Naked Science Forum
Life Sciences => The Environment => Topic started by: Leitwolf on 13/06/2018 01:32:44
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Let me skip the explanation of the GHE, it should be well known. I could point out to a couple of major and decisive flaws in the original theory, but that shall not be the scope of this posting. No, rather I want to take a look at the solid evidence for the GHE.
The GHE is observable and measureable. There are essentially two approaches to that, one is to look up the sky and detect "back radiation" and the other one is looking down from space, measuring long wafe infra red (LWIR). Both approaches show and confirm how greenhouse gases (GHG) interfere with surface emitted LWIR.
Back radiation is typically measured with pyrgeometers, which I consider somewhat untrustworthy. The problem is, pyrgeometers will react to changes in LWIR, but they are very hard to calibrate in case you are not knowing the absolute amount of LWIR. The problem is solved by calibrating pyrgeometers with other pyrgeometers, so that they give similar results. However, that brings up the question how the first pyrgeometer was calibrated. I am afraid it is more a model based measurement, than a fact based.
Anyhow, there is back radiation and thermographic cameras support that claim. Thermographic cameras detect radiation at certain wave lengths where GHGs do not absorb that radiation, also known as the "atmospheric window" (AW). That works so well, that you can even look at the moon, and it will give are relatively accurate temperature for its surface.
Let me provide two examples for such recordings, which offer a lot of interesting details if you take a closer look.
Right now I only want to direct your attention to the clear sky. It appears very cold, like -35 to -40°C, while the surface temperature was also relatively low (~10°C). Yet that means there will be a lot of radiation coming down from the clear sky. Relative that would be like (233K/283K)^4 = 46% of the amount of LWIR emitted by the surface. This result is quite consistent with other recordings of that kind, taken at different temperatures, and the GHE model itself, if you will.
The important point however is, this LWIR emitted by GHGs is also emitted in AW. Meaning that GHGs emit LWIR but hardly absorb LWIR at these wave lengths.
The other fine piece of evidence is provided by NASA. They have satellites looking onto Earth which measure outgoing LWIR. Now they not just measure the total amount, but also give us the spectrum of these emissions. What we can see very clearly, is how GHGs interfere with these emissions. You can see the wave bands where CO2 or vapour absorb LWIR, and accordingly less radiation goes into space. By hindering LWIR emissions that way GHGs warm the planet, so the story goes. Also we can see how in the range of the AW, there is almost exactly as much LWIR going outward as the theory suggests. At wave numbers from 800 to 1250 GHGs (with the exception of ozone) are very transparent to LWIR, and so the blue area mingles with the red line, which represents the theoretical emissions from the surface.
https://www.giss.nasa.gov/research/briefs/schmidt_05/curve_s.gif
So far everything makes perfect sense, and all the evidence fully supports the theory of the GHE. Keep in mind that not even "climate sceptics" are seriously doubting the existence of the GHE. So by all means, there is absolute consensus on this subject. And by looking at the evidence, it all supports the theory. So why did I choose this headline?
Well, you probably have not mentioned it, but there is a huge and disastrous mistake in all that. It is not just a mistake, a minor flaw, but a total annihilation of the GHE, well concealed in what I just said.
It is all about the AW and the amount of radiation measured by NASA. In that range the satellite is measuring just or almost as much LWIR as the surface should emit in theory. That is no surpise, as we know the atmosphere is perfectly transparent there. The problem is that we know, that GHGs are also emitting a lot of LWIR in that range. If you look down onto Earth, you will receive almost 100% of LWIR emitted by the surface, plus LWIR emitted by GHGs, which might add another 50%. So the satellite should be able to measure almost 1 1/2 times as much radiation, as the surface alone would emit in theory.
Rather than a perfect match, now we have a perfect missmatch. I am not even sure if these data have been measured, or if they were simply manufactured. For the sake of the argument let as assume they are legitimate, because that has some serious consequences.
