Bishop Hill James Annan on climate sensitivity
Feb 1, 2013 Climate: sensitivity James Annan has a must-read post on climate sensitivity today, picking up on the Norwegian study, Nic Lewis's work and the contents of the leaked IPCC report. Here are some choice excerpts:
As I said to Andy Revkin (and he published on his blog), the additional decade of temperature data from 2000 onwards (even the AR4 estimates typically ignored the post-2000 years) can only work to reduce estimates of sensitivity, and that's before we even consider the reduction in estimates of negative aerosol forcing, and additional forcing from black carbon (the latter being very new, is not included in any calculations AIUI). It's increasingly difficult to reconcile a high climate sensitivity (say over 4C) with the observational evidence for the planetary energy balance over the industrial era.
Since the IPCC can no longer defend their old analyses in any meaningful manner, it seems they have to resort to an unsupported "this is what we think, because we asked our pals". It's essentially the Lindzen strategy in reverse: having firmly wedded themselves to their politically convenient long tail of high values, their response to new evidence is little more than sticking their fingers in their ears and singing "la la la I can't hear you".
The paper I refer to as a "small private opinion poll" is of course the Zickfeld et al PNAS paper. The list of pollees in the Zickfeld paper are largely the self-same people responsible for the largely bogus analyses that I've criticised over recent years, and which even if they were valid then, are certainly outdated now. Interestingly, one of them stated quite openly in a meeting I attended a few years ago that he deliberately lied in these sort of elicitation exercises (i.e. exaggerating the probability of high sensitivity) in order to help motivate political action. Of course, there may be others who lie in the other direction, which is why it seems bizarre that the IPCC appeared to rely so heavily on this paper to justify their choice, rather than relying on published quantitative analyses of observational data.
This comment submitted by Annan to the Fifth Assessment report process is fun too:
It seems very odd to portray our work as an outlier here. Sokolov et al 2009, Urban and Keller 2010, Olson et al (in press JGR) have also recently presented similar results (and there may be more as yet unpublished, eg Aldrin at the INI meeting back in 2010). Such "observationally constrained pdfs" were all the rage a few years ago and featured heavily in the last IPCC report, there is no clear explanation for your sudden dismissal of them in favour of what seems to be a small private opinion poll.
And there are some interesting comments on Nic Lewis's work too. Great fun. Read the whole thing.
Reader Comments (56)
Good point. I forgot about diamonds. Thanks for educating me!
@Nic Lewis,
Reading the pushback you've got at Annan's blog, it would seem the thing everyone gets their knickers in a twist about is the -0.73 W/m^2 aerosol forcing estimate.
What happens if you keep all other parameters constant but vary that between, say, -0.6 and -1.1 (a range that would seem to cover pretty much every 'reasonable'/'consensus' value for that number)?
I think it would be nice to say something along the lines of ' keeping other estimates constant implies that sensitivity varies between 1.X and 2.Y for aerosol forcings in the range of -0.6 to -1.1 W/m^2' and perhaps produce a graph so we can see whether the relationship is linear etc. etc.
[If you already did this somewhere then I'm sorry for being stupid but I missed it]
FrancisT wrote:
" Reading the pushback you've got at Annan's blog, it would seem the thing everyone gets their knickers in a twist about is the -0.73 W/m^2 aerosol forcing estimate.
What happens if you keep all other parameters constant but vary that between, say, -0.6 and -1.1"
Yes, anyone who wants to believe that a central estimate for climate sensitivity (ECS) should be close to 3 K really has to insist that aerosol forcing is way (negatively) above -0.73 W/m^2. Otherwise, simple heat balance estimation (as I used) rules out such a high figure, now that ocean heat uptake is fairly well constrained at reasonably modest levels.
Regarding the effect of varying aerosol forcing assumptions, see my recent comment (3/2/13 7:54 pm) at James Annan's blog. Increasing the aerosol forcing estimate from the -0.73 W/m^2 satellite-observation based central estimate to the SOD's main composite central estimate of -0.9 W/m^2 would increase my central ECS estimate from 1.62 K to 1.77 K. The change in ECS estimate scales fairly linearly with change in aerosol forcing estimate over the -0.6 to -1.1 W/m^2 range.
Manfred wrote:
"Including black carbon would further increase net total forcing by about 20%. (where I assume there is no overlap with the adjustments already done in the new aerosol cooling, otherwise the increase would be less). Wouldn't that decrease sensitivity further to about 1.35 deg ?"
I had at first thought it might. But Bond et al. 2013 also increases the estimate of negative indirect aerosol forcing from BC, resulting in almost no change in the total forcing figure. And 'inverse' estimates of total aerosol forcing (which mainly deduce it from differences in temperature evolution between the N and S hemispheres or different latitude bands), which are unaffected by revised estimates for components of aerosol forcing, seem consistent with the -0.73 W/m^2 satellite-observation derived total aerosol forcing figure that I used. BC on snow and ice forcing is a separate matter, but Bond et al. 2013 hardly changed the estimate for that. So my current working assumption is that the new Bond et al. BC forcing estimates have little or no significance for my (or other) climate sensitivity estimates. The final version of AR5 WG1 may offer further insight into this issue.
Nic Lewis:
"Regarding the effect of varying aerosol forcing assumptions, see my recent comment (3/2/13 7:54 pm) at James Annan's blog. Increasing the aerosol forcing estimate from the -0.73 W/m^2 satellite-observation based central estimate to the SOD's main composite central estimate of -0.9 W/m^2 would increase my central ECS estimate from 1.62 K to 1.77 K. The change in ECS estimate scales fairly linearly with change in aerosol forcing estimate over the -0.6 to -1.1 W/m^2 range."
Which seems to correspond well with Annan's various comments/findings about a sensitivity in the ~2K range.
In other words, despite a bunch fo carping from various alarmists, we are seeing general agreement amongst more recent investigations that the sensistivity range tops out at about 2,5K and has a lower bound of perhaps 1K and a central estimate of maybe 1.9K. This from investigators who are using totally different methods (Annan estimating from paleo LGM temps, you via heat balance calcs, Lindzen etc.) that is.
A high end estimate of 2.5 is very very different from the 4+ estimates of previous IPCC reports and puts a very different spin on the urgency of CO2 reductions. In fact given the recent Tol paper that suggests that warming up to 2 deg C from now is actually beneficial - http://wattsupwiththat.com/2013/02/04/new-paper-by-richard-tol-targets-for-global-climate-policy-an-overview/ - it would seem that the correct path is actually to do nothing at all for a bit but invest heavily in (shale) gas for the short/medium term while sponsiring lots and lots of research into Thorium and other nuke options for a longer term solution.
IPCC doesn't care that much about CAGW.
The UN is going for the whole ball of wax.
Sustainability.
It encompasses everything on earth and beyond, including climate, if they want.
It includes your dog and your goat.
Your house and your car.
Your job and your family.
Never ever think if they get the power they will not use it.
They always do.
That's why we have the 2nd Amendment.