{"id":926,"date":"2022-02-22T18:35:23","date_gmt":"2022-02-22T18:35:23","guid":{"rendered":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/15-global-climate-change\/"},"modified":"2025-01-21T01:03:30","modified_gmt":"2025-01-21T01:03:30","slug":"15-global-climate-change","status":"publish","type":"chapter","link":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/chapter\/15-global-climate-change\/","title":{"raw":"15 Global Climate Change","rendered":"15 Global Climate Change"},"content":{"raw":"[caption id=\"attachment_4591\" align=\"aligncenter\" width=\"767\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15The_Earth_seen_from_Apollo_17.jpg\"><img class=\"wp-image-889 size-full\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2021\/12\/15The_Earth_seen_from_Apollo_17.jpg\" alt=\"Photograph of Earth, with a view of Africa and clouds.\" width=\"767\" height=\"768\"><\/a> The \u201cBlue Marble,\u201d a picture of our planet from the 1972 Apollo 17 mission, shows that our planet is a finite place with many interacting systems. While the exact photographer is unknown, it was most likely taken by the first (and only) geologist on the moon: Harrison \u201cJack\u201d Schmitt.[\/caption]\n<h1>15 Global Climate Change<\/h1>\n<strong>KEY CONCEPTS<\/strong>\n\n<b>At the end of this chapter, students should be able to:<\/b>\n<ul>\n \t<li>Describe the role of greenhouse gases in\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0change.<\/li>\n \t<li>Describe the sources of greenhouse gases.<\/li>\n \t<li>Explain Earth\u2019s energy budget and global\u00a0[pb_glossary id=\"2689\"]temperature[\/pb_glossary]\u00a0changes.<\/li>\n \t<li>Explain how positive and\u00a0[pb_glossary id=\"1714\"]negative feedback[\/pb_glossary]\u00a0mechanisms can influence\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary].<\/li>\n \t<li>Explain how we know about climates in the geologic past.<\/li>\n \t<li>Accurately describe which aspects of the environment are changing due to\u00a0[pb_glossary id=\"1717\"]anthropogenic[\/pb_glossary]\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0change.<\/li>\n \t<li>Describe the causes of recent [pb_glossary id=\"1710\"]climate[\/pb_glossary] change, particularly the role of humans in the overall [pb_glossary id=\"1710\"]climate[\/pb_glossary] balance<\/li>\n<\/ul>\nThis chapter describes the Earth systems involved in [pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0change, the geologic evidence of past\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0changes, and the human role in today\u2019s\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0change. In science, a\u00a0[pb_glossary id=\"2664\"]system[\/pb_glossary]\u00a0is a group of interacting objects and processes. <strong>[pb_glossary id=\"2670\"]Earth System Science[\/pb_glossary]<\/strong> is the study of these systems: [pb_glossary id=\"2665\"]geosphere[\/pb_glossary]\u2014rocks; [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]\u2014gasses; [pb_glossary id=\"2666\"]hydrosphere[\/pb_glossary]\u2014water; [pb_glossary id=\"2668\"]cryosphere[\/pb_glossary]\u2014ice; and [pb_glossary id=\"2669\"]biosphere[\/pb_glossary]\u2014living things. Earth science studies these systems and how they interact and change in response to natural cycles and human-driven, or [pb_glossary id=\"1717\"]anthropogenic[\/pb_glossary] forces. Changes in one Earth [pb_glossary id=\"2664\"]system[\/pb_glossary] affect other systems.\n\nIt is critically important for us to be aware of the geologic context of [pb_glossary id=\"1710\"]climate[\/pb_glossary] change processes and how these Earth systems interact, first, for us to understand how and why human activities cause present-day [pb_glossary id=\"1710\"]climate[\/pb_glossary] change and, secondly, to distinguish between natural processes and human processes in the geologic past\u2019s [pb_glossary id=\"1710\"]climate[\/pb_glossary] record.\n\nA significant part of this chapter introduces and discusses various processes from these Earth systems, how they influence each other, and how they impact global\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]. For example, Earth\u2019s [pb_glossary id=\"2689\"]temperature[\/pb_glossary]\u00a0and [pb_glossary id=\"1710\"]climate[\/pb_glossary] largely change based on atmospheric gas [pb_glossary id=\"2831\"]composition[\/pb_glossary], ocean circulation, and the land-surface characteristics of rocks, [pb_glossary id=\"2464\"]glaciers[\/pb_glossary], and plants.\n\nAlso necessary to understanding [pb_glossary id=\"1710\"]climate[\/pb_glossary] change is to distinguish between [pb_glossary id=\"1710\"]climate[\/pb_glossary] and [pb_glossary id=\"1709\"]weather[\/pb_glossary]. <strong>[pb_glossary id=\"1709\"]Weather[\/pb_glossary]\u00a0<\/strong>is the short-term [pb_glossary id=\"2689\"]temperature[\/pb_glossary] and [pb_glossary id=\"2707\"]precipitation[\/pb_glossary] patterns that occur in days\u00a0 and weeks. <strong>[pb_glossary id=\"1710\"]Climate[\/pb_glossary]\u00a0<\/strong>is the variable range of [pb_glossary id=\"2689\"]temperature[\/pb_glossary] and [pb_glossary id=\"2707\"]precipitation[\/pb_glossary] patterns averaged over the long-term for a particular region (<a href=\"https:\/\/opengeology.org\/textbook\/13-deserts\/#131_The_Origin_of_Deserts\">see Chapter 13.1<\/a>). Thus, a single cold winter does not mean that the entire globe is cooling\u2014indeed, the United States\u2019 cold winters of 2013 and 2014 occurred\u00a0 while the rest of the Earth was experiencing record warm-winter temperatures. To avoid these generalizations, many scientists use a 30-year average as a good baseline. Therefore, [pb_glossary id=\"1710\"]climate[\/pb_glossary] change refers to slow [pb_glossary id=\"2689\"]temperature[\/pb_glossary] and [pb_glossary id=\"2707\"]precipitation[\/pb_glossary] changes and trends over the long term for a particular area or the Earth as a whole.\n<h2><span style=\"font-weight: 400\">15.1 Earth\u2019s Temperature<\/span><\/h2>\nWithout an\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary], Earth would have huge [pb_glossary id=\"2689\"]temperature[\/pb_glossary] fluctuations between day and night, like the moon. Daytime temperatures would be hundreds of degrees Celsius above normal, and nighttime temperatures would be hundreds of degrees below normal. Because the Moon doesn\u2019t have much of an\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary], its daytime temperatures are around 106 \u00b0C (224\u2109) and nighttime temperatures are around -183\u00b0C (-298\u2109). That is an astonishing 272\u00b0C (522\u00b0F) degree range between the Moon\u2019s light side and dark side. This section describes how Earth\u2019s\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]\u00a0is involved in regulating the Earth\u2019s\u00a0[pb_glossary id=\"2689\"]temperature[\/pb_glossary].\n<h3><b>15.1.1 Composition of Atmosphere<\/b><\/h3>\n[caption id=\"attachment_4592\" align=\"alignleft\" width=\"200\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.1_Atmosphere_gas_proportions.png\"><img class=\"size-full wp-image-890\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_Atmosphere_gas_proportions.png\" alt=\"This figure shows the proportion of atmopheric gases at 78% for nitrogen, 21% for oxygen, 1% for argon, and less than 1% for trace components.\" width=\"200\" height=\"417\"><\/a> Composition of the atmosphere[\/caption]\n\nThe\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]\u2019s\u00a0[pb_glossary id=\"2831\"]composition[\/pb_glossary]\u00a0is a key component in regulating the planet\u2019s\u00a0[pb_glossary id=\"2689\"]temperature[\/pb_glossary]. The\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]\u00a0is 78 percent nitrogen (N<sub>2<\/sub>), 21 percent oxygen (O<sub>2<\/sub>), one percent argon (Ar), and less than one percent trace components, which are all other gases. Trace components include carbon dioxide\u00a0(CO<sub>2<\/sub>),\u00a0water vapor (H<sub>2<\/sub>O), neon, helium, and methane.\u00a0Water vapor is highly variable, mostly based on region, and composes about one percent of the\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]. Trace component gasses include several important\u00a0<strong>greenhouse gases<\/strong>, which are the gases responsible for warming and cooling the plant. On a geologic scale, [pb_glossary id=\"1181\"]volcanoes[\/pb_glossary]\u00a0and the\u00a0[pb_glossary id=\"2676\"]weathering[\/pb_glossary]\u00a0process, which bury CO<sub>2<\/sub>\u00a0in\u00a0[pb_glossary id=\"2678\"]sediments[\/pb_glossary], are the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]\u2019s CO<sub>2 \u00a0<\/sub>sources. Biological processes both add and subtract CO<sub>2<\/sub>\u00a0from the\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary].\n\nGreenhouse gases\u00a0[pb_glossary id=\"3342\"]trap[\/pb_glossary]\u00a0heat in the\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]\u00a0and warm the planet by absorbing some of the longer-wave outgoing infrared radiation that is emitted from Earth, thus keeping heat from being lost to space. More greenhouse gases in the\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]\u00a0absorb more longwave heat and make the planet warmer. Greenhouse gasses have little effect on shorter-wave incoming solar radiation.\n\n[caption id=\"attachment_4593\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.2_greenhouse-gas-molecules.jpg\"><img class=\"wp-image-4593 size-medium\" title=\"Source: NASA public domain - https:\/\/climate.nasa.gov\/system\/internal_resources\/details\/original\/249_Causes-greenhouse-gas-molecules-cropped-more-55.jpg\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_greenhouse-gas-molecules-1.jpg\" alt=\"Illustration of the molecular shape of greenhouse gases.\" width=\"300\" height=\"192\"><\/a> Common greenhouse gases[\/caption]\n\nThe most common greenhouse gases are water vapor (H<sub>2<\/sub>O), carbon dioxide (CO<sub>2<\/sub>), methane (CH<sub>4<\/sub>),\u00a0and nitrous\u00a0[pb_glossary id=\"1919\"]oxide[\/pb_glossary]\u00a0(N<sub>2<\/sub>O).\u00a0Water vapor is the most abundant greenhouse gas, but its atmospheric\u00a0abundance does not change much over time. Carbon dioxide is much less abundant than water vapor, but carbon dioxide is being added to the\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]\u00a0by human activities such as burning\u00a0[pb_glossary id=\"3336\"]fossil fuels[\/pb_glossary], land-use changes, and deforestation. Further, natural processes such as\u00a0[pb_glossary id=\"1181\"]volcanic[\/pb_glossary]\u00a0eruptions add carbon dioxide, but at an insignificant rate compared to\u00a0human-caused contributions.\n\nThere are two important reasons why carbon dioxide is the most important greenhouse gas. First, carbon dioxide stays in the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] and does not go away for hundreds of years. Second, most of the additional carbon dioxide is \u201c[pb_glossary id=\"2176\"]fossil[\/pb_glossary]\u201d in origin, which means that it is released by burning [pb_glossary id=\"3336\"]fossil fuels[\/pb_glossary]. For example, [pb_glossary id=\"2856\"]coal[\/pb_glossary] and [pb_glossary id=\"3337\"]petroleum[\/pb_glossary] are [pb_glossary id=\"3336\"]fossil fuels[\/pb_glossary]. [pb_glossary id=\"2856\"]Coal[\/pb_glossary] and [pb_glossary id=\"3338\"]oil[\/pb_glossary] are made from long-dead plant material, which was originally created by photosynthesis millions of years ago and stored in the ground. Photosynthesis takes sunlight plus carbon dioxide and creates the substances of plants. This transformation occurs over millions of years as a slow process, accumulating [pb_glossary id=\"2176\"]fossil[\/pb_glossary] carbon in rocks and [pb_glossary id=\"2678\"]sediments[\/pb_glossary]. So, when we burn [pb_glossary id=\"2856\"]coal[\/pb_glossary] and [pb_glossary id=\"3338\"]oil[\/pb_glossary], we instantaneously release the stored solar energy and [pb_glossary id=\"2176\"]fossil[\/pb_glossary] carbon dioxide that took millions of years to accumulate in the first place. The rate of release is critical to comprehend current [pb_glossary id=\"1710\"]climate[\/pb_glossary] change.\n<h3><b>15.1.2 Carbon Cycle<\/b><\/h3>\nCritical to understanding global [pb_glossary id=\"1710\"]climate[\/pb_glossary] change is to understand the carbon cycle and how Earth's own carbon-balancing [pb_glossary id=\"2664\"]system[\/pb_glossary] is being rapidly thrown off balance by human-driven activities. Earth has two important carbon cycles: the biological and the geological. In the biological cycle, living organisms\u2014mostly plants\u2014consume carbon dioxide from the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] to make their tissues and substances through photosynthesis. Then, after the organisms die, and when they decay over years or decades, that carbon is released back into the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]. The following is the general equation for photosynthesis.\n<p style=\"text-align: center\"><i><span style=\"font-weight: 400\">CO<sub>2<\/sub> + H<\/span><\/i><sub><i><span style=\"font-weight: 400\">2<\/span><\/i><\/sub><i><span style=\"font-weight: 400\">O + sunlight \u2192 \u00a0sugars + O<\/span><\/i><sub><i><span style=\"font-weight: 400\">2<\/span><\/i><\/sub><\/p>\nIn the geological carbon cycle, a portion of the biological-cycle carbon becomes part of the geological carbon cycle: plant materials into [pb_glossary id=\"2856\"]coal[\/pb_glossary] and [pb_glossary id=\"3337\"]petroleum[\/pb_glossary], tiny fragments and molecules into organic-rich [pb_glossary id=\"2839\"]shale[\/pb_glossary], and the [pb_glossary id=\"1917\"]carbonate[\/pb_glossary] bearing calcareous shells and other parts of [pb_glossary id=\"2883\"]marine[\/pb_glossary] organisms into [pb_glossary id=\"2851\"]limestone[\/pb_glossary]. Such materials become buried and become part of the slow geologic [pb_glossary id=\"2960\"]formation[\/pb_glossary] of [pb_glossary id=\"2856\"]coal[\/pb_glossary] and other sedimentary materials. This cycle actually involves most of Earth\u2019s carbon and operates very slowly.\n\n[caption id=\"attachment_4594\" align=\"aligncenter\" width=\"1024\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.2_Carbon-Cycle.jpg\"><img class=\"wp-image-892 size-large\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_Carbon-Cycle-1024x791.jpg\" alt=\"Figure shows how carbon moves between reservoirs such as the ocean, atmosphere, biosphere, and geosphere.\" width=\"1024\" height=\"791\"><\/a> Carbon cycle.[\/caption]\n\n<span style=\"font-weight: 400\">\u00a0<\/span>The following are geological carbon-cycle storage\u00a0[pb_glossary id=\"3341\"]reservoirs[\/pb_glossary]:\n<ul>\n \t<li>Organic matter from plants is stored in peat,\u00a0[pb_glossary id=\"2856\"]coal[\/pb_glossary], and\u00a0[pb_glossary id=\"1712\"]permafrost[\/pb_glossary]\u00a0for thousands to millions of years.<\/li>\n \t<li>[pb_glossary id=\"2709\"]Silicate[\/pb_glossary]-[pb_glossary id=\"2687\"]mineral[\/pb_glossary]\u00a0[pb_glossary id=\"2676\"]weathering[\/pb_glossary]\u00a0converts atmospheric carbon dioxide to\u00a0[pb_glossary id=\"2815\"]dissolved[\/pb_glossary]\u00a0bicarbonate, which is stored in the oceans for thousands to tens of thousands of years.<\/li>\n \t<li>[pb_glossary id=\"2883\"]Marine[\/pb_glossary] organisms convert [pb_glossary id=\"2815\"]dissolved[\/pb_glossary] bicarbonate to forms of [pb_glossary id=\"1918\"]calcite[\/pb_glossary], which is stored in [pb_glossary id=\"1917\"]carbonate[\/pb_glossary] rocks for tens to hundreds of millions of years.<\/li>\n \t<li>Carbon compounds are directly stored in\u00a0[pb_glossary id=\"2678\"]sediments[\/pb_glossary]\u00a0for tens to hundreds of millions of years; some end up in\u00a0[pb_glossary id=\"3337\"]petroleum[\/pb_glossary]\u00a0deposits.<\/li>\n \t<li>Carbon-bearing\u00a0[pb_glossary id=\"2678\"]sediments[\/pb_glossary]\u00a0are transferred by\u00a0[pb_glossary id=\"2602\"]subduction[\/pb_glossary]\u00a0to the\u00a0[pb_glossary id=\"2586\"]mantle[\/pb_glossary], where the carbon may be stored for tens of millions to billions of years.<\/li>\n \t<li>Carbon dioxide from within the Earth is released back to the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] during [pb_glossary id=\"1181\"]volcanic[\/pb_glossary] eruptions, where it is stored for years to decades.<\/li>\n<\/ul>\nDuring much of Earth\u2019s history, the geological carbon cycle has been balanced by [pb_glossary id=\"1181\"]volcanos[\/pb_glossary]\u00a0releasing carbon at approximately the same rate that carbon is stored by the other processes. Under these conditions, Earth\u2019s\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0has remained relatively stable. However, in Earth\u2019s history, there have been times when that balance has been upset. This can happen during prolonged stretches of above-average\u00a0[pb_glossary id=\"1181\"]volcanic[\/pb_glossary] activity. One example is the Siberian\u00a0[pb_glossary id=\"3342\"]Traps[\/pb_glossary]\u00a0eruption around 250 million years ago, which contributed to strong\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0warming over a few million years.\n\nA carbon imbalance is also associated with significant mountain-building events. For example, the Himalayan Range has been forming for about 40 million years, and over that time \u2014 and still today \u2014 the rate of\u00a0[pb_glossary id=\"2676\"]weathering[\/pb_glossary]\u00a0on Earth has been enhanced because those mountains are so huge and the range is so extensive that they present a greater surface area on which weathering takes place. The\u00a0[pb_glossary id=\"2676\"]weathering[\/pb_glossary]\u00a0of these rocks \u2014 most importantly the\u00a0[pb_glossary id=\"2814\"]hydrolysis[\/pb_glossary]\u00a0of\u00a0[pb_glossary id=\"1916\"]feldspar[\/pb_glossary]\u00a0\u2014 has resulted in consumption of atmospheric carbon dioxide and transfer of the carbon to the oceans and to ocean-floor\u00a0[pb_glossary id=\"1917\"]carbonate[\/pb_glossary]-rich\u00a0[pb_glossary id=\"2678\"]sediments[\/pb_glossary]. The steady drop in carbon dioxide levels over the past 40 million years, which contributed to the Pliocene-Pleistocene\u00a0[pb_glossary id=\"1700\"]glaciations[\/pb_glossary], is partly attributable to the\u00a0[pb_glossary id=\"2960\"]formation[\/pb_glossary]\u00a0of the Himalayan Range.\n\nAnother, nongeological form of carbon-cycle imbalance is happening today on a very rapid time scale. In just a few decades, humans have extracted volumes of\u00a0[pb_glossary id=\"3336\"]fossil fuels[\/pb_glossary],\u00a0such as [pb_glossary id=\"2856\"]coal[\/pb_glossary],\u00a0[pb_glossary id=\"3338\"]oil[\/pb_glossary], and gas, which were stored in rocks over the past several hundred million years, and converted these fuels to energy and carbon dioxide. By doing so, we are changing the\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0faster than has ever happened in the past. Remember, carbon dioxide stays in the\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]\u00a0and does not go away for hundreds of years. The more greenhouse gases in the\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary], the more heat is trapped and the warmer the planet becomes.\n<h3><b>15.1.3 Greenhouse Effect<\/b><\/h3>\nThe\u00a0<strong>[pb_glossary id=\"1715\"]greenhouse effect[\/pb_glossary]<\/strong>\u00a0<em>is<\/em> the reason our global [pb_glossary id=\"2689\"]temperature[\/pb_glossary] is rising, but it\u2019s important to understand what this effect is and how it occurs. The [pb_glossary id=\"1715\"]greenhouse\u00a0effect[\/pb_glossary] occurs because greenhouse gases are present in the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]. The [pb_glossary id=\"1715\"]greenhouse effect[\/pb_glossary] is named after a similar process that warms a greenhouse or a car on a hot summer day. Sunlight passes through the glass of the greenhouse or car, reaches the interior, and changes into heat. The heat radiates upward and gets trapped by the glass windows. The [pb_glossary id=\"1715\"]greenhouse effect[\/pb_glossary] for the Earth can be explained in three steps.\n\n<b>Step 1:<\/b><span style=\"font-weight: 400\"> Solar radiation from the sun is [pb_glossary id=\"2831\"]composed[\/pb_glossary] of mostly ultraviolet (UV), visible light, and infrared (IR) radiation. Components of solar radiation include parts with a shorter [pb_glossary id=\"3186\"]wavelength[\/pb_glossary] than visible light, like ultraviolet light, and parts of the spectrum<\/span><span style=\"font-weight: 400\">\u00a0with longer wavelengths, like IR and others.<\/span><span style=\"font-weight: 400\">\u00a0Some of the radiation gets absorbed, scattered, or reflected by the atmospheric gases <\/span><span style=\"font-weight: 400\">but about half of the solar radiation eventually reaches the Earth\u2019s surface.<\/span>\n\n[caption id=\"attachment_4595\" align=\"aligncenter\" width=\"800\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.1_Solar_Spectrum.png\"><img class=\"size-full wp-image-893\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_Solar_Spectrum.png\" alt=\"Show how different wavelengths of incoming solar radiation are absorbed, scattered, and reflected before reaching the earth's surface.\" width=\"800\" height=\"600\"><\/a> Incoming radiation absorbed, scattered, and reflected by atmospheric gases.[\/caption]\n\n<b>Step 2:<\/b><span style=\"font-weight: 400\"> The visible, UV, and IR radiation, that reaches the surface converts to heat energy. Most students have experienced sunlight warming a surface such as pavement, a patio, or deck. When this occurs, the warmer surface then emits thermal radiation, which is a type of IR radiation. So, there is a conversion from visible, UV, and IR to just thermal IR. This thermal IR is what we experience as heat. If you have ever felt heat radiating from a fire or a hot stove top, then you have experienced thermal IR. <\/span>\n\n<b>Step 3:<\/b><span style=\"font-weight: 400\"> Thermal IR radiates from the earth\u2019s surface back into the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]. But since it is thermal IR instead of UV, visible, or regular IR, this thermal IR gets trapped by greenhouse gases. In other words, the sun's energy leaves the Earth at a different [pb_glossary id=\"3186\"]wavelength[\/pb_glossary] than it enters, so the sun\u2019s energy is not absorbed in the lower [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] when energy is coming in, but rather when the energy is going out. The gases that are mostly responsible for this energy blocking on Earth include carbon dioxide, water vapor, methane, and nitrous [pb_glossary id=\"1919\"]oxide[\/pb_glossary]. More greenhouse gases in the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] results in more thermal IR being trapped. Explore this external link to an <\/span><a href=\"https:\/\/www.koshland-science-museum.org\/explore-the-science\/interactives\/what-is-the-greenhouse-effect\"><span style=\"font-weight: 400\">interactive animation on the greenhouse effect<\/span><\/a><span style=\"font-weight: 400\"> from the National Academy of Sciences.<\/span>\n<h3><b>15.1.4 Earth\u2019s Energy Budget<\/b><\/h3>\nThe solar radiation that reaches Earth is relatively uniform over time. Earth is warmed, and energy or heat radiates from the Earth\u2019s surface and lower [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] back to space. This flow of incoming and outgoing energy is Earth\u2019s energy budget. For Earth\u2019s [pb_glossary id=\"2689\"]temperature[\/pb_glossary] to be stable over long stretches of time, incoming energy and outgoing energy have to be equal on average so that the energy budget at the top of the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] balances. About 29 percent of the incoming solar energy arriving at the top of the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] is reflected back to space by clouds, atmospheric particles, or reflective ground surfaces like sea ice and snow. About 23 percent of incoming solar energy is absorbed in the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] by water vapor, dust, and ozone. The remaining 48 percent passes through the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] and is absorbed at the surface. Thus, about 71 percent of the total incoming solar energy is absorbed by the Earth [pb_glossary id=\"2664\"]system[\/pb_glossary].\n\n[caption id=\"attachment_4596\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.1_reflected_radiation.jpg\"><img class=\"wp-image-894 size-medium\" title=\"Source: NASA Public Domain - https:\/\/earthobservatory.nasa.gov\/Features\/EnergyBalance\/images\/reflected_radiation.jpg\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_reflected_radiation-300x172.jpg\" alt=\"This figure shows incoming solar radiation, 23% is absorbed in the atmosphere, 29% reflected, and 48% absorbed at the surface after passing through atmosphere.\" width=\"300\" height=\"172\"><\/a> Incoming solar radiation filtered by the atmosphere.[\/caption]\n\nWhen this energy reaches Earth, the atoms and molecules that makeup the\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]\u00a0and surface absorb the energy, and Earth\u2019s [pb_glossary id=\"2689\"]temperature[\/pb_glossary] increases. If this material <em>only <\/em>absorbed energy, then the\u00a0[pb_glossary id=\"2689\"]temperature[\/pb_glossary]\u00a0of the Earth would continue to increase and eventually overheat. For example, if you continuously run a faucet in a stopped-up sink, the water level rises and eventually overflows. However,\u00a0[pb_glossary id=\"2689\"]temperature[\/pb_glossary]\u00a0does not infinitely rise because the Earth is not just absorbing sunlight; it is also radiating thermal energy or heat <em>back <\/em>into the\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]. If the\u00a0[pb_glossary id=\"2689\"]temperature[\/pb_glossary]\u00a0of the Earth rises, the planet emits an increasing amount of heat to space, and this is the primary mechanism that prevents Earth from continually heating.\n\n[caption id=\"attachment_4597\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.1_surface_energy_balance.jpg\"><img class=\"wp-image-895 size-medium\" title=\"Source: NASA public domain - https:\/\/earthobservatory.nasa.gov\/Features\/EnergyBalance\/images\/surface_energy_balance.jpg\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_surface_energy_balance-300x200.jpg\" alt=\"This figure shows incoming solar radiation reaching the surface and changing into longwave radiation that radiates into the atmosphere.\" width=\"300\" height=\"200\"><\/a> Some of the thermal infrared energy (heat) radiated from the surface into the atmosphere is trapped by gasses in the atmosphere.[\/caption]\n\nSome of the thermal infrared heat radiating from the surface is absorbed and trapped by greenhouse gasses in the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary], which act like a giant canopy over Earth. The more greenhouse gases in the\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary], the more outgoing heat Earth retains, and the less thermal infrared heat dissipates to space.\n\nFactors that can affect the Earth\u2019s energy budget are not limited to greenhouse gases. Increasing solar energy can increase the energy Earth receives. However, these increases are very small over time. In addition, land and water will absorb more sunlight when there is less ice and snow to reflect the sunlight back to the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]. For example, the ice covering the Arctic Sea reflects sunlight back to the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]; this reflectivity is called\u00a0<strong>[pb_glossary id=\"1711\"]albedo[\/pb_glossary]<\/strong>. Furthermore, aerosols (dust particles) produced from burning\u00a0[pb_glossary id=\"2856\"]coal[\/pb_glossary], diesel engines, and\u00a0[pb_glossary id=\"1181\"]volcanic[\/pb_glossary]\u00a0eruptions can reflect incoming solar radiation and actually cool the planet. While the effect of\u00a0[pb_glossary id=\"1717\"]anthropogenic[\/pb_glossary]\u00a0aerosols on the\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u2019s\u00a0[pb_glossary id=\"2664\"]system[\/pb_glossary] is weak,\u00a0the effect of human-produced greenhouse gases is not weak. Thus, the net effect of human activity is warming due to more\u00a0[pb_glossary id=\"1717\"]anthropogenic[\/pb_glossary]\u00a0greenhouse gases associated with\u00a0[pb_glossary id=\"3336\"]fossil fuel[\/pb_glossary]\u00a0combustion.\n\n[caption id=\"attachment_4598\" align=\"alignright\" width=\"452\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.2_Net-Forcings.jpg\"><img class=\"wp-image-896\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_Net-Forcings.jpg\" alt=\"Graph shows that anthropogenic greenhouse gases have a much larger influence on temperature than other factors such as natural changes.\" width=\"452\" height=\"289\"><\/a> Net effect of factors influencing warming.[\/caption]\n\nAn effect that changes the planet can\u00a0[pb_glossary id=\"3117\"]trigger[\/pb_glossary]\u00a0feedback mechanisms that amplify or\u00a0suppress the original effect. A\u00a0<strong>positive\u00a0 feedback mechanism<\/strong>\u00a0occurs when the output or effect of a process <em>enhances <\/em>the original stimulus or cause. Thus, it increases the ongoing effect. For example, the loss of sea ice at the North Pole makes that area less reflective, reducing\u00a0[pb_glossary id=\"1711\"]albedo[\/pb_glossary]. This allows the surface air and ocean to absorb more energy in an area that was once covered by sea ice.\u00a0Another example is melting\u00a0[pb_glossary id=\"1712\"]permafrost[\/pb_glossary].\u00a0<strong>[pb_glossary id=\"1712\"]Permafrost[\/pb_glossary]\u00a0<\/strong>is permanently frozen [pb_glossary id=\"1203\"]soil[\/pb_glossary] located in the high latitudes, mostly in the Northern Hemisphere. As the [pb_glossary id=\"1710\"]climate[\/pb_glossary] warms, more [pb_glossary id=\"1712\"]permafrost[\/pb_glossary] thaws, and the thick deposits of organic matter are exposed to oxygen and begin to decay. This [pb_glossary id=\"2818\"]oxidation[\/pb_glossary] process releases carbon dioxide and methane, which in turn causes more warming, which melts more [pb_glossary id=\"1712\"]permafrost[\/pb_glossary], and so on and on.\n\nA\u00a0<strong>[pb_glossary id=\"1714\"]negative feedback[\/pb_glossary]\u00a0mechanism<\/strong>\u00a0occurs when the output or effect <em>reduces <\/em>the original stimulus or cause. For example, in the short term, more carbon dioxide (CO<sub>2<\/sub>) is expected to cause forest canopies to grow, which absorb more CO<sub>2<\/sub>. Another example for the long term is that increased carbon dioxide in the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] will cause more [pb_glossary id=\"2813\"]carbonic acid[\/pb_glossary] and [pb_glossary id=\"2812\"]chemical weathering[\/pb_glossary], which results in transporting dissolved bicarbonate and other ions to the oceans, which are then stored in [pb_glossary id=\"2678\"]sediment[\/pb_glossary].\n\nGlobal warming is evidence that Earth's energy budget is not balanced. Positive effects on Earth's [pb_glossary id=\"2689\"]temperature[\/pb_glossary] are now greater than negative effects.\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"102\"]\n\n[caption id=\"attachment_4862\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/15.1-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-897\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 15.1 via this QR Code.[\/caption]\n<h2><span style=\"font-weight: 400\">15.2 Evidence of Recent Climate Change<\/span><\/h2>\nWhile [pb_glossary id=\"1710\"]climate[\/pb_glossary] has changed often in the past due to natural causes (see <a href=\"https:\/\/opengeology.org\/textbook\/14-glaciers\/#1451_Causes_of_Glaciations\">chapter 14.5.1<\/a>\u00a0and\u00a0<a href=\"https:\/\/opengeology.org\/textbook\/15-global-climate-change\/#153_Prehistoric_Climate_Change\">chapter 15.3<\/a>), the scientific consensus is that human activity is causing current very rapid [pb_glossary id=\"1710\"]climate[\/pb_glossary] change. While this seems like a new idea, it was suggested more than 75 years ago. This section describes the evidence of what most scientists agree is <strong>[pb_glossary id=\"1717\"]anthropogenic[\/pb_glossary]<\/strong> or\u00a0[pb_glossary id=\"1716\"]human-caused climate change[\/pb_glossary]. For more information, watch this<a href=\"https:\/\/youtu.be\/dquECwUfIQg?list=PL4Wzj82Z15gzrcsvrQxDPB1o4UAUxGbBM\">\u00a0six-minute video on climate change<\/a> by two professors at the North Carolina State University.\n\n[caption id=\"attachment_4871\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/Evidence-for-Climate-Change-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-898\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Evidence-for-Climate-Change-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/dquECwUfIQg[\/embed]\n<h3><b>15.2.1 Global Temperature Rise<\/b><\/h3>\nThe land-ocean [pb_glossary id=\"2689\"]temperature[\/pb_glossary] index, 1880 to present, compared to a base reference time of 1951-1980, shows ocean temperatures steadily rising. The solid black line is the global annual mean, and the solid red line is the five-year Lowess smoothing. The blue uncertainty bars (95 percent confidence limit) account only for incomplete spatial sampling.\n\n[caption id=\"attachment_4599\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15_tempgraph.png\"><img class=\"wp-image-899 size-medium\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15_tempgraph-300x159.png\" alt=\"Graph of temperature with time showing gradual increase of 1 degree Celcius in temperature over time with minor fluctuations within the large trend.\" width=\"300\" height=\"159\"><\/a> Land-ocean temperature index, 1880 to present, with a base time 1951-1980. The solid black line is the global annual mean and the solid red line is the five-year Lowess smoothing. The blue uncertainty bars (95% confidence limit) account only for incomplete spatial sampling. The graph shows that Earth\u2019s temperature is rising.[\/caption]\n\nSince 1880, Earth\u2019s surface-[pb_glossary id=\"2689\"]temperature[\/pb_glossary] average has trended upward with most of that warming occurring since 1970 (see this NASA\u00a0<a href=\"https:\/\/svs.gsfc.nasa.gov\/4882\">animation<\/a>). Surface temperatures include both land and ocean because water absorbs much additional trapped heat. Changes in land-surface or ocean-surface temperatures compared to a reference [pb_glossary id=\"2192\"]period[\/pb_glossary] from 1951 to 1980, where the long-term average remained relatively constant, are called [pb_glossary id=\"2689\"]temperature[\/pb_glossary]\u00a0<strong>[pb_glossary id=\"1719\"]anomalies[\/pb_glossary]<\/strong>. A\u00a0[pb_glossary id=\"2689\"]temperature[\/pb_glossary]\u00a0[pb_glossary id=\"1719\"]anomaly[\/pb_glossary]\u00a0thus represents the difference between the measured [pb_glossary id=\"2689\"]temperature[\/pb_glossary]\u00a0and the average value during the reference [pb_glossary id=\"2192\"]period[\/pb_glossary]. [pb_glossary id=\"1710\"]Climate[\/pb_glossary] scientists calculate long-term average temperatures\u00a0over thirty years or more which identified the reference [pb_glossary id=\"2192\"]period[\/pb_glossary] from 1951 to 1980.