As far as I know, Semiletoc and Shakhova observed methane releases but there is as yet no evidence of increases in methane release:
http://dotearth.blogs.nytimes.com/2011/12/27/leaders-of-arctic-methane-project-clarify-climate-concerns/ The best piece I have read on likely climate effects of methane releases is: http://www.realclimate.org/index.php/archives/2012/01/much-ado-about-methane/ On Tue, Feb 21, 2012 at 10:04 AM, Stephen Salter <[email protected]> wrote: > ** > Ken > > I understand that methane concentrations are now about 1.8 parts per > million, still much less than those of CO2 but that methane accounts for > about one third of the warming of CO2. Would things change if there were > sudden large increases in the rate of methane release as suggested by > Semiletov and Shakhova? > > Stephen > > > Emeritus Professor of Engineering Design > Institute for Energy Systems > School of Engineering > Mayfield Road > University of Edinburgh EH9 3JL > Scotland > Tel +44 131 650 5704 > Mobile 07795 203 195www.see.ed.ac.uk/~shs <http://www.see.ed.ac.uk/%7Eshs> > > > On 21/02/2012 17:17, Ken Caldeira wrote: > > The higher climate sensitivities (e.g. approaching 10 C per CO2 doubling) > are highly unlikely for this century and, if such sensitivities are real > (which I also deem unlikely), likely they would be the product of feedbacks > occurring on timescales of thousands of years (e.g. ice sheets). > > The climate models include most of the feedbacks that occur on the time > scale of a century or less, and therefore likely reflect the sensitivity > that is most relevant to most people living this century (e.g., about 3 C > per CO2 doubling). > > I could believe that Earth System Sensitivity (millennial scale) is twice > that of Charney Sensitivity (decadal scale). > > ------------- > > At higher CO2 levels, due to diminished ocean CO2 uptake, each CO2 > emissions contributes more to atmospheric CO2 increase, but each increment > of increase has less of a radiative effect. These two effects largely > cancel each other but not of course precisely. There was a paper that went > into this more carefully but I cannot put my finger on it, having looked > for it. > > At the highest CO2 levels, you are of course right that essentially all of > the CO2 is partitioned into the atmosphere, but the radiative effect will > be small, so the tendency is towards decreasing radiative forcing with each > emission. But, before the radiative forcing from each emission becomes > negligible, we will be living inside of a toaster. > > For an approximation that is close enough for policy purposes, you are not > far off if you assume that each CO2 emission this century produces another > increment of warming, where this warming takes a few decades to manifest > itself. The imperfection of the chemistry/physics cancellation might be > something like a 20% error this century (although I have not recently gone > through the numbers and cannot fully attest to this). > > > On Tue, Feb 21, 2012 at 7:35 AM, Robert Chris <[email protected]>wrote: > >> Ken >> >> Thanks for replying to my email. You were right. The Google Group >> worked much quicker than I'd anticipated. >> >> There's quite a lot of technical material here for a humble social >> scientist to digest. On a quick scan the message I get is that the >> forcing is logarithmic but climate sensitivity is linear because of >> compensating feedbacks in the climate system. Although it does seem >> to me that if the forcing is logarithmic there must come a point where >> the absorptive capacity of the GHGs is so small that incremental >> emissions will not produce any more global warming. Moreover, there >> must be a point where the oceans are also largely saturated and take >> up little more CO2. However, the point where climate sensitivity does >> reduce to close to zero, might not be reached before we're all fried >> and the oceans are nigh on dead. If that brief extrapolation makes >> sense, has anyone attempted to estimate where those limits might be? >> >> What has jumped out at me from these replies is the Wasdell paper. He >> is highlighting the distinction between the Charney and ESS approaches >> to the quantification of climate sensitivity. This is not an academic >> peer-reviewed paper although he does refer to several but if he is >> correct that climate sensitivity now looks like it might be closer to >> 10degC rather than 3degC, that should send alarm bells ringing that I >> certainly don't hear. Is that because ESS is not yet sufficiently >> robust for it to replace Charney; simply because the material has yet >> to be published, or because even though CS might be three times higher >> than previously thought, the time lag before the equilibrium is >> reached is such that things won't warm up that much faster in the >> short term and therefore no one's too concerned about it yet? >> >> But if ESS does provide a more accurate valuation of CS and it is >> about 10degC, what policy implications might that have for the timing >> of geoengineering deployments? >> >> Robert Chris >> >> >> >> On Feb 20, 9:48 pm, Ken Caldeira <[email protected]> >> wrote: >> > The attached papers are relevant. >> > >> > On Mon, Feb 20, 2012 at 11:32 AM, David Mitchell < >> [email protected]>wrote: >> > >> > >> > >> > >> > >> > >> > >> > > From paleoclimate data with a geologic time-scale, climate >> sensitivity may >> > > be ~ 2.7 times larger than the Charney value of ~ 3 deg. C ( climate >> > > feedback factor 0.75 deg. C/W m2; characteristic of the fast >> feedbacks in >> > > GCMs) based on a recent paper from Jeff Kiehl: >> > > Kiehl, J., 2011: Lessons from Earth's Past. Science, Vol. 331, 14 >> Jan., >> > > 158-159, DOI: 10.1126/science.1199380. >> > >> > > David Wasdell has written about climate sensitivity featuring the >> work of >> > > Kiehl and others (see attached) but I don't know whether that >> document ever >> > > got published. Wadham's paper discusses some of the arguments Mike >> has >> > > made. >> > >> > > These papers do not indicate or suggest that climate sensitivity may >> save >> > > us from global warming. >> > >> > > David Mitchell >> > >> > > On 2/20/2012 8:57 AM, Mike MacCracken wrote: >> > >> > >> Just to be clear-- >> > >> > >> The radiative forcing due to CO2 increases is logarithmic--that is, >> the >> > >> radiative forcing going from 300 to 600 ppm is the same as going >> from 600 >> > >> to >> > >> 1200 ppm. Thus, the forcing due to the rising CO2 concentration does >> > >> decrease on a per ppm basis. >> > >> > >> However, forcing is not sensitivity, and like Tom Wigley, I recall >> papers >> > >> that have done a good bit of testing of plausible changes in >> concentration >> > >> and the sensitivity (that is, the temperature change for a doubling >> of the >> > >> CO2 concentration) is, near as it can be estimated, pretty linear. At >> > >> lower >> > >> temperatures one may have more snow/ice albedo feedback, but at >> higher >> > >> temperatures one has more water vapor and, very likely, carbon cycle >> > >> feedback (carbon cycle feedback including thawing permafrost and >> releasing >> > >> CO2/CH4, out-gassing of CO2 from warmer ocean, higher airborne >> fraction as >> > >> ocean overturning slows, etc.). Given the warmth of the Cretaceous, >> it is >> > >> hard to be sanguine about adding more and more CO2 to the >> atmosphere. And >> > >> given the heat of Venus, which absorbs less solar per square meter >> than >> > >> the >> > >> Earth even though closer to the Sun, it seems really difficult to >> argue >> > >> that >> > >> adding greenhouse gases to an atmosphere leads to a plateau in the >> > >> response. >> > >> > >> Mike MacCracken >> > >> > >> On 2/20/12 7:38 AM, "Tom Wigley"<[email protected]> wrote: >> > >> > >> Sensitivity is the equilibrium change in global-mean temperature per >> > >>> unit of radiative forcing. Linearity has been demonstrated up to >> much >> > >>> higher forcings than will ever be reached by even the most >> pessimistic >> > >>> scenarios. >> > >> > >>> Early IPCC reports might cover this. I recall work by Kiehl on this >> back >> > >>> in the mid 1980s -- too far back to recall the reference. >> > >> > >>> Tom. >> > >> > >>> +++++++++++++++++ >> > >> > >>> On 2/20/2012 5:28 AM, Robert Chris wrote: >> > >> > >>>> I am engaged in discussion with a modestly prominent climate >> skeptic >> > >>>> who argues that global warming isn't a problem because as CO2 >> > >>>> concentrations rise climate sensitivity reduces. I recall coming >> > >>>> across this notion before but I don't know how much peer-reviewed >> work >> > >>>> has been done on it. I'd appreciate some help with references to >> peer- >> > >>>> reviewed papers that address the idea that climate sensitivity may >> be >> > >>>> logarithmic rather than linear so that as atmospheric CO2 >> > >>>> concentrations rise the effective climate sensitivity reduces and >> > >>>> discuss the likely levels at which this reduction becomes >> significant >> > >>>> in terms of reducing the GWP of CO2. >> > >> > >>>> ----------------------------- >> > >>>> Robert Chris >> > >>>> The Open University >> > >>>> [email protected] >> > >> > > -- >> > > You received this message because you are subscribed to the Google >> Groups >> > > "geoengineering" group. >> > > To post to this group, send email to >> geoengineering@googlegroups.**com<[email protected]> >> > > . >> > > To unsubscribe from this group, send email to >> geoengineering+unsubscribe@* >> > > *googlegroups.com <geoengineering%[email protected]>. >> > > For more options, visit this group athttp://groups.google.com/** >> > > group/geoengineering?hl=en< >> http://groups.google.com/group/geoengineering?hl=en> >> > > . >> > >> > >> > >> > Reisinger_et_al_ERL2011.pdf >> > 570KViewDownload >> > >> > Caldeira_Kasting_Nature1993.pdf >> > 417KViewDownload >> > >> > Pagani_et_al_Science2006.pdf >> > 291KViewDownload >> > >> > Matthews_et_al_Nature2009.pdf >> > 496KViewDownload >> > >> > Matthews_Caldeira_GRL2008.pdf >> > 716KViewDownload >> >> -- >> You received this message because you are subscribed to the Google Groups >> "geoengineering" group. >> To post to this group, send email to [email protected]. >> To unsubscribe from this group, send email to >> [email protected]. >> For more options, visit this group at >> http://groups.google.com/group/geoengineering?hl=en. >> >> > -- > You received this message because you are subscribed to the Google Groups > "geoengineering" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/geoengineering?hl=en. > > > The University of Edinburgh is a charitable body, registered in > Scotland, with registration number SC005336. > > -- > You received this message because you are subscribed to the Google Groups > "geoengineering" group. > To post to this group, send email to [email protected]. > To unsubscribe from this group, send email to > [email protected]. > For more options, visit this group at > http://groups.google.com/group/geoengineering?hl=en. > > > -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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