Recent intensification of eastern Pacific ENSO is unprecedented across the last millennium

The Pacific El Niño-Southern Oscillation (ENSO) phenomenon generates climate extremes that endanger ecosystems, infrastructure, and human well-being worldwide. The response of this system to climate warming is poorly constrained, due to data scarcity and climate model biases, making projections of future climate hazards uncertain. The geochemistry of Galápagos coral skeletons across the past millennium reveals an unprecedented increase in interannual variability of sea surface temperature in the eastern equatorial Pacific that has emerged above pre-industrial levels and exceeds simulated natural variability. This increase parallels the rise in global temperature and results from stronger El Niño events. Central Pacific coral data also show increased variability, although less distinctly than in Galápagos. Our results provide long-term context for understanding ENSO variability trends, with troubling implications for future climate extremes.