Transition from multi-year La Niña to strong El Niño rare but increased under global warming

Fan Jia; Wenju Cai; Tao Geng; Bolan Gan; Wenxiu Zhong; Lixin Wu; Michael J McPhaden

doi:10.1016/j.scib.2024.12.034

Transition from multi-year La Niña to strong El Niño rare but increased under global warming

Sci Bull (Beijing). 2024 Dec 25:S2095-9273(24)00941-1. doi: 10.1016/j.scib.2024.12.034. Online ahead of print.

Authors

Fan Jia¹, Wenju Cai², Tao Geng³, Bolan Gan⁴, Wenxiu Zhong⁵, Lixin Wu⁶, Michael J McPhaden⁷

Affiliations

¹ Key Laboratory of Ocean Observation and Forecasting and Key Laboratory of Ocean Circulation and Waves, Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266000, China; Laoshan Laboratory, Qingdao 266237, China. Electronic address: [email protected].
² Laoshan Laboratory, Qingdao 266237, China; Frontier Science Center for Deep Ocean Multispheres and Earth System (FDOMES) and Physical Oceanography Laboratory, Ocean University of China, Qingdao 266100, China; State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China; State Key Laboratory of Marine Environmental Science & College of Ocean and Earth Sciences, Xiamen University, Xiamen 361005, China. Electronic address: [email protected].
³ Laoshan Laboratory, Qingdao 266237, China.
⁴ Frontier Science Center for Deep Ocean Multispheres and Earth System (FDOMES) and Physical Oceanography Laboratory, Ocean University of China, Qingdao 266100, China.
⁵ School of Atmospheric Sciences, Sun Yat-sen University, and Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), Zhuhai 519000, China.
⁶ Laoshan Laboratory, Qingdao 266237, China; Frontier Science Center for Deep Ocean Multispheres and Earth System (FDOMES) and Physical Oceanography Laboratory, Ocean University of China, Qingdao 266100, China.
⁷ NOAA/Pacific Marine Environmental Laboratory, Seattle, Washington DC 20005, USA.

PMID: 39753474
DOI: 10.1016/j.scib.2024.12.034

Abstract

El Niño-Southern Oscillation (ENSO) exhibits a strong asymmetry between warm El Niño and cold La Niña in amplitude and temporal evolution. An El Niño often leads to a heat discharge in the equatorial Pacific conducive to its rapid termination and transition to a La Niña, whereas a La Niña persists and recharges the equatorial Pacific for consecutive years preconditioning development of a subsequent El Niño, as occurred in 2020-2023. Whether the multiyear-long heat recharge increases the likelihood of a transition to a strong El Niño remains unknown. Here, we show that such a transition is rare but more likely under transient greenhouse warming. In boreal spring and early summer after a multiyear La Niña, despite a substantial recharge in the western Pacific, thermocline remains anomalously shallow and sea surface temperature (SST) remains anomalously cold in the equatorial central Pacific. The cold conditions inhibit an ensuing eastward movement of atmosphere deep convection out of the warm western Pacific, delaying onset of ocean-atmosphere coupling, and hence growth of an El Niño. Under a high emission scenario, such a transition is still rare but more than twice as likely. The projected change is consistent with a projected weakening in climatological zonal SST gradient that promotes the eastward movement of atmosphere convection and a projected intensification in upper-ocean stratification of the equatorial Pacific that enhances the ocean-atmosphere coupling. Our result provides predictive insight of El Niño after multiyear La Niña, and advances our understanding of ENSO transition under greenhouse warming.

Keywords: El Niño-Southern Oscillation transition; atmosphere deep convection; greenhouse warming; multiyear La Niña.