Sensitivity Studies of Northern Hemisphere Glaciation Using an Atmospheric General Circulation Model

Abstract

The U.K. University Global Atmospheric Modeling Programme GCM is used to investigate whether the growth of Northern Hemisphere ice sheets could have been initiated by changes of orbital parameters and sea surface temperature. Two different orbital configurations, corresponding to the present day and 115 kyr BP are used. The reduced summer solar insulation in the Northern Hemisphere results in a decrease of the surface temperature by 4° to 10°C in the northern continents and to perennial snow in some high-latitude regions. Therefore, the model results support the hypothesis that a deficit of summer insulation can create conditions favorable for initiation of ice sheet growth in the Northern Hemisphere. A decreased sea surface temperature northward of 65°N during the Northern Hemisphere summer may contribute to the maintenance of ice sheets. A simple mixed-layer ocean model coupled to the GCM indicates that the changes of sea surface temperature and extension of sea ice due to insulation changes play an important role in inception of the Fennoscandian, Laurentide, and Cordilleran ice sheets. The model results suggest that the regions of greatest sensitivity for ice initiation are the Canadian Archipelago, Baffin Island, Tibetan Plateau, Scandinavia, Siberia, Alaska, and Keewatin, where changing orbital parameters to 115 kyr BP results in the snow cover remaining throughout the warmer summer, leading to long-term snow accumulation. The model results are in general agreement with geological evidence and are the first time that a GCM coupled with a mixed layer ocean has reproduced the inception of the Northern Hemisphere ice sheets.