Nic Lewis and the UK Met Office

Nic Lewis (an independent climate scientists) and the UK Met Office seem to be having a public debate about climate sensitivities and about the Met Office’s climate models. I find it quite interesting that the Met Office are engaging in this discussion. It’s commendable that they’re willing to engage, but it’s not obvious that they should be obliged to do so. Nic Lewis has a publication record in climate science, but it’s not particularly impressive. If one of my PhD students decided to publicly criticise a major research organisation, I’d probably tell them to wind their necks in and focus on doing science. If you think they’re doing something wrong, prove it in the scientific literature.

The basic issue seems to be that Nic Lewis has been involved in a couple of studies that use recent observations to determine the Transient Climate Response (TCR) and the Equilibrium Climate Sensitivity (ECS). The TCR is the change in surface temperature at the instant when atmospheric CO2 has doubled (assuming it rises at 1% per year) and the ECS is the ultimate equilibrium surface temperature after a doubling of CO2. Nic Lewis’s work suggests that the TCR and ECS are lower than previously thought. The Met Office’s model (HadGEM2-ES) produces some of the highest values for the TCR and ECS. Nic Lewis appears to think that there is an error in their models and somehow wants them to give more recognition to his studies that produce lower climate sensitivities.

I think Nic Lewis’s work (and it’s not him alone, to be clear) is interesting. One problem, though, is that it seems to be based largely on using the recent surface temperatures (last 30 years or so). Climate sensitivities are associated with changes in atmospheric CO2 that occurs over 100 years or more. Using short time intervals (30 years or less) means that the results are quite strongly dependent on natural variability and other effects (short-lived aerosols, solar variability) that might influence surface temperatures on short timescales, but average out on the longer timescales. Therefore, that Nic Lewis’s values differ slightly from other values is not that surprising. I suspect that many would see the method used by Nic Lewis and collaborators as a sensible sanity check, rather than as a method that is somehow more robust than other methods. What would have been surprising would have been if Nic Lewis’s method had produced results very different to those produced by other methods. That it didn’t (the ranges overlap) gives some confidence that the various other methods are at least consistent. If you want to know more about this, there’s a good discussion on Skeptical Science.

The UK Met Office has already responded to Nic Lewis’s criticisms in a blog post a few days ago. You can find Nic Lewis’s original criticism here. Julia Slingo, Chief Scientist at the Met Office, has written personally to Nic Lewis and the letter is posted here. I think Julia Slingo’s letter is reasoned and balanced and makes some very valid points. Nic Lewis has responded to this letter in a post on Climate etc. called Nic Lewis vs the UK Met Office.

Given how convoluted this whole episode seems to be I thought I would just make some comments with regards to Nic Lewis’s response to Julia Slingo’s letter. He seems to be critical that they focused mainly on the estimates using the period 1970-2009 and didn’t include the results from the period 2000-2009. I don’t know if they did or didn’t, but it would seem to me that focusing on the longer time period is more sensible than focusing on the shorter time period. I’m not even sure why they bothered considering the period 2000-2009 as it seems obvious that the longer the time interval considered, the more robust the result (although maybe that’s just me).

It seems as though one of Nic Lewis’s criticisms is that the Met Office model cannot explore low values of the ECS. Julia Slingo’s response is

But the key point is that the relationship between aerosol forcing and ECS is an emergent property of the detailed physical processes sampled in the PPE simulations.

I take this to mean that the the ECS is a model result that is a consequence of the various initial conditions and the physical processes included in the model. If the model does not produce a low ECS, then that implies that a low value is not possible given those input parameters and the physical processes included. You can’t force the model to give you a low ECS. As far as I’m aware, Nic Lewis’s results are based on a short time interval compared to the total time over which CO2 will double. The models consider the entire doubling time and continue on until the ECS is reached. It’s not unreasonable that there will be differences. In some sense, all these different results are useful and interesting and should, in some sense, remain independent. You can’t insist that the Met Office model produces lower ECS values simply because you think your work has more validity than others. You might be wrong. Of course, if one can find an error in a model, it should be fixed but getting a different result using a different method does not immediately imply an error in the model.

Maybe the most confusing thing about Nic Lewis’s response was the comment below

That strength cannot overcome the basic problem that HadCM3 cannot sample low aerosol forcing, low climate sensitivity combinations and is therefore an unsuitable model for this PPE study.

