OBSERVED AND PROJECTED CHANGES IN PERMAFROST 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. 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 in its detailed characteristics, but is typically from 0.5 to 2°C.

In order to assess possible changes in the permafrost thermal state and the active layer thickness, the GIPL-1.3 permafrost model was implemented for the entire North Hemisphere permafrost domain. Simulation was performed for three time snapshots. For the present-day climatic conditions the CRU2 data set with 0.5° X 0.5° latitude/longitude resolution (Mitchell & Jones 2005) was used. The future climate scenario was derived from the MIT-2D integrated global system model (IGSM) developed at the Massachusetts Institute of Technology (Sokolov & Stone, 1998). We used the MIT-2D output for the 21^st century with a doubling gradual increase of atmospheric CO₂ concentration by the end of current century that corresponds to the IPCC SRES emission scenario A1B.

The modeling results show that, according to this specific climate scenario, by the end of the 21^st century, the mean annual ground temperatures (MAGT) at the bottom of the active layer could be above 0°C within the vast territory of the Northern Hemisphere permafrost domain and permafrost will be actively thawing within the area presently occupied by discontinuous permafrost with temperatures between 0 and -2°C. The long-term thawing of permafrost will start when the soil layer that was unfrozen during the summer above the permafrost would not refreeze completely even during the most severe winters. At this moment, permafrost will start to thaw from its top down and many processes such as thermokarst, landslide, active layer detachment etc., could be triggered or intensified. The most significant impacts on ecosystems, infrastructure, carbon cycle and hydrology will be observed in areas where permafrost contains a considerable amount of ground ice.