Which environmental factor is crucial for cloud formation?

Cloud formation is primarily influenced by the process of adiabatic cooling, which occurs when air rises and expands in the atmosphere. As air ascends, it encounters lower atmospheric pressure, which causes the air to cool. This cooling is typically characterized by a temperature decrease with altitude. As the air cools, its capacity to hold moisture decreases, leading to condensation of water vapor when the air reaches its dew point. This condensation forms the tiny water droplets or ice crystals that make up clouds.

Humidity levels, while important for the presence of moisture in the atmosphere, are secondary to the cooling process. Wind speeds can assist in the transport of humid air but do not directly cause cloud formation like the cooling of air does. High atmospheric pressure is usually associated with clear skies rather than cloud formation. Thus, understanding the relationship between temperature and altitude is key to recognizing why a decrease in temperature is essential for cloud development.