What If There Was No Greenhouse Effect?
by Roy W. Spencer, Ph. D.
The climate of the Earth is profoundly affected by two competing processes: the greenhouse effect, which acts to warm the lower atmosphere and cool the upper atmosphere, and atmospheric convection (thermals, clouds, precipitation) which does just the opposite: cools the lower atmosphere and warms the upper atmosphere.
To better understand why this happens, it is an instructive thought experiment to ask the question: What if there was no greenhouse effect? In other words, what if there were no infrared absorbers such as water vapor and carbon dioxide in the atmosphere?
While we usually only discuss the greenhouse effect in the context of global warming (that is, the theory that adding more carbon dioxide to the atmosphere will lead to higher temperatures in the lower atmosphere), it turns out that the greenhouse effect has a more fundamental role: there would be no weather on Earth without the greenhouse effect.
First, the big picture: The Earth surface is warmed by sunlight, and the surface and atmosphere together cool by infrared radiation back to outer space. And just as a pot of water warming on the stove will stop warming when the rate of energy gained by the pot from the stove equals the rate of energy loss by the pot to its surroundings, an initially cold Earth would stop warming when the rate at which solar energy is absorbed equals the rate at which infrared energy is lost by the whole Earth-atmosphere system to space.
So, let’s imagine an extremely cold Earth and atmosphere, without any water vapor, carbon dioxide, methane or any other greenhouse gases – and with no surface water to evaporate and create atmospheric water vapor, either. Next, imagine the sun starts to warm the surface of the Earth. As the surface temperature rises, it begins to give off more infrared energy to outer space in response.
That’s the Earth’s surface. But what would happen to the atmosphere at the same time? The cold air in contact with the warming ground would also begin to warm by thermal conduction. Convective air currents would transport this heat upward, gradually warming the atmosphere from the bottom up. Importantly, this ‘dry convection’ will result in a vertical temperature profile that falls off by 9.8 deg. C for every kilometer rise in altitude, which is the so-called ‘adiabatic lapse rate’. This is because rising warm air parcels cool as they expand at the lower air pressures aloft, and the air that sinks in response to all of that rising air must warm at the same rate by compression.
Eventually, the surface and lower atmosphere would warm until the rate at which infrared energy is lost by the Earth’s surface to space would equal the rate at which sunlight is absorbed by the surface, and the whole system would settle into a fairly repeatable day-night cycle of the surface heating (and lower atmosphere convecting) during the day, and the surface cooling (and a shallow layer of air in contact with it) during the night.
The global-average temperature at which this occurs would depend a lot on how reflective the Earth’s surface is to sunlight in our thought experiment. ..it could be anywhere from well below 0 deg F for a partially reflective Earth to about 45 deg. F for a totally black Earth.
So, how is this different from what happens in the real world? Well, notice that what we are left with in this thought experiment is an atmosphere that is heated from below by the ground absorbing sunlight, but the atmosphere has no way of cooling…except in a very shallow layer right next to the ground where it can cool by conduction at night.
Why is this lack of an atmospheric cooling mechanism important? Because in our thought experiment we now have an atmosphere whose upper layers are colder than the surface and lower atmosphere. And what happens when there is a temperature difference in a material? Heat flows by thermal conduction, which would then gradually warm the upper atmosphere to reduce that temperature difference. The process would be slow, because the thermal conductivity of air is quite low. But eventually, the entire atmosphere would reach a constant temperature with height.
Only the surface and a shallow layer of air next to the surface would go through a day-night cycle of heating and cooling. The rest of the atmosphere would be at approximately the same temperature as the average surface temperature. And without a falloff of temperature with height in the atmosphere of at least 10 deg. C per kilometer, all atmospheric convection would stop.
Since it is the convective overturning of the atmosphere that causes most of what we recognize as ‘weather’, most weather activity on Earth would stop, too. Atmospheric convective overturning is what causes clouds and rainfall. In the tropics, it occurs in relatively small and strongly overturning thunderstorm-type weather systems.
At higher latitudes, that convection occurs in much larger but more weakly overturning cloud and precipitation systems associated with low pressure areas.
