ISMIP6 projections of ocean-forced Antarctic Ice Sheet evolution using the Community Ice Sheet Model

Abstract. The future retreat rate for marine-based regions of the Antarctic Ice Sheet is one of the largest uncertainties in sea-level projections. The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) aims to improve projections and quantify uncertainties by running an ensemble of ice sheet models with atmosphere and ocean forcing derived from global climate models. Here, ISMIP6 projections of ocean-forced Antarctic Ice Sheet evolution are illustrated using the Community Ice Sheet Model (CISM). Using multiple combinations of sub-ice-shelf melt parameterizations and calibrations, CISM is spun up to steady state over many millennia. During the spin-up, basal friction parameters and basin-scale thermal forcing corrections are adjusted to nudge the ice thickness toward observed values. The model is then run forward for 500 years, applying ocean thermal forcing anomalies from six climate models. In all simulations, the ocean forcing triggers long-term retreat of the West Antarctic Ice Sheet, including the Amundsen, Filchner-Ronne, and Ross Basins. Mass loss accelerates late in the 21st century and rises steadily over the next several centuries without leveling off. The resulting ocean-forced SLR at year 2500 varies from about 10 cm to nearly 2 m, depending on the melt scheme and model forcing. Relatively little ice loss is simulated in East Antarctica. Large uncertainties remain, as a result of parameterized basal melt rates, missing ocean and ice sheet physics, and the lack of ice–ocean coupling.

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ISMIP6-based projections of ocean-forced Antarctic ice loss using the Community Ice Sheet Model

10.5194/egusphere-egu21-6722 ◽

2021 ◽

Author(s):

William Lipscomb ◽

Gunter Leguy ◽

Nicolas Jourdain ◽

Xylar Asay-Davis ◽

Hélène Seroussi ◽

...

Keyword(s):

Sea Level ◽

Climate Models ◽

Global Climate ◽

Ice Sheet ◽

High Sensitivity ◽

Global Climate Models ◽

Thermal Forcing ◽

Antarctic Ice Sheet ◽

Basal Friction ◽

West Antarctic

<p>The future retreat rate for marine-based regions of the Antarctic Ice Sheet is one of the largest uncertainties in sea-level projections. The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) aims to improve projections and quantify uncertainties by running an ensemble of ice sheet models with forcing derived from global climate models. Here, the Community Ice Sheet Model (CISM) is used to run ISMIP6-based projections of ocean-forced Antarctic Ice Sheet evolution. Using several combinations of sub-ice-shelf melt schemes, CISM is spun up to steady state over many millennia. During the spin-up, basal-friction and thermal-forcing parameters are adjusted to optimize agreement with the observed ice thickness. The model is then run forward to year 2500, applying ocean thermal forcing anomalies from six climate models. In all simulations, ocean warming triggers long-term retreat of the West Antarctic Ice Sheet, especially in the Filchner-Ronne and Ross sectors. The ocean-forced sea-level rise in 2500 varies from about 150 mm to 1300 mm, depending on the melt scheme and ocean forcing applied. Further experiments show relatively high sensitivity to the basal friction law, and moderate sensitivity to grid resolution and the prescribed collapse of small ice shelves. The Amundsen sector exhibits threshold behavior, with modest retreat under many parameter settings, but complete collapse under some combinations of low basal friction and high thermal-forcing anomalies. Large uncertainties remain, as a result of parameterized sub-shelf melt rates, simplified treatments of calving and basal friction, and the lack of ice&#8211;ocean coupling.</p>

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ISMIP6-based projections of ocean-forced Antarctic Ice Sheet evolution using the Community Ice Sheet Model

The Cryosphere ◽

10.5194/tc-15-633-2021 ◽

2021 ◽

Vol 15 (2) ◽

pp. 633-661

Author(s):

William H. Lipscomb ◽

Gunter R. Leguy ◽

Nicolas C. Jourdain ◽

Xylar Asay-Davis ◽

Hélène Seroussi ◽

...

