Thawing Permafrost Likely To Boost Global Warming, New Assessment Concludes

And this is not even mentioning methane emissions.

http://www.sciencedaily.com/releases/2008/09/080901084854.htm

ScienceDaily (Sep. 2, 2008) — A new assessment more than doubles previous estimates of the amount of carbon stored in permafrost, and indicates that carbon dioxide emissions from microbial decomposition of organic carbon in thawing permafrost could amount to roughly half those resulting from global land-use change during this century.