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.
What is so bothersome about this topic is that people who take it up do nothing but rehearse the Great Assumptions, such as the claim that Earth should be treated as a black body. It’s like listening to discussions among Ptolemy and his colleagues. The solution is always the same: more epicycles and maybe an eccentric or two. Yet in setting forth the Great Assumptions, you mention known facts which contradict them. Earth has albedo. Suppose for a moment that Earth’s albedo became 100%, would that motivate you to change the Great Assumptions. Is an object with 100% albedo properly treated as a black body? Can anyone state a plausible account of Earth’s radiation budget that does not treat Earth as a black body? I don’t believe anyone can and I believe that fact reveals a limitation of imagination, not the firmness of accepted science. I guess we will just have to wait for the science to advance. Anyone know somebody named Kepler?
Ted Dooley: Thanks for asking.
Simple geometry tells us that the surface area of a circle (the cross-section of the Earth) is Pi x radius^2. The equation for the surface of a sphere is 4 x Pi x radius^2. The ratio of surface area of circle/sphere is thus 1/4 = 0.25. Thus, the 1366 Watts/meter^2 Solar radiation intercepted by the Earth, when averaged and spread over the whole surface is 0.25 x 1366 = 341.5 Watts/meter^2.
The albedo of the Earth System, including the reflectivity of clouds and of the surface is estimated to be
70%30% by many experts. (Some a bit more, some a bit less, but all are close to70%30%.) Thus around 30% of the Solar energy that enters the Atmosphere is reflected back to Space without being absorbed by the Earth System. So, 341.5 x 0.7 = 239.05 which I rounded up to 240 because (as an engineer) I do not like to express results at a level of precision that grossly exceeds the accuracy.Now, one may object that there would be no clouds if the Atmosphere was pure nitrogen, and that is certainly true. Thus, my calculation assuming all else being equal is, strictly speaking, in error. However, I was doing an engineering “sanity check” on the basics of Atmospheric “greenhouse effect” science, and, in the real world, there are clouds and the Earth System does have an albedo. So, I think I was justified in my assumptions.
Those who deny the reality of the Atmospheric “greenhouse effect” say that the water vapor and carbon dioxide and other so-called “greenhouse gases”, along with Atmosphere and Surface (as they are with clouds, rain, snow, storms, and ice and other light-colored items), taken as a whole, do not cause the Earth Surface to be warmer than it would be absent the back radiation from the Atmosphere.
The point of my simplified calculation was to show that, absent back radiation from the Atmosphere, there is no good explanation for the approximately 33ºC (58ºF) temperature difference between the “light” input from the Sun and the “heat” output from an Earth that would have to be cooler than it is for the heat balance to work. In other words, if you take all else being equal except for the back radiation from the Atmosphere to the Surface, there is an unbalance which would cause the Earth Surface to cool below its actual measured mean temperature. So let us be thankful for the Atmospheric “greehouse effect”. Without it, life on Earth as we know it would be impossible.
Ira (con’t):
The first pass you need to make in accounting for this discrepancy is to take albedo into account. The moon’s albedo is constant and accurately measured at some 16% so that amount of insolation doesn’t get absorbed the surface. That will account for the theoretical difference between black-body absorption and reality. The moon would be about 5C warmer if the surface albedo was close to 0%.
The problem doesn’t go away however because the earth has a non-zero albedo too and it isn’t known nearly as well as the moon’s with, depending on who you ask, an average albedo in the range of 32% which is primarily the result of some 70% being shrouded by clouds of some sort at any given instant. The problem here is there is no satisfactory agreement between experiments attempting to measure the earth’s average albedo and estimate range from as little as 30% to as much as 40%. All the experimental attempts to measure the earth’s average albedo do agree on one thing – it isn’t constant and varies by as much 1% year over year.
One percent doesn’t seem like much variation but once again it’s a very large number when compared to anthropogenic warming. A 1% change in the amount of insolation actually reaching the surface and not being reflected directly back out into space is some 2.5 watts per square meter. The IPCC third assessment is “95%” confident that anthropogenic forcing lies in the range of 0.6 to 2.4 w/m2. Yet measured variations in earth’s albedo over just several years has it changing by more watts/m2 than the highest estimate of alleged anthropogenic warming. Worse yet, the actual albedo can’t be pinned down and estimates vary by about 7% which is 7 times greater than anthropogenic forcings.
