The ‘black carbon’ in soot – produced when wood, coal, diesel and the like are burnt – could account for as much as 60 per cent of the atmospheric warming attributed to CO2, according to Veerabhadran Ramanathan from the Scripps Institution of Oceanography at the University of California and Gregory Carmichael from the University of Iowa, the study’s authors.

Using data from satellites, aircraft and surface observatories, the pair found that while most particles in the high atmosphere help to reduce global warming by reflecting radiation back out to space, black carbon particles absorb radiation, making soot the second-highest cause of global warming after CO2.

However, the study also found that black carbon only stays airborne for a few weeks and can be leached out through precipitation, whereas CO2 remains in the atmosphere for decades. More research is needed to fully understand the interactions between black carbon and other elements in the high atmosphere, said the researchers.

June 2008