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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.

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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)

 

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 below or dig deeper via the tabs above!


Further details

Among the junk-science themes promoted by climate science deniers is the claim that the explanation for global warming contradicts the second law of thermodynamics. Does it? Of course not (Halpern et al. 2010), but let's explore. Firstly, we need to know how thermal energy transfer works with particular regard to Earth's atmosphere. Then, we need to know what the second law of thermodynamics is, and how it applies to global warming.

Thermal energy is transferred through systems in five main ways: conduction, convection, advection, latent heat and, last but not least, radiation. We'll take them one by one.

Conduction is important in some solids – think of how a cold metal spoon placed in a pot of boiling water can become too hot to touch. In many fluids and gases, conduction is much less important. There are a few exceptions, such as mercury, a metal whose melting point is so low it exists as a liquid above -38 degrees Celsius, making it a handy temperature-marker in thermometers. But air's thermal conductivity is so low we can more or less count it out from this discussion.

Convection

Convection

Figure 1: Severe thunderstorm developing over the Welsh countryside one evening in August 2020. This excellent example of convection had strong enough updraughts to produce hail up to 2.5 cm in diameter. (Source: John Mason)

Hot air rises – that's why hot air balloons work, because warm air is less dense than its colder surroundings, making the artificially heated air in the balloon more buoyant and thereby creating a convective current. The same principle applies in nature: convection is the upward transfer of heat in a fluid or a gas. 

Convection is highly important in Earth's atmosphere and especially in its lower part, where most of our weather goes on. On a nice day, convection may be noticed as birds soar and spiral upwards on thermals, gaining height with the help of that rising warm air-current. On other days, mass-ascent of warm, moist air can result in any type of convective weather from showers to severe thunderstorms with their attendant hazards. In the most extreme examples like supercells, that convective ascent or updraught can reach speeds getting on for a hundred miles per hour. Such powerful convective currents can keep hailstones held high in the storm-cloud for long enough to grow to golfball size or larger.

Advection

Advection is the quasi-horizontal transport of a fluid or gas with its attendant properties. Here are a couple of examples. In the Northern Hemisphere, southerly winds bring mild to warm air from the tropics northwards. During the rapid transition from a cold spell to a warm southerly over Europe in early December 2022, the temperatures over parts of the UK leapt from around -10C to +14C in one weekend, due to warm air advection. Advection can also lead to certain specific phenomena such as sea-fogs – when warm air inland is transported over the surrounding cold seas, causing rapid condensation of water vapour near the air-sea interface.

Advection

Figure 2: Advection fog completely obscures Cardigan Bay, off the west coast of Wales, on an April afternoon in 2015, Air warmed over the land was advected seawards, where its moisture promptly condensed over the much colder sea surface.

Latent heat

Latent heat is the thermal energy released or absorbed during a substance's transition from solid to liquid, liquid to vapour or vice-versa. To fuse, or melt, a solid or to boil a liquid, it is necessary to add thermal energy to a system, whereas when a vapour condenses or a liquid freezes, energy is released. The amount of energy involved varies from one substance to another: to melt iron you need a furnace but with an ice cube you only need to leave it at room-temperature for a while. Such variations from one substance to another are expressed as specific latent heats of fusion or vapourisation, measured in amount of energy (KiloJoules) per kilogram. In the case of Earth's atmosphere, the only substance of major importance with regard to latent heat is water, because at the range of temperatures present, it's the only component that is both abundant and constantly transitioning between solid, liquid and vapour phases.

Radiation

Radiation is the transfer of energy as electromagnetic rays, emitted by any heated surface. Electromagnetic radiation runs from long-wave - radio waves, microwaves, infra-red (IR), through the visible-light spectrum, down to short-wave – ultra-violet (UV), x-rays and gamma-rays. Although you cannot see IR radiation, you can feel it warming you when you sit by a fire. Indeed, the visible part of the spectrum used to be called “luminous heat” and the invisible IR radiation “non-luminous heat”, back in the 1800s when such things were slowly being figured-out.

Sunshine is an example of radiation. Unlike conduction and convection, radiation has the distinction of being able to travel from its source straight through the vacuum of space. Thus, Solar radiation travels through that vacuum for some 150 million kilometres, to reach our planet at a near-constant rate. Some Solar radiation, especially short-wave UV light, is absorbed by our atmosphere. Some is reflected straight back to space by cloud-tops. The rest makes it all the way down to the ground, where it is reflected from lighter surfaces or absorbed by darker ones. That's why black tarmac road surfaces can heat up until they melt on a bright summer's day.

