system
Given the following post, respond as if you're commenting on Reddit:
human
How come it's colder at 70,000ft than at 100,000ft?

Watching the Red Bull Stratos event, I noticed that at 70,000ft the temperature was near -60 Celsius, and at 100,000 ft it was -25 Celsius.
gpt
That layer of the atmosphere, from about 10 km up to 50 km, is called the stratosphere, and one of its defining properties is that temperatures increase with height.  The stratosphere has a relatively high concentration of ozone (O3).  When ozone is struck by UV rays from the sun, it splits into molecular oxygen (O2) and atomic oxygen (O).  The atomic oxygen recombines with molecular oxygen to reform ozone, and in doing so it gives off heat.  This heat warms the stratosphere.  Basically, it's a mechanism for converting energy in the form of UV rays to energy in the form of heat.