Home/BlogI’ve had several requests for evidence of the hundreds of watts of downwelling infrared sky radiation. I’ve mentioned that there are many surface radiation budget observation sites around the world (but few in oceanic areas for obvious reasons). I found this presentation summarizing comparisons that Martin Wild and co-investigators have made between these measurements and the latest CMIP5 climate models at the observation sites. It is quite informative, and includes their version of the Kiehl-Trenberth energy budget diagram to fit better to the surface radiative energy budget observations.
For example, here’s a comparison for downward IR flux at the surface between the HadCM3 model and 41 Baseline Surface Radiation Network (BSRN) stations:
In this case, the model underestimates the downwelling sky radiation by about 9 W/m2. But for something supposedly “non-existent”, there is remarkable agreement between the average model behavior and the observations for this huge (300-400 W/m2) component of the surface energy budget.
What is MOST interesting to me is the existence of multidecadal changes in sunlight (downwelling shortwave) reaching the surface, as some of the sites have such records extending back to the 1930s. For example, changes at Potsdam, Germany look somewhat like how global temperatures have changed:
The authors admit this is behavior not seen in the climate models. I suppose scientists like Trenberth or Dessler would claim these changes are positive cloud feedback in response to surface temperature changes. But the continually neglected possibility is that they have causation reversed: that natural changes in cloud cover have caused the temperature changes, and cloud feedbacks are in reality negative rather than positive.
And this is where I believe we should be spending our research time in the global warming debate. Not arguing over the existence of something (“backradiation”) which is routinely measured at dozens of observation sites around the world.
Yes, but is the downward LW incident on the surface from the atmosphere really the fundamental mechanism driving the GHE? I say it isn’t really.
Yes.
I don’t agree and see this as the primary source of confusion and/or misunderstanding.
I agree with you, RW. The “greenhouse effect” through back radiation from the atmosphere is physically absurd and impossible.
It is physically impossible that any body can get warmer or cool at a slower rate if its radiation is somehow re-directed back to it: http://www.drroyspencer.com/2013/05/imaging-the-greenhouse-effect-with-a-flir-i7-thermal-imager/#comment-77996.
We had a frost here last night … no clouds above to reflect IR back to the ground. Of course there was no frost under the deck, where the wood reflected heat back down. Also no frost around the deck where IR was reflected onto the grass.
The basic physics of this shows up all the time.
Greg H or his agent:
Firstly you talk a lot of nonsense.
Secondly you have a thick skin when a site owner has asked that you not post in his site. It is akin to entering someone’s house when not welcome and your behaviour only confirms that Dr Spencer’s decision was right to ban you.
I hope he realises you are posting to a previous post of yours and blocks it.
If ‘back radiation’ existed, we would use it via ‘back radiation collectors’ on the roofs of cars to replace hydrocarbon fuels, using it to power a ‘reverse heat engine’.
The fact is, only the net change of Irradiance can cause transfer of energy in the form of heat or vice versa. To claim that an object emits energy at the rate predicted by the single S-B equation is absurd. Unfortunately, most scientists and engineers believe it to be so because using two S-B terms to calculate net flux is assumed as meaning there are two power streams.
The problem is that Meteorologists and Climate Alchemists are taught this, so it’s very difficult for them to unlearn it. As for lower cooling on a cloudy night compared with a clear night, it’s because a 1 km base cloud stops ~94% of the IR energy loss in the atmospheric window. This assumes ground temperature = 15 °C. The result of this block on IR emission is that convection and particularly evapo-transpiration rise.
A pyrometer measures the same temperature for radiative or convective heat loss because it measures the proportion of filled vibrationally activated surface sites and these can transfer energy by radiation or to adsorbed gas molecules.
When you convert that temperature via the S-B equation to power, it is the potential energy flux the radiation field could transfer to the zero point energy of cold space, not a real energy flux.
Can you explain? There are multiple inputs to the atmosphere that can contribute to downward LW at the surface, including solar power absorbed by the atmsophere yet to reach the surface.
That is, Roy, can you explain?
RW: Thermal emission by a substance is a function of its temperature and emissivity only. It does not matter what caused it to be at that temperature.
What I’m saying is I don’t quite understand how measured downward LW at the surface specifically establishes or demonstrates there is a GHE.
Without the downward LW, the only real power input to the surface is the unreflected SW solar input, which is no where near enough to maintain the present surface temperature levels and their resulting observed upward LW radiation. While we may not be able to calculate all of these to the ~1 W/m2 accuracy to know what effect we are having on this balance, there is no way we can close the 150 W/m2 gap without this.
Gravitational potential energy, ‘Lapse Rate’, causes the lower atmosphere to be hotter than the upper atmosphere. this is why Venus is so hot.
The 160 W/m^2 average solar flux is recovered as the 17 convection, 80 evapo-transpiration, 23 W/m^2 absorbed by non self-absorbed ghgs, none of it CO2 15 µm band IR, and the 40 that goes to space via the atmospheric window.
The 333 ‘back radiation’ is a potential energy flux but with a normal temperature gradient none of it is converted to heat energy. Instead it is annihilated at the surface thereby mutually annihilating ~60% of its potential energy flux.
You can easily prove this by calculating the operational surface emissivity, the proportion of the average input energy that leaves as IR, at ~0.4 [63/160). Correcting this by the ratio of net IR to input SW gives a global average emissivity prediction of 0.158. The measured value is 63/396 = 0.159.
The measured data in the energy budget are a tour do force of experimental science. The pyrgeometer data are 100s of wasted man years: all they do is to represent temperature and that is impossible for a semi-transparent clear atmosphere by pyrometer – you must use a hot wire probe or similar.
Dr. Spencer,
What do you make of Richard Muller’s analysis of the data that shows the CO2 trend to be the best fit with the temperature trend? Is he wrong?
Thanks,
Hops
Hops – That question is really irrelevant to the question at hand.
WATERLOO, Ont. (Thursday, May 30, 2013) – Chlorofluorocarbons (CFCs) are to blame for global warming since the 1970s and not carbon dioxide, according to new research from the University of Waterloo published in the International Journal of Modern Physics B this week.
. . .
“Most conventional theories expect that global temperatures will continue to increase as CO2 levels continue to rise, as they have done since 1850. What’s striking is that since 2002, global temperatures have actually declined – matching a decline in CFCs in the atmosphere,” Professor Lu said. “My calculations of CFC greenhouse effect show that there was global warming by about 0.6 °C from 1950 to 2002, but the earth has actually cooled since 2002. The cooling trend is set to continue for the next 50-70 years as the amount of CFCs in the atmosphere continues to decline.”
see here
http://wattsupwiththat.com/2013/05/30/study-says-global-warming-caused-by-cfcs-not-carbon-dioxide/
Thanks, Dr. Spencer.
Very interesting article. Earth is covered by clouds to such an extent that they must play a fundamental role in its climate.
Clouds seem to both shade the surface and delay its radiative cooling.
They seem to be a very important piece of the climate puzzle.
The changes in sunlight due to a number of factors going forward this decade will be much greater then what happened in the 1970’s which resulted in that decade featuring cooler temperature.
CO2 was increasing then ,like it now but the temperature trend in the 1970’s was cooler.
Imagine what happens to the temp. trend if sunlight (shortwave radiation reaching the surface of the earth) becomes even lower (much lower ) then it did in the 1970’s which I think will be the case if this prolong solar minimum pans out to be as intense and long in duration as is presently thought by myself and others.
Backradiation more correctly labelled LWIR cannot be measured directly.
The pyrgeometer is often presented as being an instrument that directly measures LWIR.
It gives an inferred value which depends on the radiative theory formula used for its calibration being correct.
The real physical quantity being measured when pointed skyward is the heat flow from the sensor to the sky.
This link below sets out what is actually being measured.
It should not need saying that an instrument that is calibrated with a formula cannot then be used as the sole test of the formula.
http://tallbloke.wordpress.com/2013/04/26/pyrgeometers-untangled/
ARGHH. I really am getting tired of repeating myself. While it is true that the instrument does not “directly” measure LW radiation, it nevertheless PROVES the warming effect of the sky on the surface, because that’s exactly what the greenhouse effect DOES, and that’s how the instrument WORKS!! They BOTH involve a surface temperature change resulting from the presence of the atmosphere!!
From what I understand, there are photon well detectors which DO measure directly, but they are not used in this instrumentation.
Roy,
You previously stated that a pyrgeometer measures the temperature of a surface at which it is targeted.
If, then, it is targeted at a cloud then presumably it measures the surface temperature of the cloud. I think you stated just that.
If it is targeted at open sky then what ‘surface’ is it targeted at ?
If that open sky ‘surface’ is at a different height to the cloud then presumably it will record a different temperature due to the decline of temperature with height ?
Then again, measuring a temperature at a specific height above the pyrgeometer isn’t quite the same as measuring a downward flux is it ?
You really should learn to read before you criticize Dr. Spencers extremely simple explanations.
Try and work out what “surface” was being referred to above.
The instrument estimates the effective radiating temperature of either the cloud or the atmospheric layer which is emitting, based upon the change in the LW surface energy budget of the thermopile within the instrument. It is measuring a small temperature response on one side of the thermopile, which is then calibrated in terms of the target’s estimated temperature, assuming a certain emissivity (which can be dialed into the instrument).
The isntrument doesn’t know what the sources of LW radiation are…only that they change the temperature on one side of the thermopile.
What would be the height of the atmospheric layer measured when pointing at the open sky ?
Would that be at a different height than the height of a cloud that interposed itself ?
Stephen,
The height it samples would be strongly wavelength-dependent because the opacity of the atmosphere is strongly-wavelength dependent. At those wavelengths where the atmosphere absorbs strongly, the radiation that makes it to the detector would be coming from close to the ground. At those wavelengths where the atmosphere does not absorb strongly, the radiation that makes it to the detector would be coming from much higher up. (And, of course, this statement itself is a simplification, since the radiation would actually be coming from a distribution of heights, just as the various channels of the microwave sensors on the satellites that Roy Spencer uses to calculate temperatures come from a distribution of different heights in the atmosphere ( http://www.skepticalscience.com/pics/WeightingFunction.jpg )
Now, this is somewhere that I am prone to defer to your expertise in remote sensing…
…but I’m pretty sure when an infrared or microwave sensor detects a signal from a body cooler than the sensor itself is, the signal detected is in the form of reduced voltage through the mechanism, as it is losing more energy than it gains from the target.
Roy W. Spencer, Ph. D. says: “ARGHH. I really am getting tired of repeating myself. While it is true that the instrument does not “directly” measure LW radiation, it nevertheless PROVES the warming effect of the sky on the surface, because that’s exactly what the greenhouse effect DOES, and that’s how the instrument WORKS!!”
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Roy, if you stand in front of the mirror, your heat will be reflected back to you, but you will not feel any radiative warming effect. Except you stand very close to the mirror and suppresse convection. Otherwise no effect.
In short, Roy: radiation – yes, warming effect – no.
So, Nope, why do the manufacturers of foam insulation coat one side with Mylar?
Why do backpackers often carry a “space blanket” for emergencies?
Are they part of the conspiracy, or do these things work by reflecting radiation and thereby causing warming?
Hops
Hops says: “…why do the manufacturers of foam insulation… Why do backpackers often carry a “space blanket” … Are they part of the conspiracy, or do these things work by reflecting radiation and thereby causing warming?”
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Radiation of the source reflected back to it can not cause any warming effect on the source. This is physically impossible, see my link above.
If a manufacturer claims it is possible, it is still impossible.
Conspiracy? I do not think so. A misunderstanding can be explained otherwise, there is no reason to accuse them of conspiracy.
Noperoynope:
Have you written to your consumer affairs bureau to complain about false advertising by makers of the space blankets? How about for the makers of Dewar (Thermos) flasks? They put reflective surfaces on both sides of the vacuum gap to reduce the heat transfer.
You need to learn how to define a thermodynamic system properly and keep track of all of the energy flows in and out, distinguishing them from internal flows, before you have anything whatsoever constructive to contribute to the conversation.
Curt says: “…makers of the space blankets … makers of Dewar (Thermos) flasks? They put reflective surfaces on both sides of the vacuum gap to reduce the heat transfer.”
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You mix up two different things.
A reflective surface of a thermos flask prevents IR from getting beyond this part of a flask. But it can not keep the content warmer then it otherwise would be by reflecting IR back to the content.
Reflecting IR back to the source has no effect on its temperature. Again: http://www.drroyspencer.com/2013/05/imaging-the-greenhouse-effect-with-a-flir-i7-thermal-imager/#comment-77996
A person gets hypothermia when their internally generated metabolic power (~100W) is not sufficient to maintain body temperature. Putting a space blanket around that person, which reflects back much of the radiant energy that person is emitting, literally increases the temperature of that person. Your faulty analysis, which you can do nothing but repeat mindlessly, is simply wrong.
If you put an electric heating element inside a dewar flask with reflective surfaces in the vacuum chamber, the liquid on the inside will have a higher temperature than if the same element producing the same power were put in an otherwise identical flask but without these reflective surfaces.
You desperately need to take an engineering heat transfer course so you can learn how to set up this type of problem properly. There should be many available on-line.
Curt says: “Putting a space blanket around that person, which reflects back much of the radiant energy that person is emitting, literally increases the temperature of that person. … If you put an electric heating element inside a dewar flask with reflective surfaces in the vacuum chamber, the liquid on the inside will have a higher temperature than if the same element producing the same power were put in an otherwise identical flask but without these reflective surfaces.”
