Arguments
The greenhouse effect and the 2nd law of thermodynamics
What the science says...
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The 2nd law of thermodynamics is consistent with the greenhouse effect which is directly observed. |
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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
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.
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.
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.
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:
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
Thank you, Eclectic, for your helpful comments.
AEBanner
Perhaps this web page can help?
https://bartonlevenson.com/SecondLaw.html
[PS] You are replying to comment at is over 2 years old - but good link. Please use the Link tool in the comments editor to make links yourself.
Even we accept that buringin fossil fuels is warming the planet, the estimates are a few degrees per century. Now that might be catastrophic given enough cebtturies, but there is another doomsday scenario with which gloabl warming is mutually exclusive: Namely, Oil is nprdicted to last another 50 years, natural gas 53 years and coal 110 years - all running in parallel at the current rate of consumption. So after 50-53 years our fossil feul consumtpino is down to coal alone, and boy will we be scrambling to turn that into gasoline efficiently! So after 50 years, the rate of warming may fall or cease completely, and after 110 year (or less, as we will coal fater when the oil is gone) there will no more fossil fuels to burn and there will be nothing to stop the next ice age- although is rather a long way off !
Summary: If we do nothing there will be no catastrophe.
PaulDent @1503 ,
You seem to be trying to make two opposite arguments at once:
That: [A] fossil fuels will be exhausted in 50-100 years, and so we should simply keep using them until they're all gone (and without us developing Renewable Energy systems in the meantime).
And that: [B] we should quickly phase out the burning of fossil fuels, because they should be saved for using to counteract the next scheduled "ice-age" glaciation . . . (which is due in about 16,000 years).
Either way, you could probably better argue one case (or the opposite case) on a more appropriate thread than this one ~ 'cos this thread is for those people who have rather wacko ideas about Greenhouse and Thermodynamics.
[PS] Thank you Ecletic - more offtopic comments on this thread will be deleted. Any responses in the indicated thread please.
The underlying heat-adjustment effect works like this:
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"GREENHOUSE EFFECT", TRYING TO WARM IF THE QUANTITY INCREASES
- The "greenhouse effect" in Earth's troposphere operates like this: Some of the "LWR" aka "infrared" radiation heading up gets absorbed into cloud above instead of going to space so that's the "heat trapping" effect of a cloud. The top portion of the cloud radiates up some of the LWR radiation that's manufactured inside the cloud but it's less amount than the LWR that was absorbed into the bottom of the cloud because the cloud top is colder than below the cloud and colder things radiate less than warmer things. That is PRECISELY the "greenhouse effect" in Earth's troposphere. It's the "greenhouse effect" of liquid "water" and solid "ice" in that example. You can see that "greenhouse effect" of liquid "water" and solid "ice" for all the various places on Earth from CERES satellite instrument at https://www.youtube.com/watch?v=kE1VBCt8GLc at 7:50. It's the pink one labelled "Longwave....26.2 w / m**2" so cloud globally has a "greenhouse effect" of 26.2 w / m**2.
- Solids in the troposphere have the exact same effect as the "cloud greenhouse effect" above for the exact same reason.
- Infrared-active gases in the troposphere (H2O gas, CO2, CH4, N2O, O3, CFCs) have the exact same effect as the "cloud greenhouse effect" above for the exact same reason. Non infrared-active gases in the troposphere (N2, O2, Ar) have no "greenhouse effect" because their molecule is too simple to get the vibrational kinetic energy by absorbing a photon of LWR radiation or by collision. The "greenhouse effect" really is that simple, and it's utterly 100% certain.
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SUNSHINE REFLECTION EFFECT, TRYING TO COOL IF THE QUANTITY INCREASES
- Clouds (liquid "water" and solid "ice") absorb & reflect some sunlight and the "reflect" part has an attempt-to-cool effect, which has nothing whatsoever to do with the "greenhouse effect". You can see that "sunlight reflection attempt-to-cool effect" of liquid "water" and solid "ice" for all the various places on Earth from CERES satellite instrument at https://www.youtube.com/watch?v=kE1VBCt8GLc at 7:50. It's the blue one labelled "Shortwave....-47.3 w / m**2" so cloud globally has a sunshine reflection effect of 47.3 w / m**2.
- Solids in the troposphere absorb & reflect some sunlight and the "reflect" part has an attempt-to-cool effect, which has nothing whatsoever to do with the "greenhouse effect".
- Infrared-active gases in the troposphere (H2O gas, CO2, CH4, N2O, O3, CFCs) do not absorb or reflect any sunlight (minor note: except a tiny portion in the high-frequency ultraviolet where O2 & O3 has absorbed most of it already in the stratosphere above the troposphere).
