Why the higher the altitude, the lower the temperature?

Theoretically, high altitude is closer to the sun, but compared with the distance from the earth to the sun, this distance is very small. In other words, there is little difference in solar radiation that can be received at different atmospheric heights. Without leaving the earth, you can't feel the change of solar radiation. At high altitude, it won't let us get close to the sun, let alone the temperature rise.

The atmospheric pressure decreases with the increase of altitude, and the number of air molecules holding other molecules will decrease. This means that the higher the altitude, the more space for molecules in the air to move. This reduces the chance of collision with surrounding molecules, and makes the kinetic energy of molecules distributed in a large area, thus reducing the average temperature.

On the contrary, at low altitude, the atmospheric pressure is so high that air molecules cannot move freely. They carry a lot of energy and collide with each other more frequently, leading to an increase in temperature. Therefore, mountains are hotter than mountains. This physical law applies everywhere, whether at the equator or at the poles.

Humans live in the lowest layer of the atmosphere, that is, the troposphere, and cannot directly absorb short-wavelength solar radiation. Therefore, solar radiation can almost directly contact the ground through the atmosphere in the troposphere, and after part of the energy is reflected by the ground, the rest of the energy will be absorbed by the ground, leading to an increase in temperature. With the increase of ground temperature, the ground will emit energy like the atmosphere, and because of the low ground temperature, the emitted energy has a long wavelength, mainly infrared rays. In the troposphere atmosphere, the surface radiation dominated by infrared rays is strongly absorbed by carbon dioxide and water vapor, thus raising the atmospheric temperature. So the higher the altitude, the lower the temperature, the lower the altitude and the higher the altitude.