My thanks to Tim Folkerts, who braves the generally sceptical stance on the talkshop to fight his corner for the climate mainstream paradigm of the radiative greenhouse effect. Tim has written a pared down synopsis of the fundamental points he believes makes the existence of the radiative effect certain. I suggest we try to restrict ourselves to dealing with the specifics of the article, mentioning in passing those aspects we might feel overly restrict the debate by their omission.
Simplified Greenhouse Effect
by Tim Folkerts – Dec 2012
This is about the simplest, most intuitive, most irrefutable argument I can come up with for why gases like CO2 and H20 in the atmosphere (“greenhouse gases”) must warm the surface.
There are only three fundamental requirements for this argument:
- 1. The ground is a good emitter of thermal IR (ie it is reasonably close to a black body).
- 2. The atmosphere contains gases that can absorb and emit IR radiation (“greenhouse gases” = GHGs).
- 3. The “top of the atmosphere” (TOA) (as related to IR emissions) is cooler than the surface.
Note that all three of these are confirmed by experiment for the Earth: the emissivity of the surface (especially the oceans) is close to 1; GHGs like CO2 and H2O definitely absorb and emit IR in particular wavelength bands; the radiative “top of atmosphere” is near the top of the troposphere, where temperatures are ~ 220 K (or -55 C or -65 F)
Note also that pretty much any other details are not critical. It doesn’t matter why there is a lapse rate; there is no need to calculate averages over the surface of the earth; feedback is irrelevant; exactly where and how the sun shines does not impact the fundamental argument.
For the sake of discussion, let’s look at a specific patch of the surface where the temperature happens to be 290K. Lets further assume that patch has an emissivity of 1.00 (ie it is a perfect black body). The spectrum for the thermal IR emitted from such a patch can be calculated, and is shown by the green curve in the graph below.
If there are no GHGs in the atmosphere, then this green 290 K curve in the graph below would also be the spectrum of the thermal IR leaving the earth. It is relatively easy to determine that the total radiation in this particular case would be 401 W/m^2 — either by integrating the area under the curve on the graph, or by using the Stefan-Boltzmann Law.
If we add some GHGs that absorbs IR in a band near 15 μm but transmits other wavelengths (sort of like CO2), and if this gas is at the top of the atmosphere where the temperature is 225 K, then that gas will emit a spectrum like the blue line on the graph. My hypothetical gas happens to emit 14 W/m^2 at 225. (This value can be found by integrating under the blue curve but again, the exact value is not critical).
So what will the spectrum of the thermal IR leaving the earth look like when the GHG is present? It might be tempting to ADD the two curves, getting a total of 401 W/m^2 + 14 W/m^2 = 415 W/m^2. This would result in a net cooling effect from the extra GHGs, but this it NOT correct. The photons near 15 μm that were emitted by the surface don’t leave the earth, but rather get absorbed on the way up through the greenhouse gas. Instead, the radiation from the gases higher in the atmosphere REPLACES the radiation from the surface. The net radiation will be the dashed line. The area under this curve will be less than the radiation from the surface — 377 W/m^2 vs 401 W/m^2, for a net change of – 24 W/m^2 in our particular case.
The implications should be obvious, but let me spell it out.
For a given surface temperature, less radiation leaves a world with cool greenhouse gases than a world with no greenhouse gases. This applies to each and every patch of surface around earth (at least as long as the three conditions hold). Less radiation leaving means more energy staying. More energy staying means the world with GHGs cools more slowly at night and warms more quickly during the day. This inevitably leads to a warmer world if GHGs are present.
We could also play with the numbers to discover that world with the surface at 295 K and this GHG at 225K would radiate 401 W/m^2. Again the implications are obvious. A warmer world with GHGs can radiate away the same energy as a cooler world with no GHGs. For this particular parcel of surface in this hypothetical world, the warming effect was 5 K. Other parcels at other temperatures in other worlds with other GHGs would have different warming effects, but all parcels in all GHG worlds will have some degree of surface warming due to the presence of GHGs.
QED
A few notes …
1) The specific numbers above are presented simply to have concrete numbers to refer to. As long as the three conditions are met, the general conclusion will hold — ie that a world with GHGs can have a higher surface temperature and still radiate away the same energy as a cooler world with no GHGs.
2) The form of the curve (the bite removed from the black body curve) is confirmed by satellite measurements and by more sophisticated calculations. (NOTE: These are plotted vs wavenumber rather than wavelength, so the shape is a little different).
3) This says nothing about what might happen with MORE GHGs. If more GHGs make the “bite” deeper or wider, then the warming effect would increase, but such details are for a different discussion.
4) Water absorbs over wider bands, but tends to do this at lower altitudes (where it is not as cold). This makes for wider but less deep “bites” in the spectrum. Even if water and CO2 absorb in the same band, the CO2 will still matter because it will tend to be at a higher elevation and a lower temperature, creating a deeper “bite”.
5) Details about evaporation, convection, distribution of sunlight, lapse rate, etc are certainly interesting, and could affect the magnitude of the effect. But none of these can change that fact that GHGs do indeed radiate to space from high in the atmosphere where it is cold.
6) The spreadsheet that calculated all this is available. There are no “instructions”, but there are a few comments that should make the spreadsheet’s set-up reasonably intuitive.
The shapes and values ARE accurately calculated (for the idealized emissivities) You can try playing with the temperatures or emissivities if you are so inclined.
7) “Surface” means the physical surface of the Earth — the land and water. One could also talk about the “effective radiating surface”. The “effective radiating surface”, would be somewhere between the physical surface and the TOA and on earth would have a temperature around 255K. But this level is determined by the GHGs in the atmosphere (with no GHGs the effective radiating surface would BE the physical surface), so even this approach relies on the presence of GHGs to warm the surface.
8.) Nothing here violates any laws of thermodynamics.
I can’t really understand how anyone with even a decent understanding of science could think that GHGs have no effect (or worse yet, that GHGs cool the surface!). The ability of GHGs to warm the Earth is confirmed by multiple lines of reasoning. Furthermore, there is the simple fact that the surface is much too warm to be due to sunlight alone, with no warming from the GHGs.
“So for any given fixed KE flow rate, the system’s KE content (and therefore its temperature) is a function simply of that system’s thermal conductivity characteristics”
Hence the importance of a variable speed for the adiabatic loop which incorporates the water cycle.
Thermal conductivity is invariably altered by a change in the speed of flow.
Thank you David, that’s what I was trying to get across when I bring up the difference with the moon radiating into a vacuum and the earth radiating into an atmosphere which radiates into a vacuum.
Without going off on the other tangents, lets start with your specific disagreement
TIM >> ““5) The Stefan-Boltzmann Law is a function of temperature and emissivity, but not a function of evaporation or conduction or convection.”
MAX>> “The SB law applies to a black body. The planet is not a black body. Similarly the SB law assumes that a surface is radiating into a vacuum, you should know this.”
A quick Google check does not support this assertion. I will grant you that Google is hardly the leading authority, but not one of the top 10 hits includes “radiating into a vacuum” in the description. That is your interpretation, counter to every reference I have seen.
(I will grant you that the basic SB equation j = sigma T^4 is for a blackbody only. But inevitably, SB is extended to the more general case of a non-black body j = ε σ T^4, so that half of your objection is semantics at best.)
Could you provide links to any sources that agree with your interpretation of “radiating into a vacuum”?
Your interpretation could be made to work, I suppose, meaning something like the “effective emissivity in this particular circumstance for finding the net IR radiation when other IR sources are around”. For example, you could say that two identical surfaces facing each other at the same temperature will have a “effective emissivity” of 0 since both are emitting and absorbing the same amount, for a net emission of 0. This would be as opposed to the “raw emissivity” that simply uses j = ε σ T^4 without worrying about the other surfaces.
EVEN WITH THIS ODD INTERPRETATION, you have painted yourself into a corner! Consider a 1m x 1m surface with T=288K with that is measured to radiate 370 W when surrounded by a vacuum. We can calculate the “effective emissivity” as ε=0.95 (and the “raw emissivity” is also 0.95).
* If this surface is on the a planet with no atmosphere, it will radiate 370 W to space (pretty much by definition in either your interpretation or my interpretation).
* If this surface is on the a planet with a pure N2 atmosphere, it will radiate 370 W to space. The pure N2 has no (significant) effect on the IR coming from that. The “effective emissivity” and the “raw emissivity” are still both 0.95 (and the “effective emissivity” and the “raw emissivity” of the atmosphere are both 0.0)
* If this surface is on a planet with an atmosphere like earth, then you would say the “effective emissivity” is no longer 0.95, but more like 0.6. (and I would say the “raw emissivity” of the surface is still 0.95, but the atmosphere has an emissivity now). This change in “effective emissivity” is, of course, because the IR is no longer radiating to vacuum.
The surface is radiating to the GHGs and clouds in the atmosphere. Without the the clouds & GHGs the “effective emissivity” reverts to 0.95. So it is the presence of clouds & GHGs that change the effective emissivity. It is the presence of clouds & GHGs that changes the IR emissions to space from 370 W to 240 W. It is the presence of clouds & GHGs that allows a balanced energy flow when T=288 K and a net 240 W of sunlight are absorbed.
David says: ” I am more than a little frustrated by your reply …
I am sorry. It can be tough keeping track of who believes what parts of science and who rejects other parts. Lets see if I can make one more attempt — hopefully addressing your actual concerns.
1) “OK. If “~130W/m^2 less IR actually escapes” … where does it end up?”
I think that is the wrong way to look at the issue. It is kind of like saying “three hoses run into a tank; where does the water from the first hose end up?” Once it is in the tank, all of the water goes to raise the water level in the tank and it doesn’t matter where it came from. Similarly, once energy is thermalized by the atmosphere, it doesn’t matter where it came from !
