Making fog

Readers may remember Nic Lewis's paper demonstrating a major flaw in the UKCP09 climate predictions. In brief summary, the predictions are a weighted average of a series of virtual climates produced by the HadCM3 climate model, the weight each one gets being determined by how well it matches the observations. Nic discovered that the HadCM3 model was incapable of producing virtual climates that match the real-world climate as regards two key parameters - the climate sensitivity and the aerosol forcing. This obviously meant that the average produced is meaningless.

Nic's paper had a response from Julia Slingo which acknowledged that HadCM3 could not produce low-sensitivity/low aerosol forcing climates, explaining that this was an emergent property of the model. Nic noted that she was therefore implicitly accepting his core argument and I mentioned this in a blog post about the related UK Climate Change Risk Assessment.

Shortly afterwards I had an email from a press officer at the Met Office:

I noticed in your recent blog a line about UKCP09, as follows: “Unfortunately the UKCCRA is based on the UKCP09 climate predictions, which the Met Office has acknowledged contain a major flaw.”

The highlighted section is not accurate – no such acknowledgement has been made by the Met Office (unless you can point me to any evidence to the contrary which you think supports your statement). Could you please remove this reference from your blog?

This was a bit of a surprise to tell the truth. It was pretty hard to imagine how the Met Office could argue that the predictions were sound while acknowledging that the HadCM3 model behind it couldn't generate realistic climates. I therefore replied, trying to get some clarification of precisely what their position was:

As I understand it, the Met Office does not dispute that low CS/low aerosol forcing combinations are not possible with HADCM3. This is most likely the way the real climate system is, at least according to the current observational evidence. As the UKCP09 predictions are supposed to be a probabilistic combination of all possible CS/aerosol combinations, the fact that the model cannot sample the most likely combination is indisputably a major flaw. Prof Slingo has observed that this feature is an emergent property of the model, but this is only to recognise how the problem arose, not to dispute that it is an error.  She has also stated that this feature does not create a bias, but I fail to see how she can conclude this without actually correcting the error and finding out what effect it has on the results.

I am happy to add a note to either of both of the BH postings clarifying the Met Office's position, but I would need to be clear what this is. Are you saying that it is possible to create a valid probabilistic forecast without sampling the full CS/aerosol parameter space and, in particular, without sampling the combinations of parameters that is most likely according to observations? I assume not. If the case is simply that the flaw doesn't create a bias (and is therefore not "major") then I would ask how you have reached this conclusion.

However, the reply the following day was evasive on these questions:

From your reply below it’s clear you make a few leaps of judgement to make your conclusion, and these aren’t leaps that the Met Office, or for that matter the IPCC, would necessarily agree with. Certainly they don’t justify the concept that we have acknowledged a flaw, let alone a major one – this is very much your own language and, as such, this should not be attributed to us in the way that you have.

I understand your argument here is based on Nic Lewis’s comment piece and so I note here that Nic himself has made it clear he did no claim there was an error in HadCM3 - in a response to an article on our blog, he said: “I didn’t claim that the HadCM3 model contained an error.” You can see this here (first comment).

Again, this reinforces the point that your statement is very much your own judgement call – not ours and, it seems, not Nic Lewis’s.

As a final point, HadCM3 was not the only model used for UKCP09.

With all this in mind, I’d appreciate if you removed the comment in question or reword it to something which more accurately reflects the situation.

Readers will note the complete absence of any attempt to answer my questions. Moreover, while the criticism had been carefully aimed at the UKCP09 predictions, here the Met Office was insinuating that I had implied a flaw in the underlying HadCM3 model (the argument is more that HadCM3 is unsuitable rather than that it is flawed per se). So this was an distraction by the Met Office. Readers might also like to read the rest of the Nic Lewis comment cited by the Met Office, which reveals a naked falsehood in the report they issued on climate sensitivity.

Similarly, the point about other models being used in UKCP09 was not the kind of thing you would have found in an honest response, as my reply made clear.

