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 8:53 pm
… 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? ]]]
This is not my field of expertise, however, I don’t like treating CO2 molecules like they are magic “heat” beans. Some of the effect attributed to them I regard as speculative or a current theory. I am skeptical about this influence. Every CO2 molecule takes up a measurable space or volume in the airmass. I treat it as a simple molecule and go from there. There are not enough of them floating around to do much in my opinion. Giving CO2 special powers or as you say “proportional to the effect of the CO2” is magical thinking in my book. I suggest that CO2 might bounce energy around but it eventually escapes into space. Heat has to leave Earth otherwise it would keep building up and we would eventually ignite in flames. Our current atmosphere, land, and sea seem to have an intrinsic control mechanism that swings between certain stable limits. I do not believe that CO2 is a zombie monster out to kill us. It is a minor player in “warming”. If we do accelerate a “warming” somehow, I imagine it will just start the reverse swing sooner than it would have happened because we hit the trigger limit faster than its “natural” oscillation . This is only an opinion based on my sum of life experiences so far. I am happy to learn more or be corrected if it can be proven accurate.
Ira Glickstein says in his article above:
“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 “
No, they don’t because Kirchoff’s law of thermal radiation states that emissivity and absorptivity must be equal to each other. If the surface can emit unhindered in the 10μ band without absorption in the atmosphere than that means that absorptivity of the atmosphere is zero and therefore emissivity must also be zero. The conclusion of this is that the atmosphere cannot possibly emit in the 10μ band.
And using the argument further, the atmosphere can only loose heat by CO2 and water vapour emitting radiation in their respective bands.
The model as presented by Ira does not reflect reality!
May I suggest some consideration be given to the Maxell-Boltzmann kinetic energy distribution curves on which subject Tom Vonk made an excellent post here on WUWT a while back.
http://ibchem.com/IB/ibnotes/full/sta_htm/Maxwell_Boltzmann.htm
http://dwb.unl.edu/teacher/nsf/c09/c09links/www.kobold.demon.co.uk/kinetics/maxboltz.htm
To me these effects imply that most long wave radiation absorbed by GHGs in the atmosphere is thermalised and “back radiation” is not related to the MASS of the GHGs in the atmosphere. A simple example is compare average surface temperatures at or near the equator to the average surface temperatures in the desert regions north or south of the equator. True there is more cloud at the equator because of the higher humidity but why doesn’t the temperature rocket up when the sky is clear? I have lived for some years in Singapore and never experienced temperatures there that I experienced in the Namib desert. Yet which region has the most “greenhouse” gases?
Ira Glickstein, PhD said:
“The ~10μ photons generated by the heating of the air emerge from the top of the Atmosphere”
I am sorry, but for the sake of accuracy, CO2 in air does not have any states that interact with 10-13um band. Therefore, hot air cannot possibly generate any photons in that range. Therefore the following statement is also wrong, nothing gets “transferred” into 10-um band from “heated air”:
“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.”
As result, the entire explanation of greenhouse effect is wrong. The emission from ~7um and ~15um bands is smaller than at the surface because the overall TEMPERATURE of air is smaller at that height (of emission to space). The temperature gets lower with height because of purely mechanical property of convectively-stirred turbulent atmosphere in the field of gravity, when it HAS to form the vertical temperature gradient called “lapse rate”. No matter what kind of radiation gets diffused (and locally emitted-absorbed) through the air, this mechanics overrides (complements) the process and forms the steady (on average) gradient no matter what. The 10-13um photons just shine through without much interaction with air, all straight from the Earth surface.
In the animated picture the pink and dark blue areas should not have any 10um components.
“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.”
Has WUWT become a “lukewarmer” site and abandoned Climate Realism?
This is pure nonsense and I’m surprised that WUWT would print such rubbish. Infra Red Interacting Gasses (IRIGs) CANNOT heat the earths surface. To do so would mean the colder air is warming the hot ground and that goes against the laws of thermodynamics.
Clearly impossible! (See slaying the Sky Dragon ).
The “greenhouse effect” on earth actually does work much the same as an actual greenhouse. It is due to the relative slowness of convection that keeps the earth surface from instantly freezing at night.
