Guest Post by Willis Eschenbach
OK, a quick pop quiz. The average temperature of the planet is about 14°C (57°F). If the earth had no atmosphere, and if it were a blackbody at the same distance from the sun, how much cooler would it be than at present?
a) 33°C (59°F) cooler
b) 20°C (36°F) cooler
c) 8° C (15°F) cooler
The answer may come as a surprise. If the earth were a blackbody at its present distance from the sun, it would be only 8°C cooler than it is now. That is to say, the net gain from our entire complete system, including clouds, surface albedo, aerosols, evaporation losses, and all the rest, is only 8°C above blackbody no-atmosphere conditions.
Why is the temperature rise so small? Here’s a diagram of what is happening.
Figure 1. Global energy budget, adapted and expanded from Kiehl/Trenberth . Values are in Watts per square metre (W/m2). Note the top of atmosphere (TOA) emission of 147 W/m2. Tropopause is the altitude where temperature stops decreasing with altitude.
As you can see, the temperature doesn’t rise much because there are a variety of losses in the complete system. Some of the incoming solar radiation is absorbed by the atmosphere. Some is radiated into space through the “atmospheric window”. Some is lost through latent heat (evaporation/transpiration), and some is lost as sensible heat (conduction/convection). Finally, some of this loss is due to the surface albedo.
The surface reflects about 29 W/m2 back into space. This means that the surface albedo is about 0.15 (15% of the solar radiation hitting the ground is reflected by the surface back to space). So let’s take that into account. If the earth had no atmosphere and had an average albedo like the present earth of 0.15, it would be about 20°C cooler than it is at present.
This means that the warming due to the complete atmospheric system (greenhouse gases, clouds, aerosols, latent and sensible heat losses, and all the rest) is about 20°C over no-atmosphere earth albedo conditions.
Why is this important? Because it allows us to determine the overall net climate sensitivity of the entire system. Climate sensitivity is defined by the UN IPCC as “the climate system response to sustained radiative forcing.” It is measured as the change in temperature from a given change in TOA atmospheric forcing.
As is shown in the diagram above, the TOA radiation is about 150W/m2. This 150 W/m2 TOA radiation is responsible for the 20°C warming. So the net climate sensitivity is 20°C/150W-m2, or a temperature rise 0.13°C per W/m2. If we assume the UN IPCC canonical value of 3.7 W/m2 for a doubling of CO2, this would mean that a doubling of CO2 would lead to a temperature rise of about half a degree.
The UN IPCC Fourth Assessment Report gives a much higher value for climate sensitivity. They say it is from 2°C to 4.5°C for a CO2 doubling, or from four to nine times higher than what we see in the real climate system. Why is their number so much higher? Inter alia, the reasons are:
1. The climate models assume that there is a large positive feedback as the earth warms. This feedback has never been demonstrated, only assumed.
2. The climate models underestimate the increase in evaporation with temperature.
3. The climate models do not include the effect of thunderstorms, which act to cool the earth in a host of ways .
4. The climate models overestimate the effect of CO2. This is because they are tuned to a historical temperature record which contains a large UHI (urban heat island) component. Since the historical temperature rise is overestimated, the effect of CO2 is overestimated as well.
5. The sensitivity of the climate models depend on the assumed value of the aerosol forcing. This is not measured, but assumed. As in point 4 above, the assumed size depends on the historical record, which is contaminated by UHI. See Kiehl for a full discussion.
6. Wind increases with differential temperature. Increasing wind increases evaporation, ocean albedo, conductive/convective loss, ocean surface area, total evaporative area, and airborne dust and aerosols, all of which cool the system. But thunderstorm winds are not included in any of the models, and many models ignore one or more of the effects of wind.
