Hey, Permafrost: Put a Lid on Itby Bill Chameides | March 10th, 2010
posted by Erica Rowell (Editor)
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The “it” is methane. Global warming may be slowly melting the lid off the Arctic’s megapool of methane.
Methane (CH4) is a powerful greenhouse gas — some 25 times more potent a global warmer than carbon dioxide (CO2). An earlier GreenGrok post described the potentially catastrophic consequences that may ensue if the huge pools of carbon currently stored in permafrost (about twice as much carbon as what’s currently in the atmosphere) were to be liberated from melting permafrost as CH4.
The reason why this is so worrisome is that the process of global warming from greenhouse gases and the release of methane from melting permafrost are self-reinforcing (i.e., a positive feedback). Once the carbon gets up a head of steam, so to speak, it could be impossible to rein it in before it ran its course, releasing all that stored carbon as greenhouse gases.
Methane Leaking From More Arctic Sources?
But thawing of land-based permafrost isn’t the only potential source of methane to be concerned about: there are also releases of methane from the sediments beneath the seas of the Arctic shelf.
These regions contain huge amounts of methane. It’s been estimated that if only one percent of the methane assumed to be stored in these deposits were released, it might increase the amount of methane in the atmosphere by a factor of up to four.
Today that methane is held in place by an overlaying layer of permafrost. But could that permafrost lid melt as a result of global warming? And would that lead to the methane escaping?
Citing more than 5,000 at-sea observations of methane supersaturations in the water column as well as in the air above the sea, authors Natalia Shakhova, of the University of Alaska, Fairbanks, and her colleagues were able to document and quantify a flux of methane flowing through the water column and into the atmosphere, that almost certainly is coming from the sediments below.
What to Make of These Latest Methane FindingsThe magnitude of the methane release appears to be nontrivial but not alarmingly so. The rate of release from the East Siberian Arctic Shelf is estimated to be about eight million metric tons of carbon annually, equivalent to the total amount of methane previously estimated to come from the entire ocean, but only about two percent of the total rate of annual methane emissions to the atmosphere and roughly 10 percent of the estimated release of methane due to human activities (source).
It’s not yet clear how significant the Shakhova et al. findings are. The release rates they estimate from the East Siberian Arctic Shelf are of little global significance; at today’s rates they are little more than a scientific curiosity. And it is not even certain that the releases are part of a long-term trend caused by global warming.
Nevertheless, the work cannot be dismissed. There is that issue of a positive feedback. We can’t rule out the possibility that the authors’ measurements are just the early indications of a destabilization of the entire methane pool held in the East Siberian Arctic Shelf. In that case, the measurements reported in the Science paper could turn out to be, well, the tip of the iceberg. And, while I’m no captain, I hear that it’s always a good idea to keep careful track of the icebergs.filed under: Arctic, carbon dioxide, carbon dioxide emissions, climate change, faculty, global warming, methane, Planetary Watch
and: Alaska, Arctic shelf, East Siberian Arctic Shelf, feedback, ice, permafrost, positive feedback, Siberia