Contribution of Antarctica to past and future sea-level rise

Journal name:
Nature
Volume:
531,
Pages:
591–597
Date published:
DOI:
doi:10.1038/nature17145
Received
Accepted
Published online
Corrected online

Abstract

Polar temperatures over the last several million years have, at times, been slightly warmer than today, yet global mean sea level has been 6–9 metres higher as recently as the Last Interglacial (130,000 to 115,000 years ago) and possibly higher during the Pliocene epoch (about three million years ago). In both cases the Antarctic ice sheet has been implicated as the primary contributor, hinting at its future vulnerability. Here we use a model coupling ice sheet and climate dynamics—including previously underappreciated processes linking atmospheric warming with hydrofracturing of buttressing ice shelves and structural collapse of marine-terminating ice cliffs—that is calibrated against Pliocene and Last Interglacial sea-level estimates and applied to future greenhouse gas emission scenarios. Antarctica has the potential to contribute more than a metre of sea-level rise by 2100 and more than 15 metres by 2500, if emissions continue unabated. In this case atmospheric warming will soon become the dominant driver of ice loss, but prolonged ocean warming will delay its recovery for thousands of years.

At a glance

Figures

  1. Antarctic sub-glacial topography and ice sheet features.
    Figure 1: Antarctic sub-glacial topography and ice sheet features.

    a, Bedrock elevations13 interpolated onto the 10-km polar stereographic ice-sheet model grid and used in Pliocene, LIG, and future ice-sheet simulations. b, Model surface ice speeds and grounding lines (black lines) show the location of major ice streams, outlet glaciers, and buttressing ice shelves (seaward of grounding lines) relative to the underlying topography in a. Features and place names mentioned in the text are also shown. AS, Amundsen Sea; BS, Bellingshausen Sea; WDIC, WAIS Divide Ice Core. The locations of the Pine Island, Thwaites, Ninnis, Mertz, Totten, and Recovery glaciers are shown. Model ice speeds (b) are shown after equilibration with a modern atmospheric and ocean climatology (see Methods).

  2. Schematic representation of MISI and MICI and processes included in the ice model.
    Figure 2: Schematic representation of MISI and MICI and processes included in the ice model.

    Top-to-bottom sequences (ac and df) show progressive ice retreat into a subglacial basin, triggered by oceanic and atmospheric warming. The pink arrow represents the advection of warm circumpolar deep water (CDW) into the shelf cavity. a, Stable, marine-terminating ice-sheet margin, with a buttressing ice shelf. Seaward ice flux is strongly dependent on grounding-line thickness h. Sub-ice melt rates increase with open-ocean warming and warm-water incursions into the ice-shelf cavity. b, Thinning shelves and reduced buttressing increase seaward ice flux, backing the grounding line onto reverse-sloping bedrock. c, Increasing h with landward grounding-line retreat leads to an ongoing increase in ice flow across the grounding line in a positive runaway feedback until the bed slope changes. d, In addition to MISI (ac), the model physics used here account for surface-meltwater-enhanced calving via hydrofracturing of floating ice (e), providing an additional mechanism for ice-shelf loss and initial grounding-line retreat into deep basins. f, Where oceanic melt and enhanced calving eliminate shelves completely, subaerial cliff faces at the ice margin become structurally unstable where h exceeds 800 m, triggering rapid, unabated MICI retreat into deep basins.

  3. Ice-sheet simulations and Antarctic contributions to GMSL through the LIG driven by a time-evolving, proxy-based atmosphere–ocean climatology.
    Figure 3: Ice-sheet simulations and Antarctic contributions to GMSL through the LIG driven by a time-evolving, proxy-based atmosphere–ocean climatology.

    a, Change in GMSL in LIG simulations starting at 130 kyr ago and initialized with a modern ice sheet (blue) or a bigger LGM ice sheet representing glacial conditions at the onset of the LIG (red). A probabilistic reconstruction of Antarctica’s contribution to GMSL is shown in black3 with uncertainties (16th and 84th percentiles) as dashed lines. b, c, Ice-sheet thickness at the time of maximum retreat using modern initial conditions (b) and using glacial initial conditions (c). Ice-free land surfaces are brown. The bigger sea-level response when initialized with the ‘glacial’ ice sheet is caused by deeper bed elevations and the ~3,000-yr lagged bedrock response to ice retreat50, which enhances bathymetrically sensitive MISI dynamics. d, The same simulation as b without the new model physics accounting for meltwater-enhanced calving or ice-cliff failure27. GMSL contributions are shown at top left.

