Safe 20€ a month, which is possible for a huge chunk of the population (easily > 80%), and you can do four to eight of those flights a year and that's just the lower end of the estimation, most still just don't flight that much here, and it's IMO really not an income question.

It's more like an ecological footprint and also time question as flying adds an ineligible overhead one can often outrun by using the good train networks, well maybe apart from Germany where privatization really killed a lot of networks and quality during the last decades, plus I can get to a nice nature area within an hour easily, so why bother travelling as long to the airport to only then endure their security theater.

I hate flying, but trains are rarely a convincing option. They ought to be.

Air travel is much harder to do without fossil fuels than ground transport or electrical generation, and is essential to civilization on the basis of cargo alone. It's simply not an efficient target for change right now.

I favor carbon taxes that dig an industries grave for it: such as taxing coal to build nuclear, wind, solar. That's not feasible with air travel yet, which leaves a consumption tax, those are regressive.

Taxing dirty electricity generation is regressive taxation, too; like I said, it's an original issue. A first step would be to pay out all the generated carbon taxes on a per capita basis.

This would never happen in America because it would require Americans addressing their views on transit and addressing their pitiful consumer rail or even consumer bus industries.

An extreme example would be organs.

It is probably wiser to judge based on emissions per user.

https://www.easa.europa.eu/eaer/system/files/usr_uploaded/21... section 7.3 for the citation on aviation (gah, is the europa.eu website slow).