Is Al Gore's Presentation of Global Warming in An Inconvenient Truth Accurate?

[Andre]

Objectively, it seems simple, compare the statements and quantifications in "The Inconvenient Truth" with the suppositions of the IPCC in that period.

 

[vanesch]

Yes I see that you may or may not be speaking tongue-in-cheek there,

Well, of course !

To what end? After making the first statement to 'Bob in the street', do researchers expect to come back later and say 'just kidding then, I was being condescending for your own good, but now I really know, trust me this time, I'm a scientist?'

Just for the sake of the knowledge and the fun of doing experiments. We will have performed the experiment, and we will have seen. That's what science is about, no ?

No, seriously, the only way to establish beyond doubt that the CAUSE of global warming is human-generated CO2 ejection, is to change drastically that ejection. And how are you going to convince the world to change that ejection level ? Just by saying that you want to find out something ? Or by fear mongering ? What will obtain the desired change in CO2 ejection ?

Now, two things: OR the result is that finally there was NO cause-effect relationship. Well, then you can say that things really LOOKED that way, but it turned out not to matter, so after all, burn all that coal without fear ! Go ahead ! The scientists of the beginning of the 21th century were a bit over-cautious, but then, one can't blame them, they were probably honest. They didn't know all we know now. Look at how much smarter and more scientific we are now. Do we think badly of medical science NOW because of some silliness one century ago in the medical world ? Of course not. Yesterday, people were stupid, today they are smart.

OR the result is that there IS a causal effect: in that case, one can say that the experiment DID save the earth, and that we now also know exactly WHY. That the scientists that rang the alarm bell DID have the right intuition. They were visionaries. Nobody is going to blame their initial unscientific attitude anymore then than now. (*) People think bollocks of "scientific rigor" - most don't even understand the word.(*) There are several instances of great scientific discoveries which were correct, but which, after the fact, couldn't have been scientifically established with the initial data. Examples are Einstein's prediction of the deviation of light of a star during a solar eclipse and the first expedition who observed this, and Hubble's discovery of the expansion of the universe. When looking at their initial data, their error bars didn't really allow one to establish the fact beyond doubt!

 

[russ_watters]

Minor quibble with your method, vanesch: We are changing the injection of CO2 into the atmosphere. It's gone way, way up. So I think that regardless of what we do over the next 50 years, we'll get our answer. Maybe the global temperatures will keep going up and maybe they won't.

 

[vanesch]

Minor quibble with your method, vanesch: We are changing the injection of CO2 into the atmosphere. It's gone way, way up. So I think that regardless of what we do over the next 50 years, we'll get our answer. Maybe the global temperatures will keep going up and maybe they won't.

Ok, but what we don't know, is what is the cause, and what is the effect. Is the CO2 increasing because the temperature rises ? Is the temperature rising because the CO2 increases ? Now, I know that there is some indication that at least part of the CO2 present in the atmosphere is of fossile origin (the C-12/C-13 isotope ratio) etc...

So it would be nice to inverse one, to see whether the other follows. It would also allow much better to find out the exact system response.

 

[mheslep]

Just for the sake of the knowledge and the fun of doing experiments. We will have performed the experiment, and we will have seen. That's what science is about, no ?

Fair enough, good for you then.

 

[mgb_phys]

Surely in a democracy it should be decided by the people not a judge?
You could simply put an extra question on the ballot of the next primary.

ps If there's space I would also like a little question about P and NP resolved.

 

[vanesch]

Thanks Vanesch, I've queried this with the author of the article if he responds I'll post his reply.

Hi,

I also contacted the author of the web site. Now, as this was a private e-mail conversation, I'm not going to post his replies, but just give the summary. I will however give my message completely.

I wrote:

Hello!

I've read with some interest your contribution on:
http://www.middlebury.net/op-ed/global-warming-01.html

Now, you raise interesting points, but there seems to me to be one big elementary fallacy in the main argument you bring forward:

"But the entire atmosphere isn't composed of CO2. In fact the current concentration in the atmosphere is only about 380 parts per million. It's what we call a "trace gas". So how much heat can our trace amounts of CO2 actually absorb? The math is simple: 8% ( or .08 ) x 380 PPM ( .000380 ) = .0000304, or about thirty millionths of the radiated heat."

