But this short term figure of 3C sensitivity, is not in cooperating various of the interconnected sub feedbacks. Also the initiation timescale is now different of a view order. The Wasdell paper makes a solid case, and id like to see some more analyzing from other people. I consider the paper a must read.
I working on a blog post where i summarize the paper http://climateforce.net/2011/08/13/climate-shift-impact-risk-assessment-revisited/ Best Regards, Chris Machens On Aug 14, 3:38 am, Ken Caldeira <kcalde...@globalecology.stanford.edu> wrote: > Climate sensitivity to a doubling of atmospheric CO2 is only a well defined > term (if at all) if you state what time scales or processes you are > including and what you mean by "a doubling of atmospheric CO2". > > The higher sensitivity values seem relevant to time scales (i.e., > 10 kyr) > where ice sheets and possible biogeochemical (e.g., CH4) feedbacks can kick > in at full force. > > The lower sensitivity values seem relevant to shorter time time scales > (i.e., < 100 yr) when ice sheet feedbacks are not relevant and we assume > that CH4 feedbacks need not be considered. > > Furthermore, if you instantaneously double CO2 and then let some of the CO2 > be absorbed by the ocean and biosphere you will get less of a climate > response that if you maintain the doubled CO2 concentration. > > My take is that the longer-term response seems to be closer to 6 C whereas > the shorter-term response (assuming no big methane feedback) seems closer to > 3 C. (For my own subjective probability distribution under these > assumptions, I would suggest something like an 80% probability of being in > the range of 2/3 to 3/2 of these values , i.e., short-term in the absence of > strong methane, probably something like 2 to 4.5 C for a CO2 doubling, and > for the longer term, something like 4 to 9 C for a sustained CO2 doubling.) > > --- > > I am planning to give a semi-tutorial talk on this at AGU in the same > session that Hansen is speaking in: > > *CONTROL ID: * 1209062 > *TITLE: * Radiative Forcing and Climate Response: From Paleoclimate to > Future Climate > *PRESENTATION TYPE: * Assigned by Committee (Oral or Poster) [Invited] > *CURRENT SECTION/FOCUS GROUP: * Paleoceanography and Paleoclimatology (PP) > *CURRENT SESSION: * PP10. Earth System Sensitivity To Radiative Forcings: > Lessons From Earth History > *AUTHORS (FIRST NAME, LAST NAME): * Ken Caldeira1, Long Cao1 > *INSTITUTIONS (ALL): * 1. Dept. of Global Ecology, Carnegie Institution, > Stanford, CA, United States. > *Title of Team: > ABSTRACT BODY: * The concept of radiative forcing was introduced to allow > comparison of climate effects of different greenhouse gases. In the classic > view, radiative forcing is applied to the climate system and the climate > responds to this forcing, approaching some equilibrium temperature change > that is the product of the radiative forcing times the ‘climate sensitivity’ > to radiative forcing. > > However, this classic view is oversimplified in several respects. Climate > forcing and response often cannot be clearly separated. When carbon dioxide > is added to the atmosphere, within days, the increased absorption of > longwave radiation begins to warm the interior of the troposphere, affecting > various tropospheric properties. Especially in the case of aerosols, it has > been found that considering rapid tropospheric adjustment gives a better > predictor of “equilibrium” climate change than does the classic definition > of radiative forcing. > > Biogeochemistry also provides additional feedbacks on the climate system. It > is generally thought that biogeochemistry helps diminish climate sensitivity > to a carbon dioxide emission, since carbon dioxide tends to stimulate carbon > dioxide uptake by land plants and the ocean. However, there is potential to > destabilize carbon locked up in permafrost and at least some possibility to > destabilize methane in continental shelf sediments. Furthermore, wetlands > may provide a significant methane feedback. These and other possible > biogeochemical feedbacks have the potential to greatly increase the > sensitivity of the climate system to carbon dioxide emissions. > > As time scales extend out to millennia, the large ice sheets can begin to > play an important role. In addition to affecting atmospheric flows by their > sheer bulk, ice sheets tend to reflect a lot of energy to space. If carbon > dioxide remains in the atmosphere long enough, there is potential to melt > back the large ice sheets, which would add additional warming to the climate > system. It is likely that these millennial time-scale feedbacks could double > climate sensitivity over that estimated by century-scale models. The > inclusion of these feedbacks may be one reason why paleoclimate studies seem > to indicate a much higher climate sensitivity than do the current generation > of climate models that focus on the physics of century-scale climate change. > > What is the relevance of “equilibrium” climate change on a dynamic planet? > Each gas or aerosol has a different time evolution in the atmosphere, so > the time evolution of the climate response to a methane release, an aerosol > release, and a carbon dioxide release would be very different, even if they > had the same initial radiative forcing (or radiative forcing integrated to > some time horizon, as is done in Global Warming Potential calculations). > Furthermore, the climate response to emissions of these radiatively active > substances will depend, to some extent, on the state of the climate system > into which these substances are introduced. Changes in continental positions > and altitudes can affect snow and glacier feedbacks. Changes in ocean heat > transport can affect cloud properties and the distribution of sea-ice. > > For many applications, it may be more fruitful to focus on the > time-evolution of the climate response to emissions and abandon the concept > of climate sensitivity to radiative forcing. > > > > > > > > On Sat, Aug 13, 2011 at 4:13 PM, <rongretlar...