Why are Higher Elevations Colder?

Higher elevations are colder primarily due to the decrease in atmospheric pressure that results from the expansion of air as it rises. The concept of adiabatic cooling, a process where cooling occurs without air transferring heat to its surroundings, is crucial in understanding why higher elevations are colder than lower elevations. As a volume of air rises, it expands because there is less atmospheric pressure above it to constrain it and push it down, and this expansion leads to cooling. The rate of temperature decrease with altitude, known as the adiabatic lapse rate, is about 1 °C (1.8 °F) per 100 meters (328 feet) for dry air and 0.55 °C (1 °F) per 100 meters for saturated air (see also saturation). This cooling effect is a direct result of the air’s expansion and is a key factor in the cooler temperatures experienced at higher altitudes.

In other words, you experience warmer air walking near sea level because air molecules collide with one another rather frequently, because the pressure exerted by the mass of the atmosphere mass compresses these air molecules together. With each collision of one air molecule with another, some of this energy of movement is released as heat. If your journey takes you into the hills and up a tall mountain, atmospheric pressure of the air around you will decrease, which causes this air to expand. The air cools because the energy required to do the work of expanding is drawn from the air itself. With more space between the molecules, there are fewer collisions. This process leaves less energy available for heating the air, which results in cooler temperatures as you climb higher.