Climate Audit

One of the reasons for my recent focus on Thompson is that he was one of the 20 "wise" [my term] men (and women) who wrote here to the Barton Committee deeply concerned about your approach and expressed their "hope that as a community, we can help your committee shape public policy in the light of the best available scientific knowledge. " Some of their comments bear a little consideration.

I’ve discussed elsewhere Thompson’s non-compliance with elementary data archiving obligations, even though his series are heavily relied on for analysis of climate change. One way that he could help the committee would be to archive his data. The wise men stated:

While the 2001 report of the Intergovernmental Panel on Climate Change (IPCC) highlighted this work as a useful illustration of our understanding of the impact of fossil fuel-related emissions on climate change, in no way does the report suggest that it is an essential element of that understanding.

If the point is that there are other arguments, independent of the Mann hockey stick, as to why people should be concerned about the main issue of the effect of increased CO2 levels on climate – a Roger Pielke Jr position position, then this would be fair enough. But that’s not what they say. IPCC 2001 did not use the Mann hockey stick as a "useful illustration", the phrases "warmest year of the millennium" and "warmest decade of the millennium" were central to IPCC promotion and certainly central to Canadian government promotion. The Mann hockey stick occurs in Figure 1 of the Summary for Policymakers, in Figure 5 of the Technical Summary and again in Figure 2.20 of the running text The hockey stick was figured prominently in the public presentations as shown below (also see von Storch’s PPT). Exactly why the IPCC featured this graphic so prominently if it were inessential to the point that they were making is an interesting question that no one has really addressed.

The wise men go on to say:

However, the essential points of the Mann et al. study.that the late twentieth century likely included the warmest decades in the last millennium.are supported by numerous other studies. We refer the committee to the full reports by the IPCC, the 2001 review of the Third Assessment report by the U.S. National Academy of Sciences, and the June 7 statement from the NAS and other leading science academies for balanced assessments of the current state of the science.

I looked through these references to see whether they support the specific claim about Mann et al., as represented here by the 20 wise men. Note that their characterization of the MBH claim is shaded from the original claims that 1998 was the "warmest year" and the 1990s the "warmest decade".

First, IPCC. I’m not sure that I would describe the IPCC report as independent of the MBH study in that Mann was the lead author discussing his own study. I’ve pointed out that the IPCC stated that the MBH study has significant cross-verification "skill" even though the cross-validation R2 statistic for the controversial 15th century proxies is ~0. If this information was not made available or considered by IPCC, I fail to see how IPCC can be said to have given informed consent to the Mann findings.

Second, the 2001 review of the Third Assessment report by the U.S. National Academy of Sciences is here. The closest that I could find in this report to a discussion of the above issue is the following .

The IPCC report compares the warming of global mean temperature during the 20th century with the amplitude of climate variations over longer time intervals, making use of recent analyses of tree ring measurements from many different sites, data from the Greenland ice cores, and bore hole temperature measurements. On the basis of these analyses, they conclude that the 0.6°C (1.1°F) warming of the Northern Hemisphere during the 20th century is likely to have been the largest of any century in the past thousand years. This result is based on several analyses using a variety of proxy indicators, some with annual resolution and others with less resolved time resolution. The data become relatively sparse prior to 1600, and are subject to uncertainties related to spatial completeness and interpretation making the results somewhat equivocal, e.g., less than 90% confidence. Achieving greater certainty as to the magnitude of climate variations before that time will require more extensive data and analysis.

For what it’s worth, the above statement refers to the amount of change rather than absolute levels, although the two issues are related. More importantly, the above statement as it stands is not a statement specifically endorsing or supporting the MBH claim. It merely states what IPCC said without specifically endorsing or agreeing with it. Maybe they intended to agree with it or think that this implies agreement. But Richard Lindzen was a member of the NAS Committee and I can easily picture circumstances under which he would agree to the above langauge which takes no position; no one can assume from the above that Lindzen acquiesced to MBH. It’s possible that I’ve missed a more exact reference elsewhere in NAS and I will correct this if someone points one out to me.

The June 7 statement from the NAS and other science academies here makes many recommendation to governments. However, I am unable to locate anything in this statement that endorses the MBH claim.

I can see no basis for the 20 wise men suggesting that this statement "supported" MBH. One hopes that the 20 wise men do a better job in their scientific work than they do in writing letters to Barton.