MODELING IcE AGEs and their inception can reveal aspects of the climate system that are not able to be measured, and provide a key to the drivers of climate change. Ice age model results can also allow an analysis of the global and regional conditions at that time, and provide a comparison with proxy field evidence. Models range from simple conceptual models, to full global climate models that include vegetation growth and ocean dynamics. To simulate ice ages or their inception, modelers consider several forcing factors. Low greenhouse gas levels are critical. A continental configuration that limits the oceanic transfer of heat from the tropics to the poles is also important. Ice ages can be instigated by orbital conditions that lend themselves to cool summers in high latitude continents or by weathering processes that remove carbon dioxide from the atmosphere.
Once an area cools and an ice sheet begins to grow, there are many feedbacks that encourage its growth. These include local cooling caused by the ice itself— from the higher reflectivity (albedo) of the ice and the increasing altitude of the ice surface. There are also many feedbacks that alter the levels of atmospheric greenhouse gases. For example, marshes and other regions of vegetation can be a source of greenhouse gases; as these regions freeze or are covered in ice, that source of greenhouse gas is removed. As the globe cools and the oceans begin to cool, even more greenhouse gases are removed from the atmosphere, because a cool ocean has more capacity to absorb carbon dioxide. Feedbacks are instrumental in starting and maintaining an ice age or glacial period. In a warming world, these feedbacks occur in reverse, and evidence from ice cores indicate that warming feedbacks contribute to much more rapid changes in global climate than cooling feedbacks.
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