Recent Variabilty of Northern Hemisphere Snow Cover

Evaluation of satellite data indicates a reduction in the extent of snow cover over Northern Hemisphere lands since the late 1980s compared to the previous 20 years. Analyses of station observations over portions of Eurasia and North America suggest that the recent decreased coverage is unprecedented in spring over the past century. Weekly visible-wavelength satellite maps of Northern Hemisphere snow cover produced by the National Oceanic and Atmospheric Administration’s (NOAA) National Environmental Data and Information Service (NESDIS) are used to evaluate large-scale snow extent. To date, these maps constitute the longest satellite-derived environmental dataset available.

The tendency towards less late-season cover in recent years begins in February. During 8 of the first 20 years of record, February snow extent exceeded the January value. This has occurred only once in the past 16 years. This snow “drought” is associated with observations of warmer spring temperatures, the timing of phenologic green-up, and seasonal atmospheric CO2 levels. Clearly, the implications of the snow signals with regard to climate change are quite important. Research continues to improve our understanding of the role of snow cover in the climate system. New datasets are being prepared and empirical and modeling investigations of linkages between snow and other climate variables are underway.