Rising sea levels

A sea level rise is an increase in the volume of water in the world’s oceans, resulting in an increase in global mean sea level. Sea level rise is usually attributed to global climate change by thermal expansion of the water in the oceans and by melting of ice sheets and glaciers on land. Melting of floating ice shelves or icebergs at sea raises sea levels only slightly.

Sea level rise at specific locations may be more or less than the global average. Local factors might include tectonic effects, subsidence of the land, tides, currents, storms, etc. Sea level rise is expected to continue for centuries. Because of long response times for parts of the climate system, it has been estimated that we are already committed to a sea-level rise within the next 2,000 years of approximately 2.3 metres (7.5 ft) for each degree Celsius of temperature rise. IPCC Summary for Policymakers, AR5, 2014, indicated that the global mean sea level rise will continue during the 21st century, very likely at a faster rate than observed from 1971 to 2010. Projected rates and amounts vary. A January 2017 NOAA report suggests a range of GMSL rise of 0.3 – 2.5 m possible during the 21st century.

Sea level rises can considerably influence human populations in coastal and island regions and natural environments like marine ecosystems.

Two main mechanisms contribute to observed sea level rise: (1) thermal expansion: because of the increase in ocean heat content (ocean water expands as it warms); and (2) the melting of major stores of land ice like ice sheets and glaciers. Based on figures from between 1993–2008 two thirds (68%) of recent sea level rise has been attributed by melting ice, and roughly one third has come from thermal expansion.

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