July 14, 2006; Page A12
It is routine these days to read in newspapers or hear -- almost anywhere the subject of climate change comes up -- that the 1990s were the "warmest decade in a millennium" and that 1998 was the warmest year in the last 1,000.
This assertion has become so accepted that it is often recited without qualification, and even without giving a source for the "fact." But a report soon to be released by the House Energy and Commerce Committee by three independent statisticians underlines yet again just how shaky this "consensus" view is, and how recent its vintage.
The claim originates from a 1999 paper by paleoclimatologist Michael Mann. Prior to Mr. Mann's work, the accepted view, as embodied in the U.N.'s 1990 report from the Intergovernmental Panel on Climate Change (IPCC), was that the world had undergone a warming period in the Middle Ages, followed by a mid-millennium cold spell and a subsequent warming period -- the current one. That consensus, as shown in the first of the two IPCC-provided graphs nearby, held that the Medieval warm period was considerably warmer than the present day.
Mr. Mann's 1999 paper eliminated the Medieval warm period from the history books, with the result being the bottom graph you see here. It's a man-made global-warming evangelist's dream, with a nice, steady temperature oscillation that persists for centuries followed by a dramatic climb over the past century. In 2001, the IPCC replaced the first graph with the second in its third report on climate change, and since then it has cropped up all over the place. Al Gore uses it in his movie.
The trouble is that there's no reason to believe that Mr. Mann, or his "hockey stick" graph of global temperature changes, is right. Questions were raised about Mr. Mann's paper almost as soon as it was published. In 2003, two Canadians, Ross McKitrick and Steven McIntyre, published an article in a peer-reviewed journal showing that Mr. Mann's methodology could produce hockey sticks from even random, trendless data.
The report commissioned by the House Energy Committee, due to be released today, backs up and reinforces that conclusion. The three researchers -- Edward J. Wegman of George Mason University, David W. Scott of Rice University and Yasmin H. Said of Johns Hopkins University -- are not climatologists; they're statisticians. Their task was to look at Mr. Mann's methods from a statistical perspective and assess their validity. Their conclusion is that Mr. Mann's papers are plagued by basic statistical errors that call his conclusions into doubt. Further, Professor Wegman's report upholds the finding of Messrs. McIntyre and McKitrick that Mr. Mann's methodology is biased toward producing "hockey stick" shaped graphs.
Mr. Wegman and his co-authors are careful to point out that doubts about temperatures in the early part of the millennium do not call into question more-recent temperature increases. But as you can see looking at these two charts, it's all about context. In the first, the present falls easily within a range of natural historical variation. The bottom chart looks alarming and discontinuous with the past, which is why global-warming alarmists have adopted it so eagerly.
In addition to debunking the hockey stick, Mr. Wegman goes a step further in his report, attempting to answer why Mr. Mann's mistakes were not exposed by his fellow climatologists. Instead, it fell to two outsiders, Messrs. McIntyre and McKitrick, to uncover the errors.
Mr. Wegman brings to bear a technique called social-network analysis to examine the community of climate researchers. His conclusion is that the coterie of most frequently published climatologists is so insular and close-knit that no effective independent review of the work of Mr. Mann is likely. "As analyzed in our social network," Mr. Wegman writes, "there is a tightly knit group of individuals who passionately believe in their thesis." He continues: "However, our perception is that this group has a self-reinforcing feedback mechanism and, moreover, the work has been sufficiently politicized that they can hardly reassess their public positions without losing credibility."
In other words, climate research often more closely resembles a mutual-admiration society than a competitive and open-minded search for scientific knowledge. And Mr. Wegman's social-network graphs suggest that Mr. Mann himself -- and his hockey stick -- is at the center of that network.
Mr. Wegman's report was initially requested by the House Energy Committee because some lawmakers were concerned that major decisions about our economy could be made on the basis of the dubious research embodied in the hockey stick. Some of the more partisan scientists and journalists howled that this was an attempt at intimidation. But as Mr. Wegman's paper shows, Congress was right to worry; his conclusions make "consensus" look more like group-think. And the dismissive reaction of the climate-research establishment to the McIntyre-McKitrick critique of the hockey stick confirms that impression.