Frequently Made Errors in Climate Science - The Greenhouse Effect - Comments

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haruspex
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haruspex submitted a new PF Insights post

Frequently Made Errors in Climate Science - The Greenhouse Effect

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  • #2
Buzz Bloom
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Hi haruspex:

I very much like your Insight article. I have a question though.

The article says:
If we treat the Earth as emitting and absorbing radiation as a “black body”, ignoring the atmosphere, and treating incoming light as spread evenly over the whole Earth’s surface all the time, we can calculate the equilibrium temperature as -18C. At that temperature, black body radiation would balance insolation.

Adding a non-greenhouse atmosphere, e.g. pure nitrogen, doesn’t change this.​
I understood that N2 scatters blue light, and this is what makes the sky look blue. Wouldn't the scattering of blue photons by N2 then reduce the number of blue photons that hit the earth, since about half the scattered photons return to space? Wouldn't this reduce the equilibrium average temperature of the surface compared with no atmosphere?

Regards,
Buzz
 
  • #3
haruspex
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Hi haruspex:

I very much like your Insight article. I have a question though.

The article says:
If we treat the Earth as emitting and absorbing radiation as a “black body”, ignoring the atmosphere, and treating incoming light as spread evenly over the whole Earth’s surface all the time, we can calculate the equilibrium temperature as -18C. At that temperature, black body radiation would balance insolation.

Adding a non-greenhouse atmosphere, e.g. pure nitrogen, doesn’t change this.​
I understood that N2 scatters blue light, and this is what makes the sky look blue. Wouldn't the scattering of blue photons by N2 then reduce the number of blue photons that hit the earth, since about half the scattered photons return to space? Wouldn't this reduce the equilibrium average temperature of the surface compared with no atmosphere?

Regards,
Buzz
Yes, that's true too. From what I read, the scattering of green light in air at 1atm. is 10-5m-1, and blue light about double that. From that I calculate that about 4% of green light and 8% of blue light would never make it through. Taking the mean power loss as 6%, that would knock 1.5% off the surface temperature, or 4o K.

Edit: I forgot to allow for IR, barely scattered at all. So I would think the power lost would be no more than 4% in total.
 
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What conclusions can be drawn from such 'frequent errors". Who do you think is making such errors and what are the effects? Thanks.
 
  • #5
haruspex
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What conclusions can be drawn from such 'frequent errors". Who do you think is making such errors and what are the effects? Thanks.
They are errors I have come across in posts (not just in these forums), and, just occasionally, errors I have made myself.
This particular FME post is a bit different from my others (Friction, Moments, etc.) in that there is reason to suspect that some people making climate science errors do so disingenuously.
 
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some people making climate science errors do so disingenuously.

Oh, the horror!! Yet, one must secure government grants or perish.

In most scientific models, a single false prediction invalidates the model.

Climate models seem immune from such scrutiny.
 
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haruspex
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Oh, the horror!! Yet, one must secure government grants or perish.

In most scientific models, a single false prediction invalidates the model.

Climate models seem immune from such scrutiny.
You are wandering off the topic of what errors are commonly made and what the correct versions are. If you wish to engage in a discussion on the politicisation of science; on the relationship between scepticism, consensus, scientific progress and public policy; or on the use of models of complex systems, let's do that as a private dialogue.
 
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  • #8
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The Insight article is excellent. But I can't help making a small correction to this statement:
"Note: If something is a negative feedback it acts to dampen change; it cannot make the change go in reverse."
In systems with time delays, accumulated effects, and limiting functions, negative feedback can cause cyclic behavior that includes periodic reverse effects.
The dynamics of the system we are talking about is very complicated and includes all those features.

That being said, if the negative feedback causes a reverse effect at one time, there will probably be a contributing effect later. So it might fool us now and cause a catastrophe later.
 
  • #9
D H
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Minor comment: Please replace that image that depicts a 5250 °C blackbody curve with something else. The Sun's effective blackbody temperature is not 5250 °C, or 5523 kelvins. It is 5777 or 5778 kelvins, depending on who you read. Siting that image has become a "frequently made error in climate science." This is a good example of why wikipedia is not a good source.

Otherwise, this is a very nice insight article.
 