\u00a0Another common range is a century, for example, 1900-2000. Therefore, an\u00a0[pb_glossary id=\"1719\"]anomaly[\/pb_glossary]\u00a0of 1.25 \u2103 (34.3\u00b0F) for 2015 means that the average\u00a0[pb_glossary id=\"2689\"]temperature[\/pb_glossary]\u00a0for 2015 was 1.25 \u2103 (34.3\u00b0F) greater than the 1900-2000 average. In 1950, the\u00a0[pb_glossary id=\"2689\"]temperature[\/pb_glossary]\u00a0[pb_glossary id=\"1719\"]anomaly[\/pb_glossary]\u00a0was -0.28 \u2103 (31.5\u00b0F), so this is -0.28 \u2103 (31.5\u00b0F) lower than the 1900-2000 average. These temperatures are annual average measured surface temperatures.\n\nThis video figure of [pb_glossary id=\"2689\"]temperature[\/pb_glossary] [pb_glossary id=\"1719\"]anomalies[\/pb_glossary] shows worldwide\u00a0[pb_glossary id=\"2689\"]temperature[\/pb_glossary]\u00a0changes since 1880.\u00a0 The more blue, the cooler; the more yellow and red, the warmer.\n\n[caption id=\"attachment_4864\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/15.2.1-Global-Temperature-Rise-Video-QR-Code.png\"><img class=\"size-thumbnail wp-image-900\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2.1-Global-Temperature-Rise-Video-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this video via this QR Code.[\/caption]\n\n[video width=\"300\" height=\"200\" mp4=\"http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2017\/01\/15.2_GISTEMP_2015_sm.mp4\" autoplay=\"true\"][\/video]\n\n&nbsp;\n\nIn addition to average land-surface temperatures rising, the ocean has absorbed much heat. Because oceans cover about 70 percent of the Earth\u2019s surface and have such a high specific heat value, they provide a large opportunity to absorb energy. The ocean has been absorbing about 80 to 90 percent of human activities\u2019 additional heat. As a result, [pb_glossary id=\"2689\"]temperature[\/pb_glossary] in the ocean\u2019s top 701.4 m (2,300 ft) has increased by -17.6\u00b0C (0.3\u2109) since 1969 (<a href=\"https:\/\/climate.nasa.gov\/climate_resources\/40\/\">watch this 3 minute <\/a>video by NASA JPL on the ocean\u2019s heat capacity). The reason the ocean has warmed less than the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary], while still taking on most of the heat, is due to water\u2019s very high specific heat, which means that water can absorb a lot of heat energy with a small [pb_glossary id=\"2689\"]temperature[\/pb_glossary] increase. In contrast, the lower specific heat of the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] means it has a higher [pb_glossary id=\"2689\"]temperature[\/pb_glossary] increase as it absorbs less heat\u00a0 energy.\n\nSome scientists suggest that [pb_glossary id=\"1717\"]anthropogenic[\/pb_glossary] greenhouse gases do not cause global warming because between 1998 and 2013, Earth\u2019s surface temperatures did not increase much, despite greenhouse gas concentrations continuing to increase. However, since the oceans are absorbing most of the heat, decade-scale circulation changes in the ocean, similar to La Ni\u00f1a, push warmer water deeper under the surface. Once the ocean\u2019s absorption and circulation is accounted for, and this heat is added back into surface temperatures, then [pb_glossary id=\"2689\"]temperature[\/pb_glossary] increases become apparent, as shown in the figure. Also, the ocean\u2019s heat storage is temporary, as reflected in the record-breaking warm years of 2014-2016. Indeed, with this temporary ocean-storage effect, the twenty-first century\u2019s first 15 of its 16 years were the hottest in recorded history.\n<h3><b>15.2.2 Carbon Dioxide<\/b><\/h3>\n[pb_glossary id=\"1717\"]Anthropogenic[\/pb_glossary]\u00a0greenhouse gases, mostly carbon dioxide (CO<sub>2<\/sub>), have increased since the industrial revolution when humans dramatically increased burning [pb_glossary id=\"3336\"]fossil fuels[\/pb_glossary].\u00a0These levels are unprecedented in the last 800,000-year Earth history as recorded in geologic sources such as ice cores. Carbon dioxide has increased by 40 percent since 1750, and the rate of increase has been the fastest during the last decade. For example, since 1750, 2040<sup>9<\/sup>\u00a0tonnes (2040 gigatons) of CO<sub>2<\/sub>\u00a0have been added to the\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]; about 40 percent has remained in the\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]\u00a0while the remaining 60 percent has been absorbed into the land by plants and\u00a0[pb_glossary id=\"1203\"]soil[\/pb_glossary] or into the oceans. Indeed, during the lifetime of most young adults, the total\u00a0atmospheric\u00a0CO<sub>2<\/sub> has increased by 50 ppm, or 15 percent.\n\nCharles Keeling, an oceanographer with Scripps Institution of Oceanography in San Diego, California, was the first person to regularly measure atmospheric CO<sub>2<\/sub>. Using his methods, scientists at the Mauna Loa Observatory, Hawaii, have constantly measured atmospheric CO<sub>2 <\/sub>since 1957. NASA regularly publishes these measurements at <u><a href=\"https:\/\/scripps.ucsd.edu\/programs\/keelingcurve\/\">https:\/\/scripps.ucsd.edu\/programs\/keelingcurve\/<\/a><\/u>. Go there <strong>now<\/strong> to see the very latest measurement. Keeling\u2019s measured values have been posted in a curve of increasing values, called the Keeling Curve. This curve varies up and down in a regular annual cycle, from summer when the plants in the Northern Hemisphere are using CO<sub>2<\/sub> to winter when the plants are dormant. But the curve shows a steady CO<sub>2 <\/sub>increase over the past several decades. This curve increases exponentially, not linearly, showing that the rate of CO<sub>2<\/sub>\u00a0increase is itself increasing!\n\n<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Keeling-Curve-1-10-2022-1.jpg\"><img class=\"aligncenter wp-image-901 size-full\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Keeling-Curve-1-10-2022-1.jpg\" alt=\"Keeling curve graph of the carbon dioxide concentration at Mauna Loa Observatory\" width=\"928\" height=\"618\"><\/a>\n\nThe following Atmospheric CO<sub>2 <\/sub>video shows how atmospheric CO<sub>2<\/sub> has varied recently and over the last 800,000 years, as determined by an increasing number of CO<sub>2<\/sub> monitoring stations as shown on the insert map. It is also instructive to watch the video\u2019s Keeling portion of how CO<sub>2<\/sub>\u00a0varies by\u00a0[pb_glossary id=\"3372\"]latitude[\/pb_glossary].\u00a0This shows that most human CO<sub>2<\/sub>\u00a0sources are in the Northern Hemisphere where most of the land is and where most of the developed nations are.\n<div style=\"height: 0;padding-bottom: 56.25%\">\n\n[caption id=\"attachment_4872\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/Pumphandle-2016-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-902\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Pumphandle-2016-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/gH6fQh9eAQE[\/embed]\n\n<\/div>\n&nbsp;\n\n&nbsp;\n\n&nbsp;\n\n&nbsp;\n\n&nbsp;\n\n&nbsp;\n\n&nbsp;\n\n&nbsp;\n<h3><b>15.2.3 Melting Glaciers and Shrinking Sea Ice<\/b><\/h3>\n[caption id=\"attachment_4601\" align=\"alignleft\" width=\"400\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.2_LandIceAntarctica.png\"><img class=\"wp-image-903\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_LandIceAntarctica-300x149.png\" alt=\"Graph shows decline of Antarctic ice mass by 2,000 gigatons from 2002 to 2016.\" width=\"400\" height=\"198\"><\/a> Decline of Antarctic ice mass from 2002 to 2016[\/caption]\n\n[pb_glossary id=\"2464\"]Glaciers[\/pb_glossary]\u00a0are large ice accumulations that exist year round on the land\u2019s surface. In contrast, icebergs are masses of floating sea ice, although they may have had their origin in [pb_glossary id=\"2464\"]glaciers[\/pb_glossary] (see Chapter 14). [pb_glossary id=\"2465\"]Alpine glaciers[\/pb_glossary], [pb_glossary id=\"2467\"]ice sheets[\/pb_glossary], and sea ice are all melting. Explore melting [pb_glossary id=\"2464\"]glaciers[\/pb_glossary] at NASA\u2019s interactive Global Ice Viewer). Satellites have recorded that Antarctica is melting at 1189 tonnes (118 gigatons) per year, and Greenland is melting at 2819 tonnes (281 gigatons) per year; 1 metric tonne is 1000 kilograms (1 gigaton is over 2 trillion pounds). Almost all major [pb_glossary id=\"2465\"]alpine glaciers[\/pb_glossary] are shrinking, deflating, and retreating. The ice-mass loss rate is unprecedented\u2014never observed before\u2014since the 1940\u2019s when quality records for [pb_glossary id=\"2464\"]glaciers[\/pb_glossary] began.\n\nBefore\u00a0[pb_glossary id=\"1717\"]anthropogenic[\/pb_glossary]\u00a0warming,\u00a0[pb_glossary id=\"2910\"]glacial[\/pb_glossary]\u00a0activity was variable with some retreating and some advancing. Now, [pb_glossary id=\"3174\"]spring[\/pb_glossary]\u00a0snow cover is decreasing, and sea ice is shrinking. Most sea ice is at the North Pole, which is only occupied by the Arctic Ocean and sea ice. The NOAA animation shows how perennial sea ice has declined from 1987 to 2015. The oldest ice is white, and the youngest, seasonal ice is dark blue. The amount of old ice has declined from 20 percent in 1985 to 3 percent in 2015.\n\n[caption id=\"attachment_4873\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/Watch-25-Years-of-Arctic-Sea-Ice-Disappear-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-904\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Watch-25-Years-of-Arctic-Sea-Ice-Disappear-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/Fw7GfNR5PLA[\/embed]\n<h3><b>15.2.4 Rising Sea-Level<\/b><\/h3>\nSea level is rising 3.4 millimeters (0.13 inches) per year and has risen 0.19 meters (7.4 inches) from 1901 to 2010. This is thought largely to be from both\u00a0[pb_glossary id=\"2464\"]glaciers[\/pb_glossary] melting and thermal expansion of sea water. Thermal expansion means that as objects such as solids, liquids, and gases heat up, they expand in volume.\n\nClassic video demonstration (30 second) on thermal expansion with brass ball and ring (North Carolina School of Science and Mathematics).\n\n[caption id=\"attachment_4868\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/Ball-and-Ring-Rate-of-Expansion-and-Contraction-Youtube-QR-Code-1.png\"><img class=\"size-thumbnail wp-image-905\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Ball-and-Ring-Rate-of-Expansion-and-Contraction-Youtube-QR-Code-1-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/QNoE5IoRheQ[\/embed]\n<h3><b>15.2.5 Ocean Acidification<\/b><\/h3>\nSince 1750, about 40 percent of new [pb_glossary id=\"1717\"]anthropogenic[\/pb_glossary] carbon dioxide has remained in the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]. The remaining 60 percent gets absorbed by the ocean and vegetation. The ocean has absorbed about 30 percent of that carbon dioxide. When carbon dioxide gets absorbed in the ocean, it creates [pb_glossary id=\"2813\"]carbonic acid[\/pb_glossary]. This makes the ocean more acidic, which then has an impact on [pb_glossary id=\"2883\"]marine[\/pb_glossary] organisms that secrete calcium [pb_glossary id=\"1917\"]carbonate[\/pb_glossary] shells. Recall that hydrochloric acid reacts by effervescing with [pb_glossary id=\"2851\"]limestone[\/pb_glossary] rock made of [pb_glossary id=\"1918\"]calcite[\/pb_glossary], which is calcium [pb_glossary id=\"1917\"]carbonate[\/pb_glossary]. A more acidic ocean is associated with [pb_glossary id=\"1710\"]climate[\/pb_glossary] change and is linked to some sea snails (pteropods) and small protozoan zooplanktons\u2019 (foraminifera) thinning [pb_glossary id=\"1917\"]carbonate[\/pb_glossary] shells and to ocean coral [pb_glossary id=\"2898\"]reefs[\/pb_glossary]\u2019 declining growth rates. Small animals like protozoan zooplankton are an important component at the base of the [pb_glossary id=\"2883\"]marine[\/pb_glossary] ecosystem. Acidification combined with warmer [pb_glossary id=\"2689\"]temperature[\/pb_glossary] and lower oxygen levels is expected to have severe impacts on [pb_glossary id=\"2883\"]marine[\/pb_glossary] ecosystems and human-harvested fisheries, possibly affecting our ocean-derived food sources.\n\n[caption id=\"attachment_4865\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/15.2.5-Ocean-Acidification-Video-QR-Code.png\"><img class=\"size-thumbnail wp-image-906\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2.5-Ocean-Acidification-Video-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this video via this QR Code.[\/caption]\n\n[video width=\"300\" height=\"200\" webm=\"http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2017\/01\/15.2_Impacts_of_ocean_acidification_NOAA_EVL.webm\"][\/video]\n<h3><b>15.2.6 Extreme Weather Events<\/b><\/h3>\nExtreme\u00a0[pb_glossary id=\"1709\"]weather[\/pb_glossary]\u00a0events such as hurricanes,\u00a0[pb_glossary id=\"2707\"]precipitation[\/pb_glossary], and heatwaves are increasing and becoming more intense. Since the 1980\u2019s, hurricanes, which are generated from warm ocean water, have increased in frequency, intensity, and duration and are likely connected to a warmer\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]. Since 1910, average\u00a0[pb_glossary id=\"2707\"]precipitation[\/pb_glossary]\u00a0has increased by 10 percent in the contiguous United States, and much of this increase is associated with heavy\u00a0[pb_glossary id=\"2707\"]precipitation[\/pb_glossary]\u00a0events. However, the distribution is not even, and more\u00a0[pb_glossary id=\"2707\"]precipitation[\/pb_glossary]\u00a0is projected for the northern United States while less\u00a0[pb_glossary id=\"2707\"]precipitation[\/pb_glossary]\u00a0is projected for the already dry southwest. Also, heatwaves have increased, and rising temperatures are already affecting crop yields in northern latitudes. Increased heat allows for greater moisture capacity in the\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary], increasing the potential for more extreme events.\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"103\"]\n\n[caption id=\"attachment_4863\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/15.2-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-907\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 15.2 via this QR Code.[\/caption]\n<h2><span style=\"font-weight: 400\">15.3 Prehistoric Climate Change <\/span><\/h2>\n[caption id=\"attachment_4602\" align=\"alignleft\" width=\"250\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.3_Laurentide_Ice_Sheet_Extent.jpg\"><img class=\"wp-image-908 size-full\" title=\"Source: USGS. The maximum extent of glacial ice in the north polar area during Pleistocene time. {{PD-USGov-Interior-USGS}} http:\/\/pubs.usgs.gov\/gip\/continents\/map.jpg\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Laurentide_Ice_Sheet_Extent.jpg\" alt=\"Shows extent of last ice age with glacier covering most of Canada and some of the northern U.S. including Alaska, Wisconsin, Minnesota, the Great Lakes, and parts of other states.\" width=\"250\" height=\"417\"><\/a> Maximum extent of Laurentide Ice Sheet[\/caption]\n\nOver Earth\u2019s history, the\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0has changed a lot. For example, during the\u00a0[pb_glossary id=\"1432\"]Mesozoic[\/pb_glossary]\u00a0[pb_glossary id=\"2191\"]Era[\/pb_glossary], the Age of Dinosaurs, the\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0was much warmer, and carbon dioxide was abundant in the\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]. However, throughout the\u00a0[pb_glossary id=\"1441\"]Cenozoic[\/pb_glossary]\u00a0[pb_glossary id=\"2191\"]Era[\/pb_glossary], 65 million years ago to today, the\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0has been gradually cooling. This section summarizes some of these major past\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0changes.\n\n&nbsp;\n\n&nbsp;\n\n&nbsp;\n\n&nbsp;\n<h3><strong>15.3.1 Past Glaciations<\/strong><\/h3>\nThrough geologic history,\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0has changed slowly over millions of years. Before the most recent Pliocene-[pb_glossary id=\"1443\"]Quaternary[\/pb_glossary]\u00a0[pb_glossary id=\"1700\"]glaciation[\/pb_glossary], there were other major\u00a0[pb_glossary id=\"1700\"]glaciations[\/pb_glossary]. The oldest, known as the Huronian, occurred toward the end of the\u00a0[pb_glossary id=\"2205\"]Archean[\/pb_glossary] [pb_glossary id=\"2190\"]Eon[\/pb_glossary]-early\u00a0[pb_glossary id=\"2209\"]Proterozoic[\/pb_glossary]\u00a0[pb_glossary id=\"2190\"]Eon[\/pb_glossary], about 2.5 billion years ago. The event of that time, the\u00a0[pb_glossary id=\"2210\"]Great Oxygenation Event[\/pb_glossary], was a major happening\u00a0(see Chapter 8) most commonly associated with causing that\u00a0[pb_glossary id=\"1700\"]glaciation[\/pb_glossary]. The increased oxygen is thought to have reacted with the potent greenhouse gas methane, causing cooling.\n\nThe end of the\u00a0[pb_glossary id=\"2209\"]Proterozoic[\/pb_glossary]\u00a0[pb_glossary id=\"2190\"]Eon[\/pb_glossary], about 700 million years ago, had other\u00a0[pb_glossary id=\"1700\"]glaciations[\/pb_glossary]. These ancient [pb_glossary id=\"2218\"]Precambrian[\/pb_glossary] [pb_glossary id=\"1700\"]glaciations[\/pb_glossary] are included in the\u00a0<strong>[pb_glossary id=\"1718\"]Snowball Earth hypothesis[\/pb_glossary]<\/strong>.\u00a0Widespread global rock sequences from these ancient times contain evidence that [pb_glossary id=\"2464\"]glaciers[\/pb_glossary] existed even in low-latitudes. Two \u00a0examples are [pb_glossary id=\"2851\"]limestone[\/pb_glossary]\u00a0rock\u2014usually formed in tropical\u00a0[pb_glossary id=\"2883\"]marine[\/pb_glossary]\u00a0environments\u2014and\u00a0[pb_glossary id=\"2910\"]glacial[\/pb_glossary]\u00a0deposits\u2014usually formed in cold climates\u2014have been found together from this time in many regions around the world. One example is in Utah. Evidence of [pb_glossary id=\"2575\"]continental[\/pb_glossary]\u00a0[pb_glossary id=\"1700\"]glaciation[\/pb_glossary] is seen in interbedded [pb_glossary id=\"2851\"]limestone[\/pb_glossary]\u00a0and\u00a0[pb_glossary id=\"2910\"]glacial[\/pb_glossary]\u00a0deposits ([pb_glossary id=\"2911\"]diamictites[\/pb_glossary]) on Antelope Island in the Great Salt Lake.\n\nThe controversial [pb_glossary id=\"1718\"]Snowball Earth hypothesis[\/pb_glossary] suggests that a runaway [pb_glossary id=\"1711\"]albedo[\/pb_glossary] effect\u2014where ice and snow reflect solar radiation and increasingly spread from polar regions toward the equator\u2014caused land and ocean surfaces to completely freeze and biological activity to collapse. Thinking is that because carbon dioxide could not enter the then-frozen ocean, the ice covering Earth could only melt when [pb_glossary id=\"1181\"]volcanoes[\/pb_glossary] emitted high enough carbon dioxide into the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] to cause greenhouse heating. Some studies estimate that because of the frozen ocean surface, carbon dioxide 350 times higher than today\u2019s concentration was required. Because biological activity did survive, the complete freezing and its extent in the [pb_glossary id=\"1718\"]snowball earth hypothesis[\/pb_glossary] are controversial. A competing [pb_glossary id=\"2652\"]hypothesis[\/pb_glossary] is the <strong>Slushball Earth [pb_glossary id=\"2652\"]hypothesis[\/pb_glossary] <\/strong>in which some regions of the equatorial ocean remained open. Differing scientific conclusions about the stability of Earth\u2019s magnetic poles, impacts on ancient rock evidence from subsequent [pb_glossary id=\"2914\"]metamorphism[\/pb_glossary], and alternate interpretations of existing evidence keep the idea of [pb_glossary id=\"1718\"]Snowball Earth[\/pb_glossary] controversial.\n\n<span style=\"font-weight: 400\">[pb_glossary id=\"1700\"]Glaciations[\/pb_glossary]\u00a0also occurred in the\u00a0[pb_glossary id=\"2219\"]Paleozoic[\/pb_glossary] [pb_glossary id=\"2191\"]Era[\/pb_glossary], notably the Andean-Saharan [pb_glossary id=\"1700\"]glaciation[\/pb_glossary] in the late [pb_glossary id=\"2225\"]Ordovician[\/pb_glossary], about 440\u2013460 million years ago, which coincided with a major [pb_glossary id=\"1708\"]extinction[\/pb_glossary] event, and the Karoo\u00a0[pb_glossary id=\"1700\"]Ice Age[\/pb_glossary] during the Pennsylvanian [pb_glossary id=\"2192\"]Period[\/pb_glossary], 323 to 300 million years ago. This [pb_glossary id=\"1700\"]glaciation[\/pb_glossary] was one of the evidences cited by Wegener for his [pb_glossary id=\"2575\"]Continental[\/pb_glossary] Drift [pb_glossary id=\"2652\"]hypothesis[\/pb_glossary] as his proposed [pb_glossary id=\"3366\"]Pangea[\/pb_glossary] drifted into south polar latitudes. The Karoo [pb_glossary id=\"1700\"]glaciation[\/pb_glossary] was associated with an increase of oxygen and a subsequent drop in carbon dioxide, most likely produced by the evolution and rise of land plants<\/span><span style=\"font-weight: 400\">.<\/span>\n\n[caption id=\"attachment_4603\" align=\"aligncenter\" width=\"1024\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15_cenozoic-t-2.png\"><img class=\"size-large wp-image-909\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15_cenozoic-t-2-1024x446.png\" alt=\"Graph showing decrease of average surface temperature from 23 degrees Celsius 50 million years ago to 12 degrees Celsius near present.\" width=\"1024\" height=\"446\"><\/a> Global average surface temperature over the past 70 million years.[\/caption]\n\nDuring the\u00a0[pb_glossary id=\"1441\"]Cenozoic[\/pb_glossary]\u00a0[pb_glossary id=\"2191\"]Era[\/pb_glossary]\u2014the last 65 million years,\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0started out warm and gradually cooled to today. This warm time is called the\u00a0<strong>[pb_glossary id=\"1720\"]Paleocene-Eocene Thermal Maximum[\/pb_glossary],<\/strong>\u00a0and Antarctica and Greenland were ice free during this time. Since the Eocene,\u00a0[pb_glossary id=\"2576\"]tectonic[\/pb_glossary]\u00a0events during the\u00a0[pb_glossary id=\"1441\"]Cenozoic[\/pb_glossary]\u00a0[pb_glossary id=\"2191\"]Era[\/pb_glossary] caused the planet to persistently and significantly cool. For example, the\u00a0Indian\u00a0[pb_glossary id=\"2591\"]Plate[\/pb_glossary]\u00a0and Asian\u00a0[pb_glossary id=\"2591\"]Plate[\/pb_glossary]\u00a0collided,\u00a0creating the Himalaya Mountains, which increased\u00a0the rate of [pb_glossary id=\"2676\"]weathering[\/pb_glossary] and [pb_glossary id=\"2677\"]erosion[\/pb_glossary] of [pb_glossary id=\"2709\"]silicate[\/pb_glossary]\u00a0[pb_glossary id=\"2687\"]minerals[\/pb_glossary], especially\u00a0[pb_glossary id=\"1916\"]feldspar[\/pb_glossary]. Increased [pb_glossary id=\"2676\"]weathering[\/pb_glossary]\u00a0consumes carbon dioxide from the\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary], which \u00a0reduces the\u00a0[pb_glossary id=\"1715\"]greenhouse effect[\/pb_glossary], resulting in long-term cooling.\n\n[caption id=\"attachment_4604\" align=\"alignright\" width=\"283\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Antarctic-Circumpolar.png\"><img class=\"size-full wp-image-910\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Antarctic-Circumpolar.png\" alt=\"Map of bottom of earth showing Antarctic continent and an ocean current circulating clockwise around it.\" width=\"283\" height=\"279\"><\/a> The Antarctic Circumpolar Current[\/caption]\n\nAbout 40 million years ago, the narrow gap between the South American\u00a0[pb_glossary id=\"2591\"]Plate[\/pb_glossary]\u00a0and the Antarctica\u00a0[pb_glossary id=\"2591\"]Plate[\/pb_glossary]\u00a0widened, which opened the Drake Passage. This opening allowed the water around Antarctica\u2014the Antarctic Circumpolar Current\u2014to flow unrestrictedly west-to-east, which effectively isolated the southern ocean from the warmer waters of the Pacific, Atlantic, and Indian Oceans. The region cooled significantly, and by 35 million years ago, during the Oligocene [pb_glossary id=\"2193\"]Epoch[\/pb_glossary],\u00a0[pb_glossary id=\"2464\"]glaciers[\/pb_glossary]\u00a0had started to form on Antarctica.\n\nAround 15 million years ago,\u00a0[pb_glossary id=\"2602\"]subduction[\/pb_glossary]-related\u00a0[pb_glossary id=\"1181\"]volcanos[\/pb_glossary] between Central and South America created the Isthmus of Panama, which connected North and South America. This prevented water from flowing between the Pacific and Atlantic Oceans and reduced heat transfer from the tropics to the poles. This reduced heat transfer created a cooler Antarctica and larger Antarctic\u00a0[pb_glossary id=\"2464\"]glaciers[\/pb_glossary]. As a result, the [pb_glossary id=\"2467\"]ice sheet[\/pb_glossary]\u00a0expanded on land and water, increased Earth\u2019s reflectivity and enhanced the [pb_glossary id=\"1711\"]albedo[\/pb_glossary] effect, which created a\u00a0[pb_glossary id=\"1713\"]positive feedback[\/pb_glossary]\u00a0loop: more reflective\u00a0[pb_glossary id=\"2910\"]glacial[\/pb_glossary]\u00a0ice, more cooling, more ice, more cooling, and so on.\n\nBy 5 million years ago, during the Pliocene [pb_glossary id=\"2193\"]Epoch[\/pb_glossary], [pb_glossary id=\"2467\"]ice sheets[\/pb_glossary] had started to grow in North America and northern Europe. The most intense part of the current [pb_glossary id=\"1700\"]glaciation[\/pb_glossary] is the Pleistocene [pb_glossary id=\"2193\"]Epoch[\/pb_glossary]\u2019s last 1 million years. The Pleistocene\u2019s [pb_glossary id=\"2689\"]temperature[\/pb_glossary] varies significantly through a range of almost 10\u00b0C (18\u00b0F) on time scales of 40,000 to 100,000 years, and [pb_glossary id=\"2467\"]ice sheets[\/pb_glossary] expand and contract correspondingly. These variations are attributed to subtle changes in Earth\u2019s orbital parameters, called <strong>[pb_glossary id=\"1701\"]Milankovitch cycles[\/pb_glossary]<\/strong> (see Chapter 14). Over the past million years, the\u00a0[pb_glossary id=\"1700\"]glaciation[\/pb_glossary]\u00a0cycles occurred approximately every 100,000 years,\u00a0with many\u00a0[pb_glossary id=\"2910\"]glacial[\/pb_glossary]\u00a0advances occurring in the last 2 million years\u00a0(Lisiecki and\u00a0Raymo, 2005).\n\n[caption id=\"attachment_4605\" align=\"aligncenter\" width=\"1024\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.3-oxygen-isotope-record-Lisiecki-and-Raymo-2005.jpg\"><img class=\"wp-image-911 size-large\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-oxygen-isotope-record-Lisiecki-and-Raymo-2005-1024x768.jpg\" alt=\"Graph showing the oxygen isotope record for last 5 million years with regular cycles. More pronounced glacial cycles are in the last 1 million years.\" width=\"1024\" height=\"768\"><\/a> A Pliocene\u2010Pleistocene stack of 57 globally distributed benthic \u03b418O records (Source: Lisiecki, L. E., &amp; Raymo, M. E. (2005). A Pliocene\u2010Pleistocene stack of 57 globally distributed benthic \u03b418O records.\u00a0Paleoceanography,\u00a020(1).)[\/caption]\n\nDuring an\u00a0[pb_glossary id=\"1700\"]ice age[\/pb_glossary], [pb_glossary id=\"2192\"]periods[\/pb_glossary] of warming [pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0 are called\u00a0<strong>[pb_glossary id=\"3321\"]interglacials[\/pb_glossary]<\/strong>; during [pb_glossary id=\"3321\"]interglacials[\/pb_glossary], very brief [pb_glossary id=\"2192\"]periods[\/pb_glossary] of even warmer [pb_glossary id=\"1710\"]climate[\/pb_glossary] are called\u00a0<strong>[pb_glossary id=\"3322\"]interstadials[\/pb_glossary]<\/strong>. These warming upticks are related to Earth\u2019s\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0variations, like\u00a0[pb_glossary id=\"1701\"]Milankovitch cycle[\/pb_glossary]s, which are changes to the Earth\u2019s orbit that can fluctuate [pb_glossary id=\"1710\"]climate[\/pb_glossary] (see Chapter 14). In the last 500,000 years, there have been five or six\u00a0[pb_glossary id=\"3321\"]interglacials[\/pb_glossary], with the most recent belonging to our current time, the\u00a0[pb_glossary id=\"1444\"]Holocene[\/pb_glossary] [pb_glossary id=\"2193\"]Epoch[\/pb_glossary].\n\nThe two more recent\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0swings, the Younger Dryas and the\u00a0[pb_glossary id=\"1444\"]Holocene[\/pb_glossary]\u00a0Climatic Optimum, demonstrate complex changes. These events are more recent, yet have conflicting information. The Younger Dryas\u2019 cooling is widely recognized in the Northern Hemisphere, though the event\u2019s timing, about 12,000 years ago, does not appear to be equal everywhere. Also, it is difficult to find in the Southern Hemisphere. The\u00a0[pb_glossary id=\"1444\"]Holocene[\/pb_glossary]\u00a0Climatic Optimum is a warming around 6,000 years ago; it was not universally warmer, nor as warm as current warming, and not warm at the same time everywhere.\n<h3><b>15.3.2 Proxy Indicators of Past Climates<\/b><\/h3>\nHow do we know about past climates? Geologists use proxy indicators to understand past\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]. A\u00a0<strong>[pb_glossary id=\"3323\"]proxy indicator[\/pb_glossary]<\/strong>\u00a0is a biological, chemical, or physical signature preserved in the rock,\u00a0[pb_glossary id=\"2678\"]sediment[\/pb_glossary], or ice record that acts like a fingerprint of something in the past. Thus, they are an <em>indirect <\/em>indicator of [pb_glossary id=\"1710\"]climate[\/pb_glossary]. An indirect indicator of ancient\u00a0[pb_glossary id=\"1700\"]glaciations[\/pb_glossary]\u00a0from the\u00a0[pb_glossary id=\"2209\"]Proterozoic[\/pb_glossary]\u00a0[pb_glossary id=\"2190\"]Eon[\/pb_glossary] and\u00a0[pb_glossary id=\"2219\"]Paleozoic[\/pb_glossary] [pb_glossary id=\"2191\"]Era[\/pb_glossary] is the\u00a0[pb_glossary id=\"2687\"]Mineral[\/pb_glossary]\u00a0Fork\u00a0[pb_glossary id=\"2960\"]Formation[\/pb_glossary]\u00a0in Utah, which contains rock\u00a0[pb_glossary id=\"2960\"]formations[\/pb_glossary]\u00a0of\u00a0[pb_glossary id=\"2910\"]glacial[\/pb_glossary]\u00a0[pb_glossary id=\"2678\"]sediments[\/pb_glossary]\u00a0such as [pb_glossary id=\"2911\"]diamictite[\/pb_glossary] ([pb_glossary id=\"2483\"]tillite[\/pb_glossary]). \u00a0This dark rock has many fine-grained components plus some large out-sized clasts like a modern\u00a0[pb_glossary id=\"2910\"]glacial[\/pb_glossary]\u00a0[pb_glossary id=\"2912\"]till[\/pb_glossary].\n\nDeep-sea [pb_glossary id=\"2678\"]sediment[\/pb_glossary] is an indirect indicator of [pb_glossary id=\"1710\"]climate[\/pb_glossary] change during the [pb_glossary id=\"1441\"]Cenozoic[\/pb_glossary] [pb_glossary id=\"2191\"]Era[\/pb_glossary], about the last 65 million years. Researchers from the Ocean Drilling Program, an international research collaboration, collect deep-sea [pb_glossary id=\"2678\"]sediment[\/pb_glossary] cores that record continuous [pb_glossary id=\"2678\"]sediment[\/pb_glossary] accumulation. The [pb_glossary id=\"2678\"]sediment[\/pb_glossary] provides detailed chemical records of stable carbon and oxygen [pb_glossary id=\"2701\"]isotopes[\/pb_glossary] obtained from deep-sea benthic foraminifera shells that accumulated on the [pb_glossary id=\"2885\"]ocean floor[\/pb_glossary] over millions of years. The oxygen [pb_glossary id=\"2701\"]isotopes[\/pb_glossary] are a [pb_glossary id=\"3323\"]proxy indicator[\/pb_glossary] of deep-sea temperatures and [pb_glossary id=\"2575\"]continental[\/pb_glossary] ice volume.\n<h4><span style=\"font-weight: 400\">Sediment Cores - Stable Oxygen Isotopes<\/span><\/h4>\n[caption id=\"attachment_4606\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.3_sediment-core_hg.jpg\"><img class=\"wp-image-912 size-medium\" title=\"Source: Hannes Grobe, https:\/\/en.wikipedia.org\/wiki\/File:PS1920-1_0-750_sediment-core_hg.jpg#metadata\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_sediment-core_hg-300x290.jpg\" alt=\"Image of sediment core showing clear layering and vertical changes in color and composition.\" width=\"300\" height=\"290\"><\/a> Sediment core from the Greenland continental slope (Source: Hannes Grobe)[\/caption]\n\nHow do oxygen\u00a0[pb_glossary id=\"2701\"]isotopes[\/pb_glossary]\u00a0indicate past\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]? The two main stable oxygen\u00a0[pb_glossary id=\"2701\"]isotopes[\/pb_glossary]\u00a0are\u00a0<sup>16<\/sup>O and\u00a0<sup>18<\/sup>O. They both occur in water (H<sub>2<\/sub>O) and in the calcium\u00a0[pb_glossary id=\"1917\"]carbonate[\/pb_glossary]\u00a0(CaCO<sub>3<\/sub>) shells of foraminifera as both of those substances\u2019 oxygen component. The most abundant and lighter\u00a0[pb_glossary id=\"2701\"]isotope[\/pb_glossary]\u00a0is\u00a0<sup>16<\/sup>O. Since it is lighter, it evaporates more readily from the ocean\u2019s surface as water vapor, which later turns to clouds and\u00a0[pb_glossary id=\"2707\"]precipitation[\/pb_glossary]\u00a0on the ocean and land. This evaporation is enhanced in warmer sea water and slightly increases the concentration of <sup>18<\/sup>O in the surface seawater from which the plankton derives the [pb_glossary id=\"1917\"]carbonate[\/pb_glossary] for its shells. Thus the ratio of <sup>16<\/sup>O and\u00a0<sup>18<\/sup>O in the fossilized shells in seafloor [pb_glossary id=\"2678\"]sediment[\/pb_glossary] is a [pb_glossary id=\"3323\"]proxy indicator[\/pb_glossary] of the [pb_glossary id=\"2689\"]temperature[\/pb_glossary] and evaporation of seawater.\n\n[caption id=\"attachment_4607\" align=\"alignright\" width=\"446\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.3-Ice_Age_Temperature.png\"><img class=\"wp-image-913\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-Ice_Age_Temperature.png\" alt=\"Show clear chemical evidence for six glaciations over the past 450,000 years.\" width=\"446\" height=\"298\"><\/a> Antarctic temperature changes during the last few glaciations compared to global ice volume. The first two curves are based on the deuterium (heavy hydrogen) record from ice cores (EPICA Community Members 2004, Petit et al. 1999). The bottom line is ice volume based on oxygen isotopes from a composite of deep-sea sediment cores (Lisiecki and Raymo 2005).[\/caption]\n\n<span style=\"font-weight: 400\">Keep in mind, it is harder to evaporate the heavier water and easier to condense it.