Languages are supposed to be arbitrary. The sounds a language uses to build words bear no necessary relationship to what those words mean, to the physiology of the speakers, or to the environment they inhabit. Phonological inventories — the set of consonants and vowels a language employs — are products of cultural transmission, not physical constraint.
Warm-climate languages use more vowels. Wang, Wichmann, Xia, and Ran analyzed 9,179 language varieties representing 5,293 distinct languages and found a positive correlation between ambient temperature and sonority — the vowel-like quality of speech sounds. Languages spoken in warmer regions feature more open, resonant sounds. Languages in colder regions feature more consonants, more abrupt closures, more high-frequency noise.
The mechanism is acoustic, not cultural. Warm air absorbs high-frequency sound components more readily than cold air. Consonants — particularly fricatives and plosives — carry their distinguishing information in high-frequency bursts. In warm environments, those bursts degrade faster during transmission. Vowels, which carry information in lower-frequency formant patterns, survive warm-air transmission better. The correlation between temperature and sonority across macroareas is R² = 0.904. Within individual language families, the correlation disappears — the adaptation operates on timescales of centuries, not generations.
The environment is editing the signal before it arrives. Speakers don't choose vowels because they're easier to produce in heat. They use vowels because vowels are what listeners can still hear after the air has filtered the sound. The phonological inventory of a language is shaped not by what the mouth can produce but by what the atmosphere will transmit.