The rains and winds of the hurricane Helenewhich ravaged the southeast of the United States at the end of September and left more than 230 dead, were made approximately 10% more intense by climate change, according to the study by a reference scientific network published Wednesday.
Even if this figure of 10% “may seem relatively low, it is very important to emphasize […] that a small change in danger can really lead to a big change in impact and damage,” said Friederike Otto, head of the World Weather Attribution (WWA) network.
This work also shows that fossil fuels – the main culprits of global warming – have made hurricanes like Helene 2.5 times more likely in this region.
In other words, instead of being expected every 130 years, they are now likely to occur every 53 years on average.
To study Helenescientists focused on three distinct aspects: precipitation, winds and water temperature in the Gulf of Mexico – a key factor in its formation.
“All aspects of this event have been amplified by climate change to varying degrees,” Ben Clarke, study co-author and researcher at Imperial College London, told a news conference.
“And we will see more such phenomena as the planet continues to warm,” he added.
The study comes as the state of Florida prepares for the expected arrival of a new major hurricane on Wednesday, Miltononly ten days after being hit by Helene.
Destroyers
Helene made landfall on September 26 in northwest Florida, with winds gusting to 225 km/h. The hurricane then progressed northward, triggering torrential rains inland in several states, notably in North Carolina where it caused the most victims.
The authors of the study highlighted this now increased risk beyond just coastal areas.
Helene “was so powerful” that losing that energy took time, and the hurricane “was moving fast […] so it was able to sink quickly inland,” explained Bernadette Woods Placky, meteorologist at the NGO Climate Central.
The WWA regularly assesses the link between extreme weather events around the world and climate change. The study here was carried out by scientists from the United States, the United Kingdom, Sweden and the Netherlands.
They relied on three methods to study the three chosen aspects.
For rainfall, they used an approach based on both observations and climate models, differentiating between two regions: the Appalachian mountains inland, and coastal areas, particularly in Florida.
In both cases, according to the study, precipitation has been increased by 10% due to global warming, which already amounts to 1.3°C compared to the pre-industrial era.
For winds, which are particularly difficult to study for such brief events, the chosen approach uses hurricane data since 1900.
Result: the windsHelene were 11% louder – or 21 km/h – because of climate change, the study concludes.
Finally, the researchers looked at water temperatures in the Gulf of Mexico, where Helene formed, which was approximately 2°C above normal.
This record temperature was made 200 to 500 times more likely by climate change, they say.
However, warmer oceans release more water vapor, which provides additional energy to storms.
“If humans continue to burn fossil fuels, the United States will face even more destructive hurricanes,” Ben Clarke warned.