Model CO2 as Greenhouse Gas: Tips & Results

[chriscolose]

Really? Isn't just an explanation, disregarding/downplaying the effect of other heating processes like latent heat, convection and advection as discussed in the other thread? Yes I know, the radiation numbers seem far more bigger, but the other effects are one way only while radiation is two ways, in and out, and tending to balance and cancel out.

If the atmosphere was unable to radiate, it would still be heated by those three until a certain equilibrium, which definitely bigger than zero; especially since there is no way that the atmosphere could loose the heat without radiation, since it can't convect or advect downwards. So not all, if any of those 33 degrees can be greenhouse effect.



Could you please indicate in the Fourth assessment report of wg1of the IPCC where it substantiates a remarkable predictive and explanatory power over a broad range of planetary applications?

No one downplays the importance of other processes, and they're all included in basic discussions in textbooks and in climate models. It's just a matter of understanding the difference between the surface and top-of-atmosphere energy balances, or the fact that the surface temperature cannot exceed a certain value (determined by the incoming absorbed solar radiation) without a greenhouse effect. The 33 K greenhouse effect *is* purely from greenhouse gases and clouds.

The IPCC is not a textbook on atmospheric physics or comparative planetology. Your request is rather strange. I suspect it's a distraction, but my opinions on certain commenters here are in violation of forum conduct policy.

 

[sylas]

Really? Isn't just an explanation, disregarding/downplaying the effect of other heating processes like latent heat, convection and advection as discussed in the other thread? Yes I know, the radiation numbers seem far more bigger, but the other effects are one way only while radiation is two ways, in and out, and tending to balance and cancel out.

If the atmosphere was unable to radiate, it would still be heated by those three until a certain equilibrium, which definitely bigger than zero; especially since there is no way that the atmosphere could loose the heat without radiation, since it can't convect or advect downwards. So not all, if any of those 33 degrees can be greenhouse effect.

That can't work, Andre. Imagine you have an atmosphere that is heated by convection and latent heat, but does not absorb radiation except possibly to a much smaller extent.

The atmosphere will heat up, to be sure, and you'll get a lapse rate in the atmosphere as usual.

The surface of the planet will radiate energy governed by its temperature, and that radiation will stream out into space unimpeded. That energy will have to balance the energy received from the Sun. Now, Earth receives about 240 W/m² from the Sun. To radiate that amount of energy, the surface will have a temperature of (240/σ)^0.25, which is 255 Kelvin... about 33 degrees less than what we have at present.

This is really basic first year level thermodynamics, Andre. You cannot have a higher mean temperature than this, or else the radiation from the surface, which by hypothesis is going straight out to space, exceeds what you receive from the Sun.

If you have an atmosphere which does not absorb infrared radiation to any appreciable degree, it would come to a convective equilibrium temperature, where there is no net flow of energy. There's no energy loss out from the top of the atmosphere; by the first law you know that there's no net gain of energy coming up from the bottom either.

We are about 33 degrees warmer than that... and that is a consequence of our atmosphere's capacity to absorb and radiate infrared radiation.

Now don't take this the wrong way... but I want to take the bull by the horns here. It's not meant to be personal at all; I have no problem disagreeing strongly with someone on a matter of physics or maths, and still being friends. With that understanding, I'll not mince words; but I want to assure you I'm only speaking of the substantive physics issues.

We have not been discussing global warming theories here, or the matter of changes to atmospheric composition; this is about the existence of a greenhouse effect AT ALL. It is about the thermodynamics of a convective-radiative equilibrium in an atmosphere that absorbs infrared radiation. When an atmosphere absorbs IR radiation, it also emits IR radiation, and the net effect of that by basic thermodynamics is a higher temperature than you would have otherwise.

It's one thing to be skeptical of various matters in modern climatology. I have a frankly low opinion of most of the skeptical arguments in popular use; but in amongst all that noise there are real open questions and unsolved problems and uncertainties. There are also some splendid opportunities for learning more about the relevant physics in learning to identify bad arguments.

