Since at 2 x 10^-7 mm diameter, CO2 is a very tiny molecule, let's magnify the picture by a factor of 10 million, so that we can imagine a CO2 molecule as a 20 mm diameter marble floating in the air. However, CO2 makes up only 380 of each million molecules of air – the rest are a mixture of all the other atmospheric gases and water vapor – i.e. only one in every 2632 molecules is a CO2 molecule. Let’s imagine that all the other molecules are colored blue, and CO2 molecules are colored red. All the marbles making up our model atmosphere are equispaced at 280 mm apart. When mixed evenly into our model atmosphere (which is what the wind does) a bit more simple math shows that our red marbles are equispaced at 3900 mm (i.e. 3.9 meters) apart. In the real atmosphere, at a height of approx. 5500 meters, pressure is halved from what it is at sea level. A bit more simple math shows that at a height of 5500 meters (55 million kilometers in our model – that’s 143 times the distance from earth to the moon!), our 20 mm diameter CO2 marbles are equispaced at 4.9 meters apart. Now you know why CO2 is called a “trace” gas.
This whole picture we have drawn ( with Peter Morgan's help ) illustrates both how little CO2 there is in the atmosphere, and how relatively little of the radiation it is capable of absorbing and "heating" the atmosphere. We know that most of the other IR radiation bands slips through and doesn't get to do any heating at all. (We've all seen the nice IR photographs taken from the space station.) But some scientists such as
Dr. Heinz Hug ( 
I love that guy's name) who specialize in study of this stuff claims that all of the heat in these particular spectra are indeed absorbed in a relatively short distance, so adding more CO2 to the atmosphere can't affect anything at any rate. Other scientists, such as Dr. Roy W. Spencer at NASA - and one of the leading experts in the field of climate science - doesn't completely agree
We've decided to be exceptionally generous to all concerned in the debate and look at the worst-case scenario, where we'll say that
all of the available heat in the CO2 absorption spectrum is actually captured. We know that man is responsible for about 3 % of it, so with the simplest of math, we have .03 x .08 = .0024. And remember that 8% figure was actually larger than reality, since the two side peaks don't have much energy to capture.
Man-made CO2 doesn't appear physically capable of absorbing much more than two-thousandths of the radiated heat (IR) passing upward through the atmosphere.
And, if all of the available heat in that spectrum is indeed being captured by the current CO2 levels before leaving the atmosphere, then adding more CO2 to the atmosphere won't matter a bit.
In short, the laws of physics don't seem to allow CO2 it's currently assumed place as a significant "greenhouse gas" based on present concentrations. The other "greenhouse gases" such as methane, nitrous oxide, tetrafluoromethane, hexafluoroethane, sulfur hexafluoride, trifluoromethane, 1,1,1,2-tetrafluoroethane, and 1,1-difluoroethane exist only in extraordinarily smaller amounts and aren't even up for serious discussion by any segment of the scientific community. And, since the other components of the atmosphere (oxygen, nitrogen, and water vapor) aren't materially affected by human activity, the "greenhouse effect" is essentially a totally natural phenomenon, unaffected by human activity. We could repeat the spectral analysis and calculations for Oxygen, or O2 ( The percentage of oxygen in the atmosphere remains exactly the same at all heights up to about 85 km, and is about 20.9% by volume ) and Nitrogen (N2) which is the whopper at 78.1% - but we won't. We'll leave that as your homework problem now that you know how to do it. Just look up the atomic absorption spectra for both, and do the math. You'll discover that Oxygen and Nitrogen aren't even "greenhouse gases", so that leaves the principal greenhouse gas... you guessed it.... Water Vapor. Curiously enough, the UN IPCC reports don't even mention water vapor, since it is technically not a "gas" in the atmosphere.
Dr. Roy W. Spencer (Buck's fave) has one of the best comments we've read on this subject:
"Al Gore likes to say that mankind puts 70 million tons of carbon dioxide into the atmosphere every day. What he probably doesn't know is that mother nature puts 24,000 times that amount of our main greenhouse gas -- water vapor -- into the atmosphere every day, and removes about the same amount every day. While this does not 'prove' that global warming is not manmade, it shows that weather systems have by far the greatest control over the Earth's greenhouse effect, which is dominated by water vapor and clouds."
We can safely ballpark water vapor as being responsible for more than 95% of all the greenhouse effect, with oxygen and nitrogen playing no role and carbon dioxide being relatively insignificant... particularly the even smaller human-produced part.
TL : DR : IHTD
