Black Carbon Causes Twice As Much Global Warming Than
New findings suggest there may be untapped
potential to curb climate change by reducing soot
Jan 15, 2013
The biggest source of black carbon emissions is the
burning of forest and savannah grasslands. Photograph:
Dado Galdier / AP
Soot from burned wood and diesel exhausts may have
twice the impact on global warming than previously
thought, according to a new study published on Tuesday.
The "black carbon" is said to be the second most
important man-made agent of climate change.
The findings, published in the Journal of Geophysical
Research Atmospheres, suggest there may be untapped
potential to curb global warming by reducing soot
Huge quantities of man-made soot enter the atmosphere
every year. Around 7.5m tonnes was released in 2000
alone, according to estimates. It has a greenhouse
effect two-thirds that of carbon dioxide, and greater
The biggest source of soot emissions is the burning of
forest and savannah grasslands. But diesel engines
account for about 70% of emissions from Europe, North
America and Latin America.
In Asia and Africa, wood burning domestic fires make up
60% to 80% of soot emissions. Coal fires are also a
significant source of soot in China, parts of Eastern
Europe, and former Soviet bloc countries.
Soot warms the atmosphere by absorbing incoming and
scattered heat from the Sun.
It also promotes the formation of clouds, and generates
further warming by dimming the reflective surface of
snow and ice.
The study, which involved 31 leading experts from
around the world, reviewed all the available data on
the impact of soot on climate.
Dr David Fahey, one of the authors from the US National
Oceanic and Atmospheric Administration (NOAA), said:
"This study confirms and goes beyond other research
that suggested black carbon has a strong warming effect
on climate, just ahead of methane."
His colleague Prof Piers Forster, from the University
of Leeds' School of Earth and Environment, said: "There
are exciting opportunities to cool climate by cutting
soot emissions, but it is not straightforward.
"Reducing emissions from diesel engines and domestic
wood and coal fires is a no-brainer, as there are
tandem health and climate benefits.
"If we did everything we could to reduce these
emissions, we could buy ourselves up to half a degree
less warming – or a couple of decades of respite."
However, curbing the impact of soot may not be a simple
process, the researchers pointed out. Typically soot
was emitted along with other particles and gases that
may actually cool the climate.
Organic matter in the atmosphere produced by open
vegetation burning may have an overall cooling effect,
for instance. But other reduction targets are likely to
have a clear benefit, say the experts.
"One great candidate is soot from diesel engines," said
Forster. "It may also be possible to look at wood and
coal burning in some kinds of industry and in small
household burners. In these cases, soot makes up a
large fraction of their emissions, so removing these
sources would likely cool the climate."
Tackling soot would have an almost immediate effect,
because of the short amount of time it stays in the
While the leading greenhouse gas carbon dioxide remains
in the atmosphere for long periods, soot emissions are
washed out within a few weeks and then replaced.
"Soot mitigation is an immediate effect but helps for a
short time only," said Forster. "We will always need to
mitigate C02 to achieve long-term cooling."
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