Background
The authors write that there are "fears" that if earth's permafrost thaws, "much of the carbon stored will be released to the atmosphere," as will great quantities of the greenhouse gas methane (further exacerbating warming), as is claimed is already happening -- and at an accelerating rate -- by many climate alarmists, such as Al Gore in his 21 March 2007 testimony before the United States Senate's Environment & Public Works Committee and Michael Mann and Lee Kump (2008) in their Dire Predictions book. Quite to the contrary, however, Blok et al. report that "it has been demonstrated that increases in air temperature sometimes lead to vegetation changes that offset the effect of air warming on soil temperature [italics added]," citing the studies of Walker et al. (2003) and Yi et al. (2007) as specific examples of the phenomenon.

What was done
In an attempt to explore the subject within the context of real-world experimentation, Blok et al. conducted a study within the Kytalyk nature reserve in the Indigirka lowlands of northeastern Siberia (Russia), where they measured the thaw depth or active layer thickness (ALT) of the soil, the ground heat flux, and the net radiation in 10-meter-diameter plots either possessing or not possessing a natural cover of bog birch (Betula nana) shrubs, the latter of which set of plots had all B. nana shrubs removed from their native tundra vegetation in 2007.

What was learned
The Dutch, Swiss and Russian researchers report that "experimental B. nana removal had increased ALT significantly by an average of 9% at the end of the 2008 growing season, compared with the control plots," which implies reduced warming in the more shrub-dominated plots, and that "in the undisturbed control plots with varying natural B. nana cover, ALT decreased with increasing B. nana cover," also "showing a negative correlation between B. nana cover and ALT," which again implies reduced warming in the more shrub-dominated plots.

What it means
Blok et al. say their results suggest that "the expected expansion of deciduous shrubs in the Arctic region, triggered by climate warming, may reduce summer permafrost thaw," and that the "increased shrub growth may thus partially offset further permafrost degradation by future temperature increases," while in further support of their conclusion, the six scientists write that (1) permafrost temperature records "do not show a general warming trend during the last decade (Brown and Romanovsky, 2008), despite large increases in surface air temperature," that (2) during the decade before that, "data from several Siberian Arctic permafrost stations do not show a discernible trend between 1991 and 2000 (IPCC, 2007)," and that (3) "a recent discovery of ancient permafrost that survived several warm geological periods suggests that vegetation cover may help protect permafrost from climate warming (Froese et al., 2008)." And last of all, they note that this phenomenon "could feedback negatively to global warming, because the lower soil temperatures in summer would slow down soil decomposition and thus the amount of carbon released to the atmosphere."

References
Brown, J. and Romanovsky, V.E. 2008. Report from the International Permafrost Association: state of permafrost in the first decade of the 21st century. Permafrost and Periglacial Processes 19: 255-260.

Froese, D.G., Westgate, J.A., Reyes, A.V., Enkin, R.J. and Preece, S.J. 2008. Ancient permafrost and a future, warmer Arctic. Science 321: 1648.

IPCC. 2007. In: Intergovernmental Panel on Climate Change. Fourth Assessment Report: Working Group I Report "The Physical Science Basis" (Eds. Solomon, S., Qin, D. Manning, M. et al.), Cambridge University Press, Cambridge, United Kingdom.

Mann, M.E. and Kump, L.R. 2008. Dire Predictions: Understand Global Warming. DK Publishing Inc., New York, New York, USA.

Walker, D.A., Jia, G.J., Epstein, H.E., Raynolds, M.K., Chapin III, F.S., Copass, C., Hinzman, L.D., Knudson, J.A., Maier, H.A., Michaelson, G.J., Nelson, F., Ping, C.L., Romanovsky, V.E. and Shiklomanov, N. 2003. Vegetation-soil-thaw-depth relationships along a low-arctic bioclimate gradient, Alaska: synthesis of information from the ATLAS studies. Permafrost and Periglacial Processes 14: 103-123.

Yi, S., Woo, M. and Arain, M.A. 2007. Impacts of peat and vegetation on permafrost degradation under climate warming. Geophysical Research Letters 34: 10.1029/2007GL030550.