返回
Historical change of El Niño properties shed light on future changes of extreme El Niño
Bin Wang and co-authors
Department of Atmospheric Sciences and International Pacific Research Center, University of Hawaii, Honolulu HI 96822, USA
El Niño’s intensity change under anthropogenic warming is of great importance to society, yet current climate models’ projections remain largely uncertain. The current classification of El Niño diversity does not distinguish strong from moderate El Niño events, making it difficult to project future change of El Niño’s intensity. Here we classify 33 El Niño events from 1901 to 2017 by cluster analysis of the onset and amplification processes, and the resultant three types of El Niño distinguish the strong from moderate events and exhibit distinct development mechanisms and global climate impacts. We find El Niño onset regime has changed from eastern Pacific-origin to western Pacific-origin with more frequent occurrence of extreme events since the 1970s. This regime change is hypothesized to be a background warming in the western Pacific and the associated increased zonal and vertical SST gradients in the equatorial central Pacific, which reveals a controlling factor that could lead to increased extreme El Niño events in future. Observations shows that the development of NINO4 SST anomalies are favored by increased mean state SST gradient between the western and central Pacific. The CMIP5 models’ projections demonstrate that both the frequency and intensity of the strong El Niño events will increase significantly if the projected central Pacific zonal SST gradients enhance. If the currently observed background changes continue under future anthropogenic forcing, more frequent strong El Niño events are anticipated. The models’ uncertainty in the projected equatorial zonal SST gradients, however, remains a major roadblock for faithful prediction of El Niño’s future changes.