El Niño

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

What is El Niño? What is La Niña?

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.

Arctic sea ice concentration for the week ending February 12, 2017. The gold line shows the historic median extent for the month, showing how far behind this year’s ice cover is. Image provided by NOAA, based on NASA and NOAA satellite data provided by NSIDC.
The atmosphere and Arctic sea ice: Who’s the dog, and who’s the tail?
How much of an effect does the rapid warming of the Arctic and the corresponding reduction in Arctic sea ice have on winter across the mid-latitudes where most of us live?

How ENSO impacts humans

El Niño, La Niña, 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.

El Niño Arrives in 2015. This image shows the average sea surface temperature for February 2015 as measured by NOAA satellites. The large area of red (warmer than average) can be seen extending through the equatorial Pacific.
Coming to pay per view: Reigning champ ocean vs. the scrappy land
There’s no doubt ENSO is a major heavyweight in the battle to dominate the world’s climate

What are some of ENSO's impacts?

Ecosystems and human communities can be positively or negatively affected. For example, in the Southern 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.

El Niño and La Niña affect spring tornadoes and hailstorms
El Niño and La Niña 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 Niño, which means “the boy” in Spanish. Fishing in this region is best during La Niña 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 Niño/La Niña forecasts can benefit agriculture, natural resource managers and human communities.

Updated July 2015.