Well for fuel actually. There is a way to make a kind of gas out of corn. Also you could use water to make fuel as well. Which would be very clean. And I am not talking about steam engines either. Also there is compressed air. Though corn can make ethanol and or white-lightning as some people might call it. It runs much hotter then gas and if a engine is made for it, it could actually take over as the gas. I could very well see people growing huge crops of corn to make a kind of burnable fuel out of it..
this is off topic, in your post you have (gas out of corn,water,compressed air) as tipes of power, wut about Propane its very clean and burns hot and has alot of power. Mothers Car Care made a Propane powerd car back in 2007 the car makes over 1,000 HP http://www.autoblog.com/2007/10/31/sema-2007-1-000-hp-propane-chevelle-by-mothers/
How did i not mention this lines before
? ... well, the problem is, you can make any kind of engine you like, but the energy outcome of propane is, and by the chemistry side always will be much lower than by many stuff hiding in gasoline ... so in the end, you have to burn a lot more of it, to get the same amount, as gasoline gives up. ... CO2 isnt the real problem in crude oil fuels, its the amount of other possible out-coming gases (CO - from nonperfect burning (fuel type based engine-design thing), SOx´s - witch are there, because desulfurization of crude oil isnt still a 100% thing, NOx´s - because any living thing has nitrogen and laying around under earth for milenia doesnt change that ... ).
If count their C-count for propane gasoline, you will see, you have more carbohydrates by oil use than by propane molecules. You need more molar mass for the same energy outcome.
Second problem is the fact, there are no propane designed engines (you still have to use a mix) and those trying to do that have an pain in the ass effectivity.
Last thing is, how much space you need for the certain crops to grow for the needed amount of propane by bio-fermentation processing to make it "clean" ?
Using bio-fuels newer had any real way to achieve its goals on the physical side (our economy model doesn't give that much help aether) for an closed resource planet of our. I thing it came out of some now-days economist than from an engineer - fits the thinking model.
Of course, gasoline still hasn't their problems solved. In this manner none is right actually, but changing just the energy-type base for our society isn't going to do much, if the structure and way of usage doesn't change (witch actually should be going on right now, but still isn't).
And as for fracking :
(don't mind the over-ecologist way of explaining things)
... yes, Sulphur is gotten a similar way, but uses overheated vapor water (doesn't need all the stuff poured into it like in the fracking case).
In the end - interesting idea, badly planned and idiotically done. And protected by law. What a nice sentence to describe our kind.
We need something ....
Tesla style to get this problem solved !