ELI5: Why is it colder on mountain tops?

This is a question that has always bothered me. Valleys, like Death Valley in California, tend to be really hot. But the tops of mountains (closer to the sun!!) are snowy and very cold.

And what about that whole thing, with “heat rising?” I know for a fact that my basement (lower) is always colder than my attic (higher). So why are mountaintops always colder than valleys, even though mountains are closer to the sun?

THREE REASONS

1. Ain’t no mountain high enough

Mountains are not as close to the sun as you might think. Even though mountains seem very tall to us, we are so far away from the sun that moving from the ground to a mountain doesn’t put us that much closer to the sun. Even if you’re on Mt. Everest, 8.8km high, the sun is still 140 MILLION kilometers away. Think about it this way. You’re climbing a rope that’s 140m high (longer than a soccer field!), and you move .0000088 cm closer. Not going to make much of a difference in the weather, is it?

2. Lower pressure at higher altitudes

At higher altitudes there is less atmospheric pressure. What’s atmospheric pressure? It’s how much stuff is pushing on you. Think about it like this, when you’re at a low altitude, like at sea level, there’s a lot more stuff in the air (“atmosphere”) to push down on you. When you’re at a high altitude, you’re above a lot of air and so there’s less stuff pushing on you.

Pressure and temperature have a direct relationship. A higher pressure is like shaking up a soda bottle, you’re pushing the molecules of soda together more and more and so they heat up by rubbing together. At a high altitude, there’s less pressure, so the molecules are rubbing together less and stay at a cooler temperature.

3. Heating of the Earth

Here is something that might surprise you: the sun doesn’t heat the air, the sun heats the earth. The sun heats things by sending waves of energy down to the earth. These waves of energy pass through the air, and then hit the ground, and start heating it up! Now think about standing on a mountain, is there a lot of earth around there? No, a mountaintop is a small surface that can’t give off that much heat. But if you’re in a valley close to sea level, there’s the ground you’re standing on, plus all the mountains and hills around you that can give off heat. So mountaintops don’t get heated by the earth as much.

To sum up, mountains aren’t as tall as you think. But, mountaintops do have less atmospheric pressure, so the molecules just chill and don’t give off much energy. And because there’s less earth on mountaintops, there’s less earth giving off heat, and mountaintops become very cold places.

Have any questions? Leave them in the comments!

Micaela Deitch is a Content Developer for OpenSesame, the world’s largest elearning marketplace. She enjoys learning and learning about elearning.