Once we understand, that measured LWIR in the AW must be representing LWIR emitted from the surface plus the LWIR emitted by GHGs, and that likely in a relation of 2:1, we can draw some mighty logical conclusions.
1. The surface itself must emit far less than 390W/m2. That is no surprise, as specific emissivity is not 1 (like a perfect black body), but rather just 0.92. So the surface itself would only emit like 360W/m2, which destroys one of the foundations of the GHE theory. Next to it, clouds will sharply decrease these emissions. Just have a look at the linked video above to see how the moon drops from 400K to below 100K just because thin clouds cover it shortly.
(Correction: the scale in that first video - which we do not really see - is certainly not in K)
2. It is logical and obvious to conclude, that the surface plus clouds will emit far less than 300W/m2, likely something in the range of 240W/m2 only. Only then the relation works. Only then we can explain, why in the AW the LWIR from surface and GHGs amount to sharply less than what the surface itself should emit.
3. With the surface covered by clouds emitting just as little LWIR, there is absolutely no scope for GHGs, which of course carry the wrong name. CO2 and the others are just gases, no greenhouse related to it.
4. We start to understand how they are perfectly climate neutral, despite interfering with LWIR. Yes, so called "GHGs" do absorb LWIR and thus reduce the amount of LWIR going from the surface into space. But at the same time, they emit LWIR themselves, thereby cooling Earth. What is getting absorbed by so called "GHGs" at certain wave lengths, is being emitted additionally at other wave lengths. Reading the balance sheet correctly, the net effect must be more or less zero.
These are the only logical conclusions in line with the named observations, which ironically were meant to prove the GHE.
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In summary, you seem to be saying that clouds dominate the radiative heat transfer to and from the surface of the earth. That is obvious to anyone who has ever stood underneath one, but it seems to have escaped the notice of so-called climate scientists who persist in counting fleas like CO2 and CH4 whilst studiously ignoring the H2O elephant they are riding on. Thus leading to statements like "global warming has altered the rainfall pattern" when it is obvious that the rainfall pattern is what determines global temperature.
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Once we understand, that measured LWIR in the AW must be representing LWIR emitted from the surface plus the LWIR emitted by GHGs,
There's a law of physics* that says that things that don't absorb at a given wavelength don't emit at that wavelength.
The Atmospheric window is, more or less by definition, a region where the GHG don't absorb.
So it is also a window where they don't emit.
So this term "plus the LWIR emitted by GHGs," is zero.
Shocking as it may seem, the scientists who practically all say that the greenhouse effect is real, and man-made, are good at this sort of thing and won't have made obvious mistakes like yours.
*
https://en.wikipedia.org/wiki/Kirchhoff%27s_law_of_thermal_radiation
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So if a CO2 molecule absorbs outgoing radiation at x nanometers, it also emits at x nanometers, so has no net effect on amospheric temperature. Doesn't smell right to me.
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So if a CO2 molecule absorbs outgoing radiation at x nanometers, it also emits at x nanometers,
This bit is essentially correct. (there are several complications having to do with non-radiative energy transfer, rotational-vibrational coupling, and doppler shifts, but these wrinkles don't change the overall effect)
so has no net effect on amospheric temperature. Doesn't smell right to me.
This bit isn't correct, and shouldn't smell right :)
The key here is that the direction of the emitted light is essentially random. This means that any EM of the appropriate frequency can't have a direct path from the ground our to space. Instead, it must take a random walk in which the mean free path is determined by the molar extinction coefficient of the absorber and the concentration of the absorber--and since the molar extinction coefficient is fixed, increasing concentrations of absorbers lead to shorter mean free paths, and increasing delays before the EM leaves the atmosphere.
