Washington: A new study finds that climate change and El Niño combined to intensify Hurricane Polo, which was the longest-lasting Category 5 storm ever recorded in the Pacific. Global warming had the greater influence of the two, adding nearly 10 kph to the hurricane’s wind speed, compared with about 8 kph from El Niño, according to a joint study published on Thursday by the science teams World Weather Attribution and Climate Central.
Climate change made the conditions that fuelled the hurricane 23 times more likely, while El Niño, the natural and temporary warming of parts of the Pacific, made them 14 times more likely, the study found. The conditions were linked to sea surface temperatures of 31.2 degrees Celsius, as much as 2 degrees Celsius above normal.
This year, with an exceptionally strong El Niño, has set records for the strength and longevity of Pacific storms. Polo set a record for time spent at Category 5 intensity in the Pacific, remaining at that strength for two and a half days.
“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 who coordinates the international science team behind World Weather Attribution.
“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.
Researchers found that Polo would have been a powerful storm even without climate change and El Niño. However, every additional increase in wind speed can dramatically increase the damage caused by a hurricane.
Decoding Polo's rapid strengthening
Although Hurricane Polo weakened considerably before hitting a sparsely populated part of Mexico, scientists remain interested in how rapidly it intensified from a tropical storm into a Category 5 hurricane in about 24 hours.
The study helps put the different atmospheric influences into perspective, said Kristina Dahl, a climate scientist and vice-president of science at Climate Central, a science and journalism non-profit based in New Jersey.
“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,” she said.
The study examined the warm ocean water that fuels storms, using a measure of their potential intensity. However, it did not focus on upper-level wind shear, where El Niño has a significant influence.
El Niño typically increases high-altitude winds that can weaken storms in the Atlantic. In the Pacific, however, changes in wind patterns mean El Niño reduces the winds that weaken storms.
The two research teams measured conditions slightly differently and used different techniques, but reached the same general conclusion, increasing their confidence in the findings. However, the rapid study has not yet undergone peer review, the scientific process considered a key standard for evaluating research.
To calculate the impact of climate change on Polo, both teams used the scientifically accepted method of comparing conditions in the warmer real world with those in a hypothetical world that has not warmed by 1.4 degrees Celsius since pre-industrial times.
How El Niño and climate change interact
Study co-author Daniel Gilford, a Climate Central scientist, compared the process examined by researchers to cars travelling on a road. Wind shear associated with El Niño can act like a red light in the Atlantic or a green light in the Pacific. In the Pacific, the green light allows storms to intensify, while ocean waters warmed by climate change and El Niño act like a driver pressing the accelerator.
University at Albany atmospheric scientist Brian Tang, who was not involved in the study, said he was initially surprised that researchers found climate change to have a greater influence on Polo, “given how extreme this El Niño is, but from a long-term standpoint, perhaps the result isn't as surprising as it might seem.”
However, three other outside scientists, Jeff Masters of Yale Climate Connections, the University of Pennsylvania's Michael Mann, and North Carolina State University's Carl Schreck, said they believed the study underestimated the extent to which climate change had strengthened Polo.
Masters pointed to a 2024 study by Gilford that found climate change had added 30 kph to hurricanes in the Atlantic between 2019 and 2023.
Gilford acknowledged that Thursday's report might underestimate climate change's impact to some extent, but said he had accounted for other conditions and taken a conservative approach.