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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 1401 to 1406 out of 1406:

  1. BernhardB your misunderstanding about radiators has been addressed. Since you ignored my earlier comment, I'll ask you again the question, which was also asked before to other GHE deniers on this thread: if there is no radiative GH effect, where does the downwelling IR measured at the surface come from? No GHE denier has yet come up with a good answer, perhaps you have one.
  2. It is not often I am moved to defend Dr Spencer's reputation, but in this case I can make an exception. What Dr Spencer said, that has been misinterpreted by BernhardB, was:

    "The more you can reduce the rate of energy loss to the cold walls, the hotter the plate will get. Yes, the surrounding objects act to control the rate at which the plate can lose energy. I have no idea what happens if you can keep the plate from losing energy at all….I suspect the heater wire melts "


    I say misinterpreted because Dr Spencer is clearly discussing the case of no heat loss. The only way a convection based heat sink place in a vacuum would lose no heat is if all external surfaces emitted no thermal radiation. Of course, if they did that, then there would be no "back radiation" between adjacent fins of the heat sink so BernhardB's thought experiment would not hold. So BernhardB has taken a correct explanation by Spencer, applied it to a situation that does not satisfy the conditions Spencer specified, and then claimed that Spencer's prediction would fail, and that Spencer was talking nonsense when the prediction fails outside of the conditions in which it applies.

    I suspect Spencer would blow a fuse at this level of misrepresentation.

    Which brings me to the second point. BernardH claims that the only way the wire can be melted is by increasing the voltage. Given the large number of industrial applications for melting wires by increasing the resistance while holding the voltage constant, his claim is simply false. Perhaps the most common of those applications is electrical arc welding (most commonly as MIG welding), but others abound.


    (Image from wikipedia)

    So far BernardH shows that his arguments depend on not just miscomprehending the physics, but a complete failure to understand how common industrial processes and computer components works. It is not the esoteric, but the commonplace that shows BerhardH is ...


    (Image from BernhardB)

    Well, you get the idea.
  3. "I suspect Spencer would blow a fuse at this level of misrepresentation."

    Which is fitting since, as we all know, "blowing a fuse" is what happens when a wire designed to melt under certain conditions meets these conditions... :-)
  4. I wrote on the other thread:

    33. Steve Case at 12:03 PM on 1 April, 2012
    Tom Curftis #31 Wrote
    … Science of Doom has an extensive discussion of the difference of the ocean's response to heating by solar radiation and back radiation …

    I suppose this will be considered nit picking, but back radiation from the cooler atmosphere doesn’t do any heating of the ocean. It does slow the cooling of the ocean by canceling out part of the spectrum, but it’s the sun that does the actual heating and reestablishment of equilibrium. Yes, the effect is the same and it’s perhaps just semantics, but claiming that back radiation heats the ocean leads to erroneous thinking.

    Moderator Response: [DB] Your statement about back radiation is off-topic on this thread. Any who wish to respond to it please do so on a more appropriate thread. Thank you.

    So here I am and I find this right away:

      12. Daniel Bailey at 12:01 PM on 20 September, 2010
      ...The downward radiation adds to the energy received from the sun and heats up the surface of the earth more than if this downward radiation did not occur.
      ...
      It simply means more energy flows from the warmer surface to the colder atmosphere than in the reverse direction.

    And it doesn't mean that the colder atmosphere heats up the surface. It doesn't mean that the downward radiation heats up the surface either. It means as I stated in the other thread (see above) that part of the radiation from the surface is cancelled out and the surface cools off at a slower rate and so the sun at nearly 5800K continues to warm it up until that rate is again at equilibrium with the incoming heat energy from the sun. Perhaps this is considered trivial, but I see over and over again, statements that the ocean is being heated by the back radiation and the downward radiation heats up the surface and so on. It's not exactly right, and leads to 2+2=5 thinking.

    And what is that downward radiation that makes me say 2+2=5 is comparable to claiming the downward radiation heats up the surface? It's around 15 microns isn't it? And isn't the temperature of a body that radiates mostly at 15 microns very cold? Around 200K or so which is (-100°F/-73°C) or about as cold as dry ice.

    Having said all that and from what I read, the greenhouse effect without considering feedbacks should warm things up about 1.2°C for a doubling of CO2.
  5. Increased back radiation (from increased levels of greenhouse gases) heats the ocean by altering the thermal gradient in the 'cool skin' layer of the sea surface. See SkS post: How Increasing Carbon Dioxide Heats The Ocean.

    It's true that back radiation doesn't penetrate into and heat the ocean but, by reducing the loss of heat to the atmosphere through conductivity, the oceans store more energy from the sun and therefore become warmer. That's why the ice core records show a strong relationship (correlation) between CO2 and global temperature:

  6. Steve Case @1404, the back radiation comes from a variety of frequencies, mostly associated with H2O emissions. Typically it is close to the surface temperature in brightness temperature. Globally averaged the back radiation has an effective brightness temperatures of 277 degrees K, compared to the globaly averaged effective brightness temperature of 289 degrees K for the upward surface radiation.

    Seeing we are into nitpicks at the moment, in some circumstances the overlying atmosphere is warmer than the surface so that it does warm the surface even in your use of the term.

    More importantly, the IR radiation from the atmosphere is absorbed at the surface causing an increase vibrational or translational motion in the absorbing molecule, which vibrational and translational motion is called heat. In the popular vocabulary, that means the atmosphere heats the surface. It is true that the surface radiates energy, and hence cools faster than the atmosphere can heat it, but that is almost irrelevant to the choice of terms.

    It is only "almost irrelevant" because some physicists have defined "heat" to mean "the net transfer of thermal energy" by which definition "heat" can only mover from the hotter to the colder body, and having moved ceases to exist (although the thermal energy doesn't) because heat only exists when thermal energy is being transferred. In so doing they have defined the term so that it is strictly inconsistent with popular usage of the term (causing endless confussion), and indeed, strictly inconsistent with the usage of the term by the greats of thermodynamics including Lord Kelvine, Rankine, Clausius etc.

