From this report:
Some scientists have been reluctant to talk about the overall global warming effect of all the greenhouses gases taken together, because there is another consideration - the fact that the "aerosol", or band of dust in the atmosphere from industrial pollution, actually reduces the warming.So industrial pollution keeps the world from frying. I imagine Dana Carvey as the Church Lady at this point: "Well isn't that special?"
As Professor Shine stresses, there is enormous uncertainty about the degree to which this is happening, so making calculation of the overall warming effect problematic. However, as James Lovelock points out - and Professor Shine and other scientists accept - in the event of an industrial downturn, the aerosol could fall out of the atmosphere in a matter of weeks, and then the effect of all the greenhouse gases taken together would suddenly be fully felt.