Nitrous oxide emissions grew 40 percent from 1980 to 2020

Agricultural production accounted for 74 percent of human-driven nitrous oxide emissions in the 2010s. This is due primarily to the use of nitrogen fertilizers and animal manure on croplands, according to the report “Global Nitrous Oxide Budget 2024”.

“Nitrous oxide emissions are still increasing, and faster than expected. This is in spite of the fact that nitrous oxide is a greenhouse gas and is depleting the ozone layer. Tackling sources of nitrous oxide from agriculture and industry would also be beneficial for soil, water and air quality”, says Rona Thompson, study co-leader and one of the contributing authors.

Dr Thompson at NILU and Dr Glen Peters at CICERO Center for International Climate Research are the only Norwegian researchers contributing to the study.

Agricultural emissions increased by 67 % since 1980

We live in an era when greenhouse gas emissions must decline to reduce global warming. However, in the past few years nitrous oxide levels in the atmosphere increased at a faster rate than at any other time in history. In 2022, the atmospheric concentration of nitrous oxide reached 336 parts per billion, a 25 percent increase over pre-industrial levels.

“The rate of increase far outpaces predictions previously developed by the Intergovernmental Panel on Climate Change”, said Dr Hanqin Tian. He is the lead author of the study and director of the Center for Earth System Science and Global Sustainability at Boston College’s Schiller Institute for Integrated Science and Society.

According to the Global Carbon Project’s report, agricultural emissions reached 8 million metric tons in 2020. This is a 67 percent increase from the 4.8 million metric tons released in 1980.

Assessments for international action

The Global Carbon Project analyzes the impact of human activity on greenhouse gas emissions and Earth systems. They produce 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.

The report “Global Nitrous Oxide Budget 2024” is the most comprehensive study of global nitrous oxide emissions and sinks to date. It was produced by a team of 58 researchers from 55 organizations in 15 countries and published today in the journal Earth System Science Data.

In 1980, the world’s farmers used 60 million metric tons of commercial nitrogen fertilizers. By 2020, the agricultural sector used 107 million metric tons.

The study draws on millions of nitrous oxide measurements taken during the past four decades on land and in the atmosphere, freshwater systems, and the ocean. The researchers also examined data collected around the world for all major economic activities that lead to nitrous oxide emissions. They reported on 18 sources, including natural and human ones, and three “sinks” (removal processes) of global nitrous oxide.

Top ten emitting countries

The top 10 nitrous oxide emitting countries according to the researchers are: China, India, the United States, Brazil, Russia, Pakistan, Australia, Indonesia, Turkey, and Canada. 

Some countries have had success in reducing nitrous oxide emissions through implementing policies and changing practices, according to the report. Emissions in Europe have reduced during the past few decades, while in China the emissions are still increasing but at a slower rate since the mid-2010s.

In the U.S., agricultural emissions continue to increase while industrial emissions have declined slightly, with the net effect of no trend in the total emissions.

Industrial and agricultural measures needed

“The reductions in agricultural emissions of nitrous oxide in Europe and the US are helped by the import of food from other countries. Just as for carbon dioxide emissions, nitrous oxide is a pollutant with a long lifetime and global effect. Thus, it is critical that emission reductions do not simply shift emissions from one country to another,” says Dr Glen Peters.

A relatively straight-forward measure to reduce nitrous oxide emissions from industry is to fit chemical plants (for adipic acid and nitric acid) with catalytic removers, which are already commonplace in Europe and the U.S. In agriculture, improved practices regarding the use of nitrogen fertilizer and animal manure, and especially improved nitrogen use efficiency (the ratio of crop yield to nitrogen input) will help reduce nitrous oxide emissions and improve, soil, water and air quality.

“Nitrous oxide has been a somewhat neglected greenhouse gas. Although its contribution to warming is currently less than that of carbon dioxide and methane it is a very long-lived greenhouse gas meaning that what we emit to the atmosphere will stay there for a long time – well over 100 years. This also means a long-lasting contribution to global warming. There are options to reduce nitrous oxide emissions, and the sooner we do so the better off the climate and environment will be in the long-term," concludes Thompson.

Read the full paper Global Nitrous Oxide Budget 2024 in Earth System Science Data.