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

  1. Dec 23, 2015 #1

    haruspex

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    Last edited by a moderator: Mar 30, 2016
  2. jcsd
  3. Dec 23, 2015 #2
    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
     
  4. Dec 23, 2015 #3

    haruspex

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    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.
     
  5. Dec 24, 2015 #4
    What conclusions can be drawn from such 'frequent errors". Who do you think is making such errors and what are the effects? Thanks.
     
  6. Dec 24, 2015 #5

    haruspex

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    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.
     
  7. Dec 24, 2015 #6
    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.
     
  8. Dec 24, 2015 #7

    haruspex

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    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.
     
  9. Dec 24, 2015 #8

    FactChecker

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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.
     
  10. Dec 26, 2015 #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.
     
  11. Dec 26, 2015 #10

    haruspex

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    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.)
     
  12. Dec 27, 2015 #11

    mheslep

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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"
     
  13. Dec 27, 2015 #12

    haruspex

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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.
     
  14. Dec 27, 2015 #13

    mheslep

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    Sure, then perhaps say so? "divided into negative and positive feedbacks, such as ...". Or, "...for example"
     
  15. Dec 27, 2015 #14

    haruspex

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    Done.
     
  16. Dec 28, 2015 #15

    FactChecker

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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.
     
  17. Dec 28, 2015 #16

    haruspex

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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.
     
  18. Dec 28, 2015 #17

    FactChecker

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    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.
     
    Last edited: Dec 28, 2015
  19. Dec 28, 2015 #18
    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.
     
  20. Dec 28, 2015 #19
    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”?
     
  21. Dec 28, 2015 #20

    haruspex

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    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.
     
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