Nitrous oxide (N2O) emissions from human waste in 1970-2050

Nitrous oxide (N2O) is an important contributor to climate change. Human waste is an important source of N2O emissions in several world regions, and its share in global emissions may increase in the future. In this paper we, therefore, address N2O emission from human waste: collected (from treatment and from sewage discharges) and uncollected waste. We review existing literature on emissions and emission factors, and present region-specific estimates of N2O emissions and their past and future trends. We show that human waste may became an important source of N2O emissions in the coming years as a result of increasing urbanization. About two-thirds of the global emissions are from uncollected waste, and about half from South Asia. We argue that more research is needed to improve emission factors.