Arctic Sea Ice Reaches Year's Minimum

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The sea ice that covers the surface of the Arctic Ocean has begun to slowly increase with the end of the northern summer and the onset of fall. The National Snow and Ice Data Center (NSIDC) announced on Friday that the summer melt season reached its end on Sept. 13, with Arctic sea ice extent at 5.1 million square kilometers (1.97 million square miles).

That, notes NSIDC, is “substantially more” than last year’s record low of 3.41 million square kilometers (1.32 million square miles), “yet sea ice extent remains quite low compared to the long-term 1981 to 2010 average.”

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NSIDC observes that, whereas the previous six summers have experienced high sea level pressure over the Beaufort Sea and Greenland, and low sea level pressure over Eurasia a, combination that helps to transport warm air into the Arctic — this past summer was characterized by low sea level pressure over the central Arctic and Greenland. As a consequence, temperatures were cooler and sea ice melted less. (There was also less surface ice melt on Greenland.)

Climate change skeptics leaped on the recovery, with the Daily Mail’s in-house denier-in-chief, David Rose, claiming that “some eminent scientists now believe the world is heading for a period of cooling that will not end until the middle of this century.”

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Rush Limbaugh asserted that “there is a record amount of Arctic ice for this time of year.”

Yes, well. It’s a record since 2009, yes. Otherwise, not so much. In fact, it’s the sixth lowest on record, and would have been a record low in 2006. This Washington Post blog underlines the point with seven visuals, and Dana Nuccitelli at the Guardian provides his usual detail in this dissection of the “Arctic-ice-has-recovered-everything’s-fine” brigade.

Writing in his “Bad Astronomy” blog at Slate, Phil Plait used the analogy that a rebound from the exceptionally low levels of 2012 “is like getting a D- after getting an F.” And as this video retort by science journalist Peter Hadfield points out, “There are always peaks, dips and wobbles in every trend. So although we’ve had 35 years of declining Arctic ice cover, it obviously isn’t going to move in a straight line.”

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Prior to 2012, for example, 2007 set a record low in summer sea ice extent; but that extent increased in 2008, and then increased some more the following year, leading some skeptics to claim that there was nothing to worry about, sea ice was recovering. Then the minimum extent decreased again in 2010, declined some more in 2011 and crashed to a new low in 2012. Focusing on the inevitable occasional yearly recoveries while ignoring the long-term downward trend produces a misleading and confusing picture.

It also ignores the fact that sea ice extent is just part of the story. Sea ice volume is also decreasing rapidly, as old, thick, multi-year ice is replaced by thin, first-year ice, which is more susceptible to melt the following summer.

New data from the European Space Agency’s Cryosat satellite shows there has been a decrease in the volume of winter and summer ice over the past three years, and that the volume of the sea ice at the end of last winter was lower than any other year going into summer.

 Image: Corbis