AGW Observer

Observations of anthropogenic global warming

Papers on ice sheet collapse

Posted by Ari Jokimäki on February 3, 2016

This is a list of papers on ice sheet collapse. The list is not complete, and will most likely be updated in future in order to make it more thorough and more representative.

Potential sea-level rise from Antarctic ice-sheet instability constrained by observations – Ritz et al. (2015)
Abstract: Large parts of the Antarctic ice sheet lying on bedrock below sea level may be vulnerable to marine-ice-sheet instability (MISI), a self-sustaining retreat of the grounding line triggered by oceanic or atmospheric changes. There is growing evidence that MISI may be underway throughout the Amundsen Sea embayment (ASE), which contains ice equivalent to more than a metre of global sea-level rise. If triggered in other regions, the centennial to millennial contribution could be several metres. Physically plausible projections are challenging: numerical models with sufficient spatial resolution to simulate grounding-line processes have been too computationally expensive to generate large ensembles for uncertainty assessment, and lower-resolution model projections rely on parameterizations that are only loosely constrained by present day changes. Here we project that the Antarctic ice sheet will contribute up to 30 cm sea-level equivalent by 2100 and 72 cm by 2200 (95% quantiles) where the ASE dominates. Our process-based, statistical approach gives skewed and complex probability distributions (single mode, 10 cm, at 2100; two modes, 49 cm and 6 cm, at 2200). The dependence of sliding on basal friction is a key unknown: nonlinear relationships favour higher contributions. Results are conditional on assessments of MISI risk on the basis of projected triggers under the climate scenario A1B (ref. 9), although sensitivity to these is limited by theoretical and topographical constraints on the rate and extent of ice loss. We find that contributions are restricted by a combination of these constraints, calibration with success in simulating observed ASE losses, and low assessed risk in some basins. Our assessment suggests that upper-bound estimates from low-resolution models and physical arguments (up to a metre by 2100 and around one and a half by 2200) are implausible under current understanding of physical mechanisms and potential triggers.
Citation: Catherine Ritz, Tamsin L. Edwards, Gaël Durand, Antony J. Payne, Vincent Peyaud, Richard C. A. Hindmarsh, Nature 528, 115–118 (03 December 2015) doi:10.1038/nature16147.

Marine Ice Sheet Collapse Potentially Under Way for the Thwaites Glacier Basin, West Antarctica – Joughin et al. (2014)
Abstract: Resting atop a deep marine basin, the West Antarctic Ice Sheet has long been considered prone to instability. Using a numerical model, we investigated the sensitivity of Thwaites Glacier to ocean melt and whether its unstable retreat is already under way. Our model reproduces observed losses when forced with ocean melt comparable to estimates. Simulated losses are moderate (1 mm per year of sea-level rise) collapse in the different simulations within the range of 200 to 900 years.
Citation: Ian Joughin, Benjamin E. Smith, Brooke Medley, Science 16 May 2014: Vol. 344, Issue 6185, pp. 735-738, DOI: 10.1126/science.1249055.

Where might we find evidence of a Last Interglacial West Antarctic Ice Sheet collapse in Antarctic ice core records? – Bradley et al. (2012) [FULL TEXT]
Abstract: Abundant indirect evidence suggests that the West Antarctic Ice Sheet (WAIS) reduced in size during the Last Interglacial (LIG) compared to the Holocene. This study explores this possibility by comparing, for the first time, ice core stable isotope records for the LIG with output from a glacio-isostatic adjustment (GIA) model. The results show that ice core records from East Antarctica are remarkably insensitive to vertical movement of the solid land motion driven by a simulated hypothetical collapse of the WAIS. However, new and so far unexplored sites are identified which are sensitive to the isostatic signal associated with WAIS collapse and so ice core proxy data from these sites would be effective in testing this hypothesis further.
Citation: S.L. Bradley, M. Siddall, G.A. Milne, V. Masson-Delmotte, E. Wolff, Global and Planetary Change, Volumes 88–89, May 2012, Pages 64–75, doi: 10.1016/j.gloplacha.2012.03.004.

