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sidd

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1750 on: October 22, 2019, 10:43:29 PM »
Re: vested interests

I do not think that Clerc et al. are in anyway manipulating their results. It seems to be quite straightforward analysis. That said, i remain unconvinced until i see evidence from the field. Currently we have ice cliffs over 100m. If and when significantly taller cliffs appear, i might revisit their paper.

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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1751 on: October 23, 2019, 09:02:02 AM »
Re: vested interests

I do not think that Clerc et al. are in anyway manipulating their results. It seems to be quite straightforward analysis. That said, i remain unconvinced until i see evidence from the field. Currently we have ice cliffs over 100m. If and when significantly taller cliffs appear, i might revisit their paper.

sidd

When thinking about 'vested interests' one has to ask oneself of the roller coast ride of sea level projections indicated by the two accompanying graphs by Grinsted (2014) for both RCP 4.5 and RCP 8.5, respectively; and one has to wonder how much of the wide fluctuations in projections is due to scientific uncertainty and how much is due to political pressure.

Title: "Comparison of sea level projections" by Grinsted, 2014

https://grinsted.github.io/2014/10/23/comparison-of-sea-level-projections/

Extract: "The IPCC FAR,SAR,TAR,AR4 have all been converted to RCP scenarios using conversion factors (see below). All projections have been regularized to 100 years using plain scaling."

Edit: I note that in order for consensus climate scientists to be truly transparent about their SLR projections they should acknowledge the 'deep uncertainty' associated with their glacial models (note that none of the indicated projections consider MICI mechanisms, as they were made prior to 2014).  Unfortunately, neither the general public nor decision makers deal well the risks associated the 'deep uncertainties' associated with the risk of abrupt SLR (just think about how James Hansen lost his job for warning/protesting about the dangers of scientific reticence and abrupt climate change).
« Last Edit: October 23, 2019, 05:19:27 PM by AbruptSLR »
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1752 on: October 23, 2019, 05:20:01 PM »
The linked reference provide one example of the type of Bayesian calibration that should be used more often to better quantify the right-tail (upper tail) risk for SLR; and possibly by of AR7 consensus climate scientists might be prepared to use such methodologies on local models focused on the 50-km wide Thwaites gateway and the subglacial cavities that have been observed to be growing there to be define the right-tail risk of an MICI-type of risk (as I have outlined in many of my recent posts in this thread):

I.J. Nias et al. (15 October 2019), "Assessing uncertainty in the dynamical ice response to ocean warming in the Amundsen Sea Embayment, West Antarctica" Geophysical Research Letters, https://doi.org/10.1029/2019GL084941

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL084941?af=R

Abstract: "Ice mass loss from the Amundsen Sea Embayment ice streams in West Antarctica is a major source of uncertainty in projections of future sea‐level rise. Physically‐based ice‐flow models rely on a number of parameters that represent unobservable quantities and processes, and accounting for uncertainty in these parameters can lead to a wide range of dynamic responses. Here we perform a Bayesian calibration of a perturbed‐parameter ensemble, in which we score each ensemble member on its ability to match the magnitude and broad spatial pattern of present‐day observations of ice sheet surface elevation change. We apply an idealized melt‐rate forcing to extend the most likely simulations forward to 2200. We find that diverging grounding‐line response between ensemble members drives an exaggeration in the upper tail of the distribution of sea level rise by 2200, demonstrating that extreme future outcomes cannot be excluded."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1753 on: October 23, 2019, 05:33:47 PM »
The linked reference provides an example (assuming MISI mechanisms) of how consensus climate scientists can better present the risks associated with 'deep uncertainty' and future rapid SLR with both decision makers and the general public.  Hopefully, by the time of AR7 (or AR8) consensus climate science can make such evaluations assuming the risks of MICI-types of mechanisms in the Amundsen Sea Embayment marine glaciers this century:

Robert E. Kopp et al. (16 October 2019), "Sea‐level science on the frontier of usability", Earth's Future, https://doi.org/10.1029/2018EF001145

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018EF001145?af=R
&
https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2018EF001145

Abstract
Sea‐level rise sits at the frontier of usable climate change research, because it involves natural and human systems with long lags, irreversible losses and deep uncertainty. For example, many of the measures to adapt to sea‐level rise involve infrastructure and land‐use decisions, which can have multigenerational lifetimes and will further influence responses in both natural and human systems. Thus sea‐level science has increasingly grappled with the implications of: (1) deep uncertainty in future climate system projections, particularly of human emissions and ice sheet dynamics; (2) the overlay of slow trends and high‐frequency variability (e.g., tides and storms) that give rise to many of the most relevant impacts; (3) the effects of changing sea level on the physical exposure and vulnerability of ecological and socioeconomic systems; and (4) the challenges of engaging stakeholder communities with the scientific process in a way that genuinely increases the utility of the science for adaptation decision‐making. Much fundamental climate system research remains to be done, but many of the most critical issues sit at the intersection of natural sciences, social sciences, engineering, decision science, and political economy. Addressing these issues demands a better understanding of the coupled interactions of mean and extreme sea levels, coastal geomorphology, economics, and migration; decision‐first approaches that identify and focus research upon those scientific uncertainties most relevant to concrete adaptation choices; and a political economy that allows usable science to become used science.

Plain language summary
The impacts of sea‐level rise pose growing threats to coastal communities, economies, and ecosystems, and decisions made today ‐‐ in areas like land‐use policies, coastal development, and infrastructure investment ‐‐ will affect exposure and vulnerability for generations to come. Thus the usability of sea‐level science is a pressing concern. Ensuring the usability of sea‐level science requires grappling with deep uncertainty in long‐term sea‐level projections, the relationship between long‐term trends and the impacts of short‐lived extreme events, and the ways in which the physical coast, as well as people and ecosystems along the coast, respond to increasingly frequent flooding. At the same time, it also requires more extensive and deliberate stakeholder engagement throughout the scientific process, as well as cognizance of the political economy of linking stakeholder‐engaged science to action. This AGU Centennial Paper examines the state of the relevant science and key challenges in achieving these objectives.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1754 on: October 23, 2019, 05:43:15 PM »
The linked reference warns that current consensus global climate model projections do not adequately consider the risks associated with the potential future rapid release of carbon from permafrost eroded by seawater.  Given how flat the Arctic coastal plains are, consider how much this risk increases if an MICI-type of collapse of the WAIS were to abruptly raise sea level in the Arctic Ocean:

G. Tanski et al. (15 October 2019), "Rapid CO2 release from eroding permafrost in seawater", Geophysical Research Letters, https://doi.org/10.1029/2019GL084303

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL084303?af=R

Abstract
Permafrost is thawing extensively due to climate warming. When permafrost thaws, previously frozen organic carbon (OC) is converted into carbon dioxide (CO2) or methane, leading to further warming. This process is included in models as gradual deepening of the seasonal non‐frozen layer. Yet, models neglect abrupt OC mobilization along rapidly eroding Arctic coastlines. We mimicked erosion in an experiment by incubating permafrost with seawater for an average Arctic open‐water season. We found that CO2 production from permafrost OC is as efficient in seawater as without. For each gram (dry‐weight) of eroding permafrost, up to 4.3 ± 1.0 mg CO2 will be released and 6.2 ± 1.2% of initial OC mineralized at 4°C. Our results indicate that potentially large amounts of CO2 are produced along eroding permafrost coastlines; onshore and within nearshore waters. We conclude that coastal erosion could play an important role in carbon cycling and the climate system.

Plain Language Summary
The permanently frozen soils of the Arctic, known as permafrost, store large amounts of organic carbon, which accumulated over millennia due to slow decomposition in the cold Arctic regions. With climate warming this frozen organic carbon reservoir thaws and microbes recycle it quickly into greenhouse gases, which in turn support further warming. A slow and continuous thaw is currently used in models to project future greenhouse gas release from permafrost. Yet, along the rapidly eroding coastlines of the Arctic Ocean, which make up 34% of the Earth's coastlines, whole stretches of the coast simply collapse, sink or slide into the ocean; including the previously frozen organic carbon. We simulated greenhouse gas release in response to coastline collapse in a laboratory experiment by simply mixing permafrost with seawater. We show that large amounts of carbon dioxide are being produced during the Arctic open‐water season. Our study indicates that eroding permafrost coasts in the Arctic are potentially a major source of carbon dioxide. With increasing loss of sea‐ice, longer open‐water seasons and exposure of coasts to waves, we highlight the importance of coastal erosion for potential carbon dioxide emissions.
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gerontocrat

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1755 on: October 23, 2019, 07:11:57 PM »
COASTAL EROSION, PERMAFROST, CO2 EMISSIONS

I cannot find a comprehensive survey of coastal erosion in the Arctic and its acceleration. Loads of articles about individual places, including evidence of erosion speeding up But the data does not seem to have been put together from the satellite images, maps etc that must exist.

But the linked article from the Siberian Times is a pretty good wake-up call. Most articles also suggest it is the length of the open water season in the shoreline seas that is the killer, not so much the longer wave fetch.

http://siberiantimes.com/other/others/news/n0753-vanishing-arctic-how-warming-climate-leaves-remote-permafrost-islands-on-the-precipice/

Here are a couple of graphs I made from NSIDC Area Data on Ice-Free days and Open Water percentages for the East Siberian Sea.

Things are bad now - add SLR, AGW and longer open water seasons ...... ?
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sidd

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1756 on: October 23, 2019, 09:51:32 PM »
My previous post contained an error. The sentence "Currently we have ice cliffs over 100m" should read "Currently we have no ice cliffs over 100m"

sidd

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1757 on: October 24, 2019, 01:20:22 AM »
My previous post contained an error. The sentence "Currently we have ice cliffs over 100m" should read "Currently we have no ice cliffs over 100m"

sidd

It is my opinion that there a no observed ice cliffs much over ~100m, in the modern record; however Parizek et al. (2019) do state: "The tallest ice cliffs, which extend roughly 100 m above sea level, calve only after ice-flow processes thin the ice to near flotation. Above some ice-cliff height limit, the stress state in ice will satisfy the material-failure criterion, resulting in faster brittle failure. New terrestrial radar data from Helheim Glacier, Greenland, suggest that taller subaerial cliffs are prone to failure by slumping, unloading submarine ice to allow buoyancy-driven full-thickness calving." Thus there is some chance that recent ice cliff heights above ~100m no longer exist because they recently slumped.

Nevertheless, if Thwaites gateway does have ice cliffs with heights above sea level of much over 100m, on a retrograde bed slope, in the coming decades (say due to a collapse of the Big Ear subglacial cavity), the associated ice cliff instability may propagate upstream so fast that we all regret it.

Byron R. Parizek et al. Ice-cliff failure via retrogressive slumping, Geology (2019). DOI: 10.1130/G45880.1

https://pubs.geoscienceworld.org/gsa/geology/article/569567/Icecliff-failure-via-retrogressive-slumping

Abstract
Retrogressive slumping could accelerate sea-level rise if ice-sheet retreat generates ice cliffs much taller than observed today. The tallest ice cliffs, which extend roughly 100 m above sea level, calve only after ice-flow processes thin the ice to near flotation. Above some ice-cliff height limit, the stress state in ice will satisfy the material-failure criterion, resulting in faster brittle failure. New terrestrial radar data from Helheim Glacier, Greenland, suggest that taller subaerial cliffs are prone to failure by slumping, unloading submarine ice to allow buoyancy-driven full-thickness calving. Full-Stokes diagnostic modeling shows that the threshold cliff height for slumping is likely slightly above 100 m in many cases, and roughly twice that (145–285 m) in mechanically competent ice under well-drained or low-melt conditions.

