Greenhouse Effect Explained

It seems in spite of millions of people using the expression, "Greenhouse Effect", on a daily basis, very few people actually know how it works. Add to that, occasionally we find someone questioning whether, or not, they should "believe in" the Greenhouse Effect, which is just a little bit crazy. After all, we are talking about physical facts here. Does anyone talk about "believing in" the law of gravity?

So it seems there should be available on the web, an easily understood explanation, preferably with appended detail sections, so anyone that's interested can find out how the Greenhouse Effect works. A couple searches have turned up nothing that fits this description, so I want to write one. In doing so, I really want feedback from knowledgeable people, ultimately to come up with something that's easy to understand, simplifying perhaps, the underlying physics, but not twisting it.

So, starting with a bare sketch. All physical objects radiate energy in the form of electromagnetic waves, and the frequency of the radiation is dependent on the surface temperature of the object. Hotter objects radiate at higher frequencies.

Light is a form of electromagnetic waves, and it happens that objects that are as warm as the Earth radiate in the frequency range of infrared light. Objects that are as hot as the sun radiate in the range of blue, violet and ultra-violet. This is one of the important facts involved in the Greenhouse Effect.

Another important fact is different gases don't all allow all frequencies of light to pass equally well. This fact is a little hard to accept because we don't routinely see the effect (except for one effect, the blue sky). An important example is the fact that carbon dioxide is quite transparent to visible light, and ultra-violet light, but much less transparent to infrared light.

These two facts come together to explain the Greenhouse Effect as follows: Energy is radiated from the sun and passes rather easily through the Earth's atmosphere, and is absorbed by the Earth, which warms the Earth. The Earth, in it's turn, according to its surface temperature, radiates some of the energy back, but now the frequency of the radiation has been changed to infrared. This lower-frequency radiation runs into gases like carbon dioxide in our atmosphere, and it is scattered, or reflected back. It doesn't get away, so the surface of the Earth, and the atmosphere become slightly warmer.

This is the Greenhouse Effect. The more carbon dioxide, and other "greenhouse gases", there are in the atmosphere, the better insulated the Earth becomes. There have always been greenhouse gases in the atmosphere, and the Earth has always been insulated by them, but more greenhouse gases mean more insulation, and a warmer Earth.