[1] The East Siberian transect, which has been designated by the International Geosphere-Biosphere Program (IGBP) as its Far East transect, has unique permafrost conditions. Not only does permafrost underlie the entire transect, but also about one third of the region is underlain by an "ice complex,'' consisting of extremely ice-rich Late Pleistocene sediments. Given the possibility of a predicted future increase in global temperatures, an evaluation of the magnitude of changes in the ground thermal regime becomes desirable for assessments of possible ecosystem responses and impacts on infrastructure. A soil model developed at the Geophysical Institute Permafrost Laboratory was used to simulate the dynamics of the active layer thickness and ground temperature in this transect, both retrospectively and prognostically, using climate forcing from six global climate models (GCMs). Analysis of future permafrost dynamics showed that within the southwestern part of the transect, widespread permafrost thawing from the surface can begin as early as 2050. The spatial extent and temporal dynamics of the zone with thawing permafrost vary significantly among the different GCMs. According to all the GCMs the mean annual ground temperatures could rise by 2degrees - 6 degreesC, and the active layer thickness could increase by 0.5 - 2 m everywhere within the transect by 2099. However, the increases in mean annual ground temperature and active layer thickness are not uniform in time. Relatively cold and warm periods associated with natural fluctuations in air temperature and precipitation are superimposed on the background warming trend. The most significant increases in mean annual ground temperatures and in the active layer thickness are projected to occur in the southwestern part of the transect and in areas with coarse-grained sediments, characterized by low water content and high thermal conductivity.
