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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 51 to 75 out of 1588:

  1. h-j-m - your part 1 is very much in error. The temperature of an object does not affect absorbance, and when the object is at equilibrium (incoming = outgoing), the absorbance and emissivity are equal. At equilibrium the greenhouse gases in the atmosphere are emitting as much as they receive, but ~50% (as spherically distributed incoherent radiation) heads back down to the ground. If an object receives a 10 micron IR photon, it gains that amount of energy. Photons do not carry ID cards indicating where they came from (unlike Arizonans)! It doesn't matter whether that photon came from the inside of an icebox (a few photons) or a plasma torch (a lot more), it's a photon. Objects cannot reject photons based upon their source. Hence your argument does not hold up - it violates physics. Temperature changes are caused when incoming and outgoing energies are not equal (heat flows). But photons are flying in all directions in some numbers. If you read the Trenberth article, there is about ~0.9 W/m^2 inequality heating the planet.
  2. h-j-m - I have seen your argument in many places before. It reflects a confusion between energy movement and heat flow. Energies move in all directions - up, down, and sideways. Heat flow is the sum of energy movements, and can be positive, negative, or at equilibrium based upon the magnitudes of the various energies. This is the failure at the core of the G&T paper that sparked this thread - it is a mistake to conflate the two.
  3. h-j-m, just stop and THINK about what you are arguing. You are claiming that infrared and other EM radiation cannot travel from substance A to substance B if B is already warmer than A... instead you say it must be "reflected". So... if we were to fire a laser at a block of iron in a cold room the laser would hit the block and warm it up slightly. At which point the block is warmer than the air adjacent to it... so the laser can no longer strike the block. Instead it must reflect off. Thus our laser can never cause the block to get significantly hotter than the room around it. The laser most slowly and uniformly warm the entire room because otherwise it reflects off the warmest part and thus cannot make it any warmer. This is all clearly not the case. Ditto sunlight... if it could not pass from the cold of space to the warmth of planet Earth then we would all live in perpetual darkness (which would prevent the planet from being warm). Even a cursory examination of the world around you disproves everything you are saying.
  4. #53: "Ditto sunlight..." Also to this point, sunlight must indeed pass through the cool atmosphere to the warmer ground and ocean surface. Or else there is no such thing as weather...
  5. I think that what the arguments so far show is that if you have a simplistic understanding of 2nd Law and a simplistic understanding of greenhouse effect, then you can easily make 2+2 = 5. Is 2nd Law the most misunderstood of common physics? I can only recommend, as other have done, the excellent series at Science of Doom. Of course, if someone only wants excuses to ignore science rather than understanding, then they would run a mile from this.
  6. Re #47 CBDunkerson wrote:- "How exactly do you explain sunlight traveling from space (very cold) to the Earth (much warmer) in your world?" Taking space as a vacuum, it really does not have a temperature since heat, (measured by temperature) arises from the microscopic motions of atoms and molecules. There are of course always a few molecules knocking about in space but not normally enough to have much influence on a substantial body like a spaceship. I say not normally but every now and then the Sun has indigestion and belches out energetic particles with energy in the multi MeV (million electron volts) region. You can think of these particles as having a temperature and it would be well over 10^11K. But such temperatures are largely irrelevant since the more devastating effect of the particles is the ionisation of the atoms in your body! In space there is always some radiation energy in the form of photons which comes (mostly) from hot bodies like stars 3500K-100000K. Much less intense are the photons from planets like Earth 150K-350K. Finally there is Cosmic Background Radiation (CMB) at 2.7K, this is the 'cold of space' you are probably thinking of. If you are near a star you get hot because you intercept a large number of very hot photons. At a distance from a star, like the Earth, you still intercept very hot photons but many fewer, so you receive much less energy in total. Since the energy from the photons that you receive from the star heats you up, as your temperature rises above 0K (lets start at the bottom!) you begin to radiate heat also. Your temperature stabilises when it rises far enough for you to emit enough photons of sufficient energy to match the total energy of the incoming (hot) photons from the star. An important point is the fact that the same power (W/m^2) of light (same as electromagnetic) radiation may be a few high energy photons from the hot star or a lot of lower energy photons from a much cooler planet, so when you see an 'energy balance diagram' covered in numbers with 'W/m^2' attached like the one on this page it really doesn't mean very much because there is no mention of any temperatures - anywhere, not of the Earth's surface, the atmosphere nor even the Sun.
