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All winter I ventured across frozen lakes to set more traps above these seeps. More than once I stepped unknowingly on a bubbling hotspot and plunged into ice-cold water. Methane hotspots in lake beds can emit so much gas that the convection caused by bubbling can prevent all but a thin skin of ice from forming above, leaving brittle openings the size of manhole covers even when the air temperature reaches –50 degrees C in the dark Siberian winter. I caught as much as 25 liters (eight gallons) of methane each day from individual seeps, much more than scientists usually find. I kept maps of the hotspots and tallies of their emissions across numerous lakes. The strongest bubbling occurred near the margins of lakes where permafrost was most actively thawing. The radiocarbon age of the gas, up to 43,000 years old in some places, pointed to yedoma carbon as the culprit. From 2002 to 2009 I conducted methane-seep surveys on 60 lakes of different types and sizes in Siberia and Alaska. What scientists were not expecting was that the increase in methane emissions across the study region was disproportional to the increase in lake area over that same region. It was nearly 45 percent greater. It was accelerating.
Extrapolated to lakes across the Arctic, my preliminary estimate indicated that 14 million to 35 million metric tons of methane a year were being released. Evidence from polar ice-core records and radiocarbon dating of ancient drained lake basins has revealed that 10,000 to 11,000 years ago thermokarst lakes contributed substantially to abrupt climate warming—up to 87 percent of the Northern Hemisphere methane that helped to end the Ice Age. This outpouring tells us that under the right conditions, permafrost thaw and methane release can pick up speed, creating a positive feedback loop: Pleistocene-age carbon is released as methane, contributing to atmospheric warming, which triggers more thawing and more methane release. Now man-made warming threatens to once again trigger large feedbacks.
How fast might these feedbacks occur? In 2007 global climate models reported by the Intergovernmental Panel on Climate Change (IPCC) projected the strongest future warming in the high latitudes, with some models predicting a rise of seven to eight degrees C by the end of the 21st century. Based on numerous analyses, my colleagues and I predict that at least 50 billion tons of methane will escape from thermokarst lakes in Siberia as yedoma thaws during the next decades to centuries. This amount is 10 times all the methane currently in the atmosphere.
Even with our best efforts, our current estimates beg more sophisticated modeling as well as consideration of potential negative feedbacks, which could serve as breaks on the system. For instance, in Alaska, a record number of thermokarst lakes are draining. Lakes formed in upland areas grow until they hit a slope. Then the water flows downhill, causing erosion and further drainage, sending melted sediment into rivers and eventually the ocean. Drained basins fill in with new vegetation, often becoming wetlands. Although they produce methane when they are unfrozen in summer, their total annual emissions are often less than those of lakes. It is hard to say whether such potential processes would lessen methane release by a sizable amount or just a few percentage points. Two projects of mine, with my Fairbanks colleague Guido Grosse, Lawrence Plug of Dalhousie University in Nova Scotia, Mary Edwards of the University of Southampton in England and others, began in 2008 to improve the first-order approximations of positive and negative feedbacks. A key step is to produce maps and a classification of thermokarst lakes and carbon cycling for regions of Siberia and Alaska, which we hope to draft by early 2010. The cross-disciplinary research links ecological and emissions measurements, geophysics, remote sensing, laboratory incubation of thawed permafrost soils and lake sediments, and other disciplines. The goal is to inform a quantitative model of methane and carbon dioxide emissions from thermokarst lakes from the Last Glacial Maximum (21,000 years ago) to the present and to forecast climate-warming feedbacks of methane from lakes for the upcoming decades to centuries.
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http://www.scientificamerican.com/article.cfm?id=methane-a-menace-surfaces&page=3
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