Sea-Level Changes - Geography UPSC Notes

By changes in sea level, we mean the fluctuations in the mean sea level, i.e., the average level of the sea surface. Thus, the changes in sea level may also be termed as a relative change in sea level. During the relative rise in sea level, either the land or the sea surface may undergo upliftment or subsidence, or both may rise and fall at the same time.

Rising or lowering of sea level for a longer period [not like tides] is called sea-level changes or Eustatic Changes. 

There are two types of sea-level changes:

• Sea Level Rise
• Sea Level decrease

Sea Level Rise:

The following are the two major reasons for the sea level rise:

• Isostatic adjustment of land and ocean
• Global warming

Isostatic adjustment of land and ocean:

• Due to the overloading of glacial ice, large parts of the land sink into the ground, due to which the sea level rises.
• Sea level rises because of the huge sedimentary deposition from continents by rivers or winds.

Global Warming:

Global warming causes two major problems:

• The melting of glacial ice increases the amount of water in the ocean, due to which the sea surface rises.
• The increase in sea surface temperature leads to the thermal expansion of water leading to a rise in sea level.

Sea Level fall:

Sea level fall due to two major reasons:

• Global cooling
• Upliftment of landmass

Global cooling

• In the Global cooling period, there is a reduction of insolation due to various reasons such as large-scale volcanic eruptions, or spread of space dust, or the reduction of Green Houses Gases; which leads to the thermal contraction of ocean water and the formation of glacial ices at higher latitudes; which cause fall in sea level.  Carboniferous and Pleistocene times was global cooling time.

Upliftment of landmass: The melting of ice glaciers on landmass also causes the sea level to fall as it releases the loads from the land; that causes the rising of the landmass and an apparent fall in sea level.

For example, 

• Scandinavia is still rising due to the release of glacial ice.
• The formation of lofty mountains leads to an apparent fall in sea level.

Recent news:

Recently, a study has projected that sea levels will rise around Lakshadweep Islands due to the impact of global warming. It will affect airport and residential areas that are quite close to the present coastline. India’s smallest Union Territory, Lakshadweep is an archipelago consisting of 36 islands with an area of 32 sq km.

Three Primary Factors

• • Thermal Expansion: When water heats up, it expands. About half of the sea-level rise over the past 25 years is attributable to warmer oceans simply occupying more space.
  • Melting Glaciers: Higher temperatures caused by global warming have led to greater-than-average summer melting of large ice formations like mountain glaciers as well as diminished snowfall due to later winters and earlier springs. That creates an imbalance between runoff and ocean evaporation, causing sea levels to rise.
  • Loss of Greenland and Antarctic Ice Sheets: As with mountain glaciers, increased heat is causing the massive ice sheets that cover Greenland and Antarctica to melt more quickly, and also move more quickly into the sea.

Rate of SLR:

Global: The global sea level has been rising over the past century, and the rate has accelerated in recent decades. The average global sea level has risen 8.9 inches between 1880 and 2015. That’s much faster than in the previous 2,700 years.

Also, the Intergovernmental Panel on Climate Change (IPCC) released ‘The Special Report on the Ocean and Cryosphere in a Changing Climate’ in 2019 which underlined the dire changes taking place in oceans, glaciers, and ice-deposits on land and sea.

Regional: SLR is not uniform across the world. Regional SLR may be higher or lower than Global SLR due to subsidence, upstream flood control, erosion, regional ocean currents, variations in land height, and compressive weight of Ice Age glaciers.

Consequences of SLR:

• • Coastal Flooding: Globally, eight of the world's 10 largest cities are near a coast, which is threatened by coastal flooding.
  • Destruction of Coastal Biodiversity: SLR can cause destructive erosion, wetland flooding, aquifer and agricultural soil contamination with salt, and lost habitat for biodiversity.
  • Dangerous Storm Surges: Higher sea levels are coinciding with more dangerous hurricanes and typhoons leading to loss of life and property.
  • Lateral and Inland Migration: Flooding in low-lying coastal areas is forcing people to migrate to higher ground causing displacement and dispossession and in turn a refugee crisis worldwide.
  • Impact on Infrastructure: The prospect of higher coastal water levels threatens basic services such as internet access.
  • Threat to Inland Life: Rising seas can contaminate soil and groundwater with salt threatening life farther away from coasts.
  • Tourism and Military Preparedness: Tourism to coastal areas and military preparedness will also be negatively affected by an increase in SLR.

Steps taken to Tackle SLR:

• • Relocation: Many coastal cities have planned to adopt relocation as a mitigation strategy. For example, Kiribati Island has planned to shift to Fiji, while the Capital of Indonesia is being relocated from Jakarta to Borneo.
  • Building Sea Wall: Indonesia’s government launched a coastal development project called a Giant Sea Wall or "Giant Garuda" in 2014 meant to protect the city from floods.
  • Building Enclosures: Researchers have proposed a Northern European Enclosure Dam (NEED), enclosing all of the North Sea to protect 15 Northern European countries from rising seas. The Persian Gulf, the Mediterranean Sea, the Baltic Sea, the Irish Sea, and the Red Sea were also identified as areas that could benefit from similar mega enclosures.

Architecture to Steer Flow of Water: The Dutch City Rotterdam built barriers, drainage, and innovative architectural features such as a "water square" with temporary ponds.

Vulnerability of India:

India's 7,516-kilometre-long coastline includes 5,422 kilometers of coastline on the mainland and 2,094 kilometers on the islands belonging to nine states and four Union Territories. The coastline accounts for 90% of the country's trade and it spans 3,331 coastal villages and 1,382 islands.

India’s Efforts:

• • Coastal Regulation Zone:
    • The coastal areas of seas, bays, creeks, rivers, and backwaters which get influenced by tides up to 500 m from the high tide line (HTL) and the land between the low tide line (LTL) and the high tide line were declared as Coastal Regulation Zone (CRZ) in 1991.
    • The latest regulation also takes into account rising sea levels due to global warming.
  • National Action Plan on Climate Change:
    • It was launched in 2008 by the Prime Minister's Council on Climate Change.
    • It aims at creating awareness among the representatives of the public, different agencies of the government, scientists, industry, and communities on the threat posed by climate change and the steps to counter it.

Best Practices: In Jakarta, a $40 billion project will aim to protect the city with an 80-foot-high seawall.

Rotterdam, home to the global Center on Adaptation, has offered a model to other cities seeking to combat flooding and land loss. The Dutch city has built barriers, drainage, and innovative architectural features such as Water Square with temporary ponds.