1. 3/4 of energy usage is outside the transportation sector.
2. If we switch 3/4 of energy production away from fossil fuels, that will make a huge dent and make renewables even cheaper.
3. Once renewables get cheap enough, it may be cheaper to use a few kWh of solar to produce one kWh of ethanol than it will be to dig 1 kWh of oil out of the ground.
Hydrogen goes boom, and ethanol is already straining the corn market to the limits. I can't see us turning every square section of arable land into ethanol production.
Energy is fungible at an efficiency loss. If solar gets cheap enough we'll use it, water, and atmospheric CO2 to synthesize hydrocarbons. At that point your boats and planes are net carbon neutral. It's getting carbon-free energy that cheap that's the challenge.
EDIT: I hope the OP wasn't getting downvotes. It was a reasonable thing to worry about.
I would respectfully disagree. As liquid fuel prices climb higher alternative methods of producing liquid fuels become more and more attractive.
There is a lot of research going into ways to turn CO2 into various precursors to fuel or directly into things that are liquid fuels. And the last generation of concentrating solar plants have shown that you can gather the heat very effectively if you need that. Photovoltaics are cheap and getting cheaper if your process requires electrons instead of heat. This is likely the way things will go for airplanes.
There are also a number of companies working on harnessing the wind for ships. There's the SkySail system which I believe is being deployed commercially already that's a huge, automated kite-sail. There are also people working on rigid, self-adjusting wingsails (Saildrone). Finally the folks at Makani could probably put many, many kite plane generator systems on a boat and produce a substantial amount -- perhaps even all -- of the power needed to make a large boat go.
These might require that boats get redesigned to be slipperier but as fuel prices climb inefficient ships look less like assets and more like liabilities. Given the choice between holding less expensive assets with high operating costs and more expensive assets with low operating costs plenty of businesses can find the capital to upgrade if the economics are there. And as fuel prices climb, the economics are increasingly there.
So while I agree that in the short, short term none of this helps, in the long term things can get a lot better incrementally.
The Germans have done a lot of work on straight vegetable oil running current model COTS diesel engines.
Imagine hydroponic greenhouses in some wasteland growing canola, for example.
This is a little different than waste vegetable oil aka biodiesel mostly made from old fryer oil and needing lots of processing and filtration, but roughly the same concept.
Obviously all the oil underground came from plants initially, you can skip a lot of trouble and harvest your sunflower seeds and rapeseed seeds right on the surface and skip all that "bury it for a few million years then tunnel down and dig it up"
