Global warming: Thick, multi-year Arctic ice melting faster

More trouble in the far north …

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.

By Summit Voice

SUMMIT COUNTY — 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.

As perennial ice retreated in the last three decades, it opened up new areas of the Arctic Ocean that could then be covered by seasonal ice in the winter. A larger volume of younger ice meant that a larger portion of it made it through the summer and was available to form second-year ice. This is likely the reason why the perennial ice cover, which includes second year ice, is not declining as rapidly as the multiyear ice cover, Comiso said.

Multi-year sea ice hit its record minimum extent in the winter of 2008. That is when it was reduced to about 55 percent of its average extent since the late 1970s, when satellite measurements of the ice cap began. Multi-year sea ice then recovered slightly in the three following years, ultimately reaching an extent 34 percent larger than in 2008, but it dipped again in winter of 2012, to its second lowest extent ever.

Because the different types of ice have varying concentrations of salt, they show up differently in the satellite readings. The differences are observed as variations in brightness temperature for the different types of ice. The “brightness” data are used in an algorithm to discriminate multiyear ice from other types of ice.

Comiso compared the evolution of the extent and area of multi-year ice over time, and confirmed that its decline has accelerated during the last decade, in part because of the dramatic decreases of 2008 and 2012.

He also detected a periodic nine-year cycle, where sea ice extent would first grow for a few years, and then shrink until the cycle started again. This cycle is reminiscent of one occurring on the opposite pole, known as the Antarctic Circumpolar Wave, which has been related to the El Niño-Southern Oscillation atmospheric pattern. If the nine-year Arctic cycle were to be confirmed, it might explain the slight recovery of the sea ice cover in the three years after it hit its historical minimum in 2008, Comiso said.


7 thoughts on “Global warming: Thick, multi-year Arctic ice melting faster

  1. Gosh Bob, it’s all the algorithms fault that we have this crazy theory of global warming/climate change. How simple can you get for an answer? Don’t say it, but after reading the onslaught from the deniers to last weeks post, well, I know, go sit in the corner on the 3 legged stool and wear the pointy hat.

    1. Scottish Sceptic needs to read William Marsden book, “Fools Rule: Inside the failed politics of Climate Change”. He would think otherwise about his claim or still be a fool!

  2. There’s no doubt that this winter arctic sea ice is growing faster than it has in years and now I read this article. It’s too bad it’s so easy to write anything without actually using all the facts

  3. What can we do now ? will we be able to reverse it now ? I don’t think so but could we stop it or slow it down ? I think we should try at least and NOW !

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