The corals of the Galápagos reveal a recent change in El Niño unlike anything found during the millennium preceding industrialization.
El Niño is a periodic warming of part of the tropical Pacific. Normally, winds push warm water westward toward Australia. During an El Niño event, these winds weaken and more warm water flows back eastward. This movement alters rainfall and temperatures far beyond the Pacific.
Sea surface temperature anomalies in the Pacific on August 25, 2026, showing the band of warmer water associated with El Niño.
Credit: European Union, Copernicus Marine Service Data — Contains modified Copernicus Sentinel data 2026
The phenomenon La Niña is the opposite phase of El Niño, with colder currents. El Niño and La Niña are the two components of a recurring cycle.
To find out whether the current El Niño phenomenon is truly unusual, researchers went back in time using Galápagos corals. Their skeleton grows in successive layers and preserves chemical traces linked to water temperature. The team studied 13 living or ancient corals, prioritizing pieces covering a period of at least 20 years.
The scientists notably measured the ratio of strontium to calcium in these layers. This ratio varies with the temperature at the time of their formation. A second measurement based on different forms of oxygen complemented the analysis. Together, these indicators make it possible to reconstruct ancient variations in surface temperature around the islands.
The result published in Science mainly concerns the variability of the El Niño–La Niña system in the eastern Pacific. Over the past four decades, it has reached a level 36.5% higher than that of the studied preindustrial millennium. This increase is mainly due to El Niño events becoming stronger and more frequent in recent data.
In other words, the figure of 36.5% describes the increase in temperature fluctuations associated with the phenomenon in the region studied. The Galápagos are particularly well suited to this research because major El Niño events produce strong temperature anomalies there.
The challenge is to distinguish an evolution linked to warming from an especially long natural variation. The researchers therefore compared their data with simulations covering the last millennium. Twelve climate models reproduced natural influences, notably volcanic eruptions and variations in solar activity. None generated a rise comparable to the one observed recently on its own.
The measured increase accompanies the rise in global temperature, strengthening the connection with current warming. El Niño can shift areas of heavy rainfall, promote droughts elsewhere, and disrupt marine ecosystems. A more variable phenomenon may therefore alter the intensity of some extreme weather events, without producing the same effects in every region.
The researchers also have coral archives from the central Pacific, where an increase also appears, but less clearly than in the Galápagos. These geographical differences are now becoming an important line of inquiry: they should help determine how the El Niño–La Niña system will respond if the planet continues to warm.