So how can we possibly start talking about anthropogenic forcings and surface temperature changes wrought by same when we don’t even know to +-5C what the average temperature of the earth should be due to our albedo measurements being so imprecise and having no bloody idea how, when, and why the earth’s average albedo varies.
The earth being a dynamic water world makes all attempts to model it exercises in futility. The models are toys and should be regarded as precisely that – toys with zero credibility.
6. Now use thermodynamics expressed in the form of the lapse rate.
7. An average moist lapse rate is -6.6K/km.
8. The lapse rate has nothing to do with back radiation as even scienceofdoom admits.
9. Work back down from -18C at 5km to the Earth surface and we get 5×6.6 = 33K.
So now you have an Earth surface temperature of 15C without any “greenhouse effect”.
Exactly, the earth and atmosphere are part of the same black body. Considering them as two different black bodies, based on observation of their combined effect at the TOA without consideration of lapse rate, convection and condensation seems unlikely to provide an accurate answer.
Bryan stated that using clouds, you get a 33 C temperature difference between clouds and surface “without any greenhouse effect”. I’d say inseead, that a significant fraction of the greeenhouse effect is due to clouds.
Ira Glickstein stated that the warming due to CO2 would only be about 0.2C. Here’s a way to get a rough estimate of the figure:
We get an average of 342 watts/M^2 from the sun.
As others have pointed out, excluding clouds, the average reflectivity of earth’s surface is about 0.124
Earth is not a blackbody, most of the earth is covered by ocean, which has an emissivity between 0.92 and 0.96- I’ll use a 0.94 average. This non- blackbody emissivity means earth actually radiates away less than a blackbody at the same temperature.
A non-greenhouse earth surface would receive an average of
342 *(1-.124reflectivity)/0.94 emissivity would give an average surface flux of
342*0.876/.94 = 318.7 watts. All of the positive and negative feedbacks to the
greenhouse effect give an average temperature of 288K, or effectively 390.7 watts/m^2, for an effective magnification of 1.226
From Trenbeth’s figures,
http://content.imamu.edu.sa/Scholars/it/net/trenbert.pdf
161 watts /m^2 hit the earth’s surface, with back radiation we get a total of 492 watts, not all in sensible heat, for a magnification of
493/161 = 3.06,
Putting the two formulas together, a theoretical additional factor of 2.06 multiplier due to the greenhouse effect becomes an actual multiplier of 0.226, thanks to negative factors like increases in albedo due to clouds, decreases in lapse rate, etc.
A doubling of CO2 would supposedly increase the surface flux by something less than 3.7 watts/m^2, for a total of 496.7 watts, an increase to 335.7 from 332 over the original 161 watt/m^2 hitting the surface.
Multiply that 335.7/332 * 0.226 and we get 1.2285* 318.7 for an effective
wattage increase from 390.7 to 391.52 watts, or a temperature increase to
(391.52/390.7)^0.25 = 288.15K from 288 K – Close to Ira Glickstein’s estimate of 0.2K- a drop in the bucket.
Ira:
“The only rational explanation is the back-radiation from the Atmosphere to the Surface.”
This is the crux of the issue. It is the point of contention. You and others keep repeating the same GHE theory over and over again, with slightly different words. By now, I doubt that there are many people with any scientific background who do not understand what you are saying. The problem is that it has not been demonstrated empirically AND there are other ways to explain why the surface of the Earth is higher than -18C!
The -18 C represents the average radiation temperature which comes from an altitude of about 5 km, NOT the surface. Due to the lapse rate, it is much warmer on the surface (viola, about 33C higher!).
Now, that 33C “increase” may well be due to the GHE that you describe. However, it could also be explained simply by heat storage and the ideal gas law. So I’m still not sure.
BTW, I hope you are not still trying to say that the surface is HEATED by the backradiation from the atmosphere. The atmosphere may manage to keep the surface from cooling so fast (due to the backradiation), but it is certainly NOT heating it. A colder body cannot heat a warmer one. Period.
Thanks dr.bill for trying to explain the reason the Petty curves place the peak “Radiance” at a longer wavelength than the “Intensity” of the Carleton spreadsheet and other Internet materials. However, I did not fully understand your explanation and I am not sure where you think the peak energy really is.
