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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 701 to 725 out of 882:

  1. Tom Curtis (RE: 635), "RW1 @630, as it is difficult to carry on two discussions at once on the same thread, do you mind holding of on the discussion of the relevance of the light box until we have settled that it does not violate any law of thermodynamics? And to that end, do you agree that the light box does not violate any law of thermodynamics?" I'm not sure why you are asking me this. I do not believe that the GHE effect violates any of the laws of thermodynamics.
  2. Re 701 RickG you wrote:- "Since I asked you to post your revised edition correcting Trenberth's short-comings on how it should appear, I gather your above comment is code for you can't support your claims?" Looking at the Trenberth pdf you cite: on p5 he has:- "At the surface, the outgoing radiation was computed for blackbody emission at 15°C using the Stefan–Boltzmann law R = εσT4, (1) where the emissivity ε was set to 1." Emissivity set to 1? As John McEnroe might have said "he can't be serious" Using such a figure for the Earth's surface inevitabl gives the wrong answer because the Earth's surface does not, by any stretch of the imagination, match the specifications of a black body. Worse still he claims 333W/m^2 from clouds. Clouds are even further from being black bodies. You make no reference to the fact that GHGs absorb and emit radiation only as a function of their temperature, not of their altitude. You must attach some importance to this. These things are the very essence of heat transfer in the atmosphere and anywhere else; I do think they should be examined by climatologists.
  3. damorbel #703 Just a reference about emissivity values. ε=1 is not that bad an assumption at all.
  4. damorbel @ 703 Your basic misconception concerning Trenberth's schematic appears to be about what the schematic is not about. It is not depicting the Stefan–Boltzmann Law and black body radiation. The schematic is based on actual instrumental data showing how energy is distributed globally. Once again, please read the Trenberth et al paper. Earth's Global Energy Budget.
  5. damorbel (RE: 700), "Trenberth's diagram is deficient in so many ways it is beyond revision. The so-called 'back radiation' has the concept behind it that there is a place in the atmosphere from where 'back radiation' comes; but even John Tyndall knew that this is not the case. He measured both the emission and absorption by GHGs and found that their emitted radiation was completely absorbed by gases at a lower temperature." Yes, the Trenberth diagram is a confusing and misrepresents many things. What Trenberth refers to as 'back radiation' is really mostly downward emitted radiation - some of which last originated from the Sun, some of which last originated from the surface emitted, and some of which last originated from the kinetic energy (latent heat and thermals) moved from the surface into the atmosphere. As I was trying to explain earlier in this thread, the proper definition of 'back radiation' is the downward emitted radiation from the atmosphere that last originated from the surface emitted radiation. "This last means radiation emitted by GHGs is immediately absorbed and re-emitted by adjacent GHGs. This is so when the pressure and temperature gradient are zero; in the atmosphere the density reduces with altitude so the upwardly emitted radiation is not completely reabsorbed, an increasing %age gets ever higher until it escapes completely; that is the mechanism for heat radiation from the Earth." The key thing to note is that the 239 W/m^2 of post albedo energy entering becomes about 390 W/m^2 at the surface. The absorption and isotropic re-emission of the outgoing surface emitted infrared by GHGs and clouds is slows down the rate at which energy can leave, causing a 'back up' of energy at the surface. Essentially, what this means is it takes a 'back up' of 390 W/m^2 at the surface to allow 239 W/m^2 to leave the system, offsetting the 239 W/m^2 coming in from the Sun.
  6. RW1 & damorbel, Well guys, there is no doubt that neither of you are the slightest bit interested in discussing any science with the intent of sharing information and understanding. Both of you take a perfectly legitimate and superbly illustrated schematic showing 'Earth's Global Energy Budget' and purposely misrepresent it out of context, completely ignoring the paper that describes it in detail. If you are still troubled with Trenberth's schematic and paper, I suggest you contact him personally. His email address, fax and phone number are listed prominently the NCAR site to which I have previously linked. As for me, I am through with your hand waving and obfuscation.
