What's wrong with a bit of global warming?

[adb]

There's another thread on this site on the same topic. I've just made a post about a sunbather receiving radiant heat of 324 from the atmosphere but just 168 from the sun.

Shade the sunbather from the 168 from the sun and she feels a chill. The add shade for the 324 radiating from the rest of the sky and she feels no change !

Thieme is suggesting that any temperature change due to absorption immediately results in convection, whereas the greenhouse model assumes a static atmosphere.

Yes, I'm aware that Gerlich and Thieme are suggesting there is no greenhouse effect at all. I'm also well aware of the volumes of evidence suggesting any such effect is negligible ... although falling humidity is interesting and I've seen no explanation. I also have no doubt that "average" global humidities are as questionable as "average" global temperatures ... but this is off topic.

3. Troposphere temperatures decrease almost linearly to 190 deg K at 100mbar. How do you suggest that greenhouse, together with convective circulation as described by Heinz, effect this profile ?

"... well that is explained quite nicely by adiabatic lapse rate. "

That is my understanding ... in other words are you suggesting that "greenhouse" plays no role in this temperature profile ?

 

[sylas]

There's another thread on this site on the same topic. I've just made a post about a sunbather receiving radiant heat of 324 from the atmosphere but just 168 from the sun.

Sufficient unto each thread are the bewilderments thereof. Let's leave her in that thread. There are many ways to describe the shaded sunbather, and (as is usual in physics) most of them are incorrect. The discussion can be perused at [post=2130326]#33[/post], [post=2130349]#34[/post], [post=2131659]#47[/post], [post=2131674]#48[/post], [post=2131684]#49[/post], [post=2131737]#51[/post] (so far) of the other thread.

Yes, I'm aware that Gerlich and Thieme are suggesting there is no greenhouse effect at all. I'm also well aware of the volumes of evidence suggesting any such effect is negligible ...

There is no evidence whatsoever for the greenhouse effect being negligible. It's measured, and works out to be the be equivalent of about 33C additional warmth averaged over the globe. The only rejection of greenhouse is crank pseudoscience in conflict with basic thermodynamics. It can be a useful exercise for interested students of physics to sort out those errors, but it is not an actual scientific debate.

I think some readers may have trouble distinguishing denial of greenhouse effects that occur right now in the current atmosphere, from debate over the magnitude of changes to the greenhouse that should be expected from changes in the atmosphere.

The latter is a more subtle problem, and there is real scientific debate on such changes. But even there, there's no good evidence for changes being "negligible". It's a question of how much climate change should be expected as atmospheric composition changes, and that's uncertain. The denial of the greenhouse itself is way way out in the far fringes of pseudoscience, on a par with thinking relativity is falsified by satellites, or that you can cure cancer with magnets, or that the Earth is young.

3. Troposphere temperatures decrease almost linearly to 190 deg K at 100mbar. How do you suggest that greenhouse, together with convective circulation as described by Heinz, effect this profile ?

That profile is called the lapse rate. The greenhouse effect has only a very small effect on that... but the lapse rate has a very large effect on the magnitude of the greenhouse effect! Basically, the greenhouse effect works because infrared radiation has a limited "optical depth" in the atmosphere. This means that radiation escapes to space from somewhere sufficiently high in the atmosphere that the radiation can get through. At this level, the temperature must be about -18C, because that gives the amount of radiation needed to balance the solar input.

The magnitude of the temperature impact at the surface from the greenhouse effect is therefore a product of this characteristic emission altitude with the temperature gradient given by the lapse rate. If there was no lapse rate, there would be no greenhouse effect, because the temperature at the surface would then be about the same as the point where radiation escapes to space. But the lapse rate itself is caused by the adiabatic movement of air, as Skyhunter has said.

Cheers -- Sylas

 

[jeffsubi]

There is so much emphasis on carbon dioxide as the anthropogenic agent of climate change that I thought it would be easy to find the empirical evidence. That is, the results of controlled experiments in which infrared rays at frequencies radiated by the Earth are beamed though columns of air containing 280 -380-ppm of carbon dioxide and the temperature difference measured. So far I have only been able to find the work of John Tyndall (1861). Given the equipment he had to work with it was understandably difficult for him to detect much of an effect of CO2, at atmospheric concentrations. Arrhenius admitted he didn't have the equipment, so he use indirect methods, including the moon as an infrared source.

