Permafrost Dynamics In 20Th And 21St Centuries Along The East-Siberian And Alaskan Transects

Abstract

High latitude ecosystems where the mean annual ground surface temperature is around or below 0�C are highly sensitive to global warming. This is largely because these regions contain vast areas of permafrost, which will begin to degrade when the mean annual ground temperatures will rise above 0�C. The Alaskan and East Siberian transects, centered on the 155� WL and 135� EL, were chosen for evaluation of permafrost---atmosphere interactions. The analysis of measured data shows a significant increase in air and ground temperatures that started from the late 1960s within both these transects and the magnitude of this increase is from 0.2 to 0.5�C per decade. This trend is comparable to trends predicted by majority of global warming scenarios. A simple and accurate model for evaluating the permafrost dynamics was developed in Geophysical Institute Permafrost Lab (GIPL). The GIPL model is a fusion of the modified Kudryavtsev's approach, which is a set of analytical formulas for active layer thickness (ALT) and mean annual ground temperature (MAGT) calculations, with the Geographic Information System (GIS). The evaluation of the GIPL performance showed that when applied to long-term (decadal or longer time scale) averages, this model achieves an accuracy of +/-0.2--0.4�C for the mean annual ground temperatures and +0.1--0.3 m for the active layer thickness calculations. The GIPL model was used for the hindcast of the permafrost dynamics in the 20th century, using a combination of observationally-based and simulated monthly grids of surface air temperature. The results showed that during the 20th century there were a number of relatively cold and warm periods. These climatic variations produced 1 to 3�C changes in MAGT and up to 1 m in the ALT. The forecast for the period of 2000--2100 was performed using climatic parameters from six Global Climate Models provided by Arctic Climate Impact Assessment program. The results showed that by the end of 21st century mean annual ground temperatures will be 2 to 6�C warmer and the ALT from 0.2 to 1 m deeper. During this period, in many areas within both transects the degradation of permafrost from the surface will start. By 2100, the area with actively degrading permafrost will cover about 10--15% of the Siberian transect and up to 30% and more within the Alaskan transect.