Falsifying the Atmospheric CO2 Greenhouse Effect: G. Gerlich & R.D. Tscheuschner

[sylas]

Just to let you know - I have read your posts and explanations with huge interest. It is probably more stupid to deny greenhouse effect existence than to exagerrate its influence on the surface temperature. The latter means messing with fine details of complicated equilibria, the former - ingoring basic physics and obvious facts.

Thanks, Borek! I appreciate it.

I'll almost certainly be writing more on global warming as well, as it turns up in other threads, but as you note, this is more subtle, and a lot more difficult. It means trying to see how all the various subtle interacting equilibria respond to changes in atmospheric composition. That's hard, but by no means outside the scope of science to investigate and test. A paper like the one cited here is merely a distraction from the genuinely interesting and difficult questions. It's unfortunate that many people are getting sidetracked by it, but c'est la vie. A forum like this is a great way to help sort out such matters.

The material here isn't even especially related to carbon dioxide. The largest absolute contribution to the atmospheric greenhouse effect is from water vapour, and this denial of the greenhouse effect in general makes no distinction between which gases are actually doing the absorption and emission of radiation.

 

[jostpuur]

Sylas, IMO you are writing too long posts. You know how mathematical proofs are better when they are shorter? The same thing with posts, IMO.

I thought that my jacket example would help understanding the mistake in the greenhouse effect denying deduction, but it seems that I forgot one of the main rules of the debating: "If somebody doesn't understand one simple thing, he probably doesn't understand other simple thing either."

And even more obviously, if somebody doesn't understand a simple thing, he is not understanding a complicated thing either.

IMO the things that should be said to adb are this comment from me

adb, you want to try to explain how the temperature of the Earth would not be affected by the amount of heat radiation the Earth radiates to the space? That's pretty difficult if you want to obey the first law of thermodynamics.

and this from Xnn

The 2nd Law of thermodynamics does not prohibit "back radiation". Instead, it prohibits the "back radiation" from being greater than the "forward radiation". In other words, it's possible for insulation to work and result in objects being warmer than they would be otherwise.

Excessively longer explanations only make it easier for adb to distract the discussion with his jokes about sunbathers and politics.

abd, I'm interested to know if you have anything to say to these comments from me and Xnn.

 

[sylas]

Sylas, IMO you are writing too long posts. You know how mathematical proofs are better when they are shorter? The same thing with posts, IMO.

I agree...

abd, I'm interested to know if you have anything to say to these comments from me and Xnn.

... and if you want to include any extracts from my admittedly overly long contributions; I'd single out the postscript to [post=2130349]msg #34[/post] on the direct measurement of atmospheric backradiation made back in 1954.

Cheers -- Sylas

 

[Mike Davis]

Seeig how the Green House effect is about equalizeing temperature and not warming. You know like a real Green House. I will leave you to your opinion.
I brought up the moon as the moon show our atmosphere ocean land Intrface equalizes the temperature by retricting warmth both incoming and outgoing. Due to the day night cycles and yearly cycles with axial tilt the Earth is never in equilebrium. The green house effect is Earth's attempt to achieve that. The sad thing is some people want to use what was a good example to show warming by distorting what is actually happening.
Go out and study a green house to see what it actually does.

 

[Skyhunter]

Mike Davis,

The down welling radiative flux from the atmosphere does indeed warm the surface. Most of the energy in the atmosphere originates from the surface. This is because the atmosphere is mostly transparent to short-wave radiation. The atmosphere absorbs about 67W/m² from the Sun, much of it is absorbed by O₃ in the stratosphere. On the other hand it absorbs about 452W/m² from the surface.

The surface emits the energy it absorbs from the Sun and most of this emission is absorbed by the atmosphere. The atmosphere radiates energy in all directions, therefore the atmosphere is most definitely warming the surface to the tune of about 324W/m², during the day and also during the night. And that is nearly twice the amount of energy that is received from the Sun.

 

[Xnn]

To be more precise, sunbathers should be grateful to the IPCC for inventing a fictitious way to stay warm without the sun ...

... but then again, the IPCC and its railway engineer chief, invent all sorts of nonsense to support their political propaganda.

adb;

I disagree; so I'll simply invite you to point out any nonsense in the IPCC's report on the physical science.

http://www.ipcc.ch/ipccreports/ar4-wg1.htm

 

[jostpuur]

adb;

I disagree; so I'll simply invite you to point out any nonsense in the IPCC's report on the physical science.

http://www.ipcc.ch/ipccreports/ar4-wg1.htm

This debate is unfair, because if somebody, on his or her own, (hypothetically) finds some nonsense in the IPCC's report, he or she will not be allowed to explain it here by the forum rules.

