Need Help: Can You Model CO2 as a Greenhouse Gas (Or is This Just Wishful Thinking?)

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  • #51
mheslep
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My no recovery comment is quite valid and not refuted by your comments or examples.
Then don't do it any more. You have several posts up above on extent only.
 
  • #52
Skyhunter


Then don't do it any more. You have several posts up above on extent only.
I don't understand your criticism.

The links I provided dealt with both extent and thickness. If you have a point please state it clearly. Otherwise let's not drag this thread further off topic.
 
  • #53
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... you can't measure in an experiment is the total effect on Earth's climate. ...
We've not conducted experiments on a planet as such,...

You still get people who deny that a greenhouse effect exists at all, but that is pretty much the young Earth creationism of climate science...
the effect of changing concentrations of greenhouse gases. This means quantifying the effect, in terms of concentrations; and that is not something you can do directly in a lab either.... To quantify the effect well enough to infer the effect of changing concentrations on a planet is more difficult....
to actually measure the temperature changes due to changing atmospheric composition can't be done directly. You can't separate out the causes and effects as you can in a lab.
...
A doubling of CO2 concentrations will give a certain amount of additional energy at the surface of the planet... about 3.7 W/m2... You can't measure that number directly...

No matter how large the container, no matter which greenhouse gas, how strong the light source, how long the trial run, you can't experimentally find a temperature change from CO2's greenhouse effect. Is that because it's too small to measure or is climate mitigation inherently untestable, unfalsifiable?

And you think skeptics are like creationists?
 
  • #54
Skyhunter


No matter how large the container, no matter which greenhouse gas, how strong the light source, how long the trial run, you can't experimentally find a temperature change from CO2's greenhouse effect. Is that because it's too small to measure or is climate mitigation inherently untestable, unfalsifiable?

And you think skeptics are like creationists?
The experiments linked in this thread most definitely produce a measurable change in temperature from the radiative properties of CO2. http://www.espere.de/Unitedkingdom/water/uk_watexpgreenhouse.htm" [Broken]

If by skeptics you mean climate change deniers... yes, I do think they are like creationists. They ignore the overwhelming evidence because it does not fit their bias.
 
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  • #55
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No, by skeptics I mean folks who question the efficacy of climate change mitigation. Climate change is undeniable, the climate isn't static. If it was, it wouldn't be impossible to isolate a variable like CO2.

Do you really think that experiment is very good? How come it lasts only twenty minutes, there are only five data points for each sample, it tests CO2 at 370ppm and 1,000,000ppm but no other concentrations or other greenhouse gasses and neither the principle researcher or laboratory was identified? Has any other lab reproduced these results?
 
  • #56
Skyhunter


No, by skeptics I mean folks who question the efficacy of climate change mitigation. Climate change is undeniable, the climate isn't static. If it was, it wouldn't be impossible to isolate a variable like CO2.

Do you really think that experiment is very good? How come it lasts only twenty minutes, there are only five data points for each sample, it tests CO2 at 370ppm and 1,000,000ppm but no other concentrations or other greenhouse gasses and neither the principle researcher or laboratory was identified? Has any other lab reproduced these results?
It is not impossible to isolate the radiative effect of CO2. This experiment does just that.

If you want to deny and reject the evidence that is your perogative. Just remember... the truth does not require your belief, physics doesn't dither, and gravity always wins.
 
  • #57
Evo
Mentor
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Let's refrain from calling names. There are nuts on both sides of the AGW debate, So called "Deniers" are no better or worse than "Alarmists", both cherry pick their data. Stick to discussing facts without getting emotionally involved.
 
  • #58
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I can experimentally test gravity, how come this unknown researcher at an unknown lab wants this test to remain anonymous? What other labs are doing this work? What does the effect look like with CO2 concentrations at historic levels?
 
