Guest post By Ben Herman and Roger A. Pielke Sr.
During the past several months there have been various, unpublished studies circulating around the blogosphere and elsewhere claiming that the “greenhouse effect” cannot warm the Earth’s atmosphere. We would like to briefly explain the arguments that have been put forth and why they are incorrect. Two of the primary arguments that have been used are
- By virtue of the second law of Thermodynamics, heat cannot be transferred from a colder to a warmer body, and
- Since solar energy is the basic source of all energy on Earth, if we do not change the amount of solar energy absorbed, we cannot change the effective radiating temperature of the Earth.
Both of the above statements are certainly true, but as we will show, the so-called “greenhouse theory” does not violate either of these two statements. (we use quotation marks around the words “greenhouse theory” to indicate that while this terminology has been generally adopted to explain the predicted warming with the addition of absorbing gases into the atmosphere, the actual process is quite a bit different from how a greenhouse heats).
With regards to the violation of the second law, what actually happens when absorbing gases are added to the atmosphere is that the cooling is slowed down. Equilibrium with the incoming absorbed sunlight is maintained by the emission of infrared radiation to space. When absorbing gases are added to the atmosphere, more of emitted radiation from the ground is absorbed by the atmosphere. This results in increased downward radiation toward the surface, so that the rate of escape of IR radiation to space is decreased, i.e., the rate of infrared cooling is decreased. This results in warming of the lower atmosphere and thus the second law is not violated. Thus, the warming is a result of decreased cooling rates.
Going to the second statement above, it is true that in equilibrium, if the amount of solar energy absorbed is not changed, then the amount of IR energy escaping out of the top of the atmosphere also cannot change. Therefore the effective radiating temperature of the atmosphere cannot change. But, the effective radiating temperature of the atmosphere is different from the vertical profile of temperature in the atmosphere. The effective radiating temperature is that T that will give the proper value of upward IR radiation at the top of the atmosphere such that it equals the solar radiation absorbed by the Earth-atmosphere system.
In other words, it is the temperature such that 4 pi x Sigma T4 equals pi Re2 Fso, where Re is the Earth’s radius, and Fso is the solar constant. Now, when we add more CO2, the absorption per unit distance increases, and this warms the atmosphere. But the increased absorption also means that less radiation from lower, warmer levels of the atmosphere can escape to space. Thus, more of the escaping IR radiation originates from higher, cooler levels of the atmosphere. Thus, the same effective radiating temperature can exist, but the atmospheric column has warmed.
These arguments, of course, do not take into account feedbacks which will kick in as soon as a warming (or cooling) begins.
The bottom line here is that when you add IR absorbing gases to the atmosphere, you slow down the loss of energy from the ground and the ground must warm up. The rest of the processes, including convection, conduction, feedbacks, etc. are too complicated to discuss here and are not completely understood anyway. But the radiational forcing due to the addition of greenhouse gases must result in a warming contribution to the atmosphere. By itself, this will not result in a change of the effective radiation temperature of the atmosphere, but it will result in changes in the vertical profile of temperature.
The so-called “greenhouse effect” is real. The question is how much will this effect be, and this is not a simple question. There are also questions being raised as to the very sign of some of the larger feedbacks to add to the confusion. Our purpose here was to merely point out that the addition of absorbing gases into the atmosphere must result in warming, contrary to some research currently circulating that says to the contrary.
For those that might still question this conclusion, consider taking away the atmosphere from the Earth, but change nothing else, i.e., keep the solar albedo the same (the lack of clouds would of course change this), and calculate the equilibrium temperature of the Earth’s surface. If you’ve done your arithmetic correctly, you should have come up with something like 255 K. But with the atmosphere, it is about 288 K, 33 degrees warmer. This is the greenhouse effect of the atmosphere.
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Dr Pielke,
Has anyone looked at the spectra of C02, and the spectrum of IR radiated toward space from earth’s surface, and quantified how much IR is even available to CO2? If CO2 is in trace concentrations, what becomes the probability that this IR from earth’s surface will find a CO2 molecule to energize, and then, even if ALL of it were captured by CO2, what percentage of total re-radiated IR could this even contribute, given those bands of absorption peculiar to CO2? Would not any single humid day be orders of magnitude greater? And after C02 kinetically hands off that energy to water vapor, what mechanism is to prohibit higher energy water vapor from rising and COOLING further?
Steven Mosher said:
“C02 will warm the planet, up to limit. That limit has not been reached and the questions are:
1. how fast will we reach that limit
2. will it be damaging
3. Can and should we do anything about it.
______________
Best repsonse to this thread that I’ve seen.
