El Niño–Southern Oscillation: The Planet's Most Powerful Climate Engine Is Waking Up Again

Introduction: The Oceans Are Sending a Signal

Something is stirring beneath the surface of the Pacific Ocean. Vast reservoirs of warm water that had retreated during the recent La Niña period are advancing eastward again, guided by shifting winds and oceanic currents that have been in motion for thousands of years. The signal is clear enough that the world's leading climate agencies — NOAA, the World Meteorological Organization, and the European Centre for Medium-Range Weather Forecasts — are in rare and striking agreement: El Niño is coming back.

The timing matters enormously. It is arriving against the backdrop of a planet already stressed by human-driven warming, still recovering from the disruptions of the last major El Niño event in 2023–2024, and now bracing for what several models suggest could be a strong, potentially intense episode by the end of 2026. For billions of people across Africa, Asia, the Americas, and beyond, this is not an abstract scientific development. It is a forecast that will shape rainfall, harvests, droughts, floods, hurricanes, and temperatures — sometimes simultaneously on opposite sides of the globe.

To understand why it matters so much, you have to start at the beginning.

What Is ENSO? The Science Behind the Cycle

El Niño–Southern Oscillation — universally abbreviated as ENSO — is a recurring climate phenomenon rooted in the relationship between the ocean surface and the atmosphere over the tropical Pacific. It is not one thing but a cycle with three distinct phases: El Niño (the warm phase), La Niña (the cool phase), and a neutral period that separates the two.

Under normal atmospheric conditions, powerful trade winds blow steadily from east to west along the equator, pushing warm surface water from the coast of South America toward Asia and Australia. That warm water piles up in the western Pacific, and as it does, cooler water rises from the ocean's depths along the South American coast — a process called upwelling that is rich in nutrients and forms the biological foundation of some of the world's most productive fisheries.

During El Niño, this system breaks down. The trade winds weaken or even reverse direction. The warm water that had pooled in the west sloshes back eastward across the Pacific, raising sea surface temperatures dramatically in the central and eastern equatorial Pacific. That shift in ocean heat reorganises atmospheric circulation patterns across the entire planet — altering where it rains and where it does not, strengthening some storm systems while suppressing others, and influencing temperature patterns from the Arctic to the tropics.

The counterpart, La Niña, is in many ways the mirror image. Trade winds intensify, warm water retreats further west, and the eastern Pacific becomes anomalously cool. The atmospheric consequences are again global, and in many regions, La Niña's signature is just as dramatic as El Niño's — though the two phases do not produce perfectly symmetrical impacts in every location.

The Southern Oscillation part of the name refers to the atmospheric pressure seesaw that drives and responds to these oceanic shifts. When sea surface temperatures rise in the eastern Pacific during El Niño, atmospheric pressure over Indonesia and Australia climbs while pressure over the eastern Pacific falls. During La Niña, the pattern reverses. Scientists measure this pressure difference through an index called the Southern Oscillation Index, and its fluctuations track the rhythm of the entire cycle.

The name "El Niño" has Peruvian origins. Centuries ago, fishermen along the coasts of Peru and Ecuador noticed a warm ocean current arriving around Christmas time each year, bringing poor fishing conditions. They called it El Niño de Navidad — the Christ Child — a name that eventually came to describe the broader climate phenomenon as science caught up with what local communities had long observed.

How Strong Can It Get? Measuring ENSO

Not all El Niño events are equal. Scientists measure their intensity primarily through anomalies in sea surface temperature in a region of the equatorial Pacific called the Niño 3.4 zone, which stretches from approximately 170°W to 120°W longitude, straddling the equator. An anomaly of at least +0.5°C above the long-term average, sustained over several months, is the conventional threshold for declaring El Niño conditions.

In February 2026, NOAA made a significant methodological update by adopting a new measurement tool called the Relative Oceanic Niño Index, or RONI. Unlike its predecessor, the traditional Oceanic Niño Index, RONI accounts for the long-term warming of the global oceans driven by climate change — providing a more accurate representation of true ENSO-driven variability rather than conflating it with background warming trends. The practical effect is that RONI tends to slightly dampen measured El Niño strength while amplifying measured La Niña strength relative to the older index.

