rhoda, if you haven't already, ScienceOfDoom has a lot of articles about this.

Go to it, Dung! :) I don't know how to, though.

Because CO2 has a tiny heat capacity, I showed you the graph earlier. It emits rather than vibrate.

Case 1: CO2 doesn't backscatter IR:
100 photons enter the balloon from the left, 100 from the right.
Nothing interferes with the IR.
Result: 100 photons exit from the right, 100 photons exist from the left
Case 2: CO2 backscatters the radiation
100 photons enter the balloon from the left, 100 from the right.
50 from the left are scattered and go back out the left, 50 keep going
50 from the right are scattered and go back out the right, 50 keep going
Result: 100 photons exit from the right, 100 photons exist from the left

I proposed a simple experiment at the start of the thread that gets round this.
Hang two metal spheres in the center of two balloons, one with 'air' and one with an increase concentration of CO2, electrically heat them to the same temperature then switch the heater off.

Compare the cooling of the two spheres over time.

Then re-run the experiment with the gasses swapped to take any equipment anomalies out of the equation.

If the one in the CO2 filled balloon cools slower then this shows the CO2 is having _some_ green house/ blanketing effect.

If they cool at the same rate then....

"that gets round this."

Should read "that doesn't rely on external heating"

I would expect they'd need to be pretty big balloons to get a measurable effect, but I think the principle is sound. I'm not even sure you'd need to heat them. By definition, the one in more CO2 would settle to a higher temperature, but the cooling trends might be easier to compare than static figures.

It might be a good idea to repeat with H2O as the GHG for a more measurable effect.

Good thinking Dung. I suspect the experiment was done that way because of the popular but mistaken belief that CO2 'warms' things. So it makes sense to bag it up and measure the temperature. When they didn't find any, this said nothing about the GHE, however.

When you realise it's the backscattered IR heating the ground, not the CO2 itself, you can see why it won't work. The ground under it is already being heated by kilometers of GHGs above it, the little dense pocket of CO2 near to it won't make much of a difference. It might have worked on the moon, with no air, and a large balloon.

Dung, thanks for the thoughtful post.

Over on that thread you have said things like 'Slayers should be ignored because the science says they are wrong'.

I don't think I actually said those words, but I'm too lazy to go and check :) My thinking is more along the lines of 'slayers ARE being ignored because the science says they are wrong' - whether they should be or not is another thing. I'm a fan of science, always have been (I have three science degrees!) so although I think there has been a lot of skullduggery and ranks-closing within the scientific profession I don't let that interfere with my belief in Science. So while I'm on the side of those who want to see certain bad apples put out to pasture, I am dead against anything which seeks to attack, misuse or corrupt Science itself. This means I feel defensive now and again.

First I do not believe anyone on the planet can stand up and with any justification state that they know exactly what happens and that anyone else who disagrees is wrong,

Me neither, part of core skepticism is there are whole parts of this system we don't understand, so it is stupid of anyone to say the temperature in 2100 will be x. We don't know enough, that's why we're all here.

But even though we don't know enough about the whole system, we do know quite a lot about single mechanisms within this system. We know how the constituent parts of the hydrological cycle work. We know how pressure fronts and winds form. We understand convection. We understand the ozone layer. And we know about the radiative GHE.

We may not understand how much each of these mechanisms contribute an an overall climate temperature, in fact I would say our knowledge is woefully inadequate. But that doesn't mean the mechanisms isn't understood, just how they act in combination.

All through these questions and answer sessions, I have been explaining and defending the GHE. At no point have I claimed that it is the sole mechanism by which the average temperature of the planet is reached, because i don't believe it is the sole mechanism - it's one of many mechanisms which can have an affect on the temperature.

There seems to be a common misconception that if you 'believe' in the GHE then by definition, you have to 'believe' in the whole alarmist story, and that the only way to 'disprove' AGW is to somehow 'disprove' the GHE. They have become synonymous in people's minds. The GHE is the demon.

I'd like to separate them again in people's minds

The GHE is just that.. an effect. It's a well understood physical process, all of the constituent parts are well understood and are not in dispute by science.

The GHE as a contributor to a rising temperature trend. Unproven, in my opinion. It's a hypothesis, it has a physical basis which is feasible, but it's far from being proven.

