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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.

Convection

Convection

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

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.

Advection

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

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.

Radiation

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 October 2017:

Here is a walk-through explanation of the Greenhouse Effect for bunnies, by none other than Eli, over at Rabbit Run.

Last updated on 14 February 2023 by John Mason. View Archives

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Further reading

  • Most textbooks on climate or atmospheric physics describe the greenhouse effect, and you can easily find these in a university library. Some examples include:
  • The Greenhouse Effect, part of a module on "Cycles of the Earth and Atmosphere" provided for teachers by the University Corporation for Atmospheric Research (UCAR).
  • What is the greenhouse effect?, part of a FAQ provided by the European Environment Agency.

References

Denial101x video

Comments

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Comments 351 to 375 out of 763:

  1. “Higher is Colder”, KR,337 is not “part of the greenhouse effect”. It is the only plausible way of explaining how increasing atmospheric absorption and emission can increase the surface temperature. Incidentally, it is a mechanism which G and T did not discuss, although it was current from 1900 onwards. Think about an atmosphere without a lapse rate – an isothermal atmosphere where higher is not colder. Add greenhouse gasses, increase absorption, and you suggest that the atmospheric temperature will increase. What would happen if it did? Apply the Stefan-Bolzmann equation to the radiation to space, and energy emission will also increase (proportional to the fourth power of the atmospheric temperature). But the incoming energy, from the sun, will not change. So the atmospheric temperature will fall back to its original value. My simple model, is designed to make the same point. With a lapse rate, you can suggest that the effective emission level moves up to a colder region, reducing energy emission. All the temperatures must then increase to restore the balance. The only snag with that argument is that the evidence from the last 30 years shows that it does not happen to any detectable extent. Neither G and T (nor I) claim that AGW contradicts the second law. It is just that some of the sillier explanations of AGW do. Most of them confuse heat and energy, which is where entropy comes in. The silliest explanation, which you can still find in modern text-books, (Houghton for example) is the original greenhouse radiative effect. Consider a greenhouse made of non-absorbing material, such as rock salt. It will absorb heat from the sun, the interior will heat up, and, with convective cooling eliminated, the internal temperature will be higher than the surroundings (G and T’s car interiors, for example). The greenhouse will radiate W watts per square meter, proportional to the fourth power of its temperature. Now replace the rock salt cover with glass, which absorbs infra-red radiation. Half of the outgoing radiation will return to the interior, which, so the story goes, will heat up until it radiates 2W. The original W will then be radiated to the atmosphere, and W will be returned to the interior. The ratio of the glass interior temperature to the rock salt interior temperature will be the fourth root of 2, or 1.19. An increase of 19% of the rock-salt interior absolute temperature, or about 60 degrees C. Does that argument sound familiar? You will find it in part 1 of the Rabett paper to which SOD contributed. It is, of course, nonsense. Back radiation from the cooler glass cannot heat the warmer interior. It would breach the second law if it did. To check this R W Woods built two greenhouses – one rock salt, one glass – so that their convective warming would be identical. Any back-radiative effect would heat the glass green-house preferentially. Their temperatures were the same.
  2. damorbel - I begin to see some of your issues, and quite frankly shudder to consider where to even begin. First - Do you think thermal emission is monochromatic? It's not! It covers a broad band of photon energies, due to a large number of possible electron band transitions of different levels. Second - Absorptivity describes the spectral efficiency of absorbing a photon at any particular energy/wavelength. It turns out to be equal to emissivity when the object is at thermal equilibrium. The ground, for example, has about a 95% probability of absorbing a photon at 6 micron wavelength. The thing is, photons do not carry ID cards - a 6 micron photon may be coming from a superheated plasma or a cold atmosphere - there's still a 95% probability of the ground absorbing it, and hence receiving energy from it. The recipient of a photon cannot know and does not care what the source of the photon is. But that photon still adds to the energy of the receiving object. So your statement "The temperatures are the same because the energies of the photons from both sources are the same" is incorrect. The sun provides a bunch of photons at various energies, the atmosphere emits (downward) a smaller bunch of photons at various lower energies, and these sum up to the total energy received by the ground. Which then emits it's own photons of thermal radiation. The heat flow, the net/summed power, is from sun -> ground -> atmosphere -> space, but even a cold atmosphere adds a tiny bit of energy to the warmer ground. If you cannot understand these basics, well, I can't help you, and I can't see spending my time banging my head on the wall.