Events are broadly categorised as weak, moderate, strong, or super/very strong. The benchmarks of recorded history are the 1997–1998 and 2015–2016 events — both of which met the threshold for "super" El Niños, producing sea surface temperature anomalies of more than 2°C above normal and triggering cascading disruptions around the world. The 2023–2024 event was significant but somewhat less extreme, though it still coincided with record-breaking global temperatures.

Where Things Stand Right Now: May 2026

The ENSO system spent the first months of 2026 in a state of transition. Following the end of the 2025–2026 La Niña, the equatorial Pacific moved into a neutral phase, with sea surface temperatures hovering near their long-term average. But beneath the surface, the situation was already changing fast.

As of mid-April 2026, above-average subsurface temperatures had strengthened and spread across the Pacific basin, reaching the far eastern regions. The warming at depth is particularly telling because it feeds upward into the surface layer over subsequent weeks and months. The Niño 1+2 index — which tracks the easternmost and most sensitive zone of the equatorial Pacific — had already climbed to +1.8°C, a notably warm reading even while official ENSO declarations were still anchored in neutral territory.

NOAA's Climate Prediction Center issued its final La Niña advisory in April 2026, simultaneously declaring an El Niño Watch. The official assessment placed the probability of ENSO-neutral conditions persisting through April–June 2026 at 80%, with El Niño likely to emerge in the May–July window at a 61% probability and expected to persist through at least the end of the year.

The World Meteorological Organization's language was more direct. After a period of neutral conditions at the start of the year, the WMO stated that climate models were now strongly aligned, with high confidence in the onset of El Niño and further intensification in the months that follow. Their seasonal forecast for the May–July 2026 period indicated nearly global dominance of above-normal land surface temperatures, with the signal particularly strong over southern North America, Central America, the Caribbean, Europe, and Northern Africa.

Some forecasting centres went further still. The European Centre for Medium-Range Weather Forecasts noted that the 2026 signal was stronger at this stage of the year than the analogous signal seen in early 2023, which ultimately produced a substantial El Niño with anomalies reaching 2°C by year's end. At least one meteorological analysis warned of a potential "Super El Niño" developing by the August–October period, with ECMWF model output showing anomalies exceeding +2°C across the entire ENSO region.

The caveat to all of this is what climate scientists call the "spring predictability barrier" — a well-documented tendency for the equatorial Pacific to be especially difficult to forecast during the boreal spring. The ocean-atmosphere system is in a transitional state at this time of year, and small perturbations can tip outcomes in unpredictable directions. The events of spring 2017, when many forecast models confidently expected warming that never materialised and instead La Niña developed, remain a cautionary tale. Confidence in the El Niño forecast generally increases significantly after April.

The Global Fingerprints of El Niño

When a strong El Niño takes hold, its influence is felt on every continent. The patterns are not perfectly repeatable from one event to the next — no two El Niños are identical — but decades of observation have revealed consistent regional tendencies that guide preparedness planning around the world.

In Africa, the consequences are deeply uneven and often simultaneous. Across the Horn of Africa — Ethiopia, Somalia, Kenya, and surrounding areas — El Niño historically brings above-average rainfall during the October-to-December short rains season. While that can benefit agriculture in some areas, it also increases the risk of flooding, landslides, and the waterborne diseases that follow. At the same time, western parts of East Africa tend to experience below-average rainfall between July and September. The picture shifts dramatically in southern Africa, where El Niño is associated with significantly reduced rainfall across the main cropping season between November and March. The 2015–2016 El Niño produced drought conditions across southern Africa severe enough to affect maize yields by up to 50% compared to the five-year average, leaving more than 40 million people in crisis conditions and requiring emergency aid for over 23 million.

For West Africa and the Sahel, the relationship is more complex and subject to regional variability, but reduced monsoon precipitation and heat stress are consistent risks when El Niño strengthens.

In Asia, the disruption to the monsoon system is often the most consequential effect. Under normal or La Niña conditions, warm western Pacific waters feed intense thunderstorm activity near Indonesia, driving the chain of atmospheric dynamics that ultimately delivers life-sustaining rainfall to India, Southeast Asia, and East Asia. During El Niño, the warm water retreats eastward, thunderstorm activity near Indonesia weakens, and the monsoon can falter. Indonesia faces drought conditions and a dramatically elevated risk of forest and peat fires. The Philippines experiences reduced rainfall and elevated drought stress between December and May. India's monsoon — which irrigates the agricultural foundation of more than a billion people — is frequently weakened, creating pressure on water supplies, power generation, and food production.

