Global N<sub>2</sub>O Emissions From Cropland Driven by Nitrogen Addition and Environmental Factors: Comparison and Uncertainty Analysis
Rongting Xu, Hanqin Tian, Shufen Pan, Stephen A. Prior, Yucheng Feng, Shree R. S. Dangal
Abstract
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.