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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 251 to 275 out of 765:

  1. damorbel - Your physics are so far off it is difficult to know where to start. But I would strongly suggest that you read the following, by Dr. Roy Spencer, climate skeptic, which directly addresses this topic: Yes, Virginia, Cooler Objects Can Make Warmer Objects Even Warmer Still A quote from this, involving heated plates as a thought experiment: "Since the temperature of an object is a function of both energy gain AND energy loss, the temperature of the plate (or anything else) can be raised in 2 basic ways: (1) increase the rate of energy gain, or (2) decrease the rate of energy loss. The temperature of everything is determined by energy flows in and out, and one needs to know both to determine whether the temperature will go up or down. This is a consequence of the 1st Law of Thermodynamics involving conservation of energy."
  2. Re #251 you wrote:- " I would strongly suggest that you read the following, by Dr. Roy Spencer, climate skeptic, which directly addresses this topic:" I've read Roy Spencer on this matter, he's wrong. He uses the 'insulation' argument for CO2 etc. keeping heat 'in' (the atmosphere). This insulation/blanket argument is invalid because insulators only contain heat when it is in the container already, either because it was put there from outside, like putting hot soup in a flask, or there is a source of heat like combustion or radioactivity 'contained' by the insulation. Heat that arrives from outside the container, like the Sun/Earth arrangement is just as effecively kept out of a container (flask etc.) as it is kept inside. Eventually the contents of an insulated container revert to ambient temperature, your soup or coffee gets cold and your ice cream melts. What a shame!
  3. damorbel as I said and you apparently did not read, part of the spectrum. My impression is that you're not much confident with these simple physical concepts but you presume you know better.
  4. damorbel, If you're contesting Dr Roy's very basic physics, you need to go back there, read his post again, skip all the comments but read all Dr Roy's responses to those comments. Your argument about insulating heat being "in" the container already is irrelevant. What matters is that the earth has constant input of heat / radiation. It just happens to be from the sun. KRs reference @251 really is a fantastic one. Even if it takes you all day or longer, read it, reread it, copy it by hand, rewrite it - leave it for a while and then read it again. Whatever. If study techniques need to be applied, apply them. Dr Roy is a good teacher.
  5. damorbel - You should really read that article again. Carefully. Sunlight (like the electric heater in Spencers blog) passes through the atmosphere essentially unaffected by greenhouse gases, due to its spectra (primarily visible light). Thermal IR from the Earth, on the other hand, is strongly affected by greenhouse gas presence, which act as the 'blanket'. GHG's change the rate of loss, while input energy remains almost unchanged by them. Hence the atmosphere acts as a true "one-way mirror". Note that most sunlight passes through the atmosphere (affected mostly by Rayleigh scatter), while most IR does not (from Barrett Bellamy Climate) You've been pointed to this information multiple times, by multiple posters, yet you insist that your grasp of the physics is superior to the other contributors. I suggest you go read some of the very informative links you've been pointed to.
  6. BP "If OHC is supposed to be the true indicator of global warming and we have only seven years of reliable OHC data, then it is not cherry-picking to use what we have, is it?" Well actually I think true total OHC is long way from being tied down. However, can we assume that say 7 years down the track from here, and with good OHC data, if that OHC shows the warming trend, you will finally accept that we have a warming planet and its not just some measurement error?
  7. damorbel, you wrote:
    Even higher up in the atmosphere the gas density becomes so low and the chance of a photon being reabsorbed becomes correspondingly low. For thin atmospheres many photons emitted by H2O & CO2 do not get reabsorbed by adjacent H2O & CO2 molecules, some are reabsorbed by the surface but others are absorbed by deep space.
    I'm not sure you are thinking three dimensionally. Even way high up in thin atmosphere, H2O and CO2 molecules are emitting radiation in all directions, including down. So "adjacent" molecules include the ones below. Energy transferred by radiation down, warms the atmosphere below. That layer of atmosphere also radiates in all directions, including down, thereby warming the atmosphere below it. That cascade continues down to the surface.
  8. damorbel, you wrote "Heat transfer due to radiation goes only in one direction only, out into deep space." Yes, but the energy (via radiation) transfer in the direction down to the surface reduces the heat (net transfer of energy) from the surface up toward space. Which means that activity by greenhouse gases slows the cooling of the surface. Without greenhouse gases providing that offsetting (dare I say "back"?) radiation toward the surface, the heat (net transfer of energy) from the surface up would be larger, so the surface would cool faster, outstripping the replenishment of energy from the Sun, and consequently the surface would end up colder.
