A recent study and evolving scientific observations highlight how the natural El Niño climate cycle is interacting with human-driven global warming to influence worldwide weather patterns and the planet’s rising temperatures. Meteorologists and climate scientists explain that while El Niño and its counterpart La Niña have long been known to affect precipitation and temperature patterns around the globe, their behavior and impact are now being altered by a warming world, creating new challenges for forecasting and understanding climate trends.
El Niño and La Niña are cyclical phenomena originating in the tropical Pacific Ocean. El Niño is characterized by periodic warming of ocean surface waters along the equator, which tends to raise global temperatures and shift weather patterns, while La Niña involves cooler-than-average tropical Pacific waters, generally producing the opposite effects and temporarily suppressing global temperature rise. These cycles typically alternate every few years, shaping weather extremes such as droughts, floods, and hurricanes across the globe.
However, from 2020 to 2023, Earth experienced an unusual “triple dip” La Niña—three consecutive years of La Niña conditions without a return to El Niño in between. According to Yu Kosaka, a climate scientist at the University of Tokyo and co-author of a new study published in Nature Geoscience, this extended La Niña period contributed to an increased “energy imbalance” on Earth. The term “energy imbalance” refers to the difference between incoming energy from the sun and outgoing heat energy radiated back into space. Normally, when the Earth’s surface warms, it emits more energy outward, helping to regulate temperature. But during this prolonged La Niña, more heat became trapped in the Earth system because the cooler surface waters reduced the amount of heat escaping into space.
Kosaka likened the process to a human fever: when a person’s body temperature rises, it emits more heat outward; but in this case, the extended La Niña phase suppressed that outward emission, allowing more heat to accumulate in the Earth’s atmosphere and oceans. This unusual phenomenon meant that more energy was held within the climate system for a longer period than usual, contributing to a sharp jump in global average temperatures starting in early 2023 and continuing through 2025.
The study estimates that roughly three-quarters of the recent increase in Earth’s energy imbalance can be attributed to the combined effects of long-term human-caused climate change and the transition from the prolonged La Niña to the warming El Niño phase. About 23% of this imbalance stems directly from the extended La Niña event, while just over half is linked to greenhouse gases released by burning fossil fuels such as coal, oil, and natural gas. The remainder arises from other factors, including variations in solar activity, volcanic eruptions, and changes in atmospheric particles.
El Niño and La Niña cycles have profound implications for weather extremes and natural disasters, especially in the United States. La Niña phases tend to increase hurricane activity in the Atlantic and exacerbate drought conditions in various regions, often causing more damage. Conversely, El Niño usually suppresses hurricane formation but leads to warmer global temperatures. The recent extended La Niña phase was unusual and is believed to have contributed significantly to recent climate anomalies.
In addition to clarifying the role of the El Niño and La Niña cycles in recent global warming trends, scientists have had to rethink how these phenomena are defined and classified. For the past 75 years, meteorologists identified El Niño and La Niña events based on sea surface temperature anomalies in specific tropical Pacific regions, using a fixed baseline of what constituted “normal” temperatures. If temperatures were 0.5 degrees Celsius (about 0.9 degrees Fahrenheit) warmer than average, the event would qualify as El Niño; if cooler by the same margin, it would be La Niña.
However, the problem in today’s warming world is that the baseline itself is shifting—the ocean is warming overall, making it harder to determine what truly counts as an El Niño or La Niña event. Historically, the National Oceanic and Atmospheric Administration (NOAA) used a 30-year average to define “normal” tropical Pacific temperatures, updating this average every decade. But as oceans warmed rapidly, NOAA shortened that update period to every five years. Even that proved insufficient to account for the changing baseline, according to Nat Johnson, a meteorologist at NOAA’s Geophysical Fluid Dynamics Laboratory.
To address this, NOAA introduced a new, relative El Niño index starting in June 2024. Instead of comparing tropical Pacific temperatures