  • #59
sylas
Science Advisor
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I can experimentally test gravity, how come this unknown researcher at an unknown lab wants this test to remain anonymous? What other labs are doing this work? What does the effect look like with CO2 concentrations at historic levels?
I'm assuming good faith here as best I can, but honestly, I have no idea at all what you are talking about.

Of COURSE you can test a basic greenhouse effect. You can't test on a whole planet at once, because it's too big to fit in a lab, but you can test the basic physics of the matter in labs just fine. That's what I tried to explain for you before. It sounds like you are making objections to experiments on a rather curious basis that I am finding hard to follow.

Have you looked at the rest of this thread?

We've been describing a number of experiments that reveal aspects of the problem, including experiments where you get increasing temperature due to the greenhouse effect in a lab setting. The results don't scale linearly to a whole planet; but the physics of the matter is quite straightforward.

A simple test at the level of looking for temperature change is not really all that useful for physics now; it is the kind of experiment used in a school to help children learn more about how science works and get practice doing experiments themselves. It's an experiment where you have to be careful controlling for what you are measuring, but it is entirely doable.

The experiment where you are making speculations about the "researcher" is not actually a "researcher", so much as a simple school level experiment. It's using really basic physics and confirming a result that that is elementary thermodynamics, in no doubt whatsoever for scientists.

The page is actually German, but has been translated for use in schools in the UK. The main topic of the site is water, in fact. Water is also a very important greenhouse gas. The site has a series of simple highschool level pages going through some of the properties of water, and includes five pages of "experiments and homework"; the lab test of a CO2 greenhouse effect is one of these.

  • The index page is here: http://www.espere.de/Unitedkingdom/ukschoolweluk.html [Broken].
  • The main page for the "water" unit is here: http://www.espere.de/Unitedkingdom/water/uk_overview.htm [Broken]. Note that there is a list of contributors given here.
  • The experiment proposed is number 5 on the list of experiments and homework. The experiment is described here: http://www.espere.de/Unitedkingdom/water/uk_watexpgreenhouse.htm [Broken].

This project was initially carried out in 2001/2002 in Germany, with students aged about 14; though I can't be sure what revisions have taken place since then.

Another greenhouse experiment and worksheet from ESPERE for schools is described here: http://www.atmosphere.mpg.de/enid/4...ion___greenhouse_gases/__Worksheet_2_1gb.html as worksheet 2 in a lower atmosphere unit.

The original of this kind of experiment, in which the effect was first discovered, was conducted in the 1850s by John Tyndall. Those experiments are described in [post=2187943]msg #10[/post] of this thread.

I repeat: this style of experiment is no longer of any great relevance for working scientists. The phenomenon being measured is very elementary physics.

In another thread, I showed an experiment I found with a quick google that is more along the lines of real research: V.G. Arakcheev et al., (2008) Broadening of vibrational spectra of carbon dioxide upon absorption and condensation in nanopores, in Moscow University Physics Bulletin, Vol 63, No 6, Dec 2008. This is not about "greenhouse effect" directly, so much as studying the interactions of radiation and carbon dioxide at genuine research level of experiment. But that is where science is at: the research questions have on.

I am at a complete loss to understand what you meant in this comment in reply to me in another post:

No matter how large the container, no matter which greenhouse gas, how strong the light source, how long the trial run, you can't experimentally find a temperature change from CO2's greenhouse effect. Is that because it's too small to measure or is climate mitigation inherently untestable, unfalsifiable?

And you think skeptics are like creationists?
Um... sure, we do find temperature changes experimentally from CO2 greenhouse effect. Several examples have been given in this thread and I describe some in the post to which you are replying.

As for the creationist remark; I take Evo's point that we want to keep things polite. I was not speaking of individuals here, and I was not speaking of "skeptics" in general.

