Guest Post by Ira Glickstein
This series began with a mechanical analogy for the Atmospheric “Greenhouse Effect” and progressed a bit more deeply into Atmospheric Windows and Emission Spectra. In this posting, we consider the interaction between air molecules, including Nitrogen (N2), Oxygen (O2), Water Vapor (H2O) and Carbon Dioxide (CO2), with Photons of various wavelengths. This may help us visualize how energy, in the form of Photons radiated by the Sun and the Surface of the Earth, is absorbed and re-emited by Atmospheric molecules. 
DESCRIPTION OF THE GRAPHIC
The animated graphic has eight frames, as indicated by the counter in the lower right corner. Molecules are symbolized by letter pairs or triplets and Photons by ovals and arrows. The view is of a small portion of the cloud-free Atmosphere. (Thanks to WUWT commenter davidmhoffer for some of the ideas incorporated in this graphic.)
- During the daytime, Solar energy enters the Atmosphere in the form of Photons at wavelengths from about 0.1μ (micron – millionth of a meter) to 4μ, which is called “shortwave” radiation and is represented as ~1/2μ and symbolized as orange ovals. Most of this energy gets a free pass through the cloud-free Atmosphere. It continues down to the Surface of the Earth where some is reflected back by light areas (not shown in the animation) and where most is absorbed and warms the Surface.
- Since Earth’s temperature is well above absolute zero, both day and night, the Surface radiates Photons in all directions with the energy distributed approximately according to a “blackbody” at a given temperature. This energy is in the form of Photons at wavelengths from about 4μ to 50μ, which is called “longwave” radiation and is represented as ~7μ, ~10μ, and ~15μ and symbolized as violet, light blue, and purple ovals, respectively. The primary “greenhouse” gases (GHG) are Water Vapor (H2O) and Carbon Dioxide (CO2). The ~7μ Photon is absorbed by an H2O molecule because Water Vapor has an absorption peak in that region, the ~10μ Photon gets a free pass because neither H2O nor CO2 absorb strongly in that region, and one of the 15μ Photons gets absorbed by an H2O molecule while the other gets absorbed by a CO2 molecule because these gases have absorption peaks in that region.
- The absorbed Photons raise the energy level of their respective molecules (symbolized by red outlines).
- The energized molecules re-emit the Photons in random directions, some upwards, some downwards, and some sideways. Some of the re-emitted Photons make their way out to Space and their energy is lost there, others back down to the Surface where their energy is absorbed, further heating the Earth, and others travel through the Atmosphere for a random distance until they encounter another GHG molecule.
- This frame and the next two illustrate another way Photons are emitted, namely due to collisions between energized GHG molecules and other air molecules. As in frame (2) the Surface radiates Photons in all directions and various wavelengths.
- The Photons cause the GHG molecules to become energized and they speed up and collide with other gas molecules, energizing them. NOTE: In a gas, the molecules are in constant motion, moving in random directions at different speeds, colliding and bouncing off one another, etc. Indeed the “temperature” of a gas is something like the average speed of the molecules. In this animation, the gas molecules are fixed in position because it would be too confusing if they were all shown moving and because the speed of the Photons is so much greater than the speed of the molecules that they hardly move in the time indicated.
- The energized air molecules emit radiation at various wavelengths and in random directions, some upwards, some downwards, and some sideways. Some of the re-emitted Photons make their way out to Space and their energy is lost there, others back down to the Surface where their energy is absorbed, further heating the Earth, and others travel through the Atmosphere for a random distance until they encounter another GHG molecule.
- Having emitted the energy, the molecules cool down.
DISCUSSION
As in the other postings in this series, only radiation effects are considered because they are the key to understanding the Atmospheric “Greenhouse Effect”. I recognize that other effects are as important, and perhaps more so, in the overall heat balance of the Earth. These include clouds which reflect much of the Sun’s radiation back out to Space, and which, due to negative feedback, counteract Global Warming. Other effects include convection (wind, thunderstorms, …), precipitation (rain, snow) and conduction that are responsible for transferring energy from the Surface to the Atmosphere. It is also important to note that the Atmospheric “Greenhouse Effect” and a physical greenhouse are similar in that they both limit the rate of thermal energy flowing out of the system, but the mechanisms by which heat is retained are different. A greenhouse works primarily by preventing absorbed heat from leaving the structure through convection, i.e. sensible heat transport. The greenhouse effect heats the earth because greenhouse gases absorb outgoing radiative energy and re-emit some of it back towards earth.