I understand how aerosol forcing is an input to the models, but he seems to be implying that somehow the models should be able to probe low climate sensitivities. These, I thought, were outputs so either the model produces a low climate sensitivity or it doesn’t. You shouldn’t tune the model to probe low climate sensitivities. The models should be physically motivated. How is it even remotely acceptable to argue that the model is wrong because it doesn’t produce the result you want? If we knew what the TCR and ECS actually were, then maybe one could conclude that the model was wrong, but we don’t.

Julia Slingo finishes her response by saying

As I said we appreciate your contributions to the literature on these topics; but the implications of climate change are so profound that it is essential that scientific debate takes place in the appropriate forum. With this in mind I think it is appropriate that further discussion be subject to proper peer review, through the scientific journals.

Nic Lewis, sadly, gives the standard response to such a suggestion. This appears to represent an attempt to stifle reasoned scientific debate. No it’s not an attempt to stifle reasoned debate. It’s a recognition that public debates about science aren’t particularly valuable. Exchanging ideas at conferences, or exchanging a few emails or letters is part of the process. At the end of the day, however, you need to publish your work and have it evaluated by others in the field. It’s almost as if Nic Lewis thinks that this public debate could lead to some kind of resolution. No it can’t. It could lead to some changes in the modelling and in the studies that might ultimately resolve the issues, but until the works been done, tested, published, evaluated and checked we really won’t know.

That’s why Nic Lewis should get on with his work and should really leave the Met Office scientists to get on with theirs. I’m not suggesting that all correspondence should stop. Simply that expecting the correspondence to lead to some kind of scientific resolution is unscientific. Ask questions. Make suggestions. Engage scientifically. All fine. Don’t, however, assume that because you’ve published a paper suggesting that results obtained by others might be wrong means somehow that they all have to bend over backwards to incorporate your work. That’s not really how it works. I think what Nic Lewis is doing is interesting and valuable, it’s just not – in my opinion – more interesting and valuable than the work being done by others.

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44 Responses to Nic Lewis and the UK Met Office

  1. Rachel says:

    Excellent post! It looks like Nic Lewis is not approaching this from an unbiased perspective which I’m guessing is precisely what he criticises climate scientists of doing.

    The MetOffice is not the only group making calculations of climate sensitivity. James Hansen puts it at 3-4C in his most recent paper.

  2. Thanks. I was going to include more but realised it was getting rather long. You just need to read some of the posts on Skeptical Science (or watch the video by Andrew Dessler) to realise that the evidence for the ECS being below 2oC is very slim and that it is much more likely closer to 3oC than to 2. It’s possible that the TCR will be lower than maybe originally thought, but that really just means we have more time, not that the outcome will be different. Also, more time is likely to be decades not centuries.

  3. Rachel says:

    Yes, arguments over climate sensitivity to my mind are just distractions from the real issue which is that we need to stop digging up fossil fuels. If we have more time, then great, but the outcome still needs to be the same and that is a world without coal/oil/gas.

  4. In a sense, yes. In another sense, the climate sensitivities are kind of what’s crucial. So it would be better to focus on them (for example) than the supposed mismatch between the models and observations for the last 15 years (which is probably one reason why Lewis’s work produces lower values anyway). At the end of the day, though, you’re right. What we should be considering is the ECS, not the TCR. The ECS should – in a sense – constrain how much CO2 we’re willing to add to the atmosphere and hence how much more of the fossil fuels we should be willing to extract and use.

  5. Martin says:

    I do not agree with that. The TCR is very important for valuation. E.g. Hope’s PAGE09 is apprently very important to changes in the TCR:

  6. Yes, okay I probably just worded what I said badly. I wasn’t suggesting that a different TCR would have no short-term effect . I was simply suggesting that, ultimately, if the ECS is unchanged, then that indicates the likely long-term outcome. So, yes I agree. A different TCR does change what we might want to do and change how we might address the issues. I agree with that. However, an issue I would have is that if the ECS is unchanged, then presumably that would suggest that a lower TCR does not mean we can add more CO2 to the atmosphere (or at least not if we wish to avoid a certain amount of overall warming). If we wish to constrain overall warming, presumably that should be determined by the ECS rather than the TCR?

