by Judith Curry
On the previous two threads, we had a lively, rollicking, illuminating and often frustrating discussion on the physics of the greenhouse effect. On this thread, I try to synthesize the main issues and arguments that were made and pull some of what I regard to be the highlights from the comments.
The problem with explaining the atmospheric greenhouse effect is eloquently described by Nullius in Verba:
A great deal of confusion is caused in this debate by the fact that there are two distinct explanations for the greenhouse effect: one based on that developed by Fourier, Tyndall, etc. which works for purely radiative atmospheres (i.e. no convection), and the radiative-convective explanation developed by Manabe and Wetherald around the 1970s, I think. (It may be earlier, but I don’t know of any other references.)
Climate scientists do know how the basic greenhouse physics works, and they model it using the Manabe and Wetherald approach. But almost universally, when they try to explain it, they all use the purely radiative approach, which is incorrect, misleading, contrary to observation, and results in a variety of inconsistencies when people try to plug real atmospheric physics into a bad model. It is actually internally consistent, and it would happen like that if convection could somehow be prevented, but it isn’t how the real atmosphere works.
This leads to a tremendous amount of wasted effort and confusion. The G&T paper in particular got led down the garden path by picking up several ‘popular’ explanations of the greenhouse effect and pursuing them ad absurdam. A tremendous amount of debate is expended on questions of the second law of thermodynamics, and whether back radiation from a cold sky can warm the surface.
The Tyndall gas effect
John Nielsen-Gammon focuses in on the radiative explanation, which he refers to as the “Tyndall gas effect,” in a concurrent post on his blog Climate Abyss.
Vaughan Pratt succintly describes the Tyndall gas effect:
The proof of infrared absorption by CO2 was found by John Tyndall in the 1860s and measured at 972 times the absorptivity of air. Since then we have learned how to measure not only the strength of its absorption but also how the strength depends on the absorbed wavelength. The physics of infrared absorption by CO2 is understood in great detail, certainly enough to predict what will happen to thermal radiation passed through any given quantity of CO2, regardless of whether that quantity is in a lab or overhead in the atmosphere.
In a second post, John Nielsen-Gammon describes the Tyndall gas effect from the perspective of weather satellites that measure infrared radiation at different wavelengths.
In a slightly more technical treatment, Chris Colose explains the physics behind what the weather satellites are seeing in terms of infrared radiative transfer:
An interesting question to ask is to take a beam of energy going from the surface to space, and ask how much of it is received by a sensor in space. The answer is obviously the intensity of the upwelling beam multiplied by that fractional portion of the beam which is transmitted to space, where the transmissivity is given as 1-absorptivity (neglecting scattering) or exp(-τ), where τ is the optical depth. This relation is known as Beer’s Law, and works for wavelengths where the medium itself (the atmosphere) is not emitting (such as in the visble wavelengths). In the real atmosphere of course, you have longwave contribution from the outgoing flux not only from the surface, but integrated over the depth of the atmosphere, with various contributions from different layers, which in turn radiate locally in accord with the Planck function for a given temperature. The combination of these terms gives the so-called Schwartzchild equation of radiative transfer.
In the optically thin limit (of low infrared opacity) , a sensor from space will see the bulk of radiation emanating from the relatively warm surface. This is the case in desert regions or Antarctica for example, where opacity from water vapor is feeble. As you gradually add more opacity to the atmosphere, the sensor in space will see less upwelling surface radiation, which will be essentially “replaced” by emission from colder, higher levels of the atmosphere. This is all wavelength dependent in the real world, since some regions in the spectrum are pretty transparent, and some are very strongly absorbing. In the 15 micron band of CO2, an observer looking down is seeing emission from the stratosphere, while outward toward ~10 microns, the emission is from much lower down.
These “lines” that form in the spectrum, as seen from space, require some vertical temperature gradient to exist, otherwise the flux from all levels would be the same, even if you have opacity. The net result is to take a “bite” out of a Earth spectrum (viewed from space), see e.g., this image. This reduces the total area under the curve of the outgoing emission, which means the Earth’s outgoing energy is no longer balancing the absorbed incoming stellar energy. It is therefore mandated to warm up until the whole area under the spectrum is sufficiently increased to allow a restoration of radiative equilibrium. Note that there’s some exotic cases such as on Venus or perhaps ancient Mars where you can get a substantial greenhouse effect from infrared scattering, as opposed to absorption/emission, to which the above lapse rate issues are no longer as relevant…but this physics is not really at play on Modern Earth.
A molecular perspective
As a molecular physicist, I think it’s imperative to make sure that the dynamics of each molecule come through in these mechanistic explanations. A CO2 molecule absorbs an IR photon giving off by the thermally excited surface of the earth (earthlight). The energy in that photon gets redistributed by non-radiative relaxation processes (collisions with other molecules mostly) and then emits a lower energy IR photon in a random direction. A collection of excited CO2 molecules will act like a point source, emitted IR radiation in all directions. Some of that light is directed back at the surface of the earth where it is absorbed and the whole thing happens over again.
All of this is very well understood, though in the context of the CO2 laser. If you’re interested in these dynamics, there is a great literature on the relaxation processes (radiative and otherwise) that occur in an atmosphere-like gas.
Vaughan Pratt describes the underlying physics of the greenhouse effect from a molecular point of view:
The Sun heats the surface of the Earth with little interference from Earth’s atmosphere except when there are clouds, or when the albedo (reflectivity) is high. In the absence of greenhouse gases like water vapor and CO2, Earth’s atmosphere allows all thermal radiation from the Earth’s surface to escape into the void of outer space.
The greenhouse gases, let’s say CO2 for definiteness, capture the occasional escaping photon. This happens probabilistically: the escaping photons are vibrating, and the shared electrons comprising the bonds of a CO2 molecule are also vibrating. When a passing photon is in close phase with a vibrating bond there is a higher-than-usual chance that the photon will be absorbed by the bond and excite it into a higher energy level.
This extra energy in the bond acts as though it were increasing the spring constant, making for a stronger spring. The energy of the captured photon now turns into vibrational energy in the CO2 molecule, which it registers as an increase in its temperature.
This energy now bounces around between the various degrees of freedom of the CO2 molecule. And when it collides with another atmospheric molecule some transfer of energy takes place there too. In equilibrium all the molecules of the atmosphere share the energy of the photons being captured by the greenhouse gases.
By the same token the greenhouse gases radiate this energy. They do so isotropically, that is, in all directions.
The upshot is that the energy of photons escaping from Earth’s surface is diverted to energy being radiated in all directions from every point of the Earth’s atmosphere.
The higher the cooler, with a lapse rate of 5 °C per km for moist air and 9 °C per km for dry air (the so-called dry adiabatic lapse rate or DALR). (“Adiabatic” means changing temperature in response to a pressure change so quickly that there is no time for the resulting heat to leak elsewhere.)
Because of this lapse rate, every point in the atmosphere is receiving slightly more photons from below than from above. There is therefore a net flux of photonic energy from below to above. But because the difference is slight, this flux is less than it would be if there were no greenhouse gases. As a result greenhouse gases have the effect of creating thermal resistance, slowing down the rate at which photons can carry energy from the Earth’s surface to outer space.
This is not the usual explanation of what’s going on in the atmosphere, which instead is described in terms of so-called “back radiation.” While this is equivalent to what I wrote, it is harder to see how it is consistent with the 2nd law of thermodynamics. Not that it isn’t, but when described my way it is obviously thermodynamically sound.
In what was arguably the most lauded comment on the two threads, Nullius in Verba provides this eloquent explanation:
The greenhouse effect requires the understanding of two effects: first, the temperature of a heated object in a vacuum, and second, the adiabatic lapse rate in a convective atmosphere.
For the first, you need to know that the hotter the surface of an object is, the faster it radiates heat. This acts as a sort of feedback control, so that if the temperature falls below the equilibrium level it radiates less heat than it absorbs and hence heats up, and if the temperature rises above the equilibrium it radiates more heat than it is absorbing and hence cools down. The average radiative temperature for the Earth is easily calculated to be about -20 C, which is close enough although a proper calculation taking non-uniformities into account would be more complicated.
However, the critical point of the above is the question of what “surface” we are talking about. The surface that radiates heat to space is not the solid surface of the Earth. If you could see in infra-red, the atmosphere would be a fuzzy opaque mist, and the surface you could see would actually be high up in the atmosphere. It is this surface that approaches the equilibrium temperature by radiation to space. Emission occurs from all altitudes from the ground up to about 10 km, but the average is at about 5 km.
The second thing you need to know doesn’t involve radiation or greenhouse gases at all. It is a simply physical property of gases, that if you compress them they get hot, and if you allow them to expand they cool down. As air rises in the atmosphere due to convection the pressure drops and hence so does its temperature. As it descends again it is compressed and its temperature rises. The temperature changes are not due to the flow of heat in to or out of the air; they are due to the conversion of potential energy as air rises and falls in a gravitational field.
This sets up a constant temperature gradient in the atmosphere. The surface is at about 15 C on average, and as you climb the temperature drops at a constant rate until you reach the top of the troposphere where it has dropped to a chilly -54 C. Anyone who flies planes will know this as the standard atmosphere.
Basic properties of gases would mean that dry air would change temperature by about 10 C/km change in altitude. This is modified somewhat by the latent heat of water vapour, which reduces it to about 6 C/km.
And if you multiply 6 C/km by 5 km between the layer at equilibrium temperature and the surface, you get the 30 C greenhouse effect.
It really is that simple, and this really is what the peer-reviewed technical literature actually uses for calculation. (See for example Soden and Held 2000, the discussion just below figure 1.) It’s just that when it comes to explaining what’s going on, this other version with back radiation getting “trapped” gets dragged out again and set up in its place.
If an increase in back radiation tried to exceed this temperature gradient near the surface, convection would simply increase until the constant gradient was achieved again. Back radiation exists, and is very large compared to other heat flows, but it does not control the surface temperature.
Increasing CO2 in the atmosphere makes the fuzzy layer thicker, increases the altitude of the emitting layer, and hence its distance from the ground. The surface temperature is controlled by this height and the gradient, and the gradient (called the adiabatic lapse rate) is affected only by humidity.
I should mention for completeness that there are a couple of complications. One is that if convection stops, as happens on windless nights, and during the polar winters, you can get a temperature inversion and the back radiation can once again become important. The other is that the above calculation uses averages as being representative, and that’s not valid when the physics is non-linear. The heat input varies by latitude and time of day. The water vapour content varies widely. There are clouds. There are great convection cycles in air and ocean that carry heat horizontally. I don’t claim this to be the entire story. But it’s a better place to start from.
Andy Lacis describes in general terms how this is determined in climate models:
While we speak of the greenhouse effect primarily in radiative transfer terms, the key component is the temperature profile that has to be defined in order to perform the radiative transfer calculations. So, it is the Manabe-Moller concept that is being used. In 1-D model calculations, such as those by Manabe-Moller, the temperature profile is prescribed with the imposition of a “critical” lapse rate that represents convective energy transport in the troposphere when the radiative lapse rate becomes too steep to be stable. In 3-D climate GCMs no such assumption is made. The temperature profile is determined directly as the result of numerically solving the atmospheric hydrodynamic and thermodynamic behavior. Radiative transfer calculations are then performed for each (instantaneous) temperature profile at each grid box.
It is these radiative transfer calculations that give the 33 K (or 150 W/m2) measure of the terrestrial greenhouse effect. If radiative equilibrium was calculated without the convective/advective temperature profile input (radiative energy transport only), the radiative only greenhouse effect would be about 66 K (for the same atmospheric composition), instead of the current climate value of 33 K.
The skeptical perspectives on the greenhouse effect that were most widely discussed were papers by Gerlich and Tscheuschner, Claes Johnson, and (particularly) Miskolczi. The defenses put forward of these papers did not stand up at all to the examinations by the radiative transfer experts that participated in this discussion. Andy Lacis summarizes the main concerns with the skeptical arguments:
Actually, the Gerlich and Tscheuschner, Claes Johnson, and Miskolczi papers are a good test to evaluate one’s understanding of radiative transfer. If you looked through these papers and did not immediately realize that they were nonsense, then it is very likely that you are simply not up to speed on radiative transfer. You should then go and check the Georgia Tech’s radiative transfer course that was recommended by Judy, or check the discussion of the greenhouse effect on Real Climate or Chris Colose science blogs.
The notion by Gerlich and Tscheuschner that the second law of thermodynamics forbids the operation of a greenhouse effect is nonsense. The notion by Claes Johnson that “backradiation is unphysical because it is unstable and serves no role” is beyond bizarre. A versatile LW spectrometer used at the DoE ARM site in Oklahoma sees downwelling “backradiation” (water vapor lines in emission) when pointed upward. When looking downward from an airplane it sees upwelling thermal radiation (water vapor lines in absorption). When looking horizontally it sees a continuum spectrum since the water vapor and background light source are both at the same temperature. Miskolczi, on the other hand, acknowledges and includes downwelling backradiation in his calculations, but he then goes and imposes an unphysical constraint to maintain a constant atmospheric optical depth such that if CO2 increases water vapor must decrease, a constraint that is not supported by observations.
While there is much uncertainty about the magnitude of the climate sensitivity to doubling CO2 and the magnitude and nature of the various feedback processes, the fundamental underlying physics of the atmospheric greenhouse effect (radiative plus convective heat transfer) is well understood.
That said, the explanation of the atmospheric greenhouse effect is often confusing, and the terminology “greenhouse effect” is arguably part of the confusion. We need better ways to communicate this. I think the basic methods of explaining the greenhouse effect that have emerged from this discussion are right on target; now we need some good visuals/animations, and translations of this for an audience that is less sophisticated in terms of understanding science. Your thoughts on how to proceed with this?
And finally, I want to emphasize again that our basic understanding of the underlying physics of the atmospheric greenhouse effect does not direct translate into quantitative understanding of the sensitivity of the Earth’s energy balance to doubling CO2, which remains a topic of substantial debate and ongoing research. And it does not say anything about other processes that cause climate change, such as solar and the internal ocean oscillations.
So that is my take home message from all this. I am curious to hear the reactions from the commenters that were asking questions or others lurking on these threads. Did the dialogue clarify things for you or confuse you? Do the explanations that I’ve highlighted make sense to you? What do you see as the outstanding issues in terms of public understanding of the basic mechanism behind the greenhouse effect?
Moderation note: please keep your comments on topic, make your general comments on the Skeptics discussion thread.
This is great stuff Judith. Thank you.
So, just to be clear (to this highly interested non-scientist)…
The well-worn phrase by many on ‘both sides’ that there is a large degree of consensus in the doubling of CO2 levels from pre-industrial times leading to a temperature rise of around 1.2 degrees celcius is, in your view, not the case?
I think there is relatively widespread agreement (not consensus) that this will happen absent all other factors except the GH effect. It is in many ways the starting point for the debate.
I dont believe that this 1 C for a doubling of CO2 with no feedbacks has any basis in physics. It is a purely hypothetical and meaningless number which has never been measured.
Actually it has been tested and measured extensively for over 50 years. Many studies are still behind a paywall but this should give you some basis for further investigation.
ivpo writes “Actually it has been tested and measured extensively for over 50 years.”
I completely disagree. What you have stated is just plain wrong. The references you referred to are measurements of the radiative changes which occur when CO2 is added to the atmosphere. They are not measurements of how much these radiative changes make to global temperatures, which is what we are talking about.
If we just consider this earth and it’s atmosphere (ok Latimer?), then it is impossible to measure this number. Any attempt to do so would be confounded with the feedback effects. So not only has this number never been measured; it can never be measured with our earth.
It wasn’t my perception that anyone shifted their perspectives at all, though there were a lot of extremely interesting exchanges. There are those that accept the understanding of radiative transfer – whether or not they think the estimates of climate sensitivity are valid – and there are those that do not.
My view is that it is a matter of belief, not of understanding per se. So efforts at education – however well-intentioned – will only reach those already disposed to hear it.
This is a pretty important point.
What we see from a lot of ‘skeptics’ on blogs is true belief, ie. really believing that some is true (or false), irrespective of whether it is or not.
This needs to be distuingished from justifable true belief, ie knowledge – a true belief that can account for it’s truth based on reason or evidence.
The quality of the explanations will be irrelevant for those who will settle for belief instead of knowledge.
I don’t think it was ever going to change people’s minds, I doubt any of the discussions here will do that. But we can hope to convince those who are not convinced in either direction – I think there are some commenters who fall into that category and maybe more who read but don’t comment. So it’s not neccessarily a futile excercise.
I think you’re wrong – I haven’t changed my mind about the lunacy of various proposed mitigation policies but I must say that Maxwell’s explanation of the behaviour of photons colliding with CO2 molecules, followed by NiV has definitely changed my concept of the so-called “greenhouse effect”.
Suddenly my eyes don’t glaze over when I see equations, because I can actually conceive, at a molecular level, what might actually be going on with all those unruly charged particles from the sun.
Brilliant! If I can grasp this (Academic but not in the sciences, alas) then anyone can. Great job!
I think Judith’s summary of the science is very helpful, but it lacks empirical verification and quantification. Lots of physical effects are valid but very many are of little or no practical consequence. My own submitted paper finds no statistically significant evidence that changes in atmospheric CO2 have any impact on temperature change locally or globally as soon as natural independent variables are introduced, such as changes in atmospheric water vapour and in solar surface radiation (not ToA). Absence of evidence may not be sufficient to disprove a hypothesis, as there could be alternative specifications that are consistent with observations, and I would be glad to hear of them, but my evidence supports the alternative hypothesis that changes in non-anthropogenic water vapour are the prime mover (not merely a feedback) in explaining changes in temperature as put forward by Anthony King FRS in his seminal paper in Energy & Environment, 21.6: 611-631, October 2010 (available at http://www.multi-science.co.uk).
Ironically, until John Snow’s work in London in 1854, the dominant scientific theory was that cholera like temperature was determined by airborne “miasma” (read CO2). Snow showed empirically that it is in fact a water borne disease, just as Kelly and I have shown for temperature change.
On Snow read the post-humous work by David Freedman, Statistical Models and Causal Inference, eds . David Collier et al., CUP 2010
Judith, you have provided a definitive account of the theory of CC. How about some empirical confirmation of its substantive importance?
What is it exactly that needs “empirical verification”?
Judith merely tried to offer explanations concerning the theory of the GHG effect absent other climactic phenomenae. She was at pains to stress that the magnitude of the GHE and therefore its importance on the climate is still a matter for further research and debate. I think this will come out in later threads. From my perspective as a layman ‘lurker’ I found the proponents’ explanations persuasive and very useful. As a result, I am certainly not a greenhouse denier although I remain skeptical (but open minded) about the bigger picture! Fascinating stuff.
Professor Curry, this is OT so please read and delete. Please launch another discussion topic, O”Donnell et al 2010, JoC paper which bears on Steig, et al 2009, Nature.
(btw, I suggest that you put up a “Unthreaded” heading where posts such as this can be made.)
Ray, there is a skeptical discussion thread (a few back), which would be a good place to post this.
Great site,….compliment delivered, here is my comment
The posted comments did an excellent job of describing that, yes GHG’s can impact atmospheric temperatures. You also demonstrated that those believing the opposite do not seem to have an effectively debatable position.
I am not sure it was worth your effort, but you did it.
This is a strawman argument. The effect may be theoretically sound but still negligible or at least far less important that the other factors that were assumed unimportant.
As far as I can tell only G+T argued against a significant radiative greenhouse effect and lo and behold we discover that the main greenhouse effect turns out to be largely a convective phenomenon after all – so even their position is seemingly tenable.
Miskowski argued feedbacks, not GHG theory, and feedbacks remain the big unknown so he is vindicated on that score. But regardless of the correctness of his hypothesis, at least he tried to come up with one that explained the observations as opposed to the all too common attempts to do it the other way around.
The important IPCC/Hadley argument was that the combined models could model natural variation, and that natural variation was in decline thus that just left manmade GHGs. The wheels fell off that argument a while ago because natural variation of some sort has caused a pause that wasn’t expected and the missing heat is not apparently in the ocean either. So all existing hypotheses do indeed need looked at again with fresh eyes.
I’ve been arguing for ages against certain know-it-alls who didn’t realise that you just cannot arbitrarily calculate the radiative and convective components separately and expect the correct answer. Well it is true that you don’t know until you try it yourself: In real life and in correct 3D heat transfer modeling the feedbacks are far too great for simplistic assumptions to be made and iteration is necessary. But these overly simplistic assumptions just keep coming back because it makes hand calcs easier.
Yet apparently some climateers do know that the simple radiation balance idea is misleading and this has apparently even been known for some time! Well well! The problem is that there are just too many pretend “experts” and professional pessimists who see only what they want to see and not enough people prepared to tell the doomsayers to STFU and test the hypothesis properly. Of course if they find out there is nothing to worry about then the paymasters will soon find they don’t need quite as many people studying climate. There’s the rub!
No. The greenhouse effect is not a convective effect. It is a radiative effect made weaker by the convection in a manner described e.g. 1966 by Manabe and Wetherald.
It is a radiation insulation effect in the presence of free convection. Saying it is a radiative effect made weaker by convection is a very strange and misleading statement. I would be curious how you can defend such a statement.
Radiative transfer alone would lead to a larger temperature gradient in the troposphere. Many people have stated in these discussions that earth surface would be about 30 C warmer in the hypothetical case where atmospheric constitution and albedo would be the same, but no convection.
Manabe and Wetherland introduced the convection correctly as on upper limit on the gradient. This upper limit is influencial throughout the troposphere up the neighbourhood of tropopause.
All this tell that the convection acts to make greenhouse effect weaker than it would be without convection.
The hot ground heats the air above by conduction. The hot air rises by buoyancy. Day and night and latitude variation and planetary rotation force convection. You can’t have a case with no convection. Looking at an impossible case as an example is nonsense.
Look at a case where the gas is a near perfect absorber at all outgoing wavelengths (this is actually possible with a lot more water vapor, CO2 and other absorbing gases to fill in the “window”). In this case, the radiation heat transfer will be near zero (back radiation =radiation out). All of the heat transfer to the upper atmosphere would be by convection. At very high altitude where the air is thin enough, the radiation to space would be possible, and this would set the temperature there to balance absorbed and radiated energy. Since the altitude would almost certainly be higher than for less greenhouse gas blocking, the lapse rate would result in a hotter ground. This is just the opposite of what you claim, the larger amount of greenhouse gas forces a higher temperature due to LOWER net radiation from the ground.
I am not claiming the opposite in the way you state in your last sentence.
Conduction is indeed determining the gradient as long as radiation would make it larger than conduction allows. This leads to smaller temperature gradient and further to reduced net radiation. This is a point, where we seem to agree fully.
This does not contradict my claim that conduction weakens the greenhouse effect. On the contrary it is part of the reason for may claim to be correct as the greenhouse effect gets stronger with increasing temperature gradient.
I would like a clarification of Maxwell’s statement:
“A CO2 molecule absorbs an IR photon giving off by the thermally excited surface of the earth (earthlight). The energy in that photon gets redistributed by non-radiative relaxation processes (collisions with other molecules mostly) and then emits a lower energy IR photon in a random direction.”
