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The 2nd law of thermodynamics and the greenhouse effect

Posted on 22 October 2010 by TonyWildish

Skeptics sometimes claim that the explanation for global warming contradicts the second law of thermodynamics. But does it? To answer that, first, we need to know how global warming works. Then, we need to know what the second law of thermodynamics is, and how it applies to global warming. Global warming, in a nutshell, works like this:

The sun warms the Earth. The Earth and its atmosphere radiate heat away into space. They radiate most of the heat that is received from the sun, so the average temperature of the Earth stays more or less constant. Greenhouse gases trap some of the escaping heat closer to the Earth's surface, making it harder for it to shed that heat, so the Earth warms up in order to radiate the heat more effectively. So the greenhouse gases make the Earth warmer - like a blanket conserving body heat - and voila, you have global warming. See What is Global Warming and the Greenhouse Effect for a more detailed explanation.

The second law of thermodynamics has been stated in many ways. For us, Rudolf Clausius said it best:

"Heat generally cannot flow spontaneously from a material at lower temperature to a material at higher temperature."

So if you put something hot next to something cold, the hot thing won't get hotter, and the cold thing won't get colder. That's so obvious that it hardly needs a scientist to say it, we know this from our daily lives. If you put an ice-cube into your drink, the drink doesn't boil!

The skeptic tells us that, because the air, including the greenhouse gasses, is cooler than the surface of the Earth, it cannot warm the Earth. If it did, they say, that means heat would have to flow from cold to hot, in apparent violation of the second law of thermodynamics.

So have climate scientists made an elementary mistake? Of course not! The skeptic is ignoring the fact that the Earth is being warmed by the sun, which makes all the difference.

To see why, consider that blanket that keeps you warm. If your skin feels cold, wrapping yourself in a blanket can make you warmer. Why? Because your body is generating heat, and that heat is escaping from your body into the environment. When you wrap yourself in a blanket, the loss of heat is reduced, some is retained at the surface of your body, and you warm up. You get warmer because the heat that your body is generating cannot escape as fast as before.

If you put the blanket on a tailors dummy, which does not generate heat, it will have no effect. The dummy will not spontaneously get warmer. That's obvious too!

Is using a blanket an accurate model for global warming by greenhouse gases? Certainly there are differences in how the heat is created and lost, and our body can produce varying amounts of heat, unlike the near-constant heat we receive from the sun. But as far as the second law of thermodynamics goes, where we are only talking about the flow of heat, the comparison is good. The second law says nothing about how the heat is produced, only about how it flows between things.

To summarise: Heat from the sun warms the Earth, as heat from your body keeps you warm. The Earth loses heat to space, and your body loses heat to the environment. Greenhouse gases slow down the rate of heat-loss from the surface of the Earth, like a blanket that slows down the rate at which your body loses heat. The result is the same in both cases, the surface of the Earth, or of your body, gets warmer.

So global warming does not violate the second law of thermodynamics. And if someone tells you otherwise, just remember that you're a warm human being, and certainly nobody's dummy.

This post is the Basic Version (written by Tony Wildish) of the skeptic argument "The 2nd law of thermodynamics contradicts greenhouse theory".

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Comments 51 to 100 out of 288:

