SINGAPORE: How high will future sea levels rise? Answering this question carries great importance, particularly here in Singapore. Rising seas threaten our limited land area and developed coastlines that hold such economic, environmental and societal value.
At the Earth Observatory of Singapore, Nanyang Technological University (NTU), we have focused on this challenge for many years to better estimate how much the sea level will rise in Singapore and the surrounding region. With the recent launch of a new research centre to strengthen local capabilities and expertise in coastal protection and flood management, our new research cannot be more timely.
The future projections we presented in June show the sea level here could rise between 0.38m and 0.79m by 2100 and between 0.58m and 1.37m by 2150.
This range of values is because future sea level rise depends heavily on emission scenarios that limit or worsen global warming and is one component of a changing climate system that is difficult to predict. Sea levels are also not the same everywhere, varying from place to place and over time. For example, the impact of melting Antarctic and Greenland ice sheets will be felt greatest in tropical countries such as Singapore because of how melting water is redistributed around the Earth.
One undeniable fact remains. Every additional centimetre of sea level rise will have a significant impact on the livelihood of people who live in low elevation regions of Singapore, as 30 per cent of the country is less than 5m above mean sea level. It will also put pressure on our transport infrastructure and make the country susceptible to flooding.
As a land-scarce nation, Singapore has estimated that it will need to spend more than S$100 billion (US$73 billion) over the next century to protect the island from rising sea levels and climate change.
After all, as Prime Minister Lee Hsien Loong said in his National Day Rally speech in 2019, it’s a matter of “life and death”.
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CLUES FROM THE PAST
In our study, we show projections of sea level rise under moderate to high emission scenarios increasing at rates of up to 11mm a year were only last exceeded during past rapid ice sheet melting events and have not occurred in Singapore in at least the last 8,000 years.
If climate change triggers the collapse of ice sheets, however, the sea level could rise at rates that Singapore has not seen for over 100,000 years.
We obtained these results after reconstructing the most complete history of sea levels in tropical and equatorial latitudes over the past 22,000 years, using mangroves and corals from Singapore and the surrounding region. Using a statistical model, we used the past changes in sea levels to give context to future projections.
The coastal environments used to reconstruct sea levels in the study can be considered as Earth’s natural archives. Much like pages in a book, they reveal layer by layer a history of change, detailing how sea levels responded to climate and other factors.
Twenty-two thousand years ago, Earth’s climate was very different compared with today. Global temperatures were 5 to 7 degrees Celsius cooler and carbon dioxide levels were 55 per cent less than in 2023.
This period, known as the last glacial maximum, was Earth’s last major cooling phase. Vast ice sheets covered northern America and Europe and because of all the water locked away, the sea level in Singapore were around 120m below present-day level.
With the sea level so low, our regional landscape looked very different. Indeed, Singapore was not an island surrounded by water, but was connected by land with continental Asia and neighbouring islands such as Borneo and Sumatra. At the time, ancestral populations could migrate on foot across this now-submerged landscape.
As temperatures and carbon dioxide levels naturally began to increase, due to the northern hemisphere absorbing more solar radiation, the ice sheets started to melt and sea levels rose.
We found that the rise in sea levels, however, was not uniform. Around 14,000 and 9,000 years ago, the ice sheets in the northern hemisphere disintegrated causing sea levels to rapidly increase. Between and after these events, sea level rise slowed. This evidence shows us how sensitive ice sheets are to climate change.
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FASTER THAN EVER SEEN
One key difference between past, present and future, however, is the changes we are now observing are faster than we have seen due to anthropogenic activities. Temperatures over the past 150 years have risen faster than anything in the preceding 22,000 years and carbon dioxide levels have reached their highest level in at least 3 million years.
The projected rise in sea levels also directly threatens our coastal environments, such as mangrove forests and coral reefs.
If sea levels rise too fast, tipping points are crossed, and ecosystems may drown and become permanently submerged underwater. The geological past tells us this has happened before. For example, we know when sea levels increased at rates similar to those projected under moderate to high emission scenarios, these environments died.
Our knowledge and adaptation capabilities to defend against rising sea levels are ever improving. With Southeast Asia containing more than one-third of all the world’s most ecologically diverse mangroves and corals, careful management and intervention will be required to ensure their survival.
This is particularly important in many developed coastal regions such as Singapore where industrialisation impedes their growth and landward migration.
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WILL SINGAPORE GO UNDERWATER?
The results presented in our study also have wider reaching application to other low-lying islands and coastal regions because we know changes in past sea levels in response to the rapid ice melting events were almost universal across tropical and equatorial latitudes.
According to the United Nations, an additional 30cm sea level rise can result in 45m of landward erosion in some coastal areas of Asia. Indeed, the past can provide some analogy for the future. For example, an equivalent rise of 0.95m above present level caused the past regional landscape in Southeast Asia to reduce by 20,000 square km, or roughly 27 times the size of Singapore.
A projected rise of 5m above present that considers rapid ice sheet loss events, however, could cause the past regional landscape to reduce by 88,000 square km. That’s equivalent to over 120 times the size of Singapore.
While it is virtually certain that sea levels will continue rising throughout the 21st century, how fast and by how much is very much dependent on societal choices.
Our future climate pathways are not set in stone. We as individuals must remain optimistic and play our part to ensure a sustainable future by making conscious decisions in our daily lives that limit the effects of global warming and help not only Singapore, but the world, achieve its climate goals.
Dr Timothy Shaw is Senior Research Fellow at the Earth Observatory of Singapore at Nanyang Technological University.