Edit: The attached annotated image from Parizek et al. (2019) seems to show an ice cliff that once was temporarily about 110m above sea level.
« Last Edit: October 24, 2019, 01:28:53 AM by AbruptSLR »
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sidd

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1758 on: October 24, 2019, 06:24:26 AM »
Re: if Thwaites gateway does have ice cliffs with heights above sea level of much over 100m, on a retrograde bed slope, in the coming decades

If and when Thwaites manifests cliffs of substantially over  hundred meter, then even on nonretrograde bed the cubic to fifth range of power dependence of discharge on height implies a truly monstrous discharge rate, comparable to at least MWP1B. And destabilizing Amundsen basin destabilizes all of WAIS  as Leverman shows.

That said, a great deal depends on human behaviour. We might get 2m SLR by 2100, but we should try an ensure we dont get to 10m in 2200.

sidd

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1759 on: October 24, 2019, 01:04:59 PM »
Yes, we should start thinking ahead to 2200.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1760 on: October 24, 2019, 05:24:54 PM »
Re: if Thwaites gateway does have ice cliffs with heights above sea level of much over 100m, on a retrograde bed slope, in the coming decades

If and when Thwaites manifests cliffs of substantially over  hundred meter, then even on nonretrograde bed the cubic to fifth range of power dependence of discharge on height implies a truly monstrous discharge rate, comparable to at least MWP1B. And destabilizing Amundsen basin destabilizes all of WAIS  as Leverman shows.

That said, a great deal depends on human behaviour. We might get 2m SLR by 2100, but we should try an ensure we dont get to 10m in 2200.

sidd

Not to beat a dead horse, but:

1) Parizek et al. (2019) demonstrate that slumping can occur with an ice cliff height (above sea level) just a little over 100m; which would produce icebergs with keel depths shallow enough to float out of the Thwaites gateway without getting pinned.
2) The first composite image shows that the southern extent of the 'Big Ear' subglacial cavity in the trough in the 50-km wide Thwaites gateway already extends upstream sufficiently to already be in a bed area with a retrograde slope.
3) The second attached image shows that without deep uncertainty we could reach a SLR of 2m by 2100, but with deep uncertainty we could approach 5m of SLR by 2100.
« Last Edit: October 24, 2019, 06:59:20 PM by AbruptSLR »
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1761 on: October 24, 2019, 05:44:36 PM »
More bad news, in that the Amazon rainforest could reach an irreversible tipping point within 2 years:

Title: "Amazon rainforest 'close to irreversible tipping point'"

https://www.theguardian.com/environment/2019/oct/23/amazon-rainforest-close-to-irreversible-tipping-point

Extract: "Forecast suggests rainforest could stop producing enough rain to sustain itself by 2021"
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1762 on: October 24, 2019, 11:57:33 PM »
The linked reference (& associate article) indicate that a local strengthening of the westerly winds on the eastern Antarctic Peninsula since the early 1700s has been thinning the ice shelves in this region for over 300 years; which could cause these regional ice shelves to collapse earlier than expected by current consensus science thinking.

W.A. Dickens et al. (2019), "Enhanced glacial discharge from the eastern Antarctic Peninsula since the 1700s associated with a positive Southern Annular Mode", Scientific Reports, DOI: 10.1038/s41598-019-50897-4

https://www.nature.com/articles/s41598-019-50897-4

Abstract: "The Antarctic Peninsula Ice Sheet is currently experiencing sustained and accelerating loss of ice. Determining when these changes were initiated and identifying the main drivers is hampered by the short instrumental record (1992 to present). Here we present a 6,250 year record of glacial discharge based on the oxygen isotope composition of diatoms (δ18Odiatom) from a marine core located at the north-eastern tip of the Antarctic Peninsula. We find that glacial discharge - sourced primarily from ice shelf and iceberg melting along the eastern Antarctic Peninsula – remained largely stable between ~6,250 to 1,620 cal. yr BP, with a slight increase in variability until ~720 cal. yr. BP. An increasing trend in glacial discharge occurs after 550 cal. yr BP (A.D. 1400), reaching levels unprecedented during the past 6,250 years after 244 cal. yr BP (A.D. 1706). A marked acceleration in the rate of glacial discharge is also observed in the early part of twentieth century (after A.D. 1912). Enhanced glacial discharge, particularly after the 1700s is linked to a positive Southern Annular Mode (SAM). We argue that a positive SAM drove stronger westerly winds, atmospheric warming and surface ablation on the eastern Antarctic Peninsula whilst simultaneously entraining more warm water into the Weddell Gyre, potentially increasing melting on the undersides of ice shelves. A possible implication of our data is that ice shelves in this region have been thinning for at least ~300 years, potentially predisposing them to collapse under intensified anthropogenic warming."

Extract: "Models predict further poleward intensification of the westerlies and continued greenhouse warming around Antarctica. Given the sensitivity of the APIS (and Antarctic Ice Sheet more generally) to variations in the westerlies, it is likely that mass loss will continue to accelerate through the mid-late twenty first-century, raising global sea-level, impacting marine ecosystems and potentially leading to meltwater-induced sub-surface ocean warming which has the potential to drive even greater melting underneath ice shelves."

See also:

Title: "300-year thinning may have predisposed Antarctic ice shelves to collapse"

https://phys.org/news/2019-10-year-thinning-predisposed-antarctic-ice.html

Extract: "To investigate past drivers of ice mass loss and its effect on the present, William Dickens and colleagues constructed a 6,250 year record of glacial meltwater discharge by analysing oxygen variants (isotopes) in single-celled algae preserved within a marine sediment core from the northeastern tip of the Antarctic Peninsula. Lower isotope values correspond to higher glacial discharge of fresh water.

The authors found that an increasing trend in glacial discharge occurred after the year 1400 reaching unprecedented levels after 1706. Another marked acceleration in glacial melting was observed after 1912. The findings suggest that ice shelves in this region have been thinning at an accelerating rate for approximately 300 years, which may predispose them to collapse as anthropogenic warming intensifies."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1763 on: October 25, 2019, 03:37:23 PM »
Yes, we should start thinking ahead to 2200.

As I have time I will try to provide more information about GIS and EAIS risks for 2200, and here I start by noting that AR5 SLR projections did not consider the fact that Totten Glacier sits on top of a network of subglacial lakes that could accelerate its rate of ice mass loss raising the possibility that by 2200 Totten may contribute up to 7m to SLR by itself:

Title: "A Network of Lakes Lies Under East Antarctica’s Biggest Glacier", March 2019

https://www.smithsonianmag.com/smart-news/network-lakes-lies-under-east-antarcticas-biggest-glacier-180971813/

Extract: "The water underneath the Totten Glacier may force researchers to recalculate how quickly climate change may melt the massive ice sheet

How quickly the Totten moves toward the sea has huge global implications. While the Intergovernmental Panel on Climate Change's average projection is for the planet’s oceans to rise about a half meter by the end of this century, the calculations didn’t take into consideration the lake district sitting under Totten and could force researchers to update that estimate.

“If I took all the ice contained in the [Totten Glacier] catchment, spread it out over the global oceans, sea levels would go up seven meters [23 feet],” Galton-Fenzi tells Hayes. “We actually know for a fact that the Totten Glacier is one of the regions that's actually changing. We know there's warm water present under the glacier, so we expect this is one of the regions in east Antarctica that's going to change first.”"
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1764 on: October 25, 2019, 04:29:20 PM »
While marine terminating glaciers in Southern Greenland, such as Jakobshavn, present a significant concern for participating in a bipolar seesaw interaction with Antarctica; however, by 2200 there is significant concern about marine terminating glaciers in Northern Greenland such as 79N and Zachariae Isstrom.  Currently, the deep uncertainty associated with SLR contributions from North Greenland is currently being evaluated as cited by the linked articles:

Title: "Shelf-Basin Exchange near 79N Glacier and Zachariae Isstrom, North-East Greenland"

https://www.isaaffik.org/shelf-basin-exchange-near-79n-glacier-and-zachariae-isstrom-north-east-greenland

Extract: "The objectives of this RAPID project are to deploy an array of five moored ocean current, salinity, temperature, and two subsurface pressure sensors across the 200-400 m deep Norske Ore Trough in the summer of 2014 from aboard the R/V Polarstern, a German research icebreaker. The array will observe the circulation within this channel system at dynamically relevant time and space scales. Ultimately, the recovered data will be used to test the hypothesis that a clock-wise shelf circulation off north-east Greenland between 76N and 82N latitude provides warm Atlantic waters towards one of the last remaining stable floating ice-shelves in Greenland (Niog-halvfjerdsfjorden Gletscher called 79N Glacier) via a 20-40 km wide system of troughs. Degradation of the Greenland and Antarctic Ice Sheets is a major contributor to global sea level rise. One cause of the accelerating degradation of these ice sheets is believed to be the transport of heat from the continental slope to the face of tidewater glaciers. Models and qualitative arguments suggest that this transport is enhanced by cross-shelf channels that minimize mixing of the transported waters with cold, ambient shelf waters."

See also:

Title: "How oceans interact with Greenland’s last floating glaciers"

https://icyseas.org/2019/09/30/how-oceans-interact-with-greenlands-last-floating-glaciers/

« Last Edit: October 25, 2019, 05:47:05 PM by AbruptSLR »
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1765 on: October 25, 2019, 06:02:47 PM »
While marine terminating glaciers in Southern Greenland, such as Jakobshavn, present a significant concern for participating in a bipolar seesaw interaction with Antarctica; ...
...

I re-post the two attached images to remind readers that for the past several years that the height of the calving face of Jakobshavn Glacier above sea level has remained roughly below 100m high largely because the retreat of the grounding line up the indicate prograde bed slope has been slow enough to allow the thickness of the calving face to thin sufficiently as the ice flows forward; however, should future pulses of warm ocean water allow the calving face to retreat to the indicated retrograde bed slope, say in the coming decade, this would likely provide both a real-world case of an ice cliff height significantly greater than 100m and also might slow the MOC (via associated freshening of the North Atlantic surface waters) sufficiently to trigger an acceleration of marine glacial ice mass from the Antarctic Peninsula (via the bipolar seesaw); which might then accelerate ice mass loss from other key Antarctic marine glaciers via several other positive ice-climate feedback mechanisms.

Edit: Also, if a sufficient amount of marine glacial ice mass is lost from the WAIS to contribute multiple meters to SLR by 2100, then the associated bipolar seesaw feedback could serve to trigger multiple meters of additional SLR contribution from Northern Greenland, and/or the EAIS, by 2200
« Last Edit: October 25, 2019, 06:31:22 PM by AbruptSLR »
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1766 on: October 25, 2019, 07:58:07 PM »
Any tea leaves for 2300?
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1767 on: October 25, 2019, 10:37:43 PM »
Any tea leaves for 2300?

