Model CO2 as Greenhouse Gas: Tips & Results

[vanesch]

Now... since the main part of the atmosphere is necessarily cooler than the surface, the effect of adding a capacity to absorb and emit radiation will result in a net flow of energy from the surface into the cooler atmosphere. That follows from the second law. The additional energy going into the atmosphere will help drive additional convection, which also increases the net flow of energy into the atmosphere. This is now balanced by the loss of radiant energy out from the top of the atmosphere. What we have now is called "radiative-convective equilibrium". And that involves a higher temperature than the pure convective equilibrium.

I have to say that I'm intuitively puzzled here. I think I'm going to follow your advice and go through the book. Intuitively, I would have thought that you get BETTER heat transport (lower thermal resistance) if you have both radiation and convection, rather than convection or radiation alone. You would think that you have "resistors in parallel", no ?

 

[chriscolose]

I have to say that I'm intuitively puzzled here. I think I'm going to follow your advice and go through the book. Intuitively, I would have thought that you get BETTER heat transport (lower thermal resistance) if you have both radiation and convection, rather than convection or radiation alone. You would think that you have "resistors in parallel", no ?

I'm not quite sure I understand. This diagram (from Trenberth, Fasulo, and Kiehl) shows global energy flows. If you're referring to the surface, it loses heat both through radiation and convection.

 

[lisab]

But second guessing how that happens is beside the point. The actual argument expressed is on a par with young Earth creationism -- another field of pseudoscience with its own credential scientists also writing rock bottom crank science.

Sylas, I appreciate how much time and effort you put into your posts. They're very informative.

But for those of us who are trying (in our precious spare time) to understand this stuff, it's really distracting to get editorializing like this...I believe Evo made a post recently (in another thread, I believe) about using terms like "denier" and "warmer." I totally agree with her; it brings something akin to partisanship to the discussion, which kills the discourse.

This isn't meant as a personal attack and I hope you don't take it as such.

 

[sylas]

Sylas, I appreciate how much time and effort you put into your posts. They're very informative.

But for those of us who are trying (in our precious spare time) to understand this stuff, it's really distracting to get editorializing like this...I believe Evo made a post recently (in another thread, I believe) about using terms like "denier" and "warmer." I totally agree with her; it brings something akin to partisanship to the discussion, which kills the discourse.

This isn't meant as a personal attack and I hope you don't take it as such.

No problem; I appreciate the point and understand what you mean. I also agree -- but with some qualifications.

I'll try to explain my own policy a bit -- ironically more distraction from the business of physics. I'll make sure my next post is exclusively on the physics; and I propose to look the useful questions from vanesch.

There's a dilemma discussing the many different arguments that turn around climate science, because they are not all of the same quality. There are genuinely open questions and unsolved issues. There are also basics that are not in any credible doubt, and make up a foundation for consideration of open questions. And there is not a hard and sharp dividing line between these extremes.

1. When peer view fails

We run into a problem -- and it is not unique to climate science -- when scientists who ought to be trustworthy to tell good argument from bad are actively pushing ideas that are physically nonsense. I'm not meaning all disagreement with conventional ideas.

The situation we have in this instance is revolved using fairly easy thermodynamics. The counter view so far has been based on ideas expressed in a paper published in a science journal by a first rate scientist.

One could point out a few secondary points. It's a low impact journal. The scientist is first rate all right, but not in atmospheric physics; he's in a different field. The citation trail before and since this paper shows that the ideas have been roundly rebutted in the literature, and have not excited any apparent further interest or debate in the field of atmospheric physics itself.

My own preference is to focus on the merits of the physics itself. But the inference of that is that either my own explanations are missing something, or else the published paper has somehow made outright errors that should be apparent to a decent undergraduate student.

I think it should be okay to say so, when the situation is that stark, alongside the details of physics. Otherwise one has the impression that it is just part of the "scientific debate". And it really isn't.

2. Different levels of disagreement

I've suggested previously a crude distinction between different levels of conflict in climate science.

1. There's denial of the greenhouse effect altogether. This sidesteps any question of changes to climate; it is not about warming in response to small changes. It's about the underlying thermodynamics of temperature at all. That is, people argue that the capacity of an atmosphere to interact with thermal radiation is not, in fact, the reason for Earth having a livable climate at the surface that is well above the "effective radiating temperature" of the planet as would be observed from deep space, which is about -18C.
2. There's dispute over the effects of changing atmospheric compositions on the magnitude of Earth's energy balance. That is, given a change to the concentrations of greenhouse gases (gases that interact with thermal radiation), how much additional energy is delivered at the surface? This is called the "forcing".
3. There's dispute over the response of the whole climate system to a forcing; the climate sensitivity. That is, given a change to the flux in radiant energy, how much does the surface warm or cool in response to restore the mean energy balance? This is called the "sensitivity".

Roughly speaking, the first is comparable to creationism, and in my opinion is it best to say so, frankly. It's just not a rational scientific debate at all; it's rather a case of explaining some relevant thermodynamics, much like we explain how relativity resolves the so-called twin paradox.

The second is somewhat in between, in my view. The forcing from greenhouse gases, especially carbon dioxide, is one of the least difficult issues in the whole field of climate science. But it is quite technical, and nailing it down gets into pretty complex ideas, ultimately based on quantum physics and requiring a lot of computer power to calculate. The end result (3.7 W/m² of forcing for a doubling of CO2 concentration for conditions as on Earth) is known to within 10% accuracy or so. The guts of this dispute are whether or not carbon dioxide is a significant player in the whole game. The details are sufficiently subtle that I am sympathetic to the difficulty of sorting it out.

The third is a definite wide open research question. Theoretical and empirical evidence indicates that climate sensitivity is between 0.5 and 1.2 degrees per unit forcing, and it is possible in principle to look at arguments for values outside these bounds. A credible scientific case, however, will certainly have to deal with the evidence that has already been applied to infer these bounds.

There are other genuine open questions as well. Evaluating and refining models. Sorting out regional effects and sources of short term variation. Sorting out the carbon cycle. Looking at vertical heat transport in the ocean. Sorting out all the consequences of increasing temperature. Figuring out the details of more complex forcings, like aerosol and cloud, which are far more complex than thermal emissivity as given by something like CO2.

3. Skepticism of an onlooker

Finally, there's always legitimate skepticism for anyone not well up on the physics and wanting to learn more. There are competing voices in the public sphere especially, with extraordinary claims of incompetence and worse flying in all directions.

If anyone does feel competent to pick sides and attempt to argue specifically for certain propositions in the whole discussion, then they take a level of responsibility and their actual competence is on the line for evaluation. I'm doing that; and in all seriousness I welcome substantive challenges or criticisms that address the specifics of my posts. I don't claim special authority. I have studied this as an amateur, but as far as credentials go I have no special standing. My posts stand or fall on their own intrinsic merits; and as we've seen I do make technical errors that can be identified by other readers.

But I appreciate there are many readers who are not claiming to have any special brief to argue for one perspective or the other; they are genuinely unsure who to believe or how the details of the arguments work. It is way out of line to dismiss them with pejorative labels.

It can be very frustrating for such readers to have a debate which merely has both sides calling the other idiots. What they want is exposition of the actual arguments.

Conclusion

You make a good point. For all that, I will continue, sometimes, to suggest some of the voices in this debate are outright pseudoscience, and that some of what passes for skepticism is credulous naivety and ignorance -- but only when it takes the form of actually making judgments on the worth of different arguments.

I will not be insulting to people who are asking questions or who are simply remaining uncertain about details. I am also sympathetic to those who read material which is nonsense but who find it persuasive. This does indicate a lack of basic physical knowledge; but we've all been there, and the great majority of us remain there for great swathes of physics.

There's no sin in needing to learn more about physics, and my aim above all else is to learn more and to contribute to greater understanding of physics in others. I've managed both so far (special nod here to contributors in the cosmology forum, who have helped me significantly in recent months).

Cheers -- sylas

 

[chriscolose]

Great post by sylas.

I am not quite sure how many third-party readers we have who are not posting, but just digesting the back-and-forths going on here. It may be worthwhile for any of those readers to ask specific questions they may have; I'm sure someone will be able to either explain it in detail, or if not at least provide a starting reference.

I agree that it is necessary for those familiar with the science to make sure third-party readers can at least differentiate between legitimate skeptical arguments and that stuff which does not belong in a science forum. Admittedly, I don't have the patience (which I find admirable in sylas) for people who yell "hoax" and "fraud" and continue to insist that the greenhouse effect is not real. I'm quite happy that sylas has chosen to respond substantively to those people, as he is probably best placed (knowledge-wise) to do so.

For those third-party readers who are interested, I'd like to briefly summarize much of the discussion going on and the current status of understanding in the climate community, by way of expansion on the "three levels of skepticism" discussed by sylas.

• 
  
  The energy coming in and out of the planet (determined essentially by the output of a planet's star, the distance to that star, the reflectivity of the planet, and the composition of the planet's atmosphere) serve to define the basic boundary conditions which constrain the global climate. A starting point for those interested in the physics of climate change is to understand the energy budgets of the top of the atmosphere and the surface, and the radiative forcing ability of various agents which can potentially change Earth's temperature.

• 
  The 33K greenhouse effect is real and undisputed in legitimate scientific arenas. It is the difference between the emission temperature of the Earth (which would be the surface temperature without an atmosphere, keeping the planetary albedo at 30%), and the emission from a blackbody with the temperature of the surface of Earth.

• An observer looking at the surface from space would see an upward radiation flux of roughly 390 Watts per square meter (a form of heat loss by the planet) in the absence of an atmosphere. In reality, an observer looking down would see roughly 240 Watts per square meter being emitted at the top of the atmosphere, which means that roughly 150 Watts per square meter is absorbed by the atmosphere. The greenhouse effect does not work to warm the surface unless the atmospheric temperature decreases with altitude. The greenhouse effect thus requires convection to move the heat upward to where it can be radiated to space at a lower temperature. By Stefan-Boltzmann, this emitting temperature is much weaker than the surface value, and so basically the greenhouse effect acts to make the planet much less efficient at getting rid of its heat. Accordingly, the net radiation into the planet (by the sun) is balanced at the top of the atmosphere (not the surface) by outgoing infrared energy, and one can extrapolate down to the surface by (emission height)*(lapse rate) to achieve the surface value, which is greater with an atmosphere that is opaque to infrared radiation. It is impossible for a planetary temperature to exceed that of the net incoming solar radiation (neglecting heat fluxes from the interior, which is negligible for the terrestrial planets, but important for gaseous planets in the outer solar system) in the absence of such an atmosphere

.

