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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.

Basic rebuttal written by Tony Wildish


Update July 2015:

Here is the relevant lecture-video from Denial101x - Making Sense of Climate Science Denial

 


Update October 2017:

Here is a walk-through explanation of the Greenhouse Effect for bunnies, by none other than Eli, over at Rabbit Run.

Last updated on 7 October 2017 by skeptickev. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page

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 1451 to 1457 out of 1457:

  1. #1436 "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."

    This is what I find distressing about SkS: many people here get on their high horses in defense of science — yet show they cannot even read well enough to do it. At no time did I say the 2nd Law is actually violated. On the contrary: I explained many times that I see only an appearance of violation, and that I know from the derivation of Kirchoff's and Stefan-Boltzmann radiation laws that it is not violated.

    Why, I repeated this so many times that a moderator accused me of "excessive repetition". But what else am I to do with responses that either misread what I wrote or ignore what I already said?

  2. MattJ wrote "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."

    No, the version given in the article is perfectly adequate as the greenhouse effect does not require "some other change, connected therewith, occurring at the same time" because the back-radiation is already compensated by the upwelling IR from the surface.  The definition given in the article is also merely a rephrasing of the version given in the foot note.  It isn't wrong, the difference between the two definitions is irrelevant in this particular case, so insisting on it is ridiculous pedantry.

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

    is an equivalent statement to

    "Heat cannot of itself pass from a colder to a warmer body"

    which appears in Clausius' textbook.  Note this phrase is translated from Clausius as the footnote gives the German wording of "of itself".  "Spontaneously" is a perfectly reasonable synonym for "of itself" in this context, and the "generally" refers to the possibility of there being "some other change...", which happens not to be relevant in this case.

    Please stop digging.

  3. MattJ "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."

    Given that Clausius did not appear to have published anything himself in English, to suggest that the article presents anything as his words is utter nonsense.

    There is also the point that the statement in the book may not be the only one he made, if anyone can track down the translations of his papers, or the translation of the second edition of his textbook, you may well find them there.

  4. MattJ wrote "At no time did I say the 2nd Law is actually violated. ", no, but you were claiming that there must be "some other change" that prevents the violation.  This is not the case, as the translation of Clausius' text book explains very clearly (the interchange is "compensated").  That was the point I was getting to with the thought example that you consistently avoided engaging with.

  5. Re #1434 "Dikran Marsupial at 04:51 AM on 15 August, 2014

    "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!"

    But how can you be amazed at it? You yourself have never answered the "simple direct question" I put to you to keep you from wandering down the wrong way and disproving what I never said instead of actually addressing the real issue.

    The "simple, direct questions" I am referring to are from #1435, where I wrote: 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?

    That is three simple questions you never answered. So you are in no position to complain.

     

  6. MattJ I have already answered the question, backradiation does not "heat  up" the surface any more than a blanket "heats up" the person beneath it.  It causes it to be warmer than it would otherwise be, by reducing the rate at which heat is lost.  The net transfer is still from warmer body to cooler body.  Sadly this doesn't seem to fit within your comprehension of the problem, which appears to be because your comprehension of the second law is defficient, and sadly you have too much hubris to recognise this.

    Just to be clear:

    (i) there is indeed LWIR coming from the upper atmosphere, it is usually known as "backradiation"

    (ii) The stratosphere is cooler than the ocean surface.

    (iii) The part that I disagree with is the "heat up" bit, which is incorrect, "causes to be warmer than it would otherwise be" would be closer to being correct as the net transfer of heat is from the surface to the atmosphere.  I have already explained this to you (using a blanket as a metaphor).  It would be correct to say that upwelling IR from the surface "heats up" the upper atmosphere.

  7. Re #1444

    Thanks, Tom, for your long and thoughtful reply. You did clarify several points well. But that integral is hard to do for a climate system, isn't it? That is why I am groping for a simpler way to explain it. Using a completely different form of the 2nd law and observing entropy increasing in each step of the process still seems the best way to go rather than take the article's approach.

    Then to the skeptic who still object, "but you have heat going from cooler to hotter", we can say, "but entropy did increase, so there is no violation".

    The problem with this approach is that it requires explaining to the layman what entropy is and how to track it and estimate it. Then there is still the problem that the idea that the second law says only and exactly "heat never travels from colder to hotter" is quite entrenched in the minds of many. I have encountered many, for example, who seem to have engineering thermodynamics backgrounds who still have this entrenched.

  8. "Then to the skeptic who still object, "but you have heat going from cooler to hotter", we can say, "but entropy did increase, so there is no violation".

    or alternatively, you could just show them the pages in Clausius' book where it is carefully explained that this is O.K. as it is "compensated" by a greater flow of heat in the other direction.  There is then no need to mention entropy.

  9. MattJ - What I find most frustrating in these discussions are exactly statements like "you have heat going from cooler to hotter"

    "Heating" in colloquial usage is an increase in net energy causing an increase in temperature. Energy goes from cool objects to warm objects (in fact, to all objects within the radiative view of that cool object), not heat, not by the common use of that term. 

    Energy goes from cooler to warmer objects, which add to the sum of energy going into that warm object, an increase of incoming energy - and hence the object must warm to radiate energy equal to incoming. 

    But the net flow of energy, heat, is still from the warm object to the cool one. Adding a cool object simply reduces that net energy transfer. 

     

    To be more precise, a cooler object will cause a warmer object (or one of any temperature) to increase in temperature if that cooler object adds >0 energy, if the cool object radiates/conducts/convects more energy than an absolute zero background. The starting point is an contribution of zero, anything warmer than that will add incoming energy to an object in view, increasing the input. 

    For some reason the fact that any radiating object represents a positive contribution to incoming energy gets somehow overlooked in these discussions. 

  10. @1446

    Thank you, Dikran, for that excellent find! Sure, a footnote several times the length of the text may be intimidating, but that one was well worth reading And his formulation in that footnote, "...the warmer body never receives more heat from the colder one that it imparts to it." Is particularly good for silencing the skeptic's objection. Now the cold CO2 can impart heat to the warmer thin ocean layer as long as the latter gives more heat back.

    I wish modern texts had footnotes that explained the meaning of the various terms as well as that one did. But that is an old-fashioned practice, rarely duplicated now. They try to do the same with sidebars with only mixed results.

  11. MattJ@1460 does that mean you now agree with me on my interpretation of the second law of thermodynamics only applying to the net transfer of heat, and hence there is no need to introduce the "other changes" clause?

    BTW, the translation of the second edition suggests the footnote may not be an addition by the translator as the corresponding material is in the text of the second edition (translated by somebody else).

