Reconciling climate sensitivity estimates – part III, or IV?

I mentioned in a recent post that there was a new paper that claims to reconciles climate sensitivity estimates. The basic issue is that observationally-based climate sensitivity estimates have a range of about 1.5oC to about 3oC, while climate model estimates tend to range from about 2oC to about 4.5oC. However, if you use climate models to estimate something equivalent to an observationally-based climate sensitivity, you get something consistent with these estimates.

However, to the surprise of noone, Nic Lewis has already claimed that their analysis is wrong. His argument appears to be that they made an error (I don’t know if they have) and that the equivalent observationally-based estimates you would get from climate models is higher than they claim. Also Nic Lewis claims that the range for the actual observationally-based estimates is lower than they claimed in the paper. Therefore their claim that these different estimates have been reconciled is wrong.

I don’t know if Nic Lewis has really found an error. That it would appear impossible to publish a paper that reconciles these climate sensitivity estimates without Nic Lewis claiming to have found some kind of fundamental error might suggest caution. However, based on some tweets from Kyle Armour, even if there is an error, it would seem not as obvious as Nic is claiming (not the first time that has happened). Since, however, I don’t have the time to really work out whether he is right, wrong, or somewhere inbetween, I thought I would make some general comments.

  • A key point is that there are indications that observationally-based estimates for equilibrium climate sensitivity are biased low. This is essentially because they assume that the feedback response in the future will be the same as in the past (linear). There are lots of reasons why this is unlikely to be the case. As mentioned in this Isaac Held post, we know that some regions warm faster than others. This will manifest itself as warming faster during the final stages of approaching equilibrium, than during the early stages. There are also indications that the pattern of sea surface warming has lead to a cloud feedback response that is smaller (more negative) than what we might expect to be typical. Therefore we should treat observationally-based climate sensitivity estimates with caution; they may well be biased low.
  • In Nic Lewis’s criticism he appears to decide that what should be compared are the best estimates, rather than the ranges. He recomputes the model best estimate and claims it is higher than suggested in the paper, and then compares that to the best estimates from observationally-based estimates (which he claims is between 1.6oC and 2oC). This itself seems statistically questionable, but there are also potential issues with how some of the observationally-based best estimates are determined. Nic Lewis, for example, uses a Jeffrey’s prior in his analysis. The Jeffrey’s prior potentially allows for climate sensitivity values that are unphysically low and, consequently, could shift the distribution so that the best estimate is biased low (I think he uses the median, but I can’t quite remember). We had a lengthy discussion of this issue in this post.
  • What about some ballpark estimates? We’ve already warmed by about 1oC. If we continue increasing our emissions, we could double atmospheric CO2 by the middle of the century. The long-term warming trend suggests that we could easily have warmed by 1.5oC at that stage. Given the thermal inertia of the oceans and estimates for the planetary heat uptake rate, it seems highly unlikely that the TCR-to-ECS ratio could be larger than 0.8. Hence, if the TCR is around 1.5oC, that would probably mean the ECS is at least 2oC, which is right in line with the kind of minimum we’d expect, based on our understanding of the various feedback processes.
  • There is also an interesting potential irony to all of this. On the one hand, we sometimes see arguments that we can’t trust climate models because the climate system is non-linear and, hence, chaotic and therefore we can’t make predictions about the future. On the other hand, Lewis’s position is essentially that the system is so simple that we should trust linear models over more complex climate models.

Ultimately, I think that the observationally based estimates, some of which have been done by Nic Lewis, are very useful ways of estimating climate sensitivity. However, they are quite simple and are not really inconsistent with the other estimates (ranges from 1oC to 3oC compared to other estimates that have ranges from about 2oC to 4.5oC). Searching for errors in any attempt to further reconcile the various estimates doesn’t really make the low climate sensitivity values suggested by these observationally-based estimates more credible. To do that would really require showing that they’re consistent with our understanding of physical climatology. I would argue that there are indications that they are not.

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93 Responses to Reconciling climate sensitivity estimates – part III, or IV?

  1. @ATTP,

    Regarding:

    On the one hand, we can’t trust climate models because the climate system is non-linear and, hence, chaotic and therefore we can’t make predictions about the future.

    I’m not sure whether you were stating this as a capture of (e.g.) Lewis’ position or a strawman, or if you meant it, but this interpretation of “chaotic” is not correct. Professor Lenny Smith in his Chaos: A Very Short Introduction dismisses it in his Chapter 2, with

    One of the most pervasive myths about chaotic systems is that they are impossible to predict. To expose the fallacy of this myth, we must understand how uncertainty in a forecast grows as we predict further and further into the future … [C]haos can be easy to predict, sometimes.

    Professor Smith goes on to illustrate how ensemble forecasts offer a way out, and addresses different kinds of dynamical systems. He also paraphrases Tolstoy’s Anna Karenina in a delightful way:

    All linear systems resemble one another, each nonlinear system is nonlinear in its own way.

  2. hyper,

    I’m not sure whether you were stating this as a capture of (e.g.) Lewis’ position or a strawman, or if you meant it, but this interpretation of “chaotic” is not correct.

    Yes, I realise it is incorrect. It wasn’t really meant to represent Lewis’s position. I was simply highlighting that we sometimes see arguments that the system is too complex to model, while Lewis’ position is essentially the opposite (so simple it’s linear). Of course, Lewis’s calculations are quite reasonable, even if simple and possibly biased low, but I think you’ll find many who make the former argument, also quite happy to accept Lewis’s criticism of climate model estimates.

