El Niño, Explained

January 28, 2024
Science Magazine

The most recent onset of El Niño began in 2023. As of January 2024, we are at its peak. What does this mean for our climate?

Translating to “Little Boy” in Spanish, El Niño is a climate anomaly characterized by unusually warm waters in the eastern and central Pacific Ocean—a phenomenon caused by the weakening of trade winds that normally usher cold water from the ocean floor to the surface. South American fishermen first noticed this phenomenon in the Pacific Ocean in the 1600s and called it El Niño de Navidad, as El Niño typically peaks around December. Along with its cool phase counterpart, La Niña, scientists call this phenomenon the El Niño Southern Oscillation (ENSO) cycle. El Niño events are irregular, occurring every two to seven years, and can last from nine months to several years. 

Above: Water movement of the eastern and central Pacific Ocean contributes to El Niño climate conditions. Image courtesy of SciJinks.

El Niño has widespread effects on global weather patterns. As the warmer waters in the Pacific jet stream move south of their typical position, droughts occur in Canada, Indonesia, and Australia. On the other hand, the Gulf Coast and Southeastern United States are wetter and prone to intense flooding. Additionally, the weakened trade winds prevent ocean upwelling from bringing cold, nutrient-rich water to the surface, harming the phytoplankton and fisheries that rely on these ecosystems.

Above: A cross-section of the ocean effects caused by El Niño. Image courtesy of The Guardian.

The summer of 2023 marked the hottest summer on record, as measured by global sea surface temperature anomalies. This trend of warming is the result of climate change, driven primarily by the release of greenhouse gas emissions. At the same time, El Niño has exacerbated the effects of climate change by pumping extra warmth into the atmosphere. From longer and wetter heat waves to increased wildfires from droughts, the compounding effects of El Niño and global warming can pose an immense threat to human health, ecosystems, and economies.

Above: Changes in sea surface temperature over time, showing a marked increase in 2023 compared to measurements for past years. Image courtesy of NOAA Climate.gov.

In December 2023, the sea surface temperature in the key tropical Pacific monitoring region for El Niño measured 2.1 degrees Celsius above the average from 1991 to 2020. To put this figure into perspective, the threshold for a “very strong” El Niño event is 2.0 degrees Celsius above average. While it is typical for El Niño to peak in December/early January, impacts on climate and weather conditions in the United States could last even after the peak through April.

Beyond the spring, it’s unclear if neutral conditions will persist or if La Niña, the global cooling version of El Niño, will develop. In any event, be sure to keep an eye out for extreme weather patterns and global temperatures throughout 2024. 

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