Greg Mankiw muses about a possible solution to global warming: dumping sulfate particles into the air. These would reflect sunlight away from the planet with the accompanying cooling effects. You can visibly see this if you look at the world temperature record and note when major volcanic explosions occured. He does point out the possibility of unintended consequences, some of which I will elaborate on.
1) Breathing air contaminated with sulfur compounds will cause said compounds to bind to the surfaces of your respiratory system, increasing chances of asthma and death in general.
2) Sulfur in the atmosphere is the cause of acid rain.
However, he is not an environmentalist, he is an economist. But, he should still be familiar with this issue, because the cap-and-trade scheme devised for sulfur dioxide emissions in the United States under George HW Bush is one of the world's most successful market-based environmental initiatives.