Thanks for your email, which arrived too late in the day for me to deal with before I went away on holiday. As I have indicated before, I am happy to make clear the Met Office’s position if you will make clear to me what that position is.

You note Nic Lewis’s comments about HadCM3, but I have been careful to say only that the UKCP09 predictions are flawed. Regarding HadCM3 we therefore appear to be in agreement and my blog posts are correct.

I note also your comments with regard to the use of other computer models in the UKCP09 project. I fear that you may have misinterpreted what your colleagues are telling you. As I understand it, the use of other computer models in UKCP09 is peripheral to the predictions, since they are only used in error estimates. Their use therefore does not in any way mitigate the problems caused by the structural rigidities in HadCM3.

I asked for clarification of the Met Office’s position in my previous email, but you have not responded to the question I asked. I therefore ask again: Are you saying that it is possible to create a valid probabilistic forecast without sampling the full CS/aerosol forcing space and, in particular, without sampling the combinations of those factors that are most likely according to recent observationally-based estimates? (For the avoidance of doubt, I am referring to values in (say) the ranges 1.25–2.25°C for climate sensitivity  and -0.4 to -1.1 W/m² for total effective aerosol forcing.) It appears to me that such a position is untenable and the UKCP09 predictions are therefore flawed. Your silence on the issue seems to represent a tacit admission that I am correct. You cannot say that I am wrong while simultaneously refusing to say why.

In a similar vein, I might ask why the Met Office has failed to withdraw its July paper when the vast majority of the problems Lewis identified in it have gone unanswered.

The Met Office cannot simply try to brush these problems under the carpet by refusing to acknowledge them. Should it do so it will undoubtedly be severely criticised and I therefore urge you and your colleagues to withdraw the UKCP09 predictions and the July briefing paper on your own initiative.

That was sent at the end of October but despite my sending reminders no reply was forthcoming. At the start of December I therefore wrote once more, indicating that I would publish the correspondence and let people draw their own conclusions. This finally elicited a response: 

Sorry it has taken a while to respond, we do tend to get very busy in the winter months and I have to prioritise operational work, as I’m sure you’ll understand. With regards to our email exchanges, we appear to be going round in circles, so I thought I’d recap on how we got here.

As you’ll recall, this started when I asked you to change the following line in one of your blogs:

“Unfortunately the UKCCRA is based on the UKCP09 climate predictions, which the Met Office has acknowledged contain a major flaw.”

As I’ve said before, you are entitled to your own opinions but it’s inaccurate and misleading to ascribe your own opinions to someone else – which is what you have done in the highlighted line above. The Met Office has not said anything along the lines above, and that alone is enough to say that it is factually inaccurate.

In response, you’ve asked me numerous questions which don’t have any relevance to this straightforward request. Besides that, I understand Met Office scientists have spent a considerable amount of time over recent years dealing with similar inquiries from your correspondents, Doug Keenan and Nic Lewis in particular. In fact, Nic Lewis was here for an afternoon a few weeks ago and, as I understand, there has already been a robust, open and constructive conversation about many of the issues you raise. I think that is the appropriate forum for those discussions.

Having made my points as clear as I can, I’d once again ask you to remove or change the highlighted statement above and any other similar statements on the grounds that they are inaccurate and misleading. I think we’ve probably exhausted our respective positions, so I’d suggest that unless you have anything new to add, we bring a close to this particular line of correspondence.

If anyone is any the clearer for this response, they are cleverer than I am! Slingo has certainly admitted that the HadCM3 model can't do what it needed to do for the UKCP09 process. This is undoubtedly a major flaw. Ergo she has acknowledged the flaw.

Tiring of the word games, I decided that I would publish the correspondence anyway, but asked one last question:

Can you just give me one more detail please. You say that you think that my questions re whether the inability of HadCM3 to simulate realistic climates is irrelevant. Is this your personal opinion or the opinion of Met Office scientists (or perhaps just a corporate position)?

But unfortunately, this elicited an equally obscure reply:

We need to clarify here, as I wouldn’t want you to misunderstand or use my words out of context.

