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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

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The greenhouse effect and the 2nd law of thermodynamics

What the science says...

Select a level... Basic Intermediate

The 2nd law of thermodynamics is consistent with the greenhouse effect which is directly observed.

Climate Myth...

2nd law of thermodynamics contradicts greenhouse theory


"The atmospheric greenhouse effect, an idea that many authors trace back to the traditional works of Fourier 1824, Tyndall 1861, and Arrhenius 1896, and which is still supported in global climatology, essentially describes a fictitious mechanism, in which a planetary atmosphere acts as a heat pump driven by an environment that is radiatively interacting with but radiatively equilibrated to the atmospheric system. According to the second law of thermodynamics such a planetary machine can never exist." (Gerhard Gerlich)


At a glance

Although this topic may have a highly technical feel to it, thermodynamics is a big part of all our everyday lives. So while you are reading, do remember that there are glossary entries available for all thinly underlined terms - just hover your mouse cursor over them for the entry to appear.

Thermodynamics is the branch of physics that describes how energy interacts within systems. That interaction determines, for example, how we stay cosy or freeze to death. You wear less clothing in very hot weather and layer-up or add extra blankets to your bed when it's cold because such things control how energy interacts with your own body and therefore your degree of comfort and, in extreme cases, safety.

The human body and its surroundings and energy transfer between them make up one such system with which we are all familiar. But let's go a lot bigger here and think about heat energy and its transfer between the Sun, Earth's land/ocean surfaces, the atmosphere and the cosmos.

Sunshine hits the top of our atmosphere and some of it makes it down to the surface, where it heats up the ground and the oceans alike. These in turn give off heat in the form of invisible but warming infra-red radiation. But you can see the effects of that radiation - think of the heat-shimmer you see over a tarmac road-surface on a hot sunny day.

A proportion of that radiation goes back up through the atmosphere and escapes to space. But another proportion of it is absorbed by greenhouse gas molecules, such as water vapour, carbon dioxide and methane.  Heating up themselves, those molecules then re-emit that heat energy in all directions including downwards. Due to the greenhouse effect, the total loss of that outgoing radiation is avoided and the cooling of Earth's surface is thereby inhibited. Without that extra blanket, Earth's average temperature would be more than thirty degrees Celsius cooler than is currently the case.

That's all in accordance with the laws of Thermodynamics. The First Law of Thermodynamics states that the total energy of an isolated system is constant - while energy can be transformed from one form to another it can be neither created nor destroyed. The Second Law does not state that the only flow of energy is from hot to cold - but instead that the net sum of the energy flows will be from hot to cold. That qualifier term, 'net', is the important one here. The Earth alone is not a "closed system", but is part of a constant, net energy flow from the Sun, to Earth and back out to space. Greenhouse gases simply inhibit part of that net flow, by returning some of the outgoing energy back towards Earth's surface.

The myth that the greenhouse effect is contrary to the second law of thermodynamics is mostly based on a very long 2009 paper by two German scientists (not climate scientists), Gerlich and Tscheuschner (G&T). In its title, the paper claimed to take down the theory that heat being trapped by our atmosphere keeps us warm. That's a huge claim to make – akin to stating there is no gravity.

The G&T paper has been the subject of many detailed rebuttals over the years since its publication. That's because one thing that makes the scientific community sit up and take notice is when something making big claims is published but which is so blatantly incorrect. To fully deal with every mistake contained in the paper, this rebuttal would have to be thousands of words long. A shorter riposte, posted in a discussion on the topic at the Quora website, was as follows: “...I might add that if G&T were correct they used dozens of rambling pages to prove that blankets can’t keep you warm at night."

If the Second Law of Thermodynamics is true - something we can safely assume – then, “blankets can’t keep you warm at night”, must be false. And - as you'll know from your own experiences - that is of course the case!

Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!

Further details

Among the junk-science themes promoted by climate science deniers is the claim that the explanation for global warming contradicts the second law of thermodynamics. Does it? Of course not (Halpern et al. 2010), but let's explore. Firstly, we need to know how thermal energy transfer works with particular regard to Earth's atmosphere. Then, we need to know what the second law of thermodynamics is, and how it applies to global warming.

Thermal energy is transferred through systems in five main ways: conduction, convection, advection, latent heat and, last but not least, radiation. We'll take them one by one.

Conduction is important in some solids – think of how a cold metal spoon placed in a pot of boiling water can become too hot to touch. In many fluids and gases, conduction is much less important. There are a few exceptions, such as mercury, a metal whose melting point is so low it exists as a liquid above -38 degrees Celsius, making it a handy temperature-marker in thermometers. But air's thermal conductivity is so low we can more or less count it out from this discussion.