  12. MattJ @1450

    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.

    Unfortunately the word "generally" is there to cover Spontaneous endothermic reactions, These are reactions driven by a large increase in entropy, which can overcome a loss of enthalpy (and hence heat), and ensure that the change in Gibb free energy is still negative. This, of course, is to modify Clausius's words to cover the modern understanding of the second law of thermodynamics, which is only rigourously expressed mathematically (as Tom did @1441).

    Thus Clausius's formulation of the 2nd law is actually incomplete as we now understand it. The author of the OP could either quote him directly and expose himself to the criticism that it was incomplete, or add the word "generally" to deal (albeit rather vaguely) with our current understanding.

    I would also point out that you are (now) misrepresenting post 955, which does not object to the word "generally".

  13. Dikran @1453, while I still disagree that it is a cause of confusion, I do have to agree with Matt that the form of the 2nd law given in the article is not a quotation of Clausius, and is portrayed as such.  If it was a paraphrase, it should not have been enclosed in inverted commas and should not have been indented (but may be higlighted in italics).  By including quotation marks and indentation, the OP (whether intentional or not) has marked the statement as a quotation of Clausius, or (as it is in English) a fairly literal translation of Clausius.  Further, if it is intended as a translation, it should be identical to the translation of the apparent source given for the quote, ie, the wikipedia article linked in the sentence introducing the quote.

    As it happens, I have found a reproduction of the original Clausius article in german.  From that it can be clearly seen that footnote was not included in that article, and hence it cannot be attributed to Clausius.  On the other hand, Clausius did read and approve the proofs (footnote on page vii of the English translation).  Therefore Clausius not only endorsed the translation of the principle given in that book, and quoted by wikipedia, but he also endorsed the explanation of the second law as given in that footnote.  (He may even have written it, but we do not have proof of that and hence cannot attribute it to him.)

    Turning to the actual words of Clausius,they were:

    "es kann nie Wärme aus einem kälteren in einem wämeren Körper übergehen, wenn nicht gleichzeitig eine ander damit zussamenhängende Aenderung eintritt."

    Google translate renders that as:

    "it can never pass heat from a colder to a wämeren body, if not at the same time one other so zussamenhängende change occurs"

    From that it appears that the rendition from the English version, and as given by wikipedia is fairly literal:

    "Heat can never pass from a colder to a warmer body without some other change, connected therewith, occurring at the same time."

    Given that, and the implied endorsement of the translation mentioned above, I think it is unreasonable to not take them as his words.  The "quotation" in the original post, however, cannot be taken as anything but a loose paraphrase of those words, or a paraphrase of the English gloss from the footnote (which being originally published in English, requires no translation).

    Given all this, the OP should be editted either to include the form of Clausius words as given in the English translation as quoted in wikipedia, or the text should be modified to indicate the law as actually given is a paraphrase, or the author's own phrasing of the law.

    I do not consider this a minor matter as misquotation is academic misconduct, and therefore something SkS should never do except by accident, and in the later case the error should be corrected as soon as possible.

  14. Dikran @1461, thankyou.  In the second edition, Clausius attributes the formulation of the footnote in the first edition to himself (p78), and repeats much of the explanation from that footnote.  In particular, he mentions the passage of heat from the colder to the hotter body, which is not prohibited, provided that a greater amount of heat flows in the opposite direction.  His wording is:

    "It is true that by such a process (as we have seen by going through the original cycle in the reverse direction) heat may be carried over from colder into a hotter body:  our principle however declares that simultaneiously with this passage of heat from a colder to a hotter body there must either take place an opposite passage of heat from a hotter to a colder body, or else some change or other which has the special property that it is not reversible , except under the condition that it occasions, whether directly or indirectly, such an opposite passage of heat."

    He concludes by formulating the 2nd law as:

    "A passage of heat from a colder to a hotter body cannot take place without compensation."

    That means in editing the OP to correct the misquotation, the author may use the above formulation, or that from the footnote which is now acknowledged by Clausius as his own.  They need only include a link to the source either instead of or in addition to the link to wikipedia. 

    I need only add that the formulation given in the OP is certainly a good paraphrase of the last formulation quoted from Clausius.  Therefore there is nothing wrong with it except for the point that paraphrases should not be presented as quotations.

  15. Tom thanks for the adiditonal details, it does seem that Clasuius adopted the footnote for his second edition, as I mentioned in a previous post, but you have certainly clarified it further.

    "I do not consider this a minor matter as misquotation is academic misconduct"

    This is too strong a statement as it is only misconduct if done deliberately, if there is no intent to decieve, it is just an error and is not misconduct.  I agree that it should be change if it turns out not to be a reasonable translation of something Clausius actually wrote, however this has not yet been established.  It may be that his did write something along these lines in another work.  Performing a google search suggests this exact wording does occur in other academic papers and books, so I doubt SkS are the first to make this error, if that is what it is.  I am making enquiries...

    However, in the light of my finding, I think it may be better just to rewrite the basic rebuttal from scratch as there is now a much more straightforward refutation of the myth based on Clausius' own understanding of his second law.

     

  16. Dikran @1465, following up I have found the major revision of the wikipedia page on thermodynamics which eliminated the form of the statement quoted in the OP above, and replaced it with another version, which has since in turn been replaced.  The original replacement took place on Oct 11th, 2010, with prior versions of the article having the quote in the OP.  Evidently, therefore, the OP took its quote from the wikipedia page to which it linked.  If it is a misquote, it is then entirely inadvertent as regards SkS.  The original version on wikipedia may also explain the frequent occurence of that version on the web.

    With regards to books, google books shows just five books containing that version of the quote.  Of those, it shows the relevant contents of just three recent (2011 to 2013) textbooks, the former on "The Energy Problem", and the seond on thermodynamics, and the third being Farmer and Cook (2013).  The earlier books are one from 2010 by Lawrence Soloman discussing "The Deniers", and one from 1992 by Richard Lindzen.  Unfortunately without the text it is not possible to determine whether Lindzen attributes the version of the 2nd Law to Clausius, or whether he presents it as a quote.

    Of the five, the most interesting is Stein and Powers (2011), which attributes the quote to "Rudolf Clausius' paper in 1850" (p27).  In fact Clausius' talk to the Academy of Berlin in 150 was published in two parts in Pogendorff's Annalen, the first starting on page 368, and the second on page 500.  These were translated in 1851, and included as the first memoir in the first edition of the "Mechanical Theory of Heat".

