The Docket | Emerging Science

The Wrong Number

Building to the Wrong Number

By Seth D. Carrington— May 6, 2026

Feature image for article: Building to the Wrong Number

The tide gauge at Galveston's Pier 21 has been watching the ocean since 1904. Across the bay, the Army Corps is building the largest coastal protection system in its history, $34 billion in gates and barriers and dunes, all of it engineered to a number that traces back to instruments like that gauge. Two independent studies published in the past fourteen months say the number is wrong.

Both errors run the same direction, one in the sea surface, the other in the ground beneath it. Between those two surfaces sits a project already going to concrete, designed to a margin of safety that is narrower than anyone involved has been told.

The Wrong Number

Building to the Wrong Number

By Seth D. Carrington— May 6, 2026

The tide gauge at Galveston's Pier 21 has been watching the ocean since 1904. Across the bay, the Army Corps is building the largest coastal protection system in its history, $34 billion in gates and barriers and dunes, all of it engineered to a number that traces back to instruments like that gauge. Two independent studies published in the past fourteen months say the number is wrong.

Both errors run the same direction, one in the sea surface, the other in the ground beneath it. Between those two surfaces sits a project already going to concrete, designed to a margin of safety that is narrower than anyone involved has been told.

The Correction, Mapped

Every flood map, seawall specification, and insurance rate filing along the US coast starts from one assumed number: where the ocean sits before anything goes wrong. Three studies published in early 2026 found that number is systematically low. Measured sea level at the shoreline runs roughly ten inches higher than the modeled baseline underpinning most coastal hazard assessments. The ocean has always been there. The models just weren't measuring the right one.

What follows are five findings that make the scale of this revision concrete across US coastal geography. The numbers, and where they land.

The Correction, Mapped

Every flood map, seawall specification, and insurance rate filing along the US coast starts from one assumed number: where the ocean sits before anything goes wrong. Three studies published in early 2026 found that number is systematically low. Measured sea level at the shoreline runs roughly ten inches higher than the modeled baseline underpinning most coastal hazard assessments. The ocean has always been there. The models just weren't measuring the right one.

What follows are five findings that make the scale of this revision concrete across US coastal geography. The numbers, and where they land.

Baseline Gap

The Ocean Is Ten Inches Higher Than Modeled

A March 2026 Nature study compared measured coastal sea level at tide gauges worldwide against the two geoid models used in most hazard assessments. The measured ocean runs 0.24 to 0.27 meters higher. The models leave out winds, currents, tides, and water temperature. The starting point for nearly all US coastal flood planning sits roughly ten inches too low.

Revised Exposure

Up to 132 Million More People Below Flood Line

Correct the baseline and the exposure math changes fast. After one meter of rise, 37% more land area and up to 132 million more people worldwide fall below sea level than current assessments project. The study's co-author: impacts "will be occurring sooner than previously predicted." That meter isn't hypothetical. It's the upper range of what NOAA projects for US coasts by 2100.

Assessment Quality

Nine in Ten Coastal Studies Used Wrong Baseline

Of 385 recent coastal hazard publications evaluated in the Nature study, 90% relied on modeled rather than measured sea level. More than 99% mishandled sea level or land elevation data in some form. Two papers acknowledged the discrepancy. Two out of 385.

Facility Risk

Seven States Hold 80% of Coastal Facility Exposure

Louisiana, Florida, New Jersey, Texas, California, New York, and Massachusetts account for nearly 80% of the 5,500 hazardous facilities projected to face a 1-in-100-year flood by 2100. Some 3,800 of those facilities face flood risk by 2050. Communities designated "disadvantaged" by federal criteria have 50% higher odds of living near one.

Sinking Land

In Half of Major Deltas, Land Sinks Faster

In 18 of 40 major river deltas studied globally, subsidence outpaces sea level rise, more than doubling effective local exposure. Louisiana's Mississippi Delta sinks up to 3 centimeters per year. Houston, the fastest-sinking major US city, has 40% of its area dropping more than 5 millimeters annually, driven by the same groundwater extraction that built its suburbs.

The Research

Sea level much higher than assumed in most coastal hazard assessments

A meta-analysis of 385 coastal hazard studies reveals that 99% relied on gravity-based geoid models rather than tide gauge measurements, systematically underestimating baseline sea levels by 20–30 cm globally and over a meter across Southeast Asia. Corrected exposure figures jump 48–68%.

How large is the error?

Geoid models approximate sea level using Earth's gravitational field. Tide gauges measure it. The gap between the two averages 20–30 cm and exceeds a meter in some regions.

What's still unresolved?

A preprint critique argues the datum correction is one of several compounding baseline errors, including atmospheric loading and vertical land motion, not yet reconciled against each other.

