Scientists Revise El Niño Scale as Global Heat Surges

Villagers collect water from a temporary borehole in Mudzi, Zimbabwe, on Tuesday, July 2, 2024. The United Nations food agency says months of drought across southern Africa, driven by the El Niño weather phenomenon, have severely affected more than 27 million people and triggered the region’s worst hunger crisis in decades.

Climate scientists say the natural El Niño cycle, a major driver of global weather patterns, is both shaping and being reshaped by a rapidly warming planet.

A new study indicates that unusual shifts in the El Niño–La Niña cycle may help explain why global temperatures have spiked sharply over the past three years. Researchers also report that long-standing definitions of these climate phases are being updated as ocean conditions change under the pressure of human-driven warming.

The National Oceanic and Atmospheric Administration (NOAA) recently revised how it determines when the Pacific Ocean switches between El Niño and La Niña. Persistently warmer seas have prompted scientists to adopt a new method that compares Pacific temperatures with the rest of the tropics rather than relying on an older fixed baseline. The change is expected to result in more events being classified as La Niña and fewer as El Niño, even as ocean temperatures remain high.

Earth’s average monthly temperature surged above the long-term warming trend in early 2023 and stayed elevated through 2025. Scientists point to several possible contributing factors, including accelerating greenhouse gas emissions, reduced air pollution from shipping, an underwater volcanic eruption and increased solar activity.

Research published in the journal Nature Geoscience found that the planet’s “energy imbalance” — the difference between incoming solar energy and outgoing heat — rose significantly in 2022. This meant more heat was being trapped in the climate system. About three-quarters of that increase was linked to long-term climate change combined with a shift from a prolonged La Niña cooling phase to a warming El Niño.

El Niño refers to the periodic warming of surface waters in the equatorial Pacific Ocean, which tends to raise global temperatures and disrupt weather patterns worldwide. Its counterpart, La Niña, features cooler waters that can temporarily slow global warming but intensify extremes such as hurricanes and droughts in some regions.

Between 2020 and 2023, the world experienced a rare “triple-dip” La Niña lasting three consecutive years. Scientists say this prolonged cooling phase allowed excess heat to accumulate in the oceans. Roughly 23 percent of the recent energy imbalance has been linked to this event, while more than half stems from greenhouse gases produced by burning fossil fuels.

NOAA scientists now forecast that another El Niño could develop later this year. Such a shift may reduce Atlantic hurricane activity but is likely to push global temperatures even higher, potentially setting new heat records by 2027.