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During the past several months there have been various, unpublished studies circulating around the blogosphere and elsewhere claiming that the “greenhouse effect” cannot warm the Earth’s atmosphere.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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Willis Eschenbach on co2 and negative feedback
Part 1
Willis Eschenbach on co2 and negative feedback
Part 2
Juraj V. says:
July 23, 2010 at 12:53 pm
OK gentlemen. Whats wrong with this scheme?
http://i480.photobucket.com/albums/rr165/magellansc24/hansen_oven.jpg
😀
I call it a thermos. Maybe that’s why I don’t get grant money. 😉
Roy Spencer on clouds and negative feedback
Part 1
Roy Spencer on clouds and negative feedback
Part 2
It appears that the general assumption here is that there is an unlimited amount of radiation within the region of the resonant frequencies of CO2. This is not true according to Dr. John Nicol’s paper at the current level of CO2 virtually all of the radiation at the resonant frequencies is absorbed in the first 50 meters of atmosphere the close neigbours to those frequencies are absorbed progressivly higher but all are absorbed in the lower 2000 meters thus the so called “greenhouse gas” effect of CO2 is saturated and adding CO2 only lowers the height of the absorbtion but does not change the amount of energy absorbed once the mini Stefan Boltzman curves around each resonant frequency have overlapped which occurs far below the current levels of CO2. Thus the line broadening effect of increasing CO2 concentration which is the basis for the IPCC formula has flattened out.
It should also be understood that the CO2 molecules will only reradiate energy at its specific resonant frequencies and their mean path length according to Beer’s Law is about 2 meters which explains why there is effectively no radiation at the specific resonant frequencies remaing after 50 meters. So the CO2 molecule will absorb close neigbours to its resonant frequencies higher in the atmosphere but the reradiated energy has a very short path and can not return to the earths surface.
It should also be noted that much of the energy absorbed by the CO2 molecules is transferred to the other molecules in the atmosphere by kinetic energy transfer through collision thus there is very little reradiation anyway.
kwik says:
July 23, 2010 at 2:40 pm
Phil. says:
July 23, 2010 at 12:42 pm
“‘Suppose you have an isolated black ball which you heat so that it eventually equilibrates at a certain temperature, introduce another ball nearby at a lower temperature, the hotter one will get hotter (as will the cooler).’
Are you sure about this, Phil? That the hottest will be hotter? I allways believed that this is exactly what was impossible, according to the 2′nd law….because if it got hotter…then heat has gone from colder to hotter….. or is this Trenberts hidden heat?”
The statement bugged me at first too, but then I realized it was just poorly worded. The two balls he’s using have their own internal heat sources. If they didn’t, then both would just reach the local background temperature. Take an object in the steady state at 500k radiating into a 0K background (makes it simple). Now add another object at 250k under the same conditions. Both objects would get hotter because they would radiate some of their energy to each other instead of losing it to the 0k background. Since we want the system to be in equilibrium, each ball must raise its temperature to net out the increased energy it receives from the other. The exact amount depends on the geometry of the problem.
Dr Pielke –
I could be wrong but they say this:
and you say this:
Tell me if I am wrong, but aren’t you saying exactly the same thing they are saying?
Their point seems to be that the warmer atmospheric layer can’t absorb, and you are saying if the CO2 is there it will absorb it. Your point – that more being there means more is absorbed – doesn’t address their concern about warmer vs cooler. Without saying why it is so, you only state that it does. But that is their contention in the first place. You seem to be merely rephrasing what they are objecting to. I don’t think that is adequate as an explanation.
Myself, I would have suggested that when a molecule in the atmosphere is impinged by energy, it doesn’t give a damn where the energy came from. To the molecule, energy is energy – if the energy is there, it will absorb it if the frequency is an absorbable one.
In addition, there is much comment about what water vapor is doing, and people’s thoughts are all contending. This seems to mirror what we hear about the climate models being wrong because they don’t have a clue how to model water vapor – because they haven’t figured out what water vapor really does in toto. People are getting all energized in telling what they think is going on. And I doubt Dr Pielke can definitively disagree with most of their input here; it is probable that just about all of it is correct, but what water vapor effects are operating under what conditions, in what combinations, and in what proportions – it all seems to be anybody’s guess.
I come away from this believing that Dr Pielke’s understanding is far less than complete. That is not a slam at him. It just seems to put him in the middle of the pack in trying to understand a complex system.
Co2 has been at much higher levels in the past. It didn’t cause the warming that is proposed it should have in those times. Some of the people that say co2 causes warming are smart people. Why is there a disconnect between what the data shows about co2 in the past and what these smart people are saying about what co2 can do now?
Barry Moore says:
July 23, 2010 at 9:11 pm
I agree.
