Black Carbon: A Science/Policy Primer

December 2009

Prepared for the Pew Center on Global Climate Change
by John Bachmann, Vision Air Consulting, LLC

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Over the last decade, a growing body of evidence indicates that soot and smoke from incomplete combustion are major contributors to climate change. Black carbon, a soot component, is a potent climate driver that absorbs sunlight in the atmosphere, changes rainfall patterns, and when deposited on snow and ice, accelerates melting. In addition, soot can cause direct effects on health and agriculture. Climate and other effects of soot are magnified in broad regions where the strongest source emissions occur, but transported soot is also a major concern in the Arctic. The short atmospheric lifetime of soot particles also means that emissions reductions produce nearly immediate results, in contrast to most greenhouse gases (GHGs).

The principal source categories include diesel engines, small industrial sources, residential coal and solid biofuels for heating and cooking, and open biomass burning for agriculture and forestry. Control and mitigation approaches exist, but the small size and wide dispersion of these sources present significant challenges. The available evidence suggests that appropriately targeted soot controls have the potential to accelerate and enhance climate and air quality related public health benefits when used as a complement to overall climate strategies centered on greenhouse gases. Consideration of such controls is, however, subject to a number of scientific and technical uncertainties and complexities regarding emissions, controls, and the net effect of addressing some soot sources on both global and regional scales. This paper summarizes current knowledge on the effects of soot components—black carbon and organic particles—on climate, and identifies sources and technologies to mitigate their impacts. It also presents perspectives on the potential role of soot mitigation approaches in developing more comprehensive climate strategies.