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During the past several months there have been various, unpublished studies circulating around the blogosphere and elsewhere claiming that the “greenhouse effect” cannot warm the Earth’s atmosphere.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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P Wilson,
“In tropical deserts where temps are 45C plus, radiation leaves at 8.5 microns, which puts it even further out of the c02 micron band.”
This is incorrect, the peak may be at 8.5 microns, but the radiation is emmitted in a wide band which does indeed incompass the absorption bands of CO2.
“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…”
Poorly put. This seems to repeat the original canard of heat flowing from cold to hot, as opposed to a reduction in heat loss rate from hot to cold.
stephen richards says:
July 23, 2010 at 12:15 pm
R. Gates says:
Another of your cracked replies courtesy of the Gavin Schmidt school of answers.
Gravity does not generate energy. Energy cannot be made or destroyed einstein.
Sure, gravity is a force which creates the conditions for the creation of stars and the nuclear energy in those stars is started by the force of gravity compressing the gases.
E=mc² not F.r²/m1.m2
@ur momisugly Read Coray 11:56am
Please see my post at 10:34. The terms Greenhouse Effect & Greenhouse Gas have meanings and definitions other than those now generally used. The terms have been hijacked because of their ability to convey a message and at the same time, convey it in a perjorative way. We need terms for the effects of CO2 in the atmosphere that convey the true meaning of those effects & ‘Greenhouse Anything’ just does not do that.
I think physics major is on to something!
“The atmosphere of Mars contains about 12 times as much CO2 compared to Earth’s atmosphere and there is very little atmospheric warming on Mars. The amount of warming seems more related to the total amount of atmospheric gas and hence pressure.
Mars=low pressure, low warming
Earth=moderate pressure, moderate warming
Venus=very high pressure, very high warming”
Maybe it is pressure broadening of the CO2 absorption bands?
Reed Coray says:
July 23, 2010 at 11:56 am
I want to thank Anthony, Ben Herman, and Dr. Pielke for this post. It has increased my knowledge of the popularly named “greenhouse effect”.
I believe, however, that lacking from this discussion are formal definitions of “a greenhouse gas” and “the greenhouse effect” Without such formal definitions, there is little common ground for discussion.
Such molecules need to have bonds which can be made to vibrate or rotate by absorbing light. To do that they need a permanent dipole, i.e. a different atom at each end of the bond. (this is a simplification but as reasonable one)
This means O2 and N2, the vast majority of the atmosphere can not do this. (This is where the trace gas argument breaks down, in a dry atmosphere CO2 and O3 contribute all of the absorption, thus a spacecraft approaching a desert Earth looking at the emission spectrum would to a first approximation see an atmosphere entirely composed of CO2 and O3). At first glance you’d think that O3 couldn’t absorb, but it’s a bent molecule and does possess a dipole. Most of the ‘greenhouse gases’ in the Earth’s atmosphere are triatomic or larger i.e. CH4.
I can’t see any text by way of explanation on my computer, only the graphic on this site and the link to thye other blog page. That page just links back to this with no text. What gives?? Where is the article?? It seems to have gone missing on my computer.
Alas, very superficial and not well done.
I recommend:
Heat Transfer by Infrared Radiation In the Atmosphere: Walter Elsasser, Harvard Meteorology Studies, 5-8, 1948 Pages 1-107.
Pay particular attention to page 23, discussing his general radiation chart for the Troposphere Dr. Elsasser says:
“It may be noted that since the flux in the carbon dioxide band is EQUAL, at any level, to a definite fraction of the black body radiation corresponding to the temperature of that level in BOTH the upward and downward directions, the RESULTANT flux of the CO2 vanishes in the approximation of the chart. This is a fair approximation to the truth in the lower atmosphere (for the upper atmosphere, see Section 12).”
Section 12, as with Plass, et.al, in 1955, notes the CO2 to be a net “upflux” agent in the stratosphere.
I would like to know how the basic physics changed since 1942.
Yours, stubbornly insistent on resolution…
Max Hugoson
R. Gates wrote: “Ultimately of course, the source of all energy in our region of the universe is gravity,”
You must have missed being taught that “It’s better to keep quiet and be thought a fool than to open your mouth and prove it beyond all doubt.”
THE “GREENHOUSE EFFECT”
AS A FUNCTION OF ATMOSPHERIC MASS
http://ruby.fgcu.edu/courses/twimberley/EnviroPhilo/FunctionOfMass.pdf
jorgekafkazar says:
July 23, 2010 at 12:23 pm
“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…”
Poorly put. This seems to repeat the original canard of heat flowing from cold to hot, as opposed to a reduction in heat loss rate from hot to cold.
This is a common fallacy, radiation from cold to hot takes place all the time and is not a violation of the 2nd Law. Your interpretation would have the night side of the earth radiating into outer space but when it’s at noon it would stop radiating back towards the Sun! No net heat can be transferred from the cold body to a hot via radiation but the radiation is always going both ways.
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).
P Wilson says:
July 23, 2010 at 11:43 am
Re-radiated longwave radiation doesn’t penetrate oceans, …
Re-rediated IR does not penetrate leaves, people, snow, corn, etc. It “disappears”. So all the warming that is supposed to be caused by IR is happening on less than 30% of the earths surface.
