What is the primary temperature criterion for classifying a region as a Polar (E) climate zone?

💡 Explanation:

In the Köppen-Geiger climate classification system, the Polar (E) group is defined by the fact that the average temperature of the warmest month is below 10°C (50°F). This fundamental criterion determines that the region is too cold to support tree growth, which is a key characteristic of the polar climate. Sub-types like Ice Cap (EF) have all months below 0°C, but the general 'E' group definition uses the 10°C threshold.