Projections of 21st century sea level rise for the coast of South Africa

Abstract

As a result of planetary heating, global mean sea level has increased since the end of the 19th century. Sea level rise is accelerating and will continue to rise over the 21st century and beyond. On top of the global mean signal there are large regional variations in the magnitude of sea level rise. At a local level, reliable projections of probable and possible future sea level change are vital for coastal management planning. In this work we present an observational analysis of recent sea level variations at locations around the coast of South Africa using tide gauge records and satellite altimetry data. In recent decades, sea level around South Africa has increased at a rate of around 3 mm year−1, consistent with estimates of global mean sea level rise over that time. We apply existing methods (that are rooted in the methods of the 5th Assessment Report of the Intergovernmental Panel on Climate Change, but with a number of methodological innovations) to produce sea level projections for eight locations around the coast of South Africa under low (RCP2.6) and high (RCP8.5) emissions scenarios. In the year 2100 locations around South Africa are projected to experience sea level rise (relative to 1986–2005) of approximately 0.5 m (0.25–0.8 m) following RCP2.6, or around 0.85 m (0.5–1.4 m) following RCP8.5. These increases are around 7%–14% larger than projections of global mean sea level, due to the local amplification of increases in several components of the sea level budget. The results from this work suggest that successful mitigation efforts to reduce greenhouse gas emissions would have a clear benefit in limiting 21st century sea level rise for South Africa.