2) “The core point here is that even if radiative energy does circulate around through the earth-atmosphere-earth loop, keeping perfect energy flow arithmetic, it cannot thereby deliver additional kinetic energy to the atmosphere, thus raising its temperature. “
I think you are confusing two different sorts of “perfect energy flow arithmetic”. The TOTAL of all sorts of energy must balance (ie conservation of energy). This is what I was addressing last time.
There is NOT a separate requirement that radiative energy balance out. Indeed, there is a net flow of radiative IR energy UPWARD. If the earth sends 1 unit of IR energy to the atmosphere, in that same time the atmosphere sends maybe 0.9 units of IR energy back down. And maybe 0.5 units up to space. There is no reason that any of these numbers are the same as each other, nor any requirement that (the IR energy in) = (IR energy out).
3) “Everything balances a la Trenberth.
But is doesn’t balance a la the real world. Balancing the energy flows is a necessary but not a sufficient condition. Your “1 unit up; 1 unit down” implies a world where the atmosphere is the same temperature as the surface. Your “1 unit up; 1 unit down” does conserve energy, but doesn’t really work for the “real earth”.
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The “box with heater” analogy is interesting … I’ll get back to you on that soon. But the analogy is not incompatible with GHGs warming the surface.
http://www.thermopedia.com/content/1153/
“Stefan-Boltzmann’s law relates the integral of the spectral hemispherical density of the radiant flux with the temperature of isothermal black surface. Proceeding from the quantum theory of radiation transfer it has been shown that the spectral and hemispherical density of the radiant flux from the isothermal black surface in vacuum is expressed by Planck’s formula”
http://books.google.com/books?id=4hBTUY_2BMIC&pg=PA1977&lpg=PA1977&dq=stefan+boltzmann+vacuum&source=bl&ots=kFconGb93k&sig=M82OEcqVaPGCPzlq36Fxi3lZXzc&hl=en&sa=X&ei=a9LQUL2UGs_zqwG6voCoBg&ved=0CM4BEOgBMBk#v=onepage&q=stefan%20boltzmann%20vacuum&f=false
http://i341.photobucket.com/albums/o396/maxarutaru/Selection_101_zpsbedd1eae.png
Those are just a few, but it should be obvious when you consider the energy densities involved.
Here ya go: http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/nickel.html#c1
The radiation from a nickel at room temperature can be calculated, right?
“The air molecules in a volume of air about three times the volume of the nickel will have kinetic energy equal to the radiation from the nickel, but it takes the radiation content of a large auditorium to equal that amount. The ratio of the energy per unit volume in the molecular kinetic energy is more than 10^10 times that in radiation. ”
Would you say that a nickel could transfer the same amount of energy to a volume of air AND fill an auditorium with radiation at the same time?
That’s what I mean by double-counting energy.
Max,
This is getting rather protracted, but I’ll add a couple more things
1) When Planck’s Law is expressed in terms of wavelength, then it is important to state “in vacuum” because the wavelength will be different in other materials. Both of your references present that form of Planck’s Law, so that is the context for your references.
2) Your nickel example is mildly amusing.
Max says “The radiation from a nickel at room temperature can be calculated, right?”
Right .. it is even done in the webpage you cite. You will note that they ONLY consider the nickel and its temperature. There is no dependence on the temperature or composition of the surroundings.
“Would you say that a nickel could transfer the same amount of energy to a volume of air AND fill an auditorium with radiation at the same time?
That’s what I mean by double-counting energy.”
What??? The air already has its kinetic energy. The auditorium already has its IR flying around. Neither of these needs to have energy “transferred” every second from the nickle to maintain anything.
I am not the one confused about double-counting here.
3) These are side issues. You skipped the main point — you only get your “effective emissivity” of ~ 0.6 by appealing to the IR properties of the clouds & GHGs.
I’m trying to suggest that the transfer of energy to the atmosphere by non-radiative means would be functionally the same as reducing the emissivity.
Of course the air has it’s own energy, I never said it didn’t.
The nickel conducts/radiates enough energy to raise the temperature of said volume of air by a certain amount, whereas if the nickel was only radiating into a vacuum the energy density would be lower.
Watts per meter squared is Joules per second per meter squared, the units aren’t arbitrary, if you calculate the SB emissions for a surface at a given temperature, you’re getting a maximum value, aren’t you?
If a surface would radiate 370 W/m^2 into a vacuum, adding an atmosphere would allow the surface to conduct heat as well as radiate, right?
If it was radiating 370 W/m^2 with no conduction taking place, how could it keep radiating 370 W/m^2 with conduction taking place… where does the energy conducted away from the surface come from?
If conduction transports 25 W/m^2 to the atmosphere and latent heat transports 92 W/m^2 with 66 W/m^2 leaving directly to space that would leave what, 180 W/m^2 for radiative transfer to heat the atmosphere, wouldn’t it?
Oh, and look at that, if the atmosphere emitted around the same amount of energy to space, someone measuring the radiation from a distance would pick up right around 240 W/m^2 wouldn’t they?
Looks like I can get my effective emissivity just by subtracting the energy carried away from the surface by non-radiative processes from the potential radiation given by the SB law, doesn’t it?
Tim,
Thank you for your considered responses. I appreciate the difficulty of keeping up with the onslaught from so many directions.
On your point (1): I think is was just a linguistic issue, so can be forgotten.
On your point (2): My original comment relates only to the fraction of radiation that goes round the earth-atmosphere-earth loop, as in my example. In the course of the circularity, each photon is anihilated as its energy is converted to KE and then, in the opposite direction, a new one is created as a molecule loses KE. The only sense in which radiative energy needs to balance out is for the earth as a whole (radiation in from space = radiation out to space). Indeed, within the atmosphere, as I vigorously contend, most of it has been transformed to KE anyway.
On your point (3): My example of photons all of exactly 1 unit of energy being anihilated and then created in a circular exchange between the ground KE and the atmospheric KE, was just to draw your attention to a specific point.
My perhaps over-simplistic thought experiment was intended to illustrate that the fraction of energy returned from atmospheric KE to Earth KE via a stream of photons, will all be sent back from Earth KE to atmospheric KE by another stream of photons. Since the energy flow due to that circularity in one direction will by definition balance the energy flow due to that circularity in the other direction, there will be no net energy gain to the atmosphere as a result of that circular travel of energy around the earth-atmosphere-earth loop.
Yes of course the atmosphere does not work like that. In reality (a) there is a range of (planck curve) energy values averaging out at an unit energy value that is dependent on temperature; and (b) only some fraction of the outgoing energy (not all of it) from earth to atmosphere may be returned to the earth. But I would contend that the net atmospheric KE energy gain as a result of that energy flow circularity will still be zero.
I also await your response to my “box with heater” analogy with interest.
Thanks for your continuing engagement in all of this.
Let’s expand on David’s “heater in a box” analogy. The temperature at the interior wall of the box (once equilibrium is achieved) is not simply a function of the power of the heater and the insulation between the interior and the exterior.
We actually need to know
1) the power of the heater
2) the insulating properties between the interior surface of the walls and the exterior surface of the walls
3) the insulating properties between the exterior surface of the walls and the surroundings
4) the insulating properties between the interior surface of the walls and the surroundings directly.
5) The temperature of the surroundings
Line (2) is certainly one of the key factors. “Good” insulation will have a large lapse rate; “thick” insulation will have a large temperature difference between the interior.
Line (3) cannot be ignored. The interior of your box will have a different temperature if the room is cool than if the room is warm; if there is a fan blowing or not; if there is sunshine falling on the box or not.
Line (4) is not something we tend to consider for insulated boxes, but this would be a “heat leak” from the interior. Maybe there is a hole in the box where hot air gets out despite the insulation. Or maybe the wires that carry the electricity to the heater also conduct significant heat from the interior straight to the surroundings. (You could also think of this as simply changing the insulating properties of the wall (eg two insulators in parallel), but either way it must be included).
For earth, the “surroundings” are T=3K space, the “interior surface” is the ground (or ocean) with an emissivity of ~ 0.95, and the “exterior surface” is the “top of atmosphere”. The ONLY heat transfer to the surroundings is via thermal IR radiation.
To find the temperature of the interior, we will have a set of conditions and a set of equations to solve
power of heater
P_h = constant
Power from interior to exterior
P_ie = a function of T_i, T_e, properties between interior and exterior
Power from exterior to surroundings
P_es = a function of T_e, T_s, conditions between exterior and space
Power from interior to surroundings
P_es = a function of T_i, T_s, conditions between interior and space
In general these equations are NOT linear, but you can solve them numerically (much like Wayne did in his recent spreadsheet). The main point is that you cannot find T_i simply from the power of the heater and the thermal properties of the atmosphere.
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The earth with no atmosphere would be like a box with no insulation in the walls, and good thermal contact with surroundings.
The earth with a pure nitrogen atmosphere would be like a box with good insulation in the walls but EXCELLENT insulation between the exterior and the surroundings (ie no energy transfer from the atmosphere itself to space). No (significant) energy could leave from the TOA to space, so the surface (still being connected directly to the surroundings) would still be the same temperature as with no atmosphere.
Add some CO2, and now you have decreased the thermal contact between the ground and space, but increased the thermal contact between the TOA and space. While it might not be intuitively obvious, this will lead to a cool top, and a warm ground.
(Venus would have “thick insulation” = thick atmosphere which is what leads to the high surface temperature despite a similar heater. Venus would also have good thermal contact between the TOA & space, but no thermal contact between the ground and space.)
Tim,
I groaned when I read your incredibly over-complex reply to my ever-so-simple thought experiment. Was this perhaps an attempt to avoid facing up to the issue by overwhelming me with detail?
So let’s have a complete recap.
In your earlier comments concerning the supposed warming effect of GHGs, I thought that you were confusing the energy flow through the atmosphere with its energy content. It is of course the latter and not the former that dictates its temperature.
Hence I saw the need for a thought experiment. This involved imagining a very small flow of Kinetic Energy (say, 1 Watt) through a very well insulated box, the contents of which would therefore rise to a very high temperature (say, 1000degC) despite the smallness of the energy flow.
