It was a stunning figure: $60 trillion.
Such could be the cost, according to a recent commentary [PDF] in the journal 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.
The $60 trillion figure went everywhere, and no wonder. It's jaw-dropping. To provide some perspective, 50 gigatons is 10 times as much methane as currently exists in the atmosphere. Atmospheric methane levels have more than doubled since the industrial revolution, but this would amount to a much sharper increase in a dramatically shorter time frame.
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. "The scenario they used is so unlikely as to be completely pointless talking about," says Gavin Schmidt, a noted climate researcher at the NASA Goddard Institute for Space Studies in New York.
Schmidt is hardly the only skeptic. "I don't have any problem with 50 gigatons, but they've got the time scale all wrong," adds David Archer, a geoscientist and expert on methane at the University of Chicago. "I would envision something like that coming out, you know, over the centuries."
Still, the Nature paper is the most prominent airing yet of concerns that a climate catastrophe could be brought on by the release of Arctic methane that is currently frozen in subsea deposits -- concerns that seem to be mounting in lockstep with the dramatic warming of the Arctic. That's why it's important to put these fears into context and try to determine just how much weight they ought to be accorded.