Support the Arctic Sea Ice Forum and Blog

Show Posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.


Messages - AbruptSLR

Pages: [1] 2 3 ... 342
1
The linked (open access) reference indicates that the West Greenland ice sheet experienced elevated levels (compared to modern) of precipitation during the Holocene Thermal Maximum.  These findings increase the risks that future increases in rainfall at low elevations in coastal West Greenland may accelerate hydrofracturing of key marine terminating glaciers like at the calving front of Jakobshavn Glacier:

Downs, J., Johnson, J., Briner, J., Young, N., Lesnek, A., and Cuzzone, J.: West Greenland ice sheet retreat history reveals elevated precipitation during the Holocene thermal maximum, The Cryosphere Discuss., https://doi.org/10.5194/tc-2019-129, in review, 2019.

https://www.the-cryosphere-discuss.net/tc-2019-129/

Abstract. We investigate changing precipitation patterns in the Kangerlussuaq region of west central Greenland during the Holocene thermal maximum, using a new chronology of ice sheet terminus position through the Holocene and a novel inverse modeling approach based on the unscented transform (UT). The UT is applied to estimate changes in annual precipitation in order to reduce the misfit between modeled and observed terminus positions. We demonstrate the effectiveness of the UT for time-dependent data assimilation, highlighting its low computational cost and trivial parallel implementation. Our results indicate that Holocene warming coincided with elevated precipitation, without which modeled retreat in the Kangerlussuaq region is more rapid than suggested by observations. Less conclusive is if high temperatures during the HTM were specifically associated with a transient increase in precipitation, as the results depend on the assumed temperature history. The importance of precipitation in controlling ice sheet extent during the Holocene underscores the importance of Arctic sea ice loss and changing precipitation patterns on the future stability of the GrIS.

2
The linked reference provides evidence that it will be difficult to get politically conservative individuals to fully accept climate change risks simply by using logic and data.  This implies that it will be more difficult to get off over our current BAU pathway then many individuals believe:

Matthew S. Nurse & Will Grant (16 Jun 2019), "I’ll See It When I Believe It: Motivated Numeracy in Perceptions of Climate Change Risk", Environmental Communication, https://doi.org/10.1080/17524032.2019.1618364

https://www.tandfonline.com/doi/full/10.1080/17524032.2019.1618364?af=R

Abstract: "People’s attitudes about Anthropogenic Climate Change (ACC) risks are not only influenced by scientific data, such as the likelihood of harm, the consequences of failing to act and the cost and effectiveness of mitigation. Instead, when people receive information about controversial topics of decision-relevant science like ACC they often defer to their political attitudes. Recent research has shown that more numerate people can be more polarized about these topics despite their better ability to interpret the scientific data. In this study, we investigated whether the motivated numeracy effect originally found by Kahan, Peters, Dawson, and Slovic [2017. Motivated numeracy and enlightened self-government. Behavioural Public Policy, 1(1)] on the controversial topic of gun control laws in the United States also applies to people when assessing ACC risks. This randomized controlled experiment (N = 504) of Australian adults extends the motivated reasoning thesis by finding evidence that highly numerate people who receive scientific data about ACC use motivated numeracy to rationalize their interpretations in line with their attitudes."

3
The linked (open access) reference indicates that during the mid-Pliocene wildfires were more common in the Arctic than they are today.  Hopefully, climate models will include this climate risk into their future projections:

Fletcher, T. L., Warden, L., Sinninghe Damsté, J. S., Brown, K. J., Rybczynski, N., Gosse, J. C., and Ballantyne, A. P.: Evidence for fire in the Pliocene Arctic in response to amplified temperature, Clim. Past, 15, 1063-1081, https://doi.org/10.5194/cp-15-1063-2019, 2019.

https://www.clim-past.net/15/1063/2019/

Abstract: "The mid-Pliocene is a valuable time interval for investigating equilibrium climate at current atmospheric CO2 concentrations because atmospheric CO2 concentrations are thought to have been comparable to the current day and yet the climate and distribution of ecosystems were quite different. One intriguing, but not fully understood, feature of the early to mid-Pliocene climate is the amplified Arctic temperature response and its impact on Arctic ecosystems. Only the most recent models appear to correctly estimate the degree of warming in the Pliocene Arctic and validation of the currently proposed feedbacks is limited by scarce terrestrial records of climate and environment. Here we reconstruct the summer temperature and fire regime from a subfossil fen-peat deposit on west–central Ellesmere Island, Canada, that has been chronologically constrained using cosmogenic nuclide burial dating to 3.9+1.5/−0.5 3.9+1.5/-0.5 Ma.

The estimate for average mean summer temperature is 15.4±0.8 ∘C using specific bacterial membrane lipids, i.e., branched glycerol dialkyl glycerol tetraethers. This is above the proposed threshold that predicts a substantial increase in wildfire in the modern high latitudes. Macro-charcoal was present in all samples from this Pliocene section with notably higher charcoal concentration in the upper part of the sequence. This change in charcoal was synchronous with a change in vegetation that included an increase in abundance of fire-promoting Pinus and Picea. Paleo-vegetation reconstructions are consistent with warm summer temperatures, relatively low summer precipitation and an incidence of fire comparable to fire-adapted boreal forests of North America and central Siberia.

To our knowledge, this site provides the northernmost evidence of fire during the Pliocene. It suggests that ecosystem productivity was greater than in the present day, providing fuel for wildfires, and that the climate was conducive to the ignition of fire during this period. The results reveal that interactions between paleo-vegetation and paleoclimate were mediated by fire in the High Arctic during the Pliocene, even though CO2 concentrations were similar to modern values."

4
The linked reference discusses efforts to calibrate the Community Earth System Model, CESM, to better project the poleward migration of moisture to Antarctica.  Such work can be used to better project the risk of future rainfall events (at low elevations) in West Antarctica and their potential impact on hydrofracturing risks to destabilize West Antarctic ice shelves:

Adriana Bailey et al. (20 June 2019), "Evaluating a Moist Isentropic Framework for Poleward Moisture Transport: Implications for Water Isotopes over Antarctica", Geophysical Research Letters, https://doi.org/10.1029/2019GL082965

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL082965?af=R

Abstract: "The ability to identify moisture source regions and sinks, and to model the transport pathways that link them in simple yet physical ways, is critical for understanding climate today and in the past. Using water tagging and isotopic tracer experiments in the Community Earth System Model, this work shows that poleward moisture transport largely follows surfaces of constant moist entropy. The analysis not only provides insight into why distinct zonal bands supply moisture to high‐ and low‐elevation polar sites but also explains why changes in these source regions are inherently linked to changes in temperature and rainout. Moreover, because the geometry, and specifically length, of the moist isentropic surfaces describes how much integrated rainout occurs, the analysis provides a physical framework for interpreting the isotopic composition of water in poleward‐moving air, thus indicating how variations in moisture transport might influence Antarctic ice cores."

5
More green energy measures to fight climate change assume that energy demand will not grow as the price of their energy decreases; however, the Jevons paradox indicates that as the price of energy decreases (due to increased efficiencies) demand will increase.  This means that green energy measures will be less effective than most advocates believe:

Title: "Jevons paradox"

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

Extract: "In economics, the Jevons paradox (sometimes Jevons effect) occurs when technological progress or government policy increases the efficiency with which a resource is used (reducing the amount necessary for any one use), but the rate of consumption of that resource rises due to increasing demand. The Jevons paradox is perhaps the most widely known paradox in environmental economics. However, governments and environmentalists generally assume that efficiency gains will lower resource consumption, ignoring the possibility of the paradox arising.
 
In 1865, the English economist William Stanley Jevons observed that technological improvements that increased the efficiency of coal-use led to the increased consumption of coal in a wide range of industries. He argued that, contrary to common intuition, technological progress could not be relied upon to reduce fuel consumption."

6
While this has been discussed previously, I remind readers that about 17.7 kya Mount Takahe near the Thwaites Gateway erupted and created an Antarctic ozone hole comparable that the one that exists today.  The paleo-event lead to an abrupt acceleration of Southern Hemisphere deglaciation; in a comparable manner as I believe is occurring today:

Joseph R. McConnell et al. (September 19, 2017), "Synchronous volcanic eruptions and abrupt climate change ∼17.7 ka plausibly linked by stratospheric ozone depletion", PNAS 114 (38) 10035-10040; https://doi.org/10.1073/pnas.1705595114

https://www.pnas.org/content/114/38/10035

Significance

Cold and dry glacial-state climate conditions persisted in the Southern Hemisphere until approximately 17.7 ka, when paleoclimate records show a largely unexplained sharp, nearly synchronous acceleration in deglaciation. Detailed measurements in Antarctic ice cores document exactly at that time a unique, ∼192-y series of massive halogen-rich volcanic eruptions geochemically attributed to Mount Takahe in West Antarctica. Rather than a coincidence, we postulate that halogen-catalyzed stratospheric ozone depletion over Antarctica triggered large-scale atmospheric circulation and hydroclimate changes similar to the modern Antarctic ozone hole, explaining the synchronicity and abruptness of accelerated Southern Hemisphere deglaciation.

Abstract

Glacial-state greenhouse gas concentrations and Southern Hemisphere climate conditions persisted until ∼17.7 ka, when a nearly synchronous acceleration in deglaciation was recorded in paleoclimate proxies in large parts of the Southern Hemisphere, with many changes ascribed to a sudden poleward shift in the Southern Hemisphere westerlies and subsequent climate impacts. We used high-resolution chemical measurements in the West Antarctic Ice Sheet Divide, Byrd, and other ice cores to document a unique, ∼192-y series of halogen-rich volcanic eruptions exactly at the start of accelerated deglaciation, with tephra identifying the nearby Mount Takahe volcano as the source. Extensive fallout from these massive eruptions has been found >2,800 km from Mount Takahe. Sulfur isotope anomalies and marked decreases in ice core bromine consistent with increased surface UV radiation indicate that the eruptions led to stratospheric ozone depletion. Rather than a highly improbable coincidence, circulation and climate changes extending from the Antarctic Peninsula to the subtropics—similar to those associated with modern stratospheric ozone depletion over Antarctica—plausibly link the Mount Takahe eruptions to the onset of accelerated Southern Hemisphere deglaciation ∼17.7 ka.

