Scientific Debate Over Arctic Methane Release Emerges: Long Tail Or Large Pulse?

Over the past few years, we have seen a number of conflicting scientific reports analyzing the amplifying methane release currently underway in the Arctic. Since this field of study is relatively new, it has been difficult to develop a consensus between the various studies and observations. But now, a distinct set of camps is beginning to emerge.

With the recent publication of a report headed by Katey Anthony, a scientific view has crystalized around the notion that Arctic methane release will be gradual, linear, and result in a long tail of amplification to human caused global warming over the time-scale of decades to centuries. This view, headed by David Archer at the climate blog Realclimate, has formed one side of the Arctic Methane debate among scientists. The result, according to Archer, would be a long-term increase in atmospheric carbon.

Anthony’s study focused on methane seeps at the edge of glaciers and at the boundaries of Arctic permafrost thaw. The primary region of study was Alaska, with some secondary research occurring in Greenland. Given this focus, Anthony found that methane emissions from these sources in the Arctic were double that expected by scientists. Anthony also found that methane emission was most rapid at the leading edge of glacial melt and rapidly tapered off after melting ceased.

The result was that the findings showed that rate of methane release, from glaciers and permafrost at least, is directly tied to the overall rate of melt. So, in the context of this study, your view of the potential for methane release depends the pace of glacial and permafrost thaw.

Analysis of Anthony’s paper by David Archer led him to conclude that: “the general response time of the system is slow, decades to centuries, rather than potentially poised to release a huge pulse of methane within a few years.” This conclusion is consistent with Archer’s view of a relatively gradual and linear melt down in the Arctic glacier and permafrost system. His scientific view, thus far, has been for a gradual contribution of Arctic carbon to the climate system with the ultimate deposition of a substantial portion of the 1200+ gigatons of Arctic carbon into the atmosphere over the relative long-term.

“The 1200 Gton C of Arctic methane hydrates and the permafrost carbon stack up pretty menacingly against our 700 Gton left to go, and the comparison is relevant even if the carbon is emitted slowly, or as CO2 rather than methane, or even if it is released into the ocean rather than into the air.”

Overall, this is not an entirely optimistic view. It is instead the argument for slowly amplifying Arctic methane emissions rather than large pulse emissions. The result being that the Arctic contributes a ‘long tail’ of amplification to an already worsening climate picture. Under Archer’s model, there is more time to change, but the end results of long-term human greenhouse gas emissions are the same.

Unfortunately, there are reasons to doubt some of the premises for Archer’s view. As already noted, Archer implies that glacial and tundra melt will be gradual. Archer also seems to imply that releases from hydrates will also be gradual and not necessarily breach the sea surface. But rates of tundra and glacial melt are already amplifying. Meanwhile, observations from some regions of the Arctic already imply increases in the volume of methane reaching the air with the largest methane emissions structures seen on the East Siberian Arctic Shelf. Some of these massive structures measured more than a kilometer across.

And while there is some argument as to whether these large methane structures are new or have existed over long periods of time, we have seen satellite data that show an increasing Arctic methane emission over the past 9 years. Heating in the Arctic has been very rapid. And we have already seen nonlinear melt in the Arctic sea ice.

Overall, the context of these conditions is for a very energetic Arctic environment. One that pushes toward non-linear melt, not for a gradual loss of the icy methane cap. The result of these forces have caused some scientists, including Shakhova, to estimate that it is possible for large methane pulses to form in the Arctic during rapid periods of melt and heating. These pulses, Shakhova notes, could be as large as 50 gigatons and could occur during relatively short time-frames. Since the current atmospheric concentration of methane is only 5 gigatons, and since methane is at least 25 times as potent a greenhouse gas as carbon dioxide, a 50 gigaton pulse would have serious impacts for amplifying the already powerful forcing of human-caused warming.

The fact that non-linear responses to global warming have already been established in the recent history of Arctic melt would seem to point to a not insignificant potential for Shakhova’s view bearing out. However, this does not mean that Archer paints a rosey picture either. The two views represent a range of possibilities for Arctic melt and methane release from ratcheting long-term harm, to potential devastating releases in the relative near term — years to decades rather than decades to centuries.

Outside of climate change denial, this is the debate we should currently be having about the impacts of human climate change to the Arctic ice-methane system. And this debate, between bad and worse potentials, draws a dramatic line under the need for rapid human carbon emission reductions now.

For the near-term, years to decades, let us hope that Archer is correct and there is more time for the slow-moving human system to respond to the rather dangerous changes we’re already causing to our climate.

Links:

http://www.realclimate.org/

http://thinkprogress.org/climate/2012/09/27/501221/arctic-methane-release-the-end-of-the-world-as-we-know-it/#comment-494331

http://geosci.uchicago.edu/people/archer.shtml

http://www.skepticalscience.com/arctic-methane-outgassing-e-siberian-shelf-part2.html

 

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