• 
  Carbon Dioxide absorbs strongly at Earth-like temperatures, particularly in the 15 micron band where significant absorption occurs from about 12.5 microns to 16.7 microns. See
  
  
  
  
  
  The standard equation used today to determine the radiative forcing (essentially the change in net irradiance at the tropopause after allowing stratospheric temperatures to re-adjust to equilibrium) for carbon dioxide is given in Myhre et al 1998, and is
  
  F = \alpha * ln(C/ C_{0})
  
  Where C is the final concentration of CO2 and Co is the initial concentration (e.g., the pre-industrial value in this context) and alpha today is taken to be 5.35. This suggests that a doubling of Carbon dioxide will lead to a 3.7 W/m^2 forcing

• The actual temperature change that will result per unit forcing is essentially the sensitivity of the climate system, i.e.,
  
  \Delta T = \lambda F
  
  where lambda is the climate sensitivity paramater (in K per Watt per squar meter) and constraining this value is currently a very active topic of research. Meshed into lambda is the change in water vapor, change in ice cover, change in lapse rate, change in cloud cover, etc and other feedbacks which may influence the radiative balance of the planet. These can be further decomposed into their longwave and shortwave components. Clouds represent the largest source of uncertainty, although several decades of research has not led to a considerably different pciture of sensitivity, where lamba is taken to be between 0.5 and 1.2 K per watt per square meter, which leads to a 2 to 4.5 K increase in global mean temperature per doubling of CO2.

• CO2 is also not the only thing going on for the "forcing" part of the equation, although it must be a significant part. The relevant physics and constraints of radiative imbalance allow no other possibility. Mostly because of aerosols however, the total forcing from pre-industrial to current times is somewhat uncertain, and so there's still wiggle room for other ideas (like cosmic rays or Martian death beams or whatever else) to play a role (although probably not very big, probably much smaller than the methane forcing or aerosol influence). Detecting other influences does not make AGW invalid, it simply means other things affect climate and multiple causes are present, but anthropogenic activities continue to remain a dominant mechanism in present climate change, and will be in the near future should emissions go unabated

• 
  Lots of other interesting things are happening (or could happen) and should be discussed like the competing effects of higher SST's and wind shear on hurricane intensity anomalies, ecological impacts, the sensitivity of the Greenland ice sheet to collapse, the possibility of various "tipping points" which may occur, the best way to project sea level rises, the understanding of short-term variability and decadal scale prediction. There's a lot of open questions about this stuff, and it's a lot more interesting than whether a greenhouse effect exists or whether man is influencing climate. I don't say that because it's my opinion, just because it's the stuff that is being discussed in the literature and in academic conferences...not whether basic thermodynamics is being represented correctly in undergraduate textbooks.

 

[mheslep]

Sylas - I appreciate your position, but much of it strikes me as special pleading. The hard science sub-forums on this site deal with all these problems every day and more, from the slightly exploratory to 'zero point energy' posts and 'faster than light' theorists. Yet the mentors and scientists (some of them very well known) frequenting those forums overwhelmingly do not display a need to label the radical posters 'creationists' -attaching to them some stigma - when 'wrong' will do. It is also rare to find those leading lights spending time on discovering the 'special authority', 'credentials', or the 'category' of the writer / source. Indeed there's a requirement https://www.physicsforums.com/showpost.php?p=1385588&postcount=1", but consistently argued based on the presented arguments, not on who may or may not have credentials, and frequently including direct references to experiment.

 

[BrianG]

It's too bad we can't a greenhouse gas' ability to change temperature compared to a control sample, like any other science. We have to take it on faith that the theory is correct. Just like religious belief.

 

[Evo]

To chris, claiming to be on the "right side" and determining who is not on the right side isn't going to fly here. Either post without claiming superiority or you will be deleted. Same goes for anyone claiming to have superior knowledge to anyone else.

Chris, are you a climate scientist? A search doesn't bring up any affiliations for you. As far as I know, no one posting here is a climate scientist. I dated a notable climate scientist, but he refused to post here. He has recently retired.

 

[sylas]

To both sylas and chris, claiming to be on the "right side" and determining who is not on the right side isn't going to fly here. Either post without claiming superiority or you will be deleted. Same goes for anyone claiming to have superior knowledge to anyone else.

All my posts have consistently been based on physical arguments. I refer to experiment, measurement, scientific paper and texts, and basic theory and calculation. I don't argue from credentials, for me or others. I have, given the above concerns by various individuals, noted a bit of my own policy for the record, but as far as I am concerned, this entire page of discussion has gone way off track; and it was not driven in that direction by me.

In response to some questions recently about claims for greenhouse gases leading to cooling of the atmosphere, I have explained why those claims are incorrect from straightforward physics, and with reference to an easily accessible online textbook used in teaching atmospheric physics. THAT is the basis of my argument.

There was a citation to a paper which claims the reverse. I was asked explicitly about it. I have stated where it goes wrong, as requested, with reference to the actual content of the paper. That paper is not by a climate scientist -- since YOU are the one asking about credentials here for some reason -- but any argument from anyone stands or falls on its own actual physical merits.

It is entirely proper given conflicting claims to determine which claim is right with reference to the actual physical merits of those claims. That is what I have done.

You ask about chris also. With respect, I think your question is completely inappropriate.

We get excellent input here on many topics from people who are not professionals, and from people who are professionals, and in this and other forums contributions here are based on their merits and not on who writes them. Professionals often give the best responses, but that is never merely presumed.

Chris has given a really first rate summary of background issues above. He's quite well known on this topic, and maintains one of the better blogs on this topic, that deals with the technical science of climate science. He has received some public recognition of his ability and thoroughness in the technical side of climate science from practicing climate scientists; but he himself is a student. A damn good one, it seems to me.

----

I appreciate people's concerns, and find them baffling. My aim has always been been to give argument based on explicit physics, with explicit and cited reference to experiment, measurement, theory and calculation. I aim to not only abide by the rules and conventions of this forum, but to go above and beyond them. I welcome any official input from mentors; and you may do that either privately or publicly as you see fit.

If I am told that I have to declare my credentials, I will object. I do not claim credentials. I have some background and I would guess I know more about the relevant climate science than most contributors here, but I don't presume on that or ask others to presume on that either.

If I am told I must not even mention the fact that a cited paper is incorrect, or that the author is writing outside his field, I will object. I accept that empirical or scientific claims must be supported, and I do support them.

The topic of climate science is a hot button topic these days. It is pretty much impossible to tackle the subject without running into accusations of being a fraud or an incompetent, no matter what case you are presenting. I've had it myself, and I prefer to ignore it, mostly.

I'd like us all to return to that substantive level of discussion. Please.

I understand all your concerns. I have aimed, always, to keep to precisely the position you are arguing for. That is, to avoid argument based on credentials, or authority, or anything of that kind. I will mention when someone uses a reference that has no standing by the rules of the forum; this is a sensible rule in an area like this. In this case, we had a reference which IS permitted by the rules of the forum, but is nevertheless in truly fundamental physical error. In such a case, I give a substantive response to the claims. But it is also relevant in that case to note that the paper does not have much standing, and it is entirely sensible and useful to say so. But the major basis of response remains the actual physics.

I am working on a post which gets back to that in a big way, but it is hard work. I am pretty much having to write a tutorial on some of the relevant physics. I think it will be useful.

Sylas

 

[chriscolose]

To both sylas and chris, claiming to be on the "right side" and determining who is not on the right side isn't going to fly here. Either post without claiming superiority or you will be deleted. Same goes for anyone claiming to have superior knowledge to anyone else.

Chris, are you a climate scientist? A search doesn't bring up any affiliations for you.

This is not appropriate, and I would be happy to discuss this with another (impartial) moderator privately.

In fact, neither sylas or myself have ever claimed any special authority, have never claimed to be "on the right side," have welcomed substantive challenges and corrections insofar as they are in accord with forum guidelines, and sylas has specifically said that he doesn't expect anyone to take his (or my) word on anything on its own merit. Sylas has admitted to minor errors where applicable, and has done an excellent job laying out the basic thermodynamics behind the greenhouse effect and the radiative-convective balance which constrains the global climate. He has openly stated he is not a climate expert, and for disclosure, neither am I...I'm actually a student of the atmospheric science, and like him, have a strong interest in the science (as a hobby) and in discussion of the relevant physics.

Much of what we discussed has been done properly and with suitable references where possible, or is basic undergraduate-level physics which can be found in standard textbooks. No one goes to the homework forum to tell people "they are acting superior" for instructing others how to take derivatives or how to calculate the net force on an object, since physicsforums is an outlet to share knowledge and ideas. I remain more than happy to address disagreements or questions pertaining to what I've written.

I don't want to speak too much for sylas...but from my observation, the worst thing we've done is made our opinions known about the quality of certain references (e.g., Khilyuk and Chilingar; Gerlich and Tscheuschner), and others have expressed friendly disagreement with our approach, and I don't mind. But aside from andre, the only real scientific replies have been from someone telling us the greenhouse effect is a hoax, and another who continues to insist no experiment exists to substantiate a CO2 greenhouse effect (and is therefore a hoax) in the face of numerous correction. As such, I find it an odd situation that you choose to target us for violation of guidelines or inappropriate dialogue.

Edit-- I did write this after sylas and independent of him.

 

[Evo]

That's all that is needed. We have already discerned that no posters here have proper credentials. If you did, we would have gladly recognized you as such. We have been debating if we should just close this forum down due to lack of anyone knowledgeable enough to moderate it.

 

[Ivan Seeking]

This is not appropriate, and I would be happy to discuss this with another (impartial) moderator privately.

Feel free to send me a pm.

Welcome to our hornets nest, Chris.

 

[vanesch]

I'm not quite sure I understand. This diagram (from Trenberth, Fasulo, and Kiehl) shows global energy flows. If you're referring to the surface, it loses heat both through radiation and convection.

No, what I mean is this. Suppose that you have a gas layer (atmosphere), "cold empty space" above it, and a black (or grey) "surface" beneath it. Now, suppose that you heat the surface, and you want to know what is the relationship between power lost by the surface and temperature of the surface. If there weren't any gas layer, this would be Stefan's law. If the gas layer is entirely transparant, this would also be the case. So we consider the case where the gas contains absorbers. You could consider Stefan's law as a kind of "thermal resistance of space".