Let’s see if I have the numbers correct.
CO2 input from humans roughly 3%. (slightly less)
IR band 5 micro to 75 mirco. (pick a low to high as you see fit)
CO2 band at 14-16 micro. Allowing for bandwidth broading due to statuation.
75-5 = 70
14,15,16 are 3 numbers
3/70 = .0428
So CO2 occupies 4.28% of IR.
3% of 4.28% = .00128
Humans can only be responsible for this part of any warming etc caused by CO2.
Good post PWilson.
Herman and Pielke, Sr. write:
“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.”
Though scientists might be quite familiar with these claims and have no trouble understanding them, the actual statements in English, above, contain ambiguities. Consider the following:
“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.”
Increased downward radiation toward the surface is one thing but the fact that the rate of escape of IR radiation to space is decreased is another thing. I take it that there are two things going on here. One is that radiation has been intercepted by a CO2 molecule and, for that reason, the rate of escape of IR radiation to space is decreased. Got it. That is clear. The other thing is that there is radiation that has its source in the capturing CO2 molecule and this radiation warms the Earth. Given this radiation warming the surface of the Earth, why do the good doctors describe it all as a slowing of the cooling process. Part of the process heats the surface of the Earth. I believe that the surface of the Earth does not know or care whether the radiation comes from the Sun or elsewhere. So, why is this radiation from the CO2 molecules not treated as radiation from the sun, for the purpose of calculating Earth’s heat budget?
With all due respect, professors, if you are setting about to educate us in these matters, would you please undertake it seriously? What you have given us raises far more questions than it answers.
By the way, Trenberth (yes, that one) created a book for NASA that attempted to explain all these matters to high schoolers and he attempted to calculate all the heat added by radiation bouncing up and down between CO2 molecules and Earth. He came up with a multiplier effect of three, I believe. After some rather heavy criticism, that section of the book was removed by NASA. Check here:
http://www.climatechangefraud.com/climate-reports/7055-nasa-charged-in-new-climate-fakery-greenhouse-gas-data-bogus
Back to the basic comparison. What do you do when your greenhouse gets to hot?
And what whould mother nature do? You open the vents!
Herman and Pielke, Sr. write:
“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.”
Though scientists might be quite familiar with these claims and have no trouble understanding them, the actual statements in English, above, contain ambiguities. Consider the following:
“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.”
Increased downward radiation toward the surface is one thing but the fact that the rate of escape of IR radiation to space is decreased is another thing. I take it that there are two things going on here. One is that radiation has been intercepted by a CO2 molecule and, for that reason, the rate of escape of IR radiation to space is decreased. Got it. That is clear. The other thing is that there is radiation that has its source in the capturing CO2 molecule and this radiation warms the Earth. Given this radiation warming the surface of the Earth, why do the good doctors describe it all as a slowing of the cooling process. Part of the process heats the surface of the Earth. I believe that the surface of the Earth does not know or care whether the radiation comes from the Sun or elsewhere. So, why is this radiation from the CO2 molecules not treated as radiation from the sun, for the purpose of calculating Earth’s heat budget?
With all due respect, professors, if you are setting about to educate us in these matters, would you please undertake it seriously? What you have given us raises far more questions than it answers.
By the way, Trenberth (yes, that one) created a book for NASA that attempted to explain all these matters to high schoolers and he attempted to calculate all the heat added by radiation bouncing up and down between CO2 molecules and Earth. He came up with a multiplier effect of three, I believe. After some rather heavy criticism, that section of the book was removed by NASA. Check here:
http://www.climatechangefraud.com/climate-reports/7055-nasa-charged-in-new-climate-fakery-greenhouse-gas-data-bogus
OK gentlemen. Whats wrong with this scheme?
http://i480.photobucket.com/albums/rr165/magellansc24/hansen_oven.jpg
😀
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%
H²O 5%
They both absorp at the same hµ (approx). H²o dominates and as a probability must absorp 100 times more IR ?
In general they don’t actually, here’s the spectrum of water and CO2 in the 15 μm band.
http://i302.photobucket.com/albums/nn107/Sprintstar400/H2OCO2.gif
When a mole absorps it raises its’ instability and wants to reradiate the energy and return to the ground state a.s.a.p. This reradiation is never uni-directional? Why would it radiate in a downward direction ?
The reradiated energy is at the same hµ (nu) as the absorped unless some form energy conversion has occured (conservation of energy law)?
On absorption it will cause a change from one rotational/vibrational state to another, there is no requirement that an emitted photon would fall back to the same state so the emitted photon will usually be a different energy (hν). In fact for CO2 the time it takes to emit a photon from the excited state is much
shorterlonger than the mean time between collisions in the lower atmosphere so the most likely fate of the excited state is to transfer kinetic energy to the surrounding gases via collisions. Higher up in the atmosphere collisions become less likely and therefore emission of radiation more likely.so will be absorped by another mole at ground state.? If the other moles are already at the higher quantum level, it will radiate to space?
