As Hurricane Florence bears down on the North Carolina coast, residents of the state’s Outer Banks—the string of barrier islands sitting just offshore—are fleeing their homes for higher ground.

On Tuesday night, North Carolina Gov. Roy Cooper (D) ordered an evacuation for all the state’s barrier islands ahead of the monster storm.

The Outer Banks, and other barrier islands along the North and South Carolina shorelines, may see some of their worst storm-related damage in years as Florence approaches the coast, experts say, due to a combination of high winds and catastrophic storm surge.

In fact, these islands are doing what they’re naturally made to do—buffer the inland shore against the impact of major storms.

But scientists are worried that the barrier islands, some of the East Coast’s most important natural defenses, may be in serious jeopardy. The influence of human development on the islands, combined with the relentless progression of sea-level rise, is threatening to sweep them away.

If so, storms like Florence could have an even bigger impact on the Carolina coastline in decades to come.

According to Rick Luettich, lead principal investigator for the Department of Homeland Security’s Coastal Resilience Center, there’s “no question” that the loss of barrier islands would have a major effect on a coastline’s vulnerability to strong storms.

Barrier islands are naturally occurring landforms, made of sand that’s been shaped by waves and ocean currents. They’re typically longer than they are wide and often appear in chains up and down the coastline, with one side facing the open ocean and the other side facing lagoons that separate them from the inland shore. Because of their unique placement, they help to buffer the mainland against the impact of waves and storm surge.

Barrier islands are naturally mobile—as they’re buffeted by the sea, they tend to gradually migrate inland over long periods of time. As waves wash over them, they deposit sand that helps the islands to rebuild and maintain themselves even as they move around in the ocean.

But a combination of influences is affecting many islands’ abilities to naturally weather the waves, experts say. For one thing, human development—the construction of buildings, roads and other infrastructure on the islands—is holding the beaches in place and preventing their natural migration.

“We’re fighting like crazy to hold them in place,” Luettich said.

At the same time, sea-level rise is an ever-increasing threat. Tide gauge measurements along the North Carolina coast suggest that the sea is rising by between 2 and 4 millimeters per year, depending on the location, or around 3 millimeters annually on average, according to a state sea-level rise report.

On Twitter this week, oceanographer Stefan Rahmstorf of the Potsdam Institute for Climate Impact Research pointed to previous research suggesting that sea levels in North Carolina have risen by about a foot in the past 150 years because of human-caused climate change, and that current rates of sea-level rise are the fastest in the past 2,000 years.

And depending on the severity of future climate change, sea-level rise on the U.S. East Coast could range from about a foot by the end of the century under a minimal climate change scenario to more than 8 feet under an extreme scenario, according to a 2017 NOAA report.

That’s a big concern for barrier islands. While these landforms can naturally respond to rising sea levels to a certain extent, building back up as they gradually move landward, the rate of sea-level rise makes a big difference.

Rapidly rising ocean levels, such as the rates occurring up and down the U.S. coastlines now, increase the chances that overwash from waves, chronic flooding and major erosion occur faster than islands can migrate and rebuild. These processes may also make islands more vulnerable to damage or destruction from major storms, like Florence.

In parts of the Carolinas, these processes are already becoming evident. In 2013, for instance, South Carolina news outlets reported on new maps from the U.S. Fish and Wildlife Service that suggested hundreds of acres of land has already been lost from islands that help make up the state’s Cape Romain National Wildlife Refuge.

In other regions, trends are less consistent but still worrying. According to research from the U.S. Geological Survey on coastal change, many parts of the barrier islands off the Carolina and Virginia coastlines have lost ground over the last few decades, while other areas have stayed constant or even gained some shoreline area.

In the future, though, with sea levels rapidly continuing to rise, many experts are concerned that the islands’ rates of erosion will increase.

A recent report from the Union for Concerned Scientists, for instance, suggests that many parts of the Outer Banks will experience chronic inundation—flooding at least 26 times a year, or about every other week on average—by the end of the century or sooner. By 2060, the report suggests that at least 28 percent of the land area of the Hatteras community in the Outer Banks will experience chronic inundation.

Barrier islands make up some of the nation’s most valuable natural hurricane defense systems, and without them the impact of storms like Florence may be even more severe—and that’s to say nothing of the other ways that climate change may worsen the effects of hurricanes (Climatewire, Sept. 12).

But they’re also not the only natural hurricane buffers in trouble.

In places like Florida, for instance, coral reefs help provide similar protection against storm surge, helping to break up waves before they hit the shore. But warming waters and ocean acidification are taking a toll on reefs, not just in Florida but around the world.

Similarly, coastal wetlands such as salt marshes or mangrove forests provide protection for coastlines in many regions around the globe. But sea-level rise is threatening many of these ecosystems, as well.

Florence is likely to be a stark reminder that these natural defense systems aren’t indestructible—and that the influence of climate change is making them ever more vulnerable.

Reprinted from Climatewire with permission from E&E News. E&E provides daily coverage of essential energy and environmental news at www.eenews.net.