@empiricism

One example of a fuel that does not *directly* produce greenhouse gases is Hydrogen. When it is combusted it makes water. But of course it depends on how the H is produced and transported to the fuel tanks in the jet. The production and transport of H might produce greenhouse gases.

Also, as far as I know, they haven't made a jet that runs on H.

I personally have a tiny footprint -- as small as I can practically make it.