It gets colder the higher you go because air pressure drops with altitude, making rising air expand and cool, and thinner air cannot hold or trap heat as well as dense air near the ground.

Core idea: expanding air cools

As you go up a mountain, the weight of the atmosphere above you decreases, so the air pressure gets lower. When a blob of air rises into this lower-pressure region, it expands because there is less force squeezing it.

That expansion costs energy: the air does work as it pushes outward, and it “pays” for that work with its own internal energy, so its temperature drops without needing to touch anything colder (this is called adiabatic cooling).

Why “closer to the Sun” doesn’t matter

The distance from the ground to the top of a tall mountain is tiny compared with the distance from Earth to the Sun, so being a few kilometers higher does not noticeably increase the sunlight you get. What really matters is how the atmosphere absorbs, stores, and reradiates heat, and most of that heating happens near Earth’s surface where the air is denser and warmed from below by land and oceans.

Other reasons high places feel so cold

  • Thinner air at altitude has fewer molecules to absorb and retain heat, so it warms and cools more quickly.
  • Heat escapes to space more easily in the thin upper air, a process called radiative cooling, which helps nighttime temperatures at high elevations drop fast.
  • Winds are often stronger higher up, increasing wind chill and pulling heat away from skin and clothing more efficiently, so it feels extra cold even at the same thermometer reading.

A rule of thumb for mountains

On average, in the lower atmosphere, temperature typically falls by about 0.6–1 °C for every 100 meters you climb, depending on how moist the air is. That is why snow can sit on a mountain summit while the valley below is mild or even warm at the same time.

Information gathered from public forums or data available on the internet and portrayed here.