Widespread coastal flooding would be expected if several degrees of warming is sustained for millennia.[143] For example, sustained global warming of more than 2 °C (relative to pre-industrial levels) could lead to eventual sea level rise of around 1 to 4 m due to thermal expansion of sea water and the melting of glaciers and small ice caps.[143] Melting of the Greenland ice sheet could contribute an additional 4 to 7.5 m over many thousands of years.[143]
Changes in regional climate are expected to include greater warming over land, with most warming at high northern latitudes, and least warming over the Southern Ocean and parts of the North Atlantic Ocean.[144] During the 21st century, glaciers[145] and snow cover[146] are projected to continue their widespread retreat. Projections of declines in Arctic sea ice vary.[147][148] Recent projections suggest that Arctic summers could be ice-free (defined as ice extent less than 1 million square km) as early as 2025-2030.[149]
Future changes in precipitation are expected to follow existing trends, with reduced precipitation over subtropical land areas, and increased precipitation at subpolar latitudes and some equatorial regions.[150] Projections suggest a probable increase in the frequency and severity of some extreme weather events, such as heat waves.[151]