  1. #48, Berényi Péter; #49, Kooiti Masuda: TonyWildish is not talking about the emissivity of the gas, but the "effective emissivity" of the Earth. So the whole discussion about Kirchoff's law, etc., has nothing to do with what he's talking about. He's just saying that the Earth will "have a harder time" tossing off radiation at a specific frequency if the absorption coefficient of the atmosphere at that frequency increases. "Emittance is proportional to the product of emissivity (a dimensionless number) and the fourth power of absolute temperature." This is not quite true: the T^4 law relates to the total power integrated over all frequencies, in a case when there is no frequency-specific filtering (like absorption lines): this doesn't apply to cool gases, which have line spectra. In these situations, what is more relevant is the Planck distribution, which is multiplied with the absorption spectrum to get the emission spectrum. Maximum entropy production: I am not very familiar with this "principle," and have no clear reason to believe in it. The only other time I've heard of anyone trying to apply it to atmospheric processes was when Miskolczi was trying to disprove the possibility of the greenhouse effect. I didn't believe it then, and I have no reason to believe it now.
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  2. Berényi - Are you arguing that the climate will (by virtue of many degrees of freedom) increase entropy production in some fashion in order to avoid raising temperatures? Do you have any evidence for such an assertion? Note that if a system could reach a more entropic state by reordering internal components/relationships, but those internal elements would require a less entropic (more ordered) state, local entropy will win out and the system entropy will be the product of the local (internal) entropies. Local effects (more ordered cloud formations, less uniform water vapor distributions, etc., that you have suggested in the past) that are not locally high entropy will not occur. In short, the system is the product of the components, not the other way around. And quite frankly a warmer planet with a higher effective photosphere for portions of the emission spectra is the most entropic solution - at least, according to and supported by the data.
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  3. Berényi: I am not an expert on non-equilibrium thermodynamics. My main exposure to this MEP claim has been through Miskolczki's claim that the MEP ruled out any possibility of the enhanced greenhouse effect at all. I spent some time trying to find out what this meant, but it eventually became clear enough to me that Miskolczki was also not an expert in non-equilibrium thermodynamics, and was using this principle, that he did not fully understand, to counter well-known physics that everybody understands. This seems to me not to be the most prudent way to arrive at an understanding of phenomena. Usually, one is better advised to try to extend one's understanding from things well known to things less known.
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  4. #52 KR at 02:56 AM on 26 October, 2010 Local effects (more ordered cloud formations, less uniform water vapor distributions, etc., that you have suggested in the past) that are not locally high entropy will not occur What you are effectively saying is hurricanes, supercells or tornadoes (with their more ordered cloud formations, less uniform water vapor distributions, etc.) are impossible. I don't think you mean it. Although the moderator was kind enough to delete it once, I give it another try. MEP is nothing fancy, really. The underlying principle is the same as for water flowing downhill; it simply follows the steepest gradient available. Note it says a bit more than the 2nd law, which only states water would not flow spontaneously uphill. In systems like this local entropy fails to win out, somehow. Think about it.
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  5. nealjking "I am not an expert on non-equilibrium thermodynamics." you're in good company, I don't think you'll find many experts on non-equilibrium thermodynamics around, let alone on the MEP principle. As with the 2nd law of thermodynamics (just a reminder, it's the topic of this post) you'll find, instead, a lot of misuses. Apart from Miskolczki "theory", there's really no contraddiction between an increased GHG effect and the MEP principle. A carefull look at section 3 in Ozawa et al. 2003, and fig. 5 in particular, should make it clear.
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  6. Berényi - Thunderstorms and hurricanes are excellent examples of increasing local entropy, not decreasing it as you claim, they reduce order. A small turbulent variation in updrafts can trigger a thunderstorm, tipping a temporarily ordered system downslope. Pre-storm states are more ordered, with warm wet air present - a thunderstorm lifts and condenses approximately 5×10^8 kg of water vapor. Hurricanes do much more. The result is higher entropy, more disorder, less concentration of energy. What you have argued is that large scale fractal patterns of water vapor, or cloud formations of some kind, would form as part of local variation within the degrees of freedom of the climate system. Large scale patterns of water vapor (big enough to change the climate, certainly) would require long term persistent order to exist. That's a widespread, persistent low entropy system, and you have presented no evidence for such to exist. Your example of thunderstorms and hurricanes does not support your theory; quite the contrary. More to the point: Ozawa et al 2003, as Riccardo points out, indicates that "turbulent fluid systems adjust themselves to the states of maximum entropy production". Assuming that this is so (and it seems a reasonable hypothesis), the climate system is already adjusted to the state of maximum entropy production. Your hypothesis that the climate will adjust to increase entropy and avoid warming fails to consider this - that it's already adjusted in that fashion, and that this max entropy production is part of the existing climate and climate feedbacks. Maximum entropy production won't suddenly switch on in response to climate forcings - it's already there, already part of the system, already part of the climate sensitivity. It certainly won't kick in abruptly to save us from greenhouse gas heating.
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  7. #54, Berényi; #55, Riccardo: Looking briefly at Ozawa, I notice again and again the phrases: "the hypothesis of MEP," "that might be applicable." Why would I want to construct an understanding of the 2nd law on the basis of something that looks rather speculative?
