Climate change is causing sea level rise. How can we stop the water invading our coastal towns?
June 8 is World Oceans Day and the theme is “Life & Livelihoods”. In the United States, more and more people have been moving to coastal areas, so that 29% of the population now lives near the coast. The ocean provides resources, jobs, and amenities—such as fishing, shipping, and beaches—meaning that large parts of the coast are densely populated and are facing risks that the rising seas will bring.
As you can see, the ocean provides a lot. However, climate change is impacting the ocean. Warmer ocean waters are fueling more intense storms, resulting in damage and destruction on land. In 2020, a record number of six hurricanes and a tropical storm cost the US more than $40 billion in damages. In addition to these extreme events, there is also a slow-moving trend that puts our lives and livelihoods on the coast at risk: sea level rise.
Climate change causes the oceans to expand and creep up on the shores where we live and work, this is sea level rise. There are two processes at play: as the ocean warms by absorbing heat from a warmer atmosphere, the water expands. More water is also added to the ocean as glaciers and ice sheets melt. Scientists project that ocean water levels around the globe will have increased by 1 to 8 ft in 2100.
South Florida is one of the places where the impacts of sea level rise – about half a foot since 1994 – is already felt. As a low-lying peninsula surrounded by water, just 2ft of sea level rise would mean 10% of the land is permanently swallowed by the sea. There are two types of flooding the region is most worried about: destructive storm surge from tropical storms and hurricanes, and milder tidal flooding.
When large storms make landfall, the combined forces of high winds and storm surge can cause a lot of damage. The US Army Corps of Engineers published a report last year detailing a plan to protect Miami from storm surge. It included a proposal to build an 8 ft wall around the Brickell financial district, meaning a walk along the popular boulevard no longer would include a view of Biscayne Bay. As you can imagine there is a lot of pushback about this plan, as it would disconnect the seaside neighborhood from the sea.
Another reason for the pushback was that the tall sea wall would only serve Miami in case of storm surge, and would not protect against flooding from sea level rise. Miami is built on limestone bedrock, through which ancient sea creatures dug millions of tiny tunnels. As a result, the limestone is highly permeable. Building a sea wall can keep temporary floodwaters from a storm surge out, but in the long term, the water will seep through the limestone and push up from below the ground behind the flood protection measures.
As the sea levels rise, they exert more pressure on the water table underneath Miami. This will raise the water table, causing South Florida’s many septic tanks to become compromised. In order to operate safely, septic tank drain fields require a certain amount of dry soil to let microbes break down the waste. As the water table rises, more and more of Miami’s septic tanks will have too little dry soil to neutralize harmful bacteria in the wastewater, potentially leading to public health issues. Furthermore, the salty seawater pushes further into the Biscayne Aquifer, the underground, freshwater supply South Florida takes its drinking water from. Three million people are currently dependent on this source for their drinking water.
The increased sea levels and pushing the water table higher and higher also have another effect: tidal flooding. This mild form of flooding also referred to as nuisance flooding or sunny day flooding, is caused when high tides push seawater onto the streets. Usually not by overtopping sea walls or levees, but through the groundwater table or backflow through storm drains.
In Miami, the highest tides of the year, King Tides, cause roadways and parks to flood in the late summer and fall. This flooding does not cause any immediately visible damage to buildings but does affect cars driving through the corrosive saltwater, and brings about road closures. In response to this nuisance flooding, Miami Beach raised a section of the road to install pumps that help remove any remaining water. This keeps the streets dry for the next few decades, but not the buildings lining the street, which have not been raised.
In the Florida Keys, certain roads were flooded for more than 90 consecutive days in 2019, with people needing to canoe from their property to the dry road where their cars were parked. Raising the roads could cost more than $180 million for a 3-mile stretch. There are more than 300 miles of roads in the Florida Keys meaning that raising all of them is prohibitively expensive.
But it’s not just Florida. Nuisance flooding in Annapolis, MD, is already impacting the local economy by reducing business revenues near flood-prone locations. In New York City, Superstorm Sandy, which battered the city in 2012, kickstarted ambitious plans to protect southern Manhattan from flooding. However, the plans to elevate East River Park by burying it under 8 ft of dirt and rebuilding a new park on top is controversial. In the San Francisco Bay Area, the nine counties bordering the bay have to coordinate their flood protection measures well, as a sea wall in one municipality could easily displace the water and worsen the flooding in another community.
An increase in sea level of only a few feet might not sound too dangerous, since many of us live at elevations multiple feet above sea level. However, even a few feet of sea level rise will have significant impacts in many communities along the US coasts, including faster erosion of cliffs, more storms that cause flooding, and nuisance flooding. Many communities along the Eastern Seaboard might see tidal flooding almost every single day of the year by the end of the century. Just three feet of sea level rise could displace more than 4 million Americans, and six feet could mean more land that houses 13 million people would be permanently under water.
The severity of the impacts of sea level rise will depend on how much and how quickly the water will come, obviously 1 foot will have a much milder impact and in fewer locations than 8 feet. One major reason for the large uncertainty in the projections is that the ice shelves in Greenland and Antarctica have been melting faster and faster, and scientists do not know whether this will eventually slow down, or continue to melt at increasing speed. A second reason for this large uncertainty is the amount of greenhouse gases we will pump into the atmosphere over the coming decades – lower emissions will make lower sea level rise more likely.
Sharply reducing our emissions will mitigate climate change and reduce its dangerous impacts, including sea level rise. On Earth Day (April 22), President Biden announced a commitment to reduce US greenhouse gas emissions by 50% compared to 2005 levels. American leadership on climate action can convince other countries to also pursue higher emissions reduction commitments, reducing the risk we’ll end up with 8 feet of sea level rise. Water is already at South Florida’s doorstep. But the key to keeping Miami and other coastal cities livable communities might depend less on what local officials do, and more on what all of us decide even if we do not live on the coast.
Carolien Kraan is a doctoral researcher at the Abess Center for Ecosystem Science and Policy at the University of Miami. Her dissertation research aims to support climate change adaptation that is sensitive to a wide range of societal goals, including equity and environmental justice. She is particularly interested in the idea of making more space for the water through strategic managed retreat. She has studied managed retreat in the United States by looking at where FEMA-funded voluntary property buyout programs have taken place and has also written about policy options to address equity concerns that have been raised about buyouts. Prior to joining UM, Kraan worked at Stanford University, where she focused on integrative assessments, including on the relationship between climate and conflict. She has also worked as a researcher and policy advisor at the Energy research Centre of the Netherlands (ECN), and holds an MSc from the University of Edinburgh, UK, and a BSc from University College Roosevelt, the Netherlands.