I thought that the problem with air travel is not (just) the amount of CO2 emitted, but also the altitude, which makes the green house effect bigger per ton of CO2.
It's not about CO2 emissions, but rather the high-altitude NOx that contributes more to climate change than low-altitude emissions. However, it's debatable whether the amount is very significant, at least compared to other sources of NOx.
[1] https://en.wikipedia.org/wiki/Environmental_impact_of_aviati...