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NET EFFECT OF THE 2 ENTIRELY-DIFFERENT EFFECTS DESCRIBED ABOVE
- The net result of the 2 entirely-different "cloud" effects is that clouds have a net cooling effect of 21.1 w / m**2 as seen in the blue-hues pictorial at left on screen at either of my 2 GooglesTubes links above.
- The net result for solids in the troposphere is a net cooling effect because the change in this effect by humans is the "global dimming" atmospheric aerosols air pollution effect and that's a cooling effect (separate from its cloud change effect).
- The net result for infrared-active gases in the troposphere (H2O gas, CO2, CH4, N2O, O3, CFCs) is a warming effect because their 2nd effect above is negligible, essentially zero.
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Cartoons or text that describe a "greenhouse effect" in which photons from the surface are absorbed by infrared-active gas molecules and then are re-emitted with 50% of it going down and warming the surface are incorrect because they do not include a tropospheric temperature lapse rate which is an absolute requirement. Explanations of the "greenhouse effect" which include phrases like "the radiation from the surface does not directly heat the atmosphere" are incorrect because there are simple laboratory experiments which prove that infrared radiation does indeed heat the CO2 infrared-active gas and its surroundings (which means, of course, that molecular vibrational kinetic energy is converted on collision to molecular translational kinetic energy before it happened to "thermally relax" and emit a photon and thus no photon was "re-emitted" in that case).
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Cloudy winter nights don't cool as much as clear-sky winter nights. It is PRECISELY the "greenhouse effect" in Earth's troposphere which causes that.
Grindupbaker:
Your formatting and general writing style make it hard to understand exactly what point you are trying to make. Most of the first part seems to be bog standard radiation and cloud physics.
The point where I disagree with you is where you say "...and then are re-emitted with 50% of it going down and warming the surface are incorrect because they do not include a tropospheric temperature lapse rate which is an absolute requirement. "
The 50% up, and 50% down is entriely correct. In fact, the IR emission rate is completely independent of direction, and is equal in all directions - spherical, to be precise. One half of that sphere is summarized as "upward", and one half is summarized as "downward".
You could also do two halves going horizontally - e.g., north/south, or east/west - or any other direction you wish, but the up/down summary is the one that is most useful.
And it is most useful for the reason you touch on: the vertical temperature gradient. If you think of a single height, where you have 200 W/m2 emitted upward, and 200 W/m2 emitted downward, you need to ask "what about the layers above or below this one?"
The reason any horizontal "halves" of the IR emission sphere are of little interest is because the temperature gradients are so small. No temperature gradient - no net IR difference.
And you are correct that local heating/cooling is dependent on the aborption of that radiation - plus any exhanges of non-radiative energy (convection, evaporation/condensation of water), minus losses through emission.
Bob:
Change my "Cartoons or text that describe a "greenhouse effect" in which photons from the surface are absorbed by infrared-active gas molecules and then are re-emitted with 50% of it going down and warming the surface are incorrect because they do not include a tropospheric temperature lapse rate which is an absolute requirement".
to
"Cartoons or text that describe a "greenhouse effect" at the surface which is caused entirely, or even mostly, by photons emitted from the surface being absorbed by infrared-active gas molecules and then re-emitted with 50% of it going down and this 50% adding energy at the surface are incorrect because they do not include a tropospheric temperature lapse rate, which is an absolute requirement".
My reasoning is that I assert that >99% of photons from molecules in the atmosphere arriving at the surface were emitted by molecules of solid, liquid or infrared-active gas due to them having obtained molecular vibrational kinetic energy on collision and then relaxed and emitted a photon downward, which made it to the surface, and <1% of photons from molecules in the atmosphere arriving at the surface were emitted by molecules of solid, liquid or infrared-active gas due to the sequence of (1) photon upward from surface ---> (2) absorbed by molecule of solid, liquid or infrared-active gas making it vibrate ---> (3) spontaneously re-emitted (4) repeat (2)(3) any number of times whatsoever (5) photon arrives at the surface. Since this >99% vs <1% ratio is the case those cartoons (...and then the rest of my revised refutation of the cartoon that's bandied about).
I don't have the foggiest clue what "bog standard" is and I don't see that your second sentence informed anything about this topic. It appears to just be a weird way of typing "I agree with you".
I assume that your 2 consecutive sentences "The 50% up, ... "downward". You could also ... is most useful" refer to emissions by a single molecule analyzed over sufficient time. I agree with that of course, it's random.
