Britannica Sources used in this answer

How did lower atmospheric carbon dioxide levels reinforce cooling during glacial periods?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Map showing the extent of the Laurentide, Cordilleran, and Greenland ice sheets during the Wisconsin glaciation, roughly 100,000 to 11,000 years ago. The Laurentide Ice Sheet covers most of present-day Canada and parts of the northern United States in light blue, the Cordilleran Ice Sheet covers the Pacific Northwest in teal, and the Greenland Ice Sheet is marked in purple. Modern international and state or provincial boundaries are outlined for reference. — Pleistocene Epoch Ice sheets during the Wisconsin glacial episode penetrated deep into North America.

During the Pleistocene Epoch, lower atmospheric carbon dioxide levels reinforced cooling through the greenhouse effect.1

The greenhouse effect is the process by which gases in the atmosphere—including carbon dioxide and water vapour—trap heat (infrared radiation) near the Earth's surface. During glacial periods, concentrations of these potent greenhouse gases decreased, which reduced the atmosphere's ability to retain heat. This reduction in greenhouse gas concentrations acted as a positive feedback mechanism, amplifying the cooling trends already initiated by orbital variations.12

While orbital cycles are considered the "pacemaker" of the ice ages, these feedback processes, including the decrease in carbon dioxide, were essential to explain the magnitude of the climatic changes observed during the Pleistocene. The specific dynamics of the glacial carbon sink—the processes that remove carbon dioxide from the atmosphere during these periods—remain a significant area of ongoing paleoclimatology research.12