Permafrost in the Community Earth System Model: Present-day and projected permafrost conditions and feedbacks onto global climate

摘要

The combined impact of improvements to CLM and a more accurate climate simulation improve the representation of the permafrost in CCSM4 compared to CCSM3. Though evaluation of the permafrost simulation is limited by the availability of observations and the scale mismatch between point measurements and grid cell quantities, comparisons of model data against available observations indicate improvements in the permafrost distribution, active layer thickness, and permafrost temperatures (Figure 1 [Lawrence et al. 2012]). The area containing near-surface permafrost is projected decline substantially during the 21st century in CCSM4. The rate of degradation, however, is slower by about 35% during the first half of the 21st century in CCSM4 than it was in CCSM3 due to improved soil physics. Under the highest emission scenario (RCP8.5), the majority of present-day permafrost is projected to undergo significant active layer deepening and permafrost degradation. The total projected loss of near-surface permafrost from the end of the 20th century to the end of the 21st century is 9.0 million km~2. Under the low emissions pathway (RCP2.6), the projected near-surface permafrost area contraction is much less severe (loss of 4.1 million km~2) and the permafrost state effectively stabilizes by 2100 in response to a stabilizing climate. This result implies that the permafrost-carbon feedback could be largely constrained if a low enough emissions pathway is followed.