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  • #10
haruspex
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Minor comment: Please replace that image that depicts a 5250 °C blackbody curve with something else. The Sun's effective blackbody temperature is not 5250 °C, or 5523 kelvins. It is 5777 or 5778 kelvins, depending on who you read. Siting that image has become a "frequently made error in climate science." This is a good example of why wikipedia is not a good source.

Otherwise, this is a very nice insight article.
Thanks D H, I was not aware that was wrong. But I like the image, much clearer than most, so I've just added a note. (Is the curve wrong, or just the number? The peak seems to be in about the same place as in other images I found.)
 
  • #11
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Regardless of the current uncertainty on the subject, why no inclusion of the possibility of clouds in Negative Feedbacks? The CFMIP modeled feedback is "approximately zero", but this is not the same as saying there is none.

IPCC AR5 7.2.5.4: "The key physics is in any case not adequately represented in climate models. Thus this particular feedback mechanism is highly uncertain"
 
  • #12
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Regardless of the current uncertainty on the subject, why no inclusion of the possibility of clouds in Negative Feedbacks? The CFMIP modeled feedback is "approximately zero", but this is not the same as saying there is none.

IPCC AR5 7.2.5.4: "The key physics is in any case not adequately represented in climate models. Thus this particular feedback mechanism is highly uncertain"
I included some examples. I made no claim it was exhaustive. There are several more I could have listed (positive and negative). My purpose was to illustrate what is meant by a feedback.
The Insights post concerns aspects of climate science that are well settled and uncontentious yet often misunderstood or misrepresented. I have no plan to get into the more debatable areas. That would be beyond my expertise.
Last I checked, the general view was that whether clouds act mainly as negative or positive feedbacks depended on altitude, but I don't recall which way it worked or whether there was consensus on which dominates.
 
  • #13
mheslep
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I included some examples. I made no claim it was exhaustive. ...
Sure, then perhaps say so? "divided into negative and positive feedbacks, such as ...". Or, "...for example"
 
  • #14
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Sure, then perhaps say so? "divided into negative and positive feedbacks, such as ...". Or, "...for example"
Done.
 
  • #15
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I included some examples. I made no claim it was exhaustive. There are several more I could have listed (positive and negative). My purpose was to illustrate what is meant by a feedback.
The Insights post concerns aspects of climate science that are well settled and uncontentious yet often misunderstood or misrepresented. I have no plan to get into the more debatable areas. That would be beyond my expertise.
Last I checked, the general view was that whether clouds act mainly as negative or positive feedbacks depended on altitude, but I don't recall which way it worked or whether there was consensus on which dominates.
Negative feedback is more complicated than you imply. It can cause dynamic instability. It depends on the dynamics of the system, which is very complicated in this case.
 
  • #16
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Negative feedback is more complicated than you imply. It can cause dynamic instability. It depends on the dynamics of the system, which is very complicated in this case.
To address your earlier comment I already added a clause on time delayed feedbacks. If you feel it is necessary to mention instability specifically I'm happy to add that.
Thanks.
 
  • #17
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To address your earlier comment I already added a clause on time delayed feedbacks. If you feel it is necessary to mention instability specifically I'm happy to add that.
Thanks.
No. I like your insight post. Thanks for the addition. I think what you have is as good as it can reasonable be. Negative feedback such a can of worms that it's not realistically possible to do much better.
 
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… I understood that N2 scatters blue light, and this is what makes the sky look blue. ... Buzz
I think that is miss leading. Even if the atmosphere were argon, the sky would still be blue. On the scale of longer wave lengths, say red light wave length, there is nearly a constant number of atoms (or molecules) in a cube with edge of length equal to red wave lengths. But in a cube with half that edge length (1/8 as many molecules inside) the statistical fluctuation as a percentage in number of molecules inside the cube are more significant. The scattering is due to the greater varying index of refraction that small volumes have. Nothing to due with air being mostly N2.
 
  • #19
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Derek,

Excellent post--although I have a few quibbles. You probably would have addressed them if you were given more space, but here goes:

In your point 6, you state:

1) The Sun warms the Earth’s surface.
2) Conduction and evaporation carry this heat energy to the air at the Earth’s surface.
3) Some conduction, but mostly convection, carries the heat energy higher.