@-Ira Glickstein, PhD says:
February 28, 2011 at 10:44 pm
“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.”
That assumption may not be warrented.
The atmosphere may not be a ‘blackbody’ radiator, given Kirchoff’s law the emissivity is equal to its absorptivity(?), so the emission spectrum of the atmosphere should mirror its absorption spectrum which as you have so ably described is VERY different from a ‘blackbody’.
The emissivity of the atmosphere is going to be prefferentialy concerntrated in the H2O and CO2 bands because these are several orders of magnitude ‘better’ at absorbing and emitting at these wavelengths than the N2 AND O2 are at any wavelength.
Ira, a couple more comments.
The temperature of the sun is in fact an artifact of its radiance. The sun’s actual temperature ranges from several millions of degrees at its core to about 3 million degrees in the very diffuse corona above the “surface”. The photosphere or “surface” is sandwiched between these extremes and behaves as if it were a black body at 5840K. This can be determined approximately by its total power output and peak wavelength and accurately by its absorption lines which are temperature dependent. This does not contradict anything you said but may reassure those who look at the very low temperature and think “how can that be true?”.
Secondly I have re-read your paper and realised that there is something I do not believe is correct. It relates to the point I made in my earlier comment to George E Smith and was restated rather more strongly by Tim Folkerts when he said “I must disagree with the comments to the effect that N2 & O2 radiate (or absorb) any important amount of IR”.
You talk about the “7 and 15 micron photons” being absorbed and then some of this energy being passed to other gas molecules and being re-radiated as “10 micron photons” with some of these being lost to space. This implies that there are gas molecules around that can radiate at this wavelength. However if there were then there would not be an atmospheric window. The very reason that this window exists is that there is no absorption and therefore no radiation at these wavelengths.
Incidentally, I may be wrong but, I get the impression that some posters believe that there are two types of radiation: radiation at specific wavelengths and blackbody radiation. In reality black bodies are radiating and absorbing at specific wavelengths it is just that they do so with 100% efficiency at all wavelengths. A grey body also absorbs and radiates with the same efficiency at all wavelengths but does so with less than 100% efficiency.
The earth is close to being a grey body for the infrared part of the spectrum where it emits but it is not a grey body in the visible region. That is why the sea is blue! The atmosphere is nothing like a black or grey body and can never behave like one. As I explained in my previous post the combination of the earth’s surface and the atomosphere results in the grey body emission of the surface being modified by the absorption bands of the IR absorbing gases like H2O and CO2 to give dips in the spectrum particularly around 7 micron and 15 microns when viewed by satellites.
Why is it that everyone who attempts to create a cartoon or animation to illustrate how the “greenhouse effect” warms the planet, they always feature a big old Sun beating down. No matter which of the theories about the operation of the various component gases that comprise the atmosphere you chose to embrace, you have to recognize that when the Sun is shining on the Earth the main function of the atmosphere is to make the surface of the planet much cooler than it would be without it. If the Earth were just a larger version of the Moon, without an atmosphere, its daytime temp would be close to that of the Moon. The only difference being provided by the differing lengths of the diurnal cycle. If you compare the max, min, and mean temps for the Earth and the Moon it seems to me that, whatever the atmosphere is doing to make the Earth warmer than its theoretical blackbody temp, its doing most of it at night by increasing the min temps. I keep waiting for someone to do one of these neat climate schematics that features a big full Moon and radiative conditions that prevail when the Sun isn’t shining. It seems to me that that is where the “greenhouse effect” dwells, though I still believe that the “flywheel effect” is a more accurately descriptive analogy of what the atmosphere does for the planet.
Brian H says:
February 28, 2011 at 7:49 pm
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.
Brian, I have a real problem with that explanation in the graphic that it’s only Visible and near shortwave that heat the Earth kinetically, a.k.a. “Solar”. Your “all incoming radiation reaches the surface of the earth” isn’t addressing that, because that’s what I’m saying is happening… Because all radiation includes Thermal IR which isn’t in the chart.
