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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3800 on: October 03, 2020, 04:18:44 PM »
The linked reference concludes that:

"Our study suggests that climates like those of the Pliocene will prevail as soon as 2030 CE and persist under climate stabilization scenarios.  Unmitigated scenarios of greenhouse gas emissions produce climates like those of the Eocene, …"

This essentially confirms my proposed timeline for possibly transitioning into an equable climate state before 2150 (see the attached image) even if RCP 8.5 forcing level are only followed through about 2040 to 2050 followed by an MICI type of collapse of the WAIS (in order to maintain the effective forcing rate of the RCP 8.5 scenario).

K. D. Burke, et al. (December 26, 2018), Pliocene and Eocene provide best analogs for near-future climates", PNAS, 115 (52) 13288-13293; https://doi.org/10.1073/pnas.1809600115

https://www.pnas.org/content/115/52/13288

Significance
The expected departure of future climates from those experienced in human history challenges efforts to adapt. Possible analogs to climates from deep in Earth’s geological past have been suggested but not formally assessed. We compare climates of the coming decades with climates drawn from six geological and historical periods spanning the past 50 My. Our study suggests that climates like those of the Pliocene will prevail as soon as 2030 CE and persist under climate stabilization scenarios. Unmitigated scenarios of greenhouse gas emissions produce climates like those of the Eocene, which suggests that we are effectively rewinding the climate clock by approximately 50 My, reversing a multimillion year cooling trend in less than two centuries.

Abstract
As the world warms due to rising greenhouse gas concentrations, the Earth system moves toward climate states without societal precedent, challenging adaptation. Past Earth system states offer possible model systems for the warming world of the coming decades. These include the climate states of the Early Eocene (ca. 50 Ma), the Mid-Pliocene (3.3–3.0 Ma), the Last Interglacial (129–116 ka), the Mid-Holocene (6 ka), preindustrial (ca. 1850 CE), and the 20th century. Here, we quantitatively assess the similarity of future projected climate states to these six geohistorical benchmarks using simulations from the Hadley Centre Coupled Model Version 3 (HadCM3), the Goddard Institute for Space Studies Model E2-R (GISS), and the Community Climate System Model, Versions 3 and 4 (CCSM) Earth system models. Under the Representative Concentration Pathway 8.5 (RCP8.5) emission scenario, by 2030 CE, future climates most closely resemble Mid-Pliocene climates, and by 2150 CE, they most closely resemble Eocene climates. Under RCP4.5, climate stabilizes at Pliocene-like conditions by 2040 CE. Pliocene-like and Eocene-like climates emerge first in continental interiors and then expand outward. Geologically novel climates are uncommon in RCP4.5 (<1%) but reach 8.7% of the globe under RCP8.5, characterized by high temperatures and precipitation. Hence, RCP4.5 is roughly equivalent to stabilizing at Pliocene-like climates, while unmitigated emission trajectories, such as RCP8.5, are similar to reversing millions of years of long-term cooling on the scale of a few human generations. Both the emergence of geologically novel climates and the rapid reversion to Eocene-like climates may be outside the range of evolutionary adaptive capacity.
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nanning

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3801 on: October 04, 2020, 12:12:19 PM »
^^
Wow, that should raise some hairs.

"the rapid reversion to Eocene-like climates may be outside the range of evolutionary adaptive capacity."

I'm certain of it.
Kinda puts all human's endeavours that are not about extreme mitigation in the 'stupid' category.
I've completed my personal extreme mitigation and am no longer contributing to AGW/Biosphere collapse, but others think I'm stupid, annoying or fake.
Time for some soul-searching by rich consumers (incl. most forum members).
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Hefaistos

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3802 on: October 04, 2020, 12:52:45 PM »
The linked reference concludes that:

"Our study suggests that climates like those of the Pliocene will prevail as soon as 2030 CE and persist under climate stabilization scenarios.  Unmitigated scenarios of greenhouse gas emissions produce climates like those of the Eocene, …"

This essentially confirms my proposed timeline for possibly transitioning into an equable climate state before 2150 (see the attached image) even if RCP 8.5 forcing level are only followed through about 2040 to 2050 followed by an MICI type of collapse of the WAIS (in order to maintain the effective forcing rate of the RCP 8.5 scenario).

K. D. Burke, et al. (December 26, 2018), Pliocene and Eocene provide best analogs for near-future climates", PNAS, 115 (52) 13288-13293; https://doi.org/10.1073/pnas.1809600115

https://www.pnas.org/content/115/52/13288

Significance
The expected departure of future climates from those experienced in human history challenges efforts to adapt. Possible analogs to climates from deep in Earth’s geological past have been suggested but not formally assessed. We compare climates of the coming decades with climates drawn from six geological and historical periods spanning the past 50 My. Our study suggests that climates like those of the Pliocene will prevail as soon as 2030 CE and persist under climate stabilization scenarios. Unmitigated scenarios of greenhouse gas emissions produce climates like those of the Eocene, which suggests that we are effectively rewinding the climate clock by approximately 50 My, reversing a multimillion year cooling trend in less than two centuries.

Abstract
As the world warms due to rising greenhouse gas concentrations, the Earth system moves toward climate states without societal precedent, challenging adaptation. Past Earth system states offer possible model systems for the warming world of the coming decades. These include the climate states of the Early Eocene (ca. 50 Ma), the Mid-Pliocene (3.3–3.0 Ma), the Last Interglacial (129–116 ka), the Mid-Holocene (6 ka), preindustrial (ca. 1850 CE), and the 20th century. Here, we quantitatively assess the similarity of future projected climate states to these six geohistorical benchmarks using simulations from the Hadley Centre Coupled Model Version 3 (HadCM3), the Goddard Institute for Space Studies Model E2-R (GISS), and the Community Climate System Model, Versions 3 and 4 (CCSM) Earth system models. Under the Representative Concentration Pathway 8.5 (RCP8.5) emission scenario, by 2030 CE, future climates most closely resemble Mid-Pliocene climates, and by 2150 CE, they most closely resemble Eocene climates. Under RCP4.5, climate stabilizes at Pliocene-like conditions by 2040 CE. Pliocene-like and Eocene-like climates emerge first in continental interiors and then expand outward. Geologically novel climates are uncommon in RCP4.5 (<1%) but reach 8.7% of the globe under RCP8.5, characterized by high temperatures and precipitation. Hence, RCP4.5 is roughly equivalent to stabilizing at Pliocene-like climates, while unmitigated emission trajectories, such as RCP8.5, are similar to reversing millions of years of long-term cooling on the scale of a few human generations. Both the emergence of geologically novel climates and the rapid reversion to Eocene-like climates may be outside the range of evolutionary adaptive capacity.

Quote
The linked reference confirms that elevated trace GHGs like methane, contributed directly to polar amplification of the Pliocene climate.

Peter O. Hopcroft et al. (September 22, 2020), "Polar amplification of Pliocene climate by elevated trace gas radiative forcing", PNAS, 117 (38) 23401-23407;  https://doi.org/10.1073/pnas.2002320117

The Arctic hasn’t been this warm for 3 million years – and that foreshadows big changes for the rest of the planet
https://theconversation.com/the-arctic-hasnt-been-this-warm-for-3-million-years-and-that-foreshadows-big-changes-for-the-rest-of-the-planet-144544
Quote
Because the Arctic was much warmer in the Pliocene, the Greenland Ice Sheet did not exist. Small glaciers along Greenland’s mountainous eastern coast were among the few places with year-round ice in the Arctic. The Pliocene Earth had ice only at one end – in Antarctica – and that ice was less extensive and more susceptible to melting.

Because the oceans were warmer and there were no large ice sheets in the Northern Hemisphere, sea levels were 30 to 50 feet (9 to 15 meters) higher around the globe than they are today. Coastlines were far inland from their current locations. The areas that are now California’s Central Valley, the Florida Peninsula and the Gulf Coast all were underwater. So was the land where major coastal cities like New York, Miami, Los Angeles, Houston and Seattle stand.

However, in all comparisons with the Pliocene, it should be remembered that the Panamanian land-bridge between North and South America appeared during the Pliocene (5.3 Ma to 2.6 Ma). The closure of the Panama seaway happened from 13 Ma–2.5 Ma, so for most parts of the Pliocene it was still open. The end of the Pliocene coincides with the completion of the closure.

The closure increased the salinity contrast between Pacific and Atlantic Ocean and the northward oceanic heat transport. Warmer water increased snowfall and possibly Greenland ice sheet volume.

Another thing that changed fundamentally during the Pliocene, is that a permanent El Niño state existed in the early-mid Pliocene. Warmer temperature in the eastern equatorial pacific increased water vapor greenhouse effect and reduced the area covered by highly reflective stratus clouds thus decreasing the albedo of the planet. Propagation of El Niño effect through planetary waves  warmed the polar region and delayed the onset of the northern hemisphere glaciation. Therefore, the appearance of cold surface water in the east equatorial pacific around 3 million years ago contributed to global cooling and modified global climate response to Milankovitch cycles. Also this effect is probably attributable to the closure of the Panama seaway.

After the closure, the Atlantic is the only ocean where there is northbound heat transport across the equator, and it's by far the main ocean that communicates with the Arctic, linking both poles with the AMOC.
See attached figure, from "Estimates of Meridional Atmosphere and Ocean Heat Transports", by  TRENBERTH et al, 2001.

The two papers that ASLR refers to above don't even mention the profound climate changes brought about by the closure of the Panama seaway, which makes me suspicious of their conclusion that we will see anything resembling a Pliocene climate in such a near future as 100 years.

The papers also don't even mention the fundamental changes in the ENSO.
The same goes for the article Tom refers to, no mention of neither the changes in ENSO nor the changes in meridional ocean currents.

Please correct me if I'm wrong!

nanning

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3803 on: October 04, 2020, 05:36:51 PM »
Precautionary principle

F.U.D. - no more doubt about uncertainties.

"I want you to panic"
- Greta Thunberg

off-topic for some perhaps but not if your world-view is realistic concerning the top statement.
"It is preoccupation with possessions, more than anything else, that prevents us from living freely and nobly" - Bertrand Russell
"It is preoccupation with what other people from your groups think of you, that prevents you from living freely and nobly" - Nanning
Why do you keep accumulating stuff?

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3804 on: October 04, 2020, 05:40:26 PM »
...

Another thing that changed fundamentally during the Pliocene, is that a permanent El Niño state existed in the early-mid Pliocene.

...

Please correct me if I'm wrong!

The linked reference confirms that during the Early Pliocene Warm Period El Nino events were dampened as compared to the Holocene.