Stability of the West Antarctic ice sheet in a warming world – Joughin & Alley (2011) [FULL TEXT]
Abstract: Ice sheets are expected to shrink in size as the world warms, which in turn will raise sea level. The West Antarctic ice sheet is of particular concern, because it was probably much smaller at times during the past million years when temperatures were comparable to levels that might be reached or exceeded within the next few centuries. Much of the grounded ice in West Antarctica lies on a bed that deepens inland and extends well below sea level. Oceanic and atmospheric warming threaten to reduce or eliminate the floating ice shelves that buttress the ice sheet at present. Loss of the ice shelves would accelerate the flow of non-floating ice near the coast. Because of the slope of the sea bed, the consequent thinning could ultimately float much of the ice sheet’s interior. In this scenario, global sea level would rise by more than three metres, at an unknown rate. Simplified analyses suggest that much of the ice sheet will survive beyond this century. We do not know how likely or inevitable eventual collapse of the West Antarctic ice sheet is at this stage, but the possibility cannot be discarded. For confident projections of the fate of the ice sheet and the rate of any collapse, further work including the development of well-validated physical models will be required.
Citation: Ian Joughin, Richard B. Alley, Nature Geoscience 4, 506–513 (2011) doi:10.1038/ngeo1194.

A new projection of sea level change in response to collapse of marine sectors of the Antarctic Ice Sheet – Gomez et al. (2010) [FULL TEXT]
Abstract: We present gravitationally self-consistent predictions of sea level change that would follow the disappearance of either the West Antarctic Ice Sheet (WAIS) or marine sectors of the East Antarctic Ice Sheet (EAIS). Our predictions are based on a state-of-the-art pseudo-spectral sea level algorithm that incorporates deformational, gravitational and rotational effects on sea level, as well as the migration of shorelines due to both local sea-level variations and changes in the extent of marine-based ice cover. If we define the effective eustatic value (EEV) as the geographically uniform rise in sea level once all marine-based sectors have been filled with water, then we find that some locations can experience a sea level rise that is ∼40 per cent higher than the EEV. This enhancement is due to the migration of water away from the zone of melting in response to the loss of gravitational attraction towards the ice sheet (load self-attraction), the expulsion of water from marine areas as these regions rebound due to the unloading, and the feedback into sea level of a contemporaneous perturbation in Earth rotation. In the WAIS case, this peak enhancement is twice the value predicted in a previous projection that did not include expulsion of water from exposed marine-sectors of the West Antarctic or rotational feedback. The peak enhancements occur over the coasts of the United States and in the Indian Ocean in the WAIS melt scenario, and over the south Atlantic and northwest Pacific in the EAIS scenario. We conclude that accurate projections of the sea level hazard associated with ongoing global warming should be based on a theory that includes the complete suite of physical processes described above.
Citation: Natalya Gomez, Jerry X. Mitrovica, Mark E. Tamisiea, Peter U. Clark, Geophys. J. Int. (2010) 180(2):623-634. doi: 10.1111/j.1365-246X.2009.04419.x.

Record of a Mid-Pleistocene depositional anomaly in West Antarctic continental margin sediments: an indicator for ice-sheet collapse? – Hillenbrand & Frederichs (2009)
Abstract: Modern global warming is likely to cause future melting of Earth’s polar ice sheets that may result in dramatic sea-level rise. A possible collapse of the West Antarctic Ice Sheet (WAIS) alone, which is considered highly vulnerable as it is mainly based below sea level, may raise global sea level by up to 5–6 m. Despite the importance of the WAIS for changes in global sea level, its response to the glacial–interglacial cycles of the Quaternary is poorly constrained. Moreover, the geological evidence for the disintegration of the WAIS at some time within the last ca. 750 kyr, possibly during Marine Isotope Stage (MIS) 11 (424–374 ka), is ambiguous. Here we present physical properties, palaeomagnetic, geochemical and clay mineralogical data from a glaciomarine sedimentary sequence that was recovered from the West Antarctic continental margin in the Amundsen Sea and spans more than the last 1 Myr. Within the sedimentary sequence, proxies for biological productivity (such as biogenic opal and the barium/aluminum ratio) and the supply of lithogenic detritus from the West Antarctic hinterland (such as ice-rafted debris and clay minerals) exhibit cyclic fluctuations in accordance with the glacial–interglacial cycles of the Quaternary. A prominent depositional anomaly spans MIS 15–MIS 13 (621–478 ka). The proxies for biological productivity and lithogenic sediment supply indicate that this interval has the characteristics of a single, prolonged interglacial period. Even though no proxy suggests environmental conditions much different from today, we conclude that, if the WAIS collapsed during the last 800 kyr, then MIS 15–MIS 13 was the most likely time period. Apparently, the duration rather than the strength of interglacial conditions was the crucial factor for the WAIS drawdown. A comparison with various marine and terrestrial climate archives from around the world corroborates that unusual environmental conditions prevailed throughout MIS 15–MIS 13. Some of these anomalies are observed in the pelagic Southern Ocean and the South Atlantic and might originate in major ice-sheet drawdown in Antarctica, but further research is required to test this hypothesis.
Citation: C.-D. Hillenbrand, G. Kuhn, T. Frederichs, Quaternary Science Reviews, Volume 28, Issues 13–14, June 2009, Pages 1147–1159, doi: 10.1016/j.quascirev.2008.12.010.

