Illustrative Multi-Centennial Projections of Global Mean Sea-Level Rise and Their Application

We produce projections of global mean sea-level rise to 2500 for low and medium emissions scenarios (Shared Socioeconomic Pathways SSP1-2.6 and SSP2-4.5) relative to 2020, based on extending and combining model ensemble data from current literature. We find that emissions have a large effect on sea-level rise on these long timescales, with [5, 95]% intervals of [0.3, 4.3]m and [1.0, 7.6]m under SSP1-2.6 and SSP2-4.5 respectively, and a difference in the 95% quantile of 1.6 m at 2300 and 3.3 m at 2500 for the two scenarios. The largest and most uncertain component is the Antarctic ice sheet, projected to contribute 5%-95% intervals of [-0.1, 2.3]m by 2500 under SSP1-2.6 and [0.0, 3.8]m under SSP2-4.5. We discuss how the simple statistical extensions used here could be replaced with more physically based methods for more robust predictions. We show that, despite their uncertainties, current multi-centennial projections combined into multi-study projections as presented here can be used to avoid future lock-ins in terms of risk and adaptation needs to sea-level rise. Sea levels are predicted to rise for hundreds to thousands of years, even if emissions are reduced. Decisions about how to adapt to more frequent and severe coastal flooding need predictions showing a range of possible futures. However, few computer modeling studies of the contributing factors to sea level rise extend as far as the year 2300, and few to 2500. We present illustrative predictions of global mean sea level rise for low and medium emissions scenarios to 2500 by combining previous modeling studies and extending them where necessary. We take the widest possible range when combining studies, to show many possible futures. Predictions for global average sea level rise are 0.3-4.3 m at 2500 for the low emissions scenario, where global warming stays below around 2 degrees C. Under medium emissions, where long-term warming is predicted to be around 2-5 degrees C, the predictions are around double this: from 1.0 to 7.6 m. Our aim is to outline possible long-term futures based on physical understanding, so decision-makers can analyze potential implications for society and avoid making decisions that are difficult to change later. We describe some potential applications of our projections, as well as key knowledge gaps and future research directions. Projections of global mean sea-level rise to 2500 have [5, 95]% intervals of [0.3, 4.3]m under SSP1-2.6 and [1.0, 7.6]m under SSP2-4.5The most uncertain sea-level contributor continues to be the Antarctic ice sheet, with multiple studies considered to build a projectionDespite the uncertainties, our projections can be used to analyze their societal implications and recognize and potentially avoid lock-ins

Automated summary

We produced projections of global mean sea-level rise to 2500 for low and medium emissions scenarios. Emissions have a large effect on sea-level rise on long timescales, with the Antarctic ice sheet being the most uncertain contributor. Despite the uncertainties, these projections can be used to analyze their societal implications and potentially avoid irreversible situations.