Guest post By Tom Vonk (Tom is a physicist and long time poster at many climate blogs. Note also I’ll have another essay coming soon supporting the role of CO2 – For a another view on the CO2 issue, please see also this guest post by Ferdinand Engelbeen Anthony)
If you search for “greenhouse effect” in Google and get 1 cent for statements like…
“CO2 absorbs the outgoing infrared energy and warms the atmosphere” – or – “CO2 traps part of the infrared radiation between ground and the upper part of the atmosphere”
…you will be millionaire .
Even Internet sites that are said to have a good scientific level like “Science of doom” publish statements similar to those quoted above . These statements are all wrong yet happen so often that I submitted this guest post to Anthony to clear this issue once for all.
In the case that somebody asks why there is no peer reviewed paper about this issue , it is because everything what follows is textbook material . We will use results from statistical thermodynamics and quantum mechanics that have been known for some 100 years or more . More specifically the statement that we will prove is :
“A volume of gas in Local Thermodynamic Equilibrium (LTE) cannot be heated by CO2.”
There are 3 concepts that we will introduce below and that are necessary to the understanding .
- The Local Thermodynamic Equilibrium (LTE)
This concept plays a central part so some words of definition . First what LTE is not . LTE is not Thermodynamic Equilibrium (TE) , it is a much weaker assumption . LTE requires only that the equilibrium exists in some neighborhood of every point . For example the temperature may vary with time and space within a volume so that this volume is not in a Thermodynamic Equilibrium . However if there is an equilibrium within every small subvolume of this volume , we will have LTE .
Intuitively the notion of LTE is linked to the speed with which the particles move and to their density . If the particle stays long enough in a small volume to interact with other particles in this small volume , for example by collisions , then the particle will equilibrate with others . If it doesn’t stay long enough then it can’t equilibrate with others and there is no LTE .
There are 2 reasons why the importance of LTE is paramount .
First is that a temperature cannot be defined for a volume which is not in LTE . That is easy to understand . The temperature is an average energy of a small volume in equilibrium . Since there is no equilibrium in any small volume if we have not LTE , the temperature cannot be defined in this case.
Second is that the energy distribution in a volume in LTE follows known laws and can be computed .
The energy equipartition law
Kinetic energy is present in several forms . A monoatomic gas has only the translational kinetic energy , the well known ½.m.V² . A polyatomic gas can also vibrate and rotate and therefore has in addition to the translational kinetic energy also the vibrational and the rotational kinetic energy . When we want to specify the total kinetic energy of a molecule , we need to account for all 3 forms of it .
Thus the immediate question we ask is : “If we add energy to a molecule , what will it do ? Increase its velocity ? Increase its vibration ? Increase its rotation ? Some mixture of all 3 ?”
The answer is given by the energy equipartition law . It says : “In LTE the energy is shared equally among its different forms .”
As we have seen that the temperature is an average energy ,and that it is defined only under LTE conditions , it is possible to link the average kinetic energy <E> to the temperature . For instance in a monoatomic gas like Helium we have <E>= 3/2.k.T . The factor 3/2 comes because there are 3 translational degrees of freedom (3 space dimensions) and it can be reformulated by saying that the kinetic energy per translational degree of freedom is ½.k.T . From there can be derived ideal gas laws , specific heat capacities and much more . For polyatomic molecules exhibiting vibration and rotation the calculations are more complicated . The important point in this statistical law is that if we add some energy to a great number of molecules , this energy will be shared equally among their translational , rotational and vibrational degrees of freedom .
Quantum mechanical interactions of molecules with infrared radiation
Everything that happens in the interaction between a molecule and the infrared radiation is governed by quantum mechanics . Therefore the processes cannot be understood without at least the basics of the QM theory .
The most important point is that only the vibration and rotation modes of a molecule can interact with the infrared radiation . In addition this interaction will take place only if the molecule presents a non zero dipolar momentum . As a non zero dipolar momentum implies some asymmetry in the distribution of the electrical charges , it is specially important in non symmetric molecules . For instance the nitrogen N-N molecule is symmetrical and has no permanent dipolar momentum .
