ABSTRACT
A large fraction of the net radiation at the bottom of the atmosphere is absorbed by the oceans which cover about 71 per cent of the Earth’s surface, and that absorbed energy is mostly used in evaporating water. Heat added for evaporation makes no difference to the water’s temperature, because the energy is used in breaking bonds not in altering molecular velocities. After evaporation, the vapour contains the energy absorbed during the change of state. Evaporation from the ocean incorporates latent heat into the moistened air, and that same heat is later released downwind if the vapour forms cloud. The concept of vapour pressure is needed in order to explain why a liquid is sometimes depleted by evaporation and sometimes augmented by condensation. The evaporation rate varies with latitude for reasons associated with the Dalton evaporation equation.
