Today, anthropogenic emissions of ammonia (NH3) surpass natural emissions, causing profound impacts on radiative forcing, ecosystems, biodiversity, and human health1. Accurate estimates of emissions are imperative for effective mitigation. Currently, official NH3 inventories attribute around 95 % of European anthropogenic NH3 emissions to agriculture-related activities2, but a growing body of evidence suggests that these NH3 inventories may be inaccurate3. Here, we report the first glacially archived nitrogen isotope record for ammonium (the deposited form of NH3) from a Mont-Blanc ice core, offering an unprecedented glimpse into NH3 emissions spanning Western Europe’s pre-industrial era to the present day. This 300-year record reveals that anthropogenic NH3 emissions reflect the evolution of European economies, with the emergence of intensive agriculture and fossil fuel combustion. Most importantly, we show that, over the period 2010-2016, agriculture-related activities accounted for, at most, (78 ± 17) % of anthropogenic NH3 emissions, with the remainder being attributable to fossil fuel and biomass combustions. This less-than-assumed relative contribution from agricultural emissions strongly argue for a re-evaluation of NH3 inventories and unequivocally put forth that anthropogenic NH3 emissions cannot be reduced without limiting combustion-related activities.