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oren

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4100 on: January 18, 2021, 03:57:43 AM »
A couple of charts prepared by paolo over in the PIG thread should concern the readers here. Over the last 3 years velocity increased by more than 15%. A hard acceleration of the PIG velocity over such a short period (along with calving front retreat and loss of buttressing as documented in that thread) does not bode well for the future of sea level rise.




AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4101 on: January 18, 2021, 07:35:22 PM »
Per the linked article (& the associated image), according to GISS, the GMSTA for 2020 was 1.02C above a 1951-1980 baseline; which amounts to being +1.276C above pre-industrial (i.e. to convert 1951-1980 temp departures to pre-industrial add: + 0.256 Celsius).

Title: "2020 Tied for Warmest Year on Record, NASA Analysis Shows"

https://www.giss.nasa.gov/research/news/20210114/

Extract: "Continuing the planet’s long-term warming trend, the year’s globally averaged temperature was 1.84 degrees Fahrenheit (1.02 degrees Celsius) warmer than the baseline 1951-1980 mean, according to scientists at NASA’s Goddard Institute for Space Studies (GISS) in New York. 2020 edged out 2016 by a very small amount, within the margin of error of the analysis, making the years effectively tied for the warmest year on record."

Caption: "This plot shows yearly temperature anomalies from 1880 to 2019, with respect to the 1951-1980 mean, as recorded by NASA, NOAA, the Berkeley Earth research group, and the Met Office Hadley Centre (UK). Though there are minor variations from year to year, all five temperature records show peaks and valleys in sync with each other. All show rapid warming in the past few decades, and all show the past decade has been the warmest. (Credits: NASA GISS/Gavin Schmidt)"
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4102 on: January 19, 2021, 06:47:52 PM »
It's helpful to review DeConto and Pollard's study of the mechanisms that could lead to more rapid Antarctic ice melt and see why they needed to raise the global ocean temperatures by 2C to initiate MICI.  They covered that ground in their 2015 paper, with Richard Alley as third author, linked below:

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

Quote
Potential Antarctic Ice Sheet retreat driven by hydrofracturing and ice cliff failure
David Pollard, Robert M. DeConto, Richard B. Alley
Earth and Planetary Science Letters
Volume 412, 15 February 2015, Pages 112-121

Abstract

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

Quote
2.4. Combined hydrofracture and cliff failure

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

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


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

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

If you think this is a red herring, take it up with DeConto and Pollard by publishing your work in a peer reviewed journal.

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4103 on: January 19, 2021, 08:49:21 PM »
The linked WEF article (which is part of the up-coming Davos Forum Agenda), concurs that abrupt climate change can indeed occur sooner, and more quickly, than current consensus climate change guidance (like AR5) indicates:

Title: "Climate change will be sudden and cataclysmic. We need to act fast"

https://www.weforum.org/agenda/2021/01/climate-change-sudden-cataclysmic-need-act-fast/

Extract: "
•   Tipping points could fundamentally disrupt the planet and produce abrupt change in the climate.
•   A mass methane release could put us on an irreversible path to full land-ice melt, causing sea levels to rise by up to 30 metres.
•   We must take immediate action to reduce global warming and build resilience with these tipping points in mind.

The speed and scale of the response to COVID-19 by governments, businesses and individuals seems to provide hope that we can react to the climate change crisis in a similarly decisive manner - but history tells us that humans do not react to slow-moving and distant threats. Our evolution has selected the “fight or flight” instinct to deal with environmental change, so rather like the metaphor of the frog in boiling water, we tend to react too little and too late to gradual change."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4104 on: January 19, 2021, 09:09:31 PM »
...
If you think this is a red herring, take it up with DeConto and Pollard by publishing your work in a peer reviewed journal.

The perspective piece by Siegert, Alley, Rignot, Englander and Corel (2020), provides responses to many of the issues that you raise.

Siegert, M., Richard B. Alley, Eric Rignot, John Englander and Robert Corel (2020), "Twenty-first century sea-level rise could exceed IPCC projections for strong-warming futures", One Earth, https://doi.org/10.1016/j.oneear.2020.11.002

https://www.cell.com/action/showPdf?pii=S2590-3322%2820%2930592-3

Abstract: "While twentieth century sea-level rise was dominated by thermal expansion of ocean water, mass loss from glaciers and ice sheets is now a larger annual contributor. There is uncertainty on how ice sheets will respond to further warming, however, reducing confidence in twenty-first century sea-level projections. In 2019, to address the uncertainty, the Intergovernmental Panel on Climate Change (IPCC) reported that sea-level rise from the 1950s levels would likely be within 0.61–1.10 m if warming exceeds 4o C by 2100. The IPCC acknowledged greater sea-level increases were possible through mechanisms not fully incorporated in models used in the assessment. In this perspective, we discuss challenges faced in projecting sea-level change and discuss why the IPCC’s sea-level range for 2100 under strong warming is focused at the low end of possible outcomes. We argue outcomes above this range are far more probable than below it and discuss how decision makers may benefit from reframing IPCC’s terminology to avoid unintentionally masking worst-case scenarios."

Extract: "Ice-shelf thinning and flow acceleration in the Amundsen Sea Embayment of West Antarctica, especially Thwaites and Pine Island Glaciers, could lead to retreat into deep interior basins with as much as 3 m of sea-level rise before stabilization on the next bottleneck. Some large East Antarctic glaciers have begun changing, and those draining the Wilkes, Aurora and other basins have even greater potential to raise sea level. Similarly, in Greenland, marinebased outlets underlain by deep channels extending inland (e.g., Petermann, Humboldt, Zachariae, Nioghalvfjerdsfjorden, Jakobshavn) house enough ice to raise sea level by 2.3 m.
One model that simulated ice-shelf loss and retreat from bottlenecks, including calving from grounded ice cliffs, found that, for cases in which strong anthropogenic warming triggered major West Antarctic retreat, the marine basins largely deglaciated over the following century or so. This model restricted ice-cliff calving to rates that have been exceeded elsewhere; much of the contribution to rapid sea-level rise came from the great thickness of the West Antarctic ice and the huge width of the calving front that developed during retreat. A West Antarctic calving-cliff retreat would produce much higher and wider cliffs with much larger stresses than any that have been observed, so calving might be faster, or indeed much faster, than previously measured. Ice-shelf loss and calving-cliff retreat are well recognized at the fjord scale but often are not included well in ice-sheet models. This is partly because of inherent difficulties in simulating fracture processes. (Small differences in conditions may cause a ceramic coffee cup dropped on a hard floor to bounce unharmed or break into fragments.) Furthermore, with no recently observed catastrophic retreats on the scale of Thwaites Glacier or other major Antarctic basins, models cannot be well calibrated against observational or historical data. The transition from non-floating to floating ice, commonly called the grounding line, is really a complex grounding zone with important but poorly known processes. In addition to calving of grounded ice blocks, retreat and faster flow are promoted by preferential melting undercutting the base of marine-ending ice cliffs, a process not yet included in many ice-sheet models. More broadly, the issue of melting at grounding zones of ice shelves and grounded cliffs remains an area of active research. Ice sheet models are sensitive to basal melt rates imposed at grounding zones. Large observed fluctuations in grounding-zone position during tidal cycles promote ocean-water flushing and melting over many kilometers, and inclusion of grounding-zone melting in models is required to match some recent observations. Inclusion of such processes in models, and their interactions with cliff undercutting and calving, could amplify projected ice-sheet response to warming.  The grounding-zone transition remains the least well explored and most challenging part of the ice-ocean system, and yet is central to the future evolution of these glaciers.

In our considerable but anecdotal experience, many coastal planners, policymakers, and members of the general public fail to fully appreciate the meaning of the likely range in the assessed sea-level-rise projections. Instead, some treat the high end of the likely range as a worst-case scenario or else the upper end for practical designs. Such a situation is far from ideal because the upper limit of the IPCC likely range was never intended as a worst-case scenario.

Sea-level rise will be one of the most challenging issues faced by society in the coming decades unless we decarbonize fully by mid-century. An objective appreciation and more-effective dissemination of what sea-level rise is possible under strong warming, as opposed to what is deemed likely or is currently accounted for by numerical models, would better inform decision makers, who must increase decarbonization ambition to avoid the most severe of outcomes."

Caption: "Figure 1. Analysis of ice-sheet mass balance and IPCC sea-level projections (A) Measured ice loss from Greenland and Antarctica plotted against IPCC Fifth Assessment Report predictions. AR5 upper range relates to the business-as-usual RCP8.5 scenario, whereas the AR5 lower range corresponds to the RCP2.6 scenario of strong action on carbon dioxide emissions.32 (B) Components of observed and predicted, as in (A), annual sea-level contributions from Greenland and Antarctica between 2007 and 2017, broken into components of ice dynamics and surface mass balance."
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Sciguy

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4105 on: January 20, 2021, 06:40:55 PM »

The perspective piece by Siegert, Alley, Rignot, Englander and Corel (2020), provides responses to many of the issues that you raise.

Siegert, M., Richard B. Alley, Eric Rignot, John Englander and Robert Corel (2020), "Twenty-first century sea-level rise could exceed IPCC projections for strong-warming futures", One Earth, https://doi.org/10.1016/j.oneear.2020.11.002

https://www.cell.com/action/showPdf?pii=S2590-3322%2820%2930592-3

Abstract: "While twentieth century sea-level rise was dominated by thermal expansion of ocean water, mass loss from glaciers and ice sheets is now a larger annual contributor. There is uncertainty on how ice sheets will respond to further warming, however, reducing confidence in twenty-first century sea-level projections. In 2019, to address the uncertainty, the Intergovernmental Panel on Climate Change (IPCC) reported that sea-level rise from the 1950s levels would likely be within 0.61–1.10 m if warming exceeds 4o C by 2100. The IPCC acknowledged greater sea-level increases were possible through mechanisms not fully incorporated in models used in the assessment. In this perspective, we discuss challenges faced in projecting sea-level change and discuss why the IPCC’s sea-level range for 2100 under strong warming is focused at the low end of possible outcomes. We argue outcomes above this range are far more probable than below it and discuss how decision makers may benefit from reframing IPCC’s terminology to avoid unintentionally masking worst-case scenarios."

Extract: "Ice-shelf thinning and flow acceleration in the Amundsen Sea Embayment of West Antarctica, especially Thwaites and Pine Island Glaciers, could lead to retreat into deep interior basins with as much as 3 m of sea-level rise before stabilization on the next bottleneck. Some large East Antarctic glaciers have begun changing, and those draining the Wilkes, Aurora and other basins have even greater potential to raise sea level. Similarly, in Greenland, marinebased outlets underlain by deep channels extending inland (e.g., Petermann, Humboldt, Zachariae, Nioghalvfjerdsfjorden, Jakobshavn) house enough ice to raise sea level by 2.3 m.
One model that simulated ice-shelf loss and retreat from bottlenecks, including calving from grounded ice cliffs, found that, for cases in which strong anthropogenic warming triggered major West Antarctic retreat, the marine basins largely deglaciated over the following century or so. This model restricted ice-cliff calving to rates that have been exceeded elsewhere; much of the contribution to rapid sea-level rise came from the great thickness of the West Antarctic ice and the huge width of the calving front that developed during retreat. A West Antarctic calving-cliff retreat would produce much higher and wider cliffs with much larger stresses than any that have been observed, so calving might be faster, or indeed much faster, than previously measured. Ice-shelf loss and calving-cliff retreat are well recognized at the fjord scale but often are not included well in ice-sheet models. This is partly because of inherent difficulties in simulating fracture processes. (Small differences in conditions may cause a ceramic coffee cup dropped on a hard floor to bounce unharmed or break into fragments.) Furthermore, with no recently observed catastrophic retreats on the scale of Thwaites Glacier or other major Antarctic basins, models cannot be well calibrated against observational or historical data. The transition from non-floating to floating ice, commonly called the grounding line, is really a complex grounding zone with important but poorly known processes. In addition to calving of grounded ice blocks, retreat and faster flow are promoted by preferential melting undercutting the base of marine-ending ice cliffs, a process not yet included in many ice-sheet models. More broadly, the issue of melting at grounding zones of ice shelves and grounded cliffs remains an area of active research. Ice sheet models are sensitive to basal melt rates imposed at grounding zones. Large observed fluctuations in grounding-zone position during tidal cycles promote ocean-water flushing and melting over many kilometers, and inclusion of grounding-zone melting in models is required to match some recent observations. Inclusion of such processes in models, and their interactions with cliff undercutting and calving, could amplify projected ice-sheet response to warming.  The grounding-zone transition remains the least well explored and most challenging part of the ice-ocean system, and yet is central to the future evolution of these glaciers.

In our considerable but anecdotal experience, many coastal planners, policymakers, and members of the general public fail to fully appreciate the meaning of the likely range in the assessed sea-level-rise projections. Instead, some treat the high end of the likely range as a worst-case scenario or else the upper end for practical designs. Such a situation is far from ideal because the upper limit of the IPCC likely range was never intended as a worst-case scenario.

Sea-level rise will be one of the most challenging issues faced by society in the coming decades unless we decarbonize fully by mid-century. An objective appreciation and more-effective dissemination of what sea-level rise is possible under strong warming, as opposed to what is deemed likely or is currently accounted for by numerical models, would better inform decision makers, who must increase decarbonization ambition to avoid the most severe of outcomes."

Caption: "Figure 1. Analysis of ice-sheet mass balance and IPCC sea-level projections (A) Measured ice loss from Greenland and Antarctica plotted against IPCC Fifth Assessment Report predictions. AR5 upper range relates to the business-as-usual RCP8.5 scenario, whereas the AR5 lower range corresponds to the RCP2.6 scenario of strong action on carbon dioxide emissions.32 (B) Components of observed and predicted, as in (A), annual sea-level contributions from Greenland and Antarctica between 2007 and 2017, broken into components of ice dynamics and surface mass balance."

No, it doesn't.  That study addresses impacts from warming of 4 degrees or more.  Since we're on track for under 3 degrees of warming, with a good probability of staying under 2 degrees now in the current political and economic climate, the study is as irrelevant as any run under RCP8.5 or SSP 8.5.

