Acceleration of global N₂O emissions seen from two decades of atmospheric inversion

Nitrous oxide (N₂O) is the third most important long-lived GHG and an important stratospheric ozone depleting substance. Agricultural practices and the use of N-fertilizers have greatly enhanced emissions of N₂O. Here, we present estimates of N₂O emissions determined from three global atmospheric inversion frameworks during the period 1998–2016. We find that global N₂O emissions increased substantially from 2009 and at a faster rate than estimated by the IPCC emission factor approach. The regions of East Asia and South America made the largest contributions to the global increase. From the inversion-based emissions, we estimate a global emission factor of 2.3 ± 0.6%, which is significantly larger than the IPCC Tier-1 default for combined direct and indirect emissions of 1.375%. The larger emission factor and accelerating emission increase found from the inversions suggest that N₂O emission may have a nonlinear response at global and regional scales with high levels of N-input.