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.
Tim Folkerts asks
“The readily available spectra graphs show that this is wrong.”
Could you provide a link to specific spectra that you are referring to? What is wrong with them?
Tim, I have a spreadsheet of the Planck function similar to Ira’s
So I can call up a blackbody spectrum for any temperature.
This gives a surface up value.
I then compared the atmosphere spectrum profile from Petty(2004) as given in page 127
Physical Meteorology on line is Rodrigo Caballero’s Lecture Notes
http://maths.ucd.ie/met/msc/PhysMet/PhysMetLectNotes.pdf
With the surface continuous spectrum.
My calculation is that all the radiation shown in this chart is reduced by 25% compared to the surface up radiation.
So the maximum possible back radiation would be 75% of the surface radiation!
K&T on the other hand have the reduction of only 8%.
Thus they claim a figure of 92% of radiation is surface bound.
I used the older K&T diagram .
390 up (subtract 40 from ‘window’ as everyone agrees this radiation doesn’t come back).
This leaves 350W/m2 up and 324 W/m2 “backradiation”.
(350-324)/350 = 7.4%
Caveat’s;
1. A fairy rough and ready calculation
2. The Petty spectrum might not be representative.
However even with these reservations a reasonable conclusion can be drawn.
jae says:
Convection does not occur between the earth and space…and hence cannot get you around having to satisfy conservation of energy. Besides which, the convective-radiative models include convection. You are just spouting more nonsense.
Bryan says:
May 13, 2011 at 12:35 am
There are some things that are easily provable yet there seems to be no dearth of skeptic who don’t accept what is proven.
Point an infrared thermometer up at the clear sky at night. It shows a temperature much higher than the empty cosmos. That’s because the atmosphere glows in the far infrared. Point an infrared spectrometer up at the clear sky at night. It breaks the glow down into component frequencies and those are primarily the absorption/emission bands of water vapor and CO2. In the stronger absorption bands of water vapor when the absolute humidity is high the spectroscope will show temperatures in those bands closely approaching the ground temperature. The instrument in that case is seeing the temperature of the water vapor very close the ground.
Emergency blankets commonly known as “space blankets” are made of exceedingly thin highly reflective mylar. A blanket of this material big enough to cover your body fits folded into a package the size of a teabag. It is made of a material with a mirror finish because that material reflects infrared radiation from your body back at your body and thus keeps you warmer than the same blanket made of non-reflective material.
These things are indisputable proof of so-called “back radiation” and the FACT that back radiation slows the loss of heat from the body which it wraps whether that’s a human body on a cold night or the body of the planet.
The person denying this just looks dumber than a fifth grader and makes it impossible to move on to the bits of the global warming story that aren’t well established facts like whether clouds have a net warming effect due to them being an effective insulator at night or a net cooling effect due them shading the ground underneath during the day. Or exactly how much daytime heating of the ocean gets lifted away from the surface by evaporation and convection. Or exactly how much heating of the equatorial ocean gets transported to the poles by ocean currents. Or exactly how much the albedo of the planet changes from year to year due to variation in type and amount of cloud cover and wind driven waves which break up the ocean surface and make it less able to absorb sunlight while at the same time increasing the evaporation rate which combine to make it much cooler than it would be if the winds were calm.
There are a million details which are poorly characterized that are highly relevant to the anthropogenic global warming narrative. The basic physics of greenhouse gases are simply not one of those things that are not well-enough understood and if you don’t understand how greenhouse gases work you can’t possibly move on to any reasonable debate about other phenomena which can and do (IMO) largely negate the effects of increasing greenhouse gases and leave us in a situation where the modest increase in carbon dioxide has vast beneficial effect by warming the planet at high latitudes where warming is welcome, not warming it at low latitudes where it is already warm enough, increasing the growth rate of green plants, and decreasing the water needs of green plants at the same time.
