Check the article link for details and an interview video
MR. MYHRVOLD:The most dramatic approach is to say, "Can we cool Earth off?" The answer to that, surprisingly, is yes. And the reason goes back to it being a 1% effect. All you have to do is reflect 1% roughly of the light that hits Earth before it comes down, and you've solved the entire problem. It was recognized in the 1960s that sulfur dioxide does this naturally in the atmosphere. For relatively modest amounts of sulfur dioxide injected into the atmosphere, you could easily cool Earth by 1% or more, if you want.
Many of the people involved in the debate are anti-technology. Their argument is, "Guys like you got us in this problem; why the hell should we let you go do this again?"
And the answer to that is, of course: As soon as we developed agriculture, as soon as our population increased from a couple million across the whole planet, all of those things were unsustainable in the sense that we would have growth rates that depended on us getting smart and figuring something else out. The whole question is, do we give the human race half a chance to figure out that next smart thing.