When Susan Lyons moved to the peninsula that is downtown Charleston, South Carolina, in 2004, flooding wasn’t a major concern. The city was in a drought, and high tides typically just flooded streets around the fall king tides, when the moon is in the perfect position to ramp up high tides. Twenty years later, rain storms now cause major floods, and tidal flooding happens several days each month.
The oldest, densest, and most tourist-visited part of Charleston, where Lyons lives, is surrounded by water on three sides where the Cooper River and the Ashley River meet and flow into the Atlantic. Flooding in the downtown area is increasingly disruptive. The city’s medical district is regularly awash and kids sometimes have to walk through floodwaters to get to school. Tidal flooding alone blocks streets and forces people to move their cars to parking garages, Lyons said.
“It’s very scary to stand at your front door and watch your streets fill up with water from the harbor,” she said.
Flooding from high tides, sometimes called sunny day flooding or nuisance flooding, is directly tied to rising oceans. Charleston and other cities along the U.S. Southeast and Gulf Coasts are experiencing some of the highest rates of sea level rise in the world. Without reductions in climate-causing pollution, the seas will continue to rise and nuisance flooding could make places unlivable. But reductions in carbon pollution and adaptation measures can protect communities along the coasts.
“Just because it hasn’t touched you yet doesn’t mean it won’t,” Lyons said. “It is a critical time right now, in so many ways, in our country, in our city, in our Earth. And it’s important that people understand what’s at stake.”
What is sea level rise and what’s causing it?
The term sea level rise describes the increase in the average water levels in the world’s oceans.
The current rate of rise is unprecedented over at least 3,000 years, according to Sönke Dangendorf, a professor and sea level rise expert at Tulane University in New Orleans.
“Sea level was relatively constant in the millennia before, and it started to increase with increased CO2 emissions in the mid-to-late 19th century,” Dangendorf said.
Sea level rise is primarily caused by two factors, and global warming is responsible for both.
The average sea level has risen 103.3 millimeters since 1993
The first way that global warming causes sea level rise is through melting ice sheets. Antarctica and Greenland alone store over 68% of all the fresh water on Earth in their ice sheets.
The second way is through the thermal expansion of water: When water heats up, it takes up more space.
Because of sea level rise, coastal communities increasingly face flooding during high tides. It also makes storm surges higher and more dangerous during hurricanes.
“We tend to think of Miami, but it’s every coastal city in the world,” said John Englander, an oceanographer and the president and co-founder of the Rising Seas Insitute. “All coastal cities, from Charleston to Annapolis, to Portland, Maine, to Portland, Oregon, will be affected by sea level rise because the coastline is determined by sea level.”
Not all coastal communities are equally affected. Ocean circulation patterns, nearby ocean temperatures, infrastructure differences, and land elevation and loss all affect how much sea levels contribute to flooding.
Dangendorf has been studying sea level rise along the Southeastern and Gulf Coasts of the U.S.
“We saw that since about 2010, the rates started to increase significantly faster than the global mean – and significantly faster than anywhere else in the Atlantic,” he said.
It’s not entirely clear why this area is a hot spot, Dangendorf said. But his research points to impacts from thermal expansion and a phenomenon called Rossby waves. Rossby waves, also called planetary waves, aren’t traditional ocean surface waves. They can be hundreds of kilometers long and are caused by the Earth’s rotation. They can make sea levels several inches higher along hundreds of miles of shoreline.
Although sea level rise rates are often measured in millimeters, the impacts on people are far from small. Native communities in coastal Louisiana have begun to relocate further inland, tidal flooding regularly interrupts Lyons’ life, and Dangendorf said that in his community, sea level rise is increasing the cost of flood insurance.
“We already feel it here in New Orleans,” he said. “I don’t really know how people with a normal salary can still pay the insurance rates.”
How bad will sea level rise get?
A key predictor of how high seas will rise is how much climate pollution will be produced in the coming years and decades. Under a low-pollution scenario, the Intergovernmental Panel on Climate Change projects the global mean sea level would rise 0.43 meters (1.4 feet) by 2100. Under a high pollution scenario, that projection almost doubles to 0.84 meters (2.76 feet). The lower scenario, the panel reported, would sharply reduce but not eliminate the projected threats to low-lying communities and islands.