  7. Re #705 RickG you wrote: "Your basic misconception concerning Trenberth's schematic appears to be about what the schematic is not about. It is not depicting the Stefan–Boltzmann Law and black body radiation." I suggest that you examine the document as closely as I have. All the power figures (W/m^2) e.g. 'Surface Radiation 390W/m^2' and 'Back Radiation 333W/m^2' appear to be derived by applying Stefan's formula (with an emissivity =1) to an estimate of the local temperature. Trenberth mentions 'real' temperatures (°C or K) only seven times and then only to explain how the figures were manipulated to make them more acceptable (see box on p315) The box also contains this unused information:- "The surface emissivity is not unity, except perhaps in snow and ice regions" which beggars belief. Snow certainly has a very low emissivity (and the corresponding low absorptivity) because that is why it takes a long time to melt as ground cover. It is only when the (absorptive) dark earth underneath begins to appear that radiation has a real effect melting the snow. You wrote further:- "The schematic is based on actual instrumental data showing how energy is distributed globally." I don't think you are right here. The only measurements that Trenberth uses are satellite measurments that even he admits are unreliable (because of instrument failure) and disagree violently e.g. compare the 'Solar reflected' (p316) for KT97(Trenberth) at 107W/m^2 and JRA(Japanese re-analysis) at 95.2W/m^2. Trenberth then goes on to use the difference of these measurements to calculate the extra heating due to radiation and the figure vary from positive to negative, depending on who is doing the measurements. Of course it isn't as simple as that; no, many of the figures used have all been re-analysed (aka - they didn't meet requirements) e.g. JRA aka Japanese re-analysis; NRA aka NCEP–NCAR re-analysis and ERA-40 aka 40-yr ECWMF Re-Analysis (p316). This kind of stuff reminds me strongly of [- snip -]
    Response: [muoncounter] Edited due to political accusations in violation of Comments Policy.
  8. Rick G, "Both of you take a perfectly legitimate and superbly illustrated schematic showing 'Earth's Global Energy Budget' and purposely misrepresent it out of context, completely ignoring the paper that describes it in detail." I've read the Trenberth 2009 paper, and yes, it misrepresents the most crucial aspect of the entire GHE. That is how much of the emitted surface radiation is from 'back radiation' from the atmosphere and how much is passing through unabsorbed and going straight out to space. The paper and diagram makes it look like of the 396 W/m^2 emitted at the surface, 333 W/m^2 of it is coming back from the atmosphere. This is incorrect. Using Trenberth's numbers, only 157 W/m^2 of surface emitted radiation is from 'back radiation'. The diagram also obscures what percentage of the surface emitted radiation absorbed and re-emitted by the atmosphere is downward emitted and what percentage is upwards emitted out to space. Using his numbers, 157 W/m^2 is downward emitted toward the surface and 169 W/m^2 is upward emitted, with 40 W/m^2 passing through the clear sky atmosphere and 30 W/m^2 passing through the cloudy sky atmosphere. The total transmittance of 70 W/m^2 is not referenced in the paper and seems to only be a rough estimate or guess.
  9. 707 RickG. I completely share your sentiments - although I hope not sufficiently as to violate the comments policy ;) There's been a lot of words attacking GHE... but no physics that I can discern. I'd suggest that those who feel there's a flaw in the GHE argument construct a clear, physics based, derivation - or find a flaw in explanations such as SoDs - until which time, IMHO, it's probably best to give it a rest.
  10. Re #612 Tom Curtis you wrote:- "3) The molecules in a gas do need to have significant kinetic energy to stay aloft. That is the energy of motion that they have because of the temperature of the gas. If the gas cools" You are so close to an important fact about atmospheres in general. You write "if tha gas cools" - as a molecule rises in the atmosphere it loses kinetic energy(KE) to gravitational potential energy (GPE). But the KE of a gas (well, degree of freedom, DOF; actually) is its temperature, so when it loses KE to GPE it must cool. This is so important because it establishes the basic lapse rate of 6.5C/km(altitude).
  11. 710 les Thanks les, it is a challenge to respond to such foolishness and still keep one's cool enough to remain withing the comments policy. After writing a response I usually walk away for a while before submitting it. I almost always find myself toning my initial reply's down. It doesn't always work but for the most part it does. Contrary to contrarians beliefs, I do get posts deleted from time to time. With contrarians it is quite often difficult to figure out if they really don't understand the science or if they are just up to mischievous. I hope I'm wrong but I fear the latter is too often true.
