A Pox On Proxies (When They Are Cherry Picked)

It has been kinda fun watching Steve McIntyre over at Climate Audit pick apart the rather feeble attempts by AGW apparatchiks to defend the "Son of Hockey Stick" tree ring studies. (I blogged about it before here.)

McIntyre's latest effort, though technical is some aspects, is as thorough a take down as I've seen in awhile:

Reader Tom P observed:

If Steve really wants to invalidate the Yamal chronology [ed. i.e. the "Son of Hoickey Stick"] , he would have to find another set of cores that also gave good correlation with the instrument record, but indicated a previous climate comparable or warmer than that seen today.

As bender observed, Tom P's question here is a bit of a slow pitch, since the Polar Urals (the unreported but well-known update) is precisely such a series and since the "Yamal Substitution" (where Briffa 2000 quietly replaced the Polar Urals site with its very pronounced MWP with the HS-shaped Yamal) has been a longstanding concern and issue at Climate Audit.

Just so folks who don't read this stuff normally can follow along, I'll point out that "HS" stands for "Hockey Stick" and MWP stands for "Medieval Warm Period." Since the AGW craze got going in the late 1980's the existence of the MWP, which was quite a bit warmer than anything we have experienced in the last 100 years, was a bit of a problem. For the last 10-15 years or so an effort has been launched to remove the MWP from the books. Furthermore, after serious questions were raised about the original "Hockey Stick" graph purporting to shows current temperatures to be all out of proportion with any known readings in the last few thousand years, there was a desire to find a new "Hockey Stick" which would somehow validate the old "Hockey Stick." The Yamal data seemed to offer the best of both worlds, as it seemed to show both the HS and no MWP. So, it was "bye bye old data" (a data set which showed the MWP and no HS called Polar Urals) and "hello new data"! There was much rejoicing.

Right away, questions were raised about this substitution, and scores of scientists demanded this new data, which was provided quickly, investigated, and found to be robust.

Just kidding.

Here is what actually happened:

Briffa et al (Nature 1995), a paper discussed on many occasions here, used the Polar Urals site (Schweingruber dataset russ021) to argue that the 11th century was cold and, in particular, 1032 was the coldest year of the millennium. A few years later, more material from Polar Urals was crossdated (Schweingruber dataset russ176) and, when this crossdated material is combined with the previous material, a combined RCS [ed. Radar Cross Section] ring width chronology yields an entirely different picture - a warm MWP. Such calculations were done both by Esper (in connection with Esper et al 2002) and for D'Arrigo et al 2006, but the resulting RCS reconstruction was never published nor, as noted previously, has the resulting RCS reconstruction ever appeared in print nor were the resulting RCS reconstructions placed in a digital archive in connection with either publication.

Instead of using and publishing the updated information from Polar Urals, the Yamal chronology was introduced in Briffa 2000 url, a survey article on worldwide dendro activities, in whichBriffa's RCS Yamal chronology replaced the Polar Urals in his Figure 1. Rudimentary information like core counts was not provided. Briffa placed digital versions of these chronologies, including Yamal, online at his own website (not ITRDB). A composite of three Briffa chronologies (Yamal, Taimyr and Tornetrask) had been introduced in Osborn and Briffa (Science 1999), a less than one page letter. Despite the lack of any technical presentation and lack of any information on core counts, as noted elsewhere, this chronology was used in multiproxy study after another and was even separately illustrated in the IPCC AR4 Box 6.4 spaghetti graph.

Authors frequently purport to excuse the re-use of stereotyped proxies on the grounds that there are few millennium-length chronologies, a point made on occasion by Briffa himself. Thus, an updated millennium-length Polar Urals chronology should have been a welcome addition to the literature. But it never happened. Briffa's failure to publish the updated Polar Urals RCS reconstruction has itself added to the bias within the archived information. Subsequent multiproxy collectors could claim that they had examined the "available" data and used what was "available". And because Briffa never published the updated Polar Urals series, it was never "available".

Sure this looks a little odd, but maybe this was really OK because the Yamal series was simply obviously better. That could work, right?

Well, the trouble with that is the Yamal data was also not originally published.

Not that that stopped "scientists" from praising it.

Some claimed Yamal was superior because it was more highly replicated:

The D'Arrigo et al authors believed that Briffa's Yamal chronology was more "highly replicated" than the Polar Urals chronology, a belief that they held even though they did not actually obtain the Yamal data set from Briffa. CA reader Willis Eschenbach at the time asked the obvious question how they knew that this was the "optimal data-set" if they didn't have the data.

First, if you couldn't get the raw data … couldn't that be construed as a clue as to whether you should include the processed results of that mystery data in a scientific paper? It makes the study unreplicable … Second, why was the Yamal data-set "optimal"? You mention it is for "clear statistical reasons" … but since as you say, you could not get the raw data, how on earth did you obtain the clear statistics?

Pretty reasonable questions. The Phil Trans B archive thoroughly refuted the belief that the Yamal data set was more highly replicated than the Polar Urals data set. The graphic below shows the core counts since 800 for the three Briffa et al 2008 data sets (Tornetrask-Finland; Avam-Taimyr and Yamal) plus Polar Urals. Obviously, the replication of the Yamal data set (10 cores in 1990) is far less than the replication of the other two Briffa et al 2008 data sets (both well over 100 in 1990) and also less than Polar Urals since approximately AD1200 and far below Polar Urals in the modern period (an abysmally low 10 cores in 1990 versus 57 cores for Polar Urals. The modern Yamal replication is far below Briffa's own stated protocols for RCS chronologies (see here for example.) This low replication was unknown even to specialists until a couple of weeks ago.

It's strange isn't it?

McIntyre looks at other potential statistical reasons for preferring Yamal to the Polar Ural data.

The Polar Urals chronology has a statistically significant relationship to annual temperature of the corresponding HadCRU/CRUTEM gridcell, while Yamal does not (Polar Urals t-statistic - 3.37; Yamal 0.92). For reference the correlation of the Polar Urals chronology to annual temperature is 0.31 (Yamal: 0.14). Both chronologies have statistically significant relationships to June-July temperature, but the t-statistic for Polar Urals is a bit higher (Polar Urals t-statistic - 5.90; Yamal 4.29; correlations are Polar Urals 0.50; Yamal 0.55). Any practising statistician would take the position that the t-statistic, which takes into consideration the number of measurements, is the relevant measure of statistical significance, a point known since the early 20th century. [emphasis added]

Only in AGW science is less and incomplete data preferred over more complete data.

McIntyre sums it up thusly:

At this point, in the absence of any other explanation holding up, perhaps even critics can look squarely at the possibility that Yamal was preferred over Polar Urals because of its obvious exterior attributes. After all, Rosanne D'Arrigo told an astonished NAS panel: "you need to pick cherries if you want to make cherry pie". Is that what happened here?

...there is no compelling "inner beauty" that would require or even entitle an analyst to select Yamal over Polar Urals. Further, given the known sensitivity of important reconstructions to this decision, the choice should have been clearly articulated for third parties so that they could judge for themselves. Had this been done, IPCC reviewers would have been able to point to these caveats in their Review Comments; because it wasn't done, IPCC Authors rejected valid Review Comments because, in effect, the IPCC Authors themselves had failed to disclose relevant information in their publications.

It is posts like these, with their logical precision and sure footed understanding of the statistics involved, that drive the AGW crowd insane.

And it should. Climate Audit is making them look foolish. No, that is wrong. Climate Audit is merely pointing out that the AGW crowd has made themselves look foolish.