Influence of the Recent High-Latitude Atmospheric Circulation Change on Summertime Arctic Sea Ice

It is widely believed that the decline in Arctic sea ice coverage for the past three decades is due to increasing greenhouse gases^1-3, yet the mechanisms of this linkage are not well understood⁴. Here, we present observational and modeling evidence that the rapid melting of summertime sea ice was due to changes in the large-scale atmospheric circulation during the Northern Hemisphere summer. A strengthening upper tropospheric anticyclonic anomaly over Greenland and the Arctic Ocean increased the downwelling longwave radiation above the ice by warming and moistening the lower Arctic troposphere. Our experiments indicate that the circulation trend may have contributed as much as 60% to the decline of the September sea ice extent minimum since 1979. Because the observed circulation variability over the Arctic is inconsistent with the expected model response to anthropogenic forcing, a significant component of sea ice loss over the last three decades may have been driven by dynamical sources of natural climate variability.