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.
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Regional sea-level highstand triggered Holocene ice sheet thinning across coastal Dronning Maud Land, East Antarctica
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We thank the CMIP community for making their data openly available, and J. Lenaerts for providing present-day surface mass balance data. We are also grateful to K. Buckley (Victoria University high-performance computing cluster), C. Khroulev, T. Albrecht and the Parallel Ice Sheet Model groups at the University of Alaska, Fairbanks, and the Potsdam Institute for Climate Impact Research. This work was funded by contract VUW1203 of the Royal Society of New Zealand’s Marsden Fund, with support from the Antarctic Research Centre, Victoria University of Wellington, ANDRILL, GNS Science (NZ Ministry of Business Innovation and Employment contract C05X1001), National Science Foundation grant ANT-1043712, and the Australian Research Council (ARC). J. Renwick and D. Zwartz provided comments that improved the manuscript.
The authors declare no competing financial interests.
Extended data figures and tables
Air temperature (a–d), precipitation (e–h) and ocean temperature (i–l) changes for four RCP scenarios expressed as perturbations from present, both for hemispheric sectors and for the global mean.
Antarctic-specific (60°–90° S) projected temperature trends to 2300 ce based on CMIP5 values at 2100 ce and extended to 2300 ce following trajectories of global means from intermediate-complexity Earth system models3,47. Precipitation and ocean temperature trends are calculated to follow those of atmospheric temperatures, with magnitudes based on analysis of the CMIP5 data set indicating a 5.3% increase in precipitation per degree air temperature increase and a ratio of 0.25 for converting atmospheric to oceanic temperature changes. dT, change in air temperature.
Ice-sheet geometry and surface velocities (ma-1, metres per year) at the end of a 25,000-year evolutionary simulation. a and b, Observation-based52 (a) and modelled (b) ice-sheet extent and surface elevations. c, Comparison of ice thicknesses shown in a and b. d and e, Measured59 (d) and modelled (e) surface ice velocities. f, Comparison of the ice velocities shown in d and e. ‘MeASURES’ is the name of the published ice velocity dataset of ref. 59.
Simulated changes in ice-sheet volume (a) and ice-sheet area (b) under single-parameter and combined forcings (ΔTair, ΔPeff and ΔSST), based on simplified RCP scenarios for 100-year and 300-year forcing periods. Also shown in both panels is the control experiment (thick blue lines), illustrating little to no drift during the period of interest to 5000 ce.
Extended Data Figure 5 Multi-millennial changes in ice-sheet response to single-parameter environmental forcings.
Bias-corrected rates of sea-level-equivalent ice-mass change (s.l.e. mm a-1, millimetres of sea level equivalent per year) for each of the single-parameter simplified RCP forcing experiments. a, Rates of change under applied air temperature forcings peak at around 2240–2330 ce for both the 100-year and 300-year forcing experiments and decline thereafter, but both the 100-year and 300-year experiments exhibit rates that are still much larger than initial values by 5000 ce. b, Ice-mass rates of change as in a but forced only with precipitation changes. Maxima for the 100-year and 300-year forcing experiments occur close to the end of the forcing period, reflecting little inherent lag. c, Rates of change in response to ocean forcing show much more elevated initial peaks compared to mass-loss rates in subsequent millennia. By the end of the run, rates of mass loss for both the 100-year and 300-year forcing experiments are still higher than at the beginning of the run. Data are shown relative to zero at 2000 ce.