The denial of greenhouse effect altogether, or the claim that IR absorption would work to actually have a cooler atmosphere than otherwise, is pseudoscience. This includes the model of lapse rates proposed by Chilingar. This is not the only field or the only instance where a well qualified scientist in some other field goes off the rails into nonsense in some other area. If Chilingar's model is right, every basic textbook on atmospheric physics is wrong. But his account of the adiabat is physically nonsense.

Could you please indicate in the Fourth assessment report of wg1of the IPCC where it substantiates a remarkable predictive and explanatory power over a broad range of planetary applications?

The IPCC reports are not a textbook to introduce basic planetary physics. For that, you want an undergraduate level textbook. I suppose it is remarkable; but no more and no less than any other area of science where we have been able to learn more about how the natural world operates.

I have been learning a lot about atmospheric physics over the last year or so by studying Principles of Planetary Climate, by Professor Pierrehumbert, of the University of Chicago. The book is not yet published; but is under contract to be published by Cambridge Uni Press. A draft, complete in the first eight chapters, is available online, and it is geared towards his teaching of the unit "Geosciences 232: Climate Dynamics of the Earth and Other Planets".

I like the book because it is pretty comprehensive, and quite mathematical, which suits my learning style. It is technical and I am a long way from understanding it all, but the first few chapters are fine, and already take you through a range of diverse examples in different planets. The download is available at the above link, but it is pretty large. You might like to have a look.

There's nothing there that is particularly controversial... or at least there shouldn't be. Plenty of other undergraduate level texts do the same kind of thing, including consideration of physics sufficiently generally to apply to a range of planets.

Cheers -- sylas

PS. Wrote this offline independently, before I saw Chris' reply.

 

[BrianG]

It's the lack of an experimental test that shows a 300ppm difference in an atmosphere's CO2 causing the smallest measurable degree of warming. CO2 doesn't absorb heat from IR; it merely scatters it all around. Heat still flows from hot to cold. The greenhouse effect of a large amount of CO2 is untested in the lab or in the field.

The effects of aerosols have been tested in the field and the lab. The effect of neutrino/matter reactions have been tested and measured. The effects of climate change mitigation is purely theoretical and even the pseudo science says that doubling CO2 creates one unit of warming, though the size of that unit of warming is way too small to measure.

 

[chriscolose]

One can only hope that some day you'll read enough to create one full sentence of correct information.

 

[Andre]

You cannot have a higher mean temperature than this, or else the radiation from the surface, which by hypothesis is going straight out to space, exceeds what you receive from the Sun.

Now let's concentrate on that. How about running a null hypothesis on Earth instead of using a -perhaps too simple- model that leads to the 33 degrees?

Assume that the atmosphere of our model is completely inert, no radiative properties and that the Model- Earth acts as a radiative transmitter, but not completely like a black body, since it does not meet its qualifications (like an ideal conductor, while the Earth is a near ideal insulator).

Furthermore, we have diurnal rotation effect and a point emitter, also known as the sun, instead of a universally emitting sphere around the Earth as the 33 degree model assumes.
So at any moment in time there is a point on earth, perpendicular to the sun that receives the full ~1365 W/m2, which translates, with an albedo of 0.3, via Stefan-Boltzman, to a temperature of 360K (87C or 189F). Of course this is only a moment in time but we can also we can imagine for instance a cone of +/- 60 degrees which takes the sun 8 hrs for the sun to travel) at the border of this cone this point receives half of the total radiation in, (682.5 W/m2) which is still good for a Stefan Boltzman temperature of 303K (30C or 86F). So there is a good deal of time that any point under the zenith of the sun heats up well above the theoretical “black body” temperature every day.

Note that this heat energy is assumed to be in radiation equilibrium, as dissipation via radiation into space is already accounted for. Other ways of energy dissipation are both conduction to deeper layers under the surface and conduction to the boundary layer of the atmosphere. Conduction is a very ineffective way of losing heat. However, while heating, the atmosphere boundary layer decreases in density and gets buoyant. Via convection the heat is dissipated higher into the atmosphere. So, even without radiation absorption, there is a way to bring surface heat into the atmosphere during daytime, convection.

