Emissions of the greenhouse gas N2O have risen sharply

Emissions of N₂O (nitrous oxide), a greenhouse gas more potent than carbon dioxide or methane, increased by 40 percent between 1980 and 2020. In the latter year, more than 10 million tonnes were released into the atmosphere, mainly from agriculture. That's according to a new report by the Global Carbon Project, an international organization that studies global greenhouse gas emissions. The report was co-authored by 58 researchers from 55 organisations in 15 countries. Two researchers from Utrecht University’s Faculty of Geosciences are also involved in the research. "The nitrogen problem goes beyond soil contamination."

Agricultural production accounted for 74 percent of human-caused emissions of N₂O in the previous decade — primarily from commercial fertilizers and animal waste on cropland — according to the "Global Nitrous Oxide Budget 2024" report published today in the journal Earth System Science Data. Agricultural emissions reached 8 million tonnes in 2020, an increase of 67 per cent over the 4.8 million tonnes emitted in 1980.

Record quantity

The most alarming finding of the study: in an era when greenhouse gas emissions need to fall precisely to reduce global warming, more N₂O was released into the atmosphere in 2021 and 2022 than at any other time in history. "N₂O has a stronger warming effect than carbon dioxide," emphasises Dr Junjie Wang of Utrecht University’s Faculty of Geosciences. "And due to human activities, we are seeing significant emissions of N₂O today. Not only directly from agriculture and aquaculture, such as fish farms, but also indirectly from surface water." Previously, she signed up for a study that identified groundwater and reservoirs as important "sources" of N₂O.

N2O has a stronger warming effect than carbon dioxide

Not all nitrogen is the problematic nitrogen

Our atmosphere is naturally made up of almost 80% nitrogen, a gas molecule with the formula N₂, but from the point of view of environmental problems or climate change, "nitrogen" refers to reactive compounds that are often created by human activity. N₂O is one such compound. Another well-known example is ammonia (NH₃). "This study once again shows the breadth of the nitrogen problem," says Prof. Lex Bouwman, who was involved in the N₂O study as well as Junjie Wang. "So it's not just about the pollution of groundwater and surface water, but also about the greenhouse effect. Dutch politicians haven't even thought about that yet."

This study once again shows the breadth of the nitrogen problem

Climate agreement

"N₂O emissions from human activities must decrease to limit the global temperature increase to 2°C, as set out in the Paris Climate Agreement," said the report's lead author, Hanqin Tian, Professor of Global Sustainability at the Schiller Institute in Boston College. "Reducing N₂O emissions is the only solution, as there are currently no technologies that can remove N₂O from the atmosphere."

Millions of measurements

The concentration of atmospheric N₂O reached 336 parts per billion in 2022, a 25 percent increase from pre-industrial levels. These figures go far beyond previous estimates by the Intergovernmental Panel on Climate Change (IPCC), Tian said. The study was preceded by millions of N₂O measurements. These have been carried out over the past four decades on land and in the atmosphere, in freshwater systems and the ocean. Tian points out that the researchers have thus produced the most comprehensive global N₂O figures to date.

On a different tack

"We need to rethink a good portion of our current agriculture practices. Reducing greenhouse gas emissions and water pollution requires more rational use of fertilizers and animal manure," says Josep Canadell, Executive Director of the Global Carbon Project and researcher at Australia's CSIRO Marine and Atmospheric Research.

Successes

The top 10 N₂O producing countries are China, India, the United States, Brazil, Russia, Pakistan, Australia, Indonesia, Turkey and Canada, the survey shows. Some countries have seen success in reducing N₂O emissions, according to the report. For example, the growth of Chinese emissions has slowed since the mid-2010s, as have emissions in Europe in recent decades.

Publication

Hanqin Tian, Naiqing Pan, Rona L. Thompson et al., ‘Global nitrous oxide budget (1980–2020)’, Earth System Science Data, https://doi.org/10.5194/essd-16-2543-2024.