CCAC N20 Assessment

Global Nitrous Oxide Assessment

This Assessment presents an updated emissions budget, new projections of ozone, climate and air quality impacts under different scenarios, and the most recent evaluations of effectiveness and costs of abatement measures across all major sectors.

Nitrous oxide, considered to be a super pollutant, is the third most important greenhouse gas and the most significant ozone-layer depleting substance emitted today. Its human-induced emissions, which primarily originate from the agricultural use of synthetic fertilisers and manure, are increasing faster than previously projected. This Assessment identifies abatement measures available today that could reduce these emissions by more than 40 per cent below current levels.

Transformations in food production and societal systems could lead to even deeper reductions. Nitrous oxide is part of the nitrogen cycle – nitrogen is essential to all life on Earth and the global food system. The abatement of its anthropogenic emissions must be grounded in a sustainable nitrogen management approach which would also reduce the loss of other nitrogen compounds to the environment. Ambitious action using this approach could move the world closer to meeting its 1.5° Celsius temperature goal, protect the stratospheric ozone layer, and improve air and water quality, while protecting food security, ecosystems and human health. This approach is an important part of a super pollutant multi-benefit strategy, which, alongside efforts to achieve net zero carbon dioxide emissions by mid-century, is necessary to put the world on a sustainable path to meeting long-term climate goals.

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OPPORTUNITIES TO ACT NOW

Trends in emissions N20 assessment CCAC
Fig 2.1 Trends in atmospheric nitrous oxide levels derived from ice core or firn air (triangle) and ambient air (circle) measurements shown for the northern (dark blue) and southern (light blue) hemispheres, parts per billion by volume.

Nitrous oxide is a long-lived greenhouse gas approximately 270 times more powerful than carbon dioxide per tonne of emission at warming the Earth. 

Its anthropogenic emissions are responsible for approximately 10 per cent (around 0.1° Celsius) of net global warming to date since the industrial revolution. It is also an ozone-layer depleting substance.

Although nitrous oxide is not controlled under the Montreal Protocol, its current anthropogenic emissions are a larger threat to the ozone layer than any chemical controlled under this protocol.

Ambitious action to reduce nitrous oxide emissions could move the world closer to meeting a wide range of global climate, ozone and other environmental and human health goals.

N20 Assessment CCAC
Fig 2.1 Estimated global emissions and uncertainties based on the atmospheric levels assuming a constant lifetime of nitrous oxide of 116±9 years, nitrous oxide and carbon dioxide equivalent, megatonnes per year

BENEFITS OUTWEIGH COST OF ACTION

N20 Cycle CCAC

CLIMATE BENEFITS
 

If nitrous oxide emissions continue to increase at their current rate, there is no plausible pathway to limiting global warming to 1.5° Celsius in the context of sustainable development, as defined in the Paris Agreement. (Section 4.1.2) 

Even keeping current nitrous oxide emissions constant would constrain society’s capacity to limit global warming to 1.5° Celsius and require much greater and costlier reductions of carbon dioxide and methane emissions. (Section 4.1.2)

Ambitious nitrous oxide abatement could avoid the equivalent of up to 235 billion tonnes of carbon dioxide emissions by 2100, which is approximately 6 years of current carbon dioxide emissions from fossil fuel burning. (Section 4.1.2)

A sustainable nitrogen management approach to agricultural nitrous oxide emissions could also significantly reduce emissions of shortlived nitrogen compounds – other nitrogen oxides and ammonia – which would rapidly improve air quality but cause additional near-term warming primarily due to the reduced cooling effect of aerosols. 

Due to nitrous oxide’s long lifetime, the net effect of a sustainable nitrogen management approach would reduce warming in the longer term. This is well justified by the health benefits of improved air quality. By contrast, reductions in industrial nitrous oxide emissions provide climate benefits across all time scales. (Section 4.1.2)

 

 

OZONE LAYER PROTECTION

Nitrous oxide is currently the most significant ozone-layer depleting substance being emitted to the atmosphere. The destructive capacity of today’s nitrous oxide emissions approximately equals the sum of all other current ozone-depleting substance emissions.

Through 2050, ambitious nitrous oxide abatement could provide roughly the same ozone benefits as the 2007 Montreal Protocol agreement to accelerate the phase-out of hydrochlorofluorocarbons. Through 2100, the benefits could accumulate to more than five times those of the accelerated phase out. (Sections 4.2.1, 4.2.3)

Ambitious nitrous oxide abatement could avoid a 0.2–0.8 per cent increase in cataract cases and a 2-10 per cent increase in skin cancers by 2080-2090, depending on latitude. (Section 4.2.5)

The lowest levels of ozone this century and beyond are expected to occur if nitrous oxide emissions continue unabated and carbon dioxide and methane are abated consistent with climate goals. In such a future, by the end of the century much of the world’s population could be exposed to ultraviolet levels larger than peak ozone depletion in 1995-2005. (Sections 4.2.4)