\u00a0 As evaporated water vapor drifts toward the poles and tiny droplets form clouds and [pb_glossary id=\"2707\"]precipitation[\/pb_glossary], droplets of water with <sup>18<\/sup>O tend to form more readily than droplets of the lighter form and [pb_glossary id=\"2707\"]precipitate[\/pb_glossary] out, leaving the drifting vapor depleted in <sup>18<\/sup>O. During geologic times when the [pb_glossary id=\"1710\"]climate[\/pb_glossary] is cooler, more of this lighter [pb_glossary id=\"2707\"]precipitation[\/pb_glossary] that [pb_glossary id=\"3119\"]falls[\/pb_glossary] on land is locked in the form of [pb_glossary id=\"2910\"]glacial[\/pb_glossary] ice. Consider that the giant [pb_glossary id=\"2467\"]ice sheets[\/pb_glossary] were more than a mile thick and covered a large part of North America during the last [pb_glossary id=\"1700\"]ice age[\/pb_glossary] only 14,000 years ago. During [pb_glossary id=\"1700\"]glaciation[\/pb_glossary], the [pb_glossary id=\"2464\"]glaciers[\/pb_glossary] thus effectively lock away more <\/span><sup><span style=\"font-weight: 400\">16<\/span><\/sup><span style=\"font-weight: 400\">O, thus the ocean water and foraminifera shells become enriched in <\/span><sup><span style=\"font-weight: 400\">18<\/span><\/sup><span style=\"font-weight: 400\">O.\u00a0<\/span><span style=\"font-weight: 400\">Therefore, the ratio of <\/span><sup><span style=\"font-weight: 400\">18<\/span><\/sup><span style=\"font-weight: 400\">O to <\/span><sup><span style=\"font-weight: 400\">16<\/span><\/sup><span style=\"font-weight: 400\">O (\ud835\udeff<\/span><sup><span style=\"font-weight: 400\">18<\/span><\/sup><span style=\"font-weight: 400\">O) in calcium [pb_glossary id=\"1917\"]carbonate[\/pb_glossary] shells of foraminifera is a [pb_glossary id=\"3323\"]proxy indicator[\/pb_glossary] of past [pb_glossary id=\"1710\"]climate[\/pb_glossary]. The [pb_glossary id=\"2678\"]sediment[\/pb_glossary] cores from the Ocean Drilling Program record a continuous accumulation of these [pb_glossary id=\"2176\"]fossils[\/pb_glossary] in the [pb_glossary id=\"2678\"]sediment[\/pb_glossary] and provide a record of glacials,\u00a0 [pb_glossary id=\"3321\"]interglacials[\/pb_glossary] and [pb_glossary id=\"3322\"]interstadials[\/pb_glossary].<\/span>\n<h4><span style=\"font-weight: 400\">Sediment Cores - Boron-Isotopes and Acidity<\/span><\/h4>\nOcean acidity is affected by [pb_glossary id=\"2813\"]carbonic acid[\/pb_glossary] and is a proxy for past atmospheric CO<sub>2<\/sub> concentrations. To estimate the ocean\u2019s pH (acidity) over the past 60 million years, researchers collected deep-sea [pb_glossary id=\"2678\"]sediment[\/pb_glossary] cores and examined the ancient planktonic foraminifera shells\u2019 boron-[pb_glossary id=\"2701\"]isotope[\/pb_glossary] ratios. Boron has two [pb_glossary id=\"2701\"]isotopes[\/pb_glossary]:\u00a0<sup data-preserve-html-node=\"true\">11<\/sup>B and\u00a0<sup data-preserve-html-node=\"true\">10<\/sup>B. In aqueous compounds of boron, the relative abundance of these two [pb_glossary id=\"2701\"]isotopes[\/pb_glossary] is sensitive to pH (acidity), hence CO<sub>2<\/sub> concentrations. In the early [pb_glossary id=\"1441\"]Cenozoic[\/pb_glossary], around 60 million years ago, CO<sub>2<\/sub> concentrations were over 2,000 ppm, higher pH, and started falling around 55 to 40 million years ago, with noticeable drop in pH, indicated by boron [pb_glossary id=\"2701\"]isotope[\/pb_glossary] ratios. The drop was possibly due to reduced CO<sub>2<\/sub>\u00a0outgassing from ocean ridges,\u00a0[pb_glossary id=\"1181\"]volcanoes[\/pb_glossary]\u00a0and\u00a0[pb_glossary id=\"2914\"]metamorphic[\/pb_glossary]\u00a0belts, and increased carbon burial due to [pb_glossary id=\"2602\"]subduction[\/pb_glossary] and the Himalaya Mountains uplift. By the Miocene [pb_glossary id=\"2193\"]Epoch[\/pb_glossary], about 24 million years ago, CO<sub>2<\/sub>\u00a0levels were below 500 ppm,\u00a0and by 800,000 years ago, CO<sup>2<\/sup>\u00a0levels didn\u2019t exceed 300 ppm.\n<h4><span style=\"font-weight: 400\">Carbon Dioxide Concentrations in Ice Cores<\/span><\/h4>\n[caption id=\"attachment_4608\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.3_GISP2_1855m_ice_core_layers.png\"><img class=\"size-medium wp-image-914\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_GISP2_1855m_ice_core_layers-300x136.png\" alt=\"Image of ice core showing seasonal color changes like a tree rings.\" width=\"300\" height=\"136\"><\/a> 19 cm long section of ice core showing 11 annual layers with summer layers (arrowed) sandwiched between darker winter layers. (Source: US Army Corps of Engineers)[\/caption]\n\nFor the recent Pleistocene\u00a0[pb_glossary id=\"2193\"]Epoch[\/pb_glossary]\u2019s [pb_glossary id=\"1710\"]climate[\/pb_glossary],\u00a0researchers get a more detailed and direct chemical record of the last 800,000 years by extracting and analyzing ice cores from the Antarctic and Greenland\u00a0[pb_glossary id=\"2467\"]ice sheets[\/pb_glossary]. Snow accumulates on these\u00a0[pb_glossary id=\"2467\"]ice sheets[\/pb_glossary]\u00a0and creates yearly layers. Oxygen\u00a0[pb_glossary id=\"2467\"]isotopes[\/pb_glossary]\u00a0are collected from these annual layers, and the ratio of\u00a0<sup>18<\/sup>O to\u00a0<sup>16<\/sup>O (\ud835\udeff<sup>18<\/sup>O) is used to determine [pb_glossary id=\"2689\"]temperature[\/pb_glossary] as discussed above. In addition, the ice contains small bubbles of atmospheric gas as the snow turns to ice. Analysis of these bubbles reveals the [pb_glossary id=\"2831\"]composition[\/pb_glossary] of the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] at these previous times.\n\n[caption id=\"attachment_4609\" align=\"alignright\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.3_Air_Bubbles_Trapped_in_Ice.jpg\"><img class=\"wp-image-915 size-medium\" title=\"Source: Commonwealth Scientific and Industrial Research Organization (Australia) - https:\/\/en.wikipedia.org\/wiki\/File:CSIRO_ScienceImage_518_Air_Bubbles_Trapped_in_Ice.jpg\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Air_Bubbles_Trapped_in_Ice-300x205.jpg\" alt=\"Antarctic ice showing hundreds of tiny trapped air bubbles from the atmosphere thousands of years ago.\" width=\"300\" height=\"205\"><\/a> Antarctic ice showing hundreds of tiny trapped air bubbles from the atmosphere thousands of years ago. (Source: CSIRO)[\/caption]\n\nSmall pieces of this ice are crushed, and the ancient air is extracted into a\u00a0[pb_glossary id=\"2174\"]mass spectrometer[\/pb_glossary]\u00a0that can detect the ancient\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]\u2019s chemistry. Carbon dioxide levels are recreated from these measurements. Over the last 800,000 years, the <em>maximum<\/em> carbon dioxide concentration during warm times was about 300 parts per million (ppm), and the minimum was about 170 ppm during cold stretches. Currently, the earth\u2019s\u00a0atmospheric\u00a0carbon dioxide content is over 410 ppm.\n\n[caption id=\"attachment_4610\" align=\"aligncenter\" width=\"818\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.3_Co2_glacial_cycles_800k.png\"><img class=\"size-full wp-image-916\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Co2_glacial_cycles_800k.png\" alt=\"Graph shows concentrations of carbon dioxide around 290 ppm during warm periods and 190 ppm during glacial periods. Total time frame is about 800,000 years.\" width=\"818\" height=\"580\"><\/a> Composite carbon dioxide record from last 800,000 years based on ice core data from EPICA Dome C Ice Core.[\/caption]\n<h4><span style=\"font-weight: 400\">Oceanic Microfossils<\/span><\/h4>\nMicrofossils, like foraminifera, diatoms, and radiolarians can be used as a proxy to interpret past [pb_glossary id=\"1710\"]climate[\/pb_glossary] record. Different species of microfossils are found in the [pb_glossary id=\"3384\"]sediment[\/pb_glossary] [pb_glossary id=\"2589\"]core[\/pb_glossary]\u2019s different layers. Microfossil groups are called assemblages and their [pb_glossary id=\"2831\"]composition[\/pb_glossary] differs depending on the climatic conditions when they lived. One assemblage consists of species that lived in cooler ocean water, such as in [pb_glossary id=\"2910\"]glacial[\/pb_glossary] times, and at a different level in the same [pb_glossary id=\"3384\"]sediment[\/pb_glossary] [pb_glossary id=\"2589\"]core[\/pb_glossary], another assemblage consists of species that lived in warmer waters.\n\n[caption id=\"attachment_4870\" align=\"alignleft\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/Climatic-Evidence-From-Sediments-Youtube-QR-Code.png\"><img class=\"size-thumbnail wp-image-917\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Climatic-Evidence-From-Sediments-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access this YouTube video via this QR Code.[\/caption]\n\n[embed]https:\/\/www.youtube.com\/embed\/Yvu-g8BkkIg[\/embed]\n<h4><span style=\"font-weight: 400\">Tree Rings<\/span><\/h4>\n[caption id=\"attachment_4611\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.3_Tree.rings_.jpg\"><img class=\"size-medium wp-image-918\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Tree.rings_-300x225.jpg\" alt=\"Shows a tree cut in cross-section with tree rings. Each ring form in one year.\" width=\"300\" height=\"225\"><\/a> Tree rings form every year. Rings that are farther apart are from wetter years and rings that are closer together are from dryer years.[\/caption]\n\nTree rings, which form every year as a tree grows, are another past [pb_glossary id=\"1710\"]climate[\/pb_glossary] indicator. Rings that are thicker indicate wetter years, and rings that are thinner and closer together indicate dryer years. Every year, a tree will grow one ring with a light section and a dark section. The rings vary in width. Since trees need much water to survive, narrower rings indicate colder and drier climates. Since some trees are several thousand years old, scientists can use their rings for regional paleoclimatic reconstructions, for example, to reconstruct past [pb_glossary id=\"2689\"]temperature[\/pb_glossary], [pb_glossary id=\"2707\"]precipitation[\/pb_glossary], vegetation, streamflow, sea-surface [pb_glossary id=\"2689\"]temperature[\/pb_glossary], and other [pb_glossary id=\"1710\"]climate[\/pb_glossary]-dependent conditions. Paleoclimatic study means relating to a distinct past geologic climate. Also, dead trees, such as those found in Puebloan ruins, can be used to extend this\u00a0[pb_glossary id=\"3323\"]proxy indicator[\/pb_glossary] by showing long-term droughts in the region and possibly explain why villages were abandoned.\n\n[caption id=\"attachment_4612\" align=\"aligncenter\" width=\"1024\"]<a style=\"font-weight: bold;background-color: transparent;text-align: inherit\" href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.3_Tree-Ring-Temperature-Anamoly_Yamal50.gif\"><img class=\"wp-image-919 size-large\" title=\"Source: R.M.Hantemirov - https:\/\/en.wikipedia.org\/wiki\/File:Yamal50.gif\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Tree-Ring-Temperature-Anamoly_Yamal50-1024x224.gif\" alt=\"Tree ring data from last 7000 years showing average summer highs and lows fluctuating around a mean. Last few hundred years are slightly higher than normal.\" width=\"1024\" height=\"224\"><\/a> <span style=\"text-align: justify;font-size: 1em\">Summer [pb_glossary id=\"2689\"]temperature[\/pb_glossary] [pb_glossary id=\"1719\"]anomalies[\/pb_glossary] for the past 7000 years (Source: R.M.Hantemirov)<\/span>[\/caption]\n<h4><span style=\"font-weight: 400\">Pollen<\/span><\/h4>\n[caption id=\"attachment_4613\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.3_Misc_pollen_colorized.jpg\"><img class=\"wp-image-920 size-medium\" title=\"Source: Dartmouth Electron Microscope Facility, Dartmouth College - https:\/\/en.wikipedia.org\/wiki\/File:Misc_pollen_colorized.jpg\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Misc_pollen_colorized-300x228.jpg\" alt=\"Close up image of what pollen looks like.\" width=\"300\" height=\"228\"><\/a> Scanning electron microscope image of modern pollen with false color added to distinguish plant species.[\/caption]\n\nPollen is also a proxy [pb_glossary id=\"1710\"]climate[\/pb_glossary] indicator. Flowering plants produce pollen grains. Pollen grains are distinctive when viewed under a microscope. Sometimes, pollen is preserved in lake [pb_glossary id=\"2678\"]sediments[\/pb_glossary] that accumulate in layers every year. Lake-[pb_glossary id=\"2678\"]sediment[\/pb_glossary] cores can reveal ancient pollen. [pb_glossary id=\"2176\"]Fossil[\/pb_glossary]-pollen assemblages are pollen groups from multiple species, such as spruce, pine, and oak. Through time, via the [pb_glossary id=\"2678\"]sediment[\/pb_glossary] cores and radiometric age-dating techniques, the pollen assemblages change, revealing the plants that lived in the area at the time. Thus, the pollen assemblages are a past [pb_glossary id=\"1710\"]climate[\/pb_glossary] indicator, since different plants will prefer different climates. For example, in the Pacific Northwest, east of the Cascades in a region close to grassland and forest borders, scientists tracked pollen over the last 125,000 years, covering the last two [pb_glossary id=\"1700\"]glaciations[\/pb_glossary]. As shown in the figure (Fig. 2 from reference Whitlock and Bartlein 1997), pollen assemblages with more pine tree pollen are found during [pb_glossary id=\"1700\"]glaciations[\/pb_glossary] and pollen assemblages with less pine tree pollen are found during [pb_glossary id=\"3321\"]interglacial[\/pb_glossary] times.\n<h4><span style=\"font-weight: 400\">Other Proxy Indicators<\/span><\/h4>\nPaleoclimatologists study many other phenomena to understand past climates, such as human historical accounts, human instrument records from the recent past, lake\u00a0[pb_glossary id=\"2678\"]sediments[\/pb_glossary], cave deposits, and corals.\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"104\"]\n\n[caption id=\"attachment_4866\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/15.3-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-921\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 15.3 via this QR Code.[\/caption]\n<h2><span style=\"font-weight: 400\">15.4 Anthropogenic Causes of Climate Change<\/span><\/h2>\nAs shown in the previous section, prehistoric [pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0changes occur slowly over many millions of years. The\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0changes observed today are rapid and largely human caused. Evidence shows that\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0is changing, but what is causing that change? Since the late 1800s, scientists have suspected that human-produced, i.e. [pb_glossary id=\"1717\"]anthropogenic[\/pb_glossary] changes in atmospheric greenhouse gases would likely cause\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0change because changes in these gases have been the case every time in the geologic past. By the middle 1900s, scientists began conducting systematic measurements, which confirmed that human-produced carbon dioxide was accumulating in the\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]\u00a0and other earth systems, such as forests and oceans. By the end of the 1900s and into the early 2000s, scientists solidified the\u00a0<strong>[pb_glossary id=\"2655\"]Theory[\/pb_glossary]\u00a0of\u00a0[pb_glossary id=\"1717\"]Anthropogenic[\/pb_glossary]\u00a0[pb_glossary id=\"1710\"]Climate[\/pb_glossary]\u00a0Change<\/strong> when evidence from thousands of ground-based studies and continuous land and ocean satellite measurements mounted, revealing the expected\u00a0[pb_glossary id=\"2689\"]temperature[\/pb_glossary]\u00a0increase. The\u00a0[pb_glossary id=\"2655\"]Theory[\/pb_glossary]\u00a0of\u00a0[pb_glossary id=\"1717\"]Anthropogenic[\/pb_glossary]\u00a0[pb_glossary id=\"1710\"]Climate[\/pb_glossary]\u00a0Change is that humans are causing most of the current climate changes\u00a0by burning\u00a0[pb_glossary id=\"3336\"]fossil fuels[\/pb_glossary]\u00a0such as\u00a0[pb_glossary id=\"2856\"]coal[\/pb_glossary],\u00a0[pb_glossary id=\"3338\"]oil[\/pb_glossary], and\u00a0[pb_glossary id=\"3339\"]natural gas[\/pb_glossary]. Theories evolve and\u00a0[pb_glossary id=\"2601\"]transform[\/pb_glossary]\u00a0as new data and new techniques become available, and they represent a particular field\u2019s state of thinking. This section summarizes the scientific consensus of\u00a0[pb_glossary id=\"1717\"]anthropogenic[\/pb_glossary]\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0change.\n<h3><b>15.4.1 Scientific Consensus<\/b><\/h3>\nThe overwhelming majority of\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0studies indicate that human activity is causing rapid changes to the\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary], which will cause severe environmental damage. There is strong scientific consensus on the issue. Studies published in peer-reviewed scientific journals show that 97 percent of\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0scientists agree that\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0warming is caused from human activities. There is no alternative explanation for the observed link between human-produced greenhouse gas emissions and changing modern\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]. Most leading scientific organizations endorse this position, including the U.S. National Academy of Science, which was established in 1863 by an act of Congress under President Lincoln. Congress charged the National Academy of Science \u201cwith providing independent,\u00a0[pb_glossary id=\"2644\"]objective[\/pb_glossary]\u00a0advice to the nation on matters related to science and technology.\u201d Therefore, the National Academy of Science is the leading authority when it comes to policy advice related to scientific issues.\n\nOne way we know that the increased greenhouse gas emissions are from human activities is with isotopic fingerprints. For example,\u00a0[pb_glossary id=\"3336\"]fossil fuels[\/pb_glossary], representing plants that lived millions of years ago,\u00a0have a stable carbon-13 to carbon-12 (<sup>13<\/sup>C\/<sup>12<\/sup>C) ratio that is different from today\u2019s atmospheric stable-carbon ratio ([pb_glossary id=\"2966\"]radioactive[\/pb_glossary] <sup>14<\/sup>C is unstable). Isotopic carbon signatures have been used to identify [pb_glossary id=\"1717\"]anthropogenic[\/pb_glossary] carbon in the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] since the 1980s. Isotopic records from the Antarctic [pb_glossary id=\"2467\"]Ice Sheet[\/pb_glossary] show stable isotopic signatures from ~1000 AD to ~1800 AD and a steady isotopic signature gradually changing since 1800, followed by a more rapid change after 1950 as burning of [pb_glossary id=\"3336\"]fossil fuels[\/pb_glossary] dilutes the CO<sub>2<\/sub> in the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]. These changes show the\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]\u00a0as having a carbon isotopic signature increasingly more similar to that of\u00a0[pb_glossary id=\"3336\"]fossil fuels[\/pb_glossary].\n<h3><b>15.4.2 Anthropogenic Sources of Greenhouse Gases<\/b><\/h3>\n<span style=\"font-weight: 400\">[pb_glossary id=\"1717\"]Anthropogenic[\/pb_glossary] emissions of greenhouse gases have increased since pre-industrial times due to global economic growth and population growth. Atmospheric concentrations of the leading greenhouse gas, carbon dioxide, are at unprecedented levels that haven\u2019t been observed in at least the last 800,000 years<\/span><span style=\"font-weight: 400\">. Pre-industrial level of carbon dioxide was at about 278 parts per million (ppm). As of 2016, carbon dioxide was, for the first time, above 400 ppm for the entirety of the year. Measurements of atmospheric carbon at the Mauna Loa Carbon Dioxide Observatory show a continuous increase since 1957 when the observatory was established from 315 ppm to over 417 ppm in 2022. The daily reading today can be seen at <a href=\"https:\/\/www.co2.earth\/daily-co2\">Daily CO2<\/a>.\u00a0 Based on the ice [pb_glossary id=\"2589\"]core[\/pb_glossary] record over the past 800,000 years, carbon dioxide ranged from about 185 ppm during [pb_glossary id=\"1700\"]ice ages[\/pb_glossary] to 300 ppm during warm times<\/span><span style=\"font-weight: 400\">. View the <\/span><span style=\"font-weight: 400\">data-accurate NOAA animation below\u00a0<\/span><span style=\"font-weight: 400\">of carbon dioxide trends over the last 800,000 years.<\/span>\n\n[caption id=\"attachment_4614\" align=\"alignleft\" width=\"300\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.4_Fig-1.7-from-Pachauri-et-al-2014.jpg\"><img class=\"wp-image-922 size-medium\" title=\"Source: Pachauri et al. 2014 - IPCC Climate Change 2014 Synthesis Report - https:\/\/www.ipcc.ch\/pdf\/assessment-report\/ar5\/syr\/AR5_SYR_FINAL_All_Topics.pdf\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4_Fig-1.7-from-Pachauri-et-al-2014-300x268.jpg\" alt=\"Pie chart shows\" width=\"300\" height=\"268\"><\/a> Total anthropogenic greenhouse gas emissions (gigatonne of CO2- equivalent per year, GtCO2-eq\/yr) from economic sectors in 2010. The circle shows the shares of direct GHG emissions (in % of total anthropogenic GHG emissions) from five economic sectors in 2010. The pull-out shows how shares of indirect CO2 emissions (in % of total anthropogenic GHG emissions) from electricity and heat production are attributed to sectors of final energy use. (Source: Pachauri et al. 2014)[\/caption]\n\nWhat is the source of these\u00a0[pb_glossary id=\"1717\"]anthropogenic[\/pb_glossary]\u00a0greenhouse gas emissions?\u00a0[pb_glossary id=\"3336\"]Fossil fuel[\/pb_glossary]\u00a0combustion and industrial processes contributed 78 percent of all emissions since 1970. The economic sectors responsible for most of this include electricity and heat production (25 percent); agriculture, forestry, and land use (24 percent); industry (21 percent); transportation, including automobiles (14 percent); other energy production (9.6 percent); and buildings (6.4 percent). More than half of greenhouse gas emissions have occurred in the last 40 years, and 40 percent of these emissions have stayed in the\u00a0[pb_glossary id=\"2667\"]atmosphere[\/pb_glossary]. Unfortunately, despite scientific consensus, efforts to mitigate\u00a0[pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0change require political action.\u00a0Despite growing [pb_glossary id=\"1710\"]climate[\/pb_glossary]\u00a0change concern, mitigation efforts, legislation, and international agreements have reduced emissions in some places, yet the less developed world\u2019s continual economic growth has increased global greenhouse gas emissions. In fact, the years 2000 to 2010 saw the largest increases since 1970.\n\n[caption id=\"attachment_4615\" align=\"aligncenter\" width=\"1024\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.4_Fig-1.5-Pachauri-et-al.-2014-emissions-1850-2011.jpg\"><img class=\"wp-image-923 size-large\" title=\"Source: Pachauri et al. 2014 Fig. 1.5 IPCC Climate Change 2014 Synthesis Report - https:\/\/www.ipcc.ch\/pdf\/assessment-report\/ar5\/syr\/AR5_SYR_FINAL_All_Topics.pdf\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4_Fig-1.5-Pachauri-et-al.-2014-emissions-1850-2011-1024x396.jpg\" alt=\"Graph shows carbon emissions from fossil fuel combustion increase notable around 1950 and continue to increase consistently until the graph ends in 2011.\" width=\"1024\" height=\"396\"><\/a> Annual global anthropogenic carbon dioxide (CO2) emissions in gigatonne of CO2-equivalent per year (GtCO2\/yr) from fossil fuel combustion, cement production and flaring, and forestry and other land use (FOLU), 1750\u20132011. Cumulative emissions and their uncertainties are shown as bars and whiskers[\/caption]\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n[h5p id=\"105\"]\n\n[caption id=\"attachment_4867\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/15.4-Did-I-Get-It-QR-Code.png\"><img class=\"size-thumbnail wp-image-924\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the quiz for section 15.4 via this QR Code.[\/caption]\n<h3>Summary<\/h3>\nIncluded in Earth Science is the study of the [pb_glossary id=\"2664\"]system[\/pb_glossary] of processes that affect surface environments and [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] of the Earth. Recent changes in atmospheric [pb_glossary id=\"2689\"]temperature[\/pb_glossary] and [pb_glossary id=\"1710\"]climate[\/pb_glossary] over intervals of decades have been observed. For Earth\u2019s [pb_glossary id=\"1710\"]climate[\/pb_glossary] to be stable, incoming radiation from the sun and outgoing radiation from the sun-warmed Earth must be in balance. Gases in the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] called greenhouse gases absorb the infrared thermal radiation from the Earth\u2019s surface, trapping that heat and warming the atmosphere, a process called the [pb_glossary id=\"1715\"]Greenhouse Effect[\/pb_glossary]. Thus the energy budget is not now in balance and the Earth is warming. Human activity produces many greenhouse gases that have accelerated [pb_glossary id=\"1710\"]climate[\/pb_glossary] change. CO2 from [pb_glossary id=\"3336\"]fossil fuel[\/pb_glossary] burning is one of the major ones. While atmospheric [pb_glossary id=\"2831\"]composition[\/pb_glossary] is mostly nitrogen and oxygen, trace components including the greenhouse gases (CO2 and methane are the major ones and there are others) have the greatest effect on global warming.\n\nA number of [pb_glossary id=\"1713\"]Positive Feedback[\/pb_glossary] Mechanisms, processes whose results reinforce the original process, take place in the Earth [pb_glossary id=\"2664\"]system[\/pb_glossary]. An example of a PFM of great concern is [pb_glossary id=\"1712\"]permafrost[\/pb_glossary] melting which causes decay of melting organic material that produces CO2 and methane (both powerful greenhouse gases) that warm the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] and promote more [pb_glossary id=\"1712\"]permafrost[\/pb_glossary] melting. Two carbon cycles affect Earth\u2019s atmospheric CO2 [pb_glossary id=\"2831\"]composition[\/pb_glossary], the biologic carbon cycle and the geologic carbon cycle. In the biologic cycle, organisms (mostly plants and also animals that eat them) remove CO2 from the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] for energy and to build their body tissues and return it to the [pb_glossary id=\"2667\"]atmosphere[\/pb_glossary] when they die and decay. The biologic cycle is a rapid cycle. In the geologic cycle, some organic matter is preserved in the form of [pb_glossary id=\"3337\"]petroleum[\/pb_glossary] and [pb_glossary id=\"2856\"]coal[\/pb_glossary] while more is [pb_glossary id=\"2815\"]dissolved[\/pb_glossary] in seawater and captured in [pb_glossary id=\"1917\"]carbonate[\/pb_glossary] [pb_glossary id=\"2678\"]sediments[\/pb_glossary], some of which is [pb_glossary id=\"2602\"]subducted[\/pb_glossary] into the [pb_glossary id=\"2586\"]mantle[\/pb_glossary] and returned by [pb_glossary id=\"1181\"]volcanic[\/pb_glossary] activity. The geologic carbon cycle is slow over geologic time.\n\nMeasurements of increasing atmospheric [pb_glossary id=\"2689\"]temperature[\/pb_glossary] have been made since the nineteenth century but the upward [pb_glossary id=\"2689\"]temperature[\/pb_glossary] trend itself increased in the mid twentieth century showing the current trend is exponential. Because of the high specific heat of water, the oceans have absorbed most of the added heat. That this is temporary storage is revealed by the record-breaking warm years of the recent decade and the increase in intense storms and hurricanes. In 1957 the Mauna Loa CO2 Observatory was established in Hawaii providing constant measurements of atmospheric CO2 since 1958. The initial value was 315 ppm. The Keeling curve, named for the observatory founder, shows that value has steadily increased, exponentially, to over 417 ppm now. Compared to proxy data from atmospheric gases trapped in ice cores that show a maximum value for CO2 of about 300 ppm over the last 800,000 years, the Keeling increase of over 100 ppm in 50 years is dramatic evidence of human caused CO2 increase and [pb_glossary id=\"1710\"]climate[\/pb_glossary] change! As Earth\u2019s [pb_glossary id=\"2689\"]temperature[\/pb_glossary] rises, [pb_glossary id=\"2464\"]glaciers[\/pb_glossary] and [pb_glossary id=\"2467\"]ice sheets[\/pb_glossary] are shrinking resulting in sea level rise. Atmospheric CO2 is also absorbed in sea water producing increased concentrations of [pb_glossary id=\"2813\"]carbonic acid[\/pb_glossary] which is raising the pH of the oceans making it harder for [pb_glossary id=\"2883\"]marine[\/pb_glossary] life to extract [pb_glossary id=\"1917\"]carbonate[\/pb_glossary] for their skeletal materials.\n\nEarth\u2019s [pb_glossary id=\"1710\"]climate[\/pb_glossary] has changed over geologic time with [pb_glossary id=\"2192\"]periods[\/pb_glossary] of major [pb_glossary id=\"1700\"]glaciations[\/pb_glossary]. There was a high [pb_glossary id=\"2689\"]temperature[\/pb_glossary] [pb_glossary id=\"2192\"]period[\/pb_glossary] in the [pb_glossary id=\"1432\"]Mesozoic[\/pb_glossary] shown by fossils in high latitudes and the Western Interior Seaway covering what is now the Midwest. However, [pb_glossary id=\"1710\"]climate[\/pb_glossary] has been cooling during the [pb_glossary id=\"1441\"]Cenozoic[\/pb_glossary] culminating in the [pb_glossary id=\"1700\"]Ice Age[\/pb_glossary]. Since the [pb_glossary id=\"1700\"]Ice Age[\/pb_glossary], several proxy indicators of ancient [pb_glossary id=\"1710\"]climate[\/pb_glossary] show that the rate and amount of current [pb_glossary id=\"1710\"]climate[\/pb_glossary] change is unique in geologic history and can only be attributed to human activity. Those who ignore the consequences of increasing global warming for our planet\u2019s future do so at the peril of our posterity!\n<h3>Take this quiz to check your comprehension of this Chapter.<\/h3>\n[h5p id=\"106\"]\n\n[caption id=\"attachment_4869\" align=\"aligncenter\" width=\"150\"]<a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/Ch.15-Review-QR-Code.png\"><img class=\"size-thumbnail wp-image-925\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.15-Review-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\"><\/a> If you are using the printed version of this OER, access the review quiz for Chapter 15 via this QR Code[\/caption]\n<h2><b>References<\/b><\/h2>\n<div class=\"csl-bib-body\">\n<ol>\n \t<li class=\"csl-entry\">Allen, P.A., and Etienne, J.L., 2008, Sedimentary challenge to [pb_glossary id=\"1718\"]Snowball Earth[\/pb_glossary]: Nat. Geosci., v. 1, no. 12, p. 817\u2013825.<\/li>\n \t<li class=\"csl-entry\">Berner, R.A., 1998, The carbon cycle and carbon dioxide over [pb_glossary id=\"2217\"]Phanerozoic[\/pb_glossary] time: the role of land plants: Philos. Trans. R. Soc. Lond. B Biol. Sci., v. 353, no. 1365, p. 75\u201382.<\/li>\n \t<li class=\"csl-entry\">Cunningham, W.L., Leventer, A., Andrews, J.T., Jennings, A.E., and Licht, K.J., 1999, Late Pleistocene\u2013[pb_glossary id=\"1444\"]Holocene[\/pb_glossary] [pb_glossary id=\"2883\"]marine[\/pb_glossary] conditions in the Ross Sea, Antarctica: evidence from the diatom record: The [pb_glossary id=\"1444\"]Holocene[\/pb_glossary], v. 9, no. 2, p. 129\u2013139.<\/li>\n \t<li class=\"csl-entry\">Deynoux, M., Miller, J.M.G., and Domack, E.W., 2004, Earth\u2019s [pb_glossary id=\"2910\"]Glacial[\/pb_glossary] Record: World and Regional Geology, Cambridge University Press, World and Regional Geology.<\/li>\n \t<li class=\"csl-entry\">Earle, S., 2015, Physical geology OER textbook: BC Campus OpenEd.<\/li>\n \t<li class=\"csl-entry\">Eyles, N., and Januszczak, N., 2004, \u201cZipper-[pb_glossary id=\"2624\"]rift[\/pb_glossary]\u201d: a [pb_glossary id=\"2576\"]tectonic[\/pb_glossary] model for Neoproterozoic [pb_glossary id=\"1700\"]glaciations[\/pb_glossary] during the breakup of [pb_glossary id=\"2211\"]Rodinia[\/pb_glossary] after 750 Ma: Earth-Sci. Rev.<\/li>\n \t<li class=\"csl-entry\">Francey, R.J., Allison, C.E., Etheridge, D.M., Trudinger, C.M., and others, 1999, A 1000\u2010year high precision record of \u03b413C in atmospheric CO2: Tellus B Chem. Phys. Meteorol.<\/li>\n \t<li class=\"csl-entry\">Gutro, R., 2005, NASA - What\u2019s the Difference Between [pb_glossary id=\"1709\"]Weather[\/pb_glossary] and [pb_glossary id=\"1710\"]Climate[\/pb_glossary]? Online, <a href=\"http:\/\/www.nasa.gov\/mission_pages\/noaa-n\/climate\/climate_weather.html\">http:\/\/www.nasa.gov\/mission_pages\/noaa-n\/climate\/climate_weather.html<\/a>, accessed September 2016.<\/li>\n \t<li class=\"csl-entry\">Hoffman, P.F., Kaufman, A.J., Halverson, G.P., and Schrag, D.P., 1998, A neoproterozoic [pb_glossary id=\"1718\"]snowball earth[\/pb_glossary]: Science, v. 281, no. 5381, p. 1342\u20131346.<\/li>\n \t<li class=\"csl-entry\">Kopp, R.E., Kirschvink, J.L., Hilburn, I.A., and Nash, C.Z., 2005, The Paleoproterozoic [pb_glossary id=\"1718\"]snowball Earth[\/pb_glossary]: a [pb_glossary id=\"1710\"]climate[\/pb_glossary] disaster triggered by the evolution of oxygenic photosynthesis: Proc. Natl. Acad. Sci. U. S. A., v. 102, no. 32, p. 11131\u201311136.<\/li>\n \t<li class=\"csl-entry\">Lean, J., Beer, J., and Bradley, R., 1995, Reconstruction of solar irradiance since 1610: Implications for [pb_glossary id=\"1710\"]climate[\/pb_glossary] cbange: Geophys. Res. Lett., v. 22, no. 23, p. 3195\u20133198.<\/li>\n \t<li class=\"csl-entry\">Levitus, S., Antonov, J.I., Wang, J., Delworth, T.L., Dixon, K.W., and Broccoli, A.J., 2001, [pb_glossary id=\"1717\"]Anthropogenic[\/pb_glossary] warming of Earth\u2019s [pb_glossary id=\"1710\"]climate[\/pb_glossary] [pb_glossary id=\"2664\"]system[\/pb_glossary]: Science, v. 292, no. 5515, p. 267\u2013270.<\/li>\n \t<li class=\"csl-entry\">Lindsey, R., 2009, [pb_glossary id=\"1710\"]Climate[\/pb_glossary] and Earth\u2019s Energy Budget\u202f: Feature Articles: Online, <a href=\"http:\/\/earthobservatory.nasa.gov\">http:\/\/earthobservatory.nasa.gov<\/a>, accessed September 2016.<\/li>\n \t<li class=\"csl-entry\">North Carolina State University, 2013a, [pb_glossary id=\"2831\"]Composition[\/pb_glossary] of the [pb_glossary id=\"2667\"]Atmosphere[\/pb_glossary]:<\/li>\n \t<li class=\"csl-entry\">North Carolina State University, 2013b, [pb_glossary id=\"2831\"]Composition[\/pb_glossary] of the [pb_glossary id=\"2667\"]Atmosphere[\/pb_glossary]: Online, <a href=\"http:\/\/climate.ncsu.edu\/edu\/k12\/.AtmComposition\">http:\/\/climate.ncsu.edu\/edu\/k12\/.AtmComposition<\/a>, accessed September 2016.<\/li>\n \t<li class=\"csl-entry\">Oreskes, N., 2004, The scientific consensus on [pb_glossary id=\"1710\"]climate[\/pb_glossary] change: Science, v. 306, no. 5702, p. 1686\u20131686.