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During the past several months there have been various, unpublished studies circulating around the blogosphere and elsewhere claiming that the “greenhouse effect” cannot warm the Earth’s atmosphere.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.
Pardon an ignorant question.
I assume that a perfect thermal insulator covering the whole earth high up in the atmosphere would result in the world freezing as no radiative transfer of solar energy would reach the earth’s surface.
Then, the reason for the glass of greenhouses to have an effect is because it minimises conductive and convective heat losses.
In what way does CO2 reduce such conductive and convective losses to produce a greenhouse effect?
It is very easy to prove that backradiation has no effect on temperatures. The direct solar energy at noon on a clear summer day in an arid area is about 1000 wm-2. That’s enough to raise the temperature of a black surface to about 91 C (196 F). And that is about what happens on an asphalt roadway. If backradiation had any effect, the surface would be much hotter.
RockyRoad says:
July 23, 2010 at 3:33 pm
“Maybe instead of “greenhouse” gasses we could call them “blanket” gasses, for that is what they do.”
Why not call them “heat transporting gasses”. For they absorb and re-emit LWIR.
Tallbloke,
I am sure Mosher is saying that greenhouse gases warm the lower atmosphere and surface compared to no greenhouse gases and do it by trapping some of the solar energy (similar to a blanket trapping heat). I don’t think he is implying the energy comes from the gas. I fear that poking at details such as this make us seem nitpicking and not interested in coming to agreement.
George E. Smith says:
July 23, 2010 at 4:17 pm
“[…]You may be right on that debunk being difficult; I would say it is just about pure bunk.[…]”
Maybe this one is easier to digest; it is also about the lapse rate (the part by William Gilbert):
http://docs.google.com/viewer?a=v&q=cache:A81VTnHUPkEJ:www.tech-know.eu/NISubmission/pdf/Politics_and_the_Greenhouse_Effect.pdf+adiabatic+lapse+rate+greenhouse+effect&hl=en&pid=bl&srcid=ADGEESiwZvv2w8O-I2jVLvl_jNAyMMK0oFFvnwWm3qZAom59wDIjAF9Q5k-_voIQCmn1hoWtEBgjtFGGZ22LU9giDVTnMmCmdQ7GIUpCrHNeNm6G4nKLg14djiR6c7SgRbj7b3uck3hb&sig=AHIEtbTG1haSI1yNANL1FwkTLacvcOBU0w
Rob says:
July 23, 2010 at 3:34 pm
Too true wayne, too true.
It is almost like a propaganda post.
we want real answers to the unaswered questions, not to be patronised in a – don’t be a denier – kind of way.
We know it warms
HOW MUCH ???????
~~~~~
Exactly. That’s the big question. Though of all the question marks still in my head but most are asked by others above in one form or another. Also one great question above was how much of the 33C is from water vapor? Never have got a handle on that factor. If water vapor performs basically parallel to Co2 plus it’s additional capabilities, and doubling is close to the same at 3.7C per doubling, then the difference from a 95% humidity day and a dry desert should be huge. Right? See, put water vapor in every statement where you read CO2 and it doesn’t seem to jive by physics.
Of take Co2 and half it (-3.7C) and half it (-3.7) and… yes it is logarithmic but you very quickly place a huge drop in temperature on Co2 but all of the water vapor is still there. That definitely doesn’t jive.
Please bear with me with another novice question:
Since the atmosphere has a smoothing effect on the earth’s temperature, compared with if we did not have an atmosphere at all;
1) Of all the gases in the atmosphere, does CO2 contribute more of this effect than the other gases?
2) If CO2 contributes on average less of this effect than the other gases combined, then if CO2 concentrations increase as a proportion of all gases – how can this increase the greenhouse effect in total?
Leonard Weinstein says:
July 23, 2010 at 4:46 pm (Edit)
Tallbloke,
I am sure Mosher is saying that greenhouse gases warm the lower atmosphere and surface compared to no greenhouse gases and do it by trapping some of the solar energy (similar to a blanket trapping heat). I don’t think he is implying the energy comes from the gas. I fear that poking at details such as this make us seem nitpicking and not interested in coming to agreement.
Mosher and the warmists say co2 warms the atmosphere. Pielke and I say it slows the rate of cooling of the atmosphere. You say “it doesn’t matter”.
IT FUNDAMENTALLY MATTERS.
Am I right to think about G&T that:
A possible way for atmospheric “greenhouse gases” to warm a planet could be by temporarily delaying some escape of heat?
Infrared absorbing gases in the atmosphere could slow the cooling of the Earth?
Being just an old construction worker. All I know is that no one is trying to sell me a home climate control system based on CO2.
We stopped using “dead air space” as an insulator between inside and outside wall a long time ago. I think everyone knows why.
“”” Nylo says:
July 23, 2010 at 1:28 pm
George E. Smith wrote:
“Since the rate of loss of energy goes as T^4; so it is non-linear with temperature, the colder parts of the ball, are not doing their fair share of cooling, and the hotter parts are being overworked, and if we average the Temperature all over the ball surface that average will ALWAYS be hgher than the original case of an isothermal ball at 278 K all over”.