O=C=O is also symmetrical and has no permanent dipolar momentum . C=O is non symmetrical and has a permanent dipolar momentum . However to interact with IR it is not necessary that the dipolar momentum be permanent . While O=C=O has no permanent dipolar momentum , it has vibrational modes where an asymmetry appears and it is those modes that will absorb and emit IR . Also nitrogen N-N colliding with another molecule will be deformed and acquire a transient dipolar momentum which will allow it to absorb and emit IR .
In the picture left you see the 4 possible vibration modes of CO2 . The first one is symmetrical and therefore displays no dipolar momentum and doesn’t interact with IR . The second and the third look similar and have a dipolar momentum . It is these both that represent the famous 15µ band . The fourth is highly asymmetrical and also has a dipolar momentum .
What does interaction between a vibration mode and IR mean ?
The vibrational energies are quantified , that means that they can only take some discrete values . In the picture above is shown what happens when a molecule meets a photon whose energy (h.ν or ђ.ω) is exactly equal to the difference between 2 energy levels E2-E1 . The molecule absorbs the photon and “jumps up” from E1 to E2 . Of course the opposite process exists too – a molecule in the energy level E2 can “jump down” from E2 to E1 and emit a photon of energy E2-E1 .
But that is not everything that happens . What also happens are collisions and during collisions all following processes are possible .
- Translation-translation interaction . This is your usual billiard ball collision .
- Translation-vibration interaction . Here energy is exchanged between the vibration modes and the translation modes .
- Translation-rotation interaction . Here energy is is exchanged between the rotation modes and the translation modes .
- Rotation-vibration interaction … etc .
In the matter that concerns us here , namely a mixture of CO2 and N2 under infrared radiation only 2 processes are important : translation-translation and translation-vibration . We will therefore neglect all other processes without loosing generality .
The proof of our statement
The translation-translation process (sphere collision) has been well understood since more than 100 years . It can be studied by semi-classical statistical mechanics and the result is that the velocities of molecules (translational kinetic energy) within a volume of gas in equilibrium are distributed according to the Maxwell-Boltzmann distribution . As this distribution is invariant for a constant temperature , there are no net energy transfers and we do not need to further analyze this process .
The 2 processes of interest are the following :
CO2 + γ → CO2* (1)
This reads “a CO2 molecule absorbs an infrared photon γ and goes to a vibrationally excited state CO2*”
CO2* + N2 → CO2 + N2⁺ (2)
This reads “a vibrationally excited CO2 molecule CO2* collides with an N2 molecule and relaxes to a lower vibrational energy state CO2 while the N2 molecule increases its velocity to N2⁺ “. We use a different symbol * and ⁺ for the excited states to differentiate the energy modes – vibrational (*) for CO2 and translational (⁺) for N2 . In other words , there is transfer between vibrational and translational degrees of freedom in the process (2) . This process in non equilibrium conditions is sometimes called thermalization .
The microscopical process (2) is described by time symmetrical equations . All mechanical and electromagnetical interactions are governed by equations invariant under time reversal . This is not true for electroweak interactions but they play no role in the process (2) .
Again in simple words , it means that if the process (2) happens then the time symmetrical process , namely CO2 + N2⁺ → CO2* + N2 , happens too . Indeed this time reversed process where fast (e.g hot) N2 molecules slow down and excite vibrationally CO2 molecules is what makes an N2/CO2 laser work. Therefore the right way to write the process (2) is the following .
CO2* + N2 ↔ CO2 + N2⁺ (3)
Where the use of the double arrow ↔ instad of the simple arrow → is telling us that this process goes in both directions . Now the most important question is “What are the rates of the → and the ← processes ?”
The LTE conditions with the energy equipartition law give immediately the answer : “These rates are exactly equal .” This means that for every collision where a vibrationally excited CO2* transfers energy to N2 , there is a collision where N2⁺ transfers the same energy to CO2 and excites it vibrationally . There is no net energy transfer from CO2 to N2 through the vibration-translation interaction .
As we have seen that CO2 cannot transfer energy to N2 through the translation-translation process either , there is no net energy transfer (e.g “heating”) from CO2 to N2 what proves our statement .
This has an interesting corollary for the process (1) , IR absorption by CO2 molecules . We know that in equilibrium the distribution of the vibrational quantum states (e.g how many molecules are in a state with energy Ei) is invariant and depends only on temperature . For example only about 5 % of CO2 molecules are in a vibrationally excited state at room temperatures , 95 % are in the ground state .
