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The greenhouse effect and the 2nd law of thermodynamics

What the science says...

Select a level... Basic Intermediate

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

Climate Myth...

2nd law of thermodynamics contradicts greenhouse theory


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


At a glance

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

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

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

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

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

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

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

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

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

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

Further details

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

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

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



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

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

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


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


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

Latent heat

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


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

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


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

Energy balance

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

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

Energy Budget AR6 WGI Figure 7_2

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

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

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

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

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

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

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

Tyndall 1859

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

Update June 2023:

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

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

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Comments 926 to 950 out of 1089:

  1. les 925 "Where did the rest of the material come from" Calculated base upon GHG physics. For example, an atmosphere with LW ε=0, will reflect all terrestrial emissions. That is, until accumulated energy is sufficient for visible spectra emissions. By the way surface energy for 1.998046785(Teq) should be 120422 W/m^2.
  2. L.J. Ryan that's just your interpretation.
  3. Riccardo 927 you said: "that's just your interpretation" Be a bit more specific please. What is "that"?
  4. LJRyan @924: 1) The emissivity/absorptivity of a body varies with wave length. Therefore there is no absolute emissivity, only emissivity/absorptivity relative to a certain range of frequencies of emissions/absorptions. Hence we have: (Eq 1a') reflectivity(sw) = earth's albedo(sw) = 0.3 Eq 1a") 1 - reflectivity(sw) = emissivity(sw) = 0.7 (Eq 1b') reflectivity(lw) = earth's albedo(lw) = 0.02 (Eq 1b") 1 - reflectivity(lw) = emissivity(lw) = 0.98 Where (sw) indicates the range of wavelengths at which the Sun's radiation is most intense, and (lw) indicates the ranges of wavelengths at which the Earth's thermal radiation is most intense, and where equation (1a'and ") consider the whole Earth system, while equations (1b'and ") consider only the surface of the Earth, and do not include the effects of the atmosphere. 2) (Eq 2) is ok as it stands, provided it is indexed for wavelengths as in equation 1. 3) Equation 3 is false in that you interpret σTe^4 as dealing with the Earth's surface only, while S/4*(1-A) definitely deals with the total incoming radiation at the top of the atmosphere. Consequently, equation 3 should read: (Eq 3) σTe^4 = S/4*(1-A) where Te is the effective temperature of the outgoing radiation at the top of the atmosphere, S is the total incoming solar radiation at the top of the atmoshere and A is the Earth's Albedo. Because equation 3 is valid only for the TOA, it places no limit on surface temperature of the Earth by itself, and no limit on the maximum energy radiated by the surface per second. 4) Equation 4 is false. The maximum black body absorption at the TOA is S/4, ie, the case where the Earth's albedo is zero. In this case, it is approximately 340 w/m^2. 5) Equation 5 is false. You had already applied the shortwave emissivity by compensating for Earth's albedo. There is no need, and it is contradictory to apply a second and different emissivity value. 6) Adjusting for errors to date, equation 6 is true. Stated correctly it is that the maximum out going radiation from the Earth at the top of the atmosphere, averaged over time, is S/4 or approx 340 w/m^2. Note, this is a TOA equality, not a surface equality, so as yet it tells us nothing about the Earth's surface temperature. 7) Equation seven and comments are irrelevant because of the preceding errors. We are not screaming about forcings. We are wondering why you can't even get the simple things right. I will not comment further at this time because: a) You have not established the appropriate groundwork, and are instead working on a host of demonstrably false assumptions. b) Your tables which carry your argument have unclear symbols, and are derived by an unexplained method. In other words, they are simply bare assertions.
