Climate Science Glossary

Term Lookup

Enter a term in the search box to find its definition.

Settings

Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup

Settings


All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Home Arguments Software Resources Comments The Consensus Project Translations About Donate

Twitter Facebook YouTube Pinterest

RSS Posts RSS Comments Email Subscribe


Climate's changed before
It's the sun
It's not bad
There is no consensus
It's cooling
Models are unreliable
Temp record is unreliable
Animals and plants can adapt
It hasn't warmed since 1998
Antarctica is gaining ice
View All Arguments...



Username
Password
Keep me logged in
New? Register here
Forgot your password?

Latest Posts

Archives

The 2nd law of thermodynamics and the greenhouse effect

Posted on 22 October 2010 by TonyWildish

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.

This post is the Basic Version (written by Tony Wildish) of the skeptic argument "The 2nd law of thermodynamics contradicts greenhouse theory".

0 0

Bookmark and Share Printable Version  |  Link to this page

Comments

Prev  1  2  3  4  5  6  7  

Comments 301 to 314 out of 314:

  1. While I agree with Philippe, I do like the re-wording of the question.
    0 0
  2. Re #298 Moderator Response: [Dikran Marsupial]

    "To avoid any further obfuscation, I will re-word the question. Do you agree that body A will radiate photons in random directions at random intervals, with total power proportional to the fourth power of the temperature of body A (i.e. according to the Stefan-Boltzmann law), and that this remains true regardless of the temperature of body B?"

    Yes.
    0 0
    Moderator Response: [Dikran Marsupial] Good. Do you agree that the photons radiated from body A are carrying away some of the thermal energy from body A with them?
  3. Re #302 You wrote:-
    "Moderator Response: [Dikran Marsupial] Good. Do you agree that the photons radiated from body A are carrying away some of the thermal energy from body A with them?"

    Yes
    0 0
    Moderator Response: [Dikran Marsupial] Splendid, do you agree that some of the photons emitted by A will strike and be absorbed by B, regardless of the temperatures of A and B?
  4. Re #303 You wrote:-
    "Moderator Response: [Dikran Marsupial] Good. do you agree that some of the photons emitted by A will strike and be absorbed by B, regardless of the temperatures of A and B?"

    "regardless of the temperatures of A and B?"

    As long as A is above 0K, Yes.
    0 0
    Moderator Response: [Dikran Marsupial] Super, so those photons that strike and are absorbed by B, do they add to the thermal energy of B (i.e. cause B to have greater thermal energy that it would otherwise have done, had it not intercepted the photons from A)?
  5. Re #304 You wrote:-
    "Moderator Response: [Dikran Marsupial] so those photons that strike and are absorbed by B, do they add to the thermal energy of B?"

    Yes.
    0 0
    Moderator Response: [Dikran Marsupial] So would you agree that there has been a transfer of thermal energy from A to B, in the sense that photons have been radiated from A and been intercepted by B, these photons have taken thermal energy from A and contributed thermal energy to B? Do you also agree that this is true regardless of the temperatures of A and B (provided A is above zero Kelvin)?
  6. Re #305 You wrote:-
    "So would you agree that there has been a transfer of thermal energy from A to B, in the sense that photons have been radiated from A and been intercepted by B, these photons have taken thermal energy from A and contributed thermal energy to B? Do you also agree that this is true regardless of the temperatures of A and B (provided ....?"

    I'm afraid the question isn't clear enough for me. Perhaps you can help.

    1/Are energy carrying photons also radiated by B?
    2/If so are they intercepted by A?
    3/And if they are intercepted by A, does that mean that thermal energy is transferred from B to A?
    0 0
    Moderator Response: [Dikran Marsupial] Those are issues for a more advanced step and are irrelevant to the question. If thermal energy has been taken from A and added to B via radiation and absorption of a photon, then there has been a transfer of energy, regardless of what else is ocurring. This seems pretty much the dictionary definition of "transfer"

    The conveyance or removal of something from one place, person, or thing to another.

    In this case thermal energy (the "something") has been conveyed from A (the "place") to B (the "another [place]"), via radiation and absorption of a photon. Do you agree that this has happened and that it falls within common usage of the word "transfer", as explained above?
  7. Re #306 You wrote:-
    "If theremal energy has been taken from A and added to B via radiation and absorption of a photon, then there has been a transfer of energy, regardless of what else is ocurring."

    I wonder if it is really irrelevant? I has been said elsewhere that we should consider NET energy transfer.

    Now imagine your A and B were 100% symmetrical, both radiating photons and intercepting each other's photons, the photons of each containing energy from their source either A or B.

    Now what would your estimate energy transfer be in this situation?
    0 0
    Moderator Response: [Dikran Marsupial] We will get onto net transfer later. Please give a direct answer to the question. Note it is exactly this sort of prevarication that has made it necessary to conduct this discussion in such small steps. For convenience, I'll repeat the question:
    If thermal energy has been taken from A and added to B via radiation and absorption of a photon, then there has been a transfer of energy, regardless of what else is ocurring. This seems pretty much the dictionary definition of "transfer"

    The conveyance or removal of something from one place, person, or thing to another.

    In this case thermal energy (the "something") has been conveyed from A (the "place") to B (the "another [place]"), via radiation and absorption of a photon. Do you agree that this has happened and that it falls within common usage of the word "transfer", as explained above?
  8. Re #306 Moderator Response: [Dikran Marsupial] You wrote:-
    "We will get onto net transfer later."

