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Black carbon, or soot, is making a much larger contribution to global warming
than previously recognised, according to research.
Scientists say that particles from diesel engines and wood burning could be
having twice as much warming effect as assessed in past estimates.
They say it ranks second only to carbon dioxide as the most important
The research is in the Journal of Geophysical Research-Atmospheres.
Black carbon aerosols have been known to warm the atmosphere for many years by
absorbing sunlight. They also speed the melting of ice and snow.
Half a degree
This new study concludes the dark particles are having a warming effect
approximately two thirds that of carbon dioxide, and greater than methane.
"The large conclusion is that forcing due to black carbon in the atmosphere
is larger," lead author Sarah Doherty told BBC News.
"The value the IPCC gave in their 4th assessment report in 2007 is half of what
we are presenting in this report - it's a little bit shocking,"
The researchers say black carbon emissions in Europe and North America have been
declining due to restrictions on emissions from diesel engines. But they have
been growing steadily in the developing world. However as these type of
particles don't last very long in the atmosphere, cutting their number would
have an immediate impact on temperatures.
"Reducing emissions from diesel engines and domestic wood and coal fires is a
no-brainer as there are tandem health and climate benefits," said Professor
Piers Forster from the University of Leeds.
"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," he added.
The report warns that the role of black carbon is complex and can have cooling
and warming effects.
"Mitigation is a complex issue because soot is typically emitted with other
particles and gases that probably cool the climate," said Prof Forster,
"For instance, organic matter in the atmosphere produced by open vegetation
burning likely has a cooling effect. Therefore the net effect of eliminating
that source might not give us the desired cooling," he added.
Black carbon is said to be a significant source of rapid warming in the
northern United States, Canada, northern Europe and northern Asia. The particles
are also said to have an impact on rainfall patterns in the Asian monsoon.
Last year a six nation coalition of countries began a combined effort to curb
the impact of short lived climate agents such as black carbon.
The authors say that while cutting back on soot is important, cutting carbon
dioxide emissions is the best way to address climate change in the long term.