Why Earth’s surface is so much warmer than the Moon’s – Part 1

Posted: December 10, 2012 by Rog Tallbloke in atmosphere, Clouds, Energy, general circulation, Measurement, solar system dynamics

A lot of the climate debate is highly technical, so in order to help those less tuned in to climate science jargon and the concepts of thermodynamics and radiative theory, I’ve written this intro piece on the difference in temperature on the surface of the Moon and Earth.

Sun Earth Moon

Why Earth’s surface is so much warmer than the Moon’s
Roger Tattersall Dec 2012

The Earth and the Moon are at the same average distance from the Sun, but their average surface temperatures are different by around 91C. Very little heat is escaping from their interiors, around 10,000 times less than the heat from a 1kw electric bar fire puts into a square metre around itself so we can discount that as a significant cause. At any one time, around 60% of the Earth’ surface is shaded from the Sun by clouds, reflecting around 20% of the Sun’s energy straight back into space. So why is Earth’s surface warmer by 91C, given that, on average over the year, only around 240 watts per square metre get past the clouds, whereas the Moon is receiving around 316W/m^2, about a third of a bar fire’s worth for every square metre rather than about a quarter?

Several factors are involved. The first thing to do to help find out what they are is to put the question the other way round: Why is the Moon’s surface so much colder than the Earth’s?

The Moon’s surface near the equator on the day side gets very hot, because there are no clouds to shade it, and no atmosphere to conduct and convect heat away to cooler areas. There is no ocean to cool the surface by evaporation, or take heat away from the equatorial area to cooler areas with currents. The only way the Moon’s surface can lose heat back to space is by radiating it from the surface. This happens quickly. As a point on the Moon’s surface near the equator moves round from the day side to the night side, it’s temperature drops rapidly from nearly as hot as it ever gets to nearly as cold as it ever gets in the space of a couple of days. This is because the dust and rocks of its surface can’t hold heat for long. The surface is also a poor conductor of heat, so heat doesn’t travel through the surface from the hot day side to the cold night side. Big temperature swings mean a lower average temperature, because the relationship between temperature and radiation is not linear. Something twice as hot as something else radiates more than twice as much heat.

The Moon’s average surface temperature, averaged over a long period is stable at around -76C. If it was able to spread the heat it receives from the Sun out evenly over its surface, it would be just below freezing at -0.5C.

This discussion tells us some of the reasons why the Earth’s surface is warmer than the Moon’s. It has oceans which absorb and retain heat much better, this means the night side stays warmer as the oceans release heat they gained during the day slower than the Moon’s surface. The oceans also shift heat from the equator towards the poles making the difference between the polar and equatorial temperature much less than on the Moon. Just because Earth has oceans, we’re much nearer to spreading the incoming solar energy evenly which as we saw with the Moon, would make it’s surface 75.5C warmer. However, Earth’s clouds are reflecting around a fifth of the sunlight back into space, so even if the energy getting past the clouds was spread evenly, Earth’s surface wouldn’t get to -0.5C but only to around -18C. So we need to look for some more factors.

The other big difference, apart from oceans heat capacity and mobility, between the Moon and Earth is that the Earth has an atmosphere. Before we start considering the more complex factors arising from its composition, lets first consider its mass. All mass is affected by Earth’s gravity, which is pulling the atmosphere downwards. Because nearly all the mass of the atmosphere is between the surface and about 20km altitude, we don’t need to consider the weakening of gravity as we get further from Earth’s core. But we do need to consider the effect of the weight of the upper parts of the atmosphere on the lower parts. As we descend from the top of the atmosphere towards the surface, there is more of the atmosphere above pressing down on us. This is why air pressure increases as we descend and is much higher near the surface than it is high up.  The increase in pressure causes an increase in density too. That means the molecules that make up the atmosphere get pushed closer together as we get nearer the surface. That’s why you have to breathe harder on top of a high mountain – there are less molecules of oxygen per lungful than at sea level. But more important than the density for our discussion of temperature is heat capacity.

Down at sea level, where the pressure is high, and the molecules are more densely packed together, more of the energy from the incoming sunlight is absorbed by each litre or pint of air. This is because empty gaps between molecules don’t absorb any energy, the sunlight just goes straight through. But if the sunlight hits a molecule of a type which can absorb energy, the molecule gets hotter. About 16% of the incoming energy from the Sun is absorbed in the atmosphere and most of that absorption will take place nearer the surface. That’s where the energy is more likely to be absorbed by molecules in the air, because that’s where they are packed more closely together. Gravity acting on the mass of the atmosphere to create a pressure gradient leading to higher density and heat capacity near the surface is another reason Earth’s near surface temperature is warmer than the Moon’s. Air also spreads heat around from hotter places to cooler places, warming them up, reducing the differential in temperature between equator and poles and damping down temperature swings by helping to keep the night side warmer, along with the ocean.

The mass of the atmosphere being acted on by gravity also helps keep the ocean warmer. This is because the higher air pressure near the surface limits the rate the ocean can evaporate at. Evaporation cools the ocean surface, just like putting a wet cloth over a bottle of milk in the sunshine keeps the milk cooler. Extra energy called the latent heat of evaporation is used up when water evaporates. Less energy left behind when the evaporated water heads upwards means a cooler ocean. So by limiting the rate of evaporation, the weight of the atmosphere makes the ocean less able to lose energy back through the atmosphere into space. This causes it to warm up because sunlight carries on putting enrgy into it. By warming up, it regains its ability to evaporate, and lose energy as fast as it is arriving from the Sun, so it can stay at a stable temperature. This is another reason the surface is warm.

Time to consider another factor: Clouds. This might seem strange at first, because clouds reflect around 20% of the incoming sunlight straight back into space, preventing it from reaching the surface. But as well as this cooling effect, there are warming effects which offset the cooling effect. Clouds absorb some of the Suns energy, and also heat from warm air rising from the surface. The exact amount isn’t known, because there are problems with the physics, but we do know that half of this absorbed energy gets radiated downwards towards the surface. This is why cloudy nights feel warmer than clear nights.

Now it’s time to consider the composition of the atmosphere rather than its mass and find out why it makes a difference to surface temperature. Here’s quick breakdown of the atmospheric composition:

  • 77% Nitrogen
  • 20% Oxygen
  • 1% Argon
  • 1-4% Water vapour and water
  • 0.04% Carbon dioxide

Around 99% of the atmosphere is composed of two diatomic gases, Nitrogen and Oxygen. Nearly all the rest is the inert gas Argon. There’s some water vapour, and traces of Carbon Dioxide, Methane and other sundry gases. The Water vapour and Carbon dioxide are important, because they radiate energy much more readily than Nitrogen and Oxygen. Radiation is the only way energy can get back into space, so without them in the upper atmosphere, it would get very hot as the solar energy would have to circulate from the dayside surface through the atmosphere, back to the surface on the nightside and be radiated to space direct from the ground. In the lower atmosphere, they directly absorb some of the incoming solar energy and some of the departing long wave radiation leaving the ground and thermalise Nitrogen and Oxygen molecules in collisions. So a bit like clouds, the radiatively active gases are both part of the cooling and part of the warming factors.

Finally a small but non-zero factor is that the Moon spins only once per month, whereas the Earth spins once a day. This means the surface gets longer to cool on the Moon and bigger the swings in temperature between day and night the lower the average temperature due to the power law relating temperature to radiation.

We’ve found seven reasons why the Earth’s surface is warmer than the Moon’s.