    Any "2+2=5 thinking" as you put it, can be avoided by being aware that in the popular meaning of the term "to heat", the second law of thermodynamics must be stated as, "Net heat flow can only proceed from a warmer to a cooler body".
  7. @ RW1 at 11:08 AM on 16 December, 2011

    "There is no violation of the second law with the Greenhouse Effect, because it's not about energy going from cold to warm through a conduction process."

    You are confusing radiation (electromagnetic waves) with creation of thermal energy (heat). Heat is a process involving transfer of energy based on temperature - as opposed to generic radiation of photons. It follows that thermal radiation (a process creating heat) from a cold to a hot body (i.e. from the atmosphere to the Earth) is a physical impossibility. The Second Law prevents this because otherwise it would be possible to obtain work from transfer of heat into the atmosphere; i.e power station cooling towers. Essentially, we could then reuse the energy and build a perpetual motion machine. AGW is predicated on a misunderstanding of the Second Law which is thoroughly debunked by eminent German physicists (as opposed to climate scientists who are generally not professional physicists) Gerlich and Tscheuschner.
    Response: TC: Link to RW1's post added.
  8. Not this again!

    Silas:

    There is an enormous body of theoretical, experimental, and most importantly empirical evidence showing that the atmospheric greenhouse effect, however misnamed, is fact.

    It does not violate any law of thermodynamics, it does not allow any sort of perpetual motion machine.

    Gerlich & Tscheuschner are, simply put, wrong, wrong, wrong.

    For more in-depth information you can check out the blog Science of Doom which has some reviews of the G&T paper here. You can also check out some other important Science of Doom posts regarding the relevant physics here and here. Science of Doom relies heavily on the actual maths of the situation and basic radiative physics known for decades.
    Response: [DB] In addition to the valuable links provided by Composer99 above, please see this SkS post, Has the greenhouse effect been falsified?.
  9. Silas - I would suggest, as Composer99 recommended, to look at the Science of Doom site (search there for "Gerlich"), including such gems as On the Miseducation of the Uninformed by Gerlich and Tscheuschner (2009) and Radiation Basics and the Imaginary Second Law of Thermodynamics.

    Quite frankly, I cannot think of another paper in the field that has been so definitively and repeatedly shown to be dreck. G&T's work is absolutely horrible...
  10. KR at 05:24 AM on 24 November, 2010

    Heat flow is the unidirectional and is based upon the need for thermal equilibrium between bodies. Extremely basic physics. It is a process not a summation and therefore cannot be "negative" - an egregious nonsense. (-Snip-)
    Response:

    [DB] Please familiarize yourself with this site's Comments Policy before composing future comments.

    Egregious inflammatory snipped.

  11. @Composer99 at 05:27 AM on 27 July, 2012

    I have read the G&T paper and have a background in engineering thermodynamics.

    It is incumbant upon proponents of the GHE to demonstrate their theory through (-Snip-) prediction of events in nature - i.e. unexpected and cataclysmic consequences of global warming. Confirmations do not count in science as such 'evidence' is always easy to find. (-Snip-)

    (-Snip-)
    Response: [DB] Multiple examples of unsupported sloganeering snipped.
  12. Silas, then can I suggest then that you read the Science of Doom articles to which you have been pointed to and if that is unconvincing, then try the physics textbooks from which the author draws his points? There is nothing contradicting basic physics/thermodynamics here, just a misunderstanding of the physics at work. If G&T were right, then how would explain the MEASURED back-radiation at the surface or the drop in the energy band as measured at the TOA? (among the many experimental confirmations of normal physical theory). The experimental evidence is with conventional physical theory, not with G&Ts strange interpretation of LTE.

    You might also like to check out AP Smith rebuttal here.
  13. Silas - I would strongly recommend you read through some of the posts referred to above, some of the >1400 comments on this thread, actual reviews of what G&T presented - before deciding that all the people who have looked at the G&T claims are idiots. Science of Doom in particular is sourced by a physicist - and you seem to have prejudged his expertise.

    I would also point you to the Real Climate collection on this, which links to various commentaries and a peer reviewed comment - all rebutting the G&T nonsense. You might also look at Dr. Fred Singer's (a rather notorious skeptic of just about anything - ozone holes, 2nd hand smoking, climate change) characterizing 2nd Law objections as unsupportable and embarrassing 'denial'.

    "It is incumbant upon proponents of the GHE..."

    No, it is not; that work has already been done. The radiative greenhouse effect is supported by multiple lines of evidence, physics, observations, etc. G&T (and you, apparently) feel that all this data is incorrect - that's an extraordinary claim, and requires evidence supporting that isolated view to be taken seriously. The burden of (dis)proof is on you.
  14. Silas - I think one of the best summaries of the G&T paper comes from Gavin Schmidt, who had some of the same reactions to it that I did:

    It's garbage. A ragbag of irrelevant physics strung together incoherently. For instance, apparently energy balance diagrams are wrong because they don't look like Feynman diagrams and GCMs are wrong because they don't solve Maxwell's equations. Not even the most hardened contrarians are pushing this one....
  15. Silas, you wrote:

    "You are confusing radiation (electromagnetic waves) with creation of thermal energy (heat). Heat is a process involving transfer of energy based on temperature - as opposed to generic radiation of photons. It follows that thermal radiation (a process creating heat) from a cold to a hot body (i.e. from the atmosphere to the Earth) is a physical impossibility."


    It is difficult to interpret this in any other way than a prediction that there is no thermal (IR) radiation originating in the atmosphere and being absorbed by the Earth's surface. I like that. It is a risky prediction that is easily checked by empirical means.

