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.
davidmhoffer says:
May 8, 2011 at 9:49 am
“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.”
David, this means that at -25 deg the upper atmosphere is no more colder than the ground; an equilibrium is reached. Of course, nothing happens from there; but your premise was to show that the people who say a cold object cannot warm a warm object are somehow wrong – your example shows that two equally cold objects are in equilibrium and does not contradict those people at all. In your example, the upper atmosphere is no more colder than the ground.
I don’t want to rain on your parade but the temperature at the top of the atmosphere is in the thousands of degrees.
Then it must be back radiating a fantastic amount of energy to the earth. At thousands of degrees this radiation would be in the visible or even UV.
” 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”
temperature is not heat – you can’t measure heat with a thermometer. degrees can not be converted to watts.
the sidewalk doesn’t get hot because the air above it warmed it.
the sidewalk stores heat and warms the air above it.
incidentally, phase change from liquid to gas has no temperature change – but loads of heat is involved.
incidentally, avogadro’s ‘laws’ trump co2 fetish fantasy – co2 molecules don’t get to be hotter than everything else around them – all molecules in a local region are basically at the same temperature via kinetic transfer.
/me sick of co2 shrimpers. it’s like an old ed wood flick with fat ladies in a playpen and some old fart claiming to be the walrus. or maybe it’s like divine following that pooch.
“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.”
I recall years ago seeing a calculation that the amount of heat energy delivered to the earth by rainfall significantly exceed that delivered by bright sunlight.
Ira:
We seem to be out of synchronization. In a series of comments I left the second in the series explained why the moon is not at its theoretical black-body temperature i.e.. because it isn’t a black-body. It’s a gray body with an albedo around 12%. I found the missing heat for you in that comment. I then went on to explain that the earth is also a gray body with an albedo of 30% to 40% and pointed out the crux of the issue – the earth’s average albedo isn’t know to any better certainty than +-5% and +-5 uncertainty in albedo translates into 25 watts per square meter of uncertainty in how much insolation is actually absorbed at the surface. Moreover all actual attempts to measure albedo, while disagreeing by 10% (I actually only found 7% disagreement in actual studies but still…) all do agree that the average in any given year is not static and varies from year to year. One experiment using earthshine as a measure that went on for about five years found a 1.5% difference between year one and year five. Their methodology in that one was measuring the brightness of the new moon which is illuminated solely by light reflected from the earth. It’s a bit surprising how difficult it is to get an accurate measure of the earth’s average albedo in any one year but on the other hand it isn’t difficult to measure change from year to year. The earthshine measure might not be accurate but it is precise and consistent. Precision and consistency is all you need to identify trends.
[Thanks Dave Springer and I appologize for not remembering that detail of your earlier attempts to clarify the issues. Please continue to share your special knowledge of climate science with me and others at WUWT. Your comments are most welcome here in my threads, even when they are corrections to my mistakes. In fact, especially when they help me improve my understanding and learn more about this topic. THANKS! – Ira 9:25PM EST]
jae says:
The lapse rate is not caused by GHE’s per se. Your statement about the lapse rate is more or less correct…except that this sets a maximum lapse rate. That is, it is possible for an atmosphere to have a smaller lapse rate than you get from the stability calculation that you allude to. However, it won’ t have a steeper lapse rate because such an atmosphere becomes unstable to convection, with then brings the lapse rate down to the marginal stability value.
So, the best way to put it is that the lapse rate is caused by the fact that the atmosphere is heated from below in concert with stability arguments based on buoyancy, adiabatic expansion, and the existence of convection.
What the GHEs determine is where in the atmosphere the emitted radiation is able to escape to space. Radiative balance of the earth system then sets the temperature at this level in the atmosphere and the temperature at the surface basically follows from the lapse rate.
Dave Springer says:
May 8, 2011 at 10:23 am
“For this reason I call the warmista’s “ice huggers” in fond remembrance of their predecessors the “tree huggers”.”
Good idea. They really do love their Greenland ice and all that.
Ira,
I have been reading many posts here that discuss the blackbody radiation of the earth. You have claimed that the 33K difference is due to GHG back radiation. I don’t want to argue that with you… but I think it would be worthwhile to be very very clear on exactly what you are claiming.