Note that the climate sensitivity figure of half a degree per W/m2 is an average. It is not the equilibrium sensitivity. The equilibrium sensitivity has to be lower, since losses increase faster than TOA radiation. This is because both parasitic losses and albedo are temperature dependent, and rise faster than the increase in temperature:
a) Evaporation increases roughly exponentially with temperature, and linearly with wind speed.
b) Tropical cumulus clouds increase rapidly with increasing temperature, cutting down the incoming radiation.
c) Tropical thunderstorms also increase rapidly with increasing temperature, cooling the earth.
d) Sensible heat losses increase with the surface temperature.
e) Radiation losses increases proportional to the fourth power of temperature. This means that each additional degree of warming requires more and more input energy to achieve. To warm the earth from 13°C to 14°C requires 20% more energy than to warm it from minus 6°C (the current temperature less 20°C) to minus 5°C.
This means that as the temperature rises, each additional W/m2 added to the system will result in a smaller and smaller temperature increase. As a result, the equilibrium value of the climate sensitivity (as defined by the IPCC) is certain to be smaller, and likely to be much smaller, than the half a degree per CO2 doubling as calculated above.
Brian: I suggest that you re-read my post of (19:32:16) 19 March. It is actually not that difficult to understand if your mind is at all open to new things even if they go against your ideological predispositions.
To summarize: The net flow of terrestrial radiation is out. This still makes the temperature higher due to the greenhouse effect than it would be in an IR-transparent atmosphere because the net flow is less than it would be in that case.
I don’t know how I can explain it any simpler. There are also various toy models that you can play with to get the picture. Willis’s steel greenhouse is one. Another one, which is admittedly more abstracted from the actual system in question but is kind of fun is where you have a blackbody sphere representing the sun that is at a constant temperature T_s and then you have it surrounded by one or two blackbody concentric spherical shells (A and B, which are analogs…in a very abstract way…of the earth and the atmosphere, respectively, with the radius of B slightly larger than A). There is empty space (assumed to be at zero temperature) beyond that. The question is then: What is the steady-state temperature of spherical shell A when shell B is absent and what is the temperature of shell A when shell B is present? Also, when Shell B is present, which way is the net radiative heat flow, from A to B or B to A? (These questions can be answered exactly by a simple calculation if you assume that the radii of the sphere and the two shells are close enough that one can neglect any “self-view” that the inner surface of shell A or B has of itself.)
That’s not what I said; I suggest you might try reading it again.
The point is that such energy storage happens only very slowly. Even though we are burning those fuels at a rate that far exceeds the rate at which they were formed, we are still producing only about 0.02 W/m^2 of direct heat by doing so.
The IPCC already knows this, which is why the current concern is over the changes that we are making to the chemistry of the atmosphere by burning fossil fuels that cause it to retain more of the sun’s energy rather than concern about the effect of the waste heat that we are producing by burning fossil fuels.
I don’t see where you pointed to any such mistakes. The one specific thing that you questioned is whether Arthur is correct when he asserted that he thought an IR-transparent atmosphere would be isothermal. I would have to think more about that, but it is irrelevant to the main issue because, whether or not it is isothermal, we know in the case of an IR-transparent atmosphere what the surface temperature has to be.
I guess you too missed my post of (19:32:16) 19 March where I explained very clearly where G&T go wrong in their claim of a violation of the Second Law. It seems strange to me that neither you nor Brian Valentine have been interested in engaging me on those points, seeming to prefer instead to go around attacking strawmen.
I don’t see where I gave you a specific number. But, if you want to see my papers, all you have to do is a simple google scholar search since I post under my real name here. (Additional fact: Middle initial is D.)
Igl (03:59:11) asked: “How do you arrive at “a massive 22 to 32 W/m^2″ ?
”
Please see my post at 18:18:13, 19MAR10. In part:
“Cranking in the numbers:
Change in Forcing = 4sT^3dT + 78xdT. (s is 5.67×10^-8, dT is change in temperature, x is percentage increase in evaporation per DegC).
The big unknown in this equation is x, the increase in ebaporation. The Clausius-Clapyeron equation gives an upper limit of 6.5%, and some scientists think it is as low as 2%. It’s not 0%.
For x=2% the surface sensitivity is 0.15DegC/W/m^2, and the Change in Forcing is 22W/m^2 if the temperature rises by 3DegC.
For x=6.5% the surface sensitivity is 0.095DegC/W/m^2 and the Change in Forcing is 32W/m^2 for a temperature rise of 3DegC.”