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No, there would be no such effect in both cases, because it is physically impossible and absurd, see the explanation linked in my previous comment.
In your supposed explanation, you have a body with an internal power source. That source will cause the body’s temperature to increase until its total power losses match the input from the power source.
Anything that inhibits thoses losses for a given temperature, including reflective surfaces bouncing some of the radiative losses back to the object, will permit the temperature of the object (for the same power input from the internal source) to get higher before the losses match the input and a thermal equilibrium is reached.
You, and most of the other slayers, are confusing the temperature level with energy. There is no violation of the laws of thermodynamics here. Looking carefully at the energy balances properly must lead you to different conclusions from those you have come to. Noting what really happens with products like these that we have been discussing should show you that you must need to re-analyze.
Curt says: “In your supposed explanation, you have a body with an internal power source. That source will cause the body’s temperature to increase until its total power losses match the input from the power source.”
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Please, do not fake/misinterpret my explanation linked above.
The key point there is that the body with an internal power source is already at a stable temperature initially.
Therefore the warmists’ usual trick/obfuscation about “slowing down cooling” won’t work and they can not go around the absurd and physically impossible consequence of the “greenhouse effect”, namely endless mutual warming without any additional energy input.
You can’t even keep different scenarios straight. You say you start with a “body with an internal power source is already at a stable temperature initially”. For this condition of thermal equilibrium to hold, the body’s power losses at this temperature must match the power from the internal source. Some of these losses are radiative; in a vacuum, the radiative losses are dominant.
Now you do something to reduce those losses. One of the things you could do is to put reflective surfaces around the body to reflect back the body’s thermal radiation. Here’s where you have to distinguish between different scenarios.
The first scenario: The internal power source continues as we reduce the radiative losses with the reflective surfaces. We keep the same power into the body, but reduce the net power out, so the body increases in temperature. (Yes, it does!) Not indefinitely, because other losses increase with temperature, but it will increase.
The second scenario: The internal power source is turned off as we reduce the radiative losses with the reflective surfaces (e.g. putting the hot coffee into the thermos). Without a power source, and with some losses, its temperature will decrease. But with the reduced losses, it will cool more slowly.
In both of these scenarios, the temperature of the body at any given time in the experiment is higher in the case where the reflective surfaces are present than when they are not. And it is perfectly valid in both cases to speak of the “cooling losses” from the body, even if the temperature of the body is stable or even increasing.
Generations of engineers have been taught this absolutely standard analysis and gone on to design critical infrastructure using this. If you really think this is fundamentally wrong, you should not be wasting your time arguing on blogs. You should be out taking whatever action is necessary to shut down any industrial process using high temperatures, because it was completely misdesigned.
Oh, and I’m sure you must have filed complaints for false advertising with the FTC against the folks at Thermos and the makers of space blankets.
Curt says: “You can’t even keep different scenarios straight. … The first scenario: … The second scenario: … ndustrial process using high temperatures … “
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So, as I can see you keep faking/misinterpreting the point I linked above.
It was not about two scenarios. It was about 1(one) scenario that debunks the so-called “greenhouse effect”. The method is very easy: if an assumption logically leads to something absurd, then the assumption is false.
Therefore 1(one) scenario that is based on this assumption and logically leads to an absurd outcome is sufficient to demonstrate that the assumption is false, or equally absurd.
If you still do not understand that, then nobody can help you. If you pretend to not understand that, then you can keep doing this, apparently. The readers can read and judge for themselves: http://www.drroyspencer.com/2013/05/imaging-the-greenhouse-effect-with-a-flir-i7-thermal-imager/#comment-77996
I too encourage people to look at your old comment, so they can see how ridiculous it is. You simply say that it would lead to something that you wouldn’t expect. You are completely unable to elaborate on it, so all you can do is repeat yourself.
Your scenario is Scenario 1, with the internal power source operating throughout the scenario. (My point was that you mistakenly invoke it when people are talking about Scenario 2, when the power source is no longer present.) All you are really saying is that you don’t believe that radiation reflected back to a warmer object can contribute in any way to a temperature increase in that body.
I and others show you why you are wrong, both in theory (you have changed the energy balance so the object now has more incoming than outgoing power, so its internal energy increases, so its temperature increases), and in practice (the many everyday devices that use this to practical effect: reflectorized insulation, space blankets, Thermos containers).
All you can do in response is to invoke an incredible “crippled” form of electromagnetic radiation that is incapable of carrying energy with it. Which is what you are doing when you say “A reflective surface of a thermos flask prevents IR from getting beyond this part of a flask. But it can not keep the content warmer then it otherwise would be by reflecting IR back to the content.”
You say, “The method is very easy: if an assumption logically leads to something absurd, then the assumption is false.” The problem is that it does not lead to any thing absurd — it simply leads to something that is non-intuitive to you. It is completely intuitive to me, but then again, I have been working with this stuff professionally for 35 years now, making a good living off having my analytic predictions borne out by real-world results.
I must go now, as I need to start testing a new heat sink design, and see how we did on our projected conductive, convective, and radiative heat transfer predictions.
Curt says: “You say, “The method is very easy: if an assumption logically leads to something absurd, then the assumption is false.” The problem is that it does not lead to any thing absurd — it simply leads to something that is non-intuitive to you. It is completely intuitive to me…”
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Well, again, from the linked explanation I gave you several times, the assumption of “greenhouse effect” as presented my the IPCC (warming by back radiation from “greenhouse gases”, or “surface warms the greenhouse gases and they warm the surface back) leads logically in some cases to a mutual endless warming without any additional input of energy.
This outcome is apparently absurd and physically impossible, which proves the initial assumption of “greenhouse effect” absurd as well.
And you claim this is “completely intuitive” to you and not absurd? Well, it speaks for itself.
Roy W. Spencer, Ph. D. says: “that’s how the instrument WORKS!!”
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The instrument works essentially by optical focusing the IR from a large cold area on a very small area of the sensor, as far as I know.
I am not an expert on IR-thermometers, and neither are you, but my guess would be that exactly this focusing makes it possible for the IR from cold to overcome the natural barriers. Otherwise there would be no effect and no measurement possible.
Last time I checked there were no lenses in the atmosphere.
Now you have been told that for the second time on your blog. I hope it will help.
Nope, so you think all the engineers who make these devices can’t make a thermal detector that functions correctly?
You think the people making low-e windows are operating under some misconception? Have you ever slept under a space blanket? I have…
Of course reflected radiation isn’t going to make an object warmer than it originally was, but it is going to make it warmer than would otherwise be the case.
For you and everyone here, there’s a nice course on the topic in iTunes U, Atmosphere, Ocean and Environmental Change, where a good professor explains all of this. See especially lecture 6.
The expected temperature of Mars is around 216 Kelvin. But the measured temperature is around 230K. The reason is a thin layer of CO2 (and nothing but).
Hops says: “Of course reflected radiation isn’t going to make an object warmer than it originally was, but it is going to make it warmer than would otherwise be the case.”
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This statement of yours is absurd.
If the object is in initially at a stable temperature, then “making warmer than it is” is “making warmer than it otherwise would be”.
You contradict yourself.
Please, read this text again, it demonstrates clearly, how absurd the notion of “greenhouse effect is: http://www.drroyspencer.com/2013/05/imaging-the-greenhouse-effect-with-a-flir-i7-thermal-imager/#comment-77996
Lenses are bi-directional. They work reversibly for radiation in both directions.
In the frame of pure thermodynamics, is based solely on direct observations, there is observed only the net radiation – only for these case is the II.law of the TD applicable. As part of the TD downwelling radiation is a pure computational size that Stefan has been introduced in 1879 – i.e. long ago. That we are today in the frame of quantum theory, an idea (hardly watching -. “From what I understand, there are photon well detectors Which do measure Directly, But They are not used in this instrumentation”) can make use of the two gross flows, nothing changes on this fact.
In the frame of the observed net radiation thermodynamics only the reduction of the black body radiation, since the black body radiated not to 0K, but against a body having a higher temperature than 0K – namely the atmosphere. In the frame of thermodynamics, the question remains “how known the earth’s surface that it is a warm body against?”. With the concept of backradiation and quantum theory, this question is answered.
Sincerely yours
Jochen Ebel
“The pyrgeometer is often presented as being an instrument that directly measures LWIR. It gives an inferred value which depends on the radiative theory formula used for its calibration being correct.”
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The mercury thermometer is often presented as being an instrument that directly measures temperature. It gives an inferred value which depends of the thermal expansion theory formula used for its calibration being correct.
In the frame of pure thermodynamics, is based solely on direct observations, there is observed only the net radiation – only for these case is the II.law of the TD applicable. As part of the TD downwelling radiation is a pure computational size that Stefan has been introduced in 1879 – i.e. long ago. That we are today in the frame of quantum theory, an idea (hardly watching -. “From what I understand, there are photon well detectors Which do measure Directly, But They are not used in this instrumentation”) can make use of the two gross flows, nothing changes on this fact.
In the frame of the observed net radiation thermodynamics only the reduction of the black body radiation, since the black body radiated not to 0K, but against a body having a higher temperature than 0K – namely the atmosphere. In the frame of thermodynamics, the question remains “how known the earth’s surface that it is a warm body against?”. With the concept of backradiation and quantum theory, this question is answered.
Sincerely yours
Jochen Ebel
“But the continually neglected possibility is that they have causation reversed: that natural changes in cloud cover have caused the temperature changes, and cloud feedbacks are in reality negative rather than positive.”
Exactly.
Zonal jets = less clouds.
Meridional jets = more clouds.
Jetstream behaviour being affected by solar variability (via particle and wavelength changes) altering the vertical temperature profile of the atmosphere differently above equator and poles.
As far as the downwelling IR issue is concerned it just doesn’t matter.
Whether the surface is warmed in part by DWIR or by adiabatic heating of descending air the effects of both are already fully incorporated into the current atmospheric (and oceanic)circulation and any change in either is dealt with by a change in that circulation rather than a change in system energy content or temperature.
The elephant remaining in the room is Earth’s oceans and in particular the effect of atmospheric pressure on that water in so far as it sets the energy cost of a given amount of evaporation via the latent heat of vapourisation (which varies with pressure as witness the lower boiling point of water at the top of Everest).
That energy cost sets the temperature that the oceans must reach in order to drive a circulation that achieves ToA energy balance.
Ocean temperatures then control air temperatures.
“and any change in either is dealt with by a change in that circulation rather than a change in system energy content or temperature.”
…Because it has to be by the principle that the laws of physics behave in the way that is most conducive to Stephen Wilde’s ideological conception of how he wants them to behave.
“The elephant remaining in the room is Earth’s oceans and in particular the effect of atmospheric pressure on that water in so far as it sets the energy cost of a given amount of evaporation via the latent heat of vapourisation (which varies with pressure as witness the lower boiling point of water at the top of Everest).”
The reason that the boiling point of water at the top of Everest is lower than at sea level is because boiling occurs when the vapor pressure reaches the atmospheric pressure. I don’t think it has much if anything to do with the latent heat of vaporization varying with pressure. [There is some variation of the latent heat of vaporization with temperature but that is not horribly dramatic…On the order of a 10% change over the entire range of temperature for liquid water at 1 atm: http://en.wikipedia.org/wiki/File:Heat_of_Vaporization_%28Benzene%2BAcetone%2BMethanol%2BWater%29.png ]
At zero atmospheric pressure water boils away instantly without any addition of energy.
The higher the pressure the more energy (latent heat) needs to be added for vaporisation to occur.
As regards your personal comment I think you are projecting your state of mind onto me.
There’s pretty much zero atmospheric pressure around cometary nuclei which are known to be made mostly of water. That water doesn’t boil away, it sits tightly there as ice for millions of years until the nucleus comes close to the sun which gradually transforms it into gas by its radiative energy.
If you dump room temperature water into vacuum, part of it will instantly evaporate, drawing energy from the rest, which will turn into ice and dramatically reduce its temperature. This is one of physics trivia observed e.g. by Apollo astronauts.
So while the atmospheric pressure is sure known to affect boiling temperature of water, you should clearly still learn a bit about how physics really work.
Ice within a comet at the temperature of space doesn’t boil away but it does go straight to vapour when solar radiation is added. That is what creates comet’s tails.
Water already has enough energy in it when it is in a liquid state to boil instantly when exposed to zero pressure.
It may leave an ice residue but that doesn’t negate the fact that the value of the latent heat of vaporisation is controlled by pressure.
Zero pressure would result in a 1:1 ratio which would instantly vaporise half and leave half as ice.
At 1 bar pressure the ratio is 5:1.
At more than 1 bar pressure the ratio is more than 5:1.
Would you like to revise your last sentence ?
And, you know that it takes zero energy to boil away the water at zero pressure how exactly? What tells you that it takes zero energy to do so at zero pressure but takes a heck of a lot of energy at 1 atm of pressure? I presume you’ve measured this?
Try exposing liquid water to the vacuum of space.
The water boils away instantly leaving an ice residue which is left at the temperature of space.
It doesn’t take zero energy. It takes energy from itself plus the rest of the ice residue.
I said no ADDITION of energy which still leaves the energy available within itself until its own temperature (or rather that of the residue) is reduced to that of space.
I think you are out of your depth here.
You said:
“At zero atmospheric pressure water boils away instantly without any addition of energy.
The higher the pressure the more energy (latent heat) needs to be added for vaporisation to occur.”
