El Niño / ENSO

What it is

El Niño-Southern Oscillation (ENSO) is a naturally occurring climate pattern in the tropical Pacific Ocean that cycles between three phases, warm (El Niño), cool (La Niña), and neutral, every two to seven years. It is the most influential year-to-year climate driver on Earth, linking ocean temperatures to atmospheric circulation changes that shift rainfall, temperature, and extreme-weather risk across six continents.

The benchmark measure is the Niño 3.4 index, a three-month average sea surface temperature (SST) anomaly in a fixed swath of the central-eastern equatorial Pacific. NOAA and the WMO declare El Niño when that anomaly exceeds +0.5°C for five consecutive overlapping three-month seasons; La Niña when it falls below -0.5°C. A "very strong" event is defined by SSTs reaching +2.0°C or above. The Southern Oscillation Index (SOI), which tracks atmospheric pressure between Tahiti and Darwin, Australia, provides a complementary signal measuring the atmospheric half of the coupled system.

Key monitoring institutions: NOAA's Climate Prediction Center (CPC) in the United States issues monthly ENSO diagnostic discussions; the WMO publishes quarterly El Niño/La Niña updates; and Columbia University's International Research Institute for Climate and Society (IRI) hosts the authoritative multi-model forecast ensemble, drawing on 24 dynamical and statistical models.

History

The name "El Niño" (Spanish for "the [Christ] child") was coined by Peruvian fishermen who noticed a warm coastal current arriving near Christmas and suppressing fish catches. Systematic documentation of its global reach began in the 1960s, when Jacob Bjerknes identified the ocean-atmosphere feedback loop. The 1982-83 event caused roughly US$13 billion in damage, then the strongest on record. The 1997-98 event surpassed it, peaking above +2.5°C in the Niño 3.4 region, causing an estimated 21,000 deaths and US$36 billion in losses. The 2015-16 event matched that intensity, driving Australian drought, Indonesian forest fires, and partial failure of the Indian monsoon. Multi-year La Niña episodes followed both major events; the 2020-23 La Niña was one of the longest since systematic records began.

Current state

La Niña conditions persisted from late 2020 through early 2023, followed by a strong El Niño in 2023-24 that amplified the West African cocoa supply crisis documented in Cocoa. The Pacific returned briefly to neutral, then reversed rapidly. NOAA issued an El Niño Advisory on 11 June 2026 with the weekly Niño 3.4 index at +1.7°C, assigning a 63% probability that SSTs will exceed 2.0°C by autumn 2026, which would place the event in the very strong category. The WMO's May 2026 update confirmed the developing episode. Full detail on the 2026 transition is at NOAA declares El Nino on June 11 as the Pacific moves from La Nina with Nino 3.4 reaching plus-1.7 degrees Celsius; crop-market and food-price implications are at NOAA, 엘니뇨 선언...카카오와 열대 작물 시장, '슈퍼' 이벤트 가능성에 선제 대응.

Relationships

ENSO operates through the Walker Circulation, an atmospheric pressure gradient that drives trade winds westward across the Pacific under neutral conditions. El Niño weakens those winds, allowing warm water to accumulate in the eastern Pacific; the ocean releases heat into the atmosphere in new locations, reshuffling global rainfall. Downstream effects, called teleconnections, include drought in eastern Australia, Indonesia, and southern Africa; flooding in coastal Peru and Ecuador; reduced Atlantic hurricane activity from increased wind shear; and partial suppression of India's monsoon. That monsoon link is live for 2026 in 인도 2026년 몬순, 146년 만에 가장 건조한 6월 기록, 카리프 작물 위기. ENSO forecasts feed directly into FAO food-security early-warning systems, connecting the Pacific climate cycle to the commodity prices tracked in Wheat climbs a fourth straight month as cereals defy a stable headline index.

What to watch

• NOAA CPC monthly ENSO diagnostic discussions tracking whether the 2026-27 event reaches 1997-98 intensity
• WMO quarterly El Niño/La Niña updates on confirmed impacts in southern Africa, eastern Australia, Indonesia, and the Horn of Africa
• Atlantic hurricane activity from June through November 2026, a key El Niño suppression signal watched by insurance and reinsurance markets
• FAO food-security alerts for Zambia, Zimbabwe, the Philippines, and Indonesia, the countries most exposed to El Niño-driven crop failures