Radiation

Figure 3: Heat haze above a warmed road-surface, Lincoln Way in San Francisco, California. May 2007. Image: Wikimedia Commons.

Energy balance

What has all of the above got to do with global warming? Well, through its radiation-flux, the Sun heats the atmosphere, the surfaces of land and oceans. The surfaces heated by solar radiation in turn emit infrared radiation, some of which can escape directly into space, but some of which is absorbed by the greenhouse gases in the atmosphere, mostly carbon dioxide, water vapour, and methane. Greenhouse gases not only slow down the loss of energy from the surface, but also re-radiate that energy, some of which is directed back down towards the surface, increasing the surface temperature and increasing how much energy is radiated from the surface. Overall, this process leads to a state where the surface is warmer than it would be in the absence of an atmosphere with greenhouse gases. On average, the amount of energy radiated back into space matches the amount of energy being received from the Sun, but there's a slight imbalance that we'll come to.

If this system was severely out of balance either way, the planet would have either frozen or overheated millions of years ago. Instead the planet's climate is (or at least was) stable, broadly speaking. Its temperatures generally stay within bounds that allow life to thrive. It's all about energy balance. Figure 4 shows the numbers.

Energy Budget AR6 WGI Figure 7_2

Figure 4: Schematic representation of the global mean energy budget of the Earth (upper panel), and its equivalent without considerations of cloud effects (lower panel). Numbers indicate best estimates for the magnitudes of the globally averaged energy balance components in W m–2 together with their uncertainty ranges in parentheses (5–95% confidence range), representing climate conditions at the beginning of the 21st century. Figure adapted for IPCC AR6 WG1 Chapter 7, from Wild et al. (2015).

While the flow in and out of our atmosphere from or to space is essentially the same, the atmosphere is inhibiting the cooling of the Earth, storing that energy mostly near its surface. If it were simply a case of sunshine straight in, infra-red straight back out, which would occur if the atmosphere was transparent to infra-red (it isn't) – or indeed if there was no atmosphere, Earth would have a similar temperature-range to the essentially airless Moon. On the Lunar equator, daytime heating can raise the temperature to a searing 120OC, but unimpeded radiative cooling means that at night, it gets down to around -130OC. No atmosphere as such, no greenhouse effect.

Clearly, the concentrations of greenhouse gases determine their energy storage capacity and therefore the greenhouse effect's strength. This is particularly the case for those gases that are non-condensing at atmospheric temperatures. Of those non-condensing gases, carbon dioxide is the most important. Because it only exists as vapour, the main way it is removed is as a weak solution of carbonic acid in rainwater – indeed the old name for carbon dioxide was 'carbonic acid gas'. That means once it's up there, it has a long 'atmospheric residency', meaning it takes a long time to be removed. 

Earth’s temperature can be stable over long periods of time, but to make that possible, incoming energy and outgoing energy have to be exactly the same, in a state of balance known as ‘radiative equilibrium’. That equilibrium can be disturbed by changing the forcing caused by any components of the system. Thus, for example, as the concentration of carbon dioxide has fluctuated over geological time, mostly on gradual time-scales but in some cases abruptly, so has the planet's energy storage capacity. Such fluctuations have in turn determined Earth's climate state, Hothouse or Icehouse – the latter defined as having Polar ice-caps present, of whatever size. Currently, Earth’s energy budget imbalance averages out at just under +1 watt per square metre - that’s global warming. 

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 component to another it can be neither created nor destroyed. Self-evidently, the "isolated" part of the law must require that the sun and the cosmos be included. They are both components of the system: without the Sun as the prime energy generator, Earth would be frozen and lifeless; with the Sun but without Earth's emitted energy dispersing out into space, the planet would cook, Just thinking about Earth's surface and atmosphere in isolation is to ignore two of this system's most important components.

