Oliver Keating wrote:
"Aidan Stanger" wrote...
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.

Are you sure? I thoght it was caused by the atmosphere absorbing the
radiation.

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

Incoming radiation is a mixture of high and low frequencies.

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

I'd not heard anything about the reflection effects of CO2 before. Have
you got a source for that?

However, I had heard about the reflection effects of H2O, of which there
is quite a lot in aircraft exhaust emissions. The URL Angus supplied
confirms that H2O in the stratosphere is thought to be a problem due to
the amount of back radiation it reflects being slightly higher than the
amount of incoming radiation it reflects - although scientists are far
from certain on this.

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.

You say it's the upper atmosphere where CO2 really has its effects.
Other than reflecting some of the radiation back down towards the
ground, what harmful effect would it have?

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.