Guest Post by Ira Glickstein
This series began with a mechanical analogy for the Atmospheric “Greenhouse Effect” and progressed a bit more deeply into Atmospheric Windows and Emission Spectra. In this posting, we consider the interaction between air molecules, including Nitrogen (N2), Oxygen (O2), Water Vapor (H2O) and Carbon Dioxide (CO2), with Photons of various wavelengths. This may help us visualize how energy, in the form of Photons radiated by the Sun and the Surface of the Earth, is absorbed and re-emited by Atmospheric molecules. 
DESCRIPTION OF THE GRAPHIC
The animated graphic has eight frames, as indicated by the counter in the lower right corner. Molecules are symbolized by letter pairs or triplets and Photons by ovals and arrows. The view is of a small portion of the cloud-free Atmosphere. (Thanks to WUWT commenter davidmhoffer for some of the ideas incorporated in this graphic.)
- During the daytime, Solar energy enters the Atmosphere in the form of Photons at wavelengths from about 0.1μ (micron – millionth of a meter) to 4μ, which is called “shortwave” radiation and is represented as ~1/2μ and symbolized as orange ovals. Most of this energy gets a free pass through the cloud-free Atmosphere. It continues down to the Surface of the Earth where some is reflected back by light areas (not shown in the animation) and where most is absorbed and warms the Surface.
- Since Earth’s temperature is well above absolute zero, both day and night, the Surface radiates Photons in all directions with the energy distributed approximately according to a “blackbody” at a given temperature. This energy is in the form of Photons at wavelengths from about 4μ to 50μ, which is called “longwave” radiation and is represented as ~7μ, ~10μ, and ~15μ and symbolized as violet, light blue, and purple ovals, respectively. The primary “greenhouse” gases (GHG) are Water Vapor (H2O) and Carbon Dioxide (CO2). The ~7μ Photon is absorbed by an H2O molecule because Water Vapor has an absorption peak in that region, the ~10μ Photon gets a free pass because neither H2O nor CO2 absorb strongly in that region, and one of the 15μ Photons gets absorbed by an H2O molecule while the other gets absorbed by a CO2 molecule because these gases have absorption peaks in that region.
- The absorbed Photons raise the energy level of their respective molecules (symbolized by red outlines).
- The energized molecules re-emit the Photons in random directions, some upwards, some downwards, and some sideways. Some of the re-emitted Photons make their way out to Space and their energy is lost there, others back down to the Surface where their energy is absorbed, further heating the Earth, and others travel through the Atmosphere for a random distance until they encounter another GHG molecule.
- This frame and the next two illustrate another way Photons are emitted, namely due to collisions between energized GHG molecules and other air molecules. As in frame (2) the Surface radiates Photons in all directions and various wavelengths.
- The Photons cause the GHG molecules to become energized and they speed up and collide with other gas molecules, energizing them. NOTE: In a gas, the molecules are in constant motion, moving in random directions at different speeds, colliding and bouncing off one another, etc. Indeed the “temperature” of a gas is something like the average speed of the molecules. In this animation, the gas molecules are fixed in position because it would be too confusing if they were all shown moving and because the speed of the Photons is so much greater than the speed of the molecules that they hardly move in the time indicated.
- The energized air molecules emit radiation at various wavelengths and in random directions, some upwards, some downwards, and some sideways. Some of the re-emitted Photons make their way out to Space and their energy is lost there, others back down to the Surface where their energy is absorbed, further heating the Earth, and others travel through the Atmosphere for a random distance until they encounter another GHG molecule.
- Having emitted the energy, the molecules cool down.