  12. damorbel @711, almost right. The temperature of a gas is its mean kinetic energy. That can be expressed in terms of the sum of its kinetic energies for each of its external degrees of freedom, but that does not include internal degrees of freedom, ie, rotational or vibrational energy. The heat capacity ratio of an ideal gas, on the other hand, does depend on the internal degrees of freedom as well, so that the heat capacity ratio is just (f+2)/f where f is the degrees of freedom. The heat capacity at constant pressure and the heat capacity at constant volumes are then just simple functions of the heat capacity ratio. The interesting thing about energy in the form of external kinetic energy an energy in the form of vibrations and rotations within the molecule is that they tend to equalize, so that the energy in each degree of freedom is, on average, the same. That means that when kinetic energy in the axis perpendicular to the surface is lost due to gravity, it is partially replaced by energy from the two axis parallel to the surface, plus from rotational and vibrational energy as a result of collisions. Likewise, a molecule gaining kinetic energy perpendicular to the surface will tend to redistribute it to the other degrees of freedom as the result of collisions. So, it is not gravity alone that determines the lapse rate, but gravity and the redistribution of energy form the various degrees of freedom of the gas molecules, ie, gravity and the heat capacity of the gas. Hence, the lapse rate equals the negative gravitational acceleration divided by the specific heat for constant pressure. All of which is very interesting, but as has been pointed out before, it does not determine surface temperature. It only determines the relationship between surface temperatures and the temperatures at given altitudes. In other words, these fact could all be true about the atmosphere and the Earth's global mean surface temperature be 255 degrees K. It is the greenhouse effect which explains why it is not.
    Response: [muoncounter] Lapse rate is another favorite drum to bang; see 30 November, 525 comments up thread.
  13. RW1 @702, do you mean that you have been muddying the waters by insisting on using non-standard definitions of back radiation, and treating all radiation to space as having originated either directly or indirectly from the surface as a matter of definition for no purpose? The topic of discussion in this thread is the Greenhouse effect and the 2nd law of thermodynamics. If you do not think there is a contradiction, and are not arguing against those who think their is, you have nothing to add to this thread because you are of topic.
  14. Tom Curtis 699 You said: "I get 3.4249 * 10^-19 Joules per photon myself, and hence four times that energy contained in the box." How does a photon of 3.4249 * 10^-19 Joules outside the box increase it's energy to 1.36996E-018 Joule inside the box? And now having a wavelength 145 nm inside the magic box, the photon (as a stipulation of the filter lid) can escape to the vacuum..where it instantaneously lengthens to 580 nm. This most improbable supposition is the basis of your models and GHG theory...shown here to clearly violate the 1st law.
  15. scaddenp647 KR671 KR "If, however, you carefully add up the Trenberth numbers without rounding you get an imbalance of about 0.9 W/m^2 less leaving than arriving. That's the forcing. " scaddenp "Umm, this is about whether the GHE is consistent with thermodynamics. If it is, the adding CO2 will create forcing as KR has pointed out. (and is measured at TOA)." Low temperature, (lower energy) atmosphere adding radiative heat to the warmer surface is a violation of the 2nd law. To proclaim star sourced energy can be increase itself by it's own reflection and/or re-radiation is a violation of the 1st law. "Like conduction, thermal energy is in harmony with the second law of thermodynamics such that, in the absence of work, thermal energy is radiated spontaneously from higher temperature to lower temperature matter." M. Quinn Brewster Thermal Radiative Transfer and Properties
  16. Damorbel @703, the sentence you quote is clearly intended to describe the procedure in Kiehl and Trenberth 1997. Following that quote, Trenberth, Fasullo and Kiehl then go on to discuss the changes in method for T, F & K 2009. The most important of these is that they factor in the difference in temperatures due to latitude, which results in a significant increase in the calculated surface radiation. To achieve greater precision, they take the mean of surface radiation in a model which correlates well with surface radiation measurements around the globe. They then discuss differences in emissivity. They note that low emissivities are found in regions with high surface temperatures, ie deserts, the two factors tending to cancel each other out. The also note that low emissivity means not only reduced surface radiation, but reduced absorption of back radiation, factors which again tend to cancel each other out. T, F, & K note (from Wilber et al 1999) that differences in emissivity can result in up to a 6 w/m^2 reduction in surface radiation. That represents just 1.5% of the average surface radiation. A 1.5% reduction in back radiation absorbed would be 5 w/m^2, making a difference of just 1 w/m^2 over deserts. The total area of deserts on Earth (excluding the Artic and Antarctic) is about 20 million square kilometers, or about 4% of the Earth's surface. Therefore, correcting for the low emissivity of deserts would have altered the final figure by just 0.04 w/m^2, which given the margin of error in the calculations is to small an effect to by worried about. In addition, your claim that the atmosphere is treated as having an emissivity (and hence absorptivity) of 1 is plainly refuted by the fact that some energy escapes from the surface to space in the diagram. McEnroe's histrionics where not even amusing in his time; in the era of Hawkeye, they would have just make him look foolish. He would have been forced to win matches on skill rather than on gamesmanship. On this forum we have something better than Hawkeye. We can read the original papers, and we can think.