    The closest formulation I can find in Clausius 1850 occurs on page 45 of the English first edition of "Mechanical Theory", and page 503 in the Annalen.  In English it reads:

    "Hence by repeating both alternating processes, without expenditure of force or other alteration whatever, any quantity of heat might be transmitted from a cold body to a warm one; and this contradicts the general deportment of heat, which everywhere exhibits the tendency to annul differences of temperature, and therefore to pass from a warmer body to a cold one."

    The relevant principle is, of course, stated in the second part of the sentence.  While the quote given in the OP is a good, if abbreviate, paraphrase of that sentence, it is also clearly not direct quotation.  Interestingly, in the "Mechanical Theory" a footnote dates 1864 again glosses the principle stated in the body of the text as "... heat cannot of itself pass from a colder to a warmer body".  That, or the alternative formulation, ie, that "A passage of heat from a colder to a hotter body cannot take place without compensation" have the strongest claim to represent Clausius' true formulation of the 2nd law (ie, the one he was happiest with on reflection).

    Moving on: With misquotation, as with plagiarism, academic misconduct can exist in the absence of intent.   That is why there are fairly strict academic rules about methods of quotation, which are always relaxed outside of strict academic contexts (and apparently always in the physical sciences).  The strict rules are there to prevent inadvertent misquotation.  One of those rules is that when you quote somebody indirectly by quoting somebody else quoting them you clearly indicate that so that any error can be attributed to the source that made the error.  If you do not so attribute, you are considered as guilty of any error as if you yourself had made it.

    In this case, however, clearly SkS misquoted here inadvertently by copying somebody elses "error".  Further, they linked to their source and in a way that made it transperent that it was their source.  At least, it made it transperent until the text of wikipedia was edited.   Consequently no fault lies with the authors of the OP.  Of course, that does not mean the text should not be updated with a correct quotation of an original source (or possibly rewritten in light of the other interesting material uncovered by this excercise.

  17. Cheers Tom, I suspect you are right on the source, good detective work!

  18. @1446

    Dikran- Thanks for finding the link. I do need to point out, however, that when I right-clicked on the link labeled "Google Books", I got a broken URL. It was not hard to edit though: once I removed everything before "books.google.co", it worked (people using other browsers might have to insert/omit "http://" or "www.").

    Now that I have read that note, I consider it more reasonable than I did before, to consider using  his alternative statement of the same law "an uncompensated transmission of heat from a colder to a warmer body can never occur" and allow considering the sun's input of energy as such 'compensation'.

    It still sounds odd to consider the sun's energy input 'compensation', we would not normally use the term that way nowadays, but as I read the footnote, I see he is using the term 'compensation' that generally. For he does say it expresses the same idea as "by itself", and we all agree that the heat transfer from colder CO2 to warmer ocean thin surface layer is ultimately driven by the energy input from the sun, it is not "taking place 'by itself'".

    This has been a longer detour into the historical development of thermodynamics than any of us hoped for, but it does throw light on why the meme Science of Doom calls "the imaginary second law" is so persistent. Few thermodynamics courses at any level, even college level physics and engineering, are willing to take the time for such detours and show where misunderstandings of older thermodynamics terms and concepts still trip people up.

  19. @1466 & @1464

    That is, as Dikran said, good detective work. But I am still amazed that you can claim, "I need only add that the formulation given in the OP is certainly a good paraphrase of the last formulation quoted from Clausius. Therefore there is nothing wrong with it except for the point that paraphrases should not be presented as quotations."

    That 'formulation' still has the disastrous interpolation, 'generally'. That weakens the law to the point of total uselessness. It accomplishes nothing and destroys everything. Even just ripping out that one word would improve the original article by a lot.

    Remove that one word! That is all I ask! (though, I would also like direct quotes to be real direct quotes...)

    I should also point out that at no time did I accuse SkS of dishonesty for making this mistaken statement of  the law. But I cannot see it as anything other than negligence that it has gone uncorrected for so long, even after comment #955 pointed it out way back in 2011.

  20. @1452

    ""Spontaneously" is a perfectly reasonable synonym for "of itself" in this context, and the "generally" refers to the possibility of there being "some other change...", which happens not to be relevant in this case.

    Please stop digging."

    I am genuinely surpised at your interpretation of the word 'generally'. I would have thought English is nor your native language. Either that, or you are the one who is 'digging' and engaging in pedantry.

    No, the only reasonble interpretation of the word 'generally' here is to make the whole sentence a generalization, which may have exceptions. But this in turn weakens the law to the point of uselessness, which is exactly why Clausius did not use the word 'generally' in <b>any</b> of his formulations. Not even in the footnote you provided. Nor is it used in any of the valid restatements of the law, both old and modern.

  21. I generally disagree with you, MattJ, but only because I'm trying to get this thread to 1500 comments.  At that point, it will be taken out back and shot (and buried in an unpublished location).

  22. MattJ @1468-70:

    1)  We have established that Clausius' first statement of the 2nd Law, as translated into English was:

    "[The] general deportment of heat [is that it] everywhere exhibits the tendency to annul differences of temperature, and therefore to pass from a warmer body to a cold one."

    That was glossed by Clausius as:

     "Heat cannot of itself pass from a colder to a warmer body"

    The original purported quotation sourced from wikipedia and appearing in the OP is:

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

    It mashes the two together, taking glossing "general deportment of heat"  from the body of the text as generally, and glossing "of itself" in the footnote as "spontaneiously".  Both glosses are transparently reasonable, ie, they fairly present the information content of the phrases they gloss.  Presented as a summary of Clausius' first statement of the principle (rather than a direct quotation), it is therefore wholly unobjectionable.  If you have a problem with the use of the word "generally", take it up with Clausius.

    2)  As already noted, I would prefer the use of either of the two more considered forms of Clausius statement, and as direct quotations.  The word "generally" does not appear in either, so that should satisfy you.

    3)  As shown in my post @1444, the heat transfer processes between surface and atmosphere are not changed by the absence or presence of sunlight in the short term.  Therefore they do not involve one of the changes which are irreversible except by supplying the heat deficit from warm to cold of which Clausius was talking about in the footnotes.

    It is compensated by the direct flow of a greater quantity of heat from the warmer surface to the cooler atmosphere.  That is the other case of "compensation" that Clausius discusses and does not involve the Sun in any way except in replenishing the heat thus lost by the surface.  Discussing the Sun as compensating the supposed reverse flow of heat merely confuses the issue for not such net reverse flow occurs, and hence no such compensatory role is called for.  (As stated initially, this case is quite different to that of refrigerators, where a compensatory change in pressure of the coolant is required.)

