Background
Global warming-induced thawing of subarctic peatland permafrost has been predicted to turn boreal and tundra biomes into carbon sources extraordinaire.  According to this climate-alarmist hypothesis, the exposure and subsequent decay of vast stores of newly-thawed organic matter will release long-sequestered carbon back to the atmosphere as CO2, possibly freeing enough carbon at a sufficiently rapid rate to rival more direct anthropogenic CO2 emissions.  The end result of this scenario is a tremendous positive feedback to the ongoing rise in the air's CO2 content, which is envisioned to lead to even more serious global warming.

What was done
In a real-world evaluation of this hypothesis, Payette et al. quantified the main patterns of change in a subarctic peatland on the eastern coast of Canada's Hudson Bay - which was caused by permafrost decay between 1957 and 2003 - via detailed surveys conducted in 1973, 1983, 1993 and 2003.

What was learned
There was continuous permafrost thawing throughout the period of observation.  As the researchers describe it, "about 18% of the initial frozen peatland surface was melted in 1957," while thereafter "accelerated thawing occurred with only 38%, 28% and 13% of the original frozen surface still remaining in 1983, 1993 and 2003, respectively."  This process, in their words, was one of "terrestrialization" via the establishment of fen/bog vegetation, which nearly always results in either no net loss of carbon or actual carbon sequestration.

What it means
Payette et al. conclude that "contrary to current expectations, the melting of permafrost caused by recent climate change does not [our italics] transform the peatland to a carbon-source ecosystem."  Instead, "rapid terrestrialization exacerbates carbon-sink conditions and tends to balance the local carbon budget."