It's important to note that the scientific paper that introduced MICI, Pollard, DeConto and Alley, 2016, was done to try to determine how the sea levels could have risen by 17m during the Pliocene era. While MICI may cause the Antarctic ice sheets to collapse more quickly than they would from MISI alone, it's important to understand that the conditions that could initiate MICI are at least a century off in even the worst case business as usual emissions scenarios.
https://www.sciencedirect.com/science/article/pii/S0012821X14007961
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Note that they start the model with a 3C warmer temperature than preindustrial, and a 2C warmer ocean.
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But to initiate the higher rates of sea level rise, ocean temperatures need to reach 2C above pre-industrial with global temperatures at 3C above pre-industrial. AbruptSLR, what studies support such a rapid increase in ocean temperatures to allow for initiation of MICI by the 2040s to 2050s as you often claim?
Ken,
I am going to assume that you are not trolling me, as I know virtually nothing about you, so I will briefly (in two posts) re-post information that I provided earlier in this thread in order to try to clarify both my logic and evidence for a plausible initiation of a MICI-type of collapse of most of the WAIS circa 2040:
First, I note that, Pollard, DeConto & Alley (2018) use their Antarctic Ice Sheet, AIS, model with ice-cliff and hydrofracturing failure mechanisms together with ice mélange back pressures calibrated to that currently observed for the Jakobshavn marine terminating glacier in Greenland (see the first image). Pollard et al (2018) then assumed the abrupt imposition of warm mid-Pliocene climate conditions (which roughly have a GMSTA above pre-industrial of 2C and ocean water temperatures beneath the ice of key AIS marine glaciers comparable to those found by Bronselaer et al (2018) after 2040, as shown in the second image).
David Pollard, Robert M. DeConto, Richard B. Alley (13 March 2018), "A continuum model of ice mélange and its role during retreat of the Antarctic Ice Sheet", Geosci. Model Dev. Discuss.,
https://doi.org/10.5194/gmd-2018-28https://www.geosci-model-dev-discuss.net/gmd-2018-28/gmd-2018-28.pdf&
Bronselaer, B. et al. (2018) Change in future climate due to Antarctic meltwater, Nature, doi:s41586-018-0712-z
https://www.nature.com/articles/s41586-018-0712-z&
Second, based on my interpretation of the third & fourth linked references, I suspect that local ice cliff failures near the base of the Thwaites Ice Tongue (see the third image of a profile through this area) may begin sometime 2025 and 2033, and may be initiated due to influences from Super El Nino events in that timeframe. The fourth linked reference confirms that the ENSO is directly associated with surface air temperatures across the interior of West Antarctica, and I note that the frequency of extreme El Nino events is projected to double when the global mean surface temp. anom. gets to 1.5C:
Yu, H., Rignot, E., Morlighem, M., & Seroussi, H. (2017). Iceberg calving of Thwaites Glacier, West Antarctica: full-Stokes modeling combined with linear elastic fracture mechanics. The Cryosphere, 11(3), 1283, doi:10.5194/tc-11-1283-2017
https://www.the-cryosphere.net/11/1283/2017/tc-11-1283-2017.pdfhttps://www.the-cryosphere.net/11/1283/2017/tc-11-1283-2017-assets.html&
Kyle R. Clem, James A. Renwick, and James McGregor (2017), "Large-Scale Forcing of the Amundsen Sea Low and its Influence on Sea Ice and West Antarctic Temperature", Journal of Climate,
https://doi.org/10.1175/JCLI-D-16-0891.1http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0891.1?utm_content=buffer2e94d&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer&
Finally, the fifth and sixth linked abstracts from the WAIS 2018 workshop clearly indicate that after GMSTA reaches about 2C above pre-industrial, there is significant risk of a major MICI event initiating.
