Arguments
At a glance - The greenhouse effect and the 2nd law of thermodynamics
Posted on 25 April 2023 by John Mason, BaerbelW
On February 14, 2023 we announced our Rebuttal Update Project. This included an ask for feedback about the added "At a glance" section in the updated basic rebuttal versions. This weekly blog post series highlights this new section of one of the updated basic rebuttal versions and serves as a "bump" for our ask. This week features "The greenhouse effect and the 2nd law of thermodynamics". More will follow in the upcoming weeks. Please follow the Further Reading link at the bottom to read the full rebuttal and to join the discussion in the comment thread there.
At a glance
Although this topic may have a highly technical feel to it, thermodynamics is a big part of all our everyday lives. So while you are reading, do remember that there are glossary entries available for all thinly underlined terms - just hover your mouse cursor over them for the entry to appear.
Thermodynamics is the branch of physics that describes how energy interacts within systems. That interaction determines, for example, how we stay cosy or freeze to death. You wear less clothing in very hot weather and layer-up or add extra blankets to your bed when it's cold because such things control how energy interacts with your own body and therefore your degree of comfort and, in extreme cases, safety.
The human body and its surroundings and energy transfer between them make up one such system with which we are all familiar. But let's go a lot bigger here and think about heat energy and its transfer between the Sun, Earth's land/ocean surfaces, the atmosphere and the cosmos.
Sunshine hits the top of our atmosphere and some of it makes it down to the surface, where it heats up the ground and the oceans alike. These in turn give off heat in the form of invisible but warming infra-red radiation. But you can see the effects of that radiation - think of the heat-shimmer you see over a tarmac road-surface on a hot sunny day.
A proportion of that radiation goes back up through the atmosphere and escapes to space. But another proportion of it is absorbed by greenhouse gas molecules, such as water vapour, carbon dioxide and methane. Heating up themselves, those molecules then re-emit that heat energy in all directions including downwards. Due to the greenhouse effect, the total loss of that outgoing radiation is avoided and the cooling of Earth's surface is thereby inhibited. Without that extra blanket, Earth's average temperature would be more than thirty degrees Celsius cooler than is currently the case.
That's all in accordance with the laws of Thermodynamics. The First Law of Thermodynamics states that the total energy of an isolated system is constant - while energy can be transformed from one form to another it can be neither created nor destroyed. The Second Law does not state that the only flow of energy is from hot to cold - but instead that the net sum of the energy flows will be from hot to cold. That qualifier term, 'net', is the important one here. The Earth alone is not a "closed system", but is part of a constant, net energy flow from the Sun, to Earth and back out to space. Greenhouse gases simply inhibit part of that net flow, by returning some of the outgoing energy back towards Earth's surface.
The myth that the greenhouse effect is contrary to the second law of thermodynamics is mostly based on a very long 2009 paper by two German scientists (not climate scientists), Gerlich and Tscheuschner (G&T). In its title, the paper claimed to take down the theory that heat being trapped by our atmosphere keeps us warm. That's a huge claim to make – akin to stating there is no gravity.
The G&T paper has been the subject of many detailed rebuttals over the years since its publication. That's because one thing that makes the scientific community sit up and take notice is when something making big claims is published but which is so blatantly incorrect. To fully deal with every mistake contained in the paper, this rebuttal would have to be thousands of words long. A shorter riposte, posted in a discussion on the topic at the Quora website, was as follows: “...I might add that if G&T were correct they used dozens of rambling pages to prove that blankets can’t keep you warm at night."
If the Second Law of Thermodynamics is true - something we can safely assume – then, “blankets can’t keep you warm at night”, must be false. And - as you'll know from your own experiences - that is of course the case!
Please use this form to provide feedback about this new "at a glance" section. Read a more technical version via the link below!
Click for Further details
In case you'd like to explore more of our recently updated rebuttals, here are the links to all of them:
| Myths with link to rebuttal | Short URLs |
| Ice age predicted in the 1970s | sks.to/1970s |
| It hasn't warmed since 1998 | sks.to/1998 |
| Antarctica is gaining ice | sks.to/antarctica |
| CRU emails suggest conspiracy | sks.to/climategate |
| What evidence is there for the hockey stick | sks.to/hockey |
| CO2 lags temperature | sks.to/lag |
| Climate's changed before | sks.to/past |
| It's the sun | sks.to/sun |
| Temperature records are unreliable | sks.to/temp |
| The greenhouse effect and the 2nd law of thermodynamics | sks.to/thermo |
I took a gander at the 2010 TonyWildish original version of this and think that the revision you are offering here is a bit too dumbed down. Wildish and the related comments goes into the details of the dynamics of heat loss a bit more in-depth than your new version, while the new version focuses more on the paper that has been the source of disinformation on this topic, then says it is wrong without discussing enough the important physical details of heat loss/retention that make it wrong. I think the revision needs a bit more of those details; otherwise it's just a "they are wrong" argument without enough "why's" to really get to the heart of their mistakes.
