The Global Nitrous Oxide (N₂O) Budget, released today, reveals anthropogenic (human-induced) N₂O emissions have increased by 40 per cent in the past four decades, with the period between 2020-2022 showing an accelerated rate of growth.
N₂O is one of the three key greenhouse gases, along with carbon dioxide and methane, contributing to human-driven climate change. N₂O can remain in the atmosphere for more than 100 years and it is also an ozone-depleting substance.
The paper is a core component of global greenhouse gas assessments, coordinated by the Global Carbon Project, and was authored by an international team of researchers, including CSIRO, Australia’s national science agency.
Natural and human-induced N₂O sources
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,’ said Dr Canadell.
‘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 per cent higher than any previously observed year since 1980.’
Nitrogen fertilisers and animal manure
Agricultural production, owing to the use of nitrogen fertilisers and animal manure, contributed 74 per cent of the total anthropogenic N₂O emissions in the last decade. This was followed by fossil fuels, waste and wastewater, and biomass burning.
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 per cent, through industrial emission reductions. However, emerging economies have grown in response to growing population and food demand,’ said Dr Tian.
‘The top five country emitters by volume of anthropogenic N₂O emissions in 2020 were China (16.7 per cent), India (10.9 per cent), USA (5.7 per cent), Brazil (5.3 per cent), and Russia (4.6 per cent).’
Australia’s emissions stable
Australia’s anthropogenic N₂O emissions have been stable over the past two decades.
‘The observed atmospheric N₂O concentrations in recent years have exceeded projected levels, underscoring the importance of reducing anthropogenic N₂O emissions,’ said Dr Canadell.
‘For net-zero emission pathways consistent with the Paris Agreement to stabilise global temperatures below 2 degrees Celsius, anthropogenic N₂O emissions need to decline on average by around 20 per cent by 2050 from 2019 levels.’
CSIRO initiatives underway to measure and address agriculture N₂O emissions include 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. This project is supported with funding from the Australian Government under the National Environmental Science Program’s Climate Systems Hub.
The Global Nitrous Oxide Budget was published in Earth System Science Data.
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