  7. BBD says:

    Nic Lewis is a mischief maker. I have said this many times before elsewhere, so I feel that it would be bordering on dishonest of me not to repeat my words here. As Karsten pointed out a while back, Otto et al.’s results are not robust, and NL goes much further in his own unpublished monographs (unpublished that is except on Bishop Hill and Climate etc).

    More politics masquerading as science.

  8. BBD says:

    I should add that it’s interesting – amusing even – that the “sceptics” uncritically endorse NL’s extremely low estimate for TCR as something akin to “fact” when in fact all NL has done is demonstrate that his methodology is very sensitive to the chosen estimate of negative aerosol forcing and transient variability in ocean heat uptake.

    That would be uncertainty, would it not?


  9. Martin says:

    Yes, I agree with that. A constraint on overall warming surely has different implications. This has a lot to do with the time horizon of the problem, and goes to the heart of the problem why we are discussing discount rates so much. But whatever the ansewer to that, valuation is a real thing when it comes to policy (even if we apparently don’t really agree, yet), and there the TCR is highly important. (Can one construct a catastrophe scenario where the TCR is so low, and the ECS so high, that we’d lead world into annihilation under proper valuation criteria?)

  10. Yes, I’d forgotten that. I think Tom Curtis pointed this out on an earlier thread.

  11. It certainly seems that way. As I mentioned in the post, using recent data to determine the TCR and ECS seems fine as some kind of sanity check (i.e., one could smooth out the variability to determines trends and then estimate the TCR and ECS). Arguing that it is somehow more robust than other methods because it is based on recent observations seems (as I think Karsten was pointing out – if I remember correctly) largely unfounded.

  12. I posted a comment about Nic’s first response at Judy’s:

    Judy started to delete comments. Not that it prevents Denizens to perpetuate their abusive practices. At least for now.

    If I catch some deleted comments in my RSS feed, may I post the most precious ones here, Wott?

  13. Tom Curtis says:

    Martin, TCR of 0.5 C; ECS of 4.5; assumed positive benefits of global warming up to 2 C, and a 5% discount rate ought to about do it – particularly if the model is only run out to 2200. Halve TCR and double ECS if by “annihilation” you mean the extinction of large mammalian species rather than just the end of industrial civilization.

    Of course, we are on course for the former at TCR 2 and ECS 3 based on concerted resistance to rational policy; and reliance on economic models that indicate net benefits from global warming at temperature increases are estimating >50% extinction rates.

  14. Tom Curtis says:

    Sorry, by “former” I meant, “end of industrial civilization”.

  15. Yes, I noticed you were commenting there. Feel free to add any deleted ones here if you wish. Maybe Judith will get in touch and ask me to delete them too 🙂

  16. toby52 says:

    I am puzzled by one thing – a year or so ago, Spencer & Braswell got unparallel media hype (an appearance on Fox News for Dr Roy, no less) for a paper in Remote Sensing assuming a climate sensitivity of 0C. There was also Lindzen and Choi (2009 & revised) that found a value of 0.5C. Correct me if my memory is faulty.

    Lewis gives a minimum value of something like ~1.3C, so then Spencer and Lindzen must have been wrong somewhere, but I have seen none of their former admirers point this out. It is as if anything less than 1.5C will do, no matter what.

    Thanks to the Economist, in an otherwise fair article, deniers have treated climate sensitivity like a Moody’s credit rating – it can go up or down (mostly down) based on the last result you saw that you agreed with. They do look like a desperate crowd seizing on a figure, any figure, that temporarily boosts their case.

  17. Marco says:

    No, anything that contradicts the IPCC will do, because then “there is uncertainty!”, and hence “we should not do anything until we are sure!”

  18. Are you aware if anyone has attempted to redo some of this work using newer OHC data and maybe to illustrate how sensitive it is to these assumptions.

  19. andrew adams says:

    I think the Lindzen and Choi paper was pretty quickly debunked, to the extent that even the authors accepted it was badly flawed. IIRC they produced an updated version and had a lot of trouble getting it published and it ended up getting in some obscure journal somewhere or another. That doesn’t stop the skeptics citing it of course.

    As for the Spencer and Braswell paper, that was so bad the editor of the journal resigned over it.

  20. BBD says:

    No – although Karsten was muttering darkly about rumours that NL’s results (not Otto et al.) were not reproducible. Hopefully Karsten will pop in later, although IIRC he’s off on a jolly somewhere, doubtless spending public money like a drunken pirate because as any fule kno, climate science is a hoax etc, etc…


  21. Tom Curtis says:

    My earlier discussion was here. Karsten’s immediately follows it.

