Understanding global anthropogenic phosphorus inputs is crucial for sustainable nutrient management. We apply the Net Anthropogenic Phosphorus Input (NAPI) model to assess trends across countries from 1961 to 2020. Using a random forest (RF) model, we identify key drivers and project NAPI through 2100. Results show a 1.4-fold global NAPI increase, mainly from fertilizer (PFER: 50.0%, uncertainty: 43.0-55.7%) and food/feed inputs (PIM: 47.8%, uncertainty: 32.2-71.5%). Asia and Europe together account for 62.2% (uncertainty: 49.1-79.3%) of global NAPI (uncertainty ranges derived from Monte Carlo analysis). Feature importance and Shapley additive explanations (SHAP) analysis indicate that urban population density and GDP are the main driving forces for the increase of global NAPI. The RF model further projects future NAPI under three shared socioeconomic pathways (SSPs) from 2025 to 2100, showing that NAPI in the Middle-of-the-Road Pathway (SSP2) and Regional Rivalry Pathway (SSP3) is 20.2 and 39.3% higher, respectively, than that in the Sustainable Development Pathway (SSP1). Optimizing nutrient management and enhancing nutrient cycling (such as reusing phosphorus from livestock manure and food waste composts) are key to improving phosphorus use efficiency and reducing global phosphorus pollution.
Pei et al. (Mon,) studied this question.