Robust estimates of projected sea-level rise are not available. The IPCC (2007b) could not estimate all of the contributions of global warming in projecting sea-level rise, mostly due to uncertainties with the response of the Greenland and Antarctic ice sheets. Given recent evidence that the stability of Greenland and West Antarctic ice sheets are weakening and eroding faster than previously expected, it is likely that the IPCC estimate of 0.18m to 0.59m by 2100 is a significant underestimate.
The most recent data indicate that average sea-level rise is approximately 3.4mm per year, compared to 3.1mm per year between 1993 to 2003, and 1.8mm per year from 1961 to 2003 (Church et al, 2008; Rahmstorf, 2007). Analysis shows that the rate of sea-level rise in the 20th century could be the highest for the past 5000 years, increasing at almost twice as much since 1993 than the average in the past century (ACE CRC, 2008). Like temperature, trends in sea-level rise are at the high end of the IPCC projections (White et al, 2008). Estimates that better reflect potential ice sheet flows are now showing larger projections of sea-level rise. For example, Rahmstorf (2007) projects sea-level rise of between 0.5m to 1.4m above the 1990 level by 2100, which is more than double the IPCC estimate.
Of course, sea-level rise will not be uniform. In some locations, sea levels will increase greater than in others. It is, however, very difficult to project sea-level rises at a regional or local scale. The climate-change-driven increases in the height or frequency of extreme sea-level events, such as very high tides and storm-related surges, are already threatening some coastal and small island settlements, with relocations of some communities occurring (Green, 2008) or being planned in the Pacific region (e.g. Torres Strait Islands, Vanuatu, Maldives, Kiribati and Tuvalu).
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