There would probably still be some horizontal wind flows associated with the fact that the poles would still be cooler than the tropics, and the day-night heating cycle that moves around the Earth each day. But for the most part, most of what we call ‘weather’ would not occur. The same is true even if there was surface water and water vapor…but if we were able to somehow ‘turn off’ the greenhouse effect of water vapor. Eventually, the atmosphere would still become ‘isothermal’, with a roughly constant temperature with height.
Why would this occur? Infrared absorbers like water vapor and carbon dioxide provide an additional heating mechanism for the atmosphere. But at least as important is the fact that, since infrared absorbers are also infrared emitters, the presence of greenhouse gases allow the atmosphere — not just the surface — to cool to outer space.
When you pile all of the layers of greenhouse gases in the atmosphere on top of one another, they form a sort of radiative blanket, heating the lower layers and cooling the upper layers. (For those of you who have heard claims that the greenhouse effect is physically impossible, see my article here. There is a common misconception that the rate at which a layer absorbs IR energy must equal the rate at which it loses IR energy, which in general is not true.)
Without the convective air currents to transport excess heat from the lower atmosphere to the upper atmosphere, the greenhouse effect by itself would make the surface of the Earth unbearably hot, and the upper atmosphere (at altitudes where where jets fly) very much colder than it really is.
Thus, it is the greenhouse effect that continuously de-stabilizes the atmosphere, ‘trying’ to create a temperature profile that the atmosphere cannot sustain, which then causes all different kinds of weather as the atmosphere convectively overturns. Thus, the greenhouse effect is actually required to explain why weather occurs.
This is what makes water such an amazing substance. It cools the Earth’s surface when it evaporates, it warms the upper atmosphere when it re-condenses to form precipitation, it warms the lower atmosphere through the greenhouse effect, and it cools the upper atmosphere by emitting infrared radiation to outer space (also part of the greenhouse effect process). These heating and cooling processes are continuously interacting, with each limiting the influence of the other.
As Dick Lindzen alluded to back in 1990, while everyone seems to understand that the greenhouse effect warms the Earth’s surface, few people are aware of the fact that weather processes greatly limit that warming. And one very real possibility is that the 1 deg. C direct warming effect of doubling our atmospheric CO2 concentration by late in this century will be mitigated by the cooling effects of weather to a value closer to 0.5 deg. C or so (about 1 deg. F.) This is much less than is being predicted by the UN’s Intergovernmental Panel on Climate Change or by NASA’s James Hansen, who believe that weather changes will amplify, rather than reduce, that warming.
Nick Stokes (13:53:50) :
“But eventually, the entire atmosphere would reach a constant temperature with height.”
Why wouldn’t the adiabatic expansion mechanism then continue to convey heat downwards (the air would not be motionless because of diurnal effects and thermal inhomogeneity), to restore and maintain (nearly) the adiabatic lapse rate of -9.8 K/km? Surely this mechanism moves heat more effectively than conduction?
There won’t be any mechanical reason for convection in an isothermal atmosphere as a rising parcel would be found very quickly at a temperature lower than its surroundings. Even on a planet with pretty active convection such as ours the environmental lapse rate is not adiabatic. Another way to think of this is, the convection acts as a heat engine. It has only a hot reservoir, though. Without a cold reservoir in which to expel waste heat the engine will stop running its cycle.
bob (14:18:37) :
“Why would this occur? Infrared absorbers like water vapor and carbon dioxide provide an additional heating mechanism for the atmosphere. But at least as important is the fact that, since infrared absorbers are also infrared emitters, the presence of greenhouse gases allow the atmosphere — not just the surface — to cool to outer space.”
You don’t need the greenhouse gases to cool the atmosphere, oxygen and nitrogen are infared emitters according to the Planck black body radiation effect.
But you do need an emissivity above zero. Nitrogen and oxygen have an emissivity of effectively zero. There would be some radiation emitted in the acceleration that occurs when molecules collided, but that would be effectively nil at the temperatures we are talking about here. Anthony suggested that oxygen has some weak IR bands, and thus may have some very small emissivity. However, the atmosphere that Dr. Spenser posits would have some interaction with sunlight in the UV, and he didn’t include that effect.
