September 2023

Iowa, El Niño, and La Niña

This article is part of our series focused on the causes and consequences of a warming planet

You may have heard these terms bantered about in the media. They have strange names and impact our weather. Let’s take a look at El Niño and La Niña and how they impact us.

Before we start, let's describe how these events got their names. During the 1700s, fishermen, living on the coast of Peru, noticed the periodic onset of a warm and wet period. They named it "El Niño de Navidad" because it often began in December, around the time of Christmas. The people called the phenomenon El Niño (pronounced El Neenyo) which means "the boy child" in reference to the birth of Jesus. Later, the other event was named La Niña (pronounced La Neenya) which means "the girl child."

They are both intermediate climate phenomenon that originate in the Pacific Ocean around the equator. It is a cycle of warm El Niño and cool La Niña episodes that happen every three to seven years. It is the most dramatic year-to-year variation of the Earth’s climate system, affecting weather conditions around the world.

The two are related but cannot occur at the same time because they are the opposite of each other. There are also times when neither exist.

At the equator, trade winds blow from east to west (the opposite of here in Iowa where they blow from west to east). The trade winds are impacted by high pressure systems in the Pacific. When El Niño occurs, the trade winds weaken (or even reverse) causing the eastern Pacific next to South America to warm up more than usual and bring rainfall to the dry South American west coast. Conversely, when La Niña occurs, trade winds strengthen, pushing the warm Pacific surface water westward which causes an upwelling of deep, cold water in the eastern Pacific off the cost of South America to fill the void. The impact of El Niño is shown in Figure 1 and La Niña in Figure 2.

Figures 1-2 El nino and la nina events.

El Niño can form when ocean temperature is above average by about one degree or more. Conversely, La Niña can form when ocean temperature is below average by one degree or more. When ocean temperature is normal, neither develops.

The warm water in the Pacific Ocean transfers heat into the atmosphere through convection (warm-moist air rising from the ocean causing the forming of thunderstorms). Where this occurs is important. Warm water in the east from El Niño causes thunderstorms in the east. Warm water in the west from La Niña causes the thunderstorms to occur in the west.

These changes in atmospheric circulation can impact weather systems around the Earth. Each phase causes predictable disruptions of temperature, precipitation, and winds in the tropical Pacific Ocean. These disruptions trigger a cascade of global side effects.

Current conditions

The world has just experienced the end of three consecutive years of La Niña that ended last March. This is shown by the three years of moderate temperatures and drought conditions in the Midwest. Three years of La Niña is rare and there is some evidence that it may have been impacted by climate change. This period was followed in June, by a switch to El Niño which led to warmer conditions. El Niño, when combined with climate change, has led to record breaking temperatures in many parts of the world, including the United States.

Impact of climate change

As human-caused climate change disrupts weather patterns around the world, one overarching question is how will it affect El Niño/La Niña. One manifestation is that strong El Niño and La Niña events are becoming stronger and more frequent. There is high likelihood that these variations have increased in amplitude by up to 10% since 1960 due to the observed rise in greenhouse gas concentrations in the atmosphere. This amplified cycle translates to more extreme and frequent droughts, floods, heat waves, wildfires, and severe storms.

These variations are likely to become even stronger (by 15-20%) later this century if atmospheric greenhouse gas concentrations continue to rise.

For farmers and other Iowans, stronger and more frequent El Niño/La Niña events will cause more volatile weather extremes. Learning to cope with this volatility will be challenging.

See the Ag Decision Maker website for more from this series.


Don Hofstrand, retired extension agricultural business specialist, agdm@iastate.edu

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Don Hofstrand

retired extension agricultural business specialist
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