When Susan Lyons moved to The Peninsula in downtown Charleston, South Carolina, in 2004, flooding wasn't a major issue. The city is in the midst of a drought, and high tides typically only flood the streets around autumn tide, when the moon is in the best position to speed up the tides. Twenty years later, heavy rains now cause major flooding, with tidal flooding occurring several days a month.
Charleston, where Lyons lives, is the oldest, most densely populated and most visited part of Charleston, an area surrounded on three sides by water, where the Cooper and Ashley rivers meet and flow into the Atlantic Ocean. Flooding damage in downtown areas is increasing. The city's medical district is regularly flooded, and children sometimes have to walk through floodwaters to get to school. Tidal flooding itself blocked streets and forced people to move their cars to parking lots, Lyons said.
“It's very scary to stand at your front door and watch your street being flooded with water from the harbor,” she said.
Flooding from high tides, sometimes called fair weather flooding or nuisance flooding, is directly related to sea level rise. Charleston and other cities in the southeastern U.S. and Gulf Coast are experiencing some of the fastest rates of sea level rise in the world. If climate-causing pollution is not reduced, sea levels will continue to rise and nasty flooding could make some places uninhabitable. But reducing carbon pollution and adopting adaptation measures can protect coastal communities.
“Just because it hasn't touched you yet, doesn't mean it won't touch you,” Lyons said. “This is a critical moment in many ways for our country, our cities, and our planet. It's important that people understand what's at stake.
What is sea level rise and what are its causes?
The term sea level rise describes the rise in the average water level of the world's oceans.
Sönke Dangendorf, a professor at Tulane University in New Orleans and an expert on sea level rise, said the current rate of rise is unprecedented in at least 3,000 years.
“Sea levels had been relatively stable for thousands of years, and then started to rise in the mid-to-late 19th century as carbon dioxide emissions increased,” Dangendorf said.
Sea level rise is mainly caused by two factors, and global warming is a common cause of both.
Since 1993, mean sea level has risen by 103.3 millimeters
The first way global warming causes sea levels to rise is through the melting of ice caps. The ice sheets of Antarctica and Greenland alone store more than 68% of the earth's fresh water.
The second way is through the thermal expansion of water: when water heats up, it takes up more space.
Coastal communities are increasingly facing flooding during high tides due to rising sea levels. It also makes storm surges during hurricanes higher and more dangerous.
“We tend to think of Miami, but this is true of every coastal city in the world,” said John Englander, an oceanographer and president and co-founder of the Sea Level Rise Institute. “All coastal cities, from Charleston to Annapolis to Portland, Maine, to Portland, Oregon, will be affected by sea level rise because coastlines are determined by sea level.”
Not all coastal communities are affected equally. Ocean circulation patterns, nearby ocean temperatures, differences in infrastructure, and land elevation and loss all influence the impact of sea level on flooding.
Dangendorf has been studying sea level rise in the southeastern U.S. and Gulf Coast
“We've seen that since about 2010 this ratio started to grow significantly faster than the global average and significantly faster than the rest of the Atlantic,” he said.
Dangendorf said it's not entirely clear why the area is a hotspot. But his research points to the effects of thermal expansion and Rossby wave phenomena. Rossby waves, also known as planetary waves, are not traditional ocean surface waves. They can be hundreds of kilometers long and are caused by the Earth's rotation. They can raise sea levels several inches along hundreds of miles of coastline.
Although the rate of sea level rise is usually measured in millimeters, the impact on people will be far greater. Native communities along Louisiana's coast have begun moving inland, and tidal flooding regularly disrupts life in Lyon, where Dangendorf said rising sea levels are increasing the cost of flood insurance.
“We're already feeling this in New Orleans,” he said. “I really don’t know how someone on a regular salary can still pay insurance premiums.”
How severe will sea level rise be?
A key predictor of how the 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 predicts that global mean sea level will rise by 0.43 meters (1.4 feet) by 2100. . The lower scenario would significantly reduce but not eliminate expected threats to low-lying communities and islands, the panel reported.
