Sea Level Change

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Sea Level Change

Factors combine to increase the risk of sea level change, which threatens the lives of people who live near coasts. There are three key factors that have contributed towards sea level change over different time periods, plus climate change.

Eustatic change

Eustatic change is the rising and falling of sea levels, influenced by ice ages.
Water is stored in the form of ice when the world is experiencing an ice age, which causes the sea level to fall.
As the world moves out of an ice age, the ice melts. This results in the sea level rising again.

Isostatic change

Isostatic change refers to the level of the land, which is also influenced by ice ages.
During an ice age, the weight of the ice forces the land to sink.
When the ice age has finished, the melting of the ice causes the land to rebound back up, like a spring.

Tectonic change

Tectonic change causes land to either rise or sink at the boundaries where tectonic plates meet.
A sudden change in the movement of a plate can lead to a rise or fall in the seabed, causing a change in sea level.
Earthquakes out at sea can trigger a tsunami, causing devastating effects for people living along coastlines.

Emergent vs Submergent Coastlines

Emergent and submergent coastlines cause the formation of different landforms.

Emergent coastlines

Emergent coastlines cause the formation of raised beaches and fossil cliffs caused by isostatic rebound.
A raised beach and fossil cliff are formed when, following an ice age, the land rebounds. This causes the original height of land to increase.
This leaves behind a beach and fossil cliff higher than their original position.
E.g. in Fife, Scotland.

Submergent coastlines

Submergent coastlines cause the formation of rias, fjords and Dalmatian coasts.
A ria is a flooded river valley formed when rising sea levels flood the valley, often creating an estuary.
A fjord is an example of a flooded glaciated valley formed when a glacier erodes vertically, creating a u-shaped valley.
- E.g. Lysefjord in Norway.
Dalmatian coasts are formed because of the arrangement of alternating rock types parallel to the coast.

Global Warming and Sea Level Change

The Intergovernmental Panel on Climate Change (IPCC) acknowledge that sea levels are rising from past and present data collected. The IPCC links this to global warming. Coastal flooding is a consequence of this.

Increased frequency of storms

The strong winds caused by storms create high energy, destructive waves which have considerable erosional power.
The increased energy of the sea will mean more material can be transported and for greater distances. This could leave some areas vulnerable to erosion if they are left without much protection.
The frequency of storm surges will increase. When combined with sea level rise, these surges will reach further inland and cause more damage.

Rising sea levels

Data from the IPCC indicates from 1901 to 2010, average sea levels have increased by 0.19m.
Some of the contributing factors being linked to the melting of glaciers and ice sheets.
- E.g. the Greenland and Antarctic ice sheets have been decreasing rapidly.
Higher sea levels could cause higher tides, and this would increase the frequency of coastal flooding.
Higher tides could also remove more material from beaches, leaving cliffs less protected.

Global warming

Evidence from the IPCC indicates that the between 1983 and 2012, the Northern Hemisphere experienced the warmest 30-year period of the last 1,400 years.
Changes in the world’s atmospheric temperatures are causing thermal expansion of the oceans, melting of glaciers and ice sheets.
Global warming is largely because of anthropogenic greenhouse gas (GHG) emissions. The concentration of these gases has risen rapidly since industrialisation.