Does the Greenhouse Effect Contradict the 2nd Law of Thermodynamics?
Occasionally I hear people claim that the greenhouse effect isn't real because it would contradict the 2nd law of thermodynamics. The idea behind this is that the atmosphere is cooler than the Earth's surface, and the 2nd law of thermodynamics says that heat always goes from hot to cold. Therefore, the Earth's atmosphere can't heat the Earth's surface. Therefore, the greenhouse effect can't exist in a universe in which the 2nd law of thermodynamics is operable. A Simple Explanation The silliness of this objection can become apparent with a simple analogy. If you walk outside with a thin t-shirt on a cold day (let's say 20°F), you'll quickly feel cold, and the surface of your skin will be significantly colder than normal. If you find a winter coat outside, its temperature will be 20°F. But if you put it on, you will begin to warm. It's not that the coat is generating heat and sending it to your body. It's simply slowing down the rate at which ther...