Now imagine that the gas layer is stationary - no convection. We "glue the gas in place" so to say. We now have a purely radiative transfer through the different layers of the gas, and this will give us a greenhouse effect: the thermal resistance is higher now, we need a higher surface temperature to radiate away the same amount of heat, or, equivalently, for the same temperature, you radiate away less heat. We added a series resistance representing the radiative thermal transfer through the atmosphere.

Intuitively, I would have thought that if there was now on top of that, convection, that the thermal resistance would lower with respect to the previous case. I picture that as having put in parallel to the radiative transfer thermal resistor, a convective resistor. An extra path for heat to go from the surface to the empty space.

Other possibility, we consider only convection, and no radiative transfer. We could think of putting "reflecting foils" between the gas layers, so that there is no radiative coupling between layers. We only consider material transport (a convective flow) to do the heat transport. Intuitively, I would expect the thermal resistance to be higher than in the previous case, as now the radiative resistor is taken away.

As I said, this is how I would intuitively picture things, before doing any calculation. I'm not saying things are like this, I'm just saying that if things aren't like this, it wasn't intuitively clear to me. I went in deeper details to explain you my puzzlement, because you asked me.

 

[chriscolose]

vanesch,

Unfortunately the circuit analogies are a bit over me, so I'm still unclear as to what you're getting at, especially with the concept of "thermal resistance."

It may be useful to consider the top of the atmosphere energy balance as a separate entity as the surface energy balance. The former, at equilibrium, is the solar constant*co-albedo*0.25 = sigma T^4


The planet does not lose heat by convection to space. However, the latter involves not only radiative transfer but also the sensible and latent heat fluxes which couple the atmosphere to the surface. The former is essentially the driver of planetary climate change, while the surface budget serves to regulate the gradient between the surface and overlying air. With no convection, the surface would be considerably warmer and the atmosphere much colder

 

[sylas]

Now imagine that the gas layer is stationary - no convection. We "glue the gas in place" so to say. We now have a purely radiative transfer through the different layers of the gas, and this will give us a greenhouse effect: the thermal resistance is higher now, we need a higher surface temperature to radiate away the same amount of heat, or, equivalently, for the same temperature, you radiate away less heat. We added a series resistance representing the radiative thermal transfer through the atmosphere.

Intuitively, I would have thought that if there was now on top of that, convection, that the thermal resistance would lower with respect to the previous case. I picture that as having put in parallel to the radiative transfer thermal resistor, a convective resistor. An extra path for heat to go from the surface to the empty space.

Your intuition here is probably correct; but it's not quite that simple.

The purely radiative case in a "glued" atmosphere will have have a certain "greenhouse" effect, and you get a certain temperature gradient.

Now add convection... this will alter the lapse rate. Whether the greenhouse effect is enhanced or reduced will depend on whether the radiative gradient is more, or less, than the adiabatic lapse rate which convection gives you. For Earth, I think convection will tend to reduce the greenhouse effect.

On the other hand, previous discussion has taken this the other way around. Suppose you have a radiatively neutral atmosphere. That will develop an adiabatic lapse rate, from convection. Now add radiative transfers. That will have only a small effect, if any, on lapse rate. The adiabatic lapse rate will be maintained by the effects of convection. But the effective radiating altitude will increase, and bring in a greenhouse effect with a warmer surface and warmer atmosphere.

I'll go into this a bit more, with reference to the text on planetary climate I have mentioned, when I finally get my next major technical contribution complete. I have to crunch some numbers to be sure of what I am doing as well.

Cheers -- sylas

 

[vanesch]

vanesch,

Unfortunately the circuit analogies are a bit over me, so I'm still unclear as to what you're getting at, especially with the concept of "thermal resistance."

It may be useful to consider the top of the atmosphere energy balance as a separate entity as the surface energy balance. The former, at equilibrium, is the solar constant*co-albedo*0.25 = sigma T^4

That's maybe not so obvious, as the atmosphere is partially transparant. I agree with you that convection by itself won't cool anything to outer space ; the only way to do so is of course radiation.

But the way I picture it in my head is that each layer, even the Earth surface, can partially emit directly to outer space, and partially transmit heat to other layers. This last process can be radiative, but also convective. It is not only the upper atmosphere which radiates into outer space, I would think, because the opacity is not total (it would be, if the atmosphere were totally opaque, which it is for certain wavelengths ; then for others, the radiation depth is probably rather large - I don't know these numbers by heart).

So in my idea, any process that "gets heat easier to the upper layers" lowers the thermal resistance (allows for a higher heat flux for a given surface temperature).

With no convection, the surface would be considerably warmer and the atmosphere much colder

Eh, yes. That was what I was intuitively trying to say. I had, erroneously probably, understood from sylas' post that convection didn't affect (or affected aversely) the heat transport, and that was against my intuition - which is limited, I grant you that.

 

[sylas]

Eh, yes. That was what I was intuitively trying to say. I had, erroneously probably, understood from sylas' post that convection didn't affect (or affected aversely) the heat transport, and that was against my intuition - which is limited, I grant you that.

The lapse rate (rate at which temperature falls with altitude) is independent of thermal emissivity. Almost. There will be small second order effects.

Hence, if the radiative transfers are small, the net vertical energy transport in the atmosphere will be small. You can't have a sustained trend up or down, because there's no source or sink for the energy. Hence, without radiation transfers, convective heat transport works to maintain a lapse rate, but it does so being sometimes with energy flowing up, and sometimes down, and with no sustained trend.

Now add radiation transfers. Because of the lapse rate, the immediate effect is an upwards flow of energy, by the second law, from warmer parts to colder parts; and there is energy being lost altogether out from the top of the atmosphere. But it's not completely clear whether there is heating or cooling at a given level. Each level of the troposphere is warmer than the level above, and colder than the level below. Every level is emitting both up and down, according to its temperature. So any level will on balance lose energy by radiation to the level above, and gain it by radiation from the level below.

If there is an imbalance at any level, additional convection will apply to oppose the heating or cooling at that level, and move towards the adiabatic lapse rate again.

At the very bottom of the atmosphere, of course, the upwards radiation is from the surface; and surface has emissivity close to unity. The immediate effect of radiant transfers in the atmosphere, therefore, is a flux of thermal radiation (called backradiation) coming down to the surface which wasn't there before. And the surface will heat up, and the radiant fluxes will increase as well all up and down the column; with convection always working towards the adiabatic lapse rate.

End result; an atmosphere with a lapse rate very close to the adiabatic rate (observed) and hence an atmosphere which is hotter by a similar amount as the surface. Any changes in lapse rate, whichever way they go, have less impact that the fact that the whole thing is hotter at the start point. The net flow of radiant heat is up. The net convective flow is also observed to be upwards, and so I guess this means the net effect of radiant fluxes tends to be towards cooling upper levels and heating lower ones by comparison with prevailing temperatures; but that can't mean that adding radiant transfer gives a cooler atmosphere. The whole thing is a response to heating, and temperatures don't just depend only the lapse rate, which doesn't actually change much anyway. It's crucial that the bottom of the whole stack heats up to shed the atmospheric backradiation. Humidity feedbacks impact lapse rate, but a feedback can't change the sign of the net effect.

Cheers -- sylas

 

[Andre]

Hence, without radiation transfers, convective heat transport works to maintain a lapse rate, but it does so being sometimes with energy flowing up, and sometimes down,….

Energy flowing down? But how? Convection brings more air to upper levels, disturbing the normal atmospheric pressure distribution. So obviously on other places air has to descend for counter balance balancing anywhere else. Now Isn’t it that a parcel or air descends because of its buoyancy is less than its surroundings? Hence isn’t its relative temperature/ energy lower than the not descending air around it. So it would seem that this descending air returns less energy than the convecting air is withdrawing? Hence a net energy flow up incomplete convection cell with both up and downdraft? Under which conditions could that be different?

…Each level of the troposphere is warmer than the level above, and colder than the level below. …

I would be busted for misinformation if I said something like that.

[URL][PLAIN]http://ccrc.unh.edu/~stm/AS/Common/Subsidence_Inversion.JPG
Especially in subsidence inversions temperatures aloft can be considerably higher than below.

 

[sylas]

Energy flowing down? But how? Convection brings more air to upper levels, disturbing the normal atmospheric pressure distribution. So obviously on other places air has to descend for counter balance balancing anywhere else. Now Isn’t it that a parcel or air descends because of its buoyancy is less than its surroundings? Hence isn’t its relative temperature/ energy lower than the not descending air around it. So it would seem that this descending air returns less energy than the convecting air is withdrawing? Hence a net energy flow up incomplete convection cell with both up and downdraft? Under which conditions could that be different?

The quantity you want is "potential temperature". It's described in chapter 2 of the text on planetary climate I mentioned for you last time. There's more to the energy of a packet of air moving up or down than its measured temperature. You also need to consider the pressure difference, for example.

But the case we are speaking of here is particularly simple. It is what you described earlier as a radiatively inert atmosphere. That is also explicit in the very first sentence you have quoted in my extract. In that case, the only energy flows to worry about are convection and latent heat (sometimes bundled together). And that has to add up to zero by conservation of energy. Do you agree?

Now of course, it will vary from time to time, but the net will be zero. Sometimes the energy flow is up, sometimes it is down. First law of thermodynamics, applied to the case you proposed.

Even on Earth, you can sometimes get local convective energy transport downwards; although the net is upwards, estimated at about 17 W/m², plus 80 latent heat, in the energy flow diagrams that have been cited.

I would be busted for misinformation if I said something like that.

I hope not! It's not illegal to make errors (which means misinformation.) You'll be picked up for errors by other posters, but it's not against forum rules to be wrong about information.

However, in this case you have simply failed to look sufficiently carefully at the specifics of the case described. If you had quoted the entire paragraph, this was explicitly in the context of the standard lapse rate.

The main conclusion of the description I gave was that it's not immediately clear whether there is a net radiative heating or cooling at a given level. On Earth, on balance, it is generally a radiative cooling effect I think, but in the context of a net upwards radiant flow and a significantly raised overall temperature from what you have without the radiant transfers. Upwards convection is also strengthened when radiant transfers are present. The whole response of the planet to an atmosphere that interacts with thermal energy is that it has to work harder to get rid of the same amount of energy, and on Earth this results in surface temperatures that are, on average, about 33 degrees higher than the effective radiating temperature of the planet into space, and about that increase also up through the atmosphere as well; though not uniformly.