Figure 1: Severe thunderstorm developing over the Welsh countryside one evening in August 2020. This excellent example of convection had strong enough updraughts to produce hail up to 2.5 cm in diameter. (Source: John Mason)

Hot air rises – that's why hot air balloons work, because warm air is less dense than its colder surroundings, making the artificially heated air in the balloon more buoyant and thereby creating a convective current. The same principle applies in nature: convection is the upward transfer of heat in a fluid or a gas. 

Convection is highly important in Earth's atmosphere and especially in its lower part, where most of our weather goes on. On a nice day, convection may be noticed as birds soar and spiral upwards on thermals, gaining height with the help of that rising warm air-current. On other days, mass-ascent of warm, moist air can result in any type of convective weather from showers to severe thunderstorms with their attendant hazards. In the most extreme examples like supercells, that convective ascent or updraught can reach speeds getting on for a hundred miles per hour. Such powerful convective currents can keep hailstones held high in the storm-cloud for long enough to grow to golfball size or larger.


Advection is the quasi-horizontal transport of a fluid or gas with its attendant properties. Here are a couple of examples. In the Northern Hemisphere, southerly winds bring mild to warm air from the tropics northwards. During the rapid transition from a cold spell to a warm southerly over Europe in early December 2022, the temperatures over parts of the UK leapt from around -10C to +14C in one weekend, due to warm air advection. Advection can also lead to certain specific phenomena such as sea-fogs – when warm air inland is transported over the surrounding cold seas, causing rapid condensation of water vapour near the air-sea interface.


Figure 2: Advection fog completely obscures Cardigan Bay, off the west coast of Wales, on an April afternoon in 2015, Air warmed over the land was advected seawards, where its moisture promptly condensed over the much colder sea surface.

Latent heat

Latent heat is the thermal energy released or absorbed during a substance's transition from solid to liquid, liquid to vapour or vice-versa. To fuse, or melt, a solid or to boil a liquid, it is necessary to add thermal energy to a system, whereas when a vapour condenses or a liquid freezes, energy is released. The amount of energy involved varies from one substance to another: to melt iron you need a furnace but with an ice cube you only need to leave it at room-temperature for a while. Such variations from one substance to another are expressed as specific latent heats of fusion or vapourisation, measured in amount of energy (KiloJoules) per kilogram. In the case of Earth's atmosphere, the only substance of major importance with regard to latent heat is water, because at the range of temperatures present, it's the only component that is both abundant and constantly transitioning between solid, liquid and vapour phases.


Radiation is the transfer of energy as electromagnetic rays, emitted by any heated surface. Electromagnetic radiation runs from long-wave - radio waves, microwaves, infra-red (IR), through the visible-light spectrum, down to short-wave – ultra-violet (UV), x-rays and gamma-rays. Although you cannot see IR radiation, you can feel it warming you when you sit by a fire. Indeed, the visible part of the spectrum used to be called “luminous heat” and the invisible IR radiation “non-luminous heat”, back in the 1800s when such things were slowly being figured-out.

Sunshine is an example of radiation. Unlike conduction and convection, radiation has the distinction of being able to travel from its source straight through the vacuum of space. Thus, Solar radiation travels through that vacuum for some 150 million kilometres, to reach our planet at a near-constant rate. Some Solar radiation, especially short-wave UV light, is absorbed by our atmosphere. Some is reflected straight back to space by cloud-tops. The rest makes it all the way down to the ground, where it is reflected from lighter surfaces or absorbed by darker ones. That's why black tarmac road surfaces can heat up until they melt on a bright summer's day.


Figure 3: Heat haze above a warmed road-surface, Lincoln Way in San Francisco, California. May 2007. Image: Wikimedia Commons.

Energy balance

What has all of the above got to do with global warming? Well, through its radiation-flux, the Sun heats the atmosphere, the surfaces of land and oceans. The surfaces heated by solar radiation in turn emit infrared radiation, some of which can escape directly into space, but some of which is absorbed by the greenhouse gases in the atmosphere, mostly carbon dioxide, water vapour, and methane. Greenhouse gases not only slow down the loss of energy from the surface, but also re-radiate that energy, some of which is directed back down towards the surface, increasing the surface temperature and increasing how much energy is radiated from the surface. Overall, this process leads to a state where the surface is warmer than it would be in the absence of an atmosphere with greenhouse gases. On average, the amount of energy radiated back into space matches the amount of energy being received from the Sun, but there's a slight imbalance that we'll come to.

If this system was severely out of balance either way, the planet would have either frozen or overheated millions of years ago. Instead the planet's climate is (or at least was) stable, broadly speaking. Its temperatures generally stay within bounds that allow life to thrive. It's all about energy balance. Figure 4 shows the numbers.

