December 16, 2011

“Methane Time Bomb in Arctic Seas – Apocalypse Not”

Our headline is taken from New York Times blogger Andy Revkin’s recent DotEarth post covering the results of a new paper which investigates the relationship between higher temperatures in recent decades and methane release from the Arctic seabed off the Siberian coast. As you can probably tell from the headline, the research team, led by Igor Dmitrenko, did not find that global warming, current and future, was going to have much of a dramatic impact on the release of methane from the Arctic seas. This is a fairly significant finding because methane—which has about 20 times the impact on the greenhouse effect that carbon dioxide does on a molecule by molecule basis—has the potential to act as a large amplifier (positive feedback) to a warming climate. Consequently the specter of a large Arctic methane release plays a prominent role in many of the more alarming future climate change storylines.

On a fairly routine basis at World Climate Report, we report on the latest findings on atmospheric methane concentrations—usually based on the research of Ed Dlugokencky, from NOAA’s Earth System Research Laboratory who carefully monitors and interprets the variability and growth of atmospheric methane concentrations.

Figure 1 shows the latest methane data. After rising through the 1980s and early to mid-1990s, atmospheric methane concentrations leveled off for about a decade from the late 1990s to the late 2000s for reasons largely unknown, and then during the past few years concentrations have started to rise again.


Figure 1. Atmospheric methane concentrations (source: World Meteorological Organization)

Commenting on the possible causes of the recent return of the upward trend in methane concentration after its 10-yr pause, Dlugokencky, in a paper published in 2009, pretty much ruled out a significant contribution from the Arctic:

Near-zero CH4 [methane] growth in the Arctic during 2008 suggests we have not yet activated strong climate feedbacks from permafrost and CH4 hydrates [contained in the Arctic Ocean seabed].

Apparently, Dlugokencky’s way of thinking hasn’t changed much in the intervening two years even in light of the continued growth of atmospheric methane concentrations (Figure 1). Just a few days ago he told Andy Revkin that:

[B]ased on what we see in the atmosphere, there is no evidence of substantial increases in methane emissions from the Arctic in the past 20 years.

So despite a warming Arctic, the feared large methane release has not been manifest. Which fits very nicely into the new results from Dmitrenko and colleagues. They find that the methane observed to be bubbling up from the Arctic seafloor off the coast of Siberia to be the ongoing and long-term response to the flooding of the seabed there that occurred some 8,000 years ago and not a response to recent warming in the region. Dmitrenko et al. write:

The CH4 [methane] supersaturation, recently reported from the eastern Siberian shelf, is believed to be the result of the degradation of subsea permafrost that is due to the long-lasting warming initiated by permafrost submergence about 8000 years ago rather than from those triggered by recent Arctic climate changes.

The new Dmitrenko result pretty much throws cold water on the “shocking” news that has been making its way through the global media in recent days that reports from a recent survey of the Siberian Arctic Shelf indicate that vast quantities of methane are bubbling to the surface of the ocean and that this is “stok[ing] new global warming fears.”

Here is Andy Revkin’s response to the news reports:

But scientists who track methane in the atmosphere in the Arctic and elsewhere around the planet see no big surge that can be pinned on such releases. Before I distributed the link to the new paper above to relevant scientists, I’d already heard from Ed Dlugokencky, one of the top federal researchers tracking methane trends. He sent a detailed review of atmospheric measurements from the Arctic to the Equator and concluded, quite simply:

“[B]ased on what we see in the atmosphere, there is no evidence of substantial increases in methane emissions from the Arctic in the past 20 years.”

This all builds on what I was told in 2010, when I last visited the question of methane releases from Arctic seas. (There’s an entirely different set of questions, also with relatively reassuring answers, about the vast amounts of methane locked in permafrost on land.) I urge you to read, and pass around, the 2010 post — “The Heat Over Bubbling Arctic Methane.”

And Revkin ends with a bit of sage advice:

So the next time you see a “science stunner” about Arctic methane time bombs, reach out to a couple of scientists working on this gas before you run to the ramparts.

A generalized version of that advise applies equally well for “climate stunners” of any ilk.

References:

Dlugokencky, E. J., et al., 2009. Observational constraints on recent increases in the atmospheric CH4 burden. Geophysical Research Letters, 36, L18803, doi:10.1029/2009GL039780.

Dmitrenko, I.A., et al., 2011. Recent changes in the shelf hydrography in the Siberian Arctic: Potential for subsea permafrost instability. Journal of Geophysical Research, 116, C10027, doi:10.1029/2001JC007218.




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