Polar snow cover changes and global warming

Many general circulation models suggest that current precipitation amounts in polar latitudes will increase under double CO 2 scenarios. Even though temperatures in such high-latitude regions should also increase under a doubling of CO2, as long as those temperatures remain below freezing, the increased precipitation should accumulate as snow. A study of both current and double CO2 temperature and precipitation data for all land areas poleward of 60 latitude using three different general circulation models suggests possible changes in snow accumulation due to increasing CO2. Increased snow accumulation will occur in the Antarctic whereas a small decrease in snow depth is to be expected in the Northern Hemisphere. Total snow accumulation for all land areas poleward of latitude 60 is found to increase under a double CO2 scenario. Many of the general circulation models (GCMs) that have been used to estimate climatic responses to increasing concentrations of CO2 and other trace gases in the atmosphere suggest a marked warming in polar latitudes. Although the GCMs do not provide direct information on snow cover or even snowfall, available polar warming scenarios have been cited as evidence to suggest increased melting of polar ice masses. The present study investigates temperature and precipitation conditions in the polar regions under conditions of a doubling of CO 2 using three readily available GCMs to provide some understanding of the possible range of future estimates of snow accumulation. Evaluating snowfall amounts under current and GCM simulated conditions permits an estimate of snow depth change under possible global warming scenarios. In 1934, Sir George Simpson postulated a unique theory for the cause of ice ages in the Pleistocene that required two fairly uniform increases in solar radiation with a period of decreased radiation between the radiation maxima. He theorized that a gradual rise in solar radiation would be accompanied by a gradual rise in air temperature. This, in turn, would result in an increase in precipitation, which would fall as snow in the polar regions. The increased precipitation would result from increased evaporation (due to the warmer water temperatures) and the increased water vapour capacity of the warmer air. He reasoned that as long as air temperatures in polar regions remained below freezing the increased precipitation would fall as snow and accumulate as permanent snow fields on the ground. This would lead to advancing ice sheets and a glacial period. As temperatures finally increased too much, more precipitation would fall as rain rather than snow and, at the same time, there would be increased melting of continental ice sheets, leading to their retreat and ultimate disappearance. Although Simpson's theory linking ice-age occurrence with an increase in solar radiation and air temperature has not survived the test of time, his recognition that an increase in air temperature might lead to increased snowfall in polar regions deserves further evaluation. Thomas (1986) in identifying three major processes relating global warming to average sea-level change, suggested that although two of the processes would lead to sea-level rise (increased ice melting and thermal expansion of sea water), one process might lead to a sea-level fall. That process was increased snowfall on polar