All of these statements are misleading in some respect:

1) Some two-thirds of the radiant energy reaching the surface of the Earth comes from atmospheric molecules—mostly water molecules, the remaining third comes from the Sun. These atmospheric water molecules, of course, got their energy from the Sun in the first place. If you had simply said that, “The Sun warms the Earth”, your statement would be correct.

2) More than 90% of the heat transmitted from the surface to the atmosphere comes in the form of terrestrial infrared radiation. Again, mostly radiation from water molecules. Conduction and enthalpic cycling (condensation, not evaporation) play only very minor roles.

3) Once again, radiation plays the dominant role. Air is simply an extremely poor conductor of heat. An air mass has less thermal energy and a much lower temperature after it has been forced up than it had at its lower elevation. How does this “carry the heat energy higher”?
 
  • #20
haruspex
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2) More than 90% of the heat transmitted from the surface to the atmosphere comes in the form of terrestrial infrared radiation. Again, mostly radiation from water molecules. Conduction and enthalpic cycling (condensation, not evaporation) play only very minor roles.
You're right, I missed a chunk. But I believe the fraction reradiated is more like 80% (Kiehl and Trenberth, 1997). Most of that is radiated back down again, so convection is (just) the major escape route through the troposphere.
 
  • #21
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Haruspex,

Like you, I much admire the 1997 paper by Kiehl and Trenberth. I think it should be in every atmospheric scholar's sourcebook. I believe it to be the standard to which all subsequent global heat budget studies should be compared. Which brings me to another quibble:

In your point 7, you object to the statement, “CO2 is insignificant compared with H2O as a greenhouse gas”. I would object right along with you, but I don’t know any serious scholars of the atmosphere who would make such an unsupported statement. On the other hand, a good many atmospheric scholars would strongly agree that it is a less significant greenhouse gas. Kiehl and Trenberth [1997] are among them. They call the role of water vapor “dominant”.

1. Water vapor accounts for more than 40 Wm-2 of absorption of short-wave (solar) radiation. Carbon-dioxide accounts for less than 1 Wm-2 (none, under cloudy skies).

2. The vast majority of photons emitted by terrestrial IR sources are emitted by water molecules. Atmospheric water molecules can absorb all of these photons, atmospheric carbon-dioxide can absorb only a small fraction (the “overlap” wavelengths). Carbon-dioxide plays no significant role in the emission of terrestrial IR.

3. At 4,000 ppm compared to 400 ppm, water vapor is ten times more abundant in our atmosphere than is carbon-dioxide. In your argument you state, “Increasing the level of a relatively rare greenhouse gas has more effect than increasing the level of a more common species.” This statement is true only if the more common gas is approaching its optical saturation density. This is not true for water vapor. This fact is attested to by the common observation that ground fogs and mists are rapidly dissipated by direct sunlight.
 
  • #22
Buzz Bloom
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I think that is miss leading. Even if the atmosphere were argon, the sky would still be blue.
Hi BillyT:

Thanks for your post. I am always interested in learning something new. Can you recommend a reference that explains more about this phenomenon?

Regards,
Buzz
 
  • #23
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Hi BillyT: Thanks for your post. I am always interested in learning something new. Can you recommend a reference that explains more about this phenomenon? Regards, Buzz
Read the last paragraph of right column, page 269 here:
http://homepages.wmich.edu/~korista/colors_of_the_sky-Bohren_Fraser.pdf That gives the Einstein / Smoluchowski theory which does not even require discrete molecules - only density fluxuation, that cause refractive index spatial variation.
Prior to that Einstein / Smoluchowski theory, the scatering of molecules was used (and still usually is) to explain why the sky is blue. Basically if a plane EM wave is passing thur a dense medium the E-field will oscillate the bound electrons, and an accelerated electron produces radiation which combines with the incident radiation to change the net phase of radiation field. (Why the refractive index exist.*) This electronic radiation goes in all direction in a plain normal to the oscillator motion, but that of many electrons all driven in phase (dense medium & plain wave) only constructively interfer in the forward (or backward, but 180 scatter is weak) direction. I.e. in dense medium of uniform density there is no scattering, but add dynamic density variation on the scale of the wave length you do get scattering.

These small scale density fluxuation are percentage wise much larger in a rarified gas. So most of the scattering of blue light takes place high up in the atmosphere, but not so high that there is little there. Lower in the armosphere, most of the scattering is by small particles (dust etc.).

