WASHINGTON – Climate change and El Niño worked together to intensify Hurricane Polo, a new study says, helping fuel the Pacific’s longest-lived Category 5 storm on record.
Human-caused global warming, driven by the burning of coal, oil and gas, played the larger role. It added roughly 6 mph (nearly 10 kph) to Polo’s already extreme winds, according to a joint analysis released Thursday by World Weather Attribution and Climate Central. El Niño contributed about 5 mph (8 kph), one of the study’s authors said.
The researchers found that climate change made the conditions behind the hurricane 23 times more likely, while El Niño made them 14 times more likely. The key factor was exceptionally warm ocean water: temperatures reached about 88 degrees Fahrenheit (31.2 degrees Celsius), as much as 3.6 degrees Fahrenheit (2 degrees Celsius) above normal.
A particularly powerful El Niño has helped make this year exceptional for Pacific hurricanes, setting records for both intensity and duration. Polo remained a Category 5 storm for two and a half days, the longest such stretch ever recorded in the Pacific.
“El Niño and climate change both made this hurricane stronger than it would have otherwise been, but the effect of climate change is even bigger than the one of El Niño,” said climate scientist Friederike Otto, a study co-author and coordinator of the international World Weather Attribution team.
“El Niño comes and goes, but climate change only gets worse. That means that now every hurricane that will occur in the East Pacific has at least this climate change signal making it stronger. And as long as we keep burning fossil fuels, that will only get bigger,” Otto added.
Even without the influence of climate change and El Niño, Polo would have been a formidable hurricane, the researchers said. Still, small increases in wind speed can produce a major escalation in storm damage.
Decoding Polo’s rapid strengthening
Polo weakened substantially before reaching a sparsely populated area of Mexico. But its explosive development continues to draw scientific attention: in roughly 24 hours, the storm surged from a tropical storm into a top-tier Category 5 hurricane.
Kristina Dahl, a Climate Central climate scientist and vice president of science, said the analysis helps clarify the relative influence of the competing atmospheric factors.
“It’s a powerful reminder that even though El Niño right now is shifting hazards around the globe and changing where it’s flooding and getting dry, the really dominant signal behind all of this remains climate change,” said Dahl, whose New Jersey-based organization combines scientific research and journalism.
IN CASE YOU MISSED IT: It's Final: Sweden Officially Joins NATO – NewsFinale
The researchers examined the unusually warm water that supplies hurricanes with energy, focusing on a measure of storms’ potential strength. They did not analyze upper-level wind shear, another area where El Niño has a significant effect. In the Atlantic, El Niño generally strengthens the high-altitude winds that can tear hurricanes apart. In the Pacific, however, shifting wind patterns associated with the climate pattern tend to reduce that weakening shear.
The two research groups used somewhat different measurements and analytical methods, yet reached broadly similar conclusions—an agreement that increased their confidence in the findings. The rapid assessment has not undergone peer review, however, the standard process used to evaluate scientific research.
To estimate climate change’s contribution to Polo, both teams compared the storm’s behavior in today’s warmer world with conditions in a hypothetical world that had not experienced 2.5 degrees Fahrenheit (1.4 degrees Celsius) of warming since the pre-industrial era. This approach is widely accepted in climate attribution studies.
How El Niño and climate change interact
Daniel Gilford, a Climate Central scientist and study co-author, compared the interaction to traffic. El Niño-driven wind shear can act as a red light in the Atlantic or a green light in the Pacific. In the Pacific, that green light allows storms to strengthen, while ocean temperatures elevated by both El Niño and climate change function like a driver pressing down on the accelerator.
Brian Tang, an atmospheric scientist at the University at Albany who was not involved in the research, said he was initially surprised that climate change emerged as the stronger influence on Polo. The result seemed unexpected “given how extreme this El Niño is, but from a long-term standpoint, perhaps the result isn’t as surprising as it might seem.”
Three other outside scientists—Jeff Masters of Yale Climate Connections, Michael Mann of the University of Pennsylvania and Carl Schreck of North Carolina State University—said they believe the study may understate climate change’s contribution to Polo’s strength. Masters cited a 2024 study by Gilford that estimated climate change added 16 mph (30 kph) to Atlantic hurricanes between 2019 and 2023.
Gilford said he recognized that Thursday’s analysis might slightly underestimate the effect of climate change, but explained that the researchers accounted for other conditions and deliberately used a conservative estimate.
___
The Associated Press’ climate and environmental coverage receives financial support from multiple private foundations. AP is solely responsible for all content. Find AP’s standards for working with philanthropies, a list of supporters and funded coverage areas at AP.org.
Copyright 2026 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed without permission.