Will La Niña's cooling effect end early? Here's what scientists say

The current La Niña climate pattern that emerged in January is likely to be short-lived, with a 60 percent chance it will fade by May, according to an announcement on March 6 from the World Meteorological Organization (WMO).

Meanwhile, scientists are tracking an unexpected warming pattern called El Niño Costero or Coastal El Niño developing off the coast of Peru. This pattern could have far-reaching weather implications, including potential impacts on hurricane formation and global temperatures.

The WMO report indicates this shift could contribute to continued near-record global temperatures and might reduce the likelihood of another hyperactive Atlantic hurricane season.

An unexpected, rapid warming of ocean temperatures is occurring in the eastern Pacific. (Ben Noll/Data source: NOAA)

The developing coastal El Niño has already sent sea temperatures soaring to more than 5 degrees above average in the eastern Pacific, west of South America. This pattern differs from the well-known El Niño phenomenon but can still drive significant weather changes regionally and beyond.

"Excessive heat and unusual rainfall is typically experienced along the Peruvian Coast, where around 75 percent of the country's population reside," said Abraham Levy, director of a meteorological consulting firm in Peru.

The abrupt shift comes from a rapid change in wind patterns between January and February. According to scientists, winds went from stronger to much weaker, disrupting a process called upwelling, in which strong winds bring cold, subsurface ocean water to the surface.

La Niña, which typically has a cooling effect on global climate, has done little to break the cycle of excessive global heat that dominated during 2024 and has continued into 2025, except in the United States.

The warming off Peru is "somewhat independent" of the residual La Niña in the central equatorial Pacific, warned Ken Takahashi Guevara, a scientist at the Geophysical Institute of Peru.

The National Study of the El Niño Phenomenon (ENFEN), part of the Peruvian government, issued an "El Niño Costero Watch" last week. If elevated sea temperatures west of Peru persist for at least three months, an official El Niño Costero event will be declared.

Previous coastal El Niño events in 2017 and 2023 caused flooding rains and high rates of dengue fever in Peru. During early 2023, the phenomenon brought Peru its first cyclone in decades, followed by a dengue fever outbreak that killed nearly 400 people.

The 2023 event eventually expanded into a full-fledged El Niño that covered the tropical Pacific by the end of that year. However, current forecasts suggest a full El Niño is unlikely for 2025, with at most a one-in-five chance, according to the latest probabilities from the International Research Institute for Climate and Society.

The WMO stated the probability of full El Niño conditions emerging for the year's first half is negligible.

Levy noted that each coastal El Niño event has its unique impacts. If the event lasts until autumn in the Southern Hemisphere (March to May), it can affect fisheries and agriculture. Warm changes in coastal water temperatures can stress fish populations such as the Peruvian anchovy as they seek cooler, deeper waters.

While the coastal El Niño develops near South America, a pool of cooler-than-average seawater in the central Pacific continues to qualify as a La Niña. The WMO reports a 60 percent probability of conditions shifting to ENSO-neutral (neither El Niño nor La Niña) during this year's March-to-May period.

A lonely pool of cool water in the central Pacific Ocean continues to qualify as a La Niña as of early March. (Ben Noll/Data source: NOAA)

Takahashi suggested that La Niña may not have weakened as much as traditional metrics indicate because these measurements do not account for how much the Pacific Ocean has warmed in recent years and decades due to human-caused climate change. Without that warming influence, the central Pacific would be much colder, potentially signaling a stronger La Niña.

He acknowledged the pattern is fading but noted that effects on global weather "might not fade as fast as the traditional [La Nina] index might suggest." These effects could persist as long as key central and eastern Pacific regions remain cooler relative to other parts of the tropical ocean.

Marine heat waves continue to cover parts of all ocean basins, much like in late 2024 before La Niña officially arrived. This includes the rapidly warming area in the eastern Pacific where the coastal El Niño is developing.

Even as La Niña emerged earlier this year—later and weaker than expected—scientists warned that its cooling effects would not be enough to prevent 2025 from potentially becoming another warmest year on record.

The developing warm water pattern near South America could play a role in hurricane formation. During a typical La Niña, associated cool waters can reduce rainfall and thunderstorm activity in the tropical Pacific. As the atmosphere balances itself, this can lead to increased rainfall, thunderstorm activity, and winds conducive to hurricane formation in the tropical Atlantic.

However, as areas of warm water develop in the eastern Pacific, they can have a drying effect on the Atlantic, potentially reducing hurricane activity.

If the unexpected warming continues—and in the unlikely event it spreads across the Pacific—another near-record warm year is possible for the planet, despite the short-lived La Niña at the beginning of 2025.

According to Takahashi, the rapid warming off the coast of Peru is raising particular concern because it can bring massive rainfall to normally arid climates. In early 2017, a similar event triggered heavy rainfall, deadly flooding, and landslides that caused significant damage in Peru.

While predictive skill for El Niño and La Niña events—part of what is known as the El Niño-Southern Oscillation, or ENSO—has improved significantly in recent decades, it is not perfect, especially in the eastern Pacific where the current warming is taking place.

Based on model outlooks of sea surface temperature, there was little indication that such a rapid and dramatic warming was likely to occur, highlighting the challenges in forecasting these complex climate patterns.

Scientists continue to monitor the situation closely. The duration and intensity of the coastal El Niño will determine its impacts both regionally and globally, potentially affecting everything from local rainfall patterns to global temperature records and hurricane formation in distant ocean basins.