Estimates of February/March average sea ice thickness for 2004 to 2008 from NASA’s ICESat (left) and February/March 2012 from CryoSat-2 (right). (Ill.: American Geophysical Union)
Arctic sea ice has passed its annual maximum extent and is beginning its seasonal decline through the spring and summer. While total extent was not at record low, it remained well below average through March.
According to data from the National Snow and Ice Data Center (NSIDC), the Arctic ice cap continues to get thinner and younger. Satellite data suggests that first-year ice may now cover the North Pole area for the first time since the winter of 2008.
Arctic sea ice extent in March 2013 averaged 15.04 million square kilometers. This is 710,000 square kilometers below the 1979 to 2000 average extent, and 610,000 square kilometers above the record low for the month, which happened in 2006.
Between the 2012 summer minimum and the 2013 winter maximum, sea ice extent showed the largest increase in the satellite record. This was primarily due to the extreme record low ice extent in September 2012, which resulted in a near-record high first-year ice extent.
Over the winter, some multiyear ice recirculated into the Beaufort Sea where significant melt of multiyear ice has occurred in recent summers. Also, some multiyear ice has been lost, as it moved out of the Arctic through Fram Strait. The boundary between primarily first-year ice and multiyear ice is now near the North Pole, marking the first time since the winter of 2008 that a substantial amount of first-year ice may be covering the pole as we enter the melt season.
Levels of multiyear ice remain extremely low. While multiyear ice used to cover up to 60% of the Arctic Ocean, it now covers only 30%.
European Space Agency’s CryoSat-2 satellite, launched in April 2010, now provides estimates of sea ice thickness distribution across the Arctic Ocean. The first published results from CryoSat-2 has been compared with thickness estimates from NASA’s ICESat satellite, which operated from 2003 to 2009. The CryoSat-2 results indicate continued thinning since 2008. Significantly, ice along the north coast of Greenland appears to have thinned—in the past this has been the site of some of the thickest sea ice in the Arctic, NSIDC’s web site reads.