The environmental issue with air travel is not high fuel consumption per passenger mile, but the number of miles per passenger. A coast to coast trip by car might burn just as much fuel as coast to coast by plane, but people simply wouldn't to that all that often in a lifetime.
That's for medium and long distance travel, short distance fuel consumption per passenger mile goes up dramatically.
OT: this is actually a point where I see a big, unserved gap in the market of climate-aware air travel. A feeder plane (from regional to intercontinental airport) dedicated to the market segment of "going by road or train might be roughly as fast, but I need to go to the airport and I can't risk missing my connection due to the unpredictable nature of ground travel". So you'd want a something the size of a CRJ or even just a dash-8, but ruthlessly optimized for fuel consumption. That would imply going slower (no issue at all when the time for bording etc greatly outweighs the time spent in the air!) which would imply moving the deep point in that induced vs parasitic drag diagram as far left as possible, which would imply going wild with wingspan, something sleek, carbon, like a performance glider, as wide as a 737 or beyond. One reason I've heard suggested for why this doesn't yet exist is that on those short hops (little time spent in the air), fuel cost is actually outweighed by crew cost so much that all the cost saving from lower fuel consumption would be eaten by getting less trips per crew-day. So it's an automaton problem in disguise? Or a regulatory problem?
That's for medium and long distance travel, short distance fuel consumption per passenger mile goes up dramatically.
OT: this is actually a point where I see a big, unserved gap in the market of climate-aware air travel. A feeder plane (from regional to intercontinental airport) dedicated to the market segment of "going by road or train might be roughly as fast, but I need to go to the airport and I can't risk missing my connection due to the unpredictable nature of ground travel". So you'd want a something the size of a CRJ or even just a dash-8, but ruthlessly optimized for fuel consumption. That would imply going slower (no issue at all when the time for bording etc greatly outweighs the time spent in the air!) which would imply moving the deep point in that induced vs parasitic drag diagram as far left as possible, which would imply going wild with wingspan, something sleek, carbon, like a performance glider, as wide as a 737 or beyond. One reason I've heard suggested for why this doesn't yet exist is that on those short hops (little time spent in the air), fuel cost is actually outweighed by crew cost so much that all the cost saving from lower fuel consumption would be eaten by getting less trips per crew-day. So it's an automaton problem in disguise? Or a regulatory problem?