When I use the Carleton spreadsheet for Solar radiation, the peak energy is at 0.5μm, which we see as “green” and which I happen to know is the most sensitive part of our visual system because biological evolution has “tuned” our visual system to be most sensitive where the light energy is maximized. Thus, I am sure the real peak for solar radiation is around 0.5μm, which would make the “Intensity” of Carleton the correct peak.
So, I may be particularly dense on this topic, but I still do not understand why “Radiance” (per Perry) is used. I hasten to add that I know Perry obtained his data from real measurements from a NASA satellite sensor and I am sure that there is a good reason and rationale for using “Radiance”. I would just like to know what that rationale is. Anybody know?
Ira Glickstein, PhD says:
May 8, 2011 at 8:35 am
You say the earth’s average is pretty close to 70%.
First of all that’s the reciprocal of albedo. Albedo is a number ranging from 0-1 with 0 being dead black and 1 being a perfect mirror. Multiply by 100 for a percentage.
Now I know wikipedia is frowned on as a reference but when it comes to global warming their distinct bias is always on the warmist side so if you find something in wikipedia that is contrary to warmist dogma you can bet your bottom dollar it’s a painful admission.
I quote:
http://en.wikipedia.org/wiki/Black_body
This is exactly the figure I gave you of 30% to 40% for estimated average albedo. However I didn’t get it from wiki. I got it from much more in depth reading of the experimental attempts to measure it. Wikipedia in this instance is accurate and for the warmista it is a fatal blow with regard to the credibility of their propaganda. We don’t know the average insolation that reaches the surface of earth any closer than +-25w/m2. To start talking about anthropogenic forcings in the range of -0.6 to 2.5w/m2 is ludicrous when the error margin in experimental attempts to measure average insolation is 25 watts.
Before any toy model of the earth can begin to be given any credibility it must first have a accurate number for the earth’s average albedo down to a fraction of percent and then it must further model the observed variation in albedo down to a fraction of a percent. If it can’t do that it can’t even begin to seperate anthropogenic from natural forcing.
Ira Glickstein, PhD says:
May 8, 2011 at 8:35 am
“The point of my simplified calculation was to show that, absent back radiation from the Atmosphere, there is no good explanation for the approximately 33ºC (58ºF) temperature difference between the “light” input from the Sun and the “heat” output from an Earth that would have to be cooler than it is for the heat balance to work.”
Again: The Earth radiates from the top of the atmosphere and that’s where you find exactly the temperature needed to radiate enough. See also
Harry Dale Huffman : No Greenhouse effect on Venus
http://theendofthemystery.blogspot.com/2010/11/venus-no-greenhouse-effect.html
where Mr. Huffman does the same computations for Venus.
Probably should have read more comments before posting. fred burple already said about the same thing that I did. I think he is correct.
jae –
Someone who would benefit an understanding of ‘traveling waves’; incident and reflected waves (energy), S-Parameters (Scattering Matrix Parameters).
Falling back on the simple ‘laws of thermodynamics’ does you a disservice …
Ira Glickstein, PhD says:
“The only rational explanation is the back-radiation from the Atmosphere to the Surface.”
“absent back radiation from the Atmosphere, there is no good explanation for the approximately 33ºC (58ºF) temperature difference”
As many comments above have pointed out, the adiabatic lapse rate alone can completely explain this. Thus, Ira you need to explain why in effect you consider this to be an irrational or poor explanation.
I disagree with answer three. As a fellow systems engineer I appreciate and support your back of the envelope checks. But remember, we also have to explore all feasible answers, and the difference between black body and the actual measured radiation back to space does NOT require a ‘greenhouse’ effect.
It simply requires a long time constant between heating and radiation, which is where heat sinks and non-solar heat sources come into play.
The 33° K difference could simply be a result of a time delay between solar heating and thermal cooling. The heat capacity of the Earth could require the system to bank 33°K of heat before the there is sufficient flow of energy to the upper atmosphere to radiate.
Moreover, the inner core and the active underwater volcanoes could easily be dumping a extra wedge of gravity-friction generated heat (akin to what drives the Io system). What our massive oceans provide is a heat store, not just a heat sink. Gravity-friction (which produce wave action, which transfers kinetic energy into heat) is a source of energy transfer at the surface, as is any flowing water and its passage to the sea.