S. M. White and A. C. Ravelo (30 January 2020), "Dampened El Niño in the Early Pliocene Warm Period", Geophysical Research Letters, Volume 47, Issue 4, https://doi.org/10.1029/2019GL085504

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL085504

ABSTRACT
El Niño‐Southern Oscillation (ENSO) is the strongest mode of interannual climate variability, and its predicted response to anthropogenic climate change remains unclear. Determining ENSO's sensitivity to climatic mean state and the strength of positive and negative feedbacks, notably the thermocline feedback, will help constrain its future behavior. To this end, we collected ENSO proxy data from the early and mid‐Pliocene, a time during which tropical Pacific zonal and vertical temperature gradients were much lower than today. We found that El Niño events had a reduced amplitude throughout the early Pliocene, compared to the late Holocene. By the mid‐Pliocene, El Niño amplitude was variable, sometimes reduced and sometimes similar to the late Holocene. This trend in Pliocene ENSO amplitude mirrors the long‐term strengthening of zonal and vertical temperature gradients and verifies model results showing dampened ENSO under reduced gradients due to a weaker thermocline feedback.

Plain Language Summary
El Niño events are marked by anomalously warm sea‐surface temperatures and increased rainfall in the central and eastern equatorial Pacific and cause major changes in weather patterns across the Pacific. It is unclear whether El Niño events will strengthen or weaken with anthropogenic warming. To help elucidate El Niño's future behavior, we reconstructed changes in El Niño during the Pliocene, the most recent extended period that was warmer than today. We found that El Niño events were weaker ~3.5 to 5 Ma, compared to the late Holocene. By ~3.1 Ma, El Niño strength was sometimes weaker and sometimes similar to the late Holocene, varying on millennial timescales. The shift in El Niño behavior coincides with a long‐term cooling of tropical Pacific subsurface waters. The association between subsurface temperature and El Niño strength has also been observed for the Last Glacial Maximum and the Holocene and points to an important role of the subsurface in dictating El Niño strength.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3805 on: October 04, 2020, 06:04:44 PM »
...
The closure of the Panama seaway happened from 13 Ma–2.5 Ma, so for most parts of the Pliocene it was still open. The end of the Pliocene coincides with the completion of the closure.
...
Please correct me if I'm wrong!

It is more valuable to focus on the mid-, and late, Pliocene (and not the early Pliocene); which per the first linked Wikipedia article were from 3.3Ma to 3Ma and from 3Ma to 2.6Ma, respectively.  In this regard, the second linked reference confirms that the Panamanian land-bridge was effectively closed (to major ocean circulation patterns) by 4Ma (see the attached image with SSTA information for the mid-Pliocene). So to me it is a red herring to say that the land bridge did not 100% close until 2.6Ma.

Title: "Pliocene climate"

https://en.wikipedia.org/wiki/Pliocene_climate

Extract: "During the Pliocene epoch (5.3 Ma to 2.6 Ma) climate became cooler and drier, and seasonal, similar to modern climates.

The global average temperature in the mid-Pliocene (3.3 Ma–3 Ma) was 2–3 °C higher than today, global sea level 25m higher and the northern hemisphere ice sheet was ephemeral before the onset of extensive glaciation over Greenland that occurred in the late Pliocene around 3 Ma."

Caption for the attached image: " Mid-Pliocene reconstructed annual sea surface temperature anomaly"

&

Karas, C., Nürnberg, D., Bahr, A. et al. Pliocene oceanic seaways and global climate. Sci Rep 7, 39842 (2017). https://doi.org/10.1038/srep39842

https://www.nature.com/articles/srep39842

Abstract: " Tectonically induced changes in oceanic seaways had profound effects on global and regional climate during the Late Neogene. The constriction of the Central American Seaway reached a critical threshold during the early Pliocene ~4.8–4 million years (Ma) ago. Model simulations indicate the strengthening of the Atlantic Meridional Overturning Circulation (AMOC) with a signature warming response in the Northern Hemisphere and cooling in the Southern Hemisphere. Subsequently, between ~4–3 Ma, the constriction of the Indonesian Seaway impacted regional climate and might have accelerated the Northern Hemisphere Glaciation. We here present Pliocene Atlantic interhemispheric sea surface temperature and salinity gradients (deduced from foraminiferal Mg/Ca and stable oxygen isotopes, δ18O) in combination with a recently published benthic stable carbon isotope (δ13C) record from the southernmost extent of North Atlantic Deep Water to reconstruct gateway-related changes in the AMOC mode. After an early reduction of the AMOC at ~5.3 Ma, we show in agreement with model simulations of the impacts of Central American Seaway closure a strengthened AMOC with a global climate signature. During ~3.8–3 Ma, we suggest a weakening of the AMOC in line with the global cooling trend, with possible contributions from the constriction of the Indonesian Seaway."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3806 on: October 05, 2020, 01:13:54 AM »
The linked reference finds that current slab ocean models (SOMs) systematically underestimate ECS and concludes that:

"While ECS estimates from current generation U.S. models based on SOM and coupled annual averages of years 1–150 range from 2.6°C to 5.3°C, estimates based longer simulations of the same models range from 3.2°C to 7.0°C. Such variations between methods argues for caution in comparison and interpretation of ECS estimates across models."

If ECS is as high as 7.0C, this is a clear sign that we are likely headed for an equable climate before 2150:

John P. Dunne et al. (23 July 2020), "Comparison of Equilibrium Climate Sensitivity Estimates From Slab Ocean, 150‐Year, and Longer Simulations", Geophysical Research Letters, https://doi.org/10.1029/2020GL088852

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL088852

Abstract
We compare equilibrium climate sensitivity (ECS) estimates from pairs of long (≥800‐year) control and abruptly quadrupled CO2 simulations with shorter (150‐ and 300‐year) coupled atmosphere‐ocean simulations and slab ocean models (SOMs). Consistent with previous work, ECS estimates from shorter coupled simulations based on annual averages for years 1–150 underestimate those from SOM (−8% ± 13%) and long (−14% ± 8%) simulations. Analysis of only years 21–150 improved agreement with SOM (−2% ± 14%) and long (−8% ± 10%) estimates. Use of pentadal averages for years 51–150 results in improved agreement with long simulations (−4% ± 11%). While ECS estimates from current generation U.S. models based on SOM and coupled annual averages of years 1–150 range from 2.6°C to 5.3°C, estimates based longer simulations of the same models range from 3.2°C to 7.0°C. Such variations between methods argues for caution in comparison and interpretation of ECS estimates across models.

Plain Language Summary
Precise definition and estimation of equilibrium climate sensitivity (ECS) continues to challenge model intercomparison. While annual analyses of years 1–150 of coupled atmosphere‐ocean models agree with slab ocean model simulations, they underestimate coupled ECS estimates from multicentennial to millennial scale simulations. However, long‐term ECS estimates can be largely recovered through a combination of (1) ignoring the first 50 years of abrupt 4 times preindustrial CO2 simulation dominated by early timescales of ocean response and (2) using pentadal (5‐year) averages instead of annual ones for years 51–150. This variation between methods argues for reconsideration of ECS estimation and application acknowledging that slab ocean estimates systematically ignore potential sources of enhanced sensitivity and simulations longer than 150 years are necessary for precise estimation of the long‐term trend.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3807 on: October 06, 2020, 03:02:36 AM »
The linked reference indicates that the Mid Miocene Climate Optimum (which was warmer that the Pliocene but cooler than the Eocene as shown in the attached image), likely had a high climate sensitivity (which current climate models cannot replicate), and concludes:

"We conclude that climate sensitivity was heightened during MCO, indicating that highly elevated temperatures can occur at relatively moderate pCO2. Ever higher climate sensitivity with rising temperatures should be very seriously considered in future predictions of climate change."

Hopefully, consensus climate scientist start to very seriously consider higher climate sensitivity values in future projections of coming climate change.

M. Steinthorsdottir, P. E. Jardine and W. C. Rember (12 May 2020), "Near‐Future pCO2 during the hot Mid Miocene Climatic Optimum", Paleoceanography and Paleoclimatology, https://doi.org/10.1029/2020PA003900

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020PA003900

Abstract
To improve future predictions of anthropogenic climate change, a better understanding of the relationship between global temperature and atmospheric concentrations of CO2 (pCO2), or climate sensitivity, is urgently required. Analyzing proxy data from climate change episodes in the past is necessary to achieve this goal, with certain geologic periods, such as the mid Miocene Climatic Optimum (MCO), a transient period of global warming with global temperatures up to ~7°C higher than today, increasingly viewed as good analogues to future climate under present emission scenarios. However, a problem remains that climate models cannot reproduce MCO temperatures with less than ~800 ppm pCO2, while most previously published proxies record pCO2 <450 ppm. Here, we reconstructed MCO pCO2 with a multi‐taxon fossil leaf database from the well‐dated MCO Lagerstätte deposits of Clarkia, Idaho, USA, using four current methods of pCO2 reconstructions. The methods are principally based on either stomatal densities, carbon isotopes, or a combination of both – thus offering independent results. The total of six reconstructions mostly record pCO2 of ~450–550 ppm. Although slightly higher than previously reconstructed pCO2, the discrepancy with the ~800 ppm required by climate models remains. We conclude that climate sensitivity was heightened during MCO, indicating that highly elevated temperatures can occur at relatively moderate pCO2. Ever higher climate sensitivity with rising temperatures should be very seriously considered in future predictions of climate change.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3808 on: October 07, 2020, 09:45:05 AM »
The linked reference finds that regression to the mean only be considered when there is a mean and that:

"The pandemic and the climate crisis are presently the two most significant manifestations of the law and age of regression to the tail."

This highlights the point that I have been making that in a changing system, such as for our global climate, tail risk should be guiding our decision making process:

BentFlyvbjerg (5 October 2020), "The law of regression to the tail: How to survive Covid-19, the climate crisis, and other disasters", Environmental Science & Policy, https://doi.org/10.1016/j.envsci.2020.08.013

https://www.sciencedirect.com/science/article/pii/S1462901120308637?dgcid=rss_sd_all

Abstract
Regression to the mean is nice and reliable. Regression to the tail is reliably scary. We live in the age of regression to the tail. It is only a matter of time until a pandemic worse than covid-19 will hit us, and climate more extreme than any we have seen. What are the basic principles that generate such extreme risk, and for navigating it, for government, business, and the public?

Extract: "There is nothing as practical as a theory that is correct. Regression to the mean has been proven mathematically for many types of statistics and is highly useful in health, insurance, schools, on factory floors, in casinos, and in risk management, e.g., for flight safety.

But regression to the mean presupposes that a population mean exists. For some random events of great social consequence this is not the case.

Size-distributions of pandemics, floods, wildfires, earthquakes, wars, and terrorist attacks, e.g., have no population mean, or the mean is ill defined due to infinite variance. In other words, mean and/or variance do not exist. Regression to the mean is a meaningless concept for such distributions, whereas what one might call "regression to the tail" is meaningful and consequential.

Regression to the tail applies to any distribution with non-vanishing probability density towards infinity. The frequency of new extremes and how much they exceed previous records is decisive for how fat-tailed a distribution will be, e.g., whether it will have infinite (non-existent) variance and mean.  Above a certain frequency and size of extremes, the mean increases with more events measured, with the mean eventually approaching infinity instead of converging. In this case, regression to the mean means regression to infinity, i.e., a non-existent mean. Deep disasters – e.g., pandemics, floods, droughts, wildfires, earthquakes, landslides, avalanches, tsunamis, and wars – tend to follow this type of distribution. So do crime, terrorist attacks, blackouts, financial markets, debt, bankruptcies, and cybercrime, together with less disastrous but financially highly risky ventures like hosting the Olympics, building nuclear power plants, high-speed rail systems, hydroelectric dams, new cities, and even something as apparently innocuous as procuring new IT systems, the latter being a serious bug in current worldwide digitization efforts.

