Guest Post by Ira Glickstein
Solar “light” radiation in = Earth “heat” radiation to Space out! That’s old news to those of us who understand all energy is fungible (may be converted to different forms of energy) and energy/mass is conserved (cannot be created nor destroyed).
My Visualizing series [Physical Analogy, Atmospheric Windows, Emission Spectra, and Molecules/Photons] has garnered almost 2000 comments, mostly positive. I’ve learned a lot from WUWT readers who know more than I do. However, some commenters seem to have been taken in by scientific-sounding objections to the basic science behind the Atmospheric “Greenhouse Effect”. Their objections seemed to add more heat than light to the discussion. This posting is designed to get back to basics and perhaps transform our heated arguments into more enlightened understanding :^)
As I’ve mentioned before, during my long career as a system engineer I’ve worked with many talented mathematical analysts who always provided precise results, mostly correct, but some precisely wrong, usually due to mistaken assumptions. I got into the habit of doing a “back of the envelope” calculation of my own as a “sanity check” on their results. If their results matched within reasonable limits, I accepted them. If not, I investigated further. In those days my analysis was really done using a slide rule and scrap paper, but I now use spreadsheets.
The graphic above is based on an excellent spreadsheet from http://serc.carleton.edu/files/introgeo/models/mathematical/examples/XLPlanck.xls. It uses Planck’s Law to calculate the black body radiation spectrum from the Sun, as observed at the top of the Earth’s Atmosphere. It also may be used to calculate the radiation spectrum from the Earth System (Atmosphere and Surface, see below for explanation) at any assumed temperature. (I will refer to this spreadsheet as “Carleton” in this posting.)
I modified the Carleton spreadsheet to compute the mean Solar radiation per square meter absorbed by the Earth System, which turns out to be 240 Watts/m^2. I then used the spreadsheet to determine the effective mean temperature of the Earth System that would emit an equal amount of energy to Space, and that turned out to be 255 Kelvins (-18ºC which is 1ºF).
Since the mean temperature at the surface of the Earth is 288 Kelvins (+15ºC which is 59ºF), that leaves 33 Kelvins (33ºC which is 58ºF) to be accounted for. Guess how we acount for it?
The yellow curve (above left) shows that Solar radiation is in a tall, narrow “shortwave” range, from about 0.1μm (microns, or millionths of a meter) to about 4μm, which we call ultra-violet, visual, and near-infrared. The vertical axis is Intensity of the radiation, measured in Watts/m^2/μm, and the horizontal axis is Wavelength, measured in μm. If you divide the area under the yellow curve into vertical strips, and add up the total area, you get 240 Watts/m^2.
Since we humans sense the visual portion of this radiation as “light”, that is the name we give it, and that has led to the false assumption that it contains no “heat” (or “thermal”) energy.
The violet curve (above right) shows that, assuming a mean temperature of 255 K, Earth System radiation to Space is in a squat, wide “longwave” range, from about 5μm to beyond 40μm, which we call mid- and far-infrared. If you divide the area under the violet curve into vertical strips, and add up the total area, you get the same 240 Watts/m^2 as is under the yellow curve.
DETAILED EXPLANATION
The graph on the left shows the actual observed Solar radiation spectrum (in red) as measured at the top of the Atmosphere. It is superimposed on a black body model (in blue) showing very good correlation. Thus, while the Sun is not exactly a black body, it is OK to assume it is for this type of “sanity check” exercise.
If you calculate the area under the curve you get about 1366 Watts/m^2. That means that a square meter of perfect black body material, held perpendicular to the Sun, would absorb 1366 Watts.
However, the Earth is not a perfect black body, neither is it a flat surface perpendicular to the Sun! So, to plot the yellow curve at the top of this posting, I had to adjust that value accordingly. There are two adjustments:
- The Earth may be approximated as a sphere, with the Sun shining on only half of it at any given time. The adjustment factor for this correction is 0.25.
- The albedo (reflectiveness) of the Earth system, primarily clouds and light-colored areas on the Surface such as ice, causes some of the Solar radiation to be reflected back out to Space without contributing any energy to the Earth System. The adjustment factor for this correction is 0.7.
After applying these adjustments, the net Solar energy absorbed by the Earth System is 240 Watts/m^2.
The graph on the right shows the black body model for an Earth System at a mean temperature of 255 K, a temperature that results in the same 240 Watts/m^2 being emitted out to Space.
Of course, the Earth System is not a perfect black body, as shown by the graph in the upper panel of the illustration below, which plots actual observations from 20 km looking down. (Adapted from Grant Petty, A First Course in Atmospheric Radiation, Figure 8.2, http://www.sundogpublishing.com/AtmosRad/Excerpts/index.html.)
The actual measured radiation is the dark squiggly curve. Note that it jigs and jags up and down between the topmost dashed curve, which is the black body spectrum for a temperature of 270 K and a lower dashed curve which is the black body spectrum for 230 K. This data was taken over the Arctic, most likely during the daytime. The Petty book also has a graph looking down from over the Tropical Pacific which ranges from 300 K down to 210 K. Observations will vary by tens of degrees from day to night, summer to winter, and Tropical to Polar.
However, it is clear that my result, based on matching 240 Watts/m^2, is within a reasonable range of the true mean temperature of the Earth System as viewed from Space.