It was intended simply to illustrate, by analogy, that, when we consider a given fixed flow of Kinetic Energy (KE) through the earth’s atmosphere, the temperature that the atmosphere attains at steady state will depend entirely on the various physical ‘insulating’ characteristics of the atmospheric system that serve to impede the energy flow on its way back to space, thus allowing it to build up to a level where its mean (surface) temperature is 288K.
And how did we get into that discussion in the first place? Well, it followed on from a dialogue we had, in which I argued that GHGs do not play any part at all in heating the bulk of the atmosphere, the reasoning being as follows:
1. Yes, GHGs do play a critical role in converting incoming radiation immediately on entry to KE thus adding to the atmosphere’s KE budget.
2. Yes, the GHG molecules in the bulk of the atmosphere do take part, like all molecules do, in maintaining the correct level of KE to establish its temperature. But in that role they are simply behaving as kinetically energised molecules in just the same way as are all the non-GHG molecules.
3. Yes the GHG molecules will spontaneously emit photons, thus losing KE in the process. But, in the vast bulk of the atmosphere, those photons will quickly be absorbed by other GHG molecules, which will thereby gain KE. This obviously creates a zero KE-to-photon-to-KE energy balance. So the total KE in the bulk of the atmosphere (and hence its temperature) is statistically unaffected by these photon creation/anihilation events going on in its midst.
4. And yes, towards the top of the atmosphere the GHG molecules play a critical role in converting KE to radiation that is then lost to space, thus permanently subtracting from the atmosphere’s KE budget. And as quickly as the GHG molecules lose KE by emitting their photons, they are re-energised by kinetic collisions with the other molecules around them. This establishes a general cooling process in the upper atmosphere which in turn creates a temperature gradient from the ground upwards. Consequently, KE continually flows up the atmospheric column and out (via radiation) to space.
Tim, this is just Grade I physics. It involves nothing more than the flow of good ol’ Kinetic Energy (heat) up through the atmosphere from input to output. Nowhere in that description is there any room for any kind of warming effect due to GHGs other than their mediation role in delivering KE into the atmosphere in the first place and despatching radiation out to space at the top.
If you think GHGs do more than that, TELL US IN PLAIN LANGUAGE WHAT THEY DO AND HOW THEY DO IT.
David Socrates says:
December 19, 2012 at 10:29
Tim persistently defends the radiative theory of the GHE. This has provoked your good recap of the criticisms of that theory and an alternative explanation based on gas thermodynamics.
However you say
“general cooling process in the upper atmosphere which in turn creates a temperature gradient from the ground upwards.”
The atmospheric temperature gradient ( lapse rate ) is caused by gravity. The atmosphere cools (by radiation) because it is surrounded by colder ‘space’.
Roger,
Thanks very much for your support.
I deliberately left out the lapse rate issue. But you are absolutely correct in what you say:
Fixed gravity acting on the fixed mass of air in the atmospheric column establishes fixed pressure, fixed density and fixed temperature distributions, commensurate with the fixed rate at which energy from the Sun is flowing through. All good Gas Law and Hydrostatic Law stuff. Nothing fancy.
However, without the GHGs towards the TOA, the energy flow rate up the atmospheric column would of course be nil. So in that (restricted) sense the cooling effect of the GHGs towards the TOA is responsible for the actual slope of the temperature profile.
But progress here with Tim is tough enough without going into all that. Another blog, perhaps, another day…!
David, I like your recap of your points 1-4, but I still think you are missing a significant idea or two.
For example you say: ” …the temperature that the atmosphere attains at steady state will depend entirely on the various physical ‘insulating’ characteristics of the atmospheric system …”
My somewhat more involved analogy was you show that the “insulating characteristics” are NOT sufficient to determine the temperature! It is one important bit of the puzzle, but much more is needed to find the temperature anywhere.
You say: “Nowhere in that description is there any room for any kind of warming effect due to GHGs other than their mediation role in delivering KE into the atmosphere in the first place and despatching radiation out to space at the top. “
But in fact, that is the whole point. By restricting the flow outward, the whole system “backs up” which leads to warming.
At the risk of getting too sidetracked with another analogy, it is sort of like a water tank with some water running in and some hoses leading out. The water will fill until the depth & pressure of the water in the tank is enough to cause the water running out to equal the water running it. Now block one of the hoses .. the water out will decrease and the depth will start to increase. Eventually, the pressure will rise and the water running from the other hoses will increase, until a new equilibrium with more depth & pressure is reached.
Of course, the sunlight is the incoming water. The “pressure” is the temperature. The hoses would be different wavelengths of IR leaking to space. The GHGs block specific hoses = specific wavelengths. Other details of what happens in between the surface and the TOA are interesting, but not critical. The hose labeled “15 um” is “clogged by GHGs”. Less energy is flowing from that hose to space than we would get without the GHGs, and the “thermal pressure” will rise throughout the system until equilibrium is re-achieved. The other wavelengths will take up the slack, but only after the energy has built up and the temperature has risen.
David says: “But progress here with Tim is tough enough… “
Funny, I was thinking “But progress here with David is tough enough (but much easier than with some!) … ”
BTW, what you said about the lapse rate sounds about exactly right. There is nothing you said that is new or confusing to me.
The properties of heat capacity and gravity and convection that lead to the observed lapse rate are PART of the greenhouse effect.
The properties of GHGs that allow them to absorb and emit IR are PART of the greenhouse effect.
BOTH are essential!
Roger says: “Tim persistently defends the radiative theory of the GHE. This has provoked your good recap of the criticisms of that theory and an alternative explanation based on gas thermodynamics. “
I persist because the radiative theory is one essential PART of the “greenhouse effect”. The thermodynamic properties are also PART of the “greenhouse effect”.
You can’t explain the warm surface (~ 288 K instead of ~ 255 K) without SOME acknowledgement of the effects of IR absorbing materials in the atmosphere. Conservation of energy simply does not allow and average of 240 W/m^2 of sunlight to warm a planet with an emissivity of ~ 0.95 to ~ 288 K without some thing to block some of the outgoing IR. Pressure and gravity and convection and the ideal gas law can’t get you there. If you think you can do it, then show the numbers.
David,
Thanks very much for your recap above. This has been a most enlightening discussion for me, and I also thank Tim Folkerts for his part in the debate.
Is there any way of knowing how much warmer the atmosphere would be without the cooling effect of nGHGs from the TOA? Sorry if this has been covered previously.
Arfur, from previous context, I deduce that “nGHGs” means “non-condensing GHGs” (like CO2 & CH4), rather than simply “non-GHGs” (like N2). If that is wrong, then perhaps you can clarify.
I think you are starting from a false hypothesis. The radiative effect of GHGs certainly does cool the TOP of the atmosphere, But why do you assume that it cools the atmosphere as a whole?
The cool GHGs near the top of the atmosphere produce a “slow leak” of energy to space.
The GHGs near the bottom of the atmosphere plug up a “fast leak” of energy to space.
GHG’s cooling from the TOA is not in addition to cooling from the ground, it is instead of some of the cooling from the ground. That is the whole “bite” idea from the top post!
The net result is warming of the surface (and the lower atmosphere by contact with the ground).
Let me re-post what I posted in the “emissivity” thread, since it seems equally apropos here …
————————————————————————-
Hmmm … maybe THIS is the way to say it!
1) Currently, the CO2 at the TOA radiates very poorly because it is waaaay high up where it is very cold. Because it it radiating poorly, there is little heat leaving the TOA and consequently little heat flowing up thru the atmosphere by convection. This means convection is removing little heat from the surface, so the surface can stay fairly warm.
2) Suppose I suddenly remove 3/4 of the CO2. That is still plenty of CO2 to absorb and emit in the 15 um band, so 15 um IR does not get a “free pass” from the surface out to space. But now the “TOA” will be much lower, where it is much warmer, so the CO2 will emit MORE energy to space in that 15 um band than it did in Case 1 above. This means there will be MORE convection induced to carry that extra heat upward. The more heat that gets carried away from the surface, the cooler the surface will be!
Your “now the TOA will be much lower” assertion is completely unsupported.
Convection removes heat from the boundary layer near the surface, conduction, evaporation, and radiation remove heat from the surface.
Normally radiation is an ineffective method to cool the surface by distributing energy to the rest of the atmosphere.
Adding gases with broader absorption lines provides a new route for energy to flow from the surface to the atmosphere, cooling the surface more effectively than otherwise.
Max suggests: “Adding gases with broader absorption lines provides a new route for energy to flow from the surface to the atmosphere, cooling the surface more effectively than otherwise.”
Once again, you have this rather completely muddled. The flow from the surface to the atmosphere is controlled by how well the ATMOSPHERE can lose energy. In equilibrium, the atmosphere is has no net loss or gain, and the energy in from the surface will be limited by the energy out to space. So what we are REALLY interested in is how well the surface and the atmosphere lose energy to space.
Adding GHGs means that the overall energy to SPACE gets REDUCED. The radiation that WOULD HAVE escaped straight from the warm ground level to space is blocked. The radiation that DOES escape to space comes from the cold upper atmosphere, so the total radiation to space is REDUCED. Reducing the total energy to space means the planet has to warm up. So the upper atmosphere warms a little and the surface warms a little until balance is restored.
The first bits of GHGs have the biggest impact at WARMING (not cooling!) the atmosphere. Later bits are less important, but will still cause warming.
Even the “serious skeptics” don’t deny the warming ability of GHGs. They simply question the EXTENT of the warming.
* Typical “raw” values for CO2 are ~ 1.0 C per doubling of CO2
* “Alarmists” tend to think that feedbacks will INCREASE this number, perhaps to 3C or 4C per doubling.
* “Skeptics” tend to think that feedbacks will DECREASE this number, perhaps to 0.1C – 0.5C per doubling.
