the Air Vent

Because the world needs another opinion

The IPCC’s alteration of Forster & Gregory’s model-independent climate sensitivity results

Posted by Jeff Id on July 5, 2011

Nic Lewis has made an interesting discovery deep within AR4, he sent some information on it to me last month.   It appears that the likelihood of high climate sensitivity was a little tweaked with respect to the cited literature.  He’s asked me to carry the link as he posted it on Judith Curry’s site.  It is fairly technical so I’ve requested to repost it below here.

In the meantime, this is not a small deal.  It certainly leaves one wondering how it happens by accident in such a key portion of the report.

Check it out here.

29 Responses to “The IPCC’s alteration of Forster & Gregory’s model-independent climate sensitivity results”

  1. Kenneth Fritsch said

    I commented at CA, but I must repeat that I was most impressed with Nic Lewis’ ability to explain the misapplication of a Bayesian process by the IPCC and its consequences.

  2. stan said


    Doesn’t it seem like IPCC supporters have a real dilemma? Admit that some really bad manipulation took place. Or try to argue that this is acceptable and thereby admit that the science is nowhere close to settled.

  3. [...] grafiek legt de piek bij 1.7 graden, met een halvering van de kans…zie ook: berichten:Klimaatwetenschapper Judith Curry met wijze woorden over IPCC clinch met [...]

  4. kim said


    Heh, ‘en blift nodig’. I don’t even have to know what that means.

  5. kim said

    Meh, I should have googled; ‘schandpaal’ was the key word.

  6. The real problem for the IPCC is that it can never admit error in anything that undermines their “Big Picture”. They will simply continue using apologists to muddy the waters.

  7. Hoi "Bodge" Polloi said

    Heh, ‘en blift nodig’. I don’t even have to know what that means.

    “en het blijft nodig” = it’s still necessary

  8. Jeff,

    a.) In setting boundary conditions for
    the results of scientific investigations,

    b.) Politicians have inadvertently made
    honest science a defiance of government.

    What a heck of a mess!
    Oliver K. Manuel

  9. NikFromNYC said

    Sea level has it’s own curve stretching issue. One of the Hockey Stick team and organizers named Rahmstrof used a very odd mathematical alternative curve shape instead of just fitting a curve to his data. The difference is shown here:

    Another bizarre oddity in the paper is the fitting of a straight line to scatter plot data that does not merit a linear fit. Then he extrapolates far into the future, based on it, as shown here:

    These odd manipulations (along with added “corrections” to *actual* sea level based on water reservoirs on land, while ignoring ground water pumping) resulted in a sea level curve that shows a recent upswing:

    Tom Moriarty’s blog at has several recent entries on this fiasco.

    In other news, basic sea level data is not on the pro-AGW side at all:

  10. Yes, Nik, in keeping with the old addage,

    Figures don’t lie, but . . . .

  11. a.) In setting boundary conditions for
    the results of scientific investigations,

    b.) Politicians have inadvertently made
    honest science a defiance of government.

    Nice one!

  12. max said

    I don’t want to embarrass myself on Curry’s site, but I seem to be missing something obvious. Shouldn’t the uniform prior distribution the IPCC uses to modify the Forster/Gregory curve be something on the order of ECS between -16C to 18.5C instead of 0C to 18.5C? I’ve wasted hours since first reading the Lewis piece rereading about Baysean analysis techniques and cannot find a rational for setting a boundry of 0 for ECS. What am I missing?

  13. Just to short hand the study because its a pretty long a high on the technobabble.

    The IPCC took eight studies on climate sensitivity of which one(Forster/Gregory 06) was the only study based purely on observational evidence, with no dependence on any climate model simulations threw said study in their voodoo math machines and basically 2x the results. It then put the study up in the graph with the other studies and basically pulled the “mikes nature trick/hide the decline” game.

  14. timetochooseagain said

    12-Well a negative sensitivity is physically absurd. I can assure you that the climate system does not respond to warming influences by cooling, or vice versa. However I don’t believe it is appropriate to impose this on the distribution anymore than a higher limit for values which are also unphysical. It’s similar to quantum mechanics, wherein some aspects of the wavefunction may allow nonzero probabilities for “impossible” behaviors, but one must take them into account to preserve unitarity. Bayesians like to distort distributions with this kind of extraneous information, but it never really helps.

  15. timetochooseagain said

    I left this comment at the Climate Etc. thread, probably of interest here too, and hasn’t shown up yet:

    A few people above referenced the idea that F&G 06 studied a short period and therefore must have found only the “transient climate response”, not the equilibrium sensitivity. I believe this is a red herring. First of all, if one waits for the temperature response to equilibrate the system, the imbalance will go to zero and your diagnosed sensitivity will be infinite. Secondly, the argument being made seems to be that the fully temperature response to forcing scales up with time. But F&G were meauring not the temperature response to forcing, but the ~feedback~ response to temperature change! This should only vary in time for situations were the time period is too short for the timescales of, say, cumulus convection (weeks) or for ~very~ slow feedbacks like CO2 outgassing. Arguably for our concerns the later can be neglected as it is on the order of several centuries. The temperature change, while not full in response to the forcing, should scale about the same to the ~feedback~ as a full response would. Held’s double the TCR to get ECS applies to forcing fits to temperature responses in EBMs, if that, but has nothing to do with F&G 06.

  16. j ferguson said

    Andrew, I’ve wanted to ask you some questions for a long time, but off-line. If you don’t still have a blog, maybe Jeff can forward you my email address. no hurry, in any case.

