Richard Posner says he's got a solution for climate change:
We may indeed already have the technological fix, though mysteriously it receives little attention. Sulphur dioxide, the cause of acid rain and the poster child for cap and trade--because the cap and trade program for sulphur dioxide has been a big success--is the opposite of a greenhouse gas: it cools the atmosphere by reducing the amount of sunlight that reaches the earth's surface. Injecting relatively small quantities of sulphur dioxide into the atmosphere would offset the effect of atmospheric carbon dioxide in heating the earth's surface. The opposition of environmentalists to using a pollutant to combat global warming and therefore seeming to approve of pollution, and concern with the bad effects of increasing the amount of sulphur dioxide in the atmosphere (effects that might not be limited to a modest increase in the amount of acid rain), have thus far kept this option from serious consideration in political circles.
On behalf of the environmentalists' notoriously powerful political circles, let me say that the opposition to using a pollutant to reduce global warming does not have much to do with public relations. It does have a lot to do with "the bad effects of increasing sulphur dioxide in the atmosphere."
One problem, as Posner mentions, is an increase in acid rain. But there are two bigger issues. The first is that the ecological costs of cooling the planet with sulfur will not be distributed evenly: My colleague Graeme Wood says most of those costs will fall on Africans (who will enjoy a hotter climate) and South Asians (who will enjoy less reliable rainfall). If you believe, as I do, that the best argument for mitigating global climate change is the future plight of the developing world -- which will overwhelmingly bear the costs -- then pumping millions of tons of sulfur into the atmosphere is, er, somewhat less appetizing than it might otherwise seem.
The second problem is that sulfur engineering would be difficult (and perhaps impossible) to reverse without risking calamity. As Graeme writes, "sulfur aerosols would cool the planet, but we’d risk calamity the moment we stopped pumping: the aerosols would rain down and years’ worth of accumulated carbon would make temperatures surge." So if we began pumping sulfur into the atmosphere and then realized, after several decades that there was a large unexpected cost -- greater than foreseen fishery depletion, say -- it would be hard to turn back.
I confess there's a certain escapist fun to imagining thousands of zeppelins circling the earth, spraying sulfur into the clouds -- just as watching Minority Report or Star Wars is fun. Unfortunately, the unsexy, fuddy-duddy solution of pricing carbon (via a tax or cap & trade) has a lot to recommend it.