<\/li>\n \t<li class=\"csl-entry\">Pachauri, R.K., Allen, M.R., Barros, V.R., Broome, J., Cramer, W., Christ, R., Church, J.A., Clarke, L., Dahe, Q., Dasgupta, P., Dubash, N.K., Edenhofer, O., Elgizouli, I., Field, C.B., and others, 2014, [pb_glossary id=\"1710\"]Climate[\/pb_glossary] Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on [pb_glossary id=\"1710\"]Climate[\/pb_glossary] Change (R. K. Pachauri &amp; L. Meyer, Eds.): Geneva, Switzerland, IPCC, 151 p.<\/li>\n \t<li class=\"csl-entry\">Santer, B.D., Mears, C., Wentz, F.J., Taylor, K.E., Gleckler, P.J., Wigley, T.M.L., Barnett, T.P., Boyle, J.S., Br\u00fcggemann, W., Gillett, N.P., Klein, S.A., Meehl, G.A., Nozawa, T., Pierce, D.W., and others, 2007, Identification of human-induced changes in atmospheric moisture content: Proc. Natl. Acad. Sci. U. S. A., v. 104, no. 39, p. 15248\u201315253.<\/li>\n \t<li class=\"csl-entry\">Schopf, J.W., and Klein, C., 1992, Late [pb_glossary id=\"2209\"]Proterozoic[\/pb_glossary] Low-[pb_glossary id=\"3372\"]Latitude[\/pb_glossary] Global [pb_glossary id=\"1700\"]Glaciation[\/pb_glossary]: the [pb_glossary id=\"1718\"]Snowball Earth[\/pb_glossary], <i>in<\/i> Schopf, J.W., and Klein, C., editors, The [pb_glossary id=\"2209\"]Proterozoic[\/pb_glossary] [pb_glossary id=\"2669\"]biosphere\u202f[\/pb_glossary]: a multidisciplinary study: New York, Cambridge University Press, p. 51\u201352.<\/li>\n \t<li class=\"csl-entry\">Webb, T., and Thompson, W., 1986, Is vegetation in equilibrium with [pb_glossary id=\"1710\"]climate[\/pb_glossary]? How to interpret late-[pb_glossary id=\"1443\"]Quaternary[\/pb_glossary] pollen data: Vegetatio, v. 67, no. 2, p. 75\u201391.<\/li>\n \t<li class=\"csl-entry\">Weissert, H., 2000, Deciphering methane\u2019s fingerprint: Nature, v. 406, no. 6794, p. 356\u2013357.<\/li>\n \t<li class=\"csl-entry\">Whitlock, C., and Bartlein, P.J., 1997, Vegetation and [pb_glossary id=\"1710\"]climate[\/pb_glossary] change in northwest America during the past 125 kyr: Nature, v. 388, no. 6637, p. 57\u201361.<\/li>\n \t<li class=\"csl-entry\">Wolpert, S., 2009, New NASA [pb_glossary id=\"2689\"]temperature[\/pb_glossary] maps provide a \u2018whole new way of seeing the moon\u2019: Online, <a href=\"http:\/\/newsroom.ucla.edu\/releases\/new-nasa-temperature-maps-provide-102070\">http:\/\/newsroom.ucla.edu\/releases\/new-nasa-temperature-maps-provide-102070<\/a>, accessed February 2017.<\/li>\n \t<li class=\"csl-entry\">Zachos, J., Pagani, M., Sloan, L., Thomas, E., and Billups, K., 2001, Trends, rhythms, and aberrations in global [pb_glossary id=\"1710\"]climate[\/pb_glossary] 65 Ma to present: Science, v. 292, no. 5517, p. 686\u2013693.<\/li>\n<\/ol>\n<\/div>\n&nbsp;\n\n&nbsp;","rendered":"<figure id=\"attachment_4591\" aria-describedby=\"caption-attachment-4591\" style=\"width: 767px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15The_Earth_seen_from_Apollo_17.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-889 size-full\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2021\/12\/15The_Earth_seen_from_Apollo_17.jpg\" alt=\"Photograph of Earth, with a view of Africa and clouds.\" width=\"767\" height=\"768\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2021\/12\/15The_Earth_seen_from_Apollo_17.jpg 767w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2021\/12\/15The_Earth_seen_from_Apollo_17-300x300.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2021\/12\/15The_Earth_seen_from_Apollo_17-150x150.jpg 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2021\/12\/15The_Earth_seen_from_Apollo_17-65x65.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2021\/12\/15The_Earth_seen_from_Apollo_17-225x225.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2021\/12\/15The_Earth_seen_from_Apollo_17-350x350.jpg 350w\" sizes=\"auto, (max-width: 767px) 100vw, 767px\" \/><\/a><figcaption id=\"caption-attachment-4591\" class=\"wp-caption-text\">The \u201cBlue Marble,\u201d a picture of our planet from the 1972 Apollo 17 mission, shows that our planet is a finite place with many interacting systems. While the exact photographer is unknown, it was most likely taken by the first (and only) geologist on the moon: Harrison \u201cJack\u201d Schmitt.<\/figcaption><\/figure>\n<h1>15 Global Climate Change<\/h1>\n<p><strong>KEY CONCEPTS<\/strong><\/p>\n<p><b>At the end of this chapter, students should be able to:<\/b><\/p>\n<ul>\n<li>Describe the role of greenhouse gases in\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0change.<\/li>\n<li>Describe the sources of greenhouse gases.<\/li>\n<li>Explain Earth\u2019s energy budget and global\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a>\u00a0changes.<\/li>\n<li>Explain how positive and\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1714\">negative feedback<\/a>\u00a0mechanisms can influence\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>.<\/li>\n<li>Explain how we know about climates in the geologic past.<\/li>\n<li>Accurately describe which aspects of the environment are changing due to\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1717\">anthropogenic<\/a>\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0change.<\/li>\n<li>Describe the causes of recent <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> change, particularly the role of humans in the overall <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> balance<\/li>\n<\/ul>\n<p>This chapter describes the Earth systems involved in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0change, the geologic evidence of past\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0changes, and the human role in today\u2019s\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0change. In science, a\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2664\">system<\/a>\u00a0is a group of interacting objects and processes. <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2670\">Earth System Science<\/a><\/strong> is the study of these systems: <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2665\">geosphere<\/a>\u2014rocks; <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>\u2014gasses; <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2666\">hydrosphere<\/a>\u2014water; <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2668\">cryosphere<\/a>\u2014ice; and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2669\">biosphere<\/a>\u2014living things. Earth science studies these systems and how they interact and change in response to natural cycles and human-driven, or <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1717\">anthropogenic<\/a> forces. Changes in one Earth <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2664\">system<\/a> affect other systems.<\/p>\n<p>It is critically important for us to be aware of the geologic context of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> change processes and how these Earth systems interact, first, for us to understand how and why human activities cause present-day <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> change and, secondly, to distinguish between natural processes and human processes in the geologic past\u2019s <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> record.<\/p>\n<p>A significant part of this chapter introduces and discusses various processes from these Earth systems, how they influence each other, and how they impact global\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>. For example, Earth\u2019s <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a>\u00a0and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> largely change based on atmospheric gas <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2831\">composition<\/a>, ocean circulation, and the land-surface characteristics of rocks, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2464\">glaciers<\/a>, and plants.<\/p>\n<p>Also necessary to understanding <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> change is to distinguish between <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1709\">weather<\/a>. <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1709\">Weather<\/a>\u00a0<\/strong>is the short-term <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2707\">precipitation<\/a> patterns that occur in days\u00a0 and weeks. <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">Climate<\/a>\u00a0<\/strong>is the variable range of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2707\">precipitation<\/a> patterns averaged over the long-term for a particular region (<a href=\"https:\/\/opengeology.org\/textbook\/13-deserts\/#131_The_Origin_of_Deserts\">see Chapter 13.1<\/a>). Thus, a single cold winter does not mean that the entire globe is cooling\u2014indeed, the United States\u2019 cold winters of 2013 and 2014 occurred\u00a0 while the rest of the Earth was experiencing record warm-winter temperatures. To avoid these generalizations, many scientists use a 30-year average as a good baseline. Therefore, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> change refers to slow <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2707\">precipitation<\/a> changes and trends over the long term for a particular area or the Earth as a whole.<\/p>\n<h2><span style=\"font-weight: 400\">15.1 Earth\u2019s Temperature<\/span><\/h2>\n<p>Without an\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>, Earth would have huge <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> fluctuations between day and night, like the moon. Daytime temperatures would be hundreds of degrees Celsius above normal, and nighttime temperatures would be hundreds of degrees below normal. Because the Moon doesn\u2019t have much of an\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>, its daytime temperatures are around 106 \u00b0C (224\u2109) and nighttime temperatures are around -183\u00b0C (-298\u2109). That is an astonishing 272\u00b0C (522\u00b0F) degree range between the Moon\u2019s light side and dark side. This section describes how Earth\u2019s\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>\u00a0is involved in regulating the Earth\u2019s\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a>.<\/p>\n<h3><b>15.1.1 Composition of Atmosphere<\/b><\/h3>\n<figure id=\"attachment_4592\" aria-describedby=\"caption-attachment-4592\" style=\"width: 200px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.1_Atmosphere_gas_proportions.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-890\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_Atmosphere_gas_proportions.png\" alt=\"This figure shows the proportion of atmopheric gases at 78% for nitrogen, 21% for oxygen, 1% for argon, and less than 1% for trace components.\" width=\"200\" height=\"417\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_Atmosphere_gas_proportions.png 200w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_Atmosphere_gas_proportions-144x300.png 144w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_Atmosphere_gas_proportions-65x136.png 65w\" sizes=\"auto, (max-width: 200px) 100vw, 200px\" \/><\/a><figcaption id=\"caption-attachment-4592\" class=\"wp-caption-text\">Composition of the atmosphere<\/figcaption><\/figure>\n<p>The\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>\u2019s\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2831\">composition<\/a>\u00a0is a key component in regulating the planet\u2019s\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a>. The\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>\u00a0is 78 percent nitrogen (N<sub>2<\/sub>), 21 percent oxygen (O<sub>2<\/sub>), one percent argon (Ar), and less than one percent trace components, which are all other gases. Trace components include carbon dioxide\u00a0(CO<sub>2<\/sub>),\u00a0water vapor (H<sub>2<\/sub>O), neon, helium, and methane.\u00a0Water vapor is highly variable, mostly based on region, and composes about one percent of the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>. Trace component gasses include several important\u00a0<strong>greenhouse gases<\/strong>, which are the gases responsible for warming and cooling the plant. On a geologic scale, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1181\">volcanoes<\/a>\u00a0and the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2676\">weathering<\/a>\u00a0process, which bury CO<sub>2<\/sub>\u00a0in\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2678\">sediments<\/a>, are the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>\u2019s CO<sub>2 \u00a0<\/sub>sources. Biological processes both add and subtract CO<sub>2<\/sub>\u00a0from the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>.<\/p>\n<p>Greenhouse gases\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3342\">trap<\/a>\u00a0heat in the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>\u00a0and warm the planet by absorbing some of the longer-wave outgoing infrared radiation that is emitted from Earth, thus keeping heat from being lost to space. More greenhouse gases in the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>\u00a0absorb more longwave heat and make the planet warmer. Greenhouse gasses have little effect on shorter-wave incoming solar radiation.<\/p>\n<figure id=\"attachment_4593\" aria-describedby=\"caption-attachment-4593\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.2_greenhouse-gas-molecules.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-4593 size-medium\" title=\"Source: NASA public domain - https:\/\/climate.nasa.gov\/system\/internal_resources\/details\/original\/249_Causes-greenhouse-gas-molecules-cropped-more-55.jpg\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_greenhouse-gas-molecules-1.jpg\" alt=\"Illustration of the molecular shape of greenhouse gases.\" width=\"300\" height=\"192\" \/><\/a><figcaption id=\"caption-attachment-4593\" class=\"wp-caption-text\">Common greenhouse gases<\/figcaption><\/figure>\n<p>The most common greenhouse gases are water vapor (H<sub>2<\/sub>O), carbon dioxide (CO<sub>2<\/sub>), methane (CH<sub>4<\/sub>),\u00a0and nitrous\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1919\">oxide<\/a>\u00a0(N<sub>2<\/sub>O).\u00a0Water vapor is the most abundant greenhouse gas, but its atmospheric\u00a0abundance does not change much over time. Carbon dioxide is much less abundant than water vapor, but carbon dioxide is being added to the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>\u00a0by human activities such as burning\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3336\">fossil fuels<\/a>, land-use changes, and deforestation. Further, natural processes such as\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1181\">volcanic<\/a>\u00a0eruptions add carbon dioxide, but at an insignificant rate compared to\u00a0human-caused contributions.<\/p>\n<p>There are two important reasons why carbon dioxide is the most important greenhouse gas. First, carbon dioxide stays in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a> and does not go away for hundreds of years. Second, most of the additional carbon dioxide is \u201c<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2176\">fossil<\/a>\u201d in origin, which means that it is released by burning <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3336\">fossil fuels<\/a>. For example, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2856\">coal<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3337\">petroleum<\/a> are <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3336\">fossil fuels<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2856\">Coal<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3338\">oil<\/a> are made from long-dead plant material, which was originally created by photosynthesis millions of years ago and stored in the ground. Photosynthesis takes sunlight plus carbon dioxide and creates the substances of plants. This transformation occurs over millions of years as a slow process, accumulating <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2176\">fossil<\/a> carbon in rocks and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2678\">sediments<\/a>. So, when we burn <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2856\">coal<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3338\">oil<\/a>, we instantaneously release the stored solar energy and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2176\">fossil<\/a> carbon dioxide that took millions of years to accumulate in the first place. The rate of release is critical to comprehend current <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> change.<\/p>\n<h3><b>15.1.2 Carbon Cycle<\/b><\/h3>\n<p>Critical to understanding global <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> change is to understand the carbon cycle and how Earth&#8217;s own carbon-balancing <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2664\">system<\/a> is being rapidly thrown off balance by human-driven activities. Earth has two important carbon cycles: the biological and the geological. In the biological cycle, living organisms\u2014mostly plants\u2014consume carbon dioxide from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a> to make their tissues and substances through photosynthesis. Then, after the organisms die, and when they decay over years or decades, that carbon is released back into the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>. The following is the general equation for photosynthesis.<\/p>\n<p style=\"text-align: center\"><i><span style=\"font-weight: 400\">CO<sub>2<\/sub> + H<\/span><\/i><sub><i><span style=\"font-weight: 400\">2<\/span><\/i><\/sub><i><span style=\"font-weight: 400\">O + sunlight \u2192 \u00a0sugars + O<\/span><\/i><sub><i><span style=\"font-weight: 400\">2<\/span><\/i><\/sub><\/p>\n<p>In the geological carbon cycle, a portion of the biological-cycle carbon becomes part of the geological carbon cycle: plant materials into <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2856\">coal<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3337\">petroleum<\/a>, tiny fragments and molecules into organic-rich <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2839\">shale<\/a>, and the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1917\">carbonate<\/a> bearing calcareous shells and other parts of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2883\">marine<\/a> organisms into <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2851\">limestone<\/a>. Such materials become buried and become part of the slow geologic <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2960\">formation<\/a> of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2856\">coal<\/a> and other sedimentary materials. This cycle actually involves most of Earth\u2019s carbon and operates very slowly.<\/p>\n<figure id=\"attachment_4594\" aria-describedby=\"caption-attachment-4594\" style=\"width: 1024px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.2_Carbon-Cycle.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-892 size-large\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_Carbon-Cycle-1024x791.jpg\" alt=\"Figure shows how carbon moves between reservoirs such as the ocean, atmosphere, biosphere, and geosphere.\" width=\"1024\" height=\"791\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_Carbon-Cycle-1024x791.jpg 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_Carbon-Cycle-300x232.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_Carbon-Cycle-768x593.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_Carbon-Cycle-65x50.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_Carbon-Cycle-225x174.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_Carbon-Cycle-350x270.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_Carbon-Cycle.jpg 1100w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><\/a><figcaption id=\"caption-attachment-4594\" class=\"wp-caption-text\">Carbon cycle.<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">\u00a0<\/span>The following are geological carbon-cycle storage\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3341\">reservoirs<\/a>:<\/p>\n<ul>\n<li>Organic matter from plants is stored in peat,\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2856\">coal<\/a>, and\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1712\">permafrost<\/a>\u00a0for thousands to millions of years.<\/li>\n<li><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2709\">Silicate<\/a>&#8211;<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2687\">mineral<\/a>\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2676\">weathering<\/a>\u00a0converts atmospheric carbon dioxide to\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2815\">dissolved<\/a>\u00a0bicarbonate, which is stored in the oceans for thousands to tens of thousands of years.<\/li>\n<li><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2883\">Marine<\/a> organisms convert <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2815\">dissolved<\/a> bicarbonate to forms of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1918\">calcite<\/a>, which is stored in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1917\">carbonate<\/a> rocks for tens to hundreds of millions of years.<\/li>\n<li>Carbon compounds are directly stored in\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2678\">sediments<\/a>\u00a0for tens to hundreds of millions of years; some end up in\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3337\">petroleum<\/a>\u00a0deposits.<\/li>\n<li>Carbon-bearing\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2678\">sediments<\/a>\u00a0are transferred by\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2602\">subduction<\/a>\u00a0to the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2586\">mantle<\/a>, where the carbon may be stored for tens of millions to billions of years.<\/li>\n<li>Carbon dioxide from within the Earth is released back to the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a> during <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1181\">volcanic<\/a> eruptions, where it is stored for years to decades.<\/li>\n<\/ul>\n<p>During much of Earth\u2019s history, the geological carbon cycle has been balanced by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1181\">volcanos<\/a>\u00a0releasing carbon at approximately the same rate that carbon is stored by the other processes. Under these conditions, Earth\u2019s\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0has remained relatively stable. However, in Earth\u2019s history, there have been times when that balance has been upset. This can happen during prolonged stretches of above-average\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1181\">volcanic<\/a> activity. One example is the Siberian\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3342\">Traps<\/a>\u00a0eruption around 250 million years ago, which contributed to strong\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0warming over a few million years.<\/p>\n<p>A carbon imbalance is also associated with significant mountain-building events. For example, the Himalayan Range has been forming for about 40 million years, and over that time \u2014 and still today \u2014 the rate of\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2676\">weathering<\/a>\u00a0on Earth has been enhanced because those mountains are so huge and the range is so extensive that they present a greater surface area on which weathering takes place. The\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2676\">weathering<\/a>\u00a0of these rocks \u2014 most importantly the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2814\">hydrolysis<\/a>\u00a0of\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1916\">feldspar<\/a>\u00a0\u2014 has resulted in consumption of atmospheric carbon dioxide and transfer of the carbon to the oceans and to ocean-floor\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1917\">carbonate<\/a>-rich\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2678\">sediments<\/a>. The steady drop in carbon dioxide levels over the past 40 million years, which contributed to the Pliocene-Pleistocene\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">glaciations<\/a>, is partly attributable to the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2960\">formation<\/a>\u00a0of the Himalayan Range.<\/p>\n<p>Another, nongeological form of carbon-cycle imbalance is happening today on a very rapid time scale. In just a few decades, humans have extracted volumes of\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3336\">fossil fuels<\/a>,\u00a0such as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2856\">coal<\/a>,\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3338\">oil<\/a>, and gas, which were stored in rocks over the past several hundred million years, and converted these fuels to energy and carbon dioxide. By doing so, we are changing the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0faster than has ever happened in the past. Remember, carbon dioxide stays in the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>\u00a0and does not go away for hundreds of years. The more greenhouse gases in the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>, the more heat is trapped and the warmer the planet becomes.<\/p>\n<h3><b>15.1.3 Greenhouse Effect<\/b><\/h3>\n<p>The\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1715\">greenhouse effect<\/a><\/strong>\u00a0<em>is<\/em> the reason our global <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> is rising, but it\u2019s important to understand what this effect is and how it occurs. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1715\">greenhouse\u00a0effect<\/a> occurs because greenhouse gases are present in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1715\">greenhouse effect<\/a> is named after a similar process that warms a greenhouse or a car on a hot summer day. Sunlight passes through the glass of the greenhouse or car, reaches the interior, and changes into heat. The heat radiates upward and gets trapped by the glass windows. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1715\">greenhouse effect<\/a> for the Earth can be explained in three steps.<\/p>\n<p><b>Step 1:<\/b><span style=\"font-weight: 400\"> Solar radiation from the sun is <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2831\">composed<\/a> of mostly ultraviolet (UV), visible light, and infrared (IR) radiation. Components of solar radiation include parts with a shorter <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3186\">wavelength<\/a> than visible light, like ultraviolet light, and parts of the spectrum<\/span><span style=\"font-weight: 400\">\u00a0with longer wavelengths, like IR and others.<\/span><span style=\"font-weight: 400\">\u00a0Some of the radiation gets absorbed, scattered, or reflected by the atmospheric gases <\/span><span style=\"font-weight: 400\">but about half of the solar radiation eventually reaches the Earth\u2019s surface.<\/span><\/p>\n<figure id=\"attachment_4595\" aria-describedby=\"caption-attachment-4595\" style=\"width: 800px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.1_Solar_Spectrum.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-893\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_Solar_Spectrum.png\" alt=\"Show how different wavelengths of incoming solar radiation are absorbed, scattered, and reflected before reaching the earth's surface.\" width=\"800\" height=\"600\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_Solar_Spectrum.png 800w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_Solar_Spectrum-300x225.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_Solar_Spectrum-768x576.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_Solar_Spectrum-65x49.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_Solar_Spectrum-225x169.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_Solar_Spectrum-350x263.png 350w\" sizes=\"auto, (max-width: 800px) 100vw, 800px\" \/><\/a><figcaption id=\"caption-attachment-4595\" class=\"wp-caption-text\">Incoming radiation absorbed, scattered, and reflected by atmospheric gases.<\/figcaption><\/figure>\n<p><b>Step 2:<\/b><span style=\"font-weight: 400\"> The visible, UV, and IR radiation, that reaches the surface converts to heat energy. Most students have experienced sunlight warming a surface such as pavement, a patio, or deck. When this occurs, the warmer surface then emits thermal radiation, which is a type of IR radiation. So, there is a conversion from visible, UV, and IR to just thermal IR. This thermal IR is what we experience as heat. If you have ever felt heat radiating from a fire or a hot stove top, then you have experienced thermal IR. <\/span><\/p>\n<p><b>Step 3:<\/b><span style=\"font-weight: 400\"> Thermal IR radiates from the earth\u2019s surface back into the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>. But since it is thermal IR instead of UV, visible, or regular IR, this thermal IR gets trapped by greenhouse gases. In other words, the sun&#8217;s energy leaves the Earth at a different <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3186\">wavelength<\/a> than it enters, so the sun\u2019s energy is not absorbed in the lower <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a> when energy is coming in, but rather when the energy is going out. The gases that are mostly responsible for this energy blocking on Earth include carbon dioxide, water vapor, methane, and nitrous <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1919\">oxide<\/a>. More greenhouse gases in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a> results in more thermal IR being trapped. Explore this external link to an <\/span><a href=\"https:\/\/www.koshland-science-museum.org\/explore-the-science\/interactives\/what-is-the-greenhouse-effect\"><span style=\"font-weight: 400\">interactive animation on the greenhouse effect<\/span><\/a><span style=\"font-weight: 400\"> from the National Academy of Sciences.<\/span><\/p>\n<h3><b>15.1.4 Earth\u2019s Energy Budget<\/b><\/h3>\n<p>The solar radiation that reaches Earth is relatively uniform over time. Earth is warmed, and energy or heat radiates from the Earth\u2019s surface and lower <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a> back to space. This flow of incoming and outgoing energy is Earth\u2019s energy budget. For Earth\u2019s <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> to be stable over long stretches of time, incoming energy and outgoing energy have to be equal on average so that the energy budget at the top of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a> balances. About 29 percent of the incoming solar energy arriving at the top of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a> is reflected back to space by clouds, atmospheric particles, or reflective ground surfaces like sea ice and snow. About 23 percent of incoming solar energy is absorbed in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a> by water vapor, dust, and ozone. The remaining 48 percent passes through the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a> and is absorbed at the surface. Thus, about 71 percent of the total incoming solar energy is absorbed by the Earth <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2664\">system<\/a>.<\/p>\n<figure id=\"attachment_4596\" aria-describedby=\"caption-attachment-4596\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.1_reflected_radiation.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-894 size-medium\" title=\"Source: NASA Public Domain - https:\/\/earthobservatory.nasa.gov\/Features\/EnergyBalance\/images\/reflected_radiation.jpg\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_reflected_radiation-300x172.jpg\" alt=\"This figure shows incoming solar radiation, 23% is absorbed in the atmosphere, 29% reflected, and 48% absorbed at the surface after passing through atmosphere.\" width=\"300\" height=\"172\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_reflected_radiation-300x172.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_reflected_radiation-65x37.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_reflected_radiation-225x129.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_reflected_radiation-350x201.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_reflected_radiation.jpg 720w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-4596\" class=\"wp-caption-text\">Incoming solar radiation filtered by the atmosphere.<\/figcaption><\/figure>\n<p>When this energy reaches Earth, the atoms and molecules that makeup the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>\u00a0and surface absorb the energy, and Earth\u2019s <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> increases. If this material <em>only <\/em>absorbed energy, then the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a>\u00a0of the Earth would continue to increase and eventually overheat. For example, if you continuously run a faucet in a stopped-up sink, the water level rises and eventually overflows. However,\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a>\u00a0does not infinitely rise because the Earth is not just absorbing sunlight; it is also radiating thermal energy or heat <em>back <\/em>into the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>. If the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a>\u00a0of the Earth rises, the planet emits an increasing amount of heat to space, and this is the primary mechanism that prevents Earth from continually heating.<\/p>\n<figure id=\"attachment_4597\" aria-describedby=\"caption-attachment-4597\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.1_surface_energy_balance.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-895 size-medium\" title=\"Source: NASA public domain - https:\/\/earthobservatory.nasa.gov\/Features\/EnergyBalance\/images\/surface_energy_balance.jpg\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_surface_energy_balance-300x200.jpg\" alt=\"This figure shows incoming solar radiation reaching the surface and changing into longwave radiation that radiates into the atmosphere.\" width=\"300\" height=\"200\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_surface_energy_balance-300x200.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_surface_energy_balance-65x43.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_surface_energy_balance-225x150.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_surface_energy_balance-350x233.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1_surface_energy_balance.jpg 720w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-4597\" class=\"wp-caption-text\">Some of the thermal infrared energy (heat) radiated from the surface into the atmosphere is trapped by gasses in the atmosphere.