Now, you are trying to claim that what you meant is that some of it turns to ice and some of it boils away and the heat of vaporization necessary for the boiling away is provided by the part that freezes (but you didn’t even mention an ice residue until Kasuha brought it up).
And, what do you mean about the dependence of the height of vaporization on pressure?
I’d ask about how you came up with your 1:1 and 5:1 ratios in your response to Kasuha…but I’m not sure I want to know!
Joel Shore says:
May 13, 2013 at 11:43 AM
“The height it samples would be strongly wavelength-dependent because the opacity of the atmosphere is strongly-wavelength dependent”
Well that is my point.
For an open sky it would be measuring temperature at a different height to any cloud that interposed itself.
The temperature at the respective heights would be governed by the lapse rate.
Furthermore, measuring temperatures at given heights above the pyrgeometer is not the same as measuring a downward flux.
If one were measuring a downward flux it would manifest itself as a change in temperature of the sensor itself but that cannot be the case because at all times the temperature of the sensor is different from the temperature of the remote surface it is measuring.
Furthermore the temperature of the sensor itself and the air molecules around it are set by the lapse rate and not downward radiative flux.
Any radiative fluxes there may be flowing in whatever directions are already fully accounted for in the lapse rate.
And the lapse rate is determined by density of mass held in a gravitational field and subjected to an external (to the atmosphere) source of radiation.
I would prefer to hear from Roy on these points since he is (I think) less ideologically committed than you are.
“Furthermore, measuring temperatures at given heights above the pyrgeometer is not the same as measuring a downward flux.”
Really, what do you think the pyrgeometer is measuring? Does it have some sort of magic way of knowing the temperature up there that just happens to work out to the value obtained by applying the known equations of physics for radiation?
“If one were measuring a downward flux it would manifest itself as a change in temperature of the sensor itself but that cannot be the case because at all times the temperature of the sensor is different from the temperature of the remote surface it is measuring.”
Is there an English translation available for this sentence?
“Any radiative fluxes there may be flowing in whatever directions are already fully accounted for in the lapse rate.”
Really?
“I would prefer to hear from Roy on these points since he is (I think) less ideologically committed than you are.”
I doubt he’ll waste his time responding to such gobbley-gook but we’ll see!
Joel,
i) according to Roy the pyrgeometer is measuring the temperature of a surface remote from itself.
ii) The temperature of the surface being measured differs from the temperature of the sensor itself. If it were measuring the flux arriving at the sensor it would be show the same temperature as the sensor because the flux would warm the sensor.
iii) Why would you doubt that the net radiative flux at the surface is already incorporated in the lapse rate ?
“If it were measuring the flux arriving at the sensor it would be show the same temperature as the sensor because the flux would warm the sensor.”
Really, so if we point it at the sun, it warms to the temperature of the sun? By what principle?
“Why would you doubt that the net radiative flux at the surface is already incorporated in the lapse rate ?”
I don’t understand what that sentence even means.
i) according to Roy the pyrgeometer is measuring the temperature of a surface remote from itself.
Wrong – this demonstrates your inability to read. as I pointed out earlier.
The surface being reported on in a pyrgeometer is the surface inside it.
Roy was clear that the sensor measures the temperature of a cloud if cloud is present or the temperature of the sky if a cloud is not present.
He said this amongst other things:
“In the cloud case, the cloud has a higher emitting temperature because it is at a lower altitude, and it is more opaque in the infrared than the clear sky is.”
So he also agrees that in each case the sensor measures the temperature at different heights.
I don’t see how measurements at different heights say anything about a downward energy flux.
It just shows that there is a lapse rate which we all know anyway.
http://tinyurl.com/clyhton
Uh, that’s weird, not quite sure how that happened.
http://tinyurl.com/clyhton is the url which should have said “looks like they decided to put up rather than shut up”…
Ohhh, I think I had my auto-page adding active, so when I scrolled through this thread to get down to the next one, I forgot I can’t just jump to the first reply box I see and respond… that post was supposed to be in the next one down.
Aaaaaanyway: I don’t think it was whether downwelling IR exists or not.
I think it was whether it adds to the energy available at the surface, above and beyond that directly from the Sun.
Though, it seems the ESRL NOAA site has something weird going on because most of the DWIR measurements seem to be simply calculated from the air temperature, UWIR and net IR, rather than measured directly, despite the presence of back-to-back pyrgeometers at the stations.
“whether it (DWIR) adds to the energy available at the surface, above and beyond that directly from the Sun.”
I don’t think it does because the net radiative flux in the atmosphere is already incorporated in the lapse rate.
Surface temperature is dictated by mass gravity and insolation, That leads to IR zipping every which way in the atmosphere.
Adding GHGs doesn’t alter surface pressure or the density of the atmosphere at the surface or the level of ToA insolation so the starting temparature at the surface remains fixed.
Even expanding and contracting the atmosphere makes no difference to pressure and density at the surface.
However expanding and contracting the atmosphere does make a difference at every level above the surface and this is why:
http://en.wikipedia.org/wiki/Joule%E2%80%93Thomson_effect
“As a gas expands, the average distance between molecules grows. Because of intermolecular attractive forces (see Van der Waals force), expansion causes an increase in the potential energy of the gas. If no external work is extracted in the process and no heat is transferred, the total energy of the gas remains the same because of the conservation of energy. The increase in potential energy thus implies a decrease in kinetic energy and therefore in temperature.”
It is therefore established science that if a gas parcel rises adiabatically (no heat added or removed) which it does once detached from the surface, then the expansion arising from the reduction of the weight of gases above it must cool the gas as described above.
Some think that the continued rising of a parcel of warmed air relies on more energy constantly being added at the surface (a diabatic process).
In fact, each parcel or bubble of warmed air stops receiving energy from the surface as soon as it loses contact with the surface.
Yet it continues to rise (adiabatically) because the air around it at each new higher level has also been cooled by the reduction of density and by expansion at that new height so the warmed parcel retains its density and temperature differential with the surrounding air and keeps going up adiabatically.
It would rise to ToA unless prevented from doing so by an inversion layer where the rise in temperature with height allows the density and temperature differential to be equalised.
On Earth that happens at the tropopause but only because direct solar heating of ozone reverses the normal lapse rate in that layer.
So the effect of GHGs is only to alter densities and temperatures away from the surface by causing local expansion or contraction (depending on your belief) which instead of feeding back to a change in surface temperature merely influences the slope of the lapse rate from the fixed surface temperature.
Then, in order to maintain ToA radiative balance the overall air circulation changes to adjust the rate of energy throughput.
It’s truly amazing what sort of “theories” one can come up with for the Earth’s surface temperature when one isn’t hampered by silly details like conservation of energy!
Conservation of energy is explicitly referred to.
You never explain how the Earth’s surface can be at a temperature where it is radiating 390 W/m^2 and have the elements of the atmosphere that absorb radiation not be responsible for this. Sorry, you can’t just selectively apply conservation of energy to certain pieces and not to others.
I very much like this argument. It seems to be such a slam dunk. In spite of the decisive empirical evidence for the existence of downwelling radiation from the atmosphere, many skeptics contrive ways to explain the evidence away. But I seldom see them question the magnitude of the outgoing radiation from the Earth surface. The magical ‘radiation blocking’ mechanism (i.e. cold bodies can radiate towards warmer bodies; or warmer bodies can’t absorb radiation emitted from colder bodies) doesn’t work anymore. And now, the skeptic has indeed to contend with a gross violation of energy conservation.
Thank you for that presentation link!
The shorthand station names in the document are not very easy to guess.
This presentation of Martin Wild’s from 2010 has some full length names and data in it, though:
http://www.gewex.org/BSRN/BSRN-11_presentations/Tues-MartinWild.pdf
Roy you say
“In this case, the model underestimates the downwelling sky radiation by about 9 W/m2.”
This is quite interesting as the latest pyrgeometer report that I have finds a consistant negative bias of 12 W/m2 as well as a relative instrument error of + or – 5W/m2
(See bottom of page 1)
http://www.arm.gov/publications/proceedings/conf16/extended_abs/stoffel_t.pdf
To me this systematic error being introduced would suggest a fault in the theory details used to calibrate the instruments.
What can we trust the theoretical model or the instruments which use the same equations for calibration?
The direct effect of doubling CO2 is put at 1W/m2 as I understand it.
Then these huge uncertainties in measurement dwarf the signal that is supposed to alarm us.
Here is some of the proof:
“Radiative forcing – measured at Earth’s surface – corroborate the increasing greenhouse effect,” R. Phillipona et al, Geo Res Letters, v31 L03202 (2004)
http://onlinelibrary.wiley.com/doi/10.1029/2003GL018765/abstract
“Measurements of the Radiative Surface Forcing of Climate,” W.F.J. Evans, Jan 2006
https://ams.confex.com/ams/Annual2006/techprogram/paper_100737.htm
“A method for continuous estimation of clear-sky downwelling longwave radiative flux developed using ARM surface measurements,” C. N. Long and D. D. Turner, Journal of Geophysical Research, vol 113, D18206, doi:10.1029/2008JD009936, 2008
http://onlinelibrary.wiley.com/doi/10.1029/2008JD009936/abstract
David Appell
Your ‘C. N. Long and D. D. Turner’ link did not fill me with confidence, even though it was rather frank.
“Although there is no exact means of determining the uncertainty associated with the clear-sky LW estimations, our analyses and comparison with detailed radiative transfer (RT) model calculations suggest our estimations on average are no worse than model calculations that require temporally and spatially averaged input information.”
Wow!!!
So, they know that their models (and primarily their measurements) “require temporally and spatially averaged input information”.
Whatever they say, IMHO this is valid for TOA measurements too.
Have a nice day.
Massimo
David Appell says: “Here is some of the proof: “Radiative forcing – measured at Earth’s surface … Measurements of the Radiative Surface Forcing … clear-sky downwelling longwave radiative flux…”
===========================================
Back radiation is not a forcing on the source. It can not be. It forces nothing. It is physically absurd to call it “forcing”.
The term “forcing” refers to the fact that a change in back-radiation will lead to a radiative imbalance between what the energy that the Earth absorbs from the sun and what it emits back out into space, which will then have to lead to some sort of warming or cooling until the balance is restored.
Roy was clear that the sensor measures the temperature of a cloud if cloud is present or the temperature of the sky if a cloud is not present.
He said this amongst other things:
“In the cloud case, the cloud has a higher emitting temperature because it is at a lower altitude, and it is more opaque in the infrared than the clear sky is.”
So he also agrees that in each case the sensor measures the temperature at different heights.
I don’t see how measurements at different heights say anything about a downward energy flux.
It just shows that there is a lapse rate which we all know anyway.
One could say that there is more energy coming from the lower cloud than from the higher clear sky but in reality radiation is coming downward from all heights simultaneously and the cloud is at the same temperature as the atmosphere at its particular height.
So if the sensor measures the temperature of the air immediately in front of it then that would be at a higher temperature than a cloud above because of the lapse rate. That temperature at the lower height would not have been affected by radiation from above.
What is really happening here is that with or without cloud there is an insulating effect from the entire mass of the atmosphere above the surface whether clouds are present or not.
A cloud will only further reduce the rate of cooling of the ground if it is at a higher temperature than the air at its height would be in its absence.
Meteorologically that can happen in two situations:
i) Warmer air is advected in above from elsewhere and the cloud forms at the interface between the surface air and the higher warmer air that has been advected in.
ii) The ground cools faster than the air above so an inversion layer forms and cloud develops at the interface between the air cooled by the ground and the warmer air above.
In neither case is radiation from the cloud further reducing the cooling rate of the ground. In both cases the lapse rate gradient has been disturbed and radiation from the warmer air above is reducing the cooling rate of the ground.
The presence or absence of the cloud makes no difference as long as one measures the sky temperature at the height of the cloud.It is the presence of a layer of warmer air disturbibg the lapse rate that makes the difference.
The pyrgeometer is just measuring the radiative effect of the lapse rate (which varies) at different heights and not any difference in radiative output from air or clouds at the same height.
Dear Stephen Wilde, you are mighty wordsmith, and a keen advocate of your homespun theory about the earth’s energy balance, but you have not made a serious attempt to study the physical question here, about which you write. You cannot bluff your way here: you have to learn the basic physics. Until you do that, you may continue to deceive yourself that you understand things, and you may mislead some gullible others into thinking so too, but you will not get the physics right. What you write currently just shows that you have not understood the physics.
Then describe the error in basic physics.
Measurement of temperature at different heights is not a measurement of a change in radiative flux.
It is simply a consequence of the lapse rate.
To be of use, the pyrgeometer must measure the open sky temperature at the same height as the cloud and only if there is then a difference is one measuring a change in downward flux.
In fact, the air temperature at the height of the cloud is the same as that of the cloud and would show no difference.
Who ever heard of a cloud being hotter than the air in which it floats ?
Ridiculous.
That is nothing to do with skilled wordsmanship or homespun theory, merely simple logic.
As are the rest of my propositions.
But logic doesn’t appeal to agenda driven thinkers does it ?
Nor does data.
Dear Stephen, you still don’t get the message. It’s not for me to explain to you on a blog page the physics of radiative transfer in semi-transparent media. It’s for you to study textbooks and learn about it for yourself. Your reply is here is just more evidence that you content yourself with rhetorical questions instead of doing some serious study of the subject matter for yourself. Simple logic is a form of wordsmithing. And in reality, your reply is not simple logic, it’s just more specious wordsmithing. You can’t bluff your way here, you need to do some actual study for yourself.
