Natural variability has boosted Arctic sea ice loss

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Enlarge (credit: NASA Earth Observatory)

Sea ice around Antarctica is very variable from year to year—we’ve seen the highest winter extents of the last few decades a few years ago, but record low extents have occurred in recent months. Although the trend of shrinking sea ice in the Arctic has been clearer, this doesn’t mean natural variability isn’t significant there, too. In any given year, a few storm systems can bring warm weather or blow sea ice around, deciding whether a new record low is reached. But can some meaningful portion of the Arctic trend over the last 40 years be blamed on longer-term variability?

It’s difficult to tease apart the human-caused and natural effects precisely here, so we haven’t had a great answer to that question. A new study led by the University of California, Santa Barbara’s Qinghua Ding worked out a different way to examine the question, looking for interesting patterns of atmospheric circulation.

The researchers looked for correlations between the summer sea ice low point in September and atmospheric conditions over the preceding summer months. They found a connection between the area of fastest sea ice loss—the Beaufort, Chukhchi, and East Siberian Sea side of the Arctic Ocean—and high-level atmospheric circulation over Greenland and northeastern Canada. High pressure systems in the upper troposphere there cause air to descend as it circles around the Arctic, warming as it comes down to a lower altitude.

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