Model CO2 as Greenhouse Gas: Tips & Results

[vanesch]

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

 

[Evo]

Feel free to send me a pm.

He said impartial Ivan.

 

[chriscolose]

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

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

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



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

Vanesch,

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

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

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


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

 

[vanesch]

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

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

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

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

(current = 1/R x potential difference)

The different successive layers are series connections of these resistors.

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

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

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

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

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

 

[sylas]

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

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

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

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

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

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

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

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

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

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

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

Here is the full quote

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

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

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

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

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

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

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

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

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

Cheers -- sylas

 

[Andre]

You're too kind Sylas

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

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

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

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

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

 

[Skyhunter]

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

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

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

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

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

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

 

[sylas]

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

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

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

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

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

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

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

Cheers -- sylas

 

[BrianG]

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

 

[sylas]

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

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

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

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

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

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

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

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

For the record -- sylas

 

[BrianG]

I directly address the ESPERE experiment you cite:

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

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

 

[sylas]

I directly address the ESPERE experiment you cite:

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

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

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

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

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

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

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

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

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

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

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

Here are the basic facts.

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

Sylas

 

[Andre]

I directly address the ESPERE experiment you cite:

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

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

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

 

[BrianG]

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

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

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

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

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

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


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

 

[sylas]

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

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

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

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

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

----

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

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

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

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

Cheers -- sylas

 

[skypunter]

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

 

[chriscolose]

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

 

[sylas]

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

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

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

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

Cheers -- sylas

 

[BrianG]

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

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

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

 

[vanesch]

BrianG,

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

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

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

Thank you.

 

[BrianG]

BrianG,

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

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

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

Thank you.

If it's inappropriate, delete it.

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

 

[sylas]

If it's inappropriate, delete it.

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

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

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

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

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

Cheers -- sylas

 

[Richard111]

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

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

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

 

[sylas]

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

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

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

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

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

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

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

Cheers -- sylas

 

[Richard111]

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

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

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

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

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

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

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

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

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

Regards Richard

 

[Andre]

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

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

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

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

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

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

 

[sylas]

...

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

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

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

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

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

Energy balance

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

Forcing

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

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

Planck response

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

Feedback and sensitivity: the actual response

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

Lapse rate

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

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

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

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

Convection in basic atmospheric physics

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

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

Calculating a no-feedback Planck response to increased greenhouse gases

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

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

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

Summary

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

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

Cheers -- sylas

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

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

 

[Andre]

This is complete physical nonsense.

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

Or let's look at the individual steps

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

True / False?

 

[sylas]

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

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

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

Or let's look at the individual steps

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

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

True / False?

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

Cheers -- sylas

 

[Andre]

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

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

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

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

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

true/false?

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

Something else

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

Is convection / advection (negative) feedback or not?

Feedback is...

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

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

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