Roy,
Just to be clear on this. You’re effectively saying that if I take a cold (8C) meatball suspended in a vacuum (to insulate it from conduction) and put it in my freezer (-20C) it will cook? Is that right?
Near enough Iansview, but you really should be asking Joel Shore to clarify that.
I’m happy for any of the bloggers promoting back radiation to answer the question but hearing it from Roy would be best in my mind!
Er no. He’s saying that the meatball would end up warmer than if you suspended it in a vacuum in outer space. Your freezer may seem like a fairly cold place at -20C but it is about 250 degrees warmer than space. Which is where the meatball that we live on is currently suspended.
No, it is not right, it will not cook.
It makes no difference how much IR the meatball receives from the surroundings if it is outputting more IR itself. The net energy flow is away from the meatball. It will cool, as I suspect you fully realize, and you are deliberately asking nonsense questions.
He’s also saying that if your freezer had a window in it through which you could illuminate the meatball with the radiation from a body at 6000C the meatball would end up warmer than if it received the same radiation input while suspended in outer space.
“Just to be clear on this. You’re effectively saying that if I take a cold (8C) meatball suspended in a vacuum (to insulate it from conduction) and put it in my freezer (-20C) it will cook? Is that right?”
No. He’s saying:
1) If you put your meatball in the freezer at -20 C, it will cool a lot more slowly than if you put it in a box with walls cooled by liquid helium to near absolute zero.
2)If you supply enough heat to the meatball with an embedded heater to keep it at 8 C when inside a box held at absolute zero, and then transfer the meatball and heating arrangement to your freezer at -20 C (which is 253 C warmer), then yes, it would get warm, although it would still be a bit cool for cooking.
It’s the heat supply that keeps it warmer than its surroundings, but the surroundings that decide how high a temperature you reach for any given heat input. You need to supply 353 W/m^2 to keep a meatball at 8 C inside a box at absolute zero. But when inside your freezer, it gets 353 W/m^2 from the heater and 232 W/m^2 from the walls of the freezer, making 585 W/m^2. To radiate that much heat, it has to be at a temperature of 45 C.
If you put it in a box at 7 C (still colder than the meatball) then at would get 353 W/m^2 from the heater, 348 W/m^2 from the walls, 701 W/m^2 in total, and it would warm to 60 C, which would be enough to cook it, eventually.
Incidentally, I don’t promote backradiation as the way the greenhouse effect works in the real atmosphere, but I do agree with Roy that backradiation exists, is absorbed by opaque substances contributing to their temperature, and if convection could somehow be prevented, then the effect he describes *would* occur, warming the Earth’s surface to an average 60 C. (As calculated by Manabe and Strickler in 1964.) It breaks no laws of physics.
The best example I know of for this mechanism is a solar pond. Water is transparent to sunlight, but quite opaque to thermal IR, absorbing all the IR within about a millimetre, so it makes an ideal ‘greenhouse’ material. A pool of water is set up with a layer of fresh water on top of a layer of salty water to suppress convection, and left out in the sun. The bottom of the pool can reach over 90 C, because the sunlight enters and is absorbed at the bottom, but then cannot escape by radiating through the opaque water. The bottom still radiates, but the warm water above it radiates just as much back.
If you could suppress convection and conduction entirely, then a solar pond would reach boiling point within a few centimetres of the surface, and would theoretically reach around 900 C a metre down. Fortunately for the fish, water convects quite nicely, and an ordinary pond will be at pretty much the same temperature at the bottom as the top, despite the huge amount of backradiation going on. The backradiation certainly *exists*, and is an essential part of what’s going on, but it is the lower limit to convection that controls the temperature difference. CO2 increases surface temperature by increasing the average altitude of emission to space, not by increasing backradiation.
“CO2 increases surface temperature by increasing the average altitude of emission to space, not by increasing backradiation.”
Increasing the average altitude of emission to space involves expanding the atmosphere which reduces densities at all points above the surface (but not at the surface) so cooling results from the Joule Thomson Effect whereby KE is converted to PE as a result of work being done to oppose intermolecular attraction.
The consequence is no change in surface temperature but instead a change in lapse rate slope which is then compensated for by circulation changes elsewhere in the atmosphere.
There is a greenhouse effect but it involves the entire atmosphere and there is downward radiation from all levels simultaneously but it is a consequence of the lapse rate and causative of nothing on its own.
“Increasing the average altitude of emission to space involves expanding the atmosphere”
No it doesn’t. The addition of CO2 does not increase the volume of the atmosphere significantly, only its opacity.
The result is no change in lapse rate slope, but a translation of the entire fixed slope upwards. (As shown in figure 1 of Soden and Held 2000. http://www.gfdl.noaa.gov/bibliography/related_files/annrev00.pdf)
I’ll consider that but my initial thought is that an increase in opacity would cause expansion.
Since CO2 is such a small proportion of atmospheric mass any necessary expansion would be miniscule indeed as you suggest.
You say it doesn’t increase the volume significantly. Do you accept ANY expansion ?
Against that, Miskolczi seems to have found that opacity stays stable.
I’m doubtful about the entire fixed slope moving upwards as proposed by AGW theory because there is no significant increase in mass gravity or insolation when CO2 increases yet they are supposed to be the main (probably the only) factors in setting surface temperature.
I am aware that AGW theory proposes that GHGs raise surface temperature despite mass gravity and insolation staying the same but that is where I find the theory implausible.
I don’t think we can resolve such issues here.
There would be a very slight expansion, but not enough to result in any significant effect. If you added an equivalent amount of Nitrogen, it wouldn’t make any detectable difference.
I don’t pay any attention to Miskolczi, since it’s founded on an invalid formulation of the Virial theorem.
The slope has to stay the same because it’s determined by bulk gas properties, dominated by N2 and O2. A tiny amount of CO2 isn’t going to change the slope. Assuming we’re ignoring water vapour feedback for the moment, the slope is fixed.
In fact, this is primary argument for why backradiation internal to the atmosphere cannot result in any net transfer of heat. Backradiation from the upper atmosphere to the surface would cool the atmosphere and warm the surface, changing the lapse rate. But the adiabatic lapse rate is fixed by physical/thermal gas properties, nothing to do with radiative ones, and therefore in an adiabatically-limited convective atmosphere, backradiation has no effect. It is always exactly compensated for by a change in convection to maintain the same gradient.
In a convecting atmosphere, the surface temperature is equal to the effective radiative temperature, plus the average altitude of emission times the adiabatic lapse rate.
Solar insolation, clouds, and albedo affect the effective radiative temperature.
Greenhouse gases affect the average altitude of emission to space. (You could think of it as how far into the atmosphere you can ‘see’ if you look with infrared eyes – or equivalently, the opaque apparent ‘surface’ of the planet that radiates in equilibrium to outer space.)
Latent heat from the condensation of water vapour affects the lapse rate. (This is actually a *negative* feedback, and the real reason for the predicted tropical hotspot.)
GHGs can only affect the surface temperature via the altitude term, by translating the entire lapse rate vertically. If the lapse rate was negative (as it is in the stratosphere), then extra GHGs would actually cool the atmosphere! Again, not backradiation, but translation of the lapse rate curve upwards now results in lowered temperatures.
However, if convection is suppressed, then none of this applies and Roy’s backradiation mechanism can indeed determine temperatures. It’s not unphysical, it just ignores the full implications of the nonlinearity of convection.
I agree we’re not going to resolve the issue here. I’m just offering it as a point of view, for my own entertainment.
Nullius in Verba says: “I agree we’re not going to resolve the issue here. I’m just offering it as a point of view, for my own entertainment.”
You entertained me too, Nullius. And you also enlightened me. You cleared up a few misconceptions I had about those mechanisms. That was a wonderfully instructive post. Thank you very much.
Yes, Nullius. Your post aligns very well with my picture of how the atmospheric “greenhouse” functions. I would add that the characteristic emission altitude is primarily a function of the bulk atmospheric properties enabled and fine tuned by the radiative properties of the so called greenhouse gases. The lapse rate being independent of non-condensing greenhouse gases means that the atmospheric temperature profile is extremely insensitive to changes in CO2 concentrations above 100 ppm. The dominant factor to climate change is likely to be found in down welling short wave radiation modulation (clouds, aerosols?) rather than in long wave radiation modulation.
As to those objectors to the concept of back radiation slowing heat loss to space, can I frame this issue another way? Think of back radiation as a model for what we observe even if you dislike it for seeming lack of elegance. Does the back radiation model correspond to observation? I would say yes, so the model is useful until shown to deviate from observation.
Nullius in Verba,
I appreciate the time you have taken in responding to my question and your comments are very helpful. However they have opened up another question that would help clarify things for me.
Surely the density of the IR re-radiating must have some bearing on the rate of cooling of the warmer object? E.g. what if the meatball was surrounded by air at atm=1 @ -21C as opposed to the walls of the freezer at -21C. Would the greater density of the freezer walls mean slower cooling? Is it only the layer of the air touching the meatball that needs to be considered?
I’m guessing you’re asking about near-transparency, rather than re-introducing convection/conduction.
Yes, if you surround the meatball with a semi-transparent shell at -21 C, inside the helium-cooled chamber, then the fact that you can see through the shell means that the surroundings the meatball ‘sees’ is a mixture of surfaces at -21 C and -273 C, with an effective temperature somewhere in between.
Translucency generally makes things a little more complicated. If the translucent material is at a constant temperature, then you can take slices of the material just thick enough to absorb all the radiation, and treat it as an opaque slab. If it’s not at a uniform temperature, it’s hard to avoid having to do integrations.
It’s the optical density (opacity) that matters, not the mass density, though.
Sorry, should have said “treat *each* as an opaque slab.
Incidentally, you might find this book interesting.
http://www.gutenberg.org/files/40030/40030-pdf.pdf
Hell,all I was thinking about was cooking meatballs in a freezer.
Yep….that’s another potential invention added to the scrap pile!!
Does anybody else feel like they are in some form of alternative reality at times? How can we have such a “massive” (Roy’s word) energy source in the atmosphere delivering twice the amounts of w/m2 as solar and yet we still need to debate it’s existence? If it’s twice the amount of the solar energy hitting the surface of the earth why can we not feel it, measure it and, more importantly, use it. After all we manage to harvest solar in places like the UK even in the winter. Surely with all the knowledge and technical expertise we have gained in the last 150 years we could be using this energy? Why is government and the big energy companies not investing in this like they are wind, solar, tidal, geothermal etc. How can this be?
Iansview: You ask, “why can we not feel it, measure it and, more importantly, use it?”
We can measure it, as Dr. Spencer has been showing, first with a very cheap sensor, then with a somewhat more expensive sensor. With high-grade scientific equipment, we even know its spectrum in detail and how it varies under different conditions.
Why can we not feel it? Well, it’s there all the time, so we would really know it only by its absence. But if you are really careful, you can literally feel differences. Consider two cool nights at the same temperature but different overhead conditions. For example, a fall evening with no clouds and preferably low humidity, and a winter evening that is overcast. in each case, go outside to where you have good exposure to the night sky and lie down with few clothes on. Compare how long you can stand it in each case. I think you will find that you can last longer on the cloudy night.
If you don’t want to go that far, just observe conditions when frost forms. On a clear night, you can get frost at temperatures like +4C. On a cloudy night, this will not happen.
Whey can we not use it? Because it comes from a temperature colder than where we would want to use it, and the 2nd Law of Thermodynamics establishes that we cannot get useful work from that. It is theoretically possible to use it at temperatures below the source temperature, but that is not very useful to us.
And I was thinking frost was due to dew point.??
A cloudy night is more likely to have higher humidity, so a higher dew point temperature.
“If it’s twice the amount of the solar energy hitting the surface of the earth why can we not feel it, measure it and, more importantly, use it.”
Because whatever surface on the ground you used to collect it would itself be emitting more energy than it received.
There’s actually a simpler way to get access to it. Take a large concrete block at a constant temperature and slice it in two, but leave the two halves almost touching one another.
Each cut face radiates according to its temperature towards the other half block. Because the two halves are at the same temperature, they radiate exactly the same amount of energy, and nothing changes.
Now push the halves back together so they are touching. At no point do the surfaces stop radiating – the atoms don’t stop just because there are other atoms in the way. In this way, we can see that the situation with the two cut faces facing one another simply describes the situation inside a solid block. In fact, any opaque material is radiating internally a huge amount of radiation, but when the material is all at the same temperature this all cancels out. The net effect is as if no radiation occurred, except at the surface, and so it is quite common to ignore it, and pretend opaque solids only radiate from their outer surfaces.
Energy cannot be transported radiatively through an opaque substance, except by slow diffusion, because it is opaque. Backradiation is simply the name given to each half of this balance/exchange. You can’t use it because you can’t avoid the other half of the exchange.
Only temperature differences can be exploited to do useful work, and since the sky is colder than the surface, we generate power by radiating surface heat into the sky. The radiation we get back represents the radiative component of the thermal resistance getting in the way, and reduces our ability to do it. It’s always offset against the energy we lose by radiation due to our own temperature.
“How can we have such a ‘massive’ (Roy’s word) energy source in the atmosphere delivering twice the amounts of w/m2 as solar and yet we still need to debate it’s existence?”
I find these arguments of evidence against something based on the fact that you can find lots of people who argue against it to be very unconvincing. We know why people argue against it…They argue against it because they strongly don’t want to believe it to be the case. They argue against it for the same reason that people argue against the overwhelming evidence for evolution or an Earth many orders of magnitude older than 6000 years.
