Policy Brief: Global Sea-Level Rise: An Evaluation of the Data

According to the Working Group I contribution to the Intergovernmental Panel on Climate Change’s (IPCC) Fifth Assessment Report (IPCC, 2013), “it is very likely that the global mean rate [of sea level rise] was 1.7 [1.5 to 1.9] mm yr-1 between 1901 and 2010 for a total sea level rise of 0.19 [0.17 to 0.21] m” (p. 1139) and “it is very likely that the rate of global mean sea level rise during the 21st century will exceed the rate observed during 1971–2010 for all Representative Concentration Pathway (RCP) scenarios due to increases in ocean warming and loss of mass from glaciers and ice sheets” (p. 1140).

Also according to the IPCC (2013), mass loss from the Greenland and Antarctic ice sheets over the period 1993–2010 expressed as sea-level equivalent was “about 5.9 mm (including 1.7 mm from glaciers around Greenland) and 4.8 mm, respectively,” and ice loss from glaciers between 1993 and 2009 (excluding those peripheral to the ice sheets) was 13 mm (p. 368). The total is 23.7 mm (5.9 + 4.8 + 13), which is slightly less than 1 inch. 

Like ice melting, sea-level rise is a research area that has recently come to be dominated by computer models. Whereas researchers working with datasets built from long-term coastal tide gauges typically report a slow linear rate of sea-level rise, computer modelers assume a significant anthropogenic forcing and tune their models to find or predict an acceleration of the rate of rise. This Policy Brief reviews recent research to determine if there is any evidence of such an acceleration and then examines claims that islands and coral atolls are being inundated by rising seas.