While it is certainly true that a CO2 molecule can register a variety of quantum transitions, it is not my understanding that photon absorption (by atmospheric CO2) is routinely followed by a combination of de-excitation by collision and then emission by that same molecule of a lower energy photon. Rather, as I understand it, the most common process is the following. (1) Photon absorption by a CO2 molecule is followed by a collision with a surrounding molecule(s) that de-excites the CO2 with transfer of kinetic energy to the other molecules (N2, O2, etc.) – a heating effect. (2) A different CO2 molecule is excited by a collision (therefore temperature-dependent) and in the occasional circumstance when it can emit a photon before losing its energy to collision, the photon will generally have the energy characteristic of one of the various lines of the CO2 spectrum and its dependence on the particular quantum transition involved. In other words, I don’t visualize a progression degradation of average photon energy levels throughout the multiple energy exchanges involved.
Comments would be welcome.
My understanding is that in order to emit at e.g. 15 microns, a CO2 molecule does not have to absorb a photon first. The vibration states leading to 15 micron photons are populated according to the thermal equilibrium, along with other modes (translation, rotation). The emission occurs at 15 microns consistent with the temperature of this equilibrium. I have said elsewhere that a CO2 molecule “tries” to be a black body, but only has a few IR windows to get its photons out. However at those windows it emits at the same intensity as a black body would at those wavelengths. A picture of these molecules is one of very particular absorbers and emitters. The emission is continual, something like a laser lighthouse.
I think both processes contribute.
I also think the pertinent question is whether we can physically decipher between an emitting CO2 molecule that has been excited by a photon absorption process versus a molecular collision process. If the end result is the emission of a photon at the same or lower energy as the initial excitation, I don’t think it matters as much which process leads to a specific CO2 molecule emitting a photon in a random direction. Both processes are physically indistinguishable from the measurement of the TOA radiation. As long as we know they are both happening (photon excitation versus collision excitation) then I think we’re ok.
I do think there needs to be greater emphasis put into the fact that the ‘heating’ effect of GHG absorption of the IR light is due to thermalization. That is, at lower altitudes collisions with molecules that cannot emit radiation due to strict selection rules (N2 and O2) shifts the peak of distribution of kinetic energies (velocities), which increases the temperature.
As for lower energy IR photon being emitted as a result of collision, I again will point to the CO2 laser literature which has systematically looked into all of the possible radiative relaxation pathways of vibrationally excited CO2 molecules. Some of those pathways include collisions with different gas phase molecules. Other pathways do not.
At lower altitudes where the density of molecules is higher, we would imagine that collisions are more frequent and, therefore, radiative relaxation pathways tied to collisions would be more prevalent. At higher altitudes, we would expect something different because collision rates are smaller and, as far as I know, CO2 has no energy barrier to cross to get to the state from which it can radiatively decay, we would expect less emission from radiative pathways tied to collisions. If there is a barrier, then we would have to account for the way in which the temperature at higher altitudes affects the propensity of the excited molecules to reach that radiating state. Simple kinetic rate laws would do the trick for a gas phase molecule.
Reading your comment, I think we are essentially saying the same thing. Collisions dominate the thermalization of IR absorbed energy, but some CO2 molecules can still emit IR light, either at the same or lower energy as the initial excitation. Some of that emission is due directly to the absorption of IR light, but some of it is due to energy transferred during inelastic collisions with non-radiating molecules (N2 and O2). Some of the emission from CO2 molecules is tied directly to inelastic collisions as we see from the CO2 laser literature.
All in all, I think that Dr. Curry and others (possibly myself included) need to effectively synthesize the different ‘perspectives’ on the atmospheric greenhouse effect as presented in this post. Because none of the perspectives are correct on their own and there is a need for detail in explaining all of the possible processes that lead to the overall effect. The synthesis of all of these ‘perspectives’ needs to be highly detailed as well. Even as someone trained extensively in physical science, I still struggle with all of the details with these processes, so I imagine that we all do to some extent.
If people care about this issue, then they’ll learn the details.
You cannot see this for an individual photon, but if the emission rate exceeds what would be calculated from thermal equilibrium you would be correct. it does not. Another place to look would be at emission in the asymmetric stretching region.
‘You cannot see this for an individual photon…’
I can’t infer which process you are specifically referring to with that statement. Can you please specify what you mean?
Whether the emission is direct from the excited molecule or not.
Are you saying that the emission from photo-excited CO2 molecules doesn’t contribute to the outgoing longwave radiation?
I think that’s what you’re saying.
If it is, I’d think that your line of reasoning would be that the time between collisions is shorter than the excited state lifetime of the radiating state of CO2. I’d agree, but how would any CO2 molecules emit radiation, independent of the excitation process?
Any excited molecule is going to collide with other molecules during the excited state lifetime of CO2. So under any excitation process, there is no emission from CO2 molecules in the lower layers of the atmosphere.
There is something missing here.
I believe that what is missing is the distinction between average intervals and the permissible range of intervals. The mean inter-collision interval is much shorter than the mean relaxation time for photon emission, but as with other quantum-related transitions (e.g., radioactive decay), I expect that the latter exhibits a probability range that results in rare photon emission events before de-excitation by collision. The same would be true on the excitation side, which would involve collisions (and thus local temperature) far more often than photon absorption, and would make absorption followed by emission on the part of the same CO2 molecule very rare. I haven’t seen actual data on the numbers, but would be interested in a source providing such data.
I think we have to do some real number-crunching to figure out what contribution each of these processes play.
I think the statement
‘The same would be true on the excitation side, which would involve collisions (and thus local temperature) far more often than photon absorption…’
is a good indication of why we need explicit number-crunching.
The excitation of the CO2 state that emits 10.6 micron light corresponds to a temperature over 1000 K. Very few molecules in the Boltzmann distribution of energies peaked around 300 K will have the energy to excite to this state.
To know for sure what is happening, we have to calculate how many molecules in that energy distribution have the necessary energy to excite the transition, the flux of 10.6 micron ‘earthlight’ and the cross-section of the respective molecular excitation processes (bi-molecular collisions versus single photon absorption). Then we can see which process is more probable.
I’ve got a lot of work today, but I can hopefully start on such a calculation by tomorrow.
My favorite post here to date.
More like this!
Having contributed to the response to G&T I’m pretty familiar with some of the confusing back and forth on this. I wrote up a “proof of the atmospheric greenhouse effect” as an early response to G&T a couple of years back, that some people have found helpful – of course it’s no more than the standard radiative balance calculation with some mathematical logic to show the 33 K traditional number is a lower bound (G&T essentially showed the same thing, but claimed it was all “unphysical” for some reason). See http://arxiv.org/abs/0802.4324
The problem with understanding the atmospheric greenhouse effect is that it cannot be condensed down to a single concept that is easily grasped – it involves the interplay of molecular emission/absorption spectra, atmospheric temperature and pressure profiles, non-radiative fluxes, several different thermodynamic principles, etc. It cannot be reduced to something that can be conceptually “held in the head” by somebody unfamiliar with these details, unless you simplify to an analogy like a glass greenhouse that really gets some physical details of the problem wrong.
This isn’t an unusual situation in science. Think of explanations of the tides, for instance, a really quite simple phenomenon comparatively. Conceptually we think of tides as caused by the direct gravitational pull of, say, the Moon. But that is an over-simplification that gets some real details wrong – in particular it cannot explain why is there an equal tide on the *opposite* side of the planet. The actual explanation involves the force gradient rather than the force, and can certainly be readily understood by anybody looking into the problem for a suitable amount of time. But I’m not aware of any ready analogy that can explain it in a physically correct manner to the uninitiated. You have to “do the math” to some degree, to “get it”.
Simplified explanations of entropy abound in confusion; again it’s quite a tricky concept to understand until you’ve “done the math” on a few suitable systems to understand what it’s really all about. Much the same with relativity and quantum mechanical principles, etc. etc. There’s a reason scientific training takes years – some of this stuff really is quite hard for humans to grasp initially.
But the more explanations that are out there, the more likely I guess any given person will be to find the one that clicks for them, so I’m sure this discussion should do some good. Best wishes!
As a layman I’d like to see that youtube series of animated videos you mentioned a few threads ago. I’m an engineering graduate so I reckon I’d be ok on the maths if I could picture the physical processes a bit better. I’m interested in reading up on radiative transfer physics but as a busy working dude that will take me quite a while. A picture paints a thousand words. Anybody got the time to draw some diagrams?
Thank you for putting this together. It was a well managed discussion. We hardly felt your guiding hand.
I do propose that ‘Tyndall gas effect’ is a better description of what is going than ‘greenhouse’.
do propose that ‘Tyndall gas effect’ is a better description of what is going than ‘greenhouse’.
Good luck changing the name now.
But what’s wrong with it anyway? (Don’t quote Wikipedia, but if you must then try at least to quote its sources instead.) Right now the Louvre is struggling with severe greenhouse heating that’s compromising its microclimate.
So far the science says that the planet itself does NOT need to turn or move.
Then 1669.8 km/hr of sheer energy would fly off this planet.
I have found so far 4 planetary changes that are fluffed off to AGW but makes absolutely no sense to be in that theory.
1) Salinity changes only on the surface of the oceans.
2) Growth up mountains takes a great deal of back pressure against the atmosphere to achieve as the rotating atmosphere generate a great deal of force downward.
3)Winds diminishing Globally are generated from too many molecules accumulating in the atmosphere generating a great deal of frictional drag.
4) Light density changes. I have not look into this area too much but a great deal of dust debris and soot is generated through out the globe.
These points point out to a pressure build-up in the atmosphere.
A great job by Dr Curry summarizing scientific reasoning and evidence about the GH effect. This should take care of “denialist” positions not recognizing that such effect is theoretically coherent and empirically grounded (at least as regards its existence if not its precise magnitude in relation to other related processes and feedbacks).
However, what we may call “respectable” skeptics do not fail to understand this matter. What they usually debate are certain specific numerical values, chiefly climate sensitivity but also others, such as the feedbacks (from clouds, mostly, especially in relation to probable increase in clouds due to higher evaporation due to surface warming; some of the increased mass of evaporated water would end up in clouds, and –it is argued– the net effect of clouds is likely to be cooling. They also point out the large uncertainty surrounding estimates of those critical numerical values. The whole issue of orthodoxy vs skepticism concerning anthropogenic global warming will undoubtedly benefit from a more clear understanding of the GH effect of CO2 and other such gases, but the real debate is not about that (except from some fringe scientists and amateurs denying the whole thing).
Thus, I surmise that once the terrain is cleared of misunderstandings about the physics of CO2 GH effects, one should move to the more pressing issues underlying the more serious debates at the skeptical front: accuracy and representativeness of instrumental measurements (surface stations and recently satellites) including the re-evaluation of UHI, and the validity of indexes of mean temperature derived therefrom; measurements or assumptions about feedbacks in GCMs, and so on.
Progress is being made, and more progress is possible.
I think on some point you misinterpret Claes Johnsons argument about “back radiation”. You find very often in the literature the notion that back radiation causes the the greenhouse effect. This for my opinion is thermodynamically not correct or at best incomplete. The thermodynamic root causes for the greenhouse effect are the TOA fluxes and their balance, since they are the only ones that are able to increase the energy content of the earth system. Back radiation is an internal flux that redistributes the energy internally, but does not alter the energy content of the whole earth system.
Günter: Back radiation does not alter the whole earth system as there is no back radiation from space. Back radiation is, however, a very essential part in bringing the effedt to the earth surface. Other factors are changes in conduction and convection.
What is internal for the whole earth system is external to the continents and oceans.
Pekka: I understand, but still from a thermodynamic point of view for the whole earth system back radiation is the effect of a forcing- The forcing increases the energy content of the earth system and in turn the temperature, which in turn increases backradiation as you said. Backradiation is a function of temperature. One can explain the greenhouse effect without backradiation using the concept of emission height.
I observe even in textbooks about climate dynamics incomplete explanations using backradiation. One is from Mojib Latif: Klimwandel und Klimadynamik. I think Claes Johnsons argument is adressing such incomplete explanations. The same is true for Gerlich and Tscheuschner.
Using backradiation it is necessary to mention reduced emission in order to make the picture complete. This is often neglected.
Your argument about external to the ocean and continents is somewhat arbitrary, since the basic model says that surface and atmosphere heat up simulaneously and we have on average a falling temperature gradient between surface and atmosphere. The root cause is the forcing at TOA and not backradiation.
Ther back radiation (on the average) has no contribution to the heating. The adiabatic lapse rate combined with moving the outgoing radition source up higher in the atmosphere is the whole story. Back radiation is a consequence of the increased temperature. In order for back radiation to contribute to heating, it would have to be larger than up radiation from the ground, which (on the average) is not so.
When there is radiation up and down, one can either calculate both at their full value or one can choose to consider only their difference, the net transfer by radiation. If one makes the latter choice, one can say that there is no back radiation, but only the net radiative transfer. This seems to be your choice. Many other people, including myself, choose to consider both separately. For us there definitely is back radiation.
The physics does not change by this choice, but one choice may help better in understanding the situation correctly. I believe that discussing back radiation separately makes it easier to understand the physics. On the other hand I accept that in the case of heat conduction everybody looks only at the net effect. Nobody discusses how conduction could also be split into two parts: a stronger component from hot to cold and a weaker from cold to hot. On molecular level both occur, but as I said, nobody describes conduction this way. This example demonstrates that I see some virtue in your way at looking at radiative heat transfer, but even so, I prefer to discuss the back radiation as a physical process.
You continue to misstate what I say. I never said there is no back radiation! I said there is no back radiation HEATING (on the average). Heat transfer is based on net energy transfer, not individual components. Without back radiation HEAT transfer, there is no contribution of back radiation to heating of the surface (on the average). Obviously night time and polar winter are special cases, but I am referring to global averages.
Evidently my writing is not understandable, as I tried to say that I interpreted you exactly as you say in your last message.
I wrote that one way of looking at the situation is to consider only the net raditative energy transfer. I wrote also that I think that this is your way.
Then I wrote that this is not the only possible way of looking at the issue and that I prefer the other way.
If C = A – B, one can say C or one can say A and B and calculate their difference. Which one is easier to understand depends on the situation – and on the way each individual thinks.
Although I would count myself as a ‘skeptic’ on AGW (meaning I question that the temperature increase is predominately from CO2 – I would expect some small part of it to be because of the increase CO2), I fully accept that CO2 and H2O are the predominant ‘greenhouse’ gases, meaning they absorb longwave radiation from the earth (or from any other source for that matter, such as other CO2 and H2o molecules that are radiating longwave radiation).
They can either transfer the absorbed radiation to other molecules through collision, or re-radiate it in ANY direction. And the re-radiation back towards earth is the ‘back radiation’.
I do have a question relative to N2 and O2 – what wavelength do they radiate at (I am assuming they do), since doesn’t all matter radiate energy as a function of its temperature? Is it in a wavelength that H2o and CO2 absorb? And/or how does this play into how energy is ‘moved’ from the surface of the earth to space?
To first, second and third order N2 and O2 do not radiate or absorb in the IR. You need a little quantum mechanics to understand this, but to simplify more than a little, you can model a vibrating molecule as a vibrating spring (in physics speak, a harmonic oscillator). In the harmonic oscillator there are equally spaced energy levels. Using this model you can predict the strength of emission and absorption due to a change in energy level. Only certain changes are allowed. For example, you can only transfer between neighboring energy levels. This is called a selection rule.
Now we have to go deep into the weeds. IR transitions are driven by a change in how the charges in the molecule (the electrons and nuclei) redistribute themselves during any transition. For example, if we have a HCl molecule, the distance between the positive end (the H atom) and the negative one (the Cl) changes when we go from one vibrational state to another as the molecule stretches differently in the two states. It is this change in what is called the transition dipole moment that makes the transition allowed. In N2 and O2, there is no change in the dipole moment during a transition, because the charge distribution is totally symmetric in both. (If you want to know more google multipole distribution and magnetic dipole moment or quadrupole moment, you probably don’t want to know more tho)
CO2 is also a symmetric molecule, however there are two vibrational modes which are IR active. The first is the asymmetric vibration, where the two O atoms move in one direction and the C atom in the other. This redistributes the charges along the molecular axis. The other is the bending vibration, where the C atom moves up and down and the O atoms down and up. Again, the charges are redistributed during the transition so as to produce a transition dipole, making emission and absorption allowed.
O2 actually does have some absorption bands (at 60 and 120 GHz, in the microwave). Not N2.
I should note the other gases do have an influence on the greenhouse effect, but mostly through their ability to pressure broaden the absorption lines of the GHG’s. On Mars for example there’s a lot of CO2 by percentage but not a whole lot of atmosphere, and not much greenhouse etc.
Re: Chris Colose,
Chris do you mean not much greenhouse (effect) or not much greenhouse (gasses)?
I read somewhere once that Mars has about 5% of Earths atmosphere by volume and that 95% of it is CO2.
If 95% of that 5% is CO2, then Mars has the Earth equivalent of about 4.75% CO2. Earth currently has 0.04% CO2. That’s nearly 120 times by volume. (god I hope my math is correct)
Have any calculations been made as to what Mars T would be without that CO2 that you could point me to?
All diatomic molecules have both rotational and vibrational absorption/emission spectra, but the vibrational parts of N2 and O2 spectra are in far ultraviolet while the rotational parts are in microwave part of the spectrum. Neither affects visible or infrared parts of the spectrum.
one has to be careful in describing absorption/emission spectra. There are vibrational spectra from O2 and N2 in the UV due to Raman scattering, not emission. The energies of these vibrations are in the IR region, but IR absorption/emission is not allowed from these molecules quantum mechanically due to symmetry considerations. The UV contains the electronic absorption spectra of gas phase homonuclear diatomic molecules, which leads to the resonance enhanced Raman effect which produces vibrational information if you collect scattered light correctly.
I’m also uncertain whether there are allowed O2 rotational bands due to absorption/emission. I wonder if this is a Raman effect as well.
Because much of this discussion is centered on effectively communicating the details of these physical processes, we have to take care in the specific language we use to describe what is happening physically.
Oxygen has permanent magnetic moment, which leads to rotational transitions for the neutral oxygen molecule. For nitrogen the strongest effects are due to (diatomic) ions, which are always present in the atmosphere.
I found some older literature on magnetic dipole absorption in O2 at 64 GHz, which is one of the lines Chris is mentioning, I think. There are also some rotational spectra in the far-IR, though I haven’t found a physical model behind them at this point.
But O2 does not have a permanent magnetic moment. It is a symmetric molecule. Both oxygen atoms contribute unpaired electrons to the chemical bond. If it did have a permanent magnetic moment (dipole or higher order) it would be magnetic on its own. O2 is only paramagnetic, however, meaning it becomes magnetic only under the influence of an applied magnetic field.
It is normal for a paramagnetic material to have a permanent magnetic moment based on the spins of the unpaired electrons.
For oxygen the spins of the two unpaired electrons are aligned, Therefore O2 has a permanent magnetic moment.
I’ve found you’re definitely right about the permanent dipole moment of diatomic oxygen. I confused myself using the definition of the an electric dipole. For a magnetic moment, it is an intrinsic property of the electron itself.
Thanks for clearing that up for me.
how does O2 absorb/emit microwave radiation without a permanent dipole?
Please could someone who knows explain to me why it is that since 1972, Outgoing Longwave Radiation has had swings of up to 4W/m^2 on roughly the same timescale as the solar cycles if TSI only varies around 0.1% and it’s variability is thought to make only a small difference to Earth’s climate.
Being serious now.
Since science has not studied planetary rotation or even it’s existance. How many days would longwave radiation that hits the planet be released back out into space? We are talking of spinning around the planet. Short wave would deflect back almost immidiately.
Good Q Joe. My feeble brain won’t comprehend this either.
We’re told warming is now locked in for decades even if we halt emissions immediately.
Is this radiation zipping around, not escaping to space for long periods of time?
How does that explain T variations in the desert from day to night, or even seasonal variations?
It would be good to get a contribution from someone knowledgable and informative.
A fascinating observation and a good question, if a little O/T for this thread. May be Shaviv’s amplification factor in evidence? Can you explicitly source the OLW data please? Since you already have the data downloaded, can I ask as a favour that you plot the OLW data on the same time axis as HADCRUT3 temp data. I would suggest your doing this on the open thread. I will share with you there some analysis I did on the shape of the OLW observations (rising and falling during the satellite era), which I believe to be inconsistent with CO2 being the DOMINANT driver over this period.
I’m not so sure it is OT. Whatever signal there is from co2, it’s lost in the amplitudes of the other natural factors in the OLR data.
Source is NOAA
Well, Dr. Curry,
First, although I have sceptical leanings (about feedbacks, etc.), I didn’t really doubt the GHG effect itself since people on either side who come across with some gravitas and eschew the snide and ad-homs seem united in this.
So the debate didn’t do anything to change my mind on that. Nullius’ post was excellent in that it lifted a few veils of understanding, though It’s not quite yet all gelled, because his explanation didn’t seem to go into detail about what CO2 was actually doing beyond thickening the atmospheric “fuzzy layer”. So there’s still a bit of a disconnect in there somewhere for me, in terms of my fully understanding the GHG effect. What is the involvement precisely of CO2? Why wouldn’t any gas that thickens the atmosphere and raises the altitude of the emitting layer have the same effect?
Nullius indicated that the Manabe and Wetherall approach was used, but other contributions still bang on about the “Tyndal gas effect”, and in ways that leave my eyes glazed over.
It’s all rather frustrating, because I still don’t understand what I have so far accepted. I’m hoping that if you bring it altogether with diagrams, etc., it will finally coalesce into something coherent. If I ever do get it, I will produce something myself which I will attempt to target at the layman. I do have some experience and skill in doing this sort of thing, but of course only when I completely understand what I want to convey. I’m not there yet…
I agree, some diagrams and animations are needed, something that I am particularly poor at. I’m hoping someone else will provide some ideas on what such diagrams would look like.
What CO2 is doing that other gasses aren’t doing is blocking the earth-glow (the heat radiation trying to escape to space). Other gasses don’t do that nearly as effectively. The term used is ‘optical thickness’. CO2 increases the height of the ‘fuzzy layer’ more than other gasses because it has a greater optical thickness in the important wavelengths that keep in earth’s heat but has roughly the same optical thickness as other major atmospheric gasses in the wavelengths that let sunlight in.
For the young student of this subject, it helps to begin simply: We have a good controlled experiment with two different bodies in the same orbit around the sun — the earth and the moon. To extraordinary accuracy we know that the moon’s average surface temperature is -23C and the earth’s average surface temperature is +10C. The difference is caused almost completely by the atmosphere.
So the atmosphere acts as a blanket (better analogy than a greenhouse). But a blanket keeps humans warm only because we generate body heat internally. The earth doesn’t do that to any significant degree. So for the earth’s atmosphere to act as a blanket it has to have little gaps or holes (like window panes) that let in sunlight. These ‘panes of glass’ are composed of various materials, some are made of CO2, others of O2, N2, etc.
