The Koppen System

In 1884, climatologist Wladimir Koppen created a classification system that divides Earth's climates into five main groups based on temperature and precipitation patterns: Tropical (A), Dry (B), Temperate (C), Continental (D), and Polar (E). More than a century later, it is still the most widely used climate map in the world.

Each group is subdivided further. For example, Cfa means temperate with no dry season and hot summers (southeastern United States, eastern China). BWh means hot desert (Sahara, Arabian Peninsula). The strength of Koppen's system is that it ties climate directly to vegetation patterns, so the map of climates doubles as a rough map of the world's plant life.