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. 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