1. Altitude: As you go higher, the air becomes thinner. This means there are fewer air molecules to absorb and hold heat from the sun.

2. Lower air pressure: At higher altitudes, the atmospheric pressure is lower. This lower pressure causes the air to expand, which in turn cools it.

3. Adiabatic Cooling: As air rises, it expands and cools. This is because the air pressure decreases with altitude, causing the air molecules to spread out, decreasing their energy and temperature. This is known as adiabatic cooling.

4. Mountain Topography: Mountains act as barriers to wind flow, which often carries warm air from lower elevations. This effect can create a local cooling zone on the leeward side of the mountain.

5. Snow and Ice: High mountains often have snow and ice cover, which reflect sunlight and absorb heat, contributing to the cooler temperatures.

In summary: The combination of altitude, lower air pressure, adiabatic cooling, mountain topography, and snow/ice cover all contribute to the cooler temperatures found on mountains.