 

[sylas]

Seeig how the Green House effect is about equalizeing temperature and not warming. You know like a real Green House. I will leave you to your opinion.

Well, thanks anyhow. The great thing (in my opinion) about physics is that it is not just a matter of opinion. A productive discussion ends up actually sorting out mistaken ideas.

The greenhouse effect is about preventing the equalization of temperatures. A glass greenhouse does this with a glass barrier to stop convective heat transfer. An atmospheric greenhouse effect does this with gases opaque to radiant heat transfer. The physical mechanisms are quite different, but they both work by making it harder for heat to flow, which leads to an increased temperature difference across some barrier.

I brought up the moon as the moon show our atmosphere ocean land Intrface equalizes the temperature by retricting warmth both incoming and outgoing. Due to the day night cycles and yearly cycles with axial tilt the Earth is never in equilebrium. The green house effect is Earth's attempt to achieve that. The sad thing is some people want to use what was a good example to show warming by distorting what is actually happening.

Temperatures are equalized better when you increase the flow of heat energy, not restrict it. The way the ocean and atmosphere help equalize temperatures around the planet is by transporting heat around the surface. That's not the greenhouse effect.

The atmosphere is also opaque to thermal radiation. This is a different thing. It blocks outward radiant heat flow, but has much less impact on the inward heat flow. As a result, the Earth's surface temperature is NOT equalized with the radiation escaping into space. That's the greenhouse effect.

The Earth's surface is about 33C warmer than the radiation escaping into space. On the Moon, however, with no greenhouse effect, the surface temperature IS equalized with the radiation escaping into to space. The greenhouse effect PREVENTS that equalization.

Go out and study a green house to see what it actually does.

It works by making it harder for heat to flow from the glasshouse to the outside. The interior heats up because it is prevented from "equalizing" with cooler air outside.

Cheers – Sylas

 

[Skyhunter]

This debate is unfair, because if somebody, on his or her own, (hypothetically) finds some nonsense in the IPCC's report, he or she will not be allowed to explain it here by the forum rules.

Not at all.

Simply claiming the IPCC reports are nonsense without citing examples and supporting evidence is disallowed by forum rules. Citing specific examples and providing references in support of your argument is totally allowed.

If you know of any nonsense in the IPCC report please provide an example and evidence to support your assertion. Otherwise you are just making unfounded accusations.

 

[Mike Davis]

Mike Davis,

The down welling radiative flux from the atmosphere does indeed warm the surface. Most of the energy in the atmosphere originates from the surface. This is because the atmosphere is mostly transparent to short-wave radiation. The atmosphere absorbs about 67W/m² from the Sun, much of it is absorbed by O₃ in the stratosphere. On the other hand it absorbs about 452W/m² from the surface.

The surface emits the energy it absorbs from the Sun and most of this emission is absorbed by the atmosphere. The atmosphere radiates energy in all directions, therefore the atmosphere is most definitely warming the surface to the tune of about 324W/m², during the day and also during the night. And that is nearly twice the amount of energy that is received from the Sun.

So now you are claiming a perpetual energy as the atmosphere doubles the energy it receives from the surface or quadruples it and returns half back to the surface.
If this is true why are we useing hydrocarbons to provide energy. According to your theory we only need to capture all the extra energy being produced by the atmosphere.
I think that is called perpetual motion.

 

[sylas]

So now you are claiming a perpetual energy as the atmosphere doubles the energy it receives from the surface or quadruples it and returns half back to the surface.

Nope. Just look at the diagrams of how the greenhouse effect works, as supplied by adb. http://www.climateprediction.net/images/sci_images/ipcc_fig1-2.gif .

The atmosphere has the following averaged inputs in W/m²: 67 absorbed from the Sun, 350 absorbed from surface radiation, and 102 from convection+latent heat. Total, 519.

It radiates 324 back down to the surface (the backradiation) and emits another 195 into space. Total, 519. It's all balanced, as required by thermodynamics.

There's balance at the surface also. It absorbs 168 from the Sun, and 324 from the backradiation; which is a total of 492. The surface radiates 40 back direct to space, and 350 up into the atmosphere, plus 102 from convection+latent heat. Total, 492.

If the atmosphere was not involved, you'd have instead about 235 from space (the 168, plus 67 currently absorbed into the atmosphere) and then all that 235 would have to be radiated back out again. Which would leave the surface with a lower equilibrium temperature than it has with an atmosphere; more like what is found on the Moon.

addendum: Actually, it would be more. There's 342 coming in from space in total, and 198 received to the surface, with 30/198 reflection at the surface. Hence, without an atmosphere, the sunlight absorbed at the surface would probably be more like 342*168/198, or about 290, with all of that radiated back directly into space. And that would make things even more like what is found on the Moon.​

Cheers -- Sylas

 

[adb]

Back to our sunbather.
She gets: 324 beaming down from the atmosphere but only 168 beaming down from the sun.
Hold an umbrella over the sunbather to cast a shadow over her and block out the 168 and she immediately feels a chill.
Next hold a sheet over her (avoiding drafts) to block out that big 324 radiating from the atmosphere ... but she feels no change in heat !

