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March
14, 2007
TRANSPORTED
BLACK CARBON A SIGNIFICANT PLAYER IN PACIFIC OCEAN CLIMATE
More
than three-quarters of the particulate pollution known as
black carbon transported at high altitudes over the West Coast during
spring is
from Asian sources, according to a research team led by Professor V.
Ramanathan
at Scripps Institution of Oceanography, UC San Diego.
Though
the transported black carbon, most of which is soot, is an
extremely small component of air pollution at land surface levels, the
phenomenon has a significant heating effect on the atmosphere at
altitudes
above two kilometers (6,562 feet).
As
the soot heats the atmosphere, however, it also dims the
surface of the ocean by absorbing solar radiation, said Ramanathan, a
climate
scientist at Scripps, and Odelle Hadley, a graduate student at the
Center for
Atmospheric Sciences at Scripps. The two are lead authors of a research
paper
appearing in the March 14 issue of the Journal of Geophysical
Research.
The
dual effect carries consequences for the Pacific
Ocean region that drives much of Earth’s
climate.
“That’s the primary concern we have with these
aerosols,” said Hadley. “They can
really affect global climate.”
“The soot heating of the atmosphere exceeds the surface
dimming and as a result
the long range transported soot amplifies the global warming due to
increase in
carbon dioxide,” said Ramanathan. “We have to find
out if this amplification is
just restricted to spring time or is happening throughout the
year.”
The researchers found that transported black carbon from Asian sources
is equal
to 77 percent of North American black carbon emissions in the
troposphere
during the spring. In a follow-on study funded by the California Energy
Commission (CEC), Hadley, Ramanathan and fellow Scripps climate
scientist Craig
Corrigan are now studying how much carbon might be incorporated into
precipitation and what the effects on melt rates of Sierra Nevada snowpack could be.
The measure of high black carbon concentration from Asian sources
“is a
startling finding by itself, but its potential importance is magnified
by the
fact that black carbon is believed to have a disproportional impact on
regional
climate,” said Guido Franco, technical lead for climate
change research at the
CEC’s Public Interest Energy Research (PIER) program.
“Fortunately, we have
already started to address this issue with Scripps and more studies are
being
planned.”
The
researchers compared rarely available in-flight data collected
during the spring 2004 Cloud Indirect Effects Experiment (CIFEX), a
component
of which was a series of atmospheric meteorological measurements made
during
flights originating in Eureka,
Calif.
The team combined that information
with data from 30 West Coast meteorological stations and compared it
with
computer predictions made by the Chemical Weather Forecast System
(CFORS).
Transport of Asian black carbon, particulate pollution
generated by
automobile exhaust, agricultural burning and other sources, is heaviest
in
spring when cold Arctic
fronts dip to lower
latitudes and loft warmer air to higher levels in the atmosphere. It is
part of
a worldwide transport of aerosols that sees them remain aloft at high
altitudes
for up to two weeks.
Black carbon concentrations diminish as they move farther away from
their
sources in cities and farmlands in countries such as China
and India.
However, over the Pacific Ocean,
the particles
are in sufficient concentration to have a heating effect on the upper
atmosphere, a prediction based on output from other computer models
besides
CFORS. At the same time, the radiation-absorbing particles dim skies at
the
surface.
On a
regional level, that amount of warming, or positive radiative
forcing, the black carbon causes in the skies over the Pacific is about
40
percent of the forcing that has been attributed to the carbon dioxide
increase
of the last century, said Ramanathan. It likely has measurable effects
on a variety
of other physical and biological conditions in the areas of the Pacific
over
which the particulate pollution passes.
“It was a major surprise,” said Ramanathan,
Hadley’s adviser at Scripps. “When
we came up with the preliminary results, we had to check it and recheck
it.”
Results from Hadley’s study of black carbon’s
snowpack effects are expected by
the end of this year.
Authors of the Journal of Geophysical Research
article besides Hadley
and Ramanathan include Corrigan, Greg Roberts and Guillaume Mauger at
Scripps
Oceanography and Gregory Carmichael and Youhua Tang of the University
of Iowa.
The study was funded by the National Science Foundation, the National
Oceanic
and Atmospheric Administration (NOAA) and the California Energy
Commission.
##
Contact:
Robert
Monroe or Cindy
Clark
University of California-San
Diego
858-534-3624
This text derived from:
http://ucsdnews.ucsd.edu/newsrel/science/03-07Carbon.asp
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