Tehran is moving to restrict – or effectively close – the Strait of Hormuz to shipping, as part of the latest escalation in the war involving Iran.

Markets have reacted to the global impact of closing this incredibly busy shipping channel, focusing on the risk to oil and gas flows, the prospect of higher crude prices and the inflationary pressures that would follow.

That concern is justified. But it captures only part of the story. A sustained disruption of traffic through Hormuz would not simply constitute an energy crisis. It would also represent a fertiliser shock (where prices go up dramatically and supply goes down) – and, by extension, a direct risk to global food security.

Modern agriculture runs not only on sunlight and soil, but on natural gas. When German chemists Fritz Haber and Carl Bosch developed their nitrogen fixation method in the early 20th century, they did more than just manufacture ammonia at scale.

They launched a global chemical revolution that remains a cornerstone of modern civilization and agriculture. Through this process, methane is transformed into ammonia, and ammonia into nitrogen fertilisers such as urea – the most widely used nitrogen fertiliser. Those fertilisers allow crops to reach the yields on which today’s global population depends. Without it, harvests of wheat, maize and rice would fall dramatically.

Around a third of globally traded urea passes through the Strait of Hormuz. The Persian Gulf sits at the centre of this system for........

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