PERMAFROST ZONATION AND CLIMATE-CHANGE IN THE NORTHERN-HEMISPHERE - RESULTS FROM TRANSIENT GENERAL-CIRCULATION MODELS

Numerous studies have demonstrated that both global patterns and local details of permafrost distribution are highly responsive to climatic fluctuations, at several temporal and spatial scales. Permafrost curre ntly underlies about one fourth of the land area of the northern hemis phere, and many qualitative predictions have been made for a severe re duction of this area in response to global warming. A map of permafros t distribution compiled using the 'frost index', a dimensionless numbe r that can be related to the zonal arrangement of permafrost, shows ve ry good correspondence with a recently published empirical map. The fr ost index was used in conjunction with three transient general circula tion models to compile maps of permafrost zonation for conditions in t he mid-21st century. Although regional patterns and local details diff er substantially between the three scenarios, all result in reductions in the area occupied by each permafrost zone. Localized expansions of the area underlain by permafrost are apparent from two of the scenari os. Reductions in the areal extent of equilibrium permafrost predicted from two of the three transient models are much less than those indic ated by runs using 2 x CO models.