Warming and redistribution of nitrogen inputs drive an increase in terrestrial nitrous oxide emission factor

Anthropogenic nitrogen inputs cause major negative environmental impacts, including emissions of the important greenhouse gas N2O. Despite their importance, shifts in terrestrial N loss pathways driven by global change are highly uncertain. Here we present a coupled soil-atmosphere isotope model (IsoTONE) to quantify terrestrial N losses and N2O emission factors from 1850-2020. We find that N inputs from atmospheric deposition caused 51% of anthropogenic N2O emissions from soils in 2020. The mean effective global emission factor for N2O was 4.3 +/- 0.3% in 2020 (weighted by N inputs), much higher than the surface area-weighted mean (1.1 +/- 0.1%). Climate change and spatial redistribution of fertilisation N inputs have driven an increase in global emission factor over the past century, which accounts for 18% of the anthropogenic soil flux in 2020. Predicted increases in fertilisation in emerging economies will accelerate N2O-driven climate warming in coming decades, unless targeted mitigation measures are introduced.

Automated summary

Anthropogenic nitrogen inputs have significant negative impacts on the environment, especially through the emission of the important greenhouse gas N2O. The shifts in terrestrial nitrogen loss pathways driven by global change are highly uncertain. This study presents a model that quantifies terrestrial nitrogen losses and N2O emission factors, revealing that atmospheric deposition inputs are the main cause of anthropogenic N2O emissions from soils. The predicted increase in fertilizer use in emerging economies will further accelerate N2O-driven climate warming, unless targeted mitigation measures are implemented.