How the 4 strongest El Niño events reshaped global weather

El Niño is not one repeatable event. Each occurrence differs in strength, duration and timing. Those differences decide whether a given year brings a modest shift in rainfall or a disruption that reaches harvests, fisheries and shipping lanes across several continents at once.

Climatologists rank intensity using the Oceanic Niño Index, or ONI. It measures how far sea surface temperatures in the Niño 3.4 region of the equatorial Pacific depart from a baseline normal. NOAA's Climate Prediction Center calls an event strong when that three-month running average sits between 1.5 and 1.9 degrees Celsius above normal. At 2.0 degrees and above, an event enters a tier reached only four times since the modern instrumental record began in 1950.

Those four cases — 1982-83, 1997-98, 2015-16 and 2023-24 — form the core of any list of the strongest El Niño events on record, and each left a different mark. The 1982-83 event arrived before the monitoring networks that exist today and caught forecasters off guard, producing deadly flooding in Peru and drought across Australia and Indonesia. The 1997-98 event became the benchmark for extreme El Niño behavior for nearly two decades. Then 2015-16 edged past it with the highest ONI value yet measured. The 2023-24 event pushed into the same upper tier, this time against a warmer ocean baseline than any of its predecessors faced.

Two others sit just below the very strong line but belong in the conversation. The 1972-73 event helped collapse the Peruvian anchovy fishery and rippled through global feed and food prices. The 1991-92 event overlapped with the eruption of Mount Pinatubo, creating a tangle of warming and cooling signals that climate scientists spent years separating.

The history matters beyond the record books. Strong events serve as rough analogs for what future ones may do to agriculture, water supply, fisheries and insurance exposure. The same teleconnections that weakened India's monsoon or soaked California in past cycles tend to reappear with each new strong event, even when the timing and magnitude shift. Here is how strength is measured, and what each of the biggest events did.

Illustration: Quartz

The Oceanic Niño Index is the standard tool for ranking El Niño events. It measures sea surface temperature anomalies in the Niño 3.4 region of the central equatorial Pacific, roughly between 170 degrees west and 120 degrees west longitude, and that single figure is what allows events decades apart to be compared directly.

NOAA's Climate Prediction Center calculates the ONI as a three-month running mean of how far surface water in that box departs from a 30-year baseline. An El Niño is logged when the value reaches 0.5 degrees Celsius above normal and stays there for at least five consecutive overlapping three-month seasons. The readings are commonly grouped into bands: 0.5 to 0.9 is weak, 1.0 to 1.4 moderate, 1.5 to 1.9 strong and 2.0 or above very strong.

Only four events since 1950 have reached that top band at their peak: 1982-83, 1997-98, 2015-16 and 2023-24. Others sit just below the line, among them 1972-73 and 1991-92, and both carried consequences large enough to belong in any serious accounting of major El Niño years.

Ranking by peak ONI is useful but incomplete. The index describes the ocean, not the atmosphere's full response to it, and two events with nearly identical peaks can produce different weather depending on what else the climate system is doing. The Indian Ocean Dipole and the Madden-Julian Oscillation run on overlapping timescales and can either reinforce or mute the expected pattern in a given region.

Duration is the other variable the headline number hides. Some events spike and fade within months; others hold elevated temperatures across two Northern Hemisphere winters, which changes how long the effects on rainfall and crops persist. Timing matters as well, because El Niño's pull on North American winter weather depends on the event being mature while the jet stream is most responsive to it.

Classifications also vary by country. Agencies in Australia and Japan apply their own thresholds and monitoring regions, so the same ocean data can yield slightly different labels. The ONI still offers the most consistent yardstick available across more than seven decades of observation, which is why it anchors the events that follow.

Illustration: Quartz

The 1997-98 El Niño peaked at an ONI value near 2.4 degrees Celsius and stood as the strongest event in the instrumental record for close to 20 years. It also built at unusual speed, strengthening through the spring and summer of 1997 rather than accumulating across a full seasonal cycle. That compressed timeline left governments and relief agencies less warning than a slower onset would have given.

Indonesia and neighboring parts of Southeast Asia dried out sharply. Fires lit to clear land spread into peat and forest that would normally hold too much moisture to burn. The resulting smoke drifted across the region for months, closing schools, grounding flights and pushing air quality in Malaysia and Singapore to hazardous levels.

The reverse played out on the far side of the Pacific. Northern Peru and coastal Ecuador took torrential rain and flooding, the standard signature of a strong event. A strong El Niño pushes the heaviest tropical rainfall eastward, away from the warm pool of the western Pacific.

Across North America, the jet stream reorganized along familiar El Niño lines. California and the Gulf Coast ran wetter than normal through the 1997-98 winter, while much of the northern tier of the U.S. came through milder than usual. East Africa took heavy rain and flooding during the same months southern Africa turned dry, one continent divided by a single ocean anomaly.