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  8. nealjking and indeed you can't. First, the MEP principle says other things than the 2nd law; it says that a system out of equilibrium will follow the path that maximises the entropy production rate. Note that it does not define the final equilibrium state, which (apart from metastable states which might occur) is still given by standard thermodynamics; it just tell us the path toward it. Second, it aspires to be a principle and hence it's not demonstrated; only time will tell if it really is a general principle or if it has a limited range of validity. It is a very interesting topic, whose consequences are yet to be unveiled. Unfortunately, it currently does not add much to our knowledge of the final fate of our planet, so neatly given by standard thermodynamics.
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  9. Riccardo - So, the MEP principle doesn't affect the thermodynamic end stateto, but simply says that systems will tend to move to that state as quickly as possible? Berényi - If Riccardo is correct, this means that the MEP principle you brought up has zero effect on the equilibrium temperature change for various forcings, only (if the MEP hypothesis is true) upon the speed (time lags) at which the climate moves there.
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  10. * state *
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  11. KR very much like the equilibrium state, i.e. that of maximum entropy, in statistical thermodynamics can be defined as the most probable state, the maximization of the entropy production rate may be thought as defining the most probable path toward equilibrium. I'm not an expert on non-equilibrium thermodynamics and I can't tell if the MEP path is always the fastest possible. In simple systems I guess it probably is, it's not obvious it will be so in general.
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  12. #59 KR at 07:53 AM on 26 October, 2010 If Riccardo is correct, this means that the MEP principle you brought up has zero effect on the equilibrium temperature change for various forcings, only (if the MEP hypothesis is true) upon the speed (time lags) at which the climate moves there Wait, I can see a conceptual confusion here. The climate system is never in thermodynamic equilibrium, not even close to one and the MEP tells nothing about the path to be taken there either. It's in a steady state, which is a completely different thing altogether. In this state a pretty stable stream of energy flows through it, arriving as low entropy sunlight and (part of it) leaving as high entropy thermal IR radiation against the cosmic microwave background. So there is also a constant rate of entropy production. In fact it is not really constant, just a target value actual entropy production tends to fluctuate around in a scale invariant manner. It is much like sandpile avalanche dynamics in this respect. If you change the system by increasing baseline IR opacity of the atmosphere a bit, I have already shown you it decreases entropy production rate (along with increasing average surface temperature) if all else is held unchanged. You can depict it as a landscape defined over a phase space of climate states by the entropy production rate function. MEP means the climate state tends to linger around a peak. As soon as baseline IR opacity is increased by a small quantity, the landscape gets rearranged somewhat. If there is a maximum entropy production principle at work indeed, for a neutral feedback you need the same climate state to be found right at a peak on the rearranged landscape, which is extremely unlikely. All other positions would involve some negative feedback and there is no room for a positive one at all. Of course the MEP is only a local constraint, meaning all sufficiently small changes of the climate state relative to the actual one tend to decrease entropy production rate. It does not mean there are no higher peaks at all along the landscape, accessible only through deep valleys (that is, not accessible under normal circumstances). With an ever increasing baseline opacity of the atmosphere at some point the topological structure of attractors over this landscape may get rearranged (at which point, we have no idea), so as a previously inaccessible peak becomes accessible along a continuous path with an ever increasing entropy production rate (or at least it only needs to jump through shallow valleys). If this happens, a climate regime shift occurs, but it is a highly nonlinear process, inexpressible in the climate sensitivity formalism. It is not clear either if this new steady state would imply higher or lower average surface temperatures (or the same ones with some regional rearrangement). Unfortunately mainstream climate science failed to ask these questions so far, so for the time being we do not have a chance to get proper answers.
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  13. Berényi - I would actually have to disagree about equilibrium states. If a constant input and sink of energy are maintained (sun and the 3 degree K of space), the climate will cycle around equilibrium based on the internal variance of weather. Currently we are moving towards (but have not reached) an equilibrium - but a 'steady-state' system will still reach an entropy balance (dynamic equilibrium) where energies do not change. As Riccardo stated, the MEP indicates the path taken towards equilibrium, or as I understand it entropic balance. That affects the speed of attaining equilibrium, not the final thermodynamic state. Re-reading Ozawa et al: they are indeed speaking of speed (delta) of entropy, not the final thermodynamic states. If you disagree, please point out the sections of the paper that indicate this. You have also not addressed my point here, that high entropy production if correct is already part of the climate sensitivity - it's already incorporated into our knowledge and models of climate behavior.
