Julie Cole said a study of fossilized Galápagos corals offers “one more warning sign here of what we’re facing in a warmer world.” The research reconstructed a thousand-year ocean surface temperature record and found that the exceptional El Niño weather pattern has become stronger than at any point in that span.
“We’ve been seeing some very strong El Niño events in the late 20th and early 21st century, and what we didn’t know was how unusual those are,” Cole said. The team found that temperature variability since 1984 runs 36.5 percent higher than it did during 1000 to 1850 CE, and 16.2 percent higher than during 1851 to 1982.
Galápagos coral cores
Cole, an environmental scientist at the University of Michigan, led the work by analyzing fossilized Galápagos corals. The islands sit in the bullseye of the eastern Pacific ENSO pattern, and the corals grow one to two centimeters a year, which let the team sample coral cores millimeter by millimeter and pull more than a dozen measurements per year.
The researchers examined the strontium-to-calcium ratio and oxygen isotopes in coral skeletons because both track temperature. Living coral colonies cover recent decades and can be checked against instrument data, while dead coral heads can be dated using uranium-thorium methods to within a few years, even as far back as 500 years. Cole said, “We were also able to find corals that are dead and washed up on the beach.”
What the coral record showed
The team found 28 time-separated coral series from five islands covering scattered years back to around 1100 CE. Cole said, “The events don’t look anything like what we see in the pre-industrial era.” In the reconstructed record, events that once ran a degree or two above normal in the Galápagos now run three or four, and the corals also show a shift in skewness toward the positive direction.
Cole described that shift this way: “The skewness turned positive.”
ENSO, Peru, and Australia
El Niño and La Niña are the warm and cold swings of the El Niño–Southern Oscillation, the largest source of year-to-year climate variation on Earth. In practical terms, that means the pattern can shift rainfall across the tropics, dry out Australia, flood parts of Peru, and rearrange weather on most of the planet.
The study addresses a basic comparison with the past: whether the very strong El Niño events seen in recent decades are normal variation or something outside the preindustrial range. Cole said the coral record points toward the latter, but the reconstruction does not settle how much of the increase comes from natural variability versus warming.
For readers in places shaped by El Niño swings, the useful takeaway is not just that the modern pattern looks stronger. It is that the long coral record now gives climate scientists a benchmark that reaches far beyond the short instrument era, and that benchmark puts the last four decades in a different category from the centuries before them.
