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During the past several months there have been various, unpublished studies circulating around the blogosphere and elsewhere claiming that the “greenhouse effect” cannot warm the Earth’s atmosphere.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.
Discover more from Watts Up With That?
Subscribe to get the latest posts sent to your email.
Peter says:
July 23, 2010 at 12:07 pm
RockyRoad:
First you must defend your term “damaging”
I guess you must have missed the preceding bit which said:
…and the questions are:
(my bold)
————–Reply:
Yes, they are questions, indeed. But how a question is framed often determines the acceptable answers. Context matters.
Rick Bradford says:
Rick Bradford says:
You can’t judge whether agreement exists in the scientific community by reading a blog, particularly one such as this. If this was your way of establishing whether agreement exists, you would also have to conclude, for example, that no agreement exists on the basic point of whether the Earth is less than 10,000 or 13 million years old.
Yes, agreement exists in the scientific community on this basic point and those who continue to argue it would be taken seriously in very few places outside of this little microcosm.
Ron House says:
I assume you mean to be saying that convection dominates radiative transfer from the earth’s surface. If you are talking NET radiative transfer from the surface and you include latent heat as well as convection in the “convection” part then you are indeed correct that this is larger than the net radiative transfer (see the Trenberth and Kiehl diagram or read the discussion here: ). However, you are wrong that the models are somehow missing this…or that this matters much for determining the greenhouse effect.
That is because the dominant part of determining the greenhouse effect is determining the energy balance between the earth, sun, and space…and the only way the earth can communicate any significant amount of energy with the sun and space is via radiation. The radiative balance at the earth’s surface turns out not to matter very much in determining the temperature rise because, like you say, convection (and latent heat) play the larger role in determining the temperature structure of the atmosphere. For example, in the tropics, the temperature structure is expected to be dominated by the moist adiabatic lapse rate.
cba says:
This is essentially the same sort of argument that Willis made in this thread http://wattsupwiththat.com/2010/03/16/another-look-at-climate-sensitivity/ and it is wrong for the same reason that his argument was wrong: If you consider all radiative effects to be forcings and none to be feedbacks then you will necessarily derive the sensitivity in the absence of feedbacks. (The reason that your value differs somewhat from the sensitivity of 0.29 deg C rise per W/m^2 I think has to do with the fact that you are computing it over such a larger range of forcing…but there may be other reasons too.)
It seems to me that those who have accepted the money for research and have resorted to fraud, to promote global warming, do not believe it themselves. If they did believe why rig the system.
Peter says:
The surface is not receiving 4 W/m^2 more. The 4 W/m^2 is the radiative forcing at the top of the atmosphere. There is a reason why scientists prefer to look at the forcing at the top of the atmosphere and you have just identified it: Within the troposphere itself, radiation is not the controlling heat transfer mechanism. However, it is the only significant mechanism controlling heat transfer between the earth system, sun, and space. I suggest reading an introductory textbook on the subject, such as “Global Warming: The Hard Science” by L.D. Danny Harvey, which has an interesting calculation that demonstrates this whole idea very clearly.
I am very keen to see a resolution of the issues raised by Professor Miskolczi.
My own climate descriptions fits his findings perfectly in that I aver that the change in the speed of the hydrological cycle provides a mechanism whereby optical depth (and therefore temperature) is maintained despite changes in the quantity of greenhouse gases other than water vapour.
If the IR optical thickness of the atmosphere really has been constant at 1.87 for at least 61 years then that is game set and match to the sceptical viewpoint.
Even if the optical depth has varied somewhat the alarmist proponents still have a lot of explaining to do as regards the scale of any CO2 effect as compared to natural variability.
Is anyone in authority actively investigating the optical depth aspect ?
I get the impression that it is not the “SCIENCE” that is in question. Not really!
It is the interpretation of the science and the identification of problems which follow from these interpretations and the various proposed solutions to the various problems from these interpretations that are at issue.