And by the way, please consider this to be my "form" that you asked feedback to be submitted by, since I didn't. I presume you look at the posted comments as well...
Wild (may I call you Wild?):
This "At a Glance" version is intended to be brief. Although in this page, you only see the "At a Glance" part, the entire SkS rebuttal is available from the last link in the "Click for further details" section. This "At a Glance" has been added to the "Basic" tab in the full rebuttal (which also has an "Intermediate" tab).
Short link from above:
https://sks.to/thermo
...leads you to the long link of the actual page.
Note: the link to the full rebuttal is also included in the green box at the top of this post...
I tend to agree with Wilddouglascountry. The at a glance section was quite long. When I see "at a glance" I was hoping for a clear statement in ten lines. If a rebuttal cant be summarised clearly in ten lines, then the rebuttal probably isn't valid. Although clearly AGW and the greenhouse effect doesn't violate any laws of thermodynamics.
If any of you want to have a go at explaining why the greenhouse effect does not invalidate thermodynmaics #2 in ten lines, including (essential) an introduction to what rule #2 actually says, then feel free to have a crack at it!
My quick version of "at a glance" in about ten lines:
"A climate myth claims that greenhouse gases cannot warm the earth because the flow of energy is from cold greenhouses gases to a warm surface, and this violates the second law of thermodynamics, which states that energy can only flow from hotter to colder objects (unless energy in some form is supplied to reverse the direction of heat flow).
However the CO2 is not generating heat. It acts like a blanket to slow the transmission of heat energy from the surface and in the atmosphere to colder space. The energy still transmits from hot to cold, just less heat at a slower rate, so the second law is not violated. By analogy, if greenhouse gases violated the second law a blanket would not keep you warm."
(Its based on memory of an explanation on a realclimate.org page. Its rough and needs refining, and I do not claim to have much scientific expertise, but I believe the essentials are there in about ten lines.)
Not bad at all, although a key aim of these mostly short intros is to explain and fully introduce stuff - therefore the need to explain what thermodynamics is. Many folk "out there" do not know what the word means. Some rebuttals are therefore much easier to write in a very short fashion than others.
I'll take crack at the 3laws of thermodynamics, although I am only quoting:
1- You have to play
2- You can't win
3- You can't break even
The tricky part about rebutting a "greenhouse effect violates the 2nd law of thermodynamics" myth is that there are so many possibilities and variations of such a myth. It's kind of like trying to get someone to say what they mean by "saturated" when they start spouting the "CO2 is saturated" myth.
The specific version on the full rebuttal page is related to a specific statement from Gerhard Gerlich, and arguments made in a paper by Gerlich and Tscheuschner.
When you hear someone exclaiming "2nd law of thermodynamics!", you really need to find out exactly what they think the 2nd law means before you can point out the errors (although the Gerlich and Tscheuschner flavour is pretty common).
The 2nd law is a favourite "argument" amongst the Creation Science/Intelligent Design crowd, too - evolution "violates the 2nd law". (The argument is just as wrong there.) Back in the olden days of Usenet (before the Web and blog comments), I remember a Creation Science fan emailing me (Usenet exposed people's email addresses) with a 2nd law argument.
After several rounds of email pointing out his errors in understanding the 2nd law, he came up with this strange argument of " the flow of information content" that he claimed had a similarity to the 2nd law of thermodynamics, so evolution violated his "2nd law of information content" and that mean it also violated the 2nd law of thermodynamics. Really bizarre stuff. (He never responded to my last email, where I said that calling it "the 2nd law of thermodynamics" was a lie, and why was he lying in the name of the Lord?)
I've always suspected that the appeal of the "greenhouse effect violates the 2nd law" myth may partly be due to its familiarity as a false argument against evolution. If you believe that evolution is Bad Science, and find the 2nd law argument convincing, it's easy to accept it as an argument against the greenhouse effect when you're already convinced that climate science has it all wrong.
