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Arctic sea ice extent in context: this cool summer slowed ice melt
The National Snow and Ice Data Center has published its review of sea ice conditions in the Arctic over the course of the summer. This year’s sea ice extent minimum, which occurred on Sept. 13, was the eighth lowest on record, following temperatures near or below the long term average across much of the Arctic region. However, temperatures were slightly above average over much of the East Siberian, Chukchi and Beaufort seas. Heat flow from areas of open water probably contributed to slightly elevated temperatures in coastal areas of the Arctic Ocean and in the North Atlantic, NSIDC said.
Despite the uptick in the sea ice minimum, the long term trend for the sea ice cover in September continues its strong downward trajectory, showing a linear decline of about 13.2 percent per decade since 1981, NSIDC reported.
Decline in thick ice Particularly notable is a steady decline in the proportion of thick, multiyear ice in the Arctic seas - the marginal gain in the minimum ice extent this year can largely be attributed to ice that is two years old or younger, NSIDC said. The younger ice, which is relatively thin, tends to melt out more quickly than the thicker, older ice when temperatures rise. The proportion of thick old ice to thin young ice also impacts the total volume of the sea ice cover, as distinct from the ice extent. The University of Washington’s Polar Science Center estimated that the sea ice volume minimum in September was the fourth lowest on record, NSIDC said.
The oldest sea ice, more than four years old, has now become scarce, having dwindled from an area of some 770,000 square miles in the mid-1980s to around 58,000 square miles this year.
In a similar manner to 2016, persistent stormy weather patterns over the central Arctic Ocean characterized the summer of 2017. An area of low atmospheric pressure was centered just south of the North Pole in the Siberian sector of the Arctic. Low pressure systems of this type in the Arctic in the summer tend to have cold cores, a phenomenon that would help explain the relatively cool temperatures this year. In addition, the cyclonic wind patterns associated with the low pressure tend to spread the ice out across the sea, a factor that, combined with cool temperatures, would slow the sea ice loss, NSIDC said.
- ALAN BAILEY
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