  4. Future ice-sheet simulations and Antarctic contributions to GMSL from 1950 to 2500 driven by a high-resolution atmospheric model and 1° NCAR CCSM4 ocean temperatures.
    Figure 4: Future ice-sheet simulations and Antarctic contributions to GMSL from 1950 to 2500 driven by a high-resolution atmospheric model and 1° NCAR CCSM4 ocean temperatures.

    a, Equivalent CO2 forcing applied to the simulations, following the RCP emission scenarios in ref. 36, except limited to 8 × PAL (preindustrial atmospheric level, where 1 PAL = 280 p.p.m.v.). b, Antarctic contribution to GMSL. c, Rate of sea-level rise and approximate timing of major retreat and thinning in the Antarctic Peninsula (AP), Amundsen Sea Embayment (ASE) outlet glaciers, AS–BS, Amundsen Sea–Bellingshausen Sea; the Totten (T), Siple Coast (SC) and Weddell Sea (WS) grounding zones, the deep Thwaites Glacier basin (TG), interior WAIS, the Recovery Glacier, and the deep EAIS basins (Wilkes and Aurora). d, Antarctic contribution to GMSL over the next 100 years for RCP8.5 with and without a +3 °C adjustment in ocean model temperatures in the Amundsen and Bellingshausen seas as shown in Extended Data Fig. 5d. e–g, Ice-sheet snapshots at 2500 in the RCP2.6 (e), RCP4.5 (f) and RCP8.5 (g) scenarios. Ice-free land surfaces are shown in brown. h, Close-ups of the Amundsen Sea sector of WAIS in RCP8.5 with bias-corrected ocean model temperatures.

  5. Large Ensemble model analyses of future Antarctic contributions to GMSL.
    Figure 5: Large Ensemble model analyses of future Antarctic contributions to GMSL.

    a, RCP ensembles to 2500. b, RCP ensembles to 2100. Changes in GMSL are shown relative to 2000, although the simulations begin in 1950. Ensemble members use combinations of model parameters (Methods) filtered according to their ability to satisfy two geologic criteria: a Pliocene target of 10–20 m GMSL and a LIG target of 3.6–7.4 m. c and d are the same as a and b, but use a lower Pliocene GMSL target of 5–15 m. Solid lines are ensemble means, and the shaded areas show the standard deviation (1σ) of the ensemble members. The 1σ ranges represent the model’s parametric uncertainty, while the alternate Pliocene targets (a and b versus c and d) illustrate the uncertainty related to poorly constrained Pliocene sea-level targets. Mean values and 1σ uncertainties at 2500 and 2100 are shown.

  6. Warm mid-Pliocene climate and ice-sheet simulation.
    Extended Data Fig. 1: Warm mid-Pliocene climate and ice-sheet simulation.

    a, January (warmest monthly mean) difference in 2-m (surface) air temperature simulated by the RCM relative to a preindustrial control simulation with 280 p.p.m.v. CO2 and present-day orbit. The temperature difference is lapse-rate-corrected to account for the change in ice-sheet geometry and surface elevations. The Pliocene simulation uses 400 p.p.m.v. CO2, a warm austral summer orbit, and assumes a retreated WAIS to represent maximum Pliocene warm conditions. b, The Pliocene ice-sheet is shown after 5,000 model years, driven by the RCM climate in a, and assuming 2 °C ocean warming relative to a modern ocean climatology32. In the model formulation used here, maximum Pliocene ice-sheet retreat with default model parameters is equivalent to 11.26 m GMSL, about 6 m less than in ref. 25.

  7. LIG greenhouse gases, orbital parameters, and RCM climates.
    Extended Data Fig. 2: LIG greenhouse gases, orbital parameters, and RCM climates.

    a, Greenhouse gas concentrations9, 72 converted to radiative forcing shows the LIG interval (light red bar) and the best opportunity for ice-sheet retreat. b, Summer insulation at 70° latitude in both hemispheres73 (red, south; blue, north) and summer duration at 70° S (black)79 shown over the last 150 kyr, and the two orbital time slices (vertical dashed black lines at 128 kyr ago and 116 kyr ago). c, Table showing the greenhouse gas atmospheric mixing ratios (CO2 in parts per million by volume; CH4 and N2O in parts per billion by volume) and orbital parameters (eccentricity, obliquity, precession) used in the GCM–RCM at the LIG time slices (dashed lines 1 and 2 in a and b), respectively. df, January (warmest monthly mean) differences in 2-m surface air temperature relative to a preindustrial control simulation at 128 kyr ago (d), 116 kyr ago (e), and the present-day (2015) (f). Simulated austral summer temperatures at 116 kyr ago (e) with relatively high-intensity summer insolation is warmer than the long-duration summer orbit at 128 kyr ago (d), but unlike the Pliocene (Extended Data Fig. 1a), neither LIG climatology is as warm as the present day, producing little to no rain or surface melt on ice-shelf surfaces.

