Guest post by Ira Glickstein
The Atmospheric “greenhouse effect” has been analogized to a blanket that insulates the Sun-warmed Earth and slows the rate of heat transmission, thus increasing mean temperatures above what they would be absent “greenhouse gases” (GHGs). Perhaps a better analogy would be an electric blanket that, in addition to its insulating properties, also emits thermal radiation both down and up. A real greenhouse primarily restricts heat escape by preventing convection while the “greenhouse effect” heats the Earth because GHGs absorb outgoing radiative energy and re-emit some of it back towards Earth.
Many thanks to Dave Springer and Jim Folkerts who, in comments to my previous posting Atmospheric Windows, provided links to emission graphs and a textbook “A First Course in Atmospheric Radiation” by Grant Petty, Sundog Publishing Company.
Description of graphic (from bottom to top):
Earth Surface: Warmed by shortwave (~1/2μ) radiation from the Sun, the surface emits upward radiation in the ~7μ, ~10μ, and ~15μ regions of the longwave band. This radiation approximates a smooth “blackbody” curve that peaks at the wavelength corresponding to the surface temperature.
Bottom of the Atmosphere: On its way out to Space, the radiation encounters the Atmosphere, in particular the GHGs, which absorb and re-emit radiation in the ~7μ and ~15μ regions in all directions. Most of the ~10μ radiation is allowed to pass through.
The lower violet/purple curve (adapted from figure 8.1 in Petty and based on measurements from the Tropical Pacific looking UP) indicates how the bottom of the Atmosphere re-emits selected portions back down towards the surface of the Earth. The dashed line represents a “blackbody” curve characteristic of 300ºK (equivalent to 27ºC or 80ºF). Note how the ~7μ and ~15μ regions approximate that curve, while much of the ~10μ region is not re-emitted downward.
“Greenhouse Gases”: The reason for the shape of the downwelling radiation curve is clear when we look at the absorption spectra for the most important GHGs: H2O, H2O, H2O, … H2O, and CO2. (I’ve included multiple H2O’s because water vapor, particularly in the tropical latitudes, is many times more prevalent than carbon dioxide.)
Note that H2O absorbs at up to 100% in the ~7μ region. H2O also absorbs strongly in the ~15μ region, particularly above 20μ, where it reaches 100%. CO2 absorbs at up to 100% in the ~15μ region.
Neither H2O nor CO2 absorb strongly in the ~10μ region.
Since gases tend to re-emit most strongly at the same wavelength region where they absorb, the ~7μ and ~15μ are well-represented, while the ~10μ region is weaker.
Top of the Atmosphere: The upper violet/purple curve (adapted from figure 6.6 in Petty and based on satellite measurements from the Tropical Pacific looking DOWN) indicates how the top of the Atmosphere passes certain portions of radiation from the surface of the Earth out to Space and re-emits selected portions up towards Space. The dashed line represents a “blackbody” curve characteristic of 300ºK. Note that much of the ~10μ region approximates a 295ºK curve while the ~7μ region approximates a cooler 260ºK curve. The ~15μ region is more complicated. Part of it, from about 17μ and up approximates a 260ºK or 270ºK curve, but the region from about 14μ to 17μ has had quite a big bite taken out of it. Note how this bite corresponds roughly with the CO2 absorption spectrum.
What Does This All Mean in Plain Language?
Well, if a piece of blueberry pie has gone missing, and little Johnny has blueberry juice dripping from his mouth and chin, and that is pretty good circumstantial evidence of who took it.
Clearly, the GHGs in the Atmosphere are responsible. H2O has taken its toll in the ~7μ and ~15μ regions, while CO2 has taken its bite in its special part of the ~15μ region. Radiation in the ~10μ region has taken a pretty-much free pass through the Atmosphere.
The top of the Atmosphere curve is mostly due to the lapse rate, where higher levels of the Atmosphere tend to be cooler. The ~10μ region is warmer because it is a view of the surface radiation of the Earth through an almost transparent window. The ~7μ and 15μ regions are cooler because they are radiated from closer to the top of the Atmosphere. The CO2 bite portion of the curve is still cooler because CO2 tends to be better represented at higher altitudes than H2O which is more prevalent towards the bottom.
