1494. Can Ammonia Truly Serve as a Clean Fuel?
— A Perspective That Considers Decarbonization and the Nitrogen Cycle Together —

A commentary published in One Earth discusses the need to consider decarbonization and the nitrogen cycle simultaneously, against the background of ammonia—long used widely in agriculture as a fertilizer—being increasingly applied to energy uses in recent years.

The commentary notes that ammonia synthesis via the Haber–Bosch process was a key technology that supported food production and population growth throughout the twentieth century. At the same time, it organizes evidence showing that the growing amount of reactive nitrogen fixed through human activities has substantially altered the natural nitrogen cycle. As of 2020, global ammonia production reached approximately 185 million tonnes, with nearly 70% used in agriculture as fertilizer. Ammonia production is highly energy‑intensive, accounting for about 2% of global final energy consumption and resulting in direct CO₂ emissions of approximately 450 million tonnes per year. Moreover, the amount of reactive nitrogen produced by human activities now exceeds that generated by natural processes, and inefficient fertilizer use, low nitrogen‑use efficiency, expanding international trade, and emerging uses such as fuel combustion are leading to large nitrogen losses to the atmosphere, land, and water systems. It is estimated that in 2020 roughly one‑third of industrially produced ammonia was emitted into the atmosphere. These nitrogen losses contribute to air pollution, eutrophication, soil acidification, biodiversity loss, adverse health effects, and interact with climate change.

The commentary emphasizes that these impacts do not arise primarily from ammonia synthesis itself, but instead emerge during its use through a long “nitrogen cascade.” Disruption of the nitrogen cycle is identified as one of the most severely transgressed planetary boundaries, and governance is becoming increasingly difficult due to the spatial decoupling of production, consumption, and environmental impacts across regions.

The commentary also describes how ammonia has recently attracted attention not only as a fertilizer but also as a carbon‑free energy carrier. Ammonia produced using hydrogen derived from renewable energy sources does not emit CO₂ in principle, and compared with hydrogen it is easier to store and transport and can utilize existing infrastructure. According to scenarios from the International Energy Agency (IEA), global ammonia production could increase to two to three times its current level by 2050, particularly driven by expanded use as a marine fuel.

At the same time, the commentary stresses that many of ammonia’s environmental impacts become apparent during the use phase rather than during production. Ammonia may leak during storage, transport, and use, and its combustion or decomposition can generate nitrous oxide (N₂O) and nitrogen oxides (NOx). N₂O is a potent greenhouse gas, while NOx contributes to air pollution. These nitrogen compounds can move through the environment and enter inland waters and oceans, causing eutrophication. The commentary conceptualizes these linked processes as a “nitrogen cascade.”

The commentary clearly states that the sustainability of ammonia cannot be judged solely by its low carbon emissions. Even ammonia produced using renewable energy does not reduce pressures on the nitrogen cycle if use efficiency is low or emissions and losses are inadequately managed. Consequently, the commentary identifies four key intervention points across the nitrogen cascade:

1. limiting overall production,
2. improving nitrogen‑use efficiency,
3. promoting circular use of nitrogen, and
4. ultimately converting reactive nitrogen back to N₂.

With regard to the second point, the commentary notes that agriculture has long pursued higher nitrogen‑use efficiency (NUE) through approaches such as precision agriculture, fertilizer application based on the “4R” principles (right source, rate, time, and place), the use of slow‑ or controlled‑release fertilizers, improved feed utilization, and crop breeding. The same logic, it argues, also applies to ammonia used as an energy carrier. The commentary emphasizes that in both agriculture and energy systems, reducing nitrogen losses depends fundamentally on how effectively nitrogen inputs are used.

The central message of the commentary is that, in order for ammonia to be used sustainably in a decarbonized society, decarbonizing production and managing nitrogen impacts during the use phase must be treated as inseparable objectives.

Reference
Jan Willem Erisman, Ammonia for food and fuels in a sustainable future, One Earth (2026).
https://www.sciencedirect.com/science/article/pii/S2590332226000229?via…

Contributor: IIYAMA Miyuki, Strategic Coordination Office