So the atmosphere cools without the greehouse gases.
thanks
Cripes! Some of bob’s post got attached to the end of mine. Without an edit facility these are endless errors like this for me. The atmosphere contemplated will not cool without IR emitters.
anna v (05:42:08) :
Thanks much for the pointers. Everything you said is correct. I’m familiar with QM. Everything you have pointed I realize. I know of duality also.
How do I put this and stay very simple and pure without numbers? Can’t talk a book worth here.
But this question requires someone so versed in QM & TD they can visually and logically separate a complex system into a single special case that can be exactly (to constants precision) computed and tracked.
I am going to give that special photon’s momentum a value, one, in a transformed unit system that I am going to keep secret (really irrelevant). I have a program with all of the equation in all of science so I can compute anything to adequate precision.
That original special photon travels up X distance and interacts with a molecule because energy levels and the frequency match. All of the momentum is transferred to the molecule, no more photon. I compute molecules position after specific time. The molecule ejects two low level photons, one in this direction one in that direction and a fraction of the momentum still resides in the molecule (no added rotations). I compute. I now have three pieces of the original momentum. I add them up. It’s one with the vector pointing strait up. The molecule bumps another molecule, another split billiard style and one molecule is now spinning, compute, now five pieces. They all add to one and the vector is still strait up.
Get my gist here. It may be that science in universities has become so complex in scientists and students minds that simple core underlying cases cannot be discussed and/or computed without bringing in the hundreds of complex macro-level laws which let us compute things in the real world that otherwise would be impossible. It’s as if most I talk to are unable to go back to the basics. Maybe it’s not even taught anymore. If so, it may time for me to exit science (I’m kidding).
It takes great effort to take a complex system and refine and simplify back to the core laws. But those laws are the foundation of science. Conservation of energy and momentum still apply.
Re-read post above keeping it purely simple and see if the point being made is true (or false). Anna, I do appreciate your help.
Moderator please bear a long one.
Anna:
OK! That’s the key. I know if there are many emission lines, the momentum will be split between the photon(s) of lower wavelength and some residual momentum may reside in the molecule. But conservation of momentum must always be preserved. One place or the other(s).
Please follow. Think only of the original parcel of momentum and keep track of it.
I have read literally a hundreds of papers concerning this broad subject. But I kept having a reoccurring catch in all of the pure logic used. Let’s take this as Einstein would, one infinitesimal thing at a time.
Take a special IR photon, properties set by me, carrying energy thus momentum, leaving a spot on the equator and heading directly zenith to keep this pure.
The momentum carried by this photon, one way or the other must be preserved. The photon may be absorbed by a molecule in proximity if wavelength allows, that molecule hits other molecules so momentum of the molecule changes and is distributed, this can occur many times. But mother nature by her physics is so frugal with her accounting of her energy and her momentum that she will not miss the tiniest portion of her precious energy and momentum.
That momentum from that zenith heading photon may be divided and scattered over many molecules or subdivided into components of other photons in various directions but the SUM of the net effects of that lonely photon’s momentum will end up in portions of two states. One component’s portion (can be zero) escapes into space carried by the original OR divided between some other photon(s) in some direction(s) possibly at different wavelength(s). The other possible state is to cause an infinitesimal but real and exact expansion of Earth’s atmosphere by increased momentum of a molecule(s). This will initially manifest as an increased pressure but eventually will be expansion. The sum of the momentum of these two states (speaking only of the original photons momentum), seems to me MUST be equal to the original momentum of that lone photon to meet conservation laws.
If the above is correct, from here on only speaking of that original parcel of momentum. If the photon didn’t encounter any interaction on its way up, it merely escapes into space. End of story, momentum preserved. However, if it had any interaction and the portion of momentum escaping into space (can be zero) is less than the original, the only other possible state is an expansion of the atmosphere by the remaining portion of the original momentum.
If I’m still right to this point, you can now view that photon’s momentum generically as radiative pressure. And any layer of the atmosphere as a near spherical membrane that this momentum must cross, one way or the other to satisfy conservation of the momentum.
