3 Ways To Deal With The Deep Uncertainty Of Sea Level Rise

By Ronald Leung, Dawn McGregor 27 July, 2021

SLR uncertainty is here to stay but it can be minimised as discussed at SIWW 2021. CWR's Leung & McGregor share what the climate & planning experts advised

Can never get rid of SLR uncertainty & human action is the biggest source; but it can be reduced with regional research as global vs. local SLR projections can be very different
Also, do not blindly adopt IPCC projection as it has a tendency to underestimate; instead, consider the worst-case scenario & adjust adaptation according to your own risk appetite
Low-regret flexible & adaptive solutions that make decisions at various points in time can better adapt to future changes e.g. nature solutions that embraces natural dynamics

One of the biggest obstacles in dealing with sea level rise (SLR) is the deep uncertainty in projections. The latest scientific data from the Intergovernmental Panel on Climate Change (IPCC), its Fifth Assessment Report (AR5), Global Mean Sea Level (GMSL) has the “likely” rise range projected between 0.3-1.1m (RCP 2.6 – RCP8.5) by the end of the century, but that accounts for 17-83% probability, meaning tail-risks beyond 1.1m have not been included but are still plausible.

Sea level rise has been accelerating since the 1990s…

…yet, deep uncertainty in projections is still one of the biggest obstacles

Also, bear in mind that sea levels will not stop rising beyond 2100, which makes determining the level to protect against even more difficult. The next IPCC report, the AR6, is due for release in 2022 and many expect the numbers to have increased. As Professor Dale Barker, Director at the Centre for Climate Research Singapore (CCRS), said during a session at 2021 Singapore International Water Week (SIWW), “… [SLR has been] accelerating since the 1990s and that has continued in recent years so this is a growing issue clearly.”

SIWW 2021, a 10 day fully virtual event, concluded on July 2 – you can see our 5 key takeaways from the kick-off event, SIWW Spotlight 2021, here. The risks from SLR/ coastal threats were for the first time a focus at this year’s SIWW with five dedicated sessions that covered the UK’s coastal approach, adaptive shore protection products, delivering resilient coastal communities and more.

One of the SLR sessions that stood out to us was “Dealing with the Deep Uncertainty of Sea Level Rise”. Below are our 3 key takeaways from that event after a short review of Singapore’s stance on SLR and how the country is proactively protecting itself, as presented by Hazel Khoo, Director of Coastal Protection, PUB, Singapore’s National Water Agency, who started off the SIWW session – see box below for key points from Khoo’s introduction. It wasn’t surprising to hear how much Singapore is doing on SLR risks as Singapore was ranked top in CWR’s APAC Coastal Threat Index for 20 cities – see how others ranked and the four other reports in the series here.


Singapore gets SLR & is proactively managing the risks
Key points from Hazel Khoo’s (Director of Coastal Protection, PUB, Singapore’s National Water Agency) introduction at SIWW session.

  • Singapore PM Lee said in his 2019 State of the Nation address, “We should treat climate change defences with utmost seriousness, these are life and death matters. Everything must bend at the knee to safeguard the existence of our island nation.”
  • “… for us, sea level rise is an existential threatSea level rise is a long-term problem that requires a long-term solution spanning across multiple generations of Singaporeans. Hence, it is imperative that we start planning now and implement at a pace that is sustainable.”, Khoo
  • In the second national climate change study (2014), the Centre for Climate Research Singapore (CCRS) projected that mean sea level around Singapore will rise by up to 1m by the end of this century. Furthermore, under an extreme event where storm surges and very high tides coincide, sea levels could reach up to almost 5m above current mean sea levels by the end of this century. When this happens, it will inundate many of Singapore’s low-lying coastal areas.
  • So, to safeguard Singapore against this risk, PUB’s Coastal Protection department was set-up to lead and coordinate the whole of government efforts to develop long-term solutions to protect Singapore from the rising seas.
  • “Coastal adaptation is also a massive undertaking. So, with the use of science-based data, our next step is to explore opportunities to integrate coastal protection measures with our land use plans.”, Khoo
  • CCRS is currently working on its 3rd Climate Change study, due for release in 2022 of which PUB will use to update its holistic flood risk assessment.


“… for us, sea level rise is an existential threat… Sea level rise is a long-term problem that requires a long-term solution spanning across multiple generations of Singaporeans. Hence, it is imperative that we start planning now and implement at a pace that is sustainable.”

