Arctic sea ice reaches annual peak, but falls far short of average
By Andrew Freedman From Mashable
Arctic sea ice reached its maximum extent for the year on March 21, scientists reported Wednesday, but it did not make up for much of the ground it lost during the past several unusually mild summer melt seasons.
The sea ice cover surrounding the North Pole, which expands and thickens during the northern winter and shrinks and gets thinner during the spring and summer, was only able to grow to the fifth-lowest peak extent on record since satellite data began in 1978, according to the National Snow and Ice Data Center in Boulder, Colo. Sea ice extent is a way of measuring the area covered by sea ice, as estimated using satellite imagery.
Arctic sea ice extent has plummeted in recent years due in large part to manmade global warming, setting a record low in 2012. The relatively low sea-ice maximum comes after a winter in which much of the coldest Arctic air in the Canadian and American portions of the Arctic was redirected southward into eastern Canada and the U.S., with large portions of the Arctic having a milder than average winter.
In a statement on its website, the NSIDC said Arctic sea ice reached its maximum extent for the year on March 21 at 5.76 million square miles. This came after sea ice extent had fallen close to a record low during the middle of February. Sea ice extent climbed sharply in mid-March, preventing a record or near-record low at the end of the winter season.
Arctic sea ice was near average across most of the Arctic Ocean this winter, except in the Barents Sea off of Alaska and the Sea of Okhotsk, near far eastern Russia, where levels were below average.
The NSIDC said average sea ice extent in March averaged 282,000 square miles below the 1981-2010 average, and 127,000 square miles above the record March monthly low, which occurred in 2006. Through 2014, March sea ice extent has declined at a rate of 2.6% per decade, compared to the 1981-2010 average.
Arctic sea ice has been in a steep decline for the past two decades as manmade global warming has taken its toll. The pace of ice decline has been especially steep in recent years, which has had ramifications throughout the Arctic, and may be altering weather patterns across North America and Europe. Sea-ice loss has added heat to the Arctic Ocean, speeding up melting of more sea ice, as well as land-based ice sheets in Greenland.
The added heat in the upper layers of the Arctic Ocean has been enough to melt 3.2 to 4.2 feet of sea ice during the summer, according to a recent study. The same study found the Arctic-wide melt season has grown longer, at a rate of five days per decade, since 1979. The main factor has been a later fall freeze date. The study also found that the timing of the peak ice extent can influence how much ice melts during the melt season; this year’s peak was the fifth-latest on record.
One sign that may indicate the 2014 melt season won’t hit a new record-low ice extent — although this is far from a reliable indicator — is the presence of older, thicker ice in the Arctic basin compared to 2013. This winter, the multi-year ice makes up 43% of the icepack compared to only 30% in 2013, the NSIDC said.
Arctic sea ice extent as of April 1, 2014, along with daily ice-extent data for four previous years. 2013 to 2014 is shown in blue, 2012 to 2013 in green, 2011 to 2012 in orange, 2010 to 2011 in brown, and 2009 to 2010 in purple. The 1981 to 2010 average is in dark gray.
IMAGE: NSIDC
“While this is a large increase, and may portend a more extensive September ice cover this year compared to last year, the fraction of the Arctic Ocean consisting of multi-year ice remains less than that at the beginning of the 2007 melt season (46%) when a large amount of the multi-year ice melted,” the NSIDC said. “The percentage of the Arctic Ocean consisting of ice at least five years or older remains at only 7%, half of what it was in February 2007.”
NSIDC scientists reported that much of the multi-year ice has drifted into the southern Beaufort Sea and East Siberian Sea, both of which are more likely to see warm conditions later in the melt season.
PHOTOS:
Eureka Sound on Ellesmere Island in the Canadian Arctic seen on March 25, 2014. IMAGE: NASA/MICHAEL STUDINGERImagery from the European Advanced Scatterometer (ASCAT) show the distribution of multi-year ice compared to first-year ice for March 28, 2013 (yellow line) and March 2, 2014 (blue line).
A broad area of above-average temperatures (as measured via 500 millibar atmospheric height anomalies) occurred in the Arctic this winter, while much colder temperatures affected the U.S. and Canada.
IMAGE: NOAA/ESRL
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