Robert of Ottawa:
Not quite. If the atmosphere was completely transparent to all radiation then the surface would be the (main) effective radiating surface, not the TOA. The surface temperature would actually be a bit lower than it would be if there were no atmosphere, as some of the energy from the surface would go into warming the atmosphere through conduction and convection, but the total energy radiated by the surface plus the whole of the atmosphere (not just the TOA) would equal the incoming energy at equilibrium.
The atmosphere would still be warmer at the bottom than at the top, due to the lapse rate, but it would still be a lot colder than would be the case if greenhouse gases were present.
Surely to goodness this can be measured? On a clear night, let’s see the radiation profiles. Lets cover some of the ground and see how different the radiation is. If there is scattered longwave IR running around in the atmosphere, it can be measured, can’t it? How hard could it be to prove this once and for all? By experiment. Not only the right way, but the only right way. What does the theory predict? Can we observe it?
Juraj V. says:
July 23, 2010 at 9:06 am
I agree with Juraj here.
the two dominant climatic forces and the effect they have on climate, despite there being a large amount of research on them are: oceans and clouds/water vapour, which comprise 98% of the climate, (Oceans have over 1000 times more ability to retain shortwave heat than air does longwave, and a much greater heat capacity, and 70% of the earth surface is ocean) and then go onto make pronouncements about what it will be like in years to come. However, vapour overlaps c02 by a magnitude of 100 times, in quantity, and over three times in its spectral bandwidth, (300 times the ghg as c02) so a change in cloud or vapour of 1%, which is very common, is the equivalent of a change in c02 of several hundred ppm. IE. It swamps the entire “effect” of c02, and can be a negative “feedback”. Re-radiated longwave radiation doesn’t penetrate oceans, as it takes a great amount of energy to heat them by 1C. Far more so than solid mass and air. Water is penetrated to depths of 100 metres or more by incoming solar energy in the ultraviolet and visible wavelengths but is not penetrated by infrared (longwave) wavelengths.
One notices at the beach that when the sand and paving is hot, water waves are still cool. That means no amount of greenhouse effect can cause either thermal expansion of water, or water vapour “feedback”. Certainly, since c02 intercepts heat at 15 microns, then re=emits it in less than a billionth of a second, to oxygen and nitrogen, when its saturation window closes. This wavelength on the spectroscopic band is already in the subzero region. In other words, the energy absorbed by c02 is dependent on freezing regions, such as Antarctica. Normal IR radiation leaving the earth is around 10 microns, 0r 7-14, incidentaly at the bandwidths where water vapour intervenes which co-incides with an average 288k (15C), and which is invisible to c02. That leaves very little energy for c02 to delay – around 3-4% of subzero energy. It is so miniscule that the effect cannot, and has not been measured. In tropical deserts where temps are 45C plus, radiation leaves at 8.5 microns, which puts it even further out of the c02 micron band.
So c02 absorbtion is a rare event in the atmosphere. Its also forgotten that most heat leaves by convection and evaporation, and not from re-radiation.
the only way that global warming via ghg’s (lets take only c02)could be justified would be by Boyle’s law, or the ideal gas law. However, temperature change through air pressure depends on a closed system – if the atmosphere gains more density it expands, than increasing partial pressure – the so called Iris effect. Given the limited spectroscopic bands of c02 on the other hand, an argument can’t be developed for c02 increasing the temperature or retaining heat. In the mid to upper troposphere where it goes to from -20-45C, or 228K, that does coincide with heat absorbtion from c02. However, there is no physical mechanism by which such mid tropospheric subzero temperatures can send heat back to earth, as temperature falls with altitude. (The notion indeed violates the 2nd law of thermodynamics)
the fritz says:
July 23, 2010 at 10:30 am
Green house effect is not a source of energy; if it warms the surface, something else must cool
__________
This is the worst response I’ve seen to this thread.
No one is talking about the the GH properties of CO2 and other GH gases as being “sources” of energy. The primary (but not only) source of energy on earth is the sun. It is the sun that loses energy that is received by earth, but the net energy of the system (sun-earth) of course stays the same, however, the total entropy of the solar system increases as useful energy is lost.
Ultimately of course, the source of all energy in our region of the universe is gravity, for without it, we’d be just another cold region like the majority of the universe where not much (in fact nothing at all) exciting happens.
Robert,
I think you’re incorrectly assuming that this atmosphere which is transparent to all radiation could still emit radiation. This is a contradiction. If it can emit LWIR then it must also absorb LWIR. Which brings up something I’ve asked about a few times without getting an answer. I assume that if molecules like O2 and N2 were to interact in a collision, there’s a small possibility they could emit IR (or absorb it). The reason that O2 and N2 don’t normally absorb or emit IR is that they’re symmetric molecules and thus can’t interact with an electromagnetic field. But while they’re in the process of collision, there will be some asymmetry set up which could lead to emission. The question is just how likely this is? My guess is that it’d be quite rare since the interaction time would be much quicker than the average time it takes for a quantum of IR to be emitted from a GHG (for instance). But the math to do the calculation is likely to be quite hairy and beyond my abilities. But surely there’s someone here who’s a wizz at QM who could solve the problem?