If CO2 does not significantly increase temperature at atmospheric concentrations in controlled experiments, the whole edifice of managing GHG emissions in order to control climate collapses.

Have Tyndall's experiments been repeated with modern equipment?

If there are lots of publications, could someone post one or two key references please.

 

[adb]

There is so much emphasis on carbon dioxide as the anthropogenic agent of climate change that I thought it would be easy to find the empirical evidence.

If there was a shed of evidence that man's CO2 is causing warming, I'm sure the IPCC would also like to hear about it.

The rate of man's fossil fuel burning increased around 1200% after 1945 but the rate of warming from 1910 to 1940 is higher than any period after 1945.

While the Arctic is much discussed by alarmists, it was much warmer in the 1930's than currently.

 

[sylas]

There is so much emphasis on carbon dioxide as the anthropogenic agent of climate change that I thought it would be easy to find the empirical evidence. That is, the results of controlled experiments in which infrared rays at frequencies radiated by the Earth are beamed though columns of air containing 280 -380-ppm of carbon dioxide and the temperature difference measured. So far I have only been able to find the work of John Tyndall (1861). Given the equipment he had to work with it was understandably difficult for him to detect much of an effect of CO2, at atmospheric concentrations. Arrhenius admitted he didn't have the equipment, so he use indirect methods, including the moon as an infrared source.

If CO2 does not significantly increase temperature at atmospheric concentrations in controlled experiments, the whole edifice of managing GHG emissions in order to control climate collapses.

Have Tyndall's experiments been repeated with modern equipment?

If there are lots of publications, could someone post one or two key references please.

There are a range of simple experiments similar to what you describe intended for schools or home experiments. Beaming radiation through 400ppm CO2 is not really very sensible, however. The bottom part of the atmosphere (troposphere) is roughly 20 kilometers of air. To get temperature effects in a lab, you need to do what Tyndal did... use higher concentrations in a smaller lab setting.

There's a thread with some of the details you might like at [thread=312054]Need Help: Can You Model CO2 as a Greenhouse Gas (Or is This Just Wishful Thinking?)[/thread]. This seems to be what you are asking. It's home physics for experiments to show how thermal interaction with a gas can lead to heating.

The warming effect of gases that absorb infrared radiation is pretty fundamental physics.

Modern experiments go into much more fine detail than merely whether warming occurs; they are more concerned with nailing down the emission spectrum. An example of experiments intermediate between Tyndal and modern physics might be http://prola.aps.org/abstract/PR/v38/i11/p2000_1 (1931) by H.D. Smyth, in Phys. Rev., Vol 38, Iss 11, pp 2000-2015. This is looking at the details of what wavelengths are absorbed.

The spectrum now tends to be in part calculated from first principles, I think, using knowledge of how matter and light interacts, and I'm at a bit of a loss to give a simple experiment here; the range of experiments used to develop this level of understanding of the quantum physics is a bit daunting.

Cheers -- sylas

 

[sylas]

If there was a shed of evidence that man's CO2 is causing warming, I'm sure the IPCC would also like to hear about it.

The rate of man's fossil fuel burning increased around 1200% after 1945 but the rate of warming from 1910 to 1940 is higher than any period after 1945.

While the Arctic is much discussed by alarmists, it was much warmer in the 1930's than currently.

Let's stick with actually answering the question. If you want to discuss any of these claims you are making, I would suggest a new thread; and a credible reference to kick it off.

Cheers -- sylas

 

[jeffsubi]

Thank you sylas.

I went to the link you provided (Can you model CO2 as a greenhouse gas) and the person who tried the experiment says:

"The problem I'm having is that I haven't been able to obtain the anticipated results in any reliable way. In fact, I'm seeing no consistent variation in the temperatures of the two containers, and I'm starting to wonder if this experiment is based on wishful thinking rather than on hard science"

People who use wet methods to generate CO2 may indeed see an effect, but that could be due to the difference in water vapour and not the CO2. The same thing happens in the atmosphere, water vapour swamps CO2 as an absorber of infrared radiation.