<\/figcaption><\/figure>\n<p>Some of the thermal infrared heat radiating from the surface is absorbed and trapped by greenhouse gasses in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>, which act like a giant canopy over Earth. The more greenhouse gases in the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>, the more outgoing heat Earth retains, and the less thermal infrared heat dissipates to space.<\/p>\n<p>Factors that can affect the Earth\u2019s energy budget are not limited to greenhouse gases. Increasing solar energy can increase the energy Earth receives. However, these increases are very small over time. In addition, land and water will absorb more sunlight when there is less ice and snow to reflect the sunlight back to the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>. For example, the ice covering the Arctic Sea reflects sunlight back to the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>; this reflectivity is called\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1711\">albedo<\/a><\/strong>. Furthermore, aerosols (dust particles) produced from burning\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2856\">coal<\/a>, diesel engines, and\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1181\">volcanic<\/a>\u00a0eruptions can reflect incoming solar radiation and actually cool the planet. While the effect of\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1717\">anthropogenic<\/a>\u00a0aerosols on the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u2019s\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2664\">system<\/a> is weak,\u00a0the effect of human-produced greenhouse gases is not weak. Thus, the net effect of human activity is warming due to more\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1717\">anthropogenic<\/a>\u00a0greenhouse gases associated with\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3336\">fossil fuel<\/a>\u00a0combustion.<\/p>\n<figure id=\"attachment_4598\" aria-describedby=\"caption-attachment-4598\" style=\"width: 452px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.2_Net-Forcings.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-896\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_Net-Forcings.jpg\" alt=\"Graph shows that anthropogenic greenhouse gases have a much larger influence on temperature than other factors such as natural changes.\" width=\"452\" height=\"289\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_Net-Forcings.jpg 604w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_Net-Forcings-300x192.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_Net-Forcings-65x42.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_Net-Forcings-225x144.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_Net-Forcings-350x224.jpg 350w\" sizes=\"auto, (max-width: 452px) 100vw, 452px\" \/><\/a><figcaption id=\"caption-attachment-4598\" class=\"wp-caption-text\">Net effect of factors influencing warming.<\/figcaption><\/figure>\n<p>An effect that changes the planet can\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3117\">trigger<\/a>\u00a0feedback mechanisms that amplify or\u00a0suppress the original effect. A\u00a0<strong>positive\u00a0 feedback mechanism<\/strong>\u00a0occurs when the output or effect of a process <em>enhances <\/em>the original stimulus or cause. Thus, it increases the ongoing effect. For example, the loss of sea ice at the North Pole makes that area less reflective, reducing\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1711\">albedo<\/a>. This allows the surface air and ocean to absorb more energy in an area that was once covered by sea ice.\u00a0Another example is melting\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1712\">permafrost<\/a>.\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1712\">Permafrost<\/a>\u00a0<\/strong>is permanently frozen <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1203\">soil<\/a> located in the high latitudes, mostly in the Northern Hemisphere. As the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> warms, more <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1712\">permafrost<\/a> thaws, and the thick deposits of organic matter are exposed to oxygen and begin to decay. This <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2818\">oxidation<\/a> process releases carbon dioxide and methane, which in turn causes more warming, which melts more <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1712\">permafrost<\/a>, and so on and on.<\/p>\n<p>A\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1714\">negative feedback<\/a>\u00a0mechanism<\/strong>\u00a0occurs when the output or effect <em>reduces <\/em>the original stimulus or cause. For example, in the short term, more carbon dioxide (CO<sub>2<\/sub>) is expected to cause forest canopies to grow, which absorb more CO<sub>2<\/sub>. Another example for the long term is that increased carbon dioxide in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a> will cause more <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2813\">carbonic acid<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2812\">chemical weathering<\/a>, which results in transporting dissolved bicarbonate and other ions to the oceans, which are then stored in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2678\">sediment<\/a>.<\/p>\n<p>Global warming is evidence that Earth&#8217;s energy budget is not balanced. Positive effects on Earth&#8217;s <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> are now greater than negative effects.<\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-102\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-102\" class=\"h5p-iframe\" data-content-id=\"102\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"15.1 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4862\" aria-describedby=\"caption-attachment-4862\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/15.1-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-897\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.1-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4862\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 15.1 via this QR Code.<\/figcaption><\/figure>\n<h2><span style=\"font-weight: 400\">15.2 Evidence of Recent Climate Change<\/span><\/h2>\n<p>While <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> has changed often in the past due to natural causes (see <a href=\"https:\/\/opengeology.org\/textbook\/14-glaciers\/#1451_Causes_of_Glaciations\">chapter 14.5.1<\/a>\u00a0and\u00a0<a href=\"https:\/\/opengeology.org\/textbook\/15-global-climate-change\/#153_Prehistoric_Climate_Change\">chapter 15.3<\/a>), the scientific consensus is that human activity is causing current very rapid <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> change. While this seems like a new idea, it was suggested more than 75 years ago. This section describes the evidence of what most scientists agree is <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1717\">anthropogenic<\/a><\/strong> or\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1716\">human-caused climate change<\/a>. For more information, watch this<a href=\"https:\/\/youtu.be\/dquECwUfIQg?list=PL4Wzj82Z15gzrcsvrQxDPB1o4UAUxGbBM\">\u00a0six-minute video on climate change<\/a> by two professors at the North Carolina State University.<\/p>\n<figure id=\"attachment_4871\" aria-describedby=\"caption-attachment-4871\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/Evidence-for-Climate-Change-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-898\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Evidence-for-Climate-Change-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Evidence-for-Climate-Change-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Evidence-for-Climate-Change-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Evidence-for-Climate-Change-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Evidence-for-Climate-Change-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Evidence-for-Climate-Change-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Evidence-for-Climate-Change-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Evidence-for-Climate-Change-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Evidence-for-Climate-Change-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4871\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-1\" title=\"Evidence for Climate Change\" width=\"500\" height=\"375\" src=\"https:\/\/www.youtube.com\/embed\/dquECwUfIQg?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<h3><b>15.2.1 Global Temperature Rise<\/b><\/h3>\n<p>The land-ocean <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> index, 1880 to present, compared to a base reference time of 1951-1980, shows ocean temperatures steadily rising. The solid black line is the global annual mean, and the solid red line is the five-year Lowess smoothing. The blue uncertainty bars (95 percent confidence limit) account only for incomplete spatial sampling.<\/p>\n<figure id=\"attachment_4599\" aria-describedby=\"caption-attachment-4599\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15_tempgraph.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-899 size-medium\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15_tempgraph-300x159.png\" alt=\"Graph of temperature with time showing gradual increase of 1 degree Celcius in temperature over time with minor fluctuations within the large trend.\" width=\"300\" height=\"159\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15_tempgraph-300x159.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15_tempgraph-1024x544.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15_tempgraph-768x408.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15_tempgraph-65x35.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15_tempgraph-225x119.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15_tempgraph-350x186.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15_tempgraph.png 1130w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-4599\" class=\"wp-caption-text\">Land-ocean temperature index, 1880 to present, with a base time 1951-1980. The solid black line is the global annual mean and the solid red line is the five-year Lowess smoothing. The blue uncertainty bars (95% confidence limit) account only for incomplete spatial sampling. The graph shows that Earth\u2019s temperature is rising.<\/figcaption><\/figure>\n<p>Since 1880, Earth\u2019s surface-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> average has trended upward with most of that warming occurring since 1970 (see this NASA\u00a0<a href=\"https:\/\/svs.gsfc.nasa.gov\/4882\">animation<\/a>). Surface temperatures include both land and ocean because water absorbs much additional trapped heat. Changes in land-surface or ocean-surface temperatures compared to a reference <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2192\">period<\/a> from 1951 to 1980, where the long-term average remained relatively constant, are called <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a>\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1719\">anomalies<\/a><\/strong>. A\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a>\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1719\">anomaly<\/a>\u00a0thus represents the difference between the measured <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a>\u00a0and the average value during the reference <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2192\">period<\/a>. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">Climate<\/a> scientists calculate long-term average temperatures\u00a0over thirty years or more which identified the reference <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2192\">period<\/a> from 1951 to 1980.\u00a0Another common range is a century, for example, 1900-2000. Therefore, an\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1719\">anomaly<\/a>\u00a0of 1.25 \u2103 (34.3\u00b0F) for 2015 means that the average\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a>\u00a0for 2015 was 1.25 \u2103 (34.3\u00b0F) greater than the 1900-2000 average. In 1950, the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a>\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1719\">anomaly<\/a>\u00a0was -0.28 \u2103 (31.5\u00b0F), so this is -0.28 \u2103 (31.5\u00b0F) lower than the 1900-2000 average. These temperatures are annual average measured surface temperatures.<\/p>\n<p>This video figure of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1719\">anomalies<\/a> shows worldwide\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a>\u00a0changes since 1880.\u00a0 The more blue, the cooler; the more yellow and red, the warmer.<\/p>\n<figure id=\"attachment_4864\" aria-describedby=\"caption-attachment-4864\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/15.2.1-Global-Temperature-Rise-Video-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-900\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2.1-Global-Temperature-Rise-Video-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2.1-Global-Temperature-Rise-Video-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2.1-Global-Temperature-Rise-Video-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2.1-Global-Temperature-Rise-Video-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2.1-Global-Temperature-Rise-Video-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2.1-Global-Temperature-Rise-Video-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2.1-Global-Temperature-Rise-Video-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2.1-Global-Temperature-Rise-Video-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2.1-Global-Temperature-Rise-Video-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4864\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this video via this QR Code.<\/figcaption><\/figure>\n<div style=\"width: 300px;\" class=\"wp-video\"><video class=\"wp-video-shortcode\" id=\"video-926-1\" width=\"300\" height=\"200\" autoplay preload=\"metadata\" controls=\"controls\"><source type=\"video\/mp4\" src=\"http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2017\/01\/15.2_GISTEMP_2015_sm.mp4?_=1\" \/><a href=\"http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2017\/01\/15.2_GISTEMP_2015_sm.mp4\">http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2017\/01\/15.2_GISTEMP_2015_sm.mp4<\/a><\/video><\/div>\n<p>&nbsp;<\/p>\n<p>In addition to average land-surface temperatures rising, the ocean has absorbed much heat. Because oceans cover about 70 percent of the Earth\u2019s surface and have such a high specific heat value, they provide a large opportunity to absorb energy. The ocean has been absorbing about 80 to 90 percent of human activities\u2019 additional heat. As a result, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> in the ocean\u2019s top 701.4 m (2,300 ft) has increased by -17.6\u00b0C (0.3\u2109) since 1969 (<a href=\"https:\/\/climate.nasa.gov\/climate_resources\/40\/\">watch this 3 minute <\/a>video by NASA JPL on the ocean\u2019s heat capacity). The reason the ocean has warmed less than the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>, while still taking on most of the heat, is due to water\u2019s very high specific heat, which means that water can absorb a lot of heat energy with a small <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> increase. In contrast, the lower specific heat of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a> means it has a higher <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> increase as it absorbs less heat\u00a0 energy.<\/p>\n<p>Some scientists suggest that <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1717\">anthropogenic<\/a> greenhouse gases do not cause global warming because between 1998 and 2013, Earth\u2019s surface temperatures did not increase much, despite greenhouse gas concentrations continuing to increase. However, since the oceans are absorbing most of the heat, decade-scale circulation changes in the ocean, similar to La Ni\u00f1a, push warmer water deeper under the surface. Once the ocean\u2019s absorption and circulation is accounted for, and this heat is added back into surface temperatures, then <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> increases become apparent, as shown in the figure. Also, the ocean\u2019s heat storage is temporary, as reflected in the record-breaking warm years of 2014-2016. Indeed, with this temporary ocean-storage effect, the twenty-first century\u2019s first 15 of its 16 years were the hottest in recorded history.<\/p>\n<h3><b>15.2.2 Carbon Dioxide<\/b><\/h3>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1717\">Anthropogenic<\/a>\u00a0greenhouse gases, mostly carbon dioxide (CO<sub>2<\/sub>), have increased since the industrial revolution when humans dramatically increased burning <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3336\">fossil fuels<\/a>.\u00a0These levels are unprecedented in the last 800,000-year Earth history as recorded in geologic sources such as ice cores. Carbon dioxide has increased by 40 percent since 1750, and the rate of increase has been the fastest during the last decade. For example, since 1750, 2040<sup>9<\/sup>\u00a0tonnes (2040 gigatons) of CO<sub>2<\/sub>\u00a0have been added to the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>; about 40 percent has remained in the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>\u00a0while the remaining 60 percent has been absorbed into the land by plants and\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1203\">soil<\/a> or into the oceans. Indeed, during the lifetime of most young adults, the total\u00a0atmospheric\u00a0CO<sub>2<\/sub> has increased by 50 ppm, or 15 percent.<\/p>\n<p>Charles Keeling, an oceanographer with Scripps Institution of Oceanography in San Diego, California, was the first person to regularly measure atmospheric CO<sub>2<\/sub>. Using his methods, scientists at the Mauna Loa Observatory, Hawaii, have constantly measured atmospheric CO<sub>2 <\/sub>since 1957. NASA regularly publishes these measurements at <u><a href=\"https:\/\/scripps.ucsd.edu\/programs\/keelingcurve\/\">https:\/\/scripps.ucsd.edu\/programs\/keelingcurve\/<\/a><\/u>. Go there <strong>now<\/strong> to see the very latest measurement. Keeling\u2019s measured values have been posted in a curve of increasing values, called the Keeling Curve. This curve varies up and down in a regular annual cycle, from summer when the plants in the Northern Hemisphere are using CO<sub>2<\/sub> to winter when the plants are dormant. But the curve shows a steady CO<sub>2 <\/sub>increase over the past several decades. This curve increases exponentially, not linearly, showing that the rate of CO<sub>2<\/sub>\u00a0increase is itself increasing!<\/p>\n<p><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Keeling-Curve-1-10-2022-1.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"aligncenter wp-image-901 size-full\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Keeling-Curve-1-10-2022-1.jpg\" alt=\"Keeling curve graph of the carbon dioxide concentration at Mauna Loa Observatory\" width=\"928\" height=\"618\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Keeling-Curve-1-10-2022-1.jpg 928w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Keeling-Curve-1-10-2022-1-300x200.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Keeling-Curve-1-10-2022-1-768x511.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Keeling-Curve-1-10-2022-1-65x43.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Keeling-Curve-1-10-2022-1-225x150.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Keeling-Curve-1-10-2022-1-350x233.jpg 350w\" sizes=\"auto, (max-width: 928px) 100vw, 928px\" \/><\/a><\/p>\n<p>The following Atmospheric CO<sub>2 <\/sub>video shows how atmospheric CO<sub>2<\/sub> has varied recently and over the last 800,000 years, as determined by an increasing number of CO<sub>2<\/sub> monitoring stations as shown on the insert map. It is also instructive to watch the video\u2019s Keeling portion of how CO<sub>2<\/sub>\u00a0varies by\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3372\">latitude<\/a>.\u00a0This shows that most human CO<sub>2<\/sub>\u00a0sources are in the Northern Hemisphere where most of the land is and where most of the developed nations are.<\/p>\n<div style=\"height: 0;padding-bottom: 56.25%\">\n<figure id=\"attachment_4872\" aria-describedby=\"caption-attachment-4872\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/Pumphandle-2016-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-902\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Pumphandle-2016-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Pumphandle-2016-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Pumphandle-2016-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Pumphandle-2016-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Pumphandle-2016-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Pumphandle-2016-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Pumphandle-2016-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Pumphandle-2016-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Pumphandle-2016-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4872\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-2\" title=\"Pumphandle 2016\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/gH6fQh9eAQE?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<\/div>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<h3><b>15.2.3 Melting Glaciers and Shrinking Sea Ice<\/b><\/h3>\n<figure id=\"attachment_4601\" aria-describedby=\"caption-attachment-4601\" style=\"width: 400px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.2_LandIceAntarctica.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-903\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_LandIceAntarctica-300x149.png\" alt=\"Graph shows decline of Antarctic ice mass by 2,000 gigatons from 2002 to 2016.\" width=\"400\" height=\"198\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_LandIceAntarctica-300x149.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_LandIceAntarctica-65x32.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_LandIceAntarctica-225x111.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_LandIceAntarctica-350x173.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2_LandIceAntarctica.png 737w\" sizes=\"auto, (max-width: 400px) 100vw, 400px\" \/><\/a><figcaption id=\"caption-attachment-4601\" class=\"wp-caption-text\">Decline of Antarctic ice mass from 2002 to 2016<\/figcaption><\/figure>\n<p><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2464\">Glaciers<\/a>\u00a0are large ice accumulations that exist year round on the land\u2019s surface. In contrast, icebergs are masses of floating sea ice, although they may have had their origin in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2464\">glaciers<\/a> (see Chapter 14). <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2465\">Alpine glaciers<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2467\">ice sheets<\/a>, and sea ice are all melting. Explore melting <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2464\">glaciers<\/a> at NASA\u2019s interactive Global Ice Viewer). Satellites have recorded that Antarctica is melting at 1189 tonnes (118 gigatons) per year, and Greenland is melting at 2819 tonnes (281 gigatons) per year; 1 metric tonne is 1000 kilograms (1 gigaton is over 2 trillion pounds). Almost all major <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2465\">alpine glaciers<\/a> are shrinking, deflating, and retreating. The ice-mass loss rate is unprecedented\u2014never observed before\u2014since the 1940\u2019s when quality records for <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2464\">glaciers<\/a> began.<\/p>\n<p>Before\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1717\">anthropogenic<\/a>\u00a0warming,\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2910\">glacial<\/a>\u00a0activity was variable with some retreating and some advancing. Now, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3174\">spring<\/a>\u00a0snow cover is decreasing, and sea ice is shrinking. Most sea ice is at the North Pole, which is only occupied by the Arctic Ocean and sea ice. The NOAA animation shows how perennial sea ice has declined from 1987 to 2015. The oldest ice is white, and the youngest, seasonal ice is dark blue. The amount of old ice has declined from 20 percent in 1985 to 3 percent in 2015.<\/p>\n<figure id=\"attachment_4873\" aria-describedby=\"caption-attachment-4873\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/Watch-25-Years-of-Arctic-Sea-Ice-Disappear-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-904\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Watch-25-Years-of-Arctic-Sea-Ice-Disappear-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Watch-25-Years-of-Arctic-Sea-Ice-Disappear-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Watch-25-Years-of-Arctic-Sea-Ice-Disappear-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Watch-25-Years-of-Arctic-Sea-Ice-Disappear-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Watch-25-Years-of-Arctic-Sea-Ice-Disappear-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Watch-25-Years-of-Arctic-Sea-Ice-Disappear-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Watch-25-Years-of-Arctic-Sea-Ice-Disappear-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Watch-25-Years-of-Arctic-Sea-Ice-Disappear-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Watch-25-Years-of-Arctic-Sea-Ice-Disappear-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4873\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-3\" title=\"Watch 25 Years of Arctic Sea Ice Disappear in 1 Minute\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/Fw7GfNR5PLA?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<h3><b>15.2.4 Rising Sea-Level<\/b><\/h3>\n<p>Sea level is rising 3.4 millimeters (0.13 inches) per year and has risen 0.19 meters (7.4 inches) from 1901 to 2010. This is thought largely to be from both\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2464\">glaciers<\/a> melting and thermal expansion of sea water. Thermal expansion means that as objects such as solids, liquids, and gases heat up, they expand in volume.<\/p>\n<p>Classic video demonstration (30 second) on thermal expansion with brass ball and ring (North Carolina School of Science and Mathematics).<\/p>\n<figure id=\"attachment_4868\" aria-describedby=\"caption-attachment-4868\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/Ball-and-Ring-Rate-of-Expansion-and-Contraction-Youtube-QR-Code-1.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-905\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Ball-and-Ring-Rate-of-Expansion-and-Contraction-Youtube-QR-Code-1-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ball-and-Ring-Rate-of-Expansion-and-Contraction-Youtube-QR-Code-1-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ball-and-Ring-Rate-of-Expansion-and-Contraction-Youtube-QR-Code-1-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ball-and-Ring-Rate-of-Expansion-and-Contraction-Youtube-QR-Code-1-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ball-and-Ring-Rate-of-Expansion-and-Contraction-Youtube-QR-Code-1-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ball-and-Ring-Rate-of-Expansion-and-Contraction-Youtube-QR-Code-1-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ball-and-Ring-Rate-of-Expansion-and-Contraction-Youtube-QR-Code-1-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ball-and-Ring-Rate-of-Expansion-and-Contraction-Youtube-QR-Code-1-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ball-and-Ring-Rate-of-Expansion-and-Contraction-Youtube-QR-Code-1.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4868\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-4\" title=\"Ball and Ring: Rate of Expansion and Contraction\" width=\"500\" height=\"375\" src=\"https:\/\/www.youtube.com\/embed\/QNoE5IoRheQ?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<h3><b>15.2.5 Ocean Acidification<\/b><\/h3>\n<p>Since 1750, about 40 percent of new <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1717\">anthropogenic<\/a> carbon dioxide has remained in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>. The remaining 60 percent gets absorbed by the ocean and vegetation. The ocean has absorbed about 30 percent of that carbon dioxide. When carbon dioxide gets absorbed in the ocean, it creates <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2813\">carbonic acid<\/a>. This makes the ocean more acidic, which then has an impact on <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2883\">marine<\/a> organisms that secrete calcium <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1917\">carbonate<\/a> shells. Recall that hydrochloric acid reacts by effervescing with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2851\">limestone<\/a> rock made of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1918\">calcite<\/a>, which is calcium <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1917\">carbonate<\/a>. A more acidic ocean is associated with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> change and is linked to some sea snails (pteropods) and small protozoan zooplanktons\u2019 (foraminifera) thinning <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1917\">carbonate<\/a> shells and to ocean coral <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2898\">reefs<\/a>\u2019 declining growth rates. Small animals like protozoan zooplankton are an important component at the base of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2883\">marine<\/a> ecosystem. Acidification combined with warmer <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> and lower oxygen levels is expected to have severe impacts on <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2883\">marine<\/a> ecosystems and human-harvested fisheries, possibly affecting our ocean-derived food sources.<\/p>\n<figure id=\"attachment_4865\" aria-describedby=\"caption-attachment-4865\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/15.2.5-Ocean-Acidification-Video-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-906\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2.5-Ocean-Acidification-Video-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2.5-Ocean-Acidification-Video-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2.5-Ocean-Acidification-Video-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2.5-Ocean-Acidification-Video-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2.5-Ocean-Acidification-Video-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2.5-Ocean-Acidification-Video-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2.5-Ocean-Acidification-Video-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2.5-Ocean-Acidification-Video-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2.5-Ocean-Acidification-Video-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4865\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this video via this QR Code.<\/figcaption><\/figure>\n<div style=\"width: 300px;\" class=\"wp-video\"><video class=\"wp-video-shortcode\" id=\"video-926-2\" width=\"300\" height=\"200\" preload=\"metadata\" controls=\"controls\"><source type=\"video\/webm\" src=\"http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2017\/01\/15.2_Impacts_of_ocean_acidification_NOAA_EVL.webm?_=2\" \/><a href=\"http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2017\/01\/15.2_Impacts_of_ocean_acidification_NOAA_EVL.webm\">http:\/\/opengeology.org\/textbook\/wp-content\/uploads\/2017\/01\/15.2_Impacts_of_ocean_acidification_NOAA_EVL.webm<\/a><\/video><\/div>\n<h3><b>15.2.6 Extreme Weather Events<\/b><\/h3>\n<p>Extreme\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1709\">weather<\/a>\u00a0events such as hurricanes,\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2707\">precipitation<\/a>, and heatwaves are increasing and becoming more intense. Since the 1980\u2019s, hurricanes, which are generated from warm ocean water, have increased in frequency, intensity, and duration and are likely connected to a warmer\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>. Since 1910, average\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2707\">precipitation<\/a>\u00a0has increased by 10 percent in the contiguous United States, and much of this increase is associated with heavy\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2707\">precipitation<\/a>\u00a0events. However, the distribution is not even, and more\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2707\">precipitation<\/a>\u00a0is projected for the northern United States while less\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2707\">precipitation<\/a>\u00a0is projected for the already dry southwest. Also, heatwaves have increased, and rising temperatures are already affecting crop yields in northern latitudes. Increased heat allows for greater moisture capacity in the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>, increasing the potential for more extreme events.<\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-103\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-103\" class=\"h5p-iframe\" data-content-id=\"103\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"15.2 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4863\" aria-describedby=\"caption-attachment-4863\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/15.2-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-907\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.2-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4863\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 15.2 via this QR Code.<\/figcaption><\/figure>\n<h2><span style=\"font-weight: 400\">15.3 Prehistoric Climate Change <\/span><\/h2>\n<figure id=\"attachment_4602\" aria-describedby=\"caption-attachment-4602\" style=\"width: 250px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.3_Laurentide_Ice_Sheet_Extent.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-908 size-full\" title=\"Source: USGS. The maximum extent of glacial ice in the north polar area during Pleistocene time. {{PD-USGov-Interior-USGS}} http:\/\/pubs.usgs.gov\/gip\/continents\/map.jpg\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Laurentide_Ice_Sheet_Extent.jpg\" alt=\"Shows extent of last ice age with glacier covering most of Canada and some of the northern U.S. including Alaska, Wisconsin, Minnesota, the Great Lakes, and parts of other states.\" width=\"250\" height=\"417\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Laurentide_Ice_Sheet_Extent.jpg 250w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Laurentide_Ice_Sheet_Extent-180x300.jpg 180w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Laurentide_Ice_Sheet_Extent-65x108.