  8. Effect of Southern Ocean warming on Antarctic surface air temperatures and the ice sheet at 128 kyr ago.
    Extended Data Fig. 3: Effect of Southern Ocean warming on Antarctic surface air temperatures and the ice sheet at 128 kyr ago.

    ac, January (warmest monthly mean) differences in 2-m surface air temperature at 128 kyr ago, relative to a preindustrial control simulation (top row). GHG, greenhouse gas; SST, sea surface temperature. d, e, Ice-sheet thickness (m) after 5,000 model years, driven by the corresponding climate in ac. a and d, Without climate–ice sheet coupling (present-day ice extent and surface ocean temperatures in the RCM), and prescribed 5 °C sub-surface ocean warming felt only by the ice sheet. b and e, With asynchronous coupling between the RCM atmosphere and ice sheet, and prescribed 5 °C sub-surface ocean warming felt only by the ice sheet. c and f, With asynchronous coupling between the RCM atmosphere and ice sheet, prescribed 3 °C sub-surface ocean warming felt by the ice sheet, and ~2 °C surface ocean warming felt by the RCM atmosphere. c shows the locations of East Antarctic ice cores (EDC, EPICA Dome C; V, Vostock; DF, Dome F; EDML, EPICA Dronning Maud Land) indicating warming early in the interglacial29 and previously attributed to WAIS retreat80; this warming is similar to that simulated in c from a combination of ice-sheet retreat and warmer Southern Ocean temperatures, supporting the notion that the timing of LIG retreat was largely driven by far-field ocean influences, rather than local astronomical forcing.

  9. RCM climates used in future, time-continuous RCP scenarios and evolving ice-surface melt rates linked to hydrofracturing model physics.
    Extended Data Fig. 4: RCM climates used in future, time-continuous RCP scenarios and evolving ice-surface melt rates linked to hydrofracturing model physics.

    ad, January surface (2-m) air temperatures simulated by the RCM at the present-day (2015) (a), twice the present level of carbon dioxide, 2 × CO2 (b), 4 × CO2 (c), and 8 × CO2 (d) with the retreating ice sheet. The colour scale is the same in all panels. Yellow to red colours indicate temperatures above freezing with the potential for summer rain, and surface meltwater production. eh, Evolving ice-surface meltwater production (in metres per year) in the time-evolving RCP8.5 ice-sheet simulations, driven by a time-continuous RCM climatology (Methods) following the RCP8.5 greenhouse gas time series (Fig. 4a). Black lines show the positions of grounding lines and ice-shelf calving fronts at discrete time intervals—e, 2050; f, 2100; g, 2150; and h, 2500—with superposed meltwater production rates.

  10. NCAR CCSM4 ocean temperatures and oceanic sub-ice-shelf melt rates.
    Extended Data Fig. 5: NCAR CCSM4 ocean temperatures and oceanic sub-ice-shelf melt rates.

    a, RCP2.6 ocean warming at 400-m depth, shown as the difference of decadal averages from 1950–1960 to 2290–2300. b, Same as a but for RCP4.5. c, Same as a but for RCP8.5. d, CCSM4 RCP8.5 ocean warming from 1950–1960 to 2010–2020 showing little to no warming in the Amundsen and Bellingshausen seas. The red line shows the area of imposed, additional ocean warming. e, f, Oceanic melt rates at 2015 calculated by the ice-sheet model from interpolated CCSM4 temperatures (e), and with +3 °C adjustment in the Amundsen and Bellingshausen seas (f), corresponding to the area within the red line in d.

  11. Effect of future ocean warming only.
    Extended Data Fig. 6: Effect of future ocean warming only.

    a, Antarctic contribution to future GMSL rise in long, 5,000-yr ice-sheet simulations driven by sub-surface ocean warming simulated by CCSM4, following RCP8.5 (black line), with a +3 °C adjustment in the Amundsen and Bellingshausen seas (blue line; see Extended Data Fig. 5) and a warmer +5 °C adjustment (red line). Atmospheric temperatures and precipitation are maintained at their present values. bd, Ice-sheet thickness at model-year 5,000, driven by sub-surface ocean forcing from CCSM4 (b) and from CCSM4 with a +3 °C (c) or +5 °C (d) adjustment in the Amundsen and Bellingshausen seas. Note the near-complete loss of ice shelves, but modest grounding-line retreat in b, the retreat of Pine Island Glacier in c, and the near-complete collapse of WAIS once a stability threshold in the Thwaites Glacier grounding line is reached in d.

  12. The long-term future of the ice sheet and GMSL over the next 5,000 years following RCP8.5 and RCP4.5.
    Extended Data Fig. 7: The long-term future of the ice sheet and GMSL over the next 5,000 years following RCP8.5 and RCP4.5.

    a, Equivalent CO2 forcing following RCP8.5 until the year 2500, and then assuming zero emissions after 2500 and allowing a natural relaxation of greenhouse gas levels (red) or assuming a fast, engineered drawdown (blue) with an e-folding timescale of 100 years. b. Antarctic contribution to GMSL over the next 5,000 years, following the greenhouse gas scenarios in a. c, The same as a, except showing long-term RCP4.5 greenhouse gas forcing. d, The same as b, except following the RCP4.5 scenarios in c. The insets in b and d show the ice sheet (and remaining sea-level rise) after 5,000 model years in RCP8.5 and RCP4.5, respectively, assuming fast CO2 drawdown (blue lines), highlighting the multi-millennial commitment to a loss of marine-based Antarctic ice, even in the moderate RCP4.5 scenario. Note the different y-axes in RCP8.5 versus RCP4.5.

