Closing the global N 2 O budget: A retrospective analysis 1500–1994

We present new estimates of global nitrous oxide (N 2 O) emissions for the period 1500–1994 based on revised Intergovernmental Panel on Climate Change guidelines [ Intergovernmental Panel on Climate Change (IPCC) , 1997; Mosier et al. , 1998]. Use of these estimates as input to a simple atmospheric box model resulted in a closed N 2 O budget over time, showing that increases in atmospheric N 2 O can be primarily attributed to changes in food production systems. We hypothesize that before the ninetheenth century conversion of natural land to agriculture had no net effect on N 2 O. During the twentieth century a fast expansion of agricultural land coupled with intensification of land use may have caused a net increase in N 2 O. In our base scenario the total N 2 O emissions increased from 11 Tg N yr −1 in 1850 to 15 Tg N yr −1 in 1970 and to 18 Tg N yr −1 in 1994.