March 2011 Ice Extent Second Lowest on Record
In the Arctic Ocean and adjacent polar seas, the area covered by sea ice grows and shrinks over the course of the year. Sea ice reaches its largest extent at the end of winter (late February to early March) and its smallest extent in September, at the end of summer.
Average Arctic sea ice extent for the month of March 2011 was the second lowest in the satellite record (behind 2006), according to the National Snow and Ice Data Center. The NSIDC reported that sea ice extent reached its yearly maximum on March 7. Covering an estimated 5.65 million square miles (14.64 million square kilometers), the extent tied for the lowest winter maximum extent in the satellite record.
Arctic sea ice maximum extent has decreased by 2.7 percent per decade since 1979, a much smaller decline than the 11.5 percent per decade drop in the September minimum. The relatively small decline in winter maximum extent, however, does not mean the ice is fully recovering each winter from dramatic summer melting.
Strong summer melting in the past decade has reduced the core of thick ice that manages to survive all year long. Spring ice cover has become increasingly dominated by young and generally thinner ice that formed over the previous months. Most of the thin, first-year ice melts again in the summer.
The ice pack of March 2011 contains much less multi-year ice (light blue) than the historical average. There is almost none of the oldest-more than four years old-ice that once dominated much of the Arctic Ocean. Loss of sea ice in the summer has serious consequences for marine animals, including polar bears and seals, who depend on the ice as a floating "rest stop" for hunting and caring for their young.
Climate scientists are also concerned about the effect on the Earth's energy balance. The bright white ice surface reflects up to 80 percent of incoming sunlight. Without ice, the ocean absorbs considerably more sunlight, amplifying warming and causing more melting of ice.