Reducing nitrous oxide emissions key for achieving climate goals

Current trends show that N2O concentrations are increasing faster than the most pessimistic illustrative pathways of future trajectories used by the IPCC.
Representative Image
Representative Image

While the world’s efforts are centered around reducing carbon dioxide and methane emissions to keep global warming within 1.5 to 2 degree Celsius rise, there is another more potent greenhouse gas whose emissions are continuing unabated — nitrous oxide (N2O).

Between 1980 and 2020, nitrous oxide emissions witnessed a sharp increase of 40% largely driven by unsustainable practices in global food production, according to a new report by the Global Carbon Project.

The report titled “Global Nitrous Oxide Budget 2024”, led by researchers from Boston College and published in the journal Earth System Science Data, says the uncontrolled use of nitrogen fertilisers and animal manure in agricultural production contributed 74% of the total anthropogenic nitrous oxide emissions in the last decade. 

 In an era when greenhouse gas emissions must decline to reduce global warming, in 2020 and 2021 nitrous oxide flowed into the atmosphere at a faster rate than at any other time in history. On Earth, excess nitrogen contributes to soil, water and air pollution. In the atmosphere, it depletes the ozone layer and exacerbates climate change.

Agricultural emissions reached 8 million metric tons in 2020, a 67% increase from the 4.8 million metric tons released in 1980, according to the study. It is the most comprehensive study of global nitrous oxide emissions and sinks produced by a team of 58 researchers from 55 organisations in 15 countries.

For the study, the researchers examined data collected around the world for all major economic activities that lead to nitrous oxide emissions and reported on 18 anthropogenic and natural sources and three absorbent “sinks” of the global nitrous oxide.

“Nitrous oxide emissions from human activities must decline in order to limit global temperature rise to 2°C as established by the Paris Agreement,” said the report’s lead author, Hanqin Tian, the Schiller Institute Professor of Global Sustainability at Boston College. The study says the concentration of atmospheric nitrous oxide reached 336 parts per billion in 2022, a 25% increase over pre-industrial levels that far outpaces predictions previously developed by the Intergovernmental Panel on Climate Change (IPCC). This emission increase is taking place when the global greenhouse gases should be rapidly declining towards net zero emissions if we have any chance to avoid the worst effects of climate change.

India second largest emitter

The top five emitters by volume of anthropogenic nitrous oxide emissions in 2020 were China (16.7%), India (10.9%), USA (5.7%), Brazil (5.3%), and Russia (4.6%). The per capita emissions (Kg N2O/person) for the top five emitters are 1.3 (China), 0.8 (India), 1.7 (USA), 2.5 (Brazil), and 3.3 (Russia).

Anthropogenic nitrous oxide emissions from four emerging economies have more than doubled to 135% (China), 157% (India), 131% (Brazil) and 117% (Turkey) relative to 1980. Direct nitrogen additions in agriculture are the main cause of the increase. 

G V Ramanjaneyulu, Executive Director, Centre of Sustainable Agriculture, India, said: “This report on the nitrous oxide budget is timely and alarming. India ranks second in the world concerning N2O emissions from nitrogen fertilisers, which are all subsidised by over 80% in India. In addition to its emissions contributing to climate change, nitrogen fertilisers are polluting water bodies. It’s time India takes this wake-up call seriously and changes cropping systems and production practices. Fertiliser subsidies should be repurposed to support alternative production systems.”

Some countries have seen success in implementing policies and practices to reduce nitrous oxide emissions, according to the report. Emissions in China have slowed since the mid 2010s, as have emissions in Europe during the past few decades. In the US, agricultural emissions continue to creep up while industrial emissions have declined slightly, leaving overall emissions rather flat.

Way forward

Improved practices in agriculture around the use of nitrogen fertilisers and animal manure will help address and reduce greenhouse gas emissions and water pollution. “While there have been some successful nitrogen reduction initiatives in different regions, we found an acceleration in the rate of nitrous oxide accumulation in the atmosphere in this decade,” said Global Carbon Project Executive Director Josep Canadell, who is also a research scientist at CSIRO, Australia’s national science agency.

Tian said there is a need for more frequent assessments so mitigation efforts can be targeted to high-emission regions and economic activities. An improved inventory of sources and sinks will be required if progress is to be made toward the Paris Agreement.  “There is a strong correlation between nitrous oxide emissions use and agricultural productivity. By adopting regenerative and agroecological practices, sub-Saharan Africa can increase agricultural and livestock productivity without increasing emissions from the use of nitrogen fertilisers,” said Dr Alex Awiti, Principal Scientist, Agroecology and Policy Advisor at CIFOR-ICRAF (Center for International Forest Research – World Agroforestry).

Researchers said the biggest problem is there is no good alternative. The food production system will always have some N2O leak. The goal is to make the food system as nitrogen-efficient as possible to cut emissions.

Top 5 emitters by volume

  • China - 16.7%

  • INDIA - 10.9%

  • USA - 5.7%

  • Brazil - 5.3%

  • Russia - 4.6%

Problem size in numbers

(Million metric tons: MMT)

  • 47.3 MMT - The global annual amount of chemical nitrogen fertiliser use increased by 79% from 59.9 MMT of nitrogen in 1980 to 107.2 MMT of nitrogen in 2020

  • 21.2 MMT - Global manure production increased by 26.4% from 80.2 MMT of nitrogen in 1980 to 101.3 MMT of nitrogen in 2020

  • 40% - N2O emissions from human activities have increased by 40% in the past four decades

  • 74% - Agricultural production (due to the use of nitrogen fertilisers and animal manure) contributed 74% of the total anthropogenic N2O emissions in the last decade

Strategies for reducing N2O emissions in the agricultural sector

  • Precision agriculture with nitrogen fertilisers provided at the right time when plants need it, with the right quantity, and supplied at the right soil depth where it will be most uptaken by plant roots

  • Mixing or using alternative crops of the targeted crop (eg. commodity crop) and legumes to improve soil nitrogen fertility and require less nitrogen inputs as chemical fertiliser or manure

  • Use of alternate crops with species that have natural N2O inhibitors

  • Long-term: to integrate genetically engineered N2O inhibitors or nitrogen fixing symbiosis into main commodity crops

  • Improved manure management and use

  • Climate-smart agriculture, and more effective and holistic farming that maintains good soil health can play an important role in carbon sequestration

  • Hydroponics and urban agriculture. Reduced food waste

The arrows represent N2O fluxes: red — direct emissions from nitrogen additions in the agricultural sector (agriculture); orange – emissions
from other direct anthropogenic sources; maroon — indirect emissions from anthropogenic nitrogen additions; brown – perturbed fluxes from
changes in climate, CO2, or land cover; and green — emissions from natural sources
The arrows represent N2O fluxes: red — direct emissions from nitrogen additions in the agricultural sector (agriculture); orange – emissions from other direct anthropogenic sources; maroon — indirect emissions from anthropogenic nitrogen additions; brown – perturbed fluxes from changes in climate, CO2, or land cover; and green — emissions from natural sources

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