Tuesday, October 31, 2006

A stern review of Stern

Not really stern, more disappointed, but it was too obvious a pun to ignore. I've had a quick look at the climate science bit (the full report is here), and I don't much like what I've seen. He briefly cites our work only to ignore it - I certainly don't blame him personally for this, he can only use what climate scientists tell him and there's no doubt that our work is far from the "consensus" of the peer-reviewed publications in this area. However, it is also evident that the "consensus" is seriously flawed on this point, and it is disappointing that no-one else seems prepared to admit it or even discuss the matter in public.

From my brief glance, it seems like he uses two climate sensitivity distributions, one based on the 1.5-4.5C of Wigley and Raper (drawing on the IPCC TAR) and another higher range based on Murphy et al 2004. While he doesn't go as far as to use some of the rather silly pdfs that have been presented, he's clearly been strongly influenced by them, mentioning a 20% chance of climate sensitivity exceeding 5C a few times. Of course most of the exciting numbers being quoted from his report are those arising from the highest end of the higher range that he uses. I've said before and I'll say it again, it seems quite a hostage to fortune to base policy decisions entirely on stuff that we are all pretty confident will not happen (but merely disagree on the definition of "pretty confident").

Our work has been published for a full 6 months, and a fair number of people working in the field first saw it over a year ago, so there has been plenty of time for some sort of response (I don't necessarily mean a direct comment on it, but rather new publications which take account of the arguments we have presented here and again here). So far, we've only managed to screw out some rather limited comments from Allen and Frame, and that only through the tactic of singling them out for direct criticism. Nevertheless, they have admitted (or perhaps I should say boasted, since they seem to consider it a feature not a bug) that they do not believe the results that they themselves have generated - and note further that this admission is not merely made with reference to the particular GRL paper in question, but is a general comment on the methods they and others have widely used. One IPCC AR4 author has also admitted privately via email that he is "pretty confident that the sensitivity range is 2 to 4 K or smaller" but he's never published anything like that. Come on guys (and girls), it's time to come clean before this mess gets any worse. Just because it's in the forthcoming AR4 doesn't mean you have to defend the "consensus" to the death. At the workshop I attended this summer, someone made the (at the time) amusing comment to the effect that it would be scary what was going on in probabilistic climate prediction, were it not for the fact that it was being ignored by the politicians anyway.

Well, it's no longer being ignored.

On top of the high climate sensitivity range, Stern uses the rather extreme A2 scenario (and essentially describes it as "business as usual") for his projections, even though it is already clear even 5 years on that we are falling behind this emissions pathway. I really think it's time the economists got their act together on this. And then he adds some feedbacks on top, based on results like those of the Hadley Centre model which has an extreme Amazon dieback due to having way too little rainfall in this region even before any global warming is considered. If the Japanese model had this behaviour everyone would just say it's a crap model but because it is HADCM3 it is supposed to be alarming :-) I see RP also has some criticism of the hurricane stuff. FWIW, I don't support him 100% on his general approach (too much "its not proven" and not enough "what is a realistic estimate") but I think he's more right than wrong. Anyway, my main beef is with the probabilistic estimation, because that's what I understand best. It seems crystal clear that the methods are intrinsically faulty - indeed the errors seem rather elementary once they are stated clearly - and it is long past the time that people should have been prepared to accept this and talk about it openly. Nature's comment that our criticisms "apply more generally to a widespread methodological approach" is hardly a valid defence of the science! Stern's results appear to be heavily dependent on the small probability of extremely bad consequences, so these problems may substantially weaken the value of his report. OTOH, it might be the case that even with a climate sensitivity of 2.5C and assuming a more moderate "business as usual" emissions growth, mitigation is still amply justified (personally I think action is justifiable on a number of grounds irrespective of the supposed "climate catastrophe").

I might add some more after reading it more carefully. Or I might just let those conscientious blokes at RealClimate do it better :-)


Anonymous said...

I won't pretend I have read more than fragments of the report, but before you criticize it too much you ought to make sure you understand when Stern talks about climate sensitivity in the technical sense, i.e. the response to a forcing equivalent to a doubling of CO2, and when he talks about the total warming expected from a doubling of CO2 including all feedbacks.

"Several new studies suggest up to a 20% chance that warming could be greater than 5°C."