  3. hyper,
    I see why you thought I was suggesting that we couldn’t make predictions. I’ve slightly modified that part of the post, but I don’t think I’m quite expressing it as clearly as I would like. I was really just wanted to highlight that there do seem to be a number of inconsistent arguments against climate models, not that Nic Lewis is the one who is making these inconsistent arguments.

  4. angech says:

    “really just wanted to highlight that there do seem to be a number of inconsistent arguments against climate models,”
    “we could double atmospheric CO2 by the middle of the century.”
    Is it fair to say 270 ppm to 540 ppm in which case 35 years approx into 140 ppm equates to growth at 4 ppm from current 400 ppm approx?
    “The long-term warming trend suggests that we could easily have warmed by 1.5oC at that stage.”
    Do you mean overall for the doubling or just 0.5 C for the second half of the doubling? I would have thought linear another 1 C for the second half of the doubling”

    ” observationally based estimates are very useful ways of estimating climate sensitivity.”
    Yet
    “Make the low climate sensitivity values suggested by these observationally-based estimates more credible.”
    Surely “they’re consistent with our understanding of physical climatology.”
    Yet as you say they are not .
    So what is wrong, the observations or the models?
    Why strive so hard to adjust observations to the models.
    If by some fluke the observations are right and Nic Lewis is right on low climate sensitivity is this a bad thing?
    I hope we would all agree that low CS would be a very good thing.
    But as it is a chimera I guess you need to find the reasons for the misfit.

  5. Everett F Sargent says:

    “If we continue increasing our emissions, we could double atmospheric CO2 by the middle of the century.”

    2X280 = 560
    (560 – 410)/(2050.5 – 2017.5) = 4.5 ppmv/yr average from now to 2050???

    “The long-term warming trend suggests that we could easily have warmed by 1.5oC at that stage.”

    From Santer, et. al. (2017c) RCP8.5 36-models CMIP5 average TLT increase from 1998 to 2050.5 = Two degrees centigrade or …

    1.98/(2050.5 – 1998.0) = 0.38 degrees centigrade per decade???

    0.50/((2050.5 – 2017.5) = 0.15 degrees centigrade per decade???

    I do tend to believe the slow climate mode though and its presumed delay in reaching an ECS~3C.

  6. Uh, sorry, @Everett F Sargent, we are at 490 CO2e now, not 410.

  7. angech,

    Do you mean overall for the doubling or just 0.5 C for the second half of the doubling? I would have thought linear another 1 C for the second half of the doubling”

    I meant going from now to mid-century. Essentially, we now have a net anthropogenic forcing of about 2.3W/m^2. By mid-century it could be 3.7 W/m^2 (i.e., the same as doubling atmospheric CO2).

    So what is wrong, the observations or the models?

    Neither, necessarily (although neither will be perfect either). The observations do not cover a period over which we have doubled atmospheric CO2 and allowed the system to equilibrate.

    Everett,

    I do tend to believe the slow climate mode though and its presumed delay in reaching an ECS~3C.

    Indeed, I was really just trying to argue that it’s hard to see how it could be lower than 2oC.

  8. angech says:

    ATTP thanks
    Hypergeometric, If you introduce the CO2 equivalent argument it would be best if everyone was talking the same language equivalent.
    In which case could you define the baseline and equivalent starting time and amounts and what level you expect the doubling to be.
    If we use your argument at face value and make a lot of assumptions ie baseline CO2 280 say and equivalents zero say then you have the problem that an increase of 210 ppm has not caused as much warming based on ATTP figures. It would have to be a lot less than 2.3.
    If you argue that there was some baseline equivalent, 30ppm , the the true doubling would have to be 620 ppm so still some way to go.
    I would prefer to discuss in actual CO2 levels as they possibly reflect the equivalents rise as well.
    Could you clarify so we are all on the same page.
    As said any increasing the CO2 load by adding in equivalents with current observations risks assigning lower CO2 sensitivity and makes discussion more complex but it is an issue.

  9. verytallguy says:

    But as it is a chimera I guess you need to find the reasons for the misfit.

    Angech, I think you’re just describing the scientific process. We have a theory, let’s call it the standard model of climatology for arguments sake.

    We have observations. These are many and various, note, not just historical temperatures.

    There are differences between theory and observation. That adds to our understanding, and can result in changes or refinements to the theory, emergence of new, competing theories, or acceptance that the observations are consistent with the theory.

    Nic Lewis’ apparent view that the one true measure of climate sensitivity is his own work creates as many or more other “misfits” to other observations as it solves with his own preferred measure of correctness.

    On baseline, if we’re working from preindustrial then at that point CO2=CO2e, so CO2e should be used, or more precisely, total change in forcing, which also then factors in solar, aerosol and albedo changes.

  10. izen says:

    The Issac Held post helps makes sense of the difference in sensitivity results over different timescales and regions. VV raises the ratio of land and ocean warming and its implications for global ECS.
    It is tempting to ascribe the differences in the sensitivity estimates from different methods to the time period they cover, and therefore how much of the slow changes they capture.
    Held makes this comment –

    “Trying to think about these issues while focusing on the global mean in isolation tempts people to think about nonlinearity to explain this behaviour, whereas the explanation seems to be primarily that the spatial structure of the linear response is a function of frequency.”