  5. L.J. Ryan - Fascinating post, you've obviously put a lot of work into it. It is, unfortunately, completely incorrect. Tom Curtis has shown that far more rigorously than I could. As les noted, you have an embedded link to a Professor Jin-Yi Yu's lecture on the greenhouse effect. It's a nice presentation - I suggest you actually read it, and it's conclusions, rather than mining it for equations.
  6. LJR, I have to thank you for the link to Pr Jin-Yi Yu's lecture, which indeed could not be recommended enough. It certainly would be a nice addition to the site, or to the scientific guide.
  7. Tom Curtis 929, KR, les Did you actually comprehend my post or just offer a knee jerk retort. re 1)Your Eq1 equations confirm mine. I'll prove it to you...what is the SW flux incident on the earths SURFACE? What is the SW absorptivity of the earth SURFACE? re 3) My (e3) is "mined" directly from Jin-Yi Yu lecture...KR, les and Philippe Chantreau seem to think highly of his presentation. So if I have got it wrong so does he. Your added commentary regarding TOA blackbody temperature is specious. Two reasons: first, the quote "Energy emitted by Earth = Energy absorbed by Earth" are not my words...look it up. Notice no mention of TOA. Second, the emission as defined by Stefan–Boltzmann law are from a blackbody's surface, not some arbitrary distance in order manufacture a energy gain... your definition is complete nonsense. re 4) Ok, let's eliminated earth's albedo and re-calculate blackbody maximum....T= (340 W/ m2 *1/σ).25 = 278K. Any interested readers should note, the absolute maximum blackbody temperature, with absolute maximum possible SW input is still, 10o colder, then actual temperature. Let me repeat that, GHG physics fabricates energy sufficient enough to confer temperature 10o above that which the sun provides! Tom Curtis do you deny this fact? re 5) You want to make SW absorption by the earth SURFACE 240 W/m2, fine. Shall I recalculate with this slightly higher flux, SURFACE absorption. As I suspect you know, there will be little change to the results. re 6) Ok, lets correct the record, please provide the actual SW absorption for the earths SURFACE. re 7) Since you obfuscate GHG physics mechanics invoking earths albedo, lets remove albedo and test this falsehood. No albedo, maximizes SW input, 340 W/m2 incident to the SURFACE. Given this most fantastic crutch, do you, Tom Curtis, KR, les, Philippe Chantreau, DSL, RW1, Stu, Phil, scaddenp, e, muoncounter, John Cook, DB, any of the other { -snip- } have confidence radiative forcing will work? Any interested readers should note, I will spot GHG physics the full solar input 340 W/m2 to the SURFACE, no albedo, and I contend it can not rectify the required energy to achieve earth's mean temperature of 288K.
    Response: [muoncounter] Please read the Comments Policy more carefully; accusations such as that removed from your comment are unnecessary and unacceptable. Do not overuse the emphasis; it is tantamount to shouting.
  8. Ryan. Thanks for including me in your rant. But you will note that I have not participated in your calculation thread of argumentation. The reason I have not us that as a physicist, I know thus is not how one actually thinks about this kind if problem. I've made my remark about the blog post. Respond to that or not; but I'm not being sucked into this particular bit of kinda-garden-proifiness.
  9. les 933 I'm not sure what you are saying/asking...are you referencing your post 925 where you asked: "Where did the rest of the material come from (it is only polite to reference sources, after all)?" Assuming yes, these formula are straightforward applications of GHG physics. I know that sounds obligatory, yet this is a very true answer. It is only this "physics" charade which permits such misapplication of know laws. Do you wish to see the actual equations implicit in within data tables? If so, no problem. Please reply affirmatively and I will post later this evening.
  10. Ryan 934 Assume No. HTH.
