Emissions of the greenhouse gas nitrous oxide up 40 percent since 1980
Record growth of atmospheric concentration in 2020 - 2022
Anthropogenic emissions of nitrous oxide (N2O), a much more potent greenhouse gas per molecule than carbon dioxide or methane, increased by around 40% between 1980 and 2020. In 2020, anthropogenic emissions into the atmosphere reached more than 10 million tons per year, according to the new report "Global Nitrous Oxide Budget 2024" published by the Global Carbon Project in the journal Earth System Science Data. In the 2010s, around three quarters of man-made nitrous oxide emissions were attributable to global agricultural production, mainly due to the use of mineral fertilizers and manure on farmland.
Nitrous oxide (N2O) is produced during natural conversion processes of nitrogen in marine and terrestrial ecosystems. In the atmosphere, nitrous oxide is an important greenhouse gas that contributes to climate change. Its role in the climate system is due to its significantly stronger greenhouse gas effect per molecule compared to the more commonly known greenhouse gases CO2 and CH4 and a significantly longer residence time in the atmosphere. In addition, decay products of nitrous oxide promote the depletion of the stratospheric ozone layer.
58 scientists from 55 organizations in 15 countries have now jointly written the most comprehensive study to date on the analysis of global nitrous oxide sources and sinks. To this end, they analyzed millions of nitrous oxide measurements taken over the last four decades on land, in the atmosphere, in freshwater systems and in the ocean. "By combining measurements, statistics and modeling, we were able to gain a very detailed insight into how the regional and global sources of N2O have changed in recent decades," says Prof. Dr. Sönke Zaehle, Director at the Max Planck Institute for Biogeochemistry in Jena and co-author of the study.
The researchers examined data collected worldwide for all major economic activities and natural processes that lead to nitrous oxide emissions and found 18 anthropogenic and natural sources. They also report on three "sinks" of global nitrous oxide, as well as the contribution of various countries. The authors were particularly struck by the sharp rise in emissions from the agricultural sector.
In terrestrial ecosystems, nitrogen is used as a plant fertilizer as it increases productivity and yields. However, the mineral fertilizer or animal manure used for this purpose also increases the production of nitrous oxide in the soil. In 1980, 60 million tonnes of mineral nitrogen fertilizer were applied to fields in agriculture worldwide; in 2020, this figure had already risen to 107 million tonnes. In the same year, roughly the same amount of nitrogenous animal manure was also applied, so that in 2020 a total of over 200 million tonnes of nitrogen fertilizer were used. This is far more than natural terrestrial ecosystems absorb through biological nitrogen fixation. Nitrous oxide emissions from agriculture alone increased globally by 67% in 2020 compared to 1980, making a decisive contribution to the 40% global increase in nitrous oxide emissions.
Other important man-made industrial or land-use-related emissions also contributed to the increase in atmospheric nitrous oxide concentrations worldwide. A clear exception is the EU, where industrial and energy-related emissions fell by around 30% in the period 1980-2020 and agricultural emissions remained at a roughly constant level.
"Despite some successful nitrogen reduction initiatives, we found that nitrous oxide emissions have increased globally," says Josep Canadell, Executive Director of the Global Carbon Project and scientist at the Australian science agency CSIRO. "The increase in atmospheric nitrous oxide concentrations has accelerated noticeably in recent decades," adds Zaehle, "especially in the subsequent period of the study, from 2020 to 2022, the increase is stronger than in any other of the observed periods". As a result of this increase, nitrous oxide concentrations reached a record high of 336 ppb in 2022 compared to pre-industrial levels, thus contributing to global warming.
"This increase in nitrous oxide emissions comes at a time when global greenhouse gas emissions should be falling rapidly towards net zero emissions if we are to have any chance of avoiding the worst effects of climate change," says Hanqin Tian, Professor of Global Sustainability at the Schiller Institute at Boston College, USA, who coordinated the study on behalf of the Global Carbon Project.
According to the study, in order to limit nitrous oxide emissions, improved practices in the use of nitrogen fertilizers and animal manure in agriculture should be applied in the future. These have the additional advantage that soil, water and air pollution caused by high nitrogen use, known as eutrophication, can also be reduced.
According to Tian, more studies and analyses are needed in order to better target efforts to curb emissions to regions and economic sectors with high emissions. An improved inventory of sources and sinks is therefore necessary if progress is to be made towards achieving the goals of the Paris Agreement.
