Abstract

In both polar regions, there is strong evidence of the ongoing impacts of climate change on terrestrial and freshwater species, communities and ecosystems (very high confidence). Recent studies project that such changes will continue (high confidence), with implications for biological resources and globally important feedbacks to climate (medium confidence). Strong evidence exists of changes in species’ ranges and abundances and in the position of some tree lines in the Arctic (high confidence). An increase in greenness and biological productivity has occurred in parts of theArctic (high confidence). Surface albedo is projected to decrease and the exchange of greenhouse gases between polar landscapes and the atmosphere will change (very high confidence). Although recent models predict that a small net accumulation of carbon will occur in Arctic tundra during the present century (low confidence), higher methane emissions responding to the thawing of permafrost and an overall increase in wetlands will enhance radiative forcing (medium confidence).