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Author Topic: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)  (Read 322457 times)

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2800 on: February 18, 2020, 07:41:47 PM »
The linked reference discusses the portioning of climate projection uncertainty in three large ensembles including CMIP5 & CMIP6 (see the attached image).  I note that this reference only considers model response uncertainty internal to the ensemble, and not feedback mechanisms not fully accounted for by the ensemble (like ice-climate feedback mechanisms).  In this regard, I note:

a)  Uncertainty due to climate internal variability (like ENSO variability) are still significant thru 2030 (when say a strong El Nino event might contribute to a collapse of the PIIS and/or the Thwaites Ice Tongue by say 2030, considering the increased frequency of strong El Nino events with global warming and that the last strong El Nino was in the 2015-2016 season).
b) A significant portion of the model uncertainty in CMIP6 is due to the fact that many of the included models considered nonlinearity of several feedback mechanisms that earlier ensembles did not.
c) The SSP scenarios are tied to specific emission pathways while the RCP scenarios only considered concentration pathways, which attributes more uncertainty to the RCP scenarios than to the SSP scenaros.

Lehner, F., Deser, C., Maher, N., Marotzke, J., Fischer, E., Brunner, L., Knutti, R., and Hawkins, E.: Partitioning climate projection uncertainty with multiple Large Ensembles and CMIP5/6, Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2019-93, in review, 2020.

https://www.earth-syst-dynam-discuss.net/esd-2019-93/
https://www.earth-syst-dynam-discuss.net/esd-2019-93/esd-2019-93.pdf

Abstract. Partitioning uncertainty in projections of future climate change into contributions from internal variability, model response uncertainty, and emissions scenarios has historically relied on making assumptions about forced changes in the mean and variability. With the advent of multiple Single-Model Initial-Condition Large Ensembles (SMILEs), these assumptions can be scrutinized, as they allow a more robust separation between sources of uncertainty. Here, the iconic framework from Hawkins and Sutton (2009) for uncertainty partitioning is revisited for temperature and precipitation projections using seven SMILEs and the Climate Model Intercomparison Projects CMIP5 and CMIP6 archives. The original approach is shown to work well at global scales (potential method error < 20 %), while at local to regional scales such as British Isles temperature or Sahel precipitation, there is a notable potential method error (up to 50 %) and more accurate partitioning of uncertainty is achieved through the use of SMILEs. Whenever internal variability and forced changes therein are important, the need to evaluate and improve the representation of variability in models is evident. The available SMILEs are shown to be a good representation of the CMIP5 model diversity in many situations, making them a useful tool for interpreting CMIP5. CMIP6 often shows larger absolute and relative model uncertainty than CMIP5, although part of this difference can be reconciled with the higher average transient climate response in CMIP6. This study demonstrates the added value of a collection of SMILEs for quantifying and diagnosing uncertainty in climate projections.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2801 on: February 19, 2020, 02:41:39 AM »

The loss of ice shelves — Mercer proposed — would allow the ice sheet to thin, grounding lines to retreat and the ice sheet to disintegrate via calving. This is a much faster means of losing mass than melting in place. Mercer further commented that the loss of ice shelves on the Antarctic Peninsula, as has since been observed, would be an indicator that this process of ice sheet loss due to global warming was underway.

...

Mercer proposed that the loss of ice shelves on the Antarctic Peninsula would precede the loss of ice shelves in front of critical ice sheets like the WAIS, and the linked article presents a evidence that the George VI ice shelf and others on the Antarctic Peninsula are at risk from melt-pond failure mechanisms.  I would not be surprised to read about at least one ice shelf collapse on the Antarctic Peninsula in the 2020-2021 melt season (but likely not the George VI ice shelf itself; which is sandwiched between the Antarctic Peninsula and Alexander Island):

Title: "Widespread Melt on the George VI Ice Shelf"

https://earthobservatory.nasa.gov/images/146189/widespread-melt-on-the-george-vi-ice-shelf

Extract: "Alison Banwell, a glaciologist at the University of Colorado Boulder who currently has a three-year fieldwork project on the shelf, noticed the melt in images acquired that same day with the European Space Agency’s Sentinel-2 satellite. “This is the biggest melt event we know to have occurred on the George VI ice shelf,” she said.

“What’s worrying is if George VI looks like this, other ice shelves on the peninsula probably have plenty of meltwater too,” Banwell said. “And those ice shelves are less stable.” At the time, clouds prevented satellites from getting a good look at the other ice shelves."
« Last Edit: February 19, 2020, 06:48:43 PM by AbruptSLR »
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2802 on: February 19, 2020, 03:57:42 PM »
...
The linked reference provides paleo-evidence that supports many aspects of the ice apocalypse scenario that I have previously discussed in this thread; however, it does indicate that there is still uncertainty about the time-scale at which such a scenario might unfold.  Also, to me, this evidence supports many aspects of the scenario cited in DeConto and Pollard (2016):

Chris S. M. Turney, Christopher J. Fogwill, Nicholas R. Golledge, Nicholas P. McKay, Erik van Sebille, Richard T. Jones, David Etheridge, Mauro Rubino, David P. Thornton, Siwan M. Davies, Christopher Bronk Ramsey, Zoë A. Thomas, Michael I. Bird, Niels C. Munksgaard, Mika Kohno, John Woodward, Kate Winter, Laura S. Weyrich, Camilla M. Rootes, Helen Millman, Paul G. Albert, Andres Rivera, Tas van Ommen, Mark Curran, Andrew Moy, Stefan Rahmstorf, Kenji Kawamura, Claus-Dieter Hillenbrand, Michael E. Weber, Christina J. Manning, Jennifer Young, and Alan Cooper (February 11, 2020), "Early Last Interglacial ocean warming drove substantial ice mass loss from Antarctica", PNAS, https://doi.org/10.1073/pnas.1902469117

https://www.pnas.org/content/early/2020/02/10/1902469117.short?rss=1


 Our data indicate that Antarctica is highly vulnerable to projected increases in ocean temperatures and may drive ice–climate feedbacks that further amplify warming.

In the linked article, study co-author Zoe Thomas makes it clear that the quoted study indicates that once a certain threshold is past, ice mass loss from Antarctica will become effectively 'irreversible' for hundreds, or thousands, of years:

Title: " Global Warming Creating 'Irreversible' Ice Melt in Antarctica: Scientist"

https://www.insurancejournal.com/news/international/2020/02/19/558780.htm
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2803 on: February 19, 2020, 05:09:46 PM »
The linked open access reference evaluates limits (including ice mélange buttressing) on the rate of calving for marine glaciers with bear ice cliffs (sometimes called MICI).  To me the proposed model is more suitable for application for Greenland's marine terminating glaciers rather than to ASE marine glacier; nevertheless, the high end of calving rates are alarmingly fast:

Schlemm, T. and Levermann, A.: A simple model of mélange buttressing for calving glaciers, The Cryosphere Discuss., https://doi.org/10.5194/tc-2020-50, in review, 2020.

https://www.the-cryosphere-discuss.net/tc-2020-50/
https://www.the-cryosphere-discuss.net/tc-2020-50/tc-2020-50.pdf

Abstract. Both ice sheets on Greenland and Antarctica are discharging ice into the ocean. In many regions along the coast of the ice sheets, the icebergs calf into a bay. If the addition of icebergs through calving is faster than their transport out of the embayment, the icebergs will be frozen into a mélange with surrounding sea ice in winter. In this case, the buttressing effect of the ice mélange can be considerably stronger than any buttressing by mere sea ice would be. This in turn stabilizes the glacier terminus and leads to a reduction in calving rates. Here we propose a simple but robust buttressing model of ice mélange which can be used in numerical and analytical modeling.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2804 on: February 19, 2020, 05:42:58 PM »
The linked commentary discusses the findings that the business leads rank the urgency of climate change risks significantly lower than do consensus scientists and this goes on to discuss ways of addressing this gap in climate change risk assessment.  Unfortunately, the commentary makes statements like:

"It is essential, however, that multiplicity does not simply lead to a cacophony of diverging risk perceptions which could impede action.  Rather, a range of perspectives must be collected to better understand challenges and to drive strategies to converge around solutions."

When I read statements like this from consensus climate scientists, I hear a call to limit the range of risks considered by cutting off the right-tail risks, particularly those related to abrupt sea level rise and to ice-climate feedback mechanisms.  In this regard, I provide a second link to a Dutch reference on how they address adapting to uncertain rates of SLR due to the risk of Antarctic ice mass loss.

Matthias Garschagen et al. (12 February 2020), "Too big to ignore: Global risk perception gaps between scientists and business‐leaders", Earth's Future, https://doi.org/10.1029/2020EF001498

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020EF001498?af=R
https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2020EF001498

Abstract: "Two major reports assessing global systemic risks have been published recently, presenting large‐scale panel data on the risk perceptions of different key communities, most notably business leaders and global change scientists. While both of these global communities agree on ranking environmental risks the highest, followed by societal, geopolitical, technological and economic risks, business leaders perceive the urgency of these risks (i.e. their likelihood and potential impact) as significantly lower than scientists. This gap implies vexing questions in relation to building a shared sense of urgency and facilitating collective action. These questions need to be addressed through new ways of co‐creating risk assessments and strategic futures analysis."

See also:

M Haasnoot et al (2020), "Adaptation to uncertain sea-level rise; how uncertainty in Antarctic mass-loss impacts the coastal adaptation strategy of the Netherlands", Environmental Research Letters, Volume 15, Number 3, https://doi.org/10.1088/1748-9326/ab666c

https://iopscience.iop.org/article/10.1088/1748-9326/ab666c
https://iopscience.iop.org/article/10.1088/1748-9326/ab666c/pdf

Abstract: "Uncertainties in the rate and magnitude of sea-level rise (SLR) complicate decision making on coastal adaptation. Large uncertainty arises from potential ice mass-loss from Antarctica that could rapidly increase SLR in the second half of this century. The implications of SLR may be existential for a low-lying country like the Netherlands and warrant exploration of high-impact low-likelihood scenarios. To deal with uncertain SLR, the Netherlands has adopted an adaptive pathways plan. This paper analyzes the implications of storylines leading to extreme SLR for the current adaptive plan in the Netherlands, focusing on flood risk, fresh water resources, and coastline management. It further discusses implications for coastal adaptation in low-lying coastal zones considering timescales of adaptation including the decisions lifetime and lead-in time for preparation and implementation. We find that as sea levels rise faster and higher, sand nourishment volumes to maintain the Dutch coast may need to be up to 20 times larger than to date in 2100, storm surge barriers will need to close at increasing frequency until closed permanently, and intensified saltwater intrusion will reduce freshwater availability while the demand is rising. The expected lifetime of investments will reduce drastically. Consequently, step-wise adaptation needs to occur at an increasing frequency or with larger increments while there is still large SLR uncertainty with the risk of under- or overinvesting. Anticipating deeply uncertain, high SLR scenarios helps to enable timely adaptation and to appreciate the value of emission reduction and monitoring of the Antarctica contribution to SLR."

Extract: "The Netherlands has adopted an adaptive plan that allows for adaptation over time depending on how the future unfolds. Recent SLR observations and projections have raised concerns about the plausibility of an uncertain strong acceleration of SLR after 2050 due to rapid mass-loss of the Antarctic ice sheet, which is not accounted for in the current adaptive plan."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2805 on: February 19, 2020, 06:46:47 PM »
The linked reference indicates that anthropogenic fossil fuel related methane emissions are underestimated by "25 to 40 per cent of recent estimates".  To me this highlights the risk that fuel methane emissions from fracking operation may also be severely underestimated:

Hmiel, B., Petrenko, V.V., Dyonisius, M.N. et al. Preindustrial 14CH4 indicates greater anthropogenic fossil CH4 emissions. Nature 578, 409–412 (2020). https://doi.org/10.1038/s41586-020-1991-8

https://www.nature.com/articles/s41586-020-1991-8

Abstract
Atmospheric methane (CH4) is a potent greenhouse gas, and its mole fraction has more than doubled since the preindustrial era. Fossil fuel extraction and use are among the largest anthropogenic sources of CH4 emissions, but the precise magnitude of these contributions is a subject of debate. Carbon-14 in CH4 (14CH4) can be used to distinguish between fossil (14C-free) CH4 emissions and contemporaneous biogenic sources; however, poorly constrained direct 14CH4 emissions from nuclear reactors have complicated this approach since the middle of the 20th century. Moreover, the partitioning of total fossil CH4 emissions (presently 172 to 195 teragrams CH4 per year) between anthropogenic and natural geological sources (such as seeps and mud volcanoes) is under debate; emission inventories suggest that the latter account for about 40 to 60 teragrams CH4 per year. Geological emissions were less than 15.4 teragrams CH4 per year at the end of the Pleistocene, about 11,600 years ago, but that period is an imperfect analogue for present-day emissions owing to the large terrestrial ice sheet cover, lower sea level and extensive permafrost. Here we use preindustrial-era ice core 14CH4 measurements to show that natural geological CH4 emissions to the atmosphere were about 1.6 teragrams CH4 per year, with a maximum of 5.4 teragrams CH4 per year (95 per cent confidence limit)—an order of magnitude lower than the currently used estimates. This result indicates that anthropogenic fossil CH4 emissions are underestimated by about 38 to 58 teragrams CH4 per year, or about 25 to 40 per cent of recent estimates. Our record highlights the human impact on the atmosphere and climate, provides a firm target for inventories of the global CH4 budget, and will help to inform strategies for targeted emission reductions.

See also:

Title: "Methane emissions from fossil fuels ‘severely underestimated’"

https://www.carbonbrief.org/methane-emissions-from-fossil-fuels-severely-underestimated

Extract: "Human-caused emissions of methane from the extraction and use of fossil fuels may have been “severely underestimated”, a new study suggests.

The research indicates that “natural” emissions of fossil methane, that seeps out of deeply-held reserves, make up a much smaller fraction of total methane emissions than previously thought.
This means that the levels of fossil methane in the atmosphere are likely being driven by the methane escaping as coal, oil and natural gas are mined, drilled and transported.

The implication is that methane emissions from fossil fuels are 25-40% higher than earlier estimates suggest, the lead researcher tells Carbon Brief."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2806 on: February 19, 2020, 07:17:53 PM »
The linked article points out that the surface greening of the Arctic is only the tip of the associate positive albedo feedback 'iceberg', as the associated root development in permafrost regions could significantly accelerate permafrost degradation and associated GHG emissions:

Title: "The Arctic Is Getting Greener. That's Bad News for All of Us"

https://www.wired.com/story/arctic-greening/

Extract: "Right now the Arctic is warming twice as fast as the rest of the planet, and transforming in massively consequential ways. Rapidly melting permafrost is gouging holes in the landscape. Thousands of years’ worth of wet accumulated plant matter known as peat is drying out and burning in unprecedented wildfires. Lightning—a phenomenon more suited to places like Florida—is now striking within 100 miles of the North Pole.

All the while, researchers are racing to quantify how the plant species of the Arctic are coping with a much, much warmer world. In a word, well. And probably: too well. Using satellite data, drones, and on-the-ground fieldwork, a team of dozens of scientists—ecologists, biologists, geographers, climate scientists, and more—is finding that vegetation like shrubs, grasses, and sedges are growing more abundant. The phenomenon is known as “Arctic greening,” and with it comes a galaxy of strange and surprising knock-on effects with implications both for the Arctic landscape and the world’s climate at large.

A permafrost melt also releases more water into the soil, leading to yet more knock-on effects for the vegetation. “When the ground is frozen, plants don't have any access to water,” says Kerby. “So it's almost like being in a desert for part of the year.”

Frozen ground limits when the plants can grow. But an earlier thaw could mean that plants kickstart their growth earlier in the year. As those soils thaw deeper and deeper, they will also release gobs of nutrients that have been trapped underground for perhaps thousands of years, supercharging the growth of these increasingly abundant Arctic plant species. This means the landscape could get even greener and even more hospitable to plants that can take advantage of warmer temperatures.

And really, underground is where so much of the Arctic mystery still lies: In these tundra ecosystems, up to 80 percent of the biomass is below ground. (Remember that in the deep chill of winter, roots survive underground.) “So when you see the green surface, that's just the tip of the iceberg, in terms of the biomass in these systems,” says Myers-Smith. “So it could be that a lot of the climate change responses of these plants are actually all in the below-ground world that we have a very difficult time tracking and monitoring.”"
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2807 on: February 20, 2020, 04:18:35 PM »
With LNG suitable for replacing diesel fuel for both long-haul trucks and ships, and with CNC cars being increasingly used around the world, and with shale gas cheap and available; there is little wonder that Shell forecasts a doubling of global LNG demand by 2040.  However, due to gas leaks LNG has a heavier carbon footprint than coal so we can all expect the global atmospheric methane concentration to continue rising for some time to come:

Title: "Demand for liquefied natural gas set to double by 2040, according to Shell"

https://www.cnbc.com/2020/02/20/demand-for-liquefied-natural-gas-set-to-double-by-2040-shell.html

Extract: "Worldwide demand for liquefied natural gas, or LNG, rose by 12.5% to hit 359 million tons last year, according to Royal Dutch Shell’s annual LNG Outlook report.

