Actually, our current "fuel demand" for automobiles is the great waste-disposal opportunity given today's technology.
My personal car is a Volkswagen Golf, which I run on 100% biodiesel. This requires no modification of the car, and the fuel is produced entirely from vegetable oil. Curret farming practice yeilds oil mainly from corn & soy, but if the demand rises there's a larger potential in mustard seed and oil-bearing algae.
The algae process is particularly fascinating. Special algae are farmed in large clear-walled tanks, which allow sunlight in. Waste CO2 (from fossil-fueled power plants) and nutrients (from sewage treatment plants or farm waste) are the nutrient source. "Ripe" algae is strained off and pressed for oil - some new breeds (non-bioengineered) of algae are producing more than 50% oil by weight. This oil is processed into biodiesel. Extra bonus: the algae also absorb a lot of NOx (smog causing oxides of nitrogen) as well as CO2.
This process adds no CO2 to the atmosphere. The CO2 was captured from an existing source to form the hydrocarbon (oil) and then is re-released when burned in your car. Then it's recaptured in next year's oil-producing crop, such as corn or soybeans. Thus, a true CO2 - crop - fuel - co2 - crop - fuel... cycle, instead of a one-way fossil fuel to atmospheric co2 conveyor belt we've been riding.
The beauty of it is, this technology is here today and it works. My car/tractor/RV, my brother's car, and many of my friend's & family's cars are already using it.
Sorry for the rant, but this seems like a good time to raise awareness. Anything we can do to stop the CO2-driven acidification of the oceans, and to USE some of this excess nutrient instead of dumping it is vitally important to the future of our oceans.
More information (or PM me!)
http://www.unh.edu/p2/biodiesel/article_alge.html
http://www.americanenergyindependence.com/biodiesel.html
http://www.csmonitor.com/2006/0111/p01s03-sten.html
and
http://thefraserdomain.typepad.com/energy/2005/06/university_of_n.html
with photos of a working algae tank farm attached to a power plant!