Therefore in order to maintain the number of vibrationally excited molecules constant , every time a CO2 molecule absorbs an infrared photon and excites vibrationally , it is necessary that another CO2 molecule relaxes by going to a lower energy state . As we have seen above that this relaxation cannot happen through collisions with N2 because no net energy transfer is permitted , only the process (1) is available . Indeed the right way to write the process (1) is also :
CO2 + γ ↔ CO2* (1)
Where the use of the double arrow shows that the absorption process (→) happens at the same time as the emission process (←) . Because the number of excited molecules in a small volume in LTE must stay constant , follows that both processes emission/absorption must balance . In other words CO2 which absorbs strongly the 15µ IR , will emit strongly almost exactly as much 15 µ radiation as it absorbs . This is independent of the CO2 concentrations and of the intensity of IR radiation .
For those who prefer experimental proofs to theoretical arguments , here is a simple experiment demonstrating the above statements . Let us consider a hollow sphere at 15°C filled with air . You install an IR detector on the surface of the cavity . This is equivalent to the atmosphere during the night . The cavity will emit IR according to a black body law . Some frequencies of this BB radiation will be absorbed by the vibration modes of the CO2 molecules present in the air . What you will observe is :
- The detector shows that the cavity absorbs the same power on 15µ as it emits
- The temperature of the air stays at 15°C and more specifically the N2 and O2 do not heat
These observations demonstrate as expected that CO2 emits the same power as it absorbs and that there is no net energy transfer between the vibrational modes of CO2 and the translational modes of N2 and O2 . If you double the CO2 concentration or make the temperature vary , the observations stay identical showing that the conclusions we made are independent of temperatures and CO2 concentrations .
Conclusion and caveats
The main point is that every time you hear or read that “CO2 heats the atmosphere” , that “energy is trapped by CO2” , that “energy is stored by green house gases” and similar statements , you may be sure that this source is not to be trusted for information about radiation questions .
Caveat 1
The statement we proved cannot be interpreted as “CO2 has no impact on the dynamics of the Earth-atmosphere system” . What we have proven is that the CO2 cannot heat the atmosphere in the bulk but the whole system cannot be reduced to the bulk of the atmosphere . Indeed there are 2 interfaces – the void on one side and the surface of the Earth on the other side . Neither the former nor the latter is in LTE and the arguments we used are not valid . The dynamics of the system are governed by the lapse rate which is “anchored” to the ground and whose variations are dependent not only on convection , latent heat changes and conduction but also radiative transfer . The concentrations of CO2 (and H2O) play a role in this dynamics but it is not the purpose of this post to examine these much more complex and not well understood aspects .
Caveat 2
You will sometimes read or hear that “the CO2 has not the time to emit IR because the relaxation time is much longer than the mean time between collisions .” We know now that this conclusion is clearly wrong but looks like common sense if one accepts the premises which are true . Where is the problem ?
Well as the collisions are dominating , the CO2 will indeed often relax by a collision process . But with the same token it will also often excite by a collision process . And both processes will happen with an equal rate in LTE as we have seen . As for the emission , we are talking typically about 10ⁿ molecules with n of the order of 20 . Even if the average emission time is longer than the time between collisions , there is still a huge number of excited molecules who had not the opportunity to relax collisionally and who will emit . Not surprisingly this is also what experience shows .
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Roy Spencer says:
August 5, 2010 at 4:57 am
If local thermodynamic equilibrium exists in a certain volume of a gas, and you add more CO2 at the same temperature, it is true that the volume’s temperature will not change.
No one I know of would disagree with this.
But it’s when that volume is exposed to outside influences — like IR radiation from the solar-heated surface of the Earth passing through that volume — that a temperature change can occur as a result of adding more CO2 to the volume.
_______________________________________________________________
Tom Vonk is not talking about anything but what he has defined. Until the idea of “local thermodynamic equilibrium” and the physics that applies to it is understood you can not discuss anything else. I think this post comes under the heading of defining terms.
As you said “No one I know of would disagree with this.” but most lay people do not understand that.