How much kinetic energy is in a river flowing to the sea? How was that energy stored? It was stored as water vapor evaporating from ground and bodies of water from solar heat, which rise to be COOLED, where the kinetic energy from gravity is then brought back to Earth with the rain. Friction supplies the transfer.
You can identify numerous transitions where heat is captured, converted, released, transferred and held for days, weeks, months and years.
What is wrong with ALL these models is they lack a time constant from which a joule of solar energy can travel through our system – over any one of hundreds of energy transformation paths – before it is made available for radiation. And we never remember to include the yet still unquantified heat source that is at the core of our planet. There is NO dissipation path for that heat except through radiation. It is a massive heat source which could EASILY account for the 33°K difference.
We know so little, yet act as if we have all the answers. The minute that happens we stop being scientists and become zealots.
DirkH says:
May 8, 2011 at 7:56 am
davidmhoffer says:
May 8, 2011 at 3:19 am
“Why doesn’t it keep cooling off? After all, the atmosphere above the arctic is even colder than the arctic itself… Heck, at 25,000 feet its colder than that even at the equator! So… with 0 watts/m2 from the sun, the arctic nonetheless sticks right around -26 degrees. Hmmmmm…..wonder what keeps it from cooling off more….”
DirkH;
David, if the atmosphere above the arctic is colder than the arctic surface, do you want to imply here that this cold atmosphere is nevertheless capable of WARMING the surface? Are you sure you wanted to say that?>>>>
Dirk, I didn’t say the atmosphere made the surface warmer. I said, what keeps it from cooling off more? Why does the temp drop from 275K in July, to 240K in December, a drop of 35 degrees over 5 months, and then over the next 2-3 months, despite having 0 insolation, it drops by perhaps two degrees more. Since it isn’t getting any energy from the sun, where is the energy to keep it from cooling any further come from?
There are several possibilities. The arctic is mostly ocean covered by ice, so warm water currents could be bringing in heat. Wind from warmer latitudes could be bringing in warm air. Reflection from clouds that are high enought in altitude to catch some sunlight cold contribute. All of these have been measured in various ways, all are part of the picture, but combined they are insufficient to keep the surface at -26.
So why doesn’t it cool off more? Answer is (in part) that some of the outward bound radiance is in fact returned to the surface. In fact, the atmospheric window starts to close pretty fast right around that temperature, and by -40 it is shut tight. That’s why the very coldest nights at 80 N latitude are about -40 and the very coldest nights at 50 N latitude, where the “average” temp is MUCH higher, are around -40.
Once the temp hits -25 not only is the “colder” atmosphere above the artic backradiating, reradiating, simulating pajamas, what ever term you want, it get’s more efficient at it. So it can’t EVER cause an INCREASING temperature trend, but it can certainly recycle, reradiate, pajamas, the surface radiance to the point where continued decreases in temp slow to a crawl.
ferd berple says:
May 8, 2011 at 8:22 am
I don’t want to rain on your parade but the temperature at the top of the atmosphere is in the thousands of degrees. The TOA boundary for energy budget calculations is the top of the thermosphere. So the temperature is indeed much higher at TOA than it is at BOA.
Your argument based on lapse rate is only valid to the top of the middle atmosphere and falls apart in the upper atmosphere where temperature increases with altitude.
It’s very thin atmosphere but it’s still atmosphere and its temperature can be measured. So the temperature at the bottom of the atmosphere is indeed much colder than at the top.
In my view, the explanation of the 33°C difference is somewhat tricky.
If the atmosphere were totally transparent to radiation, the effective temperature of 280 K would be that of the ground (although, as I mentioned above, this effective temperature does not coincide with the average surface temperature). So the atmosphere must be opaque to thermal IR radiation to produce an effective temperature at the TOA different from the ground one. But absorption of IR radiation IS greenhouse effect. So “some ” greenhouse effect must be present to make the atmosphere partly opaque.
BUT the open question is to compute the average difference between ground and TOA and this is much less obvious. In the absorption lines, the outgoing LWR intensity is determined by the local temperature at the last diffusion surface – so the upper atmosphere temperature. But the heat transfer in the troposphere is a complicated mixture of convection and radiation, and is indeed dominated by convection. So the difference temperature is mainly controlled by the adiabatic law between ground and and tropopause – and this can NOT be computed only with radiative physics. So in some sense, those claiming that the difference between the ground and the TOA is mainly due to gas thermodynamics are also right – this is a very complicated mixture of convective transport and radiative opacity.
