This document discusses the factors that determine the stability or instability of the atmosphere. It explains that a stable atmosphere occurs when a rising air parcel cools more rapidly than the surrounding environment, causing it to sink back down. An unstable atmosphere happens when a rising parcel cools more slowly than the environment, allowing it to continue ascending. Specifically, stability depends on how the environmental lapse rate compares to the dry and saturated adiabatic lapse rates of a rising air parcel.