  7. damorbel - "...it really doesn't mean very much because there is no mention of any temperatures": Directly, no, indirectly, absolutely yes. The 396 W/m^2 radiated from the Earth is the power emitted from the near-blackbody (average emissivity almost 1.0) of the Earth at a temperature of 14C, including temperature variations (an earlier paper estimated 390, but with insufficient attention to local variations).
  8. Re #55 scaddenp I checked your link to 'Science of doom' and this is (some ) of what I find there:- "It’s possible that the imaginary second law has taken a strong hold because anyone who does look it up finds statements like dS/dt>=0, where S is entropy. Wow. Clever people. What’s entropy? How does this relate to candles? Candles can’t warm the sun, so I guess the second law has just proved the “greenhouse” effect wrong.. According to Wikipedia, Clausius expressed the second law (validly) like this: 'Heat generally cannot flow spontaneously from a material at lower temperature to a material at higher temperature' Again, that seems right and it doesn’t have any entropy involved in the description. I never did like entropy. It never seemed real." To me the writer appears to accept that the 2nd Law of Themodynamics may even disprove the GH effect but does not seem to be very well informed on the matter. Lets face it, if he is only happy if entropy is excluded, he must be leading a very restricted (thermodynamical) life!
  9. #56: "an 'energy balance diagram' covered in numbers with 'W/m^2' ... it really doesn't mean very much because there is no mention of any temperatures " That diagram (the familiar IPCC global radiation budget) clearly indicates the incoming radiation is solar -- and therefore has the solar energy spectrum. Hence the temperatures are known. Same for earth surface and atmosphere. So what do you mean when you say 'it doesn't mean very much'?
  10. Re: damorbel (58) If you consider Science Of Doom to not "be very well informed on the matter" then perhaps (read: no uncertainty whatsoever) you should go back to the drawing board: Learn the basics of climate science and then build on that more solid foundation rather than to spout off on that which you don't even know what you don't know. No offense. The Yooper
  11. damorbel, I think your comment 56 is okay up to the next to last paragraph where you wrote "...incoming (hot) photons from the star," and the last paragraph's "... a few high energy photons from the hot star or a lot of lower energy photons from a much cooler planet...." You might have a misconception that all the photons coming from a source have the same energy, and that single energy is higher when the source is hot than when the source is cold. Instead, the radiation from a blackbody includes photons of low energy, high energy, and shades in between. That's why each blackbody radiation "curve" is a curve rather than single vertical line at a single energy. The temperature of the source determines the relative numbers of photons at those different energies. That distribution of photons' energies is the sole extent of the relevance of the source's temperature. Each photon has no memory of the temperature of its source. (We can calculate the probability of that photon having come from a hot source versus a cold source, but that's the limit of our knowledge, and the photon doesn't know even that.) Your next to last paragraph is correct if you simply leave out the phrases "(hot)" and "from the star." The correct paragraph would be "Your temperature stabilizes when it rises far enough for you to emit enough photons of sufficient energy to match the total energy of the incoming photons from all sources." The photons don't know where they came from. Your body can't tell where the photons came from; your body accepts them all.
  12. Damorbel clearly does not believe the physics when explained to him by "warmists", so maybe Dr. Roy Spencer (a "skeptic") will be able to convince him... Please go here and here.