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  14. Concerning thermodynamics, we have several different levels of knowledge. 1. Equilibrium thermodynamics. We can compare two states of thermodynamic equilbrium of the same system, and tell in which direction spontaneous changes can occur. But this formulation cannot usually describe the processes of the changes which are non-equilibrium. 2. Local thermodynamic equilbrium. While the climate system as a whole is clearly not in a thermodynamic equilibrium, we can define thermondynamic quantities such as temperature in a certain spatial and temporal scale, which is much larger than individual molecules and individual collisions between molecules, but much smaller than the whole atmosphere. If we smooth out the microscopic variabilities, the thermodynamic quantities can be considered as functions of macroscopic space and time coordinates. (This condition does not hold in the upper atmosphere, but acceptable for the troposphere and the stratosphere.) 3. Formulation of non-equilibrium thermodynamics. We can describe the rate of change of entropy in the climate system or a certain subsytem of it as the sum of entropy exchange and entropy production. Entropy production must be positive. There is no other formal constraint at this level. 4. Dynamic steady states in the entropy balance. The climate system can be approximated as a steady-state system which exports as much entropy as is produced within it. The system may actually fluctuate around the steady state. If the external condition changes slowly, the state of the system will drift acoordingly, but it may still be be approximated as a steady state. If the external condition changes too fast, the state cannot be considered as steady. 5. The hypothesis of maximum entropy producition. Under a certain external condition, there is a range of approximately steady states which our system can take. Among them, the state which has the maximum rate (=quantity per unit time) of entropy production is likely to be realized. I think that the items 1 and 2 are shared by effectively all physical climate scientists, and that 3 and 4 are acceptable by the majority of them (though many of them do not conceive them by themselves), but that 5 is held just by a minority among them.
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  15. #63 KR at 13:28 PM on 26 October, 2010 Currently we are moving towards (but have not reached) an equilibrium - but a 'steady-state' system will still reach an entropy balance (dynamic equilibrium) where energies do not change I think you still don't get it. Here is a readable account on MEP (Maximum Entropy Production), SOC (Self-Organized Criticality), including toy models like Sandpile Avalanche Dynamics and FT (the Fluctuation Theorem). Non-equilibrium Thermodynamics and the Production of Entropy Understanding Complex Systems, 2005, 2005, 41-55 DOI: 10.1007/11672906_4 4 Maximum Entropy Production and Non-equilibrium Statistical Mechanics Roderick C. Dewar Critical systems' scaling behavior is well understood in physics. If the majority of climate scientists think climate is somehow different with a very special structure that invalidates general principles, they have to explicate this idea clearly, simple hand waving like in Ozawa 2003 would not suffice.
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  16. BP >If there is a maximum entropy production principle at work indeed, for a neutral feedback you need the same climate state to be found right at a peak on the rearranged landscape, which is extremely unlikely. Correct me if I'm missing something here: is it not possible that the rearranged landscape consists of a lowered local peak, rather than a translational shift of the landscape? In such a case, we would expect a neutral response since we would already be at the local peak. If so, is it not invalid to assume that neutral feedback is "extremely unlikely?"
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  17. #66 e at 18:35 PM on 26 October, 2010 is it not possible that the rearranged landscape consists of a lowered local peak, rather than a translational shift of the landscape? It is certainly possible, but I don't see a compelling reason it should be so. Even for infinitesimally small increases of baseline opacity the transformation the landscape suffers seems to be of some more general form than simple downscaling. But I have not done a full mathematical analysis of the situation yet, it's just an impression. Do you have anything specific in mind? BTW, as I'm peeking into the literature, I see a widespread misconception about MEP-related role of radiative transfer in the climate system in general and about Dewar 2003 specifically. Stephen Mobbs is even enumerating in a presentation among Dewar's results the following proposition: "MaxEnt is equivalent to maximising the mean entropy production rate <σ> due to internal material processes – not including radiation [emphasis mine]" Journal of Physics A: Mathematical and General 2003, Volume 36, Number 3, 631 doi: 10.1088/0305-4470/36/3/303 Information theory explanation of the fluctuation theorem, maximum entropy production and self-organized criticality in non-equilibrium stationary states Roderick Dewar What Dewar actually says is this: "For climate systems there is an additional contribution to σΓ from radiative heating at planetary temperatures, deriving from the internal energy component of Q in equations (9) and (12). This contribution is not taken into account in the purely material entropy production of equation (15), and is in fact ignored in applications of MaxEP to the climate [16, 17]. Again Jaynes’ procedure provides the rationale for ignoring this contribution – radiative heating is reversible and does not contribute to the number of paths W(Airr<λ>) in equation (24). To summarise, in applications of MaxEP to climate systems it is the irreversible, material entropy production that is maximised." It is said in the context of interpreting Paltridge's work on application of MEP on horizontal heat transport (advection) and he just tries to justify why radiation was ignored in that work. Indeed, as long as radiative heating is supposed to be reversible, it does not give a contribution to the number of paths. However, while it might have been a reasonable approximation for the specific problem Paltridge was interested in, it surely does not hold in general. In a semitransparent medium (like air) whenever radiative exchange occurs between two parcels at different temperatures, the process is irreversible and involves entropy production. It may be negligible at the center of CO2 absorption band (at 15 μm) where mean free path of IR photons is small and nearby locations are at almost the same temperature, but as we move to the wings or even to an atmospheric window with no absorption lines at all just the H2O continuum, parcels at vastly different temperatures can get into radiative contact (like hot (-50°C) Antarctic winter troposphere with cold (-80°C) surface). If one is interested in climatic effects or the radiative properties of CO2, ignoring radiation entropy is certainly the most foolish track to take. As soon as we stop treating clouds, snow cover or ocean color (induced by biological processes, determining light extinction with depth) as boundary conditions, but include them as variables in the climate system, entropy production associated with ASR (Absorbed Shortwave Radiation) also enters the game.