  • The oceans spread heat polewards
  • The oceans retain heat overnight
  • The atmosphere has a higher heat capacity near the surface due to gravity acting on its mass
  • The atmosphere’s weight due to gravity restricts the oceans ability to evaporate
  • Clouds reflect heat out to space but also re-radiate absorbed heat partly downwards
  • Water vapour and CO2 radiate heat to space but also re-radiate absorbed heat partly downwards
  • Earth spins faster than the Moon, giving less time to cool overnight, so swings in temperature are reduced

In further posts, we’ll try to quantify how much each of these factors contributes to the 91C difference between the Moon’s surface temperature and the Earth’s. There will be some surprises.

Comments
  1. Stephen Wilde says:

    An 8th reason:

    The atmosphere converts KE to PE and holds onto it as PE for a while with the holding period being variable.

  2. Entropic man says:

    The ideal gas law is

    PV = nRT

    where P is the pressure of the gas, V is the volume of the gas, n is the amount of substance of gas (also known as number of moles), T is the temperature of the gas and R is the ideal, or universal, gas constant, equal to the product of Boltzmann’s constant and Avogadro’s constant.

    In SI units, P is measured in pascals, V is measured in cubic metres, n is measured in moles, and T in kelvin (273.15 Kelvin = 0.01 degrees Celsius). R has the value 8.314 J·K−1·mol−1 or 0.08206 L·atm·mol−1·K−1 if using pressure in standard atmospheres (atm) instead of pascals, and volume in litres instead of cubic metres.

    The consequence of the ideal gas law is that kinetic energy is conserved.

  3. tchannon says:

    “0.1% Water vapour”

    I think that is at least an order too small.

  4. tallbloke says:

    Thanks Tim. We need to be careful to differentiate between water vapour by volume and total water in the atmosphere by mass.

  5. tchannon says:

    Ever heard of psu? The Pennsylvania State University or Penn State.
    Any particular association come to mind?

    This comes from psu

  6. Lance Wallace says:

    Proofreading–

    1. Clouds reflect 30% (first para); 20% (near end)
    2. 0.03% for CO2 is now 0.04%

  7. Steveta_uk says:

    How are you defining the moon’s average temperature? Is this a simple arithmetic mean, or a 4th power geometric mean, or what? It makes quite a big difference.

  8. tallbloke says:

    Thanks Lance. Total albedo 30% cloud albedo 20%, I’ll fix it.

    Steve, the Lunar average surface temperature of ~197K is derived from the Nikolov and Zeller’s spherical integration method using DIVINERS empirical data.

  9. Stephen Wilde says:

    Entropic man said:

    “The consequence of the ideal gas law is that kinetic energy is conserved”

    which suggests that he doesn’t realise that KE and PE are interchangeable within a gravitational field:

    http://www.ftexploring.com/energy/PE-to-KE.html

  10. Max™‮‮ says:

    Why did you bring up the -18 C fallacy?

    That requires one to dilute the actual power of insolation across the surface AND assume the emissivity to be 1, doesn’t it? The only thing that tells us is that acting as though the earth is a black body produces absurd results, particularly when one incorrectly averages power over a surface.

    The moon rotates slower, has higher emissivity, and lower heat capacity than the earth.

  11. wayne says:

    Here’s what NASA’s fact sheet says on Earth’s water vapor:
    “Water is highly variable, typically makes up about 1%”

    Wiki: “The percentage water vapor in surface air varies from a trace in desert regions to about 4% over oceans.[13] Approximately 99.13% of it is contained in the troposphere.”

    That 0.1% does seem at least a magnitude too low.

    I have also read it listed as 1%-4%, 2%-2.5% normally, but that is a hard number to find that you can trust and concretely define what the number is and where that figure applies.

  12. Ray C says:

    When consideration is given to clouds should you include aerosols too?

    Water vapour must be condensing on and evaporating from aerosols constantly with variable consequences.

    Clouds do not form (in Earths’ atmosphere) without the presence of aerosols. Do aerosols therefore dictate to percentage of all phases of water contained within the atmosphere?

    The movement of energy due to the presence of aerosols must be huge.

    Water is changing phase on aerosols and bare aerosols are absorbing and reflecting energy all the time , somewhere in the atmosphere.
    Energy is absorbed by solid aerosol which heat up and so drive some of the convection.

    Every cubic centimetre of air has hundreds to millions of solid or liquid particles, called aerosols, which must influence both cloud formations and atmospheric composition and so too the movement of energy within the atmosphere.

    Why are aerosol not seen as a major player? These solid and liquid lumps of stuff within the gases do not conform to the gas laws do they? They float about interacting with the gas molecules according to thermophoretic forces and velocities.
    http://aerosols.wustl.edu/Education/Thermophoresis/section01.html

    Is this a vented greenhouse full of aerosols?
    What am I missing? Apart from a load of brain cells!!
    Thanks RayC.

  13. Entropic man says:

    Stephen Wilde

    Entropic man said:

    “The consequence of the ideal gas law is that kinetic energy is conserved”

    “which suggests that he doesn’t realise that KE and PE are interchangeable within a gravitational field:”

    For objects and individual particles I would agree with you. If I dropped you from a great height your potential energy would convert to kinetic energy as you accelerated.

    For an isolated molecule of helium bombinating through the lunar atmosphere the concept might still work, as its mean free path would be long enough to be meaningfully described as a trajectory.

    Once the pressure rises enough for the gas law to apply, the concept of interchanging gravitational potential energy and kinetic energy becomes meaningless.

    The short mean free paths of the gas molecules mean that the dominant force is kinetic energy and their paths are no longer affected significantly by gravity. The behaviour of individual molecules is subsumed; their kinetic energy averages out as the temperature of the gas.

    The kinetic energy is conserved, for a given mass of gas KE remains constant as the gas changes pressure, volume or temperature according to the gas law regardless of altitude.

  14. wayne says:

    “The kinetic energy is conserved, for a given mass of gas KE remains constant as the gas changes pressure, volume or temperature according to the gas law regardless of altitude.”

    Oops… didn’t you mean ‘as the gas changes in pressure or volume but not temperature’?

    Pressure and not volume at constant mass.
    Volume and not pressure at constant mass.
    KE conserved.
    But if the temperature changes for that fixed mass the KE does change.

  15. Arfur Bryant says:

    Surely water vapour should be considered as an addition to the components of the atmosphere?

    So, the dry atmosphere is 78% Nitrogen/21%Oxygen/almost 1% Argon and the rest are trace.

    When you add water vapour to the cAGW debate, it would be an addition, eg 2% water vapour makes the atmosphere 102%, of which 2.04% are radiative…

    It may be that, taking the entire atmosphere into consideration, 0.1% water vapour is probably right but it isn’t well mixed like the others. Therefore, we’re probably comparing apples and oranges again.

  16. tallbloke says:

    And if that volume of gas changes altitude in a gravitational field, its Potential Energy changes too, because gas has mass.

  17. Stephen Wilde says:

    “But if the temperature changes for that fixed mass the KE does change”

    And if the temperature change is a result of decompression during the course of that fixed mass rising then the KE that is lost becomes PE.

    The entire AGW establishment cares not a jot about adiabatic processes so they left them out of their equations.

  18. Tim Folkerts says:

    This is a good start, but I have a couple things to think about…

    “About 16% of the incoming energy from the Sun is absorbed in the atmosphere and most of that absorption will take place nearer the surface. “
    This is an assumption, but not necessarily correct. Yes, denser particles are better at absorbing … BUT only if there is something left to absorb! For example, the UV from the gets mostly absorbed by ozone in the stratosphere where the air is VERY thin. There simply isn;t much UV left at the lower layers to get absorbed.