    I don't know of any other kind of energy transfer other than net transfer.

    What kind of 'energy transfer' do you have in mind? I do think this is a reasonable question.
    0 0
    Moderator Response: [Dikran Marsupial] The reason we are having this discussion is precisely because you don't know of any other kind of energy transfer than net transfer and I am trying to explain how there can be a bidirectional transfer. Sadly continual prevarication means that going through the argument laboriously, step-by-step seems the only way in which progress seems possible, so I will answer your (perfectly reasonable) question, provided you agree to the intermediate steps.
  9. damorbel wrote "What kind of 'energy transfer' do you have in mind? I do think this is a reasonable question."

    For this portion of the thought experiment, focus on only a single photon emitted by Object A and absorbed by Object B. That situation is a completely sensible, logical, and reasonable isolation of a portion of the total situation of objects A and B, no different in method from isolation done in scientific or engineering analysis of any other situation. That photon carried energy out of Object A and into Object B. Object A no longer had that energy as soon as the photon emitted it, and Object B now had that energy as soon as the photon was absorbed by it. The photon was the vehicle that conveyed that energy from A to B; in other words, that photon "transferred" that energy from A to B. Do you agree?
    0 0
    Moderator Response: [Dikran Marsupial] Considering a single photon is indeed a useful simplification.
  10. Re #309 Moderator Response: [Dikran Marsupial] You wrote:-
    " The reason we are having this discussion is precisely because you don't know of any other kind of energy transfer than net transfer and I am trying to explain how there can be a bidirectional transfer"

    I really do think there is no problem here.

    Let us try it this way:-
    I believe that there is a bidirectional photon transfer; from A to B simultaneously with photon transfer from B to A. (As long as both A and B are above 0 Kelvin)

    OK?
    0 0
    Moderator Response: [Dikran Marsupial] There certainly is a problem as the issue of bidirectional flow of energy has repeatedly been a sticking point in your contribution to the discussion on these threads. Starting up your own step by step discussion is merely prevarication and strongly suggests that your interest on this thread is trolling rather than legitimate discussion. It is only sensible to have one step-by-step discussion, so please stick to the one already in progress.
  11. Sorry, #310 should have read "Re #308" not "Re #309"

    Now as regards #309 Tom Dayton you wrote :-

    "For this portion of the thought experiment, focus on only a single photon emitted by Object A and absorbed by Object B. That situation is a completely sensible, logical, and reasonable isolation of a portion of the total situation of objects A and B"

    What energy of photon did you have in mind?

    Did you consider that, because of the limited speed of light, it might not be possible to make a measurement for only one photon?

    You refer to a "situation". Fair enough, but what kind of situation, wold this be a cosmic ray photon with perhaps KE of 50J?

    I am having difficulty in imagining just what is the point of departure of the thought experiment and what kind result it will deliver in terms of energy transfer. Can you help?

    Perhaps I'm just being a bit thick today, trying to imagine the effect of a single photon.
    0 0
    Moderator Response: [Dikran Marsupial] The energy of the photon is entirely irrelevant, likewise this is a thought experiment, so there is no difficulty in "measuring" the energy of the photon. This is blatant trolling.
  12. Re #311 Moderator Response: [Dikran Marsupial] you wrote:-

    "so there is no difficulty in "measuring" the energy of the photon."

    Well, please explain the significance of a single photon. What has a single photon to do with the 2nd law of thermodynamics, energy and temeprature?

    My problem is that all thermal science such as the '2nd Law' is based on statistical analysis, photons included. I do not know of any thermal science that deals with single photons.

    [snip]
    0 0
    Moderator Response: [Dikran Marsupial] Blatant trolling deleted. The remainder is merely prevarication to avoid answering the question posed to you. Please DNFTT.
  13. Dikran, thank you for your patience. This has been the most entertaining, easy to follow, and ultimately hilarious and educational thread in ages. It's been so hard to avoid interjecting, but the step-by-step flow was so undeniable and relentlessly predictable that it was perfect.

    It's particularly educational not in terms of the science (which is pretty trivially simple, and should never have required this), but rather of being able to actually watch cognitive dissonance in action, down to identifying the exact point at which logic and reality break down into a swarm of conflicting, illogical thoughts. If you put your ear up to the computer monitor, you can almost hear the limbs thrashing, the teeth gnashing and the gears grinding on the other end.
    0 0
  14. I am a Certified College Dropout and I don't find this concept all that hard to grasp. It goes something like this:

    All objects above 0K radiate energy (photons) in all directions. When one of these photons intercepts another another object that photon's energy is transferred to the object regardless of the objects temperature. The fact that more photons might be moving in the other direction has no bearing on this initial interaction.

    Are there any important points I am missing?
    0 0
    Moderator Response: [Not Dikran] If I were the Wizard of Oz, I would bestow upon you your Bachelor of Science degree!

Prev  1  2  3  4  5  6  7  

You need to be logged in to post a comment. Login via the left margin or if you're new, register here.



The Consensus Project Website

TEXTBOOK

THE ESCALATOR

(free to republish)

THE DEBUNKING HANDBOOK

BOOK NOW AVAILABLE

The Scientific Guide to
Global Warming Skepticism

Smartphone Apps

iPhone
Android
Nokia

© Copyright 2014 John Cook
Home | Links | Translations | About Us | Contact Us