Sunday, November 2, 2008

Fears mount as Arctic melt prompts historic methane rise

ATMOSPHERIC concentrations of methane, "a greenhouse gas more than 20 times more potent than carbon dioxide", have risen for the first time in eight years, prompting concern about the pace of climate change.

A global study in Geophysical Research Letters found the first increase in methane levels this century — by about 28 million tonnes since mid-2006 — was in part due to release of gas in and near the Arctic.

CSIRO senior climate scientist Paul Fraser said the data was in line with predictions that rapid melting of Arctic ice would create natural wetlands, one of the most common methane emitters. "This is not good news for global warming," he said.

Over the past decade, methane emitted from wetlands, rice fields, cattle, bushfires and coalmines had been largely offset by absorption of the gas by dry soil and through atmospheric oxidation, Dr Fraser said.

"Over the past year, the total sources have overwhelmed the total sinks and methane has started to rise," he said.

Methane is estimated to be responsible for about 20% of global warming since the Industrial Revolution.

The published study comes after British newspaper The Independent reported that scientists aboard a Russian research ship had found millions of tonnes of subsea methane was bubbling to the surface and being released into the atmosphere off the Siberian coast this northern summer.

Research published in Nature Geoscience last week found the first evidence that the rise in Antarctic temperatures in recent decades was caused by human-induced emissions of greenhouse gas.

The research, led by British scientist Nathan Gillett, compared temperature rises at the Arctic and Antarctic since 1900 with four computer simulations. Only models that factored in man-made emissions were able to reproduce the changes observed in the real world. This is a step on from last year's UN Intergovernmental Panel on Climate Change report, which identified evidence of man-made climate change on every continent except Antarctica.

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