Losing Arctic sea ice: observations of the recent decline and the long‐term context

In the past four decades Arctic sea ice has undergone a precipitous decline in both areal coverage and thickness. Since the beginning of the modern satellite record in 1979 through 2014, September sea ice extent has declined 13.3% per decade. Other months have also shown smaller, but statistically significant, declines. In virtually all seasons and regions, the Arctic has been losing sea ice. Thickness data are not as complete, but there is strong indication of a long-term thinning with the ice now about 50% thinner than in the 1970s; recent satellite data suggest an acceleration of this thinning. Sea ice age data confirm a thinner sea ice cover due to substantial losses of multi-year ice. Other notable changes include earlier onset of melt and increased sea ice drift speed.