NOTE ABOUT THE ABOVE ILLUSTRATION
WUWT readers will notice some apparent inconsistencies in the graphs above. The top and bottom panels, from Petty, peak at 15μm to 20μm, while the purple, blue, and black curves in the middle panel, and the Earth System curves from the Carleton spreadsheet I used (see above) peak in the 9μm to 11μm range. Also, the Petty black body curves peak at a “Radiance” around 100 mW/m^2/sr cm^-1 while the black body curves from Carleton peak at an “Intensity” of around 14 W/m^2/μm. Furthermore, if you look closely at the Petty curves, the labels on the black body curves are mirror image! What is going on?
Well, I know some of the reasons, but not all. (I hope commenters who are more fluent in this than I am will confirm my explanations and provide more information about the differences between “Radiance” and “Intensity”.) I have Googled and Wikied the Internet and am still somewhat confused. Here is what I know:
- The horizontal axis in Petty’s plots are what he calls “Wavenumber”, increasing from left to right, which is the number of waves that fit into a cm (centimeter, one hundredth of a meter).
- This is proportional to the frequency of the radiation, and the frequency is the inverse of the wavelength. Thus, his plots are the mirror image of plots based on wavelength increasing from left to right.
- The spreadsheet I used, and my previous experience with visual, and near-, mid-, and far-IR as used in military systems, always uses wavelength increasing from left to right.
- So, when I constructed the above illustration, I reversed Petty’s curves, which explains why the labels on the black body curves are mirror image.
- Fortunately, Petty also included a wavelength legend, which I faithfully reproduced, in non-mirror image, at the top of each plot.
But, that still does not explain why the Petty black body curves peak at a longer wavelength than the Carleton spreadsheet and other graphics on the Internet. I tried to reproduce Petty’s blackbody curves by multiplying the Carleton values by the wavelength (μm) and that did not move the peak to the right enough. So, I multiplied by the wavelength again (μm^2) and, voila, the peaks agreed! (I hope some WUWT reader will explain why the Petty graphs have this perverse effect. advTHANKSance!)
ANSWERING THE OBJECTIONS TO BASIC ATMOSPHERIC “GREENHOUSE EFFECT” SCIENCE
First of all, let me be clear where I am coming from. I’m a Lukewarmer-Skeptic who accepts that H2O, CO2 and other so-called “greenhouse gases” in the Atmosphere do cause the mean temperature of the Earth Surface and Atmosphere to be higher than they would be if everything was the same (Solar radiation, Earth System Albedo, …) but the Atmosphere was pure nitrogen. The main scientific question for me, is how much does the increase in human-caused CO2 and human-caused albedo reduction increase the mean temperature above what it would be with natural cycles and processes? My answer is “not much”, because perhaps 0.1ºC to 0.2ºC of the supposed 0.8ºC increase since 1880 is due to human activities. The rest is due to natural cycles and processes over which we humans have no control. The main public policy question for me, is how much should we (society) do about it? Again, my answer is “not much”, because the effect is small and a limited increase in temperatures and CO2 may turn out to have a net benefit.
So, my motivation for this Visualizing series is not to add to the Alarmist “the sky is falling” panic, but rather to help my fellow Skeptics avoid the natural temptation to fall into an “equal and opposite” falsehood, which some of those on my side, who I call “Disbelievers”, do when they fail to acknowledge the basic facts of the role of H2O and CO2 and other gases in helping to keep temperatures in a livable range.
Objection #1: Visual and near-visual radiation is merely “light” which lacks the “quality” or “oomph” to impart warmth to objects upon which it happens to fall.
Answer #1: A NASA webpage targeted at children is sometimes cited because they say the near-IR beam from a TV remote control is not warm to the touch. Of course, that is not because it is near-visual radiation, but rather because it is very low power. All energy is fungible, and can be changed from one form to another. Thus, the 240 Watts/m^2 of visible and near-visible Solar energy that reaches and is absorbed by the Earth System, has the effect of warming the Earth System exactly as much as an equal number of Watts/m^2 of “thermal” mid- and far-IR radiation.
Objection #2: The Atmosphere, which is cooler than the Earth Surface, cannot warm the Earth Surface.
Answer #2: The Second law of Thermodynamics is often cited as the source of this falsehood. The correct interpretation is that the Second Law refers to net warming, which can only pass from the warmer to the cooler object. The back-radiation from the Atmosphere to the Earth Surface has been measured (see lower panel in the above illustration). All matter above absolute zero emits radiation and, once emitted, that radiation does not know if it is travelling from a warmer to a cooler surface or vice-versa. Once it arrives it will either be reflected or absorbed, according to its wavelength and the characteristics of the material it happens to impact.
Objection #3: The Atmospheric “Greenhouse Effect” is fictional. A glass greenhouse works mainly by preventing or reducing convection and the Atmosphere does not work that way at all.