I suggest we name this phenomenon – that events return to the tail in sufficient size and frequency for the mean to not converge – "the law of regression to the tail." The law depicts a situation with many extreme events, and no matter how extreme the most extreme event is, there will always be an event even more extreme than this. It is only a matter of time until it appears.

I further suggest that regression to the tail is the new normal. We live in the age of regression to the tail. Tail risks are becoming increasingly important and common because of a more interconnected and fragile global system of human interaction for travel, commerce, finance, etc., but also because the walls are coming down between natural and human systems, with humans impacting nature at a global scale for the first time in history, not least in terms of climate change. The pandemic and the climate crisis are presently the two most significant manifestations of the law and age of regression to the tail."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3809 on: October 07, 2020, 09:52:56 AM »
The linked reference confirms that the CMIP6 models do a good job of reasonably matching recently observed GMSTA values:

Xuewei Fan et al. (1 October 2020), "Global surface air temperatures in CMIP6: historical performance and future changes", Environmental Research Letters, Volume 15, Number 10; https://doi.org/10.1088/1748-9326/abb051

https://iopscience.iop.org/article/10.1088/1748-9326/abb051

Abstract
Surface air temperature outputs from 16 global climate models participating in the sixth phase of the coupled model intercomparison project (CMIP6) were used to evaluate agreement with observations over the global land surface for the period 1901–2014. Projections of multi-model mean under four different shared socioeconomic pathways were also examined. The results reveal that the majority of models reasonably capture the dominant features of the spatial variations in observed temperature with a pattern correlation typically greater than 0.98, but with large variability across models and regions. In addition, the CMIP6 mean can capture the trends of global surface temperatures shown by the observational data during 1901–1940 (warming), 1941–1970 (cooling) and 1971–2014 (rapid warming). By the end of the 21st century, the global temperature under different scenarios is projected to increase by 1.18 °C/100 yr (SSP1-2.6), 3.22 °C/100 yr (SSP2-4.5), 5.50 °C/100 yr (SSP3-7.0) and 7.20 °C/100 yr (SSP5-8.5), with greater warming projected over the high latitudes of the northern hemisphere and weaker warming over the tropics and the southern hemisphere. Results of probability density distributions further indicate that large increases in the frequency and magnitude of warm extremes over the global land may occur in the future.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3810 on: October 07, 2020, 10:02:53 AM »
The linked reference indicates that:

"… CMIP6 AA simulations yield robust AMOC strengthening (weakening) in response to increasing (decreasing) anthropogenic aerosols."

So as we collectively reduce anthropogenic aerosol emissions we can expect the weakening of the AMOC to accelerate (beyond what has been observed since 1990).

Hassan, T., Allen, R. J., Liu, W., and Randles, C.: Anthropogenic aerosol forcing of the AMOC and the associated mechanisms in CMIP6 models, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2020-769, in review, 2020.

https://acp.copernicus.org/preprints/acp-2020-769/

Abstract. By regulating the global transport of heat, freshwater and carbon, the Atlantic Meridional Overturning Circulation (AMOC) serves as an important component of the climate system. During the late 20th and early 21st centuries, indirect observations and models suggest a weakening of the AMOC. Direct AMOC observations also suggest a weakening during the early 21st century, but with substantial interannual variability. Long-term weakening of the AMOC has been associated with increasing greenhouse gases (GHGs), but some modeling studies suggest the build up of anthropogenic aerosols (AAs) may have offset part of the GHG-induced weakening. Here, we quantify 1900–2020 AMOC variations and assess the driving mechanisms in state-of-the-art climate models from the Coupled Model Intercomparison Project phase 6 (CMIP6). The CMIP6 all forcing (GHGs, anthropogenic and volcanic aerosols, solar variability, and land use/land change) multi-model mean shows negligible AMOC changes up to ~1950, followed by robust AMOC strengthening during the second half of the 20th century (~1950–1990), and weakening afterwards (1990–2020). These multi-decadal AMOC variations are related to changes in North Atlantic atmospheric circulation, including an altered sea level pressure gradient, storm track activity, surface winds and heat fluxes, which drive changes in the subpolar North Atlantic surface density flux. Similar to previous studies, CMIP6 GHG simulations yield robust AMOC weakening, particularly during the second half of the 20th century. Changes in natural forcings, including solar variability and volcanic aerosols, yield negligible AMOC changes. In contrast, CMIP6 AA simulations yield robust AMOC strengthening (weakening) in response to increasing (decreasing) anthropogenic aerosols. Moreover, the CMIP6 all-forcing AMOC variations and atmospheric circulation responses also occur in the CMIP6 AA simulations, which suggests these are largely driven by changes in anthropogenic aerosol emissions. Although aspects of the CMIP6 all-forcing multi-model mean response resembles observations, notable differences exist. This includes CMIP6 AMOC strengthening from ~1950–1990, when the indirect estimates suggest AMOC weakening. The CMIP6 multi-model mean also underestimates the observed increase in North Atlantic ocean heat content. And although the CMIP6 North Atlantic atmospheric circulation responses–particularly the overall patterns–are similar to observations, the simulated responses are weaker than those observed, implying they are only partially externally forced. The possible causes of these differences include internal climate variability, observational uncertainties and model shortcomings–including excessive aerosol forcing. A handful of CMIP6 realizations yield AMOC evolution since 1900 similar to the indirect observations, implying the inferred AMOC weakening from 1950–1990 (and even from 1930–1990) may have a significant contribution from internal (i.e., unforced) climate variability. Nonetheless, CMIP6 models yield robust, externally forced AMOC changes, the bulk of which are due to anthropogenic aerosols.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3811 on: October 07, 2020, 03:56:44 PM »
Copernicus reports that September 2020 was the warmest September on record, thus increasing the probability that 2020 will be the warmest year on record, despite the fact that the Eastern Equatorial Pacific is currently experiencing La Nina-like conditions.

Title: Surface air temperature for September 2020"

https://climate.copernicus.eu/surface-air-temperature-september-2020

Extract: "Globally and in Europe, September 2020 was the warmest September on record, with the global average 0.05°C warmer than the previous warmest September in 2019. Temperatures were well above average in many regions across the globe, including off the coast of northern Siberia, in the middle East, in parts of South America and Australia. Cooler than average conditions marked the eastern equatorial Pacific Ocean, consistent with the ongoing La Niña event."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3812 on: October 07, 2020, 04:11:57 PM »
As a follow-on to my last post, Hausfather posted the three attached images both showing that September 2020 was the warmest September on record (first image) but that 2020 is likely to be the warmest year on record (see the last two images).
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3813 on: October 08, 2020, 04:10:09 AM »
The linked reference indicates that the Amazon is near a tipping point of switching from a rainforest to a savannah.  This is not good news.

Staal, A., Fetzer, I., Wang-Erlandsson, L. et al. Hysteresis of tropical forests in the 21st century. Nat Commun 11, 4978 (2020). https://doi.org/10.1038/s41467-020-18728-7

https://www.nature.com/articles/s41467-020-18728-7

Abstract: "Tropical forests modify the conditions they depend on through feedbacks at different spatial scales. These feedbacks shape the hysteresis (history-dependence) of tropical forests, thus controlling their resilience to deforestation and response to climate change. Here, we determine the emergent hysteresis from local-scale tipping points and regional-scale forest-rainfall feedbacks across the tropics under the recent climate and a severe climate-change scenario. By integrating remote sensing, a global hydrological model, and detailed atmospheric moisture tracking simulations, we find that forest-rainfall feedback expands the geographic range of possible forest distributions, especially in the Amazon. The Amazon forest could partially recover from complete deforestation, but may lose that resilience later this century. The Congo forest currently lacks resilience, but is predicted to gain it under climate change, whereas forests in Australasia are resilient under both current and future climates. Our results show how tropical forests shape their own distributions and create the climatic conditions that enable them."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3814 on: October 08, 2020, 07:23:30 PM »
The linked reference indicates that an equatorial mode of climate variability will emerge in Indian Ocean in coming decades.  While the reference focuses on the regional impacts, I note that the Equatorial Indian Ocean has a major impact on the Equatorial Pacific Ocean; which, in my opinion, identifies yet another significant climate change risk that is currently under appreciated.

Pedro N. DiNezio, Martin Puy, Kaustubh Thirumalai, Fei-Fei Jin and Jessica E. Tierney (06 May 2020), "Emergence of an equatorial mode of climate variability in the Indian Ocean", Science Advances, Vol. 6, no. 19, eaay7684, DOI: 10.1126/sciadv.aay7684

https://advances.sciencemag.org/content/6/19/eaay7684

Abstract
Presently, the Indian Ocean (IO) resides in a climate state that prevents strong year-to-year climate variations. This may change under greenhouse warming, but the mechanisms remain uncertain, thus limiting our ability to predict future changes in climate extremes. Using climate model simulations, we uncover the emergence of a mode of climate variability capable of generating unprecedented sea surface temperature and rainfall fluctuations across the IO. This mode, which is inhibited under present-day conditions, becomes active in climate states with a shallow thermocline and vigorous upwelling, consistent with the predictions of continued greenhouse warming. These predictions are supported by modeling and proxy evidence of an active mode during glacial intervals that favored such a state. Because of its impact on hydrological variability, the emergence of such a mode would become a first-order source of climate-related risks for the densely populated IO rim.

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3815 on: October 08, 2020, 07:48:41 PM »
The linked reference concludes that:

"Our findings point to growing N2O emissions in emerging economies—particularly Brazil, China and India. Analysis of process-based model estimates reveals an emerging N2O–climate feedback resulting from interactions between nitrogen additions and climate change. The recent growth in N2O emissions exceeds some of the highest projected emission scenarios, underscoring the urgency to mitigate N2O emissions."

