Most discussions about geoengineering start out with the tricky scientific issues but eventually get to the even trickier issue of governance. As we wrote in SuperFreakonomics:
As of this writing, there is no regulatory framework to prohibit anyone — a government, a private institution, even an individual — from putting sulfur dioxide in the atmosphere. (If there were, many of the world’s nearly eight thousand coal-burning electricity units would be in a lot of trouble.) Still, [Nathan] Myhrvold admits that “it would freak people out” if someone unilaterally built the thing.