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One line of evidence Schmidt cites comes from ice core records, which include two warm Arctic periods that occurred 8,000 and 125,000 years ago, he said. There is strong evidence that summer sea ice was reduced during these periods, and so the methane-release mechanism (reduced sea ice causes sea floor warming and hydrate melting) could have happened then, too. But there's no methane pulse in ice cores from either warm period, Schmidt said. "It might be a small thing that we can't detect, but if it was large enough to have a big climate impact, we would see it," Schmidt told LiveScience.
Today (July 26), Peter Wadhams, a co-author of the Nature commentary, defended the work against critics in an essay posted online.
"The mechanism which is causing the observed mass of rising methane plumes in the East Siberian Sea is itself unprecedented, and the scientists who dismissed the idea of extensive methane release in earlier research were simply not aware of the new mechanism that is causing it," wrote Wadhams, an oceanographer at the University of Cambridge in the United Kingdom.
"But once the ice disappears, as it has done, the temperature of the water can rise significantly, and the heat content reaching the seabed can melt the frozen sediments at a rate that was never before possible," Wadhams added. "David Archer's 2010 comment that 'so far no one has seen or proposed a mechanism to make that (a catastrophic methane release) happen' was not informed by the ... mechanism described above. Carolyn Ruppel's review of 2011 equally does not reflect awareness of this new mechanism," Wadhams wrote.
Originally posted by pavil
reply to post by Kali74
Yes that is the question. Methane seems to have about a 10 year shelf life in the atmosphere. The alarmist side seems to say it will be a massive release while the other scientists say it will be a lengthened release. I just hate when scientists use hyperbole in their statements like "unprecedented", "never seen before" ect, when plainly, there has been similar situations in the past, where man-made global warming wasn't even around.
It isn't hyperbole to state that something is unprecedented, especially since it's accurate. Obviously the permafrost has thawed before... but it has never happened this way because the last time it did, humans weren't around.
Peter Wadhams response
What is happening is that the summer sea ice now retreats so far, and for so long each summer, that there is a substantial ice-free season over the Siberian shelf, sufficient for solar irradiance to warm the surface water by a significant amount – up to 7C according to satellite data. That warming extends the 50 m or so to the seabed because we are dealing with only a polar surface water layer here (over the shelves the Arctic Ocean structure is one-layer rather than three layers) and the surface warming is mixed down by wave-induced mixing because the extensive open water permits large fetches.
So long as some ice persisted on the shelf, the water mass was held to about 0C in summer because any further heat content in the water column was used for melting the ice underside. But once the ice disappears, as it has done, the temperature of the water can rise significantly, and the heat content reaching the seabed can melt the frozen sediments at a rate that was never before possible.
In the more recent past, there have been a number of times when the Arctic (not necessarily globe) has been significantly warmer than today. Most recently, Early Holocene, which had significantly less summer sea ice than even 2012. Earlier, Eemian 125kyrs ago was sig. warmer. At neither of these times is there any evidence for CH4 emissions or concentrations in excess of base pre-industrial conditions.
Real Climate (can't get anymore mainstream than this)
But when will the Arctic be ice free then? The answer will have to come from fully coupled climate models. Only they can account for the non-linear behavior of the trajectory of the sea ice evolution and put longer term changes in the context of expected natural variability.
The sea ice simulations in the CMIP5 models are currently being analyzed. This analysis will reveal new insights about model biases, their causes, and about the role of natural variability in long-term change.It is possible that this analysis will change the predicted timing of the “ice free summers” but large uncertainties will likely remain.
Until then, we believe, we need to let science run its course and let previous model-based predictions of somewhere between “2040 and 2100″ stand”
A rudimentary estimate of the depth to which sediments are affected by an instantaneous, sustained temperature change DT in the overlying air or ocean waters can be made using the diffusive length scale 1 = √kt , which describes the depth (m) that 0.5 DT will propagate in elapsed time t (s). k denotes thermal diffusivity, which ranges from ~0.6 to 1x10-6 m2/s for unconsolidated sediments.
Over 10, 100, and 1000 yr, the calculation yields maximum of 18 m, 56 m, and 178 m, respectively, regardless of the magnitude of DT.
In real situations, DT is usually small and may have short- (e.g., seasonal) or long-term fluctuations that swamp the signal associated with climate warming trends. Even over 1000 yr, only gas hydrates close to the seafloor and initially within a few degrees of the thermodynamic stability boundary might experience dissociation in response to reasonable rates of warming. As discussed below, less than 5% of the gas hydrate inventory may meet these criteria.
Catastrophic, widespread dissociation of methane gas hydrates will not be triggered by continued climate warming at contemporary rates (0.2ºC per decade; IPCC 2007) over timescales of a few hundred years. Most of Earth's gas hydrates occur at low saturations and in sediments at such great depths below the seafloor or onshore permafrost that they will barely be affected by warming over even 1 kyr.