Thickest parts of Arctic ice cap melting faster: NASA

NASA image of ice cover in 2012. (IMAGE COURTESY OF NASA)

NASA image of ice cover in 1980. (IMAGE COURTESY OF NASA)

Looking at these two NASA images from 1980 and 2012 shows just how much ice coverage the Arctic Ocean has lost over the past 30 years.

And, now, a new NASA study has found that the oldest and thickest Arctic sea ice is disappearing at a faster rate than the younger and thinner ice at the edges of the Arctic Ocean’s floating ice cap.

That thicker ice, known as multi-year ice, generally survives through the summer melt, when young ice formed over the winter melts again.

The rapid disappearance of older ice makes Arctic sea ice even more vulnerable to further ice loss in the summer, said Joey Comiso, senior scientist at NASA Goddard Space Flight Center, and author of the study, recently published in the Journal of Climate.

His research looked at how multi-year ice, that is, ice that has made it through at least two summers, has diminished with each passing winter over the last 30 years.

The study found multi-year ice “extent” or coverage — which includes all areas of the Arctic Ocean where multi-year ice covers at least 15 per cent of the ocean surface — has dropped at a rate of -15.1 per cent during every 10-year period.

“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 in a Feb. 29 NASA news release. “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.”

“Perennial” ice, that is as all ice that has survived at least one summer, is also shrinking at a rate of -12.2 per cent per decade, while its overall coverage is declining at a rate of -13.5 per cent per decade.

The thickest multi-year ice appears to be declining faster than the other perennial ice that surrounds it.

For his study, Comiso created a time series of multi-year ice using 32 years of microwave data from NASA’s Nimbus-7 satellite and the U.S. Department of Defense’s Defense Meteorological Satellite Program, taken during the winter months from 1978 to 2011.

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