Reassessment of the Potential Sea-Level Rise from a Collapse of the West Antarctic Ice Sheet – Bamber et al. (2009) [FULL TEXT]
Abstract: Theory has suggested that the West Antarctic Ice Sheet may be inherently unstable. Recent observations lend weight to this hypothesis. We reassess the potential contribution to eustatic and regional sea level from a rapid collapse of the ice sheet and find that previous assessments have substantially overestimated its likely primary contribution. We obtain a value for the global, eustatic sea-level rise contribution of about 3.3 meters, with important regional variations. The maximum increase is concentrated along the Pacific and Atlantic seaboard of the United States, where the value is about 25% greater than the global mean, even for the case of a partial collapse.
Citation: Jonathan L. Bamber, Riccardo E. M. Riva, Bert L. A. Vermeersen, Anne M. LeBrocq, Science 15 May 2009: Vol. 324, Issue 5929, pp. 901-903, DOI: 10.1126/science.1169335.

The Sea-Level Fingerprint of West Antarctic Collapse – Mitrovica et al. (2009) [FULL TEXT]
Abstract: Recent projections of sea-level rise after a future collapse of theWest Antarctic Ice Sheet (for example, the Fourth Intergovernmental Panel on Climate Change Assessment Report) assume that meltwater will spread uniformly (that is, eustatically) across the oceans once marine-based sectors of the West Antarctic are filled. A largely neglected 1977 study predicted that peak values would be 20% higher than the eustatic in the North Pacific and 5 to 10% higher along the U.S. coastline. We show, with use of a state-of-the-art theory, that the sea-level rise in excess of the eustatic value will be two to three times higher than previously predicted for U.S. coastal sites.
Citation: Jerry X. Mitrovica, Natalya Gomez, Peter U. Clark, Science 06 Feb 2009: Vol. 323, Issue 5915, pp. 753, DOI: 10.1126/science.1166510.

Modelling West Antarctic ice sheet growth and collapse through the past five million years – Pollard & DeConto (2009) [FULL TEXT]
Abstract: The West Antarctic ice sheet (WAIS), with ice volume equivalent to ~5 m of sea level, has long been considered capable of past and future catastrophic collapse. Today, the ice sheet is fringed by vulnerable floating ice shelves that buttress the fast flow of inland ice streams. Grounding lines are several hundred metres below sea level and the bed deepens upstream, raising the prospect of runaway retreat. Projections of future WAIS behaviour have been hampered by limited understanding of past variations and their underlying forcing mechanisms. Its variation since the Last Glacial Maximum is best known, with grounding lines advancing to the continental-shelf edges around ~15 kyr ago before retreating to near-modern locations by ~3 kyr ago. Prior collapses during the warmth of the early Pliocene epoch9 and some Pleistocene interglacials have been suggested indirectly from records of sea level and deep-sea-core isotopes, and by the discovery of open-ocean diatoms in subglacial sediments. Until now, however, little direct evidence of such behaviour has been available. Here we use a combined ice sheet/ice shelf model capable of high-resolution nesting with a new treatment of grounding-line dynamics and ice-shelf buttressing to simulate Antarctic ice sheet variations over the past five million years. Modelled WAIS variations range from full glacial extents with grounding lines near the continental shelf break, intermediate states similar to modern, and brief but dramatic retreats, leaving only small, isolated ice caps on West Antarctic islands. Transitions between glacial, intermediate and collapsed states are relatively rapid, taking one to several thousand years. Our simulation is in good agreement with a new sediment record (ANDRILL AND-1B) recovered from the western Ross Sea, indicating a long-term trend from more frequently collapsed to more glaciated states, dominant 40-kyr cyclicity in the Pliocene, and major retreats at marine isotope stage 31 (approx1.07 Myr ago) and other super-interglacials.
Citation: David Pollard, Robert M. DeConto, Nature 458, 329-332 (19 March 2009) | doi:10.1038/nature07809.

