Before the pandemic hit, back when you could whizz over to the Med for thirty quid, thousands of climate-conscious travellers took a no-fly pledge. Spurred on by evidence that the climate emergency is a terrifying reality, from wildfires in California to drought in Australia, the movement soon swept into the consciousness of a panicked aviation industry. As Ed Bastian, CEO of Delta Air Lines, pointed out at an investor day in 2019: “Environmental stewardship is the existential threat to our future ability to grow.”