Personally, I do not expect SLR to exceed 8m by 2200 nor 9m by 2300, because I suspect that there will be a major global socio-economic contraction in the 2050 to 2070 timeframe.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1768 on: October 26, 2019, 02:43:25 AM »
While one cannot directly compare the Eocene with modern climate conditions; nevertheless, the linked reference indicates that for modern conditions that ECS is 4.2C, and that ECS increases as the Earth warms, primarily due to cloud feedback mechanisms, so who knows what the effective ECS will be by 2100:

Jiang Zhu, Christopher J. Poulsen and Jessica E. Tierney (18 Sep 2019), "Simulation of Eocene extreme warmth and high climate sensitivity through cloud feedbacks", Science Advances, Vol. 5, no. 9, eaax1874, DOI: 10.1126/sciadv.aax1874

https://advances.sciencemag.org/content/5/9/eaax1874

Abstract
The Early Eocene, a period of elevated atmospheric CO2 (>1000 ppmv), is considered an analog for future climate. Previous modeling attempts have been unable to reproduce major features of Eocene climate indicated by proxy data without substantial modification to the model physics. Here, we present simulations using a state-of-the-art climate model forced by proxy-estimated CO2 levels that capture the extreme surface warmth and reduced latitudinal temperature gradient of the Early Eocene and the warming of the Paleocene-Eocene Thermal Maximum. Our simulations exhibit increasing equilibrium climate sensitivity with warming and suggest an Eocene sensitivity of more than 6.6°C, much greater than the present-day value (4.2°C). This higher climate sensitivity is mainly attributable to the shortwave cloud feedback, which is linked primarily to cloud microphysical processes. Our findings highlight the role of small-scale cloud processes in determining large-scale climate changes and suggest a potential increase in climate sensitivity with future warming
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1769 on: October 26, 2019, 07:35:27 AM »
   The real reason some scientists downplay the risks of climate change
   by Dale Jamieson, Michael Oppenheimer and Naomi Oreskes

  Climate deniers often accuse scientists of exaggerating the threats associated with the climate crisis, but if anything they’re often too conservative

https://www.theguardian.com/commentisfree/2019/oct/25/the-real-reason-some-scientists-downplay-the-risks-of-climate-change



 Quotes:

One of the factors that appears to contribute to this trend of underestimation is the perceived need for consensus, or what we call “univocality”: the felt need to speak in a single voice.

In some cases, where there are irreconciliable differences of opinion, scientists may say nothing, giving the erroneous impression that nothing is known.

How does the pressure for univocality lead to underestimation? Consider a case in which most scientists think that the correct answer to a question is in the range one to 10, but some believe that it could be as high as 100. In this case, everyone will agree that it is at least one to 10, but not everyone will agree that it could be as high as 100. Therefore, the area of agreement is one to 10, and this will be reported as the consensus view. Wherever there is a range of possible outcomes that includes a long, high-end tail of probability, the area of overlap will lie at or near the low end.

We are not suggesting that every example of under-estimation is caused by the factors we observed in our work, nor that the demand for consensus always leads to underestimation. But we found that this pattern occurred in all of the cases that we studied. We also found that the institutional aspects of assessment, including who the authors are and how they are chosen, how the substance is divided into chapters, and guidance emphasizing consensus, also generally tilt in favor of scientific conservatism.

For political leaders and business people, we think it is important for you to know that it is extremely unlikely that scientists are exaggerating the threat of the climate crisis. It is far more likely that things are worse than scientists have said. We have already seen that the impacts of increased greenhouse gases in the atmosphere are unfolding more rapidly than scientists predicted. There is a high likelihood that they will continue to do so, and that the IPCC estimates – that emissions must be rapidly reduced, if not entirely eliminated, by 2050 – may well be optimistic. The fact that this conclusion is hard to swallow does not make it untrue.

&

Great comment by a climate scientist (professor?):
https://discussion.theguardian.com/comment-permalink/134744526
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1770 on: October 26, 2019, 08:07:02 AM »
Any tea leaves for 2300?

Personally, I do not expect SLR to exceed 8m by 2200 nor 9m by 2300, because I suspect that there will be a major global socio-economic contraction in the 2050 to 2070 timeframe.

I remind readers that Applegate et al. (2015) uses Greenland surface temperature increase (see the first image) rather than GMSTA. Thus, a 12C temperature increase over Greenland would correspond to something like a 6C GMSTA (see the second image).  The second image is for RCP 8.5 which indicates that 12C is reached over Greenland circa 2200:

Applegate, P.J., Parizek, B.R., Nicholas, R.E. et al. (2015), "Increasing temperature forcing reduces the Greenland Ice Sheet’s response time scale", Clim Dyn 45: 2001. https://doi.org/10.1007/s00382-014-2451-7

https://link.springer.com/article/10.1007/s00382-014-2451-7#citeas
&
https://static-content.springer.com/esm/art%3A10.1007%2Fs00382-014-2451-7/MediaObjects/382_2014_2451_MOESM1_ESM.pdf

Abstract: "Damages from sea level rise, as well as strategies to manage the associated risk, hinge critically on the time scale and eventual magnitude of sea level rise. Satellite observations and paleo-data suggest that the Greenland Ice Sheet (GIS) loses mass in response to increased temperatures, and may thus contribute substantially to sea level rise as anthropogenic climate change progresses. The time scale of GIS mass loss and sea level rise are deeply uncertain, and are often assumed to be constant. However, previous ice sheet modeling studies have shown that the time scale of GIS response likely decreases strongly with increasing temperature anomaly. Here, we map the relationship between temperature anomaly and the time scale of GIS response, by perturbing a calibrated, three-dimensional model of GIS behavior. Additional simulations with a profile, higher-order, ice sheet model yield time scales that are broadly consistent with those obtained using the three-dimensional model, and shed light on the feedbacks in the ice sheet system that cause the time scale shortening. Semi-empirical modeling studies that assume a constant time scale of sea level adjustment, and are calibrated to small preanthropogenic temperature and sea level changes, may underestimate future sea level rise. Our analysis suggests that the benefits of reducing greenhouse gas emissions, in terms of avoided sea level rise from the GIS, may be greatest if emissions reductions begin before large temperature increases have been realized. Reducing anthropogenic climate change may also allow more time for design and deployment of risk management strategies by slowing sea level contributions from the GIS."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1771 on: October 26, 2019, 10:01:39 AM »
More bad news, in that the Amazon rainforest could reach an irreversible tipping point within 2 years:

Title: "Amazon rainforest 'close to irreversible tipping point'"

https://www.theguardian.com/environment/2019/oct/23/amazon-rainforest-close-to-irreversible-tipping-point

Extract: "Forecast suggests rainforest could stop producing enough rain to sustain itself by 2021"

and

https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1600-0889.2011.00527.x?deniedAccessCustomisedMessage=&userIsAuthenticated=false

By 2200, the PCF strength in terms of cumulative permafrost carbon flux to the atmosphere is 190 ± 64 Gt C. This estimate may be low because it does not account for amplified surface warming due to the PCF itself and excludes some discontinuous permafrost regions where SiBCASA did not simulate permafrost. We predict that the PCF will change the arctic from a carbon sink to a source after the mid‐2020s and is strong enough to cancel 42–88% of the total global land sink. The thaw and decay of permafrost carbon is irreversible and accounting for the PCF will require larger reductions in fossil fuel emissions to reach a target atmospheric CO2 concentration.

Personally, I do not expect SLR to exceed 8m by 2200 nor 9m by 2300, because I suspect that there will be a major global socio-economic contraction in the 2050 to 2070 timeframe.

Or possibly earlier if both of these things pan out...

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1772 on: October 26, 2019, 11:52:31 AM »
If someone has a few graphs from this paper, i would be grateful (scihub is completely blocked in France) Evolution of global temperature over the past two million years https://www.nature.com/articles/nature19798 I myself see a doubling in the sea level rise rate and I do not see any reason why it would stop any time soon. So a doubling every ten years brings quite a lot of water... https://www.aviso.altimetry.fr/en/data/products/ocean-indicators-products/mean-sea-level/products-images.html
« Last Edit: October 26, 2019, 11:58:46 AM by Laurent »

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1773 on: October 26, 2019, 08:50:14 PM »
While one cannot directly compare the Eocene with modern climate conditions; nevertheless, the linked reference indicates that for modern conditions that ECS is 4.2C, and that ECS increases as the Earth warms, primarily due to cloud feedback mechanisms, so who knows what the effective ECS will be by 2100:

Abstract
The Early Eocene, a period of elevated atmospheric CO2 (>1000 ppmv), is considered an analog for future climate. Previous modeling attempts have been unable to reproduce major features of Eocene climate indicated by proxy data without substantial modification to the model physics. Here, we present simulations using a state-of-the-art climate model forced by proxy-estimated CO2 levels that capture the extreme surface warmth and reduced latitudinal temperature gradient of the Early Eocene and the warming of the Paleocene-Eocene Thermal Maximum. Our simulations exhibit increasing equilibrium climate sensitivity with warming and suggest an Eocene sensitivity of more than 6.6°C, much greater than the present-day value (4.2°C). This higher climate sensitivity is mainly attributable to the shortwave cloud feedback, which is linked primarily to cloud microphysical processes. Our findings highlight the role of small-scale cloud processes in determining large-scale climate changes and suggest a potential increase in climate sensitivity with future warming

ASLR, I have no problem with the results of this paper, that ECS might be very high during Eocene conditions.
Some very brief characteristics of the Early Eocene are equable climate; >1000 ppm CO2; sea surface temperatures in the tropics as high as 35 °C and, relative to present-day values, bottom water temperatures that are 10 °C higher.
Currently, mankind has managed to warm the oceans with a trend of approximately 0.04 °C per decade for the upper 700 meters. Or, less than half a degree per century. The warming is much less than that on deeper levels of the oceans. Thus, it will take a fairly long time to reach anything like the conditions during the Early Eocene. It's on the scale of several millenia.

I'm curious, given this background, what is the relevance of your mentioning of the year 2100 in your comment?
What is your percieved timescale for Earth to develop an Early Eocene equable climate, given the amount of warming of the oceans involved?

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1774 on: October 26, 2019, 11:30:03 PM »


Currently, mankind has managed to warm the oceans with a trend of approximately 0.04 °C per decade for the upper 700 meters. Or, less than half a degree per century. The warming is much less than that on deeper levels of the oceans. Thus, it will take a fairly long time to reach anything like the conditions during the Early Eocene. It's on the scale of several millenia.

I'm curious, given this background, what is the relevance of your mentioning of the year 2100 in your comment?
What is your percieved timescale for Earth to develop an Early Eocene equable climate, given the amount of warming of the oceans involved?