That is a good explanation, as far as it goes. However, it seems there is something else going on. The ~7μ and ~15μ radiation emitted from the bottom of the Atmosphere is absorbed by the Earth, further warming it, and the Earth, approximating a “blackbody”, re-emits them at a variety of wavelengths, including ~10μ. This additional ~10μ radiation gets a nearly free pass through the Atmosphere and heads out towards Space, which explains why it is better represented in the top of the Atmosphere curve. In addition, some of the radiation due to collisions of energized H2O and CO2 molecules with each other and the N2 (nitrogen), O2 (oxygen) and trace gases, may produce radiation in the ~10μ region which similarly makes its way out to Space without being re-absorbed.
There is less ~15μ radiation emitted from the top of the Atmosphere than entered it from the bottom because some of the ~15μ radiation is transformed into ~10μ radiation during the process of absorption and re-emission by GHGs in the atmosphere and longwave radiation absorbed and re-emitted by the surface of the Earth.
Source Material
My graphic is adapted from two curves from Petty. For clearer presentation, I smoothed them and flipped them horizontally, so wavelength would increase from left to right, as in the diagrams in my previous topics in this series. (Physical Analogy and Atmospheric Windows.)
Here they are in their original form, where the inverse of wavelength (called “wavenumber”) increases from left to right.
Source for the upper section of my graphic.
Top of the Atmosphere from Satellite Over Tropical Pacific.
[Caption from Petty: Fig. 6.6: Example of an actual infrared emission spectrum observed by the Nimbus 4 satellite over a point in the tropical Pacific Ocean. Dashed curves represent blackbody radiances at the indicated temperatures in Kelvin. (IRIS data courtesy of the Goddard EOS Distributed Active Archive Center (DAAC) and instrument team leader Dr. Rudolf A. Hanel.)]
Source for the lower section of my graphic.
Bottom of the Atmosphere from Surface of Tropical Pacific (and, lower curve, from Alaska).
[Caption from Petty: Fig. 8.1 Two examples of measured atmospheric emission spectra as seen from ground level looking up. Planck function curves corresponding to the approximate surface temperature in each case are superimposed (dashed lines). (Data courtesy of Robert Knutson, Space Science and Engineering Center, University of Wisconsin-Madison.)]
The figures originally cited by Dave Springer and Tim Folkerts are based on measurements taken in the Arctic, where there is far less water vapor in the Atmosphere.
[Fig. 8.2 from Petty] (a) Top of the Atmosphere from 20km and (b) Bottom of the Atmosphere from surface in the Arctic. Note that this is similar to the Tropical Pacific, at temperatures that are about 30ºK to 40ºK cooler. The CO2 bite is more well-defined. Also, the bite in the 9.5μ to 10μ area is more apparent. That bite is due to O2 and O3 absorption spectra.
Concluding Comments
This and my previous two postings in this series Physical Analogy and Atmospheric Windows 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 (clouds, rain, snow, etc.) that transfer a great deal of energy from the surface to the higher levels of the Atmosphere.
For those who may have missed my previous posting, here is my Sunlight Energy In = Thermal Energy Out animated graphic that depicts the Atmospheric “greenhouse effect” process in a simlified form.
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 Emissions Spectra 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 ones 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.
can you state how you generated the radiance curves for each temperature? Typically these type of figures have a fudge factor to correct for the black/white body fraction. I have never believed that one is allowed to do this from first principles.
Ira,
That is a terrific presentation.
Most interested people lose interest if an article gets too scientific and complicated.
You are fast becoming our new Isaac Asimov. [especially for GHG theory]
Thanks to you and Anthony for this.
Dr. Glickstein, I greatly appreciate your efforts, as well as those commenters who have made constructive criticisms.
In what I hope is one of the latter, I, too, will cast my vote against the electric-blanket analogy.
