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Melting permafrost switches to nasty, high-gear methane release

Result? 'Way more carbon being released into the atmosphere as methane'

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A team of researchers has discovered new evidence that as the permafrost layer that covers 24 per cent of the Northern Hemisphere continues to thaw as global temperatures increase, not only does it release more greenhouse gasses into the atmosphere, but as time goes by the ratio of carbon dioxide (CO2) to methane (CH4) changes from 10:1 to 1:1 as more and more methane is released.

Methane is a far more powerful greenhouse gas than carbon dioxide, "33 times more effective at warming the Earth on a mass basis and a century time scale relative to carbon dioxide," according to a press release announcing the results of the study.

"We've known for a while now that permafrost is thawing," said Suzanne Hodgkins of Florida State University in the release. "But what we've found is that the associated changes in plant community composition in the polar regions could lead to way more carbon being released into the atmosphere as methane."

Hodgkins is the lead author of a eight-member team that conducted the research resulting in a paper, "Changes in peat chemistry associated with permafrost thaw increase greenhouse gas production", published in the latest edition of the Proceedings of the National Academy of Sciences.

The paper explains that the proportions of CO2 and CH4 released into the atmosphere from melting permafrost depend upon a number of factors, and the one that was least understood was the changes in the chemistry of organic matter as the thaw progresses. That's what the team sought to get a handle on.

To do so, they examined a series of recently to fully thawed sites in Stordalen Mire, a thawing peat plateau in northern Sweden that has been a site for carbon-cycle research since the 1970s.

In a nutshell, when frozen peat thaws it collapses and inundates areas of permafrost below it. Organic matter in the water is degraded by anaerobic bacteria to produce carbon dioxide and methane. At first, that degradation produces far more CO2 than CH4, but over time CH4 catches up as the chemical processes and vegetation distributions change.

Or, as the paper's Abstract explains in more boffinary terms:

Thaw-induced subsidence and the resulting inundation ... led to succession in vegetation types accompanied by an evolution in organic matter chemistry. Peat C/N ratios decreased whereas humification rates increased, and [dissolved organic matter] shifted toward lower molecular weight compounds with lower aromaticity, lower organic oxygen content, and more abundant microbially produced compounds. Corresponding changes in decomposition along this gradient included increasing CH4 and CO2 production potentials, higher relative CH4/CO2 ratios, and a shift in CH4 production pathway from CO2 reduction to acetate cleavage. These results imply that subsidence and thermokarst-associated increases in organic matter lability cause shifts in biogeochemical processes toward faster decomposition with an increasing proportion of carbon released as CH4.

According to the paper's conclusions, this process could intensify the already-predicted climate-feedback cycle of increasing temperature, which melts more permafrost, which releases more CH4 and CO2, which increases the greenhouse effect, which raises temperatures further, which melts more permafrost, et cetera, et cetera, et cetera.

As one of the paper's authors, professor Jeff Chanton of Florida State University, said in the press release, "The world is getting warmer, and the additional release of gas would only add to our problems."

Although average surface and atmospheric temperatures have stabilized in recent years after peaking in 1998 – a year that was affected by the record-setting El Niño of 1997-98 – they are still at a level above that of previous decades: the global average from 2000 through 2009 was higher than the average for 1990 through 1999, which was warmer than 1980 through 1989. The average for 2010 through 2012, by the way, was warmer than the average temperatures of 2000 through 2009.

After the next muscular El Niño, it will be interesting for the international team of researchers to travel back to the Stordalen Mire to check on the mushiness of the methane-releasing not-so-permafrost. ®

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