7
At least the US House of Representative realizes that we are already in a 'Climate Crisis':

House Select Committee on the Climate Crisis

https://climatecrisis.house.gov/

8
As consensus climate scientists typically 'err on the side of least drama' (ESLD), they would undoubtable contribute more to reducing climate risks by applying 'Drama theory' to their own actions as well as that of the general-public, and decision makers, before they make recommendations such as the Carbon Budgets:

Title: "Drama theory"

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

Extract: "Drama-theorists build and analyze models (called card tables or options boards) that are isomorphic to game models, but unlike game theorists and most other model-builders, do not do so with the aim of finding a 'solution'. Instead, the aim is to find the dilemmas facing characters and so help to predict how they will re-define the model itself – i.e., the game that will be played. Such prediction requires not only analysis of the model and its dilemmas, but also exploration of the reality outside the model; without this it is impossible to decide which ways of changing the model in order to eliminate dilemmas might be rationalized by the characters.

The relation between drama theory and game theory is complementary in nature. Game theory does not explain how the game that is played is arrived at – i.e., how players select a small number of players and strategies from the virtually infinite set they could select, and how they arrive at common knowledge about each other's selections and preferences for the resulting combinations of strategies. Drama theory tries to explain this, and also to explain how the 'focal point' is arrived at for the 'game with a focal point' that is finally played. On the other hand, drama theory does not explain how players will act when they finally have to play a particular 'game with a focal point', even though it has to make assumptions about this. This is what game theory tries to explain and predict."

9
The linked article indicates that it may not be easy to correct the damage done to the climate by the Trump Administration's rollback of U.S. regulations on coal:

Title: "How the EPA's climate rule rollback could reach beyond coal"

https://www.axios.com/epa-climate-rule-coal-power-20f3bed0-aa2e-4576-9b22-82cf6ba076af.html

Extract: "A big question now that EPA has finalized climate regulations for power plants is how much they'll constrain a future president — especially a potential Democrat that wants to act way more aggressively.

"EPA's narrow approach to the power sector rulemaking could pose hurdles to future regulation of other sectors under a differently minded future administration," the consultancy ClearView Energy Partners said in a note."

10
The linked reference discusses the impact that microorganisms may have on climate change on human wellbeing, and warns that consensus climate science model projections should more fully consider the interactions between microorganisms and climate change:

Ricardo Cavicchioli et al. (2019), "Scientists’ warning to humanity: microorganisms and climate change", Nature Reviews Microbiology, DOI: https://doi.org/10.1038/s41579-019-0222-5

https://www.nature.com/articles/s41579-019-0222-5

Abstract: "In the Anthropocene, in which we now live, climate change is impacting most life on Earth. Microorganisms support the existence of all higher trophic life forms. To understand how humans and other life forms on Earth (including those we are yet to discover) can withstand anthropogenic climate change, it is vital to incorporate knowledge of the microbial ‘unseen majority’. We must learn not just how microorganisms affect climate change (including production and consumption of greenhouse gases) but also how they will be affected by climate change and other human activities. This Consensus Statement documents the central role and global importance of microorganisms in climate change biology. It also puts humanity on notice that the impact of climate change will depend heavily on responses of microorganisms, which are essential for achieving an environmentally sustainable future."

11

I'll just infer that Thwaites is one of the prime spots where we'll see MICI proved or disproved in the intermediate future.


While Thwaites is the most important marine glacier to watch, it is physically connected to the Pine Island Glacier; therefore, in the attached image I have sketched a blue line where I speculate that a calving fault will form in the Southwest corner of the Pine Island Ice Shelf. PIIS, sometime in the second half of July 2019.  While I may be wrong, it is at least worth watching, and I note that no consensus climate ice sheet model that I have seen projects such a rapid retreat of the PIIS.

Edit: This image was taken on May 22, 2019

I attach a Sentinel 1 image of the Southwest corner of the PIIS and the ice face of the SW Tributary ice shelf taken on June 19, 2019.  This image shows a minor calving event (which occurred on June 17, 2019) in this corner.  In my opinion one more such event in this Southwest corner of the PIIS should like trigger a major calving event for the PIIS sometime in the second half of July 2019.

Edit: And again I reiterate that no consensus climate ice sheet model that I have seen projects such a rapid retreat of the PIIS ice face.

12
The linked reference indicates that using current climate models '… the sum of the individual ice volume changes amounts to less than half of the full ice volume response, indicating the existence of strong nonlinearities and forcing synergy."  Also: 'Our results highlight the importance of accurately representing the relative timing of forcings of past ice sheet simulations, and underscore the need for developing coupled climate-ice sheet modeling frameworks that properly capture key feedbacks.'

Hopefully, E3SM can be upgraded sufficiently to hindcaste paleo-events such as the Quaternary.

Tigchelaar, M., Timmermann, A., Friedrich, T., Heinemann, M., and Pollard, D.: Nonlinear response of the Antarctic ice sheet to Quaternary sea level and climate forcing, The Cryosphere Discuss., https://doi.org/10.5194/tc-2019-83, in review, 2019.

https://www.the-cryosphere-discuss.net/tc-2019-83/
https://www.the-cryosphere-discuss.net/tc-2019-83/tc-2019-83.pdf

Abstract. Antarctic ice volume has varied substantially during the Quaternary, with reconstructions suggesting a glacial ice sheet extending to the continental shelf break, and interglacial sea level highstands of several meters. Throughout this period, changes in the Antarctic ice sheet were driven by changes in atmospheric and oceanic conditions and global sea level, yet so far, modeling studies have not addressed which of these environmental forcings dominate, and how they interact in the dynamical ice sheet response. Here we force an Antarctic ice sheet model with global sea level reconstructions and transient, spatially explicit boundary conditions from a 408 ka climate model simulation, not only in concert with each other but, for the first time, also separately. We find that together, these forcings drive glacial-interglacial ice volume changes of 12–14 m SLE, in line with reconstructions and previous modeling studies. None of the individual drivers – atmospheric temperature and precipitation, ocean temperatures, sea level – single-handedly explains the full ice sheet response. In fact, the sum of the individual ice volume changes amounts to less than half of the full ice volume response, indicating the existence of strong nonlinearities and forcing synergy. Both sea level and atmospheric forcing are necessary to create full glacial ice sheet growth, whereas the contribution of ocean melt changes is found to be more a function of ice sheet geometry than climatic change. Our results highlight the importance of accurately representing the relative timing of forcings of past ice sheet simulations, and underscore the need for developing coupled climate-ice sheet modeling frameworks that properly capture key feedbacks.

Edit: Until we have well calibrated models that indicate otherwise, the risk of abrupt loss of ice mass from Antarctica in the coming decades remains a real risk.

13
As Antarctic Bottom Water (AABW) formation is a major driver of the meridional overturning current; the finding of the linked reference (which in my opinion errs on the side of least drama) that projected Antarctic ice mass loss (following either RCP 4.5 or RCP 8.5) will result in '… a near complete shutdown of AABW formation within just 50 years …', is a positive ice-climate feedback mechanism that is omitted from almost all current consensus climate model projections.

Véronique Lago, and Matthew H. England (2019), "Projected slowdown of Antarctic Bottom Water formation in response to amplified meltwater contributions", Journal of Climate, https://doi.org/10.1175/JCLI-D-18-0622.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-18-0622.1?af=R

Abstract: "The sinking and recirculation of Antarctic Bottom Water (AABW) is a major regulator of the storage of heat, carbon and nutrients in the ocean. This sinking is sensitive to changes in surface buoyancy, particularly due to freshening as salinity plays a greater role in determining density at cold temperatures. Acceleration in Antarctic ice-shelf and land-ice melt could thus significantly impact the ventilation of the world’s oceans, yet future projections do not usually include this effect in models. Here we use an ocean-sea-ice model to investigate the potential long-term impact of Antarctic meltwater on ocean circulation and heat storage. The freshwater forcing is derived from present-day estimates of meltwater input from drifting icebergs and basal melt, combined with RCP2.6, RCP4.5 and RCP8.5 scenarios of projected amplification of Antarctic meltwater. We find that the additional freshwater induces a substantial slowdown in the formation rate of AABW, reducing ventilation of the abyssal ocean. Under both the RCP4.5 and RCP8.5 meltwater scenarios, there is a near complete shutdown of AABW formation within just 50 years, something not captured by climate model projections. The abyssal overturning at ∼30oS also weakens, with a ∼20 year delay relative to the onset of AABW slowdown. After 200 years, up to ∼50% of the original volume of AABW has disappeared due to abyssal warming, induced by vertical mixing in the absence of AABW ventilation. This suggests that climate change could induce the disappearance of present day abyssal water-masses, with implications for the global distribution of heat, carbon and nutrients."

14
Per the linked reference many permafrost zones of the Canadian High Arctic are already experiencing thermokarst development.  This is not good news w.r.t. to the positive feedback mechanism associated with permafrost degradation.

Louise M. Farquharson et al. (10 June 2019), "Climate change drives widespread and rapid thermokarst development in very cold permafrost in the Canadian High Arctic", Geophysical Research Letters, https://doi.org/10.1029/2019GL082187

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL082187?af=R

Abstract
Climate warming in regions of ice‐rich permafrost can result in widespread thermokarst development, which reconfigures the landscape and damages infrastructure. We present multi‐site time‐series observations which couple ground temperature measurements with thermokarst development in a region of very cold permafrost. In the Canadian High Arctic between 2003 and 2016, a series of anomalously warm summers caused mean thawing indices to be 150 – 240 % above the 1979‐2000 normal resulting in up to 90 cm of subsidence over the 12‐year observation period. Our data illustrate that despite low mean annual ground temperatures, very cold permafrost (<‐10°C) with massive ground ice close to the surface is highly vulnerable to rapid permafrost degradation and thermokarst development. We suggest that this is due to little thermal buffering from soil organic layers and near surface vegetation, and the presence of near surface ground ice. Observed maximum thaw depths at our sites are already exceeding those projected to occur by 2090 under RCP 4.5.

Key Points
•   Observed thermokarst development in very cold permafrost at 3 monitoring sites along a 700 km transect in the Canadian High Arctic.
•   Rapid landscape response to above average summer warmth is due to limited thermal buffering from overlying ecosystem components and near‐surface ground ice.
•   Change was greatest at Mould Bay where thawing index values were 240 % above historic normals causing ~90 cm of subsidence in 12 years.

