The southeast tropical Atlantic: improvements and persistent biases in CMIP models

State-of-the-art climate models simulate warmer than observed sea surface temperatures (SST) in eastern boundary upwelling systems (EBUS), generating biases with profound implications for the simulation of present-day climate and its future projections. Amongst all EBUS, the bias is largest in the southeastern tropical Atlantic (SETA). Here, we provide a comprehensive evaluation of the performance in the SETA of the Coupled Model Intercomparison Project phase 6 (CMIP6), including fine resolution (HighResMIP) and ocean-forced (OMIP) models. We show that biases in the SETA remain large in CMIP6 models but are reduced in HighResMIP, with OMIP models giving the best performance. The analysis suggests that, once local forcing errors have been reduced, the major source of the SETA biases lies in the equatorial Atlantic. This study shows that finer model resolution has helped reduce the local origin of the SETA SST bias but further developments of model physics schemes will be required to make progress.