Most of us, and by "us" I mean everyone who entered the 21st century already an adult, and is still here: most of us have at some point heard a common explanation of the causes of climate change, in terms of a greenhouse. It is this: CO2 in the atmosphere prevents infrared light from escaping into space. This means that, as in an artificial greenhouse, more light gets in than can get out, so over time the temperature rises. To this, climate change skeptics often reply: the absorption of infrared light is saturated at carbon dioxide levels well below those of the earth's atmosphere. If the saturation point is X, then the move from an X +2 level to an X + 20 level can't increase the infrared light, and so can't increase the heat. So let's get busy digging up or drilling for more of those fossil fuels! That is a fallacious argument. But it can be difficult to see this because the metaphor is faulty. A greenhouse has a single surface that blocks the infrared...