In Australia, El Niño is synonymous with drought. The 1997–1998 event and the 2015–2016 event both produced severe water deficits and fire-season amplification across large parts of the continent.

The Americas present a more varied picture. In South America, the coast of Peru and Ecuador typically receives dramatically above-average rainfall, flooding infrastructure and disrupting fisheries — the original observation that gave El Niño its name. In the southern cone, parts of Argentina, Paraguay, and Uruguay tend to see increased precipitation, which benefits agriculture but raises flooding risk. Brazil's Amazon region and its agricultural heartland generally experience reduced wet-season rainfall. Further north, the Caribbean and Central America typically see drier conditions, while the southern United States and northern Mexico often experience wetter winters with elevated storm activity. The Pacific hurricane season tends to become more active during El Niño years, while Atlantic hurricane activity is typically suppressed.

In Europe, the effects are less dramatic but still meaningful, particularly in terms of winter temperature anomalies and storm track shifts across the North Atlantic. The WMO's forecast for May–July 2026 already flags an especially strong above-normal temperature signal for Europe and Northern Africa.

El Niño and Climate Change: A Dangerous Combination

The 2026 El Niño is emerging into a world that is fundamentally different from the one that experienced the 1997–1998 super event. Global average temperatures have risen by approximately 1.3°C above the pre-industrial baseline. Ocean heat content — the energy stored in the top 2,000 metres of the world's oceans — is at record levels. The background climate against which every El Niño plays out is warmer, and that background warming amplifies the impacts.

The 2023–2024 El Niño illustrated this interaction with uncomfortable clarity. The World Meteorological Organization has documented that during that event, the combination of El Niño and underlying climate change hit Latin America and the Caribbean with greater force than previous events of similar measured intensity, worsening droughts, heat waves, wildfires, extreme rainfall, and flooding in ways that exceeded historical analogues.

The relationship between climate change and ENSO's future behaviour is one of the most actively researched questions in climate science. The IPCC's Sixth Assessment Report concluded that it is "very likely" that the precipitation variability associated with El Niño–Southern Oscillation will increase in the future — meaning swings between flood and drought will become more extreme. It is also very likely that changes in the strength and spatial reach of ENSO's atmospheric connections will produce significant changes at the regional level. In simpler terms: El Niño events may not necessarily become more frequent, but their consequences are expected to become more severe and less predictable as the planet continues to warm.

The scientific community is also grappling with how background ocean warming makes it harder to detect true ENSO-driven variability, which is precisely why NOAA's adoption of the RONI index in 2026 is methodologically significant. Measuring ENSO against the warming global tropics rather than against a fixed historical baseline allows for a cleaner separation between natural climate variability and human-caused warming.

Economic and Food Security Stakes

El Niño's consequences are not merely meteorological. Research published in Science found that El Niño patterns are linked to sluggish economic growth across many affected nations — with losses measured in the trillions of dollars in unrealised economic gains globally across major events. Economies that depend heavily on rain-fed agriculture, fisheries, hydropower, and outdoor labour are particularly exposed.

Food security is among the most acute concerns. A strong El Niño simultaneously reduces crop yields in some of the world's most food-insecure regions while increasing the risk of flooding and disease in others. The FAO has previously placed multiple countries — including Nigeria, Somalia, South Sudan, and Afghanistan — at the highest alert level during major El Niño events, a recognition that agricultural disruption can rapidly tip vulnerable populations into crisis.

Fisheries are another major casualty. El Niño-driven warming of the eastern Pacific suppresses the nutrient-rich upwelling that sustains anchovy and other commercially vital fish populations off the South American coast. The consequences ripple through global fishmeal and fish oil markets, affecting feed supply chains for aquaculture and livestock industries worldwide.

Energy systems are also exposed. Reduced rainfall during El Niño conditions affects hydroelectric generation in countries that depend heavily on it — including Brazil, Zambia, and parts of Central America — just as heat-driven electricity demand rises. Insurance markets, commodity traders, logistics operators, and sovereign fiscal planners all model El Niño scenarios into their risk assessments.

