OSLO A rise in concentrations of a powerful greenhouse gas over the Arctic after a decade of stability is stirring worries about a possible thaw of vast stores trapped in permafrost, experts said.
Levels of methane in the atmosphere rose 0.6 percent in 2008, according to preliminary data from the Zeppelin station on a remote island in the Norwegian Arctic, after a similar 0.6 percent gain in 2007, Norwegian officials said.
The 2007 rise outpaced a global rise in methane of 0.34 percent to a new record high after levels had been stable for about a decade. World data for 2008 are not yet available.
"The biggest worry is that there are emissions from the permafrost, and also from wetlands in the northern region," said Catherine Lund Myhre, senior scientist at the Norwegian Institute for Air Research.
A thaw of permafrost, such as in Siberia or Canada, could release vast amounts of trapped greenhouse gases and in turn accelerate global warming. "There may be several causes for the rise. Currently it's not solved," she told Reuters.
Methane is the second most important greenhouse gas behind carbon dioxide, accounting for about 18 percent of the heat-trapping greenhouse effect from human activities that might trigger more heatwaves, floods or rising seas.
Methane is emitted from natural sources -- such as from decaying plants in swamps or by termites -- and by human use of fossil fuels, rice paddies, landfills and from the digestive tracts of animals such as cows and sheep.
Paul Fraser, a chief research scientist at the Australian Commonwealth Scientific and Research Organization, said wetlands, both in the tropics and in the north, seemed a likely source of extra methane after a drier period.
Studies indicated that 2007 and 2008 were the wettest years in the tropics for 25 years -- perhaps prompting wetland emissions. High summer temperatures in 2007 in northern regions also led to releases from wetlands, he said.
But he dismissed deeper sources such as permafrost or other frozen deposits, known as clathrates. "Nobody believes that permafrost or deeper methane sources could be involved on such short time scales," he said.
Fraser said the world rise in methane may now be slowing.
"It's difficult to say where the methane is coming from," said Marit Viktoria Pettersen, a senior adviser at the Norwegian Pollution Control Authority, of the high Arctic measurements.
"It could be methane from thawing permafrost ... We do not know," she said.
Other possible reasons for high recordings in the Arctic could include a shift in local winds. And new Arctic industrial sources include Russian coal and natural gas activities, or flaring from a StatoilHydro gas field.
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