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  18. Berényi - I'll emphasize my primary point once more. To the extent (and this appears to be an interesting point of research) that MEP is a factor in climate dynamics, it's a factor not just in forcing deltas but in the state(s) prior to the forcing deltas. Therefore MEP is already part and parcel of the climate sensitivity to forcings. Not a new factor that will jump in, but an existing part of the system dynamics. That means that climate sensitivities to forcings still hold, that those measured 'black-box' sensitivities inherently factor in the MEP effects.
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  19. "Skeptics sometimes claim that the explanation for global warming contradicts the second law of thermodynamics." Do they? I've never ever read that till now. Seems like a great big straw-man to me.
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    Moderator Response: Many of the posts appearing on the home page recently have been posted there to call attention to that same material having newly been created and added to the regular set of "Arguments." You can tell by reading to the end of the home page's post where you will see a green box which, in this case, states "This post is the Basic Version (written by Tony Wildish) of the skeptic argument 'The 2nd law of thermodynamics contradicts greenhouse theory'." Each of those regular Arguments begins with an orange box with a quote and link to a skeptic making that skeptic claim.
  20. mistermack - Google the horror that is "Gerlich and Tscheuschner". They claimed that the radiative greenhouse effect violated the 2nd law of thermodynamics. They were wrong, of course, and their physics were appalling. But their article, published as an editors choice (i.e. not peer-reviewed) in a low impact off-topic journal, got waved about by certain skeptics for quite some time. It was very sad... I shed some tears for the educational system during that time. On the plus side, a lot of people had a chance to learn some basic physics during the arguments, and some of the more competent scientific skeptics, such as Roy Spencer, weighed in on the side of reason and dismissed it.
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  21. mistermack, you should spend some more time at Jennifer Marohasy's site, if you want to find out where that non-strawman came from. Or have a look at the 'Skeptic Links' at this link on Skeptical Science. You could have found that one yourself by searching...
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  22. #69, mistermack: Gerlich & Tscheuschner wrote a paper that claimed that. It got published, but the general consensus is that it went down in flames.
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  23. You haven't read much, then, have you mistermack? It's a thread on almost every denialist site. Here's one. Also, your claim of (great big) straw man implies that you have an alternative theory to protect against such attacks. Is this true? Where is it? Or are you simply representing the denial-o-sphere as a (internally inconsistent) whole?
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  24. #69 mistermack at 00:34 AM on 27 October, 2010 Seems like a great big straw-man to me Here is the paper nealjking says went down in flames. International Journal of Modern Physics B (IJMPB) Condensed Matter Physics; Statistical Physics; Applied Physics Volume: 23, Issue: 3(2009) pp. 275-364 DOI: 10.1142/S021797920904984X FALSIFICATION OF THE ATMOSPHERIC CO2 GREENHOUSE EFFECTS WITHIN THE FRAME OF PHYSICS GERHARD GERLICH & RALF D. TSCHEUSCHNER
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  25. @mistermack: I myself have heard that argument during debates against people opposed to AGW theory. Can we put you on record as agreeing that the greenhouse effect *doesn't* violate the 2nd law of thermodynamics? It'd be nice for us to agree for a change. :-)
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  26. I wrote "I've never read it till now". I didn't think it had never been written, just not widely argued, or taken seriously. To qualify as being a strawman, it doesn't have to be brand new. You can find strawmen, you don't have to invent them. Find a pathetic argument, hidden away somewhere, and debunk it. That's a strawman tactic to me.
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  27. @mistermack: "Find a pathetic argument, hidden away somewhere, and debunk it. That's a strawman tactic to me." We don't "find" that pathetic argument, it is brought up by some contrarians. I would rather never hear about it again. A strawman is attributing to someone an exaggerated version of their position that is easy to debunk. That's not the case here - some (not all) contrarians really do argue this. Note that nowhere did anyone here suggest that *all* skeptics believe this. However, it is undeniable that some do, and as the goal of this site is to list *all* arguments used by those challenging AGW theory, then this one must be included as well.
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  28. mistermack - This particular skeptical argument was hardly hidden away somewhere. I believe that it was discussed on almost every climate blog for about 10 months over the last year. That includes ScienceOfDoom, Deltoid, ClimateRealists, bunches of others. It also made it into any number of news outlets as mentioned by skeptic columnists. Try googling the authors and see. It didn't die down as a heavily promoted anti-AGW argument until several rebuttals appeared (including a peer reviewed one, Halpern 2010, which I believe was about the only citation for the Gerlich article). This particular argument against global warming was idiotic, but hardly a strawman, given the attention paid to it on the skeptic front.
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  29. Well, that' my problem then. I don't know any sceptical blogs. I'm sure they contain some crazy stuff. If I saw this suggestion, about the second law, my initial reaction is that it's laughable, and not worth answering.
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  30. I'm not terribly worried about the skeptical blogs, either - they tend to be self-selecting for the already convinced. But the amount of general press this horrid (and yes, laughable) article got made it significant enough to respond to.