I said (as you can see in the email below): “...you’ve asked me numerous questions which don’t have any relevance to this straightforward request” [bolded for emphasis]. So to make it absolutely clear, I’m saying that your questions are not relevant to my specific request – which is on a point of fact, namely that you assert the Met Office has said something which it has not. I’ve gone into the details of why that is the case and why it’s misleading to ascribe your own opinions to someone else.

I don’t doubt that your questions do have relevant contexts and, as I understand, these issues have already been discussed at length between people more directly involved.

As I’ve said, my point is specific and on a point of fact. I am acting in my capacity as a press officer to point out factual inaccuracies and reasonably request that those inaccuracies are corrected.

To this I signed off as follows, copying Julia Slingo:

I have asserted that the Met Office has acknowledged that there is a flaw in UKCP09. I say this because Prof Slingo has acknowledged that HadCM3 cannot simulate low climate sensitivity, low aerosol forcing climates, which are the ones that observations suggest are most likely. She says that this is an emergent property of the model.

You have not disputed that she has made this acknowledgement. I therefore assume that you are disputing that HadCM3's inability to simulate these kinds of climates means that the UKCP09 projections are flawed. This is, as your scientific colleagues no doubt realise, is a completely absurd and entirely indefensible position. It is hard to believe that anyone within the Met Office would seriously suggest that a weighted average of climates excluding those most like the real climate has any usefulness as a predictive tool. As if to confirm this conclusion, you have signally failed to answer my questions on the matter.

I assume then that your real objection is that your colleagues are embarrassed by this public airing of their errors. That really is too bad. I reiterate what I said in my earlier email: the duty of the Met Office is to withdraw the UKCP09 predictions of your own volition as soon as possible. To allow both public and private sectors to continue to spend on the basis of erroneous predictions would represent a serious breach of the Met Office's duties towards the public.

I will add a note to my earlier post as follows:

The Met Office have acknowledged Nic's points about the flaw in the UKCP09 predictions but ask me to make it clear that they deny that they have acknowledged a flaw. I don't know what they mean either.

Update on Dec 12, 2013 by Bishop Hill

In response to comments by Richard Betts, Nic Lewis writes as follows:

Fig. S2 of Harris 2013 shows nicely that the HadCM3 PPE can't generate low ECS, low aerosol forcing combinations. Aerosol forcing is about 0.3 W/m2 more negative than ΔQ_noghg, so the AR5 best estimate of aerosol forcing (-0.9 W/m2) corresponds to ΔQ_noghg = -0.6 W/m2. The only place where the
HadCM3 PPE gets close to the AR5 best estimate of aerosol forcing, let alone below it, is at ECS > 3 C.

The small diamonds show the effect of perturbing the aerosol module parameters, the big diamonds being the default settings. Most of the variation in aerosol forcing comes from perturbing the main atmospheric model parameters, which also changes HadCM3's ECS. The dotted lines are meant to show uncertainty bounds, but I think they are wrong - they should all converge at low ECS.

Comments

[KNR]

Slingo dropped the ball and the MET realising that this is one of those increasingly events when that they let science get in the way of 'politics ' and this would hurt 'the cause . Tired an very 1984 style rewriting of history . Which totally failed and so to save face their tired BS and when that did not work in true climate 'science' fashion tired more BS .

The MET not change until Slingo goes , its problem is that it is in her image and that is a rather ugly, from a scientific view point , picture .
Remember they stopped making public their long range forecasts because they were so wrong so often, and by 'lucky chance ' always wrong in favour of 'the cause '

[simon abingdon]

KNR (6:19)

As usual, right on the money.

[Skiphil]

It cannot be a "flaw" because the model behaves exactly as intended.

[omnologos]

Skiphil might be ironic/sarcastic there but really, especially when there are computers involved, the old joke of the bug sold as a feature applies. And it's still a bug.

[climatebeagle]

" ...we do tend to get very busy in the winter months.... ."

