Reduced El Niño variability in the mid-Pliocene according to the PlioMIP2 ensemble

• DOI: 10.5194/cp-17-2427-2021
• Publication Date: 2021-12-01T11:12:04Z
• Authors: Arthur M. Oldeman; Michiel L. J. Baa...; Anna S. von der H...; Henk A. Dijkstra; Julia C. Tindall; Ayako Abe-Ouchi; Alice R. Booth; Esther C. Brady; Wing-Le Chan; Deepak Chandan; Mark A. Chandler; Camille Contoux; Ran Feng; Chuncheng Guo; Alan M. Haywood; Stephen J. Hunter; Youichi Kamae; Qiang Li; Xiangyu Li; Gerrit Lohmann; Daniel J. Lunt; Kerim H. Nisancioglu; Bette L. Otto-Bli...; W. Richard Peltier; Gabriel M. Pontes; Gilles Ramstein; Linda E. Sohl; Christian Stepanek; Ning Tan; Qiong Zhang; Zhongshi Zhang; Ilana Wainer; Charles J. R. Wil...
• Keywords: Empirical orthogonal functions; Tropical Atlantic

Abstract. The mid-Pliocene warm period (3.264–3.025 Ma) is the most recent geological during which atmospheric CO2 levels were similar to historical values (∼400 ppm). Several proxy reconstructions for show highly reduced zonal sea surface temperature (SST) gradients in tropical Pacific Ocean, indicating an El Niño-like mean state. However, past modelling studies do not these gradients. Efforts understand climate dynamics have led Pliocene Model Intercomparison Project (PlioMIP). Results from first phase (PlioMIP1) showed clear Niño variability (albeit significantly reduced) and did greatly time-mean SST gradient suggested by some of proxies. In this work, we study Niño–Southern Oscillation (ENSO) PlioMIP2 ensemble, consists additional global coupled models updated boundary conditions compared PlioMIP1. We quantify ENSO amplitude, period, spatial structure “flavour”, as well annual state pre-industrial simulations. a amplitude model-ensemble (−24 %) with respect pre-industrial, 15 out 17 individual showing such reduction. Furthermore, spectral power considerably decreases 3–4-year band. dominant empirical orthogonal function shows no particular change patterns mean, pre-industrial. Although equatorial 14 (0.2 ∘C reduction ensemble mean), there does seem be correlation decrease amplitude. “El Niño-like” changes that reference, while more “La Niña-like” generally large variability. results reasonable agreement both proxies reduced, or similar,