If someone could just toss up a link to a spectrum at 800 mbar in the tropics pointing sideways so we could just blow everyone’s mind quickly and hopefully be able to rebuild what’s left outside of this insidious AGWphysics this time. ☺
Fourier’s law of heat diffusion reigns when outside the windows frequencies in the bulk of the lower atmosphere, on both sides of the spectrum. You should not have brought in “back radiation” there unless you are only speaking of the lower 100 meters or so. The term back radiation has it’s place but it is only meaningful within the window wavelengths and mainly in relation to clouds, their BB radiation near 10 µm beams down the window to warm the ground on cloudy nights (and days, but not apparent). Within the thick of the atmosphere, all radiation outside the window can be properly viewed a fast, long-range conduction, that simple. Why? The atmosphere is all but totally black to these frequencies and most radiation only travels mere meters before re-absorption. That’s my current take, and still evolving though quickly now.
Ira, E for effort. I had high hopes as you began this whole series that you were going to be more open and all here could move a notch closer in truly understanding radiation’s relations within the atmosphere. You have many points exactly correct, and your animations can be deemed correct too, but only with the correct limitations and factors applied in the surrounding words. But beyond that, the whole story-line gets off of the track, IMO.
“Well, if a piece of blueberry pie has gone missing, and little Johnny has blueberry juice dripping from his mouth and chin, and that is pretty good circumstantial evidence of who took it.”
This is why climate scientist ought not dabble in police work I think, for what if Charles was the one who nicked the piece and in passing Johnny smeared him blue with it?
But essentially the dissipation is 360˚ but mostly, naturally, concentrated at the nap of the earth, just like the stove which will burn if ones hand is too close but the farther away the hand gets the colder it gets, to the point of room temperature, the in between GHGs doing absolutely next to nothing to transfer the heat to that further away location due to it’s own dissipation rate even though the GHGs are pre-heated by being inside the house as well. But of course, eventually, the stove’ll raise the temperature in the kitchen, but only when the floor, ceiling, and the walls are more radiant, but only to a certain point (unless the stove doesn’t burst into flames the paint on the farthest wall ain’t gonna start cooking any time soon.) So whom is the construct of the thief that steals that heat? :p
Ira, read the following http://climategate.nl/wp-content/uploads/2011/02/CO2_and_climate_v7.pdf which is the basis of a presentation by Dr (Ir) Noor Van Andel to KNMI in February and based on real measurements. Then, think again. -Incoming radiation to the sea surface from the sun controlled by cloud cover, evaporation at the sea surface, convection and pressure changes causing air movements, ToA radiation to space.
Dr Van Andel is a chemical engineer who has developed efficient heat exchangers for use with air see here http://www.xs4all.nl/~fiwihex/english/ Look at some of the links if you want some information on heat transfer theory.
tallbloke says:
March 10, 2011 at 4:26 am
“the hot-water bottle effect”
But what does heat the bottle, in the first place?
It is not “green-house effect”.
http://es.scribd.com/doc/28018819/Greenhouse-Niels-Bohr
Joe Lalonde says:
March 10, 2011 at 4:49 am
First, without planetary rotation, there is no convection
But….what does the Earth rotate…..an homopolar motor?
Then….heat by resistance?
How do we measure re-emittance of IR? I know absorbtion can be measured.
We live in an upside down world.
Water vapor makes up anywhere from 1-4% of the atmosphere. I can’t find the average because the percentage is so variable. CO2 is .04% of atmosphere. So water vapor is about 100x more plentiful than CO2 in atmosphere. Do anyone know the difference between the strength of CO2 vs WV as a greenhouse gas. Also, we know CO2 gets saturated in its’ greenhouse gas ability. Does this happen to WV? Then we know that man only creates 3% of the atmosphere CO2, well we don’t really know that, it’s just another big guess/estimate. How could we know that when we have forests densities completely changing throughout our world. Here in the US our forests are growing at a very fast rate, still recovering from the clearcuts of >100 yrs ago.
Then we have a possible feedback between CO2 and WV. Is it positive or is it negative? IPCC and modern “science” says CO2 always causes a positive increase in WV, causing amplification of greenhouse effect. But measurement of humidity and water vapor apparently doesn’t show this to be reality.
http://www.climate4you.com/GreenhouseGasses.htm, in fact WV is decreasing the last few years.
