El Nino

The El Nino Southern Oscillation (ENSO) is one of the most important climatic phenomena on Earth.

El Nino and La Nina are opposite extremes of the El Nino/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, and atmospheric and ocean circulation all influence each other.

Influenza patients during the 1918 flu pandemic in Iowa.
1918 pandemic and El Nino
This study suggests a possible link between one of the strongest El Nino's of the 20th century and the 1918 flu pandemic.

An El Nino 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 Nina. During this phase of ENSO, the water is cooler than normal and the east winds are stronger. El Ninos typically occur every 3 to 5 years.

El Nino, La Nina, and the neutral condition all 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, droughtoffsite link 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.

Typical influence of El Niño on Pacific and Atlantic seasonal hurricane activity. Map by NOAA, based on originals by Gerry Bell.
El Niño and La Nina influences on hurricane season
The hurricane impacts of El Nino and its counterpart La Nina are like a see-saw between the Pacific and Atlantic oceans...

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

El Niño and La Niña affect spring tornadoes and hailstorms
El Nino and La Nina affect spring tornadoes and hailstorms
The research showed that ENSO affects tornado and hailstorm frequency by influencing the position of the jet stream...

The origin of the name

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 Christmastime. Referring to the birth of Christ, they named the warm ocean waters, El Nino, which means “the boy” in Spanish. Fishing in this region is best during La Nina years when cold upwelling ocean water brings rich nutrientsoffsite link from the deep ocean, resulting in an increase in the number of fish caught.


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 Nino/La Nina forecasts can benefit agriculture, natural resource managers and human communities.

Adapted from NOAA's Pacific Marine Environmental Laboratory and

Last modified: July 2015. Editor: Kirk Beckendorf, former Einstein Fellow, NOAA Office of Education.