Is there another Christmas Eve press release in the works ?

[Patagon]

I believe that HadCM3 was superseded by HadGEM1 which itself was superseded by HadGEM2

What unnecessary steps for a flawless model!

The Met Office paper on HadGEM2 clearly states: The HadGEM2 physical model includes improvements designed to address specific systematic errors encountered in the previous climate configuration, HadGEM1,...

Again, how can there be errors in a model without major flaws?

Doug McNeall from the Met Office boasted in this same blog about the improvements of the HadGEM2, but he never replied to my criticism, which I elaborated in the discussion section on model uncertainty.

[John Silver]

Oppress Officer , more likely.

[Jake Haye]

Unfortunately the UKCCRA is based on the UKCP09 climate predictions, which the Met Office has implicitly acknowledged contain a major flaw.

Fixed.

[ssat]

The met office has been wrong for 16 years out of the last 17. Next year, they will have been wrong 17 years out of 18. If nothing changes there then .... ad infinitum.

[Green Sand]

climatebeagle

"Is there another Christmas Eve press release in the works ?"

Another? They didn't see the need for one last year!

[John]

Which would people take BBC or Daily Mail?

[jorgekafkazar]

O: ...I wish to complain about this computer model what I purchased not half an hour ago from this very boutique.

O: Oh yes, the, uh, the HadCM3 model...What's,uh...What's wrong with it?

C: I'll tell you what's wrong with it, my lad. It's dead. It can't produce low-sensitivity/low aerosol forcing climates, that's what's wrong with it!

O: No, no, it's, uh...that's an emergent property of the model.

C: Look, matey, I know a dead model when I see one, and I'm looking at one right now.

[Billy Liar]

It is interesting to read UKCP09 just to see whether it sounds a bit, well, dated. You don't have read very far, in fact only as far as the first page of the summary (p5) in the 'Briefing Report', to see this boxed statement:

Central England Temperature has increased by about 1ºC since the 1970s; it is likely that global emissions of man-made greenhouse gases have contributed significantly to this rise.

Well, in 2007, that was true. Unfortunately, just six years later the mean CET has dropped to close to 0°C (anomaly relative to 1961-90 mean).

Such a rapid drop in CET does make one wonder whether projections such as (p6 of summary document):

Summer, winter and annual mean changes by the 2080s (relative to a 1961–1990 baseline) under the Medium emissions scenario. Central estimates of change (those at the 50% probability level) followed, in brackets, by changes which are very likely to be exceeded, and very likely not to be exceeded (10 and 90% probability levels, respectively).

• All areas of the UK warm, more so in summer than in winter. Changes in summer mean temperatures are greatest in parts of southern England (up to 4.2ºC (2.2 to 6.8ºC)) and least in the Scottish islands (just over 2.5ºC (1.2 to 4.1ºC)).

are even credible.

To see whether a pattern would emerge, I looked for UKCP09's predecessor, UKCIP02, to see whether that looked dated also. Finding a copy of Climate Change Scenarios for the United Kingdom - UKCIP02 The Scientific Report proved somewhat difficult. It appears to have been deep-sixed by the establishment, including even the UNIPCC. Lots of dead links. The wayback machine, however, produced one from 2007:

http://web.archive.org/web/20071028054257/http://data.ukcip.org.uk/resources/publications/documents/14.pdf

Here's a quote from it (p8):

The recent rise in temperature cannot be solely due to natural variability of the climate system.

Remember, these documents are projecting climate 100 years in the future. If the models are so competent, it should be unnecessary to change them substantially every 7(?) years. They should withstand the test of time. If they don't it means they were worthless in the first place..

[Billy Liar]

Working link for UKCIP02:

http://tinyurl.com/nb4fee3

or add .pdf to the one in the previous post.

[Derek]

It might be useful for Lord Donoughue to ask a question on this matter, as he seems to get his questions answered eventually.

[DocMartyn]

Models do not make predictions, they make projections.

Models are not fitted to past data, they are tuned using know previous temperatures.

