Authors of new paper report slower global sea-level rise after analyzing long-term coastal records
A peer-reviewed study using century-long observations at thousands of coastal sites finds a global average rise near 1.5 mm per year, a figure below many model-based estimates
Researchers Hessel Voortman and Rob de Vos reported in a peer-reviewed paper in the Journal of Marine Science and Engineering that global mean sea level has been rising at roughly 1.5 millimeters per year, a rate that they say is consistent with the pace observed over the past century and projects to about six inches of rise by 2100.
The paper, titled "A Global Perspective on Local Sea Level Changes," analyzes long-term observational records from coastal locations to compare measured trends with model-based projections commonly cited in recent decades. The authors said they compiled and reviewed records averaging about a century of observations at roughly 150,000 coastal sites to produce their global estimate.
Voortman, a Dutch hydraulic engineer, told colleagues and co-author Rob de Vos that his initial review was prompted by work on flood-protection and coastal-infrastructure projects in the Netherlands. According to the paper, Voortman found discrepancies between model-based global projections and local tide-gauge data for the Netherlands and then expanded the analysis internationally. The authors said they funded the broader effort themselves and subjected their findings to peer review before publication.
The study's conclusions differ from a number of recent model-based projections and assessments that report higher global average rise rates and larger cumulative increases by 2100. For example, several studies and public reports have cited satellite altimetry and model syntheses indicating global mean sea-level-rise rates closer to 3–4 millimeters per year in recent decades, and some projections have suggested one to three feet or more of rise by century's end under higher-emission scenarios. The paper notes those projections commonly incorporate modeled contributions from ice-sheet loss, thermal expansion, and other components.
Sea-level change is regionally variable and driven by multiple factors including ocean warming, melting land ice, local land subsidence or uplift, and changes in ocean circulation. Tide gauges measure relative sea level at a specific location and must be corrected for factors such as glacial isostatic adjustment; satellite altimeters measure absolute sea surface height from space and have provided near-global coverage since the early 1990s. Reconciling long-term tide-gauge records with satellite-era measurements and model outputs has been an active area of research.
The authors argue their approach — emphasizing long-term observational records at coastal sites — offers a different perspective from projections that rely heavily on model extrapolations and selected inputs. They contend that, when assessed against extensive observational data, the rate of global mean rise does not show the acceleration implied by some model-based estimates.
Independent scientists and agencies typically subject new analyses to detailed scrutiny of methods, data selection and corrections. Key issues in comparing studies include the spatial distribution of tide gauges, the length and continuity of records, the application of geophysical adjustments, and the treatment of recent changes in ice-sheet mass balance. Satellite altimetry, tide-gauge networks and climate models each provide distinct types of information about sea-level change, and researchers often use multiple lines of evidence to form assessments.
Mainstream climate assessments, including those by the Intergovernmental Panel on Climate Change and numerous peer-reviewed studies, have emphasized a broad consensus that global sea levels have risen since the 19th century and that rates have increased in recent decades largely because of ocean warming and ice loss from Greenland and Antarctica. Those assessments also note substantial regional differences and the potential for higher local impacts where land subsidence or storm surge amplify effects.
Voortman and de Vos's paper does not contest the existence of human-driven climate change, but it calls for further examination of how models and observational records are integrated to produce projections used for policy and adaptation planning. The authors said their findings underline the importance of testing model outputs against long-term measurements.
The publication is likely to prompt additional analyses and debate in the scientific community about methodological choices and the implications for coastal adaptation strategies. Public agencies, coastal planners and the broader research community frequently reassess risk estimates as new data and analyses become available, and several scientists said verifying the new study's dataset and methods will be an important next step for understanding how its conclusions relate to existing assessments.