Steve says:
May 12, 2011 at 10:13 pm
richard verney says: “According to Trenberth some 78 W/m^2 of the incoming solar energy is absorbed by the atmosphere. Since the warmists case is that CHGs are transparent to incoming solar radiation, CHGs cannot account for this absorption. ”
The GHGs are transparent to incoming visible light, not all solar radiation. I think you have read an incorrect account of the “warmists” view.
///////////////////////////////////////////
Steve. Thanks your comment. I stand corrected on that point ( I was posting at about 4:30 am and was not thinking sufficiently clearly). I do need to check whether all of the 78 W/m^2 is said to be absorbed in the absorption wavelengths of GHGs or whether some of this is component is absorbed in the absorption wavelenghts of other gases and/or by atmospheric aerosols.
Someone asked for actual spectrographs.
Looking up from the ground:
http://www.sundogpublishing.com/AtmosRad/Excerpts/AtmosRad212.pdf
Looking down from above:
http://www.sundogpublishing.com/AtmosRad/Excerpts/AtmosRad125.pdf
richard verney says: May 12, 2011 at 8:39 pm
8. That Trenberth’s energy budget is wrong. It defies commonsence …”
Richard, you make some good points, but this is a pretty bold statement: science is wrong because it defies YOUR common sense!
There are many ideas in science that defy the common sense of many people. That just means people need to look at it more carefully and THEN decide what is correct. I think the diagram is correct (at least within reasonable uncertainties). Many other commenters also think it is correct. Many scientist in many fields think it is correct.
So … what specific numbers in the diagram do you think are wrong? How would you change them and still satisfy conservation of energy and still agree with observed temperatures?
richard verney says:
May 12, 2011 at 8:39 pm
“The upshot of the above is that I do not dismiss out of hand the contention that GHGs may contribute something to the warming of the atmosphere but I am very skeptical that the Earth is 33K warmer because of the presence of GHGs in the atmosphere. I consider that such a contention is far from proven both on figures and on principles involved.”
33K appears to be accurate +-10% going by average measured temperature of the surface of the moon and the surface of the earth after taking into account difference in albedo between the two where the inaccuracy is almost soley due to lack of accuracy in determining the average albedo of the earth.
However, I question whether the GHE is soley in the atmosphere. The ocean has the same properties of being transparent to visible light and opaque to infrared light that greenhouse gases exhibit. The sun warms the ocean to a depth of about 100 meters during the day but it cannot radiate infrared from a depth greater than 1 micrometer. So the energy absorbed from the sun at depth must find its way to the surface by some means other than radiative which of course leaves only convection and conduction. The question is whether convective and conductive cooling are more or less efficient than radiative heating and under what conditions. I suspect the net effect under most circumstances is that a substantial amount of greenhouse warming is contributed by the ocean alone. Of course if the ocean surface is frozen then all bets are off and any GHG warming in that case comes from atmospheric fluids not oceanic fluids. CO2 I believe is most important in helping to raise average temperature from below freezing to above freezing then water in liquid and gaseous phase becomes the major player. CO2 is the “kindling” which ignites the water cycle.
Bryan says:
“My calculation is that all the radiation shown in this chart is reduced by 25% compared to the surface up radiation.
So the maximum possible back radiation would be 75% of the surface radiation!”
The chart in question is for “Whole-atmosphere clear-sky absorptivity”. For a cloudy sky, the clouds would absorb close to 100% of the radiation. The numbers I have seen put cloud cover at ~ 0.7 (therefore clear sky @ur momisugly ~ 0.3). The back radiation would then be limited to approximately.
(100% * 0.7) + (75% * 0.3) = 95% of the upward radiation.
This limit assumes the radiation comes back from the same temperature as the surface, which is clearly incorrect. The fact that the clouds and atmosphere are on average cooler than the surface will decrease this 95% ratio significantly. If the surface emits at an average of 270 K and the atmosphere & clouds emit at an average of 260 K, the downward radiation would be reduced by (260^4 / 270^4) = 86%. So the downward radiation would be 0.86 * 0.95 = 81% of the upward radiation.
The observed ratio of downward to upward is 324/390 = 83%. This seems within reasonable agreement with the rough estimates.
