Global warming and active-layer thickness: results from transient general circulation models

The near-surface thermal regime in permafrost regions could change significantly in response to anthropogenic climate warming. Because there is only a small lag between these two processes, the impact of warming on the active layer can be investigated using relatively simple climate-driven models. A formulation attributable to Kudryavtsev was used to study the potential increase of active-layer thickness in the permafrost regions of the Northern Hemisphere, where warming is predicted to be more pronounced than elsewhere. Kudryavtsevʹs solution was validated using contemporary data, and successfully reproduced the actual depths of frost and thaw at widely spaced locations in North America and Eurasia. Modern climatic data and scenarios of climate change for 2050, derived from three transient coupled ocean-atmosphere general circulation models (GCMs), were used in conjunction with the thaw-depth solution to generate hemispheric maps showing contemporary active-layer thickness for several soil types and moisture conditions, and its relative changes over the next century. The simulations indicate a 20–30% increase of active-layer thickness for most of the permafrost area in the Northern Hemisphere, with the largest relative increases concentrated in the northernmost locations.