Why does the Saturated Adiabatic Lapse Rate (SALR) steepen with altitude?

The correct understanding of why the Saturated Adiabatic Lapse Rate (SALR) steepens with altitude revolves around the relationship between humidity, temperature, and pressure changes in the atmosphere. The SALR decreases with altitude because as air rises, it cools due to expansion, and when it is saturated, additional cooling results from the release of latent heat during condensation of water vapour.

At higher altitudes, the air is generally colder and can hold less moisture before becoming saturated. As a result, the overall amount of water vapour available decreases with increasing altitude. This diminishing availability of water molecules means that the potential for latent heat release during condensation decreases, which results in a steeper lapse rate in saturated conditions.

Focusing on the other options: latent heat release is significant at lower altitudes where warm, moist air is present; temperature does not decrease at a constant rate due to changes in moisture and pressure gradients; and pressure actually decreases with altitude, influencing the air's ability to hold water vapour.

By understanding the properties of the atmosphere and how saturation affects the lapse rate, one can see how the decrease in water vapour availability with altitude directly influences the steepening of the SALR.