The Second Law of Thermodynamics 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. To reiterate, the qualifier term, 'net', is the important one here. In the case of the Earth-Sun system, it is again necessary to consider all of the components and their interactions: the sunshine, the warmed surface giving off IR radiation into the cooler atmosphere, the greenhouse gases re-emitting that radiation in all directions and finally the radiation emitted from the top of our atmosphere, to disperse out into the cold depths of space. That energy is not destroyed – it just disperses in all directions into the cold vastness out there. Some of it even heads towards the Sun too - since infra-red radiation has no way of determining that it is heading towards a much hotter body than the Earth,

Earth’s energy budget makes sure that all portions of the system are accounted for and this is routinely done in climate models. No violations exist. Greenhouse gases return some of the energy back towards Earth's surface but the net flow is still out into space. John Tyndall, in a lecture to the Royal Institution in 1859, recognised this. He said:

Tyndall 1859

As long as carbon emissions continue to rise, so will that planetary energy imbalance. Therefore, the only way to take the situation back towards stability is to reduce those emissions.


Update June 2023:

For additional links to relevant blog posts, please look at the "Further Reading" box, below.

Last updated on 29 June 2023 by John Mason. View Archives

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Comments 201 to 225 out of 1119:

  1. #197: "you'd be in a warm bath of air at 14C, 1/2 surrounded by radiation from the ground at 14C; 1/2 from deep space at 2.7K." Damorbel, did you just say that radiation from space at 2.7K contributes 50% to keeping that 'warm bath of air' at 14C? What would Clausius say to that?
  2. Re #196 scaddenp you wrote :- "continuing to talk about what happens and how the 2nd law works in conductive energy transfer is not helping you understand how it works in radiative energy transfer." Energy transfer by photons is amazingly similar to that in gases, both exchange momentum in collision processes; in gases it is by inelastic collisions and with photons it is by elastic collision.
  3. Damorbel wrote: "The balls will slowly approach a temperature dependent only on the distance of and the power emitted by your UV source." As I understand it: If the source is a star, and both balls are receiving UV energy, then yes--even though the balls will still exchange radiation at equilibrium. However, that's not what I said. The second ball is not receiving UV radiation. It has been given one time heat by some unknown source. It is cooler than the first ball. My argument is that such a ball is an energy source for the first ball, in addition to the UV source, and it will continue to be an energy source because it receives radiation from the first ball. In this analogy, the second ball is the atmosphere. It receives radiation from the surface, and even though it is cooler than the surface, it radiates some of that energy back toward the surface. Eventually, some of the "backradiation" is absorbed by the surface and turned into work, but most of it gets hung up dancing from molecule to molecule in the troposphere, where convection and conduction also bring it into contact with the surface or bring it to the stratosphere. The point, though, is that the upper troposphere can indeed act as an energy source for the surface and for the lower troposphere (where surface temps are measured), even though the upper troposphere is concurrently cooler. GHGs basically redirect certain frequencies of longwave radiation. The more GHGs, the more LWR is redirected, and the more time LWR stays within the system (heating, doing work, being a nuisance, etc.).
  4. Sigh. If you thought greenhouse effect was energy transfer from atmosphere to surface by conduction, then that WOULD be violation of second law. However, this is not what is happening as people repeatedly tell you. No incoming radiation, no GHG effect. You cant take the sun out of it. If you are determined not to learn physics, then we are wasting our time trying to teach you.
  5. #199: "Convection is a bit special because it won't work 'downwards'" Oh, dear. I guess plate tectonics, thermohaline ocean circulation and onshore/offshore breezes, among other things all just stopped because damorbel says 'it won't work downwards'.
