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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: November 24, 2020, 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: November 24, 2020, 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: November 24, 2020, 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: November 24, 2020, 02:05:38 AM »
It says Model year (kyr).
Doesn't that mean millennia?
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paolo

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3920 on: November 24, 2020, 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: November 24, 2020, 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: November 24, 2020, 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: November 24, 2020, 02:40:53 PM by AbruptSLR »
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Ken Feldman

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3923 on: November 24, 2020, 06:20:25 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.

AbruptSLR,

DeConto, Pollard and Alley 2015 explicitly states that hydrofracturing by surface water is required to initiate MICI.

https://www.sciencedirect.com/science/article/pii/S0012821X14007961

Quote
Potential Antarctic Ice Sheet retreat driven by hydrofracturing and ice cliff failure
DavidPollard, Robert M.DeConto, Richard B.Alley

Abstract

Geological data indicate that global mean sea level has fluctuated on 103 to 106 yr time scales during the last ∼25 million years, at times reaching 20 m or more above modern. If correct, this implies substantial variations in the size of the East Antarctic Ice Sheet (EAIS). However, most climate and ice sheet models have not been able to simulate significant EAIS retreat from continental size, given that atmospheric CO2 levels were relatively low throughout this period. Here, we use a continental ice sheet model to show that mechanisms based on recent observations and analysis have the potential to resolve this model–data conflict. In response to atmospheric and ocean temperatures typical of past warm periods, floating ice shelves may be drastically reduced or removed completely by increased oceanic melting, and by hydrofracturing due to surface melt draining into crevasses. Ice at deep grounding lines may be weakened by hydrofracturing and reduced buttressing, and may fail structurally if stresses exceed the ice yield strength, producing rapid retreat. Incorporating these mechanisms in our ice-sheet model accelerates the expected collapse of the West Antarctic Ice Sheet to decadal time scales, and also causes retreat into major East Antarctic subglacial basins, producing ∼17 m global sea-level rise within a few thousand years. The mechanisms are highly parameterized and should be tested by further process studies. But if accurate, they offer one explanation for past sea-level high stands, and suggest that Antarctica may be more vulnerable to warm climates than in most previous studies.

Quote
To trigger cliff failure, floating ice must first be removed, either entirely or at least enough to greatly reduce back pressure at the grounding line. Even very rapid melting from oceanic heat is often slower than ice-stream velocities, and is usually insufficient on its own to sufficiently reduce the major ice shelves in our model. We apply an additional mechanism accounting for increased ice-shelf calving due to hydrofracture by surface melt and rainfall draining into crevasses (Nick et al., 2013). Surface melting has been strongly implicated in the recent breakup of the Larsen B ice shelf (Scambos et al., 2003). In our warm-climate scenarios, surface melting increases calving considerably around the Antarctic margins. Our treatment of calving including hydrofracturing is described in Appendix B.

Quote
Today, cliff failure in Antarctica is prevented by (1) grounding lines at basin sills not being deep enough (<~800m), (2) insufficient surface melt to cause hydrofracturing and weakening at the grounding line, and/or (3) buttressing at the grounding lines by major ice shelves. In our warm-climate simulations, a combination of increased sub-ice ocean melt (reducing buttressing) and hydrofracturing (reducing buttressing and weakening grounding-line columns) leads to cliff failure in the major basins (Fig. 2). For deep basins, this sequence proceeds catastrophically, until either (i) surface melting and hydrofracturing lessen, strengthening ice columns at the grounding line, (ii) normal deformational ice flow across the grounding line exceeds calving and ocean melting, so that a substantial ice shelf re-forms and provides buttressing at the grounding line, or (iii) the grounding line retreats to the inner part of the basin with beds shallower than and little ice above flotation.

To initiate MICI in their model, they have to apply a warm climate.  They do this by initiating the model with current conditions and then adding +2 degrees C to the ocean temperatures.

Quote
To investigate the impact of the cliff-failure and melt-driven hydrofracture mechanisms, the ice-sheet model is run forward in time, forced by climate representative of past warm periods. Simulations are started from a previous spin-up of modern Antarctica using observed climatology. An instantaneous change to a warmer climate is applied, broadly representative of a warm Pliocene period. The past warm atmospheric climate is obtained from the RegCM3 Regional Climate Model (Pal et al., 2007) applied over Antarctica with some physical adaptations for polar regions, and with 400 ppmv CO2 and an orbit yielding particularly strong austral summers (DeConto et al., 2012). Detailed simulation of ocean warming beneath Antarctic ice shelves is currently not feasible on these time scales, so a simple uniform increment of+2 [degrees] C is added to modern observed ocean temperatures, broadly consistent with circum-Antarctic warming in Pliocene paleo-oceanic reconstructions (Dowsett et al., 2009). The climate forcings are described in more detail in Supplementary Material Section S.3.