  9. FWIW, posted some molecular visualizations of the various states of the CO2 molecule here. The Yooper
  10. damorbel, you wrote "Since emitting (GH) gases absorb also there is no chance that any imbalance in thermal energy transfer will arise as described by 'back radiation.'" You are wrong. Greenhouse gases do not absorb 100% of the radiation they emit; they do not create a closed cycle that traps the energy within the greenhouse gases. They emit radiation in all directions, including down. If other greenhouse gas molecules in that downward direction absorb that radiation, those molecules in turn radiate in all directions including down. That downward cascade of radiation continues all the way to the bottom of the atmosphere, where due to the closeness of the surface, a substantial amount of the downward radiation avoids reabsorption by other greenhouse gases and so makes it to the surface. Also, greenhouse gas molecules transfer the energy they acquire not just by radiation but also by conduction. As KR explained on another thread, a CO2 molecule on average has 1000 collisions with other molecules in which it transfers energy, before it emits a photon. Those collisions are with not just other greenhouse gas molecules, but with any molecules--non-greenhouse gas molecules, liquid molecules, solid molecules. The recipients of those energy transfer in turn collide with other molecules of all kinds, thereby transferring the energy again. Thus collision (conduction) is an additional path for greenhouse gases causing warming.
  11. Re #253 Riccardo you wrote:- " part of the spectrum. " Your argument is that something can be 'black' in part of the spectrum. No it can't. On that basis a bright yellow surface can be called 'black' because it has nothing in the blue part of the spectrum, green has nothing in the red or blue part of the spectrum. When doing thermal and energy calculations black must mean 100% of the spectrum or you will get a false answer. A black body absorbs 100% of the spectrum by definition. A black body (above 0K) emits (with different intensity) in 100% of the spectrum, by definition. 'Real' black bodies fall short of this 100% property for each of two possible reasons, they reflect like Earth or a mirror thus never quite 100%, or they transmit like glass or CO2 but never quite 100%. Glass is particularly interesting because it is obvious the reflection is where the refractive index changes. All materials, even gases, have a refractive index >1, consequently no material substance can behave according to the definition of a black body.
  12. Re #254 adelady you wrote:- " Your argument about insulating heat being "in" the container already is irrelevant." Not in reality. Read what Dr. Spencer puts in his OP:- "Imagine a heated plate in a cooled vacuum chamber, as in the first illustration, below. These chambers are used to test instruments and satellites that will be flown in space. Let’s heat the plate continuously with electricity" Dr. Spencer's model of a vacuum chamber makes nothing clear. I am familiar with the working of the type of chamber he shows. He shows an electric heat source, said to be at 160°F. How so? Lets say it is regulated but is its temperature uniform? Parts are much closer to the 0°F walls. The walls must be regulated to be a uniform 0°F over the inside surface (this is frequently done with liquid N2 but of course at −321 °F) Even if the heater is a perfectly uniform 160°F the temperature of the additional bar will only be uniform if it is a perfect (thermal) conductor, otherwise there will be a thermal gradient in it, a thermal gradient that depends greatly on the geometry of the entire installation. So is the 160°F source regulated? In which case the temperature is completely unaffected by the presence of the 2nd bar. In the case where the heater is a real heater i.e. it also has a geometrical thermal gradient, its temperature is not a uniform 160°F. But the nub of the matter is, what will change with the introduction of the brown bar? There are a number of scenarios:- 1/ Suppose the brown bar is a very good but not perfect coductor of heat and it is so big it touches the container wall and the heater so that heat has a fairly easy passage. The temperature between the heater and the bar now depends entirely where you measure it because it depends on the thermal conductivity of the materials of the heater and the bar. 2/ Let us now consider the case where the heater is a point and the bar also, so now conductivity has no role. This is a false proposition because a point has no surface area so it cannot, at 160°F or any other temperature, emit any energy. Lets ignore that and say there is a temperature gradient from a point at 160°F in the centre of Dr Spencer's container to the edge at 0°F. The temperature of the brown point in such an arrangement would depend on the position of the point and, since the point also has no surface area, it isn't affected by any emmission or absorption, just by the local photon intensity (the energy of the photons coming from the heater is not changed by the distance from the heater but the intensity i.e. photons per cm^2 is) falls according to the inverse square law. You will have noticed that there are many ifs and buts associated with my explanation but at least it tries to make something out of Dr. Spencer's quite unrealistic proposition.
