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Methane Bubbling Up From Undersea Permafrost?

Mason Inman in San Francisco, California
for National Geographic News
December 19, 2008
 
The East Siberian Sea is bubbling with methane, a powerful greenhouse gas, being released from underwater reserves, according to a recent expedition.

This could be a sign that global warming is thawing underwater permafrost, which is releasing methane that has been locked away for many thousands of years.

If these methane emissions from the Arctic speed up, it could cause "really serious climate consequences," said expedition member Igor Semiletov of the University of Alaska, Fairbanks.

(Related: "Global Warming Feedback Loop Caused by Methane, Scientists Say" [August 29, 2006].)

Semiletov and colleagues have traveled along the Siberian coast—this year they covered 13,000 miles (22,000 kilometers)—while monitoring methane concentrations in the air and observing the seas.

"According to our data, more than 50 percent of the Arctic Siberian shelf is serving as a source of methane to the atmosphere," Semiletov said.

This vast shelf is about 750,000 square miles (2 million square kilometers)—about the same size as Greenland or Mexico—and about 80 percent of it is covered with permafrost, Semiletov said.

He presented the findings from his group at an American Geophysical Union meeting in San Francisco this week.

Not-So-Permanent Permafrost

Permafrost is basically dirt that's been permanently frozen for hundreds or thousands of years, much of it since the last ice age.

Sea levels back then near the Siberian coast were about 325 feet (100 meters) lower than today, and the exposed ground froze solid down to 1,600 to 2,300 feet (500 to 700 meters) deep.

Over the past 10,000 years, sea levels rose to cover some of this permafrost, and in recent years those seas have seen increases in average temperatures.

"As a result, sub-sea permafrost has warmed up to minus 1 degree Celsius [30 degrees Fahrenheit]," Semiletov said. "It's very, very close to the thawing point."

Underneath the permafrost are stores of methane, the same as the natural gas people use for cooking and heating.

There are also methane hydrates, a solid that forms when methane and water mix in cold temperatures. The hydrates release gas as they warm.

"It was assumed that these stores of methane have not been leaking, because the sub-sea permafrost served as a lid keeping hydrates and natural gas in place," Semiletov said.

But now global warming may be starting to release these stores of methane into the atmosphere.

Drastic Increase

Regions farther from the Equator generally are experiencing more warming, and the Arctic is warming fastest of all.

"Springtime air temperatures on the East Siberian Arctic shelf [have] increased up to 5 degrees Celsius [9 degrees Fahrenheit]," Semiletov said. "It's a hot spot."

In comparison, the world as a whole has warmed about 1.25 degrees Fahrenheit (0.7 degrees Celsius) since pre-industrial times.

If abrupt methane release became widespread, it could create a feedback loop that would lead to even more drastic global warming.

"Our early observations in 1994 to 1999 didn't reveal a widespread enhanced dissolved methane concentration" along the Siberian coast, Semiletov said.

"With this newly obtained data, we suggest an increase of methane release from the East Siberian Arctic shelf," he said.

"We have obtained a drastic increase of air methane in some sites—sometimes up to four times higher than the background [global average]."

Vladimir Romanovsky, a permafrost expert also at the University of Alaska, Fairbanks, says the study is worrying.

"It has very serious implications for changes in greenhouse gases," Romanovsky said, adding that the releases described should be monitored more closely.

"It could be very important, but we still need some numbers to see how big [of a problem] it is."

Carolyn Ruppel is a geophysicist with the U.S. Geological Survey who is based in Woods Hole, Massachusetts.

"The nature of the shallow Arctic continental shelves means that they have the potential to release significant methane now and into the future," said Ruppel, who was not involved in the study.

But there are a number of places this methane could be coming from, she said.

"Quantifying the contribution of each potential methane source will be a major challenge."
 

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