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  31. BP, No, I didn't have anything specific in mind. My issue is that you implied a few times that the most likely scenario following a change in the climate landscape would be a return to an entropy maximum with a total rate of entropy production exactly equal to the previous local maximum. I don't see why you would get the impression that such a change would be the most likely scenario. In fact, given that the unknown future maximum could be either lower or higher to some degree, it is extremely unlikely that the new maximum will just happen to be identical to the previous maximum (or any specific value). You have repeated a few times that - given the MEP principle - a negative feedback is likely. I don't see any basis for this implication. MEP alone neither supports nor contradicts AGW. To suggest that MEP predicts a negative feedback is to assume that the climate will be able to arrange itself in a way that a) increases the earth's entropy production and b) is impossible today or would not lead to entropy increase today. In other words, your argument is in the exact same place it was before invoking MEP; you are proposing that some as yet unknown or misunderstood mechanism may kick into effect that will negate or diminish GW. All you are really doing is restating that hypothesis in terms of entropy and MEP rather than thermodynamics. That doesn't change the fact that we need some evidence before assuming such a mechanism, or even implying that such a mechanism is likely to exist. In fact, MEP reduces the probability that such a mechanism exists, since it adds an additional constraint to the nature of this mechanism, i.e. it is impossible today or would not lead to entropy increase today.
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  32. mistermack wrote : "If I saw this suggestion, about the second law, my initial reaction is that it's laughable, and not worth answering." Most so-called skeptical 'arguments' are laughable (as are most of those bringing them forth, e.g. Monckton), but if they are not responded to - and dismissed as the laughable nonsense they are - the so-called skeptics claim that as being a victory and 'proof' that AGW is false. Many of those 'arguments' are now regarded as zombies because, no matter how many times they are refuted, they keep coming back from the dead. But continually refuted they must be. The same goes for the laughable 'arguments' from creationists - if they weren't shown as false, more and more people would believe there was something to them, and there are more than enough people who believe that creationist nonsense as it is !
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  33. And to follow up on BP, here's at least one place where the burning of G&T takes place.
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  34. e - Your objections to the introduction of the MEP hypothesis are extremely well written. I believe that's essentially what I attempted to say here, albeit not as clearly as you did. The MEP hypothesis, even if true, won't suddenly kick in to save us from global warming. If it's present, it's always been present, and can be considered part of the current feedbacks. Berényi still appears to be searching for the "mystery mechanism" that will induce negative feedback and cancel out AGW.
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  35. #81 e at 02:54 AM on 27 October, 2010 My issue is that you implied a few times that the most likely scenario following a change in the climate landscape would be a return to an entropy maximum with a total rate of entropy production exactly equal to the previous local maximum. I don't see why you would get the impression that such a change would be the most likely scenario. In fact, given that the unknown future maximum could be either lower or higher to some degree, it is extremely unlikely that the new maximum will just happen to be identical to the previous maximum (or any specific value). No, I have not said such a thing. If you had the impression I had, it's probably my fault. What I am actually trying to say is this:
    1. If IR optical depth of the atmosphere is increased by a small amount by adding to it some well mixed greenhouse gas while everything else is held constant, entropy production rate would decrease. I do not have a rigorous proof of this statement, but based on simplified model calculations I believe it's true.
    2. If that everything else is allowed to adjust now to the new situation, it would not change in a way that leads to further reduction of entropy production rate (MEP is used at this step).
    3. Therefore this spontaneous adjustment (a.k.a. feedback) does not amplify the effect of increased IR optical depth, but either leaves it unchanged or attenuates it, that is, the feedback is either neutral or negative.
    Please note a "return to an entropy maximum with a total rate of entropy production exactly equal to the previous local maximum" is never mentioned. And you are right, in fact [...] the unknown future maximum could be either lower or higher to some degree", but it is perfectly consistent with points 1-2-3. If you still maintain there must be a positive feedback in the climate system (for example by water vapor, high clouds or whatever), you have several options to attack my reasoning.
      1. You may try to show that in some cases increased IR optical depth alone does not imply a decrease in entropy production rate.
      2. You could demonstrate the climate system has a unique structure that makes the MEP principle nonoperational in this case.
      3. Or show us while feedback on entropy production rate is indeed not positive, it can still be positive on surface temperatures.
     You may even be able to come up with something else. But please refrain from constructing strawmen. And be specific in order to facilitate understanding.
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  36. Berényi - "If you still maintain there must be a positive feedback in the climate system (for example by water vapor, high clouds or whatever), you have several options to attack my reasoning"... To be quite specific, and to repeat what both 'e' and I have written on this thread: if the MEP principle is operative, it is part and parcel of the existing climate sensitivities. Straightforward 'black-box' testing of climate sensitivity from paleo evidence, for a variety of forcings, indicates that there is no major negative feedback such as you postulate. You've been avoiding that point of both our replies for some time now. MEP does not magically prevent global warming.
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  37. BP, I was referring specifically to this comment: >If there is a maximum entropy production principle at work indeed, for a neutral feedback you need the same climate state to be found right at a peak on the rearranged landscape, which is extremely unlikely. All other positions would involve some negative feedback and there is no room for a positive one at all. If you misspoke, then that's fine. But the plain reading of this comment is that you were saying exactly what I accused you of claiming: that negative feedback is the only probable outcome assuming MEP. Please don't accuse me of constructing strawmen when I'm responding directly to a statement you made.