  6. Re #198 KR The case for warming due to back radiation has not been made. GHGs are distributed more or less uniformly up to 80km except for water, by far the dominant GHG, which drops to a low concentration above 15-20km. The relevant point about GHG emission is that it takes place throughout the atmosphere, it is highest where the gas density is highest and, most important, because the temperature at any given location does not change quickly, to a first approximation, GHGs are absorbing (locally) just as much IR as they emit. They do not collect radiation together somehow 'at the top of the atmosphere' (TOA) and send it down (or up) as in Trenberth's 'Radiation Balance' diagram. If that 'collecting at TOA' according to Trenberth were possible there might be a better case for surface warming but you are still stuck with the problem that the TOA is extremely cold and can only take heat from the surface, not send heat down to the surface. Notice that I wrote 'not send down heat to the surface', not 'not send radiation down to the surface'. Radiation is not heat, heating (or cooling) arises only when there is an imbalance between absorbed and emitted radiation. In the troposphere radiation is emitted and absorbed primarily in a balanced way, with height being the only exception. The importance of this exception means that heat transfer due to radiation goes only in one direction only, out into deep space. There are two reasons for this, the atmospheric temperature falls steadily with height according to the lapse rate (-6.5K/km), the atmospheric density also falls with height. Thus the lapse rate defines the direction of heat tansfer and the density variation also ensures that there is always less radiation 'downwards' rather than 'upwards' for the simple reason that the amount of radiating gas reduces with height due to the drop in density with height.
  7. Re #204 scaddenp You wrote:- "If you thought greenhouse effect was energy transfer from atmosphere to surface by conduction, then that WOULD be violation of second law." Yes, but no need for emphasis! And:- " However, this is not what is happening as people repeatedly tell you." Tell me? Don't I know it! then you write :- "No incoming radiation, no GHG effect. You cant take the sun out of it." What does that mean? Isn't it the GHGs that are supposed to cause the GH effect? h-j-m has been arguing successfully that the atmosphere is heated directly by GHGs absorbing energy directly from the Sun's radiation, Trenberth's diagram shows it, who is disputing it? The whole planet is heated by the Sun's radiation and very little else, if you have a problem with this could you expand on it? Heat transfer by radiation can only be from a hot body (gas etc.) to a cooler, no different from conduction diffusion or convection.
  8. damorbel wrote: "Microwaves are not 'thermal' like a grill" So... you are arguing that electromagnetic radiation in the range we designate as 'infrared' (or 'thermal' energy) behave differently than all other forms of electromagnetic radiation? While ridiculous on its face... that doesn't pass the everyday reality test either. Most remote controls use infrared signals. By your logic they would not function if the receiver, or any space leading up to it, were even a fraction of a degree warmer than the transmitter. Many pieces of electronic equipment get quite warm when they have been running for a while... yet the receivers in them still pick up infrared signals from the cooler remote. Also: "Oh alright then, not 0K, lets put 0.00000000001K." Close. Multiply that by ten and you've got the lowest temperature ever observed. However, you are missing the point. Your claim that objects at 0K emit no radiation is meaningless because there AREN'T any objects at 0K.
  9. Re #205 muoncounter You wrote:- "all just stopped because damorbel says 'it won't work downwards'." And you inserted a nice diagram showing convection by a fluid between two surfaces, the warmer one being underneath, you can see how it works by the arrows on the convective flow loops. But muoncounter, surely these loops do not have a uniform temperature all the way round? According to me the left hand part of the loop (the 'upward' part) will be warmer than the righthand (the descending) part. I really don't get what you are on about. I suggest you put some indication of the temperature distribution on your diagram, that should help to clarify what is happening energywise. It is an interesting fact that convection can take place with very small temperature differences. Have you ever come accross a heat pipe? Heat pipes have fluid inside them that transfers heat by evaporation and condensation; they are very effective, my computer has one for cooling the video driver chip(s?) You must look at Earth as a sort of giant three dimensional heat pipe that transfers heat from the tropics to the poles and the upper atmosphere by processes rather similar to those in a a heat pipe.
  10. damorbel #206 Trenberth does not say anything even near "collection at TOA"; it's just your (wrong) interpretation of Trenberth's schematic diagram.
  11. Re #208 CBDunkerson You wrote:- "So... you are arguing that electromagnetic radiation in the range we designate as 'infrared' (or 'thermal' energy) behave differently than all other forms of electromagnetic radiation?" What is call 'thermal radiation' is radiation from a thermal source, glowing metal, hot carbon are typical, they give out radiation with a broad spectrum first described by G Kirchhoff as 'blackbody radiation'. The important factor is that the emission is proportional to temperature, the implication is that any substantial body must have the same temperature throughout, that is what is meant by equilibrium. The importance of uniform temperature comes from the fact that, if the temperature is not uniform, the parts with different temperature will emit different amounts of radiation. Also heat will possibly flow by conduction etc. bteween the parts with different temperatures. Ultimately, how can you