Angus Bryant wrote:

This seems deeply concerning. If air traffic growth continues at it's
present rate, then in 50 years time air travel will account for 40% of all
CO2 (greenhouse gas) emmissions.

And it's put directly into the upper atmosphere which has more of a
detrimental effect than if it were released at ground level.

I've heard this claim an awful lot, but not an explanation as to why.
What effect does CO2 have in the upper atmosphere that it does not have
at ground level?