    So Observation based estimates are, by the extent of an accurate record of temperature and forcings, restricted to less than a century. Physical modelling of the climate can cover a much longer time period, and by multiple runs is sampling a larger database of temperature changes enabling slow responses to rise above the internal noise. Paleoclimate based estimates record the impact of the slow responses because the low resolution of the proxy data restricts the determination to much longer timescales.
    The difference in the PDF of the three methods could be ascribed to the timescale of the effect they are estimating.
    (Giving me an excuse to repost this.)

  11. izen,

    The difference in the PDF of the three methods could be ascribed to the timescale of the effect they are estimating.

    This would seem consistent with what is suggested in the paper.

  12. @angech,

    Okay, and sorry if I introduced any confusion. It’s possible, too, that I am working from a different definition of ECS than others. I have seen operational definitions in papers, ones which linearize around now, present day, and go back and forth relative to how much CO2 or CO2e has changed from now, respectively. The definition I use and prefer is the full-blown ECS from Principles of Planetary Climate (Ray Pierrehumbert), which is a ratio involving forcings, including from feedbacks (e.g., water vapor). As such it is a dynamical and theoretical thing, yes, but I prefer it because it inherently reminds that (a) there are other phenomena and forcings which are pertinent, (b) these introduce attending uncertainties, and (c) the ECS is inherently state-dependent. Defining it operationally tends to sweep these matters under the rug, and they are not a question of debate. They can’t be when the water vapor feedback is on the same order as the CO2 effect.

  13. Willard says:

    > If you introduce the CO2 equivalent argument it would be best if everyone was talking the same language equivalent.

    It would even be better if we all communed through telepathy too, Doc.

    There’s no reason to expect hippies contrarians love to punch to show the same terminological discipline as more conservative meme makers.

  14. hyper,

    which is a ratio involving forcings, including from feedbacks (e.g., water vapor).

    My understanding of the standard definition of ECS is that it it the change in temperature once equilibrium is reached after a change in external forcing equivalent to that of a doubling of atmospheric CO2 and that includes fast feedbacks only.

  15. Mitch says:

    The fundamental problem with climate sensitivity is that it wandered from its original use way back in the 70’s, to compare climate models . For that purpose sensitivity can be clearly defined.

    While it is an important concept in the real world, sensitivity to a forcing will depend on the boundary conditions. For example, one can argue that future sensitivity to surface albedo feedback will be much smaller moving forward because there is no ice sheet covering Canada now. Since the forcing via greenhouse gases is different than that via high latitude insolation the connections to feedbacks will also be different. Comparisons between the Holocene and a time where the earth warmth was stable and CO2 was at about 400 ppm like the early Pliocene (3-4 deg warmer than modern), suggest significant warming for the forcing we have exerted.

  16. Mitch,
    Indeed, you’re quite right. It was originally simply a model metric, used to compare the sensitivity of different models. You’re right that when applied to the real world it is somewhat more complicated.

  17. @ATTP,

    How fast is fast in “fast feedbacks only”? No need to answer, since, quoting James Annan from 2014, “Much ado about climate sensitivity”. (Gareth Renowden, too.)

    This may be the Holy Grail of climate science, but like the variability introduced by Isaac Held’s argument, quoted by @izen, there’s so much uncertainty in the thing that using a point estimate like it’s mean or median is completely misleading. Likelihood surfaces around these tend to look like plateaus, and you can get a big displacement of the point estimate with a little perturbation of data or of a theoretical term in the Likelihood expression. (This, incidentally, is why I do not like simple distributions used for real world data. If it’s tractable, and it often isn’t, I prefer empirical likelihoods.)

    The takeaway? Such uncertainty means there’s significant probability mass in places we don’t want it to be. Worry.

  18. hyper,
    My understanding is that fast feedbacks refers to water vapour, lapse rate, and clouds.

  19. BBD says:

    Hansen et a;. (2011):

    “Fast feedbacks” appear almost immediately in response to global temperature change. For example, as Earth becomes warmer the atmosphere holds more water vapor. Water
    vapor is an amplifying fast feedback, because water vapor is a powerful greenhouse gas. Other fast feedbacks include clouds, natural aerosols, snow cover and sea ice.

  20. frankclimate says:

    It seems to me very odd to discuss the science-paper and the blogpost of Lewis when stating “It wasn’t really meant to represent Lewis’s position. ” The core of the paper is not so enigma: They claimed that they ” resolved a major conflict in estimates of how much the Earth will warm in response to a doubling of carbon dioxide in the atmosphere.” ( https://www.eurekalert.org/multimedia/pub/144866.php ). Their approach: the faster “ICS” of the CMIP5’s could be near 2.5 K/doubling CO2 and the estimates from obs. are about 2K/doubling CO2. This is a much lower difference than this between the “slower” ECS and Obs. Lewis disagrees and calculates the “ICS” with 3 K/doubling CO2 with the code of the authors. This is well above obs. again. The authors responded and Lewis makes 5 points against this response. The point 5 is striking IMO. If there would be mistakes in the calculations of the paper (dunna) there would be a take home message: There IS a major conflict between models and obs.

  21. frankclimate,

    “It wasn’t really meant to represent Lewis’s position. ”

    I just meant that my 4th bullet point wasn’t meant to represent Lewis’s position (i.e., I don’t think he has both argued that the system is too complex too model and so simple that a linear model is all that you need consider).

    Lewis disagrees and calculates the “ICS” with 3 K/doubling CO2 with the code of the authors.

    I believe the authors disagree with this.

    There IS a major conflict between models and obs.

    Really? Is this simply because Lewis is claiming this?

  22. Willard says:

    It seems very odd that FrankB fails to distinguish between “we sometimes see arguments that we can’t trust climate models because the climate system is non-linear and, hence, chaotic” and “Lewis’s position is essentially that the system is so simple that we should trust linear models over more complex climate models.”

