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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.

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 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 776 to 800 out of 1613:

  1. But Daniel, the thread has been instructive. Pretty much every kind of wiggle imaginable has been attempted. If anyone who has any doubt about GHGs and the 2nd law after reading the entirety of this thread, they should get some sleep and try it again in the morning. Or perhaps try a more thorough explanation of a pretty simple physical interaction.
    Response:

    [DB] Anyone with the willpower to read the entirety of this thread has a cast-iron stomach and a thing for pain. Maybe that's why I'm a mod. :)

    It should be painfully obvious by now that all that is being offered up are permutations of permutations (ad nauseum) of debunked and rebunked arguments.

  2. John and moderators, I agree. Despite DSL's point (valid to an extent), I can not see how allowing the same obfuscation again and again adds anything. Most readers who are unfamiliar with the physics would only take away the impression that this is a matter of debate and their perception of the whole process might be totally confused. Obfuscation is not useful to anyone.
  3. Philippe Chantreau "Most readers who are unfamiliar with the physics would only take away the impression that this is a matter of debate and their perception of the whole process might be totally confused. Obfuscation is not useful to anyone" Said otherwise: Quick kill the debate! Uncomfortable points of contention must not be seen! Back tomorrow, if this thread is still open.
    Response:

    [DB] Despite handwaving implications to the contrary, the existence and length of this thread is mute testimony to the tolerance of non-physical points of contention. On-topic comments constructed to comply with the Comments Policy go unmoderated, as the vast majority of readership here at Skeptical Science can attest.

    You have yet to demonstrate the physical-ness of your position, as other participants have pointed out to you several times.

  4. Nonsense and more obfuscation. Your accusation would be somewhat insulting if I cared the least about your opinion. If you want to debate atmospheric physics that are obvious to all researchers in the field, you should take it to the peer-reviewed litterature. I'll be very curious to see how your first paper looks like. What you are trying to argue about is no more a matter of debate than protein encoding by DNA. I have seen nothing of value for any kind of debate in the tediousness with which you have drowned this thread.
  5. Re 769 RW1damorbel (RE: 755), ""And why the 'GH' effect is not a radiation effect... from... GH gases." OK, then what is the primary mechanism for the greenhouse effect?" Since the GHE is an explained as a radiation effect t "No amount of refocussing ...... Or, in other words, increase the temperature of.... anything. That is what the 2nd law is all about." #Responding you say:- "The second law primarily states that heat can only flow from warm to cold - not the other way around." Yes However, you say also:- ".. the rate the incoming energy can leave the system from the surface is slower than the rate it is coming into the surface." Most GHE explanations say that this 'slowing' is because of a warming effect on the surface by radiation from GH gases in the atmosphere. Since the atmosphere is colder than the surface any radiation from it will not warm the surface because its photons do not have the energy to do this. What does happen is, photons from the surface, having more energy than photons in the upper atmosphere warm it, the heat thus transferred upwards is re-radiated (by GHGs) into deep space, keeping them cool. Do you agree? Then you write:- "The effect in principle is not much different than the interior of a car heating up inside on cold day from sitting out in the Sun. The Sun's energy is mostly transparent through the windows. It's then absorbed and re-radiated by the interior car components. The rate at which the energy is entering the interior is faster than the rate the re-radiated energy can leave the interior; therefore, the interior has to heat up." What you say doesn't just apply to a car, it is the same for a greenhouse or any surface exposed directly to the Sun's output. It's well known that, in a desert, the Sun can heat a surface well above 100C, enough to fry an egg. But even the arguments for the GH effect agree that it is the average temperature that is inportant, so they account for this by saying the Sun's output (the solar constant ) is not the measured 1370W/m^2 (@5780K if they include the temperature of the photons) but 342.5W/m^2 this latter would give an average temperature of about 279K, an average taken over the entire planet - summer and winter; pole to pole. Further you have:- "Ultimately, when the rate of energy entering something is faster than rate it can leave, the something has to heat up. That's the GHE." Couldn't agree more. Are you able to say at what temperature this would stop, if at all? The only beef I have with the arguments for the existance of the GHE is that it is not supported by well established thermal physics, like focussing photons increases their energy, simply not true. If it were true mirrors would change the colour of light when they reflect it; now that would be strange!
    Response:

    [DB] "The only beef I have with the arguments for the existance of the GHE is that it is not supported by well established thermal physics"

    Then you haven't been paying attention, clearly. Read the whole post, starting at the beginning. The comments too, if necessary.