Your 3 consecutive sentences "And it is most useful ... below this one?" "The layer above this one ... downward". "The layer below this one ... downward" are self contradictory because you state that there is 199 W/m2 downward and 201 W/m2 upward at the junction (your "a single height" == junction) between the 2 layers yet there is 200 W/m2 emitted upward, and 200 W/m2 emitted downward at the junction between the 2 layers.
I see no meaning in your "at any single height the locally-emitted IR is equal up and down" because you haven't spatially defined "locally-emitted". How may molecular widths or Angstrom units is the vertical limit for the IR to be considered "locally-emitted" ? I don't know the minimum required size of the infrared-active gas parcel for the Stefan-Boltzmann radiative equation to be accurate to say 5 decimal places so I can't contribute other than stating like "I'm pretty sure 5 molecules thick is too thin to do accurate radiative assessments and I'm pretty sure 200 metres thick is thick enough to do accurate radiative assessments".
Do you agree with me that infrared-active gas molecules sometimes, probably very often, lose a molecular vibrational kinetic energy upon collision, with its energy going into increased molecular translational kinetic energy and/or molecular rotational kinetic energy ? If you don't agree and can point to physics refuting that then I'm incorrect in challenging that ubiquitous "greenhouse effect" cartoon and I'll drop that and stop describing the "greenhouse effect", but if you confidently agree with me on that then debate between us on this topic comes down to semantics and thoughts expressed a tad too casually for full accuracy.
This interchange is getting rather forensic and probably unproductive. All agree. There is a troposhperic lapse rate. Radiation from the atmosphere goes in all directions so at any point the net radiation flux emitted by the atmosphere will be 50% one way and 50% the other, this with the caviat that the lapse rate reduces temperature with altitude and thus emission reduces with altitude (at least within the troposphere).
grindupBaker @1507,
You ask for confirmation that absorbed radiation is transferred to atmosphic thermal energy through mollecular collision. This is entirely correct. The average relaxation time for an excited molecule to re-emit is measured in hundredths of seconds while the atmospheric collisions occur in microseconds. Indeed, one of the points I would have made concerning your statements @1505 was use of the term "re-emit" which you allow unchallenged. It is the temperature of the atmosphere that determines (almost all) the radiation it emits, not the radiation being absorbed by that atmosphere.
I guess your comment (not a lot to do with laws of thermodynamics) is prompted by the often dreadful descriptions of the greenhouse effect we all encounter. But I'm not sure your efforts assist in such general descriptions.
When discussing the greenhouse effect, it is usually not linked to albedo (as you do) and is best seen in terms of the effective height (and thus temperature) at which the planet radiates to space. Thus it is not so much 'cloud thickness' which you imply @1505 is the important factor, but it is the 'cloud height'.
Trying to aportion the strength of the GH-effect to particular atmospheric constituents is far from straightforward as their contributions are interdependent. Thus to say O2 & N2 have no part to play is wrong as without them you get a Martian atmosphere which has an insignificant GH-effect. And specific to Earth, while H20 (gas, liquid and solid) is bigger player than CO2, it requires the CO2 to get into the atmosphere.
Trying to aportion the sensitivity of the GH-effect to particular atmospheric constituents is also far from straightforward.
MA Rodger @1508 Your "grindupBaker @1507, You ask ... that atmosphere." Thanks. I'll put some thought this winter into wording gooder that bit because "sourced from surface re-emit" is precisely what I object to as being stated as the source of all downwelling LWR at surface and yet the Bob Loblaw glossed right past "re-emit" and focussed a challenge on 50% when I could have readily typed "most" or "some" or "a bunch" instead of "50%" without changing the meaning of my objection at all, and then you stated outright that I was silent ("unchallenged") on "re-emit" so my phrasing there is somehow poor. It isn't just a junk-science cartoon, it's one of the scam types that have served the "Skeptic" community very well the last couple of decades (Henrik Svensmark did a nice one). That junk-science cartoon is the nasty, cunning Scam of Omission (aka The Dog That Barked in The Night). A photon leaves surface, absorbed by CO2 molecule, re-emitted upward, no change, another photon leaves surface, absorbed by CO2 molecule, re-emitted downward, warming surface, got trapped (maybe a couple of repeats in cartoon). It's obvious even to an uneducated mind that this will cause warming so the "greenhouse effect" makes perfect sense. However, an uneducated mind doesn't think to wonder "so is this all that CO2 molecule does regarding photons then ?". The cartoon states outright that the CO2 molecule never gets vibration due to a collision and then sometimes emits a photon in a random direction even though it didn't absorb a photon to re-emit. I could modify that cartoon to show that CO2 molecule emitting 2 photons without absorbing a photon for every photon it absorbs and then adding a CO2 molecule increases upward radiation, so using that junk-science cartoon I could show the public how increased CO2 is actually cooling Earth and how "they" have been deliberately leaving this out to fool people as a hoax. Of course, we both know that radiation to space must decrease with increased tropospheric GHGs because the average emission level becomes higher, becomes cooler and emits less. The bods presenting that cunning Scam of Omission cartoon need to be brought to task by presenting the "greenhouse effect" correctly (like Andrew Dessler does) or the public is going to think it's all a scam when what I've pointed out here is pointed out to them in a form without explanation that's not designed at all to educate them.
