ENSO is generated by a constantly shifting relationship between the tropical Pacific Ocean and the atmosphere above it. During El Niño, unusually warm surface water spreads across the central and eastern equatorial Pacific, changing atmospheric pressure, weakening or redirecting trade winds, and reorganizing rainfall on a planetary scale. La Niña generally produces the opposite pattern, with stronger trade winds and cooler eastern Pacific waters. These alternating states influence storm tracks, monsoons, wildfire conditions, agricultural yields, disease risks, and ocean ecosystems. Because ENSO naturally varies from year to year and from decade to decade, separating a human-driven signal from the climate system’s own irregular rhythms has been one of climate science’s most difficult challenges.

Recent decades have supplied plenty of reasons for concern. Several exceptionally strong El Niño events have occurred in the modern instrumental record, including episodes associated with extraordinary global heat, destructive flooding, severe drought, and widespread coral bleaching. Yet a short observational record cannot reveal whether such events represent a temporary cluster produced by natural variability or the beginning of a persistent response to rising greenhouse-gas concentrations. Climate models have not provided a simple answer. Different simulations have projected different changes in ENSO amplitude, timing, and location, partly because the tropical Pacific involves tightly coupled processes that remain difficult to reproduce, including ocean heat storage, upwelling, cloud feedbacks, and the response of trade winds to warming.

To extend the record beyond thermometers and satellites, Julia Cole and colleagues turned to corals growing around the Galápagos Islands, an archipelago positioned near the heart of the eastern Pacific ENSO region. The researchers analyzed high-resolution geochemical signals preserved in both modern and fossilized coral skeletons, reconstructing sea-surface temperatures across roughly the past 1,000 years. Coral colonies grow in seasonal layers, and the chemical composition of those layers changes in response to the surrounding seawater. In particular, temperature-sensitive geochemical indicators can preserve a detailed history of past ocean conditions, allowing scientists to track El Niño-related warmth long before systematic instrumental measurements began.

The Galápagos record is especially valuable because the eastern equatorial Pacific is where the thermal signature of many El Niño events becomes most pronounced. As warm water accumulates and shifts eastward, the region experiences changes that can be captured in coral chemistry at seasonal resolution. The new reconstruction was compared with coral records from the central Pacific and with other paleoclimate estimates of ENSO behavior. This cross-checking allowed the researchers to test whether the Galápagos signal reflected a local anomaly or a broader change in the tropical Pacific climate system. The agreement among independent records strengthened the case that the recent increase is not simply an artifact of one site, one coral colony, or one unusual sequence of events.

The team then compared the reconstructed history with preindustrial climate simulations from 12 models. These experiments were designed to estimate how much ENSO variability could arise from natural internal fluctuations and natural external forcing in a world without modern levels of human influence. The modern increase exceeded the range produced by those simulations. According to the reconstruction, eastern Pacific ENSO variability is now about 37 percent higher than its preindustrial average, largely because El Niño events have become both more frequent and more intense. The most pronounced shift appears in the recent 40-year period, when the climate system has also experienced rapid global warming and exceptional increases in ocean heat content.

The physical explanation is not that warming mechanically creates an El Niño every year, but that it can modify the conditions governing how tropical Pacific disturbances grow. ENSO depends on feedbacks between winds, sea-surface temperatures, thermocline depth, and ocean currents. A small change in winds can alter the upwelling of cold water in the eastern Pacific; that temperature change can then influence atmospheric pressure and winds, reinforcing or suppressing the original disturbance. Warming may change the background state on which these feedbacks operate, affecting the east-west temperature gradient, the distribution of ocean heat, and the efficiency with which atmospheric disturbances trigger large oceanic responses. The precise balance of these mechanisms remains an active area of research, but the coral evidence indicates that the net effect in the eastern Pacific has recently favored stronger variability.

An intensifying ENSO would have consequences far beyond the tropical Pacific. Strong El Niño conditions can shift rainfall away from regions that depend on predictable seasonal moisture while delivering extreme precipitation elsewhere. Drought can increase the risk of wildfires, reduce water supplies, and damage crops; intense rainfall can trigger floods, landslides, infrastructure failures, and outbreaks of waterborne disease. In the ocean, warmer surface waters and altered circulation can deprive marine ecosystems of nutrients and push corals beyond their thermal limits, worsening bleaching and mortality. Fisheries may be disrupted as species track changing temperatures and food availability. The economic effects can spread through global commodity markets, insurance systems, energy demand, public health services, and supply chains, making ENSO amplification a worldwide risk rather than a regional climate story.

The findings do not mean that every future El Niño will be stronger than the last, nor do they eliminate the uncertainty surrounding long-term ENSO projections. Natural variability will continue to produce quiet periods and unusually powerful events, and the response may differ between the eastern and central Pacific. However, the new evidence establishes a longer baseline against which modern changes can be judged and gives climate models a demanding test: they must reproduce not only average tropical Pacific temperatures, but also the historical evolution of ENSO variability. By showing that recent eastern Pacific behavior is unprecedented in the last millennium of the coral record, the study suggests that climate change is no longer merely a future threat to the world’s most influential natural climate pattern. It may already be turning El Niño into a more powerful and unpredictable engine of extreme weather.

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.