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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 851 to 875 out of 1008:

  1. KR 804 I "The climate, on the other hand, is driven by a band-limited solar input which does not match the thermal emissive spectra, is not greatly affected by greenhouse gases, and hence represents a fixed input, not a match to the thermal spectra at all." To further insight lets solve stepwise. The earth SURFACE has a very high emissivity (~.96)...so solar input to the earth SURFACE of 240 W/m^2 equates to~255K. Q1)Do you agree? Solar IR re-radiation via the earth SURFACE equates to ~ 240 W/m^2 emitted at 255K...this represents the temp maximum via solar radiation. Before the apoplectic visceral post, first consider the following. One litter of gasoline contains 34.8 MJ. No matter how well the losses are retarded or how slow/fast those Joules are consumed, the max possible energy/litter is as defined. Q2)Do you agree? Q3)By "thermal spectra" do you mean "atmospheric forcing"?
  2. L.J. Ryan I'll reply to those points out of order, first noting that you keep stating "240 W/m^2 emitted at 255K" without the very important black body included. Q3 - "By "thermal spectra" do you mean "atmospheric forcing"?" No. I mean the thermal emission spectra of the objects in question. The Sun's and Earth's thermal emission spectra are not identical (#27), and in fact barely overlap. Hence what affects one region (visible, IR, etc.) may or may not affect others. Q1 - "..so solar input to the earth SURFACE of 240 W/m^2 equates to~255K." Inexact and misleading. The sun provides ~240 W/m^2 via the 70-75% of solar emissive spectra that makes it through to the surface. This amount is at different wavelengths than the Earth thermal emission. And while 240 W/m^2 may be the energy emitted by a black body at 255K, neither solar input or Earth output is an unfiltered black body curve. Q1 - Nonsense. 255K represents the maximum black body temperature, but since solar input is mostly unaffected by GHG's (except for WV/clouds, but the sum effect appears to decrease emission relative to absorption, increasing forcing) - incoming energy is essentially fixed. And in order to radiate 240W/m^2, a temperature of 255K is an absolute minimum temperature for a gray body such as the Earth, as decreasing emissivity reduces power emitted at any particular temperature. To echo your posting - Do you agree?
    Response:

    [mc] fixed unclosed bold tag

    [DB] KR, I think I guessed correctly as to which comment you were linking to & also included the Figure it seemed likely you had in mind. If I'm wrong, let me know & how to fix it & I will.

  3. KR 852 "To echo your posting - Do you agree?" somewhat Ok, "incoming energy is essentially fixed" i.e. ~240W/m^2, so what temperature should be generated via this, and only this flux. your hyperlink #27 goes nowhere..or is it the included chart
    Response: [DB] See above.
  4. L.J. Ryan - That link to #27 was intended to be the chart; sorry if I was unclear. Given a power to be radiated of 240W/m^2, the Stefan-Boltzmann relationship of Power=emissivity*Area*σ*T^4, where σ is the SB constant, and the [observed, measured!] effective emissivity from ground to space of ~0.612, I expect the surface temperature to be about 287K. A black body could emit 240W/m^2 at a much lower temperature. But: if radiated power remains fixed (by the 1st law of thermodynamics, conservation of energy), any gray body object (or planet) with a lower emissivity must necessarily have a higher temperature than a black body to radiate that power level. Which is the point I have been trying to make for the last several posts.
  5. DB - Thanks, that's where I was trying to point; I was trying to (A) refer to that graph (yes, that's the one) and to (B) make a point that this information been presented since the beginning of this thread. Sorry about the poor typing/tags; there may be more caffeine in my immediate future.
  6. KR 854 You've skipped the SW absorption step. Since you seem to be avoiding my question---Ok, "incoming energy is essentially fixed" i.e. ~240W/m^2, so what temperature should be generated via this, and only this flux?---lets try it this way. Q1)What is the SW radiation emissivity of the earths surface?
  7. L.J. Ryan - I did answer your question: 240 W/m^2 incoming flux is expected to, and does, generate a temperature of about 287K in the Earth climate system. How was I not clear about that? "Q1) What is the SW radiation emissivity of the earths surface": Irrelevant question - it's zero. The Earth is not at a temperature to glow in visible light. The Earth effective absorptivity, on the other hand, is about 70-75% for the solar spectrum. The band-limited input energy that doesn't overlap with the output IR is why input power is essentially fixed.