  13. Re #257 Tom Dayton you wrote:- "So "adjacent" molecules include the ones below. Energy transferred by radiation down, warms the atmosphere below." Only if it exceeds the photon energy coming up. This should be obvious from the formation of the stratosphere where the energy absorbed by O2 & O3 warms the atmosphere with characteristic results, there is a consequent temperature inversion (the temperature rises in the stratosphere from about -50C to about 0C, depending on where you look) and suppression of convection. This stratospheric warming phenomenon when compared with the tropospheric lapse rate should make it very clear that the role played by absorption/emission via GHGs in the tropospheric temperature profile is non existent.
  14. Tom Dayton #257: "Energy transferred by radiation down, warms the atmosphere below." damorbel #263: "Only if it exceeds the photon energy coming up." Nonsense. There is just no logical way to arrive at that conclusion. You aren't just spouting ridiculous violations of basic physics, but also basic math. Let's say the "photon energy coming up" is 5 units per time X and the energy going down is only 1 unit per time X. The down photons are less than the up photons so you claim they cannot result in a warmer surface. Put the starting energy at the surface at 100 units. Ignoring incoming energy for simplicity, after 1 X has elapsed this would yield; 100 - 5 + 1 = 96 You claim this is no warmer than; 100 - 5 = 95 Which is just wrong. 96 > 95 Adding an extra step for incoming energy would obviously yield the same result. The surface is warmer with the down photons than without them. Early grade school level mathematics. Inescapably true. Yet you deny it. That's just pathetic.
  15. Re #260 Tom Dayton you wrote:- "That downward cascade of radiation continues all the way to the bottom of the atmosphere, where due to the closeness of the surface, a substantial amount of the downward radiation avoids reabsorption by other greenhouse gases and so makes it to the surface." So you maintain that the few cold photons coming down from any altitude can counteract the effect of the larger number of warmer photons radiated upwards to the extent that they raise the temperature of the surface 33C? Forgive me if I don't agree!
  16. damorbel - A few small notes: - Photons don't have temperatures (cold, warm), they have energies. - The warm plate in Spencer's example receives a certain amount of power from the electric heater; the temperature in that example is not 'regulated' (no thermostat), but is rather the temperature where the amount of thermal radiation from the plate (determined by the object shape, emissivity, and it's temperature) match incoming power. - An object (even if rather cool) warmer than the absolute zero of space will radiate some thermal energy; when that hits the 'warm' object, the incoming power to the warm object changes. - Power in matches power out, or the temperature of an object (the accumulated energy) will change. - A cool nearby object (or atmosphere) is still much warmer than absolute zero, changes the incoming power to your 'warm' object, and the temperature of the object will change until, once again, output power matches input power. It's really that simple.
  17. No, damorbel, neither I nor anyone else has ever said that. Instead, the photons that hit the surface add energy to the surface sufficient to compensate for (replace) some of the energy lost from the surface by the photons leaving the surface. The net result is that the surface cools less than it would have without the incoming photons. Therefore the surface ends up being warmer when it has incoming photons than it would have been without incoming photons.
  18. Its almost as though damorbel views IR radiation coming up from the ground as exerting a pressure such that any back radiation downwelling from CO2 cannot overcome. A good analogy would be the Deepwater Horizon oil spill in the Gulf of Mexico earlier this year. Pressure from the oil upwelling from below made it initially difficult for engineers to force drilling mud back down the pipe to stem the spill. If up-pressure is 100 GPS, how could forcing anything back down the stack work unless it first overcame the up-pressure from below? Unfortunately for damorbel, photons can and do travel simultaneously through the same "stack"...
  19. A few more comments on "hot" and "cold" photons. - Heat is the internal energy of molecular matter due to vibrations of the atomic nuclei with respect to each other. Photons are much more basic wave-particles and so cannot hold heat. - As KR says, photons do have energy, this is equivalent to frequency (see here for example. The energy of photons emitted by any molecule are equal to the separation of their quantum states and therefore fixed under all conditions. - Temperature affects the amount of photons emitted, since in a colder substance fewer molecules are in excited quantum states. This is, of course, my first point restated slightly.
  20. Re #266 KR you wrote: "Photons don't have temperatures (cold, warm), they have energies." The temperature associated with photons comes from the Planck energy distribution, the peak of the curve tracks the Wien displacement law In the same way as a gas has a distribution of energies following the Maxwell-Boltzmann distribution according to its temperature; photon energy follows Planck's law. But, since the bulk gas has the average temperature of all the molecules, this also means that the individual (isolated) molecule has its own temperature. In the same way a photon also has its own temperature, related of course, to its energy. This goes further; a planet orbiting a star is immersed in photons emitted by the Sun, the number of photons intercepted by a planet is reduced by the inverse square law but this is the only reduction, making the equilibrium temperature of a planet a function only on the Sun's (photon) temperature and the planet's distance from the Sun. The idea that planetary temperature is affected by its albedo is quite mistaken.
