A Transition to an Ammonia Dominated World? Simulations of Future Agricultural Ammonia Emissions in an Earth System Model

Abstract:

Ammonia nitrogen (N) emissions, with their dominant agricultural component, are determined in large part by the Earth’s population and its overall demand for food. They are driven by dietary preferences and influenced by the competition between land for food production, land for biofuel production, the land necessary for forest regrowth and preservation and the pastureland necessary for the grazing of livestock. Whereas the CMIP6 scenarios show decreases in the emissions of nitrogen oxides (NOx) by 2100 ammonia emissions are projected to increase; in many cases ammonia N becomes the dominant source of reactive nitrogen emissions. As a consequence, in addition to impacts on the health and climate, the deposition of reactive nitrogen will differ significantly from the present NOx dominated world with resulting changes in the overall impact on ecosystems and the carbon cycle. Here, to our knowledge for the first time, we explicitly simulate future (circa 2100) global agricultural ammonia emissions in an Earth System Model (ESM) including the impact of climate change. In particular, we use the Flows of Agricultural Nitrogen (FANv2) embedded in the land component of the ESM to simulate the climate dependency of ammonia emissions due to future changes in temperature and soil moisture. The impact of various future agricultural scenarios are investigated as determined through the Land-Use Harmonization forcing and management datasets. Future ammonia emissions are very sensitive to assumptions with respect to agricultural practices, particularly over Africa, with climate change responsible for an increase in emissions of over 25% with respect to current emissions in some instances.