Quote
The individual contributions of the new mechanisms can be assessed by re-running the simulation with cliff failure and/or melt-driven hydrofracturing turned on or off, as shown by the sea-level curves in Fig. 4, and maps in Fig. 5. With both mechanisms turned off (Fig. 5a), the model functions much as in earlier work (Pollard and DeConto, 2009). As expected, West Antarctica undergoes major collapse driven primarily by increased sub-ice melt from the +2 [degree] C ocean warming, causing reduced buttressing at the major WAIS grounding lines, and leading to classic marine instability (MISI) into the deepening interior beds (Weertman, 1974, Schoof, 2007). The time scale of this retreat is several hundred to a thousand years (Pollard and DeConto, 2009, and Fig. 4, cyan curve). There is very minor grounding-line recession into the outer Slessor–Bailey troughs and Lambert Graben due to ice-shelf thinning and reduced buttressing, but the retreat stops, presumably due to greater side-drag and funneling of ice compared to the wider West Antarctic grounding zones. Similar minor retreat occurs in a few other East Antarctic locations, but nothing on the scale of the retreat in Fig. 3. The same is true if cliff failure is active alone (without hydrofracturing, Fig. 5b), because ice shelves still exist, which buttress grounding lines and prevent cliff failure. With hydrofracturing activated alone (without cliff failure, Fig. 5c), the drastic removal of floating ice further reduces buttressing, allowing MISI to produce partial retreat into the Wilkes and Recovery–Slessor–Bailey basins, but not into the shallower Aurora. Full collapse into all basins, and greatly accelerated collapse in West Antarctica, requires the combination of melt-driven hydrofracturing and cliff failure (Fig. 5d). More analysis on the roles of the individual retreat mechanisms, and other sensitivities and basic model tests, are included in Supplementary Material Sections S.4–S.7.

Quote
To investigate the impact of the cliff-failure and melt-driven hydrofracture mechanisms, the ice-sheet model is run forward in time, forced by climate representative of past warm periods. Simulations are started from a previous spin-up of modern Antarctica using observed climatology. An instantaneous change to a warmer climate is applied, broadly representative of a warm Pliocene period. The past warm atmospheric climate is obtained from the RegCM3 Regional Climate Model (Pal et al., 2007) applied over Antarctica with some physical adaptations for polar regions, and with 400 ppmv CO2 and an orbit yielding particularly strong austral summers (DeConto et al., 2012). Detailed simulation of ocean warming beneath Antarctic ice shelves is currently not feasible on these time scales, so a simple uniform increment of is added to modern observed ocean temperatures, broadly consistent with circum-Antarctic warming in Pliocene paleo-oceanic reconstructions (Dowsett et al., 2009). The climate forcings are described in more detail in Supplementary Material Section S.3.


Quote
Fig. 3. Ice distributions in a warm-climate simulation. The simulation starts from modern conditions, with a step-function change to a generic past warm climate applied at year 0. Atmospheric temperatures and precipitation are from a Regional Climate Model simulation with hot austral summer orbit, CO2 = 400 ppmv, and ocean temperatures are increased uniformly by 2 °C above modern. Color scale: Grounded ice elevations, m. Pink scale: floating ice thicknesses, m. The run is initialized from a previous simulation equilibrated to modern climate (panel (a), 0 yr). Both new mechanisms (cliff failure and melt-driven hydrofracturing) are active.


Quote
Fig. 4. Global mean equivalent sea level rise in warm-climate simulations. Time series of global mean sea level rise above modern are shown, implied by reduced Antarctic ice volumes. The calculation takes into account the lesser effect of melting ice that is originally grounded below sea level. Cyan: with neither cliff failure nor melt-driven hydrofracturing active. Blue: with cliff failure active. Green: with melt-driven hydrofracturing active. Red: with both these mechanisms active. Geographic ice distributions for the latter run are shown in Fig. 3, and for the other runs in Fig. 5.
« Last Edit: November 24, 2020, 06:37:28 PM by Ken Feldman »

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3924 on: November 24, 2020, 06:46:16 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.

AbruptSLR,

DeConto, Pollard and Alley 2015 explicitly states that hydrofracturing by surface water is required to initiate MICI.

https://www.sciencedirect.com/science/article/pii/S0012821X14007961

Quote
Potential Antarctic Ice Sheet retreat driven by hydrofracturing and ice cliff failure
DavidPollard, Robert M.DeConto, Richard B.Alley

Abstract

Geological data indicate that global mean sea level has fluctuated on 103 to 106 yr time scales during the last ∼25 million years, at times reaching 20 m or more above modern. If correct, this implies substantial variations in the size of the East Antarctic Ice Sheet (EAIS). However, most climate and ice sheet models have not been able to simulate significant EAIS retreat from continental size, given that atmospheric CO2 levels were relatively low throughout this period. Here, we use a continental ice sheet model to show that mechanisms based on recent observations and analysis have the potential to resolve this model–data conflict. In response to atmospheric and ocean temperatures typical of past warm periods, floating ice shelves may be drastically reduced or removed completely by increased oceanic melting, and by hydrofracturing due to surface melt draining into crevasses. Ice at deep grounding lines may be weakened by hydrofracturing and reduced buttressing, and may fail structurally if stresses exceed the ice yield strength, producing rapid retreat. Incorporating these mechanisms in our ice-sheet model accelerates the expected collapse of the West Antarctic Ice Sheet to decadal time scales, and also causes retreat into major East Antarctic subglacial basins, producing ∼17 m global sea-level rise within a few thousand years. The mechanisms are highly parameterized and should be tested by further process studies. But if accurate, they offer one explanation for past sea-level high stands, and suggest that Antarctica may be more vulnerable to warm climates than in most previous studies.