How about night time? There is no radiation in and the Earth surface starts to cool down due to radiation out. The cooling rate can be any value, and the minimum temperature reached is mostly time dependent. It’s however not very relevant for our model of the rotating earth. Remember that in our model the atmosphere is inert and does not radiate. Therefore, there is only conduction to the lower boundary layer in which heat energy can travel back to the surface, where it can be radiated. But as the cooling air boundary layer is getting denser, it will not mix well with higher layers (inversion) and the dissipation of heat from the atmosphere decreases rapidly. Only the lowermost layer is cooled effectively. Therefore the heating of the Atmosphere via convection is mostly one way. It goes up but it hardly comes down. Hence –lacking radiation- the thermal energy must accumulate day after day just as well as after million years until equilibrium with the ineffective conduction at the surface is obtained.

Now this was based on one point perpendicular under the sun. How about the poles for instance? With only very little in-radiation, the surface temperature is way, way down. For instance at a latitude of 80 degrees, the solar influx is only 17% at maximum at noon and hence the maximum value at day time is 237 W/m2 which translates to a maximum Stefan Boltzman temperature of 232K (-40C and F) So there won’t be a lot of convection going on there. However the convecting energy in the equatorial plane is the engine of a conveyer belt in the atmosphere, which is know on Earth as the Hadley cell which effectively divides the convected heat energy of the tropical regions while more complex processes bring the energy to the polar regions eventually. Obviously the same one way principles apply here, the much colder surface still cannot get a lot of energy out of the inert not radiation atmosphere via conduction of the boundary layer only, as the same physics apply.

So concluding, on a model planet with a hypothetically inert atmosphere, the atmosphere will be heated one way only. At day time, thermal energy of the surface enters the atmosphere via conduction and convection. At night time and in the Polar Regions the atmosphere only cools via conduction in the boundary layer. Obviously there is no cooling due to radiation in an inert atmosphere and thermal equilibrium is only reached when the ineffective boundary layer cooling equals the convective heating. Obviously, that will be substantially more than zero, which is assumed in the 33 degrees black body radiation model. Note that this latter model is based on linear processes, which is not valid when one way valves (convection) are added in the reality.

So, if we make the inert atmosphere in our null hypothesis radiative again with the addition of radiative gasses (mistakenly known as greenhouse gasses) more processes can take place. Now the heating of the lower atmosphere during daytime is also enhanced by the absorption of the surface out-radiation, which stimulates more convection. But also the atmosphere can radiate energy to outer space, and help cooling the atmosphere that way. Now obviously these processes act in opposite directions And then we did not add the water cycle with latent heat and clouds, adding to the complexity.

Conclusion: the 33-degrees black body radiation model is meaningless considering the more complex processes on Earth

This is basically the idea of the much quoted Chilingar et al 2008 and I would appreciate it to see what exactly is wrong with the physics of that.

 

[sylas]

Now let's concentrate on that. How about running a null hypothesis on Earth instead of using a -perhaps too simple- model that leads to the 33 degrees?

Assume that the atmosphere of our model is completely inert, no radiative properties and that the Model- Earth acts as a radiative transmitter, but not completely like a black body, since it does not meet its qualifications (like an ideal conductor, while the Earth is a near ideal insulator).

There's a very simple mathematical theorem here that applies in this case, for all possible permutations of your proposed model.

The total energy received from the Earth is the solar constant of ~1365 W/m², and 30% of that is reflected, using your numbers, with which I concur. The cross section of the Earth is one quarter of the surface area, which is why we divide by four when taking average energy inputs per unit area. But in any case, the total energy is

\pi R^2 \times 1365 \times 0.3 \approx 5.3\times10^{16} \; \text{Watts}​

Now, by the first law of thermodynamics, all that has to be radiated back to space. Because Earth distributes heat around the globe fairly well -- much better than the Moon, for example -- it is usual to give an "effective" temperature for the planet, which is the temperature that would radiate that amount of energy if uniform over the whole sphere.

You are proposing we take into account the obvious fact that temperature is NOT uniformly distributed. Here's the thing, however. The power radiated goes as the fourth power of temperature. So if you increase the temperature in some places and reduce it in others, the increase has a proportionally larger impact on the energy output. That is, you have to make the colder regions take a LARGER fall than the increase in the warmer regions. This applies for any redistribution of temperature, by any means.