    “0.1% Water vapour”
    The references I ahve seen list this at 1-4% (depending on location, time of year, etc). Others seem to have the same reservations.

    Neither of these are particularly important to the discussion, but they are worth looking into.

    Clouds reflect heat out to space but also re-radiate absorbed heat partly downwards
    Water vapour and CO2 radiate heat to space but also re-radiate absorbed heat partly downwards

    Glad to see you including “back-radiation” in your possible causes.

    In fact, these two stand out from all the others for one simple, yet critical reason. The other five simply serve to allow solar energy to be absorbed and one time and/or place on the surface, but for the earths thermal radiation to be emitted at another time and/or place on the surface. As you point out, this evens out the temperatures, which has a definite (but limited!) affect on the temperature.

    For a given emissivity and albedo, the highest temperature that the “radiatinmg surface can reach is given by
    T_earth = T_sun [ (R_sun^2)* (1-alpha) / (4 D_sun^2 Epsilon) ]^0.25
    or
    T_earth = [ (insolation/4) * (1-alpha) / (epsilon * sigma) ]

    This is the infamous equation that (for emissivity = epsilon = 1 and albedo = alpha = 0.3) gives T =255 K as the “effective black body temperature” as measured at the “effective radiating surface”.

    However, the surface is not a black body. But the surface is close, with an emissivity above 0.9 for just about any where on earth. The “effective gray body temperature” might be as high as (using 0.9 for the emissivity of the surface) 262 K

    This equation specifically assumes that the temperature is uniform — any other distribution gives a lower temperature average temperature. So the earth, which is definitely not uniform temperature, will be less than 255 K (or less than 262 K with our alternate emissivity). If it were not for all these processes listed (oceans, atmosphere heat capacity..) then the temperature would be even FARTHER below 255 K (or 262 K) at the effective radiating surface. This value is set by radiation balance, and no amount of evening out the temperature will get you above 255 K (or 262 K of the gray body calculation). Oceans, winds, etc simply cannot do it!

    Fortunately you listed the two way to warm the surface above this upper limit for the temperature — clouds and the GHGs emitting IR to space from ABOVE the ground level where it is colder. This means some of the radiated energy comes from cooler locations than 255 K (ie from the cold upper atmosphere), so some can come from WARMER locations than 255 K (ie the surface).

    Overall, I think this is a good starting point for further discussion!

  19. Doug Proctor says:

    “Something twice as hot as something else radiates more than twice as much heat.”

    Trying to remember first year physics: black bodies radiate heat as a fourth function of the temperature?

    The ideal law doesn’t apply for low pressures or high pressures, right?

    The heat redistribution system has ,more power than the differential of TOA TSI as the warmer hemisphere (the Northern) has more of its TSI during the apogee position of the orbit?

    Do idiosyncratic elements of the Earth land-sea-atmospheric setup overwhelm basic physics for heating the planet, and lead to non-ideal, non-intuitive, non-stable heating/temperature patterns? Is there evidence that we live in on a planetary surface that is somewhat chaotic, in the details, at least, the details of which we call both “weather” and, in the shorter term (<200 years), climate?

    Just asking

  20. tallbloke says:

    Tim F
    Oceans, winds, etc simply cannot do it!

    This just empty argument by assertion. You still haven’t got back to me on my ocean hypothesis. Last I heard, you were “going to think more about it”.

    You haven’t replied to my questions and points on your post either.

    There simply isn;t much UV left at the lower layers to get absorbed.

    UV is small potatoes in energy terms (but very important in upper atmosphere chemistry terms).The dense high capacity air near the surface absorbs and retains heat leaving the ocean too, further limiting the rate of evaporation, making the ocean get even warmer as it has to rise to a temperature whereby it can lose heat as fast as it acquires it.

    Overall, I think this is a good starting point for further discussion!

    That’s the general idea. It gets all the factors into play, rather than fixation on a single element.

  21. Entropic man says:

    PV = nRT applies to a gas at equilibrium.

    It is an extension of the earlier

    PV
    —– = k
    T

    If you keep n and one of P or V constant and vary the other, without adding or subtracting energy from outside, T will change in such a way as to keep k constant. The net result for a give n is that the kinetic energy of the gas mass remains constant.

    If you keep P and V and n constant, the only way to change T is by adding or subtracting energy from outside the system.

    Stephen Wilde’s hypothesis violates that, making it thermodynamically impossible.

    In an atmosphere, increasing the temperature will indeed increase the total potential energy of the air mass as it expands upwards against gravity.
    However, the extra potential energy does not come from the kinetic energy already present, it comes from the extra heat energy added to increase the temperature.

    [Moderation note] Stephen is discussing an adiabatic process

    When equilibrium is reestablished, what proportion of that added energy ends up adding to the kinetic energy of the gas, and what proportion becomes potential energy, whould need to be calculated by someone with less addled mathematical skills.

    Tim?

  22. tallbloke says:

    I’ve edited the water fraction of the atmosphere. Thanks for the feedback on this.

  23. Entropic man says:

    “[Moderation note] Stephen is discussing an adiabatic process”

    And therein lies the problem. There is no physical mechanism which can expand an atmosphere in equilibrium adiabatically in the way he describes without violating the Second Law. It is only possible by adding energy from an energy source external to that atmosphere.

  24. Stephen Wilde says:

    “However, the extra potential energy does not come from the kinetic energy already present, it comes from the extra heat energy added to increase the temperature.”

    Once a parcel of air leaves the surface it will continue to rise without further energy input and during the process KE is converted to PE so there is a cooling effect as the amount of KE drops.

    The process then goes into reverse as the air parcel falls back to the surface again until KE is returned to its maximum at the surface.

    I propose that the speed of the cycle is relevant because it effectively rations the supply of KE returning to the surface which it needs to do before it can rejoin the radiative flux to space.

    If the cycle speeds up when GHGs slow down radiative loss to space then that speeding up of the adiabatic cycle would be capable of negating the GHG effect.

    I have put a proposed post to tallbloke which puts more flesh on the bones.

  25. Tim Folkerts says:

    Tallbloke says: “This just empty argument by assertion.

    No it is a very basic result based on conservation so energy. It is the same argument Clive Best made (in another thread) when he said “Viewed from a million miles away an Infra Red bolometer measurement of the Earth’s temperature will always yield a figure of roughly 255K.”

    * The bolometer will read roughly 255 K for earth, based on overall IR radiation.
    * With no GHGs (or clouds) the IR radiation will all come from the surface.

    ∴ With no GHGs, the surface will be roughly 255 K.

    Oceans and atmosphere heat capacity cannot change this. An “oceanic green house effect” could make the water BELOW the surface warmer than 255 K, but making the surface warmer (on average) than 255 K will violate conservation of energy. (And an “atmospheric green house effect” from clouds or water vapor could make the air above sea level warmer, but then we are back to needed an atmospheric GHE.)

  26. Entropic man says:

    To Stephen Wilde
    “Once a parcel of air leaves the surface it will continue to rise without further energy input and during the process KE is converted to PE so there is a cooling effect as the amount of KE drops.

    The process then goes into reverse as the air parcel falls back to the surface again until KE is returned to its maximum at the surface.”

    This is not adiabatic. You have disturbed the equilibrium by heating a parcel of gas at the surface, which then convects because the increased temperature has expanded its volume and decreased its density.

    The air behaves adiabatically thereafter. Its volume increases further as it rises, reducing pressure and temperature as it goes in accordance with PV =nRT and maintaining a constant kinetic energy.

    When it stops rising the extra energy picked up ot the surface radiates away and it sinks adiabatically again, maintaining a constant kinetic energy.