Cheers -- sylas

 

[Andre]

The quantity you want is "potential temperature". It's described in chapter 2 of the text on planetary climate I mentioned for you last time. There's more to the energy of a packet of air moving up or down than its measured temperature. You also need to consider the pressure difference, for example.

Right, but it still requires more density for air to descent, if that air is containing more energy it must at an higher ambient temperature and/or a higher pressure. If it is at an higher pressure, it will expand and decreases in density increasing it's bouyancy, stopping the downdraft. I still can't see how in a complete convection cell the net energy flow can be downwards.

There is still more air convecting up also transfers (heat) energy into potential energy, which process is reversed in descending air

I would be busted for misinformation if I said something like that.

I hope not! It's not illegal to make errors (which means misinformation.) You'll be picked up for errors by other posters, but it's not against forum rules to be wrong about information

Not if one is a declared crook according to the moral panic principle.

However, in this case you have simply failed to look sufficiently carefully at the specifics of the case described. If you had quoted the entire paragraph, this was explicitly in the context of the standard lapse rate.

Here is the full quote

Each level of the troposphere is warmer than the level above, and colder than the level below. Every level is emitting both up and down, according to its temperature. So any level will on balance lose energy by radiation to the level above, and gain it by radiation from the level below.

If there is an imbalance at any level, additional convection will apply to oppose the heating or cooling at that level, and move towards the adiabatic lapse rate again.

A subsidence inversion is the norm above the deserts, in the downdraft regions of the hadley cells, as the descending air increases in density and heats up adiabatically, additional convection would be extremely rare and certainly not the norm.

 

[vanesch]

Thanks for the explanations. I will try to digest them "out loud".

For all clearness, I'm not talking about Earth's atmosphere (yet), only about "plateworld"s atmosphere: a black hot plate, a gaslayer on top of it, and outer space. Some magic to do things with the gas, which is normally not possible, such as switching on and off convection, radiation, and a few other things, to get an understanding of the different mechanisms and their interplay.

We start by giving our gas layer (with some magic, or gravity) a pressure profile, with pressure decreasing with altitude. I will try to see where I get.

The lapse rate (rate at which temperature falls with altitude) is independent of thermal emissivity. Almost. There will be small second order effects.

Ok, so what's understandable from this, is that if the pressure profile is given, the relative temperature curve is given if there is sufficient convection. A balloon with some gas at temperature T1, lifted in this atmosphere, will cool down adiabatically (because the pressure lowers, and the balloon expands). A balloon going down will heat up (compression). If the atmosphere is not heated or cooled (no radiative stuff in it), it would reach a certain equilibrium given by this adiabatic.

Let's play a bit with this non-radiative atmosphere. Let us say that at the surface, I've 10 degrees, and at 20 km, I have -50. (making numbers up here).
Now, suppose that with electric heaters, I bring the layer at 20 km at -30. This would mean that the less cold air at 20 km, going down in the convective stream, will now bring the surface layers to a much higher temperature (say, 40 degrees, following the adiabat from -30 and compressing). The whole atmosphere will now settle to a new equilibrium, again with an adiabat, but with the top layer now at -30, and the surface at 40.

Right. This is something I didn't realize that convection could transport heat down against a temperature gradient.

Let's play another game (this is fun!). Suppose that thermal conductivity of our atmosphere is very bad but not 0. Still no radiative stuff, we're just looking at the transparant atmosphere. We switch off the EM field (I told you we had magic!).

Now, we do the following: our initial surface is at 10 degrees, the top of the atmosphere is at -50, and there is this adiabatic equilibrium due to convection (which is driven also by magic).

Suppose now that we build a huge heat exchanger at 20 km height, and another at the surface. Suppose that the surface has a thermostat that keeps it at 10 degrees, but heat can be supplied or extracted. It's a thermal reservoir. Now, we connect our two heat exchangers with some or other liquid. We take heat from the soil at 10 degrees, and bring it to the upper layers to heat the upper layers. This is possible, because up there, it is -50.
We do this until the upper layer is now at -30. We are in the same situation as before, so now the lower part of the atmosphere is hotter than the surface !

There is something wrong. We violated the second law here: we took heat from the surface at 10 degrees, delivered it to our gas at -50 (still ok), and this heated the air to 30 degrees just above the surface. So the whole cycle took heat at 10 degrees and delivered it at 30. That's against the second law (unless we do work). So, the problem was that I introduced too much magic, and introduced convection even when the upper temperatures were above the adiabat. That forced convection (my magic) did work on the gas.

I guess that if upper layers, in one way or another, are hotter than they should be according to the adiabat, convection simply stops.

So it seems that you can't heat "downwards" using convection, no ? Violates the second law, no ?

So where's the culpritt ? I would guess that it comes from thinking that a hotter gas can convect down in a cooler gas. It will be less dense, so it will have tendency to go up, not down.

So, convection cannot really take heat down, can it ? In other words, the adiabat is defined by the temperatures in the lower layers, not in the upper layers. Am I right here ?

Hence, without radiation transfers, convective heat transport works to maintain a lapse rate, but it does so being sometimes with energy flowing up, and sometimes down, and with no sustained trend.

So, is this true ? What about my above example ?

Or is it rather: convection will transport heat up, and if it should transport heat down, it stops.

I will stop here already (didn't know it when I started typing) because I'd rather sort this out clearly before going on.

edit: I was typing this independently from the discussion with Andre, but it seems he butted on a similar difficulty after reading the exchange...

 

[Evo]

Feel free to send me a pm.

He said impartial Ivan.

 

[chriscolose]

That's maybe not so obvious, as the atmosphere is partially transparant. I agree with you that convection by itself won't cool anything to outer space ; the only way to do so is of course radiation.

But the way I picture it in my head is that each layer, even the Earth surface, can partially emit directly to outer space, and partially transmit heat to other layers. This last process can be radiative, but also convective. It is not only the upper atmosphere which radiates into outer space, I would think, because the opacity is not total (it would be, if the atmosphere were totally opaque, which it is for certain wavelengths ; then for others, the radiation depth is probably rather large - I don't know these numbers by heart).

So in my idea, any process that "gets heat easier to the upper layers" lowers the thermal resistance (allows for a higher heat flux for a given surface temperature).



Eh, yes. That was what I was intuitively trying to say. I had, erroneously probably, understood from sylas' post that convection didn't affect (or affected aversely) the heat transport, and that was against my intuition - which is limited, I grant you that.

Vanesch,

What's happening with the greenhouse and convection can be understood at a wide variety of levels. In actuality, constructs like S(1-a)/4 = sig T^4 are not actually used in sophisticated GCM's, but such simple formulas valuable way of explaining the basic physics of radiation balance, and serve as a bridge between grey-gas models and more realistic models.

One classical "layer model" which is often employed at a lower level allows one to think of several imaginary "panes of glass" floating in the atmosphere which are perfectly transparent to visible and perfectly opaque to infrared radiation.

One can then proceed to set up multiple equations and go about solving for the temperature at each layer. Generalizing, the surface temperature will end up being the top temperature (the emission layer) multiplied by (n + 1)^0.25 where n is the number of layers. So, a two layer atmosphere will have a surface temperature of 335 K. This suggests that radiative equilibrium is not a good approximation for the surface temperature, which loses substantial heat by convection and conduction as well. With radiative equilibrium, the lapse rate of temperature too large in the troposphere, the stratosphere is approximated pretty good, but the surface is too hot. With other forms of heat transfer now-- The whole troposphere is well mixed in heat, and is more or less constrained by convection to stay near the moist adiabat. In that sense, the vertical structure is largely fixed by convection and the IR heating simply sets the intercept (e.g. the lower tropospheric temperature).


In actuality, the atmosphere is semi-transparent to a differing degree at different wavelengths. The radiative transfer issue is best addressed numerically with sufficient number of vertical layers to resolve the atmospheric temperature and absorber distributions, and with sufficient resolution to pin down the spectral dependence of individual gases. Looking down from space you would indeed see radiation coming from various levels of the atmosphere, but the bulk of it comes from some location (determined by the atmospheric greenhouse composition) where opacity is strong. This is often called the \tau = 1 level and much of the radiation below here is absorbed before getting to space and much radiation from above is a small term as emissivity is weak. The effect of adding CO2 is to raise \tau = 1 to higher altitude (lower pressure) thereby warming the whole troposphere. So while a real "effective layer" doesn't exist, it's a usefuil concept for thinking about the radiation balance of the planet.

 

[vanesch]

One can then proceed to set up multiple equations and go about solving for the temperature at each layer.

Yes. However, if you take "black sheets" each time, with no radiation that transmits through a layer without being "thermalized", then you have actually a series of independent "resistors" (except that "ohm's law" is not linear but for small temperature diffs we can linearise).

If we take one such element, with on one side T1 and on the other, T2, we have a net power transmission between them of sigma (T1^4 - T2^4).

Assuming small temperature differences, we have approximately 4 sigma T^3 (T1 - T2), and we can roughly say that one such "interlayer" corresponds to a thermal resistance of
\frac{1}{4 \sigma T^3}

(current = 1/R x potential difference)

The different successive layers are series connections of these resistors.

So the more of these the radiation has to cross, the higher the total resistance, and hence the higher the temperature difference for the same thermal flux ("current").

The more radiatively absorbing gasses you have, the more of these "black" layers we have.

In fact, you also have to count the last "gap" towards outer space as a resistor of the kind, but here you can for sure not linearize anymore as T2 = 0 (or 4 K if you want to).

So this explains intuitively the greenhouse effect in a layered, static atmosphere.

I'm trying to wrap my mind around what is the influence of convection in this picture.

 

[sylas]

(In what follows, my main reference is an online undergraduate level textbook, Principles of Planetary Climate, by Ray Pierrehumbert. You can find the same material in other texts; this one has the advantage of being easily available as a shared reference by anyone who wants to look it up. If I refer to page numbers or equation numbers; they are from this text. I take full responsibility for any errors in my answers, and you can check the methods I apply with this reference.)​

I have made an error in my posts; I spoke of convection working to maintain the lapse rate. That is incorrect; I should have said convection works to decrease a lapse rate towards the adiabat, or near it. A weaker or negative lapse rate is stable against convection, so convection in the atmosphere only heads towards this point from one direction.

