Science is the process of disciplined dissent. The process of
disciplined dissent relies on evidence — evidence that can force a
change of mind by challenging the consensus that scientists had
earlier achieved.

That’s nowhere more true than in climate science, where the consensus
process used by the Intergovernmental Panel on Climate Change has
been challenging its own, earlier consensus about the speed and
seriousness of what lies ahead.  What climate researchers regarded as
mostly likely in 2001 had been seriously challenged by early 2007,
and it now looks very likely that even the better consensus climate
scientists had reached in the spring of 2007 will be seriously
challenged by new evidence expected to come out in November.

Few groups are as prepared to challenge their own consensus as the
science community is. But scientists saw need of change coming, and
you saw the preview when it was posted to this list in October ’06.

” ‘… the extreme scenarios that tend to fall out of the IPCC
process may be exactly the ones we should most worry about,’ he says.”

“Michael Schlesinger, a climate scientist at the University of
Illinois, Urbana-Champaign, points to another example. ‘Things are
happening right now with the ice sheets that were not predicted to
happen until 2100.'”

SCIENCE www.sciencemag.org
VOL 314    13 OCTOBER 2006


Trying to Lasso Climate Uncertainty

An expert on climate and population looks for a way to help society avoid a
“Wile E. Coyote” catastrophe

LAXENBURG, AUSTRIA – A few weeks ago, Brian O’Neill hunkered down
around a table with a dozen other climate scientists in Cape Town,
South Africa, to talk about the future of the planet. It was no idle
speculation: Whatever they agreed upon – they knew in advance – would
have clout. They were hammering out the final draft of a chapter on
research methods for the massive “Fourth Assessment” of the
Intergovernmental Panel on Climate Change (IPCC). The product of 3
years of consensus-building among several hundred researchers from
around the world, the IPCC report is the scientific bedrock on which
policymakers will negotiate everything from carbon taxes to long-term
greenhouse gas targets.

But for all its authority, the IPCC exercise left O’Neill with a
nagging concern: What were they leaving out? “It’s important that we
climate scientists speak with a single voice,” he said in an
interview back in his office, high up in the attic of a former
Habsburg palace outside Vienna. But “the extreme scenarios that tend
to fall out of the IPCC process may be exactly the ones we should
most worry about,” he says.

O’Neill, a climate scientist at the InternationalInstitute for
Applied Systems Analysis (IIASA) here, is frustrated to see
uncertainties in research used as a reason to delay action. At age
41, he is one of the youngest scientists in the IPCC network trying
to reformulate climate-change projections that can cope better with
uncertainty by accounting for “future learning.” O’Neill hopes the
strategy will make it clear that, even with gaps in understanding, it
pays to act now.

His work is gaining notice. Although an American, O’Neill has scooped
up one of the coveted European Young Investigator Awards (EURYI), a
$1.5 million grant meant in part to keep Europe’s most promising
scientists at home. “He is one of the brightest young scientists out
there, and we’re all watching to see what he does,” says Simon Levin,
an ecologist at Princeton University.

A winding path

O’Neill’s job is to predict the future, but his own career path has
been unpredictable. With 3 years’ training in engineering and a
degree in journalism, he became passionately involved in the 1980s in
efforts to prevent ozone depletion, working for Greenpeace in
California. After collecting a Ph.D. in earth-system sciences from
New York University, he did research stints at Brown University and
the Environmental Defense Fund in New York City. In 2002, he moved to
IIASA, a center for multidisciplinary research founded in 1972. Here,
O’Neill has built up a new program focusing on population and climate
change. The treatment of demographics in most climate-change
analyses, he says, is “simplistic at best.” With the EURYI money,
he’s assembled a team of a half- dozen demographers, economists,
statisticians, and physical scientists to sharpen the models.

A long-limbed basketball player who looks like he could be fresh out
of graduate school, O’Neill seems to peel away layers of uncertainty
as he speaks. His slow-paced answers to questions often begin with a
detailed preamble of assumptions, conditions, and footnotes. But as
the father of two daughters, he says, “thinking about how the world
will be in 50 years is not so abstract for me anymore.”

At IIASA, his work focuses on building realistic demographic
projections, and China has become his main beat. Different
predictions of how the country’s population will age and urbanize —
and how carbon-emission policies will shape Chinese consumption —
have an enormous effect on global climate change scenarios. But
obtaining accurate demographic data has been difficult. With the help
of a Chinese member of his new team, O’Neill has done an analysis
revealing that the IPCC assumptions about China’s rate of
urbanization and energy consumption could be off by a factor of 2.

Learning about learning

Earlier this year, O’Neill organized a unique meeting at IIASA,
bringing together experts from different areas of climate science,
economics, and demography to think about how they generate knowledge.
One of the most important questions that emerged, says Klaus Keller,
a climate scientist at Pennsylvania State University in State
College, is how do you avoid “the Wile E. Coyote effect?” The cartoon
coyote often doesn’t realize he’s falling off a cliff until he looks
down, too late to turn back. One of the potential cliffs in climate
change involves the ocean’s conveyer-belt system — known as the
meridional overturning circulation (MOC) — which prevents a Siberian
chill from spreading across western Europe by carrying warm water
north from the equator. Scientists worry that global warming could
abruptly change or even shut down the MOC. “These are the kind of
climate thresholds that we need to identify,” says Keller.

Scientists need to know more about the natural variability in MOC
behavior, says O’Neill. But they don’t even know “how precise your
measurements have to be” or how large an area must be studied before
uncertainty could be sufficiently reduced to spot “the edge of the
cliff.” He argues that the only way to attack such complex
uncertainties with limited time and resources is to have scientists
from different fields work together, assessing observations over many
years to learn which approaches pay off the most. O’Neill and others
did exactly this with 2 decades of research on the carbon cycle,
finding that some kinds of observations narrowed uncertainty in model
parameters far better than others. Such big-picture,
multidisciplinary studies are low on the priority scaleof funding
agencies, but this is exactly what’s needed if you want “to learn
about the potential of an MOC shutdown,” he says.

The second big question to emerge from the IIASA sessions is how can
we tell if mainstream research is headed in the wrong direction?
O’Neill, Michael Oppenheimer, and Mort Webster, climate scientists at
Princeton and the Massachusetts Institute of Technology in Cambridge,
respectively, use the term “negative learning” to describe cases in
which scientific consensus builds around the wrong model. “This is
what happened with ozone,” says Oppenheimer. People believed that
ozone’s key interactions are with other gases, until scientists
realized that the critical reactions driving ozone depletion occur on
the surfaces of airborne particles. With revised reaction rates, it
was suddenly clear that the planet’s protective ozonelayer was in
much bigger trouble than had been thought. Oppenheimer proposes that
scientists team up with philosophers and historians to find common
signs of negative scientific learning. A search for such red flags
could be built into climate science’s regular review process.

And O’Neill says more funds should be set aside to explore hypotheses
outside the mainstream. Researchers desperately need a strategy for
tackling climate uncertainties, O’Neill says. Michael Schlesinger, a
climate scientist at the University of Illinois, Urbana-Champaign,
points to another example. Polar ice sheets are melting more rapidly
than anticipated, and some observers fear that this could lead to a
catastrophic sea-level increase ( Science , 24 March, p. 1698).
“Things are happening right now with the ice sheets that were not
predicted to happen until 2100,” Schlesinger says. “My worry is that
we may have passed the window of opportunity where learning is still

Whether a catastrophe can be averted using some form of scientific
introspection — or learning about learning, as O’Neill calls it —
remains unclear. The concept, like O’Neill’s career, is still at an
early stage of development.

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