David Kieth discusses the issue of geoengineering, and TED asks "Why should you listen to him?" supplying the following answer:
Environmental scientist David Keith works at the intersection of climate science, way-new energy, and public power. His research has taken him into some far-out realms of geoengineering -- dramatic, cheap, sometimes shocking solutions to a warming atmosphere, such as blowing a Mt. Pinatubo-size cloud of sulfur into the sky to bring the global temperature down.
Keith is rightly dubious about the wisdom of countering full blown warming with a geoengineering solution, but the idea that we might use a smaller geoengineering effort to counter warming, after we have made a serious effort at reducing emissions has more merit.
We heard a lot about moral hazzard during the early stages of the Global Financial Crisis - the idea that if financiers are bailed out for their mistakes by governments, then financiers will be encouraged to continue to make dangerous and risky decisions. Moral hazzard in the context of geoengineering as a response to climate change, means that less effort will be made in reducing emissions if geoengineering solutions seem possible.
At the moment, though, it is the political difficulties and the lies of the ideological opponents of reduction of emissions that are the major forces stopping positive action.