So… I can boil this down to a simple yes or no question…
Are you claiming that if the atmosphere were replaced with a different set of gasses that do not contain GHG molecules, but still had all the other macro effects such as clouds etc in the exact same amount as our current atmosphere… are you claiming that this atmosphere would NOT cause (directly or indirectly) the surface of the earth to warm at all?
You see… it does seem as if the answer to the above question is yes. It does seem as if you are making that claim. Are you? Or, are we just misunderstanding your argument?
-Anton Eagle
John of Kent says:
Bryan says:
Okay…So it is time to debunk the Postma nonsense again, even though we already did it in the last thread that Ira wrote.
The problem with the Postma argument is that the “average emission height” depends on…you guessed it…the IR-absorbing substances, namely greenhouse gases and clouds, in the atmosphere. So, the Postma argument does not get rid of the greenhouse effect…He merely sweeps it under the rug by obfuscating the fact that this average emission height being above the earth’s surface is due to the greenhouse effect.
Think about it. If the atmosphere contained no IR-absorbing substances, then all the IR emitted by the earth’s surface would escape into space and radiative balance would dictate that the earth’s average surface temperature (or really the average of emissivity*T^4 where T is the absolute temperature and the emissivity of most terrestrial materials in the wavelength range of interest is very close to 1) is set by the condition that the earth must radiate as much energy as it absorbs from the sun.
Now…Slowly add IR-absorbing substances. What happens is that some of the radiation from the earth’s surface is absorbed in the atmosphere, which subsequently radiates it again. This absorption can even occur multiple times but once the radiation occurs high enough up in the atmosphere that the remaining IR-absorbing substances above that layer are unlikely to absorb the radiation, then it can successfully escape to space. Hence, the average emission height is what is determined by the IR-absorbing substances in the atmosphere.
As the greenhouse gases in the atmosphere increase, this average emission height rises…and because of the lapse rate…this means less radiation is emitted back out into space. As a result, the earth system heats up until radiative balance is restored.
Ira,
I have a second question regarding the two emission diagrams you show.
The upper graph, showing down-looking readings at the top of the atmosphere shows that approximately 1/2 of the 15 um radiation is absorbed. It looks as if it would be about 90 mW/m^2 without absorption, and instead is about 45 mW/m^2 or so with absorption.
Then you show the lower graph showing the up-looking readings at the surface… showing about 90-100 mW/m^2 of radiation (at 15 um) down to the surface from the atmosphere.
So, my question is… if the GH gasses are absorbing about 45 mW/m^2… how are the re-radiating almost 100 mW/m^2 back to the surface?
It doesn’t look like the sun can be the source, since according to these curves the sun doesn’t radiate hardly anything at those wavelengths. So… where is the extra energy coming from?
Thanks,
-Anton Eagle
Ira Glickstein
Do you know what the adiabatic lapse rate is?.
On page 21 of the Postma paper it is derived.
This is not a controversial point, serious IPCC advocates include this derivation as part of their narrative.
If you like I can give you a couple of such references.
The clouds at 5Km are far better radiators than gaseous CO2 or H2O .
Yet strangely enough it is the Latent Heat and high specific heat capacity of water in clouds that accounts for cloudy warmer nights rather than radiative effects.
The convection mechanism is reduced if there is a smaller temperature difference between Earth Surface and clouds.
John of Kent says:
No! The earths surface is already emitting radiation in the Infra Red. It’s atoms and molecules are ALREADY excited sufficiently to be emitting IR.
Yes..The molecules of the earth surface have kinetic energy because they are excited or are being exited with the absorption of radiation.
This excitement distorts the magnetic field of the molecules components in a way that they are not in balance as they would be if the molecule was at rest. This leads the electromagnetic field of the molecule to send out waves of electromagnetic energy into space at decreasing rates if the source of the energy is turned of.
When the source energy is turned off the emitting waves from the molecule don’t cease immediately because the molecules components have mass and it is the movement of these parts that cause the decreasing waves of electromagnetic disturbance as energy is lost.
