What the Study Found
- El Nino events grew 36.5% stronger over the past 40 years than across the previous 1,000, Galapagos coral records show.
- Coral chemistry stretching back a millennium reveals the increase rising in step with global temperature.
- A dozen climate models simulating natural variability alone could not reproduce an increase this large.
- Central Pacific corals from the Line Islands show a similar rise, about 33.8% since the pre-industrial era.
OFF Santa Barbara this month, the water climbed into the low 70s Fahrenheit, and anglers started hauling in dorado and yellowtail that usually stay south of the border. A hefty El Nino is taking shape in the tropical Pacific, and new coral records pulled from the Galapagos Islands suggest this kind of event is not a fluke. Over the last 40 years, El Nino has grown 36.5 percent stronger, on average, than it was across the previous thousand. That is not a guess dressed up as a number. It comes from something scientists rarely get to examine directly: centuries of ocean chemistry, locked inside living rock.
El Nino itself is old news. It is the warm phase of a cycle called the El Nino-Southern Oscillation, and it happens every few years when the trade winds that normally push warm Pacific water toward Australia weaken, and that warm water sloshes back east instead.
The atmosphere follows the ocean’s lead. Rain that would fall over Indonesia shifts thousands of miles east, the trade winds weaken further, and the whole pattern locks in for a year or two before it lets go, sometimes flipping into the cooler La Nina phase. None of this is new, and researchers have tracked it with satellites and ocean buoys since 1980. What that instrumental record cannot tell you is whether today’s El Nino is unusual, because a few decades of measurement is a thin slice against a phenomenon that has been cycling for millennia. Julia Cole, a paleoclimatologist at the University of Michigan who led the new study, wanted a longer ruler.
A Thousand Years Written in Coral
She found one in the Galapagos, where reef-building corals have been quietly recording the ocean’s mood for a very long time. As a coral grows, roughly a centimeter or two a year, it locks the seawater’s chemical fingerprint into its skeleton: the ratio of strontium to calcium and the balance of oxygen isotopes both shift with sea surface temperature. Cole’s team sampled thirteen corals, some living, some centuries-old boulders of dead reef, a millimeter at a time down their length, then translated that chemistry back into a temperature history stretching across the last millennium.
The result, drawn from 28 separate coral records across five Galapagos islands, is about as clean a signal as paleoclimate work gets. “We kept adding records thinking ‘well, this is going to get more complicated,’ but it really didn’t,” Cole says. “This is such a clear story.”
Variability in that thousand-year record stayed fairly flat and modest right up until the last few decades, then took off. The increase tracks the rise in global temperature closely enough that the two lines practically overlay each other, and a comparable, if noisier, signal turns up in coral records from the Line Islands further west in the central Pacific. To rule out the obvious alternative, that this is simply what El Nino does on its own now and then, Cole’s team ran the numbers past a dozen climate models simulating natural variability alone, volcanoes and solar cycles included but no human influence. The models could not reproduce an increase this large, even though a broad survey of the climate-modeling literature already leaned toward expecting El Nino to intensify under warming.
The Models Are Missing Something
That gap bothers Samantha Stevenson, a co-author at the University of California, Santa Barbara, who works on the climate models in question. “I’m concerned that none of the climate models picked up on the increase we observed in the coral record,” she says. “That probably means the models are missing something about how El Nino responds to climate change, and we need to know why that’s happening.” It is an uncomfortable position for a modeler to be in: the tool built to predict the future cannot fully explain the past.
The paper stops short of declaring the case closed. Its authors write that a formal study pinning the intensification specifically on greenhouse warming, rather than merely on natural causes being unable to explain it, is beyond what this data can settle on its own. Cole herself is blunter in conversation than the manuscript is in print: “We believe global warming is supercharging El Nino,” she says, adding that stronger climate extremes are likely to follow, with ecological, infrastructural and human costs that no country is fully equipped to absorb. The coral record, for its part, shows an association that survives every natural explanation the team could throw at it. It does not, on its own, prove the mechanism.
