Supersonic air travel is coming back: Do we really want it?

Boeing abandoned its Sonic Cruiser project 15 years ago.

The noise issue raises a bigger philosophical question around supersonic flight: How much do we really value speed, anyway? After all, the structure of our current aviation industry is the result of a series of compromises around competing values. And over the past 30 years, airlines have shown that there are a lot of other things we value more than simply going really, really fast.

Back in the 1970s, Mann explains, the industry realized that if it wanted to keep growing, it needed to be a good neighbor. That meant replacing their existing fleet of loud and dirty airplanes with much quieter models — even if it meant some trade-offs in terms of performance. Similarly, ever since the oil shocks of that decade, the industry has made a point of valuing fuel efficiency over raw speed.

“The optimal cruise speed has basically declined over the years,” Mann says. “Above about Mach 0.8, you pay so much for that speed in terms of fuel.” Today, a flight from New York to Denver or from DC to Miami actually takes longer than it did in the 1970s — because airlines have realized that the fuel savings are worth the delay.

Going forward, there’s another important value to weigh on the scale: climate change. Aviation is already the fastest-growing source of greenhouse gas emissions in the world, and the world’s airlines just agreed to a sweeping deal under the International Civil Aviation Organization to offset the growth of their emissions starting in 2020. Conventional aircraft manufacturers have worked hard to reduce fuel burn by 45 percent since 1968, and companies like Boeing and Airbus are now pushing to cut fuel use even further, through the use of lighter materials and novel engine designs. Still, this remains one of the toughest sectors to decarbonize.

And new supersonic jets that burn fuel at higher rates than conventional planes seem to go in precisely the opposite direction — even if they do save travelers time. True, a few supersonic business jets flying around wouldn’t have a major impact on emissions. But if cheap supersonic flight became ubiquitous, the global warming impact could be staggering (particularly if the planes fly at higher altitudes, due to the contrail effect). With the world already struggling to avoid dangerously large temperature increases, a new fuel-inefficient plane seems like a luxury the planet can ill afford.

When I asked NASA’s Coen about the climate consequences of a world filled with supersonic jets, he agreed that it was a real concern. But he also pointed out that there might be ways to square these different values. Future caps on aviation emissions could, for instance, spur supersonic jets to adopt low-carbon biofuels. (Or there’s another way this could all go: As Mann pointed out, it’s possible that stricter carbon caps could simply make supersonic flight unviable.)

It’s still too early to say how these issues will play out, but it’s a good reminder that our slow, boring planes have quite a few things going for them.

Even so, at the end of the day, the prospect of faster flight will remain forever tantalizing. The reduction in travel times has been one of the great technological breakthroughs of the past 200 years. This isn’t merely convenient; in some ways, it’s been the very marker of progress. Humans have long been obsessed with breaking new barriers, with going faster and faster. Even if on a purely romantic level, it would be a shame if we’re currently stuck going about as fast as we’ll ever go.

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