Leftist paradise coming soon:
Ecuador signs historic deal to “leave the oil in the soil”, with the UNITED NATIONS
http://hintadupfing.blogspot.com/2010/08/ecuador-signs-historic-deal-to-leave.html
Mike Haseler wrote:
(24) The complex bond structure within CO2 means that it can readily absorb and emit radiation in the infra-red (IR) band where thermal radiation is given off by a blackbody9 at the temperature of the earth. Much of this IR is at wavelengths at which other atmospheric constituents do not interact, so if CO2 is exposed to a warmer surface like the earth, it will absorb radiation that would otherwise pass through into the cold of space AND likewise if CO2 is exposed to the cool of outer space it will emit vast quantities of IR at wavelengths which other gases cannot emit.
(25) When CO2 is present low in the atmosphere, it tends to block transmission of these wavelengths into space and reduce heat loss to space. When CO2 is present high in the atmosphere, it helps emit IR, so causing cooling of the atmosphere acting as a vector by which other gases can lose heat into space. Like triple glazing, the system is complicated by the movement of air. Air warmed at the surface naturally tends to rise above the majority of the (blocking) atmosphere and it cannot descend until it has cooled by the emission of IR into the cool of outer space. CO2 cooling is as natural as CO2 warming, the atmosphere being a highly dynamic and complex system: a natural cooling system taking heat from the surface of the earth up into space via convective currents.
(26) Simple physics could suggest CO2 is a cooling gas as easily as warming and “obvious” assertions must be validated against real evidence, not the preconceptions of “scientists”. CO2 could impact the atmosphere in other ways: changes in specific heat capacity, density, interaction with water droplets and cloud formation. Other gases like water vapour also have their effects. It would be wrong to say that increases in CO2 can not affect the climate, but it is equally absurd, in such a complex system, to say this or that effect must dominate in the absence of the normal rigorous testing required by science.
I would recommend this simple summary to anyone who is trying to understand the effect that CO2 has or might have. I have tried to make the same points in the past but the above statements are more succinct.
Just to embelish a few of the points.
The evidence from recent ice ages suggests that periods with high CO2 concentrations correlate with periods of cooling (but could easily be coincidental). There is absolutely no correlation with warming periods.
At low altitude CO2 absorbs most 13 -18 micron radiation within a few feet and re radiates it in all directions. The energy radiated downwards warms the earth (and air) below whilst that radiated upwards gets absorbed by other CO2 molecules and reradiated… and so on. Just below the tropopause the density of CO2 is such that there is a high probability that upward directed radiation will be emitted to outer space. This radiation from just below the tropopause represents the nett loss from the earth at that wavelength. It represents 18% of all the energy radiated from the earth. Most of the remaining 82% is radiated by water vapour molecules from various heights in the atmosphere (depending on wavelength) and the surface of the earth (particularly at wavelengths around 10 micron where the atmosphere is almost transparent).The total energy radiated by all these three (plus a few other small contributors like methane) has to balance the sun’s energy absorbed by the earth during the day. If it does not the earth will either heat up or cool down until it does.
I therefore have two questions that I have yet to get answers to:
1)Has amount of energy radiated into space at 13-18 micron reduced over the past 30 years? This is what make AGW a theory because it can be disproved if there has been no decrease.
Since this cannot be easily measured until the next generation of satellites goes up this year an alternative question could be:
2) Has the CO2 layer radiating directly into space decreased in temperature? The increased number of radiating CO2 molecules will have increased the radiation into space so the temperature will have to decrease significantly to compensate for this increase and reduce radiation still further.
The climate4you website has a section on long wave radiation which is very informative. It also shows how difficult it is to answer the first question. The global average of long wave radiation measured by satellites fluctuates by +/- 20%. This fluctuation dwarfs the tiny change that we are trying to measure over the longer term.
tallbloke says:
August 5, 2010 at 8:13 am
That is almost right. Water volumetric heat capacity=4.186 Jcm-3 K-1, Soil=~2.0,
Air=0.001297 Jcm-3 K-1 (3227 times less than water)
To everyone: Try preparing your breakfast using a hair dryer 🙂
DocWat says:
August 5, 2010 at 5:23 am
Help me here… A system in equilibrium quickly returns to equilibrium at a higher level when it absorbs an IR photon: CO2+N2CO2+N2 becomes CO2*+N2CO2+N2+ (pardon the limited special character skills). This looks like heating to me, and, the temperature is controlled by the variance in the rate of absorbed and emitted IR photons for any small volume.
