Thawing permafrost and thicker active layers in sub‐arctic Sweden

Observations of active‐layer thickness from nine sites with up to 29 years of gridded measurements located in the Torneträsk region, northernmost Sweden, were examined in relation to climatic trends. Mean annual air temperatures in this area have warmed and recently rose above 0°C. Active layers at all sites have become thicker, at rates ranging from 0.7 to 1.3 cm per year. This trend has accelerated in the past decade, especially in the westernmost site where rates have reached 2 cm per year and permafrost has disappeared at 81 per cent of the sampling points. Increased active‐layer thicknesses are correlated with increases in mean summer air temperature, thawing degree‐days and, in five of the nine sites, with increases in snow depth. Copyright © 2008 John Wiley & Sons, Ltd.