  6. Re #780 it has :- "an average temperature of about 279K, an average taken over the entire planet - summer and winter; pole to pole." And of course, 'day and night'.
  7. Damorbel - still waiting to hear whether you accept that experiment is way to settle the debate. Sounds like you only want to talk, not find anything out.
  8. Re #782 scaddenp you wrote:- "still waiting to hear whether you accept that experiment is way to settle the debate." Not at all sure what experiment you have in mind. Care to describe it?
    Response: [DB] The question here, which you have conspicuously avoided answering for some time now, makes it clear that the experiment design to prove your alternative world of physics is up to you. We're still waiting.
  9. Re #783 damorbel - & Response: [DB] DB I am deeply dissappointed to have to write this, since my capabilities are definitely 'off topic' and it might be thought that some of the remarks in the cited link are 'ad hominem'. Your link has this :- "I didnt describe any experiment." You must forgive me, I was looking to you to describe an experiment to which I could agree. Next in the link it has:- I proposed that an experiment be designed such that normal understanding of physics and your understanding would calculate a different result." This of course doesn't mean I am abnormal. Then the link has:- "This is normal way to test scientific arguments." I'm afraid I do not quite understand what this means, does it also mean that I cannot achieve a scientific result? And:- "I asked if the experiment didn't go your way," As yet no experiment to 'go my way' Further in the link:- "whether you would be prepared to abandon your view and read the textbook. (ie, behave like a scientist) Interesting question. But I don't know which textbook I am suppose to read or whether it is a requirement for scientists to read text books. Personally I recommend original works, textbook contents are at least 2nd hand if not much more; at university my tutors always advised original texts, they had a low opinion of published textbooks. Finally:- "Got a yes/no? In fact, have you got an experiment that you think validates your views over mainstream physics?" I have set out clearly what the essence of how energy is transferred by means of photons and so far nobody has shown it to be incorrect.
    Response: [muoncounter] We've heard the one about textbooks before. No need recycling your old ideas when they didn't work first time around.
  10. LJ Ryan, I note that you continue to make nonsense claims about greenhouse gases being unable to redirect energy from a colder area to a warmer one while refusing to answer how a parabolic mirror does so. In short. You give every appearance of knowing that your argument is groundless and not even trying to defend it... save by obfuscating with trivialities; Like using a solar cooker to cool something. Which really applies the same principle in reverse. Infrared energy coming off the object inside the cooker is reflected away towards open space. Provided the cooker is insulated enough to limit IR coming in from other directions and the IR input from the area it is pointed towards is less than the IR being reflected away from the object you get a net cooling effect. This proves that energy can flow from warmer areas to cooler ones... just as using the cooker/parabolic mirror during the day proves that energy can also flow from cooler areas (the mirrored surface) to warmer areas (the heated object at the focal point). damorbel: I thought your arguments were too ridiculous to be actually believed back when you were just arguing things like 'the reflectivity of an object has no impact on its temperature' and 'electromagnetic waves can only travel from cold areas to warmer areas in large bandwidths'. Now that you've moved on to 'the greenhouse effect is caused by gravity' and the like we clearly live in universes too profoundly different to allow any sort of rational discussion.
  11. Damorbel @780, One last chance:
    Most GHE explanations say that this 'slowing' is because of a warming effect on the surface by radiation from GH gases in the atmosphere. Since the atmosphere is colder than the surface any radiation from it will not warm the surface because its photons do not have the energy to do this. What does happen is, photons from the surface, having more energy than photons in the upper atmosphere warm it, the heat thus transferred upwards is re-radiated (by GHGs) into deep space, keeping them cool. Do you agree?
