Black carbon, or soot particles from diesel engines, could be making a much larger contribution to climate change than previously believed, according to a study by over 30 internationally recognised climate scientists. The study, Bounding the role of black carbon in the climate system: a scientific assessment, says black carbon is second only to carbon dioxide as the most important warming gas, with a greater impact than methane. The study’s lead author said the Intergovernmental Panel on Climate Change, in its 2007 assessment, gave a value to the role of black carbon that was only half of what this new study suggests it is. The authors believe that if efforts to reduce black carbon emissions were maximised, it could mean up to half a degree less warming or two decades of delay in current predictions about global warming.