An interdisciplinary team of researchers from Nanyang Technological University (NTU) Singapore and Delft University of Technology (TU Delft), The Netherlands, have introduced groundbreaking research into the projections of sea-level rise. If global carbon dioxide (CO2) emissions continue to follow the trajectory of a high emission scenario, this study predicts that sea levels may very likely rise by between 0.5 and 1.9 meters by 2100, with the high end of this estimate exceeding the latest global projections by the United Nations.
The high-end of this projected range is striking, with a difference of 90 centimeters above the latest United Nations’ estimates. The report, which was published in the peer-reviewed journal Earth’s Future, expands the knowledge of sea-level rise by introducing projections with higher certainty than prior models. These projections come with a 90% probability of occurrence, an important distinction as compared to the 66% probability of the range assessed in the latest United Nations Intergovernmental Panel on Climate Change (IPCC) report.
This new and more informative very likely range (90% probability) aims to fill the gap for policymakers, urban planners, and researchers, giving them more reliable information than ever before. This becomes crucial as global temperatures rise, glaciers melt, and ice sheet dynamics become more unpredictable due to increasing human-induced warming.
Sea-Level Rise Projections and Their Impact
Global sea level rise has become one of the most daunting consequences of climate change, affecting millions of people and coastal ecosystems. As ice sheets melt, thermal expansion of ocean water occurs due to higher temperatures, and glaciers in regions like Greenland and Antarctica continue to shed ice into the seas, contributing to rising waters. The rate of this rise is largely influenced by emission scenarios—in particular, whether future CO2 emissions continue at a high pace or are reduced in alignment with international climate mitigation goals.
The different approaches that are currently used to project sea-level rise have relied on traditional models, incorporating well-established science concerning the behavior of glaciers, thermal expansion of oceans, and the Earth’s hydrological cycle. However, some models also attempt to predict more complex and poorly understood phenomena, such as the potential collapse of ice shelves or significant shifts in glacial dynamics. The unpredictability of these processes leads to a great deal of uncertainty in the projections.
This inherent uncertainty is why the IPCC, until now, has issued sea-level rise estimates in terms of a likely range, referring to a scenario with 66% probability. While these projections are valuable, they leave out scenarios at the high-end extremes, where sea-level rise could be more dramatic and devastating, with substantial implications for vulnerable coastal infrastructure and communities around the world.
The new projections developed by the NTU and TU Delft team are set apart because they offer a clearer and more comprehensive method for dealing with these uncertainties. The team focused on a method known as the “fusion” approach, which combines both the strengths of established models and expert opinions to give a more reliable, inclusive picture of the future.
The Fusion Approach: A New Model for Reliable Projections
The fusion approach introduced by this team blends expert judgments with statistical methods to account for the full range of possibilities in the future of sea-level rise. Their work builds upon data already incorporated in the IPCC’s Sixth Assessment Report, which simulates potential future climate scenarios under different emission pathways. The fusion approach is notably distinguished from the traditional methods by integrating a wider variety of projections that reflect different levels of confidence in the outcome.
This innovative model did not only consider the medium-confidence projections—which are better understood—but also took into account projections that have low confidence due to uncertainty about processes like the collapse of Antarctic and Greenland ice sheets. The NTU team used a carefully weighted system that placed higher priority on more reliable models, while still including data with lower confidence, to ensure that the true uncertainty of these outcomes was fully represented.
According to the results from their fusion approach, global mean sea levels are likely to rise by:
- 0.3 to 1.0 meters by 2100 under a low-emissions scenario, which is similar to projections presented by the IPCC’s likely range (0.3–0.6 meters).
- 0.5 to 1.9 meters by 2100 under a high-emissions scenario—a range 90 cm greater than the IPCC’s projected maximum (0.6 to 1.0 meters).
The broader projections put forward by the NTU team signify that previous models might have underestimated the potential for extreme outcomes. In particular, the high-emissions pathway paints an especially concerning future, where sea levels could potentially rise by up to 1.9 meters—a result that reflects a level of risk too high to ignore.
The Importance of Projections in Climate Planning
In terms of practical applications, these projections will play a vital role for government agencies, urban planners, and climate researchers who need to prepare for the worst-case scenarios. Many coastal cities, cities located on islands, or places with sensitive ecological systems could face the consequences of accelerated sea-level rise as early as 2050 or 2100, depending on emissions reduction and mitigation efforts.
The study’s lead author, Dr. Benjamin Grandey, Senior Research Fellow at NTU’s School of Physical and Mathematical Sciences (SPMS), stressed that the new approach provides actionable information regarding sea-level projections with a higher degree of certainty. He pointed out that this model bridges the gap left by other models that generate large variations in outcomes.
“Our new approach tackles a key issue in sea-level science: Different methods of projecting sea-level rise often produce widely varying results. By combining these different approaches into a single fusion projection, we can estimate the uncertainty associated with future sea-level rise and quantify the very likely range,” Dr. Grandey emphasized.
Why It Matters for Global Planning
Co-author, Professor Benjamin Horton, Director of the Earth Observatory of Singapore at NTU, elaborated further on the implications of this work. “This research represents a significant breakthrough in sea-level science. By estimating the probability of the most extreme outcomes, it underscores the severe impacts of sea-level rise on coastal communities, infrastructure, and ecosystems, which must now be addressed head-on. For policymakers and urban planners, these findings speak to the urgent need to address the climate crisis and avoid the worst outcomes of rising seas.”
Sea-Level Rise Beyond Coastal Flooding
While urban planning is one essential response to the threat of rising seas, the NTU-TU Delft team notes that the fusion approach could also be applied to broader climate-related fields. For instance, it can help evaluate:
- Coastal flood risk assessments, improving vulnerability maps and decisions for evacuations, infrastructure protection, and water management.
- Infrastructure vulnerability analysis, informing government and private sector investments in more resilient buildings and cities.
- Economic forecasting models, quantifying potential costs related to displacement, environmental degradation, and the cost of adaptation.
Co-author, Professor Chew Lock Yue, from NTU’s School of SPMS, added that the new fusion model synthesizes the best available knowledge into a unified picture, helping translate uncertainty into valuable, actionable insights for climate resilience strategies.
Associate Professor Justin Dauwels, co-author from TU Delft and expert in Signal Processing Systems, emphasized that the fusion approach isn’t limited to just sea-level projections—it has broad applications for any aspect of climate-related decision-making.
Conclusion: A Call for Mitigation Action
The new projections are crucial not just for future adaptation planning, but also for urging immediate action on mitigating climate change. As Dr. Grandey mentioned, the projected high-end scenarios under a high-emissions pathway should encourage leaders worldwide to strive towards international climate agreements with concrete steps to curb greenhouse gas emissions and put the world on a path to sustainability.
By offering a fuller picture of potential sea-level rise, the NTU-TU Delft study calls for more decisive action to tackle the root causes of climate change. Their method is a powerful tool in building the resilience needed to confront an increasingly uncertain future in our coastal regions.
Reference: Benjamin S. Grandey et al, Fusion of Probabilistic Projections of Sea‐Level Rise, Earth’s Future (2024). DOI: 10.1029/2024EF005295