Human-caused climate change boosted a devastating Hurricane Helene 's rainfall by about 10% and intensified its winds by about 11%, scientists said in a new flash study released just as a strengthening Hurricane Milton threatens the Florida coast less than two weeks later.
The warming climate boosted Helene's wind speeds by about 13 miles per hour (20.92 kilometers per hour) and made the high sea temperatures that fueled the storm 200 to 500 times more likely, World Weather Attribution calculated Wednesday from Europe. Ocean temperatures in the Gulf of Mexico were about 3.6 degrees Fahrenheit (2 degrees Celsius) above average, WWA said.
"Hurricane Helene and the storms that were happening in the region anyway have all been amplified by the fact that the air is warmer and can hold more moisture, which meant that the rainfall totals — which, even without climate change, would have been incredibly high given the circumstances — were even higher," Ben Clarke, a study co-author and a climate researcher at Imperial College London, said in an interview.
Milton will likely be similarly juiced, the authors said.
The scientists warned that continued burning of fossil fuels will lead to more hurricanes like Helene, with "unimaginable" floods well inland, not just on coasts. Many of those who died in Helene fell victim to massive inland flooding, rather than high winds.
Helene made landfall in Florida with record storm surge 15 feet (4.57 meters) high and catastrophic sustained winds reaching 140 miles per hour (225.31 kilometers per hour), pummeling Georgia, the Carolinas, Tennessee and Virginia. It decimated remote towns throughout the Appalachians, left millions without power, cellular service and supplies and killed over 230 people. Search crews in the days following continued to look for bodies. Helene was the deadliest hurricane to hit the mainland US since Katrina in 2005.
Helene dumped more than 40 trillion gallons of rain — an unprecedented amount of water — onto the region, meteorologists estimated. That rainfall would have been much less intense if humans hadn’t warmed the climate, according to WWA, an international scientist collaborative that runs rapid climate attribution studies.
"When you start talking about the volumes involved, when you add even just a few percent on top of that, it makes it even much more destructive," Clarke said.
Hurricanes as intense as Helene were once expected every 130 years on average, but today are about 2.5 times more likely in the region, the scientists calculated.
The WWA launched in 2015 to assess the extent to which extreme weather events could be attributed to climate change. The organization’s rapid studies aren’t peer-reviewed but use peer-reviewed methods. The team of scientists tested the influence of climate change on Helene by analyzing weather data and climate models including the Imperial College Storm Model, the Climate Shift Index for oceans and the standard WWA approach, which compares an actual event with what might have been expected in a world that hasn't warmed about 1.3 degrees Celsius since pre-industrial times.
A separate analysis of Helene last week by Department of Energy Lawrence Berkeley National Lab scientists determined that climate change caused 50% more rainfall in some parts of Georgia and the Carolinas, and that observed rainfall was "made up to 20 times more likely in these areas because of global warming." That study was also not peer-reviewed but used a method published in a study about Hurricane Harvey.
Kim Cobb, director of the Institute at Brown for Environment and Society, wasn't involved in either study. She said there are uncertainties in exactly how much climate change is supercharging storms like Helene, but "we know that it’s increasing the power and devastation of these storms."
She said Helene and Milton should serve "as a wake up call" for emergency preparedness, resilience planning and the increased use of fossil fuels.
"Going forward, additional warming that we know will occur over the next 10 or 20 years will even worsen the statistics of hurricanes," she said, "and we will break new records."
Analysis is already indicating climate change made possible the warmed sea temperatures that also rapidly intensified Milton. Clarke said the two massive storms in quick succession illustrates the potential future of climate change if humans don't stop it.
"As we go into the future and our results show this as well, we still have control over what trajectory this goes in as to what risks we face in the future, what costs we pay in the future," he said. "That just hinges on how we change our energy systems and how many more fossil fuels we burn."
