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.
Brian Macker (23:05:06) :
I’m a AWG skeptic. This article is just bad science.
I agree with you. False scenarios profit no one.
Nice Thought Experiment BUT:
fails to deal with the oceans effectively: lets expand his idea we have a low volatile oil on the ocean preventing evaporation, the ocean 70 % of the planets surface would be effectively a black body suface, and would heat to what ? 40 – 50 deg c during the cloudless day, but only to the depth of a metre or so, at night that heat would be released at the same rate as it was absorbed. my guess is that at night the temperatures would fall to – 40 or so deg effectively freezing the entire ocean which would then no longer be a black body.
Spend a night in the sahara desert you begin to get the idea.
A nice way of creating a usefull debate!! I will have to think about this some more
Thank you Dr. Spencer for the some deep insight. I for one can follow your gist and ignore factors obviously occurring in the real world and alter my view in a hypothetical sense to simplify a system down to the core points being discussed. Once again thanks.
Here’s a supplement paper I never had stumbled upon concerning excess radiation absorbance in clear atmosphere and clouds and handled differently in most models of that time. Have no idea if these factors have changed in current day models.
http://people.aero.und.edu/~dong/Valero_JGR_2000.pdf
Interesting. Don’t know if even more massive simultaneous tests have occurred recently. This answered the question I asked you near the top of these comments.
From Dr. Spencer’s post (emphasis added):
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.
And I am reading how many posts here saying Spencer must be wrong (or perhaps someone else is) because water vapor would…?
What am I missing?
To me, he seems to basically be describing Venus, which although it has CO2 in abundance it does not really function as a GHG in that planet’s atmosphere as CO2 does in ours, you could replace it with nitrogen for about the same effect.
Perhaps the picture above, showing oceans thus surface water, is throwing people off?
D. King (21:19:05) :
” Paul (19:34:32) :
wayne (18:51:41) :
Good question about the CO2 and the answer is not so straight forward. Although there are about the same number of molecules of CO2 above any sq meter on Mars as on Earth”
I get about 30 x as many over any square meter on Mars. Would you care to justify your number?
Mike Borgelt (23:36:40):
Exactly. Paul was saying because the low pressure on Mars, I’m assuming partial pressure, that CO2 on Mars has no effect on temperature or weather at 90% component. I’m questioning why a much lower partial pressure for CO2 on Earth would have any effect either if his statement is correct about Mars. Curiosity, isn’t it.
Robert E. Phelan (22:34:35) :
Hmmph. Frost in Florida. The Weather Channel keeps talking about some blizzard in New England. No snow here on the Connecticut Western Shore. Climate: it’s all local.
This cold in Florida was brought up ahead of time here at WUWT on 12/30/09.
http://wattsupwiththat.com/2009/12/30/major-northern-hemisphere-cold-snap-coming/
I have not read all the posts so it is possible someone else commented in a similar vein.
In the article it is mentioned that there will be thermal conduction from the heated surface to the air. If you consult text books on heat transfer (eg Perry’s Chemical Engineering Handbook) this is actually called natural convection where the heat transfer is proportional to a heat transfer coefficient determined via the Nusselt number and the temperature difference. Natural convection is the cause of thermals and these can manifest as Willi Willis or Tornadoes. If there are winds the heat transfer is called forced convection (involving the Prandtl and Reynolds numbers) which results in much higher heat transfer and can be higher than the heat transfer by radiation. Note there are winds on Mars.
Someone else mentioned that oxygen and nitrogen do absorb and emit some radiation in the infra-red wavelengths but their main absorption/emission is in the UV and visible light range. The sky has a blue colour looking up from the surface and I understand it also looks blue from space.
I think a much more interesting analysis would be if there is no CO2 and the atmosphere is composed of oxygen, nitrogen and water vapour. From the many articles I have read, discounting IPCC information, it appears the climate would be very little different.
