Saving lives with thin air - by taking nitrogen from the air to make fertiliser, the Haber-Bosch Process has been called the greatest invention of the 20th Century – and without it almost half the world’s population would not be alive today. Tim Harford tells the story of two German chemists, Fritz Haber and Carl Bosch, figured out a way to use nitrogen from the air to make ammonia, which makes fertiliser. It was like alchemy; 'Brot aus Luft', as Germans put it, 'Bread from air'.

Haber and Bosch both received a Nobel prize for their invention. But Haber’s place in history is controversial – he is also considered the 'father of chemical warfare' for his years of work developing and weaponising chlorine and other poisonous gases during World War One.

Producer: Ben CrightonEditors: Richard Knight and Richard Vadon

(Photo: A farmer sprays fertiliser. Credit: Remy Gabalda/Getty Images)