  3. Fred Staples - "“Higher is Colder”, KR,337 is not “part of the greenhouse effect”. It is the only plausible way of explaining how increasing atmospheric absorption and emission can increase the surface temperature." Quite frankly, no. It's part of the story, but certainly not the entire thing. You might find the simple Excel models I posted here and here of interest. The first is a simple iterative single-layer atmosphere model (no convection/evaporation), so the numbers won't be accurate. But it starts with the surface of the Earth emitting exactly what it receives from the sun (240 W/m^2). Some of that energy is absorbed by the atmosphere, which radiates half of it upwards and half downwards. The end result (illustrative, if not numerically accurate due to model limitations) is that 240 W/m^2 come in, 240 go out, and the surface is emitting 267 W/m^2. A greenhouse gas atmosphere raises the temperature of the surface. The second is a more accurate radiative effect only zero dimensional model, which surprisingly (on my part) gets with 3% of real values. This uses the effective emissivity of the Earth, which drops as greenhouse gases rise (more re-emitted to the ground, also higher effective emission altitudes - both effects). Given an emissivity of .612 (as measured for Earth by satellites), 240 W/m^2 comes in, 240 W/m^2 goes out, and the surface is emitting at about 392 W/m^2 - just as expected. Radiative balances and emissivity decreases caused by GHG's drive surface temperatures to measured values. I'm not interested in convective greenhouses, with or without rock salt - those are red herrings in this discussion of radiative greenhouse effects. As to back radiation - the total energy received by the ground is the sum of solar and back radiation - both impinge on the ground. Arguing that the ground doesn't receive energy from back-radiation is the violation of conservation of energy, and hence the thermodynamic no-no.
  4. A number of these 'models', designed to contradict the standard physics - as well described by SoD - reminds me of the joke: A biologist, a physicist and a mathematician were sitting in a street cafe watching the crowd. Across the street they saw a man and a woman entering a building. Ten minutes they reappeared together with a third person. "They have multiplied", said the biologist. "Oh no, an error in measurement", the physicist sighed. "If exactly one person enters the building now, it will be empty again", the mathematician concluded. (although, personally, I'd expect better of the physicist) Even though the SoD series uses simplified models here and there to explore specific aspects of the physics, overall you can only understand what's happening by understanding the full system and physics. As said above, if a body is illuminated - with photons from any part of the spectrum - from another body, it'll reflect some, absorb others. Those absorbed (depending on the absorptance and spectrum) rise the temperature... the body will always radiate photons (not the ones absorbed, of course) depending on it temp, a la Boltzman + emissivity ... some or all of which (depending on geometry) will impinge on the original body doing the illumination, which will do the same physics. Then, you must account for the spectral nature of absorptance and emissivity, so that the respective conversion to heat and reflection won't be symmetric. Build the model properly, in your mind at least, otherwise you'll end up like our trio above.
  5. "R W Woods built two greenhouses – one rock salt, one glass" Call me curious, but a rock salt greenhouse? Watering time for the plants must be interesting. The experiment by RW Wood was done in 1909. WM Connelly aka Stoat pointed out the error in comparing this exercise to the greenhouse effect here.
  6. les - "A number of these 'models', designed to contradict the standard physics..." I hope you're not talking about the simple Excel models I posted earlier. They both support standard physics, and were intended to demonstrate to various people that greenhouse gases warm the surface.
  7. KR - not at all, I was alluding to 350 damorbel (where one moment all the radiation is returning to earth and the next it's radiating to space) and 351. Your excel and SoD's series are, IMHO, spot on. That people don't find they match their thought models is, IMHO again, because those thought models are wrong.
  8. Re 357 les You wrote:- "I was alluding to 350 damorbel (where one moment all the radiation is returning to earth and the next it's radiating to space)" No les, that's what you said, not me. I agree it isn't right but of course it's your interpretation, not what I said.
  9. Re 352 KR You wrote:- "First - Do you think thermal emission is monochromatic? " No. "Second - Absorptivity describes.... ...ground, for example, has about a 95% probability of absorbing a photon at 6 micron wavelength." Probably. Further you wrote:- "The thing is, photons do not carry ID cards" They certainly do. The energy of a photon is E = hv where 'h' is Planck's constant and 'v' is the source frequency. I suggest you check a book on thermal radiation before responding on this, you are clearly lost on this one. And further you wrote:- "So your statement "The temperatures are the same because the energies of the photons from both sources are the same" is incorrect. The sun provides... " Please check my 350; I was writng about an isothermal atmosphere, one with a uniform (vertical) temperature distribution. I didn't mention the Sun because I was on about atmospheric radiation: in an isothermal atmosphere there is no heat transfer of any sort because heat transport only happens with a temperature difference - standard 2nd law of thermodynamics - don't you think?
