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CLIMATE CHANGE: Arctic Shelf Leaking Potent Greenhouse Gas

Stephen Leahy

UXBRIDGE, Canada, Mar 5 2010 (IPS) - The frozen cap trapping billions of tonnes of methane under the cold waters of the Arctic Ocean is leaking and venting the powerful greenhouse gas into the atmosphere, new research shows.

Methane venting from a seafloor mound. A greenhouse gas, it is some 25 times more potent than carbon dioxide. Credit: US Geological Survey

Methane venting from a seafloor mound. A greenhouse gas, it is some 25 times more potent than carbon dioxide. Credit: US Geological Survey

It is not known if this may be one of the first indicators of a feedback loop accelerating global warming.

Researchers estimate that eight million tonnes in annual methane emissions are being released from the shallow East Siberian Arctic Shelf, which is equivalent to all the methane released from the world’s oceans, covering 71 percent of the planet.

On a global scale of methane emissions from the land-based sources – animals, rice paddies, rotting vegetation – the newly measured emissions from the Siberian seabed are less than two percent.

“That’s still very significant,” Natalia Shakhova, a researcher at the University of Alaska in Fairbanks, told IPS. “Before, it was assumed that this region had zero emissions.”

Methane concentrations measured over the oceans are currently about 0.6 to 0.7 parts per million (ppm), but they are now 1.85 in the Arctic Ocean generally, and between 2.6 and 8.2 ppm in the East Siberian Arctic Shelf, an area roughly two million square kilometres in size, said Shakhova.

Shakhova, and her University of Alaska colleague Igor Semiletov, led eight international expeditions to one of the world’s most remote and desolate regions and published their results in the Mar. 5 edition of the journal Science.

Global methane levels have risen each year since 2007 after being constant for a decade, reports Ed Dlugokencky of the Earth System Research Laboratory in Boulder, Colorado, which is run by the U.S. National Oceanic and Atmospheric Administration (NOAA).

“We saw an increase in CH4 (methane) growth rate in 2007 in the Arctic… but it did not increase in 2008,” Dlugokencky, an expert on atmospheric methane told IPS via email.

He suspects Siberia’s subsea emissions are not new but have been underway for some time, and he also says Shakhova’s estimate of eight million tonnes needs to be verified by other means. However, he acknowledges this study represents the first direct measurements ever done in the region and stresses the urgency for more investigation.

In the last few years, researchers have been shocked to see Arctic Ocean “on the boil” in places as gases from deep below come bubbling to the surface. Large parts of the Arctic Ocean floor along coastal areas is actually permafrost that was flooded thousands of years ago after the big melt from the last ice age.

Permafrost is frozen soil and contains very large amounts of carbon and methane. The extremely cold waters of the Arctic and its ice cover kept the subsea permafrost cold enough so it has been melting extremely slowly. Until now.

Surface temperatures over much of the Arctic landscape and the Siberian landscape, particularly in summer, have jumped six to 10 degrees C above normal in recent years. That has lead to a massive increase in the flows of the many rivers that terminate in the Arctic Ocean.

Shakhova and colleagues believe this substantial increase of warmer water into the shallow East Siberian Shelf has accelerated the melting of the subsea permafrost, in effect fracturing the frozen cap and allowing methane to escape into the atmosphere. “Our concern is that the subsea permafrost has been showing signs of destabilisation already,” she said in a release.

“If it further destabilises, the methane emissions may not be teragrammes, it would be significantly larger,” she said. A teragramme is a trillion grammes, or one million tonnes.

Methane – a greenhouse gas approximately 25 times more potent than carbon dioxide – is commonly called methane hydrates when it is frozen in permafrost or under the sea. The total volumes are unknown.

“The release to the atmosphere of only one percent of the methane assumed to be stored in shallow hydrate deposits might alter the current atmospheric burden of methane up to three to four times,” Shakhova said in a release.

“The climatic consequences of this are hard to predict,” she said.

Shakhova’s study is just one of at least a dozen others that clearly show the Arctic region is not only melting but also emitting more carbon and methane.

Permafrost spans 13 million square kilometres of the land in Alaska, Canada, Siberia and parts of Europe. A new Canadian study documented that the southernmost permafrost limit has retreated 130 kilometres over the past 50 years ago in Quebec’s James Bay region.

Another Canadian study released last year showed that the region was getting darker and absorbing more heat in the summer because of a significant shift in plant growth from grasses and lichen to larger shrubs over the past 30 years due to warmer temperatures.

A permafrost “retreat” has been observed over much of the southern fringe of the permafrost zone and could result in emissions a billion tonnes of carbon per year – human emissions are seven to eight billion tonnes – by mid-century, a University of Florida study estimated.

Without major reductions in those human emissions, mainly burning of fossil fuels and deforestation, the top two to three metres of permafrost across the entire Arctic region could thaw by the end of this century, warned a major report, “Arctic Climate Feedbacks: Global Implications”, released by the World Wildlife Fund last September.

Should that happen, the volumes of carbon and methane released could be many times higher than what is presently in the atmosphere, driving up the global average temperatures by six, eight, or even 10 degrees C. The consequences are unimaginable.

“The changes we are (currently) seeing are not entirely unexpected, they are just happening far sooner,” said Mark Serreze, senior research scientist at the National Snow and Ice Data Centre in the U.S. state of Colorado and co-author of Arctic Climate Feedbacks report.

If the methane hydrates start to melt or large areas of permafrost “that will be very bad news for humanity”, Serreze told IPS in September.

“The world is a very small place and we have not been good stewards. Climate change is symptom of this poor stewardship,” he said.

“The way we’re going right now, I’m not optimistic that we will avoid some kind of tipping point.”

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