Britannica Sources used in this answer

Why are mountaintops generally colder than lower elevations according to adiabatic expansion?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Engraved portrait of Rudolf Julius Emanuel Clausius, a bearded man in formal attire with sideburns, facing forward. — thermodynamics Rudolf Clausius (1822 - 1888) is considered one of the central founders of the science of thermodynamics.

Mountaintops are colder than lower elevations primarily due to adiabatic cooling, a process where a parcel of air changes temperature without transferring heat to its surroundings.12

As air rises, it encounters lower atmospheric pressure, which allows the air parcel to expand. In thermodynamics, this expansion requires the air to perform work against the surrounding environment. Because the process is adiabatic, the energy required to perform this work is drawn from the internal energy of the air itself. As the internal energy decreases, the temperature of the air parcel drops.12

This rate of temperature change, known as the adiabatic lapse rate, is approximately 1 °C per 100 meters for dry air. Conversely, at lower elevations, higher pressure compresses the air, resulting in more frequent molecular collisions and higher temperatures.1