A study published in the journal Nature reveals a recurrent methodological error in the way sea level rise is measured.
After reviewing hundreds of research studies and risk assessments, the authors conclude that around 90% of studies underestimate the reference water height at coasts by about 30 cm.
This issue is more frequent in the Global South, the Pacific, and Southeast Asia, and less so in Europe and the Atlantic coasts.
The cause of the error
According to Philip Minderhoud, professor of hydrogeology at the Wageningen University (Netherlands), the discrepancy arises because sea and land measurement methods do not align at the critical point where they meet.
- Land models often assume that “zero” coincides with the water level.
- In reality, in Indo-Pacific areas, that level can be nearly a meter above.
- Many studies start from the idea of a calm sea, when the coast is constantly affected by waves, currents, tides, temperature changes, and phenomena like El Niño.
Impact on projections
Adjusting the reference height implies that if the sea level rises a little more than a meter by the end of the century, the waters could:
- Flood up to 37% more surface area.
- Put at risk between 77 and 132 million additional people.
This complicates the planning and financing of climate change adaptation measures.
Testimonies from the Pacific
Climate activist Vepaiamele Trief, 17, describes how on her native island in the Vanuatu archipelago, the coast has visibly receded in a few years:
- Eroded beaches.
- Coastal trees uprooted.
- Homes barely a meter from the sea at high tide.
On the island of Ambae, a coastal road had to be diverted inland due to the advancing water. Even graves have been submerged. “These studies are not just numbers; they are the real livelihoods of people,” Trief states.
Scientific debate
- Ben Strauss (Climate Central) points out that the error lies in the baseline from which elevation is calculated.
- Other experts, like Gonéri Le Cozannet (French geological service) and Robert Kopp (Rutgers University), believe the problem is identified and that local planners usually know their coastal risks well.
- Minderhoud insists that in regions like Southeast Asia and island states, the discrepancy is critical and can severely underestimate the threat.
Connection with other studies
The finding coincides with a Unesco report warning about gaps in knowledge of the ocean as a carbon sink. Models differ by 10% to 20% in their estimates, raising doubts about the accuracy of global climate projections.
The study highlights that governments might be planning coastal risks with an incomplete view of reality. Sea level rise is not a future phenomenon: it is already transforming coasts, communities, and ways of life.