Similarly when the molecule is hit by a magnetic wave it will not reach its full kinetic and radiative potential until all its parts are moving in such a way as to propagate a field of disturbance equal to the constant of the energy input over time. At this point it is at radiative equilibrium with the incoming energy and no more work can be done.
Let’s say we are on the moon so there is no overlaying gas and pick an arbitrary incoming value of 100Watts/m^2. The mass of the particles at the surface will eventually increase in temperature until the moving parts of the molecules are so excited they cause a electromagnetic disturbance that is equal to the incoming electromagnetic energy from the sun. At this point the waves of energy from the surface propagate outward and are lost to open space. 100Watts/m^2 in, 100Watts/m^2 out.
This however is not the case with our planet. The over laying gas doesn’t impede the inflow of energy to the surface but the principle remains the same as the moons surface in that in its self the surface will move toward radiative equilibrium with the incoming energy.
This time however the outgoing radiation is now blocked by a molecule of gas which of course also has mass and a state of rest.
The propagating electromagnetic wave from the earths surface is now absorbed by the molecule which in turn adopts kinetic and thereby electromagnetic properties as the state of rest is now disrupted and its components vibrate, sending out electromagnetic waves as it struggles to balance its competing internal forces.
Although free floating the rules for the gas molecule are the same as the molecules at the earths surface. It will absorb all the incoming energy from the earths surface until it radiates away the same amount of radiation it is receiving. It will do this in all directions, so as it moves to reach radiative equilibrium with the surface it will radiate half toward the surface and half away. The energy being radiated back to the surface is not kinetic, it is electromagnetic. It would be 50 Watts/m^2 in the first instance of time with the other 50 Watts radiating away. The surface doesn’t know where the 100 Watts or the 50 Watts are coming from it only knows it is receiving 150 Watts in the second instance of time.
Think of this. If we had a closed system where no energy is lost and we were to put 100 watts a second into the system we would have a system with 100 joules after the first second. Now in the next second we only put 50 Watts a second into the system we get 150 joules in the system. The system doesn’t care that the that the last second had a lower value than the first second it only knows that over two seconds it has received 150 Watts of energy.
John Marshall says:
No…It does not as I have explained above.
The prediction of tropical tropospheric amplification has nothing to do with the greenhouse effect. It has to do with the fact that in the tropics the temperature decrease with height is expected to closely follow the moist adiabatic lapse rate. Hence, this amplification is predicted for warming due to any mechanism.
It is also worth noting that tropical tropospheric amplification is well-verified by the satellite and balloon data for the temperature fluctuations that occur on monthly to yearly timescales, e.g., due to ENSO. Where the data is more ambiguous is with the long-term multidecadal trends, where such data is easily contaminated by artifacts due to changes in instrumentation over time, switches from one satellite to another, etc. The different data sets…and various analyses of the data sets tend to differ not only from the model predictions (depending on which data set you look at) but also from one another.
Even Richard Lindzen agrees that tropical tropospheric amplification follows from basic physics and has nothing to do with the greenhouse effect mechanism…and that the fact that is a problem with the observational data, not the models (and, at any rate, nothing to do with the mechanism causing the warming). His only point of departure is that he thinks the data more likely to be wrong is the surface data in the tropics whereas most others think it is the data at altitude.
The specific fingerprint of warming due to an increased greenhouse effect (at least relative to, for example, the mechanism of heating by increased solar radiation) is that the greenhouse effect is predicted to cause cooling in the stratosphere. And, this is indeed what is seen. (Some of the cooling is due also to the decrease in stratospheric ozone but the amount and altitude distribution of the cooling apparently cannot be explained solely by this mechanism.)
Ira Glickstein, PhD says:
May 8, 2011 at 10:41 am
“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. ”
Acceptable margins of error are established in context. Sometimes being within an order of magnitude is good enough and other times the proverbial nine nines isn’t good enough. But I understand your point. It’s illustrated by a trite expression that +-10% is good enough for government work. Left unsaid is that the government screws up a lot because what’s considered “good enough” by them often isn’t.
Ira:
A chain is no stronger than its weakest link. I think we can agree on that.
