# El Niño / ENSO
> The El Niño-Southern Oscillation is a Pacific Ocean climate cycle that shifts rainfall, crop yields, and hurricane frequency across six continents every two to seven years.

**Meta:** type: reference · date: 2026-07-03 · heads:  · 4 takes · 4 lenses · 2 regions

## 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](/ja/n/cocoa-dossier). 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](/ja/n/la-nina-el-nino-transition-2026); crop-market and food-price implications are at [NOAAがエルニーニョを宣言、カカオや熱帯作物の市場は「超大型」イベントを先読みへ](/ja/n/el-nino-2026-advisory).

## 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 [インド2026年モンスーン、146年ぶり最も乾燥した6月を記録、カリフ作物が危機](/ja/n/india-monsoon-2026-kharif). 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](/ja/n/fao-food-prices).

## 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

## Regional takes (batched by bias / lens)

### official ENSO monitor and explainer
- **NOAA Climate.gov, El Niño and La Niña** (United States, en) — NOAA's central public-facing ENSO resource covering current phase status, threshold definitions (Niño 3.4 index, ±0.5°C for five consecutive overlapping seasons), impact maps, and links to CPC diagnostic discussions and model forecasts.
  Source: https://www.climate.gov/enso

### UN meteorological authority
- **World Meteorological Organization, El Niño / La Niña** (global, en) — WMO's definitive topic page on ENSO: phase definitions, typical frequency of two to seven years, duration characteristics (El Niño up to 18 months, La Niña up to three years), and the mechanism linking Pacific SSTs to global rainfall and temperature anomalies.
  Source: https://wmo.int/topics/el-nino-la-nina

### current state advisory
- **WMO El Niño/La Niña Update, May 2026** (global, en) — WMO quarterly bulletin confirming the emerging 2026 El Niño episode, documenting Niño 3.4 anomaly progression through the La Niña-to-El Niño transition, with regional impact projections for the 2026-27 season.
  Source: https://wmo.int/resources/publication-series/el-ninola-nina-updates/el-ninola-nina-update-may-2026

### multi-model ensemble and research
- **International Research Institute for Climate and Society, Columbia University** (United States, en) — IRI's ENSO expertise hub at Columbia University: plume forecasts from 24-model ensembles, historical event chronology, and peer-reviewed research on ENSO teleconnections and socioeconomic impacts across agriculture and public health.
  Source: https://iri.columbia.edu/our-expertise/climate/enso/

## Across the graph
- Related: [[el-nino-2026-advisory]], [[la-nina-el-nino-transition-2026]], [[cocoa-dossier]], [[fao-food-prices]], [[india-monsoon-2026-kharif]]
- Entities: El Nino, La Nina, Noaa, Wmo, Food Prices

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Canonical: https://rbtfl.xyz/ja/n/el-nino-dossier