system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: If heat rises, why are higher altitudes generally colder?

Hello, I figured this was a simple enough question, so I searched reddit- nothing. I tried a google search, and it went RIGHT over my head.

So why is it generally warmer at sea level than it is higher up? 

As a bonus question, I was reading that the stratosphere is the opposite of us- it gets warmer the higher you go. Why is it different up there?
gpt
Think of the air as like a blanket. Closer to earth the air is denser and is a thicker blanket. Higher up the blanket gets really thin. 

It’s not actually that it is insulating you, it’s just that at higher densities, there are more molecules in a given area, and the movement of those molecules is  heat.