Look, the fact is that you have to have a pretty good understanding of the science to be able to distinguish between science and pseudoscience. If your only understanding of the 2nd Law comes from a cursory study of thermodynamics and none of the underlying statistical physics, then the arguments that are clearly ridiculous to those of us who do have this background may seem pretty compelling, especially if it is what you strongly want to believe to be true. So, in the end, people are going to decide what to believe on the basis of what they want to believe or on the basis of scientists who they are truly willing to trust (although clearly a lot of AGW skeptics around here are not willing to trust Roy Spencer even though he has impeccable AGW-skeptic credentials).
And, there’s no serious debate on this in the scientific community. Sure you can find a few people who have scientific credentials who claim that the greenhouse effect doesn’t exist, but the same goes for the other examples that I gave. Even scientists who are pretty far out on the fringe of the larger debate about AGW, like Roy Spencer and Richard Lindzen, don’t debate this point. That is because the scientific evidence for the radiative greenhouse effect is overwhelming.
I ask these ‘nonsense’ questions as I find them the best way of teasing out the answers that I’m looking for. Your responses, together with those from Stephen, Nullius and the papers that I’ve been directed to, have proven very enlightening to me and I’m sure to any others that have read them. The reason that people question whether back radiation exists is because they don’t understand the physics and, unlike sunlight and it’s evident effect, it is not obvious. I don’t think it’s because they don’t want to believe it but more that they see no direct evidence of it. Now I understand a little more and have the benefit of the combined wisdom of you three (albeit not totally in agreement), I have a much better concept of back radiation and can see that it must exist and slow the cooling of warmer objects. Previously I believed that it existed but somehow reflected off of warmer objects so my understanding has moved on. Thank you to all three of you for bothering to answer my questions and hopefully you’ll lower yourself to answer a few more when they come to me in the future.
Iansview,
Okay…Sorry that my response was a bit jaded. There sometimes seem to be so few who are really willing to consider the evidence, but I am glad to see that you are one of the minority!
salvatore del prete says:
May 11, 2013 at 11:27 AM
Dr. Spencer, your stance on this issue is so correct. You have shown through examples, through experimentation, through observational data, that the ghg effect is real and does exist.
As I said I could not address the climate issue or have any understanding of the earth/climate system if I did not think the ghg effect was real.
In the absence of a GHG effect it would be next to impossible to explain anything when it comes to the climate and atmosphere. Such as the atmospheric temp. profile,the various lapse rates, the temp. of the globe being what it is given the amounts of solar radiation coming into /leaving the earth, climatic system.
FOR EXAMPLE : As you have said the STRATOSPHERE and the characteristics of it go a very very long way in proving the GHG effect is real and operates in the manner you have suggested.
SO2 from volcanic eruptions would be another example.
Some of the questions going forward are ,if the sun does stays in this prolong minimum phase how much does that, along with all the secondary effects associated with a prolong solar minimum ( one example an increase in cosmic rays more clouds) counteract the current ghg effect?
An even better question is does a prolong solar minimum and the secondary effects associated with it, resulting in less energy in the earth/climate system have the effect of causing the ghg effect to be less effective,for lack of a better word going forward?
I am thinking yes, and some reasons but not all of my reasons ,are evaporation from the oceans would be less therefore water vapor concentrations in the atmosphere would lower,the colder oceans themselves would be able to absorb more co2 from the atmosphere both in my opinion making the ghg effect, less going forward.
In addition the OLR(IR) emitted from an earth that is cooling would shift to longer wave lengths where CO2 would not be as efficient in absorbing those longer wavelengths, in contrast to the shorter wavelengths a warmer earth now emits.
The near saturation level that CO2 absorbs some of the IR from the earth must come into play at some level.
The fact that no lower tropospheric hot spot near the equator has transpired as a result of a CO2/water vapor positive feedback to me is very telling ,and puts a very big dent in what the global warming models are trying to say about the climate going forward.
To look at this climate situation from the other side ,that being solar i have the following thoughts.
I will start with the solar conditions I feel must be meant in order to get the cooling effects from low solar conditions and limit the ghg effect gong forward. These solar effects must be sustained for a long period of time.
THEY ARE SOLAR FLUX 72 OR LESS
SOLAR WND 350 KM/SEC OR LESS
AP INDEX 5.0 OR LESS 98+ % OF THE TIME
SOLAR IRRADIANCE .015% OFF OR MORE
These solar conditions have been met since 2005 at times ,but the catch in my opinion is when they were met, three factors were coming into play which did not allow the temperatures to respond the way they should going forward to those solar conditions mentioned in the above.
These three factors are the current max. of solar cycle 24 ,(although weak it is still a max. and holding up the solar values stated above), the limited number of sub-solar years(this started oct 2005 in earnest) following over 100+years of active solar conditions, and the ocean heat content that accumulated over the last 100 years in response to the strong solar conditions which is very slow to subside.
Never the less as this decade proceeds these factors will be becoming less of a factor when it comes to keeping the temperatures higher then would otherwise be the case.
I will end this but I just to mention other important secondary effects I feel will come into play with a very quiet long prolong solar minimum period.
They are 1. increase in volcanic activity(response to cosmic rays(earth magnetic field being disturbed)
2. a more meridional atmospheric circulation (in response to ozone changes)
3. a mostly cold PDO /AMO ( Less El Ninos)
4. Greater snow cover,clouds,precip. in response to a more -AO.
5. 4 in the above, results in an albedo increase
6. increase in cosmic rays contributes to more clouds and point 1
Finally the earth’s magnetic field is weakening and will serve to magnify the effects a prolong solar minimum will exert on the earth/climate system in my opinion.
Reply
pochas says:
I had to post what I said again, it is a balanced comprehensive approach TO THE CLIMATE SITUATION, unlike others who focus on is there a GHG effect.
It goes on and on with people talkng BY eachother not to one another.
I am with Stephen Wilde on the solar side of climate and with Dr. Spencer on the CO2 side of climate for the most part but disagree with Stephen on the GHG effect or lack of it, and disagree with Dr. Spencer when it comes to the solar influences on the climate.
I have put myself on the line by giving specifics and saying if this,this ,this happens the result will be this ,this and this.
I have set myself up to be either proven correct or wrong, in contrast to those trying to debate if a GHG effect exist or does not, but can’t prove it and can’t say if this,this or this happens, then this happens which proves there is no GHG effect.
I further state that Dr. Spencer has proven there is a GHG effect, and now it is time to go forward and see how strong the GHG effect might be going forward and examine what impact a prolong solar minimum will have on the climate and the GHG effect going forward, so we can get a sense of where the climate might be heading.
I think that is the central question that should be what this board needs to address.
Nullius in verba said:
“in an adiabatically-limited convective atmosphere, backradiation has no effect. It is always exactly compensated for by a change in convection to maintain the same gradient.”
I agree with that.
but then you say:
“GHGs can only affect the surface temperature via the altitude term, by translating the entire lapse rate vertically”
How would that work in an adiabatically limited atmosphere? Why wouldn’t the thermal effect of GHGs be similarly compensated for ?
Because the adiabatic lapse rate only determines the gradient of the line, it says nothing at all about the intercept.
If you increase or reduce the temperature at every altitude by the same amount, no extra convective instability is introduced. No warmed air rises above the surrounding air because the surrounding air is warmed equally too.
The temperatures at different altitudes are tied to one another in a rigid assembly, but the whole assembly is not tied to anything else – at least, not convectively. The temperature of the layer that radiates directly to space is fixed, by the requirement for the Earth to radiate as much as it absorbs from the sun. So this layer settles at the effective radiative temperature, and then all the levels above and below it (including the surface) are tied to it by the adiabatic slope.
Ok, but the normally proposed effect of CO2 is to warm the surface via back radiation rather than changing the temperature evenly at every altitude.
In that case one would get more convection.
I get the point about the rigid assembly but my view is that if anything seeks to disturb it then a circulation change must occur to correct it.
You accept that such a correction would occur if back radiation were to have an effect on the surface.
How do you get to the view that CO2 warms the air evenly at every altitude without triggering a corrective response ?
Another point is that if one raises the effective radiating level then the system is still radiating at the same temperature as before but at a higher level which has become warmer.
AGW theory says that the system radiates at a higher colder location but I can’t see that because that higher colder location will itself have become warmer.
That would normally result in more effective radiation to space with a cooling effect wouldn’t it ?
The “normally proposed” mechanism is an unfortunate simplification that some climate scientists misunderstand. The ones who developed the theory, like Ramanathan and Manabe, describe things in terms of altitude of emission to space.
Yes, if anything disturbs the rigid assembly, circulation changes occur to restore the relationship, but these changes don’t necessarily preserve the intercept. The assembly can be restored at a higher or lower level. Convection works only on temperature differences, and translations of the whole are invisible to it.
A lot of confusion is caused by climate scientists’ tendency to talk about situations that tell half the story. If CO2 rose instantaneously without the temperature changing, then an imbalance occurs that restores the equilibrium. Climate scientists talk about this hypothetical situation so they can figure out which way the imbalance is pushing the system, so they know what will subsequently happen. But in reality, the force and its effect occur simultaneously.
It’s as if they worked out what happens when you push a child on a swing by first assuming that the child doesn’t move. You push, and compress one side of the child like a spring. This spring force is in such a direction as to accelerate the child away from the push. It is, in a sense, what actually happens on sufficiently short time scales, but it gives rise to a confusing picture. You push the child but the child doesn’t move?!
Similarly, if you simply increase CO2 then the radiation comes from a higher level which is initially colder, and so radiates less. It’s still getting the same energy from below, but is now losing less, and so warms up. That stops some of the convection from below, which warms the layer immediately below, which warms the layer below that, and so on. After a while the top layer has warmed enough to be emitting as much as it receives, and equilibrium is restored.
I find it easier to think about where the new equilibrium is. Other people seem to prefer thinking in terms of the imbalanced push. But whichever you choose, you can’t mix them. That just leads to confusion.
Sorry, that’s confusing.
“Similarly, if you simply increase CO2 then the radiation comes from a higher level which is initially colder, and so radiates less.” should say “Similarly, if you simply increase CO2 then the radiation comes from a higher level where it is initially colder, and so the atmosphere as a whole radiates less.”
Hope that helps. My apologies, I need to break off now.
Nullius in Verba: Great posts and I basically agree with almost everything you have said.
Just one elaboration and one comment: The elaboration is that the way I like to look at the question of why convection can’t negate the greenhouse effect is because convection only drives the temperature as far as the (appropriate) adiabatic lapse rate because it is only lapse rates steeper than this that are unstable to convection. If convection were able to drive the atmosphere all the way to an isothermal configuration, then it could essentially negate the entire radiative greenhouse effect. And, in fact, this is exactly why Nikolov and Zeller found that they could get rid of the greenhouse effect in the simple shell model by introducing convection in a way that, by their own description, drove the temperature of the shell (“atmosphere”) down to the temperature of the Earth’s surface. Of course, this is entirely in accord with what textbooks on radiative transfer talk about, as when Ray Pierrehumbert notes in his book that it is vital for the effective radiating layer to be colder than the surface for there to be a greenhouse effect.
The comment, related to the above elaboration, is that I tend to think to think of there as being less of a dichotomy between the “back-radiation” description and the “effective radiating level rises” description than you seem to feel there is. The way I look at it is that in an atmosphere strongly heated from below, if only radiation were present then the atmosphere at altitude would indeed be colder than the surface and the back-radiation would indeed be responsible for maintaining this situation. In the presence of convection, the atmosphere is able to compensate for an increase in back-radiation by increasing the convection (and hence it becomes much less easy and useful to think in terms of the surface energy budget), but that compensation is incomplete because of the fact that convection only drives the lapse rate down to the adiabatic lapse rate.
So, at the end of the day, the easier way to understand what is going on is to think in terms of the top-of-the-atmosphere radiation budget (and hence the rise in the effective radiating level). It is precisely because within the atmosphere, the modes of radiation transfer are varied, whereas between the Earth + atmosphere and space there is only radiation, that makes that top-of-the-atmosphere point-of-view so much more powerful. But, I don’t think that the notion that back-radiation is responsible for the surface warming is really incorrect…Just that it becomes much less useful to think of it that way.
Do you think that is a reasonable way to think of it or not?
Speaking of corrections…I said
“And, in fact, this is exactly why Nikolov and Zeller found that they could get rid of the greenhouse effect in the simple shell model by introducing convection in a way that, by their own description, drove the temperature of the shell (‘atmosphere’) down to the temperature of the Earth’s surface.”
Of course, the “down” should be “up”…Or really its more that it drove the temperature of the surface down to the temperature of the shell…Or, simply that it drove them to the same temperature.
Joel,
Yes, that’s a reasonable way of looking at it.
If the lapse rate is close to zero, you get no temperature difference because convection can drive the fluid all the way to an isothermal configuration. This is the situation in a pond of water, which has huge backradiation, but which is virtually incompressible. (Actually, it does have a slight non-zero lapse rate of around 0.1 C/km, and in the deep ocean this temperature rise is observed.)
I would agree that backradiation is a necessary part of the mechanism. The radiation of the surface up and the backradiation of the sky down are two parts of the same balance, like the radiation from each half of the split concrete block. You cannot include one and ignore the other without major problems. The warm surface radiates more energy than it gets directly from the sun, so it also has to get some back from the opaque material in the way to stop it cooling.
