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.
Looking at Ira’s animation and Wayne’s proportional image, is it not clearly evident that CO2 does not have the volume required to have any dramatic impact on the Greenhouse effect?
For example, the total Greenhouse effect represents approximately 33 degrees of warming for our planet. Simplifying the atmosphere as Wayne has done it would seem that CO2 can only add ~0.44 degrees (400ppmv CO2 / 30,000ppmv H2O x 33 degrees). This discounts other GHGs but I believe they are all in far less concentrations.
MrC
Stephen Richards: thanks for the link. I did not have enough time for reading the complete article by Postma. Perhaps tonight. My first impression is like yours: it’s over with the greenhouse theory and everything based on it.
Here’s a link to the graph I tried to display in my previous post: http://www.skepticalscience.com/images/infrared_spectrum.jpg
I tried: <img src = “http://www.skepticalscience.com/images/infrared_spectrum.jpg”> but that obviously didn’t work.
[Reply: WordPress doesn’t really like the img tag. Either cut ‘n’ paste the URL like you did here, or use the “href=” command. ~dbs, mod.]
When you adjust for atmospheric pressure the absolute atmospheric temperatures of Earth, Mars and Venus only vary by 10-20%. This is despite Venus receiving about 8x as much solar radiation as Mars and 1.9x as much as Earth and the totally different atmospheric composition on all three planets.
Measured Temperature vs Atmospheric Pressure:
0.001Bar:
Mars ~210K, Earth ~220K, Venus ~190K.
1Bar:
Mars (n/a), Earth 288K, Venus 350K.
When you adjust for the different gas composition (relative molar mass) of each planet’s atmosphere the temperature differences are even smaller.
This fact is explained far better by the Ideal Gas Law than any mythical Greenhouse Effect.
It doesn´t matter how much Greens may insist on the so called “green house effect”, the only “effect” that exists is that of “confined heat”…and, still, it can´t heat sea water up, as heat transfer goes from the denser to the less dense:
http://es.scribd.com/doc/28018819/Greenhouse-Niels-Bohr
Ira Glickstein says:
“7 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 …”
As Ira states, heated air molecules radiate. So why are we so concerned about the ‘backradiation’ from CO2? As most of the heating of the atmosphere is by conduction and convection and all gases radiate in close proportion to their temperature, then all gases are greenhouse gases. If it were otherwise, N and O could not radiate away to the vacuum of space. Consequently even if it is accepted that there is backradiation from CO2 ‘further heating the Earth’ (impossible as this means the surface is heating up itself as it is the surface that has warmed the atmosphere in the first place) this effect would be dwarfed by the radiation from the remaining 99% of the atmosphere.
Some commenters on this thread who deride those of us who keep on propounding the second law claim that we misunderstand the position. They say that the greenhouse gases ‘reduce cooling’ (rather than ‘further heating the Earth’). But reducing cooling cannot add heat. In the constant irradiance models that are used to demonstrate the greenhouse effect (e.g. Kiehl & Trenberth’s) the Earth is not cooling down. The most that can be said about the ‘reduced cooling’ theory of greenhouse gases (properly called an atmosphere effect) is that it will reduce heating during the day and cooling at night. Therefore the average temperature may be higher than it would be otherwise (e.g. on the Moon) as the possible minimum is 3K whereas the maximum is determined by the quantity of solar radiance. Those who think this is the greenhouse effect have not understood what real warmists (like K&T and Gavin Schmidt) really believe. Conventional greenhouse theory says that the downward radiation from greenhouse gases raises the Earth’s temperature higher than solar radiation can.
4. 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 isn’t true for cold (below ionization energy threshhold) dense gases. They do not exhibit spectral emission lines they only have spectral absorption lines. The reason is that in a dense gas the molecules are packed so tightly that any increase in energy in an absorption line is immediately distributed to surrounding molecules through collisions. The emissions from the GHGs and all the other gases in the lower atmosphere are approximately continuous blackbody spectrum with a peak emisson frequency corresponding to the temperature of the air.