    1) The Green House Gases in the atmosphere undoubtedly radiate in all directions as, a) this is the predicted behaviour in theory of radiation; and b) the radiation from those gases have been observed from space, and from high flying planes lookding down; and from the ground and from low flying planes looking up. An example of one such measurement is found in the intermediate version of the above article. So, as a matter of empirical fact, IR radiation is emitted by GHG in the downward direction. 2) The surface of the Earth has a very high emissivity and hence absorptivity in the wavelengths in which IR radiation is emitted by Green House Gases. This is shown very clearly (from observation) in post 703 by Alexander above. Note, the wavelength of peak emission by CO2 is 15 microns, with the "wings" of peak emission extending from 13 to 17 microns thus showing significant overlap with every type of surface shown, except coarse snow, which of course significantly overlaps with H2O emissions. Thus, over land, the vast majority of Downward Long Wave Radiation is absorbed by the surface, and at sea a significant proportion of it, in most cases the majority of it is absorbed. 3) If a photon is absorbed by a surface, the surface gains the energy that was contained in the photon (by conservation of energy). 4) If energy is absorbed by a surface, all else being equal, the temperature of the surface will rise, and the surface is warmed. 5) However, the surface of the Earth is typically warmer than the atmosphere, so it itself is radiating energy to the atmosphere, and is radiating more energy than it receives from the atmosphere. 6) Therefore, absent any other energy sources, the net effect of the interchange of photons between atmosphere and surface is that the surface cools and the atmosphere warms. 7) However, if the atmosphere was not there, or did not radiate IR radiation: (a) the total energy emitted by the surface would still be the same, because that energy is solely a function of its temperature and emissivity; but (b) the surface would receive less energy because it would not be absorbing photons emitted by the atmosphere. 8) Therefore, over a given period of time, and ignoring all other energy sources, the Earth will cool quicker without an atmosphere containing GHG than it will with one. 9) Of course, the Earth's surface is periodically warmed by a very bright energy source, the Sun. For most locations on Earth, the period it is warmed is for on average 12 hours out of every 24. 10) The amount of energy received from the Sun in any 24 hour period at any location is (to a first approximation) not a function of the temperature at that location. Therefore, the Earth at any location will be warmer if it cools less at night because it will add the Sun's energy received that day to a higher base level. 11) Therefore, because GHG slow cooling, they result in warmer temperatures on the surface of the Earth, not because they are by themselves capable of providing a net warming to the Earth, but because they slow the loss of the energy provided by the Sun. (12) This does not explain the equilibrium temperature of the Earth's surface, which is governed by the need for the Outgoing Infrared Radiation to balance the Incoming Short Wave Radiation, which balance is achieved by the interplay of upper tropospheric temperatures and surface temperatures brought about by the lapse rate and GHG concentrations. Each of (1) through (12) above is straight forward, blindingly obvious, and well confirmed by by being predicted by basic physical laws, and by being observed multiple times. Jointly, they refute your entire case. I am not entering into a discussion on this point out of deference to the moderators request that we not feed the trolls. However, laid out step by step like this, even you, Damorbel, should be able to see what absolute drivel you have been serving up.
  12. Damorbel: "Since the atmosphere is colder than the surface any radiation from it will not warm the surface because its photons do not have the energy to do this. What does happen is, photons from the surface, having more energy than photons in the upper atmosphere warm it, the heat thus transferred upwards is re-radiated (by GHGs) into deep space, keeping them cool. Do you agree?" So you're saying that the photons emitted by the atmosphere are only emitted away from the surface. No photon could possibly be emitted toward the surface, because the surface is warmer. Do you agree?
