Arctic sea ice maximum in 2013 is fifth lowest on record

Arctic sea ice reached its annual maximum extent in February this year and it was the fifth lowest in the past 35 years, according to a NASA analysis.
During the cold and dark of Arctic winter, sea ice refreezes and achieves its maximum extent, usually in late February or early March.
NASA scientists found that this year the annual maximum extent was reached on February 28 and it was the fifth lowest sea ice winter extent in the past 35 years.
The new maximum 15.09 million square kilometres is in line with a continuing trend in declining winter Arctic sea ice extent: nine of the ten smallest recorded maximums have occurred during the last decade.

The 2013 winter extent is 374,000 square kilometres below the average annual maximum extent for the last three decades.
"The Arctic region is in darkness during winter and the predominant type of radiation is long-wave or infrared, which is associated with greenhouse warming," said Joey Comiso, senior scientist at NASA Goddard Space Flight Center, Greenbelt, and a principal investigator of NASA's Cryospheric Sciences Programme.

"A decline in the sea ice cover in winter is thus a manifestation of the effect of the increasing greenhouse gases on sea ice," Comiso said.
The behaviour of the winter sea ice maximum is not necessarily predictive of the following melt season. The record shows there are times when an unusually large maximum is followed by an unusually low minimum, and vice versa, scientists said.

"You would think the two should be related, because if you have extensive maximum, that means you had an unusually cold winter and that the ice would have grown thicker than normal. And you would expect thicker ice to be more difficult to melt in the summer," Comiso said.
"But it isn't as simple as that. You can have a lot of other forces that affect the ice cover in the summer, like the strong storm we got in August last year, which split a huge segment of ice that then got transported south to warmer waters, where it melted," Comiso said in a statement.

The sea ice maximum extent analysis produced at NASA Goddard is compiled from passive microwave data from NASA's Nimbus-7 satellite and the US Department of Defense's Defense Meteorological Satellite Programme.
The record, which began in November 1978, shows an overall downward trend of 2.1 per cent per decade in the size of the maximum winter extent, a decline that accelerated after 2004.