As the world warms, wetlands in the Northern Hemisphere may shrink because of thawing permafrost. This finding complicates predictions that wetlands, which harbour methane-producing bacteria, will release more greenhouse gases as temperatures rise.

Permafrost and wetlands are often found together in the Northern Hemisphere. Using a climate model, Christopher Avis at the University of Victoria in British Columbia, Canada, and his colleagues show that, at first, permafrost degradation does increase upper-soil moisture. But as frozen subsurface soil layers continue to melt, water usually trapped near the surface drains to deeper layers, and wetland extent declines.

Nature Geosci. doi:10.1038/ngeo1160 (2011)