Guest post by Ira Glickstein
A real greenhouse has windows. So does the Atmospheric “greenhouse effect”. They are similar in that they allow Sunlight in and restrict the outward flow of thermal energy. However, they differ in the mechanism. A real greenhouse primarily restricts heat escape by preventing convection while the “greenhouse effect” heats the Earth because “greenhouse gases” (GHG) absorb outgoing radiative energy and re-emit some of it back towards Earth.
The base graphic is from Wikipedia, with my annotations. There are two main “windows” in the Atmospheric “greenhouse effect”. The first, the Visible Light Window, on the left side of the graphic, allows visible and near-visible light from the Sun to pass through with small losses, and the second, the Longwave Window, on the right, allows the central portion of the longwave radiation band from the Earth to pass through with small losses, while absorbing and re-emitting the left and right portions.
The Visible Light Window
To understand how these Atmospheric windows work, we need to review some basics of so-called “blackbody” radiation. As indicated by the red curve in the graphic, the surface of the Sun is, in effect, at a temperature of 5525ºK (about 9500ºF), and therefore emits radiation with a wavelenth centered around 1/2μ (half a micron which is half a millionth of a meter). Solar light ranges from about 0.1μ to 3μ, covering the ultraviolet (UV), the visible, and the near-infrared (near-IR) bands. Most Sunlight is in the visible band from 0.38μ (which we see as violet) to 0.76μ (which we see as red), which is why our eyes evolved to be sensitive in that range. Sunlight is called “shortwave” radiation because it ranges from fractional microns to a few microns.
As the graphic indicates with the solid red area, about 70 to 75% of the downgoing Solar radiation gets through the Atmosphere, because much of the UV, and some of the visible and near-IR are blocked. (The graphic does not account for the portion of Sunlight that gets through the Atmosphere, and is then reflected back to Space by clouds and other high-albedo surfaces such as ice and white roofs. I will discuss and account for that later in this posting.)
My annotations represent the light that passes through the Visible Light Window as an orange ball with the designation 1/2μ, but please interpret that to include all the visible and near-visible light in the shortwave band.
The Longwave Window
As indicated by the pink, blue, and black curves in the graphic, the Earth is, in effect, at a temperature that ranges between a high of about 310ºK (about 98ºF) and a low of about 210ºK (about -82ºF). The reason for the range is that the temperature varies by season, by day or night, and by latitude. The portion of the Earth at about 310ºK radiates energy towards the Atmosphere at slightly shorter wavelengths than that at about 210ºK, but nearly all Earth-emitted radiation is between 5μ to 30μ, and is centered at about 10μ.
As the graphic indicates with the solid blue area, only 15% to 30% of the upgoing thermal radiation is transmitted through the Atmosphere, because nearly all the radiation in the left portion of the longwave band (from about 5μ to 8μ) and the right portion (from about 13μ to 30μ) is totally absorbed and scattered by GHG, primarily H2O (water vapor) and CO2 (carbon dioxide). Only the radiation near the center (from about 8μ to 13μ) gets a nearly free pass through the Atmosphere.
My annotations represent the thermal radiation from the Earth as a pink pentagon with the designation 7μ for the left-hand portion, a blue diamond 10μ for the center portion, and a dark blue hexagon 15μ for the right-hand portion, but please interpret these symbols to include all the radiation in their respective portions of the longwave band.
Sunlight Energy In = Thermal Energy Out
The graphic is an animated depiction of the Atmospheric “greenhouse effect” process.
On the left side:
(1) Sunlight streams through the Atmosphere towards the surface of the Earth.
(2) A portion of the Sunlight is reflected by clouds and other high-albedo surfaces and heads back through the Atmosphere towards Space. The remainder is absorbed by the Surface of the Earth, warming it.
(3) The reflected portion is lost to Space.
On the right side:
(1) The warmed Earth emits longwave radiation towards the Atmosphere. According to the first graphic, above, this consists of thermal energy in all bands ~7μ, ~10μ, and ~15μ.
