A frequent claim by climate alarmists is that global warming due to man-made GHGs is “simple physics”. And it is true that some parts of it are simple, for instance that if more heat is coming in than is getting out the planet will warm. But most of those making this claim are not, to put it gently, well-placed to judge what is simple and what is not. Very early in CDN’s career, for instance, we did a video “The ‘Simple Physics’ Slogan“ in which we interviewed, of all things, a physicist, William van Wijngaarden of York University, who among other things discussed the various “transitions” whereby five key greenhouse gases, CO2, ozone, methane, nitrous oxide and crucially water vapour, absorb heat rather than permitting it to escape the atmosphere, explaining “we’ve considered several hundred thousand different transitions.” And we want to ask most in the “simple physics” crowd what they make of, for instance, ΔE=hv=hc/λ. (From p. 14 of Theories and Predictions on Ozone Depletion and Climate Change) by Professor Qing-Bin Lu of Waterloo, with whom we just did a webinar.) But of course it’s a difficulty for less dogmatic people as well that complex mathematics can be hard to follow. So it’s important that everyone keep an eye on something that is simple: regardless of how elegant or intimidating the math, the crucial test of a theory is whether it explains known current phenomena and predicts knowable future ones. In the case of Prof. Lu’s theory, the key empirical data is that temperature records from the last half-century fit exceptionally well with atmospheric concentrations of CFCs, not CO2. And as Jim Mason wrote in an article in C2C Journal in the fall of 2024 to which our attention was just drawn, there are good physics reasons to doubt that CO2 could explain temperature, let alone that it correlates sufficiently to justify the enforced orthodoxy of the “ruling paradigm” that it does so.

Mason’s article, of all things, discusses research by that actual physicist William van Wijngaarden along with another actual physicist, the irrepressible Will Happer of Princeton. And that research covers something that is, in principle, simple physics, even if it gets messy once the deltas and lambdas come calling. It is that once you have painted over part of a window so light cannot penetrate it, adding more paint to that part does not make the room any darker.

Oh, is that physics? Yes, by analogy. You see, the core of the “simple physics” of man-made climate change is that certain key gases, including the five listed above, are transparent to incoming solar radiation in the form of visible light. It is why you can see through the air. But those gases, crucially, are not transparent to outgoing “thermal radiation” aka sunlight that, having reached the surface of the Earth and been absorbed, has turned into infrared light aka heat. And so some of the energy that came in unhindered gets absorbed and scattered in all directions, in the process causing hundreds of thousands of transitions including “Electronic transitions”, “Molecular vibrations” and “Molecular rotations”. (We told you it got complicated.) Which is often depicted in comic-book form as the gasses forming a blanket around the earth, a highly suitable metaphor for small children.

For adults it’s a metaphor that fails where it matters most. Different gasses absorb outgoing radiation at different frequencies. So if you consider the entire spectrum as a window, CO2 paints over part of it, water vapour another part, methane another and so on. Or rather, they paint over different parts and in some cases also the same part.

Now, we said above “painted over part of a window so light cannot penetrate it”. And the question of the completeness of the coverage even in that part is crucial here. Obviously if there was only one molecule of CO2 in the atmosphere it would absorb heat at a certain frequency or set of same. But only a tiny bit. However as you add more CO2, it not only eventually covers the entire sky to some extent, it also covers it more thickly, so that there’s not just some CO2 in the way of the thermal radiation everywhere, there’s an increasingly thick column of it everywhere, so energy that gets past the first molecule in the stack will hit one higher up and so on.

Of course at no point will the CO2, no matter how much you add, start absorbing in parts of the spectrum where it doesn’t absorb. But it will get to the point that in those parts that it does absorb, the coverage is essentially complete. That bit of the window is entirely opaque. Nothing is getting through, and so adding more CO2 will not have any effect.

It does also matter that the absorption spectra of CO2 and water vapour overlap to some degree, because if there’s already enough water vapour to “saturate” at that frequency, again making that part of our metaphorical “window” opaque, it doesn’t matter how much CO2 you slap on. It’s already black. But CO2 and H20 don’t entirely overlap. And so it is indeed a crucial question how much CO2 is sufficient to absorb virtually all outgoing heat at the relevant frequencies, at which point it wouldn’t matter if the amount in the atmosphere increased. Not even if it tripled.

The amount of extra heat absorbed if you add CO2 is necessarily a logarithmic curve, which is mathematics-speak for one that grows more and more slowly until it becomes a nearly horizontal line. And though it never quite gets there, as the paper by Happer and Wijngaarden argues, from first principles, there must be a point at which half of the “LWR” (that’s “Long Wave Radiation”) that could be absorbed is absorbed. They call that point “C” (for “Concentration” but hey, it wasn’t us.) And because of the logarithmic curve it means that at 2C, ¾ of the LWR at that frequency is absorbed. At 3C it reaches 7/8ths and by 10C it’s 99.9.

You’ll notice that the fraction absorbed by each extra unit of C keeps falling; the curve bends downward. But as it does so, it approaches 100% because the reason it’s falling is that there’s less and less left to absorb. With the obvious consequence that adding more CO2 has a vanishingly small impact on warming.

The “Enhanced CO2 Effect Hypothesis,” as Javier Vinós has dubbed it, looks pretty good if you only consider the latter part of the 20^th century. But if you go backwards, or forward, it performs extremely poorly. Prof. Lu’s theory about CFCs does better on the face of it, which doesn’t mean everyone should accept it and stop thinking. It means they should think hard about it, and consider ways of testing it.

Above all, simple physics is that theories are only as good as their predictions, and are strengthened or weakened by experiment not by ranting about deniers.

There. That wasn’t so hard, was it?