I have posted many times on the numerous risks/factors/cascade-of-feedbacks that could push the Northern Hemisphere in to an equable pattern (hothouse pattern) by 2100, so those who are interested can type the word 'equable' into the search engine to learn more about my thinking on this topic.  Nevertheless, as a 'lite' summary of key considerations of this possibility I present the following:

1. The primary characteristic of an equable climate (as occurred during the Eocene) is that ocean heat energy is conveyed directly from the tropical oceans (particularly the Tropical Pacific) poleward (& particularly to the Arctic).  In this regard, Schneider et al. (2019) cites that the future risk of losing marine stratocumulus clouds (which currently produce a negative feedback) which would result in an abrupt increase in GMSTA.  While Schneider et al. (2019) showed that an increase of atmospheric carbon dioxide concentration to about 1,200ppm, would result in such a loss of marine stratocumulus cloud, I previously pointed out in Reply #652 (see also Replies: #633, #642 & #650), the risk of abruptly losing the marine stratocumulus clouds would also occur if the equatorial SST increases from about 27C to about 32C. Note that that there is not need for the entire ocean to warm-up in order for the tropical ocean SST (particularly the Tropical Pacific) to increase from 27C to 32C this century; which could occur for a variety of reasons such as:

a) An abrupt collapse of much of the WAIS due to a collapse of the 'Big Ear' subglacial cavity and an associated collapse of the Thwaites Ice Tongue say circa 2030 could slow the MOC and/or;

b) A cascade of bipolar seesaw feedbacks, such as a surge of ice mass loss from Southern Greenland marine terminating glaciers like Jakobshavn (say between now and 2030) triggering an accelerated ice mass loss from the Eastern Antarctic Peninsula marine glaciers triggering a freshening of the Southern Ocean surface waters leading to increased upwelling of warm CDW across Antarctic continental shelves (see the first image); leading to an accelerated collapse of key Antarctic ice shelves leading to a partial collapse of the WAIS; which would slow the MOC and/or;

c) An abrupt release of relatively fresh water from the Beaufort Gyre (say due to a rainfall event on significant areas of Arctic Sea Ice circa 2030) flowing into the North Atlantic; which would slow the MOC; and/or;

d) The Eastern Tropical Pacific is predisposed to warming due to radiative forcing; which would likely be the case if ECS is roughly 5C (as indicated by many CMIP6 models) as indicated by the second attached image from the Ringberg 2015 workshop.

If indeed the tropical ocean SST does indeed warm up to 32C due to slowing of the MOC, then hysteresis loops shown in the third and fourth attached images [Figures 3 & 4 from Schneider  et al. (2019)] make it clear that once the stratocumulus clouds dissipate and equable atmospheric condition in the Northern Hemisphere could occur.

Tapio Schneider , Colleen M. Kaul and Kyle G. Pressel (2019), "Possible climate transitions from breakup of stratocumulus decks under greenhouse warming", Nature Geoscience, https://doi.org/10.1038/s41561-019-0310-1

https://www.nature.com/articles/s41561-019-0310-1

2. Even though a slowing of the MOC associated with freshwater hosing events might only last for decades; it is possible that an equable condition could be stabilized even without the CO2equiv reading 1,200pm due to possible future cascades of other tipping points, including:

a) Methane feedbacks such as thermokarst lakes or rapid permafrost degradation, and/or;

b) A rapid decrease of anthropogenic aerosol emissions due say to a socio-economic collapse between 2050 to 2070 and/or;

c) A marked increase of rainfall at high latitudes as is forecast to occur with global warming

3.  The linked reference (Pistone et al 2019) calculates the radiative heating of a sea ice free Arctic Ocean during the sunlit part of the year and assuming constant cloudiness they '… calculate a global radiative heating of 0.71 W/m2 relative to the 1979 baseline state. This is equivalent to …' hastening global warming by an estimated 25 years.  If the Northern Hemisphere were to flip into an equable pattern this century, this would lead to a sea ice free Arctic Ocean during the sunlit part of the year (particularly due to rainfall on the Arctic Sea Ice); which (together with bipolar seesaw interaction between the GIS and the AIS) might well be sufficient to maintain an equable climate pattern even after the multidecadal pulse of planetary energy imbalance associated with glacial ice mass loss from the GIS & the AIS.

Kristina Pistone et al. (20 June 2019), "Radiative Heating of an Ice‐free Arctic Ocean", Geophysical Research Letters, https://doi.org/10.1029/2019GL082914

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL082914?af=R

&

4. The linked reference (Massoud et al 2019) indicates that using consensus science (CMIP5) analyses the frequency of Atmospheric Rivers (ARs) will increase in frequency by about 50% and in intensity by about 25% by 2100.  As an AR rainfall event on the GIS would greatly accelerate the bipolar seesaw mechanism, this might likely serve to maintain equable conditions for centuries past 2100:

E.C. Massoud et al. (12 October 2019), "Global Climate Model Ensemble Approaches for Future Projections of Atmospheric Rivers", Earth's Future, https://doi.org/10.1029/2019EF001249

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019EF001249?af=R

Abstract
Atmospheric rivers (ARs) are narrow jets of integrated water vapor transport that are important for the global water cycle, and also have large impacts on local weather and regional hydrology. Uniformly‐weighted multi‐model averages have been used to describe how ARs will change in the future, but this type of estimate does not consider skill or independence of the climate models of interest. Here, we utilize information from various model averaging approaches, such as Bayesian Model Averaging (BMA), to evaluate 21 global climate models from the Coupled Model Intercomparison Project Phase 5 (CMIP5). Model ensemble weighting strategies are based on model independence and atmospheric river performance skill relative to ERA‐Interim reanalysis data, and result in higher accuracy for the historic period, e.g. RMSE for AR frequency (in % of timesteps) of 0.69 for BMA vs 0.94 for the multi‐model ensemble mean. Model weighting strategies also result in lower uncertainties in the future estimates, e.g. only 20‐25% of the total uncertainties seen in the equal weighting strategy. These model averaging methods show, with high certainty, that globally the frequency of ARs are expected to have average relative increases of ~50% (and ~25% in AR intensity) by the end of the century.

Plain Language Summary
Atmospheric rivers (ARs) are storms of integrated water vapor transport that are important for the global water cycle, and also have large impacts on local weather and regional hydrology. An increase in the frequency of ARs is expected to occur by the end of the century throughout most of the globe. Usually, these types of assessments of future climate change rely on simple (i.e. equally‐weighted) multi‐model averages and do not consider the skill or independence of the climate models of interest. Here, we utilize information from various model averaging approaches to constrain a suite of 21 global climate models from the Coupled Model Intercomparison Project Phase 5 (CMIP5). The weighted model combinations are fit to reanalysis data (ERA‐Interim) and are useful because they provide higher skill as well as lower uncertainties compared to equal weighting. This work supports the claim that AR frequency will increase in the future by about ~50% (and intensity will increase by ~25%) globally by the end of the century.

Edit: If what I wrote above is not clear, let me note that for the NH atmosphere to transition to an equable pattern, there is no need for the entire ocean to warm as much as what occurred during the Eocene, there is only a need for the average surface temperature of the tropical oceans to warm by 5C from 27C to 32C.

Edit2: Furthermore, there is no need for the atmospheric C02 concentration to increase to 1,200ppm.
« Last Edit: October 27, 2019, 02:24:44 AM by AbruptSLR »
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1775 on: October 26, 2019, 11:37:18 PM »
...
Personally, I do not expect SLR to exceed 8m by 2200 nor 9m by 2300, because I suspect that there will be a major global socio-economic contraction in the 2050 to 2070 timeframe.

Or possibly earlier if both of these things pan out...

kassy,

My statement to Tom was my opinion of the most likely (mode) chain of events thru 2300 for SLR.  That said, I completely concur that sea level could rise much faster and reach much higher elevations say if a cascade of positive feedback leads to an equable atmospheric pattern at least in the NH by 2100 and possibly in the SH by say 2200.

Best,
ASLR
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1776 on: October 27, 2019, 12:08:20 AM »
...
One of the factors that appears to contribute to this trend of underestimation is the perceived need for consensus, or what we call “univocality”: the felt need to speak in a single voice.



Fritz Zwicky first developed and championed the concept of dark matter and was derided for his effort for decades by consensus astronomers for his lack of "univocality".  In response Zwicky made the attached vitriolic vituperation about consensus astronomers:
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1777 on: October 27, 2019, 08:47:08 AM »
Re: Eocene, deep ocean heating

There is no way that we heat the deep ocean to 10C in the next few hundred year. 

Surface now, that's a different matter ...

sidd

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1778 on: October 27, 2019, 06:56:03 PM »
Re: Eocene, deep ocean heating

There is no way that we heat the deep ocean to 10C in the next few hundred year. 

Surface now, that's a different matter ...

sidd

For those who are still unclear as to why increasing the SST of the tropical oceans (not the entire ocean surface but only the topical ocean surface) is a fundamental parameter that directly impacts the risk of changing the NH atmospheric circulation pattern into an equable pattern possibly as soon as 2100, I note that:

1. Most solar radiative forcing reaches the Earth's surface in the tropics, with the associated surplus of energy being redistributed to cooler regions of the Earth by both ocean and atmospheric circulation.  In particular, the first image shows that the north and south hemispheric atmospheric circulation is currently organized into three atmospheric cells (Hadley, Ferrel (Mid-latitude and Polar) as indicated in the first image.  Furthermore, I note that a great deal of the surplus solar energy in the atmosphere is in the form of water vapor (primarily from the surface of the tropical oceans), which is released when the water vapor condenses back into water droplets in clouds.

2. Furthermore, the second attached image (from Sherwood et al. 2014) shows that as/when the tropical sea surface temperature (SST) increases, the associated more energetic water vapor molecules create a local deep atmospheric circulation pattern that:
a) creates more high-altitude clouds with a positive feedback and starves low-altitude clouds that have a net negative feedback; and
b) expands the Hadley Cells poleward; which also moves the local clouds poleward and which exposes the tropical sea surface to more direct solar radiation (which creates more energetic water vapor)

3. The third image from the linked article; illustrates that if the equatorial/tropical ocean SST increases from about 27C to about 32C then the atmosphere in the North Hemisphere (NH) could be abruptly transitioned from modern to equable climate circulation pattern (or 'hot house' pattern) conditions.  Such a 5C SST increase in the equatorial oceans, could conceivable occur this century from a combination of: a) ice-climate feedbacks from the collapse of the WAIS & bipolar seesaw interaction with the Arctic & Greenland; and b) a cascade of other tipping points:

Title: "The Effects of Ocean Freshening on Marine and Atmospheric Circulation: Impacts and Solutions"

https://www.sciencebuzz.com/the-effects-of-ocean-freshening-on-marine-and-atmospheric-circulation-impacts-and-solutions/

Extract: "As studied by Piana (n.d.), should the SST rise by 1°C, the tropopause’s temperature would increase by around 7.5°C. If the equatorial SST were raised from the average 27°C to 32°C then the tropopause would be heated 37°C above average. A 5°C SST increase, combined with other factors, would hypothetically cause the Hadley cells to increase in height allowing them to reach the poles. This effect terminates Ferrel and Polar cell convection and replaces it with a large Hadley cell (Figure 5). This causes global climates to become more equable than previously existed as temperatures are more evenly distributed across the globe (Piana n.d.)."