To maintain thermal equilibrium, the rate at which energy leaves the Earth must be the same as the rate at which energy comes in (which is largely constant). So if it takes longer for a packet of IR energy to get from the ground to space, to maintain this same rate of energy going out, there must be more packets of IR energy in transit simultaneously. This is effectively the same as saying that the atmosphere must be hotter (at least where the increase photon density is). (ie it does have an effect on atmospheric temperature)
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@Bored chemist
You have a valid point to it. Indeed Kirchhoffs law is telling emissivity = absorptivity (at any given wave length). I wish that principle was a way more considered by the GHE-theory in the first place. Rather the GHE is based on the unreasonable and simply wrong assumption that absorptivity of Earth was about 0.7, while emissivity was a straight 1. Only then you get to (((0.7/1.0)*342)/5.67e-8) ^0.25 = 255K.
This basic and pointless assumption, that absorptivity was always significantly lower than 1, but emissivity was always exactly 1, will consequently always lead to a calculative "GHE" which does not and can not exist. Applying this approach to the moon, you will get a GHE, applying it to Ceres, it has a GHE, applying it to Enceladus, it even has a massive GHE. All these objects do not have any atmosphere btw. ;)
Emissivity of Earth is not 1. But what is it? You can actually calculate the emissivity of water, which covers like 70% of Earth, with the help of Fresnell equations. According to my own calculation with n2 = 1.27, allowing for the cosine law, the hemispheric(!) emissivity of water must be 0.94. However, I will be straight on that too. If I make a specific and simple mistake, the result is only 0.91. Why do I mention that? Because a well reknown physics text book (Baehr, Stephan - Wärme- und Stoffübertragung) is claiming just that figure. I think I am right and they are wrong, but in case it is the opposite, emissivity is even lower. You can see that figure in german wikipedia..
https://de.wikipedia.org/wiki/Emissionsgrad (https://de.wikipedia.org/wiki/Emissionsgrad)
Land has even lower emissivities, especially arid land like deserts, which cover around 10% of the planet. Without going through the details hereto, one could estimate an average surface emissivity of about 0.92., which I named already.
However the most significant part which drops absorptivity to only 0.7 are clouds. They reflect a huge junk of solar radiation right back into space. Without the so called "cloud albedo" effect absoptivity was well above 0.9. The "trick" now is to say, clouds are reducing absorptivity as they are counted towards the surface. But they have no impact at all on emissivity, because they are not surface!?
I am not joking, this is real. But it gets even worse. Now the positive forcing of clouds is just another greenhouse "factor", competing with other GHGs in that role. Keep in mind the GHE has a size of only about 150W/m2 (=390-240). 30W/m2 originate from putting emissivity = 1 rather than a realistic 0.92. Clouds are attributed with only 30W/m2, so that a large GHE remains due to GHGs.
The GHE theory runs into huge contradictions on this. According to the IPCC the explicit cloud forcing was 50W/m2 for the albedo effect vs. a 30W/m2 of downward emissions, resulting in a net cooling effect of 20W/m2. Bear that in mind, when you look at this NOAA chart..
(https://www.weather.gov/images/jetstream/atmos/energy_balance.jpg)
Accordingly clouds would reflect 23% of solar radiation (342W/m2) and emit another 9% into space, a negative forcing of 110W/m2 in total. This is the same model, but two different perspectives, which are completely inconsistent. How comes?
The NOAA chart is likely correct on this specific subject. The problem is, you will not get from 110W/m2 to only 30W/m2, without suggesting a massive net negative cloud forcing of 80W/m2. I could well demonstrate how cloud forcing is not negative at all, as empiric data show temperatures are always higher with clouds as opposed to clear skys. That is specifically true for low clouds in the tropics, which are the kind of clouds meant to have the strongest net cooling effect.
Anyhow, you can argue a GHE with saying clouds provided a 110W/m2 in cooling, another 110W/m2 in heating, a net effect of zero. The heating 110W/m2 would explain almost all of the GHE, with only 40W/m2 remaining, of which another 30W/m2 originating from the emissivity error. For that reason the IPCC skips the upward emissions, cuts the albedo effect from 79W/m2 to a mere 50W/m2, and introduces a net cooling effect of 20W/m2. GHE rescued, Earth doomed..