This calculation seems to be unfounded. Absorption has nothing to do with relative composition, but with the cross section times the surface density of absorbing particles. Whether or not you ADD other stuff to it.

Let us assume that, say, 1 bar of CO2 over, say, 5 meters absorbs 8% of the spectrum, just by "being black" in a certain spectral region, and that this region represents 8% of the entire spectral energy content. Fine.

Now, SPREAD this 1 bar of CO2, 5 meter thick, over a column of 20 km. We now have of the order of 0.25 mbar of CO2. Guess what ? The absorption in your 20 km of 0.25 mbar of CO2 is identical to the absorption of your 5m CO2 of 1 bar. So we still pick out 8% of the spectrum, right ?

Now, add 1 bar of nitrogen/oxygen to it. What happens ? In as much as nitrogen and oxygen can be considered transparent, NOTHING changes. There is still the same number of CO2 molecules in a column of 1 square cm. We still pick out 8%.

So I don't see how you can include the RATIO of CO2 to N2/O2 or whatever in the calculation of your maximum "blackness" of CO2...

Once you have enough molecules per cm^2 to "be black", no ADDING other stuff is going to make it more transparent.

cheers,
Patrick Van Esch.

The first reply I got was an explanation of how he didn't take into account the gaussian profile of the absorption but replaced it with square blocks for simplification, pointing out that this gives a more severe absorption than if one would have done the entire integral.

I don't object to this, but it was not my point at all!

So my second message was:

Hello again,

I think you don't understand my objection. I can live with the square
profile, and the 8% for a "black" atmosphere. What I object to, is that
you multiply this with the ratio of CO2 molecules over O2/N2 molecules.
That simply makes no sense. What counts is the amount of CO2 in the
column, not whether there is ALSO N2 or O2. And as such, you arrive at a
ridiculously low absorption (one in a million) which is entirely not
justified.

Remove all the N2/O2, while you keep the 0.3 mbar or so of CO2, and,
according to your technique, you would obtain 8% (because the ratio is 1
now). Well, the real absorption is going to be the same.

Add 1000 bar of N2, and you would, according to your estimation, even have
1000 times less absorption. That is simply not correct.

So there is no justification at all to multiply the 8% with 0.0003...

cheers,
Patrick.

This time, his reply was about the non-uniformity of the absorption in a real atmosphere, and that the real transport problem is a hairy problem to solve, about the fact that the atmosphere is not adiabatic, the lowering of pressure with altitude etc...

I have to say I was at loss at what was the relationship between all these correct complications, and my elementary objection.

I will quote one phrase:

If you add N2 and O2 to the mix, you do change the collision cross sections, because the CO2 is more "spread out" and becomes a smaller "target".

This is a wrong statement. You don't change the individual molecular cross section because the molecules are more spread out.

So I replied:

===> I'm pretty acquainted with radiation transport problems, but more in
the nuclear world. For instance, typical problems I look into is the
transport problem of neutrons generated in a radioactive source, and which
propagate through a scattering/absorbing medium.

The issue we look into here is similar (although I can understand that
some details differ), and I know that general radiation problems can be a
pain.

However, you will not convince me that a homogeneous mixture of two
substances, one of which acts as an observer, will become more transparant
as JUST the amount of absorber, in the ratio of the two substances. In
fact, all extra scattering by the second material will actually INCREASE
the overall absorption, simply because the total path length of the
radiation has become longer than the direct "exit" path from source to
escape boundary.

If you want to go for a simple estimation, you simply estimate the
absorption along a straight line by only the absorbing medium (here, CO2).
Extra elastic scattering will only increase that absorption.

I'm not nitpicking you know. I try to point out a totally absurd
calculation.

Even in your ideal lab experiment: take 10 meters of CO2 at 1 bar, and
look at the absorption. Now ADD 10 bars of N2 to your CO2 container
(while keeping the 1 bar of CO2, so total pressure 11 bars). Are you
seriously going to claim that you will absorb 10 times LESS of the IR beam
you sent in ?


The cross section for a molecule to absorb a photon is independent of the
concentration of the gas.

