What about flying?

Flying is energy-intensive per minute but not per mile. Normalized per passenger-mile traveled, it is approximately the same as driving in a car with a passenger. In the electrified future, short-haul flights (<500 miles) will be electric, enabled by increases in the power density of motors and batteries. Long-haul flights will use biofuels to get enough range.

Long answer

Flying is energy-intensive per minute but not per mile.  Normalized per passenger-mile traveled, it is approximately the same as driving in a car with a passenger. That said, reducing the number of flights taken is one of the most effective ways for individuals to reduce their energy footprints.

In the electrified future, short--haul flights (<500 miles) will be electric, enabled by increases in the power density of motors and batteries.  Long--haul flights will use biofuels to get enough range. Passenger and freight flights in the U.S. require a total of 2 quads, and military aviation is another 0.5 quads. The U.S. can produce about 10 quads of biofuel energy, easily covering the tab for flying, in addition to other hard--to--electrify things like construction and mining equipment (another 1-2 quads).

I have several friends who have electric aircraft companies; they are very bullish on flying cars. I have another colleague who accurately states that at about 80mph it starts to take more energy to keep the car on the ground than just flying it --- keeping the car's tires on the ground costs you a lot in energy! It is even possible to convince yourself that small electric aircraft will have energy efficiencies per passenger mile similar to electric cars. This is true if you fly naked, but not if you pack a lot of luggage. Also, if we could all fly everywhere quickly, we'd do it more, and lose the gains in extra miles traveled. This will remain the domain of billionaires.

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