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

[Buzz Bloom]

As air is not an ideal gas it's temperature does not only depend on translational kinetic energy but also on the energy of vibration and rotation of the molecules.

Hi DrStupid:

I think that for the concept of temperature to be meaningful, the stuff for which temperture is to be measured must be in a steady state. I accept that the vibrational and rotational energy of a gas (ideal or otherwise) may be included in averaging the energy of a mass of stuff, including a non-ideal gas like air. But how exactly is such a measurement made? A measuring device must take some time to complete the measurement. The amount of time this will take is much longer than the time for any excited molecule to spontaneously re-emit a photon which will carry away the energy of the excited state.

Can you cite any reference that shows that the temperature of a gas, ideal or otherwise, can be measured as higher when the gas is irradiated with IR?

Regards,
Buzz

 

[Buzz Bloom]

They are then transferring that energy via conduction to the Nitrogen and the Oxygen in the system.

Hi JDoolin:

This quote is incorrect. In my post # 28 I described the behavior of an excited CO₂ molecule in some detail. It very quickly gets rid of the energy of its excited state by spontaneous re-radiating it away as a IR photon. No conduction of this energy is possible to any other molecules because conduction takes longer.

Regards,
Buzz

 

[votingmachine]

Hi DrStupid:

I think that for the concept of temperature to be meaningful, the stuff for which temperture is to be measured must be in a steady state. I accept that the vibrational and rotational energy of a gas (ideal or otherwise) may be included in averaging the energy of a mass of stuff, including a non-ideal gas like air. But how exactly is such a measurement made? A measuring device must take some time to complete the measurement. The amount of time this will take is much longer than the time for any excited molecule to spontaneously re-emit a photon which will carry away the energy of the excited state.

Can you cite any reference that shows that the temperature of a gas, ideal or otherwise, can be measured as higher when the gas is irradiated with IR?

Regards,
Buzz

Surely you have seen or played with an infrared lamp? It warms things. Air is difficult to experience that warming, as it has such low heat capacity. But it does warm. If there is something in the air with higher IR absorption, then the infrared lamp will warm it more.

Hi JDoolin:

This quote is incorrect. In my post # 28 I described the behavior of an excited CO₂ molecule in some detail. It very quickly gets rid of the energy of its excited state by spontaneous re-radiating it away as a IR photon. No conduction of this energy is possible to any other molecules because conduction takes longer.

Regards,
Buzz

Critically though, the infrared that is of interest is emitted from the Earth outward, and the infrared emitted by the CO2 is in a random direction. The infrared from the Sun headed at the Earth is also intermediated by the same process.

 

[JDoolin]

The total internal energy of the gas is based on translational, rotational, and vibrational energy of the gas, but the temperature is based entirely on the translational portion of the kinetic energy.

Here's an equation from my notes.

U=n N_A \frac{df}{2}(\frac 1 2 m \overline{v^2})=\frac{df}{2}nRT=n C_v T = \frac{df}{2}PV

See the n R T is multiplied by the degrees of freedom... df=3 for an ideal monatomic gas (Argon), df=5 for an ideal diatomic gas (Oxygen, Nitrogen).

That's wrong or misleading. You forgot to mention that the IR radiation is not only absorbed but also emitted in the same order of magnitude (which is clearly not negligible). The spectra in my post #24 show that there is around 25 % of the original IR intensity left in the Sahara region and almost 50 % in the Mediterranean spectra (which is clearly significant). The reduction of the IR intensity will be further increased by additional CO2 but it will never reach 100 %. There is no such thing like CO2 saturation.

(Sorry... there are a lot of things to remember all at once. Let me repeat the question, with that in mind. I really don't think it changes the central question here, though.)

Do we have a way of defining the boundary between "negligible emission/absorption" and "significant emission/absorption"

Clearly CO2 has significant emission/absorption in the 667 cm line. I think that we can say the CO2 spectrum is "saturated" there; It's already absorbing 100% of that light (on the bottom surface) Doubling or tripling the concentration should keep it at 100%--no additional heat absorbed. (Then, it is still possible in that case that if the gaussian distribution of velocities of Carbon Dioxide were widened, you could still get more heat absorption.) (Also, if the top surface of the gas were for some reason significantly colder than 220 Kelvin it would re-emit less than 25% of the original IR intensity)

And then there's regions where there is "insignificant emission/absorption". Maybe it absorbs .01% of the light. In those areas, the gas is transparent. Insignificant means essentially zero, and doubling, tripling the concentration of the gas wouldn't change it's transparency. It would go up to .02% or .03% but it would still be insignificant.