I followed your argumentation quite well until this point, but here I think you got it backwards. The average temperature will always be colder, the bigger the temperature differences in the surface, for the same total emissions. It is because of the emisivity depending on T^4. The emission gain that you get by increasing 1K the temperature is quite bigger than the emissions you lose by decreasing the temperature 1K. So in equilibrium, for the same total emissions, the bigger the temperature differences between different parts of your blackbody, the lower the average temperature will be.
Take it to the absurd. A black body with one half at 0K and another half at 100K emits the same energy as an isotermal blackbody at 84K, yet its average temperature is only 50K, considerably colder. “””
Well Nylo; I think that you have caught me in a fox pass; fancy that; must be the third time this century that I have goofed.
yes I solved the wrong problem !!
So suppose the Temperature at some location goes through a sinusoidal cycle between T0 + a at the maximum and t0 – a at the minimum; but the average temeprature over the cycle is T0.
So I can calculate the energy radiated at a Temperature of T0.
Let’s say our Temperature follows T = T0 +a sin (2pi.t/tau) where tau is the period of the Temperature cycle (could be a spatial period).
So actually the instantaneous emittance is sigma.(T0 + a.sin (2pi.t/tau))^4
and that equals sigma.(T0^4 + 4T0^3.asin(2pit/tau) +6T0^2.a^2sin^2(2pit/tau) + 4a^3 T0.Sin^3(2pit/tau) + a^4 sin^4(2pit/tau)).
It is left to the reader to show that the sin and sin^3 terms integrate to zero when we integrate the above over a complete cycle; and only the first, third, and fifth terms integrate to a non zero value over a complete cycle and they are ALL positive; so the result is ALWAYS higher that sigma.T0^4.
And I already knew that ; so that is clearly the wrong problem.
The simplest way to see that delaying the cooling process results in a higher temperature, is that during the delay time between energy coming in, and an equivalent energy exiting, the sun is still pouring in energy at a constant rate; so an increment of energy is added to the earth system that grows linearly with the propagation delay of the cooling process, and that must result in the Temperature going up.
Good to have you watching my back there Nylo; I almost slipped that one by.
The most lovely word in the english language might be “fundamentally”.
John
Anders Boman says:
July 23, 2010 at 4:55 pm
“[….]1) Of all the gases in the atmosphere, does CO2 contribute more of this effect than the other gases?”
Absorption bands of CO2 and H2O:
http://wattsupwiththat.files.wordpress.com/2008/06/atmospheric_spectral_absorption.png
Notice that H2O vastly outperforms CO2.
“2) If CO2 contributes on average less of this effect than the other gases combined, then if CO2 concentrations increase as a proportion of all gases – how can this increase the greenhouse effect in total?”
Not very much, is the answer. Even the warmists know this; that’s why they phantasize about a small warming caused by CO2 which makes H20 evaporate, which will with its wide absorption band lead to a feedback which will make the Earth melt and the Oceans boil and we will all be down on our knees and pray for bloody mercy or somesuch.
Which is of course comple lunacy as hot places on the Earth, say in the tropics during noon, are not known for melting down due to a sudden outbreak of water vapor feedback. But sanity does not enter the skulls of the AGW boneheads.
A premise of Herman and Pielke’s description of “the greenhouse theory” is that in the infrared band and outside the window of transparency the magnitude of the downwelling radiative flux increases with concentrations of greenhouse gases while the magnitude of the upwelling flux stays stationary. Would the two authors care to comment on Miskolski’s finding that the two fluxes are equal?
“”” Phil. says:
July 23, 2010 at 12:58 pm
stephen richards says:
July 23, 2010 at 12:03 pm
I’ve got problems with all of this.
What follows is a question and not a statement;
CO² 0.04% “””
Note to Phil.
I think you made a typo in your response Phil. You said that the spoantaneous decay time of the CO2 excited state was much shorter than the collision time in the lower atmosphere.
I’m sure you meant to say much longer; so that collisional thermalisation is far more likely than re-emission from the CO2 excited State. I’m having the same sort of problem today.
Andres Valencia says:
July 23, 2010 at 4:57 pm
“Am I right to think about G&T that:
A possible way for atmospheric “greenhouse gases” to warm a planet could be by temporarily delaying some escape of heat?
Infrared absorbing gases in the atmosphere could slow the cooling of the Earth?”
Yes i think so. G&T don’t talk much about any “slowing down”; as physicists, they just compute some balance or equilibrium and are done with it; they don’t care much for some temporary upswings or downswings. See my comment above at
July 23, 2010 at 9:40 am
I’m very surprised that any meteorologist of stature would offer a radiation-only explanation of the “greenhouse effect,” dismissing all other modes of thermal energy transfer as “too complicated to discuss here and not completely understood anyway,” but nevertheless maintaining that “adding more CO2 warms the atmosphere.” In effect, they conflate a) thermodynamics (flow of thermal energy) with IR radiative transfer, b) forcing with release of stored energy, and c) energy content with thermal capacitance. And then there’s the usual reference to phantom “feedbacks” in a passive feed-through system that is entirely dependent upon insolation for its energy supply.