    You later write:
    "It is incumbant upon proponents of the GHE to demonstrate their theory through ... prediction of events in nature"


    Presumably you therefore think it is incumbent on you, since you have made a risky prediction to actually check the data to see if your risky prediction is verified, or falsified by the data. Fortunately, climate scientists believe the same thing. They have predicted the existence of downward IR radiation from the atmosphere, and have checked. Indeed, here is a comparison of some of their predictions with observations:



    (Source)

    I don't want you to notice the very good correlation between AGW predicted and observed Downward IR Radiation. I want you to notice that the downward IR radiation exists, in direct contradiction of your prediction. If you follow the link to the source of the diagram (Science of Doom), you will find many other examples of observations of this radiation you claim cannot exist.

    Indeed, even the noted "skeptic" Roy Spencer is not so foolish as to deny the existence of downward IR radiation (back radiation). In fact, he has measured it himself:

    "For instance, last night I drove around pointing this thing straight up though my sunroof at a cloud-free sky. I live in hilly territory, the ambient air temperature was about 81 F, and at my house (an elevation of 1,000 feet), I was reading about 34 deg. F for an effective sky temperature.

    If the device was perfectly calibrated, and there was NO greenhouse effect, it would measure an effective sky temperature near absolute zero (-460 deg. F) rather than +34 deg. F, and nighttime cooling of the surface would have been so strong that everything would be frozen by morning. Not very likely in Alabama in August.

    What was amazing was that driving down in elevation from my house caused the sky temperature reading to increase by about 3 deg. F for a 300 foot drop in elevation. My car thermometer was showing virtually no change. This pattern was repeated as I went up and down hills.

    The IR thermometer was measuring different strengths of the greenhouse effect, by definition the warming of a surface by downward IR emission by greenhouse gases in the sky. This reduces the rate of cooling of the Earth’s surface (and lower atmosphere) to space, and makes the surface warmer than it otherwise would be."

    (Source, this link should not be interpreted in any way as agreement with Spencer's views on other subjects.)

    So, to the extent that you have predicted that there is no back radiation, you are wrong. Perhaps you would like to show your commitment to the principles of science by stating clearly that you are wrong. If you are willing to do so, we may be able to progress in resolving your conundrum.
  16. A note to the unwary.

    'Silas' is Girma Orssengo, who has in the past displayed an astonishingly blinkered misunderstanding of science. Arguing with this ardent Ayn Rand acolyte will get one nowhere, very fast.

    On the matter of the claim that 'cool' cannot radiate to 'warm', I'd invite Silas/Orssengo to visit

    http://scienceblogs.com/deltoid/2012/05/17/tim-curtins-incompetence-with/

    where such nonsense might be kicked around the park, as was done with Tim Curtin, and thus save clogging the thread here. And as Orssengo is apparently a functioning engineer, I would invite him to explain somewhere in his discourse how energy moves through the lumen* of a Dyson sphere.


    [*Yes, it was deliberate...]
  17. Thanks Bernard. I've seen Girma's discourses on various forums so I wont waste my time. Just about anyone who jumps into this thread has to be viewed with some suspicion.
  18. @1407: "...eminent German physicists..."

    This must be a joke. A bad one.

    My turn:
    Italy once had one Gallileo. Germany must be truely blessed for it has got at least two.
  19. KR says
    ...... Science of Doom site (search there for "Gerlich"), including such gems as On the Miseducation of the Uninformed by Gerlich and Tscheuschner (2009) and Radiation Basics and the Imaginary Second Law of Thermodynamics.

    The Science of Doom site is an evolving platform.
    Leonard Weinstein has a recent guest post there.

    How the “Greenhouse” Effect Works – A Guest Post and Discussion.

    SoD agrees with the broad outlines of the post.

    Leonard Weinstein would agree with Silas that it is technically incorrect to say heat moves spontaneously from a lower temperature object to a higher temperature one.

    Why do some in climate science take issue with the technical language of thermodynamics?

    There is no debate in physics about whether or not heat can flow spontaneously from a lower to a higher temperature object.
    Thousands of physics textbooks and thousands of physics departments unanimously agree with Clausius that it cannot.
    To argue otherwise is to peddle pseudo science.

    To redirect folk to SoDs site may not have the result that KR intends.
    Response: [DB] Being argumentative, repetitive and pedantic constitutes sloganeering and is in violation of the Comments Policy. FYI.
  20. suibhne - I would refer you to the reference Chris Ho-Stuart pointed you to (his peer-reviewed reply) the last time you argued in support of G&T.

    I would note that suibhne has been repeatedly pointed to the errors in his physics (here, here), and stand by my recommendation
  21. The point of redirection to SoD is to help you understand the physics - that AGW does not in fact involve a mechanism that violates 2nd Law nor that it proposes a novel definition of 2nd law. Keep reading - try to understand what is actually happening.
  22. Soooo..did "PhysSci" ever get his paper published? We *could* have us an 'a-ha' moment from it!

    >;-D
  23. At the beginning of this thread there was b-j-m insisting that CO2 must block incoming and outgoing energy equally because both contain IR components, even after being shown that the emission spectrum of the sun and the Earth are nearly disjoint.

    Here, 1400 posts later, is suibhne, whom I remember from the the G&T debates years ago, still treating heat and energy as synonyms despite the many times that physicists and others have pointed out, with numerous familiar examples, that energy freely travels from cold to hot (and in every other direction).

    In between are numerous other examples of the same phenomenon -- simple, indisputable refutations of claims being rejected out of hand, ignored, or otherwise having no effect on the claimant, who simply repeats the claim in the same or a different form. All of the claims that the greenhouse effect is a violation of the 2LOT were already refuted in the original article, yet numerous people have simply repeated the claim. (And we even have at least participant here claiming in another thread that the assertion that people deny the greenhouse effect is a strawman.)

