By Nafeez Ahmed
5 August 2013
(The Guardian) – Debate over the plausibility of a catastrophic release of methane in coming decades due to thawing Arctic permafrost has escalated after a new Nature paper warned that exactly this scenario could trigger costs equivalent to the annual GDP of the global economy.
Scientists of different persuasions remain fundamentally divided over whether such a scenario is even plausible. Carolyn Rupple of the US Geological Survey (USGS) Gas Hydrates Project told NBC News the scenario is "nearly impossible." Ed Dlugokencky, a research scientist at the National Oceanic and Atmospheric Administration's (NOAA) said there has been "no detectable change in Arctic methane emissions over the past two decades." NASA's Gavin Schmidt said that ice core records from previously warm Arctic periods show no indication of such a scenario having ever occurred. Methane hydrate expert Prof David Archer reiterated that "the mechanisms for release operate on time scales of centuries and longer." These arguments were finally distilled in a lengthy, seemingly compelling essay posted on Skeptical Science last Thursday, concluding with utter finality:
"There is no evidence that methane will run out of control and initiate any sudden, catastrophic effects."
But none of the scientists rejecting the plausibility of the scenario are experts in the Arctic, specifically the East Siberia Arctic Shelf (ESAS). In contrast, an emerging consensus among ESAS specialists based on continuing fieldwork is highlighting a real danger of unprecedented quantities of methane venting due to thawing permafrost.
So who's right? What are these Arctic specialists saying? Are their claims of a potentially catastrophic methane release plausible at all? I took a dive into the scientific literature to find out.
What I discovered was that Skeptical Science's unusually skewed analysis was extremely selective, and focused almost exclusively on the narrow arguments of scientists out of touch with cutting edge developments in the Arctic. Here's what you need to know.
1. The 50 Gigatonne decadal methane pulse scenario was posited by four Arctic specialists, and is considered plausible by Met Office scientists
The authors of the controversial new Nature paper on costs of Arctic warming didn't just pull their decadal methane catastrophe scenario out of thin air. The scenario was first postulated in 2008 by Dr Natalie Shakhova of the University of Alaska Fairbanks, Dr Igor Semiletov from the Pacific Oceanological Institute at the Russian Academy of Sciences, and two other Russian experts.
Their paper noted that while seabed permafrost underlaying most of the ESAS was previously believed to act as an "impermeable lid preventing methane escape," new data showing "extreme methane supersaturation of surface water, implying high sea-to-air fluxes" challenged this assumption. Data showed:
"Extremely high concentrations of methane (up to 8 ppm) in the atmospheric layer above the sea surface along with anomalously high concentrations of dissolved methane in the water column (up to 560 nM, or 12000% of super saturation)."
One source of these emissions "may be highly potential and extremely mobile shallow methane hydrates, whose stability zone is seabed permafrost-related and could be disturbed upon permafrost development, degradation, and thawing." Even if the methane hydrates are deep, fissures, taliks and other soft spots create heat pathways from the seabed which warms quickly due to shallow depths. Various mechanisms for such processes have been elaborated in detail.
The paper then posits the plausibility of a 50 Gigatonne (Gt) methane release occurring abruptly "at any time." Noting that the total quantity of carbon in the ESAS is "not less than 1,400 Gt", the authors wrote:
"Since the area of geological disjunctives (fault zones, tectonically and seismically active areas) within the Siberian Arctic shelf composes not less than 1-2% of the total area and area of open taliks (area of melt through permafrost), acting as a pathway for methane escape within the Siberian Arctic shelf reaches up to 5-10% of the total area, we consider release of up to 50 Gt of predicted amount of hydrate storage as highly possible for abrupt release at any time. That may cause ∼12-times increase of modern atmospheric methane burden with consequent catastrophic greenhouse warming."
So the 50 Gt scenario used by the new Nature paper does not postulate the total release of the ESAS methane hydrate reservoir, but only a tiny fraction of it.
The scale of this scenario is roughly corroborated elsewhere. A 2010 scientific analysis led by the UK's Met Office in Review of Geophysics recognised the plausibility of catastrophic carbon releases from Arctic permafrost thawing of between 50-100 Gt this century, with a 40 Gt carbon release from the Siberian Yedoma region possible over four decades.
Shakhova and her team have developed these findings from data derived from over 20 field expeditions from 1999 to 2011. In 2010, Shakhova et. al published a paper in Science based on their annual research trips which highlighted that the ESAS was a key reservoir of methane "more than three times as large as the nearby Siberian wetland … considered the primary Northern Hemisphere source of atmospheric methane." Current average methane concentrations in the Arctic are:
"about 1.85 parts per million, the highest in 400,000 years" and "on par with previous estimates of methane venting from the entire World Ocean."
As the ESAS is shallow at only 50 metres, most of the methane being released is escaping into the atmosphere rather than being absorbed into water.
The existence of such shallow methane hydrates in permafrost - at depths as small as 20m - was confirmed by Shakhova in the Journal of Geophysical Research. There has been direct observation and sampling of these hydrates by Russian geologists in recent decades until now; this has also been confirmed by US government scientists.
2. Arctic methane hydrates are becoming increasingly unstable in the context of anthropogenic climate change and its impact on diminishing sea ice
The instability of Arctic methane hydrates in relation to sea ice retreat - not predicted by conventional models - has been increasingly recognised by experts. In 2007, a study in Eos, Transactions found that:
"Large volumes of methane in gas hydrate form can be stored within or below the subsea permafrost, and the stability of this gas hydrate zone is sustained by the existence of permafrost. Degradation of subsea permafrost and the consequent destabilization of gas hydrates could significantly if not dramatically increase the flux of methane, a potent greenhouse gas, to the atmosphere."
In 2009, a research team of 19 scientists wrote a paper in Geophysical Research Letters documenting how the past thirty years of a warming Arctic current due to contemporary climate change was triggering unprecedented emissions of methane from gas hydrate in submarine sediments beneath the seabed in the West Spitsbergen continental margin. Prior to the new warming, these methane hydrates had been stable at water depths as shallow as 360m. Over 250 plumes of methane gas bubbles were found rising from the seabed due to the 1C temperature increase in the current:
"… causing the liberation of methane from decomposing hydrate … If this process becomes widespread along Arctic continental margins, tens of Teragrams of methane per year could be released into the ocean."
The Russian scientists investigating the ESAS also confirmed that the levels of methane release they discovered were new. As Steve Connor reported in the Independent, since 1994 Igor Semilitov:
"… has led about 10 expeditions in the Laptev Sea but during the 1990s he did not detect any elevated levels of methane. However, since 2003 he reported a rising number of methane 'hotspots', which have now been confirmed using more sensitive instruments."
In 2012, a Nature study mapping over 150,000 Arctic methane seeps concluded that:
"… in a warming climate, disintegration of permafrost, glaciers and parts of the polar ice sheets could facilitate the transient expulsion of 14C-depleted methane trapped by the cryosphere cap." [more]