November 26th, 2010 by Michael Ricciardi
Methane (CH4) is the main constituent of natural gas, and is the result of natural decomposition processes. Although its lifetime in the atmosphere as a free gas is much shorter than CO2, it is 23 times more potent in terms of its heat trapping ability.
This past month, there has been a flurry of news, speculation, discussion and debate concerning methane gas escaping from Arctic permafrost and its impact on the global climate system. Add to this the estimated tens of millions of cubic meters of frozen methane sequestered beneath (warming) Arctic sea beds, and you can begin to see why all the renewed concern.
The issue of methane escaping from permafrost is a fairly recent one — so recent that it was not even mentioned as a factor in the IPCC 2007 report.
Permafrost is defined as any ground that has stayed below freezing for more that two consecutive summers. Siberia and most of the Arctic land masses (including much of Alaska, Northern Canada, Greenland, and parts of northern Scandinavia) are largely permafrost regions and have been so for thousands of years. Recent discoveries of Siberian and Alaskan lake bed sediments leaking large quantities of methane have prompted climatologists to call for more study and satellite monitoring of these regions.
It is estimated that some 50 billion tons of CH4 could be trapped in the Siberian Lake permafrost. Additionally, an unknown quantity of methane in the form of hydrates (or clathrates) lies trapped beneath the polar sea floors. Also, a recent analysis of the Eastern Siberian Arctic Shelf revealed that the shallow waters there are “out gassing” and becoming “supersaturated” with methane, with numerous underwater “hot spots” containing several thousands times the normal background concentrations of CH4 (see my previous post: Extensive Release of Methane Gas from Arctic Shelf Confirmed).
Potential methane release(s) in large quantities represents one of those great unknowns in climate change. Cold region contributions to the global climate system are complex and not completely understood. One concern here is the possibility of triggering one of those positive feedback cycles that we hear more and more about these days.
Such positive feedback (which is the opposite of negative feedback–a self-canceling effect) works this way: warming temperatures (over land) from increased CO2 cause thawing of the permafrost, allowing anaerobic bacteria to decompose the plant matter in the soil, thereby releasing CH4 into the atmosphere as a by-product of decomposition (methanogenesis). Methane in the atmosphere traps more heat near the earth’s surface, further raising temperatures, leading to more thawing, more decomposition, more CH4, etc. etc. etc.
A similar effect is possible with methane trapped beneath the ocean floor, especially from shallower regions that are more impacted by sea surface temperature increases. The difference with this scenario is that no additional bacterial action is needed, only warming of the sea environment, as the methane is already present in it’s frozen, clathrate form. Another wild card here is that there is no definitive estimate of how much methane in this hydrate/clathrate form exists in our seas and oceans. What we do know is that most of it has remained in this form, mostly unchanged, for tens, perhaps hundreds, of thousands of years.
CH4, with a net lifetime of 10 years, can also degrade the ozone layer. This allows more solar radiation to penetrate the Earth’s atmosphere, which promotes a climate forcing effect (more short wave radiation reaches the earth, warming land and sea-surface temps). Eventually, atmospheric methane reacts with hydroxil ions to form CO2 and water.
Recent surveys conducted by the Arctic Monitoring and Assessment Program, established by eight Arctic region nations, have concluded that over all, the Arctic is absorbing more carbon dioxide (CO2) than it emits. This indicates that, for now, Nature’s “carbon pump” is still functioning adequately enough to keep the thawing in check.
However, other recent studies (see my more recent post An Ice-Free Arctic Ocean Will Not Absorb More CO2) indicate that an upper limit on CO2 absorption by the Arctic ocean may be reached by 2030. A sudden release of methane could push the climate system past that “tipping point”.
More likely, however, release of methane into the atmosphere will be gradual, but steady. The effect of this steady accumulation of CH4 in the atmosphere will become the focus of more scientific study, and, increasingly, environmental policy debate.
Top Image: methane CG image, Ephemeronium / public domain
Permafrost Chart: US Gov. / public domain
Global Methane Chart: NASA
Methane Molecule Diagram: maksim / cc – by – sa 3.0
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