Sure, but the incentives are mostly already there. And they're not buying the new super-efficient large jets because they have a hard time selling enough tickets to fill them. So I don't think they're going to be physically able to reduce emissions too much further, certainly not enough to hold overall emissions steady as flights rack up 3x as many miles over the next few decades.

To put it a different way, most of the advances here will not be in more efficient ways to fly, but in more effective ways to sell carbon credits to the airlines.