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4106 on: January 22, 2021, 11:33:17 AM »
The linked reference (& associated article) indicates that observed data shows that warm CDW is '… is rising toward the ocean’s surface at the rate of about 130 feet per decade"; which, is three to ten times faster that consensus climate science previously assumed.  As indicated by the attached image, this is bad news for the stability not only of ASE marine glaciers but also for marine glaciers in the Wilkes Basin and the Aurora Basin, in the EAIS, in coming decades.

Auger, M., Morrow, R., Kestenare, E. et al. Southern Ocean in-situ temperature trends over 25 years emerge from interannual variability. Nat Commun 12, 514 (2021). https://doi.org/10.1038/s41467-020-20781-1

https://www.nature.com/articles/s41467-020-20781-1

Abstract
Despite playing a major role in global ocean heat storage, the Southern Ocean remains the most sparsely measured region of the global ocean. Here, a unique 25-year temperature time-series of the upper 800 m, repeated several times a year across the Southern Ocean, allows us to document the long-term change within water-masses and how it compares to the interannual variability. Three regions stand out as having strong trends that dominate over interannual variability: warming of the subantarctic waters (0.29 ± 0.09 °C per decade); cooling of the near-surface subpolar waters (−0.07 ± 0.04 °C per decade); and warming of the subsurface subpolar deep waters (0.04 ± 0.01 °C per decade). Although this subsurface warming of subpolar deep waters is small, it is the most robust long-term trend of our section, being in a region with weak interannual variability. This robust warming is associated with a large shoaling of the maximum temperature core in the subpolar deep water (39 ± 09 m per decade), which has been significantly underestimated by a factor of 3 to 10 in past studies. We find temperature changes of comparable magnitude to those reported in Amundsen–Bellingshausen Seas, which calls for a reconsideration of current ocean changes with important consequences for our understanding of future Antarctic ice-sheet mass loss.

See also:

Title: "Southern Ocean waters are warming faster than thought, threatening Antarctic ice"

https://www.washingtonpost.com/weather/2021/01/21/southern-ocean-warming-antarctica/

Extract: "Now a new study, published Thursday in the journal Nature Communications, finds that beneath the surface layer of waters circling Antarctica, the seas are warming much more rapidly than previously known. Furthermore, the study concludes, this relatively warm water is rising toward the surface over time, at a rate three to 10 times what was previously estimated.

This means that there is a greater potential for the waters of the Southern Ocean, which are absorbing vast quantities of added heat and carbon dioxide from the atmosphere as a result of human activities, may soon help destabilize parts of the Antarctic Ice Sheet.

The researchers found that warming under the sea surface within waters near Antarctica stands out from naturally occurring trends, with temperatures increasing at a rate of about 0.072 degrees Fahrenheit (0.04 Celsius) per decade. At the same time, the relatively warm water — usually located under a colder layer — is rising toward the ocean’s surface at the rate of about 130 feet per decade. While the temperature change within waters that move from west to east around Antarctica may appear small, the study indicates it is a “radical” change from its average state and is enough to threaten ice stability where glaciers empty into the sea via fragile floating ice shelves.

“This study shows the threat of subsurface water warming, that can affect Antarctic ice cap all around Antarctica. Our hope for future studies is a better understanding of the Southern Ocean models. Ocean models are affected by the lack of observation in the region, and a better representation of the Southern Ocean by the models would be an important step forward,” Auger wrote.

However, he called the findings about warming and rising waters “frightening” compared with findings from his own work just a few years ago, saying, if correct, these waters could have a “potentially imminent impact on several Antarctic glaciers.”"
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4107 on: January 22, 2021, 05:48:26 PM »
The linked opinion piece discusses cloud-phase climate feedback and the importance of ice-nucleating particles (INP), and it states that:

"We propose that a concerted research effort is required to reduce substantial uncertainties related to the poorly understood sources, concentration, seasonal cycles and nature of these ice-nucleating particles (INPs) and their rudimentary treatment in climate models. The topic is important because many climate models may have overestimated the magnitude of the cloud-phase feedback, and those with better representation of shallow oceanic clouds predict a substantially larger climate warming."

As consensus climate scientists (e.g. CMIP5, and see the first image) tend to discount uncertainties in cloud-phase climate feedback in their projected ranges for ECS; it is highly risky to rely on consensus climate change guidance (e.g. AR5).

Murray, B. J., Carslaw, K. S., and Field, P. R.: Opinion: Cloud-phase climate feedback and the importance of ice-nucleating particles, Atmos. Chem. Phys., 21, 665–679, https://doi.org/10.5194/acp-21-665-2021, 2021.

https://acp.copernicus.org/articles/21/665/2021/

Abstract
Shallow clouds covering vast areas of the world's middle- and high-latitude oceans play a key role in dampening the global temperature rise associated with CO2. These clouds, which contain both ice and supercooled water, respond to a warming world by transitioning to a state with more liquid water and a greater albedo, resulting in a negative “cloud-phase” climate feedback component. Here we argue that the magnitude of the negative cloud-phase feedback component depends on the amount and nature of the small fraction of aerosol particles that can nucleate ice crystals. We propose that a concerted research effort is required to reduce substantial uncertainties related to the poorly understood sources, concentration, seasonal cycles and nature of these ice-nucleating particles (INPs) and their rudimentary treatment in climate models. The topic is important because many climate models may have overestimated the magnitude of the cloud-phase feedback, and those with better representation of shallow oceanic clouds predict a substantially larger climate warming. We make the case that understanding the present-day INP population in shallow clouds in the cold sector of cyclone systems is particularly critical for defining present-day cloud phase and therefore how the clouds respond to warming. We also need to develop a predictive capability for future INP emissions and sinks in a warmer world with less ice and snow and potentially stronger INP sources.

Extract: "Liquid-only clouds in the marine boundary layer at low latitudes are generally expected to decrease in amount in a warmer world, exerting a positive feedback (Ceppi et al., 2017). However, for clouds at higher latitudes or higher altitudes where the temperature is below the freezing point of water, the response to warming can be entirely different (see Fig. 2). The key difference in “mixed-phase” clouds is that the formation and precipitation of ice crystals can strongly reduce the amount of supercooled liquid water, which accounts for most of the cloud reflectivity. If aerosol particles capable of nucleating ice, ice-nucleating particles (INPs), are present and are active at the local cloud temperature, then the supercooled liquid water content and albedo of these clouds can be dramatically reduced through ice-related microphysical processes (Vergara-Temprado et al., 2018; Komurcu et al., 2014; Storelvmo, 2017).

The strength of this feedback depends on the balance between ice and supercooled water in the present and future climate (Fig. 3); however, the cloud-phase feedback is treated in climate models with varying levels of detail.

It has become clear over the last few years that many models may overestimate the magnitude of the cloud-phase feedback, especially in the Southern Ocean. There are well-known model biases in the Southern Ocean with too much SW radiation making it to the surface due to shallow clouds not being sufficiently reflective (Bodas-Salcedo et al., 2012; Trenberth and Fasullo, 2010). In many models, these shallow clouds contain too little supercooled water, exposing the dark ocean underneath and resulting in sea surface temperatures around 2 ∘C too warm (Wang et al., 2014). This bias has profound implications for the strength of the cloud-phase feedback. Tan et al. (2016) demonstrated that the strength of the cloud-phase feedback was strongly dependent on the amount of supercooled liquid water in present-day clouds (Fig. S1 in the Supplement). The ECS in their control case, where the model was run in its default configuration, was 4.0 ∘C. But, when the amount of supercooled water in the present-day climate was increased to be more consistent with satellite data, the ECS increased to 5.3 ∘C. Similarly, Frey and Kay (2018) showed that ECS increased from 4.1 to 5.6 ∘C when they increased the amount of supercooled water to better match observations of absorbed shortwave radiation over the Southern Ocean. The fact that ECS is sensitive to the balance between supercooled water and ice in clouds means that we have to improve our understanding of ice-related microphysical processes. In particular, we need a concerted effort to understand the atmospheric abundance of INPs, the aerosol type that catalyses ice formation in mixed phase clouds and plays a major role in defining the cloud-phase feedback.

A significant input of INPs to clouds in the Southern Ocean in the present climate would imply a strong negative cloud-phase feedback and that these clouds have a strong buffering effect on warming by anthropogenic CO2. Conversely, if the INP source is weak, as contemporary measurements suggest (McCluskey et al., 2018a; Schmale et al., 2019; Welti et al., 2020), then the cloud-phase feedback would be far less negative than over the Northern Hemisphere. In addition, there is the potential that sources of INPs in the Southern Hemisphere become more prominent in the future as a response to warming, which would lead to a positive feedback.

There is substantial evidence that the cloud-phase feedback has been too negative in climate models, and the correction of this will lead to larger ECS values."


Caption for the first image: "Figure 1 The equilibrium climate sensitivity plotted against cloud feedback parameter for CMIP5 and CMIP6 models. The left plot is for total cloud feedback parameter, while the right one is for shallow clouds (< 680 hPa) that are poleward of 45∘. The data are from Zelinka et al. (2020). The correlation between low cloud feedback and ECS that has emerged in CMIP6 models indicates that the treatment of mixed-phase low clouds is critical for driving inter-model ECS variability."

Caption for the second image: "Figure 2 The cloud-phase feedback and its relationship with ice-nucleating particles (based on Storelvmo et al., 2015). For shallow marine clouds, the replacement of ice by liquid water leads to more reflective clouds and less shortwave radiation reaching the low albedo ocean surface, resulting in a negative climate feedback."

Caption for the third image: "Figure 3 Cartoons illustrating how the response of mixed-phase clouds to a changing climate is controlled by the ice-nucleating particle concentration. (a) With a relatively high INP concentration ([INP]), there is a large potential for liquid to replace ice as climate warms and isotherms shift upwards, resulting in a strong negative shortwave feedback. (b) With a relatively low INP concentration, clouds contain relatively little ice in the present climate, so there is less ice to replace with liquid water and a relatively small negative feedback. (c) Setting the temperature changes aside, there may be either increases or decreases in INP concentration in the future that clouds will respond to. We have shown the effect of an increase in INP concentration where we would expect a decrease in liquid water path and a positive feedback."
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gerontocrat

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4108 on: January 25, 2021, 03:24:35 PM »
No need to comment...

https://www.theguardian.com/environment/2021/jan/25/global-ice-loss-accelerating-at-record-rate-study-finds
Global ice loss accelerating at record rate, study finds

Quote
The rate of loss is now in line with the worst-case scenarios of the Intergovernmental Panel on Climate Change, the world’s leading authority on the climate, according to a paper published on Monday in the journal The Cryosphere.

Thomas Slater, lead author and research fellow at the centre for polar observation and modelling at the University of Leeds, warned that the consequences would be felt around the world. “Sea level rise on this scale will have very serious impacts on coastal communities this century,” he said.

About 28tn (trillion) tonnes of ice was lost between 1994 and 2017, which the authors of the paper calculate would be enough to put an ice sheet 100 metres thick across the UK. About two thirds of the ice loss was caused by the warming of the atmosphere, with about a third caused by the warming of the seas.

Over the period studied, the rate of ice loss accelerated by 65%, the paper found, from 0.8tn tonnes a year in the 1990s to 1.3 trillion tonnes a year by 2017. About half of all the ice lost was from land, which contributes directly to global sea level rises. The ice loss over the study period, from 1994 to 2017, is estimated to have raised sea levels by 35 millimetres.

https://tc.copernicus.org/articles/15/233/2021/
Quote
Abstract
We combine satellite observations and numerical models to show that Earth lost 28 trillion tonnes of ice between 1994 and 2017. Arctic sea ice (7.6 trillion tonnes), Antarctic ice shelves (6.5 trillion tonnes), mountain glaciers (6.1 trillion tonnes), the Greenland ice sheet (3.8 trillion tonnes), the Antarctic ice sheet (2.5 trillion tonnes), and Southern Ocean sea ice (0.9 trillion tonnes) have all decreased in mass. Just over half (58 %) of the ice loss was from the Northern Hemisphere, and the remainder (42 %) was from the Southern Hemisphere. The rate of ice loss has risen by 57 % since the 1990s – from 0.8 to 1.2 trillion tonnes per year – owing to increased losses from mountain glaciers, Antarctica, Greenland and from Antarctic ice shelves. During the same period, the loss of grounded ice from the Antarctic and Greenland ice sheets and mountain glaciers raised the global sea level by 34.6 ± 3.1 mm. The majority of all ice losses were driven by atmospheric melting (68 % from Arctic sea ice, mountain glaciers ice shelf calving and ice sheet surface mass balance), with the remaining losses (32 % from ice sheet discharge and ice shelf thinning) being driven by oceanic melting. Altogether, these elements of the cryosphere have taken up 3.2 % of the global energy imbalance.

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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4109 on: January 25, 2021, 04:09:02 PM »
The linked reference indicates that the availability of wind-blown mineral phosphorus (dust), regulates blooms of pigmented glacier ice algae on the Greenland Ice Sheet (GrIS).  Thus, as NH dryland regions become drier with continuing climate change, we can expect more dust being blown to the GrIS and more ice algae blooms leading to more surface ice melting.  The authors also note that this positive feedback mechanism was not included in any CMIP6 models.

McCutcheon, J., Lutz, S., Williamson, C. et al. Mineral phosphorus drives glacier algal blooms on the Greenland Ice Sheet. Nat Commun 12, 570 (2021). https://doi.org/10.1038/s41467-020-20627-w

https://www.nature.com/articles/s41467-020-20627-w

Abstract
Melting of the Greenland Ice Sheet is a leading cause of land-ice mass loss and cryosphere-attributed sea level rise. Blooms of pigmented glacier ice algae lower ice albedo and accelerate surface melting in the ice sheet’s southwest sector. Although glacier ice algae cause up to 13% of the surface melting in this region, the controls on bloom development remain poorly understood. Here we show a direct link between mineral phosphorus in surface ice and glacier ice algae biomass through the quantification of solid and fluid phase phosphorus reservoirs in surface habitats across the southwest ablation zone of the ice sheet. We demonstrate that nutrients from mineral dust likely drive glacier ice algal growth, and thereby identify mineral dust as a secondary control on ice sheet melting.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4110 on: January 26, 2021, 05:18:16 PM »
The linked reference summarizes lessons learned from 5-years of research from the Oceans Melting Greenland (OMG) mission, focused on ocean forcing (Thermal Forcing, TF), and finds that models that do not consider such ocean forcing likely underestimate the associated ice mass loss by a factor of about two.  Via the bipolar seesaw mechanisms, such GrIS ice mass loss can/will/is accelerate AIS ice mass loss.

