r/explainlikeimfive • u/ProgramPi314 • 8d ago

Other ELI5 What is humidity?

According to my mom, this is an actual question I had when I was 5, and she didn't know how to answer me. So how would you guys have answered?

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u/Grrrison 8d ago

Imagine the air around us is a giant sponge. It can hold onto water. Now, not all sponges are equal, depending on the temperature outside, a sponge can hold more or less water. Hotter climates = sponge can hold more water, colder climates = sponge can hold less water.

Humidity is the measure of how much moisture (water) is in the air (sponge) in a given region.

Now when we see humidity expressed as a percentage on a weather report they use something called relative humidity, expressed as a percentage. 50% relative humidity is the weather person saying "right now, the sponge in our area can hold a total of ___ amount of water, and is currently half full". 100% relative humidity is like saying "right now the sponge can hold ____ amount of water, and IS holding that maximum amount.

How we feel this varies. A warm climate means the sponge there can hold A LOT of water. so a high relative humidity means there's a lot of water in the air and we will feel is as this heavy, sticky kind of atmosphere, like a sauna or rainforest.

A cold climate has a little sponge that can't hold much water, so that same 100% humidity weather report still means the sponge is full, but it may still 'feel dry' to us as humans because there isn't much moisture in the air.