There are lots of things which are an environmental issue. The biggest is air traffic control and the old system of navigation points. The next biggest is the inflight magazine, duty free magazine and IFE magazine. It take 4L of water to produce 1 sheet of A4 paper, the dye in the ink is toxic and the additional weight carried on every flight is a waste of fuel. I would say the third biggest in Australia is Sydney airport, the curfew, noise abatement procedures and the cap on flight movements.
Dealing with these 3 issues alone would provide greater benefit than punishing every PAX in every class as you are suggesting.
I would also say the new lack of a free cell phone pickup parking lot at Sydney airport is another environmental hazard. Instead of having cars parked up instead they circle waiting for people to arrive curb side.