Some aspects of the cryosphere and its role in climatic change

The ice cover of the earth plays a direct and important role in climate and climatic change. Sea ice responds rapidly and sensitively, and is important because of effects on albedo, heat exchange between ocean and atmosphere, and oceanic mixing. Glaciers (including ice sheets) interact on a longer time scale, but some mechanisms for significant changes on a human time scale do exist. The possibility of rapid disappearance of the West Antarctic ice sheet with a consequent 5-m rise in sea level has received much attention. There is some evidence that the extent of the Antarctic sea ice cover had diminished in the last few decades. Evidence related to the ice sheets is ambiguous—the measured rise in sea level suggests slow melting of the ice sheets, but field glaciological measurements, incomplete though they are, indicate just the opposite. Whatever the effect of climatic warming on the marine West Antarctic ice sheet, it appears to be physically impossible for it to go afloat in as little as 200 years; a more reasonable estimate of the minimum time needed is 500 years.