Global subsidence of river deltas

Satellite radar mapping of 40 major river deltas finds land sinking faster than oceans rising in 18 of them, driven overwhelmingly by groundwater extraction. Some 236 million people live on ground that is dropping out from under them, and compacted aquifer material does not rebound.

Which coastlines are most exposed?

The Mekong, Nile, and Mississippi deltas show subsidence rates that dwarf ocean-driven rise, making the land's collapse the more immediate flood threat.

Why is this permanent?

Pumping compresses fine-grained aquifer layers irreversibly. Even if extraction stops tomorrow, the elevation already lost and the storage capacity with it are gone for good.

The Research

Sea level much higher than assumed in most coastal hazard assessments

A meta-analysis of 385 coastal hazard studies reveals that 99% relied on gravity-based geoid models rather than tide gauge measurements, systematically underestimating baseline sea levels by 20–30 cm globally and over a meter across Southeast Asia. Corrected exposure figures jump 48–68%.

How large is the error?

Geoid models approximate sea level using Earth's gravitational field. Tide gauges measure it. The gap between the two averages 20–30 cm and exceeds a meter in some regions.

What's still unresolved?

A preprint critique argues the datum correction is one of several compounding baseline errors, including atmospheric loading and vertical land motion, not yet reconciled against each other.

The Research

Global subsidence of river deltas

Satellite radar mapping of 40 major river deltas finds land sinking faster than oceans rising in 18 of them, driven overwhelmingly by groundwater extraction. Some 236 million people live on ground that is dropping out from under them, and compacted aquifer material does not rebound.

Which coastlines are most exposed?

The Mekong, Nile, and Mississippi deltas show subsidence rates that dwarf ocean-driven rise, making the land's collapse the more immediate flood threat.

Why is this permanent?

Pumping compresses fine-grained aquifer layers irreversibly. Even if extraction stops tomorrow, the elevation already lost and the storage capacity with it are gone for good.

The Delay

A Sea Level Finding Published Today Won't Reach Your Local Building Code for a Decade. Here's Where It Gets Stuck.

A corrected sea level study has to pass through at least six institutional layers before it touches a building permit: federal projections, engineering standards, model codes, state adoption, local enforcement. Each runs on its own update clock. The full chain can take two decades.

Nobody waits. Buildings get permitted to whatever number currently exists. Over half of U.S. states still enforce flood load provisions unchanged since 1998, with no sea level rise consideration at all. Those structures are designed for fifty-year service lives. The concrete cures long before the science catches up.

The Delay

A Sea Level Finding Published Today Won't Reach Your Local Building Code for a Decade. Here's Where It Gets Stuck.

A corrected sea level study has to pass through at least six institutional layers before it touches a building permit: federal projections, engineering standards, model codes, state adoption, local enforcement. Each runs on its own update clock. The full chain can take two decades.

Nobody waits. Buildings get permitted to whatever number currently exists. Over half of U.S. states still enforce flood load provisions unchanged since 1998, with no sea level rise consideration at all. Those structures are designed for fifty-year service lives. The concrete cures long before the science catches up.

Frozen standards:

ASCE 7 flood load provisions went essentially unchanged from 1998 to 2023, when Supplement 2 first required designers to account for sea level rise

Code bottleneck:

That 2023 supplement missed the 2024 International Building Code cycle and won't be proposed for adoption until the 2027 edition

Map decay:

Two-thirds of FEMA flood maps haven't been updated in five years; many coastal communities haven't seen a revision in over thirty

Political whiplash:

The Federal Flood Risk Management Standard has been revoked twice since 2017, spending just eight of the past eleven years in effect

Already diverging:

Private flood models now incorporate forward-looking climate data that FEMA maps and building codes still exclude entirely

Keep Reading

Yale Environment 360: 'A More Troubling Picture of Sea Level Rise Is Coming into View'

Fred Pearce weaves both the baseline correction and subsidence research into a single narrative, with megacity-specific projections and historical context you won't find collected ...

NPR: 'Millions more people are in the path of rising seas than previously thought'

Lauren Sommer's piece is the clearest explanation of the geoid measurement error itself, and she surfaces a detail worth sitting with: some local planners were already working from...

Undark: 'A More Troubling Picture of Sea Level Rise Comes Into View'

AP/Africanews: 'Sea level rise may threaten millions more, study finds'

Keep Reading

Yale Environment 360: 'A More Troubling Picture of Sea Level Rise Is Coming into View'Fred Pearce weaves both the baseline correction and subsidence research into a single narrative, with megacity-specific projections and historical context you won't find collected ...

NPR: 'Millions more people are in the path of rising seas than previously thought'Lauren Sommer's piece is the clearest explanation of the geoid measurement error itself, and she surfaces a detail worth sitting with: some local planners were already working from...

Quick links

Undark: 'A More Troubling Picture of Sea Level Rise Comes Into View'

AP/Africanews: 'Sea level rise may threaten millions more, study finds'

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