• Regional redistribution of GMSL

• Relative sea-level change from land movement • Changes in the temporal variability of sea level Influences on sea level Source: Milne et al. (2009) Global changes—geological past Changes in sea-level due to changes in ice sheet volume Rate of sea-level rise decreased over past 10,000 years Source: Church et al. (2008) ~10 mm yr-1 ~1 mm yr-1 Global changes—last millenium The rate of sea-level rise abruptly increased about a century ago Source: Church et al. (2008) ~0 mm yr-1 ~2 mm yr-1 Global changes—last century The rate of global mean sea level (GMSL) rise is variable, but overall has increased over the past 140 years. Most recent 20-year trends are ~3 mm yr-1. Closing the sea-level budget is an active area of research. Source: Church et al. (2008) ~3 mm yr-1 Global changes—future • Global Climate Models, in principle, can be used to project changes in global-mean sea level for a given greenhouse gas emissions scenario. • Using GCMs, the Intergovernmental Panel on Climate Change (IPCC) Third and Fourth Assessment Reports (TAR and AR4) projected global sea-level increases of 9-88 and 18-79 cm, respectively, over the 21st century (Church et al. 2001, Meehl et al. 2007). • But representation of ice sheets is poor in GCMs. • Specifically, there is concern that ice sheet stability has been overestimated in the IPCC AR4. Semi-empirical approaches, tuned to historical observations, give much higher projections, 50-140 cm (Rahmstorf 2007)