Bold opening: The science of El Niño and La Niña is shifting beneath our feet—and the data show that a warming world is remaking how these cycles behave. But here’s where it gets controversial: our labels may be changing faster than the weather itself, which could reshape how we understand climate patterns and plan for impacts.
A recent study reveals that the classic El Niño–La Niña cycle is being reshaped by overall warming, helping to explain why Earth’s average temperature surged to a new high over the last three years. In addition, rapid warming is forcing meteorologists to rethink how they label El Niño and La Niña due to faster-than-expected shifts in weather patterns. The U.S. National Oceanic and Atmospheric Administration (NOAA) has adjusted its calculation method for determining when the pattern flips into a new phase, a change driven by globally hotter oceans. This adjustment is likely to produce more La Niña events and fewer El Niño events in future assessments of tropical warming.
Why this matters: Earth’s average monthly temperature rose noticeably in early 2023 and stayed elevated through 2025, on top of the long-term warming trend caused by human activities. Scientists offer several explanations for this jump, including accelerated greenhouse gas forcing, reductions in ship-particle pollution, a volcanic eruption underwater, and fluctuations in solar output.
A Nature Geoscience study published this month analyzes Earth’s energy imbalance—the difference between incoming solar energy and the energy Earth emits back into space. The researchers find that this imbalance increased in 2022, meaning more heat is being trapped. They estimate that roughly three-quarters of the recent rise in energy imbalance results from the combination of long-term human-caused climate change and a shift from a three-year La Niña toward a warmer El Niño phase.
El Niño vs. La Niña: El Niño is a natural, cyclical warming of the equatorial Pacific that alters global weather patterns, while La Niña is characterized by cooler-than-average Pacific waters. Both disrupt precipitation and temperatures, but El Niño generally pushes global temperatures higher, whereas La Niña tends to temper the long-term warming trend. La Niña years have historically been linked to more U.S. weather extremes—more hurricanes and droughts in some cases—though the pattern is complex and varies by region.
Why the cycle flips from warm to cool: Between 2020 and 2023, the planet experienced an unusual three-year stretch without a traditional El Niño, instead seeing extended La Niña conditions. In a La Niña phase, warm surface waters retreat to deeper layers, reducing the amount of heat that escapes to space. This traps more energy in the climate system. As Yu Kosaka, a climate scientist at the University of Tokyo, explains, it’s like a fever: higher internal temperatures lead the body to emit more heat, and similarly, a warming Earth tends to lose more energy when the cycle shifts. When the transition from La Niña to El Niño occurs, the “lid” pops off, releasing stored heat and influencing global temperatures more abruptly. Former NOAA meteorologist Tom Di Liberto notes that the unusually long La Niña period contributed to a larger and more noticeable energy imbalance.
Impact and attribution: About 23% of the energy imbalance fueling the recent temperature rise came from this extended La Niña pattern, with a little over half attributed to fossil-fuel emissions (coal, oil, and gas). The remaining share involves other contributing factors. Jennifer Francis of the Woodwell Climate Research Center views the findings as a plausible explanation for the observed acceleration in warming, even though she wasn’t part of the study.
Rethinking labeling: For 75 years, El Niño and La Niña were defined by how much Pacific tropical temperatures differed from a long-running regional norm. The normal baseline was updated periodically, but the rapid ocean warming made those definitions less stable. NOAA shifted to a relative, Earth-wide tropical comparison to determine El Niño status, rather than a fixed regional benchmark. The change can swing classifications by as much as about 0.5°C (0.9°F), which matters because the climate-atmosphere coupling that drives these patterns depends on how temperatures interact with atmospheric processes.
Forecast and stakes: NOAA projects a new El Niño could emerge later this year, potentially dampening Atlantic hurricane activity while amplifying global temperatures in 2027. As Jennifer Francis notes, if El Niño develops, we’re likely to set another global temperature record. With heat already in the system, the coming years may bring more intense and frequent extreme weather events.
Thought questions for readers: Do you think updating the labeling approach is the right move if it helps forecast climate patterns more accurately, even if it adds confusion in the short term? Should policy and public communication align with the revised definitions, or should there be parallel frames to prevent public misunderstanding? Share your views on how these shifts should influence preparation and policy going forward.
