Title: Sea-Level Science in Singapore and Southeast Asia

Authors: Benjamin P. Horton¹, Yudhishthra Nathan², Fangyi Tan³, Benjamin Grandey⁴, Tanghua Li³, Tim Shaw³

Affiliations

¹ The School of Energy and Environment, City University of Hong Kong, Hong Kong.

 ²The Asian School of the Environment, Nanyang Technological University, Singapore.

³ The Earth Observatory of Singapore, Nanyang Technological University, Singapore,

⁴ The School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore.

Abstract: No matter how quickly nations lower emissions now, the world is looking at about 15 to 30 centimeters of sea-level rise through the middle of the century, given the long-drawn impact of climate change on the oceans and ice sheets. Even under a stable climate, sea-level rise is expected to continue slowly for centuries. Beyond 2050, sea-level rise becomes increasingly susceptible to the world’s emission choices. If countries choose to continue their current paths, greenhouse gas emissions will likely result in ~3°C of warming by 2100, and a sea-level rise of up to 0.8 meters. Under the most extreme emissions scenario, rapid ice sheet loss from Greenland and Antarctica could lead to a sea-level rise approaching 2 meters by the end of this century and over 5 meters by 2150.

Here we illustrate the ways in which current methodologies and historical and geological data sources from Southeast Asia can constrain future projections, and how accurate projections can motivate the development of new sea-level research questions to mitigate and adapt to climate change.

1. We showed periods of rapid ice melting accelerated sea-level rise ~14,500 and ~11,500 years ago that significantly reduced land area and forced early human migration across the region. During these periods, thresholds of coastal habitat survival were also surpassed resulting in large-scale losses. Singapore became an island at approximately 9,000 years ago.

2. We ran an ensemble of Glacial Isostatic Adjustment (GIA) models that highlight how Southeast Asia experienced sea levels higher than present-day between 7,000 and 4,000 years ago, producing a mid-Holocene highstand. Variability in the high stand magnitude is controlled by solid Earth parameters while the timing is controlled by ice sheet melting history.

3. We developed a new fusion method for estimating high end sea-level rise, providing a more reliable assessment of scientific uncertainty. We estimate that by 2100, global sea levels will likely rise between 0.3-1.0 m under low emissions and 0.5-1.9 m under high emissions.

4. We focus on the implications of rising sea levels for coastal ecosystems. Under high emissions, nearly all salt marshes, most mangrove forests, and a considerable number of coral reef islands would be beyond their sea-level rise tipping point for survival.

Biography: Professor Benjamin Horton is the Dean of the School of Energy and the Environment at City University of Hong Kong. His research concerns sea-level change. He aims to understand the mechanisms that have determined sea-level changes in the past, which will shape changes in the future. Professor Horton has won research awards from European Geosciences Union, American Geophysical Union and Geological Society of America. Professor Horton was an editor for the Intergovernmental Panel on Climate Change (IPCC) 6th Assessment Report. Professor Horton has published over 280 articles in peer-reviewed journals, including Science, Nature and Proceedings of the National Academy of Sciences. He has been awarded US$50 million in research funding.