This represents yet another climate risk that is not included in CMIP6 projections:

Tian, H., Xu, R., Canadell, J.G. et al. A comprehensive quantification of global nitrous oxide sources and sinks. Nature 586, 248–256 (2020). https://doi.org/10.1038/s41586-020-2780-0

https://www.nature.com/articles/s41586-020-2780-0

Abstract: "Nitrous oxide (N2O), like carbon dioxide, is a long-lived greenhouse gas that accumulates in the atmosphere. Over the past 150 years, increasing atmospheric N2O concentrations have contributed to stratospheric ozone depletion and climate change, with the current rate of increase estimated at 2 per cent per decade. Existing national inventories do not provide a full picture of N2O emissions, owing to their omission of natural sources and limitations in methodology for attributing anthropogenic sources. Here we present a global N2O inventory that incorporates both natural and anthropogenic sources and accounts for the interaction between nitrogen additions and the biochemical processes that control N2O emissions. We use bottom-up (inventory, statistical extrapolation of flux measurements, process-based land and ocean modelling) and top-down (atmospheric inversion) approaches to provide a comprehensive quantification of global N2O sources and sinks resulting from 21 natural and human sectors between 1980 and 2016. Global N2O emissions were 17.0 (minimum–maximum estimates: 12.2–23.5) teragrams of nitrogen per year (bottom-up) and 16.9 (15.9–17.7) teragrams of nitrogen per year (top-down) between 2007 and 2016. Global human-induced emissions, which are dominated by nitrogen additions to croplands, increased by 30% over the past four decades to 7.3 (4.2–11.4) teragrams of nitrogen per year. This increase was mainly responsible for the growth in the atmospheric burden. Our findings point to growing N2O emissions in emerging economies—particularly Brazil, China and India. Analysis of process-based model estimates reveals an emerging N2O–climate feedback resulting from interactions between nitrogen additions and climate change. The recent growth in N2O emissions exceeds some of the highest projected emission scenarios, underscoring the urgency to mitigate N2O emissions."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3816 on: October 09, 2020, 04:14:07 PM »
Ice Melt Projections May Underestimate Antarctic Contribution to Sea Level Rise
https://phys.org/news/2020-10-ice-underestimate-antarctic-contribution-sea.html

... "We know ice sheets are melting as global temperatures increase, but uncertainties remain about how much and how fast that will happen," said Chris Forest, professor of climate dynamics at Penn State. "Our findings shed new light on one area of uncertainty, suggesting climate variability has a significant impact on melting ice sheets and sea level rise."

While it is understood that continued warming may cause rapid ice loss, models that predict how Antarctica will respond to climate change have not included the potential impacts of internal climate variability, like yearly and decadal fluctuations in the climate, the team of scientists said.

Accounting for climate variability caused models to predict an additional 2.7 to 4.3 inches—7 to 11 centimeters—of sea level rise by 2100, the scientists recently reported in the journal Climate Dynamics. The models projected roughly 10.6 to 14.9 inches—27 to 38 centimeters—of sea level rise during that same period without climate variability.

... The Antarctic ice sheet is a complex system, and modeling how it will evolve under future climate conditions requires thousands of simulations and large amounts of computing power. Because of this, modelers test how the ice will respond using a mean temperature found by averaging the results of climate models.

However, that process smooths out peaks caused by climate variability and reduces the average number of days above temperature thresholds that can impact the ice sheet melt, creating a bias in the results, the scientists said.

Extensive parts of the ice sheet are in contact with ocean water, and previous studies have suggested that warming oceans could cause large chunks to break away. The process may expose ice cliffs so tall that they collapse under their own weight, inducing a domino effect that further depletes the ice shelf.

The scientists found model simulations that did not include the effects of internal climate variability significantly delayed the retreat of the ice sheet by up to 20 years and underestimated future sea level rise.


... for years, the IPCC reports have been looking at sea level rise without considering this additional variability and have been underestimating what the impact may be," ...


Time series of AIS contribution to ΔGMSL since 2000

Tsai, C.-Y., Forest, C.E., and D. Pollard, The role of internal climate variability on projecting Antarctica’s contribution to future sea-level rise,  J. Climate Dynamics,  2020
https://link.springer.com/article/10.1007/s00382-020-05354-8

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3817 on: October 09, 2020, 04:25:48 PM »
v_m:
So doing a little addition we can expect in the next 80 years (in the lifetime of children today) sea level rise 13.3 to 19.2 in (34-49 cm) beyond that of today which is already causing trouble.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3818 on: October 09, 2020, 04:27:38 PM »
That's just from Antarctica
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3819 on: October 09, 2020, 05:32:50 PM »
The linked IPCC summary (for teachers) on the ocean and cryosphere in a changing climate, provides a useful beginning point for those who do not understand the dynamic interactions (and climate feedback loops) between the ocean and the cryosphere.  However, please consider that this document errs on the side of least drama (ESLD) with regard to right-tail climate risks.  Furthermore, I note that while this summary has been edited not to alarm students, it still adds the standard consensus climate caveat that coming climate changes:

"… will continue throughout the decades and the millennia – some occurring abruptly and (others) being irreversible."

Eric Guilyardi et al. (March 2020), "THE OCEAN AND CRYOSPHERE IN A CHANGING CLIMATE SUMMARY FOR TEACHERS BASED ON THE IPCC SPECIAL REPORT ON THE OCEAN AND CRYOSPHERE IN A CHANGING CLIMATE (SROCC)"

https://www.oce.global/sites/default/files/2020-04/OCE-RAP_SROCC-EN-10-WEB.pdf

Extract: "Climate-change-induced disturbances in the ocean and cryosphere have strong impacts on human communities – particularly on those living near the coast, on small islands, in polar areas or in high mountain regions. Today, around 4 million people live permanently in the Arctic region, of whom 10% are indigenous; 680 million people live near the coast and 670 million people live in high mountain regions. The changes will continue throughout the decades and the millennia – some occurring abruptly and (others) being irreversible."

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3820 on: October 09, 2020, 05:42:04 PM »
Climate Patterns Linked in Amazon, North and South America, Study Shows
https://phys.org/news/2020-10-climate-patterns-linked-amazon-north.html



University of Arkansas researchers have established a link between climate patterns in the Amazon and large parts of North and South America using their newly developed tree-ring chronology from the Amazon River basin.

... Tree growth is a well-established climate proxy. By comparing growth rings in Cedrela odorata trees found in the Rio Paru watershed of the eastern Amazon River with hundreds of similar chronologies in North and South America, scientists have shown an inverse relationship in tree growth, and therefore precipitation patterns, between the areas. Drought in the Amazon is correlated with wetness in the southwestern United States, Mexico and Patagonia, and vice versa.

The process is driven by the El Niño phenomenon, which influences surface-level winds along the equator, researchers said. El Niño is the name given to a large-scale irregularly occurring climate pattern associated with unusually warm water in the Pacific Ocean.

"The new Cedrela chronologies from the Amazon, when compared with the hundreds of tree-ring chronologies in temperate North and South America, document this Pan American resonance of climate and ecosystem extremes in the centuries before widespread deforestation or human-caused climate change," said Dave Stahle, Distinguished Professor of geosciences and first author of a study documenting the findings in the journal Environmental Research Letters.


https://wordpressua.uark.edu/amazon/

D W Stahle et al. Pan American interactions of Amazon precipitation, streamflow, and tree growth extremes, Environmental Research Letters (2020)
https://iopscience.iop.org/article/10.1088/1748-9326/ababc6

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3821 on: October 14, 2020, 04:19:08 AM »
While the linked videos selected from the WAIS Workshop 2020 may seem academic to most people; I provide them for those who are interested:

Title: "WAIS Workshop 2020: Session 5 - Grounding Zones & Ice Shelves 1"



I think that the talk starting around 58:30, regarding the Thwaites Eastern Ice Shelf and tidal pumping at its grounding line, is interesting even though I am more concerned about the Thwaites Ice Tongue.

&

Title: "WAIS Workshop 2020: Session 6 - Grounding Zones & Ice Shelves 2"



I think that the talk by Bassis starting near 1:30 is interesting; however, he focuses on cases ice cliff failures that do not lead to MICI behavior, while he does show that a critical ice thickness gradient can lead to a rapid retreat/collapse of the Thwaites Glacier (see the attached image).

&

Title: "WAIS Workshop 2020: Session 7 - Grounding Zones & Ice Shelves 3:



I think that the talk starting near 1:30 about the TARSAN project for Thwaites is interesting


To access all of the YouTube WAIS Workshop 2020 videos you can use the following link"

https://www.youtube.com/channel/UC-nSFKCeciZh5KQtEgrJqmg

« Last Edit: October 14, 2020, 04:03:04 PM by AbruptSLR »
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3822 on: October 14, 2020, 12:25:10 PM »
Thanks, ASLR. But even though I am unemployed (on disability) I don't have the hours to watch those videos. I appreciate your posting the link, and hope others can take advantage of it. I [liked] the post in case someday i can watch them.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3823 on: October 14, 2020, 04:49:36 PM »
Despite the presences of the North Atlantic cold spot, the linked reference indicates that the North Atlantic SSTs are the warmest that they have been in the ~2,900 years:

Francois Lapointe et al. (October 12, 2020), "Annually resolved Atlantic sea surface temperature variability over the past 2,900 y", PNAS; https://doi.org/10.1073/pnas.2014166117

https://www.pnas.org/content/early/2020/10/06/2014166117

Significance
Atlantic multidecadal sea surface temperature variability (AMV) strongly influences the Northern Hemisphere’s climate, including the Arctic. Here using a well-dated annually laminated lake sediment core, we show that the AMV exerts a strong influence on High-Arctic climate during the instrumental period (past ∼150 y) through atmospheric teleconnection. This highly resolved climate archive is then used to produce the first AMV reconstruction spanning the last ∼3 millennia at unprecedented temporal resolution. Our terrestrial record is significantly correlated to several sea surface temperature proxies in the Atlantic, highlighting the reliability of this record as an annual tracer of the AMV. The results show that the current warmth in sea surface temperature is unseen in the context of the past ∼3 millennia.

Abstract
Global warming due to anthropogenic factors can be amplified or dampened by natural climate oscillations, especially those involving sea surface temperatures (SSTs) in the North Atlantic which vary on a multidecadal scale (Atlantic multidecadal variability, AMV). Because the instrumental record of AMV is short, long-term behavior of AMV is unknown, but climatic teleconnections to regions beyond the North Atlantic offer the prospect of reconstructing AMV from high-resolution records elsewhere. Annually resolved titanium from an annually laminated sedimentary record from Ellesmere Island, Canada, shows that the record is strongly influenced by AMV via atmospheric circulation anomalies. Significant correlations between this High-Arctic proxy and other highly resolved Atlantic SST proxies demonstrate that it shares the multidecadal variability seen in the Atlantic. Our record provides a reconstruction of AMV for the past ∼3 millennia at an unprecedented time resolution, indicating North Atlantic SSTs were coldest from ∼1400–1800 CE, while current SSTs are the warmest in the past ∼2,900
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3824 on: October 15, 2020, 02:46:43 AM »
For those who missed this research last month [the first attached image illustrates how the deep seafloor channels converge at the base of the TEIS and the Thwaites Ice Tongue in the seafloor trough that leads directly to the Byrd Subglacial Basin (BSB); thus guiding relatively warm modified CDW to relatively quickly form a subglacial cavity in this trough area]:

Title: "Thwaites: 'Doomsday Glacier' vulnerability seen in new maps"

https://www.bbc.com/news/science-environment-54079587

Extract: "Now, a UK-US team has surveyed the deep seafloor channels in front of the glacier that almost certainly provide the access for warm water to infiltrate and attack Thwaites' underside.

It's information that will be used to try to predict the ice stream's future.

"These channels had not been mapped before in this kind of detail, and what we've discovered is that they're actually much bigger than anyone thought - up to 600m deep. Think of six football pitches back to back," said Dr Kelly Hogan from the British Antarctic Survey (BAS).

"And because they are so deep, and so wide - this allows a lot more water to get at, and melt, Thwaites' floating front as well as its ice that rests on the seabed," she told BBC News."

