Mountains and mole hills.
How many GA flight hours are flown per year compared with the millions of ground vehicle hours driven/stuck in traffic in the UK?
During COP26 there was a list of things people could do to reduce the CO2 that were being read out on the tv news.... which conveniently skipped over the item to "keep your gardens" (i.e. not concrete/tarmac over them or replace with astro turf which many people do in the UK).
In more recent news, there is a place abroad flooded that is exacerbated by loss of natural drainage where people have removed the green space in the streets.
Several years ago a simple hedge along a busy road side in London was demonstrated to have improved the air quality inside the house. Suggests there are other green alternatives to planting trees to do our bit.