The Ammonia Paradox: Why Replacing Carbon Fuels Could Trigger a Global Nitrogen Crisis

Ammonia, a compound long associated with agricultural fertilizers, is rapidly gaining attention as a potential game-changer in the global effort to decarbonize heavy industry and maritime shipping. With its chemical formula of NH3, ammonia burns without producing carbon dioxide, making it an attractive alternative to fossil fuels for sectors that have proven stubbornly difficult to electrify. Major shipping companies and industrial firms have begun investing billions in ammonia-powered engines and infrastructure, viewing the compound as a bridge to a carbon-neutral future. However, a prominent nitrogen researcher is now sounding an urgent alarm about the unintended consequences of this transition.

Jan Willem Erisman, a leading expert on nitrogen cycling and its environmental impacts, published a cautionary analysis in the journal One Earth warning that the rush toward ammonia fuels risks trading one environmental crisis for another. According to Erisman, policymakers and industry leaders have become so focused on eliminating CO2 emissions that they have overlooked the significant dangers posed by reactive nitrogen compounds. When ammonia is burned imperfectly or released into the environment through leaks and spills, it can contribute to a cascade of ecological problems including air pollution, water contamination, biodiversity loss, and even additional greenhouse warming through nitrous oxide formation.

The nitrogen problem is not a hypothetical concern. Humanity already disrupts the global nitrogen cycle on a massive scale through fertilizer production, livestock farming, and fossil fuel combustion. Each year, human activities convert roughly 150 million metric tons of inert atmospheric nitrogen into reactive forms that circulate through ecosystems. This excess nitrogen drives algal blooms that create ocean dead zones, contaminates drinking water supplies with nitrates, generates smog-forming nitrogen oxides in urban areas, and accelerates the loss of plant species in nitrogen-sensitive habitats. Adding large-scale ammonia combustion to this picture without proper safeguards could significantly worsen these existing pressures.

The technical challenges of burning ammonia cleanly are substantial. Unlike hydrogen, which produces only water when combusted, ammonia can generate nitrogen oxides (NOx) if combustion temperatures are not carefully controlled. These NOx emissions contribute to acid rain, respiratory illness, and ground-level ozone formation. Furthermore, unburned ammonia that escapes into the atmosphere, known as ammonia slip, can deposit nitrogen onto sensitive ecosystems and react with other pollutants to form fine particulate matter. Engine manufacturers are working on catalytic systems to minimize these emissions, but the technology remains in its early stages and has not been proven at the scale required for global shipping fleets.

Erisman's analysis calls for a comprehensive lifecycle approach to ammonia fuel governance. Rather than simply measuring carbon output at the point of combustion, regulators should account for nitrogen losses throughout the entire supply chain, from production through transportation to end use. This includes the energy-intensive Haber-Bosch process used to manufacture ammonia, which currently relies heavily on natural gas and generates significant emissions of its own. Green ammonia produced using renewable electricity and electrolysis represents a cleaner option, but scaling this technology to meet global fuel demand presents enormous infrastructure and cost challenges that have yet to be resolved.

The broader lesson from this research extends beyond ammonia itself. Environmental problems are interconnected, and solutions designed to address one pollutant can inadvertently amplify others. Climate policy has historically prioritized carbon tunnel vision, measuring success primarily in terms of CO2 reductions while paying less attention to nitrogen, phosphorus, and other biogeochemical cycles that sustain planetary health. Erisman argues that sustainable energy transitions require integrated thinking that considers multiple environmental boundaries simultaneously, ensuring that the clean fuels of tomorrow do not become the pollution crises of the next decade.