Wood, M. et al. (01 Jan 2021), "Ocean forcing drives glacier retreat in Greenland", Science Advances, Vol. 7, no. 1, eaba7282, DOI: 10.1126/sciadv.aba7282

https://advances.sciencemag.org/content/7/1/eaba7282

Abstract
The retreat and acceleration of Greenland glaciers since the mid-1990s have been attributed to the enhanced intrusion of warm Atlantic Waters (AW) into fjords, but this assertion has not been quantitatively tested on a Greenland-wide basis or included in models. Here, we investigate how AW influenced retreat at 226 marine-terminating glaciers using ocean modeling, remote sensing, and in situ observations. We identify 74 glaciers in deep fjords with AW controlling 49% of the mass loss that retreated when warming increased undercutting by 48%. Conversely, 27 glaciers calving on shallow ridges and 24 in cold, shallow waters retreated little, contributing 15% of the loss, while 10 glaciers retreated substantially following the collapse of several ice shelves. The retreat mechanisms remain undiagnosed at 87 glaciers without ocean and bathymetry data, which controlled 19% of the loss. Ice sheet projections that exclude ocean-induced undercutting may underestimate mass loss by at least a factor of 2.


Caption for the attached image: "Fig. 1 Regional comparison of ocean TF and glacier retreat during 1992–2017.

The reconstruction of ocean TF (°C)—the depth-averaged difference between the in situ water temperature and the salt- and pressure-dependent freezing point of seawater—and cumulative glacier retreat (Qˆr, square kilometer) is shown for (A) all 226 marine-terminating glaciers (red; ±1σ of all regions), respectively, (B) northwest (NW), (C) central west (CW), (D) southwest (SW), (F) north (N), (G) northeast (NE), (H) central east (CE), and (I) southeast (SE) Greenland. Linear regressions in TF through stable, warming, and cooling periods are identified as three thin black lines. (E) Sample areas (thick black, numbered by region) used to evaluate TF in seven regions, with major ocean currents (white), overlaid on a reconstruction of potential temperature at 257-m depth from the MITgcm ocean model for November 2005 (3). IC, irminger current; WGC, west greenland current."

See also:

Title: "Increasing ocean temperature threatens Greenland's ice sheet"

https://phys.org/news/2021-01-ocean-temperature-threatens-greenland-ice.html

Extract: "According to the research team, the build-up of warm salty water at the bottom of fjords has been accelerated by increasing temperatures in the summer months, which heat the surfaces of glaciers, creating pools of meltwater. This liquid leaks through cracks in the ice to form subsurface freshwater rivers which flows into the sea where it interacts with salty water beneath fjords.

As the water temperature around Greenland's coastline is predicted to continue to increase in the future, these findings suggest that some climate models may underestimate glacial ice loss by at least a factor of two if they do not account for undercutting by a warm ocean.

The study also lends insight into why many of Greenland's glaciers never recovered after an abrupt ocean warming between 1998 and 2007, which caused an increase in ocean temperature by nearly 2 degrees Celsius. Although ocean warming paused between 2008 and 2017, the glaciers had already experienced such extreme undercutting in the previous decade that they continued to retreat at an accelerated rate."

Click on the image to enlarge.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4111 on: January 27, 2021, 07:08:27 PM »
The linked reference confirms that CMIP6 does a better job of projecting changes in westerly winds over the Southern Ocean, than did CMIP5, and concludes that only moderate increases in westerly wind velocities and also moderate poleward shifts, in coming decades.  This is important for reasons including that too high of increases in projected westerly wind velocities over the Southern Ocean would reduce the projected associated increase in the upwelling of warm CDW.  I also, note that changes in SH westerly wind patterns are only one reason that the upwelling of warm CDW has been observed to increase in recent decades; with a progressive freshening of the Southern Ocean's surface water near Antarctica likely being of even more importance.

Goyal, R. et al. (20 January 2021), "Historical and projected changes in the Southern Hemisphere surface westerlies", Geophysical Research Letters, https://doi.org/10.1029/2020GL090849

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL090849?af=R

Abstract
Changes to the Southern Hemisphere (SH) surface westerlies fundamentally control regional patterns of air temperature, storm tracks and precipitation, while also regulating ocean circulation, heat transport and carbon uptake. Wind‐forced ocean perturbation experiments commonly apply idealized poleward wind shifts ranging between 0.5 – 10 degrees of latitude, and wind intensification factors of between 10 – 300%. In addition, changes in winds are often prescribed ad‐hoc as a zonally uniform anomaly and can neglect important seasonal differences. Here we quantify historical and projected SH westerly wind changes based on examination of CMIP5, CMIP6 and reanalysis data. We find a significant reduction in the location bias in CMIP6 and an associated reduction in the projected poleward shift compared to CMIP5. Under a high emission scenario, we find a projected end of 21st Century ensemble mean wind increase of ∼10% and a poleward shift of ∼0.8° latitude, although there are important seasonal and regional variations.

Plain Language Summary
The westerly winds in the Southern Hemisphere have increased in speed and shifted towards Antarctica over the last few decades, with model projections suggesting further poleward intensification in the future. Changes in the westerly winds are of great importance because they control the Southern Ocean circulation, ocean carbon uptake, and ocean heat transport, with ramifications for global climate. To understand the impacts of changes in the westerlies on the Southern Ocean, ocean model simulations are often run by artificially increasing and/or shifting winds towards Antarctica to understand the ocean impact of future changes in the winds. However, there is no consistency in the way these changes are incorporated, with large variations in the applied shift and strengthening. In this study, we quantify recent observed and projected changes in the surface westerlies, aiming to provide guidance as to what wind perturbations should be applied in ocean models. We further show that the latest generation of coupled climate models show a reduction in the equatorward bias in the location of westerly winds as compared to the previous generation of models.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4112 on: January 27, 2021, 07:40:08 PM »
The linked reference indicates that numerous CMIP6 models (including Wolf Pack models) project higher effective radiative forcing (ERF) for methane (in particular) than previously estimated by consensus climate science (CCS) projections (see the attached images).

Thornhill, G. D., Collins, W. J., Kramer, R. J., Olivié, D., Skeie, R. B., O'Connor, F. M., Abraham, N. L., Checa-Garcia, R., Bauer, S. E., Deushi, M., Emmons, L. K., Forster, P. M., Horowitz, L. W., Johnson, B., Keeble, J., Lamarque, J.-F., Michou, M., Mills, M. J., Mulcahy, J. P., Myhre, G., Nabat, P., Naik, V., Oshima, N., Schulz, M., Smith, C. J., Takemura, T., Tilmes, S., Wu, T., Zeng, G., and Zhang, J.: Effective radiative forcing from emissions of reactive gases and aerosols – a multi-model comparison, Atmos. Chem. Phys., 21, 853–874, https://doi.org/10.5194/acp-21-853-2021, 2021.

https://acp.copernicus.org/articles/21/853/2021/

Abstract
This paper quantifies the pre-industrial (1850) to present-day (2014) effective radiative forcing (ERF) of anthropogenic emissions of NOX, volatile organic compounds (VOCs; including CO), SO2, NH3, black carbon, organic carbon, and concentrations of methane, N2O and ozone-depleting halocarbons, using CMIP6 models. Concentration and emission changes of reactive species can cause multiple changes in the composition of radiatively active species: tropospheric ozone, stratospheric ozone, stratospheric water vapour, secondary inorganic and organic aerosol, and methane. Where possible we break down the ERFs from each emitted species into the contributions from the composition changes. The ERFs are calculated for each of the models that participated in the AerChemMIP experiments as part of the CMIP6 project, where the relevant model output was available.

The 1850 to 2014 multi-model mean ERFs (± standard deviations) are −1.03 ± 0.37 W m−2 for SO2 emissions, −0.25 ± 0.09 W m−2 for organic carbon (OC), 0.15 ± 0.17 W m−2 for black carbon (BC) and −0.07 ± 0.01 W m−2 for NH3. For the combined aerosols (in the piClim-aer experiment) it is −1.01 ± 0.25 W m−2. The multi-model means for the reactive well-mixed greenhouse gases (including any effects on ozone and aerosol chemistry) are 0.67 ± 0.17 W m−2 for methane (CH4), 0.26 ± 0.07 W m−2 for nitrous oxide (N2O) and 0.12 ± 0.2 W m−2 for ozone-depleting halocarbons (HC). Emissions of the ozone precursors nitrogen oxides (NOx), volatile organic compounds and both together (O3) lead to ERFs of 0.14 ± 0.13, 0.09 ± 0.14 and 0.20 ± 0.07 W m−2 respectively. The differences in ERFs calculated for the different models reflect differences in the complexity of their aerosol and chemistry schemes, especially in the case of methane where tropospheric chemistry captures increased forcing from ozone production.
Extract: "The experimental set-up and diagnostics in CMIP6 have allowed us for the first time to calculate the effective radiative forcing (ERF) for present-day reactive gas and aerosol concentrations and emissions in a range of Earth system models. Quantifying the forcing in these models is an essential step to understanding their climate responses.

We find that the ERF from well-mixed greenhouse gases (methane, nitrous oxide and halocarbons) has significant contributions through their effects on ozone, aerosols and clouds, which vary strongly across Earth system models. This indicates that Earth system processes need to be taken into account when understanding the contribution WMGHGs have made to present climate and when projecting the climate effects of different WMGHG scenarios."

Caption for the first image: "Figure 8 Estimated SARF from the greenhouse gas changes (WMGHGs and ozone), using radiative efficiencies for the WMGHGs and kernel calculations for ozone (see text). Hatched bars show decreases in ozone SARF. Symbols show the modelled ERF, SARF and ERFcs,af (estimate of greenhouse gas clear-sky ERF). Uncertainties on the bars are due to uncertainties in radiative efficiencies. Uncertainties on the symbols are errors in the mean due to interannual variability in the model diagnostic."

Caption for the second image: "Figure 9 Changes in methane lifetime (%), for each experiment. Uncertainties for individual models are errors on the mean from interannual variability. Uncertainties for the multi-model mean are standard deviations across models."

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Tom_Mazanec

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4113 on: January 28, 2021, 12:11:10 AM »
AbruptSLR, does it look like CMIP6 is going to be roughly "correct", or will we have to wait for CMIP7?
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4114 on: January 28, 2021, 05:31:30 PM »
Paleo records indicate that about eight thousand years ago (8kya) the marine glaciers in the ASE advanced instead of retreating.  Some climate contrarians claimed that as what was previously called the Holocene Climatic Optimum (HCO) was previously reported to have GMSTA values close to those of modern time; that this was evidence that marine glaciers like Thwaites Glacier could not become unstable under modern conditions.  However, the linked reference (& associated article) disprove this contrarian hypothesis by shown that from 12kya to 6.5 kya ice sheet melting kept the polar oceans cold (thus allowing local marine glacier advance in the ASE), which kept the true GMSTA circa 8kya (during the Holocene thermal maximum) well below the previously estimated, but incorrect, HCO GMSTA.  This new information confirms that the marine glaciers in the ASE are indeed rapidly becoming unstable.

Bova, S., Rosenthal, Y., Liu, Z. et al. Seasonal origin of the thermal maxima at the Holocene and the last interglacial. Nature 589, 548–553 (2021). https://doi.org/10.1038/s41586-020-03155-x

https://www.nature.com/articles/s41586-020-03155-x

Abstract: "Proxy reconstructions from marine sediment cores indicate peak temperatures in the first half of the last and current interglacial periods (the thermal maxima of the Holocene epoch, 10,000 to 6,000 years ago, and the last interglacial period, 128,000 to 123,000 years ago) that arguably exceed modern warmth. By contrast, climate models simulate monotonic warming throughout both periods. This substantial model–data discrepancy undermines confidence in both proxy reconstructions and climate models, and inhibits a mechanistic understanding of recent climate change. Here we show that previous global reconstructions of temperature in the Holocene and the last interglacial period reflect the evolution of seasonal, rather than annual, temperatures and we develop a method of transforming them to mean annual temperatures. We further demonstrate that global mean annual sea surface temperatures have been steadily increasing since the start of the Holocene (about 12,000 years ago), first in response to retreating ice sheets (12 to 6.5 thousand years ago), and then as a result of rising greenhouse gas concentrations (0.25 ± 0.21 degrees Celsius over the past 6,500 years or so). However, mean annual temperatures during the last interglacial period were stable and warmer than estimates of temperatures during the Holocene, and we attribute this to the near-constant greenhouse gas levels and the reduced extent of ice sheets. We therefore argue that the climate of the Holocene differed from that of the last interglacial period in two ways: first, larger remnant glacial ice sheets acted to cool the early Holocene, and second, rising greenhouse gas levels in the late Holocene warmed the planet. Furthermore, our reconstructions demonstrate that the modern global temperature has exceeded annual levels over the past 12,000 years and probably approaches the warmth of the last interglacial period (128,000 to 115,000 years ago)."

See also:

Title: "Palaeoclimate puzzle explained by seasonal variation"

https://www.nature.com/articles/d41586-021-00115-x

Extract: "Scientists have long been baffled by the mismatch of climate simulations of the past 12,000 years with temperature reconstructions from geological records. It now emerges that seasonal biases in the records explain the disparity.

The authors also show that mean annual temperatures during the last interglacial period were more stable and higher than their estimates of Holocene temperatures. They attribute this to the near-constant greenhouse-gas concentrations and reduced extent of ice sheets during the last interglacial. Crucially, the researchers find that the current mean annual temperature exceeds those of the past 12,000 years, and probably approaches the warmth of the last interglacial period."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4115 on: February 01, 2021, 03:32:41 PM »
The linked article discusses new research that indicates that thawing permafrost is full of ice-nucleating particles (INP); which could be lifted into the atmosphere by local winds where they could nucleate snow and/or rain that would cause these low-altitude clouds to dissipate earlier and thus reflect less sunlight; which would constitute yet another positive feedback for more global warming; which is currently not considered in current (CMIP6) climate projections.