Energy Budget AR6 WGI Figure 7_2

Figure 4: Schematic representation of the global mean energy budget of the Earth (upper panel), and its equivalent without considerations of cloud effects (lower panel). Numbers indicate best estimates for the magnitudes of the globally averaged energy balance components in W m–2 together with their uncertainty ranges in parentheses (5–95% confidence range), representing climate conditions at the beginning of the 21st century. Figure adapted for IPCC AR6 WG1 Chapter 7, from Wild et al. (2015).

While the flow in and out of our atmosphere from or to space is essentially the same, the atmosphere is inhibiting the cooling of the Earth, storing that energy mostly near its surface. If it were simply a case of sunshine straight in, infra-red straight back out, which would occur if the atmosphere was transparent to infra-red (it isn't) – or indeed if there was no atmosphere, Earth would have a similar temperature-range to the essentially airless Moon. On the Lunar equator, daytime heating can raise the temperature to a searing 120OC, but unimpeded radiative cooling means that at night, it gets down to around -130OC. No atmosphere as such, no greenhouse effect.

Clearly, the concentrations of greenhouse gases determine their energy storage capacity and therefore the greenhouse effect's strength. This is particularly the case for those gases that are non-condensing at atmospheric temperatures. Of those non-condensing gases, carbon dioxide is the most important. Because it only exists as vapour, the main way it is removed is as a weak solution of carbonic acid in rainwater – indeed the old name for carbon dioxide was 'carbonic acid gas'. That means once it's up there, it has a long 'atmospheric residency', meaning it takes a long time to be removed. 

Earth’s temperature can be stable over long periods of time, but to make that possible, incoming energy and outgoing energy have to be exactly the same, in a state of balance known as ‘radiative equilibrium’. That equilibrium can be disturbed by changing the forcing caused by any components of the system. Thus, for example, as the concentration of carbon dioxide has fluctuated over geological time, mostly on gradual time-scales but in some cases abruptly, so has the planet's energy storage capacity. Such fluctuations have in turn determined Earth's climate state, Hothouse or Icehouse – the latter defined as having Polar ice-caps present, of whatever size. Currently, Earth’s energy budget imbalance averages out at just under +1 watt per square metre - that’s global warming. 

That's all in accordance with the laws of Thermodynamics. The First Law of Thermodynamics states that the total energy of an isolated system is constant - while energy can be transformed from one component to another it can be neither created nor destroyed. Self-evidently, the "isolated" part of the law must require that the sun and the cosmos be included. They are both components of the system: without the Sun as the prime energy generator, Earth would be frozen and lifeless; with the Sun but without Earth's emitted energy dispersing out into space, the planet would cook, Just thinking about Earth's surface and atmosphere in isolation is to ignore two of this system's most important components.

The Second Law of Thermodynamics does not state that the only flow of energy is from hot to cold - but instead that the net sum of the energy flows will be from hot to cold. To reiterate, the qualifier term, 'net', is the important one here. In the case of the Earth-Sun system, it is again necessary to consider all of the components and their interactions: the sunshine, the warmed surface giving off IR radiation into the cooler atmosphere, the greenhouse gases re-emitting that radiation in all directions and finally the radiation emitted from the top of our atmosphere, to disperse out into the cold depths of space. That energy is not destroyed – it just disperses in all directions into the cold vastness out there. Some of it even heads towards the Sun too - since infra-red radiation has no way of determining that it is heading towards a much hotter body than the Earth,

Earth’s energy budget makes sure that all portions of the system are accounted for and this is routinely done in climate models. No violations exist. Greenhouse gases return some of the energy back towards Earth's surface but the net flow is still out into space. John Tyndall, in a lecture to the Royal Institution in 1859, recognised this. He said:

Tyndall 1859

As long as carbon emissions continue to rise, so will that planetary energy imbalance. Therefore, the only way to take the situation back towards stability is to reduce those emissions.

Update June 2023:

For additional links to relevant blog posts, please look at the "Further Reading" box, below.

