Data-driven estimates of global nitrous oxide emissions from croplands

Tao, S., Piao, S., Canadell, J.G., Cui, X., Tian, H., Janssens-Maenhout, G., Tubiello, F.N., Jackson, R.B., Winiwarter, W. ORCID: https://orcid.org/0000-0001-7131-1496, Ciais, P., Shang, Z., Zhou, F., & Wang, Q. (2020). Data-driven estimates of global nitrous oxide emissions from croplands. National Science Review 7 (2) 441-452. 10.1093/nsr/nwz087.

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Abstract

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.

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