THE NEW “FUSION” APPROACH
To address the uncertainties in current sea level rise projections, NTU researchers developed a new, improved method which combines the advantages of existing models with expert opinions, the release stated.
“Current climate models and ice sheet models are very good at simulating well-understood processes. However, the models often neglect poorly-understood processes that could cause the ice sheets to melt much faster than we expect,” said the NTU study’s lead author, senior research fellow Benjamin Grandey.
“In contrast, experts can estimate the likelihood of these unlikely possibilities. Therefore, the models and experts offer complementary information.”
Current sea level projections had relied on a range of methods to model climate processes, with some incorporating known factors such as melting glaciers and others, more uncertain events such as abrupt ice shelf collapse.
As a result, the models produce varying projections, making it difficult to estimate reliable extreme sea level rise, the release said.
The ambiguity in projections has prevented the IPCC from providing forecasts of a higher probability, termed the “very likely” ranges for sea level projections.
Scientists from the new study used data from established projections in the IPCC’s sixth assessment report, which simulate potential future scenarios under different emissions pathways to varying degrees of confidence.
The team combined different classes of projections from the IPCC report, incorporating both “medium confidence” and “low confidence” projections, supplemented by expert assessments, to account for the poorly-understood extreme processes, such as sudden shifts in ice sheet behaviour.
The team then applied a weighting system, prioritising more reliable medium-confidence data while still including lower-confidence projections to address uncertainties.
With the approach, researchers found that under a low emissions scenario, global mean sea levels are very likely to rise between 0.3m and 1m by 2100.
The IPCC’s “likely range” had projected global mean sea level to rise by 0.32m to 0.62m.
The broader ranges indicated by the NTU model suggest that previous estimates may have understated the potential for extreme outcomes, the release said.
Dr Grandey, who is from NTU’s School of Physical and Mathematical Sciences, said the new approach addresses the uncertainty in sea level science.
“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 of sea level rise,” he said.
He added that the high-end projection of 1.9m underlined the need for critical infrastructure to be planned accordingly, and the importance of climate mitigation measures to reduce greenhouse gas emissions.
The study’s co-author, Professor Benjamin Horton, the director of the Earth Observatory of Singapore at NTU, said: “This NTU 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, emphasising the urgent need to address the climate crisis.”
