Pacific annular warming elevates the 2026/27 El Niño prediction

El Niño and La Niña climate patterns normally oscillate every two to seven years, influencing weather patterns worldwide. In the era of climate change, however, oscillations are becoming more pronounced and contribute to extreme weather across the globe.

El Niño and La Niña are climate patterns that reflect the relative surface temperature of the tropical Pacific Ocean: El Niño patterns occur when the waters are warmer than average, and La Niña temperatures are cooler than average. El Niño weakens trade winds, which alters atmospheric circulation. These changes can cause higher temperatures globally, drought patterns in parts of Australia and Southeastern Asia and excessive rainfall in both South America and the southern United States.

A team of researchers, using a state-of-the-art climate prediction system, is currently forecasting a super El Niño toward the end of 2026. The scientists suggest that rare and extreme surface annular, or ring-shaped, warming in the tropical Pacific during spring 2026 is playing a key role.

Their study is published in the journal Ocean-Land-Air Research on April 21.

“The tropical Pacific exhibits an unusual annular warming pattern in spring 2026, [which is] the largest [observed in the] past 40 years. The upper ocean [is also storing more heat than it is releasing]. We [show in] a set of model experiments that…the current heat content is [sufficient] to generate a moderate El Niño event toward the end of 2026, and the annular warming [we are currently observing in the Pacific c]ould…elevate this [El Niño] to the super category,” said Tao Lian, a professor from the Second Institute of Oceanography at the Ministry of Natural Resources in China.

The widespread impact of El Niño on the global climate greatly affects human society. It is widely accepted that the buildup of the upper ocean heat in the equatorial western Pacific precedes an El Niño by about six to nine months. Recent studies have also demonstrated that extreme warm sea-surface temperature anomalies in the off-equatorial Pacific modulate El Niño intensity considerably.

Some operational institutes alerted the potential occurrence of a super El Niño at the end of 2026 in March and April despite a lack of strong Pacific heat content in spring 2026. These forecasts were instead driven by an annular warming pattern that has developed in the tropical Pacific, characterized by strong warm sea surface temperature anomalies in the western tropical Pacific, northeastern tropical Pacific and southeastern tropical Pacific and has rarely been observed in history. The intensity of the pattern is the largest that has occurred in the past four decades.

To evaluate the potential impact of this unusual annular warming on the forthcoming El Niño, the researchers conducted a series of real-time forecast experiments. Their experiments showed that the current heat content buildup alone would generate a moderate El Niño toward the end of 2026. When the scientists add the influence of annular warming, the predicted El Niño sharply intensifies into the super category. Uncertainties arising from remote forces outside the tropical Pacific, as well as from rapid atmospheric fluctuations, were removed in the experiments to better estimate the impacts of heat content buildup and annular warming.

The team’s El Niño intensity predictions are insensitive to the initial conditions used in the experiments, suggesting that the forecasts are robust. “Our results are not simply a prediction of the upcoming event; rather, they provide an explanation for why climate models are likely to predict a super El Niño at present,” said Lian.

The team will continue refining their prediction through 2026. “High-frequency [atmospheric fluctuations] in spring and early summer play a crucial role in the intensity and structure of El Niño. [For example], we observed a strong westerly perturbation in late March, which means that the probability of a super El Niño is increasing,” said Dake Chen, senior researcher with the Second Institute of Oceanography.

Despite the robust nature of their predictions, the team acknowledges their predictions are subject to uncertainty due to inconsistencies between models, remote forces from the tropical Indian and Atlantic Oceans and the actual high-frequency fluctuations that will occur in the atmosphere. By definition, high-frequency atmospheric perturbations are unpredictable in climate models, and the short-term prediction skill for sea surface temperature in the tropical Indian Ocean and Atlantic remains relatively low across current generations of climate models.

"El Niño never ceases to surprise us," said Lian. "We can only anticipate its mysterious behavior based on known processes within current models and the boundaries of our understanding at hand."

The research team includes:

• Tao Lian and Dake Chen from the State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources; the Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai); and the School of Oceanography, Shanghai Jiao Tong University.

• Ruikun Hu and Jie Feng from the State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources.

• Ting Liu from the State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources; and the Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai).

• Youmin Tang from the College of Oceanography, Hohai University.

This research was supported by grants from the National Key Research and Development Program of China, the National Natural Science Foundation of China, and China Postdoctoral Science Foundation.