The probability of absorption in a column of gas is the amount of
molecules per square cm in that column, times the cross section.

cheers,
Patrick.

I didn't get an answer yet.

 

[drankin]

Vanesch, this is very exciting to me: debating with the middlebury.net folks and sharing the conversation (assuming good faith on your part).

I am a laymen of climate science but a sceptic of global doom as a result of human input. It makes sense that altering the chemical composition of the atmosphere should impact the climate but to what end, I'm on the fence. The global climate is always in a state of change, this is a known fact. Aside from being responsible about our "waste contribution", is there anything more as a society we are going to do? This is a political dilemna and could become a military dilemna one day I believe. Because of this, I would like see the debate brought to the public in a way they can consume fundamentally and practically. A court of law is a good forum. It won't be a the only forum and it won't be an absolute decision. But if anyone believes this is a global problem, then why wouldn't this be a good place to bring the evidence we have to date?

 

[Gokul43201]

vanesch,

Is this person saying that the total absorption cross section is different for a fixed number of molecules "X", for different levels of dilution (and that the cross section scales with the concentration of X) ?

I haven't read the original article.

 

[vanesch]

vanesch,

Is this person saying that the total absorption cross section is different for a fixed number of molecules "X", for different levels of dilution (and that the cross section scales with the concentration of X) ?

I haven't read the original article.

The main argument of his article (at least, that's how I understood it), goes as follows:
CO2 has a certain number of absorption bands of EM radiation. He replaces these absorption bands by "totally black" absorption bands and then shows that, on a black-body spectrum centered on the temperature of Earth's surface, even totally black bands only absorp 8% of the BB curve.
I can live with that - I didn't check this, but ok.
So this is an upper limit to what fraction of BB radiation at Earth's average surface temperature can be captured by a "thick layer of CO2". He then tells us that a thick layer of CO2 is of the order of 10 meters or so (I guess, at atmospheric pressure).

Fine. Although I didn't check this, there's nothing wrong in principle here.

But then comes the main point he devellops: He says that a FULL atmosphere of CO2 would hence absorb only 8% of BB radiation, but the Earth atmosphere only contains 0.38mbar of CO2, so the MAXIMUM ABSORPTION of BB radiation by the atmosphere is given by:

8% x 0.00038 = 0.0000304

So the atmosphere can at most absorb 0.0000304 times the total BB radiation from the earth.

This is then used as an argument to say that no matter what happens, CO2 cannot contribute significantly to GW.
(see the quote from his page in my first quoted e-mail to him).

Now, THAT, to me, is totally bogus. There's (even as a rough approximation) no reason at all to multiply the "black" fraction (8%) with the ratio CO2/N2-O2.
You could as well multiply the 8% with, say, the exchange ratio of the former Italian Lire over the Dollar three days before Xmas of the year 1973 or something.

PS: I see that his page has changed to try to explain this...

 

[vanesch]

I replied (to the page change) the following:

Hi again,

I saw that you modified the page :-)

However, I still don't buy the argument. You see, when you write:

===
So, let's use our imagination and tack up a million one-inch bottle caps on the side of a really big building, with them all spaced 3.3 inches apart, and with only 380 of them being red and the rest all blue. If they're evenly mixed up ( like the wind mixes the atmosphere ) then the red bottle caps (representing CO2) now are going to be spaced 8,684 inches, or 723 feet apart. Now you know why we call CO2 a "trace gas" in the atmosphere.
===

there's no objection to this, but now consider that there is ONLY this trace gas, at 0.38 mbar. Then the red caps are ALSO 723 feet apart, and we already know that this absorps ALL of the 8% (remember, the 10 meters of CO2). So in how much is ADDING the blue caps going to DIMINISH the absorption by the red caps ?

You see, it is not as if initially, you had them 3 inches apart, and you absorbed 8%. You ALWAYS had them 723 feet apart (the density of CO2 molecules per square centimeter of atmosphere column). No ADDING of blue caps is going to let the radiation get out easier.

