Dear John, > This means we've already put enough greenhouse gases into the atmosphere to > produce a 4.24 degrees C equilibrium temperature, even with no further > increase in greenhouse gases.
I argue that this is wrong or biased for at least three reasons: - Hansen's estimate of climate sensitivity of 6°C is an estimate of the 'Earth system sensitivity' that includes very long term changes (vegetation, ice sheets etc.). It is very uncertain, and only relevant on timescales of thousands of years. The estimated 'likely' range for climate sensitivity relevant for the next century or so is 1.5-4.5°C for CO2 doubling. - If we talk about current greenhouse gas equivalent then I would argue it's more appropriate to use the equivalent CO2 of the total forcing (~2.3 W/m2 in AR5), which would be about 430 ppm (assuming 3.7 W/m2 for CO2 doubling). So the equivalent CO2 considering all forcings is higher than the CO2 alone (400 ppm) but not massively. - >198 / 280 * 6ºC = 4.24ºC. Temperature is not proportional to the CO2 concentration but proportional to forcing, which is proportional to the log of CO2. RF=3.7W/m2*ln(CO2/280ppm)/ln(2) Based on the above, 450ppm CO2 equivalent would correspond to about 2.5 W/m2, which for a climate sensitivity of 3°C (center of the IPCC likely range) would imply about 2.5/3.7*3=2°C warming. We are probably below the 450pm CO2 equivalent and therefore 2°C if you consider all forcings. However, the above gives only a 50% probability to stay below 2°C. A relevant question is with what probability we want to avoid 2°C, which requires to take into account the full probability density function of climate sensitivity. The results is shown in a recent paper we published in Nature Climate Change, based on IPCC AR4 numbers (Fig2 here: http://www.iac.ethz.ch/people/knuttir/papers/rogelj12natcc.pdf). I made an earlier version in Knutti et al., GRL 2005. Of course the figure is simple once we agree on a climate sensitivity distribution. >This means we've already put enough greenhouse gases into the atmosphere to >produce a 4.24 degrees C equilibrium temperature, even with no further >increase in greenhouse gases. I disagree, at least when we consider all forcings. Keeping year 2000 concentrations (or radiative forcing) was the classic commitment experiment in IPCC AR4. See Fig. SPM.5 in IPCC AR4 (https://www.ipcc.ch/publications_and_data/ar4/wg1/en/figure-spm-5.html, yellow line). The average warming across models by 2100 when keeping current concentrations is about 0.6°C above the reference period, and maybe 0.4°C above 2000. So a rough estimate would be 1°C in the past, and 0.5°C for the future, or 1.5°C in total. And even though in 2100 we are not in full equilibrium, the models suggest we are far away from the 4.24°C quoted above. Cheers, Reto From: [email protected] [mailto:[email protected]] On Behalf Of John Nissen Sent: Sonntag, 16. März 2014 21:44 To: Hawkins, Dave Cc: [email protected]; [email protected]; geoengineering; Dan Kahan; John Davies; P. Wadhams; David Wasdell; Oliver Tickell; Rafe Pomerance; Peter Carter Subject: Re: [geo] Friends of the earth March 2014 advance briefing on AR5 Working Group 3 report Hi David, I said that the level of CO2 had to be reduced if the world was to have a chance of keeping below 2ºC warming. Perhaps the simplest way to show this is to use the climate sensitivity calculations of Prof Hansen [1] and then look at the current level of CO2 equivalent from Prof Prinn [2]. I admit being shocked when I did the maths! Hansen says: "Equilibrium sensitivity 6°C for doubled CO2 is relevant to the case in which GHG changes are specified. That is appropriate to the anthropogenic case, provided the GHG amounts are estimated from carbon cycle models including climate feedbacks such as methane release from tundra and ocean sediments." Now while we currently have 400 ppm CO2, the additional greenhouse gases bring it up to 478 ppm equivalent (CO2e) according to Prinn, so we are not so far from doubling of CO2e, which would produce 6ºC warming as equilibrium temperature according to Hansen. In fact, we are 198 ppm over the pre-industrial level of 280 ppm. 198 / 280 * 6ºC = 4.24ºC. This means we've already put enough greenhouse gases into the atmosphere to produce a 4.24 degrees C equilibrium temperature, even with no further increase in greenhouse gases. Clearly we will have to suck CO2 out of the atmosphere faster than we are putting it into the atmosphere! We also have to think about reducing CO2 because of ocean acidification. Carbon dioxide removal (CDR) using geoengineering techniques, is essential. This should be ramped up ASAP. AMEG proposes a target of CO2 reduction to below 350 ppm in 20 years, ramping up the CDR continuously over that period. The CDR will probably require a combination of: (i) CCS for all fossil fuel power stations, (ii) improved forest management, (iii) improved agricultural practice such as biochar, and (iv) improved CO2 absorption in the sea using kelp and photosynthesising algae such as diatoms. The CDR should be funded by a levy on carbon taken out of the ground, preferably at the point of extraction thus avoiding the problem of taxation further down the supply chain. Cheers, John Chair AMEG (Arctic Methane Emergency