@comcast.net> wrote: > > John - Thanks for bringing this dialog back to climate sensitivity - which > > obviously is a very key parameter for this list. You seem to have correctly > > stated the present view of Dr. Hansen as being 3 degrees C per CO2 > > doubling. But in your second citation to the work of Dr. Wasdell, Hansen's > > view is stated as this being better defined as 6. Dr. Wasdell recommends > > 7.8 (as you have reported) - and your citation [2) for his work gives 3 or > > 4 additional experimental (not model) strong endorsements of this very large > > sensitivity value. > > > Can anyone else support the larger sensitivity values? Is the difference > > only in the time domain? How does such a large fundamental difference get > > settled? Will the final authority be the IPCC? > > > Ron > > > ------------------------------ > > *From: *"John Nissen" <j...@cloudworld.co.uk> > > *To: *"marty hoffert" <marty.hoff...@nyu.edu> > > *Cc: *euggor...@comcast.net, geoengineering@googlegroups.com, > > kcalde...@globalecology.stanford.edu, anr...@nytimes.com, "Tyler Volk" < > > tyler.v...@nyu.edu>, "David Wasdell" <wasd...@meridian.org.uk>, "Alan > > Robock" <rob...@envsci.rutgers.edu>, "Stefan Rahmstorf" < > > stefan.rahmst...@pik-potsdam.de>, "John Shepherd" <john_g_sheph...@mac.com>, > > "Mark Lynas" <markly...@zetnet.co.uk> > > *Sent: *Friday, August 12, 2011 7:53:53 AM > > *Subject: *Re: [geo] Jamais Cascio-- on the problematic idea of 350 > > > Hi Marty, > > > I was just looking through some bulky emails to delete them, when I noticed > > this one on climate sensitivity. You put 2.5 degrees warming for CO2 > > doubling. It is interesting that the climate sensitivity has been > > reappraised, e.g. by Hansen giving 3 degrees [1] and by Wasdell giving a > > much higher figure of around 7.8 degrees [2]. > > > Wasdell raises a fundamental point about the behaviour of the climate > > system over recent Ice Ages when temperature has varied by 5 degrees, yet > > CO2 has only varied between 180 ppm and 280 ppm. > > > [quote from [2]] > > * > > That raises the fundamental “Emperor’s Clothes” question of climate > > science: > > > 8.5.1 “If the Charney sensitivity, supported by our modern computer models, > > projects that a doubling of the concentration of atmospheric carbon-dioxide > > leads to a temperature rise of 3ºC at equilibrium, then why, in the > > empirically measured behaviour of the planetary system, does an increase of > > only 56% in CO2 concentration (from 180 ppm to 280 ppm) lead to a 5ºC change > > in temperature?” > > * > > [end quote] > > > Now that assumes that the CO2 causes the warming (rather than the polar > > amplification of Milankovitch signals, as I would suggest [4]). However I > > think Wasdell is onto something. There does seem to have to been *systemic > > optimism* in the climate science community about the effect of CO2 > > emissions on global warming, and we are on course to reach 4 degrees or > > more, even with the most drastic CO2 cuts one could imagine through a UNFCCC > > path (especially given the political situation in US and China). > > > Furthermore the potential contribution of Arctic methane to global warming > > is being ignored. > > > Furthermore, 1.5 degrees is now being accepted as a significantly safer > > target than 2 degrees [3]. And there are calls for the CO2 level to be > > quickly brought below 350 ppm, amid concerns about ocean acidification as > > well as global warming. > > > How much evidence does the scientific community need, before accepting the > > requirement for geoengineering? Perhaps those who still say that > > geoengineering is too risky (in relation to benefits) should answer this > > question. There are some on this list! > > > Cheers, > > > John > > > [1] > >http://www.columbia.edu/~jeh1/mailings/2011/20110118_MilankovicPaper.pdf > > > [2]http://www.apollo-gaia.org/Climate%20Sensitivity.pdf > > > [3] > >http://globalwarmingisreal.com/2011/06/03/unfccc-chief-says-two-degre... > > > [4] Nissen, J "Arctic sea ice thermostatic control of global temperature", > > EGU 2011 (to be published) > > > --- > > > On 02/11/2009 17:16, Marty Hoffert wrote: > > > All: > > > David Keith & Andy Revkin are right that we should not be > > over-interpreting every perhaps natural climatic fluctuation as evidence of > > global warming however much that feeds into the human psychodrama. That in > > no way detracts from the robust finding that the secular trend of rising > > global mean temperature, polar cap melting and sea ice recession from > > continued CO2 emissions is overwhelmingly supported by data. And given our > > present fossil fuel based energy system, and independently estimated global > > climate > > ... > > read more » -- 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. To unsubscribe from this group, send email to geoengineering+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/geoengineering?hl=en.