    People have patiently explained at length the errors in these claims, to no effect. Something can surely be learned from this, some lesson about pedagogy or psychology, but other than bad news I'm at a loss as to what can be taken from it ... how we can use this knowledge to improve our situation. Anyone?
  24. jibal - Appalling, isn't it? The lesson I take from this kind of discussion is simply this:

    There are, and always will be, idjits (IMO, apologies if strongly stated) who cannot be convinced (suibhne, Damorbel, Doug Cotton, others), who have blocks against a rational discussion, who are driven more by their personal worldview than facts that might contradict those. But clearly explaining their errors, even if they themselves cannot accept the data, provides the vast majority of reasonable people rational support they (I sincerely hope) appreciate for judging the issues.

    Most people can look at a discussion and recognize who is speaking from the data, from reason, and who is denying reality. While there is an element, as Friedrich Nietzsche said, of "At times one remains faithful to a cause only because its opponents do not cease to be insipid", I honestly believe that discussing the issues in a rational fashion can only assist those in the majority who might not have the time or training or inclination to personally dig into the for/against data issues.

    While I discuss matters with the deniers who raise objections, I try (insofar as as possible) to speak to the rather more silent majority. There are those who will never be convinced, but most people can clearly distinguish (given enough context, enough of an exchange) between a presentation of facts, and someone speaking from their nether regions.
  25. There are numerous thought experiments on 2nd law argued in this thread. Here is an actual experiment for those who think the 2nd law is broken to chew on.

  26. I want to post here my admiration of the persistence of those who have kept up with almost 1000 posts rebutting a rather obviously flawed argument, that starts from failing to observe that you can’t apply the 2nd law of thermodynamics unless you have a closed system. There is a continuous influx of energy from the sun, so the ground and atmosphere aren’t a closed system. Case closed.

    If Gerlich really is physics professor at an apparently good university who has real students, they should demand a refund if this is the quality of his understanding.

    BTW there are a few dead links in the Notes:

    • http://groups.google.com/group/rabett-run-labs?hl=en
    • http://scienceblogs.com/deltoid/2009/03/gerlich_and_tscheuschner_oh_my.php
    • http://tamino.wordpress.com/2009/03/07/open-thread-11/
  27. This is a good post, but I would like to believe that a lot of the thrashing in the discussions attached to it could have been avoided if Skeptical Science would edit the article to make the correction already suggested by post#955: the citation of the Clausius formulation of the Second Law is incorrect.

    Far better would be to use Clausius's own translation of his statement of the law: "Heat can never pass from a colder to a warmer body without some other change, connected therewith, occurring at the same time."

    One of the immediate advantages of this formulation is that it immediately enables us to put the burden on the "believers in the imaginary Second Law" to show that there are no "other changes" that allow the transfer of heat from the cold atmophere to the warm earth.

    Certainly, the 'generally' of the version currently in the article is terribly confusing. What is 'generally' supposed to mean in the statement of a physical law? Would Newton ever have said "to each and every action there is generally an equal and opposite reaction"? Of course not.

    At least when Clausis said "other changes", we know he was speaking in the context of heat engines, so we know he meant changes in thermodynamic state, whether of the heat engine or in the surrounding environment. We do not know anything of the sort for 'generally'.

    Alternatively, several great physicists of more recent times, so in reference to the more complete theory of thermodynamics they themselves developed, have given formulations that might even prove more useful, e.g.:

    Wolfgang Pauli: Clausius says that heat conduction is an irreversible
    process — a process is called irreversible if the initial state
    cannot be reached from the final state without compensation

    Enrico Fermi: it is impossible to have a process whose SOLE effect is
    the transfer of heat from a colder to a hotter body

    Richard Feynman: Carnot asserted that at constant temperature it is
    impossible to extract heat out of its source and turn it into work,
    without producing other changes in the given system or its surrounding
    environment.

    Please consider these also, but at the very least, correct the Clausius quote: it can only cause unnecessary confusion, as people are still referring to this article.

  28. MattJ I think you are missing the key point which is that the net transfer of heat is from the warmer surface to the cooler atmosphere, so the second law of thermodynamics holds whether there is "some other change" or not.  If you lie under a blanket, the blanket keeps you warmer than you would otherwise be, even though the blanket (and the air beneath it) is cooler than you are.  This does not require "some other change" in the blanket (or air beneath it) and does not contravene the second law of thermodynamics.

  29. Dikran-

    No, I am not missing that point. I am addressing the point you implicitly get wrong when you say (in #1428) that "the second law of thermodynamics holds whether there is 'some other change' or not".

    The clause "whether there is 'some other change' or not" is invalid. The Second Law holds, period. But the Second Law does not say that heat, whether 'net' or not (it does not make the distinction) can never flow from colder to hotter.

    It does no good to quote the Second Law incorrectly, and then say, "it does not contravene the second law of thermodynamics". As long as you allow the "imaginary second law" to maintain a hold on the reader's mind, especially on the 'skeptical' reader, he will still keep coming back to the imaginary form and say, "but, but, heat cannot flow from cooler to hotter", even after you explain to him that you are really talking about "net transfer of heat from the warmer surface to the cooler atmosphere", since you are still requiring radiating CO2 molecules in a -20C stratosphere to heat up an ocean layer that is on average above +20C (these numbers are off the top of my head and approximate, but you get the idea: the source of the radiation is much colder than the warmed sea surface: it is still a violation of the "imaginary second law", but not of the law as Clausius really stated it).

    But if you understand that the second law forbids heat transfer from colder to hotter only as the sole result of a thermodynamic process, then the "imaginary second law" loses its hold, since now the skeptic has to show there is no other result before he can claim "it violates the second law". He can't do that, since the laws of heat radiation invoked to explain backradiation warming of the ocean are derived in accordance with Clausius's statement of the 2nd law.

    Response:

    [Rob P] - allcaps edited. If you must place emphasis on a word or text use the bold format.

