Discuss the relative importance of ice sheets, CO2, ice-free land albedo changes, and orbital parameter changes in explaining 'observed' climate changes 20,000 and 70,000 years ago.
Answers
Answer: Earth's historical environmental changes, with emphasis on the recent ice-age cycles. The chapter focuses on paleoclimate records obtained by analyzing ice cores extracted from the polar ice sheets. There are many important types of paleoclimate records, but the ice-sheet records have special importance. The ice sheets are the only significant accumulations of atmospheric sediment and, therefore, contain unique information about atmospheric composition and processes. In particular, atmospheric gases are trapped in glacial ice, so ice-core analysis can rather directly reveal changes in greenhouse gas composition through time. In the global ice-age experiment, important positive feedbacks include long-term changes in continental-ice cover, sea-ice cover, greenhouse gas concentrations, oceanic heat transport, atmospheric aerosol load, and vegetation. Strongly positive rapid feedbacks are also operative. These most likely involve atmospheric water vapor and clouds and seasonal snow cover, which together amplify temperature changes by a factor of two to four. The Earth system acts as a frequency modulator in the ice-age cycles. The dominant forcings of 20 and 40 kyr periodicity are directly expressed in environmental changes, but these are considerably over-shadowed by the 100 kyr periodicity of glacial-interglacial cycling, for which there is no significant forcing.
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