The multi-millennial Antarctic commitment to future sea-level rise

Despite computational and methodological uncertainties, and a wide range of potential greenhouse gas emissions, here millennial-scale simulations of the Antarctic Ice Sheet in a warming climate show that most of Antarctica’s fringing ice shelves will collapse, leading to a rise in sea level of up to 3 metres by 2300. Future contributions of the Antarctic ice sheet to sea-level rise are potentially enormous, but remain highly uncertain, in part due to computational restrictions. Nicholas Golledge and colleagues now provide millennial-scale simulations of the Antarctic ice sheet in a warming climate, and show that with about 0.5°C of ocean warming and 2.0°C of atmospheric warming, most of Antarctica's fringing ice shelves are likely to collapse, leading to accelerated movement of the ice sheet to the ocean. Major methodological uncertainties remain, but in these simulations, sea-level rise from Antarctic ice loss ranges from about 0.1 to 3 metres by the year 2300 and from 0.4 to 9 metres by 5000. The huge range in estimated sea level reflects the both methodological uncertainty and a wide span of potential emissions of greenhouse gases. Atmospheric warming is projected to increase global mean surface temperatures by 0.3 to 4.8 degrees Celsius above pre-industrial values by the end of this century1. If anthropogenic emissions continue unchecked, the warming increase may reach 8–10 degrees Celsius by 2300 (ref. 2). The contribution that large ice sheets will make to sea-level rise under such warming scenarios is difficult to quantify because the equilibrium-response timescale of ice sheets is longer than those of the atmosphere or ocean. Here we use a coupled ice-sheet/ice-shelf model to show that if atmospheric warming exceeds 1.5 to 2 degrees Celsius above present, collapse of the major Antarctic ice shelves triggers a centennial- to millennial-scale response of the Antarctic ice sheet in which enhanced viscous flow produces a long-term commitment (an unstoppable contribution) to sea-level rise. Our simulations represent the response of the present-day Antarctic ice-sheet system to the oceanic and climatic changes of four representative concentration pathways (RCPs) from the Fifth Assessment Report of the Intergovernmental Panel on Climate Change3. We find that substantial Antarctic ice loss can be prevented only by limiting greenhouse gas emissions to RCP 2.6 levels. Higher-emissions scenarios lead to ice loss from Antarctic that will raise sea level by 0.6–3 metres by the year 2300. Our results imply that greenhouse gas emissions in the next few decades will strongly influence the long-term contribution of the Antarctic ice sheet to global sea level.