Relationship Between Tropical Cloud Feedback and Climatological Bias in Clouds

Global climate model (GCM) projections of future climate are uncertain largely due to a persistent spread in cloud feedback. This is despite efforts to reduce this model uncertainty through a variety of emergent constraints (ECs); with several studies suggesting an important role for present‐day biases in clouds. Here, we use three generations of GCMs to assess the value of climatological cloud metrics for constraining uncertainty in cloud feedback. We find that shortwave cloud radiative properties across the Southern Hemisphere extratropics are most robustly correlated with tropical cloud feedback (TCF). Using this relationship in conjunction with observations, we produce an EC that yields a TCF value of 0.52 ± 0.34 W/m2/K, which equates to a 34% reduction in uncertainty. Thus, we show that climatological cloud properties can be used to reduce uncertainty in how clouds will respond to future warming. Plain Language Summary Different global climate models exhibit large variability in how clouds across the tropics will respond to future warming. This is largely due to the complexity and diversity of responses that differing cloud types may experience under warming. A long‐term goal of the community has been to narrow this disagreement between different models. Over the past 15 years, several studies have proposed ways in which the variability in future cloud changes might be related to errors in how these models represent present‐day properties. Here, we use three collections of models to show that variability in tropical cloud changes is closely tied to shortwave cloud radiative properties across the Southern Ocean. We then use this intermodel relationship along with observations to produce a best estimate of cloud feedback across the tropics. Key Points We find a relationship between tropical cloud feedback and mean‐state biases in Southern Hemisphere extratropical cloud properties This intermodel relationship is found to be present in three different ensembles of global climate models, a sign of robustness This relationship suggests a likely tropical cloud feedback value of 0.52 ± 0.34 W/m2/K, which equates to a 34% reduction in uncertainty