Citing forecasts, Shell said that LNG demand was expected to double by 2040 to 700 million tons, with natural gas set to play “a growing role in shaping a lower-carbon energy system.”"
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2808 on: February 20, 2020, 04:51:03 PM »
The linked article/video provides some nice color commentary about this season's ITGC field mission:

Title: "A risky expedition to study the ‘doomsday glacier’"

https://www.pbs.org/newshour/show/visiting-the-most-vulnerable-place-on-earth-the-doomsday-glacier

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2809 on: February 20, 2020, 05:07:46 PM »
...
Citing forecasts, Shell said that LNG demand was expected to double by 2040 to 700 million tons, with natural gas set to play “a growing role in shaping a lower-carbon energy system.”"

Several of my recent posts have indicated that anthropogenic methane emissions have been, and are likely to remain, higher than previously assumed.  When such relatively high anthropogenic methane emissions are combined together with possible/probable increases in natural methane emissions (say from: permafrost degradation, thermokarst lakes and/or methane hydrates) the future atmospheric concentration of methane may become high enough to increase the GWP of such atmospheric methane.  In this regard, the two images come from Isaksen et al. (2011) who used computer models to estimate methane's atmospheric burden.  Isaksen et al (2011) found (see the first image) that as the assumed emission rate increased the chemistry of the atmosphere would change, resulting in increased lifetime for methane, thus increasing the associated radiative forcing (see the second image).

Isaksen, I. S. A., Gauss M., Myhre, G., Walter Anthony, K. M.  and Ruppel, C.,  (2011), "Strong atmospheric chemistry feedback to climate warming from Arctic methane emissions", Global Biogeochem. Cycles, 25, GB2002, doi:10.1029/2010GB003845.

http://onlinelibrary.wiley.com/doi/10.1029/2010GB003845/abstract
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2810 on: February 20, 2020, 10:08:33 PM »
While the authors of the linked reference are all well regarded ice modeling scientists; to me this reference illustrates how painfully slow the consensus building process is for risk assessment associated with ice sheet modeling driven by projected future climate change scenarios.  While I concur with the reference that ice shelf response to climate change is one of the key mechanisms determining future ice mass loss from Antarctica, I believe that the cited model projections all significantly underestimated the ice shelf responses that we have seen this year in the Amundsen Sea Embayment, ASE; and the MISI models used explicitly do not consider MICI-type mechanisms.

Therefore, in my opinion, the most significant finding of the cited study is that:

"We thus have to conclude that uncertainty with respect to the ice dynamic contribution of Antarctica due to future warming is still increasing and thus that coastal planning has to take into account that multi-decadal sea level projections are likely to change with an increasing understanding of the ice dynamics and their representation in ice sheet models."

Thus the big issue is will consensus climate science officially recognize the significant risk of abrupt ice mass loss from Antarctica this century before, or after, key Antarctic marine glaciers have already crossed they thresholds for 'irreversible' continuing ice mass loss this century:

Levermann, A., Winkelmann, R., Albrecht, T., Goelzer, H., Golledge, N. R., Greve, R., Huybrechts, P., Jordan, J., Leguy, G., Martin, D., Morlighem, M., Pattyn, F., Pollard, D., Quiquet, A., Rodehacke, C., Seroussi, H., Sutter, J., Zhang, T., Van Breedam, J., Calov, R., DeConto, R., Dumas, C., Garbe, J., Gudmundsson, G. H., Hoffman, M. J., Humbert, A., Kleiner, T., Lipscomb, W. H., Meinshausen, M., Ng, E., Nowicki, S. M. J., Perego, M., Price, S. F., Saito, F., Schlegel, N.-J., Sun, S., and van de Wal, R. S. W.: Projecting Antarctica's contribution to future sea level rise from basal ice shelf melt using linear response functions of 16 ice sheet models (LARMIP-2), Earth Syst. Dynam., 11, 35–76, https://doi.org/10.5194/esd-11-35-2020, 2020.

https://www.earth-syst-dynam.net/11/35/2020/

Abstract
The sea level contribution of the Antarctic ice sheet constitutes a large uncertainty in future sea level projections. Here we apply a linear response theory approach to 16 state-of-the-art ice sheet models to estimate the Antarctic ice sheet contribution from basal ice shelf melting within the 21st century. The purpose of this computation is to estimate the uncertainty of Antarctica's future contribution to global sea level rise that arises from large uncertainty in the oceanic forcing and the associated ice shelf melting. Ice shelf melting is considered to be a major if not the largest perturbation of the ice sheet's flow into the ocean. However, by computing only the sea level contribution in response to ice shelf melting, our study is neglecting a number of processes such as surface-mass-balance-related contributions. In assuming linear response theory, we are able to capture complex temporal responses of the ice sheets, but we neglect any self-dampening or self-amplifying processes. This is particularly relevant in situations in which an instability is dominating the ice loss. The results obtained here are thus relevant, in particular wherever the ice loss is dominated by the forcing as opposed to an internal instability, for example in strong ocean warming scenarios. In order to allow for comparison the methodology was chosen to be exactly the same as in an earlier study (Levermann et al., 2014) but with 16 instead of 5 ice sheet models. We include uncertainty in the atmospheric warming response to carbon emissions (full range of CMIP5 climate model sensitivities), uncertainty in the oceanic transport to the Southern Ocean (obtained from the time-delayed and scaled oceanic subsurface warming in CMIP5 models in relation to the global mean surface warming), and the observed range of responses of basal ice shelf melting to oceanic warming outside the ice shelf cavity. This uncertainty in basal ice shelf melting is then convoluted with the linear response functions of each of the 16 ice sheet models to obtain the ice flow response to the individual global warming path. The model median for the observational period from 1992 to 2017 of the ice loss due to basal ice shelf melting is 10.2 mm, with a likely range between 5.2 and 21.3 mm. For the same period the Antarctic ice sheet lost mass equivalent to 7.4 mm of global sea level rise, with a standard deviation of 3.7 mm (Shepherd et al., 2018) including all processes, especially surface-mass-balance changes. For the unabated warming path, Representative Concentration Pathway 8.5 (RCP8.5), we obtain a median contribution of the Antarctic ice sheet to global mean sea level rise from basal ice shelf melting within the 21st century of 17 cm, with a likely range (66th percentile around the mean) between 9 and 36 cm and a very likely range (90th percentile around the mean) between 6 and 58 cm. For the RCP2.6 warming path, which will keep the global mean temperature below 2 ∘C of global warming and is thus consistent with the Paris Climate Agreement, the procedure yields a median of 13 cm of global mean sea level contribution. The likely range for the RCP2.6 scenario is between 7 and 24 cm, and the very likely range is between 4 and 37 cm. The structural uncertainties in the method do not allow for an interpretation of any higher uncertainty percentiles. We provide projections for the five Antarctic regions and for each model and each scenario separately. The rate of sea level contribution is highest under the RCP8.5 scenario. The maximum within the 21st century of the median value is 4 cm per decade, with a likely range between 2 and 9 cm per decade and a very likely range between 1 and 14 cm per decade.

Extract: "In summary, for each emission scenario the procedure works as follows (each of the items is described in more detail below and in Levermann et al., 2014).
1.   Randomly select a global mean temperature realization of the respective RCP scenario from the 600 MAGICC 6.0 realizations constrained by the observed temperature record. The time series start in 1850 and end in 2100.
2.   Randomly select one of 19 CMIP5 models in order to obtain a scaling factor and a time delay for the relation between global mean surface air temperature and subsurface ocean warming in the respective regional sector in the Southern Ocean.
3.   Randomly select a melting sensitivity in order to scale the regional subsurface warming outside the cavity of the Antarctic ice shelves onto basal ice shelf melting.
4.   Select an ice sheet model that is forced via its linear response function with the time series of the forcing obtained from steps 1–3.
5.   Compute the sea level contribution of this specific Antarctic ice sheet sector according to linear response theory.
6.   Repeat steps 1–5 20 000 times with different random selections in each of the steps in order to obtain a probability distribution of the sea level contribution of each Antarctic sector and each carbon emission scenario.

Thus, the 20 000 selections are obtained by randomly choosing one temperature time series, one CMIP5 ocean model, one melt sensitivity, and one ice sheet model. The procedure is also used for each of the ice sheet models separately. In this case the random selection in step 4 is replaced by a fixed selection of the model. The procedure is illustrated in Fig. 1. For the computation of the total sea level contribution from all Antarctic sectors together, the forcing is selected consistently for all sectors. That means that for each of the 20 000 computations of the sea level contribution one global mean temperature realization is selected, as is one ocean model for the subsurface temperature scaling and one basal melt sensitivity. Although there are other possibilities, this approach was chosen because it preserves the forcing structure as provided by the ocean models. Details of steps 1–5 are given in the upcoming subsections.

However, due to the very large potential sea level contribution of Antarctica and its high sea level commitment compared to the other contributions (Levermann et al., 2013), the rate of change increases strongly over the century. Under the RCP8.5 scenario the median rate of sea level contribution by the end of the 21st century from basal-melt-induced ice loss from Antarctica alone is with 4.1 mm yr−1 larger than the mean rate of sea level rise observed at the beginning of this century (Dangendorf et al., 2019; Hay et al., 2015; Oppenheimer et al., 2019).
Although the method described here has a large number of caveats it provides an estimate of the role of the uncertainty in the oceanic forcing for the uncertainty in Antarctica's future contribution to sea level rise. By comparison with the earlier study using the same method but only three ice sheet models of an earlier model generation, we find a shift of the sea level contribution to higher values and an increase in the ranges of uncertainty. We thus have to conclude that uncertainty with respect to the ice dynamic contribution of Antarctica due to future warming is still increasing and thus that coastal planning has to take into account that multi-decadal sea level projections are likely to change with an increasing understanding of the ice dynamics and their representation in ice sheet models. This study provides an estimate of the uncertainty in the future contribution of Antarctica to global sea level rise only based on known ice dynamics but including the full range of forcing uncertainty. It substantiates the result of the previous study that Antarctica can become the largest contributor to global sea level rise in the future, in particular if carbon emissions are not abated."

Caption: "Figure 11 Projections from all models of the future sea level contribution of the different Antarctic sectors following the procedure depicted in Fig. 1 and detailed in Sect. 2. The white line represents the median value, the dark shading the likely range (66th percentile around the median), and the light shading the very likely range (90th percentile around the median)."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2811 on: February 20, 2020, 10:27:05 PM »
With a hat-tip to baking the first attached image shows the ice mélange near the seaward outlet of the PIIS southern shear margin with the Southern Ice Shelf (circa February 20, 2020).  If/when the icebergs are released to the open ocean, the Southern Ice Shelf will be subject to calving; which might likely serve to reduce the stability of the ice shelf of the Southwest Tributary Glacier:

Caption for the first image: "Chaos where the southern shear margin of Pine Island Glacier meets the sea, seen in pre-dawn light this morning. Immense forces are at work here, shattering, rotating, tilting and thrusting large blocks of ice."

Edit: The second image shows a Sentinel 1 view of the PIIS Southern Shear Margin filled with icebergs that calved off of the PIIS South Ice Shelf and which could float-out into the ocean within the next year; which would leave an exposed calving face for the PIIS South Ice Shelf.
« Last Edit: February 21, 2020, 04:31:00 PM by AbruptSLR »
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2812 on: February 20, 2020, 11:20:44 PM »
The image from the linked reference confirms that if one is worried about crossing potential tipping points in the next few decades (as I am) that it would be a good idea to immediately start reducing methane (and other GHG) emissions:

Title: "Demonstrating GWP*: a means of reporting warming-equivalent emissions that captures the contracting impacts of short- and long-lived climate pollutants" by Lynch et al. (2020).

https://iopscience.iop.org/article/10.1088/1748-9326/ab6d7e/pdf

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2813 on: February 21, 2020, 02:47:24 AM »
The linked report indicates that by 2035 we may cross a '... tipping point, after which no practicable amount of effort can reduce the risk of a slide to a plus-2 degree C world ..'.

Title: "Global risks 2035 update: Decline or new renaissance?" Oct. 30, 2019, by Mathew Burrow

https://www.atlanticcouncil.org/in-depth-research-reports/report/global-risks-2035-update/

Extract: "Experts have been warning about the impacts of climate change for years—if not decades. The temptation—especially when the impacts are less widespread—is to take small steps toward managing the risks. Research is now showing that the world is on the verge of a tipping point, after which no practicable amount of effort can reduce the risk of a slide to a plus-2-degree C world in which life would become unbearable for a great many."
« Last Edit: February 21, 2020, 03:46:19 PM by AbruptSLR »
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2814 on: February 21, 2020, 04:02:29 PM »
While many people like to count on technological advances to fight climate change, the linked article cites just one example of how advances in fracking technology for both oil and gas is only getting started; which will likely make it difficult for policy makers from supporting a natural gas energy bridge to the future, even though natural gas has the same (or worse) carbon footprint as coal:

Title: "Water reuse could be key for future of hydraulic fracturing"

https://phys.org/news/2020-02-reuse-key-future-hydraulic-fracturing.html

Extract: "Enough water will come from the ground as a byproduct of oil production from unconventional reservoirs during the coming decades to theoretically counter the need to use fresh water for hydraulic fracturing operations in many of the nation's large oil-producing areas. But while other industries, such as agriculture, might want to recycle some of that water for their own needs, water quality issues and the potential costs involved mean it could be best to keep the water in the oil patch."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2815 on: February 21, 2020, 05:23:58 PM »
If anyone will be attending the EGU General Assembly 2020 in Vienna, Austria May 3-8, 2020; it would be nice to hear back about presentations made at any of the CR5 – Ice Sheets, ice shelves and glaciers sessions, such as:

CR5 – lce sheets, ice shelves and glaciers

CR5.2
Modelling ice sheets and glaciers

This session is intended to attract a broad range of ice-sheet and glacier modelling contributions, welcoming applied and theoretical contributions. Theoretical topics that are encouraged are higher-order mechanical models, data inversion and assimilation, representation of other earth sub-systems in ice-sheet models, and the incorporation of basal processes and novel constitutive relationships in these models.

Applications of newer modelling themes to ice-sheets and glaciers past and present are particularly encouraged, in particular those considering ice streams, rapid change, grounding line motion and ice-sheet model intercomparisons.

Share: https://meetingorganizer.copernicus.org/EGU2020/session/34957

Convener: Fabien Gillet-Chaulet Co-conveners: Stephen Cornford, Gael Durand, Sainan Sun

CR5.4
Ice-sheet and climate interactions

Ice sheets play an active role in the climate system by amplifying, pacing, and potentially driving global climate change over a wide range of time scales. The impact of interactions between ice sheets and climate include changes in atmospheric and ocean temperatures and circulation, global biogeochemical cycles, the global hydrological cycle, vegetation, sea level, and land-surface albedo, which in turn cause additional feedbacks in the climate system. This session will present data and modelling results that examine ice sheet interactions with other components of the climate system over several time scales. Among other topics, issues to be addressed in this session include ice sheet-climate interactions from glacial-interglacial to millennial and centennial time scales, the role of ice sheets in Cenozoic global cooling and the mid-Pleistocene transition, reconstructions of past ice sheets and sea level, the current and future evolution of the ice sheets, and the role of ice sheets in abrupt climate change.

