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Reprieve on global warming

A STUDY of Greenland's ice sheet has revealed that a vast store of planet-warming methane appears to be more stable than thought, easing fears of a rapid rise in temperatures, a scientist said yesterday.

Methane is about 25 times more powerful at trapping heat in the atmosphere than carbon dioxide and vast amounts of the compound are trapped in permafrost in the far northern hemisphere or in seabed deposits called clathrates.

Scientists have feared climate change could trigger a huge release of methane from the clathrate reservoir, sending global warming spiraling out of control.

An estimated 5,000 billion tons of carbon are locked up in these deposits, said 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 said.

Petrenko and an international team of scientists spent six years studying air samples from vast blocks of Greenland ice to see if a rapid rise in temperatures about 12,000 years ago was triggered by methane from clathrates or another source.

The results showed the methane was most likely to have come from wetlands rather than the clathrates, deposits which resemble ice and are held in place on the ocean bed by high pressures and relatively low temperatures.

Petrenko said temperatures in Greenland 12,000 years ago had increased about 10 degrees Celsius in 20 years.

But it took 150 years for methane levels in the atmosphere to increase by 50 percent.

The rapid warming was driving the release of methane, he said, with the most likely sources being tropical wetlands and the vast northern wetlands created after the large-scale retreat of ice sheets about 18,000 years ago.


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