A comprehensive quantification of global nitrous oxide sources and sinks

Nitrous oxide (N2O), like carbon dioxide, is a long-lived greenhouse gas that accumulates
in the atmosphere. Over the past 150 years, increasing atmospheric N2O concentrations
have contributed to stratospheric ozone depletion1 and climate change2, with the
current rate of increase estimated at 2 per cent per decade. Existing national inventories
do not provide a full picture of N2O emissions, owing to their omission of natural
sources and limitations in methodology for attributing anthropogenic sources. Here we
present a global N2O inventory that incorporates both natural and anthropogenic sources
and accounts for the interaction between nitrogen additions and the biochemical
processes that control N2O emissions. We use bottom-up (inventory, statistical
extrapolation of flux measurements, process-based land and ocean modelling) and
top-down (atmospheric inversion) approaches to provide a comprehensive
quantification of global N2O sources and sinks resulting from 21 natural and human
sectors between 1980 and 2016. Global N2O emissions were 17.0 (minimum–maximum
estimates: 12.2–23.5) teragrams of nitrogen per year (bottom-up) and 16.9 (15.9–17.7)
teragrams of nitrogen per year (top-down) between 2007 and 2016. Global human-induced
emissions, which are dominated by nitrogen additions to croplands, increased by 30%
over the past four decades to 7.3 (4.2–11.4) teragrams of nitrogen per year. This
increase was mainly responsible for the growth in the atmospheric burden. Our
findings point to growing N2O emissions in emerging economies—particularly Brazil,
China and India. Analysis of process-based model estimates reveals an emerging
N2O–climate feedback resulting from interactions between nitrogen additions and
climate change. The recent growth in N2O emissions exceeds some of the highest
projected emission scenarios3,4, underscoring the urgency to mitigate N2O emissions.