But is there something in between--bandwidths where it's currently absorbing 20% of the light, and doubling or tripling the concentration would make it absorb 40% or 60% of the light?

 

[JDoolin]

Surely you have seen or played with an infrared lamp? It warms things. Air is difficult to experience that warming, as it has such low heat capacity. But it does warm. If there is something in the air with higher IR absorption, then the infrared lamp will warm it more.

Critically though, the infrared that is of interest is emitted from the Earth outward, and the infrared emitted by the CO2 is in a random direction. The infrared from the Sun headed at the Earth is also intermediated by the same process.

I think this sort of answers what I asked in post 47... This is what my intuition says, as well. (I shouldn't say "intuition" but rather my "working model" of greenhouse gasses) If there are no greenhouse gasses present in the air, then the air won't warm up. i.e. if it is entirely made of Nitrogen, Oxygen, and Argon. But if there are greenhouse gasses in there, the greenhouse gasses would catch the infrared light, and heat up the gas.

But then again, I've not done the experiment in detail...

I know my SKIN warms up if I aim an infrared lamp at it, but I don't know for sure whether the AIR between the lamp and my skin warms up.

 

[Buzz Bloom]

Hi votingmachine:

Surely you have seen or played with an infrared lamp? It warms things.

Of course IR radiation warms "things" - SOLID and LIQUID things, not GASSES.

Critically though, the infrared that is of interest is emitted from the Earth outward, and the infrared emitted by the CO2 is in a random direction.

As I explained in detail in post #28, HALF of the IR absorbed by CO2 (and other greenhouse gases) is re-radiated back to the Earth's surface.

The infrared from the Sun headed at the Earth is also intermediated by the same process.

This is true, but the IR from the sun is a very small fraction of the radiant energy from the sun.

Regards,
Buzz

 

[Buzz Bloom]

The total internal energy of the gas is based on translational, rotational, and vibrational energy of the gas, but the temperature is based entirely on the translational portion of the kinetic energy.

Hi JDoolin:

Thanks for correcting my mistake regarding temperature. I had thought I had remembered correctly (from ages ago) that it only included translational kinetic energy, but I wasn't sure. And even if it did include rotational and vibrational energy, that didn't affect the argument because of the speed of re-radiation.

Regards,
Buzz

 

[Buzz Bloom]

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 result in 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.

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.

(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 in other ways.
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 is 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.

ADDED
I looked up the paper by Hanel & Conrath, and your typo is that "cm" should be "cm^-1". The value 667 is a frequency in this uncomfortable unit defined as the inverse of wavelenth. This means that the wavelength you intended is 15 μm.

Regards,
Buzz

 

[votingmachine]

Hi votingmachine:Of course IR radiation warms "things" - SOLID and LIQUID things, not GASSES.

I understand that the proper answer is that the energy is promptly re-radiated, and that has been well stated here. The problem with an infrared lamp is there is always some convective heating. So my bad. As I gave the answer I was puzzling over how you could eliminate the surface effects, and measure with an IR thermometer shielded from the light bulb. I was thinking that it would register temperature rise ...

Nope, I don't think I could get around the convective heat. Never mind. My mistake. The convection from the various surfaces makes me miss the re-emittance.

 

[Buzz Bloom]

I decided that a very brief history of the changes of educated opinions about the "greenhouse effect" might be of some interest in this thread.

In about 1902 (I am not sure of the exact date) a graduate student of Knut Angstrom (son of Anders Angstrom after whom the Angstrom unit was named) demonstrated that CO2 is NOT warmed by being irradiated by IR. This experiment was later reproduced by others. This result (and other work by Knut Angstrom) caused a complete reversal in educated acceptance of the "greenhouse effect" that had developed since early in the 19th century. (The term was first used in this way by Nils Gustaf Ekholm in 1901.) At the time there was no alternative mechanism known that could explain how the greenhouse effect might work.

A half century later, in 1955, Gilbert Plass published a paper titled "The Carbon Dioxide Theory of Climatic Change".
http://onlinelibrary.wiley.com/doi/10.1111/j.2153-3490.1956.tb01206.x/pdf
Besides refuting the conclusions about the greenhouse effect from Knut Angstrom's work, this paper includes an excellent history summary regarding the greenhouse effect. Plass's paper un-reversed the educated opinions against the greenhouse effect caused by Angstrom.

 

[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.