  23. DSL, I don't know about burrying it, but a strong case for locking this thread can be made, and would be supported by every SkS commentator.  Notifications of any errors in future edits could be made by email, and if somebody realy thinks they have a strong case for violation of the 2nd law, they can email a copy of a blog post as well, which can be published with or without reply should they be able to convince an "editor" and "two referrees" from the SkS team that that should be worthwhile.

    Surely everything that is worth saying on this thread has already been said repeatedly.

  24. MattJ wrote "I am genuinely surpised at your interpretation of the word 'generally'. I would have thought English is nor your native language. Either that, or you are the one who is 'digging' and engaging in pedantry."

    As it happens, English is my first language (my second being MATLAB).  In the context of the quote  the word "generally" indicates that there are exceptions to the rule as stated, see e.g. the third definition given here):

    3. without reference to or disregarding particular persons, things, situations, etc., that may be an exception:

    What could those exceptions be?  Rather obviously the exceptions are the cases where there are "some other changes...".

    This doesn't weaken the second law at all, it is just a statement of only the general case of the second law, where the exception is not relevant (such as the case for the greenhouse effect, where no "some other change" need be introduced to explain what we observe).

    The problem appears to be that you are unaware of a (perhaps idomatic English) usage of "generally", not that there is something badly wrong with the quote.  As it happens, I am working on rewriting the article, and I shall use quotations from the translations of Clausius' book.


    Now I asked: "MattJ@1460 does that mean you now agree with me on my interpretation of the second law of thermodynamics only applying to the net transfer of heat, and hence there is no need to introduce the "other changes" clause?"

    but you appear to have ignored yet another of my questions.

  25. MattJ wrote "For he does say it expresses the same idea as "by itself", and we all agree that the heat transfer from colder CO2 to warmer ocean thin surface layer is ultimately driven by the energy input from the sun, it is not "taking place 'by itself'".

    I think you still have not quite understood.  While the original source of the heat is the sun, the upper atmosphere is warmed by outboud IR radiation emitted by the surface.  Thus the interchange of heat between the surface and the upper atmosphere (no need to mention the sun at all) involves a greater transfer of heat from the surface to the atmosphere than vice versa.

    It would be more accurate to say that the backradiation is not compensated by energy from the sun, but that it is directly compensated by outbound IR from the surface.

  26. MattJ @1451 & @1455.

    @1451 you use words of mine @1436 to exemplify "many people here get on their high horses in defense of science — yet show they cannot even read well enough to do it."
    @1455 you complain of "three simple questions" that have failed to be answered here.
    It is worth considering the reasons for both these complaints as they have a common source. My input @1436 pointed to potential confusion created @1435 which is also where we find your "three simple questions."
    Perhaps I should give three simple answers - (1) What is the "it" you are asking about? (2) Who do you think we are, Sky Dragon Slayers? (3) See (2).
    And be mindful, MattJ, that @1435 there had already been a prior trail of alleged missed points and disputes over what you had actually written.

    Seeking some semblence of sound thinking, we can look back to MattJ@1429 - "It does no good to quote the Second Law incorrectly, and then say, "it does not contravene the second law of thermodynamics" ... since you are still requiring radiating CO2 molecules in a -20C stratosphere to heat up an ocean layer that is on average above +20C ... it is still a violation of the "imaginary second law", but not of the law as Clausius really stated it." (Note my editing here makes things a whole lot clearer.)
    Simply MattJ argues that the statement of the Second Law as presented in the SKS post is inadequate. He suggests using the WIkipedia version (from Clausius (1854) - an 1856 translation here) to overcome the inadequacies of the version used by the SKS post. Meeting a rebuff on this MattJ, you compound the confusion with comments that are pretty dire at describing your position and in detail packed with trollish statements.

    Now, if your "it" in your first question @1435 encompassed the whole of that '@1429 statement' presented above, then there is sensible discussion to be had. For myself, I see a lot of scope for improving the post but I am not convinced that some pre-photon eighteenth century quote will expose the nonsensical cherry-picking of Sky Dragon Slayers and their ilk, however authoritative the quote. Do note in the quote from Wikipedia and its source, Clausius still talks throughout in terms of "the interchange of heat between two bodies of different temperatures" and, beyond the implications of the word 'interchange',  never makes clear that he talks of 'net heat flow.'

    However to argue the "it" actually is the whole statement @1429 would be rather difficult as it requires some strange interpretation of the words used.
    So my response to MattJ @1451 is this - It is not my reading of the words that is at fault but instead the fault lies with the writing of the words I am being expected to read.

  27. MA Roger, while the translation doesn't explicitly use the phrase "net flow of heat", I think it is implicitly clear in the translation of the first edition of Clausius' textbook in the footnote mentioned in my post at 1146:

    "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."

    The only way for this to be satisfied (in the absence of "some other change") is for the net flow of heat to be from the warmer to the cooler body.

  28. Dikran Marsupial @1477.

    The passage you found in the Tyndall translation (actually @1446 although the link does the job) certainly makes the two-way flow explicit. It is perhaps still a bit obscure being within a footnote but I think if you also point out that the statements of the law nowhere say they aren't talking about net heat flow, then the footnote would be difficult to refute.

    Also I wonder if describing the changing size of the vibrations of atoms in a solid that result in transmited heat by conduction may also be useful to show up how brainless the 'no heat shall pass from cold to hot' interpretation really is. Just as the nutters are arguing that by magic photons don't get fired at warmer objects, they also have to be arguing that vibrations only excite adjacent atoms in the direction of net heat flow. How can a vibration only act in one single direction? A mind-boggling requirement.

  29. First of all, many thanks for all your hard work! I occassionally get involved in the debate on AGW theory and your site is a great resource for sorting out the arguments and debunking the junk science streaming out of the "denialist" camp - they are like an army of Duracell bunnies and any discussion tends to quickly turn into a crap-storm of half-truths, contradictions and downright lies. Without sites such as skepticalscience it would be impossible to keep up!