Modern equipment is sensitive enough to do the experiment at 200 - 400ppm, in dry air with no water vapour. Some one must have done it. I would like to find the reference.

Thanks,
JEFF

There are a range of simple experiments similar to what you describe intended for schools or home experiments. Beaming radiation through 400ppm CO2 is not really very sensible, however. The bottom part of the atmosphere (troposphere) is roughly 20 kilometers of air. To get temperature effects in a lab, you need to do what Tyndal did... use higher concentrations in a smaller lab setting.

There's a thread with some of the details you might like at [thread=312054]Need Help: Can You Model CO2 as a Greenhouse Gas (Or is This Just Wishful Thinking?)[/thread]. This seems to be what you are asking. It's home physics for experiments to show how thermal interaction with a gas can lead to heating.

The warming effect of gases that absorb infrared radiation is pretty fundamental physics.

Modern experiments go into much more fine detail than merely whether warming occurs; they are more concerned with nailing down the emission spectrum. An example of experiments intermediate between Tyndal and modern physics might be http://prola.aps.org/abstract/PR/v38/i11/p2000_1 (1931) by H.D. Smyth, in Phys. Rev., Vol 38, Iss 11, pp 2000-2015. This is looking at the details of what wavelengths are absorbed.

The spectrum now tends to be in part calculated from first principles, I think, using knowledge of how matter and light interacts, and I'm at a bit of a loss to give a simple experiment here; the range of experiments used to develop this level of understanding of the quantum physics is a bit daunting.

Cheers -- sylas

 

[sylas]

Modern equipment is sensitive enough to do the experiment at 200 - 400ppm, in dry air with no water vapour. Some one must have done it. I would like to find the reference.

I honestly cannot imagine why anyone would bother. It would be a meaningless experiment, with no particular useful relation to the atmosphere or Earth system. Concentration is not all that important; the total amount is a more significant quantity. I don't think you'll find any such experiment with tiny quantities of a gas, giving temperature effects so small that you'd need pretty high quality experimental controls to even see them.

Cheers -- sylas

 

[jeffsubi]

OK, I'll settle for total amount. The change in CO2 concentration being talked about is from 280ppm to 380ppm, a difference of 100ppm.

If you take 1 square meter of Earth's surface and a column of air 1km high, a 100ppm of CO2 would be a 10cm slab at the bottom. Stick such an amount of CO2 in an appropriate container, beam through infrared at wavelengths radiated by the Earth and measure the temperature change.

I still maintain that modern instruments can measure EXTREMELY small temperature differences. Even with his rather basic apparatus Tyndall in 1861 was able to get measurable effects at concentrations of 'greenhouse gases' that occur in the atmosphere.

The protagonists for CO2 as the driver of global warming rest their claim on CO2 at concentrations found in air being able to absorb infrared, and warm the air (radiative forcing). That is the relevance of my experiment - can we demonstrate CO2 does this under experimentally controlled conditions, and to what extent?

Cheers,
Jeff

I honestly cannot imagine why anyone would bother. It would be a meaningless experiment, with no particular useful relation to the atmosphere or Earth system. Concentration is not all that important; the total amount is a more significant quantity. I don't think you'll find any such experiment with tiny quantities of a gas, giving temperature effects so small that you'd need pretty high quality experimental controls to even see them.

Cheers -- sylas

 

[sylas]

Jeff, here is a direct link taken from the other thread to a specific experiment that seems to be what you are looking for. http://www.espere.de/Unitedkingdom/water/uk_watexpgreenhouse.htm .

This experiment is aimed for schools, but it has been done quite carefully in the cited page.

There's not a great deal of value for professional scientists in doing this experiment to great precision, as described. It is certainly possible to measure temperature very accurately, but I honestly can't see much benefit in knowing the temperature change to great accuracy in this kind of set up. It won't tell you much about the atmosphere; it does not scale up trivially to let you draw useful conclusions.