This can only be solve through detailed modeling – and it is quite possible that this modeling is inaccurate.
A further complication is that as I mentioned , average ground temperature is NOT the same as effective temperature, so there is no clear relationship between the two: The Earth is NOT an isothermal copper sphere ! actually the average temperature depends strongly on meridional circulation that transports a lot of heat towards the high latitudes – especially with oceans that are, to say the least, not very well described and understood. Any variability in oceanic circulation could have strong effects on local, and hence average temperature, even with a fixed energy budget. This is again totally overlooked in “simple” isothermal , radiative arguments. I would say IMHO that this is actually the less known feature of current GCM – and the main reason for doubting about their accuracy and predictive power. And I am not really surprised that they struggle so much with the “lack of warming” .. 🙂
ferd (con’t)
The reason the middle and lower atmosphere get colder with height isn’t because of compression. It’s because in the middle and lower atmosphere the sun doesn’t do any appreciable heating of it.
One must always begin with the big picture and work down to the smaller details not try to add up the details into a big picture.
In the big picture the sun heats the ocean, the ocean heats the atmosphere, and the frigid cold of the cosmic background (3K) cools the atmosphere.
The lower atmosphere is warmer than the middle atmosphere because the lower atmosphere is closer to the source of the ocean that heats it.
Again, as pointed out above: Have a look at:
The best explanation I have seen so far and one that t m o completely refutes the misnomer “greenhouse effect” for back radiation.
I would like to see a discussion of that article instead.
Ira said:
“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.”
No, by my point o f view there is another explanation. The incoming radiation from the Sun is truly measured from the radiometers because of the distance from the source we get all the parallel energy rays in the SW, while the emission of the Earth in the LW range is scattered in a spheric space around the planet, so the satellites’ radiometers can’t really measure all that energy because those rays are not parallel each other and many of them will never be perpendicular to the radiometer input slit.
I suppose this is my segue into talking about the temperature of the ocean since it is responsible for the temperature of the lower atmosphere where we live and breathe.
The average temperature of the ocean is 4C. 90% of the volume of the global ocean is at a near constant temperature of 3C. Only the surface layer comprising 10% of its volume gets any warmer (or colder) than that. It’s not a temperature/density thing either because seawater, due to its saline content, increases in density all the way down to its freezing point of about -2C.
The only possible explanation for why the average temperature of the ocean is 4C is because that is the average surface temperature of the earth taken over a period of time long enough for convection and conduction to equilibrate the entire volume.
Ostensibly I should think that period of time is about 120,000 years or once complete glacial/interglacial cycle.
Any sane person armed with the facts should find their source of angst to be that huge volume of icewater lying just below the warm thin surface layer of the ocean. The current interglacial period is getting long in tooth so again by any sane measure we should be worried about an impending ice age and if there is any merit whatsoever in anthropogenic global warming we should be glad for it and try to get as much of it as we can in the hope that it might delay the inevitable return of glaciers a mile thick covering everything north of Washington, D.C.
I wonder how many of the people I share the planet with are sane in this regard. The facts on the ground are incontrovertable. The only thing we have to fear is more ice not less ice. For this reason I call the warmista’s “ice huggers” in fond remembrance of their predecessors the “tree huggers”. The tree huggers morphed into ice huggers. Ain’t that a hoot? Trees don’t grow well in ice. They are lucky to survive where ice prevails much of the year much less thrive in such conditions. A warmer earth is a greener earth and a greener earth is what we all want, innit?
Dave Springer:
Please “debunk” the article at the link given by DirkH: http://theendofthemystery.blogspot.com/2010/11/venus-no-greenhouse-effect.html
You folks are, in essence, saying that the lapse rate is CAUSED by the GHE. That is nonsense. The lapse rate is dependent upon only two variables, gravity (g) and the heat capacity of the air (Cp) and can easily be calculated from these two variables. GHE has no “place” in this formula. The lapse rate for ANY atmosphere (even pure nitrogen or oxygen) would be calculated the same way–without “allowance” for any GHE.
