[alancalverd (OP)]

PS does anyone have an authoritative atmospheric infrared absorption spectrum (i.e. one based on verifiable recent measurements) that doesn't show the CO2 bands as saturated? All those I can find suggest that it cannot be the cause of further global warming. I'm all in favour of abandoning fossil fuels (sound political and economic sense) but future generations might question the reason why we did so, and I'd hate to be associated with bad science!

[Bored chemist]

PS does anyone have an authoritative atmospheric infrared absorption spectrum (i.e. one based on verifiable recent measurements) that doesn't show the CO2 bands as saturated?

Yes.
Any spectrum  which is at least half-competent will do that.

[alancalverd (OP)]

Please show me a competent atmospheric absorbance/wavelength spectrum that covers the requisite range. Practically all those I have found on line or in textbooks are either restricted to the visible and near infrared or have a CO2 hump that reaches saturation in the 10 - 20 micron region, and all the long wave data is traceable to Howard or Goody & Robinson in the 1950s.  Transmittance spectra all seem to be nothing but the same curve inverted, showing zero in the 10 - 20 micron CO2 area.

Now either all the published papers on CO2 absorption are wrong or plagiarised from two flawed sources, or the hypothesis that increasing p[CO2] will increase surface temperature is nonsense.

[Bored chemist]

The issue here is not the quality of the spectra, but your failure to understand the nature of saturation.
So here's a rubbish drawing to explain it to you.


bad spectrum.jpg (19.76 kB . 688x582 - viewed 3221 times)

[chiralSPO]

Now either all the published papers on CO2 absorption are wrong or plagiarised from two flawed sources, or the hypothesis that increasing p[CO2] will increase surface temperature is nonsense.

The atmosphere absorbs effectively 100% of the radiation at these wavelengths (if you're looking down the whole length of the atmosphere), but the % absorbance or % transmittance or however you choose take your IR spectrum has very little bearing on the greenhouse effect (it's mechanism, magnitude or cause).

Even if the atmosphere is treated as 100% opaque to the wavelengths absorbed by CO₂, it is straightforward to see that changing the concentration of CO₂ will still change the mean free path of the photons that are interacting with CO₂.

We can think of a photon emitted from the ground and needing to reach "space". It will start out going straight until it runs into a CO₂ molecule and gets absorbed, hangs out for a time before being re-emitted in a random direction until it bumps into the next CO₂ molecule or escapes to space. Essentially it have to take a random walk from the surface to some altitude sufficiently high. And the time it takes has nothing to do with the speed of light (we can assume it is c for this), but rather in how many stops it has to take (each one being a significant delay compared to whizzing by at c), and how much time is being spent traveling the "correct" way.

The higher the CO₂ concentration, the shorter the mean free path of the photons.
The shorter the mean free path of the photons, the more hops need to be taken to escape (exponentially so!)
The more hops needed to escape the slower the rate of energy transfer through the atmosphere.

[chiralSPO]

Think of it this way:

Let, play a game. I have a pile of quarters ($0.25 coins), let's assume they are fair. You can take one and flip it. If it comes up heads you can keep it. If it comes up tails, you owe me a quarter. Once you accrue $1.00 of winnings, you may walk away with it. How many flips will it take you to get $1 of winnings?

Here is one simulation:
THTHTHTTHTHHHHTTHTHTHTHHHTHTTHTHHTHH 36 flips

Ok, now let's play the same game, but with dimes ($0.10 coins). How many flips will it take you to get $1 of winnings?

Which game would you rather play?

The difference here is that we have decreased the mean free path from 1/4 of the way to the target to 1/10 of the way to the target. By increasing the carbon dioxide concentrations from 300 ppm to 400 ppm, we have reduced the mean free path from 1/4000 (24 m of 100 km) of the way up to 1/6250 (16 m of 100 km) (ish)

[Bored chemist]

Think of it this way:

Let, play a game. I have a pile of quarters ($0.25 coins), let's assume they are fair. You can take one and flip it. If it comes up heads you can keep it. If it comes up tails, you owe me a quarter. Once you accrue $1.00 of winnings, you may walk away with it. How many flips will it take you to get $1 of winnings?

Here is one simulation:
THTHTHTTHTHHHHTTHTHTHTHHHTHTTHTHHTHH 36 flips

Ok, now let's play the same game, but with dimes ($0.10 coins). How many flips will it take you to get $1 of winnings?

Which game would you rather play?

The difference here is that we have decreased the mean free path from 1/4 of the way to thee target to 1/10 of the way to the target. By increasing the carbon dioxide concentrations from 300 ppm to 400 ppm, we have reduced the mean free path from 1/4000 (24 m of 100 km) of the way up to 1/6250 (16 m of 100 km) (ish)

To be fair, there's an upper limit to the extent of that effect too. Eventually you reach a point where the energy is carried by the random movement of excited CO2 molecules rather than by radiation.
But we aren't there yet.

