Scientists Say: El Niño and La Niña

El Niño and La Niña together make up one of the most important climate cycles on Earth

La Niña is a weather disturbance that brings heavy rains to Asia, Australia and other parts of the western Pacific Ocean. During a La Niña event in 1999, downpours caused this mudslide in Antipolo, in the Philippines.

JAY DIRECTO/Stringer/Getty Images

El Niño (noun, “El NEEN-yo”), La Niña (noun, “Lah NEEN-yah”)

El Niño and La Niña are disturbances in Earth’s climate. These events generally take turns happening every few years. Each one lasts about nine to 12 months. Together, El Niño and La Niña make up a natural cycle called ENSO. That’s short for the El Niño-Southern Oscillation. This climate cycle can shake up weather around the world.

El Niño and La Niña both arise from unusual conditions in the Pacific Ocean. Usually, strong winds blow from east to west across the ocean near the equator. This breeze sweeps warm surface water near the Americas toward Asia. Cool water from the deep sea then wells up in the eastern Pacific, near the Americas.

El Niño occurs when those westward (from east to west) winds are weaker than normal. Instead of flowing westward, warm water flows eastward, across the Pacific. That makes the ocean water near Asia chilly and the water near the Americas toasty. Because more rain clouds form over warmer seawater, El Niño tends to dump heavy rains on South and Central America. Meanwhile, Southeast Asia and Australia often suffer droughts. Those regions may also catch fire more easily.

The opposite of El Niño is La Niña. It occurs when westward winds in the tropical Pacific are very strong. The winds drag lots of warm water toward Asia, cooling the eastern Pacific. Australia and Southeast Asia get heavy rainfall. Central and South America are more likely to face droughts.

The ENSO cycle upsets the airflow in Earth’s atmosphere in a big way. This affects the movement of heat and moisture worldwide. As a result, these events can trigger weird weather far beyond the Pacific. El Niño has been linked to snow storms across the southern United States. And La Niña is known to whip up more hurricanes in the Atlantic Ocean.

Such unusual weather patterns can put food production, water supplies and people’s safety at risk. That makes ENSO one of the most important features of Earth’s climate. And it may become more important, if human-caused climate change makes ENSO events more extreme and erratic.

In a sentence

El Niño and La Niña may be born in the Pacific Ocean, but their effects are felt around the world.

Check out the full list of Scientists Say.

Maria Temming is the assistant editor at Science News for Students. She has bachelor's degrees in physics and English, and a master's in science writing.

More Stories from Science News for Students on Climate