Title: "Thawing Permafrost Is Full of Ice-Forming Particles That Could Get Into Atmosphere"

https://theconversation.com/thawing-permafrost-is-full-of-ice-forming-particles-that-could-get-into-atmosphere-152736

Extract: "Most of the time, airborne water droplets need to freeze before they can fall to the ground as snow or rain. Ice-nucleating particles allow cloud ice to form at warmer air temperatures than normal, up to around 28 degrees Fahrenheit. Without these particles, a water droplet can supercool to about negative 36 F before freezing. When ice-nucleating particles are in a cloud, water droplets freeze more easily. This can cause the cloud to rain or snow and disappear earlier, and reflect less sunlight.

We hypothesize that ice-nucleating particles from thawing permafrost could get into lakes and rivers, make their way to coastal Arctic Ocean waters and spread over large areas. Then, winds could eject these ice-nucleating particles into the air, where they could enhance the freezing of clouds and affect weather."
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kassy

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4116 on: February 01, 2021, 04:46:13 PM »
That´s one whole new angle. Pretty cool in a scientific way since that does not happen too often.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4117 on: February 01, 2021, 05:38:08 PM »
From the itnernet:
Quote
These ice-​nucleating particles (INPs) represent a small fraction of particles in an atmospheric aerosol. One main particle type which acts as INPs are mineral dusts such as clay minerals, feldspars, and quartz. Different factors influence the ice nucleation ability of such mineral dust particles.

Wouldn't wind bringing dust from 'the terrestrial south' provide more INPs? I wouldn't imaging much 'dust' rises from the ocean surface.
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kassy

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4118 on: February 01, 2021, 06:14:01 PM »
That is only a subset and the permafrost particles are more organic.

The dust will blow as it always blows while this is possibly a whole new source. It´s not so much dust as organic compounds. They get emitted by forests but also algal blooms.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4119 on: February 02, 2021, 01:15:17 AM »
The linked reference indicates that the consensus climate science (CCS) assumption that ice mass loss from the AIS is incorrect, and finds that:

"The new analysis resolves a higher degree of variability than expected over all AIS sectors. Quantifying rate fluctuations on a range of time scales, we demonstrate that loss from the West AIS is characterized by a multidecadal trend, whereas variations of the East AIS are dominated by substantial, short‐term accumulation changes that impact AIS mass balance as whole."

Finally, I note high variability is an indicator of high sensitivity and that the multidecadal trend identified for the WAIS, parallels my position that WAIS ice mass loss will accelerate in the 2030 to 2040 timeframe due to the ENSO multidecadal cycle (which may be sufficient to initially trigger a MICI-type of collapse in the Thwaites Glacier gateway.

Wang, L. et al, Complex Patterns of Antarctic Ice Sheet Mass Change Resolved by Time‐Dependent Rate Modeling of GRACE and GRACE Follow‐On Observations, Geophysical Research Letters (2020). DOI: 10.1029/2020GL090961

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL090961

Abstract
The Antarctic Ice Sheet (AIS) is a major contributor to current global sea‐level change and the largest potential source of future sea‐level change. Variability in AIS mass balance on a wide range of spatiotemporal scales obscures secular trends, increasing the uncertainty of projections. We introduce a novel approach for analyzing satellite gravity observations to estimate time‐varying mass‐change rates and resolve the time scales and amplitudes of rate fluctuations. The new analysis resolves a higher degree of variability than expected over all AIS sectors. Quantifying rate fluctuations on a range of time scales, we demonstrate that loss from the West AIS is characterized by a multidecadal trend, whereas variations of the East AIS are dominated by substantial, short‐term accumulation changes that impact AIS mass balance as whole. These complex spatiotemporal variabilities highlight the need to include stochastic processes in estimates of loss rates.

Plain Language Summary
Characterizing ice loss from the Antarctic Ice Sheet (AIS) as a constant rate, as is typically done, ignores significant temporal variability and leads to large uncertainties in the projection of future changes. We introduce a new approach that models the AIS mass‐change rate as a time‐dependent parameter, resulting in unexpectedly high variability in rates of mass loss from all sectors. We also quantify the amplitudes for the rate fluctuations for various time scales, identifying the roles of different AIS sectors in determining total mass imbalance over time. We conclude that observations and projections of AIS mass change must account for stochastic rate processes.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4120 on: February 02, 2021, 07:02:52 PM »
The linked article indicates that the recent reducing in ASI in the Laptev Sea is leading more wave-induced mixing of the top 50 meters of surface waters; which, in turn, is accelerating the degradation of subsea permafrost that could lead to an acceleration of methane from this relatively shallow sea.  Furthermore, it is safe to assume that this feedback mechanism is currently, and will continue to, accelerate methane emissions from other relatively shallow portions of the Arctic Ocean.

Title: "Scientists in the Arctic's 'Ice Factory' Found a Worrying Sign of Climate Change"

https://www.vice.com/en/article/xgzmnn/scientists-in-the-arctics-ice-factory-found-a-worrying-sign-of-climate-change

Extract: "For 40 days last fall, an expedition collected samples that confirm the thaw of the Arctic’s mysterious subsea permafrost.

Last year, following a historic heatwave across Siberia, the Laptev Sea did not freeze in October for the first time on record, and its ice production in November was unusually “sluggish,” according to NASA.

While the absence of sea ice was striking, Chuvilin and his colleagues were most interested in the murky environment within the Arctic continental shelf, located deep under the waves and even the seafloor. The team had set out to study permafrost, a layer of frozen earth, within the submerged shelf.

Rich in organic carbons, permafrost has become an important factor in models of global climate change because it releases greenhouse gases as it thaws, which scientists worry could trigger feedback loops that will amplify global warming.

“The reduction in the area of sea ice increases wave activity; storms occur, which leads to an active mixing of water masses up to a depth of 40-50 meters,” he explained. “All these parameters accelerate the degradation of subsea permafrost and contribute to the release of methane into the atmosphere that is soluble in seawater, and methane contained in bottom sediments.”"
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4121 on: February 03, 2021, 05:34:14 PM »
The linked reference found that the temporary (for several years) impacts on GMSTA from COVID-19 related reduction in anthropogenic aerosol emissions dominated the impacts of reduced emissions of CO2 and ozone and a reduction of the contrail effect; which contributed to the increase in GMSTA observed for 2020.  This suggests that future reductions in CO2 emissions will likely also result in temporary (for several years) increases in GMSTA due to the associated reduced emissions of anthropogenic aerosols.

Gettelman, A. et al. (29 December 2020), “Climate Impacts of COVID‐19 Induced Emission Changes”, Geophysical Research Letters, DOI: 10.1029/2020GL091805

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL091805

Abstract
The COVID‐19 pandemic led to dramatic changes in economic activity in 2020. We use estimates of emission changes for 2020 in two Earth System Models (ESMs) to simulate the impacts of the COVID‐19 economic changes. Ensembles of nudged simulations are used to separate small signals from meteorological variability. Reductions in aerosol and precursor emissions, chiefly black carbon and sulfate (SO4), led to reductions in total anthropogenic aerosol cooling through aerosol‐cloud interactions. The average overall Effective Radiative Forcing (ERF) peaks at +0.29 ± 0.15 Wm−2 in spring 2020. Changes in cloud properties are smaller than observed changes during 2020. Impacts of these changes on regional land surface temperature range up to +0.3 K. The peak impact of these aerosol changes on global surface temperature is very small (+0.03 K). However, the aerosol changes are the largest contribution to radiative forcing and temperature changes as a result of COVID‐19 affected emissions, larger than ozone, CO2 and contrail effects.

Plain Language Summary
The COVID‐19 pandemic changed emissions of gases and particulates. These gases and particulates affect climate. In general, human emissions of particles cool the planet by scattering away sunlight in the clear sky and by making clouds brighter to reflect sunlight away from the earth. This paper focuses on understanding how changes to emissions of particulates (aerosols) affect climate. We use estimates of emissions changes for 2020 in two climate models to simulate the impacts of the COVID‐19 induced emission changes. We tightly constrain the models by forcing the winds to match observed winds for 2020. COVID‐19 induced lockdowns led to reductions in aerosol and precursor emissions, chiefly soot or black carbon and sulfate (SO4). This is found to reduce the human caused aerosol cooling: creating a small net warming effect on the earth in spring 2020. Changes in cloud properties are smaller than observed changes during 2020. The impact of these changes on regional land surface temperature is small (maximum +0.3 K). The impact of aerosol changes on global surface temperature is very small and lasts over several years. However, the aerosol changes are the largest contribution to COVID‐19 affected emissions induced radiative forcing and temperature changes, larger than ozone, CO2 and contrail effects.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4122 on: February 08, 2021, 07:55:49 PM »
It looks like the "Wolfpack" (models that have very high ECS) CMIP6 climate models don't do a good job of recreating the hemispheric differences in aerosol forcings observed in the 20th century.

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL091024?af=R

Quote
Wang, C., Soden, B., Yang, W., & Vecchi, G. A. (2021). Compensation between cloud feedback and aerosol‐cloud interaction in CMIP6 models. Geophysical Research Letters, 48, e2020GL091024. https://doi.org/10.1029/2020GL091024

 Abstract

The most recent generation of climate models (the 6th Phase of the Coupled Model Intercomparison Project – CMIP6) yields estimates of effective climate sensitivity (ECS) that are much higher than past generations due to a stronger amplification from cloud feedback. If plausible, these models require substantially larger greenhouse gas reductions to meet global warming targets. We show that models with a more positive cloud feedback also have a stronger cooling effect from aerosol‐cloud interactions. These two effects offset each other during the historical period when both aerosols and greenhouse gases increase, allowing either more positive or neutral cloud feedback models to reproduce the observed global‐mean temperature change. Since anthropogenic aerosols primarily concentrate in the Northern Hemisphere, strong aerosol‐cloud interaction models produce an interhemispheric asymmetric warming. We show that the observed warming asymmetry during the mid to late 20th century is more consistent with low ECS (weak aerosol indirect effect) models.

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4123 on: February 08, 2021, 10:42:42 PM »
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.

This is just a reminder that as anthropogenic aerosol (AA) emissions decrease the AMOC will continue to slow; which will induce the 'pattern effect' to increase ECS this century.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #4124 on: February 08, 2021, 10:47:04 PM »
The linked reference used simulations from the Precipitation Driver and Response Model Intercomparison Project (PDRMIP); which included a lot of high-end ESMs that also participated in CMIP6; thus, their findings imply that the high-end simulations from CMIP6 (with typically high values of ECS) do a good job of matching historical records when using effective radiative forcing (ERF) for comparisons.  Unfortunately, AR5 and AR6 include a lot of low-end energy balance model simulations that use instantaneous radiative forcing which as the following quote indicates can result in efficacies that deviate considerably from unity; which can result in the calculation of low estimates of ECS (which are averaged together with more accurate estimates of ECS to result in a low bias for ECS in AR5 and likely in AR6).

"Efficacies calculated from instantaneous radiative forcing deviate considerably from unity across forcing agents and models. Effective radiative forcing (ERF) is a better predictor of global mean near‐surface air temperature (GSAT) change."

T. B. Richardson et al. (20 November 2019), "Efficacy of Climate Forcings in PDRMIP Models", JGR Atmospheres, https://doi.org/10.1029/2019JD030581

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JD030581

Abstract
Quantifying the efficacy of different climate forcings is important for understanding the real‐world climate sensitivity. This study presents a systematic multimodel analysis of different climate driver efficacies using simulations from the Precipitation Driver and Response Model Intercomparison Project (PDRMIP). Efficacies calculated from instantaneous radiative forcing deviate considerably from unity across forcing agents and models. Effective radiative forcing (ERF) is a better predictor of global mean near‐surface air temperature (GSAT) change. Efficacies are closest to one when ERF is computed using fixed sea surface temperature experiments and adjusted for land surface temperature changes using radiative kernels. Multimodel mean efficacies based on ERF are close to one for global perturbations of methane, sulfate, black carbon, and insolation, but there is notable intermodel spread. We do not find robust evidence that the geographic location of sulfate aerosol affects its efficacy. GSAT is found to respond more slowly to aerosol forcing than CO2 in the early stages of simulations. Despite these differences, we find that there is no evidence for an efficacy effect on historical GSAT trend estimates based on simulations with an impulse response model, nor on the resulting estimates of climate sensitivity derived from the historical period. However, the considerable intermodel spread in the computed efficacies means that we cannot rule out an efficacy‐induced bias of ±0.4 K in equilibrium climate sensitivity to CO2 doubling when estimated using the historical GSAT trend.

Plain Language Summary
Does the climate respond in the same way to carbon dioxide as it does to methane or aerosol changes? The simple way of thinking about forcing and response in the Earth system assumes that it does, such that, a Watt per square meter forcing from CO2 has the same response as an equivalent forcing from aerosols. Recent work has suggested that this might not be true and that differences in how effective different forcings are at increasing surface temperature (their efficacy) may account for a low estimate of climate sensitivity when examining historical change. We show this all depends on how you estimate your Watts per meter squared forcing in the first place. Using the effective radiative forcing concept to estimate forcing strength makes temperature changes far more predictable, and a lot of these issues with efficacy variation are not as pronounced as they were with earlier definitions.

This is just a reminder that per the linked reference CMIP6 Wolf Pack models do a good job of matching historical records when using effective radiative forcing (ERF) for comparisons.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4125 on: February 08, 2021, 10:55:50 PM »
This is just a reminder that the CMIP 3 and CMIP 5 models do a better job recreating observed global temperatures than CMIP 6 models.

http://www.realclimate.org/





Quote
The issues in CMIP6 related to the excessive spread in climate sensitivity will need to be looked at in more detail moving forward. In my opinion ‘official’ projections will need to weight the models to screen out those ECS values outside of the constrained range. We’ll see if other’s agree when the IPCC report is released later this year.