Do you concur with physicist climate scientist Jennifer Kay statement at 8:09 at https://www.youtube.com/watch?v=kE1VBCt8GLc that "clouds absorb and re-emit long-wave radiation and that actually causes the surface and the atmosphere to be warm", or do you concur with me that Jennifer provides incorrect physics regarding what "actually causes the surface ... to be warm" because only a tiny portion of the photons that arrive at the surface are "clouds absorb and re-emit" photons, with the vast majority being "manufactured by H2O collisions in clouds" photons (with any number 0 to n of interim absorb-and-re-emit cycles before succeeding in achieving surface absorption) ?
grindupBaker @1509,
You ask about a particular statement within this talk by Jennifer Kay 2021 'How do clouds affect global warming?'. @6:30 the video addresses the question "How do clouds affect the mean climate?" pointing to a net global mean effect of -21.1Wm^-2 (thus cooling), this comprising -47.3 Wm^-2 (cooling effect) due to albedo and +26.2 Wm^-2 (warming effect) due to a "longwave effect." Thus the statement:-
My own objection to this statement would go no further than pick up on the use of the term "re-emit."
Your objection that "only a tiny portion" of the LW radiation arriving at the surface were 're-emitted' from clouds apparently expresses a similar concern.
But I'm not sure why you would then go beyond simply suggesting the replacement of "re-emit" with "emit". You appear to want to distance these cloud IR emissions from surface warming with description of them setting off "absorb-and-re-emit cycles before succeeding in achieving surface absorption," a description that deploys the very same objectionable "re-emit" term.
The point the video makes is that the climate system ("the surface and the atmosphere") is warm to the level it is significantly because of this long wave cloud effect. And I think we agree it is this warmth that sets the level of IR whizzing about in the atmosphere as well as the level being absorbed and emitted by the surface.
(And as a point of note: I recall that perhaps some 10% of the LWR from clouds will be due to reflection and presumably some will be directly returning surface-emitted IR back to the surface.)
Grindupbaker:
Sorry for the colloquial jargon, but yes, "bog standard" indicates agreement - basically, nothing remarkable or exceptional about the statements.
As for absorption and emission: these happen at the molecule/photon level. As soon as you start invoking Stefan-Boltzmann, Planck, etc. then you are by necessity looking at statistics of large numbers of molecules. For a single emitted photon, the direction is random. For a large collection, the emissions are isotropic. Any two halves of the sphere are "equal".
Radiation transfer is a continuous process in the real world, and anything dividing it up into layers is already a simplification. A finite difference approach to a continuous function - the same way a slope between two points compares to the derivative from calculus.
As soon as you are talking about layers, adjacent layers need to be consistent. What goes out the top of one layer goes into the bottom of the next, and vice versus. For any layer, the IR flux out of it can be either emitted from that layer, or it can be transmitted transmitted through that layer from previous layers. As all photons of the same wavelength are the same, there is no way of identifying which is the case. Flux out of a layer is not equal to emissions.
The 199, 200, 201 W/m2 example was a very simplified thought experiment to illustrate how your "it can't be 50%" argument was wrong. The flux can and does vary with height, and that does not break the equal up/down emission rule. The up/down aspect has a formal label: the two-stream approximation. The combination of the Beer-Lambert Law (for absorption) plus emissions of IR radiation, leading to a net IR flux along a temperature gradient also has formal solutions, one of which is called Schwarzschild’s equation. All of these are still approximations - but useful ones.
Eli has a good discussion of the time constants for re-emission vs. thermal collisions. If you want to distinguish between (1) energy that is absorbed and emitted by the same molecule from (2) energy that is absorbed by one molecule, transferred to another molecule and emitted from that second molecule - and want to restrict "re-emitted" to the first case - then you are welcome to add to your collection of pedant points.
Eli also has a good presentation on why you cannot think of any of this solely on the basis of radiation transfer - all energy fluxes in the atmosphere play a role.
