Why does temperature stop decreasing at the top of the troposphere?

The temperature stops decreasing at the top of the troposphere, known as the tropopause, because it marks the boundary between the troposphere and the stratosphere. In the troposphere, temperature decreases with altitude due to the decreasing pressure and density of air. However, in the stratosphere, temperature begins to increase with altitude due to the absorption of ultraviolet radiation by the ozone layer, which leads to a warming effect. This transition creates a stable layer that effectively caps the troposphere.