Does anyone know if they have measured methane levels from those eras? >From ice cores or other means? On Oct 11, 5:36 pm, John Nissen <[email protected]> wrote: > Hi Andrew, > > I've been reading through Hansen's Bjerknes Lecture slides (plus text) > that you refer to, and he mentions the possibility of thermal runaway > in connection with continuing burning coal. So I've been looking up > quantities of carbon in various forms and the effect of methane > release. Clathrates were not implicated in rapid warming periods, > coming out of the last glacial period. It's possible that they were > formed before the Ice Ages. At the thermal maximum, of the Eocene, > from 1,500 to 2000 gigatons of carbon were released into the atmosphere > [1] and the CO2 level reached around 3500 ppm. Much of that carbon went > into products of erosion, but some went into plants whose anaerobic > decomposition created methane, to be trapped in permafrost or methane > clathrates. So it's possible that release of all the methane trapped in > the Arctic could conversely lead to CO2 levels much above the present. > The problem is that the methane has a GWP (global warming potential) way > above CO2, especially if released over say 20 years when GWP = 72. > Global inventory of clathrates is estimated at 500-2500 gigatonnes > carbon (with 400 Gt C in Arctic permafrost), compared to 5000 Gt C for > other fossil fuel reserves and 700 Gt C in the atmosphere [2]. > > So only a fraction of the potential methane needs to be released quickly > (i.e. over a few decades) to cause global warming to completely swamp > anthropogenic global warming. > > The possibility of thermal runaway of Venus proportions is basically due > to water vapour being a potent greenhouse gas. As temperature > increases, I wonder whether climate forcing from increased water vapour > is normally offset by increased cloud cover and its albedo. But there > would come a point when the cloud cover approaches 100%, and then the > greenhouse effect takes over until the oceans boil. Has anybody studied > this possibility? > > As Hansen says: The Earth is truly the goldilocks planet! Not too hot, > not too cold. We have to be proactive for it to remain so. > > Cheers, > > John > > [1]http://en.wikipedia.org/wiki/Paleocene%E2%80%93Eocene_Thermal_Maximum > [2]http://en.wikipedia.org/wiki/Methane_clathrate > > > > Andrew Lockley wrote: > > There's a brief mention in the article John kindly forwarded to Jim > > Hansen's opinion that the earth will go the way of Venus, desolate and > > devoid of life. Scary stuff, which I'd dismiss out of hand if it > > wasn't for Hansen's reputation. It's a new one on me, and I hope some > > people on this list can comment. > > > The only reference I could find to Hansen's views was this link > >http://www.columbia.edu/~jeh1/2008/AGUBjerknes_20081217.pdf > > > I'd love to hear more. If this is a serious risk, we need to be > > making a lot more fuss. > > > A > > > 2009/10/3 John Nissen <[email protected]>: > > >> "It is not hard to imagine that if we fail to get a grip on the climate, > >> civilisation will collapse altogether." > > >>http://www.newscientist.com/article/mg20427282.900-earth-will-be-ok-b...- > >>Hide quoted text - > > - Show quoted text -
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