Now, when “reasonable”, “mature”, “intelligent”, people assess the matter of AGW, they get the impression that there are a lot of unreasonable, immature, idiots proposing a lot of unreasonable, simple minded, bird brain solutions to what these wierdos think are the best solutions to the various problems they believe exist based on their interpretation of the science.
Hummmmm… maybe, instead of scientists we need to here from a few psyrinks and psychologists who have expertise in delusional mass hysteria.
Note to NYLO.
I just blew away a long explanation of the error in my original post.
In short; we aren’t interested in the average Temperature of the ball; that’s a distraction. The point is that the local point (under the sun) must rise in Temperature if we delay the conductive (or other type of) cooling; which increases its radiation rate, and sets up a temperature gradient so conduction can occur to remove more heat. Yes the other parts of the ball must l;ower in temp (on the night side), and the average would go down; but that is not what we wanted to know; the sun heated point MUST get hotter.
Now on the actual earth; the earth rotates in 24 hours so each point gets cooked in turn and if normal cooling paths get delayed; all points must rise; and because the earth has a much longer thermal time constant that 24 hours, the increased Temperature is not fully dissipated before the sun gets up again tomorrow.
I was working out the wrong problem in studying the average temperature of a non-rotating thermal lagging body.
Bur if you hadn’t caught me; the mistake would have been enshrined forever.
Thats the problem with doing “stick on a sandy beach” physics live on line; it is easy to wander off to a different problem.
tallbloke says:
July 24, 2010 at 1:21 am
Back radiation can’t heat the oceans.
—
Yes it can. There are hundreds of W/m2 of back radiation at the surface. Where does it go? Any respectable ocean energy budget has to include this, otherwise the temperature would drop towards the now famous 255 K.
“”” Chad Woodburn says:
July 24, 2010 at 5:05 am
I still have a question (which I have asked before, but don’t think was clearly answered).
While CO2 blocks radiation from escaping from the atmosphere, thereby producing a positive feedback, to what degree does CO2 block radiation from entering the atmosphere, thereby producing a negative feedback? Has that negative impact (if it exists) been included in the calculations?
Clouds can have a positive feedback effect by keeping heat near the ground from escaping more quickly into the upper atmosphere, but the clouds also can create a negative feedback by keeping heat from reaching the ground in the first place by reflecting the radiation back into space. My understanding is that under some circumstances the net effect of the clouds can be negative. To what degree is CO2 like that? “””
So Chad, when was the last time that you were in the shadow zone of a cloud that passed between you and the sun; and it got hotter; meaning that the clouds were retaining heat near the ground.
Clouds (on a climate time scale) ALWAYS produce cooling; NEVER heating.
The blockage of incoming sunlight from reaching the ground during daylight hours always outweighs the slowing down of cooling during the night; so on a climatically significant time scale (30 years) any INCREASE in the average amount of global cloud cover ALWAYS results in COOLING. it NEVER EVER results in WARMING.
“John A says:
July 23, 2010 at 8:45 am
Dear Dr Pielke:
…….Water vapour clouds glow in IR because of this effect, which is why they can be pictured at night from satellites.”
You have this backwards. Clouds do not glow in IR, on the contrary, they show up on the sensor as shades of black – lack of IR. The images are reversed for display ( a negative image in film terms) to follow the same conventions as that of B&W Visible imagery, which are a positive.
“Jim D says:
July 24, 2010 at 7:22 am
tallbloke says:
July 24, 2010 at 1:21 am
Back radiation can’t heat the oceans.
—
Yes it can. There are hundreds of W/m2 of back radiation at the surface. Where does it go? Any respectable ocean energy budget has to include this, otherwise the temperature would drop towards the now famous 255 K.”
Quite simply: Latent Heat of Evaporation.
The curious thing being that evaporation has a net cooling effect because it always draws more energy from the surroundings than is required to provoke it so in theory more IR back radiation should cool the oceans rather than warm them.
Go figure.
Jim D says:
July 24, 2010 at 7:22 am (Edit)
tallbloke says:
July 24, 2010 at 1:21 am
Back radiation can’t heat the oceans.
