barlevg sends this excerpt from an article at MotherJones:
"It was a stunning figure: $60 trillion. Such could be the cost, according to a recent commentary in Nature, of 'the release of methane from thawing permafrost beneath the East Siberian Sea, off northern Russia... a figure comparable to the size of the world economy in 2012.' More specifically, the paper described a scenario in which rapid Arctic warming and sea ice retreat lead to a pulse of undersea methane being released into the atmosphere. How much methane? The paper modeled a release of 50 gigatons of this hard-hitting greenhouse gas (a gigaton is equal to a billion metric tons) between 2015 and 2025. This, in turn, would trigger still more warming and gargantuan damage and adaptation costs. ... According to the Nature commentary, that methane 'is likely to be emitted as the seabed warms, either steadily over 50 years or suddenly.' Such are the scientific assumptions behind the paper's economic analysis. But are those assumptions realistic—and could that much methane really be released suddenly from the Arctic? A number of prominent scientists and methane experts interviewed for this article voiced strong skepticism about the Nature paper.'"