One way to reconcile these constraints is to have the industry fly fewer passenger-kilometres. That is one of the long-term ways to address the travel industry’s contribution to human-caused climate change. Fewer passenger-kilometres can mean fewer takeoffs and landings, which can perhaps mean that the present set of runways is adequate. Maybe the COVID-19 slowdown is a rehearsal of that? Let’s not take it as axiomatic that passenger-kilometres flown will increase without limit.