    Now most of the arguments they tend to throw up are just regurgitations of old misunderstandings, willful or otherwise, and as such I'm usually able to answer back pretty quickly, but recently something's come up which has me scratching my head. I'm referring to the Donhoe et al. paper from the 10th of November this year; "Shortwave and longwave radiative contributions to global warming under increasing CO2". If I understand it correctly, Donohoe & co show that long-wave "trapping" by CO2 is not the main driver behind global warming, and that short-wave absorbtion by water vapour (and reduced albedo) is the real cause of long term warming. So far so in accordance with observation: the earth is getting warmer and it's caused by an increase in its ability to retain heat from the sun. Climate change 101. But what I find extremely confusing is the claim that warming from CO2 is only a temporary effect; their models show that in as little time as a decade the warming effect of CO2 is balanced out by an increase in long-wave radiation back to space, "cancelling out" the warming effect. I have to admit this is complete news to me; I was always under the impression that the CO2 content (and other greenhouse gases) of the atmosphere of any planet was directly linked to that planet's temperature, and that all other things being equal, the planet with the higher greenhouse gas concentrations would be the warmer one (e.g. Venus). Instead I see claims like this:

    "When CO2 is first added, it does act as a blanket, trapping long-wave infrared energy coming off the Earth. The atmosphere then emits less of this long-wave radiation to space because the upper atmosphere is cooler than the Earth's surface, just as the top of your blanket is cooler than your body. But the Earth gradually heats up under this blanket, and hotter objects emit more long-wave radiation, so within about a decade the effect of adding the thicker blanket has been canceled by the warmer body emitting more energy." (source)

    My admittedly limited understanding of thermal equilibrium tells me that yes, add quantity X of CO2 and you will get an increase in the ability to retain heat; the planet will warm up to temperature Y, at which point long-wave radiation back to space will balance out the heat-trapping ability, and temperature will stop rising. Add more CO2 (or other greenhouse gases) and the temperature will notch up further before again reaching equilibrium. Two objects at the same distance from a radiation source, one black, one white, the black object will be warmer as it absorbs more of the incoming radiation - and as a consequence it will also emit more long-wave radiation. Both objects are at thermal equilibrium, but one is warmer than the other due to it's ability to capture more of energy. But then I see this:

    "Most of the study's simulations involved a one-time addition of carbon dioxide into the atmosphere. One scenario simulated continuously increasing CO2, as is happening now - in that case, the long-wave radiation effect lasted about 20 years before the shortwave effect took over."

    What!? Unless my reading comprehension has suffered a sudden dramatical reduction (a distinct possibility!) it seems they are saying that even if you keep increasing the CO2 content, the effect will eventually (20 years?) be cancelled out and (apart from the warming from short-wave radiation) the planet in question would return to its earlier temperature. This just doesn't make any sense to me; if CO2 is able to "trap" long-wave radiation, surely if you keep increasing the CO2 level, the "trapping" ability will also continue to increase? I would greatly appreciate if someone could shed some light on this.

  30. Lomax, when the first quotation says, "...within about a decade the effect of adding the thicker blanket has been cancelled by the warmer body emitting more energy", the 'effect' in question is the amount of outgoing long wave radiation. The planet (i.e. "the warmer body") is still hotter... it is just that the increased heat eventually leads to the radiation flows in and out equalizing. The planet isn't going to "return to its earlier temperature" as you say... just to it's earlier OLR rate, which is happening precisely because the temperature has increased.

    "This just doesn't make any sense to me; if CO2 is able to "trap" long-wave radiation, surely if you keep increasing the CO2 level, the "trapping" ability will also continue to increase?"

    Yes, but as you 'trap' more long wave radiation within the climate system that causes/is heat buildup... which causes/is even more long wave radiation emission, until eventually the extra amount being emitted equals the extra amount being trapped and the total output returns to its original level.

    Think of it as a lake with one stream flowing in and three streams flowing out. If you block off one of the outflow streams (i.e. add CO2 to reduce OLR) then the amount coming in from the inflow stream (i.e. radiation from the Sun) now exceeds the amount going out and the water level rises (i.e. the Earth gets hotter). However, as the water level rises that causes it to flow out the two remaining outflow streams faster (i.e. the amount of longwave radiation increases) and eventually the lake water level stops rising when the inflow and outflow rates are again in balance (i.e. the temperature stops increasing when incoming and outgoing radiation again match).

    For the record, none of that is actually the 'result' found by this study... that's all basic global warming. What this study is arguing that is 'new' is that the warming effect of increasing CO2 will very quickly be overwhelmed by the feedback warming effect of a darkening planetary surface (e.g. from melting snow and ice). I'm not sure I buy that, for one thing it's a model result which doesn't seem to jibe with paleoclimate studies, but if anything it actually suggests that warming will be much greater than expected.

  31. @CBDunkerson: Great, many thanks for clarifying; I guess that summary was just poorly written - as was my post, on second read-through :) I'm relieved to hear that my understanding of thermal equilibrium was basically correct and that the greenhouse effect works the way I thought (though I'm not sure relieved is the correct word here). Indeed it does sound worrying that the feedback from reduced albedo and increased water vapour levels might be greater than previously thought - let's hope they are proven wrong!

  32. I've italicised your words. My rebuttal follows. Please explain.

    They radiate most of the heat that is received from the sun, so the average temperature of the Earth stays more or less constant.

    All energy the Earth receives from the sun is returned to space. That’s what the Law of conservation of Energy and the Climate Energy Balance states. The atmosphere cools the Earth. It does not add heat. The surface of the moon is +200F. Why, because there's not convection to draw the heat away.

    Greenhouse gases trap some of the escaping heat

    C02 does NOT “Trap” heat. Kirchhoff's law of thermal radiation clearly states that a body’s ability to absorb heat energy is equal to its ability to emit that heat energy.

    So the greenhouse gases make the Earth warmer - like a blanket conserving body heat - and voila, you have global warming. 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.

    Heat moves via convection, conduction or radiation. Gas-convection, Solid-conduction, Vacuum-radiation.

    A blanket is NOT the same as a trace gas like C02. One is a solid and one is a gas. A solid object like a blanket will impose on the rate of heat loss through the loss of convection. The blanket is NOT adding heat to one’s body. If, instead of a blanket, we set the environment to a saturated C02 level of 100%, the heat loss would be the same as if it was at zero. Your explanation using a blanket is ridiculous.

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

    It should read…. "Heat CANNOT flow spontaneously from a material at lower temperature to a material at higher temperature." The Laws of Thermodynamics are LAWS not theory.

    Response:

    [JH] Please keep it civil.

    [PS] You cannot refute an argument when you dont understand how it works. Short of opening a textbook on radiative physics, I would strongly suggest that you look over Science of Doom here and here  which takes in stages and spends whole articles on your objections. Hopefully you will admit that if an experiment produces a different result from your perception of a theory, then your perception is wrong.

  33. the master...  "The surface of the moon is +200F."

    Sorry, but the average temperature of the moon isn't 200°F. That's rather an absurd cherry pick.

  34. the master... "C02 (sic) does NOT 'Trap' heat." [Mods should probably warn about all caps.]

    CO2 absorbs and reradiates IR, thus causing more heat to remain in the climate system. That's what people mean by this phrase. 

  35. the master... "A blanket is NOT the same as a trace gas like C02 (sic)."

