A landmark study published June 13 in Science Advances warns that future sea-level rise may occur more abruptly and reach greater heights than previously anticipated. Led by Professor Andrea Dutton of the University of Wisconsin–Madison and doctoral candidate Karen Vyverberg of the University of Florida, researchers analyzed fossil corals from the Seychelles islands to reconstruct precise sea-level changes during the Last Interglacial period—when global temperatures were comparable to today’s. Their findings underscore the potential for rapid, multi-meter rises in coming decades, posing urgent questions for coastal planners and policymakers worldwide.
Last Interglacial: A Window into Our Warming World
The Last Interglacial, roughly 129,000 to 116,000 years ago, represents the most recent interval in Earth’s history when average global temperatures matched or exceeded current levels. Because the major ice sheets in Greenland and Antarctica were similarly stressed by warmer climates, this period serves as a natural analogue for projecting the long-term response of ice volume and sea level to ongoing greenhouse gas emissions.
“This is not good news for us as we head into the future,” warns Professor Dutton. “By understanding how sea levels behaved when temperatures were similar to now, we gain critical insights into what lies ahead.”
Why the Seychelles Matter
Nestled in the central Indian Ocean, the Seychelles islands offered an ideal laboratory for sea-level reconstruction. Unlike coastlines influenced by nearby ice masses, the islands’ location far from ancient ice sheets minimized local gravitational and crustal effects that can skew relative sea-level records.
More importantly, the coral species studied—shallow-water stenotopic varieties—grow only within a narrow depth range just below the sea surface. When these corals fossilize, their preserved elevation directly corresponds to past sea levels with exceptional precision.
Methodology: Dating Corals, Decoding Sediments
The international team collected two dozen coral samples from various elevations across the Seychelles archipelago. Using uranium-thorium radiometric dating, they established precise ages for each specimen. Simultaneously, sedimentological analyses of the accompanying rock layers confirmed the environmental contexts—ensuring that the corals had not been re-deposited by storms or currents.
By pairing age data with elevation measurements, the researchers charted sea-level fluctuations over a 6,000-year window leading up to the Last Interglacial peak, approximately 122,000–123,000 years ago. This high-resolution chronology allowed them to resolve both gradual trends and abrupt pulses of rise and fall.
Key Findings: Pulses of Rapid Rise Amid Oscillations
Contrary to earlier models depicting a relatively smooth ascent to Last Interglacial highstands, the Seychelles record reveals three distinct “pulses” of accelerated sea-level rise—each surging by an estimated one to two meters over mere centuries. Between these pulses, sea levels temporarily dipped, suggesting dynamic responses of disparate ice sheets to changing climatic forcings.
- Initial Pulse (c. 128,000 years ago): A sudden rise of ~1.5 meters over roughly 200 years.
- Middle Pulse (c. 125,500 years ago): A similar surge of ~1.2 meters within 150–250 years.
- Pre-Highstand Pulse (c. 123,500 years ago): The final jump of ~1.8 meters in under 300 years, immediately preceding the peak sea level.
“These abrupt jumps signal times when ice volume changed rapidly—a hazard we must reckon with today,” explains Vyverberg. “They punctuated longer intervals of relative stability, highlighting that sea level can rebound both upward and downward on centennial timescales.”
Implications for Ice-Sheet Dynamics
The pulsating pattern challenges simplified assumptions that ice-sheet melt and growth occur in unison or at steady rates. Instead, the researchers propose that asynchronous temperature shifts between hemispheres drove Greenland and Antarctic ice sheets to respond out of phase: one sheet melting while the other re-accumulated snow and ice.
“These swings suggest polar ice sheets were growing and shrinking out of phase, driven by hemispheric temperature imbalances,” says Dutton. “Today, warming is global and synchronous, implying future sea-level rise could exceed Last Interglacial extremes.”
A particularly sobering discovery emerged when one of the pulses coincided, in other proxy records, with the final collapse of residual North American ice. Previously overlooked as a contributor during the Last Interglacial, this remnant Laurentide Ice Sheet would have temporarily buffered sea levels. Its late-stage melting implies that Antarctic contributions to sea-level rise were even more substantial than documented, masked by the North American ice volume.
Projected Future Rise: Beyond 10 Meters?
Based on the amplitude of Last Interglacial changes and current warming trajectories, the team warns that global mean sea level could ultimately climb by up to 10 meters—if greenhouse gas emissions continue unabated and polar ice sheets follow similar destabilization pathways.
Such an increase would inundate low-lying coastal zones, displacing hundreds of millions of people, transforming economic centers, and overwhelming existing adaptation measures.
Impacts on Coastal Planning and Risk Management
For municipal engineers and national governments, these revelations demand a reevaluation of long-term infrastructure designs. Coastal defenses built to withstand gradual sea-level rise of under a meter by 2100 may be insufficient in the context of multi-meter increases by 2300–2500.
“These findings are hugely important for coastal planners, policy makers, and risk managers,” asserts Dutton. “We need proactive strategies that account for the possibility of abrupt sea-level jumps, not just incremental changes.”
Adaptation measures could include:
- Managed Retreat: Strategically relocating communities from high-risk zones before permanent inundation.
- Layered Defenses: Combining seawalls, natural wetlands restoration, and storm surge barriers to handle both long-term rise and sudden storm-driven flooding.
- Zoning Reforms: Implementing strict building codes and prohibiting new development below certain elevation thresholds.
- Insurance Innovations: Developing risk pools and catastrophe bonds that reflect nonlinear sea-level scenarios.
Mitigation: Emissions Reduction as the Best Defense
While adaptation is critical, the authors emphasize that the most effective way to avoid the most extreme outcomes is to curb greenhouse gas emissions as swiftly as possible.
“The more we do to draw down our emissions—and the faster we do so—the greater chance we have to prevent the worst scenarios from becoming our lived reality,” says Dutton.
International climate policy, the phasing out of coal and other fossil fuels, and large-scale deployment of carbon capture and storage will all play pivotal roles in limiting future warming and, by extension, sea-level rise.
Broader Scientific Context
The Seychelles coral record complements other paleoclimate archives—such as Greenland ice cores, Antarctic sediment drills, and tropical peat deposits—painting a more nuanced picture of Earth’s sensitivity to temperature perturbations. Improved computational models now incorporate these high-frequency sea-level changes, enhancing projections of ice-sheet stability under various emissions pathways.
Conclusions
Fossil corals from a remote archipelago have sounded a clear alarm: sea-level rise is neither gradual nor predictable. Instead, past warm periods witnessed abrupt, multi-meter increases driven by complex, asynchronous ice-sheet dynamics. As humanity confronts similar thermal stresses today, coastal communities must prepare for sudden shifts in shoreline and sea-level hazards far beyond previous estimates. Simultaneously, the imperative remains to mitigate climate change through rapid emissions reductions—our best hope for blunting the worst of future sea-level rise.
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