| Summary: | In this thesis, the sensitivity of the Earth's climate is studied by modeling past climatic variations with two-dimensional seasonal energy balance model. This thesis consists of two parts. The first part is a study of the interaction between the seasonal cycle and the small ice cap instability, which is a possible mechanism for the initiation of glaciation in the northern hemisphere and southern hemisphere. Results from a two-dimensional energy balance model with a realistic land-ocean distribution show that the small ice cap instability exists in the southern hemisphere, but not in the northern hemisphere. A series of experiments with a one-dimensional energy balance model with idealized geography is used to study the roles of the seasonal cycle and the land-ocean distribution. The results indicate that the seasonal cycle and land-ocean distribution can influence the strength of the albedo feedback, which is responsible for the small ice cap instability, through two factors: the temperature gradient and the amplitude of the seasonal cycle. The second part of this thesis is a study of the CO$\sb2$-climate feedback and its possible role in the 41 kyr sea surface temperature oscillation during the Matuyama chron (2.4 to 0.7 Myr BP). The CO$\sb2$-climate feedback is parameterized as an internal longwave radiation-polar temperature feedback in the energy balance model. Other physical processes are treated as boundary conditions. It is found that the CO$\sb2$-climate feedback can increase climate sensitivity to orbital parameters, especially to the obliquity changes, which have a 41 kyr cycle. The model results indicate that the CO$\sb2$-climate feedback is one of possible mechanisms for the dominant 41 kyr climate change during the Matuyama. (Abstract shortened with permission of author.) U of I Only ETDs are only available to UIUC Users without author permission
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