[jeffreyH]

That sounds reasonable to me.

[Bored chemist]

What I would do with the data is: publish a credible estimate of the effect of CO2 variation on mean atmospheric temperature based on a priori calculation, not a posteriori modelling. Then wait and see what happens.

If my prediction turns out to be correct, we have a rational basis for reducing CO2 emissions, or ignoring them, depending on the magnitude and sign of the predicted effect.

If my prediction turns out to be incorrect, then we have a rational basis for doing something positive about mitigating the effects of climate change rather than worrying about a non-cause. 

I must be missing something.
You want the spectra of pure CO2 at 1 atm pressure measured with 2 metre and 4 metre path lengths?
Same temperature, same pressure, no other gas present?

You don't understand why nobody has done this and published the results?

[jeffreyH]

Is this the right room for an argument?
I've told you once.
No you haven't...
https://www.nasa.gov/topics/earth/features/vapor_warming.html

[Bored chemist]

Is this the right room for an argument?
I've told you once.
No you haven't...
https://www.nasa.gov/topics/earth/features/vapor_warming.html

"Andrew Dessler and colleagues from Texas A&M University in College Station confirmed that the heat-amplifying effect of water vapor is potent enough to double the climate warming caused by increased levels of carbon dioxide in the atmosphere. "
Thanks for citing NASA's observation that, while CO2 makes things worse, water vapour makes them worse by a factor of  2.
Give that we can't directly control water vapour...

[alancalverd]

I must be missing something.
You want the spectra of pure CO2 at 1 atm pressure measured with 2 metre and 4 metre path lengths?
Same temperature, same pressure, no other gas present?

You don't understand why nobody has done this and published the results?

What interests me is a measurement of the effect of doubling the concentration of carbon dioxide in the atmosphere, with no confounding effect from water. The spectral detail doesn't matter greatly: what matters is the change in total transmittance over the infrared region.

It seems that there are two ways of approximating this, either to measure the effect of doubling the path length through pure carbon doxide at atmospheric pressure (given that 300 ppm  distributed through the entire atmosphere is roughly equivalent to 2 m of pure gas at 1000 mb pressure) or to simply double the concentration in a reasonable sample of dry ambient air and extrapolate the Beer-Lambert equation to 50 km path length. That would be a more realistic approximation as it takes into account the true pressure broadening due to nitrogen, oxygen and argon rather than just carbon dioxide, but it needs to be at least 50,000 times more accurate so might not be feasible.   

Now the first experiment is obviously feasible with kit you can find in a decent undergraduate laboratory, and the second may need a bit of instrumentation development. Alas, I don't have the facilities or the time at hand right now to do either, but it's the kind of project that could entertain a bored chemist!

[jeffreyH]

Is this the right room for an argument?
I've told you once.
No you haven't...
https://www.nasa.gov/topics/earth/features/vapor_warming.html

"Andrew Dessler and colleagues from Texas A&M University in College Station confirmed that the heat-amplifying effect of water vapor is potent enough to double the climate warming caused by increased levels of carbon dioxide in the atmosphere. "
Thanks for citing NASA's observation that, while CO2 makes things worse, water vapour makes them worse by a factor of  2.
Give that we can't directly control water vapour...

My pleasure. Glad to be of service.

[jeffreyH]

We have to accept that at some point we would find ourselves in an upward trend in temperature since this has always been the case for the cycles the planet goes through. We exacerbate it and then employ the "It's someone else's problem" strategy as individuals and as a race. A lot of profiteering happens along with denial. I think as a race we should just grow up.

[alancalverd]

It is important to distinguish between skepticism (what is the cause?) and cynicism (how can I make a career out of the effect?).

[Bored chemist]

I must be missing something.
You want the spectra of pure CO2 at 1 atm pressure measured with 2 metre and 4 metre path lengths?
Same temperature, same pressure, no other gas present?

You don't understand why nobody has done this and published the results?

What interests me is a measurement of the effect of doubling the concentration of carbon dioxide in the atmosphere, with no confounding effect from water. The spectral detail doesn't matter greatly: what matters is the change in total transmittance over the infrared region.

It seems that there are two ways of approximating this, either to measure the effect of doubling the path length through pure carbon doxide at atmospheric pressure (given that 300 ppm  distributed through the entire atmosphere is roughly equivalent to 2 m of pure gas at 1000 mb pressure) or to simply double the concentration in a reasonable sample of dry ambient air and extrapolate the Beer-Lambert equation to 50 km path length. That would be a more realistic approximation as it takes into account the true pressure broadening due to nitrogen, oxygen and argon rather than just carbon dioxide, but it needs to be at least 50,000 times more accurate so might not be feasible.   