The point I disagree with is about causality/control. You get the same sort of nonlinearity when you boil a pot of water on a stove: the temperature is always 100 C. You can turn the gas up or down, put a lid on, paint the pot black – all of these change the heat flows around the pot, but none of them change the temperature. You can’t get the equations to balance without including the backradiation from the pot lid, but it’s not the *reason* for the temperature being 100 C. It’s not the *explanation*.
I know what you mean by the TOA budget, but I’m not terribly keen on the term, because it’s really about the average emissive layer, which is only about 5 km up, not at the top. I don’t know about anyone else but I used to find that confusing. The atmosphere above the emissive layer is cooler than the blackbody -20 C, just as the air below it is warmer. It’s actually more complicated, because the atmosphere doesn’t just emit at one level, but throughout its depth. So I’m not sure that my average emission altitude is that much better either for a more sophisticated understanding. I don’t know what term would be better, though.
Nullius says: “The point I disagree with is about causality/control. You get the same sort of nonlinearity when you boil a pot of water on a stove: the temperature is always 100 C.”
There is a fundamental difference here. The process of boiling holds the temperature basically constant for some system. The process of convection hold the temperature GRADIENT relatively constant for some system.
As such, phase changes are very good at keeping temperatures near some particular value. Convection does not have that property.
PS. Like Joel, I have enjoyed reading your posts and find them very positive contributions to the discussion.
Hi Nullius in Verba,
Thank you for very informative posts and the Gutenberg-Max Planck link. Like many others, I enjoy your comments.
You wrote on a post:
“You can’t get the equations to balance without including the backradiation from the pot lid, but it’s not the *reason* for the temperature being 100 C. It’s not the *explanation*.”
Agreed. Carl Menger wrote:
“All things are subject to the law of cause and effect.”
Your question suggests a “single” causal explanation for a given temperature. Since I don’t think you seek an “ultimate” cause or theological explanation, a question arises. Which of likely several proximate causes do you seek to explain the temperature? It seems obvious that several causal and limiting factors (highest proximate energy source, type and state of matter (freezing/boiling temperature if liquid), time period, pressure, etc., etc.) may determine the ability of any given quantity of matter to record a given temperature. Which one of many do you know and/or believe limits or defines all the others? Or do you in fact believe a single proximate cause trumps all the others?
“Your question suggests a “single” causal explanation for a given temperature.”
Which do you mean? The boiling pot, or the Earth’s surface?
The ’cause’ of the pot of boiling water being at 100 C is that 100 C is the boiling point of water. So long as there is enough heat going in to it to boil it, any excess heat turns water into steam which very rapidly escapes, cooling it efficiently. But as soon as the temperature has been cooled to 100 C the boiling stops, and it cools no further. The non-linearity of heat flow with respect to temperature holds the temperature tightly against the limit.
The temperature of the Earth’s surface in an adiabatically-limited convective atmosphere is equal to the effective radiative temperature plus the average altitude of emission to space times the adiabatic lapse rate.
The effective radiative temperature is affected by clouds, aerosols, albedo, and insolation – those are the factors Roy considers to be most significant, and I find his ideas persuasive.
The average altitude of emission to space is affected by greenhouse gases. There is no doubt that in an atmosphere where the lapse rate is non-zero, they must have an effect.
The lapse rate is affected only by water vapour feedback, which given the absence of a tropical hotspot may be less significant than thought.
And there are other things that affect climate and surface temperature besides AGW, like the oceans and their oscillations and currents, geology, biology, land use, and the weather.
So I’m not identifying any one factor here. But what I was saying was that backradiation is not one of these factors. If backradiation were to have an effect it would be on the lapse rate: as radiation from sky to surface cooled the sky and warmed the surface, it would thereby change the gradient. However convection is non-linearly dependent on temperature difference, meaning that any excess gradient is relieved by convection, a very efficient cooling mechanism, but as soon as the adiabatic lapse rate is restored the convection stops, forcing the profile up against the limit.
And since backradiation is not the means by which greenhouse gases affect surface temperature, trying to argue that it somehow doesn’t exist or doesn’t work is totally misdirected effort. You can’t disprove AGW that way, because it’s not how AGW works. That’s what’s so frustrating about it all. So much time and effort is being wasted.
Dr. Spencer has demenstrated through experimentation,and data that a GHG effect does exist.
salvaotre del prete,
I posted this link on the previous thread. No one chose to address it. It concerns what researchers found in looking at polar air. They found that small ice cyrstals in the air acted like black body radiators. Heat in the air would flow to them and they would radiate the energy away but not to the surface. The surface was cooling faster than accounted for by calculation as was the air at higher levels. Both CO2 and Water Vapor allow IR to pass through these windows where neither gas will absorb some wavelengths. But ice crystals that act as black bodies act as strong cooling mechanism. They found that the cooling effect far exceeded the energy given off when water vapor turned to ice. This is a peer-reviewed article. I would hope you can explain why a material that acts as a much more efficient absorber of IR acts as a strong cooler to air temp. Why wouldn’t the radiation the ice receives be directed in all directions and cause a slowing of cooling rather than an increase?
Link to article:
http://journals.ametsoc.org/doi/pdf/10.1175/1520-0450(1965)004%3C0446%3ATEOSIC%3E2.0.CO%3B2
Roy,
Yes, you are right – Trenberth or Dessler got it all backwards! I’ve been saying this for over a year (on the blogs) now – changes in cloud cover ARE the REAL DRIVER of surface temperature variations, not the other way around!
The multi-decadal periods of global dimming and brightening are well documented in the scientific literature. JGR had a special issue on this topic in 2009, see:
http://www.agu.org/contents/sc/ViewCollection.do?collectionCode=DIMBRIGHT1
Also, cloud cover retrievals (by type) conducted by Japanese JAXA researchers in 2011 (article published in JGR) show that cloud changes always PRECEDE temperature changes by about 12 months on average during the entire available record, i.e. from 1982 to 2006 (the lag is based on my own correlation of the Japanese cloud-cover data with satellite-based LT global temperature series).
Once we realize that clouds control the amount of solar radiation reaching the surface (which is the real heating agent), then temperature changes (including ENSO cycles) become easy to explain. Yes, the El Nino/La Nina fluctuations as well as PDOs and AMOs are all caused by cyclical variations in cloud cover driven by solar activity. However, we do not currently understand the process details of this Sun-cloud connection (we only know the statistical correlation), and that’s the area we should be focusing our research efforts as you correctly pointed out!
I maintain that the entire warming of about 1.2 C from 1670 to the present has been caused by a 1.2% reduction of cloud albedo due to an increasing solar magnetic activity. The Sun became quieter in the late 1990s, which resulted in a sharp increase of low-level clouds in the late 2000. This is clearly visible in the cloud-cover data. This cloud increase was the real reason for the observed cessation of warming over the past 12 years! There is no increase of heat storage into the deep oceans as some claim. It’s the clouds, Stupid! … 🙂
Dr. Roy Spencer says “ ….that natural changes in cloud cover have caused the temperature changes, and cloud feedbacks are in reality negative rather than positive.
And this is where I believe we should be spending our research time in the global warming debate.”
Ned Nikolov says: “ It’s the clouds, Stupid! …”
Totally agree with both sentiments and would include aerosol dynamics too.
The debate should include the cloud and aerosol dynamics in more detail. Constantly they are stated as the area of greatest uncertainty in the climate change debate. Before all else the reasons for the natural changes in cloud cover needs more understanding. It seems likely that clouds drive circulation in such a way as to utilise the available energy for their own development.
Contributions of Individual Atmospheric Diabatic Heating Processes to the Generation of Available Potential Energy
http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-12-00457.1
“The results presented herein suggest that the large scale dynamics of the atmosphere organizes the spatial and temporal distribution of clouds and precipitation in such a way as to increase the energy available to drive the circulation, a kind of positive feedback.”
http://udini.proquest.com/view/investigating-the-role-of-pqid:1964714661/
“changes in cloud cover ARE the REAL DRIVER of surface temperature variations, not the other way around! ”
Agreed.
High solar activity, positive AO with a higher and stronger polar vortex with a smaller surface footprint resulting in more zonal jets, poleward shifting climate zones, larger subtropical high pressure cells, less clouds and more energy able to enter the oceans foe a warming influence.
Low solar activity, negative AO with a shallower and weaker polar vortex with a larger surface footprint resulting in more meridional jets, equatorward shifting climate zones, smaller subtropical high pressure cells, more clouds and less energy able to enter the oceans for a cooling influence.
After that, the atmospheric circulation reconfigures in a negative response to eliminate long term consequences just as it does for changes in GHG amounts.
That proposition is easy enough to verify just by comparing events after the late 70s climate shift with events after 2000.
Nullius in verba said:
“Yes, if anything disturbs the rigid assembly, circulation changes occur to restore the relationship, but these changes don’t necessarily preserve the intercept”
and:
“Because the adiabatic lapse rate only determines the gradient of the line, it says nothing at all about the intercept”
My impression is that the gradient is set by gravity because the gradient of the lapse rate depends on the reduction of pressure (and thus density) with height.
The intercept is set by mass (which determines density at the surface and insolation (which determines the height to which gas of a given density will rise).
Therefore, neither gradient nor intercept is determined by the radiative characteristics of constituent molecules so if there is a change in radiative characteristics it can only be dealt with by a compensating change in circulation.
What evidence to we have that radiative characteristics can affect either gradient or intercept ?
“My impression is that the gradient is set by gravity because the gradient of the lapse rate depends on the reduction of pressure (and thus density) with height.”
It’s because when you compress a gas the temperature rises, and when you allow a gas to expand, the temperature drops. That’s how a refrigerator works. The work done compressing the gas adds energy to it. It is not simply gravity, but the result of an external force driving gas up and down a pressure gradient, which requires a temperature difference to drive convection.
The pressure under water increases/decreases even faster with altitude than it does in air, but the lapse rate is near zero. It’s not simply pressure. Gravity works underwater, too.
“The intercept is set by mass”
No. The intercept is set by the requirement that the atmosphere radiates to space as much energy as the Earth as a whole absorbs. The surface that radiates to space, and hence approaches that temperature, is the IR-‘visible’ upper surface of the IR-opaque atmosphere. When the atmosphere gets more opaque, from adding more opaque gases to it, you can see less far into it, and hence the IR-‘visible’ surface is higher off the ground.
Get a bucket of water and pour a cupful of milk into it. You can only see so far into it. Pour another cupful in. You can see less far. The visible threshold has risen.
Why would you think it was set by the mass?
Because it is mass that slows down the throughput of solar energy.
Are you really suggesting that an optically transparent atmosphere with significant mass will have zero greenhouse effect ?
Water is not significantly compressible. You can’t apply the Gas Laws to a liquid.
Even a completely transparent atmosphere will accumulate energy from an irradiated surface by conduction and develop a circulation.
Opacity actually provides an addition radiative window to space that a transparent atmosphere does not supply.
If you increase opacity there will be more radiation directly to space from within the atmosphere and in order to maintain ToA energy balance the convective circulation will slow down since it does not need to deliver energy back to the surface as fast for radiation out from that surface.
For a completely transparent atmosphere ALL energy out to space from ToA has to come from the surface so the circulation has to work harder to deliver energy back to the surface via adiabatic processes after it has been removed from the surface by adiabatic processes.
The ‘extra’ warmth beneath an atmosphere results from energy being stored in the atmosphere as PE between adiabatic uplift and adiabatic descent and the maximum temperature that will be achieved is determined by how long the KE remains in the form of PE.
The entire 33C that AGW theory obsesses over is accounted for in that way.
In practice radiative and non radiative processes will always interact so as to maintain ToA radiative balance.
Whatever radiative characteristics achieve is offset by changes in the speed of the non radiative processes.
GHGs don’t obstruct outgoing IR. They actually short circuit the need for energy stored in the atmosphere as PE to be returned to the surface before it can be radiated out.
They assist cooling but the effect is countered by a slowing down of the non radiative processes.
No greenhouse gases mean no cooling from the upper troposphere meaning little or no convection meaning a uniform atmospheric temperature profile. Surface temperature would be controlled by black or grey body radiation to space. The atmosphere would heat to the surface temperature of the planet. Of course all this would be somewhat perturbed due to planetary rotation and reduced radiation towards the poles. Greenhouse gases are the secret sauce and water is the star as both a greenhouse gas and a condensing working fluid in the great heat engine that is our atmosphere.
“Because it is mass that slows down the throughput of solar energy.”
I have no idea what that means. It doesn’t explain anything.
“Are you really suggesting that an optically transparent atmosphere with significant mass will have zero greenhouse effect ?”
Yes. The surface temperature is the effective radiative temperature plus the average altitude of emission to space times the adiabatic lapse rate. If the height of emission to space is zero, the surface temperature will be the effective radiative temperature: the temperature where it emits as much energy as is absorbed.
“Water is not significantly compressible. You can’t apply the Gas Laws to a liquid.”
It’s not a gas law. Convection applies to fluids generally.
“Even a completely transparent atmosphere will accumulate energy from an irradiated surface by conduction and develop a circulation.”
True, it will – albeit a rather strange one. (Differential heating of different parts of the surface still drives convection.) The surface will be at the effective radiative temperature, and the atmosphere above it will be even colder.
“Opacity actually provides an addition radiative window to space that a transparent atmosphere does not supply.”
This again makes no sense.