 

[sylas]

Back to our sunbather.
She gets: 324 beaming down from the atmosphere but only 168 beaming down from the sun.

Yes. When she "sunbathes" all day and all night as well, summer and winter, rain and clear. Those figures are averages over the whole planet. And don't forget the heat coming up from the surface! That's important too.

Hold an umbrella over the sunbather to cast a shadow over her and block out the 168 and she immediately feels a chill.

Yes, she does. But she's not blocking out 168 if there's a shadow. If there's a shadow, then it must be daytime, under a clear sky. If she's sunbathing, its probably summer. So she's blocking out about 800 to 1000. I explained this for you you previously. Perhaps the post was too long...

Next hold a sheet over her (avoiding drafts) to block out that big 324 radiating from the atmosphere ... but she feels no change in heat !

You'd have to use something that blocked out the infrared but not the sun. Glass can do that. But then of course you are blocking the upward movement of air as well, which is going to trap convective heat like a glass greenhouse. AND you'll trap the larger infrared emissions coming up from the surface.

Cheers -- Sylas

 

[adb]

You'd have to use something that blocked out the infrared but not the sun. Glass can do that. But then of course you are blocking the upward movement of air as well, which is going to trap convective heat like a glass greenhouse. AND you'll trap the larger infrared emissions coming up from the surface.

She's already in the shade. We are now blocking out the major source of radiation as the next step ... from the atmosphere. Use a sheet of glass as you suggest if you wish.

She felt an instant (instant because radiation is being blocked) chill when the sun was blocked; but nothing when the radiation from the sky was blocked as well !

 

[jostpuur]

adb, can you explain, with your own words, what sylas explained in his/her post #48?

 

[sylas]

She's already in the shade. We are now blocking out the major source of radiation as the next step ... from the atmosphere. Use a sheet of glass as you suggest if you wish.

She felt an instant (instant because radiation is being blocked) chill when the sun was blocked; but nothing when the radiation from the sky was blocked as well !

Anything used to block radiation from the sky is going to reflect radiation from the surface. (Consequence of the second law.) She is in a bath of infrared radiation coming from all directions. There's a bit more coming up from the surface than back from the sky. It's thermal infrared radiation; and she's emitting it herself as well.

By the laws of thermodynamics, you are not going to be able to construct a barrier that will stop radiation getting in without also trapping inside the radiation that's already there. If you could do such a thing, you could use it to break the second law (think about it). Off hand I cannot think of any way to simply remove the infrared radiation. The glass room won't do it.

Cheers -- Sylas

 

[Borek]

So now you are claiming a perpetual energy as the atmosphere doubles the energy it receives from the surface or quadruples it and returns half back to the surface.
If this is true why are we useing hydrocarbons to provide energy. According to your theory we only need to capture all the extra energy being produced by the atmosphere.
I think that is called perpetual motion.

Mike, I don't know which one of you is right. What I know is that your "hit and run" strategy, compared with sylas efforts to explain in details his point of view, looks like if you were interested just in leaving impression that there is something wrong with sylas's explanation, no matter what the reality is.

 

[Mike Davis]

Borek:
Either I am reading what he is saying incorrectly (Which is possible). What he is saying is not what I have learned and I will leave it at that.

 

[Borek]

Borek:
Either I am reading what he is saying incorrectly (Which is possible). What he is saying is not what I have learned and I will leave it at that.

Can't you try to pinpoint why it is wrong in some more detailed manner?

 

[adb]

Anything used to block radiation from the sky is going to reflect radiation from the surface. (Consequence of the second law.) She is in a bath of infrared radiation coming from all directions. There's a bit more coming up from the surface than back from the sky. It's thermal infrared radiation; and she's emitting it herself as well.

It is not a "bath" of IR radiation. According to greenhouse, there is a hemispherical emitter (the sky) providing as much radiation to the top of the sunbather, as the sun was, before she was put in the shade.

Radiation shields are used everywhere. Your car exhaust is fitted with radiation shields. A tent acts as a radiation shield to prevent radiant heat loss to cold night skies for mountain climbers. Sit in front of an electric radiator ... feel the heat on your face ... then hold a sheet of paper in front of your face ... your face instantly feels cool because IR radiation is being blocked by the paper radiation shield.