I have never seen any serious scientist suggest that CO2 has absolutely no effect. I have certainly never seen a serious scientist suggest that CO2 actually cools the surface!
If you have a reference to some article that suggests that CO2 cools the surface level, I would be interested to see it!
Jeeesh this gets old. Tim you have it muddled.
“Adding GHGs means that the overall energy to SPACE gets REDUCED.”
No, not just adding co2 to any great amount you won’t, not when you have a huge amount of other GHG species and via thermalization, translational excitation, equipartition of energy even including Maxwell-Boltzmann distribution of molecular velocities that rule the translational excitations themselves. This is not an exact trade-off but fairly close, h2o and co2 have similar properties, the energy is going to exit by whatever means it CAN possibly use at the rates governed by that species ability. Energy is not “trapped” Tim, not in our atmosphere with water vapor and other GHGs, the vast majority of the molecules are in the ground state.
Once again you are speaking to an idealized case of an atmosphere with only carbon dioxide and zero other non-GHG species. In such a case Tim, you would be much closer to correct for there is no place for equipartition to distribute with no other vibrational/rotational lines present.
Stop the omissions of ALL of the correct science Tim. I’ve risen theses points numerous times and you wiggle like a snake to crawl out of the spot your have been placed in and you never address the actual physics, all of it, at once.
Cover the h2o lines that overlap the co2 lines and why they are not expressed… it is because of co2 being present. If there was no co2 the water lines would be then visible and there would still be a “bite”, h2o tappers off there, in those frequencies.
And no one really cares whether you have spoken to other scientists or what they said they also beliefs in, these are aspects in the foundations of modern physics.
Now do you bit and cut and paste what you can out of my words to twist it around to your view or “proper” climate “science”. If I would have seen you learn even one thing in the last three years I would not be writing to you in this manner.
You assume equilibrium.
Might help to distinguish between the illuminated side and the night side. The reason being the different results an atmosphere gives.
The moon has no atmosphere and reaches a far higher temperature on the day side, so we can rather safely say the effect of an atmosphere on the day side is to prevent the surface from reaching the potential maximum.
Similarly the night side of the moon cools fairly quickly to a very low temperature and then gradually settles towards a minimum before spiking back up the next day. So we can rather safely say the effect of an atmosphere on the night side is to prevent the surface from reaching the potential minimum.
http://www.asi.org/images/2000/asi200000020.gif
I have an experiment I performed which had a rather pronounced cooling effect from adding a bag filled with CO2 to one of my test boxes, various forms of this experiment had what I took to be anomalous results where the CO2 addition appeared to give a half a degree or even a degree of cooling, but it’s difficult to read on the thermometers, and I could never get anything significant enough to be certain.
After running a version of the test with no bags but everything else the same and then running a version with the addition of an air filled and a CO2 filled bag I found a 3 to 4 degree cooler result which I was able to replicate after switching equipment around to control for instrumental error.
http://www.keepandshare.com/doc/5332990/int1-task3fix-pdf-543k?da=y
Max Says: “The moon has no atmosphere and reaches a far higher temperature on the day side, so we can rather safely say the effect of an atmosphere on the day side is to prevent the surface from reaching the potential maximum.
No, you can’t safely say that. Consider Venus, which is MUCH warmer at the surface than “the potential maximum” due to sunlight alone.
Again … there are (at least three effects) from the atmosphere.
1) The “heat capacity effect”. The atmosphere absorbs heat during the day and releases heat during the night. This serves to make temperatures more uniform — cooling the day side a bit and warming the night side a bit. Due to some standard math and that fact the power is proportional to T^4, the average temperature will be slightly higher with an atmosphere than without one. The lack of atmosphere on the moon allows the warm side to get warmer and the cold side to get colder. An atmosphere of pure N2 would even out the temperatures a bit and warm the moon (on average) a bit.
This IS NOT the “greenhouse effect”
2) The “IR absorption effect”. Some gases (and clouds) absorb thermal IR that is leaving (but allow solar UV/visible/IR that is arriving). But blocking the “warm” upward IR from the ground but emitting “cold” IR from the upper atmosphere, they warm the surface.
This IS the “greenhouse effect”
3) The “lapse rate effect”. The ability of the GHGs to warm the surface relies on the GHGs being cooler than the surface. The “taller” the atmosphere, the cooler the top will be. This enhances the “IR absorption effect” but does not directly warm the surface.. Without GHGs, the “lapse rate effect” would not exist. This is the reason for the huge differences between Venus, Earth, & Mars. It is the thickness of the atmospheres that make the biggest difference here. The %CO2 makes some difference, but it is secondary to the total mass of the atmosphere.
As for your “Are Averaged Radiative System Inputs Realistic?”, there are a lot of interesting ideas there, but too many errors (both in the theory and the experiment) for me to consider to addressing them here. Sorry.
Wayne says: “… you never address the actual physics, all of it, at once.”
Quite true! I am addressing one simple, idealized case (a gedanken experiment) to focus on the warming effect of gases that absorb IR in the range from ~ 4-100 um.
Adding other gases with other absorptions in this range (eg H2O or CH4) will simply enhance the effect I am addressing.
To address “the actual physics, all of it, at once” would require considering the effect of …
* heat capacity of the ground
* heat capacity of the atmosphere
* heat capacity of the oceans
* rotation rate
* distribution of land and oceans around the globe
* evaporation
* ocean currents
* actual lapse rates
* reflection from clouds
* absorption by clouds
* current concentrations of all GHGs
* rate of change of all GHGs
* and about a thousand other factors large and small
These will all MODIFY the effect of GHG warming, but none of them negate warming by GHGs.
Errors in the experiment, look man, it’s an effect that can be replicated.
Set up a container to test in, add a tray with water, a transparent vented lid, and a bag with regular air.
Illuminate it with a given wattage for a given period of time.
Then replace the contents of the bag with CO2, and repeat the illumination with the same wattage for the same duration.
I am confident you will observe a cooling effect from the CO2, that paper doesn’t go into the many dozens of variations I tested, that is just the narrowed down version, as otherwise it would be 30 or so pages long if not more.
You can argue all the theory and physics and math you’d like, but you can’t handwave away a fact.
You CAN point out that my experiment is not the same thing as the atmosphere itself, but what it did do was prove that adding CO2 to a system can cool it, interpret that however you’d like, but it happened.
Tim,
You say: I have never seen any serious scientist suggest that CO2 has absolutely no effect. I have certainly never seen a serious scientist suggest that CO2 actually cools the surface!
Well I am a serious scientist. So is Harry Huffman. So are Nikolov & Zeller. And so are countless others who toil away on this and other blog sites.
Are you sure you are not equating the word “serious” with the word “climate” or the word “academic”?
Max says, 22 Dec 2012 at 12:53pm:
Your “now the TOA will be much lower” assertion is completely unsupported. Convection removes heat from the boundary layer near the surface, conduction, evaporation, and radiation remove heat from the surface. Normally radiation is an ineffective method to cool the surface by distributing energy to the rest of the atmosphere. Adding gases with broader absorption lines provides a new route for energy to flow from the surface to the atmosphere, cooling the surface more effectively than otherwise.
Max, The interesting thing about your assertions is that they provoke some useful thoughts, more by what they omit than what they include.
Over on the emissivity blog I have been having a very useful discussion with Tim Folkerts about our respective understanding of the atmospheric “model” and, in particular, which bits of it are effective in restricting the energy flow through the atmosphere, thus causing more kinetic energy to accumulate in the atmosphere, and thus raising its temperature profile (and, in particular, its surface temperature).
I notice you focus in detail on all the relevant things except the crucial radiation release mechanism that converts KE to radiation at the top of the atmosphere.
This I believe should now be the main area of attention.
Tim believes that this mechanism (which certainly depends absolutely on the presence of GHGs to do the radiating) controls the rate at which energy escapes from the atmosphere (“throttles it down” as it were) thereby creating higher atmospheric temperatures than would otherwise be the case.
Whereas I suspect it is a more-or-less open window that will easily radiate any energy coming up at it through the atmospheric column – and that the “throttling” needed to raise atmspheric temperatures is due to the (in comparison) incredibly slow processes of air convection.
I don’t focus on it because the only difference between the radiation at the top and that at the bottom is the density of the gas and the effect that has on the mean flight time for a given photon.
Deeper in the atmosphere the time between collisions with other molecules is far shorter than the time between emissions, on average of course, and the distance any photon typical flies before being absorbed is not very long, thus the lower atmosphere is dominated by non-radiative interchanges for the most part.
What the addition of gases which absorb in what were previously clear regions of the spectrum does is increase the energy available for transfer to other gases.
A CO2 molecule which absorbs a photon from the surface is probably going to collide with another molecule and exchange energy in that manner before it has an opportunity to release the energy through emission.
In general the more actively absorbing molecules in the denser lower levels of the atmosphere would rarely have an opportunity to re-emit those photons at all, and most of that energy winds up distributed among other less actively absorbing gases.
As the atmosphere thins out this ratio between collisions and emissions shifts until eventually at the upper levels most transfer is by radiation, and finally there is a point above which the energy rarely gets reabsorbed before it makes it out to space.
Max Says: “I don’t focus on it because the only difference between the radiation at the top and that at the bottom is the density of the gas and the effect that has on the mean flight time for a given photon.”
There is ALSO the difference in temperature, that also makes a difference.
“In general the more actively absorbing molecules in the denser lower levels of the atmosphere would rarely have an opportunity to re-emit those photons at all, and most of that energy winds up distributed among other less actively absorbing gases.”
You are missing the fact that the CO2 can also GAIN energy from collisions with other molecules. At equilibrium, the CO2 molecules will be GAINING energy as often as they will be LOSING energy. The collisions will maintain a fixed fraction of CO2 molecules in an excited vibrational mode (the fraction depending on the temperature of the surrounding molecules). With a fixed fraction in the excited state, the odds of re-emitting a 15 um IR photon will be fixed by the temperature of the surrounding gas. Warmer gas emits more frequently than colder gas.