—
Yes it can. There are hundreds of W/m2 of back radiation at the surface. Where does it go? Any respectable ocean energy budget has to include this, otherwise the temperature would drop towards the now famous 255 K.
As Roger Pielke Sr correctly stated, the greenhouse effect works by slowing the rate of cooling, not by heating anything up. Co2 emitted radiation is long wave, and can’t penetrate the ocean much beyond its own wavelength. This is known physics. There is all sorts of worthless speculation about conduction from the ‘skin’ of the ocean, but take it from me, the sun heats the ocean because its radiation is mostly shortwave, which penetrates to several tens of metres into the briny. Longwave radiation just causes more evaporation at the surface. Any conduction effects are second order.
It was put to the test by the realclimate alarmists, who were *desperate* to show some effect from back radiation. They got something like a 0.0002C change from cloudy to clear sky, and said that it ‘proved the principle’. What a joke. I laughed my a*se off.
Now you might think that more evaporation at the surface might cause the secondary effect on water vapour and humidity levels the alarmists are needing to bump up the sensitivity, but you’d be wrong. See the post by ninderthana on this thread.
I can’t emphasize this FUNDAMENTALLY IMPORTANT point enough. Co2 doesn’t warm the Earth, it just slows down the cooling rate. However, if Miscolczi is correct, and no-one has yet refuted his paper, then the hydrological cycle will speed up to compensate for any increase in co2, and the ‘greenhouse’ will remain in dynamic equilibrium.
Therefore, as I outlned in my previous post, it’s changes in insolation at the surface which change the global temperature through raising/lowering ocean heat content. The claim that the sun can’t be responsible for late C20th warming is refuted by analysis of the total solar originated energy retained in the oceans over the period of record of ocean heat content, and the calculation of the steric component of sea level rise.
To sea the truth of this, simply consider the relative heat capacities of the players involved, the sun, the ocean and the atmosphere. The top two meters of ocean have as much heat capacity as the entire atmosphere above. The tail does not wag the dog, as the simple time series plot of SST vs LT proves:
http://www.woodfortrees.org/plot/uah/from:2007/plot/hadsst2gl/from:2007/scale:1.7/offset:-0.3 Ocean surface warms first, atmosphere responds 2-3 months later. Cause cannot be preceded by effect.
Nutshell: The sun heats the ocean, the ocean heats the atmosphere, the extra co2 slows down the escape of the heat to space by a tiny bit, but nowhare near enough to account for global warming.
Nir Shaviv shows us that though the solar cycle might only change TSI by 1.3W/m^2 over the cycle, and on Leif Svalgaards ultra conservative estimates, the total TSI had a smaller change over the C20th, reaching peaks in the late 50’s and 80’s, that change is amplified by cloud albedo changes which make a bigger difference to insolation at the surface. This accounts for far more of the C20th warming than just changes in TSI. By the time we knock of the spurious UHI signal, there isn’t much left for co2, which is mostly along for the ride.
http://tallbloke.wordpress.com/2010/07/21/nailing-the-solar-activity-global-temperature-divergence-lie/
I have said this many times, but once more will not be too much.
This explanation of why the world is not an ice ball, named “greenhouse effect” suffers from the same misuse of physics of all other climate explanations and does lead to paradoxes like Peden’s oven .
Thermodynamics has a self consistent set of axiomatic proposals that lead to classical thermodynamic equations which are being used extensively and successfully to predict and design all sorts of heat related engines etc. There is no doubt that it works
At the same time, when one reaches the small distances, one needs statistical mechanics that treats the particle nature of matter and has a completely different axiomatic formulation and different equations of state . Because they describe the same data, one set macroscopically, the other microscopically, at the limits of large distances the systems coincide.
Thus we have the axiomatic statement: entropy stays the same or always increases an axiomatic theorem in classical thermodynamics, morphs to the highly improbable statistical ensembles that would have to evolve at the microscopic levels
for this axiom of classical thermodynamics to be falsified. As, for example, there exists a tiny probability that statistically an ensemble exists where all the molecules in the room you are in will collect themselves in one corner, or arrange themselves into a checkerboard pattern. These probabilities are so miniscule that the classical thermodynamic statement on entropy stands.