15
The linked reference (& associated article) indicates that as the Western Tropical Pacific sea surface temperature increases (say due to GHG emissions, increasingly strong El Nino events and/or ice-climate feedbacks), the associated telecommunication of energy from the Tropical Pacific will likely service to accelerate the destabilization of the WAIS:

Kyle R. Clem, Benjamin R. Lintner, Anthony J. Broccoli, James R. Miller. Role of the South Pacific Convergence Zone in West Antarctic Decadal Climate Variability. Geophysical Research Letters, 2019; DOI: 10.1029/2019GL082108

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL082108

Abstract
Regional atmospheric circulation along coastal West Antarctica associated with the Amundsen Sea Low (ASL) mediates ice shelf melt that governs Antarctica's contribution to global sea level rise. In this study, the South Pacific Convergence Zone (SPCZ) is identified as a significant driver of ASL variability on decadal time scales. Using the Community Earth System Model, we impose a positive sea surface temperature anomaly in the SPCZ that reproduces an increase in convective rainfall in the southwest SPCZ that has been observed in recent decades, consistent with the Interdecadal Pacific Oscillation (IPO). Many of the major observed climate shifts across West Antarctica during the 2000‐2014 period when the IPO was in its negative phase can be explained via a teleconnection over the ASL emanating from the SPCZ. Knowledge of these relationships significantly enhances our understanding and interpretation of past and future West Antarctic climate variability.

Plain Language Summary
Deep convective rainfall in the South Pacific Convergence Zone (SPCZ) alters the regional atmospheric circulation along coastal West Antarctica impacting the regional climate and potentially driving warm ocean water upwelling that melts ice shelves. Increases in SPCZ rainfall cause cooling on the Antarctic Peninsula and warming across the Ross Ice Shelf and portions of East Antarctica. Such conditions were observed during the 2000‐2014 period in which the phase of the Interdecadal Pacific Oscillation (IPO), a naturally‐occurring mode of tropical Pacific decadal variability, was negative. The influence of the SPCZ on West Antarctic climate is consistent with observed shifts in West Antarctic climate over the period 2000‐2014. Therefore, the SPCZ, though a tropical climate feature, is found to be an important driver of West Antarctic climate on decadal time scales governed by the IPO.

See also:

Title: "Warming waters in western tropical Pacific may affect West Antarctic Ice Sheet"

https://www.sciencedaily.com/releases/2019/06/190613095204.htm

Extract: "Warming waters in the western tropical Pacific Ocean have significantly increased thunderstorms and rainfall, which may affect the stability of the West Antarctic Ice Sheet and global sea-level rise, according to a Rutgers University-New Brunswick study."

16
It looks like accelerating methane emissions may thwart efforts to meet the Paris Agreement goal of staying well below a 2C GMSTA.  The attached image shows atmospheric methane concentration values from NOAA's South Pole facility from the beginning of 2005 until June 18, 2019:

Title: "Rising methane may thwart efforts to avoid catastrophic climate change"

https://phys.org/news/2019-06-methane-thwart-efforts-catastrophic-climate.html

Extract: "If the world were on track to meet the Paris Agreement goal of less than 2 degrees Celsius of global warming, methane levels in the atmosphere would theoretically be dropping. Instead, they have been rising since 2007, and shooting up even faster since 2014. A perspective published in the journal Science discusses the potential causes and consequences of our planet's out-of-control methane.

The emissions targets in the Paris Agreement were based largely on data from the 1990s and early 2000s, when methane levels were flatter, said Sara Mikaloff Fletcher, a climate scientist with New Zealand's National Institute of Water and Atmospheric Research in Wellington and first author of the new article. The only emissions scenario that achieves Paris Agreement goals in climate models assumes that methane levels have been declining since 2010, when in fact they have been rising since 2007, she said. There may be other ways of keeping climate change under 2 degrees Celsius, but they would involve compensating for rising methane with more drastic cuts to other greenhouse gases."

17
Boaty McBoatface has identified a mechanism that enables the Southern Ocean's Westerly winds '... to increase turbulence deep in the Southern Ocean, causing warm water a mid depths to mix with cold, dense water in the abyss.' 
Unfortunately, current models do not simulate this newly identified mechanism; which in my book increases our collective risk of potential future abrupt sea level rise:

Title: "Boaty McBoatface mission gives new insight into warming ocean abyss"

https://phys.org/news/2019-06-boaty-mcboatface-mission-insight-ocean.html

Extract: "In recent decades, winds blowing over the Southern Ocean have been getting stronger due to the hole in the ozone layer above Antarctica and increasing greenhouse gases. The data collected by Boaty, along with other ocean measurements collected from research vessel RRS James Clark Ross, have revealed a mechanism that enables these winds to increase turbulence deep in the Southern Ocean, causing warm water at mid depths to mix with cold, dense water in the abyss.

The resulting warming of the water on the sea bed is a significant contributor to rising sea levels. However, the mechanism uncovered by Boaty is not built into current models for predicting the impact of increasing global temperatures on our oceans."

Edit: I note that the new mechanism identified by Boaty McBoatface works to slow-down the velocity of the global meridional overturning current; which, then causes tropical ocean surface temperatures to increase; which, is a positive ice-climate feedback mechanism.

18
The attached image shows the 2019 UN projection of world population through 2100.

https://population.un.org/wpp/Graphs/Probabilistic/900


19
Why is it that consensus climate scientist say that we still have time to cut GHG emissions, but a growing number of climate scientists now think that geoengineering may be essential?

Title: "More Scientists Now Think Geoengineering May Be Essential"

https://www.wired.com/story/more-scientists-now-think-geoengineering-may-be-essential/

20
Notice anything unusual in this year data in the attached plot of Greenland Surface Ice Melt Extent Area thru the second week of June 2019?

21
The linked pdf of a PowerPoint presentation on recent progress in E3SMv2's cryosphere modeling effort, indicate that they believe that their model is biased because it indicates abrupt ice mass loss from the Filchner-Ronne and Avery ice shelves beginning circa 2060 (see images) just as was projected by Hellmer et al. (2012).  To me this indicates not only how difficult it is to model non-linear ice mass loss from Antarctica but also how difficult it is to get decision makers to accept the risks associated with such potential abrupt ice mass loss phenomena:

Title: "Recent Findings from the E3SM Cryosphere Science Campaign" by Comeau et al. (May 2019)

https://e3sm.org/wp-content/uploads/2019/05/Comeau-Asay-Davis-Veneziani-All-Hands-May-2019_opt.pdf


22
AR5 reports ECS values calculated using a large variety of assumptions and methodologies, and the linked reference recommends that in the future (e.g. AR6): "… that researchers should present their analysis in an explicitly Bayesian manner as we have done here, as this allows the influence of the prior and other uncertain inputs to be transparently tested."

Annan, J. and Hargreaves, J.: Bayesian deconstruction of climate sensitivity estimates using simple models: implicit priors, and the confusion of the inverse, Earth Syst. Dynam. Discuss., https://doi.org/10.5194/esd-2019-33, in review, 2019

https://www.earth-syst-dynam-discuss.net/esd-2019-33/

Abstract. Observational constraints on the equilibrium climate sensitivity have been generated in a variety of ways, but the epistemic basis of these calculations have not always been clearly presented and a number of results have been calculated which appear to be based on somewhat informal heuristics. This causes a lack of clarity about the status of such results and how they compare to other analyses, in particular whether the differences between them may be due to differences in unstated assumptions rather than observational evidence.
In this paper, we show how these problems can be resolved. We demonstrate that many of these estimates can be reinterpreted within the standard subjective Bayesian framework in which a prior over the uncertain parameters is updated through a likelihood arising from observational evidence. In many of these cases, the prior which was (under this interpretation) implicitly used exhibits some unconventional and possibly undesirable properties. We present alternative calculations which use the same observational information to update a range of explicitly presented priors.
Our calculations suggest that the heuristic methods do often generate reasonable results, in that they agree fairly well with the explicitly Bayesian approach using a reasonable prior. However, we also find some significant differences and argue that the explicitly Bayesian approach is preferred, as it both clarifies the role of the prior, and allows researchers to transparently test the sensitivity of their results to it.

23
With sea level rise it will be higher storm surge that has significant impacts first.
We have already seen New York badly impacted with tropical cyclone  sandy.
It will not be the slow  rise of sea level that causes eventual retreat it will be weather events causing catastrophic damage and sane evaluation of the costs and futility of repeated repair. The developed world is far more susceptible to such costly events than the poor regions of Bangladesh.

Seeing as I have commented on this thread.
Thanks ASLR I have been reading your output for years and appreciate the immense amount of effort  your do in constructing your well supported narrative.

There are many factors contributing to inundation risks besides eustatic SLR, and storm surge, as illustrated by the attached three images.

Edit: I also note that recent research finds that for Hurricane/Typhoon cases, wave run-up is worse than previously assumed due to larger (than previously assumed) infragravity waves.

24
The attached image shows that primary energy consumptions is growing even faster than CO2 emissions, while the linked article indicates that this is significantly due to the recent rapid growth in natural gas as a primary energy fuel.  However, it would be better if media articles reported CO2-equivalent emissions and used a GWP-100 value of 35 for methane rather than the 25 value unscientifically used by NOAA:

Title: "In-depth: BP data reveals record CO2 emissions in 2018 driven by surging use of gas"

https://www.carbonbrief.org/in-depth-bp-data-reveals-record-co2-emissions-in-2018-driven-by-surging-use-of-gas

Extract: "Gas was the largest driver of energy-use growth in 2018, responsible for more than 40% of the increase. This, along with increased use of oil and coal, led to global CO2 emissions rising by 2% in 2018, the largest year-on-year increase in seven years."

See also:

Title: "The world goes the wrong way on carbon emissions"

https://www.axios.com/carbon-emissions-energy-consumption-bp-report-2fd9a2dc-b905-433d-b347-115a132a2933.html



25
For what it is worth, the attached BoM Nino 3.4 Outlook forecast was issued today based on models runs from June 8, 2019; which projects the current mild El Nino event to last throughout 2019 (which will increase GMSTA this year).