The warm CO2 in the lower atmosphere will MORE often emit 15 um IR than the cold CO2 in the upper atmosphere!
Max,
All the points you make are true. But you have not addressed my point: whether the energy release mechanism to space at the ToA acts as a “throttle”, regulating the release of energy to space and thus maintaining a higher or lower surface temperature depending on the CO2 concentration; or alternatively as an “infinite heat sink”, capable of accepting and transforming to radiation whatever KE is pushed up the atmospheric column from below.
If the former, then Tim might be right that the concentration of CO2 could affect the degree of throttling and therefore the surface temperature.
If the latter, then the rate of upwelling (and hence the surface temperature) would depend on thermodynamic forces, principally convection, which would be independent of the CO2 concentration.
A crucial point, is it not?
Tim,
You say to Max: You are missing the fact that the CO2 can also GAIN energy from collisions with other molecules. At equilibrium, the CO2 molecules will be GAINING energy as often as they will be LOSING energy. The collisions will maintain a fixed fraction of CO2 molecules in an excited vibrational mode (the fraction depending on the temperature of the surrounding molecules). With a fixed fraction in the excited state, the odds of re-emitting a 15 um IR photon will be fixed by the temperature of the surrounding gas. Warmer gas emits more frequently than colder gas.
True but so what? The rate at which photons are emitted by GHGs makes not a jot of difference in the bulk of the atmosphere because, as fast as they are emitted, they are absorbed by other GHGs molecules. The bulk of the atmosphere may well be a seething mass of photons flying in all directions. But the GHGs are losing and gaining KE in equal quantities. It’s a zero sum game. So the aggregate effect is that the KE of the bulk of the atmosphere (and hence its temperature) is not altered at all.
Only towards the top of the atmosphere, where the probablity gets higher that an emitted photon might make it to space, does a net flow from KE to radiation occur, thus tending to lower the temperature. So I don’t know why you are focussing on photons in the higher temperature parts of the atmosphere where photons have no influence.
“The bulk of the atmosphere may well be a seething mass of photons flying in all directions. But the GHGs are losing and gaining KE in equal quantities. It’s a zero sum game. So the aggregate effect is that the KE of the bulk of the atmosphere (and hence its temperature) is not altered at all. ”
Right on David. This seems so important to I.P.C.C. that this is not publically realized, for most of the pure radiative AGW ties breakdown right there. Their co2 photons from high above all beaming down upon the surface and therefore warming it or preventing it from cooling… pure hogwash, not in a real, thick atmosphere.
“As the atmosphere thins out this ratio between collisions and emissions shifts until eventually at the upper levels most transfer is by radiation, and finally there is a point above which the energy rarely gets reabsorbed before it makes it out to space.”
When the atmosphere expands that process would result in more efficient radiative loss to space would it not ?
So if GHGs cause an expansion that would offset any warming at the surface especially since the atmosphere would also then contain more PE at the expense of KE.
Mind you, I am coming to the view that GHGs don’t have any net effect at all for the reasons being suggested here.
David, the “so what” is the rate at which photons LEAVE THE EARTH (not the rate they might percolate up within the atmosphere). . Cool CO2 molecules high in the atmosphere are cold and rarely in the excited state, so they rarely emit photons. There is little energy leaving the TOA, so there is little need to convect/radiate/conduct energy up thru the atmosphere.
If there was much less CO2, then CO2 molecules much lower (where it is much warmer) would constitute the “TOA” radiating to space. Being warmer, then then would more often be in the excited state and would more often emit radiation to space. This would cause more cooling from the “TOA”. This would be a greater need to convect/radiate/conduct energy up thru the atmosphere!
And adding CO2 would have the reverse effect … raising the TOA, cooling the TOA, reducing the fraction in the excited state, reducing hte radiation to space, reducing the convection/radiation/conduction thru the atmosphere, and leading to warming of the surface.
“There is ALSO the difference in temperature, that also makes a difference.” ~Tim
Well, no, the stratosphere warms up to 273 K, then the mesosphere profile cools up to the thermosphere and temperatures reach 1200 K or higher.
The density is the most important factor.
“You are missing the fact that the CO2 can also GAIN energy from collisions with other molecules. At equilibrium, the CO2 molecules will be GAINING energy as often as they will be LOSING energy. The collisions will maintain a fixed fraction of CO2 molecules in an excited vibrational mode (the fraction depending on the temperature of the surrounding molecules). With a fixed fraction in the excited state, the odds of re-emitting a 15 um IR photon will be fixed by the temperature of the surrounding gas. Warmer gas emits more frequently than colder gas.
The warm CO2 in the lower atmosphere will MORE often emit 15 um IR than the cold CO2 in the upper atmosphere!”
Sweetheart, don’t assume I’m missing things for me.
I’m well aware CO2 can gain energy from collisions, but if a molecule of CO2 receives extra energy by absorbing photons it will be more likely to lose energy to another molecule rather than gain energy in a collision.
You’re also completely misrepresenting my argument.
I said that photons will experience collisions far more often in the lower atmosphere than anywhere else, and thus they will experience kinetic energy exchanges rather than radiative ones more often than not.
The length of time between collisions and emission is perfectly calculable, and it is FAR shorter for collisions until the atmosphere reaches low enough density.
Yes, CO2 molecules in the lower atmosphere will emit photons now and then, but those they do emit will tend to be absorbed before they travel very far.
_______________________________________________
Statistically yes, obviously there are more opportunities to emit for warmer CO2 down in the lower atmosphere, but there are many many more opportunities for it to lose energy through collisions, and there are many many more opportunities for a stray photon to be absorbed after an arbitrarily short flight.
Upper atmosphere CO2 will emit less often, but it will lose energy through collision far less often, what it does emit will be absorbed far less rapidly, often making it out to space.
This is why there is a “bite” taken out of the spectrum.
“And adding CO2 would have the reverse effect … raising the TOA, cooling the TOA, reducing the fraction in the excited state, reducing hte radiation to space, reducing the convection/radiation/conduction thru the atmosphere, and leading to warming of the surface.”
This point comes up regularly and is part of AGW dogma.
If the height at which outgoing equals incoming rises then radiation is NOT occurring from a colder location.
What happens is that the whole atmosphere expands and becomes less dense so that radiation is from a higher level but at the same temperature as before.
The result is then the exact opposite of what Tim proposes.
Radiation from the higher equally warm location is MORE efficient so less energy is available at the surface and convection etc. slows down.
The net effect at the surface being zero because the slower convection etc (my adiabatic loop) offsets the faster radiation to space (my diabatic loop).
Stephen says: “What happens is that the whole atmosphere expands and becomes less dense so that radiation is from a higher level but at the same temperature as before.
That is one hypothesis. But that hypothesis requires the lapse rate to change exactly in sync with the expansion. And that makes little sense to me.
What would cause the atmosphere to expand to begin with? It would have to be warmer on average. You are hypothesizing that the warming and expansion ONLY occurs above the surface level (otherwise you are agreeing that the surface is warming to cause the expansion). So what mechanism will warm the mid to upper levels, but not the bottom level? What makes the lapse rate DROP in the mid to upper levels so that the top stays the same temperature at a higher altitude?
We are not going to solve this here. I suspect that the atmosphere will expand (as you conclude) AND the TOA will rise to a cooler, higher level.
For example (making up approximate numbers to illustrate the point), suppose the TOA is currently at 0.25 atm and 220 K @ 10,000 km. With more CO2 the TOA might be at 0.24 Atm and 218 K @ 10,100 m. The increased altitude is due to BOTH an over all expansion due to an over all 1K warming all the way from the surface to 10,000 m AND the increase in CO2.
“Radiation from the higher equally warm location is MORE efficient …”
I am curious why you come to this conclusion. It seems the radiation should be the same in your hypothesis, since the temperature is the same.
[Reply] “What would cause the atmosphere to expand to begin with?” Solar and cloud variation.
Tim, Stephen, all…
First of all a Happy New Year!
It seems to me that this stage of the discussion is incredibly important because the ToA is the last unswept corner of the climate model.
We have visited the very thin slice at the BoA where the upwelling radiation from the surface is met by equal downwelling radiation. So radiation in the BoA certainly isn’t doing any warming.
We have visted the bulk of the atmosphere, whose KE budget (represented by energetic GHGs and non-GHGs alike) is fixed by the rate at which energy flowing in from the Sun exactly balances the outflowing ‘loss’ to space. It is also the case that, in addition to their normal KE diffusion behaviour, the GHGs in the bulk of the atmosphere continually emit photons in all directions. But they also continually absorb them at an equal rate. The total fund of radiation is fixed in quantity and therefore cannot contribute to, or subtract from, the atmosphere’s total fund of KE. So radiation in the bulk of the atmosphere certainly isn’t doing any warming.
And now we are homing in on the third and final domain, the ToA where the GHGs act as cooling agents, receiving KE from the non-GHGs all around them and transforming that KE to a photon stream which is lost to space. So radiation in the ToA certainly isn’t doing any warming.
But then there is yet another issue which we might call Tim’s last stand. He expressed this best when he asked originally what would happen if we magically reduced the concentration of CO2 in the atmosphere by, say, 3/4. This will lower the average height at which GHGs can successfully emit photons to space because the GHG molecules will be further apart, thus allowing lower level molecules a higher statistical chance of emitting photons to space. I think he is right in logic and physics to say this.
But then there are three different ‘closing arguments’ in this line of thought:
(1) TIM SAYS: Because the new lowered average emission height is in a region of higher temperature, the emitted photons are (on average) more energetic. This will result in an increased rate of flow of energy to space, thus reducing the fund of KE in the atmosphere down to a lower steady-state level. So lowering the concentration of CO2 in the atmosphere lowers its KE fund, thereby cooling it!
