Global nitrous oxide budget

Global atmospheric nitrous oxide

Nitrous oxide (N₂O) is the third most important greenhouse gas contributing to human-driven climate change. Nitrous oxide remains in the atmosphere for over 100 years. It is also an ozone-depleting substance, meaning that it reduces the amount of ozone in the atmosphere and contributes to the annual hole in the ozone layer.

As reported in the latest global nitrous oxide budget, nitrous oxide concentrations in the atmosphere reached 331 parts per billion in 2018. This is 22 per cent above levels recorded before the beginning of the industrial era. Furthermore, the rate at which concentrations are increasing is getting faster each year. Global emissions are now 10 per cent greater than in the 1980s.

The rate at which nitrous oxide is accumulating in the atmosphere is faster than any of the key emission scenarios developed by the Intergovernmental Panel on Climate Change. This puts Earth on track for an increase in average global temperatures of well above three degrees Celsius by 2100 compared with pre-industrial temperatures. To keep global warming to the Paris Agreement target of below two degrees Celsius we urgently need to reduce nitrous oxide emissions.

Main sources and sinks of nitrous oxide

Nitrous oxide is emitted from both human-derived and natural sources. Emissions from natural sources (such as soils and oceans) have not changed much in recent decades. Whereas emissions resulting from human activities have grown by 30 per cent over the past three decades.

By far the main source of human-derived emissions is agriculture. Agriculture alone accounted for almost 70 per cent of global nitrous oxide emissions in the decade to 2016. Nitrous oxide is released following the application of nitrogen fertilisers and from livestock manure.

Other human-derived sources of nitrous oxide include the chemical industry, waste water and the burning of fossil fuels.

The main sink for nitrous oxide is solar radiation, which destroys the gas in the upper atmosphere. However, humans are emitting nitrous oxide faster than it is being destroyed. This is why nitrous oxide levels in the atmosphere are increasing.