26
The first linked reference indicates the relatively unique relationship between the African rift valley and the West Antarctic Rift, WAR, established about 180 million years ago as Gondwana (Pangaea) split apart (see first and second images).

http://www.luomus.fi/en/largest-lava-eruptions-earth

Caption for the second image: " Schematic cross-section of the Karoo continental flood basalt province c. 180 million years ago. 1) Mantle melts extensively and the 2) melts intrude the lithosphere (=crust + brittle upper mantle), where they form large magma chambers and mix with it. 3) The contaminated melts proceed upwards and 4) erupt from shield volcanoes or fissures. 5) Some rare melts do not assimilate lithosphere and preserve the original mantle-derived geochemical signature. Image: Luomus / Jussi Heinonen"

Quote: "Our latest findings indicate that the enormous melt generation was caused by at least two processes: 1) Gondwana supercontinent functioned like a "lid on a cooking pot" and prevented the cooling of the sublithospheric mantle. High amount of accumulated heat caused more efficient melting of the mantle (Heinonen et al., 2010). 2) Some portions of the sublithospheric mantle were relatively Fe-rich and melted more efficiently than ambient mantle materials. Such portions were formed by mixing with ancient parts of oceanic crust that sank in to the mantle at subduction zones (Heinonen et al., 2013, 2014)."

Furthermore, the second linked reference shows how the sub-lithospheric interconnection between Africa's rift valley and WAR may have changed with some interconnection possibly being maintained via mantle plumes, such as beneath the Erebus volcano (see the third and fourth images).  Thus as the WAIS loses ice mass, we may witness changes in mantle dynamics as far away as Central Africa and South America:

Philip J. Heron (19 November 2018), "Mantle plumes and mantle dynamics in the Wilson cycle",
Geological Society, London, Special Publications, 470, https://doi.org/10.1144/SP470.18

https://sp.lyellcollection.org/content/early/2018/11/16/SP470.18

Caption for third image: "A cartoon of a simple supercontinent, the starting point for this review. Step 1, a supercontinent is amassed through a super-downwelling. Step 2, subduction then forms on the margins of the continent, generating sub-continental plumes due to mantle return flow and warming of the mantle through continental insulation (step 3). Step 4, the continental plumes facilitate the dispersal of the supercontinent."

Edit, see also Replies #: 101, 102, 103, 113, 115, 117, 147, 167, 168, 170, 172, 178, 442, 900 & 1,149.

27
Mt. Erebus has played a key role in the WAIS past and if it is activated again (possibly by the loss of sufficient WAIS ice mass) it could play an important part in the WAIS's future, as it is an alkaline volcano.

From the following summary and image are from:

 http://erebus.nmt.edu/index.php/volcanology/51-volcanological-evolution

"Prior to the early 1990's, much was known about the geochemical evolution of lavas from Mt. Erebus. Clearly, the stratigraphically oldest lavas were of a primitive basanitic composition, while the current activity is a more chemically evolved tephriphonolite. However, only a few age dates existed for the whole of Mt. Erebus and these were limited to imprecise conventional K/Ar dates. Beginning in 1993, Dr. Philip Kyle and two of his students (Chris Harpel and Richard Esser) began utilizing the more advanced, high precision 40Ar/39Ar dating technique to determine the ages of many of the exposed lava flows on Mt. Erebus. Prior to the use of 40Ar/39Ar geochronology on Mt. Erebus, what little age data existed suggested that the volcano was several million years old, including the young-looking summit area. We now know that the entire volcano is just slightly older than 1 million years old and that the summit is significantly younger than 100,000 years old.

By combining the new geochronologic data with the existing database of geochemical data, we can better confirm an evolutionary model for the development of Mt. Erebus. Below are the summarized results from several researchers working on the evolution of the volcano.

Mt. Erebus is one of several volcanoes in the McMurdo Volcanic Group which itself consists of Late Cenozoic intraplate alkaline volcanoes."

The caption for the attached figure is:  Cross-section of the crust and upper mantle below Ross Island, Antarctica. A "hot spot" or mantle plume is theorized as the mechanism to account for the origin of Mt. Erebus and Ross Island

See also:

Title: "Antarctica's sleeping dragon: Lava lake steams amid coldest place on Earth"

https://www.mnn.com/earth-matters/wilderness-resources/stories/antarcticas-sleeping-dragon-lava-lake-steams-amid-coldest

28
As global warming leads to the retreat of more Arctic (terrestrial) glaciers, the associated high-latitude aeolian dusts may well contribute to an Arctic albedo flip due to both reduced Arctic cloud reflectivity and reduced life of Arctic clouds.  This is another climate risk that is under appreciated by consensus climate science:

Title: "How Dust From Receding Glaciers Is Affecting the Climate"

http://glacierhub.org/2019/06/05/how-dust-from-receding-glaciers-is-affecting-the-climate/

Extract: "Though the study focused on the effect of glacier dust on cloud properties and lifetime, the results suggest larger questions about the impact of glacier dust on cloud reflectivity.
A decline in the reflective capability of clouds could degrade the Earth’s ability to moderate its temperature. Paul DeMott, one of the study’s co-authors, told GlacierHub that he was careful not make conclusions about the role of glacier dust in cloud reflectivity, though he acknowledged that it is “a natural, if simplistic, way of thinking about it.”

Whether or not a cloud contains ice particles is a primary determinant of its reflective capacity, as well as heat-trapping ability. Ice crystals allow more light to pass through clouds, while effectively absorbing outgoing infrared radiation.

As warming from the human-driven climate crisis accelerates, glacier dust is expected to become more abundant, with consequences for Arctic cloud cover and the Earth’s temperature, which depends on the reflectivity and heat-trapping ability of clouds. The study’s conclusion, that ice nucleating particles in glacier dust affect cloud properties, underscores the interconnectedness of natural systems, and their sensitivities."

See also:

Yutaka Tobo  et al (2019), "Glacially sourced dust as a potentially significant source of ice nucleating particles", Nature Geoscience,  12, 253–258, DOI: https://doi.org/10.1038/s41561-019-0314-x

https://www.nature.com/articles/s41561-019-0314-x

Abstract: "Aeolian dusts serve as ice nucleating particles in mixed-phase clouds, and thereby alter the cloud properties and lifetime. Glacial outwash plains are thought to be a major dust source in cold, high latitudes. Due to the recent rapid and widespread retreat of glaciers, high-latitude dust emissions are projected to increase, especially in the Arctic region; which is highly sensitive to climate change. However, the potential contribution of high-latitude dusts to ice nucleation in Arctic low-level clouds is not well acknowledged. Here we show that glacial outwash sediments in Svalbard (a proxy for glacially sourced dusts) have a remarkably high ice nucleating ability under conditions relevant for mixed-phase cloud formation, as compared with typical mineral dusts. The high ice nucleating ability of the sediments is probably governed by the presence of small amounts of organic matter (<1 wt% organic carbon) rather than mineral components. In addition, our results from intensive field measurements and model simulations indicate that the concentrations of atmospheric ice nucleating particles over the Svalbard region are expected to be enhanced in the summertime under the influence of dust emissions from Svalbard and its surroundings. We suggest that high-latitude dust sources have the potential to significantly influence glaciation of Arctic low-level clouds."

29
The linked website provides a number of downloadable reports from the Australian 'Breakthrough National Centre for Climate Rehabilitation', including its latest report entitled: "What Lies Beneath - The Understatement of Existential Climate Risk" by Spratt & Dunlop (2019)

https://www.breakthroughonline.org.au/publications

Extract: "This latest Breakthrough report argues for an urgent risk reframing of climate research and the IPCC reports. What Lies Beneath is the inside story of how climate policy-making has become embedded in a culture of failure and scientific reticence. The report brings together the voices of some of the world’s leading scientists."

Edit: Unfortunately, none of these reports appropriately address the risks of positive ice-climate feedback mechanisms.

30
As a follow-on to my last post, the linked articles discuss how the International Ocean Discovery Program, spent January to March 2019 in the Amundsen Sea collection seabed sediment cores to better evaluate the stability of the WAIS.  The cores extend back to at least 6 million years and thus include the Mid-Pliocene period.  While the cores will take 2 years to fully evaluate.  Preliminary x-rays of the cores taken on the drill ship showed layers of abundant stones/pebbles that could only have been deposited by iceberg leaving the ASE (i.e. ice-rafted debris); which supports the possibility/probability of MICI-types of WAIS collapse during multiple periods over the past 6 million years:

Title: "Newly drilled sediment cores could reveal how fast the Antarctic ice sheet will melt" by Erik Stokstad (April 2019)

https://www.sciencemag.org/news/2019/04/newly-drilled-sediment-cores-could-reveal-how-fast-antarctic-ice-sheet-will-melt

Extract: "The West Antarctic Ice Sheet is particularly vulnerable to melting from warming ocean waters because its base lies below sea level. Computer models vary in their predictions of how quickly it will disappear, but some predict it will be responsible for driving up global sea levels by a meter or more over the next century. To improve those models, scientists want to learn about the behavior of the ice sheet during the mid-Pliocene, 3 million to 4 million years ago, when temperatures were like today’s, says Rob DeConto, a glaciologist at the University of Massachusetts in Amherst who studies the ice sheet. The new cores, he says “will have a lot to bring to the table.”

The JOIDES Resolution, a research ship operated by the International Ocean Discovery Program, spent January to March in the Amundsen Sea, off the coast of West Antarctica. The hope was to drill sediment cores in five places, ranging from the continental rise toward the shallower waters of the continental shelf. Unfortunately, the ship could not reach the drill sites closer to Antarctica because it is not equipped to travel through ice and sea ice (which grows and retreats each year) extended farther out than usual. Even in the open water, avoiding the many icebergs meant less time to drill in other places. “We simply had bad luck this year,” says Karsten Gohl, a geophysicist at the Alfred Wegener Institute in Bremerhaven, Germany, and a leader of the cruise. “Despite the icebergs, we still got fantastic cores.”

Crucially, the sediment cores preserve a complete history: The Amundsen Sea at that site is 4000 meters deep, so the seafloor dune was safe from storms that can erode sediment in shallower water. “The fact that you have a continuous record from this margin is really exceptional,” Colleoni says. Tiny fossils indicate that the oldest parts of the core date back to the late Miocene, about 6 million years ago, dates that were confirmed by the patterns of magnetism recorded in the sediments.

