This part of IEC 60721 presents classifications of open-air climates in terms of temperature and humidity. It is intended to be used as part of the background material when selecting appropriate temperature and humidity severities for product testing and application. The climates cover all areas of the world, excluding the central Antarctic and high altitudes (above 5 000 m). This presentation may be used as background material when issuing climatic environmental classes for product applications. This standard defines a limited number of open-air climate classifications, in terms of temperature and humidity, which represent the conditions most frequently met by products while being transported, stored, installed and used.