As John Mason points out, there is no real shortcut to explaining what the 2nd law (and 1st and 3rd) actually means, which makes it more difficult to debunk any (or every) bogus 2nd law argument.
John Mason @7
Thanks. I agree its useful to include general information on thermodynamics in the rebuttal. Make it a teaching session. But I just believe "at a glance" should be something reasonably short, so the full teaching session would be better in the "details" section. Seems obvious to me.
Just to clarify. My version in ten lines is very much in my own words and structured, expressed and ordered as I wished. I just used the realclimate resource as background information and a detailed point they made seemed very good. In other ways their account as a bit confusing.
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Bob Loblow @8.
I did a quick scan of the internet on the greenhouse effect violating the second law, because my own knowledge was sketchy. I found three versions. The one I mentioned was the most commonly expressed version I came across.
I agree its a complicated area and does require a lengthy explanation but for me that is better in the "details"section. Or perhaps I'm being a bit OCD about how its organised!
Part of the communication problem is the word "Law" ~ a word of great historical & cultural weight (especially among the religious).
The sight of the word Law has a mesmerizing effect on non-critical thinkers. Law seems something forever unquestionable and beyond discussion; something fixed and eternally true ~ a divine decree received directly from the Hand of God. Instead of being just a word meaning a convenient concept in the minds of physicists. The word is mistaken for the reality.
Perhaps there could be room for some brief form of words, to deflate the awesomeness of a "Law" in the discussions about GreenHouse Effect.
Ineed, Eclectic! It's like many terms in science, including a lot of mineral names, that are "grandfathered" i.e. they are not considered to systematic or ideal but because they have such frequent use they are regarded as acceptable with caveats.
Quite so, John Mason ~ but my apologies for poorly conveying my thoughts. I was not wishing to suggest terms like "Law" or other jargon of a technical or traditional type should be excised from the basic rebuttal . . . but rather that some sort of ultra-brief explanatory warning be used to put the earnest reader on guard against accepting "Laws" of physics (or anything else) as being more than a convenient summary (and nothing more real that that).
The "Laws of Thermodynamics" can sound impressively authoritative ~ and I think this usage is sometimes purposely intended, to fool the layman into believing that the Denialist's objection to AGW has some validity.
That said, I don't have a ready phrase or two which would serve.
Eclectic #13 - 'principles' would be good but I like your point about an explainer - the only issue in this case is it would lengthen the rebuttal by another paragraph! Will give it some thought once EGU is over (today's the last day).
I was still in public school when the significance of the term "law" was discussed in science class. The progression of confidence in scientific understanding used to follow the path from hypothesis (untested) to theory (well-tested) to law (extremely well-tested over a long time).
But even when I was in public school, it was explained that "law" was a traditional term and science recognized that all understanding is subject to revision as more evidence is gathered.
We have "laws" of gravity, motion, etc that have been supplanted by the "theory" of relativity, etc. We still talk of "laws" of universal gases, thermodynamics, etc. As John says, use of this terminology is grandfathered in.
In common use, even "theory" gets misused when a scientist would say "hypothesis". The put-down of "that's just a theory..." should have the caveat "but I'm not a scientist" attached to it.
nigelj @10:
I'd be curious about the three versions of the 2nd law "violations" that you found. What were the key differences between them?
I'd agree that the "energy can't flow from cold to hot" is probably the most common.
I would like to have a go at this.
All molecules above absolute zero vibrate and radiate energy. With each bend and stretch, the molecular internal energy state changes, which emits radiant energy. The amount and wavelength of the emitted energy depends on the temperature and the molecular structure. The sun emits energy at about 5,800 degrees Kelvin (6,000 C, 11,000 F) and a small fraction is intercepted by the Earth. Due to the high temperature, very little solar energy is emitted at wavelengths above about 5 microns. The Earth’ surface emits radiant energy at infrared wavelengths above 5 microns based the average surface temperature of about 288 Kelvin (15 C, 59 F). Part of that infrared energy between about 14 and 16 microns (the 15-micron band) is absorbed and re-emitted by CO2 in the atmosphere until it reaches an altitude of about 15,000 meters (25,000 feet) where it is emitted at a temperature of about 217 Kelvin (-56 C, -69 F) toward space, which is at absolute zero. As CO2 increases, the edges of the 15-micron band strengthen and energy loss to space is reduced. Nothing about this radiant energy flow violates the 2nd law of thermodynamics.
