No one disputes that, right? It's established science, yes?
One thing we can get out of the way immediately is that it doesn’t work in the same way as a greenhouse. There used to be a theory, dating back to Joseph Fourier in 1824, that visible radiation could enter through the transparent glass, but because glass is opaque to infrared, when it is re-emitted it gets trapped. Fourier proposed that gases in the atmosphere could act the same way. This theory was proved wrong for actual greenhouses in 1909 by Professor Wood of John Hopkins University. An experiment comparing a pane of glass to a pane of crystallised rock salt (Sodium Chloride) which is totally transparent to infrared found no difference in temperature. In fact, greenhouses work by preventing convection, a mechanism that is of course impossible to freely floating CO2.
The above paragraph is taken from PaAnnoyed's superb post at Counting Cats, which helpfully clarifies the physics of the so-called Greenhouse Effect: it's worth reading the whole post, but I'll present a quick summary.
Some of you might remember that, a few weeks ago, I published a piece pointing out that the approximate mass of Earth's atmosphere is...
... about five quadrillion (5x1015) tonnes, three quarters of which is within about 11 km (6.8 mi; 36,000 ft) of the surface.
This is, you will not be surprised to know, because I was researching the greenhouse gas effect myself: alas, a lack of time meant that I hadn't got around the writing the post—and now I have no need to do so.
So, if the Greenhouse Effect has nothing to do with greenhouses, then why is the Earth warmer than it should be? And why is the mass of the atmosphere relevant? Simples...
What keeps the layer at 10 km so cold? –54 C is far below the –24 C we expect on energy-balance grounds, so it can’t be by radiating to space. And the fact that there is a straight line all the way down to the ground suggests that whatever the mechanism is, it’s the same one that keeps the surface at +14 C. Straight lines don’t happen by accident.
I won’t keep you in suspense any longer. The answer is pressure. Because of the weight of air, the pressure at the surface is greater than it is higher up. This means that if air moves up and down, the pressure changes, and the air expands or is compressed. And when air is compressed its temperature increases.
Air is driven to circulate up and down by convection. As it rises, it expands and its temperature drops. As it descends, it is compressed and its temperature rises. This maintains a constant temperature gradient of about 6 C/km. (It would be bigger, but evaporation of water carries heat upwards too, which somewhat counteracts the effect.)
No heat passes in to or out of the air to effect this change. It is solely an effect of the changing pressure. (If you really want to know, the compression does ‘work’ on the gas, which increases its internal energy. It doesn’t come from any flow of heat or radiation.)
This temperature gradient is called the adiabatic lapse rate, and is an absolutely standard bit of physics.
Is that all clear? Good. Now, let's move onto the second part...
When we look at the Earth in infrared wavelengths, we see it merrily glowing away, like a coal ember, radiating all the heat it has absorbed from the sun. But unlike the view in visible light, where we can clearly see the surface, in infrared the atmosphere is fuzzy and opaque. It is full of water vapour, and a few other trace gases, that fog our view of the surface. And so when we ask what temperature the surface of the Earth should radiate at, the surface we see isn’t solid ground, but this fuzzy layer high up in the air. And therefore, it is this surface that settles down to –24 C, to radiate exactly the right amount of heat away.
It is about 4 km up, and held at –24 C by the heat rising from below balancing radiation directly to space. Below it, compression increases the temperature. Above it, decompression lowers it. The actual mechanism and explanation for the Greenhouse Effect is in fact pressure. To be specific, it is the pressure difference between the surface and the average altitude from which heat radiates to outer space. Moreover, it is the exact same mechanism by which the upper atmosphere is cooled to –54 C, and there is no way you can explain a massive cooling by heat being in any sense “trapped”.
Heat is not trapped by absorption by CO2. That is Wrong, Wrong, Wrong! Such trapping does go on, but it has no long-term effect on the temperature because the adiabatic lapse rate has overriding control. You can even theoretically get a greenhouse effect with no greenhouse gases at all! All you need is some high altitude cloud to radiate heat to space.
So, given that the standard Greenhouse Effect model is... well... let's call it "simplified" rather than "a colossal pack of lies", why are people still banging on about CO2 trapping warm the heat?
Well, because CO2 does have some minor effects.
Now supposedly, according to rather more complicated calculations, doubling CO2 levels in Earth’s atmosphere will raise the average altitude of emission about 150 m, which will therefore raise the pressure difference and hence the surface temperature about 1.1 C. If we raise CO2 by only 40%, surface temperature will go up about half that. So we had half a degree last century (an amount too small to reliably measure). We’ll have half a degree next century. And that’s all the standard Greenhouse Effect can give you.
As PaAnnoyed points out, to get any more than that requires that you factor in a whole bunch of other, less well understood effects—as well as a bunch of Chaotic modelling (which are, by their very nature, not closely understood or predicted).
And no, as PaAnnoyed also explains, Venus is not an example of "runaway global warming"—anyone who tells you that "Venus is what will happen to Earth" is either ignorant or lying. Or both.
As I said, you really need to go and read the whole post, but I do think that we can put to bed the whole concept of CO2 "trapping" heat. Further, I think that we really ought to stop talking about the "Greenhouse Effect" because, having come to mean what it does, it is entirely misleading.
In the meantime, Kerry McCarthy has put an inflammatory title to a post by Next Left that—quite reasonably—points out that many Tory bloggers (and some non-Tories, such as your humble Devil) are somewhat at odds with the stated policy of the Conservative front bench on the issue of climate change.
But the simple fact is that the Tory front bench is extraordinarily short of anyone with any kind of scientific credentials whatsoever. In fact, like the LibDim and NuLabour benches, the Tories' representatives are only really experts in how to steal money off the taxpayers of Britain.
The anthropogenic climate change hoax gives our irredeemably corrupt politicos ample excuse to do precisely that—are you surprised that they have wholeheartedly embraced this massive fraud?
UPDATE: Timmy has commented on this piece and what he says about the IPCC is quite correct: his error lies in ascribing certain motives to your humble Devil.
The result of which is that this explanation of atmospheric physics is not some great “gotcha” showing that the whole climate change set of prognostications is wrong.
Indeed. As I have said over there, I was not intending this as yet another proof that anthropogenic climate change is a colossal hoax—surely I have published enough of those by now.
No, what I intended to do was merely to educate: to show people that the Greenhouse Effect has nothing to do with greenhouses, and that CO2 does not affect the Earth's temperature in the way that most people think it does.
The desire to do so was inspired by reading a number of posts in which bloggers or MSM reporters stated something like "the Greenhouse Effect is not in dispute" or "everyone agrees that CO2 is a Greenhouse Gas" or "no one denies that CO2 traps heat in the atmosphere", and then proceeded to show that they didn't understand how the Greenhouse Effect actually operates.
So, as I said, this article was not supposed to be a "gotcha"—merely educational. After all, I doubt that they teach the truth in schools anymore...