D’Arrigo presented their new study. I went over and introduced myself and said that I thought that their new study was much better than Osborn and Briffa and that it was too bad that they hadn’t received the same publicity. She said – Well, I guess that’s a compliment of sorts. I was trying to be nice, but the compliment was sincere. I missed much of her presentation as I went to a back office at NAS to download some information to edit our own PPT presentation, but a couple of interesting things, including one issue related to Briffa and familiar to readers getting firmly on the table.
I don’t have the exact words here. (I’ll edit it if I get better notes.) But, for certain, D’Arrigo put up a slide about "cherry picking" and then she explained to the panel that that’s what you have to do if you want to make cherry pie. The panel may have been already reeling from the back-pedalling by Alley and Schrag, but I suspect that their jaws had to be re-lifted after this. Hey, it’s old news at climateaudit, but the panel is not so wise in the ways of the Hockey Team. D’Arrigo did not mention to the panel that she, like Mann, was not a statistician, but I think that they already guessed.
I posted up a long time ago – scroll down – about Jacoby’s answer explaining why he would not archive or disclose the other sites besides the 10 most “Å“temperature sensitive” out of 36 that they reported on. But it’s also about making cherry pies. Here’s an excerpt:
If we get a good climatic story from a chronology, we write a paper using it. That is our funded mission. It does not make sense to expend efforts on marginal or poor data and it is a waste of funding agency and taxpayer dollars. The rejected data are set aside and not archived. As we progress through the years from one computer medium to another, the unused data may be neglected. Some [researchers] feel that if you gather enough data and n approaches infinity, all noise will cancel out and a true signal will come through. That is not true. I maintain that one should not add data without signal. It only increases error bars and obscures signal. As an ex- marine I refer to the concept of a few good men. A lesser amount of good data is better without a copious amount of poor data stirred in. Those who feel that somewhere we have the dead sea scrolls or an apocrypha of good dendroclimatic data that they can discover are doomed to disappointment. There is none. Fifteen years is not a delay. It is a time for poorer quality data to be neglected and not archived. Fortunately our improved skills and experience have brought us to a better recent record than the 10 out of 36. I firmly believe we serve funding agencies and taxpayers better by concentrating on analyses and archiving of good data rather than preservation of poor data.
The Divergence Problem
While there’s lots to complain about in D’Arrigo et al , it is both a better and a more candid study than Briffa and Osborn . I had started a post on this a couple of weeks ago, but it got overtaken by getting ready for NAS. You remember about “bring the proxies up to date! Well, D’Arrigo et al. carries proxies up to 1995 in a decent sized network. After 1985, their verification fails, so they go through some contortions to re-calibrate up to 1978 and make some (IMO) unsupportable statements about the relationship between medieval and modern periods, given the out-of-sample failure. But they at least showed the divergence in their graphic (rather than snipping it off a la Briffa). Here’s a graphic from DWJ06 (which D’Arrigo showed.)
The discrepancy between the forecast and the actual caught Cuffey’s eye and he asked D’Arrigo about it. She said “Oh that’s the “Divergence Problem”‘?. Cuffey wanted to know exactly how you could rely on tree ring proxies to register past warm periods if they weren’t picking up modern warmth “questions dear to the heart of any climateaudit reader. D’Arrigo explained that it had all been discussed by Briffa et al. I think that D’Arrigo said that the "divergence problem" only applied to a few sites.
I’ve discussed Briffa’s approch to the "Divergence Problem" before – see for example here – and we modified our presentation to respond to concerns about the "Divergence Problem". First, we showed the following graphic, reporting that the "Divergence Problem" was not limited to a few sites, but applied to an entire network of 387 sites selected to be temperature-sensitive.
Then we presented a graphic showing the following direct quotation from Briffa, "explaining" the Divergence Problem":
In the absence of a substantiated explanation for the decline, we make the assumption that it is likely to be a response to some kind of recent anthropogenic forcing. On the basis of this assumption, the pre-twentieth century part of the reconstructions can be considered to be free from similar events and thus accurately represent past temperature variability.
I’ve been trying to figure out a proper term for Briffa’s explanation – would you agree that it’s a cargo cult explanation of "divergence"?
Also see posts 529, 586.