As climate change continues to occur, some of the strongest storms in American history have ravaged coastal cities. 

A record high of 60 inches of rain fell in some parts of Texas in Hurricane Harvey earlier this year. Hurricane Irma broke a record, sustaining winds speeds of 185 mph or greater for 37 consecutive hours. More than 200 died in Irma and Harvey, and countless homes and cities on the Atlantic seaboard were destroyed, affecting many people, including Duke students who called the impacted areas—be it Texas or Florida—home.

And though hurricane season is supposed to start June 1, Hurricane Arlene became only the second Atlantic tropical storm to occur in April in the satellite era. 

But sufficient evidence does not exist to say that climate change is causing these record-setting storms, one expert said. 

“The type of hurricanes that we’ve seen—Harvey, Irma, Maria—are the type of hurricanes we can expect as our world continues to warm. But we can’t at this point make any attribution of those to climate change,” said Susan Lozier, Ronie-Richelle Garcia-Johnson professor of earth and ocean sciences, at a talk on campus Monday sponsored by the Forum for Scholars and Publics. 

Lozier is, however, not a climate change denier and acknowledges that over time, climate change will cause hurricanes to become more deadly. 

“To maintain scientific credibility is incredibly important because if we rush to name all these events as climate change and lose that credibility, that’s really damaging to the overall message of what we’re trying to say about the impacts it has,” Lozier said.

As ocean temperatures rise, hurricanes will inevitably grow in strength because they are fueled by warm water, Lozier said. Ninety percent of the warming on Earth has presented in the oceans, not in the atmosphere as many believe, she said. 

Additionally, they will produce more rain because a warming atmosphere is able to hold more water—basic physics, she said. In the summer, the air is more humid as a result of the water it's holding, she said, which could apply to the atmosphere as a whole.

However, these changes might not be as big as some may fear—Lozier projected that hurricanes will only become more intense by 10 to 15 percent, while rainfall will increase five to 10 percent.

But climate change can’t be connected to recent hurricanes yet for three reasons, even though some seem to “almost want to believe that they are,” she said.

First, the overall group of hurricanes in the 21st century is comparable to those in the 20th century in terms of strength and rainfall.

“We wouldn’t be able to find any difference between those groups right now,” Lozier said. “There’s such a strong overlap between those groups that just judging by one hurricane, you wouldn’t be able to tell. In the decades ahead, we expect some separation in those groups—the more intense hurricanes we would be able to pick out from the group.”

Although Irma was one of the strongest recorded storms ever, Hurricane Allen in 1980 had higher wind speeds. Also, six recorded hurricanes in the 20th century were in the same range of strength as Irma.

Second, hurricanes are such rare events that the sample size is not large enough to make any conclusions with a strong sense of statistical confidence, Lozier noted.

Finally, because hurricanes are intricate beings, they can be difficult to understand and record, she said. Although things like sea level and temperature are easy to record, hurricanes are dynamically complex, she said.

“Hurricanes are not so clear,” Lozier said. “It’s not all that clear that just if you have a temperature increase, the hurricane will get stronger. The wind shear matters. This year in particular was a strong hurricane season because we had unusually high tropical temperatures and La Niña year.”

La Niña refers to the periodic weather pattern during which there is more hurricane activity in the Atlantic. 

Still, just because scientists can’t chalk up these strong storms to climate change doesn’t mean Americans and politicians should be complacent about mitigating the effects of hurricanes, another expert at the talk said.

“From a public policy standpoint, we don’t need to make that linkage,” said Danielle Spurlock, assistant professor of city and regional planning for the University of North Carolina at Chapel Hill. “We need to take action based on the repeated loss of life and damage that we’ve seen and change what our actual development patterns are.”

One of the major flaws Spurlock pointed to was the safe development paradox—levees to regulate water levels can actually hurt communities by causing water to be retained in the city.

“We need to take the lessons from decades before,” Spurlock said. “We have data and evidence from decades before that we haven’t used to shape our federal, state and local policies. At the federal level, we have a lot of risk reduction through levees. However, we don’t have the same motivation to talk about risk elimination, which would be changing how we develop and making us aware of areas which are physically vulnerable.”

What complicates the issue is that coastal cities thrive economically on property developments that put people at risk, forcing constituents to have difficult conversations and make tough choices, she said.

“As an elected official, I’m thinking that [a hurricane] will be a rare, large magnitude event, but I still need to provide services to my community on an everyday basis. It’s very easy for a mayor to psychologically discount it,” Spurlock said. “We want to hold our elected officials’ feet to the fire to tell them that this isn’t actually how we want to do development.”