“…For large aircraft, there is currently no drop-in replacement for emissions-free air travel. There have been proposed replacements of conventional fuel with biomass fuel, hydrogen, or emissions-free synthetic carbon (Oakleaf et al 2022), but these efforts have mostly targeted business-as-usual air travel, which maintain the challenges related to large aircraft air travel (FAA 2015;Blakey, Rye, and Wilson 2011).…”