NASA: Old Arctic sea ice continues to melt

Tuesday, March 18, 2008

This ice concentration map dated March 9, 2008, indicates maximum ice extent in the Northern Hemisphere and the contour of the ice edge in 2006 (when the maximum extent was least extensive during the satellite era) is shown in red while that for the 28-year average is shown in gold.
Image: NASA.

NASA has stated that recent satellite images have shown that despite an unusually cold winter in the Arctic, the old or perennial ice on both the North and South Poles has continued to melt while the level of 'new ice' has increased as compared to last March.

On March 18 the scientists said they believe that the increased area of sea ice this winter is due to recent weather conditions, while the decline in perennial ice reflects the longer-term warming climate trend and is a result of increased melting during summer and greater movement of the older ice out of the Arctic.

According to NASA-processed microwave data, whereas perennial ice used to cover 50-60 percent of the Arctic, this year it covers less than 30 percent. Very old ice that remains in the Arctic for at least six years comprised over 20 percent of the Arctic area in the mid to late 1980s, but this winter it decreased to just six percent.

"Although this March the area is slightly larger than last March, the area of [thick] perennial ice has reached an all time low. So the volume of Arctic ice continues to decrease," said NASA's Cryospheric Sciences Program manager Seelye Martin.

Arctic sea ice grows and declines seasonally, ranging from an average minimum extent in September of 2.5 million square miles (6.5 million squeare km) to an average winter maximum extent of 5.9 million square miles (15.3 million square km) in March. This March, instruments on NASA’s Aqua satellite and National Oceanic and Atmospheric Administration (NOAA) and the United States Defense Department satellites showed the maximum sea ice extent slightly increased by 3.9 percent over that of the previous three years, but it is still below the long-term average by 2.2 percent. Increases in ice extent occurred in areas where surface temperatures were colder than the historical averages. At the same time, as a result of the export of ice from the Arctic, the area of perennial ice decreased to an all-time minimum.

Joey Comiso of NASA's Goddard Space Flight Center in Greenbelt, Md., the lead author of a 2007 related study, used data from NASA's passive microwave data set to establish that the perennial ice cover at the summer Arctic ice minimum in 2007 was about 40 percent less than the 28-year average. According to the latest observations from the National Snow and Ice Data Center (an organization partially funded by NASA), perennial sea ice dropped from about 40 percent of the total ice pack last year to 30 percent of total ice this winter. The perennial ice is also growing younger, meaning that it is thinner and will be more vulnerable during the summer melt period.

According to Walt Meier of the National Snow and Ice Data Center at the University of Colorado, Boulder, as ice ages it continues to grow and thicken, so that older ice is generally also thicker ice. This winter the ice cover is much thinner overall and thus in a more vulnerable state heading into the summer melt season.

"It's becoming thinner and thinner and much more susceptible to melting during the summer - much more likely to melt away. It may look OK on the surface, but it's like looking at a Hollywood movie set - you see the facade of a building and it looks OK, but if you look behind it, there's no building there," said Meier.

NASA’s ICESat satellite has contributed to understanding of the changes in ice thickness. To get a better understanding of the behavior of sea ice, NASA is planning a follow-on satellite mission, ICESat II, to launch in 2015.