Marine ecosystems in peril: Time to prepare for super El Niño

A new El Niño has begun and is projected to develop later this year into one of the strongest on record (1). The El Niño Southern Oscillation is a cyclical climate phenomenon driven by complex interactions between the ocean and the atmosphere. During the warm El Niño phase, surface temperatures in the central and eastern tropical Pacific can rapidly increase by ~5 °C or more. Super El Niños are especially strong events in which the peak Oceanic Niño Index (ONI) exceeds 2 °C (2). Whether anthropogenic climate change is directly influencing this amplitude remains an active area of research. What is clear is that the long-term warming trend, driven by greenhouse gas emissions, is increasing the ocean’s temperature baseline, so that each successive El Niño peaks from a higher starting point and pushes temperature extremes still higher. The combination of natural El Niño oscillations and anthropogenic warming is leading to more frequent and stronger marine heatwaves, i.e., discrete, prolonged periods of anomalously warm water at specific locations (3–5).