7. 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.
This is correct except for the part about “heating the earth”. That phrase justifiably causes people with a basic understanding of the laws of thermodynamics to balk. In the big picture this simple phrase (courtesy tallbloke) describes what’s happening: the sun warms the ocean and the ocean warms the air. So-called back radiation, which is what you’re describing, does not warm the surface except in limited and exceptional circumstances where a mass of air transported convectively (read winds) is warmer than the surface over which it blows and even then it is limited because the air has so little heat capacity compared to the surface – imagine trying to heat a cup of coffee by stirring it with a hot feather.
What actually happens is the back radiation slows down the rate of surface cooling. This is because radiative transfer between two objects of different temperature is a two-way street. Say the warmer object is emitting 10 watts per square meter. The cooler object, unless it is at absolute zero, is also emitting energy. Say it’s emitting 5 watts per square meter. So the warmer object is emitting 10w/m and absorbing 5w/m while the cooler object is absorbing 10w/m and emitting 5w/m. The net transfer of energy is 5w/m from warmer to cooler.
Absent greenhouse gases essentially all the radiation from the surface charges through the atmosphere at nearly the speed of light and is absorbed by the virtually infinite heat sink of the cosmic void. The cosmic void is 3 Kelvins – just a few degrees above absolute zero so the back-radiation from the cosmos is just about nil. Put some greenhouse gases in between the surface and the cosmic void and then you have some significant back radiation which slows down the surface cooling rate.
At the end of the day because the ocean doesn’t cool as quickly at night with GHGs in play it’s a little warmer in the morning than it would be absent the greenhouse gases. The sun does its thing during the day warming the ocean and because the ocean was a little warmer at sunrise it’s a little warmer at the end of the day too. The cosmic void doesn’t change temperature but now that the surface is a bit warmer than it would be absent GHGs it cools more quickly at night – the higher the difference in temperature between two objects the faster warmer object loses energy to the cooler object. Thus a new equilbrium temperature is obtained where the energy received by sun during the day is emitted at night in perfect balance.
In the real world equilibrium is moving target due to other factors like clouds (which reduce the amount of solar energy reaching the surface), convection (which mechanically transports energy from one place to another both horizontally and vertically), evaporation, and conduction. But the one thermodynamic fact is always operative in the real world – the farther out of equilibrium the system is the harder it tries to move back to the theoretical equlibrium temperate. So when everything is said & done and absent any feedbacks – GHGs raise the theoretical surface equilbrium temperature and for non-condensing (read everything except water vapor) GHGs which are well mixed and slow to change in concentration the change in theoretical surface equilibrium temperature is calculable and works out to about a 1C rise for every doubling of CO2.
A 1C rise in surface equilibrium temperature per CO2 doubling is a very good thing especially when one considers that the bulk of the warming actually occurs at night, at higher latitudes, and in the winter. This has the beneficial effect of extending growing seasons when and where longer growing seasons are most needed. Add to that that higher CO2 concentration means plants grow faster/larger (provided sunlight, nutrients, and water are not limiting factors) and they use less water per unit of growth in higher CO2 as well.
The whole brouhaha over scary global warming rests on the wholly fabricated idea that CO2 greenhouse warming puts more water vapor in the atmosphere and that, because water vapor is a powerful greenhouse gas, it constitutes a positive feedback that turns 1C per doubling into 3C per doubling. There isn’t a shred of empirical evidence to support that belief and IMO overwhelming evidence that the feedback is actually negative – the water cycle speeds up which serves to mechanically transport heat from the surface by evaporation and convection to the cloud deck where it then has an easier radiative path out to space. It also results in slightly greater cloud cover which reflects more sunlight back out into outer space before it can reach the surface to warm it. This prevents any chance of a runaway greenhouse and this is borne out by there never having been a runaway greenhouse in the earth’s history even though CO2 concentration in the past was as much as 20x greater than present. In fact the l paucity of CO2 today, relative to most of the earth’s history, is IMO undoubtedly a major factor in why the earth has been in an ice age for the past 3 million years – ice ages are rare but there is a tipping point where factors can combine that allow ice and snow to dominate the surface through positive feedback mechanisms – ice reflects a lot more sunlight than ocean or unfrozen land surface thus reducing the amount of solar surface heating (which makes conditions even better for glacier expansion) and because cold air holds less water vapor than warm air it also greatly reduces what’s normally our primary greenhouse gas in a viscious cycle of cold begetting even more cold. There is substantial but controversial evidence that glaciations in the remote past have frozen everything from pole to equator – appropriately called “snowball earth”. So global cooling, especially now with the Holocene interglacial overdue for its ending, should be our greatest concern and we should be welcoming whatever global warming we can get with wide open arms.