Answer #3: I always try to put “scare quotes” around the word “greenhouse” unless referring to the glass variety because the term is misleading. Yes, a glass greenhouse works by restricting convection, and the fact that glass passes shortwave radiation and not longwave makes only a minor contribution. Thus, I agree it is unfortunate that the established term for the Atmospheric warming effect is a bit of a misnomer. However, we are stuck with it. But, enough of semantics. Notice that the Earth System mean temperature I had to use to provide 240 Watts/m^2 of radiation to Space to balance the input absorbed from by the Earth System from the Sun was 255 K. However, the actual mean temperature at the Surface is closer to 288 K. How to explain the extra 33 K (33ºC or 58ºF)? The only rational explanation is the back-radiation from the Atmosphere to the Surface.
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How do scientists determine what the average temperature for the whole globe is anyway? – It seems to me to be pure guesswork, or maybe it is a “comparison-standard to work by”, i.e. one standard set by taking the temperatures at x numbers of stations y number of times each year.
I just took some quite random temperatures, – or rather – I found them on my favourite weather site Yr.no
Tomorrow the temperature on the North Pole is supposed to be minus (-) 2 °C, and on the South Pole – 61 °C. In Death Valley + 35 °C and in a place called Azebe (in the Gabon – very close to the Equator and at an elevation of 18 m.) it was to be +28 °C.
Now then if you take the average of those few temperatures you are not going to find yourself too far away from zero °C. However if I substitute The Death Valley + 35 °C with another one, this time from Quito in Ecuador which – just like Azebe is very close to the Equator but this time the elevation is 2108 meter (m). The Quito temperature however is to be 17 °C. So, why is an average temperature of – 18 °C unsuitable for us mammals?
And of course “My Average” is obviously not right but that could equally go for anybody else’s. – Pray tell me who has got a record of every temperature for every spot on Earth for a constant period of the past 150 years.
(Hands up those who have heard Azebe and Quito before)
Robert Clemenzi:
Hottel’s paper with Mangelsdorf was entitled ‘Heat transmission by radiation from non-luminous gases. Experimental study of carbon dioxide and water vapour’. Emissivities were evaluated experimentally based on direct measurement of total emission for a number of gases including CO2 and water vapour; these gases absorbed in certain regions of the IR spectrum and this was the data which was used.
Robert Clemenzi:
Robert Stevenson says: I use “Principles of Heat Transfer” by Krieth, 1958 (4th printing June 1961) which has 6 pages on Hottel’s methods. Perry’s Chemical Engineers’ Handbook (7th Edition 1997) has a section 5 ‘Heat and Mass Transfer’ written among others by Hoyt C Hottel and Adel F Sarofim. I don’t know much this costs but you could probably get it out of the library. You can also write to McGraw Hill on technical queries, in the past I have had some very helpful replies after spotting some errors in texts.
It looks like even Joel Shore has given up n these pages now, which means life – for me – is getting a bit less interesting.
I, of course, – have no ill feelings or aggravated “Blood Pressure problems” just because I disagree with those who “believe” in what is called “The Greenhouse Theory”. –
After all the theory is good and convincing – which it should be – as it has been “honed and fitted” to suit all new climate evidence – as it emerges.
However as I am not “The Naturally Born Orator” I cannot convince you all that there is something wrong with any statements from the state of Denmark or from the “Copenhagen Treaty 2009”
Suffice to say that if “all objects that have a temperature higher than 0 Kelvin (K) must emit thermal radiation – (Basic Stuff)- . Then, – if it is basic stuff – why do Nitrogen, Oxygen and Argon not radiate anything at all towards the Earth’s surface?
Well, oxygen does absorb and emit towards the Surface in the ~10μm range, as shown in the Petty graphics in my earlier topic http://wattsupwiththat.com/2011/03/10/visualizing-the-greenhouse-effect-emission-spectra/
Have a close look at the surface looking up and you will see the oxygen/ozone signature as a bump in the ~10μm range and a corresponding “bite” taken out of the Space looking down curve in the same area. N2 has a signature around the ~4μm range, I believe, which is outside the range of the Perry curves. As for Argon, I am not sure, but I do believe that all materials above 0 Kelvin do absorb and emit radiation at some wavelengths.
I finally got around to reading the Postma paper in detail and I found it intriguing!
The most impressive part is where Postma (pages 20-21) derives the adiabatic lapse rate by considering that the total energy of a parcel of air is the sum of its thermal energy (a function of its heat capacity multiplied by its temperature in Kelvins) plus its potential energy (a function of its height above the Surface). Reasoning that the total energy remains constant, he differentiates the equation and uses the result to calculate the correct adiabatic lapse rate which is about 9.8K/km (Kelvin per kilometer) for dry air and about 6.5K/km for moist air. Using that lapse rate, he correctly calculates the mean Surface temperature of 14.5ºC.
Prior to reading that part of his paper in detail, I (and seemingly other commenters) had incorrectly assumed Postma was simply assuming that the well-known rise of temperature that occurs when air is compressed (and drop in temperature when it is de-compressed) was the cause of the 33ºC temperature rise we attribute to the Atmospheric “greenhouse effect”.
If anyone more knowledgeable than I (such as Joel or Dave or Tim, etc.) is still following this thread, now at over 930 comments which is a near record for WUWT, I would appreciate it if they would properly debunk Postma’s explanation, which seems to me to be “putting the cart before the horse”.
