The El Niño-Southern Oscillation (ENSO), alternating between El Niño and La Niña events, is the dominant and most consequential climate phenomenon affecting extreme weather, ecosystems, and agriculture around the world. For example, during El Niño, sea surface temperature (SST) is anomalously high in the central and eastern equatorial Pacific; the warm anomaly shifts the rain band over the tropical western Pacific eastward, leading to droughts in north-eastern Australia; in contrast, during La Niña, SST is lower than normal in the equatorial central Pacific, the west Pacific rain band is more intense and concentrated, causing floods over north-eastern Australia. Determining how ENSO SST variability may respond to greenhouse warming is one of the most important issues in climate change science, and has challenged scientists for decades. I will present recent findings showing that the frequency of extreme La Niña and variability of eastern Pacific El Niño SST are expected to increase in response to unabated greenhouse gas emissions. With this projected increase, we may expect more occurrences of extreme weathers associated with ENSO events, with pronounced implications for the twenty-first century climate, extreme weather, and ecosystems.
Infographic of an El Niño, with the upper portion depicting warming, rising sea level and loss of fisheries in the eastern equatorial Pacific Ocean, and the lower portion outlining the terrestrial impacts in the western Pacific region, including drought, drying rivers, crop failure, and wild forest fires.