===
Some of the sharper physics students out there are probably asking themselves, "Hey what about scattering?" If your physics professor ever gave you the question, "Why is the sky blue?", then you're familiar with Raleigh scattering theory and you've probably already done the math and learned that in the temperature ranges we're dealing with here, the scattering is so small as to be negligible.
===

Granted. So the N2/O2 doesn't play a role. So the blue caps are in fact infinitesimally small, compared to the red caps. In what way does adding infinitesimally small blue caps to a certain density of red caps diminish the probability to hit a red cap ?


===
Now, to finish this problem, we need to estimate a "capture cross section" - the probability that a particular CO2 molecule mixed in with everything else in the air will ever encounter one of the highly specific IR photons in the absorption spectrum. We'll assume the mixing is homogeneous, and set the geometry for capture based on the known percentage of CO2 in the air, which is 380 PPM. So based on this highly simplified picture, how much heat can our trace amounts of CO2 actually absorb? The math is simple: 8% ( or .08 ) x 380 PPM ( .000380 ) = .0000304, or about thirty millionths of the radiated heat.
===


You are STILL making the same error! The RATIO of CO2 to N2/O2 has nothing to do here.
The confusion can be of several types. The most evident one is that you seem to think that you have red caps (CO2), and blue caps (N2/O2) "of the same size" (same cross section, which isn't true but that doesn't matter), and IF WE HIT A BLUE ONE, WE WON'T HIT A RED ONE. But that's not true ! If you hit a blue one, this doesn't change your probability of hitting a red one! It would indeed be a correct reasoning if N2/O2 were just as absorbing as CO2. Then you are right. Then the probability of being absorbed by CO2 INSTEAD OF being absorbed by N2/O2 would depend on their ratio. In other words, the O2/N2 are IN COMPETITION with the CO2, and have similar cross sections. But we take the hypothesis here that N2/O2 doesn't absorb (in the same band) as CO2, and, at most, scatters (leaving the photon intact to be again absorbed by CO2). But then, you even make the hypothesis that this N2/O2 scattering is neglegible.

The other possible confusion is that you seem to think that there is a linear relationship between the amount of radiation absorbed in different situations, and the ratio of absorbant in both. This is not true, because it is an exponential relationship (Beer's law). So the error might be: if a FULL atmosphere of 1 bar of CO2 can absorp 8% (spectral selection), then an atmosphere of only 0.38 mbar of CO2 can only absorb proportionally: 8% x 0.000038.
But that is not true. If you have a light source which emits red light and blue light, and you put 500 pieces of red glass behind it, then only the red light gets true, so, say, 50%. But that doesn't mean that if you put only one piece of red glass behind it, that you will only absorb 0.1% of the light, and let 49.9% of the blue light get past it! One piece of red light already absorbs all of the blue light, hence 50%. If you add 499 extra pieces, this won't change a thing.

What is absorbed is given by 1 - exp(- d rho sigma) where d is the thickness, rho the particle density per volume element, and sigma the microscopic cross section. d times rho gives you the number of particles in the column. Now, if d rho sigma is, say, 20000, then you absorb everything, and if you now divide d rho sigma by 20, you STILL absorb about everything, not 20 times less.

cheers,
Patrick.

 

[vanesch]

Another exchange.

In the first part of the response, the author claims that the "blue caps" act as *spacers* between the CO2 molecules.

I reply:

===> In what way does ADDING molecules INCREASE the space of others ??

You see, the thing I'm disputing is that you seem to make a difference in total absorption between:
a) an atmosphere consisting solely of 0.35 mbar of CO2 (which, I presume, you accept that it can potentially absorb 8% of the BB spectrum, because 0.35 mbar of CO2, over several km, comes down to 1 bar of CO2 over a few meters in surface density)

b) an atmosphere consisting of 0.35 mbar of CO2 (partial pressure) PLUS 1 bar of N2/O2.

I can assure you that the average distance between CO2 molecules in BOTH cases is the same.

So now you need to explain me how it comes that ADDING 1 bar of N2/O2 to a 0.35 mbar CO2 atmosphere is going to DECREASE the absorption of the CO2, and is going to INCREASE the distance between individual CO2 molecules...

The other part of his reply comes down to a discussion of the mechanism of the heat transfer absorbed by CO2 to water vapor.

