Model Answer
0 min readIntroduction
Sea level change, defined as the rise or fall of the average sea surface height, is a critical indicator of climate change and has profound implications for coastal communities and ecosystems. These changes aren’t uniform globally; they vary regionally due to a complex interplay of factors. Historically, sea levels have fluctuated due to natural processes, but anthropogenic activities are now significantly accelerating the rate of change. Understanding these factors – categorized as Eustatic, Isostatic, and those contributing to Relative sea level change – is vital for effective coastal management and mitigation strategies.
Eustatic Changes
Eustatic changes refer to global sea level changes caused by alterations in the volume of water in the ocean basin or changes in the ocean’s capacity to hold water. These are broadly categorized into:
- Thermal Expansion: As ocean water warms, it expands, contributing to sea level rise. The IPCC Sixth Assessment Report (2021) attributes approximately 50% of observed sea level rise to thermal expansion.
- Addition of Water: Melting glaciers and ice sheets (Greenland and Antarctica) and increased precipitation add water to the ocean, raising sea levels. The Greenland ice sheet is losing mass at an accelerating rate, contributing significantly to sea level rise.
- Glacio-Eustatic Changes: During glacial periods, vast amounts of water are locked up in ice sheets, causing sea levels to fall. Conversely, during interglacial periods, melting ice sheets cause sea levels to rise. The last glacial maximum (around 20,000 years ago) saw sea levels approximately 125 meters lower than present.
Isostatic Changes
Isostatic changes are local or regional sea level changes caused by the vertical movement of landmasses. These are primarily driven by:
- Post-Glacial Rebound: After the removal of the immense weight of ice sheets, landmasses slowly rebound upwards. This causes a relative fall in sea level in these areas. Scandinavia and Canada are experiencing significant post-glacial rebound.
- Subsidence: The sinking of landmasses due to geological processes like sediment compaction, tectonic activity, or extraction of groundwater/oil/gas. Venice, Italy, is sinking due to sediment compaction and groundwater extraction.
- Tectonic Activity: Uplift or subsidence due to plate tectonics can also cause isostatic changes.
Relative Sea Level Changes
Relative sea level change refers to the change in sea level experienced at a specific location, combining both eustatic and isostatic factors, as well as local oceanographic conditions.
- Ocean Currents & Wind Patterns: Changes in ocean currents (e.g., the Gulf Stream) and wind patterns can redistribute water, causing regional variations in sea level.
- Land Movement: As mentioned in Isostatic changes, local land subsidence or uplift significantly impacts relative sea level.
- Local Geological Processes: Volcanic activity or earthquakes can cause localized changes in land elevation and, consequently, relative sea level.
Example: The Maldives are particularly vulnerable to sea level rise due to a combination of eustatic rise and their low elevation. The islands are experiencing increased coastal erosion and saltwater intrusion, threatening their freshwater resources and habitability.
| Type of Change | Cause | Example |
|---|---|---|
| Eustatic | Thermal Expansion | Pacific Ocean warming contributing to sea level rise in Kiribati |
| Isostatic | Post-Glacial Rebound | Uplift in the Baltic Sea region |
| Relative | Land Subsidence | Jakarta, Indonesia sinking due to groundwater extraction |
Conclusion
Sea level changes are a complex phenomenon driven by a multitude of interconnected factors. While natural processes have always caused sea level fluctuations, the current rate of change is unprecedented due to anthropogenic climate change. Understanding the interplay between eustatic, isostatic, and relative sea level changes is crucial for developing effective adaptation and mitigation strategies to protect vulnerable coastal regions and communities. Continued monitoring, research, and international cooperation are essential to address this growing global challenge.
Answer Length
This is a comprehensive model answer for learning purposes and may exceed the word limit. In the exam, always adhere to the prescribed word count.