(2) OTHERS SAY: Because there are fewer photons to do the emitting, the overall energy flow to space is reduced, not increased. So lowering CO2 in the atmosphere raises its KE fund, thereby warming it!
(3) I SAY: The ToA does not behave like a “throttle” limiting the rate of flow. It behaves more like an “open window”, converting whatever KE is thrown at it into radiation that is lost to space. But if this is so, what IS limiting the rate of energy flow? It is the physics of convection which limits the rate at which KE can flow up the atmospheric column. So lowering CO2 in the atmosphere does not affect its KE fund, thereby maintaining exactly the same temperature as before!
Trouble is, (1), (2) and (3) are all good qualitative, logical arguments. What we now need is some quantitative work to prove the issue one way or another. This needs help from people with a good knowledge of statistical thermodynamics.
Any offers?
I think the point that is being missed here is that although the adiabatic loop has a zero effect on net energy flow at equilibrium it can have a non zero effect when the system is in the process of moving from one point of equilibrium to another.
That is implicit in my assertion that an expanded atmosphere changes the relationship between KE and PE.
If the atmosphere expands then the same amount of KE and PE is being cycled over a greater distance so the time delay between energy leaving the surface and arriving back at the surface increases and during that extra time more energy can leak out to space via the diabatic loop.
Thus an expanded and less dense atmosphere will return less KE to the surface after the adjustment process than it was doing before the initial disruption.
That makes sense if one considers extreme scenarios. Substantially contracting an atmosphere to make it more dense would return more KE to the surface and substantially expanding an atmosphere to greatly reduce density would return much less KE to the surface.
Venus gets lots of KE returned to the surface and Mars hardly any.The Moon, none at all.
Jupiter and Saturn as gas giants have more KE returned to their cores from the atmosphere than they receive from solar input.
The fact is that an atmosphere with more GHGs will energise the adiabatic / thermodynamic processes giving a higher atmosphere so the amount of KE being returned to the surface will reduce and it is that reduction of KE to the surface that offsets any additional warming at the surface that would otherwise have occurred from more GHGs.
Perhaps I should explain it this way:
i) The surface actually receives energy from three sources, solar input, DWIR and returning KE.
ii) Solar input comes straight in and goes straight out at equilibrium hence radiative balance high up in the atmosphere.
iii) All else remaining the same any increase in DWIR reaching the surface via the diabatic loop will result in an equal reduction in KE returning to the surface via the adiabatic loop because of atmospheric expansion and increased energy leakage to space.
Of course the position is different if the atmospheric expansion results from more energy circulating through both of the two loops but one can only achieve that from more insolation, more atmospheric mass or a stronger gravitational field.
Just changing composition only involves a shift in the balance between DWIR and returning KE and that in turn is mediated by the KE / PE balance up through the vertical column.
That is why it is wrong to focus on DWIR as a significant driver of surface temperature. Changes in DWIR alone are irrelevant to the temperature that a surface can attain beneath an atmosphere.
A faster adiabatic loop, as provoked by more GHGs, then results in less KE returning to the surface as a result of atmospheric expansion.
So we now have a clear mechanism whereby a slowing down of energy throughput by GHGs can be offset by a speeding up of energy throuhgput by thermodynamics.
The speeding up of the thermodynamic processes within an expanded atmosphere results in a reduction in the amount of KE getting back to the surface via the adiabatic loop.
Max says: “I’m well aware CO2 can gain energy from collisions, but if a molecule of CO2 receives extra energy by absorbing photons it will be more likely to lose energy to another molecule rather than gain energy in a collision.
Max, Darling, you still are not quite “getting it”. If the atmosphere is the same temperature as the ground, then the likelihood is the same. Several people have mentioned the “equipartition theorem” in this thread, which is exactly the idea at play here. If the CO2 molecule was more likely to absorb photons (and pass that energy to the surrounding molecules) than to emit photons (by absorbing KE from the surrounding molecules) it would be easy to violate the 2nd Law of thermodynamics.
Now, it is true that the atmosphere absorbing the 15 um photons is slightly cooler than ground emitting the 15 um photons, so there will be a VERY SMALL net gain of energy by the atmosphere (ie slightly more IR photons absorbed than emitted) due to the lapse rate. If there is a temperature inversion, then the CO2 molecules would be MORE likely to gain energy from collisions and emit a photon, than to absorb a photon and pass energy along to the molecules nearby.
“I said that photons will experience collisions far more often in the lower atmosphere than anywhere else, and thus they will experience kinetic energy exchanges rather than radiative ones more often than not.”
Now you have confused me. The first half I follow, but is “they” photons or molecules? Or perhaps you meant “molecules” at the start of the sentence?
“The length of time between collisions and emission is perfectly calculable, and it is FAR shorter for collisions until the atmosphere reaches low enough density.
True, but “until the atmosphere reaches low enough density” is well above the tropopause if my estimates are correct. And the “TOA” for CO2 15 um photons is below the tropopause.
This is actually a bit of a challenging problem. The simple estimate is that the mean time between collisions is proportional to
t ∝ P / T^0.5
At the TOA near the top of the troposphere, the pressure is ~ P = 0.2 Atm and the temperature is about 75% of the surface temperature, so the collision time increases by only a factor of about 6. If the collision time was “FAR shorter” (say 1% as long) at the surface, then multiplying by ~ 6 will probably STILL leave it shorter than the time for IR emissions.
Then there is the issue of pressure broadening. The lower pressure at the TOA will sharpen the line width, which will (according to Heisenberg) increase the time the atom can spend in the excited state. In other words, as the pressure decreases, the frequency of collisions decreases AND the frequency of emission decreases. This should mostly wipe out the effect of pressure changes, leaving only the relatively small temperature change to affect the odds of emission vs collision.
(This is probably why it is hard to Google info about the time for photon emission for CO2 — it depends strongly on pressure and temperature).
Pretty good Summary, David.
Of course, I still hold with Option (1).
Very briefly (once again)
(2) suffers from going against Planck’s Law and the physics of thermal radiation. With 1/4 as much CO2, the “view from space” would see much warmer CO2 (but still still “thick” enough to emit photons effectively in the 15 um band) and hence MORE photons, not fewer! Rather than perhaps a 1,000 m thick layer at 10,000 m altitude with a temperature of 220 K emitting few photons to space (and blocking all the 15 um photons coming up from below), you might have a 1,000 m thick layer at 5,000 m altitude with a temperature of 240 K emitting more photons to space (and still blocking all the 15 um photons coming up from below).
(3) suffers from the fact that GHGs (and clouds) are what let the energy “leak out the top” so naturally they should control the energy out the top of the atmosphere and hence the energy up thru each layer of the atmosphere.
“(3) suffers from the fact that GHGs (and clouds) are what let the energy “leak out the top” so naturally they should control the energy out the top of the atmosphere and hence the energy up thru each layer of the atmosphere”
Not so fast.
The extra energy leaking out from the expanded atmosphere reduces the amount of KE being returned to the surface via adiabatic compression.
That KE reduction offsets any extra energy reaching the ground from more DWIR.
“Trouble is, (1), (2) and (3) are all good qualitative, logical arguments. What we now need is some quantitative work to prove the issue one way or another. This needs help from people with a good knowledge of statistical thermodynamics.”
Agree. Also, very important I think, you cannot just ignore stimulated emissions for these emissions are directional in nature and there is an upward bias in the atmosphere and it is quite large. Both you and Tim are only looking at the collisional excitation and dwell times. Remember, a ~15 micron emission is 8.5 billion times more likely to be by stimulation than by spontaneous emission. Stimulation emissions are directional, the spontaeous ones are isomorphic (1/2 upward, 1/2 downward).
Steven Wilde says: I think the point that is being missed here is that although the adiabatic loop has a zero effect on net energy flow at equilibrium it can have a non zero effect when the system is in the process of moving from one point of equilibrium to another. That is implicit in my assertion that an expanded atmosphere changes the relationship between KE and PE.
Maybe. But the model I am discussing assumes that the atmosphere always contains the same total fixed amount of KE – and then we examine whether or not it remains so after changes in CO2 concentration.
I think it is best to offer a model at KE equilibrium and then demonstrate (as I have attempted to do) that the reason is at equilibrium is simply due to the fixed flow rate of KE up the atmospheric column and not due to a “throttling” effect at the output end at the ToA. If the former is the controlling factor (as I believe), then radiative gases can have no effect because the rate of KE flow is purely to do with the physics of convection of air. If the latter is the controlling factor (as Tim believes), then I would have to concede to Tim that the rate of throttling could indeed be influenced by CO2 concentration.
That is why I suggest our focus now should be wholly on this one area where we appear to have a major and crucial difference of opinion with Tim so that (collectively) we can try and settle it one way or the other.
So in those circumstances, I am not sure that your responses about transient effects relate to the model I am putting forward.
Wayne says: Also, very important I think, you cannot just ignore stimulated emissions for these emissions are directional in nature and there is an upward bias in the atmosphere and it is quite large.
Wayne,
This is something new to me. I thought stimulated emission was something that happened in lasers, and not in the atmosphere!
Tim says: (3) suffers from the fact that GHGs (and clouds) are what let the energy “leak out the top” so naturally they should control the energy out the top of the atmosphere and hence the energy up thru each layer of the atmosphere.
Tim,
Your comment doesn’t move us forward. It is just a re-statement of your sincerely held view.
As I say, to resolve the issue we need some quantitative statistical thermodynamics now…
“Maybe. But the model I am discussing assumes that the atmosphere always contains the same total fixed amount of KE – and then we examine whether or not it remains so after changes in CO2 concentration. ”
That’s fine for a starting point but would only apply in a static atmosphere with no convection.
In reality the total energy content of an atmosphere is represented by PE plus KE and as per my contentions the proportions can vary.
The difference with Tim is that he allows for a throttling effect from more GHGs but then fails to allow for de-throttling from less KE coming back from the adiabatic compression of descending air.
He only considers half the equation.
