With nearly 500 comments on the thread on the Second Law of Thermodynamics there is obviously a need for people to discuss the basic greenhouse theory. Here’s a new thread on that theme.
So what is the Second Darn Law?
But there are variations
As with all these Laws of science there is no exact wording, because There Is No God Who Issues Science Decrees*. What we have are human efforts to best explain the world around us. Note that the two well known versions of the Second Law both contain the phrase “whose sole result”, meaning that heat transfer can certainly move from a colder to a warmer body if there is some other compensating movement where more heat is transferred from a hotter body to a colder one. Voila… whatever heat transfer goes from greenhouse gases to the Earth is more than countered by the heat moving from the Sun to Earth and on to space. Greenhouse gases can heat the Earth as long as the entropy of the whole system increases.
Clausius statement:
No process is possible whose sole result is the transfer of heat from a body of lower temperature to a body of higher temperature.
Kelvin Statement
No process is possible in which the sole result is the absorption of heat from a reservoir and its complete conversion into work.
Behind the scenes I’m still getting many emails from people wondering about this topic. I’m sorry I can’t reply to them all. Joseph Postma kindly replied to my last post on this topic in comment #97, and in reply to him I say this (his comments are in blue):
“The 2nd Law of Thermodynamics applies to net flows of heat, not to each individual photon, and it does not prevent some heat flowing from a cooler body to a warm one.”
JP: The laws of heat transfer DO forbid a cold body from raising the temperature of a warmer body. This is a much more physically unambiguous clarification. “Flows of heat” is ambiguous and confusing. It is obviously correct to say that a cold body does not raise the temperature of a warmer body. “Flows of heat” is ambiguous and not important, in terms of what has the ability to raise who’s temperature.
The “ability to raise temperature” is not proscribed by the 2nd law, merely by your interpretation of it. The second law does not mention “abilities” of anything.
“Net heat flows” is not ambiguous. It is the Net heat flow. Are more photons going in one direction? Yes, but the ones coming back the other way affect the NET heat flow.
JP: It is obviously correct to say that a cold body does not raise the temperature of a warmer body.
No it isn’t. It’s obviously correct to say that the heat stored in a cold object can’t raise the temp of a warmer object, but the heat is not coming from a cold object. The heat is coming from the sun. The cold body just stops it leaving the warmer object at the rate it was previously.
Why do you keep ignoring the sun? There is a continuous input of energy into the Earth?
JP: But there IS a restriction on which body can raise the temperature of its neighbours. Only the hotter body can raise the temperature of a colder neighbour.
This is preposterous. God doesn’t make rules like “photons can travel in any direction except the way it came”. Atoms radiate photons randomly and some return in the same direction.
“Technically, strictly, greenhouse gases don’t “warm” the planet (as in, they don’t supply additional heat energy), but they slow the cooling, which for all pragmatic purposes leaves the planet warmer that it would have been without them.” — Jo Nova
JP: This statement is fraught with contradiction. Is it technical or is it real? I mean this is very important! If GHG’s, as you correctly point out cannot raise the planets temperature because they are not actually sources of additional energy, then how do we arrange some logic in which they do exactly what we just said they cannot do?
The technical part is the language use, the reality part is the temperature.
The difference between whether we ascribe the raised temperature to the GHG gas or to the SUN is “technical” the reality of the warming is real. Think of the blanket analogy. Technically a blanket on your body does not heat you (if you want to be a pedant) your own body heats you. In reality, you put on a blanket and your temperature goes up.
What if we put it this way: Greenhouse gases don’t warm^ the planet but they do create a situation where the Sun can warm the world to a temperature above where it previously was without the gases?
That doesn’t break the second law, and it describes reality with a technical accuracy.
^(I don’t like this phrasing at all: the word “warm” here specifically means something other than it’s usual use — here it implies no additional heat energy is supplied that is new to the Earth-atmosphere system. Normally “to warm” means… well you know… . Life doesn’t have to be this complicated.)
In the end this boils down to the energy flows in a whole system, and people who think that the addition of greenhouse gases to our atmosphere won’t warm the planet (due to a conflict with the Second Law) are forgetting that the system includes the sun, and the extra energy flowing in continuously is what drives the system. CO2 may have little effect on Planet Earth, but that’s for other reasons. You can’t just make a comment about “the Earth-Atmosphere” part of the system and ignore the plasma ball that’s 1.4 million kilometers across and 13 million degrees in the middle.
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UPDATE #1 From Michael Hammer
Michael Hammer has suggested this as a line of reasoning that may help people discuss this. If you don’t agree with the end conclusion (that greenhouse gases can’t warm earth because they are not hotter than Earth), point out exactly which step in the sequence is the one you think is wrong and explain it so we can understand why.
- Do you agree that if you stand surrounded by cold objects (say a ring of huge ice blocks) you feel cold?
- Do you agree that the colder the object you are surrounded by the colder you feel? eg: if they were blocks of frozen CO2 (dry ice) instead of water ice would you feel colder?
