As given by A. Supan in 1879, a belt around the earth within which the annual mean temperature is less than 20°C (68°F) and the mean temperature of the warmest month is higher than 10°C (50°F).
These limits separate this belt from the hot belt and cold caps, respectively.
See climatic classification.
Supan, A. 1879. Die Temperaturzonen der Erde. Petermanns Geog. Mitt.. 25. 349–358.