“It's clear what we can avoid by going to net-zero emissions,” Dangendorf said.
A big question mark currently facing scientists on rising sea levels is what will happen to the Antarctic and Greenland ice sheets in the coming decades. Englander said there is enough ice on the ice sheet that if it all melted, sea levels would rise 65 meters (213 feet). A rise of just three meters (9.84 feet) would have a huge impact on all coastal cities, including major cities such as Jakarta, Mumbai, Miami and Los Angeles.
Sharon Gray, director of education and science communications at the Sea Level Rise Institute, added that some Greenland glaciologists believe the ice sheet has reached a point of no return and melting is inevitable. Research suggests Antarctica may have reached a similar tipping point. But there are many uncertainties about when or how much the ice will melt.
“It's like predicting when the next earthquake or the next mudslide or the next avalanche will happen in San Francisco,” Englund said. “These things are impossible to predict with precision, and the same goes for the collapse of Antarctica and Greenland.”
Significant collapse of one or both of these ice sheets could raise sea levels beyond model predictions.
“Overall, I should say, actual sea level rise has been exceeding various projections or models over the past 20 years,” Englund said.
Sea level rise is certainly an ongoing problem, although uncertainty remains about how high it will be and how much coastal communities will be affected. Sea levels will continue to rise for centuries due to stored heat and thermal expansion in the oceans.
“Sea levels are already rising. We are committed to combating sea level rise. We need to adapt, but we also need to mitigate to avoid uncontrollable sea level rise,” Dangendorf said.
How can communities adapt to sea level rise?
Adaptation looks different in every community. Geology can play a role in the types of measures available, Gray noted.
“In Florida, for example, seawalls don't work because we're on limestone, so the water comes up from below,” she said. “Each place really needs to think individually about the resources they have.”
Englund points out that it's difficult for individuals to think about sea level rise on these time scales because it happens so slowly, like drops of water in a bucket.
“In Miami, real estate is booming. These high-rises are sprouting like weeds, these fancy, expensive condos. But the streets are flooding more and more,” he said. “People rationalize that in five years, if there's a flood or water levels rise, they're going to sell their house.”
Real estate and tourism are also booming in Charleston, Lyons said. She began organizing with her neighbors in 2017 after flooding from heavy rains and hurricanes led to her third consecutive flood insurance claim. Neighbors, who call themselves “Groundswell,” are working together to push political leaders to take Charleston's vulnerability to flooding seriously and build infrastructure to protect residents.
For a while, the group was successful, albeit more slowly than members had hoped. The city hired Dutch experts from flood-prone areas and established a resilience office to study and plan for flooding. In 2023, the U.S. Army Corps of Engineers released the Peninsula Perimeter Protection Project, a flood control study that recommended an 8-mile storm surge structure, natural-based features such as living shorelines and 10 water pumps. The city and the Army Corps have begun preliminary negotiations on a design agreement. With momentum building, Groundswell members decided it was safe to continue the hiatus.
“Unfortunately, we had a mayoral election last November and the mayor who supported all of these efforts lost by 500 votes,” Lyons said. “The new mayor, both publicly and even in private conversations during his campaign and since taking office, has been very skeptical of this peninsula conservation project.”
So, in late June 2024, Groundswell was back in action and Lyons was trying to breathe life into the team. Solidarity with neighbors has given the 81-year-old a new perspective.
“It actually became a new dimension in my life,” she said. “It's a horrific situation, so this is a completely honest endeavor for me. I'm with all of them. But it's comforting because I've found so many like-minded people who are smart and thoughtful , care, and work hard to find solutions in their own areas.
Englander said the Sea Level Rise Institute encourages policymakers and infrastructure planners to look further into the future when planning for sea level rise.
“The real short-term question is, what can we do to stop our homes from flooding this year?” he said. “This is just short-term flooding, and it's very important. But if we're trying to study the effects of sea level change, we should be thinking about 25, 50 and 100 years.
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