The Impact of Changing Climate on Ammonia Emissions from Agriculture and the Associated Climate Forcings

Abstract:

Agriculture is the largest anthropogenic source of ammonia (NH₃) on a global scale with major contributions from the application of synthetic fertilizer and manure from livestock. While strict controls are placed on the emissions of many industrial pollutants, NH₃ concentrations are expected to increase this century. In addition to future expansion of agricultural activities that could lead to greater NH₃ emissions, NH₃ emissions are affected by changes in temperature and precipitation. Here we use a newly developed agricultural N pathways model running in a global terrestrial model (Community Land Model v4.0) to estimate future NH₃ emissions from manure and synthetic fertilizer application, and the impact of changing climate on these emissions and other N pathways (runoff, denitrification, etc.). We include future increases in the application of manure and synthetic fertilizer that are consistent with a middle-of-the-road projection of population growth and per capita caloric intake. Combined with atmospheric forcing that follows RCP8.5, NH₃ emissions increase by about 50% and 90% between years 2010 and 2100 from synthetic fertilizer and manure, respectively. Roughly 25% of this increase can be attributed to the changing climate, mainly increased global temperatures over the 21^st century. We show associated changes in ammonium nitrate and ammonium sulfate aerosol concentrations and radiative forcings, the results of a set of additional simulations using the Community Atmosphere Model v5.0 and an offline radiative transfer scheme. This work suggests that projections of global NH₃ concentrations need to take changes in climate into account.