Edit: For ease of comparison I provide the last three images from earlier posts in this thread; where the second image shows how in 2012-13 the ice surface dropped abruptly when a portion of the subglacial cavity collapsed in this area.

Edit2: For those who forgot, or have not scrolled back through this thread, I note that the last two images show that the southside of what I have termed the 'Big Ear' subglacial cavity has an ice surface that is about 140m above sea level and that the ice over the 'Big Ear' subglacial cavity is essentially floating.  Thus, a surge of the Thwaites Ice Tongue (as occurred in the 2013-14 season, and which I believe may likely occur again well before 2040) could unpin the ice over the 'Big Ear' Subglacial cavity (thus allowing this ice to float away); which would likely expose a bare ice cliff face (potentially about 140m above the water surface); which according to Bassis' 2020 WAIS Workshop analysis, would be sufficient to trigger an MICI-type of collapse leading straight into the BSB.
« Last Edit: October 15, 2020, 06:30:38 PM by AbruptSLR »
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3825 on: October 15, 2020, 05:28:32 PM »
As a follow-on to my last post, Hausfather posted the three attached images both showing that September 2020 was the warmest September on record (first image) but that 2020 is likely to be the warmest year on record (see the last two images).

I note that if the 2020-21 season is eventually officially recorded as an La Nina season, and if 2020 eventually has a GMSTA close to that of 2016 (see the first image from Hausfather); then the second image from Hansen indicates that the recent warming trend of La Nina years portends a relative high climate sensitivity value.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3826 on: October 15, 2020, 06:20:37 PM »
The linked reference indicates that the majority of Antarctic ice shelves are susceptible to meltwater-driven fracturing with continued local surface warming.  Furthermore, I note that a major freshwater hosing event (such as due to a temporary reversal of the Beaufort Gyre) would abruptly increase the atmospheric advection of heat from the Tropical Pacific to West Antarctica; which, would abruptly increase the risk of meltwater-driven hydrofracturing of the ice shelves in this region.

Lai, C., Kingslake, J., Wearing, M.G. et al. Vulnerability of Antarctica’s ice shelves to meltwater-driven fracture. Nature 584, 574–578 (2020). https://doi.org/10.1038/s41586-020-2627-8

https://www.nature.com/articles/s41586-020-2627-8

Abstract
Atmospheric warming threatens to accelerate the retreat of the Antarctic Ice Sheet by increasing surface melting and facilitating ‘hydrofracturing’, where meltwater flows into and enlarges fractures, potentially triggering ice-shelf collapse. The collapse of ice shelves that buttress the ice sheet accelerates ice flow and sea-level rise. However, we do not know if and how much of the buttressing regions of Antarctica’s ice shelves are vulnerable to hydrofracture if inundated with water. Here we provide two lines of evidence suggesting that many buttressing regions are vulnerable. First, we trained a deep convolutional neural network (DCNN) to map the surface expressions of fractures in satellite imagery across all Antarctic ice shelves. Second, we developed a stability diagram of fractures based on linear elastic fracture mechanics to predict where basal and dry surface fractures form under current stress conditions. We find close agreement between the theoretical prediction and the DCNN-mapped fractures, despite limitations associated with detecting fractures in satellite imagery. Finally, we used linear elastic fracture mechanics theory to predict where surface fractures would become unstable if filled with water. Many regions regularly inundated with meltwater today are resilient to hydrofracture—stresses are low enough that all water-filled fractures are stable. Conversely, 60 ± 10 per cent of ice shelves (by area) both buttress upstream ice and are vulnerable to hydrofracture if inundated with water. The DCNN map confirms the presence of fractures in these buttressing regions. Increased surface melting could trigger hydrofracturing if it leads to water inundating the widespread vulnerable regions we identify. These regions are where atmospheric warming may have the largest impact on ice-sheet mass balance.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3827 on: October 15, 2020, 07:30:24 PM »
The linked Wired article reminds us that the current rapid warming of the Arctic dynamically impacts both the Beaufort Gyre and the Arctic Ocean SSTA.  To me this raises the risk that due to some future perturbation that the Beaufort Gyre could temporarily reverses; which would release large volumes of relatively fresh water into both the Arctic Ocean and the North Atlantic; which would have serious and abrupt impacts on global climate:

Title: "Why the Arctic Is Warming So Fast, and Why That’s So Alarming"

https://www.wired.com/story/why-the-arctic-is-warming-so-fast/

Extract: "Ocean currents normally bring in warmer water from the Pacific, and colder water exits out of the Arctic into the Atlantic. But those currents may be changing because more melting ice is injecting the Arctic Ocean with freshwater, which is less dense than saltwater, and therefore floats above it. The missing ice also exposes the surface waters to more wind, speeding up the Beaufort Gyre in the Arctic, which traps the water it would normally expel into the Atlantic. This acceleration mixes up colder freshwater at the surface and warmer saltwater below, raising surface temperatures and further melting ice."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3828 on: October 15, 2020, 09:05:57 PM »
In the linked article, Hansen & Sato discuss how in the past five years, GMSTA has accelerated from the trend line from the past half century:

Title: "Accelerated Global Warming"

http://www.columbia.edu/~jeh1/mailings/2020/20201014_AcceleratedWarming.pdf

Extract: "In the past five years global temperature has jumped well above the trend which has been stable at about 0.18°C per decade for the past half century (see figure above). This deviation is too large to be explained by unforced climate variability."
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RoxTheGeologist

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3829 on: October 16, 2020, 03:28:04 AM »
In the linked article, Hansen & Sato discuss how in the past five years, GMSTA has accelerated from the trend line from the past half century:

Title: "Accelerated Global Warming"

http://www.columbia.edu/~jeh1/mailings/2020/20201014_AcceleratedWarming.pdf

Extract: "In the past five years global temperature has jumped well above the trend which has been stable at about 0.18°C per decade for the past half century (see figure above). This deviation is too large to be explained by unforced climate variability."

They make the conclusion that the increased forcing is down to aerosols, because all other major sources of rapid forcing have been eliminated. I'm looking forward to reading chapter 33.

My initial thought is if a presumed reduction in aersols has lead to such rapid warming then the ECS has been underestimated.

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3830 on: October 16, 2020, 04:57:18 PM »
...

My initial thought is if a presumed reduction in aerosols has lead to such rapid warming then the ECS has been underestimated.

I concur, and as we continue to reduce anthropogenic aerosol emissions the true value of climate sensitivity will become more evident.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3831 on: October 16, 2020, 09:53:47 PM »
more positive feedback ...

Arctic Ocean Sediments Reveal Permafrost Thawing During Past Climate Warming
https://phys.org/news/2020-10-arctic-ocean-sediments-reveal-permafrost.html

Sea floor sediments of the Arctic Ocean can help scientists understand how permafrost responds to climate warming. A multidisciplinary team from Stockholm University has found evidence of past permafrost thawing during climate warming events at the end of the last ice age. Their findings, published in Science Advances, caution about what could happen in the near future: That Arctic warming by only a few degrees Celsius may trigger massive permafrost thawing, coastal erosion, and the release of the greenhouse gases carbon dioxide (CO2) and methane (CH4) into the atmosphere.

... "Our new study shows for the first time the full history of how warming at the end of the last ice age triggered permafrost thawing in Siberia. This also suggests the release of large quantities of greenhouse gases," says Jannik Martens, Ph.D. student at Stockholm University and lead author of the study. "It appears likely that past permafrost thawing at times of climate warming, about 14,700 and 11,700 years ago, was in part also related to the increase in CO2 concentrations that is seen in Antarctic ice cores for these times. It seems that Arctic warming by only a few degrees Celsius is sufficient to disturb large areas covered by permafrost and potentially affect the climate system."

In the current study, the scientists used an eight meters long sediment core that was recovered from the sea floor more than 1 000 meters below the surface of the Arctic Ocean during the SWERUS-C3 expedition onboard the Swedish icebreaker Oden back in 2014. To reconstruct permafrost thawing on land, the scientists applied radiocarbon (14C) dating and molecular analysis to trace organic remains that once were released by thawing permafrost and then washed into the Arctic Ocean.

"From this core we also learned that erosion of permafrost coastlines was an important driving force for permafrost destruction at the end of the last ice age. Coastal erosion continues to the present day, though ten times slower than during these earlier rapid warming period. With the recent warming trends, however, we see again an acceleration of coastal erosion in some parts of the Arctic, which is expected to release greenhouse gases by degradation of the released organic matter," says Örjan Gustafsson, Professor at Stockholm University and leader of the research program. "Any release from thawing permafrost mean that there is even less room for anthropogenic greenhouse gas release in the earth-climate system budget before dangerous thresholds are reached.

Gustafsson, Martens and their colleagues are now again in the Arctic Ocean as part of the International Siberian Shelf Study (ISSS-2020) onboard the Russian research vessel Akademik Keldysh. The expedition left the port of Arkhangelsk on September 26 and is currently in the East Siberian Sea, seeking more answers to how changing climate may trigger release of carbon, including greenhouse gases, from Arctic permafrost systems, including coastal erosion and permafrost below the sea bottom preserved from the past ice age.



Remobilization of dormant carbon from Siberian-Arctic permafrost during three past warming events. Sci. Adv. 6, eabb6546 (2020)
https://advances.sciencemag.org/content/6/42/eabb6546



... This demonstrates that Arctic warming by only a few degrees may suffice to abruptly activate large-scale permafrost thawing, indicating a sensitive trigger for a threshold-like permafrost climate change feedback.
“There are three classes of people: those who see. Those who see when they are shown. Those who do not see.” ― Leonardo da Vinci

Insensible before the wave so soon released by callous fate. Affected most, they understand the least, and understanding, when it comes, invariably arrives too late

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3832 on: October 18, 2020, 05:29:22 PM »

The first linked Master's Thesis presents evidence from the IODP Expedition 374 (in the Ross Sea, see the second linked reference) that the WAIS most likely collapsed during the MIS 5e (Eemian).  I also remind readers ice-rafter debris (IRD) can only occur due to MICI-types of marine glacier collapse and that there is plenty of evidence IRD in the coastal Southern Ocean in this timeframe.

Master's Thesis: "PLIO-PLEISTOCENE PALEOCEONOGRAPHY OF THE ROSS SEA, ANTARCTICA BASED ON FORAMINIFERA FROM IODP SITES U1523, U1522, AND U1521" by JULIA L. SEIDENSTEIN May 2020

https://scholarworks.umass.edu/cgi/viewcontent.cgi?article=1988&context=masters_theses_2

Abstract: "The West Antarctic Ice Sheet (WAIS) is currently thinning and retreating because shifting oceanic currents are transporting warmer waters to the ice margin, which could lead to a collapse of the ice sheet and global sea level rise. International Ocean Discovery Program (IODP) Expedition 374 sailed to the Ross Sea in 2018 to study the history of the WAIS over the last 20 million years. Previous geologic drilling projects into Ross Sea sediments that record the history of the WAIS (DSDP Leg 28, RISP, MSSTS, Cape Roberts Drilling Project, ANDRILL), as well as modeling studies, show considerable variability of ice-sheet extent during the Neogene and Quaternary including ice sheet collapse during times of extreme warmth.