Positive cloud forcing however is more likely in the three digit region. Look up the cloud video I posted above. The surface temperature was up to 10°C (I checked the weather records) at time of the recording. Clouds appear to have about the same temperature, which means low, opaque clouds provide just or almost as much LWIR as the surface does. If the surface did emit like 390W/m2, you only need to guess a reasonable percentage for average cloud cover, and you can roughly estimate positive cloud forcing. With a 30% average cover you would get to 0.3 * 390 = 117W/m2. That is all of the GHE. On the other side .. 30W/m2? No way!
Let us get back to the original question. Do GHGs emit where they absorb? I do not know! As I interpret it, they will emit at a wide spectrum, but we can play it through. If GHGs emitted specifically where they absorb and most LWIR going outward (look up the NOAA chart, which says 49% of 342 = 168W/m2, or 70% of total LWIR going outward), with only a tiny atmospheric window (12% or 41W/m2), then it is still not working.
Then, TOA, we would have massive amounts of LWIR where for instance CO2 absorbs BUT also emits. Rather than less LWIR at this absorption wave lengths, we should be seeing just as much, or even more LWIR. So, I am afraid, it is just another iteration of argument to save the theory, short lived as the all the others once we check for logical consistency.
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So if a CO2 molecule absorbs outgoing radiation at x nanometers, it also emits at x nanometers, so has no net effect on amospheric temperature. Doesn't smell right to me.
What?
Where did you get that from?
There's no logical reason for
"no net effect on amospheric temperature"
to be linked to
"if a CO2 molecule absorbs outgoing radiation at x nanometers, it also emits at x nanometers".
One does not imply the other.
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Only then you get to (((0.7/1.0)*342)/5.67e-8) ^0.25 = 255K.
Where's that from?
255K is a lot colder than the freezing point of water, so it's clearly colder than the surface of most of the Earth.
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According to Wikipedia, and it concurs with my recollection of long-ago geology lessons:
An estimated 45 to 90 percent of the heat escaping from the Earth originates from radioactive decay of elements mainly located in the mantle.
Some of the rest is "primordial" heat from the molten core.
So the planet is mostly warm because it is....mostly warm!
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Only then you get to (((0.7/1.0)*342)/5.67e-8) ^0.25 = 255K.
Where's that from?
255K is a lot colder than the freezing point of water, so it's clearly colder than the surface of most of the Earth.
That is the GHE in its essence. Let me explain it. You take the solar radiation, which is about 1368W/m2 at the position of Earth. The surface of Earth, as it is a sphere, is four times the area of a disc with the same radius. So .. 1368 / 4 = 342. To determine what amount of radiation a perfect black body emits at any temperature we use the Stephan Boltzmann constant 5.67e-8. That goes like 288^4 * 5.67e-8 = 390W/m2. Or it goes the opposite way, where have the amount of radiation, and want to know temprature that will yield. With 342W/m2 that would be (342/5.67e-8)^0.25 = 278.7K.
Finally we may allow for the deviation from a perfect black body with regard to absorptivity and emissivity. However, to argue the GHE, only the deviation on absorptivity is allowed for, not the one on emissivity. Absorptivity = 1 - albedo (with albedo ~0.3) by the way. So ususally that formula above would look like (((1 - 0.3)*342)/5.67e-8) ^0.25 = 255K. As 1 - 0.3 = 0.7 / 1 that will not make any difference. However I strongly prefer the latter version, as it reminds us, that it is about relation of absorptivity to emissivity, and emissivity is explicitly (but wrongly) put equal 1.
The GHE itself, just to mention it, is of course the difference between the observed 288K and the theoretical 255K and thus 33K.
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So what happened to the primordial and radiogenic heat?
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Rather the GHE is based on the unreasonable and simply wrong assumption that absorptivity of Earth was about 0.7, while emissivity was a straight 1.
Did it occur to you that the values of 1 and 0.7 might be measured, rather than assumed?