Share: https://meetingorganizer.copernicus.org/EGU2020/session/34963

Co-organized by CL4
Convener: Heiko Goelzer Co-conveners: Alexander Robinson, Ricarda Winkelmann, Philippe Huybrechts, Stefanie Mack

CR5.7
Ice shelves and tidewater glaciers - dynamics, interactions, observations, modelling

Ice shelves and tidewater glaciers are sensitive elements of the climate system. Sandwiched between atmosphere and ocean, they are vulnerable to changes in either. The recent disintegration of ice shelves such as Larsen B and Wilkins on the Antarctic Peninsula, current thinning of the ice shelves in the Amundsen Sea sector of West Antarctica, and the recent accelerations of many of Greenland's tidewater glaciers provide evidence of the rapidity with which those systems can respond. Changes in marine-terminating outlets appear to be intimately linked with acceleration and thinning of the ice sheets inland of the grounding line, with immediate consequences for global sea level. Studies of the dynamics and structure of the ice sheets' marine termini and their interactions with atmosphere and ocean are the key to improving our understanding of their response to climate forcing and of their buttressing role for ice streams. The main themes of this session are the dynamics of ice shelves and tidewater glaciers and their interaction with the ocean, atmosphere and the inland ice, including grounding line dynamics. The session includes studies on related processes such as calving, ice fracture, rifting and mass balance, as well as theoretical descriptions of mechanical and thermodynamic processes. We seek contributions both from numerical modelling of ice shelves and tidewater glaciers, including their oceanic and atmospheric environments, and from observational studies of those systems, including glaciological and oceanographic field measurements, as well as remote sensing and laboratory studies.

Share: https://meetingorganizer.copernicus.org/EGU2020/session/36133

Co-organized by OS1
Convener: Adrian Jenkins Co-conveners: Rachel Carr, Angelika Humbert, Nicolas Jourdain, Inga Monika Koszalka

CR5.8
Hydrology of ice shelves, ice sheets and glaciers - from the surface to the base

Dynamic subglacial and supraglacial water networks play a key role in the flow and stability of ice sheets. The accumulation of meltwater on the surface of ice shelves has been hypothesized as a potential mechanism controlling ice-shelf stability, with ice-shelf collapse triggering substantial increases in discharge of grounded ice. Observations and modelling also suggest that complex hydrological networks occur at the base of glaciers and these systems play a prominent role in controlling the flow of grounded ice. This session tackles the urgent need to better understand the fundamental processes involved in glacial hydrology that need to be addressed in order to accurately predict future ice-sheet evolution and mass loss, and ultimately the contribution to sea-level rise .
We seek contributions from both the modelling and observational communities relating to any area of ice-sheet hydrology. This includes but is not limited to: surface hydrology, melt lake and river formation; meltwater processes within the ice and firn; basal hydrology; subglacial lakes; impacts of meltwater on ice-sheet stability and flow; incorporation of any of these processes into large-scale climate and ice-sheet models.

Share: https://meetingorganizer.copernicus.org/EGU2020/session/34964

Co-organized by HS2.1
Convener: Sammie Buzzard Co-conveners: Ian Hewitt, Amber Leeson, Martin Wearing

CR5.9
Subglacial Environments of Ice Sheets and Glaciers

Subglacial environments are among the least accessible regions on Earth and represent one of the last physical frontiers of glaciological research, while emerging as a unique ecological habitat. The subglacial environment is a key component in the dynamic behaviour of ice sheets and glaciers, involving complex and precise mass and energy transfers between the ice and its substrate of water, air, bedrock, or sediment, and the oceans at ice sheet boundaries. In particular, determining the distribution and nature of water flows at the ice-mass bed is highlighted as a priority for understanding and predicting ice dynamics. For example, both remote sensing and ground-based observations across Antarctica and Greenland highlight the existence of subglacial water in a variety of forms, ranging from vast subglacial lakes (providing distinctive habitats for potentially unique life forms) to mm-thick water flows at the ice-substrate interface. Feedbacks between increased surface melting, glacier bed conditions and ice flow also affect alpine glaciers, potentially contributing to increased glacial retreat in low and mid-latitude mountain regions.

It is clear that subglacial processes impact ice dynamics, transcending ice-mass scales from valley glaciers to large ice sheets and, through feedback loops, contribute to changes in sea level, ocean circulation, and climate evolution. Quantitative characterisation of the basal environment therefore remains an outstanding glaciological problem, as does scaling of this knowledge for use in modelling ice sheet and glacier behaviour.

We invite scientific contributions that include, but are not limited to, measurements and/or modelling of: (i) flow of subglacial water at the bed and through subglacial sediments; (ii) linkages between subglacial hydrology and ice dynamics; (iii) theoretical-, field-, or laboratory-based parameterisation of subglacial processes in numerical ice-flow models; (v) formation, geometry and potential hydrological linkages between subglacial lakes; (v) subglacial and supraglacial lake drainage and subglacial floods from ice margins; and (vi) geomorphological evidence of subglacial water flows from contemporary ice-sheet margins and across formerly glaciated continental-scale regions.

Share: https://meetingorganizer.copernicus.org/EGU2020/session/34965

Convener: Adam Booth Co-conveners: Robert Bingham, Christine Dow, Bryn Hubbard, Harold Lovell


See also:

CR – Cryospheric Sciences

https://meetingorganizer.copernicus.org/EGU2020/sessionprogramme/CR?cosession=5e4ffc4ae69d84-89874115-m#s34964

   CR1 – The State of the Cryosphere: Past, Present, Future
   CR2 – Instrumental and paleo-archive observations and analysis of the cryosphere
   CR3 – Snow and ice: properties, processes, hazards
   CR4 – Frozen ground, debris-covered glaciers and geomorphology
   CR5 – lce sheets, ice shelves and glaciers
   CR6 – Sea Ice
   CR7 – The cryosphere in the Earth system: interdisciplinary topics
   CR8 – Short courses
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2816 on: February 21, 2020, 05:40:52 PM »
The linked Nature magazine editorial re-emphasizes a major theme of this thread that:

“If carbon emissions are not drastically reduced by 2030, we will be entering uncharted territory, including the possibility (…) of passing irreversible tipping points such as the widespread loss of Antarctic ice.”

Title: "Nature Magazine Editorial: Research decade must focus on climate"

https://www.pik-potsdam.de/news/in-short/nature-magazine-editorial-research-decade-must-focus-on-climate

“The pace of warming means that the window for avoiding temperature rises of 1.5 or 2°C is now frighteningly small. The 2020s will be a make-or-break,” Nature maintains in unequivocal terms. “If carbon emissions are not drastically reduced by 2030, we will be entering uncharted territory, including the possibility (…) of passing irreversible tipping points such as the widespread loss of Antarctic ice.”

See also:

Title: "The scientific events that shaped the decade"

https://www.nature.com/articles/d41586-019-03857-x

Extract: "The 2010s have seen breakthroughs in frontiers from gene editing to gravitational waves. The coming one must focus on climate change."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2817 on: February 21, 2020, 10:16:37 PM »
It looks like JP Morgan agrees with the primary theme of this thread:

Title: "World's Biggest Fossil Fuel Funder Notes Climate Change Could End 'Human Life as We Know it'"

https://earther.gizmodo.com/worlds-biggest-fossil-fuel-funder-notes-climate-change-1841835204

Extract: "The finance industry is issuing some of the direst warnings about climate change while funding the industry most responsible for it. Today’s example: JP Morgan.

The bank is the single biggest funder of fossil fuels in the world. But its economists wrote an internal report leaked to Extinction Rebellion on Friday stating that they “cannot rule out catastrophic outcomes where human life as we know it is threatened.”

The analysis is most worried about the tail risks of climate change. In plain language, that’s the less likely but utterly catastrophic outcomes of the climate crisis that keeps economists and scientists up at night.

We’re talking things like the sudden collapse of the West Antarctic Ice Sheet, sending sea levels more than 10 feet higher and displacing millions of people. Or a feedback loop where melting permafrost releases more carbon dioxide that causes more warming that causing more thawing and carbon emissions. These things are already happening but at a rate, we can somewhat handle. What’s worrisome is that we could cross a tipping point where they happen suddenly and humanity is left having to deal with a new, unsteady state.

“Although precise predictions are not possible, it is clear that the earth is on an unsustainable trajectory,” the JP Morgan analysts wrote. “Something will have to change at some point if the human race is going to survive.”

In a logical world, this would be enough to convince world leaders to act. The report calls for a global price on carbon as the single, most effective climate policy the world could pursue. Instead, governments are basically engaged in a game of chicken with the climate as they approve more fossil fuel development that will almost surely screw future generations."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2818 on: February 21, 2020, 11:43:02 PM »
Seeing is believing: Antarctic Peninsula ice melt from February 4th to the 13th, 2020.

Title: "'Antarctica Melts,' NASA Says, Showing Effects Of A Record Warm Spell"

https://www.npr.org/2020/02/21/808187601/-antarctica-melts-nasa-says-showing-effects-of-record-heat

Extract: "Where there was a white ice cap, there are now brown blotches of land; melted snow and ice have created ponds of water. Those are the effects of the recent record high temperatures in Antarctica, according to NASA, which on Friday released stunning before-and-after satellite images of northern Antarctica.

The photos center on Eagle Island, part of the northern tip of the Antarctic Peninsula that stretches toward South America. Satellites took the images just nine days apart, on Feb. 4 and Feb. 13. But dramatic changes took place in that timespan. Two days after the first photo was taken, the area hit 18.3 degrees Celsius (64.9 degrees Fahrenheit) — matching that day's temperature in Los Angeles, NASA notes."

Caption: "Satellite images show the effects of a prolonged warm spell on Eagle Island, in the far north of the Antarctic Peninsula, NASA says. An inch of snowpack melted in just one day, the agency says. The blue areas in snow on the right are ponds of melted water."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2819 on: February 22, 2020, 12:39:44 AM »
I provide a better reference citation for my Reply #2128.

Forster, P.M., Maycock, A.C., McKenna, C.M. et al. Latest climate models confirm need for urgent mitigation. Nat. Clim. Chang. 10, 7–10 (2020). https://doi.org/10.1038/s41558-019-0660-0

https://www.nature.com/articles/s41558-019-0660-0#citeas
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2820 on: February 22, 2020, 10:16:18 PM »
First, I re-post (in quotes immediately below) my Reply #5 in the Surge thread from February 21, 2013:

"Attached is a figure of output from a hydraulic circulation model [taken from numerical simulations conducted at CCPO (St-Laurent, Klinck and Dinniman)] for the Amundsen Sea Embayment, ASE, indicating that warm CDW flows through a trough in the continental shelf from the Amundsen Sea to the Pine Island Glacier, PIG, ice shelf, a portion of this water then flows Westward through a submerged rift valley that parallels the coast down to the postulated cavity at the threshold of Thwaites, where I believe that the warm CDW bottom water flows into the cavity beneath fresher seawater (diluted by melt water from the glacier), and I believe that the colder fresher water continues flowing to the Northwest.  If so this would set-up both vertical and horizontal saline pumping actions for the combine PIG/Thwaites glacial system; which would promote this inflow of warm CDW flow to accelerate the melting of the glacial ice at the groundling line of both PIG and Thwaites."

Second, the following linked article from 2020 confirms that warm CDW is indeed being advected from the Pine Island Ice Shelf to beneath the Thwaites East Ice Shelf, TEIS.  Also, the second attached image shows the path taken (indicated by arrows) of two more streams of warm CDW to beneath both the TEIS and the Thwaites Ice Tongue, following the seabed troughs shown in the third attached image.  The fourth image shows the bathymetry near the Thwaites Gateway that shows the seabed channels that the modified warm CDW follow from the PIIS to beneath the TEIS and the Thwaites Ice Tongue.

Title: "Antarctica's Thwaites Glacier 'Has Got Three Guns Pointed Right At It'"

https://www.msn.com/en-us/weather/topstories/antarcticas-thwaites-glacier-has-got-three-guns-pointed-right-at-it/ar-BB10flKO?li=BBnb7Kz

Extract: "Scientists have discovered three channels of warm water under Antarctica's Thwaites Glacier mixing underneath the ice, threatening the glacier's collapse. "Thwaites has got these three guns pointed right at it," Erin Pettit, a glaciologist at Oregon State University in Corvallis, told Nature. "There is warm water coming from all directions."

Pettit's team deployed an underwater robot named Rán, after the Norse goddess of the sea. It obtained data on ocean conditions underneath the shelf, plus information that has since informed detailed seafloor maps of the area.

Information collected over the last two years suggests warm water is hitting Thwaites from Pine Island Glacier to its north. This warm water is merging with two more streams of warm water coming from different directions underneath the ice shelf, Nature reports.

The warm water streams threaten to destabilize Thwaites' traditionally more stable eastern side—which flows at approximately 2,000 feet per year, compared to 1.2 miles per year on the western side.

One of the most surprising finds to come out of the project, said Pettit, is the discovery that the Thwaites glacier contains a rich and complex landscape of channels, ridges and cliffs on its underside, forged by warm water currents, showing that the glacier is not melting uniformly.

Pettit and her team are just two years into a five-year mission. At the end, scientists expect to know more about the risks and vulnerabilities of the Thwaites glacier and its future. "We've never seen an ice sheet disintegrate in a warming climate, so we're struggling to project how it could happen," Ted Scambos, a glaciologist at the National Snow and Ice Data Center in Boulder, Colorado, told Nature."

Third, the following linked abstract from Pettit et al's 2020 AGU Oceans Meeting provides more details about these three measured streams of CDW and how they may soon destabilize both the TEIS and the Thwaites Ice Tongue.

Title: "HE21B - Ice-Ocean Interactions and Circulation Around the Antarctic Margins I"

https://agu.confex.com/agu/osm20/meetingapp.cgi/Session/92341

Processes occurring at or close to the ice-ocean interface around Antarctica influence the state and circulation of a large proportion of the global ocean. The annual cycle of sea ice formation, export and melt is critical to the formation of both Antarctic Bottom Water and Antarctic Intermediate Water, which together fill more than half of the global sub-surface ocean. Inflow of warm Circumpolar Deep Water beneath floating shelves of marine-terminating glaciers promotes retreat of the grounded portion of the ice sheet, and thus sea level rise. Though historically limited by the prohibitive costs of in situ observations and high-resolution models, recent field campaigns and focused model development efforts are now rapidly advancing our understanding of these processes. This session will showcase recent advances in understanding the physical processes occurring in the Antarctic marginal seas, across the Antarctic continental shelf and slope, and within the ocean cavities beneath floating ice shelves. Studies based on observations, numerical models and theory are all welcome. The authors particularly encourage submissions addressing ocean-sea ice interactions, warm water pathways from continental slope to grounding zones, and inter-connectivity between sectors of the Antarctic margins and the broader Southern Ocean.

Title: "HE21B-01 - Vulnerability of Eastern Thwaites Ice Shelf, West Antarctica to Warm Ocean Water: Insights from First AUV Exploration of Sub-Ice-Shelf Environment"

https://agu.confex.com/agu/osm20/meetingapp.cgi/Paper/656253

Abstract
Thwaites and neighboring glaciers and ice shelves in West Antarctica are rapidly losing mass and perceived as vulnerable to warm ocean water entering the sub-ice-shelf cavity. Predictions of future ice-shelf and glacier dynamic behavior still lack understanding of the dominant processes and feedbacks, particularly the spatial and temporal variability of ice melt and its atmospheric and oceanic drivers. Here we present the first direct observations of ocean temperature and salinity underneath Thwaites ice shelf collected by an autonomous underwater vehicle as part of the TARSAN (Thwaites-Amundsen Regional Survey and Network) Project. We provide an initial interpretation in the context of nearby ship-based temperature and salinity profiles, recently improved bathymetric maps, radar-derived ice geometry, and related data. Our analyses suggests that deep water (> 1000 m) underneath the central part of the Thwaites ice shelf originates in Pine Island Bay, which suggests more complex deep water circulation than previously understood. Further, mid-depth water (700 - 1000 m) enters the cavity from both sides of a buttressing point for the Eastern Thwaites Ice Shelf. We observe large spatial gradients of density and temperature and infer that this is a region of strong current shear and active mixing processes. The findings highlight a vulnerability of the main buttressing point to warm water inflow from all sides and challenge conceptual models of ice-ocean interactions at glacier grounding zones. Finally, we provide an initial assessment of the possible local short-term dynamic response of the ice shelf to loss of this buttressing point. The Thwaites and other West Antarctic glaciers and ice shelves are rapidly changing; the potential for complex flow patterns that generate localized melting and loss of buttressing to feed back onto and alter those flow patterns remains a large uncertainty in predicting sea-level rise through the next decades.