Hazel Khoo, Director of Coastal Protection, PUB,



Below are our 3 key takeaways from the “Dealing with the Deep Uncertainty of Sea Level Rise” session:

1. Uncertainty is here to stay… so accept it but minimise with regional research

Climate models have a similar set-up to weather models, they try to represent the whole grid area but there are many complexities, be it the water cycle, a volcano or differing land surface, all of which present uncertainty. But the biggest uncertainty is how humans are going to deal with climate change – “So, this is the biggest source of uncertainty we have. The 1.5°C versus business as usual…”, Professor Barker, Director at the Centre for Climate Research Singapore.

We can never get rid of uncertainty, but we can minimise it and measure it as Professor Barker said, “… one needs to reduce uncertainty…. but we recognise that we will never get rid of uncertainty. Uncertainty will always be there.  We will try and reduce it but at the same time as reducing it, we need to estimate what it is… as that will help us estimate what the risks are.”

“The biggest uncertainty is the green… how we are going to deal with climate change. So, this is the biggest source of uncertainty we have. The 1.5°C versus business as usual…”

Professor Dale Barker, Director at CCRS

One way to reduce the uncertainties is through running multiple climate models – mostly done already – and another is through robust regional research. Global versus local SLR projections can be very different, especially if one is in Asia, which is most at risk from SLR making it even more important to run regional and local SLR research.

Singapore is running it’s 3rd climate change study; the first regionally to use CMIP6

Singapore is doing just that. The country is already on its third national climate change study that also includes the surrounding region, the results are due next year. It will be the first regional climate projection in the world to use the latest global climate model CMIP6. It will also be done to a higher resolution so will have more local data than the previous version. This isn’t a small task. The study is using the latest science and computing resources from Singapore’s national supercomputer centre but is a priority for the nation and so is getting done. However, it is also important to know what to do with the data, which leads us to the next point.

2. Risk appetite matters but don’t ignore the worst-case scenario

SLR risk appetite differs depending who you are and the decisions you have to make – scientists use the “most likely” scenarios while insurers tend to use the “worst case” scenarios. But a key takeaway from this session is that whatever your appetite, one should not blindly adopt the IPCC’s “likely” projection and also one can’t afford to not consider the worst-case scenario or as Professor Barker called it, the “high impact low-likelihood” (HHLL) scenario.

Do not blindly adopt IPCC’s “likely” scenario; also need to check against “high impact low-likelihood” scenario

This aligns with what IPCC suggested in its 2019 Special Report on the Ocean and Cryosphere in a Changing Climate, “the range of SLR to be considered in decisions depends on the risk tolerance of stakeholders, with stakeholders whose risk tolerance is low, should also be considering SLR higher than the likely range”.

SLR expected to be adjusted higher in the upcoming AR6

While considering risk appetite, all stakeholders should also be mindful of the changing nature of climate science as more global focus and resources are deployed and climate conditions change. As PUB’s Khoo said during the session, “we expect SLR projections to be adjusted higher in the upcoming AR6”. And actually, a study co-authored by SLR expert Dr Nicole Khan also suggested that IPCC’s projections are conservative to many experts, see our interview with her in 2020 here. So, what is the best way to plan with uncertainty in the projections and different risk appetites? We look at this below.

3. Start planning flexible & adaptive solutions now

Conventional planning, with everything done up front and none, if any room, for contingencies is not the way forward as said by Assistant Professor, Naomi Hanakata from the Department of Architecture at the National University of Singapore. Adding that projects that follow this planning paradigm, will likely see their functional lifetime decrease due to the changing climate.

To build real resilience, need to adopt adaptive planning as its flexible to change

Instead, Hanakata suggested implementing adaptive planning, which creates a dynamic and responsive model that does not have everything planned out and brings together different datasets (including climate data) at various points in time thus building resilience by responding to changes and the future environment. Hanakata added that this approach is particularly applicable for SLR.

An adaptive approach was also the recommendation of Laura Vonhögen-Peeters, Associate Director Singapore Operations, Deltares – NUSDeltares who said, “stakeholders need to act now with low-regret flexible measures”, adding that this will save from overspending to protect against worst-case scenarios. Vonhögen-Peeters went further saying that building with nature should also be in plans as “building with nature embraces natural dynamics and thus adapts to a changing environment.”

Coastal adaptation strategies should embrace an adaptive approach that includes nature solutions & diversifications

Both Hanakata and Vonhögen-Peeters were clear, due to the deep uncertainties in SLR, coastal adaptation strategies should embrace an adaptive approach that includes nature solutions, diversifications and has multiple strategies to provide extra layers of protection.

