US coastal cities at risk? What a new study warns about sea levels surging by 2100

Major U.S. coastal cities could face far greater flooding, property damage and pressure to abandon vulnerable neighborhoods if global sea levels approach 6.2 feet of rise by the end of the century, according to research that raises the upper limit well beyond widely used United Nations projections.

From Miami and New Orleans to New York and communities along the California coast, higher seas could magnify storm surges, overwhelm existing flood defenses and expose homes, roads, ports and other critical infrastructure to more frequent inundation. Saltwater could also penetrate farther into freshwater supplies and agricultural areas, while some low-lying communities may eventually have to consider managed retreat.

The warning stems from research by scientists at Nanyang Technological University (NTU) in Singapore and Delft University of Technology in the Netherlands. Their modeling suggests that under a high greenhouse gas emissions scenario, global mean sea level rise by 2100 could fall within a “very likely” range of approximately 1.6 to 6.2 feet.


The 6.2-foot figure is not a prediction that oceans will definitely rise by that amount. Rather, it represents the upper end of a broader probability range designed to capture severe outcomes that could be missed when planners rely on narrower projections.

That distinction is especially important for the United States, where trillions of dollars in homes, businesses and infrastructure are concentrated along coastlines. Decisions being made now about sea walls, drainage networks, ports, highways and new construction could have consequences lasting well into the next century.

Why the new sea level estimate matters for the US

The implications of rising seas extend well beyond beaches disappearing beneath the water.

As the average sea level increases, coastal flooding can begin from a higher baseline. That means hurricanes and other storms do not necessarily need to become stronger for their storm surges to reach farther inland.

Low-lying roads, airports, sewage facilities and electrical infrastructure could consequently face greater exposure. Properties that rarely flood today could experience increasingly regular inundation, while insurance and adaptation costs could rise alongside the physical threat.

The effects will not be identical across the United States. Local land movement, ocean circulation and changes associated with melting polar ice can cause relative sea levels to rise faster in some locations than the global average.

Subsidence poses an additional problem in places where the land itself is sinking, compounding the impact of rising water.

Researchers combine two approaches to calculate future risk

Scientists have long faced difficulties determining exactly how high oceans could rise because different forecasting methods can produce noticeably different results.

Physics-based models simulate processes including glacier loss, ice-sheet changes and the expansion of seawater as oceans warm. While grounded in known physical processes, these models may have difficulty representing some highly uncertain events capable of producing rapid changes.

Expert assessments provide another source of information, particularly for potentially high-impact processes that are harder to model.

A research team led by NTU senior research fellow Benjamin Grandey developed a statistical “fusion” approach designed to bring those sources together rather than choosing one over the other.

The work, involving researchers from NTU and Delft University of Technology, was published in Earth’s Future in December 2024 and used underlying data associated with the Intergovernmental Panel on Climate Change’s Sixth Assessment Report.

How high could sea levels actually rise?

Under a lower-emissions pathway, the fusion model produced a 90% probability range of roughly 1.0 to 3.3 feet of sea level rise by 2100.

Under high emissions, the range widened considerably to approximately 1.6 to 6.2 feet.

The researchers’ probability framework differs from the one used for some headline IPCC projections, so the figures cannot simply be compared as equivalent forecasts. The IPCC’s comparable high-emissions range reaches roughly 3.3 feet at a 66% probability threshold.

The significance of the new work lies largely in its treatment of uncertainty. By widening the range, researchers can account for potentially devastating outcomes that may have relatively low probabilities but enormous consequences.

Flood defenses may need to prepare for worse scenarios

For U.S. cities, a wider range of possible sea level rise could change how officials think about infrastructure built to last for many decades.

A seawall, bridge or transit system designed around a lower estimate could prove inadequate if actual sea level rise approaches the higher end of the range.

Coastal planners can instead use severe scenarios to stress-test projects and determine whether defenses would continue functioning under more extreme conditions.

Rising seas could also worsen saltwater intrusion into freshwater aquifers and agricultural land and accelerate the loss of wetlands that naturally provide some protection against storms.

In the most vulnerable communities, repeatedly rebuilding after floods may eventually become more expensive than relocating people and infrastructure — a process generally known as managed retreat.

The researchers do not argue that such an outcome is inevitable across U.S. coastal cities. Instead, the expanded projections underline the scale of uncertainty confronting communities making long-term decisions today.

For cities with infrastructure expected to remain in use through 2100 and beyond, the question is no longer only how much sea levels are likely to rise. Planners may increasingly have to consider what happens if the more extreme projections become reality.