Last updated on 29 June 2023 by John Mason. View Archives

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Comments 951 to 975 out of 1089:

  1. L.J. Ryan - "To claim effective LW emissivity of 0.612 is measured, is specious. How do measure “effective emissivity”? " That's quite a statement you're making there, L.J., and quite unsupportable. (A) The effective emissivity is quite simply measured by looking at the surface temperature (well known, well measured, etc., not to mention being what we're interested in) and the integrated power emitted at the top of the atmosphere (about 240 W/m^2). The tool used for those measurements is an infra-red spectroscope, incidentally. That's about 61% of the power that a black body at 15C would radiate, and hence the effective emissivity is 0.61. (B) That number matches the physics, as per line-by-line spectral modelling of the atmosphere such as in the MODTRANS and more up to date computations. It's always nice when the model matches the data - it's excellent support for the model being correct. So - that's the data, and it's supported by the (correct) models. You also have stated that "Delta T must be a function (of) a non-radiative input", rather than the well understood greenhouse effect. Just what non-radiative input would that be??? Invisible volcanos? Little green men? Accumulated friction from the hand-wringing of climate skeptics? I quite simply cannot take your argument seriously when you invoke Mysterious Unknown Forces (MUF's) as a replacement for the last 150 years of science. Please, L.J.Ryan - read some of the references you have equation-mined. Learn a bit more about the science. You're approaching the issue with a lot of erroneous preconceptions, and those are leading you to incorrect conclusions.
  2. CBDunkerson 950 I should have addressed my post to les 948 & 914...914 is linked within 948.
  3. 949 Ryan. You can paraphrase what you like. But I would rather advise learning the meaning of the orriginal phrasing, put together by better physicists than you or I. But you really should not invent things like that that is my "revised position". I revised nothing. And you really cannot put a paraphrase into quotation marks! Yes, clearly the 2nd law is universal. But it doesn't say that energy can not flow from cold to hot. it says that energy can not flow from cold to hot without work being done. Any one who doesn't realise that should get a cold beer from the fridge and think about it.
  4. les 953 So when you said:

    884 KR
    " The "2nd law" objection to the greenhouse effect is based upon a mistaken notion.." I don't disagree with you. However I'd like to suggest there is another problem. In the post, the statement of the 2nd law has missed out the phrase: "whose sole result". This is a statement that the 2nd law only applies to a closed system. For practical purposes, the system which consists of: the sun, outer space, the solid earth and the earths atmosphere is not a closed system.