  11. L.J. Ryan - The most important issues I see with your postings are: - Absorptivity/albedo vary with wavelength; your initial problem statement did not incorporate that. - 240 W/m^2 enters the climate at TOA (boundary condition), including all SW albedo effects. The appropriate satisfaction of that boundary condition is that 240 W/m^2 leave the TOA. However, you make the (false) assumption that this power level is a boundary condition on the surface. That boundary condition misapplication is a huge error, and leads you in the wrong directions, and to ridiculous results. As stated before, given a known amount of outgoing radiation, the black body temperature is an absolute minimum on the temperature of an equivalently radiating graybody, due to the relationship of emissivity and temperature. The following is a rough zero dimensional calculation, but actually is quite close to measured effects: Without GHG's (ignoring affects on SW albedo), 240 W/m^2 of SW would enter the climate, and the only exit would be LW radiation from the surface through LW transparent atmosphere, average surface LW emissivity of 0.98, hence a temperature of -16.7C. With GHG's and an effective LW emissivity of 0.612 (that's measured, L.J., not made up, from the LW spectra to low orbit), the temperature is: T = [ P / ( ε * σ ) ]^0.25 K (Stefan-Boltzmann equation) or [ 240/(0.612 * 5.6704*10^-8 ]^0.25 - 273.15 = 15.2C Which, not surprisingly, matches our experience; ~15C surface temperature. Those are the measurements and the math, with an appropriately applied boundary condition of 240 in/240 out. If your hypothesis does not match the measurements, it's probably time for a new hypothesis!
  12. - 240 W/m^2 enters the climate at TOA (boundary condition), including all SW albedo effects. The appropriate satisfaction of that boundary condition is that 240 W/m^2 leave the TOA. However, you make the (false) assumption that this power level is a boundary condition on the surface. That boundary condition misapplication is a huge error, and leads you in the wrong directions, and to ridiculous results. Surely this assumption that LJR makes is equivalent to assuming that there >is no Greenhouse effect. In other words LJR's argument is circular: he's assuming what he's trying to prove.
  13. LJR is banging the table based on his notion that 'the blackbody temp at a given flux represents the maximum temperature.' Putting this unsubstantiated phrase into the google machine, there are no occurrences of it other than in these SkS comments. There don't even appear to be any denier blogs sourcing this sentence. However, there are multiple occurrences of statements which say, in essence, 'the wavelength of maximum flux represents (in this case via an inverse proportion) the blackbody temperature.' Are we simply witnessing a case of reversed word order? If so, this is truly much ado about nothing.
  14. I am sorry not to have responded before this, damorbel (872). Sadly, in the interval, we seem to have left basic thermodynamics (and G and T) behind. Heat is not what is measured by temperature. Internal energy is what is measured by temperature. Before internal energy can do anything (create work or raise temperature elsewhere) it must be transferred from a higher to a lower temperature, from a source to a sink. It will then become heat, which is the net transfer of energy, and the work it generates, or the warming it produces, will conform to the second law. That is why we must use the net transfer of energy to the atmosphere, e 873, from the surface, and not the back transfer (the negative term in Stefan Bolzmann) to calculate any possible GHG effects. From the source, surface, to the sink, atmosphere, most of the energy transfer is via conduction, convection and evaporation. From the source, atmosphere, to the final sink, space, all the transfer is radiative. However, the first and second laws are not concerned with transfer mechanisms. The final outgoing energy, atmosphere to space, must balance the incoming solar energy (first law). If we make the simplifying assumption of an effective emission level in the atmosphere, this fixes the outgoing radiative temperature (at 255K as it happens). Anything which increased that temperature would increase outgoing radiation, and the atmosphere would cool down. Anything which reduced that temperature would have the opposite effect. So why is the surface temperature about 33 degrees C higher? Because of the lapse rate. As damorbel has pointed out, gravity compresses the atmosphere and the work done in the compression warms it up. This has nothing to with radiative effects. It is a function of gravity and specific heat (page 45 of Elementary Climate Physics by Taylor), and is about 6K per kilometre of altitude. So, we if we can accept: 1) that there is sufficient water vapour in the atmosphere to absorb all, or nearly all, of the net outgoing energy, and 2) the effective radiative temperature of the atmosphere to space is 255K at an effective altitude of about 5 kilometres, there is no need to pursue greenhouse theory into the realms of quantum electrodynamics. G and T are right, and the simplistic “back-radiation” theories of AGW are wrong. However, there is one more explanation that is more difficult to refute: the “higher is colder” theory which suggests that increased absorption in the atmosphere will raise the effective radiative altitude to a higher and colder level via the lapse rate. This will reduce outgoing radiation, and the atmosphere and surface will warm to compensate. Effectively, the lapse rate will shift to the right. Does the evidence support this theory? The radio-sonde and satellite data should show this effect over the past 40 years when CO2 has been increasing relatively rapidly. I will down-load the data to try to find out. Please don’t expect anything conclusive.
