Food from Air. Half your nitrogen came from a factory.

Plants need nitrogen. Air is 78% nitrogen, but in a form no plant can use. In 1909 Fritz Haber worked out how to pull it out under heat and pressure, and Carl Bosch built it at industrial scale. Synthetic fertiliser now feeds roughly half the people alive. It is the least famous invention of that size.

• The process is hungry for energy, so fertiliser prices track natural gas prices. That is the route by which an energy shock turns into a food shock.
• The same nitrogen that grows the crop runs off into rivers and feeds algae instead. The gain and the damage come out of one chemistry.