You're better off using nuclear power or renewable energy to create carbon-neutral jet fuel than anything else. I doubt there's any other way to fly than hydrocarbons (or equivalent chemical energy). Nuclear planes are also a joke (I believe they are theoretically physically possible, but have to be huge, and of course there's the little issue of flying nuclear reactors around in the sky), all the other alternate energies are right out, and none of the non-rocket alternate thrust methods have anywhere near enough specific impulse to get a plane off the ground, to say nothing of the unpleasantness of something like ion drives taking off in the middle of populated metropolises all the time. (Any ion drive that could drive a plane would sterilize quite a bit of landscape in the process.) Rockets might theoretically work but obvious jet engines win out in practice in this use case.