    As your parcel of air rises, it displacing air downwards elsewhere. The potential energy of this gas parcel increases, as that of the downgoing air decreases. The overall potential energy change is zero .

    There is no need for any kinetic energy of the gas parcel to convert into potential energy. The gas law and radiative physics explain its behaviour perfectly well on their own.

  27. Max™‮‮ says:

    That is indeed empty assertion.

    In between your first and second point you forgot to put “a wizard does something”, I think.

  28. Tim Folkerts says:

    [biting my tongue ... ]

    Max, apparently it is the 2nd statement you disagree with, so what is wrong with it? With no GHGs or clouds, where will the radiation come from besides the surface? Do you think that N2 or O2 will produce enough IR to make a difference? (HINT: look at an IR spectrum looking UP from the surface and tell me what IR you see. Look at an IR spectrum looking DOWN from above and tell me what you see. Do you see any IR that comes from N2 or O2?)
    http://www.skepticalscience.com/images/infrared_spectrum.jpg

  29. tchannon says:

    Anyone point to *global* diurnal temperature profile in K ?

  30. Max™‮‮ says:

    Tim F., what is the location where that measurement was made?

    Why is it cut off?

    If the atmosphere couldn’t radiate at a lower temperature due to GHG’s, it would need to be warmer for N2/O2 to radiate the same amount of energy, wouldn’t it?

    For the record, these are the two regions where N2 and O2 are strongest:

    http://i341.photobucket.com/albums/o396/maxarutaru/guest975820037.png from UV to 6 microns, and: http://i341.photobucket.com/albums/o396/maxarutaru/Selection_033.png from 25 to 1000 microns.

    Black body curves for 255 K and 288 K:

    http://scienceofdoom.files.wordpress.com/2010/03/blackbody-radiation-255k-transmittance.png

    http://scienceofdoom.files.wordpress.com/2010/03/blackbody-radiation-288k2.png

    These are similar measurements to yours, taken from Chile:
    http://i341.photobucket.com/albums/o396/maxarutaru/Selection_049.png

    http://i341.photobucket.com/albums/o396/maxarutaru/Selection_050.png

    Also, skepticalscience link? Really? I’m allergic to things which are that ironic.

  31. wayne says:

    Here is TimF again speaking of a high surface emissivity. FAIL.

    “However, the surface is not a black body. But the surface is close, with an emissivity above 0.9 for just about any where on earth. The “effective gray body temperature” might be as high as (using 0.9 for the emissivity of the surface) 262 K”

    Try about an effective emissivity = 0.67 Tim if you have moved from your thread to here, see: http://tallbloke.wordpress.com/2012/12/06/tim-folkerts-simple-argument-supporting-a-radiative-greenhouse-effect/#comment-37860

    Tim, if you really know physics and thermodynamics as well as you say you do, you should have come off of this train of logic long, long ago, but, it just keeps a’going on, and on, and on ….

    I’m curious if you are going to deny a “now-balanced Trenberth energy budget” since that is always your templeate of dicussions. For about half goes up and half goes down, right?

  32. tallbloke says:

    Wayne:
    The figures I remember for emissivity are about 0.7 for various land surfaces and 0.983 for the ocean. Since the ocean covers a large proportion of the globe, that would raise the overall emissivity well above 0.7. Maybe there’s something in your ‘effective’ emissivity I don’t understand, so please elaborate.

    Max asked earlier why I ‘brought up the -18C fallacy’. At that point in the article we hadn’t yet brought the atmosphere into play.

  33. Max™‮‮ says:

    Even with no atmosphere, -18 C requires unity emissivity which is unphysical.

    The ocean emissivity is only .9 in certain wavelengths, not across the entire spectrum, and it is even more dependent on angle than the land is, such that trying to apply a single value is… troublesome to say the least.

    [Reply] It also requires uniform temperature across the surface to be as high as -18, which doesn’t pertain. Tim F’s point is that with no GHG’s, the surface has to do all the emitting to space, and because there is on average 240W/m^2 coming in (after albedo which wouldn’t be there with no water vapour) there can’t be more than 240W/m^2 on average going out.

  34. tallbloke says:

    Tim Folkerts (and the whole of mainstream climate science), is fixated on balancing the books with radiation alone. This is false. GHG’s cool the Earth to space from high in the atmosphere where the radiatively active molecules can radiate directly to space. But they do not warm the surface with ‘downwelling radiation’ which can’t penetrate the ocean anyway.

    The surface is warmer than the final ‘back to space’ average emission temperature because of the other factors I have outlined. The average surface temperature of the ocean is a couple of degrees higher than the average near surface air temperature. Changes in the globally averaged near surface air temperature lag changes in sea surface temperature by a couple of months. This tells you everything you need to know about the direction of causality.

    Tim F’s long continued studious ignorance of those two facts tells you everything you need to know about his inability to use simple logic or understand the basics of thermodynamics. He continues to ignore and fail to respond to the points and questions I raised on his own thread, and hurries over to this one to propagandise his ‘radiation only’ world view. I hope he will be responding in full to my comments on his own thread, and is ready to respond fully to the points raised in this comment.

    For my part, I have no problem in accepting that GHG’s losing heat to space from high in the atmosphere are an essential part of the Earth’s system which are necessary for the surface to have the potential to be warmer than the final emission temperature on average.

    But a necessary condition isn’t the same thing as a sufficient condition. Just because it is necessary for the high altitude GHG’s to be there for the surface to have the potential to be warmer than the emission temperature doesn’t mean they are the sufficient cause of the surface being warm. In fact they can’t be, because most of the downwelling radiation is soon absorbed in the denser region of the troposphere below and carried upwards again by convection. What little reaches the surface from high altitude is absorbed in the top 10 nanometres of the ocean surface where it promotes the evaporation which cools the ocean. The primary role of GHG’s is to cool the planet and provide a necessary, but not sufficient condition for the surface to have the potential to be warmer than the average emission-to-space temperature of ~255K or -18C. On average, the net radiation flux is upwards, away from the surface, thereby cooling it, not downwards thereby warming it.

    My contention is that the surface warming above ~255K is done by the Sun and the way matter with heat capacity is organised into gradients by gravity and convection. The high altitude GHG’s play a small role in the changing temperature gradient at the top of the atmosphere, but the contribution radiative gases make to the setting of the lapse rate diminishes with falling altitude. Heat capacity, density, pressure and the throughput of solar energy dominate the energy balance at the surface and are the primary factors in setting both its temperature, and the temperature of most of the troposphere.

    Tim Folkerts needs to learn some simple logic.

  35. Stephen Wilde says:

    Entropic man said:

    “When it stops rising the extra energy picked up ot the surface radiates away and it sinks adiabatically again, maintaining a constant kinetic energy.”

    No it doesn’t. It warms up again adiabatically on the descent.

    That is where you guys go wrong.

  36. Bryan says:

    Its interesting that Tim Folkers is using a skeptical science link.

    Perhaps Tim lives a very sheltered life.
    Even so, surely a hermit must know that skeptical science have been caught red handed altering posts.

    Posts that skeptical science cannot handle simply disappear even after being shown for several hours.
    Other critical posts are edited and even altered.
    The intention is to make the loyal skeptical science hacks look smart and critics ineffective.

    Such blatant propaganda methods are however counterproductive and skeptical science has become the laughing stock of the climate blogs.

    Would they alter a chart or graph?
    Why not……… if its in a ‘good cause’.

    How the ‘skeptical’ science hacks can look themselves in the mirror is beyond me!