The sensitivity at the hot, massive Surface is very different to the sensitivity of the thin cold atmosphere at the Tropopause. The system has to work much harder to heat the surface and keep it hot than it does at the Tropopause.
Joel Shore (06:46:04, 21MAR10) said:
“It is just that the heat flow into space is less than it would be if the atmosphere were transparent to IR radiation (and the Earth’s surface were still at its current temperature).”
I think that statement may be wrong. At equilibrium (planetary and atmospheric temps stable) the energy flux radiated to space equals the energy flux received from space (neglecting any flux from the centre of the planet.), regardless of the state of the greenhouse.
My understanding is: Some of the radiated energy from the Earth (according to KT around 40W/m^2) is at the “window” frequencies and passes directly out to space. The rest of the energy which is going into the atmosphere (a small amount of net radiated energy, about 25W/m^2, plus the directly conducted energy about 25W/m^2 plus the latent heat in evaporated water about 80W/m^2, plus the absorbed sunlight about 75W/m^2) can only leave the planet by radiation. It gets radiated from two primary bands:
1. The band of water vapour. The effective level is somewhere near the top of the clouds. Most of the radiation (at least two thirds) is from here.
2. The CO2 in the mid Tropopause to Stratosphere. About 20-25% comes from here.
Here’s an even simpler toy model from about p200 of An Inconvenient Truth (and about all he has to say about how it works):
“CO2 acts like a blanket that keeps the Earth too warm.”
Tell me about it, Joel.
Folks, if some fish that Al Gore or Joel want to sell you don’t smell too good,
DON’T BUY
Brian –
I know I am new to this thread – and to this site (I have been lurking for awhile while studying), but you cannot be seriously quoting Al Gore on thermodynamics or physics, rght? I mean really?
This is a guy who shows a glass of water with Ice in it, that does not protrude above the rim of the glass, and then shows it melting with the result that the water flows out of the glass onto the table the glass sits on…really? Hardly Mr. Wizard, I don’t think he is worth a quote. A Nobel Prize maybe, but that’s politics, not what is being discussed here.
Mike
Re: Joel Shore (Mar 19 19:32),
Joel I agree with 1) and 2)
For
(3) Despite the fact that the net flow is from earth to atmosphere, the effect of an IR-active atmosphere is still to produce warming relative to the case of an IR-transparent atmosphere. This may be the point that trips the most people up….It seems like an almost unstated assumption in many arguments of a Second Law violation that in order for the greenhouse effect to occur, the net flow must be from atmosphere to Earth. ****THIS IS WRONG.**** The reason that this is wrong is because in the comparison case, of an IR-transparent atmosphere, all the radiation emitted by the earth escapes into space. Hence, anything that causes some of that radiation to be returned to the earth will cause warming relative to that case.
I come to think that it is the semantics that causes the confusion at this point.
The active energy role given to the atmosphere . Instead of “returned” one should state “retained” .
This misuse, as standard thermodynamics goes, is enhanced by the terminology of “forcings”.
Radiation is the dominant way energy leaves this ball and enters this ball, and can be used instead of total energy balance with small errors.
Within this ball, earth, the equivalence given and imposed to think in terms of “radiations” and “forcings” when a multitude of other heat transport involving processes exist, leads to errors, ( at least in temperature estimates) imo . It is wrong to state the problem in terms of Watts/m^2 as if all processes are perpendicular to the surface of the earth.
It is true that when one integrates to solve a problem, one can turn it into shells dx and consider the forces acting on this , but one does not go around making a terminology : the central part of the earth give A contribution to gravity, the magma adds B, the mantle C, in order to describe to the layman scientist how gravity works on the surface. ( remember the mechanics problem of a marble falling in hole that goes completely through the center of the earth to the other side?) It would be confusing and not useful for calculations involving gravity on the surface where people need a formula.
I believe this sort of confusion has been introduced by the climate terminology and makes it difficult to see the forest for the trees and introduces errors in actual calculations.
One, imo, should be saying: the heat capacity of the atmosphere is increased by the existence of H20 and CO2 etc, from x to y, and thus heat transport to space is delayed by z , instead of handwaving watts/m^2.
