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Arctic methane release is the release of methane from seas and soils in permafrost regions of the Arctic. While a long-term natural process, it may be exacerbated by global warming. This results in a positive feedback effect, as methane is itself a powerful greenhouse gas. The feedback of the undisturbed process is comparably weak, however, because the local release leads to a warming spread over the whole globe. The Arctic region is one of the many natural sources of the greenhouse gas methane. Global warming accelerates its release, due to both release of methane from existing stores, and from methanogenesis in rotting biomass. Large quantities of methane are stored in the Arctic in natural gas deposits, permafrost, and as submarine clathrates. Permafrost and clathrates degrade on warming, thus large releases of methane from these sources may arise as a result of global warming. Other sources of methane include submarine taliks, river transport, ice complex retreat, submarine permafrost and decaying gas hydrate deposits. During interglacials, average atmospheric methane concentrations are nearly twice the lowest values in the depths of glacial. Concentrations in the Arctic atmosphere are higher by 8–10% than that in the Antarctic atmosphere. During cold glacier epochs, this gradient decreases to practically insignificant levels.〔Climate Change 2001: The Scientific Basis (Cambridge Univ. Press, Cambridge, 2001)〕 Land ecosystems are considered the main sources of this asymmetry, although it has been suggested that "the role of the Arctic Ocean is significantly underestimated." Soil temperature and moisture levels have been found to be significant variables in soil methane fluxes in tundra environments. ==Contribution to climate change== The release of methane from the Arctic is in itself a major contributor to global warming as a result of polar amplification. Recent observations in the Siberian arctic show increased rates of methane release from the Arctic seabed.〔 Land-based permafrost, also in the Siberian arctic, was estimated in 2013 to release 17 million tonnes of methane per year - a significant increase on the 3.8 million tons estimated in 2006 and estimates before then of 0.5 million tonnes. This compares to around 500 million tonnes released into the atmosphere annually from all sources.〔 In the plot showing the global atmospheric methane concentration (the significant measure from the viewpoint of global warming and radiative forcing), however, the rate of the increase in atmospheric methane has been slowing until 2004, indicating that the contribution from Arctic release is currently not the dominant factor in the global picture. Shakhova et al. (2008) estimate that not less than 1,400 Gt of Carbon is presently locked up as methane and methane hydrates under the Arctic submarine permafrost, and 5-10% of that area is subject to puncturing by open taliks. They conclude that "release of up to 50 Gt of predicted amount of hydrate storage () highly possible for abrupt release at any time". That would increase the methane content of the planet's atmosphere by a factor of twelve.〔N. Shakhova, I. Semiletov, A. Salyuk, D. Kosmach (2008), (Anomalies of methane in the atmosphere over the East Siberian shelf: Is there any sign of methane leakage from shallow shelf hydrates? ), EGU General Assembly 2008, ''Geophysical Research Abstracts'', 10, EGU2008-A-01526〕 In 2008 the United States Department of Energy National Laboratory system〔(IMPACTS: On the Threshold of Abrupt Climate Changes ), Lawrence Berkeley National Laboratory News Center, 17 September 2008〕 identified potential clathrate destabilization in the Arctic as one of the most serious scenarios for abrupt climate change, which have been singled out for priority research. The U.S. Climate Change Science Program released a report in late December 2008 estimating the gravity of the risk of clathrate destabilization, alongside three other credible abrupt climate change scenarios.〔(CCSP, 2008: Abrupt Climate Change. A report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research ) (Clark, P.U., A.J. Weaver (coordinating lead authors), E. Brook, E.R. Cook, T.L. Delworth, and K. Steffen (chapter lead authors)). U.S. Geological Survey, Reston, VA, 459 pp.〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「arctic methane release」の詳細全文を読む スポンサード リンク
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