The climate mitigation of global forestation: Constrained by land availability and policy

Large-scale forestation, a profound form of land cover change, is widely proposed for climate mitigation. Its full Earth system impact, however, depends on complex trade-offs between carbon sequestration in biomass and soils and other biogeophysical feedbacks, alongside stringent land availability constraints. This study assesses the global potential and limits of forestation as a land use change strategy by integrating high-resolution simulations of soil organic carbon dynamics with spatially explicit constraints on land availability designed to prevent adverse impacts on surface albedo, water resources, and biodiversity. Our analysis reveals that when forestation is restricted to these ecologically viable lands, its scale and consequent carbon sequestration potential are substantially lower than previous estimates that did not fully account for these Earth system trade-offs. Furthermore, when land use is limited only to areas aligned with existing national policy commitments, the feasible scope for forestation and its associated carbon sink becomes drastically reduced. Realizing significant climate benefits from forestation requires navigating critical land use trade-offs and expanding ambitious, spatially optimized land-use policies, particularly in regions with high potential.