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #4126 on: February 08, 2021, 11:33:56 PM »
While I don't have time to properly evaluate the linked reference which evaluates ENSO simulations by both CMIP5/PIMP3 and CMIP6; it seems to me that CMIP6/PMIP4 exhibits more skill in hind casting ENSO than CMIP5/PIMP3:

Brown, J. R., Brierley, C. M., An, S.-I., Guarino, M.-V., Stevenson, S., Williams, C. J. R., Zhang, Q., Zhao, A., Braconnot, P., Brady, E. C., Chandan, D., D'Agostino, R., Guo, C., LeGrande, A. N., Lohmann, G., Morozova, P. A., Ohgaito, R., O'ishi, R., Otto-Bliesner, B., Peltier, W. R., Shi, X., Sime, L., Volodin, E. M., Zhang, Z., and Zheng, W.: Comparison of past and future simulations of ENSO in CMIP5/PMIP3 and CMIP6/PMIP4 models, Clim. Past Discuss., https://doi.org/10.5194/cp-2019-155, in review, 2020.

https://www.clim-past-discuss.net/cp-2019-155/
https://www.clim-past-discuss.net/cp-2019-155/cp-2019-155.pdf

Abstract. El Niño-Southern Oscillation (ENSO) is the strongest mode of interannual climate variability in the current climate, influencing ecosystems, agriculture and weather systems across the globe, but future projections of ENSO frequency and amplitude remain highly uncertain. A comparison of changes in ENSO in a range of past and future climate simulations can provide insights into the sensitivity of ENSO to changes in the mean state, including changes in the seasonality of incoming solar radiation, global average temperatures and spatial patterns of sea surface temperatures. As a comprehensive set of coupled model simulations are now available for both palaeoclimate time-slices (the Last Glacial Maximum, mid-Holocene and Last Interglacial) and idealised future warming scenarios (one percent per year CO2 increase, abrupt four times CO2 increase), this allows a detailed evaluation of ENSO changes in this wide range of climates. Such a comparison can assist in constraining uncertainty in future projections, providing insights into model agreement and the sensitivity of ENSO to a range of factors. The majority of models simulate a consistent weakening of ENSO activity in the Last Interglacial and mid-Holocene experiments, and there is an ensemble mean reduction of variability in the western equatorial Pacific in the Last Glacial Maximum experiments. Changes in global temperature produce a weaker precipitation response to ENSO in the cold Last Glacial Maximum experiments, and an enhanced precipitation response to ENSO in the warm increased CO2 experiments. No consistent relationship between changes in ENSO amplitude and annual cycle was identified across experiments.

Caption: "Table 1: List of models included in study and length of simulations based on number of years of data available for NINO3.4 in the CVDP archive. Additional information about CMIP6/PMIP4 models (indicated in bold) is provided in the Supplementary Material."

I thought that it would be good to remind readers that CMIP6 generally demonstrate higher skill levels than do earlier CMIP projections.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #4127 on: February 08, 2021, 11:40:32 PM »
The linked article by Gavin Schmidt indicates that the CMIP6 models with relatively high ECS values (for values thru August 2019 see the attached image) collectively show higher skill scores than those for earlier models (like CMIP5).  We will all have to wait and see what AR6 does with this new information:

Title: "Sensitive But Unclassified"

http://www.realclimate.org/index.php/archives/2019/11/sensitive-but-unclassified/

Extract: "Why might the numbers be correct? All the preliminary analyses I’ve seen with respect to matches to present day climatologies and variability indicate that the skill scores of the new models (collectively, not just the high ECS ones) are improved over the previous versions. This is discussed in Gettelman et al. (2019) (CESM2), Sellar et al (2019) (UKESM1) etc. Indeed, this is a generic pattern in model development.

What is clear is that (for the first time) the discord between the GCMs and the external constraints is going to cause a headache for the upcoming IPCC report. The deadline for papers to be submitted for consideration for the second order draft is in December 2019, and while there will be some papers on this topic submitted by then. I am not confident that the basic conundrums will be resolved. Thus the chapter on climate sensitivity is going to be contrasted strongly with the chapter on model projections. Model democracy (one model, one vote) is a obviously a terrible idea and if adopted in AR6, will be even more problematic. However, no other scheme has been demonstrated to work better."

This is just a reminder to readers that even Gavin Schmidt agrees that the CMIP6 models (thru August 2019; which include most Wolf Pack models) have higher skill ratings than earlier models (like CMIP5 or CMIP3).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4128 on: February 09, 2021, 06:12:09 PM »
This is just a reminder that Transcient Climate Response (TCR) is a measure of how the climate models respond to a 1% annual increase in CO2 for 70 years as opposed to Equilibrium Climate Sensitivity (ECS), which is a measure of how models respond to an instantaneous 4 times increase of CO2.



https://advances.sciencemag.org/content/6/26/eaba1981

Quote
Context for interpreting equilibrium climate sensitivity and transient climate response from the CMIP6 Earth system models

By Gerald A. Meehl, Catherine A. Senior, Veronika Eyring, Gregory Flato, Jean-Francois Lamarque, Ronald J. Stouffer, Karl E. Taylor, Manuel Schlund

Science Advances
24 Jun 2020

Abstract

For the current generation of earth system models participating in the Coupled Model Intercomparison Project Phase 6 (CMIP6), the range of equilibrium climate sensitivity (ECS, a hypothetical value of global warming at equilibrium for a doubling of CO2) is 1.8°C to 5.6°C, the largest of any generation of models dating to the 1990s. Meanwhile, the range of transient climate response (TCR, the surface temperature warming around the time of CO2 doubling in a 1% per year CO2 increase simulation) for the CMIP6 models of 1.7°C (1.3°C to 3.0°C) is only slightly larger than for the CMIP3 and CMIP5 models. Here we review and synthesize the latest developments in ECS and TCR values in CMIP, compile possible reasons for the current values as supplied by the modeling groups, and highlight future directions. Cloud feedbacks and cloud-aerosol interactions are the most likely contributors to the high values and increased range of ECS in CMIP6.

Note again that cloud feedbacks and cloud-aerosol interactions are the most like cause of the high ECS in the models that run hot.  As noted in this paper posted on interhemispheric differences in observed aerosol forcings, the models that run hot do a much poorer job of simulating those differences:

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL091024?af=R

Quote
The most recent generation of climate models (the 6th Phase of the Coupled Model Intercomparison Project – CMIP6) yields estimates of effective climate sensitivity (ECS) that are much higher than past generations due to a stronger amplification from cloud feedback. If plausible, these models require substantially larger greenhouse gas reductions to meet global warming targets. We show that models with a more positive cloud feedback also have a stronger cooling effect from aerosol‐cloud interactions. These two effects offset each other during the historical period when both aerosols and greenhouse gases increase, allowing either more positive or neutral cloud feedback models to reproduce the observed global‐mean temperature change. Since anthropogenic aerosols primarily concentrate in the Northern Hemisphere, strong aerosol‐cloud interaction models produce an interhemispheric asymmetric warming. We show that the observed warming asymmetry during the mid to late 20th century is more consistent with low ECS (weak aerosol indirect effect) models.

TL, DR:  The high sensitivity (ECS, not TCR which is similar to other models from CMIP 6 and earlier) CMIP6 models have ECS because of cloud feedbacks and cloud-aerosol interactions and they do a poor job replicating observed aerosol and cloud-feedback observations.  This puts thier high ECS values in doubt.


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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4129 on: February 10, 2021, 02:28:56 AM »
The linked reference indicates that CMIP5 likely underestimated how negative aerosol forcing has been and indicates that the mean values of aerosol forcing and of TCR from CMIP6 are closer to matching the observed regional land temperatures.  If so, this indicates that the relatively high mean climate sensitivity values (both TCR and ECS) determined in CMIP6 are more likely than so far acknowledged by consensus climate documents like AR5.  I note that while the TCR value of 2.0K determined by this reference is relatively high, this value does not consider the impacts of freshwater hosing on TCR and that when E3SMv1 did so it projected a value of 2.95K for TCR.

Zhaoyi Shen,Yi Ming and Isaac M. Held (05 Aug 2020), "Using the fast impact of anthropogenic aerosols on regional land temperature to constrain aerosol forcing", Science Advances, Vol. 6, no. 32, eabb5297, DOI: 10.1126/sciadv.abb5297

https://advances.sciencemag.org/content/6/32/eabb5297.full

Abstract
Anthropogenic aerosols have been postulated to have a cooling effect on climate, but its magnitude remains uncertain. Using atmospheric general circulation model simulations, we separate the land temperature response into a fast response to radiative forcings and a slow response to changing oceanic conditions and find that the former accounts for about one fifth of the observed warming of the Northern Hemisphere land during summer and autumn since the 1960s. While small, this fast response can be constrained by observations. Spatially varying aerosol effects can be detected on the regional scale, specifically warming over Europe and cooling over Asia. These results provide empirical evidence for the important role of aerosols in setting regional land temperature trends and point to an emergent constraint that suggests strong global aerosol forcing and high transient climate response.

Extract: "One can further estimate the global aerosol forcing at −1.4 ± 0.7 W m−2 by subtracting the nonaerosol forcings (2.9 ± 0.2 W m−2 in the three models) from the inferred total forcing (1.5 ± 0.7 W m−2). This value is appreciably stronger than the best AR5 estimate (−0.9 W m−2) but well within the 90% confidence interval (−0.1 to −1.9 W m−2). It is also within the 68% confidence interval of −0.65 to −1.60 W m−2 provided by (27). The best estimate is at the lowest end of the Coupled Model Intercomparison Project Phase 6 (CMIP6) aerosol ERF range (−0.63 to −1.37 W m−2) (28).

The transient climate response (TCR; defined as the surface temperature change in response to a 1% per year increase of CO2 at the time of doubling), a quantity crucial for near-term climate projection, can be calculated from the historical warming (δT, 0.80 K) (29) and ERF (F) as F2XδT/F, where F2X is the ERF of CO2 doubling (3.8 W m−2) (29). At a historical forcing of 1.5 W m−2 as estimated here, the implied TCR is 2.0 K. This is at the higher end of the AR5 likely range of 1 to 2.5 K (30) but is close to the median TCR of 1.95 K based on CMIP6 models (31)."

This is just a friendly reminder that CMIP5 likely underestimate how negative aerosol radiative forcing has been and that CMIP6 did a fairly reasonable job of estimating TCR (without considering possible impacts on TCR from possible significant future freshwater hosing events).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4130 on: February 10, 2021, 02:34:01 AM »
The linked website/article indicates that HadGEM3-GC3.1 has a TCR of about 2.7C and an ECS of about 5.5C; while E3SMv1 has a TCR of 2.93C and an ECS of 5.3C.  As HadGEM3-GC3.1 does a better job of modeling Arctic melt ponds on sea ice and E3SMv1 does a better job of assessing the impacts of freshwater on the AMOC; I am concerned that E3SMv1's TCR value of 2.93C may be more correct while HadGEM3-GC3.1's ECS value of 5.5C maybe more correct.  If so them the CMIP6 'Wolf Pack' may be erring on the side of least drama with regard to climate sensitivity this century.

Title: "New flagship climate models - UKESM1 and HadGEM3-GC3.1"

https://www.metoffice.gov.uk/research/approach/modelling-systems/new-flagship-climate-models

Extract: "Analysis shows the climate sensitivity of the models is high. For both models the Transient Climate Sensitivity (TCR) is about 2.7 °C, while the Equilibrium Climate Sensitivity (ECS)  is about 5.4°C for UKESM1 and about 5.5°C for GC3.1. Future projections using the new models are in progress. When these have been analysed, we will have a better understanding of how the climate sensitivity affects future warming and associated impacts."

This is just a reminder that there is a real chance that the CMIP6 Wolf Pack is underestimating both TCR and ECS (particularly when considering the fact that all CMIP6 Wolf Pack models do not consider the extent of ice-climate feedback projected by Hansen et al 2016).
« Last Edit: February 10, 2021, 05:42:27 PM by AbruptSLR »
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4131 on: February 10, 2021, 05:41:47 PM »
The linked reference uses AI to confirm that there is: '… a clear but variable clockwise circulation …' in the Pine Island Bay; which to me indicates that some mCDW coming out from beneath the PIIS is advected toward the Thwaites Ice Shelf and the Thwaites Ice Tongue.

Lars Boehme & Isabella Rosso (06 February 2021), "Classifying Oceanographic Structures in the Amundsen Sea, Antarctica", Geophysical Research Letters, https://doi.org/10.1029/2020GL089412

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL089412

Abstract
The remote and often ice‐covered Amundsen Sea Embayment in Antarctica is important for transporting relatively warm modified Circumpolar Deep Water (mCDW) to the Western Antarctic Ice Sheet, potentially accelerating its thinning and contribution to sea level rise. To investigate potential pathways and variability of mCDW, 3809 CTD profiles (instrumented seal and ship‐based data) are classified using a machine learning approach (Profile Classification Model). Five vertical regimes are identified, and areas of larger variability highlighted. Three spatial regimes are captured: Off‐Shelf, Eastern and Central Troughs. The on‐shelf profiles further show a separation between cold and warm modes. The variability is higher north of Burke Island and at the southern end of the Eastern Trough, which reflects the convergence of different mCDW pathways between the Eastern and the Central Trough. Finally, a clear but variable clockwise circulation is identified in Pine Island Bay.

Plain Language Summary
The glaciers of West Antarctica are melting and could change sea level by about 30 cm or more by 2100. Pine Island and Thwaites Glaciers, both flowing into the Amundsen Sea, are currently retreating partly driven by warm water melting the glaciers from below. This water sits only a few degrees above freezing, but can still accelerate the melt and sea level rise. This warm water comes from the deeper Southern Ocean further north and travels through deep channels onto the shallower Amundsen Sea shelf following deeper troughs until reaching the glaciers further south. Understanding the pathways and the variability of this warm water on its way south is of high importance. Here, we use a machine learning method to identify different pathways from a large number of observations.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4132 on: February 10, 2021, 06:47:59 PM »
The linked reference discusses a new nondestructive method to study periods of potentially abrupt climate change during the PETM; which should help modern researchers to better project how our current oceans may respond (potentially in an abrupt manner) to continuing forcing.