I was describing three levels of confidence in the details of the greenhouse effect. They are:

  • Is there a greenhouse effect at all? That is, does an atmosphere containing greenhouse gases help maintain a warmer surface temperature than otherwise?
  • What is the consequence of a CHANGE in greenhouse gas concentrations, and specifically carbon dioxide, in terms of the additional energy available to the surface?
  • What is the consequence of the additional energy at the surface in terms of a temperature response?

It was the denial of greenhouse effect at all that I compared with creationism -- point "A" above. I stand by that without hesitation; but it's not meant to be a put down of individuals here; just a clarification of what parts of the question are really really basic.... and that IS a relevant point for the physicsforums rules, consistently applied.

As far as physics forums is concerned, I think a consistent application of the rules would mean that this forum is not a place for that level of denial of basic physics. There are some people who will think this is unreasonable or unfair or ignoring scientific criticism; and there's not much point in debating them, frankly. For various reasons this topic is one where public debate does include a lot of really nonsensical physics, but I would hope that the physicsforum mentors are not at that level. I think physics confirmed from over 150 years ago is not what we should be debating here.

The next level of "skepticism" is about quantifying changes in greenhouse gas concentrations. This is at a rather different level; although still actually quite basic and not in credible doubt. On the other hand, the physics now becomes much more subtle, and certainly something that could be usefully explained and discussed in these forums.

The final level is about quantifying a temperature impact, and this is wide open cutting edge science. There are some papers proposing rather extreme outlier values for the effect, but that's the game in science, and I don't have a problem with it.

My main interest here, by the way, is education. I'm not a physicist myself; nor a physics teacher; though I do a bit of tutoring on physics and maths as a sideline. I engage here in topics like cosmology, relativity, climate, because these are topics in which people are genuinely interested and on which there is a lot of public confusion sorting out some matters which are not really matter of confusion in the mainstream of science. That's where I get interested; in topics where there is a disconnect between working science, and public perceptions or policy.

Cheers -- sylas
 
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  • #60
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Sorry, I thought this forum was about experimental tests of CO2's effect on temperature when exposed to IR.

Bye.
 
  • #61
sylas
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Sorry, I thought this forum was about experimental tests of CO2's effect on temperature when exposed to IR.

Bye.
Well... that clarifies what is going on, and answers my confusion.

You've been given several examples of precisely that here in the thread; and they are linked in the post to which you reply. I do assume good faith as long as possible, and will continue to assume that for other readers. But not beyond reason, and not for you. You've established that you are not even trying to be sensible, and are just refusing to even read what is right in front of your nose.

