Chicago (IL) – NASA’s Ice, Cloud and land Elevation Satellite (ICESat) provides new clues about the presence of ice in the Arctic and you already know the picture isn’t pretty. Critical thick ice coverage has dropped by a staggering 595,000 square miles, more than the land size of the U.S.’ largest state - Alaska - in just four years.
NASA found that Arctic sea ice is thinning much faster than previously thought. The area covered by thick ice, which is ice that survives several summers, apparently decreased by 42%. That number translates into 595,000 square miles, which exceeds Alaska’s 570,374 square miles and is more than twice the size of Texas (260,914 square miles), almost four times the size of California (155,973 square miles) or about ten times the size of Georgia (57,919 square miles).
Thick ice coverage is being viewed as an indicator of the health of the ice cover. As the ice cover in the Arctic grows thinner, it grows more vulnerable to melting in the summer. "Ice volume allows us to calculate annual ice production and gives us an inventory of the freshwater and total ice mass stored in Arctic sea ice," said Ron Kwok of NASA's Jet Propulsion Laboratory in Pasadena, California.
"Ice volume allows us to calculate annual ice production and gives us an inventory of the freshwater and total ice mass stored in Arctic sea ice," said Kwok. "Even in years when the overall extent of sea ice remains stable or grows slightly, the thickness and volume of the ice cover is continuing to decline, making the ice more vulnerable to continued shrinkage. Our data will help scientists better understand how fast the volume of Arctic ice is decreasing and how soon we might see a nearly ice-free Arctic in the summer."
Using ICESat measurements, scientists found that overall Arctic sea ice thinned about 7 inches a year, for a total of 2.2 feet over four winters. During the study period, the relative contributions of the two ice types to the total volume of the Arctic's ice cover were reversed. In 2003, 62% of the Arctic's total ice volume was stored in multi-year ice, with 38% stored in first-year seasonal ice. By 2008, 68% of the total ice volume was first-year ice, with 32% multi-year.
"The near-zero replenishment of the multi-year ice cover, combined with unusual exports of ice out of the Arctic after the summers of 2005 and 2007, have both played significant roles in the loss of Arctic sea ice volume over the ICESat record," said Kwok.
NASA said that the amount of ice replaced in the winter has not been sufficient to offset summer ice losses. The result is more open water in summer, which then absorbs more heat, warming the ocean and further melting the ice.