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

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?

Up to this point you are reasonably correct, but it is not possible for CO2
to reflect radiation. It absorbs infra-red in well-defined bands, as does
water vapour. Water droplets in the form of clouds can reflect radiation,
which is why it is cooler on cloudy days. What can happen is that CO2 can
absorb short wavelength radiation and re-emit it as longer wavelength
radiation, but that depends on temperature, and is unlikely to occur in the
atmosphere.

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.

Because the atmosphere contains a lot more H2O than it does CO2, the effect
of water vapour is considerably more than that of CO2, but the processes of
condensation and re-evaporation tend to balance it out. CO2 absorption
depends more on photosynthesis than anything else, although some will
dissolve in water droplets.

Scientists know exactly what happens. Pseudo-scientists don't.
--
Terry Harper
http://www.terry.harper.btinternet.co.uk/