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.
Ira –
I have grappled with the ‘basic physics’ for some time – having concluded from studying the flux data (courtesy of NASA), that CO2 can be accounting for at most 20% of the observed warming between 1980-2010. The main driver is very clearly percentage changes in cloud cover – I deal with this at length in my book ‘Chill: a reassessment of global warming theory’ – which calls for a re-analysis of the models. Obviously, if I am right, then there is something seriosuly wrong with the ‘basic physics’.
But I think you could be focussing your energy on an area of far greater importance than the emission spectra. It took me a long time to realise that the Radiative Forcing (RF) that is at the heart of the model calculations is centred on a notional point toward the top of the troposphere…defined by the temperature at which the earth will reradiate the balancing energy – which is -19 C and about 10km up. This is the point of notional equilibrium – a necessary condition for model initiation (it is very difficult to build in long term cycles and the reality of non-equilibrium when the causes of those cycles, as well as their amplitude and frequency are so poorly known).
So – the model calculations show that an RF of say 1.6 watts/square metre for current carbon dioxide levels will thus radiate downwards – this is a ‘forcing’ because it has moved the system from its pre-AGW (and fictitious) equlilibrium state.
This value , and the value for ‘doubling’ CO2 – at about 4 watts/square metre, is quoted everywhere you look – but just try to find the science of RF calculations to back it up!!! It took me a long time to find references in IPCC – I had to go back to 1990. Their special publication on RF is very unhelpful (and hard to find). I still found no academic scientific references. Eventually I realised that the IPCC reference to ‘offline computer codes’ meant the MODTRANS formulae which are produced by the USAF and can be accessed for $300! There may be others, but this unit seems to have the monopoly. I have no idea if there are error margins – but they do all the ‘basic physics’ calculating the heat transfers and photons and all that jazz at any altitude…and this model will allow you to input changes in greenhouse gases.
It is clear the MODTRANS RF model is LOG…..as many have posted on WUWT.
There may be nothing wrong with this level of the basic science – But references to this log relationship are VERY sparce in the literature. One colleague of mine persistently asked – ‘how can you say there is a log relationship between concentration of CO2 and its RF, when everything I see in the literature refers to a linear one?’ Eventually, I found him a point in IPCC where the (ln) equation was stated (but not referenced to an academic paper).
But then the Rf must be translated to a surface temperature – and that is far from basic physics.
I believe the first equations relating RF to temperature at the surface were courtesy of James Hansen – but I may not have the whole story. It is in THIS relationship that assumptions of linearity come in.
THUS….modtans calculates the RF at 10 km…..and say for a doubling we have an excess of 4 watts/sq metre of downwelling IR radiation.
Warmist science then has to translate this value into Temperature at the surface – and compare this to the observed T, and arrive at an equation T at surface = X (RF) where X is the factor that translates RF to T on a degrees C per watt basis. Remember, the RF has a log relation to concentration and Modtrans already assumed this, so the RF does not increase linearly with concentration. In calculating the RF we have to assume – in the absence of any critical scientific review of the privately produced modtrans model – that the asymptotic point has been calculated correctly. Actually, by the time you approach 200ppmv for CO2, you have already reached the break point in the curve, beyond which additional CO2 has much less impact on the RF – and this is close to the glacial value – suggesting that CO2 changes do not drive the glacial cycles (CO2 changes are supposed to amplify T rise during deglaciation, but there is scant evidence for this and the assumption that it did also underlay the IPCC belief – and a great many references in academic papers give a T degrees C per ppmv CO2 without stating over which range of concentrations this is meant to apply.
So – this X-factor must take account of everything that goes on beneath the calculated RF at 10km…..all the varying cloud and aerosol and water vapour. Values seem to vary between 0.4 and 0.8. This is the assumed ‘linear’ relationship that is always mentioned, whereas the original log relationship gets buried.
I suspect that given the paucity of knowledge in relation to clouds and aerosols (not to mention cycles)…the original X factors for the equation ranged through values that at the lower end produced no scary warming scenarios for the future doubling (ie at or lower than 1.5 C) to those that were very scary at 3-4.5 C – or even 6 C if you add strong feedbacks from melting ice, permafrost and emissions of methane. Hansen (and others?) was faced with such a range and chose the high ones – perhaps out of a genuine sense of precaution.