Thanks, Charlie_Brown.
But permit me a grumble or two. What is this 15,000 meters (25,000 feet) business of equivalence? One, or two, typos/errors ?
And 15-micron band broadening . . . is over-technical and of minimal relevance to the basic topic.
Charlie #17:
There you portray the dilemma in an illustrative way. Now go back through it and, critically, add an asterisk after every single word/acronym that, to your knowledge, the typical "consumer" has not meaningfully encountered before.
The vast majority of folk are slightly to non-curious about global warming until one of its effects comes a-banging on their door. We have to reach them - they ARE the majority here. Deniers and activists are in contrast a small percentage at two ends of a spectrum- although I figure activists are far more populous these days but at the same time some deniers still have a disproportionare noise-allowance. But it's the everything-in-between we have to reach and explain what's happening.
Eclectic@18:
Good catch. The conversion was my mistake. It should be 15,000 meters (50,000 feet) for the cold layer of the atmosphere between the troposphere and the stratosphere.
Clearly countering a highly technical argument using non-technical explanations poses a difficult problem. I don’t think that I am capable of meeting the objective of simplifying this to the level necessary for the non-technical reader. As stated above, the Gerlich & Tscheuschner paper contains many technical errors and distractions. Primarily, they misrepresent the technical basis of the greenhouse effect and then criticize the erroneous description. In particular, they criticize the use of thermal conductivity when thermal conduction has nothing to do with the greenhouse effect. They also spend a lot of time criticizing the radiative explanation. This becomes a problem for non-technical people because they have trouble figuring out which scientist to believe. Interestingly, G&T argue that there are many examples of consensus scientists being wrong, but make no mention that individual contrarians, such are themselves, might be the ones who are wrong.
The first law of thermodynamics, conservation of energy, is relatively easy to understand. The second law is much more difficult. In its shortest oversimplified form, it says that entropy increases, which doesn’t mean much to most people. It has the Kelvin-Planck and Clausius statements and several corollaries, which are helpful concepts. The Clausius statement is: “No process is possible whose sole result is the removal of heat from a reservoir at one temperature and the absorption of an equal quantity of heat by a reservoir at a higher temperature.” This statement does not say that it is impossible to transfer heat from a cold body to a hot body (Look and Sauer, Thermodynamics, 1982). As stated above in the “At A Glance” description, it is “the net sum of the energy flows will be from hot to cold”.
G&T oversimplifies the Clausius statement to:
“– Heat cannot move itself from a cooler body into a warmer one.
– A heat transfer from a cooler body into a warmer one cannot happen without compensation.”
G&T continue their argument by addressing and discounting potential criticisms of their paper. They quote climatologist Stefan Rahmstorf, who has it right, then proceed to reject Rahmstorf with some undefined nonsense about the distinction between heat and energy.
G&T quotes Rahmstorf: “Some ‘sceptics’ state that the greenhouse effect cannot work since (according tothe second law of thermodynamics) no radiative energy can be transferred from a colder body (the atmosphere) to a warmer one (the surface). However, the second law is not violated by the greenhouse effect, of course, since, during the radiative exchange, in both directions the net energy flows from the warmth to the cold.”
Then G&T counters: “Rahmstorf’s reference to the second law of thermodynamics is plainly wrong. The second law is a statement about heat, not about energy. Furthermore, the author introduces an obscure notion of “net energy flow”. The relevant quantity is the “net heat flow”, which, of course, is the sum of the upward and the downward heat flow within a fixed system, here the atmospheric system. It is inadmissible to apply the second law for the upward and downward heat separately redefining the thermodynamic system on the fly.”
Unfortunately it is G&T who are plainly wrong, even after very clear and accurate explanations are provided for them. How can it be resolved when two scientists are called "plainly wrong" when both should be knowledgeable on the technical issues?
Maybe an example would help. Consider two walls of different temperature facing each other, perhaps as a large radiant heating panel in a room. The net flow of radiant heat will be from the hot wall to the cold wall. All objects above absolute zero radiate energy (heat), so the cold wall must be radiating heat in the direction of the hot wall. Raise the temperature of the cold wall to warm, so now the flow of energy from the warm wall is increased and the net flow of heat is reduced. One can go to the extreme of making the temperatures equal and the net heat flow will be zero, but both walls will be radiating.