  37. tallbloke says:

    Bryan, spot on as usual. I caught them red handed altering the Y axis labelling on a cloud cover graph to make its variation appear much less than it has been. I emailed John Cook about it three times to give him the opportunity to correct it. Nada.

    I’ve inset another graph with a correct scale here. You do the math.

    http://tallbloke.files.wordpress.com/2010/08/cloud-earthshine1.png

    No further links to ‘skepticalscience.com’ will be published here.

  38. wayne says:

    tallbloke, sorry if this was to be atmosphere-less so far. If so that emissivity works to be 0.883. Read on.

    The “effective” emissivity has two different processes setting that one 0.67 value. One is the sensible and evapo-transpiration that are moving energy from the surface. At the very skin molecules of the surface you can’t have both non-radiative and radiative energy leaving the same surface all at each at their own measured or maximum theoretical rates.

    S-B assumes ONLY radiative transfer is in action from a surface, no wet surface and no convective thermals also sapping the heat that also causes the radiation. The second part is the surface’s normally stated emissivity (dry, no convection) of around .9, that is the weighted mean of water, sea water, rock, soil, plants, etc, etc. average of the world.

    Hope you looked very closely at that spreadsheet, a gift to TimF.
    http://i46.tinypic.com/21931xt.png

    All of that ends up being (396 – 17.0 – 80.0) * 0.883 = the 264 W/m2 that actually leaves the surface. Ok, we differ 1.9% on the surfaces raw emissivity instead of 0.9.

    Just remember what “emissivity” is. It is the fraction lowering S-B’s absolute maximum energy that a black-body surface can even emit per second and per meter squared, and here against absolute zero (the downwelling radiation, 197.8 W/m2 must be subtracted from this to get the net radiation moving upward to space, not much).

    Repeat and let it sink in:
    Seems from the average and weighted matter of Earth’s surface the radiation is 88.3% of S-B if and only if the surface is dry and no convection, but wait, we have 80 W/m2 of water evaporating from that surface of Earth and an additional 17 W/m2 of sensible heat also leaving the surface, all simultaneously. That is the equation above. Now we are very close to T&K’s ‘reality’ that they hid very well behind the curtain.

  39. tallbloke says:

    Hi Wayne:
    my comment about the -18C figure was directed to Max. At the moment, I’m inclined to think that while your reduction of ‘effective’ emissivity is correct, the GHG’s at high altitude emitting to space are still a necessary, though not a sufficient condition for the surface to get as warm as it does.

    I guess Tim would respond to you by pointing out that without the emission to space, there would not be such a large amount of convection or evaporation going on. On his thread, he calculated that something like 128W/m^2 of energy would be transferred into the GHG free atmosphere on the dayside, and that would be transferred back to the surface on the nightside.

    It would be interesting to know how much that calculation would change in view of your revised emissivity.

    I have a feeling the atmosphere would get very hot without emission to space from high altitude. That would suppress evaporation. Depending on what happens to the lapse rate, convection would be reduced (but advection to the nightside increased).

  40. Entropic man says:

    Stephen Wilde

    “It warms up again adiabatically on the descent.”

    Of course it does! Pressure increases, volume decreases and temperature increases as air descends, all in accordance with PV =nRT. The potential energy decreases, transferred to other, rising, packets, and the kinetic energy content of your parcel of air stays constant throughout the descent.

    Think of a bucket chain lifting sand. The sand is carried upwards from the quarry in bucket sized parcels and taken away. The buckets are carried back down. The potential energy of individual buckets changes as they go up and down, but the potential energy of the bucket chain stays constant. Ignoring friction, the energy input driving the bucket chain equals the potential energy gained by the sand.

    Transpose this into the atmosphere. Think of a thermal as a bucket of sand. The packet of air is the bucket. The extra kinetic energy added when the air is warmed by the surface is the sand.
    The extra KE warms and expands the air packet (PV =nRT), which becomes bouyant and rises, the equivalent to whatever drives the bucket chain. At the tropopause the extra energy radiates away into the OLR, unloading the bucket. The packet of air drops, increasing in temperature and pressure as its volume decreases but at constant KE.

    I’m starting to become concerned. You seem to have built a whole new hypothesis around a simple misunderstanding of how gases behave, and taken Wayne and tallbloke with you.

    [Reply] Heh, if only you knew the history.

  41. Entropic man says:

    tallbloke

    To Tim Folkerts “You still haven’t got back to me on my ocean hypothesis. Last I heard, you were “going to think more about it”.”

    If I recall, we had reached the point at which we had calculated that your hypothesis was not thermodynamically impossible and established the minimum size of the necessary change in AMO temperatures over the cycle.

    You now have a hypothesis and a prediction, and are ready to validate it empirically against measured AMO and global temperature behaviour.
    You also need a mechanism to explain why it would happen.

    Put up a new post discussing validation and mechanism and we can take it from there as a dedicated thread.

    [Reply] Thanks for the advice. ;)

  42. [...] tallbloke on Why Earth’s surface is s… [...]

  43. wayne says:

    LOL, tallbloke, I bet I am giving you the wrong impression where I am positioned on all of these topics right now. T&K is junk, I just have to maintain a “dual” tie to those who are still firmly bound to their logic. The radiative-only wall is crumbling. And I say junk, that’s not completely true, the data in their papers is just that, data, and probably some of the best to date so I’ll use those values, it’s their interpretations and assumptions I have trouble with (and his AGW activism).

    For Tim’s 128 wm-2, making the T&K now day and night?? I’m really not interested now, been there, done that. Except for the five data inputs and OLR value most of all of the other numbers are most likely not real at all except in a balanced radiative-only world.

    Later on what I have uncovered on co2 in the low and mid troposphere, but not related here. (it’s qm and it seems Dr. Vonk was right all along in a comment at TheAirVent)

    Tallbloke, I believe I’m pretty close to you most of these topics (or I’d holler at you! :) ) I may not place so much weight on things like the oceans right now, but I’m currently looking at atmospheres, and many don’t even have an ocean.

    A hot GHG-less atmosphere? Count me in. Maybe not right at the surface in the inversion at night but the bulk seems that way.

  44. Stephen Wilde says:

    Entropic man:

    How does air increase in temperature with the KE staying the same ?

    What actually happens is that as the air falls the PE is converted to KE on a molecule by molecule basis.

    Here is a simplified account of the interchangeability of kinetic energy and potential energy:

    http://www.ftexploring.com/energy/PE-to-KE.html

    What stays the same is the total energy of all types i.e. KE plus PE.

    The adiabatic process stores PE out of sight of the radiative exchange and the amount of PE tied up at any given moment can vary but:

    PE + KE = constant.

    And the constant is set by mass, gravity and insolation.

    So anything that changes PE to KE or KE to PE must do so at the expense of the other if the constant remains the same.

    That swapping to and fro between KE and PE is what stabilises the radiation budget but it is achieved by a non radiative process.

    “The extra KE warms and expands the air packet (PV =nRT), which becomes bouyant and rises, the equivalent to whatever drives the bucket chain”

    No.

    You overlook the fact that once an air packet leaves the ground it keeps rising with no additional input of energy.That is quite unlike the bucket chain which does need a constant energy input.

    I have previously found AGW proponents severely ignorant about the process of evaporative phase changes of water and now I find them equally clueless about adiabatic processes.

  45. Stephen Wilde says:

    “The potential energy decreases, transferred to other, rising, packets,”

    Entropic man thinks that rising molecules ‘acquire’ their increasing PE from falling molecules.

    How would that work ?

    Is there another form of energy transfer whereby potential energy can move from one molecule to another ?