We should now be able to ascribe a real figure to the X-factor. If we can trust the RF calculation in the absence of effective peer-review – and using the observed global rise in T (criticism of urban heat islands and dodgy grid homogenising algorithms not-withstanding), then 0.7 = X (RF), where the RF for CO2 is…..? Do we take the final cumulative figure at the end of the observation period at 1.6? Or the increase since the beginning of the observation period? Taking the former – the RF given by IPCC for the CO2 is 1.6 watts (this is also the more approximate net forcing when all other GHG, cloud and aerosol factors are taken into account).
Using these values, the X-factor would be 0.43 with the proviso that it is determined over a century and that the system is at equilibrium (Warmists like to have it both ways here, ie that it was at equlibrium to start with, but not at the end, where there is ‘warming in the pipeline’ due to absorption and release of heat by the oceans). If we apply this value to the future predicted total net RF in 2050 of 3.7 watts/sq metre due to the mix of GHGs, then the resultant surface T is 1.59 C – and not at all a scary climate story.
Thus, observations tend to support a low factor X. Even this assumes that ALL the change in T from 1900 to 2010 was caused by the net downward flux or RF – the forcing, and there was no variation in any of the factors that contribute to that X factor such as clouds and aerosols, or warming and cooling cycles in the ocean heat reservoir – which is unlikely. The defending argument is that any such variables will be compensated for over the time period.
It is this X factor that needs attention – where is the peer-reviewed science? I assume it IS there, just not so readily available to the non-specialist scientific reviewer.
And actually, my final conclusion is that there is nothing actually ‘wrong’ with the basic science – it already includes these lower factors and a low prediction for doubling in 2050, but there is an assumption that this low prediction is very unlikely. This is not a problem with the basic science, rather a lack of awareness and bias on the part of the reviewers at IPCC and just about every academic institution that has supported their faulty analysis.
By the way – the IPCC Summary for Policy Makers has a graphic that has on the left side concentration of CO2 and on the right, the RF in wats/square metre – the right hand axis is shown as linear. This may account for the difficulty the IPCC has in accepting that future increases in CO2 will have very small impacts – they believe that graphic. The relationship is not of course linear, but logarithmic.
Robert Clemenzi says:
………”Several people have said that a cold sky can not heat a warm surface. The truth is that it can.”……
A warmer surface will radiate more of every wavelength than it absorbs from the colder surface.
How then can we say the colder surface “heats” the warmer surface?
Heat means to “increase the temperature of “.
In fact it is more correct to say that the colder surface slows the rate of heat loss from the warmer surface.
In other words it insulates the warmer surface to some extent.
The igloo example will insulate the person inside to some extent.
Myrrh, you really need to get outside more and sit in the Sunshine and feel the warmth! That is how visible and near-visible (“shortwave”) light warms he Earth.
If you don’t or cannot get outside, turn on an old-fashioned incandescent light bulb and hold yourhand near it (not too close, you will get burned). Feel the heat? That is shortwave light because the filament is heated to temperatures similar to the Sun’ surface. You can tell it is shortwave because you can see the light.
Tim Folkerts says:
February 28, 2011 at 7:23 pm
“However, it is an observed fact (supported by theory) that monatomic gases (like argon) or symmetric diatomic gases (like N2 and O2) do not have vibration modes or rotation modes that would allow them to absorb (or emit) IR photons.
… IR is not absorbed or emitted by N2 & O2.”
A hot body that won’t radiate infrared?? That’s gotta be the best-kept secret in physics, if it’s true.
In reply to Katherine and to Phil’s dad. When the Earth’s temperature increases
from 1 to 1 + p, the total radiation increases by a factor of (1 + p) ^4,
Outgoing radiation increase at all wavelengths, but the PERCENTAGE increase at
short wavelengths, which are not affected by CO2, increases at a much larger rate.
So if CO2 results in 40 watts/500 total watts, with a 1% increase in the total to
505 watts, CO2 will absorb less than 40.4 watts. There’s a negative feedback due to that 4th power increase in radiation with respect to temperature, as you discovered, there’s also a negative feedback with respect to CO2 due to a larger percentage of increased outgoing radiation in wavelengths not affected by CO2.
I think you have it summarized quite well. IMHO, the initial Alarmists, like “Chicken Little” who REALLY thought the sky ws falling, were honest, if a bit mistaken. In the case of Global Warming, they really thought that we were heading for a “tipping point” that would lead us over the cliff into “runaway warming”. I believe James Hansen of NASA GISS and Phil Jones of the UK CRU were true believers, at least in the beginning, convinced they were annointed to SAVE THE WORLD AND HUMAN CIVILIZATION AND ANIMAL AND PLANT POPULATIONS.