Charlie Brown
Your comment @21 "This statement does not say that it is impossible to transfer heat from a cold body to a hot body (Look and Sauer, Thermodynamics, 1982). As stated above in the “At A Glance” description, it is “the net sum of the energy flows will be from hot to cold”."
Makes sense. This is my understanding as follows as a lay person. Its probably naive. If you shine a weak radiant heat source at a warmer surface than the source then surely the radiant heat source heats the warmer surface? I mean the radiant heat isnt going to bounce off the warmer molecules. But over time the warm surface will loose its total energy to a colder surface somewhere so the second law isn't violated.
If however you had a warm and colder sufaces physically touching each other so you have conduction, then heat flow would be from warmer to colder.
Am I right or wrong?
Nigelj, Thanks for the question.
You are almost correct, although I would rephrase "... the (weak) radiant heat source heats the warmer surface". "Heats" implies raising the temperature of the warmer surface, which would be a violation of the second law. Since the warmer surface radiates more energy away than it receives from the weak source, the temperature will drop unless there is another source of energy keeping it warm. Rephrase it to "... the radiant heat source directs (or sends or radiates) energy to the warmer surface."
Yes, touching surfaces changes the mode of heat transfer from radiant to conduction. The net heat flow between the two surfaces is from warm to cold in either case, but with conduction there is no flow toward the warmer surface.
I think you guys are illustrating the difficulty of specialized terminology versus common usage. In day-to-day conversation, "heat" and 'energy" are almost interchangeable, but the difference is important at a technical level.
For conduction, you are still looking at bulk properties what talking about heat flow from warm to cold. Temperature only has meaning as the average kinetic energy level of a large number of molecules. Individual molecules will be transferring energy from one to another via collision, and individual collisions can transfer energy in any physical direction. It will always be from the higher energy molecule to the lower energy molecule, but that is not dictated by the bulk properties of "hot" versus "cold". It's only when you get to the average of a large number of collisions that you can say "heat/energy goes from warm to cold"
So, even "conduction" is a net transfer result. For radiation, if you have two plates facing each other with a vacuum between, the net radiative transfer will be from the hot plate to the cold plate - but there will be photons travelling in both directions. The photons emitted from the cold plate have no knowledge of the existence of the hot plate and its emitted energy. What individual photons do is not limited to matching the net result of many photons - just as individual molecular collisions are not limited to matching the net result of conduction.
The "heated by..." phrasing is also ambiguous in common usage. People can imaging being "heated by" an electric blanket that is warmer than they are. A regular blanket that is cooler than the person? "Heated by" make a little less sense, but "kept warm by" is perfectly reasonable. The use of "heated by" instead of "kept warm by" isn't enough to say that a regular blanket violates the laws of thermodynamics, though.
Likewise for IR radiation and the greenhouse effect. The surface is "heated by" back-radiation? Maybe a bit sloppy in terminology? How about "kept warmer by.."? But to make sense, you really have to get into the overall energy balance and some mathematical descriptions. The main article for this thread includes a link to an excellent post by Eli Rabbet on The Green Plate Effect. It has a loooong comments thread, but in it you can see some of the die-hard denialists at work. The extreme cases are people that claim that downward-directed IR from the atmosphere to the surface simply does not exist - usually with some "2nd Law" faulty logic involved.
As I mentioned earlier, countering a "2nd law" argument depends hugely on exactly what flavour of "2nd law" the person is claiming. The only common element is that the person making the claim has misunderstood something - what they call "2nd law" is not actually the real 2nd law..
Excellent comment, Bob. Far too many words are spent on misunderstanding technical distinctions. Concepts need to be conveyed succinctly at understandable levels. That requires knowing just what is being misunderstood. Input from a non-technical person is helpful. To understand the point of view of denialists, I have been working my way through the comments on the main aarticle for this thread. I now understand Philippe's comment @8 above, (@1112 in the main thread. I just saw your reference to Manabe & Wetherald @1134 which you provided to me a little while ago. I am thinking of having another go at drafting something as input for at-a-glance. I am hopeful that I can distill and limit the 2nd law myth into something managable. It's a tall order, but maybe my 2-cents would help.
There is a huuuge number of comments on the main post, so that's one tough slog you've made for yourself, Charlie!
My apologies to anyone that followed the link to Eli's Green Plate Effect post, read the comments, and had their head explode. I re-read them this morning, and boy do you need a head vice for the weapons-grade idiocy from a few of the determined commenters. Same goes for the comments Charlie is reading on the main article here at SkS. Take your head vice, don't drink coffee while reading...