The radiation upwards from an opaque atmosphere only replaces the radiation upwards from the surface that it blocks. There’s nothing ‘additional’ about it. If you suspend an opaque plate a foot above the surface, it creates a new opportunity to radiate to space, but only does so by blocking the old one.
“The ‘extra’ warmth beneath an atmosphere results from energy being stored in the atmosphere as PE between adiabatic uplift and adiabatic descent and the maximum temperature that will be achieved is determined by how long the KE remains in the form of PE.”
I’m afraid I have no idea what this means. It doesn’t sound like real physics to me.
I’ve explained how it works. I’m very pleased to see a couple of people have understood. (I appreciate the feedback, guys!) But I don’t have the time or interest at the moment to pursue the question, and given that Roy has asked people to stop posting Slayer nonsense, it would be rude to do it here.
But I’ve enjoyed the conversation, for which I’d like to thank everybody. It’s been fun!
Perhaps Stephen means that the altitude of the upper troposphere radiating layer is set by atmospheric density, not mass. Adding mass to the atmosphere would raise the altitude of the characteristic emitting layer. Raising the emitting layer means a higher surface temperature via the lapse rate extended over a greater vertical distance.
Yes, and density has an effect on opacity.
For a given atmospheric composition, the infrared optical depth of the atmosphere will increase with pressure. As a result, a rise of [pressure] will always lead to a rise of the [radiative] greenhouse effect and temperature.
from here:
http://wwwuser.oats.inaf.it/astrobiology/docs/EBM_EGU2012.pdf
I don’t subscribe to the conclusuons of that paper but that point sounds right to me.
The point that pressure-broadening affects the IR absorption bands of those elements of the atmosphere that do absorb IR is not controversial. However, I don’t see what that has to do with anything.
We are not making any significant changes in the pressure in the atmosphere…We are making significant changes in its IR opacity by the addition of CO2 (and, through the water vapor feedback) water vapor.
“Perhaps Stephen means that the altitude of the upper troposphere radiating layer is set by atmospheric density, not mass.”
Again, what does this mean, precisely? What do you mean by “set by”? Proportional to? With what constant of proportionality? Some other function of density? Quadratic? Exponential? What?
So if you’ve got a completely IR-transparent atmosphere of Xenon, which is extremely dense, and you replace part of it with water vapour, which is much lighter, then the density goes down. Does the IR-opacity therefore go down too? Or up? Or what?
Water vapour is lighter than air (nitrogen/oxygen) which is lighter than carbon dioxide – but water vapour is the most opaque, followed by CO2, and oxygen/nitrogen is transparent. So does the opacity-density relationship have a dip in the middle? If you compress pure nitrogen does it become opaque to IR?
We always get this talking to slayers. They throw out assertions that are untrue, unclear, undefined and/or unrelated to any identifiable physical principle. Then when you ask them about it, you get an unclear answer and another half dozen sciency-sounding assertions. Or a link to a brain-numbing hundred-page document telling you at great length how badly deluded everybody else is, packed with yet more unclear assertions.
It’s just throwing out anything to avoid the obvious conclusion – that if you add more of an IR-opaque gas to a mixture then the mixture will get more opaque.
If you can first connect it to some other quantity like density by talking about the density of an opaque substance, and then silently switch definitions/context to mass density of substances generally, then it’s easy to say that adding a few ppm of CO2 isn’t going to change the density of the atmosphere so it can’t have any effect on the opacity either. Or something. It’s a technique called equivocation, and it relies on being imprecise about meaning.
The only thing I can’t make my mind up about is whether it’s deliberate. I suspect it’s not intentional – people can genuinely believe some very strange things – but it’s hard to tell.
Anyway, I’m not going to bother any more. I’m happy to talk to anyone who is interested in how it really works, but only if they can make some sort of sense.
I can simplify that.
the gradient is set by gravity because the gradient of the lapse rate depends on the reduction of pressure (and thus density) with height.
The intercept is set by mass (which determines density at the surface).
Insolation sets the distance through which the gradient must travel to reach ToA.
So,
Gravity gives gradient.
Mass gives intercept.
Insolation gives height.
What role is left for radiative characteristics ?
Give us an equation. The values for mass, gravity, and insolation are well-known. If that is all there is to it, then you should be able to calculate the height and the surface temperature from just the numbers you discuss (and basic parameters like the specific heat of air, the emissivity of the ground, etc).
I will bet you cannot do it without including *something* about the radiative properties of the atmosphere. In particular, how do you find the “effective radiating level”? You can’t just say “the experimental value is ~ 5 km up, so the theoretical value is ~ 5 km up”. You need to be able to say “I calculated the altitude using f(m,I,g, …) and found it to be ~ 5 km up, which agrees with experiment”.
[Even the name “effective radiating level” assumes that the radiative properties of the atmosphere are an indispensable part of the process and an indispensable part of the calculations].
Prove that radiative properties make a difference.
The ability of the effective radiating level to vary suggests a negative system response.
You are proposing that it does make a difference. Back it up.
Bets not enough.
A completely transparent atmosphere effects ALL radiation from the surface. In reality that would involve no atmosphere at all.
A completely opaque atmosphere effects ALL radiation from ToA. In reality that would involve ToA being a solid surface.
An atmosphere in between radiates from somewhere in between and obviously the height at which it radiates will depend on opacity.
What you miss is that none of that matters for surface temperature.
The level of opacity simply alters the effective radiative height – correct.
But that is countered by a negative system response.
The more energy is radiated out by a higher effective radiating level the less energy needs to be radiated from the surface and the circulation slows down to deliver less energy back to the surface.
The less energy is radiated out by a lower effective radiating level the more energy needs to be radiated from the surface and the circulation speeds up to deliver more energy back to the surface.
Note that I an accepting a climate effect from GHGs because there is a change in circulation which affects climate zones and jet streams.
However, the effect is miniscule because such a tiny proportion of atmospheric mass is involved and it is the entire atmospheric mass that determines the scale of the greenhouse effect.
Furthermore solar and oceanic variability makes vastly larger differences to the circulation as a matter of routine.
Yes…You simplify it by ignoring conservation of energy. It is simply wrong to say, “the intercept is set by mass (which determines density at the surface)”. Conservation of energy tells us that the constraint is going to be set by the fact that the Earth system has to be in radiative balance (or, more precisely, that it will always be driven toward radiative balance).
That is why science is done by writing down equations and actually showing mathematically how things work out. It is not done, as you guys like to do at Tallbloke’s, by just talking off the top of your heads. The laws of physics severely constrain the mathematical models that can be written down.
Your “models” are not constrained in this way because you never demonstrate mathematically that basic things hold like conservation of energy. And, of course, they don’t because it is impossible to relegate radiative characteristics to having no effect when it is the only way in which the Earth + atmosphere communicates energy to space! You end up with absurdities like the claim that the discrepancy between the 390 W/m^2 the surface of the earth radiates and the 240 W/m^2 that the Earth system radiates as seen from space can be explained without referring to the radiative characteristics of the atmosphere!!!!
240 is exchanged between atmosphere and space.
150 is exchanged between surface and atmosphere by non radiative processes.
The observed radiative fluxes are simply a consequence of that.
Conservation of energy fully complied with.
You keep not understanding: The 390 W/m^2 is emitted as radiation. It is not exchanged between the surface and atmosphere by non-radiative processes. Any non-radiative processes are above and beyond the 390 W/m^2.
Lets take it one parameter at a time.
i) gradient – If GHGs alter the gradient then they alter density at every point from the surface which changes the rate of energy transport through the system to negate their effect.
ii) intercept – if GHGs alter the intercept point then radiative characteristics trump mass. I challenge you to prove that the effect is significant at a proportion of 0.004%.
iii) height – If GHGs alter height then again they alter density at every point from the surface which changes the rate of energy transport through the system to negate their effect.
So the whole issue turns on the intercept point. I am indifferent as to whether the effect on the intercept point is zero (which I think it is after a period of transition) or 0.004% (being insignificant).
I call for evidence that changing 0.004% to 0.008% (a doubling) has any measurable effect on the intercept point set by total atmospheric mass.
You want to change global energy policy. You do the proving.
“ii) intercept – if GHGs alter the intercept point then radiative characteristics trump mass. I challenge you to prove that the effect is significant at a proportion of 0.004%.”
The proof is in the fact that the Earth’s surface is at a temperature where it emits 150 W/m^2 more than it could possibly emit in the absence of IR-absorbing elements…in, in fact, 150 W/m^2 more than we know is actually being emitted out to space. And, the spectra of the emission to space, showing the absorption lines due to CO2 and H2O and CH4 and what-have-you just happen to agree very well with the radiative transfer calculations, hardly surprising since these radiative transfer calculations underlie the entire field of remote sensing, including the very methods by which Spencer and Christy determine the temperature in the troposphere from satellite measurements.
I think that 150W/m2 is simply being exchanged between surface and atmosphere by adiabatic uplift and descent involving the entire mass of the atmosphere rather than just GHGs.
Steven,
That doesn’t make any sense: 390 W/m^2 is being radiatively emitted. It can’t magically turn into “adiabatic uplift”. The only way that the atmosphere can interact with it is by absorbing the radiation.
It does absorb it by conduction.
Adiabatic uplift and descent is not magic. It arises from density differentials in the horizontal plane so that air parcels of different densities move vertically relative to one another after acquiring KE by conduction from the surface.
The entire atmospheric mass acquires energy by conduction and then moves it up and then down adiabatically via convection.
That gives your 150W/m2 between surface and atmosphere and in turn raises surface temperature by 33C.
The 150W/m2 radiation is a consequence of the conductive and convective exchange between surface and atmosphere.
The atmosphere doesn’t need to react with the radiation. The radiation is a consequence of the non radiative processes and not a cause of them.
Stephen,
What you are saying is just utter and complete nonsense. The issue isn’t exchange between the surface and the atmosphere. The issue is that the surface is emitting 390 W/m^2 of radiation and no amount of sophistry on your part can convert that into 240 W/m^2 of emission as seen from space. The only thing that can cause this reduction of 150 W/m^2 in the radiation is absorption of the radiation by the atmosphere.
“The entire atmospheric mass acquires energy by conduction and then moves it up and then down adiabatically via convection.”
(1) This violates the 2nd Law of thermodynamics. How is convection going to transfer heat in net downward from the colder upper atmosphere to the warmer surface?
(2) It is irrelevant anyway because, despite your refusal to understand, the issue is not how the surface gets enough energy to emit 390 W/m^2. The issue is that 390 W/m^2 can’t be emitted by the Earth + atmosphere as a system because it is only absorbing 240 W/m^2 from the sun. And, a further issue is that we know that the Earth + atmosphere is in fact not emitting 390 W/m^2 to space, it is only emitting 240 W/m^2. The only way this can be true is if the atmosphere is absorbing some of the radiation emitted by the surface. (And, coincidently enough, the spectrum of radiation emitted to space looks exactly like what is predicted on the basis of radiative transfer calculations.)
This ought not be that difficult to understand.
Let me explain why I think you are now in a bind.
There are actually 4 parameters involved in determining surface temperature.
Gradient of the lapse rate slope, intercept point (surface temperature),atmospheric height and ToA insolation.
The critical point is that ToA insolation is fixed whereas the other 3 are variable.
Whatever happens, an atmosphere can only be retained long term if OLR is the same as ToA insolation over time.
So you cannot alter any of the other three without altering all three. If you alter any one then the others will adjust to negate the effect.
Assuming for a moment that GHGs affect the intercept point. That obviously affects the gradient which will put OLR out of line with ToA insolation unless height changes too.
However, changes in height or in the gradient alter the way density varies with height and so that changes the rate at which energy flows through the system.
One key issue is the way that atmospheric contraction and expansion alter the relative proportions of KE (heat) and PE (not heat)
Another, is that reduced density converts KE to PE via the Joule Thomson effect
but for brevity I won’t go into those matters here.
The only way for ToA insolation to remain matched to OLR is for the gradient and/or height to change to negate any effect from GHGs on the intercept point.
Now there is a refinement to the AGW theory that I have encountered elsewhere.
The idea is that GHGs warm the lower layers but cool the upper layers in order to maintain ToA balance despite an increase in the intercept point.
The problem with that is that it is just shifting the essential problem behind a ‘curtain’.
If one cools the upper layers compared to the lower layers then temperature differentials increase (a steeper average lapse rate in the lower, warmed portion of the atmosphere) and so the rates of convection and/or evaporation increase and can then negate the change in the intercept point.
With a fixed radiative balance at ToA the three variable parameters will do whatever is necessary to retain the atmosphere whatever the specific radiative characteristics of the constituents of a given atmosphere.
You can introduce all sorts of kinks in the lapse rate at different levels but in the end the netted out gradient of all lapse rates must mesh with the intercept point and the height of the atmosphere to ensure that OLR equals ToA insolation over time.
As to the practical implications for the climate at the surface I have dealt with that elsewhere.
Stephen says:
Did you really just say that you are using the surface temperature to determine the surface temperature? I suspect you meant something slightly different, but I can’t tell just what else you might have meant.
I come back to the simple point — if the atmosphere was completely devoid of IR sources (meanly mostly GHGs and clouds) then what difference can the atmosphere make on the energy balance? The OLR will all come from the surface, and, as you just said, this cannot change long term. So the (average) surface temperature will be fixed, independent of the atmosphere above it. No amount of mass can change the average OLR from the surface, so no amount of mass will raise the average temperature.