Now the first experiment is obviously feasible with kit you can find in a decent undergraduate laboratory, and the second may need a bit of instrumentation development. Alas, I don't have the facilities or the time at hand right now to do either, but it's the kind of project that could entertain a bored chemist!

Sorry, but I'm not that bored and I hope I never will be.
You probably don't realise it, but you are proposing an experiment to determine whether or not photons have a memory.
Since there's no plausible mechanism for that, and no evidence to suggest that it's true, there's no point doing the experiment.

[alancalverd]

What utter drivel - unworthy of you, BC.

Do they really hand out chemistry degrees at Trump University? Or have you just had a bad night?

[Bored chemist]

I don't know, but they hand them out at Oxford, which is where I studied.

You posted a picture of the absorption spectrum of the atmosphere. There are wavelengths where CO2 absorbs almost all the incident IR, and there are wavelengths where it absorbs practically none.
So, do you accept that there are wavelengths where it absorbs (to any given degree of accuracy) exactly half the  IR that goes through it?

And, since you are proposing to use a path length of 2 metres of CO2 at a atmosphere as a mimic for the absorption in the air, I presume that you accept that there are wavelengths where a 2 metre column of CO2 absorbs half the incident IR.

Now imagine that I connect a pair of 2 meter pipes together to make a 4 metre pipe.
I shine IR at this wavelength into one end of the pipe.
Half of the radiation is absorbed  in transit through the first metre of CO2.
And half the remaining IR is absorbed in transit through the second metre.
This is the thing you didn't understand.
The fraction absorbed has to be independent of  what has happened before- because photons do not have a memory.
So the 4 metre pipe, at this wavelength absorbs exactly 3/4 of the radiation (and the other 1/4 goes through.

Do you accept that?

Now lets imagine choosing a different wavelength.
We measure the absorbance for the 2 metre column of gas. and we find that some fraction- let's call it Z -gets absorbed.
Obviously 1-Z gets through
And if we now put a second 2 metres of CO2 in the way it absorbs exactly the same fraction (Z) of the IR.
So the amount that gets through both  columns of gas is (1-Z)(1-Z)

If I know the fraction that's absorbed by a 2 metre column of gas at any wavelength I can calculate- mathematically exactly- the absorbed fraction by a 4 metre column. I don't get any additional information from the second 2 metres of gas.
In fact, if I use the units for measuring absorbance of light (rather unoriginally called absorption units) all I have to do is multiply the absorption by 2.

If I use the units that are of interest to spctroscopists- who aren't particularly concerned about the size  and pressure of the kit, but about the properties of the molecules themselves, the absorption spectrum (expressed as a capture cross section per molecule) is exactly the same for a 2 metre tube as for a 4 metre tube.
https://en.wikipedia.org/wiki/Absorption_cross_section
The reason why nobody publishes the results of the experiment you have talked about is that, depending on the units, the difference either looks exactly the same as the absorbance of the 2 metre pipe, or the difference is exactly zero.

Now, since you have made it abundantly clear that you not only don't know hat you are talking about, but you think that I'm wrong- precisely because I do know my subject- you have proved that your problem is this.
https://en.wikipedia.org/wiki/Dunning%E2%80%93Kruger_effect
And we can safely ignore anything else you say about it.

[alancalverd]

I strongly recommend you to review your undergraduate notes on absorption and practical spectroscopy.

[Bored chemist]

I strongly recommend you to review your undergraduate notes on absorption and practical spectroscopy.

OK I did. It turns out that I got rid of them decades ago.
Now  was there anything in particular you needed me to help you with?
Or do you still think that light somehow behaves differently when it travels through a second column of gas after going through the first one?
If so, how does it know?
How does it "remember" where it has been?

[alancalverd]

Perhaps they missed this bit out at Oxford, but there are plenty of elementary texts on the internet.

When light passes through a selective absorber, fewer photons of the selected energies remain. That is how stained glass works (and there's no shortage of that in the college chapels).  So the spectrum changes along the path length. Suppose we had a filter that absorbed red but not blue light. If you increase the thickness of the filter, the red part of the spectrum weakens but the blue part is unaffected.  At some thickness, adding more path length has very little apparent effect because there isn't much red left.