What I really don’t understand is why water and CO2 are better, by a factor of 20, at this as N2 and O2
___________________________________________________________
I am going to go out on a limb and drag up my physics from forty years ago (Eeek is was that long ago?!)
The absorption of a photon does not translate to heat it is the VELOCITY of the gas translates to heat. PV=nRT
Temperature: A measure of the amount of heat in a system
[K] or [◦ C]. More precisely, it is a measure of the average velocity
of the particles in matter (see §XIII.G). from PHYS-2010: General Physics I: Course Lecture Notes: Section XIII
Hope that helps.
bushy,
There isn’t any question that the greenhouse effect is real and that CO2 is a contributor. Places that have very little GHG (i.e. South Pole) also have very cold temperatures.
Jan K. Andersen says:
August 5, 2010 at 5:23 am
I am sorry to say that this was a rather disappointing article on this otherwise excellent blog.
The fact that CO2 absorbs infrared energy and heat the atmosphere is no theory,, it is a fact. The flaw in the article is that it does not take into account that the absorbed radiation is outgoing, but the emitted radiation go in all directions.
_____________________________________________________________-
There IS no flaw. Tom Vonk carefully defined the case he was discussing. I again defined the simple case under discussion here: http://wattsupwiththat.com/2010/08/05/co2-heats-the-atmosphere-a-counter-view/#comment-448340
tallbloke says:
“The sun hits the sea more than the land, penetrates it up to a depth of tens of metres, gives up it’s heat energy to it, and then the ocean emit’s longwave IR into the atmosphere. It heats it mainly by convection, and the latent heat of evaporation and condensation. Then the atmosphere loses the heat to space, after bouncing it up and down to the surface a few times.”
So anything that warms up the oceans (eg, sunlight, IR emitted downward by water vapor in the atmosphere, or IR emitted downward by CO2) will also warm the atmosphere.
Even without going into the atmospheric physics, that seems to kill the OP right there.
A few questions for Tom Vonk:
Is it fair to say CO2 is an insulator that slows down how fast the ground cools at night?
Is it also fair to say that like any other insulator each fixed incremental addition of more insulation is less effective than the previous increment – so that like having on five layers of clothing in the arctic winter adding a sixth won’t help keep you warm nearly as much as going from no clothes to adding the first layer?
Does a 25ppm increase in CO2 from 1880 to 1950 have about the same net surface warming effect as the 50ppm increase from 1950 to 2000?
The big questions though are the ones you can’t answer. Is there a negative feedback to increasing CO2 (in the water cycle) that will negate its insulating effect? Latent heat of vaporization at the surface, especially over the oceans, carries a tremendous and not easily quantifiable amount of energy straight through the CO2 like it wasn’t there and releases it much higher up where the path out the door to space has much less resistance compared to ground level. Is the effect of higher concentration of CO2 i.e. the CO2 signal or fingerprint, hopelessly swamped by other variables, some cyclic and some chaotic, some probably unknown and possibly unknowable and greatly variable in just about any timeframe from minutes to millions of years?
I guess I’ll finish up with a biology and geology question. What is the global optimum average temperature for maximum productivity of the primary producers (green plants) in the food chain? What is the optimal concentration of CO2 for the same producers?
It seems clear enough from evidence of the geologic past that before the earth started ringing like a bell every 120K years from glacial to interglacial with the former dominating the other 10:1 in persistence, the Eocene optimum 50 million years ago the earth was ice-free, green from pole to pole, it was about 11F warmer overall, with the most dramatic warming in the highest latitudes (right where you’d want it if you could ask for it), and atmspheric CO2 was several times what it is today, which makes sense in light of much warmer global ocean not able to hold as much CO2. Happily enough, terrestrial also plants also require less water per unit of growth as CO2 rises because they don’t have to open their stomata as much to get the respiratory exchange of gases.
So what am I supposed to fear from rising CO2? A warmer, greener earth? I’m more looking forward to it!