West Antarctic Ice Sheet collapse – the fall and rise of a paradigm – Vaughan (2008) [FULL TEXT]
Abstract: It is now almost 30 years since John Mercer (1978) first presented the idea that climate change could eventually cause a rapid deglaciation, or “collapse,” of a large part of the West Antarctic ice sheet (WAIS), raising world sea levels by 5 m and causing untold economic and social impacts. This idea, apparently simple and scientifically plausible, created a vision of the future, sufficiently alarming that it became a paradigm for a generation of researchers and provided an icon for the green movement. Through the 1990s, however, a lack of observational evidence for ongoing retreat in WAIS and improved understanding of the complex dynamics of ice streams meant that estimates of likelihood of collapse seemed to be diminishing. In the last few years, however, satellite studies over the relatively inaccessible Amundsen Sea sector of West Antarctica have shown clear evidence of ice sheet retreat showing all the features that might have been predicted for emergent collapse. These studies are re-invigorating the paradigm, albeit in a modified form, and debate about the future stability of WAIS. Since much of WAIS appears to be unchanging, it may, no longer be reasonable to suggest there is an imminent threat of a 5-m rise in sea level resulting from complete collapse of the West Antarctic ice sheet, but there is strong evidence that the Amundsen Sea embayment is changing rapidly. This area alone, contains the potential to raise sea level by around ~1.5 m, but more importantly it seems likely that it could, alter rapidly enough, to make a significant addition to the rate of sea-level rise over coming two centuries. Furthermore, a plausible connection between contemporary climate change and the fate of the ice sheet appears to be developing. The return of the paradigm presents a dilemma for policy-makers, and establishes a renewed set of priorities for the glaciological community. In particular, we must establish whether the hypothesized instability in WAIS is real, or simply an oversimplification resulting from inadequate understanding of the feedbacks that allow ice sheets to achieve equilibrium: and whether there is any likelihood that contemporary climate change could initiate collapse.
Citation: David G. Vaughan, Climatic Change, November 2008, Volume 91, Issue 1, pp 65-79, DOI: 10.1007/s10584-008-9448-3.

Glacier Surge After Ice Shelf Collapse – De Angelis & Skvarca (2003) [FULL TEXT]
Abstract: The possibility that the West Antarctic Ice Sheet will collapse as a consequence of ice shelf disintegration has been debated for many years. This matter is of concern because such an event would imply a sudden increase in sea level. Evidence is presented here showing drastic dynamic perturbations on former tributary glaciers that fed sections of the Larsen Ice Shelf on the Antarctic Peninsula before its collapse in 1995. Satellite images and airborne surveys allowed unambiguous identification of active surging phases of Boydell, Sjögren, Edgeworth, Bombardier, and Drygalski glaciers. This discovery calls for a reconsideration of former hypotheses about the stabilizing role of ice shelves.
Citation: Hernán De Angelis, Pedro Skvarca, Science 07 Mar 2003: Vol. 299, Issue 5612, pp. 1560-1562, DOI: 10.1126/science.1077987.

Risk Estimation of Collapse of the West Antarctic Ice Sheet – Vaughan & Spouge (2002) [FULL TEXT]
Abstract: Complete collapse of the West Antarctic Ice Sheet (WAIS) would raise global sea level by around 5 m, but whether collapse is likely, or even possible, has been `glaciology’s grand unsolved problem’ for more than two decades. Collapse of WAIS may result from readjustments continuing since the last glacial maximum, or more recent climate change, but it is also possible that collapse will result from internal flow instabilities, or not occur at all in the present inter-glacial. Such complexity led the Intergovernmental Panel on Climate Change to conclude in its Second Assessment Report that `estimating the likelihood of a collapse during the next century is not yet possible’. However, a refusal by scientists to estimate the risk leaves policy-makers with no sound scientific basis on which to respond to legitimate public concerns. Here we present a discussion of the likelihood of WAIS-collapse, drawing input from an interdisciplinary panel of experts. The results help to summarise the state of scientific knowledge and uncertainty. While the overall opinion of the panel was that WAIS most likely will not collapse in the next few centuries, their uncertainty retains a 5% probability of WAIS causing sea level rise at least 10 mm/year within 200 years. Since this uncertainty reflects both the unpredictability of the physical system and the scientific uncertainty, it will undoubtedly change as a better understanding is established.
Citation: David G. Vaughan, John R. Spouge, Climatic Change, January 2002, Volume 52, Issue 1, pp 65-91, DOI: 10.1023/A:1013038920600.

