Sea levels are rising and are projected to continue increasing, with notable regional differences. Regional mean sea-level projections can be produced by assuming that all contributing processes combine linearly. While IPCC-style, process-based projections offer valuable insights at large spatial scales (>100 km), mostly derived from global climate models, they fall short in resolving finer-scale regional and local processes (5–10 km). However, end-users urgently require more detailed sea-level projections for effective adaptation planning, and recent progress in regional projections has begun to address this need.

High-resolution coupled global climate model simulations have been attempted recently, but only for limited scenarios due to high computational costs. Despite these limitations, they provide valuable insights into the differences and similarities in sea-level distribution between coarse- and high-resolution simulations. Additionally, dynamical downscaling using high-resolution regional ocean models is rapidly advancing, offering a practical method for obtaining finer-scale sea-level information. With significantly lower computational demands, this approach allows for the downscaling of an ensemble of climate models across various future scenarios, with uncertainties properly quantified.

The melting of the Antarctic Ice Sheet remains the largest uncertainty in global sea-level projections over the coming centuries, primarily due to limited observations and an incomplete understanding of ice sheet dynamics. Recent advancements include the production of high-resolution sea-level fingerprints that resolve the fine structures of both melting sources and coastal impacts at kilometer-scale resolution, driven by the latest ice sheet simulations from the Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6).

Vertical land motion (VLM) is another critical factor affecting relative sea-level changes, contributing on a comparable scale to other sea-level processes. However, VLM observations are limited—either directly through GNSS/InSAR satellite measurements or indirectly through differences between satellite altimetry and tide gauge data—resulting in significant discrepancies across different products and observations. How to robustly represent VLM in future sea-level projections remains an open question.

While most current projections focus on mean sea levels, the need for projections of extreme sea levels is becoming more pressing. The impacts of mean sea-level rise will often manifest through an increased frequency of extreme sea-level events. Pioneering regional studies are beginning to explore the interactions among multiple factors, such as mean sea-level rise, high-frequency atmospheric forcing, tides, and waves, providing valuable insights into future extremes.
 

sea-level rise