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Methane mischief: misleading commentary published in Nature

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A catastrophic release of the potent greenhouse gas methane in the Arctic could cause a sudden warming with massive economic consequences says a commentary published in the esteemed scientific journal Nature Wednesday. Yet most everything known and published about methane indicates this scenario is very unlikely. This piece should never have been published without discussing this critical point.

The commentary speculates methane hydrates, ice-like substances where the gas is stored in the East Siberian Arctic shelf (among other places), could unleash a 50 gigatonne “pulse” of methane between 2015-2025 (leading to an atmospheric concentration six times current levels) as undersea permafrost thaws. This abrupt increase in the gas, 20 times as effective at trapping heat as carbon dioxide, would accelerate global warming 15-35 years ahead of current projections, setting off a so-called “economic time bomb” of some $60 trillion (roughly the size of the 2012 global economy, writes Climate Central) the commentary estimates.

But what do scientists and the scientific literature say about the likelihood of such a methane “pulse”?

In the 2008 U.S. government (Climate Change Science Program) assessment on abrupt climate change, the authors stress the uncertainty of the size of the methane “hydrate reservoir” but say a dramatic abrupt release appears “very unlikely”.

“…modeling and isotopic fingerprinting of ice-core methane do not support such a release to the atmosphere over the last 100,000 years or in the near future,” the report says.

On the climate science blog Real Climate, in 2010, climate scientist David Archer writes:

“For methane to be a game-changer in the future of Earth’s climate, it would have to degas to the atmosphere catastrophically, on a time scale that is faster than the decadal lifetime of methane in the air. So far no one has seen or proposed a mechanism to make that happen.”

And, here’s the kicker: Nature, the same organization which published Wednesday’s commentary, published a scientific review of methane hydrates and climate change by Carolyn Ruppel in 2011 which suggests the scenario in said commentary is virtually impossible. The review states:

Catastrophic, widespread dissociation of methane gas hydrates will not be triggered by continued climate warming at contemporary rates (0.2ºC per decade; IPCC 2007) over timescales of a few hundred years. Most of Earth’s gas hydrates occur at low saturations and in sediments at such great depths below the seafloor or onshore permafrost that they will barely be affected by warming over even [1,000] yr.

I emailed NOAA methane expert Ed Dlugokencky and asked him if he could reconcile what the climate science literature says about methane versus the assumptions guiding Wednesday’s Nature commentary. His response:

“…our lab measures CH4 [methane] in air samples collected from sites around the world, including the Arctic. So far, we do not detect a permanent increase in CH4 emissions from natural Arctic CH4 sources (wetlands in permafrost regions and ocean hydrates) from our data, despite Arctic warming over the past couple decades. I tend to agree with the conclusions of Carolyn Ruppel [see above] and USCCSP SAP 3.4 Chapter 5 [the abrupt climate change report mentioned above] that increases in emissions as large as those suggested in the Nature article are unlikely.”

Climate scientist Gavin Schmidt took to Twitter to criticize the commentary. Here are a couple of his tweets:

In a piece in the Guardian Wednesday, Peter Wadhams, one of the authors of the Nature commentary, defends the choice of methane scenario.

“Those who understand Arctic seabed geology and the oceanography of water column warming from ice retreat do not say that this is a low probability event,” Wadhams says.

Wadhams is likely referring to work  done by Natalia Shakhova, whose studies published in 2010 (one of which his commentary cites) proposed the possibility of a sudden release of methane  with “catastrophic consequences for the climate system.”

But even Shakhova’s work was heavily qualified.

“There remains substantial uncertainty regarding several aspects of the CH4 [methane] release from the ESAS [East Siberian Arctic Shelf],” she writes in an article published in Science.

Ultimately, the devastating flaw in the Nature commentary is its failure to include more than a cursory discussion of the plausibility of such a high impact event. Here’s its one line on the issue:

“It [methane] is likely to be emitted as the seabed warms, either steadily over 50 years or suddenly,” the commentary says.

Gavin Schmidt’s tweets below nicely speak to the problems with this unsatisfactory treatment:

Convincing climate science needs evidence-based, carefully articulated communication, not speculative, unqualified hype.

Related story: How likely is a huge Arctic methane pulse? We find disagreement among scientists

Correction, 10:04 p.m., July 25:  The originally published blog post indicated the journal Nature published the Carolyn Ruppel review described above.  A reader clarified that the review was not published in Nature’s journal, but rather the Nature Education Knowledge Project. The Education Knowledge Project content is peer reviewed, but via a different process than the journal.  The text was updated to clarify the Ruppel review originated from the organization Nature, rather than the journal.

Post script, 11:49 a.m., July 26: Peter Wadhams, one of the authors of the Nature commentary, sent me a rebuttal to my argument, which I’ve published separately: Rebuttal to “Methane mischief: Misleading commentary published in Nature”