January 17, 2011

Arctic Thaw Fans The Flames Of Global Warming

The Northern Hemisphere's shrinking ice and snow cover is causing less and less sunlight to reflect back into space in a previously underestimated mechanism that could add to global warming, according to a new study on the subject.

Satellite data indicated that Arctic sea ice, glaciers, winter snow pack and Greenland's ice were reflecting less energy back into space between 1979 and 2008. The dwindling amount of reflective energy exposes the ground and water, both of which are darker and absorb more heat.

The study estimated that ice and snow in the Northern Hemisphere, especially in the Arctic, were now reflecting on average 3.3 watts per square meter of solar energy back into the upper atmosphere, a reduction of 0.45 watts per square meter since the late 1970s.

"The cooling effect is reduced and this is increasing the amount of solar energy that the planet absorbs," Mark Flanner, an assistant professor at the University of Michigan and lead author of the study, told Reuters.

"This reduction in reflected solar energy through warming is greater than simulated by the current crop of climate models," Flanner said of the findings, published in the journal Nature Geoscience Sunday.

"The conclusion is that the cryosphere (areas of ice and snow) is both responding more sensitively to, and also driving, stronger climate change than thought," he said.

As ground and water are increasingly exposed to sunlight, the absorbed heat in turn speeds up the melting of snow and ice nearby.

The United Nation's panel of climate experts blames the shrinking of Arctic sea ice mainly on greenhouse gases from man's burning of fossil fuels.

Many studies forecast that the Arctic sea ice could disappear altogether in the summer months later this century. Such an occurrence would destabilize the hunting cultures of indigenous peoples and threaten many of the Arctic's animal species, as well as add to global climate change.

Although, Flanner said it was impossible to come to such conclusions based on the study about the rate of future melting, for instance of Arctic sea ice, since it was based on only 30 years of data.

"There are a lot of other things that determine climate ... this is just one of them," he said.

Other factors include whether more clouds will be around in a warmer climate, which also reflects sunlight. There also could be more water vapor that traps heat in the atmosphere.

The study estimated that a rise in temperature of just one degree Celsius (1.8 degrees Fahrenheit) would equal a decline in solar energy reflected out into space of 0.3 to 1.1 watts per square meter from the Northern Hemisphere's snow and ice.

Temperatures have risen nearly 0.75 degrees Celsius in the Northern Hemisphere in the past 30 years. The study did not look at the Southern Hemisphere, where Antarctica has much more ice and there are fewer signs of warming.

"On a global scale, the planet absorbs solar energy at a rate of about 240 watts per square meter averaged over a year. The planet would be darker and absorb an additional 3.3 watts without the Northern Hemisphere cryosphere," Flanner told Reuters. 


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