  13. damerol - You said According to Wikipedia, Clausius expressed the second law (validly) like this: 'Heat generally cannot flow spontaneously from a material at lower temperature to a material at higher temperature'. That is NOT what wikipedia quotes. Their translation of Clausius is: "No process is possible whose sole result is the transfer of heat from a body of lower temperature to a body of higher temperature". This statement is correct within the context for which he made it. Again, that seems right and it doesn’t have any entropy involved in the description. I never did like entropy. It never seemed real. What do mean by "seems right"? And entropy has very precise definition from Clausius (as does 2nd law) in mathematics. You cant go drawing wild conclusions from imprecise english statements excerpted from context and claim this overturns application of a very precise mathematical framework from which the statement is derived. As I said, half-grasped ideas just lead to 2+2=5
  14. damorbel - Your last post left me a bit stunned. If you honestly feel that SoD "does not seem to be very well informed on the matter", then you are suffering from what is known as the Dunning-Kruger effect. You need to go back and review the basics - you've certainly been directed to them repeatedly. Until you do, the points you raise won't even be wrong.
  15. KR, sorry, I did not know that meanwhile our technology is advanced enough to observe directly what happens when photons hit matter or are emitted by it. I'd really like to see that. Then I will gladly accept that your notions about emissivity and absorptivity. That a photon is a photon regardless of it's origin is outright wrong unless they are at the same energy level (wavelength). But the wavelength of a photon depends on the temperature of their source (hence different black body radiation curves for different temperatures) and yes, so to speak, they do carry their ID cards (sort of). No, I do not confuse between energy movement and heat flow, I just state that temperature plays a dominant role. While you seemingly argue that taking temperature out of the game will leave no room for the violation of thermodynamic laws. I just looked up the science of doom page that scaddenp referred to and noticed the same trick. But a bit bolder as the author eliminates the term temperature and speaks of amounts of energy instead. Unfortunately temperature is not a measurement of energy amounts. It is a measurement of energy intensity. CBDunkerson, if you would read more carefully and reply to what I wrote you might be able to get a point. And yes sunlight can never reach the earth if its source is cold and empty space, but if it's source is the far hotter sun, I think that might change things a bit.
  16. h-j-m, I'm glad you wrote that two photons are equals if their wavelengths are the same. Now you need to understand that a photon of a given wavelength can come from a range of different-temperature sources. Imagine those two identical-wavelength photons hitting their target. The target absorbs them identically, because as you wrote, they are effectively identical. Which means the temperature difference between the source and the target is irrelevant.
  17. I just looked up the science of doom page that scaddenp referred to and noticed the same trick. But a bit bolder as the author eliminates the term temperature and speaks of amounts of energy instead. Unfortunately temperature is not a measurement of energy amounts. It is a measurement of energy intensity. Firstly, SoD is text-book stuff. Secondly, I am sorry but I fail to understand your comments on temperature. Temperature of say a gas is linearly related to average kinetic energy of the gas particles. Energy in those diagrams isnt measured - its derived from temperature. Can you express what you mean by "energy intensity" in mathematical terms and relate it to temperature please?
  18. h-j-m - I read your last post, and spent some time thinking about it. I think you are approaching the issues with a great deal of common sense, but not much technical background. That is a reasonable first approach, but leads to the Common Sense logical error - applying day-to-day reasonable responses to problem domains outside that experience. The Stefan–Boltzmann law (also here) is one of the more established properties of thermal radiation - it applies to all objects with a temperature above absolute zero. But it's not intuitive - it required detailed spectroscopy to establish this basic behavior. In direct response to your post, temperature sets the amount of thermal radiation, as per P=e*s*A*T^4 (Power, emissivity as a ratio to a theoretic black body [always 1 or less], Area, and Temperature). The thermal mass, and hence the total energy, are set by the particular object in question. But the amount of radiation is set by emissivity, area, and temperature. Nothing else. That's why everyone talks about temperatures in regard to climate. Thermal mass and total energy affect how fast temperatures change. But temperatures and emissivity differentials (primarily temperatures) affect how total energy changes - at whatever rate. And the direction of change is directly dependent on energy emission/absorption, not total heat content. We really worry about the directions, although we're also interested in the rate of change. I hope these comments are helpful. I would suggest looking into the Science of Doom site as a resource - search on "greenhouse", "2nd law of thermodynamics", etc. He has a good way with explaining these issues. Also look at Dr. Roy Spencer (noted 'skeptic'), here and here