Earlier in his paper, Postma (page 5) states: “If the source of light is constant, meaning it shines with the same unchanging brightness all the time, then the blackbody absorbing that light will warm up to some maximum temperature corresponding to the energy in the light, and then warm up no further. When this state is reached it is called ‘radiative thermal equilibrium’, which means that the object has reached a stable and constant temperature equilibrated with the amount of radiation it is absorbing from the source of light.”
While true, this seems to ignore the reason for the maximum temperature, which is that the black body has been radiating, according to T^4, all along as its temperature had been rising, and its temperature levels off at the point that the incoming radiation equals the outgoing. In other words Postma “puts the cart before the horse” ignoring the direction of causality.
This is confirmed when he later says (also page 5): “When a blackbody has reached thermal equilibrium, it can no longer absorb more light for heating and therefore has to re-emit just as much light-energy as it is absorbing. Because the blackbody can‟t just reflect the light, it has to re-emit it as thermal radiation.”
Later in his paper (pages 27 to 28) he raises total misconception of the role of CO2 and other so-called “greenhouse gases” in the Atmospheric “greenhouse effect”. He says (again correctly) that, if the vacuum of a thermos is replaced by CO2, the hot liquid in the thermos will cool faster. That, he thinks (incorrectly) proves that “CO2 does not ‘trap’ any radiative heat” in the Atmosphere. Of course, a Thermos bottle works by blocking both convection and conduction (by the vacuum) and radiation (by metalic coating), so the comparison is totally misleading.
Still later (page 29) he gives the also misleading example that adding even a large quantity of 5ºC water (which, since it is way above the absolute zero of -273ºC contains a great deal of thermal energy) to a bathtub of water that is at 40ºC, will not raise its temperature. On the other hand, he notes that even a tiny bucket of water at a bit over 40ºC will raise the temperature of the tub, at least a little bit. Again correct, but absolutely no evidence against the ability of downwelling radiation from the Atmosphere to the Surface to cause the Surface to be warmer than it would be absent the “greenhouse gases”.
These two “red herring” examples, and his earlier “cart before the horse” indicate to me that Postma either does not properly understand the Atmospheric “greenhouse effect” -or- that he is misusing his knowledge of physics to “pull our leg” in a practical joke.
Concerning Postma – http://www.globalwarmingskeptics.info/forums/attachment.php?aid=327
It should be pointed out immediately that the “Greenhouse Effect” is indeed a theory – it is not a benign empirical fact, such as the existence of the Sun, for example.
Baloney – By definition, the Greenhouse Effect is what makes the surface of the Earth different than the surface of the Moon. Immediately below that statement, he provides a *gravity* analogy – gravity is an observed fact, the theory is in how it works. I suggest that the Greenhouse Effect is identical, the difference between the Earth and the Moon is an observed fact – the theory is in how it works.
As a result, he makes the mistake of assuming that there is only one Greenhouse Effect theory. There are, in fact, many.
On page 6, he misses the point when describing blackbodies.
the blackbody is already in radiative thermal equilibrium with a hotter source of energy
That is simply wrong – That might be true if the blackbody was surrounded by a perfect insulator but is definitely not true for planets in space. In that case, the blackbody is in radiative thermal equilibrium with a hotter source of energy and with the cold microwave background radiation.
Next he suggests that adding a mirror can not make the blackbody hotter. Again, he misses the point that the mirror shields the blackbody from the cold of space. This is even more important when a planet is rotating.
You cannot make something warmer by introducing to it something colder
Absolutely true. However, the mirror is effectively warmer than what is available without the mirror.
Kirchhoff’s Law of Thermal Radiation … states: “At radiative thermal equilibrium, the emissivity of a body equals its absorptivity.”
Wrong – that statement is true for each individual frequency, but not for the body as a whole.
For Ira – He completely messes up the bit about lapse rates. As you said, he has the DALR correct, but the rest makes no sense. He obviously missed the fact that the troposphere is much warmer than predicted by the DALR.
Additionally, the direction of heat flow is always only from hot (the ground), to cold (upper atmosphere),
Everyone should look at the lapse rate over Antarctica – during the winter (night), the atmosphere is ALWAYS warmer than the surface. The only reason the surface stays so “warm” at night is because of back radiation from the warm atmosphere to the cold ground.
Infrared energy leaves the atmosphere in only a few milliseconds
If that were true, the atmosphere would drop significantly below freezing every night. Everywhere.
There are numerous additional errors in the last few pages .. such as the repeat of his bucket analogy (p29). I agree that adding a 5C bucket of water will not warm a 40C tub of water. However, to complete the analogy, he needs to compare the results to adding a -273C bucket of water. In that case, there is a real difference in the final average temperature of the two experiments.
Ira says:
If anyone more knowledgeable than I (such as Joel or Dave or Tim, etc.) is still following this thread, now at over 930 comments which …
Didn’t think Joel was very knowledgeable, he hasn’t said anything sensible yet.
Robert Clemenzi seems to have a clear mind on the physical world. Here are some comments on Roberts analysis of Postma’s paper:
Greenhouse Effect – check! There are many theories.
A blackbody in equilibrium – check! Does not imply equilibrium at all, overall radiative equilibrium is but one possible state.
On the mirror – check, but, in the case with space on the backside of the mirror the planet side would be warmer of course, BUT, the space side would also be equally cooler, shielded from the warm planet. It’s called radiative insulation, like aluminum radiative barrier in homes. Both sides of this effect must always be accounted for.
