Taking planetary nutrient boundaries seriously: Can we feed the people?

Recent research suggests that anthropogenic nutrient flows may have transgressed the regulatory capacity of the earth. Agrifood systems account for most of the flows, and the food supply is limited more by reducing the excessive flows than by phosphorus (P) reserves or population growth. The food supply is limited primarily by the P flow tolerated by freshwater ecosystems and next by the needed reduction in the conversion of nitrogen (N) to reactive form in fertilizer manufacture, legume cultivation and fossil fuel combustion. The required reduction in P and N flows would reduce the food supply to 250 and 710 kcal capita−1 d−1, respectively, in the current agrifood systems. Dietary changes, waste prevention and nutrient recycling are parts of the necessary transformation.