    What did you mean?
  5. 954 Ryan I meant
    " The "2nd law" objection to the greenhouse effect is based upon a mistaken notion.." I don't disagree with you. However I'd like to suggest there is another problem. In the post, the statement of the 2nd law has missed out the phrase: "whose sole result". This is a statement that the 2nd law only applies to a closed system. For practical purposes, the system which consists of: the sun, outer space, the solid earth and the earths atmosphere is not a closed system.
    HTH. I even already posted another phrasing of the same point from here
    "The planetary warming resulting from the greenhouse effect is consistent with the second law of thermodynamics because a planet is not a close system"
    what bit are you struggling with?
  6. les 955 "This is a statement that the 2nd law only applies to a closed system."...Ok applies only to closed systems "For practical purposes, the system which consists of: the sun, outer space, the solid earth and the earths atmosphere is not a closed system. "...Ok the earth's system is not closed These together suggest you are saying the earth's open system does NOT have to follow the 2nd law. Otherwise, why would have "another problem" or for that matter the entirety of 914?
  7. Moderators - I'm noticing a similarity in approach, in some word choices, and the use of terms I previously used replying to one poster appearing in another; are damorbel and L.J Ryan the same person? We appear to be getting "trolled" again... Please delete this post if I am incorrect.
  8. 956 Ryan. As mentioned above, everything obeys the 2nd law and the 2nd law states "bla bla sole result bla bla ... " or words to that affect. But now I see you confusion. "another problem" refers to the observations of KR 849. I should have hyperlinked that as the numbering of the comments tends to change from time to time. I must say I can see absolutely no reason to infer from any of my remarks that I believe the 2nd law doesn't hold. The reason for my comment was, on the contrary, to suggest that because the important "sole result" or close system clause is missing from the blog post, many people seem to be very very confused. Be that as it may. Now we have cleared up to your confusion I am confident that you will agree that the green house affect does not violate the 2nd law and we can bring a stop to the physics abuse of this thread. Great!
  9. KR 951 re (A) As I stated, it is not measured. Rather effective emissivity is calculated by solving solving for emissivity with given temperature and power...and the assumption GHG mechanics are correct. So when you calculate for unknown X and then turnaround and use X to calculate one of the given variables, you have simplified verified your formula ([ 240/(0.612 * 5.6704*10^-8 ]^0.25 - 273.15 = 15.2C). The problem is with your given variables. If you are measuring radiation via atmosphere, should not the temperature variable also be that of the atmosphere. Why use temp. from one source and use it to calculate emissivity of another? re(B) I assume the modals would match the data because both assume the wrong input variable..namely surface temperature and atmosphere radiation to measure atmos. effective emissivity. I refer the above reply, why not use atmosphere temperature? KR: I am not damorbel.
  10. addendum: In truth, I can see that when I pointed out that the 2nd law as stated in the blog doesn't hold, it may be read as "the 2nd law doesn't hold"... but, really, that is a bit silly given that I mentioned the "sole result" clause...
  11. les 958 We agree it must follow. The physics used to validate GHG theory however, is at odds with this tenet.
  12. 961 Ryan. "The physics used to validate GHG theory however, is at odds with this tenet." Not at all. Although I've yet to see much discussion of physics in these posts. Never the less, if it's of help, I refer you, again, to the paper of Prof. Pierrehumbert for illustration.
  13. wot? Where's Ryan? I'm expecting something like: You say "Not at all", let me rephrase "yes exactly". Do I understand? Well?
  14. L.J. Ryan - If you feel that integrated spectra are not measurements, well, then, I'll pass that on to the spectroscope manufacturers I work with. That should be good for a laugh. "Effective emissivity" is a useful summary of surface temperatures, atmospheric temperatures, band blocking, emission altitudes, and the lapse rate. You get the same results from either orbital measures of emitted spectra compared to surface emitted spectra, or from computationally modelling the entire atmospheric physics. That's the fractional efficiency of TOA energy radiation due to surface temperatures, relative to a black body. Incidentally, do you recognize that the black body temperature required to radiate a fixed power is the absolute minimum temperature required for a gray body to radiate the same power? With the gray body temperature going up as emissivity goes down? I've raised that point a few times with you, but you have not responded. Your objections to this are beginning to consist of nothing but flat denials with no backing; until and unless you post a physical argument that actually makes sense, preferably with references that support it, I don't believe I'll bother replying to any more of your posts. After almost 1000 posts, I believe there's more than enough information present for anyone who isn't sticking their fingers in their ears and singing "La la la la la..." Do some reading, L.J. Ryan, including the sources you yourself have linked to.
  15. les#948: "we pay respect to this great moment by giving up on this assault on the nodal discipline of physics by attempting to prove/disprove another of it's great achievements" That's a great point. Perhaps this will be the year when the deniers swear off the 'I am right and all of physics is wrong' arguments. Out of respect for past great physics achievements ... probably not. But maybe for their own self-respect?
  16. LJRyan @932: First, anybody who has read anything that I have written knows I am not given to knee jerk responses from my writing style alone, even if they do not understand the content. The fact that you are so completely wrong does not make a post which points that out a knee jerk response. Perhaps it is time you reconsidered your arrogance which believes, on this topic, that you alone have the truth, and the world's physicists from Arrhenius on have been barking up the wrong tree. A little humility is the first step to wisdom, so it is about time you learnt some. Second, my equations (1xx) are not equivalent to yours. That is because the Earth absorbs most of its energy in as visible light, but emits most of it as IR light. I would of course be delighted for you to prove me wrong. Don't just cite Kirchoff. Apply his proof to the actual situation on Earth and prove that his results have the consequences you claim. To do so remember that you must use all of the following sinks and sources: i) The Sun; ii) The Earth's surface; iii) The Earth's