Now to the earth’s body heat, once generated by sun coming in those different panes of glass tries to escape back out. But the CO2 pane of glass has a unique property. It is transparent to letting sunlight in, but it is partially opaque to letting the earth’s body heat out–it’s like a transistor, letting the energy flow only in one direction — in. The more CO2 there is, the more opaque it is to letting the earth’s body heat escape. The other panes don’t have this same effect. They largely let sunlight in as effectively as they let earth glow out.
To keep the explanation simple, it is useful to leave out the secondary roles of the oceans and ice, of changing land cover, and of clouds, none of which occur on the moon. But if these are to be mentioned, the beginning point is to say that our planet has had wildly different amounts of all three of these things over geologic history, and none have produced temperature variations as large as the 33C difference between the earth’s and the moon’s average surface temperature. So these effects are of lesser importance than the net effect of the Atmospheric Blanket of gasses.
Are you forgetting anything about H2O in your explanation?
H2O is another of the panes of glass, and as a feedback effect, adds a complexity to the discussion that would obscure the message without changing it.
I must correct myself — I said that the CO2 ‘pane of glass’ is like a transistor, but I should have said diode. (and yes, Methane, CFCs, H2O are other such selective ‘panes of glass’ that let in sunlight but resist letting out the earth’s ‘body heat’.
But is not H2O a rather thick and highly variable pane, and in each of its phases that exist in the atmosphere, 3 panes that act differently?
Also, since it horticultural hot houses that use panes of glass or fiberglass to hold down convection is it really useful after so much work on the last few threads to use greenhouse metaphors at all?
H2O is all you describe. But the effects on AGW are feedbacks. Because of the short half life of residency of H2O in the atmosphere, human activity is not causing a build-up of H2O the way it is of CO2.
My ‘hybrid’ analogy invokes a blanket with embedded panes of glass. The analogy allows convection to get around the panes of glass because they are not continuous like a greenhouse would be. As an analogy, it’s not a model. The goal is to create a mental picture that is simple to conceptualize.
Dr. Pielke, Sr. would disagree with you. H2O is anthro-influenced, and we ahve built up quite a bit of it in formerly arid regions where we have changed the regional humidity levels by way of dam building.
Also, calling H2O a feedback, when it is infact the largest Tyndall gas in the atmosphere seems more than a bit dodgey.
It’s effects are much more complex, since you get ice, water and vapor all in the atmosphere at once.
I invite you to rewrite the explanation to satisfy your objection, and see if it improves the simplicity and understandability. Good luck.
Dam building, irrigation using fossil water, rain forest clearing all alter the water vapor balance in the atmosphere, some effects are positive, some negative. Overall, through the 20th century, what percentage change in the radiative transfer is produced by the observed change in atmospheric H2O in (using any model of your choice) compared to the percentage change induced by the change in atmospheric CO2 in the atmosphere?
And that proven percentage Is? observed not model ie real measured.
I like your explanation because it provides a simple sensible inuitive entry point based on emprical data from which to advance into quantitative analysis.
To improve the explanation I suggest incuding some narrative on the daytime and nightime temperature extremes on the moon and the moderating effect of the Tyndall gases.
So the atmosphere acts as a blanket (better analogy than a greenhouse).
It’s a worse analogy because blankets aren’t transparent and don’t feature triatomicity. Solid triatomic molecules like transparent glass are a great solid-state analogue of triatomic molecules like CO2 and H20 (whether as high-temperature water vapor or cooler liquid).
Your summation reminds me of several consultation exercises I have been involved in.
The appearance of open debate is encouraged.
Then some threads are drawn together.
The prearranged position of the “executive” is then presented as if it has been overwhelmingly agreed by all concerned.
It fools no one but the “executive” and is a fairly tired method that should be dropped.
I must confess rather guiltily that the same thought did fleetingly cross my mind – I must have attended the same kind of “consultation exercises” that you mention :-)
However, I did not voice it because there was the counter-thought that this particular issue is one of the few that experts on all sides seem to agree on. Especially, for me, Richard Lindzen. Dr. Curry is probably speaking from a position of understanding, in which case, her verdict is most likely correct.
One can quibble about the way she chose to express that, but if she’s right, well, that’s a strong mitigating factor. In those consultation exercises we’ve seemingly both experienced, I’ve found that usually, the idea is to sell one on what the boss really wants to happen and may bear no relation to what actually should happen, or what action the facts actually justify.
Bryan, there is no serious debate about the basic physics of the GH effect, and I certainly did not see any serious exposition on that thread of the few skeptical papers on this topic that have gotten published. The challenge is how to explain it in a way that is easily understood. I think some progress in this regard was made on the thread.
I wonder Ms Curry, should we be making a distinction between the radiative properties of GHGs (no reasonable skeptic argues against) and the Greenhouse effect. (No I don’t mean it’s magnitude or feedbacks)
Afterall, in some instances at least, what happens on the lab table may not manifest itself in the real world to any discernable degree.
I wonder Ms Curry, should we be making a distinction between the radiative properties of GHGs (no reasonable skeptic argues against) and the Greenhouse effect.
Fascinating Australian train of thought. I’d been assuming up to now that the notion of a
reasonable skepticwas an oxymoron. Their existence is almost on a par with that of God.
Oh please, no need to compare me to deity.
Speaking of things Aussie, there is also the “chopping down tall poppies” and “get your head out of your a$$ mate”
I’m glad to sense you’re feeling quite good about yourself right about now. I don’t begrudge that of anybody.
Speaking of things Aussie, there is also the “chopping down tall poppies” and “get your head out of your a$$ mate”
Quite right. (No fair my dishing it out if I’m not willing to take it.)
I noticed that as well, but it is important to separate out the idea that gasses in the atmosphere act to regulate energy flows and let those who see this basic physics is credible get on board.
Additionally, having attended the same style of meetings in the past, I can see the difference between what our good Dr. is doing here and the heavy handed suppression used in the sorts of corporate/governmental potemkin meetings you are referring to.
Skepticism in the climate catastrophe promotion industry does not rest on the physics of H2O and CO2 in the atmosphere.
Getting a common understanding of the Tyndall gas effect/greenhouse effect is a good way to get on with it.
Venus: No Greenhouse Effect
The radiating temperature of Venus should be 1.176 times that of the Earth.
Without ANY greenhouse effect as promulgated by the IPCC, at any given pressure within the range of the Earth atmosphere, the temperature of the Venus atmosphere should be 1.176 times that of the corresponding Earth atmosphere.
at 1000 millibars (mb), T_earth=287.4 (K), T_venus=338.6, ratio=1.178
at 900 mb, T_earth=281.7, T_venus=331.4, ratio=1.176
at 800 mb, T_earth=275.5, T_venus=322.9, ratio=1.172
at 700 mb, T_earth=268.6, T_venus=315.0, ratio=1.173
at 600 mb, T_earth=260.8, T_venus=302.1, ratio=1.158
at 500 mb, T_earth=251.9, T_venus=291.4, ratio=1.157
at 400 mb, T_earth=241.4, T_venus=278.6, ratio=1.154
at 300 mb, T_earth=228.6, T_venus=262.9, ratio=1.150
at 200 mb, T_earth=211.6, T_venus=247.1, ratio=1.168
(Venus temperatures are +/- 1.4K, Earth temp. are from std. atm)
The actual ratio overall is 1.165 +/- 0.015 = 0.991 x 1.176. It does not vary from the no-greenhouse theoretical value at any point by so much as 2%.
The Venus atmosphere, in the range of Earth’s atmosphere, shows no sign whatsoever of a greenhouse enhancement due to its composition of 96.5% carbon dioxide. The fact that the temperature ratios are so close to that predicted by mere relative distances from the Sun tells us that both atmospheres must be warmed, overall, essentially in the same way, by direct IR solar irradiation from above, not by surface emissions from below. Keeping it simple, the atmospheres must be like sponges, or empty bowls, with the same structure (hydrostatic lapse rate), filled with energy by the incident solar radiation to their capacity to hold that energy.
There is no greenhouse effect on Venus with 96.5% carbon dioxide, and none on the Earth with just a trace of carbon dioxide.
This is the rock hard bottom line. This is the true standard from which to proceed.
Your argument is that the greenhouse effect is the same on earth as venus, not that there is no greenhouse effect on either.
Your link compares the temperatures on earth with a greenhouse effect to those on Venus, finds them simular and then concludes there is no greenhouse effect. A logical failure.
Harry’s argument appears to me to be:
The compared atmospheric temperatures on Earth and within similar pressure levels on Venus are the same once the difference in received solar energy is accounted for. BUT this is a strange result because the atmospheric concentrations of gases is very different.
I’m not planning on reading the Dragon book, but this particular comparison between the Earth’s atmosphere and, the 1 bar to space layer of Venus’ atmosphere, is very intriguing in my humble opinion.
I had not seen this argument before, but it sounds to me to be a very good scientific inquiry, worthy of study. So I would like to respectfully ask how this comparison fits into our above theories. If there is a better rebuttal to Harry’s argument, please point me in the right direction.
You used the wrong albedo numbers. The bond albedo is the correct one for total energy absorbed by the planets, and Earth’s is 0.29, while Venus is 0.75. These result in Venus actually receiving an average of only 0.67 times as much energy per area as Earth! Thus there is a strong greenhouse gas effect. In addition, the lapse rates are slightly different due to different gravity and gas composition. Venus is the classic greenhouse gas affected planet. However it is the combination of high altitude of outgoing radiation (nearly 10 times as high as for Earth) and lapse rate that gives the high surface temperature. Venus would be nearly as hot with much less greenhouse gases as long as the total atmospheric mass were the same, but some greenhouse gases are necessary.
Maybe you can help me understand a couple of things. Doesn’t a gas radiate it’s own particular IR wavelengths and isn’t it relatively opaque to those wavelengths? It seems to me that the opacity of an atmosphere would be determined by some simple formula of atmospheric thickness and not necessarily whether the atmosphere is CO2, N2 or other.
Also, if the radiation of IR from the surface of the earth is an efficient means of getting the heat through the atmosphere to space, then wouldn’t the air be cooler in a layer near the earth? Since the overwhelming bulk of heat is stored in the air the bulk of the radiation to space must be coming from the air. It seems unlikely to me that CO2 is a good absorber of IR from O2 and N2 at least in comparison to O2 and N2 absorbing their own frequencies.
Whether a gas radiates or not depends on the distribution of electric charge around the molecule. Light can be thought of like a wave of electromagnetism, that pushes and pulls on any electric charges as it passes. If the molecule is symmetrical, it pushes/pulls on all parts equally, and the molecule simply ‘bobs’ on the wave, unaffected. But if there are different charges on different parts, then the wave can stretch and bend the molecule, as the different parts are pushed and pulled differently with respect to one another.
So N2 and O2 which are symmetrical are not easily affected by light waving at frequencies similar to those at which molecules naturally vibrate, but CO2 and H2O both have a big negative charge on the central oxygen/carbon atom, and positive charges on the hydrogen atoms to either side. This is why CO2 and H2O interact strongly with IR, but O2 and N2 do not.
However efficient IR might be at getting through the atmosphere, the less atmosphere it has to go through, the easier it is. But as I said in an earlier discussion (that Judith has kindly quoted above) the temperature structure of the atmosphere near the Earth’s surface has a lot more to do with compression because of air pressure than it does radiation.
Nullius–Thanks. I knew about polarized molecules like H2O but didn’t know its connection to IR absorption efficiency. One question that comes to my mind arises from what I think is true about efficient absorbers. Aren’t they also efficient radiators at the same wavelengths? When CO2 absorbs IR from the ground it immediately within a few collisions transfers that energy to the O2 and N2 in the immediate vicinity. By the same token, warm air maintains the temperature of the CO2 mixed with it. If CO2 is an efficient radiator, doping the atmosphere with CO2 should provide a fairly efficient conduit for the heat stored in the atmosphere to be delivered to space. Wouldn’t CO2 be on net a cooling factor? Thanks–Robert
Efficient absorbers are indeed efficient radiators at the same wavelengths.
Greenhouse gases in the atmosphere do make cooling of the atmosphere more efficient, but it’s the temperature of the ground that we’re more interested in. Also, the efficiency of cooling doesn’t have anything to do with the temperature; molten steel cools more efficiently than snow, because it is a good thermal conductor.
With the atmosphere, it doesn’t matter how efficient the IR-visible surface is at cooling, what matters is where it is. If it is high up in the atmosphere, then it is the high atmosphere that settles at the equilibrium temperature. If it is at the solid surface, then the solid surface will attain this temperature. Exactly the same amount of heat is radiated to outer space, wherever it is and whatever its efficiency. The radiator is cooled to exactly the same temperature to output just that amount of heat.
If our planetary cooler is higher up in the atmosphere, we get let benefit from it down here at the surface. The further away it is from us, the less cooling we get.
Efficient absorbers are indeed efficient radiators at the same wavelengths.
This was the prevailing sentiment prior to 1950. How do you reconcile this with Kasha’s rules and the Stokes shift?
That’s a very good point! I like it when someone teaches me something new!
Yes. The normal rule or absorption corresponding to emission is based on the concept of the time-reversibility of the microscopic laws of quantum physics. I think in this case it doesn’t apply because there isn’t a thermodynamic equilibrium. To take the simple example of photons being absorbed, then some of the energy lost as heat before re-emission occurs, it relies on there being a heat sink available to stop the heat from building up until the reverse process starts to occur. I’m not sure, but I think that at equilibrium you would get a single broad peak identical for absorption/emission encompassing both the peaks, and that in a sense what is happening is that emission is occurring preferentially from one side wing of the same peak as the absorption.
But I could be wrong; I haven’t thought about it for very long.
It’s going to be tricky to explain at a basic level, though.
I enjoyed this post a lot, I’m a details person so I find it much easier to follow arguments which make their point and then go through the detail of it.
In terms of the debate I have some problems with this post. It is almost entirely devoted to trying to get the explanation of the GH effect right. If this is so difficult how can it be non-problematic? When we finally get to the skeptical arguments they are merely dismissed as “nonsense” and “beyond bizarre.” One would hope for as detailed an explanation and discussion as for the AGW side but no, there is nothing. Then, to add insult to injury, skeptics are told to read the ultra-AGW RealClimate (!) and Chris Colose for the details.
Overall this comes across as yet another example of the AGW argument that the science is settled and skeptics are stupid. The skeptics obvious response is that if we are so stupid why don’t you respond to our arguments? Why indeed?
The basic science of the GH effect is straightforward. Explanation of GH to audiences with various levels of understanding is a challenge. Skeptics on this particular topic have built up straw dogs to knock down or make arguments that are patently incorrect. These have been debunked many places in the blogosphere, and skeptics showing up here to make these arguments didn’t make a particularly strong showing, although the comment on the milne/eddington argument was definitely a cut above the others.
There are many skeptical arguments on a range of topics that I think are valid and interesting (see skeptics make your best case thread). I don’t recall that any of the arguments on that thread saying the GH effect doesn’t exist, etc.
The debate should be focused on the feedbacks and sensitivity, and the relative magnitude of the GH impact on climate change compared to natural variability. There is enough uncertainty on these topics to keep everyone on both sides very busy. But persistent skepticism of the GH effect itself, made with weak arguments, isn’t getting us anywhere.
One question I asked in this was in reference to a claim that a reflecting layer over a radiating surface would heat it up. My question was for the person asserting this to show it. I do not believe I received a response.
Can you please clear that up for me?
If I may ask another question: After these Climate Etc. discussions and Dr. N-G’s interesting posts on this, do you still think ‘greenhouse’ is a proper descriptive basis for what H2O, CO2 and the rest do to the energy flows of the atmosphere?
See Dr. Spencer’s website on this topic, and an example:
Some of the issue in my opinion is the choice of words, specifically the words ‘heating it up’. What is happening is that the loss of heat is slowed down with the an object (or reflecting layer) adjacent to the radiating surface in question.
It is important to note that the surface/object in question is being heated itself initially from another source (Dr. Spencer’s example has the plate being heated electrically). This is an important point. There is an initial equilibrium temperature of the object by itself, and a different equilibrium temperature with another body/surface next to the original object. The heated object doesn’t cool as rapidly with something next to it as it would if nothing were there. Thus from a ‘comparative’ point of view, the heated object it is hotter with something adjacent to it than it would be without it.
Martin- I agree. But a surprisng number of people in the AGW community do not seem to realize this.
My background, as someone who grew up in the insulation industry, and having a grandfather who was an MIT engineer and liked to teach his grandchildren about things like insulation properties, makes this clear to me. Frank, I believe, was someone talking about the property of heating things up by way of reflectors reflecting back heat from a source, and that is a bit dubious.
I think there is a problem with the way you’re setting the problem up.
In your wording, I infer you’re saying that given a finite amount of energy, how does reflecting energy back at a source add more energy to that system?
I may be mistaken for which you can clarify what you mean.
Assuming my interpretation is correct, I think the question needs to be rephrased to if I slow down a system’s ability to dissipate heat, will that system increase its temperature?
For example, I heat up a pot of water to a specific temperature such that the water comes to a thermal equilibrium between the heating element and the surrounding air (let’s assume no water is evaporating for the moment). This temperature equilibrium means that the water is losing energy to the surrounding air at the same rate it is gaining energy from the heating element. The is no net change in energy.
Now, if I take a piece of aluminum and place it 6 inches from the top of the pot, then some of the energy dissipated away from the water in the form of IR light is being reflected back toward the water. We have now changed the equilibrium between the energy gained by the water and the energy lost. By reflecting heat back at the water, it is now losing less energy.
The water, however, ‘wants’ to lose energy at the same rate it is losing energy, based on the second law of thermodynamics (heat engines are good example of this idea). So to increase the rate at which it is losing energy, the water will increase in temperature. This increase in temperature will continue until the amount of energy lost per unit time equals the amount of energy gained.
So we’re NOT adding any additional energy to the water. We are simply impeding its ability to cool itself. By doing so the water increases in temperature until it has balanced the energy in to the energy out.
You should be able to try that experiment at home with the a burner on low and a small pot of water. Any metal lying around will work, but it should be a pretty big piece. Digital thermometers would likely be better than their mercury counterparts, but that’s just a guess.
Maxwell, good points. But if you are at boiling, you will only only act to slow loss of energy/ retain energy in the pot, and not change temps. The system is always going to seek to shed energy and ultimately- when the heat source turns off- cool off. But the one thing that never happens is that a run away tipping point is found to make the pot explode.
I test your experimental proposal every Saturday when I use the nice shiny aluminum dome lid to make the lovely Mrs. hunter an omellette and use the reflective properties of the lid to the get cheese to melt just right. I think we will have a fetta cheese and spinach omellete tomorrow.
I think you’re assuming too much in your responses.
First, I assumed we were not vaporizing liquid in the example above, so we can’t be boiling water.
Second, if the pot were made to keep in more heat, then adding more and more and more energy would lead to an explosion at some point. It’s just that commercial pots are specifically designed with fail-safes to ensure the safety of consumers.
You’re trying to draw the conclusion that because your pot that is designed to fail-safe can’t explode, there can’t be runaway global warming. Unfortunately, the implicit assumptions in your argument make the two situations uncomparable.
It may still be the case that global warming can’t runaway, but it’s not for the reasons you claim.
Water is always vaporizing, down to very low temps, if I recall correctly. The evaporatoin rate can be very low, but is non-zero.
I simply thought you were putting a cover on a pot, not sealing it.
I am pretty sure that even in a sealed pot you will get no explosion unless boiling does occur. I don’t believe the pressure will rise enough to do much of anything unless you are getting boiling or pressurizing enough to suppress boiling below really high temps.
I was not using this little kitchen experiment to talk about Hansen’s tipping points but about the idea of reflector raising the temperature as frank asserted in another thread.
So….I think, depsite our disagreements, we agree that even a really good reflector will not cause temps to increase, but will instead slow the cooling, or make the heating occur more quickly.
One question I asked in this was in reference to a claim that a reflecting layer over a radiating surface would heat it up. My question was for the person asserting this to show it. I do not believe I received a response.
Here’s a relevant experiment I did myself a few months ago. I took two sheets of cardboard, one white and one black, put a sheet of glass in front of each with a 1/4″ air gap, and faced both to the Sun for ten minutes. I then picked up the sheets of glass and transferred them back and forth between my hands to feel if there was any temperature difference.
The glass in front of the black sheet was warmer. (Taking the precaution of labeling the glass sheets with a laundry marker avoids losing track of which was which, which can easily happen with this sensitive method of detecting heat differences.
The effect was enhanced by wrapping every component in one thickness of saran wrap to protect against convective cooling. Saran wrap lets both visible and FIR pass while keeping what it’s wrapped around from cooling by convection.
The glass simulated a greenhouse gas while the cardboard simulated high and low albedo.
I agree on one point, namely that the technical papers presenting arguments against the greenhouse effect were never competently presented, much less defended. Presumably no one was qualified to do so, except the Dragon Slayer and he seems to have been driven off by being called a fraud.
Beyond that, the confusion and disagreements displayed by those defending the GH effect makes it hard to accept that the science is straightforward. Two disagreements, among many, that seemed prominent were the relative roles of back radiation and convection. It seems clear that the detailed science is complex, perhaps even controversial, not straightforward. I also agree that there may be better things to discuss, but my assessment is that the GH discussion failed because the skeptical arguments were never presented.
There is no role for back radiation (on the average). It is a result of the process, not a driver. Please read Nullius or Tyndell or even my versions. The heating at the surface (which results in more surface and back radiation) is due to the radiation insulation property of greenhouse gases moving the average location of radiation to space to a higher altitude and this combined with the adiabatic lapse rate results in the higher surface temperature.
I agree with Leonard about the radiative transfer theory, but I think the rise in co2 has been offset by the drop in humidity. Whether this is due to a self balancing effect such as that proposed by Miskolczi or whether it is due to reduction in solar activity since the 60’s I’m not sure, but I’m tending towards the latter on the basis of my own research.
What’s your take on the contribution of methane on the total GHG effect? I see it as one major related skeptic issues often raised.
Some claim that its absorption bands are relatively narrow (around three and eight microns) and thus cannot have that much effect on anything. The first three micron band is claimed to reside outside the relevant LW emission spectrum and the eight micron is too narrow to have any significant effect.
Additionally, I have seen claims that methane is quickly destroyed by UV light. Other sources suggest that its atmospheric lifetime is in the order of 10 years.
How does it compare with CO2 overall? For example, we have (unreliable) Wikipedia, stating that it has “global warming potential of 72”, and many articles that state its effect is 21-times, or even more that of CO2. What is the total effect of the projected methane concentration on the back radiation, or what has been the assumption when building projections?
I don’t agree with any of the ‘anti-warming’ nonsense discussed by ‘skeptics’. I also don’t agree that they are skeptics. The greenhouse basic effect is very much real and very much simple physics. What I consider a true skeptic is one who understands the basics of heat capture/retardation and still doesn’t buy into the magnitude of the warming. In fact the typical blackboard, CA, tAV, Lubos and even WUWT reader is fully aware of and in agreement with the basic effects.
