What is the role of humidity in cloud formation?

Humidity plays a crucial role in cloud formation primarily by increasing the air's capacity to hold moisture. When air is saturated with water vapor, it reaches a point where it can no longer hold all the moisture, leading to condensation. This condensed moisture forms clouds. The higher the humidity, the more water vapor is present in the air, which promotes cloud development.

While humidity does contribute to cooling effects when the air rises and expands, the key aspect in cloud formation is that higher humidity increases the moisture content in the air, leading to condensation and subsequently, cloud formation. Other options mention effects that do not address the primary function of humidity directly related to the process of clouds forming. For instance, while cooling can influence weather conditions, it is not the main factor in the cloud formation process itself compared to the role of moisture saturation.