A groundbreaking international study by marine scientists based in Singapore has revealed that sea-level rise in the Indian Ocean began accelerating far earlier than previously thought, with corals providing an unbroken natural record of ocean change stretching back to the early 20th century.

Published in Nature Communications, the study was led by Professor Paul Kench from the Department of Geography, at the National University of Singapore’s (NUS) Faculty of Arts and Social Sciences, in collaboration with researchers from NUS and Nanyang Technological University (NTU).

By analysing coral samples from the Maldives in the central Indian Ocean, the scientists reconstructed a century-long chronology of sea-level changes and climate shifts with remarkable precision.

They were able to extend the sea-level record for the Indian Ocean back a further 60 years, all the way to the early 1900s, offering a much longer and clearer historical context for interpreting modern sea-level changes.

The study yielded two significant findings.

The first is the pronounced acceleration of rising sea levels in the Indian Ocean from around 1959 – earlier than indicated by coastal tide gauges or satellite observations. The timing aligns closely with global temperature increases and accelerated glacial melt driven by human activity, showing that the Indian Ocean has been highly responsive to climatic changes for over half a century.

The second is that sea levels in the Indian Ocean, which covers approximately 30% of the world’s ocean area and supports around 30% of the global population, have risen significantly by 30cm since the middle of the 20th century.

“What we’re seeing is a clear fingerprint of human-driven climate change etched into the skeletons of corals. The early acceleration in sea-level rise is a warning sign that the ocean has been responding to global warming far earlier and more strongly than we thought,” said Prof Kench.

Accelerating sea-level rise threatens millions living in coastal areas with increased flooding, erosion, saltwater intrusion, and damage to vital ecosystems like mangroves and coral reefs.

The effects of sea-level changes in the Indian Ocean ripples beyond Asia to the rest of the world, underscoring the need for international cooperation to address global challenges such as water security, agriculture, and disaster preparedness.

For Singapore and its Southeast Asian neighbours, the uncovering of long-term patterns of sea-level changes can improve climate models and strengthen the region’s ability to plan for future risks under continued global warming.

For example, the new coral-derived data from the study offers a historical baseline that can enhance the efforts that Singapore already has in place to guard against rising sea levels, such as the Coastal-Inland Flood Model and Climate Impact Science Research Programme, by improving the accuracy of sea-level projections and informing adaptive strategies.

Corals confirmed as trusted recorders of sea-level and climate history

This research sets a new standard for how scientists can use coral to look back in time and understand how our oceans have changed.

As corals grow, they build their skeletons layer by layer similar to how trees form rings. Each layer captures details about the ocean at that time, such as temperature, salt levels, and even sea level.

To make sure data from the coral samples from the Indian Ocean that were analysed was reliable, the team compared it with real sea-level measurements from tide stations and satellites, and found that they matched up closely.

The successful calibration of coral proxies against instrumental sea-level records means that we can trust corals to tell us about past sea-level changes, with their coral growth rates validated to be reliable indicators of relative sea-level changes, making them a powerful tool for climate research.

In addition to tracking long-term sea-level changes, the coral records also captured signs of extreme climate events such as unusual warming and cooling periods, as well as droughts. These signals closely match historical weather records, offering valuable insight into the frequency and severity of past climate extremes.

Prof Kench said, “These findings have far-reaching implications for climate adaptation planning globally, especially for low-lying and densely populated coastal regions. We hope this work contributes meaningfully to the global dialogue on resilience and preparedness.”

This pioneering research deepens our understanding of how oceans respond to climate change, while setting a new standard for using natural archives to reconstruct environmental history. As coastal nations around the world confront the realities of rising seas, the insights uncovered by Singapore’s marine scientists offer both a clearer view of the past and a critical guide for planning a more resilient future.

About the Study

The study titled “Coral growth records 20th Century sea-level acceleration and climatic variability in the Indian Ocean” was published in Nature Communications (link: https://rdcu.be/euiYQ) on 1 July 2025. It represents a milestone in paleoclimate science, combining marine biology, geochemistry, and oceanography to produce the most detailed Indian Ocean sea-level record to date.

The interdisciplinary approach taken for this study, combining marine biology, geochemistry, climatology, and oceanography, demonstrates the power of collaborative science in tackling complex global challenges. It also highlights the role of Singapore’s research institutions in contributing to world-class climate science.

The paper was also recently presented at the Asia Oceania Geosciences Society 2025 conference and picked up by Science Magazine (link: https://scienmag.com/coral-records-reveal-20th-century-sea-level-rise/).