Sulphur prices are soaring, flashing a warning sign about geopolitical disruptions and hidden dependencies. More than 90% of global sulphur supply is a byproduct of oil and gas refining, with a third originating in the Middle East. The potential closure of the Strait of Hormuz therefore threatens sulphur even more than oil, as 20% of global oil passes through versus an even greater share of sulphur. Prices were already spiking due to Russian export curbs.

This is not an abstract market move. Mosaic, a major fertiliser producer, idled plants in Brazil late last year as costs surged. The benchmark price exceeded $500 per tonne by year-end, compared to a historical norm of $200 or less. In Africa, where sulphur is used for metal leaching, prices jumped nearly 20% this month. The US, which imports one-third of its sulphur, is also feeling the boom, directly raising fertiliser production costs.

Higher fertiliser prices will hit poor nations first and hardest, with spillover into global food inflation. The crisis provides an accidental preview of a post-oil future. For decades, the fossil fuel industry provided a de facto subsidy of cheap sulphur. As the world shifts to batteries and green energy, demand for sulphuric acid could more than double by 2040 while supply from refining declines. The last US sulphur mine closed in 2000, leaving few alternatives. Current turmoil exposes a looming vulnerability.