Rising seas swell in southeastern U.S. — study

By Chelsea Harvey | 04/11/2023 06:37 AM EDT

People lean into the wind and waves as the outer bands of Hurricane Ivan pound Pensacola, Fla., in September 2004.

People lean into the wind and waves as the outer bands of Hurricane Ivan pound Pensacola, Fla., in September 2004. Stephen Morton/Getty Images

Sea levels have surged along the coastlines of the southeastern United States, new research finds — hitting some of their highest rates in more than a century.

They’ve risen more than a centimeter a year over the last decade — about triple the global average — and the effects on communities near the Gulf of Mexico and Atlantic Ocean already are being observed in the form of increased flooding, more severe hurricanes and eroding shorelines.

“We have seen the impacts quite significantly,” said Sönke Dangendorf, an expert in coastal engineering at Tulane University and lead author of the new study.


The study, published Monday in the journal Nature Communications, is the latest to point out the trend. Another study, published earlier this month in the Journal of Climate, highlighted a similar pattern — sea-level rise of more than a centimeter per year since 2010 along the Gulf and Southeast coasts.

The studies indicate that the affected region spans from the western Gulf up to Cape Hatteras in North Carolina.

The flurry of interest dates back to a 2022 NOAA report on sea-level rise, according to Dangendorf. The report presented projections for U.S. coastlines in the coming decades, predicting about a foot of sea-level rise on average around the country by midcentury. It also projected higher-than-average sea-level rise along the East and Gulf coasts.

Still, the amount of sea-level rise observed in the Southeast and the Gulf exceeds the model’s projections for the next 30 years — and scientists wanted to know why.

The latest study, led by Dangendorf, analyzed 66 tide gauge records up and down the East and Gulf coasts, alongside satellite observations and model simulations for a closer examination. The researchers separated out the extra influence of sinking land, a notable issue in some parts of Texas and Louisiana.

They found that sea levels are rising rapidly throughout the regions, even without the influence of sinking land levels. In Pensacola, Fla., for instance, they found rates exceeding 11 millimeters per year.

The researchers began analyzing possible causes for the rapid increase. Meltwater from the world’s shrinking glaciers and ice sheets has contributed to a global acceleration in sea-level rise — but it doesn’t fully explain the pattern happening on U.S. coastlines.

The researchers suggest that warming waters and changing wind patterns have altered the ocean’s circulation in parts of the North Atlantic and the Caribbean, changing the way masses of water flow up to U.S. coastlines. These changes can be attributed partly to human-caused global warming and partly to natural climate variations, they say.

And if the changes are partly natural cycles, then the accelerating sea-level rise should slow back down eventually, they add — although it’s uncertain how long it might take.

There’s still some scientific debate about the exact causes behind the acceleration, and other research groups have raised other theories. The recent Journal of Climate study suggested that the increase may be driven by changes in a warm-water current passing through the Gulf of Mexico. And these changes may in turn be fueled by a recent slowdown in a major Atlantic Ocean current, driven by human-caused climate change.

Despite the differences in theories about the mechanisms, scientists do generally agree that the acceleration is caused by changes in physical ocean dynamics, according to Dangendorf.

“I wouldn’t say that they disagree, necessarily,” he said. “All of them agree that it’s a dynamic factor — that’s pretty much set in stone.”

But more studies will be needed to determine the exact causes and what they mean for future sea-level rise rates on the Gulf and Southeast coasts.

In the meantime, studies demonstrate the influence that rising oceans have had in both regions.

The Journal of Climate study notes that the rising rates have coincided with record-breaking hurricane seasons in recent years, and that coastal flooding and damage have likely intensified as a result. Higher sea levels can worsen the outcomes of hurricanes by increasing storm surge, which can result in catastrophic coastal flooding.

High-tide flooding also is accelerating at most locations along the Gulf and East coasts, according to NOAA. And the total number of high-tide flooding days has increased by as much as 400 percent in the Southeast and 1,100 percent in the Gulf compared with the year 2000.

At the same time, flood damages are rising and insurance costs are spiking. And coastal communities are watching their shorelines gradually slip into rising waves.

“We need to prepare for that; we need to adapt,” Dangendorf said. “It affects us all.”