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NASA's greenhouse effect not correct?

  1. Dec 22, 2015 #1
    NASA says Earth's greenhouse effect makes Earth 33 C hotter than the Moon. All of that warming can be explained by Earth having 1 bar of pressure compared to the Moon having no pressure. Going from the Moon to Earth is like going from the top of the troposphere to sea level, roughly speaking.

    This shows the increase in temperature as pressure increases.

    http://www.engineeringtoolbox.com/air-altitude-temperature-d_461.html

    As you can see, going from 16,000 feet to sea level, temperature increases from -17 C to 15 C. That's an increase of 32 C.

    This is NASA saying Earth is 33 C hotter than the Moon because Earth has greenhouse gases and the Moon does not.

    http://www.giss.nasa.gov/research/briefs/ma_01/

    I also do not agree with NASA's claim that Earth's temperature is driven by the level of greenhouse gases in the air. If that were the case, Earth would be much hotter than it is today.
     
    Last edited: Dec 22, 2015
  2. jcsd
  3. Dec 22, 2015 #2

    BvU

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    So why the question mark in the title of your thread ?
     
  4. Dec 22, 2015 #3

    mfb

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    Where is the question?
    The atmospheric composition is relevant there as well.

    Note that the Moon does not have a single temperature, its surface temperatur varies wildly over the 1-month day/night cycle.
     
  5. Dec 22, 2015 #4

    Bandersnatch

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    No, it's not wrong. You're just comparing apples and oranges.

    The 33 C difference often talked about in this context comes from calculating the equilibrium temperature the surface of a spherical black body at 1 AU would have, while taking into account albedo.
    For a body without an atmosphere, this is the same as average temperature of the actual surface - this is the only thing that can and must emit all the received energy back into space. No thermal radiation escapes directly from the deeper regions of the planet, as the surface is opaque.
    For bodies with atmospheres, there is an intervening layer of partially-transparent atmosphere. The total energy received from the Sun is the same, and when measured at sufficiently high altitude - the reradiated energy is also the same. But only parts of it come directly from the surface. The outgoing thermal radiation is the sum of unabsorbed radiation from the surface, and from each consecutive layer of the atmosphere.
    All layers will have varying temperature, density, transparency to both in and outgoing radiation, composition, and generally contribute different amounts to the reradiated total. You will have layers with much lower, as well as layers with much higher average temperature than both the equilibrium equivalent of a black body, and the surface temperature.

    What you did, is look at one atmospheric layer at some distance, treat it as if it were a completely opaque, solid surface of a black body at equilibrium temperature - which it obviously isn't - and wonder why you get nonsensical results.



    What is this claim based on?
     
  6. Dec 22, 2015 #5
    Are you saying that the entire proposition of warming being caused by CO2 and other gases is misconcieved?
    It is experimentally proven that gases have thermodynamic properties which can cause heat to be absorbed or reflected in different ways.
    It's not a theory being propagated by NASA either, these properties of gases were studied long before NASA even existed.
    The details of how different concentrations of gases might affect climate is debatable, but the fact that some gases do have 'greenhouse' properties isn't
     
  7. Jan 4, 2016 #6
    How do you come to this conclusion?
     
  8. Jan 9, 2016 #7
    Golddust:

    All your engineeringtoolbox reference shows is that the Earth's atmosphere is warmer where it is denser. This is not universally true, but is true on the average. This is not because of any causal relationship between the two parameters. In the free atmosphere, temperature is independent of pressure. (Indeed, very hot areas often have lower atmospheric pressures than very cold ones.) It is true because the denser air (close to the surface) gets a great deal of heat from the warmer surface. This makes it hotter. As the elevation increases (and the density decreases), it gets less surface energy. This makes it cooler. It is the change in distance from the heat source that makes it cooler, not the change in pressure.

    Bandersnatch (post #4) summed it up very succinctly.
     
  9. Oct 15, 2016 #8
    Interesting post. The 33K difference for Earth is attributed to greenhouse gases and the measured area weighted mean temperature for Earth's surface being warmer than its effective mean radiative temperature. Apply 'exactly' the same rules to the much simpler moon and the area weighted mean (measured by diviner) is some 70+K lower than the quoted effective radiative mean. NASA quote 271K for BB temp (273K grey) but the 'measured' average is more like 200K. Ie incorrect by 70+K, due to the non-linearity of radiation and temperature.
     
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