Email from Alan Siddons, a former radiochemist, to Greenie Watch (h/t):
...it's not only the Second Law (heat always flows to a cooler zone) which invalidates trace gas heating theory but the First Law as well (energy can neither be created nor destroyed).
"Heat-trapping gases," you hear, and "Radiation goes in but can’t get out." Well then, what is every explanation of the greenhouse effect pointing at but a radiation valve? Since heat rays are prevented from exiting to space, it is claimed, they have nowhere else to go but back to the earth which, by absorbing them, becomes warmer.
The notion of a radiation valve snaps these concepts into focus: Without such a valve, it is imagined, infrared rays from the earth's solar-heated surface will pass freely into space. For every unit of sunlight going in, therefore, one unit of infrared goes out. Ergo, 1 - 1 = 0, zero referring to the heat gain. But with a proper valve in place no infrared is lost and the trapped rays are absorbed by the emitting surface, so the process goes thusly:
As you see, if the tenets of this theory are valid there can be no outcome other than a doubling of surface energy (a doubling at minimum, that is, since there's no reason to suppose that radiation from the now-warmer surface would not continue to be back-radiated, absorbed, and amplified in a "runaway" heating cascade).
As a real world application, such a valve could be approximated by common window glass or a dichroic filter. The irradiated surface could be anything similar to a blackbody, an ideal absorber-emitter, and a radiative heat gain of something above 0 would be observed. A working model of the greenhouse effect couldn't be made any simpler.
Simple as it is, though, no scientist in the world is able to construct a model that exhibits any radiative gain because the theory's tenets (called "the basic science") are not valid. On a theoretical basis alone, conservation of energy (the First Law) forbids a model like this from working. You can't obtain more energy than you put in. On an empirical basis too, however, as demonstrated by laboratory blackbodies, confined radiation only induces temperatures close to a theoretical blackbody limit, not a degree hotter. (The premise of greenhouse theory, remember, is that radiative confinement raises the earth's temperature above a blackbody limit, yet a laboratory blackbody --which is little more than a light trap -- exemplifies radiative confinement! The premise is self-contradictory.)
I urge you to notice that the valve's efficiency doesn't actually matter, either, because physical laws are violated even in a modest case. In some sense, in fact, the crimes get worse. For instance, let's install a 20% valve, so that 80% of the infrared escapes and 20% back-radiates.
In this case, 0.8 exits while 0.2 is "retained" by the surface. But 0.2 also radiates back to the surface, so it gains 0.4 in total (again, as a minimum: further back-radiation effects must arbitrarily be halted). In other words, even when the oft-mentioned "net flow" favors the outward movement of thermal energy (a modeling effort to satisfy the Second Law), the alleged heating effect still contradicts the First Law because you're getting more energy than you put in. Any furnace manufacturer would eagerly exploit such a loophole in the law if it existed.
But the problems don't stop there. Since the valve allows 80 percent of the infrared to escape, the same applies to the 40 percent that's been gained. So sum up the amount of radiation getting past the valve: 1.12 units -- more energy than is going in!
The whole model is nonsense. Here are two corollaries I can think of.
• Just like temperature, radiant energy flows do not add. Lumping two 70° balls of clay together doesn't result in a single ball that's 140°, nor do 70 watts per square meter beaming back onto a body that's radiating 70 raise it to 140. Frankly, it is stupid to think otherwise.
• Back-radiation cannot be absorbed by the emitter or else the conservation of energy law is meaningless. As I've noted before, the output of a weak battery can't be used as an input to recharge it.
Related: A greenhouse effect on the moon?