NASA/Goddard - Loss Of Multi-Year Arctic Sea Ice Running About 15%/Decade

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The bright white central mass shows the perennial sea ice while the larger light blue area shows the full extent of the winter sea ice including the average annual sea ice during the months of November, December and January. The data shown here were compiled by NASA senior research scientist Josefino Comiso from NASA's Nimbus-7 satellite and the U.S. Department of Defense's Defense Meteorological Satellite Program. Credit: NASA/Goddard Scientific Visualization Studio.

Along with the steady decline (3.2 percent per decade) in overall Arctic sea ice extent, a new NASA study shows that the oldest and thickest multi-year ice is melting at a much faster pace — about 15 percent per decade — than the thin ice that forms anew each year. The rapid decline of older ice makes the Arctic Ocean’s floating ice cap even more vulnerable to further decline in the summer, according to Joey Comiso, a senior scientist at NASA Goddard Space Flight Center.

“The average thickness of the Arctic sea ice cover is declining because it is rapidly losing its thick component, the multi-year ice. At the same time, the surface temperature in the Arctic is going up, which results in a shorter ice-forming season,” Comiso said. “It would take a persistent cold spell for most multi-year sea ice and other ice types to grow thick enough in the winter to survive the summer melt season and reverse the trend.”

Scientists differentiate multi-year ice from both seasonal ice, which comes and goes each year, and “perennial” ice, defined as all ice that has survived at least one summer. In other words: all multi-year ice is perennial ice, but not all perennial ice is multi-year ice (it can also be second-year ice).

Comiso found that perennial ice extent is shrinking at a rate of -12.2 percent per decade, while its area is declining at a rate of -13.5 percent per decade. These numbers indicate that the thickest ice, multiyear-ice, is declining faster than the other perennial ice that surrounds it.

EDIT

http://summitcountyvoice.com/2012/03/01/global-warming-thick-multi-year-arctic-ice-melting-faster/