Bye. Sylas
 
  • #62


Repeating what I've been saying "The greenhouse gas effect" is a fairy -tale There is no scientific proof that it exists.
The experiment that claims to prove the ghg Effect is junk. below are a list of thing that are questionable or wrong with the experiment and the results.
1. Are the two containers the same size, shape and type of glass? Different types of glass
absorb different wave lengths of IR and heat up differently.
2. Where are the thermometers located relative to the light? Are they in the light path
were they would absorb some of the IR thus skewing the data.
3. If the greenhouse gas effect exists there should be a different temperature of the black
cardboard in the CO2 container. The temperature was not measured therefore this
experiment only illustrates that the CO2 heats up. Does it heat from absorption or from
conduction of different heating of the container?
4. Was the experiment done with other “greenhouse gases?” as CH4 butane, natural
cooking gas, Nitrogen trifluoride ?
5. Did the experimenters reverse the gases to the other container to evaluate differences
in the set-up.?
6. Was more than one set of test done? Is there more data to evaluate?
7. Did you monitor the temperature of the water in the trays? If the trays are in contact
with the gases there is conduction of heat from the bottom of the glass trays to the gases.
8. I can not be sure from the photos but it appears that the top of C1 container is closed ,if
this is true then you have created a confined space heating container (greenhouse effect).
It has been proved by R.W. Wood and others that the heating in a greenhouse is caused
by the restriction of heat convection and not back radiation of IR. The top of C2 appears
open thus keeping the temperature lower by convection. Good job of cheating..
9. What you have shown is what has been known from IR spectroscopes that different
gases absorb different wave lengths of IR but in accordance to Niels Bohr that absorption of IR does not cause the gas to heat up
10. I have done a similar experiment except I used clear Mylar balloons (very little or no
absorption of IR as opposed to glass) Based on IR thermometer reading and available
data on IR absorption by glass much of the heating in the experiment was from the glass.
This was not measured in the experiment. By using Mylar balloons in bright sunlight
there was no heating of the gases inside 4 balloons above ambient temperature (measured
with an IR thermometer reading to O.1 degrees F. The contents were 100% CO2, 100%
butane, natural gas (CH4 and CO2) and air. The black cardboard I used did not show any
differential heating between areas in the “shadow” of the balloons compared to “unshadowed”
areas –no back radiation from the “greenhouse gas effect” The black
cardboard did increase in temperature from ambient of 95 degree F to 175 degree F.
uniformly across the surface.
11. If the greenhouse gas effect exist why hasn’t it been applied to something useful like
thermopane window filled with a “greenhouse gas” that would back radiate IR into the
house and create insulated windows with R=30 values.
You ask the question “Why can it be warmer at night than during the day? Any
elementary school students that can read a weather report know that daily temperature are
effected by hot or cold air masses moving across the area. It is also obvious that
on a clear night the temperature will cool down much faster that on a cloudy night. Water
is not a greenhouse gas in spite of what many people say- it has known properties that
explain temperature differences 24/7/365. There is no back radiation –there is reflection
of light or blockage of light(clouds) energy release as lightening and other thermo effects
that are within the Laws of physics and thermodynamic.
When you find reliable experimental data that proves that the “greenhouse gas effect
exists please share it with the world.
In the mean time read “Falsification of the Atmospheric CO2 greenhouse effects within
the frame of Physics” by Gerhard Gerlich and Ralf D. Tscheuschner and when you
understand it in five or ten years( a PhD level –way above your level of intelligence) and
the global temperature has dropped by the 0.6 degrees that it has gone up over the passed
120year you will realize that man-made global warming is a hoax.
Posted by: cleanwater | May 14, 2009 3:09 PM
Below are the intro and abstract to very relevant technical papers.

Greenhouse Gas Hypothesis Violates Fundamentals of Physics*
by Dipl.-Ing. Heinz Thieme*
*
Deutsche Version siehe:*http://freenet-homepage.de/klima/index.htm
*
The relationship between so-called greenhouse gases and atmospheric temperature is not yet well understood.* So far, climatologists have hardly participated in serious scientific discussion of the basic energetic mechanisms of the atmosphere.* Some of them, however, appear to be starting to realise that their greenhouse paradigm is fundamentally flawed, and already preparing to withdraw their theories about the climatic effects of CO2 and other trace gases.
At present, the climatological profession is chiefly engaged in promoting the restriction of CO2 emissions as a means of limiting atmospheric warming.* But at the same time, they admit that the greenhouse effect - i.e. the influence of so-called greenhouse gases on near-surface temperature - is not yet absolutely proven (Grassl et al., see: http--www.dmg-ev.de-gesellschaft-aktivitaeten-pdf-treibhauseffekt.pdf ).* In other words, there is as yet no incontrovertible proof either of the greenhouse effect, or its connection with alleged global warming.
This is no surprise, because in fact there is no such thing as the greenhouse effect: it is an impossibility.* The statement that so-called greenhouse gases, especially CO2, contribute to near-surface atmospheric warming is in glaring contradiction to well-known physical laws relating to gas and vapour, as well as to general caloric theory.
The full paper is available on line.

