ARCTIC ENVIRONMENTAL-CHANGE OF THE LAST 4 CENTURIES

A compilation of paleoclimate records from lake sediments, trees, glac iers, and marine sediments provides a view of circum-Arctic environmen tal variability over the last 400 years. From 1840 to the mid-20th cen tury, the Arctic warmed to the highest temperatures in four centuries. This warming ended the Little Ice Age in the Arctic and has caused re treats of glaciers, melting of permafrost and sea ice, and alteration of terrestrial and lake ecosystems. Although warming, particularly aft er 1920, was likely caused by increases in atmospheric trace gases, th e initiation of the warming in the mid-19th century suggests that incr eased solar irradiance, decreased volcanic activity, and feedbacks int ernal to the climate system played roles.