  13. Freshwater input to the Southern Ocean.
    Extended Data Fig. 8: Freshwater input to the Southern Ocean.

    Total freshwater and iceberg flux from 1950 to 2500, following the future RCP scenarios shown in Fig. 4b. Freshwater input calculations include contributions from ice loss above and below sea level and exceed 1 Sv in RCP8.5.

Tables

  1. Summary of Antarctic contributions to GMSL during the Pliocene, LIG, future centuries, and future millennia
    Extended Data Table 1: Summary of Antarctic contributions to GMSL during the Pliocene, LIG, future centuries, and future millennia
  2. Ensemble simulations of Pliocene, LIG, and future Antarctic contributions to GMSL
    Extended Data Table 2: Ensemble simulations of Pliocene, LIG, and future Antarctic contributions to GMSL

Videos

  1. RCP2.6 ice-sheet thickness (m) from 1950 to 2500 CE
    Video 1: RCP2.6 ice-sheet thickness (m) from 1950 to 2500 CE
    This video shows various aspects of our ice-sheet simulations from 1950 to 2500 CE, following future greenhouse-gas emission scenarios: RCP2.6, RCP4.5, and RCP8.5. Animations show the time-evolution of ice sheet thickness (m), oceanic melt rates (m a-1) driven by NCAR CCSM4 ocean temperatures, and surface melt-water production (m a-1) driven by our atmospheric RCM. Surface ice speeds (m a-1) illustrate the evolution of ice streams during ice-sheet retreat in the RCP8.5 scenario. The simulations in the videos use default model parameters and correspond to the simulations shown in Figure 4.
  2. RCP4.5 ice-sheet thickness (m) from 1950 to 2500 CE
    Video 2: RCP4.5 ice-sheet thickness (m) from 1950 to 2500 CE
    This video shows various aspects of our ice-sheet simulations from 1950 to 2500 CE, following future greenhouse-gas emission scenarios: RCP2.6, RCP4.5, and RCP8.5. Animations show the time-evolution of ice sheet thickness (m), oceanic melt rates (m a-1) driven by NCAR CCSM4 ocean temperatures, and surface melt-water production (m a-1) driven by our atmospheric RCM. Surface ice speeds (m a-1) illustrate the evolution of ice streams during ice-sheet retreat in the RCP8.5 scenario. The simulations in the videos use default model parameters and correspond to the simulations shown in Figure 4.
  3. RCP8.5 ice-sheet thickness (m) from 1950 to 2500 CE
    Video 3: RCP8.5 ice-sheet thickness (m) from 1950 to 2500 CE
    This video shows various aspects of our ice-sheet simulations from 1950 to 2500 CE, following future greenhouse-gas emission scenarios: RCP2.6, RCP4.5, and RCP8.5. Animations show the time-evolution of ice sheet thickness (m), oceanic melt rates (m a-1) driven by NCAR CCSM4 ocean temperatures, and surface melt-water production (m a-1) driven by our atmospheric RCM. Surface ice speeds (m a-1) illustrate the evolution of ice streams during ice-sheet retreat in the RCP8.5 scenario. The simulations in the videos use default model parameters and correspond to the simulations shown in Figure 4.
  4. RCP2.6 oceanic melt rates (m a-1) from 1950 to 2500 CE
    Video 4: RCP2.6 oceanic melt rates (m a-1) from 1950 to 2500 CE
    This video shows various aspects of our ice-sheet simulations from 1950 to 2500 CE, following future greenhouse-gas emission scenarios: RCP2.6, RCP4.5, and RCP8.5. Animations show the time-evolution of ice sheet thickness (m), oceanic melt rates (m a-1) driven by NCAR CCSM4 ocean temperatures, and surface melt-water production (m a-1) driven by our atmospheric RCM. Surface ice speeds (m a-1) illustrate the evolution of ice streams during ice-sheet retreat in the RCP8.5 scenario. The simulations in the videos use default model parameters and correspond to the simulations shown in Figure 4.
  5. RCP4.5 oceanic melt rates (m a-1) from 1950 to 2500 CE
    Video 5: RCP4.5 oceanic melt rates (m a-1) from 1950 to 2500 CE
    This video shows various aspects of our ice-sheet simulations from 1950 to 2500 CE, following future greenhouse-gas emission scenarios: RCP2.6, RCP4.5, and RCP8.5. Animations show the time-evolution of ice sheet thickness (m), oceanic melt rates (m a-1) driven by NCAR CCSM4 ocean temperatures, and surface melt-water production (m a-1) driven by our atmospheric RCM. Surface ice speeds (m a-1) illustrate the evolution of ice streams during ice-sheet retreat in the RCP8.5 scenario. The simulations in the videos use default model parameters and correspond to the simulations shown in Figure 4.
  6. RCP8.5 oceanic melt rates (m a-1) from 1950 to 2500 CE
    Video 6: RCP8.5 oceanic melt rates (m a-1) from 1950 to 2500 CE
    This video shows various aspects of our ice-sheet simulations from 1950 to 2500 CE, following future greenhouse-gas emission scenarios: RCP2.6, RCP4.5, and RCP8.5. Animations show the time-evolution of ice sheet thickness (m), oceanic melt rates (m a-1) driven by NCAR CCSM4 ocean temperatures, and surface melt-water production (m a-1) driven by our atmospheric RCM. Surface ice speeds (m a-1) illustrate the evolution of ice streams during ice-sheet retreat in the RCP8.5 scenario. The simulations in the videos use default model parameters and correspond to the simulations shown in Figure 4.
  7. RCP2.6 surface melt-water production (m a-1) from 1950 to 2500 CE
    Video 7: RCP2.6 surface melt-water production (m a-1) from 1950 to 2500 CE
    This video shows various aspects of our ice-sheet simulations from 1950 to 2500 CE, following future greenhouse-gas emission scenarios: RCP2.6, RCP4.5, and RCP8.5. Animations show the time-evolution of ice sheet thickness (m), oceanic melt rates (m a-1) driven by NCAR CCSM4 ocean temperatures, and surface melt-water production (m a-1) driven by our atmospheric RCM. Surface ice speeds (m a-1) illustrate the evolution of ice streams during ice-sheet retreat in the RCP8.5 scenario. The simulations in the videos use default model parameters and correspond to the simulations shown in Figure 4.
  8. RCP4.5 surface melt-water production (m a-1) from 1950 to 2500 CE
    Video 8: RCP4.5 surface melt-water production (m a-1) from 1950 to 2500 CE
    This video shows various aspects of our ice-sheet simulations from 1950 to 2500 CE, following future greenhouse-gas emission scenarios: RCP2.6, RCP4.5, and RCP8.5. Animations show the time-evolution of ice sheet thickness (m), oceanic melt rates (m a-1) driven by NCAR CCSM4 ocean temperatures, and surface melt-water production (m a-1) driven by our atmospheric RCM. Surface ice speeds (m a-1) illustrate the evolution of ice streams during ice-sheet retreat in the RCP8.5 scenario. The simulations in the videos use default model parameters and correspond to the simulations shown in Figure 4.
  9. RCP8.5 surface melt-water production (m a-1) from 1950 to 2500 CE
    Video 9: RCP8.5 surface melt-water production (m a-1) from 1950 to 2500 CE
    This video shows various aspects of our ice-sheet simulations from 1950 to 2500 CE, following future greenhouse-gas emission scenarios: RCP2.6, RCP4.5, and RCP8.5. Animations show the time-evolution of ice sheet thickness (m), oceanic melt rates (m a-1) driven by NCAR CCSM4 ocean temperatures, and surface melt-water production (m a-1) driven by our atmospheric RCM. Surface ice speeds (m a-1) illustrate the evolution of ice streams during ice-sheet retreat in the RCP8.5 scenario. The simulations in the videos use default model parameters and correspond to the simulations shown in Figure 4.
  10. RCP8.5 ice-surface speeds (norm of ice-surface velocities (m a-1)) from 1950 to 2500 CE
    Video 10: RCP8.5 ice-surface speeds (norm of ice-surface velocities (m a-1)) from 1950 to 2500 CE
    This video shows various aspects of our ice-sheet simulations from 1950 to 2500 CE, following future greenhouse-gas emission scenarios: RCP2.6, RCP4.5, and RCP8.5. Animations show the time-evolution of ice sheet thickness (m), oceanic melt rates (m a-1) driven by NCAR CCSM4 ocean temperatures, and surface melt-water production (m a-1) driven by our atmospheric RCM. Surface ice speeds (m a-1) illustrate the evolution of ice streams during ice-sheet retreat in the RCP8.5 scenario. The simulations in the videos use default model parameters and correspond to the simulations shown in Figure 4.

