Statistics needed
The Deniers -- Part I
The National Post
Friday, February 02, 2007
Tuesday, November 28, 2006
In the global warming debate, there are essentially two broad camps. One
believes that the science is settled, that global warming is serious and
man-made, and that urgent action must be taken to mitigate or prevent a future
calamity. The other believes that the science is far from settled, that
precious little is known about global warming or its likely effects, and that
prudence dictates more research and caution before intervening massively in the
economy.
The "science is settled" camp, much the larger of the two, includes
many eminent scientists with impressive credentials. But just who are the
global warming skeptics who question the studies from the great majority of
climate scientists and what are their motives?
Many in the "science is settled" camp claim that
the skeptics are untrustworthy -- that they are either cranks or otherwise at
the periphery of their profession, or that they are in the pockets of Exxon or
other corporate interests. The skeptics are increasingly being called Deniers,
a term used by analogy to the Holocaust, to convey the catastrophe that could
befall mankind if action is not taken. Increasingly, too, the press is taking
up the Denier theme, convincing the public that the global-warming debate is
over.
In this, the first of a series, I examine The Deniers, starting with Edward Wegman.
Dr. Wegman is a professor at the Center for Computational Statistics at
Wegman became involved in the global-warming debate after the energy and
commerce committee of the U.S. House of Representatives asked him to assess one
of the hottest debates in the global-warming controversy: the statistical
validity of work by Michael Mann. You may not have heard of Mann or read Mann's
study but you have often heard its famous conclusion: that the temperature
increases that we have been experiencing are "likely to have been the
largest of any century during the past 1,000 years" and that the
"1990s was the warmest decade and 1998 the warmest year" of the
millennium. You may have also heard of Mann's hockey-stick shaped graph, which
showed relatively stable temperatures over most of the last millennium (the
hockey stick's long handle), followed by a sharp increase (the hockey stick's
blade) this century.
Mann's findings were arguably the single most influential study in swaying the
public debate, and in 2001 they became the official view of the International
Panel for Climate Change, the UN body that is organizing the worldwide effort
to combat global warming. But Mann's work also had its critics, particularly
two Canadians, Steve McIntyre and Ross McKitrick, who published peer-reviewed
critiques of their own.
Wegman accepted the energy and commerce committee's assignment, and agreed to
assess the Mann controversy pro bono. He conducted his third-party review by
assembling an expert panel of statisticians, who also agreed to work pro bono.
Wegman also consulted outside statisticians, including the Board of the
American Statistical Association. At its conclusion, the Wegman review entirely
vindicated the Canadian critics and repudiated Mann's work.
"Our committee believes that the assessments that the decade of the 1990s
was the hottest decade in a millennium and that 1998 was the hottest year in a
millennium cannot be supported," Wegman stated, adding that "The
paucity of data in the more remote past makes the hottest-in-a-millennium
claims essentially unverifiable." When Wegman corrected Mann's statistical
mistakes, the hockey stick disappeared.
Wegman found that Mann made a basic error that "may be easily overlooked
by someone not trained in statistical methodology. We note that there is no
evidence that Dr. Mann or any of the other authors in paleoclimate studies have
had significant interactions with mainstream statisticians." Instead, this
small group of climate scientists were working on their own, largely in isolation,
and without the academic scrutiny needed to ferret out false assumptions.
Worse, the problem also applied more generally, to the broader climate-change
and meteorological community, which also relied on statistical techniques in
their studies. "[I]f statistical methods are being used, then
statisticians ought to be funded partners engaged in the research to insure as
best we possibly can that the best quality science is being done," Wegman
recommended, noting that "there are a host of fundamental statistical
questions that beg answers in understanding climate dynamics."
In other words, Wegman believes that much of the climate science that has been
done should be taken with a grain of salt -- although the studies may have been
peer reviewed, the reviewers were often unqualified in statistics. Past
studies, he believes, should be reassessed by competent statisticians and in
future, the climate science world should do better at incorporating statistical
know-how.
One place to start is with the American Meteorological Society, which has a
committee on probability and statistics. "I believe it is amazing for a
committee whose focus is on statistics and probability that of the nine members
only two are also members of the American Statistical Association, the premier
statistical association in the
While Wegman's advice -- to use trained statisticians in studies reliant on
statistics -- may seem too obvious to need stating, the "science is
settled" camp resists it. Mann's hockey-stick graph may be wrong, many
experts now acknowledge, but they assert that he nevertheless came to the right
conclusion.
To which Wegman, and doubtless others who want more rigourous science, shake
their heads in disbelief. As Wegman summed it up to the energy and commerce
committee in later testimony: "I am baffled by the claim that the
incorrect method doesn't matter because the answer is correct anyway. Method
Wrong + Answer Correct = Bad Science." With bad science, only true
believers can assert that they nevertheless obtained the right answer.
LawrenceSolomon@nextcity.com.
- Lawrence Solomon is executive director of Urban Renaissance Institute, a
division of Energy Probe Research Foundation.
THE CV OF A DENIER
Edward Wegman received his Ph.D. degree in mathematical statistics from the