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December
15, 2006 Just as
overconfidence in a
teenager may lead to unwise acts, overconfidence in projections of
climate
change may lead to inappropriate actions on the parts of governments,
industries and individuals, according to an international team of
climate
researchers. "Climate researchers
often
use a scenario approach," says Dr. Klaus Keller, assistant professor of
geosciences, The
Intergovernmental Panel on
Climate Change, which is in its third round of climate assessment, uses
models
that scenarios of human climate forcing drive. These forcing scenarios
are, the
researchers say, overconfident. "One key question is
which
scenario is likely, which is less likely and which they can neglect for
practical purposes," says Keller who is also affiliated with the Penn
State
Institutes of Energy and the Environment. "At the very least, the
scenarios should span the range of relevant future outcomes. This
relevant
range should also include low-probability, high-impact events." The researchers
provide evidence
that the current practice neglects a sizeable fraction of these low
probability
events and results in biased outcomes. Keller; Louis Miltich, graduate
student;
Alexander Robinson, Penn State research assistant now on a Fulbright
Fellowship
in Berlin, and Richard Tol, senior research officer, Economic and
Social
Research Institute, Dublin, Ireland, developed an Integrated Assessment
Model
to derive probabilistic projections of carbon dioxide emissions on a
century
time scale. Their results extended far beyond the range of previously
published
scenarios, the researchers told attendees today (December 15) at the
fall
meeting of the American Geophysical Union in Noting that
overconfidence is an
often observed effect, Keller cites a study reviewing estimates of the
weight
of an electron as an example. The reported range for the weight of an
electron
from 1955 to the mid-1960s did not include the weight considered
correct today.
On a more closely related topic, the range of energy use projections in
the
1970s typically missed the observed trends. "We need to identify
key
sources of overconfidence and critically reevaluate previous studies,"
says Keller. According to their
study, past
scenarios of carbon dioxide emissions can miss as much as 40 percent of
probabilistic
projection, missing a large number of low-probability events. The
omitted
scenarios may include low-probability, high-impact events. "If low-probability,
high-impact events exist, such as threshold responses of ocean currents
or ice
sheets, omitting these scenarios can lead to poor decision making,"
says
Keller. "We need to see the full range of possible scenarios, because
the
actual outcome may not be contained in the central estimate. "New tools and
faster
computers enable a considerably improved uncertainty analysis," he
adds.
"If you do not tell how likely the probability of a scenario is, people
are left to guess. A sound scientific analysis can at least tell how
consistent
these guesses are with the available observations and simple, but
transparent
assumption."
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