SENSITIVITY STUDIES OF NORTHERN-HEMISPHERE GLACIATION USING AN ATMOSPHERIC GENERAL-CIRCULATION MODEL

The U.K. University Global Atmospheric Modeling Programme GCM is used to investigate whether the growth of Northern Hemisphere ice sheets co uld have been initiated by changes of orbital parameters and sea surfa ce temperature. Two different orbital configurations, corresponding to the present day and 115 kyr BP are used. The reduced summer solar ins olation in the Northern Hemisphere results in a decrease of the surfac e temperature by 4 degrees to 10 degrees C in the northern continents and to perennial snow in some high-latitude regions. Therefore, the mo del results support the hypothesis that a deficit of summer insolation can create conditions favorable for initiation of ice sheet growth in the Northern Hemisphere. A decreased sea surface temperature northwar d of 65 degrees N during the Northern Hemisphere summer may contribute to the maintenance of ice sheets. A simple mixed-layer ocean model co upled to the GCM indicates that the changes of sea surface temperature and extension of sea ice due to insolation changes play an important role in inception of the Fennoscandian, Laurentide, and Cordilleran ic e sheets. The model results suggest that the regions of greatest sensi tivity for ice initiation are the Canadian Archipelago, Baffin Island, Tibetan Plateau, Scandinavia, Siberia, Alaska, and Keewatin, where ch anging orbital parameters to 115 kyr BP results in the snow cover rema ining throughout the warmer summer, leading to long-term snow accumula tion. The model results are in general agreement with geological evide nce and are the first time that a GCM coupled with a mixed layer ocean has reproduced the inception of the Northern Hemisphere ice sheets.