re: Thomas says:
March 29, 2011 at 5:39 am
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)
If you totally ignoreevery factor including albedo, atmospheric composition and incident solar radiation there is still a <10% temperature variation between the atmospheres of Mars and Venus at the same pressure. This is despite Venus receiving 8x as much solar energy as Mars.
I prefer to accept an irrefutable Ideal Gas Law than the idea of "magical greenhouse gases" which defy virtually every basic principle of chemistry.
The calculated value of -19C for Earth without an atmosphere is based on absurd reasoning.
if I am reading it correctly (probably not) #7 violates the 2nd Law … the cooler air cannot heat up a warmer body …
if you mean it slows down the rate of heat loss of the earth then I am with you but it cannot “heat” the earth …
My impression is that there is confusion between thermal transfer between molecules (rotation, vibration etc) and radiation emission/absorption. The first depends on the thermodynamics, the second on quantum physics.
As far as I remember, the absorption of a photon concerns only the electrons which can gain a higher (not stable) energy level. After some time the excited electron will re-emit the received excitation energy as a photon and fall back into the stable configuration. The radiation energy balance would be zero. But may be I have forgotten some essential laws of physics.
Anders says:
March 29, 2011 at 2:25 am
If all that is going on is absorption and re-emitting radiation there would be no heating of the atmosphere. Heating happens because of the re-distribution of energy through collisions between molecules. The “simple” visualization is thus too simple. The temperature of a gas IS the average kinetic energy of the gas molecules, this is something Roger Pielke Sr. has pointed out a number of times and for many years.
Your comments are as close to what makes me uncomfortable with this representation of the absorbtion and re-radiation of a photon. The kinetic energy seems like it could be represented as the mean free path and temperature. What I have a problem with is the absorbtion and re-radiation at the same wavelength. You can’t have that and warm the molecule as well. If warming occurs, then the re-radiation must be at a different wavelength, lower energy. Otherwise, energy is created from nothing.
This article is incompetent, in the face of definitive experimental data that simply invalidates its premise:
Venus: No Greenhouse Effect
The simple analysis I did, within hours of finding the data on the internet, should have been done nearly 20 years ago. Every scientist who promulgates the greenhouse effect is incompetent. You will find the simplest, clearest discussions about the greenhouse effect on my website. My presentation of the definitive evidence, the first and only such presentation to date as far as I know, should be properly confronted and accepted by the entire science community; I have submitted it to “Physics Today” to get it before that community, but have received no response, which shows a complete lack of integrity and professional commitment to scientific self-correction — a fundamental failing of scientific institutions today.
There is no longer any validity to arguments for the greenhouse effect. The science is settled, and what is needed is re-education of all those like Ira Glickstein who are promulgating false science.
If the “greenhouse effect” had increased, a hot spot would be found over the tropics. This hot spot has not been measured.
Now, let’s see where warming has been measured: mostly where you can find snow or ice. Maybe it could be good to evaluate the “greenhouse effect” inside of snow. First, it is wrong to think that snow reflects light like a giant mirror. Most of the light does enter inside of the snow where it is reflected in all directions by pieces of ice, and after a while, most of the light is reflected out of the snow. So it is similar to a “greenhouse effect”.
