Shortly after the water condenses, the air finds a level of matching buoyancy and stops rising. This is the stratosphere, a zone of low water content where we’ll have none of the weather nonsense that we deal with down at sea level. It's called the stratosphere because it is stably stratified. Planes fly in the lower stratosphere for this reason. There are no storms, but it’s colder: minus forty to fifty degrees on average. (Celsius or Fahrenheit? At this point it doesn’t matter; -40 degrees is the temperature at which both temperature scales are the same.) The air will warm up if you keep rising, however, because the stratosphere, gets warmer the farther you go up. As such, it is stable: the thermodynamic equivalent of setting ping pong balls on top of your bathwater, rather than below it. But what causes heating at the top, something which would solve so many of our weather woes down in the troposphere? We started by saying that sunlight can’t warm the air because air is transparent. This is true for most of the visible wavelength light we receive, but not for ultraviolet wavelengths, which cause ozone formation. Ultraviolet light from the sun splits molecular oxygen (O 2 ) into two oxygen atoms, which can bond with another molecule of oxygen to form ozone (O 3 ). This process releases enough heat so that at the top of the stratosphere, where the air receives the most amount of ultraviolet radiation, the temperature hovers around freezing -- cold by tropospheric standards, but quite warm by local standards. The UV radiation is mostly absorbed in this part of the atmosphere, thankfully, and so doesn’t make it down to the surface where it can have truly deleterious effects on our DNA.