Asymmetric impacts of forest gain and loss on tropical land surface temperature

Forest gain in the tropics can cool the land surface by altering the energy budget through biophysical processes. Many countries have adopted forestation as part of their strategies for tackling climate warming. However, the biophysical effects of forest gain have generally been estimated based on the symmetrical reversal of ongoing tropical forest loss. Here we use multiple sources of satellite remote sensing data to explore the sensitivities of land surface temperature to forest gain and loss, and find forest loss warming the surface by 0.56 ± 0.12 °C and forest gain cooling the surface by 0.10 ± 0.09 °C. This asymmetry indicates weaker biophysical effects of forest gain on local temperature, which we attribute to contrasting changes of vegetation properties, such as leaf area and greenness. We find that current Earth system models fail to capture the observed asymmetry and thus could overestimate the cooling effect of afforestation in future. This highlights the need to improve representation of forest demographic impacts on biophysics-related vegetation properties, such as leaf area index, albedo and canopy structure, to better estimate the effects of tropical forestation on surface temperature. The impact of forest loss on land surface temperature in the tropics is five times greater than the response to forest gain, according to satellite observations of temperature and land cover.