Perhaps, as you say, they each focussed on their narrow, fragmented, domain of expertise (Hansen’s PhD is in Astronomy) and missed the “big picture”.
As a system engineer on military avionics, I dealt with many wonderfully dedicated and intelligent and good natured specialty engineers and scientists and mathematicians who were so deep into their area of expertise that they could “not see the forest for the trees”. Sometimes, when they ventured into the overall system aspect, they made amazing errors in judgment (as I sometimes did when I ventured into their specialties).
These specialists were so used to being expert in their area (and they were) that they thought they also had perfect insight into all areas, including stuff where their knowledge level was almost childish. As a system engineer, I knew my limitations and that my knowledge of many specialized areas was fairly shallow. Therefore, I was not so sure I was right all the time. When a given specialized domain became of critical importance to the system as a whole, I summoned up my admittedly limited knowledge of physics and math (though, of course, I passed those courses in engineering college) and sat at the feet of these experts, and begged them to explain their stuff to me. I would usually say, “I want to know ‘what time is it’ not ‘how to build a clock'”. Most were quite patient with me since I was modest and fairly quick on the uptake. I am now trying to do the same with climate science and I appreciate those on WUWT who have corrected and instructed me so well.
Even now, Hansen and Jones and others on the official climate Team may still be able to force and delude themselves to believe this stuff (“Strange is man when he seeks after his gods.”) I give former VP Al Gore a (nearly) free pass because he simply accepted what established scientists told him and ran with it. His idea that the Earth’s core is at “millions of degrees” (high by a factor of a thousand) illustrates his lack of any real scientific knowledge. But he did have some great political allies and and mainstream media connections. Amazing what that man can do with only half a brain :^).
On the other hand, I believe some percentage of climate scientists are opportunists, in it for the money, who will give scientific support to almost any exaggeration to get more government grants. Then there are those politicians and professional enviromentalists who are in it for opportunistic political reasons. (“Half the air pollution is due to burning fossil fuels and the other have due to the incessant spouting of nonsense by environmentalists” :^)
That is the problem when the government gets involved in complex stuff that would better be left to the privae sector. (“If the government was in charge of hte Sahara Desert, in six months there would be a shortage of sand.” :^)
However, some of the alarmist and warmist advocates are honestly convinced that the advance of technolology and transnational corporations and globalization will do us all in. I tend to be an optimist on these issues, as expressed in my free online novel and predictions about life, liberty, and technology in the second half of this century.
@-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 vast majority of the energy direct from the Sun that heats the Earth is in the visible spectrum, NOT the IR. If you doubt that visible light can heat things consider the car on a sunny day. The glass of the windows blocks IR but lets through visible light that is absorbed by the (usually) dark plastic/leather interior. The hot steering wheel and seat are warmed by the visible light not any IR.
You are correct of course that the surface is ALSO heated by the 7um and 15um IR emissions from the H2O and CO2 in the atmosphere that has been warmed by the IR emissions from the surface….
cal says:
February 28, 2011 at 4:58 pm
“As I read it you seem to imply that the greenhouse molecules pass all their energy to the O2 and N2 molecules which then radiate into space. However they can’t since there is a law which says that a bad absorber cannot be a good radiator.
The rule is that you cannot have a net energy transfer in this direction but there is always energy being radiated from any body above absolute zero.”
OK which is it. N2 and O2 “can’t since there is a law” or “there is always energy being radiated from any body above absolute zero.”
You can’t have it both ways.
Ira,
usefull schematics. However, some posters have pointed out that, according to Kirchoff’s law, if the atmosphere cannot absorb at 10 micro thingies, it can’t emit at that wavelength either, and therefore by implication, cannot this wavelength cannot appear as the result of being warmed by other wavelengths. I don’t pretend to know anything about Kirchoff’s laws, but if they are correct, this does present an issue with your model. Care to comment?
John of Kent,
“To do so would mean the colder air is warming the hot ground and that goes against the laws of thermodynamics.”
Wow. Against the laws of thermodynamics. Which laws of thermodyamics did you have in mind? First law says that energy can be changed from one form to another but cannot be destroyed. That can’t be it then. What about the second law? Perhaps that’s what you meant. Let’s see. Here’s a quote about that from Wiki:
“The second law of thermodynamics is an expression of the tendency that over time, differences in temperature, pressure, and chemical potential equilibrate in an isolated physical system. From the state of thermodynamic equilibrium, the law deduced the principle of the increase of entropy and explains the phenomenon of irreversibility in nature. The second law declares the impossibility of machines that generate usable energy from the abundant internal energy of nature by processes called perpetual motion of the second kind.”