  8. KR Q2) What is the LW radiation emissivity of the earths surface? Note: I'm not asking about the effective surface to space emissivity but rather the surface emissivity.
  9. L.J. Ryan "What is the LW radiation emissivity of the earths surface?" About 0.98 on average. This is known data; I've stated that as well in this thread. Effective emissivity from the surface to the top of the atmosphere, however, is still 0.612, as shown as the integral of the Earth emission spectra. Incidentally, I would appreciate something longer than three sentence postings in this discussion, rather, a post long enough to have some content worth discussing, perhaps a statement of what your hypothesis is rather than a drawn out, multiple day, QA cycle. This is especially important in this case - if you feel that the radiative greenhouse effect actually violates thermodynamics, then please point out what effect does not, in a way consistent with the very large amount of evidence from multiple investigatory pathways that supports the greenhouse effect. The surface of the Earth averages 14C, and without the GHE it would run at about -20C. What alternative to the GHE do you propose that accounts for that?
  10. damorbel (RE: 780), "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." But the temperature is about 288K - not 279K. How is that so? Here are more questions for you: Do you agree that all of the Sun's emitted energy is radiative? Do you agree that the Sun's emitted energy is transparent through space to the Earth? Do you agree that the Sun's energy is mostly transparent through Earth's atmosphere? Do you agree that space is colder than than the Earth's atmosphere? Do you agree that the atmosphere of the Earth is colder than the surface of the Earth? Do you agree that of the roughly 390 W/m^2 emitted at the Earth's surface, all of it is radiative? Do you agree that the emitted 390 W/m^2 is a result of the Earth's surface temperature and nothing else? Do you agree that the emitted radiation from the surface is mostly NOT transparent to the atmosphere? Do you agree that a lot of the surface emitted radiation is absorbed and re-emitted isotropically by the atmosphere?
  11. damorbel, Do you know that the 2nd law does not apply to photons? Thermal energy by definition is kinetic and not radiative. The kinetic energy in the atmosphere is not what's heating the surface. It cannot as the 2nd law dictates. It's the photons emitted from the surface and re-emitted isotropically by the atmosphere that is heating the surface. The net effect the kinetic energy in the atmosphere has on the radiative budget is zero, as I explained earlier in this thread. It seems to be a significant source of confusion in a multitude of issues - not this one.
  12. At the end of 861, I mean to say "not just this one."
  13. LJR: "Q1)What is the SW radiation emissivity of the earths surface?" What? Why would one even ask such a question is baffling.
  14. Phillippe @863 - Didn't you know - Global Warming is caused by glow-worms. :-)
  15. Re #861 RW1 you wrote:- "Do you know that the 2nd law does not apply to photons? Thermal energy by definition is kinetic and not radiative" I suggest a few moments contemplation will reveal that it does. Anything that radiates heat also absorbs heat and, if two bodies are near each other, they are thermally linked by the exchange of photons, in the absence of other heat sources (and heat sinks) the two will arrive at a common temperature, purely by means of radiation. However radiation is not heat, it is a way of transmitting energy that does not involve mechanical contact, so to that extent you are correct.
  16. Re #865 I wrote:- "they are thermally linked by the exchange of photons" Which is true. But the link does't have to have a thermal spectrum according to the Planck law; even if there was a filter that allowed only part of the spectrum to pass between the two bodies (there normally is a filter of some sort) they would eventually reach the same temperature, the filter just slows things down; it slows them down a great deal if the filter is a highly reflective mirror.
  17. Attractive hypothesis Phil, and as plausible as much of the stuff that has been thrown around on this thread...
  18. Philippe, Phil - My personal suspicion is that global warming is due to an overabundance of hotheaded naked ice borers reducing polar ice, increasing albedo. Obviously in this crisis we should organize large hunting parties to reduce this overpopulation of dangerous animals. Oh, and /sarcasm...
