Estimating Tropical Upper-Level Cloud Feedback Based on Radiative-Convective Equilibrium Framework

Tropical upper-level cloud (TUC) feedback remains highly uncertain because TUC fraction and its radiative effect respond in complex ways to sea surface temperature (SST) warming. Using a radiative–convective equilibrium (RCE) model, we isolate the radiative impact of TUC changes by adjusting the relative occurrence of clouds and water vapor across the tropics. The resulting TUC feedback parameter, estimated from RCE experiments with observationally constrained versus CMIP6-derived TUC fractions, is more negative for observational inputs (−1.66 to −1.24 W m⁻² K⁻¹) and spans a much broader range for CMIP6 inputs (−1.34 to +1.78 W m⁻² K⁻¹). The stronger negative feedback with observational inputs likely reflects a larger reduction in TUCs with SST warming. In contrast, CMIP6-based parameters indicate weaker radiative effects of SST-driven TUC reductions, suggesting that climate models may underestimate this negative feedback.