As CO₂ rose in a warm ancient climate, study shows El Niño peaked then weakened

The Miocene, beginning approximately 23 million years ago, represents a canonical "warm-Earth" interval characterized by elevated atmospheric CO2 and a warmer global climate. The El Niño–Southern Oscillation (ENSO), as a leading mode of interannual climate variability, exerts pronounced influences on global precipitation patterns and the occurrence of climate extremes. Investigating ocean–atmosphere variability under Miocene-like high-CO2 background states therefore provides a valuable framework for evaluating climate-model performance in warm climates and for informing expectations of ENSO behavior under continued anthropogenic warming.