No evidence for a Pleistocene collapse of the West Antarctic Ice Sheet from continental margin sediments recovered in the Amundsen Sea – Hillenbrand et al. (2002)
Abstract: Records of glaciomarine deposition recovered from the West Antarctic continental margin in the Amundsen Sea allow the reconstruction of the behaviour of the West Antarctic Ice Sheet (WAIS) in response to the natural climatic changes of the last 1.8 million years. Contents of gravel-sized and lithogenic components represent the input and redeposition of glaciogenic debris, whereas variations in the proportions of the calcareous sediment fraction reflect palaeoproductivity changes. All proxies, which are regarded as sensitive to a WAIS collapse, changed markedly during the global climatic cycles, but do not confirm a complete disintegration of the WAIS during the Pleistocene.
Citation: Claus-Dieter Hillenbrand, Dieter K. Fütterer, Hannes Grobe, Thomas Frederichs, Geo-Marine Letters, July 2002, Volume 22, Issue 2, pp 51-59, DOI: 10.1007/s00367-002-0097-7.

Pleistocene Collapse of the West Antarctic Ice Sheet – Scherer et al. (1998)
Abstract: Some glacial sediment samples recovered from beneath the West Antarctic ice sheet at ice stream B contain Quaternary diatoms and up to 108 atoms of beryllium-10 per gram. Other samples contain no Quaternary diatoms and only background levels of beryllium-10 (less than 106 atoms per gram). The occurrence of young diatoms and high concentrations of beryllium-10 beneath grounded ice indicates that the Ross Embayment was an open marine environment after a late Pleistocene collapse of the marine ice sheet.
Citation: Reed P. Scherer, Ala Aldahan, Slawek Tulaczyk, Göran Possnert, Hermann Engelhardt, Barclay Kamb, Science 03 Jul 1998: Vol. 281, Issue 5373, pp. 82-85, DOI: 10.1126/science.281.5373.82.

Active volcanism beneath the West Antarctic ice sheet and implications for ice-sheet stability – Blankenship et al. (1993)
Abstract: IT is widely understood that the collapse of the West Antarctic ice sheet (WAIS) would cause a global sea level rise of 6 m, yet there continues to be considerable debate about the detailed response of this ice sheet to climate changel–3. Because its bed is grounded well below sea level, the stability of the WAIS may depend on geologically controlled conditions at the base which are independent of climate. In particular, heat supplied to the base of the ice sheet could increase basal melting and thereby trigger ice streaming, by providing the water for a lubricating basal layer of till on which ice streams are thought to slide4,5. Ice streams act to protect the reservoir of slowly moving inland ice from exposure to oceanic degradation, thus enhancing ice-sheet stability. Here we present aerogeophysical evidence for active volcanism and associated elevated heat flow beneath the WAIS near the critical region where ice streaming begins. If this heat flow is indeed controlling ice-stream formation, then penetration of ocean waters inland of the thin hot crust of the active portion of the West Antarctic rift system could lead to the disappearance of ice streams, and possibly trigger a collapse of the inland ice reservoir.
Citation: Donald D. Blankenship, Robin E. Bell, Steven M. Hodge, John M. Brozena, John C. Behrendt, Carol A. Finn, Nature 361, 526 – 529 (11 February 1993); doi:10.1038/361526a0.

Irregular oscillations of the West Antarctic ice sheet – Macayeal (1992) [FULL TEXT]
Abstract: Model simulations of the West Antarctic ice sheet suggest that sporadic, perhaps chaotic, collapse (complete mobilization) of the ice sheet occurred throughout the past one million years. The irregular behaviour is due to the slow equilibration time of the distribution of basal till, which lubricates ice-sheet motion. This nonlinear response means that predictions of future collapse of the ice sheet in response to global warming must take into account its past history, and in particular whether the present basal till distribution predisposes the ice sheet towards rapid change.
Citation: Douglas R. MacAyeal, Nature 359, 29 – 32 (03 September 1992); doi:10.1038/359029a0.

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