What it does do is reframe the stakes. A stronger El Nino means wetter winters for Southern California and drier ones for Indonesia, and it drags droughts, floods, wildfire and disease risk along for the ride wherever the pattern reaches. Some forecasts, Cole notes, put global warming as high as 1.7 or 1.8 degrees Celsius above pre-industrial temperatures in the coming years, a level she calls “quite a bit higher than the current record.” If El Nino keeps scaling with that warming the way the coral record suggests it has for the last forty years, the version of the pattern now forming off the California coast may end up looking modest by comparison.
Stevenson’s group is already digging into why the models undersell it, comparing them piece by piece to find where the physics diverges from the coral chemistry. Cole, for now, is watching the ocean do what her data said it would.
Reference
Cole, J. E., Thompson, D. M., Dyez, K. A., Tripp, C. J., Tudhope, A. W., Lofverstrom, M., Stevenson, S., Okun, J. M., Lawman, A. E., Conroy, J. L., Overpeck, J. T., Jimenez, G., & Edwards, R. L. (2026). Recent strengthening of eastern Pacific ENSO in the last millennium paleorecord. Science. https://doi.org/10.1126/science.ady2660
- Study type: Peer-reviewed paleoclimate reconstruction, published in Science.
- Sample size: 28 coral time series across 5 Galapagos islands, plus a comparison set of Line Islands coral records.
- Material examined: Living coral colonies and centuries-old dead coral boulders, sampled at millimeter resolution for strontium-calcium ratios and oxygen isotopes.
- Comparison basis: 12 climate model simulations of natural (pre-industrial) variability, used to test whether volcanic and solar forcing alone could explain the trend.
- Period covered: Circa 1000-2015 CE, spanning preindustrial, 20th-century and modern intervals.
- Funding / conflicts of interest: US National Science Foundation and UK Natural Environment Research Council grants; authors declare no competing interests.
- Data availability: Archived at the NOAA-NCEI World Data Service for Paleoclimatology.
- Main limitation: The authors state that a formal study attributing the increase specifically to greenhouse warming, rather than simply ruling out natural causes, is beyond this paper’s scope; the climate models used for comparison also failed to reproduce the full size of the observed increase.
FAQ
How can coral reveal what the ocean was doing hundreds of years ago?
Coral can reveal centuries of ocean history because it grows in visible layers, much like tree rings, and each layer locks in a chemical record of the water it grew in. As a coral adds roughly a centimeter or two of skeleton each year, the ratio of strontium to calcium and the balance of oxygen isotopes in that new layer shift depending on the sea surface temperature at the time. Sampling down through a coral a millimeter at a time turns that chemistry into a year-by-year temperature timeline, which is exactly how the Galapagos team reconstructed a thousand years of El Nino behavior that no thermometer was around to measure.
Why would a warmer planet make El Nino stronger in the first place?
A warmer planet may make El Nino stronger because the pattern runs on temperature contrasts across the Pacific, and warming does not spread evenly: the eastern Pacific, where El Nino’s warm pool forms, appears to be more sensitive to rising background temperatures than the rest of the ocean. One proposed mechanism points to warming-driven changes in how sharply ocean layers separate near the equator, which lets the ocean and atmosphere reinforce each other’s swings more than they used to. That uneven warming can sharpen the swings between El Nino and La Nina rather than just raising the baseline. The new coral data show the intensification happening in step with global temperature, though the researchers stop short of saying the mechanism is fully worked out.
Could El Nino keep getting more intense from here?
El Nino could keep getting more intense if the warming trend that has tracked its strengthening over the last forty years continues, since the coral record shows no sign of the relationship leveling off. Samantha Stevenson and her colleagues are now digging into why the climate models used to project the future underestimate the increase already visible in the coral chemistry. Until that gap is closed, projections of how much stronger El Nino could get carry real uncertainty.
If climate models cannot reproduce this trend, why trust the coral data instead?
Trusting the coral data over the models on this point makes sense because the corals are a direct physical record of what actually happened, while the models are simulations of what should happen under a given set of assumptions. When the two disagree, the honest conclusion is not that the coral data are wrong but that the models are missing a mechanism, which is exactly the interpretation Stevenson and Cole draw. That gap is now driving new work to figure out which piece of El Nino physics the models have underweighted.
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