This photo provided by the journal Nature shows Sergey Zimov, director of the Northeast Science Station in Siberia, examining a cross-section of yedoma, carbon trapped in permafrost, along the bank of the Kolyma River in Siberia. The shiney surface of the cliff represents massive ice wedges. The dark sections in between are soil inclusions which contain ice-age organic carbon, left over from the Pleistocene steppe-tundra ecosystem, which, when deposited into lake bottoms, provided food for bacteria, that produce methane. (AP Photo/Nature, Katey Walter)