Longwave Scattering Effects on Radiative Kernels

Abstract Longwave (LW) scattering, the redirection of infrared radiation by cloud and aerosol particles, is often neglected in current global climate models (GCMs). However, studies have suggested that LW scattering can influence the Earth's energy budget and climate sensitivity, indicating a need to improve the representation and understanding of this radiative effect. In addition to mean radiative fluxes, LW scattering can also change radiative sensitivities as quantified by radiative kernels. This aspect of the LW scattering effect, especially on the radiative sensitivity of non‐cloud variables, has remained largely unexplored. In this study, we use the Canadian Atmospheric Model (CanAM) which accounts for LW scattering to investigate how it affects broadband and spectral flux radiative kernels and subsequently biases kernel‐diagnosed climate feedbacks. Our results show that LW scattering generally weakens the non‐cloud kernels, reducing the sensitivity of TOA and surface radiative fluxes to non‐cloud feedback variables, with the reduction being stronger at the TOA than at the surface. The largest impact occurs in the water vapor TOA kernel, especially in the far‐infrared region. Consistent with these radiative kernel changes, non‐cloud radiative feedbacks diagnosed using radiative kernels are weaker when LW scattering is included. On the other hand, the cloud feedback is enhanced, corroborating earlier findings.