I've referred to the Manabe and Wetherald paper a number of times over the years. There is a reason it's a classic. I sometimes find these older papers do a better job of covering some of the basics - stuff that won't be included in later papers because it's all old and well-established.
The same can be said for the IPCC reports - start with number 1, if your climatology background is limited. It could be used as the basic text for an undergraduate climatology course. The newer reports leave so much of that "old ground" out, because they assume that the reader has taken (and passed) the prerequisites.
Charlie Brown @23
Thanks. Makes sense.
Just my two cents worth on communications style. I believe this website is well written overall and would be reasonably intelligible to the general public. It avoids complex jargon and when it uses jargon there are definitions. It has beginner and advanced sections in the myths. This is a great feature.
In comparison realclimate.org is too technical.
It's a very hard balance to strike. The thing is its only possible to simplify science to a certain extent before it starts to become meaningless. And science is hard and some people will never understand.
Of course its always possible to refine and improve things. I'm just saying that theres probably not a whole lot more that can be done to communicate the science better. The real problem is people who don't want to understand or receive the message, or who don't see climate change as an urgent threat. Just writing the science differently won't solve those particular problems.
I thought Charlie Browns original comment on radiation physics and the second law @17 was rather good, and sounded technically correct and would be reasonably intelligible to a lay person. People do undertand numbers and probably have some understanding of the terms used enough to get the right message. I liked its brevity so you wouldnt want it to get too much longer.
I think with a little bit of refining the comment would be 100%.
The only real criticism I would have Is your final statement was "Nothing about this radiant energy flow violates the 2nd law of thermodynamics" It might have helped to briefly explain why and define the law. It left me sort of hanging, for want of a better word. I understood why but others may not have put two and two together.
NigelJ #28 - yes it is a complex challenge achieving balance in this business. The deniers have the advantage that they can make stuff up. We cannot!
Also, some myths are very straightforward to rebut - e.g. "it hasn't warmed since 1998". This particular one we are discussing here is something of a pig by contrast!
Realclimate has improved by strides since its inception. I was working on "Further details" about the Urban Heat Island effect - a debate largely triggered by a paper by Ross McKitrick and Pat Michaels in 2004. Realcimate's response was robust but only undererstandable to someone with serious statistical training. I nevertheless linked to it but with a note to that effect.
Fortunately, most of the myths on the database can be laid to rest in the At-a-glance pieces in less than 500 words, that being the ideal word limit for that class of rebuttals. Like I said, the one we are commenting on is a bit of an outlier in this respect because so much needs introducing to the layperson. But I firmly believe we need to be near-absolutely inclusive in this business - near because I accept that there are people out there who have reading difficulties, but nevertheless reaching the biggest possible audience is the aim here.
Here is my next attempt for the At-A-Glance section. It is 356 words. I will start by copying the "Myth" from the top of the main page. That saves trying to paraphrase it in the discussion.
"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)
The Clausius statement of the 2nd law of thermodynamics is: “It is impossible to operate a cyclic device in such a manner that the sole effect external to the device is the transfer of heat from one heat reservoir to another at a higher temperature” (Wark, Thermodynamics, 4th ed., 1983). The myth claims that back radiation or downward infrared (IR) radiation emitted by greenhouse gases (GHG) is the mechanism that increases the temperature of the Earth’s surface. Since that would not be possible according to the 2nd law, the myth concludes that global warming is false. However, the myth overlooks the fact that the sun is the external energy source that drives global warming and outer space is the external cold reservoir. The sole external effect is transferring heat from the hot sun to cold outer space. If heat loss to space is reduced, the planet will get warmer. Some take the myth even further to claim that thermal radiation cannot transfer energy from a cold body to a warmer one. Consider two walls facing each other and that all objects above absolute zero radiate energy. The warm wall radiates more energy toward the cold wall, but the cold wall will still radiate some energy toward the warm wall.