Plain Language Summary
Glaciers are not good swimmers. As soon as they reach the ocean, they tend to breakup into icebergs and float away. Some glaciers do manage cautiously to "swim," extending out into the ocean as floating ice shelves, at least as far as they have some rock to hold on. Because they require rock to be stable, they are particularly vulnerable to environmental changes. The less rock they have to hold on to, the easier it is for small changes in ocean water currents, to push them off that rock, causing the glacier ice to flow more quickly, fracture, and ultimately collapse into a bunch of icebergs. At its farthest extent, the Eastern Thwaites Ice Shelf is mainly holding on to just one rock right now. We show some initial data from a submarine the explored the cavity beneath the ice shelf and discuss our ideas about it's potential for getting kicked off its rock and drowning. It's hard to teach a glacier to swim.
« Last Edit: February 22, 2020, 10:43:50 PM by AbruptSLR »
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2821 on: February 22, 2020, 10:24:49 PM »
The AGU Ocean Sciences Meeting is always a good source of information about ice-ocean interactions and associated climate risks. Therefore, I provide the first two links to the sessions descriptions for the 2020 meeting (held in San Diego), and following that I provide an abstract from an associated session:

Title: "Ocean Sciences Meeting 2020"

https://www.agu.org/Ocean-Sciences-Meeting
https://agu.confex.com/agu/osm20/meetingapp.cgi/Home/0

The following provides an abstract about measurements of seawater beneath the Dotson Ice Shelf, that indicates both seasonal influx of relatively warm seawater into the east side of the ice shelf and synergy of this seawater flux between the Dotson and the Crosson ice cavities:

Title: "HE21B-02 - Seaglider and Float Observations Beneath Dotson Ice Shelf, West Antarctica"

https://agu.confex.com/agu/osm20/meetingapp.cgi/Paper/653697

Abstract
In Antarctica and Greenland, interactions between Oceans and Ice sheets are crucial to the regulation of the global overturning circulation and the current acceleration of ice flow into the ocean and associated global sea-level rise. Satellite and moored ocean observations demonstrate with increasing temporal and spatial resolution that the interaction is complex, and occurs on broad ranges of scales. But the establishment of clear relationships between ocean and ice sheet will remain elusive until we obtain direct, sustained in-situ observations beneath and near the ice shelves. Three Seagliders and four EM-APEX floats sampled oceanic properties near and under the Dotson ice shelf in West Antarctica in January 2018, with observations continuing through the winter into summer 2018/2019, covering several hundreds of kilometers under the ice shelf. Observed water properties generally confirm expected features of under ice shelf circulation, with deep inflowing warmer water on the eastern side of the cavity and shallower outflowing meltwater on the western side. Initial analysis also reveal new and potentially important features for ice/ocean interactions: (i) bathymetric inversion from airborne gravity observations are significantly improved by using in-situ constraints; (ii) large intraseasonal and seasonal variability along the ice shelf calving front, of the order of the interannual variability shown previously, is rapidly transferred inside the cavity; and (iii) a float slipped through a wide gap between Dotson and Crosson ice cavities, implying broader connectivity between basins, and potential implications for ice dynamics. The technology used for this project offers tantalizing prospects for future explorations.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2822 on: February 22, 2020, 10:38:15 PM »
Here is another abstract from the AGU Ocean Sciences Meeting 2020 that focuses on a model that is relevant to how warm CDW could get beneath the FRIS in coming years/decades.  The first two images are from the associated poster presentation and the last two image show conceptually how warm CDW was, until recently, blocked from getting beneath FRIS and how in the future it could penetrate all the way to the grounding line:

Title: "HE24B-1962 - Role of Tides in Ice-Ocean Interactions Over the Antarctic Continental Shelf and Slope"

https://agu.confex.com/agu/osm20/meetingapp.cgi/Paper/647193

Abstract
Tides are key contributors to the circulation and water mass exchange around the Antarctic margins. Previous studies indicate that the rectification of tidal currents on the continental slopes plays a crucial role in setting the structure of the Antarctic Slope Current (ASC). Tides make large contribution to the across-shelf heat transport towards the Antarctic coast, and also affect the dense-water outflows on the continental shelf and slope. However, the interactions between tidal flows, sea ice drift and the structure and transport of the ASC remain poorly understood. In this study our primary aim is to understand how tides and wind forcing drive the ocean/sea-ice system of the ASC. We are also investigating the role of tides in modulating cross-slope exchanges.

We utilize high-resolution process modeling in idealized settings to perform a series of experiments with varying tidal amplitude, wind speed, atmospheric forcing and sea ice parameters. To better understand the dynamics of tidally-forced ice/ocean flows, we also develop a 1D model to simulate a barotropic ocean overlaid by viscous-plastic sea ice, driven by tidal forcing and wind stress. We use this 1D model to explore the effects of drag coefficients, ice rheology parameters, wind stress and tidal forcing, and quantify the stress terms at ice-ocean interface and ocean bottom. Our results show that sea ice plays a role in redistributing tidal-input along-slope momentum away from the slope current, which affects the structure of the ASC and overturning of the slope front. The rectification of tidal currents enhances the ocean-ice heat flux, modulating the upper ocean stratification, as well as the formation and export of dense shelf water. We discuss the implications of our findings for circum-Antarctic variations in the structure and overturning of the ASC, and for redistribution of water masses and sea ice around Antarctica.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2823 on: February 22, 2020, 10:55:02 PM »
I provide the following three abstracts from the first linked AGU Ocean Science Meeting session on the Beaufort Gyre.  Selected findings from these three presentations include:

1. The Beaufort Gyre has progressively accumulated an unusually large amount of relatively warm fresh water between at least 2003 and 2018.

2. The Beaufort Gyre currently contains a sufficient accumulation of relatively warm fresh water to likely slow the MOC if/when it is released from the gyre.

3. Models of the Beaufort Gyre are improving and are providing new insights on the interactions between the Beaufort Gyre, the Arctic Ocean and the North Atlantic:

Title: "HE14B - New Insights into the Beaufort Gyre of the Arctic Ocean: Scientific Questions, Observing Technologies, and Modeling Capabilities I Posters"

https://agu.confex.com/agu/osm20/meetingapp.cgi/Session/84248

Title: "HE14B-1940 - Variability of the Beaufort Gyre freshwater content in 2003-2018 from observations and model results"

https://agu.confex.com/agu/osm20/meetingapp.cgi/Paper/494011

Abstract: "Hydrographic data collected from research cruises, moorings, Ice-Tethered Profiler observations and satellite altimetry in the Beaufort Gyre document an increase of more than 6,400 cubic km of liquid freshwater content from 2003-2018, a 40% growth relative to the climatology of the 1970s. This freshwater accumulation was a result of persistent anticyclonic atmospheric wind forcing accompanied by sea ice melt, wind-forced redirection of Mackenzie River discharge, and a contribution of waters of Pacific Ocean origin via Bering Strait. The fresh water input to the Beaufort Gyre region from Siberian rivers in 2003-2018 was negligible. Remnants of Siberian river waters detected by geochemical analysis, presumably penetrated into the region in 1989-1996 during a cyclonic circulation regime. A slight decrease of freshwater content in the region between 2010 and 2013 was associated with a relaxation of anticyclonic winds; however, in 2015-2016, the volume of freshwater content was greater than ever measured previously due to the combination of reintensified anticyclonic winds and continued fresh water supply from both ice melt and North American rivers discharge. In 2017 and 2018, the freshwater content remained high due to a complex variability of winds resulting in forcing favorable for freshwater content stabilization."

&

Title: "HE11A-04 - Impact of the Beaufort Gyre freshwater release on deepwater formation in the North Atlantic"

https://agu.confex.com/agu/osm20/meetingapp.cgi/Paper/656421

Abstract: "The Beaufort Gyre (BG) is the largest liquid freshwater reservoir of the Arctic Ocean. Observations show a significant increase of its freshwater content over the past 15 years, with the increase reaching 40% of its climatology in 2017. If the freshwater is released into the North Atlantic, the magnitude would excess that of the Great Salinity Anomaly of the 1970s, raising the specter of slowing global ocean circulation. However, whether the BG freshwater can ultimately perturb the North Atlantic deepwater formation is highly uncertain. Here, we assess the impact of a potential BG freshwater release during the historical period, using an eddy-permitting ocean-sea ice model with passive tracers that explicitly track the BG volume and freshwater transport.

Our simulations suggest that more BG-sourced freshwater (36 mSv) reached the North Atlantic during a release phase (1983-1995) of the BG freshwater content than during an accumulation phase (1996-2008), when most BG-sourced water recirculated within the Arctic basin. 70% of this BG-sourced freshwater routed through Davis Strait, while 30% routed through Fram Strait. This BG-sourced freshwater was able to bring down the surface salinity by 0.35 psu in the western Labrador Sea towards the end of the release phase. Although the historical release was not able to induce obvious impact during the phase of harsh winters with very strong convection in the early 1990s, the current BG freshwater content anomaly has almost doubled its historical maximum and a future release may become large enough to dampen the deepwater formation once in conjunction with mild winters."

&

Title: "HE14B-1927 - Comparison of High-Resolution Model Output in the Beaufort Gyre"

https://agu.confex.com/agu/osm20/meetingapp.cgi/Paper/646599

Abstract: "We compare ice and circulation patterns in the Beaufort Gyre from several products of the HYbrid Coordinate Ocean Model (HYCOM). The first two are from the Naval Research Laboratory’s Global Ocean Forecast System (GOFS), an assimilative, coupled ocean-ice model that produces global operational model forecasts. GOFS 3.1 has a nominal resolution of 1/12.5°, or roughly 3.5 km in the Beaufort Gyre region, while GOFS 3.5 has a nominal resolution of 1/25°, or roughly 1.8 km in that same region. These will be compared with a non-assimilative, regional version of HYCOM coupled with the ice model CICE, referred to as BFG (Beaufort Gyre). This regional version also has a resolution of 1/25°, and is the first attempt at a coupled HYCOM+CICE at high latitudes such that ice is transported through the boundaries. The two GOFS products agree closely on assimilated quantities such as ice edge, while differences with BFG in ice concentration and surface temperature are evident during the melting season. However, at depths below approximately 200 m, GOFS 3.5 and BFG agree closely, demonstrating a subsurface layer of warm, Atlantic water that matches observations, while the Atlantic water in the lower resolution GOFS 3.1 model is thinner and cooler. All differences in melting, refreezing, and subsurface circulation between these three depictions of the Arctic region from May 2017 through April 2018 will be examined."

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2824 on: February 23, 2020, 05:15:43 PM »
With a hat-tip to baking the first attached image shows the ice mélange near the seaward outlet of the PIIS southern shear margin with the Southern Ice Shelf (circa February 20, 2020).  If/when the icebergs are released to the open ocean, the Southern Ice Shelf will be subject to calving; which might likely serve to reduce the stability of the ice shelf of the Southwest Tributary Glacier:

Caption for the first image: "Chaos where the southern shear margin of Pine Island Glacier meets the sea, seen in pre-dawn light this morning. Immense forces are at work here, shattering, rotating, tilting and thrusting large blocks of ice."

Edit: The second image shows a Sentinel 1 view of the PIIS Southern Shear Margin filled with icebergs that calved off of the PIIS South Ice Shelf and which could float-out into the ocean within the next year; which would leave an exposed calving face for the PIIS South Ice Shelf.

As the attached Sentinel 1 image of the PIIS-SIS-SWT interface area after grixm from Feb 23 2020 is clearer than the image that I previously posted I provide it here (as I can no longer modify the original post).  The red line added by grixm shows the existing rift extending from the SIS into the SWT ice shelf that would likely become activated if/when the SIS calves locally once the icebergs in the Southern Shear Margin float out to sea (as has the bergy bit indicated by the red circle drawn by grixm).
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2825 on: February 23, 2020, 06:21:25 PM »
The linked open access reference discusses how climate tipping points can be modelled to produce 'extreme sensitivity' (see the associated first attached image).  This reference indicates that it is difficult to simulate this behavior in conventional climate models like those in CMIP5 and/or CMIP6.  However, just because it is difficult to model such dynamical behavior due not mean that nature does not behave this way as indicated by the second image (by Tobias Friedrich et al. 2016); which could be the result of a cascade of tipping points (see the third image) resulting in a progressive ratcheting up of quasi-static equilibrium states due to perturbations such as a Beaufort Gyre discharge and/or an Extreme El Nino event as illustrated by the fourth image.

Ashwin, P., von der Heydt, A.S. Extreme Sensitivity and Climate Tipping Points. J Stat Phys (2019). https://doi.org/10.1007/s10955-019-02425-x

https://link.springer.com/article/10.1007/s10955-019-02425-x

Abstract: "A climate state close to a tipping point will have a degenerate linear response to perturbations, which can be associated with extreme values of the equilibrium climate sensitivity (ECS). In this paper we contrast linearized (‘instantaneous’) with fully nonlinear geometric (‘two-point’) notions of ECS, in both presence and absence of tipping points. For a stochastic energy balance model of the global mean surface temperature with two stable regimes, we confirm that tipping events cause the appearance of extremes in both notions of ECS. Moreover, multiple regimes with different mean sensitivities are visible in the two-point ECS. We confirm some of our findings in a physics-based multi-box model of the climate system."

Extract: "Recent work [35] suggests we are at a crossroads in terms of the future earth system state. On the one hand, looking at the palaeoclimate record for the last 1 million years suggests that we are overdue descent into an ice age. On the other hand, comparison of anthropogenic CO22 emissions with the palaeo record suggest the next tipping point may be to much warmer ‘hothouse’ earth. A better understanding of improved indicators such as two-point ECS and what they say about the climate response to changes in greenhouse gases, together with a better understanding of hothouse earth climate states that may have existed in the past (e.g. the Palaeocene climate [3, 21]) should help our understanding and guide future generations in their need to avoid dangerous climate change."

Caption for the first image: "Temperature versus a atmospheric CO2 concentration and b ΔR of radiative forcing by CO2, for the time series in Fig. 3. The red line corresponds to the steady solution of (15) with dependence on CO2 (Color figure online)"
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2826 on: February 23, 2020, 10:48:42 PM »
The linked reference concludes that ESS during the Pliocene (which had radiative forcing comparable to what we will likely reach circa 2030) Epoch was about 53% higher than ECS (including due to the loss of large areas of the AIS in the Pliocene) .  While consensus assume that the marine glaciers in Antarctica will be lost gradually (over centuries to millennia), their assumptions do not mean that these marine glaciers may be lost abruptly (in less than a century) due to MICI-type of behavior

"There is a statistically significant relationship between ECS and Pliocene global annual average temperature change. The PlioMIP2 ensemble finds that ESS is greater than ECS by a best estimate of 53%."

Haywood, A. M., Tindall, J. C., Dowsett, H. J., Dolan, A. M., Foley, K. M., Hunter, S. J., Hill, D. J., Chan, W.-L., Abe-Ouchi, A., Stepanek, C., Lohmann, G., Chandan, D., Peltier, W. R., Tan, N., Contoux, C., Ramstein, G., Li, X., Zhang, Z., Guo, C., Nisancioglu, K. H., Zhang, Q., Li, Q., Kamae, Y., Chandler, M. A., Sohl, L. E., Otto-Bliesner, B. L., Feng, R., Brady, E. C., von der Heydt, A. S., Baatsen, M. L. J., and Lunt, D. J.: A return to large-scale features of Pliocene climate: the Pliocene Model Intercomparison Project Phase 2, Clim. Past Discuss., https://doi.org/10.5194/cp-2019-145, in review, 2020.

https://www.clim-past-discuss.net/cp-2019-145/
https://www.clim-past-discuss.net/cp-2019-145/cp-2019-145.pdf

Abstract. The Pliocene epoch has great potential to improve our understanding of the long-term climatic and environmental consequences of an atmospheric CO2 concentration near ~ 400 parts per million by volume. Here we present the large-scale features of Pliocene climate as simulated by a new ensemble of climate models of varying complexity and spatial resolution and based on new reconstructions of boundary conditions (the Pliocene Model Intercomparison Project Phase 2; PlioMIP2). As a global annual average, modelled surface air temperatures increase by between 1.4 and 4.7 °C relative to pre-industrial with a multi-model mean value of 2.8 °C. Annual mean total precipitation rates increase by 6 % (range: 2 %–13 %). On average, surface air temperature (SAT) increases are 1.3 °C greater over the land than over the oceans, and there is a clear pattern of polar amplification with warming polewards of 60° N and 60° S exceeding the global mean warming by a factor of 2.4. In the Atlantic and Pacific Oceans, meridional temperature gradients are reduced, while tropical zonal gradients remain largely unchanged. Although there are some modelling constraints, there is a statistically significant relationship between a model's climate response associated with a doubling in CO2 (Equilibrium Climate Sensitivity; ECS) and its simulated Pliocene surface temperature response. The mean ensemble earth system response to doubling of CO2 (including ice sheet feedbacks) is approximately 50 % greater than ECS, consistent with results from the PlioMIP1 ensemble. Proxy-derived estimates of Pliocene sea-surface temperatures are used to assess model estimates of ECS and indicate a range in ECS from 2.5 to 4.3 °C. This result is in general accord with the range in ECS presented by previous IPCC Assessment Reports.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2827 on: February 24, 2020, 05:07:26 PM »
Key parts of the US fossil fuel industry will not 'go quietly into the night':

Title: "The Oil Industry Is Quietly Winning Local Climate Fights"

https://www.theatlantic.com/science/archive/2020/02/oil-industry-fighting-climate-policy-states/606640/

Extract: "In the past few years, the American Petroleum Institute and its allies have fought against climate-friendly policies in at least 16 different states.