 

N20 Infographic CCAC

Abatement of nitrous oxide emissions under a sustainable nitrogen management approach would significantly improve air quality through the concurrent abatement of ammonia and nitrogen oxide emissions that form harmful fine particulates and ground-level ozone. This would have multiple health benefits, especially for the most vulnerable in society, ultimately avoiding approximately 20 million premature deaths globally by 2050, of which roughly 4 million would be saved in the next decade. (Section 4.1.3)

A sustainable nitrogen management approach would deliver significant additional benefits for water quality, soil health and the structure and functioning of ecosystems. Reducing nitrogen run-off would, for example, lower the risk of eutrophying water bodies and contaminating drinking water supplies, while reducing such associated human health impacts as decreasing the risk of colon cancer.

Nitrous oxide abatement measures could be implemented while simultaneously meeting future food demand, consistent with existing food security goals. Achieving this will require significant efforts to increase the efficiency of agricultural nitrogen use and reduce excessive nitrogen application in many parts of the world. (Section 4.1.4)

SOLUTIONS

Currently available abatement measures that could reduce global anthropogenic nitrous oxide emissions by more than 40 per cent below current levels. Industrial emissions provide an opportunity for rapid nitrous oxide abatement.

There are a number of cost-effective technologies that can effectively eliminate industrial nitrous oxide emissions and do not require significant changes to existing production processes. Ambitious abatement in these sectors alone could reduce emissions by approximately 2.5 billion tonnes of carbon dioxide equivalent and 160,000 tonnes of CFC-11 equivalent.

Figure 2.3 Global N20 Assessment
Figure 2.3 Nitrous oxide sources and sinks, megatonnes of nitrous oxide per year. Values shown are the mean for 2010–2019. Source: Tian et al. 2024

 

Currently available measures (~40% reduction potential)

Chemical Sector

Acid Production

Adipic acid production: Catalytic reduction and thermal destruction 

Nitric acid production: Catalytic reduction and thermal destruction

Waste management

Waste Treatment

  • Improving wastewater treatment to increase the N2/N2O ratio
  • Reducing biomass burning and fossil fuel combustion.
Agricultural sector

Farm Management Efficiency

  • Nitrogen testing: Soil and plant nitrogen testing 
  • Nitrogen application: Split application using controlled-release fertilisers; urease and nitrification inhibitors; reduced application rates; and increased manure recycling 
  • Crop management: Integrating nitrogen-fixing crops in rotations; reduced tillage; and the use of cover crops 
  • Livestock diets: Optimising protein intake 
  • Grazing: Rotational grazing 
  • Manure storage/process: Solid/slurry separation; storage under dry conditions and rapid drying; anaerobic digestion
  • Drainage control: Buffer strips 
  • Planning: Integration of crop and livestock production

Avoiding Trade-Offs


Several emerging decarbonisation measures could result in increased nitrous oxide emissions. 

There is a considerable risk that increasing the use of ammonia as a fuel for marine shipping and biofuels derived from fertilised crops could produce significant nitrous oxide emissions, partially or completely offsetting their intended climate benefits. 

For example, recent studies suggest that nitrous oxide emissions from the use of ammonia as a shipping fuel could, if not managed properly, exceed agricultural nitrous oxide emissions. (Section 6.3.3)

The trade-offs between carbon dioxide, methane and nitrous oxide abatement in all sectors need to be better understood so that technologies can be improved and policies developed to manage the risks. (Section 6.3.3)

MULTILATERAL OPTIONS FOR ACTION ON NITROUS OXIDE 

Nitrous oxide’s impacts on the ozone layer and climate, coupled with its close links to other nitrogen compounds, means that it falls under the remits of several multilateral environmental agreements, including the Paris Climate Agreement and the Vienna Convention for the Protection of the Ozone Layer. (Section 6.4) 

Moreover, an integrated approach through sustainable nitrogen management including ambitious nitrous oxide abatement would enable associated reductions in other nitrogen compounds and contribute to achieving several other international targets. 

These include: 

  • Target 7 of the Global Biodiversity Framework: at least halving nutrient losses to the environment by 2030; 
  • The Gothenburg Protocol targets on ammonia and nitrogen oxides under the Convention on Long Range Transboundary Air Pollution;
  • A number of the Sustainable Development Goals, notably including: 

Goal 2: End hunger, achieve food security and improved nutrition, and promote sustainable agriculture; 

Goal 6: Ensure availability and sustainable management of water and sanitation for all; 

Goal 12: Ensure sustainable consumption and production patterns; 

Goal 13: Take urgent action to combat climate change and its impacts by regulating emissions and promoting developments in renewable energy. 

Ultimately, the successful implementation of any multilateral effort to reduce nitrous oxide or nitrogen losses more broadly will require concerted action at national and sub-national scales.

Download the full assessment here.