Is Greenhouse Gas the Main Cause of Global Warming? Experiments and Evidence

[JDoolin]

Clearly CO2 has significant emission/absorption in the 667 cm line. I think that we can say the CO2 spectrum is "saturated" there
Hi JDoolin:

I tried to find online some information about the CO2 absorbsion spectrum, but my search seems to resulti n a saturation by stuff put out by skeptics. Somewhere in my files I have this information, but right now it is "lost". "667 cm" cannot be right. That's 6.67 meters. That's a radio wave length. Probably a typo. For the purpose of this post, I am going to designate the wavelength you intended as w.

Typo, yes. I meant 667 /cm. or more commonly written 667 cm^-1 I guess it's around 15 micrometers.

I am not sure what "saturated" means here. I have seen this term used in two ways:
1. All of the IR from Earth at wavelength w is currently 100% absorbed.
2. The current CO2 in the atmosphere has absorbed all of the IR radiation at wavelength w from the Earth that this CO2 can hold.

(1) has been used by greenhouse effect skeptics to argue that more CO2 cannot have any effect. I belief this argument has been thoroughly discredited. I will try to find some references and cite them in a separate post.

What I mean by "saturated" is that the Carbon Dioxide is 100% opaque in some wavelengths, and 100% transparent in other wavelengths. If it is 100% opaque, then you wouldn't be able to make out any ground-detail in that color. You would just be able to see the upper surface of the gas in that color. (re-emitted light)

If there are any wavelengths where the Carbon Dioxide is 20%, 40% or 60% opaque, then I would be effectively convinced that the spectrum is not saturated. If it is not perfectly opaque, then I think you would still be able to see some ground detail in that color. (light from the ground)

(2) may have been demonstrated, but I am not sure. It should be a testable proposition. In any case, I think the concept needs a clearer definition.
If (2) is true, it would strongly support the concept that more CO2 will cause more IR photons at wavelenth w from Earth to be absorbed, and thereby more heating of the Earth.
If (2) is false, then this would mean that the current level of IR radiation at wavelength w from the Earth (and also from the sun?) is insufficient to saturate the current amount of CO2. This could be interpreted as not all CO2 molecules are in an excited state at the same time, which seems quite plausible. It might also be interpreted inotherways.
Each IR photon from the Earth at wavelength w has a chance of being absorbed by a CO2 molecule if the photon passes within the molecule's absorbsion cross section area, and the molecule not already excited. I understand that this cross section depends on several variables which I do not understand very well. In any case, whatever the IR radiance is from Earth, and what ever the relative density of CO2 is in the air, it is plausible that some (perhaps a small) fraction of absorbable photons at wavelength w will escape into space without being absorbed. That means, at least in some reasonable sense, that more CO2 is still likely to absorb more such photons.

Regards,
Buzz

You've been saying that the Carbon Dioxide atoms don't "hold onto the photon for very long, but immediately re-emit it." I don't think that's the way it works in my model. That vibrational mode of kinetic energy at the 15 micrometer wavelength allows the Carbon Dioxide molecule to interact electromagnetically. But it can convert that energy from that vibrational mode into transverse or rotational kinetic energy, which causes the temperature of the molecules to rise.

Conversely, at the top layer of the atmosphere, that translational and rotational kinetic energy occasionally turns into the vibrational mode, which then emits a photon, in the relevant frequency.

So in that case, of course, the Carbon Dioxide can't become saturated in that way. If the photon can be converted into the vibrational mode, and the vibrational mode can be converted into translational mode, then the photon can raise the temperature of the gas, and the temperature of the gas can go up and up without saturating.

But if the vibrational mode can't do anything except re-emit a photon, then what you're saying makes sense; that the infrared light can't raise the temperature... And then all of the extra energy would have to be held by higher densities of infrared photons throughout the space (I guess?)

 

[D H]

Thread locked for moderation. I've been too busy as of late, and this thread has spun out of control.