What is El Niño and What are Causes and Effects of El Niño


El Niño is a natural phenomenon experienced in the equatorial Pacific which causes temporary alterations in the world climate. It is normally characterized by complex and abnormally warm ocean temperatures in the Pacific Ocean in the area near the equator which results in global weather events and sea-surface temperature changes.

In practical sense, the ocean surface around the equator region warms up by small degrees Celsius along with very heavy thunderstorms. The small rise in temperatures is influenced by change in the normal wind direction. Scientist also prevails that the temperature increases may be intensified by the effects of greenhouse gases and consequent global warming. This small difference in temperature increase has a substantial impact on the world’s climate.

El Niño reportedly takes place every 2 to 7 years and can last from months to a period of up to two years. It is also referred to as the warm phase of the El Niño-Southern Oscillation cycle (ENSO). The ocean warming off South American coast is a prime example of an El Niño event.  The unusual rainfall and flooding in Peru, Southern California, and Chile are also usually tied to the El Niño climatic conditions.

According to NOAA,

El Niño is characterized by unusually warm ocean temperatures in the Equatorial Pacific, as opposed to La Niña, which is characterized by unusually cold ocean temperatures in the Equatorial Pacific. El Niño is an oscillation of the ocean-atmosphere system in the tropical Pacific having important consequences for weather around the globe.

Primary Causes of El Niño

In normal conditions, the wind blow from the east to the west along the equator in the Pacific. These are the trade winds which blow towards the west along the equator. This results in the piling of water in the western side of the Pacific to a sea surface area of up to 18 inches high.

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In the eastern side, deeper water (which is cooler compared to the sun-heated warm surface water) gets pulled up from beneath to substitute the water pushed to the west. So, the normal difference in temperature across the equatorial Pacific is cold water (about 22 degrees Celsius) in the east and warm water (about 30 degrees Celsius) in the west.

In El Niño conditions, the winds propelling the water get weaker and as an outcome, some of the warm water collected in the west is heavily drawn towards the east. At the same time, not so much cold water is pulled up from beneath. Accordingly, these elements make the water in the pacific warmer which results in El Niño events.

Besides, the warmer ocean successively affects the winds which make the winds weaker. Weaker winds means the ocean gets warmer and this process happens interchangeably and consecutively thus making the El Niño bigger and bigger. In other words, El Niño is caused by the weakening of the trade winds which results in pushing of warm surface water to the west and less cold water to the east.

The outcome of the eastward displacement of the atmospheric heat source lying on top of the warmest water is drastic change in the global wind cycle circulation. In turn, the end results are severe changes in weather and temperatures around the world. For instance, the weakening of the trade winds allows the waters along the coast of Peru and Chile to warm and brings about unusual warm conditions in the South American coasts, contributing to heavy rains and flooding.

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Drastic Effects of El Niño

  1. Effect on aquatic species and sea birds

In normal situations, the ocean water carry nutrients that lie beneath the ocean to the top thereby allowing the fish species living in the upper waters to feed on the planktons that rely on these nutrients. Seaweeds also rely on cool and nutrient-rich water for survival and growth. An El Niño lessens the upwelling of cold water and the uplift of nutrients from the bottom of the ocean.

As a result, fish either migrate to other regions or die during an El Niño because they lack adequate food for growth and survival. When fish have migrated or reduced in number, other aquatic creatures namely the sea birds and seals that feed on the fish are also affected. Off the coast of California, the aquatic populations such as fish, seals, sea lions, and sea birds are normally affected and deaths are registered during El Niño events.

  1. Drought and dry conditions

As much as El Niño presents differently from one occasion to another, the surest characteristic is that it creates tremendous changes in weather patterns. On occasion, this may result in extreme dry spells and drought. Indonesia, the Philippines, and Australia mostly witness much drier conditions than usual together with droughts, forest fires and poor crop yields.

These conditions are experienced when the winds that fetch rain to these regions become weaker. It is believed that the most deadly global famine in 1876 that contributed to the millions of deaths was due to the effects of El Niño.

  1. Flooding and impact on local/commercial fishing
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The change in El Niño conditions prevail for many months and with the ocean temperatures evening out, the resultant rainy weather patterns in the oceans bring about heavy floods that last for extended periods. The heavy floods are experienced far beyond the ocean shores in the main land, destroying property and rendering people homeless for months.

Consequently, local and commercial fishing is many times severely affected. In Peru, South America, and Ecuador, heavier rains witnessed sometimes during El Niño events between January and May often bring about flooding and impacts commercial fishing negatively.

  1. Occurrence of Hurricanes, Typhoons, and very cold weather

The warm pacific air is tied to some of the occurrences of serious hurricanes, typhoons, and very cold weather in various parts of the world. In South America, thunderstorms and severe tropical cyclones (hurricanes) are frequently associated with the drastic change in the global wind cycle circulation because of the eastward displacement of atmospheric heat.

Besides, during times when hurricanes are fewer, wetter weather and very cold weather is witnessed during winter and autumn. Some meteorological evidence indicates that the very cold weather in Europe is promoted by the El Niño. For instance, the 2009 severe winter in the UK was party linked to the effects of El Niño. In South Korea and Japan, the resultant warm Pacific wind currents are believed to cause the more intense typhoons.

References: PMEL , NASA
Photo by: tonynetone

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