PS. I disagree with your thinking when you say “subtract 40 from ‘window’ as everyone agrees this radiation doesn’t come back”.
The EM radiation from the surface is determined by the surface temperature and surface emissivity. Whether that energy is absorbed or reflected or transmitted by the atmosphere doesn’t change how much IR the ground emits. The ground emits ~ 390 W/m^2 of thermal IR at its current average temperature, so that is the number that should be used.
Dave Springer says:
May 12, 2011 at 4:40 pm
mkelly says:
May 12, 2011 at 12:00 pm
Sorry I totally disagree. What a thing is named is important.
A rose by any other name smells as sweet. ~Wm. Shakespeare
Your lack of education evidently isn’t confined to science and extends into classic literature as well.
Mr. Springer, you cannot call temperture back radiation. In science words have meanings. Velocity is not distance although it is intertwined with distance. I subscribe to the Mark Twain version. see below
“If we call a dogs tail a leg how many legs does a dog have? Four just because you call a tail a leg does not make it one.” Mark Twain.
richard verney says: May 12, 2011 at 8:39 pm
“9. That if DWLIR of the magnitude as indicated by Trenberth really existed, we would be able to extract energy from this and/or there would be considerable research into exploiting this natural green resource. After all, this DWLIR would have potential exceeding that of solar and wind.”
Once again, your common sense is incorrect. The diffuse IR radiation from the atmosphere cannot be concentrated in the way you suggest. No matter how you concentrate the energy, this IR by itself cannot heat something above the temperature of the material emitting the light.
In the same way, you cannot heat something above 5700 K no matter how you arrange lenses & mirrors to focus sunlight. If you had a furnace at 5700 K, you could not use sunlight to warm it any further (although you could reduce the amount of other energy required to heat the oven).
Dave Springer you will need to read the posts before you launch into a rant.
I said …… show significant radiative heating in a volume of the atmosphere.
This they cannot do.
Did you notice the word SIGNIFICANT ?
Ive made it larger so that you can read it.
You then go on to give a whole pile of irrelevant tripe.
Of course CO2 and H2O radiate in the Infra Red but does this amount to a 33K increase in the atmosphere of the planet
You go on “These things are indisputable proof of so-called “back radiation” ”
Who are you arguing with here?
If you had read any of my previous posts you would know that I have always maintained that colder surfaces can radiate to warmer surfaces but they cannot HEAT them.
I will send a second post with experimental evidence that the radiative heating of a volume of air the size of a greenhouse is so small that it is almost negligable
Roy W. Spencer, Ph. D. says in his own blog on May 11, 2011 at 9:15 AM as a response to comments to his posting “UAH Temperature Update for April, 2011: +0.12 deg. C”:
“EVERYONE:
It turns out the stratosphere is responsible for the difference between the Discover ch 5 data and our official LT data. There was an abrupt switch from a westerly QBO to easterly last month, with strong lower stratospheric cooling in the tropics, which then influenced ch. 5.
ALSO:
You are making too much out of month-to-month temperature variations. We have computed before that these large changes can be caused by less than 1% fluctuations in the convective heat transport from ocean to atmosphere.
Stop thinking in terms of only radiation causing temperature changes.”
============================
I hope Dr. Spencer does not mind me sharing his comment with you here on WUWT but I thought the line; “Stop thinking in terms of only radiation causing temperature changes.” is a significant one when it comes from him. I have known for a long time that Dr. Spencer has always considered factors other than radiation. But I have also had the impression; “That not a lot of people know that”
I am also one who happen to think too many people – by far, are making too much of radiation. – The so-called “Back radiation” is also “just” radiation and cannot possibly just radiate back to whence it came.
Tim Folkerts
Why is it that IPCC advocates have a tendency to “bend” the numbers?
We were talking about the KT diagram
You say……. If the surface emits at an average of 270 K
Tim the actual surface temperature for this diagram is +15C = 288K
You say …… atmosphere & clouds emit at an average of 260 K
A more realistic figure particularly if you are stressing the clouds would be 240K.
