Recently I've run across a couple of presentations on technological solutions to reverse global warming. The most interesting is to put stuff into the upper atmosphere to block UV light. Not only does this reduce warming due to sunlight, it has an immediate payoff in terms of reduction in skin cancer. Analyses suggests that it would actually pay for itself in terms of just that effect, independent of the benefits for climate change.
Here is one presentation, a 7-minute audio interview with UCI physicist
(and science fiction author) Greg Benford:
And here is a paper by Dr. Edward Teller of Livermore Labs on the subject, which I think is the work Benford is referring to:
Teller's paper actually describes two mitigation schemes, one involving putting stuff in the stratosphere, and the other a more ambitious plan to station material at the Earth-Sun L1 point. This is a semi-stable orbital point approximately a million miles towards the Sun from the Earth. Teller et al calculate that only 3000 tons of smart material located at L1 would diffract away enough sunlight from Earth to eliminate global warming. Of course it will be some time before we can put or manipulate this much material in space.
Benford suggests (in his interview) beginning a pilot scheme to put 100 micron particles into the arctic stratosphere during the summer, in order to try to reverse the loss of arctic sea ice and save the polar bears. By design (and in fact, it's hard to avoid) these would snow out every year so they have to be replaced each summer, at an annual cost of about $100 million, he estimates.
The bottom line is, as Benford notes, "we're going to have to run this planet." Sooner or later the message will sink in that Kyoto and other conservation efforts are too little, too late (and too expensive).
Geo-engineering will be forced on the human race, luddites and all,by the climate change threat of the 21st century.