Falsification Of The Atmospheric CO2 Greenhouse Effects Within The Frame Of Physics
Version 1.0 (July 7, 2007)
Gerhard Gerlich &
Ralf D. Tscheuschner
Abstract
The atmospheric greenhouse effect, an idea that authors trace back to the traditional
works of Fourier 1824, Tyndall 1861 and Arrhenius 1896 and 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. Nevertheless, in almost
all texts of global climatology and in a widespread secondary literature it is taken for
granted that such mechanism is real and stands on a firm scientific foundation. In
this paper the popular conjecture is analyzed and the underlying physical principles are
clarified. By showing that (a) there are no common physical laws between the warming
phenomenon in glass houses and the fictitious atmospheric greenhouse effects, (b) there are no calculations to determine an average surface temperature of a planet, (c) the frequently mentioned difference of 33 _C is a meaningless number calculated wrongly,(d) the formulas of cavity radiation are used inappropriately, (e) the assumption of a radiatively balance is unphysical, (f) thermal conductivity and friction must not be set to zero, the atmospheric greenhouse conjecture is falsified.
The full paper is available on line.
Going back to 1909 -R.W.Wood proved the gh effect as discribed is confined space heating and the ghg effect does not exist.
 
  • #63
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It's a real shame our educational system has sunk so low, this is the state of our popular science:

 
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  • #64
sylas
Science Advisor
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Repeating what I've been saying "The greenhouse gas effect" is a fairy -tale There is no scientific proof that it exists.
The experiment that claims to prove the ghg Effect is junk. below are a list of thing that are questionable or wrong with the experiment and the results.
No, they aren't questionable issues. You are making up spurious objections asking if the experiments used elementary common sense.

The simple fact that carbon dioxide absorbs thermal radiation much better than ordinary air (mainly Nitrogen and Oxygen) has been known for well over 150 years, and the physics of is now well understood.

11. If the greenhouse gas effect exist why hasn’t it been applied to something useful like
thermopane window filled with a “greenhouse gas” that would back radiate IR into the
house and create insulated windows with R=30 values.
R values are a measure of insulation; which is not the relevant quantity. The relevant quantity here would be the thermal emissivity, with the added requirement that it be transparent to visible light.

Glass is already somewhat opaque to infrared, and treated glass can enhance this effect; which does have some benefits. But it is not the same as insulation quantified with an R-value.

You could get a similar effect with a very strong greenhouse gas like some of the fluorocarbons, but it is more efficient to use treated glass. A window is a bit thinner than the atmosphere. It is idiotic to compare an atmosphere with a thin layer of gas that could be reasonably placed inside a window cavity.

You ask the question “Why can it be warmer at night than during the day? Any
elementary school students that can read a weather report know that daily temperature are
effected by hot or cold air masses moving across the area. It is also obvious that
on a clear night the temperature will cool down much faster that on a cloudy night. Water
is not a greenhouse gas in spite of what many people say- it has known properties that
explain temperature differences 24/7/365. There is no back radiation –there is reflection
of light or blockage of light(clouds) energy release as lightening and other thermo effects
that are within the Laws of physics and thermodynamic.
My actual remarks are in the thread; and I did not say it is warmer at night than in the day. (Good grief!)

Water most certainly is a strong greenhouse gas, and that is a major reason why clear nights are colder.

Atmospheric backradiation is directly measured, and has been for over 50 years. It is very elementary thermodynamics that a warm gas which is opaque to thermal radiation -- like the atmosphere -- will also radiate thermal radiation. An early direct measurement of this is described in 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. (http://ams.allenpress.com/perlserv/...&issn=1520-0469&volume=011&issue=02&page=0121)

The measurements are made in the night, and in the day. There is a large flux of radiation coming to the surface of the earth from the atmosphere day and night, though of course the flux is larger in the daytime. It's measured. It's real. And basic thermodynamics means that the atmosphere is emitting radiation; which by Kirchoff's laws means that it also absorbs those same wavelengths.

When you find reliable experimental data that proves that the “greenhouse gas effect
exists please share it with the world.
Done already in the thread. You merely invented a bunch of wholly unfounded objections, which is why people like you are "deniers" rather than "skeptics".

