Reconciling global-model estimates and country reporting of anthropogenic forest CO2 sinks

Abstract

Achieving the long-term temperature goal of the Paris Agreement requires forest-based mitigation. Collective progress towards this goal will be assessed by the Paris Agreement’s Global stocktake. At present, there is a discrepancy of about 4 GtCO2 yr−1 in global anthropogenic net land-use emissions between global models (reflected in IPCC assessment reports) and aggregated national GHG inventories (under the UNFCCC). We show that a substantial part of this discrepancy (about 3.2 GtCO2 yr−1) can be explained by conceptual differences in anthropogenic forest sink estimation, related to the representation of environmental change impacts and the areas considered as managed. For a more credible tracking of collective progress under the Global stocktake, these conceptual differences between models and inventories need to be reconciled. We implement a new method of disaggregation of global land model results that allows greater comparability with GHG inventories. This provides a deeper understanding of model–inventory differences, allowing more transparent analysis of forest-based mitigation and facilitating a more accurate Global stocktake.

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Fig. 1: Conceptual diagram of the impact of mismatches in anthropogenic land flux estimates on the gap between country pledges and what is required to meet climate targets.
Fig. 2: Comparison of the global net anthropogenic land-related CO2 fluxes estimated by AR5 and countries’ GHGIs.
Fig. 3: Summary of the main conceptual differences in defining the anthropogenic land CO2 flux between IPCC AR5 and countries’ GHGIs.
Fig. 4: Comparison and reconciliation of developed countries’ forest net CO2 fluxes and forest area for 1990–2014.
Fig. 5: Comparison and reconciliation of global forest net CO2 fluxes and forest area for 2005–2014.

Data availability

The data that support the findings of this study are available from the corresponding author upon request.

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Acknowledgements

The authors thank J. Pongratz for discussing an early stage of the analysis, V. Korotkov for checking our analysis on Russia, and G. M. Domke for checking our analysis on the United States. J.H. was supported by EU FP7 through project LUC4C (GA603542) and the UK NERC project GGRiLS-GAP. G.G. was supported by Administrative Arrangement Number 340203/2016/742550/SER/CLIMA.A3. A.K.J. was supported by the NSF (AGS 12-43071) and DOE (DE-SC0016323). J.E.M.S.N. was supported by the German Research Foundation’s Emmy Noether Programme (grant number PO1751/1-1). G.G., J.H., G.P.P. and L.P. received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement number 776810 (VERIFY). C.D.K. was supported by the US DOE under Contract DE-AC02-05CH11231 as part of their RGMA (BGC-Feedbacks SFA) and TES Programs (NGEE-Tropics). A.K.J. was supported under the US NSF (NSF-AGS-12-43071).

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Contributions

G.G. designed the analysis with J.H. and W.A.K., and all three drafted the manuscript. G.G. coordinated all of the inputs, executed the calculations and made the figures. A.C., R.A.H., G.P.P. and M.J.S. contributed to the analysis and provided inputs to the manuscript. F.D. contributed by commenting and editing the manuscript. R.A.V., S.R., S.F. and D.L. contributed to collecting data and information on country GHGIs. R.A. post-processed the DGVM results. R.A.H. and A.A.N. provided data from bookkeeping models. L.P. provided comments on the Global stocktake. A.A., A.B., M.F., P.F., A.K.J., E.K., C.D.K., J.E.M.S.N., S.S., N.V., A.W. and S.Z. provided the original DGVM results and inputs to the manuscript. All authors read and approved the final manuscript.

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Correspondence to Giacomo Grassi.

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Supplementary methods and data 1–4, Supplementary analysis and results 5-8, Supplementary tables 1–12, Supplementary figures 1–9, Supplementary references

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Grassi, G., House, J., Kurz, W.A. et al. Reconciling global-model estimates and country reporting of anthropogenic forest CO2 sinks. Nature Clim Change 8, 914–920 (2018). https://doi.org/10.1038/s41558-018-0283-x

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