  10. 358 damorbel: Clearly that's what I said - and for good reason. Given (for the sake of argument): 1/ "Let us imagine for a moment that the surface and the upper atmosphere are at the same temperature. In this situation both surface and the UA are emitting photons with the same energy" and the assumption it requires... Then, this 2/ "The temperatures are the same because the energies of the photons from both sources are the same;" is a tautology - The spectrum of photons energies would be the same if the temperature, emissivity etc. are the same (said assumptions) - and we ignore it. So, two 'bodies', sufficiently identical to emit the same amount and spectrum of e-m radiation, and, we assume, the same absorptivity, so they identically absorb the energy will, by definition 3/ "there would be thermal equilibrium i.e. no energy transfer and no temperature change." Clearly, without interpretation, implies that no energy is escaping to space or any where else. You couldn't possibly mean that the surface is being headed by anything, like the sun, because you would have said so. yet in your "real" model: "bla bla... it is further radiated into deep space." QED. But really the problem is that you have given a qualitative description of how you feel things work and this leaves the door open to a range of errors - whether interpretation on one side, missing assumptions or just poor physics on the other. As SoD has shown, it is completely possible to build up mathematical models to describe how this works. If someone doesn't agree, the thing to do is present either alternative maths or, at least, show which assumptions or derivations are wrong in the original.
  11. Re 360 les You wrote:- "The temperatures are the same because the energies of the photons from both sources are the same;" is a tautology " Indeed it is a tautology because that s how you measure temperature remotely Then you wrote:- "So, two 'bodies', sufficiently identical to emit the same amount and spectrum of e-m radiation, and, we assume, the same absorptivity, so they identically absorb the energy will, by definition" And "Clearly, without interpretation, implies that no energy is escaping to space or any where else" "no energy is escaping"? That is not the case, the upper atmosphere (UA) is less dense than the surface and will exchange fewer photons with the lower atmospheric layers (and the surface) than pass through (the UA) on their way into space. Having a different density does not mean they cannot have the same temperature but 'the different densities' does translate directly into different amounts of energy. What you are missing is the fact that, with a uniform temperature, the lower atmosphere exchange photons but without any change in their relative energy.
  12. 361 : first, it's not "tautology because that s how you measure temperature remotely", it's a tautology because first you suggest, to paraphrase for clarity: that the em radiation is the same because the temp is the same, then you suggest that the temp is the same because the em radiation is the same. Nothing to do with measuring anything. Anyway, as you then go on to say that in fact they're exchanging "fewer photons", clearly the above is irrelevant, as I pointed out. Then, I'm sure I miss a lot in the real physics, but in this context I'm only looking at your description of how you see things. If something is missing, improve your description. e.g. in "Having a different density does not mean they cannot have the same temperature but 'the different densities' does translate directly into different amounts of energy." Clearly two bodies of the same temperature but different densities contain a different amount of energy. Equally clearly, if they are ideal Boltzmann black bodies they will radiate the same amount of em radiation per unit area. Then at two extremes there are: 1/ If both where in free space, the denser would take longer to cool than the less dense. But eventually both would cool to with a Planks whisker of absolute zero. 2/ If, somehow, all the radiation from each was absorbed by the other, they wouldn't cool. In between 3/ If the radiation from the denser was absorbed fully by the less dense, which in turn lost some energy to free space and some was radiated to the denser object, then, obviously, the amount of energy radiate into space wouldn't be going back to the denser object... it would cool - at some rate depending on it's energy density and the proportion lost in space - etc. till both where again withing a Planks whisker of absolute zero. Of course neither the earth (denser object) nor any part of the atmosphere are anything like that. They are not ideal Boltzmann black bodies. Nor are the em radiation flows so arranged... again, I recommend the SoD series to walk through the incremental complexities of reality.