Talks about a tendency of temperatures to equilibriate and the impossibility of perpetual motion machines. Ok, if the colder air is supposed to be radiating towards the warmer ground, is that against the second law of thermodynamic?
Not necessarily. As long as the warmer ground is radiating more back towards the cold air than the cold air is radiating towards the warmer ground, their temperatures would equilibriate (if the ground wasn’t being continually warmed by the sun). Does this mechanism constitute a perpetual motion machine? No, because again, their temperatures would equilibirate over time so no more work could be done.
By this definition of the second law, GHG back radiation to earth does not violate it. Care to elaborate?
davidmhoffer says:
March 1, 2011 at 3:04 am
John of Kent says:
“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.”
By the same token insulation in your attic can’t heat your house. But that doesn’t mean attic insulation does nothing at all. It slows down the rate of heat exchange between inside the house and outside the house. That’s what greenhouse gases do except that GHGs are more one-way than attic insulation. They impede very little energy coming from the sun to the earth’s surface but impede a lot of energy going from the earth’s surface to the frigid cold of outer space. This should not be difficult to understand. Arguments to the contrary always have two defining characteristics: they are convoluted and untrue.
Anthony, I wish WUWT would follow Max Hugoson’s advice — atmospheric effect. Truth in science.
Max Hugoson says:
February 28, 2011 at 7:34 pm
PS: Because of Robert Woods 1909 experiment with two miniature “greenhouses”, one with a “rock salt” (i.e., transparent to the longwave IR material) window and the other with a glass window, showing NO MEASURABLE DIFFERENCE in the final equilibrium temperatures in both boxes, we’ve known SINCE 1909 that to ascribe the warming of greenhouses to the allegation of a “one way valve” due to the regular sodium silica glass, is in error.
Real “Meteorological” textbooks for many years have noted this and used the prefered term: “Atmospheric Effect”.
I think the WUWT crowd needs to realize this fact and steadfastly refuse to use the terms “Greenhouse gases” or “Greenhouse Effect”.
Truth needs to win!
THANKS Tim Folkerts for the link. I knew some WUWT reader would be alert enough to answer Fred Souder’s good question . GREAT LINK, let me repeat it: http://www.skepticalscience.com/images/infrared_spectrum.jpg
Here it is for all to see:
Ira Glickstein
http://www.scribd.com/doc/34962513/Elsasser1942
Again I give you this link to a paper on radiative heating of the atmosphere via IR. It may help.
Great question DccMartyn. I think that some part of the UV spectrum, like its close cousin visible light, is mostly reflected rather than absorbed and re-emitted, so it would go back out to Space like the visible light that strikes clouds. Other parts are 100% absorbed by oxygen and ozone, or are scattered, see http://en.wikipedia.org/wiki/File:Atmospheric_Transmission.png. Some of the UV gets through and gives us happy residents of Florida our nice natural tans.
“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.”
No, Mars isn’t at a “beyond supporting life” distance from the sun. The Martian atmosphere would be warm enough to support life if it wasn’t so thin , at about 1% the density of Earth’s atmosphere. The density of the atmosphere ties in directly with it’s heat capacity. Mars has little to no magnetosphere, so the solar wind stripped much of the atmosphere away over billions of years.
Enough already with the argument that certain gases that don’t absorb infrared can’t emit it. This is not true for dense gases. The troposphere is a mixture of cold dense gases. Please review Kirchoff’s Laws:
http://www.physics.rutgers.edu/~matilsky/documents/kirchoff.html
Nitrogen doesn’t absorb infrared radiation but it can certainly gain kinetic energy by excited molecules of CO2 and H2O bumping into nitrogen molecules. The kinetic energy gained by the nitrogen molecules will be lost in a continuous blackbody spectrum characteristic of the temperature of the gas.
Any argument to the contrary is simply wrong and ignores basic laws of physics formulated 150 years ago.
What’s hilarious is watching people who have less understanding of classical laws of physics than 19th century physicists start babbling about 20th century quantum mechanics.
Ira Glickstein, PhD says:
March 1, 2011 at 7:19 am
If you’d paid attention to MY comments you’d have found that image months ago. I have posted it several times including last night on THIS thread.
http://www.sundogpublishing.com/fig8-2.pdf
It’s from the 2006 textbook “A First Course in Atmospheric Radiation” by Grant Petty.
