But our time scale is not the long run anymore. It is the next few decades. Even carbon that is part of the carbon recycling process can thus hurt because of time lags--say, cutting down trees that take fifty years to regrow. Isn't that methane in the same category? Bill
William H. Calvin [email protected] WilliamCalvin.org On Jul 30, 2013, at 12:33 PM, Andrew Lockley <[email protected]> wrote: I have a couple of concerns about the logic here. Firstly, the release of methane to the atmosphere is not the same as the release of stored carbon, even if that stored carbon is itself methane. Dissolution into a well oxygenated water column, or a passage through damp, aerated soils, results in a significant conversion of (reduced) methane carbon to (oxidized) CO2. There's a strong evolutionary imperative for this energy-releasing process to happen as effectively as possible. Secondly, the release mechanism discussed by Wadhams is based on the work of Shakhova et al. I'm interested to know whether the work of Schaeffer et al into carbon fluxes from terrestrial reservoirs have been considered. These postulated releases are assumed by Schaeffer to be as CO2, but this is a conservative assumption. It would be useful to understand if and how possible warming-induced terrestrial methane releases to atmosphere could be incorporated into this or similar modelling work. A On Jul 30, 2013 5:12 PM, "Greg Rau" <[email protected]> wrote: > http://www.cam.ac.uk/research/discussion/a-response-to-methane-mischief-misleading-commentary-published-in-nature > > The 24 July news story about the potential cost of Arctic methane release has > provoked widespread coverage, including a critique in the Washington Post. > Here, Professor Peter Wadhams responds to some of the comments that were > made. > > The 25 July post by Jason Samenow on the global economic impacts of methane > emissions in the East Siberian Sea portrays the findings of our research as > misleading, a statement with which I strongly disagree. Our work is based on > a prediction of the magnitude and timing of methane emissions from the > thawing of Arctic offshore permafrost by a scientist who has done extensive > field work on this part of the ocean bed and is a globally recognized expert. > We calculated the financial implications of these emissions for the world > economy over a century and also considered the effect of the emissions on > increasing overall global warming, obtaining a 0.6C figure by 2040. We > rightly consider these to be substantial figures, which deserve wide > circulation among climate scientists, and Nature and its referees agreed with > us. > > In our analysis we showed that the overall cost of a given volume of methane > release is relatively insensitive to the rate of release or, within limits, > its timing, BUT that the cost is roughly proportional to the overall volume > of release. Thus, even if you worked with a different projection by a lesser > qualified scientist than Shakhova, and revised down the figure and scale of > the 60 trillion dollars accordingly, I suspect the cost will still be > substantial – and that is one clear finding: The planetary cost of Arctic > warming far outstrips any possible benefits to shipping or natural resource > exploration. > > In support of its skepticism about methane emissions the article quoted > authors who wrote before the enormous retreat of summer Arctic sea ice and > its oceanographic effects became so evident. 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. > > 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. > > The 2008 US Climate Change Science Program report needs to be seen in this > context. Equally, 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 Semiletov/Shakhova field experiments and the > mechanism described above. Carolyn Rupple’s review of 2011 equally does not > reflect awareness of this new mechanism. > > Therefore I robustly defend our research and commentary, and hope that rather > than dismiss the substantial risk such a methane release poses, the response > might be to support more intensive research on this problem. > > - See more at: > http://www.cam.ac.uk/research/discussion/a-response-to-methane-mischief-misleading-commentary-published-in-nature#sthash.0ULHFzzl.dpuf > -- > You received this message because you are subscribed to the Google Groups > "geoengineering" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To post to this group, send email to [email protected]. > Visit this group at http://groups.google.com/group/geoengineering. > For more options, visit https://groups.google.com/groups/opt_out. > > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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