That's actually a major part of the problem. Efficiency (or more accurately: low opportunity costs) lead to higher induced demand via the Jevons paradox. Fast flights => more passenger miles, at roughly 40 gallons per passenger.

World Bank, passenger growth 1970--2018: 0.3 to 4.2 billion.

(Not paxmiles, but closely related, and available data.)

https://data.worldbank.org/indicator/IS.AIR.PSGR