The other site, which yielded cores from four holes, is some 60 kilometers away from the first one and close to a submarine channel. When deep currents travel down such channels, they often carry and deposit sediment that was eroded from nearby land. (The currents passing over the drift, in contrast, are thought to carry sediment from much farther away.) Researchers can trace the origin of sediment by studying the mineralogy and chemistry of individual grains, comparing them to rocks on land. By combining various lines of evidence, the team hopes to infer when the ice sheet retreated.

The cores from both sites also contain pebbles or larger stones that were transported from the continent by icebergs. An abundance of such stones is another, more straightforward sign of a retreating ice sheet that is calving many icebergs.

A key question is how the waxing and waning of the ice sheet correlates with records of ocean temperatures, which the researchers can estimate from the abundance of certain chemical isotopes in the fossilized shells of tiny organisms called foraminifera.

The research team expects to spend the next 2 years coaxing this history out of the cores.:

See also:

Title: "The sensitive Achilles heel of the white continent" by Dagmar Rohrlich (March 2019)

https://translate.google.com/translate?sl=de&tl=en&u=https%3A%2F%2Fwww.deutschlandfunk.de%2Fwestantarktischer-eisschild-die-sensible-achillesferse-des.676.de.html%3Fdram%3Aarticle_id%3D446200

Extract: " To do this, one would have to know how much the ice sheet has melted off in the warm phases – and this can be seen in the deep-sea sediments of the Amundsen Sea. …
"We can already say that in the past millions of years the central part of the West Antarctic Ice Sheet has repeatedly extended far out to the sea before retreating, …

How long these cycles last exactly, the evaluations have yet to show.  Then the researchers hope, it will also prove where the ice sheet could completely collapse during warm periods. If man triggered it, he would cause sea level rise of three to six meters."

31
With a hat-tip to bligh8, the linked articles present paleo-evidence that the WAIS likely collapsed during the Eemian.  Such findings indicate that the WAIS contribution to SLR during the Eemian was much more significant than that of the GIS.  Furthermore, since some records indicate that for periods of the Eemain, sea level rose at a rate of 2.5 m per century, these new findings provide support that an MICI-type of collapse may have occurred in at least portion of the WAIS during the Eemian (I note that we are currently headed towards Mid-Pliocene conditions):

Title: "Discovery of recent Antarctic ice sheet collapse raises fears of a new global flood"

https://www.sciencemag.org/news/2018/12/discovery-recent-antarctic-ice-sheet-collapse-raises-fears-new-global-flood

Extract: "Some 125,000 years ago, during the last brief warm period between ice ages, Earth was awash. Temperatures during this time, called the Eemian, were barely higher than in today’s greenhouse-warmed world. Yet proxy records show sea levels were 6 to 9 meters higher than they are today, drowning huge swaths of what is now dry land.

Scientists have now identified the source of all that water: a collapse of the West Antarctic Ice Sheet. Glaciologists worry about the present-day stability of this formidable ice mass. Its base lies below sea level, at risk of being undermined by warming ocean waters, and glaciers fringing it are retreating fast. The discovery, teased out of a sediment core and reported last week at a meeting of the American Geophysical Union in Washington, D.C., validates those concerns, providing evidence that the ice sheet disappeared in the recent geological past under climate conditions similar to today’s. “We had an absence of evidence,” says Anders Carlson, a glacial geologist at Oregon State University in Corvallis, who led the work. “I think we have evidence of absence now.”

If it holds up, the finding would confirm that “the West Antarctic Ice Sheet might not need a huge nudge to budge,” says Jeremy Shakun, a paleoclimatologist at Boston College. That, in turn, suggests “the big uptick in mass loss observed there in the past decade or two is perhaps the start of that process rather than a short-term blip.” If so, the world may need to prepare for sea level to rise farther and faster than expected: Once the ancient ice sheet collapse got going, some records suggest, ocean waters rose as fast as some 2.5 meters per century."

See also:

Title: "PP11A-05: Absence of the West Antarctic ice sheet during the last interglaciation" Carlson et al (2018)

https://agu.confex.com/agu/fm18/meetingapp.cgi/Paper/421418

Summary: "During the last interglaciation (LIG; ~129-116 ka), global mean sea level (GMSL) was >6 m above present. Based on evidence of only modest LIG Greenland ice-sheet retreat, Antarctic ice sheets may also have contributed to LIG GMSL, but direct data for a contribution is lacking. Here we investigate the LIG extent of the West Antarctic (WAIS) and Antarctic Peninsula (APIS) ice sheets using Sr-Nd-Pb isotopes of silt from ODP Site 1096 in the Bellingshausen Sea. Based on our shelf Sr-Nd-Pb provenance data and a stable-isotope age model, we document WAIS-APIS erosion of all radiogenically-discernable terranes from the latter part of marine isotope stage (MIS) 5 up through the Holocene, consistent with independent ice-margin chronologies showing ice presence on all of these terranes from MIS 2 through the Holocene. For the LIG/early MIS 5, we only find evidence of silt sourced from the erosion of the APIS and the mountain ranges that rim the northern modern WAIS, with an absence of silt from Pine Island glacier. Ice-sheet models link Pine Island glacier absence to full WAIS collapse into ice caps on mountains. Our record thus provides the first direct indication of a much smaller LIG WAIS, providing paleo-context for the susceptibility of the WAIS to collapse."

32
Just to be clear species extinction is a real, and accelerating, problem; and is a positive feedback for the acceleration of climate change:

Title: "Rise of the Extinction Deniers"

https://therevelator.org/extinction-deniers/

Extract: "Extinction’s not a problem, right?

That’s actually a point made quite a bit lately by a group of “extinction deniers” — people who use the relatively low number of confirmed extinctions to say there’s no such thing as an extinction crisis. These industry shills came out of the woodwork in the wake of the recent Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services report that predicts the world faces up to one million extinctions in the coming decades due to human activity."

33
Thanks again AbruptSLR for this research.

As a service, I provide a link to a pdf of Vakulenko and Sudakov (2019) "Complex bifurcations in fast-slow climate dynamics"

https://arxiv.org/pdf/1902.07936.pdf

Extract: "Then, we consider the dynamic model with random parameters for the climate-biospher coupling to explain why the climate may stay stable over long-time intervals.  The model shows that climate stability can be explained by mutual annihilation of many independent factors.  One of the important consequences is that if biodiversity decreases then the random evolution of the biosphere can lead to global climate changes."

Also, of Dortmans et al (2018) "An Energy Balance Model for Paleoclimate Transitions", first cited in Reply #349:

https://www.clim-past.net/15/493/2019/cp-15-493-2019.pdf

Caption for the attached image: "Figure 7. Pliocene Arctic EBM (36)(37). Parameter values δ = 0.67, FA = 115; other parameters as in Table 1. Subfigure a): CO2 takes valuesµ = 1200, 1000, 800, 600, 400, 200ppm,from top to bottom on the blue curves, with fixed FO = 50 Wm−2. The warm equilibrium state disappears as µ decreases. Subfigure b): Bifurcation Diagram for the Pliocene Paradox. Here, CO2 concentration µ and ocean heat transport FO decrease simultaneously, with increasing ν, (0≤ν ≤1), as given by equations (42). As ν increases, the warm equilibrium solution (τS > 1) disappears in a saddlenode bifurcation, at approximately ν = 0.9, corresponding to forcing parameter µ = 343 ppm and FO = 51 Wm2. To the right of this point, only the frozen equilibrium state exists. To the left of this point, the frozen and warm equilibrium states coexist, separated by the unstable intermediate state."

34
Just to follow-up on my last post on hysteresis and climate change (see Reply #1207); the linked Wikipedia article indicates that mathematically, tipping points are any type of climate bifurcation with hysteresis, such as the abrupt collapse of a marine ice sheet and/or the abrupt slowdown of the MOC:

Title: "Tipping points in the climate system"

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

Extract: "Tipping point behaviour in the climate can also be described in mathematical terms. Tipping points are then seen as any type of bifurcation with hysteresis. Hysteresis is the dependence of the state of a system on its history. For instance, depending on how warm and cold it was in the past, there can be differing amounts of ice present on the poles at the same concentration of greenhouse gases or temperature.

In the context of climate change, an "adaptation tipping point" has been defined as "the threshold value or specific boundary condition where ecological, technical, economic, spatial or socially acceptable limits are exceeded."

35
Re: hysteresis

Yes, there are such effects. ASLR has posted on many, not a few on this very thread.

sidd

For convenience, the following are some selected extracts from some of my posts in this thread on hysteresis:

Furthermore, the hysteresis loops in Figures 3 & 4 make it clear that once the stratocumulus clouds dissipate (say partially due to a temporary decades-long perturbation like the collapse of the WAIS and associated feedbacks, and partially due to a temporary pulse of methane emission from Arctic thermokarst lakes [as well as a rapid reduction in anthropogenic aerosols]), it is difficult for them to reestablish themselves even at CO2-equivalent levels well below 1,200ppm.

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

Abstract: "Stratocumulus clouds cover 20% of the low-latitude oceans and are especially prevalent in the subtropics. They cool the Earth by shading large portions of its surface from sunlight. However, as their dynamical scales are too small to be resolvable in global climate models, predictions of their response to greenhouse warming have remained uncertain. Here we report how stratocumulus decks respond to greenhouse warming in large-eddy simulations that explicitly resolve cloud dynamics in a representative subtropical region. In the simulations, stratocumulus decks become unstable and break up into scattered clouds when CO2 levels rise above 1,200 ppm. In addition to the warming from rising CO2 levels, this instability triggers a surface warming of about 8 K globally and 10 K in the subtropics. Once the stratocumulus decks have broken up, they only re-form once CO2 concentrations drop substantially below the level at which the instability first occurred. Climate transitions that arise from this instability may have contributed importantly to hothouse climates and abrupt climate changes in the geological past. Such transitions to a much warmer climate may also occur in the future if CO2 levels continue to rise."