By the laws of thermodynamics, you are not going to be able to construct a barrier that will stop radiation getting in without also trapping inside the radiation that's already there. If you could do such a thing, you could use it to break the second law (think about it). Off hand I cannot think of any way to simply remove the infrared radiation. The glass room won't do it.

The above examples show it is easy to block IR radiation. Adding additional isolated shields will further reduce radiation transmission between the radiation source and the cold body.

Of course all the above examples have IR radiation flowing from hot bodies to colder ones. I'm still mystified by how radiation shields are supposed to work (or not work) when you claim IR radiation traveling from a cold body (the sky) to our warm sunbather (now in the shade).

 

[sylas]

Borek:
Either I am reading what he is saying incorrectly (Which is possible). What he is saying is not what I have learned and I will leave it at that.

There's another possibility, which is that our differences come about in actually applying what we have both learned to a couple of specific situations.

We've both learned some basic physics, obviously. We both agree on laws like conservation of energy, and the second law of thermodynamics, and so on. We both know how to calculate the radiant energy coming from a blackbody. We both agree on the solar constant, and temperatures on the Moon, and so on. We both agree that an atmospheric greenhouse effect is different from a glass greenhouse effect. We both agree that the atmosphere helps to equalize temperatures around the Earth's surface.

In fact, when you really look at it, I think we agree on a lot more of the fundamentals than we disagree!

Is it going to possible to make a simple statement of any points of difference? I think if you make a deliberate effort to single out the points of real difference, you'll be able to resolve them, and you'll even find that you are not in fact "unlearning" much at all! All you really need is to apply what you've learned already just a little bit more accurately.

I'll propose two points where I think rapid progress should be possible.

(A) The association between greenhouse and equalization of temperatures

You have said that a greenhouse works by equalizing temperatures. Is that right? But were you ever actually taught that anywhere?

I think you may be mixing up two different but real effects, and simply labeling them the wrong way around.

The main process by which a glass greenhouse works is that it prevents hot air from rising out through the roof. Sunlight comes in, and heats up the floor, which in turn heats up the air above the floor. Now normally, hot air would rise up away from the floor, and cooler air from up higher in the atmosphere would be circulated back down again. It's why we have thermals and air circulation out in the open. Basically, there is a convective flow of heat up from the surface into the atmosphere caused by moving air masses. But in the greenhouse, the hot air is trapped near the floor. The glass roof prevents the processes by which temperatures are equalized between air at different heights above the ground, and results in a larger temperature difference between air in the green house, and in the atmosphere above it.

The circulation of air horizontally is also important for equalizing temperatures. This does not have much to do with a greenhouse. A greenhouse with no walls will continue to work, despite loss of heat out the sides; but a greenhouse with no roof can't even get started.

Horizontal circulation is important for equalizing temperatures around the planet. Winds tend to blow from a hot high pressure area into a cooler low pressure area. You see this on daily weather maps. So we agree that the atmosphere helps equalize temperatures around the Earth. The thing is... that is not the greenhouse effect! I suspect you've just associated the wrong label with the phenomenon. The greenhouse (glass greenhouse) prevents circulation (mainly vertical circulation, and also horizontal if you have walls). The equalizing effect around the Earth is caused by circulation.

As for the atmospheric greenhouse effect, this is not the same as a glass greenhouse. What they have in common is that they both work by inhibiting movement of heat up from the surface. But they do it by very different processes. The atmospheric greenhouse works by blocking radiant heat flow from moving up into space. The glass greenhouse works by blocking convective heat from moving up into the atmosphere.

(B) Perpetual motion

You've suggested that the atmospheric greenhouse effect is described as a kind of perpetual motion machine.

In this case, we all agree that energy is conserved, and you can't get a continuous flow, or circulation, without a continuous source of energy from somewhere. Of course, the energy coming in from the sun drives all kinds of continuous cycles. The water cycle, with water circulating continuously up into the atmosphere and back down to the surface, through rivers to the sea, is basically "perpetual", for as long as the Sun shines on the ocean, and we can use this to drive, for example, a hydroelectric power station.

We've spoken of atmospheric "backradiation"; which is a continuous flow of radiant heat from the atmosphere back down to the surface. You've apparently taken this as a "perpetual motion" in violation of the first law, since it is being driven from the surface.

But in this case, the problem goes away as soon as we take into account the flow of heat in both direction; just like we explain why the apparently endless flow of water from rivers doesn't overflow the ocean. There's another flow of water in reverse to consider.

In the greenhouse effect, there is a larger flow of radiant heat up from the surface than there is backradiation from the atmosphere down to the surface. When you include also the energy exchange from the atmosphere out into space, it all balances. The atmosphere receives exactly as much energy as it emits. The flow of energy through the atmosphere proceeds mainly from the surface and out into space, with a balance between the total energy in and total energy out, and this flow will continue as long as the Sun shines.

