Reto, etal
I thought your probability paper below was very well done; nice graphics.
No disagreements with anything you have below.
I wonder if it is possible to use the same (and additional new modeling
data if easy) to somehow give more weight (Bayesian sense) to those models that
provide earlier predictions of the disappearance of Arctic ice? My impression
is that almost all are seriously too conservative and that those that show
September ice extent and thickness would also be giving higher and more
accurate climate sensitivity numbers. Not asking for any new runs, just
somehow taking advantage of the experimental evidence on Arctic ice behavior.
(as seen in
http://www.theguardian.com/environment/2014/feb/21/arctic-ice-melt-video)
Ron
On Mar 17, 2014, at 7:19 AM, Knutti Reto <[email protected]> wrote:
> 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]>> 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]>> 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).
>
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