Introduction

Sea-level rise is one of the most significant consequences of global warming, threatening ecosystems, economies, and human settlements. In the Indian Ocean, recent findings based on coral microatolls suggest that sea levels began rising rapidly as early as the 1950s, decades before satellite and tide-gauge data had indicated. This challenges existing assumptions in climate change studies and raises critical questions about preparedness for vulnerable island states like Maldives, Lakshadweep, and the Chagos archipelago.

Coral Microatolls as Natural Recorders of Sea-Level History

• Unique natural recorders: Coral microatolls are disk-shaped colonies that stop growing upwards once constrained by the lowest tide, making their surface a natural reflection of long-term sea-level change.
• Longevity and accuracy: They can survive for decades or centuries, providing high-resolution, continuous data.
• Study site: Research conducted on Mahutigalaa reef, Huvadhoo Atoll (Maldives), measured a Porites microatoll covering 1930–2019.

Acceleration and Scale of Sea-Level Rise in the Indian Ocean

• Accelerated rise: Data showed a 0.3 metre increase over 90 years.
• Rates of rise:
  • 1930–1959: 1–1.84 mm/year
  • 1960–1992: 2.76–4.12 mm/year
  • 1990–2019: 3.91–4.87 mm/year
• Striking revelation: Sea-level rise began in the late 1950s, not around 1990 as earlier assumed.
• Cumulative impact: Maldives, Lakshadweep, and Chagos have witnessed 30–40 cm rise in half a century, worsening flooding and erosion risks.

Climate Variability and Environmental Signals Captured in Corals

• Climate variability: Slow or interrupted coral growth coincided with El Niño and negative Indian Ocean Dipole (IOD) events.
• Astronomical influence: The 18.6-year lunar nodal cycle was reflected in the growth bands, showing tidal and sea-level oscillations.
• Tectonic stability: Critical factor ensuring that coral growth data reflects sea-level change rather than land movement.

Regional Significance of Findings for the Indian Ocean Basin

• Above-average warming: The Indian Ocean is heating faster than the global average, amplifying sea-level fluctuations.
• Strategic gaps: Despite its ecological and geopolitical importance, the central Indian Ocean is one of the least-monitored basins.
• Regional variations: Coastal areas saw recent acceleration, but the central basin experienced earlier, stronger rise, influenced by shifts in Southern Hemisphere westerlies, ocean heat uptake, and the Intertropical Convergence Zone.

Vulnerabilities and Adaptation Imperatives for Island Nations

• Existential threat: Infrastructure and communities are concentrated just above sea level in Maldives and Lakshadweep.
• Adaptation strategies: Understanding historic timing and magnitude of sea-level rise is vital for coastal planning, disaster preparedness, and climate resilience.
• Scientific value: Microatolls cannot replace tide gauges or satellites but offer a vital complementary tool to refine projections in data-sparse regions.

Conclusion

The discovery that sea-level rise in the Maldives and Lakshadweep began decades earlier than thought is a wake-up call for policymakers and communities. Coral microatolls, silent sentinels of the ocean, have revealed the urgency of accelerating adaptation and resilience measures. As the Indian Ocean warms faster than global averages, the survival of low-lying nations will depend on proactive international cooperation and evidence-based planning.

PYQ Relevance

[UPSC 2023] The Intergovernmental Panel on Climate Change (IPCC) has predicted a global sea level rise of about one metre by AD 2100. What would be its impact in India and the other countries in the Indian Ocean region?

Linkage: The article’s findings on coral microatolls show that sea-level rise in the Maldives, Lakshadweep, and Chagos began as early as the 1950s, much earlier than assumed. This reinforces IPCC projections of accelerated rise, highlighting existential risks for low-lying islands. For India and the wider Indian Ocean region, the impacts include intensified coastal erosion, loss of habitats, and the need for urgent adaptation strategies.

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