The purpose of this study is to reconstruct paleoenvironments on the Ross Sea and confirm modeling studies that show warming waters in the Southern Ocean led to the loss of Antarctic ice in the past. Site U1523 is a key site as it is located close to the shelf break and therefore sensitive to warm water incursions from modified Circumpolar Deep Water (mCDW) onto the Ross Sea continental shelf as the Antarctic Slope Current weakens with a changing climate. Shelf sites U1522 and U1521 provide perspective for what was happening closer to the Ross Ice Shelf. Multiple incursions of subpolar or temperate planktic foraminifera taxa occurred during the latest Pliocene and early Pleistocene prior to ~1.8 Ma at Site U1523 indicating times of warmer than present conditions and less ice in the Ross Sea. Especially high abundances of foraminifera are recorded in the late Pleistocene associated with Marine Isotope Stage (MIS) 31, MIS 11, and MIS 5e might also indicate reduced ice and relatively warmer conditions. The interval of abundant foraminifera around MIS 31 (MIS 37 to 21) suggests multiple warmer interglacials during the Mid-Pleistocene Transition (MPT). A change in benthic foraminiferal assemblages and a large increase in foraminiferal fragments after the MPT (~800 ka) indicate stronger currents at the seafloor and perhaps corrosive waters, suggesting a major change in water masses entering (mCDW) or exiting the Ross Sea (AABW) since the MPT."

Extract: "Increased foram abundances at MIS 11, and particularly during MIS 5, suggest that these periods were also much less ice covered. We suspect MIS 5 rather than MIS11 32 could be associated with collapse of the West Antarctic Ice Sheet (Scherer et al., 1998)."

&

McKay, R.M., De Santis, L., Kulhanek, D.K., and the Expedition 374 Scientists (August 10, 2019), " Proceedings of the International Ocean Discovery Program Volume 374", https://doi.org/10.14379/iodp.proc.374.101.2019

http://publications.iodp.org/proceedings/374/101/374_101.html

Abstract
The marine-based West Antarctic Ice Sheet (WAIS) is currently locally retreating because of shifting wind-driven oceanic currents that transport warm waters toward the ice margin, resulting in ice shelf thinning and accelerated mass loss. Previous results from geologic drilling on Antarctica’s continental margins show significant variability in ice sheet extent during the late Neogene and Quaternary. Climate and ice sheet models indicate a fundamental role for oceanic heat in controlling ice sheet variability over at least the past 20 My. Although evidence for past ice sheet variability is available from ice-proximal marine settings, sedimentary sequences from the continental shelf and rise are required to evaluate the extent of past ice sheet variability and the associated forcings and feedbacks. International Ocean Discovery Program Expedition 374 drilled a latitudinal and depth transect of five sites from the outer continental shelf to rise in the central Ross Sea to resolve Neogene and Quaternary relationships between climatic and oceanic change and WAIS evolution. The Ross Sea was targeted because numerical ice sheet models indicate that this sector of Antarctica responds sensitively to changes in ocean heat flux. Expedition 374 was designed for optimal data-model integration to enable an improved understanding of Antarctic Ice Sheet (AIS) mass balance during warmer-than-present climates (e.g., the Pleistocene “super interglacials,” the mid-Pliocene, and the Miocene Climatic Optimum). The principal goals of Expedition 374 were to
•   Evaluate the contribution of West Antarctica to far-field ice volume and sea level estimates;
•   Reconstruct ice-proximal oceanic and atmospheric temperatures to quantify past polar amplification;
•   Assess the role of oceanic forcing (e.g., temperature and sea level) on AIS variability;
•   Identify the sensitivity of the AIS to Earth’s orbital configuration under a variety of climate boundary conditions; and
•   Reconstruct Ross Sea paleobathymetry to examine relationships between seafloor geometry, ice sheet variability, and global climate.
To achieve these objectives, postcruise studies will
•   Use data and models to reconcile intervals of maximum Neogene and Quaternary ice advance and retreat with far-field records of eustatic sea level;
•   Reconstruct past changes in oceanic and atmospheric temperatures using a multiproxy approach;
•   Reconstruct Neogene and Quaternary sea ice margin fluctuations and correlate these records to existing inner continental shelf records;
•   Examine relationships among WAIS variability, Earth’s orbital configuration, oceanic temperature and circulation, and atmospheric pCO2; and
•   Constrain the timing of Ross Sea continental shelf overdeepening and assess its impact on Neogene and Quaternary ice dynamics.
Expedition 374 departed from Lyttelton, New Zealand, in January 2018 and returned in March 2018. We recovered 1292.70 m of high-quality core from five sites spanning the early Miocene to late Quaternary. Three sites were cored on the continental shelf (Sites U1521, U1522, and U1523). At Site U1521, we cored a 650 m thick sequence of interbedded diamictite and diatom-rich mudstone penetrating seismic Ross Sea Unconformity 4 (RSU4). The depositional reconstructions of past glacial and open-marine conditions at this site will provide unprecedented insight into environmental change on the Antarctic continental shelf during the late early and middle Miocene. At Site U1522, we cored a discontinuous late Miocene to Pleistocene sequence of glacial and glaciomarine strata from the outer shelf with the primary objective of penetrating and dating RSU3, which is interpreted to reflect the first continental shelf–wide expansion of East and West Antarctic ice streams. Site U1523, located on the outer continental shelf, targeted a sediment drift beneath the westward-flowing Antarctic Slope Current (ASC) to test the hypothesis that changes in ASC vigor regulate ocean heat flux onto the continental shelf and thus ice sheet mass balance.
We also cored two sites on the continental rise and slope. At Site U1524, we recovered a Plio–Pleistocene sedimentary sequence from the levee of the Hillary Canyon, one of the largest conduits of Antarctic Bottom Water from the continental shelf to the abyssal ocean. Site U1524 was designed to penetrate into middle Miocene and older strata, but coring was initially interrupted by drifting sea ice that forced us to abandon coring in Hole U1524A at 399.5 m drilling depth below seafloor (DSF). We moved to a nearby alternate site on the continental slope (Site U1525) to core a single hole designed to complement the record at Site U1524. We returned to Site U1524 after the sea ice cleared and cored Hole U1524C with the rotary core barrel system with the intention of reaching the target depth of 1000 m DSF. However, we were forced to terminate Hole U1524C at 441.9 m DSF because of a mechanical failure with the vessel that resulted in termination of all drilling operations and forced us to return to Lyttelton 16 days earlier than scheduled. The loss of 39% of our operational days significantly impacted our ability to achieve all Expedition 374 objectives. In particular, we were not able to recover continuous middle Miocene sequences from the continental rise designed to complement the discontinuous record from continental shelf Site U1521. The mechanical failure also meant we could not recover cores from proposed Site RSCR-19A, which was targeted to obtain a high-fidelity, continuous record of upper Neogene and Quaternary pelagic/hemipelagic sedimentation. Despite our failure to recover a continental shelf-to-rise Miocene transect, records from Sites U1522, U1524, and U1525 and legacy cores from the Antarctic Geological Drilling Project (ANDRILL) can be integrated to develop a shelf-to-rise Plio–Pleistocene transect.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3833 on: October 18, 2020, 06:49:14 PM »
I have previously noted that in a changing climate it is generally incorrect for consensus climate scientists to use regression to the mean analysis when interpreting observed data because the mean is changing with time.

In this post, I point-out that when assess the risks of an 'Ice Apocalypse' it is incorrect for consensus scientists to assume a normal probability distribution; as in situations where tail-risk dominates it is much more appropriate to assume a Pareto distribution (see the accompanying image [showing a large right-tail risk] and the linked Wikipedia article).  This is the case because most climate scenarios have little impact on climate risk, while climate scenarios such as the following have major impacts on climate risk:

The Byrd Subglacial Basin, BSB, initiates a MICI-type of collapse in the 2035-2040 timeframe because the nominally 140m high ice cliff face currently extant on the southern side of the 'Big Ear' (see the line B-B' for the Thwaites Ice Tongue in the second image from Jordan et al. 2020) subglacial cavity abruptly loses the restraint from the almost buoyant downstream ice (see the profile of line B-B' in the third image) due to both subsurface ice melting from relatively warm modified CDW, the continued growth of the 'Big Ear' subglacial caveat (see the fourth image), and a surge of ice flow along line B-B', historically happens for the Thwaites Ice Tongue every 25 to 30 years and which last happened circa 2012-2013.

Title: "Pareto distribution"

https://en.wikipedia.org/wiki/Pareto_distribution

Extract: "The Pareto principle or "80-20 rule" stating that 80% of outcomes are due to 20% of causes was named in honour of Pareto, but the concepts are distinct. Pareto distributions with shape value of log45 ≈ 1.16. Empirical observation has shown that this 80-20 distribution fits a wide range of cases, including natural phenomena and human activities."

&

Jordan, T. A., Porter, D., Tinto, K., Millan, R., Muto, A., Hogan, K., Larter, R. D., Graham, A. G. C., and Paden, J. D.: New gravity-derived bathymetry for the Thwaites, Crosson and Dotson ice shelves revealing two ice shelf populations, The Cryosphere Discuss., https://doi.org/10.5194/tc-2019-294, in review, 2020.

https://www.the-cryosphere-discuss.net/tc-2019-294/

Extract: "Airborne gravity provides a good first order estimate of sub-ice-shelf bathymetry. Despite the relatively high uncertainty (~100 m standard deviation) comparisons with different gravity inversion techniques, and new observational bathymetric data, indicate that the pattern of sub-ice-shelf bathymetry is well resolved.

Thwaites Glacier is connected to the deep ocean by a major trough >800 m deep and 20 km wide. In contrast the grounding lines of the of Dotson and Crosson ice shelves are accessible through relatively narrow channels and thin sub shelf cavities. In the Thwaites, Dotson and Crosson region, areas of ice shelf which developed before and after 1993 form distinct populations. The most recently un-grounded areas are underlain by thin cavities (average 112 m) where the ice shelf base closely tracks the underlying bed topography."

Caption of image 2: "Figure 2: New bathymetry and cavity maps. a) Final topography from terrain shift method. White lines A-D mark profiles in Fig. 3. Yellow outline encloses region constrained by gravity data. Pink line shows -800m depth contour. Light grey lines mark grounding lines and ice shelf edge."

Caption of image 3: "Figure 3: Profiles across ice shelves. Upper panel shows ice surface from REMA DEM (Howat et al., 2019) and base of ice shelf calculated assuming hydrostatic equilibrium, together with gravity-derived bathymetric estimates. Second panel shows input freeair gravity anomaly. Third panel shows magnetic anomalies derived from ITGC survey data (REF data doi) and ADMAP2 (Golynsky et al., 2018). a) Thwaites Eastern Ice Shelf. b) Thwites Glacier Tongue. c) Crosson Ice Shelf. d) Dotson Ice Shelf. Note 520 thin cavity in regions of ice sheet grounding line retreat since 1993 (grey boxes)."

