http://www.nytimes.com/2008/02/19/sc...ss&oref=slogin
Clever concept (which doesn't exist yet unfortunately) which could use CO2 in the atmosphere and synthesize it into more complex hydrocarbon fuels. The only problem is that it would need a completely clean power plant (i.e. non-coal) to keep net CO2 emissions 0. Might not work but it is definately worth researching.