Köppen climate classification

First recorded in 1950–55; named after Wladimir Köppen (1846-1940), who invented the system in 1884

The Köppen climate classification is named after its creator, Wladimir Köppen. It's sometimes called the Köppen-Geiger climate classification, with credit to Rudolf Geiger as well, who introduced significant changes to Köppen’s classification.
In this system, there are six basic groups, each one marked by a capital letter: “A” (tropical), “B” (arid), “C” (temperate), “D” (continental), and “E” (polar). Each group also has one or two additional letters to further indicate how dry the climate is and, where applicable, how hot or cold it is.
For example, an “Af” (tropical, rainforest) climate is an area like the Amazon with little variation in temperature and a lot of precipitation, and since there's no such thing as a cold tropical rain forest, “Af” doesn't need a third letter. An “EF” (polar, ice cap) climate is a dry, freezing area like Antarctica—always cold, so it also has only two letters. “BWh” (arid, desert, hot) is an area like the Sahara—an arid desert that's always hot. “Dfa” (continental, no dry season, hot summer) is a climate with high seasonal temperature variation, a hot summer, and year-round precipitation, like Chicago in the United States.
There have been further modifications to the Köppen climate classification over time, but it's still one of the most widely-used systems for classifying climates.