Unpacking the potential: How proposed reforestation scenarios shape global and regional temperature

Large-scale reforestation is a prominent proposed climate mitigation strategy, yet our understanding of its impact on global and regional temperature remains incomplete. Here, we present the first comparison of temperature responses to three distinct reforestation potentials – Bastin et al. (2019), Moustakis et al. (2024), and Hurtt et al. (2020) – integrated into a fully-coupled Earth System Model (CESM2) under an SSP2-4.5 warming trajectory. Our simulations reveal that while all scenarios achieve a net global cooling ranging from -0.13°C to -0.25°C by 2100, the cooling from carbon uptake is partially offset by biogeophysical warming. Consequently, a comparable net global cooling can be achieved with substantially less reforested area (up to 450 Mha) if planting locations are better suited for regional-scale cooling. Reforestation locally cools the tropics but triggers albedo-driven warming in higher latitudes, which is further amplified by non-local effects. Thus, tropical and subtropical regions emerge as high-potential climate mitigation areas where local cooling dominates, whereas reforestation in mid-to-high latitudes can be climatically counterproductive due to this amplified local warming. Regional temperature outcomes diverge most significantly due to non-local responses, illustrating how specific reforestation patterns reshape the climate through large-scale circulation and oceanic adjustments. Interestingly, despite these divergent temperature patterns, we find that precipitation changes remain surprisingly consistent across the different reforestation scenarios. Our findings underscore the importance of "climate-smart" policies that prioritize the geographical placement of reforestation over total area, accounting for both biogeochemical and biogeophysical effects to maximize global cooling benefits.

Reference to preprint: https://doi.org/10.21203/rs.3.rs-7714264/v1