Ice sheet contributions to future sea-level rise from structured expert judgment

• Published in: Proceedings of the National Academy of Sciences
• Main Authors: Bamber, Jonathan L., Oppenheimer, Michael, Kopp, Robert E., Aspinall, Willy P., Cooke, Roger M.
• Format: Text
• Language: English
• Published: National Academy of Sciences 2019
• Subjects: Physical Sciences; East Antarctica; Antarc*; Antarctica; Ice Sheet
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6561295/; http://www.ncbi.nlm.nih.gov/pubmed/31110015; https://doi.org/10.1073/pnas.1817205116

Despite considerable advances in process understanding, numerical modeling, and the observational record of ice sheet contributions to global mean sea-level rise (SLR) since the Fifth Assessment Report (AR5) of the Intergovernmental Panel on Climate Change, severe limitations remain in the predictive capability of ice sheet models. As a consequence, the potential contributions of ice sheets remain the largest source of uncertainty in projecting future SLR. Here, we report the findings of a structured expert judgement study, using unique techniques for modeling correlations between inter- and intra-ice sheet processes and their tail dependences. We find that since the AR5, expert uncertainty has grown, in particular because of uncertain ice dynamic effects. For a +2 °C temperature scenario consistent with the Paris Agreement, we obtain a median estimate of a 26 cm SLR contribution by 2100, with a 95th percentile value of 81 cm. For a +5 °C temperature scenario more consistent with unchecked emissions growth, the corresponding values are 51 and 178 cm, respectively. Inclusion of thermal expansion and glacier contributions results in a global total SLR estimate that exceeds 2 m at the 95th percentile. Our findings support the use of scenarios of 21st century global total SLR exceeding 2 m for planning purposes. Beyond 2100, uncertainty and projected SLR increase rapidly. The 95th percentile ice sheet contribution by 2200, for the +5 °C scenario, is 7.5 m as a result of instabilities coming into play in both West and East Antarctica. Introducing process correlations and tail dependences increases estimates by roughly 15%.