To explain why, I'll give a brief discussion of how an atmospheric greenhouse effect works later in this post.

Nevertheless, there are more careful professional experiments with "gas cells" and the transmission of radiant energy. They are more concerned with measuring the properties of a gas than with trying to reproduce an atmosphere or prove a greenhouse effect in the atmosphere. You seem to be wanting some kind of experimental proof of the greenhouse effect. Tyndal's work gives you that, and though there may well be more or less equivalent experiments in more modern settings, I can't cite you one quickly that does precisely that; other than teaching experiments like the one cited above.

What I am wanting to say, without appearing snarky or discouraging, is that the atmospheric greenhouse is really basic physics. It's pretty much an immediate consequence of simple thermodynamics, given a gas with frequency dependent emissivity. There are all kinds of experiments confirming the details of thermodynamics and interaction of gases with radiation, and measurements of our own atmosphere that only make sense in the light of an atmospheric greenhouse effect.

What is more subtle is precisely how temperature profiles change with changes in concentrations of greenhouse gases, and for the atmosphere that depends on much much more than just the greenhouse gases themselves. That is, you need to distinguish between the matter of whether there is a greenhouse effect at all, with the question of how the effect changes as concentrations of gas change, in a complex climate system.

Gas cell experiments

One of the standard tools used for studying gases is a "gas cell"; a container of carefully measured gas within which transmission of radiation can be studied.

Just looking quickly, I can give you a reference to a paper showing a modern use of such a cell. See V.G. Arakcheev et al., (2008) Broadening of vibrational spectra of carbon dioxide upon absorption and condensation in nanopores, in Moscow University Physics Bulletin, Vol 63, No 6, Dec 2008. It's not what you want, but it does show the nature of the gas cells and the precisions of experiments. I picked that up with a quick google.

Another tool I've used a bit myself to play around is a simulator for gas cells. See Gas cell simulator at spectralcalc.com

(There's also a tool for calculating transmission in the atmosphere: http://geosci.uchicago.edu/~archer/cgimodels/radiation.html , at the University of Chicago.)

OK, I'll settle for total amount. The change in CO2 concentration being talked about is from 280ppm to 380ppm, a difference of 100ppm.

If you take 1 square meter of Earth's surface and a column of air 1km high, a 100ppm of CO2 would be a 10cm slab at the bottom. Stick such an amount of CO2 in an appropriate container, beam through infrared at wavelengths radiated by the Earth and measure the temperature change.

Sure, you could do that; but it wouldn't have a whole heck of a lot to do with the atmospheric greenhouse effect. Here's why:

Quick summary of atmospheric greenhouse

What actually happens in the atmosphere is that you get solar radiation coming in, and infrared being radiated up from the surface. When there's a gas in between which is opaque to certain infrared frequencies, it absorbs the radiation coming back from the surface, and heats up. Then, by virtue of having a temperature, the gas radiates in the same frequencies that it absorbs. This is radiated in all directions, back down as well back up out to space. And, of course, that radiation is absorbed again in turn. Each frequency of radiation has its own "optical depth"... the mean path length of a photon before it is absorbed.

We can measure directly the thermal "backradiation" that returns to the surface from the atmosphere; there are descriptions of this earlier in the thread. One way to think of the heating effect at the surface is to consider the additional radiation coming to the surface from the heated atmosphere, on top of the solar radiation.

But note... the backradiation depends on the temperature of the atmosphere as well as its emissivity, and so the net effect depends on other forms of energy transport, including latent heat and convection. Hence you can't represent an atmosphere either by having a small amount at the same concentration, or at the same total partial pressure.

Hence there's not really much point in an experiment just to measure a temperature change in a small amount of gas, apart from a teaching tool for practice in doing simple experiments and learning about radiative transfer in a gas.

I still maintain that modern instruments can measure EXTREMELY small temperature differences. Even with his rather basic apparatus Tyndall in 1861 was able to get measurable effects at concentrations of 'greenhouse gases' that occur in the atmosphere.

