How Are El Niño and La Niña Impacted by Climate Change?
As the impacts of human-induced climate change reshape global weather patterns, its worth examining the impact of El Niño and La Niña on these processes.
Several years ago, a diligently researched book delved into the future of the El Niño Southern Oscillation (ENSO), a dominant force in Earth's climate system. Titled El Niño Southern Oscillation in a Changing Climate, the book, by Michael McPhaden, Senior Scientist at NOAA’s Pacific Marine Environmental Laboratory in Seattle and co-editor of the volume, was released by the American Geophysical Union. It offers insights from 98 authors representing 58 research institutions across 16 countries.
ENSO, a cyclical phenomenon alternating between warm El Niño and cool La Niña episodes in the tropical Pacific Ocean, exerts a profound influence on worldwide climate variations. It significantly affects agriculture, public health, freshwater availability, power generation, and economic activities globally. The book encompasses 21 chapters exploring the latest theories, models, and observations related to ENSO. It also addresses the challenges of forecasting El Niño and La Niña events in the context of a changing climate.
ENSO's influence extends across the globe, impacting regions differently during El Niño and La Niña events. For instance, El Niño often leads to increased drought risks in India, Indonesia, Australia, and parts of the Amazon, while La Niña brings wetter conditions to these areas and dry spells to the southern United States.
Understanding the diverse nature of these events adds complexity to predicting how climate change will influence future ENSO occurrences.
The book traces the historical development of ENSO concepts, explores underlying physical processes, and presents the latest scientific findings on how external factors, including climate phenomena, volcanic eruptions, and greenhouse gas forcing, influence ENSO.
Looking ahead, the authors project that extreme El Niño and La Niña events may become more frequent in a warming climate, potentially increasing from one every 20 years to one every 10 years by the end of the 21st century. The strongest events may also intensify. Rainfall patterns are anticipated to shift during El Niño and La Niña events, impacting equatorial regions in the Pacific Ocean.
In January 2024, elevated sea surface temperatures (SST) persisted across the equatorial Pacific Ocean, although anomalies weakened in the eastern and east-central regions. Weekly Niño index values reflected a slight decrease in SST anomalies. Notably, subsurface temperature anomalies approached zero, indicating significant changes below the equatorial Pacific Ocean's surface.
While above-average temperatures prevailed in the upper 100 meters of the equatorial Pacific, below-average temperatures were observed at greater depths. Atmospheric anomalies in the tropical Pacific displayed a weakening trend during January, with near-average low-level winds and easterly upper-level wind anomalies over the east-central Pacific. Convection remained slightly enhanced near the Date Line and approached average levels around Indonesia, signaling an overall weakening El Niño.
The latest International Research Institute for Climate and Society (IRI) plume suggests a shift to ENSO-neutral conditions during spring 2024, with the potential development of La Niña in the subsequent summer. Despite the inherent lower reliability of forecasts through the spring season, historical patterns indicate a tendency for La Niña to follow strong El Niño events. The forecast team aligns with current model guidance, acknowledging some uncertainty regarding the timing of transitions to ENSO-neutral and La Niña.