Change history

Corrected online 05 April 2016
A couple of missing citations to the Extended Data Tables were corrected in the HTML on 5 April 2016.

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Author information

Affiliations

  1. Department of Geosciences, University of Massachusetts, Amherst, Massachusetts 01003, USA

    • Robert M. DeConto
  2. Earth and Environmental Systems Institute, Pennsylvania State University, University Park, Pennsylvania 16802, USA

    • David Pollard

Contributions

R.M.D. and D.P. conceived the model experiments, developed the models, and wrote the manuscript.

Competing financial interests

The authors declare no competing financial interests.

Corresponding author

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Extended data figures and tables

Extended Data Figures

  1. Extended Data Figure 1: Warm mid-Pliocene climate and ice-sheet simulation. (258 KB)

    a, January (warmest monthly mean) difference in 2-m (surface) air temperature simulated by the RCM relative to a preindustrial control simulation with 280 p.p.m.v. CO2 and present-day orbit. The temperature difference is lapse-rate-corrected to account for the change in ice-sheet geometry and surface elevations. The Pliocene simulation uses 400 p.p.m.v. CO2, a warm austral summer orbit, and assumes a retreated WAIS to represent maximum Pliocene warm conditions. b, The Pliocene ice-sheet is shown after 5,000 model years, driven by the RCM climate in a, and assuming 2 °C ocean warming relative to a modern ocean climatology32. In the model formulation used here, maximum Pliocene ice-sheet retreat with default model parameters is equivalent to 11.26 m GMSL, about 6 m less than in ref. 25.