a, Modelled ice volume changes relative to the control run (in sea-level equivalent) for simulations in which only the grounding-line parameterization is altered. ‘SG’ and ‘Slip’ denote respectively the sub-grid and reduced traction grounding-line schemes employed in our simulations; ‘no SGmelt’ indicates an experiment in which only the sub-grid basal melt interpolation scheme is turned off (see Methods for details). Grey shading denotes period of applied forcing. b and c, Domain-integrated grounded (gr.) ice area (b) and sea-level-equivalent ice volume (c) trajectories under RCP 8.5 conditions for simulations in which the full sub-grid scheme is used and only the model resolution is changed. The 5-km simulation was not run beyond 3100 ce owing to the large computational overhead. d, Grounding-line positions at 2500 ce for the experiments shown in b and c. The greatest differences occur in the Siple Coast area (SC). Note the very close agreement between the 10-km and 5-km simulations. e–g, Grounding-line locations under RCP 8.5 conditions at 2100 ce (e), 2300 ce (f) and 5000 ce (g) for experiments using the full grounding-line parameterization (‘SG+Slip’) compared to those in which the sub-grid basal melt interpolation is turned off (‘no SGmelt’). h–j, Grounding-line locations under RCP 8.5 conditions at 2100 ce (j), 2300 ce (i) and 5000 ce (j) for 10-km and 20-km simulations that use the full grounding-line parameterization and resolution-specific stress balance tunings.
a, Geometry of the modelled Antarctic ice sheets under RCP 8.5 at 5000 ce, using both variants of the grounding-line scheme. Bold values and those in italics denote magnitudes and rates of sea-level contributions respectively. Leading values and those in parentheses relate to ‘low’ and ‘high’ scenarios respectively. Panels show ice extent for ‘low’ simulations; blue lines show grounding-line locations for ‘high’ simulations. Pale blue shading shows grounded ice lost in ‘high’ simulations but present in the ‘low’ scenario. b, Duplicate simulation to a but using a 2 × amplification of Antarctic temperatures beyond 2300 ce. Note the greater sea-level contribution compared to a. c, The full equilibrium response of the polar amplification scenario shown in b. Note the greater loss of ice from the Wilkes Basin (WB) and eastern Weddell Sea (WS), resulting in a higher total sea-level contribution. Black areas denote ice-free land. d, Rate of ice loss for the 2 × amplification scenario for ‘low’ (black) and ‘high’ (blue) scenarios, illustrating that although the fastest contribution to sea level (2–4 m per century) occurs during the first millennium, slower mass loss continues for many millennia thereafter.
a, Predicted sea-level contribution from the AIS for ‘high’ and ‘low’ simulations (coloured lines) under each of the four RCP scenarios as well as one that includes 2 × amplification of Antarctic temperatures by 2300 ce (darker shading), based on coeval climatic and oceanic perturbations. The forced response (grey shading) represents 20% to 42% of the committed response by 5000 ce. Lighter shading between coloured lines shows rates of sea-level-equivalent ice loss for each scenario. b, Long-term sea-level commitment as a function of atmospheric warming (blue shading with squares). Intermediate response curves for the ‘low’ simulations are shown in dotted lines. Red shading with triangles shows relationship between ice-shelf area and atmospheric warming for the near-equilibrium response and for intermediate stages (dotted lines). All curves in b are based on data from the four RCP scenario simulations, as well as one that includes 2 × amplification of Antarctic temperatures by 2300 ce, and two additional experiments whose maximum air temperature forcings are 1.5 °C and 3.35 °C. Pink shading defines the temperature range within which an ice-shelf extent less than 50% of present is simulated.
Main graphic shows ice extent for 'low' simulations; blue lines show grounding-line locations for 'high' simulations. Pale blue shading shows grounded ice lost in 'high' simulations but present in the 'low' scenario. Grey shading denotes ice shelves. Note the increasing divergence between 'high' and 'low' beyond 2300 CE. Bold values and those in italics denote magnitudes and rates of sea-level contributions respectively. Leading values and those in parentheses relate to 'low' and 'high' scenarios respectively. WAIS: West Antarctic Ice Sheet; EAIS: East Antarctic Ice Sheet. (MP4 6204 kb)
Main graphic shows ice extent for 'high' simulations. Warmer colours indicate areas of relatively faster-flowing ice. WAIS: West Antarctic Ice Sheet; EAIS: East Antarctic Ice Sheet. Graph shows the Antarctic contribution to global sea-level. (MP4 5638 kb)
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Golledge, N., Kowalewski, D., Naish, T. et al. The multi-millennial Antarctic commitment to future sea-level rise. Nature 526, 421–425 (2015). https://doi.org/10.1038/nature15706
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