In the mean time read “Falsification of the Atmospheric CO2 greenhouse effects within
the frame of Physics” by Gerhard Gerlich and Ralf D. Tscheuschner and when you
understand it in five or ten years( a PhD level –way above your level of intelligence) and
the global temperature has dropped by the 0.6 degrees that it has gone up over the passed
120year you will realize that man-made global warming is a hoax.
Actually, I have a PhD already, thanks. The main benefit of that is that you appreciate just how facile it is to argue by credentials. An argument stands or falls on its intrinsic merits. The paper by Gerlich and Tscheuschner is one of the worst failures of peer review I have ever seen in a physics journal. It is gross pseudoscience.

In fact, the paper was published without the normal peer review processes normally used in the journal. I sent a message to the journal advising them of its errors after it came out, on my own behalf. It was suggested I reply formally to the journal. I have since done so, as a co-author of a reply that has been submitted to the same journal pointing out some of the many errors; but in my view this should not have been necessary. There's no need to refute the paper for people who know basic atmospheric thermodynamics; the main problem is the failure of the journal editors to pick up such arrant nonsense before publication.

Going back to 1909 -R.W.Wood proved the gh effect as discribed is confined space heating and the ghg effect does not exist.
Wood explained the mechanisms of a glasshouse. He shows, correctly, that it works mainly by limiting convection; not by trapping infrared radiation. That is, he showed that a glasshouse does not work in the same way as an atmosphere opaque to infrared radiation.

This is basic stuff from the first lecture in an introductory course on atmospheric physics. To treat Wood's work as a refutation of the atmospheric greenhouse in the atmosphere is bizarre.

Sylas
 
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  • #65
negitron
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Water most certainly is a strong greenhouse gas, and that is a major reason why clear nights are colder.
Eh, I have to disagree with the underlined portion (and only with that; I agree with the thesis statement). Cloud cover is an excellent reflector of IR; this works in both directions, obviously. At night, with little incoming energy, the ground and everything on it radiates its usual blackbody spectrum, peaking in the IR. On clear nights, this IR just mostly passes through the atmosphere, with a small portion being absorbed and re-radiated by various atmospheric gases--nothing special here. However, on cloudy nights, the ground-radiated IR is largely reflected from the cloud bottoms back down to the ground where a percentage of it is subsequently re-absorbed; the warmer ground heats the air above it and, voila, you've got a warmer-than-expected night. No greenhouse property of water vapor (which I agree is a real effect, don't get me wrong) is required.
 
  • #66
sylas
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Eh, I have to disagree with the underlined portion (and only with that; I agree with the thesis statement). Cloud cover is an excellent reflector of IR; this works in both directions, obviously. At night, with little incoming energy, the ground and everything on it radiates its usual blackbody spectrum, peaking in the IR. On clear nights, this IR just mostly passes through the atmosphere, with a small portion being absorbed and re-radiated by various atmospheric gases--nothing special here. However, on cloudy nights, the ground-radiated IR is largely reflected from the cloud bottoms back down to the ground where a percentage of it is subsequently re-absorbed; the warmer ground heats the air above it and, voila, you've got a warmer-than-expected night. No greenhouse property of water vapor (which I agree is a real effect, don't get me wrong) is required.
My understanding is that the effect you are describing is not "reflection", but absorption and re-emission of radiation... and that is a greenhouse effect. Clouds are good at this because they are made of water.

But I'll check a bit further.

Thanks -- sylas
 
  • #68
negitron
Science Advisor
842
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My understanding is that the effect you are describing is not "reflection", but absorption and re-emission of radiation...
That's what reflection is thought to be, at a fundamental level. However, clouds are not water vapor, but liquid water droplets. These are MUCH better at reflecting light, including IR, than water vapor (or any transparent gas, for that matter).
 