  30. MattJ wrote "since you are still requiring radiating CO2 molecules in a -20C stratosphere to heat up an ocean layer that is on average above +20C"

    This is incorrect, this is not what is required for the enhanced greenhouse effect to cause the surface to be warmer than it would be in the absence of greenhouse gasses in the atmosphere.  Nor does a blanket that is slightly cooler "heat up" a warmer body that is under the blanket.  You need to understand the problem first, before seeing how the second law applies.


    Consider two black body objects A and B, in a vacuum, where object A is marginally warmer than object B.  Do you agree that object B will emit IR photons that will be absorbed by A?  "Yes" or "No".  If "No" please explain why.

  31. Dirkan-

    Please read what I actually wrote and respond to that instead of rebutting a climate-denial argument I never used or supported. I am not talking about nor implying that "a blanket heat up a warmer body that is under the blanket". Unlike certain denialists, I understand that the heat transfers in the blanket example are all from higher temperature to lower, so that there is no need to invoke the "without some other change" clause in Clausius's statement of it. Nor do I doubt that in your black body example, both objects emit photons absorbed  by the other.

    I thought I made that clear when I said that " it [radiative heat transfer from cooler to hotter] is still a violation of the "imaginary second law", but not of the law as Clausius really stated it".

    Rather, the point I am trying to make is that different from that. Actually, I am trying to make three points: 1) the statement of the Second Law attributed to Clausius in the article is incorrect: it is not what Clausius said, nor is it even correct 2) you simply cannot build a correct scientific explanation/argument on an incorrect version of one of the fundamental laws 3) partly because of this mis-statement, the article has <b>not</b> explained why the cold CO2 in the stratosphere can transfer heat to the warmer earth and ocean surface without violating the Second Law.

    There was a good article on ScienceOfDoom that I always have trouble findiing when I look for it, it did explain why this transfer can take place — but only by referring to Kirchoff's Law and the Stefan-Boltzmann Law, pointing out that since these law were themselves derived from the Second Law, the results must be consistent with it.

    This approach is sound, it is correct, but it is awfully indirect. And it too relied on getting the statement of the Second Law correct, which this Skeptical Science article does NOT do.

    That is why I say that as a bare minimum, the article should correct the Clausisus quote and state the Second Law correctly. But it would be so much better if in addition to this, it can directly state what the "some other change" is when cold GHGs manage to transfer heat to the warmer thin surface layer of the ocean.

  32. MattJ wrote"Please read what I actually wrote"

    I did, you wrote "since you are still requiring radiating CO2 molecules in a -20C stratosphere to heat up an ocean layer that is on average above +20C" and I pointed out that is not the case.  A blanket is just a useful metaphor I introduced to illustrate why that is not necessarily the case.  Now it seems the fastest way to reach agreement is by consideration of the thought experiment.

    Now you agree that body B emits photons that are absorbed by A.  Do you agree that this photon takes away some energy from B and adds it to A?  yes or no, if no, explain why.

  33. Dikran-

    Yes, you did "point out that is not the case", but then you immediately switched to talking about something else, the several heat transfers that <b>are</b> in the direction of decreasing temperature, without addressing the real issue. That is why I asked you to "read what I actually wrote".

    Nor are you addressing the issue by asking about photons. The question is not "do photons take energy away from B and add it to A". The question is how this can happen without violating the Second Law. You should have not even asked the question not only for this reason, but because I already made it clear that I do undestand that the energy transfer you refer to is real. But simply acknowledging that it takes place does not address the issue: how can it take place without violating the Second Law?

  34. MattJ wrote "but then you immediately switched to talking about something else" no, as I said it was a metaphor to help you to understand the issue.  It is a shame that you did not engage with it.

    "Nor are you addressing the issue by asking about photons" you assume you understand the point I was making, which evidently you do not.  The fact that you refuse to answer the question suggests to me that you are not willing to have your argument put to the test, and therefore should not be surprised if you are not taken seriously.

    As it happens, for radiative transfer, it is exactly what happens to the photons and energy they carry that is important.

    I am always amazed how rare it is in discussions of climate change for people to be willing to answer simple direct questions and will go to such great lengths to avoid doing so!

  35. Dikran-

    Also, simply answering "since you are still requiring radiating CO2 molecules in a -20C stratosphere to heat up an ocean layer that is on average above +20C" with "I pointed out this is not the case is not helpful. Which part of it do you disagree with? Are you going to claim there is no LWIR coming from the stratosphere? Or that the stratosphere is warmer than the ocean surface? Even if the backradiation were mostly coming from the troposphere, it would still be going from cooler to warmer, yet transfering heat to the warmer ocean surface. The only difference is that the temperature difference is not as dramatic. But it is still there, and with the inconvenient sign.

    Now glancing back through the comments on this article, I noticed some tried to explain this by saying that the Second Law applies only to a closed system, or to "net heat". But Clausius never made a distinction between 'heat' and "net heat". And in the statement of the Second Law itself, he does not state any restriction to "closed systems" (but since he was speaking in the context of heat engines, one can make a case for that). So one must either prove that Clausius's statement either appies only to closed systems, generalizes to "net heat" or use a more modern form of the Second Law that is already known to apply to "net heat". Or take the Science of Doom approach, which as I already mentioned, works, but is awfully indirect; it is difficult to use in discussion with laymen or skeptics because of the long winding path through Kirchoff and Stefan-Boltzmann.

    But this Skeptical Science article takes none of these routes; it doesn't even get the statement of the Second Law correct. That is a serious shortcoming.

    Response:

    [JH] You are now skating on the thin ice of escessive repetition which is prohibited by the SkS Comments Policy. Please read the policy and adhere to it.