You cannot make something warmer by introducing to it something colder – check!
Kirchhoff’s Law of Thermal Radiation – check on each frequency, but I would add to the statement: “but not for the body as a whole UNLESS ALL individual frequencies are also in radiative thermal equilibrium”. I’m sure that was just a slip.
Lapse rates – can’t compare yet – hasn’t jelled for me.
Infrared energy leaves the atmosphere in only a few milliseconds – check, I agree, no! Five-sixth by simple geometry is colloquially ‘trapped’ in either the case of conduction OR radiation if the mean free path is rather small in comparison to the scale of the entire system.
Follow Robert Ira. I concur with him point by point.
You are certainly entitled to your opinion, Robert Stevenson, but I disagree. Ever hear the expression “don’t throw the baby out with the bathwater?” Well, Joel, as what I would call a Warmist, has some opinions at variance with mine. However, in this thread and on others I’ve read here at WUWT, Joel has been remarkably restrained in the face of IMHO unjustified personal attacks and postings by commenters who have not read his previous explanations and simply -thoughtlessly- repeat their Disbeliever mantra. I congratulate Joel for not hectoring us here on his (again IMHO) mistaken belief in the dangers of modest increases in mean temperatures and CO2 levels. He, along with others whose opinions are closer to mine, have taught me much on this Blog and I thank them, one and ALL.
Ira Glickstein, PhD said on Visualizing the “Greenhouse Effect” – Light and Heat
May 29, 2011 at 8:04 pm
“…. I would appreciate it if they would properly debunk Postma’s explanation, which seems to me to be “putting the cart before the horse”.”
Alleyne replies:
Good to know you don’t have any pre-conceived ideas about this Ira 🙂 I too would like to hear some rational, factual, scientific discussion about it, but I have no vested interest in the outcome. This is not meant as a personnal attack, Ira, just an observation. I expect that it will turn out that both CO2 and adiabatic heating will prove to be mexhanisms in the atmosphere’s temperature profile. In systems as dynamic and complex as the atmosphere it rarely turns out that a single parameter accounts for everything.
Ira Glickstein, PhD said on Visualizing the “Greenhouse Effect” – Light and Heat
May 29, 2011 at 8:04 pm
Earlier in his paper, Postma (page 5) states: “If the source of light is constant, meaning it shines with the same unchanging brightness all the time, then the blackbody absorbing that light will warm up to some maximum temperature corresponding to the energy in the light, and then warm up no further. When this state is reached it is called ‘radiative thermal equilibrium’, which means that the object has reached a stable and constant temperature equilibrated with the amount of radiation it is absorbing from the source of light.” While true, this seems to ignore the reason for the maximum temperature, which is that the black body has been radiating , according to T^4, all along as its temperature had been rising, and its temperature levels off at the point that the incoming radiation equals the outgoing. In other words Postma “puts the cart before the horse” ignoring the direction of causality.
Alleyne replies:
I must disagree, though it may just be semantics getting in the way again, the reason for the maximum temperature is not that it has been radiating all along, but that it has reached radiative equilibrium. His statement makes no comment one way or the other as to the radiative state of the BB before it reaches equilibrium. Furthermore, perhaps I am misunderstanding, but the conclusion in your last sentence makes no sense to me. I really don’t see how he ignores the direction of causality which surely is from the source to the BB. The BB radiation doesn’t determine the energy level of the source, though it will determine the rate at which the source’s energy level will decrease. The cause of the BB radiation is obviously the energy from the source mediated by the BB Absorbtivity and Emissivity (which at certain wavelengths will be equal once radiative equilibrium is reached)
Ira Glickstein, PhD said on Visualizing the “Greenhouse Effect” – Light and Heat
May 29, 2011 at 8:04 pm
“This is confirmed when he later says (also page 5): “When a blackbody has reached thermal equilibrium, it can no longer absorb more light for heating and therefore has to re-emit just as much light-energy as it is absorbing. Because the blackbody can‟t just reflect the light, it has to re-emit it as thermal radiation.”
Again, I don’t understand what your point is or how you see this as putting the cart before the horse.
Ira Glickstein, PhD said on Visualizing the “Greenhouse Effect” – Light and Heat
May 29, 2011 at 8:04 pm
“Later in his paper (pages 27 to 28) he raises total misconception of the role of CO2 and other so-called “greenhouse gases” in the Atmospheric “greenhouse effect”. He says (again correctly) that, if the vacuum of a thermos is replaced by CO2, the hot liquid in the thermos will cool faster. That, he thinks (incorrectly) proves that “CO2 does not ‘trap’ any radiative heat” in the Atmosphere. Of course, a Thermos bottle works by blocking both convection and conduction (by the vacuum) and radiation (by metalic coating), so the comparison is totally misleading.”
I agree that this is a very poor example to use, though it would be an interesting experiment to run. Replacing the vaccuum with CO2 would no doubt reduce the conductive and convective insulation (ie increase conductive & convective heat loss) theoretically radiative heat loss should remain the same. An interesting question is whether the heat loss would be less than if the vaccuum were replaced with Nitrogen.