The gist of the above is to say that energy, thus momentum, of outgoing photons cannot be absorbed and re-radiated IN A NADIR direction without also expanding the atmosphere, thus, by thermodynamic laws cooling the atmosphere in an equal amount of the heat trapped.
I’m stuck on this point. Reoccurs in my mind every paper I read and until I can get a understandable answer, I don’t feel an added portion of CO2 that traps additional heat can help but to expand the atmosphere thus cancelling any effect. Some papers support this view but from other directions. I tried to make mine simple.
Any help, corrections or comments?
Phil. (08:21:46) :
Sorry about the error — yes there is more CO2 per sq m, but as your spectrum shows, the low total pressure greatly reduces the radiative forcing by CO2 compared to earth.
But this is really all beside the point — the main point about reference to Mars is that in the absence of heavy dust, the surface temperature is close to the planetary radiative equilibrium temperature (such that IR emission from the surface is balanced by solar heating == e.g the definition of an inefficient greenhouse). Despite this, Mars has a highly dynamic atmosphere.
[The main reason Mars has such an inefficient greenhouse, is 1) very low humidity (therefore IR opacity is very low in the thermal IR; CO2 absorption covers only ~10% of the thermal emission spectrum even on earth with its larger pressure broadening) and 2) the low total pressure reduces the efficiency of all greenhouse gases (including H2O and CO2). ]
Alex Harvey (08:00:19) :
“The situation with mixtures of gases is a little more complicated as radiation absorbed by CO2 can be passed thermally to H2O and emitted at frequencies that CO2 simply could not.”
There’s something in that observation. However, the colling of c02 leads surrounding molecules to warm up, and can only do so when it emits at the bandwidth that receiving molecules like oxygen can accept them, though this isn’t the case with H2o, so co2 doesn’t thermalize with h2o – mainly because the thermal excitation of c02 is a tiny part of total heat in the system. In a given volume of air, for each co2 molecule there are about 3000 nitrogen and oxygen molecules, and only around 5% of c02 molecules will be excited at 15C – so the chances of c02 colliding with anoter c02 are quite rare, and it is like molecules which are the most efficient t transmitting radiation. That changes the entire ration of excited cow molecules in a volume of air to the nitrogen and oxygen ones. c02 in th ebending mode doesn’t have the energy to excites a h2o molecule, although it does in the symmetric streching mode – only it has to be at such a high energy that isn’t even found at 35C. As said above, radiation and molecules move in 3 dimensions so for c02 molecules in the upper troposphere where the greenhouse effect is said to be at its mst active, we run into another conundrum: There are even fewer c02 molecules per volume of air that oxgen and nitrogen and the temperature in the mid-upper troposphere indicates that c02 absorbs heat outside of its peak 15 microns, to the shoulders where it coincides with the small peaks of oxygen and nitrogen’s small heat retaining effect – and then there are millions more molecules that co2 has to compete with.
Incidentally, there can be up to 31% h20 in a volume of air and this is where heat is intercepted by h20, leaving c02 little, if any heat to intercept. water vapour like molecules tend to collide and vibrate more with each other, and transfer energy to each other more efficiently. (C02 capture of heat is quite a rare occurence in the atmosphere)
Well… having spent about 2 hrs on this post and blog, I can only come to one conclusion: while it has all been very entertaining, it only shows how intensely complicated it all is, and how far-fetched it is to imagine that the entire thing can be driven merely by small changes to CO2 levels. Most of the above still seems seriously counter-intuitive to me. Methinks the chaotic nature of earth’s systems (per definition as I understand it: multiple non-linear mathematical models interacting) will ultimately prove to be beyond man’s intellect.
As for the (patently extremely simplistic) current state of the art: After initially starting out, some years ago, as merely skeptical, I now doubt even the fundamental premises. I doubt that CO2 levels have actually increased due to man’s efforts… I doubt that earth’s temperature has recently increased beyond margin of error… I doubt the very veracity of the greenhouse effect in this context. Data is suspect.. analyses flawed… motives uncertain.