    It may not be odd that he fails to address the incompatiblity between the two lines from the Contrarian Matrix, as AT underlines.

  23. frankclimate says:

    ATTP: Please cite complete! The whole sentence of mine was:
    “If there would be mistakes in the calculations of the paper (dunna) there would be a take home message: There IS a major conflict between models and obs.”
    And the last claim was from the PR of the authors: They claimed that they have solved a major conflict and if they didn’t ( DUNNA) the conflict goes on. What’s wrong with this deduction??

  24. Willard says:

    > What’s wrong with this deduction??

    There’s nothing wrong with stating truisms like “if A, then A.” And yet A may still be trivial, e.g. “what if you were wrong?” More generally, counterfactual thinking can serve a social function among luckwarm contrarians:

    [A]t a group level, counterfactual thinking can lead to collective action. According to Milesi and Catellani (2011), political activists exhibit group commitment and are more likely to re-engage in collective action following a collective defeat and show when they are engage in counterfactual thinking. Unlike the cognitive processes involved at individual level, abstract counterfactuals lead to an increase in group identification, which is positively correlated with collective action intention. The increase in group identification impacts on people’s affect. Abstract counterfactuals also lead to an increase in group efficacy. Increase in group efficacy translates to belief that the group has the ability to change outcomes in situations. This in turn motivates group members to make group-based actions to attain their goal in the future.

    https://en.wikipedia.org/wiki/Counterfactual_thinking#Collective_action

    If you have any other rhetorical question, FrankB, feel free to ask.

  25. frankclimate says:

    Willard: What nonlinear and chaotic behaviour of the climate system describes the CMIP5 mean?

    It describes IMO the GMST controlled by GHG with TWO key figures: TCR (1.8) and ECS ( about 3). The problem: from 1850…2015 we see from obs. a TCR of about 1.3 and a ECS near 2. No chaos, no non-linearity!

  26. frankclimate,

    Please cite complete! The whole sentence of mine was:

    Okay, apologies, I misread.

    No chaos, no non-linearity!

    It’s clear that the system is non-linear and, hence, chaotic. However, as has already been pointed out, this means that we can’t predict the exact future state because of the sensitivity to initial conditions. It doesn’t, however, approximate the average state. The point I was making in the post is that it is probably not exactly linear (as would be required if we want to trust Lewis’s projections over the climate model projections) but it’s probably not so non-linear that we can’t estimate the response to external perturbations.

  27. Willard says:

    > What nonlinear and chaotic behaviour of the climate system describes the CMIP5 mean?

    Which part of AT’s we sometimes see arguments that we can’t trust climate models because the climate system is non-linear and, hence, chaotic would imply such thing, and why would you suggest any such thing if not to put words into AT’s mouth to peddle stuff without acknowledging you misread him, FrankB?

  28. Willard says:

    What if I told you that CS may not be 9C?

  29. frankclimate says:

    ATTP: No problem at all, shit happens 🙂 The CMIP5 mean from which were deduced the key figures TCR and ECS is quite linear dependend of the GHG content of our atmosphere ( on longer time spans) which nobody with some brain will deny. I can’t replicate the difference when looking at the obs. which show some different behaviour AFAIK. This seems to be the core of the PH17 paper: they try to resolve this difference and Lewis disagrees and has some strong arguments. Dunna which result it gives in the end, wait’n see!

  30. frankclimate,

    The CMIP5 mean from which were deduced the key figures TCR and ECS is quite linear dependend of the GHG content of our atmosphere ( on longer time spans) which nobody with some brain will deny.

    Maybe, but that misses the point. If you use climate model results to determine something equivalent to an observationally-based climate sensitivity, you tend to get a result that is lower than their full ECS.

    This seems to be the core of the PH17 paper: they try to resolve this difference and Lewis disagrees and has some strong arguments.

    That Lewis disagree is barely worth mentioning (would be remarkable if he didn’t). However, this misses the point that there are many studies that indicate that feedbacks are not strictly linear (either because of the variations in regional warming, or the pattern of sea surface warming) and, hence, observationally-based estimates will tend to be biased low.

  31. Magma says:

    The Proistosescu & Huybers Science Advances paper came out July 5. On July 8, Nic Lewis posted a 3300 word comment on it at Climate etc. and a longer 5000 word version at Climate Audit.

    Unless he was given a preprint and maintained an embargo, I find that short period difficult to reconcile with a thorough review.

  32. Willard says:

    > The CMIP5 mean from which were deduced the key figures TCR and ECS is quite linear dependend of the GHG content of our atmosphere ( on longer time spans) which nobody with some brain will deny.

    FrankB, meet teh Keenan:

    Stationarity is not the only assumption. Your paper also includes some assumptions about linearity … I do not see how [linearity] can be justified….

    http://www.bishop-hill.net/blog/2014/9/29/keenan-on-mckitrick.html

    Someone named “Frank” commented in that thread and wonders “whether a linear model is a suitable model,” FrankB. Is it your evil twin?

  33. Magma,

    Unless he was given a preprint and maintained an embargo, I find that short period difficult to reconcile with a thorough review.

    Yes, it was rather rapid.

  34. frankclimate says:

    ATTP: “That Lewis disagree is barely worth mentioning (would be remarkable if he didn’t).”
    If you really want to deal with this subject ( and not only rhetoricaly) you should read both the paper and the post of Lewis and make some reflections with regards to content. The hint to other papers ( not the subject here under your introduction?) isn’t so helpful IMO.

