Michael Mann (2002), "Climate Reconstruction: The Value of Multiple Proxies":
Rich Muller emails:
I enjoyed skimming through your discussion of the hockey stick. I was a referee on the National Academy Report on the hockey stick (I am named in their report for this service), and so I am very familiar with what the report actually says. It is frequently misrepresented as "verifying" the hockey stick. That is very inaccurate.
The report concluded that Mann's assertion that there was no medieval warm period was not supported by the data. (Mann really did have an error in his analysis.) The National Academy explicitly concluded that the most we can say about the last 2000 years is that we are now in the warmest period of the last 400 years. They criticized Mann for greatly underestimating his error bars on the data prior to 1600, and they concluded that nothing of value could be concluded for that period.
The fact that we are now in the warmest period of the last 400 years was well known to everybody prior to Mann's work. That is not disputed. What Mann had "shown" was that there was no little ice age -- the cold period preceding the 20th century had extended back 800 -- then 1000 -- then 2000 years. But this conclusion is not valid according to the NAS review.
The NAS review said, in effect, that the hockey stick still exists, but that it extends back only 400 years. That was known in all the earlier IPCC reports. It was the extension to 1000 AD that lead to the dramatic metaphor of the "hockey stick". So some Mann supporters are still defending him. But, in fact, there is nothing left of his publications that is new, or that disagrees with what the IPCC was saying back in 1995.
Mann has defended his work by claiming that the hockey stick is still there when he does the analysis after removing the program bug. But if you read his paper, you discover that the hockey stick component that he is claiming is no longer the principle component of the analysis. (I think it was the 3rd component.) The excitement over his data was largely over the fact that the principal component, typically the only one with small error uncertainties, was hockey stick in shape.
I am also amused to see that I am not considered a climate expert. I did spend over ten years of my life studying climate cycles, the details of the data and methods of analysis. I published a series of papers in Science, Nature, and elsewhere, and wrote a highly respected technical book on climate change titled "Ice Ages and Astronomical Causes." That is not a popular book. As I mentioned earlier, I was chosen by the National Academy of Sciences to be an expert reviewer on their review of Mann's work. Michael Mann, who had a major mathematical error in his published analysis, is considered an expert but I am not? Michael Mann, who has (I believe) not done any experimental work in the field, is considered an expert, but I am not? (I've analyzed Greenland ice cores for their climate record.)
I guess some people pick their experts by looking at the conclusions first, and then eliminating the people who do not agree with them.
I am definitely a believer in the Medieval Warm Period. In a middle ages in which the stone to build Norwich Castle is shipped by sea from France, it makes absolutely no sense to argue that high costs of transport from France made it efficient to grow wine grapes in England if England then had the same climate that England does today or had in the Little Ice Age. And I am definitely not a believer in principal components analyses like those used by Mann et al.--we economists have a religious faith instead in Bayesian Kalman filters.