  22. Martin says:

    [Mod – a rather unnecessarily sarcastic response]

  23. Tom Curtis says:

    [Mod – a rather personally insulting response]

  24. That might be too cocksure, Tom.

    Try “you may be” instead of “you are”.

  25. Hmmm, I step out for a few minutes and everything falls to pieces. Trying out my newly implemented moderation policy I see. Martin, I don’t know what motivated your comment (did you think Tom was being sarcastic?- although maybe best you don’t actually answer that). Tom, possibly not strictly “vitriolic personal attack” (i.e., I’ve heard much worse) and possibly Martin’s comment was deserving of some response. Anyway, unless anyone objects, maybe we can just move on.

  26. Seems that Nic’s “has implicitly accepted” might come handy:

    > In effect, AK has implicitly accepted that Nic Lewis wrote a political hit job, just like his other op-ed.

  27. Martin says:

    Yes, Wotts. I object.

    1) You think that somebody who has to ‘throw up’ (or whatever it was) when reading ‘Pielkish’ has not actually made an “ad hominem” attack (be it vitrioic or not). That was already a bit strange and a very narrow definition, but OK – at least, it’s technically true (though I think that you are pussyfooting around calling out an obvious insult by adhering to such literal interpretations.)
    2) Now you have somebody with a track record calling other names calling me an arsehole, and you make excuses for him. I note that you take such track records of bad behavior very important, even if they happened outside this blog (you include them in your blog posts if they concern, say, Tol). This is, btw, the same Tom Curtis who just linked (in another comment section) to a Tol comment about Pachauri being allegedly unfit or whatever for his job (a comment not containing strong language – but now, for some reason you “have heard much worse”; and we are talking about the word “arsehole”!) as a vitriolic personal attack. And you agreed without further ado (I somehow do not remember you making excuses for Tol, and I’d say that you were exactly right.).

    Do you take your comment on this here seriously? Really? Tom Curtis (maybe) couldn’t help but calling me an arsehole, because, in some way, you can at least imagine that I more or less asked for it? May I also assume that you think it was fair play from your and Curtis’ part as long as I do not clarify my comment? That it’s my responsibility to put my comment in a light so that maybe it do not “derserve a response”, namely “Martin, your an arsehole!”. If you do not think that this is what you defended (and that’s exctly what you did), in effect, I suggest your read your last comment again.

    I repeat: Are you taking yourself seriously at this point?

    I’d also note that no, of course I am not an arsehole, and I am pretty sure about it. But given how the notion is not so bad (or certainly not the worst), after all, I will feel free to use it whenever I feel like it in this comment section (we can always “move on” after you clarified that maybe I had a reason to do so?). I’d be interested, at this point, why I shoudln’t. Like, really.

    Now, I do not mean to criticize you for not always being 100 % consistent (because, who is). But if you could be a bit less blatantly biased, that would reallly be nice. What do you think?

  28. Martin, I actually thought my response was actually quite balanced. I didn’t actually make an excuse for Tom. I pointed out that maybe your comment deserved some kind of response. You made what was fairly clearly a very sarcastic response to a comment by Tom. He responded in a manner that was not particularly polite (and somewhat against my general “Let’s be civil” mantra). What kind of response did you expect for your comment? What would you like me to do? Moderate Tom’s comment on the basis that it’s technically an ad hom and leave yours alone? Moderate both? I was actually hoping that those involved could simply see this as some kind of spat and move on. I can’t see the point of doing something about this. So, if you really object, I’ll just delete the whole series of comments. I don’t really have time to mediate a lengthy discussion on this.

  29. Martin says:


    your threshold for a vitriolic personal attack was calling someone an idiot. Your “balanced” response after Tom calling somebody an arsehole was:”Tom, possibly not strictly “vitriolic personal attack” (i.e., I’ve heard much worse) and possibly Martin’s comment was deserving of some response.” You must be kidding. You repeat the same excuses.

    I wish you good luck with your BBFs here, this is ridiculous.

  30. Martin, maybe you could clarify which possible version of BBF you were intending in your comment.

    To go a bit further my “Possible not a ‘vitriolic attack'” was meant to convey that it was still a personal attack but maybe not as bad as it could have been, not an attempt to say “well done”. I was trying to find something negative to say about both comments. Maybe I failed in that, but that was the intent.