Ira Glickstein, PhD said on Visualizing the “Greenhouse Effect” – Light and Heat
May 29, 2011 at 8:04 pm
“Still later (page 29) he gives the also misleading example that adding even a large quantity of 5ºC water (which, since it is way above the absolute zero of -273ºC contains a great deal of thermal energy) to a bathtub of water that is at 40ºC, will not raise its temperature. On the other hand, he notes that even a tiny bucket of water at a bit over 40ºC will raise the temperature of the tub, at least a little bit. Again correct, but absolutely no evidence against the ability of downwelling radiation from the Atmosphere to the Surface to cause the Surface to be warmer than it would be absent the “greenhouse gases”.”
Agreed. But given that the presence of any gas will cause the surface to be warmer than it would otherwise be, all we are talking about is the slight amount of endogenous (if I can put it that way) warming from CO2, most of which has already occured.
The real question is whether climate feedbacks are positive or negative. In other words will the small amount of warming cause the powerful GHGs (like water vapour) to increase the amount warmed or is the climate system stable such that there are feedback mechanisms which works to dampen and/maintain the climate in a ‘steady state’. So far the evidence, as I understand it, seems to indicate that this is the case.
I would like to second your thanks to all those who have contributed positively to the discussion and specifically to Joel, Tim and Dave Springer who all helped me with my understanding of the way in which “back radiation” works.
I still have some reservations and thinking to do about that Trenberth diagram and the whole Postma thesis, but that is for another day.
As a person who spends quite a bit of time commenting online, this is my first experience with WordPress and I must say I find it very unwieldly to use. Firstly it is very difficult to search and find anything so even if one were inclined to try, it would be laborious and probably fruitless trying to find and read previous explanations. Secondly I find it awckward trying to reply online instead of from my inbox, which is more immeadiate and flexible – but then I guess that is just the way it is and no reflection on WUWT or the people here.
Ira Glickstein and others – there are many things about this I frankly do not understand.
1) As I mentioned on May 29, 2011 at 1:37 pm: “If it is correct that all objects that have a temperature above Zero Kelvin (0K) must emit energy by radiation, then why do Nitrogen, Oxygen and Argon not radiate anything at all towards the Earth’s surface?” And also why do these other 3 gases not seek equilibrium with GHGs?
2) I have no problem understanding that energy radiation from a warmer source can warm a cooler object (one that receives and absorbs that energy). Nor have I any problem with the idea that a colder object is radiating its energy towards a warmer one, – but, of course, – any reduction in cooling of that warmer object can then only take place at the side facing the cooler object.
Therefore I understand perfectly well that radiation from the surface can warm the atmospheric GHGs that absorb it. – What I can not understand however is this: “How can it even be considered possible that energy that was removed from the surface, by radiation in the first place, thus causing the surface to cool can ‘warm the original source’, i.e. the surface – just because some gas or other sends it all back.” – It seems perfectly reasonable to me that if we imagine the surface never emits that energy in the first place,- energy that is stored in the surface and just below, i.e. oceans, lakes, rivers, ground, and air, – just to mention a few, then any surface temperature change would be completely reliant on variations in Solar irradiation and advection mainly by Water Vapor (WV) but also by other GHGs that have the ability to contain more heat than the rest of the atmospheric gases. –
To my way of thinking “atmospheric heat can only be trapped, or slowed down, by a reduction in convection. –
In other words the atmosphere’s energy radiation back to space – is delayed.
The two lapse rates should smack you in the face – DALR is fixed – The Moist Adiabatic Lapse (MALR) rate is not. It varies (a scale is used) depending on the atmosphere’s moisture content.
The much belowed CO2, by the way, has not got a lapse rate of its own. (The MALR (Moist Adiabatic Lapse Rate) is also called the wet or saturated adiabatic lapse rate. It is the temperature trajectory a parcel of saturated air takes. The dry adiabatic lapse rate is a near constant of 9.8 C/km, however, the wet adiabatic lapse rate is much less of a constant. The wet adiabatic lapse rate varies from about 4 C/km to nearly 9.8 C/km.)
But, having said all that, I would like an answer from those who believe that GHGs supply the surface with additional heat, to explain why I am wrong.
I am now begging all you AGW enthusiasts to explain where I do go wrong. Because if you are right – then – I am WRONG.
–
Ira, having said all that, it does not matter much whether we agree or disagree on the correctness of the GHG theory.
However, I do not think it is impossible that if you agree with the theory that says CO2 rules our world’s well being,, then it may not be long before you admit that the melting of the North Pole will not liberate Siberian and other frozen landmasses but instead fry us all (on the top of the surface this time), unlike down below – as stokers of hell fires – as envisaged it just a few years ago
O H Dahlsveen says:
May 30, 2011 at 1:58 pm
Ira Glickstein and others – there are many things about this I frankly do not understand.
1) As I mentioned on May 29, 2011 at 1:37 pm: “If it is correct that all objects that have a temperature above Zero Kelvin (0K) must emit energy by radiation, then why do Nitrogen, Oxygen and Argon not radiate anything at all towards the Earth’s surface?” And also why do these other 3 gases not seek equilibrium with GHGs?
Your premise isn’t true, gases are not ‘objects’ and N2, O2 & Ar don’t emit in the IR due to the lack of a dipole.
