From today’s LA Times, by Margot Roosevelt, original story is posted here

Carbon dioxide (C02) is the most prevalent greenhouse gas that is trapping heat in the atmosphere, warming the planet to what most climate scientists consider dangerous levels. But methane, a greenhouse gas that is 25 times more powerful than CO2, has also been growing at an alarming rate, with concentrations more than doubling since pre-industrial times.

A paper published Thursday in the journal Science reveals that parts of the East Siberian continental shelf, which extends up to 1000 miles out into Arctic waters, show concentrations of methane in surface waters that are 100 times higher than expected. And in the air, more than 5,000 measurements taken by scientists on Russian icebreakers and on helicopters document methane levels more than four times higher than elsewhere in the Arctic basin.

The researchers, led by Natalia Shakhova of the University of Alaska, along with Swedish and Russian colleagues, found that the amount of methane seeping into the atmosphere from below the Arctic Ocean is comparable to previous emissions estimates for all the world’s oceans. The Arctic is warming faster than any other part of the planet, and scientists fear that methane emissions could rise even more dramatically in a feedback loop: As the atmosphere warms, the permafrost that has locked in methane gas in wetlands and beneath continental shelves melts, releasing more methane, which then warms the planet more.

“Wetlands and permafrost soils, including the subsea permafrost under the Arctic Ocean, contain at least twice the amount of carbon that is currently in the atmosphere as carbon dioxide,” Martin Heimann wrote in an article accompanying the paper. “Release of a sizeable fraction of this carbon as carbon dioxide and/or methane would lead to warmer atmospheric temperatures, causing yet more methane to be released.” The researchers recommend that their data be immediately incorporated into current assessments of how fast the Arctic is likely to warm in the near future.

And a  perspectives piece in Science by Martin Heimann us partially reprinted below:

Methane is, after water vapor and carbon dioxide, the third most important greenhouse gas in the atmosphere. Its concentration in the atmosphere has more than doubled since preindustrial times. Human energy production and use, landfills and waste, cattle raising, rice agriculture, and biomass burning are considered responsible for this increase (1). However, 40% of current global methane sources are natural. Most natural emissions come from anaerobic decomposition of organic carbon in wetlands, with poorly known smaller contributions from the ocean, termites, wild animals, wildfires, and geological sources. Two observational studies now shed light on how these natural sources are changing in today’s changing climate (2, 3).

Ice core studies have shown that the natural methane sources must have changed substantially during the glacial cycles. How stable are they under global warming? Wetlands and permafrost soils, including the sub-sea permafrost under the Arctic Ocean, contain at least twice the amount of carbon that is currently in the atmosphere as carbon dioxide. Release of a sizable fraction of this carbon as carbon dioxide and/or methane would lead to warmer atmospheric temperatures, causing yet more methane to be released. It would thus create a positive feedback loop that amplifies global warming. However, observational evidence for such release on regional and global scales has been elusive.

On page 1246 of this issue, Shakhova et al. (2) report convincing evidence of methane outgassing from the Arctic continental shelf off northeastern Siberia (Laptev and East Siberian Sea), based on painstaking repeated surveys using Russian ice breakers between 2003 and 2008. In this region, the relatively shallow continental shelf extends up to 1000 km north of the coastline. The seabed consists of relict permafrost from the last glaciation (4), when sea levels were considerably lower than today. The permafrost layer contains substantial amounts of organic carbon and also traps methane seeping up from underneath. In the permafrost, the methane forms relatively stable methane hydrates, but warming of the seawater or a decrease in pressure by a reduction in sea level will destabilize the hydrates, releasing methane into the ocean waters (5).

Shakhova et al. now document large areas with surface waters that are highly supersaturated in methane; in some places, methane concentrations are more than 100 times as high as expected in equilibrium with the ambient atmosphere. Based on their extensive data set, the authors estimate an annual outgassing to the atmosphere of 8 x 1012 grams of carbon (8 Tg C) as methane from the East Siberian Arctic Shelf waters. Consistent with this, concurrent atmospheric concentration measurements on the ship and with a helicopter document methane levels up to four times as high as recorded elsewhere in the Arctic basin.


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