* As the earlier theory which does consider the individual atomic / molecular scattering gives almost the correct results, few of the papers found by Google have much to say about Einstein / Smoluchowski theory, but it clearly does not depend upon the existance of atoms or molecules - Certainly not what they are. Why I could say that an argon amosphere would also make the sky blue.
 
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  • #24
Buzz Bloom
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That gives the Einstein / Smoluchowski theory which does not even require discrete molecules - only density fluxuation, that cause refractive index spatial variation.
Hi @BillyT:

Thanks very much for the reference. I am a bit confused by your quote relative to what I read in the reference.

The quote above seems to be saying that the Einstein / Smoluchowski theory about fluxuations explains the blue sky. The following is a quote from the reference.
Einstein stated that "it is remarkable that our theory does not make direct use of the assumption of the discrete distribution of matter" . . .
There is no dispute, then, about what really causes the sky to be blue? Is it "really" scattering by molecules? Or, if you want to be more precise, scattering by electrons. Even more precise, scattering by bound electrons: free electrons would not give us a blue sky. The preposition "by" indicates an agent, and molecular scattering is the agent responsible for the sky's blueness.​
This seems to contradict your quote's suggestion that molecules are not responsible for the blue sky. Your quote seems to support the Einstein / Smoluchowski theory, and the references seems to say it's wrong. Or have I misinterpreted what you said? Or what the article says?

ADDED
Now that I have read the whole article, I get that any molecule of sufficiently small size, e.g. argon, would also make the sky blue, provided such molecules have no specific energy levels in its spectrum that would absorb blue light. So the reason that NO2 makes the sky blue is that NO2 makes up most (~80%) of the atmosphere. Since O2 makes up most of the remainder, I am curious. Does O2 also scatter light with smaller wavelengths like blue and violet?

Regards,
Buzz
 
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  • #25
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Hi @BillyT:

Thanks very much for the reference. I am a bit confused by your quote relative to what I read in the reference.

The quote above seems to be saying that the Einstein / Smoluchowski theory about fluxuations explains the blue sky. The following is a quote from the reference.
Einstein stated that "it is remarkable that our theory does not make direct use of the assumption of the discrete distribution of matter" . . .
There is no dispute, then, about what really causes the sky to be blue? Is it "really" scattering by molecules? Or, if you want to be more precise, scattering by electrons. Even more precise, scattering by bound electrons: free electrons would not give us a blue sky. The preposition "by" indicates an agent, and molecular scattering is the agent responsible for the sky's blueness.​
This seems to contradict your quote's suggestion that molecules are not responsible for the blue sky. Your quote seems to support the Einstein / Smoluchowski theory, and the references seems to say it's wrong. Or have I misinterpreted what you said? Or what the article says?

ADDED
Now that I have read the whole article, I get that any molecule of sufficiently small size, e.g. argon, would also make the sky blue, provided such molecules have no specific energy levels in its spectrum that would absorb blue light. So the reason that NO2 makes the sky blue is that NO2 makes up most (~80%) of the atmosphere. Since O2 makes up most of the remainder, I am curious. Does O2 also scatter light with smaller wavelengths like blue and violet? Regards, Buzz
Note I said:
"EM wave is passing thur a dense medium the E-field will oscillate the bound electrons, and an accelerated electron produces radiation which combines with the incident radiation to change the net phase of radiation field. (Why the refractive index exist.*) "

So yes there must be some matter (especially bound electrons) to make a refractive index. O2, N2,NO2, & argon all supply "bound electrons" for the incident sunlight's E-field to shake.

If the bound electronic density were exactly the same every where, so would be the index of refration and there would be only forward (and bckward) scattering. What Einstein / Smoluchowski theory does is to note that all you need is variation of the index of refraction on wave lenght scale. - you don't really need to get into the facts relating to how the index of refraction is created, but that was the approach used to explain blue sky originally. Einstein / Smoluchowski skipped the real details about atoms having bound electrons, but they must be present to make the index of refracion, and if their density is varying on the wave length scale, then so will th index of refraction. - One is a high-level POV and the standard, older one is a more detailed POV, but they are essentially the same.

Sort of like the difference between: The IC motor makes torque that turns the wheels vs The vaporized gasoline volume and presure greatly increases as it oxidizes and they forces the pistons down ..."
 

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