Your habit of referring to diagrams as "cartoons", and your desire to "..challenge the ubiquitous 'greenhouse effect'..." suggests that you think that you have something new to add. You don't. You are taking simplified explanations, criticizing them for their incompleteness ("All models are wrong. Some are useful."), and replacing them with your own incomplete explanations. To quote MA Rodger in #1508, "I'm not sure your efforts assist in such general descriptions."
And as MA Rodger has also pointed out, this is really getting off topic for this particular climate myth, which is supposed to be about the second law of thermodynamics.
Can someone please share the math equation showing exactly how infrared radiation being trapped by CO2 is raising the temperature of the earth?
Frankamungus:
For the basics, you can read about the Beer-Lambert Law (atmospheric absorption of IR radiation) on this page:
https://skepticalscience.com/from-email-bag-beer-lambert.html
Relating this absorption to increasing temperature is not the result of a single equation. It involves a system of equations relating the complete energy balance. Comment #15 on that blog post includes references to two early papers that do the math in one dimension (vertical).
Manabe and Strickler, 1964
Manabe and Wetherald, 1967
The comments in that Beer's Law post also provide a lot of relevant discussion, Frankamungus. I suggest that you post further questions on that thread, unless you have questions specifically related to the 2nd Law (this post).
Frankamungus @1512 One interpretation of your question is that you simply want to see a formula such as:
f = 5.35 * ln (CO2<now>/CO2<before>) w / m**2 for the heater of a CO2 increase in Earth's atmosphere from CO2<before> to CO2<now>.
If so, that's the one on NASA Web site and I've vague recollections of seeing assertions of values other than the 5.35 over the years.
Note that the equation dF = 5.35 ln(C/Co), provided by GrindupBaker in comment 1515, is a simple approximation of radiative forcing due to changing CO2, based on more complex radiative transfer models. The original source is Myhre, 1998.
More information is available on this SkS page:
https://skepticalscience.com/empirical-evidence-for-co2-enhanced-greenhouse-effect-advanced.htm
Please note: the basic version of this rebuttal has been updated on Feb 14, 2023 and now includes an "at a glance“ section at the top. To learn more about these updates and how you can help with evaluating their effectiveness, please check out the accompanying blog post @
https://sks.to/at-a-glance
Thanks - the Skeptical Science Team.
Seems to me the main paradox between AGW and the 2nd law of thermo is not about radiation transfer but about attribution. The greenhouse effect says higher average CO2 over decades causes higher average temperatures. But how does a 2°C temperature rise over a century cause a 20°C heat wave for a week in Toronto? Humans have gotten a bit taller over the past century, but no one would consider that a satisfactory explanation of a village where everyone is 8 feet tall.
As summer arrives in the northen hemisphere, we're due for another season of news stories that claim such causality without asking whether it makes any sense. Was CO2 especially dense in Toronto that week?
One can obviously handwave that Earth is a heat engine not constrained by the 2nd law, or that climate is a chaotic system that does weird things we can't explain, but that undermines the claims we can attribute the heat wave to anything in particular. Or one can point to computer simulations where similar weird things happen, but that just relocates the paradox from Toronto to SimToronto.
Gootmud @1518... Probably the best way to understand this is to watch what happens over time with the shifting distribution of temperature events. Here is a great animated graph from the NASA Scientific Visualization Studio.
And here is a simple graphic explaining it as well.
Gootmud @1518:
The 2C rise does not cause the 20C heat spike, it turns an 18C heat spike into a 20C heat spike. Rob's diagram @1520 shows this shift in the overall distribution.
Rob's diagram also assumes that the spread around the mean remains constant. This may or may not be the case, and may vary locally. Another plausible scenario is that a location used to go +/-16C from it's mean, and now it goes +/-18C around its new mean that is +2C, so +20C (from the old mean) is the result of a 2C shift in the mean, and a +/-2C expansion around the mean. The +20C spike compares to a system that only saw +16C in the past.
Rob @1520...that looks like "climate does weird things" presented as a graph. It suggests heat waves are the result of some random process that we can't explain causally. We can only talk about the distribution, and we expect that as the mean shifts the tails will shift along with it. That contradicts the idea of attribution.
Gootmud @ 1522:
The diagram and explanation provide does not at all mean "some random process we can't explain causally". We can explain variation about the mean. It's called weather.
If you think that every single normally-distributed measurement is a purely random process, you need to think again.
Also note that this conversation is getting of the proper topic, which is the 2nd Law myth.
Gootmud @ 1522,
Hot weather tends to be associated with a high pressure system situated in a position to a) allow maximum insolation and b) to permit warm air advection. That's not "some random process". With global warming, in the synoptic situation I describe, it can be expected to be a bit hotter again. This should not be too difficult to visualise.