Models are based on fundamental physics of the Earth system, for a non-rotating planet without a phase transition between liquid and solid water.

[Lynn Clark]

Met Office responses sound a lot like the non-responses offered by liberal politicians everywhere. They actively misunderstand questions and instead answer questions that weren't asked. As Steve McIntyre is fond of saying, you have to carefully watch the pea under the pod when their "lips are moving".

[ATheoK]

Chandra, Julia darling! How nice of you to know exactly where to look.

Interesting exchange and absolute waste of time by the Meto. Reminds me of the terrific Abbott and Costello routine "Who's on First"

[amoorhouse]

It is one of those irregular verbs:

I flaw
You logically assert
She assigns an emergent property

[omnologos]

If they get busy during the winter months, does it mean when finally global warming will reach our shores, we can save money by reducing the size of the Met Office workforce?

[Richard Betts]

Bishop Hill

Chandra (Dec 11, 2013 at 1:54 PM) is correct - your statement on what Julia said appears to be inconsistent with what Julia actually said.

To clarify, please can you quote the exact phrase from Julia's letter which you think "acknowledged that HadCM3 could not produce low-sensitivity/low aerosol forcing climates"?

Thanks

Richard

[Bishop Hill]

Richard

"It is certainly the case that versions of HadCM3 with low climate sensitivity and strongly negative aerosol forcing are incompatible with the broad range of observational constraints. 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."

As I understand it, when the climate sensitivity is low, the model takes on strongly negative aerosol forcing. She says that this relationship is an emergent property of the model.

[omnologos]

Richard -the letter is quoted extensively at http://judithcurry.com/2013/09/25/nic-lewis-vs-the-uk-met-office/

[Richard Betts]

BH

Thanks. Exactly which words in this paragraph does this mention "low aerosol forcing"?

NB. "Strongly negative" is opposite to "low" - assuming you are using the standard definition of "low" which means "small in magnitude, irrespective of sign" - Nic Lewis appeared to use this standard definition in his comment (see Figure B.1 and accompanying text).

Strongly negative means large negative numbers.

[Bishop Hill]

Richard

While you are here, perhaps you would like to answer the question about the validity of the projections given that they do not sample low-CS/low AF climates.

Everyone in the Met Office seems to take the view that if they say nothing, somehow everything will turn out right.

[Richard Betts]

BH

Let's get the key point out of the way first! Exactly which words of Julia's mention "low-sensitivity/low aerosol forcing climates"?

Let me answer it for you - they don't. Julia does not say that. If you disagree, please tell me where she says this.

[matthu]

You need to read Julia's statement in the context of Nic Lewis's original letter that she was replying to.

Nic wrote

When significantly lower values for ECS – as suggested by recent observational studies – are obtained, HadCM3′s aerosol forcing takes on highly negative values. The observational data strongly contraindicate aerosol forcing being highly negative, so parameter combinations resulting in significantly reduced model ECS levels (and thus highly negative aerosol forcing) are heavily down-weighted. As a result, whatever the actual level of ECS, HadCM3-derived ECS estimates are bound to be high.

Julia justified this by saying:

"It is certainly the case that versions of HadCM3 with low climate sensitivity and strongly negative aerosol forcing are incompatible with the broad range of observational constraints. 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."

Julia did not dispute the fact that when significantly lower values for ECS – as suggested by recent observational studies – are obtained, HadCM3′s aerosol forcing takes on highly negative values. Instead she tried to justify it.

[Bishop Hill]

Richard

What Matthu said.

[omnologos]

Can we avoid discussing the meaning of LOW please...

Richard - when the climate sensitivity is low, the model takes on strongly negative aerosol forcing - is this true, or false?

[Richard Betts]

There seems to be some misunderstandings here. Julia is saying that on the basis of observations, we can probably rule out the possibility of both climate sensitivity being small and aerosol forcing being large (ie: strongly negative).

