By conventional measures, Jitbhai Chowdhury is a model farmer. He uses organic manure and natural pesticides. He grows fruit trees round the edge of his alfalfa fields and tends his dairy cattle with care. Every day he produces 25 litres of milk which he sends to a collection point in the nearby village of Kushkal in Gujarat, India, for delivery to the state dairy. It’s because of people like him that India isn’t starving.

But for all its virtues, Chowdhury’s 2-hectare farm is sowing the seeds of a global disaster. To grow the fodder that he needs to feed his cows, he is entirely dependent on irrigation water pumped from deep underground. Over the course of a year, his small electric pump sucks twice as much water from beneath his fields as falls on the land as rain. No wonder the water table in the village is 150 metres down and falling by 6 metres a year.

Chowdhury is one of millions of farmers doing this across the world. From China to Argentina, and Australia to the US, people are increasingly dependent on “fossil” water extracted unsustainably from deep underground. Collectively, our actions are threatening to revive a spectre that nobody has seriously worried about for the best part of 40 years – mass global starvation.

Back in the 1960s, the world was gripped by a Malthusian nightmare. The planet’s population was set to double in a generation, and nobody knew how everyone would be fed. Scare stories abounded. In 1968, for example, Stanford University biologist Paul Ehrlich wrote in his best-selling book The Population Bomb that “the battle to …