  19. Re #865 RW1 you wrote:- 1/"But the temperature is about 288K - not 279K. How is that so?" Apart from the fact that this 'average' temperature is not accurately known (NASA have a webpage somewhere with +-5K on some median temperature) - all gravitatioally bound concentrations of gas have a temeperature that rises towards the (gravitational) centre, in a star it reaches somewhere between 10^10K and 10^15K, hot enough for thermonuclear ignition. Even the paltry 85km of the Earth's atmosphere shows a temperature profile due to the planet's gravity. It is interesting to note that this gravitational temperature increase is a feature of very deep mines where, in addition to the increasing heat from the Earth (which is very variable with depth) a mine of 3km depth can have additional temperature rise of between 10 and 18K purely due to the higher air pressure at that depth. 2/"Do you agree that all of the Sun's emitted energy is radiative?" - Both electromagnetic and particulate radiation. 3/"Do you agree that the Sun's emitted energy is transparent through space to the Earth?" - I think the nswer is yes. 4/"Do you agree that the Sun's emitted energy is transparent through space to the Earth?" - No. the Earth's atmosphere absorbs all UV <0.3 microns, about 10% of the Sun's output and I believe about 30% in the infrared. 5/"Do you agree that space is colder than than the Earth's atmosphere?" - Space does not have a temperature. Different locations get heat from stars in varying amounts. At night the sky without the Sun has an apparent temperature of 2.7K, this is called the Cosmic Microwave Background or CMB for short. 6/"Do you agree that the atmosphere of the Earth is colder than the surface of the Earth?" - Over a given location - most of the time (except in the stratosphere). (Havn't I seen this stuff before somewhere?) 7/"Do you agree that the atmosphere of the Earth is colder than the surface of the Earth?" - No. 8/"Do you agree that the emitted 390 W/m^2 is a result of the Earth's surface temperature and nothing else?" - See 7. 9/"Do you agree that the emitted radiation from the surface is mostly NOT transparent to the atmosphere?" - See above. 10/"Do you agree that a lot of the surface emitted radiation is absorbed and re-emitted isotropically by the atmosphere?" - Yes Now be so good as to answer my question:- What % of the heat tranferred to the atmosphere from the ground by radiation:- 14%?......40%?.......90%? (You can make your own suggestion if you like.)
  20. Heat. It is much easier to say what heat is not, than what it is. It is not energy, although it is measured in the same units. Because it is not energy, it cannot be trapped, stored or transferred. The internal energy of a system can be defined and measured; it is a property of a system. Heat is not a property of a system. There is no such thing as the internal heat of a system. Most of the confusion in climate science explanations arises because heat and energy are treated as synonymous. Unfortunately, it is conventional to speak of heat transfer when we mean net energy transfer. It works if we keep the definition in mind. Heat is a process. It is energy in transit. It is the net energy transferred across the boundary of system due to a difference in temperature between a system and the surroundings of a system. The idea of net energy transfer is crucial. At the microscopic level, energy can travel in both directions between a higher and a lower temperature. The rate of transfer will be greater from the higher to the lower, so the net transfer will be from the higher to the lower and, risking confusion, we can call this heat transfer. By definition, therefore, it is uni-directional. Spontaneously, heat transfer will cool the higher temperature system and warm the lower temperature. Eventually, all systems in thermal contact will come to equilibrium at the same temperature. This does not necessarily stop energy transfer. It does stop heat transfer. That is why the “back-radiation” explanations of AGW are misleading at best, or wrong. All the explanations which claim direct warming of the surface from back-radiation violate the second law. Heat, net energy, travels only from a source to a sink; from a higher to a lower temperature. This is the only way that raw energy can actually do anything, either generate useful work or warm something. Heat (useful energy) cannot go backwards. For global warming, the first source is the sun, and the earth is the sink. For the atmosphere, the earth is the source and the atmosphere (at a lower temperature) is the sink. Finally, the atmosphere becomes a source and space (close to absolute zero) is the ultimate sink. Quite simple, indeed obvious. No-one would contradict that, surely. Have a look at the version of the Trenberth diagram at post 50, which is quoted all over the blogosphere: Outgoing Radiation: 396 watts per square meter Direct to Space : 40 watts per square meter Back Radiation : 333 Watts per square meter, absorbed by surface (it says) Quite absurd. The correct version is at page 6 of A First Course in Atmospheric Radiation by Grant W Petty. The net outgoing radiation is 21% of the solar energy entering the atmosphere, or 71.7 watts per square meter. This is, of course, a surface cooling effect, alongside conduction and convection (23.9 watts per square meter), and evaporation (78.5 watts per square meter). All these combined are atmospheric warming effects. So have climate scientists made an elementary mistake, as this thread suggests in the introduction? G and T are undoubtedly correct as far as most journalistic, political, and blogosphere posts are concerned. However, G and T did not address the interaction between outgoing radiation to space and the lapse rate, which is the favoured explanation of some of the climate scientists and the RC blog. Before we try to decide, we will have to examine the lapse rate.