Quote
To trigger cliff failure, floating ice must first be removed, either entirely or at least enough to greatly reduce back pressure at the grounding line. Even very rapid melting from oceanic heat is often slower than ice-stream velocities, and is usually insufficient on its own to sufficiently reduce the major ice shelves in our model. We apply an additional mechanism accounting for increased ice-shelf calving due to hydrofracture by surface melt and rainfall draining into crevasses (Nick et al., 2013). Surface melting has been strongly implicated in the recent breakup of the Larsen B ice shelf (Scambos et al., 2003). In our warm-climate scenarios, surface melting increases calving considerably around the Antarctic margins. Our treatment of calving including hydrofracturing is described in Appendix B.

Quote
Today, cliff failure in Antarctica is prevented by (1) grounding lines at basin sills not being deep enough (<~800m), (2) insufficient surface melt to cause hydrofracturing and weakening at the grounding line, and/or (3) buttressing at the grounding lines by major ice shelves. In our warm-climate simulations, a combination of increased sub-ice ocean melt (reducing buttressing) and hydrofracturing (reducing buttressing and weakening grounding-line columns) leads to cliff failure in the major basins (Fig. 2). For deep basins, this sequence proceeds catastrophically, until either (i) surface melting and hydrofracturing lessen, strengthening ice columns at the grounding line, (ii) normal deformational ice flow across the grounding line exceeds calving and ocean melting, so that a substantial ice shelf re-forms and provides buttressing at the grounding line, or (iii) the grounding line retreats to the inner part of the basin with beds shallower than and little ice above flotation.

To initiate MICI in their model, they have to apply a warm climate.  They do this by initiating the model with current conditions and then adding +2 degrees C to the ocean temperatures.

Quote
To investigate the impact of the cliff-failure and melt-driven hydrofracture mechanisms, the ice-sheet model is run forward in time, forced by climate representative of past warm periods. Simulations are started from a previous spin-up of modern Antarctica using observed climatology. An instantaneous change to a warmer climate is applied, broadly representative of a warm Pliocene period. The past warm atmospheric climate is obtained from the RegCM3 Regional Climate Model (Pal et al., 2007) applied over Antarctica with some physical adaptations for polar regions, and with 400 ppmv CO2 and an orbit yielding particularly strong austral summers (DeConto et al., 2012). Detailed simulation of ocean warming beneath Antarctic ice shelves is currently not feasible on these time scales, so a simple uniform increment of+2 [degrees] C is added to modern observed ocean temperatures, broadly consistent with circum-Antarctic warming in Pliocene paleo-oceanic reconstructions (Dowsett et al., 2009). The climate forcings are described in more detail in Supplementary Material Section S.3.

Quote
The individual contributions of the new mechanisms can be assessed by re-running the simulation with cliff failure and/or melt-driven hydrofracturing turned on or off, as shown by the sea-level curves in Fig. 4, and maps in Fig. 5. With both mechanisms turned off (Fig. 5a), the model functions much as in earlier work (Pollard and DeConto, 2009). As expected, West Antarctica undergoes major collapse driven primarily by increased sub-ice melt from the +2 [degree] C ocean warming, causing reduced buttressing at the major WAIS grounding lines, and leading to classic marine instability (MISI) into the deepening interior beds (Weertman, 1974, Schoof, 2007). The time scale of this retreat is several hundred to a thousand years (Pollard and DeConto, 2009, and Fig. 4, cyan curve). There is very minor grounding-line recession into the outer Slessor–Bailey troughs and Lambert Graben due to ice-shelf thinning and reduced buttressing, but the retreat stops, presumably due to greater side-drag and funneling of ice compared to the wider West Antarctic grounding zones. Similar minor retreat occurs in a few other East Antarctic locations, but nothing on the scale of the retreat in Fig. 3. The same is true if cliff failure is active alone (without hydrofracturing, Fig. 5b), because ice shelves still exist, which buttress grounding lines and prevent cliff failure. With hydrofracturing activated alone (without cliff failure, Fig. 5c), the drastic removal of floating ice further reduces buttressing, allowing MISI to produce partial retreat into the Wilkes and Recovery–Slessor–Bailey basins, but not into the shallower Aurora. Full collapse into all basins, and greatly accelerated collapse in West Antarctica, requires the combination of melt-driven hydrofracturing and cliff failure (Fig. 5d). More analysis on the roles of the individual retreat mechanisms, and other sensitivities and basic model tests, are included in Supplementary Material Sections S.4–S.7.