Caption for the third image: "Figure 5: a. This shows the Hadley, Ferrel, and Polar Cells in the troposphere. For a Hadley cell warm air rises near the equator and falls after cooling at 30° latitude, creating a convection cell. b. This illustrates a single large Hadley cell due to increased SST (Hagerman design)."

4.  The fourth attached image shows that during the Eocene there were no ice sheets (Antarctic or Greenland) whose collapse would temporarily slow ocean circulation (which leaves warm surface water in the tropics longer where it creates more water vapor and associated high-altitude clouds); thus during the Eocene the tropical ocean SST warmed more slowly than is occurring in the modern world.  Also, the fourth image shows that during the Eocene the atmospheric CO2 concentration may have ranged as low as 680ppm while sustaining an equable climate pattern; thus if ice-climate feedbacks were to temporarily (for multiple decades) push the NH atmosphere into an equable circulation pattern (with one big Hadley Cell) then hysteresis might make this pattern stable for several centuries as by 2050 atmospheric CO2-eq may be in the 680ppm range if we continue on a BAU pathway to 2050 (possibly followed by a major global socio-economic contraction).
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1779 on: October 28, 2019, 01:42:42 AM »
The linked graphic from Gavin Foster (of Foster Lab) compares CMIP6 ECS projections as of August 2019 to earlier projections; showing that the CMIP6 ECS projections are still running hot.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1780 on: October 28, 2019, 02:39:29 PM »

I have posted many times on the numerous risks/factors/cascade-of-feedbacks that could push the Northern Hemisphere in to an equable pattern (hothouse pattern) by 2100, so those who are interested can type the word 'equable' into the search engine to learn more about my thinking on this topic.  Nevertheless, as a 'lite' summary of key considerations of this possibility I present the following:

1. The primary characteristic of an equable climate (as occurred during the Eocene) is that ocean heat energy is conveyed directly from the tropical oceans (particularly the Tropical Pacific) poleward (& particularly to the Arctic).  In this regard, Schneider et al. (2019) cites that the future risk of losing marine stratocumulus clouds (which currently produce a negative feedback) which would result in an abrupt increase in GMSTA.  While Schneider et al. (2019) showed that an increase of atmospheric carbon dioxide concentration to about 1,200ppm, would result in such a loss of marine stratocumulus cloud, I previously pointed out in Reply #652 (see also Replies: #633, #642 & #650), the risk of abruptly losing the marine stratocumulus clouds would also occur if the equatorial SST increases from about 27C to about 32C. Note that that there is not need for the entire ocean to warm-up in order for the tropical ocean SST (particularly the Tropical Pacific) to increase from 27C to 32C this century; which could occur for a variety of reasons such as:

a) An abrupt collapse of much of the WAIS due to a collapse of the 'Big Ear' subglacial cavity and an associated collapse of the Thwaites Ice Tongue say circa 2030 could slow the MOC and/or;

b) A cascade of bipolar seesaw feedbacks, such as a surge of ice mass loss from Southern Greenland marine terminating glaciers like Jakobshavn (say between now and 2030) triggering an accelerated ice mass loss from the Eastern Antarctic Peninsula marine glaciers triggering a freshening of the Southern Ocean surface waters leading to increased upwelling of warm CDW across Antarctic continental shelves (see the first image); leading to an accelerated collapse of key Antarctic ice shelves leading to a partial collapse of the WAIS; which would slow the MOC and/or;

c) An abrupt release of relatively fresh water from the Beaufort Gyre (say due to a rainfall event on significant areas of Arctic Sea Ice circa 2030) flowing into the North Atlantic; which would slow the MOC; and/or;

d) The Eastern Tropical Pacific is predisposed to warming due to radiative forcing; which would likely be the case if ECS is roughly 5C (as indicated by many CMIP6 models) as indicated by the second attached image from the Ringberg 2015 workshop.

If indeed the tropical ocean SST does indeed warm up to 32C due to slowing of the MOC, then hysteresis loops shown in the third and fourth attached images [Figures 3 & 4 from Schneider  et al. (2019)] make it clear that once the stratocumulus clouds dissipate and equable atmospheric condition in the Northern Hemisphere could occur.

/snip/

Edit: If what I wrote above is not clear, let me note that for the NH atmosphere to transition to an equable pattern, there is no need for the entire ocean to warm as much as what occurred during the Eocene, there is only a need for the average surface temperature of the tropical oceans to warm by 5C from 27C to 32C.

Edit2: Furthermore, there is no need for the atmospheric C02 concentration to increase to 1,200ppm.

ASLR, you provide a long list of factors that you claim might trigger a deep climate change so that we will have an equable climate already by 2100. This is a fascinating hypothesis, worth pondering upon.

I will here comment manly on your first point, in which you mention various ways in which the MOC might shut down; this in turn would trigger an equable climate as the tropics would 'overheat' with SSTs rising some 5 degrees C.

I think you are correct to focus on the oceans and more specifically on the MOC. The oceans of the world contain 99.9% of the surface thermal energy on the Earth, while the dry atmosphere contains a mere  0.07% of the energy. While atmospheric processes often dominate the weather, the climate is dominated by the oceans. While oceans drive our climate, what drives changes in the oceans? They have no interior energy source. They collect most of the solar energy that makes its way to the Earth’s surface, as well as most of the thermal energy radiated toward the Earth by GHG. The atmosphere is not heating the ocean.

There are (at least) two critical factors that might make your hypothesis of an equable climate by 2100 less plausible, the first one is about the MOC, the second is about clouds in the tropics.

1. How to trigger a shutdown of the MOC? The main engine of the MOC is the downwelling in the polar regions. The critical issue here seems to be the ongoing loss of Arctic sea ice and whether it will be enought to stop the MOC in a <100 years timeframe. (I think we can agree that not much will happen in the Antarctic in this time frame that might affect MOC.)

The MOC is a gigantic sea water mixer. Huge quantities of dense water sink and cool at high latitudes (Arctic/Antarctic). This is offset by equal quantities of water rising in lower latitudes. Cold water in polar zones sink relatively rapidly over a relatively small area, while warm water in temperate and tropical zones rise more gradually across much larger areas. The continual diffuse up-welling of deep water maintains the existence of the permanent thermocline found in the low and mid-latitudes. The up-welling of deep water is in the order of 1 cm per day over most of the ocean. The water that has up-welled is warmed and the surface streams then transport the heat away from the tropics.

The dense water masses that sink into the deep basins are formed in specific areas of the North Atlantic and the Southern Ocean. In the North Atlantic, seawater at the surface of the ocean is intensely cooled by the wind and low ambient air temperatures.

But even if the MOC would stall, the heat transfer in the ocean wouldn't stop. You cannot heat the top of the ocean without the heat travelling into the deep ocean. This is basic thermodynamics. Heat at the surface percolate down through the depths - whether there are currents below the surface or not. The entire volume of the ocean must be taken into account in order to account for the thermodynamics. I conclude that your premise that it is feasible to heat the top layer of the ocean some 5 degrees C without having to heat the rest of the water mass is false.

The ocean circulation has inherently long time scales, up to millennia. An unusually large amount of cold bottom water formed at the surface in the Arctic in one century might take 100s or even 1000s of years before it re-emerges at the surface, say in the tropics. Climate can change all by itself and we still lack a lot of data on what's going on in the oceans.

2. Clouds in the tropics. The second necessary prerequisite for your hypothesis of an equable climate by 2100 is that the atmospheric conditions in the tropics somehow must change, to allow for dramatically increased solar radiation reaching the ocean, in order to heat at least the top layer 5 degrees C. You write: "Schneider et al. (2019) cites that the future risk of losing marine stratocumulus clouds (which currently produce a negative feedback) which would result in an abrupt increase in GMSTA.  While Schneider et al. (2019) showed that an increase of atmospheric carbon dioxide concentration to about 1,200ppm, would result in such a loss of marine stratocumulus cloud, I previously pointed out in Reply #652 (see also Replies: #633, #642 & #650), the risk of abruptly losing the marine stratocumulus clouds would also occur if the equatorial SST increases from about 27C to about 32C. "

If we accept the hypothesis that we might lose sufficient marine stratocumulus cloud to support the positive feedback that will keep tropical oceans at 32C, we still need to demonstrate how we can reach such a state in the first place, given that we will stay way below the postulated 1,200 ppm of CO2 within the postulated timeframe of <100 years. At the current climate conditions in the tropics /current CO2 levels/ an incrementally increased temperature is unlikely to have a strong positive feedback, and might even have a negative feedback, working through the water vapor convection /phase changes of H2O. Theories and results vary between researchers and there is still a lot of research to be done in this field as there is not only a lack of theory, but also a lack of data. It would be very interesting if you could provide some scientific evidence demonstrating the atmospherical process that might take us from the current climate  to an equable climate in less than 100  years.

« Last Edit: October 28, 2019, 05:21:43 PM by Hefaistos »

Tom_Mazanec

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1781 on: October 28, 2019, 03:00:50 PM »
Hefaistos:
Doesn’t warm water tend to stay above cold water? Wouldn’t the surface heated water just float there?
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1782 on: October 28, 2019, 05:22:35 PM »
...
1. How to trigger a shutdown of the MOC? The main engine of the MOC is the downwelling in the polar regions. The critical issue here seems to be the ongoing loss of Arctic sea ice and whether it will be enought to stop the MOC in a <100 years timeframe. (Not much will happen in the Antarctic in this time frame that might affect MOC.)



I disagree with many of your assumptions but the one that I highlight in bold underline above is the most important.  You are posting in the Ice Apocalypse thread and the vast majority of posts in this thread provide supporting evidence that at least significant portions of the WAIS may collapse prior to 2100, possibly due to MICI-mechanisms.  If you care to respond to all of that evidence then I might take your highlighted assumption more seriously, but until then I believe that you are merely repeating consensus science assumptions/caveats on this matter (all of which err on the side of least drama).
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1783 on: October 28, 2019, 05:28:14 PM »
Hefaistos:
Doesn’t warm water tend to stay above cold water? Wouldn’t the surface heated water just float there?

You can heat water on the top of the ocean but the heated top layer of water will lose energy as it continously warms the lower lying layers. These are simple thermodynamic principles. You can demonstrate it in a lab with simple means.
It helps if you have a thermocline layer to separate the top layer from the lower layers.

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1784 on: October 28, 2019, 07:01:15 PM »
Hefaistos:
Doesn’t warm water tend to stay above cold water? Wouldn’t the surface heated water just float there?

You can heat water on the top of the ocean but the heated top layer of water will lose energy as it continously warms the lower lying layers. These are simple thermodynamic principles. You can demonstrate it in a lab with simple means.
It helps if you have a thermocline layer to separate the top layer from the lower layers.
A post about something where my lack of knowledge is almost total.

Overall, ocean temperatures from 0 to 100 metres depth have increased by about 0.6 degrees celsius since 1955 (0.11 degrees per decade and accelerating), compared with only about 0.2 degrees for 0 to 700 metres. It seems there is something called the pycnocline that separates the top 100 metres from the ocean depths, except in polar regions.

