Excessive Negative Surface Heat Flux Feedback in CMIP6 Models

Abstract

Local surface heat flux feedback plays a critical role in modulating sea surface temperature (SST) variability. Here we estimate local surface heat flux feedbacks using an observational and a reanalysis data set, and outputs from 27 CMIP6 models. We find that CMIP6 models systematically overestimate the magnitude of negative net surface heat flux feedback by 22%–27% globally. This excessive damping mainly arises from overly strong latent heat flux feedback globally, with an additional contribution from stronger shortwave feedback in the tropics. Despite these strong negative feedbacks, SST variability in CMIP6 models does not show clear signs of excessive overdamping, as both SST variance and persistence are broadly consistent with observations. This apparent inconsistency suggests compensating oceanic processes, potentially related to underestimated ocean damping or biases toward overly deep mixed layer depths.