I mean we didn't even close borders (freight & genuinely essential travel excepted) during a deadly pandemic. People were clamouring for their foreign holidays because they couldn't possibly go without just once or twice. It doesn't bode well for reduced flights.
It's likely the only way planet earth will survive is the human race dying out (naturally, as opposed to death by COVID).
But I don't see most people agreeing to be The Last Humans On Earth (with robot end of life care). So at the end of the day there's no harm in trying to mitigate against the damage.
With flights, rationing would be fairer than higher taxes because the latter would see the rich continued to pollute whilst locking out the poor from a one off holiday or visit to family abroad.
Flying aside, one of the simplest ways we could help - and it's something that would save people money rather than adding a financial burden to already struggling people. Call for better made more durable consumer products. Eg. Longer lasting phones and computers (built to cope with software updates, etc).
We need to move to a less throwaway society. Recycle when necessary yes, but I the first instance whenever possible reuse.
Next up another cheap and therefore easy action. Encourage smaller families, through education and free access to contraception.
Moving on to cryptocurrency. Hugely energy hungry. Not the most environmentally friendly option.
So that's three actions to get us going with.