Human-caused climate change played at least as large a role as El Niño in creating the conditions that helped Hurricane Polo reach extraordinary strength over the eastern Pacific Ocean, according to a new scientific analysis published on October 15, 2026.
The research found that global warming made the extreme oceanic and atmospheric conditions associated with Polo approximately 23 times more likely, while El Niño increased their likelihood by a factor of about 14 under a different comparison. The findings offer new insight into how long-term climate warming and natural climate variability can combine to influence exceptionally powerful hurricanes.
The analysis, conducted by international researchers associated with World Weather Attribution and Climate Central, examined the conditions surrounding Polo's explosive intensification in September 2026. Crucially, the results describe the likelihood of environmental conditions favorable for extreme hurricane intensity—not the probability of Hurricane Polo itself forming or reaching Category 5.
What the Study Found About Climate Change and El Niño
In its October 15 attribution analysis, World Weather Attribution examined a meteorological measurement called potential intensity, which estimates the maximum wind speed that environmental conditions could theoretically support.
By combining observational data with climate models, researchers estimated that human-induced warming made environmental conditions as favorable as those surrounding Polo about 23 times more likely than they would have been in a climate without human-caused warming. The same analysis estimated that global warming increased potential intensity by approximately 5 meters per second, or 11 mph.
El Niño also contributed substantially. Compared with neutral El Niño–Southern Oscillation conditions in the present climate, the researchers estimated that the prevailing El Niño increased the likelihood of similarly extreme potential-intensity conditions by approximately 14 times. Its estimated contribution to potential intensity was about 4.2 meters per second, or 9 mph.
These figures use different reference conditions and cannot be directly interpreted as each factor's percentage contribution to the hurricane. Nor should the likelihood multipliers be multiplied together to calculate the probability of a Category 5 storm.
A complementary analysis estimated that human-caused climate change increased Polo's actual peak wind speed by approximately 2.7 meters per second, equivalent to about 6 mph. That result is distinct from the larger estimates describing changes in theoretical potential intensity.
How Hurricane Polo Became a Category 5 Storm
Polo developed into a tropical depression on September 20, 2026, before intensifying rapidly over the eastern Pacific. By September 22, the storm had reached Category 5 strength, the highest classification on the Saffir-Simpson Hurricane Wind Scale.
According to the National Hurricane Center's advisory records, Polo's maximum sustained winds increased by approximately 90 knots—about 104 mph—within 24 hours. An advisory issued on September 22 reported sustained winds of 165 mph, with subsequent aircraft observations indicating even greater intensity.
Polo remained exceptionally powerful for several days, fluctuating between Category 4 and Category 5 strength. The Associated Press reported that its cumulative time at Category 5 established a Pacific record of approximately two and a half days.
Exceptionally warm ocean conditions helped support the storm. NASA Earth Observatory documented sea-surface temperatures reaching approximately 32°C (90°F) along parts of Polo's development region, around 2–3°C above the usual temperature for September 23.
However, ocean warmth was not the only ingredient. Weak vertical wind shear, abundant atmospheric moisture, favorable upper-level outflow and high ocean heat content also supported rapid intensification. El Niño can alter these conditions through changes in tropical atmospheric circulation, sometimes making the eastern Pacific more favorable for hurricane development.
Polo eventually weakened before striking Baja California Sur around September 28–29 as a Category 2 hurricane. It subsequently reached mainland Mexico east of Guaymas as a Category 1 storm. Although its strongest winds remained offshore, the hurricane caused flooding, infrastructure damage and disruptions in affected communities.
How Scientists Measured the Influence of Global Warming
To investigate climate change's contribution, researchers compared conditions observed in the modern climate with estimates of conditions in a hypothetical world without human-induced global warming. They examined sea-surface temperatures, atmospheric properties and potential intensity using observational records and climate-model simulations.
Ocean-temperature observations formed an important part of the evidence. NASA's Multiscale Ultrahigh Resolution Sea Surface Temperature dataset combines satellite measurements with observations from ships and ocean-monitoring buoys. These records help scientists identify unusually warm waters and compare temperatures with historical reference periods. NASA's September 23 temperature-anomaly analysis, for example, used a 2003–2014 reference period, distinct from the preindustrial baseline used in climate-attribution estimates.
The attribution team estimated that the waters Polo crossed before reaching peak strength were approximately 1.4°C warmer than they would have been in a preindustrial climate. Its analysis indicated that sea-surface temperatures this high had become dramatically more likely because of human-caused warming.
Researchers also compared observed and modeled changes in potential intensity across the eastern Pacific. Although the observational record showed a stronger historical increase than many models, both lines of evidence supported an increase associated with climate change.
The different approaches provided complementary evidence, but they did not amount to independent experimental proof of exactly how much each environmental factor strengthened Polo. Tropical cyclones result from interacting atmospheric and oceanic processes, making precise attribution of an individual storm inherently challenging.
What the Research Cannot Yet Explain
The October 15 analysis was a rapid attribution study and had not undergone peer review at the time of publication. Its findings therefore remain open to further scientific scrutiny, even though the researchers used established attribution techniques.
One important limitation concerns rainfall. Observational datasets suggested substantial historical increases in extreme rainfall across the study region, but the climate models did not adequately reproduce those trends. Consequently, researchers could not reliably quantify how much human-caused climate change contributed to Polo's rainfall.
The analysis also did not comprehensively isolate the influence of upper-level wind shear, an important factor in determining whether tropical cyclones strengthen or weaken. As AP's reporting noted, several independent scientists suggested that the study might underestimate climate change's contribution, although that interpretation has not been established as a correction to its results.
These uncertainties do not invalidate the findings. Instead, they define what the available evidence supports and where more detailed research is needed.
What Polo Reveals About Future Hurricane Risks
Hurricane Polo illustrates how exceptionally warm oceans can raise the potential intensity of tropical cyclones while interacting with shorter-term climate patterns such as El Niño.
As greenhouse gas concentrations increase, warmer ocean waters and atmospheric conditions can provide more energy and moisture for powerful storms. Nevertheless, the actual intensity of an individual hurricane also depends on wind shear, internal storm structure, ocean heat beneath the surface and other environmental influences.
Polo's impacts further demonstrate why peak wind speed alone cannot determine disaster severity. The storm weakened before reaching relatively sparsely populated areas, while flooding and other hazards continued to affect communities away from its most intense winds.
The new research strengthens the evidence that human-caused warming can substantially influence conditions supporting extreme tropical cyclone intensity. It does not establish that every future hurricane will intensify at Polo's extraordinary rate. Understanding that distinction is essential as scientists investigate how a warming climate may alter hurricane hazards and the risks faced by coastal communities.
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