Extract: "The CO2 level at which the instability occurs depends on how largescale dynamics change with climate, which is heuristically parameterized in our simulations and hence is uncertain. In particular, the large-scale subsidence in the troposphere weakens under warming, which lifts the cloud tops and counteracts the instability. Indeed, when we weaken the parameterized large-scale subsidence by 1 or 3% per Kelvin of tropical SST increase (within the range of GCM responses to warming), the stratocumulus instability occurs at higher CO2 levels: around 1,400 ppm with 1% K–1 subsidence weakening, and around 2,200 ppm with 3% K–1 (Fig. 4). The hysteresis when the CO2 levels drop thereafter remains, but it narrows: stratocumulus decks reform once the CO2 levels drop below 500 ppm for a 1% K–1 subsidence weakening, and once they drop below 1,900 ppm for one of 3% K–1.

For the future, our results suggest that stratocumulus decks may break up if CO2 levels continue to rise. Equivalent CO2 concentrations around 1,300 ppm—the lowest level at which the stratocumulus instability occurred in our simulations—can be reached within a century under high-emission scenarios. However, it remains uncertain at which CO2 level the stratocumulus instability occurs because we had to parameterize rather than resolve the large-scale dynamics that interact with cloud cover. To be able to quantify more precisely at which CO2 level the stratocumulus instability occurs, how it interacts with large-scale dynamics and what its global effects are, it is imperative to improve the parameterizations of clouds and turbulence in climate models."


If nothing else, the findings of the linked reference could be used to better calibrate state-of-the-art ESM climate change projections w.r.t. 'the role of the Southern Ocean in abrupt transitions and hysteresis' in the MOC:

Sophia K.V. Hines, Andrew F. Thompson, Jess F. Adkins (15 March 2019), "The Role of the Southern Ocean in Abrupt Transitions and Hysteresis in Glacial Ocean Circulation", Paleoceanography and Paleoclimatology, https://doi.org/10.1029/2018PA003415

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018PA003415

Abstract: "High‐latitude Northern Hemisphere climate during the last glacial period was characterized by a series of abrupt climate changes, known as Dansgaard‐Oeschger events, which were recorded in Greenland ice cores as shifts in the oxygen isotopic composition of the ice. These shifts in inferred Northern Hemisphere high‐latitude temperature have been linked to changes in Atlantic meridional overturning strength. The response of ocean overturning circulation to forcing is nonlinear and a hierarchy of models have suggested that it may exist in multiple steady state configurations. Here, we use a time‐dependent coarse‐resolution isopycnal model with four density classes and two basins, linked by a Southern Ocean to explore overturning states and their stability to changes in external parameters. The model exhibits hysteresis in both the steady state stratification and overturning strength as a function of the magnitude of North Atlantic Deep Water formation. Hysteresis occurs as a result of two nonlinearities in the model—the surface buoyancy distribution in the Southern Ocean and the vertical diffusivity profile in the Atlantic and Indo‐Pacific basins. We construct a metric to assess circulation configuration in the model, motivated by observations from the Last Glacial Maximum, which show a different circulation structure from the modern. We find that circulation configuration is primarily determined by North Atlantic Deep Water density. The model results are used to suggest how ocean conditions may have influenced the pattern of Dansgaard‐Oeschger events across the last glacial cycle."

&

The linked reference finds that:
"… Labrador Sea deep convection and the AMOC have been anomalously weak over the past 150 years or so (since the end of the Little Ice Age, LIA, approximately AD 1850) compared with the preceding 1,500 years.

We suggest that enhanced freshwater fluxes from the Arctic and Nordic seas towards the end of the LIA – sourced from melting glaciers and thickened sea ice that developed earlier in the LIA – weakened Labrador Sea convection and the AMOC.  The lack of a subsequent recovery may have resulted from hysteresis or from twentieth-century melting of the Greenland Ice Sheet."

These findings support Hansen's ice-climate feedback mechanism.

Thornalley et al. (2018), "Anomalously weak Labrador Sea convection and Atlantic overturning during the past 150 years", Nature, doi:10.1038/s41586-018-0007-4

https://www.nature.com/articles/s41586-018-0007-4
&

E. Gasson, R.M. DeConto, D. Pollard, and R.H. Levy (2016), "Dynamic Antarctic ice sheet during the early to mid-Miocene", Proceedings of the National Academy of Sciences, pp. 201516130, doi: 10.1073/pnas.1516130113

http://www.pnas.org/content/early/2016/02/17/1516130113

Significance: "Atmospheric concentrations of carbon dioxide are projected to exceed 500 ppm in the coming decades. It is likely that the last time such levels of atmospheric CO2 were reached was during the Miocene, for which there is geologic data for large-scale advance and retreat of the Antarctic ice sheet. Simulating Antarctic ice sheet retreat is something that ice sheet models have struggled to achieve because of a strong hysteresis effect. Here, a number of developments in our modeling approach mean that we are able to simulate large-scale variability of the Antarctic ice sheet for the first time. Our results are also consistent with a recently recovered sedimentological record from the Ross Sea presented in a companion article."



36
While I have no problem with those who like to be positive; in my book being positive does not mean ignoring the honest evaluation of right-tailed climate risks:

Title: "Paris + 2: Climate jolted faster than projected"

https://www.axios.com/two-years-since-trump-withdrew-paris-climate-agreement-2a680e45-0c87-4dbf-81d7-6b8d55feee40.html

Extract: "While virtually all countries except the U.S. remain committed to the 2015 Paris Climate Agreement, many aren’t on track to meet their targets — which are mostly too weak anyway, according to the Climate Action Tracker, a research group following the Paris deal pledges.

Diringer said. “I’d say it’s a fair bet that over time continued U.S. inaction will have a corrosive effect on political will globally.”"

37
One should remember that the Ross Ice Shelf, RIS, not only buttresses key WAIS marine glaciers but also key EASI marine glaciers.  Thus, its potential abrupt loss this century could potentially trigger up to 11.6 m of ice contribution to SLR.  In this regards, the linked reference indicates that the RIS stability is currently in something of a 'Goldie Locks' condition, and that relatively small changes in local conditions might trigger a rapidly rapid reduction in RIS stability:

K. J. Tinto, L. Padman, C. S. Siddoway, S. R. Springer, H. A. Fricker, I. Das, F. Caratori Tontini, D. F. Porter, N. P. Frearson, S. L. Howard, M. R. Siegfried, C. Mosbeux, M. K. Becker, C. Bertinato, A. Boghosian, N. Brady, B. L. Burton, W. Chu, S. I. Cordero, T. Dhakal, L. Dong, C. D. Gustafson, S. Keeshin, C. Locke, A. Lockett, G. O’Brien, J. J. Spergel, S. E. Starke, M. Tankersley, M. G. Wearing, R. E. Bell. Ross Ice Shelf response to climate driven by the tectonic imprint on seafloor bathymetry. Nature Geoscience, 2019; DOI: 10.1038/s41561-019-0370-2

https://www.nature.com/articles/s41561-019-0370-2

Abstract: "Ocean melting has thinned Antarctica’s ice shelves at an increasing rate over the past two decades, leading to loss of grounded ice. The Ross Ice Shelf is currently close to steady state but geological records indicate that it can disintegrate rapidly, which would accelerate grounded ice loss from catchments equivalent to 11.6 m of global sea level rise. Here, we use data from the ROSETTA-Ice airborne survey and ocean simulations to identify the principal threats to Ross Ice Shelf stability. We locate the tectonic boundary between East and West Antarctica from magnetic anomalies and use gravity data to generate a new high-resolution map of sub-ice-shelf bathymetry. The tectonic imprint on the bathymetry constrains sub-ice-shelf ocean circulation, protecting the ice shelf grounding line from moderate changes in global ocean heat content. In contrast, local, seasonal production of warm upper-ocean water near the ice front drives rapid ice shelf melting east of Ross Island, where thinning would lead to faster grounded ice loss from both the East and West Antarctic ice sheets. We confirm high modelled melt rates in this region using ROSETTA-Ice radar data. Our findings highlight the significance of both the tectonic framework and local ocean–atmosphere exchange processes near the ice front in determining the future of the Antarctic Ice Sheet."

See also:
Title: "Study uncovers surprising melting patterns beneath Antarctica's Ross Ice Shelf"

https://www.sciencedaily.com/releases/2019/05/190527111724.htm

Extract: "Using the new map of the seabed under the ice shelf, the team ran a model of ocean circulation and its effect on ice shelf melting. Compared with the Amundsen Sea to the east, where warm water crosses the continental shelf to cause rapid melting of the ice shelves, little warm water reaches the Ross Ice Shelf. In the Ross Sea heat from the deep ocean is removed by the cold winter atmosphere in a region of open water, called the Ross Shelf Polynya, before flowing under the ice shelf. The model showed that this cold water melts deeper portions of east Antarctic glaciers, but it is steered away from the west Antarctic side by the depth change at the ancient tectonic boundary.

In a surprise twist, however, the team found that the polynya also contributes to a region of intense summertime melting along the ice shelf's leading edge. This melting was confirmed in the radar images of the ice shelf's internal structure. "We found that the ice loss from the Ross Ice Shelf and flow of the adjoining grounded ice are sensitive to changes in processes along the ice front, such as increased summer warming if sea ice or clouds decrease," said Laurie Padman, a co-author and senior scientist at Earth and Space Research.

Overall, the results indicate that models used to predict Antarctic ice loss in future climates must consider changing local conditions near the ice front, not just the large-scale changes in the circulation of warm deep water. "We found out that it's these local processes we need to understand to make sound predictions," said Tinto."

38
We need to make changes today to stop worse things from happening further down the road and committing the system to Eemian era sea levels.

Rich, I suspect stopping Eemian sea levels is a train that has already left the station.

Paleoclimate scientists seem to recognize great SLR risk than does consensus climate science, as indicated by the linked reference and the accompanying image.  The image shows a comparison of an unreasonable linear (by Alley 2010, in a consensus science effort to discount the risk of abrupt SLR) projected rate of SLR to achieve a eustatic sea level change of five meter by 2100, vs a more feasible 10-year doubling time (by Hansen & Sato 2011) projected rate of SLR to achieve the same change by 2100, Hansen.