Quote
To investigate the impact of the cliff-failure and melt-driven hydrofracture mechanisms, the ice-sheet model is run forward in time, forced by climate representative of past warm periods. Simulations are started from a previous spin-up of modern Antarctica using observed climatology. An instantaneous change to a warmer climate is applied, broadly representative of a warm Pliocene period. The past warm atmospheric climate is obtained from the RegCM3 Regional Climate Model (Pal et al., 2007) applied over Antarctica with some physical adaptations for polar regions, and with 400 ppmv CO2 and an orbit yielding particularly strong austral summers (DeConto et al., 2012). Detailed simulation of ocean warming beneath Antarctic ice shelves is currently not feasible on these time scales, so a simple uniform increment of is added to modern observed ocean temperatures, broadly consistent with circum-Antarctic warming in Pliocene paleo-oceanic reconstructions (Dowsett et al., 2009). The climate forcings are described in more detail in Supplementary Material Section S.3.

Ken,

You are mixing up DeConto & Pollard et al.'s MICI model assumptions with reality.  All current MISI and MICI model projections are all wrong, but some model projections provide useful warmings.

Just because DeConto & Pollard et al.'s MICI model assumes that hydrofracturing is necessary to expose bare ice cliffs for Thwaites Glacier, does not mean that a bare ice cliff with over 100-feet of freeboard cannot occur without hydrofracturing.  Similarly, because their model limits the rate of retreat of the calving ice face to a fraction of that observed for the Jakobshavn Glacier does not mean that a bare ice cliff face for Thwaites Glacier will not exceed that retreat rate by several times.

In any event, I do not see any global decision makers taking anywhere near enough action to stop the MICI-type of collapse scenario for the WAIS that I have cited in numerous posts; so in my opinion we will all likely need to wait until the 2030 to 2040 timeframe to see where an MICI-type of collapse of the Thwaites Glacier is initiated, or not, in that timeframe.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3925 on: November 24, 2020, 08:16:59 PM »
Quote
To initiate MICI in their model, they have to apply a warm climate.  They do this by initiating the model with current conditions and then adding +2 degrees C to the ocean temperatures.

Quote
... An instantaneous change to a warmer climate is applied, broadly representative of a warm Pliocene period. ... Detailed simulation of ocean warming beneath Antarctic ice shelves is currently not feasible on these time scales, so a simple uniform increment of+2 [degrees] C is added to modern observed ocean temperatures, broadly consistent with circum-Antarctic warming in Pliocene paleo-oceanic reconstructions (Dowsett et al., 2009). .

Quote
As expected, West Antarctica undergoes major collapse driven primarily by increased sub-ice melt from the +2 [degree] C ocean warming, ... The time scale of this retreat is several hundred to a thousand years (Pollard and DeConto, 2009, and Fig. 4, cyan curve).

Ken,
... in my opinion we will all likely need to wait until the 2030 to 2040 timeframe to see where an MICI-type of collapse of the Thwaites Glacier is initiated, or not, in that timeframe.

The models quoted apply a uniform and instantaneous increase of ocean temperatures by 2 K in order to trigger MICI events, and this is one of the factors needed to initiate MICI events.

You give it 10 to 20 year to reach your "2030 to 2040 timeframe" until MICI events are initiated.
 
ASLR, how long time might it take in reality to get a uniform increase in ocean temperatures of 2 K?

(currently, SST's are warming with 0.07 K per decade, and deeper ocean layers warm at considerably lower rates.)
« Last Edit: November 24, 2020, 08:23:50 PM by Hefaistos »

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3926 on: November 24, 2020, 10:29:20 PM »
...
The models quoted apply a uniform and instantaneous increase of ocean temperatures by 2 K in order to trigger MICI events, and this is one of the factors needed to initiate MICI events.

You give it 10 to 20 year to reach your "2030 to 2040 timeframe" until MICI events are initiated.
 
ASLR, how long time might it take in reality to get a uniform increase in ocean temperatures of 2 K?

(currently, SST's are warming with 0.07 K per decade, and deeper ocean layers warm at considerably lower rates.)

While I am too busy to make a detailed response, I note the following:

1.  I believe that their model assumes the ASE ice shelves to be in a more robust condition than they actually are today.  Thus, I believe that it will take less oceanic heat input on the underside of these currently fragile ice shelves to get them to collapse circa 2030 to 2040.

2. How much the entire ocean warms-up is not relevant to this topic, as what matters is the temperature of the modified CDW reaching the undersides of the ASE ice shelves as shown in the first attached image; which, is a function of upwelling of the CDW.

3. As shown in the second attached image, the amount of upwelling of CDW is projected to increase with time.

4. The third image shows how the influx of warm water into the ASE changes with the ENSO phases; which rapidly impacts the buttresses offered by the associated ice shelves to the ice flux out of the marine glaciers in the ASE.