The Moon is without an atmosphere. It’s daytime temperature is around 400K (+/-) and it’s night time temperature is about 120K (+/-). So how does one arrive at a temperatiwhere does the 255K temperature of the Earth without an atmosphere. Actually this would be really cool sine the oceans would freeze during the night and boil during the day. Nice model.
I want to thank Anthony, Ben Herman, and Dr. Pielke for this post. It has increased my knowledge of the popularly named “greenhouse effect”.
I believe, however, that lacking from this discussion are formal definitions of “a greenhouse gas” and “the greenhouse effect” Without such formal definitions, there is little common ground for discussion. For you electrical engineers, it’s kind of like discussing Signal-to-Noise Ratio (SNR) without a formal definition of “Signal Power” and/or the bandwidth in which the “Noise Power” is defined.
Therefore, I request that Ben Herman and Dr. Pielke provide formal definitions of these entities. Something like:
A greenhouse gas is a gas whose molecular electron structure is such that (a) it possesses electron energy states whose energy difference is in the IR band, and (b) when excited from a lower energy state to a higher energy state by an IR photon, a portion of the stored energy when released will be transformed into thermal energy of the molecule and/or the surrounding gas molecules.
For a body whose rate of thermal energy input is fixed, the greenhouse effect is the phenomenon by which a greenhouse gas solely by virtue of its ability to transduce IR photon energy into molecular thermal energy will induce a rise in the temperature of the gas surrounding the body.
I make no claim that the above are valid definitions. They are meant only to be examples. But before I can decide if the “greenhouse effect” is real or figment of the imagination, I need explicit definitions of these two entities.
The statement that taking away the atmosphere and calculating the expected temperature keeping the albedo the same is nonsense. Most of the albedo effect is the result of the oceans and the atmosphere. Without the atmosphere there can be no ocean and without them the earth would look like the moon with an albedo in the range of 10-12 percent. If you then calculate the expected equilibrium temperature you will get something about 273-278 degrees Kelvin. Thus the “greenhouse effect of 33 degrees” is utterly false. The best that can be said is that the ocean-atmosphere system causes the earth to be 5-10 degrees warmer that it would otherwise be. The term greenhouse is also a nonsense as no greenhouse works in the way suggested by the proponents of the term.
If those who oppose the greenhouse theory are right, then we not only must reinvent climate theory, but meteorology itself. On a clear calm night, temperatures drop rapidly at the surface boundary layer as IR heat radiates into space. On a calm cloudy night, the temperatures drop more slowly because that IR heat is re-radiated downward by water droplets in the clouds.
Now apply this concept to daytime heating: Greenhouse gases don’t add heat, but retard its loss by reradiating. During the day the ground temperature may easily exceed 100F in the summer while the air temperature may only 75F. We rely on radiation and convection to transport this heat away from the surface. Additional greenhouse gases will retard surface cooling (though ever so slightly in my view) causing the air temperature to be closer to the ground temperature. So the surface air temperature increases without adding any heat to the system. All the heat needed to do the job is already present.
“The bottom line here is that when you add IR absorbing gases to the atmosphere, you slow down the loss of energy from the ground and the ground must warm up. ”
crazy. backwards.
improve the heat capacity of a convective heat exchange system and you increase efficiency.
2 words:
phase change
I’ve got problems with all of this.
What follows is a question and not a statement;
CO² 0.04%
H²O 5%
They both absorp at the same hµ (approx). H²o dominates and as a probability must absorp 100 times more IR ?
When a mole absorps it raises its’ instability and wants to reradiate the energy and return to the ground state a.s.a.p. This reradiation is never uni-directional? Why would it radiate in a downward direction ?
The reradiated energy is at the same hµ (nu) as the absorped unless some form energy conversion has occured (conservation of energy law)? so will be absorped by another mole at ground state.? If the other moles are already at the higher quantum level, it will radiate to space?
Bill DiPuccio says:
You are of course correct. The problem with the greenhouse theory is that the planet is not a greenhouse. The greenhouse theory just is no applicable. The big question is what happens to the energy absorped by a CO² molecule in a system as complex as this planet (not just the atmos).
RockyRoad:
I guess you must have missed the preceding bit which said:
(my bold)
Reed Coray says:
July 23, 2010 at 11:56 am
An intelligent question. The more you try to make a precise mechanistic definition of a “greenhouse gas”, the clearer one will see the holes in the hypothesis, what seemed intuitively simple proves more complex and elusive.
