The main reason to keep hydrocarbon fuels in a green-energy future is for their energy density. Rockets and airplanes will always want the best density and weig

The main reason to keep hydrocarbon fuels in a green-energy future is for their energy density. Rockets and airplanes will always want the best density and weight available, and that’s hydrocarbon fuel for now, barring some order-of-magnitude battery improvements. Hydrogen rockets are a thing, but their tanks are huge compared to methane or kerosene rockets.