Sea Level
Introduction
Sea level refers to the average height of the ocean's surface, also known as mean sea level (MSL). It serves as the reference point from which elevations and depths on Earth are measured. The sea level is a critical factor in various scientific and societal contexts, including geodesy, cartography, oceanography, and climate change studies.
Determining Sea Level
Determining the sea level is not as straightforward as it might seem. The sea is not static, and its surface is influenced by a myriad of factors. These include tides, winds, atmospheric pressure, ocean currents, and temperature. Therefore, to obtain a reliable measure of sea level, scientists average sea-surface height over a period of time and over large spatial scales.
Sea Level Change
Sea level change refers to the rise or fall in the average level of the sea over time. This change can be local (relative sea level change) or global (eustatic sea level change).
Eustatic Sea Level Change
Eustatic sea level change is a global change in sea level due to an alteration in the volume of water in the world's oceans or a change in the volume of the ocean basins. The primary factors contributing to eustatic sea level change include thermal expansion of seawater due to global warming and the addition or removal of water from the ocean basins due to the melting or formation of glaciers and ice sheets.
Relative Sea Level Change
Relative sea level change refers to local changes in sea level relative to the land. It is influenced by eustatic changes and vertical land movements. Land can rise (uplift) due to tectonic forces or sink (subsidence) due to various processes such as compaction of sediments, extraction of groundwater, or isostatic adjustment following the melting of land-based ice.
Impact of Sea Level Change
Changes in sea level have significant impacts on human societies and natural environments. Rising sea levels due to climate change pose a particular threat to low-lying coastal areas, where they can lead to coastal erosion, flooding, and the intrusion of saltwater into freshwater resources. These impacts can have severe consequences for human settlements, agriculture, and ecosystems.
Future Sea Level Change
Predicting future sea level changes is a complex task that involves understanding and modeling the many factors that contribute to sea level change. Most projections indicate that sea levels will continue to rise throughout the 21st century due to ongoing global warming. However, the rate and magnitude of this rise remain uncertain and depend on a range of factors, including future greenhouse gas emissions and the response of glaciers and ice sheets to warming.