Wolfwalker
“The opening paragraphs of this article give me the same tingling-down-the-back-of the-neck feeling as those creationist arguments about thermodynamics. It doesn’t feel right. The slightly patronizing writing style, the drastic simplifying of a very complex subject, the theme of ‘armchair genius uses basic facts to prove a major field of science wrong’ — all just like any pseudo-scientific creationist tract. ”
No need to get your spidey senses tingling, Wolf. I think you’ll find that far from trying to prove a major field of science wrong, Tom’s article is just an explanation of how greenhouse gases work at the molecular level.
Watch how fast Liquid Nitrogen absorbs infrared radiation/gains energy from the rest of the molecules in its space.
http://www.youtube.com/watch?v=uQJOj0PkFZU&NR=1
Julio says:
August 5, 2010 at 7:15 am
“This is an amazing exercise in disinformation: how to thoroughly muddle the waters while pretending to clarify………..
Well, since in equilibrium we need to balance things, we need the total radiation out to equal the radiation in,
Iout = Iin
but Iout is only 80% of the radiation emitted upwards by the sphere,
Iout = 0.8*Iup
so we end up with
Iup = Iin/0.8 = 1.25 Iin
which means the “earth” has to radiate more with the glass in place, which means it has to get hotter.
Now tell me exactly what part of “CO2 traps part of the infrared radiation in the atmosphere” you think is untrue.”
Julio, I think you’re taking the wrong message from the posting. Admittedly, I’m rather ignorant of chemistry, especially, this type. What I took from the posting, given the equal distribution of emission of the CO2 molecule, of course there would be a part that is emitted back downward towards the earth. However, I think you have the equation wrong. You’re representing the percentage back out as a constant. It isn’t. Now hang with me as I attempt to clarify while over simplifying.
I’m going to assign a value to the infrared coming in as 10. For no particular reason other than it is a easy number to work with. As it hits the CO2 part of our atmosphere, the CO2 absorbs and then emits. Some back out, some downward towards the earth. Right? So, 10 goes to CO2 and 5 goes out and 5 goes in. So, you’re correct as far as you’re assertion goes, only my constant is 0.5. But that’s not where the story ends. But so far, the equation looks like this;
10—>CO2= 5up and 5 down. But, 10 is the constant representing atmospheric infrared constantly bombarding the earth. So the 5 up is gone back out harangue some other planet. the 5 down is now bouncing back up to combine with the constant 10 so 10 +5 —> CO2 = 7.5 up and 7.5 down. This appears to validate most of the CO2 warming crowd, let’s continue. the 7.5 bounces back up, so now we have 10+7.5 –>CO2 = 8.75 up and 8.75 down. Still going, 10+8.75—>CO2= 9.375 up/down…..10+9.75—>CO2 = 9.875 up/down. Lets see what CO2 is adding to the earth. First is was 5, the 2.5, then 1.25, then 0.625, o.3125…………
Yes, it’s adding, at least that’s my take on the multi-directional emission properties of CO2, but also, do you see how much it is adding? And do you see where you’ll never get. My take in the simplest of terms. If I over simplified, I apologize, if someone thinks I took the wrong bit of information from the post, feel free to correct.
Best wishes.
Folks, it would be fun to try grading all the responses. The fact is that Tom has made a fundamental error. Roy Spencer has pointed it out, as you might expect. Werner Weber and Edvin have added more detail on where he went wrong. There are probably others who have gotten it right but I didn’t notice as I read them.
OTOH, a lot of people have either taken Tom’s words as gospel or gone off on tangents. I’m interested in seeing if Anthony gets it right or not.
BTW, in case you didn’t get it, the basic error by Tom is demanding that there be LTE at all times, even when a photon of IR from outside the local area is absorbed. In fact, he’s also misleading when he claims that a violation of LTE means the temperature of the local area is undefined. I’d like to see it worked out quantitatively, but in any case, if we’re talking a reasonable size local area, the uncertainty of temperature by one or a few IR photons being absorbed is too small to worry about. It’s only when there’s a constant input of such outside photons being absorbed that the local area must warm to produce a new LTE eventually.
One more thing. when we’re talking warming the atmosphere by added GHGs, the initial action is that a local area will absorb a larger % of the (unchanged at this point) IR entering it. This will, despite what Tom says, warm the local area and cause it to, when a new LTE is reached, emit more IR in all directions. The added IR which reaches the surface will warm it (See Roy Spencer’s site if you’re one of those who don’t think a colder body [atmosphere] can warm a hotter body [the surface] via radiation) and this is the raw material of the climate change theory. The CAGW crowd then make a number of wrong assumptions at this point, but I think all the skeptics here are quite aware of that.