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  38. Berényi Péter #85 there's something I don't get in your point #1. What do you mean by "everything else held constant"? Will you let the system evolve? By changing what? And the entropy production rate of what, in first place? Also, in #3 I do not understand why restoring the "right" entropy production rate cannot be a positive feedback in climate terms, i.e. an increase in surface temperature as opposed to in entropy production rate. Can't you increase entropy production rate by increasing surface temperature? Maybe it's just a consequence of the problem in #1. I've never heard anyone claiming the impossibility of positive feedback based on MEP principle.
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  39. #87 e at 07:43 AM on 27 October, 2010 the plain reading of this comment is that you were saying exactly what I accused you The key phrase is you need the same climate state to be found right at a peak on the rearranged landscape (otherwise there is a direction in the phase space along which a small displacement of the climate state would increase entropy production). I have no idea how "a total rate of entropy production exactly equal to the previous local maximum" would follow from it. But maybe I was not clear enough.
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  40. BP, Ok, I think I see what you're doing. You're basically saying that an increase in water vapor is a decrease in entropy, so this feedback is impossible given MEP. Of course, if this claim was true, atmospheric water vapor could never increase. Of course, we know from empirical evidence, that water vapor does increase. In a more general sense, how do you distinguish between a movement along the potential entropy production landscape, and a wholesale change to that landscape? Is it simply a matter of external forcings vs. internal? If so, is not the ocean "external" with respect to the atmosphere?
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  41. #88 Riccardo at 08:14 AM on 27 October, 2010 What do you mean by "everything else held constant"? I mean what is ordinarily called a no feedback situation. That is, cloudiness, snow cover, atmospheric water vapor distribution, winds, ocean currents, vegetation, etc. are not allowed to change in response to increased IR optical depth. I say in this specific case entropy production rate gets smaller than it was before optical depth was increased. And the entropy production rate of what, in first place? The global entropy production rate in W/K, measured as difference between entropy of outgoing longvawe vs. incoming shortwave radiation. Can't you increase entropy production rate by increasing surface temperature? No, I can't. Not as if I have not tried, but all simplified radiative or radiative-convective models I have checked so far have this vexing property. As surface temperatures are increased, entropy production rate declines. I conjecture a general principle is at work in the background. The MEP usually also implies minimum entropy contents of the system and higher temperatures mean higher entropy. But I do not have a formal proof (yet). Anyway, if you could show us an understandable climate model that goes against this conjecture, that would be informative. I've never heard anyone claiming the impossibility of positive feedback based on MEP principle You are welcome :)
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  42. #90 e at 08:30 AM on 27 October, 2010 You're basically saying that an increase in water vapor is a decrease in entropy, so this feedback is impossible given MEP. No, I would never claim such a thing. Water vapor is free to do whatever it is inclined to. I just say given MEP some rearrangement of the climate state is likely in response to increased IR opacity in order to approach maximum entropy production rate under the new circumstances. This rearrangement would counteract GHG effect on entropy production rate (like a negative feedback). Water vapor redistribution is just a possibility. Average opacity of the atmosphere can decrease happily in weak H2O IR absorption bands even with increasing average moisture, provided its distribution gets a bit more uneven (higher moments are increased). It can happen on all scales, including sub-grid ones relative to computational climate models. how do you distinguish between a movement along the potential entropy production landscape, and a wholesale change to that landscape? It is a matter of convention to some extent. What you usually consider a forcing is supposed to rearrange the landscape while so called feedbacks only push the climate state around in the phase space. Is it simply a matter of external forcings vs. internal? If so, is not the ocean "external" with respect to the atmosphere? I don't think there are internal forcings, I would rather call changes not forced by external agents unforced ones. As the climate system is close to a critical state (see SOC - Self-Organized Criticality) one would expect the correlation length go up implying large spontaneous (unforced) fluctuations on all scales. And no, the ocean is in no way external to the climate system. In fact most of the climate happens in the oceans, there's thousands of times more mass in them than in the atmosphere.
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  43. Berényi - Once again you are proposing a complex hypothesis of negative feedback that will defeat global warming: "This rearrangement would counteract GHG effect on entropy production rate (like a negative feedback)". And once again this is contradicted by the actual data. Such a MEP effect would already be in effect now, and in the past, and would be part of measured climate sensitivities. There is no such negative feedback observed in the data. And if your hypothesis is contradicted by the data, it's time for a new hypothesis. This entire MEP side excursion is a red herring.
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  44. KR @93, I have been following this debate with interest from the side lines. I think your last sentence sums everything up nicely-- a very elaborate red herring at that. So this "debate" all seems an effort by BP to distract form the subject at hand. Or does BP agree with G&T's misunderstanding that the so-called "greenhouse effect" somehow contradicts the second law of thermodynamics? There is really nothing to debate concerning the validity of G&T's work, b/c the science on that is settled-- G&T have been shown to be wrong. If BP is trying to argue that the climate system has some alleged significant negative feed backs, surely that debate belongs on a more appropriate thread, and not here.
