The Efficiency of Water Vapor on Top‐of‐Atmosphere Radiation

Abstract Earth's climate sensitivity is greatly affected by the compensation between temperature feedback and water vapor (WV) feedback. Using abrupt 4xCO 2 experiments, we show that the global‐mean WV feedback is nearly a linear function of the temperature feedback, the slope of which is explained by the longwave radiative efficiency of WV . Although remains constant across models in the global mean, it exhibits substantial spatial variations and is particularly weak in Antarctica, where near‐surface inversions decouple the surface from the free troposphere. We introduce a surface–free troposphere temperature difference (SFTD) metric, showing that positive SFTD (e.g., high lifting condensation level) amplifies , while negative SFTD (e.g., strong surface inversion) suppresses it. These findings provide a clear explanation of how local climate conditions modulate the radiative compensation between temperature and WV feedbacks.