You know, I've just noticed this whole argument is not about physics at all. It's about the definition of the word "warm".

To me, "to warm" means "make less cold"

To ssat, "to warm" means to "raise the temperature"

My definition is straight out of vector physics, a definition which doesn't care about the starting point only the direction. ssat's definition requires that to "warm" something, the thing must get hotter that it was when it started.

Admittedly, ssat's definition matches more closely the everyday use of the word.

Using ssat's more everyday definition of the word warm, a colder body can never "warm" a hotter body. If you turn on an electric fire and it's so weak that it fails to raise your temperature, then the fire didn't "warm" you, even if the fire itself is warm. To me, used to vector physics, the fire still warms the person even if they don't get any hotter, because warm just means to me "add a positive temperature vector"

I understand now, and taking the word "warm" the way you define it, I agree back-radiation does not (and never can) warm the ground. Only the sun can do that. But back-radiation can stop it getting cold !

Sandy S,Jan 15, 2014 at 10:10

Mars may well serve to advance understanding but its all a bit beyond my budget and time! I would prefer to stay with the point I originally made on this thread which was about a different way of looking at how a temperature rise of Earth and its atmosphere may come about other than the one we are constantly pushed toward accepting - energy as heat, having entered the system circulates backwards radiatively and is the Greenhouse Effect.

My contention is that the energy entering the system warms the system not only by radiation transfer but also by conduction, specifically to whole atmosphere, via the radiative gasses. This process is slower than the speed-of-light incoming and outgoing of the system. We have 2-speed energy transfer. Therefore, over time, energy has accumulated in the system raising its average temperature over that of our moon, which, without an atmosphere, cannot experience this Greenhouse Effect. Eventually, nothing else changing, the system reaches an equilibrium: energy ceases to accumulate and outgoing radiative energy = incoming from the sun.

Now we change one variable by adding a small quantity of a radiative gas and let that be CO2. If that gas, by conduction, were to raise the temperature of the whole atmosphere (and my assertion here is that it would and by the mechanism I have described) then the difference between the atmosphere's temperature and the sink of space has increased. It would be possible to conclude that it will then merely radiate faster in order to attain equilibrium; to cool to its prior temperature. But that would be erroneous as it ignores Greenhouse Effect, we have caused lower speed energy to accumulate in the system by adding the additional CO2. What will happen is the effective radiating diameter of the atmosphere will change to maintain the temperature difference between it and space while accumulated energy maintains its, now raised, temperature. This is because temperature changes with height in the atmosphere and the added energy as heat has moved the emitting height higher, increasing the radiating diameter.

But what of surface temperatures? They increase also so that the difference between them and atmosphere is maintained. We see that additional CO2 has warmed both the surface and the atmosphere. It is the conservation of the flux through the system that has modified temperatures within it. It does not require flux reversals or unrealistic single-speed energy transfer to explain it.

What I hope the above will do is lead to a discussion about GE, not about whether it exists or not for that is a different argument, but about how it occurs, has Climate Science reached a correct understanding of it and if not, what are the implications to modelled projections of future climate?

ssat

about how it occurs, has Climate Science reached a correct understanding of it

No.

Martin, I expect so.

A lot of challenges to physics I see on these boards seem to be people quoting the 'classical' laws of physics. Unfortunately, the wording of these sometimes leaves a lot to be desired, meanings can be gleaned which weren't intended. The 2nd Law of Thermodynamics is a favourite.

Now: Jan 15, 2014 at 12:57 PM | TheBigYinJames

You know, I've just noticed this whole argument is not about physics at all. It's about the definition of the word "warm".
To me, "to warm" means "make less cold"

Then: Jan 13, 2014 at 5:32 PM | TheBigYinJames

A colder object can cause a warmer object to become warmer.

To ssat, "to warm" means to "raise the temperature"

A colder object can cause a warmer object to become warmer.

Yes, that was naughty of me. I always attach my ".. than it would be otherwise" to my statements, but appear to have forgotten on that sentence.

The full line should be

A colder object can cause a warmer object to become warmer than it would be otherwise (by stopping it cooling down so fast)

Having attempted to follow the above discsussion (from someone whose physics education ended with doing a couple of modules as a first year undergraduate as a subsidiary subject to my geology degree), I got the impression that ssat and BigYin were essentially agreeing but stuck on some semantic definition - it seems there is agreement that both agree that 'back radiation' reduces the rate of heat loss from a warmer (warmed by an external source) surface.

