One may question the greenhouse effect on the grounds that it doesn't show up in the laboratory and hasn't been able to account for any historic climate change. And this is a most valid objection, after all, ultimately science is about explaining observed phenomena. But it is often said that the greenhouse effect is a necessary consequence of "the laws of nature". Also, many people skeptical to the conclusions of the IPCC believe that CO2 will cause some warming, just not that much. It is in fact plausible that by changing the composition of the atmosphere, living in that altered atmosphere will be somewhat different from living in the old atmosphere, but that is a truism and has nothing to do with science. The question is, will this change be adequately described by the so called "greenhouse effect"?
We will now go a step further and make an attempt to figure out what went wrong. Why isn't the greenhouse effect a necessary consequence of the laws of nature?
Let's first review some basic physics. We need to distinguish bewteen organized energy, for example translational kinetic energy, and disorganized energy in the form of heat. A single particle cannot possess disorganized energy, but a collection of particles can do that. Organized energy can be transformed into heat by dissipation. We can also extract work (organised energy) from heat but the second law of thermodynamics puts a limit to that process, not all heat can be converted into work.
Above you have an illustration of these concepts applied to an ideal gas enclosed in a rectangular volume. Lets now have a look at the greenhouse effect:
The arrows indicate electromagnetic radiation that is absorbed and emitted by the atmospheric layers. The atmosphere is in equilibrium when each layer emits the same amount of energy as it absorbs, and we recall that emmision is dependent on emmisivity/absorption and temperature, while absoption is not dependent on temperature. Now have a look at the first image again. See any similarities?
Marcus Aurelius once said "Of each particular thing ask: What is it in itself, what is its nature?". So let's ask that question about the arrows in the greenhouse diagram above. To me they indicate radiation pressure. You may respond, but the pressure is so insignificant compared to the atmospheric pressure. I respond, ok let's neglect it then.
If you throw a ball up in the air it doesn't suddenly stop and convert its kinetic energy into heat energy by itself. It can only do so by dissipation, which means interaction with the environment. An atmospheric layer can of course collide with the adjacent upper layer, but that layer is busy colliding with another layer and so on ad infinitum.
Other partly similar explanations has already been proposed by G&T (distinction between energy and heat) and Miskolci (saturated greenhouse effect). Also, check out Claes Johnson's article on blackbody radiation.