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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3900 on: November 19, 2020, 09:44:33 PM »
For what it is worth, an abrupt slowdown of the MOC due to a freshwater hosing event (or a chain of events) would increase hypoxia conditions in large portion of the ocean.  In this regard, I wonder whether future SSTA values may be higher that projected due to reduced biological mixing of the upper layers of the ocean due to such possible increased hypoxia conditions in many regions (see the linked reference about current trends of hypoxia conditions):

Deutsch, C., Penn, J.L. & Seibel, B. Metabolic trait diversity shapes marine biogeography. Nature 585, 557–562 (2020). https://doi.org/10.1038/s41586-020-2721-y

https://www.nature.com/articles/s41586-020-2721-y

Abstract
Climate and physiology shape biogeography, yet the range limits of species can rarely be ascribed to the quantitative traits of organisms. Here we evaluate whether the geographical range boundaries of species coincide with ecophysiological limits to acquisition of aerobic energy for a global cross-section of the biodiversity of marine animals. We observe a tight correlation between the metabolic rate and the efficacy of oxygen supply, and between the temperature sensitivities of these traits, which suggests that marine animals are under strong selection for the tolerance of low O2 (hypoxia). The breadth of the resulting physiological tolerances of marine animals predicts a variety of geographical niches—from the tropics to high latitudes and from shallow to deep water—which better align with species distributions than do models based on either temperature or oxygen alone. For all studied species, thermal and hypoxic limits are substantially reduced by the energetic demands of ecological activity, a trait that varies similarly among marine and terrestrial taxa. Active temperature-dependent hypoxia thus links the biogeography of diverse marine species to fundamental energetic requirements that are shared across the animal kingdom.

Edit: I note that the current poleward migration of marine life with likely further accelerate the increase of SSTA in the equatorial oceans with continued global warming.
« Last Edit: November 20, 2020, 10:32:10 AM by AbruptSLR »
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3901 on: November 20, 2020, 03:47:29 PM »
Consensus climate scientists has noted that the Thwaites, and Pine Island, Glacier catchment basins respectively could contribute about 2-ft and 1-ft to sea level rise.  However, these facts distract from the fact that if a MICI-type of collapse begins in the Thwaites Glacier gateway, it will not stop at the limits of the Thwaites Glacier catchment basin but will continue on into the backsides of all of the adjoining catchment basins (see the attached image) right up to the Transantarctic Mountain Range, including into the PIG catchment basin.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3902 on: November 20, 2020, 04:00:11 PM »
Also, I note that the recent acceleration of the ice velocity for the SWT Glacier is continuing to degrade the adjoining section of the Pine Island Southern Ice Shelf, PISIS, as shown in the first attached image from the Sentinel-2 satellite on November 17, 2020; while the second and third images show that when the PISIS no longer restrains the SWT Glacial ice velocity, the eastern shear margin of the Thwaites Glacier will offer less restraint and the ice velocities of the Thwaites Glacier will accelerate.
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Stephan

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3903 on: November 20, 2020, 05:37:07 PM »
I just tried to add the actual calving position into your second picture to demonstrate that the connection between SWT (and, partly SIS) with the PIIS got lost in the last years.
No guarantee for the correctness of the calving position (white line in the upper picture).

See attached picture, may need a click to enlarge.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3904 on: November 21, 2020, 01:17:43 AM »
I just tried to add the actual calving position into your second picture to demonstrate that the connection between SWT (and, partly SIS) with the PIIS got lost in the last years.
No guarantee for the correctness of the calving position (white line in the upper picture).

See attached picture, may need a click to enlarge.

Stephan,

Thanks for helping to orientate readers.  At the current rate that both the SWT ice shelf and the PIIS are calving, I believe that we will likely see ice mass loss accelerated marked for both the PIG and the Thwaites Glacier sometime between 2035 and 2040.

Best,
ASLR
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3905 on: November 21, 2020, 03:42:37 PM »
The linked SciAm article discusses many of the uncertainties associated with the consequences of waking up hibernating Arctic microbes with continued global warming, and here I remind readers that greater uncertainty mean greater risk:

Title: "Deep Frozen Arctic Microbes Are Waking Up"

Deep Frozen Arctic Microbes Are Waking Up - Scientific American

Extract: "Thawing permafrost is releasing microorganisms, with consequences that are still largely unknown.