  13. Re 362 les First you wrote:- "Clearly two bodies of the same temperature but different densities contain a different amount of energy." Then you wrote:- "Equally clearly, if they are ideal Boltzmann black bodies they will radiate the same amount of em radiation per unit area." Which is not the case at all. You are applying Kirchhoff's concept of a black body as a perfect absorber and emitter of radiation and it doesn't apply in this case, GHGs in the atmosphere get nowhere near this model because no gas, in any circumstances behaves like a black body. About your 'two extremes' 1/'free space' Really? Far too undefined; a gas in a vacuum? 2/'If, somehow, all the radiation from each was absorbed by the other, they wouldn't cool' Only if the density was the same and this is absolutely not the case for the vertical profile of the atmosphere. 3/'If the radiation from the denser was absorbed fully by the less dense' Simply impossible; see #2 From what you write 'Of course neither... ' you are clearly questioning the matter, like I am. Good luck! PS I have looked at SoD but he is far from having a good grip of the thermal characteristics of atmospheres - too much sloppy thinking.
    Response: [Daniel Bailey] If you believe SoD to be incorrect, please address that there, as SoD is well-established as an online reference tool known for accuracy in these matters. Until corrected, that status will remain.
  14. 363.... "Which is not the case at all. You are applying Kirchhoff's concept of a black body as a perfect absorber and emitter of radiation " Clearly. I was starting, as you observe, from an ideal model... always good to go back to basics - trying to clarify, at least for my self, your 'model'. which is why, in line with "and it doesn't apply in this case, GHGs in the atmosphere get nowhere near this model because no gas, in any circumstances behaves like a black body." I said that the earth and atmosphere are, indeed, not ideal black body objects. Did you actually read that?!?!? Just for clarity... 1/ no, I think it's clear the radiation is lost. end of. I said nothing of gases - I said 'object', it matters not what the object is made of (p.s. the atmosphere is a gas in a vacuum, but that's by-the-by) 2/... no. Read again they hypothetical - situation. In this highly simple model, not meant to represent the real world, but trying to clarify your 'explanation'... they are the same temp, the same surface area, same everything... except density... They would radiate and absorb the same amount of energy. simple. 3/ no it isn't. if I enclose a dense ball in a less dense shell, the shell will absorb all the radiation from the ball... where else is it going to go!?!? I am certainly not questioning the matter, nor - in general terms - the SoD model, with I rather like. But if you think his thermodynamics is amiss, I'd suggest you concentrate more on that then the e-m radiation bit... which, seems to me, you're struggling with.
  15. 364- in 2/ "same amount of energy" should read "same amount of energy / unit time".
  16. Re 364 les You wrote:- "Clearly. I was starting, as you observe, from an ideal model" If you start your model as a gas 'behaving like a black body' you really have nowhere to go because the odd CO2 (or H2O) molecule (at the density in the atmosphere - think of the thickness when brought to the surface and liquified) will never get anywhere near absorbing all the radiation from the surface. Even this observation is utterly irrelevant because any radiation absorbed by CO2 & H2O in the atmosphere is promptly re-emitted, if it wasn't the temperature of the intermediate layers would change. The atmosphere really is not, as far as radiation is concerned, different from a solid. Radiating solids also need internal heat transport to get the heat to the emitting suface. The emitting surface of solids is not an ideal, theoretical model; it is very complex and depends on the exact composition of the surface, which is seldom the same as the bulk material, it is an oxide or dirt or something.
  17. 366... clearly, and again, we all appreciate the complexities. And, again, I never said gas, I said 'body'. Boltzmann et al don't care what it's made of. Introducing both complexities and irrelevant factors (prompt photon emission? 'prompt' for e-m radiation, is a technical term regarding decay from excited states; does that matter here do you think?) prevent one from seeing the basic facts of the matter which bound such problems - which is the point of idealized models. I really did think going back to basics would help. But I can see that the road is to long and, really, rather than nowhere to go, I have better places to go!
  18. Re 363 You wrote:- "Response: [Daniel Bailey] If you believe SoD to be incorrect, please address that there, as SoD is well-established as an online reference tool known for accuracy in these matters. Until corrected, that status will remain." Sorry if I have upset anyone but I do not use links to put arguments I cannot support myself. Nor do I have any general position on what third party writers say; they may well be very good but giving a general approval seems to be fundamentally insecure since the question of interpretation arises. To put it another way, I require provable and reproduceable facts.
  19. damorbel The theory of evolution by natural selection is neither a provable nor reproducable fact; however that doesn't prevent the majority of biologists accepting that it is correct. Asking for definitive proof of any theory regarding the real world is unreasonable, as demonstrated by David Hume in the 18th century. We cannot observe causality, only correlation, and to move from an observation of correlation to assertion of causation we need to make assumptions. It is impossible to prove any theory about climate, they can only be disproved.
  20. Re 369 Dikran Marsupial Thank you for your contribution. I'm afraid I really don't see the connection between what you write and the application of the 2nd Law of thermodynamics to radiative heat transfer. I might add that the whole of quantum physics was started with the nummerous attempts to explain 'black body' radiation as identified by Gustav Kirchhoff in a way that matched experimental results.