DISCUSSION
As in the other postings in this series, only radiation effects are considered because they are the key to understanding the Atmospheric “Greenhouse Effect”. I recognize that other effects are as important, and perhaps more so, in the overall heat balance of the Earth. These include clouds which reflect much of the Sun’s radiation back out to Space, and which, due to negative feedback, counteract Global Warming. Other effects include convection (wind, thunderstorms, …), precipitation (rain, snow) and conduction that are responsible for transferring energy from the Surface to the Atmosphere. It is also important to note that the Atmospheric “Greenhouse Effect” and a physical greenhouse are similar in that they both limit the rate of thermal energy flowing out of the system, but the mechanisms by which heat is retained are different. A greenhouse works primarily by preventing absorbed heat from leaving the structure through convection, i.e. sensible heat transport. The greenhouse effect heats the earth because greenhouse gases absorb outgoing radiative energy and re-emit some of it back towards earth.
That said, how does this visualization help us understand the issue of “CO2 sensitivity” which is the additional warming of the Earth Surface due to an increase in atmospheric CO2? Well, given a greater density of CO2 (and H2O) molecules in the air, there is a greater chance that a given photon will get absorbed. Stated differently, a given photon will travel a shorter distance, on average, before being absorbed by a GHG molecule and be re-emitted in a random direction, including downwards towards the Surface. That will result in more energy being recycled back to the Surface, increasing average temperatures a bit.
Stephen Richards (2:05)
the article in Climate Realists makes exactly the same mistakes as all those that think back-radiation somehow violates 2nd law thermodynamics. The last-but-one paragraph sums up his errors quite nicely – it’s basically completely wrong.
Oddly, he describes a thought experiment with a black body and mirrors that he could easily try out, and which would show him he is wrong, Clearly he knows he is right, so doesn’t bother to actually test it.
The other indicator that he is wrong is the massive introduction that is just waffle, before reaching any solid science. Why bother with all that if you are right?
“where their energy is absorbed, further heating the Earth”
That phrase is the crux of the difficulty that some have with the greenhouse effect.
There is no ‘further’ heating.
What happens is that the downward longwave radiation reduces the net upward flow by partially offsetting it until the temperature rises and a new equilibrium is reached.
There is always a net energy flow from a warmer body to a cooler body in accordance with the Laws of Thermodynamics but in fact both bodies still radiate towards each other.
A cooler body doesn’t stop radiating just because it is in the presence of a warmer body.
It is the net rate of energy transfer between the two that changes with no need for the cooler body to effect any direct warming of the warmer body.
The suggestions that the greenhouse effect somehow offends the Laws of Thermodynamics is a non starter and a hindrance to scepticism of the theory of AGW.
Ira doesn’t seem to make that mistake but he has used a form of words that perpetuates the misunderstanding.
Ira,
Thanks for this, but for me the animation is way too fast to follow. Any chance you could slow it down?
Ira,
Good presentation!!!
You’ve only touched partially on the tip of the iceberg of how complex this planets climate system is.
Thermodynamics is garbage in being too simple and too broad in coverage so that simple minded scientists can grasp some hope of understanding.
This planet is a globe and not a tube, that rotates and has gravity. From the equator to the poles, there are different factors going on besides the introduction of solar radiation, CO2, gases, water vapor, etc. Cold compression and superheated compression has very different areas in complexity as well as storing energy on a planet that is thrown through space at 300km/sec. We have yet to understand infused energy into the planet and solar system at creation and what that accomplishes in storing energy for slow release.
Our current problem is that science can only grasp one area at a time and fails in understanding a multi-understanding of many areas into a super complex system.
Following temperatures in a 150 year time period is ridiculous in the 4.5 billion year time frame and for what? To know what clothes to wear?
Ira,
I know you have the caveat paragraph “As in the other postings in this series, only radiation effects are considered because they are the key to understanding the Atmospheric “Greenhouse Effect”…… ”
But in comparison to the power of the hydrologic cycle your ‘radiation only’ approach is not unlike saying you are only looking at the retardation effects on the locomotive of hitting insects.
The AGW CO2 warms the world hypothesis depends on the hydrologic cycle. It only works if they can show the ‘water vapor feedback’ which all the GCMs show as a tropospheric hotspot that in the real world does not exist therefore all the models are falsified. You cannot disregard the locomotive of the hydrologic cycle whose effects nobody has been able to quantify but is accepted as the main transport of heat from the surface to the tropopause and the ‘iris’ that increases albedo reducing incoming energy and only worry about the insect collisions of outgoing IR with CO2 in three small radiation bands.
