Land-atmosphere feedbacks reduce positive albedo forcing of afforestation

Thanks to their carbon uptake potential, which produces a negative radiative forcing, forests are considered a major natural mitigation strategy for global warming. Because of their relatively low albedo, however, previous assessments have shown that the effectiveness of afforestation rapidly decreases with latitude. Here, we revisit the problem by taking land-atmosphere feedbacks into account and especially the impact of vegetation on the timing of cloud formation and the probability of convective precipitation. Using a soil-plant-atmosphere continuum model coupled to a mixed layer model of the atmospheric boundary layer (ABL), we explore variations in the local surface energy balance and diurnal evolution as a function of biomes and latitude. We show that the increased evapotranspiration from forests causes an anticipation in the crossing between the ABL and the lifting condensation level a phenomenon that can lead to earlier cloud formation. This provides an extra cooling effect, which counterbalances the positive forcing of land-surface albedo. As a result, the negative effects of albedo changes appear less limiting, making afforestation a more viable strategy in a wider range of latitudes.