[alancalverd (OP)]

So here's a rubbish drawing to explain it to you.

Now show me an authoritative atmospheric absorption spectrum that doesn't look like that in the range 10 - 20 microns.

[chiralSPO]

This is roughly what air looks like by IR (transmittance).


background.png (78.73 kB . 754x415 - viewed 3289 times)

The large feature around 2350 cm^–1 is from CO₂ the other major peaks are from H₂O (it appears there may also be some organics in there too... I see stuff around 2900...

There was a time when I saw some form of this every day (I always subtracted it out as background, because I was interested in what was on the sample holder, not what was in the air. But I always needed to make sure that this is what the background looked like)

[Bored chemist]

I also used to spend a lot of time looking at that sort of thing.
I wonder; is that spectrum from a Perkin Elmer system 2000 FTIR?

Now show me an authoritative atmospheric absorption spectrum that doesn't look like that in the range 10 - 20 microns.

I can't show you one that doesn't look like that, because, as I said, even a half competent one will look like that.
They all look more or less like that somewhere in that range
10 to 20 µM  is 500 to 1000 cm^-1 (The units used on Chiral's spectrum)
The big absorption in the middle is about 4.25 µM
And here's what the spectrum looks like at a much higher resolution From here
https://wiki.anton-paar.com/fi-en/infrared-spectrum-of-carbon-dioxide/##data-imagegroup-64300


better spectrum.JPG (84.16 kB . 1482x546 - viewed 3193 times)

And I took a clip of it zoomed in  and labelled it for Alan

Big better spectrum.jpg (30.14 kB . 444x762 - viewed 3189 times)

[Petrochemicals]

background.png (78.73 kB . 754x415 - viewed 3289 times)

Why is this graph not flat? Or at least linear? Does the sun do a particularly good job in issuing IR around the peak?

[alancalverd (OP)]

That's a very pretty absorption spectrum of a sample of CO2, and there's no disputing that it looks like it should. But what we need is the absorption spectrum of the atmosphere, i.e. showing how much of the surface black body radiation is absorbed in the atmosphere per wavelength. All the plots I have seen indicate that damn near 100% of 10 - 20 micron photons are absorbed by a 60 km air column containing 300 ppm of CO2, i.e. the bands are saturated and have been for at least 100 years Now what happens to total absorption if you add stuff to a mixture that is already saturated at that wavelength? Not a lot, IIRC.

The anthropogenic problem as I see it is that every emission of CO2 is accompanied (apart from burning clean coal) by an emission of H2O, whose absorption bands are very broad and generally not saturated. This is particularly bad news because substituting methane for town gas or coal generates a lot more H2O per molecule of CO2,and likewise diluting heavy alkanes like gasoline or diesel with ethanol similarly increases the H2O/CO2 ratio and the total H2O emission per joule of useful energy generated.

I've often cautioned against doing the right thing for the wrong reason, but it looks as though some intermediate "carbon reduction" processes may actually be doing the wrong thing for an irrelevant reason. Funny that all the scary populist images  of power stations show plumes emanating from stacks and cooling towers, and condescending scientists snort and say "it's only water - you can't see the CO2". But AFAIK water is indeed the problem, and as the ice core data shows, always has been.

[chiralSPO]

But what we need is the absorption spectrum of the atmosphere, i.e. showing how much of the surface black body radiation is absorbed in the atmosphere per wavelength. All the plots I have seen indicate that damn near 100% of 10 - 20 micron photons are absorbed by a 60 km air column containing 300 ppm of CO2, i.e. the bands are saturated and have been for at least 100 years Now what happens to total absorption if you add stuff to a mixture that is already saturated at that wavelength? Not a lot, IIRC.

Yes, the top maximum of the absorption is saturated if you take the whole column of air. But, as Bored chemist points out, there's also the bits of the peak that are not the maximum, and will continue to increase in inensity.

And, as I mentioned, and you conveniently ignored, the total absorption of the atmosphere is not actually relevant. It also happens to increase with increasing CO₂ concentration, but is not the cause of greenhouse effect:

Even if the atmosphere is treated as 100% opaque to the wavelengths absorbed by CO2, it is straightforward to see that changing the concentration of CO2 will still change the mean free path of the photons that are interacting with CO2.

We can think of a photon emitted from the ground and needing to reach "space". It will start out going straight until it runs into a CO2 molecule and gets absorbed, hangs out for a time before being re-emitted in a random direction until it bumps into the next CO2 molecule or escapes to space. Essentially it have to take a random walk from the surface to some altitude sufficiently high. And the time it takes has nothing to do with the speed of light (we can assume it is c for this), but rather in how many stops it has to take (each one being a significant delay compared to whizzing by at c), and how much time is being spent traveling the "correct" way.