However, it was also agreed that of the outgoing LWIR energy absorbed by CO2 (so the spike around 14 microns wavelength) is not all re-emitted as long wave photons, but some (presumably most in the lower atmosphere, lessening with altititude and consequent lowering of gas pressure in the upper layers of the atmosphere) is transfered by collision with the hugely more abundant N and O in the air. Basic physics - hot gases rise (at least on a macro scale), so surely some/most (?) of the increased energy from GHG absorption is transferred to enhanced convection, leaving only a small fraction to be re-emitted to the surface, and which can therefore have an influence on the surface temperature.

The implied question to this is how much does this matter?

A second question is based on the assumption that the lower atmosphere would not be thermalised in the absence of GHGs (including water vapour). From my practical experience of spectrometry and spectroscopy, I am unconvinced by this assumption, and think that all the gases in the atmosphere absorb some 'background' energy across all wavelengths (hence the need for vacuum in AES spectroscopes), although accept that the absorption is much higher for specific molecules and wavelengths. When integrated across the range of wavelengths in the outgoing longwave radiation, how important is this background absorption, compared to the absorption at specific wavelengths?

Ian

A second question is based on the assumption that the lower atmosphere would not be thermalised in the absence of GHGs (including water vapour). From my practical experience of spectrometry and spectroscopy, I am unconvinced by this assumption

As usual in physics, there are few absolutes. The majority of the atmosphere (O2 and N2) don't thermalize much with insolation - but 'much' isn't 'nothing'. Obviously 'some' radiation will be absorbed - emissivity is not a step graph, it's a distribution curve - but we're on the tail end of the emissivity spectrum with those gases, the amounts compared with the total are small - so can be ignored when trying to explain the mechanism.

It's not 'missed' when doing energy budget calcs, though. if you look at the diagrams, e.g.

http://www.cgd.ucar.edu/cas/Topics/Fig1_GheatMap.png

You'll see the atmosphere does absorb some incoming insolation. the reason it's usually omitted from the explanation is that once it's thermalized, it's identical to longwave that has been to the ground first.

Ian,

Missing from the energy budget diagrams of the type linked to by me and later by TBYJ at 12:04, is time. Your observation that N and O are abundant is important in that regard because energy transfer via them is a slower process than radiative transfer. That slower process increases the energy within the system. Hence higher temperatures achieved over time.

Note that the diagram shows a net absorption of 0.9W. That would be a warming system as outgoing < incoming. For an equilibrium system, net absorbed would be 0.0W. How does the diagram describe GE with no changes in existing GHG? I don't see how it can and by extension, don't see how it explains anything.

ssat,

The diagram is not meant to demonstrate changes to the fluxes when changing atmospheric concentration. The diagram is merely there to show the main energy flows in and out of the main systems. It's snapshot in time. Trenberth's original one has been recently updated with new values, but the magnitudes are pretty much understood.

Who knows if changing the concentration of GHG change the fluxes at all? Who knows if they change to balance each other out (e.g. more back radiation, but more cloud albedo)? I don't know, nobody does. Especially not climate scientists, even if they pretend to. The science is so far away from understanding it, it's laughable.

(Note the diagram doesn't mention heat going into the deep ocean - haha! - so much for that being the big 'explanation' )

Although I understand the IR absorbance of CO2 (standard IR spectroscopy) I have always had doubts about the magnitude of the GHG effect. These doubts seem to be justified, given the recent temperature plateau. If for argument sake, the net consequence of GHG warming is much lower than expected then either negative feedbacks are reducing the warming, the GHG effect is less than expected or a combination of both.

Starting with the suggestion that the GHG effect is less than expected, I have been interested in trying to understand how the magnitude of the effect is arrived at.

It seems that they use the SB radiation from the sun (1367m/m2) and calculate how much impinges on the earth, assuming the earth to be a disc with an albedo of 0.3. This gives the 255 degrees about 33 less than measured at the surface.

If what I have said so far is accurate, then the next step would be to examine the above sentence in more detail to understand the assumptions that are implicit in the approach. For example, if two thirds of the earth is oceans and SW solar radiation penetrates the oceans to a depth of say 100m then does that not suggest massive energy consumption to warm a huge volume of sea that is not taken into account when just considering the warming of the surface of a disc?

How does the presence of an atmosphere interfere with the solar warming? They assume it is a window to the visible light, but I think it interacts with the UV component which is the high energy portion of the incoming spectrum.

These are just initial thoughts to illustrate my thinking.

http://earthobservatory.nasa.gov/Features/SORCE/sorce_02.php

This short article explains that 46-50% of the TSI is taken in by land and oceans. About 1% (UV) is removed by the upper atmosphere, 20-24% by the lower atmosphere (mainly IR) and 30% reflected back to space.

Schroedinger

Starting with the suggestion that the GHG effect is less than expected, I have been interested in trying to understand how the magnitude of the effect is arrived at.