say a body, whose parts are at different temperatures, has 'one' temperature? But radiation comes in all sorts and sizes from DC(?) to beyond blue light I have heard. Thermal radiation has a characteristic Planckian spectrum that comes from a black body and it is related to the temperature of this 'black body' (yes I know it isn't black if it's radiating!) Radiation from other sources such as lasers, microwave ovens and radio and television transmitters is largely monochromatic they have only one frequency. All these forms of radiation get converted to heat when absorbed; this heat tends to raise the temperature of the irradiated object. This heat tends to be dissipated in the surroundings by any process you care to mention, radiation; convection; conduction etc. or even into chemical energy e.g. plant growth. The important point is that not all sources of radiation have a temperature.
  12. Re #210 Riccardo You wrote:- "Trenberth does not say anything even near "collection at TOA"; it's just your (wrong) interpretation of Trenberth's schematic diagram." It is an expression used all over the place in climatology, Trenberth has it here If it is any comfort to you it is a meaningless concept not least because the TOA is completely undefined, temperature? pressure? altitude? All are unidentified.
  13. damorbel wrote: "What is call 'thermal radiation' is radiation from a thermal source, glowing metal, hot carbon are typical, they give out radiation with a broad spectrum first described by G Kirchhoff as 'blackbody radiation'." So... 'sunlight'. Which is the broad spectrum of radiation given off by a thermal source known as the Sun. Yet sunlight travels from the cold of space to the warmer upper atmosphere to the warmer still lower atmosphere. damorbel wrote: "The important point is that not all sources of radiation have a temperature." Which is an oxymoron. All sources of radiation have a temperature... otherwise they couldn't be sources of radiation. The theoretical 'no temperature' of 0 Kelvin is defined as the point at which matter emits no radiation.
  14. damorbel could you please point me where Trenbrth said such thing? I couldn't find it.
  15. #206: "GHGs are distributed more or less uniformly up to 80km except for water, by far the dominant GHG, which drops to a low concentration above 15-20km. ... the atmospheric temperature falls steadily with height according to the lapse rate (-6.5K/km), the atmospheric density also falls with height." Multiple sources show CO2 and H2O concentrations vary considerably with altitude. Temperature isn't uniformly decreasing with altitude. Density isn't linear with altitude. #209: "surely these loops do not have a uniform temperature all the way round?" Who suggested that they did? You said 'convection won't work downwards'; most people associate 'convection' with some sort of circulation - including the return trip down. There's no subduction of lithospheric plates without it. "I suggest you put some indication of the temperature distribution on your diagram," The 'heat input' on the bottom and 'fluid cools' at the top would be enough for Wikipedia-level readers to get the point. Apparently you require additional notation? "Isn't it the GHGs that are supposed to cause the GH effect?" Duh; but without solar heat input, there's no surface IR radiation for GHGs to absorb. Deflecting the discussion with these irrelevancies was just tedious some hundred comments ago; now it's pointless clutter, but I suspect that's your actual goal here.
  16. Re #213 CBDunkerson you wrote:- "So... 'sunlight'. Which is the broad spectrum of radiation given off by a thermal source known as the Sun. Yet sunlight travels from the cold of space to the warmer upper atmosphere to the warmer still lower atmosphere." Of itself a vacuum contains no material so it can have no temperature, since temperature is a measure of the heat content of molecules and atoms. Electromagnetic (EM) radiation is produced by the vibration (more accurately the acceleration) of electric charge (electrons and protons), so it always is associated with matter how ever far away that matter happens to be. EM radiation starts and finishes with matter, it moves at the speed of light and it cannot be stored or otherwise conserved like energy. Since EM radiation is produced by matter which in turn has a temperature there is a sort of connection between temperature and radiation. But only a connection. If the connection is to be strong the radiation must at least have a spectrum according to the Planck radiation formula. Just having the spectrum is not sufficient, it must have the right intensity also. If the intensity is weakened, say because a star is at a distance then, even though the spectrum remains the same, the temperature is reduced because the intensity is no longer that given by Planck's formula. Further you wrote:- "The important point is that not all sources of radiation have a temperature." Which is an oxymoron. All sources of radiation have a temperature... otherwise they couldn't be sources of radiation." Lasers, radio and television transmitters, microwave ovens are all sources of radiation that does not conform to the Planck spectrum, so the source is not related to matter having a temperature (be careful, the radiation output of a microwave oven etc. is (more or less) independent of its physical temperature). When this 'non-Planckian' radiation is absorbed (by matter) the temperature of the absorbing matter increases - the stored energy is thermal in character, the matter has a temperature.
