‘Black carbon’ rated as second largest cause of global warming

Black carbon is the second most significant contributor to climate change with only CO2 having a greater human-induced warming effect on the atmosphere.

A new paper published in the Journal of Geophysical Research: Atmospheres says that the effect of black carbon could have been underestimated in existing climate change models by as much as a factor of three.

Black carbon, of which soot is one form, is produced by diesel engines and the burning of wood, peat and other solid fuels.

The science behind the issue is further complicated by the cooling effect that some of the gases frequently emitted in tandem by fuels rich in black carbon.

Landfill fires, diesel engines and solid fuel burning are major sources of black carbon other short-term climate forcers. (Source: Flickr/ksimonsays)

Despite this, there are still some source of black carbon that if reduced, could deliver significant cuts in warming.

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

“In these cases, soot makes up a large fraction of their emissions, so removing these sources would likely cool the climate.”

The US has spearheaded the Climate and Clean Air Coalition (CCAC) in partnership with UNEP and more than 20 governments including Australia, Bangladesh, Ghana and the EU.

Health benefits

Particulate matter, sulphur dioxide and other emissions related to diesel and wood burning are also bad for human health delivering benefits for air pollution and the climate.

“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’,” said Prof Alastair Lewis, Professor of Atmospheric Chemistry at the University of York.

“In practice, many governments have been extremely successful in tackling their national air pollution problems, in contrast to global attempts to deal with CO2.”

Despite the study’s focus on black carbon, Forster was keen to stress the importance of continuing to focus climate mitigation efforts on CO2.

“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.”

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