The main energy transfer of an excited CO2, or H2O will be through cascading to lower levels, and thus not reproducing the input frequency anyway, and also rotational and vibrational levels, all these being the process of thermalization of the atmosphere which is composed mainly N2 and O2.
The whole concept leading to the energy oven of Peden as shown by TskTsk above is based on what happens when one mixes ones physics systems. In this case thermodynamic theory and quantum statistical theory. Temperatures, the way they are used in climate with black body radiation etc are thermodynamic quantities. When one starts to go into the quantum statistical picture, one has to remain in that. One cannot hand wave back radiation and stuff like that. One has to describe quantum statistical ensembles and treat them appropriately to get the average energy from the exponential expressions where it is hiding. One cannot treat radiation in quantized systems as if it is billiard balls bouncing around and expect consistent results.Mixing two systems of physics/reference results in paradoxes, like the oven above.
As one of the earlier commentators remarked, the responses to this post are almost enough to drive me to the other side of the argument. The authors put “greenhouse gases” in quotes and are criticized for misunderstanding greenhouses. They state that greenhouse gases raise temperatures leaving all other factors aside and are criticized for not considering other factors. They say that the Second Law is not violated and, good Lord, I don’t even follow what happens next!
Several people have suggested that the scientists should rephrase their explanations in terms that they can understand. Sorry, but this is clearly not going to be possible.
kwik says:
July 23, 2010 at 2:40 pm
Phil. says:
July 23, 2010 at 12:42 pm
“Suppose you have an isolated black ball which you heat so that it eventually equilibrates at a certain temperature, introduce another ball nearby at a lower temperature, the hotter one will get hotter (as will the cooler).”
Are you sure about this, Phil? That the hottest will be hotter? I allways believed that this is exactly what was impossible, according to the 2′nd law….because if it got hotter…then heat has gone from colder to hotter…..
That’s exactly right, the version of the 2nd Law you quote is not applicable to radiation as George, I and others have pointed out above. Consider this thought experiment, for the cooler ball not to radiate to the hotter would require the surface of that ball ‘know’ that the photon it is about to emit will hit a hotter ball and so not emit! As far as radiation is concerned it is the net transfer that is governed by the 2nd law, but energy is transferred in both directions continuously (just at a higher rate from the hotter one).
This is not something that’s limited to climate science, it’s used every day in radiation heat transfer in engineering.
I believe that if someone made a balloon ascent wearing a set of IR goggles that could *only* see CO2 radiation, they would soon lose sight of the ground and be lost in a uniform fog of dimming CO2 ‘light’ as the temperature cooled at the adiabatic lapse rate until they reached the tropopause where they would finally see the darkness of outer space opening out from above. The sun, as it became visible, would not appear to be much brighter than the pale CO2 ‘cloud’ below illuminated by Earthshine.
REPLY: Actually, that’s an easily reproducible experiment with a hi altitude balloon and a video camera – Anthony
DirkH says:
July 23, 2010 at 5:18 pm
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.
Only if we lived on a planet where Planck’s radiation law does not apply, i.e. on this planet the radiation from the surface is not uniform from the UV to the microwave, if you want to look at what the absorption curve actually looks like see here:
http://i302.photobucket.com/albums/nn107/Sprintstar400/Atmos.gif
An explanation that includes convection.
Start with an atmosphere of nitrogen and oxygen (negligible GH effect). The surface will be 255 K, and the atmosphere above it would be cooler with height (negative lapse rate) due to convective equilibrium and pressure variation. Add transparent GHG slowly which now leads to the atmosphere starting to produce its own longwave flux up and down. Now, from no downward longwave before, the surface has both solar and longwave downward fluxes, and it has to warm because its net radiation input has increased. This leads to more convection, spreading the warming through the troposphere, but maintaining the convective lapse rate. Eventually a new warmer equilibrium is reached determined by the incoming/outgoing radiation balance at the top of the atmosphere. This is why the surface is now 288 K instead of 255 K. [For simplicity, I have assumed albedo stays the same here, but of course with no water vapor, it would be warmer than 255 K due to no clouds, and water vapor also modifies the way the lapse rate develops due to clouds].
Re: The Saturation Argument.
The accumulation of CO2 in the atmosphere means that the average height at which IR is emitted to space is higher.
Higher -> Colder
Colder -> reduced emitted energy (by S-B law)
There will be a imbalance between incoming (solar) and outgoing (IR) which will cause the surface and the lower atmosphere to warm – until it he incoming=outgoing balance is restored. How much will it warm?
Equations (based on Beer-Lambert and Planck) which model EM transmission through the atmosphere suggest that doubling CO2 in the atmosphere will reduce the outflow of energy at TOA (top of the atmosphere) by ~4 watts/m2. These equations form the basis of programs such as Modtran which have been validated against numerous different atmospheric profiles.