(2) The ~10μ portion passes through the Atmosphere with litttle loss. The ~7μ portion gets absorbed, primarily by H2O, and the 15μ portion gets absorbed, primarily by CO2 and H2O. The absorbed radiation heats the H2O and CO2 molecules and, at their higher energy states, they collide with the other molecules that make up the air, mostly nitrogen (N2), oxygen (O2), ozone (O3), and argon (A) and heat them by something like conduction. The molecules in the heated air emit radiation in random directions at all bands (~7μ, ~10μ, and ~15μ). The ~10μ photons pass, nearly unimpeded, in whatever direction they happen to be emitted, some going towards Space and some towards Earth. The ~7μ and ~15μ photons go off in all directions until they run into an H2O or CO2 molecule, and repeat the absorption and re-emittance process, or until they emerge from the Atmosphere or hit the surface of the Earth.
(3) The ~10μ photons that got a free-pass from the Earth through the Atmosphere emerge and their energy is lost to Space. The ~10μ photons generated by the heating of the air emerge from the top of the Atmosphere and their energy is lost to Space, or they impact the surface of the Earth and are re-absorbed. The ~7μ and ~15μ generated by the heating of the air also emerge from the top or bottom of the Atmosphere, but there are fewer of them because they keep getting absorbed and re-emitted, each time with some transfered to the central ~10μ portion of the longwave band.
The symbols 1/2μ, 7μ, 10μ, and 15μ represent quanties of photon energy, averaged over the day and night and the seasons. Of course, Sunlight is available for only half the day and less of it falls on each square meter of surface near the poles than near the equator. Thermal radiation emitted by the Earth also varies by day and night, season, local cloud cover that blocks Sunlight, local albedo, and other factors. The graphic is designed to provide some insight into the Atmospheric “greenhouse effect”.
Conclusions
Even though estimates of climate sensitivity to doubling of CO2 are most likely way over-estimated by the official climate Team, it is a scientific truth that GHGs, mainly H2O but also CO2 and others, play an important role in warming the Earth via the Atmospheric “greenhouse effect”.
This and my previous posting in this series address ONLY the radiative exchange of energy. Other aspects that control the temperature range at the surface of the Earth are at least as important and they include convection (winds, storms, etc.) and precipitation that transfer a great deal of energy from the surface to the higher levels of the Atmosphere.
I plan to do a subsequent posting that looks into the violet and blue boxes in the above graphic and provides insight into the process the photons and molecules go through.
I am sure WUWT readers will find issues with my Atmospheric Windows description and graphics. I encourage each of you to make comments, all of which I will read, and some to which I will respond, most likely learning a great deal from you in the process. However, please consider that the main point of this posting, like the previous one in this series, is to give insight to those WUWT readers, who, like Einstein (and me :^) need a graphic visual before they understand and really accept any mathematical abstraction.
[[[ D. J. Hawkins says:
February 28, 2011 at 5:52 pm
… All things being equal, add more balls to the pool and you can heat the water to a higher temperature. In point of fact, people actually do this to help their pools warm up in early spring. You just add a pool cover to reduce re-radiation at night. ]]]
If we covered the earth in a pool cover, the heat increase would kill us in short order.
That would create an environment similar to a real greenhouse which becomes scorching in the summer sun and use water spray, windows, and fans to cool down. They can be deadly for plants and people trapped in them in the summer if they are not managed properly. A pool cover is not an accurate representation of CO2.
My point with the black balls is that the ratio to the volume of water is miniscule… they cannot have much effect due to the small quantity…. same as CO2 is only a trace gas in the atmosphere. The black balls should actually be drifting under the water to be a more accurate representation of CO2 floating in the atmosphere. You are creating a non-representative condition by covering the surface of the pool with black balls, (and also interfering with surface cooling by radiation/evaporation) and…
1) That is also creating an overrepresentation of CO2. and..
2) CO2 does not float at the top of the atmosphere, but is homogenized in.
I suggest again that there are not enough black balls floating around in the pool to make any measurable change in water (atmospheric) temperature.
