[jabl]

As another poster pointed out, the climate forcing due to high altitude emissions is about a factor of 2.6 worse than the CO2 alone. So 2.6 becomes about 6.8%, and rising fast. And to make it even worse, we basically know how to decarbonize other forms of transportation and electricity production, heating, some major industrial processes etc., meaning that when those solutions start rolling out at scale, air travel will rise even faster as the proportion of the total.

By all means, let's continue developing aerospace technology, but I think it's a fantasy that we'd be able to have anywhere close to the same volume of flights as today in a decarbonized world.