Water vapor plays a large role in the weather on our planet. It is critical for cloud formation, lightning, and keeping the surface of the Earth warm. However, the amount of water in the atmosphere changes frequently. Above deserts, only a trace amount is found. Above the oceans one will find that water vapor accounts for about 4% of the air.

Of the 1.39 billion cubic kilometers (331 million cubic miles) of water on Earth, just a thousandth of 1% (1.39 million cubic km) exists as water vapor. Yet this tiny amount of water has an outsized influence on the planet: It is a potent greenhouse gas and a major driver of weather and climate.

This map shows the distribution of water vapor in Earth’s atmosphere during August 2010. Even the wettest regions would form a layer of water only 60 millimeters (2.4 inches) deep if the entire column of air was condensed from the top of the atmosphere to the surface. The map was compiled from observations by the Atmospheric Infrared Sounder (AIRS) and the Advanced Microwave Sounding Unit (AMSU-A) on NASA’s Aqua satellite.

via A Little Water Goes a Long Way : Image of the Day.