United Nations’ World Water Day 2025 carries the theme of Glacier Preservation. Sea level rise is known to be accelerating, but it is not too late to avoid the worst outcomes. More can, and must, be done, Dr Jamin Greenbaum and Erol Yayboke write.
Global mean sea level is rising at an accelerating rate and rose faster in the 20th century than at any time in the last three thousand years; mass loss from glaciers and ice sheets contributed the most to sea level rise starting in 2006 (IPCC Sixth Assessment Report).
Given these dramatic recent changes, it is prudent to ask how much worse could these changes get and what could the impacts be on our global society?
Geological evidence provides some clues to the first question: studies utilising palaeoclimatological data have shown that sea level today is actually 6 to 9 metres (~20 to 30 feet) lower than it was the last time conditions on Earth were similar to what they are today (Kopp et al., 2009), at a time roughly 125,000 years ago called the Last Interglacial period (LIG).
The LIG is interesting because, in climatic (e.g. global average temperature) and geological (e.g. when considering tectonic motion and erosion) terms, Earth was essentially identical to what it is today; the only meaningful difference is that hominids had not yet industrialised.
Global mean sea level rose faster in the 20th century than at any time in the last three thousand years.
Photo: Shutterstock
Given that sea level rose so much higher at a time when climate conditions were similar to today, predicting what it will do during the rest of this interglacial is obviously urgent, especially for the 11% of the global population in low-lying coastal zones (Neumann et al., 2015), which generate 14% of global Gross Domestic Product (Magnan et al., 2022).
Projections estimate ~190 million people live in areas that could be below high tide by 2100 under low emissions scenarios, rising to ~630 million (Kulp & Strauss, 2019) under high emissions scenarios that include potential glacier instabilities from Antarctica (DeConto & Pollard, 2016). In the United States alone, relative sea level rise could threaten 273,000 people and 171,000 properties by 2050 (Ohenhen et al., 2024).
Major uncertainties remain in the physical models used in those studies (Edwards et al., 2019) and the IPCC acknowledges that higher than predicted rates of sea level rise are possible due to ice sheet instability processes that had not yet been included at the time of the 6th Assessment Report.
These uncertainties are the foundation of many ongoing research projects supported by international funding agencies like the National Science Foundation in the United States.
As a low-lying coastal city, Miami is particularly vulnerable to climate change impacts including rising sea levels.
Source: Shutterstock
Tragically, like climate change more broadly, sea level rise occurs disproportionately in places that are less prepared to deal with its impacts.
Miami and Copenhagen will undoubtedly incur costs and periodic catastrophic climate events, but similar challenges in places like Jakarta and Lagos could have longer lasting impacts, particularly on the people who live there.
These people are well aware of the consequences of climate change. Rising seas not only impact those who live within a few kilometres of the coast, it can result in saltwater intrusion for inland farmers and can contaminate groundwater sources critical for humans and animals alike.
Indonesia is building a new capital city called Nusantra on the island of Borneo in response to the risk posed by rising sea levels on Jakarta.
Photo: Shutterstock
Though rapid urbanisation, overcrowding, and other sociological factors contributed to its decision (not to mention have their own solutions), Indonesia recently decided to move its capital city to the island of Borneo in large part because sea level rise and other ecological factors will soon make Jakarta unable to meet the needs of its residents.
Significant chunks of Jakarta fall within those areas that could be below high tide by 2100 and coastal farmland in critical rice-producing regions like Central Java could face significant soil salinity issues. Indonesians directly or indirectly impacted by these challenges are looking for sustainable solutions…not always in productive places.
Nigerians are also paying close attention. Communities along Nigeria’s 853 km coastline deal with extreme weather and rising seas with increasing frequency. And when damaging – and also increasingly frequent – inland flooding inundated large swaths of the country and caused a major dam to collapse in September 2024, analysis of discursive and conversational data by FilterLabs.AI showed a substantial negative shift in sentiment. Nigerians were not happy, and they clearly (and accurately) blamed the disastrous flooding on climate change.
Figure 1: How Nigerians feel about climate change can fluctuate drastically based on real world events.