[SNIP] Repeated use of the d-word made your posting effort a waste of time. Read the site policy. ~dbs, mod.]
Here is my reply cleared up a bit.
http://noconsensus.wordpress.com/2010/08/05/a-simple-word-experiment-proves-radiative-effects-of-co2/
Fun post.
I think too many folk get caught up in detail (e.g. considering individual molecule interaction vs homogeneous ‘energy’ interaction in the composite atmosphere); rather it would simplify things to consider energy flux flows in 3-D and apply the concepts of S-Parameters (Scattering matrix parameters) to the analysis problem.
A similar problem was manifest years ago when electrical engineers attempted to characterize device (transistor) performance at RF/microwave frequencies using the usual I and E (or e) quantities but encountered shortcomings using that approach until the discovery a revolutionary new way of ‘handling’ a myriad of interactions at very high frequencies … the S-Parameter method of device characterization was born.
http://www.microwaves101.com/encyclopedia/sparameters.cfm
http://en.wikipedia.org/wiki/Two-port_network#Scattering_parameters_.28S-parameters.29
http://www.die.uniroma1.it/personale/pisa/CIRCUITI_MICROONDE/CAD/HP-SEMINARS/S_PARAMETER_MWJ.pdf
.
Gail Combs says:
August 5, 2010 at 8:27 am
“Tom Vonk is not talking about anything but what he has defined. Until the idea of “local thermodynamic equilibrium” and the physics that applies to it is understood you can not discuss anything else. I think this post comes under the heading of defining terms.”
No system that has net radiative energy flows can be in LTE. It may be quite close to LTE, but the departures from LTE cannot be neglected when considering radiative heating and cooling. LTE is not a valid or relevant assumption for discussing the greenhouse effect. It is important to distinguish LTE (local Thermodynamic Equilibrium) from LDE (Local Dynamic Equilibrium), which merely means the temperatures, pressures, composition, inputs, outputs, etc., aren’t varying (or varying only on timescales much greater than that of the molecular processes concerned).
Note that within Earth’s troposphere, the gross molecular flow of heat energy through any surface is of order 100MW/m2 (heat content times molecular speed). The net energy flows (radiation, convection, etc.) are however only ~300W/m2, a few millionths of the total. Being so comparatively small, they normally produce only very slight departures from LTE. Nevertheless, they are quite adequate to create and maintain strong vertical temperature gradients and major temperature differences across the globe.
Love it! Expression in my culture is “the tail does not wag the dog”.
What’s the optical depth of 15um earth vs. Mars atmosphere?
I think the biggest effect the atmosphere has on climate is 14.7psi at the surface raises the vaporization point of water enough that can have a global ocean covering 70% of the surface to an average depth of 4000 meters.
The the big picture becomes “the sun heats the ocean, the ocean heats the atmosphere, and the atmosphere radiates it into the frigid depth of outer space.
Everything else is a minor detail in comparison. The ocean is the dog. The atmosphere is the tail.
DocWat says:
August 5, 2010 at 5:23 am
Help me here…
What I really don’t understand is why water and CO2 are better, by a factor of 20, at this as N2 and O2
________________________________________________________
It has to do with the shape of the molecule. CO2 is
O-C-O and can bend a little in collisions so it is no longer symmetrical
Water, H2O, is not linear like CO2 but shaped in a V (hope the drawing works)
H…. H
\ O /
N2 is N =N (triple bond) and O2 is O=O (double bond)
O2 and O3 grabs much higher energy wavelengths from the sun
This gives a picture of what molecules grabs which wavelength of energy from where (sun or earth) and a ball park of how much.
http://upload.wikimedia.org/wikipedia/commons/7/7c/Atmospheric_Transmission.png
Gail, you point out again that much of chemistry is engineering design and physics, not chemical properties. Which is why I prefer to teach chemistry from a visual building blocks perspective. I wish Legos would sell a chemistry set. That would be so cool.
