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

Abstract

Anthropogenic nitrogen inputs cause major negative environmental impacts, including emissions of the important greenhouse gas N ₂O. 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 N ₂O emission factors from 1850-2020. We find that N inputs from atmospheric deposition caused 51% of anthropogenic N ₂O emissions from soils in 2020. The mean effective global emission factor for N ₂O 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 N ₂O-driven climate warming in coming decades, unless targeted mitigation measures are introduced.

Abstract

Soil nitrogen isotopic composition is used to drive the IsoTONE model, which is constrained with measurements of tropospheric nitrous oxide isotopic composition. The model results reveal causes of rising mean global nitrous oxide emission factor.