http://www.livescience.com/environment/051220_permafrost.html

Ground Frozen Since Ice Age Thaws and Collapses

Melting permafrost is damaging roads and buildings in Alaska and Russia and threatens to get much worse as the planet grows warmer, researchers said this week.

Up to 90 percent of the permafrost at the surface of the Northern Hemisphere could melt by the end of this century, leaving gaping holes in the ground and collapsed structures, roads and railways in northern regions.

In what scientists predict to be a vicious cycle, the thaw will release more greenhouse gases into the atmosphere, further exacerbating global warming.

The meltdown of northern soil is already underway. Other teams have noted sunken railways, damaged structures and increased numbers of rock-falls at high elevations owing to thawed boulders.