Water vapor is known as a variable gas which means its percent abundance in the air at any one place in the troposphere is not constant. This variation results due to influences from temperature, altitude, and availability of water to evaporate into the air. As temperature increases, then an increasing amount of liquid or solid water can vaporize into the air. This is limited though by the availability of water to evaporate. The warmest places on earth may or may not have abundant moisture in the air depending on availability. Hot temperatures and warm ocean waters are the best combination for high amounts of moisture. Even at these locations the maximum amount of water vapor as a percentage of the air is a few percent. Very cold and very dry locations will have a water vapor percentage of close to 0%. The amount of water vapor is the air tends to decrease with altitude. This is because temperatures decrease with height and the availability of a moisture source is farther away.

Although water vapor is typically just a small percentage of the total air, it is the critical component to producing the Earth’s weather such as clouds and thunderstorms. This variable gas has vast influences on latent heat release and absorption as well as distributing water over the Earth. Water has the unique property that it can exist as a liquid, solid and gas within the temperatures experienced on Earth. This allows it to be readily distributable by wind currents, ocean currents, groundwater, rivers/streams, and glaciers. Water is in all three phases within a thunderstorm (water vapor advected into the storm, water vapor condensed to liquid as in rain formation, and ice such as in the formation of hail). The unique properties of water are a reason for the magnificence of Earth’s weather.