Sea Level Change

Sea Level Rise

Eustatic- change in the sea level due to the amount of water in the oceans changing.

Isostatic- change in the sea level because of the movement of land in response to loss or gain of mass.

Sea levels can rise because of two reasons:

  • Increasing amounts of water in the oceans.
  • Thermal expansion of the oceans water.

Why is it difficult to predict future changes in the sea level?

- You cannot fully predict our future greenhouse emissions because we do not know how the world's population will develop and change their culture.

- We do not know if levels will continue as they are or change.

- It is difficult to predict the impact of thermal expansion of oceans and melting ice caps and glaciers as they will all contribute to changes in sea levels.

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Features of Sea Level Change

Emergent - emergent landforms occur when isostatic rebound takes place faster than a eustatic rise in sea level. The land's height rises faster than the sea's.

Submergent these are often formed when eustatic rise in sea level takes place faster than the isostatic rebound. The water starts to flood the land and fills up landforms on the land.

A 15m rise in sea level will be caused by 4 factors:

  • Melting of West Antarctic ice sheet = 5m rise
  • Complete melting of Greenland ice sheet = 7m rise
  • Collapse and melting of the world's glacier system = 2m rise
  • Continued thermal expansion of oceans = 1m rise

Three types of areas which are most at risk?

1. The world's large river deltas (e.g. Nile & Mississippi).

2. Areas that lie close to sea level and are already defended.

3. Small, low-lying islands in the Pacific and Indian Oceans.

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1. Bangladesh + Egypt

A country with 70% of land being floodplains less than 6m above sea level.

- Bangladesh could lose 20% of its land, displacing up to 40 million people.

- Rising sea level threatens to reduce supplies of food and fresh drinking water and it can damage agricultural land in a country where 65% of the rapidly growing population are subsistance farmers.

- Bangladesh is a multiple hazard zone (river floods, coastal floods, storm surges, typhoons) and climate change is likely to make things worse.

- Solutions are very complex as the coast is too long to fully defend espiecally for an LEDC.

> A similar situation exists in the Nile delta in Egypt, where local subsidence exacerbates the impact of the rising sea level.

> A 1m rise in sea level could affect 15% of the countries habitable land which accounts for 7 million people.

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2. The Netherlands

A country which lies close to the sea level and is already defended.

Once known as Holland, the Netherlands is located in Western Europe and in contrast to Bangladesh, it is one of the richest countries in the world.

- The Netherlands has a population of around 16.8 million.

- It is largely made up of coastal lowlands, over 50% of which are polders (reclaimed land), below the present sea level.

- This densely populated, heavily developed area is defended by a complex system of dykes and coastal sand dunes. 

- A 1m rise in sea level would cost the Netherlands $12,000 million to defend.

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3. Pacific Islands

A collection of small, low-lying islands in the Pacific Ocean which are already feeling the affects of sea level rise.

Islands like these in the Pacific Ocean have common vulnerabilities:

  • Small physical size
  • Low elevation
  • Prone to natural disasters
  • A dense and growing population
  • Increasing degradation of natural environments
  • Vulnerability of groundwater to contamination by sea water
  • Wide geographic distribution and remoteness
  • Limited resources

- Carteret Island, Marshall Islands, Kiribati, Tuvalu and Vanuatu are the islands in the Pacific Ocean which are most at threat of the rising sea levels.

- The small island of Tegua, 100km north of Vanuata, was nearly abandoned in December 2005 and is likely to be the first community in the world to be forced out by rising sea levels.

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