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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 626 to 650 out of 1254:

  1. L.J.Ryan, I forgot in my post 615 to mention the equalities only apply in the equilibrium condition. To explore the non-equilibrium condition, let us assume time steps equal to the average time it takes light to cross the depth of the box once. We use the average time because the photons may be at different angles, and hence have different path lengths. Let us also assume that 100 photons enter the box in each time step. We set the initial time step,0, to the time photons first start entering the box, but before they strike the back wall of the box. In that case, the number of photons in each of A, B, C, and D for progressive time steps are: Following Phil's suggestion, I have modeled this on a spreadsheet, using the following formulars: Column B2 and subsequent: 100, column C2: 0, Column C3 and subsequent is the sum of columns B and D for the preceding row. Column's D and E2: 0; and for columns D and E3 and subsequent, 0.5 times the value of column C in the preceding row. The first twelve steps show as follows: STEP A B C D 0 100 0 0 0 1 100 100 0 0 2 100 100 50 50 3 100 150 50 50 4 100 150 75 75 5 100 175 75 75 6 100 175 87.5 87.5 7 100 187.5 87.5 87.5 8 100 187.5 93.75 93.75 9 100 193.75 93.75 93.75 10 100 193.75 96.875 96.875 11 100 196.875 96.875 96.875 12 100 196.875 98.4375 98.4375 Clearly there is a problem for the spreadsheet that it allows fractional photons. What would happen in the real case is that occasionally 99 photons would leave the box, and occasionally 101, but typically 100 would leave the box. Furthermore, the mean value of photons leaving the box once the equilibrium state is reached would be 100. So, ignoring the quirk of fractional values, it is plain the system quickly approaches the state described in my 615. Do you have any problems with that?
  2. C Truth @627, the ideal gas law is included in atmospheric physics in calculating the lapse rate, as shown in this university lecture, and as explained by me very briefly in 563 above. It is also included in analysis of convection, but as convection in the atmosphere is what establishes (on average) the lapse rate, that is saying the same thing. It follows that any explanation of the green house effect that incorporates the environmental lapse rate already incorporates the gas law. As previously discussed in this thread, the standard theory of the greenhouse effect incorporates the lapse rate as an essential element of the theory. So, yes, understanding the gas law can provide insights into the greenhouse effect, and those insights were discovered decades ago, and are the basis of the modern understanding of the greenhouse effect.
  3. Tom Curtis @626 "Do you have any problems with that?" As I said A=C, so with that we agree. However, energy can NOT accumulate within the box, B can not equal 2A, no way can't happen. Your scenario is a light/energy doubler. If you change your filter to reflect 75% what happens? Take it further, enclose a flashlight within a completely and perfectly reflective box, at what point is there infinite energy therein?
  4. Tom Curtis (RE: 615), "By simplifying the situation, ie, by getting rid of any concerns about convection and light absorbed by the atmosphere etc, we should be able to raise any issues you have with the consistency of the GHE with the laws of thermodynamics without getting hung up on trivia. Do you agree?" No, I don't agree that it is trivia. Understanding the energy flows relative to the radiative balance is absolutely fundamental to the entire GHE and ultimately surface temperatures (i.e. how much surface emitted radiation is coming back from the atmosphere and how much is passing through). All I'm saying is latent heat and thermals are just redistributing energy around the thermal mass of the system - mostly from the tropics to the higher latitudes. The bulk of this energy condenses to form clouds, weather systems and returns as precipitation. Any amount of it that ends up radiated out to space is equally offset at the surface by a lesser amount returning, which cools the surface. All the energy flows are constant, thus this effect is already accounted for in the 396 W/m^2 emitted at the surface.
  5. LJ@629>However, energy can NOT accumulate within the box, This is not correct. Don't forget that the flashlight is continuously outputting radiative energy (converted from energy stored in batteries). If the energy cannot escape, then yes of course the radiative energy accumulates in the box. Otherwise you would violate conservation of energy, because if the flashlight is outputting energy and it does not escape and it does not accumulate, then it must have been destroyed. It would of course stop accumulating after the flashlight runs out of battery or shuts off. Fortunately in the earth system analogy our "flashlight" will not run out of juice for a very long time.
  6. e @631 Let's assume the flashlight radiates with a 1W bulb for 100 hrs. How much energy is contained within the box at the end of a 100 hrs? How long to accumulate a gigawatt?
  7. 1J/s for 100 hours, thats 360kJ accumulated. Of course your torch also absorbs energy so guess that is going melt at some point. RW1 - this lightbox example is simple demo of how not to make inappropriate inference about energy from energy flux through different surfaces. Do you agree with light box as TC has set it up?
  8. Keep in mind, everyone, that the gain of the box is 0.5, less than one, and hence a run-away feedback is not possible. Please see Does positive feedback necessarily mean runaway warming for details. Tom Curtis, I like your example. I did much the same thing on this thread earlier, except adding a value (which could be a column) of emissivity (0.612 for Earth, as measured), where your "C" was (1.0 - emissivity) * B, and "D" was emissivity * B. If you do that with 240 as input, the results are quite interesting, as per Trenberth 2009.
  9. 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?
  10. scaddenp @633 360kJ is at minimum expended by the batteries. Surely you would accumulate more then 360kJ within the box. After all, the claim is reflected light (B from Tom Curtis's diagram) is twice the input. Why the discrepancy? So lets step it back, if your box was fully enclosed such all surfaces are reflective save two small aperture. One aperture to receive light the second to radiate light. Close the output while receiving 1W at the input. The energy accumulated within the box after 100 hrs is what, 360kj? If the first aperture is then closed does the box now contain 360kj of light?
  11. L.J.Ryan @629, let us consider this step by step: 1) Consider the box as described, but without any lid. In this case all the light will reflect of the wall of the box and exit through the aperture where the lid was. Is that correct? 2) Now consider the case in which we place the lid on the box, but at an angle so that all light reflected of the lid will leave the box through some other aperture. In this case, the amount of light leaving the box through the lid will be half of that which enters, while the amount that is reflected by the lid and leaves through the other aperture will also be half of that which enters the box. Is that correct? Do either of these scenarios violate any law of thermodynamics?
  12. 636 Ryan "One aperture to receive light the second to radiate light" Ah, some more thermodynamics... ... have you met Maxwells Demon?
  13. CTruth @627 said I agree with RW1 and a few others that observational data seem to indicate the availability of a significant kinetic energy content in the lower troposphere than cannot be accounted for by the solar input alone. CTruth, my position (and if I may be so bold to suggest, I think the position of Tom Curtis, KR, scaddenp et al) is this; ... that observational data indicates the availability of a significant energy content in the lower troposphere than cannot be accounted for by the solar input alone but is accounted for by an exchange of heat between the surface and the atmosphere. This heat has accumulated in the planetary system in the distant past in the process of reaching (approximate) thermal equilibrium If you tried the spreadsheet model I suggested earlier (and Tom Curtis improved @626), one thing you can discover from it is that at the time P(in) = P(out) then ΣTP(in) - ΣTP(out) is at its maximum and is equal to the capacity of the system to hold P (so as to conserve energy or matter) These statements hold true for Tom's half-mirrored box (where P is photons), KR's rivers running in and out of a reservoir (where P is water) and the earths energy budget (where P is heat). T is time, of course, and - heads up to les @623 - yes of course the summations should really be integrals !
  14. Phil, interesting point @639. I have included two new columns in my spreadsheet. One, titled Gain, is Bx-Dx for each row, x. The second, titled "Stored" is the sum of the values in the Gain column from row 2 to row x, for each row, x. The exact formula is "=SUM(G$2:G2)" where G is the column for Gain. As expected, with each progressive iteration, Gain falls to 0 while Stored increases to 400 when the number of photons exiting the box matches the number entering the box. When the incoming photons are reduced to zero, the Gain immediately becomes -100 before slowly increasing to zero, which it reaches approximately as Stored reaches zero and photons leaving the box reaches zero.
  15. Tom @640 Cool - thats shows it nicely - but hey I don't need convincing :-( Kudos has to go to KR, who first alerted me to the idea of using spreadsheets to do these sort of simple iterative demonstrations. On a more general note I wonder if the SkpSci team have considered trying to let contributers share "live" spreadsheets via "cloud" providers like GoogleDocs. It would need to protect the documents from abuse and hide users email addresses, but it might be a useful additional resource if it could be made to work.
  16. LJ >After all, the claim is reflected light (B from Tom Curtis's diagram) is twice the input. Why the discrepancy? Amount reflected off a surface is not the same as accumulated energy in the box. If a single photon "bounces" back and forth from one wall to another, then you are going to count multiple reflections even though the energy content is still a single photon. The amount reflected tells us how many times photons have bounced off the walls, while the accumulated energy tells us how many photons are in the box. Do you see the distinction?
  17. Re #580 RickG You wrote "The diagram is not about temperature. Its about incoming solar radiation expressed in W/m^2 and how it is distributed throughout the Earth's climate system, which is the proper unit of measure for that particular type of energy (Incoming Solar Radiation)." The thread is about 2nd Law of Thermodynamics which states the direction energy is transferred WRT temperature. Trenberth's diagram is all about energy transfer (W/m^2) without any reference to temperature anywhere, thus it says absolutely nothing about atmospheric thermodynamics or the possibility of CO2 having any influence on climate in any way. You write further:- "Why would Ternberth or anyone for that matter want to use 12 year old data when more up to date data is available? And again, the diagram is about the distribution of energy, not temperature." The age of the data has no relevance, Trenberth's diagram does not present any useful information for any discussion on climate change (anthropogenic global warming - AGW) because it is completely deficient in temperature information, the driving parameter in the 2nd law of thermodynamics.
  18. 643 damorbel - "Trenberth's ... is completely deficient in temperature information" Someone might correct me; but, seems to me, the diagram includes "surface radiation", "back radiation" from GHGs, "Emitted by Atmosphere" ... all of which are temperature dependent.
  19. Tom Curtis@637 You are avoiding questions posed @636. If your box was fully enclosed such that all surfaces are reflective save two small aperture. One aperture to receive light the second to radiate light. Close the output while receiving 1W at the input. The light source occludes the reflected light from "leaking" out the input. The energy "accumulated" within the box after 100 hrs is what, 360kj? If the first aperture is then closed, does the box now contain 360kj of light? Asked otherwise, can the "accumulated" energy in the box be captured?
  20. e@642 You asked: "The amount reflected tells us how many times photons have bounced off the walls, while the accumulated energy tells us how many photons are in the box. Do you see the distinction? " Using Tom Curtis 615, what is the value of each at equilibrium i.e. 1. accumulated energy 2. reflected energy..if you can quantify it
  21. LJRyan @645, in an ideal fully mirrored box, the accumulated energy would be 360 kilojoules. Of course, in practise you would not have perfectly reflecting walls, and given the high speed of light, and consequent very large number of reflections in a short period, the light would decay to zero very quickly. Likewise, again because of the high speed, the light would escape the aperture before you could close it. But practical difficulties do not prevent us from exploring theoretical possibilities in ideal cases. @646, let the time interval be the time it takes a photon to travel from the lid to the back wall. Then 1) the accumulated photons at equilibrium is 4 times the number of photons that enter the light box at each time interval (see 640); and 2) at equilibrium the number of photons reflected in each time interval is 3 times the number that enter the light box in each time interval. Of those, 2 times that number are reflected of the back wall, and a number of photons equal to the number that enter are reflected of the lid. This ignores reflections of the side walls which are irrelevant to the overall issue. The answer has to be in terms of photon numbers, not energy because the wavelength of the photons has not been specified. If we specify that all photons have the same wavelength, then the multipliers for photons in the answers above can be used for energy. Now, can you answer my questions @637
  22. Re #644 les you write:- "... all of which are temperature dependent." Too true, I couldn't agree with you more. So do you not think, to make a useful contribution to a discussion on temperature change, the temperatures should be mentioned? Also, the emitting materials do not all have the same emissivity; Trenberth should have inserted the emissivity that applies.
  23. damorbel 648 - fine. We agree on so much including, it would seem, that the diagram is not "completely deficient in temperature information". Why don't people say what is apparent without exaggeration? The diagram doesn't explicitly mention temperatures and piles of other information. Indeed it's a cartoon. It clearly does "present ... useful information for any discussion on climate change (anthropogenic global warming - AGW) ". Why the hysteria, then? Same with LJRyan, giles et al. If you guys where half the scientist scientists you'd have be to participate in tgis discussing, you'd be far more easy with the shorthand notations, use of approximations, anstract models,partial perspectives and all the other tool we use on a daily basis to understand things. Take a chill pill.
  24. damorbel @ 643, I'm well aware of the title of the thread. However, my original comment was about Trenberth's diagram and what you said about it. For what Trenberth is demonstrating temperature is neither necessary or relevant in that diagram. I have no problem understanding the diagram myself. Trenberth has a presentation in which that diagram is described here on pages 13 & 14. Other diagrams with "temperature" are described in the presentation as well, in their appropriate place. If you still have a problem with the diagram, then perhaps you should contact him personally and take the matter up with him at the National Center for Atmospheric Research (NCAR).. I'm sure he is open to new ideas and wants to be sure his diagrams convey the proper information and documentation.
    Response: [Muoncounter] damorbel has been given this suggestion a number of times to little if any effect. Instead, we have more pointless repetition of the same tedious argument, which we may surmise is damorbel's actual intent.
  25. Tom Curtis@647 "accumulated energy would be 360 kilojoules" So the accumulated "boxed" light would radiate 1W for a 100 hrs, once the second aperture is opened? "the light would decay to zero very quickly" Sounds like a violation of the 1st law...remember perfectly reflective walls. Sounds as if you don't believe your own answer. "The answer has to be in terms of photon numbers, not energy because the wavelength of the photons has not been specified. If we specify that all photons have the same wavelength, then the multipliers for photons in the answers above can be used for energy." ok lets assign three wavelengths and redo @646 1. 11364 nm 2. 10062 nm 3. 2898 nm @637 questions 1) Consider the box as described, but without any lid. In this case all the light will reflect of the wall of the box and exit through the aperture where the lid was. Is that correct? 1a)I not sure I understand your question...if the lid included the aperture wouldn't it also be removed with the lid...? 2) Now consider the case in which we place the lid on the box, but at an angle so that all light reflected of the lid will leave the box through some other aperture. In this case, the amount of light leaving the box through the lid will be half of that which enters, while the amount that is reflected by the lid and leaves through the other aperture will also be half of that which enters the box. Is that correct? 2a)Again, I'm not sure I understand your question. Is the box partially open? How open?

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