2011-07-05 22:48:28Another IPCC error? this time in WG1 over climate sensitivity


It looks like another statistical hand waving activity over the McIntyrists inability understand the priors in used in climate science.  But since I'm not a math guy, perhaps we can get an explanation from someone else before this goes viral.  Another IPCC ERROR!!!!!!  CLimate sensitivity over estimated!!!!!


Here's the article by Nic Lewis, at Judith's, of O'Donnell / Steig fame


Here's the relevant section in the IPCC 


Here's Forster/Gregory 06


Here's Frame 05

2011-07-06 02:10:05
Dana Nuccitelli

The way I read it, the IPCC just used a different statistical approach than Forster and Gregory, and slightly changed their probability distribution as a result.  But in the paper, Forster and Gregory found climate sensitivity within the IPCC range, though slightly lower than most studies.  Looks to me like another mountain out of a molehill, but my statistics aren't that strong either.

2011-07-06 02:15:33


I can't imagine how anything too revolutionary can come out of someone reading a paper first published 5 years ago.

2011-07-06 02:35:01


I can say that the set up for that post - IPCC error - or anything of the sort is total bullshit.  Whether or not the use of priors is sufficient is a judgement call, well described in the report and appendices.  Otherwise I have no idea what Lewis is basing his conclusions on.  This was discussed in the review comments in the IPCC, which I pointed out on the Curry thread, and has now made to an update on McIntyre's thread.  Perhaps Lewis' own "priors" on climate science policy decisions is a likely culprit.  

2011-07-09 21:30:10


In case someone missed it, Forster reply @ Curry's site.

2011-07-10 02:51:37
Dana Nuccitelli

I just emailed Forster to see if he'd be intersted in doing a guest post on the subject.

2011-07-10 03:30:03
Julian Brimelow

Dr. James Annan has also weighed in on this, and he agrees that there was no error per se and nothing nefarious going on.  lewis is also behind the times....  

Scientists do not always agree (lots of egos, lots of nit picking), so the fact that they did not all agree is nothing unusual, especially when it is not clear or obvious which approach is best at the time. Also, science advances and they will very likely deal with the issue differently next time round as some progress has been made.  This is yet another storm in a tea cup, fabricated and perpetuated by people who do not understand how science operates.  They are really scraping the bottom of the barrel here....i mean at the nano-scale-- the fact that the results are still robust is not of interest to the "skeptics", all they are concerned with is undermining the credibility of the IPCC by faricating controversy, fabricating doubt and escalating uncertainty.

Some comments by Dr. Annan (from his blog).

"´╗┐From my point of view, the problem is not particularly in the treatment of the Forster and Gregory result - the authors had already in that paper pointed to the choice of prior as an important factor in the specific results they generated. More, the error was in the IPCC's endorsement and rigid adherence to the use of uniform prior, despite the existence of very straightforward arguments that this approach is simply not tenable:

(also here:
http://www.jamstec.go.jp/frsgc/research/d5/jdannan/probrevised.pdf )

These arguments (which as you saw I made during the IPCC review process [here here here]) were basically brushed aside. The IPCC authors exclusively relied on and highlighted the results that had been generated using uniform priors, and downplayed alternative results, which already existed in the literature, that had been generated with different priors.

However, with the passage of time I believe my arguments have now become more widely (if grudgingly) accepted, so I look forward with some interest to see how the IPCC authors deal with the subject this time.

I should also add that I'm not at all convinced by the author's claims that a prior which is uniform in feedback (1/sensitivity) is "correct", rather, it is something that people have to think about, and may reasonably disagree. Such is life. It is theoretically possible that someone could even present a plausible argument for a uniform prior in sensitivity, but I've not yet seen one..."



"Steve, yes it looks to me that Lewis is basically rediscovering something that was well known, and widely accepted as appropriate, at least according to the majority view at the time. I'm not sure they would do the same thing now."




"I think that the scientists working in this area were dead wrong to promote a uniform prior so monomaniacally; I think the IPCC authors emphasised and reinforced this likewise; however given that context, the specific reinterpretation of FG's result was not IMO particularly contentious, especially as FG had themselves alluded to this in the paper (and G was a co-author on the Frame et al paper on which this uniform prior obsession was explicitly codified).

Also: what jules said, though the averaging thing hasn't been part of this particular kerfuffle.

7/7/11 10:27 PM"


2011-07-10 12:10:42
Rob Honeycutt


It never ceases to amaze me the number of comments that Curry gets on any of her posts.

It gets so bad over there that I rarely post there and when I do I post under a pseudonym (Buzz Fledderjohn... from a Tom Waits song of the same name).