Colder Eastern Equatorial Pacific and Stronger Walker Circulation in the Early 21st Century: Separating the Forced Response to Global Warming From Natural Variability

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