I'm quite sure you've never actually been taught that there's a perpetual motion machine in the atmosphere. I think you have picked this up from incomplete descriptions, which don't attempt a complete account of all the energy flows involved. If you take a full description of the energy flows as given in energy balance diagrams for sunlight and the atmosphere, it's quite clear that there's no perpetual motion machine involved.

-------

If there are other points where you think I am saying something different from what you have learned, just try to spell it out as carefully as you can, identifying where the difference arises. I'm a pretty friendly chap, and I won't abuse you when I think I can see a point of error. I'll just point it out, and if you find real problems with my descriptions I'll take them on board gratefully. Getting things right is a win/win situation.

One difficulty is that discussion can be confused by use of poor quality reference material. If you use conventional reference books on Earth science, or climate, or thermodynamics, or astronomy, you are pretty safe for the most part. Sometimes a description can be incomplete or poorly expressed, but you won't get errors at the level of violating fundamental laws of physics. On the other hand, there are some webpages or articles that are completely wrong, even outright pseudoscience. Sometimes they come from individuals who ought to know better, and who have legitimate scientific credentials (usually exaggerated). Usually they'll mix in a bit of real physics with some completely counter factual claims or bad errors in analysis, in such a way that it can look superficially plausible. From your posts, I think you have enough physics background to engage a discussion of such articles on their own merits, and that you won't actually be "unlearning" anything in the process. Just clearing up how to apply what you know already.

Good luck with it. Don't give up! Cheers -- Sylas

 

[adb]

We've spoken of atmospheric "backradiation"; which is a continuous flow of radiant heat from the atmosphere back down to the surface.

We're both intelligent people and I'd like to tie things down. I don't work in the industry and have nothing to gain whether greenhouse exists or not.

No question that real greenhouses have no analogy with the atmosphere.

The above is the crux on which I am trying to understand your thinking. The amount of IR "back radiation" from the atmosphere is claimed by greenhouse theory to be comparable to the total radiation from the sun.

Radiation from the atmosphere or anywhere else travels in straight lines. Our sunbather will experience downward radiation from the sun as well claimed downward radiation from the hemispherical sky source. If the sunbather is shielded from the sun (ie placed in shadow), she will feel it immediately, as expected. However, there is no effect on subsequently shielding from the second source, the sky.

We can only conclude that any "back radiation" is insignificant.

This is as expected. Where temperature differences are small, heat transfer is primarily by convection and conduction. Radiation becomes more significant as temperature differences increase.

It is also interesting that you agree that greenhouse does not have a significant effect on atmospheric temperature profiles. This agrees with what Thieme suggests.

 

[sylas]

It is not a "bath" of IR radiation. According to greenhouse, there is a hemispherical emitter (the sky) providing as much radiation to the top of the sunbather, as the sun was, before she was put in the shade.

The notion of a "bath" of radiation is standard, and it applies here because there are large flows in both directions. Any IR detector is going to see radiation coming from all sides, and that is called a bath of radiation.

If you want to know what occurs according to the greenhouse, use the description of the greenhouse you've provided already. Here it is again, inserted visually.
http://www.climateprediction.net/images/sci_images/ipcc_fig1-2.gif

(Source: http://www.climateprediction.net/content/basic-climate-science at climateprediction.net.)​

Remember, that is averaged over night and day, summer and winter, poles and equator, clear and cloudy. If you want to get concrete numbers for the sunbather, you'll have to adjust the numbers for some typical daylight sunbathing.

OK. Let's do some physics! I'll welcome corrections to my numbers; but they have to stay consistent with basic physics.

You can skip over this indented section at first reading. It's only here because I want to use more realistic daytime numbers. The real answer to the puzzle is simply that you can't block the backradiation without trapping the upwards radiation also.

We're looking at transfers at the beach. The 198 W/m² (168+30) sunlight coming down will be roughly 1000 W/m². This is a scaled up by four for the sun being overhead; plus a bit more for clear sky and reduced atmospheric reflection. This corresponds well to measurements of summer sunlight at midday on a clear day. The ground reflection scales the same way, up from 30 to 150.

The surface radiation upwards relates to ground temperature. 390, by Stefan-Boltzmann, corresponds to about 15C. But in the day, when sunbathing, it will be more like 30C, which would be radiation of about 480. To stick with rough figures, I'll use 500 W/m² upwards, which is a surface temperature of 33C (or 92F if you like Fahrenheit). This also has the benefit of keeping temperatures close to body skin temperature; because we want to ignore complications of body heat.

The radiation down from the atmosphere tends to remain roughly in proportion to surface air temperature. (See the paper I cited previously on measurements of backradiation.) So we can scale the 324 backradiation to roughly 400.

