Hockey Stick again

0 Comments – Welkom bij Natuurwetenschap & Techniek – February 2005

This is a fairly long article by Marcel Crok that has been translated into english. It is full of statistical analysis. It declares that much of the underlining assumptions for the rapid increase in global temperatures is quite flawed from a statistical standpoint. A few points:

They carefully studied the script and found something very unusual. McIntyre:“In a conventional PC calculation in a high-level language, the mean of each series is subtracted from each column prior to the rest of the algorithm. Instead of doing this, Mann’s Fortran program had only subtracted the 1902-1980 mean from each column. This is a highly unusual procedure and had not been mentioned in the Nature article.”

The seemingly small change has major consequences for the end result and explains most of the difference between the graph of McIntyre and McKitrick and the hockey stick for the 15th century. McIntyre:“The effect is that tree ring series with a hockey stick shape no longer have a mean of zero and end up dominating the first principal component (PC1); in effect, Mann’s program mines for series with a hockey stick shape. In the crucial period of 1400-1450, in the critical PC1 of the North American network, the top-weighted Sheep Mountain series, with a hockey stick shape gets over 390 times the weight of the least weighted series, which does not have a hockey stick shape.”

After studying McIntyre’s finding at our request,Von Storch agrees that “simulations with red noise do lead to hockey sticks. McIntyre and McKitrick’s criticism on the hockey stick from 1998 is entirely valid on this particular point.”

We were able to show that the fourteen bristlecone pine series that effectively made up Mann’s PC1 (and six others) had been excluded from the PC calculations in the censored folder.Without the bristlecones sites, there were no hockey sticks for Mann’s method to mine for, and the results came out like ours.The calculations used in Mann’s paper included the controversial bristlecone pine series, which dominate the PC1 and impart the characteristic hockey stick shape to the PC1 and thereafter to the final temperature reconstruction. Mann and his colleagues never reported the results obtained from excluding the bristlecone pines, which were adverse to their claims.”

McIntyre and McKitrick draw far reaching conclusions from their research:“When the IPCC decides to base their policy on such studies, triggering the spending of billions of dollars, there should be more thorough checks.At some point, some one should have done an elementary check on the principal component calculations.This never happened and there is no excuse for this.”

Rob van Dorland of the KNMI has read the article that will appear in Geophysical Research Letters and is convinced it will seriously damage the image of the IPCC.“For now, I will consider it an isolated incident, but it is strange that the climate reconstruction of Mann has passed both peer review rounds of the IPCC without anyone ever really having checked it. I think this issue will be on the agenda of the next IPCC meeting in Peking this May.”

This brings climate research back to square one. McIntyre:“ Our research does not say that the earth’s atmosphere is not getting warmer. But the evidence from this famous study does not allow us to draw any conclusions about its extent, relative to the past thousand years, which remains as much a mystery now as it was before Mann’s article in 1998

You can read the PDF of the article here

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