Observed and Projected Changes in Permafrost Thermal State in the Northern Hemisphere

Climate projections for the 21st century indicate that there could be a pronounced warming and degradation of permafrost in the arctic and sub-arctic regions. Thawing and freezing of soils is affected by many factors, with air temperature, vegetation, snow accumulation and soil moisture among the most significant. Recent observations indicate a warming of permafrost in many northern and mountain regions with a resulting degradation of ice-rich and carbon-rich permafrost. Permafrost temperature has increased by 1 to 2°C in northern Eurasia during the last 30 to 35 years (e.g. Romanovsky et al., 2008). This observed increase is very similar to what has been observed in Alaska where the warming varies between locations, but is typically from 0.5 to 2°C. In the last 30 years, warming in permafrost temperatures observed in the Russian North and Alaska has resulted in the thawing of permafrost in natural, undisturbed conditions in areas close to the southern boundary of the permafrost zone. Thawing of Little Ice Age permafrost is ongoing at many locations. There are some indications that older late-Holocene permafrost has begun to thaw as well as some undisturbed locations in northeastern Europe, in northwest Siberia and in Alaska.

To assess possible changes in the permafrost thermal state and the active layer thickness we implemented the GIPL2/MPI (Geophysical Institute Permafrost Lab) parallel transient model for the entire Northern Hemisphere permafrost domain. Input parameters to the model are spatial datasets of mean monthly air temperature and precipitation, prescribed vegetation and thermal properties of the multilayered soil column, and water content, which are specific for each vegetation and soil classes and geographical location. As a climate forcing, we used ensemble of five IPCC Global Circulation Models that performed the best in the Arctic and sub-Arctic: ECHAM5, GFDL21, CCSM, HADcm and CCCMA (A1B emission scenario) produced by the researchers from University of Illinois at Urbana-Champaign. The outputs from these five models have been scaled down to 0.5 degree latitude/longitude horizontal resolution. According to this specific climate scenario, projections of future changes in permafrost suggest that by the end of the 21st century, late-Holocene permafrost in Northern Eurasia and Alaska may be actively thawing at all locations and some late Pleistocene permafrost could start to thaw at some locations.