Since the two processes cancel out the net effect is as you say. The total amount of KE stays much the same because any attempts by GHGs to change it are cancelled out by an adjustment of the relative proportions of KE and PE.
“This is something new to me. I thought stimulated emission was something that happened in lasers, and not in the atmosphere!” ~David Socrates
David, a few month’s ago I thought the same but it turns out that is very, very wrong.
There are two types of emissions in all gases and all radiation and always occur whether electronic, rotational or vibrational, makes no difference. Lasing is just a special case. Unfortunately 99 of every 100 mentions in articles and papers of stimulated emission jump to lasers which is just one very special case… that makes it hard to get the low down.
Stimulated emissions must equal absorptions if in TE at all times, not so for isotropic spontaneous emissions, it is just that these emissions leave as two photons and are directional in all gases and e/m fields. Look it up, took me month’s to go through enough sites (use the “site:edu” selector when searching, that helps) to get a starting handle on the subject.
I’ll post some links and further info on this later as I can re-gather it.
Stephen,
You say: That’s fine for a starting point but would only apply in a static atmosphere with no convection.
I don’t understand your point. My model, the one that has been under discussion for some time on this thread, is averaged over sufficient time and space to iron out all short term, and spacial, variations such as those that occur all the time in a real atmosphere. All energy balance models have to be like that – otherwise nobody could have a sensible conversation about long term energy balances! My model is certainly not intended to exclude the thermodynamic effects of convection.
You say: The difference with Tim is that he allows for a throttling effect from more GHGs but then fails to allow for de-throttling from less KE coming back from the adiabatic compression of descending air. He only considers half the equation. Since the two processes cancel out the net effect is as you say. The total amount of KE stays much the same because any attempts by GHGs to change it are cancelled out by an adjustment of the relative proportions of KE and PE.
Well perhaps that’s a good alternate theory to put up to Tim if my ‘Closing Argument (3)’ fails and his ‘Closing Argument (1)’ prevails! If so I shall have to make a bigger effort to understand it, but I must confess that it does not currently make much sense to me. Maybe that’s because I missed out on an elaboration elsewhere?
David Socrates, I’ve left you a further comment on the emissivity thread about stimulated emission. I don’t want to mess up Tim’s and this doesn’t really seem to apply to his anyway.
Tim, I did mean molecules in the first part of the second quote of mine above.
“ If the CO2 molecule was more likely to absorb photons (and pass that energy to the surrounding molecules) than to emit photons (by absorbing KE from the surrounding molecules) it would be easy to violate the 2nd Law of thermodynamics.” ~Tim
This has nothing to do with what I was saying.
The exchange from CO2 molecules jostling other molecules will work out to be roughly balanced, while the exchange from the ground to CO2 can not work out to be roughly balanced, as the ground is warmer than the atmosphere.
The time between a CO2 molecule absorbing a photon and emitting a photon is shorter than the average time between collisions.
It is unlikely that a CO2 molecule would absorb a photon and remain in that state without colliding with another molecule for a long enough time to emit that photon again.
There would be cases where a CO2 molecule collides with another molecule and then emits a photon, and a portion of those cases would involve emission towards the ground, and some portion of those cases would involve those emitted photons reaching the surface.
Max, you say: The time between a CO2 molecule absorbing a photon and emitting a photon is shorter than the average time between collisions.
It is unlikely that a CO2 molecule would absorb a photon and remain in that state without colliding with another molecule for a long enough time to emit that photon again.
Er, did you mean that? Surely those two statements contradict one another!
In any case I thought it had been clearly established that, at least in the lower atmosphere, the probability of an energised GHG molecule emitting a photon before it loses its energy in a collision is quite low.
Or is this just another ‘climate science’ myth?
The first part should have been “between absorbing and emitting is longer than the average time between collisions”, was distracted while posting.
I meant the same thing you said, I just had it phrased oddly: the probability of a molecule emitting a photon before it loses that energy in a collision is quite low.
David.
Going by your comments on the other thread we are pretty much in agreement.
The points I raised and which puzzled you were just a couple of steps further on in considering the logical implications.
More detail is contained in my thread about adiabatic processes.
In effect one needs some component of the system to respond quickly and negatively to any attempt at thermal forcing from GHGS.
One cannot alter the amount of energy tied up in the adiabatic loop because that is fixed by mass, gravity and available energy (from sun, geothermal or as a consequence of pressure).
However one can alter the speed at which the adiabatic loop circulates and it is that variability which can accelerate or decelerate energy lost to space from the diabatic loop thereby negating the thermal effects of GHGs.
Once we have a clear explanation as to why GHGs cannot heat up the system then that is game over.
Max says, January 4, 2013 at 1:35 am: I meant the same thing you said, I just had it phrased oddly: the probability of a molecule emitting a photon before it loses that energy in a collision is quite low.
OK, so how do you square that with your comment of January 3, 2013 at 1:32 am: …exchange from the ground to CO2 can not work out to be roughly balanced, as the ground is warmer than the atmosphere.
The atmosphere at surface level is NOT cooler than the ground. It is in contact with the ground. So the atmosphere at the surface must generate exactly the same downwelling LWIR as the earth generates upwelling LWIR. In other words, the ground and the atmosphere at the surface are in radiative balance. And, by Prevost’s Theory of Exchanges (1790), there will therefore be no net radiant energy to convert to KE in the atmosphere.
If you accept this argument, the only energy contribution from the ground that is generating KE (i.e. heat) in the atmosphere is via conduction/diffusion and by the latent heat of vaporisation (the latter being subsequently converted to KE when it is converted to KE during precipitation). To this must be added the energy that is received directly into the atmosphere from the Sun’s incident IR radiation which is also absorbed immediately as KE.
So the KE flowing into the atmosphere (and hence its temperature) is not affected by the concentration of atmospheric GHGs, providing that there is at least enough concentration of GHGs (which there is) to convert the portion obtained from the Sun’s incoming LWIR radiation to KE.
Mod: For the record, LWIR above should read SWIR.
[Reply] The page is too long for my lappy to load, and I don’t know when you made the comment above. In order to get you and Tim to write the new articles you have promised, I will close comments on this thread soon.
[...] of the AGW theory and frequent blogger. He bravely agreed with TB to write an article entitled: Tim Folkerts: Simple argument supporting a radiative greenhouse effect. The other thread was initiated on 14 Dec 2012 by TB himself entitled: Emissivity puzzle: energy [...]
There is a love of theoretical minutia, coupled with a disragard for observation, in many of these comments. The discussion of gravity is a case in point. The density and pressure of the atmosphere are largely determined by gravity. However, the temperature dependence of the atmosphere is dominated by the absorption of solar radiation. The temperature drops in the troposphere, rises in the stratosphere, drops again in the mesosphere and rises again in the thermosphere. This W cannot be understood except in terms of solar wind and ozone’s UV absorption. So handwaving about radiation and the kinetic energy of gasses, enthalpy etc. without calculations to show that you are ‘in the ballpark’ with observation are akin to metaphysics. Please focus on the empirical and observation.
The discussion of Prevost’s Theory, which predates any modern understanding of radiation or the atomic theory of matter, is woefully inappropriate for a discussion of the interaction of radation and matter in an atmosphere, espeically when there is a absorption spectra involved. In what sense does IR radiation behave like a ‘rare fluid’ in the presense of a molecule with an aabsoption line in the midle of the frequencies in question? So rather than looking to thermodynamic arguements of dubious applicability, why not pay more attention to observations of the atmosphere? The point of a simple theory, as Tim presented, it to give a reasonable explanation of observation. It is to capture the essence, not to demonstrate a knowledge of every aspect of a physical system.
To my mind, TIm has provided a concise explanation of how the green house effect does manage to warm the Earth. That the greenhouse effect of carbon dioxoide does warm the Earth has been non-controversial since the time of Arrhenius. Without a greenhouse effect, we would still be living on a snowball Earth. Why is the Earth currently warmer than 255 K? The Earth has seen several episodes of snowball earth, as evidenced by drop stones on the equator. But greenhouse warming resulted in the habitable world that made the Cambrian explosion, and our modern world, possible.
Max stated:
“I have an experiment I performed which had a rather pronounced cooling effect from adding a bag filled with CO2 to one of my test boxes, various forms of this experiment had what I took to be anomalous results where the CO2 addition appeared to give a half a degree or even a degree of cooling, but it’s difficult to read on the thermometers, and I could never get anything significant enough to be certain.”
As far as I know, dry ice is the only practical way to get a ‘bag full of CO2′ (Carbon dioxide at room temperature, is of course a gas,and bags of gas are not very common. An inflated diver’s vest would count, so perhaps you did actually have a bag of CO2 gas. Please explain your bag of CO2 and include the relative volumes of the test box and CO2 bag. Also discuss your experience with calorimetry.) Adding anything at −78.5 °C to a test box at room temperature is likely to cool the test box, this would explain your observations but has nothing to do with the greenhouse effect. As a self-described climate skeptic, I’m sure you understand the importance of healthy skepticism of claimed experiments that contradict published results.
I suggest that you watch following experiment from Mythbusters, which was conveniently recorded on Youtube: http://www.youtube.com/watch?v=pPRd5GT0v0I (or search youtube for “Mythbusters greenhouse”, it will be your first link). Apparently, they have a bigger budget for thermometers than you do since were able to measure the temperature increase.
It should be easy to convince me of your claims – I am a skeptic, not a contrarian. Write up your experiment with enough detail that it can be reproduced. We can then discuss the results and determine the correctness and relevance of your claims. If there are questions about the experimental results, we can simply repeat the measurements to confirm your results.
Steven Wilde states,
“The total amount of KE stays much the same because any attempts by GHGs to change it are cancelled out by an adjustment of the relative proportions of KE and PE.”