Dear Ben and Roger,
In principle, your article is correct.
However.
1. It is unclear why you should compare the <> temperature of the Earth with and without atmosphere and claim this should be the “greenhouse effect”. Most of the Earth albedo results from clouds. So, you <> compare the temperature somewhere around clouds. And it is around 233 K, as it should be according to the albedo!
2. The temperature below the clouds (actually in the whole troposphere) is simply the adiabate. The higher pressure = higher temperature. Nothing with “greenhouse”.
3. If you descent down into a deep shaft, you know the temperature increases. Do you think this is “greenhouse effect”, or may be, rather the adiabatic temperature lapse?
One must be very careful with the so called “greenhouse”.
Your tried explanation is too naive!
R. Gates says:
July 23, 2010 at 11:44 am
the fritz says:
July 23, 2010 at 10:30 am
Green house effect is not a source of energy; if it warms the surface, something else must cool
__________
This is the worst response I’ve seen to this thread.
Climate is a zero sum game – didn’t you read the memo?
Bill DiPuccio>> You use clouds as observational evidence for the validity of the GHG theory, but your example actually reinforces the notion that GHG:s are poor isolators compared to for example clouds.
The air humidity can be identical on the two nights you mention, but the one with clouds will always be the warmest – by far…
R. Gates says:
Another of your cracked replies courtesy of the Gavin Schidt school of answers.
Gravity does not generate energy. Energy cannot be made or destroyed einstein.
Sure, gravity is a force which creates the conditions for the creation of stars and the nuclear energy in those stars is started by the force of gravity compressing the gases.
RuhRoh says:
July 23, 2010 at 9:35 am
Mr. Juraj V;
Are you saying there is more CO2 on Mars than on Earth, yet there is no discernible ‘greenhouse warming’ on Mars? Yikes!
From those very handy links,
Mars atmosphere is ~2.5 x 10**16 kg, @ur momisugly950,000 ppm CO2, yes?
Earth atmosphere is ~5 x 10**18kg, @ur momisugly 400ppm CO2.
This seems to be a very potent issue for the greenhouse advocates.
Maybe RC can answer this one.
No need to go there, the absorption of CO2 (or any absorber) depends on it’s temperature, concentration and pressure. On Mars the absorption lines of CO2 are very narrow ( a bit like a picket fence with relatively large gaps) whereas the conditions on Earth broaden the lines (so the gaps in the fence narrow). This means that the same mass of CO2 is more effective absorber on Earth. I have compared the partial spectra below at the respective surface conditions.
http://i302.photobucket.com/albums/nn107/Sprintstar400/Mars-Earth.gif
P Wilson says:
July 23, 2010 at 11:43 am
the two dominant climatic forces and the effect they have on climate, despite there being a large amount of research on them are: oceans and clouds/water vapour, which comprise 98% of the climate
Which aspect of climate ??
In reply to Cedarhill, the effective radiating temperature of the Earth is the temperature that prevails at what is called the characteristic-emission altitude, defined as the altitude (varying with latitude) at which the ingoing and outgoing fluxes are equal. If we remove the atmosphere, biosphere, hydrosphere and cryosphere, and retain only the lithosphere, also artificially retaining today’s Earth albedo, then the mean characteristic-emission temperature will be as follows:
[(S/4)(1-a)/s]^(1/4) = 255 K,
where S = 1368 W/m2 is the total incoming solar radiation, which is divided by 4 to allow for the ratio of the surface area of the disk presented to the Sun’s rays by the Earth and the surface area of the rotating sphere; a = 0.3 is the albedo, artificially held at today’s value; and s = 5.67 x 10^(-8) is the Stefan-Boltzmann scaling constant.
The effective radiating temperature of the Earth today is of course exactly the same, but the characteristic-emission altitude is no longer at the surface but several miles up, and the surface is some 33 K warmer than the characteristic-emission altitude.
To calculate the mean surface temperature of the lithosphere without artificially pretending that clouds and ice are still present, halve the albedo to 0.15, about the same as that of Mars today. Then the true surface temperature of the naked lithosphere today would be 268 K, or around 20 K cooler than today’s measured mean surface temperature. Hope this helps.
This implies that the presence of the atmosphere causes 33 degrees of warming, but it doesn’t imply that IR absorbing gases are responsible for all (or any) of the 33 degrees.
The atmosphere of Mars contains about 12 times as much CO2 compared to Earth’s atmosphere and there is very little atmospheric warming on Mars. The amount of warming seems more related to the total amount of atmospheric gas and hence pressure.
Mars=low pressure, low warming
Earth=moderate pressure, moderate warming
Venus=very high pressure, very high warming