  13. Re #785 DB you wrote:- "This proves that energy can flow from warmer areas to cooler ones... " The basic 2nd Law. Further you wrote:- "just as using the cooker/parabolic mirror during the day proves that energy can also flow from cooler areas (the mirrored surface) to warmer areas (the heated object at the focal point)." When a mirror focusses the Suns image on the food you are saying... that the energy comes from the ....mirror? Ahem, CBD I think this is not right. Doesn't the energy come from the Sun and is just redirected by the mirror? A mirror is about as far from a black body as it is possible to get, it doesn't absorb radiation. A mirror's temperature is not changed by incident radiation because it is reflected without being absorbed; that is why a mirror is used to block radiation to and from a vacuum flask. Likewise mirrors do not emit radiation; you claim that heat (in a solar cooker) 'goes from the mirror' but the temperature of a mirror is not changed when the sun shines on it, only the food is cooked!
  14. Re #787 DSL you wrote:- "you're saying that the photons emitted by the atmosphere are only emitted away from the surface. " No, I didn't say that. The photons emitted downwards have lower energy than those at the surface so there is no warming of the surface, it is the emitting gases in the upper atmosphere that are warmed by by the (more energetic) photons emitted by the surface. And further you wrote:- "No photon could possibly be emitted toward the surface, because the surface is warmer. Do you agree?" No I don't agree. See the first answer.
  15. Damorbel: "No, I didn't say that. The photons emitted downwards have lower energy than those at the surface so there is no warming of the surface, it is the emitting gases in the upper atmosphere that are warmed by by the (more energetic) photons emitted by the surface." So the natural question, then, is "what happens to these lower-energy photons?" Are they or are they not absorbed by the surface? If not, what happens to them?
  16. Damorbel: "Doesn't the energy come from the Sun and is just redirected by the mirror?" Irrelevant gibber-gabber. The source of the radiation does not change its behavior, but even if it did... the energy being redirected by the greenhouse gases 'came from the Sun' too. The object at the focal point of the parabolic mirror is warmer than the air around it, which is in turn warmer than the mirror. Yet energy moves through space from the cold mirror to the warmer air to the warmer still object. This is exactly what you claim violates the 2nd (and/or 1st) law of thermodynamics when greenhouse gases do it. So how is this commonly observed phenomena possible? It violates what you claim to be a fundamental law of physics, but it is observed reality. Ergo... your claims about thermodynamic laws must be false.
  17. DSL 760 "The reflective surface focuses incoming radiation." --yes, solar radiation when cooking. "That radiation could be coming from the atmosphere." ---from the sun for cooking...that is how it works. If you point away from the sun the target COOLS below ambient temperature. "Your argument is that we can't differentiate between radiative transfer and conduction/convective transfer." ---I'm not sure what you mean. "In other words, why doesn't the solar cooker cool to near absolute zero when pointed at the open night sky?" ---It fact, it's temp. drops well below ambient. However the atmosphere, as you know, is not absolute zero. Thus potential drop is limited by atmos. temp. and the rate of drop is determined by delta T between cooker contents and the sky. If the atmosphere is same temp as the cooker no cooling occurs. If the atmosphere is warmer then the cooker, the contents warm.
  18. CBDunkerson 785 "LJ Ryan, I note that you continue to make nonsense claims about greenhouse gases being unable to redirect energy from a colder area to a warmer one while refusing to answer how a parabolic mirror does so." Where/when did I say this?
  19. Philippe Chantreau 772 "Considering that the body in question is continuously receiving energy at a more or less constant rate, it does not seem so difficult to imagine that its temperature will increase if the rate at which it can radiate that energy is decreased. In fact, I would have a hard time to understand if it did not warm up under these conditions. " Philippe, blackbody radiation is based upon a "constant rate". Adding more radiation of less magnitude does NOT change the output. Adding more radiation of the same magnitude does NOT change output. Adding more radiation of higher magnitude DOES change the output. Do you agree? Any interested readers should note your evasion, and that you do not feel confident enough to discuss the case on its merits.