atmosphere; and iv) Space. For greater realism, you must also include clouds. For greater realism still you must split the atmosphere into about 30 odd layers, treating each as a separate sink/source, and treating clouds in each layer distinctly; but we won't expect that from you (though it is what we expect, and more, from climate scientists). I note that nobody understands a law of physics unless they can use the proof of the law to set up an appropriate model to model any situation in which it applies. So if you cannot make the argument called for above, it is because you do not know what you are talking about when you cite Kirchoff. Of course, if you do set up an argument as called for above, you will find that either your model contains obvious, and obviously relevant disanalogies with real life; or that it simply confirms the theories of the physicists. I am also not interested in any other argument from you because, quite frankly, I am tired of your bullshit and obfustication. For your help in setting up the model, the SW absorptivity of the surface is, on average 0.875, although if you exclude clouds for simplicity, you may want to treat it as 0.7. Third, you certainly did quote mine Professor Jin-Yi Yu's lecture slides. The thing about lecture slides is that they are never self explanatory. They are designed to be accompanied by a lecture which explains the slides, and without that lecture you are always missing crucial information, including, in this case, the definition of the symbols. lecture notes are much better, but not ideal because they are often too compressed. Text books are best of all, but rather hard to directly link to. However, despite the deficiency of lecture slides, even the slides you quote contain enough information to prove you wrong. Specifically on the slide titled "Greenhouse Effect"(about page 15), we have the following two formulas: a) Ta = Te = 255K b) Ts = (2^0.25)*Ta = 303 K Clearly the effective temperature (Te) does not equal the surface temperature (Ts) as you require for your version of equation 3 to be correct. Note that your comment about black body surfaces is irrelevant. The effective temperature is the temperature of a theoretical black body the would radiate the same power as is actually radiated from the the top of the atmosphere. It does not imply that the TOA has that temperature, or that all the OLR at the TOA is radiated from a surface at that point. It is no wonder you are so confused if you do not even understand basic terms of the science. Fourth, nothing else in your post is worth responding to IMO. This is because of your tantrum. I am not going to dignify your "shouted" comments and those bracketed by them with anymore response than to note that it is irrational to treat a tantrum thrower as both a tantrum thrower and a rational disputant at the same time. If you want to debate, be polite.
  17. Gosh . I dislike quoting the luminaries directly, but here are quotes from RC and Open Mind: RayPierre Humbert In a nutshell, then, here is how the greenhouse effect works: From the requirement of energy balance, the absorbed solar radiation determines the effective blackbody radiating temperature Trad. This is not the surface temperature; it is instead the temperature encountered at some pressure level in the atmosphere prad, which characterizes the infrared opacity of the atmosphere, specifically the typical altitude from which infrared photons escape to space. The pressure prad is determined by the greenhouse gas concentration of the atmosphere. The surface temperature is determined by starting at the fixed temperature Trad and extrapolating from prad to the surface pressure ps using the atmosphere’s lapse rate, which is approximately governed by the appropriate adiabat. Since temperature decreases with altitude over much of the depth of a typical atmosphere, the surface temperature so obtained is typically greater than Trad, as illustrated in Figure 3.6. Increasing the concentration of a greenhouse gas decreases prad, and therefore increases the surface temperature because temperature is extrapolated from Trad over a greater pressure range. It is very important to recognize that greenhouse warming relies on the decrease of atmospheric temperature with height, which is generally due to the adiabatic profile established by convection. The greenhouse effect works by allowing a planet to radiate at a temperature colder than the surface, but for this to be possible, there must be some cold air aloft for the greenhouse gas to work with. Tamino “If a parcel of air rises, because of the reduced pressure the parcel will expand. It generally takes much longer for a parcel of air to absorb/emit heat from/to its surroundings than to expand/contract, so during its expansion it will, for all practical purposes, exchange no heat with its surroundings; in other words, the expansion of the parcel of air will be adiabatic” For a text book derivation I quoted page 45 of Elementary Climate Physics by FWTaylor (mentioned in the far distant introduction). The lapse rate is a function of gravity and specific heat and is about 6K per kilometre of altitude. If we cannot accept this very basic Physics, we are entitled to ask who are the denialists in this debate. Anyone can see the compression/decompression effect for themselves by inflating a bicycle tyre or releasing the pressure in a gas cylinder. The question of the transparent atmosphere is frequently raised. An atmosphere which was totally transparent to radiant energy, unable to absorb or emit, would still have a lapse rate. Its low pressure at altitude would be colder than its high pressure at the surface. However, it would be a very strange gas indeed. Unlike everything else in nature with a temperature, it would not radiate. It would allow the surface to be in radiative equilibrium at 255 K, and would not affect this temperature by thermal insulation, convection, conduction, or evaporation. Not worth debating, I think. As I said in a previous response "The explanation you offer, Very Tall Guy, is the only plausible explanation of the AGW effect. It is the preferred explanation of the founding fathers over at RC, and you can find it in the Rabbet rebuttal of the G and T paper, (immediately following their absurd multi-layer, back-radiation explanation). It begins with the lapse rate, a function of gravity and specific heat, which has nothing to do with radiative effects. Without this lapse rate there would be no possibility of AGW. The argument is that increasing CO2 in the cold, dry, upper atmosphere, impedes outgoing radiation, and moves the effective radiation point to higher (and therefore) colder temperatures. Outgoing radiation is reduced, incoming radiation remains the same, and the whole atmosphere and surface warms up to restore the balance. As your drawing demonstrates, the lapse rate moves to the right". The dominance of water vapour in the AGW stakes (often quoted by the sceptics)is not a factor because, at this altitude, the air is dry. This is a plausible explanation, unlike all the others. It implies that AGW is a top of the atmosphere effect, and that the temperature increase (right shift of the lapse rate) should be greater at altitude than at the surface. More subtly, it suggests that increasing the concentration of CO2 in the stratosphere will absorb and emit energy more efficiently, and thus cool the stratosphere.