When it comes to trying to sort out natural forcings from unnatural forcings we run into a link in the chain where we have a 25w/m2 range of uncertainty in surface forcing from natural factors. We might reliably know that unnatural forcings fall in the range 0.6 – 2.5w/m2. So that’s a strong link but it’s strength is meaningless when there’s a link in the chain with only a tenth of that strength. See what I’m saying?
Martin Mason:
Ira, the Second Law of thermodynamics works at every level and you cannot transfer heat from a colder body to a warmer body. A black body cannot also reabsorb and re-emit lower intensity radiation that it has already emited.
You clearly do not know the basis for the Second Law, which is statistical physics. You seem to believe in some sort of magical version of the Second Law. The actual Second Law is based on the fact that although energy transfers occur in both directions, by simple statistics it becomes essentially astronomically improbable that the net flow of energy, what we call “heat” will be from the hotter body to the colder body for any macroscopic bodies.
In particular, applied to two radiating objects at different temperatures, the Second Law simply states that the amount of radiation from the hotter body that is absorbed by the colder body is always larger than the amount of radiation from the colder body that is absorbed by the hotter body. The laws of radiative transfer automatically satisfy the Second Law when applied correctly and all models of the greenhouse effect, be they toy models or advanced radiative-convective codes, satisfy the Second Law.
No…That doesn’t happen because of simple conservation of energy. The steak is not producing thermal energy or receiving it from a hotter object. So, all that the reflective interior can do is slow the cooling of the steak.
The earth is receiving lots of thermal energy from a hotter object, namely the radiation that it receives from the sun. Its steady-state temperature is set by the balance of what it receives and what it emits back out into space. The greenhouse effect, by affecting the rate at which the earth emits radiation back out into space for a given surface temperature, causes the earth’s temperature to warm in order to maintain radiative balance.
Insulation in general does help you to save on heating bills. The reason that CO2 in particular does not is for a variety of reasons, one being that the heat loss from a house is due to many mechanisms besides radiation. (For the earth system as a whole, the only way it can lose heat is via radiation, although heat can be transferred between different parts of the system, e.g., surface to atmosphere by convection and evaporation/condensation.) Another is that, as discussed above, the full picture of how adding CO2 affects the greenhouse effect relies on the fact of the lapse rate in the troposphere, something that is not applicable in your example.
Dave Springer says: May 8, 2011 at 10:23 am
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.
Dave,
Wouldn’t the explanation be that the surface temperature where there are down-welling currents must be around 4C?
Currently (no pun intended) the major down-welling current is the gulf stream in the north Atlantic. As long as the north Atlantic is ~4 C, the currents along the bottom will be ~ 4 C. It is reasonable to speculate that down-welling currents would always be in cold regions, since that is where the surface water is most dense. (Add in the fact that evaporation of warm water as it heads pole-ward will increase salinity and increase density and we have a stronger reason for down-welling currents are in the polar regions.)
Several commenters maintained that a colder body cannot heat a warmer body. They may have confused heat with temperature. Heat can be transferred from a cold body to a hotter body, but a colder body cannot increase the temperature or heat content of a hotter body. However, a colder body can decrease the rate of cooling of the hotter body by radiation to the hotter body. Electrons jumping orbitals and producing radiation don’t know if there is a warmer or colder body out there somewhere, therefore the total instantaneous radiation from any body is independent of the temperature of the surroundings.
Something I did not see in the comments was mention of emissivity, which would have a direct impact on the sensible temperature of the air and surface of the earth. Good emitters (high emissivity) both absorb and emit energy better (grass, leaves, black bodies) than low emitters (most light colors, stainless steel). Emissivity will vary greatly from year to year depending on snow cover, clouds, crops, deforestation, etc.
Dr. Glickstein’s discussion is interesting, but I think is too simplified to convince any warmist that CO2 is not cooking the earth.
A couple of things that I am curious about that directly affect the emissions balance, and which have not appeared in any discussion I have read, are:
1. Energy is absorbed and converted to chemical energy through photosynthesis. I have no idea how much energy that would be (probably not much), but with higher CO2 levels, vegetation is growing faster so it is logical that more radiation is being converted to plant material than in the past, which is stored energy that will not be re-emitted until the material is burned or otherwise reverts to it’s former state.