Some of the most important fights over climate change aren’t being waged in Washington. They’re happening state by state, in a melee of utilities, fossil-fuel companies, state legislators, and persuaded voters."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2828 on: February 24, 2020, 05:29:08 PM »
I have not discussed the bipolar seesaw mechanism for a while, so I present the two linked references that present paleo-finding about the bipolar seesaw and the Southern Ocean.  These references confirm that cooling of the Southern Ocean surface (possibly/probably from an armada melting icebergs) leads to warming of the Northern Hemisphere over a period of more than a century.  Nevertheless, I suspect that possible future bipolar seesaw activity could happen this century for reasons including:

a) radiative forcing is currently increase at a rate of several hundreds to several thousands of times faster than in the paleo cases cited in the two references;

b) the current ozone hole was not extant in the cited paleo cases; which is upwelling relatively warm CDW faster now than in the past, and

c) rapid climate change (as is currently occurring) would give Antarctic marine glaciers less time to thin, which may well lead to taller ice cliffs in coming decades; which may likely result in faster MICI propagation in the WAIS in coming decades:

Andrew F. Thompson et al. (2019), "Southern Ocean Mechanism for the Interhemispheric Coupling and Phasing of the Bipolar Seesaw", JCLI, https://doi.org/10.1175/JCLI-D-18-0621.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-18-0621.1

Abstract: "The last glacial period is punctuated by abrupt changes in Northern Hemisphere temperatures that are known as Dansgaard–Oeschger (DO) events. A striking and largely unexplained feature of DO events is an interhemispheric asymmetry characterized by cooling in Antarctica during periods of warming in Greenland and vice versa—the bipolar seesaw. Methane-synchronized ice core records indicate that the Southern Hemisphere lags the Northern Hemisphere by approximately 200 years. Here, we propose a mechanism that produces observed features of both the bipolar seesaw and the phasing of DO events. The spatial pattern of sea ice formation and melt in the Southern Ocean imposes a rigid constraint on where water masses are modified: waters are made denser near the coast where ice forms and waters are made lighter farther north where ice melts. This pattern, coupled to the tilt of density surfaces across the Southern Ocean and the stratification of the ocean basins, produces two modes of overturning corresponding to different bipolar seesaw states. We present evolution equations for a simplified ocean model that describes the transient adjustment of the basin stratification, the Southern Ocean surface density distribution, and the overturning strength as the ocean moves between these states in response to perturbations in North Atlantic Deep Water formation, which we take as a proxy for Greenland temperatures. Transitions between different overturning states occur over a multicentennial time scale, which is qualitatively consistent with the observed Southern Hemisphere lag. The volume of deep density layers varies inversely with the overturning strength, leading to significant changes in residence times. Evidence of these dynamics in more realistic circulation models is discussed."

&

Svante Björck et al. (2019), "A south Atlantic island record uncovers shifts in westerlies and hydroclimate during the last glacial", Climate of the Past, https://doi.org/10.5194/cp-2019-65

https://www.clim-past-discuss.net/cp-2019-65/

Abstract. The period 36–18 ka was a dynamic phase of the last glacial, with large climate shifts in both hemispheres. Through the bipolar seesaw, the Antarctic Isotope Maxima and Greenland DO events were part of a global concert of large scale climate changes. The interaction between atmospheric processes and Atlantic meridional overturning circulation (AMOC) is crucial for such shifts, controlling upwelling- and carbon cycle dynamics, and generating climate tipping points. Here we report the first temperature and humidity record for the glacial period from the central South Atlantic (SA). The presented data resolves ambiguities about atmospheric circulation shifts during bipolar climate events recorded in polar ice cores. A unique lake sediment sequence from Nightingale Island at 37° S in the SA, covering 36.4–18.6 ka, exhibits continuous impact of the Southern Hemisphere Westerlies (SHW), recording shifts in their position and strength. The SHW displayed high latitudinal and strength-wise variability 36–31 ka locked to the bipolar seesaw, followed by 4 ka of slightly falling temperatures, decreasing humidity and fairly southern westerlies. After 27.5 ka temperatures decreased 3–4 °C, marking the largest hydroclimate change with drier conditions and a variable SHW position. We note that periods with more intense and southerly positioned SHW are correlated with periods of increased CO2 outgassing from the ocean. Changes in the cross-equatorial gradient during large northern temperature changes appear as the driving mechanism for the SHW shifts. Together with coeval shifts of the South Pacific westerlies, it shows that most of the Southern Hemisphere experienced simultaneous atmospheric circulation changes during the latter part of the last glacial.

The linked abstract from the AGU Ocean Sciences Meeting (February 2020 in San Diego); reminds us that the bipolar seesaw mechanism(s) is not (are not) limited to oceanic feedbacks but includes a good number of atmospheric feedbacks including shifts in the South Atlantic Subtropical Dipole. So a relatively warm freshwater release from the Beaufort Gyre into the North Atlantic would rapidly impact several different regions of the globe, including the Amazon Rainforest, via the atmosphere.

Title: "PL14A-2610 - Early-Holocene South Atlantic thermal structure and the control of South American Monsoons."

https://agu.confex.com/agu/osm20/meetingapp.cgi/Paper/645981

Abstract
The early Holocene is characterized by the final collapse of North American ice sheets, thus reorganizing the freshwater budget in the North Atlantic. The increasing summer insolation is thought to accelerate Laurentide Ice Sheet melting, resulting in the freshwater outburst of the Lake Agassiz and rerouting of Canadian basin discharge. Those early-Holocene meltwater events are linked to shifts in South American monsoonal system, through a change in the South Atlantic Subtropical Dipole (SASD). Here, we propose a mechanism by which freshwater addition to the North Atlantic strengthens the South American monsoons through a shift of the SASD in early Holocene. Using Ekman dynamics and a 1.5 layer model approach, we derived the wind effect on the South Atlantic isothermal displacement in two early Holocene (9-7ka) simulations: Simulation of Transient Climate Evolution over the last 21,000 years (TraCE-21ka) and the Community Climate System Model Version 3.0 (CCSM3) run for the 8.2 ka. The South Atlantic Subtropical Dipole (SASD) index was used in order to evaluate the state of the monsoonal system and the AMOC index used to check the state of the bipolar seesaw. In both simulations, as AMOC index decays, i.e. overturning slows down, heat builds up in the South Atlantic and the southern trade winds system weakens. The 1.5 Layer isothermal displacement results show that weak trade winds push isotherms upwards, with highest isothermal displacement of up to 20m in western South Atlantic. The wind-driven isothermal uplift then disperse heat from west towards the eastern South Atlantic, pushing SASD towards negative values.

Hence, we propose that while AMOC decelerates, the weakening of southern hemisphere trade winds displaces the South Atlantic isothermal structure, and concentrates heat in northeast South Atlantic. Finally, a warmer northeast South Atlantic enhances evaporation and increase continental moisture delivery, strengthening the South American monsoons.

Plain Language Summary
Rain over South America oscillated in the past due to changes in Atlantic Ocean Circulation. Shifts in rain intensity over South America in the past are connected to ocean surface temperature changes. In this study we propose a mechanism by which rain over northeastern South America is intensified while Atlantic circulation slows down by nine thousand yeas ago. The mechanism relies in changes on surface ocean temperature along South Atlantic, increasing evaporation over South Atlantic and driving precipitation increase in South America.

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2829 on: February 24, 2020, 06:31:29 PM »
The linked article cites research that not only links the increased accumulation of freshwater in the
Beaufort Gyre (in recent decades) to Arctic Sea Ice loss, but also identifies a positive feedback between associated increased turbulence from the Beaufort Gyre and increasing Arctic Sea Ice loss.  This is not good news.

Title: "Arctic Ice Melt Is Changing Ocean Currents", February 6, 2020 by NASA - JPL

https://www.jpl.nasa.gov/news/news.php?feature=7590

Extract: "A major ocean current in the Arctic is faster and more turbulent as a result of rapid sea ice melt, a new study from NASA shows. The current is part of a delicate Arctic environment that is now flooded with fresh water, an effect of human-caused climate change.

Using 12 years of satellite data, scientists have measured how this circular current, called the Beaufort Gyre, has precariously balanced an influx of unprecedented amounts of cold, fresh water - a change that could alter the currents in the Atlantic Ocean and cool the climate of Western Europe.

But the since the 1990s, the gyre has accumulated a large amount of fresh water - 1,920 cubic miles (8,000 cubic kilometers) - or almost twice the volume of Lake Michigan. The new study, published in Nature Communications, found that the cause of this gain in freshwater concentration is the loss of sea ice in summer and autumn. This decades-long decline of the Arctic's summertime sea ice cover has left the Beaufort Gyre more exposed to the wind, which spins the gyre faster and traps the fresh water in its current.

Scientists have been keeping an eye on the Beaufort Gyre in case the wind changes direction again. If the direction were to change, the wind would reverse the current, pulling it counterclockwise and releasing the water it has accumulated all at once.

"If the Beaufort Gyre were to release the excess fresh water into the Atlantic Ocean, it could potentially slow down its circulation. And that would have hemisphere-wide implications for the climate, especially in Western Europe," said Tom Armitage, lead author of the study and polar scientist at NASA's Jet Propulsion Laboratory in Pasadena, California.
...
"We don't expect a shutting down of the Gulf Stream, but we do expect impacts. That's why we're monitoring the Beaufort Gyre so closely," said Alek Petty, a co-author on the paper and polar scientist at NASA's Goddard Space Flight Center in Greenbelt, Maryland.

The study also found that, although the Beaufort Gyre is out of balance because of the added energy from the wind, the current expels that excess energy by forming small, circular eddies of water. While the increased turbulence has helped keep the system balanced, it has the potential to lead to further ice melt because it mixes layers of cold, fresh water with relatively warm, salt water below. The melting ice could, in turn, lead to changes in how nutrients and organic material in the ocean are mixed, significantly affecting the food chain and wildlife in the Arctic. The results reveal a delicate balance between wind and ocean as the sea ice pack recedes under climate change."

Edit, see also:

Armitage, T.W.K., Manucharyan, G.E., Petty, A.A. et al. Enhanced eddy activity in the Beaufort Gyre in response to sea ice loss. Nat Commun 11, 761 (2020). https://doi.org/10.1038/s41467-020-14449-z

https://www.nature.com/articles/s41467-020-14449-z?utm_medium=affiliate&utm_source=commission_junction&utm_campaign=3_nsn6445_deeplink_PID8099906&utm_content=deeplink

Abstract: "The Beaufort Gyre freshwater content has increased since the 1990s, potentially stabilizing in recent years. The mechanisms proposed to explain the stabilization involve either mesoscale eddy activity that opposes Ekman pumping or the reduction of Ekman pumping due to reduced sea ice–ocean surface stress. However, the relative importance of these mechanisms is unclear. Here, we present observational estimates of the Beaufort Gyre mechanical energy budget and show that energy dissipation and freshwater content stabilization by eddies increased in the late-2000s. The loss of sea ice and acceleration of ocean currents after 2007 resulted in enhanced mechanical energy input but without corresponding increases in potential energy storage. To balance the energy surplus, eddy dissipation and its role in gyre stabilization must have increased after 2007. Our results imply that declining Arctic sea ice will lead to an increasingly energetic Beaufort Gyre with eddies playing a greater role in its stabilization."

Edit 2:
Caption for the attached image: "a Before and b after 2007, including the wind work, W (comprised of atmosphere-ocean, Wao, and ice–ocean, Wio, components), available potential energy (APE), and eddy dissipation, Weddy. The atmosphere and ocean circulations are illustrated by ua and ug, respectively. The size of the arrows/vectors represents their relative strength. The loss of sea ice after 2007 led to increased wind energy input to the BG, increased APE, and increased energy dissipation and freshwater stabilization by eddies."

I wanted to point out that if several key Greenland marine terminate glaciers (like Jakobshavn) where to surge a small armada, the associated local ice melt might be sufficient to temporarily restore of the recently lost Arctic Sea Ice Extent.  If so, Armitage et al (2020)'s finding indicate that such a temporary restoration of Arctic Sea Ice Extent would likely trigger a release of relatively warm freshwater from the Beaufort Gyre; which would compound the slowing of the MOC; which might then trigger an MICI-type of collapse of the WAIS; which might lead to a scenario similar to that indicate by Hansen et al. (2016) by the red curves in the attached plot where both the Northern Hemisphere and the Southern Hemisphere experience concurrent freshwater hosing events.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2830 on: February 24, 2020, 08:48:51 PM »
I think that it the linked reference is important for a better understanding of the differences between a marine ice cliff instability, MICI, event and a marine ice cliff calving event.  In this regard, Jakobshavn Glacier '... likely has the highest un-buttressed ice cliffs on Earth'; which occasionally has an ice cliff front height of around 130m; and which have not yet lead to an MICI event.  The reference indicates that in recent decades the calving face of Jakobshavn has retreated or advanced in a correlation with the Atlantic Multidecadal Oscillation (AMO) index that influences the ocean water temperature in Disko Bay.  Furthermore, the reference states:

"Our point is not that cliff failure is irrelevant but rather that any glacier that reaches terminus heights where cliff failure may be a significant effect must already be in a state of rapid retreat. Far more important to long-term outlet glacier stability is how seasonal variability and oceanographic/atmospheric trends influence the calving rates of grounded glacier termini. In Antarctica and northern Greenland there are additional atmospheric temperature sensitivities (e.g. meltwater ponding and hydrofracture) that influence ice shelf stability (Scambos et al., 2000). In summary, while brittle failure cliff instability may be important in some circumstances, it is far more likely to play a role in a late-stage retreat than to serve as the process that would initiate such a retreat."

Ian Joughin et al (2020): "A decade of variability on Jakobshavn Isbræ: ocean temperatures pace speed through influence on mélange rigidity", The Cryosphere, 14, 211–227, https://doi.org/10.5194/tc-14-211-2020

https://www.the-cryosphere.net/14/211/2020/

Abstract: "The speed of Greenland's fastest glacier, Jakobshavn Isbræ, has varied substantially since its speed-up in the late 1990s. Here we present observations of surface velocity, mélange rigidity, and surface elevation to examine its behaviour over the last decade. Consistent with earlier results, we find a pronounced cycle of summer speed-up and thinning followed by winter slowdown and thickening. There were extended periods of rigid mélange in the winters of 2016–2017 and 2017–2018, concurrent with terminus advances ∼6 km farther than in the several winters prior. These terminus advances to shallower depths caused slowdowns, leading to substantial thickening, as has been noted elsewhere. The extended periods of rigid mélange coincide well with a period of cooler waters in Disko Bay. Thus, along with the relative timing of the seasonal slowdown, our results suggest that the ocean's dominant influence on Jakobshavn Isbræ is through its effect on winter mélange rigidity, rather than summer submarine melting. The elevation time series also reveals that in summers when the area upstream of the terminus approaches flotation, large surface depressions can form, which eventually become the detachment points for major calving events. It appears that as elevations approach flotation, basal crevasses can form, which initiates a necking process that forms the depressions. The elevation data also show that steep cliffs often evolve into short floating extensions, rather than collapsing catastrophically due to brittle failure. Finally, summer 2019 speeds were slightly faster than the prior two summers, leaving it unclear whether the slowdown is ending."

Extract: "The depressions that lead to the calving events described above represent just one of a variety of failure modes that can cause calving. Recent work has raised concerns about ice cliff instability contributing to rapid ice sheet collapse (DeConto and Pollard, 2016). With ice cliffs more than 130 m above the waterline at times (see Fig. 7), Jakobshavn Isbræ provides an interesting case study for understanding the effect of such potential instabilities. In actuality, however, ice sheet or glacier instability arises when the calving and discharge rates fall out of sync (Amundson and Truffer, 2010), rather from the actual failures themselves (i.e. calving events). Whether it initiates above or below the water line, it is important to note that some kind of material failure must occur to produce calving events even in steady state. It is also important to consider that while the Jakobshavn terminus is advancing at ∼40 m d−1 and typically calving in ∼100 m slabs, any ice cliff has a limited lifespan (∼2.5 d on average, though clustering of calving events may keep some cliffs intact up to weeks; see Fig. 7). Here we examine evolution of the front, following the formation of steep calving faces.

