A comparison of Northern Hemisphere snow extent climatologies derived from passive microwave and visible remote sensing data

The extent and variability of seasonal snow cover are recognized as important parameters in climate and hydrologic systems. At its average maximum extent snow covers more than 45 percent of the land surface of the Northern Hemisphere and is the single greatest source of annual and interannual albedo fluctuations, both in terms of magnitude as well as spatial extent. Trends in snow cover are also expected to serve as an indicator of global climatic changes. Any decrease in snow resulting from a warming trend results in increased absorption of solar radiation and additional heat to melt additional snow. This results in the classic positive temperature albedo feedback mechanism which is included in nearly all climate models. In addition to the albedo effect, snow cover represents a significant heat sink during the warming period of the seasonal cycle due to a relatively high latent heat of fusion. As a result, the seasonal snow cover provides a major source of thermal inertia within the total climate system as it takes in and releases large quantities of energy with little or no fluctuation in temperature.