We've been considering the case of an "optically thin" atmosphere, with minimal thermal emissivity. If there is no energy exchange with the surface, then the atmosphere in this simple case would be isothermal (one temperature) at 2^-0.25 = 0.84 of the surface temperature. (p 142) This is called the "skin temperature". But because there is an energy exchange where the atmosphere is in contact with the surface, the bottom of the atmosphere is heated by the surface; and this proceeds up the atmospheric column to establish a temperature gradient, up to the point where the "skin temperature" is again established, and from there you get an isothermal stable stratosphere (p 143). Radiant energy transfers make life more complex; but the radiatively inert case in this example is simpler. Here's a diagram from the book.

The lapse rate is therefore directly linked to the height of the tropopause, given a surface temperature balanced with solar input, and a stratosphere at the skin temperature. If the tropopause is at low altitude, the mean lapse rate is large; and unstable. This leads to heating, by transfer from the surface and then by convection; that raises the tropopause, until you get to the adiabatic lapse rate, which is now stable.

Given the small loss of energy from the atmosphere, on the assumption of being optically thin, or radiatively inert, this equilibrium state has negligible net flow of energy up or down, and that does mean convection processes will sometimes transport energy up, and sometimes down, however this is presuming that you have a bit variance in conditions, rather than always being right at an equilibrium.

I think you really only get energy flux downwards by "forced convection", or a mechanical result of wind or other movements that do work. But I'll accept guidance from others on this point. The major point is that the net upwards energy flux into a radiatively inert atmosphere is zero.

Right, but it still requires more density for air to descent, if that air is containing more energy it must at an higher ambient temperature and/or a higher pressure. If it is at an higher pressure, it will expand and decreases in density increasing it's bouyancy, stopping the downdraft. I still can't see how in a complete convection cell the net energy flow can be downwards.

Net isn't downwards. In the radiatively inert case, the net is effectively zero. But that suggests that as you introduce a bit more complexity, like horizontal wind and so on, there's going to transient periods of a downward flux of energy, occasionally, with other periods of a net upwards flux... sometimes up, sometimes down. I know that a downwards energy flux is not a stable situation.

And in particular, any implication I gave that you get a spontaneous movement of energy downwards against the temperature gradient of the conventional lapse rate was my mistake. Such movement may occur, I believe, as a result of mechanical work from winds, but they are not sustained.

Not if one is a declared crook according to the moral panic principle.

I don't panic, and will be happy to back you up if you get unfairly disciplined for simply being presumed to be in error. I do appreciate your substantive engagement, whether I agree with it or not.

Here is the full quote

Now add radiation transfers. Because of the lapse rate, the immediate effect is an upwards flow of energy, by the second law, from warmer parts to colder parts; and there is energy being lost altogether out from the top of the atmosphere. But it's not completely clear whether there is heating or cooling at a given level. Each level of the troposphere is warmer than the level above, and colder than the level below. Every level is emitting both up and down, according to its temperature. So any level will on balance lose energy by radiation to the level above, and gain it by radiation from the level below.

If there is an imbalance at any level, additional convection will apply to oppose the heating or cooling at that level, and move towards the adiabatic lapse rate again.

Um... with respect, you continue to omit the initial sentences of the paragraph which describe the lapse rate being assumed. I have taken the liberty of inserting the rest of the paragraph in bold, where the lapse rate is mentioned explicitly; and adding the link to the post through the quote tag.

It's quite true that you can get inversions within the troposphere. They tend to be of a limited depth; less than a kilometer. The majority of the troposphere in a real planet is still with the positive lapse rate (falling temperature with altitude) and this is the case in the simple example I was explicitly discussing.

The point is that in the troposphere, any layer tends to be gaining radiant heat with respect to lower levels, and losing it with respect to higher levels, by virtue of the temperature gradient that occurs in the troposphere, and so you can't presume net heating or cooling immediately.

However, I can't quibble too much here, because the big error here in my post is in the second paragraph you've quoted. Convection does not necessarily work to oppose heating or cooling. It is only an overly large lapse rate above the adiabatic rate that is unstable to spontaneous convection.

This doesn't alter the main point that increasing the capacity of an atmosphere to interact with thermal radiation will give higher temperatures at the surface and in the troposphere; even though the normal equilibrium at those higher temperatures may show radiative cooling at that level, balanced by the special heat flux.

But it's still another screwup, and I am glad to acknowledge it and fix it. Thanks.

A nod to vanesch as well for picking up the problem also; you get the kudos for being first, and I sneak in third.

Cheers -- sylas

 

[Andre]

You're too kind Sylas

So the more of these the radiation has to cross, the higher the total resistance, and hence the higher the temperature difference for the same thermal flux ("current")...The more radiatively absorbing gasses you have, the more of these "black" layers we have.

Would the band saturation decrease that effect? If that frequency band is 'saturated' it appears that it won't make that much difference anymore how many times radiation energy is absorpted and re-emitted.

I'm trying to wrap my mind around what is the influence of convection in this picture.

Ah let's try some ideas, especially with wet convection, involving latent heat. So, as a wet surface heats up, water evaporates (latent energy -which reduces the temperature increase). Conduction and radiation heat up the lower layer(s) of the troposhere, causing the well discussed convection. Heat- and latent energy -water vapor- are now transported up. Due to expansion the updraft cools adiabatically and water condenses forming clouds and releasing the latent heat again. Clouds are good radiators as they radiate on all water IR- frequencies. So this energy is radiated outwards in al directions as it would have done on the Earth surface without convection. But the difference is that energy -on water frequencies) emitted upwards will find less water vapor molecules because the upper levels are much drier than the surface levels. Evidently, the CO2 frequency bands are also less relevant here. Consequently the energy emitted by clouds (tops), on water frequencies, has more chance to escape into space than energy emitted by the surface in all bands including the CO2 frequencies.

Now if the greenhouse gas concentration was to increase then the heating of the lower atmosphere by radiation was also to be increased, this would enhance the convection rate, transporting more energy upwards, where more energy can radiate into space. Consequently it appears that convection acts as a negative feedback on greenhouse gas variation

 

[Skyhunter]

Would the band saturation decrease that effect? If that frequency band is 'saturated' it appears that it won't make that much difference anymore how many times radiation energy is absorpted and re-emitted.

This makes no sense. Absorption and re-emission makes a difference everytime it happens.

Clouds are good radiators as they radiate on all water IR- frequencies. So this energy is radiated outwards in al directions as it would have done on the Earth surface without convection. But the difference is that energy -on water frequencies) emitted upwards will find less water vapor molecules because the upper levels are much drier than the surface levels. Evidently, the CO2 frequency bands are also less relevant here. Consequently the energy emitted by clouds (tops), on water frequencies, has more chance to escape into space than energy emitted by the surface in all bands including the CO2 frequencies.

Why do you say it is evident that CO₂ absorption is less relevant at higher altitudes?

If the emission frequency is in the active CO₂ bands, (which you are saying it is) then it will be absorbed, since CO₂ is well mixed.

I agree that the scarcity of WV in the upper troposphere and stratosphere leaves larger windows for radiation to escape into space. But the concentrations of CO₂ are fairly uniform.

 

[sylas]

(As before, any references are pages or equations in Principles of Planetary Climate)[/size]​

Would the band saturation decrease that effect? If that frequency band is 'saturated' it appears that it won't make that much difference anymore how many times radiation energy is absorpted and re-emitted.

Actually, it does make a difference; because of the lapse rate.

The example described here is completely saturated, even with a single "pane"; the stated assumption is that each successive pane is completely opaque to the upwards thermal radiation. Each pane is warmer than the one above it, and the more successive panes you have, the higher the temperature of the bottom pane; since the uppermost is the one that it at the effective radiating temperature to balance to short wave input.

This kind of effect is seen, for example, in the atmosphere of Venus, which is profoundly saturated. The topmost level of the atmosphere on Venus is at the effective radiating temperature... which is actually colder than Earth, because Venus has a very high albedo. Despite being closer to the Sun, Venus actually absorbs less solar energy per unit area than Earth! It is so hot because of a super greenhouse effect; thermal radiation is absorbed and re-emitted many times up that dense carbon dioxide atmosphere, and all the way the lapse rate is maintained, so that right at the bottom you are far hotter than the effective radiating temperature at the top of the atmosphere.

The big omission of this example is convection, and vanesch also asked about that. In a profoundly optically thick atmosphere like this, there is a natural radiative lapse rate, which corresponds directly to the successively lower temperature on higher panes of glass in our example. At the same time, there is also the natural convective lapse rate, which is determined by the adiabat. Convection will be at work if the radiative lapse rate is greater than the adiabatic lapse rate. In that case, convection will relax the lapse rate, and that will reduce the temperature difference between top and bottom from the purely radiative case. I'll consider than some more later on.

In the meantime, note that the Earth is rather different to Venus. (p253) On Venus, increasing greenhouse gas concentrations works mainly by raising the emission altitude. On Earth, increasing concentrations works mainly by widening the saturated bands; additional absorption occurs in the "wings" of those bands, more than by raising the emission altitude of the saturated regions.

Cheers -- sylas

 

[BrianG]

The greenhouse effect is so weak, it's impossible to duplicate AGW in the lab or the field. These experiments aren't peer reviewed, can't be duplicated and no responsible researcher or lab has claimed credit.

 

[sylas]

The greenhouse effect is so weak, it's impossible to duplicate AGW in the lab or the field. These experiments aren't peer reviewed, can't be duplicated and no responsible researcher or lab has claimed credit.

The original experiments which demonstrated how the greenhouse effect works with directly measured temperature differences were conducted about 150 years ago by John Tyndall, one of the great Victorian experimental scientists. His experiments are described in message [post=2187943]msg #10[/post] of this thread, with a link to John Tyndall's book online that describes them in more detail.

In fact, the greenhouse effect is very strong indeed, and it is responsible for the Earth having a livable climate at all. This is not in any credible dispute, and is widely discussed in basic textbooks dealing with the Earth's climate. Extracts from John Tydall's lecture on this are presented in [post=2294440]msg #76[/post].

The nineteenth century was a productive period in experimental physical science; and the basics of thermodynamics and temperature were established then, and have been extensively developed since. Thermodynamics at this level is not in the slightest physical doubt, and continues to be given in elementary textbooks on the subject.