I think that one area of misunderstanding is that, although the presence of greenhouse gases permits the surface to be warmer than otherwise, it does not necessarily cause the surface to be warmer.
Well the Herman Pielke note, as clearly stated, does not invite controversy and simply and clearly gives the basis for (informed) AGW statements about “greenhouse gas” warming. Some of the ensuing comments demonstrate that this is needed and that this very basic assertion is misunderstood. In particular they note that this is not the full story of very complex processes.
However, I note that the Stefan-Boltzmann formula for thermal radiation is somehow misquoted lacking R^2 and the very-important (near-inscrutable) emissivity factor..??
Herman and Pielke end their dissertation with the following pragraph:
“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.”
______________________________________________
Now, apart from the fact that without CO2, life as we know it would be non existent on this planet, can Ben Herman and Roger A. Pielke Sr. please tell us what the temperature would be like if we remove only the CO2 component from the atmospheric mix and keep all else unchanged? How much less the temperature of our planet would be? Wouldn’t this hypothetical removal of all CO2 be the reverse of doubling CO2, or would the logarithmic ‘diminishing returns’ characteristic come into play? If the latter is true (logarithmic diminishing return), then why the GE increase due to increase in CO2? Is it tru that the effect of increased CO2 is practically capped at 50ppm?
I m waiting with baited breath.
‘If you’ve done your arithmetic correctly, you should have come up with something like 255 K.’
All the above sounds great and convincing, a fundamental question should be how did you come up with the value of 255 K for the earth without an atmosphere ? Is this fundamental equation correct – how do we know, shouldn’t this be the first point that is debated and resolved ?
I doubt anyone realistically doubts the IR absorbing effect – but there must get a point when at some point all IR leaving the surface at the absorbing wavelengths of CO2 is absorbed – at what concentration of CO2 does this happen, and are we at that point already ? If not, when ?
P Wilson says:
July 23, 2010 at 11:43 am
One notices at the beach that when the sand and paving is hot, water waves are still cool. That means no amount of greenhouse effect can cause either thermal expansion of water, or water vapour “feedback”. Certainly, since c02 intercepts heat at 15 microns, then re=emits it in less than a billionth of a second, to oxygen and nitrogen, when its saturation window closes. This wavelength on the spectroscopic band is already in the subzero region. In other words, the energy absorbed by c02 is dependent on freezing regions, such as Antarctica. Normal IR radiation leaving the earth is around 10 microns, 0r 7-14, incidentaly at the bandwidths where water vapour intervenes which co-incides with an average 288k (15C), and which is invisible to c02. That leaves very little energy for c02 to delay – around 3-4% of subzero energy. It is so miniscule that the effect cannot, and has not been measured. In tropical deserts where temps are 45C plus, radiation leaves at 8.5 microns, which puts it even further out of the c02 micron band.
So c02 absorbtion is a rare event in the atmosphere. Its also forgotten that most heat leaves by convection and evaporation, and not from re-radiation.
Sorry but this is complete nonsense. Here’s a set of spectra showing the relative absorption of various GHGs.
The first panel shows the total effect and progressively each gas is removed.
http://i302.photobucket.com/albums/nn107/Sprintstar400/Atmos.gif
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
You forgot the sun, it should look like this.
http://en.wikipedia.org/wiki/File:GSO.JPG
Juraj V:
I think you know the answer to that already, but, for the benefit of those who might not:
This is not about heat flow (which would violate the 2nd law of thermodynamics) but rather nett energy flux A warmer body can absorb radiation from a cooler body because, being warmer, it must still be emitting more energy than it’s receiving from the cooler body. In other words, the nett energy flux is still away from the warmer body and towards the cooler body – it’s just that the nett energy flux from the warmer body is less than it would be in the absence of the cooler body. This does not warm the body, but rather slows down the rate of its cooling (if it’s cooling) or increases the rate of its warming (if it’s warming)
“Bill DiPuccio says:
July 23, 2010 at 11:58 am
…On a clear calm night, temperatures drop rapidly at the surface boundary layer as IR heat radiates into space. On a calm cloudy night, the temperatures drop more slowly because that IR heat is re-radiated downward by water droplets in the clouds.”
Another explanation is, that clouds partially block the natural convection of warm air upwards, thus slowing down the night time cooling.
Here is a real measurement of solar, and upwelling+downwelling IR radiation, made probably by pyrgeometer.
Clear sky: the downwelling IR does not react on fact, that the surface warms and emits more IR upwards during the day.
http://www.srrb.noaa.gov/cgi-bin/surf_check?ptype=gif&site=desr&date=17-jun-2008&p1=dpsp&p5=dpir&p6=upir
My take is, that downwelling IR is a sign, that the atmosphere above has certain temperature and radiates accordingly.
Cloudy sky:
http://www.srrb.noaa.gov/cgi-bin/surf_check?ptype=gif&site=desr&date=17-sep-2008&p1=dpsp&p5=dpir&p6=upir
When solar radiation is limited by cloud, upwelling IR goes down (as the surface cools in shade) and now the downwelling IR increases at this very time. Hard to say whether the night was cloudy as well, but the downwelling IR radiation is fairly constant, like during the clear night above.