The Xiamen Symposium on Marine Environmental Sciences (XMAS 2025)

Today, we live in a largely coastal society with growing coastal population densities already more than twice the global average. As well as large coastal megacities, shipping and related transport activities, agriculture on rich coastal and deltaic soils, fishing, and recreation activities all have a major focus on the coastal zone. At the same time that this coastal development is continuing, sea-level rise is accelerating along most of the world’s coastline, resulting in growing impacts on our coastal society. Our knowledge and understanding of sea-level change has improved significantly over recent decades but there remain many uncertainties about how sea levels will evolve through the 21^st century and beyond. Understanding paleo and historical sea-level change is a prerequisite for building confidence in useful and accurate projections of future changes. For many decades, our limited knowledge of the contributions to sea-level change could not adequately explain the rise measured by coastal tide gauges – the sea level enigma. New and improved in situ and satellite observations of the ocean, improved understanding of the “solid Earth”, and better understanding and improved modelling of the climate system have helped resolve this enigma. The major contributions to 20^th century sea level change come from ocean thermal expansion and loss of mass from glaciers, with accelerating ice-sheet contributions over recent decades and contributions from changes in land-water storage. However, some discrepancies remain with the sum of contributions prior to 1940 larger than observations and slightly smaller after 1970. There are significant uncertainties surrounding projected sea-level rise through the 21^st century and beyond, particularly from the ice sheet contributions. Of critical interest to society in the upper end of the projection range. Resolving these uncertainties will rely on improved estimates and understanding of paleo and historical sea-level changes, and the contributions to these changes. I will discuss these issues and give some personal views about future sea level, for the 21^st century and beyond. What is clear though is that we need to urgently mitigate our emissions to avoid the worst case scenarios of several metres over coming centuries, and that we will need to adapt to long-term sea-level rise that we can no longer prevent.

sea level rise, sea level projection