Courtney L. Wagner, C.L., et al. (February 9, 2021), "In situ magnetic identification of giant, needle-shaped magnetofossils in Paleocene–Eocene Thermal Maximum sediments", PNAS, 118 (6) e2018169118, https://doi.org/10.1073/pnas.2018169118

https://www.pnas.org/content/118/6/e2018169118

Significance
Giant magnetofossils are the preserved remains of iron-biomineralizing organisms that have so far been identified only in sediments deposited during ancient greenhouse climates. Giant magnetofossils have no modern analog, but their association with abrupt global warming events links them to environmental disturbances. Thus, giant magnetofossils may encode information about nutrient availability and water stratification in ancient aquatic environments. Identification of giant magnetofossils has previously required destructive extraction techniques. We show that giant, needle-shaped magnetofossils have distinct magnetic signatures. Our results provide a nondestructive method for identifying giant magnetofossil assemblages in bulk sediments, which will help test their significance with respect to environmental change.

Abstract
Near-shore marine sediments deposited during the Paleocene–Eocene Thermal Maximum at Wilson Lake, NJ, contain abundant conventional and giant magnetofossils. We find that giant, needle-shaped magnetofossils from Wilson Lake produce distinct magnetic signatures in low-noise, high-resolution first-order reversal curve (FORC) measurements. These magnetic measurements on bulk sediment samples identify the presence of giant, needle-shaped magnetofossils. Our results are supported by micromagnetic simulations of giant needle morphologies measured from transmission electron micrographs of magnetic extracts from Wilson Lake sediments. These simulations underscore the single-domain characteristics and the large magnetic coercivity associated with the extreme crystal elongation of giant needles. Giant magnetofossils have so far only been identified in sediments deposited during global hyperthermal events and therefore may serve as magnetic biomarkers of environmental disturbances. Our results show that FORC measurements are a nondestructive method for identifying giant magnetofossil assemblages in bulk sediments, which will help test their ecology and significance with respect to environmental change.

See also:

Title: "Mysterious magnetic fossils offer past climate clues"

https://www.eurekalert.org/pub_releases/2021-02/uou-mmf012721.php

Extract: "There are fossils, found in ancient marine sediments and made up of no more than a few magnetic nanoparticles, that can tell us a whole lot about the climate of the past, especially episodes of abrupt global warming.

During a few periods in the Earth's past, at the beginning and middle of the Eocene epoch from 56 to 34 million years ago, some of these biologically-produced magnets grew to "giant" sizes, about 20 times larger than typical magnetofossils, and into exotic shapes such as needles, spindles, spearheads and giant bullets. Because the bacteria used their magnetic supersense to find their preferred levels of nutrients and oxygen in the ocean water, and because the giant magnetofossils are associated with periods of rapid climate change and elevated global temperature, they can tell us a lot about the conditions of the ocean during that rapid warming, and especially how those conditions changed over time.

Beyond that, though, the information contained in magnetofossils helps scientists understand how oceans responded to past climate changes--and how our current ocean might respond to ongoing warming."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4133 on: February 11, 2021, 09:14:45 PM »
The linked open access reference provides paleo-data that indicates that significant portions of the Svalbard-Barents Sea ice sheet (composed of marine glaciers) mostly collapsed virtually instantly (under the right conditions); which, could only have happened due MICI-type of collapses.  This research increases the risk that many of the marine glaciers in the WAIS could undergo similar MICI-types of collapse given continued global warming and increased upwelling of relatively warm mCWD (modified Circumpolar Deepwater), in coming decades.

Rasmussen, T.L. et al, Climate and ocean forcing of ice-sheet dynamics along the Svalbard-Barents Sea ice sheet during the deglaciation ∼20,000–10,000 years BP, Quaternary Science Advances (2020). DOI: 10.1016/j.qsa.2020.100019

https://www.sciencedirect.com/science/article/pii/S2666033420300198?via%3Dihub

Abstract
The last deglaciation, 20,000–10,000 years ago, was a period of global warming and rapidly shrinking ice sheets. It was also climatically unstable and retreats were interrupted by re-advances. Retreat rates and timing relative to climatic changes have therefore been difficult to establish. We here study a suite of 12 marine sediment cores from Storfjorden and Storfjorden Trough, Svalbard. The purpose is to reconstruct retreat patterns and retreat rates of a high northern latitude marine-based ice stream from the Svalbard-Barents Sea Ice Sheet in relation to paleoceanographic and paleoclimatic changes. The study is based on abundance and composition of planktic and benthic foraminiferal assemblages, ice rafted debris (IRD), lithology, and 70 AMS-14C dates. For core 460, we also calculate sea surface and bottom water temperatures and bottom water salinity. The results show that retreat rates of the ice shelf and ice streams of Storfjorden Trough/Storfjorden (‘Storfjorden Ice Stream’) closely followed the deglacial atmospheric and ocean temperature changes. During the start of the Bølling interstadial retreat rates in Storfjorden Trough probably exceeded 2.5 km/year and more than 10,000 km2 of ice disappeared almost instantaneously. A similarly rapid retreat occurred at the start of the Holocene interglacial, when 4500 km2 of ice broke up. Maximum rates during the deglaciation match the fastest modern rates from Antarctica and Greenland. Correlation of data show that the ice streams in several fjords from northern Norway retreated simultaneously with the Storfjorden Ice Stream, indicating that temperature was the most important forcing factor of the Svalbard-Barents Sea Ice Sheet during the deglaciation.

Extract: "The retreat was not uniform over time. About haft of the ice disappeared in two almost instantaneous collapses. The first occurred at the beginning of the Bølling interstadial, when more than 11,000 km2 of ice sheet from Storfjorden Trough and the outer fjord disintegrated. The second collapse took place at the beginning of the early Holocene and comprised about 4500 km2 of ice from the inner fjord system. During both break-ups, the ice front retreated about 100 km. Instant disintegration is the most likely scenario for the early Bølling and early Holocene collapses."
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Sciguy

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4134 on: February 11, 2021, 09:15:28 PM »
A recently published study finds that the high-sensitivity CMIP6 model (one of the "Wolfpack") overestimates cooling in the last glacial maximum.  This is due to the way it (and other Wolfpack models) treat cloud feedbacks and thus  "the projected future warming in CESM2, and models with a similarly high ECS, is thus likely too large."

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020GL091220?af=R

Quote
Zhu, J., Otto‐Bliesner, B. L., Brady, E. C., Poulsen, C. J., Tierney, J. E., Lofverstrom, M., & DiNezio, P. (2021). Assessment of equilibrium climate sensitivity of the Community Earth System Model version 2 through simulation of the Last Glacial Maximum. Geophysical Research Letters, 48, e2020GL091220. https://doi.org/10.1029/2020GL091220

 Abstract

The upper end of the equilibrium climate sensitivity (ECS) has increased substantially in the latest Coupled Model Intercomparison Projects phase 6 with eight models (as of this writing) reporting an ECS > 5°C. The Community Earth System Model version 2 (CESM2) is one such high‐ECS model. Here we perform paleoclimate simulations of the Last Glacial Maximum (LGM) using CESM2 to examine whether its high ECS is realistic. We find that the simulated LGM global mean temperature decrease exceeds 11°C, greater than both the cooling estimated from proxies and simulated by an earlier model version (CESM1). The large LGM cooling in CESM2 is attributed to a strong shortwave cloud feedback in the newest atmosphere model. Our results indicate that the high ECS of CESM2 is incompatible with LGM constraints and that the projected future warming in CESM2, and models with a similarly high ECS, is thus likely too large.


Quote
Model‐data comparison of the GMST response (ΔGMST) in the LGM simulations. The black line and the gray shading indicate the mean and the 95% confidence intervals respectively for the proxy estimates compiled by Tierney et al. (2020b). GMST, global mean surface temperature; LGM, Last Glacial Maximum.

Quote
The [SW cld feedback factor] in LGM simulations is closely connected to that in abrupt 4×CO2 simulations, which largely determines intermodel differences in ECS under the present‐day climate (Bacmeister et al., 2020; Gettelman et al., 2019). Compared to CESM1, CESM2 global mean [SW cld feedback factor] is larger by ∼0.4 W m‒2 K‒1 in both the LGM and 4×CO2 simulations (Table 1). For both simulations, the intermodel difference in [SW cld feedback factor] is most prominent over the Southern Ocean and the Southern Hemisphere subtropics (red vs. blue lines in Figure 3e), likely reflecting a Southern Ocean origin of the different model behavior (Bacmeister et al., 2020) that impacts the lower latitudes through ocean and atmosphere processes (Zhu & Poulsen, 2020a). These results suggest that the cloud processes that give rise to the higher ECS in CESM2 (in the 4×CO2 simulation) act in a similar way to produce the larger LGM cooling.


Quote
The shortwave cloud feedback (units: W m‒2 K‒1) in (a) CESM2 and (c) CESM1 LGM simulations. (b) and (d) As (a) and (c), but for the abrupt 4×CO2 simulations. (e) The zonal mean shortwave cloud feedback in each simulation. (f) Difference in the zonal mean shortwave cloud feedback between LGM and 4×CO2 simulations in CESM2 and CESM1.


Quote
5 Conclusions

In this study, we performed a CESM2 simulation of the LGM and found that the simulated global cooling exceeds ‒11°C, which is at least 5°C colder than the median of the latest proxy‐based estimates (Tierney et al., 2020b). LGM tropical mean ΔSST is ‒7°C in CESM2, which is also much colder than the proxy data estimate (‒2°C – ‒3°C). At individual proxy SST sites, CESM2 LGM is on average 4°C–5°C colder than the proxy. In comparison, global and regional cooling in CESM1 (predecessor to CESM2) is much smaller and agrees better with proxies. The larger LGM cooling in CESM2 is attributed to the new physical parameterizations in the atmosphere model (CAM6), which simulates a stronger shortwave cloud feedback than its predecessor (CAM5 in CESM1).

Quote
Our study suggests that the ECS in CESM2 is too high and closely related to the large model‐data discrepancy in the LGM cooling. This result indicates either that the shortwave cloud feedback in CESM2 is too strong or that current climate models are missing important physical processes that counter the shortwave cloud feedback and stabilize the climate. Whichever is true, the projected future warming using high‐ECS models, such as CESM2, is likely overestimated. This conclusion from constraints using a past cold climate is the same as our previous studies using past extreme warm climate of the Early Eocene (Zhu et al., 2019, 2020). Our findings are also consistent with independent studies, which show that the warming trends in high‐ECS models including CESM2 are too large than that in the instrumental record (Brunner et al., 2020; Nijsse et al., 2020; Tokarska et al., 2020). Here, we emphasize the unique strength of the paleoclimate constraint as a true “out‐of‐sample” test and its advantage of being independent on the transient climate change and internal variability.

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4135 on: February 11, 2021, 09:59:59 PM »
As most current ESMs (including most CMIP6 models) do not adequately account for potential upcoming significant freshwater hosing events, I believe that the first attached image (from the first linked website) is only relevant to current conditions.

Title: "Disequilibrium and the AMOC"

https://www.gfdl.noaa.gov/blog_held/64-disequilibrium-and-the-amoc/

Caption for the first image: "The strength of the Atlantic Meridional Overturning Circulation (AMOC) at 26N , in units of Sverdrups (106 m3/s), plotted against the ratio of the Transient Climate Response to the Equilibrium Climate Sensitivity (TCR/ECS) in a set of coupled atmosphere-ocean climate models developed at GFDL over the past 15 years.  Redrawn from Winton et al 2014. Also shown is the strength of  the AMOC as observed by the RAPID array at 26N,  from McCarthy et al 2015."

Next, I remind readers that the second linked reference finds that part of the E3SM version 1 projected high value of TCR of 2.93C (see the second attached image) is due to its projected slowing of the AMOC; and that E3SMv1 projected an ECS value of 5.3C; which gives a TCR/ECS ratio of 0.553; which is close to the TCR/ECS ratio given in the first image for the AMOC mass flux measured by RAPID.  In my opinion this provides some substantiation of the E3SMv1 projections.

Aixue Hu et al. (17 April 2020), "Role of AMOC in transient climate response to greenhouse gas forcing in two coupled models", Journal of Climate, https://doi.org/10.1175/JCLI-D-19-1027.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-19-1027.1?af=R

Abstract
As the greenhouse gas concentrations increase, a warmer climate is expected. However, numerous internal climate processes can modulate the primary radiative warming response of the climate system to rising greenhouse gas forcing. Here the particular internal climate process that we focus on is the Atlantic Meridional Overturning Circulation (AMOC) – an important global scale feature of ocean circulation that serves to transport heat and other scalars, and we address the question of how the mean strength of AMOC can modulate the transient climate response. While the Community Earth System Model version 2 (CESM2) and the Energy Exascale Earth System Model version 1 (E3SM1) have very similar equilibrium/effective climate sensitivity, our analysis suggests that a weaker AMOC contributes in part to the higher transient climate response to a rising greenhouse gas forcing seen in E3SM1 by permitting a faster warming of the upper ocean and a concomitant slower warming of the subsurface ocean. Likewise the stronger AMOC in CESM2 by permitting a slower warming of the upper ocean leads in part to a smaller transient climate response. Thus, while the mean strength of AMOC does not affect the equilibrium/effective climate sensitivity, it is likely to play an important role in determining the transient climate response on the centennial timescale.

Edit: As Hu et al. (2020) indicates that TCR (but not ECS) increases when the AMOC slows due to freshwater hosing.  Thus, the first image indicates that if the AMOC were to slow due to future freshwater hosing events that TCR would likely increase relatively rapidly.

This is just a reminder that:

First, the E3SMv1 (a member of the CMIP6 Wolf Pack) hind-castes accurately matched the measured AMOC values and

Second, that Hu et al. (2020) states:

"While the Community Earth System Model version 2 (CESM2) and the Energy Exascale Earth System Model version 1 (E3SM1) have very similar equilibrium/effective climate sensitivity, our analysis suggests that a weaker AMOC contributes in part to the higher transient climate response to a rising greenhouse gas forcing seen in E3SM1 by permitting a faster warming of the upper ocean and a concomitant slower warming of the subsurface ocean."

