El Niño and La Niña: the two climatic phenomena of the Pacific

Contrasting illustration of the El Niño phenomenon (warm waters in the eastern Pacific) and La Niña (anomalously extensive cold waters) — On the left, **El Niño**, for at least several millennia, has been distorting the surface of the Pacific Ocean with a tongue of warm water that blocks the upwelling of cold water. On the right, **La Niña** amplifies equatorial cooling and accentuates drought around the Pacific rim.
Image source: astronoo.com (new window) - AI-generated image, public domain.

Scientific summary

The Astronoo article presents the ENSO phenomenon (El Niño-Southern Oscillation), the most powerful driver of interannual climate variability. It describes how the trade winds of the tropical Pacific, by weakening or strengthening, alternately tip the ocean into two opposing states: El Niño, which abnormally warms the eastern Pacific, and La Niña, which cools it. The article details the ocean-atmosphere feedback mechanisms discovered by Jacob Bjerknes, traces extreme episodes since 1950, and highlights global consequences: droughts, floods, food crises and monsoon disruptions.

What makes El Niño and La Niña the most powerful drivers of the global climate?

This article is devoted to the ENSO phenomenon (El Niño-Southern Oscillation), the coupled oscillation between the tropical Pacific Ocean and the Earth's atmosphere. But what makes El Niño and La Niña the most powerful drivers of the global climate? The answer lies in the immensity of the equatorial Pacific, which stores and redistributes a colossal amount of heat. Under normal conditions, the trade winds push warm waters toward Indonesia, allowing cold, nutrient-rich waters to rise off the coast of Peru—essential for fishing. When El Niño occurs, these trade winds weaken, warm water spreads eastward and disrupts rainfall across several continents, causing droughts and floods. La Niña, conversely, intensifies the trade winds and excessively cools the eastern Pacific, altering storm tracks and monsoons. These two opposing phases form a climatic pendulum whose repercussions affect agriculture, fisheries, health and the global economy. Understanding ENSO means deciphering the chaotic breathing of our planet, a precarious balance perpetually rewritten by the dance of the ocean and the sky.

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The tropical Pacific: epicenter of climate variability

An irregular and planetary rhythm

Without a fixed rhythm, generally every two to seven years, the largest ocean on the planet tips from one state to another. Sometimes its waters run wild, becoming abnormally warm and pouring torrential rain on usually arid deserts. Other times they freeze in excessive cold, pushing back clouds and strangling monsoons. These two opposing pulsations bear Spanish names inherited from South American fishermen: El Niño (the Christ child, because it often occurs around Christmas) and La Niña (the little girl). Together they constitute the ENSO phenomenon (contraction of "El Niño / Southern Oscillation"), the most intense climatic driver coupling the ocean and the Earth's atmosphere.

The discovery of Jacob Bjerknes

Far from being isolated catastrophes, El Niño and La Niña are the two facets of the same implacable 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.

How does the ENSO pendulum work?

The fragile equilibrium of the Pacific under normal conditions

The trade winds always blow from east to west, along the equator (from Peru toward Indonesia). Under normal conditions, the trade winds push warm waters toward Indonesia and Australia. This movement brings deep, cold waters to the surface off the coast of Peru: this is upwelling, a nutrient-rich phenomenon that feeds one of the most abundant fisheries on the planet.

Normal: Indonesia/Australia ← (warm waters) ← Pacific ← (trade winds) ← Peru (cold upwelling)

When the trade winds falter: El Niño enters the scene

During El Niño, the belt of trade winds and rain shifts eastward, pushing warm waters toward the central and eastern Pacific, blocking the Peruvian upwelling. The consequences follow one another: torrential rain on the west coast of South America, intense droughts in Indonesia and Australia, disruptions of the Indian monsoon, and even a weakening of the jet stream that disrupts European winters.

El Niño: Indonesia/Australia ← (warm waters) ← Pacific ← (weakened trade winds) ← Peru (rain)

When the trade winds race: La Niña triggers the cold machine

La Niña, conversely, occurs when the trade winds accelerate abnormally. Warm water is violently driven back westward, the upwelling becomes hyperactive, and the eastern Pacific cools well below normal. Rain stops 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)

The most notable events of the past century

A chronology of extreme episodes

Oceanographic and satellite records now allow us to trace with precision the history of ENSO episodes. The table below presents the most extreme events since 1950, each with its average thermal anomaly in the NINO 3.4 region, located at the heart of the equatorial Pacific between 170°W and 120°W. This is the oceanic region whose temperature deviation from normal officially diagnoses an El Niño episode (anomaly >+0.5 °C) or La Niña (anomaly <-0.5 °C).

Chronology of extreme ENSO episodes (1950-2024)
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 episode documented with modern data
1965-1966	Moderate El Niño	+0.9 °C	Failure of the Indian monsoon, famine	Aggravated the Indo-Pakistani war
1972-1973	Strong El Niño	+1.4 °C	Collapse of Peru's anchovy fisheries	Brutal decline of 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 super El Niño of 1982-1983
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 over 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 to 1997-1998 in intensity
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

The remarkable case of the 2020-2023 "triple dip"

N.B.:
A "triple dip" episode (three consecutive winters of La Niña) is rare in the records. The last one dated back to the 1973-1976 period. The 2020-2023 occurrence surprised the models.

Key takeaways

Very real consequences

Beyond the climate anomaly figures, El Niño and La Niña concretely translate into food crises, epidemics, forced migrations and colossal economic losses, for several millennia.

The chaotic breathing of the planet

El Niño and La Niña are not meteorological whims. They embody the chaotic breathing of our planet. Climatic stability does not exist: there is only a precarious balance, perpetually rewritten by the dance of the ocean and the sky.

References

FAQ: Everything you need to know about El Niño and La Niña

What is the ENSO phenomenon?

ENSO is the acronym for El Niño-Southern Oscillation, that is, the coupled oscillation between the tropical Pacific Ocean and the atmosphere. It refers to the irregular alternation of two opposing phases: El Niño (warm phase) and La Niña (cold phase). This phenomenon is the main mode of interannual climate variability on a global scale.

What is the difference between El Niño and La Niña?

El Niño corresponds to an abnormal warming of surface waters in the central and eastern Pacific, accompanied by a weakening of the trade winds. La Niña, conversely, is characterized by an abnormal cooling of these same waters and a strengthening of the trade winds. The two phases are the extremes of the same ocean-atmosphere pendulum.

How often do El Niño and La Niña episodes occur?

ENSO episodes occur irregularly, generally every two to seven years. Their duration varies from a few months to more than two years. Some particularly long episodes, such as the 2020-2023 "triple dip" La Niña, can persist over three consecutive winters.

What are the main impacts of El Niño on the global climate?

El Niño causes torrential rain on the west coast of South America, droughts in Indonesia and Australia, disruptions of the Indian monsoon and a weakening of the jet stream that influences European winters. It can also foster epidemics and food crises in tropical regions.

What are the main impacts of La Niña?

La Niña brings drier conditions on the South American coast, floods in Australia and Southeast Asia, as well as a surge in Atlantic hurricanes. It can also cause droughts in the southern United States and Patagonia.

Does climate change modify the ENSO phenomenon?

Scientists observe that global warming could intensify extreme ENSO episodes, particularly El Niño, by increasing the amount of heat stored in the ocean. However, projections remain uncertain regarding the future evolution of the phenomenon's frequency and amplitude.