  35. Willard says:

    > If you really want to deal with this subject […]

    Thank the lords of ClimateBall for FrankB’s concerns. They’re way more interesting than his dodging.

  36. frankclimate,
    As I mentioned in the post, I don’t really have the time to try and work out who is right and who is wrong (or if it is something in between). That Nic Lewis found an “error” is entirely unsurprising. In some sense, what he is doing is scientifically unsound. Carry out what is clearly quite a simple calculation that has various underlying assumptions that may not be correct. Spend the rest of your time finding fault with any other study that suggests that your results may not be all the appropriate for projecting climate change into the future (or, maybe more correctly, that it is a bit more complicated that his analysis suggests).

    The hint to other papers ( not the subject here under your introduction?) isn’t so helpful IMO.

    I don’t know what this refers to?

  37. frankclimate says:

    Willard, I can’t take you seriously anymore! “Someone named “Frank” commented in that thread and wonders “whether a linear model is a suitable model,” FrankB. ”
    Perhaps it was Sinatra! How many Franks you know? It lowers the bar, really!

  38. Willard says:

    I think FrankB is referring to the bulleted “general comments” that FrankB evades, AT.

    Be thankful for his “but NicL’s no 5” peddling and be done with it.

  39. frankclimate says:

    ATTP: ” I don’t really have the time to try and work out who is right and who is wrong (or if it is something in between). ” You should spend all the time (also the time for writing your post!) if you are not interested in the truth.

  40. frankclimate,

    You should spend all the time (also the time for writing your post!) if you are not interested in the truth.

    Really? A couple of comments.

    1. Science is a process that is often quite lengthy.

    2. The truth (by which I assume you mean some kind of scientific truth, rather than an absolute truth) tends to emerge slowly.

    3. It’s extremely unlikely that we will determine the truth by carefully analysing this paper and Nic Lewis’s response (which is not to say we learn nothing, though).

    3. I write blog posts about things I find interesting and that might provoke some interesting discussions. I don’t claim that they produce some kind of truth, they’re just blog posts.

  41. I should probably add that one reason I find it hard to spend too much time on this is that it’s more a part of the blog wars, than a part of serious scientific research. There’s a pattern. Paper suggests it can reconcile climate sensitivity estmiates. Nic Lewis immediately (within days) finds fundamental flaw. Repeat.

  42. RealClimate just pushed a discussion on updates to climate sensitivity titled “Climate Sensitivity Estimates and Corrections”, by Gavin Schmidt.

  43. niclewis says:

    Magma
    “Unless he was given a preprint and maintained an embargo, I find that short period difficult to reconcile with a thorough review.”

    I was and I did. And I obtained from the lead author the computer code used for the paper (good on him for supplying it), analysed it and ran the code both unchanged and modified to correct the two main errors that I found in it. Read my analysis at Climate Audit for details. I only make a post criticising a study after studying and analysing it in depth.

  44. Willard says:

    > I can’t take you seriously anymore!

    Thank you for the kind words, FrankB. They mean a lot to me.

    Unless you can claim that teh Keenan is a zombie, I duly submit that your “nobody with some brain will deny” is a bit premature.

    Admittingly, Keenanian zombies would seem less dangerous than Boltian ones.

    ***

    > How many Franks you know?

    The question is rather how many Franks are your evil twins.

    You know why I call you FrankB, right?

    No entity without identity, and no identity with sockpuppetry.

  45. izen says:

    @-“What if I told you that CS may not be 9C?”

    What if I suggested it maybe, at least on a regional basis.

    Consider Issac Helds’ suggestion that polar amplification may be much greater than we predict, but the response time is much slower than we expect. If doubling CO2 shifts the energy budget, the 1st & 2nd LoT require that is re-balanced.
    A climate sensitivity of 3C could do that, or a climate sensitivity of 2c if the poles warm disproportionately (9C!) for the SAME amount of extra Joules.

    The observations may fail to capture the full extent of polar amplification if it is large but slow because of coverage issues and internal variability still exceeding the magnitude of the signal.

    This is one reason why I always find the importance ascribed to climate sensitivity a pinhead-angel ratio problem.
    I may stand corrected, but the 2deg-3deg range that is in contention does not represent a large difference in the amount of Joules accumulated by the doubling of CO2 and subsequent feedbacks. How much the global mean surface temperature increases to offset the energy imbalance is a modelling metric that has been co-opted (badly) into a shorthand for the impact of climate change.

    But a lower climate sensitivity, or rate of return to energy equilibrium does not scale to climate impacts. Regional changes, polar amplification and radical alterations in long established ocean currents may generate a lower GMST in reality than in models. Although paleoclimate suggests the opposite. But the assumption that restoring a common energy imbalance would be less damaging if ECS is 2C rather than 3C seems Panglossian.

  46. Willard says:

    > I obtained from the lead author the computer code used for the paper

    When?

  47. frankclimate says:

    ATTP: “Paper suggests it can reconcile climate sensitivity estmiates. Nic Lewis immediately (within days) finds fundamental flaw.” And this says that Lewis is wrong? When somebody knows his field very well nothing is to say against a short time span for the subsumption of the facts IMO. Anyway… what I’m missing in your post is a real consideration of the facts. Perhaps you come to the clue that Lewis is wrong after you have weighted the arguments. But a post without arguments seems to be a bit to poor.

  48. frankclimate,

    And this says that Lewis is wrong?