Ira says that Visible is the largest part of the Sun’s spectrum, wrong, it’s actually the smallest, and compared with the others, very very small. Light is not hot, it is Reflective not Absorptive, and your use of “absorbed by matter of one form of the other” is misleading. The radiation that penetrates to heat the Earth is Thermal IR. And that is not in the Chart.
So, not only is downwelling Thermal IR taken out of the equation, it is replaced by the very strange notion that Visible light and its two other cool neighbours, by themselves heat the Earth, called “Solar”. I can sit infront of the TV all day in a cold room, it won’t heat me.
What I want here is conclusive proof that it this narrow band of non-thermal light energy which is the sole cause of the ground and rocks and me heating up from the Sun. That’s basic premise to the AGW Energy Balance claim as shown in the Charts.
And no, it does not require the source to be as hot as the sun to radiate out Thermal IR, the electric plate on your stove doesn’t have to be even hot enough to produce red light for you to feel the IR it is radiating, but that doesn’t mean that the Sun isn’t radiating our Thermal IR! That’s reaching the Earth at the same time as Solar. And is better going through water vapour, fog and mist, than Visible Light.
The Earth being heated by kinetic energy alone by Solar without any mention of of the Absorptive energies from the Sun of Thermal IR is nonsense, which is the AGW claim. I’m asking for proof it isn’t nonsense.
“The ~10µ photons generated by the heating of the air emerge from the top of the Atmosphere and their energy is lost to Space,”
“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 transferred to the central ~10µ portion of the longwave band.”
Complete nonsense. The reason that the 10µ photons from the surface are able to reach space is because the atmosphere does not absorb them. For exactly the same reason, the atmosphere also does not emit radiation at the wavelength.
Jim D does point out one exception, clouds.
I also agree with Jim D that greenhouse gases have a net cooling effect. When convection from the surface is included in the analysis, it is obvious that increasing the amount of CO2 cools the atmosphere more than it adds heat.
In addition to the problems in the main post, there are numerous errors in the comments.
George E. Smith says:
“The AGW types, like the frequency scale, because that puts the CO2 frequencies near the peak of the curve”
Actually, the frequency (wavenumber) scale gives a more intuitive plot when discussing the amount of energy. Note, the wikipedia graph uses log of wavelength which completely distorts the plot.
“the actual amplitude of the thermal spectrum should be about 80 times smaller than it is.”
Well, that depends on the x-axis selection. When frequency (wavenumber) is selected, it is the solar spectra that is about 28 times too high. When wavelength is selected, the 300K curve should be about 10 times smaller.
“The only function of the GHG molecules is to heat the atmospheric gases; along with all the other mechanisms that are heating it. After that, the GHG molecules serve no function in the climate process whatsoever.”
True, they do heat the atmosphere .. however, they also cool it. In fact, greenhouse gases provide the only method to cool the atmosphere. Note that some of the energy they release returns to the surface producing the greenhouse effect.
wayne says:
“where in the heck did 5525K for the sun’s temperature come from?”
Scientists have measured the spectra of the Sun and temperatures near 5,777 K produce a similar blackbody spectrum. However, the references use many different values. For instance, the wikipedia plot above references ~5500 K.
There are several very good reasons why the references don’t agree
* The real spectra is not very close to any blackbody spectra (slightly different shape)
* The measurement devices do not agree
* The radiation temperature of the center of the solar disk is higher than the apparent temperature near the edge
* The temperature of the outer corona is more than 1,000 hotter than the “surface”
* The Sun does not have a surface
* The distance between the Earth and Sun varies (the orbit is an ellipse), and different references handle this differently
However, what is known fairly well is the number of watts at the top of the atmosphere (TOA).
John of Kent says:
Has WUWT become a “lukewarmer” site and abandoned Climate Realism?
This is pure nonsense and I’m surprised that WUWT would print such rubbish. Infra Red Interacting Gasses (IRIGs) CANNOT heat the earths surface. To do so would mean the colder air is warming the hot ground and that goes against the laws of thermodynamics.>>>
Oh my.