And estimate of the 'magnitude' or at least the 'proportion' of the back radiation effect from CO2 can be arrived at by looking at the actual measured spectrum. e.g. http://scienceofdoom.files.wordpress.com/2010/07/dlr-spectrum-wisconsin-ellingson-1996.png

The measured graph will be flat apart the places we have emitting molecules - the so called 'atmospheric window', with peaks corresponding to different molecules. In this way we can measure the 'proportion' that CO2 contributes compared with the others, and it's usually estimated to be about 20%-30% of the whole. It's complicated by the H2O and CO2 bands overlapping to some extent.

Since CO2 concentration compared with H2O concentration is small, this is a large 'bang-for-buck' for CO2, which is why it is more important, and why "trace gas" arguments are bogus.

If back radiation is in addition to incoming radiation is it detectable as a peak/peaks at specific frequencies are these measurable when compared incoming solar radiation? I have always assumed this to be the case but have never actually seen a definitive statement as to a measured value.

sandy,

they always measure it at night, so it's only back radiation they are measuring. I'm sure you could probably pick out the peaks from a daytime graph, but the stuff shorter than 5 nm would be huge solar peaks, making the back radiation peaks look much smaller by comparison.

Posting problems this last few days, apologies.

He does have a point that the CO2 band (14-16 nanometres) where the big emission peak is represents a temperature below that of near the surface. But CO2 emission doesn't have much of a width, it can only absorb and emit in specific ranges of wavelengths - just because most of the atmosphere is warmer doesn't mean CO2 can suddenly start emitting at that higher temperature - it can only emit in the bands it can emit in. Also, up near the mesopause, the atmosphere is EXACTLY within this temperature range requires to emit 14-16 nanometres.

So not exactly a rebuttal, but more surprise that he uses the fact that CO2 only emits in specific frequencies which represent a temperature band which is below near surface temperatures as a way to 'disprove' the fact that they are doing so. It makes no sense to me. We can measure the photons, they are coming back. Does it really matter if they are colder than he expects?

stewgreen - what's the rebuttal ?

Can't do anything but support the man;

Consider a planet in space with an atmosphere of non-radiating gas and an internal heat source. The atmosphere will attain an average temperature from conduction and convection and the surface an average temperature by conduction from the interior. Its average radiating temperature will be that dictated by S-B law, total flux will be equal to total internal energy production and its radiating diameter will that of the planet's surface.

The same planet with an addition of a radiating gas to the atmosphere will have the same average radiating temperature as before as dictated by the same S-B Law, flux will equal internal energy production as before but radiating diameter will have increased.

As the surface no longer radiates to the cold temperature of space but to the warmer temperature of the atmosphere which then radiates to space then the Greenhouse Effect will manifest itself as an increased surface temperature (from Newton's Law of Cooling) and which can only be measured at the surface: from space, the increased surface temperature would be concealed behind the unchanged average radiating temperature, now at some height in the atmosphere.

From the above we can see that any changes measured in average radiating temperature would come only from changes in internal energy production. If energy production was now moved to outside the atmosphere to a sun, and the same procedure followed as described above, changes in average radiating temperature would indicate variance in that sun's output. In neither scenario would that change indicate increased surface temperature from Greenhouse Effect.

As outgoing radiation (excluding reflected) is in the infra-red spectrum, viewing the two scenarios from outside the atmosphere with night-vision, the observer would notice the increase in diameter but see no change in intensity of illumination (OLR).

Currently popular climate science considers changes in OLR to be caused by a continually increasing concentration of (mainly CO2) radiative gasses in the atmosphere. This is basic mistake number 1. It is total concentration that matters. As anthropogenic sources of greenhouse gasses are tiny then so is their effect on average radiating diameter.

Martin A

In my post, Jan 14, 2014 at 11:57 AM and the one directly before yours I use the term to indicate that it is the proportionality of temperature difference that is important in the rate of heat energy transfer from a body to its surroundings. That holds true for a body in a vacuum or in a living room even though one might use different formulae when calculating for each scenario. In the former, the basic S-B Law modified* for a grey body radiating to the surrounding temperature of space and receiving radiation back from it would be apposite whereas in the latter, conduction and convection should be additionally considered.

* q = ε σ [T1^4 - T2^4] A Where q is in Watts, ε is grey-body emissivity, σ is S-B constant, T1 & T2 are the different temperatures and A is area. The variables between a planet with a non-radiative atmosphere and then a radiative one are ε and A. Fixed are q (conservation of energy) and T (S-B Law relative to absolute zero).

Martin, if I might quote you;
“I've noticed that, when thinking about physics problems, it's often better to avoid discussions of what-causes-what and simply figure out what happens.”

Martin, I know you skipped most of this thread because it looked like bickering, but try to read it all before committing to this new exchange. You may choose not to afterwards.