- Our research is profiled in the cover story of the Feb. 1, 2005 edition of Natuurwetenschap & Techniek (NWT), a prominent European science magazine. Dutch and English versions of the article will be at www.natutech.nl. NOTE: NWT will make web editions available later. Media representatives may contact NWT (redactie@natutech.nl or +31 20 5310 919) to request copies of the article and accompanying editorials.
- The NWT article is also being published in two parts starting today in the National Post along with a front-page news article discussing our work.
- Our article “Hockey Sticks, Principal Components and Spurious Significance” has been accepted for publication in Geophysical Research Letters, the same journal that published the version of the Mann et al. hockey stick used by the IPCC. A pre-publication version is available here, copyright 2005 American Geophysical Union (doi: 2004GL012750). Further reproduction or electronic distribution is not permitted.
- A second article, “The M&M Critique of the MBH98 Northern Hemisphere Climate Index: Update and Implications”, has been accepted for publication by Energy & Environment and is available here by kind permission of the publisher.
- NWT has reported that the Dutch Organization for Science Research (NOW) and the Dutch National Meteorological Agency (KNMI) have announced plans for a special conference this Spring to assess the implications of our work.
- NWT also quoted Dr. Rob van Dorland, an IPCC Lead Author and climate scientist at the Dutch National Meteorological Agency, as saying it will “seriously damage the image of the IPCC.” He added: “It is strange that the climate reconstruction of Mann 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.”
- The articles show what appears to be a serious computer programming error in the original calculations, affecting a step called principal component analysis (PCA). We showed that the PCA method as used by Mann et al. effectively mines a data set for hockey stick patterns. Even from meaningless random data (red noise), it nearly always produces a hockey stick. Professor Hans von Storch, an IPCC Contributing Author and internationally-renowned expert in climate statistics at the Center for Coastal Research in Geesthacht, Germany, is quoted as saying that our criticism on this point is “entirely valid.” Dr Mia Hubert, a statistician at the Katholieke Universiteit Leuven in Belgium, examined the materials at the request of NWT and agreed with our conclusions, saying: “Tree rings with a hockey stick shape dominate the PCA with this method.”
- The figure above shows 3 simulated PC1s generated by feeding random numbers (red noise) into the Mann et al. algorithm, as well as the MBH98 reconstruction: can you pick out the reconstruction?
- Professor Richard Muller of the University of California at Berkeley examined our work last fall. In an essay published in the MIT Technology Review, he said the findings “hit me like a bombshell, and I suspect it is having the same effect on many others. Suddenly the hockey stick, the poster-child of the global warming community, turns out to be an artifact of poor mathematics.”
- Our GRL article showed that the original study erred in only applying one statistical test for significance. If a second standard test had been also applied, it would have shown that the results lack statistical significance and that the other significance test was calculated incorrectly. Because the results lack statistical significance, contrary to previous understanding, the Mann et al. reconstruction is not usable for claims comparing 20th century climate to earlier periods.
- By tracing the effect of the incorrect PCA method, we found that the distinctive hockey stick shape of MBH98 was simply an imprint of a strong 20th century growth spurt from a small group of bristlecone pine trees in the western USA. But the specialist literature (including papers by Mann, Hughes and others) has not attributed this growth to temperature. The MBH98 reconstruction lacks statistical significance, even when the errors are corrected. Moreover had it been done correctly it would have suggested high early 15th century temperatures, as shown in the Figure below. Contrary to previous understanding, the Mann et al. reconstruction is not usable for claims that the Earth is experiencing unprecedented climate change.
- In our E&E article we showed that the MBH98 reconstruction has high early 15th century values, as shown in the Figure below, after applying two changes: (1) using the archived version of the Gaspé tree ring series rather than the version with ad hoc editing by Mann et al.; (2) using exactly the same number of series as MBH98, but with standard centered PC calculations rather than the data mining method of MBH98. However, neither reconstruction has any statistical significance.
- BACKGROUND MATERIAL: Please see Climate2003.com. It presents a summary of our new papers, a set of FAQs, and a listing of the responses, presented to date by Mann and his colleagues to our analyses. Much of the material in our new papers was first debated between us and MBH during an exchange at Nature magazine. More recently Mann and others have advanced some specific arguments at realclimate.org. We explain their arguments and show how our new papers rebut them.
We have also prepared a pdf version of the "backgrounder", available here.
- The R scripts used in the GRL and E&E papers can be accessed at Steve's web page; also GRL will archive the scripts used for that paper.
- We have also prepared a short explanatory note on PC analysis as it relates to the MBH98 issues.
MEDIA CONTACT:
If you are interested in witing a story on this topic, please begin by reading the papers referred to above and the backgrounder, as the issues are rather technical. For interviews you can contact Steve McIntyre at (647) 287-5425 or email him at stephen.mcintyre@utoronto.ca.
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