When one reaches dimensions of hbar, and those are the dimensions where one sees the spectral lines of radiation and absorption, a new system is needed, and that is quantum statistical mechanics which also treats the aggregate particles as statistical ensembles but now with quantized properties. This formulation also at the limit, falls back to simple statistical mechanics, which fall back to classical thermodynamics macroscopically.
Now radiation consists of photons, and photons are quantum mechanical entities. Classical thermodynamics has radiation, and has the black body formula, treating radiation as heat loss with classical Maxwell equation pointing vectors that carry the energy. One of the reasons quantum mechanics was invented was that the black body formula was not describing the data and showed the necessity of another system in the microscopic domain that impinged on the macroscopic description, but that is another story.
About paradoxes. Paradoxes arise when axiomatic systems are mixed up inconsistently. There is the famous Cretan paradox from ancient greek philosophy:
All Cretans are liars, said a Cretan. Since he is a Cretan he is lying, so all Cretans are not liars, but if he is telling the truth? Then he is lying.
These paradoxes are solved in modern times by the concept of meta-levels: The Cretan is in one level , the statement is a meta-level.
In a similar way, classical thermodynamics is one level, quantum statistical mechanics is another level, and if a paradox, as Peden’s oven, appears, it means the two system have been mixed up inconsistently.
Hotter body and cooler body are statements from classical thermodynamics. If one sticks to that then one cannot be talking of radiation levels and absorption lines. In classical thermodynamics there is just heat capacity and heat retention. CO2 and H2O change the heat capacity of the atmosphere ( among a number of other things the H2O does). There is no need to play ball with photons absorbed and reradiated in a hand waving manner because that does lead to Peden’s oven and the accusation of violating the second law. Of course in the quantum statistical picture there are ensembles with a probability where the second law is violated, similar as with the entropy I described above. But the fact that quantum statistical mechanics smoothes over to statistical mechanics which smoothes over to thermodynamics means that when talking about average behavior, and temperature, heat etc are average descriptions of statistical ensembles, a colder body cannot heat a warmer body. Period. It is really introducing paradoxes in the soup and should be avoided.
And I am not repeating what a number of people have pointed out here, that ,that one lonesome CO2 molecule surrounded by 150 N2 and O2 ones will transfer any excited energy into thermal energy before it manages to cascade to ground level and reradiate anything in the funny world view of climate plots.
I’m still puzzled:
(1) The heat of an object is a function of the total amount of thermal radiation directed upon it.
(2) During the day, when the sun is shining, the surface of, say, a piece of asphalt is heated by the sun to a temperature that is higher than the air temperature.
(3) The standard GHG theory says that there is backradiation, which affects the temperature of the atmosphere (preventing it from cooling off as fast as it would without GHGs). This backradiation would have to be ADDED to the solar radiation during daytime to determine the total energy being received by the asphalt. That would HAVE to lead to an even higher temperature than produced by the sun alone (see (1) above).
(4) But that cannot happen because of the Second Law; the cooler atmosphere cannot contribute heat to the warmer surface.
(5) Therefore, something’s wrong with the “GHG hypothesis” as explained in this post.
Can someone explain where I am wrong?
“””
Reed Coray says:
July 23, 2010 at 6:51 pm
George E. Smith says:
July 23, 2010 at 5:08 pm
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.
If you have a well-mixed mixture of distilled water and ice, the temperature of the mixture will be 0 degrees Centigrade. As you add heat to the mixture, the temperature will stay at 0 degrees Centigrade until the ice has melted. If you add enough heat the ice will melt and the temperature of the water will rise. But during the interval the ice is melting, the added heat does NOT raise the temperature. So I don’t believe that the claim “an increment of energy” must result in “the Temperature going up” is correct. “””
Reed, You are welcome to live in a well mixed mixture of distilled water and ice.