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  45. BP, ok sorry I misunderstood the water vapor point somewhat. RE the convention of moving along the landscape vs. changes to the landscape: it seems to me that distinguishing these concepts is somewhat important to your hypothesis is it not? MEP states that the system will tend towards the maximum path of entropy production given the constraints. As I understand it, it says nothing about whether a change in constraints can raise or lower the entropy production of the system. If positive feedbacks are thought of as changes in the constraints of the system (as the net consequence of the initial forcing), then there is no reason to predict that entropy production must increase (or stay the same) as a result of these changes. In this way, positive feedbacks can reduce entropy production with no contradiction to MEP. In short, how do you determine whether positive feedbacks are changes to the path of entropy production or changes to the constraints of the system?
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  46. The message of the main text of this thread is that such assertion that "greenhouse effect contradicts the 2nd law of thermodynamics", as Gerlich and Tscheuschner made in their paper published in 2009, is false. I think that there is no objection to this message among the commenters here. The story of the principle of maximum entropy production (MEP) is related to the general title "The 2nd law of thermodynamics and the greenhouse effect", but MEP is something distinct from the 2nd law, and is much less estabilished. I think that it is an interesting subject of academic science to discuss whether it holds in the real world. But I think that formulations of the model systems that should represent the real world is different among scientists (e.g. between Berényi Péter and Ozawa et al.), and that the answer to the preliminary question "maximum among what?" is different accordingly. So MEP does not seem to me helpful as a piece of policy-relevant science of climate at present.
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  47. Albatross - I agree. Berényi - MEP discussions probably belong on How sensitive is our climate, not here. The 2nd law of thermodynamics is quite secure, and the nonsense of Gerlich and Tscheuschner well disproven. MEP is off-topic here.
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    Moderator Response: Agreed. Take it to that other thread, please.
  48. KR The second law is about entropy, heat flows from hot to cold is just sticking this in the most simple terms. If you state the second law as chaos increases, you are mostly just going to get blank stares back, but its not a bad approximation of the second law. But entropy increases or stays the same, is the second law... now if you modify the system however?
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  49. #98, Joe Blog: However you define the 2nd law, the usual model of the greenhouse effect is "in compliance" with it.
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  50. #96 Kooiti Masuda at 12:53 PM on 27 October, 2010 The story of the principle of maximum entropy production (MEP) is related to the general title "The 2nd law of thermodynamics and the greenhouse effect", but MEP is something distinct from the 2nd law, and is much less established [...] the formulations of the model systems that should represent the real world is different among scientists [...] and that the answer to the preliminary question "maximum among what?" is different accordingly Yes. MEP, even if related, is distinct from the 2nd law. I also agree proper definition of boundary conditions is crucial. Anyway, I move discussion of MEP and its suggested relevance on climate sensitivity to the How sensitive is our climate thread. All interested parties are invited to continue there. The message of the main text of this thread is that such assertion that "greenhouse effect contradicts the 2nd law of thermodynamics", as Gerlich and Tscheuschner made in their paper published in 2009, is false Slow down, please. The statement you've put in quotation marks is not found in the Gerlich and Tscheuschner paper. It is important to get quotations right, otherwise you can easily get what others have got in [2]: "Since Halpern et al. communicate our arguments incorrectly, their comment is scientifically vacuous." These guys may be physicists, but not fools. Perhaps it's worth checking out what they've actually said. I don't think their paper has got properly refuted either. I know there was much talk about it in the blogosphere, but according to the standards of this blog, only peer reviewed papers can be relied on and of those we do not have too many, just one (along with a counter-refutation from the original authors). [1] International Journal of Modern Physics B Vol. 24, No. 10 (2010) 1309–1332 DOI: 10.1142/S021797921005555X COMMENT ON “FALSIFICATION OF THE ATMOSPHERIC CO2 GREENHOUSE EFFECTS WITHIN THE FRAME OF PHYSICS” JOSHUA B. HALPERN, CHRISTOPHER M. COLOSE, CHRIS HO-STUART, JOEL D. SHORE, ARTHUR P. SMITH & JÖRG ZIMMERMANN [2] International Journal of Modern Physics B Vol. 24, No. 10 (2010) 1333–1359 DOI: 10.1142/S0217979210055573 REPLY TO “COMMENT ON ‘FALSIFICATION OF THE ATMOSPHERIC CO2 GREENHOUSE EFFECTS WITHIN THE FRAME OF PHYSICS’ BY JOSHUA B. HALPERN, CHRISTOPHER M. COLOSE, CHRIS HO-STUART, JOEL D. SHORE, ARTHUR P. SMITH, JÖRG ZIMMERMANN” GERHARD GERLICH & RALF D. TSCHEUSCHNER "Naturally, from our own experience we know — and we often point this out in discussions — that individuals, who — escaped from the science department — flew to and finally got lost in the domains of global climatology often suffer from a barely modest infection by mathematics and physics." Quite rude. Although not a peer reviewed paper, but this one from the same authors may be of some interest too: arXiv.org > physics > arXiv:1003.1508 Physics > Atmospheric and Oceanic Physics (physics.ao-ph) Cite as: arXiv:1003.1508v2 [physics.ao-ph] On The Barometric Formulas And Their Derivation From Hydrodynamics and Thermodynamics Gerhard Gerlich & Ralf D. Tscheuschner "Since the measurable thermodynamic quantities of a voluminous medium, in particular the specific heat and the thermodynamic transport coefficients, naturally include the contribution from radiative interactions, we cannot expect that a change of concentration of a trace gas has any measurable effect"
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