  17. Anonymous said

    # 15 TTCA

    This is a good point. It seems to me that one cannot wave away the best estimate of sensitivity from analysis like F&G06 without also waving away GCM’s, etc. It seems like this argument is advanced to merely dismiss the results of an analysis like F&G without asking critical questions. If the weight of 2C to 5C climate sensitivity (for example) is from long term feedbacks, then how can there be evidence of a climate response beyond the direct forcing of CO2?

  18. Layman Lurker said

    #17 was from me.

  19. max said

    14 – a negative absolute sensitivity is absurd, but in this case that doesn’t apply. ECS, while it is a form of sensitivity, is Equilibrium Climate Sensitivity, that Equilibrium word is important, negative values are those in which the temperature is decreasing while atmospheric CO2 concentration is increasing. Since global temperature has gone down while atmospheric CO2 concentration has gone up (see the 1950s and 1960s), it certainly is possible for the ECS to be negative, and the climate system is able to respond during increasing warming influences by cooling.

  20. max said

    Argh, that line about equilibrium is confusingly written. Ignore it while I try to think of a more readable explanation.

  21. j ferguson said

    19. substitute “increase in CO2 concentration for “warming influences” in last sentence?

  22. Anonymous said

    Jeff Id,

    you said: “In the meantime, this is not a small deal. It certainly leaves one wondering how it happens by accident in such a key portion of the report.”

    Since someone had to read the paper and modify the results to place in the WG1 AND reject comments on it, I think you are being WAAAAAAAAAAY too polite using the term accident.

  23. Jeff Id said


    You couldn’t be more right about that. Nic is understated in an extreme. When I wrote the post above, I had only skimmed the paper he referenced but I have found several impolite nuances since that time. Despite having over a month to review from Nic’s first contact, there simply isn’t time to fit climate in my schedule. I tried to quit blogging but that simply was not going to work either. I am too busy to put new material up, yet I’ve gathered a half dozen good posts in my head.

    I’ve got a guest post which needs placement and SteveM has a good one which I have just got to vent on.

    Time is far more important than money.

  24. timetochooseagain said

    16-The blog is still running:

    Everyone feel free to inundate my email if you feel like it!

    link crazy 543 @ hotmail . com

    Just remove the spaces. I try to check as often as possible but fall off the face of the net frequently, especially during the school year.

    19-I think I know what you are getting at. But basically physically what I’m saying is that the climate shouldn’t cool when the net energy flow is into it, nore warm when the net flow is out. During the midcentury, something bigger than the CO2 forcing caused the Earth to cool slightly. Warmers think (despite their models not actually showing!) that “aerosols” were responsible (which is little better than handwaving) I think that it was a natural ocsillation (to be fair, also handwaving!) but either way the climate cooled because something caused it to lose energy faster than it comes in (which could mean the cause slowed energy gain or enhanced loss). The climate reacted by slowing it’s loss of radiation to space, that is, it got colder. If this relationship were reversed the climate would be a bizzare system indeed.

    17-Interestingly, the “proof” offered for high sensitivities almost always references long timescale changes, totally ignoring this alleged issue. There are other problems with those studies (and even F&G 06!) but I think this “issue” is minor at best.

    But supposing it were true that the fast feedback gave a sensitivity half of the equilibrium value (ie “for the sake of argument”) and put aside that if that equilibrium value is unrealized for millenia or longer it is irrelevant to AGW “crisis”…My analysis of the fast feedback is that it yeilds a sensitivity of about .6 K for 2*CO2, which if doubled arbitrarily is 1.2 K per doubling, which is just below the IPCC lower bound!

  25. Neil Fisher said

    “Well a negative sensitivity is physically absurd. I can assure you that the climate system does not respond to warming influences by cooling, or vice versa.”

    Don’t be absurd – it is quite possible for TCS to be positive while ECS is LESS or even negative! In fact, given the relative stability of the climate and it’s chaotic nature, it seems to me that this is actually likely. I can think of several possible explanations for such behaviour off the top of my head – eg, the north polar ice cap may prevent heat escaping from the ocean, so melting it with a TCS would increase IR loss and result in a cooling; TCS is positive, ECS is negative. Such behaviour is “consistent with” recent climate as well.

  26. timetochooseagain said

    25-”the north polar ice cap may prevent heat escaping from the ocean, so melting it with a TCS would increase IR loss and result in a cooling”
    More IR loss, but also shortwave gain from a less reflective surface. I still have a hard time seeing how a feedback could generate response that would alter the sign of the change. If cooled more than the warming that prompted it to do so, or vice versa, that change itself would be fed back upon in such a way as to produce a warming (if the initial circumstance were warming, the reverse if cooling) that was proportional to the difference, and again a slight cooling and again a slighter warming…I could be wrong but such sum tends to zero, I think, which means zero sensitivity, but not negative. I’ll check the math to be sure however.

  27. kayla said

    I don’t understand why this issue is not generating more comments here at WUWT. It certainly has generated lots of comments at Bishop Hill and Climate Etc. and I think this is one of the most important developments in the fight against CAGW in the last year.

  28. mishawelsh said

    It is truly difficult to defend Bayesian reasoning. And I do not mean to criticize you. But to defend Bayesian reasoning, you select a case where Rules of Thumb have been deployed and developed for generations. That is what explains the success, not the Bayesian reasoning. In any case, you agree with me that Bayesian reasoning does not force one to make explicit their assumptions, unlike the method of hypothesis, inference, and test.

  29. Upper Darby…

    [...]The IPCC’s alteration of Forster & Gregory’s model-independent climate sensitivity results « the Air Vent[...]…

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