This is a necessary consequence of Hölder's inequality, which means:

\frac{1}{S} \int_S T dS \leq \left( \frac{1}{S} \int_S T^4 dS \right)^{0.25}​

Added in edit. The above formula was originally incorrect; I had omitted the normalization with area S. See [post=2296963]msg #99[/post] by vanesch for the original incorrect version, and why it needed fixing. I've updated this post with the corrected formula he provided.​

The above represents a surface integral. One is the integral of temperature; the other is an integral of power emission. The power integral is constrained to balance the solar input by the first law.

What that means is that the value 255K (-18C) as an effective surface temperature is a strong upper bound on the average temperature, given any redistribution of temperature around the globe at all which maintains the energy output.

The only way you can actually get higher temperatures than a 255K average; the ONLY way, is if the energy radiated from the surface can't actually get directly out into space. In other words, the 33 degrees is a strong [strike]UPPER[/strike] LOWER BOUND on the consequence of absorption of radiant energy in our atmosphere.

That's a theorem; as strong as any result you can get in physics. Given your stated assumptions, of a radiatively inert atmosphere, and the unstated assumption of a surface emissivity of close to unity (which it certainly is, at the relevant wavelengths; I include this for completeness) the 33 degrees falls out from the laws of thermodynamics. It's that fundamental.

Note that this heat energy is assumed to be in radiation equilibrium, as dissipation via radiation into space is already accounted for. Other ways of energy dissipation are both conduction to deeper layers under the surface and conduction to the boundary layer of the atmosphere. Conduction is a very ineffective way of losing heat. However, while heating, the atmosphere boundary layer decreases in density and gets buoyant. Via convection the heat is dissipated higher into the atmosphere. So, even without radiation absorption, there is a way to bring surface heat into the atmosphere during daytime, convection.

But not out into space. Convection can heat up the atmosphere, but if the atmosphere cannot absorb infrared radiation then it cannot emit it either. There's nowhere for the heat to go. By the first law of thermodynamics, such a planet has an atmosphere which reaches a pure convective equilibrium. The atmosphere may heat up and cool down with the diurnal day night cycle or seasons, in various complex ways, but only through an exchange of energy to the surface. There's no way the atmosphere can actually be a net sink for heat from the surface; so ALL the radiation from the surface goes to space; and that means the surface is at a temperature to balance solar input. By Holder's inequality, this is necessarily an average temperature of -18 degrees, or less.

That is, the greenhouse effect -- absorption of IR radiation -- accounts for AT LEAST 33 degrees of extra surface warmth.

This is not advanced physics. This is very elementary thermodynamics.

I sympathize with people who get confused on these points, because there is a lot of outright pseudoscience expressed on this topic, which can easily lead the unwary astray. It's not always easy to pick the pseudoscience at first sight, for a non-professional. There are even a couple of cases where scientists have managed to express such ideas in the actual scientific literature. This is really unusual, and represents a startling failure of the journal to manage basic quality control; but it happens, in this and other fields. The cases I know of are in low impact journals, with authors who are not active in the relevant fields of physics. Even that is not enough to explain how this happens... I am honestly at a loss to account for how anyone could possibly write papers like Gerlich and Tscheusner, or Chilingar et al.

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.

So, if we make the inert atmosphere in our null hypothesis radiative again with the addition of radiative gasses (mistakenly known as greenhouse gasses) more processes can take place. Now the heating of the lower atmosphere during daytime is also enhanced by the absorption of the surface out-radiation, which stimulates more convection. But also the atmosphere can radiate energy to outer space, and help cooling the atmosphere that way. Now obviously these processes act in opposite directions And then we did not add the water cycle with latent heat and clouds, adding to the complexity.

The "complexity" here is smoke and mirrors. There is certainly plenty of complexity and a whole pile of open research questions here that can be legitimately a focus for more rational skepticism of various conclusions.