Further Reading

  • Sea Level Rise – What The Science Tells Us – What’s the latest on sea level rise projections? HKU’s Dr. Nicole Khan shares key findings from her survey of 100+ sea level experts, as well as talks risks to Hong Kong and what we should take away from COVID-19
  • Future SLR Projections & Biggest Worries – In this follow up interview, HKU’s Dr. Nicole Khan shares her biggest concerns on how future SLR projections are rising higher & faster than thought & shares the best approach for building realistic scenarios
  • Existential Coastal Threats: 8 Things You Must Know – Rapid SLR will happen sooner than we think, yet we are still driving investments to vulnerable locations. CWR’s Debra Tan shares 8 things you need to know about the existential threat from SLR – from glaciers in the mountains to ice sheets in our poles, permafrost + more
  • The CWR Survival Guides to Avoiding Atlantis – Sea levels can be 3m by 2100, putting urban real estate equivalent to 22 Singapores underwater in just 20 APAC capitals & cities. With US$5.7trn of annual GDP at stake, get on top of the new risk landscape to survive
  • Surviving Rising Seas – 20 APAC Cities: Who’s ahead & Who’s Behind? – The homes of 28mn to 100mn+ residents could be submerged in just 20 APAC cities. Which cities are more prepared? We walk you through the Top 5 Most Proactive & the Bottom 5 Laggards in our CWR APACCT 20 Index

More on Latest

  • SIWW Spotlight 2021 Key Takeaways – Impressed with the frank conversations & SLR focus for the first time at the 2021 SIWW Spotlight, see what other takeaways CWR’s Dawn McGregor has from the centerpiece sessions
  • A Conversation with SIWWs Ryan Yuen – It was a different SIWW this year due to the pandemic & a more holistic agenda with hot new topics. We sat down with SIWW’s Ryan Yuen to get the SIWW2021 scoop & see what’s next
  • Why Isn’t Water Top Of The Climate Agenda? – If water risks were properly valued, they would be much greater than the energy transition risks so, why isn’t water at the top of the agenda asks Eco-Business’ Sonia Sambhi who caught CWR’s Debra Tan & other water experts at SIWW 2021
  • Game Changers: 6 Lee Kuan Yew Water Prize Laureates – We would be fools not to tackle 3 game changers for our future water & climate according to 6 LKY laureates. CWR’s Dawn McGregor breaks them down
  • Behind Phnom Penh’s Water Success Story – PPWSA, a once-bankrupt utility now outperforms those in LA or London. CWR’s Soomin Park & Dawn McGregor shares 2 keys to its miraculous transformation & 2 new challenges it faces
Ronald Leung
Author: Ronald Leung
Hailing from Hong Kong, Ronald’s interest in geopolitical and economic issues led him to understand that climate change is one of the most pressing challenges of our times, yet politically, the topic lacked urgency and societal attention. This motivated him to join CWR upon graduation from the Master of Global Political Economy at The Chinese University of Hong Kong. He assists the team in research across various focus areas and sectors that CWR covers and works on the publication of CWR’s monthly newsletter. He also helps manage and expand our network of contributors plus keeps the content on our website updated. Prior to CWR, Ronald focused on market and competitor research in a property conglomerate and a travel tech start-up. Besides, he conducted country analysis and co-published geopolitical articles with his professor in CUHK. He hopes to use his experiences as a debate team captain in the University of Hong Kong (where he obtained a Bachelor in Accounting & Finance) to raise public awareness towards climate change in Hong Kong.
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Dawn McGregor
Author: Dawn McGregor
Dawn leads CWR’s work to help corporates navigate increasingly disruptive & material risks from water & climate threats, as well as transitional risks in the supply chain arising from new regulations in China. Here, Dawn engages extensively with the global fashion industry delivering on-ground workshops in China to keynotes and strategic input at European HQs. She has written at length on the end of dirty and thirsty fast fashion and her report to overcome gaps between brands and manufacturers for a clean and circular future inspired the industry to create a new wastewater tool. Dawn also works closely with the property and tourism sectors where she not only conducts strategic assessments of their exposure but builds collective action toward resilience via closed door working groups and invite-only events. Having helped build CWR, Dawn is a frequent keynote, panellist & moderator at events, including being twice selected as the lead-rapporteur at World Water Week. Her articles are cited in various industry publications including the UN’s ‘World Without Water’. Dawn previously worked in a global investment bank assessing geo-political risk, crisis management and business resiliency. She was born and bred in Hong Kong and has lived in France, England, Singapore and Beijing.
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