Thanks to Willis Eschenbach for the amusing spoof ‘reconstructed’ photo of Michael Mann.
No doubt many blog readers will be familiar with the infamous ‘Hockey Stick’ graph, which used ‘proxy’ reconstructed temperature data up to 1980, grafted onto Hadley CRU instrumental data. The IPCC liked it so much that it appeared several times in the Third Assessment Report of 2001, thus enhancing the man-made global warming scare. A very different graph was used in the 1995 report, which clearly showed a Medieval Warm Period and the Little Ice Age.
To cut a long story short, Steve McIntyre and Ross McKitrick published critiques of the Michael Mann et al ‘Hockey Stick’ in 2003, which were updated in further publications in 2005 (GRL and E&E), followed in 2006 by a presentation to the National Academy of Sciences Expert Panel, “Surface Temperature Reconstructions for the Past 1,000-2,000 Years.”
Steve McIntyre and Ross McKitrick wrote on the Nature blog:
In their summary of the change in consensus over the hockey stick, von Storch and Zorita (VZ) at first did not mention our work, then, in light of criticism, they dismissed our contributions as minimal and largely irrelevant.
We note with some pride that the NAS took a very different and more favorable view of our work, even crediting us with a revival of research on fundamental methodological issues, saying :
“A second area of criticism focuses on statistical validation and robustness. McIntyre and McKitrick (2003, 2005a,b) question the choice and application of statistical methods, notably principal component analysis; the metric used in the validation step of the reconstruction exercise; and the selection of proxies, especially the bristlecone pine data used in some of the original temperature reconstruction studies. These and other criticisms, explored briefly in the remainder of this chapter, raised concerns that led to new research and ongoing efforts to improve how surface temperature reconstructions are performed. (p.110)”
While we are pleased that some of our observations, in particular, about verification statistics and non-robustness, have attracted academic interest (e.g. from Bürger), it was not our intent to develop methodological innovations or tell paleoclimatologists how to do their job.
Our initial objective was simpler: despite the prominence of the MBH98 reconstruction, no one seemed sure how it was done, and nobody had verified the results. Did the reconstruction possess the claimed “statistical skill”? Did it have the claimed “robustness” to the presence/absence of all dendroclimatic indicators? Had the proxies been “rigorously” selected according to objective criteria?
Notwithstanding claims in the MBH papers (e.g. verification r2 skill as shown in MBH98 Figure 3), we showed the answer was, in every case, No. Early segments of the MBH reconstruction fail verification significance tests, a finding later confirmed by Wahl and Ammann and accepted by the NAS Panel. Far from being “robust” to the presence or absence of all dendroclimatic indicators, we showed that results vanished just by removing the controversial bristlecones, a result also confirmed by Wahl and Ammann and noted by the NAS Panel. We showed that the PC method yielded biased trends, an effect confirmed by the NAS and Wegman panels. We showed that pivotal PC1 was not a valid temperature proxy due to non-climatic contamination in the dominant-weighted proxies (bristlecones, foxtails). Here again the NAS panel concurred, saying that strip-bark bristlecones should not be used in climate reconstructions.
VZ criticize us for supposedly only publishing one peer-reviewed study; however, the IPCC AR4 cites five peer-reviewed studies by us, one of which contains the requested discussion of bristlecones.
While we believe that VZ’s views are unjustified, we believe that they hold them in good faith. Almost uniquely among climate scientists, they have been cordial to us both publicly and privately and we would have no hesitation in requesting either of them as a reviewer. However, we deserve more credit than they give us and we do not agree that their GRL Comment overturned our results.
Steve McIntyre and Ross McKitrick
The NAS Panel said that strip bark trees should be avoided, a policy then disregarded in recent paleoclimate studies (Osborn and Briffa 2006; Hegerl et al 2007; anything by Mann and/or Rutherford; and, of course; Juckes et al 2007).
Now we come to Steve McIntyre’s ‘Little Secret:’
Don’t you think that someone on the Team might have been a little curious as to what bristlecone ring widths have done during the past 25 years? For this, we have the classic excuse of Michael Mann and the Team for not updating bristlecone and proxy records is that it’s not practical within the limited climate budgets:
“While paleoclimatologists are attempting to update many important proxy records to the present, this is a costly, and labor-intensive activity, often requiring expensive field campaigns that involve traveling with heavy equipment to difficult-to-reach locations (such as high-elevation or remote polar sites). For historical reasons, many of the important records were obtained in the 1970s and 1980s and have yet to be updated.”
……..I’ve continued to satirize this failure pointing out that several of Graybill’s classic bristlecone sites were easily accessible from UCAR world headquarters in Boulder and that no heroic expedition was required to update, for example, the Graybill sites to the west of Colorado Springs.
To make a long story short, last summer, when my wife and I visited my sister in Colorado Springs……..
…….Prior to the trip, I obtained a permit from the U.S. Forest Service to take dendrochronological samples from bristlecones on Mount Almagre and we did more than look at pretty views; we obtained up-to-date bristlecone samples. I only went up Almagre on the first day. Our permit lasted a month and Pete and Leslie spent two more days on Almagre, finally locating and sampling tagged Graybill trees on the third day.
Before writing this blog piece, I emailed Steve McIntyre. He replied:
“In one sense, it was just testing that needed to be done, and I stated ahead of time that I would archive the results promptly whatever they showed and would archive them when they became available as opposed to when and if I published an academic article on them. Given the reliance both on strip bark bristlecones/foxtails and secondarily on Graybill’s chronologies (although Graumlich’s foxtails are also used), you’d think that even climate scientists would be curious.
I’m not sure that the results can be said to be “unexpected”. However so far they show that (1) there is a “divergence problem” with the bristlecones; (2) more speculatively, supposedly “anomalous” 20th century bristlecone growth may not be due to CO2 fertilization but actually not exist and merely be an artifact of strip bark selection.”
Read more over at Climate Audit where donations can be made via the ‘Tip Jar’ to help Steve cover the costs of this project:
21st October 2007