I realize this is not a perfect analogy. CO2 purports to reflect certain wavelengths back to the planet. I visualize CO2 in the atmosphere like a screen door on a submarine…. Some of the energy waves will get reflected back, but there are so many holes in the CO2 cover that after a couple bounces, all will make it out into space. Net gain…. not much. Screen doors on submarines don’t keep the water out. CO2 is a screen door… too many holes in the coverage to do much benefit.
Brief note to Myrrh;
All incoming radiation that reaches the surface heats the Earth. It is absorbed by one form of matter or another, which causes kinetic agitation — i.e., heat. It can’t be re-radiated at those same wavelengths because that would require being as hot as the source, the Sun. It gets emitted at the wavelengths matching the temperature of the matter/material emitting. That’s in the IR band for the temps we experience.
In deep space, much material is much colder, and emits at even lower wavelengths, down in the radio bands. Other higher frequency radiation also comes in on those bands after being “red-shift” stretched by the relative recession of the sources from our POV. Such as the putative “Big Bang” cosmic background patterns.
bubbagyro writes:
“CO2 is generated on the earth’s surface. It becomes more dilute as it diffuses upward. The models, similar to Ira’s, assume it is a narrow band. This is not true. The very dilute CO2 and water even in the stratosphere absorb radiation. The higher that occurs, the more is lost to space.”
Please expand on this. My understanding is that the modelers assume that concentrations of CO2 are the same wherever they occur in the atmosphere – all the way up. In addition, they assume that the behavior of CO2 molecules regarding radiation is the same throughout the atmosphere. It has always seemed to me that these “uniformity” assumptions were just evidence of an unwillingness to do the necessary empirical research. In plain and simple terms, I would like someone to address the linked questions of “where are the CO2 concentrations and how does radiative behavior change depending on where they are?”
Correction/refinement of above: “All incoming radiation that reaches the surface and is not reflected …”
bubbagyro says:
February 28, 2011 at 7:11 pm
Oh, no!
I did it again, misspelled my /unbolding. It was only meant for one word.
Sorry.
=======================================================
They are some really nice guys! They fixed it for you!
“I plan to do a subsequent posting that looks into the violet and blue boxes in the above graphic and provides insight into the process the photons and molecules go through.”
Please don’t go into quantum electrodynamics. The scales involved don’t warrant it and I guarantee you no good will result from it unless further confusion and unending arguments even between the PhD physicists here is your goal.
Oh, one other observation for Ira, by continuously mentioning Albert Einstein’s name in all of your posts you are in fact doing yourself a disservice. You may think that it increases your credibility and more people will automatically accept your arguments since you “drop” Al’s name, but it only works for a small portion of the audience.
I for one evaluate your posts based solely on their merit. Just because you make nice graphics in the “spirit of Albert Einstein” does not make me give your arguments any more weight. If my garbage collector makes a good argument I consider it with just as much logical analysis as I do yours.
Just an observation, you might want to go heavy on the LOGIC and light on the “Al Einstein agrees with me” thing.
Cheers, Kevin.
You know Ira, there’s a quantum explanation for why you squint your eyes in bright lights. There’s also no good reason to ever try to explain it in quantum terms when a macroscopic explanation is far simpler and completely adequate for any practical purpose. The same goes for the greenhouse effect. Quench that desire. Just say no.
When the up-going long-wave radiation gets reflected back to the earth, how long does it take for it to “bounce off” the earth and return to the level where it was previously reflected back to the earth? (Or does it not work that way?)
How long does it take for the long-wave radiation to completely dissipate during the night? (If it does not, how much of it is still there when “new” long-wave radiation joins it after sunrise?)
How long does it take after sunrise for the GHG in the upper atmosphere to again get saturated with long-wave radiation?
If the long-wave inventory returns to negligible levels by morning, what difference would that make to average global temperatures in contrast to the inventory staying relatively high (or static)?
This was sort of what I was alluding to regarding the behavior of CO2 in the atmosphere. Your black ball can’t be based on the proportion (molar volume) of CO2 in the atmosphere; it has to be proportional to the effect of the CO2 in the atmosphere. You say it’s a “couple bounces.” I say…does anyone know for sure? Or have a defensible WAG?