  17. LJRyan @715, the photon does not increase its energy. Rather, if you feed in one photon per time interval, at equilibrium there will be four photons in the box, each with the same energy, and hence the total radiant energy in the box will be four times that which is fed in in each time interval. You cannot, apparently, manage even simple reading comprehension, yet you purport to lecture the world's atmospheric physicists about the relation between thermodynamics and the greenhouse effect.
  18. LJRyan @ 716 - you assert that "Low temperature, (lower energy) atmosphere adding radiative heat to the warmer surface is a violation of the 2nd law" That's actually not correct. The 2nd law only talks about NET heat transfer. You can have heat radiating from an object at 500º to an object at 1000º. Obviously, the warmer object will be radiating *more* heat back the other way, but it's still receiving heat from the cooler object. Anyway, don't take our word for it. Ask Dr Roy Spencer, one of the most prominent opponents of human-caused global warming. He discusses it here, and again in more detail here. Dr Spencer may hold views on the causes of global warming that are at odds with the vast majority of climate scientists, but he certainly understands radiative heat transfer (and that, to be honest, makes it really puzzling why he so strongly disagrees with the consensus view on this matter).
  19. LJRyan @716:
    "Low temperature, (lower energy) atmosphere adding radiative heat to the warmer surface is a violation of the 2nd law."
    The energy increase comes from the sun, not the atmosphere. All the GHG in the atmosphere do is decrease the efficiency with which the energy is radiated away. There is a very simple model of this. Suppose you have an electrical stove with a pot of water on it. The pot has no lid. You heat the pot until it is gently simmering, and stably so. In this situation, the heating element will be glowing slightly red, showing a temperature of about 500 degrees C. The water will be just of the boil, indicating a temperature of about 100 degrees C. We now place a lid on the pot, leaving only a small gap. Even though the we do not adjust the heating element, the water will commence to boil vigorously and may even boil over. It you look at the inside of the lid, however, you will see water condensing on it, showing clearly that it is below 100 degrees C in temperature. So, addition of a cooler part, the lid, has caused a hotter part (the water) to gain heat. In thermodynamic terms, the analogy between this and the greenhouse effect is exact. So, anytime anyone on Earth boils some rice, they prove you wrong about thermodynamics.
    "To proclaim star sourced energy can be increase itself by it's own reflection and/or re-radiation is a violation of the 1st law."
    See 718
    ""Like conduction, thermal energy is in harmony with the second law of thermodynamics such that, in the absence of work, thermal energy is radiated spontaneously from higher temperature to lower temperature matter." M. Quinn Brewster Thermal Radiative Transfer and Properties"
    This quote is quiet accurate, but refers to the net energy transfer. It is plainly not true that a cooler body cannot radiate energy towards a warmer body. What it cannot do is radiate more energy that is absorbed than does the warmer body toward it. Ie, radiated energy from the warmer body - radiated energy from the cooler body is always positive. That it is not simply prohibiting any radiation from the cooler body is shown simply, and aptly by the actual measurement of back radiation. The atmosphere is, in nearly all cases, cooler than the surface. Despite this radiation from the atmosphere to the surface has been measured many times. Here is one example: From Science of Doom. See also this and this.
  20. Re #717 Tom Curtis you wrote:- "The[y]also note that low emissivity means not only reduced surface radiation, but reduced absorption of back radiation, factors which again tend to cancel each other out." Yes indeed. And so did Gustav Kirchhoff writing in 1862. From that he concluded that the temperature of a body black or or otherwise, is not affected by its emissivity as long as it has no internal heat source (or heat sink) i.e. it is in thermal equilibrium. This is the basis of his argument that emissivity and absorptivity are the same for any given body. The only internal heat source* the Earth has is the radioactivity in is rocks and (possibly) some residual heat from the formation of the planet. Measurements have shown these internal heat sources contribute not more than 0.1W/m^2 to the outgoing radiation, a negligible amount. The meaning of this is clear, the size of the albedo has no affect on the temperature of the Earth, the position of climatologists, that the Earth's equilibrium temperature is lowered by 33K from 288K to 255K has no scientific basis. What the albedo does is reduce the rate of change of temperature, this follows because a high albedo reduces both the absorptivity and the emissivity by exactly the same amount. Common experience shows the reality of this; an every day vacuum flask has a highly reflective coating that produces this effect exactly. I apologise to muoncounter if I have mentioned this before but he should take note that, as yet, the argument about the vacuum flask has not been countered by anyone and the comparisin with a planet heated entirely by energy from the Sun is 100% valid. And, incase you are wondering, Kircchoff's proof of this is based entirely on the 2nd Law of Thermodynamics. * The Earth has a heat sink, chemical change. Some of the Sun's energy is converted into chemical energy, but not very much.
  21. L.J. Ryan. We have measures (ie real world) of 341W/m2 incoming at TOA and 396W/m2 being irradiated from surface. Wow, 1st law violation? Are you trying to say nature is breaking the 1st law? The measurement must wrong? Well no. Tom and others have very patiently been explaining to what is really happening. Ditto, this whole thread on 2nd law where you are jumping on the premise that atmosphere is heating the planet. Nope. Thermodynamics is not flawed. Understanding is.
  22. 712 RickG I guess there are several issues. The one I have with this form of argumentation (not particularly this one, but ones like it) is that it's very often to appear to knock down an argument using broad bush-strokes, appeal to "common experience", focusing on missing details etc. What is harder, and rarely done, is to build up an argument - and specifically to build an argument up to the level to be usable for policy... that is the role, e.g. of the IPCC. Now, "do nothing" is a policy. It just isn't good enough to base this policy - which is potentially very very expensive and life threatening - on a level of analysis which is no more than waffle-words. Something much stronger must be built to attack the science as shown on a site like this... ... you just cannot cut steal with chewing-gum. The tools need to be sharper and harder than the thing you're attacking;you need maths, detail, consistency etc. And these things are, by and large, the unknown-unknowns of a lot of "denilists" - all the stuff along the road that ends in a diagram, a graph or a couple of numbers.
  23. Tom Curtis 718 You said: " the photon does not increase its energy. Rather, if you feed in one photon per time interval, at equilibrium there will be four photons in the box, each with the same energy, and hence the total radiant energy in the box will be four times that which is fed in in each time interval." I did not specify a rate, you did. A single photon will transverse the box and/or absorbed and re-radiated countless times within a second...so why no increase in energy? Is there a minimum energy for your box?
  24. Tom Curtis 720 You said: "In this situation, the heating element will be glowing slightly red, showing a temperature of about 500 degrees C." Do you really think the water boils because of "lid" forcing. If you made the lid transparent to IR from 100C to 500C, would the water still boil? I say yes. But before I endeavor to explain this scientifically sound principle, I'll let you reconsider your latest GHG analogy. hint...pressure cooker. What if we removed the pot of water and simply inverted a larger empty pot over the red hot burner, i.e. no conduction. By your supposition, the burner should get hotter...correct? What is the temperature of the top (actual bottom) of the pot? What if we directed the burner toward your magic box. Would the burner get hotter then 500C?
  25. 725 Tom Curtis 720 partial re-post What if we removed the pot of water and simply inverted a larger empty pot over the red hot burner, i.e. no conduction. By your supposition, the burner should get hotter...correct? What is the temperature of the top (actual bottom) of the pot? Would the burner get hotter then 500C? What if we directed the burner toward your magic box. Would the outside of the box, insulation pulled back for sampling, be hotter then 500C

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