    "A blanket" is a metaphor. No metaphor is intended to be exactly like anything, otherwise it wouldn't be a metaphor. As a metaphor, a blanket is a good way to explain how greenhouse gases work.

    [Again with the all caps "not."]

  36. The Master:

    Interesting choice of names.  

    Answering your points in order, your words in italics:

    "All energy the Earth receives from the sun is returned to space."  Some energy is absorbed by the surface and not returned to space for a period of time.  That can range from a day or two up to centuries.  A great deal of ice has melted from Greenland and the Antarctic the past few years.   The heat to melt that ice came from the sun.  It will not be returned for centuries (or more likely thousands of years) when the ice freezes again.  On average over a very loong period of time all the energy is re-emitted but for shorter times (like the life of a human) some is absorbed and raises the temperature of the Earth.  At other times more energy is emitted than absorbed as the Earth goes into a glacial period.

    The surface of the moon is .+200C during the day but it is -200C at night  The average temperature is not 200F as you claim.  The temperature of the moon is as predicted by scientists.  The colder average temperature of the Moon shows that the Earth is heated by greenhouse gases.  This has been known by scientists since 1850.

    " Kirchhoff's law of thermal radiation clearly states that a body’s ability to absorb heat energy is equal to its ability to emit that heat ." At 5 kilometers above the surface the temperature is about 30C less than at the surface.  If the surface emits IR radiation proportional to its temperature some of that energy will be absorbed by CO2 at 5 km.  Since the CO2 is colder than the surface it cannot radiate the energy outward as fast as it absorbs it, even though it follows Kirchhoff's law.  You need to pay more attention to the temperature of the emitting and absorbing surfaces.  Mistakes like this make it appear that you have not thought through the physics enough yet.

    "If, instead of a blanket, we set the environment to a saturated C02 level of 100%, the heat loss would be the same as if it was at zero."   Many videos on You Tube show that bottles filled with CO2 heat up faster than bottles filled with air.  The heat loss is lower when the atmosphere is CO2.

    You have me with an example of heat flowing from a cold area to a warmer area, but that statement is not used in the argument so it is moot.  

    In general it is easier to discuss your misunderstandings of the scientific arguments if you limit your arguments to one problem at a time.  Once that issue is resolved we can move on to the next misunderstanding.  When there is a long list like yours the replies become difficult to read.  

  37. tm @ 1482:

    "The surface of the moon is +200F. Why, because there's not convection to draw the heat away."

    200 Fahrenheit is approximately 366.5 Kelvin.  To put your claim into context, the most thorough scientific examination of the surface temperature of the Moon says:

    "The mean temperature at the equator is 215.5 K with an average maximum of 392.3 K and average minimum of 94.3 K (Fig. 19), representing an average change in temperature of ∼300 K. Average maximum and minimum temperatures in the polar regions (poleward of 85°) are 202 K and 50 K respectively; with a mean average temperature 104 K. Mean maximum temperatures in the south polar region are ∼11 K warmer than the north polar region, however the average minimum temperatures are the same at both poles."

    In other words, your estimate of the Moon's temperature over estimates the mean equatorial temperature by 155 K (279oF).  It overestimates the mean lunar surface temperature by much more.

    You will also note that the lunar mean equatorial temperature is about 72 K less than the Earth's Global Mean Surface Temperature.  As the equator of the Moon has the warmest mean temperature of any latitude, it follows that the Global Mean Surface Temperature of the Moon is much more than 72 K less than the Earth's.  That is despite the fact that the Moon's albedo of 0.136 is less than half of that of the Earth's.  It follows, even by your reasoning, that the Earth's atmosphere heats it relative to what it would be as an airless body.

    As it happens, the major part of that warming is due to the thermal inertia of the atmosphere, and the oceans (in particular), along with the poleward heat transport by both, results in much more equal temperatures.  However, the Earth's Global Mean Surface Temperature is about 33 K warmer than would be possible with its albedo, even if its surface were a uniform temperature.  That means the combined effect of the atmosphere (radiative and convective energy transfer) warms the Earth's surface.  As it happens, it has been shown that the radiative effect warms it, while convection cools the surface relative to what it would be with the radiative effect (ie, the greenhouse effect) alone.

  38. Further to tm @ 1482

    "It should read…. "Heat CANNOT flow spontaneously from a material at lower temperature to a material at higher temperature." The Laws of Thermodynamics are LAWS not theory."

    The term "heat" is used ambiguously.  Some people use it to mean the thermal energy.  Used with that meaning, it is unambiguously the case that thermal energy (in the form of IR radiation) can flow from a colder body to a warmer body, although more must flow in the reverse direction.

    The other (possibly more scientifically accurate) meaning is "net thermal energy flow", under which meaning it is unambigously the case that "net thermal energy flow" must be from the warmer body to the colder body (something that can be deduced from the preceding paragraph).  

    Needless to say, the sentence you find offensive uses the first, and more common in popular usage, meaning.

    Under either definition, the 2nd Law of thermodynamics is no bar to the Greenhouse Effect which predicts that net energy flow will be from the Sun to the surface, and then surface outwards.  This can be clearly seen in the standard model used to teach the mathematics of the Greenhouse effect:

    You will notice that the downward IR radiation at each level is less than the upward IR radiation from the level below, so that the net energy flow is upward.  You will also notice that, as the model shows an equilibrium condition, the net IR energy flow between each level is an upward flow equal to the downwar flow from solar radiation.  However, to maintain this condition (which conforms with all energy conservation laws), the ground level upward flux must be (in this example), four times the incoming flux from the solar radiation, implying a very strong greenhouse warming.  It is only able to do this in compliance with the laws of thermodynamics because of the downward IR flux from the layer above.

    Note: this is just a toy model used to illustrate imortant concepts, and introduce a very basic level of the maths involved.  It is in no way meant to represent a real situation.  In real situations, atmospheres do not conveniently divide themselves into layers like that, and convection is a crucial element.  However, in real life the Earth's surface is warmer than can be accounted for by solar radiation and the the Earth's albedo alone, and the net energy flow upwards from all sources matches the downward energy flow from the incoming solar radiation at all levels (although not all levels are shown below):

    That is, there is a greenhouse effect, but it is in complete confirmation with the laws of thermodynamics (which is no surprise given that it was predicted by some of the key figures in determining those laws.)

