More bad news from the warming Arctic.

It's been known for some time that global warming is thinning Arctic sea ice, threatening to increase temperatures across the polar region and melt the on-shore permafrost that serves as a huge frozen store of greenhouse gases.

But the threat from melting permafrost on land could pale in comparison to the threat of undersea permafrost melting and releasing methane – a gas with far greater global warming impacts than carbon dioxide.

That's the warning Igor Semiletov, a scientist with the Russian Academy of Sciences' Pacific Oceanological Institute, delivered Tuesday at the American Geophysical Union's fall meeting in San Francisco.

"Based on newly obtained data, we suggest an increased methane release from the East Siberian Arctic Shelf," said Semiletov, who conducted his research as a visiting scientist at the International Arctic Research Center at the University of Alaska Fairbanks.

While governments grapple with ways to reduce man-made greenhouse gases, natural resources such as these could threaten said efforts (see Obama Names Energy and Environment Leaders, California Approves Climate Change Master Plan, U.N. Climate Talks Poses Big Impact on Greentech and Can You Spare $45T to Curb Global Warming?).

The undersea shelf off the northern Siberian coast, mostly less than 100 meters deep, contains permafrost, or permanently frozen soil, that was frozen beneath rising ocean water many thousands of years ago – permafrost that scientists expected would not release its store of frozen methane and other greenhouse gases.

But Semiletov, who has studied methane releases from permafrost for 15 years, wanted to find out why recent measurements of atmospheric methane above the arctic were up to 10 percent higher than worldwide averages.

His research indicates that "we've just detected the first signs of release of deep methane" from sub-sea permafrost beds in the East Siberian Sea and Laptev Sea, driven by a slow warming of ocean waters that may or may not be connected to global warming, he said.

But whether or not global warming plays a cause in the methane releases, there's little doubt that they could accelerate it, he said.

While Semiletov said he couldn't predict the worst would happen based on his current data, the melting of the world's subsea permafrost could triple the atmosphere's current share of methane, which would be "enough for a climate catastrophe," he said – that is, an average global temperature increase of up to 6 degrees Celsius.

More research is needed to find out whether recent warming trends, rather than the slow warming the ocean has been undergoing over thousands of years, is playing a role in the release of methane, Semiletov said. It's possible that rising temperatures of water flowing from rivers that feed the Arctic sea could be playing a role, he said.

But when it comes to the link between rising temperatures and the shrinking Arctic ice sheet, there's a clear feedback loop in place, said Julienne Stroeve, a research scientist at the National Snow and Ice Data Center at the University of Colorado in Boulder, Colo.

The shrinking of sea ice – a trend that received a lot of attention in 2007, when the Arctic saw a 36 percent drop in ice cover – means there is less white ice and snow to reflect sunlight, and more dark water to absorb it, she said.

As the shrunken core of summer ice is smaller and thinner, it fails to grow as much during the winter, which means the next summer's shrinking is even worse – a feedback loop that may represent "a new stage" for the polar ice cap, she said.

Not only that, but the ocean water that absorbssolarenergy in the summer releases the heat it's absorbed back into the atmosphere in the fall, Stroeve said. That's having an effect on land temperatures along the North American and Eurasian arctic coasts, where temperatures have grown fastest next to sea areas that have lost ice, she said.

And this is worrisome because those land areas contain lots of permafrost, she said. Arctic permafrost holds within its frozen surface an estimated 950 gigatons of carbon, compared to an estimated 730 gigatons of carbon in the atmosphere today, she said.

As if the threat of massive greenhouse-gas emissions from a melting Arctic wasn't enough bad news, there are other climate effects to consider, Stroeve said. "The arctic is basically the air conditioner of the northern hemisphere," and "when you start losing that sea ice, you lose that air conditioner," she said.

Losing this natural air conditioner could lead to changes in North American climate and weather patterns, including the possibility of a much drier American Southwest, Stroeve said, though she cautioned that the research predicting those climate changes is "still in its infancy."