text: This is where most of the earth's infrared radiation is being lost. It is from clear air, in between the clouds, that is sinking. Its the humidity of this layer that is most important to global warming theory. OK? The humidity of this layer. Where does this layer get its humidity? It gets it from these rainfall systems. If you watch the next thunderstorm that you see, the top of the thunderstorm spreads out; that anvil material spreads out in the clouds. The clouds spread out in the upper troposphere out to the side and then disappear. That's because they are re-evaporating - that's what moistens the troposphere. It is the detrain cloud material from these rain systems that then moistens this layer. This layer and how moist it is the moisture mostly controls how much infrared radiation is lost to space.