  17. #213 CBDunkerson at 00:13 AM on 1 December, 2010 All sources of radiation have a temperature... otherwise they couldn't be sources of radiation. The theoretical 'no temperature' of 0 Kelvin is defined as the point at which matter emits no radiation Which is an oxymoron. damorbel is obviously talking about radiation sources very far from thermal equilibrium. Such systems do not have a unique well defined temperature, yet they may emit radiation. Otherwise how would you explain laser cooling? (Heat never moves spontaneously from a cold place to a hot one, so in a sense laser light has to be cold indeed to be able to cool down things to several nanokelvins.) LED lamp is another example. Or is the common glow-worm (Lampyris noctiluca) hot? For that matter neither has OLR (Outgoing Longwave Radiation) at TOA (Top of Atmosphere) a well defined blackbody temperature. Partly because Earth is not a blackbody, partly because due to heavy frequency dependence of atmospheric transparency, layers of very different temperature give contributions to OLR. Again, Earth is a system very far from thermodynamic equilibrium.
  18. damorbel - As I stated before, greenhouse gases reduce cooling of the surface, which has the result of the Earth's surface heating up in order to radiate in balance with the incoming solar energy. The observed backradiation from lower atmosphere GHG's is part of the energy balance, which Trenberth listed in his 2009 paper - it's an energy exchange, part of the balance sheet including incoming solar, outgoing top of atmosphere (which as a point of demarcation is chosen as somewhere above the majority of GHG's), surface IR, back IR, thermals, etc etc. You are obviously familar with EM, heat, energy exchanges, etc. Your description of lapse rates, thermal radiation, etc., seem reasonable, except for your somehow deciding that backradiation doesn't have a role. You have, however, put up repeated strawman and red herring points, such as dying due to lack or H2O in thought experiments, quibbling about monochromatic sources, etc. At this point I consider you to just be objecting for the sake of objecting. If you have actual issues, fine - otherwise I'm leaving this thread.
  19. damorbel, imagine there are two stars, named Miami and Anchorage. Both are 100,000 light years from our Sun. From hottest to coolest, Miami > Sun > Anchorage. Miami and Anchorage's radiation emission curves overlap, and intersect at a wavelength W, so the two stars emit the same number of photons having wavelength W. Simultaneously 100,000 years ago, Miami emitted a photon named Sally, and Anchorage emitted a photon named Greg. Sally and Greg both have wavelength W. 100,000 years later, Sally and Greg arrive at our Sun. Our Sun is cooler than Miami but hotter than Anchorage. All physicists in the world agree that both Sally and Greg are absorbed by the Sun. The Sun has no way of knowing that Sally's source was hotter than the Sun, and that Greg's source was cooler than the Sun, because Sally and Greg have the same wavelength W. I believe that in stark contrast you have been claiming that the second law of thermodynamics requires the Sun to absorb Sally but not absorb Greg. Here is a simple question for you: What happens to Greg?
  20. Berényi - Well written post on non-thermal radiation, thank you. Directly inferring temperature from EM spectra only works when the spectra is sufficiently similar to a blackbody curve, whether it has band-gaps or not. Monochromatic and 'cold-light' sources have an inherent energy, but since they are not thermal emitters that doesn't directly correspond to a temperature. However, when you say that "...Earth is a system very far from thermodynamic equilibrium", I would like to point out that as far as we can tell (again from Trenberth 2009, although I'm sure there are slightly different estimates out there) the balance sheet is currently tipped only about 0.9 W/m^2 from dynamic equilibrium. If we can reduce or prevent further GHG emissions, we can reduce that imbalance, and the resulting shift in global temperatures.
  21. BP, you are arguing (correctly) that not all rectangles are squares. Damorbel is arguing (incorrectly) that not all squares are rectangles. That is... yes, there is such a thing as non-thermal radiation. However, there is NOT such a thing as radiation from a source with no temperature. Two very different arguments. damorbel writes: "EM radiation starts and finishes with matter, it moves at the speed of light and it cannot be stored or otherwise conserved like energy." So... EM radiation is not energy. Fascinating stuff. However, setting that aside... your dodge about the vacuum of space being empty (it isn't) doesn't address the fact that sunlight travels through the Earth's atmosphere. How does sunlight hit gas molecules in the stratosphere, which is very cold, and then continue from there down to the troposphere, which is much warmer? Your argument would make this impossible... yet it obviously happens. Sunlight travels from a cold region of the atmosphere to a warmer one... indisputable fact. The whole 'broad spectrum' bit was nonsense to begin with because there is no reason a wide range of EM emissions should behave differently than a narrow band... and sunlight shows that it doesn't. There are countless examples of EM radiation traveling from cold areas to warmer ones... and it makes no difference whether it is individual wavelengths vs a wide band or the emissions source is thermal or non-thermal. Examples have been provided of ALL of these behaving the same way... there is no magical 'warmth barrier' to radiation. It's pure nonsense and observably so in the everyday world all around us.
