Grendel wrote on May 2^nd, 2010 at 2:23am:


Yeah, let's do that. Nobody is winning or losing anything here.

Re the upper atmosphere, it's reasonably correct, but think in terms of the low density of the atmosphere at that level and think in terms of specific heat capacity (remember SMDelta T from physics? )

Now when you look at the relative mass of that part of the atmosphere compared to the troposphere, the fact that it's cooler up there will have 4/5 of very little effect on the troposphere.

Now that's probably an ill-considered response but I'll read that article in more detail and comment further.

ok.... (edit)

Just imagine a CO2 molecule at the level of the mesosphere. An infrared photon hits it and it re-emits it in a random direction. Thinking back to the dandelion seed head analogy, at that level the probability of the IR photon escaping to space is much higher because of the curvature of the Earth and the fact that there are very few CO2 molecules to hit (and practically zero water molecules). Even if it's emitted slightly below "waist" level it only has a very thin layer of atmosphere to pass through before it ends up in space. So it's correct to state that it actually radiates more energy to space than it redirects downwards.

However, as I stated before, it's an incredibly small effect, and by the time the IR photons reach the mesosphere, it's all over red rover. The main warming effect is happening lower in the atmosphere.

I have a friend in the States who is an Atmospheric Physicist. If you think that explanation is lame, I'll get a more detailed explanation from him.

Grendel wrote on May 2^nd, 2010 at 4:11pm:


That argument is ancient history. It was argued out during the 1930's and 40's. I'll obviously need to expand on that answer, but I'm busy at the moment.
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It actually 'gets hit' last. The Long Wave Infrared is the key to the whole thing. That's coming from the earth (black body radiation). No disrespect intended, but I thought you knew that. Sorry if I haven't made that clear.

The effect on Incident sunlight is miniscule by comparison to the effect on emitted LW infrared.

I can see I'm going to come up with some good references instead of shooting from the hip here. Leave it with me and I'll provide a fuller explanation, but if you look at the diagram, the red represents downgoing Solar radiation (mostly visible and near IR), and the blue represents emitted blackbody radiation (Long wave infrared)

The Greenhouse effect acts on the latter.  Make sense?

Also note the spectrum of CO2. You notice how there is a heavy absorption band around 10 microns? That's what we're talking about.

The same applies to water as we said before. Water accounts for about double the greenhouse effect of CO2.  Every climate scientist in the world knows this

I can see that you don't quite grasp the Greenhouse Effect.  (I don't mean that in any sense other than factual)

The Sun's radiation is mostly in the visible spectrum. Look at the CO2 contribution and you'll see how much of that is absorbed (4/5 of FA) Basically the radiation hits the troposphere and Earth's surface where it's absorbed and it heats up the Earth.

OK so far?

The Earth emits blackbody radiation and that's where the Greenhouse effect comes in. Now as far as CO2 in the upper atmosphere is concerned, that has a negligible effect on incident radiation (Look at the spectrum and you'll see why.) Water vapour on the other hand has a considerable effect. It's the main reason for absorption of Solar Energy, and that occurs mainly in the troposphere.

As well as that, there are albedo effects (eg clouds and ice), which mean that approximately 30% of the solar radiation is reflected back into space, but that has nothing to do with CO2.

Looking at that red curve, do you see the chunks missing from it? Take a look at the relative contributions (The graphs below) and you'll see what's responsible for that effect. (The upper stratosphere is bone dry.)

Can you see now why CO2 has very little effect on incident solar radiation?  Again not trying to be sarcastic, but can you interpret the spectra? (That's a genuine question - if you can't, I'll break down the explanation further)

Incidentally, do you notice the curve for Rayleigh scattering up on the UV end? Ever wonder why the sky is blue? - there's your answer.

Grendel wrote on May 2^nd, 2010 at 8:29pm:


The input is the incident radiation from the sun (no brainer), however the overwhelming reason that the Earth retains its heat is the Greenhouse effect, and that is connected with how much of the Earth's radiation is radiated into space.

Do you understand why the Sun emits mainly around the visible while the Earth radiates in the Long wave portion of Infrared?

The key is the The Stefan–Boltzmann law.  The frequency, which is proportional to Energy [E = H(nu)],   is proportional to the fourth power of the temperature of the object.

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Correct. Hopefully we're on te same wavelength here. I've tried to explain this before. See the sticky notes. Nobody is claiming that it's simple. If it was simple, you wouldn't need general circulation models to predict future climate scenarios - accurately.

Climate models are just systems of differential equations based on the basic laws of physics, fluid motion, and chemistry.  

If you want accurate answers, you have to take a lot of variables into account.

The radiative forcing equations alone incorporate a great deal of  physics,  and chemistry.

What we do understand extremely well is what happens when you change one variable in a complex system, and in the case of global warming,  the variable that we are currently changing is atmospheric CO2 (and other GHG's) concentration.  

You are a patient man, Muso (applies to both topics)