The fourth image shows conceptual models for the formation of the subglacial cavities for the key ASE marine glaciers.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3834 on: October 18, 2020, 08:49:49 PM »
As a follow-on to my last post, where I noted that the Thwaites Ice Tongue tends to surge every 25 to 30 years, I did not note that I believe that this surge is primarily related to the periodic drainage a upstream subglacial lakes (that take about 25 to 30 years to refill after being drained).  However, in this post, I note that in addition to the periodic drainage of upstream subglacial lakes, the Thwaites Ice Tongue is likely to surge in the 2035 to 2040 due to the current (on-going) reduction in buttressing from the Pine Island Southwest Tributary (SWT) glacier on the eastern shear margin of the Thwaites Glacier (see the first attached image from MacGregor et al 2013).  As shown in the second image of an Oct 16 2018 Sentinel 1 image, in 2018 the main PIIS (see the third image from 2012) stopped directly blocking the SWT, but which left shear restraint from the PIIS Southern Ice Shelf (SIS).  However, the fourth image of Oct 12, 2020 Sentinel 2 image (by paolo) shows that currently the SIS adjoining the SWT is currently being fractured to the extent that in the next year, or two, the restraint from the SIS on the SWT ice shelf will be greatly reduced; which in turn will reduce the restraint that the SWT presents to the Thwaites eastern shear margin.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3835 on: October 19, 2020, 06:05:10 PM »
I post the attached image from Fig 1 of Milillo et al. (2019) to remind readers that ice downstream of the 'Big Ear' subglacial cavity only has a few meters of ice surface elevation above flotation (see panel D of the attached image), and that this amount of ice surface elevation could easily be lost by 2035 to 2040; and if this were to happen the ice floating above the 'Big Ear' subglacial basin could merely float away; which could abruptly expose a bare ice cliff face susceptible to a MICI-type of failure.

Caption: "Fig 1 …. (D) Height of the ice surface above flotation, hf, in meters. (E) Change in ice surface elevation, dh, between decimal years 2013.5 and 2016.66 color-coded from red (lowering) to blue (rising). (F) Ice surface speed in 2016 – 2017 color-coded from brown (low) to green, purple, and red (greater than 2.5 km/year), with contour levels of 200 m/year in dotted black."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3836 on: October 20, 2020, 01:14:46 AM »
The Tsunami from the Alaska Peninsula will soon reach the ice shelves in West Antarctica:

Title: "Tsunami warning issued following 7.5 magnitude earthquake off Alaska Peninsula"

https://www.adn.com/alaska-news/2020/10/19/tsunami-warning-issued-following-74-magnitude-earthquake-near-sand-point/

Edit: A long-period tsunamic can reach beneath an ice shelf far upstream from the calving face; which might contribute to flexural cracking of such ice shelves.
« Last Edit: October 20, 2020, 02:37:32 AM by AbruptSLR »
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3837 on: October 20, 2020, 09:43:56 PM »
The linked article reminds us that project demands for future cooling presents a hidden threat for climate change:

Title: "Cooling: The hidden threat for climate change and sustainable goals"

https://phys.org/news/2020-10-cooling-hidden-threat-climate-sustainable.html

Extract: "Past research suggests growing international demand for cooling has the potential to drive one of the most substantial increases in greenhouse gas emissions in recent history.

Research from the International Energy Agency has shown that the energy needed for space cooling alone is projected to triple by 2050—the equivalent of adding 10 new air conditioners every second for the next 30 years. This would require additional electricity generation similar to that of the US, the EU and Japan combined."

“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Tom_Mazanec

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3838 on: October 21, 2020, 12:34:35 AM »
Of course rising temperatures will increase the demand for cooling technology and infrastructure.
SHARKS (CROSSED OUT) MONGEESE (SIC) WITH FRICKIN LASER BEAMS ATTACHED TO THEIR HEADS

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3839 on: October 21, 2020, 02:39:14 AM »
Of course rising temperatures will increase the demand for cooling technology and infrastructure.

But the point is that current projections underestimate not only the increased power demand, but also the risk of increased HFC emissions.
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Tom_Mazanec

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3840 on: October 21, 2020, 11:55:00 AM »
I know that. I was just highlighting the vicious circle effect.
SHARKS (CROSSED OUT) MONGEESE (SIC) WITH FRICKIN LASER BEAMS ATTACHED TO THEIR HEADS

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3841 on: October 21, 2020, 03:41:50 PM »
The linked article indicates that the Antarctic ozone hole grew in size in 2020 as compared to 2019; which confirms that this ozone hole (which is currently accelerating circumpolar winds and associated upwelling of warm CDW for the Southern Ocean) will take longer to heal (assuming strict adherence to the Montreal Protocol, w.r.t. both CFCs and HFCs) than many consensus climate scientists were hoping.  This increases the risk of an MICI-type of collapse of the WAIS in coming decades:

Title: "The Ozone Hole Over Antarctica Has Grown Much Deeper And Wider in 2020"

https://www.sciencealert.com/the-ozone-hole-over-antarctica-has-grown-to-one-of-its-largest-sizes-in-recent-times

Extract: "The hole in the ozone layer over Antarctica has expanded to one of its greatest recorded sizes in recent years.

In 2019, scientists revealed that the Antarctic ozone hole had hit its smallest annual peak since tracking began in 1982, but the 2020 update on this atmospheric anomaly – like other things this year – brings a sobering perspective.

"Our observations show that the 2020 ozone hole has grown rapidly since mid-August, and covers most of the Antarctic continent – with its size well above average," explains project manager Diego Loyola from the German Aerospace Center.

New measurements from the European Space Agency's Copernicus Sentinel-5P satellite show that the ozone hole reached its maximum size of around 25 million square kilometres (about 9.6 million square miles) on 2 October this year.

That puts it in about the same ballpark as 2018 and 2015's ozone holes, which respectively recorded peaks of 22.9 and 25.6 million square kilometres.

"There is much variability in how far ozone hole events develop each year," says atmospheric scientist Vincent-Henri Peuch from the European Centre for Medium-Range Weather Forecasts.

"The 2020 ozone hole resembles the one from 2018, which also was a quite large hole, and is definitely in the upper part of the pack of the last 15 years or so."

"After the unusually small and short-lived ozone hole in 2019, which was driven by special meteorological conditions, we are registering a rather large one again this year, which confirms that we need to continue enforcing the Montreal Protocol banning emissions of ozone depleting chemicals."

The Montreal Protocol was a milestone in humanity's environmental achievements, phasing out the manufacturing of harmful chlorofluorocarbons (CFCs) – chemicals previously used in refrigerators, packaging, and sprays – that destroy ozone molecules in sunlight.

While we now know that human action on this front is helping us to fix the Antarctic ozone hole, the ongoing fluctuations from year to year show that the healing process will be long."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3842 on: October 21, 2020, 04:06:50 PM »
The linked reference indicates that two CESM ensembles project a continuing poleward shift of atmospheric river (AR) events in the Southern Hemisphere.  In the past few decades several AR events in East Antarctica have contributed to local snow accumulations; leading some consensus climate scientists to imply that the risk of next ice mass loss from Antarctica in coming decades is less that that indicated by such researchers as Hansen et al. (2016).  However, in my opinion such a consensus climate science position errs on the side of least drama for reasons including:

1. Increasing snow accumulations in East Antarctica do not change the risk of a potential MICI-type of collapse of the WAIS.

2. Increasing snow accumulations in West Antarctica increase the inland thickness of key marine glaciers (like Thwaites and PIG); which increases the thickness gradient; which is the most important factor in predicting a MICI-type of collapse of such key West Antarctic marine glaciers.

3. The condensation of clouds into either snow, or rain, introduces heat into the local atmosphere; which is not good for AIS stability.

4. At some point in the global warming trend, AR events over Antarctica will have precipitation in the form of rain, instead of snow; which will rapidly melt surface snow and ice and which will contribute to increased hydrofracturing.

Weiming Ma, Gang Chen and Bin Guan (19 October 2020), "Poleward Shift of Atmospheric Rivers in the Southern Hemisphere in Recent Decades", Geophysical Research Letters, https://doi.org/10.1029/2020GL089934

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL089934?af=R

Abstract
The atmospheric river (AR) frequency trends over the Southern Hemisphere are investigated using three reanalyses and two Community Earth System Model (CESM) ensembles. The results show that AR frequency has been increasing over the Southern Ocean and decreasing over lower latitudes in the past four decades, and that ARs have been shifting poleward. While the observed trends are mostly driven by the poleward shift of the westerly jet, fully‐coupled CESM experiments indicate anthropogenic forcing would result in positive AR frequency trends over the Southern Ocean due mostly to moisture changes. The difference between the observed trends and anthropogenically driven trends can be largely reconciled by the atmosphere‐only CESM simulations forced by observed sea surface temperatures (SSTs): SST variability characteristic of the negative phase of the Interdecadal Pacific Oscillation (IPO) strongly suppresses the moisture‐driven trends while enhances the circulation‐induced trends over the Southern Ocean, thus bringing the simulated trends into closer agreement with the observed trends.

Plain Language Summary
Atmospheric rivers (ARs) are “rivers” in the sky that carry a huge amount of water vapor equivalent to the world’s largest rivers on the ground. Because of the amount of water vapor they carry, ARs can cause extreme rainfall and floods upon landfall when the moisture is condensed out by mountain barriers or other favorable conditions. Most of the studies so far have focused on ARs in the Northern Hemisphere. In this study, we found that ARs in the Southern Hemisphere have been occurring at increasingly higher‐latitude regions in the past four decades, and that this observed trend is mostly due to winds getting stronger at higher‐latitude regions in the Southern Hemisphere. Using results from climate model simulations, we show that the observed AR trends in the Southern Hemisphere are driven by both human activities, such as greenhouse gas increases and ozone depletion, and the internal variability of sea surface temperatures due to the coupled atmosphere‐ocean system. The poleward shift of ARs in the Southern Hemisphere may have major implications for the amount of moisture and heat transported into Antarctica, thus may also have profound impacts on the Antarctic, and in turn, global climate.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3843 on: October 21, 2020, 05:24:04 PM »
Both the Deep Weddell Sea, and the Weddell Gyre, are key features that have a significant impacts on climate change risk, and the linked reference indicates that these features, below 2000 m, are warming approximately 5 times faster than the rest of the global deep ocean, for reasons including:

1. The reference indicates that the Weddell Gyre is entraining more warm water, along its northern edge, from the ACC and is advecting this warm water into the coastal current that leads toward the FRIS (which should progressively decrease the stability of the FRIS in coming decades).