Perhaps some sense will ultimately come from disciplines other than climate research, hopefully less tainted by agendas other than science. Here’s hoping… (but still reading all this! Keep up the good work!)
“cow” molecules should be c02 molecules in that 2nd paragraph. If cows could fly…
I believe the most likely source of outgoing radiation from the upper atmosphere is from solid or liquid particles at the cloud-tops as I believe they emit radiation over a much broader spectrum of wavelengths than gases as a result of their solid or liquid bonding energy states. The problem I see for emissions from the primary gases in the atmosphere is the high probability of re-absorption by the same gases higher up. Perhaps this is the reason for the progressive warming below the stratopause.
I expect that radiation from trace gases just below the tropopause would have a higher chance of getting out because this radiation would be less likely to have an absorption encounter with another molecule of the same gas.
A transmission plot for outgoing radiation emitted from the equatorial tropopause (at 55,000 ft) should show much wider transmission windows as I estimate that over 90 percent of the mass of the atmosphere is below 55,000 ft. based on the reduced pressure at that altitude.
As I said earlier, perhaps the best real approximation of Dr. Spencer’s conjecture is the ancient ice-cube or Ice-Ball Earth climate catastrophe indicated in the geological record.
At the end of Dr. Spencer’s thought experiment world, “the rest of the atmosphere would be at approximately the same temperature as the average surface temperature”. If the average surface temperature turned out to be around the freezing point of water, then the N2 and O2 at, say 30,000 feet elevation, would be floating around happily at 273 deg Kelvin day after day right there on the edge of space.
Re: P Wilson (11:17:15) :
“Alex Harvey (08:00:19) :
“The situation with mixtures of gases is a little more complicated as radiation absorbed by CO2 can be passed thermally to H2O and emitted at frequencies that CO2 simply could not.”
There’s something in that observation. However, the colling of c02 leads surrounding molecules to warm up, and can only do so when it emits at the bandwidth that receiving molecules like oxygen can accept them, though this isn’t the case with H2o, so co2 doesn’t thermalize with h2o – … ”
Sorry, it is a mixture of gases, so they also strive for thermal equilibrium through contact, i.e. collisions. Even if two gases have no overlap in their spectra when mixed that is still the case.
Alex
Ron House (05:31:04) :
Sometimes I don’t write enough to be clear, not wanting to be too long in post!
Precision is the key. This is somewhat theoretical. If I have a conglomerate of gases, and at one instance I know the temperature is exactly 20.000… to 99 places. Along comes a photon that is totally captured by one of the molecule. I know the temperature has increased no matter how tiny its influence may be, maybe in the 63rd digit. The pressure after one pico second will be increased pressure locally but since Earth has no top on its atmosphere, that pressure over time will be expressed as expansion of volume (but maybe not totally, would have to look that up). That’s what I mean when I silently ‘mix’ systems.
JER0ME (17:56:12) :
sorry I have lived Norht AND South of the equator and can assure you that Coriolis affects the way the water drains down th plug hole.
Aged 16 went from UK (54N) to Zambia (12S) – almost the very 1st thing I did was confirm that the water went down the plug in the opposite direction to the UK.
Experimental science by observation,
Later over the years I repeated the test – on ships – so I do not know what & why the experiments you cite produced anomalous results.
However easy experiment if you are not on/near the equator :
go to the kitchen/bathroom fill a sink with water – pull the plug – observer which way the water spins.
repeat several times – repeat at friends houses work etc.
Next experiment :
Fill sink with water (very full) stir water so there is a gentle flow in the OPOSITE direction to that observed above – pull plug & observe what happens.
Now – if the Coriolis force is NOT responsible explain the OBSERVED result (every time I have done this is results in the flow direction being reversed as the water drains down the plug hole)
Observation by repeating the experiment trumps/confirms theory every time
Paul (19:34:32) :
“there are about the same number of molecules of CO2 above any sq meter on Mars as on Earth”
No. The surface pressure on Mars ranges from 30 Pa (Olympus Mons) to 1155 Pa (Hellas Planitia), with a mean nominal pressure of 600 Pa. 95.72% of the atmosphere is carbon dioxide, so the partial pressure can be as low as 29 Pa and as high as 1105 Pa. The surface gravity of Mars is 0.376 g. Should we place this atmosphere in a terrestrial gravity environment, the pressure range would be 76 Pa – 2940 Pa, with a mean of 1527 Pa.
