The Wall Street Journal editorial: Hockey Stick Hokum
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.
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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.
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