Climate models exaggerate the impact of greenhouse gases on recent interhemispheric temperature contrast and tropical climate

The interhemispheric thermal contrast (IHTC), represented by sea surface temperature (SST) differences between the northern (NH) and southern (SH) hemispheres, crucially influences the tropical climate. Current CMIP6 climate models, however, struggle to accurately simulate the IHTC and associated tropical climate variability. Here, we show that simulated long-term trends since 1950 in models are consistently higher, with more warming in the NH compared to the SH, than in observations. This systematic discrepancy arises from overly dominant role of greenhouse gases in models that yields a positive IHTC through wind-evaporation-SST feedback. Conversely, the observed trend, primarily driven by anthropogenic and natural aerosols, is negative. This discrepancy suggests that current models is overly sensitive to greenhouse gases, and actual equilibrium climate sensitivity (ECS) may be lower than CMIP6 model predictions. Nevertheless, the modeled multidecadal IHTC variability aligns with observations, enabling a constrained estimate of effective radiative forcing due to aerosol-cloud interactions (ERFaci) at -0.6±0.3 W/m^2, with a “likely” range 57% narrower than the latest IPCC report. Our study further suggests that future tropical rain belt shifts are likely to be less pronounced than predicted by CMIP6 models with the high ECS.