@Thomas says:
March 29, 2011 at 1:57 am
bananabender. Go ahead, try to explain the temperature of the Earth using only the ideal gas law! It can’t be done, you see, if you actually start to think about what you do.
I agree with John Kehr says:
March 29, 2011 at 12:11 am
What he is describing is the Maxwell-Boltzmann kinnetic energy effect in the atmosphere.
Hmm… from my second reading I note that no mention is made of energy absorbed being passed directly to nearby air molecules (collisions) and warming those before the absorbing molecule can fire off a photon and cool itself that way.
[taunting is not an attractive color on you. go ahead and reply, some other moderator will not know why I deleted your little attempt at a
humoroushumorless polemic. ~ ctm]A quibble:
Ira says:
I say:
The vast majority of downward radiation coming from the atmosphere is longer wavelength than 13 um. The area under the curve around 10 um looks like about 5 percent of the area under the curve greater than 13 um. In other words, the vast majority of the energy coming back at us is explainable as blackbody radiation. Note that the graphs I am attempting to display here are for arctic data.
If I interpret the graphs correctly, even if CO2 absorbed all the energy around 10 um, and that energy was immediately passed to other molecules to re-radiate around 15 um, the energy absorbed by the CO2 wouldn’t account for much of the back radiation.
This ‘GHG physics’ is bunkum. Let’s take the 15 micron band. 95% is absorbed in 1 m air. That’s why mirages exist – the air above a hot surface is warmed by IR absorption.
OK, the air does re-radiate downwards but a lot of the hot air is convected upwards thus ensuring most of that original IR radiation from the ground never makes it back.
What GHGs do is to increase the adiabatic lapse rate a bit, also raise the tropopause. And because more latent heat means more efficient precipitation, the upper atmosphere dries and it’s easier for the heat to radiate to space.
So, GHG warming is controlled to a near constant level independent of [CO2]. it’s about time that ‘climate scientists’ and politicians realised it.
bananabender. That calculation starts off with the simple mistake of forgetting to include albedo, that Earth reflect some of the sunlight, and thus gets a too high non-greenhouse temperature. (This temperature is measurable as the blackbody temperature of Earth as seen from space and is -19 C)
Then the author come up with an altitude of 1600 meters that he for some reason thinks is important. Multiplying this arbitrary altitude with the temperature gradient and adding the (faulty) base temperature does give the right answer, but only because he picks that altitude to get the right answer.
Now take a look at what the real atmosphere looks like:
http://apollo.lsc.vsc.edu/classes/met130/notes/chapter1/vert_temp_all.html
Still think you can explain it?
…rubbish !
John Kehr says:
March 29, 2011 at 12:11 am
“I like that animation. ”
I find Dr. Glickstein’s animations (this isn’t his first) to be annoyingly distracting. Since it interfered with my focusing on the text, I decided to skip the essay.
Did I miss an interesting and important post? Maybe. But it just wasn’t worth my effort.
Ira,
There are a few reasons that I do not trust “averaged out global mathematical calculations”.
One time frames. Our current calculations fail due to the calculation do not include adjusting for planetary motion, slowdown or unknown surprising factors(such as solar flares, massive eruptions, salt changes, ocean current changes, impacts, etc.).
Next, planetary positioning. Since the suns diameter at it’s equator is the greatest mass and the poles are much smaller to the drifting of the planet between the two.
Thirdly is planetary shape of having a huge diameter equator and smaller diameter poles on a rotating planet.
So, where on this planet or atmosphere does make a difference to any other place taking a measurement.
