Speaker: Chengfei He
Our understanding of climate largely relies on state-of-the-art Earth system models that have been shown to faithfully simulate global mean sea surface temperature (SST). However, largely independent of the global mean, the interhemispheric thermal contrast (IHTC) — defined as the SST difference between the NH and SH — remains poorly constrained. In this talk, I will show that current CMIP6 models produce a substantial positive trend in the IHTC, while observations reveal a negative trend since 1950. This discrepancy arises from differing dominant forcings. Models respond primarily to greenhouse gas increases, which preferentially warm the NH through wind-evaporation-SST feedback, whereas the real world has been predominantly shaped by anthropogenic aerosol forcing. The divergent long-term IHTC trends suggest that real-world equilibrium climate sensitivity (ECS) may be lower than CMIP6 predictions. Nevertheless, the multidecadal variability of the IHTC is well reproduced by the models, enabling a novel constraint on the effective radiative forcing from aerosol–cloud interactions.
This seminar can also be viewed via our live stream.