green + house

Greenhouse is a compound: green (from Old English grēne) plus house (from Old English hūs). The first greenhouses in England, in the seventeenth century, were called 'green houses' — two words — because they housed 'greens,' meaning evergreen plants, particularly citrus trees and other tender specimens that could not survive English winters outdoors. The green was the plants. The house was the structure that kept them alive.

The technology evolved rapidly. By the 1700s, glass-walled structures heated by stoves allowed wealthy estate owners to grow tropical fruits year-round. The great conservatories of the Victorian era — Kew's Palm House (1848), the Crystal Palace (1851) — pushed greenhouse technology to its limits. Joseph Paxton's Crystal Palace, built for the Great Exhibition, was essentially a greenhouse the size of a cathedral.

In 1827, Joseph Fourier described the mechanism by which the earth's atmosphere traps heat — comparing it to the glass panes of a hotbed. In 1896, Svante Arrhenius calculated that doubling atmospheric carbon dioxide would raise global temperatures by about 5°C. Neither used the phrase 'greenhouse effect,' but the metaphor was implicit. By the 1930s, 'greenhouse effect' was the standard English term for atmospheric heat trapping.

The word greenhouse now names both a building and a planetary crisis. The greenhouse effect, greenhouse gases, greenhouse emissions — the metaphor has consumed the original meaning. When most people hear 'greenhouse' today, they think of climate change, not of a glass building full of orchids. The building that protected tender plants from cold gave its name to the process that is making the whole planet warmer.