I understand your need for an experiment to prove definitively that the GHE is a real effect, I'd love to see one as well. The large balloon on the moon would be a great one, but expensive. But to say we're swapping theories is giving the alternative theories more scientific credibility than they've earned. It's more a case of 'refute this or it's true' which is an adversarial legalistic tactic I don't really like.

When papers such as N&Z come along, they never say "here's another effect that might contribute part of the observed warming" No they always have to be a replacement mechanism, GHE has to be rejected COMPLETELY. This is what always gets my "bad smell" sensors out. As soon as the GHE is required to be completely abandoned by a theory, then I start to wonder why it's so important to them that it be rejected. Can't a new mechanism explain part of it? Why does it need to be all?

I really like your final paragraph about the effect of adding more CO2 won't have any more effect since it's all already being intercepted and scattered. I'm not going to try to counter it, because it has nothing to do with the defence of the GHE itself. It's actually an argument which takes the reality of the GHE as its base. Given the GHE, what does adding more CO2 do? There is a stream of skepticism which revolves completely around this 'optical depth' argument, and it's very interesting.

On a more general note, people seem to have enjoyed this thread. I think it's because, as the ancient Greeks found out, a dialogue of questions and answers is a fantastic learning tool. The protagonist gets to make a case, and an antagonist gets to ask a lot of awkward questions. At the end, a reader can judge the 'performance' of the theory and get a feel in their minds if it holds together. Thank you very much Dung (and others, lapogus etc) for being my antagonists :)

This is going to be my final word on the GHE. I think everyone knows by now I put it right in the middle of the 'confirmed' set of theories along with gravity, kinetics et al. Others may still be in doubt about how 'real' it is, which is fine, and if someone could come up with an experiment which could confirm the GHE, as an educational tool in itself would be a massive boon for everyone. Obviously I believe it would confirm the GHE :) AGW is a completely different kettle of fish....

From now on, I'll restrict my comments here to discussing and commenting on actual proposed experiments, feasibility and theoretical basis.

Thanks for a great thread!

I'm quite happy to chip in on discussions about whether an experiment would or wouldn't test an aspect of the GHE, I could have saved the guy with the balloons a lot of time :)

At the moment, the best suggestion is the heated sphere in a mylar balloon of GHG and one in normal air, or an N2/O2 mix. It would be interesting to see if we could work out what volume of CO2 would produce say 1 degree of heat difference purely from gas absorption equations etc. I have a hunch it would need to be a pretty massive balloon.

I know it's not a linear relationship, but for a laugh....10km of GHG produces 33K warming, so to get 1/2 degree we'd need a balloon.... 300m wide.... that's a big balloon :)

Is it possible to measure, at the surface, the total w/sqm of radiation and also the w/sqm of radiation in the wavelengths that CO2 can absorb?

Yes, you'd need a spectrum analyser.

Is it possible to measure the amount of that wattage absorbed by a cubic metre of atmospheric CO2 at various altitudes?

Well apart from the problem of getting the kit to the actual altitude, yes. Might be easier to reproduce the pressure, composition and temperature in the lab. Remember it's absorbed and re-emitted, it doesn't just disappear. Here's a paper you may want to read (skip the GW crap at the start)

Your tube experiment would only measure absorption of IR by CO2, something already proven in the lab. It wouldn't show any GHE.

Popular science video demonstrating IR absorption - yes they could have faked it, but easy to check, looks like less than £500's worth of equipment.

Yeah I know, I wasn't commenting on him as such, I find popularist science presenters like him and Cocksy annoying, but as a repeatable experiment it looks kind of cheap to do.

The reason I don't think that is faked is when you look at the candle, you can see it's mylar/clingfilm covering the end of the tube - something he didn't mention but is relevant to the experiment. Also, not all the image disappeared, the lighter outer area of the candle (cooler) remained on the screen, which was a wavelentgh effect he also didn't mention, but which added believability to it for me.

Remember, mindless advocates can be complete ****s but the science still be right!

Can't we witness, every day, an experiment that shows the greenhouse effect and the contribution of CO2. I speak of the night time temperatures in the desert compared to the night time temperatures in the tropics and sub-tropics.

The desert tempertures, where there is no water vapour drip by 30C or so when the sun goes down, while the tropics, with plenty of water vapour barely drop at all.

Or am I talking complete bollocks, as usual?