So it may only be semantics, but thermodynamics says that a cooler body cannot warm a hotter body unless work is done. I can imagine the gigantic system of convection precipitation evaporation etc in the atmosphere/ocean system to be described as an equivalent heat pump where the energy is supplied by the sun and the the work is done by the winds gravity tides and the chemistry. A passive ball as is described with forcings and watts/m^2 and an atmosphere actively warming violates the second law , imo always of course.
CO2 has maybe a tiny role in this heat engine, by changing the heat capacity.
Igl wrote(06:50:50, 21MAR10):
“But only 20% of the energy transport from the surface is non-radiative. Why would suddenly most of the added 10 W be returned as non-radiative? Still sounds very strange.”
It is important to note that it is the NET radiative transfer (absorbed – radiated) which heats the air, not the absorbed radiation. So the actual transfer of energy from the Surface into the Atmosphere is:
Net Absorbed Radiation (= IR Radiated from the Surface(390) – The portion which is not absorbed and escapes straight to space (40) – The Back Radiation (324), the figures come from K&T 1997 from the IPCC AR4, Chapter 1) = 26W/m^2
+ Direct Conduction into the air = 24W/m^2
+ Latent Heat in Evaporated Water = 78W/m^2
So about one fifth of the energy transferred from the surface is radiated,
one fifth conducted,
and three fifths is in water vapour as latent heat.
When the surface warms further, evaportion increases, and the NET surface radiation absorbed by the atmosphere falls by exactly the same amount. At a 3 DegC increase, the evaporation increases by between 6 and 16 W/m^2 (scientists are unsure) to 84 to 94W/m^2, and the NET radiation drops by that amount to between 10 and 20W/m^2.
Joel Shore wrote (19:16:13, 21MAR10)
“The net flow of terrestrial radiation is out. This still makes the temperature higher due to the greenhouse effect than it would be in an IR-transparent atmosphere because the net flow is less than it would be in that case”
That is incorrect I think.
The net flow is identical in all cases of the atmosphere. Neglecting the flows into and out of the solids/liquids of the planet, (which for clarity only I ignore by claiming an equilibrium which I acknowledge never exists in practice) the incoming solar radiation is always balanced by the outgoing radiation.
This outgoing radiation comprises reflected sunlight, IR “through the window” direct from the surface, and IR from the gases in the atmosphere, primarily Water Vapour, and to a considerably less extent, CO2.
It is reasonably obvious that the higher one goes in the atmosphere the more chance a photon emitted by a water molecule will have of NOT being absorbed by a higher water molecule. If one is very low down then any radiation from water molecules is completely blocked by the overlying water molecules. It is only where the water vapour thins out (top of the clouds) that emissions from water vapour have a good chance of making it to space. (Note that the intensity from this layer is much higher than from the CO2, as it is relatively warm – around minus10DegC and water vapour has a much more exrensive spectrum).
Similarly for CO2, but in this case the extinction horizon is deep in the Tropopause, and the majority of emissions are coming from the stratosphere. (The gas is much colder, around -45DegC, and CO2 has less spectrum, so it emits much less energy than the water vapour).
If you increase the concentration of either gas, the level at which extinction occurs changes. For an increase in gas concentarition this is higher in the atmosphere. The resultant energy imbalance is called “Radiative Forcing” (or “Feedback” in the case of water vapour, which the IPCC doesn’t like very much). That imbalance causes local cooling or heating of the atmosphere until a balance is restored. This is called the “Greenhouse Effect”.
That’s my understanding, which means it is probably wrong!
Joel
Here is the direct link you require I hope you read the whole piece so as not to say I pulled this out of context.
Its easy to make a slip when responding in a blog but what alarms me is that Arthur did not take the chance to set the record straight.
It seems an elementary mistake – draw your own conclusions.
Try to cut down on the insult throwing.
If you think about it it is more the language of the football terraces than of science.
Rational debate and adherence to the scientific method is the only way to make progress.
