Hi Ken, Carbon Tracker Initiative has taken Potsdam figures for allowed CO2 emissions to achieve 2 degrees with 20% chance of failure [1]. The Potsdam figures are derived from a range of climate models and climate sensitivities [2] - so their budget figure (886 GtCO2 between 2000 and 2050) might need to be revised downward in the light of Hansen and Wasdell.
As you say, the climate sensitivity as an equilibrium far in the future is not as important as the effect of GHG levels on warming over the coming decades, to achieve a plateau of 1.5 or 2 degrees - preferably the former. But acheiving the former is extremely tough, as we are on 0.75 degrees already, and have 1.6 W/m-2 forcing from CO2, which won't go away quickly due to CO2's long effective lifetime. How much budget have we already used since 2000? According to [1]: "*By 2011, the global economy has already used up over a third of that 50 year budget in the first decade alone. Calculations of global emissions published in Nature indicate 282 GtCO2 have already been emitted in the first decade of this century from burning fossil fuels, with land use change contributing a further 39 GtCO2. This leaves a budget of around 565 GtCO2 for the remaining 40 years to 2050. This budget could be further contracted if a position is adopted to limit global warming to 1.5°C or even lower.*" It looks from this as if geoengineering to remove carbon dioxide will be required. (I'm copying this to Stefan Rahmstorf at the Potsdam Institute to comment on the figures.) But worse still, we have to include methane in the equation. The direct forcing per given weight of methane is over 100 times that of CO2, though the average over time comes down (e.g. to 72 times over 20 years or 25 over 100 years), due to the decay of methane - mainly by reaction with OH ions. However 1 Gt of methane maintained in the atmosphere gives equivalent forcing to over 100 Gt CO2. An annual emission of 0.1 Gt of methane would be sufficient to maintain 1 Gt in the atmosphere. But 100 Gt CO2 would make a big dent in the budget for CO2 emissions. So on the basis of the Potsdam budget, we need to keep methane emissions from rising more than 0.1 Gt per annum at most. Current emissions are estimated at 0.6 Gt per annum. But, according to Shakhova et al, there is 50 Gt of methane that could be released from the East Siberian Arctic Shelf [3]: [quote] *They conclude that "release of up to 50 Gt<http://en.wikipedia.org/wiki/Gigatonne>of predicted amount of hydrate storage [is] highly possible for abrupt release at any time". That would increase the methane content of the planet's atmosphere by a factor of twelve.<http://en.wikipedia.org/wiki/Arctic_methane_release#cite_note-12> * Ken, don't we come to the inescapable conclusion that geoengineering/intervention is required, both (a) to reduce the CO2 level through carbon dioxide removal (CDR); and (b) to prevent a methane excursion through a combination of solar radiation management (SRM) and local management of the methane environment - if that is at all possible? Cheers, John [1] http://www.carbontracker.org/wp-content/uploads/downloads/2011/07/Unburnable-Carbon-Full-rev2.pdf [2] http://www.nature.com/nature/journal/v458/n7242/full/nature08017.html [3] http://en.wikipedia.org/wiki/Arctic_methane_release --- On Sun, Aug 14, 2011 at 7:23 AM, Ken Caldeira < [email protected]> wrote: > In the attached paper, we provide evidence for a long-term climate > sensitivity of 6.8 to 7.8 C per CO2 doubling, but this probably depends on > having strong functioning methane feedbacks in the Eocene. > > My point below was that there is not a right and wrong way to define > climate sensitivity, radiative forcing, and so on, but there are different > ways. Depending on what you count as a feedback and what you count as a > forcing, and what timescales and processes you consider, you come up with > different numbers. > > I haven't gone through the Wasdell writing in great detail but it seems to > be a mostly reasonable, if somewhat imprecise, review of the literature. > > An important question is how fast and how powerfully will various feedbacks > come into play and how fast will anthropogenic forcing on the climate system > be removed by natural processes. If the timescale of concern is short or > feedbacks end up being weak, then Charney sensitivity is probably > appropriate for current policy. If timescales of concern are longer or > feedbacks end up being more rapid or more powerful than generally > anticipated or atmospheric CO2 adjustment time ends up longer than > anticipated, then the climate sensitivities estimated from paleo climates > become more relevant. > > In any case, it is important to separate issues that have to do with > differences in definitions from issues that have to do with uncertainty > about the facts. > > > ________________ > Ken Caldeira > > Carnegie Institution Dept of Global Ecology > 260 Panama Street, Stanford, CA 94305 USA > +1 650 704 7212 [email protected] > http://dge.stanford.edu/labs/caldeiralab @kencaldeira > > See our YouTube: > Carbon dioxide emissions embodied in international > trade<http://www.youtube.com/watch?v=JOj_YScv7WY> > Past land use decisions and the mitigation potential of > reforestation<http://www.youtube.com/watch?v=Bmyek4gYEUk> > > > > On Sat, Aug 13, 2011 at 10:48 PM, Prokaryotes <[email protected]> wrote: > >> 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 >> <[email protected]> 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, <[email protected]> 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" <[email protected]> >> > > *To: *"marty hoffert" <[email protected]> >> > > *Cc: *[email protected], [email protected], >> > > [email protected], [email protected], "Tyler >> Volk" < >> > > [email protected]>, "David Wasdell" <[email protected]>, "Alan >> > > Robock" <[email protected]>, "Stefan Rahmstorf" < >> > > [email protected]>, "John Shepherd" < >> [email protected]>, >> > > "Mark Lynas" <[email protected]> >> > > *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 [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. > -- 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.
