I thought I read that hydrogen is the perfect fuel; very clean and effecient. Unfortunately, in order to produce hydrogen, you currently need to use lots of hydrocarbons to convert the raw material (H2O ??).
The stats on air transport using only around 4% of hydros is surprising to me. I would have guessed much higher - say 20%.
So the real problem with limiting fossel burns is to find a viable alternative to oil/gas for ground transport.
...interesting.