Ira Glickstein says:
‘Joel’s mistaken belief in the dangers of modest increases in mean temperatures and CO2 levels. He, along with others whose opinions are closer to mine, have taught me much on this Blog and I thank them, one and ALL.’
This absurd fixation with CO2 as the sole driver of global warming is my main reason for blogging; even the BBC in their bulletins now speak of too much carbon in the atmosphere hoping that listeners will not realise the link with CO2 (the considerable benefits to plant growth are well documented).
The principal emission bands of CO2 and water vapour are as follows:
CO2 2.64 to 2.84 4.13 to 4.5 13 to 17 microns
Water vapour 2.55 to 2.84 5.6 to 7.6 12 to 25 microns
Because of its high concentration, water vapour absorbs to extinction first generation photons (hv) in the main waveband in 120m of traverse (as many contributors have pointed out) and CO2 absorbs very little, due to its small concentration.
This means that 63.3% (248Wm-2) of the 391Wm-2 emitted as LWIR radiant energy from the surface is absorbed by water vapour in 120m of traverse and the remainder 140Wm-2 leaves the atmosphere as it is transparent to it. Increases in CO2 have very little effect in this water vapour dominated environment as it is a very weak absorber.
Opposition to CO2AGW does not mean we do not care about the environment, we do and hate to see the rural landscape despoiled by ugly noisy wind farms for instance. These installations cost enormous sums but generate only a fraction of their installed capacity.
Ira,
Further to previous post – in the table I wanted to high light the spectral overlap between CO2 and water vapour in the main band thus:
Carbon dioxide – 13 to 17 microns
Water vapour – 12 to 25 microns
but it didn’t come out too well
Robert Stevenson says:
May 31, 2011 at 2:20 am
Ira,
Further to previous post – in the table I wanted to high light the spectral overlap between CO2 and water vapour in the main band thus:
Carbon dioxide – 13 to 17 microns
Water vapour – 12 to 25 microns
but it didn’t come out too well
Yeah, not particularly accurate either, a few weak spread out lines hardly constitutes ‘overlap’!
Your calculation of H2O absorption is way too high.
http://i302.photobucket.com/albums/nn107/Sprintstar400/H2OCO2.gif
Robert Stevenson said on Visualizing the “Greenhouse Effect” – Light and Heat
May 31, 2011 at 2:07 am
“Opposition to CO2AGW does not mean we do not care about the environment, we do and hate to see the rural landscape despoiled by ugly noisy wind farms for instance. These installations cost enormous sums but generate only a fraction of their installed capacity.”
Alleyne replies:
Not to get off topic, but I whole heartedly agree with you Robert. The damage to endangered species, habitat and biodiversity done in the name of ‘saving the planet’ by proponents of ‘Greed’ Energy is tragic.
They plan on installing almost 800 IWT in this area I live in which is in large part unspoiled habitat for Peregrines, Golden Eagles, Bald Eagles, Sand Hill Cranes as well as various species of endangered and threatened plants and reptiles. Some of these are recognized as species at risk and supposedly protected by any number of Provincial, Federal and International laws. Yet the Ministry is turning a blind eye in the name of so-called green energy (only thing green about it are the profits being made)
Phil, your spectracalc graphs are meaningless because they lack the
pressure, molar concentration, and path length
Graphs of a typical atmosphere show a very different picture. For one thing, the CO2 fine structure disappears because more than 95% (3-sigma) of the photons from 650 to 690 cm-1 are absorbed in the first 80 meters. Based on what I see, I feel safe assuming that the spectracalc CO2 path length was about 1 meter. It also appears that the water vapor concentration was about 500 ppm, where the actual value in the lower troposphere is about 10,000 ppm (yes, ten thousand ppm, aka 1% or 62% RH at 15C/59F).
Robert Stevenson says:
The reason why the radiative forcing of ~4 W/m^2 due to doubling CO2 is-what-it-is is well-understood: : http://www.realclimate.org/index.php/archives/2007/06/a-saturated-gassy-argument/ and is again something that is not disputed by any serious scientist (i.e., even Spencer and Lindzen accept it).
O H Dahlsveen says:
Solids and liquids have essentially continuous emission and absorption spectra. However, gases are different: An individual molecule of nitrogen or oxygen is non-polar and even its modes of oscillation are non-polar. As a result, oscillation and rotation modes of the molecule do not “couple” with electromagnetic radiation, which means the molecule can not emit or absorb radiation over these (IR) wavelengths. The only way that O_2 and N_2 can couple at all with IR radiation is through molecular collisions and, while these can become important at high pressures, at atmospheric pressures, any such absorption or emission of IR radiation through such processes is essentially negligible.
I think you are getting confused about what the comparison case is: Yes, the surface of the earth is not warmer than it would be if it never emitted radiation in the first place. However, if that were the case, it would be absorbing radiation from the sun and not emitting radiation and its temperature would be constantly rising. In fact, as Ray Pierrehumbert has pointed out, under such a counterfactual situation, the amount of energy that the earth receives from the sun over the time of a million years is enough to raise the temperature of the ENTIRE EARTH (fr0m core to skin) by ~800 K!
