Embargoed until 2:00 p.m., EDT
NSF PR 01-58 - July 19, 2001
Media contacts:
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Cheryl Dybas, NSF
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(703) 292-8070
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cdybas@nsf.gov
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Anatta, NCAR
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(303) 497-8604
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anatta@ucar.edu
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Program contact:
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Cliff Jacobs, NSF
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(703) 292-8521
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cjacobs@nsf.gov
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This material is available primarily
for archival purposes. Telephone numbers
or other contact information may be out
of date; please see current contact information
at media
contacts.
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Global 4 to 7 Degree Temperature Rise Likely by
2100
Overwhelming odds point to global average temperatures
that will rise 4 to 7 degrees over the coming century,
according to a new probability analysis by scientists
in the United States and Europe. As early as 2030
the planet is likely to heat up 1 to 2 degrees, say
the scientists. A one-degree temperature rise was
observed over the past century. The study is funded
in part by the National Science Foundation (NSF) and
appears in the July 20 issue of the journal Science.
"We are assigning probabilities to long-term projections
to aid policy makers in assessing the risks that might
accompany various courses of action or non-action,"
says Tom Wigley of the U.S. National Center for Atmospheric
Research (NCAR) in Boulder, Colorado. "If all scenarios
are believed to be equally likely, it’s difficult
to plan." NCAR's primary sponsor is the National Science
Foundation.
"NSF has supported climate research for well over a
decade," adds Cliff Jacobs, program director in NSF’s
division of atmospheric sciences, which funds NCAR.
"Our goal from the beginning has been to improve our
understanding of the Earth's systems and ultimately
provide useable science to society. This study is
another step in that direction."
An estimated global warming range of 2.5 to 10.4 degrees
F was announced earlier this year by the Intergovernmental
Panel on Climate Change (IPCC), composed of hundreds
of scientists around the world. But the likelihood
that the earth’s temperature would warm only 2.5 degrees
or as much as 10.4 degrees is very low, say NCAR’s
Wigley and co-author Sarah Raper of the University
of East Anglia in England and the Alfred Wegener Institut
for Polar and Marine Research in Germany.
Even warming of 4 to 7 degrees F, however, is very
large compared with the observed warming over the
past century, they write. "Whether or not such rapid
warming will occur . . . depends on actions taken
to control climate change," they continue.
In arriving at their estimates, the scientists assumed
that no policies would be implemented to curb climate
change before 2100. If a rapid warming and its expected
impacts occur in the near future, even swift societal
attempts at control would yield little immediate success,
say the authors. “The climate’s inertia would lead
to only a slow response to such efforts and guarantee
that future warming would still be large,” they write.
New estimates of sulfur dioxide and other emissions,
along with updated information on carbon storage,
ocean circulation, radiation, and other components
of the earth system have improved computer models
of the earth’s climate and led the IPCC to both raise
and widen its estimated range of global temperature
increase. The latest range of 2.5 to 10.4 degrees
F is up significantly from the panel’s 1995 estimates
of 1.4 to 6.3 degrees.
In their analysis, Wigley and Raper attempted to interpret
the likelihood of the new estimates, taking into account
wide uncertainty about future human activities and
the climate’s response to them. They identified the
main sources of uncertainty and estimated the probability
of their values falling within defined ranges. They
then used these results to "drive" a simplified climate
model and combined the various model results into
probability ranges for temperature increases.
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