    Response: [muoncounter] Please do not quote long passages from other blogs; we are fully capable of following links to them. And to avoid the possibility that you might be quoting selectively or out of context, you must provide those links anyway.
  18. What others (explanations of AGW) someone may ask. I collected the following explanations from one thread at RC: Ekholm in his 1901 paper: . . . radiation from the earth into space does not go directly from the ground, but on the average from a layer of the atmosphere having a considerable height above sea-level. . . The greater is the absorbing power of the air for heat rays emitted from the ground, the higher will that layer be. But the higher the layer, the lower is its temperature relatively to the ground; and as the radiation from the layer into space is the less the lower its temperature is, it follows that the ground will be hotter the higher the radiating layer is. Chris Colose This is one of the problems I have with the simple layer model as it is introduced in some textbooks, such as Dennis Hartmann’s or David Archer’s “Understanding the Forecast.” This is where you simply add up the influence from successive blackbody “layers” with a final result of something that usually ends up looking like T_s=T_eff*(N+1)^0.25, where N is the number of layers, and T_s and T_eff are the surface and effective temperatures, respectively. Archer discusses some of the incompleteness of this model in his class lectures (lack of convection, layers are not fully transparent in the shortwave nor fully opaque in the longwave) but I think the whole presentation misses the point completely Barton Paul Levenson Your CO2 absorbs an infrared photon, one of its electrons jumps a level, and it either radiates another photon of the same level, or more likely, crashes into a nearby nitrogen or oxygen molecule and transfers some of the new stuff as kinetic energy. Temperature is a measure of kinetic energy at the molecular level; the faster the molecules jiggle, the hotter the object. Thus the atmosphere warms up. Those collisions transfer energy *back* to the CO2, which radiates by the (wavelength-specific) Stefan-Boltzmann law. Some of the energy goes back down to the surface and heats it above what it would be from sunlight alone. Eli Rabett The short answer to the question of where the energy comes to warm the surface is from energy that left the surface but was turned around by backradiation. Without the greenhouse gases it would just keep going And RayPierre “The way the greenhouse effect really works is that adding CO2 reduces the infrared out the top of the atmosphere, which means the planet receives more solar energy than it is getting rid of as infrared out the top. The only way to bring the system back into balance is for the whole troposphere to warm up. It is the corresponding warming of the low level air that drags the surface temperature along with it” Settled Science?
    Response: [Dikran Marsupial] Some of those explanations are completely consistent with the "Top of the atmosphere" explanation, particularly that of Ekholm, Rabbet and RayPierre. Colose seems to be merely arguing a point on the details and Levinson is discussing part (anl only a part) of the same mechansim.
  19. Certainly it's settled science. No need to post from another blog to show that there are folks who misunderstand part or,indeed, all of it; just read the posts here! Mind you, if you want to understand the science your self you'll need to read one of those book things, possibly with the support of a physics (or physical science) degree. If you haven't done that, probably tre next best thing is to pist rubbish on a blog... ... Oh!
  20. Fred, You're making much of the perception that there are somehow two contradictory theories of GHE. As Tom and others have tried to explain to you, this is a false perception. The explanation relying only on backradiation is often referred to as the idealized or simple greenhouse model. It is a simplification, not a contradiction. The full explanation relies on both backradiation and the altitude of effective TOA radiation. I don't understand why you're having so much difficulty grasping this. Do you believe that atomic theory is in dispute because the Bohr model is still taught in elementary school?
  21. Fred Staples @967 & 968, you quote a number of well informed people expounding the theory of the GHE which I expounded @944, and which is the only theory of the GHE expounded by regular defenders of climate science on this site. You also quote three people who may be considered to be defending a grey slab model (which is physically false), if that quote was all you knew of there opinions. However, Ray Pierre fully and explicitly defends the lapse rate theory in your first quote, and Tamino quotes Eli Rabbett as defedning it in your second; so we know that your selected quote does not represent their whole opinion, which is in agreement with Ray Pierre's first exposition. So, on the evidence you present, there is a consistently accepted theory of the GHE which has been expounded since at least 1901 - as shown by earliest quote. So yes, that part of the theory is settled science. And while even settled science is always up for grabs if a better theory comes along, given that this settled science rests on such fundamental theories as quantum mechanics and the laws of thermodynamics, and literally millions of observations including some on systems as diverse as Venus, Earth, and Mars, if any better theory every comes along, it will be a close observational approximation of the current theory. So what is your point? (Please find a thread relevant to this discussion to answer this question, for it is plainly not relevant here.)
  22. The real problem in fitting Greenhouse Theory to observation is comparing a planet with an atmosphere to a planet with no atmosphere; this is not possible. A hypothetical atmosphere that contained no GHGs is still held in place by gravity and it will still have a temperature like any other gas in contact with an illuminated surface that can absorb and emit radiation from a star. When considering a planet with an atmosphere without any radiating/absorbing GHGs (or with, for that matter) it is important to remember that the rocky surface is no longer the planetary surface but it is the atmosphere; leaving the problem of deciding where the atmospheric surface is exactly located. The concept of an atmosphere without GHGs is perfectly valid; such an atmosphere would still have a temperature gradient due to the effect of gravitational compression, any satisfactory theory needs also to account for the gradient.