But at what latitude does the pycnocline break down? Is the West Antarctic Peninsula at low enough latitudes for the pycnocline to persist?  Fascinating stuff.

https://www.britannica.com/science/pycnocline
Pycnocline, in oceanography, boundary separating two liquid layers of different densities. In oceans a large density difference between surface waters (or upper 100 metres [330 feet]) and deep ocean water effectively prevents vertical currents; the one exception is in polar regions where pycnocline is absent. Formation of pycnocline may result from changes in salinity or temperature. Because the pycnocline zone is extremely stable, it acts as a barrier for surface processes. Thus, changes in salinity or temperature are very small below pycnocline but are seasonal in surface waters.
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Hefaistos

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1785 on: October 28, 2019, 07:12:29 PM »
...I believe that you are merely repeating consensus science assumptions/caveats on this matter (all of which err on the side of least drama).

Yes, I am.
That said, i believe all scenarios and forecasts of dramatic climate changes, like the one you propose, should obey basic laws of thermodynamics and/or physics. Pathways to reach an equable climate have to be demonstrated in a way that doesn't conflict what is physically possible, e.g.


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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1786 on: October 28, 2019, 10:54:32 PM »
...
1. How to trigger a shutdown of the MOC? The main engine of the MOC is the downwelling in the polar regions. The critical issue here seems to be the ongoing loss of Arctic sea ice and whether it will be enought to stop the MOC in a <100 years timeframe. (Not much will happen in the Antarctic in this time frame that might affect MOC.)



I disagree with many of your assumptions but the one that I highlight in bold underline above is the most important.  You are posting in the Ice Apocalypse thread and the vast majority of posts in this thread provide supporting evidence that at least significant portions of the WAIS may collapse prior to 2100, possibly due to MICI-mechanisms.  If you care to respond to all of that evidence then I might take your highlighted assumption more seriously, but until then I believe that you are merely repeating consensus science assumptions/caveats on this matter (all of which err on the side of least drama).

Please keep in mind that not even the authors of the MICI hypothesis believe it will occur before the end of this century.

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1787 on: October 29, 2019, 03:17:10 AM »

Please keep in mind that not even the authors of the MICI hypothesis believe it will occur before the end of this century.

I concur that DeConto, Pollard and Alley have publicly acknowledged that their MICI model merits further calibration work and that they are currently proceeding with research work to do just that; but I disagree that they have ever said that significant portions of the WAIS cannot collapse per the MICI mechanism prior to 2100.  Indeed they (and others) have warned that to avoid hydrofracturing and cliff failures in the WAIS, GMSTA should not go above 2C and might become unavoidable if GMSTA reaches 2.7C and in this regards I note the following.

First, I note that, Pollard, DeConto & Alley (2018) use their Antarctic Ice Sheet, AIS, model with ice-cliff and hydrofracturing failure mechanisms together with ice mélange back pressures calibrated to that currently observed for the Jakobshavn marine terminating glacier in Greenland (see the first image).  Pollard et al (2018) then assumed the abrupt imposition of warm mid-Pliocene climate conditions (which roughly have a GMSTA above pre-industrial of 2C and ocean water temperatures beneath the ice of key AIS marine glaciers comparable to those found by Bronselaer et al (2018) after 2040, as shown in the second image). 

David Pollard, Robert M. DeConto, Richard B. Alley (13 March 2018), "A continuum model of ice mélange and its role during retreat of the Antarctic Ice Sheet", Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2018-28

https://www.geosci-model-dev-discuss.net/gmd-2018-28/gmd-2018-28.pdf
&

Bronselaer, B. et al. (2018) Change in future climate due to Antarctic meltwater, Nature, doi:s41586-018-0712-z

https://www.nature.com/articles/s41586-018-0712-z

Finally, the fifth and sixth linked abstracts from the WAIS 2018 workshop clearly indicate that after GMSTA reaches about 2C above pre-industrial, there is significant risk of a major MICI event initiating.

Title: "Climatic Thresholds for WAIS Retreat: Onset of Widespread Ice Shelf Hydrofracturing and Ice Cliff Calving in a Warming World", by Rob DeConto, David Pollard, Knut Christianson, Richard B. Alley & Byron R. Parizek

https://www.waisworkshop.org/sites/waisworkshop.org/files/webform/2018/abstracts/WAIS2018.pdf

Abstract: "The loss or thinning of buttressing ice shelves and accompanying changes in grounding zone stress balance are commonly implicated as the primary trigger for grounding line retreat, such as that observed in Amundsen Sea outlet glaciers today. Ice-shelf thinning is mostly attributed to the presence of warm ocean waters beneath the shelves. However, climate model projections indicate that summer air temperatures could soon exceed the threshold for widespread meltwater production on ice-shelf surfaces. This has serious implications for the future stability of ice shelves, because they are vulnerable to the propagation of water-induced flexural stresses and water-aided crevasse penetration, often referred to as ‘hydrofracturing’. Once initiated, the rate of shelf loss through hydrofracturing can far exceed that caused by sub-surface oceanic melting, and could result in the complete loss of some buttressing ice shelves, with marine-terminating grounding lines suddenly becoming calving ice fronts. In places where those exposed (unbuttressed) ice fronts are thick enough (>900m), deviatoric stresses can exceed the strength of the ice, and the cliff face will fail through brittle processes leading to rapid calving like that seen in analogous settings on Greenland such as Jakobshavn and Helheim. 
 
Here we explore the implications of hydrofacturing and subsequent ice-cliff collapse in a warming climate, by parameterizing these processes in a hybrid ice sheet-shelf model. Model physical parameters controlling sensitivity of surface crevasse penetration to meltwater and ice-cliff calving rate (a function of cliff height above the stress-balance threshold for brittle failure) are based on observations of calving in analogous settings, and model performance relative to observed mass loss and paleo sea-level estimates. Including these processes and exploring a range of atmospheric and ocean climate forcing scenarios, we find the potential for major future WAIS retreat if global mean temperature rises more than ~2ºC above preindustrial. We also find that strict mitigation, with net negative carbon emissions initiated ~2060 substantially reduces the magnitude and rate of long-term WAIS retreat. In simulations following a ‘worst case’ RCP8.5 scenario, the model produces rates of equivalent sea level rise that would be measured in cm per year by the end of this century. Importantly, parameterized Antarctic calving rates at thick ice fronts are not allowed to exceed those observed in Greenland today. This may be an overly conservative assumption, considering the very different spatial scales and physical settings of Antarctic outlet glaciers like Thwaites. Clearly the potential for mechanical/brittle processes to deliver ice to the ocean, in addition to viscous and basal processes, needs to be better constrained through more complete, physically based model representations of calving."
&

Title: "Across the Great Divide: The Flow-to-Fracture Transition and the Future of the West Antarctic Ice Sheet", by Richard B. Alley, Byron R. Parizek, Knut Christianson, Robert M. DeConto, David Pollard and Sridhar Anandakrishna

https://www.waisworkshop.org/sites/waisworkshop.org/files/webform/2018/abstracts/Alley_R.pdf

Abstract: "Physical understanding, modeling, and available data indicate that sufficient warming and retreat of Thwaites Glacier, West Antarctica will remove its ice shelf and generate a calving cliff taller than any extant calving fronts, and that beyond some threshold this will generate faster retreat than any now observed. Persistent ice shelves are restricted to cold environments. Ice-shelf removal has been observed in response to atmospheric warming, with an important role for meltwater wedging open crevasses, and in response to oceanic warming, by mechanisms that are not fully characterized. Some marine-terminating glaciers lacking ice shelves “calve” from cliffs that are grounded at sea level or in relatively shallow water, but more-vigorous flows advance until the ice is close to flotation before calving. For these vigorous flows, a calving event shifts the ice front to a position that is slightly too thick to float, and generates a stress imbalance that causes the ice front to flow faster and thin to flotation, followed by another calving event; the rate of retreat thus is controlled by ice flow even though the retreat is achieved by fracture. Taller cliffs generate higher stresses, however, favoring fracture over flow. Deformational processes are often written as power-law functions of stress, with ice deformation increasing as approximately the third power of stress, but subcritical crack growth as roughly the thirtieth power, accelerating to elastic-wave speeds with full failure. Physical understanding, models based on this understanding, and the limited available data agree that, above some threshold height, brittle processes will become rate-limiting, generating faster calving at a rate that is not well known but could be very fast. Subaerial slumping followed by basal-crevasse growth of the unloaded ice is the most-likely path to this rapid calving. This threshold height is probably not too much greater than the tallest modern cliffs, which are roughly 100 m."
&

For those who do not understand the implications of Alley et al. (2018)'s comment that ice deformation is a power-function of stress, I attach the third image that translates this underlying ice-cliff behavior into terms of calving rate (deformation) per year for various values of marine glacier freeboard (ice face height minus water depth) and relative water depth (which combine determine the primary stresses near the ice cliff face).
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1788 on: October 29, 2019, 03:36:45 AM »
...
Yes, I am.
That said, i believe all scenarios and forecasts of dramatic climate changes, like the one you propose, should obey basic laws of thermodynamics and/or physics. Pathways to reach an equable climate have to be demonstrated in a way that doesn't conflict what is physically possible, e.g.

In addition to gerontocrat's comments about the upper 100m of the oceans; it is widely accepted by consensus climate science that with continued global warming that key portions of the oceans (including the tropical oceans) will become more stratified as noted even in AR3 (TAR) era references as cited below:

Antonietta Capotondi, Michael A. Alexander, Nicholas A. Bond, Enrique N. Curchitser, James D. Scott (25 April 2012), "Enhanced upper ocean stratification with climate change in the CMIP3 models", Journal of Geophysical Research: Oceans/Volume 117, Issue C4, https://doi.org/10.1029/2011JC007409

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2011JC007409

Abstract: "Changes in upper ocean stratification during the second half of the 21st century, relative to the second half of the 20th century, are examined in ten of the CMIP3 climate models according to the SRES‐A2 scenario. The upper ocean stratification, defined here as the density difference between 200 m and the surface, is larger everywhere during the second half of the 21st century, indicative of an increasing degree of decoupling between the surface and the deeper oceans, with important consequences for many biogeochemical processes. The areas characterized by the largest stratification changes include the Arctic, the tropics, the North Atlantic, and the northeast Pacific. The increase in stratification is primarily due to the increase in surface temperature, whose influence upon density is largest in the tropical regions, and decreases with increasing latitude. The influence of salinity upon the stratification changes, while not as spatially extensive as that of temperature, is very large in the Arctic, North Atlantic and Northeast Pacific. Salinity also significantly contributes to the density decrease near the surface in the western tropical Pacific, but counteracts the negative influence of temperature upon density in the tropical Atlantic."
« Last Edit: October 29, 2019, 08:32:39 AM by AbruptSLR »
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1789 on: October 29, 2019, 08:50:04 AM »
The linked reference helps to explain why it is that with continued global warming the tropical oceans surface layer warms quickly as 'ocean barrier layers' help isolate the surface layer from deeper cold thermocline water:

J. E. Jack Reeves Eyre et al. (20 June 2019), "Ocean Barrier Layers in the Energy Exascale Earth System Model", Geophysical Research Letters/Vol. 46, Issue 14, https://doi.org/10.1029/2019GL083591


https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL083591

Abstract
Ocean barrier layers (BLs) separate the mixed layer from the top of the thermocline and are able to insulate the mixed layer from entrainment of cold thermocline water. Here, we provide the first global BL assessment in E3SMv1 and two other Earth system models. Compared to observations, models reproduce the global distributions as semipermanent features in some tropical regions and seasonal features elsewhere. However, model BLs are generally too thin in tropical regions and too thick in higher latitudes. BLs' ability to insulate the ocean surface from entrainment of cold thermocline water is most apparent in the tropics. Thus, E3SMv1s BL thickness biases most affect entrainment here. Tropical BLT biases appear driven by atmosphere biases, mainly through the effect of precipitation minus evaporation on mixed layer depth. At higher latitudes BL thickness biases are dominated by thermocline depth errors related to ocean circulation and vertical mixing.