This seems to refer to the latter number and thus doesn't contradict your results for climate sensitivity.

James Annan said...

Well it's probably also worth my re-emphasising that I haven't checked it all thoroughly either, but it seems clear to me that in Chapter 1 he must be talking about climate sensitivity when he mentions "up to a 20% chance" of sensitivity greater than 5C. The wording on p2 (p1 of the pdf) is perhaps a little ambiguous but the repeat of the same numbers on p9 is surely not.

Anonymous said...

>"He briefly cites our work only to ignore it - I certainly don't blame him personally for this, he can only use what climate scientists tell him and there's no doubt that our work is far from the "consensus" of the peer-reviewed publications in this area. However, it is also evident that the "consensus" is seriously flawed on this point"

I wondered what you would make of the review's citing your work. It appeared to me that it was really only mentioned because it took a different approach. So 'briefly cites' seems reasonable.

I thought it was possible you might criticise

"These studies [Forest et al 2006, Knutti et al 2002, Murphy et al 2004, Stainforth et al 2005, and Annan and Hargreaves 2006] provide an important first attempt to apply a probabilistic framework to climate projections."

more heavily. That a sensitivity estimate isn't really a 'projection' is not terribly significant. I thought you might have a go at saying that only your work is such a first attempt as the others are not using all the lines of evidence available and therefore cannot be viewed as a realistic probabilistic framework.

Maybe you felt that "only to ignore it" covered the situation and you didn't want to go over the same old ground yet again?


jules said...

>Maybe you felt that "only to ignore it" covered the situation and you didn't want to go over the same old ground yet again?

Oh yes, please don't encourage him to go over the same old ground again again! :-)


James Annan said...


What I think that extract illustrates is that your attempted "save" (ie, the explanation that these people were not actually estimating S at all) is a rather strained misreading of what they said and meant :-)

EliRabett said...

I have to say that the graph they used drove me nuts. Do you know if the Meinshausen paper is available on line. I really want to see if the paper simply plop the pdfs down or attempts a critical evaluation of them.

James Annan said...


The whole "Avoiding dangerous climate change" book is available for free here (a surprisingly difficult google to find it, so I'll forgive you). It's a big download but IIRC the Meinshausen paper does indeed simply plop down the pdfs.

That book also contains a paper by all the usual suspect in which they consider the 20th century, LGM, and volcanic evidence separately, and conclude that none of them rules out high sensitivity individually...

EliRabett said...

Thanks. One would hope for better, but that is only a hope. I'll look it up for giggles.

Hank Roberts said...

This is "pretty confident" versus "ugly worried" I think. The closest analogy for the political process is probably the CFC ban. I wonder if there was a 'sensitivity' estimate used in that process.

Anonymous said...

The work of yourself and your colleague will doubtless find publication since it shows a way to restrict rather wide uncertainties. But the Stern report says various things need to be done but yesterday. If the scientists who have been waving a red flag on AGW are correct, then that is what is to be done and none of them have any business at all in now passing over to the defensive and beginning to sound like denialists.
Look at the Nordhaus review of Stern and you will see the game that is shaping up. He is actually trying to seize control of the agenda for the economists for what he calls "...the central questions about global warming policy.. how much, how fast, and how costly..remain open..." he says.
Like bloody hell they do. The central questions of animal ecology (shall we survive, all us animals in our present habitats) depend upon an ecological understanding of what needs be done to sustain us all. Did anyone sit around calculating costs in order to decide whether to build the bomb, in the USA of the early 1940s. Did the Canadian House of Commons call for an economic cost benefit analysis before voting on whether to support England in the Second World War, in 1939? And do you suppose there is any significant number of climate scientists who will decide whether or not to publish articles favoring action or not on AGW based on where the grant money is?
I said any "significant" number.

James Annan said...


I don't object at all to the idea of reducing fossil fuel use. In fact I am sure there are a large number of good practical reasons for it irrespective of climate change, and I also think that we are entitled to make an essentially ethical and moral decision to do so in order to preserve our environment. I am, however, disturbed at the quality of arguments which are commonly put forward as to why climate change is such a big threat. If there really is such a clear-cut case, then why is there so much specious and erroneous argumentation?

Furthermore, the willingness of climate scientists to look away (or even contribute) when distortions are presented, makes for a rather uncomfortable situation for genuine research!