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 currently underlies about one fourth of the land area of the northern hemisphere, and many qualitative predictions have been made for a severe reduction of this area in response to global warming. A map of permafrost distribution compiled using the 'frost index', a dimensionless number that can be related to the zonal arrangement of permafrost, shows very good correspondence with a recently published empirical map. The frost index was used in conjunction with three transient general circulation models to compile maps of permafrost zonation for conditions in the mid-21st century. Although regional patterns and local details differ 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 scenarios. Reductions in the areal extent of equilibrium permafrost predicted from two of the three transient models are much less than those indicated by runs using 2 x CO models.