The partial pressure of the same gas on Earth as of now is about 57 Pa. So there are 1.34 – 51.58 times more molecules of CO2 above any sq meter on Mars than on Earth, mean value 26.8.
An up to fifty times thicker carbon dioxide envelope more than makes up for lack of pressure line broadening. Even the highest point has more CO2 above it than on Earth, sea level. The same can not be said about highest point of Earth, Mt. Qomolangma, where CO2 partial pressure is only 18 Pa. Olympus Mons has four times as much carbon dioxide above it, although it is the highest mountain in the entire solar system, peak 27 km above mean surface level.
Spector (05:44:30) :
RE: kadaka (23:28:44)
I believe you are missing the point. Dr. Spencer is describing a planet with a *perfectly transparent* atmosphere — no greenhouse gasses, no clouds, and no dust in the upper atmosphere.
Nah, not really. Spencer concludes the Earth would be essentially isothermal, as Venus is. There is the lack of water vapor, as with Venus. The CO2 atmosphere is basically an inert gas. From there, examining this simpler system without the preconceptions of how Earth’s atmosphere operates, I can see better what he is talking about. The sulphuric acid clouds and haze do act as an insulator, but then that is only one layer to remove for the thought experiment. Without it the planet would likely be cooler, but otherwise resemble the thought experiment model.
Then, the questions begin. Here it is proposed convective overturning would cease. Yet convection is what drives the Venusian climate. Do the properties of the CO2 as an infrared absorber and emitter make the difference? Here it is argued the Earth would become isothermal. Venus is isothermal, with the convective overturning. Are the sulphuric clouds and haze keeping Venus isothermal? Etc. Just doing the thought experiment from a different starting point, ditching certain preconceptions, and examining what different questions, and what same ones, will arise.
Folks, I think Mars is a good planet for comparison to Earth as far as greenhouse effect goes. At least most of the confounding factors (water, clouds)are not present, the atmosphere is transparent in visible light and the planet has about the same axial tilt and rotational period.
My point about the amount of CO2 on Mars vs Earth is that the calculation is easy to do properly so we should at least get that right when talking about greenhouse effect on Mars.
If what Paul (10:10:58) said in his post is true then Mars might approximate Roy’s hypothetical Earth with obvious problems for Roy’s little thought experiment.
It also raises problems for the warmies if CO2 covers only 10% of the IR spectrum on Earth and the pressure broadening depends on total pressure not partial pressure of CO2. Doubling CO2 will only increase total pressure on Earth from 1013.25 hPa to 1013.69hPa at most but in reality less than that as the “O2” part of the CO2 comes from the oxygen in the atmosphere at least in part.
My question is, does doubling CO2 and causing a total pressure increase by a factor of 4 parts in 10,000 really cause a significant increase in pressure broadening ?
I think this is a significant question as a large part of the warmie case seems to depend on this.
Robert E. Phelan:
If you actually read the link I provided, you’d notice that it is Spencer’s own article describing his belief that the biblical creation story is plausible. But I’m glad that you agree that anyone who is a young earth creationist should not be trusted to have either a brain nor an understanding of science. So we can safely ignore anything that Spencer says.
Not that the article above is actually wrong, but it most certainly is a red herring.
Roy W. Spencer.
You wrote: “Importantly, this ‘dry convection’ will result in a vertical temperature profile that falls off by 9.8 deg. C for every kilometer rise in altitude, which is the so-called ‘adiabatic lapse rate’.”
I don’t see how this can be ‘adiabatic’ any more as you’ve taken out all the water and water vapour (WV) that provides the stability for the atmosphere to act as an adiabat. We’re looking ‘mostly’ at low stratospheric properties here aren’t we, but at surface altitudes where convection ‘will’ occur.
You wrote: “This is because rising warm air parcels cool as they expand at the lower air pressures aloft, and the air that sinks in response to all of that rising air must warm at the same rate by compression.”
