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Methane Belches in Lakes Supercharge Global Warming, Study Says

Richard A. Lovett
for National Geographic News
September 6, 2006
 
Global warming is causing Siberian lakes to bubble methane, a greenhouse
gas, into the atmosphere at an alarming rate, scientists say.

Because methane in the atmosphere warms the planet, the Russian pools are intensifying the climate change that boosted their belching in the first place.

It all adds up to a feedback loop in which warming begets even more warming.

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

Rotting organic matter in wetlands or beneath lakes can give rise to methane, which is a much more powerful greenhouse gas than the usual culprit, carbon dioxide.

Until recently most scientists believed that lakebeds were a minor source of the gas.

Methane bubbles have long been known to rise from the depths of Siberian lakes. But the bubbles were intermittent and difficult to measure.

Recently, though, an international team of U.S. and Russian scientists realized that the best time to look for bubbles was in winter. In the cold season researchers can walk across the frozen lakes, peering at bubbles trapped in the ice.

What they found is that lakebed emissions are large enough that taking them into account increases the total estimated level of Arctic emissions by 10 to 63 percent. The scientists report their findings in tomorrow's issue of the journal Nature.

Not So Permafrost

The methane appears to be produced from the thawing of permafrost—what should be a permanently frozen layer of earth—due to global warming, says the study's lead author, Katey Walter of the University of Alaska Fairbanks's Institute of Arctic Biology.

Overall, she says, there is as much organic matter buried in the Siberian tundra—rolling treeless plains with mucky soil and mosses at the surface—as is contained in all of the world's tropical rain forests.

As global warming melts the permafrost, bacteria eat the thawed organic matter, then belch methane into the lakes.

Using radiocarbon dating, Walter's team determined that the methane being produced beneath the lakes comes from organic matter that died as long as 42,900 years ago but that is only now decomposing, presumably due to recent temperature increases.

Melting permafrost has caused lakes to increase in area by 14 percent in recent decades, she adds.

"It's a time bomb."

Increasing Feedbacks

The new paper is important, says Walter Oechel of the Global Change Research Group at California's San Diego State University. It helps quantify the degree of climate-warming feedbacks from Arctic warming, he says.

"They're not only significant but larger than expected," Oechel said.

In addition to increasing methane production from lakebeds, he says, there is also a risk that global warming might lead to the melting of methane-containing ice in the permafrost.

"Those are huge stores of methane," Oechel said. "If those came out, they would swamp the current warming [that is] due to carbon dioxide from all sources."

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