International study: Where there's smoke or smog, there's climate change
S. Doherty, Univ. of Washington |
In
addition to causing smoggy skies and chronic coughs, soot -- or black carbon --
turns out to be the number two contributor to global warming. It's second only
to carbon dioxide, according to a four-year assessment by an international
panel. The new study concludes that black carbon, the soot particles in smoke
and smog, contributes about twice as much to global warming as previously
estimated, even by the 2007 Intergovernmental Panel on Climate Change.
"We
were surprised at its potential contribution to climate," said Sarah
Doherty, a University of Washington atmospheric scientist and one of four
coordinating lead authors. The silver lining may be that controlling these
emissions can deliver more immediate climate benefits than trying to control
carbon dioxide, she said.
The paper was made freely available online Jan. 15 in the Journal of Geophysical Research-Atmospheres.
Some
previous research had hinted that models were underestimating black-carbon
emissions, Doherty said, from such things as open burning of forests, crops and
grasslands, and from energy-related emissions in Southeast Asia and East Asia.
Black
carbon's role in climate is complex. Dark particles in the air work to shade
Earth's surface while warming the atmosphere. Black carbon that settles on the
surface of snow and ice darkens the surface to absorb more sunlight and
increase melting. Finally, soot particles influence cloud formation in ways
that can have either a cooling or warming impact.
The
report surveyed past studies and included new research to quantify the sources
of black carbon and better understand its overall effect on the climate.
Doherty
was executive director of the International Global Atmospheric Chemistry
Project in 2009 when policy groups were seeking better information on the benefits
of reducing black-carbon emissions. The scientific body undertook a
comprehensive assessment, supported by IGAC and the U.S. National Oceanic and
Atmospheric Administration.
"Because
of a lack of action to reduce carbon dioxide emissions, the policy community is
asking what else we can do, particularly to help places like the Arctic that
are melting much more quickly than we had anticipated," Doherty said.
"We hope reducing black-carbon emissions buys us some time. But it doesn't
replace cutting back on CO2 emissions."
While
carbon dioxide has a half-life of 100 years, black carbon stays in the
atmosphere for only a few days.
The
authors investigated various sources of black carbon to see which reductions
might have the most short-term cooling impact. Regulating emissions from diesel
engines followed by replacing some wood- and coal-burning household stoves,
authors find, would have the greatest immediate cooling impact.
"If
you're just thinking about impact on climate, you would want to be strategic
about which sources you cut back on," Doherty said. "We looked at the
overall impact because some of these sources also emit associated particles
that can have counteracting effects."
Black
carbon contributes to climate change in the mid to high latitudes, including
the northern United States, Canada, northern Europe and northern Asia, as well
as affecting rainfall patterns of the Asian Monsoon.
The
report incorporates data that Doherty and co-author Stephen Warren, a UW
professor of atmospheric sciences, gathered between 2007 and 2009 to measure
soot on Arctic snow. Calculating black carbon deposits in the Arctic is
difficult, so data are essential for testing and correcting models.
First
author Tami Bond, now at the University of Illinois, earned a doctoral degree
at the UW in 2000 that combined engineering, chemistry and atmospheric science
to measure emissions from burning that have atmospheric importance.
"Mitigating
black carbon is good for curbing short-term climate change, but to really solve
the long-term climate problem, carbon dioxide emissions must also be
reduced," Bond said.
In
related research, Doherty, Warren and UW graduate student Cheng Dang will
travel next month to Colorado, Wyoming, the Dakotas, Saskatchewan, Manitoba and
elsewhere to collect snow samples and investigate black carbon's effects on
North America's Great Plains.
Source: University
of Washington
Posted by Unknown
on Saturday, January 19, 2013.
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