If aerosol radiative forcing were strongly negative, the net anthropogenic forcing would be weakly positive (ie: small overall forcing). If climate sensitivity were low (ie: the response to the small +ve forcing is also small) then this would result in a small overall warming.

However, observations show that this has not happened. The observed warming over several decades has been larger than would be expected if net forcing were small and climate sensitivity were small.

[SteveW]

"...When significantly lower values for ECS – as suggested by recent observational studies – are obtained, HadCM3′s aerosol forcing takes on highly negative values..."

So for low values of ECS the model produces what you, Richard, have just affirmed to be an unrealistic set of values for aerosol forcing?

[omnologos]

Richard - as Nic Lewis was talking about ECS and models, are you implying that Julia's answer was not about ECS and models, rather about ECS and observations, iow just another case of the MetOffice refusing to answer by talking about something else?

[rhoda]

[Sorry, I'd like to keep this tightly on topic. Otherwise everyone piles onto Richard, which isn't fair.]

[Nic Lewis]

Richard B

> To clarify, please can you quote the exact phrase from Julia's letter which you think "acknowledged that HadCM3 could not produce low-sensitivity/low aerosol forcing climates"?

Julia is perfectly well aware that HadCM3 cannot produce low-sensitivity/low aerosol forcing climates, and her statement that "the relationship between aerosol forcing and ECS is an emergent property of the detailed physical processes sampled in the PPE simulations" reflects that she does not seek to dispute the fact, but rather to justify it.

Julia has more sense than to try to deny that HadCM3 cannot produce low-sensitivity/low aerosol forcing climates. The Harris et al (2013) paper (the work underlying UKCP09) actually represents aerosol forcing in the HadCM3 Perturbed Physics Ensemble as a mathematical function of climate sensitivity (ECS), in equation S9, and shows the resulting relationship in Figure S2. It makes clear that the HadCM3 PPE can only explore a relatively narrow set of combinations of ECS and aerosol forcing, which excludes low-sensitivity/low aerosol forcing climates.

[Bishop Hill]

Richard

No, no misunderstanding. Everyone seems to agree that low ECS/large negative AF climates don't match observations. Nic's position is that low ECS, small negative AF climates cannot be generated by HadCM3. He has just sent me a graph extracted from the Sexton paper which confirms that this (I'll post as an update to the header post). Slingo does not deny it either. How could she when Sexton confirms it? Instead, as Matthu notes, she seeks to justify it, saying that it is an emergent property of the model.

So we can see that everyone agrees on the central fact, but in Slingo's case we have a sideways acknowledgement rather than a clear statement. In essence then we are arguing whether a sideways acknowledgement is an acknowledgement. This is wordplay.

If you or Prof Slingo wants to issue a clear and unequivocal statement saying that Sexton is wrong and why, and a detailed explanation of how you can get a valid set of predictions without sampling the full CS/AF space then we'd love to hear it.

[Don Keiller]

[Sorry, I'm trying to keep this strictly on topic]

[Paul in Sweden]

[Snip - O/T]

[omnologos]

It seems that "emergent property of the model" means "on the left side of the formula", i.e. they compute the aereosols forcing from ECS rather than the other way around

[Mickey Reno]

...but can you not also build UKCP09 out of stone?

[omnologos]

Upon looking at the FigS2 graph, I have this nagging feeling that the divergent uncertainty bounds are not a plotting or computational error, rather another "emergent property of the model"....emergent, that is, from it being completely useless below the uncertainty's "elbow" points (2.5C upper bound, 3.5C lower bound).

[Richard Betts]

BH

OK, I think we're getting there! We actually agree that the combination of small net forcing and small climate sensitivity is unrealistic. Good! But it turns out that this is not really the point in question anyway.

The point is what to make of Julia's sentence which mentions emergent properties, and what is actually being said and what is being inferred.

To return to what my colleague in the press office wrote to you - he disagrees that the Met Office has "acknowledged [the UKCP09 climate projections contain a major flaw". Looking at what Nic Lewis writes, I think this confirms that the press officer is right to disagree with you.