- OK now if you have been standing surrounded by extremely cold objects and then move so that you are now surrounded by merely cool objects does the move make you feel less cold than you were before?
- In the absence of green house gases the earth is surrounded by an extremely cold object – outer space at 4K (-269C). Green house gases make the atmosphere opaque at some wavelengths. With these in place the earths surface is in effect surrounded by a merely cool atmosphere instead of the truly frigid outer space. Because the surface is now surrounded by a less cold object than it was before it is less cold.
- Since warm and cold are opposites, less cold is the equivalent of warmer. Surrounding earth’s surface with an opaque cool atmosphere make it warmer than it would be if exposed directly to the ultra frigid outer space.
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*Which doesn’t mean there is No God at all. I’m staying right out of that one.
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UPDATE#2 Joseph Postma in Comment #47
[My comments in reply inline in green. –JN]
Thanks for posting my comments, Jo.
Firstly, I would like to re-iterate that in my paper, “Understanding the Thermodynamic Atmosphere Effect”, I in fact refer to the Laws of Heat Transfer (i.e. thermodynamics) in total, not just the 2nd Law. You may have an earlier pre-edit copy which had the reference to the 2nd Law specifically.
Secondly, the 2nd Law isn’t even the most important one when it comes to understanding how the atmosphere actually works. Conservation of energy is actually much more important, in terms of the physics. Your diagram from NASA shows just how obscure the 2nd Law can be.
Lastly, the brief mention of the Laws of heat transfer, around page 6-7 of “Understanding…”, is NOT central in any way to the paper! There are MUCH more important issues discussed within.
Now to your post:
“heat transfer can certainly move from a colder to a warmer body if there is some other compensating movement where more heat is transferred from a hotter body to a colder one.”
This was never disputed…it is unclear why there is so much focus on this issue. What is undisputable is that more heat transfers from the warm body to the cold body and so the warm body has to cool down. That is, a cold body does not raise the temperature of a warmer body.
JN: Exactly – the greenhouse gases don’t warm the sun and the sun gets cooler (albeit slowly).
There is too much ambiguity and invitation to equivocation when using terms like “heat transfer” when what is more important is how the temperature is actually controlled. “Heat” does not equal “higher temperature”. 1 Kelvin has “heat”.
“Voila… whatever heat transfer goes from greenhouse gases to the Earth is more than countered by the heat moving from the Sun to Earth and on to space.”
And so by extension the GHG’s cannot increase the temperature of the ground. Because the net heat transfer is from the ground (warmest), outward (coolest).
“Greenhouse gases can heat the Earth as long as the entropy of the whole system increases.”
Not without an additional source of energy, could they do this*. GHG’s do not represent an additional source of energy. Re-emitted, or “back-IR” radiation from GHG’s, do not represent additional energy – this is rather the RESULT of the original Solar energy insolated into the system. The Laws of Thermodynamics, in total, tell you that this energy can’t be replicated for further heating. Never mind the 2nd Law all by itself. The IR and back-IR, etc, is a RESULT of what has already happened…they’re not the cause.
JN: *Never once have I said that GHGs are a source of new energy. Have I not explained at length and repeatedly that the heat comes from the sun, and the GHG’s slow the heat loss from Earth? Remember if the Earth didn’t radiate the heat away it’s final equilibrium temperature would be much higher… what would 4 billion years of input do with no heat loss?
“Why do you keep ignoring the sun? There is a continuous input of energy into the Earth?”
This is unfortunate. If my paper would actually be read it can be learned that I spend a GREAT deal of time discussing the Sun and its continuous input into the Earth system. When understood properly, as I qualitatively and partially quantitatively explained, you discover there is no need to postulate a radiative greenhouse theory in the first place because 1) there’s more than enough Solar insolation to explain the ground temperature, and 2) back-IR heat amplification is not supported experimentally – not that we should have ever expected it to be so, if one utilizes all 3 laws of thermo.
JN: This is a whole new point. If you have other reasons to think CO2’s effect is minimal, lets discuss those but the only way to get past the focus on the Second Law is to admit that as a point of reasoning, there is nothing about the second law which precludes GHGs from theoretically causing an increase in the Earths temperature. Then we can move on and discuss the other reasons. And if I can be so bold — people will find your other reasons more compelling if there is no erroneous reference to the Laws of Thermodynamics being broken at the start.
“This is preposterous. God doesn’t make rules like “photons can travel in any direction except the way it came”. Atoms radiate photons randomly and some return in the same direction.”
Obviously I did not say that. [No, but that’s the implication of a Law that “stops” this happening.–JN] I said there is a restriction on cold bodies raising the temperature of a warmer body. [Only in a closed system where there is not a third body involved like The Sun –JN] If you surrounded yourself by an entire “death star” of ice – you were placed right in the center of it – ALL of that IR energy from the ice-star, which would be tremendously more energy than you radiate at ~30C (or whatever skin temperature humans are), would not raise your temperature. It could be emitting one-billion times more thermal-IR than you do, and you could be right at the center of the sphere, but it would still not warm you. You would still cool. Even if the “death-star” you were in the center of were 29C, you would still cool.