I may present more information when I have more time.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3927 on: November 24, 2020, 11:27:11 PM »
The linked 2020 article by Caroline Weiss (and the two associated attached images) help to explain how CDW is currently contributing to the destabilization of both PIG and Thwaites Glaciers:

Title: "Thwaites and Pine Island Glaciers Rapid Melting Could Cause Four Foot Global Sea Level Rise"

https://www.climatecenter.pitt.edu/news/thwaites-and-pine-island-rapid-melting-could-cause-four-foot-global-sea-level-rise

Extract: "Besides its structure, a widely accepted theory explains why Thwaites is losing so much ice: warmer ocean water beneath Antarctica’s colder surface layer has started to come in contact with the bottom of the glacier calving front. This encroachment of the warm and salty Circumpolar Deep Water (CDW) into Pine Island Bay through submarine glaciated valleys has catalyzed the ice shelf thinning by pulling warm water toward Thwaites (Figure 2). Since most of the glacier is below sea level, the glacier’s thickness increases further inland and more ice is exposed as the glacier recedes (Figure 3). Climate change is implicated in Thwaites’ instability crisis, as it is culpable for the changing wind patterns around Antarctica that are linked to altered atmospheric circulation and warming tropics. Shifting winds are drawing the warm offshore CDW ocean current toward the shore, where it can melt the ice.

Between Thwaites and Pine Island, the amount of ice lost from Antarctica’s ice shelves is rapid and indicates a serious future threat. Both are susceptible to the encroachment of warm sea level because the “grounding line,” where the glaciers meet bedrock, lies below sea level. These two glaciers form the gateway to a large supply of frozen water on land that if released into the sea would cause global sea levels to rise by an estimated four feet."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3928 on: November 25, 2020, 11:53:52 AM »
...
The models quoted apply a uniform and instantaneous increase of ocean temperatures by 2 K in order to trigger MICI events, and this is one of the factors needed to initiate MICI events.

You give it 10 to 20 year to reach your "2030 to 2040 timeframe" until MICI events are initiated.
 
ASLR, how long time might it take in reality to get a uniform increase in ocean temperatures of 2 K?

(currently, SST's are warming with 0.07 K per decade, and deeper ocean layers warm at considerably lower rates.)

While I am too busy to make a detailed response, I note the following:

1.  I believe that their model assumes the ASE ice shelves to be in a more robust condition than they actually are today.  Thus, I believe that it will take less oceanic heat input on the underside of these currently fragile ice shelves to get them to collapse circa 2030 to 2040.

2. How much the entire ocean warms-up is not relevant to this topic, as what matters is the temperature of the modified CDW reaching the undersides of the ASE ice shelves as shown in the first attached image; which, is a function of upwelling of the CDW.

3. As shown in the second attached image, the amount of upwelling of CDW is projected to increase with time.

4. The third image shows how the influx of warm water into the ASE changes with the ENSO phases; which rapidly impacts the buttresses offered by the associated ice shelves to the ice flux out of the marine glaciers in the ASE.

I may present more information when I have more time.

You didn't reply to my question regarding the necessary temperature increase in the Antarctic seas to initiate MICI events.
Circumpolar deep water is between 1–2 °C of temperature. If we apply Pollard/DeConto's assumed increase with 2 K, it means at least a doubling of the CDW temperature. I'm just curious as to the needed timeframe for such an enormous increase of CDW temperature.

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3929 on: November 25, 2020, 12:35:15 PM »
Quote
Circumpolar deep water is between 1–2 °C of temperature. If we apply Pollard/DeConto's assumed increase with 2 K, it means at least a doubling of the CDW temperature. I'm just curious as to the needed timeframe for such an enormous increase of CDW temperature.
That's not how temperature ratios go, Hefaistos. 2ºC is actually 275.15ºK and a two degree rise is actually less than one percent change.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3930 on: November 25, 2020, 03:42:54 PM »
...

You didn't reply to my question regarding the necessary temperature increase in the Antarctic seas to initiate MICI events.
Circumpolar deep water is between 1–2 °C of temperature. If we apply Pollard/DeConto's assumed increase with 2 K, it means at least a doubling of the CDW temperature. I'm just curious as to the needed timeframe for such an enormous increase of CDW temperature.

It is my opinion that the regional ocean water in and around the ASE does not need to increase at all for a MICI-type of collapse to initiate in the Thwaites Gateway circa 2030 to 2040.  Furthermore, I believe that the natural variability of the ENSO and ABSL (or ASL or LAS in the attached image) will determine whether sufficient warm CDW will be advected into the ASE to drive a MICI-type of collapse by 2030 or not.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3931 on: November 25, 2020, 07:24:16 PM »
While the linked preprint reference focuses on data from Europe, it does imply that a positive feedback loop Arctic sea ice area reached an abrupt tipping point between 1985 and 1991; which, if so, would contribute to a worldwide increase in climate sensitivity, due to an associated acceleration of Arctic Amplification.