  2. Extended Data Figure 2: LIG greenhouse gases, orbital parameters, and RCM climates. (398 KB)

    a, Greenhouse gas concentrations9, 72 converted to radiative forcing shows the LIG interval (light red bar) and the best opportunity for ice-sheet retreat. b, Summer insulation at 70° latitude in both hemispheres73 (red, south; blue, north) and summer duration at 70° S (black)79 shown over the last 150 kyr, and the two orbital time slices (vertical dashed black lines at 128 kyr ago and 116 kyr ago). c, Table showing the greenhouse gas atmospheric mixing ratios (CO2 in parts per million by volume; CH4 and N2O in parts per billion by volume) and orbital parameters (eccentricity, obliquity, precession) used in the GCM–RCM at the LIG time slices (dashed lines 1 and 2 in a and b), respectively. df, January (warmest monthly mean) differences in 2-m surface air temperature relative to a preindustrial control simulation at 128 kyr ago (d), 116 kyr ago (e), and the present-day (2015) (f). Simulated austral summer temperatures at 116 kyr ago (e) with relatively high-intensity summer insolation is warmer than the long-duration summer orbit at 128 kyr ago (d), but unlike the Pliocene (Extended Data Fig. 1a), neither LIG climatology is as warm as the present day, producing little to no rain or surface melt on ice-shelf surfaces.

  3. Extended Data Figure 3: Effect of Southern Ocean warming on Antarctic surface air temperatures and the ice sheet at 128 kyr ago. (418 KB)

    ac, January (warmest monthly mean) differences in 2-m surface air temperature at 128 kyr ago, relative to a preindustrial control simulation (top row). GHG, greenhouse gas; SST, sea surface temperature. d, e, Ice-sheet thickness (m) after 5,000 model years, driven by the corresponding climate in ac. a and d, Without climate–ice sheet coupling (present-day ice extent and surface ocean temperatures in the RCM), and prescribed 5 °C sub-surface ocean warming felt only by the ice sheet. b and e, With asynchronous coupling between the RCM atmosphere and ice sheet, and prescribed 5 °C sub-surface ocean warming felt only by the ice sheet. c and f, With asynchronous coupling between the RCM atmosphere and ice sheet, prescribed 3 °C sub-surface ocean warming felt by the ice sheet, and ~2 °C surface ocean warming felt by the RCM atmosphere. c shows the locations of East Antarctic ice cores (EDC, EPICA Dome C; V, Vostock; DF, Dome F; EDML, EPICA Dronning Maud Land) indicating warming early in the interglacial29 and previously attributed to WAIS retreat80; this warming is similar to that simulated in c from a combination of ice-sheet retreat and warmer Southern Ocean temperatures, supporting the notion that the timing of LIG retreat was largely driven by far-field ocean influences, rather than local astronomical forcing.

  4. Extended Data Figure 4: RCM climates used in future, time-continuous RCP scenarios and evolving ice-surface melt rates linked to hydrofracturing model physics. (849 KB)

    ad, January surface (2-m) air temperatures simulated by the RCM at the present-day (2015) (a), twice the present level of carbon dioxide, 2 × CO2 (b), 4 × CO2 (c), and 8 × CO2 (d) with the retreating ice sheet. The colour scale is the same in all panels. Yellow to red colours indicate temperatures above freezing with the potential for summer rain, and surface meltwater production. eh, Evolving ice-surface meltwater production (in metres per year) in the time-evolving RCP8.5 ice-sheet simulations, driven by a time-continuous RCM climatology (Methods) following the RCP8.5 greenhouse gas time series (Fig. 4a). Black lines show the positions of grounding lines and ice-shelf calving fronts at discrete time intervals—e, 2050; f, 2100; g, 2150; and h, 2500—with superposed meltwater production rates.

  5. Extended Data Figure 5: NCAR CCSM4 ocean temperatures and oceanic sub-ice-shelf melt rates. (373 KB)

    a, RCP2.6 ocean warming at 400-m depth, shown as the difference of decadal averages from 1950–1960 to 2290–2300. b, Same as a but for RCP4.5. c, Same as a but for RCP8.5. d, CCSM4 RCP8.5 ocean warming from 1950–1960 to 2010–2020 showing little to no warming in the Amundsen and Bellingshausen seas. The red line shows the area of imposed, additional ocean warming. e, f, Oceanic melt rates at 2015 calculated by the ice-sheet model from interpolated CCSM4 temperatures (e), and with +3 °C adjustment in the Amundsen and Bellingshausen seas (f), corresponding to the area within the red line in d.