The 1st law of thermodynamics is conservation of energy – input = output + accumulation. The global system can be defined as from the Earth’s surface to the top of the atmosphere. The input to the global system is the sun. The surface temperature is regulated by balancing heat input from the sun with heat loss from the top of the atmosphere toward space. There are three output energy pathways: 1) infrared (IR) radiation at wavelengths that are transmitted from the surface directly to outer space (the transparent range). 2) IR radiation at wavelengths that are emitted by GHG in the cold atmosphere, and 3) solar energy reflected by clouds and the surface. As the concentration of GHG increases, energy output to space (path 2) is reduced. This upsets the global energy balance. Energy accumulates and the surface temperature rises. As the surface temperature rises, energy output from the surface through the transparent range (path 1) increases until the balance is restored. This is how global warming works.
Going in way over most people's heads, Charlie. Introduce, introduce!
Also note that when each rebuttal page is updated with these, it will retain the fact-myth-fallacy structure we've used all along.
My next attempt. I hope this is getting better. I changed the first part quite a bit to emphasize that the key problem with G&T, often overlooked, is their assumption that the input solar and output IR radiation are balanced (see Fig 32). I think these are worthwhile revisions. The structure seems fact-myth-fallacy-fact because I wanted to begin by separating the 1st & 2nd laws, but bring back the 1st law facts to seal the deal. Please feel free to edit and use the input as you deem suitable.
The 1st law of thermodynamics is conservation of energy. The 2nd law describes limitations on how energy can be used in forms of heat and work. It is difficult to express without introducing the concept of entropy - a state of disorder that is hard to understand. Instead, the 2nd law can be expressed practically in the form of statements and corollaries. One translation of the Clausius statement is: “It is impossible to operate a cyclic device in such a manner that the sole effect external to the device is the transfer of heat from one heat reservoir to another at a higher temperature” (Wark, Thermodynamics, 4th ed., 1983). A key phrase is “sole effect external to the device.” A cyclic device can be a heat engine and the classic example is a refrigerator that requires adding external energy, electricity, to make it work. Gerlich & Tscheuschner’s paper describes modern global warming theory as a perpetual heat engine that transfers heat from the cold stratosphere and the warm surface. That would violate the 2nd law, but that is an incorrect description of global warming. They assume that the radiant energy input from the sun is equal to the radiant heat loss to space and the system is “radiatively balanced”. That would be true for the greenhouse effect before the industrial revolution but increasing greenhouse gases (GHG) upsets the balance and causes global warming.
Some take the myth even further to claim that thermal radiation cannot transfer energy from a cold body to a warmer one. Gerlich & Tscheuschner steer the discussion into distraction by emphasizing the technical distinction between heat and energy. Consider two walls facing each other. All objects above absolute zero radiate energy. The warm wall radiates more energy toward the cold wall, but the cold wall still radiates some energy toward the warm wall. The debate amounts to whether it is energy or heat that moves towards the warm wall.
Conservation of energy for any defined system is:
Input = Output + Accumulation
The global system can be defined as from the Earth’s surface to the top of the atmosphere. The input to the global system is the sun. The surface temperature is regulated by balancing heat input from the sun with heat loss from the top of the atmosphere toward space. When balanced, accumulation is zero. There are three output energy pathways: 1) Infrared (IR) radiation from the surface at wavelengths that are transmitted directly to outer space (the transparent range). 2) IR radiation from GHG in the colder atmosphere at wavelengths that are emitted by GHG, and 3) solar energy reflected by clouds and the surface. As the concentration of CO2 increases, energy output to space (path 2) is reduced. This upsets the global energy balance. Energy accumulates and the surface temperature rises. As the surface temperature rises, energy output from the surface through the transparent range (path 1) increases until the balance is restored. This is how global warming works.
It is getting better. That latest one is pretty good, especially the analysis of G&T's trick, which is nothing more than a sophisticated straw man.
Thank you, Philippe.
I want to make two edits to emphasize a key point about the external energy of the sun and to clarify G&T's assumption about being radiatively balanced. Try this.
Insert after “… requires adding external energy, electricity, to make it work. The sun is the external source of energy to increase or to maintain the Earth’s temperature given the external energy loss to cold outer space. There is no violation of the 2nd law.”
Replace: “… incorrect description of global warming. They assume that the radiant energy input from the sun is equal to the radiant heat loss to space and the system is “radiatively balanced”. That would be true for the greenhouse effect before the industrial revolution but increasing greenhouse gases (GHG) upsets the balance and causes global warming..”
With: “... incorrect description of global warming as well as the Earth as a cyclic device in perpetuum. They ignore the energy flows from external hot reservoir of the sun and to the cold reservoir of space by stating that the heat transfer between the Earth’s surface and the stratosphere is “radiatively balanced.”"