47 5.6 Weathering and Climate Change — Physical Geology – 2nd Edition
During much of Earth’s history, the geological carbon cycle has been balanced, with carbon being released by volcanism at approximately the same rate that it is stored by the other processes. Under these conditions, the climate remains relatively stable.
During some periods of Earth’s history, that balance has been upset. This can happen during prolonged periods of greater than average volcanism. One example is the eruption of the Siberian Traps at around 250 Ma, which appears to have led to strong climate warming over a few million years because of the slow but steady input of extra volcanic CO2 into the atmosphere.
A carbon imbalance is also associated with significant mountain-building events. For example, the Himalayan Range was formed between about 40 and 10 Ma and over that time period—and still today—the rate of weathering on Earth has been enhanced because those mountains are so high and steep and the range is so extensive. The weathering of these rocks—most importantly the hydrolysis of feldspar—has resulted in consumption of atmospheric carbon dioxide and transfer of the carbon to the oceans and to ocean-floor carbonate minerals. The steady drop in carbon dioxide levels over the past 40 million years, which led to the Pleistocene glaciations, is partly attributable to the formation of the Himalayan Range.
A non-geological form of carbon-cycle imbalance is happening today on a very rapid time scale. We are in the process of extracting vast volumes of fossil fuels (coal, oil, and gas) that was stored in rocks over the past several hundred million years, and then converting these fuels to energy and carbon dioxide. By doing so, we are changing the climate faster than has ever happened in the past, and putting both ecosystems and our descendants at significant risk.
Media Attributions
- Figure 5.6.1: © Steven Earle. CC BY.
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