In the modern era, you are not likely to find much in the way of experimental work specifically measuring temperature change, except in high schools or undergraduate lab work. A number of such experiments have been given in the thread, and they can easy show a temperature difference in controlled conditions. A selection of such experiments is given in [post=2291727]msg #59[/post].

The actual strength of the greenhouse effect on Earth is well known from basic comparison of the radiation measured from the surface, and from what escapes to space. The total effect is about 33 degrees Celsius (about 60 degrees Fahrenheit). The calculation of this magnitude is shown in [post=2296677]msg #96[/post]. The actual amount of radiation coming to the Earth from the atmosphere is very large... hundreds of watts per square meter, day and night. This is measured directly, and has been for 50 years. Citations for such measurements are given in [post=2293770]msg #64[/post].

Brian has not actually directly addressed any of these experiments or calculations or measurements. He has, however, insisted that an experiment should use concentrations of carbon dioxide equivalent to that in the atmosphere... which is a bit less than 1/2500 by volume. But he wants to see the effect in a lab... in a few meters of air. This is, of course, absurd; and that has been pointed out. He's effectively demanding to see the greenhouse effect using much less than one thousandth of the actual amounts of greenhouse gases that apply to give us a livable climate. This is explained in [post=2295700]msg #85[/post].

There's nothing wrong with disagreement over fundamental points. We can explain the relevant physics. But at this point, Brian has long since stopped engaging the discussion and the evidence, and has taken to repetitive posting of a couple of lines that just make the same point which has been demolished many times over in the thread.

For the record -- sylas

 

[BrianG]

I directly address the ESPERE experiment you cite:

http://www.espere.de/Unitedkingdom/water/uk_watexpgreenhouse.htm

The data is extremely limited, reduced to one twenty minute run with four data points for each of the two samples. The work isn't peer reviewed, isn't attributed to any specific lab or principle researcher.

 

[sylas]

I directly address the ESPERE experiment you cite:

http://www.espere.de/Unitedkingdom/water/uk_watexpgreenhouse.htm

The data is extremely limited, reduced to one twenty minute run with four data points for each of the two samples. The work isn't peer reviewed, isn't attributed to any specific lab or principle researcher.

Of course it isn't. It's a simple experiment intended for students; not a research report. This has been explained many times now. I don't think you'll find such basic teaching experiments in a formal scientific paper any more. It's not that trivial to get a scientific paper published, you know!

Experiments to measure temperature directly from thermal interaction of a gas with radiation have not been particularly important now for over a hundred years. Those experiments can be repeated -- and ARE repeated, as shown in these simple teaching experiments -- and they do show temperature effects very easily.

The state of science now is that the basic thermodynamics is nailed down solidly, and what is important for physics is measuring the properties of how light and matter interacts; how energy is absorbed and emitted. Even the spectral emissivity of CO2 -- which is the quantity of relevance -- is not something determined by experiment any more.

But for some reason you have dismissed those details, saying you don't dispute spectral characteristics. Apparently, you just dispute the basic consequences which follow from this when applied to something too big to fit in a lab.

Trying to reproduce the entire atmosphere is not something you do in a lab. Trying to have a couple of meters of gas with 500ppm CO2 has less than a thousandth of the effect of an atmosphere -- yet that is apparently what you think should be done. It's not a sensible experiment. It bears little relation to an entire atmosphere, and it doesn't just scale simply even if you could measure the tiny impact as a temperature. You can EASILY get a temperature difference using an amount of CO2 similar to that in the atmosphere -- but that doesn't scale easily either, because of the importance of lapse rate that has been discussed.

You most certainly can measure the energy effects of even small amounts of CO2; but you don't do that by measuring temperature. You measure the radiation directly.

For some reason which you have not explained, you apparently don't think that is good enough.

Here's another example of what a relevant experiment does in modern physics. (And note that even THIS is simply a confirmation of the basic quantum theory used to calculate the interactions of light and matter.)

• Roy, S. et al. (2002) Mid-infrared polarization spectroscopy of carbon dioxide, in Applied Physics B: Lasers and Optics, Volume 75, Number 8 / December, 2002.

Here are the basic facts.

• The experimental measurement of the effects of gasses on thermal radiation, determined by measuring temperature effects directly, were conducted by John Tyndall in the mid nineteenth century. Nobody, ever, has claimed that these experiments are somehow incorrect or don't measure what is described. That would be absurd.
• Similar experiments continue to be conducted now, although in modern days they are teaching experiments used in schools. It's not something you bother with in a research paper.
• To measure temperature effects, you need a fair amount of carbon dioxide to absorb sufficient thermal radiation to have an impact. That means you can't do it usefully with 500ppm CO2 in a lab. You can measure the backradiation from the sky directly. It is very large, and has been cited in the thread. Or you can do experiments like those that have been described.
• The impact of CO2 on energy transmission continues to be studied. You measure the radiant energy directly, as this gives you much better resolution than trying to measure temperature. That some individuals are apparently dubious of how energy and temperature are related is not the problem of working scientists, but is rather a problem of education. That is what I am trying to help with here.

Sylas

 

[Andre]

I directly address the ESPERE experiment you cite:

http://www.espere.de/Unitedkingdom/water/uk_watexpgreenhouse.htm

The data is extremely limited, reduced to one twenty minute run with four data points for each of the two samples. The work isn't peer reviewed, isn't attributed to any specific lab or principle researcher.

Interesting and straight forward, but isn't half the story? What happenes if the light is turned off? After all, the sun shines only half a day.

 

[BrianG]

You say, "Trying to reproduce the entire atmosphere is not something you do in a lab." then you cite an experiment that would necessarily be faulty:

http://www.espere.de/Unitedkingdom/water/uk_watexpgreenhouse.htm

And you say this is a teaching tool in schools? What are they teaching, bad science?

Then you insist we ignore temperature differences and look at spectroscopy.

The preview to your link says nothing about the results of varying concentrations of CO2.

http://www.springerlink.com/content/phcvdcmce4y2hff7/


Our key question is, what does a few parts per million of manmade CO2 emissions do to atmospheric temperature? Not, what color is the sky.

 

[sylas]

Our key question is, what does a few parts per million of manmade CO2 emissions do to atmospheric temperature? Not, what color is the sky.

The combination of CO2 and H2O as the two major greenhouse gasses results in about 33 degrees of additional warmth over what you would have otherwise.

It's not possible to divide the warming between the two gases, or other smaller contributors, as if in a linear sum. Each one in part compensates for the other; so that the impact of the two together is less that the sum of each one acting alone. But as a rough comparison it is fair enough to say that H2O is roughly twice as significant as CO2 for the total greenhouse effect on Earth.

The 33 degree impact of Earth's greenhouse effect is a comparison of what temperature we actually have and what temperature would be required to radiate directly into space, as occurs on the Moon. This was explained earlier in the thread. This also fits with the hundreds of watts per square meter which is measured as radiation coming to the surface from the atmosphere; energy that would not be available without gases in the atmosphere to radiate it. The spectrum of this backradiation aligns with the bands where Earth's greenhouse gases are active; and measurement of the emission spectrum from above the atmosphere also shows clearly the major bands where greenhouse absorption occurs, and the emission is coming from the higher cooler altitudes in the atmosphere.

Andre asks what happens at night. The answer is that the greenhouse effect has a hugely significant role for keeping nighttime on Earth a moderate temperature. The atmosphere has a substantial capacity to hold energy as heat, and so it keeps emitting thermal radiation all night, and this is a major source of warmth. This is measured directly in the experiments I cited previously of backradiation, which includes night and day measurements.

----

One problem with this discussion is that it can easily be mixed up with the idea of global warming. In fact, this is quite a distinct problem.

Global warming and climate change is not simply about the greenhouse effect -- it is about the impact of CHANGES to composition of the atmosphere. What happens when you get additional greenhouse gases in the atmosphere? There are a host of real and interesting scientific questions related to this -- and all of that debate is sidestepped with what is essentially an irrelevant distraction in this rejection of the very idea of any greenhouse effect at all.

This is why I said earlier that denial of the greenhouse effect is comparable to creationism. I did not mean that as an attack on individuals, but as a characterization of the scientific argument itself. All the ideas about the genuinely open questions -- like the measure of climate sensitivity, or the impact of other non-greenhouse forcings, or the regional distribution of impacts from a changing climate and constraining of feedbacks and much else besides is a whole different level.

Suggesting that the the greenhouse effect doesn't exist, or that CO2 or H2O have no effect on temperature by virtue of thermal emissivity, or that there's some source of energy somehow giving the surface the extra 33 degrees over Earth's effective emission temperature into space other than the measured heat from the atmosphere, is all really an attack on fundamental thermodynamics established in the nineteenth century and now quite fundamental in physics education; and absolutely misses completely any serious examination of the genuinely open questions in climate.

Cheers -- sylas

 

[skypunter]

What happens when water vapor is carried aloft and is condensed?
Isn't a great deal of heat radiated above the densest layers of greenhouse gases?
Wouldn't this result in a large net outflow of energy?
How is this seemingly random thermodynamic process handled by computer models?

 

[chriscolose]

This mode of heat transfer was understood since at least the 1960's, looking through some of Manabe's work (and maybe before that, but I don't know) and can even be treated in simple radiative-convective models.

 

[sylas]

This mode of heat transfer was understood since at least the 1960's, looking through some of Manabe's work (and maybe before that, but I don't know) and can even be treated in simple radiative-convective models.

It was known well before that. The earliest global energy balance diagram of which I am aware is from 1917, by Dines, and this includes the latent heat flux, with about the right value.

(Dines, W. H., 1917: The heat balance of the atmosphere. Quart. J. Roy. Meteor. Soc., 43, 151–158.)

The value given is 140 cal/cm².day, which is about 70 W/m². It follows pretty immediately from values for global precipitation. The 1917 work also includes the conventional greenhouse effect, as the atmospheric back radiation. The relevant physics for all of this was worked out in the nineteenth century.