The protagonists for CO2 as the driver of global warming rest their claim on CO2 at concentrations found in air being able to absorb infrared, and warm the air (radiative forcing). That is the relevance of my experiment - can we demonstrate CO2 does this under experimentally controlled conditions, and to what extent?

Cheers,
Jeff

The experiments listed in the other thread do show that absorption of radiant energy by a gas can result in warmer temperatures than otherwise. As I've tried to show above, for studying climate we need a bit more than simply knowing a gas can heat up when it absorbs infrared radiation.

There is a paper mentioned in this thread which attempted to deny that there's a greenhouse effect at all. That's frankly outright pseudoscience; the climate equivalent of young Earth creationism. But sorting out how much temperatures on Earth change in response to changes in greenhouse gas concentrations is much more difficult. It can't be measured as a simple lab experiment, and constraints from actual empirical studies of the Earth itself only constrain the "sensitivity" of climate to comparatively crude precision.

I suspect this is not exactly what you were looking for, but I hope it might be some help.

Cheers -- sylas

 

[jeffsubi]

Dear Sylas,

Thank you so much for your detailed reply. I didn't mean to put you to so much trouble.

I am aware of the wealth of spectoscopic data on the absorption of infrared by CO2. The HITRAN database is the key reference for that. Yes, absorption of infrared by CO2 definitely will cause some warming. But how much? Maybe hardly any at atmospheric concentrations?

The student experiment you referred me to is very nice. Better than the many others on a similar theme that I have seen on the Web. I shows a heating effect of a few degrees for 100% CO2

Doubling CO2 concentration in air from 280ppm to 560ppm should also cause some warming - but maybe hardly any? My contention is that a change of a few hundreds of parts per million CO2 will cause a miniscule amount of temperature change in an air mix, (no matter how large or small the volume), and that this should be verifiable by empirical experiment with modern equipment.

So far I have found only the publication by Tyndall (1861) and this one:

http://www.john-daly.com/artifact.htm

Both of which seem to support the idea that CO2 at atmospheric concentrations does not warm very much with infrared radiation. And yes, this is only the first step in understanding the complex behaviour of gases in the atmosphere.

Certainly I think that the effect of any CO2 change will probably be swamped by changes in heat distribution, and concentrations of the major 'greenhouse gas', namely water vapour, which we humans definitely have altered by land clearing, river diversion, irrigation etc. Also, burning oil and coal produces water vapour as well as carbon dioxide.

A bigger warming effect occurs in the northern hemisphere than the south because there is a larger land mass there and larger human populations. Correspondingly, we see more evidence of warming in the form of melting glaciers, ice caps and Arctic sea ice in the Northern Hemisphere than in the Southern.

I am not challenging the phenomenon of global warming, or the 'greenhouse effect'. I just think proof that atmospheric CO2 is the MAJOR driver of climate change is unconvincing. At least I am yet to find any empirical evidence in support.

I don't mean to tire you any further with my pesky questions and replies because you are probably a busy professional and I am an amateur in this field.

I shall explore this website, expand my understanding of the issues, and keep looking!

Cheers,
Jeff

 

[sylas]

I don't mean to tire you any further with my pesky questions and replies because you are probably a busy professional and I am an amateur in this field.

I shall explore this website, expand my understanding of the issues, and keep looking!

Cheers,
Jeff

Actually, I am not busy and not professional, and I enjoy exploring the issue. I've looked into this topic in a fair amount of detail, but as an interested amateur, as part of a general interest in physics and issues where it interacts with public education.

I wrote a post which attempts to explain the conventional picture of quantification of the warming effect of carbon dioxide. In brief, there is about 3.7 W/m² "forcing" for every doubling of CO2 concentrations (fairly accurately known) and roughly 0.8 degrees warming for every W/m² of forcing (only crudely known). That works out to about 3 degrees warming per doubling of CO2; though the uncertainties mean it could be anything from 2 to 4.5.

The post is: [thread=307685]Estimating the impact of CO2 on global mean temperature[/thread].

There is, of course, more than CO2 involved. It's the largest single factor in present times, but there are plenty of other factors involved, long and short term, which mean that climate change considers a lot more than this one factor.