The use of "acknowledged" makes it sound like something has been unearthed by someone else (e.g. Nic) and that the Met Office agreed with this afterwards. But this is not the case - the relationship between aerosol forcing and climate sensitivity in the model had already been published by the Met Office before Nic even looked at it. So this is hardly "acknowledged" - we said it first!

It then comes down to whether this leads to a "flaw" in UKCP09 or not. Nic is clearly of the opinion that it is, on the basis of his own idea of what combination of climate sensitivity and aerosol forcing are realistic. However, this combination cannot be measured - as I've discussed here previously, climate sensitivity cannot be observed, it can only be estimated using various assumptions. Same goes for aerosol forcing. Nic's has made his own estimates, but the Met Office (and indeed everyone else as far as I am aware) thinks these are unrealistic since the assumptions behind them don't seem to stand up.

So, the issue of this leading to a "flaw" in UKCP09 rest entirely on Nic's opinion.

Therefore the statement "the UKCP09 climate predictions, which the Met Office has acknowledged contain a major flaw." simply is not true. A more correct version would be "Nic Lewis is of the opinion that the published behaviour of HadCM3 is unrealistic, but the Met Office disagrees".

Thanks for talking it through though.

[rhoda]

"If aerosol radiative forcing were strongly negative, the net anthropogenic forcing would be weakly positive (ie: small overall forcing). If climate sensitivity were low (ie: the response to the small +ve forcing is also small) then this would result in a small overall warming."

"OK, I think we're getting there! We actually agree that the combination of small net forcing and small climate sensitivity is unrealistic. Good! But it turns out that this is not really the point in question anyway."

Are we equating anthropogenic forcing with net forcing? That is, are we saying that forcings are anthropogenic by definition and other things affecting the climate are all in some other category? And that aerosol also falls into that anthro bucket?

Are we all sure about that? I seem to recall some recent work about previously unacknowledged sources of natural aerosols.

[omnologos]

Nic Lewis has found a major flaw and the Met Office instead of countering the claim has come up with excuses

[Dolphinlegs]

Thanks for talking it through though.

And that dear friends is meant to be the end of the discussion.

Climate scientists do so love to talk at us!

[Nic Lewis]

Richard

I think you may have misread what BH wrote? In any event, you make some unwarranted statements.

Julia/the Met Office originally claimed that uncertainty in the response of the climate system to CO2 forcing is comprehensively sampled in Harris 2013.

The relationship in the HadCM3 PPE between ECS and aerosol forcing was not mentioned at all in the scientific report relating to the UKCP09 projections. Harris 2013 did mention this relationship, but obscured its importance by pointing out that the aerosol uncertainty distribution was a good match to that in IPCC AR4 and showing that use of an independent-of-ECS aerosol forcing distribution in line with the AR4 one did not change the results very much. The match with the AR4 distribution was based on a highish ECS range, and so is not relevant to sampling the lowish climate sensitivity, lowish aerosol forcing combination. In any case, the AR4 aerosol distribution is nearly 50% more negative than the new AR5 one. Moreover, I pointed out that the use of the independent-of-ECS aerosol forcing distribution came too late in the Harris 2013/ UKCP09 method to overcome the strong relationship in the HadCM3 PPE between ECS and aerosol forcing.

So there is no doubt that the claim by Julia/the Met Office that uncertainty in the response of the climate system to CO2 forcing is comprehensively sampled in Harris 2013 was incorrect.

"Nic is clearly of the opinion that it is, on the basis of his own idea of what combination of climate sensitivity and aerosol forcing are realistic."

No, my opinion is on the basis of what the IPCC AR5 forcing and ocean heat uptake best estimates imply as to the most realistic combinations of climate sensitivity and aerosol forcing. UKCP09 doesn't sample those combinations to any extent.

"Nic's has made his own estimates, but the Met Office (and indeed everyone else as far as I am aware) thinks these are unrealistic since the assumptions behind them don't seem to stand up."