Some of these microbes are known to scientists. Methanogenic Archaea, for example metabolize soil carbon to release methane, a potent greenhouse gas. Other permafrost microbes (methanotrophs) consume methane. The balance between these microbes plays a critical role in determining future climate warming."
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kassy

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Þetta minnismerki er til vitnis um að við vitum hvað er að gerast og hvað þarf að gera. Aðeins þú veist hvort við gerðum eitthvað.

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3907 on: November 22, 2020, 02:42:56 AM »
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ShortBrutishNasty

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3908 on: November 23, 2020, 03:07:48 AM »
ASLR wrote:  "This linked reference indicates that it is likely that [snipped].  This is not good news."

Repetitive much?   :-\ ::)

On a serious note, I understand ice doesn't like to be stacked more than about 100 meters high.
 How quickly would a MICI-type collapse be detected?

A) Is it subject to seismic measurement?

B) Or do satellite photos reveal it in a matter of days?

C) Or does some guy in Biscayne Florida go down to his dock in the morning and notice he's got an extra 1.3mm on his tide gauge?

Thanks again for your undying efforts.

SBN
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sidd

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3909 on: November 23, 2020, 05:23:55 AM »
Re: I understand ice doesn't like to be stacked more than about 100 meters

Technically, 100 meter freeboard on exposed cliff face. Slitely less for non marine stack of ice. You can have a mile thick ice sheet sloping down to a  hundred meter face.

A) yes
B) yes
C) no

I will let ASLR fill in the caveats. But it might be more useful if one were to search the previous posts on this thread and others. For example, that 100m number comes from a Bassis and Walker paper in 2011,
doi:10.1098/rspa.2011.0422

sidd
« Last Edit: November 23, 2020, 06:16:18 AM by sidd »

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3910 on: November 23, 2020, 03:10:23 PM »
While the linked reference is a couple of years old, it is still a good reminder of the threat that the projected abrupt emissions of methane and CO2 from thermokarst lakes represent as an accelerant (by a factor of two) to permafrost carbon feedback model projections of radiative forcing from circumpolar permafrost-soil carbon fluxes this century.

Walter Anthony, K., Schneider von Deimling, T., Nitze, I. et al. 21st-century modeled permafrost carbon emissions accelerated by abrupt thaw beneath lakes. Nat Commun 9, 3262 (2018). https://doi.org/10.1038/s41467-018-05738-9

21st-century modeled permafrost carbon emissions accelerated by abrupt thaw beneath lakes | Nature Communications

Abstract: "Permafrost carbon feedback (PCF) modeling has focused on gradual thaw of near-surface permafrost leading to enhanced carbon dioxide and methane emissions that accelerate global climate warming. These state-of-the-art land models have yet to incorporate deeper, abrupt thaw in the PCF. Here we use model data, supported by field observations, radiocarbon dating, and remote sensing, to show that methane and carbon dioxide emissions from abrupt thaw beneath thermokarst lakes will more than double radiative forcing from circumpolar permafrost-soil carbon fluxes this century. Abrupt thaw lake emissions are similar under moderate and high representative concentration pathways (RCP4.5 and RCP8.5), but their relative contribution to the PCF is much larger under the moderate warming scenario. Abrupt thaw accelerates mobilization of deeply frozen, ancient carbon, increasing 14C-depleted permafrost soil carbon emissions by ~125–190% compared to gradual thaw alone. These findings demonstrate the need to incorporate abrupt thaw processes in earth system models for more comprehensive projection of the PCF this century."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3911 on: November 23, 2020, 03:57:31 PM »
Re: I understand ice doesn't like to be stacked more than about 100 meters

Technically, 100 meter freeboard on exposed cliff face. Slitely less for non marine stack of ice. You can have a mile thick ice sheet sloping down to a  hundred meter face.

A) yes
B) yes
C) no

I will let ASLR fill in the caveats. But it might be more useful if one were to search the previous posts on this thread and others. For example, that 100m number comes from a Bassis and Walker paper in 2011,
doi:10.1098/rspa.2011.0422

sidd

If anyone is interested in the numerous caveats on the topic of different combinations of key parameters necessary to trigger an MICI type of collapse then I recommend searching for "WAIS Workshop 2020" and for Reply #3821 watch Session 6 starting at 1:30 for the Bassis findings with numerous caveats.  That said, when considering all of Bassis' numerous caveats it remains clear to me that the Thwaites Gateway near the base of the Thwaites Ice Tongue is likely poised to initiate an MICI-type of collapse of the entire Byrd Subglacial Basin ,BSB, (& beyond) likely sometime between 2030 and 2040 (which could well raise sea level by over 1m in less than a year).   Reasons to single out the Thwaites Gateway include:

