Nitrous Oxide

Nitrous Oxide (N2O) is now the most significant ozone-depleting substance (ODS) and is projected to remain so throughout the 21st century. It is also the third most important greenhouse gas (GHG) and is 273 times more potent than carbon dioxide (CO2) on a tonne for tonne basis over a 100-year period. The vast majority of our N2O emissions come from agriculture, largely through the overuse of fertilisers, with wastewater, biomass burning, transport and industrial emissions also contributing significantly to the total human-caused output. Largely unchecked, N2O emissions simultaneously undermine global efforts to reverse depletion of the ozone layer under the Montreal Protocol, and to limit global surface temperature increases to 1.5°C under the Paris Climate Agreement.

The problem

N2O is intrinsically linked to the wider nitrogen cycle, which has been radically disrupted from its natural state by human activity. This disruption has accelerated over the last century with the advent of synthetic fertilisers, leading to significant environmental damage that links ozone depletion, global warming, air and water pollution, biodiversity loss and soil degradation. N2O and its impacts are only one element in this “cocktail of nitrogen pollution”.

In the last four decades, human-caused N2O emissions have increased by 30 per cent. The Montreal Protocol’s Scientific Assessment Panel (SAP) has stated that, “the accelerating increase of N2O abundances and emissions is a serious threat for stratospheric ozone”, while the latest IPCC assessment report estimates that N2O emissions have already contributed 0.1°C to global average warming. To remain consistent with the 1.5°C pathway, annual emissions of N2O must be reduced by 22 per cent by 2030 and 25 per cent by 2050, compared to 2015 levels.

  • 1/5

    N2O emissions in 2020 were equivalent to more than a fifth of peak CFC emissions in terms of

    ozone depleting potential

  • 0.1°C

    of global warming so far

    has been caused by N2O emissions

  • 25%

    Emissions of N2O need to be reduced by 25 per cent by 2050

    to keep warming below 1.5°C

Moving forward

Although its ozone depleting potential was first recognised more than 40 years ago N2O is not controlled under the Montreal Protocol, and it has received only limited attention in the Nationally Determined Contributions (NDCs) of UNFCCC member states.

Increasingly, however, the interconnectedness of environmental challenges linked to the nitrogen cycle has been recognised. In 2019 the first-ever UN Resolution on Sustainable Nitrogen Management was adopted by the UN Environment Assembly (UNEA), followed by a second in 2022. On the recommendation of these resolutions, a UNEP Nitrogen Working Group was established, tasked with facilitating cooperation between states on nitrogen policies, and providing them with guidance and support in drafting National Action Plans (NAPs) for addressing nitrogen pollution.

Technologies and practices that can mitigate N2O emissions exist across all sectors, and in particular, the technologies for tackling emissions from transport, energy and chemical production are already proven and well-established. When deployed properly and at scale, these highly effective technologies have the potential to mitigate more than 80 per cent of our current N2O emissions in these sectors. The introduction of policy requirements to abate industrial N2O emissions is a clear, cost-effective and immediate opportunity to prevent a substantial quantity of unnecessary emissions. EIA believes that the Montreal Protocol should play an important role in this, for the benefit of both the ozone layer and the climate.

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