The Haber–Bosch process is one of the greatest inventions in modern human history. It enables industrial-scale production of ammonia from atmospheric N2using energy. From ammonia,various synthetic nitrogen (N) fertilizers are manufactured, without which nearly half of the world’s population would not be alive today (1). However, synthetic N fertilizer has become “too much of a good thing”because much of the N applied to cropland escapes the agricultural system and becomes a pollutant, which disrupts terrestrial and aquatic ecosystem functions and contributes to global climate change. The environmental cost is considerable, betweenV70 billion andV320 billion per year just for the European Union according to a recent 5-y European nitrogen assessment (2). This 200-member expert panel considered N emission reductions a central environmental challenge in the 21st century and called for a global interconvention N protocol to address the issue. Indeed, coordinated global efforts are particularly critical when dealing with N-related greenhouse gas (GHG) emissions, because such emissions and their impacts recognize no borders.