The Beer-Lambert equation applies to each and every frequency individually.

Carbon dioxide is a frequency-selective ("comb")  filter.

So the question is, at what thickness of filter, whether you measure it as path length through pure carbon dioxide or mean atmospheric concentration, does adding more have a negligible effect?  Or, if you like, what would be the effect on the incident and radiated IR spectra, of doubling the present concentration?

Your help would be greatly appreciated in answering this question.

[Bored chemist]

Perhaps they missed this bit out at Oxford, but there are plenty of elementary texts on the internet.

When light passes through a selective absorber, fewer photons of the selected energies remain. That is how stained glass works (and there's no shortage of that in the college chapels).  So the spectrum changes along the path length. Suppose we had a filter that absorbed red but not blue light. If you increase the thickness of the filter, the red part of the spectrum weakens but the blue part is unaffected.  At some thickness, adding more path length has very little apparent effect because there isn't much red left.

The Beer-Lambert equation applies to each and every frequency individually.

Carbon dioxide is a frequency-selective ("comb")  filter.

So the question is, at what thickness of filter, whether you measure it as path length through pure carbon dioxide or mean atmospheric concentration, does adding more have a negligible effect?  Or, if you like, what would be the effect on the incident and radiated IR spectra, of doubling the present concentration?

Your help would be greatly appreciated in answering this question.

You say "Your help would be greatly appreciated in answering this question."
But I already gave you a lot of help  on that. You called me rude names for my trouble.
The help I gave you was to point out that, once you have the spectrum at one concentration or pathlength, you can calculate it at others- you don't need to do any more measurements.
When I explained that this was the case - and teh reason- which is that photons have no memory- you said "What utter drivel - unworthy of you, BC.

Do they really hand out chemistry degrees at Trump University? Or have you just had a bad night?"

Now, let's try again.
For example, lets's consider some stained glass- since you brought it up.
If I choose a wavelength I can measure the amount of light that gets through the glass.
And I can express that as a fraction of the amount of light I shone onto it in the first place.

(It seems that the important difference is that Oxford doesn't just teach you that "When light passes through a selective absorber, fewer photons of the selected energies remain. ", they also tell you how to calculate the fraction that will get through two pieces of glass (as long as you know the fraction that gets through one piece).
Now I don't know where you leaned this stuff, (you clearly did because you cited it earlier in the form of teh Beer Lambert law) but it seems you don't understand it.

The BL law applies, exactly, at any given wavelength.

So, when you proposed ( a while back) that I did an experiment
"Anyway. as you are a spectroscopist, you can easily do the experiment. Isolate a metre or so of dry air, measure the transmittance in the CO2 spectrum, and add another 400 ppm of CO2. Now extrapolate to 5000 m or whatever you consider to be the effective thickness of the atmosphere, and see what happens."
I pointed out that there's no point.
I can calculate the result.
Because you don't understand what you are talking about you said "What I find surprising about the CO2 debate is that nobody seems to have published the experimental result, which would be a lot easier to obtain than a model prediction, and a lot more credible since all the models to date seem to have been wrong or dependent on suspiciously "adjusted" data."

Nobody has done the experiment, and nobody has published the result, because it is pointless.
It would provide no additional information.

That only leaves the other thing which you say you are hoping to find ...
"So the question is, at what thickness of filter, whether you measure it as path length through pure carbon dioxide or mean atmospheric concentration, does adding more have a negligible effect? "
And the answer to that is simple.
Define "negligible".
And answering that question is the point of all the models- how big a change in energy flux does it take to make a difference.

So, do you now understand that, unless photons have a memory, you were repeatedly  suggesting doing something pointless?

[alancalverd]

Excellent! You say that the experiment will provide no additional information, so I presume that you already have the information I seek.

If you know the comb linear absorption coefficients for pure CO2 at 1 atm pressure from NIR to about 10 microns, I'd be grateful for the numbers. However if you think the presence of other gases significantly alters the pressure broadening (your definition of significant will do!) then we need to consider  what actually happens to the IR absorption when we increase the CO2 content from say 300 to 600 ppm.

These are the numbers I haven't been able to find on line, but I think you will agree they are important if we want to make a scientific prediction of climate change rather than extrapolate a model.

The reason for proposing the experiments is because it seems that many people do not understand the implications of the BL law. It's fundamental to radiology, but from some 25 years of teaching it, I know that however well a class of radiographers manages to calculate the entry/exit dose ratio for a patient, they never believe it until they have measured it!   

