Last week, several prominent scientific organizations confirmed what had been predicted for months: 2024 was the hottest year on record.
This sparked renewed calls for countries to rein in emissions of greenhouse gases, which superheat the planet and drive the climate crisis. Amid those pleas, experts urged nations not to forget about one often-overlooked gas: nitrous oxide.
The compound warms the planet hundreds of times faster than carbon dioxide and, at the same time, destroys the stratospheric ozone layer, the barrier which protects the planet from harmful solar radiation.
“Nitrous oxide is not as well known by the public as some other greenhouse gases, but it can be a remarkably destructive substance,” says Martina Otto, Head of Secretariat of the Climate and Clean Air Coalition, which is convened by the United Nations Environment Programme (UNEP). “The good news is that with strong policymaking and international cooperation, it is possible to slow emissions of this super pollutant – and save millions of lives around the world.”
Here is everything you need to know about the hidden perils of nitrous oxide and how humanity can curb its impact on the planet.
What is nitrous oxide?
Nitrous oxide is a molecule comprised of two nitrogen atoms and one oxygen atom. While it has long been used in medical settings as an anaesthetic colloquially known as laughing gas, at elevated levels, it’s a super-pollutant. Nitrous oxide traps heat in the atmosphere, contributing to climate change. It also breaks down the molecules that form the stratospheric ozone layer, which shields Earth from damaging ultraviolet radiation from the sun.
What are the main sources of nitrous oxide?
Nitrous oxide is part of the nitrogen cycle. It occurs naturally in soil and water when bacteria break down nitrogen through processes called nitrification and denitrification.
It is also common byproduct of agriculture. When too much nitrogen-based fertilizer is used on crops, nitrogen can leach out of the soil and into the broader environment, forming nitrous oxide. Some 75 per cent of human-made nitrous oxide emissions since 1980 have come from the farming sector. Industrial sources account for 5 per cent of human-caused releases, while the remaining 20 per cent comes from fossil fuel combustion, wastewater treatment and other sources.
Are nitrous oxide emissions rising?
Yes, and much faster that had been thought, found a report released last year by UNEP and the Food and Agriculture Organization (FAO) of the United Nations. More than 28 million tonnes of nitrous oxide were emitted in 2020, compared to 17 million tonnes in an average year before the industrial revolution. A key driver of this spike is the increased use of synthetic fertilizers to feed the world’s surging population, the report says.
Where does nitrous oxide rank in the pantheon of greenhouse gases?
Nitrous oxide is the third-most prevalent human-produced greenhouse gas, behind carbon dioxide and methane. It has been responsible for around 10 per cent of global warming since the industrial revolution. While it remains in the atmosphere for around 120 years, about a tenth as long as carbon dioxide, it traps 270 times more heat per tonne than its fellow greenhouse gas. Nitrous oxide is also the most significant ozone-layer-depleting substance emitted today, not controlled by the Montreal Protocol, a global agreement to protect the ozone layer.
Why is nitrous oxide often overlooked compared to carbon dioxide and methane?
Carbon dioxide alone is responsible for more than half of the global warming we experience today. It also accumulates in the atmosphere, so it has been a focus of climate activists for decades. Methane, which is short-lived, is increasingly in the world’s crosshairs because it is responsible for at least a third of current warming. It is also 80 times more potent than carbon dioxide in the first 20 years after its emission.
Compared to these two powerful greenhouse gases, tackling nitrous oxide has fallen through the cracks. But cutting emissions is vital to keeping alive the world’s hopes of limiting global warming to 1.5°C above pre-industrial levels, a key target of the Paris Agreement, says David Kanter, co-chair of the UNEP-FAO report, the Global Nitrous Oxide Assessment.
“Only through addressing all three of these greenhouse gases do we stand a chance of staving off the most devastating effects of climate change, from extreme heat, to droughts, to more frequent and more intense storms,” he said.
How can countries reduce nitrous oxide emissions?
There are several ways. The quickest and most cost-effective solutions lie in eliminating nitrous oxide releases from the industrial sector. Using existing low-cost technologies, industry could slash its emissions by 2.5 billion tonnes of carbon dioxide equivalent by 2050.
In the agriculture sector, improving fertilizer management and better managing crops could limit nitrous oxide emissions without jeopardizing food security.
Importantly, nitrous oxide falls under the purview of several international environmental accords, including the Paris Agreement on climate change. So, ambitious countries can create reduction targets for nitrous oxide in their Nationally Determined Contributions and other climate plans.
Would this improve public health?
Yes. Measures to address nitrous oxide emissions would tackle other air pollutants, improving air quality and preventing deaths around the world. It would also protect the ozone layer, reducing the potential proliferation of skin cancers and cataracts.
UNEP is at the forefront of supporting the Paris Agreement goal of keeping global temperature rise well below 2°C, and aiming for 1.5°C, compared to pre-industrial levels. To do this, UNEP has developed the Sectoral Solution, a roadmap to reducing emissions across sectors in line with the Paris Agreement commitments and in pursuit of climate stability. The six sectors identified are: energy; industry; agriculture and food; forests and land use; transport; and buildings and cities.
The UNEP-convened Climate and Clean Air Coalition is a partnership of over 190 governments, intergovernmental organizations, and non-governmental organizations. It works to reduce powerful super pollutants that drive both climate change and air pollution. It connects ambitious agenda setting with targeted mitigation action within countries and sectors. Robust science and analysis underpin its efforts and bolstered by its Trust Fund, the CCAC has given rise to high-level political commitment, in-country support, and a range of tools that support the case for action and implementation.
