Ammonia is being considered as a fuel for the future of shipping because it releases no carbon when burned. But does it really cut emissions as much as it seems to, and could it harm the environment in ways nobody intended? Those were the questions at the webinar Beyond Carbon: Environmental considerations of ammonia as a marine fuel, hosted by Opportunity Green and Environmental Defense Fund (EDF) on 7 October 2026. The speakers followed ammonia from the production plant to the ship’s engine. OPP Co-Founder and Director of Policy & Research Dr. Lucy Gilliam joined Dr. Sofia Esquivel Elizondo (EDF), Yuanrong Zhou and Dr. Bryan Comer (International Council on Clean Transportation), Prof. Mark Zondlo (Princeton University) and Dr. James Kershaw (Opportunity Green).
The session focused on reactive nitrogen, which can escape at every stage. In production, Yuanrong Zhou showed how uncertain the greenhouse gas figures for “blue” ammonia are, since it still depends on natural gas. Mark Zondlo explained that ammonia is hard to measure, so emissions from production plants may be up to twice what is currently recorded. On board, James Kershaw described “ammonia effluent”: water used to flush fuel lines that ends up full of reactive nitrogen. He argued it should be stored on board until it can be treated at proper facilities at berth. In the engine, Bryan Comer showed that unburned ammonia can escape (“ammonia slip”) and that nitrous oxide (N₂O) emissions depend heavily on how the engine is run.
In her talk, Reactive Nitrogen: One Element, Many Harms, Lucy looked at what happens once these molecules reach the environment. About 80% of man-made reactive nitrogen already leaks into the environment, three times the planetary safe limit. She named three threats from ammonia fuel. First, eutrophication: nitrates feed algal blooms that create dead zones like those already found in the Baltic and the Gulf of Mexico. Second, direct toxicity to marine life, especially corals. Third, more N₂O, a greenhouse gas 273 times more potent than CO₂ over 100 years, which microbes in the ocean can produce from ammonia. Nutrient-poor and low-oxygen waters are the most vulnerable. Lucy also explained that the IMO’s Life Cycle Assessment guidelines do not yet count this indirect N₂O. OPP has raised this with the IMO and has called for it to be included in the IMO’s fifth Greenhouse Gas Study, so far without success. That is why OPP works with partners to gather the evidence and put it in front of IMO delegates and the GESAMP experts revising the process.
Audience questions showed how much is still unknown. Lab tests only covered engines running at 25% load or more, but in emission control areas such as the North Sea and the Baltic, ships spend about a third of their time below that. According to Bryan Comer, N₂O alone can come close to the tank-to-wake CO₂ emissions of LNG at the high end of the range. That could make ammonia worse than conventional fuels. James Kershaw stressed that strict regulation is needed, because shipping companies follow the rules and what pays. The conclusion: ammonia may have a future as a ship fuel, but only if the whole chain, from production and combustion to effluent handling, is closely monitored. Otherwise marine life pays the price, and the climate gains could be lost to nitrous oxide.
Lucy Gilliam’s research on this topic has now been published. As lead author, she wrote the review article Beyond carbon: reactive nitrogen emissions from ammonia as a marine fuel and implications for ocean ecosystems together with researchers from Opportunity Green and EDF, published in Frontiers in Marine Science. On 3 November she will present it at the 10th International Nitrogen Conference (N2026) in Kyoto, Japan.
