An Op-Ed article in the Wall Street Journal
a month ago claimed that a published study affirming the existence of a
scientific consensus on the reality of global warming had been refuted.
This charge was repeated again last week, in a hearing of the House
Committee on Energy and Commerce.
I am the author of that study, which appeared two years ago in the journal Science, and I'm here to tell you that the consensus stands. The argument put forward in the Wall Street Journal
was based on an Internet posting; it has not appeared in a
peer-reviewed journal — the normal way to challenge an academic
finding. (The Wall Street Journal didn't even get my name right!)
My
study demonstrated that there is no significant disagreement within the
scientific community that the Earth is warming and that human
activities are the principal cause.
Papers
that continue to rehash arguments that have already been addressed and
questions that have already been answered will, of course, be rejected
by scientific journals, and this explains my findings. Not a single
paper in a large sample of peer-reviewed scientific journals between
1993 and 2003 refuted the consensus position, summarized by the
National Academy of Sciences, that "most of the observed warming of the
last 50 years is likely to have been due to the increase in greenhouse
gas concentrations."
Since
the 1950s, scientists have understood that greenhouse gases produced by
burning fossil fuels could have serious effects on Earth's climate.
When the 1980s proved to be the hottest decade on record, and as
predictions of climate models started to come true, scientists
increasingly saw global warming as cause for concern.
In
1988, the World Meteorological Assn. and the United Nations Environment
Program joined forces to create the Intergovernmental Panel on Climate
Change to evaluate the state of climate science as a basis for informed
policy action. The panel has issued three assessments (1990, 1995,
2001), representing the combined expertise of 2,000 scientists from
more than 100 countries, and a fourth report is due out shortly. Its
conclusions — global warming is occurring, humans have a major role in
it — have been ratified by scientists around the world in published
scientific papers, in statements issued by professional scientific
societies, and in reports of the National Academy of Sciences, the
British Royal Society and many other national and royal academies of
science worldwide. Even the Bush administration accepts the fundamental
findings. As President Bush's science advisor, John Marburger III, said
last year in a speech: "The climate is changing; the Earth is warming."
To be sure, there are a handful of scientists, including MIT professor Richard Lindzen, the author of the Wall Street Journal
editorial, who disagree with the rest of the scientific community. To a
historian of science like me, this is not surprising. In any scientific
community, there are always some individuals who simply refuse to
accept new ideas and evidence. This is especially true when the new
evidence strikes at their core beliefs and values.
Earth
scientists long believed that humans were insignificant in comparison
with the vastness of geological time and the power of geophysical
forces. For this reason, many were reluctant to accept that humans had
become a force of nature, and it took decades for the present
understanding to be achieved. Those few who refuse to accept it are not
ignorant, but they are stubborn. They are not unintelligent, but they
are stuck on details that cloud the larger issue. Scientific
communities include tortoises and hares, mavericks and mules.
A
historical example will help to make the point. In the 1920s, the
distinguished Cambridge geophysicist Harold Jeffreys rejected the idea
of continental drift on the grounds of physical impossibility. In the
1950s, geologists and geophysicists began to accumulate overwhelming
evidence of the reality of continental motion, even though the physics
of it was poorly understood. By the late 1960s, the theory of plate
tectonics was on the road to near-universal acceptance.
Yet
Jeffreys, by then Sir Harold, stubbornly refused to accept the new
evidence, repeating his old arguments about the impossibility of the
thing. He was a great man, but he had become a scientific mule. For a
while, journals continued to publish Jeffreys' arguments, but after a
while he had nothing new to say. He died denying plate tectonics. The
scientific debate was over.
So it
is with climate change today. As American geologist Harry Hess said in
the 1960s about plate tectonics, one can quibble about the details, but
the overall picture is clear.
Yet
some climate-change deniers insist that the observed changes might be
natural, perhaps caused by variations in solar irradiance or other
forces we don't yet understand. Perhaps there are other explanations
for the receding glaciers. But "perhaps" is not evidence.
The
greatest scientist of all time, Isaac Newton, warned against this
tendency more than three centuries ago. Writing in "Principia
Mathematica" in 1687, he noted that once scientists had successfully
drawn conclusions by "general induction from phenomena," then those
conclusions had to be held as "accurately or very nearly true
notwithstanding any contrary hypothesis that may be imagined…. "
Climate-change
deniers can imagine all the hypotheses they like, but it will not
change the facts nor "the general induction from the phenomena."
None
of this is to say that there are no uncertainties left — there are
always uncertainties in any live science. Agreeing about the reality
and causes of current global warming is not the same as agreeing about
what will happen in the future. There is continuing debate in the
scientific community over the likely rate of future change: not
"whether" but "how much" and "how soon." And this is precisely why we
need to act today: because the longer we wait, the worse the problem
will become, and the harder it will be to solve.
Naomi Oreskes is a history of science professor at UC San Diego.
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