  36. Dikran Marsupial @1434.

     

    You might find the comment @1435 a bit odd as you are, I think, confused by the comment @1433. The implication you make from the beginning of the final paragraph is contrary to the less ambiguous statements later in that paragraph. "...I already made it clear that I do undestand that the energy transfer you refer to is real. But simply acknowledging that it takes place does not address the issue: how can it take place without violating the Second Law?"
    MattJ is saying that photons do really pass from B to A but in so doing the 2nd Law of Thermodynamics is violated and this phenomenon thus requires explanation.

    Goodness!! It appears the 2nd Law of Thermodynamics is breached!!!

  37. MA Roger, the point I was heading towards was that if photons from B that are abosorbed by A do transfer heat energy from a cooler object to a warmer one, then for MattJ's interpretation of the second law to be obeyed, there must be "some other change, connected therewith, occurring at the same time" and I was going to ask what it was.

    Of course if you adopt the modern statistical intepretation, there is no need to find the "some other change" as the second law only applies to the net transfer of heat, and there is no problem. The reason why we don't need to explain why it doesn't violate the second law of thermodynamics is because it is not precluded by more modern interpretations of the second law in the first place.

    I suspect the problem is that Clausius would have been easily able to measure temperatures of objects (and hence the net transfer), but how would he be able to detect the fact that the radiation is bi-directional between the objects?   Not too surprising then that he didn't make the distinction between transfer of heat and net transfer.

    The funny thing is the Science of Doom page gives exactly the same definition of Clausius' second law as the SkS page does.

    Anyway, MattJ has exhausted my patience, some people are fundamentally unable to see any point of view other than their own, and being unwilling to engage in a thought experiment designed to highlight where the disagreement lies suggests that they don't want to see any point of view other than their own.  This is a pity, as if  MattJ were right, it would be the most efficient way of demonstrating it.

  38. MattJ's original request:

    Far better would be to use Clausius's own translation of his statement of the law: "Heat can never pass from a colder to a warmer body without some other change, connected therewith, occurring at the same time."

    is adequetly met by the word "spontaneously" in the OP version.

     

    but I would like to believe that a lot of the thrashing in the discussions attached to it could have been avoided if Skeptical Science would edit the article to make the correction

    In this I think you are naive; G&T's misformulation was too attractive for climate change deniers to resist, and they have continued to try and make it stick no matter how the 2nd Law was formulated.

    My own observation on the ensuing exchanges is that MattJ appears terribly confused about the distinction between energy and heat transfer; he should get that straight first.

  39. MattJ, the exceptions that Clausius allows for with his clause "without some other change, connected therewith, occurring at the same time" covers situations such as those found in refridgerators, in which heat is pumped from a colder interior to a warmer exterior, but only at the expense of pumping additional heat from a still warmer furnace (via power generation) to drive the process with a net increase in entropy for the entire process.  What you are missing is that the "warming" of the Earth by greenhouse gases is not analogous to that case.  Rather, it is analogous to the far simpler case of decreasing the efficiency of heat transfer outwards from a body warmed by a still warmer source.  Therefore, the exception is not involved.  Including a more explicit statement of the exception (more explicit because it is mentioned in the OP as noted by Phil) would therefore in no way help decrease scientific confusion about the greenhouse effect and thermodynamics.  Rather, trying to explain the greenhouse effect by analogy to refrigerators will increase that confusion.

  40. Hi, Tom-

    Thanks for your reply. For sure, Clausius was including such systems as you describe as "without some other change, connected therewith, occuring at the same time". He was even thinking primarily if not entirely of such systems. But how can we be sure that those are the only such changes he had in mind? I had the impression, based on discussions of the Second Law and its various forms in thermodynamics texts by Fermi, Feynman, Pauli and others, that the law, even in Clausius's form of it, covers a more general class of 'changes'. Thus, for example, Pauli paraphrases it as being equivalent to saying "heat conduction is irreversible". But the concepts of irreversibility and reversibility are more general than providing heat or work from outside, as in your refrigerator example. If when you go around the cycle, some thermodynamic variable must be different from the beginning when you get back, the process is irreversible, a change has occurred. It is not just the two thermodynamic variable heat and work that are under consideration.

    I also have to point out that I am not assuming "that the 'warming' of the Earth by greenhouse gases is analogous to the refrigerator case." Rather, I am pointing out that even when you say that it is based on "the  far simpler case of decreasing the efficiency of heat transfer outwards from a body warmed by a still warmer source", you are still leaving something out.

    That is, sure, once one understands that backwave radiation occurs resulting in IR being absorbed and turned into heat, yes, the hottest point is the sun itself, and all the other surfaces heat moves to are colder than that. But there is still the case of the cold atmosphere transfering heat to the warm surface to accomplish that "decrease of efficiency of transfer". Explaining that event's consistency with the Second Law is what is left out.

    Let me try to put that another way: sure in the overall system, all the heat comes from the sun with the heat/temperature of the earth depending on both how quickly heat comes in and how quickly it goes out, so that slowing the rate of outflow raises the temperature. But to explain how this happens involves explaining how the hotter ocean surface can be heated by the cooler atmosphere, an <b>apparent</b> violation of the Second Law: this article 'explains' it only be getting the Second Law wrong, so that it really hasn't explained anything relevant.

    If you really think Clausius' statement was meant to apply only in the context of heat engines and closed cycles, then it is useless to use his statement of the Second Law in this article, since, as you yourself point out, the analogy of a refrigerator (a heat engine of a particular sort) and the climate system is not very good, and can be quite misleading. The article should then use a completely different formulation, one that has been proved to generalize to the climate system, such as "in an isolated system, entropy is non-decreasing". But this particular option has its own difficulties, I think I understand why the author chose not to use it.

    Finally, concerning Phil's point. Yes, it was mentioned, but only later, and the author did not even seem to notice that he was contradicting himself, putting an unnecessary burden on the reader to resolve the contradiction, all still without a clear and correct statement of the law. Good expository prose does not do this: you get the statement exactly right the first time, and then explain as necessary the technical or otherwise surprising sense of the expressions used. Or you use a special case as a stepping stone to the final, full generalization. But even the appearance of self-contradiction defeats the purpose of the article — and creates a lot of room for the quibbling and carping we saw in 1400 posts.

