Since the early 1990s the Pacific Walker circulation shows a multi-decadal strengthening, contradicting future model projections. Whether this trend, evident in a range of indices especially before the 2015 El Niño, reflects the coupled ocean-atmosphere response to global warming or the negative phase of the Pacific Decadal Oscillation (PDO) remains debated. Here we show that sea surface temperature (SST) trends during 1980-2020 are dominated by three signals: a spatially uniform warming trend, a negative PDO pattern, and a Northern Hemisphere/Indo-West Pacific warming pattern. The latter pattern, which closely resembles the transient ocean thermostat-like response to global warming emerging in a subset of CMIP6 models, shows cooling in the central-eastern Pacific but warming in the western Pacific and tropical Indian ocean. This pattern contributes to the Walker circulation strengthening along with the PDO. Historical simulations appear to underestimate this pattern, contributing to the models’ inability to replicate the Walker cell strengthening.