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THE HOCKEY STICK REVISITED
December 9, 2009

Posted by: David Lungren David_Lungren@epw.senate.gov

EPW POLICY BEAT: THE HOCKEY STICK REVISITED

"The story behind the hockey stick provides a cautionary tale about the need to recognize the limited function of journal peer review and the dangers of proceeding with major policy decisions without applying a further level of due diligence equivalent to an audit or an engineering study."  Ross McKitrick, "Shattered Consensus: The True State of Global Warming" 

Who is Michael Mann?  In the rarified world of paleo-climatology (the study of climate conditions, including their causes and effects, in the geologic past), he's a big deal.  And now he's at the center of Climategate.  

Mann is an international climate superstar.  He was a "Lead Author" of the Intergovernmental Panel on Climate Change's Third Assessment Report (TAR), and was selected by Scientific American as one of 50 leading "visionaries" in science and technology.  That vision helped produce the infamous "hockey stick" graph, which showed relatively stable temperatures going back to 1000 AD (the shaft), and then a sharp increase beginning in 1900 (the blade).  For some, the conclusion was crystal clear: anthropogenic emissions were causing global warming.  The graph, and Mann himself, received international acclaim, and it was featured prominently in the TAR.  Governments throughout the world relied on Mann's temperature reconstructions to formulate policy.

But that was then-today the hockey stick is broken (more on that below), and Penn State University, Mann's employer, is investigating his role in Climategate.  The Climategate emails seem to suggest that Mann at times was more interested in politics than science. "As we all know," Mann wrote in one email, "this isn't about truth at all, it's about plausibly deniable accusations." The emails also appear to suggest that Mann advocated bullying scientific journals that published work contrary to his own.  "So what do we do about this?" he asked.  "I think we have to stop considering ‘Climate Research' as a legitimate peer-reviewed journal. Perhaps we should encourage our colleagues in the climate research community to no longer submit to, or cite papers in, this journal. We would also need to consider what we tell or request of our more reasonable colleagues who currently sit on the editorial board..."

None of this is surprising.  Back in 2003, Stephen McIntyre, a Canadian mining consultant, and Ross McKitrick, an economics professor at the University of Guelph (Ontario), believed Mann's hockey stick was unsound.  They were right.  After their persistent efforts-Mann refused time and time again to share his underlying data-the empirical basis of the hockey stick melted away.  McIntyre and McKitrick's critique sparked considerable controversy, prompting a review by the National Research Council.  The NRC said Mann's work was "plausible," but it lacked "confidence" in his central claim that temperatures in the 1990s, and 1998 in particular, were "unprecedented":   

"The Research Council committee found the Mann team's conclusion that warming in the last few decades of the 20th century was unprecedented over the last thousand years to be plausible, but it had less confidence that the warming was unprecedented prior to 1600; fewer proxies-in fewer locations-provide temperatures for periods before then. Because of larger uncertainties in temperature reconstructions for decades and individual years, and because not all proxies record temperatures for such short timescales, even less confidence can be placed in the Mann team's conclusions about the 1990s, and 1998 in particular."

Along with the NRC, an independent committee led by Dr. Edward Wegman of George Mason University, and past chair of the NRC's Committee on Applied and Theoretical Statistics, concluded that Mann's hockey stick research was "obscure and incomplete," while the critiques by McIntyre and McKitrick were "valid and compelling." Link to Wegman Report. "Overall," the committee found, "Mann's assessments that the decade of the 1990s was the hottest decade of the millennium and that 1998 was the hottest year of the millennium cannot be supported by his analysis."

Thus, it's no wonder that Mann stubbornly refused to open his books to McIntyre and McKitrick. We found a fascinating account of Mann's obstruction by McKitrick himself in "Shattered Consensus: The True State of Global Warming."  The account is not a flattering one: it shows a scientist who is defensive, arrogant, evasive, and utterly uninterested in transparency, or, for that matter, the scientific method.  Below are highlights from McKitrick's account, with the bold showcasing Mann's obstruction:

A Tale of Obstruction (2003-2004)

"In this case, [McIntyre] found that there were large amounts of missing data and [principal components] calculations wouldn't go through.  In early September 2003, he e-mailed Mann to ask how he had dealt with missing data.  He received no reply." (p. 25)

 "He e-mailed Rutherford [Mann's assistant] about the problem, but Rutherford said that the data were from before his time and that Steve would have to contact Mann himself." (p. 26)

"At lunch, to avoid any possible misunderstandings, we agreed that it was time to send the entire data set to Mann and ask him for confirmation that this was the data actually used in MBH98.  Steve did this.  In reply, Mann said that he was too busy to respond to this or any further inquiries and referred us to a publication by Zorita et. al., who, he said, had had no trouble in replicating his methods." (p. 26)

"In the aftermath of our later E&E publication, we took some flak for not giving MB&H more opportunity ahead of time to address our concerns before our paper was published.  But the fact is that Mann had categorically terminated our correspondence without answering reasonable questions about his methodology and the provenance of the data set...Indeed later, Mann continued to refuse to provide information on his data and methods." (p. 26)

"In the aftermath of publication, the resulting publicity forced Mann to disclose much previously unavailable information, including the location of the vast amount of FTP data unavailable to [McIntyre and McKitrick]."  (p. 28)

"Mann also gave out a new and different URL for the location of the MBH98 data, a URL that was not referred to at Mann's own website or in any public source to that date."  (p. 29)

"Mann's statements were untrue.  Steve had not originally asked for a data file but for an FTP site.  Mann had told him he had forgotten where it was and referred the request to Rutherford.  Rutherford said the data were scattered over several sites, not just one.  Eventually Rutherford gave us a URL at Mann's FTP site, which pointed to a plain text file, not an Excel file..." (p. 29)

"A few days after the publication of MM03, Mann apparently erased the file, removing the evidence of its age, but we had verified the date just before it was deleted.  Now Mann was saying that the ‘right' data were at a different URL, which, despite several previous inquiries, he had never disclosed and we could not have accessed given the information we had to that date." (p. 29)

"We asked Mann for details, but he refused to enlighten us, saying that we should be able to figure it out from his FTP site.  Yet there were hundreds of PC series listed there, many of which were obviously not used."  (p. 31)

"Since Mann had redone his calculations in writing his response, we knew he had the source code at hand.  We asked for it, but Mann refused to send it, or any more information for that matter." (p. 33)

"Needless to say, the first comment in the referee report was that Mann et al. had failed to comply with the supposedly mandatory requirement to supply their data and supporting calculations.  We haven't heard any more about this file."  (p. 34)

"At Mann's FTP site, there is a folder in the NOAMER directory called BACKTO_1400-CENSORED.  You can imagine how intrigued we had been by this folder...Given [Mann's] subsequent furious excoriation and accusations of ‘selective censoring,' we were amused to find results similar to ours lurking on his FTP site in a folder called ‘CENSORED'."  (. 42)

Related:

EPW POLICY BEAT: CLIMATEGATE: WHO, WHAT, WHEN, WHERE

Roger Pielke Jr.: Your Politics are Showing

WSJ: Op-Ed: Climategate: Science Is Dying

Wall Street Journal Editorial: Global Warming With the Lid Off

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