Keyword(s):

Sea Level ◽

Climate Models ◽

Global Climate ◽

Ice Sheet ◽

High Sensitivity ◽

Global Climate Models ◽

Thermal Forcing ◽

Antarctic Ice Sheet ◽

Basal Friction ◽

Basin Scale

Abstract. The future retreat rate for marine-based regions of the Antarctic Ice Sheet is one of the largest uncertainties in sea-level projections. The Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6) aims to improve projections and quantify uncertainties by running an ensemble of ice sheet models with atmosphere and ocean forcing derived from global climate models. Here, the Community Ice Sheet Model (CISM) is used to run ISMIP6-based projections of ocean-forced Antarctic Ice Sheet evolution. Using multiple combinations of sub-ice-shelf melt parameterizations and calibrations, CISM is spun up to steady state over many millennia. During the spin-up, basal friction parameters and basin-scale thermal forcing corrections are adjusted to optimize agreement with the observed ice thickness. The model is then run forward for 550 years, from 1950–2500, applying ocean thermal forcing anomalies from six climate models. In all simulations, the ocean forcing triggers long-term retreat of the West Antarctic Ice Sheet, especially in the Filchner–Ronne and Ross sectors. Mass loss accelerates late in the 21st century and then rises steadily for several centuries without leveling off. The resulting ocean-forced sea-level rise at year 2500 varies from about 150 to 1300 mm, depending on the melt scheme and ocean forcing. Further experiments show relatively high sensitivity to the basal friction law, moderate sensitivity to grid resolution and the prescribed collapse of small ice shelves, and low sensitivity to the stress-balance approximation. The Amundsen sector exhibits threshold behavior, with modest retreat under many parameter settings but complete collapse under some combinations of low basal friction and high thermal forcing anomalies. Large uncertainties remain, as a result of parameterized sub-shelf melt rates, simplified treatments of calving and basal friction, and the lack of ice–ocean coupling.

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Climate, the Antarctic ice sheet and ground heat flux

Annals of Glaciology ◽

10.3189/s0260305500015731 ◽

1995 ◽

Vol 21 ◽

pp. 144-148

Author(s):

Garth W. Paltridge ◽

Christopher M. Zweck

Keyword(s):

Heat Flux ◽

Steady State ◽

Climate Models ◽

Global Climate ◽

Ice Sheet ◽

Global Climate Models ◽

Balance Model ◽

Antarctic Ice Sheet ◽

Ground Heat Flux ◽

The Antarctic

A simple steady-state energy and mass-balance model of the Antarctic ice sheet is developed. Basically it is a set of two equations with two unknowns of steady-state height h and potential basal temperature Tb. Tb determines whether, and to what extent, there is liquid water at the base of the ice which in turn affects the values of h and Tb. Simultaneous changes of sea-level temperature and precipitation (changes related to each other as might be expected from global climate models) indicate a maximum in the field of possible steady-state ice volumes which may not be far from the presently observed conditions. The possibility of cyclical variation in ground heat flux associated with convection of water and heat in the continental crust is discussed. The mechanism might be capable of generating cycles of ice-sheet volume with relatively short periods similar to those of Milankovitch forcing.

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Climate, the Antarctic ice sheet and ground heat flux

Annals of Glaciology ◽

10.1017/s0260305500015731 ◽

1995 ◽

Vol 21 ◽

pp. 144-148 ◽

Cited By ~ 1

Author(s):

Garth W. Paltridge ◽

Christopher M. Zweck

Keyword(s):

Heat Flux ◽

Steady State ◽

Climate Models ◽

Global Climate ◽

Ice Sheet ◽

Global Climate Models ◽

Balance Model ◽

Antarctic Ice Sheet ◽

Ground Heat Flux ◽

The Antarctic

A simple steady-state energy and mass-balance model of the Antarctic ice sheet is developed. Basically it is a set of two equations with two unknowns of steady-state heighthand potential basal temperatureTb.Tbdetermines whether, and to what extent, there is liquid water at the base of the ice which in turn affects the values ofhandTb. Simultaneous changes of sea-level temperature and precipitation (changes related to each other as might be expected from global climate models) indicate a maximum in the field of possible steady-state ice volumes which may not be far from the presently observed conditions. The possibility of cyclical variation in ground heat flux associated with convection of water and heat in the continental crust is discussed. The mechanism might be capable of generating cycles of ice-sheet volume with relatively short periods similar to those of Milankovitch forcing.