My reply:

I'm not discussing climate change or anything, I'm trying to point out an elementary but gross error in a single step, which is the deduction that the maximum BB energy absorption can at most be 8% times the CO2/N2-O2 ratio. This step is wrong *in principle*.

The reason is that if it were true (but it isn't) then indeed, the discussion stops there, and anyone going further is indeed a total ignoramus of elementary physics. This is what you present on your page. But unfortunately, it is not correct *in principle*. No matter whether or not there is climate change, whether or not in the end CO2 plays a role or whatever. The *reasoning* is faulty.

The simple statement that a pure CO2 atmosphere (of what thickness and pressure ?) would absorb 8%, and the fact that in the real atmosphere there is about 3000 more N2-O2 added to it, DOESN'T IMPLY that the atmosphere can at most absorb 8% / 3000.

Again, this is simply demonstrated by your lab experiment: take 10 meters of 1 bar of CO2, and a beam of IR radiation. You find that you absorb 8% of the spectrum totally. Now ADD 10 bars of N2 to your gas. Do you really expect now that you only absorb 0.8 % of the spectrum ? Of course not. You will STILL absorb 8%.

From that point on, any further argument made is put in doubt too (in the same way as the erroneous arguments in Gore's movie put everything else in doubt). It is like in an interview for a job: once you've found ONE erroneous statement by the candidate about his CV, you don't believe a word anymore for any other argumentation he might devellop.

Cheers,
Patrick.

 

[ecofan]

Well, I see one big blunder already:

It's reasonably valid to use partial pressure arguments to estimate "collision cross sections", since the radiation is diminishing per the inverse square law and the target molecules are thinning at an even faster rate. Lab science and the real world aren't always in agreement, and the real atmosphere simply can't be replicated in the lab. Straightforward linear absorption just doesn't apply to the atmospheric geometry.

http://www.middlebury.net/op-ed/global-warming-01.html"

This fellow is writing for the layman, not the geek. His approximations are rough... some are generous, some are thin. It tends to balance out. It's a pretty good conclusion, at any rate, and better than anything else I've seen written so the ordinary non-scientist can understand.

 

[vanesch]

It's reasonably valid to use partial pressure arguments to estimate "collision cross sections", since the radiation is diminishing per the inverse square law and the target molecules are thinning at an even faster rate. Lab science and the real world aren't always in agreement, and the real atmosphere simply can't be replicated in the lab. Straightforward linear absorption just doesn't apply to the atmospheric geometry.

http://www.middlebury.net/op-ed/global-warming-01.html"

This fellow is writing for the layman, not the geek. His approximations are rough... some are generous, some are thin. It tends to balance out. It's a pretty good conclusion, at any rate, and better than anything else I've seen written so the ordinary non-scientist can understand.

No, it is fundamentally wrong.
At no point, the RATIO of absorber to "filling gas" plays any role. What plays a role is the partial pressure of the absorber, PERIOD.

What I tried to explain is that one shouldn't use ERRONEOUS arguments, even as approximations. It is as if I wrote:

Given that the current is 20 amps, and the weight of the resistor is 3 kg, this means that the voltage over the resistor is 20 x 3 = 60 volts.

The MASS has nothing to do with the resistance a priori. In the same way, if the total black absorption represents 8% for a sufficiently thick CO2 layer (he cites 10 meters of some undefined pressure of CO2), then NOTHING allows me to multiply this with a ratio of a CO2 partial pressure and a neutral gas partial pressure to estimate the absorption in a gas mixture!

 

[Gokul43201]

This fellow is writing for the layman, not the geek. His approximations are rough... some are generous, some are thin. It tends to balance out. It's a pretty good conclusion, at any rate, and better than anything else I've seen written so the ordinary non-scientist can understand.

Really! Did you get past this paragraph (quoted below), or like me, gag at the nonsense and give up?

Atoms and molecules are very tiny things, and the distances between them are therefore also very small. Physicists like to use a unit of measure called an Angstrom, which is a nano-meter, or a billionth of a meter. A molecule like CO2 has a size of around 2 Angstroms, and in an "Ideal Gas", the spacing is about 3.3 Angstroms apart. The so-called Ideal Gas is one in which 10 to the 24th power number of molecules occupies a space of about 22 liters, at a pressure of 760mm of mercury and 273 degrees Kelvin - called the "standard temperature and pressure".

