The Haber-Bosch process, which converts atmospheric nitrogen into chemicals for synthetic fertilizer, feeds roughly 4 billion people. Because natural gas feeds the Haber-Bosch process, many of the world’s largest fertilizer production facilities are located near energy sources in the Persian Gulf; fertilizer factories elsewhere also depend on raw materials and gas from the region. When the United States and Israel’s attack on Iran shut down the Strait of Hormuz in late February, it cut off 20% of the global supply of natural gas and one-third of the planet’s raw materials for fertilizer. Without a durable peace, poor countries could experience an unprecedented level of acute hunger this year.

All nitrogen fertilizers start with ammonia, about a quarter of which passes through the Strait of Hormuz. Some add sulfur, whose supply has potentially fallen by more than half since the start of the war. Iran is the world’s fourth-largest exporter of urea, the most popular nitrogen fertilizer by far, and the chaos across the region has disrupted 35% of global urea exports. A single company in Qatar accounts for 14% of the world’s urea supply; its factories went idle after Iran struck a Qatari natural gas plant in March. There is no substitute for these synthetic fertilizers, which support half of global food production and have enabled a massive increase in the human population over the past century.

For Americans and other residents of rich countries, the shock will likely lead to higher food prices. Australia, whose farmers count on Gulf fertilizer shipments in April and June, may face particularly stiff increases. In the Global South, however, the war could mean famine. African countries such as Malawi, Tanzania, Uganda, Kenya, and Sudan are highly dependent on fertilizer imports from the Gulf, as are South Asian countries like Sri Lanka, Pakistan, and Bangladesh. India, the world’s most populous country, gets 25% of its fertilizer from the region, plus raw materials and natural gas for its own fertilizer production facilities. Its farmers receive generous fertilizer subsidies from the government in normal years, and a rise in prices may test the resilience of its agricultural sector and the capacity of the state; the loss of Qatari natural gas supplies has shuttered fertilizer plants in India, Bangladesh, and Pakistan.