An interdisciplinary group of researchers is warning that if global CO2 emissions keep rising and hit a high emission scenario, sea levels could likely increase between 0.5 and 1.9 meters by the year 2100. Notably, the upper estimate of this projection exceeds the latest United Nations forecast by 90 centimeters, which estimates an increase of 0.6 to 1.0 meters.
A diverse team of researchers from Nanyang Technological University in Singapore (NTU Singapore) and Delft University of Technology in the Netherlands (TU Delft) has forecasted that continued growth in global CO2 emissions could lead to a very likely rise in sea levels of between 0.5 and 1.9 meters by 2100. This upper limit is 90 centimeters greater than the most recent United Nations projection of 0.6 to 1.0 meters [1].
The very likely range, which indicates a 90% chance of occurrence, was shared by the NTU team in the academic journal Earth’s Future. This work enhances the sea-level rise forecasts made by the Intergovernmental Panel on Climate Change (IPCC), which considered only a likely range (66% probability).
Current estimations for sea-level rise are based on various techniques that consider different climate processes. Some methods account for well-known factors like melting glaciers, while others include more unpredictable events such as sudden collapses of ice shelves.
This leads to diverse projections, creating challenges in reliably predicting severe sea-level rises. The inconsistencies in projections from various methods have prevented the IPCC from providing very likely estimates for sea-level rises, which are crucial for risk management.
To tackle this issue and clarify uncertainties in current sea-level rise predictions, NTU researchers devised a novel projection methodology known as the “fusion” approach. This method merges the strengths of current models with expert insights, resulting in a clearer and more dependable forecast for future sea-level rise.
According to the study’s lead author, Dr. Benjamin Grandey, a Senior Research Fellow at NTU’s School of Physical and Mathematical Sciences (SPMS), “Our innovative approach addresses a significant challenge in sea-level science, where different forecasting methods yield vastly different outcomes. By merging these methods into a unified fusion projection, we can better estimate the uncertainties associated with future sea-level rise and clearly define the very likely range of expected increases.”
The research team believes this new method fills an important void in providing reliable data, serving as a complement to the IPCC’s recent findings.
The fusion approach: Merging the strengths of existing models
The multidisciplinary NTU team comprising physicists and climate specialists developed the fusion model by combining statistical techniques with expert opinions. They utilized data from established models showcased in the IPCC’s Sixth Assessment Report, which outlines various potential future scenarios based on differing emissions paths.
The researchers integrated various categories of projections from the IPCC report, using both ‘medium confidence’ and ‘low confidence’ estimates while incorporating expert views to cover less understood extreme phenomena, like sudden changes in ice sheet dynamics. A weighting system was applied, favoring more reliable medium-confidence data, while still including lower-confidence projections to address the uncertainties involved.
Forecasts derived from this fusion method indicate that under a low-emissions scenario, global mean sea levels are very likely to rise between 0.3 and 1.0 meters by 2100, while the IPCC’s likely range suggests a 0.3 to 0.6-meter rise.
In a high-emissions scenario, the NTU fusion model suggests global mean sea levels could very likely climb between 0.5 and 1.9 meters by 2100, compared to the IPCC’s likely estimate of 0.6 to 1.0 meters.
The broader estimates presented by the NTU model imply that prior predictions may have underestimated the risks of extreme outcomes, with potential rises reaching up to 90 cm beyond the upper limit of the IPCC’s likely estimates under high emissions.
Current emission patterns indicate that the world is currently between the low-emission and high-emission projections.
“Our very likely projections underscore the substantial uncertainties related to sea-level rise,” Dr. Grandey noted. “The top estimate of 1.9 meters highlights the necessity for planners to prepare critical infrastructure accordingly. More importantly, these findings stress the urgent need for climate mitigation by lowering greenhouse gas emissions.”
Co-author Professor Benjamin Horton, Director of the Earth Observatory of Singapore at NTU, stated, “This NTU research marks a major advancement in the field of sea-level science. By evaluating the probability of the most extreme scenarios, it illustrates the profound implications of sea-level rise on coastal communities, infrastructure, and ecosystems, underscoring the urgent need for action on the climate crisis.”
The significance of the new projection method
Providing accurate projections of sea-level rise is crucial for preparing against climate change. The NTU team firmly believes their method presents valuable, actionable insights for urban planners and governments, enabling them to devise protective strategies for at-risk communities, especially in extreme scenarios of sea-level rise.
Co-author Professor Chew Lock Yue from NTU’s SPMS emphasized, “By effectively combining the best available sea-level data across different confidence levels into a unified distribution, we have crafted a new way to illustrate the full range of uncertainty regarding future sea-level rise.”
Co-author Associate Professor Justin Dauwels at TU Delft added, “Our novel approach to projecting future sea-level rise’s uncertainty range could also be utilized for other climate projections and related assessments, such as evaluating coastal flood risks, analyzing the vulnerability of infrastructure, and forecasting economic impacts.”
This study highlights NTU’s dedication to advancing climate science research and contributing to global sustainability efforts, supported by the National Research Foundation of Singapore and the National Environment Agency under the National Sea Level Programme Funding Initiative (Award No. USS-IF-2020-3).
[1] This projection is derived from the Intergovernmental Panel on Climate Change’s (IPCC) Sixth Assessment Report. The IPCC is a UN body responsible for providing authoritative scientific assessments regarding climate change. Visit https://www.ipcc.ch/report/ar6/wg1/chapter/chapter-9/ for more information.
