Question.
With suitable examples, explain the factors causing sea level changes.
( UPSC 2024: Geography Optional (Oceanography); NCERT: Class XI ( Geography) Chapter-12)
Answer.
Introduction:
Sea level changes refer to the rise or fall of the global or local sea surface relative to the land. These changes can be short-term or long-term and are influenced by both natural and anthropogenic factors. In the modern context, global warming and climate change are significant contributors to sea level variation.
Major Factors Causing Sea Level Changes:
1. Climate Change:
Cause: Melting of glaciers and polar ice due to rising global temperatures.
Example: Rapid ice melt in Greenland and Antarctica is contributing to global sea-level rise.
2. Thermal Expansion of Seawater:
Cause: When ocean water warms, it expands and occupies more volume.
Example: According to IPCC reports, about 50% of recent sea-level rise is due to thermal expansion.
3. Tectonic Activities:
Cause: Plate tectonics can uplift or subside land, leading to relative sea-level changes.
Example: The 2004 Indian Ocean earthquake caused parts of Indonesia to subside, resulting in an increase in local sea level.
4. Glacial-Interglacial Cycles:
Cause: During ice ages, sea levels fall due to water being stored in ice sheets; in interglacial periods, melting ice causes sea levels to rise.
Example: Since the Last Glacial Maximum (~20,000 years ago), sea level has risen by ~120 meters.
5. Anthropogenic Activities:
Cause: Excessive groundwater extraction, deforestation, and urbanization near coasts accelerate subsidence and impact sea levels.
Example: Jakarta (Indonesia) is sinking due to over-extraction of groundwater, worsening sea-level impacts.
6. Local Geomorphic and Oceanic Factors:
Cause: Sedimentation in deltaic regions, coastal erosion, tides, ocean currents, etc.
Example: The Sundarbans delta region is experiencing land erosion due to rising sea levels and frequent storms.
Conclusion:
Sea level change is a complex process resulting from a combination of climatic, tectonic, and human-induced factors. It poses serious challenges including coastal erosion, submergence of low-lying islands, biodiversity loss, and climate migration. Hence, a scientific understanding of its causes is vital for framing resilient coastal policies and climate mitigation strategies.
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