(a) Global temperature change from increased CH4 emission due to the warming and expansion of thawed, inundated areas for the low and high TCR of the GST scenario
Figure 4. (a) Global temperature change from increased CH4 emission due to the warming and expansion of thawed, inundated areas for the low and high TCR of the GST scenario. IE refers to the CH4 inundation emission. (b) The sensitivity of global temperature change (° C) to the increased CH4 inundation emission for the high TCR of the GST scenario. 10, 25, 50, and 100 refer to the CH4 inundation emission increases scaled by 10-, 25-, 50-, and 100-fold, respectively. Also shown is the global temperature change with the UCE scenario.
Climate change and permafrost thaw have been suggested to increase high latitude methane emissions that could potentially represent a strong feedback to the climate system. Using an integrated earth-system model framework, we examine the degradation of near-surface permafrost, temporal dynamics of inundation (lakes and wetlands) induced by hydro-climatic change, subsequent methane emission, and potential climate feedback. We find that increases in atmospheric CH4 and its radiative forcing, which result from the thawed, inundated emission sources, are small, particularly when weighed against human emissions. The additional warming, across the range of climate policy and uncertainties in the climate-system response, would be no greater than 0.1 ° C by 2100. Further, for this temperature feedback to be doubled (to approximately 0.2 ° C) by 2100, at least a 25-fold increase in the methane emission that results from the estimated permafrost degradation would be required. Overall, this biogeochemical global climate-warming feedback is relatively small whether or not humans choose to constrain global emissions.