Washington: After a record melt season last year, the Arctic Ocean`s icy cover shrank to its lowest extent on record, continuing a long-term trend and diminishing to about half the size of the average summertime extent from 1979 to 2000.
During the cold and dark of Arctic winter, sea ice refreezes and achieves its maximum extent, usually in late February or early March.
According to a NASA analysis, 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 -5.82 million square miles (15.09 million square kilometers)- 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 144,402 square miles (374,000 square kilometers) 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," Joey Comiso, senior scientist at NASA Goddard Space Flight Center, Greenbelt, Md., and a principal investigator of NASA`s Cryospheric Sciences Program, said.
"A decline in the sea ice cover in winter is thus a manifestation of the effect of the increasing greenhouse gases on sea ice," he said.
Satellite data retrieved since the late 1970s show that sea ice extent, which includes all areas of the Arctic Ocean where ice covers at least 15 percent of the ocean surface, is diminishing.
This decline is occurring at a much faster pace in the summer than in the winter; in fact, some models predict that the Arctic Ocean could be ice-free in the summer in just a few decades.