Geological Perspectives of Future Sea-Level Rise in Singapore

Tropical latitudes of Southeast Asia are especially vulnerable to relative sea-level rise (RSLR) that is virtually certain (>99% probability) to increase over the 21st century. Singapore, a small (~730 km2) island in Southeast Asia, is vulnerable to RSLR with populations, industry, urban, and transport infrastructure within 5 m elevation of present sea level. Here, we review RSL changes spanning the last glacial maximum (LGM) towards the present using geological reconstructions and instrumental RSL records from Singapore and the Sunda Shelf. We applied an Error-In-Variables Integrated Gaussian Process model to quantify magnitudes and rates of RSL change through time and provide probability perspectives to IPCC AR6 projections to 2100.

At the end of the LGM, RSL rose from -115 m at 19.5 ka BP to -67 m at ~13 ka BP during which the average rate of RSLR accelerated to 18 ± 6 mm/yr associated with meltwater pulse 1A. Between the early and mid-Holocene, RSL rose from -21 m at 9.5 ka BP to ~1 m at 6.5 ka BP at rates up to ~14 mm/yr primarily driven by deglaciation of Northern Hemisphere ice sheets. RSL reached a highstand of ~4 m at 5.5 ka BP and fell below present to -2 m at 1.5 ka BP at rates of ~-2 mm/yr driven by hydro-isostatic processes. Between 1915 and 2020 CE, RSL rose 0.15 m at a rate of 1.7 ± 1 mm/yr increasing to 2.2 ± 1 mm/yr driven by ocean volume and mass changes.

Projections to 2100 show RSL rising 0.37 m to 0.78 m at rates of 4 mm/yr to 13.5 mm/yr that may be exacerbated by ice sheet, ocean, and atmospheric processes. Rates of RSL exceeding 4 mm/yr were virtually certain and very likely (>90% probability) exceeded 13.5 mm/yr between 14.5 ka and ~13 ka BP and between 9.5 ka and ~8 ka BP. These periods are associated with the disintegration of ice sheets in response to climate warming. During the last ~5.5 ka, it was unlikely (<33% probability) RSL exceeded 4 mm/yr and exceptionally unlikely (<1% probability) RSL exceeded 13.5 mm/yr during last ~8.5 ka.