Then of course we have the oceans and their cylces, the sun and planetary alignment, undersea volcanoes etc etc etc. But THEY know everything. The SCIENCE is settled.
Yet after 11 years of increasing CO2 and amplification models, their data shows we are back where we started from in temperature with no trend whatsoever.
http://www.woodfortrees.org/plot/hadcrut3vgl/from:1999
We don’t know nothing about climate!
1 – Ira has presented us with curves showing the measured values of upward and downward radiation.
2 – One of the graphs shows the energy leaving the planet. The only way energy can leave the planet is by radiation.
3 – The other graph shows radiant energy arriving at the surface in the far infra-red region of the spectrum. Most of this energy is radiated by the atmosphere. It is explained by the heating of the atmosphere by the sun and by heating of the atmosphere caused when the atmosphere is heated by radiation, conduction, evaporation, etc. from heat leaving the surface of the planet.
4 – Under some conditions, upward radiation probably explains most of the heat leaving the surface. The graph comparing Barrow with Nauru is pretty dramatic. There isn’t a lot of heat from the atmosphere beaming down on Barrow. 😉 There also isn’t a lot of heat moving up through the atmosphere in the form of thunder storms in Barrow in November (when the graph was created). Most of the heat leaves Barrow as radiation and little of it heats the atmosphere and returns as back radiation in the range between 13 um and 8 um. (It looks like much/most of it comes back around 15 um.)
On the other hand, the effect of thunderstorms in tropical regions is huge. Evaporation takes heat from the surface and deposits it higher in the atmosphere. From there it can be carried elsewhere or be radiated.
5 – For those who doubt that back radiation exists, consider this: Infra-red radiation is electromagnetic radiation. It is the same as radio waves and light. Here are two examples of radiation from a weaker source going toward a stronger one: a) If I stand with my back toward the sun, I will be able to see a flashlight being shone at me. Nothing about the sun’s radiation will prevent the radiation from the flashlight from reaching me. b) If I stand near a strong radio transmitter, I can still tune in weaker transmitters. Nothing about the stronger transmitter’s signal prevents the weaker signal from getting to me. The net energy flux will still be from the stronger source toward the weaker one. It is a net flux though, in other words, the net flux is the difference between the two signals.
6 – The discussion totally ignores heat removed from the tropics by ocean currents and moved toward the poles. The effect of that heat is also huge. Compare, if you will, the climate of Regina Saskatchewan and London England. In the winter, Regina is a lot colder than London in spite of the fact that London is somewhat further north. The average low January temperature in London is 2.4 deg. C. In Regina, the same figure is -21.6 deg. The difference is entirely explained by heat transported by the ocean.
7 – Ira’s article made stark the difference between a tropical humid atmosphere and an arctic dry one.
8 – Many commenters might spend more time carefully reading Ira’s article and less automatically gainsaying it on the basis of any preconceived notions they may have. It is what it is. It explains one aspect of climate science and doesn’t pretend to be encyclopedic. My only quibble is that it leaves the impression that most of the heat in the atmosphere is caused by radiation.
william gray says:
March 10, 2011 at 5:16 am
How do we measure re-emittance of IR? I know absorbtion can be measured.
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You should be able to get pretty close by taking a spectrum at say 800 mbar in the tropics aimed sideways at night. ☺ That’s the only way I can think of doing it. Wouldn’t that be close?
Ira
I applaud your efforts, but you should start off with the simplest case first.
The Tropical western Pacific spectrum is not fixed. You have presented a simple snapshot of of it, I believe. Or is it an average? I don’t see any definition here of what that spectrum really means.
The tropics are EXTREMELY dynamic from a radiational heat transfer point of view. The absorption, transmission, and reflections, are constantly shifting due to water vapor. Everything changes from moment to moment, and it can be drastic. Just imagine lying on a beach on a sunny day, and a thick cloud passes overhead. The temperature you feel on your skin immediately plunges. That’s an immediate change in radiational heat transfer. Those curves you present are actually dancing around dramatically.
