On Tue, 22 Jul 2008 15:17:29 -0700 (PDT), Mel Rowing
wrote:

CO2 is probably the best known molecule in terms of its infra-red
absorption spectrum.

From this we know that CO2 molecules do not totally block infra red
light regardless of any level of CO2 present.

Essentially (and simply) CO2 molecules absorb IR in a specific wave
band (15 microns) that amounts to ~8% of the energy radiated from the
earth surface. That is not theory it is fact observed on countless
occasions.

That particular band of IR is absorbed to extinction (blocked) The
energy from it is converted to heat which is why, as AGW enthusiasts
never tire of telling us that earth is warmer than it otherwise would
be if CO2 were not present.

However, all other IR wavebands are not blocked. A CO2 molecule blocks
just this specific area of IR and not any other. It therefore not the
case that the more CO2 there is in the atmosphere the more IR will be
blocked. Natural CO2 levels are sufficient to block all the IR that
CO2 is capable of blocking.

This may be true for the centre of the 15 micron band but there are
several fundamental bands of CO2 absorption. There is another strong
one about 4 microns, plus there are numerous weaker overtones,
combination bands, hot bands and isotopic bands. Many of these bands
are not saturated and increading levels of CO2 in the atmosphere will
lead to increased absorption.

These bands do not have a sharp edge as they are made up of many
individual absorption lines. The weaker lines at the edge of the 15
micron band are not saturated and increasing CO2 will cause this band
to broaden the region it absorbs over.