Paul (19:34:32) :
“Good question about the CO2 and the answer is not so straight forward. Although there are about the same number of molecules of CO2 above any sq meter on Mars as on Earth, they are not nearly as effective as a greenhouse gas because the total atmospheric pressure is much lower. ”
I believe you are flat out wrong about this:
Assuming a Mars surface partial pressure of CO2 of 6hPa on average (this is at the low end of the variable surface pressure on Mars and 95% of the atmosphere is CO2) and Earth at 1013hPA of which the partial pressure of CO2 is 0.58hPa (390ppmv and CO2 has 1.51 times the molecular mass as oxy-nitrogen) this would make the number of molecules of CO2 above each square meter of mars TEN times that over each square meter on Earth, however pressure is WEIGHT and Mars has only 0.38 the surface gravity of Earth so you need 2.63 times as much mass to get the pressure so we get at least 26.3 times as many molecules of CO2 over each square meter of Mars as on Earth. And that was the low end of the martian surface pressure so around 30 x seems reasonable.
And yet the greenhouse effect on mars is “feeble”?
As for this:
“The higher density of gas in Earth’s atmosphere works to spread the absorption of IR by CO2 over more of the wavelength scale. The same amount of CO2 (or H2O) is more efficient on earth because of all the N2 and O2 colliders (this is called pressure broadening. There is a reasonable wiki page http://en.wikipedia.org/wiki/Spectral_line but it could use to be updated to discuss the role of broadening on climate.”
OK great, but isn’t one of Gavin’s arguments at RC that extra CO2 in Earths atmosphere causes extra pressure broadening? Just how much extra pressure broadening do you get by doubling CO2 from a partial pressure of 0.44hPa to 0.88 hPa(corresponding to CO2ppmv going from 290 to 580ppmv) out of a total pressure of over 1000hPa?
I’m really pleased you’ve cleared that up that it is the TOTAL pressure that causes pressure broadening of absorption spectra minor constituent gases of the atmosphere like CO2 and not the partial pressure of CO2.
Denis Wingo might like to comment on this.
OT Galeras Columbia has large eruption:
http://scienceblogs.com/eruptions/2010/01/galeras_has_large_eruption_-_1.php
This is a very good article. I wonder anyone has ever attempted to model or estimate the state of the atmosphere during the ancient period, very similar to Dr. Spenser’s thought experiment, when geological evidence indicates that the earth may have frozen over all the way to the equator. Is it possible that the tropopause descended all the way to the surface in this event?
As it has become fashionable of late to assume carbon dioxide to be the cause of all things related to the greenhouse effect, I now wonder if volcanic CO2 was really the most likely reason for the end of the ice-cube earth period.
Mike Borgelt (23:36:40):
Also you asked about the numbers:
The 1/100th atmospheric pressure came from Google on Mars atmosphere stating 10 mbar. Earth is about 1000mbar. Didn’t write down the source.
The 90% CO2 on Mars is commonly cited, I just followed suit.
The 380PPM of CO2 on Earth was rough average of what I tend to see on cite and current papers and articles.
Exactness here is not necessary to press the question.
I would like to point out here that thermodynamics is a self contained description of nature and works wonderfully well until it hits dimensions of hbar or coherent effects as in superconductivity, superfluidiy etc.
Thermodynamics treats radiation well, and this at a time where nothing was known of infrared absorption bands and dipole molecules and such, all in the realm of quantum mechanics and hbar sizes.
To say that a body of matter will only radiate heat away only if the molecules consisting it have infrared absorption lines is making a total confusion between classical thermodynamics and quantum mechanics, that displays the confusion in the heads of climatologists and I suspect leads to double countings, like that nice oven by Peden, http://www.vermonttiger.com/content/2008/07/nasa-free-energ.html .
I want to remind everybody that the ideal gas is really tiny billiard balls, not heat factories of infrared, and the heat of the ideal gas is the motion of these within it.
The radiation is given by Wien’s law (~1890 before quantum mechanics) http://en.wikipedia.org/wiki/File:Wiens_law.svg and the black body radiation are all classical thermodynamics.
I hope this settles that all things that have temperature radiate.
It is not that there does not exist a statistical quantum mechanical description of what really happens when molecules and photons shake hands. Tom Vogt once gave me a dense precis of what happens and how finally infrared photons absorbed and being held tight by a molecule end up as kinetic motion and heat of the gas . It is not simple, it is not just dipole, it is complicated. BUT all matter radiates according to the laws of classical thermodynamics.
javs (14:51:17) :
Hans Jelbring, The “Greenhouse Effect” as a Function of Atmospheric Mass
http://www.ingentaconnect.com/content/mscp/ene/2003/00000014/F0020002/art00011
Nice try but it’s behind a pay wall. Does any one have a paper on this subject?