  31. toby52 says:

    You mean (gasp!) he might be an … an …. (words fail me!) an activist?

  32. @BBD: I don’t have much to add to what Julia Slingo (MetOffice) und wotts have already been saying. I find Nic’s paper not particularly exciting and Alex’ paper should best be seen as an observationally constrained lowest bound on ECS. There is a hint of information with regard to the current TCR, which itself is not necessarily constant over time. For both, TCR and ECS, only the 40 year interval would be of relevance given the huge decadal variability. The figure in my earlier comment (following Tom’s discussion in the link he provided) is an extension of Alex’s work using a more realistic aerosol forcing time series (note that the current value of -0.9W/m2 is basically the same) and more recent OHC data from Balmaseda et al. 2013. Not surprisingly, TCR/ECS for the last 40 years increases. However, this is too simplistic an approach which is why it remains a rather futile exercise if the OHC of the earlier period is unknown. Only models can help to get a better handle on that. Something I’d like to explore in more detail if time allows.

    Re jolly: You got it absolutely right 😀

  33. BBD says:

    Thanks for the response and recap of your earlier comments Karsten. Also thanks to Tom for linking back to the relevant discussion for interested readers (something I neglected to do).

    * * *

    There has been some editorialising about climate blogs recently. Here we have a good example of how the best can make a positive contribution to the “debate”.

  34. Onto Nic’s second point:

    Notice how Nic does not discuss Dr. Slingo’s claim that “Observations alone cannot provide that information.”

    Does that mean Nic implicitly accepts it?

  35. BBD says:

    Given that Dr. Slingo is correct, he has no choice but to accept it. Unless he wishes to appear overtly irrational, that is. But NL is a mischief-maker. So he carries on making…

  36. Just a minor nit – I wouldn’t call Lewis a climate scientist. I probably have more climate publications than he does, but I’m certainly not a climate scientist. I don’t think publishing a paper every now and then is sufficient to qualify. Personally I define the term as somebody who does climate research on a professional basis, i.e. for a living, constantly doing research, not just putting together a paper in one’s spare time every now and again. That’s just my definition of course, your mileage may vary.

  37. I have no real issue with calling someone who’s published a paper in the general area of climate science, a climate scientist. That doesn’t mean that I think that it makes them any good or that it gives them any real credibility or that it means that they should be given some kind of platform. For that, they would have to at least satisfy your definition.

  38. An update: Nic’s third point omits two full paragraphs from Slingo’s letter:

    Nic’s empiricism is showing.

  39. Onto Nic’s fourth point:

    There seems to be an interesting standoff. Nic claims that his argument has not been refuted, and tries to build up a KO argument out of this stand-off.

    But he can’t. This may explain why we are having the Berthold Brecht’s reference at the end of Nic’s response, as I explain to miker.

  40. Onto Nic’s fifth point, where the burden of proof is being reversed:

    I really like the idea of reflecting the real climate.

  41. BBD says:

    As you say, Lewis’s empiricism is showing ;-). He is mischief-making in the gap between observations and the totality of evidence. Slingo nails it (and Lewis omits it!):

    What you omit to say is that observations of the real world, including those you need to compute TCR and ECS are themselves seriously incomplete and therefore inherently uncertain. Indeed one could argue that models provide a more physically consistent representation of the real world than spatially sparse and poorly sampled observational data. This is why we should look across all estimates and not claim that one method is superior to another. IPCC has correctly used all the evidence to set the range.

  42. Onto Nic’s sixth point, where we see that an whole paragraph is being omitted, except for a sentence:

    The fact that “more models are better” is not being discussed, nor the idea that a greater range of observational constraints can reduce uncertainty.

    The first fact may be tough for Nic’s whole line of argument.

  43. BBD says:

    Since Lewis’s mischief-making depends *entirely* on incomplete measurements, he will do everything he can to divert attention away from this fact. But Dr Slingo nailed his mischief very ably, hence the further argument by omission you deftly illustrate at JC’s.

    I’m sorry I stopped commenting there, but I couldn’t stand the thuggery or tolerate the way Curry repeatedly deleted and moderated me while allowing astonishingly transgressive behaviour unchecked in certain other commenters.

  44. I’ve never tried commenting there and I’m minded not to bother. I can’t imagine that it will go well 🙂

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