    Of course not.

    The process of rising converts KE to PE on a molecule by molecule basis and the process of falling converts PE to KE on a molecule by molecule basis.

    The warmed surface is caused by returning KE being released by the adiabatic process as air descends.

    A mechanical process keeping the surface warm and nothing whatever to do with radiation because radiation already gets a free pass straight through the system due to every molecule in the atmosphere already being at the maximum temperature permitted by the combination of gravity, mass and insolation.

    AGW theory has made a serious acounting error:

    http://climaterealists.com/index.php?id=10704&linkbox=true&position=2

  46. Stephen Wilde says:

    Entropic man said:

    “At the tropopause the extra energy radiates away into the OLR, unloading the bucket. ”

    How does PE radiate away ?

    It doesn’t. It has been taken out of the radiative exchange until it converts back to KE on the down cycle.

    The energy lost to space is radiative only but the two way net zero energy exchange between top of atmosphere and surface is mechanical energy.

    What radiates out by way of OLR is radiation from the ground surface plus radiation released higher up as a result of the water cycle releasing latent heat at the tropopause, plus a little radiation from the non condensing GHGs.

    You don’t need downward IR at all if you correctly apply a figure to the PE being returned to the surface by the adiabatic process.

  47. Tim Folkerts says:

    Wayne’s model boils down to “ For about half goes up and half goes down, right?

    Nope, that is NOT right .. not for the atmosphere as a whole. The bottom of the atmosphere (being warmer) radiates MORE energy down than the top of the atmosphere (being cooler) radiates up.

    If the atmosphere were a single layer with the same the temperature at the top and bottom, then you would be right about “1/2 up, 1/2 down”. But we know all sorts of things (latent heat, convection, conduction, radiation) occur WITHIN the atmosphere. We know there is a lapse rate. These force us to model the atmosphere with at LEAST two layers in order get even close to reality.

    [PS It is certainly possible to get a "GHE" from a single layer model and it is a good academic exercise to start to learn the basics. But there is no reasons to expect that the numbers from this simple model would match the actual earth, so, for example, such a model would not be appropriate to try to estimate the earth's emissivity.]

  48. Tim Folkerts says:

    Bryan says: “Its interesting that Tim Folkers is using a skeptical science link.

    (( sigh )) I KNEW someone wouldn’t be able to resist making an ad hominin attack.

    Bryan, attack the MESSAGE not the messenger! Whatever else SkS my have said has no bearing on this particular data. The data was simply REPOSTED at SkS from a textbook. Unless you have evidence that SkS “doctored” the data, then tells us what is wrong with the DATA, not with the letters in the URL!

    PS The data is also posted at Wattsupwiththat: http://wattsupwiththat.com/2011/03/10/visualizing-the-greenhouse-effect-emission-spectra/
    Would you have complained “Its interesting that Tim Folkers is using a s̶k̶e̶p̶t̶i̶c̶a̶l̶ ̶s̶c̶i̶e̶n̶c̶e̶ WattsUpWithThat link.”? :-)

  49. Hans Jelbring says:

    Entropic man says: December 11, 2012 at 12:27 pm

    Stephen Wilde, “It warms up again adiabatically on the descent.”

    “Of course it does! Pressure increases, volume decreases and temperature increases as air descends, all in accordance with PV =nRT. The potential energy decreases, transferred to other, rising, packets, and the kinetic energy content of your parcel of air stays constant throughout the descent.”

    Warming adiabatically means that dT/dz = -g/Cp. This can be derived by using the adiabatic condition, the Ideal Gas Law and the Hydrostatic Equation. To understand the derivation needs good understanding of meteorology which you seem to lack when wrongly stating “… in accordance with PV = nRT.” The approximate adiabatic heating at fast descent of air (about 2-30 minutes but not 24 hours) does not follow from the application of the Ideal Gas Law alone. The fact that adiabatic heating is often observed and important in nature is that vertical mechanical motion of air is mostly a fast process and in such situations energy exchange by radiation can be dismissed sonce it affect the temperature much less than the motion of air.

  50. Tim Folkerts says:

    Wayne says: “Just remember what “emissivity” is. It is the fraction lowering S-B’s absolute maximum energy that a black-body surface can even emit per second and per meter squared,̶ ̶a̶n̶d̶ ̶ h̶e̶r̶e̶ ̶ a̶g̶a̶i̶n̶s̶t̶ ̶ a̶b̶s̶o̶l̶u̶t̶e̶ ̶ z̶e̶r̶o̶ ̶ (̶t̶h̶e̶ ̶ d̶o̶w̶n̶w̶e̶l̶l̶i̶n̶g̶ ̶ r̶a̶d̶i̶a̶t̶i̶o̶n̶,̶ ̶ 1̶9̶7̶.̶8̶ ̶ W̶/̶m̶2̶ ̶ m̶u̶s̶t̶ ̶ b̶e̶ ̶s̶u̶b̶t̶r̶a̶c̶t̶e̶d̶ ̶f̶r̶o̶m̶ ̶ t̶h̶i̶s̶ ̶ t̶o̶ ̶g̶e̶t̶ ̶ t̶h̶e̶ ̶ n̶e̶t̶ ̶ r̶a̶d̶i̶a̶t̶i̶o̶n̶ ̶ m̶o̶v̶i̶n̶g̶ ̶ u̶p̶w̶a̶r̶d̶ ̶ t̶o̶ ̶ s̶p̶a̶c̶e̶,̶ ̶ n̶o̶t̶ ̶ m̶u̶c̶h̶)̶.̶

    You started out well. :-)

    Emissivity is a property of a surface, independent of the incoming radiation, independent of conduction or convection or evaporation. It only depends on the surface material and the temperature.

    A blackbody at 300 K emits 459.3 W/m^2 of thermal radiation. Period.
    If an object at 300 K emits 436.3 W/m^2 of thermal radiation, the emissivity is 0.95. Period.

    If doesn’t matter if they are heated by sun light or an electric heater of an IR lamp or nuclear reactions.
    It doesn’t matter if there is evaporation or convection or conduction (other than the fact that more total energy input will be required to maintain the 300 K temperature and hence the thermal IR).

    ε = (radiated power) / ( σ * T^4 * A)

    That is the whole equation!

  51. Stephen Wilde says:

    “vertical mechanical motion of air is mostly a fast process”

    Not sure about that since there is the Brewer-Dobson circulation in the stratosphere which is very slow.

    Also in the troposphere there are indeed small areas of fast uplift in depression centres and fast descent in the middle of intense high pressure cells but globally and on average it is all much more sedate.

    Generally, with average pressure being 1000 mbars anything above that is descending and anything above that is rising and not always quickly.

    But generally I agree that radiation exchange within an atmosphere can be dismissed in comparison to radiation from the surface where the atmosphere is made up mostly of non GHGs.

  52. Hans Jelbring says:

    Stephen Wilde says: December 11, 2012 at 4:33 pm

    I did mention the time span I consider “fast” so you can check it up. I must admit that I restricted my comment to the troposphere where the bulk mass of the atmosphere and stored atmosphere energy reside.

    Every day over land when sun is shining and air is raising the adiabatic temperature lapse rate will develop (dry ot wet) from the surface to the inversion level. That is quite often. Add to that the always existing katabatic wind system in Antarctica (windiest palces on earth), plus any low pressure vortex and you will include quite a lot. The adiabat develops in many windy conditions as well where intense mechanical mixing exists. However during night cooling over land when air descend in calm conditions the radiative cooling will exceed the change produced by mechanical vertical flows. Radiative cooling to space is then about 1 C/24 hour which can be observed in the troposphere in equatorial regions.

