An analysis of living and fossil corals from the Galapagos Islands found that the variability of the El Niño–La Niña system in the eastern Pacific Ocean is now 36.5% higher than it was during the pre-industrial millennium. The increase is largely due to stronger and more frequent El Niño events, and natural climate models alone have failed to reproduce a change of this magnitude.
Events El Niño The extremes of recent decades no longer appear to be a normal part of the fluctuations that have characterized the Pacific Ocean for centuries. A new study, based on Coral Life and fossils fromGalapagos Islands, found that the interannual variability of the El Niño–Southern Oscillation system (ENSO) in the Eastern Pacific Ocean is currently 36.5% higher than it was in the pre-industrial millennium.
The study, published in Science, shows that the increase is largely due to more frequent and stronger El Niño events. The researchers found that the most dramatic change has occurred in the past four decades, coinciding with global warming.
This does not mean that every El Niño event in the last 40 years has been 36.5% stronger than a previous event. The number refers to the increase in the variability of the ENSO system—that is, the range of oscillations of Sea surface temperature Year after year. But according to the researchers, most of this increase stems from the warm end of the cycle: stronger El Niño events.
El Niño is natural—but the background has changed
El Niño is a natural phase of the ENSO cycle. Under normal conditions, the trade winds along the equator push warm water westward, towards Indonesia and Australia, allowing colder water to rise in the eastern Pacific.
As the trade winds weaken, warm water spreads eastward toward the coast of South America. The change in the ocean affects the atmosphere, shifting rainfall areas and altering flow patterns on a global scale. The results can include droughts, floods, fires, crop failure and disease outbreaks in different parts of the world.
El Niño itself is not caused by human-made climate change. The question that has preoccupied climate researchers is whether a warmer world is changing the strength of the natural oscillation—and, in particular, whether it is allowing El Niño events to become more extreme.
The problem is that instrument records only provide a detailed picture for a relatively short period. To know whether the last forty years are truly exceptional, you have to compare them to centuries when there were no thermometers and satellites.
Corals maintain the sea temperature
To do this, the researchers turned to the Galapagos Islands, which are located in the heart of the region where the El Niño signal in the eastern Pacific Ocean is particularly strong.
The team drilled cores from 13 corals—both living colonies and ancient coral blocks that had been washed ashore. Corals build their skeletons layer by layer, at a rate of about one to two centimeters per year. The chemical composition of each layer depends on the seawater conditions at the time it was formed, so the skeleton serves as a natural climate archive.
The researchers sampled the cores at millimeter intervals and examined two independent chemical indices. The first is the ratio of strontium to calcium in the coral skeleton, which varies with water temperature. The second is the ratio of different oxygen isotopes, which also serves as an indirect measure of temperature and water conditions.
Because ENSO events occur in cycles of several years, the researchers focused on records that each span at least 20 years. Combining the records provided a window into changes in sea surface temperature in the eastern Pacific Ocean over large parts of the last millennium.
The last forty years stand out immediately
When the researchers compared the periods, a clear picture emerged: in the pre-industrial millennium, a lower level of variation was maintained, while in recent decades the fluctuations have strengthened sharply.
According to the researchers, modern variability is 36.5% higher than that of the pre-industrial millennium. The change is largely due to more frequent and stronger El Niño events, with the most pronounced increase occurring in the last four decades.
Coral records from the central Pacific also indicate an increase in diversity, although the signal there is less sharp than that found in the Galapagos.
The researchers emphasize that the strength of El Niño increases in parallel with global temperatures. Julia Cole, professor and head of the Department of Earth and Environmental Sciences atUniversity of Michigan And the lead author of the study, said that the large El Niño events of the last forty years do not seem normal in the context of the last millennium.
Could this just be a natural fluctuation?
Correlation with warming alone is not enough to determine what is causing the change. ENSO is an inherently variable system, and is also influenced by natural factors such as volcanic activity and changes in solar radiation.
So the researchers compared the coral records to simulations of the pre-industrial climate from 12 climate models. The simulations included the known effects of volcanic eruptions, changes in solar radiation, and internal variability of the climate system.