Now, the impurities inside of the snow and the spectrum of light will probably have an effect on how much light is absorbed. Up to now, I have not seen any study about this.
I think a more accurate animation will look like tsunami open sea wave models like this (where the islands represent GHG molecules):
http://www.amath.washington.edu/~dgeorge/talks/movies/TsunamiMovies/IndianOceanAmrMV.gif
It certainly is not like a bunch of projectiles flying around.
Thermodynamics gives us an idea of the direction of energy transfer. The transfer mechanism controls the rate. The rates of convection, evaporation/condensation, freezing/thawing are much slower than radiative energy transfer that can be considered “line of site, speed of light”. Model the energy input/output of a column of air in winter, over Arctic sea ice considering all these processes. Test your model by analyzing the reanalysis data. Take a guess as to the relative contributions of each process to slowing down the loss of energy to space. In your model design, don’t forget to include the insulating qualities of sea ice (thermal conductivity and thickness change). Energy is being transferred from water below the ice to the upper surface, as it freezes.
Spartacusisfree, if you have any evidence for your claims I suggest you publish them. The general view is that H2O increases as temperature go up, and that seems much more reasonable to me. If you look at different areas of the Earth with different temperature the trend is definitely that warmer areas have more water vapor, so why should the trend be in the opposite direction if the warming comes from AGW? (But at least you don’t violate any obvious law of nature unlike most of the geniuses here)
Thomas says:
“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.”
Ideal gas law PV=nRT can be rewritten as P/R=rho T . Ascending in altitude through the troposphere, the density decreases at a lesser rate than pressure
steveta_uk says:
March 29, 2011 at 3:15 am
You need to explain in the same terms and manner as to why back radiation doesn’t violate black body theory not wave your arms around. I have read the entire doc twice and compared it to the BB theory and can find no problem with what he says. So, explain yourself using the known laws of physics and perhaps we can come to consensus 🙂
Stephen Richards BSc Physic MSc Solid state Physics.
bananbender, again I ask you to look at that figure of the real atmosphere. Where is the 0.001 bar altitude on Earth? It’s around the stratopause, and according to the standard atmosphere the temperature at that altitude is 270 K, not 220 K as you claim. You just make up your numbers to make them fit! I think I prefer the regular kind of science.
steveta_uk says:
March 29, 2011 at 2:56 am
“…Surely they can only re-emit much lower energy photons, of similar energy levels to the black-body curve at -20C.
Yes, however the temperature of a gas is actually defined as the average kinetic energy of the gas molecules, for example at -20C and not the amount of radiant energy it is emitting. In fact the laws of black body radiation only have a good fit to solid blackbodies which are in thermal equilibrium – something that seldom happens in our chaotic weather systems. The tiny effect the odd molecule of CO2 has is swamped by other processes which drive our turbulent, non-linear system.
I think Cassandra King nailed it. To me, this is a problem of scale which, of course, is not represented in the original graphic.
I would use the following analogy to visualise the scale:
.
Let us take a large sports stadium such as the Melbourne Cricket Ground. Capacity 100,000 seats. Although the concentrations of ghgs are by ppm by volume, let us approximate to 10.000 molecules per percentage volume (1 million divided by 100). This means that of the 100,000 spectators in the MCG, only 40 (wearing red for GHGs) are able to both hear the tannoy (LW radiation) and re-transmit what it says. Another 250 spectators (wearing blue for water vapour) can hear the tannoy but cannot re-transmit the message (because they are mute). The rest (wearing white) are deaf-mute. Let us now pretend the tannoy message was a very funny joke. The only way that the 99,710 spectators in white can even realise something funny has been said is by ‘conduction’ withthe 290 people, who are shaking with laughter (vibration). If they are touching the laughing people, they may well laugh in sympathy – but maybe with less conviction. As most of the ‘water’ spectators are in the lower stand, that is where most of the shaking is done. Back in 1850, the number of emitting spectators was only 28 (probably 29 if you include all the other dry ghgs). Therefore, according to the radiative forcing theory, the addition of 12 spectators (of any type of ghg) has increased the degree of overall shaking by 2.5% (0.8 C). According to the IPCC, doubling the number of emitters to 56 will lead to a ‘best estimate’ increase of 10% (3 C).
