[holding answer 12 October 2009]: Research reported in the intergovernmental panel on climate change’s fourth assessment report suggest a small, but significant, total warming effect since 1750 from black carbon emitted into the atmosphere by fossil fuel (the main source), biofuel and biomass burning. This effect is estimated to be the equivalent of about one seventh of the total climate warming effect from long lived greenhouse gases. There is also an additional but smaller warming effect due to the deposition of black carbon on surface snow and ice. Recent work by the Met Office Hadley Centre, funded by DECC, suggests black carbon emissions have potentially the second largest warming influence on climate, after greenhouse gases.
The “Air Quality and Climate Change: A UK Perspective, 2007” report by the Air Quality Expert Group considered the effects of air pollutants on air quality and climate change. Improvements in air quality will have a complex influence on climate change, as some pollutants have a direct or indirect warming effect while aerosol emissions other than black carbon have a cooling effect.