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February
17, 2007 As climate change
scientists
develop ever more sophisticated climate models to project an expected
path of
temperature change, it is becoming increasingly important to include
the
effects of aerosols on clouds, according to Joyce E. Penner, a leading
atmospheric scientist at the That's because
aerosols, fine
particles such as smoke and dust that form droplets in clouds and
change cloud
thickness, affect how much sun is able to pass through the cloud to
Earth, as
well as the amount of moisture that's returned to Earth. Both moisture
and
sunlight play significant roles in climate change. "Think of it as
having two
clouds--one made of cotton and the other of Styrofoam," Penner said.
"More sunlight and moisture will pass through a cloud of cotton as
opposed
to the denser cloud of Styrofoam. This difference is becoming more
critical in
terms of modeling future changes in the climate as we continue to
produce more
and more aerosols that form thicker and thicker clouds." Penner will
present a talk on this topic, "Aerosol-Cloud Interactions and Climate
Projections" during panel at a meeting of the American Association for
the
Advancement of Science in By comparing the
observed
temperature change record since 1850 with two different climate models,
one
that has low climate sensitivity and small amounts of aerosols and one
that has
high climate sensitivity and high amounts of aerosols, Penner's group
showed
that both models follow almost identical predictive paths in the past,
but
diverge significantly when predicting the temperature in the future Penner's
presentation also looks
at the predictive capability of three climate models, a US NCAR-Oslo
model, a
French model and a Japanese model, and shows that differences are
large,
especially when the models predict both aerosols and their cloud
effects in the
assumed level of aerosols at the time, significantly changes the
results. The
differences are large partly because these models do not have high
enough
resolution to reproduce observations. "We know that
aerosol
effects on clouds need to be included in climate models," Penner said,
"but we need more research to reach optimum predictive properties for
climate models."
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