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During the past several months there have been various, unpublished studies circulating around the blogosphere and elsewhere claiming that the “greenhouse effect” cannot warm the Earth’s atmosphere.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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Good article Dr. Pielke. It is unfortunate that this needs saying at all, but I fear the infamous G&T paper has done a bit of damage to the credibility of sceptical science.
Greenhouse Gases emitted in all directions. Also into outer space. Seems to forget this detail.
Hi there,
well .. I usually describe it the following way:
It is a fact, that with increasing CO2 the characteristic CO2 emission into space comes from a greater atmosphere layer (measured by the temperature of the emitting molecule via the spectrum width).
In layman terms this means the lower layer losses one way to transport energy and thus has a lower thermal conductivity (which means it warms)
This effect is well understood and can be calculated to the 3.7 W/m^2 cited by IPCC, the question reamins, what this means to the temperature.
All the best regards,
LoN
The amount of warming from the greenhouse effect varies by a large amount between the tropics and the poles, due to the amount of water vapour in the atmosphere. The tropics experience much more more greenhouse effect than the south pole, because there is almost no water vapour in the atmosphere over the south pole.
My guess is all of the feedback ‘constants’ are driven by the variables “The rest of the processes, including convection, conduction, feedbacks, etc. are too complicated to discuss here and are not completely understood anyway.” Without understanding those variables ones instrumentation is left to quantify the dynamics. Empirical prediction?
The conditions forcing the escape of radiation the atmosphere must also force the escape of atmospheric gases. As such, wouldn’t the conditions for escape of those gases be the determinant of the rate of the greenhouse effect
….There is dusted together water on the moon and mars………
Rubbish…
Surely the ultimate question is – Is the Earth sensitive to changes in CO2 levels?
The earth has had much higher levels of CO2 in the past so the knee jerk reaction to this must be NO, or else we would not be here to talk about it.
Is industrialisation altering our atmosphere to such an extent that we face imminent virtually immediate doom?
Again looking at the last 20 years I would say NO. So whatever we need to do whatever we need to measure and calculate we can do rationally and sensibly and slowly and openly.
Is this happening? NO ….
You have to add the trapping effect of the clouds and you have the basic story complete.
Anyway, it looks like Kevin Trenberth’s backradiation hop (up, down, up, down) as described here
http://johnosullivan.livejournal.com/19541.html
vastly overestimates back radiation because they just didn’t follow the established vector calculus rules (subtracting energy that goes into the opposite direction).
http://hockeyschtick.blogspot.com/2010/07/new-unphysical-agw-simulator-available.html
The atmosphere is due to the density of CO2 a dense fog for the absorption bands of CO2 even where there is no water vapor, and this was so even before the increase in CO2 emissions. The light (or LWIR) from a diffuse surface like the Earth’s surface must be diffuse. The fog will re-emit the light into all directions equally. What does it matter whether a ray from the surface is intercepted after 23 m on the average or after 15 m the first time, to be re-emitted? Nothing at all when the atmosphere is 10,000 times as high.
slowing down the cooling of an object cannot cause it temperature to rise … THAT would violate the 2nd law …
if a black box is warmed to x degrees by the sun then its temperature cannot rise above x no matter how much greenhouse gas it is surrounded by …
x becomes the upper threshhold of the objects temperature (assuming no other energy inputs …)
yes, it may REMAIN at some temperature between x and zero longer than it would but it can never rise above x … it may be relatively warmer because of slowed cooling but it has certainly not “warmed” up …
if you say something has warmed you are implying that its temperature has RISEN … not cooled slower …
Good article. In a way it reminded me of another item I read today, not exactly on the subject, but interesting, about Enrico Fermi, and connections.
This connection is CO2 causing GW simply because CO2 was increasing and some recent warming. This idea was noted in similar to a train of thought that Enrico Fermi discussed with his friends Teller, John von Neumann, and others over lunch at Los Alamos. The subject was the recent disappearance of NY trashcans and increased appearance of flying saucers. The logical, but not necessarily correct, conclusion was aliens were stealing NY trashcans.
http://www.firstthings.com/onthesquare/2010/07/et-phone-here
“The rest of the processes, including convection, conduction, feedbacks, etc…. are not completely understood anyway. … There are also questions being raised as to the very sign of some of the larger feedbacks to add to the confusion. ”
Dr Pielke, I note you talked about warming the ground, but carefully avoided reference to the ocean, the really big dog on the climate block. Since longwave radiation can’t penetrate the ocean, but only causes increased evaporation at its surface, and since as you note, there’s lots we don’t know about convection etc, what makes you so sure adding more co2 will cause warming? Is Miscolzci to be ignored forever?