Thus, Hu et al (2020) indicates that CESM2 ignores the influence of freshwater hosing on climate sensitivity; while E3SMv1 finding that freshwater hosing events make a significant contribute to climate sensitivity and cannot be ignored.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4136 on: February 14, 2021, 05:36:26 PM »
The linked research indicates that the recovery of the Antarctic Ozone Holes contributes to relatively high Antarctic sea ice extents.  As Antarctic sea ice extent is one of the mechanisms contributing to positive ice-climate feedback, this research increases the calculated probability of an ice apocalypse.

Xia, Y., Hu, Y., Liu, J. et al. Stratospheric Ozone-induced Cloud Radiative Effects on Antarctic Sea Ice. Adv. Atmos. Sci. 37, 505–514 (2020). https://doi.org/10.1007/s00376-019-8251-6

https://link.springer.com/article/10.1007/s00376-019-8251-6

Abstract: "Recent studies demonstrate that the Antarctic Ozone Hole has important influences on Antarctic sea ice. While most of these works have focused on effects associated with atmospheric and oceanic dynamic processes caused by stratospheric ozone changes, here we show that stratospheric ozone-induced cloud radiative effects also play important roles in causing changes in Antarctic sea ice. Our simulations demonstrate that the recovery of the Antarctic Ozone Hole causes decreases in clouds over Southern Hemisphere (SH) high latitudes and increases in clouds over the SH extratropics. The decrease in clouds leads to a reduction in downward infrared radiation, especially in austral autumn. This results in cooling of the Southern Ocean surface and increasing Antarctic sea ice. Surface cooling also involves ice-albedo feedback. Increasing sea ice reflects solar radiation and causes further cooling and more increases in Antarctic sea ice."
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Tom_Mazanec

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4137 on: February 14, 2021, 05:40:38 PM »
AbruptSLR:
How does more ice in the Southern Ocean mean global warming is worse?
SHARKS (CROSSED OUT) MONGEESE (SIC) WITH FRICKIN LASER BEAMS ATTACHED TO THEIR HEADS

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4138 on: February 18, 2021, 04:28:34 PM »
The linked reference provides a conceptual model that indicates that with continued global warming the MOC could abruptly slowdown due to oceanic mechanisms in both polar regions. Also, note that: meteoric freshwater flux is that from precipitation minus evaporation, river runoff, oceanic glacial ice melt and iceberg calving, that PO = Polar Water and that OW = Overflow Water.

Haine, T.W.N. (2021), "A Conceptual Model of Polar Overturning Circulations", Journal of Physical Oceanography, DOI: https://doi.org/10.1175/JPO-D-20-0139.1

https://journals.ametsoc.org/view/journals/phoc/51/3/JPO-D-20-0139.1.xml

Abstract: "The global ocean overturning circulation carries warm, salty water to high latitudes, both in the Arctic and Antarctic. Interaction with the atmosphere transforms this inflow into three distinct products: sea ice, surface Polar Water, and deep Overflow Water. The Polar Water and Overflow Water form estuarine and thermal overturning cells, stratified by salinity and temperature, respectively. A conceptual model specifies the characteristics of these water masses and cells given the inflow and air–sea–land fluxes of heat and freshwater. The model includes budgets of mass, salt, and heat, and parameterizations of Polar Water and Overflow Water formation, which include exchange with continental shelves. Model solutions are mainly controlled by a linear combination of air–sea–ice heat and freshwater fluxes and inflow heat flux that approximates the meteoric freshwater flux plus the sea ice export flux. The model shows that for the Arctic, the thermal overturning is likely robust, but the estuarine cell appears vulnerable to collapse via a so-called heat crisis that violates the budget equations. The system is pushed toward this crisis by increasing Atlantic Water inflow heat flux, increasing meteoric freshwater flux, and/or decreasing heat loss to the atmosphere. The Antarctic appears close to a so-called Overflow Water emergency with weak constraints on the strengths of the estuarine and thermal cells, uncertain sensitivity to parameters, and possibility of collapse of the thermal cell."

Extract: "
•   For the Arctic, specifically the transfer across the Fram Strait and Barents Sea Opening, the real system appears vulnerable to heat crisis (Fig. 10a). The estuarine cell vanishes for increased meteoric freshwater flux to the ocean, or increased AW heat flux, or decreased ocean heat loss flux. The first two factors are anticipated under global warming (Rawlins et al. 2010; Vavrus et al. 2012; Collins et al. 2013), pushing the Arctic closer to heat crisis and collapse of the estuarine cell. This may relate to Arctic Ocean “Atlantification” (Polyakov et al. 2017).

•   For the Antarctic, the real system appears close to OW emergency (Fig. 10b) with weak constraints on the strengths of the estuarine and thermal cells, although most solutions show a stronger estuarine cell. This result suggests that the Antarctic system is more susceptible to unforced variations than the Arctic. The sensitivity of the Antarctic solutions to changes in flux parameters is unclear because the system appears close to switching between strong and weak shelf circulation modes. Loss of parts of the estuarine cell may relate to loss of sea ice and PW in Weddell Sea polynyas (Comiso and Gordon 1987; Gordon 2014). Such offshore polynyas are linked to climate variations that are projected to strengthen with anthropogenic climate change (Campbell et al. 2019). Loss of the thermal cell may relate to loss of AABW formation due to increased land ice melt in future climate projections (Lago and England 2019). Warming CDW (Smedsrud 2005) pushes the Antarctic system toward the entrainment-dominated solution with warm OW and weak shelf circulation (Fig. 10a).

The most important lessons from this conceptual polar overturning model are probably these: The model Arctic regime is being driven toward heat crisis and collapse of the estuarine overturning cell by flux changes associated with anthropogenic climate change. Approaching the heat crisis, entrainment and shelf salinity are high, shelf circulation is weak, and variability in OW flux and temperature is small. Sea ice does not disappear prior to the heat crisis. The model Antarctic regime shows large intrinsic variability between OW and PW fluxes and between strong and weak shelf circulations. The magnitude and sign of the sensitivity to changes in ocean heat loss, freshwater gain, and CDW heat flux are uncertain. But sensitivity is weak to changes due to oceanic melting of glacial ice."

Caption for the attached image: "Schematics of the four main solution modes: (a) heat crisis for small Q (like experiment 1), (b) OW emergency for intermediate Q (like experiment 6 and the middle of experiment 3), (c) salt crisis for large Q (like experiment 2), and (d) entrainment emergency for fresh PW and/or aW (like the small PW salinity end of experiment 5). These main solutions are determined by the forcing, indicated by the ocean heat loss flux Q (Figs. 6 and 8), and by the aW salinity (Fig. S2). See also Fig. S3."

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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4139 on: February 18, 2021, 04:34:46 PM »
AbruptSLR:
How does more ice in the Southern Ocean mean global warming is worse?

Tom,

More sea ice extent in the Southern Ocean means both that the MOC radiates less heat to the atmosphere at high latitudes and that more warm CDW is directed towards oceanic melting of marine glacial ice (both for ice shelves and at the grounding line) as indicated by the three attached images.  Also, see my last post about Haine (2021)'s research.

Edit: I note that an associated abrupt slowdown of the MOC in coming decades would increase ECS and thus contribute to more warming for the GHG in the atmosphere.
« Last Edit: February 18, 2021, 04:49:13 PM by AbruptSLR »
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4140 on: February 18, 2021, 05:04:41 PM »
The linked reference confirms that CMIP6 models that include interactive ozone chemistry modules have better skill at forecasting SAM behavior than do 'no-chemistry' models; and I note that all of the Wolf Pack CMIP6 models include interactive ozone chemistry modules.  This is an important modeling issue for forecasting the telecommunication of equatorial heat to southern high latitudes (particularly from the Tropical Pacific to Western Antarctica).

Morgenstern, O. (08 February 2021), "The Southern Annular Mode in 6th Coupled Model Intercomparison Project models", JGR Atmospheres, https://doi.org/10.1029/2020JD034161


https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020JD034161?af=R

Abstract
I analyze trends in the Southern Annular Mode in CMIP6 simulations. For the period 1957‐2014, simulated linear trends are generally consistent with two observational references but seasonally in disagreement with two other reconstructions of the SAM. Using a regression analysis applied to model simulations with interactive ozone chemistry, a strengthening of the SAM in summer is attributed nearly completely to ozone depletion because a further strengthening influence due to long‐lived greenhouse gases is almost fully counterbalanced by a weakening influence due to stratospheric ozone increases associated with these greenhouse gas increases. Ignoring such ozone feedbacks would yield comparable contributions from these two influences, an incorrect result. In winter, trends are smaller but an influence of greenhouse gas‐mediated ozone feedbacks is also identified. The regression analysis furthermore yields significant differences in the attribution of SAM changes to the two influences between models with and without interactive ozone chemistry, with ozone depletion and GHG increases playing seasonally a stronger and weaker, respectively, role in the chemistry models versus the no‐chemistry ones.

Plain Language Summary
The Southern Annular Mode consists of a see‐saw of atmospheric mass between southern middle and high latitudes. It is subject to human influences due to ozone loss (esp. the ozone hole) and global warming. Here I show, using a regression analysis performed on simulations recently produced by present‐generation climate models, that the ozone loss influence is dominant in summer because the influence of global warming is largely offset by the impact on the mode of stratospheric mid‐ and high‐latitude ozone increases caused by greenhouse gas increases, causing a weakening. Models simulating ozone as part of chemistry schemes on average show a larger influence on the mode due to ozone loss and a smaller influence of greenhouse gases than models that prescribe ozone. The results suggest that only relying on such "no‐chemistry" models for the attribution of trends in the mode can lead to incorrect results.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4141 on: February 18, 2021, 05:52:54 PM »
The linked reference provides paleo-data that indicates that Ross Sea sea ice and the Ross Ice Shelf (RIS) may be susceptible to rapid ice retreat during warming conditions.

Yan, Y., Spaulding, N. E., Bender, M. L., Brook, E. J., Higgins, J. A., Kurbatov, A. V., and Mayewski, P. A.: Enhanced Moisture Delivery into Victoria Land, East Antarctica During the Early Last Interglacial: Implications for West Antarctic Ice Sheet Stability, Clim. Past Discuss. [preprint], https://doi.org/10.5194/cp-2021-7, in review, 2021.

https://cp.copernicus.org/preprints/cp-2021-7/

Abstract. The S27 ice core, drilled in the Allan Hills Blue Ice Area of East Antarctica, is located in Southern Victoria Land ~80 km away from the present-day northern edge of the Ross Ice Shelf. Here, we utilize the reconstructed accumulation rate of S27 covering the Last Interglacial (LIG) period between 129 and 116 thousand years before present (ka) to infer moisture transport into the region. The accumulation rate is based on the ice age-gas age differences calculated from the ice chronology, which is constrained by the stable water isotopes of the ice, and an improved gas chronology based on measurements of oxygen isotopes of O2 in the trapped gases. The peak accumulation rate in S27 occurred at 128.2 ka, near the peak LIG warming in Antarctica. Even the most conservative estimate yields a six-fold increase in the accumulation rate in the LIG, whereas other Antarctic ice cores are typically characterized by a glacial-interglacial difference of a factor of two to three. While part of the increase in S27 accumulation rates must originate from changes in the large-scale atmospheric circulation, additional mechanisms are needed to explain the large changes. We hypothesize that the exceptionally high snow accumulation recorded in S27 reflects open-ocean conditions in the Ross Sea, created by reduced sea ice extent and increased polynya size, and perhaps by a southward retreat of the Ross Ice Shelf relative to its present-day position near the onset of LIG. The proposed ice shelf retreat would also be compatible with a sea-level high stand around 129 ka significantly sourced from West Antarctica. The peak in S27 accumulation rates is transient, suggesting that if the Ross Ice Shelf had indeed retreated during the early LIG, it would have re-advanced by 125 ka.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4142 on: February 18, 2021, 11:15:14 PM »
I have previously posted about the last flipping of the Earth's magnetic poles some 42kya during the Laschamps Excursion; however, the linked reference provides evidence that this geomagnetic reversal, combined '… with Grand Solar Minima, caused substantial changes in atmospheric ozone concentrations and circulation, driving synchronous global climate shifts that caused major environmental changes, extinction events, and transformations in the archaeological record.'

I note that if abrupt ice mass loss in coming decades were to trigger another geomagnetic reversal this century, then this would likely contribute to greater climate changes than currently projected by consensus climate science (CCS).

Cooper, A. et al. (19 Feb 2021), "A global environmental crisis 42,000 years ago", Science, Vol. 371, Issue 6531, pp. 811-818, DOI: 10.1126/science.abb8677

https://science.sciencemag.org/content/371/6531/811

Abstract
Geological archives record multiple reversals of Earth’s magnetic poles, but the global impacts of these events, if any, remain unclear. Uncertain radiocarbon calibration has limited investigation of the potential effects of the last major magnetic inversion, known as the Laschamps Excursion [41 to 42 thousand years ago (ka)]. We use ancient New Zealand kauri trees (Agathis australis) to develop a detailed record of atmospheric radiocarbon levels across the Laschamps Excursion. We precisely characterize the geomagnetic reversal and perform global chemistry-climate modeling and detailed radiocarbon dating of paleoenvironmental records to investigate impacts. We find that geomagnetic field minima ~42 ka, in combination with Grand Solar Minima, caused substantial changes in atmospheric ozone concentration and circulation, driving synchronous global climate shifts that caused major environmental changes, extinction events, and transformations in the archaeological record.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #4143 on: February 18, 2021, 11:31:15 PM »
For those who doubt that the Earth's geomagnetic field can reverse at a very rapid rate, consider that during the Laschamp event (or Laschamps event for purists) the magnetic polarity flipped twice in only 250 years, or about 125 years per flip.

Title: "An extremely brief reversal of the geomagnetic field, climate variability and a super volcano"

https://phys.org/news/2012-10-extremely-reversal-geomagnetic-field-climate.html

Extract: "41,000 years ago, a complete and rapid reversal of the geomagnetic field occurred.

What is remarkable is the speed of the reversal: "The field geometry of reversed polarity, with field lines pointing into the opposite direction when compared to today's configuration, lasted for only about 440 years, and it was associated with a field strength that was only one quarter of today's field," explains Norbert Nowaczyk. "The actual polarity changes lasted only 250 years.