Good luck with it all -- sylas

 

[cleanwater]

Sylas your statement "The warming effect of gases that absorb infrared radiation is pretty fundamental physics." is pure crap. It was proved by Niels Bohr that a gas is not heated by absorption of IR. If your statement were correct then the temperature in the atmosphere would increase with altitude and it is well known that it decreases.

 

[chriscolose]

Sylas your statement "The warming effect of gases that absorb infrared radiation is pretty fundamental physics." is pure crap. It was proved by Niels Bohr that a gas is not heated by absorption of IR. If your statement were correct then the temperature in the atmosphere would increase with altitude and it is well known that it decreases.

Actually the way the greenhouse effect works is pretty fundamental physics, and as people have pointed out already, the relevant spectrometry has been well tested in the lab. Unfortunately it involves a little more than just "gases heating up" when they absorb radiation, which isn't exactly how it works. The reason the temperature decreases with altitude is also something covered in the first week of undergraduate atmospheric science classes.

 

[sylas]

Sylas your statement "The warming effect of gases that absorb infrared radiation is pretty fundamental physics." is pure crap. It was proved by Niels Bohr that a gas is not heated by absorption of IR. If your statement were correct then the temperature in the atmosphere would increase with altitude and it is well known that it decreases.

Good grief, that is clueless.

A greenhouse gas is one that absorbs infrared radiation but is mostly transparent to the visible wavelengths. Hence a greenhouse gas is one that is heated by radiation from the surface.

And if you heat something from the surface, then you get temperature DECREASING with altitude.

There's actually a lot more to the temperature profile than this, as chris colose points out.

Even so, your comment is breathtakingly ignorant of basic physics. And I don't mind being a bit blunt in saying so if you use rude language with so little knowledge of physics yourself.

Cheers -- sylas

 

[Andre]

It should also be considered that a greenhouse gas emits infrared radiation, losing energy in the process, as much as it gains energy by absorpting infrared radiation.

So, since we have two more agents for transfer of 'heat'-eneregy, conduction, convection; it would be interesting to see what kind of role they play in the temperature of the atmosphere. The importance of convexion is generally estimated to be low, compared to radiation. However, radiation balances heating and cooling of the atmosphere but convection does not.

Parcels of surface air are heated by conduction (and radiation) decreasing their density so they will rise up (convection). A similar effect have horizontally moving air masses of different temperatures, where the warmer, less dense, air is forced over the cooler air (advection). Also this transport of energy higher into the atmosphere is enhanced considerably by the http://daphne.palomar.edu/jthorngren/latent.htm due to evaporation and condensation. Meanwhile, cooler air descends balancing the pressure. But there is no such thing as back convection or back advection, transferring the energy back down to the Earth surface.

So, without radiative greenhouse gasses, this convected heat would have accumulated in the atmosphere and it could be argued that this one way traffic of convection contributes significantly towards accumulating heating of the atmosphere, while the radiative greenhouse gasses moderate its heating effect, cooling it down again. See also Chilingar et al 2008 which is discussed in this thread.

these processes may also put the 'certainty' of heating or cooling effects in perspective, due to the variation in concentration of radiative gasses in the atmosphere.

*G. V. CHILINGAR, L. F. KHILYUK, and O. G. SOROKHTIN, 2008, Cooling of Atmosphere Due to CO2 Emission, Energy Sources, Part A, 30:1–9, 2008 ISSN: 1556-7036 print/1556-7230 online DOI: 10.1080/15567030701568727

 

[sylas]

It should also be considered that a greenhouse gas emits infrared radiation, losing energy in the process, as much as it gains energy by absorpting infrared radiation.

Good point. This is also known as Kirchoff's law; the emissivity of a radiator is equal to its absorptivity. This is frequency dependent. That is, a gas (or any other material) will interact with some wavelengths better than others... and that interaction applies for both emission and absorption. This is crucial for the basic physics of the atmospheric greenhouse effect.

We can see this on Earth... and in fact this is one of the ways we can be confident that temperature changes in the present are being driven by these atmospheric greenhouse interactions of certain gases with thermal radiation!

