ARLINGTON, Va.—The National Center for Atmospheric Research
(NCAR) in Boulder, Colo., is unveiling a powerful new version of
a supercomputer-based system to model Earth's climate and to
project global temperature rise in coming decades. Scientists
will contribute results to the next assessment by the
Intergovernmental Panel on Climate Change (IPCC), an
international research body that advises policymakers on the
likely impacts of climate change. The system, known as the
Community Climate System Model, version 3 (CCSM3), indicates in a
preliminary finding that global temperatures may rise more than
the previous version had projected if societies continue to emit
large quantities of carbon dioxide into the atmosphere.
NCAR developed the model in collaboration with researchers at
universities and laboratories across the country, with funding
from NSF as well as the Department of Energy, the National
Oceanic and Atmospheric Administration, and the National
Aeronautics and Space Administration. It is releasing the model
results and the underlying computer codes to atmospheric
researchers and other users worldwide.
"The release of CCSM3 marks a significant milestone in
development of climate models," said Jay Fein, director of NSF's
climate dynamics program. "The investment by the NSF, the
Department of Energy and the scientific community is yielding new
insight into the complexities of the Earth system and the likely
responses of our planet to natural and anthropogenic influences."
CCSM3 shows global temperatures could rise by 2.6 degrees Celsius
(4.7 degrees Fahrenheit) in a hypothetical scenario in which
atmospheric levels of carbon dioxide are suddenly doubled. That
is significantly more than the 2 degree Celsius (3.6 degree
Fahrenheit) increase that had been indicated by the preceding
version of the model.
William Collins, an NCAR scientist who oversaw the development of
CCSM3, says researchers have yet to pin down exactly what is
making the model more sensitive to an increased level of carbon
dioxide. But he says the model overall is significantly more
accurate than its predecessor.
"This model makes substantial improvements in simulating
atmospheric, oceanic and terrestrial processes," Collins says.
"It has done remarkably well in reproducing the climate of the
last century, and we're now ready to begin using it to study the
climate of the next century."
As scientists learn more about the atmosphere, the world's most
powerful climate models generally agree about the climatic
effects of carbon dioxide, an important greenhouse gas emitted by
motor vehicles, power plants, and other sources. Observations
show that atmospheric levels of carbon dioxide have increased
from 280 parts per million by volume (ppmv) in preindustrial
times to more than 370 ppmv today, and the increase is
continuing. A doubling of carbon dioxide over present-day levels
would significantly increase global temperatures, according to
all the major models. The models do not always agree, however,
on the complex impacts of clouds, sea ice, and other pieces of
the climate system.
CCSM3 is one of the world's leading general-circulation climate
models, which are extraordinarily sophisticated computer tools
that incorporate phenomena ranging from the effect that volcanic
eruptions have on temperature patterns to the impact of shifting
sea ice on sunlight absorbed by the oceans. Climate models work
by solving mathematical formulas, which represent the chemical
and physical processes that drive Earth's climate, for thousands
of points in the atmosphere, oceans, sea ice, and land surface.
CCSM3 is so complex that it requires about 3 trillion computer
calculations to simulate a single day of global climate.
With CCSM3, scientists were able to add four times as many points
for the land and atmosphere than had existed in the previous
version of CCSM, thereby producing far more information about
regional variations in climate and climate change. The new
version also captures such features as continental land
temperatures and upper atmospheric temperatures far more
accurately than the previous version. In a test,
the model closely simulated changes in global temperatures over
the last century.
In addition to simulating temperatures over the next century,
scientists will use the model to study climate patterns of the
past, such as the peak of the last ice age 21,000 years ago.
They will also use it to probe chemical processes and the cycling
of carbon between the atmosphere, ocean, and land, as well as the
localized impacts of sulfates and other pollutants on climate.