There’s so many things wrong with those few sentences that it would take paragraphs to correct them all. I sometimes wonder why it is that when science is well explained on this site, by highly technical people, who then engage in well informed debate and discussion with other highly technical people, the bulk of whom are skeptics or mild luke warmers at best, there is always some troll jumping in, spouting rage and ridicule, and denouncing the explanation as fraudulent? And why does the criticism almost always include the exact same two statements?
1. Cold things can’t heat up warm things.
2. That breaks the laws of thermodynamics.
Is there some secret troll society somewhere, a cabal of warmists perhaps, determined to mess up every serious discussion of greenhouse effect by shouting those two statements? Are they on a web site someplace worded a dozen different ways so that volunteers can just copy and paste to distract everyone else? Or maybe it is completely automated?
OK Kent, cold things can’t heat up warm things. Igloos freeze everything inside them to death, that’s why the Inuit are extinct. The laws of thermodynamics don’t allow for net energy transfer. That’s why if you take two very hot things at the exact same temperature and put them side by side, there’s no energy transferring between them so you won’t burn yourself if you stick your hand between them, the laws of thermodynamics say you’ll be just fine. Kent…KENT KKKKEEEENNNNTTTT don’t actually do it!!! Phew. I thought you were going to try it. Would have felt bad about that.
There’s dozens of threads and hundreds of comments on this site from very well informed skeptics (amongst others) explaining the facts. You would do well to read many of them before popping off with comments that can be falsified by building an igloo.
Several people have said that a cold sky can not heat a warm surface. The truth is that it can. What they miss is that the “cold sky” is much warmer than the colder microwave background. So, while it may be true that a cold body won’t heat a warmer one, it will slow down the heat loss if the cold body wasn’t there.
In addition, at night the air in the lower 1,000 meters is warmer than the surface.
When it comes to our little blue planet, all this hypothetical analysis of incoming and outgoing radiation in various wave lengths, and how much is reflected back and how much escapes is neatly summed up by by Humphrey Bogarde, It does not amount to a hill of beans. The amount of heat our world receives and its reaction to it gives us our chaotic but wonderfully variable climate. I find it some what incongruous that people find small changes in things like CO2 can cause warming and cooling besides drought and floods, not to mention no snow or massive snow. The entire argument is total nonsense. It is and always will be the sun and solar mechanics that control climate, anything else will be but a bit player and not relevant to our climate.
We have a heat pump Earth that uses water and water vapour as a control mechanism every thing else is irrelevant. It is time to ask our great sun god Sol to awaken for the energy balance is tipping to the cool side. As our moderating fluid in the oceans cool as it would seem is happening no amount of nit picking as to what IR radiation is going up or down is going to be diddlysquat as far as our well being is concerned.
The world has suffered a concerted propaganda effort by the by so called experts to brain wash the west into believing that we are evil polluting monsters, AGW never was about global warming, it was about control power and wealth distribution.
Discussing radiative imbalances is a digression to keep those with cognitive thought busy whilst evil is committed.
Those here on this site show huge education and intelligence but this subject has nothing to do with global warming the IPCC is totally political with no real science involved. Confound the science of global warming all you like but the politics and the lies will keep overwhelming you in the compliant MSM.
It is time for a different tack for the science is becoming irrelevant as the brainwashing of the young is total in the schooling system. I have no answer but many on this site are far more intelligent than I and may have an antedote to this modern day grab for control. Cheers Wayne
Ira,
I think the explanation of the atmospheric window that you posted is reasonably sound, but I think the discussion has wandered off the most important aspect of it. Yes, sensitivity and greenhouse effect and what molecules radiate at what frequencies are all parts of the discussion, and necessary for understanding the climate as a whole. But in relation to the atmospheric window, I think these are relatively minor. The atmospheric window has an effect on earth temperature that I think is far more significant than how it interacts with the greenhouse effect. The important aspect of the atmospheric window is how it interacts with ALL upward bound radiance regardless of source.