    Response: Not gravity again :( See, among other rebuttals, Tamino's little gem, the detailed response (be sure to read the comments, too) by Chris Colose, and the lengthier series of posts on Science of Doom. If that's not enough, start searching the intertubes for "Steven Goddard Venus."
  15. LJR, your shouting is not impressive. As for this question " have confidence radiative forcing will work?" Answer is yes. Muoncounter above summarizes well some of your confusion. You should look again at Pr Jin-Yi Yu's lecture. This statement:"So if I have got it wrong so does he" does not follow from logic at all.
  16. Fred Staples, "Please don’t expect anything conclusive." Fear not.
  17. Fred Is the atmosphere being actively compressed by gravity? Is it more dense here at the surface than it was yesterday? The answer, of course, is no. Therefore no work is being done. Indeed, we can experience this in everyday life. Pump up your bicyle tyres quickly to 60psi. You've done work on them and they've gotten hotter due to compression. Leave the bike alone for a bit and come back later. The tyres are now at the ambient temperature. How did that happen? They're still at 60psi (the force analagous to gravity here is the tension of the inner tube) but the fact that they're at significantly higher pressure than their surroundings doesn't make them hotter*. Gravity, like the tension of an inner tube, is no substitute for thermodynamics. *PS I had one 'sceptic' argue back that when you cycle around the tires get hot. Apparently not familiar with friction!
  18. A tiny Excel exercise for L.J.Ryan and others: Create a new spreadsheet. Enter the values below: A1: 1.0 A2: A1-0.01 Copy A2, paste from A3 to A50. B1: =(240/(A1 * 5.6704*10^-8 ))^0.25- 273.15 Copy B1, paste from B2 to B50. Explanation: With 240 W/m^2 (fixed) radiated as power, and varying emissivities, what gray body temperature (in degrees C) is required to radiate that 240 W/m^2, using the Stefan-Boltzmann relationship? An emissivity of 1.0 represents a perfect black-body, 0.98 represents the Earth's surface with no GHE, and an emissivity of 0.61 is quite interesting.
  19. Fred Staples @939, first let me surprise everyone and congratulate you on being almost entirely correct. I notice that you indicate that: 1) The effective temperature of the outgoing radiation is 255 K; 2) That the effective altitude of radiation to space is about 5 km. From these it follows that 3) The (average) temperature of the atmosphere at about 5 km is about 255 K. You also note that: 4) The lapse rate (in the troposphere) is entirely determined by the local gravitational accelerationg, g, and the specific heat of the atmosphere; and that 5) The lapse rate is approximately 6 degrees per km (6.5 is more accurate). Therefore: 6) The average surface temperature is (5 * 6.5) + 255 = 288 K. That is the greenhouse effect in a nutshell. To see this, consider an example in which the atmosphere absorbs (and radiates) no IR radiation. In that case the effective altitude of radiation to space would be 0 km, and hence the surface temperature would be (0 * 6.5) + 255 = 255 K. It is not the lapse rate, therefore, which is responsible for the elevated surface temperatures, for it is (near) constant in both scenarios. Rather it is the presence of IR absorbing and radiating gases in the atmosphere. We can consider the case where the concentration of GHG in the atmosphere decreases. This will lower the effective altitude of radiation to space, and consequently lower the surface temperature (but not the effective temperature of radiation to space). Conversely, if we increase the concentration of GHG, that will raise the effective altitude of radiation to space, the surface temperature will rise, all else being equal. Hence, from principles you have just espoused, the green house effect follows by simple logic. Back radiation does come into the picture. Without the return of some energy from the atmosphere to the surface, thus reducing the net transfer of energy from surface to atmosphere, an increase of the Earth's surface temperature would be impossible. But that transfer (in keeping with the 2nd law of thermodynamics) can never exceed the energy transfer from the surface to the atmosphere (except locally and temporarily). If it rises to a level which would warm the surface by more than the amount indicated by the lapse rate and the effective altitude of radiation to space, the result is simply an increase of of convection and evapo/transpiration, thus nullifying the effect.
  20. KR You said : However, you make the (false) assumption that this power level is a boundary condition on the surface. and T = [ P / ( ε * σ ) ]^0.25 K [ 240/(0.612 * 5.6704*10^-8 ]^0.25 - 273.15 = 15.2C from where does the P (240W/m^2) LW originate....the surface? This very flux is the sole source of LW...without the 240 W/m^2 of SW input the there will be no LW. So save changes to albedo or solar radiation, this IS a boundary condition for radiative energy. Said otherwise, because P input to the surface must equal P output at can not get more LW flux out then SW flux in. Re-radiating Pout can not increase Pin. Delta T must be a function a non-radiative input. To claim effective LW emissivity of 0.612 is measured, is specious. How do measure “effective emissivity”? Emissivity with the qualifier effective, only aids in obfuscation. “Don't bother looking a the real mechanics of GHG physics, it can all be explained by effective emissivity"
