There is observational evidence in high northern latitudes that increasing temperatures are having an effect on permafrost and seasonally frozen ground regions. During the last 50 years in Russia, the depth of the freezing layer has decreased, and active layer depths have been increasing. In this study, a new version of the Goddard Institute for Space Studies (GISS) global coupled atmosphere-ocean-ice model is used to examine the seasonal freeze/thaw depths in northern Russia during the last 150 years and how they might change in the next 100 years as atmospheric greenhouse gases (GHGs) continue to increase. Two 250-year model simulations will be analyzed; one is a control with fixed levels of atmospheric GHGs and the other is a transient experiment with increasing GHGs. For the present climate, the results will be compared with observations and other model studies where possible. Changes in other hydrologic variables, such as ground water storage, precipitation, evaporation, snow cover, and river discharge, will also be analyzed to determine how they are related to changes in seasonal freeze/thaw depths.