Water vapor consists of tiny clouds, which form where there’s no atmosphere, in a region of space where there is some kind of liquid. This vapor is held there by pressure.
This water vapor is known as an atmospheric gas. For the purposes of explaining how much is too much, let’s just say there is a little water vapor in our atmosphere. In fact, our atmosphere contains around 40 pounds of water vapor. (That’s just under 400 ml.) The average amount of water we get from sunlight is 0.17 percent, but your body doesn’t feel the effects of the sun’s heat at all.
The amount of water in the air you breathe comes from the amount of water vapor in the air. When clouds form, more water vapor is absorbed by them than it is lost. What’s left is moisture in the form of clouds and rain.
How much water vapor does the atmosphere really contain? The answer isn’t terribly precise because of its delicate balance.
You can’t measure just how much atmospheric water exists. There’s no point. You can’t even use a vacuum to get an accurate measure because the amount of air under your nose is an exact fraction of your body’s volume. You can’t even estimate. You’d have to measure exactly how much water vapor is being lost, and then figure out the amount of moisture that’s remaining. We’re basically just speculating here about the amount of water vapor remaining in our atmosphere, and it’s unlikely we’ll ever know precisely how much there is.
That’s not to say that all of that cloud is water vapor. Clouds can hold other kinds of gas and liquids too.
In a few cases, such as the tropics, the amount of water in an atmosphere can be quite large. In part, that’s because so much of our atmosphere is made up of greenhouse gases that hold water. This water can act as a greenhouse gas, or as a refrigerant which reduces global warming by making a planet a bit cooler and reducing pollution from burning fossil fuels.
Water vapor levels in the upper atmosphere are affected by the amount of carbon dioxide. If carbon dioxide levels in the atmosphere are increasing (as they are currently) because of humans’ burning of fossil fuels causing climate change (the second effect is the reason that we can’t say precisely how much water is remaining), rain will fall as much in the tropics as in the United States.
One of the things many people think about when they think about water vapor
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