“It’s pretty clear what we can avoid by getting to net-zero emissions,” Dangendorf said.
A big question mark for sea level rise scientists right now is what will happen with the Antarctic and Greenland ice sheets in the coming decades. The ice sheets hold enough water that they would raise sea levels 65 meters (213 feet) if it all melted, Englander said. Only three meters (9.84 feet) of rise would have a dramatic effect on all coastal cities, including major cities like Jakarta, Mumbai, Miami, and Los Angeles.
Sharon Gray, the director of education and science communication at the Rising Seas Institute, added that some Greenland glaciologists believe that the sheets have reached the point of no return where melt is inevitable. Studies show Antarctica may have reached similar tipping points. But there’s a lot of uncertainty about when, or how much, that ice will melt.
“It’s like predicting when the next San Francisco earthquake will happen or the next mudslide or the next avalanche,” Englander said. “Those things are not predictable to any precision, nor is the collapse of Antarctica and Greenland.”
Significant collapse of either, or both, of these ice sheets could make sea level rise surpass modeled predictions.
“In the last 20 years the actual sea level rise, generally speaking, I should say, as a broad statement, keeps exceeding the various projections or models,” Englander said.
Though uncertainty remains in how high oceans will rise and how much coastal communities will be affected, sea level rise promises to be an ongoing problem. Because of the heat stored in the oceans and thermal expansion, sea levels will continue to rise for centuries.
“We have already sea level rise. We are committed to sea level rise. We need to adapt, but we also need to mitigate to avoid unmanageable sea level rise,” Dangendorf said.
How can communities adapt to sea level rise?
Adaptation looks different for every community. Geology, Gray pointed out, can play a role in the types of measures that are available.
“For example, in Florida, sea walls don’t work because we’re on limestone, so the water comes up from underneath,” she said. “Each place really needs to look individually at the resources that they have available.”
For individuals, Englander noted, it can be hard to think about sea level rise on those time scales because it is happening slowly, like drips in a bucket.
“In Miami, real estate is booming. These high rises just sprout out like weeds, these gorgeous, incredibly expensive condominiums. But the streets are flooding more and more,” he said. “And people will rationalize that, well, in five years, they’ll sell their place if it’s flooding or the water is getting higher.”
Lyons said real estate and tourism are booming in Charleston, too. She began organizing with her neighbors in 2017 after flooding from heavy rains and hurricanes led her to file flood insurance claims three years in a row. The neighbors call themselves Groundswell, and together, they push political leaders to take Charleston’s vulnerability to flooding seriously and build infrastructure to protect residents.
For a while, the organization found success, albeit slower than the members would have liked. The city brought in experts from flood-prone Netherlands and created a resilience office to study and plan for flooding. In 2023, the U.S. Army Corps of Engineers published the Peninsula Perimeter Protection Project, a flood-protection study that recommended an eight-mile storm surge structure, nature-based features such as living shorelines, and 10 pumps. The city and the Army Corps began preliminary negotiations on a design agreement. With momentum gaining, Groundswell members thought it was safe to go on hiatus.
“Unfortunately, we had a mayoral election this past November, and the mayor who was supportive of all these efforts lost by 500 votes,” Lyons said. “The new mayor, both in his campaign, and since he’s taken office, has been very skeptical overtly, and apparently in private conversation, about this peninsula protection project.”
So in late June 2024, Groundswell came out of retirement and Lyons is trying to re-energize the group. Banding together with her neighbors has given the 81-year-old a new perspective.
“It kind of became a new dimension to my life actually,” she said. “It is a scary situation, so this is a completely honest endeavor on my part. I am with them all. But it has been gratifying because I have found any number of like-minded people who are smart and thoughtful and concerned and working in their own realms toward trying to find solutions.”
Englander said that the Rising Seas Institute encourages decision-makers and infrastructure planners to look further into the future when planning for sea level rise.
“Real short term is like, what do we do to stop our house from flooding this year?” he said. “That’s just short-term flooding, and really important. But if we’re trying to look at the impacts of sea level change, we should be thinking about 25, 50, and 100 years.”
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