In that one paragraph, the author has produced more high school level errors than I've seen in any single paragraph by any high schooler.

1. Atoms and molecules are small. Therefore, distances between them are small? Hello? I'm currently sitting near a chamber where molecules are several inches apart.

2. 1 Angstrom = 1nm? Really? I recommend the first chapter or inside cover of any high school physics text.

3. Intermolecular spacing at STP is about 33 Angstroms, not 3.3 Angstroms. But I can see how you'd make that mistake if you don't know your Angstroms from your nanometers!

4. The definition of a mole of a gas is independent of whether or not it is ideal. The author thinks he's providing a definition of an ideal gas, while he is simply defining a mole, and in no way whatsoever, describing a "so-called Ideal Gas."

I sure hope this person does not have a degree in the physical sciences - that would be embarrassing!

 

[ecofan]

I wrote your objections to the guy and got an almost immediate reply, thanking me for pointing out the error. He also says he's using the published intermolecular spacing for N2 as a substitute for CO2, and if we have a better reference, he'd be pleased to know about it.

If it turns out to be 33 angstroms instead of 3.3, he'll likely correct it, as it appears he has already done with the tenth-off nanometer thing.

And even I know that an ideal gas is also defined by molar volume and stp - so what's the rub there? Are you guys a bunch of Al Gore worshipers?

You catch more flies with honey than with vinegar.

 

[Gokul43201]

I wrote your objections to the guy and got an almost immediate reply, thanking me for pointing out the error. He also says he's using the published intermolecular spacing for N2 as a substitute for CO2, and if we have a better reference, he'd be pleased to know about it.

Oh boy! For any given temperature and pressure, you can calculate the intermolecular spacing of gas molecules on the back of a very small envelope, and you'll see that the quoted number is off by an order of magnitude. You don't need to look up any references for it!

If it turns out to be 33 angstroms instead of 3.3, he'll likely correct it, as it appears he has already done with the tenth-off nanometer thing.

Is this something that really needs deep investigation? The lattice parameter of diamond is about 3.5 angstroms. Does this person really need to be given a reference to be shown that the intermolecular of a gas at STP should not be comparable to that of a solid with similar atomic make-up?

And even I know that an ideal gas is also defined by molar volume and stp - so what's the rub there?

No, it is not. It is defined by how the molar volume scales with temperature and pressure.

Are you guys a bunch of Al Gore worshipers?

Not I. Are you a worshipper of crackpottery?

You catch more flies with honey than with vinegar.

The day I start growing a fondness for flies, I'll be sure to use that advice.

 

[Art]

Really! Did you get past this paragraph (quoted below), or like me, gag at the nonsense and give up?



In that one paragraph, the author has produced more high school level errors than I've seen in any single paragraph by any high schooler.

1. Atoms and molecules are small. Therefore, distances between them are small? Hello? I'm currently sitting near a chamber where molecules are several inches apart.

2. 1 Angstrom = 1nm? Really? I recommend the first chapter or inside cover of any high school physics text.

3. Intermolecular spacing at STP is about 33 Angstroms, not 3.3 Angstroms. But I can see how you'd make that mistake if you don't know your Angstroms from your nanometers!

4. The definition of a mole of a gas is independent of whether or not it is ideal. The author thinks he's providing a definition of an ideal gas, while he is simply defining a mole, and in no way whatsoever, describing a "so-called Ideal Gas."

I sure hope this person does not have a degree in the physical sciences - that would be embarrassing!

Congratulations on presenting a quintessential example of an ad-hominem attack

btw high schooler should be high schooler or high-schooler. So based on your logic and your error it follows everything you have ever done or written is wrong.

 

[Gokul43201]

Congratulations on presenting a quintessential example of an ad-hominem attack

Ad hominem? Pointing out gross mathematical/scientific errors is an ad hominem attack?

btw high schooler should be high schooler or high-schooler. So based on your logic and your error it follows everything you have ever done or written is wrong.

Was that really the only typo in my post? I'm surprised!