My own issues lie in the magnitudes of the warming, feedback to warming, and even more so with the alleged dangers and fake solutions. I wouldn’t be surprised at all to find that feedback was negative or strongly negative. I also wouldn’t be surprised to find out that warming from doubling of CO2 even with no feedback has been incorrectly estimated. I haven’t found a good reference for the 1C calculation as yet. The only stuff out there is too basic to correctly capture the magnitude IMO. But none of this changes the fact that the warming effect does and in fact MUST exist. Some will never be convinced, but they would be very unhappy people if they were correct.
I agree, this is where the skepticism should be directed.
This leads on from a point I tried to make on the previous post about the basic GHG premise. I understand your admirable desire to find a way to explain in simple terms these well-accepted mechnisms: I just don’t think it’s necessary. I agree with Jeff Id – the vast majority of ‘sceptics’ are concerned with feedback mechanisms and overstated confidence levels.
Those that seriously question the basic ‘greenhouse’ properties of CO2 are perfectly entitled to air their theories but, by definition, they cannot participate in the main areas of scientific contention that involve most ‘sceptics’ because this requires acceptance of the very premise they dispute.
Sorry if I’m flogging this point to death but I’m really keen to fast-forward to debates on feedback, cosmic radiation, enso etc and I find all this stuff a bit of a distraction. I want to learn about the nature of the trees, not whether people think the forest exists in the first place.
I will keep building on this overall topic, with a post next week on the direct CO2 forcing, and the 1C issue (the point raised by Jeff Id, and I concur with Jeff on this).
The other area that really needs to be handled is the effect of clouds. I’ve read a lot of the comments here and elsewhere and they nearly all give some great explanation and then say something like “of course could cover affects this by …” or “clouds make the interaction more complex” or similar. Furthermore it seems to me (though I’m not an expert and will be pleased to be corrected) that most (all?) of the climate models run by the various research groups also handle clouds poorly.
from my understanding clouds do two things. They stop more radiation from leaving the warm surface below thus heating it up. They also reflect solar (and other extra atmosphere) radiation from above thus reducing the energy reaching the surface from outside. A clarification of how these two effects interact (e.g. higher clouds reflect more than they block from below, lower clouds the opposite) and how widespread the effects are is key because without it you end up with something that is only marginally better than the famous mathematical spherical cow.
Moreover the lack of cloud detail is an instant point where the more desperate out and out “skeptics” can claim that the whole GH effect is a lie because it misses this detail.
If the fact that CO2 and H2O absorb and emitt in the Infra Red makes you a believer in the Greenhouse Effect then I suppose we are all believers.
If however you think the magnitude of such an effect has no great influence on our climate I think you are a sceptic.
The last thing I want to see is a list of “approved sceptics” drawn up by a supporter of the IPCC position.
This would then be followed by a list of “approved topics” and you will then be permitted to choose whether you favour the mild IPCC projection or the extreme version of CAGW outlook.
Thank you for the comments about the average reader! I am one of those people that read many of the blogs regularly but rarely make any comments.
I would like to know whether the option of an atmosphere which has no CO2 has been discussed (here or elsewhere)? I wonder if it is possible to prove whether a greenhouse atmosphere can be sustained water vapour alone?
I would like to know whether the option of an atmosphere which has no CO2 has been discussed (here or elsewhere)
The vegetarians would starve to death in a month.
Boom boom. Good one.
I got 18 vegetarians at my place, so more CO2 is good for me.
You counting the mice, or are you running an ashram?
Jeff Id: “I haven’t found a good reference for the 1C calculation as yet”
Jeff, the 1C value for a forcing of 3.7 W/m^2 (the canonical value for doubled CO2 based on radiative transfer equations and spectroscopic data) is derived by differentiating the Stefan -Boltzmann equation that equates flux (F) to a constant (sigma) x the fourth power of temperature. We get dF/dT = 4 sigma T^3, and by inversion, dT/dF = 1/(4sigmaT^3). Substituting 3.7 for dF and 255 K for Earth’s radiating temperature, and assuming a linear lapse rate, dT becomes almost exactly 1 deg C. In fact, however, the models almost uniformly yield a slightly different value of about 1.2 C, based on variations that occur with latitude and season.
I work in my day job as an optical engineer. How is the 3.7W/m^2 calculated? I’ve seen several estimates done very crudely but never seen the true absorption/re-emission timing and pressure taken into consideration nor have I seen good measured data on the matter. It’s important to note that because it is the smaller end effect we’re talking about, I haven’t really spent any significant time looking for it either. I have seen a bunch of crappy stuff tho.
Jeff – This is clearly an area complicated enough so that its entirety can’t be encompassed within one or a few references. As a start, though, you might want to look at Myhre et al’s 1998 GRL paper and then work your way backwards via the references.
The link is Radiative Forcing and Table 3 provides the basis for the 3.7 W/m^2 value.
Fred: I’ve raised the same point as Jeff at SOD, been sent to the same reference and looked at the abstracts of some of the preceding papers. One of them says that the radiative forcing due to 2X CO2 varies with the altitudes at which the forcing is calculated. What is the correct altitude for calculating forcing? Obviously the altitude that is most relevant for claiming that surface temperature will rise by a similar amount (which one can correct for lapse rate feedback if you like – assuming that there IS a constant lapse rate between the surface and the altitude at which forcing is calculated – which there probably isn’t). My skeptical antennae are quivering rapidly over the fact that all of this information is buried behind pay walls, spread over a half a dozen linked papers, and is cited, hasn’t been independently re-developed by any other researcher and is never discussed at proAGW websites. At the moment, I’d say that the radiative forcing for 2X CO2 is 3.7 W/m^2 (the IPCC says +/-10%, a joke) could be termed a hypothesis. (SOD once replied that he would post on this subject, but I won’t be surprised if a post doesn’t appear. Belittling G&T and the like is much easier than scrutinizing non-transparent work like Myhre’s.)
PDF of Myhre 1998
So, since many journal articles are behind paywalls (including Science, Nature, Geophysical Research Letters, astrophysical journals, chemistry journals, biology journals, medical science journals, social science journals, etc), I presume you’re skeptical of the content of all of them?
You’re angry because you can’t find a blog that talks about technical issues (just as an aside though there are several which talk about radiative forcings, including my own). You actually have to find academic resources?!?!
A 10% uncertainty claimed in a particular set of references is a ‘joke?’
With all due respect, have you ever taken science courses at a college level, especially in the physical sciences?
Instead of being silly, you could actually spend 5 seconds doing a google scholar search of “Myhre et al 1998” to find a full text PDF of the paper. Many papers behind paywalls are available if you look hard enough, often through an authors web page. Sometimes I have e-mailed authors for papers, and generally are very happy to have their paper read.
This is all much more rational and it works much better than pouting that climate science is unfair
Yes, a body will radiate ~3.7W/m2 more energy if its temperature is increased by ~1c. However, that does not mean that increasing the energy flow to the body by that amount is going to increase its temperature by ~1C. Any increase in the temperature has to increase the energy flow away from the body by all means it can, ie conduction, convection, evaporation as well as radiation. When the outflow of energy equals the inflow then thermal equilibrium exists with the body at a higher temperature. But that temperature cannot be as much as ~1C higher, as the radiative outflow has to be less than the total outflow.
There also seems to be confusion between energy and temperature. They’re not the same thing. This confusion seems to exist on both sides of the fence, as well as in some of those who sit on the fence.
Before I get jumped upon, I should qualify my previous post by saying that the radiative outflow can only equal the total outflow at the TOA.
So all the air rising and falling stuff is part and parcel of the ‘greenhouse effect’ then?
I agree with what you say, but from the comments here and on the previous thread, there are still many that think the skeptical position on the existence of the GH effect is correct or at least plausible.
Dr Curry, it may be good to state, as in this post, the basics of the GH effect, if only for the sake of die-hard ultra-skeptics that deny its validity or existence. But please let us move on to the real skeptical views, which are all about the magnitude of the effect, the feedbacks, the measurements, etc. And then we could also move on to discuss the alleged impacts, which are also a matter of great debate on the skeptical front (and on this matter the IAC report on the IPCC does agree that WG2 has a quite flawed approach). The two main issues, then are
1. OK, but how much?
2. So what?
I agree with Hector. I haven’t doubted the Tyndall gas effect since someone at WUWT directed me to a tutorial on the adiabatic lapse rate. The real uncertainties concern feedbacks and the underlying mechanism of the climate. Then there is the political part which will be a sticky wicket no matter what the science says.
A greenhouse cannot generate a pressurizing effect.
The salt changes on the surface of the oceans WILL interfere with radiation penetration. This then means more solar radiation is reflected back rather than absorbed.
Just one question: Are you doing a parody?
Yes and no.
Gases are building but the solar energy is being reflected back more making the planet become colder.
The corollary to that is that for many of the believers in the AGW catastrophe, anyone who does not agree with their view also does not believe in the actions of H2O, CO2, etc. in the atmosphere. One scientist, when I asked if it was possible to falsify AGW(referring to the idea of climate crisis), replied (parphrasing) it was only possible to do so if the understood physics of CO2 were proven to be wrong.
This sort of view makes distinguishing between known physics and the applications of those physics to come up with a world wide crisis demanding huge changes in our economies and technologies very difficult.
Thank you Judith. This is most encouraging thing I have seen on this blog.
I’m not sure, but it seems like replies are ending up at the bottom of the thread. If mine also falls through: Dr. Curry, who were you responding to at December 3, 2010 at 8:02 am?
let me try to see what is going on.
(Not sure the reply function is working right. This got posted further down so I am reposting it.) There is no single skeptical position, rather we have several distinct challenges. Each appears scientific so it is plausible to that extent. Most importantly, merely reciting GH theory is not a counter argument to any of them. There is a possible irony here, as Tyndall was himself a revolutionary, part of a group of skeptics who successfully questioned the accepted view that heat was a substance. His book “Heat as a Mode of Motion” is a classic.
An interesting thread. I share with many correspondents the view that the existence of the GH effect is not really central ground for the debate on AGW. There is de facto more radiation leaving the Earth’s surface than leaving TOA to balance net solar incoming flux.
Having said that, however, I do conclude from the various comments that there is a want of a single authoritative description that represents our current best understanding of the effect expressed in both qualitative and quantitative terms. I share your view that the existence and widespread acceptance of such a description would help focus conversations onto areas of genuine scientific disagreement.
H2O is another of the panes of glass, and as a feedback effect, adds a complexity to the discussion that would obscure the message without changing it.
I must correct myself — I said that the CO2 ‘pane of glass’ is like a transistor, but I should have said diode. (and yes, Methane, CFCs, H2O are other such selective ‘panes of glass’ that let in sunlight but resist letting out the earth’s ‘body heat’.
There are two hypothesis. The first (the radiation absorbtion by CO2) is used to say that if you believe this then you must believe AGW. The problem is the unstated and unsubstantiated second hypothesis that there is a strong positive feedback from very small change caused by the CO2. This is the problem and yet as at RC here is no real discussion about this hypothesis; it is just assumed and you are called a “skeptic” if you question it and then the first hypothesis is trotted out to show how “stupid” you are. Let’s get to discussing the real issue, hypothesis two, climate feedbacks.
No, at RC you are a ‘denier’ paid by big oil and anti-science, to boot.
Jeff Id December 3, 2010 at 7:53 am writes
“My own issues lie in the magnitudes of the warming, feedback to warming, and even more so with the alleged dangers and fake solutions.”
Could I really support this message. It is not only the feedbacks that are in question. It is also the magnitude of the warming that should be given equal prominence.
I have limited time the next two weeks to develop lengthy posts, but I would like to move this dialogue along. I am proposing the following topics for the next two greenhouse threads, let me know what you think:
1. why we have confidence in the radiative transfer models used in climate models
2. the magnitude of the direct CO2 forcing in terms of temperature increase (and why I think there is uncertainty and how we might go about addressing this issue in a different way).
Bravo!!! However, with respect to “1. why we have confidence in the radiative transfer models used in climate models”, the obvious question is, to do what? There are some things which radiative transfer models are very useful for. Whether estimating the change in radiative forcing for a doubling of CO2 is one of these, I am not sure. I would certainly like to see an explanation as to why radiatve transfer models are suitable to estimate change in radiatve forcing.
With respect to “2. the magnitude of the direct CO2 forcing in terms of temperature increase (and why I think there is uncertainty and how we might go about addressing this issue in a different way).” as so many people have observed, this is THE key issue. Both how much effect CO2 has without feedbacks, and what is the sign and magnitude of the feedbacks are.
Sounds great to me – I’m looking forward to reading them!
I am hoping #2 can also compare the 3.7 W/m2 forcing from CO2-doubling with other forcings such as the solar 11-year cycle (0.2 W/m2) and the longer term variability causing the MWP and LIA (0.5 W/m2). I think there are some salient points to be made here, given that these others do appear to have had significant positive feedbacks. Even without talking about feedbacks it is instructive to compare forcings like these.
Regarding your suggestion for topic 1, will this aim to discuss the whole radiative budget thing? I see this as very much a cross-discipline process, in the sense that it should involve measurements and observations covering atmospheric particulates, So2, Methane, clouds, albedo, clouds, algal blooms, cosmic radiation and all manner of biological ‘importers’ and ‘exporters’ of CO2…….and I’m sure there are heaps of other checks and balances that I can’t think of, all of which should play a part in GCMs.
I see little value in pursuing 1. as the main scientific acceptance on both sides is 1 C to 1.2 C per CO2 doubling without any feed back, and the difference is not a big deal, and not worth a separate long debate. The discussion on 2. should mainly be on forcing and feedback, i.e., total effect. That is the only issue of main concern.
I view that there is sufficient room for an interesting discussion on the nonfeedback sensitivity, lets see if i convince you. Also, 20% is quite a large discrepancy. Firmly and unambiguously addressing this problem is needed before moving onto the feedbacks, IMO. stay tuned. I hope to have this next post ready within a few days, but testimony may get in the way. stay tuned.
Judith on reading the title of this post I thought you might have answered a nagging doubt I’ve been developing. You write an awful lot about doubt, uncertainty and what we don’t know. I thought this article was going to be the antithesis of the “skeptics make your best case” and contain information on where you think AGW or CAGW where on a strong footing. Which datasets and anlysis show a clear AGW fingerprint? Where does the certainty lie? What is indisputable beyond CO2 is a GHG? etc. etc.
Imagine my disappointment.
Any chance of such a post?
First, let me say that I have enjoyed the discsussions here. I’ve been quite intrigued by some of the different explanations and personalities, e.g. Prof Vaughan Pratt’s dancing molecules, etc.
Perhaps my brain works differently, but I’m a great deal more intrigued by quantifying what’s unknown than going over why we think we know something. I tend to assess information quality by seeing a big picture and then noting the gaps. From there I can better assess whether or not a gap needs exposition or is important enough to worry about, etc.
What I think would be helpful isn’t necessarily explanation re how it works so much as listing of observations or experiments (if any) that counter the prevailing theory. And I mean real ones from real players, no crackpot stuff.
In the case of GHE there’s probably not that much counter observation. I don’t know, though, because your summaries concentrate on explaining how we know stuff. Are there any serious counter theories and/or serious observations that suggest a gap in understanding?
What I have in mind would show the argument/counter-argument ratio at each step. If a series of graphs show this then it’s a quick visual showing what we know vs what we don’t. If need be, in gap format. The gap thing shows where we are fuzzy. In this manner I don’t have to wade through a great deal of explanation re back radiation etc unless I want to really explore the knowledge gap. If presented graphically (IFA?) then a climate layman like me at least knows what things are important to look at. Those coming to the discussion later would see things like GHE and note that there’s not much of a gap (if any) meaning that there’s nto much gold to be mined from that particular argument.
I use my approach at work. Although I have yet to fill the “denizens” info I’m an engineer doing mostly software modeling (stuff that lets other engineeers do designs.) Even in areas as mundane as UI what I want to know is what doesn’t work, what people don’t like. I can infer what does work and what is liked from that. From this persepective, to me anyway, much of what’s been discussed is affirmation of what works rather than what’s not right, and it becomes more difficult to for me zero in precisely on what needs attention.
I’m hoping that you perceive this as constructive, and not a criticism.
GLA is correct, I think. It would be good to present empirical evidence of the Tyndall gas effect. Someone on an earlier thread mentions the actual measurement of absorption of radiation by some instrument; from the ground, from high in the atmosphere in an airplane, and pointed “sideways.” These sorts of measurements certainly bolster the case, if support is necessary for some people.
Read Dr. N-G over at his Climate Abyss blog. His Tyndall gas part II post does exactly this with some excellent satellite filtered photos to show the CO2 in action.
Only ran across this just now, whence the month-long delay.
Dr. N-G acknowledges my comment at his Climate Abyss blog, and offers a solution. In the following response I argue that he’s missing the basic point of how greenhouse gases work, namely that there’s a 20x wavelength lengthening when the radiation comes back off the ground.
I tried posting the following there just now, but without success since in the meantime it seems to have been closed to further comments.
(Incidentally I realize now that I’ve been underestimating the difficulty of the reasoning here. Just because something’s obvious to a physics honours major with no explanation does not guarantee it’s equally obvious to everyone without a clear explanation.)
My apologies for not returning to this site until just now. (I should have made a note to do so sooner.)
N-G: “In Pei’s pyramid, if the glass were transparent to solar radiation, it would not be able to attain a temperature warmer than the floors and walls.”
This is dramatically contradicted by measurements I’ve performed on Wood-type boxes where the inside of the window (whether glass or salt) is 20 degrees C hotter than the bottom of the box. I don’t understand where your statement comes from.
N-G: “Your observed effect must be due either to the semi-opacity of the glass to visible radiation (the glass is tinted so that the indoor sunlight is not too harsh)”
You may be missing the point that the glass already *is* heavily tinted, in fact pretty much opaque, to the radiation coming back at it from the floor, whose wavelength is 20x longer than that of sunlight.
As far as visible light is concerned there is no noticeable tinting whatsoever. The “infrared tinting” such as it is sets in about an octave or two below visible red light, and is entirely due to molecular properties of compounds such as silicon dioxide (analogous to atmospheric carbon dioxide) and not to any absorbent tinting materials.
N-G: “or a tendency of the human body to be so used to infrared radiation warming us from below that we can’t notice it.”
How does that explain the sudden sensation of tremendous heat from above when you enter the pyramid? The ground outside the pyramid is receiving the same sunlight as inside, which should therefore warm it by the same amount.
The difference is that outside there is nothing to trap the large amount of outgoing thermal radiation which keeps Earth cooler than the Sun. The Pei pyramid glass intercepts that outgoing radiation, heats up, and radiates that heat both up and down. Greenhouses work the same way (in addition to retaining the air thereby warmed, which the Louvre air conditioners desperately try to remove with only partial success).
this post rings a bell, anyone interested in entropy of radiation? I have a subsection in my book on this, here is concluding paragraph of that subsection:
Radiation from a hot emission temperature (e.g. the Sun) and subsequent scattering is associated with small entropy relative to radiation from a cool emission temperature (e.g. the Earth). In fact, the entropy exported by the outlong longwave radiation is found to be about two orders of magnitude larger than the entropy associated with the net solar radiation. This negative entropy stream at the top of the atmosphere allows internal production of entropy by the Earth while at the same time maintaining order in the atmosphere. If the overall entropy of the atmosphere were increasing, the atmosphere would approach a state of maximum entropy leading to a uniformity of the climate.
I have a few links posted here. This first link over there has full papers are available at no cost.
This issue of Philosophical Transactions of The Royal Society B: Biological Sciences, May 12, 2010; 365 (1545):
Theme Issue ‘Maximum entropy production in ecological and environmental systems: applications and implications’ compiled and edited by Axel Kleidon, Yadvinder Malhi and Peter M. Cox. doi:10.1098/rstb.2010.0018
And this morning I assembled the following:
Sean Wright, David Scott, and James Haddow,On Applied Thermodynamics in Atmospheric Modeling, Int.J. Applied Thermodynamics, Vol.3, (No.4), pp.171-180, December 2000.
W. Wu and Y. Liu (2010), Radiation entropy flux and entropy production of the Earth system, Rev. Geophys., 48, RG2003, doi:10.1029/2008RG000275.
Wei Wu and Yangang Liu, A new one-dimensional radiative equilibrium model for investigating atmospheric radiation entropy flux, Phil. Trans. R. Soc. B (2010) 365, 1367–1376. doi:10.1098/rstb.2009.0301
thanks very much for these, i clearly have much to catch up on. I will try to get something up on this topic later next week.
Nullius in Verba’s explanation was a real eye-opener for me. I spent several hours going over it and analyzing it. It is very logical and accessible to anyone with a basic understanding of physics. That I found that information here is a huge compliment to your blog. It is also a mystery to me why it took me so long to find it, I do read a fair amount of science magazines and web sites.
You now appear to have won over most of us into accepting the greenhouse effect as explained by Nullius in Verba. The debate now focuses on what degree will a doubling of CO2 affect the Earth’s temperature. Nullius in Verba stayed clear from that prediction for good reason. Good luck and keep up the good work!
The debate now focuses on what degree will a doubling of CO2 affect the Earth’s temperature.
I can answer that. Assuming the CO2 had been stationary for a few centuries, and within a day you doubled the CO2, then the surface temperature on the following day would be indistinguishable from that on the previous day.
In other words, the “instantaneous climate sensitivity” would be zero degrees per doubling.
But if instead of a step function you gingerly raised anthropogenic CO2 (the part nature isn’t adding and removing) by an amount that doubled every 32.5 years, then you would find that the instantaneous climate sensitivity in the above sense was 1.83 °C, because the temperature was responding to the increase of several decades ago.
I know that because it pretty much describes what’s being going on for the past two centuries, since 1790 to be precise. It can be seen spelled out at this Elementary Model of Multidecadal Climate Change.
If however you judged the dependence of temperature on the CO2 added 20 years ago, still assuming the 32.5-year doubling period for anthropogenic CO2, you would find that the climate sensitivity was around 2.7 °C. The dependence of Earth’s surface temperature on changing greenhouse gases is itself heavily dependent on how long you wait before observing the effect.
While this point is implicit in the IPCC’s distinction between “equilibrium climate sensitivity” (which for me has the status of the tooth fairy) and “transient climate response” (whose 20-year delay would be reasonable were it not for the inscrutable 1% p.a. increase of atmospheric CO2), nowhere near enough attention has been paid to the influence of these parameters, especially the delay, on that magic number referred to as “climate sensitivity.”
More posts like this excellent one — accompanied by illuminating diagrams (static and video, hopefully) and experimental data — and you will have created the first highly-collaborative online textbook on climate science. Keep going!
These quotes are what I have read before, so no not confusing.
However, their explanations is simple. Simple in that the atmosphere is far more complex than what a simple “greenhouse” effect will have one think should happen. Examples include cyclones and hurricanes. They transfer heat from the oceans into the atmosphere which travel into cooler regions. Thus some of that radiated tropical energy is being sent to the temporate zones where it cools. Same with warm fronts from the tropics which sends, for example, Gulf warm air up into Canada where it cools. Cold Arctic air comes down mixes with this warm air, causing storms, again further cooling the atmosphere.