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Laurentide_Ice_Sheet_Extent-225x375.jpg 225w\" sizes=\"auto, (max-width: 250px) 100vw, 250px\" \/><\/a><figcaption id=\"caption-attachment-4602\" class=\"wp-caption-text\">Maximum extent of Laurentide Ice Sheet<\/figcaption><\/figure>\n<p>Over Earth\u2019s history, the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0has changed a lot. For example, during the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1432\">Mesozoic<\/a>\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2191\">Era<\/a>, the Age of Dinosaurs, the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0was much warmer, and carbon dioxide was abundant in the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>. However, throughout the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1441\">Cenozoic<\/a>\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2191\">Era<\/a>, 65 million years ago to today, the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0has been gradually cooling. This section summarizes some of these major past\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0changes.<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<h3><strong>15.3.1 Past Glaciations<\/strong><\/h3>\n<p>Through geologic history,\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0has changed slowly over millions of years. Before the most recent Pliocene-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1443\">Quaternary<\/a>\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">glaciation<\/a>, there were other major\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">glaciations<\/a>. The oldest, known as the Huronian, occurred toward the end of the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2205\">Archean<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2190\">Eon<\/a>-early\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2209\">Proterozoic<\/a>\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2190\">Eon<\/a>, about 2.5 billion years ago. The event of that time, the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2210\">Great Oxygenation Event<\/a>, was a major happening\u00a0(see Chapter 8) most commonly associated with causing that\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">glaciation<\/a>. The increased oxygen is thought to have reacted with the potent greenhouse gas methane, causing cooling.<\/p>\n<p>The end of the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2209\">Proterozoic<\/a>\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2190\">Eon<\/a>, about 700 million years ago, had other\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">glaciations<\/a>. These ancient <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2218\">Precambrian<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">glaciations<\/a> are included in the\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1718\">Snowball Earth hypothesis<\/a><\/strong>.\u00a0Widespread global rock sequences from these ancient times contain evidence that <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2464\">glaciers<\/a> existed even in low-latitudes. Two \u00a0examples are <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2851\">limestone<\/a>\u00a0rock\u2014usually formed in tropical\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2883\">marine<\/a>\u00a0environments\u2014and\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2910\">glacial<\/a>\u00a0deposits\u2014usually formed in cold climates\u2014have been found together from this time in many regions around the world. One example is in Utah. Evidence of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2575\">continental<\/a>\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">glaciation<\/a> is seen in interbedded <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2851\">limestone<\/a>\u00a0and\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2910\">glacial<\/a>\u00a0deposits (<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2911\">diamictites<\/a>) on Antelope Island in the Great Salt Lake.<\/p>\n<p>The controversial <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1718\">Snowball Earth hypothesis<\/a> suggests that a runaway <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1711\">albedo<\/a> effect\u2014where ice and snow reflect solar radiation and increasingly spread from polar regions toward the equator\u2014caused land and ocean surfaces to completely freeze and biological activity to collapse. Thinking is that because carbon dioxide could not enter the then-frozen ocean, the ice covering Earth could only melt when <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1181\">volcanoes<\/a> emitted high enough carbon dioxide into the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a> to cause greenhouse heating. Some studies estimate that because of the frozen ocean surface, carbon dioxide 350 times higher than today\u2019s concentration was required. Because biological activity did survive, the complete freezing and its extent in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1718\">snowball earth hypothesis<\/a> are controversial. A competing <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2652\">hypothesis<\/a> is the <strong>Slushball Earth <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2652\">hypothesis<\/a> <\/strong>in which some regions of the equatorial ocean remained open. Differing scientific conclusions about the stability of Earth\u2019s magnetic poles, impacts on ancient rock evidence from subsequent <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2914\">metamorphism<\/a>, and alternate interpretations of existing evidence keep the idea of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1718\">Snowball Earth<\/a> controversial.<\/p>\n<p><span style=\"font-weight: 400\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">Glaciations<\/a>\u00a0also occurred in the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2219\">Paleozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2191\">Era<\/a>, notably the Andean-Saharan <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">glaciation<\/a> in the late <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2225\">Ordovician<\/a>, about 440\u2013460 million years ago, which coincided with a major <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1708\">extinction<\/a> event, and the Karoo\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">Ice Age<\/a> during the Pennsylvanian <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2192\">Period<\/a>, 323 to 300 million years ago. This <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">glaciation<\/a> was one of the evidences cited by Wegener for his <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2575\">Continental<\/a> Drift <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2652\">hypothesis<\/a> as his proposed <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3366\">Pangea<\/a> drifted into south polar latitudes. The Karoo <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">glaciation<\/a> was associated with an increase of oxygen and a subsequent drop in carbon dioxide, most likely produced by the evolution and rise of land plants<\/span><span style=\"font-weight: 400\">.<\/span><\/p>\n<figure id=\"attachment_4603\" aria-describedby=\"caption-attachment-4603\" style=\"width: 1024px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15_cenozoic-t-2.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-large wp-image-909\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15_cenozoic-t-2-1024x446.png\" alt=\"Graph showing decrease of average surface temperature from 23 degrees Celsius 50 million years ago to 12 degrees Celsius near present.\" width=\"1024\" height=\"446\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15_cenozoic-t-2-1024x446.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15_cenozoic-t-2-300x131.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15_cenozoic-t-2-768x334.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15_cenozoic-t-2-65x28.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15_cenozoic-t-2-225x98.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15_cenozoic-t-2-350x152.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15_cenozoic-t-2.png 1243w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><\/a><figcaption id=\"caption-attachment-4603\" class=\"wp-caption-text\">Global average surface temperature over the past 70 million years.<\/figcaption><\/figure>\n<p>During the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1441\">Cenozoic<\/a>\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2191\">Era<\/a>\u2014the last 65 million years,\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0started out warm and gradually cooled to today. This warm time is called the\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1720\">Paleocene-Eocene Thermal Maximum<\/a>,<\/strong>\u00a0and Antarctica and Greenland were ice free during this time. Since the Eocene,\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2576\">tectonic<\/a>\u00a0events during the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1441\">Cenozoic<\/a>\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2191\">Era<\/a> caused the planet to persistently and significantly cool. For example, the\u00a0Indian\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2591\">Plate<\/a>\u00a0and Asian\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2591\">Plate<\/a>\u00a0collided,\u00a0creating the Himalaya Mountains, which increased\u00a0the rate of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2676\">weathering<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2677\">erosion<\/a> of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2709\">silicate<\/a>\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2687\">minerals<\/a>, especially\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1916\">feldspar<\/a>. Increased <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2676\">weathering<\/a>\u00a0consumes carbon dioxide from the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>, which \u00a0reduces the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1715\">greenhouse effect<\/a>, resulting in long-term cooling.<\/p>\n<figure id=\"attachment_4604\" aria-describedby=\"caption-attachment-4604\" style=\"width: 283px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/Antarctic-Circumpolar.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-910\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Antarctic-Circumpolar.png\" alt=\"Map of bottom of earth showing Antarctic continent and an ocean current circulating clockwise around it.\" width=\"283\" height=\"279\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Antarctic-Circumpolar.png 283w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Antarctic-Circumpolar-65x64.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Antarctic-Circumpolar-225x222.png 225w\" sizes=\"auto, (max-width: 283px) 100vw, 283px\" \/><\/a><figcaption id=\"caption-attachment-4604\" class=\"wp-caption-text\">The Antarctic Circumpolar Current<\/figcaption><\/figure>\n<p>About 40 million years ago, the narrow gap between the South American\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2591\">Plate<\/a>\u00a0and the Antarctica\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2591\">Plate<\/a>\u00a0widened, which opened the Drake Passage. This opening allowed the water around Antarctica\u2014the Antarctic Circumpolar Current\u2014to flow unrestrictedly west-to-east, which effectively isolated the southern ocean from the warmer waters of the Pacific, Atlantic, and Indian Oceans. The region cooled significantly, and by 35 million years ago, during the Oligocene <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2193\">Epoch<\/a>,\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2464\">glaciers<\/a>\u00a0had started to form on Antarctica.<\/p>\n<p>Around 15 million years ago,\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2602\">subduction<\/a>-related\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1181\">volcanos<\/a> between Central and South America created the Isthmus of Panama, which connected North and South America. This prevented water from flowing between the Pacific and Atlantic Oceans and reduced heat transfer from the tropics to the poles. This reduced heat transfer created a cooler Antarctica and larger Antarctic\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2464\">glaciers<\/a>. As a result, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2467\">ice sheet<\/a>\u00a0expanded on land and water, increased Earth\u2019s reflectivity and enhanced the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1711\">albedo<\/a> effect, which created a\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1713\">positive feedback<\/a>\u00a0loop: more reflective\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2910\">glacial<\/a>\u00a0ice, more cooling, more ice, more cooling, and so on.<\/p>\n<p>By 5 million years ago, during the Pliocene <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2193\">Epoch<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2467\">ice sheets<\/a> had started to grow in North America and northern Europe. The most intense part of the current <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">glaciation<\/a> is the Pleistocene <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2193\">Epoch<\/a>\u2019s last 1 million years. The Pleistocene\u2019s <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> varies significantly through a range of almost 10\u00b0C (18\u00b0F) on time scales of 40,000 to 100,000 years, and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2467\">ice sheets<\/a> expand and contract correspondingly. These variations are attributed to subtle changes in Earth\u2019s orbital parameters, called <strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1701\">Milankovitch cycles<\/a><\/strong> (see Chapter 14). Over the past million years, the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">glaciation<\/a>\u00a0cycles occurred approximately every 100,000 years,\u00a0with many\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2910\">glacial<\/a>\u00a0advances occurring in the last 2 million years\u00a0(Lisiecki and\u00a0Raymo, 2005).<\/p>\n<figure id=\"attachment_4605\" aria-describedby=\"caption-attachment-4605\" style=\"width: 1024px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.3-oxygen-isotope-record-Lisiecki-and-Raymo-2005.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-911 size-large\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-oxygen-isotope-record-Lisiecki-and-Raymo-2005-1024x768.jpg\" alt=\"Graph showing the oxygen isotope record for last 5 million years with regular cycles. More pronounced glacial cycles are in the last 1 million years.\" width=\"1024\" height=\"768\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-oxygen-isotope-record-Lisiecki-and-Raymo-2005-1024x768.jpg 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-oxygen-isotope-record-Lisiecki-and-Raymo-2005-300x225.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-oxygen-isotope-record-Lisiecki-and-Raymo-2005-768x576.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-oxygen-isotope-record-Lisiecki-and-Raymo-2005-65x49.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-oxygen-isotope-record-Lisiecki-and-Raymo-2005-225x169.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-oxygen-isotope-record-Lisiecki-and-Raymo-2005-350x263.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-oxygen-isotope-record-Lisiecki-and-Raymo-2005.jpg 1058w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><\/a><figcaption id=\"caption-attachment-4605\" class=\"wp-caption-text\">A Pliocene\u2010Pleistocene stack of 57 globally distributed benthic \u03b418O records (Source: Lisiecki, L. E., &amp; Raymo, M. E. (2005). A Pliocene\u2010Pleistocene stack of 57 globally distributed benthic \u03b418O records.\u00a0Paleoceanography,\u00a020(1).)<\/figcaption><\/figure>\n<p>During an\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">ice age<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2192\">periods<\/a> of warming <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0 are called\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3321\">interglacials<\/a><\/strong>; during <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3321\">interglacials<\/a>, very brief <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2192\">periods<\/a> of even warmer <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> are called\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3322\">interstadials<\/a><\/strong>. These warming upticks are related to Earth\u2019s\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0variations, like\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1701\">Milankovitch cycle<\/a>s, which are changes to the Earth\u2019s orbit that can fluctuate <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> (see Chapter 14). In the last 500,000 years, there have been five or six\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3321\">interglacials<\/a>, with the most recent belonging to our current time, the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1444\">Holocene<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2193\">Epoch<\/a>.<\/p>\n<p>The two more recent\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0swings, the Younger Dryas and the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1444\">Holocene<\/a>\u00a0Climatic Optimum, demonstrate complex changes. These events are more recent, yet have conflicting information. The Younger Dryas\u2019 cooling is widely recognized in the Northern Hemisphere, though the event\u2019s timing, about 12,000 years ago, does not appear to be equal everywhere. Also, it is difficult to find in the Southern Hemisphere. The\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1444\">Holocene<\/a>\u00a0Climatic Optimum is a warming around 6,000 years ago; it was not universally warmer, nor as warm as current warming, and not warm at the same time everywhere.<\/p>\n<h3><b>15.3.2 Proxy Indicators of Past Climates<\/b><\/h3>\n<p>How do we know about past climates? Geologists use proxy indicators to understand past\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>. A\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3323\">proxy indicator<\/a><\/strong>\u00a0is a biological, chemical, or physical signature preserved in the rock,\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2678\">sediment<\/a>, or ice record that acts like a fingerprint of something in the past. Thus, they are an <em>indirect <\/em>indicator of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>. An indirect indicator of ancient\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">glaciations<\/a>\u00a0from the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2209\">Proterozoic<\/a>\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2190\">Eon<\/a> and\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2219\">Paleozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2191\">Era<\/a> is the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2687\">Mineral<\/a>\u00a0Fork\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2960\">Formation<\/a>\u00a0in Utah, which contains rock\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2960\">formations<\/a>\u00a0of\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2910\">glacial<\/a>\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2678\">sediments<\/a>\u00a0such as <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2911\">diamictite<\/a> (<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2483\">tillite<\/a>). \u00a0This dark rock has many fine-grained components plus some large out-sized clasts like a modern\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2910\">glacial<\/a>\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2912\">till<\/a>.<\/p>\n<p>Deep-sea <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2678\">sediment<\/a> is an indirect indicator of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> change during the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1441\">Cenozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2191\">Era<\/a>, about the last 65 million years. Researchers from the Ocean Drilling Program, an international research collaboration, collect deep-sea <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2678\">sediment<\/a> cores that record continuous <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2678\">sediment<\/a> accumulation. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2678\">sediment<\/a> provides detailed chemical records of stable carbon and oxygen <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2701\">isotopes<\/a> obtained from deep-sea benthic foraminifera shells that accumulated on the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2885\">ocean floor<\/a> over millions of years. The oxygen <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2701\">isotopes<\/a> are a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3323\">proxy indicator<\/a> of deep-sea temperatures and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2575\">continental<\/a> ice volume.<\/p>\n<h4><span style=\"font-weight: 400\">Sediment Cores &#8211; Stable Oxygen Isotopes<\/span><\/h4>\n<figure id=\"attachment_4606\" aria-describedby=\"caption-attachment-4606\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.3_sediment-core_hg.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-912 size-medium\" title=\"Source: Hannes Grobe, https:\/\/en.wikipedia.org\/wiki\/File:PS1920-1_0-750_sediment-core_hg.jpg#metadata\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_sediment-core_hg-300x290.jpg\" alt=\"Image of sediment core showing clear layering and vertical changes in color and composition.\" width=\"300\" height=\"290\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_sediment-core_hg-300x290.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_sediment-core_hg-1024x990.jpg 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_sediment-core_hg-768x743.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_sediment-core_hg-1536x1486.jpg 1536w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_sediment-core_hg-65x63.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_sediment-core_hg-225x218.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_sediment-core_hg-350x339.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_sediment-core_hg.jpg 1558w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-4606\" class=\"wp-caption-text\">Sediment core from the Greenland continental slope (Source: Hannes Grobe)<\/figcaption><\/figure>\n<p>How do oxygen\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2701\">isotopes<\/a>\u00a0indicate past\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>? The two main stable oxygen\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2701\">isotopes<\/a>\u00a0are\u00a0<sup>16<\/sup>O and\u00a0<sup>18<\/sup>O. They both occur in water (H<sub>2<\/sub>O) and in the calcium\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1917\">carbonate<\/a>\u00a0(CaCO<sub>3<\/sub>) shells of foraminifera as both of those substances\u2019 oxygen component. The most abundant and lighter\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2701\">isotope<\/a>\u00a0is\u00a0<sup>16<\/sup>O. Since it is lighter, it evaporates more readily from the ocean\u2019s surface as water vapor, which later turns to clouds and\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2707\">precipitation<\/a>\u00a0on the ocean and land. This evaporation is enhanced in warmer sea water and slightly increases the concentration of <sup>18<\/sup>O in the surface seawater from which the plankton derives the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1917\">carbonate<\/a> for its shells. Thus the ratio of <sup>16<\/sup>O and\u00a0<sup>18<\/sup>O in the fossilized shells in seafloor <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2678\">sediment<\/a> is a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3323\">proxy indicator<\/a> of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> and evaporation of seawater.<\/p>\n<figure id=\"attachment_4607\" aria-describedby=\"caption-attachment-4607\" style=\"width: 446px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.3-Ice_Age_Temperature.png\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-913\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-Ice_Age_Temperature.png\" alt=\"Show clear chemical evidence for six glaciations over the past 450,000 years.\" width=\"446\" height=\"298\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-Ice_Age_Temperature.png 564w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-Ice_Age_Temperature-300x201.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-Ice_Age_Temperature-65x43.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-Ice_Age_Temperature-225x150.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-Ice_Age_Temperature-350x234.png 350w\" sizes=\"auto, (max-width: 446px) 100vw, 446px\" \/><\/a><figcaption id=\"caption-attachment-4607\" class=\"wp-caption-text\">Antarctic temperature changes during the last few glaciations compared to global ice volume. The first two curves are based on the deuterium (heavy hydrogen) record from ice cores (EPICA Community Members 2004, Petit et al. 1999). The bottom line is ice volume based on oxygen isotopes from a composite of deep-sea sediment cores (Lisiecki and Raymo 2005).<\/figcaption><\/figure>\n<p><span style=\"font-weight: 400\">Keep in mind, it is harder to evaporate the heavier water and easier to condense it.\u00a0 As evaporated water vapor drifts toward the poles and tiny droplets form clouds and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2707\">precipitation<\/a>, droplets of water with <sup>18<\/sup>O tend to form more readily than droplets of the lighter form and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2707\">precipitate<\/a> out, leaving the drifting vapor depleted in <sup>18<\/sup>O. During geologic times when the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> is cooler, more of this lighter <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2707\">precipitation<\/a> that <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3119\">falls<\/a> on land is locked in the form of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2910\">glacial<\/a> ice. Consider that the giant <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2467\">ice sheets<\/a> were more than a mile thick and covered a large part of North America during the last <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">ice age<\/a> only 14,000 years ago. During <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">glaciation<\/a>, the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2464\">glaciers<\/a> thus effectively lock away more <\/span><sup><span style=\"font-weight: 400\">16<\/span><\/sup><span style=\"font-weight: 400\">O, thus the ocean water and foraminifera shells become enriched in <\/span><sup><span style=\"font-weight: 400\">18<\/span><\/sup><span style=\"font-weight: 400\">O.\u00a0<\/span><span style=\"font-weight: 400\">Therefore, the ratio of <\/span><sup><span style=\"font-weight: 400\">18<\/span><\/sup><span style=\"font-weight: 400\">O to <\/span><sup><span style=\"font-weight: 400\">16<\/span><\/sup><span style=\"font-weight: 400\">O (\ud835\udeff<\/span><sup><span style=\"font-weight: 400\">18<\/span><\/sup><span style=\"font-weight: 400\">O) in calcium <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1917\">carbonate<\/a> shells of foraminifera is a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3323\">proxy indicator<\/a> of past <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>. The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2678\">sediment<\/a> cores from the Ocean Drilling Program record a continuous accumulation of these <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2176\">fossils<\/a> in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2678\">sediment<\/a> and provide a record of glacials,\u00a0 <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3321\">interglacials<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3322\">interstadials<\/a>.<\/span><\/p>\n<h4><span style=\"font-weight: 400\">Sediment Cores &#8211; Boron-Isotopes and Acidity<\/span><\/h4>\n<p>Ocean acidity is affected by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2813\">carbonic acid<\/a> and is a proxy for past atmospheric CO<sub>2<\/sub> concentrations. To estimate the ocean\u2019s pH (acidity) over the past 60 million years, researchers collected deep-sea <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2678\">sediment<\/a> cores and examined the ancient planktonic foraminifera shells\u2019 boron-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2701\">isotope<\/a> ratios. Boron has two <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2701\">isotopes<\/a>:\u00a0<sup data-preserve-html-node=\"true\">11<\/sup>B and\u00a0<sup data-preserve-html-node=\"true\">10<\/sup>B. In aqueous compounds of boron, the relative abundance of these two <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2701\">isotopes<\/a> is sensitive to pH (acidity), hence CO<sub>2<\/sub> concentrations. In the early <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1441\">Cenozoic<\/a>, around 60 million years ago, CO<sub>2<\/sub> concentrations were over 2,000 ppm, higher pH, and started falling around 55 to 40 million years ago, with noticeable drop in pH, indicated by boron <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2701\">isotope<\/a> ratios. The drop was possibly due to reduced CO<sub>2<\/sub>\u00a0outgassing from ocean ridges,\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1181\">volcanoes<\/a>\u00a0and\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2914\">metamorphic<\/a>\u00a0belts, and increased carbon burial due to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2602\">subduction<\/a> and the Himalaya Mountains uplift. By the Miocene <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2193\">Epoch<\/a>, about 24 million years ago, CO<sub>2<\/sub>\u00a0levels were below 500 ppm,\u00a0and by 800,000 years ago, CO<sup>2<\/sup>\u00a0levels didn\u2019t exceed 300 ppm.<\/p>\n<h4><span style=\"font-weight: 400\">Carbon Dioxide Concentrations in Ice Cores<\/span><\/h4>\n<figure id=\"attachment_4608\" aria-describedby=\"caption-attachment-4608\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.3_GISP2_1855m_ice_core_layers.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-medium wp-image-914\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_GISP2_1855m_ice_core_layers-300x136.png\" alt=\"Image of ice core showing seasonal color changes like a tree rings.\" width=\"300\" height=\"136\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_GISP2_1855m_ice_core_layers-300x136.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_GISP2_1855m_ice_core_layers-65x29.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_GISP2_1855m_ice_core_layers-225x102.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_GISP2_1855m_ice_core_layers-350x158.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_GISP2_1855m_ice_core_layers.png 741w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-4608\" class=\"wp-caption-text\">19 cm long section of ice core showing 11 annual layers with summer layers (arrowed) sandwiched between darker winter layers. (Source: US Army Corps of Engineers)<\/figcaption><\/figure>\n<p>For the recent Pleistocene\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2193\">Epoch<\/a>\u2019s <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>,\u00a0researchers get a more detailed and direct chemical record of the last 800,000 years by extracting and analyzing ice cores from the Antarctic and Greenland\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2467\">ice sheets<\/a>. Snow accumulates on these\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2467\">ice sheets<\/a>\u00a0and creates yearly layers. Oxygen\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2467\">isotopes<\/a>\u00a0are collected from these annual layers, and the ratio of\u00a0<sup>18<\/sup>O to\u00a0<sup>16<\/sup>O (\ud835\udeff<sup>18<\/sup>O) is used to determine <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> as discussed above. In addition, the ice contains small bubbles of atmospheric gas as the snow turns to ice. Analysis of these bubbles reveals the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2831\">composition<\/a> of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a> at these previous times.<\/p>\n<figure id=\"attachment_4609\" aria-describedby=\"caption-attachment-4609\" style=\"width: 300px\" class=\"wp-caption alignright\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.3_Air_Bubbles_Trapped_in_Ice.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-915 size-medium\" title=\"Source: Commonwealth Scientific and Industrial Research Organization (Australia) - https:\/\/en.wikipedia.org\/wiki\/File:CSIRO_ScienceImage_518_Air_Bubbles_Trapped_in_Ice.jpg\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Air_Bubbles_Trapped_in_Ice-300x205.jpg\" alt=\"Antarctic ice showing hundreds of tiny trapped air bubbles from the atmosphere thousands of years ago.\" width=\"300\" height=\"205\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Air_Bubbles_Trapped_in_Ice-300x205.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Air_Bubbles_Trapped_in_Ice-1024x701.jpg 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Air_Bubbles_Trapped_in_Ice-768x526.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Air_Bubbles_Trapped_in_Ice-1536x1051.jpg 1536w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Air_Bubbles_Trapped_in_Ice-2048x1401.jpg 2048w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Air_Bubbles_Trapped_in_Ice-65x44.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Air_Bubbles_Trapped_in_Ice-225x154.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Air_Bubbles_Trapped_in_Ice-350x239.jpg 350w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-4609\" class=\"wp-caption-text\">Antarctic ice showing hundreds of tiny trapped air bubbles from the atmosphere thousands of years ago. (Source: CSIRO)<\/figcaption><\/figure>\n<p>Small pieces of this ice are crushed, and the ancient air is extracted into a\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2174\">mass spectrometer<\/a>\u00a0that can detect the ancient\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>\u2019s chemistry. Carbon dioxide levels are recreated from these measurements. Over the last 800,000 years, the <em>maximum<\/em> carbon dioxide concentration during warm times was about 300 parts per million (ppm), and the minimum was about 170 ppm during cold stretches. Currently, the earth\u2019s\u00a0atmospheric\u00a0carbon dioxide content is over 410 ppm.