The rest of us don’t; so your observation has no relation to the greenhouse effect on earth; that stops us from being at 255K.
So believe whatever you want. I’m too busy trying to help people who want to learn to bother with straw man arguments.
George E. Smith said:
“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.”
I’m not sure we understand the same thing regarding “delaying the cooling process”. And I am also not sure that you agree with me that the average temperature of your lead-filled bb ball, after reaching the new equilibrium temperature, would be lower. Perhaps it could raise the temperature a little bit while reaching the new equibirium, I don’t know, I didn’t do the maths. But in the new equilibrium, the average temperature will be lower. In the new equilibrium, the hot part of the ball will have increased its temperature by a lesser ammount than the cold part will have reduced it. Putting it in formulae, and using k for the 4*pi*sigma constant, divided by 2 for convenience of considering the 2 halves of the ball separately,
(k*(t0+t1)^4 + k*(t0-t1)^4) > 2k*(t0^4), for any k, t0, t1. Therefore, if
E=2k*(t0^4) = the original incoming energy, which doesn’t change, and
E = (k*(t0+t2)^4 + k*(t0-t3)^4) after the new equilibrium, then it follows that
t2<t3 and, therefore the avg temperature drops: ((t0+t2) + (t0-t3))/2 < t0.
The delay in the cooling process causes the temperature to rise LOCALLY, in the side which receives the incoming energy, but causes the global temperature, the average, to drop.
Your example with the sinusoidal change of temperature around T0 causing the radiated energy to be higher than it would correspond to an isotermal T0 only proves my point. An isotermal condition is the least effective way of radiating your accumulated energy. Therefore, if you have little or no changes in your bb temperature, the average temperature will have to be higher in order to be able to radiate the same energy. Remember the example, 0k and 100k vs 84k.
That's why I say that the mere presence of the oceans increases the Earth's average temperature. Because oceans make the Earth more isotermal than it would be without them. They reduce the temperature variability of the planet. So they make the planet need to be hotter on average, in order to radiate back all the energy being received from the sun. And the effect is probably bigger than any warming we may be getting from GHGs because of their radiative properties.
Joel Shore said:
“Within the troposphere itself, radiation is not the controlling heat transfer mechanism.”
Well precisely. There you have it.
If. within the troposphere itself, the other mechanisms of convection conduction and the speed of the hydrological cycle vary (and indeed dominate) then that must affect the energy being supplied to the higher levels for radiation to space.
So if one varies, for example, the speed of the hydrological cycle then the energy made available for radiation to space will also vary and the temperature of the troposphere will vary and the temperature of the stratosphere will likewise vary but in the opposite direction as the energy available to it from the troposphere varies.
Now the speed of the hydrological cycle (in the troposphere) is set primarily by the rate of energy release from the oceans.
But the rate of energy release from tropopause to space seems to be set to some degree by the levels of solar activity.
To maintain the balance between the two influences the air circulation systems move latitudinally and the shift of the cloud bands affects global albedo.
The outcome is global climate variability in regional terms but the global temperature as a whole (including the ocean heat content) remains pretty much stable.
Get away from tropospheric temperatures as the definitive measure of global warmth.
As the oceans release energy the troposphere may warm but total energy content for the system remains the same because the ocean heat content declines.
As the oceans withold energy the troposphere may cool but total energy content for the system remains the same because the ocean heat content increases.
As the sun gets more active the troposphere may warm but total energy content for the system remains the same because the stratosphere cools.
As the sun gets less active the troposphere may cool but total energy content for the system remains the same because the stratosphere warms.
The mechanism in the middle regulating the independent solar and oceanic influences is the speed of the hydrological cycle represented by latitudinal shifts in the air circulation systems and consequent effects on global albedo.
It all works. Just engage brains and check it out.
tallbloke
July 24th 2010 at 7.50 am
Nice to see so much basic agreement. Just add my stuff about those latitudinal shifts in the air circulation systems and the consequent albedo effects and I think we’ve nailed it.
