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Wednesday, January 2, 2013

Albedo flip in Arctic speeding up sea ice melt

Light Absorption Speeding Arctic Ice Melt

Green: Science
The record-setting disappearance of Arctic sea ice this fall was an indication to many climate scientists and ice experts that the pace of climate change was outstripping predictions.
Geophysical Research LettersThe rate of the ocean’s heat absorption is depicted along a color spectrum, with red representing the highest levels and green the lowest.
Now a new study published this week in the journal Geophysical Research Letters provides a look at a dynamic that may further accelerate the process: the rate at which the ocean underneath the ice absorbs sunlight.
The bottom line of the study, which was done by four scientists, three at the Alfred Wegener Institute for Polar and Marine Research in Bremerhaven, Germany, and one from the department of aerospace engineering sciences at the University of Colorado, Boulder, is that the ocean under newly formed ice (“first-year ice” in the scientists’ terminology) absorbs 50% more solar energy than the ocean beneath older ice (“multiyear ice”).
This means that the more the ice melts in late summer, the more first-year ice replaces multiyear ice, and the warmer the ocean beneath the ice becomes, accelerating the melting process. One sentence of the study says it all: “a continuation of the observed sea-ice changes will increase the amount of light penetrating into the Arctic Ocean, enhancing sea-ice melt and affecting sea-ice and upper-ocean ecosystems.”

The study, the first of its kind, used a remotely driven undersea vehicle equipped with spectral radiometers, devices capable of measuring light. It then produced a map of the distribution of light under the summer ice across the Arctic.
The rapid loss of Arctic ice has been a matter of escalating concern to climate scientists. And, as my colleague Justin Gillis explained in this blog earlier this year, the notion that it is offset by increases in Antarctic ice is belied by data showing that the northern melting during the summer, based on the total amount of ocean covered, is progressing far faster than the rate of the southern increase in ice.
The authors of the new study say their data allows them to predict that the trend will only accelerate as the feedback loop continues.

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