Getting nations to agree to cut their greenhouse pollution has proved to be the ultimate free-rider problem, as the biggest nations must all cooperate or the planet will keep getting warmer. The Pinatubo option creates the opposite dilemma: As the discussions in Lisbon made clear, any of a dozen nations could change the global temperature all by itself.
I'm huge on the idea of Unintended Consequences. It's a key feature of many of my lectures. This one's a whopper. Instead of nuclear blackmail, we could face climatological blackmail over global warming which may prove ultimately to have been Not Entirely Our Fault.