the best renewable fuel will wind up being methane... it's easy to make biologically without wasting more valuable resources to produce it.

the problem with any of the combustable fuels other than hydrogen is carbon byproducts.

the ultimate solution is probably the "air car" using compressed air to drive around town, the most minimal use of resources...

more than global warming, there is a limit to the number of people the world can support in a reasonable quality of life. over population was never a real problem. the current # of people can't stay on earth and not destroy the place...

all the solutions seem very expensive.