AGW Observer and SkS have the link. Money quote:
The global relationship between annual mean temperature and terrestrial net CH4 exchange (Fig. 9 for the baseline simulation) showed a significant weak to moderately strong linear relationship (R2 = 0.38, P < 0.01). On the basis of the results of this regression, net terrestrial CH4 emission has increased at a rate of 41.6 Tg CH4 yr−1 per 1 ◦C of warming, suggesting the existence of a positive biogeochemical feedback in response to climatic warming (and partly in response to historical land-use change in parallel with temperature change). On the basis of the 100-yr Global Warming Potential for CH4 (=25; IPCC, 2007), this responsiveness of the CH4 budget corresponded to an increase of 283 Tg C yr−1 in the climate–carbon (CO2) cycle feedback. As implied by a study using an Earth System model (Gedney et al., 2004), the interaction between climate and the methane cycle can exert a positive feedback as a result of human-induced climate change. The feedback would be accelerated by additional emissions from permafrost melting and methane hydrates (O’Connor et al., 2010).