Thermally-Conditioned Paleo-Permafrost Variations from Global Climate Modeling

The permafrost distribution under Quaternary climate conditions is investigated by a frozen ground classification method based solely upon the near surface air thermal indices as a diagnosing analysis of the Paleoclimate Model Intercomparison Project 2 (PMIP2) output. The methodology is constructed using the present-day distribution of the frozen ground and the thermal (freeze and thaw) index, and showed reasonable capability for large-scale mapping. The frozen ground distribution was reconstructed for 0 ka (pre-industrial), 6 ka (mid-Holocene), and 21 ka (the last glacial maximum; LGM) conditions. The Holocene simulations (0 ka and 6 ka) produced largely similar results. The LGM outputs showed substantial increase of the permafrost area by 49.6% relative to the pre-industrial conditions in median among the models, but also showed insufficient cooling during the cold season in some regions. Across-model variations illustrate the regions that need careful examination in using PMIP2 outputs for further subsurface thermal regime calculations.