Well, I hope you are going to act as a responsible scientist and back up this allegation about my work with some details, so that I can respond to it properly. Please can you clarify what estimates of mine the Met Office (and everyone else you are aware of) thinks are unrealistic. And what assumptions of mine don't seem to stand up?

[Derrick Byford]

This paper looks as though it will be interesting:

The myopia of imperfect climate models: the case of UKCP09

Frigg, Roman, Smith, Leonard A. and Stainforth, David A. (2014) The myopia of imperfect climate models: the case of UKCP09. Philosophy of science . ISSN 0031-8248 (In Press)

The United Kingdom Climate Impacts Program’s UKCP09 project makes high-resolution forecasts of climate during the 21st century using state of the art global climate models. The aim of this paper is to introduce and analyze the methodology used and then urge some caution. Given the acknowledged systematic errors in all current climate models, treating model outputs as decision relevant probabilistic forecasts can be seriously misleading. This casts doubt on our ability, today, to make trustworthy, high-resolution predictions out to the end of this century.

http://eprints.lse.ac.uk/54818/

David Stainforth attached to the Grantham RI

[Pharos]

Derrick
There's a thread on one of the authors of that paper, Leonard Smith, in the current blog train here

http://www.bishop-hill.net/blog/2013/12/11/on-the-limits-to-climatology.html

[kim]

Richard Betts talks through his hat in an effort to make it palatable.
==========

[Richard Betts]

Hi Nic

Thanks for responding.

For the scientific community’s views on your estimates of climate sensitivity and aerosol forcing, there’s a number of sources I could quote, but let’s go for James Annan’s view. He’s a specialist in climate sensitivity. He is also noted for being sceptical of higher estimates of climate sensitivity, and has been critical of the IPCC, so hopefully we can agree that he’s a fair choice for commenting on your estimates.

On your estimates of climate sensitivity, Annan says:

I have some doubts about Nic Lewis' analysis, as I think some of his choices are dubious and will have acted to underestimate the true sensitivity somewhat. For example, his choice of ocean heat uptake is based on taking a short term trend over a period in which the observed warming is markedly lower than the longer-term multidecadal value. I don't think this is necessarily a deliberate cherry-pick, any more than previous analyses running up to the year 2000 were (the last decade is a natural enough choice to have made) but it does have unfortunate consequences. Irrespective of what one thinks about aerosol forcing, it would be hard to argue that the rate of net forcing increase and/or over-all radiative imbalance has actually dropped markedly in recent years, so any change in net heat uptake can only be reasonably attributed to a bit of natural variability or observational uncertainty.

On your aerosol forcing estimates, he says:

Lewis has also adjusted the aerosol forcing according to his opinion of which values are preferred - concidentally, he comes down on the side of an answer that gives a lower sensitivity. His results might be more reasonable if he had at least explored the sensitivity of his result to the assumptions made. Using the last 30y of ocean heat data and simply adopting the official IPCC forcing values rather than his modified versions (since after all, his main point is to criticise the lack of coherence in the IPCC report itself) would add credibility to his analysis. A still better approach would be to use a model capable of representing the transient change, and fitting it to the entire time series of the various relevant observations.

You could also read IPCC AR5 WG1 Chapter 10 section 10.8.2. I won’t quote it here as it’s too extensive, but similar points are made.

Cheers

Richard

PS. Bishop Hill, thanks for the tight moderation on this thread. It’s important that we have these discussions on the scientific detail, and I appreciate your efforts in facilitating this by avoiding distractions.

[Paul Matthews]

Richard & Julia & The Met Office have decided a priori that the the warming of the 80s and 90s must be attributed to a response to a forcing (their models are too crude and overdamped to allow anything else), and that that forcing must be anthropogenic. So either there has to be low GHG sensitivity and aerosol influence, or both can be larger.
The IPCC seems to be using the same argument, with its figure 10.5 showing high confidence in total anthro influence but lower confidence in its constituent parts. Scientifically this is a ridiculous and backwards argument of course, but it shows have far the climate science community has gone in fooling itself.