Remember also that this post was in answer to your initial contention that all downwelling LW radiation is really back radiation.
Hence my calculation ignored the window radiation which nobody thinks “comes back” or do they?
I don’t think that that is a tenable position
Dave Springer as promised two experiments that show the radiative heating of the atmosphere is very small.
The first experiment was the classic experiment by R W Wood.
He was was probably the best experimental physicist that America ever produced.
Wood nailed two points in this experiment.
1. Greenhouses(glasshouses) work by stopping convection.
2. The radiative effects of CO2 are very weak at atmospheric temperatures.
G&T did an experiment to confirm the conclusions of Wood and also give an account of his experiment.
“Falsification Of the atmospheric CO2 greenhouse effects within the frame Of Physics” by Gerhard Gerlich and Ralf D. Tscheuschner; International Journal of Modern Physics B, Vol. 23, No. 3 (2009) pages 275-364.
http://arxiv.org/PS_cache/arxiv/pdf/0707/0707.1161v4.pdf
The second experiment is an interesting paper especially as it comes from a source with no “spin” on the AGW debate.
The way I read the paper is it gives massive support for the conclusions of the famous Woods experiment.
Basically the project was to find if it made any sense to add Infra Red absorbers to polyethylene plastic for use in agricultural plastic greenhouses.
Polyethylene is IR transparent like the Rocksalt used in Woods Experiment.
The addition of IR absorbers to the plastic made it equivalent to “glass”
The results of the study show that( Page2 )
…”IR blocking films may occasionally raise night temperatures” (by less than 1.5C) “the trend does not seem to be consistent over time”
http://www.hort.cornell.edu/hightunnel/about/research/general/penn_state_plastic_study.pdf
Now if you think that the “greenhouse theory” has any evidence that the radiative effects of CO2 and H2O can significantly heat a volume of air at STP please let us know.
Joel Shore says:
“Convection does not occur between the earth and space.”
As a matter of fact, convection does occur between the earth and space. Warmer air both rises and radiates. That area is called the atmosphere, and convection provides a mechanism for dumping heat into space.
Tim Folkerts:
“So … what specific numbers in the diagram do you think are wrong? How would you change them and still satisfy conservation of energy and still agree with observed temperatures?”
It doesn’t make sense to me because it suggests that the only way the surface temperature can average 288 K (and therefore emit 390 wm-2) is through backradiation from a colder sky. It is hard to believe that so many scientists think that is correct.
But then, that seems to be the only way that the magic 33 C increase from “black body earth” can really be explained by radiatiation. How funny!
Smokey:
““Convection does not occur between the earth and space.”
As a matter of fact, convection does occur between the earth and space. Warmer air both rises and radiates. That area is called the atmosphere, and convection provides a mechanism for dumping heat into space.”
I think you are actually saying the same thing as Joel is: the only way that energy can actually move from the atmosphere to outer space is through radiation.
But then Joel said in reply to my:
“Convection might (and probably does) wipe out any GHE effects, just like with the “real greenhouse” effects. ”
that
“Convection does not occur between the earth and space…and hence cannot get you around having to satisfy conservation of energy. Besides which, the convective-radiative models include convection. You are just spouting more nonsense.”
Which is a total (willful?) misunderstanding of my comment.
Yeah, the “convective-radiative” models include convection, but my position is that they don’t treat it properly.
Bryan says: May 13, 2011 at 8:35 am
>>You say……. If the surface emits at an average of 270 K
OK, that number is low, but that is not the main point. I will grant that 285 K is a better number
>>You say …… atmosphere & clouds emit at an average of 260 K
>A more realistic figure particularly if you are stressing the clouds would be 240K.
I don’t agree. A large faction of clouds are within 2000 m of the surface. Based on lapse rates, these must be no more than 20 K cooler than the surface. Many would be within 10 K of the surface temperature. Very few clouds would have their bases high enough to be 285K – 240K = 45 K colder than the surface that you suggest as more realistic.
