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Water cycle: Image and animation from the Scientific Visualization Studio, NASA Goddard Space Fight Center.

Steaming the Air is an apt title for this module as we look at the second phase of the water cycle. Water vapor is created during evaporation, when water transforms from a liquid or solid to vapor. The water vapor is then available for precipitation. Approximately 78 percent of water vapor comes from the ocean, as it holds 97 percent of the world's water.

According to the National Research Council's report on Research Pathways for the Next Decade, the impacts of climate change take place principally through the water cycle. Water vapor affects weather and climate as it is an important greenhouse gas. During evaporation, the water molecules pick up latent heat. This cools the ocean's surface waters. When the water vapor transforms back to liquid or solid - during precipitation - this heat is released.

Some interesting details concerning the water cycle are worthy of note: Water molecules stay in the atmosphere approximately nine days after evaporation; about 434,000 cubic km of water evaporate from the ocean each year; 71,000 cubic km of water come from land through evaporation and transpiration. The impact of climate change on water vapor, clouds and precipitation is of particular interest to researchers.

 

This module is based on the NASA Visualization Application, The Water Cycle: Steaming the Air

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