Theo Goodwin says:
February 28, 2011 at 7:51 pm
I did not want to elaborate, because it is an onion skin, that keeps revealing more layers of variables. More variables than explanatory equations. For example, CO2 is never free. When water vapor is present, depending upon humidity, it is associated reversibly into carbonic acid: CO2 + H2O ⇌ H2CO3. This is a highly radiation absorptive species, probably across most of the bands. The higher the humidity, the more the CO2 is associated. This will absorb incoming radiation at most UV, visible, and IR wavelengths.
Then there is quenching. (Thanks for mentioning, David). If a molecule is excited by a wavelength, then it can reradiate at higher wavelength (always higher, because lower energy—2nd Law). OR, it has another choice. Another species can “steal” the energy of the π to π* transition state, and excite itself (I’m getting excited). OR, it can do chemistry.
If a CO2 molecule is excited by IR, let’s say from below, then it can reradiate a higher wavelength IR (direction of that photon is up, down, or sideways, on average). OR, it can have the energy stolen (quenched) by SO2, or CFCs, or chloride, or water, or ozone, or carbon particulates, or dust, or…
The trouble with the models is that they do not test all of the available permutations of all the species present at all locations and levels of the atmosphere.
Hence, they simplify, and show us the absorption spectrum of pure CO2 in a vial under ideal conditions.
Then their is the horrendous problem of diffusion and diffusivity of gases.
Then we have the states of matter, especially water. Water associates in complex ways, forming structures in the low atmosphere. It is most dense when it is at 4°C, yet expands pronouncedly when it is cooled to 0*C.
Many variables, few equations. Chaos for models.
What is the source of that data and the accuracy of measurement in 1950? Assuming the change is actual, I would think it would impact the “greenhouse effect”, but I do not know which way because relative humidity considers both the temperature and water content. Are there any more expert than me out there with an answer?
DccMartyn,
the ozone is broken down by the radiation it absorbs. I am told there is no energy radiated from this interaction.
Dave Springer,
You use a common graph of the Arctic. I was wondering why you would use a graph of the second dryest place on earth, the dryest being the Antarctic. These would seem to show a much larger absorption by CO2 when water vapor is the largest effect in most other areas on the surface especially since the poles have a lot less energy to radiate.
Dave Springer says:
February 28, 2011 at 7:36 pm
I strongly suspect that the GCR’s are a variable, and that variable is modulated by the level of Solar Activity.
To be very blunt, the level of incoming GCR’s would vary even if the Sun were to remain constant in activity.
You could have low GCR levels coupled with low Solar Activity or high GCR levels with high Solar Activity, and both cases would produce much the same result.
” Whence arises this uniformity in all their outward shapes but from the counsel & contrivance of an Author? Whence is it that the eyes of all sorts of living creatures are transparent to the very bottom & the only transparent members in the body, having on the outside an hard transparent skin, & within transparent juyces with a crystalline Lens in the middle & a pupil before the Lens all of them so truly shaped & fitted for vision, that no Artist can mend them? Did blind chance know that there was light & what was its refraction & fit the eys of all creatures after the most curious manner to make use of it? These & such like considerations always have & ever will prevail with man kind to believe that there is a being who made all things & has all things in his power & who is therfore to be feared.” —- Isaac Newton…….(emphasis mine)
It is basic Science 101 that any mass with a temperaure above absolute zero emits radiation in all directions at wavelengths that peak according to their “blackbody” temperature. The air and clouds in the Atmosphere are over 200ºK, which is well above absolute zero (0ºK), so they emit radiation accordingly.
I also did a search and did not find any specific mention of test results, but I am sure they exist and I hope some WUWT reader will provide a link.
This NASA site (not GISS :^) http://earthobservatory.nasa.gov/Features/Clouds/, is about clouds and says, in part: “When a cloud absorbs longwave radiation emitted by the Earth’s surface, the cloud reemits a portion of the energy to outer space and a portion back toward the surface. ”
Why believe this site? Well, because they get it that clouds are a net NEGATIVE feedback. That is, if warming, say due to increased CO2, produces more evaporation and therefore more water vapor and thus more clouds, that will feed back and reduce the amount of warming somewhat. Here is what they say: “The balance between the cooling and warming actions of clouds is very close although, overall, averaging the effects of all the clouds around the globe, cooling predominates.”