  39. Rob Honeycutt @1485,

    You say the descrption "blanket" is but a metaphor. I would disagree. The convection within the atmosphere is very very slow. How else could it be? Convection contributes directly only 4% of the surface cooling (as conveniently illustrated @1488 above). And that is because the circulation of the atmosphere is very slow. Outside cyclones it takes something like two weeks for a parcel of air to move from surface to tropopause and back. The atmosphere is not static but neither is a greenhouse hermetically sealed. And blankets are far from air-tight. Just like with the planet surface and the GH effect, a blanket's main mode of operation is not preventing cooling convection but in trapping radiant heat loss. So I would suggest that both 'greenhouse' and 'blanket' are analogies and not metaphors.

  40. MA Rodger @1489, the energy balance diagram only shows energy movement between realms - ie, from the surface to the atmosphere, or from the atmosphere to the surface.  It does not show energy transfer within the atmosphere itself.  For that reason, the figure is not a good guide for estimated what Global Mean Surface Temperature (GMST) would be like in the absence of convection.

    A better guide is Fig 4 from Manabe and Strickler (1964):

    As you can see, from their model, an absence of latent heat transfer (ie, dry-adiabatic lapse rate) would lift GMST by about 10oC, while the complete absence of convection would lift it by about 45oC relative to current conditions.  As the greenhouse effect on Earth raises GMST by over 33oC, the presence of convection cools the Earth by over 50%  of the temperature increase that would occur from a greenhouse effect without convection.  

    Eliminating latent heat transfer within the atmosphere by the condensation of water would eliminate just under 25% of the greenhouse effect coupled with convection.  That is an esoteric figure, however, given that 75% of the greenhouse effect is from water vapour and clouds.  Consequently the combined effect (greenhouse and lapse rate) of water vapour in the atmosphere is to warm the Earth; although at a lower GMST it might be to cool it given the reduced greenhouse effect but near constant cloud albedo effect. 

  41. MA Rodgers...  I suppose that would be a function of how you referred to it. You can make it a simile, metaphor or an analogy. I think TM was attempting to dismiss it on a more literal basis and that, I believe, was deliberately missing the point.

  42. Rob Honeycutt @1491,

    I agree that when explaining the GH effect, at a minimum there is a willful prejudice being employed when an immutable counter-argument wielded against both "blanket" and "greenhouse" as an analogy (or metaphor or whatever) is of the form as presented @1482 (ie - "One is a solid and one is a gas.").

    But my thought is to break that immutable nonsense rather than live with it. Thus my position trying to revitalise both the "blanket" and the "greenhouse" as strong analogies for the GH effect.

    Thus I would argue as follows.

    Note the follow-on comment @1482 "A solid object like a blanket will impose on the rate of heat loss through the loss of convection." A blanket does not trap air anything like as well as the lower atmosphere. The plume of hot gas passing through a blanket is travelling at quite a rate (as this test shows - note 400ft/min =2m/s)  And greenhouses are not hermetically sealed but are actually far more leaky that the lower atmosphere, even commercial ones. The lower atmosphere retains parcels of air for a week or more. The same cannot be said for either any blanket or any greenhouse.

    And this slow action of the atmosphere circulation is probably best explained by the planet Earth being so big and tha atmosphere so shallow. In the tropics a latitudinal band measuring say 1,000 km is heated and so it is wanting to rise up and displace the cooler air above it. This creates a Walker Cell which will flow away from the tropics at the top of the atmosphere where it cools by radaition into space and so cooled drops back down to the surface outside the tropics. The problem for the "big convetion" argument is that the longitudinal winds at the top of the atmosphere (and the balancing ones in the lower atmosphere) are much less than 10m/s. This speed of wind is the result of the upward convetion flow from the tropics but the <10m/s represents a massive acceleration from the vertical convetion speeds - because comparatively the tropics are very broad but the atmosphere is rather shallow. If the vertical motion feeding this <10m/s is 1,000km wide, the upward speed has to be <0.02m/s which means the air in any "big convetion" cooling circulation will take >600,000 seconds or seven days to reach the top of the atmosphere. Radiation, on the other hand, is flying about at the speed of light. So it's not much of a contest, is it? Thus the values of the various fluxes in the Earth Energy Balance diagram as shown @1488 show very small quantities of convection in operation.

    Now this last bit referring to the diagram is a bit of a throw-away remark. The diagram in its original form did describe the sensible heat flux as "thermals" (eg in Trenberth et al 2009 figure 1) which is wrong. But I'm not sure it is entirely wrong.

  43. Tom Curtis @1490,

    The Manabe & Strickler model presents interesting findings but I'm not sure that I would accept them without a fight. Likewise, the figure of 5% convection contribution deriving from the figure presented @1488 is also not well established. (The 5% is more the value for the conduction of sensible heat from surface to atmosphere and certainly is not a good value to rely on.)

    While the Manabe & Strickler non-convection calculation of atmospheric temperature profile is a useful calculation, I do not see it as the final word. Firstly, it is being compared with two other profiles which pre-suppose the lapse rate. Thus the model Manabe & Strickler were developing is really just testing their model above the troposphere. So is the non-convection version a fair one? It assumes only a single value for the H2O profile which may not be (probably isn't) a good choice for a global average. Indeed, what model should be set up to calculate a non-convective atmospheric GH effect? That is the start point. I think you would have to freeze representative GHG levels (& presumably cloud) over the whole globe to calculate it. I would suggest that the result would show that it is the holes in the H2O blanket that are responsible for a very large portion of the energy balance. This is why the Wanabe & Strickler graph without such a hole shows the large increase in temperature for non-convection at low altitudes where in their modelled H2O is high.

    And a quick back-of-fag-packet argument. If we look at average surface temperatures, if half the cooling were convective, would we see a significant temperature differential between equator & 30 degrees? If we look at TOA outward IR (eg Trenberth & Stepaniak (2004) fig 3a&b) would there be a sign of a cooler upper atmosphere above the outer limit of the Hadley cells? Of course, what we see is more LR at the outer limits and less over the tropics which suggests it is the GH effect which continues to dominate the outward energy budget through the thickness of the troposphere with the dry atmosphere sinking in the gentle Hadey cell flow allowing big energy fluxes to flow out from the planet, averaging perhaps roughly 270W/sq m. Over the equator the H2O GH effect keeps that energy flux down to say 225W/sq m. Of course, all this very much first-cut response to the Manabe & Stickler model.

  44. This does not seem a good explanation for how greenhouse theory is not at odds with the second law of thermodynamics. A body will lose heat at a rate relative to the surrounding temperature. If it is much colder and your body loses heat quickly you feel cold. The blanket does slow the transfer of heat from your warm body to the cold atmosphere, making you feel warmer, or more correctly less cold. You do not actually get hotter just colder slower, whereas greenhouse theory States the earth gets hotter, not colder slower.