Somehow it has not occurred to them, that LATENT heat transfer is the principal mode of cooling the surface over oceans. And is the PRESENCE of an atmosphere, rather than trace chemical concentration, that is the key to the “greenhouse effect,” because that’s what makes backradiation possible. That radiation comes largely NOT from CO2, or even water vapor, but from the far-more massive constituents of the atmosphere radiating collisionally transferred energy in the seldom-shown regions of the thermal spectrum.
Hmmm? So the science isn’t settled, after all?
Are clouds part of the greenhouse effect?
tallbloke: In running through the above comments, only a dozen or so even think to mention the oceans. Kind of odd, don’t ya think? But a few noted that the temperature of the earth would be much cooler if not for the oceans.
The oceans, of course, have their own “greenhouse effect”; that is, downward shortwave radiation can warm the oceans as deep as 100 meters but the oceans can only release heat at the surface. So all in all, most of the arguments miss the obvious.
I want the theory and this whole discussion to move to the level where all of this happens – at the quantum level. It operates with photons and molecules and the speed of light (300,000 km/sec) and the EM spectrum (from infrared to ultraviolet) and the molecular collision rate (6.9 billion per second).
There is too much Macro and note enough Micro.
from Ben and Roger’s guest-post:
“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.”
This is a very important point, and I don’t mind reiterating it in my own words. Real greenhouses keep the flowers, fruits, and veggies inside of them warm by goofing up convection cells. Atmospheric IR-absorbing gases, like gas-phase H2O, and to a much lesser extent CO2, cause warming by an entirely different mechanism.
It’s a mistake for skeptics to jump on the buzzword, “greenhouse”. It’s not a conversation-stopper. On the other hand, AGW buffs are mistaken in their belief that recent increases in atmospheric levels of CO2 are causes for concern. The experience of the last 30 years demonstrates beyond all reasonable doubt, that the actual warming effect of moderately increased atmospheric concentrations of CO2–together with all of the intertwined positive and negative feedback mechanisms–is *immeasurably* small. CO2 is *not* the 800-pound gorilla of climate change.
In principle, the AGW buffs may be *qualitatively* correct about the warming effects stemming from IR-absorbing gases. However on a *quantitative* level, it’s a different story.
We should courageously face the facts about those with whom we strongly disagree. They are simply not smart enough to be wrong about everything. And knee-jerk reactions to each and every AGW expression is counterproductive; it makes all of Skepticdom look foolish.
In order to minimize confusion, I propose that the atmospheric-warming mechanism of interest to us be rechristened as the Larry Effect. One of these days, I really should catalog and number all of the Larry Effects. 🙂
DirkH says:
July 23, 2010 at 5:18 pm
“Not very much, is the answer. Even the warmists know this; that’s why they phantasize about a small warming caused by CO2 which makes H20 evaporate, which will with its wide absorption band lead to a feedback which will make the Earth melt and the Oceans boil and we will all be down on our knees and pray for bloody mercy or somesuch.”
Thanks for the answers, much appreciated.
Is it really correct that the AGW alarmists think that CO2 will indirectly cause an increase in water vapour which will create an even greater greenhouse effect? That does not make much sense.
I just find that cloudy days are cooler than clear days. So there must be a large difference in the greenhouse effect of water vapour depending on whether atmospheric H2O is in gaseous form or in aerosol form as clouds? Surely more water vapour in the atmosphere would result in increased cloud formation also?
It just seems likely that the earth is a stable system with biodiversity having survived this long. If the system was inherently unstable (that is, having dangerous positive feedback loops), then it seems statistically unlikely for a world as old as ours to have thrived so much.
I read somewhere that the earth has already experienced periods with significantly higher CO2 concentrations in the atmosphere in the past. What was the climate and biodiversity like during those periods?
NickB. says: “I’ve always wondered if the equation that comes up with 33 degrees of greenhouse effect took into account that space really isn’t absolute zero – if I recall correctly it’s 3 or so K. Not that it really matters, just curious if anyone knew”
Yeah, I heard (a few decades ago) that it was an average of 4°K. (Or 4 K, if you wish, and don’t mind people thinking you mean 4,000). I’m not so sure, given the recent order-of-magnitude changes in the thermosphere, that it’s a constant. But as you suggest, it doesn’t matter much for most purposes, since there’s not a lot of difference between, say:
q = AFσ(298^4) and q = AFσ(298^4 – 4^4)
Note that the thermosphere’s temperature can be range from 200°K (at lower altitudes) to as high as 2800°K during the day (high altitudes). The thermosphere is extremely tenuous, so it’s not considered to have a measurable effect on the Earth’s heat balance. This may be in error.
I was amazed when I read the succession of recent papers saying that the ‘greenhouse effect’ violated established laws of physics, as I understood this to be the bedrock of global warming theory.
I am even more amazed after reading this thread; after 30 years and tens of billions of dollars in ‘climate research’, we still don’t have agreement on even this basic point?
What have the scientists been doing all these years?