The central role of diminishing sea ice in recent Arctic temperature amplification

Climate change does not occur uniformly around the world: instead, in a process called polar amplification, the Arctic warms more rapidly than the tropics or mid-latitudes. Recent work published in Nature suggested that upper-atmospheric transport processes accounted for much of the recent polar amplification, but this conclusion proved controversial. Using updated reanalysis data from the past two decades, James Screen and Ian Simmonds now show that reductions in sea ice cover and thickness, rather than upper atmosphere processes, are responsible for most of the recent polar amplification. These findings reinforce suggestions that strong positive ice–temperature feedbacks are at work in the Arctic, and suggest that rapid warming and sea ice melting are likely to continue in the near future. Climate change does not occur symmetrically; instead, in a process called polar amplification, polar areas warm faster than the tropics. Recent work indicated that transport processes in the upper atmosphere account for much of the recent polar amplification, but this conclusion proved controversial. Here, updated reanalysis data have been used to show that reductions in sea ice are instead responsible. The rise in Arctic near-surface air temperatures has been almost twice as large as the global average in recent decades1,2,3—a feature known as ‘Arctic amplification’. Increased concentrations of atmospheric greenhouse gases have driven Arctic and global average warming1,4; however, the underlying causes of Arctic amplification remain uncertain. The roles of reductions in snow and sea ice cover5,6,7 and changes in atmospheric and oceanic circulation8,9,10, cloud cover and water vapour11,12 are still matters of debate. A better understanding of the processes responsible for the recent amplified warming is essential for assessing the likelihood, and impacts, of future rapid Arctic warming and sea ice loss13,14. Here we show that the Arctic warming is strongest at the surface during most of the year and is primarily consistent with reductions in sea ice cover. Changes in cloud cover, in contrast, have not contributed strongly to recent warming. Increases in atmospheric water vapour content, partly in response to reduced sea ice cover, may have enhanced warming in the lower part of the atmosphere during summer and early autumn. We conclude that diminishing sea ice has had a leading role in recent Arctic temperature amplification. The findings reinforce suggestions that strong positive ice–temperature feedbacks have emerged in the Arctic15, increasing the chances of further rapid warming and sea ice loss, and will probably affect polar ecosystems, ice-sheet mass balance and human activities in the Arctic2.