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So what happened to the primordial and radiogenic heat?
We leave where it is. It is negligible for surface temperatures, unless you are sitting on a volcano.
Rather the GHE is based on the unreasonable and simply wrong assumption that absorptivity of Earth was about 0.7, while emissivity was a straight 1.
Did it occur to you that the values of 1 and 0.7 might be measured, rather than assumed?
I thought was quite explicit on that. While the precise value of the albedo (and thus absorptivity) is both in discussion and a matter of ongoing research, I do not question its dimension. It will be around 0.3. Emissivity however is not being discussed, nor being measured. It is a dogma that it shall be 1, any discussion or research on the subject will be considered heretic.
But, as always, let us try a dialectic approach. One could use the secretive devide called "google" to argue the opposite. Here we have an article of NASA on the subject.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19990100634.pdf
"To date, however, high quality surface emissivity data have not been readily available for global applications. As a result, many remote sensing and climate modeling efforts have assumed the surface to radiate as a blackbody (surface emissivity of unity)."
Right, it is all based on an assumption. But NASA comes to help. So they simply put a satellite into space to measure emissivity, which should clarify the subject once and for all.
But wait a moment! How could you measure emissivity? You can measure LWIR which will depend on a) surface temperature, b) its emissivity, c) GHGs absorbing and emitting it and d) even LWIR reflected by the surface. How will you know what is what? Seems the attempt is doomed before it started.
"The resulting broadband emissivities were used with a surface longwave model to examine the differences resulting from the use of the emissivity maps and the blackbody assumption"
Ok, here we have it. A model will do the trick. To models however the old programming rule applies: garbage in, garbage out. Ultimately even NASA "measurements" are based on .. assumptions. Just read the article, it is discussing assumptions and models back and forth.
What is worse, we even know they got it all wrong. They made a pretty childish mistake in this paper. On page 4 they quote labratory measurements on the emissivity of water (among others), which may be quite accurate. But the emissivity of water is a way more complicated than what they assumed, as it all depends on the angle of observation. You will need Fresnel equations to derive the hemispheric emissivity, which is much lower than vertical emissivity. It is not so hard to do, and it is a great starting point for any complicated model, if you have some "knowns" to compare with the "unknowns", just like in a crossword.
You can not see that in the ill fated grey maps in that named article, but they also have a shorter version with a map that is actually readable. There they have ocean water with an emissivity of 0.99-0.995. And that is simply untrue.
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20040086575.pdf
Now that is bad science. I could also point towards some more reasonable data like in the link below.
https://www.star.nesdis.noaa.gov/smcd/spb/LANDEM/prod_AMSRE.php
In a nutshell: yes, there are attempts being made to "measure" emissivity, which is hard to do for the named reasons. In any case emissivity is lower than 1 by a disputed margin. How does the church of climatology account for it? Not at all, they hold on to the assumption emissivity = 1, period. And that is very bad science too.
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But wait a moment! How could you measure emissivity?
You don't bother.
You measure the reflectivity- because that's easy.
The stuff that's not reflected is absorbed, so it's easy to find the absorptivity.
And then Kirchhoff's law tells you that the emissivity is the same as the absorptivity.
That's why I told you about that rather useful law.
Why are you ignoring it?
Is it that it undermines your viewpoint?
While the precise value of the albedo (and thus absorptivity) is both in discussion and a matter of ongoing research, I do not question its dimension.
It is a ratio, so it is dimensionless.
Emissivity however is not being discussed, nor being measured. It is a dogma that it shall be 1,
Once you actually understand Kirchhoff's law, you realise that your statement makes no sense.
If you know how well the surface reflects then you know how well it emits. (at any given wavelength)
From a distance (I'm told) the Earth looks blue.
That observation tells me that the Earth reflects short wave light better than it reflects long wave light.