But not the question of "cooling". That is not an open question at all. As you give the atmosphere a capacity to interact with thermal radiation, you inevitably find that the atmosphere heats up; it gets more energy from the surface than when radiatively inert. What complexity means is that you can't easily derive how much it will heat up, nor whether you'll get local reductions offset by larger increases elsewhere, in complex ways. But the net effect of additional heating is a necessary consequence of basic thermodynamics, entirely independent of any concerns about the acknowledged complexity.

In a convective equilibrium, you will find temperatures fall with altitude. That is because pressure falls with altitude; as packets of air move up or down, they expand or contract, giving lower temperatures at altitude. There's a well developed theory for the "dry adiabat" that derives this relation, using basic thermodynamics. Note that this result is independent of the thermal emissivity. It depends simply on the "potential temperature", which is the temperature that air at a certain pressure would have if compressed in a return to surface levels. Allowing the atmosphere to absorb and emit radiation will drive stronger convection, certainly; but the adiabat is unaffected because the potential temperature is unaffected.

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 repeat, this is basic first year level physics. It's not in any doubt whatsoever. It is also completely irrelevant to most expressions of skepticism about conventional climatology; it's part of the rock bottom lunatic fringe of denial, in conflict with fundamentals of physics that are a basis for even to starting to look at the real complexities and uncertainties that exist in the field.

Conclusion: the 33-degrees black body radiation model is meaningless considering the more complex processes on Earth.

This is on a par with claiming that the conservation of momentum model is meaningless given the complexities of interactions of orbits in a multi-body gravitationally bound system.

On an exam, your comment could only be marked wrong. The 33 degrees is a necessary lower bound on the impact of the atmosphere's capacity to absorb infrared radiation, that holds by basic physics no matter how complex the processes you invoke. Complexity can't overrule the basic laws like conservation of energy; and that's the level of fundamentals from which the 33 degree bound follows.

This is basically the idea of the much quoted Chilingar et al 2008 and I would appreciate it to see what exactly is wrong with the physics of that.

The idea that adding a capacity to interact with thermal radiation has a net cooling effect.

(And by the way: you say "much quoted"... but by whom? You know the citation count on that paper? Zero. There's a handful of citations in an earlier error ridden paper he wrote in 2006; most importantly a devastating rebuttal response. In my opinion, finding the people who quote Chilingar is a good way to identify people whose skepticism is grounded in a profound lack of comprehension of the relevant physics... mainly amongst bloggers or the like. But scientists? Not so much...)​

Chilingar ignores the standard and completely uncontroversial thermodynamics of lapse rate, and comes up with his own definitions, without any experimental or observation support, without any refutations of the conventional thermodynamics of potential temperature and lapse rate, and in complete conflict with what should be learned in first year uni by anyone studying atmospheric physics.

I don't expect you to believe me on my own authority here. I'm making strong criticisms of Chilingar's competence in basic physics, despite the acknowledged fact he is a prominent and successful scientist in his own field. That may give you pause before accepting my analysis above. Good! That's skepticism, and skepticism is good. The thing is, you should on the same basis be skeptical of Chilingar's claims.

It is possible to be a "climate skeptic", but many people who identify themselves that way are better described as credulous naifs. My suggestion is... don't take my word for anything, and don't presume Chilingar's word either. After all, if Chilingar's lapse rate ideas have any merit then we'll have to rewrite all the physics of the dry adiabat! That's possible in principle, but a genuine skeptic should be cautious of jumping on that bandwagon too quickly!

Instead, take a bit of time to check the background. I cited for you an online text above. Try reading through chapter 2, of Principles of Planetary Climate, by Professor Ray Pierrehumbert. This chapter is "Thermodynamics in a Nutshell", and it includes derivations of the dry and the moist adiabat. Pretty much any other text on atmospheric physics should deal with this topic as well. I appreciate that this will take time; and I am not demanding you simply accept my claims at once. I anticipate we'll eventually wind up this discussion without reaching a mutual recognition the implications of thermodynamics for the hard bounds on properties of a complex climate system, and that's fine with me. But I hope I might have shaken your confidence enough to look into the physics more thoroughly over coming months, offline.