Mike Borgelt (00:05:29) : “The same amount of CO2 (or H2O) is more efficient on earth because of all the N2 and O2 colliders (this is called pressure broadening. …”
What I don’t get is at the point after IR absorption, a CO2 molecule will ‘braoden’ to ANY other molecule, O2, N2 and CO2 molecules also. So I see this as a null statement. Am I wrong?
wayne (23:59:15) :
Mike Borgelt (23:36:40):
Would you care to justify your number?
http://hyperphysics.phy-astr.gsu.edu/HBASE/Solar/venusenv.html#c2
Don’t miss the Water section where they mention the runaway
greenhouse effect.
kuhnkat (16:08:26) :
kuhnkat, thank you for leading me here;
http://climatechange1.wordpress.com/
I have bookmarked it, and will read it again and again. Never
before have I found a more interesting article about what drives the climate.
Finally someone that understand that the most important thing is to understand whether the wheels drive the pistons, or whether the pistons drive the wheels.
The AGW’ers thinks the wheels drives the pistons.
Wayne: see my post at 00:05:29.
I think a factor of 30 is worth resolving.
D. King (00:48:54) I thought we were talking about Mars not Venus and it is rather surprising that the Martian atmosphere has around 30 times as many molecules of CO2 above each square meter of surface as has Earth.
anna v (00:14:54) :
You sound more versed in thermodynamics than myself. Honestly. Please help clarify my view if you know.
Real but somewhat a thought experiment. Take a single molecule in empty space at rest, no momentum. A photon at correct frequency is absorbed by that molecule, knocking an electron a shell higher. I assume that until it drops back the molecule now has momentum. When the electron drops back down, here my big question, seems it must be ejected exactly in the same direction that it was traveling before it was absorbed cancelling the momentum. Is that a correct view? The answer eludes me.
According to your answer, I might have a following question.
Here is a link to an article at RealClimate.org that shows that total CO2 absorption is saturated on earth over the spectrum range of about 13.5 to 17 microns at 1xCO2 (280 ppm, I believe) and would be saturated over the range of 13 to 17.5 microns at 4xCO2 (1120ppm). This is why I prefer to think of CO2 as a scarf rather than a blanket.
I believe that total CO2 overhead is equivalent to a layer of pure CO2 about ten feet thick at sea-level.
http://www.realclimate.org/index.php/archives/2007/06/a-saturated-gassy-argument-part-ii/
Here is a naked link to an image that shows the full picture of radiation through the atmosphere.
http://www.globalwarmingart.com/images/7/7c/Atmospheric_Transmission.png
Nick Stokes:
” the adiabatic lapse rate of -9.8 K/km? Surely this mechanism moves heat more effectively than conduction?”
By definition, no. Adiabatic implies without exchange of heat.
Mike Borgelt (01:01:05) :
For one Mike, I’m agreeing with your flow. The 30x is your computation and number. Are you asking for me to check your math/logic? Maybe you can answer D. King.
D. King (00:48:54) :
Yes, I was speaking of Mars. Nothing to do with Venus.
My question was on statement by Paul way back. No one has posted a yes or no yet. Refollow from Paul down. Keep logic simple. It’s a simple question.
I have heard personally from Prof. Taro Matsuno (one of the best theoretical meteorologists in Japan) that there has been no simulation in which CO2 concentration is set to be zero. He said that such simulation had to be carried out although researchers had interests only in cases with increased CO2.
>Roy is talking about the planet Mars.
But Mars has weather. It has both local scale (e.g. dust devils) and synoptic scale (planet wide dust storms) weather.
I really wonder where the energy comes from for those dust storms without the storage capacity of water vapor, but they do happen.
++PLS
Mike Borgelt (01:01:05) :
Well, the thread title is:
Spencer: Earth sans greenhouse effect – what would it be like?
So we’re off thread, but I was trying to point to Venus as the
origin of the AGW runaway greenhouse effect scare. They beat
this drum and always leave out pressure, as part of the equation.
Mars is another good example. The pressure on Mars is 1/100-150th
that of Earth. So I don’t think Mars is in any danger of thermal
runaway or reaching a “Tipping Point”.