Experiments show (and the theoretical basis backs them up) that this trend continues into the IR.
http://envisat.esa.int/workshops/mavt_2006/MAVT-2006-0901_MBabin.pdf
Since the Earth isn't hot enough to emit visible light, it's only the IR spectral properties that matter.
And in the IR the Earth is pretty dark.
However the radiation from the Sun is rich in much shorter wavelengths - notably visible light.
And it is a moderately good reflector of visible light- about 30% bounces off.
So, in reality the numbers 0.7 and 1 are based on things that you know about, but don't understand- like the fact that the Sun is much hotter than the Earth, and the sky is blue.
It's not the climatologists who are making a stupid mistake...
"To date, however, high quality surface emissivity data have not been readily available for global applications. As a result, many remote sensing and climate modeling efforts have assumed the surface to radiate as a blackbody (surface emissivity of unity)."
That report is nearly 20 years old and is likely to have been superseded but the graphs in fig 1 show actual measured emissivity data and all the measurements are above 0.96 and fig 2 gives values consistently above 0.985
So, calling it 1 isn't a massive error.
Stop trying to pretend that this is a problem.
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So what happened to the primordial and radiogenic heat?
We leave where it is. It is negligible for surface temperatures, unless you are sitting on a volcano.
Only a climate "scientist" would call 90% "negligible".
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So what happened to the primordial and radiogenic heat?
We leave where it is. It is negligible for surface temperatures, unless you are sitting on a volcano.
Only a climate "scientist" would call 90% "negligible".
The heat flow arising from the Earth's primordial heat is sufficient, over the course of a year, to melt an ice layer a centimetre or two thick. A good burst of sunshine can do that in an hour or two. That amounts to "negligible" in my book.
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Without radiogenic heating the Earth would be an iceball and we wouldn't be here to talk about it.
Only a climate change denier would ordinarily call that "negligible".
However, like the Earth's emittivity, radiogenic heating is fixed (at least on a human timescale) so it can't be responsible for changes in the Earth's temperature.
The issue is not that it is negligible, but that it is irrelevant.
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It isn't irrelevant when people are trying to calculate absolute surface temperature from radiative exchange alone.
Most people's dynamic bank balance is fairly close to zero - we tend to spend about as much as we earn over a year - but the actual bottom line surely includes the million you inherited, which is neither negligible nor irrelevant to your lifestyle.
The effect of climate on living things depends on the state and distribution of atmospheric water. This would be very different if the mean global temperature were 5 degrees higher or lower than at present, so I think it is important to calculate the "underlying" surface temperature of a body which is 75% water and 25% rock, heated from the inside, with no atmosphere, before trying to fit a guess at mean emissivity to a static atmospheric model that ignores at least half of the input power.
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It isn't irrelevant when people are trying to calculate absolute surface temperature from radiative exchange alone.
True- that's why I pointed out that, without it, we would be frozen solid.
But the thread is about the greenhouse effect and the daft idea that the calculations of radiative gain and loss are somehow wrong because they have no accurate value for the impassivity (spoiler alert- they have).
And radiogenic heating has no direct relevance to those measurements.
Obviously, it has an indirect effect. Without radioactive heat from the earth, we would be looking for data on the emissivity of sheet ice.
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Without radiogenic heating the Earth would be an iceball and we wouldn't be here to talk about it.
Only a climate change denier would ordinarily call that "negligible".
However, like the Earth's emittivity, radiogenic heating is fixed (at least on a human timescale) so it can't be responsible for changes in the Earth's temperature.
The issue is not that it is negligible, but that it is irrelevant.
I am calling it negligible and am most assuredly not a climate change denier.
Given that the heat derived at the surface from terrestrial heat flow (radiogenic heating + primordial heat) is substantially less than 1% of that acquired from solar radiation I find the term negligible to be wholly appropriate and accurate.
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I am calling it negligible and am most assuredly not a climate change denier.
That's why I said "ordinarily".
In any event, it's irrelevant to the discussion in hand.
I'm more interested in hearing Mt Leitwolf's latest missive.