P.Y. Groisman, T.R. Karl, and R.W. Knight
263 (5144), 198-200 Jan. 14, 1994
Analysis of satellite-derived snow cover, radiative balance, and surface air temperature over Northern Hemisphere extratropical land shows that the retreat of the Northern Hemisphere's extent of spring snow cover over the past 20 years parallels a change in the influence of snow cover on the radiative balance and an observed increase of spring temperatures over the same area. These results help explain why the long-term (20th century) increase in surface air temperature over Northern Hemisphere land has been greater in spring than in any other season relative to the interannual variability.