Your statement about a delay is true but is simply not the most useful way to look at it because it doesn’t really lead to intuition about what happens as a result. The best way to look at it is to consider the fact that the rate at which the earth emits radiation is reduced and that the earth will then increase its temperature until it reaches the point where the amount of radiation it emits back out into space matches the amount it receives from the sun.
To make an analogy: It would be wrong to argue that a beaver dam can’t produce a pond because all the dam does is delay slightly the flow of the water down the stream. The fact is that such a dam causes a pond to form until such a point that the additional water flow produced by the pressure from the pond causes the amount of water flowing out to once again balance the amount coming in.
I don’t understand what you are even trying to say in regards to the lapse rate. To the first approximation, additional CO2 does not change the lapse rate. What it does do, however, is raise the effective radiating level in the atmosphere…i.e., the level at which the temperature has to average about 255 K. As a result, if you use the lapse rate to extrapolate the temperature to the surface, you find that the surface temperature is now higher.
(In the second approximation, additional CO2 does actually change the lapse rate…because of the fact that the temperature profile in the tropics follows the moist adiabatic lapse rate. This actually turns out to be a negative feedback…i.e., the lapse rate is reduced slightly so the temperature at the surface does not have to rise quite as much as would be predicted by just considering the change in the effective radiating level and a fixed lapse rate.)
mkelly says:
I am not sure exactly what we are supposed to take from this 1942 book. Note that this book was written before the 1950s, which is when the importance of the wings of the absorption band and of where in the atmosphere the absorption is significant was first widely understood. Again, see http://www.realclimate.org/index.php/archives/2007/06/a-saturated-gassy-argument/ See also the second, more technical part of the discussion: http://www.realclimate.org/index.php/archives/2007/06/a-saturated-gassy-argument-part-ii/ The physics of radiative transfer in the atmosphere has advanced over the last 70 years.
Joel, I enjoyed reading
http://www.realclimate.org/index.php/archives/2007/06/a-saturated-gassy-argument-part-ii/
It is almost correct.
First problem – it focuses on the energy going thru the atmosphere. However, that is totally irrelevant. The focus should be on the energy returning to the surface.
Second problem – it assumes that adding CO2 will increase the temperature of the atmosphere. If radiation was the only source of energy, then that would be a valid assumption. However, because of conduction/convection and the latent heat of vaporization (to evaporate water), the paper’s assumption is wrong. In fact, adding CO2 (or any other IR active gas) to the lower atmosphere will cause it to cool. Those few gases that do cause the atmosphere to get hotter (such as ozone in the stratosphere) also cause the surface to be cooler.
Third problem – the paper focuses only on the wings of a single gas spectrum. When a second gas is added, the analysis changes. If the CO2 only eats red MM’s while water vapor eats all colors, once the total number of MM’s is gone, adding more of either gas will have no effect. Once it is realized that greenhouse gases cool the atmosphere, then it becomes obvious that the atmosphere is already emission saturated, that the “wing” argument does not apply, and that the system is (nearly) stable.
Fourth – The paper does not indicated that the CO2/water vapor overlap reduces the effect by about half. Adding clouds reduces it by another half. Thus, the net effect of increasing CO2 would be about one fourth the amount suggested in the paper .. except that the emissive saturation reduces it to almost zero.
Robert Clemenzi says:
Or, perhaps, the scientists who have studied this much more than you ever have are in fact basically completely correct and it is you who suffers from misconceptions. It continues to amaze me how many people on this website seem to be so much more knowledgeable than all the experts in the field!
Oh boy…What you fail to understand is that your first problem and second problem are in fact problems with your view of things and that the two taken together represent the solution to the problem of each viewed in isolation. There is a good reason why scientists have focused on the energy that is emitted back to space (i.e., the energy budget at the top of the atmosphere) and that is precisely the issue that you bring up: the energy budget at the surface is strongly influenced by convection and latent heat transfer. Hence, the easiest way to figure out what is going to happen to the surface temperature is actually to look at the energy budget at the top of the atmosphere (where we know the only energy transfers are via radiation) and then to incorporate convection and latent heat transfer essentially through understanding the constraints that they set on the lapse rate.
As for adding CO2 causing the atmosphere to cool: this is only true if the amount of energy that is absorbed from the surface by this CO2 is less than the amount that is emitted into space, which is not going to be the case. (A more complicated version of your argument is used to explain why the addition of greenhouse gases does lead to the prediction that the stratosphere will cool.)
Water vapor and CO2’s absorption lines overlap less than you think, especially once those lines are well-resolved. And, as is explained, as you go up in the troposphere water vapor concentration rapidly decreases and so CO2 becomes more important. What you don’t realize is that behind the description that is given are actual calculations. You can criticize the description for explaining things in an over-simplified way; however, ultimately what it comes down to is who is solving the equations correctly. Can you tell me what is wrong with the standard solution of the equations for radiative transfer in the atmosphere and how you know this and where you are planning to publish it? Otherwise, you are just talking nonsense.
Nonsense. The radiative forcing for additional CO2 is already calculated taking into account the effects of which you speak. Your 1/4 number might be correct about the amount that the effect is reduced relative to a hypothetical calculation that assumed that CO2 was the only IR-absorber in the atmosphere. But, such a calculation is not what is actually made to determine the radiative forcing due to additional CO2.
[snip – multiple violations of policy – rephrase and resubmit – Anthony]