Spartacusisfree, the amount of energy the Earth has to radiate to remain in thermal equilibrium is constant. Since we have GHG:s in the atmosphere only a small part of the radiation emitted into space comes from the surface, the rest comes from the atmosphere, and we can assign an “effective altitude” from which the average radiation is emitted. If you add more GHG:s radiation will have a harder time escaping and thus this effective altitude will increase, but since the amount of energy has to be constant its temperature has to remain the same. Now take the lapse rate into account. If the layer of constant temperature rises, the temperature at the surface has to increase as the lapse rate multiplied by the increase in altitude. If more GHG:s raises the tropause by 100 meters the temperature at the surface rises 0.7 degrees as a first approximation.
Ira
Carbon dioxide is a linear molecule. You show it with a bent structure like H2O
Fix that mistake. It makes you look stupid.
When a CO2 or H2O molecules absorbs an IR photon, its linear velocity does not increase. The absorbed photon causes an increase in the vibrational frequency of a bond or combination of bonds (e.g, bending). Fix that mistake.
A vibrationally- excited CO2 or H2O molecule in the troposphere will not re-emit the absorbed photon but will undergo immediate collision deactivation with N2, O2, Ar or H2O. This causes an increase in the speed of these, i.e., they become slightly warmer.
The collision frequency at 1 atm and room temp is about 100 billion collision per sec. Incidently, this is why nat gas in air explodes with great violence, i.e., the reaction goes at the collision frequency.
FYI: CO2 is a weak absorber of IR because it does not have a permanent electric dipole like H2O.
All of this is totally unnecessary. All we need is one valid graph of long-term temperature vs CO2 concentration, showing the lack of correlation. And we already have plenty of valid graphs like that.
The greenhouse effect hypothesis, and specifically the warming caused by increasing CO2 in the atmosphere goes back to 1896, when Svante Arrhenius wrote an article and then a book that postulated the theory. All kinds of people ran with it afterwards although the theory was later found to be based on grossly erroneous spectra. These gross spectroscopy errors can be seen as conclusively proven wrong in MODTRAN(R) simulations. For a list of references to Arrhenius, including some by people that still believe it to be true look here:
http://www.lycos.com/info/svante-arrhenius.html
For the MODTRAN(R) simulations disproving the theory look here:
http://members.casema.nl/errenwijlens/co2/arrhrev.htm
Although I disagree with his conclusions (he is a warmist), Spencer Weart wrote a pretty thorough history of how this whole AGW thing evolved over the last century, ending with Charles (Dave) Keeling, before going into the modern research and model predictions that are so questionable.
Regardless of his conclusions, I give Weart credit for being quite thorough and his book is worth a read because it encapsulates all the early prominent research that went into building AGW theory as we know it in it’s present form. This book is also a great place to look at all this greenhouse research in one place and to see where the all the holes and leaps of faith are. A pretty complete condensation of the book can be found here:
http://www.aip.org/history/climate/co2.htm
Sadly, and contrary to the whole point of the book, which should have been citations and discussions of the history of AGW research, Weart himself takes the ultimate leap of faith and joins the warmist camp, tainting a great read with his own conclusions. You can see that in his personal notes:
http://www.aip.org/history/climate/SWnote.htm
Best,
Jose
rusureuwant2know
“I thought Al Gore got his graph backwards and the increase of CO2 followed warming – why are we still working with the assumption it creates it???”
Greenhouse gasses definitely do warm the planet, there is no question of that. And, increasing the amount of CO2 in the atmosphere will increase the amount of heat retained here on Earth. The real question is, how much will the change be as a result of a doubling of the CO2? First order effects seem to point to a change of 0.8 to 1.5 degrees. All of the other warming the alarmists are trumpeting is from second order effects that are definitely not known. Will the H2O in the atmosphere increase significantly, thereby significantly warming the planet? or perhaps there is negative feedback and the H2O is reduced and the planet cools. I don’t know.
As to your other point about the CO2 following temperature, there is definitely evidence of that too. Warmer oceans can’t hold as much CO2 so more of it ends up in the atmosphere. It’s a complicated system.
Stephen Wilde
Although there clearly is a greenhouse effect it is infinitesimal compared to the energy retaining effect of the oceans.