  6. Extended Data Figure 6: Effect of future ocean warming only. (241 KB)

    a, Antarctic contribution to future GMSL rise in long, 5,000-yr ice-sheet simulations driven by sub-surface ocean warming simulated by CCSM4, following RCP8.5 (black line), with a +3 °C adjustment in the Amundsen and Bellingshausen seas (blue line; see Extended Data Fig. 5) and a warmer +5 °C adjustment (red line). Atmospheric temperatures and precipitation are maintained at their present values. bd, Ice-sheet thickness at model-year 5,000, driven by sub-surface ocean forcing from CCSM4 (b) and from CCSM4 with a +3 °C (c) or +5 °C (d) adjustment in the Amundsen and Bellingshausen seas. Note the near-complete loss of ice shelves, but modest grounding-line retreat in b, the retreat of Pine Island Glacier in c, and the near-complete collapse of WAIS once a stability threshold in the Thwaites Glacier grounding line is reached in d.

  7. Extended Data Figure 7: The long-term future of the ice sheet and GMSL over the next 5,000 years following RCP8.5 and RCP4.5. (187 KB)

    a, Equivalent CO2 forcing following RCP8.5 until the year 2500, and then assuming zero emissions after 2500 and allowing a natural relaxation of greenhouse gas levels (red) or assuming a fast, engineered drawdown (blue) with an e-folding timescale of 100 years. b. Antarctic contribution to GMSL over the next 5,000 years, following the greenhouse gas scenarios in a. c, The same as a, except showing long-term RCP4.5 greenhouse gas forcing. d, The same as b, except following the RCP4.5 scenarios in c. The insets in b and d show the ice sheet (and remaining sea-level rise) after 5,000 model years in RCP8.5 and RCP4.5, respectively, assuming fast CO2 drawdown (blue lines), highlighting the multi-millennial commitment to a loss of marine-based Antarctic ice, even in the moderate RCP4.5 scenario. Note the different y-axes in RCP8.5 versus RCP4.5.

  8. Extended Data Figure 8: Freshwater input to the Southern Ocean. (130 KB)

    Total freshwater and iceberg flux from 1950 to 2500, following the future RCP scenarios shown in Fig. 4b. Freshwater input calculations include contributions from ice loss above and below sea level and exceed 1 Sv in RCP8.5.

Extended Data Tables

  1. Extended Data Table 1: Summary of Antarctic contributions to GMSL during the Pliocene, LIG, future centuries, and future millennia (346 KB)
  2. Extended Data Table 2: Ensemble simulations of Pliocene, LIG, and future Antarctic contributions to GMSL (527 KB)

