Upper bounds on twenty-first-century Antarctic ice loss assessed using a probabilistic framework

• Published in: Nature climate change Vol. 3; no. 7; pp. 654 - 659
• Main Authors: Little, Christopher M., Oppenheimer, Michael, Urban, Nathan M.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.07.2013; Nature Publishing Group
• Subjects: 639/705/531; 704/106/125; Climate adaptation; Climate Change; Climate Change/Climate Change Impacts; Climatology. Bioclimatology. Climate change; Earth, ocean, space; Environment; Environmental Law/Policy/Ecojustice; Environmental risk; Exact sciences and technology; External geophysics; Ice; Intergovernmental Panel on Climate Change; letter; Marine; Mathematical models; Meteorology; Physics of the oceans; Risk assessment; Snow. Ice. Glaciers; Surface waves, tides and sea level. Seiches; polar regions; Antarctica; Century 21st; mass balance; climate warming; Glacier variation; Atmosphere cryosphere interaction; Sea level rise; Climate prediction; ice sheets; global change; Ice shelf; Polar region; collapse; sea level; climate change
• ISSN: 1758-678X; 1758-6798
• DOI: 10.1038/nclimate1845

Estimating the probable magnitude of future sea-level rise under global warming is complicated by a limited understanding of long-term ice-sheet dynamics. This study presents a probabilistic approach for assessing upper bounds on twenty-first-century Antarctic ice-sheet loss, and its effect on sea level. Climate adaptation and flood risk assessments 1 , 2 have incorporated sea-level rise (SLR) projections developed using semi-empirical methods 3 , 4 , 5 (SEMs) and expert-informed mass-balance scenarios 2 , 6 . These techniques, which do not explicitly model ice dynamics, generate upper bounds on twenty-first century SLR that are up to three times higher than Intergovernmental Panel on Climate Change estimates 7 . However, the physical basis underlying these projections, and their likelihood of occurrence, remain unclear 8 , 9 , 10 . Here, we develop mass-balance projections for the Antarctic ice sheet within a Bayesian probabilistic framework 10 , integrating numerical model output 11 and updating projections with an observational synthesis 12 . Without abrupt, sustained, changes in ice discharge (collapse), we project a 95th percentile mass loss equivalent to ∼13 cm SLR by 2100, lower than previous upper-bound projections. Substantially higher mass loss requires regional collapse, invoking dynamics that are likely to be inconsistent with the underlying assumptions of SEMs. In this probabilistic framework, the pronounced sensitivity of upper-bound SLR projections to the poorly known likelihood of collapse is lessened with constraints on the persistence and magnitude of subsequent discharge. More realistic, fully probabilistic, estimates of the ice-sheet contribution to SLR may thus be obtained by assimilating additional observations and numerical models 11 , 13 .