Nearly 75% of oil and gas methane emissions can be abated with existing technologies. These can often be deployed at a relatively low cost. Considering natural gas prices so far in 2021, we estimate that almost 50% of oil and gas methane emissions can be avoided with measures that would have no net cost because the value of the captured methane is sufficient to cover the costs of the abatement measure. The technical solutions available to avoid emissions of coal mine methane are more limited, especially after the start of operations, and often entail higher costs due to the dispersed nature of coal mine methane. However, actions to minimise leaks in coal mines can drive a reduction of almost 45% in the methane intensity of coal supply.

This topic is covered in more detail in other IEA analyses, including Curtailing Methane Emissions from Fossil Fuel Operations

Impacts on water, soil, air and ecosystems

Inefficient use of fertilisers – including both mineral and organic fertilisers – has considerable impacts on water quality and aquatic ecosystems. Run-off from agricultural fields carries excess nutrients to lakes and oceans, leading to eutrophication of freshwater and marine ecosystems. In the process of eutrophication, a high influx of nutrients into a body of water leads to a large increase in growth of plant organisms such as phytoplankton, more commonly known as algae. When the phytoplankton die, bacterial decomposition of the dead phytoplankton depletes oxygen levels in the water. This creates a low-oxygen (hypoxic) environment that is inhospitable to fish and other animal life.

Researchers have found that more than 500 sites in coastal waters have reported hypoxic conditions since 1950. An example of the impact is the Gulf of Mexico hypoxic zone, which has become an annual summer occurrence. The Mississippi River drains a 3.2 million km2 catchment area from Canada down through the central United States – the third-largest in the world – into the gulf. Nitrogen and phosphorus fertilisers, animal manure, human waste and industrial waste all contribute to the nutrient enrichment. The size of the hypoxic zone can vary considerably from year to year. Over the past 36 years of measurement, the average size has been 14 000 km2, approximately the area of Northern Ireland. Other examples around the world abound, from the world’s largest hypoxic zone in the Baltic Sea to algal blooms in one-third of China’s lakes. In addition to their impacts on oxygen availability, algal blooms can have direct toxic effects. The

toxins created can affect smaller fish and shellfish that consume the algae, and they can also be passed up the food chain to other fish, birds, marine mammals, and reptiles.

Nitrogen pollution can also have impacts on soils and terrestrial ecosystems. Long-term excessive fertilisation can cause soil acidification and salinisation, reducing crop productivity and potentially resulting in loss of arable land. Nitrogen pollution also contributes to acid rain and direct ammonia deposition, which can damage forests and grassland ecosystems, in addition to negatively affecting aquatic ecosystems. Ammonia – both when applied directly on agricultural fields, and when volatised and redeposited further away – can have localised effects directly toxic to soil organisms.

Nitrogen fertiliser use also contributes to air pollution. The air pollutants involved include: nitrogen oxides (NOx), which are directly emitted from agricultural fields; particulate matter, which can be formed from NH3 emitted from agriculture; and ground-level ozone, which can be formed from NOx emitted from agriculture. These air pollutants contribute to a variety of human health problems, including cardiovascular and respiratory disease.

Various efforts are underway to improve nutrient use efficiency and thus reduce the environmental impacts of nitrogen fertiliser use, including efforts led by the industry itself. Nonetheless, according to the United Nations, much stronger efforts are needed to reduce nutrient pollution. See Chapter 3 for examples of existing initiatives and recommendations for accelerating progress.

The environmental benefits that arise from using fertiliser should also be acknowledged. Fertilisers enable higher crop yields relative to organic agriculture, and thus can produce the same amount of food and fibre from a smaller land area. As a result, less land needs to be brought into agricultural production when using mineral fertilisers. Preserving more natural ecosystems, such as forests and grasslands, has the benefit of preserving biodiversity and maintaining natural carbon sinks. Reduced land use requirements can also prevent agriculture from encroaching on less suitable land, thus reducing degradation of soils and desertification.

This is not to say that organic agriculture should not be pursued due to its higher land use requirements. Indeed, researchers point out that there are other ways to reduce land use requirements. Measures could be taken to reduce food wastage, and diets could be shifted towards lower reliance on animal products, thus reducing livestock feed requirements. As such, total crop production requirements could be lowered while sustaining the same human population. All things