The Water Cycle: Steaming The Air

This second part of our series on the water cycle illustrates the way in which evaporation and winds combine to move water from the ocean to the land. The ocean loses water to the air when the water evaporates and turns into water vapor (steam). If the air over the ocean didn't move, the ocean water would reabsorb much of the steam. But the ocean surface air moves constantly and increases the transfer of water vapor to the air to roughly 440 trillion tons of water per year (just like blowing on hot liquid cools it off faster). Evaporation of water from the land only moves about 66 trillion tons of water to the air every year, mostly during the day. The winds in the atmosphere mix up the water vapor over the land and ocean, so that there is a net movement of water from land to ocean of 37 trillion tons of water per year. Surprisingly, only about 12 trillion tons of water is in the air at any one time because water vapor only stays in the air for an average of 10 days.