资源环境科技发展态势分析平台

Recent explorations of the state‐dependence of Earth's equilibrium climate sensitivity (ECS) have revealed a pronounced peak in ECS at a surface temperature of approximately 310 K. This ECS peak has been observed in models spanning the model hierarchy, suggesting a robust physical source. Here we propose an explanation for this ECS peak using a novel spectrally‐resolved decomposition of clear‐sky longwave feedbacks. We show that the interplay between spectral feedbacks in H₂O‐ and CO₂‐dominated portions of the longwave spectrum, along with moist‐adiabatic amplification of upper‐tropospheric warming, conspire to produce a minimum in the feedback parameter, and a corresponding peak in ECS, at a surface temperature of 310 K. Mechanism denial tests highlight three key ingredients for the ECS peak: 1) H₂O continuum absorption to quickly close spectral windows at high surface temperature; 2) moist‐adiabatic tropospheric temperatures to enhance upper‐tropospheric warming; and 3) energetically‐consistent increases of CO₂ with surface temperature.