Sea-level rise: understanding the past and improving projections for the future.
Around the world, rising sea levels, as a result of human-induced climate change, are already having an impact.
The oceans are changing
Many observations show that the ocean has been changing over the past several decades. One aspect of this is a warming ocean resulting in increase of ocean volume through thermal expansion. There has also been addition of water from glacier and ice sheets and changes in storage of water on or in the land (e.g. retention of water in man-made dams and extraction of water from aquifers). Together these result in changes in sea level.
Human-induced climate change
Sea-level rise is a response to increasing concentrations of greenhouse gases in the atmosphere and the consequent changes in the global climate. Sea-level rise contributes to coastal erosion and inundation of low-lying coastal regions, particularly during extreme sea-level events. It also leads to saltwater intrusion into aquifers, deltas and estuaries.
These changes impact on coastal ecosystems, water resources, and human settlements and activities. Regions at most risk include heavily populated deltaic regions, small islands (especially coral atolls), and sandy coasts backed by major coastal developments.
Observed changes in sea level
Over the last 140,000 years, sea level has varied over a range of more than 120 metres. The most recent large change was an increase of more than 120 metres as the last ice age ended. Sea level stabilised over the last few thousand years, and there was little change between about 1AD and 1800AD. Sea level began to rise again in the 19th century and accelerated again in the early 20th century. Satellite altimeter measurements show a rate of sea-level rise of about 3 mm/year since the early 1990s – a further increase in the rate.