…..In fact, I stated earlier that the atmosphere would be essentially isothermal, at the surface temperature. So your claim that I think the “temperature at top of the N2/O2 atmosphere would be about 30 degrees C below the surface” is wrong. Not that I see any significant logical conclusion you are drawing from the issue. http://arthur.shumwaysmith.com/life/content/the_arrogance_of_physicists
Anna V(22:13:06, 21MAR10) wrote:
“One, imo, should be saying: the heat capacity of the atmosphere is increased by the existence of H20 and CO2 etc, from x to y, and thus heat transport to space is delayed by z , instead of handwaving watts/m^2.”
I think that is only partially correct. The “heat capacity” is presumably the amount of energy it takes to heat a certain mass of air by a certain amount. The concentrations of Water vapour and CO2 in the air make almost no difference to the heat capacity.
But I said partially correct. Where I think the statement is sort of correct is that if water vapour concentration is increased then the air is actually carrying much more energy – due to the increased latent heat.
So I think it is untrue to say that if CO2 concentration is increased the heat capacity of the air is increased.
But if the surface temperature goes up and as a result there is more evaporation, then the air is holding more energy.
It’s quite interesting – as the surface temperature increases, less energy is being transported into the lowest levels of the atmosphere (by radiation and convection), and more is going to the middle levels (the clouds) in evaporated water vapour.
Colin Davidson (20:21:36) :
Sorry Colin. I did search your name… well, bad excuse
Then we pretty much agree. Correcting for the evaporation I’m ending in the area 1.3 C per CO2 doubling. So if K/T budget is right then IPCC is wrong. Cleary it can’t be us two being wrong 🙂
But I totally disagree with your (01:01:42) …
anna v
I have no idea where they get the lunar temperate data in those quotes you keep using. The reference is not published by NASA and it contains no references to the actual data returned by the sensors in the boreholes.
The full data record is not public yet but NASA says it will be available for anonymous FTP download “soon”. If you had checked my original comment on this you’d find I got my data from the link below which has the data plotted at low resolution for Apollo 15 & 17. Apollo 17, by the way, recorded a constant regolith temperature of 18C. 23C was the constant temperature recorded at the Apollo 15 site. Apollo 17 was closer to the moon’s equator (20 degrees n. latitude vs. 26) and the regolith there was also darker, both of which combine to make the average surface temperature there 5C warmer. I used the Apollo 15 site as it’s more representative of the typical lunar surface in albedo and equidistant between pole and equator.
http://education.ksc.nasa.gov/esmdspacegrant/LunarRegolithExcavatorCourse/Chapter5.htm#OtherPhysicalProperties
That said, there should be no argument from any physicist that once the borehole depth is deep enough to smooth out the diurnal heating/cooling fluctuations the constant temperature obtained is the average of the surface temperature. This is pretty simple stuff. The calculations are not simple if you are trying to go backward from watts/meter^2 at the surface to the temperature at any particular depth. Then you need to know the thermal diffusion characteristics of the substrate and because any real world substrate is not going to be homogenous the calculated result will never be quite as good as a measured result. When you have a thermocouple buried at a certain depth you don’t need to do any calculations as the thermocouple is giving you the correct result of those calculations with the actual dirt doing the integration of the heat flow equations for you. The actual dirt does the calculation for every quantum particle in the whole system which is something you cannot hope to do on paper. The best you can do on paper is use statistical thermodynamics to predict bulk behaviors of systems with many many particles. This is how experimental science works. You produce hypothetical results based on your perception of how things work then you obtain actual results from the real world and compare to your hypothetical results. Experiments can yield bogus data of course but in this case (the Apollo heat flux experiment) the results are quite reliable as the instrumentation was nothing new, the deployment rather simple, and no uncontrolled variables of any significance to worry about (the interior of the moon is geologically dead, no atmosphere, no water transport of heat through the soil, no seasons, etc.)
Evidently you’ve never worked on the experimental side or it’s been so long you’ve forgotten what it’s like because a thermocouple is as basic a piece of lab equipment as test tubes, centrifuges, litmus paper, and bunsen burners. The principle of operation of thermocouples is basic high school physics and, if nowhere else, you had to have used thermocouples in high school and college science courses where there was any laboratory work included in the course. I was shocked when you didn’t know what one was.
