Drivers of CMIP Tropical Pacific Warming Pattern Diversity

Abstract Anthropogenic changes in sea surface temperature relative to the tropical mean (relative SST) play a pivotal role in influencing atmospheric stability and circulation. In the tropical Pacific, CMIP5/6 multi‐model mean (MMM) projections by the end of the 21st century show a southeastern relative cooling and a reduced equatorial SST gradient, although individual models exhibit considerable diversity. Using a simplified heat budget framework, we analyze the processes driving these relative SST changes across 63 CMIP5/6 models under historical and most pessimistic future scenarios. In the southeastern tropical Pacific, MMM relative SST cooling is driven by intensified winds that enhance latent heat flux, with inter‐model diversity explained by variations in clouds and winds. Conversely, the MMM equatorial SST gradient reduction arises from reduced evaporative cooling efficiency in the climatologically cold eastern Pacific. A heat budget covariance analysis reveals that inter‐model diversity in equatorial Pacific warming is predominantly driven by ocean dynamical processes, challenging previous studies that emphasized cloud feedback mechanisms. Clouds instead mitigate inter‐model spread. The inter‐model spread in ocean dynamics is linked to two factors: trade wind relaxation and the cold tongue bias. Stronger trade wind relaxation amplifies western Pacific warming, while a weaker cold tongue indicates a less effective ocean thermostat, enhancing eastern Pacific warming. During the present‐day period, only a subset of models captures the observed equatorial SST gradient strengthening, but the mechanisms vary across these models, complicating the identification of robust drivers of this observed trend.