1. As shown in the first attached image from Milillo et al 2019 (Fig 1, panels D&F) the southern side of the subglacial cavity in this gateway already has a ~140m high ice face freeboard (hf) that is buttressed by icebergs floating over the subglacial cavity with the icebergs pinned by lightly ground downstream ice (that is subject to becoming ungrounded by 2030 2040 due both to thinning of the ice at the base of the Thwaites Ice Tongue due to a likely acceleration of the ice velocities when the chain of upstream subglacial lakes drain [projected to occur circa 2035, & see the second and third attached images] and due to warm modified CDW melting the grounded ice perimeter from below, particularly during a Super El Nino events [projected to occur circa 2035-36]).

2. As the Thwaites Gateway is about 50km wide, there is relatively little lateral restraint to limit MICI-behavior as I note that Jakobshavn Glacier already exhibits ice cliff failures but only very limited MICI-behavior because its ice face is currently positioned on a positive bed slope and the ice cliff propagation is restrained by lateral restraint from the sides of the relatively narrow fjord that Jakobshavn is located in.

3. Bassis (WAIS Workshop 2020) finds that the dominant factor/parameter for sustaining MICI-propagation upstream is the rate of increase of ice thickness upstream of the bare ice cliff face, and the fourth attached cartoon illustrates that there is both a steep negative bed slope upstream of this area as well as a relatively rapid increase in ice surface elevation upstream of this Thwaites Gateway area.
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Tom_Mazanec

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3912 on: November 23, 2020, 05:02:23 PM »
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3913 on: November 23, 2020, 05:14:54 PM »
In note that in the Sinclair video in the linked Skeptical science article about Thwaites Glacier all of the model projections that these climate scientists discuss only consider MISI behavior (with consensus values of climate sensitivity) and their only consideration of a MICI-type of behavior is in the colorfully/vague discussion of a potential "Runaway Positive Feedback".  We should all remember that with regard to the risks of abrupt sea level rise and abrupt climate change that uncertainty is not our friend and that true 'hard science' embraces deep uncertainty and does not discount it; while consensus climate science does discount fat, right-tail climate risks in order to pretend to be 'hard' science.

Title: "Can shearing of Thwaites glacier slow or stop if humans control greenhouse gas emissions?"

Can shearing of Thwaites glacier slow or stop if humans control greenhouse gas emissions? (skepticalscience.com)

Extract: "Let’s face it: Thwaites has the makings of being the lead role in an upcoming cli-fi thriller, one strong on emotion and drama but lacking something when it comes to hard science."

Edit: See the following active link.

https://skepticalscience.com//shearing-thwaites-slow-or-stop.html
« Last Edit: November 23, 2020, 05:32:02 PM by AbruptSLR »
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Tom_Mazanec

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3914 on: November 23, 2020, 07:53:37 PM »
Quote
hat said, when considering all of Bassis' numerous caveats it remains clear to me that the Thwaites Gateway near the base of the Thwaites Ice Tongue is likely poised to initiate an MICI-type of collapse of the entire Byrd Subglacial Basin ,BSB, (& beyond) likely sometime between 2030 and 2040 (which could well raise sea level by over 1m in less than a year).   
AbruptSLR, assume for the sake of discussion you are wrong about the timing and the year is actually 2021.
How will that affect, for example, me in Twinsburg, Ohio?
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3915 on: November 23, 2020, 11:20:10 PM »
Quote
hat said, when considering all of Bassis' numerous caveats it remains clear to me that the Thwaites Gateway near the base of the Thwaites Ice Tongue is likely poised to initiate an MICI-type of collapse of the entire Byrd Subglacial Basin ,BSB, (& beyond) likely sometime between 2030 and 2040 (which could well raise sea level by over 1m in less than a year).   
AbruptSLR, assume for the sake of discussion you are wrong about the timing and the year is actually 2021.
How will that affect, for example, me in Twinsburg, Ohio?

Tom,

There is no way for me to give you a precise answer to your question so I will just throw-out the following hypothetical possible impact on you assuming that an MICI-type of collapse of the Thwaites Glacier began in January 2021, and increase eustatic sea level by 1m by January 2022, with the BSB emptied of glacial ice.

1. The MICI-type of collapse would likely continue beyond the BSB contributing about a total 3.6m of SLR over the subsequent 10 to 15 years from the WAIS.