So we can be more accurate. I am not a meteorologist, but …
* the surface average would be ~ 285K (using pretty much anyone’s numbers)
* the observed environmental lapse rate is 6.5 K/km, which we will use a a rough estimate.
* 0 m and 3000 m will be 6.5 K – 20 K cooler than the surface.
* many common types of clouds (stratus, stratocumulus, cumulus, cumulonimbus, fog) have their base between 0 – 3000 m above the ground.
* therefore, the bases of many clouds are 0-20 K cooler than the surface.
* therefore estimating the temperature drop between ground and clouds as 10K is not too far off.
I’d be happy to see either more accurate estimates or experimental data for the typical temperatures of cloud bases. There are definitely clouds above 2000 m (6500 ft) and a more accurate analysis would need to include a better average of the cloud heights.
Furthermore, estimates I have seen for CO2 & H2O vapor suggest most of the absorption (and hence emission) comes in the first few 100 m where the temperature is within a few K of the surface temperature. So for the 75% you were looking at, we can use about the same temperature for the back radiation as for the forward radiation for CO2 & H2O. (And the satellite data at the very beginning of this post confirms that)
Whether the the numbers are (270 K surface and 260 K clouds & GHG) or (285 K surface and 275 K clouds & GHG), the basic result is the same.
Bryan then says: “Why is it that IPCC advocates have a tendency to “bend” the numbers?”
1) I don’t consider myself an “IPCC advocate” — just a scientist interested in the subject of climate change and interested in seeing the basic science presented correctly.
2) I admit I presented one inaccurate number (270 K vs 285) — it must have been too late when I wrote that. However, that doesn’t actually make a fundamental difference in the final results because it is primarily the temperature DIFFERENCE that matters. I think the estimate of 10 K temperature difference is closer than your estimate of 45 K.
3) You missed the effect of clouds entirely! That would seem to be much more egregious than “bending” one or two numbers.
Joel Shore says:
May 12, 2011 at 2:11 pm
mkelly says:
q = ε*σ*(Th^4 – Tc^4) Ah
“Perhaps the most fundamental thing to understand about that equation is that if Tc was zero then there would be more heat going from the hotter object to the colder object than when Tc is not zero.
It is sort of amazing how such a simple concept seems to illusive for some people!”
So you agree with me that there is no back radiation only temperature gradient. Two things must exist for heat transfer to take place 1. path 2. temperature gradient. Temperature is not back radiation. A simple concept Joel.
However the must fundamental thing to note is that if both objects have the same temperature there is zero back radiation as you call it. The back radiation from the atmosphere cannot heat the ground higher it takes a temperature change in the atmosphere.
Please now specify the temperature you would like to use for the atmosphere and we can proceed.
By the way that should be “too illusive” not “to illusive”.
Bryan says: “Hence my calculation ignored the window radiation which nobody thinks “comes back” or do they?”
That suggest a fundamental misconception. (Or else I have some fundamental misconceptions! 🙂 ) Here is what I think …
* Nobody thinks (or at least nobody should think) that any of the 390 W/m^2 radiation “comes back”.
* The earth emits radiation. Once the energy leaves, it is gone; it is no longer the earth’s energy. All that matters is the surface’s emissivity and the surface’s temperature. Whether the atmosphere lets 40 W/m^2 thru or 390 W/m^s will not matter (at least not until the surface starts to cool off).
* The atmosphere emits its own energy. Wherever that energy may have come from (from the sun, from the water cycle, from the surface’s radiation, from convection), it is the atmosphere’s energy. All that matters is the temperature and emissivity (complicated by the fact that emissivity is a function of wavelength and that IR can travel considerable distances, so there is not a clear “surface” for calculations).
* Some of the energy from the atmosphere heads left; some head right; some heads up; some heads down. Since the radiation heading down is heading “back toward us” we call it “backradiation” (not because any photons are heading back where they came from).
The surface currently emits ~ 390 W/m^2 in a generally upward direction.
The atmosphere current emits ~ 324 W/m^2 in a generally downward direction.
