Is climate change making hurricanes worse? Yes, here’s why.
Dorian hit the Bahamas as one of the strongest storms in Atlantic history, once again whipping up social media banter about whether hurricanes in a warming world are getting too strong for Category 5 to capture just how bad they can get.
“It resurfaces every time we have one of these,” said Brian McNoldy, senior research associate at the University of Miami’s Rosenstiel School of Marine and Atmospheric Research. “It’s one of the things people like to talk about.”
On Sunday, as Dorian hit peak power in the Bahamas, meteorologist Ryan Maue walked his nearly 100,000 Twitter followers through his calculations on how the hurricane might qualify for a hypothetical Category 6 designation.
While any hurricane with sustained winds above 155 mph is labeled Category 5 under the 1971 Saffir-Simpson scale, Maue said the progression between categories 1 and 5 suggests the next tier would start at 182 mph. Dorian’s sustained wind speeds maxed out at 185 mph Sunday, tying a handful of other hurricanes for the second-strongest storm in the Atlantic since 1950. The strongest was 1980’s Allen, with sustained winds hitting 190 mph.
The Miami Herald sent a freedom of information request last month to the National Oceanic and Atmospheric Administration regarding potential changes to the Saffir-Simpson Scale. As of Tuesday, the Herald has not received a response.
The famous scale was first developed by Herb Saffir, a Coral Gables structural engineer and longtime advocate for tougher building codes, who envisioned a rating system similar to the Richter scale used for earthquakes. That explains its focus on linking wind speed to building damage as a measure of hurricane force. In the early 1970s, it was embraced and co-developed by Robert Simpson, then director of the National Hurricane Center, as a handy way to issue warnings about the severity of storms.
The categories have since become ingrained with the public and weather forecasters but in the last few decades, monster storms have seemed a bit too common.
The record-setting stretch of hurricanes in 2004 and 2005, when Katrina ravaged New Orleans and Florida suffered nine hurricane landfalls, helped raise questions about the ratings. In the past few years, Maria, which slammed Puerto Rico and the Keys in 2017, reached Cat 5 at one point before reaching land. Hurricane Michael, which bulldozed the Florida Panhandle last year, hit as a Cat 4 but was later upgraded to a Cat 5. Now, there’s even stronger Dorian.
And some climate change studies suggest the future could be worse, with some researchers predicting future 200 mph storms will render Category 5 as an inadequate scale of the extreme. For instance, one 2018 study from the National Center for Atmospheric Research found that in a warmer world, it’s more likely that hurricanes will be stronger, slower and wetter. While the total number of storms would not necessarily change, research suggests that more of the storms we do get will be higher categories.
“There’s every reason to expect hurricanes will get stronger,” said Hugh Willoughby, former director of NOAA’s Hurricane Research Division. “It’s well validated.”
That said, it’s also hard to find a scientist who sees a pressing need to mess with the venerable Saffir-Simpson rating system.
Professional meteorologists and hurricane experts say they already rely on things like maximum sustained winds, peak gusts and barometric pressure as the key measures of hurricane intensity.
Since the top of the scale, a Category 5, describes a landscape where virtually everything has been flattened or shredded, McNoldy for one sees no need to add more numbers to the top — other to make monster storms sound more menacing.
“Does it really do anything? I don’t think so,” he said.
One knock against Saffir-Simpson is that the wind-based scores don’t always adequately capture the dangers a storm can bring from heavy rains or storm surge. Boosting the cap beyond Category 5 wouldn’t eliminate that shortcoming, leaving weather experts to dismiss the idea as misplaced tinkering.
“The argument on whether to use the Saffir-Simpson at all is a more worthwhile argument,” said Adam Sobel, professor of environmental science and climate physics at Columbia University. He said the Category 5 designation hasn’t really been tested by recent strong storms. “We’ve seen some records broken. But not in a way that would leave the scale irrelevant yet.”
As far as climate impacts on the scale, Timothy Hall, a NASA researcher, said the clearest link between that and hurricanes is that rising sea levels will lead to more storm surge, the deadliest part of a hurricane. It’s also “almost certain” that these future storms will be wetter, he said, since a warmer atmosphere can hold more water vapor and dump more rain — a la Hurricane Harvey.
Some recent research, including a paper Hall published, suggests there could be a link between a warmer planet and slower storms that stall out like Dorian did. But Hall said much more research is needed.
“That relationship is really at the edge of what we can say right now,” he said. “There’s a lot to be worked out.”
For now, these extremely strong storms are rare. Hall said only four Category 5 storms have made landfall in the U.S. in modern history, with Hurricane Michael in the Florida Panhandle as the most recent. If there were a Category 6, it wouldn’t have many storms in it.
“You would do that if there were so many storms that occurred in that upper category that it was inconvenient to lump them together and you wanted to separate them into new bins,” he said. “I don’t think that’s necessary.”
Phil Klotzbach, a research scientist with Colorado State University’s department of atmospheric science, doesn’t see the point of a new category either.
He pointed out the NHC description of a Category 5: “A high percentage of framed homes will be destroyed, with total roof failure and wall collapse. Fallen trees and power poles will isolate residential areas. Power outages will last for weeks to possibly months. Most of the area will be uninhabitable for weeks or months.”
“I don’t really see how you could categorize damage from a Category 6 that would be any worse. At some point, we just have to have a high point for the scale and leave it at that, even if climate change does make for stronger hurricanes,” he said.
The current system already works well as a public relations tool, said Willoughby, a professor at Florida International University. It makes it easy to communicate damage with people who don’t pay attention to hurricanes very often. And changing it might backfire in delivering a public safety message, he said.
People might dismiss the severity of a Category 5 storm, since it would then be only the second-worst-case scenario available.
“Category 6 would make a big splash the first time it was used and then people would relax for category fives,” he said. “Cat 5 communicates it pretty much doesn’t get worse.”
Miami Herald staff writer Alex Daugherty contributed to this report.