Whatever the oceans do and whatever the sun does and whatever CO2 does the air circulation systems just shift a bit to maintain the optical depth (and therefore temperature) set by the combination of:
i) Solar energy output
ii) Total atmospheric density (and thus pressure at the surface)
iii) The properties of the phase changes of water
That’s it in a nutshell and it would have been sorted twenty years ago but for the CO2 distraction.
Tallbloke explains:
“Back radiation can’t heat the oceans.”
And a mighty interesting explanation it is too. However, consider the plight of the non-climate scientist who is trying to understand the AGW theory. Schmidt and Trenberth swear that back radiation is the source of global warming. Yet the essay by Pielke, Sr, did not advance to the level of addressing this question. Answers are dribbling out in the discussion but dribbles are very unsatisfying. What is needed is a simple graph or graphs of Earth’s energy budget, as theorized by different parties, that addresses the issues of global warming at the level of CO2 molecules; that is, a graph of “Radiation’s Quest for Space and How CO2 Interferes with It.” Schmidt and Trenberth says that radiation emitted from CO2 goes to the surface of the Earth. How does it not cause warming? If it does not cause warming, how does radiation from black asphalt contribute to the cooling of the black asphalt? We do not need some textbook chapters on all the equations and the various spectra. We need a model along the lines of that ancient fossil known as “Rutherford’s Model of the Atom.”
Short of the kind of information that I have suggested, maybe we should direct everyone to the intense debate that Schmidt held on “Real Climate” some time back. In that debate, he did not satisfy his critics. We could take that as our starting point.
Joel Shore:
So then what does warm the surface? The nett energy flow to the surface must increase for the surface to warm, so where does it come from? It cannot receive energy from convection or evaporation, so it must be from radiation. (Admittedly, it can receive extra nett energy from the inhibition of convection etc, but you can’t blame CO2 for that) If it is from back-radiation then the surface must be receiving at least 4W/m2 in radiation in order to warm by 1.2 deg. Just because there’s a radiative imbalance at the TOA does not provide a mechanism for the surface to warm.
Posted this on the wrong thread earlier:
—————–
I need to clarify a point. It is true that the adiabatic temperature gradient dominates the temperature profile – but this would not occur without the greenhouse effect.
If greenhouse gases did not exist, the atmosphere would remain nearly uniformly cold and would not convect. Without convection, the adiabatic lapse rate would be zero.
RE: MattN: (July 24, 2010 at 5:32 am) “Logic would dictate that *if* 100% of the longwave IR is already being absorbed in the bandwidths CO2 does its absorbing, than increasing concentration can not absorb anymore because there is no more IR left in that bandwidth to absorb!”
That would be true if these absorption bands had sharp edges. As it is, there are fringe effects. That is why each doubling of the CO2 concentration, such as 280 to 560 ppm or 560 to 1120 ppm, is expected to cause a nominal one degree C increase in temperature.
So far, with all our modern industrial activity, the CO2 concentration has only increased from about 280 ppm to about 390 ppm.
The results from one online absorption effect calculation tool based on MODTRAN data suggests that there may be an additional temperature effect proportional to the seventh power of the log of the CO2 concentration that would kick in around 7200 ppm, but I have not seen any explanation of why this might be the case.
Stephen Wilde says:
July 24, 2010 at 8:25 am (Edit)
tallbloke
July 24th 2010 at 7.50 am
Nice to see so much basic agreement. Just add my stuff about those latitudinal shifts in the air circulation systems and the consequent albedo effects and I think we’ve nailed it.
Yes. With my engineers hat on (stuff you sphaerica) I can see that those shifts and the consequential changes to the hydrological cycle will have far bigger effects than anythng co2 gets up to. If you consider the Earth as a good old fashioned heat engine, these forces make a 0.011% change in the chemical compostion of the atmosphere utterly inconsequential.
But since the folks we are trying to get to see the sunlight only comprehend W/m^2 we’ll have to get some numbers nailed down in order to win the day.
We’ve been having ths conversation for over a year now, so let’s get cracking. 🙂