Impact of tropical eastern Pacific warming bias on Caribbean climate.

During the last decades, CMIP5 models simulate a warming trend in the tropical eastern Pacific that has not been present in observations (Seager et al., 2019). Associated with this, the Walker circulation has experienced a westward migration while CMIP5 models simulate an eastward migration. This mismatch is still present in CMIP6 models and might affect climate projections worldwide through different teleconnections.

In the Caribbean region, CMIP6 models project a strong drying at the end of the 21st century. El Niño-like changes in the Walker circulation are the dominant processes driving the Caribbean drying. The models that project a strong Caribbean drying also simulate generally a strong equatorial eastern Pacific warming trend over the recent decades. Thus, the mismatch between observed and simulated warming trends over the equatorial eastern Pacific questions the reliability of the Caribbean precipitation projections. The warming bias might also have implications for tropical cyclones’ projections in the Atlantic and Pacific through the effect of vertical wind shear, which is related to shifts in the Walker circulation. In addition, the double Intertropical Convergence Zone (ITCZ) bias might be influenced by the mismatching trends. Based on our understanding of the physical processes affecting Caribbean drying, we carry out an emergent constraint analysis to reduce the projected Caribbean precipitation spread. We find that the future drying in the Caribbean might be weaker than the one projected by CMIP6 models.

The strong influence of El Niño-Southern Oscillation (ENSO) dynamics on the world’s climate through different teleconnections demands more in-depth studies addressing the drivers of the Walker circulation and the equatorial Pacific warming bias.