The ocean rarely announces its changes loudly. Most days it appears steady and familiar — waves arriving in patient rhythm, tides rising and falling with a quiet certainty that seems timeless. Yet beneath that calm surface lies a system shaped by subtle forces: winds, currents, gravity, and heat moving slowly through the planet’s waters.

For years, scientists have tried to capture that complexity through models and measurements, building projections that help communities understand what rising seas may mean for coastlines. But new research suggests that one important detail may have been overlooked. In some places, the ocean may already be higher than scientists previously believed.

A recent study published in Nature examined hundreds of scientific papers on coastal flood risk and sea-level rise. By reviewing 385 peer-reviewed studies produced between 2009 and 2025, researchers discovered that many assessments relied on simplified assumptions about sea level rather than using direct local measurements.

These assumptions often used what scientists call “geoid models.” In simple terms, these models estimate sea level based on Earth’s gravity and rotation. They are useful for understanding the general shape of the ocean’s surface across the globe. Yet the real ocean is influenced by many other factors — from winds and ocean currents to temperature and salinity — which can raise or lower water levels in different regions.

When the researchers compared the models with measured coastal sea levels, they found a noticeable gap. On average, sea levels used in many studies were about 24 to 30 centimeters lower than actual measurements, though the difference varied depending on location and modelling method.

In parts of the Global South — particularly Southeast Asia and the Indo-Pacific — the difference could be even greater. Some coastal areas may have sea levels one meter or more higher than previously assumed, according to the study’s analysis.

At first glance, a few tens of centimeters might seem modest compared with the vast scale of the ocean. But for coastal planning, such differences matter greatly. Sea-level projections are used to design flood defenses, plan infrastructure, and estimate how many people may be exposed to coastal flooding in the future.

If the baseline sea level used in calculations is already too low, then projections of future risk may also be understated.

Using revised measurements, the researchers estimated that if global sea levels rise by one meter — a possibility often discussed in long-term climate projections — up to 37 percent more land could fall below sea level than previously projected. This could place 77 million to 132 million additional people in vulnerable coastal zones.

The findings do not necessarily mean that previous studies were careless. Instead, scientists describe the issue as a kind of disciplinary gap — where ocean measurements and land-elevation data were not always combined in a way that reflected real coastal conditions.

For many coastal cities and island nations, especially those already experiencing flooding during high tides or storms, the research adds another layer of urgency to understanding the changing relationship between land and sea.

Sea-level rise itself remains driven by well-known forces: melting glaciers and ice sheets, along with the expansion of seawater as it warms. The Intergovernmental Panel on Climate Change has estimated that global sea levels could rise between about 28 centimeters and one meter by 2100, depending on future emissions and climate responses.

What the new research suggests is that the starting point — the present-day height of the sea relative to the land — may need a closer look.

For scientists, that means refining models and integrating more detailed local measurements. For policymakers and coastal planners, it may mean reassessing flood maps, infrastructure plans, and long-term adaptation strategies.

The ocean, after all, moves slowly but persistently. And sometimes the most important discoveries about its future begin with a quiet correction to how we measure the present.

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Sources The Guardian Associated Press (AP) Financial Times Vox Nature (Journal)