None of the models naturally produced an increase in ENSO variability of the magnitude found in the coral records, which the researchers say reinforces the argument that the current change is not well explained by the natural forces that operated in the millennia before industrialization.
However, the result also raises a problem for the models themselves. Samantha Stevenson of the University of California, Santa Barbara, one of the study's authors, noted that the fact that the models did not reproduce the strengthening seen in corals may indicate that they are still missing some of how ENSO responds to warming.
Why are corals in the Galapagos so important?
The Galapagos Islands are located in the eastern equatorial Pacific Ocean, where El Niño-related temperature changes are particularly strong, so even a relatively small change in ENSO dynamics leaves a clear signature there.
Corals also allow us to go far beyond the period of direct measurements. This is important because strong ENSO events do not occur every year. A record of only a few decades can make a rare event seem unprecedented even though it is part of a long oscillation. Thousands of years of connection make such a claim much stronger.
The study does not rely on a single coral or a single chemical index. The use of multiple corals, at different times, and with two chemical temperature indices provides cross-checking between the records.
2026 provides a real-time test
The study was published as a particularly strong El Niño develops in the Pacific Ocean. As early as the summer of 2026, abnormal temperatures were measured in the eastern Pacific Ocean, and NASA identified a large reservoir of warm water beneath the ocean surface—conditions that could fuel the event’s continued strengthening.
A single event should not be used to prove a long-term trend. The strength of the new study comes from exactly the opposite direction: It starts with a thousand years of data and shows that the past few decades as a whole have fallen outside the range of variation seen in the past.
If the link between global warming and ENSO intensification continues, very strong El Niño events could become more common in an already warmer world. Such a combination could exacerbate heat waves, droughts, floods, fires, damage to agriculture and infrastructure, and risks to public health.
El Niño also warms — and warming may strengthen it
El Niño has been known for years as a mechanism that can temporarily raise global temperatures, as heat stored in the ocean is released into the atmosphere. In years of strong El Niño, global temperature records are often broken.
The new study suggests that the relationship also works in the opposite direction: long-term warming of the climate system may increase ENSO oscillations and strengthen El Niño events themselves.
This is not a simple cycle in which each warm year immediately strengthens the next El Niño. ENSO is influenced by complex processes in the ocean and atmosphere, and researchers emphasize that models still do not fully capture the change. But the coral record provides long-term evidence that the Pacific climate system is already behaving differently than it did in the pre-industrial millennium.
Questions and Answers
What did the new study on El Niño find?
Chemical records from corals in the Galapagos show that ENSO variability in recent decades is 36.5% higher than that of the pre-industrial millennium. Much of the increase is due to stronger and more frequent El Niño events.
How can we know what the strength of El Niño was hundreds of years ago?
Coral skeletons are formed in layers, and their chemical composition depends on the temperature of the seawater during growth. Measuring the ratio of strontium to calcium and oxygen isotopes allows us to reconstruct changes in sea surface temperature throughout the life of the coral.
Is El Niño caused by global warming?
No. ENSO is a natural oscillation of the ocean and atmosphere. The research suggests that global warming may be changing the strength of the oscillation and causing stronger El Niño events, rather than that climate change created the phenomenon itself.
How did the researchers verify that this was not a normal natural oscillation?
They compared the coral record to simulations of the pre-industrial climate in 12 models that included volcanic activity, solar radiation changes, and internal variability. The simulations did not produce a change as large as that found in the modern record.
The scientific article
Recent strengthening of eastern Pacific ENSO in the last millennium paleorecord — JE Cole et al., Science, August 27, 2026.
More on the subject on the science website
- NASA: Large heat reservoir developing under the Pacific Ocean, strengthening El Niño
- Super El Niño: Earth is gaining heat at a record rate, the energy balance has doubled in recent decades
- El Niño approaches for a warmer world: Scientists warn of heat waves, fires and severe flooding
- El Nino - will 2014 be the new 1997?
- The disturbance in the wind circulation in the Pacific Ocean that causes the El Niño phenomenon
For the original publication: Opening the original publication