2. The deep Weddell Sea is at the southernly tip of the AMOC and the rapid warming of the deep water in this region results in a relatively rapid slowing of the AMOC; which could rapidly increase ECS in coming decades

Volker H. Strass et al (2020), "Multidecadal Warming and Density Loss in the Deep Weddell Sea, Antarctica", J. Climate, 33 (22): 9863–9881, https://doi.org/10.1175/JCLI-D-20-0271.1

https://journals.ametsoc.org/jcli/article/33/22/9863/354273/Multidecadal-Warming-and-Density-Loss-in-the-Deep

Abstract
The World Ocean is estimated to store more than 90% of the excess energy resulting from man-made greenhouse gas–driven radiative forcing as heat. Uncertainties of this estimate are related to undersampling of the subpolar and polar regions and of the depths below 2000 m. Here we present measurements from the Weddell Sea that cover the whole water column down to the sea floor, taken by the same accurate method at locations revisited every few years since 1989. Our results show widespread warming with similar long-term temperature trends below 700-m depth at all sampling sites. The mean heating rate below 2000 m exceeds that of the global ocean by a factor of about 5. Salinity tends to increase—in contrast to other Southern Ocean regions—at most sites and depths below 700 m, but nowhere strongly enough to fully compensate for the warming effect on seawater density, which hence shows a general decrease. In the top 700 m neither temperature nor salinity shows clear trends. A closer look at the vertical distribution of changes along an approximately zonal and a meridional section across the Weddell Gyre reveals that the strongest vertically coherent warming is observed at the flanks of the gyre over the deep continental slopes and at its northern edge where the gyre connects to the Antarctic Circumpolar Current (ACC). Most likely, the warming of the interior Weddell Sea is driven by changes of the Weddell Gyre strength and its interaction with the ACC.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3844 on: October 22, 2020, 01:44:23 AM »
The linked reference indicates that observation are just now entering the just entering the `detection window’ to determine whether the AMOC is slowing:

D. Lobelle et al. (17 October 2020), "Detectability of an AMOC decline in current and projected climate changes", Geophysical Research Letters, https://doi.org/10.1029/2020GL089974

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL089974?af=R

Abstract
Determining whether the Atlantic Meridional Overturning Circulation (AMOC)'s transport is in decline is challenging due to the short duration of continuous observations. To estimate how many years are needed to detect a decline, we conduct a simulation study using synthetic data that mimics an AMOC time series. The time series' characteristics are reproduced using the trend, variance, and autocorrelation coefficient of the AMOC strength at 26.5°,N from 20 Coupled Model Intercomparison Project Phase 5 (CMIP5) models under the RCP8.5 future scenario, and from RAPID observations (2004‐‐2018). Our results suggest that the 14‐year RAPID length has just entered the lower limits of the trend’s `detection window’ based on synthetic data generated using CMIP5 trends and variability (14‐‐42 years; median = 24 years), but twice the length is required for detectability based on RAPID variability (29‐‐67 years; median = 43 years). The annual RAPID trend is currently not statistically significant (‐0.11 Sv yr‐1, p>0.05).

Plain Language Summary
There are ongoing discussions in the scientific community about whether the Atlantic Meridional Overturning Circulation transport is slowing down. This is of interest due to the importance of this circulation in transporting heat from the tropics to the northern latitudes. A consensus about its decline is hard to reach due to the limited direct observational data available; with the longest continuous data being 14 years long from 2004 to 2018. We therefore conduct a simulation experiment to examine how many years of data are required to detect a decline in the circulation. We create simulations of the North Atlantic transport based on statistical properties from 20 general circulation models with future climate change projections (until 2100) and from the RAPID array observations (since 2004). Our results demonstrate that the length of data we currently have from observations has just entered the `detection window’ of 14—42 years (based on model simulations). However, the RAPID observations do not currently exhibit a statistically significant trend.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3845 on: October 22, 2020, 01:51:54 AM »
The linked reference discusses the use of icequake monitoring to both confirm the existence of, and to study the nature of, hydraulically-force crevassing in ice shelves and ice sheets:

T. S. Hudson et al. (19 October 2020), "Breaking the ice: Identifying hydraulically‐forced crevassing", Geophysical Research Letters, https://doi.org/10.1029/2020GL090597

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL090597?af=R

Abstract
Hydraulically‐forced crevassing is thought to reduce the stability of ice shelves and ice sheets, affecting structural integrity and providing pathways for surface meltwater to the bed. It can cause ice shelves to collapse and ice sheets to accelerate into the ocean. However, direct observations of the hydraulically‐forced crevassing process remain elusive. Here we report a novel method and observations that use icequakes to directly observe crevassing and determine the role of hydrofracture. Crevasse icequake depths from seismic observations are compared to a theoretically derived maximum‐dry‐crevasse‐depth. We observe icequakes below this depth, suggesting hydrofracture. Furthermore, icequake source mechanisms provide insight into the fracture process, with predominantly opening cracks observed, which have opening volumes of hundredths of a cubic meter. Our method and findings provide a framework for studying a critical process that is key for the stability of ice shelves and ice sheets, and therefore future sea‐level rise projections.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3846 on: October 22, 2020, 05:19:00 PM »
While the mid-Pliocene is not a perfect model for our coming climate, and while the PlioMIP2 ensemble does not offer perfect simulations of the mid-Pliocene; nevertheless, the linked reference offers some indications of where the Arctic may well be headed in coming decades:

de Nooijer, W., Zhang, Q., Li, Q., Zhang, Q., Li, X., Zhang, Z., Guo, C., Nisancioglu, K. H., Haywood, A. M., Tindall, J. C., Hunter, S. J., Dowsett, H. J., Stepanek, C., Lohmann, G., Otto-Bliesner, B. L., Feng, R., Sohl, L. E., Tan, N., Contoux, C., Ramstein, G., Baatsen, M. L. J., von der Heydt, A. S., Chandan, D., Peltier, W. R., Abe-Ouchi, A., Chan, W.-L., Kamae, Y., and Brierley, C. M.: Evaluation of Arctic warming in mid-Pliocene climate simulations, Clim. Past Discuss., https://doi.org/10.5194/cp-2020-64, in review, 2020.

https://cp.copernicus.org/preprints/cp-2020-64/
https://cp.copernicus.org/preprints/cp-2020-64/cp-2020-64.pdf

Abstract. Palaeoclimate simulations improve our understanding of the climate, inform us about the performance of climate models in a different climate scenario, and help to identify robust features of the climate system. Here, we analyse Arctic warming in an ensemble of 16 simulations of the mid-Pliocene Warm Period (mPWP), derived from the Pliocene Model Intercomparison Project Phase 2 (PlioMIP2).

The PlioMIP2 ensemble simulates Arctic (60–90° N) annual mean surface air temperature (SAT) increases of 3.7 to 11.6 °C compared to the pre-industrial, with a multi-model mean (MMM) increase of 7.2 °C. The Arctic warming amplification ratio relative to global SAT anomalies in the ensemble ranges from 1.8 to 3.1 (MMM is 2.3). Sea ice extent anomalies range from −3.0 to −10.4 × 06 km2 with a MMM anomaly of −5.6 × 106 km2, which constitutes a decrease of 53 % compared to the pre-industrial. The majority (11 out of 16) models simulate summer sea ice-free conditions (≤ 1 × 06 km2) in their mPWP simulation. The ensemble tends to underestimate SAT in the Arctic when compared to available reconstructions. The simulations with the highest Arctic SAT anomalies tend to match the proxy dataset in its current form better. The ensemble shows some agreement with reconstructions of sea ice, particularly with regards to seasonal sea ice. Large uncertainties limit the confidence that can be placed in the findings and the compatibility of the different proxy datasets. We show that, while reducing uncertainties in the reconstructions could decrease the SAT data-model discord substantially, further improvements are likely to be found in enhanced boundary conditions or model physics. Lastly, we compare the Arctic warming in the mPWP to projections of future Arctic warming and find that the PlioMIP2 ensemble simulates greater Arctic amplification, an increase instead of a decrease in AMOC strength compared to pre-industrial, and a lesser strengthening of northern modes of variability than CMIP5 future climate simulations. The results highlight the importance of slow feedbacks in equilibrium climate simulations, and that caution must be taken when using simulations of the mPWP as an analogue for future climate change.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3847 on: October 22, 2020, 06:42:19 PM »
The linked reference (& associate article) indicates that the 'Antarctic is estimated to contain as much as a quarter of earth's marine methane …'.  Thus an abrupt MICI-type of collapse of the WAIS (and/or Totten Glacier) could release major amounts of methane into the atmosphere.

Andrew R. Thurber, Sarah Seabrook  and Rory M. Welsh (22 July 2020), "Riddles in the cold: Antarctic endemism and microbial succession impact methane cycling in the Southern Ocean", Proceedings of the Royal Society B, https://doi.org/10.1098/rspb.2020.1134

https://royalsocietypublishing.org/doi/10.1098/rspb.2020.1134

Abstract
Antarctica is estimated to contain as much as a quarter of earth's marine methane, however we have not discovered an active Antarctic methane seep limiting our understanding of the methane cycle. In 2011, an expansive (70 m × 1 m) microbial mat formed at 10 m water depth in the Ross Sea, Antarctica which we identify here to be a high latitude hydrogen sulfide and methane seep. Through 16S rRNA gene analysis on samples collected 1 year and 5 years after the methane seep formed, we identify the taxa involved in the Antarctic methane cycle and quantify the response rate of the microbial community to a novel input of methane. One year after the seep formed, ANaerobic MEthane oxidizing archaea (ANME), the dominant sink of methane globally, were absent. Five years later, ANME were found to make up to 4% of the microbial community, however the dominant member of this group observed (ANME-1) were unexpected considering the cold temperature (−1.8°C) and high sulfate concentrations (greater than 24 mM) present at this site. Additionally, the microbial community had not yet formed a sufficient filter to mitigate the release of methane from the sediment; methane flux from the sediment was still significant at 3.1 mmol CH4 m−2 d−1. We hypothesize that this 5 year time point represents an early successional stage of the microbiota in response to methane input. This study provides the first report of the evolution of a seep system from a non-seep environment, and reveals that the rate of microbial succession may have an unrealized impact on greenhouse gas emission from marine methane reservoirs.


See also:

Title: "Scientists studied microbes feeding on Antarctica’s first methane leak – here’s what they found"

https://www.weforum.org/agenda/2020/08/antarctica-methane-leak-microorganisms/

Extract: "Antarctica is thought to contain up to a quarter of the planet’s marine methane – a greenhouse gas far more potent than carbon dioxide.
Some scientists are concerned that as the region continues to warm, dormant methane deposits trapped beneath age-old ice could escape into the atmosphere, triggering rapid and irreversible climate change."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3848 on: October 23, 2020, 12:14:53 AM »
I provide the attached profile (& associated ice velocities) of the Thwaites Glacier from Docquier, Pollard and Pattyn (2014) to illustrate how in a worse case scenario we could be witnessing ice cliff failures deep in the Byrd Subglacial Basin with nearly 2,000m high ice faces above the water line as soon as 2050.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

sidd

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #3849 on: October 23, 2020, 07:31:30 AM »
Re: 2000 m freeboard

At 100 m freeboard the cliff face collapses, as we see in Jacobshawn.  So we are gonna have a giant melange slope at the critical angle for giant chunks of ice, that melange will be melted and cleared as in Jacobshawn.

Except of course,there ain't no fjord walls and Thwaites is 10 times or more as wide as Jacobshawn, and it doesn't even make sense to talk of width when you consider PIG, Thwaites are both one icechunk grounded submarine and collapse will extend into Ross and Weddel.

So much s i would like to see 2km high icecliffs with base in water, i fear that might have to be in another life ... on another planet ... with about ten times lower surface gravity ...

sidd