  • #69


Actually reflection is a much different process, and sylas is right that it is not an important term for Earth's clouds (in the IR, obviously this not apply in the visible). In a lot of planetary applications though (like early Mars, Venus) scattering of IR light is very important. And water vapor or clouds are both very important considerations, whether it be day or night.
 
  • #70
negitron
Science Advisor
842
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Actually reflection is a much different process, and sylas is right that it is not an important term for Earth's clouds (in the IR, obviously this not apply in the visible)
I don't believe this is correct. See the following chart:
spectra.jpg
 
  • #71
sylas
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I don't believe this is correct. See the following chart: (chart removed... see above... sylas)
That's not thermal infrared. Look at the wavelengths. The wavelength for thermal infrared radiation is more like 10 microns, way off to the right of the diagram where reflectance drops off sharply. The AVHRR channel 1 band in your chart is pretty much centered on visible light, I think.

I may not get back to this for a bit; but a quick look at my references confirms my opinion that the warmth of a cloudy night is a very strong greenhouse effect from cloud; meaning it is due to thermal emissions, not reflection. A detailed cloud model does consider infrared reflectance; but it is not a major factor, and not the main factor for why cloudy nights are warmer.

I'm not totally confident on this; but for the time being I still think my original statement is correct as given.

Cheers -- sylas
 
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  • #72
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I may not get back to this for a bit; but a quick look at my references confirms my opinion that the warmth of a cloudy night is a very strong greenhouse effect from cloud; meaning it is due to thermal emissions, not reflection.
But who is paying the energy bill? If clouds emit IR sponaneously, then they would cool rather strongly, which would facilitate the condensation process, hence generating more clouds.

However most clouds tend to dissipate in the night.
 
  • #73
sylas
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But who is paying the energy bill? If clouds emit IR sponaneously, then they would cool rather strongly, which would facilitate the condensation process, hence generating more clouds.
EVERYTHING radiates infrared spontaneously. It's a basic property of matter. What I am describing is not any different to what you are used to; I'm describing the thermodynamics of the world you and I experience right now. This includes cooling at night, and condensation on the washing I forget to bring in this afternoon.

The Sun pays all the energy bills that matter.

It may help to bear in mind that the backradiation from the sky is real. It's measured. It's significant; night time included. Hence as you try to work on the physics of what happens to clouds and temperatures, you know for a fact you are going wrong somewhere if you think the atmosphere doesn't provide radiation to the surface at night, all night. That follows anyway from the physics; but it's still a handy sanity check to keep us on track.

With that in mind as an empirical fact about the world, lets see how the physics works.

The atmosphere does cool down at night; but the heat capacity of air is sufficiently high (about 1 kJ/kg/K) that it easily remains warm all night. There is about 104 kg of air per m2, so the heat capacity of the atmosphere is roughly 107 Joules/m2/K.

This radiates to space about 240 W/m2; which is offset by a net energy flow up from the surface. Don't be confused by physically naive descriptions which suggest that greenhouse warming means that there's a net flow of energy from atmosphere to the surface. Its the other way around. The atmosphere is heated from the surface, at night as well as in the day. The effect is analogous to a blanket, which keeps you warmer even though it is colder than you are, and the net flow of energy is still from you into the blanket. The atmosphere is warmed by the surface, or a blanket is warmed by a body; and that means you are warmer than if you were radiating direct to space without impediment.

I don't know the rate at which heat energy is lost from the atmosphere at night, but will be less than 240 W/m2. Over 11 hours we have about 40000 seconds; so the energy lost at night should be, ball park, 107 J/m2, or less; which is enough of itself to lower temperatures about a degree.

This is not an attempt to actually calculate the temperature change; just give a bit of basic thermodynamics to show that there's plenty of heat in the atmosphere to keep things mild over the span of a night. In more detail, we would find that night time usually brings an "inversion" in the lower part of the atmosphere close to the surface, so much of the temperature drop occurs low in the atmosphere, which makes good sense thermodynamically. And this means, by the way, that the clouds don't actually drop in temperature as much; most of the changes to cloud will probably be related to the inversion and currents.

