El Niño Intensified More in 40 Years Than Any Previous Millennium

An El Niño event of historic proportions is taking shape in the tropical Pacific, bringing unusually warm ocean conditions and renewed attention to a climate pattern capable of reshaping weather across the planet. In late August, seawater temperatures off Santa Barbara rose into the low 70s Fahrenheit, while anglers reported catching dorado and yellowtail near the Channel Islands—species more commonly associated with warmer waters. The immediate event is striking, but a new reconstruction published in Science suggests that its significance extends far beyond one season. By analyzing modern and ancient corals from the Galápagos Islands, researchers found that El Niño events have been nearly 40 percent stronger during the past 40 years than they were during the pre-industrial era. They also found that recent events were more intense than any El Niños recorded in the preceding millennium.

El Niño is part of the El Niño–Southern Oscillation, or ENSO, a natural climate cycle centered in the tropical Pacific. Under typical conditions, easterly trade winds push warm surface water westward along the equator, allowing cooler, nutrient-rich water to rise near the coasts of Ecuador and Peru. During El Niño, those trade winds weaken. Warm water that has accumulated in the western Pacific spreads eastward, increasing sea-surface temperatures across the central and eastern equatorial Pacific. The warmer ocean then changes atmospheric pressure, convection and rainfall, creating feedbacks that can further weaken the winds and reinforce the event. These interactions can maintain abnormal conditions for one or two years, while their atmospheric effects travel far beyond the Pacific basin.

The consequences are global because the tropical Pacific acts as a powerful engine for atmospheric circulation. During a strong El Niño, rainfall commonly shifts away from Indonesia and the western Pacific toward the central and eastern Pacific, increasing the risk of drought in some regions and flooding in others. In the western United States, altered circulation can push the jet stream southward and redirect atmospheric-river storms toward California rather than the Pacific Northwest. Southern California may therefore experience an exceptionally wet winter, while other locations face heat, dryness or disrupted seasonal rainfall. Across the world, ENSO-related changes have been associated with crop failures, wildfire conditions, disease outbreaks, ecological stress and damage to infrastructure. When a strong El Niño occurs on top of human-caused global warming, the combined effect can produce temperatures and climate extremes that exceed what either influence would generate alone.

To determine whether recent El Niños are unusual, the research team turned to corals in the Galápagos, a strategically important location because it lies near the eastern Pacific region where ENSO-driven temperature changes are especially pronounced. The investigators collected cores from 13 corals, including living colonies and massive fragments of ancient coral preserved as boulders. Corals grow incrementally, generally adding one to two centimeters of calcium-carbonate skeleton each year. As they grow, they incorporate chemical signatures from the seawater around them. Those signatures form a natural archive of past ocean conditions, allowing scientists to reconstruct temperature variations long before thermometers, ships and satellites began monitoring the Pacific.

The researchers measured the ratio of strontium to calcium in successive layers of the coral skeleton. Because strontium is incorporated differently from calcium as a function of temperature, changes in the strontium-to-calcium ratio can be calibrated as a proxy for the temperature of the surrounding seawater. The team also examined oxygen isotopes, different forms of oxygen atoms whose proportions are influenced by temperature and by the balance between evaporation and precipitation. Combining the two chemical indicators helped the researchers distinguish temperature signals from other environmental influences. Each core was sampled at millimeter-scale intervals and had to span at least 20 years, ensuring that the record was long enough to capture multiple El Niño events rather than isolated warm episodes.

Together, the coral records revealed a consistent pattern. El Niños occurring during the most recent four to five decades reached substantially greater intensities than those recorded in the earlier portions of the reconstruction. In contrast, events before roughly the modern period showed a relatively stable pattern of lower intensity across much of the previous 1,000 years. The result was notable because the researchers expected that adding more coral records might produce a more complicated history, with different sites revealing conflicting trends. Instead, the records from the Galápagos produced what the scientists described as a clear signal: the eastern Pacific ENSO system has intensified in parallel with the rise in global temperature.

The study also examined whether natural factors could explain the change. Volcanic eruptions can temporarily cool the climate and alter atmospheric circulation, while fluctuations in solar activity can affect the amount of energy reaching Earth. To test these possibilities, the researchers used climate models that incorporated historical changes in volcanic activity and solar variability. Those simulations did not provide a convincing explanation for the large increase in El Niño strength seen in the coral record. The findings therefore point toward a connection with long-term warming, although the precise physical mechanisms remain unresolved. The authors emphasize that their results do not mean every future El Niño will be stronger than every event in the past, but they do indicate that the background climate is becoming more favorable for unusually powerful episodes.

An important warning emerged when the coral evidence was compared with climate-model simulations. The models used by scientists to study past and future climate change did not reproduce the increase in El Niño intensity observed in the coral data. That mismatch suggests that some aspect of the tropical Pacific system may be missing or insufficiently represented in current models. Possible explanations could involve the representation of ocean mixing, atmospheric convection, cloud processes, thermocline behavior or feedbacks between the ocean and atmosphere. Resolving the discrepancy is urgent because models are central to projections of rainfall, drought, storm risks and heat extremes. If they underestimate how ENSO responds to warming, societies may also be underestimating the hazards associated with future climate variability.

The developing El Niño illustrates why the distinction between natural variability and climate change is increasingly difficult to separate in practical terms. ENSO itself is not caused by greenhouse-gas emissions; it has operated for centuries as a natural oscillation. However, the new reconstruction indicates that global warming may be amplifying the intensity of the cycle, effectively adding extra energy to an already powerful climate mechanism. Some forecasts for the current event suggested that global temperatures could temporarily reach 1.7 or 1.8 degrees Celsius above pre-industrial levels, potentially exceeding the existing record by a substantial margin. Such warmth would not be produced by El Niño alone, but by the combination of elevated greenhouse-gas concentrations and the ocean-atmosphere redistribution associated with the event.

If the observed trend continues, so-called super El Niños could become more frequent or more damaging, increasing risks to food systems, water supplies, ecosystems, public health and built infrastructure. Floods can destroy homes, roads and railways, while drought can reduce harvests and intensify wildfire danger. Shifts in rainfall can also influence the spread of waterborne diseases such as cholera. The researchers stress that no nation can fully isolate itself from these cascading effects. The coral record provides a long-term perspective showing that the strongest El Niños of recent decades are not typical of the last thousand years. It also delivers a direct challenge to climate science: explain why the models miss this intensification, improve predictions, and account for the possibility that continued warming will supercharge one of Earth’s most consequential natural climate cycles.