 

[ecofan]

Looks like he's bought your 33 angstrom argument. Maybe it was a typo? 3.3 vs 33 sounds like too much of a coincidence.

Not to change the subject, but has anyone read Lisa Randall's really great summary of particle physics, Warped Passages? Most of physics hasn't budged a lot in the last 50 years, but the particle theorists are really dancing in 9 ( or is it 10 ) dimensions..

 

[Gokul43201]

Looks like he's bought your 33 angstrom argument.

I looked again, and I see now that he's also removed the entire paragraph about the short extinction length for atmospheric CO2 (quoted by vanesch in post #20) which essentially is all you need to see to realize that his rationale for multiplying by 380ppm is flawed. Without this paragraph, it is now still conceivable that dilution could result in a reduction of absorption if the extinction length is much greater than the thickness of the atmosphere. But this is not the case, as he had himself pointed out before ... but new readers will no longer be able to tell, because he's removed the very statements that debunk the rest of his argument.

And even if he does arrive at a correct number, he still needs to show how this number proves his subsequent statement about CO2 not being a "significant greenhouse gas".

 

[vanesch]

I didn't get any reply anymore in my mailbox...

 

[vanesch]

I looked again, and I see now that he's also removed the entire paragraph about the short extinction length for atmospheric CO2 (quoted by vanesch in post #20) which essentially is all you need to see to realize that his rationale for multiplying by 380ppm is flawed. Without this paragraph, it is now still conceivable that dilution could result in a reduction of absorption if the extinction length is much greater than the thickness of the atmosphere. But this is not the case, as he had himself pointed out before ... but new readers will no longer be able to tell, because he's removed the very statements that debunk the rest of his argument.

The funny thing is that another claim that CO2 increase will almost not affect any greenhouse effect, is to be found here:
http://www.john-daly.com/artifact.htm

is based on exactly the opposite conclusion: the CO2 in the atmosphere ALREADY absorbs ALL of the IR radiation in the band, so adding more to it won't change anything.

Now, I have to say that I don't find any gross error in principle here (assuming the numbers cited are correct).

 

[ecofan]

I talked him into forgetting the whole absorption cross section argument and just going with a worst-case scenario, a la Heinz Hug, to which he was agreeable. He seems to want to give the maximum benefit of the doubt to the AGW panic crowd... which was smart, because the results still show CO2 to be a small player in the greenhouse gas orchestra. And if the comment "the CO2 in the atmosphere ALREADY absorbs ALL of the IR radiation in the band, so adding more to it won't change anything" from PF Mentor is correct, then we can all go out and buy a SUV without having any guilt.

 

[vanesch]

And if the comment "the CO2 in the atmosphere ALREADY absorbs ALL of the IR radiation in the band, so adding more to it won't change anything" from PF Mentor is correct, then we can all go out and buy a SUV without having any guilt.

Uh, that's not MY comment, this is how I understand the argument put forward in the cited page. At least it doesn't contain any *gross* errors like multiplying with a factor that is not justified in not one case. I only pointed out the page in that it stance is the same (CO2 doesn't play a role), and that in order to arrive at that conclusion, it concludes that it absorbs already everything, while our friend claimed exactly the opposite, and he couldn't accuse this site of being pro-AGW.

Personally, I would think that the CO2 effect ITSELF and its radiative forcing would be not so open to doubt. After all, it is a radiation transport problem, which is rather well mastered, and is way simpler than things like ground feedback, cloud formation and so on.

It is difficult to estimate the real impact of CO2 by a hand calculation, because of several effects I can think of. One is the re-emission of thermal radiation. As such, the entire atmosphere is not simply considered as a filter, but is also an emitter. An absorbed line will then be re-emitted as a BB spectrum again after thermalisation within a gas layer. There are effects like Doppler broadening of the line. All this can be done using radiation transport codes, but is difficult to estimate by hand. I would think - but I try to find this and I don't, that *this* part would be more or less correctly handled.

My doubts about AGW reside more in the much bigger uncertainties of the feedback mechanisms, and of the entire CO2 cycle. But even there, there are suggestive data. What I don't like in the IPCC-hype is that suggestions from scientific data are sold as scientific facts.

