Sea-level changes | Oceanography | Principle Of Geography

Oceanography

Principle Of Geography

Geography Complete Study Material

(Paper - I)

Sea-level Changes

             The base level for determining height and depth on Earth is the sea level. As a result, sea-level changes are a climate change event in which the volume of ocean water increases or decreases, primarily due to ice sheets and glaciers melting and water thermal expansion, or vice versa. Coastal life worldwide is threatened as a result of sea-level rise, and adaptation policies must be formed to prevent further and faster catastrophic impacts. As the climate changes, the sea level rises. Due to local factors such as ground settling, upstream flood management, erosion, regional ocean currents, and if the land is still rebounding from the crushing weight of ice age glaciers, past and future sea-level rise at specific sites on land may be more or less than the average of the world.

        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.

Factors of Sea-level Changes

            The change in sea levels is linked to three primary factors, all induced by ongoing global climate change:

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: Large ice formations such as mountain glaciers naturally melt a bit each summer. In the winter, snows, primarily from evaporated sea water, are generally sufficient to balance out the melting.  Recently, though, persistently higher temperatures caused by global warming have led to greater than average summer melting 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 Antarctica’s ice sheets: As with mountain glaciers, increased heat is causing the massive ice sheets that cover Greenland and Antarctica to melt more quickly. Scientists also believe that meltwater from above and seawater from below is seeping beneath Greenland's ice sheets, effectively lubricating ice streams and causing them to move more quickly into the sea. While melting in West Antarctica has drawn considerable focus from scientists, especially with the 2017 break in the Larsen C ice shelf, glaciers in East Antarctica are also showing signs of destabilizing.