Rising Sea Levels Threaten More Coastal Communities Than Previously Thought

As the climate warms, sea levels are rising globally, impacting coastal communities. New research indicates that the number of people at risk of inundation may be significantly higher than previous estimates, potentially affecting up to 132 million more individuals than initially projected.

Underestimation of Sea Level Rise

A study published in the journal Nature reveals that previous scientific research may have underestimated current sea levels by approximately 10 inches. This discrepancy stems from the starting point used in most studies, which relies on ocean heights that are lower than actual measurements. If sea levels rise by three feet from where they were from 1995-2014, this could happen by the middle of the next century, depending on emissions reductions.

Regional Impacts

The underestimation is most pronounced in Southeast Asia and the Indo-Pacific region, where sea levels are already more than three feet higher than assumed in many research models. This means a larger land area and population are vulnerable to the effects of rising seas in these regions.

Global Sea Level Trends

Globally, sea levels have risen 8 to 9 inches since 1880. This rise is driven by two primary factors: the melting of glaciers and polar ice caps, which adds freshwater to the ocean and the thermal expansion of water as ocean temperatures increase. The effect is amplified in areas where land is sinking, such as the U.S. East Coast.

Impacts on Coastal Communities

Coastal communities are already experiencing the consequences of rising sea levels, including increased flooding during storms and hurricanes, and more frequent “sunny day” flooding during high tides.

The Role of Geoid Models

The study identifies a “methodological blind spot” in the computer models used to estimate current sea levels. These models, known as geoid models, simulate the ocean’s surface in calm conditions, but do not fully account for factors like tides, ocean currents, and trade winds. Researchers found that 90% of studies from 2009 to 2025 were starting with current sea levels that were too low.

Correcting the Data

By using actual measurements of current sea level, researchers found that up to 37% more land area and 68% more people would be affected by a three-foot rise in sea levels compared to previous estimates. Recent studies are beginning to incorporate this corrected data.

Implications for Climate Negotiations

Accurate global impact assessments are crucial for vulnerable countries advocating for increased emissions reductions and financial assistance from wealthier nations during international climate negotiations.

Local Adaptation Planning

While the new study provides a more accurate global picture, local communities typically rely on detailed, localized data for adaptation planning. This includes assessing land and sea elevations, infrastructure, and coastal dynamics to determine specific vulnerabilities and implement appropriate measures like building sea walls, restoring natural coastal protections, or relocating populations.