Switching airplanes to hydrogen has a much higher cost than replacing fossil fuel with carbon-neutral biofuels in the existing planes and engines. This is by far the easiest way forward. Still tremendously difficult - it does need electrification of bio-fuel production, something which we haven't made outside of a lab setting.

But the same tech is necessary for carbon neutral food production anyway. Today's agriculture is fully dependant on fossil fuel energy, both for running the machines and for creating the many inputs like fertilizers and pesticides.