Alasdair Skelton, Nina Kirchner and Ingrid Kockum (2020), "Skewness of Temperature Data Implies an Abrupt Change in the Climate System between 1985 and 1991", https://doi.org/10.1002/essoar.10503828.1

https://www.essoar.org/doi/10.1002/essoar.10503828.1
https://www.essoar.org/pdfjs/10.1002/essoar.10503828.1

Abstract
Instrumental records of mean annual temperature extend back to the seventeenth and eighteenth centuries at multiple sites in Europe. For such long time series, we expect and find that histograms of mean annual temperature data become skewed towards higher temperatures with time because of global warming. However, we also find that skewness changed abruptly and started increasing between 1985 and 1991 (95% confidence) at 17 sites. We argue that this finding may imply an abrupt change in the climate system affecting Europe which probably occurred at this time. One possible cause is a climate tipping point having been passed. Of known tipping elements, we find Arctic sea ice loss, potentially linked to reduced sulfate aerosol emissions and coupled to temperature by an albedo feedback mechanism, a likely candidate. This is based on good correlations of sea ice extent and sulfate aerosol emissions with skewness of mean annual temperature data.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3932 on: November 25, 2020, 07:50:05 PM »
The linked reference discusses the "Larger Sensitivity of Arctic Precipitation Phase to Aerosol than Greenhouse Gas forcing", and it indicates that under RCP8.5 the rainfall over both Greenland and the eastern Arctic Ocean will increase rapidly.  To me this implies accelerated ice mass loss from the GIS and accelerated degradation of Siberian permafrost and increased freshwater inflow into the Arctic Ocean (which will likely work to destabilize the halocline in that ocean):

Shifeng Pan et al. (20 November 2020), "Larger Sensitivity of Arctic Precipitation Phase to Aerosol than Greenhouse Gas forcing", Geophysical Research Letters, https://doi.org/10.1029/2020GL090452

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL090452?af+R

Abstract
The sensitivity of the Arctic precipitation phases (solid and liquid) to the forcings from greenhouse gases (GHGs) and aerosols over 2016‐2080 was investigated by using the Community Earth System Model version 1. Results show that the warming caused by the two forcings results in an increasing trend in total precipitation and a solid‐to‐liquid precipitation transition in the Arctic. Under RCP8.5 scenario, the increased rate of Arctic mean precipitation with global warming forced by aerosol reduction (7.7%/°C) is twice greater than that by increased GHG emission (3.5%/°C). The sensitivity of rainfall to precipitation ratio (RPR) to various forcings is much higher than that of total precipitation in the Arctic. The increased rate of RPR due to global aerosol forcing (8.4%/°C) is approximately three times that due to GHG forcing (2.9%/°C) in the Arctic, the differences even larger over Greenland and the eastern Arctic Ocean, resulting in more rainfall in these areas.

Plain Language Summary
The precipitation phase is extremely sensitive to temperature changes, especially in the Arctic. Solid and liquid precipitation have almost the opposite effect on the ground energy budget. The changes in precipitation phase can greatly affect snow and ice mass balance, regulating the regional hydrological cycle. The transition from solid precipitation to liquid precipitation can even promote carbon release over the permafrost through changing the rate of snow melting. We evaluated the impacts of the two most important anthropogenic forcing agents (Greenhouse gases and aerosols) on the changes of precipitation phases in the Arctic using a state‐of‐art earth system model. We found that the warming forced by global aerosol reduction and increased Greenhouse gas emission leads to a solid‐to‐liquid precipitation transition and therefore more rainfall events in the Arctic. Under RCP8.5 scenario, the sensitivity of Arctic precipitation phase to global aerosol forcing is approximately three times that to the GHG forcing, and the most sensitive phase changes of Arctic precipitation to the aerosol forcing are observed in Greenland and the eastern Arctic Ocean. Understanding the impact of human activities on the changes in the Arctic precipitation phase will help formulate reasonable emission reduction policies and better adapt to the rapid Arctic climate changes in the future.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Tor Bejnar

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3933 on: November 25, 2020, 10:48:32 PM »
ASLR,
How would " increased freshwater inflow into the Arctic Ocean ... work to destabilize the halocline in that ocean"?  I've read elsewhere (other ASIF threads, and maybe this one, too) that rivers (dumping fresh water into the Arctic) support the reestablishment of the halocline where storms and currents have somewhat mixed the top 30 or 50 meters.
Arctic ice is healthy for children and other living things.

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3934 on: November 25, 2020, 11:28:55 PM »
While the linked reference discusses millennial-scale variability; it nevertheless confirms that during deglacial periods (such as now) that Northern Hemisphere sea-level forcing accelerates grounding-line retreat in marine-based sectors of the Antarctic Ice Sheet

Gomez, N., Weber, M.E., Clark, P.U. et al. Antarctic ice dynamics amplified by Northern Hemisphere sea-level forcing. Nature 587, 600–604 (2020). https://doi.org/10.1038/s41586-020-2916-2