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Influence of Continental Ice Retreat on Future Global Climate

Journal of Climate ◽

10.1175/jcli-d-12-00102.1 ◽

2013 ◽

Vol 26 (10) ◽

pp. 3087-3111 ◽

Cited By ~ 15

Author(s):

Aixue Hu ◽

Gerald A. Meehl ◽

Weiqing Han ◽

Jianjun Yin ◽

Bingyi Wu ◽

...

Keyword(s):

Sea Level ◽

North Atlantic ◽

Global Climate ◽

Ice Sheet ◽

Greenland Ice Sheet ◽

Meridional Overturning Circulation ◽

Antarctic Ice Sheet ◽

Climate System Model ◽

West Antarctic Ice Sheet ◽

West Antarctic

Abstract Evidence from observations indicates a net loss of global land-based ice and a rise of global sea level. Other than sea level rise, it is not clear how this loss of land-based ice could affect other aspects of global climate in the future. Here, the authors use the Community Climate System Model version 3 (CCSM3) to evaluate the potential influence of shrinking land-based ice on the Atlantic meridional overturning circulation (AMOC) and surface climate in the next two centuries under the Intergovernmental Panel on Climate Change (IPCC) A1B scenario with prescribed rates of melting for the Greenland Ice Sheet, West Antarctic Ice Sheet, and mountain glaciers and ice caps. Results show that the AMOC, in general, is only sensitive to the freshwater discharge directly into the North Atlantic over the next two centuries. If the loss of the West Antarctic Ice Sheet would not significantly increase from its current rate, it would not have much effect on the AMOC. The AMOC slows down further only when the surface freshwater input due to runoff from land-based ice melt becomes large enough to generate a net freshwater gain in the upper North Atlantic. This further-weakened AMOC does not cool the global mean climate, but it does cause less warming, especially in the northern high latitudes and, in particular, in Europe. The projected precipitation increase in North America in the standard run becomes a net reduction in the simulation that includes land ice runoff, but there are precipitation increases in west Australia in the simulations where the AMOC slows down because of the inclusion of land-based ice runoff.

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Drivers of abrupt Holocene shifts in West Antarctic ice stream direction determined from combined ice sheet modelling and geologic signatures

Antarctic Science ◽

10.1017/s0954102014000613 ◽

2014 ◽

Vol 26 (6) ◽

pp. 674-686 ◽

Cited By ~ 16

Author(s):

C.J. Fogwill ◽

C.S.M. Turney ◽

N.R. Golledge ◽

D.H. Rood ◽

K. Hippe ◽

...

Keyword(s):

Flow Direction ◽

Ice Sheet ◽

Weddell Sea ◽

Last Deglaciation ◽

Ice Streams ◽

Antarctic Ice Sheet ◽

West Antarctic Ice Sheet ◽

West Antarctic ◽

Ice Stream ◽

Ice Sheet Modelling

AbstractDetermining the millennial-scale behaviour of marine-based sectors of the West Antarctic Ice Sheet (WAIS) is critical to improve predictions of the future contribution of Antarctica to sea level rise. Here high-resolution ice sheet modelling was combined with new terrestrial geological constraints (in situ14C and 10Be analysis) to reconstruct the evolution of two major ice streams entering the Weddell Sea over 20 000 years. The results demonstrate how marked differences in ice flux at the marine margin of the expanded Antarctic ice sheet led to a major reorganization of ice streams in the Weddell Sea during the last deglaciation, resulting in the eastward migration of the Institute Ice Stream, triggering a significant regional change in ice sheet mass balance during the early to mid Holocene. The findings highlight how spatial variability in ice flow can cause marked changes in the pattern, flux and flow direction of ice streams on millennial timescales in this marine ice sheet setting. Given that this sector of the WAIS is assumed to be sensitive to ocean-forced instability and may be influenced by predicted twenty-first century ocean warming, our ability to model and predict abrupt and extensive ice stream diversions is key to a realistic assessment of future ice sheet sensitivity.