 

[Gokul43201]

The funny thing is that another claim that CO2 increase will almost not affect any greenhouse effect, is to be found here:
http://www.john-daly.com/artifact.htm

is based on exactly the opposite conclusion: the CO2 in the atmosphere ALREADY absorbs ALL of the IR radiation in the band, so adding more to it won't change anything.

Now, I have to say that I don't find any gross error in principle here (assuming the numbers cited are correct).

I haven't read the content at that url vanesch, but I think the scientific community is pretty coherent about one thing - the absorption increases logarithmically with CO2 concentration in the vicinity of present day concentrations. In the absence of any positive feedback mechanism (coming from other places than just the atmospheric composition), it would take exponential increases in CO2 concentration to produce the similar increases in warming.

All these naive "first principle" calculations are really trying to reinvent the wheel, in an age where we already have self-lubricating bearings.

 

[Gokul43201]

If anything, it is clear that the author of the blog linked to by art and ecofan is not a physicist or climatologist, and that the url in question be treated as a crackpot link.

After making all of the gross errors that have been pointed out here, he still has the gall to leave these gems in place:

Side note: Both Oxygen and Nitrogen don't like to live alone. They prefer to find another and stick together into a diatomic ( 2 atom ) molecule. Thus the molecular weight of atmospheric oxygen or nitrogen is approximately twice that of one of them alone. We say "approximately", because it takes energy to bind them together, and mass and energy are equivalent stuff, as our good friend Dr. Einstein explained with his famous equation E=MC2.

Wow! That completely unnecessary and totally misleading description is positively embarrassing!

Now, you can sit back and give yourself a pat on the back, because you now know more pure physics of the atmosphere than a lot of so-called "climate scientists", and likely know more than almost all of the non-scientist Popular Journalists and other writers churning out panic-stricken books and newspaper articles on the subject.

And that's a joke!

 

[ecofan]

Interesting paper here

GEOPHYSICAL RESEARCH LETTERS, VOL. 34, L15707, doi:10.1029/2007GL029698, 2007

written by Roy W. Spencer, William D. Braswell, John R. Christy, and Justin Hnilo

titled
Cloud and radiation budget changes associated with tropical intraseasonal oscillations

which discusses feedback mechanisms in some detail. Worth a read.

 

[vanesch]

All these naive "first principle" calculations are really trying to reinvent the wheel, in an age where we already have self-lubricating bearings.

I know, but I would like to see a nice explanation of what principles are at work, and what makes the difference between the simple "straight line" analytical estimate which seems to be presented in the page I linked to, and what corrections are at work in a more elaborate model.

For instance, there is a web interface to MODTRAN, a radiation transport code in a plane-parallel atmosphere:
http://geosci.uchicago.edu/~archer/cgimodels/radiation.html

where you can play around with a black body earth, and other features, and you get out the radiation at a certain altitude. But it is still black box.

Personally, when I have to do a computer calculation, I first like to have a back-of-the-enveloppe hand estimation. It gives me more of a feeling of what I should obtain. If the computer code does different things, then I try to switch off all effects one by one until I only simulate my own hand calculation. If I still don't find agreement, there's a bug somewhere.

 

[ecofan]

Side note: Both Oxygen and Nitrogen don't like to live alone. They prefer to find another and stick together into a diatomic ( 2 atom ) molecule. Thus the molecular weight of atmospheric oxygen or nitrogen is approximately twice that of one of them alone. We say "approximately", because it takes energy to bind them together, and mass and energy are equivalent stuff, as our good friend Dr. Einstein explained with his famous equation E=MC2.

I think that's a lead-in to the fact that he calculates the relative molecular weights of the other gases to show that CO2 is the heaviest of the bunch... thus, it is relative.

And the spike at the "climate scientists" is probably aimed at the "modelers" who are churning out all the "predictions" which are simply elaborate fairy tales.

And, putting 2+2 together, the "Popular Journalist" he constantly refers to is probably Bill McKibben, a scientific illiterate who is currently a "visiting scholar" at Middlebury College and who churns out environmental panic books by the shovel full, using his background as a former gossip columnist at the New Yorker.

You seem to be eternally angry at everything in the world. Is that the most productive way to discuss physics or any other subject?