Source: FilterLabs.AI
Geological data shows sea level rise could get much worse while discursive and conversational data shows that the real-world consequences could make things even worse.
Much can be done to decelerate climate change and to help people adapt and prepare for even more challenging times ahead. From innovative Senegalese efforts to limit coastal erosion to the restoration of San Francisco’s tidal marshes to the physical relocation of people (in Indonesia and other vulnerable places like Fiji), positive adaptation examples abound. But the bottom line is that more must be done in more places, and that doing so is not only a humanitarian imperative.
Whether in Jakarta or Lagos or countless other places disproportionately negatively impacted by climate change, sentiment analysis demonstrates that providing immediate and longer-term solutions is crucial for maintaining stability in some of the most populous countries (including Indonesia at number 4 and Nigeria at number 6) in the world.
Dr Greenbaum and his team want to understand what is driving Antarctic Ice Sheet melt and how to better predict global rising sea levels.
It is not too late to avoid the worst projected outcomes of sea level rise through climate mitigation efforts. However, two centuries of industrialisation have made costly adaptation measures inevitable.
Prioritising and planning these projects will become more straightforward as scientists continue improving our understanding of coupled atmosphere-ice-ocean instability processes that drive rapid glacier melt and retreat.
The value of these efforts cannot be overstated: the IPCC estimates that just 1 metre of sea level rise could put about a trillion dollars in global GDP at risk, with approximately 50% of the impact concentrated in Asia and another 30% in Europe. We must know when to expect these impacts along our coastlines and we need to know as soon as possible.
Dr. Jamin Greenbaum is a polar geophysicist at the Scripps Institution of Oceanography at the University of California San Diego. His work focuses on observing and understanding areas of the polar regions that are important for predicting sea level rise but are difficult to access using conventional approaches. He has led or supported 18 internationally collaborative polar expeditions using a combination of airborne and marine platforms in Antarctica and Greenland.
Erol Yayboke leads research for a growing data analytics firm, FilterLabs.AI and is a Senior Fellow (non-resident) at the Center for Strategic and International Studies (CSIS). He completed his service in the Biden-Harris Administration as the Deputy Chief of Staff to the Deputy Secretary of Defense, before which he was a Senior Advisor in the Administration at USAID/BHA. Before government, Yayboke was a senior fellow with the International Security Program and director of the Project on Fragility and Mobility at CSIS.
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IPCC. 2023. Summary for Policymakers. In Climate Change 2023: Synthesis Report. Contribution of Working Groups I, II, and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change, edited by Core Writing Team, H. Lee, and J. Romero, 1–34. Geneva, Switzerland: IPCC.
DeConto, R. M., & Pollard, D. (2016). Contribution of Antarctica to past and future sea-level rise. Nature, 531(7596), 591–597.
Edwards, T. L., Brandon, M. A., Durand, G., Edwards, N. R., Golledge, N. R., Holden, P. B., et al. (2019). Revisiting Antarctic ice loss due to marine ice-cliff instability. Nature, 566(7742), 58–64.
Kopp, R. E., Simons, F. J., Mitrovica, J. X., Maloof, A. C., & Oppenheimer, M. (2009). Probabilistic assessment of sea level during the last interglacial stage. Nature, 462(7275), 863–867.
Kulp, S. A., & Strauss, B. H. (2019). New elevation data triple estimates of global vulnerability to sea-level rise and coastal flooding. Nature Communications, 10(1), 4844.
Magnan, A. K., Oppenheimer, M., Garschagen, M., Buchanan, M. K., Duvat, V. K. E., Forbes, D. L., et al. (2022). Sea level rise risks and societal adaptation benefits in low-lying coastal areas. Scientific Reports, 12(1).
Neumann, J. E., Emanuel, K., Ravela, S., Ludwig, L., Kirshen, P., Bosma, K., & Martinich, J. (2015). Joint effects of storm surge and sea-level rise on US Coasts: new economic estimates of impacts, adaptation, and benefits of mitigation policy. Climatic Change, 129(1–2), 337–349.
Ohenhen, L. O., Shirzaei, M., Ojha, C., Sherpa, S. F., & Nicholls, R. J. (2024). Disappearing cities on US coasts. Nature, 627(8002), 108–115.