    Not at all, just commenting on a pattern. One thing to consider is that Nic Lewis’s work can really tell you little about whether or not the feedbacks are indeed linear. That is simply an assumption of his method. If he really wanted to show that his projections are indeed more likely to be correct than those of climate models, he will probably need to do something to indicate why we might expect the response in the future to be the same as its been in the past. Also, bear in mind that his work suggests that the ECS is more likely below 2K, than above, and it doesn’t rule out an ECS < 1K. Almost all other estimates indicate that an ECS below 1K is almost impossible and that it is more likely above 2K, than below. Reconciling this kind of discrepancy is quite important. Nit picking at individual studies is not really doing it.

    Perhaps you come to the clue that Lewis is wrong after you have weighted the arguments. But a post without arguments seems to be a bit to poor.

    I didn’t say he was wrong. My post is simply some comments, which you can consider, or ignore. It’s up to you.

  49. frankclimate says:

    ATTP: ” One thing to consider is that Nic Lewis’s work can really tell you little about whether or not the feedbacks are indeed linear. That is simply an assumption of his method.”
    I don’t thing that there is fundamental discrepancy between CMIP5 and the approach of Lewis as I showed it here: http://frank3867.wordpress.com/ . An ECS below 1K/doubling CO2 is unlikely, we agree!

  50. Willard says:

    > I showed it here

    Indeed:`

    Im angeforderten Archiv wurden leider keine Ergebnisse gefunden. Eine Suche findet eventuell einen verwandten Beitrag.

    Care to try again?

  51. frankclimate says:

    Willard: some kind of kidding, isn’t it?

  52. frankclimate,

    I don’t thing that there is fundamental discrepancy between CMIP5 and the approach of Lewis as I showed it here

    I don’t quite get what you’re suggesting. What is being suggested in the paper is that if you use climate model results to reproduce an observationally-based estimate, then it does indeed agree with Nic Lewis and somewhat underestimates the actual equilibrium climate sensitivity. Nic appears to disagree and suggests that the climate model estimates that for observationally-based sensivities are still quite a bit higher than what you get from the actual observations. I must admit that I do find this a little odd in that climate models appear to reseasonably represent the observed historical temperature. The might slightly over-estimate the TOA flux (which would give a higher CS) but I didn’t think it was so great as to be almost twice as high as Nic Lewis’s best estimate.

  53. frankclimate says:

    ATTP: “Not at all, just commenting on a pattern.” Don’t you think that your sampling is too low for recognizing patterns? I don’t say that he’s right, I’m unable to weight the arguments. BUT I don’t make a post out of this!

  54. frank,
    I think you’re taking my comment a bit too seriously. On the other hand, there seem to be two constants in the online climate debate. Publish a paper about millenial temperature reconstructions and Steve McIntrye will find something to criticise. Publish a paper apparently reconciling model and instrumental climate sensiviity estimates and Nic Lewis will find something to criticise. Of course, the response may not be linear and so we can’t use this to accurately predict what will happen in the future 🙂

  55. Willard says:

    > Don’t you think that your sampling is too low for recognizing patterns?

    That’s why the wording was “pattern” not “frequecies” or “oscillations”.

  56. Willard says:

    > BUT I don’t make a post out of this!

    “This” may not refer to AT’s “general comments,” which you have yet to address, FrankB.

  57. Susan Anderson says:

    While I may not be technically able to follow the scientific arguments, and may find Willard’s sense of humor a bit erratic, I keep coming back because I find kernels of intelligence and honesty which are of value in this present. Willard is an education in himself.

    This is not about “tactics”. It is about finding the truth and acting on it. Various and sundry argumentations, particularly if based on bias, are wasting valuable time.

  58. Susan Anderson says:

    Try Occam’s razor. if the truth hurts, face it, don’t explore every possible means to escape it.

  59. Everett F Sargent says:

    Three very recent papers …

    “Prospects for narrowing bounds on Earth’s equilibrium climate sensitivity”
    Bjorn Stevens, Steven C. Sherwood, Sandrine Bony, Mark J. Webb
    http://onlinelibrary.wiley.com/doi/10.1002/2016EF000376/abstract
    (open access, This article was corrected on 4 MAY 2017)

    “Objectively combining AR5 instrumental period and paleoclimate climate sensitivity evidence”
    (Nicholas Lewis, Peter Grünwald, paywalled, Boo, Nicholas H. C. Lewis, Boo! First Online: 19 June 2017)
    https://link.springer.com/article/10.1007%2Fs00382-017-3744-4

    “On the meaning of independence in climate science”
    (James D. Annan and Julia C. Hargreaves, Published: 21 Mar 2017, open access of course)
    http://www.earth-syst-dynam.net/8/211/2017/esd-8-211-2017.html

    Last paper, see section 7 (Part 2 – Independence of constraints on climate system behaviour) …

    “While we emphasise that Bayesian probability is at its heart a fundamentally subjective concept, it is quite usual to use numerical or mathematical models as a tool to represent and understand our uncertainties.”

    “While the subjective nature of Bayesian priors (i.e. p(S) D p(Sjp), where p is the researcher’s personal background knowledge) has been regularly discussed in the literature, it is less widely appreciated that the likelihood p(AjS) D p(Ajp \ S) is also a fundamentally subjective concept within the Bayesian paradigm.”

    “Therefore, while the likelihood should give a reasonable prediction of the evidence A when the correct value of S is used, there is no objective constraint or check on what the likelihood should predict for some alternative incorrect choice of S.”

