Last year I wrote about the controversial McIntyre and McKitrick paper that disproved the fanmous IPCC hockeystick that originated in a couple of papers by Michael Mann. Well, just in time to make Tony Blair happy, Geophysical Research Letters which published the second (1999) Mann paper, has now published McIntyre and McKitrick's devastating rebuttal.
For those who dislike the idea of reading the dense technical science, Canada's National Post reproduced a two part translation of the leadarticle in the Dutch magazine Natuurwetenschap & Techniek (NWT), which is also available in PDF format from the McIntyre and McKitrick website. The appearence in Geo Res Letters does rather blow a hole in the attempts by other climate scientists (such as Stephen Schneider) to discredit the credibility of McIntyre and McKitrick. In this page on his website Schneider writes:
Although Mann and his colleagues were not given the chance to peer review the McIntyre and McKitrick paper, they did immediately prepare a couple of rebuttals, one that was posted on Michael Mann's website, and one that was posted on Quark Soup. Tim Osborn, Keith Briffa, and Phil Jones of the Climatic Research Unit of the University of East Anglia also prepared a rebuttal. The main counter-evidence presented in all four rebuttals is summarized below:
McIntyre and McKitrick selectively censored some important data used by Mann et al. (by either eliminating it completely or substituting other data for it), especially for the period from 1400-1600 AD, where their results deviate most from Mann's. Much of the data censored were key proxy indicators that added to cooling in the fifteenth century.
McIntyre and McKitrick claimed that some of their data omissions/substitutions were due to the fact that not all of the Mann et al. data were available to them. However, Mann says his datasets were actually available online and have been for the last couple years.
McIntyre's and McKitrick's methodology also had technical problems. For example, they used a decomposition based on one surface temperature data set with standardization factors based on a different temperature data set, effectively mashing together two sets of incompatible data.
McIntyre and McKitrick requested a spreadsheet of the Mann et al. (1998) proxy data, and the data they received from one of Mann's colleagues were incorrect. Mann takes the blame for this but also wonders why the authors didn't visit the website containing all the data sets in the first place. This inaccurate data set could explain why McIntyre and McKitrick could not reproduce the Mann et al. (1998) "hockey stick" reconstruction. In addition, the data provided to McIntyre and McKitrick contained only 112 proxy indicator series, whereas Mann's work actually had 159.
Unfortunately as all the evidence gathered by McIntyre and McKitrick, such as the fact that Mann had an entire directory named "BACKTO_1400-CENSORED" which has data showing similar results to those produced by McIntyre and McKitrick, seems to indicate that Mann was indeed sloppy in his statistics and that the fourth accusation - about cherry picking only some of the series is a case of the pot calling the kettle black. As McIntyre says in the NWT article:
“Imagine the irony of this discovery.After we published our findings in Energy and Environment,Mann accused us of selectively deleting North American proxy series.Now it appeared that he had results that were exactly the same as ours, stuffed away in a folder labeled CENSORED.”
Indeed the NWT article is truly devastating. The authors got confirmation from many people who are clearly qualified to comment on particular aspects of the matter under question. For example:
At our request, Dr Mia Hubert of the Katholieke Universiteit Leuven in Belgium, who specializes in robust statistics, checked to see if the Mann’s unusual standardization influenced the climate reconstruction. She confirms:“Tree rings with a hockeystick shape dominate the PCA with this method.”
This is worrying because it seems that Mann's hockey stick and the data series he has used are repeated in numerous "independant" papers, and that many of these have less raw data available to verify whether there is any funny business going on.
At this point, McIntyre has growing doubts about the other studies as well. His initial impression is that they are also dubious. It is almost certain, or so he states, that the other studies have not been checked either. McIntyre:“Mann’s archiving may be unsatisfactory, but other researchers, including Crowley, Lowery,Briffa, Esper, etc, are even worse.After twenty-five emails requesting data, Crowley advised me that he had misplaced his original data and only had a filtered version of his data. Briffa reported the use of 387 tree ring sites, but has not disclosed the sites. Other researchers haven’t archived their data or methods or replied to requests.”
“Mann speaks of independent studies, but they are not independent in any usual sense.Most of the studies involve Mann, Jones,Briffa and/or Bradley. Some datasets are used in nearly every study.Bristlecone pine series look like they affect a number of other studies as well and I plan to determine their exact impact. I’m also concerned about how the proxies are selected. There is a distinct possibility that researchers have either purposefully or subconsciously selected series with the hockey stick shape. .."
As the article concludes, if we are going to try and implement about Kyoto then the IPCC data that it was based upon need to be very very solid. It worries me that climate science has accepted such complex statistical methods apparently without checking and that it has fallen to outsiders, such as McIntyre, McKitrick and Skeptical Environmentalist Bjorn Lomborg to find the faults. One thing that does jump out is that the skeptics are frequently statistcians (Lomborg and McIntyre), presumably true statisticians just look at the maths and the numbers not the meaning behind them when they do their sums.
Intriguingly, the NWT article reports that another paper was published in Science last year - von Storch, H., E. Zorita, J. Jones, Y. Dimitriev, F. González-Rouco, and S. Tett, 2004: Reconstructing past climate from noisy data, Science 306, 679-682, 22 October 2004 (Sciencexpress, doi 10.1126/science.1096109) - which also criticises different parts of the Mann methodology. This is particularly interesting since on of the authors, von Storch, was involved in a bizarre episode where he resigned as Editor-in-Chief of Climate Research in protest at shoddy way Climate Research had published another anti-global warming article. It is heartening that Dr von Storch was willing to stand up for science not politics in both cases, one wonders when Scheider, Mann and the rest will follow suit.