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The problem lies in the type of sand we are using. Desert sand is largely useless to us. The overwhelming bulk of the sand we harvest goes to make concrete, and for that purpose, desert sand grains are the wrong shape. Eroded by wind rather than water, they are too smooth and rounded to lock together to form stable concrete.

The sand we need is the more angular stuff found in the beds, banks, and floodplains of rivers, as well as in lakes and on the seashore. The demand for that material is so intense that around the world, riverbeds and beaches are being stripped bare, and farmlands and forests torn up to get at the precious grains. And in a growing number of countries, criminal gangs have moved in to the trade, spawning an often lethal black market in sand.

“The issue of sand comes as a surprise to many, but it shouldn’t,” says Pascal Peduzzi, a researcher with the United Nations Environment Programme. “We cannot extract 50 billion tonnes per year of any material without leading to massive impacts on the planet and thus on people’s lives.”

The main driver of this crisis is breakneck urbanisation. Every year there are more and more people on the planet, with an ever growing number of them moving from the rural countryside into cities, especially in the developing world. Across Asia, Africa, and Latin America, cities are expanding at a pace and on a scale far greater than any time in human history.

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