The potential energy of a molecule near the surface of the Earth is given by mgh, e.g. it’s height. The KE is determined by it’s translational and vibrational degrees of freedom. When a molecule absorbs radiation, it can gain vibrational energy. This can be transferred to other molecules by collisions. This will tend to increase the kinetic energy of all the molecules in the gas. This will also cause the atmosphere to rise slightly. (statistically speaking, the molecules go up slightly)
So the radiant energy, along with the kinetic energy and potential energy of the molecule all follow the Boltzmann distribution. See http://courses.physics.illinois.edu/phys213/lectures/lecture12.pdf for lecture notes on this; I’m sure there are many more discussions of this on the internet or in general texts of undergraduate physics. There simply is no ‘canceling out’ – if you dump energy into a system, it will be distributed between all available degrees of freedom in accord with the Boltzmann distribution.
David Socrates states,
“This obviously creates a zero KE-to-photon-to-KE energy balance. So the total KE in the bulk of the atmosphere (and hence its temperature) is statistically unaffected by these photon creation/anihilation events going on in its midst.”
There are two subtile, but fundamental, mistakes in these two sentences.
1. If the energy of the photons is higher than the average kinetic energy of the gas, the effect of atom/photon interactions is to increase the temperature of the gas. If the gas has a higher temperature (average energy per degree of freedom), the gas will loose energy to the photons. So we will head toward a thermal equilibrium as long as there is a mechanism to achieve thermal equilibrium. (if the gas is transparent to the photons, there need not be a thermal equilibrium between them.) So the temperature of the gas is affected by KE-photon-KE interactions.
2. As the gas heats, the distribution of the height of the molecules, which obey the Boltzmann distribution, e.g. exp(-mgh/kT), will also increase. It is not only the KE that increases with temperature, the PE also reaches thermal equilibrium. So all of the arguments that equate temperature with only kinetic energy are simply incorrect.
Have a look on YouTube under ‘Yalecourses’; they have the lectures for the class “The Atmosphere, the Ocean and Environmental Change” (GG 140). Episode 04 is “Vertical Structure of the atmosphere; residence time.” The density of the atmosphere decreases with exp(-gh/RT). (h=height, g=acceleration of gravity, R is gas constant and T is temperature). Why is this exponential and why does this vary with g, h and 1/T? It can all be derived in a few lines from the Boltzmann distribution and the ideal gas law. This can also be found in all the standard texts. This is not controversial or fringe, this is well established by theory and confirmed by measurement.
The Feynman Lectures have a wonderful discussion of thermal equilibrium using a ratchet and pawl (in Vol 1, as I recall.) Or just read about the ‘Brownian ratchet’ on Wikipedia. This is fun stuff, so read it if you want to refine your arguments about statistical physics.
—–
As you may have guessed from our names and similar ages, Tim is my more patient brother. I also have a daughter with a recent degree in Earth Sciences who is currently experiencing and combatting some of the consequences of global warming near the Sahel. I thank everyone on this forum who has avoided pseudonyms; our children and grandchildren will be able to go back and Google our words. If they have to deal with the increasing consequences of climate change, they can understand why nothing was done sooner. Or maybe mainstream science is wrong; then our children and grandchildren can look back and laugh at me for being such a Henny Penny. You know how I am betting.
Robert Folkerts says:
Some good points there, until the last paragraph. The theories of Arrhenius were debunked 100 years ago by a simple experiment.
http://greenhouse.geologist-1011.net/
[see para. 3.3]
Hi Robert and welcome. My name is Roger Tattersall, I’m a Mech Engineer with a degree in the history and philosophy of science. Just a quick point about the ‘mythbusters’ experiment. While none of us here are in any doubt that a doubling of co2 in a test like this will produce around a K of warming of the control volume, we doubt whether this fact has much relevance in the open where convection and latent heat control the temperature of the bulk atmosphere. Without getting into discussion of the Maxwell distribution, it’s worth pointing out that the PE contained in water vapour is a much more efficient energy store than gravity is. This is because as Peter Berenyi pointed out, the the latent heat required to evaporate a molecule of water is equivalent to the amount of energy used in raising that molecule 264km from the surface aganst gravity. Given that the troposphere is only about 18km high at the equator…. well, I won’t insult your intelligence by labouring the point.
Mythbusters has nothing whatsoever to say about water vapour and their experiment is therefore utterly worthless in relation to an understanding of the real atmosphere. It’s effectiveness as propaganda is a different question, which we don’t need to clutter this thread with.
Robert asks: “Why is the Earth currently warmer than 255 K”
Actually, the question is: Why is the Earth warmer than ~206K – The average surface temperature of the Moon, which is at the same distance from the Sun. That’s an issue I started investigating here:http://tallbloke.wordpress.com/2012/12/10/why-earths-surface-is-so-much-warmer-than-the-moons-part-1/
Oldbrew,
Arrhenius had the microscopic mechanism wrong; given that the infrared spectrum of CO2 was published on Jun 17, 1932, I think that is understandable.
But it is certainly the case that infrared (of certain frequencies) will excite CO2 which is then very likely to reemit the photon in a random direction. However, it is also possible that the molecule in question will suffer a collision and the energy will be converted to the motion of the other atoms of the gas.
The first mechanism results in a very long random walk of IR photons that will form a ‘gas’ in their own right. This gas exchanges energy with the gas of molecules. Within the range of frequencies where a molecule (or water droplet, or aerosol…) can absorb and reemit, the radiation and molecules in the gat will come to a thermal equilibrium. The details of the mechanism are not important to thermodynamic arguments. Arrhenius was certainly a master of chemical thermodynamics; as anyone who has studies rate equations in chemistry should recall. Disproving Arrhenius’ mechanism does not necessarily disprove his thermodynamic arguments.
So let us return to our microscopic picture of solar radiation. You have a photon of visible light that is absorbed on a rock, heats the rock. The hot rock is now a blackbody in its own right. If it emits a photon is of a a frequency that is not absorbed, the photon will freely escape into space. If the photon is of a frequency that is absorbed, its energy will reside longer in the atmosphere until it is either emitted into space or converted into molecular motion (or increasing the distance between water molecules, or any of the other things that energy can do in the atmosphere.
How is that not an insulating layer? An insulator does not function to add or remove heat, it simply slows the transfer of heat. A random walk in three dimensions is vastly longer than than a straight path. That makes it an insulator. During this long random walk, the energy of the photon is likely to be exchanged with other degrees of freedom. So we have a microscopic mechanism that does work as Arrhenius predicted from thermodynamic reasoning.
Tallbloke states:
“While none of us here are in any doubt that a doubling of co2 in a test like this will produce around a K of warming of the control volume…”
Max stated:
“I have an experiment I performed which had a rather pronounced cooling effect from adding a bag filled with CO2 to one of my test boxes…”
So at least one of us here does have doubts about CO2 producing warming and goes so far as to say he has an experiment that showed cooling. I realize that this is a public forum and Tallbloke is not responsible for the content of Max, but he did go on to claim a community norm that clearly is not shared by all members of this community.
I am standing by Tim’s analysis, not only because he is kin but because his arguments are based upon well established thermal physics AND they are largely consistent with observation. I have challenged the arguments of others based upon the physical principles as understood by physicists and most climate scientists. I will not appeal to community norms to make an argument about a physical system.
Tallbloke states,
” it’s worth pointing out that the PE contained in water vapour is a much more efficient energy store than gravity is. This is because as Peter Berenyi pointed out, the the latent heat required to evaporate a molecule of water is equivalent to the amount of energy used in raising that molecule 264km from the surface aganst gravity. ”
It comes as no surprise that a van der Waal’s (electrostatic) attraction id much stronger than gravity at the molecular level. Since the mean free path of a molecule in the atmosphere is well under 264 km, I’m pretty sure that the water will reach thermal equilibrium with the surrounding molecules well before it travels that far. So even if you postulate a mechanism to transfer this potential energy to kinetic energy, I don’t see how that changes much. As long as we have a mechanism to exchange energy, we should expect the system to approach thermal equilibrium by purely statistical arguments. After all, the density of the atmosphere does obey exp(-mgh/kT).
It is also clear that because of this van der Waal attraction, the water in the atmosphere does condense and it largely found in the bottom 10 km of the atmosphere, e.g. the troposphere. By contrast, carbon dioxide is much more evenly distributed throughout the atmosphere. So in the stratosphere, CO2 is interacting with the infrared radiation and providing an insulating effect even when there is (relatively) no water to be found. So I will gladly grant you that the PE due to the latent heat of water is much greater than the gravitational energy between the earth and a molecule. Will you agree that this latent heat is the reason that water is largely restricted to the troposphere? By contrast, carbon dioxide remains at about 330 ppm up to an altitude of 80 km.
Hi Robert and thanks for your reply. It’s always interesting when new people come along and make novel arguments about the greenhouse effect. Up until now the theoreticians have been saying that additional co2 will cause the troposphere to warm and the stratosphere to cool. Now you seem to be saying that the ‘insulation’ of additional co2 in the stratosphere will cause it to warm. The data says the stratosphere has been neither warming nor cooling since 1995 when the after-effects of Pinatubo wore off. There does seem to be a deal of confusion over absolute temperature levels however:
http://tallbloke.wordpress.com/2013/01/17/met-office-in-new-controversy-undocumented-stratosphere-dataset-2c-warmer-than-noaa-met/
Given the much wider open ‘window’ up there (due to low density), I would expect the co2 above the tropopause to do a pretty efficient job of cooling the planet by radiating to space. Maybe you can point us to some technical information on this?
You said:
“I’m pretty sure that the water will reach thermal equilibrium with the surrounding molecules well before it travels that far. So even if you postulate a mechanism to transfer this potential energy to kinetic energy, I don’t see how that changes much.”
The mechanism is condensation, and I don’t need to postulate it, because what goes up must come down. Water vapour sneaks energy in the form of PE locked up in the latent heat of evaporation up past the co2 in the lower troposphere and condenses out, releasing that heat at an altitude where LW radiates pretty freely to space from the cloud-tops. Thus the hydrological cycle is in dominant control of the troposphere.