How much atmospheric radiant energy is lost into the ground when it rains?
Lastly there was no dicussion on whether or not there is a thermostat that keeps the planet from overheating due to the GHE such that no matter how much more GHG’s are added, it does not add any more warming to the planet. It would add warming to the cold regions of the world, but not the tropics. That temp range in the tropics is stable, no increasing trend in the maximum temperature.
I agree generally with everything you’ve stated. I’m not sketpical that the greenhouse effect exists; my remaining skepticisism is based on the degree of heating from man-made CO2 and impact of other variables.
Good explanation even for those of with just BS degrees.
1. why we have confidence in the radiative transfer models used in climate models
Use something like Nullius in Verba’s explanation. Then we need data like density and (average) temperature of the atmosphere by altitude.
2. the magnitude of the direct CO2 forcing in terms of temperature increase (and why I think there is uncertainty and how we might go about addressing this issue in a different way).
This is the main issue for me. I have two suggestions. First, what real measureable effect will doubling the CO2 content have to Nullius in Verba’s model? Half of the CO2 increase will be in the first 5km where all IR is already absorbed. Above that the atmosphere is thin. How much effect will doubling the CO2 there have?
Second, I find it short-sighted to try and extract meaning about climate change from temperature flat files. My suggestion is to have some smart student design a small (relatively) inexpensive box of known conductive properties. Keep the internal temperature of this box constant and record the amount of energy that is required to do so. Place several hundred of these devices distributed around the world. Have satellite hook-ups to monitor them periodically. The amount of energy required to heat and cool these devices will provide accurate information about current climate change.
I think all you will find out is how much energy it takes to heat or cool a box at a particular location. Temperature is only one of many factors about climate. It may be not be the most important.
Unlike a thermometer, the box’s energy usage will react to wind, precipitation and sunlight. This will provide more information about climate than temperature data alone. Tracking the total averaged energy usage could give us a baseline on whether the current climate trend is heading warmer, colder or staying the same.
But I think it will have trouble giving distinctive data as to wind, humidity or temperature.
It has been a fascinating discussion – thanks.
The fact that highly intelligent people like Nullius and ScienceofDoom are still in disagreement about how the greenhouse effect works (after 465 comments) shows that it is still not very clearly understood.
I still feel that the role of convection is underestimated in all these explanations. For example, when a region of the atmosphere gets warmer due to absorption of IR, it is claimed that this heat must be re-radiated (up or down with equal probability). The possibility that the warmer air might rise (leading to an UPward heat flux) does not seem to occur to people!
I’m a lurker with an undergraduate degree in engineering and an interest in global warming. I really enjoy this blog and I definitely learned something from this thread.
For me, the convection/adiabatic lapse explanation by Nullius in Verba provides really good insight into the greenhouse effect. Unless someone shoots a hole in his logic, it clarifies for me how the greenhouse effect works. But it did leave me with a question. In my perhaps simple-minded view, I think of the greenhouse effect as the increase in Earth’s surface temperature relative to that expected from a similar-sized blackbody. From my understanding of what Nullius wrote, this temperature increase is due to a heating of the atmosphere above the Earth by the solid body of the Earth. As long as there is heat transfer from the Earth to the atmosphere, convection (which moves the warmed air to a higher altitude) will cause a greenhouse effect. If so, then, because heat transfer between the Earth and its atmosphere can also take place through conduction, doesn’t this imply that a greenhouse effect will occur even if there are no greenhouse gases present at all?
Willb – For practical purposes, heat can escape into the almost complete vacuum of space only by radiation. If there are no greenhouse gases to intercept radiation from the Earth’s surface and return some of it downwards, the Earth will balance the energy it receives from the sun by radiating at the temperature given by the Stefan-Boltzmann equation. That turns out to be about 33 deg C cooler than the current circumstance (if one neglects changes in albedo for the purpose of illustration). Conduction would alter this only minimally, because its ability to warm the atmosphere is slight and because non-greenhouse gas molecules in the atmosphere radiate very little energy at the temperature of our climate.
Thanks for the explanation. I guess I had incorrectly assumed that a gas could behave like a blackbody. So when CO2 is heated, it radiates energy. But when nitrogen is heated, not so much?
Regarding conduction, I was expecting that this would be a primary mode of heating the atmosphere. Wouldn’t there be significant heat transfer from wind blowing through sea spray, through dust and sand, and through vegetation? Conduction using heatsinks and fans certainly seems to beat out radiation when air-cooling electronics.
It turns out conduction is not very important in the atmosphere, except when there are very large temperature gradients over very small distances (i.e., at the surface). This represents one term of the surface energy budget which helps maintain the temperature gradient between the ground and overlying air (which is distinct from the *planets* energy budget, which is almost 100% purely radiative). Over the globe though, evaporation is a much larger term.
It also turns out greenhouse gases are horrible blackbodies! They are very selective absorbers, which is why you see such a complicated looking spectrum looking down from space (or up from the surface).
Another way to think of it is as raising the surface of the black body up into the middle of the atmosphere. (Due to inclusion of gases that look opaque when looked at in the IR spectrum.) The black body still approaches the black body temperature, exactly as before. But as air moves from this altitude down to the solid surface it gets compressed by increasing air pressure (the weight of all the air above it) and compressing a gas (without allowing the heat to escape into its surroundings) raises its temperature.
One of the things I like about your explanation is that it IS so easy to visualize the blackbody surface being raised up. The logic seems quite straightforward to me. The air is heated at the Earth’s surface and through convection rises. As it rises the greenhouse gases in the air radiate energy, presumably in all directions but most importantly (at least from my perspective) out into space. To maintain equilibrium with the Sun’s incident radiant energy, the Earth + atmosphere must radiate an equivalent amount of energy back out into space. As long as some of this energy is emanating from greenhouse gases at altitude, then the mean position for the Earth’s radiation must be somewhere above the surface of the Earth itself.
I don’t think we reached a fair conclusion on this – but I think Nullius’ focus on convection exclusively without taking into account the backradiation muddied the waters a bit. The flow chart used by Manabe and Wetherald is illustrative – there are two separate constraints that both have to be satisfied – the presence of GHGs that conform to radiation laws and in the space of all possible atmospheric temperature profiles the constraint of a maximum permissible lapse rate as determined by convection. Both are causes of the tropospheric and surface temperatures as observed, both of the constraints imposed by the two separate phenomena have to be satisfied. In other words it is a joint optimization problem, but you first need GHGs in the atmosphere to absorb and re-radiate the IR radiation in the first place.
I’ll copy my post from down below here.
“The lapse rate is crucial to the explanation. If the temperature increased with height, adding CO2 would lead to a cooling instead of warming. Indeed this is why the stratosphere cools when CO2 is added, because that has a reverse lapse rate (due to the ozone layer).”
In the troposphere convection determines the lapse rate and in the stratosphere ozone heating does. So I like this lapse-rate explanation because it unifies the stratospheric cooling with tropospheric warming.
You’re a smart lady and from the tone of this thread you will by now have understood the technical consensus shared by people like me who have scientific, engineering and mathematical acheivements in the real world. Your task, should you care to accept it, is to move the guild of climate alarmists into this state of uncertainty and enlightenment. En route please do not insult folk like me by terms like citizen scientist. Good luck and good wishes. DavS
query, pls provide preferred term if you don’t like citizen scientist. I have also used the words “auditor” and “extended scientific peer community.” there are different nuances for these three terms, and i am certainly open to other ideas on this.
‘Citizen scientist’ suits me. Captures it rather nicely I think.
As a European with a long memory, I’m a bit resistant to sociological or adjectival prefixes to scientific enquiry. I certainly react anything that suggests I’m anything else other than mainsteam. I hope I didn’t appear rude in my comments. I wish you very good luck with this extraordinary task.
Sifting through the comments, I don’t understand why the canonical “good skeptical position” is to accept the existence of the greenhouse effect but reject several decades of research constraining climate sensitivity. Perhaps because you can’t work out the full answer on a napkin? Because it’s theoretically conceivable (i.e., a low sensitivity doesn’t violate the laws of physics?) Because a couple of scientists like Lindzen or Spencer have a new opinion?
While one would like to narrow the range given in the AR4 (which is now 2 to 4.5 C for a doubling of CO2), it’s a range nonetheless, and doesn’t allow people to mindlessly make things up– either on the very low or very high end. People arguing for a very low climate sensitivity have to pull a lot of strings, do some tap-dancing, look sideways at the data a couple of times, get the very right data set, etc to make their case. At this point, the position is just as much faith-based as believing in the flying spaghetti monster, and often the leaps of faith to justify the position are no less dogmatic than denying the greenhouse effect. Some people are still arguing that there is no evidence for a positive water vapor feedback for instance, which is just a boast of ignorance in theoretical, observational, and modeling developments over the last couple of decades.
The same logic of dogma would apply to someone arguing for 10 C per doubling, though I’m not aware of anyone actually doing that. Meanwhile, the Earth’s history provides a treasure chest of climate change events, across multiple timescales and under different types of forcing, along with events for which we have records for such as the responses to Mt. Pinatubo, or how ocean heat content has changed in time. Multiple lines of evidence have converged to paint a coherent template for how Earth’s climate has the capacity to change, and while details must always be worked out, a very insensitive Earth system is found to be a bankrupt hypothesis.
As an add-on to Chris’ post, I’ll cross post a list of climate sensitivity studies that use past and present observation and do NOT use models for estimating climate sensitivity using a wide variety of methods.
A conversation such as “as long as we all agree on a greenhouse effect we’re good” is somewhat vacuous without an expansion as to what that means for the climate.
Deriving global climate sensitivity from palaeoclimate reconstructions — MARTIN I. HOFFERT* & CURT COVEY†
The ice-core record: climate sensitivity and future greenhouse warming — C. LORIUS, J. JOUZEL, D. RAYNAUD, J. HANSEN & H. LE TREUT
Aerosol radiative forcing and climate sensitivity deduced from the Last Glacial Maximum to Holocene transition — Petr Chylek
<a href="http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo578.html"Carbon dioxide forcing alone insufficient to explain Palaeocene–Eocene Thermal Maximum warming — Richard E. Zeebe
An Observationally Based Estimate of the Climate Sensitivity — J. M. GREGORY
<a href="http://www.amath.washington.edu/research/articles/Tung/journals/solar-jgr.pdf"Solar-Cycle Warming at the Earth’s Surface and an Observational Determination of Climate Sensitivity — Tung
Effect of climate sensitivity on the response to volcanic forcing – Wigley
The equilibrium sensitivity of the Earth’s temperature to radiation changes – Knutti and Hegerl
How sensitive is the World’s Climate — Hansen
fixing links, hopefully.
Carbon dioxide forcing alone insufficient to explain Palaeocene–Eocene Thermal Maximum warming — Richard E. Zeebe
Solar-Cycle Warming at the Earth’s Surface and an Observational Determination of Climate Sensitivity — Tung
You are asking the question in the same arrogant tone that eugenics promoters talked about how evolution proved their position on the rightness of eugenics policies.
Consider the skeptical position on this as early intervention before you burn through another ~$50 billion or so and impose some even dumber policies that the ones the climate crisis promotion industry has stuck us with so far.
The low sensitivity climate happens to look a lot like what people see out the window and in the rocks, by the way.
chriscolose writes “While one would like to narrow the range given in the AR4 (which is now 2 to 4.5 C for a doubling of CO2), it’s a range nonetheless, and doesn’t allow people to mindlessly make things up– either on the very low or very high end”
This is true if the science presented in AR4 is correct. If the science presented in AR4 is just plain wrong, as I suspect, then no such range has been established. And that, surely, is what we skeptics are urging Judith to discuss.
I note that both Jim and hunter’s responses consist solely of statements of faith, which rather bolsters Chris’s point.
There are more scientific reasons, but given that this is a thread about basic mechanisms, and Judith has already said that she plans another post later on sensitivity, to expand on this extremely complicated debate here would be off-topic.
That may be the reason for the terse replies.
I notice that you managed to miss (or ignore) my point completely, which bolsters my historical comparison of climate catstrophism to eugenics.
From the articles I’ve seen, I’d accept a doubling range up to 1.5 C from human produced causes. There is too much play in the higher spread.
Sifting through the comments, I don’t understand why the canonical “good skeptical position” is to accept the existence of the greenhouse effect but reject several decades of research constraining climate sensitivity.
Is the research data driven (i.e. real hard data from instruments) or that which is derived from modeling (data + assumptions)?
Link, no joy. Tried parsing url and the www …. no joy either.
“Perhaps because you can’t work out the full answer on a napkin? Because it’s theoretically conceivable (i.e., a low sensitivity doesn’t violate the laws of physics?) Because a couple of scientists like Lindzen or Spencer have a new opinion?”
On occasion in the past, I’ve considered myself surrounded by mental midgets and made an objectionable pillock of myself by making no secret of it to them. Looking back at specific examples, some of them from decades ago, I still find myself blushing.
The usual explanation for my behaviour, with the benfit of hindsight and a little of the extra wisdom that comes with age, was that actually, I was only being so disdainful because I needed to convince myself that I was right. Somewhere deep down, I actually had doubts, but couldn’t let them surface because so much ego was tied up in being right and beyond challenge.
I can’t remember a single time when I behaved like this when I was actually as right as I believed. Moreover, such right as I might have had on my side was ignored because of my attitude, so I usually achieved very little.
very well said Mr Larkin!
I find your “Flying Spaghetti Monster” reference very interesting, given that most projections of higher range temperature increases rely on GCMs rather than observational evidence from the records (though I must admit there is a fascinating discussion to be had concerning what the time span of such observations should be) – these seem to indicate a far more modest rise…..which means that, if the “several decades of research” to which you refer are correct, you would have to agree that something other than the mechanisms in this “research” is constraining the actual observed temperature trend – which is sort of the whole argument, is it not?
With the greatest respect it seems to me that you may be the one supporting the existence of Dawkins’ favourite creature.
Chris, as others have mentioned, your attitude leaves a lot to be desired.
Why do many have great doubts about the IPCC range of 2-4.5 C range? Evidence around us. The fact that the rate of rise from around 1910 to 1940 was very similar to the rise from around 1975 to 2005 (http://hadobs.metoffice.com/hadcrut3/diagnostics/hemispheric/northern/
The fact that the PDO, AMO, and solar cycles are more correlated to temperature than CO2
Because Hansen’s predictions (or projections if you like) based on models is not close to reality
Because Dr. Spencer’s paper (http://www.drroyspencer.com/wp-content/uploads/Spencer-Braswell-JGR-2010.pdf) discusses the position that cause and effect may have been mixed up when evaluating climate sensitivity.
AND because after the 2007 IPCC report, so many ‘experts’ claimed the science was settled, we MUST do something to lower CO2, when it is clearly not.
Dear Prof. Curry,
I thank you for your candour.
You leave me utterly perplexed. I don’t know whether I should feel humbled or scream out obscenities.
Unlike yourself, I am not the head of a university department.
Unlike yourself I have not even managed to complete my PhD, nor earn any other postgraduate degree.
I have published 4 papers, the first of which being in climatology is of such a great embarrassment to me (rightly or wrongly) that I dare not mention it. I have already mentioned the other 2 papers which were substantially my own effort.
Here is another paper for which I am listed as a co-author. I was blind, ignorant and fully guided. Including me as co-author was being embarrassingly generous .
Prof Kapral went to considerable effort to instill in me one specific fact.
He said (paraphrased) “You do know that the only reason this effect can occur is because the system is nonlinear (rather than linear)? You do appreciate that crucial aspect don’t you?
To be honest, I am flabbergasted. Convection arises from consequential nonlinear components in the description of the dynamic process. That changes the outcome substantially.
Those who put forth an non-convective model to explain the GHG effect willfully mislead.
Why has such an obvious and overt misnomer been allowed to persist, unchallenged and uncorrected?
The misrepresentation sickens me fully. Research climatologists cannot be trusted. THEY DELIBERATELY MISREPRESENT. The science is a farce. The reality is consequential confusing and muddled.
I am being lied to.
I have no more patience for such nonsense. Sorry.
Raving. I don’t understand what you mean. The lapse rate explanation can be given a physical interpretation by imagining a parcel of air convecting upwards to the top of atmosphere. As it ascends, it cools due to expansion. There, didn’t use any radiation.
The lapse rate is crucial to the explanation. If the temperature increased with height, adding CO2 would lead to a cooling instead of warming. Indeed this is why the stratosphere cools when CO2 is added, because that has a reverse lapse rate (due to the ozone layer).
Oh. That would help stabilize the polar inversions.
Further comments on Ferenc Miskolczi’s greenhouse analysis:
For all the hoopla about using a line-by-line computer program to calculate his results, reading Miskolczi’s paper makes it abundantly clear that Miskolczi does not fully understand the basics of radiative transfer, or the greenhouse effect.
He calculates what he calls “the true greenhouse-gas optical thickness” computed from the Planck-weighted spectral hemispheric transmittance using M=3490 spectral intervals, K=9 emission angle streams, N=11 molecular species, and L=150 homogeneous atmospheric layers. I don’t know how exactly he performs his line-by-line spectral interval calculations, but let us assume that those are being calculated accurately.
Unfortunately, his greenhouse optical thickness number is a useless quantity that is lacking even academic interest. It is relevant to the roughly 15% of the outgoing LW flux that goes directly to space from the ground surface (mostly within the LW window region, and little affected by CO2). This concept of a spectrally integrated optical depth for the entire atmosphere might have been relevant to the way radiative transfer was handled in the early 1900s before anyone had access to numerical computation. No GCM radiation model would take this approach to radiative transfer modeling.
Calculating atmospheric transmission is the easy part. What Miskolczi fails to do is calculate is the transfer of radiation through the atmosphere, i.e., the upward and downward atmospheric emitted radiation – that is the essential radiative transfer needed to define the greenhouse effect.
What Miskolczi should have done is to keep the calculated flux going out to space that was transmitted through the atmosphere after being emitted by the ground surface. This is the ground surface contribution to the outgoing LW flux (and forget about the greenhouse optical depth stuff). Next, he should compute the flux emitted upward by the first atmospheric layer, and calculate the fraction of that flux that is transmitted out to space. Then do the same for layer two, three, . . . all the way to layer N=150. Upon summing up all of the layer-by-layer flux contributions, he then would have calculated the total outgoing LW flux.
For these calculations, it is necessary to have specified an atmospheric temperature profile. If this temperature profile was representative of the global mean temperature profile, and if representative global mean profiles for water vapor and the other greenhouse gases were used, including some adjustment for the fact that global cloud cover is about 50% – had Miskolczi done all this, he would have gotten about 240 W/m2 for the outgoing LW flux at the top of the atmosphere. Further, if he had used a temperature of about 288 K for the ground surface, the LW flux emitted by the ground surface would have been about 390 W/m2. This would result in a difference of about 150 W/m2 between the ground and TOA fluxes, which represents the strength of the current terrestrial greenhouse effect.
The downward atmospheric flux incident on the ground surface can be calculated by a similar layer by layer procedure, starting from the top of the atmosphere where the starting LW flux from space is zero.
Instead of calculating these atmospheric fluxes, Miskolczi instead assumes that the downwelling atmospheric flux is simply equal to the flux (from the ground) that is absorbed by the atmosphere. He then goes on to further assume that the ratio of the downward emitted atmospheric flux (at ground) to the upward emitted flux (at TOA) is simply equal to 5/3!
There is absolutely nothing in this paper that is remotely useful for reaching a better understanding of either the greenhouse effect, or of radiative transfer in general. A total waste of time to read.
Andy, this analysis is very helpful.
It appears you have failed to read Miskolczi’s original papers, but criticize his subsequent simplifications and summaries accusing him of not having done the earlier detailed work.
From my reading, he has done most or all of the steps you propose and accuse him of not doing. You have interpreted him absolutely backwards. He started with the detailed quantitative calculations based on original data. Then from the results he worked to discover simplifications.
This is generally summarized in Zagoni’s presentation.
AL1: “I don’t know how exactly he performs his line-by-line spectral interval calculations”. See:
F.M. Miskolczi et al.: High-resolution atmospheric radiance-transmittance code (HARTCODE). In: Meteorology and Environmental Sciences Proc. of the Course on Physical Climatology and Meteorology for Environmental Application. World Scientific Publishing Co. Inc., Singapore, 1990.
For performance of HARTCODE see Zagone slides 16-19.
AL2: “For these calculations, it is necessary to have specified an atmospheric temperature profile.”
DONE: Miskolczi went to the original radiosonde data and recalculated the temperature profile. See Zagoni’s summaries slides 16-21.
In doing so, he found significant errors in USST76. See Zagoni slide 67.
There were major errors in water column. See Zagoni Slide 68
AL3: “spectrally integrated optical depth for the entire atmosphere”
You totally misread him. He specifically does the vertical integration, not a lumpsum atmosphere.
AL4: “Next, he should compute the flux emitted upward by the first atmospheric layer, and calculate the fraction of that flux that is transmitted out to space. Then do the same for layer two, three, . . . all the way to layer N=150”
Again Miskolczi has done the detailed integration, calculating the radiation at each layer from layers above and below.
“The atmosphere up to 61 km was stratified using 32 exponentially placed layers with about 100 m and 10 km thickness at the bottom and the top.”
Exponential spacing should give better results than linear layers.
See Zagoni slide 30. Each dot is the integration over a TIGR integrated across these 32 layers.
Then in the latest paper, he expands from 32 layers to 150 layers.
““the true greenhouse-gas optical thickness” computed from the Planck-weighted spectral hemispheric transmittance using M=3490 spectral intervals, K=9 emission angle streams, N=11 molecular species, and L=150 homogeneous atmospheric layers.”
AL5: “For these calculations, it is necessary to have specified an atmospheric temperature profile.”
He went way beyond this, calculating profiles for differing latitudinal regions for 11 groups and 228 profiles. See Zagoni slides 18-21.
AL6: “representative global mean profiles for water vapor and the other greenhouse gases were used,”
He calculated for ALL significant greenhouse gases, not just water vapor co2, pressure and temperature along the profiles
See Zagoni slide 28 for water etc.
AL7: “Further, if he had used a temperature of about 288 K for the ground surface, ” –
Done: See Slide 28 where Miskokczi calculates from 230K-310K for three different radiation regions and total.
See Slide 29 for calculating up and down flux as function of surface temperature. Each dot is a separate atmospheric profile. Then he fits curves to those results.
AL8: “the LW flux emitted by the ground surface would have been about 390 W/m2. ”
See Slide 30 – calculated for 230K to 310K
AL9: “Miskolczi instead assumes that the downwelling atmospheric flux is simply equal to the flux (from the ground) that is absorbed by the atmosphere”
False and backwards.
AL10: “his greenhouse optical thickness number is a useless quantity that is lacking even academic interest.”
Miskolczi calculates the total optical depth quantitatively across all 150 layers for all greenhouse species, based on original data.
See definition Slide 32
Miskolczi then compares his theoretical value from his simplifying assumptions to the original data based optical depth. See slide 53.
