Climate change made Hurricane Helene more powerful, rainier, and significantly more likely. And as temperatures continue to warm, the U.S. can expect more storms like Helene in the future.
Those are the findings of a study released Wednesday by researchers with World Weather Attribution, an international network of scientists who conduct rapid studies to assess the impact of climate change on major weather events.
The study found that rainfall from Helene was about 10% heavier due to human-caused climate change. That’s a massive amount of additional precipitation, and similar to other damaging, climate-fueled hurricanes in the past decade, like Hurricanes Harvey and Ian.
Climate change also made such heavy rainfall up to 70% more likely in central and southern Appalachia, where catastrophic flooding washed away roads, destroyed homes and businesses, and left thousands of people still without power two weeks later. So far, 230 people have died from the storm, though the true human toll will take years to fully determine.
“We found that essentially all aspects of this event [were] amplified by climate change to different degrees,” says Ben Clarke, an extreme weather researcher at Imperial College, London, and an author of the study. “We'll see more of the same as the world continues to warm.”
Many of those same conditions are now fueling Hurricane Milton, which is currently headed toward Florida as a major, life-threatening storm.
Warmer ocean temperatures drive more powerful storms
A key factor in Helene’s intensity was extraordinarily high water temperatures in the Gulf of Mexico. Sea surface temperatures reached about 85 degrees Fahrenheit as Helene was forming.
Such temperatures were 200 to 500 times more likely because of climate change, the study found.
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Warmer ocean temperatures are perhaps the most important driver of more powerful storms, says Michael Wehner, a climate scientist at the Lawrence Berkeley National Laboratory who was not involved in the WWA study.
“It's all about sea surface temperatures, at the end of the day,” Wehner says.
Wehner worked with a team on a similar analysis to fingerprint the impact of climate change on the storm, using different statistical techniques. His team found that climate change could have boosted Helene’s rainfall by up to 50% along parts of its pathway.
When ocean waters are hotter, storms can suck up additional moisture. That drives heavier rainfall – but it also acts as a power source for the storm: when water turns from vapor to liquid, it releases energy.
That, in turn, drives even more rainfall and potentially allows a storm to travel further inland.
“Simply put, the storm is more violent,” Wehner says.
Hurricane Helene eventually unleashed more than two feet of rain on some towns in North Carolina. Such an event would have been very unlikely without the 1.3 degrees Celsius (1.8 degrees Fahrenheit) of warming from human-caused climate change, the WWA analysis found.
Communities need to prepare for more intense storms
As warming continues, storms like Helene will become more common, the WWA analysis found.
Communities need to prepare for more intense storms in the future – even communities well outside historical hurricane zones, says Julie Arrighi, an author of the study and director of programs at the Red Cross Red Crescent Climate Centre.
“We need to really be adapting and preparing for these unprecedented, very extreme events,” Arrighi says.
Ultimately, the only way to head off more storms like Helene is to limit global warming, says Bernadette Woods Placky, chief meteorologist for Climate Central, who worked on the WWA analysis.
“We know what's causing these increases,” Woods Placky says. “And we know if we don’t accelerate climate action, storms are only going to get stronger, wetter, and more frequent.”
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