The Sensitivity of an Energy Balance Climate Model to Variations in the Orbital Parameters

The responses of a zonally symmetric model of the global energy balance to perturbations in incident solar radiation are anaLYzed. The model is forced with seasonally varying insolation and incorporates in a simple way the positive feedback due to the high albedo of snow and sea ice. Meridional em:rgy transport due to atmospheric motions is simulated with lateral diffusion of heat. Meridional energ} transport by oceanic currents is ignored, as are possible variations in cloudiness. Emphasis is placed on the model's sensitivity to the latitudinal and seasonal redistribution of insolation produced by variations in the obliquity, the eccentricity, and the longitude of perihelion of the earth's orbit. It is found that when albedos are allowed to vary, increased seasonal variation of insolation leads to increased tt:mperature in the northern hemisphere. I n all cases considered, the latitudinal extent of perennial sno~ covc:r in the northern hemisphere is particularly sensitive to the perturbations, a response suggesti'{c of the large fluctuations of continental glaciers during the Pleistocene. When the mode! is forced wilh the orbital variations of the past 150, years, its response is qualitatively similar to the geologic r:cord of that period.