COS 164-1 - The Potential Climate Change Mitigation of a Circular Nitrogen Economy in the Food System

Abstract: The food system has tremendous potential to contribute to climate change solutions while helping to meet global food demand, reduce dependence on inorganic nitrogen (N) fertilizers, improve soil and human health, and achieve sustainable development goals. Currently, the food system is the largest global source of N₂O and inorganic N fertilizer is an important emitter of fossil fuel CO₂. One of the greatest opportunities for emissions reduction in the food system is reducing and repurposing food loss and waste (FLW). We used literature data and country-level reporting to analyze FLW mass and nitrogen content and determine the potential carbon and greenhouse gas savings from repurposing FLW into organic fertilizers for the U.S. and China. At the field scale, eliminating inorganic nitrogen overfertilization would result in a reduction in N₂O emissions from soils and a savings of 32 and 37 MMT of CO₂e for the U.S. and China, respectively. Composted or anaerobically digested FLW used as fertilizer, could decrease the amount of inorganic nitrogen fertilizer needed to 3.5 and 4.9 MMT of nitrogen annually in China and the U.S., respectively. This would result in annual savings at the field scale of 60 MMT CO₂e in China and 40 MMT CO₂e in the U.S. from decreased N₂O emissions alone.
Using less inorganic nitrogen fertilizer confers fossil fuel savings from fertilizer manufacturing. Estimates suggest up to 50% of applied inorganic fertilizer is not taken up by plants. If land application of inorganic nitrogen fertilizer is reduced by 50%, the fossil fuel emissions reduction alone would amount to 80 and 20 MMT CO₂e for China and the U.S., respectively. Eliminating overfertilization combined with the substitution of composted or digested FLW fertilizer could theoretically save 97 MMT CO₂e for China, and 11 MMT CO₂e for the U.S. Combined savings from just these two actions could save 157 and 51 MMT CO₂e from China and the U.S., respectively. TAdditional emissions reduction could be achieved from the diversion of FLW from landfilling and incineration, and land application of FLW compost or anaerobic digestate for soil carbon sequestration. Our results show that taking advantage of a circular economy in the food system could significantly lower emissions and contribute to climate change mitigation.