Figure 7 illustrates the evolution of what begins as an initially ∼130 m high sheer ice front (see 22 August in Fig. 7). Rather than a brittle failure event leading to a rapid collapse, the strong extension near the terminus instead causes evolution from a sheer grounded cliff to a heavily crevassed floating tongue with a ∼5 % slope (see 30 September in Fig. 7). In some sense this progression represents the failure of the cliff but as a process that evolves over weeks likely involving multiple small failures (e.g. crevasse events) rather than a single catastrophic failure. Furthermore, the stability of the floating extension depends on environmental factors. As our data suggest, cooler ocean temperatures, perhaps supplemented by colder air temperatures, could allow such a tongue to advance over the colder part of the year. Conversely, when more summer-like conditions prevail, such a tongue should disintegrate far more rapidly, as was the case for the transient tongue shown in shown in Figs. 7 and 8. In this case, in addition to the lack of rigid mélange, submarine melt may contribute to the breakup by thinning the floating section at rates of up to a few metres per day. Thus, stability likely is governed more by environmental conditions than by a single height-dependent mechanical failure criterion that could yield rapid collapse (Parizek et al., 2019).

Our data also reveal that once the summer speed-up commences, near-terminus surface thinning rates can exceed 50 m over the course of a few months (see M6 elevations in Fig. 2). Thus, even without cliff failure, the high stretching rates associated with an un-buttressed terminus on a retrograde bed slope can cause rapid thinning to flotation, which if unabated will lead to further calving and rapid retreat. Were it not for the seasonal cycle that produces readvance and winter thickening (see Figs. 2 and 3), the terminus of Jakobshavn Isbræ would have receded far deeper inland than it has thus far, even without ice cliff collapse as such.

Finally, it is important to note that, to the best of our knowledge, Jakobshavn Isbræ has the deepest un-buttressed calving face in Greenland or Antarctica, leading to the fastest marine-terminating glaciers speeds (Joughin et al., 2014). As such, it has been out of balance at times by more than a factor of 3 seasonally (Joughin et al., 2014) and a factor of 2 annually (Mouginot et al., 2019). Nearly all glaciers in Greenland and Antarctica have steady-state speeds well below that of Jakobshavn Isbræ (Joughin et al., 2010; Rignot et al., 2011). Thus, given that speed scales non-linearly with terminus depth (Schoof, 2007), any glacier that evolves to the point where the height of its un-buttressed calving face rivals that of Jakobshavn Isbræ will already be well out of balance, yet likely will maintain heights well below those needed to exceed a material failure criterion (∼200 m) that would lead to rapid brittle failure (Parizek et al., 2019). Our point is not that cliff failure is irrelevant but rather that any glacier that reaches terminus heights where cliff failure may be a significant effect must already be in a state of rapid retreat. Far more important to long-term outlet glacier stability is how seasonal variability and oceanographic/atmospheric trends influence the calving rates of grounded glacier termini. In Antarctica and northern Greenland there are additional atmospheric temperature sensitivities (e.g. meltwater ponding and hydrofracture) that influence ice shelf stability (Scambos et al., 2000). In summary, while brittle failure cliff instability may be important in some circumstances, it is far more likely to play a role in a late-stage retreat than to serve as the process that would initiate such a retreat.

We have assembled and produced a comprehensive time series of terminus position, surface flow velocity, surface elevation, and mélange rigidity for Jakobshavn Isbræ over the last decade. The data show a strong degree of variability, including a potentially brief (a few years) slowdown that coincided with cooler ocean temperatures (see also Khazendar et al., 2019). The time series of elevation provides an unprecedented level of detail, which clearly shows a pattern of summer thinning partially offset by winter thickening in response to seasonal changes in flow speed over most of the record. At least from autumn 2016 through spring 2019, winter thickening outpaced summer thinning, leading to net thickening and elevations approaching those observed in 2010. These data also provide observational evidence to support theoretical development describing how necking proceeds as basal crevasses form (Bassis and Ma, 2015). The elevation data also show that although Jakobshavn Isbræ likely has the highest un-buttressed ice cliffs on Earth, at this point they do not appear to be subject to sustained catastrophic brittle failure. Most importantly, our observations reinforce earlier findings on the influence of mélange rigidity on calving (Amundson et al., 2010; Joughin et al., 2008b; Krug et al., 2015; Todd et al., 2018) and help establish an apparent connection to ocean temperature. Ocean temperatures are expected to rise over the next century (Stocker et al., 2013), which will likely produce further retreat of Jakobshavn Isbræ. Superimposed on any trend for the last century, however, there is substantial multi-decadal scale variability of ocean temperatures in Disko Bay that correlates well with the Atlantic Multidecadal Oscillation (AMO) index, which has been linked to past changes on Jakobshavn Isbræ (Lloyd et al., 2011). Thus, whether Jakobshavn Isbræ can stabilize, at least temporarily, likely depends on whether a cycle similar to that of the last century produces an extended period (several more years to decades) of cooler waters in Disko Bay. While our results should be applicable to glaciers with high calving rates that yield a thick mélange (Bevan et al., 2019; Kehrl et al., 2017), more work is needed to understand the influence of thinner mélange on smaller glaciers that calve less rapidly."

Caption for first image: "Figure 2(a) Terminus position (T: black circles) and position 1 km upstream of annual minimum terminus extent (Tmax−1 km: brown dots). Terminus positions are given as distances measured relative to the seaward origin of our reference profile (see Fig. 1), and the arrows show the direction of retreat and advance. Two points in 2014 were excluded in determining Tmax−1 km (see text). The blue squares indicate when rigid mélange was present in front of the terminus at the locations indicated by the blue boxes in Fig. 1. (b) Elevations of the points M6 (red) and M9 (gold) extracted from all available DEMs along with the inferred flotation height, hfT (grey), at the terminus. (c) Surface speeds through time extracted from a TerraSAR-X/TanDEM-X velocity time series, with a few points from summer 2019 derived using COSMO-SkyMed data. See Fig. 1 for the locations of points M6–M26. The black circles indicate the speed at Tmax−1 km. Because this minimum position is updated annually, unlike the static points, there are discontinuities at each year boundary since the sampling point location changes (e.g. brown points in the top plot). The average summer (1 June to 30 September) speeds are shown as red bars for the five summers when the terminus was most retreated (2012–2016). A linear fit (r2=0.91, p=0.013) to these summer averages is shown with a black line that extrapolates the trend through 2019."

Caption for second image: "Figure 3 Plots for each year from 2010 through 2018 showing the available near-terminus elevation profiles, with three 2019 profiles included in the 2018 plot (see Fig. S2 for separate 2018 and 2019 plots). Profiles are labelled by date (MM-DD), and the profile location is shown in Fig. 1. For reference, the initial 2010 profile (12 August 2010) is included in each plot. All elevations are relative to nominal mean sea level (EGM2008 geoid). The grey line indicates the flotation height as estimated using bed elevations (Fig. S1) from BedMachine v3 (Morlighem et al., 2017)."

Caption of third image: "Figure 7Elevation and velocity profiles for summer 2015 illustrating the evolution of an advecting transverse surface depression. The legends give the nominal dates (MM-DD) in 2015. As in Fig. 3, the grey line indicates nominal height of flotation. The triangles show the estimated locations (see text) of the parcel of ice that evolved to form the bottom of the depression discussed in the text (white circles in Fig. 8), which served as a detachment point for a calving event (or events) that occurred between 30 September and 11 October."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2831 on: February 25, 2020, 02:21:19 AM »
As a follow on to my last post, I note that:

1. While Jakobshavn's calving front is current advancing (away from the retrograde section of bed), the glacier is also becoming thicker, so if the ocean water in Disko Bay were to warm in the next few years (say due to a change in the AMO trend) the thicker ice might provide sufficient driving force for the calving front to retreat into the retrograde section of bed.

2. If the surface of Jakobshavn were to experience a heat wave of sufficient duration/intensity to create ice melt-ponds, then hydrofracturing at the calving front could act to provide more driving forces towards a possible MICI-type of event if/when the calving front reaches the retrograde section of bed.

3. As noted in the linked NSIDC article confirms that the melt-albedo feedback helps to accelerate surface ice melting.

Title: "Large ice loss on the Greenland ice sheet in 2019"

http://nsidc.org/greenland-today/2019/11/large-ice-loss-on-the-greenland-ice-sheet-in-2019/

Extract: "The key factors for surface mass loss and melting for Greenland in 2019 included: 1) exceptional persistence of anticyclonic conditions (high pressure) during the 2019 summer, promoting dry and sunny weather that enhanced the surface melt thanks to the melt-albedo feedback, and 2) low snowfall in the preceding fall-winter-spring, particularly in the high-melt areas of western Greenland."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2832 on: February 25, 2020, 05:46:56 PM »
I think that it the linked reference is important for a better understanding of the differences between a marine ice cliff instability, MICI, event and a marine ice cliff calving event.  In this regard, Jakobshavn Glacier '... likely has the highest un-buttressed ice cliffs on Earth'; which occasionally has an ice cliff front height of around 130m; and which have not yet lead to an MICI event.  The reference indicates that in recent decades the calving face of Jakobshavn has retreated or advanced in a correlation with the Atlantic Multidecadal Oscillation (AMO) index that influences the ocean water temperature in Disko Bay.  Furthermore, the reference states:

"Our point is not that cliff failure is irrelevant but rather that any glacier that reaches terminus heights where cliff failure may be a significant effect must already be in a state of rapid retreat. Far more important to long-term outlet glacier stability is how seasonal variability and oceanographic/atmospheric trends influence the calving rates of grounded glacier termini. In Antarctica and northern Greenland there are additional atmospheric temperature sensitivities (e.g. meltwater ponding and hydrofracture) that influence ice shelf stability (Scambos et al., 2000). In summary, while brittle failure cliff instability may be important in some circumstances, it is far more likely to play a role in a late-stage retreat than to serve as the process that would initiate such a retreat."

Ian Joughin et al (2020): "A decade of variability on Jakobshavn Isbræ: ocean temperatures pace speed through influence on mélange rigidity", The Cryosphere, 14, 211–227, https://doi.org/10.5194/tc-14-211-2020

https://www.the-cryosphere.net/14/211/2020/

...

While correctly evaluating the stability of the Jakobshavn Glacier is important; the real concern is the parallels that the Thwaites Glacier exhibits w.r.t. lessons about ice cliff failure mechanisms learned from the Jakobshavn Glacier.  In this regard, I post the following concerns that I have regarding the lessons learned by Joughlin et al. (2020):

1. Near ice cliff failure conditions Jakobshavn temporarily formed a fractured ice tongue that temporarily helps to stabilize it until the critical ice cliff conditions dissipated.  Similarly, the Thwaites Ice Tongue is highly fractured but is currently serving to stabilize any potential ice cliff failure mechanism that might try to form at the base of the Thwaites Ice Tongue.  Thus, if in sometime in the next ten (or so) years an Extreme El Nino event were to both cause the fractured Thwaites Ice Tongue to disperse and to abruptly transfer the base of the residual ice tongue to the south edge of the subglacial cavity (Big Ear) at the current base of the Thwaites Ice Tongue; then to me it is probable that conditions for a full MICI-type of failure of the Thwaites Glacier could occur as supported by paleo-evidence of ice-rafted debris, IRD, from the ASE marine glaciers.

2. The probability of the scenario outlined in item 1 occurring increase when one considers that: a) ice-climate feedbacks are currently accelerating the upwelling of warm CDW into the ASE; b) any possible future bipolar seesaw mechanism caused by a freshwater hosing event into the North Atlantic would also accelerate both local upwell of CDW and local surface warming due to interactions with the Tropical Pacific; and c) the likely continued activation of the SWT Glacier would add stress to the Thwaites Glacier's Eastern Shear Margin.

3. To me it looks like the TEIS could collapse abruptly due to combined: ice stress, basal melting and hydrofracturing sometime between 2030 and 2040; which would also accelerate the Thwaites ice flow velocities.

4. The Thwaites Gateway is much wider than the Jakobshavn's ice calving front; which makes Thwaites more susceptible to ice cliff failure mechanisms.

5. The Thwaites Glacier has a subglacial hydraulic system that includes subglacial lakes that are currently filling up with basal meltwater, and which statistics indicate should support an abrupt outburst of basal meltwater at the base of the Thwaites Ice Tongue sometime in the next ten to fifteen years.

6.  Advection of atmospheric heat from the Tropical Pacific to the ASE via Rossby Waves may likely reduce local sea ice extents in the next teen to fifteen years.

7.  The intensity of local cyclones is currently increasing with continued global warming, which can drive storm surge into the ASE which would work to destabilize both the TEIS and the Thwaites Ice Tongue.

8.  The Amundsen Sea Low, ASL, (see the linked website below) can also work to temporarily drive ocean water (including CDW) into the ASE; which can also work to destabilize both the TEIS and the Thwaites Ice Tongue.

Hosking, Scott & National Center for Atmospheric Research Staff (Eds). Last modified 14 Jan 2020. "The Climate Data Guide: Amundsen Sea Low indices ." Retrieved from https://climatedataguide.ucar.edu/climate-data/amundsen-sea-low-indices.

Title: "AMUNDSEN SEA LOW INDICES"
https://climatedataguide.ucar.edu/climate-data/amundsen-sea-low-indices

Captions from the attached image:

Upper panel: "An example of seasonal mean sea level pressure around Antarctica with the location of the ASL marked with a '+' symbol. The sector used to derive the ASL indices (version 2) is enclosed by the black line box.(contributed by S. Hosking)" and

Lower panel: "Time series of monthly mean ASL longitudinal location derived from ERA- Interim data (grey line) and the corresponding 11-month smoothed time series (black line). (contributed by S. Hosking)"
« Last Edit: February 26, 2020, 06:32:26 PM by AbruptSLR »
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2833 on: February 25, 2020, 09:18:25 PM »
Many people do not appreciate that West Antarctica is among the most rapidly warming regions on Earth, with a rate of warming that is approximately three times higher than the global average.  This has significant bearing on the risk of ice shelf collapse in this area this century.

Bromwich, D., Nicolas, J., Monaghan, A. et al. Central West Antarctica among the most rapidly warming regions on Earth. Nature Geosci 6, 139–145 (2013). https://doi.org/10.1038/ngeo1671

https://www.nature.com/articles/ngeo1671

Abstract: "There is clear evidence that the West Antarctic Ice Sheet is contributing to sea-level rise. In contrast, West Antarctic temperature changes in recent decades remain uncertain. West Antarctica has probably warmed since the 1950s, but there is disagreement regarding the magnitude, seasonality and spatial extent of this warming. This is primarily because long-term near-surface temperature observations are restricted to Byrd Station in central West Antarctica, a data set with substantial gaps. Here, we present a complete temperature record for Byrd Station, in which observations have been corrected, and gaps have been filled using global reanalysis data and spatial interpolation. The record reveals a linear increase in annual temperature between 1958 and 2010 by 2.4±1.2 °C, establishing central West Antarctica as one of the fastest-warming regions globally. We confirm previous reports of West Antarctic warming, in annual average and in austral spring and winter, but find substantially larger temperature increases. In contrast to previous studies, we report statistically significant warming during austral summer, particularly in December–January, the peak of the melting season. A continued rise in summer temperatures could lead to more frequent and extensive episodes of surface melting of the West Antarctic Ice Sheet. These results argue for a robust long-term meteorological observation network in the region."

See also:

Title: "Research shows rapid warming on the West Antarctic Ice Sheet"

https://phys.org/news/2012-12-rapid-west-antarctic-ice-sheet.html

Extract: "The temperature record from Byrd Station, a scientific outpost in the center of the West Antarctic Ice Sheet (WAIS), demonstrates a marked increase of 4.3 degrees Fahrenheit (2.4 degrees Celsius) in average annual temperature since 1958—that is, three times faster than the average temperature rise around the globe."

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2834 on: February 26, 2020, 04:08:06 PM »
Really cool long article:

How boulders in Mongolian mountains reveal the pace of climate change

...

The samples they’ve already studied from trips around the world hint that the shift in climate was not only synchronous in both hemispheres, but also occurred at a much faster rate than many previously suspected. “We had always had this conception that it was a slow process, but as we acquire more data, we developed a clearer picture of how glaciers behaved, and we realized that it was a really sudden event,” said Putnam. “It was so fast that you would have noticed it.”

https://thebulletin.org/2020/02/how-boulders-in-mongolian-mountains-reveal-the-pace-of-climate-change/

Don´t think the science on it is out yet but it should be interesting.
His research with Strand only shows the other regions mentioned in the article.

https://aaroneputnam.weebly.com/publications.html

A cosmogenic 10Be chronology for the local last glacial maximum and termination in the Cordillera Oriental, southern Peruvian Andes: Implications for the tropical role in global climate.