  21. Damobel. Matching experimental results does not prove that the quantum explanation of black body radiation is correct (however it is repeatable). Quantum theory may be a very persuasive explanation for blackbody radiation, but it is not a provable fact. The point I was making is that if you require provable facts abdout the real world, you require the impossible. Science generally concentrates on the most plausible explanations, proof is generally reserved for mathematics. You wrote: "But all that you write makes it increasingly clear that the idea that the upper atmosphere (UA) can raise the surface temperature simply doesn't work." Nobody claims that the upper atmosphere does raise surface temperatures. The energy that causes the temperature of the surface to rise is from the sun, not the upper atmosphere, the upper atmosphere being warmer than outer space just means the surface looses energy to outer space less quickly and hence its equilibrium temperature is higher.
  22. Re 371 Dikran Marsupial, you wrote:- "Matching experimental results does not prove that the quantum explanation of black body radiation is correct (however it is repeatable)." I'm afraid I do not understand what you expect of quantum theory other than 'matches experimental results'. The essence of a good theory is that it enables new experiments to be devised which produce results that could not have been predicted with previous theories. Do you feel that quantum theory is deficient in this respect? Also you wrote:- "Nobody claims that the upper atmosphere does raise surface temperatures. The energy that causes the temperature of the surface to rise is from the sun" All significant climate energy comes from the Sun. The question is about how it is distributed. When you write:- "the upper atmosphere being warmer than outer space just means the surface looses energy to outer space less quickly and hence its equilibrium temperature is higher" Now there are various explanations for this and the presence of gases that radiate towards the surface in the infrared (GHGs) is the matter in hand. It is well established that matter cools when there is a net transfer of energy away from it. Correspondingly its temperature rises when energy is transferred into it. When you say "looses energy to outer space less quickly and hence its equilibrium temperature is higher", you are of course talking about a change in energy distribution. Now according to the 2nd law of thermodynamics a temperature difference is needed for a change of energy distribution and the also other way round, a change in energy distribution is always accompanied by a temperature difference. You seem to agree that it the CO2 in the atmosphere causes a surface temperature rise and many say that it is radiation from increases in CO2 that causes this. However this explanation would need the CO2 in the atmosphere to be warmer than the surface otherwise it will be the CO2 that is warmed by the surface (2nd Law). Personally I can see no other effect of CO2 that comes anyway near explaining temperature changes of any sort. Is there any other effect, in your opinion?
  23. damorbel - The point I was making is that you can reject any scientific theory regarding the nature of reality by demanding provable facts - but that doesn't make it rational or scientific behaviour. Consider a thought experiment, a blackbody object exists in a hard vaccum; initially the object is 273 degrees Kelvin (for the sake of argument), but it will cool by radiation to its environment which is at zero degrees kelvin. Now consider a second identical black body, also initially at 273 degrees kelvin, but now enveloped by a concentric hollow sphere of a blackbody material, leaving a gap all around of 1mm containing a hard vaccum. The shell is maintained at 272 degrees Kelvin. Which object will cool faster and why?
  24. Re 373 Dikran Marsupial, you wrote:- "Which object will cool faster and why?" The first because it radiates to a fixed 0K. Because of this it will eventually reach 0K The 2nd black body cools much less quickly because it radiates to a fixed 272K. Eventually the 2nd black body will reach the fixed 272K of the shell. Only a few people on the second body will notice much difference, 1K change is not very much. Those on the first body will not be caring much, they will have been frozen to death long ago! I am sorry but I can see no point in these examples. However there are interesting observations to be made. The first body has no heat source, internal or external and because it is 'black' it will cool at the maximum possible rate to 0K. If it is not black it will cool at a lesser rate, dependent on the surface emissivity. This could be very low indeed if it had a highly polished surface or even multiple surfaces; that is the principle behind using multilayer foil insulation (MFI) on spacecraft. The point is the MFI stops heat getting out of the craft by reflecting it back into it, so the craft does not cool down quickly. The MFI also reflects incoming radiation away from the craft, which is convenient because it stops the Sun heating it up too quickly. For these reasons MFI is sometimes called 'a thermal blanket'.
  25. damobel how does the first body know that it is radiating to 0K and know to emit fewer photons? BTW, this was the first stage in the thought experiment, lets not get ahead of ourselves, if we take it in small steps it will be easier to find out where our views diverge. The point of the examples is to find the point of divergence, which is the first step in determining which position is correct.

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