Group) [1] http://arxiv.org/ftp/arxiv/papers/0804/0804.1126.pdf [2] http://oceans.mit.edu/featured-stories/5-questions-mits-ron-prinn-400-ppm-threshold -- On 16/03/2014 13:19, Hawkins, Dave wrote: John, You say-- the level of CO2 in the atmosphere has to be reduced if the world is to have any chance of keeping below 2 degrees C warming. If you are referring to today's level of CO2 in the atmosphere, what paper(s) can you point to that support this conclusion? As for the FOE comments about geoengineering, I think it is worth noting that FOE says it opposes only one form of geoengineering, SRM, and appears to be primarily concerned about one form of SRM, stratospheric particle injection. David Sent from my iPad On Mar 16, 2014, at 4:50 AM, "John Nissen" <[email protected]<mailto:[email protected]><mailto:[email protected]><mailto:[email protected]>> wrote: Hi all, FoE says the WG2 report on climate impacts will be published on March 29th and the WG3 report on "pathways to avoid dangerous climate change" will be published on April 11th. To quote from the WG3 summary by FoE: "It is still possible to reduce global carbon pollution fast enough and deep enough to make 2 degrees of global warming unlikely and provide a small chance of avoiding 1.5 degrees of warming, but only by making far-reaching socio-economic changes." This is complete twaddle and wishful thinking by people whose solidarity is clearly with the "egalitarians" (see posting by Dan Kahan on polarities). It is twaddle because the level of CO2 in the atmosphere has to be reduced if the world is to have any chance of keeping below 2 degrees C warming. There is no way that some vague collection of "socio-economic changes" can reduce the CO2 in the atmosphere as required. Only geoengineering can do this. It is also twaddle because the situation in the Arctic is completely ignored. Best scientific evidence points to a vicious cycle of warming and melting in the Arctic as albedo is lost. The only way to break this cycle, and halt the slippery slide into complete Arctic meltdown, is to cool the Arctic. The sooner that IPCC accepts geoengineering as a logical necessity for both CO2 removal and cooling the Arctic, the sooner that the twin dangers from excess CO2 and Arctic overheating will be accepted by politicians and society at large. The talk of geoengineering will make everyone aware that the situation we find ourselves in is already dangerous - really dangerous. The only sensible "pathways to avoid dangerous climate change" must involve geoengineering to remove CO2 and geoengineering to cool the Arctic. The pathway proposed by WG3 is suicidal lunacy. Cheers, John On Sat, Mar 15, 2014 at 12:34 AM, Oscar Escobar <[email protected]<mailto:[email protected]><mailto:[email protected]><mailto:[email protected]>> wrote: IPCC AR5 WG2 report - advance briefing Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment, Working Group 3 report Questions and answers in advance of publication http://www.foe.co.uk/sites/default/files/downloads/advance-briefing-ipcc-report-climate-mitigaton-45694.pdf (Excerpt) Reasons to be worried Although the WG3 report will show that the potential to cut carbon pollution sufficiently to make 2 degrees warming unlikely exists, it will also illustrate the very significant socio-economic changes that are needed to do so. Currently the political will to make these changes, for example reducing fossil fuel use or reducing inequalities between and within countries, is sorely lacking. Because of current and past failures to reduce carbon pollution it is not surprising that the IPCC has investigated geoengineering options. However, by doing so it potentially normalises these approaches alongside energy efficiency, renewables, etc. The risks of particularly solar radiation management are very high and this will need to be made clear. What are others likely to say? It is likely that climate deniers will identify the high costs of mitigation whilst ignoring the considerable benefits which outweigh the costs. It is also possible that right-wing think tanks and the media focus on the potential for geoengineering as a potentially low cost response to climate change, particularly regarding the extremely risky strategy of injection of aerosols into the stratosphere as a form of solar radiation management. Friends of the Earth is opposed to the deployment of solar radiation management. There is also the danger that some commentators also reject all negative emissions technologies in addition to rejecting solar radiation management. This is simplistic and could create opposition to development of necessary technologies to remove carbon pollution from the atmosphere (e.g. air capture of carbon utilising carbon capture and storage). -- You received this message because you are subscribed to the Google Groups "geoengineering" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]<mailto:[email protected]><mailto:[email protected]><mailto:[email protected]>. To post to this group, send email to [email protected]<mailto:[email protected]><mailto:[email protected]><mailto:[email protected]>. Visit this group at http://groups.google.com/group/geoengineering. For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "geoengineering" group. 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