The process responsible for most of the water vapor that enters the atmosphere is evaporation. Evaporation occurs when water from oceans, lakes, rivers, and other bodies of water is heated by the sun and turns into water vapor. This water vapor then rises into the atmosphere.
Another significant contributor is transpiration, which is the process by which plants release water vapor through their leaves. Together, evaporation and transpiration are often referred to as evapotranspiration.
These processes are crucial components of the Earth’s water cycle, helping to regulate the climate and distribute water across the planet.