Quote from futurecurrents:
All right. Maybe Republicans are offended by having to listen to ten year old kids tell them stuff.
So here. Check it out. It's pretty cool. Really.
<iframe width="420" height="315" src="//www.youtube.com/embed/SeYfl45X1wo" frameborder="0" allowfullscreen></iframe>
Actually, that's only part of the story, the less important part relative to what we call the greenhouse effect. I didn't intend to get into this here as many would have trouble understanding it, but I guess I'll make an attempt, particularly because jem has been so confused by that NASA (or was it NOAA) article re CO2 cooling effect.
The demonstration in the video is showing you that CO2 absorbs infra red radiation. (It also coincidentally demonstrates that the guys detector is tuned or filtered so that it is not an extremely broad band IR detector, nor can it detect visible emr.
There are two separate properties of CO2 to consider. The first is its ability to absorb and re-radiate a portion of the ir, emr spectrum. The second property is the transparency of CO2 to the entire visable spectrum, some of the uv spectrum, and some of the IR spectrum.
First the IR absorption properties of CO2. (This is where "jems cooling effect" comes from with regard to CO2 in the outer atmosphere.) CO2 has a simple IR band structure. It has two stretching modes, symmetrical and asymmetrical. Only the asymmetrical leads to absorbtion in the ir region. When an infrared photon, of energy corresponding to an energy encompassed by the ir absorption band of a CO2 molecule, strikes a molecule there is a non-zero probability that it will be "absorbed"; hence the molecule's asymmetrical stretching vibration will undergo a transition to a higher energy state and then spontaneously relax to its ground state by emitting an infrared photon.
A collection of these molecules will emit in all directions, hence molecule in the outer atmosphere will emit some of the absorbed ir back toward outer space and some will be emitted toward Earth where they will eventually strike another molecule and the absorption-emission will be repeated.
If you think of the atmosphere as composed of layers like an onion, you will see that each subsequent layer moving toward earth is exposed to less and less ir so that eventually that portion of the ir spectrum radiated by the sun and absorbed by CO2 is mostly absorbed before it reaches the Earths surface.
But the sun radiates ir over a very broad spectral region, so that ir that is not absorbed by the atmosphere does reach the Earths surface, and we feel that as heat. (the same phenomenon occurs with the other greenhouse gases such as water and methane, but they have more ir active modes of vibration and are hence somewhat better ir absorbers. (Note also that these same gasses also have reflective properties since not all photons will have the correct phase to be absorbed, even if they have the correct energy.)
Now, this is the important point. The phenomenon I have just describes is NOT the greenhouse effect and does not cause the greenhouse effect. In fact what I have just described has somewhat of a cooling effect, because just as the CO2 in the video shielded the detector from the candles heat, the CO2 in our atmosphere, partially shields the Earths surface from direct ir radiation from the sun, but only partially. When you walk outside on a sunny day you are playing the role of the detector in the video experiment, and the sun is playing the role of the candle. You get warm, but not nearly so warm as you would were the atmosphere not there.
I will explain the green house effect in a subsequent post. This requires that the greenhouse gas be transparent (non-absorbing) to part of the solar spectrum and opaque to another lower energy part.
