Nonlinear Coupling Between Longwave Radiative Climate Feedbacks

Abstract

AbstractThe radiative feedbacks of such climate variables as air temperature, water vapor, and clouds influence the energy budget of the climate system. Measuring the strength of each feedback is of critical importance for understanding the climate sensitivity and its spread in climate models. Most feedback analyses to‐date, such as those using the kernel method, have been based on a linear decomposition of the radiation budget and neglect the nonlinear effects between the feedbacks. In this work, we quantify the coupling effects between different longwave radiative feedbacks based on partial radiative perturbations using a radiative transfer model. Two climate change scenarios, the El niño‐Southern Oscillation (ENSO) and the quadrupling CO2 (4xCO2), are examined. We find that the coupling effect between water vapor and cloud is the strongest among all the coupling effects and can amount to 50% or greater of the univariate cloud feedback. This significant coupling effect results from the masking effect of the two feedbacks on each other and can be well explained by a simple analytic model.