https://www.nature.com/articles/s41586-020-2916-2

Abstract: "Sea-level rise due to ice loss in the Northern Hemisphere in response to insolation and greenhouse gas forcing is thought to have caused grounding-line retreat of marine-based sectors of the Antarctic Ice Sheet (AIS). Such interhemispheric sea-level forcing may explain the synchronous evolution of global ice sheets over ice-age cycles. Recent studies that indicate that the AIS experienced substantial millennial-scale variability during and after the last deglaciation (roughly 20,000 to 9,000 years ago) provide further evidence of this sea-level forcing. However, global sea-level change as a result of mass loss from ice sheets is strongly nonuniform, owing to gravitational, deformational and Earth rotational effects, suggesting that the response of AIS grounding lines to Northern Hemisphere sea-level forcing is more complicated than previously modelled. Here, using an ice-sheet model coupled to a global sea-level model, we show that AIS dynamics are amplified by Northern Hemisphere sea-level forcing. As a result of this interhemispheric interaction, a large or rapid Northern Hemisphere sea-level forcing enhances grounding-line advance and associated mass gain of the AIS during glaciation, and grounding-line retreat and mass loss during deglaciation. Relative to models without these interactions, the inclusion of Northern Hemisphere sea-level forcing in our model increases the volume of the AIS during the Last Glacial Maximum (about 26,000 to 20,000 years ago), triggers an earlier retreat of the grounding line and leads to millennial-scale variability throughout the last deglaciation. These findings are consistent with geologic reconstructions of the extent of the AIS during the Last Glacial Maximum and subsequent ice-sheet retreat, and with relative sea-level change in Antarctica."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3935 on: November 26, 2020, 12:14:20 AM »
ASLR,
How would " increased freshwater inflow into the Arctic Ocean ... work to destabilize the halocline in that ocean"?  I've read elsewhere (other ASIF threads, and maybe this one, too) that rivers (dumping fresh water into the Arctic) support the reestablishment of the halocline where storms and currents have somewhat mixed the top 30 or 50 meters.

Tor,

While you are correct that increasing influx of fresh riverine water into the Arctic Ocean increases the thickness of the halocline layer; which reduces heat flux from the Atlantic layer to the Arctic atmosphere. 

Nevertheless, as the first linked reference cites, excess fresh surface water is frequently heated in the northern Chukchi Sea and then stored in the interior of the Beaufort Gyre.  So more freshwater discharge into the Arctic Ocean will increase the heat stored in the Beaufort Gyre; which when released (during a temporary reversal of the Beaufort Gyre) will melt large areas of Arctic sea ice; which, will destabilize the halocline releasing more heat from the Atlantic layer into the Arctic atmosphere thus accelerating Arctic Amplification.

Mary-Louise Timmermans, John Toole and Richard Krishfield (29 Aug 2018), "Warming of the interior Arctic Ocean linked to sea ice losses at the basin margins", Science Advances , Vol. 4, no. 8, eaat6773, DOI: 10.1126/sciadv.aat6773

http://advances.sciencemag.org/content/4/8/eaat6773

Abstract: "Arctic Ocean measurements reveal a near doubling of ocean heat content relative to the freezing temperature in the Beaufort Gyre halocline over the past three decades (1987–2017). This warming is linked to anomalous solar heating of surface waters in the northern Chukchi Sea, a main entryway for halocline waters to join the interior Beaufort Gyre. Summer solar heat absorption by the surface waters has increased fivefold over the same time period, chiefly because of reduced sea ice coverage. It is shown that the solar heating, considered together with subduction rates of surface water in this region, is sufficient to account for the observed halocline warming. Heat absorption at the basin margins and its subsequent accumulation in the ocean interior, therefore, have consequences for Beaufort Gyre sea ice beyond the summer season."

&

Also, the second linked reference indicates that in addition to the freshwater accumulated in the Beaufort Gyre the entire Arctic Ocean surface layer has been accumulating atypically high volumes of freshwater that are only recently beginning to leak atypically high volumes of freshwater into the North Atlantic.  This implies that for many years now the full impacts of unusually high (anthropogenically driven) discharges of freshwater into the Arctic Ocean (and then on to the North Atlantic) have been masked.  As thick layers of freshwater in the Arctic Ocean reduce the rate of heat flux from the deeper/warming layers of ocean water into the Arctic atmosphere, this atypically high accumulation of freshwater in the Arctic Ocean surface layers implies that in recent years the Arctic has been cooler than it otherwise would have been (without this atypically high accumulation).  Thus if/when the Beaufort Gyre finally reverses it will likely not only release excessively high freshwater volumes accumulated in the Gyre into the North Atlantic, but it would likely also flush excess freshwater from the atypically high accumulations from the ocean surface layers in much of the Arctic Ocean and would likely melt large portions of the existing sea ice; which, would flush even more freshwater into the North Atlantic where this additional freshwater flux would serve to rapidly slow the AMOC:

Alexandra Jahn and Rory Laiho (27 July 2020), "Forced Changes in the Arctic Freshwater Budget Emerge in the Early 21st Century", Geophysical Research Letters, https://doi.org/10.1029/2020GL088854

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL088854?af=R

Abstract
Arctic liquid freshwater (FW) storage has shown a large increase over the past decades, posing the question: Is the Arctic FW budget already showing clear signs of anthropogenic climate change, or are the observed changes the result of multi‐decadal variability? We show that the observed change in liquid and solid Arctic FW storage is likely already driven by the changing climate, based on ensemble simulations from a state‐of‐the‐art climate model. Generally, the emergence of forced changes in Arctic FW fluxes occurs earlier for oceanic fluxes than for atmospheric or land fluxes. Nares Strait liquid FW flux is the first to show emergence outside the range of background variability, with this change potentially already occurring. Other FW fluxes have likely started to shift but have not yet emerged into a completely different regime. Future emissions reductions have the potential to avoid the emergence of some FW fluxes beyond the background variability.