The higher the CO2 concentration, the shorter the mean free path of the photons.
The shorter the mean free path of the photons, the more hops need to be taken to escape (exponentially so!)
The more hops needed to escape the slower the rate of energy transfer through the atmosphere.

I know you're no dullard Alan... but you seem to have a particularly strong mental block on this topic. It's not water.

[Bored chemist]

water is indeed the problem, and as the ice core data shows, always has been.

Got evidence?

[Bored chemist]

The anthropogenic problem as I see it is that every emission of CO2 is accompanied (apart from burning clean coal) by an emission of H2O,

Which falls out of the sky almost immediately as rain.
Or, in the case of my condensing boiler, it doesn't even reach the atmosphere

[Petrochemicals]

But what we need is the absorption spectrum of the atmosphere, i.e. showing how much of the surface black body radiation is absorbed in the atmosphere per wavelength. All the plots I have seen indicate that damn near 100% of 10 - 20 micron photons are absorbed by a 60 km air column containing 300 ppm of CO2, i.e. the bands are saturated and have been for at least 100 years Now what happens to total absorption if you add stuff to a mixture that is already saturated at that wavelength? Not a lot, IIRC.

Yes, the top maximum of the absorption is saturated if you take the whole column of air. But, as Bored chemist points out, there's also the bits of the peak that are not the maximum, and will continue to increase in inensity.

And, as I mentioned, and you conveniently ignored, the total absorption of the atmosphere is not actually relevant. It also happens to increase with increasing CO₂ concentration, but is not the cause of greenhouse effect:

Even if the atmosphere is treated as 100% opaque to the wavelengths absorbed by CO2, it is straightforward to see that changing the concentration of CO2 will still change the mean free path of the photons that are interacting with CO2.

We can think of a photon emitted from the ground and needing to reach "space". It will start out going straight until it runs into a CO2 molecule and gets absorbed, hangs out for a time before being re-emitted in a random direction until it bumps into the next CO2 molecule or escapes to space. Essentially it have to take a random walk from the surface to some altitude sufficiently high. And the time it takes has nothing to do with the speed of light (we can assume it is c for this), but rather in how many stops it has to take (each one being a significant delay compared to whizzing by at c), and how much time is being spent traveling the "correct" way.

The higher the CO2 concentration, the shorter the mean free path of the photons.
The shorter the mean free path of the photons, the more hops need to be taken to escape (exponentially so!)
The more hops needed to escape the slower the rate of energy transfer through the atmosphere.

I know you're no dullard Alan... but you seem to have a particularly strong mental block on this topic. It's not water.

If carbon dioxide has increaced 25 percent in 100 years, the temperature of the earth was 300k in 1900, why has earth not increaced in temperature to 400k?

[Bored chemist]

If carbon dioxide has increaced 25 percent in 100 years, the temperature of the earth was 300k in 1900, why has earth not increaced in temperature to 400k?

This sort of thing is the reason why his signature says "For reasons of repetitive antagonism, this user is currently not responding to messages from;
BoredChemist"

He posts stuff that shows he's clueless, and then complains when people point it out.

[chiralSPO]

If carbon dioxide has increaced 25 percent in 100 years, the temperature of the earth was 300k in 1900, why has earth not increaced in temperature to 400k?

One reason is that it is not a linear relationship between average temperature and CO₂ concentration. (the relationship is complex enough there is not just one equation that can be used to model it well, but we can know for sure that it isn't linear)

Another major issue is that the Earth's average temperature is still increasing because of the excess carbon dioxide put out last century, and even if the carbon dioxide concentration were to suddenly stop and remain constant right now, temperatures would still continue to increase for decades (the earth is a big place and it takes a while for it to warm up)

[Petrochemicals]

If carbon dioxide has increaced 25 percent in 100 years, the temperature of the earth was 300k in 1900, why has earth not increaced in temperature to 400k?

One reason is that it is not a linear relationship between average temperature and CO₂ concentration. (the relationship is complex enough there is not just one equation that can be used to model it well, but we can know for sure that it isn't linear)

Another major issue is that the Earth's average temperature is still increasing because of the excess carbon dioxide put out last century, and even if the carbon dioxide concentration were to suddenly stop and remain constant right now, temperatures would still continue to increase for decades (the earth is a big place and it takes a while for it to warm up)

In that case there must be more more than co2 responsible for the vast majority of heat retention.

[Bored chemist]

In that case there must be more more than co2 responsible for the vast majority of heat retention.

Not really.