Cheers -- sylas

 

[BrianG]

Full Text of Translated Letter By 61 German Scientists:
Open Letter - Climate Change
Bundeskanzleramt
Frau Bundeskanzerlin Dr. Angela Merkel
Willy-Brandt-Strabe 1
10557 Berlin
#
Vizerprasident
Dipl. Ing. Michael Limburg
14476 Grob Glienicke
Richard-Wagner-Str. 5a

Grob Glienicke 26.07.09
To the attention of the Honorable Madam Angela Merkel, Chancellor of Germany
When one studies history, one learns that the development of societies is often determined by a zeitgeist, which at times had detrimental or even horrific results for humanity. History tells us time and again that political leaders often have made poor decisions because they followed the advice of advisors who were incompetent or ideologues and failed to recognize it in time. Moreover evolution also shows that natural development took a wide variety of paths with most of them leading to dead ends. No era is immune from repeating the mistakes of the past.
Politicians often launch their careers using a topic that allows them to stand out. Earlier as Minister of the Environment you legitimately did this as well by assigning a high priority to climate change. But in doing so you committed an error that has since led to much damage, something that should have never happened, especially given the fact you are a physicist. You confirmed that climate change is caused by human activity and have made it a primary objective to implement expensive strategies to reduce the so-called greenhouse gas CO2. You have done so without first having a real discussion to check whether early temperature measurements and a host of other climate related facts even justify it.
A real comprehensive study, whose value would have been absolutely essential, would have shown, even before the IPCC was founded, that humans have had no measurable effect on global warming through CO2 emissions. Instead the temperature fluctuations have been within normal ranges and are due to natural cycles. Indeed the atmosphere has not warmed since 1998 - more than 10 years, and the global temperature has even dropped significantly since 2003.
Not one of the many extremely expensive climate models predicted this. According to the IPCC, it was supposed to have gotten steadily warmer, but just the opposite has occurred.
More importantly, there's a growing body of evidence showing anthropogenic CO2 plays no measurable role. Indeed CO2's capability to absorb radiation is already exhausted by today's atmospheric concentrations. If CO2 did indeed have an effect and all fossil fuels were burned, then additional warming over the long term would in fact remain limited to only a few tenths of a degree.
The IPCC had to have been aware of this fact, but completely ignored it during its studies of 160 years of temperature measurements and 150 years of determined CO2 levels. As a result the IPCC has lost its scientific credibility. The main points on this subject are included in the accompanying addendum.
In the meantime, the belief of climate change, and that it is manmade, has become a pseudo-religion. Its proponents, without thought, pillory independent and fact-based analysts and experts, many of whom are the best and brightest of the international scientific community. Fortunately in the internet it is possible to find numerous scientific works that show in detail there is no anthropogenic CO2 caused climate change. If it was not for the internet, climate realists would hardly be able to make their voices heard. Rarely do their critical views get published.
The German media has sadly taken a leading position in refusing to publicize views that are critical of anthropogenic global warming. For example, at the second International Climate Realist Conference on Climate in New York last March, approximately 800 leading scientists attended, some of whom are among the world's best climatologists or specialists in related fields. While the US media and only the Wiener Zeitung (Vienna daily) covered the event, here in Germany the press, public television and radio shut it out. It is indeed unfortunate how our media have developed - under earlier dictatorships the media were told what was not worth reporting. But today they know it without getting instructions.
Do you not believe, Madam Chancellor, that science entails more than just confirming a hypothesis, but also involves testing to see if the opposite better explains reality? We strongly urge you to reconsider your position on this subject and to convene an impartial panel for the Potsdam Institute for Climate Impact Research, one that is free of ideology, and where controversial arguments can be openly debated. We the undersigned would very much like to offer support in this regard.
Respectfully yours,
Prof. Dr.rer.nat. Friedrich-Karl Ewert EIKE
Diplom-Geologe
Universität. - GH - Paderborn, Abt. Höxter (ret.)
#
Dr. Holger Thuß
EIKE President
European Institute for Climate and Energy
http://www.eike-klima-energie.eu/
Signed by…

http://www.climatedepot.com/a/2282/Consensus-Takes-Another-Hit-More-than-60-German-Scienti%20sts-Dissent-Over-Global-Warming-Claims-Call-Climate-Fears-Pseudo-Religion-Urge-Chancellor-%20to-reconsider-views

 

[vanesch]

BrianG,

The previous post doesn't have its place here: this is part of the political and sociological debate, eventually, but it is not science as it is understood here.

It is a very touchy subject, and we try to keep a balance here, based upon mostly peer-reviewed material, and keeping away from the political and sociological aspects of it as much as we can.

This is a very difficult forum to moderate, so please bear with us.

Thank you.

 

[BrianG]

BrianG,

The previous post doesn't have its place here: this is part of the political and sociological debate, eventually, but it is not science as it is understood here.

It is a very touchy subject, and we try to keep a balance here, based upon mostly peer-reviewed material, and keeping away from the political and sociological aspects of it as much as we can.

This is a very difficult forum to moderate, so please bear with us.

Thank you.

If it's inappropriate, delete it.

I'm just looking for a single experiment on CO2 and temperature, and if I can't find one, I want to know why. I think my post is helpful, we disagree. You decide.

 

[sylas]

If it's inappropriate, delete it.

I'm just looking for a single experiment on CO2 and temperature, and if I can't find one, I want to know why. I think my post is helpful, we disagree. You decide.

You've been given lots of experiments. The most important is John Tydall's experiments in the nineteenth century, described in message #10, with references to a detailed account of his work.

This is basic thermodynamics, which stands alongside work by Carnot, Clausius, Maxwell, Thompson (Kelvin), Boltzmann, Gibbs. All this nineteenth century physics established the basics of thermodynamics as a science. The experiments demonstrating the particular details of emissivity and thermal radiant absorption in different gases are here in the thread, and they do use temperature.

As thermodynamics has developed as a science, the ongoing work tends to measure energy rather than temperature, in the interaction of light or infrared radiation in a gas; since this is actually the fundamental basis from which temperature arises as a consequence.

Be that as it may, you have your experiments described for you here in the thread. See especially [post=2187943]msg #10[/post].

Cheers -- sylas

 

[Richard111]

A lot of heavy reading for me here so I gave up after page five. Apologies if my question has been asked and answered.

The current rate of increase of CO2 is well documented. The rate and extent for the change of water vapour can be huge even on a daily basis.

Assuming a relative humidity of anything less than 100% why is the DRY ADIABATIC LAPSE RATE a constant? Or is it not and what makes it change?

 

[sylas]

A lot of heavy reading for me here so I gave up after page five. Apologies if my question has been asked and answered.

The current rate of increase of CO2 is well documented. The rate and extent for the change of water vapour can be huge even on a daily basis.

Assuming a relative humidity of anything less than 100% why is the DRY ADIABATIC LAPSE RATE a constant? Or is it not and what makes it change?

If you raise a parcel of gas in an atmosphere slowly, it will expand due the reduced pressure. When a packet of gas expands, it cools.

The adiabatic lapse rate is simply the temperature change with pressure that corresponds exactly the temperature change of a parcel of gas expanding adiabatically as it rises... a change with constant energy for the gas parcel.

This rate can be calculated given from the gas law, if you know the molecular weight of the gas molecules and the heat capacity. It corresponds to a constant "potential temperature". The "dry adiabiat", by definition, applies when there is no moisture in the air. With added moisture, there's an extra energy term from latent heat of condensation, giving the "moist adiabat".

Hence the lapse rate depends mostly on the moisture content of the air. The real lapse rate can vary from the corresponding dry or moist adiabat. A lapse rate that is greater than the adiabatic lapse rate is unstable, because rising air becomes more bouyant as it rises. A smaller lapse rate, or negative lapse rate is stable against convection, although there is a tendency in this case for radiant heat flows to increase the lapse rate... a slower process.

Cheers -- sylas

 

[Richard111]

Thanks for that. The Gas Laws rule.
Having no formal education in this subject I must rely on intuition and common sense (I hope) and reading blogs.

The title of this thread, "Can You Model CO2 as a Greenhouse Gas", caught my attention because of a thought experiment I have been musing on. Imagine a column of air on a one square meter base. Accept the assumption that the sides of the column are impervious, no energy in or out. We know the mass of the column, about 10,333kg, the mass of contained CO2 about 4.13kg (0.04% say), and for water vapour we can choose any value from zero to say 4% and assume the base temperature and dry lapse rate is selected to ensure no physical water droplets will be in the column. We may need to limit our attention to some defined height of the column, say 300mb level or so.

Having defined the properties of our column (heh!), we consider the nature and properties of the base. We are free to choose water, land, grass whatever. Initially I have chosen a "greybody" with a surface temperature of 15C. Now the pips begin to squeak.

Ignoring convection from the surface and assuming the only "greenhouse" gas present is CO2 we should be able to surmise how much radiated energy is intercepted by the CO2, how much is transferred to the surrounding air molecules and how much is reradiated up and back down.

Definitive information on how long any CO2 molecule can remain in its energised state seems hard to come by. It would seem that at high densities, low altitude, where molecular spacing is closer, transfer by conduction is more likely. At higher altitudes the molecule may radiate a photon before encountering an air molecule. At this point my confusion index starts rocketing. Does the molecule radiate an equivalent photon? Or will the "new" photon be at a different wavelength/frequency? Anyway, to my thinking, (assuming there is no such thing as a free lunch) the "rate" of radiation will be less as the atmosphere cools with altitude.

I think I'll stop here. We know how much is being radiated up from the surface, we know CO2 can absorb at 2.7, 4.3 and 15 micrometers (µm), (I understand that this equates to about 8% of the available outgoing radiation). We do not, at this moment, know exactly how much is converted in heating the surrounding atmosphere. The remaining energy can be radiated isotropically such that about half will return to the surface.

So my present understanding is that under ideal conditions any surface radiation can expect something less than 4% of its output back again due entirely to CO2 thus slowing down the cooling of the surface by that amount.

Above, I used the word "intercepted" as I fail to see any energy "trapped". The rate of transfer is seriously changed from the speed of light to the dry adiabatic lapse rate but trapped it is not. When I move the column to over water, well... I get overcome by an urgent desire to grab a beer from the fridge.

Lots and lots left out like optical depth of the atmosphere at different LW wavelengths for different mixes. Ah well, hope the experts get round to an understandable explanation in due course.

Regards Richard

 

[Andre]

Now Richard, if you allow me, we could erect a second column of that air right next to yours, with openings in between the two at surface level and high in the top somewhere.

The difference is that the greybody underneath is somewhat less grey and more white. So as the different grey bodys get different temperatures after sun rise, due to different albedos, your column has more IR emission and warms the air directly above it more strongly than the the second column. So this air expands more than the other and in the top of the column, the air is pushed from the first column, through the hole into the second. As the buoyancy of the first colum is better, it start acting as a chinmey this way, transporting the warmer air up while it travels down again in the second column.