[Update 7PM EST – I just noticed that I misunderstood the direction of Dave Springer’s 5ºC delta. I am sorry about my error. The following is unchanged from what I originally posted. As you read it, please mentally reverse the sign of the 5ºC delta. Ira]
Great to hear from you again Dave Springer and thanks again for putting me on to the radiation measurement curves in the Perry book in your comment on a previous thread. That information (from you and Tim Folkerts) was the basis for another one of my postings in this series. My only claim to special knowledge here at WUWT is as a system engineer and system scientist, and I appreciate it when those more familiar with climate science add to my knowledge.
You make a great point about using the experimental reality of the Moon as a reference. That would reduce the 33ºC I calculated in my simplified “sanity check” by 5ºC, so it would be about 28ºC.
How to explain the difference? Well, 28ºC is pretty close to 33ºC for a “sanity check”. Furthermore, the Moon’s albedo is about 0.12 compared to the albedo of the Earth which is about 0.37. If we assume all else is equal except the subject of this posting, namely the Atmospheric “greenhouse” effect, and assign the Earth System an albedo equal to that of the Moon, using my modified Carleton spreadsheet, that would increase my 255 K to about 272 K, reducing the 33ºC to be accounted for down to about 16ºC. OOPS, we have over-corrected your 5ºC on the Moon and we are now off by 12ºC in the opposite direction! Clearly there are other differences between the Moon System and the Earth System. If anything, your Moon example adds credibility to the reality of the Atmospheric “greenhouse effect” on Earth.
I hasten to add that engineers are not as picky about precision of estimates as scientists and mathematical analysts are about their data. If we get estimates within 15% (33ºC vs 28ºC) that is usually close enough, since other uncertainties are likely to be in the mix. You may have noticed that I am unusually sensitive when mathematical analysts state their results to more decimal places than is justified by the accuracy of the assumptions that have gone into their models.
I never claimed that my “sanity check” was more than just that, a way for a system engineer to double-check the rationality of the more exacting calculations of the supoosed experts. From that point of view, I think the 33ºC due to all Atmospheric effects (‘greenhouse” as well as others that are unknown at present to me) holds up pretty well. It is definitely in the ballpark of the truth.
Thus, it seems you are correct that there are factors in addition to the Atmospheric “greenhouse effect” that account for the Surface being warmer than it would be absent that back radiation. Thanks for your input.
No mention is made of ocean and atmospheric heat transport. With one side of the Earth exposed to near absolute zero temperatures and the other exposed to the Sun; any theory has to take into account the movement of vast amounts of heat energy from hot to cold and vice versa. Although the Earth may lose heat at night, there is still substantial heat transfer from the day side to the night side keeping the night side warmer than it would be otherwise. The true “greenhouse effect” is a perfect example. Without convective heat transport a greenhouse becomes much hotter than its unenclosed environment. Simplistic models with lots of fudge factors to make the numbers fit are insufficient to describe the climate.
More on heating and cooling of gases due to compression and expansion.
Heat and cooling only takes place as the gas pressure is changing. When the pressure stops changing so does the temperature. There is very little dynamic variation of atmospheric pressure at any constant altitude so there is very little heating or cooling taking place due to pressure variation.
In a real world example I have an air compressor in my shop. If the air in the tank is not compressed and I run the compressor to bring up to 10 atmospheres the tank will get much warmer than the air in my shop and if I quickly bleed it back to 1 atmosphere the tank will get colder than the air in my shop.
However (this is the key) if I leave the tank full of compressed air it won’t stay warmer than the air in my shop for long. That’s because the pressure is constant.
Ferd’s assertion that atmospheres get warmer as you go deeper into them because of compression is quite wrong. If there were some mechanism that were taking volumes of air high in the atmosphere and transporting them lower in the atmosphere his thesis would have some merit but there is no such mechanism at work on Venus, Earth, or Mars. The pressure gradient is nearly static and if an actual volume of gas is neither expanding nor contracting there is no associated change in temperature.
“A warmer earth is a greener earth and a greener earth is what we all want, innit?”
It certainly is surprising that people fear the earth getting warmer, yet when it comes to spending their hard earned money to go on vacation, few it any head towards the poles. If warming is something to be feared, where did the term “tropical paradise” come from? Why isn’t it “polar paradise”?