    Response:

    [PS] This is the longest thread at Sks and it seems to be because people have simultaneously have a very poor grasp of thermodynamics and a great reluctance to improve it. Science of Doom have an excellent series on the textbook basics as well as good article on Second Law. But please be clear that if you are going to insist on a description of thermodynamics that is not in accordance with experimental results, then this is not site for you.

  45. I suspect the informal article with the jacket analogy, the intermediate article and the video all help resolve any confusion for most people. Actually seeing pyrgeometers measuring downward infra-red radiation adds to the knowledge of how we know. Intuition can be more important to non-experts than logic. On which subject, the intermediate page is very good, but my intuition tells me that a big atmospheric window from 10 to 13 µm should allow more than 40 Wm¯² of surface radiation (about 10% of it) to directly escape to space. What's the best way of doing that calculation?

    Maybe rather than starting with the overall behaviour, it is good to show that each component in the system is behaving according to physical laws. Would presenting the simple equations for conduction and for radiation help, as it would clarify that heat transfer is proportional to temperature difference in the case of conduction, but not in the case of radiation? Some people seem to disbelieve Stefan-Boltzmann, asserting that an object somehow knows it should cease to radiate towards a warmer object.

    Anyway, I wanted to mention to more 'grey literature' online resources helping to clarify the confusion, rather than textbooks. Science of Doom provides basics (mentioned in response to 1494) for those willing to go through them, but goes beyond them: here's a 2017 challenge to anyone arguing against the greenhouse effect on thermodynamic grounds: explain your own view numerically.

    More simple, intuitive understanding of the principles is provided by Eli Rabbett's Green Plate Effect. In particular, here's a video by izen.

    Response:

    [PS] Thank you. Those are all good resources.

  46. I'm fairly new to this site and just catching up on a lot of articles and comment streams. Is this myth still used? The way I explain it to laymen is...

    The CO2 greenhouse effect was discovered in the 1890's. Much of its fundamental underpinnings were discovered and confirmed with Cold War era military research. So I find it exceptionally hard to believe that this theory was studied for ~90 years before the existence of the IPCC and nobody noticed that it violated basic laws of physics.

  47. AFT, anyone who thinks seriously about it undertands that thermodynamics are not violated. This argument is just part of larger campaign undertaken by some actors because they know where the morally defensible position is and that people will in their majority adopt the morally right position if there is no doubt about it.

    The depth of the denial is compounded by numerous factors. Some scientists, like G&T, are unscrupulous enough to write such nonsense. The general population is science illiterate and innumerate enough to buy into it. The ambient attitude that anyone is free to have whatever opinion they choose is stretched to the point that it implies said opinion has validity. The overall anti elite and anti intellectual sentiment has been cultivated by crooks purely for the fostering of their financial interest.

    There is little to gain by arguing with those who go for the 2nd law argument; they are ready to cling to any straw, no matter how feeble and likely won't be convinced by any level of reasoning or evidence. Look how long this thread is. Waddle in it if you want, it's saddening. Almost 1500 post devoted to the least valid "skeptic" argument of all. It says something.

  48. So I just encountered this one, which appears to be a variant of "AGW violates basic physics"...

    "It ends up being trivially easy to understand that gravity, not spectrum , is why and by how much bottoms of atmospheres are hotter than their tops. See my website which includes links to my Heartland Inst talk showing the impossibility of explaining Venus's surface temperature , 400c hotter than what it absorbs from the Sun, as a spectral effect."

    Response:

    [PS] Doesnt like a 2nd law argument. More like the Postma nonsense. Surface temperature is end result of all relevant physics including GHE. Actually I think the author is Bob Armstrong who has some times demonstrated his grasp of physics here. Try https://www.google.com/search?q=bob+armstrong+site%3Askepticalscience.com

  49. Greenhouse Gas Theory does not violate the Second Law of Thermodynamics

    Attempts have been made to discredit the GHG theory by claiming that it violates the Second Law of Thermodynamics and so the theory cannot be valid. I have seen some rebuttals on this site, but I was not convinced; so I now offer my own approach which I hope will be helpful.

    The claims of violation are based on the idea that heat cannot flow from a cold object to a hotter one. In general, with heat transfer by conduction and convection, this idea is very true. But the Second Law does not actually state that idea. In fact, it deals with another property of the system, known as entropy, which is the degree of disorder of the system. If the system is very “tidy”, the disorder is small, and so is the entropy. Great “untidiness” means high entropy.

    The Second Law of Thermodynamics states that the entropy of a system will increase.
    It does not mention Heat.

    In the case of heat transfer, it is readily seen that the Law is obeyed by conduction and convection between objects in contact. Higher temperatures mean that the atoms and molecules are moving/vibrating more rapidly and to a greater extent than at colder temperatures, and so have high entropy. Some of the greater movements in the hot object can be passed into the cold object, so increasing the overall degree of disorder, or entropy, of the system. But, the reverse cannot happen, according to the Law, because the colder object has smaller entropy.

    Therefore, heat can flow from hot to cold, but not from cold to hot. And it is only for conduction and convection transfer.

    This leaves us to consider heat transfer by radiation.
    This is the method by which heat is claimed to flow, according to the GHG theory, from the carbon dioxide in the atmosphere to the Earth’s surface. But the atmosphere is cooler than the Earth’s surface, so how can this happen? Does it not violate the Second Law? And this is the big problem the GHG theory has to overcome.

    Not a problem. Consider photons of infrared energy emitted downwards from carbon dioxide molecules in the atmosphere. These are neat little wave-packets of electromagnetic energy, and have no charge. Very neat and tidy. The entropy involved is small because they are not continually in vibrational contact with each other, as are the atoms in a solid, or the molecules in a gas. Once emitted, they will continue in their motion until they are absorbed by the Earth’s surface, (although some may collide with molecules in the air). Upon absorption, the energy given to the surface atoms and molecules causes them to increase vibration and movement, and so the entropy, the degree of disorder, increases. OK, and the surface gains energy and so the temperature rises.

    The entropy increases. This is in agreement with the Second Law. No violation, but the temperature of the surface of the Earth also increases. This is what the GHG theory says.

  50. AEBanner @1499 ,

    Well said.   Including your description of entropy as "untidiness".

    This particular thermodynamic "Law" is a source of endless trouble to some people, because (as you have said) they do not look at the basic physical entities involved.   Instead, they stand back and try to view the universe as ruled and directed by "Laws" . . . laws which are actually simply abstract conceptions in the human mind.   It's all a very Nineteenth Century religion-like viewpoint.   Very pre-Einstein, pre-quantum-mechanics way of thinking.    Mistaking the concept for the reality.   ( Can we blame Plato for this? )

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