2. This would likely lead to an abrupt slowing of the MOC no later than 2031; which would likely trigger very large Hurricanes (say Cat 6) soon thereafter as well as large changes in the ENSO patterns that would impact rainfall in Ohio; which would likely produce local rain related flood evens.  Also, ECS would likely increase rapidly, and might likely trigger a reversal of the Beaufort Gyre; which in addition to further slowing the MOC would also trigger an abrupt reduction in boreal summertime Arctic sea ice extent.

3. The world economic system would likely fall into a Great Depression; which would likely trigger warfare around the world within decades.

Many other impacts are likely such as food shortages, etc. but I need to go now.

Best,
ASLR
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Tom_Mazanec

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3916 on: Today at 12:33:49 AM »
Just think how many million SLR refugees there would be in America.
Would some go to Ohio?
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Ken Feldman

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3917 on: Today at 01:13:46 AM »
Recently published research from a team including Robert Deconto and David Pollard indicates that the timeframes for the onset of Marine Ice Cliff Instability (MICI) were 25 years too early in their 2015 and 2016 papers.  And they acknowledge that MICI is still speculative, not required for paleo-climate ice sheet loss rates, and may not occur in Antarctica if ice shelf loss isn't instantaneous.

https://agupubs.onlinelibrary.wiley.com/doi/pdfdirect/10.1029/2019JF005418

Quote
Gilford, D. M., Ashe, E. L., DeConto, R. M., Kopp, R. E., Pollard, D., & Rovere, A. (2020). Could the Last Interglacial constrain projections of future Antarctic ice mass loss and sea-level rise?. Journal of Geophysical Research: Earth Surface, 125, e2019JF005418.

Accepted article online 5 OCT 2020

Quote
Abstract
Previous studies have interpreted Last Interglacial (LIG;∼129–116ka) sea-level estimates in multiple different ways to calibrate projections of future Antarctic ice-sheet (AIS) mass loss and associated sea-level rise. This study systematically explores the extent to which LIG constraints could inform future Antarctic contributions to sea-level rise. We develop a Gaussian process emulator of an ice-sheet model to produce continuous probabilistic projections of Antarctic sea-level contributions over the LIG and a future high-emissions scenario. We use a Bayesian approach conditioning emulator projections on a set of LIG constraints to find associated likelihoods of model parameterizations. LIG estimates inform both the probability of past and future ice-sheet instabilities and projections of future sea-level rise through 2150.  Although best-available LIG estimates do not meaningfully constrain Antarctic mass loss projections or physical processes until 2060, they become increasingly informative over the next 130years. Uncertainties of up to 50cm remain in future projections even if LIG Antarctic mass loss is precisely known (±5cm), indicating that there is a limit to how informative the LIG could be for ice-sheet model future projections.  The efficacy of LIG constraints on Antarctic mass loss also depends on assumptions about the Greenland ice sheet and LIG sea-level chronology. However, improved field measurements and understanding of LIG sea levels still have potential to improve future sea-level projections, highlighting the importance of continued observational efforts.

Quote
MICI is not well understood and is difficult to parameterize. While it has not yet been observed in Antarctica, there is some modern evidence consistent with cliff instability, such as the documented calving events of Greenland glaciers (DeConto & Pollard, 2016; Parizek et al., 2019). Newly discovered iceberg-keel plough marks also provide evidence for MICI in Pine Island Bay in the early Holocene,∼12ka (Wise et al., 2017).  However, a recent reanalysis of DeConto and Pollard (2016) showed that MICI is not well constrained and is unnecessary for ice-sheet model projections to be consistent with modern and paleoclimate estimates of AIS mass loss (Edwards et al., 2019). Clerc et al. (2019) examined how ice cliffs deform following removal of their buttressing ice shelves. They found that∼90-m-tall ice cliffs would have to be lost near instantaneously after shelf collapse to trigger MICI—on longer timescales viscous relaxation dominates the response. Furthermore, Olsen and Nettles (2019) found that seismic measurements of the aforementioned Greenland glaciers were not indicative of subaerial ice-cliff failure expected with MICI. These findings cannot preclude MICI as a primary mass loss mechanism in Antarctica, but they demonstrate the paucity of observations to constrain this process.

