Chen et al. (2025) El Niño-like warming underestimated in a warmer climate due to ENSO rectification effect

Identification

• Journal: npj Climate and Atmospheric Science
• Year: 2025
• Date: 2025-11-17
• Authors: Yue Chen, Ping Huang, Jun Ying
• DOI: 10.1038/s41612-025-01250-2

Research Groups

• Anhui Province Key Laboratory of Atmospheric Science and Satellite Remote Sensing, Anhui Institute of Meteorological Sciences, Hefei, China
• Huaihe River Basin Typical Farm Eco-meteorological Experiment Field of CMA, Shouxian National Climatology Observatory, Shouxian, China
• State Laboratory of Earth System Numerical Modeling and Application, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
• Center for Monsoon System Research, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
• State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, State Oceanic Administration, Hangzhou, China

Short Summary

This study reveals that traditional climate models underestimate El Niño-like warming in a warmer climate by 14.5% ± 11.9% due to a weakening El Niño–Southern Oscillation (ENSO) asymmetry-related rectification effect. By employing a normalized mean state framework, the research clarifies how ENSO nonlinearity shapes tropical Pacific warming patterns and provides an improved basis for climate projections.

Objective

• To clarify how ENSO nonlinearity, specifically the rectification effect stemming from ENSO asymmetry, shapes the tropical Pacific sea surface temperature (SST) warming pattern under global warming.
• To quantify the underestimation of El Niño-like warming in traditional climate projections and provide an improved framework for future climate projections.

Study Configuration

• Spatial Scale: Tropical Pacific (20°S–20°N, 120°E–80°W, with specific regions for eastern and western Pacific), global for normalization.
• Temporal Scale: Historical runs (CMIP5: 1976–2005; CMIP6: 1985–2014) and future scenarios (CMIP5: Representative Concentration Pathway 8.5 (RCP8.5), 2071–2100; CMIP6: Shared Socioeconomic Pathway 5 (SSP5-8.5), 2071–2100).

Methodology and Data

• Models used: 21 CMIP5 models (7 selected for analysis) and 23 CMIP6 models (8 selected for analysis).
• Data sources:
  • Hadley Center Sea Ice and Sea Surface Temperature dataset version 1.1 (HadISST v1.1) reanalysis (1980–2020) for evaluating ENSO asymmetry.
  • CMIP5 and CMIP6 model outputs for SST, precipitation, shortwave radiation, latent heat flux, sensible heat flux, net longwave radiation, and ocean dynamical processes (including vertical current and temperature).
  • A newly defined "normalized mean state framework" was used to isolate the ENSO rectification effect.
  • Sea surface heat energy budget analyses were performed to quantify contributing mechanisms.
  • Box–Cox power transformation method was used for data normalization.

Main Results

• Traditional methods underestimate El Niño-like warming in the tropical Pacific by 14.5% ± 11.9% in multi-model ensemble means of CMIP models.
• This underestimation is attributed to the ENSO asymmetry-related rectification effect, which diminishes under global warming.
• The reduction in ENSO asymmetry induces La Niña-like influences, primarily through cloud radiative and atmospheric convection processes in the equatorial western Pacific.
• Energy budget analyses show that the cloud radiation suppression effect (ΔQ0 SW) and the ocean dynamical thermostat effect (ΔQ0 w2) exhibit the most significant differences between traditional and normalized mean states.
• The underestimation of cloud radiative feedback suppression in the traditional mean state is most pronounced in the western Pacific.
• ENSO SST asymmetries, along with ENSO-related precipitation and shortwave radiation anomalies, show a marked decrease under global warming in both traditional and normalized mean states.
• The uncertainty in the contribution of the ENSO rectification effect to the tropical Pacific SST warming pattern (TPSWP) is significantly correlated with the simulated historical ENSO asymmetry in climate models.

Contributions

• Introduced and applied a novel "normalized mean state framework" to accurately isolate and quantify the ENSO rectification effect, which was previously entangled with the climatological background state.
• Quantified the underestimation of El Niño-like warming in the tropical Pacific by traditional climate models, providing a more accurate projection of future warming patterns.
• Clarified the critical role of ENSO nonlinearity and its weakening asymmetry under global warming in shaping tropical Pacific SST warming patterns.
• Identified cloud radiative and atmospheric convection processes as dominant factors in how ENSO asymmetry impacts the TPSWP.
• Highlighted the importance of improving the simulation of ENSO skewness in climate models for more reliable climate projections.

Funding

• National Natural Science Foundation of China (42425504)
• Scientific Research Fund of the Second Institute of Oceanography, Ministry of Natural Resources (Grant SOEDZZ2504)

Citation

@article{Chen2025El,
  author = {Chen, Yue and Huang, Ping and Ying, Jun},
  title = {El Niño-like warming underestimated in a warmer climate due to ENSO rectification effect},
  journal = {npj Climate and Atmospheric Science},
  year = {2025},
  doi = {10.1038/s41612-025-01250-2},
  url = {https://doi.org/10.1038/s41612-025-01250-2}
}