Anyhow, if you want the equations which apply to soil physics and heat flow I suggest going here:
http://soilphysics.okstate.edu/software/SoilTemperature/index.html
The above is a downloadable software package that does the math for you, either calculating average surface air temperature taken from from soil temperature readings at depth or going the other way and predicting soil temperature at depth from average air temperature. The documentation with the software lays out the equations used by the software. This is important stuff when doing things like designing energy efficient earth-insulated buildings and using heat pumps with heat exchangers in boreholes. For instance, if you’re in upstate New York the constant soil temperature, when you have enough thermal mass to smooth out seasonal temperature change, is about 52 degrees. In south-central Texas where I’m at the average soil temperature is 72 degrees. That’s a big difference if you’re sinking a house in the ground or piling dirt around it to leverage the thermal inertia of the earth for heating/cooling or drilling a hole in the ground to drop an HVAC heat exchanger into. Same goes for the moon should we ever start having buildings there. It’s a very handy fact to know that burying a habitat one meter deep at 26 degrees north latitude on the moon with regolith similar to Apollo 15 landing site would produce a stable inside temperature of -23C absent any internal heating or cooling or -18C for a similar habitat at 20 degrees north latitude under regolith with an albedo like that at Apollo 17 landing site.
And back to the main point – if the earth didn’t have an atmosphere it would be quite similar to the moon as far as average surface temperature. I’m sure Willis knows this even if he won’t admit it and now he appears to be sulking. What the heck is it about the internet that makes people so unwilling to admit mistakes?
Colin Davidson says:
Re: Dave Springer (Mar 22 04:10),
I am tired of this one upmanship.
I was not questioning the term “thermocouple”. I was questioning your assigning it to the 50cm layer of the moon surface.
from wiki
A thermocouple is a junction between two different metals that produces a voltage related to a temperature difference.
Which is what I remembered and has nothing to do with your model of the ground integrating global temperatures of the moon.
It must be the “couple” that is confusing.
That there will be a functional connection, there will be. But until one integrates the skin surface temperatures ( which are the ones responsible for radiation and its balance) and has the average moon temperature I will not be convinced that the 50cm layer temperature gives the average moon temperature, and not the 1m or 2m. The steadiness in day night changes is a necessary condition if you are talking of an integrator, but not a sufficient one, always in my opinion. It is the differences that are eliminated but that does not fix the absolute value.
After all, if the regolith were a complete insulator, the 50cm layer would be at close to 0K while the average skin surface would still be -23 ( with the numbers above for the sake of argument ). Raise the heat conductivity incrementally and the temperature will rise correspondingly, but in no way it will be the surface average energy, though the change will be functionally connected ( if the average temperature became -20C correspondingly the 50cm level would rise by a calculable increment).
Re: Dave Springer (Mar 22 04:10),
That said, there should be no argument from any physicist that once the borehole depth is deep enough to smooth out the diurnal heating/cooling fluctuations the constant temperature obtained is the average of the surface temperature.
This is one physicist who doubts it, as I explained in my previous post.
There are more with me I guess.
If this were true, why go through the trouble of surface thermometers and not grid the land with boreholes?
Our disagreement lies in the absolute value of the temperature, when first the seasonal/time variation stops being evident. You are saying it is the average temperature over the seasons/times and I am doubting this identity.
For example, in:
http://www-personal.umich.edu/~shaopeng/science98.pdf
They are talking of deltaT. Not absolute T. I have no quarrel with that.
“The question I thought we were talking about is whether the atmospheric greenhouse effect violates the Second Law ”
The answer is, I can’t go any farther to convince you, and apparently, conversely.
If you really think about it this greenhouse gas idea causing global warming in the sense that it applied has to be completely erroneous. CO2 has been in the air since the Earth had an oxidizing atmosphere, probably less than a billion years after the first appearance of life on Earth, and and from all appearances of the geologic record, the rise and fall of CO2 in the air has never been associated with true climactic change. It has been the result of it, related to ocean solubility of it.
