Scientists warned this week that feedback effects in global warming might tip the Earth into a “hothouse state”, recovery from which could be impossible, even by reductions in CO2 emissions. How frightened should we be about moving from a greenhouse to a hothouse?

The mechanism by which atmospheric gases warm the planet has been well understood since the 19th century. High CO2 levels early in the Earth’s history, wrote the geologist Thomas Sterry Hunt in 1867, had created the sort of climate that would have resulted if we “had covered the Earth with an immense dome of glass, had transformed it into a great orchid house”. The term “greenhouse effect” was coined in 1907.

But a “hothouse” sounds far more intense. From the 16th century, a hothouse was a bathhouse or a brothel, or a heated room for drying linen, and then a heated greenhouse for cultivating exotic species, metaphorically extended to an environment in which anything (including minds) grows very quickly. Its products are often said to be highly delicate, if not sickly. We are already wilting like hothouse flowers this summer, and there might be no way to smash the glass.