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Cooler in the Mountains

Cooler in the Mountains

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 Here’s a riddle: If heat rises, and mountains are closer to the sun, why are they always colder? The answer may surprise you. The heat of the sun can’t actually radiate through space. There would need to be particles of some element to conduct its heat; but space is a vacuum. Instead, the sun emits electromagnetic energy: ultraviolet, visible and infrared light, X-rays, and radio waves. When this solar radiation finally meets Earth’s surface, it warms it. And that radiates heat back upward, warming the atmosphere from the bottom up. So is that why it’s warmer lower and cooler higher? Not exactly. It has more to do with air pressure. Like all gases, the air in our atmosphere is a poor conductor—because it’s not dense with particles. However, the atmosphere does have mass. And its weight bearing down on the air at the surface compresses it more than the air at altitude. The compressed air is denser with molecules, which are more likely to collide, and these collisions produce heat. That means the air near the surface is not only better able to conduct Earth’s reflected heat but generates its own heat because it’s dense. This hot air can indeed rise. But as it does, the atmospheric pressure decreases, the air expands, and it cools. So, even though they’re closer to the sun, thin air in the mountains keeps them colder than the thicker air in the lowlands surrounding them.
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