I didn’t know you could get a PhD in Obfuscation & Convolution but you’re living proof that it happens.
Max, you are quite correct, technically. Yes greenhouse (even with ‘scare quotes’ as “greenhouse effect”) is a misnomer for what you prefer to call the “Atmospheric effect”.
On the other hand, when we speak to the general public, and even to those who are into climate science like the WUWT crowd, we need to use the terms that, for whatever reason, have become established in the language. The popular usage term “Greenhouse effect” is what my PhD advisor calls a “frozen accident” – something that has been accepted and is now dominant, though other alternatives might be equally good or even better. There are many aspects of the genetic DNA code, for example, that, as a computer and programming savy guy, I would change if I could, but Evolution and Natural Selection has chosen those somewhat accidental codes and fixed them so firmly that to change them would be futile. The best is the enemy of the good enough.
I try to use ‘scare quotes’ and I mention, right at the top of my topics, that the Atmospheric “greenhouse effect” works differently from a physical greenhouse. If I simply said “Atmospheric effect” who, except for you and some subset of Meteorologist specialists, would know what I was talking about?
Perhaps we can get the agriculturalists to change the name of their transparent boxes to “Hot House” or “Limited Convection Containment Houses” or “Temperature Enhancement Houses” or some other more descriptive term? :^)
If I am right (see CO2 is Plant Food) we will see captured CO2 from clean coal powerplants pumped into real greenhouses, since elevated levels of CO2, up to 1400 ppm or even higher, aid the growth of most plants. Greenhouses are also usually quite humid. Thus, even the term “Greenbouse gases” (GHG) will apply both to the “Amospheric effect” and the inside of real greenhouses.
Ira Glickstein, PhD says:
February 28, 2011 at 11:08 pm
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.
I’m wondering then if the above is true, then what is the minimum altitude (bold section mine) that actually has any discernable effect on either the earth’s surface or the climate?
Also, while it radiates in all directions, doesn’t whatever becomes warmer rise, moving away from the surface?
Just wondering.
etudiant says:
February 28, 2011 at 2:18 pm
Relative humidity in the upper atmosphere (300mb level) has fallen from around 55% in 1950 to about 45% now.
Should this not have a material impact on the greenhouse effect? …
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?
Dr Glickstein,
The source of the data is NOAA, here
http://www.esrl.noaa.gov/psd/cgi-bin/data/timeseries/timeseries1.pl
I do not know how good the pre satellite data is.
Presumably it represents balloon measurements.
The striking thing is the apparent monotonicity of the trend, unlike that at 600mb, which has seen a recovery in recent years.
It does underscore the tremendous complexity of the atmosphere, that this kind of longer term change happens without us even being much aware of it, much less able to explain it.
Dave Springer says:
March 1, 2011 at 7:53 am
Nitrogen doesn’t absorb infrared radiation but it can certainly gain kinetic energy by excited molecules of CO2 and H2O bumping into nitrogen molecules. The kinetic energy gained by the nitrogen molecules will be lost in a continuous blackbody spectrum characteristic of the temperature of the gas.
Agreed. My point to Cal earlier. If N2 and O2 could not shed energy (trapping it) then we would have a problem.
But that leads to a question: what difference is there between the spectrum of N2 and O2 both at the exact same temperature and radiating. I have not found anything on that.
The peak wavelength of human body emission is at 9500 nm (9.5 microns) and according to the diagram, passes through the Long-wave Window with small loses.
It is interesting to note that nearly all Earth-emitted radiation is between 5 to 30 microns and is centered at about 10 microns.
It seems that most of the thermal energy emitted by Earth and its inhabitants gets a free pass through the Pass-Through Window.
One of the few articles that recognizes the specific heat capacities of the major atmospheric gases – Nitrogen, Oxygen, Ozone and Argon – as well as the atmospheric trace gases – water vapor and Carbon Dioxide.
The charts from skepticalscience are very interesting.
They do not appear to be readings taken at the north pole on January 7th., nor at Tucson on July 9th.
I would be very interested in reading how they are put together.
Dave Springer
…….”The kinetic energy gained by the nitrogen molecules will be lost in a continuous blackbody spectrum characteristic of the temperature of the gas.”……
Could you provide a chart showing a continuous black body spectrum for nitrogen gas.
I dont think such a thing exists.