We write as a group that include authors, chapter scientists, and review editors of the Intergovernmental Panel on Climate Change (IPCC)'s most recent assessments of sealevel and ice-sheet changes, as well as scholars of the IPCC process and developers of tools to communicate IPCC sea-level projections.The IPCC is a United Nations (UN) body established to assess the science of climate change. By providing governments with a common, rigorously reviewed, scientific fact base for policy discussions, rather than leaving scientific disagreements to play out in more politicized, policy-making venues, it plays a critical role in global climate governance.Unfortunately, a recent UN secretariat technical brief on sea-level rise attempts to update the IPCC Sixth Assessment Report (AR6)’s assessment without the benefits of the IPCC’s established assessment processes. In concluding that “since the publication of the IPCC AR6 [report] in 2021, a growing number of scientific studies on ice-sheet loss are raising alarm among scientists that future [sea-level rise] could indeed be much larger and occur sooner” than AR6 assessed, it misunderstands the IPCC AR6 presentation of future sea- level rise and presents an unbalanced perspective on literature published since AR6.

Projections of future sea-level change are characterized by both quantifiable uncertainty and by ambiguity. Both types of uncertainty are relevant to users of sea-level projections, particularly those making long-term investment and planning decisions with multigenerational consequences. Communicating information about both types is thus a central challenge faced by scientists who generate sea-level projections to support decision-making. Diverse approaches to communicating uncertainty in future sea-level projections have been taken over the last several decades, but the literature evaluating these approaches is limited and not systematic. Here, we review how the Intergovernmental Panel on Climate Change (IPCC) has approached uncertainty in sealevel projections in past assessment cycles and how this information has been interpreted by national and subnational assessments, as well as alternative approaches used by recent US subnational assessments. The evidence reviewed here generally supports the explicit approach to communicating both types of uncertainty adopted by the IPCC Sixth Assessment Report (AR6).