What's left? 850 in from the sun, 400 in from the atmosphere, and 500 out from the surface; we have 750 W/m² unaccounted for. This will be divided between absorbed energy heating up the surface (which will be given back again at night time, so it doesn't show up in the diagram) plus convection and latent heat from the surface (which is 102, on average, in the diagram).

Grabbing the back of an envelope: air has heat capacity of about 1000 J/kg/K. At night, you can get an "inversion", or reversal of the atmospheric temperature gradient, up to about 500m or so. This is the air giving heat back to the surface at night. Density is about 1.2 kg/m^3. Hence the upper 500m of the atmosphere is about 6e5 J/K/m^2. Assuming a temperature difference of about 20 degrees from night to day, we get about 1.2e7 J/m^2 stored energy difference. Assuming a transfer of this over 8 hours, or about 2.9e4 seconds, I get a bit over 400 W/m² flux. That sounds plausible as about the flux of excess energy up into the daytime sky to heat the air, storing energy that is given back at night. So in the daytime, there's about 400 W/m² energy actually being soaked up in the air. The 350 still unaccounted for needs to show up as convection and latent heat… and this looks a credible value also, because the average over night and day is given in the diagram as 102. If anyone has actual measurements of daytime energy balance, I'd love to see them for comparison with this guesstimate for division of the remaining 750.

Final numbers I propose for the midday sunbather, all in W/m².

• 1000 downwards as sunlight.
• 400 downwards as infrared backradiation.
• 150 upwards as reflected sunlight.
• 500 upwards as infrared surface emission.
• 350 upwards as convection and special heat.
• 400 excess being absorbed to heat up the air.

​

OK. The real question is, can't we make the sunbather feel cold by shielding her from the 400 Wm² backradiation? The answer is… no, because there's no physical way to remove that without trapping the radiation she emits herself.

Radiation shields are used everywhere. Your car exhaust is fitted with radiation shields.

Right; and this is useful, because the exhaust pipe is so much hotter than the air outside. What you CAN'T do is make a shield that keeps all the thermal heat inside at the exhaust pipe, but still let's in heat from the other direction. If you could make such a shield, you could take a warm brick, which is cooler than the exhaust pipe, put it next to the radiation shield, and have heat from the brick flowing in through the barrier, while heat from the exhaust pipe was prevented from flowing the other way. You could use such a shield to heat up a hot object from a colder one, in violation of the second law.

As I said previously, we CAN block infrared radiation with glass. It does make a very good shield for IR radiation. So what happens if we put a glass sheet over the sunbather?

Sure enough, we've blocked out the 400 W/m² atmospheric backradiation. But the sunbather, who is at a nice comfortable 33C, is radiating herself, upwards, at 500 W/m²! And we've trapped that inside! She gets HOTTER as a result. You simply cannot block out the 400 W/m² down without also blocking the 500 W/m² going up.

All your examples of cooling something by blocking radiation work because they are shielding you from something hotter than you are. But in the greenhouse effect, the surface (and the sunbather) is hotter than the atmosphere. If you put in a block, you're actually making it harder for the sunbather to shed the thermal radiation she needs to emit to keep cool.

It's the same problem in all these discussions. All the attempts to portray greenhouse, or backradiation, as some kind of violation of thermodynamics or perpetual motion are ignoring the energy flows in the other direction.

The paper by G&T is just the same. It may look superficially plausible, but it's not going to take in anyone who works with atmospheric thermodynamics for a second. If they were first year physics students, we'd simply say that they need to learn a bit more about basic physics. But these clowns have had their errors pointed out to them at length, for years. The paper came out ages ago in arxiv, and the errors were identified quickly and publicly. Recently, they actually managed to get their paper into a small mainstream journal, bypassing the normal technical review by appearing in an "invited" category. Whichever editors made the invitation have slipped up badly, and G&T are plainly pseudoscientific cranks – on this topic, at least. Neither one of them has any publication record in climate or basic thermodynamics, nor indeed do they have much of a publication record at all. They are very minor players in real science, with a sideline in gibberish. It's not unheard of, and there are plenty of other isolated examples in other fields of science. From time to time such individuals do manage to get some of their stuff into the scientific literature, because editors are not infallible.

------

And also, in response to your next post:

We're both intelligent people and I'd like to tie things down. I don't work in the industry and have nothing to gain whether greenhouse exists or not.

Thanks muchly; I feel the same way. I'll add that there's no animosity between us either, as far as I am concerned, and I'm sure you feel the same. We're just having an "energetic" discussion of points of physics. It's fun, and hopefully it's educational. I expect we'll be able to tie most of it down. The point about radiation shields working in both directions will be crucial.

