<b>The Russia−Ukraine war exposed a hidden food−climate vulnerability</b>

Whether abrupt fertilizer scarcity delivers climate benefit, however, remains unclear. Here we exploit cross-country differences in pre-war dependence on fertilizer supplies from Russia and Belarus to quantify the food and climate consequences of the 2022 Russia−Ukraine war.

Combining international fertilizer trade, country-level agricultural data, event-study analysis and process-based soil-carbon model, we identify that supplier concentration, rather than overall import dependence, best predicted post-war declines in N use. A one-standard-deviation increase in pre-war Russia−Belarus import share reduced N application by 5.5% on average during 2023−2024, corresponding to an estimated annual reduction of 4.36 Tg N. Lower N use reduced crop production and plant-derived carbon (C) inputs, causing global cropland soil organic carbon losses of 22.5−30.8 Tg C yr⁻¹ during 2022−2024.