Scientists Redefine El Nino as Climate Change Alters Weather Patterns

New index aims to better track shifts in tropical Pacific temperatures and their global impacts.

Published on Feb. 21, 2026

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Meteorologists have had to update how they label the El Nino and La Nina weather patterns due to rapid changes caused by global warming. The U.S. National Oceanic and Atmospheric Administration has altered its calculation method, likely leading to more La Nina and fewer El Nino events being identified. Researchers also found that the unusually long La Nina period from 2020-2023 contributed significantly to the recent spike in global temperatures, accounting for about 23% of the increase in Earth's energy imbalance.

Why it matters

El Nino and La Nina events have major impacts on weather patterns worldwide, affecting precipitation, temperatures, and the frequency of extreme weather like hurricanes and droughts. As the climate continues to warm, these natural cycles are becoming more volatile and harder to define using traditional methods, requiring scientists to adapt their tracking and forecasting approaches.

The details

The new El Nino index developed by NOAA compares tropical Pacific temperatures to the rest of the Earth's tropics, rather than using a fixed 30-year average. This relative approach better captures how the ocean-atmosphere interactions have been changing. The researchers also found that the unusually long 3-year La Nina period from 2020-2023 contributed about 23% of the recent spike in global temperatures, by trapping more heat on Earth.

  • From 2020 to 2023, Earth experienced an unusual 'triple dip' La Nina without an El Nino in between.
  • NOAA updated its El Nino/La Nina definition this month to use a relative index rather than a fixed 30-year average.

The players

NOAA

The U.S. National Oceanic and Atmospheric Administration, the government agency that monitors and studies the Earth's oceans, atmosphere, and climate.

Yu Kosaka

A climate scientist at the University of Tokyo and co-author of the study on the impact of the recent La Nina period.

Jennifer Francis

A scientist at the Woodwell Climate Research Center who commented on the study's findings.

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What they’re saying

“When El Nino develops, we're likely to set a new global temperature record. '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.”

— Jennifer Francis (Email)

“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 Nina, it's opposite.”

— Yu Kosaka, Climate Scientist, University of Tokyo (Nature Geoscience)

What’s next

NOAA forecasts an El Nino to develop later this year in the late summer or fall, which could dampen Atlantic hurricane activity but also lead to warmer global temperatures in 2027.

The takeaway

As the climate continues to warm, the natural El Nino-La Nina cycle is becoming more volatile and harder to define using traditional methods. Scientists have had to adapt their tracking and forecasting approaches, including NOAA's new relative index, to better capture how these ocean-atmosphere interactions are changing and their cascading global impacts.