How climate change is intensifying storms like Hurricane Helene

Climate change is making hurricanes like Hurricane Helene more intense, scientific research shows. 

Helene has unleashed high winds, heavy rain and a dangerous storm surge in the Southeast after making landfall in Florida as a Category 4 hurricane Thursday night. As of Friday afternoon, the estimated death toll of the storm had climbed to more than 40 across four states. 

It follows roughly two and a half months after Hurricane Beryl — which peaked as a Category 5 storm — tracked destruction across the Caribbean as well as the United States, killing dozens of people.

The proportion of hurricanes that fall into these more intense categories 4 and 5 are expected to increase as the planet heats up, according to the most recent report from the Intergovernmental Panel on Climate Change, a well-respected climate science authority from the United Nations. Peak hurricane wind speeds are also expected to rise.

“These hurricanes are getting bigger and stronger and that is due to simple energy transfer,” said Claudia Benitez-Nelson, a climate scientist at the University of South Carolina.

Benitez-Nelson explained that a hotter planet means more energy can transfer from the ocean to the atmosphere. 

“And what are hurricanes? They're big balls of energy and so that energy is now feeding into these tropical storms,” she said. 

That transferring effect is expected to continue and worsen as the planet heats up.

Estimates of just how much it will do so can vary. But if the planet warms up by about 3.6 degrees Fahrenheit (2 degrees Celsius) above preindustrial levels, a hurricane’s maximum wind speeds could increase by about 5 percent, according to Tom Knutson, a senior scientist at the National Oceanic and Atmospheric Administration’s (NOAA) Geophysical Fluid Dynamics Lab.

Noting the increase in wind speeds, earlier this year scientists suggested adding a Category 6 to the Saffir-Simpson hurricane wind scale, saying that the currently used categories 1 through 5 are “inadequate” as hurricanes continue to intensify. 

In addition to making hurricanes overall more intense, Benitez-Nelson noted that climate change is also causing hurricanes to intensify more quickly, potentially giving people less time to prepare.

Hurricane Helene went from a Category 1 storm to a Category 4 in less than a day amid unusually warm ocean temperatures. 

Benitez-Nelson, who is a member of the climate education group Science Moms, said increased global temperatures lead to increased ocean temperatures that in turn lead to a “more effective transfer of heat.”

She added that this “really helps to spin up a hurricane that moves from a tropical storm to a hurricane, and then makes these hurricanes even stronger and intensify more rapidly.”

As well as fueling increased wind speeds, Knutson noted that climate change is also likely causing more rainfall to occur during hurricanes.

"With the warmer climate, the atmosphere is holding more water vapor systematically, and that's leading the storms to become basically bigger, more intense rain producers,” Knutson said. “The air is holding more moisture than previously, so that causes some increase in the rainfall rates.”

He added that modeling shows that every additional degree Celsius (1.8 degrees Fahrenheit) in the regional sea surface temperatures where the hurricane is leads to an average of 7 percent more rainfall. 

The Earth’s surface has already warmed by an average of about 2 degrees Fahrenheit (1 degree Celsius) when compared to preindustrial levels, but the actual level of warming can vary across regions and between lands and oceans. 

Benitez-Nelson added that as hurricanes become stronger they also don’t dissipate as quickly and can move further inland, including to places that are not used to dealing with them. 

“Hot air can hold more water,” she said. “And it's dumping massive amounts of water in places that simply are ill prepared to handle that amount of rainfall.”

She pointed to impacts from Hurricane Beryl’s remnants that made their way to Vermont earlier this year. “That's ridiculous ... but that is our future,” she said.

And beyond climate change’s own impacts on hurricanes, these storms can combine with other climate impacts like sea level rise to bring about more damage. 

“Our ocean has been rising, and so, of course it has an impact when a hurricane comes along because now the height of your water is already higher and then you've got the storm surge on top of that,” said Jennifer Collins, a professor at the University of South Florida School of Geosciences. 

Collins expressed concern that going forward, this will cause significant harm, as people tend to pay more attention to a hurricane’s wind speed than its flood potential. 

“We've seen other storms in the past that have had significant flooding from one of these weaker storms,” Collins said. “I am very concerned about those type of storms, honestly, because people made their evacuation decisions sometimes purely based on the Saffir-Simpson hurricane wind scale.”

Climate change is caused by human activity releasing greenhouse gases like carbon dioxide, which get trapped in the atmosphere and create a greenhouse effect that warms the planet. The burning of fossil fuels is the main driver of climate change, though other parts of the economy like agriculture and landfills are also major contributors.

Benitez-Nelson said that to prevent climate-related harm going forward, “the biggest thing that we can do is reduce emissions.”