So, this site confirms re-emission from clouds to Earth at least.
As you know, the “temperature” of a gas, such as the Atmosphere, is an abstraction of the average speed of the N2, O2, O3, H2O, CO2 and other molecules that make up that gas. When GHGs absorb a photon, they do not hold onto it forever. Rather, in their energized state, they may re-emit it or they may move faster and, by colliding with non-GHGs (such as N2) they will raise the temperature of the gas. Any mass, including a mass of gas, that has a temperature above absolute zero, will emit longwave radiation in random directions and at a variety of wavelengths, peaking at the wavelength corrresponding to the temperature of that gas, as indicated in the first graphic.
Thus, once the temperature of any portion of the Atmosphere stabilizes, ALL the photons that are absorbed from the Earth are re-emitted in all directions and a variety of wavelengths (~7μ, ~10μ ~and 15μ).
The ~7μ and ~15μ photons rattle around between GHG molecules until some emerge at the top of the Atmosphere and go off into Space, and others strike the Earth and are absorbed, further warming the Earth. The ~10μ photons get an almost free pass and zip through the GHGs and off to Space or, if they happen to be emitted downward, strike the Earth and get absorbed, further warming the Earth until it stabilizes in temperature, re-emitting the same number of photons as it receives.
If the density of CO2 molecules is increased, the ~15μ photons will get absorbed and re-emitted after moving a shorter distance, on average, through the Atmosphere. That results in a bit more being re-emitted towards Earth and the others spending more time in the Atmosphere which raise the temperature of both the Earth and the Atmosphere accordingly, until they too stabilize, but at higher average temperatures.
The key question is about the sensitivity to a doubling of CO2, not to the fact that it is a GHG that, all else being equal, tends to raise the mean Earth temperatures. Is the CO2 sensitivity high (2ºC to 5ºC) as the official climate Team claims, or only (0.25ºC to 1ºC) as some skeptics claim.
A second key question is the logarithmic parameter of successive doubling. Everyone agrees that subsequent doublings will have less and less effect, in a logarithmic manner, but the specific reduction seem to be a matter of controversy.
Thanks for your kind comment. I have seen that value, in various versions (5,500ºK, 6,000ºK, 9,500ºF, 10,000ºF, …) so I am sure it is approximately correct. The source http://en.wikipedia.org/wiki/File:Atmospheric_Transmission.png seems to say they assume the Sun is a “blackbody” (which, while not absolutely true is close enough for government work) and they run the numbers to get the corresponding “blackbody” temperature, which is the red curve. The solid red area is what actually gets through the Atmosphere to the surface, which includes cloud-tops and the white roof of Energy Secretary Chu’s home.
A useful post and an important topic not often given an airing.
For an alternative view of the long wave effect have a look at:
http://www.climatedata.info/Forcing/Emissions/introduction.html
With regard to the question on variability of outgoing radiation have a look at:
http://www.climatedata.info/Forcing/Forcing/albedo.html
Great questions jknapp! I am sure convection, including the rise of warmed air as well as wind and storms is the major driver of energy transmission out. But, for convection to take place, you need the warming due to radiation to preceed it.
As for the idea that each molecule has a particular wavelength where it absorbs and emits, that is what I used to think. If you look at the source http://en.wikipedia.org/wiki/File:Atmospheric_Transmission.png for my first graphic, where I used only the top part, the lower part shows the absorption bands for H2O and CO2 and they are quite wide, spanning around 13μ to 17μ for CO2 and, for H2O, from around 5μ to 8μ plus around 15μ to 70μ. So, clearly, these molecules are not that selective. I do not know about nitrogen (N2). However, since the Sun and the Earth act pretty much like “blackbody” emitters, with a wide range peaking at a characteristic wavelength based on temperature, I now think the Atmosphere is about the same.
