By Brad Plumer – Washington Post – December 19, 2011

One of the least understood — and one of the more unnerving — facets of climate change is the question of what will happen as the Arctic region heats up and permafrost in places like Alaska and Siberia thaws out.  There's a whole lot of carbon locked up in all that frozen soil and organic matter. And, as the frost melts, that carbon will enter the atmosphere, most of it as carbon dioxide, but some of it transformed by bacteria into methane, an even more powerful heat-trapping greenhouse gas. That, in turn, will warm the planet further. It’s a potent feedback mechanism, and scientists still aren’t sure just how potent it might be. For full story, click here.