For what it's worth, my usual interpretation of a "negligible" effect is "indistinguishable from  the variance due to other, uncontrollable causes". This  is the basis for most legislation around potential risks and estimated probability of causation.

[Bored chemist]

Excellent! You say that the experiment will provide no additional information, so I presume that you already have the information I seek.

Why make that presumption?
It's not correct, and it's not a logical deduction.
I said essentially "measuring the same thing a second time will not give you any more information".
That is not an indication that anyone has made the measurement, not that I know what that measured data will be.
It just says that your proposal to measure it twice was silly.

However you have already posted graphs of the data.
What you haven't got is a model for heat transfer in the atmosphere.
You also need to look at the change in the spectrum with temperature and pressure.
Those are the difficult bits.
Have fun.
Here's a hint- the people who have studied these things recon  that the change from 300 ppm to 400 ppm is significant.
Since you didn't seem to even know what you needed to look at to determine whether or not that change is significant, it's fair to say that their assessment is better judged than yours.

[alancalverd]

Perhaps you would be so good as to point me to the numbers used by the people who have studied these things, as distinct from the people who have attempted to model them from historic "adjusted" data. I haven't judged anything as I don't pretend to have the data on which to make a judgement. I'm simply asking for it. 

You will recall that the change of CO2 absorption spectrum with temperature and pressure can be calculated for any given spectral line, and both  broadening effects are proportional to absolute T & P. It is quite clear that atmospheric pressure won't change  by more than 100 ppm if we double the quantity of CO2, and a surface temperature change of  less than 5 degrees isn't going to affect the total absorption measurably. I'm more than happy to look at these second-order effects, but we need the first-order data first!

Heat transfer in the atmosphere is dominated by the condensation and freezing of water, as you well know. Problem is that nobody has a global model because of the singularities inherent in a rotating atmosphere.  But we can at least calculate the radiant inputs and outputs of an idealised dry, stationary atmosphere if we know the linear attenuation coefficients of the filters.   

[Bored chemist]

... the people who have studied these things, as distinct from the people who have attempted to model them from historic "adjusted" data. I haven't judged anything as ...

You will recall that the change of CO2 absorption spectrum with temperature and pressure can be calculated for any given spectral line, and both  broadening effects are proportional to absolute T & P. It is quite clear that atmospheric pressure won't change  by more than 100 ppm if we double the quantity of CO2, and a surface temperature change of  less than 5 degrees isn't going to affect the total absorption measurably. I'm more than happy to look at these second-order effects, but we need the first-order data first!

Heat transfer in the atmosphere is dominated by the condensation and freezing of water, as you well know. Problem is that nobody has a global model because of the singularities inherent in a rotating atmosphere.  But we can at least calculate the radiant inputs and outputs of an idealised dry, stationary atmosphere if we know the linear attenuation coefficients of the filters.   

I think you have judged it.
Temperature induced broadening in terms of the doppler effect depends on the square root of the temp so, in saying it's proportional you are you are (once again) wrong.

The actual spectrum of the absorbance also varies with temperature (exponentially)  because the occupation of the various energy levels is temperature dependent.
You seem not to have taken note of that.

The actual spectrum can be found here- it's a JCAMP file which isn't that commonly used.
http://webbook.nist.gov/cgi/cbook.cgi?ID=C124389&Type=IR-SPEC&Index=1#IR-SPEC
Obviously, it's just data on how CO2 absorbs IR so there's no way it can be " historic "adjusted" data" whatever that might mean.
However , as you say, the temperature and pressure dependence is fairly small.
The other thing you say is this "Heat transfer in the atmosphere is dominated by the condensation and freezing of water"
Well, it's a big effect, a lot of the time and so you can't usually ignore it.
However, by exactly the same argument that you have adopted for ignoring the difference in CO2 spectra,- i.e. the atmosphere isn't changing much-you can say that the water in that atmosphere isn't changing much.

I look forward to seeing:
Your apology for your earlier comments about my education
Your explanation of why you have posted so many things that just are not true and, of course
your model for heat transfer in that atmosphere.

By the time you have drawn up a sensible model I should be able to get some nice IR data for you.
Would a .csv file do?

[jeffreyH]

It's nice to see physicists and chemists working towards mutual cooperation. Even if in a round about way. The results may be very interesting.