Evapotranspiration is the transfer of energy from the Earth's surface to the atmosphere in the form of latent heat, due to the evaporation of water from the ground and bodies of water, and the transpiration of water from plants. The transpiration aspect of evapotranspiration accounts for about 10% of the moisture in the atmosphere, with evaporation from oceans and other bodies of water accounting for nearly 90% and a tiny amount coming from sublimation (ice changing into water vapour without first becoming liquid).
Evapotranspiration is an important part in the Earth's hydrologic cycle. About 30% of the total ocean volume evaporates each year. Wind carries this water vapour to higher elevations where it cools and condenses, and finally precipitates. About 76% of it goes right back to the ocean, and the rest hits land and drives the life cycles there.
Evapotranspiration is a key factor in Earth's heat balance. The radiant heat coming from the Sun must be rid of by the Earth in order for its temperature to remain constant, and this is partly done by evapotranspiration. This happens because it requires energy to change a substance from liquid to gas, so as the water on the Earth evaporates and transpires it uses some of this solar energy. The contribution of evapotranspiration to Earth's energy budget is displayed in Figure 2 below.