The Goddard Institute for Space Studies climate model is used to investigate whether the growth of ice sheets could have been initiated by solar insolation variations. Three different orbital configurations are used, corresponding to 116 and 106 kyr B.P., and a modified insolation field with greater reductions in summer insolation at high northern latitudes. The time periods chosen are those in which geophysical evidence suggests ice sheets may have been growing rapidly. The reduced summer insolation field characteristic of all the experiments is though to be a necessary condition for allowing snow to last through the summer, and ice sheets to build. The results show that the model fails to maintain snow cover through the summer at locations of suspected initiation of the major ice sheets, despite the reduced summer and fall insolation. When 10-m-thick ice was inserted in all locations where continental ice sheets existed during the Last Glacial Maximum, the model failed to maintain it as well, producing energy and mass imbalances which would remove the ice within 5 years. Only when the ocean surface temperatures were adjusted to their peak ice age values was the model able to keep any of the additional ice, and then only in a very restricted region of north Baffin Island.

The experiments indicate there is a wide discrepancy between the model's response to Milankovitch perturbations and the geophysical evidence of ice sheet initiation. As the model failed to grow or sustain low-altitude ice during the time of high-latitude maximum solar radiation reduction (120--110 kyr B.P.), it is unlikely it could have done so at any other time within the last several hundred thousand years. If the model results are correct, it indicates that the growth of ice occurred in an extremely ablative environment, and thus demanded some complicated strategy, or else some other climate forcing occurred addition to the orbital variation influence (and CO2 reduction), which would imply we do not really understand the cause of the ice ages and the Milankovitch connection. If the model is not nearly sensitive enough to climate forcing, it could have implications for projections of future climate change. ¿ American Geophysical Union 1989