  19. Oh, and 's' is the Stephen-Boltzmann constant, which scales this relationship. Sorry about that...
  20. Re #66 Tom Dayton You wrote:- "Now you need to understand that a photon of a given wavelength can come from a range of different-temperature sources." That is true but misses an important factor, a thermal source has a broad spectrum that is determined by the temperature. We are all familiar with the Planck spectrum, the amplitude of which is a function of the temperature, But taking one photon (with energy a function of frequency), or even one spectral component, does not represent the entire spectrum thus the temperature is not defined. Although a single photon has energy it does not have a temperature. You can say the same for a laser, a laser's beam may contain a great deal of energy which is all squashed into one frequency, all its photons have the same energy. If the laser beam is absorbed its single frequency energy is converted into thermal energy with its characteristic temperature dependent Maxwell-Boltzmann energy distribution.
  21. damorbel, you completely missed my point. And your reply seems to be gobbledygook.
  22. Re #60 Daniel Bailey You wrote:- "you should go back to the drawing board: Learn the basics of climate science" But 'Science of Doom' write weird things like:- "What’s entropy? How does this relate to candles? Candles can’t warm the sun, so I guess the second law has just proved the “greenhouse” effect wrong.." Of course a candle can warm the Sun if the candle's temperature is high enough, difficult to achieve I know but not impossible. It won't warm it much because the energy available from any reasonable candle is rather small compared with the Sun. But if the candle is hot enough and you have a large enough (very large!) number of them there will be a visible effect! Perhaps this is not found in the 'basics of climate science' but nevertheless it is the 2nd Law of Thermodynamics.
  23. Re #71 Tom Dayton "And your reply seems to be gobbledygook." The bit about lasers having photons with the same energy? Or something else?
  24. Re #61 Tom Dayton you wrote:- "I think your comment 56 is okay up to the next to last paragraph where you wrote "...incoming (hot) photons from the star," and the last paragraph's "... a few high energy photons from the hot star or a lot of lower energy photons from a much cooler planet...." " And then:- "You might have a misconception that all the photons coming from a source have the same energy, and that single energy is higher when the source is hot than when the source is cold." No misconception here, the average energy of the photons from a hot source is higher than the average energy of those from a cooler source. But you must recognise that the power (W/m^2 or J/s/m^2) in a stream of photons is proportional to the number of photons/s times hv, their energy. For example the photons from the Sun come from a high temperature source (5780K) these have enough hv to split O2 molecules and thus allow the formation of ozone. The power in this stream of photons from the Sun is 1370W/m^2, which averages to 342.5W/m^2 over the surface. This average power, when converted to heat, produces a temperature in the region of 280K. The Earth then radiates photons with an average energy based on this 280K, keeping the Earth's temperature stable while being bombarded with photons from a high energy photon source at 5780K. The photons radiated from the Earth also have a thermal (Planck) distribution which also allows a very small probability of splitting O2 molecules but the proportion of photons emitted by the Earth at 280K with sufficient energy to do this is very very small, many times smaller than the proportion in sunlight
  25. Did anyone notice we now have a case of skeptical whiplash? In this thread, #65: "I do not confuse between energy movement and heat flow, I just state that temperature plays a dominant role." In a comment on another thread we read, "Temperature is not a useless metric in given circumstances. It, by itself tho, is a useless metric when talking about climate. ... When talking about climate one must think in terms of heat content. " This seems to summarize the universe of the skeptic: It is what they say it is; until they say something else and believe that too -- even if it contradicts their prior position.

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