    Fast processes will always help in producing a dry or wet adiabatic since it will locate equal amount of energy per atmospheric mass unit (2 law of thermodynamics at work). Descending air (for whatever reason) will mostly produce inversions and these are often slow moving and upset the local or regional equalization of energy per mass unit.

  53. Bryan says:

    Tim Folkerts says:

    “Bryan says: “Its interesting that Tim Folkers is using a skeptical science link.”

    (( sigh )) I KNEW someone wouldn’t be able to resist making an ad hominin attack.

    Bryan, attack the MESSAGE not the messenger! Whatever else SkS my have said has no bearing on this particular data. ”

    I was not attacking you though it appears you don’t get out much.

    Why would anyone want to source material from SkS?

    They have been caught red handed tampering with posts and graphs.

    Why would anyone want to waste time checking out if this is yet another fiddle?

    Use reputable sources for your links.

    WUWT lists them as unreliable
    This must be one of the most understated descriptions of the SkS site

  54. tallbloke says:

    Entropic Man unwisely compared me to a young earth creationist, and is now winding down for a Christmas holiday break from commenting.

    Happy holidays Entropic. :)

  55. Max™‮‮ says:

    ” because there is on average 240W/m^2 coming in (after albedo which wouldn’t be there with no water vapour) there can’t be more than 240W/m^2 on average going out.”~ Tallbloke

    I thought there was 480 W/m^2 (after albedo) coming in, but the only constraint which 240 W/m^2 out places is a minimum temperature, isn’t it?

  56. paulinuk says:

    The Earth absorbs light from the sun and emits at peak IR of 10.1um at 15c. Why have the Skeptical Science graphs the shifted the x-axis 10um to the left and show the Earth radiating at 20.1um?

  57. paulinuk says:

    Oh, and once gases/ plasmas are thermalised, they must emit radiation to cool down, the wavelength being dependent on the temperature alone and not the spectral absorbtion characteristics of the molecules/atoms. Prove otherwise.

  58. paulinuk says:

    Tim Folkerts asks “Look at an IR spectrum looking DOWN from above and tell me what you see. Do you see any IR that comes from N2 or O2?”

    Yes, since all matter that’s Thermalised emits IR at a peak wavelength of 10.1 um at 15c

  59. Tim Folkerts says:

    >>Tim Folkerts asks “Look at an IR spectrum looking DOWN from above
    >>and tell me what you see. Do you see any IR that comes from N2 or O2?”

    >Paulinuk replies: “Yes, since all matter that’s Thermalised emits IR at a
    >peak wavelength of 10.1 um at 15c”

    No, all matter emits thermal radiation less than or equal to the curve given by the Planck’s Law (http://en.wikipedia.org/wiki/Planck%27s_law#Different_forms), which has a peak at 10.1um at 15 C.

    But the actual amount radiated at any given wavelength will be smaller for any object that is not a black body. And N2 is about as far from a black body as you can get. The emission (and absorption) from N2 in the earths atmosphere are ORDERS OF MAGNITUDE smaller than those emitted (or absorbed) by a black body at any and all wavelengths.

    In other words, 10.1 um IR emitted by the surface will pass up thru all the N2 in the atmosphere without getting absorbed by N2. And equally, N2 in the atmosphere will not emit any (significant) amount or IR either up or down. That is what is in the measured spectra, if you take a look. The “proof” is in the measured spectra!

  60. Tim Folkerts says:

    Max ponders: ” I thought there was 480 W/m^2 (after albedo) coming in …

    * There are ~ 1370 W/m^2 coming in from the sun (measured perpendicular to the direction of travel)

    * There are ~ 0.7 * 1370 W/m^2 = ~ 960 W/m^2 after albedo (measured perpendicular to the direction of travel)

    * The half of the earth facing the sun is not always perpendicular to the direction of travel (it is a sphere!). Averaged over the sun-facing side, you get (960 W/m^2) / 2 = 480 W/m^2 on the sunny side after albedo.

    * Averaged over both the sunny and the night side, you get (480 W/m^2) / 2 = 240 W/m^2 after albedo.

    It is all elementary geometry.

  61. paulinuk says:

    I’m don’t trust wiki links as that Connelly and others are notorious for changing pages to suit their AGW perspective. I see Wiens Law has changed since I last looked at it and is now just an approximation and only really applies to hot gases. I prefer the links from real scientists who actually measure things and seem to know what they’re talking about and can communicate in plain English:

    http://www.nrao.edu/index.php/learn/radioastronomy/radiowaves#blackbody

    Tim, when a ball of gas is in deep space the only way for it to lose heat is by radiation. If isolated nitrogen gas were heated up in deep space you say it will stay hot since it can’t radiate. Care to put that to the test and take your spaceship up close to a ball of hydrogen or nitrogen gas heated up in stages to 1c,10c, 100c,1000c, 10000c, 100000c and see what happens.

  62. paulinuk says:

    Tim says “In other words, 10.1 um IR emitted by the surface will pass up thru all the N2 in the atmosphere without getting absorbed by N2″

    I don’t agree: 10.1 um IR is emitted by the surface AND all the atmospheric gases – part of that IR is absorbed by GHG in their respective absorbtion bands. In other words you don’t know where the 10.1um IR came from.

  63. paulinuk says:

    Tim says “That is what is in the measured spectra, if you take a look. The “proof” is in the measured spectra!

    You haven’t supplied any proof other than a graph of what a satellite sees from outside the atmosphere of which I accept reservedly ( as I stated the x-axis looks out of place). What I see from that graph is the satellite looking down at 10.1um broadband IR emitted from the atmosphere (N2 and O2 mainly) AND ground with parts of the broadband IR absorbed by GHG’s.

    Also test tube “proof” isn’t the same as the real world proof.

  64. Max™‮‮ says:

    Tim, you said “* Averaged over both the sunny and the night side, you get (480 W/m^2) / 2 = 240 W/m^2 after albedo.”, right?

    The energy from the sun is never actually averaged over the planet, you are choosing to do this for whatever reason.

    Like I said elsewhere, 1×10^22 Joules is absorbed by half of the surface per second (approximately), 1×10^22 Joules is emitted by all of the surface per second (approximately), and these can not actually be sensibly averaged as you are doing there.

    The planet emits roughly 240 W/m^2 from the top of the atmosphere, approximately, which works out to 1×10^22 Watts over the entire surface.

    The planet receives that same amount of power across one hemisphere, which produces a much higher theoretical maximum than your average would suggest.

    The only thing your value tells us is what the minimum temperature could theoretically be.

    If the surface was a black body, the planet could be no colder than 255 K.

    If the day side was absorbing all of the energy with no reflection or atmospheric cooling effects (as I explained in your thread) then the day side would reach temperatures similar to those found on the day side of the moon, 390 K in parts, and easily 330+ K across a large portion of the surface.

    The moon absorbs a similar amount of energy and distributes it across roughly a 2 dimensional surface which then emits to space.

    The earth distributes that energy through a 3 dimensional atmosphere, and the entire system emits to space in parts.

    I wonder…

    Does anyone here think distributing a given amount of energy across a square meter will raise it to the same temperature as distributing the same amount of energy throughout a cubic meter?

    I’ve been doing a home experiment for a class which is related to the first point, to sum it up I have two styrafoam boxes set up in my bathroom beneath a row of four light sockets, if I can I will try to find four 30 watt bulbs to eliminate any ambiguity, but so far I have four 60 watt bulbs, I’ve set up the system in various ways along with a control system that is near but not directly illuminated by the bulbs, a thermometer in each, and then I have been systematically adjusting a variable, then comparing the temperature changes after a period of time with two 60 watts and the temperature changes after half the above period of time with four 60 watts and half the period with the lights off.