That said, how does this visualization help us understand the issue of “CO2 sensitivity” which is the additional warming of the Earth Surface due to an increase in atmospheric CO2? Well, given a greater density of CO2 (and H2O) molecules in the air, there is a greater chance that a given photon will get absorbed. Stated differently, a given photon will travel a shorter distance, on average, before being absorbed by a GHG molecule and be re-emitted in a random direction, including downwards towards the Surface. That will result in more energy being recycled back to the Surface, increasing average temperatures a bit.
Tim Folkerts says, amongst other things:
April 18, 2011 at 12:38 pm
“(2) is tougher, since the term “catastrophic” is ill-defined. “One man’s blessing is another man’s curse.” Proving an ill-defined term is pretty nearly impossible! 🙂 ”
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For quite an eloquent post, this conclusion was hard for me to understand.
You are saying that the warmists can throw out an ill-defined term that is nearly impossible to prove, and then require people who think they are full of snip to prove them wrong ?? Given how ridiculous that is on its face, this would seem to me to be supporting Smokey’s view, not rebutting it.
Why wouldn’t you recommend that they come up with accurately defined parameters of “catastrophicness” that can be tested using the scientific method ??
Even with the ill-defined term, the real world data shows that there hasn’t been any catastrophic anything at a 40% increase in CO2 (other than the unintended – some might say “intended” – consequences of fake global warming hysteria that is).
Bryan: You continue to nitpick wording and refuse to engage in substance. So, what is the substance of what G&T said in reference to the greenhouse effect and the 2nd Law of Thermodynamics? We are waited with baited breath for you to enlighten us.
philincalifornia says: April 18, 2011 at 5:11 pm
“You are saying that the warmists can throw out an ill-defined term that is nearly impossible to prove, and then require people who think they are full of snip to prove them wrong ?? Given how ridiculous that is on its face, this would seem to me to be supporting Smokey’s view, not rebutting it.”
Actually, I do significantly agree with Smokey — the burden of proof DOES lie with scientists. However, almost by definition, that burden of proof has been met for “established science”, at which point the skeptic has the burden of proof to show the established science is wrong. The challenge here is deciding where to draw the line between “new science” and “established science”.
* The basic GHG theory is IMHO “established science”.
* That the increase in CO2 over the last century is primarily due to people is IMHO “established science”.
* The extent to which additional CO2 affects global temperatures is IMHO not quite “established science” and needs to be further researched and tested before it is nailed down, especially the feedbacks. Here ALL sides should be finding support for their specific hypotheses.
* The levels at which in CO2 and/or global temperature increases become “catastrophic” are IMHO fuzzy and would need considerable research before we could have confidence in the predictions.
The last point is doubly true since there is no obvious scientific definition of “catastrophic”. I can define “polar covalent bonds” in terms of specific electronegativity values; I can define “Thermal IR” in terms of specific wavelengths. I can define “mammal” in terms of specific characteristics. But there is number or test to determine “catastrophic”. Thus, proving “CAGW” (or disproving) is pretty much a fool’s errand, since no one can delineate precisely what the “C” means!
“Why wouldn’t you recommend that they come up with accurately defined parameters of “catastrophicness” that can be tested using the scientific method ??”
Actually, I think that is a mostly reasonable idea, although it would be easier to stick to more easily defined parameters for the statement of the hypothesis. Rating earthquakes on a Richter Scale is well-defined; rating climate change on a “catastrophicness scale” would be nigh unto impossible since there are so many different ways a change could be catastrophic.
It would be better to stick to hypotheses about sea level rise or global tempeature or rainfall patterns.
Tim Folkerts says:
April 18, 2011 at 9:04 pm
philincalifornia says: April 18, 2011 at 5:11 pm
“You are saying that the warmists can throw out an ill-defined term that is nearly impossible to prove, and then require people who think they are full of snip to prove them wrong ?? Given how ridiculous that is on its face, this would seem to me to be supporting Smokey’s view, not rebutting it.”