Cheers -- sylas

 

[mheslep]

... I'm making strong criticisms of Chilingar's competence in basic physics, despite the acknowledged fact he is a prominent and successful scientist in his own field. ...

In the case of peer reviewed publications by reputable scientists, isn't the place for that kind of criticism in the literature itself and not here?

 

[sylas]

In the case of peer reviewed publications by reputable scientists, isn't the place for that kind of criticism in the literature itself and not here?

That's an important question of policy. I am strongly opposed to any such notion. I think both venues are legitimate for strong criticism of peer reviewed papers.

I've taken time to set out some of my thoughts in more detail... its a bit long, sorry!

1. Responses in physicsforums

Criticism of peer reviewed papers in this forum should be held to the highest possible standard. It should not be prohibited as a general rule; but it had better be well founded. I will gratefully accept any substantive comment on the actual physics I explained in my post. It has long been a deliberate policy of mine to seek out and welcome corrections to any of my posts, and to publicly retract my errors as fast as possible, with thanks and recognition to anyone who helps me find them.

In all honesty, I am not in the slightest doubt of the physics I explained previously. But I'll never take offense at a genuine and substantive critique, whether valid or not. I aim to learn from mistakes, and hence anyone willing to help me find them is my friend. I've put a bit of work over the last year or so into learning more about atmospheric physics and thermodynamics, and I now feel pretty comfortable with it at the level I am using here. But it would be great to have a well informed second opinion especially from a colleague with a strong background specifically in atmospheres and thermodynamics.

As context for your question, there are two points I'd like to make.

1. Peer review isn't perfect. Sometimes it can fail quite spectacularly. Bad papers do get published occasionally, and we cannot simply presume that a paper published in a scientific journal is above criticism. So if we insist such criticism is not permitted here, it must be for some other general policy reason. If you recognize that it does happen occasionally that a physically invalid paper gets past peer review; such a policy would risk a window for physically invalid ideas to be introduced without fear of correction.
2. On this discussion in particular; the main substance of my post was not, in fact, criticism of the paper. It was on a very specific example and question proposed by Andre. I explained the whole thing, without mention of the paper at all, using only very straightforward physical thermodynamics. The paper came up because it was the basis for Andre's claim that interaction with thermal radiation leads to a cooler atmosphere than otherwise.

Andre cannot be faulted on policy. We disagree on some physics, which is not a problem so much as an opportunity for a useful substantive exchange. I think an exchange like this is really useful in this kind of forum, and I appreciate Andre's willingness to be part of it, and the way he engages the topic. Andre's claim, for all that it is IMO physically incorrect, is properly based on a published paper, and so permitted in the forum.

In my own reponse, I first explained why 33 degrees is entirely proper as an expression of the magnitude of Earth's greenhouse effect. This number is widely used in introductory material on atmospheric physics. That first part is self-contained. After that, I also went on to answer his question of why Chilingar gets a physically incorrect result... which he certainly does.

It is mainly because Chilingar (who is a petroleum geologist; not an atmospheric physicist) invents a completely invalid theory of lapse rate. That's not the end of the problems, but it's a start and easily checked by comparison with any simple introduction to thermodynamics of the adiabat.

2. Published responses

Now in fact, there IS published criticism of Chilingar's work, though not of the 2008 paper specifically. My own post is not based on that; I wrote my post independently and from my own working knowledge of atmospheric physics, and after reading Chilingar for myself. But you can find quite blistering refutations of Chilingar in the literature... in reference to a slightly older paper with many of the same errors repeated.

References:

• Khilyuk, L.F., and Chilingar, G.V. (2006) On global forces of nature driving the Earth’s climate. Are humans involved? in Environmental Geology Vol 50, No 6, Aug 2006.
• Aeschbach-Hertig, W. (2007) Rebuttal of “On global forces of nature driving the Earth's climate. Are humans involved?” by L. F. Khilyuk and G. V. Chilingar in Environmental Geology Vol 52, No 5, May 2007.

