Global Nitrous Oxide (N₂O) Assessment Report

The Global Nitrous Oxide Assessment has recently been published by the United Nations Environment Programme & the Food and Agriculture Organization.

• It is the first international report focused solely on N2O in more than a decade. 

Crucial Insights on the Global Nitrous Oxide (N₂O) Assessment Report

Key Findings

• Global Warming Impact:
  • N₂O currently contributes 0.1°C to global warming.
  • Its continued increase in emissions makes it impossible to limit warming to 1.5°C.
• Anthropogenic Emissions:
  • Increased by 40% since 1980, with 75% originating from agriculture (synthetic fertilizers and manure).
• Ozone Depletion and Health Risks:

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• • N₂O is the leading ozone-depleting substance, increasing harmful UV exposure.
  • Raises risks of cataracts (0.2–0.8%) and skin cancer (2–10%).
• Abatement measures: The report highlighted that currently, available abatement measures could reduce N2O emissions by more than 40 per cent below current levels.
• Emissions Sources:
  • Agriculture: It is currently the source of 75% of those emissions, of which approximately 90% comes from the use of synthetic fertilisers and manure on agricultural soils and 10% from manure management.
  • Industry: Industrial sources account for approximately 5% of emissions, and the remaining 20% come from fossil fuel combustion, wastewater treatment, aquaculture, biomass burning, and other sources.
• Rise in Emissions: Atmospheric abundance of the gas has risen by over 20% since pre-industrial era; its mean annual growth rate over the past five years (2017–2021) was 1.2 parts per billion a year and was nearly twice that of the early 2000s (2000–2004).

Suggested Measures

• Agriculture: Use of enhanced-efficiency fertilisers, nitrification inhibitors, & slow-release formulations can reduce emissions.
• Industry: Industries can eliminate N2O emissions by adopting existing and relatively low-cost abatement measures that could cost $1,600-6,000 per tonne of nitrous oxide. 
• Fossil Fuel Reduction: Transition to renewable resources in transportation & energy production.
• Manure Management: Balance nutrient inputs in animal feed, reduce grazing intensity, & apply anaerobic digestion of manure.
• Multilateral Options:  Adopting targets like the Gothenburg Protocol on ammonia & nitrogen oxides under the Convention on Long Range Transboundary Air Pollution.
• Transformations in food production: Transformations in food production and societal systems could lead to even deeper reductions in  Nitrous Oxide emissions.

Nitrous Oxide and Its Absorbent Sinks

About Nitrous Oxide (N2O)

• It is a Greenhouse gas (GHG) 300 times more potent than carbon dioxide (CO2).
• It has the third-highest concentration, after CO2 and methane (CH4), in Earth’s atmosphere among GHGs responsible for global warming.
• It can live in the atmosphere for up to 120-125 years and is approximately 270 times more powerful than carbon dioxide per tonne of emission at warming the Earth.

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Absorbent “Sinks” of Nitrous Oxide

• Soils: Microbial processes in soils can consume and reduce N₂O emissions. 
  • Denitrifying bacteria convert N₂O to nitrogen gas (N₂) under anaerobic conditions.
• Oceans:  Deeper and subsurface oceans absorb N₂O from the atmosphere through dissolution at the air-sea interface.
  • Marine phytoplankton play a role in consuming dissolved N₂O
• Stratosphere: N₂O reacts with ozone (O₃) which leads to the formation of nitrogen oxides (NOx) and ultimately nitrogen gas (N₂).