Hurricane Polo formed in the eastern Pacific off Mexico in late September 2026 and, in roughly 24 hours, exploded from a tropical storm into a top-of-the-chart Category 5 hurricane with winds above 252 kph (156 mph), per EL PAÍS.

The Associated Press reports it was the longest-lasting Category 5 storm ever recorded in the Pacific, spending two and a half days at that intensity — the second most powerful tropical cyclone recorded in the basin to date.

Polo later weakened before striking Baja California Sur as a Category 2 storm, leaving torrential rains, floods and infrastructure damage across northwest Mexico and the southwestern United States, with five deaths linked to flooding in Mexico.

The striking finding is the ordering: a joint rapid study by World Weather Attribution and Climate Central concluded that human-caused climate change, not the record-strength El Niño sitting under the storm, was the larger culprit in Polo's intensification.

The Associated Press reports that burning coal, oil and gas added about 6 mph (nearly 10 kph) to the storm's strength, while El Niño contributed a bit less, about 5 mph (8 kph).

Given how extreme this year's El Niño is, University at Albany atmospheric scientist Brian Tang said he was initially surprised by the result, though from a long-term standpoint it may not be so unexpected. The study, published October 14, has not yet been peer-reviewed.

Both research teams compared the real, warmed world with a hypothetical world that has not warmed by about 1.4 degrees Celsius since pre-industrial times.

They found climate change made the conditions feeding Polo roughly 23 times more likely, while El Niño made them 14 times more likely, according to EL PAÍS. The fuel was ocean water of 31.2°C (88°F) — as much as 2 degrees Celsius above normal, the Associated Press reports.

The two teams measured conditions somewhat differently and used different techniques but reached the same general conclusion, which strengthens confidence in the result, though outside scientists including Jeff Masters, Michael Mann and Carl Schreck told AP they think the study may understate warming's contribution.

The study did not focus on upper-level wind shear, where El Niño has a large footprint. In the Atlantic, El Niño typically increases the storm-decapitating high-altitude winds, but in the Pacific it decreases the winds that weaken storms.

Study co-author Daniel Gilford of Climate Central likened the setup to cars on a road: El Niño's wind shear acts as a green light in the Pacific saying go, and water warmed by both climate change and El Niño acts like a driver flooring the accelerator.

Climate scientist Friederike Otto, who coordinates the WWA team, said El Niño comes and goes but climate change only worsens, meaning every East Pacific hurricane now carries at least this warming signal.

Despite Polo's explosive strengthening at sea, human losses were limited thanks to a successful emergency response and because the storm struck a sparsely populated region, scientists noted in the EL PAÍS account.

Researchers emphasize that Polo would have been a monster storm even without the added influences, but every extra bit of wind speed can dramatically increase damage.

UN climate chief Simon Stiell said the El Niño phenomenon is already raising the risk level for the Pacific hurricane season, and that the study shows how climate change is increasing the danger and costs of storms as humanity keeps burning vast amounts of coal, oil and gas.

Early warning systems are being stressed as the key protection for events growing more frequent, more intense, or both.

The rapid study awaits peer review, the gold standard of science, and Gilford acknowledged it could be somewhat underestimating climate change's impact while being deliberately conservative.

This year, with a super-strong El Niño, has already set records for the strength and longevity of Pacific storms, and scientists say the relationship between El Niño and climate change remains under study with no clear conclusions about their links.

Still, as Imperial College London researcher Ben Clarke put it, every El Niño now happens in a warmer world.

Stiell's prescription: accelerate the transition to clean energy and invest in early warning systems and resilient infrastructure to protect people and economies exposed to these intensifying threats.