2. The earth might correct temperature variations by moderating emissions, especially in the Arctic. When the northern oceans are warmer than normal, they freeze later in the season, and since they emit to an almost perfect black body (deep space with no sunlight) they release much more heat and take up very little, esp. in winter, helping to correct the global temperature. Ice and snow are poor emitters and also insulate the warmer ocean beneath whereas a dark ocean is a very good emitter. A change in ocean currents, for example diversion of a warm pacific current to the Arctic for a prolonged period, could cause global cooling by eliminating ice in the Arctic all year. I have no idea how significant this cooling would be, but suspect it is substantial. Perversely, an abnormally warm current to the Arctic would cause warming of the atmosphere while reducing heat content in the ocean, making it appear as if the earth is warming when in fact it is cooling. Do the GCM’s address this?
As there are multiple periods in the geological record of tens of millions years in duration when CO2 levels were high and the planet was cold and when CO2 levels were low and the planet was warm, it appears there is a basic fundamental assumption in the model of atmospheric radiation that is incorrect or there is an omission of another mechanism from the standard models of atmosphere radiation.
One possibility is the greenhouse mechanism saturates such that the initial CO2 causes most of the warming.
Gas molecules transfer energy from molecule to molecule by collisions in addition to radiation.
As one moves higher in the atmosphere there are more ions due to galactic cosmic rays striking the atmosphere. An ion radiates continuously due to motion of the ion in addition to the band specific radiation that is emitted when an ion captures an electron. It is possible that radiation from ions provides the leak to cause the CO2 mechanism to saturate.
Atmospheric carbon dioxide levels for the last 500 million years
http://www.pnas.org/content/99/7/4167.full
Using a variety of sedimentological criteria, Frakes et al. (18) have concluded that Earth’s climate has cycled several times between warm and cool modes for roughly the last 600 My. Recent work by Veizer et al. (28), based on measurements of oxygen isotopes in calcite and aragonite shells, appears to confirm the existence of these long-period (_135 My) climatic fluctuations. Changes in CO2 levels are usually assumed to be among the dominant mechanisms driving such long-term climate change (29).
Superficially, this observation would seem to imply that pCO2 does not exert dominant control on Earth’s climate at time scales greater than about 10 My. A wealth of evidence, however, suggests that pCO2 exerts at least some control [see Crowley and Berner (30) for a recent review]. Fig. 4 cannot by itself refute this assumption. Instead, it simply shows that the ‘‘null hypothesis’’ that pCO2 and climate are unrelated cannot be rejected on the basis of this evidence alone.
http://www.nature.com/uidfinder/10.1038/nature01087
Despite these successes in linking variations in greenhouse gas concentrations to climate change in the geologic past, the oxygen isotope palaeotemperature record from 600 Myr ago to the present displays notable intervals for which inferred temperatures and pCO2 levels are not correlated1. One of these occurred during the early to middle Miocene (about 17 Myr ago), a time well established as a warm interval (relative to today), but with proxy evidence for low atmospheric pCO2 (ref. 2). Moreover, whereas climate models predict tropical warming in response to elevated pCO2, geologic data — in particularly the oxygen isotope record — indicate muted warming or even cooling at low latitudes while higher latitudes warm (the ‘cool tropicsparadox’10–11).
Bryan,
The 2.66 grams per square inch figure is considering the whole air column.
http://www.wolframalpha.com/input/?i=14.7+lbs+*+400%2F1000000
Alan D. McIntire,
The solar radiation hitting the earths surface is 184 W/m^2 per Trenberth 2009 or 198 W/m^2 per Trenberth 1997. The surface albedo must be applied to this to get the net gain. Back radiation adds another 333 or 324 W/m^2 respectively. Since Trenberth’s diagram don’t show any reflection at these wavelengths , it is unclear whether he has applied the albedo that corresponds to these wavelengths. The albedo of surfaces varies with wavelength, and for some surfaces like snow the variation is quite significant.