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Grounding-line retreat of the West Antarctic Ice Sheet from inner Pine Island Bay

Geology ◽

10.1130/g33469.1 ◽

2012 ◽

Vol 41 (1) ◽

pp. 35-38 ◽

Cited By ~ 51

Author(s):

C.-D. Hillenbrand ◽

G. Kuhn ◽

J. A. Smith ◽

K. Gohl ◽

A. G. C. Graham ◽

...

Keyword(s):

Ice Sheet ◽

The West ◽

Antarctic Ice Sheet ◽

West Antarctic Ice Sheet ◽

West Antarctic ◽

Grounding Line

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Dynamical processes involved in the retreat of marine ice sheets

Journal of Glaciology ◽

10.3189/172756501781832269 ◽

2001 ◽

Vol 47 (157) ◽

pp. 271-282 ◽

Cited By ~ 95

Author(s):

Richard C.A. Hindmarsh ◽

E. Le Meur

Keyword(s):

Ice Sheets ◽

Ice Sheet ◽

Ice Shelf ◽

Ice Streams ◽

Antarctic Ice Sheet ◽

West Antarctic Ice Sheet ◽

West Antarctic ◽

Grounding Line ◽

Neutral Equilibrium ◽

Generally True

AbstractMarine ice sheets with mechanics described by the shallow-ice approximation by definition do not couple mechanically with the shelf. Such ice sheets are known to have neutral equilibria. We consider the implications of this for their dynamics and in particular for mechanisms which promote marine ice-sheet retreat. The removal of ice-shelf buttressing leading to enhanced flow in grounded ice is discounted as a significant influence on mechanical grounds. Sea-level rise leading to reduced effective pressures under ice streams is shown to be a feasible mechanism for producing postglacial West Antarctic ice-sheet retreat but is inconsistent with borehole evidence. Warming thins the ice sheet by reducing the average viscosity but does not lead to grounding-line retreat. Internal oscillations either specified or generated via a MacAyeal–Payne thermal mechanism promote migration. This is a noise-induced drift phenomenon stemming from the neutral equilibrium property of marine ice sheets. This migration occurs at quite slow rates, but these are sufficiently large to have possibly played a role in the dynamics of the West Antarctic ice sheet after the glacial maximum. Numerical experiments suggest that it is generally true that while significant changes in thickness can be caused by spatially uniform changes, spatial variability coupled with dynamical variability is needed to cause margin movement.

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A Potential Disintegration of the West Antarctic Ice Sheet: Implications for Economic Analyses of Climate Policy

The American Economic Review ◽

10.1257/aer.p20161103 ◽

2016 ◽

Vol 106 (5) ◽

pp. 607-611 ◽

Cited By ~ 16

Author(s):

Delavane Diaz ◽

Klaus Keller

Keyword(s):

Climate Policy ◽

Expert Knowledge ◽

Ice Sheet ◽

The West ◽

Antarctic Ice Sheet ◽

West Antarctic Ice Sheet ◽

Threshold Response ◽

West Antarctic ◽

Climate Forcings ◽

Economic Analyses

The Earth system may react in a nonlinear threshold response to climate forcings. Incorporating threshold responses into integrated assessment models (IAMs) used for climate policy analysis poses nontrivial challenges, for example due to methodological limitations and pervasive deep uncertainties. Here we explore a specific threshold response, a potential disintegration of the West Antarctic Ice Sheet (WAIS). We review the current scientific understanding of WAIS, identify methodological and conceptual issues, and demonstrate avenues to address some of them through a stochastic hazard IAM framework combining emulation, expert knowledge, and learning. We conclude with a discussion of challenges and research needs.

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