  21. damorbel #270: "The idea that planetary temperature is affected by its albedo is quite mistaken." Your belief that you have any idea what you are talking about is quite mistaken. If albedo is irrelevant to temperature... why exactly is it that black asphalt gets hotter than white cement on sunny days? Or what magical property would be at work such that a planet with no atmosphere covered in white cement would be just as hot as an otherwise identical planet covered in black asphalt? That's the thing which gets me about nearly everything you say here... it isn't just that it is wrong, it is that any person capable of observing the world around them should know it is wrong. First you argue that a non-zero energy flow produces zero heating... now that reflection and absorption yield the same result. It's gibberish.
  22. Re #270 CBDunkerson you wrote:- "If albedo is irrelevant to temperature... why exactly is it that black asphalt gets hotter than white cement on sunny days? " You must not confuse 'rate of heating' with 'final temperature'. Highly absorptive materials heat up quickly because they absorb a large % of the incoming radiation. Switch the radiation off and they cool correspondingly quickly. Highly reflective materials (high albedo) heat up slowly and cool down slowly in the absence of input; an example of this is a thermos flask with its highly polished surfaces. In either case, black or shiny, the final temperature, after stabilisation from whatever the initial temperature was, will be the average of the fluctuating sunshine or whatever thermal input there is. You must see from this that, with a fluctuating radiation input, the temperature of the asphalt will fluctuate about the average temperature far more than the contents of the flask but both will have the same average temperature.
  23. damorbel, I understand what you believe. I also know it is false. How you can not know it is false is a great mystery to me. If you fire identical lasers at a black iron plate and a mirror the black iron plate is going to get hotter than the mirror... no matter how long you wait. This is basic and obvious, because the mirror reflects more of the laser light and thus absorbs less energy than the black iron plate. Less incoming absorbed energy means a lower temperature at which the emitted radiation equals the incoming radiation (i.e. equilibrium point). The same is true of sunlight or any other radiation and any other matter it is striking. The lower the energy absorption rate the lower the final temperature of the object will be. Again, let's look at it mathematically; Incoming radiation: 100 units Object A reflectivity: 90% Object B reflectivity: 25% Object A reflects 90 units and absorbs 10. That 10 absorption heats up the object until it is emitting 10 units. At that point the 90 units reflected + 10 units emitted equals the 100 units incoming and the object is at equilibrium. Object B reflects 25 units and absorbs 75. That 75 absorption heats up the object until it is emitting 75 units. At that point the 25 units reflected + 75 units emitted equals the 100 units incoming and the object is at equilibrium. At equilibrium object A is emitting 10 units of energy and object B is emitting 75 units. Object B is thus much hotter than object A. Albedo has a direct and obvious impact on temperature.
  24. damorbel, the law about equilibrium temperature uses only the energy that the object actually absorbs. Energy contained in photons that reflect off the object is excluded by that law. Think about it: Energy that the object did not absorb does not exist inside the object, and so cannot be emitted by the object. The object does not "need" to emit energy it never absorbed.
  25. damorbel writes: This goes further; a planet orbiting a star is immersed in photons emitted by the Sun, the number of photons intercepted by a planet is reduced by the inverse square law but this is the only reduction, making the equilibrium temperature of a planet a function only on the Sun's (photon) temperature and the planet's distance from the Sun. The idea that planetary temperature is affected by its albedo is quite mistaken. damorbel then explains this idea further: Highly reflective materials (high albedo) heat up slowly and cool down slowly in the absence of input; an example of this is a thermos flask with its highly polished surfaces. Look, this is just wrong. It really is. If you're (understandably) reluctant to accept that from a bunch of anonymous strangers on the Internet, please just stop by whatever university is nearest to where you live and talk to someone in the physics, atmospheric science, astronomy, or earth science departments, and see if they can explain it to you. The earth receives short-wavelength radiation from the sun, and radiates away long-wavelength radiation. If the albedo of the earth increased, it will receive less short-wavelength radiation (visible, near-infrared). But this doesn't imply an immediate, corresponding reduction in outgoing long-wavelength radiation. Instead, the planet will gradually cool. As it cools, the flux of outgoing long-wavelength radiation will gradually decrease, in accordance with Stefan-Bolzmann, until incoming and outcoming radiation fluxes are once again in equilibrium, with the planet at a lower temperature.

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