Not quite. A ‘rising warm air parcel’ cools by ‘expansion on rising, mixing and radiation’, but you’ve taken out the radiative gasses so it cools more slowly! Thus, convection is doubly enhanced as there can be no latent factor either without water in the atmosphere.
You wrote: “Eventually, the surface and lower atmosphere would warm until the rate at which infrared energy is lost by the Earth’s surface to space would equal the rate at which sunlight is absorbed by the surface, and the whole system would settle into a fairly repeatable day-night cycle of the surface heating (and lower atmosphere convecting) during the day, and the surface cooling (and a shallow layer of air in contact with it) during the night.”
Completely nonsensical. Without radiative gasses in an atmosphere, the atmosphere reacts as a ‘black body’ also, but with a variable depth. The atmosphere also plays its part in cooling the planet!
I’ll not go on. While I tend to concur with your desire to convey understanding, this surely can’t be the way to do it!
The whole point is that just by removing radiative gasses from a model doesn’t remove all of the ‘greenhouse effect’ (GHE). For example! If another mass object (the atmosphere) is interposed between the void and a body radiating as a ‘black body’ (the Earth), the interposing body (the atmosphere) always shares some of the energy from the radiating ‘black body’ (the Earth). Thus, the atmosphere radiates a black body radiation at a reduced rate. This is a property of ‘insulation’!
Much as I’ve tried to, I really can’t follow your scenario.
Best regards, suricat.
Maybe we should start refering to CO2 as an Ice Age inhibitor.
Re: suricat (16:15:19) :
“Without radiative gasses in an atmosphere, the atmosphere reacts as a ‘black body’ also, but with a variable depth. The atmosphere also plays its part in cooling the planet!”
The atmosphere does not react like a black body and if it does not have a significant emission/absorption spectra when at earthlike temperatures it will not significantly radiate and will not significantly cool the planet.
There is a belief that all warm masses must radiate when at earthlike temperatures, but some gases do not unless you want to nit-pick over miniscule amounts. If a gas does not absorb thermal radiation from a source with an earthlike temperature it will not radiate when at an earthlike temperature.
Gases don’t just radiate, they have to have a machanism by which they radiate, and if they have a mechanism by which they can radiate at a specific frequency and they must have a mechanism to absorb at that frequency.
Alex
“Berényi Péter (13:51:12) :
Paul (19:34:32) :
“there are about the same number of molecules of CO2 above any sq meter on Mars as on Earth”
No. The surface pressure on Mars ranges from 30 Pa (Olympus Mons) to 1155 Pa (Hellas Planitia), with a mean nominal pressure of 600 Pa. 95.72% of the atmosphere is carbon dioxide, so the partial pressure can be as low as 29 Pa and as high as 1105 Pa. The surface gravity of Mars is 0.376 g. Should we place this atmosphere in a terrestrial gravity environment, the pressure range would be 76 Pa – 2940 Pa, with a mean of 1527 Pa.
The partial pressure of the same gas on Earth as of now is about 57 Pa. So there are 1.34 – 51.58 times more molecules of CO2 above any sq meter on Mars than on Earth, mean value 26.8.
An up to fifty times thicker carbon dioxide envelope more than makes up for lack of pressure line broadening. Even the highest point has more CO2 above it than on Earth, sea level. The same can not be said about highest point of Earth, Mt. Qomolangma, where CO2 partial pressure is only 18 Pa. Olympus Mons has four times as much carbon dioxide above it, although it is the highest mountain in the entire solar system, peak 27 km above mean surface level.”
the pressure broadening is affected by both the broadening of the same molecule type and the composite of all the other molecular types in the atmosphere. My recollections are that the Earth composite or air broadening is on about the same order of magnitude as that of the self broadening or the effect of other co2 molecules upon a co2 molecule. That being the case, then an atmosphere at 1 atm. (Earth sea level) has a much greater broadening effect than a maximum Martian pressure of 0.01 atm.
while I’ve never tried to run a full calculation on the martian atmospheric column, what I’ve seen from Earth’s is something along the lines of 3.5 W/m^2 for a co2 doubling at 70km with clear skies – which is ballpark of the warmer claims. Despite this significant effect on Earth that appears to be good for possibly almost a degree rise in temperature, the effect on Mars with the equivalent of 5 extra doublings over that of the Earth’s co2 amount is evidently around 1 degree or less for the total ghg contribution which is essentially totally co2. This shows that the actual pressure lower down in the atmosphere is important as well as the fact that co2 itself has rather little effect on temperature, even when there is no h2o vapor to reduce the co2 effects.