    “Within the Bayesian paradigm, therefore, the likelihood can only reflect the researcher’s subjective beliefs and modelling choices rather than any physical truth.”

    I do have my own copy of the LG17 paper, but what 1st caught my eye was the 1st word in said titled paper “Objectively … ” just because you put certain words in your paper’s title does not necessarily imply that the paper itself is objective per se.

  60. Everett,
    Thanks, those look interesting.

  61. Actually, I’ve written about the first paper already.

  62. ATTP, from a ‘lay’ perspective, is there a problem with the language used? I am thinking how I might use this result within a local community setting, for example.

    If Nic Lewis says “I am using observations, you are using models”, then the untutored ear might say “well that sounds reasonable”. Why would we trust models over observation? (notwithstanding the little matter of being far away from a new equilibrium, so ‘short term’ “observations” having limitations).

    Of course, the paleo data was deduced from experiment also, and as @izen showed nicely above, it’s been known for a while that it is key to the shift that the paper identifies. The paper discusses “Centennial modes display stronger amplifying feedbacks” as a basis for reconciling data and models.

    Would it not be better to talk about a comparison of “empirical data” and “model projects”, where empirical includes the direct/ recent observations (last 100 years or so) and any data (including paleo) from which prior GMST etc. have been deduced? If the paper’s claims are accepted, we (us ‘lay’ communicators) could then make the statements:

    “Empirical temperature measurements and model-based projections are consistent with each other”

    “Using the empirical data available, the average of the model projections suggest a temperature increase in the atmosphere* from doubling** of CO2 concentrations of roughly*** between 2° and 6°C, and most likely, nearly 3.5°C”

    * Global Mean Surface Temperature (GMST) relates to the atmosphere.
    ** The word “doubling” is often, and here, used as short-hand for increasing CO2 concentrations from pre-industrial levels at 280 ppm to 580 ppm.
    *** Strictly, the paper […] indicates a 5 to 95% confidence of being between 2.2° and 6.1°C and a median value of 3.4°C

  63. Richard,
    I’m not quite sure what you’re suggesting. I think it’s rare that some analysis can be completely free of models, and – similarly – few models are completely free of observations/measurements. Even the observationally-based (energy balance) estimates are not model free. I think my own view is that we just have to be clear about what it is that is being estimated and how, rather than necessarily trying to come up with simplifying terminology.

  64. I was thinking about how better to communicate the conclusions, and avoid long-winded technical qualifications (for a general audience). I appreciate I may not have nailed it, but welcome any other others. A short, non-technical statement you would use in a church hall if a heckler shouted “but the observation data shows that the Earth won’t warm as much as the climate scientists are saying; the models are running too hot!”. Over to you …

  65. Richard,
    Okay, that would be useful. My cynical side feels that there isn’t a way that wouldn’t be pedantically criticised by those who would like to do so. I guess my view is that the observations do not support that models are running too hot since there are models that can match the observations. This does not mean that they aren’t running hot, but that we don’t yet have sufficient evidence to claim that they are.

  66. Maybe something more pithy in a rowdy hall …

    Sir, it isn’t the models running too hot; it’s the observations running too slow!

  67. izen says:

    @-Richard Eskine

    “Using Observations is like predicting the score after 20 minutes of a game. Models predict a lot of late goals.
    That’s the way climate has played out in the past.”

  68. Chubbs says:

    The climate etc post below sheds some information on the EBM method by regressing surface temperature data against CMIP5 forcing for the period 1951 to 2015. The plots clearly show non-linearity with observed temperatures below the trend line early and above the trend-line late with non-random u-shaped residuals. The blog attributed the non-linearity to AMO but non-linear response to forcing or some other systematic factor would also explain. In any case, assuming linearity is questionable and projecting forward with this or related methods will underestimate future warming.

    https://judithcurry.com/2016/10/26/taminos-adjusted-temperature-records-and-the-tcr/

  69. @Everett F Sargent, and all,

    On the Bayesian prior point, okay, but just don’t forget the Bernstein-von Mises Theorem, as long as Cromwell’s rule and infinite priors are avoided. Also Wikipedia, but it’s not their best entry on statistics and probability, even though they have a good many fine ones.

  70. frankclimate says:

    Chubbs:in a follow up post ( https://climateaudit.org/2017/06/19/the-effect-of-atlantic-internal-variability-on-tcr-estimation-an-unfinished-study/ ) is shown the linkage between the residuals of the forcing dependend delta T of the oserved record and the as good as possible forcing- cleaned AMO/AMV as the most important part of the internal variability on decadal timescales (fig. 6). After removing this part one gets the results for TCR shown there in fig.8. For the forced part ( this is the important part for every sensivity estimation) there are no non-linearities neither in obs nor in the CMIP5-mean.

  71. Steven Mosher says:

    Willard.

    When?

    Best jaq ever!

    Nice attempt to cover for the slimy innuendo others engaged
    In.

    I suggest to folks here that they do science. Get the code.
    Get the data. Or just speculate. Crap the wuwt disease knows no boundaries.

  72. @Everrett F Sargent,

    … it is less widely appreciated that the likelihood p(AjS) D p(Ajp \ S) is also a fundamentally subjective concept within the Bayesian paradigm.”

    Therefore, while the likelihood should give a reasonable prediction of the evidence A when the correct value of S is used, there is no objective constraint or check on what the likelihood should predict for some alternative incorrect choice of S.

