By SETH BORENSTEIN

WASHINGTON (AP) — The natural phenomena of El Niño and La Niña significantly influence global weather patterns, and they are both impacted by and contribute to the planet’s warming, according to meteorologists.

Recent research has delved into an unusual recent variation in the El Niño-La Niña cycle, shedding light on why Earth’s temperatures have soared to unprecedented levels over the past three years. This study offers insights into the ongoing scientific puzzle regarding the sudden spike in global temperatures already on the rise due to climate change.

In light of rapid climate shifts, scientists are revisiting how they define El Niño and La Niña events. The U.S. National Oceanic and Atmospheric Administration (NOAA) has amended its criteria for identifying these weather patterns, influenced by increasingly warm ocean waters worldwide. This alteration suggests a future where La Niña events might become more frequent, while El Niño occurrences may diminish.

In early 2023, Earth’s average monthly temperature experienced a notable increase, diverging from the long-standing upward trend linked to human-induced climate change, and this pattern persisted through 2025. Various theories attempt to explain this phenomenon, including a potential acceleration in greenhouse gas effects, decreased particle pollution from maritime activities, an underwater volcanic eruption, and heightened solar activity.

A recent publication in Nature Geoscience by Japanese scientists explores the concept of Earth’s energy imbalance—the discrepancy between energy entering and leaving the planet. In 2022, this imbalance intensified, leading to more heat being trapped and, consequently, rising temperatures. The study estimates that around 75% of the increase in this imbalance is due to a combination of ongoing human-induced climate change and the transition from a three-year cooling period dominated by La Niña to a warming phase with El Niño.

El Niño vs. La Niña

El Niño is a cyclical and natural warming of patches of the equatorial Pacific that then alters the world’s weather patterns, while La Niña is marked by cooler than average waters.

Both shift precipitation and temperature patterns, but in different ways. El Niños tend to increase global temperatures and La Niñas depress the long-term rise.

La Niñas tend to cause more damage in the United States because of increased hurricane activity and drought, studies have shown.

Why weather cycles switch from warm to cool

From 2020 to 2023, Earth had an unusual “triple dip” La Niña without an El Niño in between. In a La Niña , warm water sticks to a deeper depth, resulting in a cooler surface. And that reduces how much energy goes out into space, said study co-author Yu Kosaka, a climate scientist at the University of Tokyo.

She compared it to what happens when people have fevers.

“If our body’s temperature is high then it tends to emit its energy out, and the Earth has the same situation happening. And as the temperatures increase, it acts to emit more energy outward. And for three-year La Niña , it’s opposite,” Kosaka said.

So more energy — which becomes heat — is trapped on Earth, she said. La Niñas more typically correspond to a one- or two-year buildup of extra energy imbalance, but this time it was longer so the difference was more noticeable and included hotter temperatures, Kosaka said.

“When there is a transition from La Niña to El Niño , it’s like the lid is popped off,” releasing the heat, explained former NOAA meteorologist Tom Di Liberto, who’s now with Climate Central.

About 23% of the energy imbalance driving the recent higher temperatures comes from this unusually long La Niña pattern, with slightly more than half coming from gases from the burning of coal, oil and gas, the study authors said. The rest can be other factors.

Scientist Jennifer Francis of the Woodwell Climate Research Center, which wasn’t involved in the study, said the research makes sense and explains an increase in energy imbalance that some scientists were attributing to accelerated warming.

Changing how El Niños and La Niñas are labeled

For 75 years when meteorologists calculated El Niños and La Niñas , it was based on the difference in temperature in three tropical Pacific regions compared to normal. An El Nino was 0.5 degrees Celsius (0.9 degrees Fahrenheit) warmer than normal and La Nina was cooler than normal by the same amount.

The trouble in a warming world is what’s considered normal keeps shifting.

Until now, NOAA used the 30-year average as normal. It updated the 30-year average every decade, which is how often it updates most climate and weather measurements. Then the water warmed so much for El Niños and La Niñas that NOAA updated its definition of normal every five years, but that wasn’t enough either, said Nat Johnson, a meteorologist at NOAA’s Geophysical Fluid Dynamics Lab.

So NOAA came up with an El Niño index that’s relative, starting this month. This new index compares temperatures to the rest of Earth’s tropics. Recently that difference between the old and new methods has been as much as half a degree Celsius (0.9 degrees Fahrenheit), and “that’s enough to have an impact,” Johnson said.

That’s because what really matters with El Niños and La Niñas is the way the waters interact with the atmosphere. And recently the interactions didn’t match the old labeling, but they do match the new method, Johnson said.

This will likely mean a bit more La Niñas and fewer El Niños than in the old system, Johnson said.

Here comes another El Niño

NOAA’s forecast is for an El Niño to develop later this year in the late summer or fall. If it comes early enough, it could dampen Atlantic hurricane activity. But it would also mean warmer global temperatures in 2027.

“When El Niño develops, we’re likely to set a new global temperature record,” Woodwell’s Francis said in an email. “’Normal’ was left in the dust decades ago. And with this much heat in the system, everyone should buckle up for the extreme weather it will fuel.”

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