WHAT CAUSES EVAPORATION?
It would be difficult to find a more important process in our weather and climate system than evaporation. Evaporation is the change of water from a liquid to a gas. Water is continuously evaporating from the surface of the Earth, literally pumping more and more water vapor into the atmosphere. Averaged across the entire Earth, water evaporates from the surface at a rate of about 3 millimeters per day (about 1/8 of an inch). Over the tropical oceans, the value is much larger; over cold surfaces, it is much lower; and over deserts it is almost zero, since there is little or no water to evaporate. This change of phase (from a liquid to a gas) requires heat, called the “latent heat of condensation”. When water evaporates, it removes heat, lowering the temperature of the surface. For both water and land surface, most of this heat energy comes from the surface, not from the air. Evaporative cooling, along with convection, helps keeps the surface of the Earth from getting too hot. What is co
