Nitrous oxide emissions surge by 40% over four decades, report finds

A new report reveals a 40% increase in anthropogenic nitrous oxide emissions over the past 40 years, bringing into sharp focus the urgent need for emission reductions to meet climate goals.

Chimney emissions

In the past 40 years, human activities have increased nitrous oxide (N₂O) emissions by 40%, with a notable acceleration from 2020 to 2022, according to the Global Nitrous Oxide Budget released today. This report, coordinated by the Global Carbon Project and authored by an international team including researchers from CSIRO, Australia’s national science agency, highlights the pressing issue of N₂O emissions.

Dr Pep Canadell of CSIRO explained that the report uses data from 1980 to 2020 to account for both natural and human-induced N₂O sources.

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

The report finds that N₂O levels in the atmosphere have accelerated in the last four decades, with growth rates from 2020-2022 being 30% higher than any previous year since 1980.

Agricultural activities, including the use of nitrogen fertilizers and animal manure, have been the primary sources of anthropogenic N₂O emissions, contributing 74% of the total in the past decade. Other sources include fossil fuels, waste, wastewater, and biomass burning.

Dr Hanqin Tian from Boston College, who led the study, noted, "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."

In 2020, the largest emitters of anthropogenic N₂O by volume were China (16.7%), India (10.9%), the USA (5.7%), Brazil (5.3%), and Russia (4.6%). Australia's emissions have remained stable over the past two decades.

Dr Canadell emphasized the need for reduction, saying, "The observed atmospheric N₂O concentrations in recent years have exceeded projected levels."

“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 is actively working on initiatives to measure and reduce agricultural N₂O emissions, including efforts to improve nitrogen fertilizer efficiency in cotton production and studies on the N₂O footprint in the grains sector. These efforts aim to make the food system more nitrogen-efficient.

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

The report was published in Earth System Science Data, read it here.

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