After an unusually cold summer in the northernmost latitudes, Arctic sea ice appears to have reached its annual minimum summer extent for 2013 on Sept. 13, the NASA-supported National Snow and Ice Data Center (NSIDC) at the University of Colorado in Boulder has reported. Analysis of satellite data by NSIDC and NASA showed that the sea ice extent shrunk to 1.97 million square miles (5.10 million square kilometers).
This year's sea ice extent is substantially higher than last year's record low minimum. On Sept.16, 2012, Arctic sea ice reached its smallest extent ever recorded by satellites at 1.32 million square miles (3.41 million square kilometers). That is about half the size of the average minimum extent from 1981 to 2010.
This summer's minimum is still the sixth lowest extent of the satellite record and is 432,000 square miles (1.12 million square kilometers) lower than the 1981-2010 average, roughly the size of Texas and California combined.
The 2013 summertime minimum extent is in line with the long-term downward trend of about 12 percent per decade since the late 1970s, a decline that has accelerated after 2007. This year's rebound from 2012 does not disagree with this downward trend and is not a surprise to scientists.
"I was expecting that this year would be higher than last year," said Walt Meier, a glaciologist at NASA's Goddard Space Flight Center in Greenbelt, Md. "There is always a tendency to have an uptick after an extreme low; in our satellite data, the Arctic sea ice has never set record low minimums in consecutive years."
The ice cap covering the Arctic Ocean shrinks and expands with the passing of the seasons, melting in the summer and refreezing during the long, frigid Arctic winter. This year, cooler weather in the spring and summer led to a late start of the melt season and overall less melt.
This year, Arctic temperatures were 1.8 to 4.5 degrees Fahrenheit (1 to 2.5 degrees Celsius) lower than average, according to NASA's Modern Era Retrospective analysis for Research and Applications, a merging of observations and a modeled forecast. The colder temperatures were in part due to a series of summer cyclones. In August 2012, a big storm caused havoc on the Arctic Ocean's icy cover, but this summer's cyclones have had the opposite effect: under cloudier conditions, surface winds spread the ice over a larger area.
http://www.sciencedaily.com/releases/2013/09/130921092243.htm
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