Originally Posted by
GerryinHouston
Hot air rises, as any hot air balloon knows. So, it is less dense than cold air...
Correct...but low density air is extremely cold too.
Because of the lower pressure [at high altitude], the air expands as it rises, which causes it to cool. Thus, high altitude air is cold, which causes a characteristic alpine climate. This climate dramatically affects the ecology at high altitude.
https://en.wikipedia.org/wiki/Altitude