Diminished biophysical cooling benefits of global forestation under rising atmospheric CO₂

Forestation is a proposed solution for mitigating global warming through carbon sequestration. However, its biophysical effects through surface energy modulation, particularly under rising CO₂ levels, is less understood. Here we investigate the biophysical effects of global potential forestation on near-surface air temperature (T_a) under increasing CO₂ concentrations using a land-atmosphere coupled model with slab ocean module. Our findings reveal that, under current climate conditions, the biophysical effect of global full-potential forestation can reduce land surface T_a by 0.062 °C globally. However, this cooling benefit diminishes as CO₂ rises. While elevated CO₂ slightly alters evaporative local cooling via stomatal closure and adjustments in forestation-driven rainfall regimes, the dominant reduction stems from non-local mechanisms. Background climate shifts reorganize forestation-induced horizontal temperature advection, weakening remote cooling in the Northern Hemisphere. These findings highlight the necessity of incorporating dynamic forest management strategies to optimize mitigation potential under a changing climate.