Quite a lot of denial of reality going on here, isn't there?
One obvious measure is minimum fuel-burn per bum-mile, which also turns out to be quite good for profits.
The other big win is probably more in ATC and routing, rather than anything any individual airline can do.
I wonder why people are so sure that all concern about climate change is bullcrap? Surely it could not be that it is inconvenient? Maybe they just like to position the airline industry in opposition to most of the world's governments, which I am sure is a very good strategy for preserving jobs.