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Summer Arctic Ice-Melt Rate Slows But Long-Term Trend Still "Strongly Downward"

posted 23 Aug 2013, 07:30 by Mpelembe   [ updated 23 Aug 2013, 07:31 ]

NASA scientists say the rate of ice-melt in the Arctic this summer is unlikely to set a record but that it is in line with the sustained decline observed over the last several decades. The space agency has produced a new animated video to illustrate the latest figures.

ANIMATION (NASA) -  The animation is based on data, collected by NASA and other satellites, that shows the rate of Arctic ice-melt between May 16 and August 15. It shows that the melting of sea ice in the Arctic was well on its way toward its annual "minimum," although scientists say it is unlikely to set a new record.

However, they say the downward, long-term trend is unchanged.

"Even if this year ends up being the sixth- or seventh-lowest extent, what matters is that the 10 lowest extents recorded have had during the last 10 years," said Walt Meier, a glaciologist with NASA's Goddard Space Flight Center in Greenbelt, Md. "The long-term trend is strongly downward."

On August 21, ice cover of the Arctic Ocean was measured at 2.25 million square miles (5.83 million square kilometers). On the same date in 2012, it was measured at 1.67 million square miles (4.34 million square kilometers). The record low came on September 16, 2012 when Arctic sea ice coverage was recorded by satellites at 1.32 million square miles (3.41 million square kilometers), about half the size of the average extent from 1979 to 2010.

NASA says this year's melting season included a fast retreat of the sea ice during the first half of July. But low atmospheric pressures and clouds over the central Arctic kept temperatures up north cooler than average, slowing down the plunge.

The sea ice minimum extent analysis is compiled from passive microwave data from NASA's Nimbus-7 satellite, which operated from late October 1978 to August 1987, and the U.S. Department of Defense's Defense Meteorological Satellite Program, which has been used to extend the Nimbus 7 sea ice record onwards from August 1987.

The record, which began in November 1978, shows an overall downward trend of 14.1 percent per decade in the size of the minimum summer extent, a decline that accelerated after 2007.