<\/p>\n<figure id=\"attachment_4610\" aria-describedby=\"caption-attachment-4610\" style=\"width: 818px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.3_Co2_glacial_cycles_800k.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-full wp-image-916\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Co2_glacial_cycles_800k.png\" alt=\"Graph shows concentrations of carbon dioxide around 290 ppm during warm periods and 190 ppm during glacial periods. Total time frame is about 800,000 years.\" width=\"818\" height=\"580\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Co2_glacial_cycles_800k.png 818w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Co2_glacial_cycles_800k-300x213.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Co2_glacial_cycles_800k-768x545.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Co2_glacial_cycles_800k-65x46.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Co2_glacial_cycles_800k-225x160.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Co2_glacial_cycles_800k-350x248.png 350w\" sizes=\"auto, (max-width: 818px) 100vw, 818px\" \/><\/a><figcaption id=\"caption-attachment-4610\" class=\"wp-caption-text\">Composite carbon dioxide record from last 800,000 years based on ice core data from EPICA Dome C Ice Core.<\/figcaption><\/figure>\n<h4><span style=\"font-weight: 400\">Oceanic Microfossils<\/span><\/h4>\n<p>Microfossils, like foraminifera, diatoms, and radiolarians can be used as a proxy to interpret past <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> record. Different species of microfossils are found in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3384\">sediment<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2589\">core<\/a>\u2019s different layers. Microfossil groups are called assemblages and their <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2831\">composition<\/a> differs depending on the climatic conditions when they lived. One assemblage consists of species that lived in cooler ocean water, such as in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2910\">glacial<\/a> times, and at a different level in the same <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3384\">sediment<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2589\">core<\/a>, another assemblage consists of species that lived in warmer waters.<\/p>\n<figure id=\"attachment_4870\" aria-describedby=\"caption-attachment-4870\" style=\"width: 150px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/Climatic-Evidence-From-Sediments-Youtube-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-917\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Climatic-Evidence-From-Sediments-Youtube-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Climatic-Evidence-From-Sediments-Youtube-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Climatic-Evidence-From-Sediments-Youtube-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Climatic-Evidence-From-Sediments-Youtube-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Climatic-Evidence-From-Sediments-Youtube-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Climatic-Evidence-From-Sediments-Youtube-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Climatic-Evidence-From-Sediments-Youtube-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Climatic-Evidence-From-Sediments-Youtube-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Climatic-Evidence-From-Sediments-Youtube-QR-Code.png 1155w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4870\" class=\"wp-caption-text\">If you are using the printed version of this OER, access this YouTube video via this QR Code.<\/figcaption><\/figure>\n<p><iframe loading=\"lazy\" id=\"oembed-5\" title=\"Climatic Evidence From Sediments - Exploring the Science of Climate (3\/5)\" width=\"500\" height=\"281\" src=\"https:\/\/www.youtube.com\/embed\/Yvu-g8BkkIg?feature=oembed&#38;rel=0&#38;rel=0\" frameborder=\"0\" allowfullscreen=\"allowfullscreen\"><\/iframe><\/p>\n<h4><span style=\"font-weight: 400\">Tree Rings<\/span><\/h4>\n<figure id=\"attachment_4611\" aria-describedby=\"caption-attachment-4611\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.3_Tree.rings_.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"size-medium wp-image-918\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Tree.rings_-300x225.jpg\" alt=\"Shows a tree cut in cross-section with tree rings. Each ring form in one year.\" width=\"300\" height=\"225\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Tree.rings_-300x225.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Tree.rings_-1024x766.jpg 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Tree.rings_-768x575.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Tree.rings_-1536x1149.jpg 1536w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Tree.rings_-65x49.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Tree.rings_-225x168.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Tree.rings_-350x262.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Tree.rings_.jpg 1800w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-4611\" class=\"wp-caption-text\">Tree rings form every year. Rings that are farther apart are from wetter years and rings that are closer together are from dryer years.<\/figcaption><\/figure>\n<p>Tree rings, which form every year as a tree grows, are another past <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> indicator. Rings that are thicker indicate wetter years, and rings that are thinner and closer together indicate dryer years. Every year, a tree will grow one ring with a light section and a dark section. The rings vary in width. Since trees need much water to survive, narrower rings indicate colder and drier climates. Since some trees are several thousand years old, scientists can use their rings for regional paleoclimatic reconstructions, for example, to reconstruct past <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a>, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2707\">precipitation<\/a>, vegetation, streamflow, sea-surface <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a>, and other <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>-dependent conditions. Paleoclimatic study means relating to a distinct past geologic climate. Also, dead trees, such as those found in Puebloan ruins, can be used to extend this\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3323\">proxy indicator<\/a> by showing long-term droughts in the region and possibly explain why villages were abandoned.<\/p>\n<figure id=\"attachment_4612\" aria-describedby=\"caption-attachment-4612\" style=\"width: 1024px\" class=\"wp-caption aligncenter\"><a style=\"font-weight: bold;background-color: transparent;text-align: inherit\" href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.3_Tree-Ring-Temperature-Anamoly_Yamal50.gif\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-919 size-large\" title=\"Source: R.M.Hantemirov - https:\/\/en.wikipedia.org\/wiki\/File:Yamal50.gif\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Tree-Ring-Temperature-Anamoly_Yamal50-1024x224.gif\" alt=\"Tree ring data from last 7000 years showing average summer highs and lows fluctuating around a mean. Last few hundred years are slightly higher than normal.\" width=\"1024\" height=\"224\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Tree-Ring-Temperature-Anamoly_Yamal50-1024x224.gif 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Tree-Ring-Temperature-Anamoly_Yamal50-300x66.gif 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Tree-Ring-Temperature-Anamoly_Yamal50-768x168.gif 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Tree-Ring-Temperature-Anamoly_Yamal50-1536x336.gif 1536w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Tree-Ring-Temperature-Anamoly_Yamal50-2048x448.gif 2048w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Tree-Ring-Temperature-Anamoly_Yamal50-65x14.gif 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Tree-Ring-Temperature-Anamoly_Yamal50-225x49.gif 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Tree-Ring-Temperature-Anamoly_Yamal50-350x77.gif 350w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><\/a><figcaption id=\"caption-attachment-4612\" class=\"wp-caption-text\"><span style=\"text-align: justify;font-size: 1em\">Summer [pb_glossary id=\"2689\"]temperature[\/pb_glossary] [pb_glossary id=\"1719\"]anomalies[\/pb_glossary] for the past 7000 years (Source: R.M.Hantemirov)<\/span><\/figcaption><\/figure>\n<h4><span style=\"font-weight: 400\">Pollen<\/span><\/h4>\n<figure id=\"attachment_4613\" aria-describedby=\"caption-attachment-4613\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.3_Misc_pollen_colorized.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-920 size-medium\" title=\"Source: Dartmouth Electron Microscope Facility, Dartmouth College - https:\/\/en.wikipedia.org\/wiki\/File:Misc_pollen_colorized.jpg\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Misc_pollen_colorized-300x228.jpg\" alt=\"Close up image of what pollen looks like.\" width=\"300\" height=\"228\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Misc_pollen_colorized-300x228.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Misc_pollen_colorized-1024x780.jpg 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Misc_pollen_colorized-768x585.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Misc_pollen_colorized-65x49.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Misc_pollen_colorized-225x171.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Misc_pollen_colorized-350x266.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3_Misc_pollen_colorized.jpg 1228w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-4613\" class=\"wp-caption-text\">Scanning electron microscope image of modern pollen with false color added to distinguish plant species.<\/figcaption><\/figure>\n<p>Pollen is also a proxy <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> indicator. Flowering plants produce pollen grains. Pollen grains are distinctive when viewed under a microscope. Sometimes, pollen is preserved in lake <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2678\">sediments<\/a> that accumulate in layers every year. Lake-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2678\">sediment<\/a> cores can reveal ancient pollen. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2176\">Fossil<\/a>-pollen assemblages are pollen groups from multiple species, such as spruce, pine, and oak. Through time, via the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2678\">sediment<\/a> cores and radiometric age-dating techniques, the pollen assemblages change, revealing the plants that lived in the area at the time. Thus, the pollen assemblages are a past <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> indicator, since different plants will prefer different climates. For example, in the Pacific Northwest, east of the Cascades in a region close to grassland and forest borders, scientists tracked pollen over the last 125,000 years, covering the last two <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">glaciations<\/a>. As shown in the figure (Fig. 2 from reference Whitlock and Bartlein 1997), pollen assemblages with more pine tree pollen are found during <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">glaciations<\/a> and pollen assemblages with less pine tree pollen are found during <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3321\">interglacial<\/a> times.<\/p>\n<h4><span style=\"font-weight: 400\">Other Proxy Indicators<\/span><\/h4>\n<p>Paleoclimatologists study many other phenomena to understand past climates, such as human historical accounts, human instrument records from the recent past, lake\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2678\">sediments<\/a>, cave deposits, and corals.<\/p>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-104\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-104\" class=\"h5p-iframe\" data-content-id=\"104\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"15.3 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4866\" aria-describedby=\"caption-attachment-4866\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/15.3-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-921\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.3-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4866\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 15.3 via this QR Code.<\/figcaption><\/figure>\n<h2><span style=\"font-weight: 400\">15.4 Anthropogenic Causes of Climate Change<\/span><\/h2>\n<p>As shown in the previous section, prehistoric <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0changes occur slowly over many millions of years. The\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0changes observed today are rapid and largely human caused. Evidence shows that\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0is changing, but what is causing that change? Since the late 1800s, scientists have suspected that human-produced, i.e. <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1717\">anthropogenic<\/a> changes in atmospheric greenhouse gases would likely cause\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0change because changes in these gases have been the case every time in the geologic past. By the middle 1900s, scientists began conducting systematic measurements, which confirmed that human-produced carbon dioxide was accumulating in the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>\u00a0and other earth systems, such as forests and oceans. By the end of the 1900s and into the early 2000s, scientists solidified the\u00a0<strong><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2655\">Theory<\/a>\u00a0of\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1717\">Anthropogenic<\/a>\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">Climate<\/a>\u00a0Change<\/strong> when evidence from thousands of ground-based studies and continuous land and ocean satellite measurements mounted, revealing the expected\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a>\u00a0increase. The\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2655\">Theory<\/a>\u00a0of\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1717\">Anthropogenic<\/a>\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">Climate<\/a>\u00a0Change is that humans are causing most of the current climate changes\u00a0by burning\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3336\">fossil fuels<\/a>\u00a0such as\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2856\">coal<\/a>,\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3338\">oil<\/a>, and\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3339\">natural gas<\/a>. Theories evolve and\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2601\">transform<\/a>\u00a0as new data and new techniques become available, and they represent a particular field\u2019s state of thinking. This section summarizes the scientific consensus of\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1717\">anthropogenic<\/a>\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0change.<\/p>\n<h3><b>15.4.1 Scientific Consensus<\/b><\/h3>\n<p>The overwhelming majority of\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0studies indicate that human activity is causing rapid changes to the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>, which will cause severe environmental damage. There is strong scientific consensus on the issue. Studies published in peer-reviewed scientific journals show that 97 percent of\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0scientists agree that\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0warming is caused from human activities. There is no alternative explanation for the observed link between human-produced greenhouse gas emissions and changing modern\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>. Most leading scientific organizations endorse this position, including the U.S. National Academy of Science, which was established in 1863 by an act of Congress under President Lincoln. Congress charged the National Academy of Science \u201cwith providing independent,\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2644\">objective<\/a>\u00a0advice to the nation on matters related to science and technology.\u201d Therefore, the National Academy of Science is the leading authority when it comes to policy advice related to scientific issues.<\/p>\n<p>One way we know that the increased greenhouse gas emissions are from human activities is with isotopic fingerprints. For example,\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3336\">fossil fuels<\/a>, representing plants that lived millions of years ago,\u00a0have a stable carbon-13 to carbon-12 (<sup>13<\/sup>C\/<sup>12<\/sup>C) ratio that is different from today\u2019s atmospheric stable-carbon ratio (<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2966\">radioactive<\/a> <sup>14<\/sup>C is unstable). Isotopic carbon signatures have been used to identify <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1717\">anthropogenic<\/a> carbon in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a> since the 1980s. Isotopic records from the Antarctic <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2467\">Ice Sheet<\/a> show stable isotopic signatures from ~1000 AD to ~1800 AD and a steady isotopic signature gradually changing since 1800, followed by a more rapid change after 1950 as burning of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3336\">fossil fuels<\/a> dilutes the CO<sub>2<\/sub> in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>. These changes show the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>\u00a0as having a carbon isotopic signature increasingly more similar to that of\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3336\">fossil fuels<\/a>.<\/p>\n<h3><b>15.4.2 Anthropogenic Sources of Greenhouse Gases<\/b><\/h3>\n<p><span style=\"font-weight: 400\"><a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1717\">Anthropogenic<\/a> emissions of greenhouse gases have increased since pre-industrial times due to global economic growth and population growth. Atmospheric concentrations of the leading greenhouse gas, carbon dioxide, are at unprecedented levels that haven\u2019t been observed in at least the last 800,000 years<\/span><span style=\"font-weight: 400\">. Pre-industrial level of carbon dioxide was at about 278 parts per million (ppm). As of 2016, carbon dioxide was, for the first time, above 400 ppm for the entirety of the year. Measurements of atmospheric carbon at the Mauna Loa Carbon Dioxide Observatory show a continuous increase since 1957 when the observatory was established from 315 ppm to over 417 ppm in 2022. The daily reading today can be seen at <a href=\"https:\/\/www.co2.earth\/daily-co2\">Daily CO2<\/a>.\u00a0 Based on the ice <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2589\">core<\/a> record over the past 800,000 years, carbon dioxide ranged from about 185 ppm during <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">ice ages<\/a> to 300 ppm during warm times<\/span><span style=\"font-weight: 400\">. View the <\/span><span style=\"font-weight: 400\">data-accurate NOAA animation below\u00a0<\/span><span style=\"font-weight: 400\">of carbon dioxide trends over the last 800,000 years.<\/span><\/p>\n<figure id=\"attachment_4614\" aria-describedby=\"caption-attachment-4614\" style=\"width: 300px\" class=\"wp-caption alignleft\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.4_Fig-1.7-from-Pachauri-et-al-2014.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-922 size-medium\" title=\"Source: Pachauri et al. 2014 - IPCC Climate Change 2014 Synthesis Report - https:\/\/www.ipcc.ch\/pdf\/assessment-report\/ar5\/syr\/AR5_SYR_FINAL_All_Topics.pdf\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4_Fig-1.7-from-Pachauri-et-al-2014-300x268.jpg\" alt=\"Pie chart shows\" width=\"300\" height=\"268\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4_Fig-1.7-from-Pachauri-et-al-2014-300x268.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4_Fig-1.7-from-Pachauri-et-al-2014-65x58.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4_Fig-1.7-from-Pachauri-et-al-2014-225x201.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4_Fig-1.7-from-Pachauri-et-al-2014-350x312.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4_Fig-1.7-from-Pachauri-et-al-2014.jpg 725w\" sizes=\"auto, (max-width: 300px) 100vw, 300px\" \/><\/a><figcaption id=\"caption-attachment-4614\" class=\"wp-caption-text\">Total anthropogenic greenhouse gas emissions (gigatonne of CO2- equivalent per year, GtCO2-eq\/yr) from economic sectors in 2010. The circle shows the shares of direct GHG emissions (in % of total anthropogenic GHG emissions) from five economic sectors in 2010. The pull-out shows how shares of indirect CO2 emissions (in % of total anthropogenic GHG emissions) from electricity and heat production are attributed to sectors of final energy use. (Source: Pachauri et al. 2014)<\/figcaption><\/figure>\n<p>What is the source of these\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1717\">anthropogenic<\/a>\u00a0greenhouse gas emissions?\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3336\">Fossil fuel<\/a>\u00a0combustion and industrial processes contributed 78 percent of all emissions since 1970. The economic sectors responsible for most of this include electricity and heat production (25 percent); agriculture, forestry, and land use (24 percent); industry (21 percent); transportation, including automobiles (14 percent); other energy production (9.6 percent); and buildings (6.4 percent). More than half of greenhouse gas emissions have occurred in the last 40 years, and 40 percent of these emissions have stayed in the\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a>. Unfortunately, despite scientific consensus, efforts to mitigate\u00a0<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0change require political action.\u00a0Despite growing <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>\u00a0change concern, mitigation efforts, legislation, and international agreements have reduced emissions in some places, yet the less developed world\u2019s continual economic growth has increased global greenhouse gas emissions. In fact, the years 2000 to 2010 saw the largest increases since 1970.<\/p>\n<figure id=\"attachment_4615\" aria-describedby=\"caption-attachment-4615\" style=\"width: 1024px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/02\/15.4_Fig-1.5-Pachauri-et-al.-2014-emissions-1850-2011.jpg\"><img loading=\"lazy\" decoding=\"async\" class=\"wp-image-923 size-large\" title=\"Source: Pachauri et al. 2014 Fig. 1.5 IPCC Climate Change 2014 Synthesis Report - https:\/\/www.ipcc.ch\/pdf\/assessment-report\/ar5\/syr\/AR5_SYR_FINAL_All_Topics.pdf\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4_Fig-1.5-Pachauri-et-al.-2014-emissions-1850-2011-1024x396.jpg\" alt=\"Graph shows carbon emissions from fossil fuel combustion increase notable around 1950 and continue to increase consistently until the graph ends in 2011.\" width=\"1024\" height=\"396\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4_Fig-1.5-Pachauri-et-al.-2014-emissions-1850-2011-1024x396.jpg 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4_Fig-1.5-Pachauri-et-al.-2014-emissions-1850-2011-300x116.jpg 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4_Fig-1.5-Pachauri-et-al.-2014-emissions-1850-2011-768x297.jpg 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4_Fig-1.5-Pachauri-et-al.-2014-emissions-1850-2011-65x25.jpg 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4_Fig-1.5-Pachauri-et-al.-2014-emissions-1850-2011-225x87.jpg 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4_Fig-1.5-Pachauri-et-al.-2014-emissions-1850-2011-350x135.jpg 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4_Fig-1.5-Pachauri-et-al.-2014-emissions-1850-2011.jpg 1477w\" sizes=\"auto, (max-width: 1024px) 100vw, 1024px\" \/><\/a><figcaption id=\"caption-attachment-4615\" class=\"wp-caption-text\">Annual global anthropogenic carbon dioxide (CO2) emissions in gigatonne of CO2-equivalent per year (GtCO2\/yr) from fossil fuel combustion, cement production and flaring, and forestry and other land use (FOLU), 1750\u20132011. Cumulative emissions and their uncertainties are shown as bars and whiskers<\/figcaption><\/figure>\n<h3>Take this quiz to check your comprehension of this section.<\/h3>\n<div id=\"h5p-105\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-105\" class=\"h5p-iframe\" data-content-id=\"105\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"15.4 Did I Get It?\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4867\" aria-describedby=\"caption-attachment-4867\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/15.4-Did-I-Get-It-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-924\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4-Did-I-Get-It-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4-Did-I-Get-It-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4-Did-I-Get-It-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4-Did-I-Get-It-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4-Did-I-Get-It-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4-Did-I-Get-It-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4-Did-I-Get-It-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4-Did-I-Get-It-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/15.4-Did-I-Get-It-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4867\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the quiz for section 15.4 via this QR Code.<\/figcaption><\/figure>\n<h3>Summary<\/h3>\n<p>Included in Earth Science is the study of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2664\">system<\/a> of processes that affect surface environments and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a> of the Earth. Recent changes in atmospheric <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> over intervals of decades have been observed. For Earth\u2019s <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> to be stable, incoming radiation from the sun and outgoing radiation from the sun-warmed Earth must be in balance. Gases in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a> called greenhouse gases absorb the infrared thermal radiation from the Earth\u2019s surface, trapping that heat and warming the atmosphere, a process called the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1715\">Greenhouse Effect<\/a>. Thus the energy budget is not now in balance and the Earth is warming. Human activity produces many greenhouse gases that have accelerated <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> change. CO2 from <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3336\">fossil fuel<\/a> burning is one of the major ones. While atmospheric <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2831\">composition<\/a> is mostly nitrogen and oxygen, trace components including the greenhouse gases (CO2 and methane are the major ones and there are others) have the greatest effect on global warming.<\/p>\n<p>A number of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1713\">Positive Feedback<\/a> Mechanisms, processes whose results reinforce the original process, take place in the Earth <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2664\">system<\/a>. An example of a PFM of great concern is <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1712\">permafrost<\/a> melting which causes decay of melting organic material that produces CO2 and methane (both powerful greenhouse gases) that warm the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a> and promote more <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1712\">permafrost<\/a> melting. Two carbon cycles affect Earth\u2019s atmospheric CO2 <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2831\">composition<\/a>, the biologic carbon cycle and the geologic carbon cycle. In the biologic cycle, organisms (mostly plants and also animals that eat them) remove CO2 from the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a> for energy and to build their body tissues and return it to the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">atmosphere<\/a> when they die and decay. The biologic cycle is a rapid cycle. In the geologic cycle, some organic matter is preserved in the form of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3337\">petroleum<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2856\">coal<\/a> while more is <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2815\">dissolved<\/a> in seawater and captured in <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1917\">carbonate<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2678\">sediments<\/a>, some of which is <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2602\">subducted<\/a> into the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2586\">mantle<\/a> and returned by <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1181\">volcanic<\/a> activity. The geologic carbon cycle is slow over geologic time.<\/p>\n<p>Measurements of increasing atmospheric <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> have been made since the nineteenth century but the upward <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> trend itself increased in the mid twentieth century showing the current trend is exponential. Because of the high specific heat of water, the oceans have absorbed most of the added heat. That this is temporary storage is revealed by the record-breaking warm years of the recent decade and the increase in intense storms and hurricanes. In 1957 the Mauna Loa CO2 Observatory was established in Hawaii providing constant measurements of atmospheric CO2 since 1958. The initial value was 315 ppm. The Keeling curve, named for the observatory founder, shows that value has steadily increased, exponentially, to over 417 ppm now. Compared to proxy data from atmospheric gases trapped in ice cores that show a maximum value for CO2 of about 300 ppm over the last 800,000 years, the Keeling increase of over 100 ppm in 50 years is dramatic evidence of human caused CO2 increase and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> change! As Earth\u2019s <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> rises, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2464\">glaciers<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2467\">ice sheets<\/a> are shrinking resulting in sea level rise. Atmospheric CO2 is also absorbed in sea water producing increased concentrations of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2813\">carbonic acid<\/a> which is raising the pH of the oceans making it harder for <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2883\">marine<\/a> life to extract <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1917\">carbonate<\/a> for their skeletal materials.<\/p>\n<p>Earth\u2019s <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> has changed over geologic time with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2192\">periods<\/a> of major <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">glaciations<\/a>. There was a high <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2192\">period<\/a> in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1432\">Mesozoic<\/a> shown by fossils in high latitudes and the Western Interior Seaway covering what is now the Midwest. However, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> has been cooling during the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1441\">Cenozoic<\/a> culminating in the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">Ice Age<\/a>. Since the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">Ice Age<\/a>, several proxy indicators of ancient <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> show that the rate and amount of current <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> change is unique in geologic history and can only be attributed to human activity. Those who ignore the consequences of increasing global warming for our planet\u2019s future do so at the peril of our posterity!<\/p>\n<h3>Take this quiz to check your comprehension of this Chapter.<\/h3>\n<div id=\"h5p-106\">\n<div class=\"h5p-iframe-wrapper\"><iframe id=\"h5p-iframe-106\" class=\"h5p-iframe\" data-content-id=\"106\" style=\"height:1px\" src=\"about:blank\" frameBorder=\"0\" scrolling=\"no\" title=\"Chapter 15 Review\"><\/iframe><\/div>\n<\/div>\n<figure id=\"attachment_4869\" aria-describedby=\"caption-attachment-4869\" style=\"width: 150px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/slcc.pressbooks.pub\/app\/uploads\/sites\/35\/2022\/03\/Ch.15-Review-QR-Code.png\"><img loading=\"lazy\" decoding=\"async\" class=\"size-thumbnail wp-image-925\" src=\"https:\/\/pressbooks.ccconline.org\/accdigitalmarketing\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.15-Review-QR-Code-150x150.png\" alt=\"\" width=\"150\" height=\"150\" srcset=\"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.15-Review-QR-Code-150x150.png 150w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.15-Review-QR-Code-300x300.png 300w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.15-Review-QR-Code-1024x1024.png 1024w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.15-Review-QR-Code-768x768.png 768w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.15-Review-QR-Code-65x65.png 65w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.15-Review-QR-Code-225x225.png 225w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.15-Review-QR-Code-350x350.png 350w, https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-content\/uploads\/sites\/222\/2025\/01\/Ch.15-Review-QR-Code.png 1147w\" sizes=\"auto, (max-width: 150px) 100vw, 150px\" \/><\/a><figcaption id=\"caption-attachment-4869\" class=\"wp-caption-text\">If you are using the printed version of this OER, access the review quiz for Chapter 15 via this QR Code<\/figcaption><\/figure>\n<h2><b>References<\/b><\/h2>\n<div class=\"csl-bib-body\">\n<ol>\n<li class=\"csl-entry\">Allen, P.A., and Etienne, J.L., 2008, Sedimentary challenge to <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1718\">Snowball Earth<\/a>: Nat. Geosci., v. 1, no. 12, p. 817\u2013825.<\/li>\n<li class=\"csl-entry\">Berner, R.A., 1998, The carbon cycle and carbon dioxide over <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2217\">Phanerozoic<\/a> time: the role of land plants: Philos. Trans. R. Soc. Lond. B Biol. Sci., v. 353, no. 1365, p. 75\u201382.<\/li>\n<li class=\"csl-entry\">Cunningham, W.L., Leventer, A., Andrews, J.T., Jennings, A.E., and Licht, K.J., 1999, Late Pleistocene\u2013<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1444\">Holocene<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2883\">marine<\/a> conditions in the Ross Sea, Antarctica: evidence from the diatom record: The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1444\">Holocene<\/a>, v. 9, no. 2, p. 129\u2013139.