The purpose of this webpage is to provide supplementary information and comments to ongoing research on the use of proxy information to develop temperature reconstructions.  To date, most of my effort has been in the analysis of the "hockey stick graph" developed by Mann et al. [1998, 1999], which was relied upon by the IPCC to claim that the 1990s were the warmest decade of the millennium. However, I've been examining some of the other major multiproxy studies and hope to comment on them in the future. To contact me: Email: Stephen McIntyre.  I will be posting some comments at the following URL/blog - look there for followup - and feel free to post any views that you may have. I'll try to respond.

www.climateaudit.org

The hyperlinks at left provide a summary chronology for the main documents in this research.  A more complete listing, together with URLs to various archived information is at the URL page. Below we have listed some blog-sites and chatgroups which are commenting on the papers.

Jan. 27, 2005. Three New Articles

We (McIntyre and McKitrick) are profiled in the cover story of the Feb. 1, 2005 edition of Natuurwetenschap & Techniek (NWT), a prominent European science magazine (both Dutch and English versions at www.natutech.nl ). The cover story is based on two new peer-reviewed papers being published in the well-known science journals Geophysical Research Letters and Environment and Energy.  The NWT story has also been published by the National Post in two parts Part 1 and Part 2. See links below. 

Our article “Hockey Sticks, Principal Components and Spurious Significance” has been accepted for publication in Geophysical Research Letters, copyright 2005 American Geophysical Union (doi: 2004GL012750). A pre-publication version is at http://www.climate2003.com/pdfs/2004GL012750.pdf. Further reproduction or electronic distribution is not permitted.

Our 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 at http://www.multi-science.co.uk/mcintyre-mckitrick.pdf.

Our research shows fundamental flaws in the “hockey stick graph” used by the Intergovernmental Panel on Climate Change (IPCC) to argue that the 1990s were the warmest decade of the millennium. The original hockey stick study was published by Michael Mann of the University of Virginia and his coauthors Raymond Bradley and Malcolm Hughes. The main error affects 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.

This “backgrounder” provides a road map and summary of the 3 articles. While these papers have been under review, Mann et al. have opened up their own weblog realclimate.org and criticized some of our earlier work. We have some responses to MBH here on this commentary and some FAQ. Below we have listed some blog-sites and chatgroups which are commenting on the papers.

Natuurwetenschap & Techniek

The NWT article (National Post online Part 1; Part 2) presents a history of our original interest in the problem, proceeding through our first analysis of MBH98 in 2003, the responses by Mann et al., our counter-responses and so on up to the present. In addition, there is an NWT editorial and commentary and a National Post editorial. 

As part of the NWT due diligence for the article, they showed our research to referees of their choosing for detailed assessment.

One was Dr. Rob van Dorland, IPCC Lead Author and climate scientist at the Dutch National Meteorological Agency. In the NWT article he is quoted saying it will “seriously damage the image of the IPCC.” He added: “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.”

Another was Dr Mia Hubert, a statistician at the Katholieke Universiteit Leuven in Belgium. She also agreed with our results, observing: “Tree rings with a hockey stick shape dominate the PCA with this method.” Professor Hans von Storch, an IPCC Contributing Author and internationally-renowned expert in climate statistics at the Institute for Coastal Research in Geesthacht, Germany, concurred, calling McIntyre and McKitrick’s criticism on this point “entirely valid.”

Geophysical Research Letters

Our article, <Hockey Sticks, Principal Components and Spurious Significance > has been accepted for publication in Geophysical Research Letters, copyright 2005 American Geophysical Union (doi: 2004GL012750). Further reproduction or electronic distribution is not permitted. 

This article identifies what is almost certainly a computer programming error in the principal components method used in MBH98. The error causes their PC method to nearly always identify hockey stick shaped series as the “dominant pattern” in a data set (the so-called “first Principal Component” or PC1), even when the data are just random numbers. We carried out 10,000 simulations in which we fed “red noise”, a form of trendless random numbers, into the MBH98 algorithm and, in over 99% of the cases, it produced hockey stick shaped PC1 series. The figure below shows 3 simulated PC1s and the MBH98 reconstruction: can you pick out the reconstruction?

Figure 1. Three simulated PC1s and the MBH98 reconstruction.

The GRL article also examines the statistical significance of the MBH98 reconstruction in the controversial 15th century step. Although the Reduction of Error (RE) statistic is sometimes said to be “preferred” by paleoclimatologists, we show that it is necessary to look at more than one statistic before coming to a conclusion of statistical significance, because these simulated hockey sticks tend to have spuriously high RE statistics when compared to Northern Hemisphere temperatures during the calibration and verification periods of MBH98. The original article reported only one of the usual verification statistics used in paleoclimate studies. Mann et al. have not archived supporting data for this step and have refused to provide supporting calculations for this step. However, we report on emulations of MBH98, which indicate that the R2 and other verification statistics for MBH98 lack statistical significance. Using more accurate benchmarks for the RE statistics under the actual conditions of MBH98, we show that the MBH98 reconstruction lacks statistical significance in its early portion. 