Miskolczi then calculates from NOAA data annually taking the variations for the last 61 years, Slides 58-61.
Note that the average optical depth over all 61 years of NOAA data is 1.868.
For Clouds See Slide 61 Miskolczi
“Below the cloud layer there is radiative equilibrium, over the cloud there is clear-sky greenhouse effect.”
See Zagoni slides 69-71 with vertical profiles for H2O, CO2, O3 components from ground to TOA.
Note: “K=9 emission angle streams,”
Not only does he do the full integration from original data across 150 layers, he also calculates for 9 angles, not just vertically.
Weighting: He weights by Plank distribution, not flat.
AL11: “goes on to further assume that the ratio of the downward emitted atmospheric flux (at ground) to the upward emitted flux (at TOA) is simply equal to 5/3!”
You read it backwards. From the data he fits the curves. From those he makes simplifying assumptions to arrive at the 5/3.
Slide 72 is his simplified conclusions from the detailed quantitative calculations from original data (NOT his a priori assumptions.)
AL12: “There is absolutely nothing in this paper that is remotely useful”
I can find hardly anything in your post that is useful.
Miskolczi has already performed far more detailed original calculations in far greater depth and variation than you have proposed.
You have read him exactly backwards and then trashed his paper with no understanding of his method or detailed quantitative development.
Please withdraw your comments and start over by actually reading Miskolczi and Zagoni from the beginning on through.
So was this helpful too, Judith?
I’ve noticed a tendency of certain researchers not to bother actually even reading papers that they are ideologically predisposed to reject. And so it continues……
Just how many climate researchers have read Lindzens fairly reasonable scientific points? The pessemists sure as heck cannot effectively debate him…..he wins every time!
It took about a day (and a long time away from an university environment) for the full meaning of this to sink in.
Ho hum, another boring useless piece of nonsense. If the topic of the paper wasn’t skeptical of AGW (?assuming it is such?) , the contents would pass by, unnoticed and ordinary.
What seems remarkable is the lack of *even* a ‘hypothetical’ contrarian argument. There is something deathly about this absence of credible opposition. It’s a very complicated topic and even a vague indication of the future trend is an accomplishment.
Don’t suggest that the lack of a credible counter argument “proves” the veracity of climatology. Rather the warmists have terrorized and spooked away all the opposition. For example, Currey gets herself labeled a ‘heretic’ in SciAm.
Show me credible criticism of the AGW hypothesis and I will feel more confident that the results are balanced. Dragging out a shoddy piece of criticism and flogging it in public doesn’t make the AGW hypothesis believable IMO. It indicates that opposing informed opinion has been savagely suppressed. YMMV.
> It indicates that opposing informed opinion has been savagely suppressed.
Does it? Or is it that “opposing informed opinion” is nonsense?
How many flat-earth papers do you read in “Journal of Geodesy”? How many creationist papers do you read in evolutionary biology journals?
Or is it that “opposing informed opinion” is nonsense?
Quite so. It is forbidden to question dogma.
I guess geodesists and biologists are dogmatic because they “suppress” flat earthers and creationists. Darn them!
CO2 is a secondary GHG. Water vapor is a greater factor.
More importantly both CO2 and H2O increase the lapse rate. (Yes that means to increase the temperature at the surface. I.E. ‘Greenhouse Effect’)
Thereafter Chicken Little clucks out “The CAGW!! The CAGW!!!!!!!” and doesn’t bother to consider further.
Increased global warming —> Increased lapse rate.
Increased lapse rate –> Increased convection,
—> increased turbulence
—> early onset of convection +turbulence
Increased CO2 –> Increased biological response.
(You can pretty much bet the farm that plants and animals will swiftly adapt to exploit the opportunity of more abundant and valuable ‘trace gas’ CO2 and follow on consequences. This biological response is in the order of years, NOT thousands of years. )
The adaptations to increased CO2 levels have already been evolved and revisited multiple times in the past. They are nascent, primed and rolling out at this very moment.
The increase of CO2 helps to set in motion multiple dynamic processes.
Which way it goes and switches and goes and switches and goes and switches and goes … ????
A fortune teller could provide an “informed opinion”. … The CFD OTOH merely describe the opening movement. Beyond that first linear opening fluctuation, the models are insensitive and blind. They do not predict, nor anticipate the alteration in their own design.
So it’s warming. …. What comes next?
What comes next is crucial and changes everything.
… and what happens after that “next” occurs is equally crucial and changes everything afresh. … and so on and so forth
From the guarded comments on this blog (i.e. silence … implied “no comment”) the informed opinions are struggling real hard to gain confidence in the opening CFD model.
Throw in the active, dynamically evolving boundary conditions [ocean currents, sea ice, water reservoirs, atmospheric, terrestrial and hydrological chemistry, biological adjustment and adaptation + other boundary qualities which are as yet unknown and/or unappreciated] and there is no way of predicting where and how things go when it breaks from the ‘linear’ trend.
The whole structure is so poorly modeled and understood that not even the initial trend can be strongly demonstrated.
I don’t intend to say that the trend doesn’t exist. Rather I emphasize that the underlying model used to describe/predict the trend is poorer than the faint anticipated trend signal itself.
And you want me to accept that underlying scientific structure for AGW as being robust? Maybe you wish that I should write a paper claiming “creationism” is primary and try to publish it in The Auk
You forgot one thing – water vapor is a feedback, not a forcing. Take away the CO2, and water vapor alone won’t keep the planet warm – in fact, it will condense out very quickly. Bye-bye, habitable planet.
Sure, plants can adapt to more CO2 – whether or not those are the relatively few plants our entire agricultural productivity depends on is a big question. You may look at a southeastern US entirely overrun by kudzu and claim “see, plants do fine with more CO2”, but most others wouldn’t be so sanguine.
Kudzu is edible. It would probably support a bunch of cows.
X amount more CO2 may make good plant Y grow Z% better. It may also make bad plant W grow 50% better. Is that a win?
Raving also overlooked the impact of warming on the hydrological cycle. Even if total precipitation stays the same, its frequency and intensity may be different, which could wreak havoc. Likewise, rain isn’t the same as snow.
I would say none of that is predictable.
CO2 is a secondary GHG. Water vapor is a greater factor
Water vapor is only a factor for climate, not for climate change. Unless water vapor changes it has no relevance to climate change. Currently no evidence has been found for significant change in water vapor.
CO2 is relevant to climate change because the anthropogenic component of it doubles every 32.5 years. This is due in part to the Malthusian exponential population growth, and in part to the the exponential growth in deployment of technology by each individual on the planet.
The evidence for significant change in atmospheric CO2 level can be seen in the Keeling curve, by all except ostriches.
Currently no evidence has been found for significant change in water vapor.
Well, that was uninformed of me. For the record let me retract that in favour of the fifth paragraph of my December 22 post. This quotes Trenberth et al 2007 as saying “The strong relationships with sea surface temperatures (SSTs) allow estimates of column water vapor amounts since 1970 to be made and results indicate increases of about 4% over the global oceans, suggesting that water vapor feedback has led to a radiative effect of about 1.5 W m 2 (Fasullo and Sun 2001), comparable to the radiative forcing of carbon dioxide increases (Houghton et al. 2001).”
Convection cannot work by itself!
Centrifugal force has to be the main carrier for convection to raise from the planets surface.
This is where science has been hitting brick walls in not understanding the energy that this planet creates on it’s own.
Joe, centrifugal force has NOTHING to do with convection in the atmosphere. In addition, centrifugal force is the force BY the object in cirular motion ON the object creating that circular motion. Centrifugal force is not trying to ‘throw’ the atmosphere away from the earth due to earth’s rotation.
There are 3 physical energy forcings. 2 exert to the planet’s surface and one to the atmosphere or even the Earth’s crust for that matter.
Electromagnetic field(gravity) and atmospheric pressure exert down to the planets surface and beyond. And if we did not have this other force exerting out, we would not have the enery to rise from the planets surface. We would still be a pile of chemicals. Centrifugal force exerts outward. If there is a barrier, such as the planets crust, then the accumulated gases are compressed into a liquid(stored energy). Centrifigal force is directly tied with the speed of planetary rotation. As the planet slows, the compression relaxes and energy is released still after 4.5 billion years.
Joe, centrifugal force has NOTHING to do with convection in the atmosphere.
POV. How about Coriolis force? Would you say that has nothing to do with convection in the atmosphere?
Centrifugal force has to be the main carrier for convection to raise from the planets surface.
This is where science has been hitting brick walls in not understanding the energy that this planet creates on it’s own.
Not following. Are you saying people don’t understand how the Hadley cells work?
Scientists pick the most stupid time to announce that this is one of the hotest years ever. Before the end of the year and in the middle of a major cold spell. Governments have gone on what scientists have predicted for the future on their preperations of not preparing for snow. PEOPLE ARE DYING!!! How many lawsuits do you think are going to be generated by this?
If this cold keeps going, by spring you would not want to admit to being a climate scientist.
PEOPLE ARE DYING!!!
Beats family planning.
Where is this government that failed to prepare for snow in November and December?
There are a number of aspects about the greenhouse effect (and the radiative transfer involved) that are a bit subtle. One of these is the question of why does the stratosphere cool while the ground and troposphere warm in response to increased CO2.
The reason for this non-intuitive behavior arises because of the spectral non-grayness of the gaseous opacity, i.e., the LW window. If the atmospheric opacity where spectrally uniform, there would be no cooling of the stratosphere. Or, as happens with crude radiative transfer models which use spectrally averaged absorption across the spectrum, such models cannot get the stratosphere to cool as greenhouse gases are increased.
In a radiative greenhouse, as atmospheric opacity is increased, the temperature difference between the top of the atmosphere and the bottom of the atmosphere increases. However if the solar energy input remains fixed, the temperature at the top of the atmosphere (from where radiation is emitted to space) must also remain fixed, even as the surface temperature is increasing. In the terrestrial greenhouse, as CO2 increases, the temperature differential between the top of the atmosphere and the ground will increase. But with the spectral window region available, the stratosphere can keep getting colder and colder without upsetting the solar-thermal energy balance because addition thermal flux from a warmer surface can go directly to space and thus maintain the global energy balance. If a climate model does not show stratospheric cooling in response to increased CO2, it needs to upgrade its radiative transfer modeling to incorporate spectrally resolved radiation.
Another aspect of atmospheric radiation that seems to produce misunderstanding is the nature of gaseous absorption. The GHGs only absorb (and emit) radiation at their characteristic spectral line positions. Thus N2 and O2 don’t directly interact with thermal radiation. (They do produce line broadening by colliding with H2O and CO2 molecules while they are trying to radiate. Why then does an air parcel at a higher temperature radiate more energy than an air parcel at a lower temperature if they both have the same number of GHG molecules, and these GHG molecules can only radiate at their fixed wavelengths?
This question does not have a simple answer. The answer is related to the population of the different rotational and vibrational energy states of the GHGs as a result of collisions incurred with other molecules in local thermodynamic equilibrium at the local temperature T of the air parcel.
It is no doubt easier to accept that a solid surface at some temperature T will radiate according to Planck law (sigmaT^4) until the emitted radiation matches the input radiation to that surface (thus establishing an equilibrium temperature). But what about an air parcel with, say 390 ppm CO2, at temperature T. How much is that supposed to radiate?
To get a better feel for this, we can invoke Kirchhoff’s radiative law in an isothermal cavity (at temperature T) with a viewing pinhole through which the radiation in the cavity can be observed. The emerging radiation is Planck radiation (at temperature T) no matter if the cavity is empty or filled with some greenhouse gas. Maintaining the condition of isothermality is not trivial. It means that every possible transition for absorption and emission must be precisely balanced, otherwise some part of the isothermal cavity will either be heating or cooling. Full thermodynamic equilibrium is achieved when everything within the isothermal cavity is at the same temperature and all emissions and absorptions precisely balance each other (as averaged over some finite time period).
We can perform a radiative transfer thought experiment for the air parcel in the isothermal cavity. In an empty cavity, the Planck radiation, B, emerging from the pinhole comes from the back wall (B=sigmaT^4). With the air parcel within the cavity, and in the way of the light path, there will be a transmitted component B exp(-TAUv) emerging from the pinhole, where TAUv is optical depth (molecular cross-section at wavelength v, times the number of molecules per unit area) of CO2 at the wavelength v. There will also be a component, E, that is emitted by the air parcel. Since the total radiation emerging from the pinhole must be equal to B, it follows that E = B [ 1 – exp(-TAUv) ], which is the Planck radiation B times the absorptivity of the air parcel.
If this air parcel is removed from the isothermal cavity and placed into the context of the real atmosphere, it will no longer be in full thermodynamic equilibrium, but in what is called local thermodynamic equilibrium – which is close enough to ensure that the thermodynamic population of molecular energy levels will be maintained by molecular collisions at the local atmospheric temperature T. The air parcel will then absorb atmospheric radiation according to its absorptivity [ 1 – exp(-TAUv) ], and will radiate according to E = B(T) [ 1 – exp(-TAUv) ] at the local temperature T.
As a further point, atmospheric radiation happens virtually instantaneously. For the given atmospheric temperature profile, surface temperature, and vertical distribution of GHGs and/or clouds and aerosols, the radiation model calculation gives the instantaneous atmospheric radiative heating and cooling rates, including the radiative fluxes going out to space and incident on the ground surface.
The instantaneous radiative heating and cooling rates plus the thermodynamic and advective energy contributions will then serve to redefine the atmospheric temperature profile in time for the next radiative time step in the time marching process of GCM operation.
The greenhouse effect is simply the result of radiative interactions with the atmospheric absorber structure. The difference between the upward flux emitted by the ground surface, and what eventually makes it out to space at the top of the atmosphere is a quantitative measure of the greenhouse effect.
Andy, thanks for the very good description.
This has been brought up before at RC, but there’s a slightly esoteric point of contention: if you pick the right SW absorbers to put in the stratosphere, you can still get stratospheric cooling even with a grey gas; if you add more greenhouse gas, you get more cooling (at a given temperature) balancing the same solar heating. By locally getting rid of more of the absorbed solar, the stratosphere is allowed to cool.
That’s all very well but the stratosphere hasn’t warmed since 1995, the oceans haven’t warmed for the entire length of time there have been accurate instruments measuring them (2003), the outgoing radiation measurements only prove either negative feedback (Lindzen) or that they are in error (Trenberth), the radiosondes back up Miscolskis theory, not yours, and the “missing heat” remains elusive, (the nonsensical guess that it somehow bypasses the surface and goes into the deep ocean being more laughable than scientific).
The upshot is, it is not the physics you think you know but the physics that remain neglected that need to be considered rather more. And the starting point for that is the realization that your model is totally inadequate for the task…. Not exactly an earth shattering realization considering the utter magnitude and sheer difficulty of the task. When will we hear less of the theory and more of the comparison with unambiguous observations? You don’t need to make a temporal forecast; getting something spatially correct would be a good start!
The Stratosphere hasn’t cooled I meant :), ie the one true signature of AGW according to the IPCC.
Clearly those measurements are wrong, since the models are supported by the consensus and the consensus in climate science can never be wrong.
After all, the only thing it can be is that CO2 is causing a global climate disruption.
So this means you are in the employ of big oil, or the Koch family, or both, and want your grandchildren to die.
Except for the fact that the stratosphere is not cooling and the troposphere is not heating, your model is great.
Thanks for the description. For a quantitative thermodynamic model of this process, see:
Prediction of the Standard Atmosphere Profiles of Temperature, Pressure, and Density with Height for the Lower Atmosphere by Solution of the (S−S) Integral Equations of Transfer and Evaluation of the Potential for Profile Perturbation by Combustion Emissions
Robert H. Essenhigh
Energy Fuels, 2006, 20 (3), 1057-1067 • DOI: 10.1021/ef050276y
In reply to Michael who said In response to T R C Curtin on December 2, 2010 at 8:53 pm:
I think Judith’s summary of the science is very helpful, but it lacks empirical verification and quantification. Lots of physical effects are valid but very many are of little or no practical consequence. My own submitted paper finds no statistically significant evidence that changes in atmospheric CO2 have any impact on temperature change locally or […]
What is it exactly that needs “empirical verification”?
That there is any statistically significant relationship between changes in atmospheric concentration of greenhouse gases (which is tiny at less than 0.5% of the atmosphere, and growing almost imperceptibly, just 0.4% p.a. in the case of CO2, and 0.0% p.a. in the case of CH4) and changes in global mean temperature. There is no such relationship that I have been able to find using regression analysis, and what little there is, is swamped by changes in atmospheric water vapour, which are clearly the prime mover, not merely a source of feedbacks. Theories unfounded in or supported by evidence are worthless. It is sad but true that the IPCC team in their AR4, WG1, chap.9 (Hegerl & Zwiers et al) abjure any use of regression analysis to determine the relative contributions of non-H2O GHG and atmospheric water vapour (they ignore the latter completely perhaps because it is 90% non-anthropogenic although it is a greenhouse gas) to temperature changes either globally or anywhere on earth.
First I apologize for getting too steamed up in my previous post.
Re: THE STABLE STATIONARY VALUE OF THE EARTH’S GLOBAL AVERAGE ATMOSPHERIC PLANCK-WEIGHTED GREENHOUSE-GAS OPTICAL THICKNESS
Ferenc M. Miskolczi ENERGY & ENVIRONMENT VOLUME 21 No. 4 2010
In Miskolczi’s 2010 Energy/Environment paper, he takes the actual atmospheric profiles for each of the 61 years for which NOAA data is available, and calculates the optical depth, using all greenhouse species, with full atmospheric composition and temperature profiles.
Note that he is using a full Planck weighted total optical depth
ta “that is computed from the Planck-weighted spectral hemispheric transmittance and therefore represents the true spectral feature of the infrared absorption coefficient.”
“Note that this quantity is conceptually different from the Planck mean optical thickness as usually defined for thin gray atmospheres;”
He finds “the variation in the annual mean optical thickness anomaly is largely caused by the H2O, , the linear correlation coefficient between Δt (u) and Δt is 0.9948.” By contrast, the optical depth correlations are: 0.131 for CO2, and −0.494 for the temperature.”
I understand that to be ALL empirical optical depths, without any “unphysical constraints”.
Miskolczi states: “The fact that the virtual change is about four times the actual change is strong empirical evidence that there is a very strong dynamic compensation that stabilizes the atmospheric energy transport process against a potential perturbation by CO2 change.”
This is based on the consequences of the results of optical depth calculations on on the empirical data, NOT on “imposing an unphysical constraint energy constraint”.
PS on clouds Miskolczi assumes:
“that the atmospheric vertical thermal and water vapor structures are implicitly affected by the actual cloud cover, and that the atmosphere is at a stable steady state of cloud cover; the present quasi-all-sky protocol refers to dynamic cloud processes only by implicit assumption.”
In terms of attention to detail, note that Miskolczi even compensates for the variation in atmospheric heating with changes in temperature
by: “subtracting the trend in the top altitude (7.6750×10−4 km/year)”
Note Fig 5. The atmosphere absorption Aa (Su – St) is within 3% of downward atmospheric emmittance Ed.
The primary controversy in his previous papers appears to be when he subsequently simplifies and assumes Aa = Ed. etc. to obtain simplifying assumptions.
I think it would be more useful to explicitly keep as a difference function and to explore these differences between Aa and Ed etc.
Look forward to your reevaluation of the actual variations of the Planck weighted optical depth that Miskolczi finds with the best available data for this 61 year period.
“Andy Lacis summarizes:”
Unless I have misunderstood Miskolczi, I think you have your interpretation reversed from too brief a reading colored by other posts.
See Zagoni Slide 77. Greenhouse Effect in Planetary Atmospheres.
The green dots are calculated from the actual data.
The curves are calculated from his fitting the data and consequent relationships.
The green humped curve f-Ta is the result. From this he interprets that the atmosphere will stabilize around the maximum of that f-Ta curve.
Miskolczi appeals to entropy maximization principles for this. That region has an optical depth of 1.87, which is what Miskolczi finds from all his detailed integrated atmospheric profile calculations.
Zagoni interprets that as the atmosphere is “locked” to that value. Without digging back into Miskolczi’s papers, I understand this statement to be a consequence and interpretation, not an a priori imposed constraint.
Having found the simplifying correlations, he then interprets that stable atmospheric configuration as being a result of entropy maximization. However, all that is at the end of the voyage of discovery from applying HARTCODE.
I also encourage giving some slack for non-native speakers. (i.e.., my Hungarian is atrocious).
Andy already replied in greater detail to Ferenc’s fluff piece
It’s just like G&T…obvious nonsense. Even if you don’t have the background to see the nonsense in his theoretical setup, you can confirm its nonsense by looking at observations (e.g., water vapor changes), Venus, or whatever….
Before jumping to conclusions see my earlier post above responding in detail to A. Lacis.
Please clarify where I have misunderstood or misquoted either Lacis or Miskolczi.
Zagoni provides a summary presentation.
Re: “you can confirm its nonsense by looking at observations ”
See Zagoni Slide 30 showing martian vs earth atmospheres.
He takes the actual atmospheric profile data, then calculates the detailed quantitative Planck weighted optical depth for all greenhouse absorbers, individually for 150 atmospheric layers, including 9 different angles (not just vertical.) What has he left out? What step in Miskolczi’s actual method needs correcting?
(NOT Lacis’ backwards interpretation of what he must have done.)
Andy has hit the nail directly on the head concerning the ultimate point of Miskolczi’s theoretical framework.
The entire basis of Miskolczi’s model is that atmosphere ‘knows’ how to condense water when the atmosphere’s IR optical depth gets to some threshold level. Unfortunately, every single lab experiment concerning the IR absorption of gas phase molecules disconfirms this hypothesis. No experiments concerning molecules that can condense have shown something similar to what Miskolczi claims will happen in the atmosphere. That being the case, why should the atmosphere be different from a tube of IR absorbing gas in the lab?
In that sense, as far as we can tell from highly controllable and reproducible experiments over the past 50 years, what Miskolczi proposes is HIGHLY UNPHYSICAL. More than that it’s nonsensical because there are much less concentrated condensing gases than water that will give you ‘a bigger bang for your buck’ in IR absorption through condensation.
I’m not up to speed on the radiative transfer aspects of this research, but I know the physical basis of his theory makes no sense.
I agree that this is the main thing in Miskolczi’s paper that makes no sense.
maxwell and judith
Thanks for clarifying your concerns.
I agree that optical depth does not condense molecules. I don’t think that is what Mikolczi is saying.
First separate out his detailed quantitative solar (Planck) weighted optical depth evaluation. That shows that the total global optical depth has remained remarkably constant over the last 61 years based on both the TIGR data and the NOAA reconstruction.
Miskolczi then begins to fit curves to the detailed flux data.
From that he finds relationships to make a simplifying 1 D planetary greenhouse model. The important takeaway is that:
1) Miskolczi provides the first quantitative detailed evaluation of global optical depth. See Zagoni slides 58-61
2) Both TIGR and NOAA data provide very similar global optical depths.
3) Optical depth has changed very little over the last 61 years.
