Future Projections of the El Niño—Southern Oscillation and Tropical Pacific Mean State in CMIP6

Journal Article · 01 November 2023 · Journal of Geophysical Research. Atmospheres

DOI: https://doi.org/10.1029/2022jd037563 · OSTI ID:2204447

Erickson, Nathan E. ^[1]; Patricola, Christina M.  ^[2]

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1. Iowa State University, Ames, IA (United States)
2. Iowa State University, Ames, IA (United States); Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). Climate and Ecosystem Sciences Division

The El Niño—Southern Oscillation (ENSO) is an important mode of tropical Pacific atmosphere-ocean variability that drives teleconnections with weather and climate globally. However, prior studies using state-of-the-art climate models lack consensus regarding future ENSO projections and are often impacted by tropical Pacific sea-surface temperature (SST) biases. We used 173 simulations from 29 climate models participating in the Coupled Model Intercomparison Project, version 6 (CMIP6) to analyze model biases and future ENSO projections. We analyzed two ENSO indices, namely the ENSO Longitude Index (ELI), which measures zonal shifts in tropical Pacific deep convection and accounts for changes in background SST, and the Niño 3.4 index, which measures SST anomalies in the central-eastern equatorial Pacific. We found that the warm eastern tropical-subtropical Pacific SST bias typical of previous generations of climate models persists into many of the CMIP6 models. Future projections of ENSO shift toward more El Niño-like conditions based on ELI in 48% of simulations and 55% of models, in association with a future weakening of the zonal equatorial Pacific SST gradient. On the other hand, none of the models project a significant shift toward La Niña-like conditions. The standard deviation of the Niño 3.4 index indicates a lack of consensus on whether an increase or decrease in ENSO variability is expected in the future. Finally, we found a possible relationship between historical SST and low-level cloud cover biases in the ENSO region and future changes in ELI; however, this result may be impacted by limitations in data availability.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER); National Science Foundation (NSF); Iowa State University; USDOE
• Grant/Contract Number: AC02-05CH11231; AGS-2043272
• OSTI ID: 2204447
• Alternate ID(s): OSTI ID: 2204448; OSTI ID: 2350920
• Journal Information: Journal of Geophysical Research. Atmospheres, Vol. 128, Issue 21; ISSN 2169-897X
• Publisher: American Geophysical UnionCopyright Statement
• Country of Publication: United States
• Language: English