Rare deglacial-aged corals point to weaker El Niño in a colder world

Robert Domeyko, Judson Partin, Yuko Okumura, Kaustubh Thirumalai , Pedro DiNezio, Allison Lawman, Frederick Taylor, Dunyu Liu , Lael Vetter, Christopher Maupin, Esline Garaebiti, Abel Kalo, Krisna Kotra, Lisa Zuraw, Hsun-Ming Hu, Mayuri Inoue, Larry Edwards, Chuan-Chou Shen

Extreme El Niño events, the warm phase of the El Niño–Southern Oscillation (ENSO), have increased in frequency since the late 20th century, intensifying concerns about ENSO’s response to a changing climate and its far-reaching impacts on global weather. Yet climate model projections of future ENSO behaviour remain divergent, and simulations under past glacial boundary conditions likewise lack consensus. Past climate simulations are distinctive in that they can be directly evaluated against subannually-resolved palaeoclimate archives; however, such archives remain scarce beyond the Holocene. Here we combine the first monthly-resolved, multidecadal fossil coral oxygen isotope records spanning the last deglaciation with new climate model experiments to evaluate ENSO amplitude and extreme event frequency under colder climates. The new coral data from Vanuatu – where a significant portion of interannual changes are driven by ENSO – reveal a reduction in interannual variance and extreme-event frequency ~12–15 thousand years ago relative to the late Holocene. The climate simulations reveal systematic increases in interannual variance and extreme-event frequency from the cold deglacial to the warm Holocene, with further intensification under anthropogenic warming. The concordance of natural archives with climate model simulations demonstrates a robust climate state dependence of ENSO and strengthens confidence in projections of more frequent extreme El Niño events in a warming future.