From a phenomenological standpoint, it MUST violate the second law Joel OR CLIMACTIC CHANGE FROM CO2 IN THE AIR WOULD HAVE HAPPENED IN THE PAST
can’t you see that? It’s Cold Fusion all over again. If Cold Fusion were possible at anything exceeding quantum tunneling there would be no such thing as an ocean.
If greenhouse CO2 were possible at ANY level the atmosphere would have saturated with water vapor long ago. There is no way it could be stopped
Don’t you have any appreciation for what three billion years of geologic history is?
Fleishman and Pons could be stopped because nobody could build their little cold fusion test tube thing (not that anybody need to try). This AGW thing cannot be so easily stopped because there is nothing but rational thought to counter it and that’s JUST NOT ENOUGH for some folks who for one reason or another actually like the idea and will go to the end of the Earth to defend it
Igl wrote (02:38:39, 22MAR10):
“Then we pretty much agree. Correcting for the evaporation I’m ending in the area 1.3 C per CO2 doubling. So if K/T budget is right then IPCC is wrong. Cleary it can’t be us two being wrong 🙂
But I totally disagree with your (01:01:42) …”
I think what Igl may disagree with is my statement that the atmosphere is heated by NET absorbed surface radiation, rather than the actual amount of radiation absorbed.
You are standing in a room. It feels neither hot or cold. You are receiving around 325 W/m^2 of radiation from all directions. Why don’t you warm up? Because you are also radiating about the same out to your surroundings.
Replace the person with some air. looking to the side, the air absorbs about the same radiation as it emits, so it does not heat or cool from that source. Looking down at the ground however, it absorbs somewhat more than it emits, so it warms slightly. It is not the absolute anmount of radiation but the NET which counts.
In my post I calculated the relative strengths of the surface fluxes which heat the atmosphere. These are:
CONDUCTION (24W/m^2) which heats the air in direct contact with the surface
NET ABSORBED RADIATION (26W/m^2) which heats the air up to about 500m, but over half that radiation is absorbed within the first 50m
LATENT HEAT IN WATER VAPOUR (78W/m^2) which heats the air when the water vapour condenses into water droplets, ie in the clouds.
If the surface temperature increases by 3DegC, these values alter and become:
CONDUCTION (24W/m^2)
NET ABSORBED RADIATION (Between 10 and 20 W/m^2)
LATENT HEAT IN WATER VAPOUR (Between 84 and 94W/m^2)
I must point out that my posts are really only trying to explain and extend the physics of the ficticious world depicted by Kiehl &Trenberth, particularly their 1997 version which is the one used by the IPCC AR4 Chapter 1. The reason for doing this is to remove all of the variables (non-equilibrium, night/day, cloud/not, land/sea, latitude, season, wind, precipitation, altitude, sea currents, energy from the centre of the earth) from the discussion so that the basic physics can be explored without the complications that these other factors involve.
Going back to that ficticious world, I have a problem, enunciated in my posts at (14:10:34, 20MAR10) and (00:21:13, 21MAR10). That is that the additional downwelling radiation in a 3DegC higher temperature world, is much less than what is required to keep the surface at a 3DegC higher temperature. The surface is much less sensitive to downwelling radiation than the air at the tropopause for two major reasons:
1. It is much hotter than the Tropopause , so the increase in temperature yields a much greater increase in surface radiation.
2. Any temperature increase increases the rate of evaporation, so there is an additional flux required to supply the energy of latent heat in the evaporated water.
The IPCC claims that a doubling of CO2 prodduces an additional 4W/m^2 of “Radiative Forcing”, which through the controversial positive feedback due to water vapour and clouds turns into about 12W/m^2. It claims this warms the upper atmosphere by about 3DegC, and that this local warming gets transmitted to the surface by the magic of constant lapse rate. OK, suppose all that is true.
Where does the additional 22 to 32 W/m^2 downward radiation required to maintain the surface temperature at an additional 3DegC come from? (I note in passing that these are minimum, not maximum estimates, as the additional cloud produced due to the additional evaporation would tend to increase these figures).