Even Barrow, Alaska is a rather complex situation.
I suggest trying to model and understand the interior Antarctic Polar region (Amundsen-Scott, Vostok, etc) first from a radiational heat transfer point of view. There is virtually no water in the atmosphere there. It is dominated by radiational heat transfer. And there are reliable surface temperature data, as well as documented of increased CO2 from 1957 to data.
You have to learn how to simply walk before you can dance the tango with its infinite complexities and beauty.
Ira,
You should stop saying the greenhouse gases in the atmosphere warm the earth to this crowd. Too may engineers running around here. The atmosphere slows the rate at which the earth loses energy to deep space. Thus, the earth in the sun-earth-space system has a higher equilibrium temp. The “old” rules of thermodynamics still apply: a warm object cannot gain net thermal energy from a cold object.
Thank you for posting the good data though, especially of the IR toward and away from earth at the arctic. I am curious what the ground temperature was on the days that this data was collected, since at the arctic you often have an inverted lapse rate and the atmosphere could indeed “heat” the ground. I am curious if the ground temps are cold enough at the poles, and the lapse rate is positive instead of negative, so that the atmosphere could indeed “heat” the Earth, at least in these specific conditions and locations.
After reading all the comments I am, again, uncertain.
There are so many contradictory statements about frequency and wavelength, heat transfers, conduction, radiation etc., etc., …….
Has anyone presented a theory based on photons?
I know……… stupid question
Sorry but this article is filled with misinformation.
“Perhaps a better analogy would be an electric blanket that, in addition to its insulating properties, also emits thermal radiation both down and up.”
no a much better analogy is a blanket. There is no additional heating coming from the atmosphere.
They seem to give out degrees and doctorates in corn flakes boxes these days.
I too have been enjoying your articles. From prior posters, I thought of an additional analogy. Consider traffic flow over a section of road. The number of vehicles in the section being monitored represents joules. Joules are constantly entering the section at one end- radiation from the sun, and leaving at the other end-outgoing raiation cooling off the earth. Now, thanks to greenhouse gases, suppose there’s a traffic accident or a road construction crew closing one of the outgoing lanes The amount of traffic coming into the intersection-radiation from the sun, continues at the same rate, but the outflow due to fewer exit lanes results in a buildup of traffic- joules, in the system.
Note the NET effect is not a warming from the sky, which tends to confuse some posters here, but a constriction of outgoing radiation and a buildup of heat from the sun.
As in virtually all such articles focusing on longwave emissions/apsorption/etc, no account is given for the effect of the oceans which are the main determinant of global temperatures on this planet. The oceans absorb the vast majority of solar radiation on this planet and they do so to a considerable depth. Water is a relatively slow conductor of heat and therefore tends to hold it for a good length of time. Ocean currents and temperature layering cause the heat to move from the equator to the poles. Atmospheric temperatures in the tropics are nearly what one would expect from a black body analysis. The so called “green house effect” is really only visible at higher latitudes. This is due almost entirely to the redistribution of heat by the oceans. Atmospheric effects are quite small in comparison. This is not a new idea. until a few years ago oceanic scientists such as Doctor Robert Stevenson could have described all of this in considerable detail. Unfortunately, “climate scientists” with a poor understanding of the influence of the oceans have completely ignored it.
Ira, there’s a problem here. as P. van der Meer says at 3:15 am. The blackbody curves are showing a peak at about 18 micron when they should be peaking at about 10 micron for a 300K blackbody.
In fact, if you refer to your previous post ‘Visualising the Greenhouse Effect – Atmospheric Windows’, you have the peak correct at 10 microns.
So, the current graphs don’t make sense – unless I am missing something? I have looked at the source material and that appears to be wrong also.
Has anyone got an explanation for this?
tallbloke says: March 10, 2011 at 4:26 am
“….The greenhouse effect works by *SLOWING DOWN THE RATE THE EARTH COOLS AT*, by raising the altitude at which the atmosphere radiates to space . There is more than a semantic difference. Understanding it this way enables you to understand that it was reduced albedo 1979-1998 allowing more Solar energy to enter the oceans that caused the majority of the global warming at the end of the last millenium.
http://tallbloke.wordpress.com/2011/03/03/tallbloke-back-radiation-oceans-and-energy-exchange/
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Thanks for the link to your article. I was one of those who was arguing similar points with Willis and I have not seen your article before today. It is an interesting read.