http://tallbloke.wordpress.com/2010/01/04/why-the-sun-is-so-important-to-climate/
Earth warmed while solar activity was high, and cloud albedo diminished, and ocean heat-energy content has been dropping since 2003 when the sunspot count dropped below its long term average of 40, and cloud increased again.
http://tallbloke.wordpress.com/2010/07/21/nailing-the-solar-activity-global-temperature-divergence-lie/
I guess I have a problem with the over simplistic model. Yes, absorbing gasses in the atmosphere ‘slow’ the cooling because the radiated heat bounces a like a pinball from molecule to molecule before it actually radiates to space.
However, the movement of air columns can shorten or lengthen that wayward path, as can precipitation which tends to absorb heat and drop it back into the oceans.
When air heats it rises, but the atmosphere also expands (something easily detected in satellite orbits, which experience changes in atmospheric drag constantly as the atmosphere expands and contracts – sometimes regionally). An expanding atmosphere lowers the density as volume increases. Already ‘thin’ air becomes even thinner, which means the chances of IR radiation bouncing back into the atmosphere should decrease and radiation rates escaping should increase.
If the Earth’s atmosphere actually has built in thermal balancing – which must be the case given it has survived for billions of years – then the combination of precipitative cooling and increased radiative cooling because of lower density and greater surface area to space would seem to more robust than many climate alarmists would consider.
This becomes even more true if recent human actions on climate are driven by the UHI and expanding population centers (changing the basic reflective/absorptive characteristics of the Earth’s surface). I seriously doubt CO2 or any GHG can go into a ‘runaway’ mode. If you look at Mars, Earth & Venus it is not the GHG gas necessarily that drives their climate, but the distance from the Sun (i.e., solar flux intensity) and their mass (how much atmosphere they can hold gravitationally) which dictated their atmospheric stability point.
No one has proved reducing GHG on Venus or increasing it on Mars would change a damn thing. These kinds of theories border on the science fiction concept of terra forming – something never proved even slightly.
The billion year stability of our atmosphere, through massive eruptions, massive (but slow) changes in content, though large impact events, would indicate the cross-checking balancing mechanism always bring the system back to a nominal range of climate. A range we have seen for millions of years and a wide range of CO2 and GHG concentrations.
While it doesn’t refute your argument, I want to point out that assertion #2, technically, is not correct. There are many sources of energy on Earth that are not sun related. Simply because it has mass, the Earth contains ~5^41 J of energy. It creates a vast gravitational well that imparts energy on all objects on the planet. Additionally, a lot of our energy sources have no ties to solar energy (e.g. fission reacts on Uranium which is, most likely, a remnant of a distant supernova).
However, if you were to say that the sun is the source of all BIOLOGICAL energy, I wouldn’t argue.
“The rest of the processes, including convection, conduction, feedbacks, etc. are too complicated to discuss here and are not completely understood anyway.”
But that’s the crux of the matter. For starters, there cannot be a proper greenhouse effect in the presence of constant convection. And the biosphere is a temperature regulating mechanism that constantly changes the chemical composition of atmosphere, therefore defining, where the equilibrium will be.
Therefore, all this talk about “greenhouse effect being real” is nonsense. No, it’s not “real,” it exists only within the simplistic framework of intentional misunderstanding.
How much of the 33 degrees is due to heat escaping from the Earth’s core and tidal forces?
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.
A bit misleading, this last paragraph.
The dry atmosphere consists of:
N2 78.084%
O2 20.946%
Ar 0.934%
rest 0.03768%
and if there is humidity around, H2O 0.4% and more near the surface.
The trouble is not with whether the atmosphere keeps temperatures temperate, but whether the tiny amount of CO2 can contribute significantly to this, considering also that H2O covers most of the spectrum and CO2 only some windows.
I am curious if anybody has calculated a toy earth with only N2 and O2 as an atmosphere. Deserts do get cold at night and hot in the day, but on average would not be too far off current global averages.
I question the analysis by Herman and Pielke in
http://claesjohnson.blogspot.com/2010/07/blackbody-radiation-by-ockhams-razor.html
Comments from Herman and Pielke are particularly wellcome.
