Twentieth-century global-mean sea level rise: is the whole greater than the sum of the parts?

• Published in: Journal of Climate
• Main Authors: Gregory, JM, White, NJ, Church, JA, Bierkens, MFP, Box, JE, van den Broeke, MR, Cogley, JG, Fettweis, X, Hanna, E, Huybrechts, P, Konikow, LF, Leclercq, PW, Marzeion, B, Oerlemans, J, Tamisiea, ME, Wada, Y, Wake, LM, van de Wal, RSW
• Format: Article in Journal/Newspaper
• Language: English
• Published: Amer Meteorological Soc 2013
• Subjects: Earth Sciences; Atmospheric Sciences; Climate Change Processes; Antarctic; The Antarctic; Greenland; Antarc*; glacier; Ice Sheet
• Online Access: https://doi.org/10.1175/JCLI-D-12-00319.1; http://ecite.utas.edu.au/122066

Confidence in projections of global-mean sea level rise (GMSLR) depends on an ability to account forGMSLRduring the twentieth century. There are contributions from ocean thermal expansion, mass loss from glaciers andice sheets, groundwater extraction, and reservoir impoundment. Progress has been made toward solving theenigma of twentieth-century GMSLR, which is that the observedGMSLRhas previously been found to exceedthe sum of estimated contributions, especially for the earlier decades. The authors propose the following: thermalexpansion simulated by climatemodels may previously have been underestimated because of their not includingvolcanic forcing in their control state; the rate of glacier mass loss was larger than previously estimated and wasnot smaller in the first half than in the second half of the century; the Greenland ice sheet could have madea positive contribution throughout the century; and groundwater depletion and reservoir impoundment, whichare of opposite sign, may have been approximately equal inmagnitude. It is possible to reconstruct the time seriesof GMSLR from the quantified contributions, apart from a constant residual term, which is small enough to beexplained as a long-term contribution from the Antarctic ice sheet. The reconstructions account for the observationthat the rate of GMSLR was not much larger during the last 50 years than during the twentieth century asa whole, despite the increasing anthropogenic forcing. Semiempiricalmethods for projectingGMSLR depend onthe existence of a relationship between global climate change and the rate of GMSLR, but the implication of theauthors closure of the budget is that such a relationship is weak or absent during the twentieth century.