    The claim that lapse rate or gravitational compression is responsible for the GHE is not directly relevant to this thread, as has already been addressed in multiple links provided. Please take this particular point of discussion elsewhere.

    Edit: "responsible for the GHE" should read "responsible for the warming attributed to the GHE"

  23. damorbel @973: Are you saying that we cannot test GH theories because we cannot compare planets with and without atmospheres? In that case, the presence of the moon refutes the claim. Such comparisons are easily made. Or are you saying that we can only test GH theories by comparing planets with GHG concentrations in their atmospheres to planets with atmospheres but no GHG? Again, you are wrong; for we can certainly compare planets with different concentrations of GHG, and that is sufficient. Continuing on, certainly the concept of an atmosphere without GHG is perfectly valid. Let us assume, for example, a planet with only nitrogen in it's atmosphere so that, for practical purposes, it is transparent at all wavelengths. It will be heated slowly at the surface until energy flow from the surface matches that to the surface (on average). The atmosphere above the surface will have a temperature gradient defined by g/c(p) = 9.81/1.039 = 9.44 K/km. I know this because we already have a theory that accounts for the gradient. That theory is independent of GH theory in the same way that the laws of thermodynamics. IE, it is an independent theory from which (along with some other theories) GH theory is derived. Curiously, the derivation is a logical derivation. Therefore, the standard theory of the GHE cannot be false unless at least one of: The laws of thermodynamics; The ideal gas laws; Quantum mechanics; The relativistic version Maxwell's theory of electricity; or The theory of gravitation, is false. So would you please acknowledge (after having been told inumerable times) that there is a well grounded theory of the lapse rate, and hence a theory that incorporates gravitation into the physics of atmospheres; and tell us just which fundamental branch of physics you think needs to overthrown by your no doubt brilliant, but never revealed proof of an error in GH theory.
    Response: [muoncounter] In keeping with above moderator responses, please do not attempt re-starting the lapse rate conversation ad nauseum.
  24. If anyone is feeling that their science-senses have been badly assaulted and would like some reading for restoration, SoD has started a new series Simple Atmospheric Models which is part one. I have no doubt we can look forward to some elegant prose and explanations.
  25. In a series of posts, I have tried to demonstrate that “higher is colder” is the only theory of AGW that does not contradict basic thermodynamics. Sadly, it is the only theory that G and T do not address. It is a top-of-atmosphere theory (where CO2 effects are not swamped by water vapour) and it depends on the existence of the lapse rate. The climate models are based on this theory, (which does not mean that it is correct, Tom) and predict mid-troposphere temperatures trends about about 20% higher than surface trends (50% higher in the tropics, where increased evaporation should produce the famous missing hotspot). To test the theory, we can look at the satellite data (from 1979) and, separately, radio-sonde data compiled by the Hadley Centre. At first sight, any debate is settled by the satellite data, which shows trends in the opposite direction to the models (wikipedia - satellite temperature measurements): Mid Troposphere : 0.52 degrees per century Lower Troposphere : 1.4 degrees per century However, the commentators cast doubt on the upper atmosphere results because they are contaminated by readings weighted from the stratosphere, which is said to have cooled (see below). A more straightforward source is the radio-sonde data from the Hadley Centre, which provides data at all levels. The trends over the satellite era, in degrees C per century, are as follows: Lower Troposphere 1.45 kilometers : 1.54 Mid Troposhere 5.56 kilometers : 1.58 Upper Troposphere 9.13 kilometers : 1.27 Lower Stratosphere 11.74 kilometers: -0.28 (not significantly different from zero) Upper Stratosphere 21 kilometers : -8.10 Has the stratosphere cooled? In the upper reaches, unquestionably, but these tenuous regions will not effect satellite readings. The lower stratosphere has not cooled significantly, but the more or less constant temperatures might mask (to some extent) warming in the troposphere as viewed by the satellites. Those whose business it is are working on this. I tested the significance of all the data (the use of second decimal places presumably shows that scientists have a sense of humour), and there is 1 chance in 18 that the trend difference between the lower and upper troposphere arose by chance, (ie from random fluctuations in the data) which is just less than the conventional 5% level. What can we conclude from this data? Warming there has certainly been but the data lends no support to any theory of causation. If I were an AGW enthusiast I would be particularly worried about the lower trend in the upper troposphere. And the satellite data would be conclusive (against “higher is colder”) were it not for the constant (ie not cooling) lower stratosphere temperatures. The data also confirms another piece of conventional sceptical wisdom. Working back from the latest data, we can ask how far we must go to detect a statistically significant period of warming. The answer, for the mid and lower troposphere, is 15 years. For the upper troposphere, 19 years.

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