Title: "Paleoclimate Implications for Human-Made Climate Change"

http://www.columbia.edu/~jeh1/mailings/2011/20110118_MilankovicPaper.pdf

39
We are in general, including the experts, notoriously overconfident and optimistic when it comes to predictions.



The linked scientific reference finds that AR5 (as a reflection of consensus climate science) does not adequately communicate the trur level of climate change risks:

Salvador Herrando-Pérez, Corey J A Bradshaw, Stephan Lewandowsky, David R Vieites. Statistical Language Backs Conservatism in Climate-Change Assessments. BioScience, 2019; 69 (3): 209 DOI: 10.1093/biosci/biz004

https://academic.oup.com/bioscience/article/69/3/209/5382637

Abstract: "The scientific evidence for anthropogenic climate change is empirically settled, but communicating it to nonscientific audiences remains challenging. To be explicit about the state of knowledge on climate science, the Intergovernmental Panel on Climate Change (IPCC) has adopted a vocabulary that ranks climate findings through certainty-calibrated qualifiers of confidence and likelihood. In this article, we quantified the occurrence of knowns and unknowns about “The Physical Science Basis” of the IPCC's Fifth Assessment Report by counting the frequency of calibrated qualifiers. We found that the tone of the IPCC's probabilistic language is remarkably conservative (mean confidence is medium, and mean likelihood is 66%–100% or 0–33%), and emanates from the IPCC recommendations themselves, complexity of climate research, and exposure to politically motivated debates. Leveraging communication of uncertainty with overwhelming scientific consensus about anthropogenic climate change should be one element of a wider reform, whereby the creation of an IPCC outreach working group could enhance the transmission of climate science to the panel's audiences."

40
Climate change is complicated, as is the modeling of its subparts like the Arctic Ocean and the Beaufort Gyre.  In previous posts I have raised the prospect of, in a warming world, the Beaufort Gyre releasing a large volume of relatively freshwater into the North Atlantic Ocean; which would both slow the MOC, and weaken the Arctic's halocline which would cause deeper relatively warm ocean water to rise up in the water column, which would melt more Arctic sea ice.  Clearly, this ice-climate feedback mechanism would serve to increase ECS (by both warming the tropical sea surface temperatures due to the slowing MOC and by the albedo flip associated with the accelerated loss of Arctic sea ice); and thus climate science has begun to focus more on this very real and significant climate risk as illustrated by the numerous related paper collected in the first linked JGR: Oceans Special Issue, and by the associated selected linked references (note the JGR: Oceans Special Issue has too many papers to be summarized in this post):

JGR: Oceans Special Issues (2019), "Forum for Arctic Modeling and Observational Synthesis (FAMOS) 2: Beaufort Gyre phenomenon"

https://agupubs.onlinelibrary.wiley.com/doi/toc/10.1002/(ISSN)2169-9291.FAMOS2

See also:

Proshutinsky, A., and R. Krishfield (2019), In a spin: New insights into the Beaufort Gyre, Eos, 100,https://doi.org/10.1029/2019EO119765. Published on 08 April 2019.

https://eos.org/editors-vox/in-a-spin-new-insights-into-the-beaufort-gyre

Extract: "Although the Beaufort Gyre is located in the Arctic region, it has impacts on the climate further afield in two ways:
•   First, fresh water accumulates in the Beaufort Gyre which results in a deficit of fresh water flowing into the North Atlantic. This deficit creates the conditions for deep convection of ocean waters and heat release from the ocean to atmosphere in the subpolar regions; it also promotes intensification of the Atlantic Ocean Meridional Circulation (AOMC).
•   Second, when there are prevailing counter-clockwise winds over the Arctic, fresh water released from the Beaufort Gyre region inhibits the processes of deep convection, reduces intensity of the AMOC and results in climate cooling. Such periodical releases of fresh water from the Arctic Ocean, which have occurred in the 1970s, 1980s, and 1990s, are known as ‘Great Salinity Anomalies’ (Dickson et al., 1988; Belkin et al., 1998)."
&

Edward W. Doddridge et al. (01 April 2019), "A Three‐Way Balance in the Beaufort Gyre: The Ice‐Ocean Governor, Wind Stress, and Eddy Diffusivity", JGR Oceans,
https://doi.org/10.1029/2018JC014897

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2018JC014897

Abstract: "The Beaufort Gyre (BG) is a large anticyclonic circulation in the Arctic Ocean.  Its strength is directly related to the halocline depth, and therefore also to the storage of freshwater.  It has recently been proposed that the equilibrium state of the BG is set by the Ice-Ocean Governor, a negative feedback between surface currents and ice-ocean stress, rather than a balance between lateral mesoscale eddy fluxes and surface Ekman pumping.  However, mesoscale eddies are present in the Arctic Ocean; it is therefore important to extend the Ice-Ocean Governor theory to include lateral fluxes due to mesoscale eddies.  Here, a non-linear ordinary differential equation is derived that represents the effects of wind stress, the Ice-Ocean Governor, and eddy fluxes.  Equilibrium and time-varying solutions to this three-way balance equation are obtained and shown to closely match the output from a hierarchy of numerical simulations, indicating that the analytical model represents the processes controlling BG equilibration.  The equilibration timescale derived from this three-way balance is faster than the eddy equilibration timescale and slower than the Ice-Ocean Governor equilibration timescales for most values of eddy diffusivity.  The sensitivity of the BG equilibrium depth to changes in eddy diffusivity and the presence of the Ice-Ocean Governor is also explored.  These results show that predicting the response of the BG to changing surface forcing and sea ice conditions requires faithfully capturing the three-way balance between the Ice-Ocean Governor, wind stress and eddy fluxes."

&

Gianluca Meneghello, John Marshall, Jean-Michel Campin, Edward Doddridge, Mary-Louise Timmermans. The Ice-Ocean governor: ice-ocean stress feedback limits Beaufort Gyre spin up. Geophysical Research Letters, 2018; DOI: 10.1029/2018GL080171

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL080171

Abstract
The Beaufort Gyre is a key circulation system of the Arctic Ocean and its main reservoir of freshwater. Freshwater storage and release affects Arctic sea ice cover, as well as North Atlantic and global climate. We describe a mechanism that is fundamental to the dynamics of the gyre, namely, the ice‐ocean stress governor. Wind blows over the ice, and the ice drags the ocean. But as the gyre spins up, currents catch the ice up and turn off the surface stress. This governor sets the basic properties of the gyre, such as its depth, freshwater content, and strength. Analytical and numerical modeling is employed to contrast the equilibration processes in an ice‐covered versus ice‐free gyre. We argue that as the Arctic warms, reduced sea ice extent and more mobile ice will result in a deeper and faster Beaufort Gyre, accumulating more freshwater that will be released by Ekman upwelling or baroclinic instability.

Plain Language Summary
The Beaufort Gyre, located north of Alaska and Canada, is a key circulation system of the Arctic Ocean. Changes in its depth and circulation influence the evolution of the Arctic sea ice cover, the North Atlantic circulation, and the global climate. The gyre is driven by persistent, ice‐mediated winds, accumulating surface freshwater toward the center, deepening the gyre, and spinning up its currents. We describe a mechanism, dubbed here the ice‐ocean governor, in which the interaction of surface currents with the ice regulates the depth of the Beaufort Gyre: The spinning up of the gyre reduces the relative speed between the ocean and the ice, and hence the freshwater accumulation. This competes with, and we argue is more important than, the release of freshwater by flow instability, which moves water from the center toward the periphery. In the current climate the depth and speed of the Beaufort Gyre are mainly set by the governor, but this may change in a warming world where reduced ice cover will render the ice‐ocean governor less effective. The resulting deeper, swifter gyre will likely exhibit more variability in its freshwater storage and flow speeds.

See also:

Title: "Arctic ice sets speed limit for major ocean current"

https://www.sciencedaily.com/releases/2018/10/181017140925.htm

Extract: "There have been a handful of times in the recorded past when the Beaufort Gyre has spilled over, beginning with the Great Salinity Anomaly in the late 1960s, when the gyre sent a surge of cold, fresh water southward. Fresh water has the potential to dampen the ocean's overturning circulation, affecting surface temperatures and perhaps storminess and climate.

Similar events could transpire if the Arctic ice controlling the Beaufort Gyre's spin continues to recede each year.

"If this ice-ocean governor goes away, then we will end up with basically a new Arctic ocean," Marshall says.

In this new paper, the researchers studied the interplay of ice, wind, and ocean currents in more depth, using a high-resolution, idealized representation of ocean circulation based on the MIT General Circulation Model, built by Marshall's group. They used this model to simulate the seasonal activity of the Beaufort Gyre as the Arctic ice expands and recedes each year.
They found that in the spring, as the Arctic ice melts away, the gyre is exposed to the wind, which acts to whip up the ocean current, causing it to spin faster and draw down more fresh water from the Arctic's river runoff and melting ice. In the winter, as the Arctic ice sheet expands, the ice acts as a lid, shielding the gyre from the fast-moving winds. As a result, the gyre spins against the underside of the ice and eventually slows down.

Marshall and Meneghello note that, as Arctic temperatures have risen in the last two decades, and summertime ice has shrunk with each year, the speed of the Beaufort Gyre has increased. Its currents have become more variable and unpredictable, and are only slightly slowed by the return of ice in the winter.

"At some point, if this trend continues, the gyre can't swallow all this fresh water that it's drawing down," Marshall says. Eventually, the levee will likely break and the gyre will burst, releasing hundreds of billions of gallons of cold, fresh water into the North Atlantic.

An increasingly unstable Beaufort Gyre could also disrupt the Arctic's halocline -- the layer of ocean water underlying the gyre's cold freshwater, that insulates it from much deeper, warmer, and saltier water. If the halocline is somehow weakened by a more instable gyre, this could encourage warmer waters to rise up, further melting the Arctic ice."

Edit: It goes without saying that a pulse of cold, relatively fresh, water from the Beaufort Gyre into the North Atlantic, would trigger a bipolar seesaw mechanism that would contribute to the destabilization of key Antarctic marine glaciers.

41
As a follow on to my comments in Reply #1175:

The first image shows the turbulent convective mixing of the warm modified CDW and the fresh basal meltwater in front of an ice cliff in Antarctica.  In my opinion this type of turbulent convection is significantly contribution to the observed expansion of the subglacial cavity in the trough area between the Big and Little Ears of the Thwaites Ice Shelf/Ice Tongue.

