trade winds

Trade in 'trade winds' derives from Middle English trade, meaning 'a path, a track, a regular course,' from Middle Low German trade (track). The compound trade wind meant 'wind that blows on a track' — a wind so reliable that it always came from the same direction. The commercial meaning of 'trade' (buying and selling) developed separately, from the same root's sense of 'a regular practice or course of business.' The winds were named for their consistency, not their economic utility.

The trade winds blow from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere, converging near the equator in the Intertropical Convergence Zone. Edmond Halley — the astronomer who calculated the comet's orbit — published the first scientific explanation of the trade winds in 1686, attributing them to differential solar heating of the equatorial and temperate zones. George Hadley refined the theory in 1735, adding the Coriolis effect.

The coincidence that trade winds facilitated maritime trade reinforced the false etymology. Columbus used the northeast trades to cross the Atlantic in 1492. Portuguese, Spanish, Dutch, and English merchants rode the trades to Africa, the Americas, and Asia. The winds that blew on a constant track made oceanic commerce possible. The wrong etymology felt right. The winds did enable trade, even if that is not why they are called trade winds.

The trade winds have weakened measurably since the mid-twentieth century, a phenomenon linked to climate change. Reduced temperature gradients between the equator and the poles weaken the atmospheric circulation that drives them. The most reliable winds in human navigation are becoming less reliable. The word 'trade' — meaning constant, predictable, on a track — is slowly losing its accuracy.