I read an interesting thing the other day about how sunlight has been decreased by a good margin on our fair planet due to that all the pollution in the air. I believe the word "particulate" was used, though I'm certainly no scientist.
It was a bit of a doomsday scenario in that global warming would be a lot worse if some of that pollution wasn't blocking the sun's rays and as we move to cleaner fuels, the same/more carbon dioxide is produced but the benefits of smoke and ashes and other more visible crap aren't pumped out then we get more sunlight and that heats things up a little more, or a lot more.
EDIT:
Here's The Link!