There are two kinds of difficult ethical problems: situations where it is genuinely hard to work out what the right course of action is, and situations where the right course of action is fairly clear but people are unwilling to do it.
Air travel is an example of the second type. I think it’s pretty unarguable that our excessive emissions of greenhouse gas pollution are unethical. Long flights produce excessive amounts of CO2, and many (perhaps most) of those long flights serve morally unimportant purposes. As such, people should fly less, because their decisions to fly harm innocent strangers. And yet, few people are willing to do that. They put their own preferences and convenience ahead of the interests of others. Eating most types of meat and dairy products probably falls into this category too – at least if you think the suffering of non-human animals has any moral importance.
The international distribution of the costs of dealing with climate change may be an ethical problem of the first type. It’s not entirely clear what the ethical status of historical emissions is, what the relevance of population is, the importance of per capita emissions, etc. While it may not be entirely clear who should pay exactly what, I do think it is clear that every country needs to take action – far more action than they are taking now.