Does anyone think the original 28 red people can have a significant effect, and will the addition of another 12, or even doubling the original figure, be likely to incur catastrophic warming (laughter)?
.
A lighthearted analogy, I admit…
“The greenhouse effect heats the earth because greenhouse gases absorb outgoing radiative energy and re-emit some of it back towards earth”.
To be true doesn’t this mean that CO2 must act like a mini sun with an energy multiplying effect.
As an example if the earth contains 1 trillion units of energy. If 100,000 leave the earth’s surface as radiation. Somehow even though half or move does not return to the surface the energy that does return must be greater than 100,000 units. Otherwise there can not be a heating of the earth.
But even this example is not correct as the radiation returning has a cooler energy impact than the earth and a cooler body can not heat a warmer one.
Ira, you do keep pluggin’ away.
1. If you are going to have H2O in the mix then you also need to recognize that it has a much higher specific heat than CO2. water vapor about 1.9 CO2 about .84. Water vapor can hold on to the heat. CO2 cannot.
2. You should show the area under the curve. (this was mentioned before) It is about 8% for the 15 micro. People are only a small protion (3%) of the 8%. So our effect if any is small.
3. You should define “surface”. If a proton of IR strikes me it disappears. If it hits a leaf or a blade of grass it is gone. So there is a huge portion of the downward IR that never gets to the surface. Again, the oceans cover 2/3 of planet. So your claim is that 1/3 of the surface area of the planet heats the other 2/3’s of the atmospher over water due to backradiation. I have my doubts.
4. Heat transfer is totally and only dependent on temperature difference. q/A=(emissivity * sigma*(T^4-T^4)) If both e and sigma are the same no heat transfer but that does not cause either to stop radiating at its temperature. If I take a blow torch at 3000 C and add a second torch so the flame is exactly opposite I don’t get 0 at any point. If I combine the flames tips in the same direction I don’t get 6000 C. 3000 C is it.
5. What is the emissivity of CO2 at partial pressure and the temperatures you list? Without that knowledge you cannot figure heat transfer and I bet it is very tiny. My heat transfer book does not go that low in temperature so I have to extrapolate to less than .1.
6. PV=nRT for the air temperature at or near the surface is valid since the critical temperture of N2 is so far away. (Paul please note I said at or near. ;)) If this was not valid why do we have STP, standard temperture and pressure. Using standard pressure and 273 K the equation is in balance.
7. Because of the equation in my #4 and the atmosphere under almost all conditions being at a lower temperature than the ground no heating of the surface by air can take place. Not to mention the mass diparity of both and the heat capacity difference.
Please try again.
Where Argon ?
“”””” Jan Oortwyn says:
March 29, 2011 at 7:29 am
My impression is that there is confusion between thermal transfer between molecules (rotation, vibration etc) and radiation emission/absorption. The first depends on the thermodynamics, the second on quantum physics.
As far as I remember, the absorption of a photon concerns only the electrons which can gain a higher (not stable) energy level. After some time the excited electron will re-emit the received excitation energy as a photon and fall back into the stable configuration. The radiation energy balance would be zero. But may be I have forgotten some essential laws of physics. “””””
In the lower regions of the atmosphere where weather happens, the mean time between intermolecular collisions, is much shorter than the mean lifetime of the molecular excitted states; so before an excited molecule gets to spontaneously decay to some lower state, it collides wiht another molecule or atom (of Argon) and energy is redistributed between the collision participants. That is what temperature is all about, so that original photon energy, becomes a melange of thermal energy of kinetic motion of the gas molecules. As a result of those collisions eventually some IR active species will receive enough kinetic energy from a collision, to put it into soe excited state from which it can radiate (before the next collision).
Only in the rarified stratospheric regions, is the lifetime of the excited states shorter than the mean collision time.