The normal lapse rate to temperature Earth's atmosphere drops to 0oC at the

The Earth's atmosphere is divided into layers based on temperature gradients. In the troposphere, the temperature decreases at a normal lapse rate of approximately 6.4°C per km [1], reaching about -57°C at the tropopause [1]. Above this, in the stratosphere, the temperature increases with altitude due to the absorption of ultraviolet radiation by the ozone layer. This warming trend continues until the stratopause, located at approximately 50 km altitude, where the temperature rises back to nearly 0°C (273 K). Beyond the stratopause, in the mesosphere, the temperature begins to drop again, reaching its minimum at the mesopause. Therefore, the point where the temperature returns to 0°C after the initial drop in the troposphere is the upper boundary of the stratosphere, known as the stratopause.

Sources

1. [1] Environment and Ecology, Majid Hussain (Access publishing 3rd ed.) > Chapter 1: BASIC CONCEPTS OF ENVIRONMENT AND ECOLOGY > Structure of the Atmosphere > p. 7