Amplified local cooling effect of forestation in warming Europe.

Forests exhibit local cooling or warming effects compared to adjacent openlands through biophysical processes. These temperature effects are predicted by earth system models to evolve in response to climate change. However, such temporal patterns remain unconstrained by observations and have not been detected in historical records. Here, by comparing the satellite observations of spatially nearby forests and openlands over the last two decades, we quantify temporal trends in local land surface temperature (LST) effects of forest change in Europe. During winter, the daytime warming effect of potential forestation weakens and reverses to cooling (-0.142 K/decade) with decreasing snow cover, as forests show less pronounced surface darkening trends than openlands. During summer, the daytime cooling effect intensifies (-0.188 K/decade) because forests remain more physiologically and hydrologically resilient to increasing soil dryness. These negative trends are broadly supported by state-of-the-art earth system models, though substantial inter-model variability persists. Given continued climate change, we emphasize the need to consider the dynamics of biophysical effects when comprehensive forest-related climate policies are formed.