Plain Language Summary
The surface waters of the Arctic Ocean are fresher than the rest of the world oceans, due to the input of large amounts of river runoff. The very fresh surface ocean affects the ocean circulation and climate not just in the Arctic Ocean, but also at lower latitudes, especially in the North Atlantic. The last two decades have seen a freshening of the surface Arctic Ocean, for reasons that are currently unknown. Here we demonstrate that this freshening is likely already driven by climate change. Furthermore, we find that due to man‐made climate change, Arctic freshwater fluxes to the North Atlantic are also likely to soon start showing signs of change beyond the range of the variability we have observed in the past. The information provided here about the expected timing of the emergence of climate change signals will allow us to monitor upcoming changes in real time, to better understand how changes in the Arctic Ocean can impact climate worldwide.

Key points
•   The observed increase in Arctic liquid freshwater (FW) storage is likely already driven by climate change
•   A forced change in liquid FW flux through Nares Strait is likely to emerge within the next decade
•   The already changing nature of many FW budget terms can delay detection of shift and emergence from observations

Best,
ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Tor Bejnar

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3936 on: November 26, 2020, 01:57:02 AM »
Thanks.
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Hefaistos

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3937 on: November 26, 2020, 12:00:20 PM »
Quote
Circumpolar deep water is between 1–2 °C of temperature. If we apply Pollard/DeConto's assumed increase with 2 K, it means at least a doubling of the CDW temperature. I'm just curious as to the needed timeframe for such an enormous increase of CDW temperature.
That's not how temperature ratios go, Hefaistos. 2ºC is actually 275.15ºK and a two degree rise is actually less than one percent change.

To be more precise, we have to consider the specific heat capacity of ocean water (about 4000 J/KgK) multiplied with the mass of ocean water in consideration, the CDW. From this we can calculate how much energy is required to raise the temperature by 2K.
The heat capacity of the entire Ocean is 5.6x10^24 Joules/Degree Kelvin, so we would need about
11 x 10^24 Joules to heat ALL water 2K.
I have no idea how big part the CDW is of all Ocean water. But let's say that it is e.g. 1% of the total. So we'd need about 10^23 Joules to heat all CDW water 2K. This is an enormous amount of energy.
As comparison, the upper 3.5 meters of the ocean hold as much heat as the entire atmosphere above it.

The question is, where is that very considerable energy going to come from?

(Not much can come from below, as the avg temp of Oceans at depth 2000-3688 m is about 3.6C. The 2000 m temp is from the Argo floats, and bottom water is assumed to be at 0 degrees C.)

I guess my point is just to question the model makers' assumption of an abrupt temperature increase of 2K. - even if it only refers to the CDW. In reality I presume this would take 100's of years with the current forcings.

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3938 on: November 26, 2020, 07:26:43 PM »
....

I guess my point is just to question the model makers' assumption of an abrupt temperature increase of 2K. - even if it only refers to the CDW. In reality I presume this would take 100's of years with the current forcings.

The model makers state that the reason that they increased the regional ocean temperature in their model by 2K is that their model does not allow them to correctly detail the simulation of ocean warming beneath Antarctic ice shelves, as indicated by the statement below.

"Detailed simulation of ocean warming beneath Antarctic ice shelves is currently not feasible on these time scales, so a simple uniform increment of+2 [degrees] C is added to modern observed ocean temperatures, broadly consistent with circum-Antarctic warming in Pliocene paleo-oceanic reconstructions (Dowsett et al., 2009)."

Therefore, instead of asking the modelers to explain how the regional ocean water could possibly abruptly increase in temperature by 2K, you would do better by asking why it is that decision makers do not grant DeConto and Pollard et al. more money so that they can refine their model in order to run detailed simulation of ocean warming beneath Antarctic ice shelves.

Is it possible that decision makers do not want to know the answer so they refuse to provide the resources necessary to properly model the true climate risk associated with the potential MICI-type of collapse of key marine glaciers in the WAIS?
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3939 on: November 27, 2020, 09:43:46 PM »
The linked article indicates that a large Sahara dust storm the peaked from June 14 to 19, 2020 contributed Arctic sea ice loss this year.  If such large Sahara dust storm increase in frequency and/or magnitude, then this phenomena would likely contribute to future Arctic Amplification.

Title: "Godzilla Sahara dust storm linked to melting Arctic sea ice"

www.newscientist.com/article/2261073-godzilla-sahara-dust-storm-linked-to-melting-arctic-sea-ice/
« Last Edit: November 27, 2020, 09:53:45 PM by AbruptSLR »
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kassy

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3940 on: November 28, 2020, 12:00:03 AM »
Also invoking the heat capacity of the entire ocean is a fallacy. That did not matter for meltwater pulse 1A etc.

The meaningful exchange is at the surfaces.
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