Salzer, Hughes et al (PNAS 2009) is in the news. It reports that “unprecedented” high-altitude bristlecone growth, citing increased growth at Sheep Mountain, Mount Washington and Pearl Peak, but especially Sheep Mountain. pdf PNAS SI Salzer SI
CA readers are obviously familiar not just with bristlecones, but with Sheep Mountain. As pointed out in the MM articles, Sheep Mountain was the most important single series in the Mann PC1. Bristlecone chronologies had been introduced by Donald Graybill and arch-skeptic Sherwood Idso as supposed evidence of CO2 fertilization at high latitudes and IPCC 2AR in 1995 included a caveat.
Idso was startled, to say the least, when he learned, as a result of our work, that these chronologies were so influential in MBH.
Indeed, in retrospect, the primary “innovation” of MBH was probably their introduction of these HS-shaped series in temperature reconstructions.
As observed at CA on prior occasions, multiproxy authors quickly became addicted to bristlecone chronologies; the IPCC 2AR caveat was ignored and these chronologies were used in one multiproxy study after another.
Bristlecones were discussed at the NAS panel in 2006, who recommended that strip bark trees (especially bristlecones and foxtails) be “avoided” in temperature reconstructions. This recommendation was totally ignored by paleoclimatologists, who, if anything, actually increased their use of both strip bark chronologies and even Mann’s PC1 as a sort of solidarity against third party criticism. Subsequent to the NAS panel report, strip bark chronologies were applied in Hegerl et al 2006, Juckes et al 2007, Mann et al 2007, Mann et al 2008 and most recently in Tingley and Huybers (submitted).
We discussed bristlecones at considerable length in the MM articles, especially McIntyre and McKitrick 2005b (EE), neither of which is cited by Salzer et al, although the present interest in bristlecones surely owes something to do these articles.
We observed that there were a variety of issues surrounding whether bristlecone chronologies were unique antennae for world climate. In addition to being stressed by cold, Sheep Mountain bristlecones are in an extremely arid environment and subject to more than one stress.
These issues are not canvassed in Salzer et al; instead, they argue that the chronologies are correlated to modeled high-altitude temperature- something that will be discussed on another day.
Today, I want to discuss the chronologies themselves and more particularly the claim highlighted at RC that Salzer had shown that the Graybill-Idso wholebark-stripbark thing was merely a matter of inappropriate standardization.
CA readers are aware that Linah Ababneh’s 2007 Ph D thesis (Hughes was one of her supervisors) was placed online did a major update of the Sheep Mountain bristlecone data and did not replicate the Graybill HS chronology (opposite to Salzer’s result). Ababneh’s Sheep Mountain chronology, as shown in her PhD thesis and Ababneh (Quat Int 2007) did not have an anomalous 20th century. (Needless to say, it was not applied in Team multiproxy reconstructions. For example, Mann et al 2008 continued to use the Graybill chronologies from the 1980s.)
At the AGU 2007 convention in December, I attended a presentation by Malcolm Hughes that, contrary to Ababneh’s results, reported unprecedented bristlecone growth – see the CA discussion here in a post entitled Malcolm Hughes and the Witness Protection Program. This presentation contained the main elements of Salzer et al 2009.
Despite Ababneh’s recent work on bristlecones, Ababneh’s name did not pass Hughes’ lips. Nor did Hughes make any effort to reconcile her results with the opposing results that he presented at AGU.
In my 2007 AGU report, I reported these bizarre events as follows:
Malcolm Hughes coauthor Matthew Salzer) made a presentation entitled “Twentieth Century Bristlecone Pine Tree Rings near Upper Tree Limit Wider than in Recent Millennia”. This included a report on Sheep Mountain. He showed a picture of Matthew Salzer on Sheep Mountain and praised his work. He said that there was no difference between strip bark and whole bark chronologies and showed a graphic up to 2005 with relatively wide recent ring widths. Linah Ababneh’s name did not pass his lips (the Ababneh thesis showing non-nomalous 20th results discussed here, here here), nor did he discuss her work. In Ryan Maue’s felicitous phrase, it was as though she had been put in witness protection. The words “CO2 fertilization” also did not pass his lips in a discussion of possible explanations for the recent behavior.
The situation is no better in Salzer et al. Ababneh is mentioned only in passing, and only as supposed authority in the SI for the assertion that “the divergence in modern period [between strip and whole bark] is clearly a result of the standardization technique used by Graybill and Idso (1)” – an assertion that (see below) is neither justified by the facts of the situation nor by Ababneh’s statements.
This failure to cite and reconcile opposite results is another instance of both shoddy practice by the scientists and all too typical indolent reviewing by senior journals. How could a competent reviewer of this article either be unaware of Ababneh’s contrary results or not require a reconciliation? Another frustrating aspect of this study is its failure to discuss seemingly discordant findings from Millar et al (2006) – findings which were noted in the NAS panel report (though IPCC refused to mention them.) Millar et al had observed subfossil stumps well above present treelines and reported: http://www.climateaudit.org/?p=585
Deadwood tree stems scattered above treeline on tephra-covered slopes of Whitewing Mtn (3051 m) and San Joaquin Ridge (3122 m) show evidence of being killed in an eruption from adjacent Glass Creek Vent, Inyo Craters. Using tree-ring methods, we dated deadwood to 815-1350 CE, and infer from death dates that the eruption occurred in late summer 1350 CE….Using contemporary distributions of the species, we modeled paleoclimate during the time of sympatry [the MWP] to be significantly warmer (+3.2 deg C annual minimum temperature) and slightly drier (-24 mm annual precipitation) than present.