This post is an insult to honest climate skepticism. The author’s thesis is correct, but incomplete, and therefore totally irrelevant to climate. “A volume of gas in Local Thermodynamic Equilibrium (LTE) cannot be heated by CO2” UNLESS MORE PHOTONS ENTER THAT VOLUME THAN LEAVE. WHEN more photons enter than leave, then that gas will heat up until it radiates away as many photons as it receives. Of course, carbon dioxide can’t heat the atmosphere by itself – it needs an outside source of energy!
Radiant energy is constantly FLOWING from the sun to the earth’s surface and atmosphere and from the earth’s surface and atmosphere to space. Within the atmosphere energy flows by both radiation and convection. The temperature at various locations in the atmosphere and on the surface of the earth is determined by the net flux of energy at that location (and never reaches true equilibrium because the energy input from the sun changes with night/day and the seasons). We are now conducting a planet-wide experiment to see what happens when we double the concentration of the most important molecule mediating the flow of energy from the upper atmosphere to space. (There is little water vapor in the upper atmosphere and most energy leaves the lower atmosphere by convection to or radiation to the upper atmosphere.)
Tom Vonk is correct when he says that the following statements are over-simplifications and need corrections (in caps): “CO2 absorbs AND EMITS the outgoing infrared energy and warms the atmosphere TO A HIGHER TEMPERATURE THAN IT WOULD HAVE WITHOUT CO2” – or – “CO2 traps part of the infrared radiation between ground and the upper part of the atmosphere” AND IS THE MAJOR SOURCE OF INFRARED RADIATION FROM THE UPPER ATMOSPHERE TO SPACE. The credibility of the skeptical community is not helped when Tom makes similar over-simplifications and then buries the important qualifications in Caveat 1: “The concentrations of CO2 (and H2O) play a role in [the] dynamics [of the Earth-atmosphere system] but it is not the purpose of this post to examine these much more complex and not well understood aspects.” What is the purpose of Vonk’s post: To correct the over-simplifications of CAGW’s or to confuse readers into thinking that CO2 plays no role in the temperature of the atmosphere? The future climate of the planet depends on these “much more complex and not well understood aspects”.
This article is misleading. If one assumes constant equilibrium conditions then indeed nothing changes because, well, you have assumed constant equilibrium conditions. The collisional frequency and excited decay times are important because the collisions are so frequent that local equilibrium exists in the bulk of the the atmosphere. All excited states of all the gasses are in equilibrium in the lower atmosphere. This is not true 100 km up. Adding CO2 does increase the adsorption of IR in a closed cell and the temperature must go up to until the IR emission equals the absorption at a new equilibrium.
Closed cells are not at all like the open atmosphere. Adding IR absorption will increase convection and how this affects the hydrodynamic cycle is the critical process. My pet theory says that the tropopause will rise slightly due to CO2 increases and dry out the stratosphere so that the net optical density remains constant per Miskolczi.
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I’ve only skimmed this, and will take a closer look after I’ve had some grub, but if this is all standard text book stuff, and has been for 100years, why don’t Jones, Hansen, Mann et al know about it….Actually, thinking about it, thats probably a stupid question.
Paul Birch says:
August 5, 2010 at 9:43 am
No system that has net radiative energy flows can be in LTE. It may be quite close to LTE, but the departures from LTE cannot be neglected when considering radiative heating and cooling. LTE is not a valid or relevant assumption for discussing the greenhouse effect. It is important to distinguish LTE (local Thermodynamic Equilibrium) from LDE (Local Dynamic Equilibrium), which merely means the temperatures, pressures, composition, inputs, outputs, etc., aren’t varying (or varying only on timescales much greater than that of the molecular processes concerned)…..
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I do not disagree. However you still have to define LTE (local Thermodynamic Equilibrium) and its physical characteristics before you can go on to describe LDE (Local Dynamic Equilibrium) were things ARE varying.
I think both side of the discussion should be looking at Tom’s definition of the LDE (Local Dynamic Equilibrium) AS an Equilibrium. Jump on him if his definition of LDE (Local Dynamic Equilibrium) and the physics of that state is incorrect otherwise jump on him when he finishes defining his terms and goes on from there.
Many of us have little or no thermodynamics or even physics or chemistry background so I find this definition of terms highly useful in advancing my knowledge.
So please stick to the very small portion of Thermodynamics, LDE (Local Dynamic Equilibrium) Tom has described. Is Tom’s description of this equilibrium state wrong and if so where and why.