January 15, 2013

expert reaction to new research into the impacts of ‘black carbon’ on the climate

A study published in the Journal of Geophysical Research Atmospheres, said the direct warming effect of black carbon, the term used by scientists to describe soot, could be about twice previous estimates.

Prof Alastair Lewis, Professor of Atmospheric Chemistry at the University of York, said:

“This new study helps us see the bigger picture: that we need to tackle air pollution and climate change as one joined-up problem.  

“In the past there has been a rather artificial separation between science and policy that deals with ‘pollution’ – meaning the impact of dirty air on health – and climate, which is often CO2-focused and considered to be on such a large global scale that it induces policy ‘despair’.  In practice, many governments have been extremely successful in tackling their national air pollution problems, in contrast to global attempts to deal with CO2.  

“It has long been known that diesel engines and combustion of wood and coal contribute to both kinds of pollution.  This new work shows us that careful selection of air pollution control at national level could be an effective means to create climate benefits in the future.

“This study shows us that black carbon – or ‘soot’ – has a significant role in climate change, and reducing its concentrations would have a fast and significant effect.  But this does not mean that CO2 has a lesser effect; and most certainly should not allow us to lose sight of essential reduction of CO2 emissions.  It simply tells us we must do both – and fast.”

Professor Piers Forster from the University of Leeds’ School of Earth and Environment, who co-led the study, 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.

“Mitigation is a complex issue because soot is typically emitted with other particles and gases that probably cool the climate.  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.

“One great candidate is soot from diesel engines. 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.

“Soot mitigation is an immediate effect but helps for a short time only.  We will always need to mitigate CO2 to achieve a long-term cooling.”

‘Bounding the role of black carbon in the climate system: A scientific assessment’ by T. C. Bond et al. is published in Journal of Geophysical Research-Atmospheres