A new study from the USGS on ocean bed methane release. Study was received Aug 2016 and is online now.
The Physorg versionhttps://phys.org/news/2017-02-gas-hydrate-breakdown-massive-greenhouse.html
Gas hydrate breakdown unlikely to cause massive greenhouse gas release
From towards the end
"Our review is the culmination of nearly a decade of original research by the USGS, my coauthor Professor John Kessler at the University of Rochester, and many other groups in the community," said USGS geophysicist Carolyn Ruppel, who is the paper's lead author and oversees the USGS Gas Hydrates Project. "After so many years spent determining where gas hydrates are breaking down and measuring methane flux at the sea-air interface, we suggest that conclusive evidence for release of hydrate-related methane to the atmosphere is lacking."
The source study online at AGU "Review of Geophysics" - non paywalled. http://onlinelibrary.wiley.com/doi/10.1002/2016RG000534/full
I am not sure, but I believe this is the first time I have seen the 84 times more potent than CO2 in the 20 year time frame (IPCC 2013) in a refereed journal. Read in the first paragraph of the introduction.
It is really large, large and my shortest quick take away is that it is not
disputing methane emissions from the ocean and especially the Arctic Ocean. It ls laying some of the emissions onto submerged permafrost - more research needed.
From the second paragraph of Conclusions.
At high latitudes, the key factors contributing to overestimation of the contribution of gas hydrate dissociation to atmospheric CH4 concentrations are the assumption that permafrost-associated gas hydrates are more abundant and widely distributed than is probably the case [Ruppel, 2015] and the extrapolation to the entire Arctic Ocean of CH4 emissions measured in one area. Appealing to gas hydrates as the source for CH4 emissions on high-latitude continental shelves lends a certain exoticism to the results but also feeds catastrophic scenarios. Since there is no proof that gas hydrate dissociation plays a role in shelfal CH4 emissions and several widespread and shallower sources of CH4 could drive most releases, greater caution is necessary.
From 6.3 Gas Hydrates in Glaciated areas.
Figure 11 shows nominal conditions for permafrost evolution and gas hydrate stability beneath cold and warm-base ice sheets. Even where permafrost is lacking beneath warm-base ice, gas hydrate is stable at shallow depths in the sedimentary section for ice sheets a mere 500 m thick. Such shallow hydrates could form from microbial gas instead of the thermogenic gas thought to be sourcing many contemporary PAGH [Ruppel, 2015]. Anomalously shallow gas hydrates have been postulated for the Yamal Peninsula [Chuvilin et al., 2002] and invoked to explain some observations on the East Siberian Arctic Shelf [Shakhova et al., 2010a], as discussed above. Neither area was glaciated at the LGM, and the shallow gas releases on which the anomalous hydrate interpretation is based [Chuvilin et al., 2002] are common in permafrost areas during drilling and thought to be unrelated to gas hydrate dynamics. Even if proof for anomalous gas hydrates is eventually found, it remains uncertain how the pressure and temperature conditions at shallow depths (e.g., less than 100 m) could have been within the gas hydrate stability field absent recent glacial loading or a highly unusual mixture of hydrocarbons.
Intact arctic continental shelf gas hydrate certainly remains today within or beneath subsea permafrost, but distinguishing hydrate- from ice-bearing sediments based on geophysical data is nearly impossible without direct sampling.
Some will read this and think that the USGS is severely underestimating the methane emissions from the oceans and others will read the "conclusive evidence for release of hydrate-related methane to the atmosphere is lacking" and mentally black out "hydrate-related" and mentally scrub out methane impacts to CO2Equiv. But for a quick read, my opinion is not a bad distillation.
For me - it is not a counterpoint to the possibility of spiking methane emissions, but a caveat specific to methane hydrate emissions via the clathrate gun scenario. Must read more..