And given that the cooling is pretty limited, effects on cloud are going to depend on a lot more than the simple measured facts of backradiation and associated cooling. The physics of cloud is actually pretty complex.

Cheers -- sylas
 
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  • #74


Guys, much of this is basic physics or atmospheric stuff, and shouldn't really feature much disagreement. Reflection is not the same thing as absoprtion and re-radiation. The physics is different. Clouds tend to have a cooling effect in daytime (depends on the cloud type, altitude, etc) and warm during the night time. Clouds especially have a warming effect in the polar night. Clouds or greenhouse gases also do not reflect IR light to any significant degree at Earth-like conditions. When an absorbing surface is present, the average emission temperature is less than the surface value, and the loss of energy to space is much less efficient than the infrared emission from the surface. Thus you can define the greenhouse effect as [tex]\sigma T^{4}_{s} - \sigma T^{4}_{eff} \approx 150 W m^{-2}[/tex]

One significant difference between an absorbing greenhouse effect and a scattering greenhouse effect (the latter requires considerations in many alien planets) is that one's magnitude is essentially dependent on the temperature profile vertically, wheras in a scattering case you have near independence of the cloud altitude.
 
  • #75
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With that in mind as an empirical fact about the world, lets see how the physics works.
It appears that the problem is more terminology and definitions. So we agree that the noctural cooling of the atmosphere due to radiation amounts to an order of magnitude of one degree. However there is a distinct difference between Earth surface cooling with or without cloud cover, at least an order of magnitude higher in no wind conditions. Why?

Before it was called greenhouse effect, it was explained that the clouds reflected the surface heat radiation, and the clear dark night did not. Hence, what's in a name?

.more detail, we would find that night time usually brings an "inversion" in the lower part of the atmosphere close to the surface, so much of the temperature drop occurs low in the atmosphere, which makes good sense thermodynamically.
We won't find so much of an inversion under a cloud cover, it's more a clear air property like shown http://www.myoops.org/twocw/usu/Forest__Range__and_Wildlife_Sciences/Wildland_Fire_Management_and_Planning/Unit_7__Atmospheric_Stability_and_Instability_2.html [Broken]:

http://www.myoops.org/twocw/usu/Forest__Range__and_Wildlife_Sciences/Wildland_Fire_Management_and_Planning/inversion2.jpg [Broken]

See also this post:

But the first thing in greenhouse effect is understanding how it works.

The global warming hypothesis assumes that the difference between basic Earth black body temperature and actual atmospheric temperature is caused by radiative properties of the greenhouse gases, of which water vapor is the most important, basically nullifying all other mechanisms. In reality it is convection and latent heat transport, which heats the atmosphere from the surface at daylight, while there is no comparable mechanism at night to cool it again. So this mechanism is one way only. This can be demonstrated when comparing day and night lapse rates in the atmosphere, where the difference between day and night is greatest at the Earth surface

http://mtp.jpl.nasa.gov/missions/texaqs/austin_poster/Image11.gif [Broken]

http://mtp.jpl.nasa.gov/missions/texaqs/austin_poster/MTP_Austin_Paper.htm [Broken]

Hence the upper levels hardly cool at night as the only cooling mechanism is .... greenhouse effect, radiation out. And at those levels, with strongly reduced water vapor, radiation escapes to outer space much easier. This effect appears to be neglected in the IPCC endorsed literature and if you don't account for it in the models, you're basically stuck to the GIGO principle.

It is all in this thread, discussing the Chilingar et al 2008 study.

https://www.physicsforums.com/showthread.php?t=252066

In this mechanism the concentration of greenhouse gasses for temperature is strongly reduced. More greenhouse warming simply increases the convection rate, removing the excess heat again from the surface.
 
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