<\/li>\n<li class=\"csl-entry\">Deynoux, M., Miller, J.M.G., and Domack, E.W., 2004, Earth\u2019s <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2910\">Glacial<\/a> Record: World and Regional Geology, Cambridge University Press, World and Regional Geology.<\/li>\n<li class=\"csl-entry\">Earle, S., 2015, Physical geology OER textbook: BC Campus OpenEd.<\/li>\n<li class=\"csl-entry\">Eyles, N., and Januszczak, N., 2004, \u201cZipper-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2624\">rift<\/a>\u201d: a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2576\">tectonic<\/a> model for Neoproterozoic <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">glaciations<\/a> during the breakup of <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2211\">Rodinia<\/a> after 750 Ma: Earth-Sci. Rev.<\/li>\n<li class=\"csl-entry\">Francey, R.J., Allison, C.E., Etheridge, D.M., Trudinger, C.M., and others, 1999, A 1000\u2010year high precision record of \u03b413C in atmospheric CO2: Tellus B Chem. Phys. Meteorol.<\/li>\n<li class=\"csl-entry\">Gutro, R., 2005, NASA &#8211; What\u2019s the Difference Between <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1709\">Weather<\/a> and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">Climate<\/a>? Online, <a href=\"http:\/\/www.nasa.gov\/mission_pages\/noaa-n\/climate\/climate_weather.html\">http:\/\/www.nasa.gov\/mission_pages\/noaa-n\/climate\/climate_weather.html<\/a>, accessed September 2016.<\/li>\n<li class=\"csl-entry\">Hoffman, P.F., Kaufman, A.J., Halverson, G.P., and Schrag, D.P., 1998, A neoproterozoic <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1718\">snowball earth<\/a>: Science, v. 281, no. 5381, p. 1342\u20131346.<\/li>\n<li class=\"csl-entry\">Kopp, R.E., Kirschvink, J.L., Hilburn, I.A., and Nash, C.Z., 2005, The Paleoproterozoic <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1718\">snowball Earth<\/a>: a <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> disaster triggered by the evolution of oxygenic photosynthesis: Proc. Natl. Acad. Sci. U. S. A., v. 102, no. 32, p. 11131\u201311136.<\/li>\n<li class=\"csl-entry\">Lean, J., Beer, J., and Bradley, R., 1995, Reconstruction of solar irradiance since 1610: Implications for <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> cbange: Geophys. Res. Lett., v. 22, no. 23, p. 3195\u20133198.<\/li>\n<li class=\"csl-entry\">Levitus, S., Antonov, J.I., Wang, J., Delworth, T.L., Dixon, K.W., and Broccoli, A.J., 2001, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1717\">Anthropogenic<\/a> warming of Earth\u2019s <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2664\">system<\/a>: Science, v. 292, no. 5515, p. 267\u2013270.<\/li>\n<li class=\"csl-entry\">Lindsey, R., 2009, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">Climate<\/a> and Earth\u2019s Energy Budget\u202f: Feature Articles: Online, <a href=\"http:\/\/earthobservatory.nasa.gov\">http:\/\/earthobservatory.nasa.gov<\/a>, accessed September 2016.<\/li>\n<li class=\"csl-entry\">North Carolina State University, 2013a, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2831\">Composition<\/a> of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">Atmosphere<\/a>:<\/li>\n<li class=\"csl-entry\">North Carolina State University, 2013b, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2831\">Composition<\/a> of the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2667\">Atmosphere<\/a>: Online, <a href=\"http:\/\/climate.ncsu.edu\/edu\/k12\/.AtmComposition\">http:\/\/climate.ncsu.edu\/edu\/k12\/.AtmComposition<\/a>, accessed September 2016.<\/li>\n<li class=\"csl-entry\">Oreskes, N., 2004, The scientific consensus on <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> change: Science, v. 306, no. 5702, p. 1686\u20131686.<\/li>\n<li class=\"csl-entry\">Pachauri, R.K., Allen, M.R., Barros, V.R., Broome, J., Cramer, W., Christ, R., Church, J.A., Clarke, L., Dahe, Q., Dasgupta, P., Dubash, N.K., Edenhofer, O., Elgizouli, I., Field, C.B., and others, 2014, <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">Climate<\/a> Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">Climate<\/a> Change (R. K. Pachauri &amp; L. Meyer, Eds.): Geneva, Switzerland, IPCC, 151 p.<\/li>\n<li class=\"csl-entry\">Santer, B.D., Mears, C., Wentz, F.J., Taylor, K.E., Gleckler, P.J., Wigley, T.M.L., Barnett, T.P., Boyle, J.S., Br\u00fcggemann, W., Gillett, N.P., Klein, S.A., Meehl, G.A., Nozawa, T., Pierce, D.W., and others, 2007, Identification of human-induced changes in atmospheric moisture content: Proc. Natl. Acad. Sci. U. S. A., v. 104, no. 39, p. 15248\u201315253.<\/li>\n<li class=\"csl-entry\">Schopf, J.W., and Klein, C., 1992, Late <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2209\">Proterozoic<\/a> Low-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_3372\">Latitude<\/a> Global <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1700\">Glaciation<\/a>: the <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1718\">Snowball Earth<\/a>, <i>in<\/i> Schopf, J.W., and Klein, C., editors, The <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2209\">Proterozoic<\/a> <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2669\">biosphere\u202f<\/a>: a multidisciplinary study: New York, Cambridge University Press, p. 51\u201352.<\/li>\n<li class=\"csl-entry\">Webb, T., and Thompson, W., 1986, Is vegetation in equilibrium with <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a>? How to interpret late-<a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1443\">Quaternary<\/a> pollen data: Vegetatio, v. 67, no. 2, p. 75\u201391.<\/li>\n<li class=\"csl-entry\">Weissert, H., 2000, Deciphering methane\u2019s fingerprint: Nature, v. 406, no. 6794, p. 356\u2013357.<\/li>\n<li class=\"csl-entry\">Whitlock, C., and Bartlein, P.J., 1997, Vegetation and <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> change in northwest America during the past 125 kyr: Nature, v. 388, no. 6637, p. 57\u201361.<\/li>\n<li class=\"csl-entry\">Wolpert, S., 2009, New NASA <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_2689\">temperature<\/a> maps provide a \u2018whole new way of seeing the moon\u2019: Online, <a href=\"http:\/\/newsroom.ucla.edu\/releases\/new-nasa-temperature-maps-provide-102070\">http:\/\/newsroom.ucla.edu\/releases\/new-nasa-temperature-maps-provide-102070<\/a>, accessed February 2017.<\/li>\n<li class=\"csl-entry\">Zachos, J., Pagani, M., Sloan, L., Thomas, E., and Billups, K., 2001, Trends, rhythms, and aberrations in global <a class=\"glossary-term\" aria-haspopup=\"dialog\" aria-describedby=\"definition\" href=\"#term_926_1710\">climate<\/a> 65 Ma to present: Science, v. 292, no. 5517, p. 686\u2013693.<\/li>\n<\/ol>\n<\/div>\n<p>&nbsp;<\/p>\n<p>&nbsp;<\/p>\n<div class=\"glossary\"><span class=\"screen-reader-text\" id=\"definition\">definition<\/span><template id=\"term_926_1710\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1710\"><div tabindex=\"-1\"><p>Long term averages and variations within the conditions of the atmosphere.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2689\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2689\"><div tabindex=\"-1\"><p>The measure of the vibrational (kinetic) energy of a substance.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1714\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1714\"><div tabindex=\"-1\"><p>A system which reverts back to a baseline when it deviates.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1717\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1717\"><div tabindex=\"-1\"><p>Having to do with humans.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2664\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2664\"><div tabindex=\"-1\"><p>An interconnected set of parts that combine and make up a whole.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2670\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2670\"><div tabindex=\"-1\"><p>The study of the interaction of the spheres within the system that is the Earth, mainly the study of the hydrosphere, atmosphere, geosphere, and biosphere.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2665\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2665\"><div tabindex=\"-1\"><p>The solid, rocky parts of the Earth, including the crust, mantle, and core.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2667\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2667\"><div tabindex=\"-1\"><p>The gases that are part of the Earth, which are mainly nitrogen and oxygen.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2666\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2666\"><div tabindex=\"-1\"><p>The water part of the Earth, as a solid, liquid, or gas.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2668\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2668\"><div tabindex=\"-1\"><p>The part of the hydrosphere (water) that is frozen, found mainly at the poles.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2669\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2669\"><div tabindex=\"-1\"><p>The living things that inhabit the Earth.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2831\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2831\"><div tabindex=\"-1\"><p>The mineral make up of a rock, i.e. which minerals are found within a rock.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2464\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2464\"><div tabindex=\"-1\"><p>A body of ice that moves downhill under its own mass.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1709\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1709\"><div tabindex=\"-1\"><p>Current conditions within the atmosphere.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2707\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2707\"><div tabindex=\"-1\"><p>The act of a solid coming out of solution, typically resulting from a drop in temperature or a decrease of the dissolving material.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1181\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1181\"><div tabindex=\"-1\"><p>Place where lava is erupted at the surface.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2676\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2676\"><div tabindex=\"-1\"><p>Breaking down rocks into small pieces by chemical or mechanical means.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2678\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2678\"><div tabindex=\"-1\"><p>Pieces of rock that have been weathered and possibly eroded.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_3342\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_3342\"><div tabindex=\"-1\"><p>A geologic circumstance (such as a fold, fault, change in lithology, etc.) which allows petroleum resources to collect.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1919\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1919\"><div tabindex=\"-1\"><p>Minerals in which ions are bonded to oxygen, such as in ice, H2O.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_3336\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_3336\"><div tabindex=\"-1\"><p>Energy resources (typically hydrocarbons) derived from ancient chemical energy preserved in the geologic record. Includes coal, oil, and natural gas.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2176\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2176\"><div tabindex=\"-1\"><p>Any evidence of ancient life.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2856\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2856\"><div tabindex=\"-1\"><p>Former swamp-derived (plant) material that is part of the rock record.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_3337\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_3337\"><div tabindex=\"-1\"><p>A fossil fuel derived from shallow marine rocks. Consists of oil and natural gas.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_3338\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_3338\"><div tabindex=\"-1\"><p>A dark liquid fossil fuel derived from petroleum.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2839\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2839\"><div tabindex=\"-1\"><p>A very fine-grained rock with very thin layering (fissile).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1917\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1917\"><div tabindex=\"-1\"><p>Mineral group in which the carbonate ion, CO3-2, is the building block. This can also refer to the rocks that are made from these minerals, namely limestone and dolomite (dolostone).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2883\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2883\"><div tabindex=\"-1\"><p>Places that are under ocean water at all times.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2851\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2851\"><div tabindex=\"-1\"><p>A chemical or biochemical rock made of mainly calcite.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2960\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2960\"><div tabindex=\"-1\"><p>An extensive, distinct, and mapped set of geologic layers.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_3341\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_3341\"><div tabindex=\"-1\"><p>Rocks which allow petroleum resources to collect or move.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1712\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1712\"><div tabindex=\"-1\"><p>Soil and rock which is below freezing for long periods of time.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2709\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2709\"><div tabindex=\"-1\"><p>Mineral group in which the silica tetrahedra, SiO4-4, is the building block.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2687\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2687\"><div tabindex=\"-1\"><p>A natural substance that is typically solid, has a crystalline structure, and is typically formed by inorganic processes. Minerals are the building blocks of most rocks.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2815\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2815\"><div tabindex=\"-1\"><p>The process in which solids (like minerals) are disassociated and the ionic components are dispersed in a liquid (usually water).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1918\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1918\"><div tabindex=\"-1\"><p>CaCO3. Pure form is clear, but can take on many different colors with impurities. It is soft, fizzes in acid, and has three cleavages that are not at 90\u00b0. Thus, it can form slanted blocks, though it is visually common to be without any structure. Found in many sedimentary rocks from marine settings, rarely in igneous rocks, in the metamorphic rock marble, but is common as a secondary mineral throughout surface rocks.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2602\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2602\"><div tabindex=\"-1\"><p>A process where an oceanic plate descends bellow a less dense plate, causing the removal of the plate from the surface. Subduction causes the largest earthquakes possible, as the subducting plate can lock as it goes down. Volcanism is also caused as the plate releases volatiles into the mantle, causing melting.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2586\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2586\"><div tabindex=\"-1\"><p>Middle chemical layer of the Earth, made of mainly iron and magnesium silicates. It is generally denser than the crust (except for older oceanic crust) and less dense than the core.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2814\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2814\"><div tabindex=\"-1\"><p>Water breaking into ions and replacing ions in minerals; a major type of chemical weathering in silicates.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1916\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1916\"><div tabindex=\"-1\"><p>Consisting of three end members:&nbsp;potassium feldspar (K-spar, KAlSi3O8), plagioclase with calcium (CaAl2Si2O8, called anorthite), and plagioclase with sodium (NaAlSi3O8, called albite). Commonly blocky, with two cleavages as ~90\u00b0. Plagioclase is typically more dull white and grey, and K-spar is more vibrant white, orange, or red. The most common mineral found within the crust, and a major component of almost all igneous rocks, some sedimentary rocks, and some metamorphic rocks. Structure is a three-dimensional framework of silica tetrahedra, with locations open for cations (K, Na, Ca).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1700\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1700\"><div tabindex=\"-1\"><p>A period of cooler temperatures on Earth in which ice sheets can grow on continents.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1715\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1715\"><div tabindex=\"-1\"><p>The ability for the atmosphere to absorb heat that is emitted by a planet's surface.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_3186\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_3186\"><div tabindex=\"-1\"><p>The distance between any two repeating portions of a wave (e.g., two successive wave crests).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1711\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1711\"><div tabindex=\"-1\"><p>The amount of light that is reflected off of an object like the Earth.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_3117\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_3117\"><div tabindex=\"-1\"><p>An event that causes a landslide event. Water is a common trigger.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1203\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1203\"><div tabindex=\"-1\"><p>A type of non-eroded sediment mixed with organic matter, used by plants. Many essential elements for life, like nitrogen, are delivered to organisms via the soil.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2818\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2818\"><div tabindex=\"-1\"><p>Certain metallic elements (like iron) take in oxygen, causing reactions like rust.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2813\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2813\"><div tabindex=\"-1\"><p>An acid that forms from carbon dioxide and water. It is a large contributor to chemical weathering.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2812\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2812\"><div tabindex=\"-1\"><p>Breaking down of mineral material via chemical methods, like dissolution and oxidation.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1716\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1716\"><div tabindex=\"-1\"><p>Climate changed caused by human activity, namely, the burning of fossil fuels.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2192\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2192\"><div tabindex=\"-1\"><p>The third largest span of time recognized by geologists; smaller than a era, larger than a epoch. We are currently in the Quaternary period. Rocks of a specific period are called systems.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1719\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1719\"><div tabindex=\"-1\"><p>Data which is out of the ordinary and does not fit previous trends.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_3372\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_3372\"><div tabindex=\"-1\"><p>The measure of degrees north or south from the equator, which has a latitude of 0 degrees.&nbsp; The Earth's north and south poles have latitudes of 90 degrees north and south, respectively.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2465\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2465\"><div tabindex=\"-1\"><p>Glaciers that form in cool or mountainous areas.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2467\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2467\"><div tabindex=\"-1\"><p>Thick glaciers that cover continents during ice ages.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2910\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2910\"><div tabindex=\"-1\"><p>Deposition and erosion tied to glacier movement.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_3174\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_3174\"><div tabindex=\"-1\"><p>A place where pressurized groundwater flows onto the surface.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2898\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2898\"><div tabindex=\"-1\"><p>A topographic high found away from the beach in deeper water, but still on the continental shelf. Typically, these are formed in tropical areas by organisms such as corals.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1432\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1432\"><div tabindex=\"-1\"><p>Meaning \"middle life,\" it is the middle era of the Phanerozoic, starting at 252 million years ago and ending 66 million years ago. Known as the Age of Reptiles.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2191\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2191\"><div tabindex=\"-1\"><p>The second largest span of time recognized by geologists; smaller than a eon, larger than a period. We are currently in the Cenozoic era. Rocks of a specific era are called eratherms.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1441\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1441\"><div tabindex=\"-1\"><p>The last (and current) era of the Phanerozoic eon, starting 66 million years ago and spanning through the present.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1443\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1443\"><div tabindex=\"-1\"><p>The most recent, and current, period within the Cenozoic era, starting 2.58 million years ago.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2205\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2205\"><div tabindex=\"-1\"><p>Eon defined as the time between 4 billion years ago to 2.5 billion years ago. Most of the oldest rocks on Earth, including large portions of the continents, formed at this time.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2190\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2190\"><div tabindex=\"-1\"><p>The largest span of time recognized by geologists, larger than an era. We are currently in the Phanerozoic eon. Rocks of a specific eon are called eonotherms.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2209\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2209\"><div tabindex=\"-1\"><p>Meaning \"earlier life,\" the third eon of Earth's history, starting at 2.5 billion years ago and ending at 541 million years ago. Marked by increasing atmospheric oxygen and the supercontinent Rodinia.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2210\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2210\"><div tabindex=\"-1\"><p>A period of the early Proterozoic (around 2.5-2 billion years ago) where atmospheric oxygen levels dramatically increased, killing many non-oxygen-breathing organisms and allowing oxygen-breathing organisms to thrive.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2218\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2218\"><div tabindex=\"-1\"><p>A term for the collective time before the Phanerozoic (pre-541 million years ago), including the Hadean, Archean, and Proterozoic. Known for a lack of easy-to-find fossils.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1718\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1718\"><div tabindex=\"-1\"><p>A controversial hypothesis which states the entire ocean froze and continental glaciation covered the planet about 700 million years ago.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2575\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2575\"><div tabindex=\"-1\"><p>The layers of igneous, sedimentary, and metamorphic rocks that form the continents. Continental crust is much thicker than oceanic crust. Continental crust is defined as having higher concentrations of&nbsp;very light elements like K, Na, and Ca, and is the lowest density rocky layer of Earth. Its average composition is similar to granite.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2911\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2911\"><div tabindex=\"-1\"><p>A sedimentary rock containing two distinct grain sizes, typically cobbles (or larger) mixed with mud.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2652\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2652\"><div tabindex=\"-1\"><p>A proposed explanation for an observation that can be tested.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2914\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2914\"><div tabindex=\"-1\"><p>Rocks and minerals that change within the Earth are called metamorphic, changed by heat and pressure. Metamorphism is the name of the process.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2219\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2219\"><div tabindex=\"-1\"><p>Meaning \"ancient life,\" the era that started 541 million years ago and ending 252 million years ago. Vertebrates (including fish, amphibians, and reptiles) and arthropods (including insects) evolved and diversified throughout the Paleozoic. Pangea formed toward the end of the Paleozoic.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2225\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2225\"><div tabindex=\"-1\"><p>The second period of the Paleozoic era, 485-444 million years ago.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1708\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1708\"><div tabindex=\"-1\"><p>When a species no longer exists.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_3366\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_3366\"><div tabindex=\"-1\"><p>The most recent supercontinent, which formed over 300 million years ago and started breaking apart less than 200 million years ago. Africa and South America, as well as Europe and North America, bordered each other.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1720\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1720\"><div tabindex=\"-1\"><p>A warm climate spike, the warmest in the recent past, occurring about 55 million years ago.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2576\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2576\"><div tabindex=\"-1\"><p>The theory that the outer layer of the Earth (the lithosphere) is broken in several plates, and these plates move relative to one another, causing the major topographic features of Earth (e.g. mountains, oceans) and most earthquakes and volcanoes.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2591\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2591\"><div tabindex=\"-1\"><p>A solid part&nbsp;of the lithosphere which moves as a unit, i.e. the entire plate generally moves the same direction at the same speed.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2677\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2677\"><div tabindex=\"-1\"><p>The transport and movement of weathered sediments.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2193\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2193\"><div tabindex=\"-1\"><p>The second smallest span of time recognized by geologists; smaller than a period, larger than as age. We are currently in the Holocene epoch. Rocks of a specific epoch are called series.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1713\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1713\"><div tabindex=\"-1\"><p>A system which adds into itself.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1701\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1701\"><div tabindex=\"-1\"><p>A series of changes to the Earth's orbit which can fluctuate climate.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_3321\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_3321\"><div tabindex=\"-1\"><p>Period of warming within a glacial or ice age cycle.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_3322\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_3322\"><div tabindex=\"-1\"><p>A very brief period of warming, even warmer than a interglacial, within a glacial or ice age cycle.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_1444\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_1444\"><div tabindex=\"-1\"><p>The most recent epoch of geologic time, from 11,700 years ago to present.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_3323\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_3323\"><div tabindex=\"-1\"><p>A measurement which can specify a change in another system. For example, changes in climate can change the amount of certain isotopes of oxygen and carbon in sea creatures.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2483\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2483\"><div tabindex=\"-1\"><p>Term for a rock made definitively of glacial till.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2912\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2912\"><div tabindex=\"-1\"><p>General term for very poorly sorted sediment that is of glacial origin.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2701\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2701\"><div tabindex=\"-1\"><p>An atom that has different number of neutrons but the same number of protons. While most properties are based on the number of protons in an element, isotopes can have subtle changes between them, including temperature fractionation and radioactivity.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2885\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2885\"><div tabindex=\"-1\"><p>Relatively flat ocean floor, which accumulates very fine grained detrital and chemical sediments.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_3119\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_3119\"><div tabindex=\"-1\"><p>Detached, free-falling rocks from very steep slopes.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2174\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2174\"><div tabindex=\"-1\"><p>A device that can determine the amounts of different isotopes in a substance.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_3384\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_3384\"><div tabindex=\"-1\"><\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2589\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2589\"><div tabindex=\"-1\"><p>The innermost chemical layer of the Earth, made chiefly of iron and nickel. It has both liquid and solid components.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2655\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2655\"><div tabindex=\"-1\"><p>An accepted scientific idea that explains a process using the best available information.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_3339\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_3339\"><div tabindex=\"-1\"><p>Gaseous fossil fuel derived from petroleum, mostly made of methane.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2601\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2601\"><div tabindex=\"-1\"><p>Place where two plates slide past each other, creating strike slip faults.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2644\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2644\"><div tabindex=\"-1\"><p>An observation that is completely free of bias, i.e. anyone and everyone would make the same observation.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2966\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2966\"><div tabindex=\"-1\"><p>The process of atoms breaking down randomly and spontaneously.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2217\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2217\"><div tabindex=\"-1\"><p>Meaning \"visible life,\" the most recent eon in Earth's history, starting at 541 million years ago and extending through the present. Known for the diversification and evolution of life, along with the formation of Pangea.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2624\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2624\"><div tabindex=\"-1\"><p>Area of extended continental lithosphere, forming a depression. Rifts can be narrow (focused in one place) or broad (spread out over a large area with&nbsp;many faults).<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><template id=\"term_926_2211\"><div class=\"glossary__definition\" role=\"dialog\" data-id=\"term_926_2211\"><div tabindex=\"-1\"><p>The supercontinent that existed before Pangea, about 1 billion years ago. North America was positioned in the center of the land mass.<\/p>\n<\/div><button><span aria-hidden=\"true\">&times;<\/span><span class=\"screen-reader-text\">Close definition<\/span><\/button><\/div><\/template><\/div>","protected":false},"author":83,"menu_order":15,"template":"","meta":{"pb_show_title":"on","pb_short_title":"","pb_subtitle":"","pb_authors":[],"pb_section_license":""},"chapter-type":[48],"contributor":[],"license":[],"class_list":["post-926","chapter","type-chapter","status-publish","hentry","chapter-type-numberless"],"part":19,"_links":{"self":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapters\/926","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapters"}],"about":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/wp\/v2\/types\/chapter"}],"author":[{"embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/wp\/v2\/users\/83"}],"version-history":[{"count":3,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapters\/926\/revisions"}],"predecessor-version":[{"id":3416,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapters\/926\/revisions\/3416"}],"part":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/parts\/19"}],"metadata":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapters\/926\/metadata\/"}],"wp:attachment":[{"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/wp\/v2\/media?parent=926"}],"wp:term":[{"taxonomy":"chapter-type","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/pressbooks\/v2\/chapter-type?post=926"},{"taxonomy":"contributor","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/wp\/v2\/contributor?post=926"},{"taxonomy":"license","embeddable":true,"href":"https:\/\/pressbooks.ccconline.org\/accintrogeology\/wp-json\/wp\/v2\/license?post=926"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}