The Methane Bomb Thing Isn't Really A Thing (Global Warming)
Peter Sinclair has done some nice work to clarify the famous Methane Bomb thing. Briefly, the Methane Bomb is where methane trapped on the floor of the Arctic ocean gets out in large quantities because it is warm. This makes more warming. So, more of this Methane comes out, causing it to get warmer, then this cycle keeps up for a while and in short order civilization collapses and we all die.
Source: scienceblogs.com