new version of CCSM aids in climate analysis
Scientists studying global climate patterns have
a new and important tool at their disposal: NCARs Community
Climate System Model, version 2 (CCSM-2).
The latest version of the powerful model, unveiled
in the spring, has passed a major test with flying colors with
a hypothetical 1,000 year simulation of Earths climate.
Researchers are now preparing to use the model to simulate 20th-century
climate and to explore what if scenarios, such as
the impact of continuing carbon dioxide emissions on future climate.
CCSM-2 represents a significant improvement
in simulating phenomena with worldwide climate implications, such
as El Niño, says CGDs Jeff Kiehl, who played
a leading role in the models development. Researchers
can use it to study past climate shifts such as the last glacial
maximum, and they can examine the changing atmosphere of the future.
CCSM-2 belongs to the elite group of climate tools
known as general circulation models, which run on some of the
worlds most powerful computers. These models use mathematical
formulas to analyze the climatic impact of the atmosphere, oceans,
Increasingly, they are depicting more subtle natural
features such as the formation of sea ice and the volume of fresh
water deposited into the oceans by major rivers. These models
provide a sort of numerical laboratory for conducting experiments
on Earths climate, since scientists are unable to conduct
actual experiments with the climate system.
None of these models is perfect, both because of
gaps in our understanding of the small-scale processes in the
climate system and because of the limited power of computers.
But CCSM stands apart from the other models in its ability to
simulate 1,000-year of climate without drifting from
real-world conditions and requiring scientists to correctp its
CCSM also is unique because it has been developed
by an unusually broad collaboration of scientists at NCAR, other
national laboratories, andp universities. The underlying computer
code of CCSM is freely available on the Web to researchers worldwide.
Data from the 1,000-year control simulation are also openly available
to the research community. Indeed, NCAR scientists have been refining
global climate models for researchers worldwide since 1983. The
first version of CCSM was released in 1998.
The CCSM effort is a great example of the
trend toward increasing collaboration among research institutions
on complex and important scientific problems. says UCAR
president Rick Anthes.
New and improved
CCSM-2 offers higher resolution than the original
version, and is far more successful in reproducing such phenomena
as the El NiñoSouthern Oscillation and the annual
expansion and contraction of sea ice in polar regions. This
1,000-year run was a real achievement, says CGDs Peter
Gent. He notes that scientists used the original version of CCSM
to model the climate for no more than a 350-year period per run.
Many scientists in CGD have contributed to CCSM-2.
At the 2002 CCSM workshop held in June in Breckenridge, discussion
leaders included Peter (ocean), Gordon Bonan (land), Bill Collins
(atmosphere), Jim Hurrell (climate variability), Bette Otto-Bliesner
(paleoclimatology), and Jerry Meehl and Warren Washington (climate
change and assessment). SCDs Cecelia DeLuca co-leads a working
group on software engineering.
The next step
Now that CCSM-2 has proved its worth by simulating
many natural modes of climate variability, researchers will use
it to probe past and future climate shifts.
For example, the model will peer back in time to
replicate conditions during the last glacial maximum, a time about
18,000 years ago when much of North America and Europe lay under
vast sheets of ice and the atmosphere contained far less carbon
dioxide than it does today. CCSM-2 also can help researchers understand
other climate shifts, such as the correlation between the North
Atlantic Oscillation (a see-saw in atmospheric pressure) and the
Little Ice Age that cooled temperatures during the 17th, 18th,
and early 19th centuries.
Looking to the future, CCSM-2 likely play an integral
role in the fourth of the major climate assessments issued every
few years by the Intergovernmental Panel on Climate Change.
And the models increased capabilities will
permit new types of studies, such as the Flying Leap
experiment. This multi-institutional, multiyear effort will track
fossil fuel carbon emissions as they are dissolved in the oceans,
processed by the terrestrial ecosystem, and subsequently released
back into the atmosphere.
But scientists note that, even with the latest
version, CCSM lacks the power to capture all the subtle forces
that affect world climate. For example, the model does not yet
include active chemistry or capture fine-scale ocean processes.
Far from stopping at version 2, scientists are working toward
future versions that will offer much more detail, possibly even
enabling researchers to make climate predictions for specific
Nature is inherently complex, and our models
will inevitably evolve in their complexity to more realistically
represent Earths climate system, Jeff explains. David
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