  22. Re #218 KR You write:- "greenhouse gases reduce cooling of the surface, which has the result of the Earth's surface heating up in order to radiate in balance with the incoming solar energy." And:- "The observed backradiation from lower atmosphere GHG's is part of the energy balance, which Trenberth listed in his 2009 paper" And crucially:- "except for your somehow deciding that backradiation doesn't have a role" Back radiation would have a role in raising raising the surface temperature if it exceeded the output from other sources. But Trenberth himself has back radiation at 333W/m^2 and the surface sourcing 356W/m^2 to the atmosphere, thus the net upward radiation to the atmosphere is just 26W/m^2 and since it 'is net upward radiation' it is cooling the surface, not heating it! Trenberth has a total of 198W/m^2 going into the atmosphere and 169W/m^2 plus 30W/m^2 = 199W/m^2 leaving to deep space; leaving 1W/m^2 to raise the temperature of the surface by 30K. I may have got some of the figures wrong but without any temperatures on the diagrams it is quite impossible to make any check of the claimed warming effect, so without any question it is a scientifically unsound explanation, I have no idea how you manage to have such faith in it.
  23. damorbel - Aha, I think I see the issue you're having. Without greenhouse gases, the atmosphere would not emit much IR at all - nitrogen and oxygen don't have the structure to emit in the thermal IR bands. So, without the 333 W/m^2 backradiation, the surface of the Earth at current temperatures would still radiate upwards to space at net 356 W/m^2, not net 26 W/m^2. Don't you think this would have a cooling effect? If greenhouse gases were to go away the Earth would rapidly cool towards -18C, where outgoing top of atmosphere IR would be in balance with incoming solar energy, rather than the current +14C average temperature. Of course, that would lead to glaciation, increasing albedo, and reducing the temperature even further - the -18C thought experiment is just a first pass example. Backradiation greatly reduces cooling efficiency of the Earth - it has to be hotter to remain in energy balance with the sun. Backradiation doesn't have to exceed surface radiation in order to change the net heat loss, which you yourself have shown. The whole issue of backradiation and thermal balance is still based upon energy coming in from the sun, net energy flow to space, and the temperature of the Earth. Reduce the net cooling energy flow to space (reduced emissivity from GHG's), and the system is imbalanced until the temperature rises to compensate. I've pointed you to the very straightforward Thermal Radiation writeup on this, and the governing equation P = e * s * A * T^4. To put it bluntly, if you don't understand that, I don't think I can help you.
  24. Re #221 CBDunkerson You write:- "How does sunlight hit gas molecules in the stratosphere, which is very cold, and then continue from there down to the troposphere, which is much warmer? Your argument would make this impossible... yet it obviously happens. Sunlight travels from a cold region of the atmosphere to a warmer one... indisputable fact." When sunlight hits the atmosphere the UV component at 200 microns and below splits the O2 molecules into two O atoms which then join other O2 molecules to form ozone - O3 O3 further absorbs UV at 300 microns and shorter, thus the sunlight proceeds to the surface shorn of its dangerous UV. But what do you mean when you write this:- "Sunlight travels from a cold region of the atmosphere to a warmer one... indisputable fact."? The sunlight that passes through the atmosphere is not affected by it. The absorbed UV heats the stratosphere and generates the Ozone layer. The heating by UV causes a massive temperature inversion which makes the stratosphere very calm in comparison with the troposphere. Oh, and the temperature at the stratopause is not that low, just about freezing, 0C.
  25. Other have covered some of your points BUT "Heat transfer by radiation can only be from a hot body (gas etc.) to a cooler, no different from conduction diffusion or convection. " Missing word in here is NET heat transfer. Energy is transferred from cold to hot - a photon isnt magically not absorbed because the absorption surface is hotter than its source. The energy warming from surface of earth is from sun, the ghg are merely backscattering outgoing radiation.
    Response: Sorry to nag, but please refrain from using all caps.

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