It would be tempting, and easy, to go into a cheap attack looking at secondary matters of the journal and citations and so on. But in brief, the paper has no impact on climate science. The formally published rebuttal gives the reason as a closing paragraph:

It is astonishing that the paper of Khilyuk and Chilingar (2006) (as well as Khilyuk and Chilingar 2004, for that matter) could pass the review process of a seemingly serious journal such as Environmental Geology. Such failures of this process, which is supposed to guarantee the quality of published literature, are likely to damage the reputation of this journal.

-- (Aeschbach-Hertig 2007)​

There's also a second aspect to your question about the proper place for criticism.

There's a problem with trying to refute work that is this bad within the scientific literature; it's not automatically a useful thing to do.

This paper has no prospect of any impact whatever on atmospheric physics in practice... so why would you bother? The one possible reason is to put out an explanation for people who aren't familiar with the field. But that can backfire. If anyone was actually serious about understanding these issues, they'd be reading basic texts on the subject. If someone feels all at sea with the subject matter, they'll just come away with the misleading impression that this is a scientific debate on a par with other disagreements between working scientists. But it isn't.

Professor Aeschbach-Hertig, who actually IS an environmental physicist specifically involved in climate research and paleoclimate in particular, also has his own blog; which is not a legitimate reference in the forum. Those who care can find it; and see what he thinks of the new paper. The criticisms go well beyond being merely incompetent at physics.

In all honesty, there's nothing in Chilingar's paper that deserves to be taken seriously in the scientific literature. That it got published at all, even in a low impact journal like Environmental Geology, is an indication of problems at the journal itself; and there's actually more to the story than just a bad publication. However, I can't just presume that here in physicsforums.

Cards on the table; that's my view of the whole debacle. But for discussion here at physicsforums, I will aim to be scrupulous in focusing on the merits of the physics itself.

I am not particularly interested in contributing to a situation where people work out who to cheer for on the basis of secondary ideas like "consensus" or "impact" or credentials or publication venue or the presumed allegiances of the author. My main interest is physics and physics education. I'm interested mainly in contributing to a situation where people know a bit more about the actual physics... in climate, in cosmology, in relativity, in any area of science where there's public interest and/or confusion.

Cheers -- sylas

 

[vanesch]

Ok, if you allow me to nitpick, although I agree with what you write concerning the black (or grey body) body temperature of the Earth without greenhouse effect: non-uniform irradiation can only result in a still lower surface-averaged temperature. This is because the "penalty" is a stronger-than-linearly rising function of T, so for constant "penalty", the maximum overall T you can achieve is when T is uniform. When it varies, you "pay" more. That's like tax: for a given amount of tax over 10 years to pay, best is to have as uniform an income a year. If you have all your income in 1 year, and nothing else in the 9 others, your overall 10-year income for the same tax will be lower than if you had a uniform income.
That's why it is a bookkeeping advantage of being able to spread extra income over as many accountancy years as possible.

This is a necessary consequence of Hölder's inequality, which means:

\int_S T dS \leq \left( \int_S T^4 dS \right)^{0.25}​

The above represents a surface integral. One is the integral of temperature; the other is an integral of power emission. The power integral is constrained to balance the solar input by the first law.

However there must be a typo in the formula you gave, because set T = 1 and S = 10 and you see the problem:

10 < (10)^(0.25) ??

The Hoelder inequality requires you to have 1/p + 1/q = 1.

We can fix this, by taking q = 4, p = 4/3, f = 1 and g = T.

We then have:
\int_S T dS \leq \left( \int_S 1^{1.33} dS\right)^{0.75} \left( \int_S T^4 dS \right)^{0.25}
or:

\int_S T dS \leq \left(S\right)^{0.75} \left( \int_S T^4 dS \right)^{0.25}

or:

\frac{1}{S} \int_S T dS \leq \left(\frac{1}{S} \int_S T^4 dS \right)^{0.25}

So there was a normalization missing.

It doesn't change your argument.

I was hesitating to report this nitpicking, but since you asked for it...

 

[sylas]

I was hesitating to report this nitpicking, but since you asked for it...

I did indeed, and you are quite correct. The integral as I gave it was not an average temperature at all, or an "effective" temperature (which can be considered as a kind of weighted average). I had left out the normalization. Urk. I've made a brief addendum to my post pointing to your correction.

Thanks -- Sylas

 

[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.