What is the phenomenon of El Niño?

El Niño is a climatic phenomenon named by Peruvian fishermen who noticed a warm current occurring around Christmas time (hence its name El Niño, "the child"). It is a complex climatic phenomenon that occurs irregularly in the tropical Pacific Ocean. It is characterized by an abnormal increase in the sea surface temperature, leading to significant changes in weather conditions on a global scale.

The temperature in the western Pacific, near Indonesia and Australia, is warm, reaching around thirty degrees. It is called the Indonesian Warm Pool. In the eastern Pacific, temperatures range between 24 and 25 degrees. This temperature difference creates a disparity in atmospheric pressure, which generates trade winds. The trade winds cause warm water to accumulate in the west and cold water to rise in the east, as part of their inherent process.

During an El Niño episode, there is a decrease in high pressure in the southern Pacific. The trade winds, which are regular east-to-west winds, weaken or even change direction. This leads to a reversal of warm surface waters, accompanied by clouds and precipitation, from west to east. This natural thermal anomaly has significant impacts on ocean and atmospheric circulations, winds, and precipitation patterns across the planet, especially in the tropics.

El niño

The consequences of El Niño are varied and affect different regions of the world. Coastal regions of South America can experience heavy rainfall and flooding, while other regions such as Southeast Asia and Australia may endure prolonged droughts. Weather disruptions, such as tropical storms and hurricanes, can also occur in different parts of the world.

To learn more about how to teach the phenomenon of El Niño, refer to the "Scientific Overview" section of the teacher's manual "The climate in our hands - Ocean and Cryosphere."


What are the impacts of El Niño on human beings?

"During El Niño, fishing in Peru is directly affected, leading Peruvians to not deploy their fishing fleet during those years." Eric Guilyardi, climatologist and El Niño expert.

The El Niño phenomenon has significant impacts on human beings:

  • Agriculture and food security: El Niño can lead to prolonged droughts in certain regions, thereby reducing water availability for irrigation of crops. This can result in crop losses, decreased food production, and increased food prices. Populations that rely on subsistence agriculture are particularly vulnerable to these disruptions.


Address the impact of climate change on agriculture with your students using the session "C2 - Climate Change and agriculture."

C2billes de sciences


  • Extreme events: During El Niño episodes, certain regions may experience an increase in extreme weather events such as tropical storms, hurricanes, floods, and landslides. Others may see a decrease in risk, such as in the tropical Atlantic. Natural disasters associated with these extreme events can result in loss of life, forced population displacement, material destruction, and deterioration of critical infrastructure.


Discover the nature of extreme events with your students through the session "C3 - Extreme Events and Land Degradation."



  • Economy: Disruptions caused by El Niño can have significant economic consequences. Sectors related to agriculture, fishing, tourism, and infrastructure may suffer substantial financial losses.


To learn more about the links between the economy and climate change, watch the replay of the webinar "Ecological Transition and Development" with OCE and Esther Duflot. (in French)

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"The impacts of El Niño vary from one region to another depending on geography, vulnerability, and the exposure of local populations, available infrastructure, and implemented adaptation measures. Continuous monitoring and early warning systems are essential to mitigate the adverse effects of El Niño on human communities."


"Discover more information about the phenomenon in the 'Scientific Overview’ section of the educational guide 'The climate in our hands - Ocean and Cryosphere'."

éclairage scientifique


Initiate the discussion in class with your students by watching the CLIM video "El Niño."



Teach the El Niño phenomenon in class with the session "C5 - Marine currents and climate regulation" from the teacher’s guide book "The climate in our hands - Ocean and Cryosphere."


How can the arrival of the El Niño phenomenon be predicted?

To predict future occurrences of the El Niño phenomenon, scientists rely on their understanding of climate variability mechanisms in the tropical Pacific Ocean, observation networks, and computer models for seasonal forecasting.

A precursor to El Niño is the buildup of heat in the Western Pacific, extending deep into the ocean up to 300 to 400 meters. A network of buoys equipped with thermometers helps detect this heat buildup. Once the event is triggered, this heat then propagates along the equator in the Pacific, emerging at the surface in the East and Central regions, thus causing the El Niño phenomenon. Currently, based on climate scenarios and observations, there is no observed average change in the intensity or frequency of the El Niño phenomenon.


Interview with Eric Guilyardi: President of the Office for Climate Education, Lead Author for IPCC AR5, and expert on the El Niño phenomenon.


Eric Guilyardi is a French researcher specializing in climate science. He currently serves as a research director at the National Centre for Scientific Research (CNRS) and works at the Laboratory of Oceanography and Climate: Experimental and Digital Approaches (LOCEAN) in Paris, France.

Eric Guilyardi's work primarily focuses on studying the interactions between the ocean and the atmosphere in the context of climate change. His research aims to improve our understanding of the climate system and provide valuable insights for climate prediction and the assessment of climate change impacts.


"Can you tell us about your professional journey and your relationship with the study of the El Niño climate phenomenon?"

"After completing my thesis on the role of ocean eddies in climate, I became drawn to a particular climate phenomenon: El Niño. I was intrigued by its cyclic nature and its impact on global weather events. I subsequently joined several research groups specializing in the study of oceanic and atmospheric phenomena at the core of El Niño's evolution. I have particularly developed advanced computer climate models and compared them with observations. I am fortunate to collaborate with scientists from around the world and participate in exciting research projects.

I embarked on my first postdoctoral research in the United States, where I focused on modeling ocean-atmosphere interactions in the tropical Pacific. This allowed me to deepen my understanding of the physical mechanisms underlying El Niño. Later, I pursued a second postdoc at the University of Reading in the United Kingdom, working with Julia Slingo's team, which specifically focused on the atmospheric mechanisms of El Niño. Since then, I have continued to work on El Niño and deepen my knowledge of this fascinating and complex subject. To learn more, I invite you and your students to watch the CLIM episode titled 'El Niño'."


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Office for Climate Education OCE