El Niño vs. La Niña: Definitions and Climate Implications

El Nino, illustration
El Nino, illustration.


Weather’s most popular twins, El Niño and La Niña, are both naturally occurring events associated with the El Niño-Southern Oscillation (ENSO) — a climate cycle having to do with changes in sea surface temperatures across the equatorial Pacific Ocean. But while they’re both related to the same climate cycle and influence seasonal climate around the world, they work in opposite ways; El Niño refers to the warming of the waters of the Pacific, whereas La Niña refers to their cooling.

Why care about the atmospheric conditions in the equatorial Pacific if you don’t live there? Because no matter how far away it is, the changes occurring there can have a domino effect on weather patterns around the world. 

The ENSO Cycle

What Is the ENSO Cycle?

ENSO is the acronym for the term “El Niño-Southern Oscillation” — the see-saw shift in ocean temperatures across the equatorial Pacific Ocean (El Niño and La Niña) and in air pressure over the Pacific’s eastern and western halves (Southern Oscillation). It’s a blanket term that is used whenever referring to this cycle in its entirety, as opposed to naming its three individual phases — El Niño, La Niña, and neutral conditions.

ENSO affects weather around the world by causing increased rainfall, an increased risk of drought and wildfires, atmospheric warming, and more. During an El Niño phase, for example, very warm Pacific Ocean waters pump more moisture into the air, causing an increase in storminess over a large area. The event can be so severe that it disrupts major wind currents in the upper air, which can shift typical storm paths and, as a result, a location’s normal air temperatures and precipitation patterns. These changes in environmental conditions caused by the ENSO cycle can also lead to agricultural, public health, political, and economic consequences.

El Niño vs. La Niña

During El Niño episodes, the trade winds — surface winds over the tropical ocean that blow from east to west along the equator — weaken or reverse course altogether, blowing the warm, western Pacific waters east along the equator. Rainstorms follow the warm water to the central and eastern Pacific, while drier-than-normal conditions impact northern Australia and southeast Asia. In the U.S., milder weather tends to move into northern areas, while wetter weather soaks the south. 

One of the first signs of the arrival of El Niño is warm water off the coast of South America near Christmastime, which is how it got its name — “El Niño” is Spanish for “the boy,” referring to the Christ child. Waters usually reach peak warmth during late autumn of the following year and, after peaking, will gradually cool throughout the upcoming winter and spring.

La Niña is characterized by the opposite setup: The trade winds strengthen, and warm water and rainstorms are pushed to the western half of the Pacific. This results in cooler waters in the central and eastern tropical Pacific Ocean. La Niña produces drier-than-normal conditions over the Pacific coast of South America and much wetter weather over Indonesia, northern Australia, and southeast Asia. This event can impact U.S. weather, bringing cooler weather to the northwest and warmer weather to the southeast.

Both El Niño and La Niña conditions generally occur every three to eight years and last one to two years at a given time. That said, no two El Niños or La Niñas are exactly alike. Their strength, duration, and even weather can vary from one event to another.

In the United States, NOAA is responsible for declaring when an El Niño or La Niña event begins. NOAA operates a network of satellites and ocean buoys that measure temperature, currents, and winds in the equatorial Pacific region to detect when an El Niño or La Niña will arrive. When conditions look favorable, NOAA’s Climate Prediction Center issues a “watch” or an “advisory” to alert the public of possible development.

In years when neither El Niño nor La Niña conditions are active, conditions across the tropical Pacific Ocean return to their neutral state. That is, trade winds blow east to west, bringing warm moist air and warmer surface waters toward the western Pacific and keeping the central Pacific relatively cool. 

The Effects of El Niño and La Niña

As for how El Niño and La Niña affect the overall global climate, El Niño is associated with weather extremes (droughts, floods, etc.), while La Niña impacts cooler global temperatures. But El Niño and La Niña don’t just influence the weather; the weather changes they stir up can disrupt ecosystems, public health, food production, and the global economy. 

The 2020 La Niña event, for example, contributed to a record-breaking Atlantic hurricane season that boasted 30 named storms and 13 hurricanes instead of the 12 named storms and six hurricanes expected during a typical season. AccuWeather estimated that the 2020 Atlantic hurricane season’s 12 U.S. landfalling storms caused a combined $60-$65 billion in economic damages. 

One of the strongest El Niños on record led to a multi-year global food crisis that began in 2015. It triggered severe droughts in Africa that were described as some of the driest in 30 years, while it brought prolonged flooding to Asia and Latin America. Together, these extreme conditions ruined harvests and left over 60 million people facing food and water insecurities. Lingering floodwaters, which are a breeding ground for disease-carrying insects, also increased vulnerability to illness, including the Zika virus. 

As our world continues to warm, ENSO is likely to exacerbate climate issues by increasing the frequency and intensity of droughts and wildfires. Likewise, our changing climate will undoubtedly impact future ENSO events, too. While scientists are still exploring the complex interactions between climate change and the ENSO cycle, they predict strong El Niño and La Niña events might become more frequent, occurring every 10 years by the end of the 21st century. It’s also possible the strongest events could become several times stronger than those experienced today.