Consider the black curve in your diagram, which represents the distribution of LW radiation emitted by a surface at 210 degrees Kelvin, or -63 C. The peak of the black curve is BEYOND the atmospheric window. Guestimating from the drawing, a surface at -63 C would be only emitting about 30% of its radiance in a spectrum that can escape freely to space. The rest is impeded by absorption and re-emission. But the centre curve, at 260 Kelvin, or -13 C, is smack dab in the middle of the sweet spot. For argument’s sake, let’s call that 50% going straight out the window. Then look at that pink line…uh oh….310 K… 27 C….. the percentage going out to space is dropping back down, the hotter it gets, the less surface radiance is in the escape window…25%? Less? Can you hear the tipping point argument sneaking up on you?
Of course the tipping point argument is ludicrous. Falsified by no other means than the conditions that supposedly would create it have existed multiple times in the geological record, yet no tipping point occured. The question is not if the tipping point is possible, the question is why ISN’T is possible, and the atmospheric window is a big part of that. As another commenter alluded to earluer, the geological record shows that the earth varies between certain upper and lower temperature bounds, and the atmospheric window has much to do with that also.
The lower end is in my mind the easier of the two to understand, and also easier to demonstrate. Once the earth surface cools below a certain temperature, it loses heat via radiance that is increasingly outside of the atmospheric window. In brief, the colder it get in that temperature range, the more effective the atmosphere is as insulation. You can see this easily in the temperature record. Anyone who lives in a cold climate, say Winnipeg, at 50 degree N latitude will talk with a certain amount of pride about surviving -40 C. Thompson, well north of that they will talk about…. -40 C. Keep going north. In fact, let’s go right to the arctic circle and take a look at the temperature record from DMI:
http://ocean.dmi.dk/arctic/meant80n.uk.php
Pick any year you want. Winnipeg in the depths of winter gets a few hours of sunshine every day. The arctic circle gets none for WEEKS. Yet look at the lows. Hardly ever gets past -40. The window is closed to the heat being radiated at that temperature.
What of the high end? Why no tipping point? That’s more complicated of course. For starters, you can actually see that in fact the atmospheric window does start to close as earth surface warms up. Here’s a snapshot of ERBE:
http://knowledgedrift.files.wordpress.com/2010/01/erbe-zonal-1986.gif
The tropics are for the most part slightly positive in terms of net radiation, they absorb more heat than the radiate (which is why its hot there!) and they would in fact ignite if they couldn’t get rid of that heat via convection and other processes. But you can see that the atmospheric window is pretty much closed to the wavelengths being emitted by the warm tropics. Then take a look at the arctic zones. Holy cow grandma, them windas is wide open, look at all them photon torpedos justa leakin’ out ta space, no wonder its so darn cold here, we gots ta build us an igloo right fast or we gonna freeze solid….what’s that grandma? igloos won’t work because they violate the laws of thermodynamics and cold stuff can’t keep warm stuff warm? Ya been datin’ that troll Kent agin’?
So part of the answer (sorry Kent, had to take that shot) is that convection at the tropics raises warm air upward where it eventually spills toward the poles. As it cools, it is radiating increasingly into the atmospheric window. Cool air from the poles works its way to the equator to replace the rising hot air picking up heat as it goes. For the most part it starts out cold, below the atmospheric window, and warms, radiating to space more efficiently until it gets “too” warm. But the hotter the tropics get, the faster the cycle goes. Check out the GISS or HadCrut broken down by latitude and you’ll find the tropics are VERY stable, even though they are the net retainers of heat for the planet. Any variation in solar or anything else gets pushed to the temperate and arctic zones for mandatory expulsion to space.
Of course there are other factors too. Those curves represent the RELATIVE distribution of wavelength radiated, they do NOT represent ABOSLUTE magnitude. Since the amount of energy the surface radiates is proportional to the temperature in degrees K raised to the power of FOUR (squared squared!) there’s an awfull lot more photon torpedoes pointed at space from the +27 C tropics than there are at the -63 C poles. So part of the reason for -40 being a sort of bottom end is that the atmospheric window is nearly closed AND there’s less photons being fired upward besides.
However, at the top end, even at 27 C, there’s still a healthy percentage of that curve radiating within the window, and the total being radiated is MUCH bigger. Grab a calculator and do 210^4 then do 310^4. Even if only 25% of the torpedoes at 310 get fired off within the range of the window, that’s still more than 100% of the torpedos at 210. Does that mean a tipping point is impossible? YES! You’d have to heat the planet to the point where even the POLES are more than 300 degrees K warmer than the top end of that window. Do the net radiation calculation for THAT temperature. OK, NOW we have a violation of the laws of thermodynamics.