4) The magnitude of the global warming effect is not explained by changes in global optical depth.
5) That means we need to look to clouds etc. for the major causes.
6) Miskolczi conducted detailed evaluations of numerous radiative flux parameters in the atmosphere – based on empirical data. See slides 73-76.
7) Miskolczi identified errors in Milne 1922, resulting in an improved 1D global lapse rate model that fits empirical lapse data and surface temperature much better than Milne.
8) He fit the flux parameters and found simplifying ratios between them.
9) From these he developed a 1D planetary greenhouse model.
10) Miskolczi’s two theoretical methods provide very similar optical depths indicating a first level quantitative explanation for optical depth.
11) His modeling compared to highly stable optical depth evaluations suggests that the atmosphere acts in a way that effectively maintains a fairly constant optical depth. See Slides 55, 56 and Slide 77.
There is alot yet to digest in his models. My expectation is that with warming/cooling, the atmospheric profiles /lapse rate and surface temperature will vary. They also impacts the tropic-polar temperature differences and winds. That in turn affects the cloud level and precipitation/ice formation. Those change the moisture profile.
I understand Miskolczi to appeal to entropy maximization as the “physical” description for the atmosphere coming to its new equilibrium configuration. That in turn results in staying near a configuration of maximum optical depth that he found from TIGR and NOAA data. Miskolczi finds a very similar global optical depth from his theoretical model. That suggests that he is on to something.
Yes it needs better explaining, and some refinement. (Real surface absorptivity/emissivity, and Essenhigh’s themodynamic atmospheric lapse rate model.)
From that to develop a pseudo 2D model to with full latitudinal variation rather than assuming the experimental models.
I give him alot of credit for very detailed, quantitative evaluations of the best available.
PS Maxwell. I think Any Lacis read Miskolczi’s paper backwards – assuming his started with his simplifying conclusions rather then the actual detailed development. See my response above.
Having taken a look at the slides you linked in your comment, I still am not convinced. Whatever theoretical relations he seems to compute using whatever assumptions he uses, he is still proposes a physical process that is not observed in controlled, lab experiments.
I think that point matters the most at the moment.
If he can propose something that we can observe in the lab, then maybe it’s a theory worth looking into. Until then, it seems like a waste of time to me.
Sorry for this lengthy post, but I wanted to put all my basic thoughts in order. Perhaps this is helpful also for somebody else.
Here I go through all steps that I consider most relevant without going to smallest details.
The radiation of the sun contains most of its energy at wavelengths that pass with little absorption through the atmosphere to the surface of the earth or to the clouds that stop its progress reflecting much of it back to space. Part of the solar radiation is stopped already in the stratosphere (e.g. UV by ozone) and this is the reason for its high temperature. A fraction is absorbed in troposphere.
The direct radiation would heat the surface of the earth to approximately 255 K without the help of the additional radiation coming from the atmosphere.
The surface of the earth radiates infrared radiation at wavelengths and intensity determined by its temperature. The balance of incoming radiation, outgoing radiation, convection and conduction determines the temperature of the earth. On the average all other factors lower the temperature, only incoming radiation in heating on the average. Direction of convection and conduction varies over time and between locations, but average effect is to cool the surface, because the radiation from the sun is by far the main source of heat to the earth surface and atmosphere. Other sources (heat from the interior of the earth and tidal effects) are minuscule.
The greenhouse gases in the atmosphere (water vapor, CO2 and others) absorb infrared. Each gas absorbs only certain wavelength bands and has some bands where its influence is important. Oxygen and nitrogen do not absorb radiation at visible or infrared wavelengths.
One basic law of physics (Kirchoff’s law of radiation) tells that all matter that absorbs radiation at a specific wavelength also emits radiation at this same wavelength and that the coefficients of absorption and emissivity are equal. The strength of emission depends also strongly on the temperature. The atmospheric gases radiate uniformly to all directions.
That part of radiation from atmosphere that comes back to the surface of the earth raises its temperature up from 255 K.
The heated surface heats atmosphere through radiation, conduction and convection. Lowest layers are heated most by the repeated absorption and emission within the atmosphere, which leads on most of the earth (excluding polar regions) to a large temperature difference between different layers of the atmosphere. The temperature difference becomes so large that the atmosphere becomes unstable and large scale convection results.
The convection sets an upper limit on the temperature gradient. This limit is the typical lapse rate of 5-9 degrees C/km altitude. The actual limit depends on the moisture content of air. The lapse rate is so large because air expands when going up and compresses coming down and because expanding air cools and compressing warms.
The lapse rate is approximately constant up to the altitude where the local conditions are stable without convection, i.e. the lapse rate based on radiation is less than that creating instability. Where this occurs depends on the level of solar radiation, infrared radiation from other parts of the atmosphere and the concentration of greenhouse gases it the atmosphere. The limiting level is tropopause. In the actual atmosphere the tropopause is at an altitude of roughly 10 km and its temperature is about 60 C lower than at the earth surface.
Looking from the space, the earth must radiate as much as it receives radiation. Earth radiates directly from the surface at some limited wavelength bands and from all levels of the atmosphere at wavelengths that are not too strongly absorbed at upper layers. The upper troposphere close to the tropopause is very important in this, because the water vapor and CO2 in these layers block most of the radiation coming from lower troposphere. Also the direct radiation from surface and from clouds is important as temperature affects the intensity very strongly and as this radiation occurs also at wavelengths not blocked efficiently by greenhouse gases.
The whole earth system heats or cools until the total outgoing radiation becomes equal to the incoming radiation. This means that the effective radiative temperature of the earth must be 255 K. The effective radiative temperature is a weighted average of the earth surface and various layers of the atmosphere. This requirement leads to the actual temperatures of the earth and its atmosphere.
The amount of CO2 affects the resulting temperatures by reducing the share of radiation from the earth surface and lowest atmosphere. As the share of the warmest parts is reduced, the temperatures must rise to keep the weighted average unmodified.
What happens to that radiation trapped in the stratophere? There is nothing that can deflect it directly. So, it must be absorbed and pulled around to the colder dark of night to be cooled and released.
Stratosphere is essentially in local radiative balance. It is heated by the sun and by the earth (surface and atmosphere) and cooled by the infrared radiation of its constituents which include also ozone. The temperature is higher, because heating by sun is so strong that the balance requires more infrared emission and this in turn requires higher temperature. Under these conditions an increase in CO2 lowers the temperature, because it makes the cooling emission stronger.
But, Co2 is a heavier gas and 85% is concentrated in the lower atmosphere closer to the planet’s surface.
We have the misconception that there is no ceiling so all the gases generated will escape. This is not the case. From Ice Age to Ice Age, gases build-up and physical changes of salt on the oceans generate more feed back radiation. There are less winds in this period due to more molecules in the atmosphere. After an Ice Age, much of the gases are bled out over the years whihc means less molecules in the atmosphere and more winds.
There are two things: one, several posts have claimed the oceans have not warmed since 2003; and two, I believe none of the explanations of the GHE have mentioned the word (I apologize if I missed it:)
To be fair, they have been included in surface or ground, but I think oceans need a bit of attention.
Does the GHE result in warmer oceans? If so, how? With respect to ocean heat content, what has actually happened since 2003?
David L Hagen,
You are right in stating that I have not gone and read all of Miskolczi’s previous publications. Having read two of his papers was sufficient to convince me that Miskolczi does not fully understand radiative transfer, or the greenhouse effect. For whatever else Miskolczi may be expert in, I did not care to investigate further.
The fact that one has a capable radiative modeling tool in hand (such as the line-by-line radiative transfer code), does not mean that that individual will be able to take full advantage of the model’s capabilities. In my comments I stated that while I didn’t know how he performed his line by line calculations, let us assume that he did that correctly.
The problem is that his “greenhouse optical depth” that he calculates is a quantity that while it may be numerically “correct”, this quantity has no useful application in analyzing atmospheric radiative transfer, or the greenhouse effect. The other problem is Miskolczi imposing unwarranted constraints that the downwelling atmospheric flux is equal to the flux (from the ground) that is absorbed by the atmosphere, and that the ratio of the downward emitted atmospheric flux (at ground) to the upward emitted flux (at TOA) is equal to 5/3! This makes it impossible to perform an objective analysis with his “greenhouse theory” of how the real atmosphere is going to respond to imposed radiative forcings such as increased CO2.
Let me try to describe the situation in terms that you find easier to relate to. Science is without doubt the most dog-eat-dog free enterprise system that has ever existed. Ideas and concepts that are in agreement with the laws of physics are going to survive. Those ideas that are contrary to the laws of physics will inevitably be exterminated. There is no basis for compromise between that which is “correct”, and that which is “incorrect”. Imposing arbitrary constraints, aka arbitrary government regulations on the economy (particularly when these constraints happen to be wrong) does not lead either to better understanding, or to a more accurate prediction of what happens with the climate system when CO2 is increased.
When calculating radiative transfer in the atmosphere, you do not impose arbitrary constraints on any of the fluxes. You take the atmospheric structure as given (temperature profile, surface temperature, water vapor distribution, etc.), and perform the radiative transfer calculations according to the applicable and well established physical principles. Then you look at the results and interpret them accordingly. This is a far more objective approach to take, and one that gives us a more accurate picture of what is happening with global climate.
Andy, please distinguish between Miskolczi’s discoveries of those relationships and his consequent modeling fitting those assumptions to see where they lead.
1) He does NOT “impose unwarranted constraints” – he discovered them.
2) Then he models using that correlation and finds explanations for them.
He does NOT impose those arbitrary constraints. Stop repeating that mantra. Read his radiative calculations based on the raw data.
I AGREE. Miskolczi HAS done so. Please reread the presentation and papers.
I think you have still taken a biased presumption as to what he is doing – you are still putting have the cart he discovered before the horse of his raw data and quantitative absorption calculations.
I am encouraging him to retain the actual empirical ratios and keep the differences in his future developments.
“Miskolczi, on the other hand, acknowledges and includes downwelling backradiation in his calculations, but he then goes and imposes an unphysical constraint to maintain a constant atmospheric optical depth such that if CO2 increases water vapor must decrease, a constraint that is not supported by observations.”
On the contrary, the thesis is supported by the empirical data Miskolczi used and by the tiny trend in OLR since 1974. I don’t think he is so easily dismissed.
There a couple more points regarding Miskolczi’s paper that need further thought and contemplation.
First, consider his assumption (or supposedly demonstrated proof) that the downward directed flux from the atmosphere is equal to the fraction absorbed by the atmosphere of flux emitted by the ground (Ed = Su * A). When there is solar radiation also being absorbed in the atmosphere, not just the ground, it is not easy to spot the fallacy of this assumption. In an optically thick atmosphere it is actually close to being true. But consider an atmosphere where all of the solar radiation is absorbed by the ground, with the atmosphere only supporting a thermal radiation greenhouse. In this case, if the downward flux from the atmosphere were equal to the ground flux absorbed by the atmosphere, this would leave zero thermal flux emitted to space by the atmosphere. (The atmosphere also needs to conserve energy, not just the Earth as a whole.)
The reason this “Miskolczi equality” is close to being true is that in an optically dense atmosphere (the atmospheric temperature being continuous) there will be but a small difference in the thermal flux going upward from the top of a layer compared to the flux emitted downward from the bottom of the layer above. Doubled Co2 is after all only 4 W/m2 of forcing, while the flux emitted by the ground surface is about 390 W/m2, with the down flux from the atmosphere being somewhat smaller. One needs to be careful in not forcing an equality where there shouldn’t be one, lest the baby get thrown out with the bath water.
Whenever somebody claims to have performed detailed radiative transfer calculations on real atmosphere data, be VERY skeptical about the conclusions that may be drawn from such analyses. This is because it is beyond the capabilities of any measurement system to fully (and accurately) measure the entire atmospheric temperature profile, the entire water vapor profile – ground through stratosphere, the entire ozone profile, also the vertical distribution (and radiative properties) of aerosols and clouds. Also, the top-of-the-atmosphere ERBE OLR measurements are not really a measurement of outgoing LW flux (that is impossible to do). Instead, the SW and LW TOA “fluxes” are inferred from theoretical and empirical “angle” models based on inferred atmospheric cloud structure and the observed radiance measurements. Also note that the ERBE inferred fluxes are highly unlikely to coincide with any radiosonde or ground based measurements, and even if they did, they would have incompatible spatial resolution. This is why it is not possible to have a credible set of “closure” measurements to directly “validate” climate GCM performance.
There is no recourse then but to rely on statistical analysis and correlations to extract meaningful information. However, any conclusions, particularly if they do not have a clear physical basis, will be subject to large uncertainties.
On the other hand, radiative analyses performed in the context of climate GCM modeling, have the capability of being self-consistent in that the entire atmospheric structure (temperature, water vapor, ozone, etc. distributions) is fully known and defined. Clearly, the GCM atmosphere is not an exact replica of the real world – consider it an ‘Earth-like’ atmosphere.
This makes it possible to establish physical relationships within the climate system (such as the global warming caused by increasing CO2), rather than having to deduce them from a noisy climate system using incomplete and imperfect measurements that require considerable statistical analysis and modeling input to extract the relevant information.
‘This makes it possible to establish physical relationships within the climate system (such as the global warming caused by increasing CO2), rather than having to deduce them from a noisy climate system using incomplete and imperfect measurements that require considerable statistical analysis and modeling input to extract the relevant information.’
Yes, I think it’s hard for people who haven’t worked with noisy observational data to understand this point. That said, I think it’s the point most strongly made in the context of Miskolczi’s work. His reliance on data of unknown certainty and quality makes the work, however mathematical straightforward, very dubious.
In response to A Lacis on December 5, 2010 at 1:20 am
“This is why it is not possible to have a credible set of “closure” measurements to directly “validate” climate GCM performance. There is no recourse then but to rely on statistical analysis and correlations to extract meaningful information.”
Then why do Lacis et al (2010) and all others in their team NEVER undertake statistical analysis and correlations?
My own exhaustive regressions of changes in temperature as a function of changes in atmospheric concentrations of both CO2 [CO2] and water vapour [H2O] find that despite all the tortuous physics described on this thread, it is [H2O] that best explains temperature change locally, and thence by aggregation and averaging, globally. This should be obvious from the linear upward progression of [CO2] while changes in [H2O] vary non-linearly in step with observed temperature changes which worldwide show a polynomial, i.e. up and down cyclical, trend closely associated with the ENSO, PDO, etc, none of which are related to changes in [CO2]. However plotting MONTHLY levels of [CO2] from 1958 to 2010 shows an interesting correlation with ENSO, because of the impact of that on atmospheric uptakes of CO2 emissions.
The physics adumbrated here has provided no explanation for why NH summer temperatures are inversely correlated with declines in CO2 during the NH summer that are larger (6.14 ppm between May and September 2010) than the annual end-of year increases in [CO2] (1,73 ppm between Decembers 2008 and 2009), any more than NH winter temperatures correlate with higher [CO2] in the autumn and winter. Clearly there are other factors at work, but Hegerl Zwiers et al.(2007) along with Lacis et al. (2010) dismiss them (AR4, WG1, ch.9), although WG1 does admit it can find no link between ENSO and rising [CO2].
T R C, I am quite sure you are handling the statistics properly, but this does not translate into a physical understanding. Have you spent any time looking a bit into this? Both, your results of H2O tracking temperature changes, and NH summer coinciding with a local minma in CO2 are very easy explainable, and are done so in introductory global warming material.
I really don’t understand this rationale of questioning the climate community when it’s clear that the questioner has not even done the most basic of research, or completely misrepresent the papers they address. And we’re the ones being dogmatic…
In response to Derecho64 on December 5, 2010 at 12:31 am:
X amount more CO2 may make good plant Y grow Z% better. It may also make bad plant W grow 50% better. Is that a win? […]
How then does Derecho64 explain why world food production has grown faster than world population since 1960? What is tragic is that people like Derecho64 and Jim Hansen’s protégés Lacis and Schmidt neither know nor it seems care that the end of 2008 atmosphere contained 827.97 GtC, equal to 16.34 GtC per hectare of the total land surface, which falls to only 14.83 if Hansen’s aspiration of max [CO2] of only 350 ppm. is achieved at Cancun. That will reduce cereal and all other crop yields pro rata.
Congratulations to all our physicists here.
In response to chriscolose | December 5, 2010 at 2:45 am | Reply T R C, I am quite sure you are handling the statistics properly, but this does not translate into a physical understanding. Have you spent any time looking a bit into this? Both, your results of H2O tracking temperature changes, and NH summer coinciding with a local minma in CO2 are very easy explainable, and are done so in introductory global warming material.
Well, all the physics here implies a one on one relationship between changes in [CO2] and changes in global temperature. When that is not confirmed by the observations, what of the physics? Answer: the physics is beautiful but trivial and irrelevant.
Moreover all the few statistics on global temperature advanced by the physicists of the IPCC and here are fatally flawed by the non-random nature of the sampling of global temperature by Hadley-CRU and GISS, whereby a “globe” with Africa and other tropical areas absent from the instrumental record in 1900 is deemed to be comparable with a globe post-1950 when they are brought to account.
That is incompetence too close to Madoff for comfort.
Please find anyone here, in the literature, or in the IPCC report that says (or even implied) CO2 is the only thing that matters…once you fail, I will glady accept the apology for the straw man.
Once you are ready to stop making things up, then I will be happy to answer questions you may still have (please give a little effort though to google for 3 minutes)
Chris Colosse makes the following request: “Please find anyone here, in the literature, or in the IPCC report that says (or even implied) CO2 is the only thing that matters…”
On p.665 of AR4 WG1 (executive summary of Chapter 9: Understanding and attributing climate change, co-ordinating lead authors GC Hegerl and FW Zwiers) we read: “Greenhouse gas forcing has very likely caused most of the observed global warming over the last 50 years.” This statement seems to me to come close to implying that greenhouse gases – presumably including methane as well as carbon dioxide – are the only thing that matters in recent climate change, as far as the IPCC is concerned. It unambiguously states that in the view of the IPCC other causes of recent global warming are very likely of minor importance. Does this amount to saying they don’t matter? Not quite, but some readers might certainly understand it that way.
Andy Lacis: | December 5, 2010 at 1:20 am
“radiative analyses performed in the context of climate GCM modeling, have the capability of being self-consistent in that the entire atmospheric structure (temperature, water vapor, ozone, etc. distributions) is fully known and defined. Clearly, the GCM atmosphere is not an exact replica of the real world – consider it an ‘Earth-like’ atmosphere.
This makes it possible to establish physical relationships within the climate system (such as the global warming caused by increasing CO2)”
No. It makes it possible to establish computed relationships within the model. Not only are the models not an exact replica of the Earth’s climate, they do not provide us with anything we can draw conclusions with regarding the cause of global warming, for all the reasons stated in Andy Lacis’ preceding paragraphs.
This is another example of Andy Lacis’ belief that nature follows the laws of physics as interpreted by Andy Lacis, and incorporated into models by his colleagues.
Nature does not follow the laws of physics Andy. The laws of physics attempt to emulate nature, and are under constant revision. Miscolczi’s discovery that 60 years worth of empirical data shows that the atmosphere maintains an almost constant optical thickness is a valuable contribution to our knowledge, and shouldn’t be wrongly dismissed because it doesn’t fit the current global warming paradigm.
Why would we expect the rest of the atmosphere-ocean system to maintain some mythical balance while co2 increases anyway?
In response to chriscolose | December 5, 2010 at 3:45 am |
“Please find anyone here, in the literature, or in the IPCC report that says (or even implied) CO2 is the only thing that matters…once you fail, I will glady accept the apology for the straw man.”
How about “most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations” (IPCC, AR4, WG1, 2007, passim, but especially p.666)?
As you seem to have a real name, email me at tcurtin [at] bigblue.net.au and I will send you a copy of my submitted Regressions paper, which obviously goes into all this at greater depth than is possible in a blog post.
Re: JamesG (undefined NaN NaN:NaN),
So was this helpful too, Judith?
Yes I’d like to hear a response to that question as well and it’s been many hours.
This is not the only time either Ms Curry. I’ve noticed you respond with kind to a comment, but when a cogent counter point is put, silence from you.
I find these threads difficult to follow due to their structure, so hopefully you just miss the counter points? I hope so.
This is what I mean, my comment above should have been in-line with James Gs comment at [ JamesG | December 4, 2010 at 7:31 am]
I respond to posts when they come across my dashboard, so I look at the 30 or so most recent comments, and reply to the extent that I have time to. On technical threads, when I have time, I go back through the entire thread when it is relatively mature (I will be going through the best of the greenhouse thread this morning). I can’t comment on everything, nor do I even try.
Thankyou and please disregard my first 2 paragraphs.
The explanations given here are wonderful, but frankly most skeptics, including myself, do understand all of this and do not disagree with it. What matters are the magnitudes (how much does solar influence, what about Svensmark’s theory, why is S pole sea ice increasing if the globe is warming, etc) and the feedbacks. In the context of everything Colose et al say, feedbacks still need not be positive. If warming speeds up the tropical hydrologic cycle causing more vertical heat dissipation and more descending dry air and changes in clouds, the result could damp out the warming due to GHG. Furthermore, the model representation of the physics is not necessarily as pure as the presentation here. For example, GCMs differ in global mean temperature by as much as 4 deg C (see The Blackboard for documentation of this last year I think) which points to some serious issues and is why alarmists only want to show anomalies with these models. Same goes for absolute precipitation or frequency distributions of precip. Just because the “concept” is right does not mean the models are.
Yes, I will second this. Climate modeling is a very ambitious and worthwhile project, but has been taken over by political and economic goals.
There is no error propagation, see chapter 184.108.40.206 of AR4 :” The above studies show promise that quantitative metrics for the likelihood of model projectionsmay be developed, but because the development of robust metrics is still at an early stage, the model evaluations presented
in this chapter are based primarily on experience and physical
reasoning, as has been the norm in the past.”
The spaghetti outputs are just to fool the eye of the nonexperts that there is an error width, whereas it is just a dispersion of the models according to the taste of the modelers. The dispersion is worse for the temperatures, and you are right, that is why anomalies are the fashion.
One does not make a successful cake by throwing ingredients haphazardly in the oven, and even though the physics inputs are there in the models the outputs show that this is not enough.
In addition I believe the present models have an inherent problem that will be hard to overcome. They are numerical solutions of nonlinear coupled differential equations where the first order approximations are used at initialization . This means that as the time increases in the program, the higher order terms ignored by the approximations will kick in and the results will diverge from the true solutions . This is true for the weather programs, and that is why they are good for a few days only, and it is true for the GCMs used for climate which are just the weather programs adjusted for the time scales of climate.
In my opinion one has to consider true chaotic models , as Tsonis et al have done, or, alternatively, design an analogue computer which in principle should solve differential equations correctly.
Actually everything that happens in nature, does so ACCORDING to the laws of physics. To think otherwise is being self-delusional.
If ever there are observations that APPEAR to be contrary to the accepted laws and concepts of physics (think dark matter, dark energy, quantum entanglement), then that is really big news, and it becomes the central focus for intense investigation until such observation is understood in terms of existing physical understanding, or it requires the development of a new and improved understanding of physics.
