Change in snow-cover duration for autumn (snow-cover onset period) and spring (snow-cover melt period) between 1972/73 and 2008/09

Snow-cover duration and snow-cover extent, which can both be measured from satellites, have decreased. There is less certainty about changes in snow depth because this has to be measured on the ground, so the observations are less extensive. The maps show how the number of days with snow cover has changed between 1972 and 2008, as measured every week from images taken by satellites. Decreases in snow-cover duration are much more widespread and marked in spring than in autumn. The greatest reductions in the duration of snow cover (dark orange/red) are seen in coastal regions, particularly coastal Alaska, northern Scandinavia and northern Canada. On average across the entire Arctic, the period of winter snow cover has become four days shorter every decade between 1972/73 and 2008/09. Since 1978, the duration of snow cover has decreased by between 4 and 9 days per decade in all Arctic coastal areas except for the Kara Sea and the Chukchi Sea coasts. The area covered by snow is decreasing too. Satellite images show that the Arctic land area covered by snow in May and June shrank by 18% between 1966 and 2008.