Grandma… GRANDMA… ya can come out now, yu and Kent there done melted that igloo.
Dave Springer comments at February 28, 2011 at 7:36 pm are well worth a read, especially the point he makes aboud clouds (a point I made in my earlier post).
Whilst CGR may be an explanation for changes in clouds/cloud seeding/ cloud patterns, there may be other explanations for these changes. Indeed, in a chaotic system (such as weather/our atmosphere) one would expect there to be changes in clouds and their patterns. Further, given that we are looking at such a small time scale (circa 100 years) it would not be surprising if during such a short period there was a tendancy (ie., a trend) for less cloudiness and hence a slight upward trend in temperature. This might be nothing more than natural variation on the time scales that we are looking at.
Personally, I consider that an explanation along these lines is a more plausible explanation (by many orders of magnitude) over that of CO2 being responsible for the warming. Given that current computer models do such a poor job with clouds, we cannot rule this out.
I think etudiant has an interesting point concerning the jetstream (300mb level) and the reduction in its relative humidity. Following the reasoning of Steven Wilde a link may be considered concerning the temperature gradients at these heights in the atmosphere and the position (or changes therein) of the high speed vortices around the world driving the weather patterns and ultimately the climate.
Tim Folkerts says:
February 28, 2011 at 7:23 pm
I must disagree with the comments to the effect that N2 & O2 radiate (or absorb) any important amount of IR.
Look at a somewhat similar and more familiar idea – visible light emitted by a Hydrogen atom (the Bohr model covered in freshman chem & physics around the world). It is easy to observe that H only emits very specific energies of light which are “easily” predicted by the quantum mechanics of the orbiting electrons and the allowed transitions between energy levels of those orbits.
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But the Sun emits mostly like a blackbody.
It is not being emitted in the Hydrogen frequencies only, it is emitting across the entire spectrum close to what the blackbody curve predicts. If anything the Hydrogen spectra are suppressed (much like the CO2 spectra is suppressed on Earth) and it emits a little more energy in the non-specific-absorption frequencies (more in the visible).
The absorption and emission spectra bear special attention, but not all the attention.
http://commons.wikimedia.org/wiki/File:EffectiveTemperature_300dpi_e.png
http://en.wikivisual.com/index.php/Image:Solar_irradiance_spectrum_1992.gif
Ira Glickstein, PhD says:
February 28, 2011 at 10:02 pm
Kevin says:
February 28, 2011 at 2:52 pm
“From the looks of that first chart, ~100% of 7μ and 15μ radiation gets absorbed by the atmosphere on the way back to space, mainly by H20 and CO2. Maybe a tiny trickle bounces its way from molecule to molecule and makes it to space.”
If that’s so, then doubling or even tripling the values of H2O in our atmosphere should have no effect on absorbtion. You can’t absorb more than 100% of the radiation, right?
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.
No, gases such as N2, O2 and Ar possess no dipole and are unable to emit in the IR. Gases do not emit as black bodies, they can only emit in certain wavelength bands which correspond to transitions between certain rotational/vibrational states. This is well established physical chemistry.
Unfortunately the text in the figure is incorrect.
It says: Downgoing solar radiation 70-75% transmitted. The part not transmitted (but reflected) is not downgoing anymore. This may seem pedantic (it probably is) but it informs the howler at the right: Upgoing thermal radiation 15-30% transmitted. This has to be: All, that is 100%, of the upgoing thermal radiation is transmitted (else it would not be upgoing anymore). The atmosphere is in long-term equilibrium which means that all thermally emitted radiation is in balance with the loss at the top of the atmospher to space. The semantic mistake is an indication that the maker of the figure confused the outgoing flux with the local source function.
Chad Woodburn says:
February 28, 2011 at 8:38 pm
“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?)”
Maybe instantly maybe 10,000 years. You can’t track energy by naming each photon and following them like airplanes on a radar display.
