Search

Low elevation equatorial and tropical coastal regions are highly vulnerable to sea level rise. Here we provide probability perspectives of future sea level for Singapore using regional geological reconstructions and instrumental records since the last glacial maximum ~21.5 thousand years ago. We quantify magnitudes and rates of sea-level change showing deglacial sea level rose from ~121 m below present level and increased at averaged rates up to ~15 mm/yr, which reduced the paleogeographic landscape by ~2.3 million km2. Projections under a moderate emissions scenario show sea level rising 0.95 m at a rate of 7.3 mm/yr by 2150 which has only been exceeded (at least 99% probability) during rapid ice mass loss events ~14.5 and ~9 thousand years ago. Projections under a high emissions scenario incorporating low confidence ice-sheet processes, however, have no precedent during the last deglaciation. Ministry of Education (MOE) National Environmental Agency (NEA) National Research Foundation (NRF) Published version This research was supported by the Earth Observatory of Singapore grants M4430132.B50- 2014, M4430139.B50-2015, M4430188.B50-2016, M4430245.B50-2017 and M4430245.B50-2018. T.A.S., T.L., S.C., J.M.M., A.D.S. and B.P.H. were supported by the Singapore Ministry of Education Academic Research Fund MOE2019-T3-1-004 and MOE- T2EP50120-0007, the National Research Foundation Singapore, the Singapore Ministry of Education under the Research Centers of Excellence initiative, and by Nanyang Techno- logical University. This Research/Project is supported by the National Research Foundation, Singapore, and National Environment Agency, Singapore under the National Sea Level Programme Funding Initiative (award No. USS-IF-2020-1). Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not reflect the views of the National Research Foundation, Singapore and the National Environment Agency, Singapore. N.C. research is conducted with the financial support of Science Foundation Ireland and co-funded by Geological Survey Ireland under Grant number 20/FFP-P/8610. R.E.K. and G.G.G. were supported by U.S. National Science Foundation award ICER-2103754 as part of the Megalopolitan Coastal Transformation Hub (MACH) and by the National Aeronautics and Space Administration (award 80NSSC20K1724 and JPL task 105393.509496.02.08.13.31).

Supplemental material, sj-docx-1-hol-10.1177_09596836221131696 for A 5000-year record of relative sea-level change in New Jersey, USA by Jennifer S Walker, Tanghua Li, Timothy A Shaw, Niamh Cahill, Donald C Barber, Matthew J Brain, Robert E Kopp, Adam D Switzer and Benjamin P Horton in The Holocene

Singapore is a small (728 km2) island nation that is vulnerable to rising sea levels with 30% of its land surface area less than 5 m above present sea level. Rising relative sea level (RSL), however, is not uniform with regional RSL changes differing from the global mean due to processes associated with vertical land motion (e.g., glacial-isostatic adjustment) and atmospheric and ocean dynamics. Understanding magnitudes, rates, and driving processes on past and present-day sea level are therefore important to provide greater confidence in accurately quantifying future sea-level rise projections and their uncertainty. Here, we present a synopsis of Singapore’s past and present RSL history using newly developed proxy RSL reconstructions from mangrove peats, coral microatolls and tide gauge data and conclude with probabilistic projections of future RSL change.Past RSL is characterized by rapid rise during the early Holocene driven primarily by deglaciation of northern hemisphere ice sheets. Sea-level index points (SLIPs) from mangrove peats show sea levels rose rapidly from -20.7 m at 9.5 ka BP to -0.6 m at 7 ka BP at rates of 6-12 mm/yr. This is substantially greater than predicted magnitudes of RSL change from the ICE-6G_C GIA model which shows RSL increasing from -6.4 m at 9.5 ka BP to a ~2.8 m highstand at ~7 ka BP. SLIPs show the mid-Holocene highstand of ~4 ± 3.6 m at 5.2 ka BP before falling towards present at rates up to -2 mm/yr driven by hydro-isostatic processes. The nature of RSL changes during the mid- to late-Holocene transition remains poorly resolved with evidence of sea levels falling below present level to -2.2 ± 2.0 m at 1.2 ka BP. Present RSL reconstructions from coral microatolls coupled with tide-gauge data extend the limited instrumental period in this region beyond ~50 years. They show RSL rose ~0.03 m from 1915 to 1990 at 0.7 ± 1.4 mm/yr before increasing to 1.5 ± 2.1 mm/yr after 1990 to 2019. Future RSL change from probabilistic projections to 2100 under low (RCP 2.6) and high (RCP 8.5) emission scenarios show sea levels rising 0.43 m (50th percentile) (0.06 – 0.96 m; 95% credible interval) and 0.74 m (0.28 – 1.4 m), respectively. However, projected magnitudes of sea-level rise driven by rapid ice sheet dynamics and the unknown contribution of atmospheric and ocean dynamics in Southeast Asia have the potential to exacerbate projection magnitudes.