Closing the evapotranspiration–cloud gap: A mechanistic framework for forest biophysical cooling

Recent observations show planetary albedo reached record lows in 2023 due to reduced tropical cloud cover since December 2020, contributing 0.23°C to global warming (Goessling et al., 2025). We describe a mechanism—the Stomata–Cumulus Cooling Chain—where groundwater availability acts as a binary prerequisite for light-triggered stomatal opening. This "light-gate" initiates a thermodynamic pump that transports moisture and biogenic aerosols to altitudes exceeding 10 km. Our multi-regional analysis across Amazonas West and Congo Basin reveals an observed pattern where minimal forest degradation (~5%) coincides with disproportionate regional convection reduction (~30%). This suggests that tropical forest tipping points may be reached much earlier than biomass-based models suggest, occurring as soon as groundwater access is compromised. The convergence of a temperature inversion and evapotranspiration suppression during the 2020–2022 La Niña wet phase indicates that this resilience threshold has already been crossed in key basins, providing mechanistic plausibility for the unexplained global cloud loss documented in 2023.