The ocean, like all things with a temperature above absolute zero, is constantly radiating energy out to the environment and absorbing energy from the environment at the same time. When an object and its environment are at different temperatures there is a net flow of energy from warmer to colder. The larger the difference the greater the net flow rate. So say the ocean at night is radiating 400 watts per square meter upward but greenhouse gases absorb 100 watts and half of that is radiated downward towards the ocean. So you have the ocean radiating 400w and absorbing 50w at the same time for a net flow of 350w out of the ocean. Now say we have a doubling of greenhouse gases such that they absorb 200w and radiate half of that downward. Now the ocean is radiating 400w and absorbing 100w for a net flow of 300w out of the ocean.
What this results in is a lower rate of cooling for the ocean. Like coffee in an insulated versus an uninsulated cup.
The net result of all this is that when the sun warms the ocean during the day greenhouse gases reduce the rate at which that energy can escape. So the ocean gets warmer than it would have absent the greenhouse gases. The warmer ocean radiates heat faster than a cooler ocean due to the larger temperature differential between the cold of outer space and the warm ocean surface. Thus a new equilibrium point is established where energy received during the day is lost at night. In the long haul all energy absorbed by the ocean is radiated back out into space. However there are many other dynamic things happening that keep changing the daily energy flow so that equilibrium becomes a moving target that can be approached but never hit. Some days are cloudy, some are not, so some days the ocean receives more energy and some days less. Evaporation, convection, ocean and wind currents move energy around mechanically from one place to another. But the bottom line remains that greenhouse gases slow down the rate of energy loss to space which causes a higher surface equilibrium temperature the system will target.
Myrrh says: March 1, 2011 at 2:45 am
“Ira says that Visible is the largest part of the Sun’s spectrum, wrong, it’s actually the smallest, and compared with the others, very very small. Light is not hot, it is Reflective not Absorptive, and your use of “absorbed by matter of one form of the other” is misleading. The radiation that penetrates to heat the Earth is Thermal IR. And that is not in the Chart. ”
The issue here is the “size of the energy”, not the wavelength. There is a handy table at http://en.wikipedia.org/wiki/Planck%27s_law that shows the energy distribution of sunlight (above the atmosphere).
* A little over 10% of the ENERGY is in ultraviolet photons or shorter wavelengths.
* Close to 40% of the ENERGY is visible light photons
* Over 40% is “near IR” (from 0.7 – 3 um). (So Ira’s claim that visible is the biggest is not quite right, but it is not far off. On the other hand, the atmosphere is still mostly transparent to these wavelengths, so his arguments still hold).
* Only a few % is above 3 um (“thermal IR”) so it cannot possibly be the main source for heating the earth.
Greenhouses primary design is not to trap heat, but to control the environment, which includes to control the in house atmosphere which, of course, constitutes of gases.
So what you have in a greenhouse is a triple layer between the plants and the god ol’ Sol. You got the outside atmosphere (that apparently is working as a greenhouse effect), the glass (which apparently the outside atmosphere is functioning as), and the denser inside atmosphere (which apparently the outside atmosphere’s affect is the warming effect of.)
And greenhouses do not retain the heat very well, no insulation to keep the heat inside really and the much denser atmosphere does a really poor job of trapping the heat since the heat “escapes” so easily.
A greenhouse is in effect trying to mimic earth’s “summer effect” in a controlled manner. However, other ‘an summer days you usually have to add heat by other means since the heat “evaporates” so quickly to the outside, even with the inside having the denser atmosphere.
So I still claim that using the “greenhouse effect” as defined as something that gets warmer is just silly. Although if more people sported their greenhouses all through winter the power and gas companies would be ecstatic. :p
Mars is a lot further from the Sun than is the Earth, which is the main reasion it is too cold to support life as we know it, despite all the CO2 in its Atmosphere. Your analogy of the black balls in the pool does not work because the mechanism is not at all like that of the “greenhouse effect” GHG in the atmosphere. There is more H2O (the main GHG) in the Atmosphere than CO2, but the percentage of H2O is also miniscule, yet, the tiny percentage of GHGs (mostly H2O but also CO2) are responsible for the Earth being at livable temperatures.