"Aidan Stanger" wrote in message
...
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?

The green house effect is caused by CO2 in the upper atmosphere bouncing
back infra-red radiation to the earth.

The fact is, incoming radiation from the sun is high frequency because the
sun is very hot. CO2 is transparant to high frequency radiation.

The Earth is much cooler, so it emits low-frequency radiation, which CO2
absorbs and reflects - hence greenhouse.

CO2 at ground level has little effect, but in the upper atmosphere its where
it really has it's effects. So in theory, a pollution source that puts CO2
straight up there, rather than at ground level will do more harm.

The argument is slightly spurious because atmospheric gases have an
excellent mixing coefficient, and any local high concerntrations of CO2 will
be rapidly mixed until the concerntration is nearly uniform - indeed recent
analysis found that the concerntration of CO2 was extremely constant around
the world.