Coral reefs registered the heat as well. Sustained ocean warmth during 1997-98 drove widespread bleaching, with heavy mortality documented in the Indian Ocean and across parts of the Pacific. The event also lifted global surface temperatures in the short term, helping make 1998 the warmest year measured to that point, on top of the longer warming trend already underway.

For nearly two decades afterward, meteorologists used 1997-98 as the reference case when explaining what a severe El Niño could do to rainfall, fisheries and food supply. It held that role until the 2015-16 event registered a higher peak.

Illustration: Quartz

The 2015-16 El Niño peaked at an ONI value of roughly 2.6 degrees Celsius above normal, the highest figure in NOAA's record, narrowly surpassing 1997-98. It built through 2015 and held its strength into the opening months of 2016.

Southern Africa took some of the heaviest damage. Drought cut maize harvests across South Africa, Zimbabwe and Zambia, forcing South Africa — normally a regional exporter of the crop — to import grain and leaving neighboring countries that depend on its surplus short of food. Ethiopia and parts of the wider Horn of Africa faced crop failure tied to the same displacement of tropical rainfall, and millions needed food assistance.

Ocean heat left a visible record on reefs. Widespread bleaching struck Australia's Great Barrier Reef, Hawaiian waters and reef systems across the Indo-Pacific. Those losses formed part of a global bleaching episode that ran from 2014 through 2017, the most geographically extensive documented up to that point. Indonesia turned dry again, raising fire risk across its peatlands, while heavy rainfall hit stretches of South America's Pacific coast.

California entered the 2015-16 winter after several years of severe drought, and the season delivered more precipitation than the preceding years had. The relief was uneven. Northern California fared better than the southern half of the state, and reservoir and groundwater deficits built up over the dry period were not erased in a single wet season. The Pacific Northwest and the northern tier of the U.S. trended milder, matching the jet stream configuration that strong El Niño winters typically impose on North America.

The event also coincided with a stretch of record global heat, and 2016 ranked as the warmest year measured at the time, reflecting both the long-term warming trend and the temporary boost a strong El Niño adds to global average temperature. 2015-16 now serves as the practical ceiling of observed El Niño intensity, the case against which newer events are measured.

Illustration: Quartz

A peak Oceanic Niño Index value of about 2.1 made the 1982-83 El Niño the first event of the modern era recognized as very strong. It developed almost entirely unannounced. Forecasters did not identify it until it was already underway, because the monitoring network and model guidance available today did not yet exist.

Detection was complicated further by the eruption of El Chichón in Mexico in 1982. Volcanic aerosols filled the stratosphere and skewed satellite readings of sea surface temperature, masking the warmth building across the tropical Pacific. By the time the scale of the anomaly was clear, the atmosphere had already reorganized.

Northern Peru absorbed some of the worst of it. Desert districts that normally see almost no rain were inundated for months, washing out roads, bridges and farmland. The cold, nutrient-rich upwelling that sustains the anchoveta fishery off Peru and Ecuador shut down as warm water pushed in. Catches collapsed, and so did the fishmeal trade built on them. Seabird colonies that feed on the same fish crashed alongside the stocks.

On the opposite side of the basin, Australia and Indonesia endured severe drought. Australian wheat output fell sharply, and dry pastures forced heavy livestock losses. The hot, parched conditions of that summer preceded the Ash Wednesday bushfires of February 1983 in Victoria and South Australia.

California faced the reverse problem. A storm track pushed far south by the warm Pacific delivered repeated winter systems, bringing coastal erosion, high surf that damaged piers and homes, and inland flooding. Bolivia recorded flooding in some departments and drought in others over the same months, which shows that one event does not deliver one kind of weather.

Reefs in the eastern Pacific, including those around the Galápagos Islands, suffered extensive bleaching and mortality. They became among the earliest well-documented cases linking coral die-off to El Niño warmth.

The surprise carried a lasting consequence. Failure to anticipate 1982-83 pushed scientists to build a permanent ocean observing system. That effort produced the array of moored buoys set across the tropical Pacific under the TOGA program, still the backbone of El Niño monitoring.

Illustration: Quartz

The 2023-24 El Niño peaked at an ONI value of about 2.0, placing it alongside 1982-83, 1997-98 and 2015-16 in the small group of events that reached the very strong tier. It built through 2023 and persisted into the first half of 2024 before conditions returned to neutral.

The event overlapped with 2023 becoming the warmest year measured globally up to that point. A strong El Niño releases heat from the ocean into the atmosphere, adding a short-term lift on top of the longer warming trend, and 2023 carried both signals at once.

