Arctic methane: Is catastrophe imminent? – ‘Pushing the climate system harder than at any time in Earth’s history’
By JUSTIN GILLIS
20 December 2011
In my article over the weekend about the climate risks from buried Arctic carbon, I omitted any discussion of one issue that sometimes appears in the news: methane deposits under relatively shallow seawater near the coasts of Siberia, Canada and Alaska. It was a purposeful omission because my piece focused on carbon buried on land, which presents a climate risk if it eventually emerges as methane or carbon dioxide. However, given the alarming headlines about methane in the ocean, as seen here and here for example, I did some additional reporting. What I learned about ocean methane was reasonably reassuring, with the caveat that scientists would like to know a great deal more about these deposits before declaring for certain that the hazard is minimal. On land in the Arctic and sub-Arctic regions, we are primarily worried not about methane that already exists but about carbon locked in permafrost that may decompose into methane or carbon dioxide once it thaws. The ocean deposits are different: large quantities of methane already exist there. Both gases are risky, but methane especially so, as it is roughly 25 times as potent at trapping heat as carbon dioxide over the course of a century. The offshore methane is typically locked up as methane hydrate or clathrate, essentially a type of ice that is only stable at certain combinations of temperature and pressure. (Many readers may remember this type of ice forming during the Deepwater Horizon spill last year and blocking efforts to cap the well.) The basic worry is that as the climate changes, the ocean temperature could rise enough to destabilize many of these offshore methane deposits, sending them into the atmosphere. If you go beyond the Arctic and count deposits that exist off the margins of all the continents, there’s probably enough methane that a rapid release could turn the earth into a hothouse. But senior scientists I spoke with told me they considered any such rapid release to be highly unlikely, at least for the deeper deposits. A United States government report came to basically the same conclusion a few years ago. While examples can already be found of warmer ocean currents that are apparently destabilizing such deposits—for example, at this site off Spitsbergen, an island in the Svalbard archipelago in the Arctic—the scientists explained that a pervasive ocean warming sufficient to destabilize a lot of methane hydrates would almost certainly take thousands of years. And even if that happened, many scientists say that the methane released would largely be consumed in the sea (by bacteria that specialize in eating methane) and would not reach the atmosphere. That is what seems to be happening off Svalbard. “I think it’s just dead wrong to talk about ‘Arctic Armageddon,’ ” said William S. Reeburgh, an emeritus scientist at the University of California, Irvine, who spent decades studying such matters and says the likely consumption of methane within the ocean should not be underestimated. “Most of this methane is never going to see the atmosphere.” Nobody regards the case as closed, and more research is necessary, but most of the methane deposits lining the margins of continents would seem to be fairly low on the list of scientific concerns about global warming. The methane hydrate deposits in the Arctic Ocean may represent a somewhat greater hazard because the Arctic is warming so rapidly. Considerable attention was devoted to a paper published last year that found methane bubbling out across large areas of ocean above the East Siberian Shelf, which has some of the Arctic’s largest methane hydrate deposits. […] Martin J. Kennedy, a researcher at the University of Adelaide in Australia, points out that geological evidence from the earth’s long history suggests that the climate has substantial instabilities and is capable of rapid change—sometimes on human, not geological, time scales. He studies extreme climate events from the earth’s history and is among the scientists who suspect that methane hydrates represent one of the planet’s instabilities. “We are pushing the climate system harder than at any time in earth’s history, probably,” Dr. Kennedy said. “Are we not going to cross one of those thresholds soon?”
The East Siberian Arctic Shelf is very vast and very shallow, so the trillion or so tons of methane on its seabed could easily start a cycle of dissociation that would be impossible to stop.