Human-caused climate change boosted the wind speeds of recent Atlantic hurricanes, making them more damaging and costly, according to a pair of scientific reports released today.

Research published in the journal Environmental Research: Climate, “Human-caused ocean warming has intensified recent hurricanes,” found that between 2019 and 2023, the maximum sustained winds of Atlantic hurricanes were 19 mph (31 km/h) higher because of human-caused ocean warming.

And a parallel report by Climate Central, a nonprofit scientific research organization, applied the techniques developed in the Environmental Research paper to the 2024 hurricane season, finding that climate change increased maximum wind speeds for all 11 Atlantic hurricanes in 2024, increasing their highest sustained wind speeds by nine to 28 mph (14-45 km/h). 

This increase in wind speeds moved seven of the hurricanes into a higher Saffir-Simpson Hurricane Wind Scale category and strengthened Hurricanes Debby and Oscar from tropical storms into hurricanes. The report found that without human-warmed ocean temperatures, Hurricane Beryl and Milton would have been Category 4 storms, but the extra human-caused warming increased their winds by 18 mph (29 km/h) and 23 mph (37 km/h), respectively, lifting them to Category 5 strength.

“Every hurricane in 2024 was stronger than it would have been 100 years ago,” said Daniel Gilford, climate scientist at Climate Central and lead author of the new research. “Through record-breaking ocean warming, human carbon pollution is worsening hurricane catastrophes in our communities.”

A 10% increase in hurricane winds leads to a doubling in damage

Rather than running a detailed high-resolution model of each hurricane to study how it would have changed with and without human-caused ocean warming, the study used “potential intensity” theory to estimate how climate change has affected hurricanes. Potential intensity theory was pioneered in 1987 by MIT hurricane scientist Kerry Emanuel, who theorized that the wind speeds in hurricanes can be expected to increase about 5% for every increase of one degree Celsius (1.8°F) in tropical ocean temperature, assuming that the average wind speed near the surface of the tropical oceans does not change. Computer modeling has found a slightly smaller magnitude (4%) for the increase.

World Weather Attribution, an international scientific group, released in October 2024 a report showing that Hurricane Milton’s winds were increased by about 10% from human-caused climate change. And researchers at the Imperial College of London separately determined that climate change increased Hurricane Helene’s wind speeds at landfall by about 13 mph or 11%, and Milton’s by almost 11 mph, or 10%.

Although a 10% increase in hurricane winds because of climate change may not sound like a big deal, it matters a lot because hurricane damage increases exponentially with wind speed. For example, according to NOAA, a Category 2 hurricane with 100 mph (161 km/h) winds will cause 10 times the damage of a Category 1 hurricane with 75 mph (121 km/h) winds. This includes damage not only from winds but also from storm surge, inland flooding, and tornadoes. Bottom line: A 10% increase in winds yields about a doubling in hurricane damage (Fig. 2).

Using a previously published damage function and data on the exposed value of global assets, the researchers determined that 44% of the economic damages caused by Helene and 45% of those caused by Milton could be attributed to climate change. They added that the analysis “likely underestimates the true cost of the hurricanes because it does not capture long-lasting economic impacts such as lost productivity and worsened health outcomes.”

In an interview with CNN, retired NOAA hurricane expert Jim Kossin said, “I see this paper as a good way to estimate how multiple anthropogenic [human-caused] factors have increased hurricane intensities in the Atlantic, but I do not think that these estimates can be projected into the future,” because ocean temperatures are influenced by various factors other than carbon pollution, and the impact of temperature changes on hurricanes could differ in the future.

What about Sara?

The new research hinges on the warming oceans associated with climate change that can make hurricanes more powerful. But sometimes a potential hurricane won’t develop at all because other factors get in the way, keeping it from taking advantage of those climate-change-warmed waters. This was the case with Tropical Storm Sara, which dumped more than 90 inches of rain at one location in Honduras in early November and took at least seven lives. Forecast models a few days in advance showed that Sara had the potential to be a major hurricane because of exceptionally warm waters in the Caribbean. However, the disturbance that gave birth to Sara ended up moving closer to land sooner than originally expected. The resulting land interaction kept Sara from developing the structure that otherwise could have taken advantage of record-warm water and resulted in a truly devastating hurricane.

Bob Henson contributed to this post.