On other occasions, I’ve expressed my view that reconciliation of regional results is something that should be of high priority if this field is to advance and it is disappointing that Salzer didn’t do so.
There are definitely some aspects of Salzer et al that deserve commendation. Like Ababneh, Salzer has updated the Graybill measurement data from the 1980s. Updating of proxies is something that has been urged here for some time but it would have been so much better if Salzer had discussed and reconciled to Ababneh.
Salzer’s article is virtually unprecedented in one respect: Salzer archived measurement data concurrent with publication – perhaps even responding in some measure to CA influence. Full marks to Salzer in this respect. I’ve downloaded the data and re-saved it at CA here .
Less satisfactory is the non-archiving of proper metadata. Information on the exact location of samples, altitudes, exposures and photos are important if one is to independently interpret the results of this sort of study. Pete Holzmann and I (particularly Pete) were able to provide this sort of documentation of our Almagre samples, complete with a detailed online photo inventory of individual trees. It is disappointing that Salzer did not take the opportunity to properly archive the metadata as well.
I’ll comment on several aspects of this paper, but I’ll comment in a little more detail today on one point that attracted attention over at RC, where they relied on a very strange analysis of strip versus whole bark as follows:
One final note: bristlecone pines often have an unusual growth form known as “strip bark morphology” in which annual growth layers are restricted to only parts of a tree’s circumference. Some studies have suggested that such trees be avoided for paleoclimatic purposes, a point repeated in a recent National Academy of Sciences report (Surface temperature reconstructions for the last 2,000 years. NRC, 2006). However Salzer et al’s study shows that there is no significant difference in their results when the data are divided into two classes—strip bark and non-strip-bark cases –when the raw unstandardized data are compared. So that particular issue has apparently had people barking up the wrong tree…
Once again, the folks at RC did not carry out even the most elementary due diligence on Salzer’s claims, which don’t hold up to the simplest scrutiny.
For the record, I’m not sold on claims that bristlecone growth pulses are due to CO2 fertilization as argued by Graybill and Idso. My comments below are directly only at Salzer’s incorrect claim that use of raw unstandardized data resolves anything.
First, here is the original graphic from Graybill and Idso, showing the difference between strip bark and whole bark chronologies at Sheep Mt.
Figure 2 showing Graybill and Idso 1993 Figure 5, Sheep Mt strip bark and whole bark chronologies
Salzer, to his credit, archived the original Graybill measurement data used in the comparison – a mere 16 years after publication. (Hopefully this will inspire Lonnie Thompson.)
Salzer emulated this figure in his Supplementary Figure 4B – which is an extremely muddy graphic, to say the least. I’ve done up a RCS chronology which in this case yields a virtually identical result to the original Graybill-Idso chronology and to the Salzer Figure, as shown below.
Salzer stated that the difference between strip and whole bark chronologies arose from standardization and that comparison “in an appropriate manner” “without artifacts introduced by standardization” leads to “very similar” results:
The apparent divergence of their strip- and whole-bark chronologies from the mid-19th century to the late-20th century is the result of the standardization scheme they used (Fig. S4B). When compared in an appropriate manner, without artifacts introduced by standardization, recent growth rates of strip-bark and whole-bark trees from the same environment are very similar. In light of these results, the suggestion that strip-bark pines should be avoided during analysis of the last 150 years (27) should be reevaluated.
As noted above, their Figure S4, shown below, is extraordinarily muddy. The chronologies shown in the lower panel are a dilated version of the graphic shown above. (I’ll show the corresponding ring width plot below.)
Here is a replot showing their Figure S4 in a non-muddy format. The change from a chronology plot to a plot of average widths is, in this case, a difference without a distinction. In the chronology plot, the difference between the strip bark and whole bark series manifests itself as divergence in the 20th century. In the ring width plot, the difference between the strip bark and whole bark series manifests itself as a divergence in earlier periods.
Going from a standardized chronology to mean width has nothing to do with the price of eggs. The effect arises only from re-centering the series and not because of “inappropriate” standardization.
Interestingly, the differences between centering on the 20th century and centering on the pre-20th century period was discussed at CA here in connection with the difference between the Ababneh version and the Graybill version, where it was noted that if the two series were centered on the long period up to 1900, then there was a divergence in the 20th century; but if they were centered on the 20th century, the divergence was in the earlier period.
Doing the analysis using Graybill and Idso data simply squeezes the balloon, so that the divergence moves from one period to another. The authors have simply deluded themselves into thinking that they “explained” something and RC is too uncritical to notice.
For reference, I’ve posted up pdfs plotting ring width series by tree for all six sites plus the two Graybill-Idso series as http://climateaudit.files.wordpress.com/2009/11/sheep_mt.pdf and similar names, all shown for the 1500-2000 period only and all shown with a common y-scale.