Actually, I do significantly agree with Smokey — the burden of proof DOES lie with scientists. However, almost by definition, that burden of proof has been met for “established science”, at which point the skeptic has the burden of proof to show the established science is wrong. The challenge here is deciding where to draw the line between “new science” and “established science”.
* The basic GHG theory is IMHO “established science”.
* That the increase in CO2 over the last century is primarily due to people is IMHO “established science”.
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Basic GHG theory is exactly what it says on the can but, being basic, how does it relate to the more complex problem of planet earth’s temperature/climate ?? Not very well, as I view the data.
http://img576.imageshack.us/img576/2681/temperaturewithrealbase.gif
The slope of the line doesn’t seem to change a whole lot, with or without an increase of 40% in CO2 levels since 1950. Do you have some magical theory that the slope would’ve gone level at around 1950ish ??
Otherwise, what’s the CO2 doing exactly ?? ….. besides nothing measurable.
* The basic GHG theory is IMHO “established science”.
This seems correct. But this might (or might not) be a slight embarrassment to science and others who accepted this GHG back-radiation theory without question in the not too distant future.
* That the increase in CO2 over the last century is primarily due to people is IMHO “established science”.
Surely not. I’m not a scientist so would like other viewpoints on this.
* The extent to which additional CO2 affects global temperatures is IMHO not quite “established science” and needs to be further researched and tested before it is nailed down, especially the feedbacks. Here ALL sides should be finding support for their specific hypotheses.
Not quite established science?
Surely it is not even close to established science. If it was there would not be all the debates on this subject with scientists on both sides. The impact of CO2 v water vapour being just one of them.
Tim Folkerts says of my comment here;
……”Joel Shores simple world consists of an earth without oceans and a land surface that does not retain heat.”
Tim says;
…..”By any standard thermodynamic definition (like the ones you gave), it is impossible to “retain” heat (Q), any more than you can “retain” work (W). Both are processes that happen; but internal energy (U) is what is contained within a system. “….
My reply;
This seems a much more robust comment than I have come to expect from Tim.
I meant here that the heat retention process is akin to insulation.
However you seem to have “caught on” very quickly.
This raises the possibility that you know fine well that a lot of your input at this site is without a firm scientific basis.
Is it that you post in order to confuse?
How do you feel morally about that?
Tim Folkerts says
* The basic GHG theory is IMHO “established science”.
Tim could you point us to a copy of this ;
…….”The basic GHG theory”……
As there seems to be several versions.
Which is the orthodox version, held to be true by the fervent believers.
Joel says of
University Physics by Young and Freedman
….”Speaking of which, would you care to enlighten us about what that textbook has to say on the subject of the greenhouse effect and global warming? I have a copy of the latest edition back in my office, so I can tell you tomorrow if your edition is too old to mention it or if you would rather not tell us here.”…..
My reply
My edition is the ninth in which they say;
Energy transfer that takes place soley because of a temperature difference is called heat flow or heat flow transfer and energy transferred in this way is called heat .
page 470
Heat always flows from a hot body to a cooler body never the reverse. page 559
This statement is impossible to reconcile with the conclusion reached in your “comment” paper page 15
….”the surface is now HEATED not only by the sun but also by the downward emission of terrestrial radiation from the atmosphere”…..
The colder atmosphere HEATING a warmer Earth surface!
I dont think so!
Joel perhaps to you the actual direction of heat flow is as you say “nitpicking”, however if you read your textbook carefully you will find that this is a very isolated viewpoint and one that would fail an examination question in physics.
“[1] “Falsification Of the atmospheric CO2 greenhouse effects within the frame Of Physics” by Gerhard Gerlich and Ralf D. Tscheuschner; International Journal of Modern Physics B, Vol. 23, No. 3 (2009) pages 275-364.
http://arxiv.org/PS_cache/arxiv/pdf/0707/0707.1161v4.pdf”
Bryan.
Thanks for posting these papers (and for your other comments).
Bryan says: “This raises the possibility that you know fine well that a lot of your input at this site is without a firm scientific basis.”
Could you give a lot of examples??? Or just one or two specific examples???
In fact, you just admitted that your own statement was without firm scientific basis — that you mis-used the word “heat”.
Is it that YOU post in order to confuse?
How do YOU feel morally about that?
