Earth Today | Nitrous oxide challenge looms large

A RECENT global assessment has called attention to nitrous oxide (N2O) as a super pollutant requiring collaborative best efforts to thwart the effect on global warming and the ozone layer while also protecting food security and improving air quality.

According to the 2024 Global Nitrous Oxide Assessment of the United Nations Environment Programme (UNEP) and the Food and Agriculture Organisation (FAO) of the United Nations, “If nitrous oxide emissions continue to increase at their current rate, there is no plausible pathway to limiting global warming to 1.5 degrees Celsius in the context of sustainable development, as defined in the Paris Agreement”.

“Even keeping current nitrous oxide emissions constant would constrain society’s capacity to limit global warming to 1.5 degrees Celsius and require much greater and costlier reductions of carbon dioxide and methane emissions. Ambitious nitrous oxide abatement could avoid the equivalent of up to 235 billion tonnes of carbon dioxide emissions by 2100, which is approximately six years of current carbon dioxide emissions from fossil fuel burning,” the report added.

Nitrous oxide is part of the nitrogen cycle. Nitrogen, of note, is essential to all life on Earth and the global food system, according to the report. The super pollutant is also the third most important greenhouse gas and the most significant ozone-layer depleting substance emitted.

The emission of greenhouse gases, which include carbon dioxide and methane, is fuelling the warming of the planet while triggering other climate change impacts.

These impacts include sea level rise and extreme weather events, such as extreme hurricanes,the likes of which have devastated sections of the Caribbean over recent years.

The human-induced emissions of N2O, meanwhile, comes mainly from the agricultural use of synthetic fertilisers and manure and, according to the report, are increasing faster than previously projected.

The report has, therefore, called for a sustainable nitrogen management approach to agricultural nitrous oxide emissions, which is anticipated to “significantly reduce emissions of short-lived 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,” the report added.

There are also significant ozone benefits to be gained.

“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,” the UNEP-FAO report explained.

“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,” it added.

According to the report, “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”.

“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,” the report said further.

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