Dec 8, 2021 7:00 AM

Climate Change May Make Hurricanes Hit Sooner and Last Longer

A new study modeling storm behavior under a warmer climate finds Boston and Norfolk will face higher risk from floods as they crawl along the East Coast.

This past hurricane season was a pretty nasty one. With 21 storms from June 1 to November 30, for the second year in a row the National Oceanic and Atmospheric Administration ran out of names on their official list and had to swap over to a backup. Eight hurricanes hit the United States, and one—Ida—killed at least 82 people and caused an estimated $60 billion in damage as it churned its way from Louisiana to New Jersey, according to federal officials.

But unless things change in a big way, the future will be even worse. In a warmer climate, hurricanes will speed toward the Northeast coast more quickly and then slow down once they arrive, causing more damage and floods in vulnerable coastal communities. In a study published in November in the journal Earth’s Future, a team from three universities examined storm tracking data from the past 100 years and used it in a global climate model that takes into account changes in environmental conditions caused by heat-trapping greenhouse gases, such as carbon dioxide and methane.

The researchers focused on the Northeast US, which has the largest population centers living along the coast. “We found that storms are forming a little more north and west in the Atlantic, moving faster toward the Southeast coast and traveling their slowest along the East Coast,” says lead author Andra Garner, an assistant professor of environmental science at Rowan University in New Jersey. “It was a surprising finding.”

The study finds that Norfolk, Virginia and Boston will be more at risk from tropical storms by the end of this century, while New York City residents will face slightly less risk. That’s because future storm tracks will likely shift slightly east or west as the hurricanes emerge from their warm-water nursery in a big patch of ocean between the Caribbean and Western Atlantic and are then driven northward by high-level winds, ocean currents, and the curve in their path caused by the rotation of the planet, known as the Coriolis Effect.

While previous studies have looked at how climate change may make hurricanes more intense or cause them to drop more rain, this is one of the first to look at how future climate conditions may change their direction and speed. Garner had previously worked on modeling what would happen to New York City if a powerful storm like 2012’s Hurricane Sandy struck under future climate conditions. After looking at the effects of a sea-level rise on New York, she decided to see how these same conditions would affect the path of hurricanes in the Atlantic.

Garner and her colleagues simulated 35,000 storms under conditions that assume the world’s societies fail to take drastic action to curb carbon emissions, known as the Representative Concentration Pathway 8.5 scenario (RCP8.5). Under this scenario, humans would pump enough carbon into the atmosphere to boost global warming an average of 8.5 watts per square meter across the planet and raise atmospheric temperatures 4.3 degrees Celsius (or 7.7 degrees Fahrenheit) by the year 2100. This is the so-called “business as usual” scenario that scientists with the International Panel on Climate Change warned nations about in their latest report issued in August, one that United Nations Secretary-General António Guterres called "a code red for humanity.”

In their study, Garner and colleagues compared where storms formed, how fast they moved, and where they ended. Comparing data from pre-industrial times to simulations stretching to the end of the 21st century, the study found tropical storms will be 15 percent more likely to begin their life closer to the US Southeast coast. Under the model simulation, storms are more likely to travel within 100 kilometers (62 miles) of both Boston and Norfolk than toward New York City.

But Garner says the results don’t mean New Yorkers can breathe easy. While the analysis showed the average storm may stay further out to sea, any individual storm will still pose a risk to the region. She says these future super-storms will move fast while at sea, covering more territory until they hit land and slow down. This means they could make landfall faster. “One of the impacts we see is that it takes less time to travel to within 100 kilometers of these cities,” she says.

In addition, the team's analysis found there will be more storms along the East Coast, and because they will be moving more slowly they will produce stronger wind and more water damage to homes and businesses. In fact, the longest-lived hurricanes will last twice as long as today’s storms. “Norfolk saw the biggest impact in how long storms last, but all three cities see impacts that would lead one to think about how they are preparing for these events in the future,” Garner continues.

Hurricanes need warm water to survive, and most of them tend to die out once they cross the northern boundary of the Gulf Stream, a wide, fast-moving ocean current that brings warm tropical water from the Gulf of Mexico past south Florida, along Cape Hatteras and North Carolina, and then across the Atlantic to Europe. Two recent hurricanes, Dorian in 2019 and Matthew in 2016, were so powerful that they actually slowed the current by 50 percent for several weeks, according to a paper published last year in the Journal of Marine Systems.

That study’s author, Tal Ezer, a professor of earth and ocean sciences at Old Dominion University in Norfolk, believes that if future hurricanes also change their direction and speed, that may wreak even more havoc on the Gulf Stream. Ezer says the new study is a reasonable analysis of the possible future ocean system. “If these hurricanes can actually change tracks, that could have a significant impact on the Gulf Stream and ocean circulation,” he says. That’s important because the Gulf Stream helps moderate temperatures in England and southern Europe, which would be much colder if it were to slow or stop.

In the US, coastlines were hit by 19 tropical storms that qualified as billion-dollar disasters between the years 2010 and 2020, for a total of $480 billion in damages, adjusted for inflation. Slow-moving storms will likely run up a bigger price tag, and that has some state and local officials worried. Norfolk and the surrounding Hampton Roads, Virginia area are home to the world’s largest naval base, and rising sea levels have caused daytime flooding in many neighborhoods during the past 15 years.

“Flooding is creating problems for us now, so any big storm that comes along is going to be that much worse,” says Rear Admiral Ann Phillips, first special assistant to the governor of Virginia for coastal adaptation and protection. “More water on top of that is going to expand the floodplain.”

Phillips has been working with town and city officials in Virginia for the past year on planning for the future climate threat of coastal flooding, as well as bigger and more intense rainstorms. “We know that’s coming. The challenge is how do we get ahead of it,” she says. “It’s a slow, insidious threat, and it’s going to keep getting worse.”