Magnitudes and Rates of Past, Present and Future Sea-Level Change in Singapore

Low-lying nations, including Singapore, are vulnerable to rising relative sea level (RSL) with ~30% of its total land surface area (728 km2) less than 5 m above present sea level. Furthermore, paleo proxy archives suggest coastal ecosystems (e.g., mangroves and corals reefs) will likely collapse once thresholds in RSL rate are surpassed. Past and present records of sea level have varied in response to a wide range of boundary conditions and climate forcings and can serve as a valuable guide to projecting future sea-level rise. However, using past and present records in this manner requires a robust understanding of regional variability and rigorous quantification of uncertainty. Here, we reconstruct magnitudes and rates of RSL change since the last glacial maximum (~20 ka), through the Holocene and present using paleo proxy RSL reconstructions and tide-gauge records from Singapore and the Sundaland Shelf. We will conclude with IPCC AR6 projections to 2100 using newly adopted Shared Socioeconomic Pathways aligned with increasing global temperature levels. During the last deglacial transition (18 to 11 ka), RSL rose from -111 m to -51 m at rates of 210 mm/yr, accelerating up to ~40 mm/yr between 14.5 to 14 ka in response to meltwater pulse 1A. During the early Holocene (11.6 to 6.5 ka), RSL rose from -21 m to ~1 m at rates up to ~14 mm/yr driven by deglaciation of northern hemisphere ice sheets. RSL continued to rise during the mid-Holocene (6.5 to 5.5 ka), reaching a highstand of ~4 m at rates of 0.53 mm/yr before falling thereafter at a maximum rate of -2 mm/yr driven by hydro-isostatic processes. Present RSL change shows RSL increased ~0.2 m at rates of 2.52.8 mm/yr between 1980 and 2016, increasing to ~4 mm/yr after 1993. Future RSL change to 2100 driven primarily by thermal expansion and mass loss from glaciers and ice sheets may be exacerbated due to uncertainties related to marine ice sheet and cliff instability and atmospheric and ocean dynamics.