Weather and Atmosphere

El Niño



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Real World Data

Background Information

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ENSO is one of the most important climatic phenomena on Earth. By influencing global temperatures and precipitation, ENSO significantly impacts Earth’s ecosystems and human societies.

Pacific Equitorial sea temperature of El Niño and La Nina
Caption- “El Niño, warmer than average waters in the Eastern equatorial Pacific (shown in orange on the map), affects weather around the world.”

El Niño and La Niña are opposite extremes of the El Niño/Southern Oscillation (ENSO); which refers to cyclical environmental conditions that occur across the Equatorial Pacific Ocean. These changes are due to natural interactions between the ocean and atmosphere. Sea surface temperature, rainfall, air pressure, atmospheric and ocean circulation all influence each other.

An El Niño condition occurs when surface water in the equatorial Pacific becomes warmer than average and east winds blow weaker than normal. The opposite condition is called La Niña . During this phase of ENSO, the water is cooler than normal and the east winds are stronger.  El Niños typically occur every 3 to 5 years. 

Both El Niño and La Niña (and the neutral condition) produce important consequences for people and ecosystems across the globe. The interactions between the ocean and atmosphere alters weather around the world and can result in severe storms or mild weather, drought or flooding. Beyond “just” influencing the weather, these changes can produce secondary results that influence food supplies and prices, forest fires, and create additional economic and political consequences. Famines and political strife can result from these environmental conditions.

The origin of the name “El Niño” dates to the 1800’s, when fishermen on the Pacific coast of South America would notice that a warm ocean current would appear every few years. Fish catches would drop drastically, negatively affecting the food supply and livelihood of the communities of coastal Peru. This warm water would arrive around Christmas-time. Referring to the birth of Christ, they named the warm ocean waters, El Niño, which means “the boy” in Spanish. Fishing in this region is best during La Niña years when cold up-welling ocean water brings rich nutrients from the deep ocean, resulting in an increase in the number of fish caught.

Ecosystems and human communities can be positively or negatively affected.  For example, in the Southern part of the United States, during the fall through spring, El Niño usually causes increased rainfall and sometimes destructive flooding. La Niña , however, usually causes drier weather in the South, but the Northwest tends to be colder and wetter than average. Even though El Niño occurs in the Pacific Ocean, it often reduces the number of hurricanes that form in the Atlantic Ocean.  Conversely, La Niña events tend to be related to an increase in the number of Atlantic hurricanes.

Food production is impacted by ENSO. Changes in ocean temperatures and currents that happen during El Niño impact marine life. This can impact individuals who make a living fishing and consumers who depend on certain fish for food. Agriculture is of course very dependent on climate and weather, as a result ENSO’s influence on rainfall and temperature have important consequences for food production and availability.

Education Connection
ENSO provides teachers with the opportunity to have students discover ways that the oceanic and atmospheric systems interact and how those interactions can impact ecosystems and human society. The resources in this Collection can be used to help learn about the basics of ENSO, the inter-relationship of Earth systems, the consequences of these interactions, and how to use and analyze data. These resources can be used to teach students how scientists study the complexity of the Earth’s systems and why better El Niño/La Niña forecasts can benefit agriculture, natural resource managers and human communities.

Adapted from el-nino-story  and
Last Modified: Jul 2015. Editor: Kirk Beckendorf, former Einstein Fellow, NOAA Office of Education

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