Butterfly effect and a self-modulating El Niño response to global warming

Area of Science:

• Climate Science
• Oceanography
• Atmospheric Science

Background:

• El Niño and La Niña, known as the El Niño-Southern Oscillation (ENSO), are highly consequential and nonlinear climate phenomena.
• ENSO exhibits asymmetry, with El Niño's warm anomalies being larger than La Niña's cold anomalies.
• Greenhouse warming is projected to increase ENSO event frequency, but model projections vary significantly due to internal variability.

Purpose of the Study:

• To investigate the impact of initial infinitesimal perturbations on ENSO variability.
• To understand how initial ENSO variability systematically affects its response to future greenhouse warming.
• To explore the self-modulating mechanism linking ENSO variability across different timescales.

Main Methods:

• Utilized large ensembles of climate models, including those from the Coupled Model Intercomparison Project.
• Introduced infinitesimal random perturbations to identical initial conditions to simulate the butterfly effect.
• Analyzed the cumulative oceanic heat loss from ENSO thermal damping and its impact on ocean stratification.

Main Results:

• Infinitesimal perturbations to initial conditions induce vastly different initial ENSO variability.
• Higher initial variability leads to greater oceanic heat loss, reducing upper ocean stratification.
• This self-modulation results in a smaller increase in ENSO variability under subsequent greenhouse warming in some scenarios.

Conclusions:

• A self-modulating mechanism links ENSO variability across time, influencing its response to climate change.
• If greenhouse-warming-induced ENSO variability is initially suppressed by internal variability, future ENSO variability may be enhanced.
• This finding offers a new perspective on ENSO dynamics across multiple timescales in a changing climate.