Concerning increase in nitrous oxide emissions

Human-induced nitrous oxide (N₂O) emissions have increased by 40% in the past 40 years, an international paper has revealed.

The Global Nitrous Oxide Budget report was coordinated by the Global Carbon Project and authored by an international team of researchers, including scientists from CSIRO. Published in Earth System Science Data, the Budget forms a core component of global greenhouse gas assessments.

CSIRO’s Dr Pep Canadell said the report incorporates both natural and human-induced N₂O sources using data from 1980 to 2020.

“N₂O in the atmosphere contributes to global warming as well as depleting the ozone layer. It is a long-lived potent greenhouse gas and has been accumulating in the atmosphere since the pre-industrial period,” Canadell said.

“Our report shows N₂O accumulation in the atmosphere has accelerated in the last four decades. Growth rates over the past three years — from 2020–2022 — are 30% higher than any previously observed year since 1980.”

74% of the total anthropogenic N₂O emissions in the last decade were from agricultural production, due to the use of nitrogen fertilisers and animal manure. This was followed by fossil fuels, waste and wastewater, and biomass burning.

Graph of 2000 years of atmospheric nitrous oxide concentrations. Observations taken from ice cores and the atmosphere. ©Bureau of Meteorology/CSIRO/Australian Antarctic Division.

Dr Hanqin Tian from Boston College, who led the study, said the report provided a comprehensive quantification of global N₂O sources and sinks in 21 natural and anthropogenic categories from countries across the globe.

“The once top emitter, Europe, has reduced its emissions since the 1980s by 31%, through industrial emission reductions. However, emerging economies have grown in response to growing population and food demand,” Tian said.

“The top five country emitters by volume of anthropogenic N₂O emissions in 2020 were China (16.7%), India (10.9%), USA (5.7%), Brazil (5.3%) and Russia (4.6%).”

Australia’s anthropogenic N₂O emissions have been stable over the past two decades.

Globally, Canadell said that he observed atmospheric N₂O concentrations in recent years had exceeded projected levels, underscoring the importance of reducing anthropogenic N₂O emissions.

“For net-zero emission pathways consistent with the Paris Agreement to stabilise global temperatures below 2°C, anthropogenic N₂O emissions need to decline on average by around 20% by 2050 from 2019 levels,” he said.

There are various CSIRO initiatives underway to measure and address agricultural N₂O emissions, including reducing loss of nitrogen fertiliser for cotton production and studies on the N₂O footprint of the grains sector to make the food system more nitrogen efficient.

The Global Nitrous Oxide Budget 2024 is the second budget of its kind. It is supported with funding from the Australian Government under the National Environmental Science Program’s Climate Systems Hub.

Top image credit: iStock.com/zetter