Elsewhere  Mann et al. have insisted that climate reconstructions must pass a number of statistical verification tests or else they should not be considered. Applying that criterion, the MBH98 hockey stick graph should henceforth be considered invalid.

The computer script used to generate the simulations, figures and statistics in the GRL article has been archived with GRL, together with sample hockey stick shaped PC1s. A mirror is located here. 100 sample simulated PC1s are here .  

Energy & Environment

The Energy & Environment article, <The M&M Critique of the MBH98 Northern Hemisphere climate Index: Update and Implications> examines the effect of two methodological changes on the Northern Hemisphere climate index of MBH98: using the version of a Gaspé tree ring series as archived by the originating researchers rather than as emended by MBH; and using a conventional (centered) principal components methodology rather than the nonstandard methodology applied in MBH98. Our emulation methodology fully implements all the details reported in the July 2004 Corrigendum by Mann et al., including the actual steps for their stepwise principal components calculation and the gridcell standard deviations from the (now obsolete) HadCRU data previously unavailable. The result is, as we had found in our 2003 study, relatively high early 15th century values as shown in Figure 2 below.

Figure 2. Northern Hemisphere temperature reconstructions: MBH98 and MM05 emulation of MBH98 using (a) centered principal components; (b) archived version of Gaspé series. Both series smoothed.

The E&E article canvasses various permutations and combinations of methodology now advocated by MBH98 in an attempt to avoid our criticism, showing how slight variations in methodology sometimes lead to high early 15th century results and sometimes to low early 15th century results. For example, the presence or absence of the PC4 in centered calculations determines early 15th century results. We point out that this is inconsistent with MBH98 claims that their method is “robust” to the presence or absence of dendroclimatic indicators.

The common factor in the bifurcation of 15th century temperatures is traced to the effect of bristlecone pines. There is an undoubted growth pulse for a small network of bristlecone pines in the Western USA in the late 19th and 20th centuries, and their ring width “chronologies” thus have a hockey stick shape. While these series represent only a small fraction of the MBH98 data base the resulting hockey stick shape is essentially an imprint of this bristlecone pine growth pulse. If world climate history is held to be uniquely characterized by the growth of bristlecone pines, we think that there should be a clear exposition of all the issues involved. We survey specialist literature on bristlecone pines and show that the original authors of the sites that dominate the MBH98 PC1 stated clearly that the 20th century growth pulse was not due to temperature. Even Mann’s co-author, Hughes, has stated in print that the bristlecone pine growth pulse is a “mystery”.

MBH98 data mining methods resulted in the selection of these hockey stick shaped series into the PC1, thereby ranking them as the “dominant pattern of variability”, whereas they appear in neither the PC1 nor the PC2 under a centered calculation. Regardless of the role of the data mining method, it is important to recognize and fully assess the role of these series in imprinting a hockey stick shape and to completely assess whether they are the correct way of measuring world climate history.

The computer script used to generate the figures and statistics in the E&E here will be located here [in a couple of days].

FAQ

Responses to MBH Comments: this responds to the main points at realclimate.org

Discussions and Comments: these are some that I've noticed

David Appell short comment and forum - David Appell is an arch-supporter of Mann. Discussion is open. Some interesting points.

sci.environment - this is current thread. The archives have much prior discussion. Most of the posters are very pro-Mann, some are quite belligerent and include realclimate coauthor Connolley.

UK Weatherworld - this board has followed the topic for a long time and is quite civil, relatively evenly balanced between supporters and opponents.

Real Climate - peer review #2 - This is Mann's first response comment to our GRL paper. The forum is moderated and only a couple of posts on this topic (neither significant), although other topics are active.

Real Climate - what if? - also a moderated. Discussion of what it means to IPCC if MBH98 is discredited. A preview of the future. Quite a few comments. 

Climatesceptics  - moderated discussion group to which I belong. Not much discussion on our current material. 

Debunkers  - there is ongoing discussion with opposing views - not as active as the other chargroups.

Roy Spencer in Tech Central Station  Forum  - supportive comment; forum comments have little to do with our situation

Lubos Motl - comment by physicist who has excellent grasp of dispute and who's followed it for a while; no blog discussion.

Some discussions at time of Muller article (Oct 2004)

MIT Technology Review Richard Muller article (Oct. 2004)  Forum  - Muller article was very supportive and made a big difference to our reception. It was what interested the Dutch magazine, NWT.

Brothers Judd  - no current postings on the topic. Mostly supportive at the time.

Slashdot  - mostly supportive at the time. Topic inactive.

Tim Lambert  - an arch opponent mostly criticizing unrelated work in which I'm not involved. I haven't seen any substantive criticisms.

William Connolley  - a realclimate.org coauthor and arch-opponent. Currently (Jan. 30, 2005) takes pride in not having read our current material, but nonetheless believes fervently that it is unimportant.

Brad deLong  - another arch opponent. Mostly rhetorical and none of the criticisms are substantive.

Crooked Timber - another very rhetorical arch opponent. 

Citycomfortsblog  - mostly supportive