Hence more warm air (adiabatically cooled of course) will get to higher parts of the atmosphere where there are less molecules as you said, less heat is transferred to molecules and more is reradiated. Moreover, the (optical) distance to outer space is reduced, hence the chance for a photon to escape is increased and the upper atmosphere cools effectively by radiation out, the cooler air can descend again in the second column (where it heats up adiabatically, cancelling out the both adiabatic components).

So with this convection, we have basically made an heat pump that removes more heat from the atmosphere than radiation alone. It appears that this process can't really be ignored. Because...

If you increase the concentration of "greenhouse" gasses, the heating of the lower atmosphere becomes more effective by nett absorption, as does the cooling of the upper atmosphere by nett radiation out. This enhances the convection and more heat is transported upwards, effectivily reducing the warmin effect at the surface, aka negative feedback.

So sure if there was no convexion then there would likely be a certain increase in surface temperature, but this is reduced by the negative feedback of the convection heat transport, a process that isn't really identified in the IPCC reports.

 

[sylas]

...

So sure if there was no convexion then there would likely be a certain increase in surface temperature, but this is reduced by the negative feedback of the convection heat transport, a process that isn't really identified in the IPCC reports.

This is complete physical nonsense, sorry. I don't mean this as a personal attack; but as a correction to really fundamental errors in basic atmospheric physics.

Note that this account is not only ignored in the IPCC reports. It's also ignored in basic texts of atmospheric physics. The only source of which I am aware for this kind of account is an error-ridden paper by a petroleum geologist -- and ironically one of the criticisms of this geologist is that HE ignores basic background information on atmospheric physics. This notion of a convection related negative feedback is ignored in actual working science, as can be seen by citations. We've discussed this earlier in the thread, with references. This idea should be ignored; and it can only distract from a basic understanding of real atmospheric physics.

It can be useful, however, to try and explain the errors, and WHY this notion doesn't actually appear in atmospheric science.

It's going to be necessary to get some basic terms and concepts defined.

Energy balance

The Earth receives energy from the Sun and radiates effectively the same amount of energy back to space. The "energy balance" at the top of the atmosphere is the difference between the energy coming in and the energy going out.

Forcing

A forcing is anything which has as its immediate effect a change in the energy balance. For example, more reflection of light will increase the amount of outgoing energy. More thermal absorption will decrease the amount of outgoing energy.

For various reasons, it is convenient to define a forcing as a change in energy balance at the tropopause after stratosphere temperatures have responded to the forcing but before the surface and troposphere have changed in response. (See also [post=2162699]msg #1[/post] of "Estimating the impact of CO2 on global mean temperature" for some more background on this, and references.)

Planck response

As a result of a change in the energy balance, the Earth will heat up, or cool down; until energy balance is restored. The "Planck reponse" is a simplified ideal in which all changes in atmospheric composition or surface are ignored. It is the amount of temperature increase which would restore the energy balance with all other secondary effects, like cloud, or humidity, or vegetation, or ice cover, remaining fixed.

Feedback and sensitivity: the actual response

Of course, the Earth is not that simple. When temperature changes, so does vegetation, ice cover, humidity, cloud, weather patterns, etc, etc. All of these can lead to additional impacts on energy balance, and hence work as feedbacks in the climate system. The actual response, as a temperature change, is the combination of the basic Planck response plus all the feedbacks.

Lapse rate

The lapse rate is the change in temperature with altitude in the atmosphere.

The troposphere is the lower part of the atmosphere, within which convection is at work. In this region, the lapse rate tends towards the "adiabatic lapse rate". This is determined simply by the natural buoyancy of air. As air rises into altitudes with lower pressure, it expands and cools. The adiabatic lapse rate is when temperature gradients match the natural adiabatic cooling of rising air. If the lapse rate is greater than this, then rising air increases in buoyancy as it rises. This is an unstable state, and convection drives the warmer air upwards until the adiabatic lapse rate is restored.

The lapse rate of the atmosphere has only a negligible dependence on temperature. It depends rather on the heat capacity of air, and on its molecular weight. It can be derived from first principles and the gas law.

The lapse rate has a strong dependence on humidity, because of the energy changes that result as moisture condenses. A moist lapse rate is significantly less than a dry lapse rate. Moisture related effects are an example of a feedback, because they rely on changes to the composition of the atmosphere.

Convection in basic atmospheric physics

The fundamental feature of convection in atmospheric physics is that it works to maintain the adiabatic lapse rate; or more particularly, to decrease lapse rate until it approaches an adiabatic rate. That's HOW YOU CALCULATE the expected consequence of convection under changing conditions.

You can only think the effects of convection are ignored if you don't know the basic underlying fundamentals, in which convection is crucial, or if you have a physically incorrect notion of what convection does.

Calculating a no-feedback Planck response to increased greenhouse gases

The no-feedback climate response is taken by finding a new temperature at the surface and in the troposphere that restores energy balance, without changing the composition of the atmosphere or surface. The lapse rate is therefore unchanged for this calculation.

In a greenhouse forcing, the change is basically because there is a reduced path length for thermal radiation. Radiation in the absorption bands of the spectrum escapes into space from higher altitudes, where the atmosphere is cooler, and so less radiation is emitted.

When the temperatures adjust, and balance is restored, the surface is warmer, and hence the whole atmosphere is warmer at any given altitude, because the same lapse rate still applies.

Summary

Any changes in convection are not a feedback. A feedback would have to alter the lapse rate. (Humidity does this, for example.) Convection is an integral part of the first level Planck response in changing temperature, because it IS convection that maintains lapse rate. This is a simple consequence of how climate feedbacks are defined. To say that this is "ignored" by the IPCC is to profoundly misunderstand at the most basic level how feedback and non-feedback climate response is defined.

This is indeed the fundamental problem. The paper that proposed this curious notion does indeed show a profound lack of comprehension of basic climate science.

Cheers -- sylas

PS. Added in edit. For more detail on the concepts discussed in this post, the best bet is simply to read up more on atmospheric science in a conventional undergraduate textbook. I don't expect people to take my word on this; but I do assert that this is not advanced level climate science. I encourage those who find the competing claims confusing to proceed not by picking a side to trust, but by learning this background. The specific idea proposed by Andre (due to Chillingar) is not addressed directly; but there is a discussion of lapse rates, convection, radiant-convective balance, feedbacks, and so on; which is what you need to start looking at claims like Chillingar's so-called feedback by convection on their own real merits.

There's a good text on available online that I have recommended. It's fairly demanding in total, but the first two chapters are pretty readable. Chapters 2 and 3 in particular covers most of what is needed here. The book is "Principles of Planetary Climate", by R.T. Pierrehumbert at the Uni of Chicago.

 

[Andre]

This is complete physical nonsense.

This is followed by a plethora of words, none of which seem to actually explain why it is complete physical nonsense. Wouldn't it be better to refer to the peer reviewed rebutal of the peer reviewed paper with these principles? Why is it physical nonsense? Could that be explained in less than 100 words?

Or let's look at the individual steps

Step one: the initial heating of the atmosphere due to IR radiation of the warmer Earth at daytime takes places in the lower layers of the atmosphere because of nett IR absorption, assuming that the agitated radiative molecules transfer kinetical energy to the other molecules. There is of course a lot more to that concerning the total radiation energy flow, but the nett process is that most warming due to IR reradiation takes place in the lower levels initially.

True / False?

 

[sylas]

This is followed by a plethora of words, none of which seem to actually explain why it is complete physical nonsense. Wouldn't it be better to refer to the peer reviewed rebutal of the peer reviewed paper with these principles? Why is it physical nonsense? Could that be explained in less than 100 words?

Because the no-feedback response already includes the effects of convection. Because convection is what maintains lapse rate.

It might well not show up in a peer reviewed article essentially because it is not the role of peer reviewed literature to correct undergraduate homework. Sometimes a response is given when material this bad shows up in the scientific literature, sometimes not. In this case, the low grade of Chillingar's atmospheric physics has already been shown in a response to an older paper. It's a reasonable approach (IMO) to ignore a new round of errors. They don't have any impact on science; and for people who are not actually involved in the science, responses can backfire by giving the incorrect impression that this is actually a scientific debate.

Or let's look at the individual steps

The error is in the way you break up the individual steps.

Step one: the initial heating of the atmosphere due to IR radiation of the warmer Earth at daytime takes places in the lower layers of the atmosphere because of nett IR absorption, assuming that the agitated radiative molecules transfer kinetical energy to the other molecules. There is of course a lot more to that concerning the total radiation energy flow, but the nett process is that most warming due to IR reradiation takes place in the lower levels initially.

True / False?

True, but this "initially" very rapidly gets fixed back to the standard lapse rate by convection. So rapidly, in fact, that there is no sensible "initial" response. Any such division of steps is already lost in the usual diurnal cycles. The whole atmosphere responses much much faster than greenhouse compositions can change. Same with cooling by increasing albedo. That is why, as I explained previously, it is already a part of the no-feedback response, as these terms are used in atmospheric physics.

Cheers -- sylas

 

[Andre]

The error is in the way you break up the individual steps.

If one cannot break this process down in steps, which process can be broken down anway?

True, but this "initially" very rapidly gets fixed back to the standard lapse rate by convection.

Really and how rapidly? we are talking diurnal effects here, matter of parts of day, but in case of advection, several days to weeks, the life cycle time of frontal systems.

Yes, convection or advection, because the rising air is less dense and hence more buoyant than the surrounding layers, due to a higher temperature with equal pressure (in principle) the next question is, if this process effectively transports energy ( regardless in what form) from surface layers to higher layers.

true/false?

Perhaps that the devastation power of Hurricanes, Tornadoes and other storms give a hint towards the answer.

Something else

This notion of a convection related negative feedback is ignored in actual working science, as can be seen by citations. We've discussed this earlier in the thread, with references. This idea should be ignored;

Is convection / advection (negative) feedback or not?

Feedback is...

the process in which part of the output of a system is returned to its input in order to regulate its further output

Well, convection is an output of the Earth surface warming up, which is the output of the sun warming the surface. So convection is output. It's effect is to take energy/heat away that is in direct contact with the Earth surface. This air is replaced with cooler air which in turn does return less radiation to the surface, and hence is 'returned to its input in order to regulate its further output'. And since the sign (cool air) is opposite to the original input (warming sun) it is negative feedback.

So what exactly is wrong with the complete convection process, that it is not negative feedback?