Given a scientific passage and an answer, generate a question for the given answer.
Q: Passage: Air in the troposphere is warmer closer to Earth's surface. Warm air is less dense than cool air, so it rises higher in the troposphere. This starts a convection cell. Convection mixes the air in the troposphere. Rising air is also a main cause of weather. All of Earth's weather takes place in the troposphere. Answer: it is less dense than cool air
A:
Why does warm air rise higher in the troposphere?