Public release date: 23-Mar-2008
University of California – San Diego
Contact: Rob Monroe, Mario Aguilera
Black carbon pollution emerges as major player in global warming
Soot from biomass burning, diesel exhaust has 60 percent of the
effect of carbon dioxide on warming but mitigation offers immediate
Black carbon, a form of particulate air pollution most often produced
from biomass burning, cooking with solid fuels and diesel exhaust,
has a warming effect in the atmosphere three to four times greater
than prevailing estimates, according to scientists in an upcoming
review article in the journal Nature Geoscience.
Scripps Institution of Oceanography at UC San Diego atmospheric
scientist V. Ramanathan and University of Iowa chemical engineer Greg
Carmichael, said that soot and other forms of black carbon could have
as much as 60 percent of the current global warming effect of carbon
dioxide, more than that of any greenhouse gas besides CO2. The
researchers also noted, however, that mitigation would have immediate
societal benefits in addition to the long term effect of reducing
greenhouse gas emissions.
The article, “Global and regional climate changes due to black
carbon,” will be posted in the online version of Nature Geoscience on
Sunday, March 23.
“Observationally based studies such as ours are converging on the
same large magnitude of black carbon heating as modeling studies fromStanford, Caltech and NASA,” said Ramanathan. “We now have to examine
if black carbon is also having a large role in the retreat of arctic
sea ice and Himalayan glaciers as suggested by recent studies.”
In the paper, Ramanathan and Carmichael integrated observed data from
satellites, aircraft and surface instruments about the warming effect
of black carbon and found that its forcing, or warming effect in the
atmosphere, is about 0.9 watts per meter squared. That compares to
estimates of between 0.2 watts per meter squared and 0.4 watts per
meter squared that were agreed upon as a consensus estimate in a
report released last year by the Intergovernmental Panel on Climate
Change (IPCC), a U.N.-sponsored agency that periodically synthesizes
the body of climate change research.
Ramanathan and Carmichael said the conservative estimates are based
on widely used computer model simulations that do not take into
account the amplification of black carbon’s warming effect when mixed
with other aerosols such as sulfates. The models also do not
adequately represent the full range of altitudes at which the warming
effect occurs. The most recent observations, in contrast, have found
significant black carbon warming effects at altitudes in the range of
2 kilometers (6,500 feet), levels at which black carbon particles
absorb not only sunlight but also solar energy reflected by clouds at
Between 25 and 35 percent of black carbon in the global atmosphere
comes from China and India, emitted from the burning of wood and cow
dung in household cooking and through the use of coal to heat homes.
Countries in Europe and elsewhere that rely heavily on diesel fuel
for transportation also contribute large amounts.
“Per capita emissions of black carbon from the United States and some
European countries are still comparable to those from south Asia and
east Asia,” Ramanathan said.
In south Asia, pollution often forms a prevalent brownish haze that
has been termed the “atmospheric brown cloud.” Ramanathan’s previous
research has indicated that the warming effects of this smog appear
to be accelerating the melt of Himalayan glaciers that provide
billions of people throughout Asia with drinking water. In addition,
the inhalation of smoke during indoor cooking has been linked to the
deaths of an estimated 400,000 women and children in south and east
Elimination of black carbon, a contributor to global warming and a
public health hazard, offers a nearly instant return on investment,
the researchers said. Black carbon particles only remain airborne for
weeks at most compared to carbon dioxide, which remains in the
atmosphere for more than a century. In addition, technology that
could substantially reduce black carbon emissions already exists in
the form of commercially available products.
Ramanathan said that an observation program for which he is currently
seeking corporate sponsorship could dramatically illustrate the
benefits. Known as Project Surya, the proposed venture would provide
some 20,000 rural Indian households with smoke-free cookers and
equipped to transmit data. At the same time, a team of researchers
led by Ramanathan would observe air pollution levels in the region to
measure the effect of the cookers.
Carmichael said he hopes that the paper’s presentation of the
immediacy of the benefits will make it easier to generate political
and regulatory momentum toward reduction of black carbon emissions.
“It offers a chance to get better traction for implementing
strategies for reducing black carbon,” he said.
The National Science Foundation, the National Oceanic and Atmospheric
Administration and the National Aeronautics and Space Administration
funded the review.
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MARCH 23, 2008, 11 A.M. U.S. PACIFIC DAYLIGHT TIME
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Scripps Institution of Oceanography, at UC San Diego, is one of the
oldest, largest and most important centers for global science
research and graduate training in the world. The National Research
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atmospheric studies of the earth as a system. Hundreds of research
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