    Not to mention there is still this crippling problem of the word 'generally' being used in the alleged statement of Clausius' form: no law of physics has such weasel words as 'generally', that makes the 'law' useless for generalization. No wonder Clausius himself never said that!

  41. MattJ @1440:

    "Let me try to put that another way: sure in the overall system, all the heat comes from the sun with the heat/temperature of the earth depending on both how quickly heat comes in and how quickly it goes out, so that slowing the rate of outflow raises the temperature. But to explain how this happens involves explaining how the hotter ocean surface can be heated by the cooler atmosphere, an apparent violation of the Second Law: this article 'explains' it only be getting the Second Law wrong, so that it really hasn't explained anything relevant."

    But the cold atmosphere does not warm the warmer ocean, and nor is their any apparent violation of the second law.  The second law, stated mathematically is that for a closed system:

    ΔS ≥ ∫δQ/T

    where S is the entropy, δQ is the incremental transfer of heat, and T is the temperature.

    Therefore to determine the entropy change we need to integrate over all incremental heat transfers.  In the case of the relationship between atmosphere and surface under the greenhouse effect, we need to integrate over all energy transfers between atmosphere and surface.  From the Fasullo and Trenberth, we have this summary of those transfers:

    Summing over all such transfers, we find that 356+80+17 =  453 W/M^2 is transfered from the surface to the atmosphere, while only 333 W/m^2 is transfered trom the atmosphere to the surface.  Integrated over all energy transfers from between surface and atmosphere, that is a net transfer of +120 W/m^2 from the warmer surface to the cooler atmosphere.  That transfer involves in increase in entropy proportional to the inverse of the reduction of temperature involved, ie, proportional ratio of surface to atmospheric temperatures.

    There is only an "appearance" of a violation of the 2nd law because people insist on considering the back radiation in complete isolation, ie, not as part of a system of transfers including those from the surface to the atmosphere.  If you intergrate all such transfers, as is required by the 2nd law, there is transparently no violation of the 2nd law involved.

  42. That is, sure, once one understands that backwave radiation occurs resulting in IR being absorbed and turned into heat, yes, the hottest point is the sun itself, and all the other surfaces heat moves to are colder than that.

    And there's your answer as to why the greenhouse effect doesn't violate the 2nd Law, Matt.  You have to include the Sun's continuing contribution of energy.  If you don't everything else seems to violate the 2nd Law. 

  43. Re 1441: Not that awful Trenberth diagram again! Sure, I know the diagram is correct, but people who are climate scientists simply have no idea how confusing it is to people who are not familiar with it. It looks like lots of things should add up that don't.

    But you say one has to do the integration — but then you don't do it. You are doing a sum of watt/m2, which is not even the right units for entropy. Nor are you doing the sum over a cycle/process, which is what the expression you gave for delta S requires.

    But rather than ask for that integration, what I think you really need, so what I will ask for is a clarification of the grounds of your assertion that "But the cold atmosphere does not warm the warmer ocean, and nor is their any apparent violation of the second law." That there is an apparent violation is pretty clear, since lots of people find it apparent. But more important: when you say, "the cold atmosphere does not warm the warmer ocean" what do you think happens to the IR photons from CO2 high in the cold stratosphere when they meet the surface of the earth or of the ocean? Aren't they almost entirely absorbed? And once absorbed, isn't all their energy converted to heat? How could these steps be anything other than "the cold atmosphere warming the warm ocean?

    At this point, I think Robert Murphy is a lot closer to answering my question. I have suspected it has a lot to do with the low entropy energy input from the sun driving the whole process, but even this leaves unanswered questions.

    In particular, if we follow a more modern statement than Clausius's (an idea I have been mentioning for a while), then the increasing wavelength of each of these stages of radiative transfer each shows an increase in entropy, so that entropy is non-decreasing, as the second law requires. It is even still non-decreasing in the case of cold stratosphereic CO2 adding heat energy to the thin but warmer surface layer on the ocean.

    It is much harder to make the same argument from Clausius's form, especially when the author does not even state his form correctly. Clausius NEVER said "Heat <b>generally</b> cannot flow spontaneously".

  44. MattJ @1443, the formula for the Clausius inequality is:

     

    That only applies to cyclical processes, and is integrated over the cycle.  You will notice the variant integration symbol used to indicate that fact.

     

    The formula, ΔS ≥ ∫δQ/T, which I gave above is for any closed system, and uses a conventional integration.  That is, it sums over all energy transfers in the region under consideration, and for the time under consideration.

    The Fasullo and Trenberth diagram provides us with total average energy flows per unit time.  From that we can integrate over area and time if we want to, but the result will be the same as simply summing over the power flows in showing that the 2nd law is not violated by the exchange of energy between surface and atmosphere.

    Importantly for this discussion, this is shown without bringing in extraneous factors like the energy input from the Sun, or the energy outflow to space.  In fact, we can model a genuinely closed surface/atmosphere system and the principles involved in the energy exchanges will be the same.  The actual values integrated will not be, for the energy flows will change over time as the surface and atmosphere equalize in temperature.  Such a process would involve every means of energy exchange that actually exists in the atmosphere, including back radiation, and would result in a net increase in entropy.  Further, the surface would cool over time while the atmosphere warms over time.  It follows that back radiation does not violate the 2nd law of thermodynamics, and that neither does it warm the surface.

    We can extend this model by opening it to space, and compare to situations, ie, one with an atmosphere containing greenhouse gases, and one without.  If we do so we can show that the surface in the case with the atmosphere will cool slower than the surface without an atmosphere.  However, it will still cool so there will be no question of any violation of the 2nd law of thermodynamics or the atmosphere warming the surface.