Also, studying climate change with climate GCMs is not the only thing that we do. We also analyze an awful lot of climate related observational data. Data analysis probably takes up most of our research time. Observational data is often incomplete, poorly calibrated, and may contain spurious artifacts of one form or another. This is where statistics is the only way to extract information. This is where empirical orthogonal functions along with joint probability distributional analyses are the only means to separate fact from artifact.
As you may well appreciate, observation and experiment are the essentials for verifying and validating our understanding of reality. And climate modeling is specifically formulated on such such observational and experimental results. All absorption coefficients, refractive indices, heat capacities, thermodynamic relationships, fluid dynamics, that are part of the climate model “physics” are all based on laboratory measurements that have been repeated and verified countless times. The concentrations of GHGs and their trends have been precisely measured in the field. What we do is to incorporate all this together in the form of a general circulation climate model by means of mathematics. And this climate model does a damn good job in reproducing the behavior of the terrestrial climate system, including reproducing the global surface temperature trend over the past century, predicting the global surface temperature decrease due to the large Pinatubo volcanic eruption, and understanding the basic climate response to radiative forcings and the role of water vapor, cloud, and surface albedo feedback effects that magnify the direct temperature effect of the applied forcings.
But when you look at what is happening with the global climate, you should be aware that the climate system is very complex. If you look at a few sample years of climate data where you see that atmospheric CO2 has increased, but the global temperature has decreased, and you have heard it said that CO2 causes global warming, it is much too simplistic to jump to the conclusion that climate models don’t work. That is because you have never really looked (and understood) at what climate models predict, nor at what the climate system does.
Both the real world and climate models produce what is referred to as “natural variability” that statistically looks like chaotic behavior. Natural variability arises in the climate system because the climate system processes of evaporation and condensation, as well as dynamical transport of heat within the ocean system greatly overshoot the radiative forcings that try to bring the system to equilibrium. It is only in a global multi-year sense that global energy balance is maintained.
Yes, nature does keep precise track of the global energy balance (as do climate models). Chaotic behavior is by no means random behavior. There is a steadily increasing component (global warming due to GHG increases) upon which are superimposed a more variable component due to small changes in solar cycle energy output, and somewhat uncertain changes in atmospheric aerosols, on top of all of which there is the natural variability component.
In looking at the observational record of global climate change, you need a physical climate model to separate out the global warming component due to increasing GHGs from the natural variability such as El Ninos, La Nina, and longer time scale Pacific and Atlantic decadal oscillations. The observed climate record is too short to convincingly separate out all of the contributing components by statistical means only. That is why you need a climate model to find out what is happening with global climate.
Andy, first of all, thank you for your reply. There are a lot of points in it I want to address, and so this will also be long. Apologies to Judith for hogging the bandwidth. Just to be upfront with you, since you are well known and I use a screen name, I am a qualified engineer with experience in fluid dynamics, metrology and I also have a degree in the history and philosophy of science. I have been studying current climate theory and developing my own alternative theory for the last five years.
Actually everything that happens in nature, does so ACCORDING to the laws of physics. To think otherwise is being self-delusional.
If ever there are observations that APPEAR to be contrary to the accepted laws and concepts of physics (think dark matter, dark energy, quantum entanglement), then that is really big news, and it becomes the central focus for intense investigation until such observation is understood in terms of existing physical understanding, or it requires the development of a new and improved understanding of physics.
This is quite hard to untangle, but I think you are confusing ‘physics’ with nature. Which laws do you think nature followed before man arrived with numbers and concepts of ‘physics’?
Nature follows the laws of nature. Our laws of physics represent our current best shot at characterising the way nature operates.
Dark matter and dark energy are not ‘observations’ (show me the dark matter!) but are logical necessities to save a gravity only cosmological theory.
this climate model does a damn good job in reproducing the behavior of the terrestrial climate system, including reproducing the global surface temperature trend over the past century
As Craig Loehle points out above, the absolute surface temperatures produced by a number of GCM’s vary by as much as 4C. As Willis Eschenbach points on in his recent article, only the UKMET GCM produces realistic temperature variation and rates of change. As Nicola Scaffeta points out, the hindcasts, even after playing around with aerosol forcings don’t follow historical temperature well at all.
But when you look at what is happening with the global climate, you should be aware that the climate system is very complex.
It looks a lot less complex when you stop trying to drive the whole thing with a trace gas and look at the big picture. The 4W/m^2 swings in OLR show that the oceans release more energy when the sun is below it’s average output. El nino more frequently occurs after solar minimum, raising tropical humidity levels, keeping atmospheric heat in as it spreads to higher latitudes. This shows that the oceans accumulate energy on long timescales, and the multidecadal oceanic oscillations show that succesive el ninos can warm the climate more than the interspersed la ninas cool it over those timescales. And vise versa.
The observed climate record is too short to convincingly separate out all of the contributing components by statistical means only. That is why you need a climate model to find out what is happening with global climate.
you need a physical climate model to separate out the global warming component due to increasing GHGs from the natural variability such as El Ninos, La Nina, and longer time scale Pacific and Atlantic decadal oscillations.
I’m very, very pleased to hear GCM’s are now accounting for longer term oceanic oscillations. What is the mathematically quantified figure for the contribution of the positive phases of the Pacific and Atlantic oceans to the warming from 1975 to 2003 you have been able to calculate from your GCM please?
Actually everything that happens in nature, does so ACCORDING to the laws of physics. To think otherwise is being self-delusional.
Well, almost always (> 99.999% of the time). I would put it as being either ignoble or Nobel. (But not Ig Nobel, which differs from ignoble in not taking itself seriously. Key distinction there.)
scienceofdoom has a new post up on Does Back Radiation Heat the Ocean – Part III http://scienceofdoom.com/2010/12/05/does-back-radiation-heat-the-ocean-part-three/. Its a good post.
That is a superb three-part SOD series.
Without trying to distract from its main points, but just out of curiosity, I have one question/quibble about the statement, “the ocean heats the boundary layer via convection”, which may overstate the case slightly. As far as I know, the balance between radiation and convection depends somewhat on latitude, with convection strongly dominant over the warm tropical ocean, but radiation more important at cooler latitudes with less atmospheric water. Even in the tropics, I would ask whether convection alone would suffice, given that the air above the sea surface is close to 100 percent water-saturated, and should remain so if not warmed, and that conduction followed by sensible heat transfer via convection would probably warm rather little. Is there any reason to exclude radiative heating of the boundary layer as an additional means of increasing the ability of air above the surface to accept more water and thereby facilitate evaporative cooling with a consequent convective transport upward of latent heat? Perhaps someone familiar with up to date model results can answer this.
Perhaps surprisingly, the net effect of radiation (shortwave plus longwave) is generally negative (i.e. cooling) all the way to the surface. The equilibrium is between convective warming and radiative cooling, so the radiation just ensures that convection persists.
In the polar night, and even the nighttime in general, there is often convective decoupling, and radiative transfer dominates. When you see a temperature inversion forming with its base at the ground, that is radiative transfer dominating the lower atmospheric heat budget.
Thnx for the link, very interesting and deserving of a closer read.
My initial observations (NOT criticisms)
*Those of us who own swimming pools will need to take a close look at these series of articles based on models. There is a distinct thermal decoupling in the oceans, (and in my pool) quite different to the way the atmosphere behaves.
*I especially found the graph which showed oceans freezing to -15DegC within a few years with solar heating only. Interesting prospect.
*It’s been about 10,000yrs since the end of the last ice age. The mean atmospheric T is ~15DegC. The mean ocean T is ~3DegC. Seems 10,000yrs hasn’t been quite long enough for the atmosphere to heat the oceans.
Anyway, interesting as I said. Will be well worth the read when he finishes the series.
The whole concept is backasswards. The sun warms the ocean, especially when cloud cover drops as it did from 1980 to 1998 as measured by ISCCP. The ocean warms the atmosphere. The rise in co2 is cancelled by the fall in humidity measured by radiosonde balloons, and calculated by Miscolczi.
There’s your global warming.
You’ll be better off with a solar pool heater. I wouldn’t bother running it at night to collect back radiation though.
Not my concept Tall
Being a pool owner, and a large one at that, I’m yet to be convinced that back-radiation will warm any substantial body of water let alone the oceans.
I prefer this version
Sure, I was agreeing with you and reinforcing the point.
Try your link again, it doesn’t work.
learning html tags
Excellent, many thanks.
Just found Daly’s submission to the Oz govt prior o Kyoto.
According to Kiehl & Trenberth 1997, the transfer of incoming_solar_energy_absorbed_by_the_surface to the atmosphere is effected by 3 mechanisms:
1. Conduction (one fifth)
2. Radiation (one fifth)
3. Evaporated water (Three fifths)
All three mechanisms convert to atmospheric kinetic energy, just at different levels. If the surface and atmosphere warm up by the same amount, the same amount of energy is transported into the atmosphere, but the relative strengths of the transport mechanisms change, evaporation increasing at the expense of radiation (people get hung up on the absolutes – both surface radiation and back radiation increase, what we are talking about here is the net radiation) which decreases.
Because the same energy is put into the atmosphere whatever the temperature, the overall lapse rate does not alter.
If there is a negative radiative imbalance at the tropopause due to an increase in CO2 concentration, I would expect this to be balanced by:
1. A positive radiative imbalance at wavenumber 670 in the Stratosphere, plus
2. A warming of the tropopause area,propagating to the surface due to the constant lapse rate, but this is unstable: a warmer atmosphere means increased radiation from the radiative top of the water vapour. So the temperature increase is much less than one would think based on calculations at the Tropopause.
What we are being asked to believe is that an initial 4W/m^2 of radiative imbalance at the Tropopause leads to a 1 degC incease in atmospheric temperature (nofeedbacks). I hope that the necessarily increased radiation from the top of the water vapour, and the increased radiation from the stratosphere have been taken into account, ie that this is the true balance neglecting those pesky and contentious feedbacks…
It translates to 1 C effective radiative temperature at the top of the atmosphere, which by-passes all those things you mentioned. They come into play when you try to get the effect at the bottom of the atmosphere. My understanding is it stays of the same order there, but you do have to consider the stratosphere (small) and lapse-rate change effects.
That was a reply to novandilcosid.
Thanks for the reply, Jim
[In my post I inadvertently omitted the radiation from the surface direct into space, which I assume is essentially constant (the small decrease in the window size as GHG concentration increases being offset by the small increase in intensity due to surface temperature increase).]
The essential point is that if there is no change in albedo, there is no change in the solar energy absorbed by the planet. This solar energy escapes as surface radiation through the window and as conducted heat, NET radiation absorbed by the atmosphere and evaporated water which later condenses in the atmosphere releasing its latent heat.
So assuming no change in albedo, and no change through the window, the sum of the other three components is a constant whatever the temperature.
If we make another assumption, that the relative temperature difference between the atmosphere and the surface stays the same, then the energy conducted is also a constant, meaning that the sum of the net radiation from the surface to the atmosphere and the energy in evaporated water is a constant.
But when the temperature rises we know that the evaporation rate must rise. So as temperature goes up the NET energy radiated from the surface into the atmosphere falls. (Another way of saying this is that for the surface temperature to rise the back-radiation must rise FASTER than the rise in the surface radiation, implying that there must be a tightening of the “window” by a narrowing or by a lowering of the mean height from which the radiation occurs.)
I do not buy any change in the lapse rate UNLESS it can be shown that the amount of energy being pumped into the atmosphere from the surface has changed. [The transport mechanism doesn’t matter – the energy whether radiative, conductive or latent all ends up as kinetic energy in the atmosphere.]
You can do anything you like to the tropopause or stratosphere. These cannot directly affect the surface. The only ways the surface temperature can be maintained at a new, higher level, is for
1. the change in back-radiation to exceed the change in suface radiation, or
2.the absorbed solar radiation to increase, or
3.the temperature differential between the atmosphere and the surface to permanently change to a lower value.
One or all of these is required to offset the necessarily increased evaporation, an increase which is agreed by most (even though there is dissent as to by how much.)
If the models do not do this, then the surface is unbalanced and the result is nonsense. So either:
1. Cloud cover massively DECREASES (why would this happen, given increased evaporation is likely to mean more clouds?)
2. Snow and Ice cover massively DECREASES (oh really? There’s no sign of that for the last degree of warming, and no main-stream scientist is buying the Hansonite catastrophe version of future events.)
3. The atmosphere through some unkown mechanism becomes relatively hotter in relation to the surface. I can’t see that happening or a mechanism by which it would be maintained.
4. The radiative imbalance at the Tropopause translates to an increase in near earth GHGs (since the great majority of back-radiation is from near the surface), greatly lowering the mean height of the back-radiation (thereby increasing the temperature and therefore the intensity).
It seems to me that 4. above is the only logical possibility.
For the Enhanced Greenhouse Effect to work AT ALL therefore REQUIRES an increase in GHG concentration NEAR THE SURFACE.
Note that it is not sufficient to say “the atmosphere has warmed therefore so must the surface by the same amount”. The surface can’t warm by the same amount – it needs to supply extra energy into evaporating water molecules, and this energy has to come from somewhere.
Nova – I wonder whether you might not be failing to distinguish between a transient imbalance and an evenual restoration of a steady state. During the unbalanced state of CO2-mediated forcing (probably amplified by the greenhouse effects of rising atmospheric water), back radiation does increase faster than surface radiation, and the result is a warming. No “tightening” of the window is required, and in fact, total radiative escape via the window probably increases slightly, because the surface is warmer. Once a new steady state is achieved, surface radiation has been increased because of the higher temperature. Increased evaporation and convective latent heat loss also increases, moderating but not nullifying the temperature rise.
One way to think about it is to consider an Earth without greenhouse gases, radiating without impediments to space at a temperature of 255 K to balance solar absorbed energy (we’ll neglect albedo to keep things simple). Now add some CO2. All of sudden, some of the outward radiation is intercepted and returned to Earth. Balance is not restored until the surface warms sufficiently so that radiation ultimately escaping to space at a higher altitude once again balances the absorbed radiation. You can add in a little water and thereby partition the increased heat loss between radiation and convection/latent heat transfer. But the Earth still warms up.
(Not that although radiation to space in wavelengths intercepted by greenhouse gases actually declines as more of the total radiation escapes via the window, that radiation occurs at a higher mean altitude, requiring that all layers below heat up to provide sufficient temperature at that new, colder altitude to permit the requisite level of escape.)
I would like to thank Fred Moolton for his response.
I have been considering two steady state “planets” , one with a doubled CO2 concentration and therefore an increased temperature.
If the albedo is constant and the temperature differential between the atmosphere and the surface is the same:
1. The intensity of surface radiation will be higher
2. The intensity of back-radiation will be higher. [As Dr Strangelove points out below, back-radiation is coming from near the surface, which is why surface radiation LESS surface radiation direct to space LESS back radiation is such a small number – the temperatures are close].
3. Conduction will be the same (same temperature differential)
4. Evaporation will go up (hotter = more evaporation.)
So, since absorbed sunlight = (surface radiation LESS surface radiation direct to space LESS back radiation) + evaporation +conduction
is true in both planets,
difference in (surface radiation LESS surface radiation direct to space LESS back radiation) = – difference in evaporation
ie as surface temperature goes up, evaporation goes up, so necessarily (surface radiation LESS surface radiation direct to space LESS back radiation) goes down. The only way this can happen is if either the “window” widens (doubtful), or the back radiation increases more than the surface radiation, which implies an increased concentration of IR active gases.
It should be noted that the surface cannot maintain an increased temperature without a reduction in net radiation into the atmosphere to counteract the increased evaporation rate.
There is a post discussing the new Koutsogiannis et al paper over at Wattsup , which shows what Lucia has shown for temperatures from the GCMs and for precipitation, that the models do very poorly.
The Koutsoyiannis paper is interesting, but I think WUWT that (and the authors themselves) overinterpreted it. It examined multiple land-based locations and found rather poor correlation with models over the past century. However, most of the data related to the U.S., and the relative inability of models to simulate regional as opposed to global scenarios is well recognized. The models actually performed not badly from 1970 onward, whereas earlier eras including mid-century variations whose attribution is still being debated fared less well.
More importantly, perhaps, global simulations have involved far more data points. Most importantly, ocean temperatures (SSTs) are the most important contributor to global temperature anomalies, given that the oceans occupy about 70 percent of the Earth’s surface and store most of its heat. The paper lacks SST data. Its findings reinforce the need for better modeling of regional, particularly land-based, data, but don’t invalidate the utility of models, despite their imperfections, as a guide in understanding long term global phenomena. A number of interesting threads in this blog have already discussed models, and I expect that there will be more.
IMO, the molecular perspective is the simplest and easiest to understand model of the greenhouse effect for the layman. It is also physically accurate and can easily explain the confusion of G&T. When I first read G&T paper, I immediately saw that it is technically accurate but does not falsify the “atmospheric greenhouse effect” which is a misnomer.
“Back radiation” is not a very useful picture since from a quantum mechanics view, which is similar to the molecular perspective, the infrared photons only travel less than 10 m before they get absorbed by greenhouse gas molecules in the atmosphere. Therefore it is not as if there is a “back radiation’ coming from the upper troposphere hitting the earth’s surface causing heating, the conventional picture of the greenhouse effect.
Acutally the absorption and re-emission of photons are happening all throughout the troposphere. Since earth’s surface has higher temp. than higher altitute troposphere, the surface emits more infrared photons according to the Stefan-Boltzmann radiation law. Low altitude also has denser atmosphere – more gas molecules per unit volume of air. Hence more absorption and re-emission of photons happen in low than high altitudes, and it follows warmer in low altitudes and cooler in higher altitudes.
The temp. gradient or lapse rate in the atmosphere is consistent with radiative heat transfer in quantum mechanics as well as convective heat transfer in classical mechanics. There is no violation of the 2nd law of thermodynamics as G&T claims. Overall, heat is transferred from the warm low altititude to the cold high altitude whether by radiation, convection or conduction. However, adding more greenhouse gas molecules in the atmosphere will slow down the heat transfer as the photons will get absorbed and re-emitted more times before they reach the upper troposphere and eventually escape into space.
So strictly speaking, G&T is correct. There is no way the cold upper troposphere can heat the warm earth’s surface. But greenhouse gases can slow down the cooling of the warm surface causing an increase in temp. If you find this explanation a bit confusing, here is a very good analogy. There is no way a car’s radiator cooling system can heat the engine because the radiator is at 100 C and inside the engine is 1,500 C. It would violate the 2nd law of thermodynamics if heat is flowing from the radiator to the engine. But we all know that if the radiator malfunctions, the engine would overheat. A malfunctioning radiator decreases the heat flow (cooling) and causes engine temp. to rise.
The problem is that our intuitive understanding of heat flow fails to describe radiative heat transfer. Consider the following thought experiment.
A flat plate heated by an external source of energy suspended in empty space heats up to some temperature determined by the Stefan-Boltzmann equation. If we now place a second identical plate with no external heat source next to the first one, it is quite easy to show that the mere presence of the second plate will result in the first plate getting hotter. There is no violation of the laws of thermodynamics, and no violation of the conservation of energy. Yet apparently, heat is “flowing” from the unheated colder plate to the heated one.
Excellent summary, well done Dr S.
Agree, very evocative of the other Dr. S.
Reply to Vaughan Pratt said on Best of the greenhouse
December 10, 2010 at 5:15 am
“Water vapor is only a factor for climate, not for climate change. Unless water vapor changes it has no relevance to climate change. Currently no evidence has been found for significant change in water vapor.”
Not true. NOAA data for 1200+ locations across the USA shows very significant changes in atmospheric water vapour that account by a factor of 5 more than changes in atmospheric CO2 for chnages in annual mean temperatures at those locations, and the same is true in Australia and elsewhere.
“CO2 is relevant to climate change because the anthropogenic component of it doubles every 32.5 years.”
Not true, in fact a lie. The growth rate of the atmospheric concentration of
CO2 has been 0.296 percent p.a since 1958 (check CDIAC for the Mauna LOa data), which means it would take 236 years to double from the 1958 level.
Like all climate scientists you confuse the growth rate of emissions (say 3% p.a on c.10 GtC or 0.3 GtC p.a.) with the growth rate of the atmospheric concentration (i.e. 0.3 GtC p.a is only about 0.3 % p.a. of the 827 GtC in the atmosphere as of end 2009). Go CDIAC for the latest exact numbers.
But to be fair, when NO climate scientists are aware of that distinction I do not expect you to be any the wiser than they are.
Then you said “This is due in part to the Malthusian exponential population growth, and in part to the the exponential growth in deployment of technology by each individual on the planet”
Nonsense. See my ANU seminar paper on Malthus and all that at my website (www.timcurtin.com).
“The evidence for significant change in atmospheric CO2 level can be seen in the Keeling curve”
Yes, at just 0.296% p.a. since he began in 1958. If my stock broker offers me only a 0.3% p.a. return on my portfolio, he’s fired (Madoff offered 20%).
“CO2 is relevant to climate change because the anthropogenic component of it doubles every 32.5 years. …” – Vaughan Pratt
Dear Dr. Strangelove:
With all due respect, the car radiator analogy does not apply to the earth’s surface and atmosphere: when car radiator malfunctions, its temperature increases and car engine’s temperature increases as a consequence, basic thermodynamics. In contrast and for the atmosphere, air temperature above six kilometers is presently cooling, yet the temperature of the surface of the earth is increasing. A totally different phenomenon and can not be compared with car engine. How do greenhouse gases switch behavior from cooling mode above six kilometers to heat trapping mode below six kilometers? Any scientific explanation?
Dr Pratt: you said “.. still assuming the 32.5-year doubling period for anthropogenic CO2, you would find that the climate sensitivity was around 2.7 °C. The dependence of Earth’s surface temperature on changing greenhouse gases is itself heavily dependent on how long you wait before observing the effect.”. Where do you get the 32.5 year doubling period?
The actual observed rate of growth of the atmospheric concentration of CO2 at Mauna Loa since 1958 has been only 0.3 to 0.5 % p.a. and that does not imply doubling after only 32.5 years, far from it (I have given the answer previously here).
For visualization, the word greenhouse is a misleading analogy. Since CO2 only absorbs IR in two narow bands, representing about 10% of the spectrum, it’s like a greenhouse with 90% of the glass missing. You may argue about the percentage due to the wings, but it is nonetheless rather small.
My main question is: Since incoming and outgoing radiation is a nearly constant, fixed amount, how much CO2 does it take to absorb all of the available radiation? According to some sources, half the IR is absorbed with as little as 80 ppm of CO2. The remainder is absorbed and diminished logarithmically till most all of it is absorbed by the time the concentration reaches 250-300 ppm. You can argue the details, but at some point an equilibrium has to be reached.
Why does there need to be an “atmospheric greenhouse”? Water has a high specific heat. It heats up in the day and cools slowly overnight, not radiating all its absorbed energy immediately the sun goes down.
If, as I read, the ice measurements show that CO2 rises several centuries after temperature I would have thought that the game is over. Empirical evidence rather than models and theories.