JN: People keep warmer in Igloos, not because the heat comes from the ice, but because it comes from burning fat internally, and the ice cuts the heat loss. Why continually ignore the real heat inputs? No one is suggesting that ice or GHG’s raise the temp of a warmer body above what it would have been without another energy source…. I’m stuck in ground-hog day: the sun … the sun … the sun…. ?
“What if we put it this way: Greenhouse gases don’t warm^ the planet but they do create a situation where the Sun can warm the world to a temperature above where it previously was without the gases?”
The Sun can only warm the planet to whatever its insolation temperature is. If a planet surface is warmer it is because of additional physical contributions, such as adiabatic compression and convection, etc. Any IR energy as a result of these processes are just that – the RESULT. They cannot self-amplify the temperature or energies of the system as they are the consequence of what has already happened, not the cause of what has already happened.
Also, the discussion of the actual solar insolation and resulting expected temperature can be read about in “Understanding…”. The input insolation upon the Earth is NOT -18C…it is actually +30C on average with a maximum of around +121C, depending on local effects and extinction. It is only the “effective”, or mathematically and theoretically averaged energy OUTPUT of the entire system, as compared to a Black Body, which equates to -18C. This does not mean this is the actual kinetic temperature you should find, nor does it say where you should actually find it even if it was.
“… it describes reality with a technical accuracy.”
Well, I disagree 
It isn’t accurate, ENOUGH.
JN: I’m talking about a principle – not an exact number. The principle is right or wrong. Your calculations are a different thing, and accuracy matters there, but if the principles are wrong, there’s no point doing a calculation.
In regard to Hammer’s post, I will just say this:
The effect of an atmosphere on a planet is to modulate the surface temperature from the extremes it would otherwise experience, as is the case on the moon compared to Earth. ANY atmosphere, independent of GHG’s, has a thermal capacity and ability to retain heat, and so it will ALWAYS be the case that the presence of an atmosphere keeps the “bottom-of-atmosphere” average temperature higher than the effective mathematical equivalent (as just discussed). If adiabatic effects are added to this then the “bottom-of-atmosphere” temperature can rise even further – even to well above the original Solar insolation, as is the case on Venus.
So consider then what the strongest GHG, H2O vapour, does in contribution to this effect: it is the best modulator of temperature that we have in our atmosphere. Under the Sun, in the tropics with lots of H20 vapour, the temperature will raise to LESS-than whatever the Solar insolation says it should. For some reason all the H2O doesn’t amplify the temperature. Very telling.
Then at night, comparing a tropic region to a desert, the tropic region cools by only a fraction of what a desert does. They likely have roughly the same “daily-average” temperature.
So the strongest GHG actually kept it cooler under the Sun than it should have been, and cooler than a desert, even with all the extra back-IR “heating”, of which a desert experiences very little.
There’s nothing wrong with being kept warm at night…but there is a significant concern if Solar insolation heating is modulated downwards by GHG’s.
The only extra heating more CO2 could provide is that contribution to increasing the atmospheric depth and density, such as to increase the physical heating effects.
I think we agree that ideally, CO2 concentration should be above at least 1000ppmv, in order to sustain the biosphere and improve its productivity. I am not sure this can be attained via fossil fuel burning…but I DO think we should try! Even if it DID warm the planet…well that would be great. The climate has always changed and it is only the intellectually inept, and the physically lazy, who now try to use other-people’s MONEY to avoid doing the work and economic improvements to adapt to it.
But as it is, the GH postulate is borne out of an incorrect application of the Stefan-Boltzmann equation, and worse, an illogical interpretation of its result. Under such a scenario, a logician EXPECTS non-physical postulates and theories to be borne out of an illogical premise. Applying the Laws of Thermodynamics, and trying to figure out how the 2nd Law applies, is secondary to this more fundamental physical mistake. Though, again, we should expect to find an inability to agree on the correct application under such a scenario.
We (the Slayers of the Sky-Dragon) will be publishing a new paper in the coming weeks which quantitatively will put this issue to rest…if logic is allowed back into the paradigm. We will also outline (and carry out) the proper physics experiment which anyone can perform, to actually prove or disprove the thesis on either side – such is the way science actually works.
JN: Joseph, you can’t quantitatively put to a rest an argument of reason which is not based on logic. The reasoning underpins everything. Maybe CO2 doesn’t heat the Earth (for other reasons unrelated to this post), but if that’s the case — it’s not anything to do with “Laws of Thermodynamics”. Can you at least acknowledge that in the Sun-Earth-Atmosphere system it is possible that energy flows which are always going from the hot sun to cold space, could be changed by a colder entity (GHGs) which would allow a warmer entity (Earth) to get even warmer, given that a third source (the Sun) is continually adding energy?