    Finally, we can add in the Sun and find an equilibrium situation.  In that case, the surface equilibrium will be warmer with the atmosphere than without.  That, however, is because the slower rate of cooling for a given surface temperature with an atmosphere requires a warmer surface temperature for the outgoing radiation to match in energy the incoming energy from the Sun.  Thus, in this case, it is true to say that the surface is warmer than it would have been without the greenhouse gases, but it is the Sun that warms the surface, not atmosphere.  

    We might say colloquially that the greenhouse gases warmed the surface, just as we might say colloquially that a blanket warms us at night.  In both cases, however, it is strictly inaccurate.  A blanket will not "warm" a cold stone, and greenhouse gases will not "warm" in the absense of the incoming solar radiation because they do not warm at all, they merely slow the loss of heat.

    You comment:

    "But more important: when you say, "the cold atmosphere does not warm the warmer ocean" what do you think happens to the IR photons from CO2 high in the cold stratosphere when they meet the surface of the earth or of the ocean?"

    No.  I do not mistake the net flow of heat with the individual flows of energy.  Nor am I unaware that in the superior formulation of statistical thermdynamics the 2nd law holds only on average, and that the shorter the time interval the higher the probability that it is violated for that short term.  Thus, there are IR photons from the atmosphere that strike the ocean and transfer energy, but there are more IR photons from the ocean that do the reverse so that the the net heat flow is from ocean to atmosphere (and hence it is the ocean warming the atmosphere rather than the reverse).

    Finally:

    "[The] increasing wavelength of each of these stages of radiative transfer each shows an increase in entropy, so that entropy is non-decreasing, as the second law requires. It is even still non-decreasing in the case of cold stratosphereic CO2 adding heat energy to the thin but warmer surface layer on the ocean."

    The wavelength of IR radiation exchanged between atmosphere and surface is approximately the same for any specific atmospheric component, but the difference in wavelength between incoming SW radiation and outgoing IR radiation does indeed show the process to involve an increase in entropy, and to not violate the 2nd law of thermodynamics.

     

  45. MattJ:

    Finally, concerning Phil's point. Yes, it was mentioned, but only later, and the author did not even seem to notice that he was contradicting himself,

    I'm sorry, but I cannot understand this point;  the OP correctly formulates the 2nd Law using the word "spontaneously" to indicate that exceptions to the flow of heat require "work". It does so in the 3rd paragraph, not "only later". I would suggest that you actually re-read the OP.

    I would re-iterate the my point,  that you seem to be having great trouble distinguished heat from energy flows. Dikran tried to help you with this, but you refused to let him, Tom is having another attempt; but fundamentally your remarks show that you know less about the physics of the greenhouse effect than you think you do.

  46. O.K., well I thought I'd go and look up Clausius' statement, and I found a translation of his works here:

    "The Mechanical Theory of Heat, with its Application to the Steam Engine, and to the Physical Properties of Bodies", by R. Clausius, Translated by John Tyndall, Edited by T Archer Hurst, 1867 (available via Google books)

    Yes, it was indeed that John Tyndall!

    Clausius' statement of the second law mentioned by MattJ can be found on page 117, and has an interesting footnote, which I have reproduced below:

    The footnote makes it very clear that I was wrong in that Tyndall, and I presume also Clausius (as he has an author's preface published in the volume) were well aware that there is a bidirectional transfer of heat between two bodies of different temperatures:


    "In the first place this implies that in the immediate interchange of heat between two bodies by conduction and radiation, the warmer body never receives more heat from the colder one that it imparts to it."


    However, it is in complete agreement with what I wrote about the second law applying only to the net flow of heat,


    "now it is to these compensations that our principle refers; and with the aid of this conception the principle may also be expressed thus 'an uncompensated transfer of heat from a cooler to a warmer body can never occur' "


    and thus the greenhouse effect does not violate the second law of thermodynamics because the surface imparts more radiation to the upper trophosphere than in receives in back radiation.  In Tyndall's terms it is fully compensated.

    Update: It seems unclear whether the translation was by Tyndall or Hirst, or possibly a bit of both as Tyndall translated the original papers and apparently worked with Hirst.  Tyndall certainly wrote the introduction.  However the central point remains as Clausius obviously approved the translation.

  47. Very interesting. This formulation makes the G&T paper completely moot. Their entire demonstration relies on faulty interpretation of the law.

  48. PhilippeChantreau indeed, but it is still able to generate a thread of 1448 comments! ;o)

    I really don't understand why there is so much skeptic [sic] interest in the very weakest skeptic [sic] arguments, such as this one, and the idea that the rise in CO2 is natural, where in both cases a bit of common sense is all that is required.

  49. Re #1448 Dikran says, "I really don't understand why there is so much skeptic [sic] interest in the very weakest skeptic [sic] arguments, such as this one, and the idea that the rise in CO2 is natural, where in both cases a bit of common sense is all that is required."

    Well, look at how long it took for you to recognize that I was right, my quote of Clausius is correct (in #1446), the author's version is not. That alone should show you that it does take more than just "common sense". When you put forth an alleged scientific explanation that can't even quote the Second Law correctly, you should expect enough dispute to generate a 1448 comment thread. By starting out with such a blunder, you make the weak skeptic's argument look much stronger than it actually is.

  50. Re #1445

    No, Phil, he does NOT "get it right". Nor am I the first to point out this error. It was pointed out long ago (#955), yet nothing was done about it.

    What the article actually says is: "Heat generally cannot flow spontaneously from a material at lower temperature to a material at higher temperature."

    Do you see the difference now between what you said and what the article actually says? If, as you say, he had only used the word 'spontaneously', you would be correct. But he also put in the word 'generally', making it useless as a physical law.

    But there is another problem which I also pointed out: the wording, despite what the article claims, is NOT even from Clausius. Yet the article presents this as his own words.

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