Supplementary information

Video

  1. Video 1: RCP2.6 ice-sheet thickness (m) from 1950 to 2500 CE (470 KB, Download)
    This video shows various aspects of our ice-sheet simulations from 1950 to 2500 CE, following future greenhouse-gas emission scenarios: RCP2.6, RCP4.5, and RCP8.5. Animations show the time-evolution of ice sheet thickness (m), oceanic melt rates (m a-1) driven by NCAR CCSM4 ocean temperatures, and surface melt-water production (m a-1) driven by our atmospheric RCM. Surface ice speeds (m a-1) illustrate the evolution of ice streams during ice-sheet retreat in the RCP8.5 scenario. The simulations in the videos use default model parameters and correspond to the simulations shown in Figure 4.
  2. Video 2: RCP4.5 ice-sheet thickness (m) from 1950 to 2500 CE (523 KB, Download)
    This video shows various aspects of our ice-sheet simulations from 1950 to 2500 CE, following future greenhouse-gas emission scenarios: RCP2.6, RCP4.5, and RCP8.5. Animations show the time-evolution of ice sheet thickness (m), oceanic melt rates (m a-1) driven by NCAR CCSM4 ocean temperatures, and surface melt-water production (m a-1) driven by our atmospheric RCM. Surface ice speeds (m a-1) illustrate the evolution of ice streams during ice-sheet retreat in the RCP8.5 scenario. The simulations in the videos use default model parameters and correspond to the simulations shown in Figure 4.
  3. Video 3: RCP8.5 ice-sheet thickness (m) from 1950 to 2500 CE (585 KB, Download)
    This video shows various aspects of our ice-sheet simulations from 1950 to 2500 CE, following future greenhouse-gas emission scenarios: RCP2.6, RCP4.5, and RCP8.5. Animations show the time-evolution of ice sheet thickness (m), oceanic melt rates (m a-1) driven by NCAR CCSM4 ocean temperatures, and surface melt-water production (m a-1) driven by our atmospheric RCM. Surface ice speeds (m a-1) illustrate the evolution of ice streams during ice-sheet retreat in the RCP8.5 scenario. The simulations in the videos use default model parameters and correspond to the simulations shown in Figure 4.
  4. Video 4: RCP2.6 oceanic melt rates (m a-1) from 1950 to 2500 CE (593 KB, Download)
    This video shows various aspects of our ice-sheet simulations from 1950 to 2500 CE, following future greenhouse-gas emission scenarios: RCP2.6, RCP4.5, and RCP8.5. Animations show the time-evolution of ice sheet thickness (m), oceanic melt rates (m a-1) driven by NCAR CCSM4 ocean temperatures, and surface melt-water production (m a-1) driven by our atmospheric RCM. Surface ice speeds (m a-1) illustrate the evolution of ice streams during ice-sheet retreat in the RCP8.5 scenario. The simulations in the videos use default model parameters and correspond to the simulations shown in Figure 4.
  5. Video 5: RCP4.5 oceanic melt rates (m a-1) from 1950 to 2500 CE (691 KB, Download)
    This video shows various aspects of our ice-sheet simulations from 1950 to 2500 CE, following future greenhouse-gas emission scenarios: RCP2.6, RCP4.5, and RCP8.5. Animations show the time-evolution of ice sheet thickness (m), oceanic melt rates (m a-1) driven by NCAR CCSM4 ocean temperatures, and surface melt-water production (m a-1) driven by our atmospheric RCM. Surface ice speeds (m a-1) illustrate the evolution of ice streams during ice-sheet retreat in the RCP8.5 scenario. The simulations in the videos use default model parameters and correspond to the simulations shown in Figure 4.
  6. Video 6: RCP8.5 oceanic melt rates (m a-1) from 1950 to 2500 CE (809 KB, Download)
    This video shows various aspects of our ice-sheet simulations from 1950 to 2500 CE, following future greenhouse-gas emission scenarios: RCP2.6, RCP4.5, and RCP8.5. Animations show the time-evolution of ice sheet thickness (m), oceanic melt rates (m a-1) driven by NCAR CCSM4 ocean temperatures, and surface melt-water production (m a-1) driven by our atmospheric RCM. Surface ice speeds (m a-1) illustrate the evolution of ice streams during ice-sheet retreat in the RCP8.5 scenario. The simulations in the videos use default model parameters and correspond to the simulations shown in Figure 4.
  7. Video 7: RCP2.6 surface melt-water production (m a-1) from 1950 to 2500 CE (477 KB, Download)
    This video shows various aspects of our ice-sheet simulations from 1950 to 2500 CE, following future greenhouse-gas emission scenarios: RCP2.6, RCP4.5, and RCP8.5. Animations show the time-evolution of ice sheet thickness (m), oceanic melt rates (m a-1) driven by NCAR CCSM4 ocean temperatures, and surface melt-water production (m a-1) driven by our atmospheric RCM. Surface ice speeds (m a-1) illustrate the evolution of ice streams during ice-sheet retreat in the RCP8.5 scenario. The simulations in the videos use default model parameters and correspond to the simulations shown in Figure 4.
  8. Video 8: RCP4.5 surface melt-water production (m a-1) from 1950 to 2500 CE (594 KB, Download)
    This video shows various aspects of our ice-sheet simulations from 1950 to 2500 CE, following future greenhouse-gas emission scenarios: RCP2.6, RCP4.5, and RCP8.5. Animations show the time-evolution of ice sheet thickness (m), oceanic melt rates (m a-1) driven by NCAR CCSM4 ocean temperatures, and surface melt-water production (m a-1) driven by our atmospheric RCM. Surface ice speeds (m a-1) illustrate the evolution of ice streams during ice-sheet retreat in the RCP8.5 scenario. The simulations in the videos use default model parameters and correspond to the simulations shown in Figure 4.
  9. Video 9: RCP8.5 surface melt-water production (m a-1) from 1950 to 2500 CE (779 KB, Download)
    This video shows various aspects of our ice-sheet simulations from 1950 to 2500 CE, following future greenhouse-gas emission scenarios: RCP2.6, RCP4.5, and RCP8.5. Animations show the time-evolution of ice sheet thickness (m), oceanic melt rates (m a-1) driven by NCAR CCSM4 ocean temperatures, and surface melt-water production (m a-1) driven by our atmospheric RCM. Surface ice speeds (m a-1) illustrate the evolution of ice streams during ice-sheet retreat in the RCP8.5 scenario. The simulations in the videos use default model parameters and correspond to the simulations shown in Figure 4.
  10. Video 10: RCP8.5 ice-surface speeds (norm of ice-surface velocities (m a-1)) from 1950 to 2500 CE (918 KB, Download)
    This video shows various aspects of our ice-sheet simulations from 1950 to 2500 CE, following future greenhouse-gas emission scenarios: RCP2.6, RCP4.5, and RCP8.5. Animations show the time-evolution of ice sheet thickness (m), oceanic melt rates (m a-1) driven by NCAR CCSM4 ocean temperatures, and surface melt-water production (m a-1) driven by our atmospheric RCM. Surface ice speeds (m a-1) illustrate the evolution of ice streams during ice-sheet retreat in the RCP8.5 scenario. The simulations in the videos use default model parameters and correspond to the simulations shown in Figure 4.

Additional data