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Saturday, August 21, 2010

DeepClimate eviscerates McShane and Wyner 2010

McShane and Wyner 2010

by DeepClimate, August 19, 2010

Over at ClimateAudit and WUWT they’ve broken out the champagne and are celebrating (once again) the demise, nay, the shattering into 1209 tiny splinters, of the Mann et al. “hockey stick” graph, both the 1998 and 2008 editions. The occasion of all the rejoicing is a new paper by statisticians Blakely McShane and Abraham Wyner, entitled A Statistical Analysis of Multiple Temperature Proxies: Are Reconstructions of Surface Temperatures Over the Last 1000 Years Reliable? [PDF]. The paper, in press at the Annals of Applied Statistics, purports to demonstrate that randomly generated  proxies of various kinds can produce temperature “reconstructions” that perform on validation tests as well as, or even better than,  the actual proxies.

My discussion of McShane and Wyner is divided into two parts. First, I’ll look at the opening background sections. Here we’ll see that the authors have framed the issue in surprisingly political terms, citing a number of popular references not normally found in serious peer-reviewed literature. Similarly, the review of the “scientific literature” relies inordinately on grey literature such as Steve McIntyre and Ross McKitrick’s two Environment and Energy [which cannot be called a real jouranl] articles and the (non peer-reviewed) Wegman report.

Even worse, that review contains numerous substantive errors, some of which appear to have been introduced by a failure to consult cited sources directly, notably in a discussion of a key quote from Edward Wegman himself.

With regard to the technical analysis, I have assumed that McShane and Wyner’s applications of statistical tests and calculations are sound. However, here too, there are numerous problems. The authors’ analysis of the performance of various randomly generated “pseudo proxies” is based on several questionable methodological choices. Not only that, but a close examination of the results shows clear contradictions with the findings in the key reconstruction studies cited. Yet the authors have not even mentioned these contradictions, let alone explained them.

In a late breaking development, Blakeley McShane’s website advises that the paper has been accepted, but that the draft available at the Annals of Applied Statistics (AOAS) is not final. However, the available document does acknowledge the input of two anonymous reviewers as well as that of the AOAS editor Michael Stein (whose purview includes “physical science, computation, engineering, and the environment”). Thus, we can expect the final version to be reasonably close, but not identical, to the one available at the AOAS website. With those caveats in mind, let’s take a closer look.

The AOAS guidelines call for authors to introduce their topic in “as non-technical a manner as possible.” [Well, for Heaven's sake!] After a brief introduction of paleoclimatology concepts, McShane and Wyner have taken this directive to heart and framed the issue in terms not unlike those found on libertarian websites:
On the other hand, the effort of world governments to pass legislation to cut carbon to pre-industrial levels cannot proceed without the consent of the governed and historical reconstructions from paleoclimatological models have indeed proven persuasive and effective at winning the hearts and minds of the populace. … [G]raphs like those in Figures 1, 2, and 3 are
featured prominently not only in official documents like the IPCC report but also in widely viewed television programs (BBC, September 14, 2008), in film (Gore, 2006), and in museum expositions (Rothstein, October 17, 2008), alarming both the populace and policy makers.
After a passing reference to three Wall Street Journal accounts of “climategate,” McShane and Wyner start in on the history of the controversy “as it as it unfolded in the academic and scientific literature.” With a backing citation of all three McIntyre and McKitrick papers (an obvious warning sign), the authors state categorically:
M&M observed that the original Mann et al. (1998) study … used only one principal component of the proxy record.
This is nonsense – the famous PC1 was the leading principal component of one proxy sub-network (North American tree rings) for one period of time (the 1400 step that represents the start of the original MBH98 reconstruction). And even for that sub-network, two PCs were used, not one.

[Readers, there is much more to this in depth deconstruction of a terrible article at the link below.]


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