There He Goes Again: Mann Claims His Hockey Stick was Affirmed by the NAS

Spinmeister Michael Mann has fired off a reply to the editor of  a newspaper which published an article critical of his work, again claiming his hockey stick graph, one of the most thoroughly discredited papers of the modern age, was affirmed by the National Academy of Sciences (NAS): 

"...the National Academy of Sciences, affirmed my research findings in an exhaustive independent review published in June 2006 .."

The NAS report did nothing of the sort, and in fact validated all of the significant criticisms of McIntyre &  McKitrick (M&M) and the Wegman Report:


1. The NAS indicated that the hockey stick method systematically underestimated the uncertainties in the data (p. 107).

2. In subtle wording, the NAS agreed with the M&M assertion that the hockey stick had no statistical significance, and was no more informative about the distant past than a table of random numbers. The NAS found that Mann's methods had no validation (CE) skill significantly different from zero. In the past, however, it has always been claimed that the method has a significant nonzero validation skill. Methods without a validation skill are usually considered useless. Mann’s data set does not have enough information to verify its ‘skill’ at resolving the past, and has such wide uncertainty bounds as to be no better than the simple mean of the data (p. 91). M&M said that the appearance of significance was created by ignoring all but one type of test score, thereby failing to quantify all the relevant uncertainties. The NAS agreed (p. 110), but, again, did so in subtle wording.

3. M&M argued that the hockey stick relied for its shape on the inclusion of a small set of invalid proxy data (called bristlecone, or “strip-bark” records). If they are removed, the conclusion that the 20th century is unusually warm compared to the pre-1450 interval is reversed. Hence the conclusion of unique late 20th  century warmth is not robust—in other word it does not hold up under minor variations in data or methods. The NAS panel agreed, saying Mann’s results are “strongly dependent” on the strip-bark data (pp. 106-107), and they went further, warning that strip-bark data should not be used in this type of research (p. 50).

4. The NAS said " Mann et al. used a type of principal component analysis that tends to bias the shape of the reconstructions", i.e. produce hockey sticks from baseball statistics, telephone book numbers, and monte carlo random numbers.

5. The NAS said Mann downplayed the "uncertainties of the published reconstructions...Even less confidence can be placed in the original conclusions by Mann et al. (1999) that ‘the 1990s are likely the warmest decade, and 1998 the warmest year, in at least a millennium.’

Mann never mentions that a subsequent House Energy and Commerce Committee report chaired by Edward Wegman totally destroyed the credibility of the ‘hockey stick’ and devastatingly ripped apart Mann’s methodology as ‘bad mathematics’. Furthermore, when Gerald North, the chairman of the NAS panel -- which Mann claims ‘vindicated him’ – was asked at the House Committee hearings whether or not they agreed with Wegman’s harsh criticisms, he said they did:

CHAIRMAN BARTON: Dr. North, do you dispute the conclusions or the methodology of Dr. Wegman’s report?

DR. NORTH [Head of the NAS panel]: No, we don’t. We don’t disagree with their criticism. In fact, pretty much the same thing is said in our report.

DR. BLOOMFIELD [Head of the Royal Statistical Society]: Our committee reviewed the methodology used by Dr. Mann and his co-workers and we felt that some of the choices they made were inappropriate. We had much the same misgivings about his work that was documented at much greater length by Dr. Wegman.

WALLACE [of the American Statistical Association]: ‘the two reports [Wegman's and NAS] were complementary, and to the extent that they overlapped, the conclusions were quite consistent.’ 

Mann uses the 5 rules of propaganda in his defense, including the rule of orchestration: endlessly repeating the same messages in different variations and combinations [e.g. the NAS gave my hockey stick a clean bill of health].


Sources: M&M, Spectator, Wikipedia, Wattsupwiththat, Foxnews,