The "methane boils out of the tundra and cooks the earth" meme was debunked in 2011 by the U.S.G.S.  Two lines of evidence:  One was a numerical simulation that failed to demonstrate runaway hydrate melting (Live by the Computer Model; Fall by the Computer Model); the second is observation of the geologic/ice core record that fails to show any huge methane spikes or wholesale permafrost melting in any of the (numerous) interglacials we've had previously, that were just as warm as anything predicted for the rest of the 21st Century.  See this reference:  Ruppel, C. D. (2011), "Methane Hydrates and Contemporary Climate Change", in _Nature Education Knowledge_ 3(10):29.