Nitrous oxide greenhouse emissions increase by 40% in 40 years

CSIRO Head Office

Wednesday, 12 June, 2024

Nitrous oxide greenhouse emissions increase by 40% in 40 years

The Global Nitrous Oxide (N2O) Budget has been released, and reveals anthropogenic (human-induced) N2O emissions have increased by 40% in the past four decades, with the period from 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.

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 to 2022 — are 30% higher than any previously observed year since 1980.”

Agricultural production, due to the use of nitrogen fertilisers and animal manure, contributed 74% 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%, 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.

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

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

“The observed atmospheric N2O concentrations in recent years have exceeded projected levels, underscoring the importance of reducing anthropogenic N2O emissions,” Canadell said. “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.”

CSIRO initiatives underway to measure and address agricultural 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. The 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.

Top image credit: iStock.com/Olga Kostrova

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