But it's impractical reality to use productive farm land to fill up petrol tanks.
Ignorant piffel, Jatropa doesn't need to be grown on "productive" farmland..unlike palm oil, and the various other soya based crops.
Algae, Jatropa, and to some extent perhaps some form of wild grass (which don't, won't and will never compete with food production) may well be the next leap in alternative aviation fuels. I can't help thinking though that given aviation produces 2% of the worlds emissions...the "anti" progress lobby certainly are targetting the lowest hanging fruit of all.