After spending two years and about $5,000 of his own money trying to double-check the influential graphic, Stephen McIntyre says he has found significant oversights and errors. He claims its lead author, climatologist Michael Mann of the University of Virginia, and colleagues used flawed methods that yield meaningless results.
Dr. Mann vigorously disagrees. On a Web site launched with the help of an environmental group (www.realclimate.org1), he has sought to debunk the debunking, and counter what he calls a campaign by fossil-fuel interests to discredit his work. "It's a battle of truth versus disinformation," he says.
But some other scientists are now paying attention to Mr. McIntyre. Although a scientific outsider, the 57-year-old has forced Dr. Mann to publish a minor correction. Now a critique by Mr. McIntyre and an ally is being published in a respected scientific journal. Some mainstream scientists who harbored doubts about the hockey stick say its comeuppance is overdue.
The clash has grown into an all-out battle involving dueling Web logs (www.climateaudit.org2), a powerful senator and a score of other scientists. Mr. McIntyre's new paper is circulating inside energy companies and government agencies. Canada's environment ministry has ordered a review.
Many skeptics contend that liberal environmental agendas are behind alarming global-warming headlines, though often skeptics bring policy agendas of their own. Think tanks backed with funding from the energy industry have waged a wide campaign to cast doubt on key scientific results. "Climate science today is fully politicized," says Roger Pielke Jr., head of the University of Colorado's Center for Science and Technology Policy Research. Mr. McIntyre says he hasn't received any industry funding.
The hockey stick was a highlight of a 2001 report by the U.N.'s Intergovernmental Panel on Climate Change. That is an advisory body through which the world's scientists try to reach consensus on man-made climate change and provide advice on how to limit it. Because the graph showed only minor temperature changes before the industrial age and then an upward slant -- the hockey-stick shape -- it became an oft-cited argument that human activity was raising temperatures.
The problem, says Mr. McIntyre, is that Dr. Mann's mathematical technique in drawing the graph is prone to generating hockey-stick shapes even when applied to random data. Therefore, he argues, it proves nothing.
Statistician Francis Zwiers of Environment Canada, a government agency, says he now agrees that Dr. Mann's statistical method "preferentially produces hockey sticks when there are none in the data." Dr. Zwiers, chief of the Canadian agency's Center for Climate Modeling and Analysis, says he hasn't had time to study Dr. Mann's rebuttals in detail and can't say who is right.
Dr. Mann, while agreeing that his mathematical method tends to find hockey-stick shapes, says this doesn't mean its results in this case are wrong. Indeed, Dr. Mann says he can create the same shape from the climate data using completely different math techniques.