One Earth (2026). DOI: 10.1016/j.oneear.2026.101621"> Global fixation of reactive nitrogen in oxidized and reduced form until 2010. Credit: One Earth (2026). DOI: 10.1016/j.oneear.2026.101621 Ammonia has been feeding the world for decades as a fertilizer and is now rapidly emerging as a carbon-free fuel for shipping and industry. But if we focus only on CO₂ emissions, we risk creating new nitrogen problems, warns nitrogen expert Jan Willem Erisman in an article published in the journal One Earth . Ammonia is one of the most important inventions of the last century. Thanks to the Haber-Bosch process , nitrogen from the air can be converted into ammonia. This made large-scale plastic production possible and contributed to a huge increase in global food production. But the invention also has a downside. Large-scale use has disrupted the natural nitrogen cycle —the balance of nitrogen in soil, water and air. This has led to biodiversity loss, poorer water and air quality, and extra warming of the planet.…