Climate Dynamics Group
 at the University of California, Santa Cruz

The efficiency of water vapor on top-of-atmosphere radiation

research paper
  • Jing Feng
  • David Paynter
  • Nicole Feldl
  • Zhihong Tan
  • Pu Lin
updates ↓

08/16/25 Feng, J., D. Paynter, N. Feldl, Z. Tan, and P. Lin (2025), Geophysical Research Letters, 52, e2025GL115210, doi:10.1029/2025GL115210.

Earth’s climate sensitivity is greatly affected by the compensation between temperature feedback and water vapor (WV) feedback. Using abrupt 4xCO2 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 (ε). Although ε 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 ε, 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.