Or perhaps we are both trying to present scientific information in a very non-scientific setting (recent awards to this site not withstanding) to people with a wide variety of scientific backgrounds. By necessity we cannot be 100.000% scientific 100.000% of the time in 200 word posts created in moments of free time. We could only use “heat” in the sense of “dQ = dU+dW”. But in a setting like this, you often have to meet people half way.
“Which is the orthodox version [of the GH effect], held to be true by the fervent believers.”
Well, I can’t speak for “fervent believers” because I try to stick to science, not religion, in these discussions.
I don’t have time to spell out all the details (I have a real job to deal with), but by “basic GH effect” I mean something like:
The IR properties of gases in the atmosphere (notably H2O and CO2) cause the earth’s surface to be warmer than it would be in the absence of those IR properties.
Tim and Joel,
is this a valid radiative heat transfer equation? q/A= emissivity * SB * (T1-T2)
If you agree please point to where back radiation is entered to account for it.
Also if two identical plates are at identical temperatures how much radiation goes back and forth and what is the heat transfer?
Tim Folkerts says:
“The IR properties of gases in the atmosphere (notably H2O and CO2) cause the earth’s surface to be warmer than it would be in the absence of those IR properties.”
Do you have measured, real world evidence to support that statement? No?
That’s OK, no one else does, either.
For example, Dr Muller preposterously claims that .6° of the .7°C rise over the past century is due to AGW. But the naturally rising trend line since the LIA would suddenly go almost flat without the added CO2 emissions if Muller was correct. Taking that reasoning to its logical conclusion, it is clear that CO2* has a negligible effect as the primary cause of [naturally] rising temperatures. The effect of CO2 is simply too small to measure, but people like Muller talk as if it is settled science. It is not; it is just evidence-free speculation.
[*Specifically CO2. “GHG” is an attempt to disassociate the AGW claims from the demonization of “carbon”, which is the basic reason for the scare: “carbon” [by which the illiterati mean carbon dioxide] is a minor trace gas that is emitted by almost every economic activity. Thus, economic activity can be taxed using CO2 emissions as a proxy, whereas water vapor – by far the major GHG – cannot be similarly taxed. In the interest of honesty, the discussion is really about CO2, not GHGs.]
Tim Folkerts version of the Greenhouse Theory
……..”The IR properties of gases in the atmosphere (notably H2O and CO2) cause the earth’s surface to be warmer than it would be in the absence of those IR properties.”…
There’s not much to this “theory”, is there Tim!
Is this what the scientific world has rallied around!
G&T say that the heating effect of CO2 at atmospheric temperatures is so small that it can be ignored for most practical purposes.
But according to Tim’s “theory” they too can be included as believers in his modest formulation of the Greenhouse Theory.
“Do you have measured, real world evidence to support that statement? No? ”
* There is measured, real-world data that CO2 & H2O absorb IR.
* There is measured, real-world data that IR photons matching the measured spectra of H2O & CO2 shine down from the atmosphere to the surface.
* There is measured, real-world data that the earth’s surface absorbs IR.
* There is measured, real-world data that absorbed photons of any sort add energy to the object absorbing them.
* There is measured, real-world data that objects like rocks and lakes and that absorb more energy get warmer.
* And there are well-developed theories including conservation of energy and black-body radiation and quantum mechanical vibrations of triatomic molecules that support these observations.
My hypothesis was “GHGs as a whole have SOME warming effect.”
The null hypothesis would be “GHG’s as a wholehave NO warming effect.”
Note that I was not referring specifically to sources or to types. To me, the experiments and theory outlined above (along with lots of other supporting information like the measured surface temperature of the moon) provide sufficient support of the hypothesis that the natural ~2% water vapor and ~0.4 % CO2 (and throw in some natural O3 and CH4 for good measure) keep the earth dramatically warmer than it would be without those gases.
Do you think that GHGs as a whole have no measurable effect at all?
You are perfectly welcome to then go on and address FURTHER hypotheses that address how much temperature change should be expected from ADDITIONAL GHGs (and any associated feedback mechanisms). And as I specifically said, that question IS NOT “settled science”. It is actively being pursued my many people who are exploring many different lines of attack to try to get a better answer.
Bryan says: “There’s not much to this “theory”, is there Tim!”
