Linear trends of the length of snow-cover season in the Northern Hemisphere as observed by the satellites in the period 1972-2000

The dataset of Northern Hemisphere EASE-Grid weekly snow cover and sea-ice extent (U.S. National Snow and Ice Data Center) for the period September 1972-August 2000 is analyzed to examine the possible influence of recent global warming on the seasonal change of snow cover in the Northern Hemisphere. It is found that the 2 total snow-cover area in the 1980s and 1990s is diminished by 3 x 106 kin, and the length of snow-cover season is reduced by 2-3 weeks, as compared with the 1970s. In general, the contribution from earlier snowmelt is greater than that from delayed snow accumulation. In addition, the maximum snow-cover area during January-February has gradually decreased by about 3 X 10(6) km(2) within the two decades. Geographically, the rate of decrease of snow-cover duration is < 0.1 week per year (wpy) in the high-latitude regions such as the Siberian Plains and Northwest Territories of Canada and > 0.2 wpy in the high-elevation regions such as the Scandinavian Peninsula, Tibetan Plateau and Rocky Mountains. The earlier snowmelt in the high-elevation regions suggests that the snowfall amounts there are decreasing owing to global warming.