J. Geophys. Res. http://dx.doi.org/10.1002/jgrd.50171 (2013)

Black carbon aerosols — tiny soot particles suspended in the atmosphere — are a by-product of the incomplete combustion of fossil and biomass fuels, and are mainly emitted by the transport, industrial and residential sectors. These aerosols play an important and complex role in the climate system, where they absorb solar radiation, influence clouds and alter snow and ice thaw processes.

Tami Bond at the University of Illinois, at Urbana-Champaign, US, and a multidisciplinary team of 30 co-workers assessed the influence of black carbon on radiative forcing — the balance of radiant energy received and lost by the Earth — in the most comprehensive study so far. Their results indicate that black carbon has around twice the direct warming effect conventionally expected, giving it the dubious privilege of being the second most important warming agent after CO2.

The ways in which black carbon and co-emitted pollutants influence the climate are complicated, making it difficult to predict the success of blanket policies that cut black carbon emissions. Nevertheless, decreases in some categories of emissions, such as those from diesel engines and domestic wood and coal fires, are expected to reduce short-term warming and have important health co-benefits.