Plain Language Summary
Most regions of the Earth's oceans exhibit a thermocline, separating relatively warm surface water from colder water below. In some regions, salinity varies sharply within the warm layer, displaying a fresh layer at the surface and a salty warm layer, termed a barrier layer, between the surface layer and the thermocline. Here we assess barrier layers in three Earth system models, focusing on the Energy Exascale Earth System Model. We show the following: Earth system models can capture barrier layers, albeit with errors in thickness; barrier layers affect exchange of water and heat between the surface and the thermocline in the tropics, but not at midlatitudes; and barrier layer model errors are not purely due to the ocean model component but are caused by several model components (ocean, atmosphere, land, and river runoff) and interactions between them.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1790 on: October 29, 2019, 03:53:16 PM »
Who knows whether after 2100 the world might head towards an abrupt transition into a Canfield Ocean event:

Rick Bartlett, Maya Elrick, James R. Wheeley, Victor Polyak, André Desrochers, and Yemane Asmerom (June 5, 2018), "Abrupt global-ocean anoxia during the Late Ordovician–early Silurian detected using uranium isotopes of marine carbonates", PNAS, 115 (23) 5896-5901; first published May 21, 2018 https://doi.org/10.1073/pnas.1802438115

https://www.pnas.org/content/115/23/5896

Significance
The Late Ordovician mass extinction (LOME) terminated one of the greatest biodiversity radiations in Earth history eliminating ∼85% of marine animals, and it is coincident with the first major glaciation of the Phanerozoic. To evaluate LOME origins, we use uranium isotopes from marine limestones as a proxy for global-ocean redox conditions. Our results provide evidence of an abrupt global-ocean anoxic event coincident with the LOME onset and its continuation after the biologic recovery, through peak glaciation, and the following early Silurian deglaciation. These results also provide evidence for widespread ocean anoxia initiating and continuing during icehouse conditions.

Abstract
Widespread marine anoxia is hypothesized as the trigger for the second pulse of the Late Ordovician (Hirnantian) mass extinction based on lithologic and geochemical proxies that record local bottom waters or porewaters. We test the anoxia hypothesis using δ238U values of marine limestones as a global seawater redox proxy. The δ238U trends at Anticosti Island, Canada, document an abrupt late Hirnantian ∼0.3‰ negative shift continuing through the early Silurian indicating more reducing seawater conditions. The lack of observed anoxic facies and no covariance among δ238U values and other local redox proxies suggests that the δ238U trends represent a global-ocean redox record. The Hirnantian ocean anoxic event (HOAE) onset is coincident with the extinction pulse indicating its importance in triggering it. Anoxia initiated during high sea levels before peak Hirnantian glaciation, and continued into the subsequent lowstand and early Silurian deglacial eustatic rise, implying that major climatic and eustatic changes had little effect on global-ocean redox conditions. The HOAE occurred during a global δ13C positive excursion, but lasted longer indicating that controls on the C budget were partially decoupled from global-ocean redox trends. U cycle modeling suggests that there was a ∼15% increase in anoxic seafloor area and ∼80% of seawater U was sequestered into anoxic sediments during the HOAE. Unlike other ocean anoxic events (OAE), the HOAE occurred during peak and waning icehouse conditions rather than during greenhouse climates. We interpret that anoxia was driven by global cooling, which reorganized thermohaline circulation, decreased deep-ocean ventilation, enhanced nutrient fluxes, stimulated productivity, which lead to expanded oxygen minimum zones.

See also:

Donald Canfield (December 1998), "A new model for Proterozoic ocean chemistry", Nature 396(6710):450-453,DOI: 10.1038/24839

Abstract
Widespread marine anoxia is hypothesized as the trigger for the second pulse of the Late Ordovician (Hirnantian) mass extinction based on lithologic and geochemical proxies that record local bottom waters or porewaters. We test the anoxia hypothesis using δ238U values of marine limestones as a global seawater redox proxy. The δ238U trends at Anticosti Island, Canada, document an abrupt late Hirnantian ∼0.3‰ negative shift continuing through the early Silurian indicating more reducing seawater conditions. The lack of observed anoxic facies and no covariance among δ238U values and other local redox proxies suggests that the δ238U trends represent a global-ocean redox record. The Hirnantian ocean anoxic event (HOAE) onset is coincident with the extinction pulse indicating its importance in triggering it. Anoxia initiated during high sea levels before peak Hirnantian glaciation, and continued into the subsequent lowstand and early Silurian deglacial eustatic rise, implying that major climatic and eustatic changes had little effect on global-ocean redox conditions. The HOAE occurred during a global δ13C positive excursion, but lasted longer indicating that controls on the C budget were partially decoupled from global-ocean redox trends. U cycle modeling suggests that there was a ∼15% increase in anoxic seafloor area and ∼80% of seawater U was sequestered into anoxic sediments during the HOAE. Unlike other ocean anoxic events (OAE), the HOAE occurred during peak and waning icehouse conditions rather than during greenhouse climates. We interpret that anoxia was driven by global cooling, which reorganized thermohaline circulation, decreased deep-ocean ventilation, enhanced nutrient fluxes, stimulated productivity, which lead to expanded oxygen minimum zones.

See also:

Title: "Canfield ocean"

https://en.wikipedia.org/wiki/Canfield_ocean
« Last Edit: October 29, 2019, 04:53:31 PM by AbruptSLR »
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1791 on: October 29, 2019, 04:20:14 PM »
When evaluating future climate risk, one not only needs to evaluate the right-tail portion of the Probability Density Function (PDF), but also the impact of such right-tail events should they occur; which in turn is a function of the strength, or weaken, of governance of countries around the world, as discussed in the linked reference:

Marina Andrijevic et al. (2019), "Governance in socioeconomic pathways and its role for future adaptive capacity", Nature Sustainability , DOI: https://doi.org/10.1038/s41893-019-0405-0

https://www.nature.com/articles/s41893-019-0405-0

Abstract: "Weak governance is one of the key obstacles for sustainable development. Undoubtedly, improvement of governance comes with a broad range of co-benefits, including countries’ abilities to respond to pressing global challenges such as climate change. However, beyond the qualitative acknowledgement of its importance, quantifications of future pathways of governance are still lacking. This study provides projections of future governance in line with the Shared Socioeconomic Pathways. We find that under a ‘rocky road’ scenario, 30% of the global population would still live in countries characterized by weak governance in 2050, while under a ‘green road’ scenario, weak governance would be almost entirely overcome over the same time frame. On the basis of pathways for governance, we estimate the adaptive capacity of countries to climate change. Limits to adaptive capacity exist even under optimistic pathways beyond mid-century. Our findings underscore the importance of accounting for governance in assessments of climate change impacts."
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Ken Feldman

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1792 on: October 29, 2019, 05:18:55 PM »
From DeConto and Pollard 2018:

https://www.geosci-model-dev-discuss.net/gmd-2018-28/gmd-2018-28.pdf

Quote
4.3 Antarctica
We now use the coupled model to examine the role of mélange during rapid retreat of Antarctic ice. Starting from the ice-sheet model state equilibrated to modern climate (with no mélange), an instantaneous change to a warm ~3 Ma mid Pliocene climate is imposed. As described in Pollard et al. (2015), atmospheric forcing is provided by a regional climate model with a warm austral-summer orbit and atmospheric CO2 level of 400 ppm, and circum-Antarctic ocean temperatures are assumed to warm 2 oC above modern climatology.

Note the bolded assumption.  Ocean temperatures around Antarctica need to be 2 degrees C warmer than they are currently (not warmer than pre-industrial) for MICI to begin.  So how fast are the waters around Antarctica currently warming? 

https://tos.org/oceanography/article/southern-ocean-warming

Quote
outhern Ocean Warming
Jean-Baptiste Sallée 
Published Online: August 15, 2018

Article Abstract
The Southern Ocean plays a fundamental role in global climate. With no continental barriers, it distributes climate signals among the Pacific, Atlantic, and Indian Oceans through its fast-flowing, energetic, and deep-reaching dominant current, the Antarctic Circumpolar Current. The unusual dynamics of this current, in conjunction with energetic atmospheric and ice conditions, make the Southern Ocean a key region for connecting the surface ocean with the world ocean’s deep seas. Recent examinations of global ocean temperature show that the Southern Ocean plays a major role in global ocean heat uptake and storage. Since 2006, an estimated 60%–90% of global ocean heat content change associated with global warming is based in the Southern Ocean. But the warming of its water masses is inhomogeneous. While the upper 1,000 m of the Southern Ocean within and north of the Antarctic Circumpolar Current are warming rapidly, at a rate of 0.1°–0.2°C per decade, the surface sub­polar seas south of this region are not warming or are slightly cooling. However, subpolar abyssal waters are warming at a substantial rate of ~0.05°C per decade due to the formation of bottom waters on the Antarctic continental shelves. Although the processes at play in this warming and their regional distribution are beginning to become clear, the specific mechanisms associated with wind change, eddy activity, and ocean-ice interaction remain areas of active research, and substantial challenges persist to representing them accurately in climate models.

At current observed rates of warming (with GMSTA around 1C above pre-industrial), the oceans around Antarctica are warming at 0.05 degrees C per decade.  At that rate, it would take 400 years to hit one of the necessary triggers for MICI to start.

That may be why DeConto and Pollard are urging more caution now about the MICI models.  They are still claiming that hydrofracturing could begin as GMSTA approaches 2C above pre-industrial, but that results in centimeters of sea level rise, not meters as MICI would project.

https://agu.confex.com/agu/fm18/meetingapp.cgi/Paper/458431

Quote
Climatic Thresholds for Widespread Ice Shelf Hydrofracturing and Ice Cliff Calving In Antarctica: Implications for Future Sea Level Rise

Monday, 10 December 2018

Here we explore the implications of hydrofacturing and subsequent ice-cliff collapse in a warming climate, by parameterizing these processes in a hybrid ice sheet-shelf model. Model sensitivities to meltwater production and to ice-cliff calving rate (a function of cliff height above the stress balance threshold triggering brittle failure) are calibrated to match modern observations of calving and thinning. We find the potential for major ice-sheet retreat if global mean temperature rises more than ~2ºC above preindustrial. In the model, Antarctic calving rates at thick ice fronts are not allowed to exceed those observed in Greenland today. This may be a conservative assumption, considering the very different spatial scales of Antarctic outlets, such as Thwaites. Nonetheless, simulations following a ‘worst case’ RCP8.5 scenario produce rates of sea-level rise measured in cm per year by the end of this century. Clearly, the potential for brittle processes to deliver ice to the ocean, in addition to viscous and basal processes, needs to be better constrained through more complete, physically based representations of calving.

