A climate change scenario experiment conducted with the state-of-the-art coupled atmosphere-ocean general circulation model ECHAM4/OPYC3 is analysed with the objective to quantify changes in present-day Arctic permafrost conditions. An efficient procedure is adopted which overcomes the many problems associated with an explicit treatment of soil freezing and thawing processes. The zero degree soil temperatures as well as induced permafrost index characteristics simulated by the model for present day conditions match well the observed permafrost zonation. For a future scenario of greenhouse gas emissions (SRES A2 issued by IPCC), we estimate the amounts that the permafrost zones moves poleward and how the thickness of the active layer deepens in response to the global warming by the end of the 21st century. The simulation indicates a 30--40% increase in active-layer thickness for most of the permafrost area in the Northern Hemisphere, with largest relative increases concentrated in the northernmost locations.