Quote
Future simulations of AIS mass loss under RCP8.5 forcing are very similar across the ensemble in the early21st century; 158 of 196 simulations have loss rates within 1 standard deviation of IMBIE2 observed rates over 1992–2017 (15–46mm/yr IMBIE-Team, 2018). In∼2060 ice discharge dramatically accelerates among ensemble members with higher CLIFVMAX values, and simulations markedly diverge. Across the simulations ice loss continues to accelerate through 2100 and well into the 22nd century; 86% of the simulated peak loss rates occur after 2130. By 2150, the ensemble's median rate of sea-level equivalent mass loss is 54mm/yr, and the median AIS sea-level contribution is 2.3m. Mean RCP8.5 ensemble AIS sea-level contributions are 42cm in 2100 and 2.3m in 2150. These values are lower than DeConto and Pollard (2016) large-ensemble projections (without bias corrections and with default model parameters, see their Extended Data Table 1)in both 2100 (77cm) and 2150 (2.9m). Differences are largely due to improved model synchronicity in atmospheric forcing, which slows the onset of surface meltwater production and ice-shelf hydrofracturing by∼25 years compared to DeConto and Pollard (2016).

Note that they are still running simulations under RCP 8.5, which has become increasingly unrealistic as the energy transition has accelerated since it was shown we were closer to RCP 4.5 last year.  Current atmospheric concentrations of Carbon Dioxide are consistent with RCP 2.6 and methane concentrations are around RCP 4.5.  See the graphs at the following links:

Carbon Dioxide 2020 RCP 2.6 is 412.1 ppm, RCP 8.5 is 415.8 ppm, 2019 annual average (globally) was 409.85.
https://forum.arctic-sea-ice.net/index.php/topic,2994.msg288256.html#msg288256

Methane 2020 RCP 4.5 is 1801 ppb, RCP 8.5 is 1924 ppb, 2019 annual average was 1866.55:
https://forum.arctic-sea-ice.net/index.php/topic,2994.msg288258.html#msg288258

And future fossil fuel emissions assume very little renewable energy and, for RCP 8.5, continued increases in coal consumption.  (Global coal consumption peaked in 2013 and looks to be headed to zero by 2050).




AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3918 on: Today at 02:03:47 AM »
Recently published research from a team including Robert Deconto and David Pollard indicates that the timeframes for the onset of Marine Ice Cliff Instability (MICI) were 25 years too early in their 2015 and 2016 papers.  And they acknowledge that MICI is still speculative, not required for paleo-climate ice sheet loss rates, and may not occur in Antarctica if ice shelf loss isn't instantaneous.

https://agupubs.onlinelibrary.wiley.com/doi/pdfdirect/10.1029/2019JF005418

Quote
Gilford, D. M., Ashe, E. L., DeConto, R. M., Kopp, R. E., Pollard, D., & Rovere, A. (2020). Could the Last Interglacial constrain projections of future Antarctic ice mass loss and sea-level rise?. Journal of Geophysical Research: Earth Surface, 125, e2019JF005418.

Accepted article online 5 OCT 2020
...

Ken,

Thank you for the linked reference; and there is a lot of deep uncertainty about when/whether an MICI-type of collapse might be initiated in the WAIS; nevertheless, the attached image from DeConto et al. 2020 indicates that if/when an MICI-type of collapse is trigger then it will most likely proceed very quickly (on the order of years not decades) to contribute multiple meters of SLR.

Best,
ASLR
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3919 on: Today at 02:05:38 AM »
It says Model year (kyr).
Doesn't that mean millennia?
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3920 on: Today at 08:48:33 AM »
TM,
The confusion results from the fact that ASLR published only half of the figure, the half referring to the LIG simulation and forgetting the half relating to the RCP8.5 scenario. Below is the full figure

Click to enlarge

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3921 on: Today at 12:20:11 PM »
Thanks, paolo.
And I apologize, AbruptSLR.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3922 on: Today at 02:17:47 PM »
It says Model year (kyr).
Doesn't that mean millennia?

Yes, but as paolo points out it also says LIG simulation with very low radiative forcing.

Edit: To add some clarity to the second panel of the image that paolo posted, it assumes that in order to obtain a bare ice cliff face their model assumes that the regional air temperature must have warmed sufficiently for hydrofracturing to occur to remove the associated ice shelves that were previously buttressing the ice cliff face.  First, this is a very conservative assumption as the ice shelves in the Amundsen Sea Embayment are currently rapidly degrading without any hydrofracturing and second, their model assumes CMIP5 values for climate sensitivity which are much lower than the wolfpack values from CMIP6.  This explains why the second panel in the image that paolo posted assumes that it will take many decades from now before MICI-type mechanisms occur.  However, the attached image shows that ice cliff rates of retreat follow the power law and can reach rates of well over 100 km per year for freeboard and relative water depth conditions associated with the Thwaites Glacier.
« Last Edit: Today at 02:40:53 PM by AbruptSLR »
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