Authors: 
Robert M Deconto
University of Massachusetts Amherst
 
David Pollard
Pennsylvania State University
 
Knut A Christianson
University of Washington
 
Richard B Alley
Pennsylvania State University

I'd also note that given trends in the decline of the coal industry and the rate of renewable energy installations in the past two years (the period in which renewables became cheaper than coal and are threatening to overtake natural gas), it's virtually impossible for us to burn enough fossil fuels to hit the RCP8.5 scenario.


nanning

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1793 on: October 29, 2019, 05:28:13 PM »
Thanks again for your brilliant posts AbruptSLR :).

I fear and expect that all warnings, science and efforts will not bring about the required changes.
I ask myself: Is this it? Is it just going to be: Doing the same things without radical change? When is enough, enough? Until collapse.
"It is preoccupation with possessions, more than anything else, that prevents us from living freely and nobly" - Bertrand Russell
   Simple: minimize your possessions and be free and kind    It's just a mindset.       Refugees welcome

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1794 on: October 29, 2019, 05:42:03 PM »
From DeConto and Pollard 2018:

https://www.geosci-model-dev-discuss.net/gmd-2018-28/gmd-2018-28.pdf

Quote
4.3 Antarctica
We now use the coupled model to examine the role of mélange during rapid retreat of Antarctic ice. Starting from the ice-sheet model state equilibrated to modern climate (with no mélange), an instantaneous change to a warm ~3 Ma mid Pliocene climate is imposed. As described in Pollard et al. (2015), atmospheric forcing is provided by a regional climate model with a warm austral-summer orbit and atmospheric CO2 level of 400 ppm, and circum-Antarctic ocean temperatures are assumed to warm 2 oC above modern climatology.

Note the bolded assumption.  Ocean temperatures around Antarctica need to be 2 degrees C warmer than they are currently (not warmer than pre-industrial) for MICI to begin.  So how fast are the waters around Antarctica currently warming? 


For this discussion what really matters in DeConto, Pollard and Alley (2018)'s model is the warming of the ocean in their model beneath the ice shelves and at the grounding line of the marine glaciers in the ASE (Amundsen Sea Embayment); which the attached image reminds us should increase by over 1.5C from 1960's temperatures to circa 2070 (i.e. the warm CDW advected over the continental shelf).  Furthermore, I note that their model does not include the influence of the subglacial cavity at the base of the Thwaites Ice Tongue.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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vox_mundi

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1795 on: October 29, 2019, 06:12:26 PM »
Rising Sea Levels Pose Threat to Homes of 300 Million People – Study
https://www.theguardian.com/environment/2019/oct/29/rising-sea-levels-pose-threat-to-homes-of-300m-people-study

More than three times more people are at risk from rising sea levels than previously believed, research suggests.

Land that is currently home to 300 million people will flood at least once a year by 2050 unless carbon emissions are cut significantly and coastal defences strengthened, says the study, published in Nature Communications. This is far above the previous estimate of 80 million.

Open Access: Scott A. Kulp, et.al. New elevation data triple estimates of global vulnerability to sea-level rise and coastal floodingNature Communications (2019)
https://www.nature.com/articles/s41467-019-12808-z

“There are three classes of people: those who see. Those who see when they are shown. Those who do not see.” ― Leonardo da Vinci

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

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1796 on: October 29, 2019, 07:23:43 PM »
While the linked reference does not project a pending shutdown of the AMOC in coming decades; neither can it rule-out such a possible shutdown this century:

W. Weijer et al. (24 July 2019), "Stability of the Atlantic Meridional Overturning Circulation: A Review and Synthesis", JGR Oceans, https://doi.org/10.1029/2019JC015083

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2019JC015083

Abstract: "The notion that the Atlantic Meridional Overturning Circulation (AMOC) can have more than one stable equilibrium emerged in the 1980s as a powerful hypothesis to explain rapid climate variability during the Pleistocene. Ever since, the idea that a temporary perturbation of the AMOC—or a permanent change in its forcing—could trigger an irreversible collapse has remained a reason for concern. Here we review literature on the equilibrium stability of the AMOC and present a synthesis that puts our understanding of past and future AMOC behavior in a unifying framework. This framework is based on concepts from Dynamical Systems Theory, which has proven to be an important tool in interpreting a wide range of model behavior. We conclude that it cannot be ruled out that the AMOC in our current climate is in, or close to, a regime of multiple equilibria. But there is considerable uncertainty in the location of stability thresholds with respect to our current climate state, so we have no credible indications of where our present‐day AMOC is located with respect to thresholds. We conclude by identifying gaps in our knowledge and proposing possible ways forward to address these gaps."

Extract: "Over decadal to centennial timescales, the AMOC decreases in response to an CO2 increase. This weakening may be exacerbated by potential positive freshwater perturbation from the Greenland Ice Sheet (Bakker et al., 2016; Böning et al., 2016; Luo et al., 2016; Rahmstorf et al., 2015) and the Arctic Ocean (Gelderloos et al., 2012; Giles et al., 2012).

Drijfhout et al. (2015) and Sgubin et al. (2017) investigated AMOC shut down within CMIP5 projections. In two climate models the AMOC shut down (reached a state with very weak AMOC) by 2100, …"

Edit: I note that a partial collapse of the WAIS in coming decades would actually push the AMOC's warm waters further northward (thus increasing Artic Amplification) and would increase tropical ocean SSTAs; via the bipolar seesaw mechanism.
« Last Edit: October 29, 2019, 07:42:33 PM by AbruptSLR »
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Lennart van der Linde

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1797 on: October 29, 2019, 08:15:35 PM »
At current observed rates of warming (with GMSTA around 1C above pre-industrial), the oceans around Antarctica are warming at 0.05 degrees C per decade.  At that rate, it would take 400 years to hit one of the necessary triggers for MICI to start.

That may be why DeConto and Pollard are urging more caution now about the MICI models.  They are still claiming that hydrofracturing could begin as GMSTA approaches 2C above pre-industrial, but that results in centimeters of sea level rise, not meters as MICI would project.

Hansen et al 2016 write:
https://www.atmos-chem-phys.net/16/3761/2016/

"We use numerical climate simulations, paleoclimate data, and modern observations to study the effect of growing ice melt from Antarctica and Greenland. Meltwater tends to stabilize the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in the Southern Ocean and North Atlantic, thus increasing Earth's energy imbalance and heat flux into most of the global ocean's surface. Southern Ocean surface cooling, while lower latitudes are warming, increases precipitation on the Southern Ocean, increasing ocean stratification, slowing deepwater formation, and increasing ice sheet mass loss. These feedbacks make ice sheets in contact with the ocean vulnerable to accelerating disintegration. We hypothesize that ice mass loss from the most vulnerable ice, sufficient to raise sea level several meters, is better approximated as exponential than by a more linear response. Doubling times of 10, 20 or 40 years yield multi-meter sea level rise in about 50, 100 or 200 years. Recent ice melt doubling times are near the lower end of the 10–40-year range, but the record is too short to confirm the nature of the response. The feedbacks, including subsurface ocean warming, help explain paleoclimate data and point to a dominant Southern Ocean role in controlling atmospheric CO2, which in turn exercised tight control on global temperature and sea level. The millennial (500–2000-year) timescale of deep-ocean ventilation affects the timescale for natural CO2 change and thus the timescale for paleo-global climate, ice sheet, and sea level changes, but this paleo-millennial timescale should not be misinterpreted as the timescale for ice sheet response to a rapid, large, human-made climate forcing. These climate feedbacks aid interpretation of events late in the prior interglacial, when sea level rose to +6–9 m with evidence of extreme storms while Earth was less than 1 °C warmer than today. Ice melt cooling of the North Atlantic and Southern oceans increases atmospheric temperature gradients, eddy kinetic energy and baroclinicity, thus driving more powerful storms. The modeling, paleoclimate evidence, and ongoing observations together imply that 2 °C global warming above the preindustrial level could be dangerous. Continued high fossil fuel emissions this century are predicted to yield (1) cooling of the Southern Ocean, especially in the Western Hemisphere; (2) slowing of the Southern Ocean overturning circulation, warming of the ice shelves, and growing ice sheet mass loss; (3) slowdown and eventual shutdown of the Atlantic overturning circulation with cooling of the North Atlantic region; (4) increasingly powerful storms; and (5) nonlinearly growing sea level rise, reaching several meters over a timescale of 50–150 years. These predictions, especially the cooling in the Southern Ocean and North Atlantic with markedly reduced warming or even cooling in Europe, differ fundamentally from existing climate change assessments."

If this ice melt feedback indeed exists, what would this mean for the rate of warming of the subsurface ocean waters? When would this warming reach 2 degrees C above current temperatures? Have DeConto & Pollard taken this potential feedback into account? How likely or unlikely is this feedback and what level of risk does this uncertainty imply?

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1798 on: October 29, 2019, 09:00:53 PM »
Thanks again for your brilliant posts AbruptSLR :).

I fear and expect that all warnings, science and efforts will not bring about the required changes.
I ask myself: Is this it? Is it just going to be: Doing the same things without radical change? When is enough, enough? Until collapse.

I would recommend being true to yourself, no matter what situation you find yourself in within a constantly changing world.
« Last Edit: October 31, 2019, 03:52:23 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #1799 on: October 29, 2019, 09:36:17 PM »

If this ice melt feedback indeed exists, what would this mean for the rate of warming of the subsurface ocean waters? When would this warming reach 2 degrees C above current temperatures? Have DeConto & Pollard taken this potential feedback into account? How likely or unlikely is this feedback and what level of risk does this uncertainty imply?

Lennart,

I is always a pleasure to read your posts; particularly when you quote James Hansen et al.

That said, while your questions are good they seem to me to lack focus in such matters as:

1. That ice-climate feedbacks exist is beyond question; rather what matters is how fast, how high and how far they occur for a given radiative forcing scenario.
2. It is a red herring to think about the rate of subsurface ocean waters in generic terms; which is why global climate models are required to both include such ice-climate feedbacks and to interpret the consequences of such feedbacks.
3. DeConto & Pollard included some ice-climate feedbacks in some of their projections (which did increase ice mass loss); but they did not include all such feedbacks and they did not include the current existing boundary conditions in the ASE; which have much more deteriorated ice shelves than they assumed and have much greater existing grounding line retreats than they modeled; and also they assumed that ECS is around 3C, rather than closer to the 5C value indicated my many CMIP6 model projections.
4. As to how much risk ice-climate feedbacks entail, I believe that the attached image from Hansen et al. (2016) showing that they could essentially double planetary energy imbalance for multidecadal periods only represents part of the risks, primarily as this attached image likely does not indicate the risk that such a perturbation in energy imbalance could trigger a cascade of following feedbacks (like rapid permafrost degradation etc.) that could lock key Earth Systems in a 'hot house' state for multiple centuries (in my opinion).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson