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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)

 

Skeptics sometimes claim that the explanation for global warming contradicts the second law of thermodynamics. But does it? To answer that, first, we need to know how global warming works. Then, we need to know what the second law of thermodynamics is, and how it applies to global warming. Global warming, in a nutshell, works like this:

The sun warms the Earth. The Earth and its atmosphere radiate heat away into space. They radiate most of the heat that is received from the sun, so the average temperature of the Earth stays more or less constant. Greenhouse gases trap some of the escaping heat closer to the Earth's surface, making it harder for it to shed that heat, so the Earth warms up in order to radiate the heat more effectively. So the greenhouse gases make the Earth warmer - like a blanket conserving body heat - and voila, you have global warming. See What is Global Warming and the Greenhouse Effect for a more detailed explanation.

The second law of thermodynamics has been stated in many ways. For us, Rudolf Clausius said it best:

"Heat generally cannot flow spontaneously from a material at lower temperature to a material at higher temperature."

So if you put something hot next to something cold, the hot thing won't get hotter, and the cold thing won't get colder. That's so obvious that it hardly needs a scientist to say it, we know this from our daily lives. If you put an ice-cube into your drink, the drink doesn't boil!

The skeptic tells us that, because the air, including the greenhouse gasses, is cooler than the surface of the Earth, it cannot warm the Earth. If it did, they say, that means heat would have to flow from cold to hot, in apparent violation of the second law of thermodynamics.

So have climate scientists made an elementary mistake? Of course not! The skeptic is ignoring the fact that the Earth is being warmed by the sun, which makes all the difference.

To see why, consider that blanket that keeps you warm. If your skin feels cold, wrapping yourself in a blanket can make you warmer. Why? Because your body is generating heat, and that heat is escaping from your body into the environment. When you wrap yourself in a blanket, the loss of heat is reduced, some is retained at the surface of your body, and you warm up. You get warmer because the heat that your body is generating cannot escape as fast as before.

If you put the blanket on a tailors dummy, which does not generate heat, it will have no effect. The dummy will not spontaneously get warmer. That's obvious too!

Is using a blanket an accurate model for global warming by greenhouse gases? Certainly there are differences in how the heat is created and lost, and our body can produce varying amounts of heat, unlike the near-constant heat we receive from the sun. But as far as the second law of thermodynamics goes, where we are only talking about the flow of heat, the comparison is good. The second law says nothing about how the heat is produced, only about how it flows between things.

To summarise: Heat from the sun warms the Earth, as heat from your body keeps you warm. The Earth loses heat to space, and your body loses heat to the environment. Greenhouse gases slow down the rate of heat-loss from the surface of the Earth, like a blanket that slows down the rate at which your body loses heat. The result is the same in both cases, the surface of the Earth, or of your body, gets warmer.

So global warming does not violate the second law of thermodynamics. And if someone tells you otherwise, just remember that you're a warm human being, and certainly nobody's dummy.

Last updated on 22 October 2010 by TonyWildish.

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Related Arguments

Further reading

  • Most textbooks on climate or atmospheric physics describe the greenhouse effect, and you can easily find these in a university library. Some examples include:
  • The Greenhouse Effect, part of a module on "Cycles of the Earth and Atmosphere" provided for teachers by the University Corporation for Atmospheric Research (UCAR).
  • What is the greenhouse effect?, part of a FAQ provided by the European Environment Agency.

References

Comments

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Comments 201 to 250 out of 1406:

  1. #197: "you'd be in a warm bath of air at 14C, 1/2 surrounded by radiation from the ground at 14C; 1/2 from deep space at 2.7K."

    Damorbel, did you just say that radiation from space at 2.7K contributes 50% to keeping that 'warm bath of air' at 14C? What would Clausius say to that?
  2. Re #196 scaddenp you wrote :-

    "continuing to talk about what happens and how the 2nd law works in conductive energy transfer is not helping you understand how it works in radiative energy transfer."

    Energy transfer by photons is amazingly similar to that in gases, both exchange momentum in collision processes; in gases it is by inelastic collisions and with photons it is by elastic collision.
  3. Damorbel wrote: "The balls will slowly approach a temperature dependent only on the distance of and the power emitted by your UV source."

    As I understand it:

    If the source is a star, and both balls are receiving UV energy, then yes--even though the balls will still exchange radiation at equilibrium. However, that's not what I said. The second ball is not receiving UV radiation. It has been given one time heat by some unknown source. It is cooler than the first ball. My argument is that such a ball is an energy source for the first ball, in addition to the UV source, and it will continue to be an energy source because it receives radiation from the first ball.

    In this analogy, the second ball is the atmosphere. It receives radiation from the surface, and even though it is cooler than the surface, it radiates some of that energy back toward the surface. Eventually, some of the "backradiation" is absorbed by the surface and turned into work, but most of it gets hung up dancing from molecule to molecule in the troposphere, where convection and conduction also bring it into contact with the surface or bring it to the stratosphere. The point, though, is that the upper troposphere can indeed act as an energy source for the surface and for the lower troposphere (where surface temps are measured), even though the upper troposphere is concurrently cooler. GHGs basically redirect certain frequencies of longwave radiation. The more GHGs, the more LWR is redirected, and the more time LWR stays within the system (heating, doing work, being a nuisance, etc.).
  4. Sigh. If you thought greenhouse effect was energy transfer from atmosphere to surface by conduction, then that WOULD be violation of second law. However, this is not what is happening as people repeatedly tell you. No incoming radiation, no GHG effect. You cant take the sun out of it. If you are determined not to learn physics, then we are wasting our time trying to teach you.
  5. #199: "Convection is a bit special because it won't work 'downwards'"

    Oh, dear. I guess plate tectonics, thermohaline ocean circulation and onshore/offshore breezes, among other things all just stopped because damorbel says 'it won't work downwards'.

  6. Re #198 KR The case for warming due to back radiation has not been made.

    GHGs are distributed more or less uniformly up to 80km except for water, by far the dominant GHG, which drops to a low concentration above 15-20km.

    The relevant point about GHG emission is that it takes place throughout the atmosphere, it is highest where the gas density is highest and, most important, because the temperature at any given location does not change quickly, to a first approximation, GHGs are absorbing (locally) just as much IR as they emit. They do not collect radiation together somehow 'at the top of the atmosphere' (TOA) and send it down (or up) as in Trenberth's 'Radiation Balance' diagram.

    If that 'collecting at TOA' according to Trenberth were possible there might be a better case for surface warming but you are still stuck with the problem that the TOA is extremely cold and can only take heat from the surface, not send heat down to the surface.

    Notice that I wrote 'not send down heat to the surface', not 'not send radiation down to the surface'. Radiation is not heat, heating (or cooling) arises only when there is an imbalance between absorbed and emitted radiation. In the troposphere radiation is emitted and absorbed primarily in a balanced way, with height being the only exception. The importance of this exception means that heat transfer due to radiation goes only in one direction only, out into deep space.

    There are two reasons for this, the atmospheric temperature falls steadily with height according to the lapse rate (-6.5K/km), the atmospheric density also falls with height. Thus the lapse rate defines the direction of heat tansfer and the density variation also ensures that there is always less radiation 'downwards' rather than 'upwards' for the simple reason that the amount of radiating gas reduces with height due to the drop in density with height.
  7. Re #204 scaddenp You wrote:-
    "If you thought greenhouse effect was energy transfer from atmosphere to surface by conduction, then that WOULD be violation of second law."

    Yes, but no need for emphasis!

    And:-

    " However, this is not what is happening as people repeatedly tell you."

    Tell me? Don't I know it!

    then you write :-
    "No incoming radiation, no GHG effect. You cant take the sun out of it."

    What does that mean? Isn't it the GHGs that are supposed to cause the GH effect?

    h-j-m has been arguing successfully that the atmosphere is heated directly by GHGs absorbing energy directly from the Sun's radiation, Trenberth's diagram shows it, who is disputing it?

    The whole planet is heated by the Sun's radiation and very little else, if you have a problem with this could you expand on it?

    Heat transfer by radiation can only be from a hot body (gas etc.) to a cooler, no different from conduction diffusion or convection.
  8. damorbel wrote: "Microwaves are not 'thermal' like a grill"

    So... you are arguing that electromagnetic radiation in the range we designate as 'infrared' (or 'thermal' energy) behave differently than all other forms of electromagnetic radiation?

    While ridiculous on its face... that doesn't pass the everyday reality test either. Most remote controls use infrared signals. By your logic they would not function if the receiver, or any space leading up to it, were even a fraction of a degree warmer than the transmitter. Many pieces of electronic equipment get quite warm when they have been running for a while... yet the receivers in them still pick up infrared signals from the cooler remote.

    Also: "Oh alright then, not 0K, lets put 0.00000000001K."

    Close. Multiply that by ten and you've got the lowest temperature ever observed. However, you are missing the point. Your claim that objects at 0K emit no radiation is meaningless because there AREN'T any objects at 0K.
  9. Re #205 muoncounter You wrote:-
    "all just stopped because damorbel says 'it won't work downwards'."

    And you inserted a nice diagram showing convection by a fluid between two surfaces, the warmer one being underneath, you can see how it works by the arrows on the convective flow loops.

    But muoncounter, surely these loops do not have a uniform temperature all the way round? According to me the left hand part of the loop (the 'upward' part) will be warmer than the righthand (the descending) part.

    I really don't get what you are on about. I suggest you put some indication of the temperature distribution on your diagram, that should help to clarify what is happening energywise.

    It is an interesting fact that convection can take place with very small temperature differences. Have you ever come accross a heat pipe? Heat pipes have fluid inside them that transfers heat by evaporation and condensation; they are very effective, my computer has one for cooling the video driver chip(s?)

    You must look at Earth as a sort of giant three dimensional heat pipe that transfers heat from the tropics to the poles and the upper atmosphere by processes rather similar to those in a a heat pipe.
  10. damorbel #206
    Trenberth does not say anything even near "collection at TOA"; it's just your (wrong) interpretation of Trenberth's schematic diagram.
  11. Re #208 CBDunkerson You wrote:-
    "So... you are arguing that electromagnetic radiation in the range we designate as 'infrared' (or 'thermal' energy) behave differently than all other forms of electromagnetic radiation?"

    What is call 'thermal radiation' is radiation from a thermal source, glowing metal, hot carbon are typical, they give out radiation with a broad spectrum first described by G Kirchhoff as 'blackbody radiation'.

    The important factor is that the emission is proportional to temperature, the implication is that any substantial body must have the same temperature throughout, that is what is meant by equilibrium.

    The importance of uniform temperature comes from the fact that, if the temperature is not uniform, the parts with different temperature will emit different amounts of radiation. Also heat will possibly flow by conduction etc. bteween the parts with different temperatures.

    Ultimately, how can you say a body, whose parts are at different temperatures, has 'one' temperature?

    But radiation comes in all sorts and sizes from DC(?) to beyond blue light I have heard. Thermal radiation has a characteristic Planckian spectrum that comes from a black body and it is related to the temperature of this 'black body' (yes I know it isn't black if it's radiating!)

    Radiation from other sources such as lasers, microwave ovens and radio and television transmitters is largely monochromatic they have only one frequency. All these forms of radiation get converted to heat when absorbed; this heat tends to raise the temperature of the irradiated object. This heat tends to be dissipated in the surroundings by any process you care to mention, radiation; convection; conduction etc. or even into chemical energy e.g. plant growth. The important point is that not all sources of radiation have a temperature.
  12. Re #210 Riccardo You wrote:-
    "Trenberth does not say anything even near "collection at TOA"; it's just your (wrong) interpretation of Trenberth's schematic diagram."

    It is an expression used all over the place in climatology, Trenberth has it here

    If it is any comfort to you it is a meaningless concept not least because the TOA is completely undefined, temperature? pressure? altitude? All are unidentified.
  13. damorbel wrote: "What is call 'thermal radiation' is radiation from a thermal source, glowing metal, hot carbon are typical, they give out radiation with a broad spectrum first described by G Kirchhoff as 'blackbody radiation'."

    So... 'sunlight'. Which is the broad spectrum of radiation given off by a thermal source known as the Sun. Yet sunlight travels from the cold of space to the warmer upper atmosphere to the warmer still lower atmosphere.

    damorbel wrote: "The important point is that not all sources of radiation have a temperature."

    Which is an oxymoron. All sources of radiation have a temperature... otherwise they couldn't be sources of radiation. The theoretical 'no temperature' of 0 Kelvin is defined as the point at which matter emits no radiation.
  14. damorbel
    could you please point me where Trenbrth said such thing? I couldn't find it.
  15. #206: "GHGs are distributed more or less uniformly up to 80km except for water, by far the dominant GHG, which drops to a low concentration above 15-20km. ... the atmospheric temperature falls steadily with height according to the lapse rate (-6.5K/km), the atmospheric density also falls with height."

    Multiple sources show CO2 and H2O concentrations vary considerably with altitude. Temperature isn't uniformly decreasing with altitude. Density isn't linear with altitude.

    #209: "surely these loops do not have a uniform temperature all the way round?"

    Who suggested that they did? You said 'convection won't work downwards'; most people associate 'convection' with some sort of circulation - including the return trip down. There's no subduction of lithospheric plates without it.

    "I suggest you put some indication of the temperature distribution on your diagram,"

    The 'heat input' on the bottom and 'fluid cools' at the top would be enough for Wikipedia-level readers to get the point. Apparently you require additional notation?

    "Isn't it the GHGs that are supposed to cause the GH effect?"

    Duh; but without solar heat input, there's no surface IR radiation for GHGs to absorb.

    Deflecting the discussion with these irrelevancies was just tedious some hundred comments ago; now it's pointless clutter, but I suspect that's your actual goal here.
  16. Re #213 CBDunkerson you wrote:-

    "So... 'sunlight'. Which is the broad spectrum of radiation given off by a thermal source known as the Sun. Yet sunlight travels from the cold of space to the warmer upper atmosphere to the warmer still lower atmosphere."

    Of itself a vacuum contains no material so it can have no temperature, since temperature is a measure of the heat content of molecules and atoms.

    Electromagnetic (EM) radiation is produced by the vibration (more accurately the acceleration) of electric charge (electrons and protons), so it always is associated with matter how ever far away that matter happens to be. EM radiation starts and finishes with matter, it moves at the speed of light and it cannot be stored or otherwise conserved like energy.

    Since EM radiation is produced by matter which in turn has a temperature there is a sort of connection between temperature and radiation. But only a connection. If the connection is to be strong the radiation must at least have a spectrum according to the Planck radiation formula.

    Just having the spectrum is not sufficient, it must have the right intensity also. If the intensity is weakened, say because a star is at a distance then, even though the spectrum remains the same, the temperature is reduced because the intensity is no longer that given by Planck's formula.

    Further you wrote:-

    "The important point is that not all sources of radiation have a temperature."
    Which is an oxymoron. All sources of radiation have a temperature... otherwise they couldn't be sources of radiation."

    Lasers, radio and television transmitters, microwave ovens are all sources of radiation that does not conform to the Planck spectrum, so the source is not related to matter having a temperature (be careful, the radiation output of a microwave oven etc. is (more or less) independent of its physical temperature).

    When this 'non-Planckian' radiation is absorbed (by matter) the temperature of the absorbing matter increases - the stored energy is thermal in character, the matter has a temperature.
  17. #213 CBDunkerson at 00:13 AM on 1 December, 2010
    All sources of radiation have a temperature... otherwise they couldn't be sources of radiation. The theoretical 'no temperature' of 0 Kelvin is defined as the point at which matter emits no radiation

    Which is an oxymoron. damorbel is obviously talking about radiation sources very far from thermal equilibrium. Such systems do not have a unique well defined temperature, yet they may emit radiation.

    Otherwise how would you explain laser cooling? (Heat never moves spontaneously from a cold place to a hot one, so in a sense laser light has to be cold indeed to be able to cool down things to several nanokelvins.)

    LED lamp is another example. Or is the common glow-worm (Lampyris noctiluca) hot?



    For that matter neither has OLR (Outgoing Longwave Radiation) at TOA (Top of Atmosphere) a well defined blackbody temperature. Partly because Earth is not a blackbody, partly because due to heavy frequency dependence of atmospheric transparency, layers of very different temperature give contributions to OLR. Again, Earth is a system very far from thermodynamic equilibrium.
  18. damorbel - As I stated before, greenhouse gases reduce cooling of the surface, which has the result of the Earth's surface heating up in order to radiate in balance with the incoming solar energy.

    The observed backradiation from lower atmosphere GHG's is part of the energy balance, which Trenberth listed in his 2009 paper - it's an energy exchange, part of the balance sheet including incoming solar, outgoing top of atmosphere (which as a point of demarcation is chosen as somewhere above the majority of GHG's), surface IR, back IR, thermals, etc etc.

    You are obviously familar with EM, heat, energy exchanges, etc. Your description of lapse rates, thermal radiation, etc., seem reasonable, except for your somehow deciding that backradiation doesn't have a role. You have, however, put up repeated strawman and red herring points, such as dying due to lack or H2O in thought experiments, quibbling about monochromatic sources, etc.

    At this point I consider you to just be objecting for the sake of objecting. If you have actual issues, fine - otherwise I'm leaving this thread.
  19. damorbel, imagine there are two stars, named Miami and Anchorage. Both are 100,000 light years from our Sun. From hottest to coolest, Miami > Sun > Anchorage.

    Miami and Anchorage's radiation emission curves overlap, and intersect at a wavelength W, so the two stars emit the same number of photons having wavelength W.

    Simultaneously 100,000 years ago, Miami emitted a photon named Sally, and Anchorage emitted a photon named Greg. Sally and Greg both have wavelength W.

    100,000 years later, Sally and Greg arrive at our Sun. Our Sun is cooler than Miami but hotter than Anchorage. All physicists in the world agree that both Sally and Greg are absorbed by the Sun. The Sun has no way of knowing that Sally's source was hotter than the Sun, and that Greg's source was cooler than the Sun, because Sally and Greg have the same wavelength W.

    I believe that in stark contrast you have been claiming that the second law of thermodynamics requires the Sun to absorb Sally but not absorb Greg. Here is a simple question for you:

    What happens to Greg?
  20. Berényi - Well written post on non-thermal radiation, thank you. Directly inferring temperature from EM spectra only works when the spectra is sufficiently similar to a blackbody curve, whether it has band-gaps or not. Monochromatic and 'cold-light' sources have an inherent energy, but since they are not thermal emitters that doesn't directly correspond to a temperature.

    However, when you say that "...Earth is a system very far from thermodynamic equilibrium", I would like to point out that as far as we can tell (again from Trenberth 2009, although I'm sure there are slightly different estimates out there) the balance sheet is currently tipped only about 0.9 W/m^2 from dynamic equilibrium. If we can reduce or prevent further GHG emissions, we can reduce that imbalance, and the resulting shift in global temperatures.
  21. BP, you are arguing (correctly) that not all rectangles are squares. Damorbel is arguing (incorrectly) that not all squares are rectangles.

    That is... yes, there is such a thing as non-thermal radiation. However, there is NOT such a thing as radiation from a source with no temperature. Two very different arguments.

    damorbel writes: "EM radiation starts and finishes with matter, it moves at the speed of light and it cannot be stored or otherwise conserved like energy."

    So... EM radiation is not energy. Fascinating stuff. However, setting that aside... your dodge about the vacuum of space being empty (it isn't) doesn't address the fact that sunlight travels through the Earth's atmosphere.

    How does sunlight hit gas molecules in the stratosphere, which is very cold, and then continue from there down to the troposphere, which is much warmer? Your argument would make this impossible... yet it obviously happens. Sunlight travels from a cold region of the atmosphere to a warmer one... indisputable fact.

    The whole 'broad spectrum' bit was nonsense to begin with because there is no reason a wide range of EM emissions should behave differently than a narrow band... and sunlight shows that it doesn't. There are countless examples of EM radiation traveling from cold areas to warmer ones... and it makes no difference whether it is individual wavelengths vs a wide band or the emissions source is thermal or non-thermal. Examples have been provided of ALL of these behaving the same way... there is no magical 'warmth barrier' to radiation. It's pure nonsense and observably so in the everyday world all around us.
  22. Re #218 KR You write:-

    "greenhouse gases reduce cooling of the surface, which has the result of the Earth's surface heating up in order to radiate in balance with the incoming solar energy."

    And:-
    "The observed backradiation from lower atmosphere GHG's is part of the energy balance, which Trenberth listed in his 2009 paper"

    And crucially:-
    "except for your somehow deciding that backradiation doesn't have a role"

    Back radiation would have a role in raising raising the surface temperature if it exceeded the output from other sources. But Trenberth himself has back radiation at 333W/m^2 and the surface sourcing 356W/m^2 to the atmosphere, thus the net upward radiation to the atmosphere is just 26W/m^2 and since it 'is net upward radiation' it is cooling the surface, not heating it!

    Trenberth has a total of 198W/m^2 going into the atmosphere and 169W/m^2 plus 30W/m^2 = 199W/m^2 leaving to deep space; leaving 1W/m^2 to raise the temperature of the surface by 30K.

    I may have got some of the figures wrong but without any temperatures on the diagrams it is quite impossible to make any check of the claimed warming effect, so without any question it is a scientifically unsound explanation, I have no idea how you manage to have such faith in it.
  23. damorbel - Aha, I think I see the issue you're having.

    Without greenhouse gases, the atmosphere would not emit much IR at all - nitrogen and oxygen don't have the structure to emit in the thermal IR bands.

    So, without the 333 W/m^2 backradiation, the surface of the Earth at current temperatures would still radiate upwards to space at net 356 W/m^2, not net 26 W/m^2. Don't you think this would have a cooling effect? If greenhouse gases were to go away the Earth would rapidly cool towards -18C, where outgoing top of atmosphere IR would be in balance with incoming solar energy, rather than the current +14C average temperature.

    Of course, that would lead to glaciation, increasing albedo, and reducing the temperature even further - the -18C thought experiment is just a first pass example.

    Backradiation greatly reduces cooling efficiency of the Earth - it has to be hotter to remain in energy balance with the sun. Backradiation doesn't have to exceed surface radiation in order to change the net heat loss, which you yourself have shown.

    The whole issue of backradiation and thermal balance is still based upon energy coming in from the sun, net energy flow to space, and the temperature of the Earth. Reduce the net cooling energy flow to space (reduced emissivity from GHG's), and the system is imbalanced until the temperature rises to compensate. I've pointed you to the very straightforward Thermal Radiation writeup on this, and the governing equation P = e * s * A * T^4.

    To put it bluntly, if you don't understand that, I don't think I can help you.
  24. Re #221 CBDunkerson You write:-

    "How does sunlight hit gas molecules in the stratosphere, which is very cold, and then continue from there down to the troposphere, which is much warmer? Your argument would make this impossible... yet it obviously happens. Sunlight travels from a cold region of the atmosphere to a warmer one... indisputable fact."

    When sunlight hits the atmosphere the UV component at 200 microns and below splits the O2 molecules into two O atoms which then join other O2 molecules to form ozone - O3

    O3 further absorbs UV at 300 microns and shorter, thus the sunlight proceeds to the surface shorn of its dangerous UV.

    But what do you mean when you write this:-

    "Sunlight travels from a cold region of the atmosphere to a warmer one... indisputable fact."?

    The sunlight that passes through the atmosphere is not affected by it. The absorbed UV heats the stratosphere and generates the Ozone layer. The heating by UV causes a massive temperature inversion which makes the stratosphere very calm in comparison with the troposphere.

    Oh, and the temperature at the stratopause is not that low, just about freezing, 0C.
  25. Other have covered some of your points BUT
    "Heat transfer by radiation can only be from a hot body (gas etc.) to a cooler, no different from conduction diffusion or convection. "
    Missing word in here is NET heat transfer. Energy is transferred from cold to hot - a photon isnt magically not absorbed because the absorption surface is hotter than its source.

    The energy warming from surface of earth is from sun, the ghg are merely backscattering outgoing radiation.
    Response: Sorry to nag, but please refrain from using all caps.
  26. Re #223 KR You write:-

    "So, without the 333 W/m^2 backradiation, the surface of the Earth at current temperatures would still radiate upwards to space at net 356 W/m^2, not net 26 W/m^2. Don't you think this would have a cooling effect?"

    The real cooling effect of radiation is the 239W/m^2 leaving the top of Trenberth's diagram for deep space.

    The net 26W/m^2 due to GHGs is trivial in comparison with the 175W/m^2 total contributed by the sun (78W/m^2), water vapour (80W/m^2) and convection (17W/m^2).
  27. damorbel - Without greenhouse gases to radiate from the upper atmosphere, the 17 convection and 80 evaporative W/m^2 would quickly saturate and cycle back to the ground, reducing net transport to space via those pathways to zero, as it would have nowhere to go - the 169 emission from the atmosphere would be zilch without GHG's.

    And the 396 W/m^2 IR would go straight into space, rather than the 239 W/m^2 currently. Net would be 156-157 W/m^2 imbalance towards space, as opposed to the current 1 W/m^2 imbalance towards the ground.

    What do you think - would a negative balance of 156 W/m^2 have (as you seem to claim) no effect, or would it rather cool the earth about 150x faster than it's currently warming?
  28. Re #223 bis KR You write:-
    "the surface of the Earth at current temperatures would still radiate upwards to space at net 356 W/m^2,"

    I have done detective work on this and it is based on "the Earth emitting like a black body", yet another piece of GHE folklore that has no foundation.

    It is very obvious that the Earth is not a black body radiator at any wavelength. A blackbody radiator would have an emissivity (e) of 1, whereas the Earth has an emissivity of 1-a, where 'a' is the albedo. Thus the Earth's emisivity is about 0.7, giving an equilibrium temperature of about 279K

    Yet another shocker for you to think about, the Earth's equilibrium temperature (279K) is completely independent from the albedo!

    In support of this you can look at the Trenberth diagram where you will find that the total power absorbed by the Earth from incoming Sunlight is 161+78 = 239W/m2, the same as the total outgoing 239W/m2 - even with a surface temperature of 288K!

    Pure blackbody radiators do not exist, they are a hypothetical concept introduced to distinguish absorption from reflection (or scattering - to use a better term).
  29. Here's an analogy to the greenhouse effect, that incorporates a few critical items:

    Imagine a reservoir behind a dam. There is a constant stream running into the dam (solar input), output pipes at the bottom of the dam (size = Earth area), with some fractional screens (emissivity) over them. Outflow rate is determined by area of the pipes, screen blockage, and primarily by water pressure/reservoir depth (temperature), which for the sake of discussion will scale with depth^4th.

    Flow = screen * constant * Area * depth^4

    We'll start with the reservoir at a level where water pressure pushes an output flow through the pipes and screens equal to the amount coming in from the stream.

    Leaves block parts of the output screens (greenhouse gases), reducing output flow (cooling energy flow to space). The leaves increase the back-pressure at the output pipes (back-radiation). What happens? Well, output flow is now lower than input flow, and the reservoir level rises until increased pressure makes output flow equal to input again (temperature rises).

    That, in a nutshell, describes the greenhouse gas effect.
  30. Actually, damorbel, the surface IR emissions are measured observational data, as are the downward back-radiation numbers. You are quite simply incorrect.

    And greenhouse gases still reduce emissivity to space, sending just under 50% of the Earth emissions back down rather than to space.
  31. Re #227 KR You write:-
    "Without greenhouse gases to radiate from the upper atmosphere, the 17 convection and 80 evaporative W/m^2 would quickly saturate and cycle back to the ground, reducing net"

    This is not very sensible, is it? How can you write about "absence of GHGs" and "80 evaporative W/m^2" in the same breath - so to speak? The "80 evaporative W/m^2" comes from the oceans, you know!

    A completely passive atmosphere, let us say helium (and no water), would still have a temperature gradient due to compression by gravity and it would still circulate heat from the tropics to the poles, it may not be so efficient as water vapour and there would be no liquid water to perform the same circulation but a helium atmosphere would not be some sort of passive participant.
  32. Re #230 KR You write:-
    "Actually, damorbel, the surface IR emissions are measured observational data, as are the downward back-radiation numbers. You are quite simply incorrect."

    Measured or not, the net radiation is from the surface to the atmosphere, is that what you mean when you say "You are quite simply incorrect."?
  33. Emissivity of the ground is in the range of 0.96 to 0.99, with cloud albedo at 0.5 accounting for a combined emissivity (relative to a blackbody) of ~0.612.

    An effective emissivity change of 1.4% (from that same link, with a very simple climate model) will result in a 1°C temperature change. And greenhouse gases directly affect the emissivity of the Earth.


    As to your "helium atmosphere", total removal of greenhouse gases is a Gedankenexperiment. It's not intended to fully determine an end state, but rather serve as an illustration of how changing a parameter would cause a change from the current state, thus illustrating the importance of that parameter. Arguing about the endpoint of a Gedankenexperiment is quite simply a red herring.
  34. damorbel - You are incorrect when you state that IR from the Earth without GHG's (at current temperatures) would be anything but 396 W/m^2.
  35. damorbel - Also, you're incorrect in your statement about equilibrium temperature being unconnected to albedo. Even a simple climate model indicates about a 1°C temperature change for 3.3% change in albedo, 1.4% change in solar constant, or 1.4% in emissivity (for independent changes of a single value).
  36. damorbel, people have asked you, repeatedly, the simple and essential question "What happens to the photons from sources cooler than the target?"

    You have ignored those repeated questions, despite them being at the heart of the topic of this thread.

    Please answer my most recent version of that question: What happens to the photon named Greg?
  37. Re 236 Tom Dayton you wrote:

    "What happens to the photons from sources cooler than the target?"

    All bodies (that emit and absorb radiation) exchange photons all the time.

    The photons from a hotter body have more energy E (because E = h x v = Planck's constant times frequency) the cooler body emits lower energy photons because the peak emission frequency is, according to Wien's law, a direct function of temperature.

    Do not forget that all thermal bodies (those with an identifiable temperature - not monochromatic etc. like a laser) emit a broad spectrum of frequencies according to Planck's law.

    It is just that the hotter body emits photons with a higher energy and higher number of photons also.

    Whatever the configuration of the hot and cold bodies, the cold body will always absorb more photon energy (no. x E) from the hot body than the other way round.

    Betwen the surface the atmosphere and deep space it goes like this: the surface emits photons at 288K, these are absorbed somewhere in the troposphere, primarily by H2O & CO2 at, let us say at an average temperature of 255K.

    All the time the H2O & CO2 are emitting photons at 255K and absorbing photons from deep space at 2.7K, not very many and with very low energy (E = h x v ), so the balance is by far in favour of the energy going into deep space.

    If that was all, the H2O & CO2 in the troposphere would cool down PDQ but do not forget that these two gases are kept at the same temperature as the N2 & O2 also present in the atmosphere as well as absorbing photons from the surface.

    As well as absorbing surface photons and emitting photons to deep space, H2O & CO2 emit and absorb photons to and from each other.

    The extent to which this happens depends on where they are in the atmosphere; in the lower troposphere they exchange photons with the surface; since the surface and the lower troposphere have only a small difference of temperature the net energy exchange is small, a vast number of photons but, on average, a very small energy difference.

    Higher up the balance shifts from the surface exchange as the % H2O & CO2 intermediate between the emission/absorption altitude increases from zero.

    Even higher up in the atmosphere the gas density becomes so low and the chance of a photon being reabsorbed becomes correspondingly low.

    For thin atmospheres many photons emitted by H2O & CO2 do not get reabsorbed by adjacent H2O & CO2 molecules, some are reabsorbed by the surface but others are absorbed by deep space.

    Because it is the net transfer of photon energy between objects that determines the energy transfer you should realise that radiative transfer on Earth from the surface into the atmosphere is only about 26W/m^2, small in comparison with the 78W/m^2 put in directly by the Sun the 80 W/m^2 from evaporation and 17W/m^2 by convection (numbers from Trenberth's diagram). This is the heat that is transferred to the H2O & CO2 by O2 & N2 in the upper atmosphere for subsequent radiative transfer into deep space.
  38. Re 235 Tom Dayton you wrote:

    "Even a simple climate model indicates about a 1°C temperature change for 3.3% change in albedo"

    That is what is wrong with the climate models, they are based on the assumption that the Earth 'emits like a black body', an assumption I have seen many times. Not only is this assumption never justified it is self evidently incorrect because Earth reflects quite a portion of the incoming solar radiation, a portion that is called the albedo; so Earth can never be considered as 'a black body'!

    Worse still, this 'back body' assumption makes the planet's equilibrium temperature a function of its albedo which is simply not the case, there is nothing in modern physics that allows for such a conclusion.

    If you calculate the average temperature of any planet on the assumption that it is a black body then you will definitely get an erroneous temperature, unless of course it really is a black body.

    In the case of Earth this 'black body' assumption gives the average temperature as 255K when it should be 279K, a temperature that disposes with the GH effect entirely.
  39. Re 233 KR you wrote:
    "Emissivity of the ground is in the range of 0.96 to 0.99, with cloud albedo at 0.5 accounting for a combined emissivity (relative to a blackbody) of ~0.612"

    I could discuss the ground if you like but just think of the oceans which cover 70% of the planet. The oceans reflect light mostly by specular reflection but they do not reflect very much, that is why they generally look rather dark. Mostly the incoming sunlight energy is absorbed and causes evaporation of water, the heat from the Sun then goes into the atmosphere when condensation (rainfall!) takes place thus there is not much of a 'black body' factor in the transfer of heat from watery surfaces to the atmosphere.

    Water evaporation from land is also an important mechanism for heat transfer into the atmosphere. Including it as part of radiation from the surface like your truly amazing "Emissivity of the ground is in the range of 0.96 to 0.99" figures would appear to do, is definitely an odd way of calculating heat transfer. Even graphite and charcoal never get near these emissivities!
  40. damorbel #238
    any body may behave like a blackbody in a frequency range and not in others. In particular, the earth surface is very near a blackbody in the IR range of interest.
  41. damorbel #224: "Sunlight travels from a cold region of the atmosphere to a warmer one... indisputable fact."?

    Just what it says. The stratosphere is between the Sun and the troposphere. The stratosphere is colder than the troposphere. Ergo, for sunlight to reach the troposphere (and us to be able to see it) it passes from a colder area to a warmer one.

    Also: "The sunlight that passes through the atmosphere is not affected by it."

    Nonsense. In the same post you went off on an inexplicable tangent about sunlight causing ozone formation. That alone proves that sunlight is affected by the atmosphere.

    Also: "Oh, and the temperature at the stratopause is not that low, just about freezing, 0C."

    First, the stratopause is the boundary between the stratosphere and the mesosphere. Second, it is the warmest point throughout the mesosphere and stratosphere. Third, 0C is still significantly colder than the ~15C average surface temperature.

    Also in #237: "Whatever the configuration of the hot and cold bodies, the cold body will always absorb more photon energy (no. x E) from the hot body than the other way round."

    True... but here you finally admit that the 'hotter' body is absorbing photon energy from the colder one. Ergo, the hotter body must have more photon energy with the colder body than without it. Take the colder body away and the hotter is emitting the same amount of energy but not receiving any... ergo, it has less energy and is colder than it would have been with the colder body there.

    In other words, yes more energy flows from the warm surface of the Earth to the cooler sky than vice versa, but the IR photon energy flowing from the greenhouse gases in the atmosphere down to the surface means the surface is warmer than it would be without those gases.
  42. #220 KR at 02:59 AM on 1 December, 2010
    However, when you say that "...Earth is a system very far from thermodynamic equilibrium", I would like to point out that as far as we can tell (again from Trenberth 2009, although I'm sure there are slightly different estimates out there) the balance sheet is currently tipped only about 0.9 W/m^2 from dynamic equilibrium. If we can reduce or prevent further GHG emissions, we can reduce that imbalance, and the resulting shift in global temperatures.

    Thermodynamic equilibrium and steady state are very different concepts. Earth is not in thermodynamic equilibrium in any sense of the word, because its environment is not in thermal equilibrium. About one part in 184,801 of the skies around it has an effective temperature of 5777 K, while the rest is at 2.725 K. In first, second and third approximation there is only radiative coupling between Earth and its cosmic environment. In spite of the fact the Sun occupies only a tiny portion of the sky, due to the T4 dependence of thermal radiation flux, in excess of a hundred million times more radiative energy comes from it than from CMB (Cosmic Microwave Background).

    What you call dynamic equilibrium has nothing to do with thermal equilibrium proper, when entropy of the system is supposed to be at its maximum. Quite the contrary. The overall entropy content of the climate system (which includes at least the atmosphere and hydrosphere of Earth, probably the biosphere as well) is kept at the smallest possible value by continuously getting rid of the entropy produced inside the system (OLR has a much higher entropy flux than ASR).

    This low entropy state can only be maintained by working as hard as possible, that is, producing entropy at the highest possible rate (then radiating it away into outer space as soon as possible). This is what MEPP (Maximum Entropy Production Principle) is about.

    Obviously an energy balance has to hold in the long run and on average, otherwise sooner or later the system would enter some absolutely crazy state (contrary to observations). But this balance is best described by the concept of steady state, not as a dynamic equilibrium, because it's only too easy to mix up the latter one with thermal equilibrium.

    It is easy to show that whenever the climate system is in a MEP state, increasing the opacity of the atmosphere in thermal IR (that's what so called GHGs do) decreases rate of entropy production if all else is held unchanged. At the same time entropy content of the system goes up. That's what is described as warming, because warmer stuff has higher entropy in general.

    BTW, if the climate system were in some suboptimal state by having less IR opacity in the atmosphere than required by MEPP, adding GHGs would increase overall entropy production and decrease entropy content, hence temperature. Saying the addition of some more GHG causes warming is equivalent to insist current IR opacity is already at or above the value implied by MEPP.

    The fictitious value of 0.9 ± 0.15 W/m2 TOA energy flux imbalance from Trenberth 2009 has nothing to do with reality. What is actually measured by ERBE and CERES satellites, is 6.4 W/m2 (which is obviously wrong beyond repair). Therefore they apply all kinds of adjustments to the measured dataset so as to match computational model projections and this is how they arrive at the value which was assumed to be the correct one from start. The logic behind this exploit surely makes one's head spinning.

    J. Climate, 2008, 21, 2297–2312.
    doi: 10.1175/2007JCLI1935.1
    The Annual Cycle of the Energy Budget. Part I: Global Mean and Land–Ocean Exchanges.
    Fasullo, John T., Kevin E. Trenberth

    J. Climate, 2008, 21, 2313–2325.
    doi: 10.1175/2007JCLI1936.1
    The Annual Cycle of the Energy Budget. Part II: Meridional Structures and Poleward Transports.
    Fasullo, John T., Kevin E. Trenberth

    The only measurement having a chance to shed some light on the true value of energy imbalance at TOA is ARGO Ocean Heat Content data, and only after mid 2003, not before (because OHC measuring network before that date was far too sparse, with serious undersampling as a result).



    An energy imbalance of 0.9 W/m2 is equivalent to a heat accumulation rate of 1.45×1022 J/annum. In seven years (between mid 2003 and mid 2010) it would be more than 10×1022 J. The NOAA/NODC figure above shows somewhat less than zero J went into the upper 700 m of oceans, so more than 1023 J had to go somewhere else. But there is no place on Earth where such a huge quantity could possibly hide, therefore it is not hiding anywhere, but has left the terrestrial climate system by crossing TOA (as outgoing thermal radiation). In other words, there is no energy imbalance whatsoever, Trenberth's speculations are falsified along with the computational climate model calculations they were based on (which means Trenberth's famous "missing heat" is nowhere to be found at the moment, but it used to be in the oceans earlier, unobserved by the much less reliable XBT/MBT system, making steep parts of the NOAA/NODC OHC graph wanting). Present climate is as close to a steady state as it can possibly be. It is as simple as that.

    And now back to theory. The most lucid point to have is that Earth is not getting any heat from the Sun, just short wave EM radiation. This radiation is turned into heat when and if it is absorbed by either the atmosphere or the surface (accompanied by a huge increase in entropy).

    Concerning the effect of GHG addition, the "if all else is held unchanged" clause above is an all-important one. Of course there is no one there to hold things unchanged as some more CO2 is added to the atmosphere, making it more opaque in a restricted thermal IR band. The real climate system has an astronomical number of degrees of freedom (vastly more than any computational climate model can possibly have), so it can adjust itself in any number of ways if a single parameter (like IR opacity in the 14-16 μm band) is changing.

    If CO2 addition has decreased entropy production rate initially (that is, if the system was close to a MEP state), it will readjust itself to increase its entropy production rate if possible, but under no circumstances would readjustment decrease entropy production rate further. That is, there is a strong tendency to counteract climatic effects of CO2, but MEPP would not allow any change which would amplify it.

    And indeed, that's what is observed. In the 7 years considered atmospheric carbon dioxide content went up from 376 ppmv to 390 ppmv, which is 5.3% of the radiative effect of a CO2 doubling. Yet, it has induced neither "radiative imbalance" nor "heat accumulation" in the system, as it is indicated by actual measurements (as opposed to computational models).
  43. Berényi - You are correct, I should have used the term "steady-state", rather than "thermodynamic equilibrium".

    However - the essential I extract from your post is your statement that "...there is a strong tendency to counteract climatic effects of CO2, but MEPP would not allow any change which would amplify it".

    In other words, you claim that there is only negative feedback, not positive feedback to a CO2 forcing. Sorry to say, the data proves this not to be the case. Feedback is positive, your assertion is quite simply not supportable. MEPP is either not a correct description or it does not have the effects you claim. You have been pointed to before, and have failed to address this issue with your MEPP claims. You keep saying that "degrees of freedom will override climate forcings to maintain the status quo", and that is observationally, patently not the case.

    As to your claim that the last 7 years disprove CO2 forcing, that would be cherry-picking - if this holds for 20-30 years, and acquires statistical significance, then we have something worth discussing.
  44. In my previous post, "degrees of freedom will override climate forcings to maintain the status quo" is not a quote, but rather my interpretation of a number of postings on this subject.

    My apologies - I don't mean to put words into other peoples mouths.
  45. damorbel, like CBDunkerson (his last three paragraphs), I am pleased to see your agreement that photons from a cooler source are indeed absorbed by a warmer target. So you agree that the greenhouse gas effect does not violate the second law of thermodynamics, which is the topic of this thread, right?
  46. #243 KR at 01:46 AM on 2 December, 2010
    that would be cherry-picking

    If OHC is supposed to be the true indicator of global warming and we have only seven years of reliable OHC data, then it is not cherry-picking to use what we have, is it?

    What is more (and it is independent of MEPP), even if we assume heat is accumulating in the climate system on an annual rate of 1.45×1022 J, it takes more than 300 years to warm the ocean up by 1°C. It is clearly inconsistent with a 2+°C warming by the end of this century.
  47. Re #245 Tom Dayton, you wrote:-

    " I am pleased to see your agreement that photons from a cooler source are indeed absorbed by a warmer target"

    Tom they would be absorbed by any 'target'. But do you agree that they are absorbed by adjacent CO2 (H2O, CH4 etc.) more or less at the altitude where they are emitted? Or do they make it to the Earth's surface as 'backradiation', as in Trenberth's diagram?

    Further, do you think the cold photons raise the surface temperature 33K from 255K to 288K?

    And finally, what would be the average surface temperature without the H2O & CO2 etc.?
  48. damorbel #247: "Tom they would be absorbed by any 'target'."

    That's a yes. Ergo, global warming theory does not violate the second law of thermodynamics.

    Now you are just quibbling about the magnitude of the effect. Which, as various people have pointed out, is a measured fact. Heck, Fourier made a pretty good stab at estimating it nearly two hundred years ago when he discovered the temperature discrepancy and first proposed what we now call the greenhouse effect as a possible explanation.
  49. Re #240 Riccardo you wrote:-

    "any body may behave like a blackbody in a frequency range and not in others. In particular, the earth surface is very near a blackbody in the IR range of interest."

    Not so. IR is just a colour the same as red, yellow, green etc. and there is an albedo (reflection) in the IR also.

    The IR emissions from H20, CO2 etc. do not follow the smooth black body emission spectrum, instead the spectrum is highly irregular
    meaning that, for substantial parts of Earth's emission spectrum there is no radiation from the GHGs.

    Now you could argue that radiation from Earth 'fills in the gaps' but you will also have to explain why the material that reflects the sunlight to give Earth an albedo doesn't also reflect radiation originating in coming from Earth.

    There is no real 'one way' reflection effect, what you have for the ladies changing room is a cunning lighting effect that gives the impression of a 'one way' mirror. The cause of Earth's 30% albedo also causes a reflection of 30% (inwards) of the radiation coming out from the planet. That is why the temperature of a planet like Earth is independent of the albedo.
  50. Re #248 CBDunkerson you wrote:-

    "damorbel #247: "Tom they would be absorbed by any 'target'."
    That's a yes. Ergo, global warming theory does not violate the second law of thermodynamics."

    You are going too fast. Since emitting (GH) gases absorb also there is no chance that any imbalance in thermal energy transfer will arise as described by 'back radiation' (i.e. W/m^2, J/s/m^2) as claimed by Trenberth. Not just 'insufficient' to cause 33K increase in surface temperature but none at all., the thermal energy transfer is going from the surface to the troposphere, cooling the surface as it goes.

    You must realise that with a full transparent atmosphere (no GHGs) the cooling radiation would all come from the surface, so what's the big deal? The surface would have just the same temperature it has now.

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