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La Niña is coming. This is how it could change the weather.

La Niña is coming. This is how it could change the weather.
La Niña is coming. This is how it could change the weather.

The planet is officially on alert for La Niña, the counterpart to the climate phenomenon El Niño, scientists said Thursday. The phenomenon could have a cooling effect on the ongoing record heat and will likely help spawn a series of major hurricanes in the Atlantic this fall.

The chance that La Niña will develop between August and October is 70 percent, and the chance that La Niña will occur this winter is nearly 8 in 10, scientists at the National Oceanic and Atmospheric Administration wrote in a weather forecast accompanying their La Niña warning.

The climate pattern associated with cool conditions in the Pacific would have ripple effects on regional weather extremes that are largely the opposite of what a strong El Niño pattern brought during its peak last winter. In the United States, it may produce droughts in some places and heavy snow in others; elsewhere, its most dangerous effects could be drought in East Africa and flooding in Indonesia.

However, there is some uncertainty about what impact this La Niña event might have, as it comes amid more than a year of record-high global average temperatures and unprecedented ocean surface warming.

Climate scientists will be watching closely to see whether the global cooling effect typical of La Niña plays out as usual — and if not, what sign it might be of how humans have altered Earth’s systems by burning fossil fuels and emitting planet-warming greenhouse gases.

“It will be interesting to see how this La Niña intersects with the generally very warm oceans,” said Nathan Lenssen, a climate scientist at the University of Colorado. “We are in truly uncharted territory globally.”

Here are answers to some frequently asked questions about La Niña and its impact on the planet.

What is La Niña?

La Niña is a global climate phenomenon in which cool waters from the depths of the eastern Pacific rise to the surface, creating a pool of cooler than normal water along the equator in the central and eastern Pacific. At the same time, stronger trade winds blow from east to west across the Pacific, driving warm surface water toward Asia and causing this colder water to rise in the east.

The pattern affects conditions around the world because it shifts the atmospheric forces that control weather patterns in the middle and upper latitudes. The contrast between the hot and stormy conditions in the western Pacific and the cooler-than-normal conditions in the central and eastern Pacific helps drive changes in the normal course of weather patterns such as heat waves and storm systems.

What does La Niña mean for global weather?

Some effects of La Niña may be imminent. The pattern is known for fueling tropical storm activity in the Atlantic. Among the changes it brings to atmospheric patterns is a reduction in wind shear – a difference in wind speed and direction at different altitudes – over the Atlantic basin, creating an environment more conducive to the organization and strengthening of tropical systems.

Due to the La Niña outlook, meteorologists this week revised upward a key forecast for hurricane season, now predicting a near-record 25 named storm systems, including 12 hurricanes and six “major” hurricanes of Category 3 or higher.

In the United States, La Niña is best known for warm and dry conditions throughout the southern part of the country during the winter—including Southern California, the Southwest, and the Gulf Coast—as well as wet and snowy conditions from the Pacific Northwest to the northern Plains.

Elsewhere in the world, the impacts could include flooding in northern South America and across Indonesia, and drought in East Africa – conditions that could exacerbate a famine amid civil war in Sudan.

What is the difference to El Niño?

El Niño is associated with warmer than average temperatures in the eastern and central Pacific Ocean. During El Niño, the trade winds are weaker than normal unless they reverse eastward, creating a cycle that causes warm surface water to pool in the eastern Pacific Ocean and warm it dramatically.

El Niño often ushers in La Niña episodes because it releases enormous amounts of heat from the eastern Pacific, allowing a rapid transition to the cooler conditions of La Niña.

How could this episode of La Niña be different?

Many parts of the world’s oceans experienced temperatures that exceeded expectations last year, including the western Pacific. This may be exacerbating the natural contrast between the hot waters on one side of the ocean and the cold waters on the other, amplifying an otherwise relatively mild La Niña episode, says Nathaniel Johnson, a NOAA scientist involved in La Niña forecasting.

“Due to the high temperatures in the western Pacific, this event could be of above-average magnitude,” said Johnson, a researcher at NOAA’s Geophysical Fluid Dynamics Laboratory.

Research is currently underway to determine whether climate change could alter the behavior of La Niña and El Niño, Lenssen said. El Niño, known to raise temperatures across the planet, last July helped push the planet to what scientists say are its hottest temperatures in more than 100,000 years — and closer than ever to a dangerous warming threshold of 1.5 degrees Celsius above pre-industrial temperatures.

Climate scientists will be closely watching whether and to what extent La Niña can counteract this acceleration of global warming.

How long will La Niña last?

La Niña usually lasts nine to twelve months, but can sometimes last three years. It is too early to say how long this phenomenon will last.

Currently, long-term climate models suggest that a period of so-called “neutral” conditions – the absence of El Niño or La Niña – could occur next, but those forecasts are far from reliable, Lenssen said. A two-year La Niña is “definitely possible,” he said.

The stronger the previous El Niño was, the longer a La Niña can last, Lenssen said. After an El Niño pattern became one of the strongest observed in the winter of 2015-16, weak La Niña conditions persisted for two years.

But amid a relatively weak and brief El Niño in 2018 and 2019, La Niña persisted for three years, from 2020 to 2023, in what climate scientists called a rare “triple-dip” La Niña.

This time, the planet is experiencing a historically strong El Niño phenomenon – although not quite as intense as the strongest episodes since weather records began, including 2015-2016, 1997-1998 and 1982-1983.

Why is it called La Niña?

The pattern’s name comes from a legend related to El Niño, a Spanish name meaning baby Jesus. Fishermen off the coast of Peru noticed periods of unusually warm water in the eastern Pacific, sometimes occurring in winter, that changed fishing conditions around Christmas. La Niña is simply the opposite of El Niño.

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