Data-driven estimates of global nitrous oxide emissions from croplands
© 2020 The Author(s) 2019. Published by Oxford University Press on behalf of China Science Publishing & Media Ltd. Croplands are the single largest anthropogenic source of nitrous oxide (N2O) globally, yet their estimates remain difficult to verify when using Tier 1 and 3 methods of the Intergovernmental Panel on Climate Change (IPCC). Here, we re-evaluate global cropland-N2O emissions in 1961-2014, using N-rate-dependent emission factors (EFs) upscaled from 1206 field observations in 180 global distributed sites and high-resolution N inputs disaggregated from sub-national surveys covering 15593 administrative units. Our results confirm IPCC Tier 1 default EFs for upland crops in 1990-2014, but give a ∼15% lower EF in 1961-1989 and a ∼67% larger EF for paddy rice over the full period. Associated emissions (0.82 ± 0.34 Tg N yr-1) are probably one-quarter lower than IPCC Tier 1 global inventories but close to Tier 3 estimates. The use of survey-based gridded N-input data contributes 58% of this emission reduction, the rest being explained by the use of observation-based non-linear EFs. We conclude that upscaling N2O emissions from site-level observations to global croplands provides a new benchmark for constraining IPCC Tier 1 and 3 methods. The detailed spatial distribution of emission data is expected to inform advancement towards more realistic and effective mitigation pathways.
Wang, Q; Zhou, F; Shang, Z; Ciais, P; Winiwarter, W; Jackson, RB; Tubiello, FN; Janssens-Maenhout, G; Tian, H; Cui, X; Canadell, JG; Piao, S; Tao, S
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