Global N2O Emissions From Cropland Driven by Nitrogen Addition and Environmental Factors: Comparison and Uncertainty Analysis

Abstract Human activities have caused considerable perturbations of the nitrogen (N) cycle, leading to a ~20% increase in the concentration of atmospheric nitrous oxide (N 2 O) since the preindustrial era. While substantial efforts have been made to quantify global and regional N 2 O emissions from cropland, there is large uncertainty regarding how climate change and variability have altered net N 2 O fluxes at annual and decadal time scales. Herein, we applied a process‐based dynamic land ecosystem model (DLEM) to estimate global N 2 O emissions from cropland driven by synthetic N fertilizer application and multiple environmental factors (i.e., elevated CO 2 , atmospheric N deposition, and climate change). We estimate that global cropland N 2 O emissions increased by 180% (from 1.1 ± 0.2 to 3.3 ± 0.1 Tg N year −1 ; mean ±1 standard deviation) during 1961–2014. Synthetic N fertilizer applications accounted for ~70% of total emissions during 2000–2014. At the regional scale, Europe and North America were two leading regions for N 2 O emissions in the 1960s. However, East Asia became the largest emitter after the 1990s. Compared with estimates based on linear and nonlinear emission factors, our results were 150% and 186% larger, respectively, at the global scale during 2000–2014. Our higher estimates of N 2 O emissions could be attributable to the legacy effect from previous N addition to cropland as well as the interactive effect of N addition and climate change. To reduce future cropland N 2 O emissions, effective mitigation strategies should be implemented in regions that have received high levels of N fertilizer and regions that would be more vulnerable to future climate change.