Ice and Snow Feedbacks and the Latitudinal and Seasonal Distribution of Climate Sensitivity

Abstract

A new parameterization of snow and ice area and albedo as functions of surface temperature is presented based on recent satellite observations of snow and ice extent. This parameterization is incorporated into a seasonal energy-balance climate model. Experiments are conducted with the model to determine the effects of this parameterization change on the latitudinal and seasonal distribution of model sensitivity to external forcings of climate change, such as solar constant variations and changes in the atmospheric carbon dioxide amount. The sea ice-thermal inertia feedback is found to be the determining factor in this sensitivity pattern, producing enhanced sensitivity in the polar regions in the winter and decreased sensitivity in the polar regions in the summer. The albedo feedbacks (snow-area and snow/ice-meltwater) are weak and produce a small amount of additional sensitivity, but do not change the pattern. The response pattern is the same as that found by Manabe and Stouffer (1980) with a general circulation model. The enhanced sensitivity in the summer found by Ramanathan et al. (1979) is shown to be due to a surface albedo feedback parameterization which does not allow the thermal inertia to change. The sensitivity of an annual average version of the model is approximately the same as that of the seasonal model.