Nonlinear Dynamics of El Niño–Southern Oscillation Events

The El Niño–Southern Oscillation (ENSO) embodies a complex interplay of oceanic and atmospheric processes that give rise to irregular warming (El Niño) and cooling (La Niña) episodes in the tropical Pacific. Its nonlinear character stems from threshold behaviours in feedback loops, notably the Bjerknes feedback, whereby sea surface temperature anomalies amplify wind and thermocline responses. The classical recharge–discharge oscillator paradigm describes how equatorial heat content builds up and releases, yet observations and models reveal departures from this idealised cycle, including multi-year La Niña episodes, regime shifts between strong and moderate El Niño types, and hysteresis under changing greenhouse-gas forcing. Interactions with other tropical basins, variations in ocean heat content and mean state warming further modulate event onset, duration and intensity. These dynamics underpin far-reaching teleconnections that alter precipitation, temperature extremes and ecosystem health across continents. Improved understanding of ENSO’s nonlinear behaviour is essential for enhancing seasonal forecasts, anticipating climate extremes and informing adaptation strategies in a warming world.

Research from Nature Portfolio

Recent studies have revealed a marked rise in consecutive multi-year La Niña events under future warming scenarios. Model intercomparisons indicate that subtropical and equatorial Pacific mean-state warming broadens easterly wind anomalies northward, slowing heat recharge and favouring second-year cooling persistence. Observational analyses challenge the notion that only strong El Niño precursors trigger multi-year La Niña, instead highlighting the role of off-equatorial modes such as the North Pacific Meridional Mode in extending cold anomalies and initiating repeat La Niña cycles. Complementary work shows that two distinct pathways link El Niño strength and spatial pattern to subsequent La Niña persistence, with central Pacific and eastern Pacific warming each invoking different feedbacks. Large ensemble simulations further demonstrate that enhanced western Pacific warming amplifies zonal advective and thermocline feedbacks, accounting for the recent acceleration in multi-year cold events.

Nonlinear Dynamics of El Niño–Southern Oscillation Events publication trend

The graph below shows the total number of articles in nonlinear dynamics of el niño–southern oscillation events across all publications each year (not limited to Nature Index journals).

Technical terms

El Niño–Southern Oscillation (ENSO): A coupled ocean-atmosphere phenomenon characterised by interannual variations in tropical Pacific sea surface temperatures and atmospheric circulation.

Bjerknes feedback: A positive loop in which warm sea surface temperature anomalies weaken trade winds, deepen the thermocline and further amplify warming.

Recharge–discharge oscillator: A conceptual model describing how equatorial heat content accumulates (recharge) and is released (discharge) to drive ENSO cycles.

Thermocline: The subsurface layer in the ocean marking the rapid transition between warm surface water and cooler deep water, whose depth fluctuations influence ENSO intensity.

Ocean heat content (OHC): The integrated thermal energy stored in the upper ocean, serving as a precursor signal for forthcoming ENSO events.

References

1. Increased occurrences of consecutive La Niña events under global warming. Nature (2023).
2. Overemphasized role of preceding strong El Niño in generating multi-year La Niña events. Nature Communications (2023).
3. Understanding the recent increase in multiyear La Niñas. Nature Climate Change (2023).
4. A multiyear tropical Pacific cooling response to recent Australian wildfires in CESM2. Science Advances (2023).
5. ENSO skewness hysteresis and associated changes in strong El Niño under a CO2 removal scenario. npj Climate and Atmospheric Science (2023).
6. A Strong 2023/24 El Niño is Staged by Tropical Pacific Ocean Heat Content Buildup. Ocean-Land-Atmosphere Research (2023).
7. Strong and moderate nonlinear El Niño regimes. Climate Dynamics (2015).
8. Single- and multi-year ENSO events controlled by pantropical climate interactions. npj Climate and Atmospheric Science (2022).