Alex Harvey.
You wrote: “The atmosphere does not react like a black body and if it does not have a significant emission/absorption spectra when at earthlike temperatures it will not significantly radiate and will not significantly cool the planet.”
I concur. Though we’re stuck with the presentation that precludes emission/absorption as made by Prof. Spencer!
You wrote: “There is a belief that all warm masses must radiate when at earthlike temperatures, but some gases do not unless you want to nit-pick over miniscule amounts. If a gas does not absorb thermal radiation from a source with an earthlike temperature it will not radiate when at an earthlike temperature.”
When at an Earth-like temperature does what? An Earth-like temperature is way above the temperature of the ‘void’, but seeing as any radiative energy transfer is prohibited in this model I guess it must defer to kinetic contact (with the void?). Ask Roy for clarification. Though I’ve not seen his participation in this thread yet.
I reiterate that; any mass above absolute zero temperature radiates its temperature signature until its mass temperature returns to absolute zero (though this is unobtainable).
Your last paragraph has no meaning here. Radiative theory is by-passed with this model. Perhaps we can link up elsewhere.
Best regards, suricat.
Radioactive Man (Norway) (07:14:37) :
Oh no… someone posted a link above (http://theevolutioncrisis.org.uk_testimony2.php) where one can read Dr Spencer’s less than enlightened views on evolution and the historicity of the Biblical Gospels, among other things. I must admit I was quite shocked by what I read. I can’t avoid being sceptical of anything he writes on climate science from now on, even if it isn’t related to his religious/anti-evolutionist views.
Well, you’d be shocked at what Clerk Maxwell had to say about origin of Earth and its age, and scripture, etc., etc., and yet he was “pretty good” physicist–I think he helped organize a few things in electrodynamics.
I read my earlier post and it seemed quite unclear, so let me try again.
I hadn’t thought of the impact of GHGs on convection until I read Spencer’s speculation here. It is a very fruitful thought I believe, because there is the idea that convection is inevitable as long as there is a warm surface, which we find through Spencer’s model atmosphere, is not so. There won’t be any mechanical reason for convection in an atmosphere with a lapse rate even slightly below the adiabatic value, as a rising parcel would be found very quickly at a temperature lower than its surroundings, and conduction, even though a slow process, would make the environmental lapse rate slightly below adiabatic (eventuall isothermal). However, I suggested that another way to think of this is as follows: Convection is a heat engine. Without greenhouse gases, though, it would have only a hot reservoir (the surface). Greenhouse gases provide the cold reservoir for this heat engine and without a cold reservoir in which to expel waste any heat engine will stop running its cycle (to do otherwise would violate the second law). Without greenhouse gases the only possible temperature structure is isothermal up until, at great height in Spencer’s model atmosphere, nitrogen and oxygen absorb UV, and make a temperature structure like our stratosphere.
Just some comments on Spencer’s model. Since it excludes water in any form that means no clouds or ice, I’ll assume a N2 atmosphere since any O2 allows for O3 which of course is a GHG. In that case our first issue is the albedo, in the absence of clouds etc it’s reasonable to use the lunar value (~0.15). Given that you’d expect a Lambertian temperature distribution (cos^0.25) with a maximum near local noon of about 350K and about 200K at the edge of the illuminated disc. The major loss from the surface by far will be bb radiation which will not interact with the atmosphere on its way out. While illuminated the surface will transfer some heat to the atmosphere via conduction, but this will be very thin because of the low thermal conductivity of air, when the surface passes out of illumination it will cool by radiation and cool the layer above it by conduction causing an inversion (such as happens at the poles). It’s likely that there would be circulation due to differential heating but its scale will be very small.