Abstract
Abstract. Climate change causes global mean sea level to rise due to thermal expansion of seawater and loss of land ice from mountain glaciers, ice caps and ice sheets. Locally, sea level can strongly deviate from the global mean rise due to changes in wind and ocean currents. In addition, gravitational adjustments redistribute seawater away from shrinking ice masses. However, the land ice contribution to sea level rise (SLR) remains very challenging to model, and comprehensive regional sea level projections, which include appropriate gravitational adjustments, are still a nascent field (Katsman et al., 2011; Slangen et al., 2011). Here, we present an alternative approach to derive regional sea level changes for a range of emission and land ice melt scenarios, combining probabilistic forecasts of a simple climate model (MAGICC6) with the new CMIP5 general circulation models. The contribution from ice sheets varies considerably depending on the assumptions for the ice sheet projections, and thus represents sizeable uncertainties for future sea level rise. However, several consistent and robust patterns emerge from our analysis: at low latitudes, especially in the Indian Ocean and Western Pacific, sea level will likely rise more than the global mean (mostly by 10–20%). Around the northeastern Atlantic and the northeastern Pacific coasts, sea level will rise less than the global average or, in some rare cases, even fall. In the northwestern Atlantic, along the American coast, a strong dynamic sea level rise is counteracted by gravitational depression due to Greenland ice melt; whether sea level will be above- or below-average will depend on the relative contribution of these two factors. Our regional sea level projections and the diagnosed uncertainties provide an improved basis for coastal impact analysis and infrastructure planning for adaptation to climate change.
Highlights
Since the IPCC Fourth Assessment Report (AR4) (Bindoff et al, 2007), significant progress has been made toward understanding current sea level rise (SLR), in particular with the closure of the sea level budget over the last four decades (Church et al, 2011)
We have derived regional sea level projections that result from a broad range of ocean warming, circulation changes and land ice melting during the 21st century
Our method is designed to explore the various uncertainties of each process contributing to SLR, and to be flexible with respect to emission scenarios based on a combination of global mean contributions to sea level change and their regional “fingerprints”
Summary
Since the IPCC Fourth Assessment Report (AR4) (Bindoff et al, 2007), significant progress has been made toward understanding current sea level rise (SLR), in particular with the closure of the sea level budget over the last four decades (Church et al, 2011). Projections of future SLR are still very uncertain (Lowe and Gregory, 2010; Rahmstorf, 2010). Current coupled model projections can reasonably simulate ocean thermal expansion and the retreat of mountain glaciers and ice caps (MGIC). Changes in ocean dynamics and density structure due to water temperature and salinity changes (so-called steric changes) have sizeable effects (Landerer et al, 2007; Pardaens et al, 2010; Yin et al, 2009, 2010). The projected regional distribution of steric SLR is highly non-uniform, and deviations from the global SLR can be similar in magnitude as the global thermal expansion (Yin et al, 2009).
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