Daily Dose · Maps / Sep 5, 2026 / Climate Zones
Five Letters for Every Climate on Earth
In 1884 a Russian-born German climatologist named Wladimir Köppen tried to sort the world's weather the way a botanist sorts plants — by where things can grow. The alphabet he arrived at, A through E, is still the colour key under almost every climate map you have ever seen.
Köppen–Geiger climate types are enough to label every square kilometre of land on Earth. One of them — Csc, cold-summer Mediterranean — turns up nowhere at all.
PEEL, FINLAYSON & McMAHON 2007 · HESS 11, 1633–1644
The world by Köppen–Geiger main class · schematic, equirectangular
01 · The alphabet
Five letters, and a couple of thresholds
Köppen's system is almost brutally simple: look at the coldest month, the warmest month, and whether rain outpaces evaporation. Three numbers — 0 °C, 10 °C, 18 °C — cut the planet into five families. A second letter describes the rain, a third the summer heat. Three characters, and you have named a climate.
MONTHLY MEAN AIR TEMPERATURE. CLASS BOUNDARIES AS APPLIED IN PEEL ET AL. 2007; KÖPPEN'S OWN C/D BOUNDARY WAS ORIGINALLY −3 °C.
02 · The split
The biggest climate on Earth is dry
Ask people to picture the planet's dominant climate and they think of forest. The land says otherwise: arid B climates cover more ground than any other family, and a single sub-type — BWh, the hot desert — is the most widespread climate on Earth.
THE TWO MOST EXTENSIVE INDIVIDUAL CLIMATE TYPES, AS SHARES OF GLOBAL LAND AREA. BARS SCALED TO BWh. SOURCE: PEEL ET AL. 2007.
03 · Continents
Every continent has a favourite letter
Globally the five classes are surprisingly balanced. Zoom in and the balance collapses: each landmass is overwhelmingly one thing. Australia is a desert with a wet rim; South America is a rainforest with a cold tail; North America and Asia are, above all, cold.
SHARE OF EACH CONTINENT'S LAND AREA HELD BY ITS SINGLE DOMINANT MAIN CLASS. CONTINENTAL BOUNDARIES AS DEFINED IN PEEL ET AL. 2007.
04 · The rare ones
Two codes that almost don't exist
The grammar of the system allows 30 combinations. The planet declines to build them all. Csc — a Mediterranean climate with a cool short summer — appears in exactly zero grid cells worldwide. Cwc, its dry-winter cousin, survives in 25 cells out of a whole world.
THE Cwc BAR IS EXAGGERATED 25× FOR VISIBILITY AND IS LABELLED AS SUCH; ALL OTHER BARS ARE TO SCALE. SOURCE: PEEL ET AL. 2007.
05 · Resolution
The same idea, a thousand times sharper
Köppen drew his zones by hand from a scattering of stations. The modern version is a raster: Beck and colleagues published the classification at 0.0083° — about 1 km at the equator — for 1980–2016, and checked it against every long-record weather station they could find.
CLASSIFICATION ACCURACY AGAINST 22,078 WEATHER STATIONS (GHCN-D AND GSOD). SOURCE: BECK ET AL. 2018, SCIENTIFIC DATA 5:180214.
06 · Drift
The map is quietly moving
A climate classification is a snapshot, and the snapshot is going out of date. Comparing 1901–1930 with 1991–2020, about a twentieth of the ice-free land has already crossed into a different main class. The projections for the end of this century depend almost entirely on which emissions path the world takes.
SHARE OF GLOBAL LAND SURFACE (EXCLUDING ANTARCTICA) TRANSITIONING TO A DIFFERENT MAIN KÖPPEN–GEIGER CLASS. FUTURE VALUES ARE MODEL PROJECTIONS, NOT MEASUREMENTS. SOURCE: BECK ET AL. 2023, SCIENTIFIC DATA 10:724.
What to notice on the map
- The desert belts are symmetric. Ochre sits at roughly 20–30° north and south on both sides of the equator — the Sahara, Arabia, the Thar, the Sonoran, the Kalahari, the Australian interior, the Atacama. That is the descending arm of the Hadley circulation drawn in sand.
- The cold class is a Northern Hemisphere phenomenon. D covers 24.6% of all land, and virtually none of it lies south of the equator — there is simply no continent at those southern latitudes to hold it.
- West coasts and east coasts disagree. At the same latitude the western edge of a continent tends to run Mediterranean or cool-oceanic and the eastern edge humid-subtropical: compare Portugal with Beijing, or California with Georgia.
- Mountains punch holes in the pattern. The pale patch inside Asia is the Tibetan Plateau — polar climate at 30° north, purely because it stands five kilometres up.
- It is a vegetation map in disguise. Köppen built the thresholds to match where plants stop growing, which is why the boundaries land so close to the edges of rainforest, steppe, taiga and tundra.