    I should have also commented that (a) it is also key for maximum likelihood estimation, which is the Frequentist main, and (b) there are empirical likelihood techniques (Owen) and devices like ABC. I did not because I thought I already did, but then recalled I mentioned in in connection with a trends discussion on Tamino’s blog. (So many blogs, so little time …)

  73. Willard says:

    > Best jaq ever!

    NicL has been quite circumspect in providing a timeline.

  74. Willard says:

    > in a follow up post […] is shown

    Not “is shown,” FrankB.

    You show.

    You are the author of that post, FrankB.

    Own it.

    No more sockpuppetry, please.

  75. frankclimate says:

    Willard: You do everything to make you childish, don’t you? If it’s shown by me it’s also shown? And congrates for finding out the identity of “frankclimate” which was never hidden. You have the format of Sherlock Holmes at least! A Shelock Holmes for absolute beginners 🙂

  76. Willard says:

    A simple “this is the website of Frank Bosse and my ClimateBall handle is frankclimate” on your empty website would suffice, FrankB.

    Otherwise start publishing your ClimateBall posts under the name “frankclimate.”

  77. frankclimate says:

    Willard: “NicL has been quite circumspect in providing a timeline.” Do you really think this would change anything in the content? You are not interested in the content (science) IMO, you only try to make ad homs.

  78. Willard says:

    Dear FrankB,

    I asked you to acknowledge something. Your next comment better acknowledge it, or else you’ll have to raise concerns elsewhere.

    Is that clear?

  79. Willard says:

    Oh, and speaking of content, dear FrankB:

    A few days ago Tamino (aka Grant Foster) released a blogpost with all the data (thank you for this, Tamino) in which he introduced a “sophisticated adjustment” to eliminate the influences of ENSO, solar TSI- changes and volcanic activities on the temperatures from 1951 to the present ( 8/2016) in many records.

    https://judithcurry.com/2016/10/26/taminos-adjusted-temperature-records-and-the-tcr/

  80. @izen – I like it. I will bank that for future use!

  81. Joshua says:

    frankclimate –

    =={ You should spend all the time (also the time for writing your post!) if you are not interested in the truth. }==

    ??

    Did you really mean to put hat not in there?

    Did you mean to imply that the depth of effort taken to write this post indicates that Anders is not interested in “the truth?”

    If so, what was that you were saying about ad homs?

    [No need to expect an answer. FrankB’s concern peddling reached a dead end. – Willard]

  82. Chubbs says:

    Frankclimate:

    Tamino has written about pitfalls in using amo as a measure of ocean variability independent of ghg warming.

    https://tamino.wordpress.com/2011/01/30/amo/

    He cites the wikipedia write-up on the AMO:

    “The AMO signal is usually defined from the patterns of SST variability in the North Atlantic once any linear trend has been removed. This detrending is intended to remove the influence of greenhouse gas-induced global warming from the analysis. However, if the global warming signal is significantly non-linear in time (i.e. not just a smooth linear increase), variations in the forced signal will leak into the AMO definition. Consequently, correlations with the AMO index may mask effects of global warming.[4]”

    So the linked blog doesn’t provide any useful information on the whether the linear assumption in the EBM is valid, since any global warming non-linearity bleeds into the AMO and confounds the analysis.

  83. frankclimate says:

    Chubbs: “So the linked blog doesn’t provide any useful information on the whether the linear assumption in the EBM is valid, since any global warming non-linearity bleeds into the AMO and confounds the analysis”

    Please note that for the AMV(AMO) was used another index which is not linear:
    “Atlantic variability: In S. 17 they use an Index from this study. There are some disadvantages from the inclusion of the tropical part of the Atlantic it’s shown in v. Oldenborgh et.al (2009). Therefore I use the SST 25…60°N; 70…7°W (HadSST3) regressed on the forcing (NOT on the GMST) to generate the AMO index.”

  84. izen says:

    @-“Therefore I use the SST 25…60°N; 70…7°W (HadSST3) regressed on the forcing (NOT on the GMST) to generate the AMO index.”

    Doesn’t that require that SST in the chosen region have a linear response to forcings to retrieve and remove an independent AMO influence ?

  85. frankclimate says:

    izen, indeed there is implied that the forcing is also working in the area of the extratropical northern atlantic and the SST response linear to this forcing.

  86. JCH says:

    More AMO spoon bending.

  87. frankclimate says:

    [You failed to address AT’s points and you have yet to acknowledge what you were asked to acknowledge, FrankB. Thank you for your concerns. – Willard]

  88. Chubbs says:

    Frankclimate

    It still appears to me that the amo adjustment is removing some of the ghg forcing signal. A TCR of 1.33 would lead to warming of roughly 0.12C per decade using the CMIP5 forcing.

  89. Uli says:

    It is possible to test observationally-based estimates for equilibrium climate sensitivity by using the output of a climate model with known equilibrium climate sensitivity instead of the real world observations. Then compare the observationally-based estimates for equilibrium climate sensitivity ,estimated with the same method as for real world observation, from the “observations” of the model output with the know equilibrium climate sensitivity of the model.

    I did this with a model with an equilibrium climate sensitivity of 2.9 °C/2xCO2. I run a simulation from 1850 to 2014.
    The observationally-based estimate for the equilibrium climate sensitivity form this model run was 2.0 °C/2xCO2.

  90. Willard says:

    Better late than never:

    frankclimate | July 29, 2017 at 1:01 pm | Reply

    […]

    I think it’s clear that I’m the author of the post […]

    https://judithcurry.com/2017/07/29/update-on-the-strength-of-aerosol-forcing/#comment-855044

  91. Pingback: A bit more about clouds | …and Then There's Physics

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