… It is also interesting that you agree that greenhouse does not have a significant effect on atmospheric temperature profiles. This agrees with what Thieme suggests.

Sure. Thieme's errors – and his essay is full of them – are on other matters. His comments on convection are merely a distracting non-sequitur. He might as well point out that greenhouse has no effect on atmospheric scattering of light, and the consequent colour of the sky.

Cheers -- Sylas

 

[adb]

OK. The real question is, can't we make the sunbather feel cold by shielding her from the 400 Wm² backradiation? The answer is… no, because there's no physical way to remove that without trapping the radiation she emits herself.

How about reflective foil, blackened on the sunbather side ?

I'm an engineer, not a physicist ... I still find the concept of heat traveling from cold bodies to hot bodies difficult to get my head around.

 

[sylas]

How about reflective foil, blackened on the sunbather side ?

It makes no difference. If it is "black" then it is absorbing and emitting thermal radiation. Think of a thermodynamic "blackbody". There's still energy coming out. It's just the that all the energy is emitted as thermal radiation, with a spectrum depending on temperature. It can't just soak up all the thermal radiation and give nothing back, unless it is initially cooled to absolute zero.

If you use a super cold glass shield you could just soak up all the IR radiation, and emit nothing in return, and still let though the sunlight.

With a supercold shield, you would indeed cool down the sunbather. But it's not because of "cold" flowing from the shield to the sunbather.

Add in a second transparent vacuum shield to prevent any loss into the cold shield by conduction, or (equivalently) to trap a small layer of warm air around the sunbather. She's still going to feel significantly cooler as a result. It's not because she's actually touching anything cold; there's still a layer of warm air around her trapped by the vacuum shield.

Of course, this is far from equilibrium. The cold shield will soon heat up again, unless you apply refrigeration. But the immediate effect of moving the cold shield into place should have the effect of soaking up the downwards flux without reflecting any of the upwards flux, which is what we want. When I previously said this was impossible, I should have said it was impossible at equilibrium.

I'm an engineer, not a physicist ... I still find the concept of heat traveling from cold bodies to hot bodies difficult to get my head around.

Think in terms of a warm brick next to a hot brick. From above the two bricks, you can feel heat coming from each one. There's more coming from the hot one. They are both radiating in all directions. Drop a cold slab of insulating material between the bricks. Both sides will warm up; and the side facing the hotter brick will warm up more quickly.

Evidently, there's heat from the hot brick moving towards the warm brick, and also visa versa.

Cheers -- Sylas

 

[adb]

Instead of a sunbather, suppose we have a box made of thin IR transparent material. The box is evacuated and has a thick insulated base. It is placed so that the top of the base can only view the sky. A shade is positioned some distance away to block the sun. Only 400 watts of back radiation should be entering the box. We place a small beaker of water in the box and measure the time it takes to heat via back radiation.

Unfortunately the walls of the box will be at ambient temperature and will radiate to the beaker.

Somehow this setup seems similar to a pyranometer measuring the (low) temperature of the sky. If so, the water would cool rather than heat.

Is there any way that the 400 watts back radiation can be verified experimentally ?

 

[sylas]

Is there any way that the 400 watts back radiation can be verified experimentally ?

Yes, there is. It's quite routine, and was first done over 50 years ago. I previously cited Stern, S.C., and F. Schwartzmann, 1954: An Infrared Detector For Measurement Of The Back Radiation From The Sky. J. Atmos. Sci., 11, 121–129. (online). I commented further in [post=2128781]msg #73[/post] in the other thread.

What the instrument actually detects directly is the difference between forward and backradiation. But because we know the forward radiation (using the blackbody relation), the backradiation can be obtained directly. I don't know much at first hand about the workings of these instruments, but here are the wikipedia links. A pyranometer is for measuring solar irradiance, and a pyrgeometer is for measuring the IR backradiation, by measuring the difference between backradiation and the warmer surface temperature.

Cheers -- Sylas

 

[adb]

Instruments such as pyrometers bring the discussion full circle. They focus radiation from an object onto a thermocouple or an FPA array to determine its temperature by comparison to some standard, based on the amount of radiation it is emitting or absorbing. We point it at the sky and measure a temperature of say -40, we point it at the ground and measure a temperature of 20. From these values we can calculate the heat flow from the hot to the cold body taking into account radiation, view factors, transparency etc; convection; conduction; and latent heat.

 

[sylas]

I made a dumb mistake in giving numbers for daytime energy balance. It has pretty much no effect on all the discussions of temperature and radiation; but I did not need to worry about the heat capacity term... and I'd like to get the correction on record for posterity. Here's what I said previously:

We're looking at transfers at the beach. [...]