Quite true! Most good theories are quite simple — it makes them more easily testable.
I supported this hypothesis in the previous post to Smokey. Is there something there you disagree with? Many people seem to disagree with even this most simple version, so I wanted to get a common starting point. But perhaps even this most basic of theories is not what you think is correct?
mkelly says: April 19, 2011 at 6:40 am
“is this a valid radiative heat transfer equation? q/A= emissivity * SB * (T1-T2)”
I’m not sure how you are defining all your variables.
Is “SB” = σ = Stefan–Boltzmann constant?
and do you mean T1^4 – T2^4 where T1 & T2 are the temperatures?
so q would be power (J/s = W) (as opposed to the more standard nomenclature where q is heat (J))?
Tim Folkerts says;
….”Quite true! Most good theories are quite simple — it makes them more easily testable.”….
Testing a theory is of central importance in determining if it is within the area of science.
There is a feeling amongst sceptics that there are so many “greenhouse theories” that the “theory” is incapable of falsification and hence is more like a religious belief.
Tim could you expand a little on what kind of test would falsify your version of the “greenhouse theory”.
For instance if the average surface temperature of the planet stayed constant or decreased over the next ten years would it be falsified?
Bryan says:
Well, my edition is the 13th and they have about a page on the greenhouse effect and climate change right in the part of the chapter that discusses radiation. Here is some of what they says:
(And, yes, I agree that their equating the 33 C rise all to CO2 specifically is not correct in the simple sense of its own radiative contribution to the total greenhouse effect, although it could be correct…or even an underestimate…once feedbacks due to water vapor, clouds, and ice albedo are included.)
It then goes on to talk about the burning of fossil fuels, the increase in CO2, and the increase in temperatures, ending with these two sentences:
Do you still think YOUR source supports your point of view?
Bryan says:
Those would be excellent statements and questions if only they were directed at you rather than Tim.
I have never seen a better example of sophistry than you are displaying in this thread.
mkelly says:
As Tim pointed out, you forgot to raise each temperature to the 4th power. The term that has been given the name “back radiation” is the second term. Think of it this way: This equation tells you that the heat transfer between objects 1 and 2 depends not only on the temperature of 1 (presumably the warmer object) but also 2. So, if T2 were at 3 K (the radiative temperature of space) then the heat transfer away from object 1 the earth (for a given temperature T1) will be larger than if T2 is the temperature of the upper atmosphere (say, 255 K). This means that when you try to figure out what temperature the surface of the earth has to be to achieve radiative balance, it has to be higher if the temperature T2 of the atmosphere is higher.
The heat transfer is zero. That means that no heat is being transported away from object 1, presumably the earth. Since it is receiving lots of radiation from the sun, it is going to heat up until the heat transfer away from it balances what it is receiving from the sun.
Bryan says:
What is nitpicking is to object to a single word that, if it bothers you, can easily be replaced by another word that makes the language more precise but makes no material difference to what we were saying. Replace the word “heated” by “receiving radiation” if it bothers you.
Frankly, Bryan, this sort of gamesmanship is scientifically childish. Yes, of all the thousands of words in our paper, some may have not been the optimal words to choose. However, we got the physics right. By contrast, G&T got the physics completely wrong and yet you continue to defend them. Pathetic.
Bryan says:
Well, my edition is the 13th and they have about a page on the greenhouse effect and climate change right in the part of the chapter that discusses radiation. Here is some of what they says:
(And, yes, I agree that their equating the 33 C rise all to CO2 specifically is not correct in the simple sense of its own radiative contribution to the total greenhouse effect, although it could be correct…or even an underestimate…once feedbacks due to water vapor, clouds, and ice albedo are included.)
It then goes on to talk about the burning of fossil fuels, the increase in CO2, and the increase in temperatures, ending with these two sentences:
Do you still think YOUR source supports your point of view?
Joel Shore says:
April 19, 2011 at 1:11 pm
Joel it tells you only that there must be a gradient and that no radiation back and forth is considered. period.
My apologizes for missing the ^4 on each T.
You keep talking about back radiation inhibiting a surface from cooling and there is no place in any heat transfer equation where you can enter that to show it happens. The only thing is temperature.
If back radiation can suppress an object from radiating the it must have an R-value so what is the R-value of CO2 15 micro radiation.