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El Niño-Southern Oscillation (ENSO) sea surface temperature (SST) anomaly skewness encapsulates the nonlinear processes of strong ENSO events and affects future climate projections. Yet, its response to CO2 forcing remains not well understood. Here, we find ENSO skewness hysteresis in a large ensemble CO2 removal simulation. The positive SST skewness in the central-to-eastern tropical Pacific gradually weakens (most pronounced near the dateline) in response to increasing CO2, but weakens even further once CO2 is ramped down. Further analyses reveal that hysteresis of the Intertropical Convergence Zone migration leads to more active and farther eastward-located strong eastern Pacific El Niño events, thus decreasing central Pacific ENSO skewness by reducing the amplitude of the central Pacific positive SST anomalies and increasing the scaling effect of the eastern Pacific skewness denominator, i.e., ENSO intensity, respectively. The reduction of eastern Pacific El Niño maximum intensity, which is constrained by the SST zonal gradient of the projected background El Niño-like warming pattern, also contributes to a reduction of eastern Pacific SST skewness around the CO2 peak phase. This study highlights the divergent responses of different strong El Niño regimes in response to climate change.
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This content will become publicly available on December 1, 2026
Distinct anthropogenic aerosol and greenhouse gas effects on El Niño/Southern Oscillation variability
Abstract El Niño/Southern Oscillation variability has conspicuous impacts on ecosystems and severe weather. Here, we probe the effects of anthropogenic aerosols and greenhouse gases on El Niño/Southern Oscillation variability during the historical period using a broad set of climate models. Increased aerosols significantly amplify El Niño/Southern Oscillation variability primarily through weakening the mean advection feedback and strengthening the zonal advection and thermocline feedbacks, as linked to a weaker annual cycle of sea surface temperature in the eastern equatorial Pacific. They prevent extreme El Niño events, reduce interannual sea surface temperature skewness in the tropical Pacific, influence the likelihood of El Niño/Southern Oscillation events in April and June and allow for more El Niño transitions to Central Pacific events. While rising greenhouse gases significantly reduce El Niño/Southern Oscillation variability via a stronger sea surface temperature annual cycle and attenuated thermocline feedback. They promote extreme El Niño events, increase SST skewness, and enlarge the likelihood of El Niño/Southern Oscillation peaking in November while inhibiting Central Pacific El Niño/Southern Oscillation events.
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- PAR ID:
- 10579111
- Publisher / Repository:
- Communications Earth & Environment
- Date Published:
- Journal Name:
- Communications Earth & Environment
- Volume:
- 6
- Issue:
- 1
- ISSN:
- 2662-4435
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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