The Late Great John Daly was writing about this kinda stuff (and of “Fraunhofer bands”) over a decade ago in his excellent book “The Greenhouse Trap – why the Greenhouse Effect will not end Life on Earth” … of which I’ve had a copy of for nearly as long.
regarDS
Dave Springer
Thanks for the thorough reply. It is helpful to me. Of course, I’m not completely satisfied with this answer about empirical measurements replacing theoretical ones.
I was thinking about Einstein’s (and others) investigations of Brownian motion as something to give me a lead into better understanding of the movement of heat through the atmosphere. I am guessing that heat radiating from the surface molecules of a solid also radiate in the same way within the solid. This talk of radiation conflicts with my understanding of heat conduction being vibrational. Although I suppose the two aren’t mutually exclusive; I’ve never thought of it that way.
From what I’ve read Big Bear observatory has data demonstrating that albedo is variable even on the scale of decades using a technique conceived of by DaVinci. … Fascinating.
http://www.sciencedaily.com/releases/2001/04/010418072342.htm
http://www.sciencedaily.com/releases/2004/05/040527233052.htm
http://www.sciencedaily.com/releases/2009/04/090407105156.htm
I am just a lay reader of science, and it is important to understand something about models to gauge whether the scientific consensus that I read about is real, or whether there is a large group of scientists that have fashioned their views and taken a stance because an important moral matter is at hand. Do you think it really possible that there is a large number of scientists that have delved into the working of these models and formed their judgments on climate change based on what they understand about the workings and the reliability of models.
Thanks Philip Peake for starting me down this trail of bouncing balls with your “trucks” comment way back in Willis Eschenbach’s topic. Do you have any idea how much work you (as “PJP”) , and your co-conspirator “davidmhoffer”, have induced me to undertake? Thanks! It has been a learning pleasure and that is why I am up at 2AM Florida time answering your most recent comment, ignoring the fact I have to lead a bicycle ride this morning at 8AM and do water aerobics at 9AM – Oh, the harried life of the retired engineer, never a day off :^) Thanks also for your kind comments.
What the 100% absorption means is that 100% of the photons in the appropiate bands are 100% likely to be absorbed by an H2O or CO2 molecule before they travel all the way through the Atmosphere. Indeed, I believe, even at the historical 270 or 280 ppm level of CO2, each photon traveled a small fraction of the height of the Atmosphere before being absorbed and re-emitted. So, with the current level of CO2 around 390 ppm, the photons, on average, will travel a shorter distance before getting absorbed and re-emitted. That means that newly emitted longwave radiation from the Earth’s surface will spend more time in the lower reaches of the Atmosphere and therefore contribute to heating the N2 and O2 and other components of the air more than before. Thus, the air nearest the surface of the Earth will, being a bit warmer, re-emit a bit more longwave radiation in all directions, including towards the surface. Hence, more CO2 = a bit more warming. Fortunately, this is a logarithmic process, so subsequent doublings have less and less effect – but they do have an effect.
Fred Souder says:
February 28, 2011 at 2:31 pm
“Ira,
Are there any experiments which detect the incoming re-emitted radiation from the atmosphere? Did a quick search and only came up with models. It seems like we should be able to detect the radiation coming back at us from the atmosphere if this model is valid.”
Try this –
http://www.gewex.org/bsrn.html
Baseline Surface Radiation Network (BSRN)
About BSRN
Because of the important role radiation plays in the climate system, the Baseline Surface Radiation Network (BSRN) was established to provide a worldwide network to continuously measure radiative fluxes at the Earth’s surface.
Or-
http://ams.confex.com/ams/Annual2006/techprogram/paper_100737.htm
Measurements of the Radiative Surface Forcing of Climate
W.F.J. Evans, North West Research Associates, Bellevue, WA; and E. Puckrin
The earth’s climate system is warmed by 35 C due to the emission of downward infrared radiation by greenhouse gases in the atmosphere (surface radiative forcing) or by the absorption of upward infrared radiation (radiative trapping). Increases in this emission/absorption are the driving force behind global warming.