Millennial-scale pulsebeat of glaciation in the Southern Alps of New Zealand.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2835 on: February 26, 2020, 05:55:51 PM »
The linked August 2016 Special Edition of Past Global Changes (PAGES) Magazine examines paleo evidence for multiple different mechanisms for tipping points including the synergistic interactions between various mechanism resulting in a chain reaction leading to abrupt climate change.  While the entire issue is valuable, I extract from two article in the Special Edition by Fogwill et al (2016), and Praetorius & Mix (2016); which highlight the importance of ice (or freshwater hosing)-climate interaction.  The first image, from Fogwill et al (2016), shows that for Pliocene conditions (which we might reach without adequate mitigation), it is impossible to reproduce the paleo reported ice mass loss from Antarctica (both West and East) without invoking both cliff failures and hydrofracturing.  The second image, from Praetorius & Mix (2016), highlight paleo evidence that oceanic feedback mechanisms can synchronize warming of both the North Atlantic and the North Pacific in order contribute to relatively high Arctic Amplification:

Eds: Turney C, Fogwill C, Lenton T, Jones R & von Gunten L (August 2016), "Tipping Points", Past Global Changes Magazine (PAGES), vol. 24(1), 1-52, https://doi.org/10.22498/pages.24.1

http://www.pages-igbp.org/products/pages-magazine/7018-24-1-tipping-points
&
http://www.pages-igbp.org/download/docs/magazine/2016-1/PAGESmagazine_2016(1)_Full_HighREs.pdf

Christopher J. Fogwill, N.R. Golledge, H. Millman and C.S.M. Turney (August 2016), "The East Antarctic Ice Sheet as a source of sea-level rise: A major tipping element in the climate system?", Past Global Changes Magazine (PAGES), Vol 24, No. 1,

Extract: "Sea-level reconstructions suggest significant contributions from the East Antarctic Ice Sheet may be required to reconcile high interglacial sea levels. Understanding the mechanism(s) that drove this loss is critical to projecting our future commitment to sea-level rise."

&

Summer K. Praetorius and Alan C. Mix (August 2016), "Did synchronized ocean warming in the North Pacific and North Atlantic trigger a deglacial tipping point in the Northern Hemisphere?", Past Global Changes Magazine (PAGES), Vol 24, No. 1, 

http://pastglobalchanges.org/download/docs/magazine/2016-1/PAGESmagazine_2016%281%29_10-11_Praetorius.pdf

Extract: "Rapid Northern Hemisphere warming during the last deglaciation involved synchronization of the North Pacific and North Atlantic. Threshold-like transitions to hypoxia occurred in conjunction with abrupt ocean warming, implying synergistic ocean heat transport triggered both physical and ecological tipping points.

Outlook
New high-resolution paleoceanographic records from the subpolar North Pacific document rapid changes during the last deglacial transition similar in timing to those observed in the Greenland ice cores. Rather than deglacial changes in the North Pacific merely reflecting a downstream response to changes in the North Atlantic region, interactions between basins may be a key element in the emergence of abrupt climate transitions in the Northern Hemisphere."

This is a lot of paleo-evidence of the abrupt synchronization of positive feedback mechanisms that can drive abrupt climate such as this previously cited post.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2836 on: February 26, 2020, 05:59:57 PM »
Also, there is paleo-evidence, such as the linked research, that indicates that meltwater from the Wilkes Basin (see the attached image) can help destabilize the Weddell Sea Sector of the WAIS; which to me indicates that a partial collapse of the BSB will help to destabilize the Amery Ice Shelf sector.  Neither of these probable occurrences this century are considered by either AR5, or AR6:

Steven J. Phipps, Christopher J. Fogwill, and Christian S. M. Turney (2016), "Impacts of marine instability across the East Antarctic Ice Sheet on Southern Ocean dynamics", The Cryosphere Discuss., doi:10.5194/tc-2016-111

http://www.the-cryosphere-discuss.net/tc-2016-111/tc-2016-111.pdf

Abstract: "Recent observations and modelling studies have demonstrated the potential for rapid and substantial retreat of large sectors of the East Antarctic Ice Sheet (EAIS). This has major implications for ocean circulation and global sea level. Here we examine the effects of increasing meltwater from the Wilkes Basin, one of the major marine-based sectors of the EAIS, on Southern Ocean dynamics. Climate model simulations reveal that the meltwater flux rapidly stratifies surface waters, leading to a dramatic decrease in the rate of Antarctic Bottom Water formation. The surface ocean cools but, critically, the Southern Ocean warms by more than 1oC at depth. This warming is accompanied by a Southern Ocean-wide ‘domino effect’, whereby the warming signal propagates westward with depth. Our results suggest that melting of one sector of the EAIS could result in accelerated warming across other sectors, including the Weddell Sea sector of the West Antarctic Ice Sheet. Thus localized melting of the EAIS could potentially destabilise the wider Antarctic Ice Sheet."

Extract: "Remarkably, we therefore find that the largest changes in convective depth occur on the opposite side of the continent from the region of freshwater input. Furthermore, this outcome occurs despite the fact that the salinity signal in the Weddell Sea is weak; the average decrease in SSS over the eastern half of the sea, where the greatest reduction in convective depth occurs, is only 0.13psu. This demonstrates that the Weddell Sea is extremely sensitive to freshwater input within the model and can be significantly impacted by melting on the other side of the continent, as a result of the surface freshening being carried westwards by the coastal counter-currents.



Furthermore, recent work has highlighted the sensitivity of the Weddell Sea sector of the WAIS to changes in local ocean circulation (Hellmer et al., 2012). This is exacerbated by the presence of steep reverse slope beds in regional ice streams (Ross et al., 2012), making this sector particularly vulnerable to warming (Humbert, 2012; Fogwill et al., 2014a).We have established in this study that melting of the EAIS can lead to reduced convection and warming at depth in the Weddell Sea, suggesting that localised melting of one sector of the EAIS might be sufficient to destabilise at least one key sector of the WAIS as well."

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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2837 on: February 26, 2020, 06:14:27 PM »
While I have previously posted the attached image of the SLR fingerprint effect of the WAIS collapsing in order to cite how regional sea level rise in the NH would be higher than the global mean sea level rise (should the WAIS collapse); however, in this post I focus on the SH and I note that if the ASE marine glaciers were to collapse abruptly due MICI-type mechanism; the associated drop in sea level in both the FRIS and RIS ice shelves would cause flexural stresses and associated ice fractures that would serve to quickly destabilize these large ice sheets; which would contribute to the accelerated collapse of the rest of the WAIS.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2838 on: February 26, 2020, 08:32:08 PM »
This post is to remind readers of the risk that future oceanic infragravity waves (especially considering that storm activity in the Pacific Ocean should become more intense with continuing climate change) could contribute to (or trigger) a sudden collapse of key West Antarctic ice shelves such as the Ross Ice Shelf (RIS):

Title: "OCEAN-ICE SHELF INTERACTIONS – GRAVITY WAVES"

https://scripps.ucsd.edu/centers/iceshelfvibes/ocean-ice-interactions/

Extract: "The flexing of ice shelves by infragravity waves could provide the additional external forcing needed to extend existing fractures (rifts), thereby triggering sudden ice shelf collapse."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2839 on: February 26, 2020, 08:45:31 PM »
I thought that some people would like some color commentary on ice-rafted debris, IRD, in action:

Title: "21 February 2020 Ice Rafted Debris - Virtual Base Camp / Thwaites Offshore Research"

https://www.polartrec.com/expeditions/thwaites-offshore-research/journals/2020-02-21

Extract: "Disappointingly, the object I saw would only be thought of as a treasure by a very small subset of the population (although a substantial number of people on this ship would consider themselves part of that subset). It is something called Ice Rafted Debris - small rocks and bits of sediment that get trapped in a glacier as it scours (or scrapes) the face of a continent, and are then carried off to sea by the chunk of ice into which they become frozen. When we take long cores of sediment from the bottom of the ocean, we often find pebbles buried many meters deep, and the explanation for them is that they were dropped by an iceberg floating above - former ice rafted debris that gets dumped when its raft melts. This piece was unusually large and it is hard to imagine where it came from and where it will end up. Eventually, the ice holding it will melt and this large boulder (or still, maybe, treasure chest) will sink to the bottom of the Amundsen Sea, likely never to be seen again. Fortunately, I got a decent picture to remember it by."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2840 on: February 26, 2020, 11:02:18 PM »
The linked article discusses the findings of the second linked survey report of risks perceived by scientists in 2020.  The associated first image ranks the perceived impact and likelihood of the global risks while the second associated image shows the perceived highly synergistic nature of the identified global risks.  I would expect that in future years the findings of such survey reports will become progressively more alarming.

Title: "Humanity's greatest risk: Cascading impacts of climate, biodiversity, food, water crises: scientists"

https://www.eurekalert.org/pub_releases/2020-02/tca-hgr020520.php

Extract: "The greatest threat to humanity hides in the potential cascading of impacts of five highly-related, highly-likely risks -- a collision that can amplify these effects catastrophically, according to a new survey of 222 leading scientists from 52 countries."

See also:

Title: "Risks Perception Report 2020"

https://futureearth.org/initiatives/other-initiatives/grp/
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2841 on: February 27, 2020, 12:39:53 AM »
The linked article cites research that indicates that changing patterns of the westerlies over the Southern Ocean is likely reducing the net amount of CO2 absorbed by the Southern Ocean; which is not good.

Title: "Out of Antarctica, churnings of climate change"

https://www.knowablemagazine.org/article/physical-world/2020/southern-ocean-carbon-sink

Extract: "The interplay of carbon dioxide, winds and Southern Ocean waters could be reaching an environmental tipping point

There’s growing evidence that, at least in the winter months when the westerlies are at their most violent, some parts of the Southern Ocean are giving off more of the gas than was previously estimated. It has all the makings of a vicious cycle.

Because the AMOC transports heat from the south to the north, a slowdown effectively cools the Northern Hemisphere and heats up the Southern Hemisphere. This warming also intensifies the westerlies and shifts them toward the South Pole, leading to a greater vertical churning of the Southern Ocean, which may contribute to global warming by weakening the ocean’s ability to absorb CO₂. Since the likely result is even more glacial meltwater flowing into the North Atlantic, this could further weaken the AMOC. It has all the makings of a system that’s slipping out of control."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2842 on: February 27, 2020, 04:15:34 PM »
As we are near GHG conditions comparable to the Pliocene Climatic Optimum, I provide the linked reference that confirms that Earth System responses during the Pliocene were driven by relatively slow orbital cycles while the current rate of change of radiative forcing is thousands of time faster than what occurred during this paleo-case with a high climate sensitivity.

Gonzalo Jiménez-Moreno et al. ( September 2019), "Early Pliocene climatic optimum, cooling and early glaciation deduced by terrestrial and marine environmental changes in SW Spain", Global and Planetary Change, Volume 180, Pages 89-99; https://doi.org/10.1016/j.gloplacha.2019.06.002

https://www.sciencedirect.com/science/article/pii/S0921818119301560

Abstract
The Pliocene is a key period in Earth's climate evolution, as it records the transition from warm and stable conditions to the colder and more variable glaciated climate of the Pleistocene. Simultaneously, climate became more seasonal in the Mediterranean area, and Mediterranean-type seasonal precipitation rhythm with summer drought established. These climatic changes presumably had significant impacts on terrestrial environments. However, the response of terrestrial environments to such climate changes is still not fully understood due to the lack of detailed studies dealing with this period of time. In this study, multiproxy analyses of continuous core sampling from La Matilla (SW Spain) shows detailed and continuous record of pollen, sand content and abundance of benthic foraminifer Bolivina spathulata to describe paleoenvironmental and paleoclimate trends during the early Pliocene. This record shows warmest, most humid climate conditions and highest riverine nutrient supply at ~ 4.35 Ma, coinciding with the Pliocene climatic optimum and high global sea level. A climate cooling and aridity trend occurred subsequently and a significant glaciation occurred at ~ 4.1–4.0 Ma, during a period known by very little terrestrial evidence of glaciation. Our multiproxy data thus indicate that terrestrial and marine environments were significantly variable during the early Pliocene and that major glaciation-like cooling occurred before the intensification of northern hemisphere glaciation at the beginning of the Pleistocene (~2.7 Ma). This major climate cooling and aridity maxima between 4.1 and 4.0 Ma is independently validated by a coeval sea-level drop (third order Za2 sequence boundary). This sea level drawdown is supported by enhanced coarse sedimentation and minima in riverine nutrient supply, showing paired vegetation and sea-level changes and thus a strong land-ocean relationship. This study also shows that long-term climatic trends were interrupted by orbital-scale cyclic climatic variability, with eccentricity, obliquity and precession acting as the main triggers controlling climate and environmental change in the area.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2843 on: February 27, 2020, 04:38:21 PM »
While the linked reference is from 2013, it nevertheless observed a freshening of the Antarctic Bottom Water, AABW, feeding into the southern end of the AMOC.  Fresher AABW entering the AMOC means less driving force and an associated slowing of the AMOC; and it is clear that since 2012-2013 the AABW entering the AMOC in the Weddell Sea is still fresher than that of 2012-2013 as more local ice melting has been measured.

Jullion, L., A.C. Naveira Garabato, M.P. Meredith, P.A. Holland, P. Courtois and B.A. King (2013) Decadal Freshening of the Antarctic Bottom Water Exported from the Weddell Sea. Journal of Climate, 26(20): 8111–25. https://doi.org/10.1175/JCLI-D-12-00765.1

https://journals.ametsoc.org/doi/10.1175/JCLI-D-12-00765.1

Abstract
Recent decadal changes in Southern Hemisphere climate have driven strong responses from the cryosphere. Concurrently, there has been a marked freshening of the shelf and bottom waters across a wide sector of the Southern Ocean, hypothesized to be caused by accelerated glacial melt in response to a greater flux of warm waters from the Antarctic Circumpolar Current onto the shelves of West Antarctica. However, the circumpolar pattern of changes has been incomplete: no decadal freshening in the deep layers of the Atlantic sector has been observed. In this study, the authors document a significant freshening of the Antarctic Bottom Water exported from the Weddell Sea, which is the source for the abyssal layer of the Atlantic overturning circulation, and trace its possible origin to atmospheric-forced changes in the ice shelves and sea ice on the eastern flank of the Antarctic Peninsula that include an anthropogenic component. These findings suggest that the expansive and relatively cool Weddell gyre does not insulate the bottom water formation regions in the Atlantic sector from the ongoing changes in climatic forcing over the Antarctic region.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2844 on: February 27, 2020, 05:16:00 PM »
The linked article makes a number of good points about the climate sensitivity findings of CMIP6 (especially about the projected amount of cover from mid to high latitude supper-cooled liquid (SCL) clouds) & see the first image; however, be very careful about the stated caveats such as research that uses observational data from the faux 'warming hiatus' period to bias the finding of their relatively short-term observations.  In my opinion, considering the findings of CMIP6 in terms of climate risk associated with climate sensitivity (see the second image, which is based on CMIP5 not CMIP6) is good science communication as it illustrates the significant impact on our global socio-economic system from even relatively small increases in climate sensitivity:

Title: "Climate Sensitivity in CMIP6: some initial findings"

https://www.crescendoproject.eu/climate-sensitivity-in-cmip6-causes-consequences-and-uses/

Extract:
•   "In CMIP6 a significant number of Earth system models exhibit ECS values greater than 4.5°C, with 5 models (so far) suggesting an ECS greater than 5°C (figure 1).
•   While such high ECS values are considered highly unlikely, they cannot be ruled out and therefore remain as; low probability, high impact futures.
•   A new paper, to appear soon, suggests models with ECS greater than ~5°C overestimate post-1990 warming rates compared to observations, suggesting their future warming may also be overestimated. A caveat to this finding is that the post-1990 observed warming includes the highly unusual “warming hiatus” from ~ 1999 to 2012, so the observed record may not fully constrain future warming.
•   At least two CMIP6 models (UKESM1/HadGEM3 and CESM2) have higher ECS than predecessor versions due to an increase in the amount of mid to-high latitude super-cooled liquid (SCL) clouds simulated for the present-day. SCL clouds form at temperatures below 0°C but are composed primarily of super-cooled liquid droplets rather than ice crystals. Such clouds are most common in clean regions such as the Southern Ocean.
•   Earlier models (as in CMIP5) systematically overestimated (underestimated) the amount of ice (super-cooled liquid) in these clouds. The two CMIP6 models do a better job in this regard and are closer to observations.
•   In CMIP5 models, these (erroneous) ice clouds melt and become liquid clouds as the climate warms in the future. For an equivalent amount of water, changing from ice to liquid leads to these clouds being more reflective to solar radiation (liquid clouds are composed of a larger number of smaller droplets than ice clouds that are composed of fewer, large crystals).
•   Increasing cloud reflectivity as the climate warms is a (cooling) negative feedback. In CMIP5 models, this negative (mid-latitude) cloud feedback opposed other, predominantly (warming) positive, cloud feedbacks in the tropics and subtropics.
•   The negative mid-latitude cloud feedback is likely spurious in CMIP5 models, as they start from an erroneous present-day, ice-rich cloud state, leading to an unrealistic amount of ice to liquid melt as the climate warms.
•   The improved CMIP6 models do not exhibit this spurious negative cloud feedback. Therefore, the positive (tropical) cloud feedbacks that are still present in these models, are no longer balanced by this negative feedback, resulting in a larger positive net cloud feedback and an increase in climate sensitivity.
•   The improved evaluation of mid-latitude clouds in the CMIP6 models makes us confident the reduced negative cloud feedback is more realistic in these models than their predecessor CMIP5 versions."

