Human activities have caused considerable perturbations of the nitrogen (N) cycle, leading to a ~20% increase in the concentration of atmospheric nitrous oxide (N2O) since the preindustrial era. While substantial efforts have been made to quantify global and regional N2O emissions from cropland, there is large uncertainty regarding how climate change and variability have altered net N2O fluxes at annual and decadal time scales. Herein, we applied a process‐based dynamic land ecosystem model (DLEM) to estimate global N2O emissions from cropland driven by synthetic N fertilizer application and multiple environmental factors (i.e., elevated CO2, atmospheric N deposition, and climate change). We estimate that global cropland N2O 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 N2O 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 N2O 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 N2O 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.
Climate change is impacting global crop productivity, and agricultural land suitability is predicted to significantly shift in the future. Responses to changing conditions and increasing yield variability can range from altered management strategies to outright land use conversions that may have significant environmental and socioeconomic ramifications. However, the extent to which agricultural land use changes in response to variations in climate is unclear at larger scales. Improved understanding of these dynamics is important since land use changes will have consequences not only for food security but also for ecosystem health, biodiversity, carbon storage, and regional and global climate. In this study, we combine land use products derived from the Moderate Resolution Imaging Spectroradiometer with climate reanalysis data from the European Centre for Medium-Range Weather Forecasts Reanalysis v5 to analyze correspondence between changes in cropland and changes in temperature and water availability from 2001 to 2018. While climate trends explained little of the variability in land cover changes, increasing temperature, extreme heat days, potential evaporation, and drought severity were associated with higher levels of cropland loss. These patterns were strongest in regions with more cropland change, and generally reflected underlying climate suitability—they were amplified in hotter and drier regions, and reversed direction in cooler and wetter regions. At national scales, climate response patterns varied significantly, reflecting the importance of socioeconomic, political, and geographic factors, as well as differences in adaptation strategies. This global-scale analysis does not attempt to explain local mechanisms of change but identifies climate-cropland patterns that exist in aggregate and may be hard to perceive at local scales. It is intended to supplement regional studies, providing further context for locally-observed phenomena and highlighting patterns that require further analysis.more » « less
- NSF-PAR ID:
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Environmental Research Letters
- Page Range / eLocation ID:
- Article No. 064010
- Medium: X
- Sponsoring Org:
- National Science Foundation
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