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Arctic Ocean ice melt smashes previous record: frozen area falls well below 2007 minimum extent.

The future looks bleak for the floating skin of ice at the top of the world. Ice covered less of the Arctic Ocean this September than in any year since satellite records began in 1979.

At its low point on September 16, Arctic sea ice covered 3.41 million square kilometers, according to the National Snow and Ice Data Center in Boulder, Colo. That's 760,000 square kilometers below the previous modern record from 2007 and 3.29 million square kilometers less than the average annual minimum from 1979 to 2000--an area nearly twice the size of Alaska.

In 2007, scientists described that year's record minimum as shocking and unprecedented. Now, they say, the 2012 melt shows that the Arctic sea ice cover has shifted to a profoundly different regime.

"The ice cover is now just so thin and weak in the springtime that large parts of it can't survive the melt season," says NSIDC director Mark Serreze.

Arctic sea ice grows in winter and melts partly away each summer. Overall, more sea ice has been lost each year, a sign of changing Arctic climate. From i979 to 2011, the amount of sea ice left in September at the end of each melt season dropped by an average of 12 percent per decade.

The ice isn't just shrinking; it's also thinning. The Arctic used to contain lots of thick ice--some 3 to 4 meters thick--that survived year after year. Now it's dominated by thinner ice only 1 to 2 meters thick and just one to two summers old. "It's almost like parts of the Arctic have become a giant Slushie at this time of year," says Walt Meier, a sea ice expert at NSIDC.

Even so, the average Arctic sea ice thickness actually increased during August, according to computer modeling of sea ice volume. That's because so much thin ice melted away completely that the remaining ice got thicker on average, says Axel Schweiger, a polar scientist at the University of Washington in Seattle.

In 2007 winds, cloud cover and other weather conditions were just right for a lot of ice to melt. "There were a number of people saying [2007] was a one-off-and you'll never see this perfect storm again," says Serreze. "What Mother Nature is telling us is that you don't need a perfect storm anymore, just because the ice is so thin now."

This year, ice cover stayed pretty much on track with 2007 levels through July, after which it rapidly nose-dived. One possible factor was a strong Arctic storm that spun up north of Alaska in early August, around the same time a lot of ice melted in the East Siberian Sea. Serreze and others say it's too early to know how the storm might have been related to that sea ice loss--whether the storm broke ice apart and made it more susceptible to melting, or whether the two events just happened to coincide.

"My gut feeling is that it was probably not critical and we would have reached a new record regardless," says James Screen, a climate scientist at the University of Melbourne in Australia who has studied the role of Arctic storms in sea ice loss.

Nevertheless, says Meier, storms that thicker sea ice might once have weathered now rank a knockout punch for thin, unconsolidated ice. "The Arctic is becoming like a fighter with a glass jaw," he says.

During August, nearly 92,000 square kilometers of ice disappeared each day on average, the fastest rate ever observed for that month.

The six lowest sea-ice extents in the satellite record have now occurred in the last six years, according to the NSIDC. More melt means more open water exposed to sunlight; that water absorbs more heat and causes feedback loops that heat the Arctic even more.

NSIDC counts an area as ice-covered if it has at least 15 percent sea ice, as seen by microwave instruments aboard satellites. This approach can over- or underestimate how much ice is really there, thanks to changes in factors such as clouds, fresh ice or the overall ice reflectivity.

To help improve the measurements, center scientist Julienne Stroeve traveled to the Arctic for the record ice melt. On September 11, she wrote online that ice concentrations at 83 degrees north were less than 40 percent--even though satellite data suggested that ice should cover nearly 100 percent at that spot.

Other research groups in Europe and Japan that monitor sea ice cover using different techniques confirm this year's record melt.

For now, the ice is beginning to refreeze. But the small amount lingering from the record summer melt probably means less ice next spring. "It sets us up for another world of hurt next year," says Serreze.


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Title Annotation:STORY ONE
Author:Witze, Alexandra
Publication:Science News
Geographic Code:1USA
Date:Oct 6, 2012
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