Edit: I provide the third image in order to emphasize that per the indicated 10 model group of CMIP6 results, following a SSP5 - 8.5 path could possibly (right-tail risk) result in an 8C increase in GMSTA by 2100.
« Last Edit: February 27, 2020, 06:19:49 PM by AbruptSLR »
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2845 on: February 27, 2020, 06:11:43 PM »
The linked reference provides evidence that changes in the Atlantic Ocean abruptly results in synchronized changes in the North Pacific (which is strongly related to the ENSO cycle), via atmospheric telecommunications (see the attached image & associated caption).  This likely means that a freshwater hosing event in the North Atlantic (such as a release of relatively warm fresh water from the Beaufort Gyre) would abruptly lead to a synchronized response in the North Pacific Ocean; which to me means that climate sensitivity is much more responsive to freshwater hosing events than assumed by consensus climate scientists.

Wu, C., Lin, Y., Wang, Y. et al. An Atlantic-driven rapid circulation change in the North Pacific Ocean during the late 1990s. Sci Rep 9, 14411 (2019). https://doi.org/10.1038/s41598-019-51076-1

https://www.nature.com/articles/s41598-019-51076-1

Abstract: "Interbasin interactions have been increasingly emphasized in recent years due to their roles in shaping climate trends and the global warming hiatus in the northern hemisphere. The profound influence from the North Atlantic on the Tropical Pacific has been a primary focus. In this study, we conducted observational analyses and numerical modeling experiments to show that the North Atlantic has also strongly influenced the Extratropical North Pacific. A rapid and synchronous change in the atmospheric and oceanic circulations was observed in the North Pacific during the late 1990s. The change was driven by the transbasin influence from the Atlantic Ocean. During the positive phase of the Atlantic Multidecadal Oscillation (AMO) since the 1990s, the anomalously warm North Atlantic triggers a series of zonally symmetric and asymmetric transbasin teleconnections involving the Inter-tropical Convergence Zone (ITCZ), Walker and Hadley circulations, and Rossby wave propagation that lead to a decrease in wind stress curls over the Pacific subtropics, resulting in an abrupt weakening in the North Pacific subtropical gyre (NPSG) and the Kuroshio Current."

Extract: "As schematized in Fig. 5, our observational analyses and climate model experiments suggest that the change of the AMO to a positive phase in the middle 1990s can trigger a series of zonally symmetric and asymmetric transbasin processes to give rise to a late-1990s abrupt change of the North Pacific circulation that is manifested as a weakening of the NPSG and Kuroshio. This Atlantic or AMO control of the North Pacific circulation was not noted in earlier periods of instrumental observations. This can be an indication of an emerging change of climate dynamics due to global warming that deserves attention."

Caption for image: "Diagram of the linkage between the Atlantic and North Pacific. The anomalously warm North Atlantic and cold South Atlantic (right) leads to weakened Hadley cell in the Northern Hemisphere but strengthened Hadley cell in the Southern Hemisphere, resulting in a northward displacement of the ITCZ not only in the Atlantic but also in the Pacific. The weakened Hadley cell leads to a positive WSCA in the Pacific subtropical region, resulting in a weakened NPSG (left). The tropical North Atlantic warming associated with the positive AMO phase can also trigger a zonally-asymmetric circulation mechanism to weaken the NPSG. The Atlantic warming can induce an anomalous Walker circulation that descends over the tropical central Pacific and suppresses deep convection there, the anomalous cooling resulting from which can then excite a Rossby wave response to higher latitudes inducing a low-level anomalous cyclone and low pressure over the subtropical Pacific, and an anomalous high pressure over the North Pacific (i.e. Aleutian Low weaker, contours), which also result in a weakened NPSG and Kuroshio. The colors are wind stress curl (left, in units of 10−8 N m−3) and SST (right, in units of °C) difference (1999–2013 minus 1993–1998) from NCEP r2 and AVHRR OISST data. The green/purple colors denote the cyclonic/anticyclonic anomaly (left). The contours are sea level pressure (left, in units hPa) difference (1999–2013 minus 1993–1998) from NCEP r2. The solid/dash contours denote positive/negative anomaly. The arrows indicate the surface wind field and atmospheric meridional overturning circulation (left). The AL denotes the Aleutian Low."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2846 on: February 27, 2020, 08:27:47 PM »
The linked reference examines: 'The role of Northeast Pacific meltwater events in deglacial climate change".  While we are not currently at risk of major freshwater hosing events into the Northeast Pacific (such as the paleo Columbia River megafloods); nevertheless, this research clarifies the synchronization of the North Pacific and the North Atlantic due to freshwater hosing event; and I draw attention to  the abrupt onset of the Bølling-Allerød (BA)  warming at 14.7 thousand years (ka) as shown in the attached image (& see the associated caption):

Summer K. Praetorius et al. (26 Feb 2020), "The role of Northeast Pacific meltwater events in deglacial climate change", Science Advances, Vol. 6, no. 9, eaay2915, DOI: 10.1126/sciadv.aay2915

https://advances.sciencemag.org/content/6/9/eaay2915.full

Abstract
Columbia River megafloods occurred repeatedly during the last deglaciation, but the impacts of this fresh water on Pacific hydrography are largely unknown. To reconstruct changes in ocean circulation during this period, we used a numerical model to simulate the flow trajectory of Columbia River megafloods and compiled records of sea surface temperature, paleo-salinity, and deep-water radiocarbon from marine sediment cores in the Northeast Pacific. The North Pacific sea surface cooled and freshened during the early deglacial (19.0-16.5 ka) and Younger Dryas (12.9-11.7 ka) intervals, coincident with the appearance of subsurface water masses depleted in radiocarbon relative to the sea surface. We infer that Pacific meltwater fluxes contributed to net Northern Hemisphere cooling prior to North Atlantic Heinrich Events, and again during the Younger Dryas stadial. Abrupt warming in the Northeast Pacific similarly contributed to hemispheric warming during the Bølling and Holocene transitions. These findings underscore the importance of changes in North Pacific freshwater fluxes and circulation in deglacial climate events.

Extract: "Abrupt increases in SST and reduction of the apparent radiocarbon age of abyssal waters were paralleled between the North Pacific and North Atlantic during the transitions into the BA and Holocene, supporting a dual role for North Pacific and North Atlantic heat transport in abrupt Northern Hemisphere warming events (17).

While the timing of major meltwater events from the Cordilleran and Laurentide ice sheets appears to have been somewhat asynchronous during the early deglaciation, cooling during the YD was generally synchronous and of similar magnitude between sites in the Northeast Pacific and midlatitude North Atlantic, pointing to essentially synchronous meltwater influences in both ocean basins in this abrupt Northern Hemisphere cooling event. While dates for the submergence of the Bering Strait remain controversial, our results suggest that if the strait was breached at the beginning of the YD (30, 32), then some of the meltwater funneled into the Northeast Pacific may have been transported through the Arctic and into North Atlantic deepwater formation regions. Thus, major meltwater pulses to the Northeast Pacific and attendant impacts on ocean circulation and sea-ice formation may have played a hitherto underrepresented role in abrupt deglacial climate variability."

Caption: "Fig. 5 Global SST anomalies for various deglacial climate intervals.
Climate intervals shown are early HS1 relative to the LGM (A and B), late HS1 relative to early HS1 (C and D), the BA relative to early HS1 (E and F), the YD relative to the BA (G and H), and the early Holocene relative to the YD (I and J) (see Materials and Methods for data references and dates of climate intervals). SST anomalies for each core site are plotted on the left panels, and an interpolated version using a weighted average grid scheme is shown in the right panels. Maps were generated using Ocean Data View (82)."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2847 on: February 27, 2020, 08:56:51 PM »
The linked article/reference confirm that it is anthropogenic forcing (& not natural variability) that is driving the high rate of warming of the Southern Ocean (which is not only melting Antarctic marine ice but is also changing precipitation & evaporation patterns in the Southern Ocean as shown in the attached image):

Title: "What’s Causing Antarctica’s Ocean to Heat Up? New Study Points to 2 Human Sources"

https://insideclimatenews.org/news/23092018/antarctica-warming-southern-ocean-human-greenhouse-gas-ozone-ice-loss-study

Extract: "With help from floating data-collectors, a new study reveals the impact greenhouse gas emissions and ozone depletion are having on the Southern Ocean."

See also:

Swart et al. (2018), "Recent Southern Ocean warming and freshening driven by greenhouse gas emissions and ozone depletion", Nature Geoscience, DOI: https//doi.org/10.1038/s41561-018-0226-1

https://www.nature.com/articles/s41561-018-0226-1

Abstract: "The Southern Ocean has, on average, warmed and freshened over the past several decades. As a primary global sink for anthropogenic heat and carbon, to understand changes in the Southern Ocean is directly relevant to predicting the future evolution of the global climate system. However, the drivers of these changes are poorly understood, owing to sparse observational sampling, large amplitude internal variability, modelling uncertainties and the competing influence of multiple forcing agents. Here we construct an observational synthesis to quantify the temperature and salinity changes over the Southern Ocean and combine this with an ensemble of co-sampled climate model simulations. Using a detection and attribution analysis, we show that the observed changes are inconsistent with the internal variability or the response to natural forcing alone. Rather, the observed changes are primarily attributable to human-induced greenhouse gas increases, with a secondary role for stratospheric ozone depletion. Physically, the simulated changes are primarily driven by surface fluxes of heat and freshwater. The consistency between the observed changes and our simulations provides increased confidence in the ability of climate models to simulate large-scale thermohaline change in the Southern Ocean."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2848 on: February 28, 2020, 09:23:48 PM »
Plants (particularly forests) emit volatile organic compounds (VOCs) that chemically transform in the atmosphere (particularly in clouds) into secondary organic aerosols (SOAs) that serve as cloud condensation nuclei (CCN); which generally promote the formation of relatively low altitude clouds; which produce negative feedback for global warming (see the first linked reference).  Thus, VOCs and SOAs play a complex role in climate change including that:

a) Forest extents have been progressively reduced since at lead the beginning of the 20th Century this may mean that values of climate sensitivity determined from observations in the first half of the 20th Century may be biased on the low end of the range by the negative cloud feedback that is now dissipating.

b) Atmospheric new particle formation (NPF) are 'nanoparticles' of both natural and anthropogenic origin that participate in the formation of SOAs, and they result in positive feedback for global warming (see the second linked reference).  However, the role of NPF in climate change is still poorly understood.

c) The third linked reference indicates that anthropogenic air pollution can serve to promote SOA formation in rainforest areas; which may explain why cloud formation over rainforests have not yet been significantly reduced.  However, the relatively fragile nature of this source of SOA promoted clouds could easily be disrupting in coming years due to climate change stress of socio-economic distress; which could lead to a premature collapse of rainforests and an associated abrupt net increases in positive feedback for more global warming.

Roldin, P., Ehn, M., Kurtén, T. et al. The role of highly oxygenated organic molecules in the Boreal aerosol-cloud-climate system. Nat Commun 10, 4370 (2019). https://doi.org/10.1038/s41467-019-12338-8

https://www.nature.com/articles/s41467-019-12338-8

Abstract: "Over Boreal regions, monoterpenes emitted from the forest are the main precursors for secondary organic aerosol (SOA) formation and the primary driver of the growth of new aerosol particles to climatically important cloud condensation nuclei (CCN). Autoxidation of monoterpenes leads to rapid formation of Highly Oxygenated organic Molecules (HOM). We have developed the first model with near-explicit representation of atmospheric new particle formation (NPF) and HOM formation. The model can reproduce the observed NPF, HOM gas-phase composition and SOA formation over the Boreal forest. During the spring, HOM SOA formation increases the CCN concentration by ~10 % and causes a direct aerosol radiative forcing of −0.10 W/m2. In contrast, NPF reduces the number of CCN at updraft velocities < 0.2 m/s, and causes a direct aerosol radiative forcing of +0.15 W/m2. Hence, while HOM SOA contributes to climate cooling, NPF can result in climate warming over the Boreal forest."

&

Veli-Matti Kerminen et al. (27 September 2018), "Atmospheric new particle formation and growth: review of field observations", Environmental Research Letters, Volume 13, Number 10, https://doi.org/10.1088/1748-9326/aadf3c

https://iopscience.iop.org/article/10.1088/1748-9326/aadf3c/meta

Abstract: " This review focuses on the observed characteristics of atmospheric new particle formation (NPF) in different environments of the global troposphere. After a short introduction, we will present a theoretical background that discusses the methods used to analyze measurement data on atmospheric NPF and the associated terminology. We will update on our current understanding of regional NPF, i.e. NPF taking simultaneously place over large spatial scales, and complement that with a full review on reported NPF and growth rates during regional NPF events. We will shortly review atmospheric NPF taking place at sub-regional scales. Since the growth of newly-formed particles into larger sizes is of great current interest, we will briefly discuss our observation-based understanding on which gaseous compounds contribute to the growth of newly-formed particles, and what implications this will have on atmospheric cloud condensation nuclei formation. We will finish the review with a summary of our main findings and future outlook that outlines the remaining research questions and needs for additional measurements."

&

Shrivastava, M., Andreae, M.O., Artaxo, P. et al. Urban pollution greatly enhances formation of natural aerosols over the Amazon rainforest. Nat Commun 10, 1046 (2019). https://doi.org/10.1038/s41467-019-08909-4

https://www.nature.com/articles/s41467-019-08909-4

Abstract: "One of the least understood aspects in atmospheric chemistry is how urban emissions influence the formation of natural organic aerosols, which affect Earth’s energy budget. The Amazon rainforest, during its wet season, is one of the few remaining places on Earth where atmospheric chemistry transitions between preindustrial and urban-influenced conditions. Here, we integrate insights from several laboratory measurements and simulate the formation of secondary organic aerosols (SOA) in the Amazon using a high-resolution chemical transport model. Simulations show that emissions of nitrogen-oxides from Manaus, a city of ~2 million people, greatly enhance production of biogenic SOA by 60–200% on average with peak enhancements of 400%, through the increased oxidation of gas-phase organic carbon emitted by the forests. Simulated enhancements agree with aircraft measurements, and are much larger than those reported over other locations. The implication is that increasing anthropogenic emissions in the future might substantially enhance biogenic SOA in pristine locations like the Amazon."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2849 on: February 28, 2020, 09:25:14 PM »
Per the linked article, the increasingly probably collapse of the Thwaites Glacier by 2050 may '… taint the legacy of a largely ignorant Congress', not to mention tainting the legacy of the Trump Administration:

Title: "What, exactly, does Congress understand about the world's most threatening glacier?"

https://mashable.com/article/thwaites-glacier-what-congress-knows/

Extract: "How quickly will Thwaites melt? Even 10 years out, we don't know what Thwaites will look like. "It's completely unclear," said Anandakrishnan.

What's clear, however, is Thwaites' relentless retreat, ultimately driven by a warming atmosphere. These changes are far outside the realm of what most members of Congress — empowered to make supreme laws of the land that determine the nation's fate — can easily grasp. There's good news and pretty bad news when it comes to what the 535 members of Congress realize about the most threatening glacier on Earth — and critically, the necessity to rapidly slash carbon emissions to potentially curb Thwaites' melt.

And by 2050, Thwaites may have already collapsed.

But Thwaites promises to keep receding, whether or not we're able to watch up close. How fast this happens as the planet continues to relentlessly warm is a question that won't go away, may haunt our descendants, and might taint the legacy of a largely ignorant Congress."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson