The atmosphere is the superhighway in the sky that moves water everywhere over the Earth. Water at the Earth's surface evaporates into water vapor, then rises up into the sky to become part of a cloud which will float off with the winds, eventually releasing water back to Earth as precipitation.
• Water Science School HOME • The Water Cycle •
Water cycle components » Atmosphere · Condensation · Evaporation · Evapotranspiration · Freshwater lakes and rivers · Groundwater flow · Groundwater storage · Ice and snow · Infiltration · Oceans · Precipitation · Snowmelt · Springs · Streamflow · Sublimation · Surface runoff
The atmosphere is full of water
The water cycle is all about storing water and moving water on, in, and above the Earth. Although the atmosphere may not be a great storehouse of water, it is the superhighway used to move water around the globe. Evaporation and transpiration transform liquid water into vapor, which ascends into the atmosphere due to rising air currents. Cooler temperatures aloft allow the vapor to condense into clouds. Strong winds move the clouds around the world until the water falls as precipitation, replenishing the earthbound parts of the water cycle. About 90 percent of water in the atmosphere is produced by evaporation from water bodies, while the other 10 percent comes from transpiration from plants.
There is always water in the atmosphere. Clouds are, of course, the most visible manifestation of atmospheric water, but even clear air contains water — water in particles that are too small to be seen. One estimate of the volume of water in the atmosphere at any one time is about 3,100 cubic miles (mi3) or 12,900 cubic kilometers (km3). That may sound like a lot, but it is only about 0.001 percent of the total Earth's water volume of about 332,500,000 mi3 (1,385,000,000 km3), as shown in the table below. If all the water in the atmosphere rained down at once, it would only cover the globe to a depth of 2.5 centimeters, about 1 inch.
How much does a cloud weigh?
Do you think clouds have any weight? How can they, if they are floating in the air like a balloon filled with helium? If you tie a helium balloon to a kitchen scale it won't register any weight, so why should a cloud? To answer this question, let's explore first if air has any weight. A barometer and air pressure will tell us that air does have weight! At sea level, the weight (pressure) of air is about 14 ½ pounds per square inch (1 kilogram per square centimeter).
Since air has weight, it must also have density, which is the weight for a specific volume, such as a cubic inch or cubic meter. If clouds are made up of particles, then they must have weight and density.
But why do clouds float? The density of the same volume of cloud material is less than the density of the same amount of dry air. Just as oil floats on water because it is less dense, clouds float on air because the moist air in clouds is less dense than dry air.
We still need to answer the question of how much a cloud weighs. Before we do, there's one more thing to consider. The weight depends on how you define it:
- The weight of the water droplets in the cloud
- The weight of the water droplets plus the weight of the air (mostly above the cloud, pressing down)
We're only going to look at the weight of the actual cloud particles. One estimate of cumulus cloud density is given at https://www.sciencealert.com/this-is-how-much-a-cloud-weighs, as a density of about 0.5 gram per cubic meter. A 1 km3 cloud contains 1 billion cubic meters.
Doing the math: 1,000,000,000 x 0.5 = 500,000,000 grams of water droplets in our cloud. That is about 500,000 kilograms or 1.1 million pounds (about 551 tons). But that "heavy" cloud is floating over your head because the air below it is even heavier— the lesser density of the cloud allows it to float on the dryer and denser air.
Global distribution of atmospheric water
| Water source | Water volume, in cubic miles | Water volume, in cubic kilometers | Percent of total freshwater | Percent of total water |
|---|---|---|---|---|
| Atmosphere | 3,094 | 12,900 | 0.04% | 0.001% |
| Total global fresh water | 8,404,000 | 35,030,000 | 100% | 2.5% |
| Total global water | 332,500,000 | 1,386,000,000 | -- | 100% |
Source: Gleick, P. H., 1996: Water resources. In Encyclopedia of Climate and Weather, ed. by S. H. Schneider, Oxford University Press, New York, vol. 2, pp. 817-823.
Related content:
The little cloud that could—but why?
Why is this tiny cloud the only one in the sky?
