Permafrost in this area is melting in response to the rapid warming of the Arctic. The most likely cause of this crater is a methane explosion. [...] If Dr Kurchatova's explanation is correct, the consequences are profound. It means that there are vertical structures where salt accumulated as methane ices formed in permafrost. Layers of permafrost may have salty vertical zones of weakness in them that will allow sudden release of methane trapped below the permafrost layer as the climate warms. Vast quantities of methane trapped in river deltas in the Arctic ocean on the Siberian shelf may be unstable. This crater appears to be evidence that the methane is not protected by a very slowly melting solid layer of permafrost. Methane bubbles recently observed in the Laptev Sea, reported on by the National Science Foundation, could be the beginning of the release of an enormous amount of subsea methane.
Methane is a way more effective greenhouse gas than CO2, so cue the feedback loops.