At any given altitude, at equilibrium the energy flowing up is equal to the energy flowing down. Any excess or deficit will go to heating up or cooling down the gas, driving it towards an equilibrium. Since the atmosphere interacts very weakly with visible light, the solar energy flowing down is mostly unimpeded. The Earth's surface radiates back up in thermal wavelengths; and the atmosphere is opaque to most of this radiation... mostly because of interactions with water and with carbon dioxide.

There is also energy flowing up from the surface by convection, and also by latent heat of evaporation of water. The atmosphere is thus mainly heated from below; and then it radiates also in turn, with the same wavelengths that it absorbs. The energy radiated from the atmosphere goes both upwards, and back down. This is the guts of the greenhouse effect. The surface receives most of the solar input, plus an additional flux of thermal radiation from the atmosphere.

If the atmosphere was dry nitrogen and oxygen only, then it would still be heated by convection; but the thermal radiation would escape straight out to space. The atmosphere would still be heated; but it would radiate very inefficiently; there would be minimal backradiation coming back down to the surface. Earth's temperature would be an equilibrium with solar radiation, substantially below the freezing point of water.

There's one very illuminating feature of how the atmospheric profile has been changing over recent decades as the planet has heated up somewhat. The stratosphere actually cools... very strongly... and this is driven mostly by greenhouse gases and their capacity to radiate more efficiently. In the atmosphere, temperatures fall with altitude up to the tropopause, which is extremely cold. Above this level, the radiation escaping to space is strongly depleted in infrared radiation, and this is directly measured. You can see great chunks cut out of the spectrum, particularly with the effects of water and carbon dioxide.

You DO still get radiation coming up at the wavelengths that interact with CO2... but that radiation is not coming from the surface. It comes mainly from the upper atmosphere, because the mean path length of thermal radiation is much reduced. Hence the radiation coming into the stratosphere which is able to interact with CO2 or H2O is weak and cold... colder indeed that the stratosphere itself. Hence the net effect of more effecient interaction with thermal radiation is that the stratosphere SHEDS heat more effectively than otherwise, and is becomes cooler as greenhouse gas concentrations increase.

I've given some descriptions of this, with references, in other threads. See, for example [post=2170740]msg #23[/post] of "Estimating the impact of CO2 on global mean temperature"; the first page of that thread also shows some spectra and energy flow diagrams ([post=2165483]msg #3[/post]).

So, since we have two more agents for transfer of 'heat'-eneregy, conduction, convection; it would be interesting to see what kind of role they play in the temperature of the atmosphere. The importance of convexion is generally estimated to be low, compared to radiation. However, radiation balances heating and cooling of the atmosphere but convection does not.

The thread I mention above gives some numbers, with references, that give a good idea of the magnitude of energy flows, as global averages. At the surface, the Earth absorbs about 161 W/m² of incoming solar radiation. By virtue of its own temperature, the surface radiates about 396 W/m² of radiation; and there is also a flux of about 17 W/m² as convection and 80 W/m² as latent heat of evaporation. So you are quite right; in terms of actual energy flux convection and latent heat is about 20% of the total. The thermal backradiation from the atmosphere is about 333 W/m²; less than the upwards radiation because of course it is cooler than the surface; but still actually the largest energy flux to the surface, on average.

Often, people just consider the difference between the up and down flux, in which case there is about 63 W/m² net radiation into the atmosphere from the surface; this is less than convention, but it is certainly positive; which means that the net effect of interaction with radiation is to heat the atmosphere. Another approach is to remove the radiation that escapes direct to space, in which case you have just 23 W/m² into the atmosphere from the surface.

Of course, this is a net positive; the net effect of interactions with radiation is to heat up the atmosphere, not to cool it.

As for "balance"... ALL these energy flows balance together; energy conservation does not distinguish. Also, the flux of thermal radiation reduces with altitude, because temperatures fall with altitude. So I don't think there's any real difference between radiant and other energy fluxes in terms of balance. Energy balance calculations have to consider special and radiant energy on the same footing.

Cheers -- sylas