April 24, 2009

Ice Study Reveals Methane’s Effect On Global Warming

According to scientists, Greenland's icesheet has revealed a store of methane that appears to be more stable that previously thought, easing tensions over a rapid rise in global temperatures.

Vast amounts of methane, a gas that is 25 times more powerful than carbon dioxide (CO2) at trapping heat within the atmosphere, is trapped within the permafrost in the far northern hemisphere, and in seabed deposits called clathrates.

Scientists have feared that the release of the clathrate reservoir could trigger a downward spiral of global warming that could not be stopped.

Roughly 5,000 billion tons of carbon are stored in these deposits says Vasilii Petrenko of the Institute of Arctic and Alpine Research at the University of Colorado.

"That's about equal to all of the oil, coal and gas reserves that we think we have," he told Reuters.

Petrenko and a team of researchers studied blocks of Greenland ice for six years to see if a rapid rise in temperature 12,000 years ago was triggered by methane from clathrates.

The results of the testing showed that most of the methane likely came from wetlands rather than clathrates.

According to Petrenko, temperatures in Greenland 12,000 years ago increased about 10 degrees Celsius in 20 years, but it took 150 years for methane levels in the atmosphere to increase by 50 percent.

Tropical wetlands and vast northern wetlands drove the release of methane after the large-scale retreat of icesheets about 18,000 years ago.

Petrenko and his team measured an isotope called carbon-14 (C14) in methane extracted from air bubbles trapped in Greenland ice going back 12,000 years.

Scientists can use C14 to determine the age of the ice because it deteriorates at a known rate.

Wetlands methane has a different C14 "signature" than clathrate deposit methane.

"The project involved pushing the analytical techniques to a level no one has taken them before," Petrenko said.

Only one trillionth of the methane from the air bubbles contained the carbon-14 isotope.

"The results definitely help us to say that it doesn't seem methane clathrates respond to warming by releasing lots of methane into the atmosphere, which is really good news for global warming."

"We're warming now and we know that there's evidence of northern wetlands becoming more productive. If it's not clathrates, the wetlands might still drag the methane up," he said.


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