Multi-gas and multi-source comparisons of six land use emission datasets and AFOLU estimates in the Fifth Assessment Report, for the tropics for 2000-2005

The Agriculture, Forestry and Other Land Use (AFOLU) sector contributes with ca. 20-25 % of global anthropogenic emissions (2010), making it a key component of any climate change mitigation strategy. AFOLU estimates remain, however, highly uncertain, jeopardizing the mitigation effectiveness of this sector. Global comparisons of AFOLU emissions have shown divergences of up to 25 %, urging for improved understanding on the reasons behind these differences. Here we compare a diversity of AFOLU emission datasets (e.g. FAOSTAT, EDGAR, the newly developed AFOLU "Hotspots", "Houghton", "Baccini", and EPA) and estimates given in the Fifth Assessment Report, for the tropics (2000-2005), to identify plausible explanations for the differences in: i) aggregated gross AFOLU emissions, and ii) disaggregated emissions by sources, and by gases (CO2, CH4, N2O). We also aim to iii) identify countries with low agreement among AFOLU datasets, to navigate research efforts. Aggregated gross emissions were similar for all databases for the AFOLU: 8.2 (5.5-12.2), 8.4 and 8.0 Pg CO2e. yr-1 (Hotspots, FAOSTAT and EDGAR respectively), Forests: 6.0 (3.8-10), 5.9, 5.9 and 5.4 Pg CO2e. yr-1 (Hotspots, FAOSTAT, EDGAR, and Houghton), and Agricultural sectors: 1.9 (1.5-2.5), 2.0, 2.1, and 2.0 Pg CO2e. yr-1 (Hotspots, FAOSTAT, EDGAR, and EPA). However, this agreement was lost when disaggregating by sources, continents, and gases, particularly for the forest sector (fire leading the differences). Agricultural emissions were more homogeneous, especially livestock, while croplands were the most diverse. CO2 showed the largest differences among datasets. Cropland soils and enteric fermentation led the smaller N2O and CH4 differences. Disagreements are explained by differences in conceptual frameworks (e.g. carbon-only vs multi-gas assessments, definitions, land use versus land cover, etc), in methods (Tiers, scales, compliance with Intergovernmental Panel on Climate Change (IPCC) guidelines, legacies, etc) and in assumptions (e.g. carbon neutrality of certain emissions, instantaneous emissions release, etc) that call for more complete and transparent documentation for all the available datasets. Enhanced dialogue between the carbon (CO2) and the AFOLU (multi-gas) communities is needed to reduce discrepancies of land use estimates.

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DOI:

https://doi.org/10.5194/bg-13-5799-2016

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