    I’ve tweaked the CO2 content, convection, I’ve tried using a (ziploc freezer) bag of water with the thermometers above it, and so forth.

    I have tweaked the airflow through the bathroom, but always make sure that the two 60/four 60 samples are done in the same manner, just differing in time/wattage.

    I’ve done samples with the different wattage for the same time, and I’ve even done the opposite, with two 60 for half the time as four 60, just to eliminate as many variables as I can think of.

    So far, nothing has changed the general result: 120 Watts for time=x does not produce the same peak, or end temperature as 240 Watts for time=x/2 + 0 Watts for time=x/2.

  65. Brian H says:

    Yeah, surprise, the Earth violates all the preconditions and assumptions for S-B analysis, so it’s simplification doesn’t apply.

  66. Brian H says:

    Oog. typo: “its simplification”.

    I’m so ashamed!

  67. paulinuk says:

    TB says “The Water vapour and Carbon dioxide are important, because they radiate energy much more readily than Nitrogen and Oxygen. Radiation is the only way energy can get back into space, so without them in the upper atmosphere, it would get very hot as the solar energy would have to circulate from the dayside surface through the atmosphere, back to the surface on the nightside and be radiated to space direct from the ground. In the lower atmosphere, they directly absorb some of the incoming solar energy and some of the departing long wave radiation leaving the ground and thermalise Nitrogen and Oxygen molecules in collisions. So a bit like clouds, the radiatively active gases are both part of the cooling and part of the warming factors.”

    You are effectively saying that the Earths surface with just N2 and O2, and without H2O and CO2, would be much hotter.

    Wouldn’t the Earths’ surface be just 91c colder (ref. Niklov and Zeller) as all the radiating to space would occur at the surface at -76c and the temperature of the N2 and O2 would never get higher than -76c just by conduction at the surface?

  68. tallbloke says:

    Hi Paul:
    N&Z’s gray body calculations are for airless planets. Earth with an N2 O2 atmosphere is a different case. The atmosphere would get heated by the surface by conduction. This would set up convection and advection as the higher atmospheric temperature on the dayside would have a differential with the atmospheric temperature on the nightside, which would be cooled by conduction back to the surface.

    Because hot air rises, and there is no escape for energy at the top of the atmosphere without radiation, the atmosphere would get very hot indeed higher up. This high temperature would conduct back to the surface due to mixing induced by advection..

    In reality the winds would be fierce, and this would raise a lot of dust into the atmosphere capable of radiating to space from above the ground. That dust would be hot in the superheated atmosphere and would radiate effectively, mitigating the heat accumulation at altitude.

    It would have to be modelled properly to see what the outcome would be for surface temperature. Not an easy task.

  69. Max™‮‮ says:

    The atmosphere would still radiate way up high, but the surface wouldn’t be able to transfer energy to the atmosphere through radiation or evaporation/condensation, leaving only conduction/convection/a few scattered absorption lines.

    The same amount of energy coming in and leaving, but it wouldn’t be distributed as effectively into the atmosphere, so the surface should be hotter.

  70. tallbloke says:

    Hi Max:
    Not much radiation could take place to space from N2 and O2, so most radiation would have to come from the ground surface. Since the planet can only radiate out as much as comes in and remain in equilibrium, it would be at a temperature commensurate with its emissivity and distance from the Sun, about 0.88 for a Moon like surface getting around 316W/m^2 from memory. We’d be getting as much as the Moon due to lack of cloud albedo, so surface T would be around 5C according to Tim F.

  71. Max™‮‮ says:

    The moon hits 390 K during the day, we have an atmosphere which takes the energy responsible for that same potential daytime peak and spreads it over a large volume of gas and ocean.

    If you remove any of the methods by which energy leaves the surface, it would become warmer, would it not?

    N2 and O2 radiate fine, they just don’t absorb strongly in terrestrial emission wavelengths so they can’t contribute a significant cooling effect by themselves.

    In fact, the main contribution from N2 and O2 is due to their mass alone, though they do absorb a not insignificant amount of energy from the sun, the main effect we see from those two gases is the surface pressure and the corresponding temperature.

    Adding H2O and CO2 provides two avenues for energy transfer from the surface to the atmosphere, and thus are largely responsible for distributing energy more effectively to the other gases, lowering the overall temperature.

    You can’t forget that an atmosphere with only N2 and O2 will still have a lapse rate, so there is no reason to think the surface would be cooler.

  72. tallbloke says:

    Thanks Max
    I’ll look into how well they radiate.

  73. Stephen Wilde says:

    “Because hot air rises, and there is no escape for energy at the top of the atmosphere without radiation, the atmosphere would get very hot indeed higher up”

    Molecules have the same total energy at the top as at the bottom but during the rising process KE gets replaced by PE and the temperature FALLS.

    PE doesn’t radiate out so energy cannot be lost to space as a result of the rising process.

    It is different for latent heat of evaporation because condensed out water droplets radiate upward very effectively.

    It is different too for GHGs since they can radiate out as well.

    As for all the rest of the energy which is hidden away as PE it can only be released as the air descends again and converts PE back to KE. That reconversion process is strongest back at the surface which heats up because the reconverted energy has to be ADDED to the incoming insolation.

    The PE / KE relationship is the key to the whole thing.

  74. Tim Folkerts says:

    Max says: “If you remove any of the methods by which energy leaves the surface, it would become warmer, would it not?

    That depends on which “it” you are referring to. And how the energy “leaves the surface”.

    If you remove a method that TRANSFERS energy from the warm surfaces of the planet to cooler parts of the planet (and transfers energy to the cooler surfaces from warmer parts) (eg convection), then …
    * if “it” = “the warm areas” — then “it” will indeed warm up as less energy is carried away
    * if “it” = “the cold areas” — then “it” (for example on the night side) will cool off because convection is not returning any of that energy back to the surface.
    * if “it” = “the whole world” — then “it” will cool down.

    To repeat the point with fewer double negative, the more you can spread the energy around (keeping the hot parts cooler and the cold parts warmer), the warmer the world AS A WHOLE will be.

    ********************************************************************************

    On the other hand, if you remove a method by which energy leaves the planet as a WHOLE, then you will can indeed make the surface as a whole warmer. GHGs reduce the energy leaving the planet as a whole, so they can warm the surface (until the surface warms enough to restore the balance).

  75. paulinuk says:

    Kirchoff’s first of law radiation: ” A hot solid, liquid, or dense gas emits radiation at all wavelengths (“a continuous spectrum of radiation”). For example, a perfect blackbody does this. If the light were passed through a prism, you would see the whole rainbow of colors in a continuous band”

    So the dense N2, O2 atmosphere of Earth emits black body radiation with a peak of 10.1um at a temperature of 15c or 288k. This adds to the upward reading of BB radiation from the surface. What goes up goes down as well so they must add to downward IR radiation and raise the surface temperature. Looking at the atmosphere side on you’d be able to detect the thermal radiation. Looking from above with the aid of a satellite you’d see the absorbtion bands of the greenhouse gases missing from the thermal BB radiation from the air and land combined as the air is cooler than the ground and can absorb at the internal energy absorbtion bands of CO2, H20 .

    See fig1 in Science of Doom; Part 1 , visualizing atmospheric radiation (NB : ignore his interpretation and just reason for yourself)

  76. […] average surface temperature above that of the Moon. I covered some of the possibilities in a non-technical essay a while […]