Atmospheric nitrous oxide emissions grew 40% from 1980 to 2020, new study finds

Southern Cross University

Emissions of nitrous oxide – a greenhouse gas more potent than carbon dioxide and methane – has continued to increase over the past 40 years, according to a new report by the Global Carbon Project which includes a Southern Cross University member.

Australia is among the top 10 nitrous oxide emission-producing countries, the report found.

Further, farming practices were primarily responsible for releasing more than 10-million metric tons of nitrous oxide into the atmosphere in 2020.

The report “Global Nitrous Oxide Budget 2024“, led by researchers from Boston College and including Southern Cross University’s Dr Judith Rosentreter, is published today in the journal Earth System Science Data.

The report found agricultural production accounted for 74 percent of human-driven nitrous oxide (N2O) emissions in the 2010s. The emissions can be attributed primarily to the use of commercial fertilisers and animal waste on croplands.

Excess nitrogen contributes to soil, water, and air pollution. In the atmosphere, it depletes the ozone layer, and exacerbates climate change.

Southern Cross University Senior Research Fellow Dr Judith Rosentreter is one of the co-authors of this global effort.

“We live an era when greenhouse gas emissions must decline to reduce global warming,” said Dr Rosentreter.

“We are alarmed to see that the growth rates of atmospheric nitrous oxide in 2021 and 2022 were more than 30 percent higher than the average rate of increase in the previous decade.”

Agricultural emissions reached 8-million metric tons in 2020, a 67 per cent increase from the 4.8- million metric tons released in 1980, according to the study, the most comprehensive study of global nitrous oxide emissions and sinks produced by a team of 58 researchers from 55 organisations in 15 countries.

“Nitrous oxide emissions from human activities must decline in order to limit global temperature rise to 2°C as established by the Paris Agreement,” said the report’s lead author, Hanqin Tian, the Schiller Institute Professor of Global Sustainability at Boston College.

“Reducing nitrous oxide emissions is the only solution since at this point no technologies exist that can remove nitrous oxide from the atmosphere.”

The concentration of atmospheric nitrous oxide reached 336-parts-per-billion in 2022, a 25 per cent increase over pre-industrial levels that far outpaces predictions previously developed by the Intergovernmental Panel on Climate Change.

“This emission increase is taking place when the global greenhouse gasses should be rapidly declining towards net zero emissions if we have any chances to avoid the worst effects of climate change,” said Dr Tian, who coordinated the research on behalf of the Global Carbon Project.

The world’s farmers used 60 million metric tons of commercial nitrogen fertilisers in 1980. By 2020, the sector used 107 million metric tons. That same year, animal manure contributed 101 million metric tons for a combined 2020 usage of 208 million metric tons.

The unfettered increase in a greenhouse gas with a global warming potential approximately 300 times larger than carbon dioxide, presents direct policy implications.

Drawing on millions of nitrous oxide measurements taken during the past four decades on land and in the atmosphere, freshwater systems, coastal waters and the ocean, Tian said the researchers have generated the most comprehensive assessment of global nitrous oxide to date.

The researchers examined data collected around the world for all major economic activities that lead to nitrous oxide emissions and reported on 18 anthropogenic and natural sources and three absorbent “sinks” of global nitrous oxide.

Australia's anthropogenic N2O emissions
The Global Carbon Project has assessed Australia’s anthropogenic N2O emissions.

The top 10 nitrous oxide emission-producing countries are: China, India, the United States, Brazil, Russia, Pakistan, Australia, Indonesia, Turkey, and Canada, the researchers found.

“Anthropogenic nitrous oxide emissions from Australia have been relatively stable over the past two decades. Although we find high fluctuations of emissions from biomass burning such as wildfires from year to year,” said Dr Rosentreter.

Some countries have seen success implementing policies and practices to reduce nitrous oxide emissions, according to the report. Emissions in China have slowed since the mid-2010s; as have emissions in Europe during the past few decades.

Established in 2001, The Global Carbon Project analyses the impact of human activity on greenhouse gas emissions and Earth systems, producing global budgets for the three dominant greenhouse gases – carbon dioxide, methane, and nitrous oxide – that assess emissions and sinks to inform further research, policy, and international action.

Improved practices in agriculture around the use of nitrogen fertilizers and animal manure will help to address and reduce greenhouse gas emissions and water pollution.

“While there have been some successful nitrogen reduction initiatives in different regions, we found an acceleration in the rate of nitrous oxide accumulation in the atmosphere in this decade,” said Global Carbon Project Executive Director Josep Canadell, who is also a research scientist at CSIRO, Australia’s national science agency.

Dr Tian said there is a need for more frequent assessments so mitigation efforts can be targeted to high-emission regions and economic activities. An improved inventory of sources and sinks will be required if progress is going to be made toward the objectives of the Paris Agreement.

Study details

Global nitrous oxide budget (1980–2020) by H Tian, et al

Published in Earth System Science Data journal


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