The greenhouse effect and the energy retaining effect of the oceans are different things. The atmosphere and the ocean may retain heat, but the atmospheric heat retention is infinitesimal compared to the heat retention of the oceans. The greenhouse effect changes the amount of heat that flows out of the system.
Perhaps you could think of the heat retention of the ocean as a bucket of water. Then, you have a stream of water flowing into the bucket and a hole in the bottom of the bucket that lets an equal amount of water flow out. The system is in equilibrium because the same amount of water is going out as is coming in, the water level remains constant. When you change the greenhouse gases you change the amount of water flowing out so the water level will raise of lower as a result.
MikeEE
To be thorough, there’s also an “anti-greenhouse” effect. See
http://en.wikipedia.org/wiki/Anti-greenhouse_effect
The atmosphere of Titan is transluctent to some wavelengths, and translucent to part of the surface radiation.
This results in a surface cooler than a surface with NO atmosphere
sun —–> 4 watts 2 watts 2 watts Titan surface 2 watts4 2 watts from atmosphere<——-
2 watts from surface 2 watts from atmosphere
4 watts 2 watts Earth
The earth heats up, reradiating the 2 watts to the atmosphere, which will also heat up. The final
balanc will be
Sun —> 4 watts to atmosphere 4 watts to earth from atmosphere
–>4 watts from sun, 4 watts from earth4 watts from atmosphere to earth
<—4 watts to earth from atmosphere
So the net effect of the surface warming from an infrared absorbing atmosphere is the same as the effect of NO atmosphere.
See Trenbeth's figures here:
http://stephenschneider.stanford.edu/Cl … lance.html
Note that the zero greenhouse effect would apply for those 67 watts absorbed directly by the atmosphere.
Caveats: Working out the temperature drop in a purely radiation
cooled atmosphere, it can be shown that the temperature drop would be
greater than the
moist pseudoadiabetic lapse rate, making a purely radiation
controlled atmosphere unstable. The adiabetic lapse
rate places an upper limit on drop in temperature with height.
Nice animation and explanation. But I think it is giving ony a passing thought to a very important component countering any heating effect of more CO2 — convection. As noted, a warmer molecule will be moving faster and hence have a faster Mean Free Velocity and it will rise. That warmer air will cool as it rises and condenses water pulled up with that rising mass, losing even more energy. Hence transporting ground air heat to the cooler higher atmosphere.
Also missing from this, is that this affect in the animation is only when the sun it at noon in the location where the sun is directly over head. Daytime everywhere else gets lower energy from the sun because of the angle. Nighttime, more of that stored daytime heat is lost into space. Also, the warmed portions of the planet intermix that warm air to the colder regions of the planet (causing storms which disapates even more heat).
In other words, the atmospheric system has a buffering affect and is why the planet have never “cooked” when CO2 was 20 times today.
The planet is not suseptable to over heating, it’s suseptable to significant cooling, which is bad.
Reply to Thomas: I agree that as the adiabatic lapse rate and the tropopause rise, surface temperature will increase. However, the reduction of [H2O] in the upper atmosphere will allow easier radiative heat transport to space. The interaction of this radiative heat transport with the ALR is actually quite interesting.
The evidence of lower [H2O] is fairly conclusive. So, I expect GHG warming from CO2 to be very low.
Igl
What a lot of nonsense. Here is how it really works…
Don’t believe everything you read. He says it’s not reradiation because “When the atmosphere emits radiation, it is not the same radiation”.
What is ‘the same radiation’? that’s just nonsense. Any material (CO2 for example) that is not at absolute zero emits radiation to stay at equilibrium. If you raise the amount of energy that you put into that material you will raise it’s temperature and the amount of energy that it radiates. Whether it is the same of different energy is irrelevant.
MikeEE
Although this article mentions CO2 absorbing energy through collisions and radiating that energy (half to space) it does not mention that this is a cooling effect. And, when you add more CO2 you increase this cooling effect. So, what is the trade-off here. How much warming vs. how much cooling. I’ve never seen this tackled anywhere.