I too respect Willis’ views but he was unable to even begin to explain the physics involved in how heat could be entrained by the oceans given the wavelength of DLR and its penatrative depth and thus become well mixed.
The only point he came up with (which did not answer the question) was that but for GHGs, the oceans would freeze and he referred to a link on scienceofdoom which suggested that without GHGs, the oceans would freeze within about 4 years. The underlying data and codes were not attached to the scienceofdoom article so that that assessment could not be verified. However, as I tried to point out to Willis, it is too simplistic looking at average temperatures and average conditions. The oceans are extremely complex and act as both a huge storage reservoir and a huge heat pump. For example, if one looks at the Baltic, in late summer, the sea temp is 16 to 18C and yet within about 4 months, it freezes over notwithsanding GHGs. There are many parts of the oceans (and inland lakes/seas) that freeze within months and this will tend to give the impression that when viewed on an average basis the seas would freeze within years. However, of course, there are great swathes of the Pacific, Indian Ocean, Atlantic etc receiving immense amounts of solar energy which energy is then pumped around by currents etc. It is almost certainly the case that it is this input and distribution that stops the majority of oceans from freezing over within seasons. Further, one may enquire rhetorically as to what causes the ice to melt/recede on these frozen seas/lakes? It is not an increase in GHCs but rather an increase in solar energy either directly and/or indirectly (via currents/circulation patterns).
I consider it probable that the vast majority of recent warming is due to natural variations and one of the key contenders for this being changes in cloud cover and changes in albedo allowing more solar energy to have penatrated the oceans.
I’ve been working with a combination of the reanalysis data and CO2 data to quantify the relative effects of atmospheric water and CO2 on OLR from the top of the atmosphere (click on my name). I think that a better approach would be to consider the average optical thickness of that blanket of atmosphere. First estimate the temperature at the top of the atmosphere using the S-B law. Then using skin surface temperature (SST) and lapse rates to calculate average optical thickness. (wet in the tropics and dry near the poles). Regress the calculated thickness on precipitation rate, precitatable water, and CO2. This method measures the effects of non-radiative processes of energy transfer as well as the “greenhouse effect”. (the formation of clouds, rain, and snow). You will find that any minor effect of CO2 is lost in the variability in the combination of effects of atmospheric water (vapor, clouds, rain, and snow).
Scarlet Pumpernickel says:
March 10, 2011 at 3:30 am
So what concentration of CO2 saturates these wavelengths?
There is already proof from Venus that the Greenhouse effect is not exponential http://theendofthemystery.blogspot.com/2010/11/venus-no-greenhouse-effect.html
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Thanks Scarlet, one impressive analysis. Also since NASA lists Venus’s *average* temperature at 464 C and if the surface was as high as 505 C then the natural dry lapse rate matches the graviation acceleration almost exactly, as it should. (778K-339K)/49.5km = ~8.87 °C/km (g=8.87 m/s2). Neat, 96.5% CO2 and no greenhouse effect at all. Now that’s some pure simple logic!
But the radiation from the Sun has an even smaller wavelength. How come solar radiation can heat the Earth but re-emitted radiation?
funny all this blanket stuff, we know that without greenhouse gases the surface can get very hot during the daytime – the moon, though at night leads to rapid cooling.
Seems to me that greenhouse gases lead to cooling during the day, and at night leads to a slow cooling , or in the desert, rapid due to less moisture.
After all if the sun didn’t come up next day how quick before the planet froze.
Such a simple elegant explanation.
The commentary for this article is pure gold. Mr. Watts, please continue a series of posts on basic planetary science processes; I’m very eager to see what your readership can come up with. I’d love some insight on, for example, how the Coriolis effect really works.
I suggest we rid the atmosphere of o2 also. I mean it has this fat absorption/emission band at 50-70 GHz. One cannot be too careful you know.