(Certainly the mass of the atmosphere will help even out the temperature by conduction & convection, so in those ways it will boost the average temperature a bit, but not to 288 K. And the mass of the atmosphere in conjunction with the GHGs will raise the surface temperature.)
“if the atmosphere was completely devoid of IR sources (meanly mostly GHGs and clouds) then what difference can the atmosphere make on the energy balance?”
The atmosphere would still absorb energy from the surface by conduction.
The heating of the air above the surface would be uneven.
There would still be a lapse rate with height due to declining density with height.
Air would still convect upward then downward as it does in the global circulation that we can observe.
Upward convection converts KE to PE and cools both surface and the atmospheric column. Downward descending air would convert PE to KE to warm both the surface and the atmospheric column.
The returning KE reaching the surface must be added to incoming solar energy and that gives the greenhouse effect.
ToA energy in and out is balanced.
Surface / atmosphere energy exchange is balanced.
Surface is 33C warmer.
All without radiative gases.
The initial source of the energy that gives the 33C warming is the time delay in energy flowing through the system which was created when the mass of the atmosphere first developed.
I think the conceptual problem here is with radiative physicists envisaging that 150W/m2 as a flow in a particular direction.
I don’t think there is a net flow in any direction.
It is just a haze of radiation flowing in all directions equally and the intensity of the haze is a consequence of the temperature at any given height.
The radiation in an atmosphere isn’t going anywhere. The amount of radiation at any given moment at any given height is simply a by-product of non-radiative conductive and convective processes within the atmosphere.
That is why energy out equals energy in over the long term at ToA.
The surface/atmosphere energy exchange is independent of the flow of solar energy straight through the system.
There is no net radiative flow of 150W/m2 going anywhere. that radiation just sits there maintaining the KE required to keep the atmosphere elevated above the surface.
As soon as one stops looking at that 150W/m2 as a flow in a particular direction then it seems to all make sense so far as I can see.
Indeed, there is an energy equivalent of 150W/m2 distributed evenly from surface to ToA and it is a permanent feature.
The temperature declines between surface an ToA only because reducing density with height progressively converts more of the KE to PE as one goes up.
A molecule at the surface has just the same energy content as one at ToA. The only difference is the relative proportions of KE and PE.
Taking KE and PE together there is a uniform store of energy in any atmosphere whether radiative or not and it is derived from conduction and convection.
The only reason for the warmer surface is that more of the energy is in KE form.
That 150W/m2 flows nowhere other then from KE to PE and back again.
That 150W/m2 does not represent a radiative flow at all and all science that assumes that it does is therefore wrong.
And if there is zero net flow then GHGs can’t slow the flow down.
Nullius nearly got there when he pointed out that the energy that GHGs radiate to space is balanced by the radiation that they block from escaping the surface.
It appears that the thermal effect of GHGs is therefore zero and that 150W/m2 is a permanent,stable consequence of the mass of our atmosphere restrained by gravity and irradiated from outside.
Not only no net flow but no net effect from GHGs either.
Non sequitur.
I don’t think so.
I said only that you ‘nearly’ got there.
Briefly, the radiative effects of GHGs (or any form of opacity) whether up or down will be faster than the non radiative processes so the net effect would be cooling if it were not the fact that the potentially faster radiative loss to space results in slower non radiative processes to negate the effect.
Ultimately the average global lapse rate stays the same despite changes in opacity. I think you accepted the principle of compensating mechanisms at some point.
There are some characteristics of GHGs that can affect the local lapse rate such as direct solar irradiation of ozone in the stratosphere and phase changes of water in the troposphere but they get cancelled out by circulatory changes elsewhere.
No, I meant it was a non sequitur to jump from the energy GHGs radiate to space matching those they block to saying the effect on the surface temperature is therefore zero. I already explained that. You just ignored it.
The lapse rate stays the same (excluding H2O feedbackl), but that does NOT imply there is no effect on the surface temperature. There is. The gradient doesn’t change but the intercept does.
And if the height changes without increased ToA insolation ?
In that case the gradient stays the same as does the intercept point but the increased height converts more KE to PE for a cooling effect that offsets any potential warming effect from whatever caused the rise in height in the first place.
Assuming gravity sets the gradient, mass sets the intercept point and ToA insolation sets the height then any change in height from a cause such as more CO2 reduces density right up the vertical column (but crucially not at the surface) in a self cancelling process as far as any thermal effect is concerned.
You said that the effective radiating height can rise from more CO2 but you got the sign of the thermal response wrong by ignoring the thermal cooling effect of increasing height and so reducing density.
Dr Spencer,
The close agreement between model and observation is at first surprising, the model being an idealisation of the chaotic reality being observed. However, closer inspection reveals “observation” to be misleading. What the instrument observes, and all that it observes, is temperature change in a detector plate. The instrument’s reading or measurement is a creation, built on the observation, using the same radiative transfer theory applied in creating the model. The close agreement between model and instrumental “observation” is then quite unsurprising. It is a bit of a stretch to hold up the self-referencing agreement as validating the theory.
So, what you are saying is if you deny enough physics, you can dispute this (or any) experiment. Sure. Do we have to start at the basics and prove all physical laws relevant to this experiment?
More to the point, the instrument measures the gain or loss of energy by the sensor, not the “sensor being warmed by incident radiation, regardless of the source” as Roy has claimed, despite it being utter nonsense.
Max,
How many times can you mindlessly repeat this mantra without making any effort to actually understand? Why is it difficult to comprehend that TWO sources of energy can warm something more than one source by itself?
If the body of the instrument is 300 K and it is aimed at a 0 K target, the sensor will be cooler than 300 K because the sensor is radiating lots of IR an absorbing none. The sensor will not cool to 0 K because there will be conduction from the body of the instrument.
DOES THAT SOUND REASONABLE SO FAR? If not, what do you object to?
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For the sake of argument suppose the temperature of the sensor is 260 K when aimed at 0 K. There will be ~ 260 W/m^2 of IR leaving the sensor, with 0 W/m^2 entering from the 0 K target. This must mean that the 40 K temperature gradient for the sensor must be enough to conduct 260 W/m^2 from the body of the instrument.
DOES THAT SOUND REASONABLE SO FAR? If not, what do you object to?
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Now aim the instrument at some warmer object — say 250 K. There will now be ~ 220 W/m^2 entering the sensor. Initially the sensor will be losing 260 W/m^2 by IR, gaining 260 W/m^2 by conduction AND gaining the new 220 W/m^2. The net flow into the sensor will cause it to warm up — to approximately 280 K. At this point, the conduction into the sensor has dropped sufficiently for the net power to be zero.
DOES THAT SOUND REASONABLE SO FAR? If not, what do you object to?
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The only change was the target. The ’cause’ of the temperature change of the cool (260 K) sensor was the change of the even-cooler-yet target (form 0 K to 250 K). OF COURSE, everyone knows that it was the COMBINATION of the target and the body of the sensor that determined the temperature of the sensor. OF COURSE, the target cannot by itself warm the sensor above the temperature of the target.
The science is painfully obvious. The sensor changes temperature from 260 K to 300 K as the target changes from 0 K to 300 K. The only issue is the semantics — should this process be called “warming” or “slowing the cooling” or “influencing” or “contributing to the temperature change of” or something else. The semantics are secondary to the physics.
“DOES THAT SOUND REASONABLE SO FAR? If not, what do you object to?”
I object to the sensor warming up, because it doesn’t work that way.
Until the target is warmer than the sensor it is measuring smaller and smaller losses of energy from the sensor to the target.
A microbolometer does not detect the sensor being warmed by a colder target, if it did this would be the breakthrough of all time, because we could generate energy for free with this mechanism.
In the real world, these devices detect the difference in voltage through the sensor, negative values indicate a colder target, positive values indicate a warmer target.
If the sensor was gaining energy from all targets it would register all targets as warmer than it is, herp-a-derp!
Stop spreading nonsense, please.
“I object to the sensor warming up, because it doesn’t work that way.”
Specifically, what do you think is wrong? Do you think that the sensor will stay at 300 K regardless of the temperature of the target (for the target cooler than the body of the sensor)? How do you think that the sensor knows to produce a negative voltage without a negative temperature change in the detector? Are you saying the detector simply “knows” that the target is colder, but that the sensor itself does not change in any way?
I think the sensor loses more energy than it receives from a cold target, and recevies more than it loses from a warm target.
Roy says that the sensor is warmed by any input and then translates that into a measurement.
Max,
Roy is talking about warming COMPARED TO THE 2.7 Cosmic Microwave Background radiation. If you point the detector at
[Accidentally submitted half way throught]
… If you point the detector at “empty space”, that will cause the detector to be as cold as possible. Pointing the detector at ANYTHING ELSE in nature will cause the detector to be warmer than if it is pointed at “empty space”.
Yes yes, which is a bunch of nonsense trying to get around the 2nd law without seeming like you are.
If you point it at empty space it will lose energy at what is probably a greater rate than it is calibrated for and it will return a value at or below the bottom end of the calibrated range.
If you point it at a target the same temperature as the internal temperature it will register no change and should return the same value as the internal temperature.
It isn’t “warmer than x” after pointing at a target the same temperature, is it?
So why would it be “warmer than y” after pointing it at a cold target? The proper phrasing would be “colder than x”, but set that aside for a moment.
________________________
If it was simply a matter of “any incoming IR adds to the energy of the detector, and thus makes it ‘warmer than it would be’ if pointed at empty space”, then why exactly would we need to cool detectors for low temperature sensing?
If they work the way Roy claims, then there would not be a calibrated range for a given instrument, would there? If any incoming IR was sufficient to give a positive signal, then any instrument would be as good as any other, wouldn’t it?
The IR sensor is basically a thermometer in a box at a known temperature with an aperture in the front. The thermometer receives radiation both through the aperture, and from the surrounding box, in proportion to the respective area of its view of each.
So if the box is at temperature X, and the view out of the front is at temperature Y, and the aperture occupies 10% of the thermometer’s total 360 degree view, then it receives radiation from its surroundings sigma * (0.9 * X^4 + 0.1 * Y^4) = sigma * Z^4 for some temperature Z. It gains or loses heat until it is radiating as much as it is receiving, which will be when its temperature is Z.
Z = FourthRoot(0.9*X^4 + 0.1*Y^4)
hence
Y = FourthRoot(10*Z^4 – 9*X^4)
The temperature of the thermometer is intermediate between X and Y. When Y = X, Z = X too. But when Y is less then X, Y is less than Z is less than X.
Y can report values all the way down to zero, but it becomes less sensitive to small changes as Y drops below X. It’s less accurate for any given amount of measurement error. So cooling the sensor improves the sensitivity to small changes at low temperatures.
Good answer, Nullius. 🙂
(There is also the issue of thermal noise in the electronics. For small signals, this can be quite significant, so sometimes cooling the circuits connected to the sensor can help.)
Hey Roy,
What about climate sensitivity determined by INSOLATION?
Northern Hemisphere insolation flux around 170 wm-2
Northern Hemisphere SST flux around 4 deg C
Southern Hemisphere insolation flux around 180 wm-2
Southern Hemisphere SST flux around 3 deg C
Global insolation flux around 50 wm-2
Global SST flux around 1 deg C
Based on this, 4 wm-2 (x2 CO2) is going to give you about 0.1 deg C!
Haha
Why don’t you do it by the insolation difference and SST difference between day and night?!? You’d get an even lower value.
What are you learning? That if you have a system with a relaxation time and you force it at a period much shorter than the relaxation time, the oscillations will be damped. (And, you made it especially bad by using SST rather than global temperatures…because the time constant is much slower for the oceans than for the land.)
Amazing what lengths people will go to come up with bad arguments to support what they want to believe!
Ha ha
I actually don’t have much idea, but think the comparison between “principle radiative components” maybe interesting. And help explain the GHE to people like myself.
INSOLATION at the TOA is not the same as at the surface as a lot is reflected away…….by the system. I guess I’m not of the tribe that believes a trace gas stops the world freezing over. If its negative on the outside why not the inside?
“If its negative on the outside why not the inside?”
This question is completely cryptic to me at the moment. (What is negative…and outside or inside of what?) Care to elaborate on what you are talking about?
I look upon the atmosphere as a thermal insulator. The effect must be passive because the atmosphere is not a source of energy. At thermal insulator is rally a thermal resistor. So greenhouse gasses must work as a radiant energy resistor, retarding the flow of radiant energy. So an increase in the radiant energy resistance of the atmosphere will cause the lower atmosphere to appear warmer because it decreases the rate of energy loss but it will cause the upper atmosphere to appear cooler.
OK, so : if this GHE exists, and is capable of warming up things, then why do solar thermal collectors show 0.00 (zero) energy output during nightime ? I’m talking of thermal (not PV) collectors, that have a blackbody-like behaviour. According to NASA, earth absorbs (on average) only 163 W/m2 solar radiation, while it’s warmed by a whopping 340.3 W/m2 infrared backradiation from GHG. During nights, obviously the sun provides zero input. But all those gases up there, keep doing their job of absorbing and back-radiating earth infrared electromagnetic waves, and they do that at such stunning intensity. According to NASA, GHG heating effect should be not less than double that of the sun alone. But I still see 0.00 W/m2 being provided by my thermal collector during night time (not surprisingly indeed, since everytime I get out at nights, I do not feel any heat whatsoever on my head, like I do when I stay in the sun. Double heating than the sun, but I steel need my wool cap). Engineers must be idiots, not being able to exploit this marvelous heating potential.
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