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El Nino is a weather phenomenon caused when warm water from the western Pacific Ocean flows eastward. In this lesson, we’ll see how the effects of El Nino can be noticed in many parts of the world, with different regions experiencing varying weather anomalies.

Definition of El Ni;o

When we notice different weather patterns, we usually think of what’s in the air. But did you know that a lot of what happens in the air is because of the temperature of the oceans? El Niño is an abnormal weather pattern caused by the warming of the Pacific Ocean near the equator, off the coast of South America. The sun warms the water near the equator, which can make more clouds and, therefore, more rain.

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However, normally there are trade winds, which blow that warm water west. During El Niño, though, those trade winds weaken, or even reverse, which lets the warm water that is usually found in the western Pacific remain or flow east. This warm water displaces the cooler water that is normally found near the surface of the eastern Pacific, setting off atmospheric changes that affect weather patterns in many parts of the world.A temperature increase of least 0.9 F (0.5 C) needs to occur in the waters of the eastern Pacific Ocean near the equator for it to be considered an El Niño year. Although El Niño does not occur in a perfectly regular pattern, it seems to happen every 2 to 7 years.

Following an El Niño, an opposite phenomenon occurs, called La Niña. During La Niña, the eastern Pacific Ocean experiences cooler than normal temperatures around the equator.The effects of El Niño are strong and can wreak havoc on weather systems around the world. The changes vary drastically around the globe.

Storm Effects

Along the Pacific coast of the Americas, El Niño can cause severe storms and flooding. Peru and Ecuador usually receive the brunt of the force of El Niño.

During the months of April – October, this area experiences increased rain fall. El Niño’s effects are not only felt through rain. In normal years, along the coast of Peru, cool, nutrient-rich water is pushed up from the deep waters off the Pacific coast, and this nutrient-rich water is a food source for marine life. However, during an El Ni;o year, this cold water is replaced by warmer water that lacks those important nutrients.

The nutrient-deficient water starves the bottom of the food chain and the effects cause a die-off of larger fish.El Ni;o is not all bad in the Americas, though. Away from the Pacific coast, North America actually tends to have milder winters during El Ni;o years, and it is even thought that El Ni;o reduces the number and intensity of hurricanes in the Atlantic.

Drought Effects

While the Pacific coast of the Americas receives more rain, on the other side of the Pacific, the islands of Melanesia receive drought-like conditions.

This is very problematic throughout Melanesia, because many of the islands receive their water supply almost exclusively from rainfall. During El Ni;o years, fresh water is flown in to stave off dehydration.


In order to better understand and try to predict El Ni;o, scientists have set up a system of buoys across the Pacific Ocean that record daily temperatures both above and below the surface.

The predictions are especially useful to help farmers decide what crops to plant. For example, cotton grows better in drier conditions, but in a wet El Ni;o year, it may benefit the farmer to plant rice since it grows better in wet conditions. Since El Ni;o is a worldwide weather phenomenon, climate researchers are still working to try to understand its full effect.

Lesson Summary

When the Pacific Ocean waters near the equator warm, they are normally pushed by trade winds to the west. When El Ni;o occurs, the trade winds are weak and there is nothing to push the warm waters away from the east.

This can change the weather drastically; heavy rains hit the western Americas, especially Peru and Ecuador, while drought is rampant in the Melanesian islands. It helps to know when this will happen, so climate researchers are trying to better predict and understand this phenomenon.

Notes on El Ni;o

El Nino is caused by the warming of the Pacific Ocean near the Equator.
Map with warm Equator
El Nino
*An abnormal weather pattern caused by the warming of the Pacific Ocean and the displacement of normally cold water *Affects global weather patterns *Can be responsible for flooding and drought conditions *Occurs every 2 to 7 years *An El Ni;o year is indicated by a temperature increase of least 0.9 F (0.5 C)

Learning Outcomes

Thoroughly examine this lesson on El Ni;o, and you could go on to accomplish these goals:

  • Cite the cause of El Ni;o
  • Discuss the wet and dry effects of El Ni;o
  • State the reasons that it is important to study climates and daily temperatures

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