I like to travel. This is going to be a long post, because the carbon footprint of airplanes is a complicated subject.
Compared to cars, airplanes are actually surprisingly fuel-efficient. Depending on the plane capacity and distance traveled, each individual passenger moves about 100 miles per gallon of fuel. That’s about the same as a car carrying three people. Shorter flights with fewer seats are less efficient, but even a 300-mile flight with 20 passengers gets about 40 passenger-miles per gallon. Not bad!
First, cars are not a strong baseline to compare against. It’s hard to get solid numbers to compare modes of transportation, because unfortunately (1) they depend on ridership and on production and maintenance costs, which are hard to account for, and (2) most of the relevant articles found on Google are sponsored by one or another politically or economically motivated association. But for the sake of having at least one strong baseline, this paper mentions that the French TGV Dasye high-speed train uses 20 kWh/km. It has 508 seats. Elecricity currently costs about one pound of carbon dioxide per kWh, compared to 20 pounds per gallon of gas. This means that at full capacity, TGV travels the equivalent of 318 passenger-miles per gallon.
Second, airplanes cannot yet be powered by renewable energy. A person can cross the Atlantic with roughly 100 kilograms of jet fuel, but to get an equivalent amount of energy, they would need 4500 kilograms of batteries. Of course, to transport that much extra weight, they’d need way more energy. The technology for long-haul electric flight is at least 50 years away.
Finally, the problem is not with airplanes per se—it’s with traveling long distances. Even if you could somehow cross the Atlantic (3500 miles) on a fully loaded high-speed electric rail, the round trip would still release 200 kilograms of carbon dioxide (given current sources of electricity). That’s how much the average Tanzanian produces in an entire year. For reference, flying would release 636 kilograms. (That’s according to my calculations. By contrast, this Guardian article calculates that it would release 1,972 kg, which is almost half of the global per capita annual emissions. This is what I mean about the difficulty of obtaining solid numbers.)
So what’s the solution? It seems cruel to demand that everyone stop traveling. Many people live very far from their loved ones. International travel builds valuable global awareness. But taking even one fewer trip per year has an enormous impact on carbon emissions, so here are some ideas.
- Reduce discretionary travel. A good rule of thumb might be to limit non-local vacations to once per year, even if you have the economic means to travel more frequently.
- Avoid putting yourself in situations that require you to travel. Unfortunately, opportunities to do this are rare and usually coincide with major life decisions. For instance, you could choose to move nearer to your relatives. You might also consider avoiding long-distance relationships, or choosing a job that does not require business trips.
Unlike my previous posts, I have not yet implemented these ideas in my own life. To my chagrin, I’ve already taken six flights in the last six months. Comment below if you have other ideas that might help, and we’ll work on this together.
- Here are two sources that compare transportation energy efficiency in the U.S. They seem objective, but they’re a bit hard to interpret.
- In addition to electric flight, this article discusses a few other options for climate-friendly airplanes, including biofuels and electrofuels.
- This long report reviews many arguments for and against high-speed trains in the U.S. Here’s a similarly long report from the other side of the argument. Also see the International Energy Agency report on rail transportation.