What Preparedness Looks Like

The advance warning that modern climate science provides — typically several months — is one of humanity's most valuable tools for limiting El Niño's damage. Early warnings allow farmers to adjust planting calendars and crop choices, governments to pre-position food and medical supplies, water utilities to draw down reserves before drought conditions arrive, and disaster management agencies to prepare evacuation and relief infrastructure.

The WMO has scheduled a Global Seasonal Climate Outlook Briefing for UN and humanitarian agencies, covering ENSO and other climate drivers and flagging key areas of concern. Seasonal forecasts are described by the WMO as vital instruments for guiding preparedness actions in climate-sensitive sectors including agriculture, water resource management, energy, and public health.

For regions where El Niño is already bringing above-normal temperature forecasts for the May–July 2026 season — including southern North America, Central America, the Caribbean, Europe, and Northern Africa — preparedness is not a future consideration. It is an immediate one.

Conclusion: Watching the Ocean Watch Us Back

The El Niño–Southern Oscillation has shaped the rhythm of human civilisation for as long as there have been communities dependent on predictable seasons — which is to say, for as long as there has been settled agriculture. The Peruvian fishermen who named it understood that the warm ocean current changed everything: the fish left, the rains came, and life reorganised itself accordingly.

What is different now is the scale of our vulnerability and the depth of our knowledge. We have satellite systems that track subsurface ocean temperatures in real time. We have atmospheric models that detect the Bjerknes feedback — the positive reinforcement loop between weakening trade winds and warming seas — as it unfolds. We have historical records that tell us, region by region, what an El Niño of a given strength is likely to do to rainfall, temperature, and food production.

What we do not yet have is the institutional and political will to use that knowledge as aggressively as the coming months will likely demand. The ocean is sending a clear signal. The question now is whether the world's governments, planners, and communities will receive it clearly enough — and act on it in time.

News and Scientific Sources

1. World Meteorological Organization — "Likelihood increases of El Niño" (April 2026) https://wmo.int/media/news/wmo-likelihood-increases-of-el-nino
2. NOAA Climate Prediction Center — ENSO Diagnostic Discussion, Final La Niña Advisory / El Niño Watch (April 9, 2026) https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.shtml
3. IRI (International Research Institute for Climate and Society), Columbia University — April 2026 ENSO Quick Look https://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/
4. ECMWF (European Centre for Medium-Range Weather Forecasts) — "How confident should we be in a prediction of El Niño?" Science Blog, 2026 https://www.ecmwf.int/en/about/media-centre/science-blog/2026/el-nino-2026
5. Severe Weather Europe — "Summer 2026 Forecast Shift: New Data Shows a Stronger El Niño Impact Than Previously Expected" (May 2026) https://www.severe-weather.eu/long-range-2/summer-2026-forecast-shift-super-el-nino-stronger-seasonal-weather-united-states-canada-europe-fa/
6. Yale Climate Connections — "Five things you need to know about El Niño's likely comeback" (May 2026) https://yaleclimateconnections.org/2026/05/five-things-you-need-to-know-about-el-ninos-likely-comeback/
7. NOAA Drought.gov — "New NOAA El Niño-Southern Oscillation Index Supports Drought Early Warning" (March 11, 2026) https://www.drought.gov/news/new-noaa-el-nino-southern-oscillation-index-supports-drought-early-warning-2026-03-11
8. FAO — El Niño: Food Security and Agriculture https://www.fao.org/el-nino/en
9. Zero Carbon Analytics — "Are we heading towards a Super El Niño in 2026?" (April 2026) https://zerocarbon-analytics.org/insights/briefings/el-nino-and-climate-change/
10. DTN/Progressive Farmer — "5 Global Regions Hit Hard by a Super El Niño" (May 8, 2026) https://www.dtnpf.com/agriculture/web/ag/news/article/2026/05/08/5-global-regions-hit-hard-super-el
11. Wikipedia — El Niño–Southern Oscillation (updated May 2026) https://en.wikipedia.org/wiki/El_Ni%C3%B1o%E2%80%93Southern_Oscillation
12. Journalist's Resource — "El Niño: Economic devastation and how it intersects with climate change" https://journalistsresource.org/environment/el-nino-economic-devastation-climate-change/