The most visible economic disruption appeared at the Panama Canal. Drought across the canal watershed drew down Gatun Lake, the reservoir that supplies the water used for every lock transit, and the Panama Canal Authority reduced daily crossings well below normal capacity. Shipping lines rerouted around the bottleneck or bid heavily in slot auctions. The restrictions lasted months before rainfall restored lake levels.

Southern Africa recorded severe drought through the 2023-24 growing season. Maize harvests fell across Zambia, Zimbabwe and Malawi, and each government declared a national disaster as food shortages widened. The same maize belt had absorbed comparable losses during the 2015-16 event.

Indonesia and parts of Southeast Asia ran drier than normal, matching the way El Niño pulls convection and rainfall eastward from the western Pacific warm pool. In the U.S., an active storm track brought repeated rain to California over the winter of 2023-24 and built a Sierra Nevada snowpack near average.

Coral reefs faced renewed heat stress during the same window. In April 2024, NOAA and the International Coral Reef Initiative confirmed a fourth global bleaching event, driven by El Niño warmth stacked on an already elevated ocean baseline.

Rankings place 2023-24 third or fourth among the strongest events depending on which version of the ONI dataset is used, because periodic revisions to the 30-year baseline shift peak values by roughly a tenth of a degree. Across those versions, the event stays inside the top four.

Illustration: Quartz

The 1972-73 El Niño reached the upper end of the strong range on the Oceanic Niño Index, and it hit global food and feed markets more directly than several events that ran hotter in the Pacific. Its defining consequence was the collapse of the Peruvian anchoveta fishery, at the time the largest single-species fishery in the world.

Anchoveta thrive on the cold, nutrient-dense water that wells up along the Peruvian coast and feeds the plankton at the base of the food chain. The warm surface layer that arrives with El Niño shuts that upwelling down. A harvest that had reached roughly 12 million metric tons in 1970 dropped to about two million tons by 1973. Heavy fishing in the preceding seasons had already thinned the stock, so warm water was not the sole cause. It pushed an overexploited population past the point of recovery, and the fishery never regained its former scale.

The collapse registered far beyond Peru because anchoveta was ground into fishmeal, a protein input for poultry and livestock feed on several continents. Buyers shifted toward soybean meal and other substitutes, tightening a market already under pressure. Grain and oilseed prices climbed through 1973, part of a wider food price shock with several converging causes rather than a single one.

The atmospheric side followed the pattern El Niño usually imposes. Australia and Indonesia turned dry as the main belt of tropical rainfall shifted east, away from the western Pacific. India's 1972 monsoon underdelivered, cutting harvests in a country where seasonal rain governs staple crop output for hundreds of millions of people.

What sets 1972-73 apart in the record is the chain it made visible: a shift in tropical Pacific sea surface temperatures turning up months later in the cost of chicken feed on another continent. The event arrived before El Niño had any broad public profile, and before any system existed to watch the equatorial Pacific in real time. It strengthened the case for sustained ocean monitoring — a case that drew serious funding only after the 1982-83 event developed a decade later with almost no warning.

Illustration: Quartz

The 1991-92 El Niño peaked at an ONI value of about 1.6, placing it in the strong category rather than the very strong tier. Its lasting significance comes from timing. It developed in the same window as the June 1991 eruption of Mount Pinatubo in the Philippines, one of the largest volcanic eruptions of the 20th century.

Pinatubo pushed a large volume of sulfur dioxide into the stratosphere. There it converted into sulfate aerosols that scattered incoming sunlight and pulled global average surface temperature down for roughly two years. That cooling worked against the warming an El Niño normally delivers to global temperatures. The two signals overlapped almost exactly, and separating them became a central problem for anyone reading the 1991 and 1992 temperature record at face value.

The regional weather signatures still appeared despite the volcanic interference. Drought struck southern Africa through the 1991-92 growing season, one of the region's most severe of the century, cutting grain harvests across several countries. Peru and Ecuador recorded heavier rainfall along their coasts as warm water displaced the cold Humboldt Current. Eastern Australia trended drier across its farming districts, matching the suppressed rainfall that Pacific warming tends to produce on the western side of the basin.

The event also ran long. Elevated sea surface temperatures in the tropical Pacific persisted in a sequence stretching into 1994-95. Climatologists have debated whether that period amounted to one unusually protracted El Niño or several closely spaced events. The ambiguity is part of why peak ONI values alone are an incomplete ranking tool.

Climate research still treats 1991-92 as an attribution case study. Isolating a volcanic cooling signal from an El Niño warming signal occurring in the same months forced refinements in the statistical methods used to pull individual drivers out of a single temperature series. Those methods now shape how researchers account for volcanic and oceanic influences when assessing long-term warming. The event's scientific legacy outweighs its ONI peak, which sits well below the figures recorded in 1982-83, 1997-98, 2015-16 and 2023-24.