The Myth of the Climate Change '97%'
What is the origin of the false belief—constantly repeated—that almost all scientists agree about global warming?
May 26, 2014 7:13 p.m. ET
Last week Secretary of State
John Kerry
warned graduating students at Boston College of the "crippling
consequences" of climate change. "Ninety-seven percent of the world's
scientists," he added, "tell us this is urgent."
Where
did Mr. Kerry get the 97% figure? Perhaps from his boss, President
Obama,
who tweeted on May 16 that "Ninety-seven percent of scientists
agree: #climate change is real, man-made and dangerous." Or maybe from
NASA, which posted (in more measured language) on its website,
"Ninety-seven percent of climate scientists agree that climate-warming
trends over the past century are very likely due to human activities."
Yet
the assertion that 97% of scientists believe that climate change is a
man-made, urgent problem is a fiction. The so-called consensus comes
from a handful of surveys and abstract-counting exercises that have been
contradicted by more reliable research.
One frequently cited source for the consensus is a 2004 opinion essay
published in Science magazine by
Naomi Oreskes,
a science historian now at Harvard. She claimed to have examined
abstracts of 928 articles published in scientific journals between 1993
and 2003, and found that 75% supported the view that human activities
are responsible for most of the observed warming over the previous 50
years while none directly dissented.
Ms.
Oreskes's definition of consensus covered "man-made" but left out
"dangerous"—and scores of articles by prominent scientists such as
Richard Lindzen,
John Christy,
Sherwood Idso and
Patrick Michaels,
who question the consensus, were excluded. The methodology is
also flawed. A study published earlier this year in Nature noted that abstracts of academic papers often contain claims that aren't substantiated in the papers.
Getty Images/Imagezoo
Another widely cited source for the consensus view is a 2009 article in
"Eos, Transactions American Geophysical Union" by
Maggie Kendall Zimmerman,
a student at the University of Illinois, and her master's thesis
adviser
Peter Doran.
It reported the results of a two-question online survey of
selected scientists. Mr. Doran and Ms. Zimmerman claimed "97 percent of
climate scientists agree" that global temperatures have risen and that
humans are a significant contributing factor.
The
survey's questions don't reveal much of interest. Most scientists who
are skeptical of catastrophic global warming nevertheless would answer
"yes" to both questions. The survey was silent on whether the human
impact is large enough to constitute a problem. Nor did it include solar
scientists, space scientists, cosmologists, physicists, meteorologists
or astronomers, who are the scientists most likely to be aware of
natural causes of climate change.
The
"97 percent" figure in the Zimmerman/Doran survey represents the views
of only 79 respondents who listed climate science as an area of
expertise and said they published more than half of their recent
peer-reviewed papers on climate change. Seventy-nine scientists—of the
3,146 who responded to the survey—does not a consensus make.
In
2010,
William R. Love Anderegg,
then a student at Stanford University, used Google Scholar to
identify the views of the most prolific writers on climate change. His findings
were published in Proceedings of the National Academies of Sciences.
Mr. Love Anderegg found that 97% to 98% of the 200 most prolific writers
on climate change believe "anthropogenic greenhouse gases have been
responsible for 'most' of the 'unequivocal' warming." There was no
mention of how dangerous this climate change might be; and, of course,
200 researchers out of the thousands who have contributed to the climate
science debate is not evidence of consensus.
In
2013,
John Cook,
an Australia-based blogger, and some of his friends reviewed
abstracts of peer-reviewed papers published from 1991 to 2011. Mr. Cook reported that
97% of those who stated a position explicitly or implicitly suggest
that human activity is responsible for some warming. His findings were
published in Environmental Research Letters.
Mr. Cook's work was quickly debunked. In Science and Education in
August 2013, for example,
David R. Legates
(a professor of geography at the University of Delaware and
former director of its Center for Climatic Research) and three coauthors
reviewed the same papers as did Mr. Cook and found "only 41 papers—0.3
percent of all 11,944 abstracts or 1.0 percent of the 4,014 expressing
an opinion, and not 97.1 percent—had been found to endorse" the claim
that human activity is causing most of the current warming. Elsewhere,
climate scientists including
Craig Idso,
Nicola Scafetta,
Nir J. Shaviv
and Nils-
Axel Morner,
whose research questions the alleged consensus, protested that
Mr. Cook ignored or misrepresented their work.
Rigorous international surveys conducted by German scientists
Dennis Bray
and
Hans von Storch
—most recently published in Environmental Science & Policy
in 2010—have found that most climate scientists disagree with the
consensus on key issues such as the reliability of climate data and
computer models. They do not believe that climate processes such as
cloud formation and precipitation are sufficiently understood to predict
future climate change.
Surveys of
meteorologists repeatedly find a majority oppose the alleged consensus.
Only 39.5% of 1,854 American Meteorological Society members who
responded to a survey in 2012 said man-made global warming is dangerous.
Finally,
the U.N.'s Intergovernmental Panel on Climate Change—which claims to
speak for more than 2,500 scientists—is probably the most frequently
cited source for the consensus. Its latest report claims
that "human interference with the climate system is occurring, and
climate change poses risks for human and natural systems." Yet
relatively few have either written on or reviewed research having to do
with the key question: How much of the temperature increase and other
climate changes observed in the 20th century was caused by man-made
greenhouse-gas emissions? The IPCC lists only 41 authors and editors of
the relevant chapter of the Fifth Assessment Report addressing
"anthropogenic and natural radiative forcing."
Of the various petitions on global warming circulated for signatures by scientists, the one by the Petition Project,
a group of physicists and physical chemists based in La Jolla, Calif.,
has by far the most signatures—more than 31,000 (more than 9,000 with a
Ph.D.). It was most recently published in 2009, and most signers were
added or reaffirmed since 2007. The petition states that "there is no
convincing scientific evidence that human release of . . . carbon
dioxide, methane, or other greenhouse gases is causing or will, in the
foreseeable future, cause catastrophic heating of the Earth's atmosphere
and disruption of the Earth's climate."
We
could go on, but the larger point is plain. There is no basis for the
claim that 97% of scientists believe that man-made climate change is a
dangerous problem.
Mr. Bast is
president of the Heartland Institute. Dr. Spencer is a principal
research scientist for the University of Alabama in Huntsville and the
U.S. Science Team Leader for the Advanced Microwave Scanning Radiometer
on NASA's Aqua satellite.
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