Sources and more information:
How much does a cloud weigh? - National Oceanic and Atmospheric Administration
The atmosphere is the superhighway in the sky that moves water everywhere over the Earth. Water at the Earth's surface evaporates into water vapor, then rises up into the sky to become part of a cloud which will float off with the winds, eventually releasing water back to Earth as precipitation.
• Water Science School HOME • The Water Cycle •
Water cycle components » Atmosphere · Condensation · Evaporation · Evapotranspiration · Freshwater lakes and rivers · Groundwater flow · Groundwater storage · Ice and snow · Infiltration · Oceans · Precipitation · Snowmelt · Springs · Streamflow · Sublimation · Surface runoff
The atmosphere is full of water
The water cycle is all about storing water and moving water on, in, and above the Earth. Although the atmosphere may not be a great storehouse of water, it is the superhighway used to move water around the globe. Evaporation and transpiration transform liquid water into vapor, which ascends into the atmosphere due to rising air currents. Cooler temperatures aloft allow the vapor to condense into clouds. Strong winds move the clouds around the world until the water falls as precipitation, replenishing the earthbound parts of the water cycle. About 90 percent of water in the atmosphere is produced by evaporation from water bodies, while the other 10 percent comes from transpiration from plants.
There is always water in the atmosphere. Clouds are, of course, the most visible manifestation of atmospheric water, but even clear air contains water — water in particles that are too small to be seen. One estimate of the volume of water in the atmosphere at any one time is about 3,100 cubic miles (mi3) or 12,900 cubic kilometers (km3). That may sound like a lot, but it is only about 0.001 percent of the total Earth's water volume of about 332,500,000 mi3 (1,385,000,000 km3), as shown in the table below. If all the water in the atmosphere rained down at once, it would only cover the globe to a depth of 2.5 centimeters, about 1 inch.
How much does a cloud weigh?
Do you think clouds have any weight? How can they, if they are floating in the air like a balloon filled with helium? If you tie a helium balloon to a kitchen scale it won't register any weight, so why should a cloud? To answer this question, let's explore first if air has any weight. A barometer and air pressure will tell us that air does have weight! At sea level, the weight (pressure) of air is about 14 ½ pounds per square inch (1 kilogram per square centimeter).
Since air has weight, it must also have density, which is the weight for a specific volume, such as a cubic inch or cubic meter. If clouds are made up of particles, then they must have weight and density.
But why do clouds float? The density of the same volume of cloud material is less than the density of the same amount of dry air. Just as oil floats on water because it is less dense, clouds float on air because the moist air in clouds is less dense than dry air.
We still need to answer the question of how much a cloud weighs. Before we do, there's one more thing to consider. The weight depends on how you define it:
- The weight of the water droplets in the cloud
- The weight of the water droplets plus the weight of the air (mostly above the cloud, pressing down)
We're only going to look at the weight of the actual cloud particles. One estimate of cumulus cloud density is given at https://www.sciencealert.com/this-is-how-much-a-cloud-weighs, as a density of about 0.5 gram per cubic meter. A 1 km3 cloud contains 1 billion cubic meters.
Doing the math: 1,000,000,000 x 0.5 = 500,000,000 grams of water droplets in our cloud. That is about 500,000 kilograms or 1.1 million pounds (about 551 tons). But that "heavy" cloud is floating over your head because the air below it is even heavier— the lesser density of the cloud allows it to float on the dryer and denser air.
Global distribution of atmospheric water
| Water source | Water volume, in cubic miles | Water volume, in cubic kilometers | Percent of total freshwater | Percent of total water |
|---|---|---|---|---|
| Atmosphere | 3,094 | 12,900 | 0.04% | 0.001% |
| Total global fresh water | 8,404,000 | 35,030,000 | 100% | 2.5% |
| Total global water | 332,500,000 | 1,386,000,000 | -- | 100% |
Source: Gleick, P. H., 1996: Water resources. In Encyclopedia of Climate and Weather, ed. by S. H. Schneider, Oxford University Press, New York, vol. 2, pp. 817-823.
Related content:
The little cloud that could—but why?
Why is this tiny cloud the only one in the sky?
Sources and more information:
How much does a cloud weigh? - National Oceanic and Atmospheric Administration