What's left? 850 in from the sun, 400 in from the atmosphere, and 500 out from the surface; we have 750 W/m² unaccounted for. This will be divided between absorbed energy heating up the surface (which will be given back again at night time, so it doesn't show up in the diagram) plus convection and latent heat from the surface (which is 102, on average, in the diagram).

Grabbing the back of an envelope: air has heat capacity of about 1000 J/kg/K. At night, you can get an "inversion", or reversal of the atmospheric temperature gradient, up to about 500m or so. [...]
​

Now actually, if I am just considering energy flow at the beach, energy going to heat up the lower part of the atmosphere is simply a part of the upwards convection and latent heat. There's a little bit heating the ground that I could consider, I think, but it's small and can be ignored at this approximate level.

Hence what I should have said is simply that the upwards convection and latent heat processes would be about 750 W/m² at midday.

The average upwards convection and latent heat is given in the diagram, but since we are considering the sun is overhead, this is effectively a tropical summer, and so the geometric ratio for mean input solar radiation should be pi, rather than 4, at this latitude. The average convection is hence probably closer to 160 than the 100 shown for a global average. If the daytime peak is 750, then the nighttime minimum under the night inversion is probably about -430; or a net flow of special heat from the atmosphere back to the surface.

I'm still curious to know if my estimated flow of special heat fits any published estimates.

The radiant energy flows I am much more confident about. So my revised estimates for an example midday sunbather, all in W/m².

• 1000 downwards as sunlight.
• 400 downwards as infrared backradiation.
• 150 upwards as reflected sunlight.
• 500 upwards as infrared surface emission.
• 750 upwards as convection and special heat.

The paper I cited for measurement of backradiation has numbers which I previously quoted in [post=2130349]msg #34[/post], measured from Frederick, Maryland. Night time backradiation ranged from 206 to 312; daytime ranged from 314 to 405. Interpreted as a temperature of the sky, as seen at the surface, this would be a night time temperature from -28C to -1C, and a daytime temperature from -0.5 to 17.5. Even the -28C is surprising to me. It may be an outlier. A sky temperature of -40C would be really hard to understand, I think.


Cheers -- Sylas

 

[Phrak]

http://www.climateprediction.net/images/sci_images/ipcc_fig1-2.gif

(Source: http://www.climateprediction.net/content/basic-climate-science at climateprediction.net.)​

That's a very nice diagram, sylas.

My attention is drawn to the gray layer called Greenhouse Gases with some sort of unlabeled cloud in it. There must be 7 items running in and out of it. If you were to take a wild guess, how much of this grayed-in area is due to the greenhouse gas, water vapor?

 

[Borek]

What are 165/30 emitted by atmosphere? Why split?

 

[sylas]

That's a very nice diagram, sylas.

My attention is drawn to the gray layer called Greenhouse Gases with some sort of unlabeled cloud in it. There must be 7 items running in and out of it. If you were to take a wild guess, how much of this grayed-in area is due to water vapor?

Including cloud as water vapour, I would guess that something from 65% to 85% of the absorption is to water vapour. Water is the most important part of the net greenhouse effect on Earth.

Just as a caution, however, it's not the the percentage absorption that really matters. This gets rapidly very technical, but basically, you can think of the consequences for temperature as following from the altitude at which radiant heat can escape to space, rather than simply the fraction of radiation absorbed.

And Borek, I believe the split is between thermal emissions from the atmosphere, and thermal emissions from cloud. I think.

Cheers -- Sylas

PS. Credit goes to adp for this diagram. He was the one who found it for us and posted the links to the thread. I just supplied some img tags to his link.

 

[Phrak]

Including cloud as water vapour, I would guess that something from 65% to 85% of the absorption is to water vapour. Water is the most important part of the net greenhouse effect on Earth.

With 20 percent of the solar insolation absorbed by greenhouse gases, water vapor contributes a lot. It must vary -99 to +200% or so, from place to place, day to day, year to year, and century to century. I imagine it's as predictable as next week's weather.

Any toy model of global weather prediction would be useless if the propagated error of the input data should become larger than the predicted change, wouldn't it?

Just as a caution, however, it's not the the percentage absorption that really matters. This gets rapidly very technical, but basically, you can think of the consequences for temperature as following from the altitude at which radiant heat can escape to space, rather than simply the fraction of radiation absorbed.

Go ahead; get technical. This is a physics forum.

 

[Count Iblis]

It must vary -99 to +200% or so, from place to place, day to day, year to year, and century to century. I imagine it's as predictable as next week's weather.

The average effect does not fluctuate much, otherwise the Earth's climate would be very unstable.

 

[Phrak]

The average effect does not fluctuate much, otherwise the Earth's climate would be very unstable.

How long is the coast line of California? I'm sorry, but that's not a meaningful statement. 'Average' means nothing without a timescale.