  21. Wow. Comment 945 and counting! Not to intrude too much on everyones fun, but a few questions for Fred: "From the source, surface, to the sink, atmosphere, most of the energy transfer is via conduction, convection and evaporation." Source please! Radiation transfer from an object at temerature x is determined only by its temperature, not other parallel heat transfer mechanisms. "and the simplistic “back-radiation” theories of AGW are wrong. ". Oops. Small problem here Fred. Back Radiation has been observed for decades and has been increasing in the radiation frequencies of the GH gases. Damn pesky thing observations aren't they. A beautiful theory derailed by a mere observation. "That is why we must use the net transfer of energy to the atmosphere, e 873, from the surface, and not the back transfer (the negative term in Stefan Bolzmann) to calculate any possible GHG effects" Wrong Fred. Yes the net of the two flows will be what determines (is) the actual energy flux. However this is made up of several different phenomena that occur because of different mechanisms. Radiation flux from the surface is driven solely by surface temperature. Absorption by the atmosphere depends of the absorption properties the GH gases alone. Back Radiation depends on the temperature of the lower atmosphere at an altitude where the path back to the surface is not 'optically thick'. Several phenomena coming together to create the GH Effect, rather than the GH Effect being caused by the net of the heat flux.
  22. Fred "If we make the simplifying assumption of an effective emission level in the atmosphere, this fixes the outgoing radiative temperature (at 255K as it happens). Anything which increased that temperature would increase outgoing radiation, and the atmosphere would cool down. Anything which reduced that temperature would have the opposite effect." You are missing several factors here Fred. As GH Gas levels increase, then the altitude at which emitted photons have a clear path out to Space increases. With altitude Temperature decreases so the emission temperature decreases so less radiated because the altitude of radiation increases. To use a simple analogy, its like a Cloud Bank. At the bottom of the 'cloud' a photon can 'see' the ground so can reach it. At the top of the 'cloud' a photon can 'see' Space and can reach it. One of the two effects of increased GHGas levels is to increase the upper altitude of the 'cloud'. So when a photon can reach Space it will be emitted from air that is colder. There is an excellent article on the radiative physics of the GH Effect by Prof Ray PierreHumbert in Physics Today here Have a look at his figure 3a, modelled and measured spctrum of radiation leaving the Earth. At around wavenumber 670, right in the highest absorption region for CO2, the amount of energy reaching space spikes up. Right in the middle of the highest absorption part of the CO2 band the emission temperature spikes back up! Why? Because the altitude at which the path to Space at that wavenumber is clear because of the high levels of absorption is SO high that it is above the altitude where lapse rate causes a temp drop with altitude and is high enough that atmospheric temps are climbing in the upper stratosphere. The models of radiative transfer are so accurate that they capture this altitude dependent temperature behaviour superbly. That graph is a thing of transcendent beauty.
  23. 947 - Glenn. Nice article link. As an aside, and of only the slightest relevance to this blog post, I note his statement "The planetary warming resulting from the greenhouse effect is consistent with the second law of thermodynamics because a planet is not a close system"... as noted above and to which 934 Ryan should have assumed I was alluding. Now, I suggest that as, as noted by the Economist, this is the 150th anniversary of some relevant and great physics (the unification of Electric and Magnetic fields) - we pay respect to this great moment by giving up on this assault on the nodal discipline of physics by attempting to prove/disprove another of it's great achievements (the laws of thermodynamics) through bean-counting and pseudo-modelling.
  24. les 948 Let me see if understand your revised position on the GHG physics and the 2nd law. I paraphrase you (maybe): Because the earth's radiative energy system is not a "closed loop system" and the 2nd law applies only to "closed loop systems", GHG physics therefore does not follow nor is required to follow the 2nd law. Do I have this right?
  25. L.J. Ryan, you 'quote' the phrase "closed loop system" twice in your comment above, yet I cannot find it anywhere in the preceding comments. I assume this is meant to be a reference to comments about over-simplified versions of the 2nd law of thermodynamics (e.g. 'energy can only flow from hot to cold') only being applicable to 'closed systems'. The 2nd law of thermodynamics is universal (so far as we know)... however, poorly stated versions of it require qualification.

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