Air and ground temperatures measured in Eastern Siberia has been compiled and analyzed. The analysis of mean annual air temperatures measured at 52 meteorological stations within and near the East-Siberian transect during the period from 1956 through 1990 demonstrates a significant and statistically significant (at 0.05 level) positive trend ranging from 0.065 to 0.59 degrees C/ 10 yr. A statistically significant (at 0.05 level) positive trend was also observed in mean annual ground temperatures for the same period. The permafrost temperature reflects changes in air temperature on a decadal time scale much better than on an interannual time scale. Generally, positive trends in mean annual ground temperatures are slightly smaller in comparison with trends in mean annual air temperatures, except for several sites where the discordance between the air and ground temperatures can be explained by the winter snow dynamics. The average trend for the entire region was 0.26 degrees C/10 yr for ground temperatures at 1.6 in depth and 0.29 degrees C/10 yr for the air temperatures. The most significant trends in mean annual air and ground temperatures were in the southern part of the transect, between 55 degrees and 65 degrees N. Numerical modeling of ground temperatures has been performed for Yakutsk and Tiksi for the last 70 yr. Comparing the results of these calculations with a similar time series obtained for Fairbanks and Barrow in Alaska shows that similar variations of ground temperatures took place at the same time periods in Yakutsk and Fairbanks, and in Tiksi and Barrow. The decadal and longer time scale fluctuations in permafrost temperatures were pronounced in both regions. The magnitudes of these fluctuations were on the order of a few degrees centigrade. The fluctuations of mean annual ground temperatures were coordinated in Fairbanks and Yakutsk, and in Barrow and Tiksi. However, the magnitude and timing of these fluctuations were slightly different for each of the sites. (C) 2006 Elsevier B.V. All rights reserved.

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 2°–6°C, 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.

At the northernmost three sites, annual mean air and ground temperatures vary significantly in a cyclic manner with high temperatures in the late 1980s and late 1990s and maxima in 1989 and in 1998-1999. Temperatures were colder earlier in mid-1980s and slightly colder in the early 1990s. There was a long-term increase in temperatures during the entire period of measurements. Annual mean air temperatures at all three sites are very similar, while the ground and permafrost temperatures at West Dock are several degrees colder than at Deadhorse and Franklin Bluffs. A significantly shallower and slightly more conductive snow cover and a smaller range in seasonal air temperature variations at the West Dock site are responsible for these differences. The recent warming increased soil temperatures about 3degreesC over long-term averages. Annual mean temperatures of the ground and permafrost surfaces near Ivotuk are about -2 to -3degreesC, which is 2 to 3degreesC warmer than at the Deadhorse and Franklin Bluffs sites. This probably attributes to the differences in the snow cover thickness and its thermal properties.