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The Warming-Induced Release of Greenhouse Gases from High-Latitude Permafrost
Reference
Delisle, G. 2007. Near-surface permafrost degradation: How severe during the 21st century? Geophysical Research Letters 34: 10.1029/2007GL029323.

Background
The author writes that "concern has been raised by Lawrence and Slater (2005) and others -- e.g., Zimov et al. (2006) -- over a much accelerated release of greenhouse gases following rapid degradation of permafrost," as well, we might add, as by Al Gore and James Hansen, the former in his testimony of 21 March 2007 before the U.S. Senate's Environment and Public Works Committee, and the latter in his testimony of 26 April 2007 before the Select Committee of Energy Independence and Global Warming of the U.S. House of Representatives.

What was done
In an important study that broaches this high-profile subject, Delisle (2007) employs a "unidimensional long-term permafrost temperature model of general application" that incorporates "all relevant thermal processes within the active layer and the permafrost, and between the permafrost and the non frozen ground below," to determine what we might expect to occur in this regard if surface temperatures were to rise at a rate as high as 0.8C per decade for a full century.

What was learned
The German researcher finds that "permafrost will mostly prevail in this century in areas north of 70N," even for an unbelievable total warming of 8C, and that "permafrost will survive at depth in most areas between 60 to 70N."

What it means
According to Delisle, "based on paleoclimatic data and in consequence of this study, it is suggested that scenarios calling for massive release of methane in the near future from degrading permafrost are questionable," where the reference to paleoclimatic data pertains, in the researcher's words, to the "limited amount of organic carbon that had been released from permafrost terrain in previous periods of climatic warming such as e.g. the Medieval Warm Period or during the Holocene Climatic Optimum," when "there appear to [have been] no significant CH4 excursions in ice core records of Antarctica or Greenland during these time periods (see e.g., Chappellaz et al., 1997), which otherwise might serve as evidence for a massive release of methane into the atmosphere from degrading permafrost terrains."

References
Chappellaz, J., Blunier, T., Kints, S., Dallenbach, A., Barnola, J.-M., Schwander, J., Raynaud, D. and Stauffer, B. 1997. Changes in the atmospheric CH4 gradient between Greenland and Antarctica during the Holocene. Journal of Geophysical Research 102: 15,987-15,997.

Lawrence, D.M. and Slater, A.G. 2005. A projection of severe near-surface permafrost degradation during the 21st century. Geophysical Research Letters 32: 10.1029/2005GL025080.

Zimov, S.A., Schuur, E.A.G. and Chapin III, F.S. 2006. Permafrost and the global carbon budget. Science 313: 1612-1613.

Reviewed 26 November 2008