“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.”
Um, what about an atmosphere devoid of greenhouse gases? What about the dry adiabatic lapse rate?
That is a very good simple explanation of the greenhouse effect.
Can you tell me, does atmospheric CO2 currently absorb 100% of the longwave IR in the bandwidths which apply?
If so, at what altitude is the saturation achieved?
Assuming that additional CO2 would lower that altitude, what sort of effect would this actually have on surface T? I mean, given what we know about the atmosphere I would think convection would distribute this additional atmospheric heat well enough to prevent a significant increase to the ground temp and probably keep the increased surface atmospheric temp from increasing a great deal as well. I guess what I’m really asking is, if all of the IR that CO2 can absorb is already being absorbed by CO2 within the first several tens of meters above the surface (to my understanding), what additional impact can more CO2 have on the overall heat content of the atmosphere, and does it really make a difference if that heat is added in the first 50 meters or the first 5?
Maybe this isn’t so, I do not know for a fact if the CO2 is currently absorbing 100% of the IR it is capable of, though I’ve read and been told that this is true. Maybe science doesn’t yet know the answer to these other questions, which would seem plausible as this is almost bordering on chaos theory; (everything’s just so, you have all of the measurements and can accurately predict what will happen forever, then a butterfly flaps it’s wings and all of your calculations go awry.)
Or maybe I’m just way off base in my line of thinking here.
Please let me know your thoughts.
And again, this is a really good article in describing the greenhouse theory of global warming to someone (like me) who hasn’t the scientific background to do the math, but is really trying to understand and keep up with the debate.
Dr. Pielke
For your demonstration of the greenhouse effect WUWT has used the Arctic part of the globe, which is currently very popular with many researchers. In a way of a modest contribution, I think I may have found an important correlation as shown here.
http://www.vukcevic.talktalk.net/NFC1.htm
You may not agree with the explanation for this unusual phenomenon, but in the interest of science and the readers of WUWT (well over 3000) who viewed this graph, I would very much appreciate your comment.
Thank you.
This is entirely reasonable. For me, that we have greenhouse affects on the planet is rather boring (not that your presentation was). It’s kind of a stable thing and of not much complexity relatively speaking.
It’s the feedbacks and turbulent nature of the thermosphere that fascinates me. Much harder to simply explain and therefore endlessly fascinating to me. If each of our gasses and particulates in our overturning thermosphere (warm to cold in height so it wants to be turbulent) were colored, it would be a right pretty ever changing kaleidoscope of swirling color topped with a ribbon-like fairly stable stratospheric layer (cold to warm in height so those layers don’t want to be turbulent), and so on. If one were to try to demonstrate AGW increases in any one color in that thermosphere, stratosphere, etc, you would be hard pressed to do so. But regardless I could stare at such a presentation for hours.
DirkH says:
July 23, 2010 at 8:20 am
“[…]The atmosphere is due to the density of CO2 a dense fog for the absorption bands […]”
Such a re-emitting fog must tend towards an equilibirum, and that’s why its exact density does little to change the overall distribution of re-emittance towards the ground or space; just like adding another 15m of atmosphere does not change the distribution. I’m assuming a 100% re-emittance here. If the re-emittance is smaller, energy will just be distributed to non-LWIR-emitting molecules like O2 which results in heating where we enter the area of “not well understood anyway” convection and conduction so that would steal some more energy from Kevin Trenberth’s beloved backradiation, torpedoing his assumptions further.
I don’t think that most of the arguments circulating (such as Lubos’s or mine) are contradicting what you said. Their point is that, at least for Venus, it is mainly the fact that the atmosphere is very tall due to much higher mass of the atmosphere that causes the very high surface temperature. There still needs to be greenhouse gas and clouds, but they could be a far lower percent of the composition and still get most of that high temperature as long as the mass of the atmosphere is high enough to maintain the approximate altitude where outgoing radiation leaves the atmosphere. If the Earth had 100,000 ppm CO2 rather than 390 ppm, the temperature would only be a few degrees higher that at present, due to the limited size of our atmosphere. In other words, it is the COMBINATION of mass of the atmosphere that is resulting in it’s thickness combined with the trapping effect of greenhouse gases and clouds that result in the ground temperature. The concept that had been often stated, of a “runaway” greenhouse effect, is what brought that point up. There is no runaway, just straightforward fluid dynamics and radiation heat transfer.