Abstract
Abstract. Emissions from land use and land cover change are a key component of the global carbon cycle. However, models are required to disentangle these emissions from the land carbon sink, as only the sum of both can be physically observed. Their assessment within the yearly community-wide effort known as the “Global Carbon Budget” remains a major difficulty, because it combines two lines of evidence that are inherently inconsistent: bookkeeping models and dynamic global vegetation models. Here, we propose a unifying approach that relies on a bookkeeping model, which embeds processes and parameters calibrated on dynamic global vegetation models, and the use of an empirical constraint. We estimate that the global CO2 emissions from land use and land cover change were 1.36±0.42 PgC yr−1 (1σ range) on average over the 2009–2018 period and reached a cumulative total of 206±57 PgC over the 1750–2018 period. We also estimate that land cover change induced a global loss of additional sink capacity – that is, a foregone carbon removal, not part of the emissions – of 0.68±0.57 PgC yr−1 and 32±23 PgC over the same periods, respectively. Additionally, we provide a breakdown of our results' uncertainty, including aspects such as the land use and land cover change data sets used as input and the model's biogeochemical parameters. We find that the biogeochemical uncertainty dominates our global and regional estimates with the exception of tropical regions in which the input data dominates. Our analysis further identifies key sources of uncertainty and suggests ways to strengthen the robustness of future Global Carbon Budget estimates.
Highlights
The annual flux of carbon dioxide (CO2) to the atmosphere caused by land use and land cover change (LULCC) is a key part of the Global Carbon Budget (GCB; Friedlingstein et al, 2019)
The goal of this paper is threefold: first, it is to provide another bookkeeping estimate of global and regional LULCC emissions – that will hopefully be used in the future GCB – obtained with an original model; second, it is to revise and further investigate the loss of additional sink capacity” (LASC) estimates that we provided in an earlier version of the GCB (Le Quéré et al, 2018b); and, third, it is to investigate the uncertainty range in both these fluxes along the three axes of analysis shown in Table 1: the inclusion of the LASC, the driving LULCC data sets, and the biogeochemical parameterization
We find global LULCC emissions of 1.36 ± 0.42 PgC yr−1 on average over the 2009–2018 period, which is consistent with the Global Carbon Budget 2019 (GCB2019) estimate (Friedlingstein et al, 2019) of 1.5 ± 0.7 PgC yr−1
Summary
The annual flux of carbon dioxide (CO2) to the atmosphere caused by land use and land cover change (LULCC) is a key part of the Global Carbon Budget (GCB; Friedlingstein et al, 2019). The Global Carbon Budget 2019 (GCB2019) assessment (Friedlingstein et al, 2019) estimated that LULCC emissions were 1.5 ± 0.7 PgC yr−1 (1σ range) on average over the 2009–2018 period. This value relied on two lines of evidence: dynamic global vegetation models (DGVMs), which are complex process-based and spatially explicit models of the terrestrial carbon cycle (and related processes), and bookkeeping models, which are parametric models that convolute time series of LULCC areal
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