  21. #869. Stunning. Please show us your sums for calculating the average surface temperature and lapse rate for say earth, venus, mars by this incredible piece of physics. I am really interested. After all this can be done by normal climate science. Any alternative explanation that you think avoids such "errors as violation of 2nd Law" has to do so as well. Physci claim he/she could though we are still waiting.
  22. Re #870 Fred Staples you wrote:- 1/"It is much easier to say what heat is not, than what it is." - Heat is what is measured by temperature, don't you think? 2/"Back Radiation : 333 Watts per square meter, absorbed by surface (it says)....Quite absurd" - Fred, what I like about 'Back Radiation' is that it goes straight into the surface, nothing is reflected, even though most of the surface is water with a refractive index of 1,33; I'm sure Fresnel is weeping in his grave!
  23. Fred, The back-radiation in Trenberth's original diagram illustrates the gross flow of energy from atmosphere to surface. If you want to see the net energy flow (heat transfer), just subtract it from the gross flow of energy from surface to atmosphere: 356 - 333 = 23 W/m^2 net radiative energy transfer from surface to atmosphere. Where exactly do you see a violation of the 2nd law? Oh and the "correct" version you cited is derived by doing this exact type of math on Trenberth's results. It is the same information, not a corrected version. All they did was sum the gross inputs/outputs into the atmosphere. Also don't forget that Trenberth's diagram documents measured values, it is not a theoretical whimsy. If you doubt that back-radiation exists, go buy an infrared thermometer, point it at space on a clear night, and prove your point.
  24. damorbel @872: 1) Surely you mean that Heat is what is measured by temperature multiplied by heat capacity. "Heat capacity"? How about that. It appears to be implicit to the language of physics (as it has always been to natural languages) that heat is something that can be stored. I think the revisionist physicists who want to outlaw the use of "heat" to describe internal energy are merely sowing confusion for themselves and their students. 2) Any back radiation that is reflected from the surface is simply part of the Surface Radiation. This is because, fairly obviously, IR detectors cannot distinguish between IR radiation emitted and reflected at the same frequency. The amount reflected is, of course, very small, and probably not large enough to include even if you designed instruments that could reliably distinguish it. Therefore there is no problem in treating emitted surface radiation plus reflected back radiation as a single bulk quantity. In this case you are scoffing at ant hills while swallowing mountains of denier nonsense.
  25. Re #874Tom Curtis you wrote:- "1) Surely you mean that Heat is what is measured by temperature multiplied by heat capacity" That would be energy - Joules. Heat capacity is 'C' (Cp; Cv) which is in Joules/Kelvin (J/K) The 2nd law requires for equilibrium, that T is uniform, i.e. no temperature diffences, no teperature gradients. Further you wrote:- "I think the revisionist physicists who want to outlaw the use of "heat" to describe internal energy are merely sowing confusion for themselves and their students." I have noticed this too but it isn't consistent. Since heat is only a function of temperature, it is only a function of molecular motion, the harder they vibrate the hotter things are! The devil in the matter seems to be latent heat which really is a misnomer. Let us take ice; when ice is formed the operative change is the loss of vibrational energy as the molecules line up to form crystals. Crystals have energy stored in the the lattice bonds. This is of course is 'energy in Joules' but it does not affect the temperature as ice forms/melts so it is not really heat but it is part of the internal energy of a water/ice thermal system. I suspect you knew all of this before reading it here. But there seem to be a number of contributors who need reminding! You wrote:- " Any back radiation that is reflected from the surface is simply part of the Surface Radiation." In kinetic theory molecules exchange energy by collision, thus on any (imaginary) surface introduced in a volume of gas the molecules on either side of this imaginary surface exchange energy (momentum, really), (T>0) all the time; so, if you were being pedantic, you could describe this energy exchange as 'forward' energy and 'back' energy and it is going on all the time, at every imaginable 'surface' in the volume. Energy exchange by radiation is not much different, but in this case the collisions are replaced by the emission and absorption of photons. Just like kinetic theory where the 'collisions' are between adjacent molecules. This is where the concept of 'back radiation' fails because it relies on radiation acting over large distances whereas it is actually very local, just the same as kinetic energy exchange. I have referred to this in previous posts, at the time I mentioned Einstein's paper 'Strahlungs-Emission und Absorption nach der Quantentheorie (german 1916) It is available on line in english and it is fairly easy to read and it firmly disposes of the idea that radiating gases can make any difference to the distribution of energy in a gas.

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