Title: "Climatic Thresholds for WAIS Retreat: Onset of Widespread Ice Shelf Hydrofracturing and Ice Cliff Calving in a Warming World", by Rob DeConto, David Pollard, Knut Christianson, Richard B. Alley & Byron R. Parizek
https://www.waisworkshop.org/sites/waisworkshop.org/files/webform/2018/abstracts/WAIS2018.pdfAbstract: "The loss or thinning of buttressing ice shelves and accompanying changes in grounding zone stress balance are commonly implicated as the primary trigger for grounding line retreat, such as that observed in Amundsen Sea outlet glaciers today. Ice-shelf thinning is mostly attributed to the presence of warm ocean waters beneath the shelves. However, climate model projections indicate that summer air temperatures could soon exceed the threshold for widespread meltwater production on ice-shelf surfaces. This has serious implications for the future stability of ice shelves, because they are vulnerable to the propagation of water-induced flexural stresses and water-aided crevasse penetration, often referred to as ‘hydrofracturing’. Once initiated, the rate of shelf loss through hydrofracturing can far exceed that caused by sub-surface oceanic melting, and could result in the complete loss of some buttressing ice shelves, with marine-terminating grounding lines suddenly becoming calving ice fronts. In places where those exposed (unbuttressed) ice fronts are thick enough (>900m), deviatoric stresses can exceed the strength of the ice, and the cliff face will fail through brittle processes leading to rapid calving like that seen in analogous settings on Greenland such as Jakobshavn and Helheim.
Here we explore the implications of hydrofacturing and subsequent ice-cliff collapse in a warming climate, by parameterizing these processes in a hybrid ice sheet-shelf model. Model physical parameters controlling sensitivity of surface crevasse penetration to meltwater and ice-cliff calving rate (a function of cliff height above the stress-balance threshold for brittle failure) are based on observations of calving in analogous settings, and model performance relative to observed mass loss and paleo sea-level estimates. Including these processes and exploring a range of atmospheric and ocean climate forcing scenarios, we find the potential for major future WAIS retreat if global mean temperature rises more than ~2ºC above preindustrial. We also find that strict mitigation, with net negative carbon emissions initiated ~2060 substantially reduces the magnitude and rate of long-term WAIS retreat. In simulations following a ‘worst case’ RCP8.5 scenario, the model produces rates of equivalent sea level rise that would be measured in cm per year by the end of this century. Importantly, parameterized Antarctic calving rates at thick ice fronts are not allowed to exceed those observed in Greenland today. This may be an overly conservative assumption, considering the very different spatial scales and physical settings of Antarctic outlet glaciers like Thwaites. Clearly the potential for mechanical/brittle processes to deliver ice to the ocean, in addition to viscous and basal processes, needs to be better constrained through more complete, physically based model representations of calving."
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Title: "Across the Great Divide: The Flow-to-Fracture Transition and the Future of the West Antarctic Ice Sheet", by Richard B. Alley, Byron R. Parizek, Knut Christianson, Robert M. DeConto, David Pollard and Sridhar Anandakrishna
https://www.waisworkshop.org/sites/waisworkshop.org/files/webform/2018/abstracts/Alley_R.pdfAbstract: "Physical understanding, modeling, and available data indicate that sufficient warming and retreat of Thwaites Glacier, West Antarctica will remove its ice shelf and generate a calving cliff taller than any extant calving fronts, and that beyond some threshold this will generate faster retreat than any now observed. Persistent ice shelves are restricted to cold environments. Ice-shelf removal has been observed in response to atmospheric warming, with an important role for meltwater wedging open crevasses, and in response to oceanic warming, by mechanisms that are not fully characterized. Some marine-terminating glaciers lacking ice shelves “calve” from cliffs that are grounded at sea level or in relatively shallow water, but more-vigorous flows advance until the ice is close to flotation before calving. For these vigorous flows, a calving event shifts the ice front to a position that is slightly too thick to float, and generates a stress imbalance that causes the ice front to flow faster and thin to flotation, followed by another calving event; the rate of retreat thus is controlled by ice flow even though the retreat is achieved by fracture. Taller cliffs generate higher stresses, however, favoring fracture over flow. Deformational processes are often written as power-law functions of stress, with ice deformation increasing as approximately the third power of stress, but subcritical crack growth as roughly the thirtieth power, accelerating to elastic-wave speeds with full failure. Physical understanding, models based on this understanding, and the limited available data agree that, above some threshold height, brittle processes will become rate-limiting, generating faster calving at a rate that is not well known but could be very fast. Subaerial slumping followed by basal-crevasse growth of the unloaded ice is the most-likely path to this rapid calving. This threshold height is probably not too much greater than the tallest modern cliffs, which are roughly 100 m."
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For those who do not understand the implications of Alley et al. (2018)'s comment that ice deformation is a power-function of stress, I attach the fourth image that translates this underlying ice-cliff behavior into terms of calving rate (deformation) per year for various values of marine glacier freeboard (ice face height minus water depth) and relative water depth (which combine determine the primary stresses near the ice cliff face).