Nitrogen (N) is a naturally abundant element and forms nearly 80% of the Earth’s atmosphere as the inert gas di-nitrogen (N2), indeed being primarily responsible for the sky appearing blue. However, reactive nitrogen compounds (Nr) – chemically active forms of nitrogen that interact with the environment and support plant growth – are typically scarce in the natural environment. Since the 1960s, human use of synthetic Nr fertilizers has increased 9-fold globally and a further substantial increase of around 40-50% is expected over the next 40 years based on current trends (Full Report (FR) Section 1.1). Together with increased fossil fuel combustion, humans have now created excess Nr pollution that spans all environmental compartments with multiple threats, to the extent that the disruption of the natural nitrogen cycle is now one of the greatest global threats to the environment of the 21st century.
Key N threats and estimates for the UK from Section 1.1 in the full report include:
- Reductions in biodiversity (i.e. degradation of sensitive habitats) – the area of N-sensitive habitats in the UK with exceedance of nutrient N critical loads was 57.6% (42,049 km2) in 2017;
- Accelerated climate change via the production of nitrous oxide gas (N2O) – representing 5% of UK GHG emissions in 2019;
- Widespread air pollution leading to growing incidences of upper respiratory disease and cancer in humans, including the role of oxidized N in tropospheric (ground-level) ozone formation (a potent GHG that can also impact on human health and crop yields) – current estimate of the mortality burden of air pollution in the UK is equivalent to nearly 29,000 deaths and an associated loss of 340,000 life years across the population annually of which nitrogen oxide (NOx) and ammonia (NH3) pollution plays a significant role (FR Section 1.1.2);
- Depletion of stratospheric ozone layer via the production of nitrous oxide gas (N2O);
- Eutrophication of aquatic ecosystems and hypoxic “dead zones” in the coastal ocean – around 55% of England in 2019 was designated as a Nitrate Vulnerable Zone (NVZ) due primarily to elevated nitrate concentrations in groundwater and rivers; in England, only 16% of water bodies meet the criteria for ‘good’ ecological status, 50% and 40% of water bodies achieve good status in Scotland and Wales respectively;
- Acidification of soils and forests of natural ecosystems – the area of acid- sensitive habitats in the UK with exceedance of acidity critical loads was 38.8% (27,253 km2) in 2017.
The main drivers contributing to the overuse of N, its loss to the environment in a wider context and the resulting impacts can be categorized as:
- Inefficient farming practices – the inefficient and unsustainable use of N-fertilizer and manure leading to large Nr losses to the atmosphere and to terrestrial and aquatic ecosystems;
- Fossil fuel combustion – increased demand for fossil fuels, increasing of Nr release to the atmosphere during combustion;
- Geographic concentration in urban sewerage via food – concentration of Nr food system flows in towns and cities producing wastewaters high in Nr which are lost to the aquatic environment;
- Protein consumption (multiplier of preceding drivers) – increased global consumption levels as a result of human population growth, increase in per capita consumption and a diet shift towards more protein-rich and animal derived food and a rise in the use of N-fertilizers.
The report shows that tackling nitrogen pollution by tightening the nitrogen cycle will have multiple benefits across the environmental, economic and social pillars of sustainable development. These include meeting key Sustainable Development Goals of supplying the food needs of the world, while tackling the climate crisis and reversing the loss of nature, while also protecting human health, the ozone layer and ecosystems through improved air and water quality.
To obtain these multiple benefits, while avoiding trade-offs, the report recommends a full-cycle and integrated approach to quantifying nitrogen use and losses, including transboundary imports and exports embedded in food, feed and fertilizer, as well as transboundary pollution via air and water.
The report shows that we can achieve change holistically, rather than unintentionally shifting problems from one form of pollution to another, or, geographically by importing goods and inputs produced to lower environmental standards.
The report is divided into three sections:
- Firstly, it sets out the impacts of our current misuse of nitrogen at a range of scales, from global to local, on the natural environment, on people and on the economy.
- Secondly, it identifies the key ways of reducing nitrogen use and waste, including adapting to regenerative forms of farming, reducing demand for animal feed, changing diets, reducing waste and cutting other combustion sources.
- And thirdly, it sets out the policy responses needed as part of a comprehensive package, from agreeing global priorities to introducing national nitrogen budgets and targets to guide action to halve nitrogen waste by 2030.