Joel
You either did not follow the link or you failed to understand it.
The link shows that Arthur Smith thinks that if CO2 and H20 vapour were removed from the atmosphere.
The atmosphere would then become isothermal from the surface to a height of 30Km.
I certainly do not believe in such nonsense.
Any person that had a clue about the Kinetic Theory (and/or ) had climbed a hill would be in no doubt that the temperature drops steadily.
I thought that he would correct the record once someone had pointed out how foolish it was.
There was no correction and perhaps he still believes it!
Since you are a friend of his perhaps you could have a word with him and explain why this is physical nonsense.
Brian G Valentine says:
One doesn’t “prove” 2nd Law violations from a phenomenological standpoint (especially when one’s interpretation of the phenomenology disagrees with most of the the people who, you know, actually publish in the field).
Or maybe it is because those who who are arguing against it don’t really have very coherent scientific arguments and just put up a bunch of nonsense, like G&T did, that then gets swallowed by people who want to believe it even though it is easy to demonstrate what nonsense it is. If that is “rational thought”, I think you should try something else!
Joel, the only suggestion I have right now is to go “prove” your point with some more condescension and arrogance at people who write papers you don’t like and who question you on the web logs.
With some practice, maybe you can get as arrogant as Eli Rabbit!
Hey – maybe you and Eli can do some joint research together to answer the question
Which of the following is the stinkiest fraud?
– Gerlich and Tscheuschner
– Gerhard Kramm
– Brian Valentine
Publish your results in a reputable journal
Joel Shore (05:15:45, 22MAR10) wrote:
“Yeah…There is always some confusion when talking about the greenhouse effect regarding at what point in time one is talking about. When I said that the net flow out is reduced, I am imagining instantaneously “turning on” the greenhouse effect and seeing the immediate result. But, of course, once the net flow out of the system is reduced, the result will be that the earth heats up until radiative balance is restored. And, once that occurs, what you have is, as you note, that the net terrestrial radiation that escapes is the same as before but the earth has to be warmer in order to produce this result.”
I would like to thank Joel for his answer.
I have a problem with”Radiative Forcing” which is described as a step change to a stable system (The imbalance at the Tropopause if all change in the Stratosphere is complete but no change has happened to the Troposphere). This is because we are imposing a step change on the static, imperfect model that is described by K&T.
I want to understand, instead, the final state, not the transition. I want to see the K&T diagram for a +3DegC world, and I want the surface balance explained in detail. For example, I want to know what the REDUCTION in sunlight absorbed by the Surface is (because it’s cloudier). I want to know how much extra back radiation there is due to a warmer atmosphere. I want to know how much surface radiation is predicted to escape direct to space. I want to know what the amount of direct conduction there is, and if it has changed from the +0DegC world, why. I want to know how much evaporation there is going to be, and why. I want to know how much extra back radiation there is due to the increase in concentration of the two main gases, with a justification.
I guess it’s not really important, because we are only talking about the really simplified, unrealistic model. But I’m curious. I can’t get a surface balance in that world – not one that’s driven by 2xCO2, unless the First or Second Laws are in abeyance.
Bryan:
I don’t see how the climbing a hill notion proves anything: Arthur is talking about a hypothetical case. He knows that the lapse rate exists in our current atmosphere. I also am not clear as to what kinetic theory dictates as to the thermal structure of the atmosphere. Care to enlighten me?
I honestly don’t have a “dog in this fight”. What the thermal structure of the atmosphere would be in the absence of IR-absorbing gases is not obvious to me. However, the one thing that I do know is that the temperature of the surface would be dictated by radiative balance, which I think was Arthur’s main point, the entire thermal structure being somewhat of a side discussion.
Brian Valentine:
It is certainly a bizarre world we live in where those people who call others “arrogant” are those like you and G&T who somehow feel that they know climate science much better than most of the world’s climate scientists. I sort of associated arrogance with having a sense of the correctness and importance of one’s own ideas that is way out of balance relative to the ideas of those who have clearly studied these things much more closely and have the track record of accomplishments to show for this. But, perhaps you have a very different definition.