There seems to be some debate about whether particulate matter has a net-warming or net-cooling effect. It's difficult to estimate empirically, because there ar

There seems to be some debate about whether particulate matter has a net-warming or net-cooling effect. It's difficult to estimate empirically, because there are so many uncontrolled variables. http://en.wikipedia.org/wiki/Global_dimming http://en.wikipedia.org/wiki/Global_dimming http://en.wikipedia.org/wiki/Global_cooling#Aerosols http://en.wikipedia.org/wiki/Global_cooling#Aerosols