  20. KR 773-775 A bit sleight of hand KR. Power input is also based on emissivity. Lower emissivity, higher reflectivity, thus less power input. Lower "fixed" input lower base temp i.e. lower then 255K. So GHG effect must account for more then 33K. Said differently, a body does not absorb one emissivity and radiate at another. Regarding the Alan Siddon post, neither he nor I believe earth is a blackbody. The gist of the post, blackbody represent max radiation input and max output. Regardless of reflection and re-radiation, max radiation output cannot be exceeded less higher energy input. Very simple concept, proven by years of actual data measurements. Do you agree?
  21. DB "You have yet to demonstrate the physical-ness of your position, as other participants have pointed out to you several times." Physical-ness of MY argument. Yet you proponents contradict one another when TRYING to explain the lack of "physical-ness" of my contentions. You press for answer on behalf of whom you agree. Yet chastise skeptics for re-posting question which remain unanswered.
  22. You can't formulate anything in a coherent fashion. You're the one evading my question with irrelevant gibberish. I am not talking about adding radiation of any magnitude, whatever that means. I am talking about a spherical blackbody receiving solar radiation at a constant rate in w/sq m, in the solar spectrum. If, by any means, that blackbody's ability to radiate energy out is impaired, what will happen to its temperature? About this: "it's temp. drops well below ambient" How does it square with this? "If the atmosphere is same temp as the cooker no cooling occurs." It drops below "ambient" but then if the temp is the same as the ambient atmosphere, no cooling occurs? More incoherence and more nonsense.
    Response: Let's end the sniping here, there is nothing constructive coming from it.
  23. LJ, Please clarify your statements where you say "Adding more radiation of the same magnitude does NOT change output". What precisely do you mean by "more" radiation of the same "magnitude"? By magnitude are you referring to the frequency of the radiation? Let's say we have an object in a vacuum absorbing one photon per second with a wavelength of 1um for all photons. If we increase the rate of incident energy to two photons per second, but they all remain at a wavelength of 1um, are you saying the amount of radiation emitted by the object does not change?
  24. LJR: "neither he nor I believe earth is a blackbody." Now that's a radical change of heart, as you specifically described earth's blackbody temperature here. And you've totally ignored the complete defenestration of your argument by KR (#773-775) and CBD (#785). As far as 'fundamental flaws' (#797), you haven't proven them; a reference to someone else's blog and 'google solar cooker' do not cut it as scientific source material.
  25. Me: "In other words, why doesn't the solar cooker cool to near absolute zero when pointed at the open night sky?" LJ Ryan: It fact, it's temp. drops well below ambient. However the atmosphere, as you know, is not absolute zero. Thus potential drop is limited by atmos. temp. and the rate of drop is determined by delta T between cooker contents and the sky. If the atmosphere is same temp as the cooker no cooling occurs. If the atmosphere is warmer then the cooker, the contents warm. Or, rather, if the cooker is radiating energy at the same rate that the atmosphere is radiating at it (removing conducted energy from the equation), then the cooker will remain at the same temperature. If the atmosphere is not adding radiated energy to the cooker, the cooker--if unable to shed via conduction (e.g., in a vacuum box)--will cool to near absolute zero when pointed at the night sky. But, of course, all atmospheric layers do radiate, and some of this radiation is absorbed by warmer surfaces and warmer atmospheric layers. Here's the key, though: the current temperature of any atmospheric layer or material within the system is that specific temperature because the atmosphere is already adding its radiated energy. The system is dynamic. if we take away the atmosphere, the surface eventually (quickly) reaches a lower equilibrium temperature. That the atmosphere doesn't heat the surface or warmer atmospheric layers is false. The heating is already taking place, and the result is the equilibrium temp. It's a mistake to think that this equilibrium temp is a baseline temp to which atmospheric energy is added. If we increase the radiative density of the atmosphere, the radiation has a greater chance of being redirected (in all directions). The maze is more complex, the pachinko machine has more pins, the dam is higher, etc. etc. The amount of available, usable energy in the lower layers increases because it's around longer in those layers. Do I have this right?

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