Without a fixed rhythm, generally every two to seven years, the planet's largest ocean shifts from one state to another. Sometimes, its waters overheat, become abnormally warm, and unleash torrential rains on usually arid deserts. Other times, they freeze in excessive cold, push clouds away, and strangle monsoons. These two opposing pulses have Spanish names inherited from South American fishermen: El Niño (the Christ Child, as it often occurs around Christmas) and La Niña (the little girl). Together, they form the ENSO phenomenon (El Niño/Southern Oscillation), the most intense climate engine coupling the ocean and Earth's atmosphere.
Far from being isolated disasters, El Niño and La Niña are two facets of the same relentless mechanism. Jacob Bjerknes (1897-1975), a Norwegian meteorologist, was the first to understand, in the mid-20th century, that the tropical Pacific Ocean and the atmosphere are linked by a vertiginous feedback loop. Breaking this dance would be like trying to stop the Earth's rotation.
The trade winds always blow from east to west, along the equator (from Peru to Indonesia). Normally, the trade winds push warm waters toward Indonesia and Australia. This movement causes cold, deep waters to rise off the coast of Peru: this is upwelling, a nutrient-rich phenomenon that feeds one of the planet's most abundant fisheries.
Normal: Indonesia/Australia ← (warm waters) ← Pacific ← (trade winds) ← Peru (cold upwelling)
During El Niño, the belt of trade winds and rains shifts eastward, pushing warm waters toward the central and eastern Pacific, blocking the Peruvian upwelling. The consequences follow: torrential rains on the west coast of South America, intense droughts in Indonesia and Australia, disruptions to the Indian monsoons, and even a weakening of the jet stream that disrupts European winters.
El Niño: Indonesia/Australia ← (warm waters) ← Pacific ← (weakened trade winds) ← Peru (rains)
La Niña, on the other hand, occurs when the trade winds accelerate abnormally. Warm water is violently pushed westward, upwelling becomes hyperactive, and the eastern Pacific cools well below normal. Rains stop on the South American coast while Australia and Southeast Asia are submerged by recurrent floods.
La Niña: Indonesia/Australia ← (very warm waters) ← Pacific ← (strengthened trade winds) ← Peru (intense upwelling + drought)
Oceanographic and satellite records now allow us to accurately trace the history of ENSO events. The table below shows the most extreme episodes since 1950, with the average thermal anomaly in the NINO 3.4 zone, located in the heart of the equatorial Pacific between 170°W and 120°W. This is the oceanic region whose temperature deviation from the norm is used to officially diagnose an El Niño episode (anomaly > +0.5 °C) or La Niña (anomaly < -0.5 °C).
| Years | ENSO Type | Average NINO 3.4 Anomaly | Major Impacts | Comment |
|---|---|---|---|---|
| 1957-1958 | Strong El Niño | +1.2 °C | Drought in India, floods in Peru | First documented episode with modern data |
| 1965-1966 | Moderate El Niño | +0.9 °C | Failure of the Indian monsoon, famine | Worsened the Indo-Pakistani War |
| 1972-1973 | Strong El Niño | +1.4 °C | Collapse of Peru's anchovy fisheries | Sudden decline in the fishmeal industry |
| 1982-1983 | Very Strong El Niño | +2.1 °C | Drought in Australia, cyclones in Polynesia | Deadliest of the 20th century (over 2,000 deaths) |
| 1988-1989 | Strong La Niña | -1.6 °C | Drought in the American Great Plains | Followed the 1982-1983 super El Niño |
| 1997-1998 | Extreme El Niño | +2.4 °C | Fires in Indonesia, floods in Kenya | The most intense ever measured at the time |
| 1999-2000 | Moderate La Niña | -1.1 °C | Active monsoons in India, Atlantic hurricanes | Prolonged the impacts of the previous El Niño |
| 2010-2012 | Prolonged La Niña | -1.3 °C | Floods in Queensland, drought in Texas | One of the longest ever recorded |
| 2015-2016 | Very Strong El Niño | +2.3 °C | Massive coral bleaching, record heat episodes | Comparable in intensity to 1997-1998 |
| 2020-2023 | Triple-Dip La Niña | -1.0 °C (three-year average) | Drought in Patagonia, exceptional rains in Southeast Asia | Rare phenomenon: three consecutive winters |
Note: A "triple-dip" episode (three consecutive La Niña winters) is rare in the records. The last one dates back to 1973-1976. The 2020-2023 occurrence surprised the models.
Beyond the numbers of climate anomalies, El Niño and La Niña translate into food crises, epidemics, forced migrations, and colossal economic losses, for several millennia.
El Niño and La Niña are not meteorological whims. They embody the chaotic breathing of our planet. Climate stability does not exist: there is only a precarious balance, perpetually rewritten by the dance of the ocean and the sky.
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