Executive Summary
A new Nature Geoscience study argues that coastal land does not simply rise or sink at a steady pace, and that this matters because local sea-level change is measured relative to the land. By comparing tide-gauge records with a probabilistic reconstruction of climate-related sea level from 1900 to 2021, the researchers found that vertical land motion is often nonlinear and can significantly amplify relative sea-level rise in some coastal communities. The practical message is that coastal risk cannot be assessed from ocean change alone: where the ground is sinking, flood exposure can grow faster than expected, especially in places already vulnerable to high tides and storm surge.
The New Finding Is That Coastal Land Motion Often Changes In Phases
The central development is not simply that land subsides or uplifts, which scientists have understood for decades, but that the rate of that movement often changes over time rather than remaining constant. The new study found previously unreported temporal variations in vertical land motion at a global set of tide-gauge stations, showing that local relative sea-level trends can shift materially when the ground itself speeds up or slows down in its sinking or rising. That makes local sea-level rise a more dynamic problem than conventional linear assumptions suggest.
The Study Reconstructed A Century Of Local Change From Tide Gauges
To isolate that signal, the researchers compared tide-gauge observations with a probabilistic reconstruction of climate-related sea level from 1900 to 2021. In the study’s framework, the difference between the reconstructed climate-driven sea-level signal and the observed tide-gauge record primarily reflects vertical land motion. The paper concludes that linear extrapolations can introduce systematic median projection errors of up to 7.6 millimeters per year at sites influenced by seismic or volcanic activity and 5.6 millimeters per year at other sites, which is large enough to matter for local planning and coastal projections.
Louisiana And The Mississippi Delta Stand Out As High-Impact Examples
The paper and the accompanying Phys.org coverage both highlight pronounced impacts in Louisiana and along the Mississippi Delta, where sinking land can dominate the local sea-level story. Thomas Wahl, a University of Central Florida researcher and co-author, said that in places like Louisiana, sea level may be rising by roughly 1 to 3 millimeters per year, while the land is sinking 10 to 15 times faster. That interaction compounds relative sea-level rise and increases the risk of flooding from high tides and storm surge for homes, businesses, and critical infrastructure.
Human Activity And Natural Processes Both Help Drive The Nonlinearity
The researchers argue that this variability is linked to both anthropogenic and natural processes. The Nature Geoscience paper identifies subsurface fluid withdrawal, seismic activity, and volcanic processes as key drivers of time-varying land motion, while the Phys.org article highlights groundwater extraction as a key human cause in some cities. The study also reports that decadal fluctuations in regional relative sea-level trends can exceed those driven by climate-related processes by an order of magnitude, helping explain why local coastal change can diverge sharply from broader ocean trends.
The Planning Implication Is That Linear Assumptions Are Becoming Riskier
One reason the study matters now is that many future sea-level projections still assume that ground motion behaves linearly over time. The authors explicitly challenge that assumption, arguing that time-varying vertical land motion should be incorporated more carefully into local projections. In practical terms, that means coastal communities may be underestimating future relative sea-level rise if they rely on a steady-rate model in areas where the ground is moving in phases or responding to changing human activity.
There Is A Policy Silver Lining In The Case Of Manageable Subsidence
The article also highlights a limited but important source of optimism: some forms of vertical land motion can be slowed. Wahl notes that Tokyo and Shanghai experienced extreme subsidence of several centimeters per year in the mid-20th century, but later substantially reduced that sinking after imposing stricter groundwater-extraction controls and related land-management policies. That does not make every coastal setting equally manageable, but it does suggest that at least part of the local sea-level problem can be influenced by policy rather than treated as immutable.
The Coastal Takeaway Is To Treat Land Motion As Part Of Sea-Level Risk
The most important takeaway from the new study is that coastal sea-level risk is not only about how fast the ocean is rising globally. It is also about how fast the land beneath a community is shifting locally and whether that motion is stable or changing over time. For coastal planners, engineers, and local governments, the implication is straightforward: place-specific monitoring of vertical land motion needs to be much closer to the center of flood-risk planning, adaptation strategies, and long-term infrastructure design.
Frequently Asked Questions (FAQs)
- What is vertical land motion? Vertical land motion is the upward or downward movement of the ground surface. In coastal areas, it matters because local sea level is measured relative to the land. Sinking ground worsens relative sea-level rise, while uplift can offset part of it.
- What is new about this study? The study’s main advance is demonstrating that vertical land motion is often nonlinear over time rather than steady. By inferring land motion at tide gauges worldwide, the authors identified temporal changes that conventional linear assumptions have not fully captured in twentieth-century sea-level budgets or future projections.
- Why do nonlinear land shifts matter for coastal communities? They matter because they can accelerate local relative sea-level rise, thereby worsening flood exposure. In areas with strong subsidence, the land can be sinking fast enough to materially amplify the effect of ocean-driven sea-level rise.
- What causes these changing rates of land motion? The study and article identify multiple causes, including groundwater and other subsurface fluid withdrawal, as well as seismic and volcanic processes. Because these drivers can intensify or ease over time, local land motion can also shift in phases rather than remain constant.
- Can communities do anything about subsidence? In some cases, yes. The Phys.org article notes that Tokyo and Shanghai significantly slowed earlier extreme subsidence by implementing stricter groundwater-extraction controls and related land-management measures, suggesting that some human-driven subsidence can be reduced.
Sources
- Dangendorf, S., Oelsmann, J., Mitrovica, J. X., Tornqvist, T. E., Piecuch, C. G., Creel, R., Coronel, W., Thompson, P. R., Ebinger, C., & Wahl, T. (2026). Variable contributions of vertical land motion to sea-level change inferred at tide gauges. Nature Geoscience. https://www.nature.com/articles/s41561-026-02005-1
- Ramiccio, M. (2026, June 10). Coastal land shifts reveal faster local sea level rise than expected. Phys.org. https://phys.org/news/2026-06-coastal-shifts-reveal-faster-local.html
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