Weakening vegetation control on global terrestrial evapotranspiration in a warmer world

Widespread vegetation greening enhances terrestrial evapotranspiration (ET) by increasing evaporative surfaces, yet their dynamics and the underlying ecological mechanisms under projected warming scenarios remain unclear. Here, we quantify changes in the sensitivity of ET to growing-season averaged leaf area index (∂ET/∂LAI) through 2100 across emission scenarios by integrating satellite retrievals and CMIP6 Earth system model simulations within a machine-learning framework. Results show that the current positive ∂ET/∂LAI (71.53 ± 12.01 mm m2m-2) is projected to weaken over about 80% of global land, driven by a declining vegetation control on transpiration, particularly in warm regions and under higher‑emission scenarios (−0.121 ± 0.026 and −1.247 ± 0.075 mm m2m-2 decade-1 under SSP1-2.6 and SSP5-8.5, respectively). Conductance-based diagnostics indicate that the suppressing effect of reduction in stomatal conductance increasingly outweighs the positive CO2 fertilization effect with the elevated CO2 concentration. Consequently, the LAI-driven evaporative cooling is expected to diminish under future conditions for the benefit of enhanced water conservation. The positive sensitivity of terrestrial evapotranspiration to growing-season averaged leaf area index is projected to weaken over about 80% of global land area by 2100, according to integration of satellite data and CMIP6 Earth system model simulations.