There would only be radiation “coming back” if the atmosphere acted as a reflector, which is not the case (to any appreciable extent).
Tim
Regarding your post at 5:32 am regarding Trenberth’s energy diagram. I am not saying that his diagram is wrong, merely that I am fairly confident that when more is known and understood about the system (this may be 20, 30, 50 years hence – hopefully not that long), it will be found to be wrong.
As an engineer, you often have a ‘feel’ for what will or will not work. Hopefully, one’s ‘feel’ for something is right although I accept that inevitably there will be cases when it is not right (or not fully right).
I know that this is unscientific, but to me, the Trenberth energy budget does not have the right ‘feel’. The fact that there is famously ‘missing heat’ may indicate that his energy budget is wrong, but I am not going to carp on about that.
Tim
Perhaps, I should have added to my last comment that I accept that I am not in a position to put forward alternative figures (partly because I consider that there is a lack of accurate empirical data on a number of aspects that affect the budget) but in general, I consider that the use of average figures is not simply an over simplification of the system but more significantly it disguises and distorts what is in practice going on thereby leading to a failure to properly understand how the system works as a whole. My gut tells me that it underplays the effect of solar and overplays the effect of DWLIR.
The real driver of the Earth’s climate is the oceans and the solar energy being poured into these which is then distributed around the globe by currents (both ocean currents and air currents). Until this is properly understood (which will involve a proper understanding of clounds), we will never properly understand the Earth’s climate.
>>> Richard says “8. That Trenberth’s energy budget is wrong. It defies commonsence ”
>> Tim replies: “There are many ideas in science that defy the common sense”
>>”So … what specific numbers in the diagram do you think are wrong?”
> JAE replies: “It doesn’t make sense to me ”
I obviously didn’t my point about common sense, since more people are claiming their common sense is being violated, as if violations of common sense are remarkable in science.
Once again, science does not always make sense, especially if you don’t really dig into it.
Let me try one more time on radiation…. Using the way over-simplified equation as a starting point:
q = ε*σ*(Th^4 – Tc^4) Ah
We could call the term related to Th^4 (390 W/m^2) the “up-radiation” or “away-from-us radiation” from the surface and we could call the term related to Tc^4 ( 324 W/m) the “down-radiation” or “back-toward-us radiation” from the atmosphere.
Or we could call the net result (390 W.m^2 – 324 W/m^2 = 66 W/m^2) the net radiation. I really don’t care.
The bottom line is that the surface has a net lost of thermal IR radiation of 66 W/m^2.
The surface has a loss of energy via convection and evaporation as well.
All these together add to the other energy input (primarily the sun’s visible light) and the energy of the surface is pretty well balanced. Any slight change in these numbers will lead to global warming/cooling.)
(And yes, there are other inputs/outputs of energy from the surface. There is geothermal energy flowing out at a rate I have seen estimated as 0.1 W/m^2 — pretty insignificant it would seem. The much bigger factor would be ocean currents eg El Nino/La Nina. Over the course of years or decades, changes in the oceans currents could have a major impact on surface temperatures because of the huge heat capacity of the oceans.)
Tim Folkerts .
I’m afraid you did not get it quite right even on the second attempt.
>>You say……. If the surface emits at an average of 270 K
OK, that number is low, but that is not the main point. I will grant that 285 K is a better number
I didn’t mention 285K, the actual number is 288K and corresponds to the average surface temperature of 15C
This is from my post above…………….
“Tim the actual surface temperature for this diagram is +15C = 288K”
I don’t think it is worth pursuing this rather trivial point as I have better things to do.
However I think that you should review your opinion that all downwelling Long Wavelength radiation is backradiation.
Why not instead of “bending” the numbers to suit an IPCC position try bending them the other way and take an average.
Tim Folkerts
Your tying yourself up in knots here;
You say ……… “Some of the energy from the atmosphere heads left; some head right; some heads up; some heads down. Since the radiation heading down is heading “back toward us” we call it “backradiation” (not because any photons are heading back where they came from). “………
So by this definition, the Solar Radiation is also “backradiation”!!!