The second image shows the conceptual degradation of methane hydrates from the paleo-bed of the retreating paleo-marine ice sheet in the Barents Sea during the last interglacial.  I note that as it is believed that the bed beneath the Thwaites Glacier also contains methane hydrates, and abrupt retreat of the Thwaites grounding line in the relatively shallow Thwaites Gateway, could result in a similar release of methane into the atmosphere from the potential degradation of methane hydrates in the Thwaites Gateway, in the coming decades.

42
I provide the linked article to remind readers that eight of the most sophisticated ESMs for CMIP6, are projecting ECS values will increase to over 5C in the coming decades, and that
increasing ECS values means increasing climate variability, which means increased risk of a coming abrupt change in climate state (such as occurred in the Mid-Pliocene period due to an Arctic albedo flip, e.g. see my last post).

Title: "New climate models predict a warming surge"

https://www.sciencemag.org/news/2019/04/new-climate-models-predict-warming-surge

Extract: "But a host of global climate models developed for the United Nations' next major assessment of global warming, due in 2021, are now showing a puzzling but undeniable trend. They are running hotter than they have in the past.

But in at least eight of the next-generation models, produced by leading centers in the United States, the United Kingdom, Canada, and France, that “equilibrium climate sensitivity” has come in at 5°C or warmer."

43
The linked reference adds information to the relationship between two types of ENSOs and Arctic surface temperatures in the boreal winter.  The associated improved understanding of the relationship between ENSO events and Arctic sea ice melting could provide more accurate projections for the risk of an Arctic albedo flip in the coming decades:

Zhiyu Li et al. (2019), "Different effects of two ENSO types on Arctic surface temperature in boreal winter", Journal of Climate, https://doi.org/10.1175/JCLI-D-18-0761.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-18-0761.1

Abstract

The present work investigates different responses of Arctic surface air temperature (SAT) to two ENSO types based on reanalysis datasets and model experiments. We find that eastern Pacific (EP) ENSO events are accompanied by statistically significant SAT responses over the Barents-Kara Seas in February, while central Pacific (CP) events coincide with statistically significant SAT responses over northeastern Canada and Greenland. These impacts are largely of opposite sign for ENSO warm and cold phases. During EP El Niño February, the enhanced tropospheric polar vortex over Eurasia and associated local low-level northeasterly anomalies over the Barents-Kara Seas lead to anomalously cold SAT in this region. Simultaneously, the enhanced tropospheric polar vortex leads to enhanced sinking air motion and consequently reduced cloud cover. This in turn reduces downward infrared radiation (IR), which further reduces SAT in the Barents-Kara Seas region. Such a robust response cannot be detected during other winter months for EP ENSO events. During CP El Niño, the February SAT over northeastern Canada and Greenland are anomalously warm and coincide with a weakened tropospheric polar vortex and related local low-level southwesterly anomalies originating from the Atlantic Ocean. The anomalous warmth can be enhanced by the local positive feedback. Similar SAT signals as in February during CP ENSO events can also be seen in January but they are less statistically robust. We demonstrate that these contrasting Arctic February SAT responses are consistent with responses to the two ENSO types with a series of atmospheric general circulation model experiments. These results have implications for the seasonal predictability of regional Arctic SAT anomalies

44
As a follow-on to my last post:

The first image reminds readers that there are troughs in the seafloor of the Amundsen Sea Embayment, ASE, that direct the warm modified CDW water from offshore of the local continental shelf to the Thwaites ice shelves (where the CDW both accelerates basal ice melting and when appropriate to burn through basal crevasses in the ice shelves).

The second image reminds readers that the basal melt water from the entire Thwaites Glacier catchment basin is channeled through the bed trough between the Little and Big Ear area, which is dynamically working to grow the subglacial cavity in this area (particularly where the light freshwater meltwater mixes with the relatively dense warm modified CDW).

The third and fourth images reminds readers that the basal meltwater drainage system from beneath the Thwaites Glacier contains subglacial lakes that periodically drain (say every 20 to 25 years).  Furthermore, the last such drainage event (from June 2013 to January 2014) may have been triggered by the partial collapse of the subglacial cavity between the Big & Little Ears sometime in 2012.  Also, I note that the next Thwaites subglacial lake drainage event may happen as early as 2033 to 2038.

45
As a follow-on to my posts in Replies #1170 and #1171, on how I expect ice cliff failure mechanism to first initial in the Thwaites Gateway, between what I label in those posts, the Big and Little Ear bed locations.  Furthermore, I believe that within this limited area of the trough that leads directly into the Byrd Subglacial Basin, that ice cliff failure mechanism could be formed sometime between 2028 and 2035, without the need for hydrofracturing, once the ice mélange has been cleared-out from in front of this area.

The first image (of a Landsat-7 photograph from January 2013) shows how many crevasses there were (& are) in the ice between the grounding line (in green & showing the Big Ear) and the caving front (orange line).  This is the ice mélange region at the base of the Thwaites Ice Tongue that I mentioned must be cleared away by warm modified CDW water associated with Super El Nino events that may occur circa 208 & 2035.

The second image shows a computer analysis of projected basal crevasse development in the bottom of the ice shelf in this Big Ear area at the base of the residual Thwaites Ice Tongue.

The third image (from Bassis & Ma 2015) shows how warm modified CDW water can entering into such basal ice shelf crevasse, and then burns through the basal crevasse up to the top surface of the ice shelf.  Furthermore, the second image shows that these basal crevasses for the Thwaites ice shelf near the Big Ear are concentrated at the base of the ice shelf, so that if/when the warm modified CDW burns through the crevasse, this would leave a bear ice cliff that could initial an ice-cliff failure just upstream of the Big Ear.

The fourth image shows that the subglacial ice cavity is growing at the Big Ear (shown in the bottom panel of this image).  The growth of this cavity decreases the stability of the ice shelf in this area.

46
As a follow on to my last post, I present four images in an attempt to get readers oriented in the area where I first expect ice cliff failures for Thwaites Glacier between to bed areas that I have labelled Big Ear and Little Ear in this series of images.

With a hat tip to Sleepy, the first image shows the ear relative to the growth of the subglacial cavity at the base of the Thwaites Ice Tongue (near the Big Ear)

The second image shows the locations of the Big & Little Ears relative to a collapse of the cavity that lead to a surge of the Thwaites Ice Tongue after January 2012.

The third image shows the location of Big & Little Ears on a Sentinel 1 image from May 23, 2019.  This image shows ice bergs floating near the Little Ear location.

The fourth image shows the bathymetry of the Thwaites Gateway prior to 2013, where the location of the Big & Little Ears is self-evident, so I have not labelled them.

47
At the risk of being imprecise, I present four images in this post and four images in the next post, in an attempt to get readers oriented in the area where I first expect ice cliff failures for Thwaites Glacier between to bed areas that I have labelled Big Ear and Little Ear in this series of images.

The first image comes from Kim et al. (2018).
https://www.mdpi.com/2072-4292/10/8/1236

The second image comes from Tinto Bell (2011), that shows the bed trough leading to the BSB

The third and fourth images show the alignment A-B that Rignot believes has low stability

48

I'll just infer that Thwaites is one of the prime spots where we'll see MICI proved or disproved in the intermediate future.


While Thwaites is the most important marine glacier to watch, it is physically connected to the Pine Island Glacier; therefore, in the attached image I have sketched a blue line where I speculate that a calving fault will form in the Southwest corner of the Pine Island Ice Shelf. PIIS, sometime in the second half of July 2019.  While I may be wrong, it is at least worth watching, and I note that no consensus climate ice sheet model that I have seen projects such a rapid retreat of the PIIS.

Edit: This image was taken on May 22, 2019

49
It's my experience so far in California that a 'carbon' tax isn't doing what it's supposed to do, and that is because the oil companies wont sell the farm. I am SERIOUSLY worried that the carbon tax will fail to cut emissions, here is NO guarantee it will work. We don't need some wishy-washy idea of tax and dividend that makes everyone seem like we are saving the planet but it turns out to be greenwashing.


Not all Carbon Fee and Dividend plans are the same (& it is definitely not a cap & trade plan; which Hansen does not support), but the linked plan by 'Citizens' Climate Lobby' is supported by James Hansen and many others:

Title: "The Basics of Carbon Fee and Dividend"

https://citizensclimatelobby.org/basics-carbon-fee-dividend/


50
Some people think that this thread is too doom and gloom;"
.
The truth of climate change is mostly gloomy. Someone has to tell the truth.

I value what I'm finding here.

BTW - the equations in that SLR paper on crevasses at Thwaites are way above my pay grade. I'll just infer that Thwaites is one of the prime spots where we'll see MICI proved or disproved in the intermediate future.

For what it's worth, I've watched a bunch of YouTube videos with Eric Rignot. He comes across as pretty credible and a good example of a scientist who is doing his best to wake people up.

Rich,

I concur that Eric Rignot is a straight shooter, as are all of his co-authors in the linked reference (with Hansen as a lead author); which, does not consider the details of how abrupt ice sheet mass loss might occur, but rather on the consequences:

James Hansen, Makiko Sato, Paul Hearty, Reto Ruedy, Maxwell Kelley, Valerie Masson-Delmotte, Gary Russell, George Tselioudis, Junji Cao, Eric Rignot, Isabella Velicogna, Blair Tormey, Bailey Donovan, Evgeniya Kandiano, Karina von Schuckmann, Pushker Kharecha, Allegra N. Legrande, Michael Bauer, and Kwok-Wai Lo (2016), "Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous", Atmos. Chem. Phys., 16, 3761-3812, doi:10.5194/acp-16-3761-2016

http://www.atmos-chem-phys.net/16/3761/2016/acp-16-3761-2016.html

Abstract: "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. We discuss observations and modeling studies needed to refute or clarify these assertions."


Also, you might want to scroll through the following linked thread:

Title: "Hansen et al paper: 3+ meters SLR by 2100"
https://forum.arctic-sea-ice.net/index.php/topic,1327.0.html

Finally, I provide the attached image, which illustrates the concept of an 'ice plug' temporarily preventing MICI events in key Antarctic marine glaciers & you are correct that the Thwaites Glacier is most at risk of losing its 'ice plug' first in Antarctica.

Best,
ASLR

Pages: [1] 2 3 ... 342