New Study Warns US Coastal Cities Could Face 6.2 Feet of Sea Level Rise by 2100

Why a New Sea-Level Model Upends US Coastal Planning

Coastal cities from Miami to New York and along the California shoreline may need to prepare for far more severe flooding than is currently assumed in most long-range plans. A new study by scientists from Nanyang Technological University in Singapore and Delft University of Technology warns that, under a high greenhouse-gas emissions scenario, global mean sea-level rise by 2100 could fall within a 90% probability range of approximately 1.6 to 6.2 feet. That upper figure is not a prediction but a deliberately widened estimate meant to capture extreme outcomes that narrower projections often miss.

The research, published in Earth’s Future, combines physics-based models with expert assessments of uncertain ice-sheet processes. The result is a statistical “fusion” that produces a wider and more comprehensive view of possible sea-level futures than the headline ranges used by the Intergovernmental Panel on Climate Change, whose comparable high-emissions rise reaches roughly 3.3 feet at a 66% probability threshold. The expanded range could fundamentally change how US officials set building codes, design flood defenses and decide where to rebuild after disasters.

For the United States, the stakes are enormous. Trillions of dollars in homes, businesses, roads, ports, drainage networks and other infrastructure are concentrated along the coast. Higher seas do not just submerge beaches; they lift the baseline from which storm surges start, meaning hurricanes and nor’easters can push water farther inland even if they do not intensify. Properties that today flood only in rare events could face regular inundation, while saltwater intrusion threatens drinking water supplies and farmland.

What the Expanded Range Means for Property and Infrastructure

A Probability Framework That Forced a Wider Lens

The team, led by NTU senior research fellow Benjamin Grandey, built a model that merges detailed physical simulations with structured expert judgment about processes such as rapid ice-sheet collapse. The approach acknowledges that highly uncertain, low-probability events can still have enormous consequences. By reporting a 90% probability range rather than a narrower central estimate, the researchers effectively told planners: the upper tail is wider than you think, and ignoring it could be catastrophic. The 1.6-foot lower bound is already serious; the 6.2-foot upper bound would redraw maps of every US coastal city.

How the US Coastline Is Uniquely Exposed

Sea-level rise will not be uniform. Some areas, such as the Gulf Coast, face additional subsidence — the land itself is sinking — which compounds the effect. In parts of Louisiana and Texas, relative sea-level rise could be 2 to 3 feet higher than the global average. Low-lying roads, airports, sewage treatment plants and electrical substations could be exposed to regular tidal flooding long before a major storm hits. The study’s core message is that “very likely” ranges used up to now may have lulled decision-makers into underestimating the worst case.

Property, Insurance and Infrastructure: A Trillion-Dollar Gap

If the full 6.2-foot rise materialises, the consequences for real estate are drastic. Many properties in current flood-insurance maps would essentially become uninsurable or unlivable. Mortgage lenders backing 30-year loans on coastal properties would need to factor in the higher end of sea-level projections. Beyond homes, the infrastructure that makes coastal cities functional — ports that handle billions of dollars in trade, bridges, underground transit — was not designed for such water levels. Replacing or retrofitting it would cost hundreds of billions of dollars, and failing to prepare early could leave entire communities as stranded assets.

The Managed Retreat Question Moves into Mainstream

The study does not predict mass relocation, but it makes the conversation about “managed retreat” harder to avoid. When the cost of repeatedly rebuilding after floods exceeds the value of staying, buyout programs and relocation become economically rational — even if politically fraught. The expanded probability range arms local governments with the scientific justification to start zoning changes and infrastructure divestment in areas that cannot be defended.

What Coastal Stakeholders Should Do in a 6.2-Foot World

The implications for different coastal stakeholders are immediate and specific.

• Property developers and homebuyers: Re-evaluate flood-zone reliance on current FEMA maps, which are based on historical rather than forward-looking probabilities. Insist on elevation certificates and long-term flood-risk disclosures for any property within the 6.2-foot surge zone.
• City planners and municipal bond issuers: Stress-test all infrastructure projects with a 6.2-foot sea-level scenario by 2100, even if it exceeds current regulatory requirements. Bond rating agencies are beginning to scrutinise climate risk; a failure to plan could raise borrowing costs.
• Mortgage lenders and insurers: Update catastrophe models to incorporate the 90% probability range, not just the IPCC median. Overconcentration in high-risk ZIP codes, especially in subsidence-prone areas of the Gulf, could become a systemic portfolio risk.
• Federal and state agencies: Use the NTU/Delft fusion framework to guide revisions of the National Flood Insurance Program and coastal infrastructure grants, so that public money is not repeatedly spent defending areas that are likely to be abandoned later in the century.