Besides giving evidence for a geomagnetic field reversal 41,000 years ago, the geoscientists from Potsdam discovered numerous abrupt climate changes during the last ice age in the analysed cores from the Black Sea, as it was already known from the Greenland ice cores. This ultimately allowed a high precision synchronisation of the two data records from the Black Sea and Greenland. The largest volcanic eruption on the Northern hemisphere in the past 100 000 years, namely the eruption of the super volcano 39400 years ago in the area of today's Phlegraean Fields near Naples, Italy, is also documented within the studied sediments from the Black Sea. The ashes of this eruption, during which about 350 cubic kilometers of rock and lava were ejected, were distributed over the entire eastern Mediterranean and up to central Russia. These three extreme scenarios, a short and fast reversal of the Earth's magnetic field, short-term climate variability of the last ice age and the volcanic eruption in Italy, have been investigated for the first time in a single geological archive and placed in precise chronological order."

For those who do not remember, during the Laschamps Excursion the magnetic pole flipped twice in 250 years, or 125 years per flip.  So if the WAIS were to sustain a MICI-type of collapse beginning say in 2035, and if the associated abrupt SLR were to trigger another geomagnetic reversal, then shortly after say 2100 the atmospheric ozone concentrations could be sharply decreased.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« Reply #4144 on: February 19, 2021, 05:53:53 AM »
Re: abrupt SLR were to trigger another geomagnetic reversal

do tell ...

sidd

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #4145 on: February 19, 2021, 03:37:28 PM »
As sidd has questions about why abrupt sea level rise from ice mass loss might increase the risks of flipping the Earth's magnetic poles, I am reposting the following from the 'Adapting to the Anthropocene' thread:

"In my opinion, a collapse of the WAIS this century would likely accelerate schedule for the long overdue flipping of the Earth's magnetic poles.  So I hope people prepare accordingly:

Title: "Earth's Magnetic Poles Are Overdue For a Switch And We're Not Prepared"

https://www.sciencealert.com/earth-magnetic-poles-reversal-switch-overdue-turbulent

Extract: "Within the last 20 million years, Earth has fallen into the pattern of pole reversal every 200,000 to 300,000 years, and between successful swaps, the poles sometimes even attempt to reverse and then snap back into place.

About 40,000 years ago, the poles made one such unsuccessful attempt, and the last full swap was about 780,000 years ago, so we're a bit overdue for a pole reversal based on the established pattern.

The planet's magnetic field is already shifting, which could signify the poles are preparing to flip, and while we can't yet confirm that a reversal is on the near horizon, it is well within the realm of possibility.

To try to determine whether or not a flip is imminent, scientists have begun using satellite imagery and complex calculations to study the shifting of the magnetic field.

They've found that molten iron and nickel are draining energy from the dipole at the edge of the Earth's core, which is where the planet's magnetic field is generated.

They also found that the north magnetic pole is especially turbulent and unpredictable. If the magnetic blocks become strong enough to sufficiently weaken the dipole, the poles will officially switch.

Again, while it is not a certainty that the switch will happen soon, this activity at the Earth's core suggests that it is possible in the near future.""
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #4146 on: February 19, 2021, 03:38:14 PM »
Here is another repost regarding possible increased risks of flipping the Earth's magnetic poles


": sidd  Today at 02:26:20 AM

"In my opinion, a collapse of the WAIS this century would likely accelerate schedule for the long overdue flipping of the Earth's magnetic poles. "

Interesting. What leads you to this opinion ? Do tell.

sidd




Here is some background references:


1. Adam C. Maloof Galen P. Halverson Joseph L. Kirschvink Daniel P. Schrag Benjamin P. Weiss Paul F. Hoffman (2006), "Combined paleomagnetic, isotopic, and stratigraphic evidence for true polar wander from the Neoproterozoic Akademikerbreen Group, Svalbard, Norway",  GSA Bulletin, 118 (9-10): 1099-1124, DOI: https://doi.org/10.1130/B25892.1

https://pubs.geoscienceworld.org/gsa/gsabulletin/article-abstract/118/9-10/1099/125331/combined-paleomagnetic-isotopic-and-stratigraphic?redirectedFrom=fulltext

Abstract: "We present new paleomagnetic data from three Middle Neoproterozoic carbonate units of East Svalbard, Norway. The paleomagnetic record is gleaned from 50 to 650 m of continuous, platformal carbonate sediment, is reproduced at three locations distributed over >100 km on a single craton, and scores a 5–6 (out of 7) on the Van der Voo (1990) reliability scale. Two >50° shifts in paleomagnetic direction are coincident with equally abrupt shifts in δ13C and transient changes in relative sea level. We explore four possible explanations for these coincidental changes: rapid plate tectonic rotation during depositional hiatus, magnetic excursions, nongeocentric axial-dipole fields, and true polar wander. We conclude that the observations are explained most readily by rapid shifts in paleogeography associated with a pair of true polar wander events. Future work in sediments of equivalent age from other basins can test directly the true polar wander hypothesis because this type of event would affect every continent in a predictable manner, depending on the continent's changing position relative to Earth's spin axis."

2. J. R. Creveling, J. X. Mitrovica, N.-H. Chan, K. Latychev & I. Matsuyama (08 November 2012), "Mechanisms for oscillatory true polar wander", Nature, volume 491, pages 244–248,
doi:10.1038/nature11571

http://www.nature.com/articles/nature11571

Abstract: "Palaeomagnetic studies of Palaeoproterozoic to Cretaceous rocks propose a suite of large and relatively rapid (tens of degrees over 10 to 100 million years) excursions of the rotation pole relative to the surface geography, or true polar wander (TPW). These excursions may be linked in an oscillatory, approximately coaxial succession about the centre of the contemporaneous supercontinent. Within the framework of a standard rotational theory, in which a delayed viscous adjustment of the rotational bulge acts to stabilize the rotation axis, geodynamic models for oscillatory TPW generally appeal to consecutive, opposite loading phases of comparable magnitude. Here we extend a nonlinear rotational stability theory to incorporate the stabilizing effect of TPW-induced elastic stresses in the lithosphere. We demonstrate that convectively driven inertia perturbations acting on a nearly prolate, non-hydrostatic Earth with an effective elastic lithospheric thickness of about 10 kilometres yield oscillatory TPW paths consistent with palaeomagnetic inferences. This estimate of elastic thickness can be reduced, even to zero, if the rotation axis is stabilized by long-term excess ellipticity in the plane of the TPW. We speculate that these sources of stabilization, acting on TPW driven by a time-varying mantle flow field, provide a mechanism for linking the distinct, oscillatory TPW events of the past few billion years."

3. To learn how much the North Pole has shifted in the recent decades due to rapid ice mass loss, see Chen, J..L., C.R. Wilson, J.C. Ries, B.D. Tapley, Rapid ice melting drives Earth's pole to the east, Geophys. Res. Lett., Vol. 40, 1-6, DOI: 10.1002/grl.50552, 2013; which can be found at the prime author's website at the University of Texas, where you can download a preprint (made available by the author):

http://www.csr.utexas.edu/personal/chen/publication.html

and here is a link directly to the preprint pdf:

ftp://ftp.csr.utexas.edu/pub/ggfc/papers/2013GL056164_preprint.pdf

"
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #4147 on: February 19, 2021, 03:38:53 PM »
Here is my last repost from the 'Adapting to the Anthropocene' thread about increased risk of flipping the Earth's magnetic pole due to abrupt sea level rise associated with abrupt ice mass loss this century:


": sidd  Today at 06:55:23 AM

Do you mean magnetic pole or rotational pole ? both the papers you cite talk about the rotational pole.

sidd




sidd,

I will move this line of discussion to the 'Ice Apocalypse' thread (see the link below) in the Antarctic folder as this topic was meant to be just a word of warning here.  However, my general point is that a some portion of the changes in the magnetic pole can be associated with changes in the rotational pole (the attached image illustrates how fast this is currently changing), due to changes in the magma flow associated with ice mass redistribution.  Furthermore, my point is that due to the current exceptionally high rate of anthropogenic forcing and the bipolar seesaw mechanism that possible abrupt changes in ice mass loss can make faster changes in tectonic behavior than observed in the paleorecord.

https://forum.arctic-sea-ice.net/index.php/topic,2205.50.html

ASLR"
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #4148 on: February 19, 2021, 03:44:23 PM »
As a follow on to my last series of re-posts about correlating true polar wander (shifting of the Earth's rotational axis) and magnetic field reversals and mass redistribution around the Earth; I provide the first linked reference that provides paleo evidence that during periods of little polar wander the is reduced activity of magnetic pole flipping; while the second linked article makes it clear that polar wander is associated with all mass (ice, sea level, groundwater, isostatic rebound) redistribution.  Also, Hansen's ice-climate feedback results in changes in precipitation patterns that will affect polar wander.

I recommend that scientists with the appropriate Earth models that include Earth's interior core-mantle-lithosphere mechanisms should assume some up-bound scenarios for possible future abrupt mass redistributions around the Earth (including: a WAIS ice mass collapse and associated isostatic rebound, increased rainfall at both poles; changes in groundwater distributions, etc.) and then see what happens to tectonic activity (including magnetic fields, volcanism and seismic activity):

Courtillot V & Besse J. (1987 Sep 4), "Magnetic field reversals, polar wander, and core-mantle coupling", Science vol 237, issue (4819), pp 1140-7, DOI:10.1126/science.237.4819.1140

http://science.sciencemag.org/content/237/4819/1140

Abstract: "True polar wander, the shifting of the entire mantle relative to the earth's spin axis, has been reanalyzed. Over the last 200 million years, true polar wander has been fast (approximately 5 centimeters per year) most of the time, except for a remarkable standstill from 170 to 110 million years ago. This standstill correlates with a decrease in the reversal frequency of the geomagnetic field and episodes of continental breakup. Conversely, true polar wander is high when reversal frequency increases. It is proposed that intermittent convection modulates the thickness of a thermal boundary layer at the base of the mantle and consequently the core-to-mantle heat flux. Emission of hot thermals from the boundary layer leads to increases in mantle convection and true polar wander. In conjunction, cold thermals released from a boundary layer at the top of the liquid core eventually lead to reversals. Changes in the locations of subduction zones may also affect true polar wander. Exceptional volcanism and mass extinctions at the Cretaceous-Tertiary and Permo-Triassic boundaries may be related to thermals released after two unusually long periods with no magnetic reversals. These environmental catastrophes may therefore be a consequence of thermal and chemical couplings in the earth's multilayer heat engine rather than have an extraterrestrial cause."

&

Title: "Climate Change Is Moving the North Pole"

https://news.nationalgeographic.com/2016/04/160408-climate-change-shifts-earth-poles-water-loss/

Extract: "As ice melts and aquifers are drained, Earth's distribution of mass is changing—and with it the position of the planet's spin axis."


Edit, also see which indicates that about 66% of the polar wander over the indicated period was due to rapid changes in ice mass loss:

Surendra Adhikari and Erik R. Ivins (08 Apr 2016), "Climate-driven polar motion: 2003–2015", Science Advances, Vol. 2, no. 4, e1501693, DOI: 10.1126/sciadv.1501693

http://advances.sciencemag.org/content/2/4/e1501693

Abstract: "Earth’s spin axis has been wandering along the Greenwich meridian since about 2000, representing a 75° eastward shift from its long-term drift direction. The past 115 years have seen unequivocal evidence for a quasi-decadal periodicity, and these motions persist throughout the recent record of pole position, in spite of the new drift direction. We analyze space geodetic and satellite gravimetric data for the period 2003–2015 to show that all of the main features of polar motion are explained by global-scale continent-ocean mass transport. The changes in terrestrial water storage (TWS) and global cryosphere together explain nearly the entire amplitude (83 ± 23%) and mean directional shift (within 5.9° ± 7.6°) of the observed motion. We also find that the TWS variability fully explains the decadal-like changes in polar motion observed during the study period, thus offering a clue to resolving the long-standing quest for determining the origins of decadal oscillations. This newly discovered link between polar motion and global-scale TWS variability has broad implications for the study of past and future climate."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #4149 on: February 19, 2021, 03:46:31 PM »
While I am not a scientist, the fact that the linked reference associates climate change with a Cambrian true wander event and associated changes in the paleomagnetic data, indicates to me that qualified scientist should model what impacts that abrupt sea level rise this century would have on both Earth's rotational and magnetic axes:

Wen-Jun Jiao et al. (16 January 2018", "Paleomagnetism of a well-dated marine succession in South China: A possible Late Cambrian true polar wander (TPW)", Physics of the Earth and Planetary Interiors, https://doi.org/10.1016/j.pepi.2018.01.009

https://www.sciencedirect.com/science/article/pii/S0031920117301905

Abstract: "The Cambrian true polar wander (TPW) hypothesis remains controversial largely because of the uncertainties in the quality and/or fidelity of the paleomagnetic data as well as their chronological control. Testing the TPW hypothesis requires high-quality paleomagnetic data of sufficient spatial and temporal resolutions. Here, we present paleomagnetic results of a continuous Cambrian shallow marine succession from South China where available detailed biostratigraphy provides exceptional chronological constraints. Forty-three sites of paleomagnetic samples were collected from this limestone-dominated succession. Stepwise thermal demagnetization generally reveals three-component magnetizations. Low- and intermediate-temperature components can be cleaned by ∼330°C, and the high-temperature component (HTC) was isolated typically from ∼350 to ∼450°C. A positive fold test and the presence of reversed polarity in the strata, together with rock magnetic data as well as the scanning electron microscopic (SEM) and transmission electron microscopic (TEM) results, collectively suggest that the HTCs are likely primary. A directional shift of the HTCs occurs between the lower-middle Cambrian and the upper Cambrian strata in the succession and is tentatively interpreted to indicate a ∼57° polar wander from ∼500.5 to 494 Ma. Because the rate of polar wander is too fast to be a tectonic origin, this polar wander is interpreted to represent a Late Cambrian TPW. This TPW appears coeval with the Steptoean positive carbon isotope excursion (SPICE) and the major trilobite mass extinctions, suggesting a potential link between the TPW and the Late Cambrian biotic and climatic changes. Because the proposed TPW event is exceptionally well-dated, it should be testable through examination of other worldwide sections."
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