The overlooked local air warming mitigation of potential tree restoration

Abstract Forestation, as a key component of Nature-based solutions, has the potential to cool or warm local climate through biophysical feedbacks, thereby enhancing or offsetting the global warming mitigation from carbon assimilation. Currently, the magnitude of such biophysical feedback on local climate remains unconstrained, as most previous observational studies rely on land surface temperature (Ts), rather than the policy-relevant air temperature (Ta). Based on multi-scale observational evidence, we show that Ta response to tree cover change is significantly lower, ranging from 15% to 30%, compared to Ts response, suggesting the overestimation of forestation’s local climate effect in previous Ts-based studies. In-situ observations further show that this discrepancy is attributed to the reduced aerodynamic resistance and the resultant flatter near-surface temperature profiles in forested areas. Despite the reduced Ta sensitivity, we find potential tree restoration in hotspot countries could still offer substantial climate benefits, which are equivalent to about 50% of the carbon sequestration-related cooling effects (biochemical effect) under the fully restored scenario. The biophysical cooling can be comparable to the biochemical effect in terms of daytime maximum temperature. Our Ta-based assessment underscores the strong potential of local climate mitigation from tree restoration practices, an aspect often overlooked in current forest-related pledges and policies against global warming.