An international group of 28 sea-level scientists and practitioners of the World Climate Research Programme’s Grand Challenge on Regional Sea Level Change and Coastal Impacts has released a new estimate for high-end sea-level rise. High-end sea-level rise projections represent what might happen rather than representing the most likely outcome. They are of particular interest for stakeholders engaged in long-term adaption planning where such uncertainties are important, such as long-life infrastructural projects or coastal land use. The findings were published in Earth Future on Saturday, 22 October. 
30 cm lower
The new estimates are based on multiple lines of evidence and physical plausibility for each sea-level component, including the critical Antarctic ice sheet contribution. This approach leads to substantially lower numbers than the structured expert judgement used in the latest IPPC-AR6 report for strong warming scenarios at the end of the century: a difference of around 30 cm lower compared to the high impact low likelihood scenarios of IPCC-AR6. The high-end global mean sea-level rise is now projected to be up to 1.3-1.6 meter for strong warming in 2100.
Fulfillment Paris Agreement
The collapse of major Antarctic ice shelves at the end of this century followed by increased discharge of ice may lead to a 9-10 meter catastrophic sea-level rise by 2300, under the same strong warming scenario. Fulfilling the Paris Agreement will greatly reduce the potential of high-end sea-level rise to 2.2-2.5 m. However, it will not stop sea-level rise until 2300. Hence, we need to be prepared to both mitigate climate change, and adapt in coastal areas. Luckily, such adaptations are feasible for this magnitude of change over multiple centuries in many places.
Application of the results
Prof. Robert Nicholls from University of East Anglia, who was one of the leaders of the exercise, says: “I think we have found a robust rationale for developing transparent high-end estimates of sea-level rise”. He adds: “This type of information is critical for planning future coastal flood management in our coastal areas, especially cities and urban areas. They show that there is a major challenge in the future even with climate mitigation, and adaptation plans need to be ready for this. In London this is the case, but most coastal cities are not prepared. This assessment process could and should be repeated periodically as the science improves”.
A high-end estimate of sea-level rise for practitioners: R. S. W. van de Wal, R. J. Nicholls, D. Behar, K. McInnes, D. Stammer, J. A. Lowe, J. A. Church, R. DeConto, X. Fettweis, H. Goelzer, M. Haasnoot, I. D. Haigh, J. Hinkel, B. P. Horton, T. S. James, A. Jenkins, G. LeCozannet, A. Levermann, W. H. Lipscomb, B. Marzeion, F. Pattyn, T. Payne, T. Pfeffer, S. F. Price, H. Seroussi, S. Sun, W. Veatch, K. White, Earth Future.