Global Warming, Rising Seas, and Coral Reefs

Why in News?

Recent studies have thrown light on how rising sea levels due to Global Warming are affecting coral reefs and how coral reefs can be used to assess rising sea levels and associated changes.

UPSC Relevance 

Geographical and Environmental phenomena and issues are important for both Prelims and Mains.

GS1- Important Geophysical Phenomena such as earthquakes, Tsunami, Volcanic activity, cyclone etc., geographical features and their location-changes in critical geographical features (including water-bodies and ice-caps) and in flora and fauna and the effects of such changes.

GS 3 – Conservation, Environmental Pollution and Degradation, Environmental Impact Assessment.

PYQ

2012

The acidification of oceans is increasing. Why is this phenomenon a cause of concern?

1. The growth and survival of calcareous phytoplankton will be adversely affected.
2. The growth and survival of coral reefs will be adversely affected.
3. The survival of some animals that have phytoplanktonic larvae will be adversely affected.
4. The cloud seeding and formation of clouds will be adversely affected.

Which of the statement(s) given above is/are correct?

 (a) 1, 2 and 3 only

 (b) 2 only

 (c) 1 and 3 only

 (d) 1, 2, 3 and 4

2024, GS1

What is sea surface temperature rise? How does it affect the formation of tropical cyclones?

2021, GS1

How does the melting of the Arctic ice and glaciers of the Antarctic differently affect the weather patterns and human activities on the Earth? 

2023,GS3

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?

The Impact of Rising Sea Levels on Coral Reefs

• Vulnerability: Coral reefs are highly sensitive to changes in their environment, making them particularly vulnerable to rising sea levels.
• Coral Bleaching: As sea levels rise, sunlight may no longer penetrate the water to reach corals, a process that can lead to coral bleaching.
• Additional Stressors: Changes in tide patterns and increased coastal erosion further stress reef ecosystems, compounding the effects of warmer waters and ocean acidification.

Sea-Level Rise in the Indian Ocean

• Above-Average Rise: According to India’s Ministry of Earth Sciences, the Indian Ocean’s sea level is rising at an average of 3.3 mm/year, which is higher than the global average.
• Accelerated Warming: The Indian Ocean is also experiencing above-average warming, which can amplify atmospheric and oceanic changes that contribute to coral bleaching.
• Significant Data Gaps: Despite ongoing monitoring efforts, there are significant gaps in sea-level records, particularly in the central tropical Indian Ocean.

A New Method Using Coral Microatolls

• Natural Recorders: A new study by a team led by Paul Kench used coral microatolls as a natural structure to create high-resolution, long-term sea-level records.
• How They Work: Coral microatolls are disk-shaped colonies whose upward growth is limited by the height of the lowest tide. Their flat upper surface closely reflects the lowest water levels over time, providing a historical record.
• Study Site: The study was conducted on a Porites microatoll on Mahutigalaa, a reef platform in the Maldives’ Huvadhoo Atoll.
• Data Extraction: Researchers painstakingly surveyed the coral’s structure, X-rayed a slab to reveal annual growth bands (like tree rings), and used uranium-thorium dating to determine its historical elevation.

Groundbreaking Findings from the Coral Study

• Earlier Acceleration: The study’s data, which extends back to 1930, indicates that sea levels in the region began accelerating as early as the late 1950s, decades earlier than previously believed.
• Challenging Assumptions: This finding challenges the common assumption in climate change and adaptation work that significant sea-level rise began only around 1990.
• Magnitude of Rise: The data showed a total sea-level rise of around 0.3 meters (30-40 cm) over the 90-year period.
• Increased Rate: The rate of rise has increased markedly over time:
  • 1930-1959: 1-1.84 mm/year
  • 1960-1992: 2.76-4.12 mm/year
  • 1990-2019: 3.91-4.87 mm/year

Historical and Regional Context

• Environmental Signals: The coral microatoll also preserved environmental signals, showing that periods of slowed growth corresponded with major El Niño and negative Indian Ocean Dipole (IOD) events.
• Lunar Influence: The data also revealed the influence of the 18.6-year lunar nodal cycle on tides and sea levels.
• Tectonic Stability: The study’s findings were robust because the research site was tectonically stable, ensuring that changes in the coral’s elevation were due to sea-level fluctuations and not land movement.
• Role of Microatolls: While not a substitute for tide gauges or satellite observations, coral microatolls are a valuable complementary tool, providing historical context and filling critical data gaps in remote regions.

6. Policy and Future Implications

• Regional Differences: The study highlighted notable differences in sea-level rise across the Indian Ocean basin, with the central ocean showing an earlier, higher rise compared to coastal areas.
• Informing Adaptation Strategies: For vulnerable island nations like the Maldives, Lakshadweep, and the Chagos archipelago, understanding the timing and magnitude of historic sea-level changes is crucial for developing effective adaptation strategies.
• Continued Role: Coral microatolls are expected to play a growing role in helping scientists reconstruct sea-level histories, especially in the central Indian Ocean, which remains one of the least-monitored basins.

 Read more about corals