Modern El Niño Events Are the Strongest in a Millennium, Coral Records Reveal

An El Niño of historic proportions is currently taking shape in the tropical Pacific, and new research from the University of Michigan suggests that such powerful events are not merely unusual—they are unprecedented in the context of the past thousand years. The study, published in the journal Science, found that El Niño events over the last four decades have become nearly 40 percent stronger than they were during the pre-industrial era, before humans began altering the climate system with greenhouse gas emissions. By reading the chemical archives preserved in modern and ancient corals from the Galápagos Islands, the researchers assembled a temperature history stretching back a millennium, and what they found was a clear and troubling signal: the El Niños of the recent past exceed anything recorded in the natural variability of the last 1,000 years prior to roughly 1850.

Lead author Julia Cole, professor and chair of the University of Michigan Department of Earth and Environmental Sciences, emphasized that the comparison between past and present is strikingly unambiguous. According to Cole, there is no period in the reconstructed record where El Niños were as strong as they are today, and the strength of El Niño appears to change in parallel with the warming of global temperatures. The findings, she noted, demonstrate that the large El Niño events of the last 40 years are not normal within the context of the last thousand years. This conclusion carries significant weight because El Niño is one of the most influential sources of year-to-year climate variability on the planet, capable of reshaping weather patterns across entire continents and driving droughts, floods, wildfires, and disease outbreaks far from its tropical Pacific origins.

Understanding why the researchers turned to corals requires an appreciation of both the phenomenon itself and the remarkable natural recorders that grow in the waters surrounding the Galápagos. El Niño is a natural climate oscillation that, every few years, causes the tropical Pacific to become warmer than usual. Under normal conditions, trade winds blow steadily along the equator from east to west, pushing sun-warmed surface water from the coast of South America toward Australia and Indonesia. When these trade winds weaken, the warm water sloshes back eastward toward South America, setting an El Niño event in motion. The atmosphere responds in turn: strong rainfall shifts from the Indonesian region into the central Pacific, leaving the western Pacific in drought, which further weakens the trade winds and locks in El Niño conditions that can persist for one to two years.

Although these temperature and precipitation fluctuations originate in the tropical Pacific, their consequences ripple across the entire globe. Storm tracks over the United States shift southward, bringing more rain to the desert Southwest and less to the Pacific Northwest. Similar circulation changes around the world produce droughts and flooding that contribute to crop failure, wildfires, waterborne disease, and other crises affecting human health and well-being. The Galápagos Islands sit at a geographic sweet spot for recording these shifts, a location where El Niño exerts its largest influence. The archipelago is famous for its astounding biodiversity, a product of high nutrient availability and the mixing of cool and warm waters, and its corals grow in an environment that faithfully registers every swing of the eastern Pacific climate system.

To reconstruct the history of El Niño intensity, Cole and her colleagues sampled cores from 13 corals, drawing on both living colonies and boulders of ancient coral collected from the Galápagos. Corals grow by secreting layers of calcium carbonate at a rate of roughly one to two centimeters per year, and the chemistry of each layer preserves a record of the seawater temperature in which the coral grew. Because El Niño extremes occur every few years, the team focused on core samples spanning at least 20 years, ensuring that each record captured multiple events. Sampling the cores a millimeter at a time, the researchers measured two independent aspects of the skeleton’s chemistry, building a robust proxy archive of past ocean conditions.

The first measurement targeted the ratio of strontium to calcium in the coral skeleton, a geochemical parameter that depends directly on the temperature at which the coral formed its skeleton. The team supplemented these results with an analysis of oxygen isotope ratios, which at this particular site also serve as a reliable measure of temperature. Together, these two proxies yielded a detailed history of temperature variability in the Galápagos region. The pattern that emerged was remarkably consistent: strong El Niños appeared throughout the last 40 to 50 years, whereas the El Niños recorded prior to that period displayed a steady pattern of lower intensity. Cole described the experience of adding record after record and expecting the story to grow more complicated, only to find that it did not—the signal was that clear.

A critical next step was to rule out the possibility that natural processes alone could have produced a strengthening of this magnitude. The researchers turned to climate models that simulate the last thousand years using reconstructions of volcanic eruptions and solar variability, the two dominant natural forcings of pre-industrial climate. When the models were run with these natural drivers, they produced no large shifts in El Niño behavior that could account for the magnitude of change documented in the coral records. This absence of a natural explanation, combined with the timing of the intensification after about 1850, points toward human-driven global warming as the most plausible cause of the observed strengthening, a conclusion consistent with the finding that El Niño intensity tracks rising global temperatures.

The timing of the study’s release gives its conclusions particular urgency. As a powerful El Niño develops atop an already warmed climate system, Cole noted that the relevant question is not whether the event will happen but how severe it will become and how damaging its impacts will be. Because the event is superimposed on global warming, it is likely to supercharge the temperature increase that would normally be expected from greenhouse gases alone. Forecasts cited in connection with the study suggest global temperatures could reach as much as 1.7 or 1.8 degrees Celsius above pre-industrial levels during this period, which would be considerably higher than the current record. The research was supported by the U.S. National Science Foundation and the United Kingdom Natural Environmental Research Council, with additional support from the Galápagos National Park and the Charles Darwin Research Station.

The implications extend well beyond the immediate forecast. El Niño is a major source of climate extremes, and if the phenomenon is intensifying, then its impacts intensify with it: droughts, floods, wildfire, and food insecurity. Changes in the hydrologic cycle also translate into damage to infrastructure, including floods that destroy homes, highways, and railroads, as well as public health consequences such as outbreaks of diseases like cholera. Cole and her colleagues argue that global warming is supercharging El Niño, and if that is correct, stronger climate extremes should be expected to amplify ecological, infrastructural, and human losses. No country, she cautioned, has the resources to be fully protected from these impacts, a reality that makes the strengthening of El Niño a global concern rather than a regional one.

For the research team, the ultimate takeaway is a call for mitigation. The coral archives of the Galápagos have delivered one of the clearest long-term pictures yet of how a major climate oscillation is responding to human influence, and the message is that the recent strengthening of El Niño represents one more reason to move away from fossil fuels, which the researchers identify as the root cause of the problem. The study’s co-authors include University of Michigan researchers Kelsey Dyez, Cameron Tripp, Jonathan Overpeck, and alumnus Jake Okun; University of Arizona researchers Diane Thompson and Marcus Lofverstrom; Samantha Stevenson-Karl of the University of California, Santa Barbara; Sandy Tudhope of the University of Edinburgh; Allison Lawman of Colorado College; Jessica Conroy of the University of Illinois; Gloria Jimenez of Moody’s Risk Management Services; and R. Lawrence Edwards of the University of Minnesota. Together, their work transforms a string of tropical islands into a millennium-scale warning system, one that indicates the powerful El Niños of recent decades stand alone in a thousand years of climate history.

Subject of Research: Unprecedented strengthening of El Niño events over the last four decades reconstructed from Galápagos coral paleoclimate records

Article Title: El Niños more intense over last 40 years than previous 1,000, according to U-M study

Article References: El Niños more intense over last 40 years than previous 1,000, according to U-M study. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: El Niño, ENSO, coral proxies, paleoclimatology, Galápagos Islands, climate change, global warming, tropical Pacific, strontium-to-calcium ratio, oxygen isotopes, climate models, University of Michigan