If the emission from a surface is blocked from escaping in some parts of its spectral emission range, then, everything else being equal, it must increase in temperature until enough of its spectrum is in the ranges that do allow the energy to escape. That would be its equilibrium temperature. Of course, everything else isn’t equal, it will never have to reach that temperature, because conduction, evaporation, convection, poleward heat transport, etc. will assist in transporting the heat away.
Energy in = energy out is not technically true though, the heat that reaches the surface is attenuated as the surface warms and cools, for example heating of the ocean surface and ground surface. When the sun first hits them in the morning they are not instantly at thermal equilibrium and radiating what they recieve straight back upwards, plus the deeper ocean can store and release energy – I know over time energy in = energy out, but it doesnt actually apply to any moment during a day, its why the coldest temps are night are the early morning, and why its warming in the afternoon, not when the sun is highest. I think the diurnal pattern of energy release is also something worth considering, as it does not match the incoming diurnal pattern.
I think to further peoples understanding the impact of surface attenuation and the affect on the ocean on the global energy flow need to be discussed, as the greenhouse effect doesnt quite hold if these affects are not considered when looking at a point in time on the earth
The issue at hand here is not that co2 can absorb energy, but what occurs and how does it contributes to AGW, and specific man’s co2 output.
If I suspend in the middle of my room a 4 foot by 6 ft by 2 inch thick lead plate in the middle of my room (not touching the walls), then while that lead plate has huge ability to absorb energy (1000’s of times more than co2), that introduction of the lead plate will NOT cause the room to warm up. So, any energy absorbed by this lead plate will be re-emitted back into the room.
If the above lead plate could heat up the room, the we would all purchasing big lead plates to suspend in the middle of the room for free heat.
On the other hand, increasing the insulation of the WALLS of the room is a different matter.
So, at the end of the day is not that co2 can absorb energy, but what occurs with that effect. As the lead plate example shows, just because physics says something can absorb energy does not necessary mean it affects the inflows and outflows of energy in a given system.
And in fact it not the co2 that holding this energy anway, but the other substances such as ground and ocean and other parts of atmosphere that represents the bulk of the “mass” of the atmosphere to hold that heat energy.
In fact, this explains why engine blocks and especially motor cycle heads are often painted black, not silver in color. The choice of black paint on the engine can cause the engine to cool better! In other words, placing black paint on an engine block INCREASES cooling effect yet black paint is known to absorb energy better!
In effect, since black is a good absorber of energy it’s also thus becomes a good emitter of energy. Black objects emit more radiant energy (cools faster) than a white or silver to its cooler surroundings.
The issue here never been that co2 can absorb energy, but the issue is not the slam dunk as to what effect this has in terms warming the overall system, or even as some claimed can in fact cause cooling of the system based on the same reasons why black paint on engines can help cooling!
Super Turtle
“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.”
Hadley cells transport volumes of atmosphere from high up to lower down. Don’t confuse the motion of the fluid with its pressure distribution. The fluid can move across a pressure gradient, expanding and contracting as it goes, while the pressure at every point remains constant.
If there were no convection loops on Venus, it wouldn’t be so windy there.
It seems that for incoming sunlight there is one surface (where sunlight strikes) but for the outgoing radiation there is another surface (at the top of the atmosphere for some wavelengths). One might say that the heat that consumes time migrating from the incoming surface to the outgoing surface represents the heat of greenhouse warming.
I always wonder about the 15 degree C number quoted as the earth’s surface temperature. It seems that this is the just the air temp nearest the surface struck by sunlight (assuming I don’t misunderstand the source of the number). Why wouldn’t it be more appropriate to attempt to average all temps (air, sea, and land) inside the regions somehow touched by solar radiation (but excluding deep earth temps influenced by heat of radioactivity).
Ron House wrote:
Whether or not it’s directly measureable doesn’t matter. What matters is whether or not it’s happening.
If molecules follow ballistic trajectories, the minimum KE will occur at zenith and be higher at all other points.
A short MFP just means that equipartitioning will be rebalanced (on average) every MFP.
Assuming air (a diatomic gas with 5 degrees of partitioning), for a given delta-h, the thermal energy will be reduced by 1/5th of the energy required to lift molecules by that delta-h.
My point is that Objection #2 is not, in fact, correct.