Is methane really a $60 trillion climate crisis?


Chris Mooney at Mother Jones pushes back against a recent report in Nature that suggested methane from warming arctic sea floors could cost the global economy $60 trillion.

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.

To be clear, methane is a serious problem that needs to be researched and addressed, in particular with the methane being released by the natural gas boom, but Mooney speaks to a number of scientists that are skeptical that such an enormous amount of methane could ever be released suddenly or in a short amount of time.

Moreover, even if subsea permafrost methane hydrates do thaw, the liberated gas still has to travel through layers of sediment just to get to the ocean floor. So how does that happen? "That's kind of mysterious," says Archer. Perhaps there will be open pathways for gas in some places, but perhaps there won't. Archer also notes that there have been undersea explosions or landslides that release methane in bursts, but "those kinds of things seem like they would be relatively small compared to 50 gigatons, and they would happen sporadically in time over centuries, not everything blows up in a few years."

Nonetheless, imagine that methane gas from melted hydrate makes it to the sea floor. It now exists as bubbles with, say, 50 meters to go before they reach the sea surface. Most of the bubbles won't make it, say scientists: They'll be dissolved in seawater, and then the methane will be broken down by microorganisms over a period of months. "If methane is in the ocean water column, most of it doesn't get out," explains Bill Reeburgh, a professor of earth system science at the University of California-Irvine who has spent his career studying methane. "Most of it is oxidized" by bacteria, which turn it into carbon dioxide and water, Reeburgh continues. "So all these stories about seeps, people seem to think the bubbles go straight to the atmosphere, and they don't."

In other words, while the waters of the East Siberian Sea may be full of dissolved methane, for many scientists that doesn't prove that hydrates have been disturbed, or that the Arctic is starting to vent large amounts of methane from below the sea floor into the atmosphere. Not yet, anyway.

Read the rest.

Andy Revkin also raised concerns on Twitter (see tweet above) over the attention given to the $60 trillion figure. He's compiled a number of critiques of the Nature piece, as well as a response from the author here.

Tags: Global Climate Change | Global Warming Science

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