Is a warming climate changing El Niño?

Every few years the trade winds over the equatorial Pacific weaken, warm water spreads east from the western Pacific, and the ocean releases heat into the atmosphere. This is El Niño. Its opposite, La Niña, brings stronger trade winds and a cooler eastern Pacific. Together they form the El Niño–Southern Oscillation (ENSO), the largest source of year-to-year variation in the global climate.

El Niño changes the position of the great tropical rain systems, and through them the weather on every inhabited continent. It typically brings drought to Indonesia, eastern Australia, southern Africa, Central America and northern South America, and heavy rain and flooding to coastal Peru and Ecuador, parts of East Africa and southeastern South America. It also raises global average temperature for a year or so.

Scientists track El Niño with sea-surface temperatures in a box of the central-eastern Pacific called Niño-3.4. Because the whole tropics are now warmer than in the past, NOAA and Australia’s Bureau of Meteorology have moved to relative indices, which compare the Niño-3.4 region with the tropical average. The relative index captures the east-west contrast that drives El Niño’s effects.

A strong El Niño developed in 2026. NOAA declared El Niño conditions and, in its October 2026 discussion, kept an El Niño Advisory in place. In October 2026 Niño-3.4 temperatures passed +3°C, among the highest weekly values in NOAA’s record since 1981. On the relative index, which removes the warming of the whole tropics, the event had not passed the 1982–83 peak. The latest values are on The ocean now.

Longer records suggest El Niño has already strengthened. Fossil corals from the Galápagos Islands record eastern Pacific temperatures over the past thousand years. They show a large recent increase in year-to-year variability, driven by stronger El Niño events, that exceeds simulated natural variability and parallels rising global temperature (Cole et al., 2026).

At the same time, the average state of the Pacific has moved the other way. Since the mid-twentieth century the east-west temperature contrast along the equator has strengthened, which is more La Niña-like (Seager et al., 2019). Most climate models simulate the opposite over that period, and the difference is unlikely to be explained by natural variability alone (Seager et al., 2022; Sugiura et al., 2026). Why models and observations disagree is one of the main open questions in climate science.

The IPCC concludes that El Niño will remain the dominant mode of year-to-year variability, and that it is very likely that the rainfall swings it causes will become larger in the second half of this century under intermediate and high emissions. Models do not agree on whether El Niño’s temperature swings will grow (IPCC, 2021). Studies that select the models best able to reproduce El Niño find an increase in its temperature variability and in the frequency of extreme events (Cai et al., 2014; Cai et al., 2022).

Over longer periods, most models and theory expect the eastern Pacific to warm faster than the west, weakening the east-west contrast. This would move the Pacific towards a more El Niño-like average state (IPCC, 2021; Watanabe et al., 2024). A study published in October 2026 used nine Earth system models and a set of 1,000-year simulations to ask what happens after emissions reach net zero. It found that continued warming of the deep and Southern Ocean sustains the El Niño-like state for centuries, with more frequent extreme El Niños, and that reaching net zero later makes the shift larger and longer-lasting (Sengupta et al., 2026). The long simulations come from a single model with known biases, and the authors note that observations so far show the opposite trend.

Under very high emissions, some models eventually produce what has been called a permanent El Niño-like state, in which the year-to-year oscillation itself weakens after 2100 (Geng et al., 2024; Callahan et al., 2021). This is a slow, forced change in the Pacific’s background state. The Global Tipping Points Report assesses, with medium confidence, that El Niño is not a tipping system, because there is no evidence of a self-sustaining shift within its own dynamics (Global Tipping Points Report, 2025).

El Niño’s costs are large and long-lasting. One study links the 1982–83 and 1997–98 events to global income losses of US$4.1 trillion and US$5.7 trillion, because growth in affected countries stayed lower for years afterwards (Callahan & Mankin, 2023). Another estimates losses of US$2.1 trillion and US$3.9 trillion for the 1997–98 and 2015–16 extreme events (Liu et al., 2023). Losses are concentrated in tropical, agriculture-dependent economies.

Food security is the most direct channel. El Niño lowers yields of maize, rice and wheat in many producing regions, although soybean benefits on average (Iizumi et al., 2014). In June 2026, FAO and the World Food Programme launched their first joint anticipatory appeal, for US$202 million to protect 8.8 million people in 22 countries ahead of El Niño impacts (FAO & WFP, 2026). Across the tropics, the chance of new civil conflicts has historically been twice as high in El Niño years as in La Niña years (Hsiang et al., 2011).

El Niño also drives marine heatwaves. In October 2026 Peru’s Ministry of Production decided not to open the second anchovy fishing season of the year in the main north-central zone, after the marine institute IMARPE found that juveniles made up 79% of the stock by number (Forbes Perú, 2026). The fishery supplies much of the world’s fishmeal and fish oil. Strong El Niños have triggered mass coral bleaching across the tropics, and severe bleaching events now recur on average every six years (Hughes et al., 2018).

El Niño will keep happening, and its effects on rainfall are expected to become larger. Models and theory agree on this.

Less certain is how El Niño’s own strength will change. Coral records, recent observations and the models that best simulate El Niño point to stronger and more frequent extreme events (medium confidence). Whether the Pacific’s average state will turn lastingly more El Niño-like is contested (low confidence). Climate models favour an El Niño-like future, but the observed trend in the Pacific’s background state points towards La Niña, and models fail to reproduce that trend, which limits confidence in them. Resolving this matters for the rainfall projections of billions of people around the Pacific and Indian oceans.

El Niño is the ocean change that countries can best prepare for, because it can be forecast several months ahead. The 2026 event was anticipated from mid-year, which allowed early action: pre-positioning food, releasing water from reservoirs, adjusting planting and fishing plans and triggering pre-arranged finance. Turning forecasts into action requires agreed triggers, funds that can be released before impacts, and plans that reach the people most exposed.

For longer-term planning, the useful assumption is that El Niño-related droughts and floods will become more severe, even if the size of the change is uncertain. Water storage, crop insurance, social protection and food reserves sized for past El Niños may prove too small. Observations of the tropical Pacific, from the moored buoy array along the equator to satellites and Argo floats, underpin both the seasonal forecasts and the long-term picture, and need sustained funding.