What does 4 watts/m2 mean for surface temperature? A ‘quick and dirty’ method of calculation follows:
Surface Temp @ur momisugly ~15 deg C (288K) emits ~390 watts/m2
TOA emits ~240 watts/m2
IR Transmission = 240/390 = 0.615
Reduce outgoing IR at TOA by 4 watts/m2 then
IR Transmission = 236/390 = 0.605
But to maintain/restore incoming=outgoing balance we still need to emit 240 w/m2, so rearrange Transmission equation to give
Emission from Surface = 240/0.605 = 396.6 watts/m2
which equates to a surface temperature of ~289.2K or an increase of 1.2 deg. Usual caveat applies, i.e. does not include feedbacks.
Theo Goodwin says:
July 23, 2010 at 7:22 pm
[–snip for brevity–]
So, Tallbloke, is it wrong to say that CO2 molecules capture radiation from Earth’s surface and then emit radiation randomly so that near half what they admit goes to Earth’s surface? If this description is correct then how can it be that the emitted radiation does not heat the Earth’s surface?
THIMK: If the Earth is first heated by energy released from a gas molecule, and then the Earth releases that energy to a gas molecule, then how does the gas molecule ‘reheat’ the Earth?
Monckton of Brenchley says:
July 23, 2010 at 9:13 am
[–snip–] The true debate in the scientific community is not about whether there is a greenhouse effect (there is), nor about whether additional atmospheric CO2 causes warming (it does),[–snip rest–]
No, CO2 does no such thing, and I challenge YOU to produce incontrovertible proof of any such contention.
You’ll be doing that, won’t you? Real soon now?
In the interim, there are those bits of ‘inconvenient truth’ referred to as the Vostok Ice Cores which COMPLETELY refute your statements: In every case of a temperature rise, CO2 lagged, i.e., followed AFTER an interval of time.
Consonantly, in every case where the temperature fell, the CO2 lagged the temperature fall.
A poster on Treehugger forums totally destroyed AGW with a simple experiment. Take Two Kilner Jars. Fill one with pure C02 and the other with reasonably humid but otherwise standard atmosphere. Heat both from the same heat source and then turn off the heat source after a while. Then measure the rate of heat loss within the Jars. The C02 loses it’s heat much faster than the humid standard atmosphere.
REPLY: We don’t live in a pure CO2 atmosphere, so the comparison isn’t valid – Anthony
I never see mention as to what becomes of the more than 45% of solar radiation which is IR. Is most of it absorbed by greenhouse gasses before reaching the surface? What affect would that have on the amount of surface radiation that can be absorbed?
Monckton of Brenchley says:
[–snip–] The true debate in the scientific community is not about whether there is a greenhouse effect (there is), nor about whether additional atmospheric CO2 causes warming (it does),[–snip rest–]
Sounds a little bit like the argument put forward by the alarmist, i.e. I think your argument holds no merit so I’m not going to discuss it any further. I’m no scientist but now that somebody has deconstructed the greenhouse theory, I’m almost embarrassed that I never properly questioned it myself. Frankly, GH theory clearly has problems faced with empirical evidence and fudges such as talk of sensitivity and forcings merely explain the oberservation rather than the science. I don’t think we can so easily laugh or dismiss the alternative and challenging ideas – at least not in their entirety and certainly not yet.
Anthony, the experiment referred to by Darren Parker is COMPLETELY valid and more so. The experiment demonstrates the properities of Co2. You can check for yourself, the specific heat of Co2 is slightly less than aluminum. Aluminum dissipates heat rapidly. Co2 shares this same property and that is what is observed in the experiment. Poor at absorption, fast at reemission when compared to air. It also illustrates the high specific heat of water. In fact this experiment pits a 100% concentration of Co2 up against water vapor and Co2 falls flat on its face.
Instead of the focus on co2 there should be a focus on producing food for poor countries against the cooling that has already started in the earth. It is sad what could happen, and what has already begun to happen.
274 comments, this one touched a nerve
Tallbloke:
First, the statements in italics were not my words (scienceofdoom.com’s), but I will stand by them. GHG’s absorb and re-emit longwave radition back to earth.
What you’re stating in terms of ‘cooling slower’ is less clear statement than the specific role of GHG’s in reflecting back energy. If this didn’t happen we’d be much colder (-18C, see the previous post) Pretty nitpicky statement on your part for you ending up being less clear.
So the sun’s energy just passes through like they don’t exist, but when the earth emits its radiation, these gases absorb energy and then re-emit, so that the earth’s energy doesn’t just fly off into space but instead it’s absorbed and re-transmitted, some of it back down to earth.