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Author Topic: Supporting Paleo-Evidence/Calibration for WAIS Collapse Hazard Scenarios  (Read 85669 times)

AbruptSLR

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It is likely that many of readers consider my hazard analysis posts on the potential for abrupt SLR from a complete, or partial, collapse of the WAIS this century, as constituting an improbable chain of events.  Nevertheless, it is well known that people heavily discount the future, and as a result are frequently surprised by "Black Swan" events; which, as discussed in the "Philosophical" thread, happen much more frequently than most people are willing to entertain.  Therefore, I am opening this thread to discuss the consideration that the available paleo-evidence  may be adequate to serve as a form of calibration or as a "guarantor"  that the risk of such abrupt SLR scenarios are sufficiently likely, for authorities to enact regulations requiring that susceptible infrastructure should be evaluated for resiliency against such a Maximum Credible (slr) Event, MCE.

What I mean by a "guarantor" is something akin to the "invisible-hand" of capitalism, or more accurately, closer to a chain of positive feedback mechanisms that create a strange attractor (such as the "Lorenz Attractors", see Chaos Theory [also note that the Black Swan Theory, BWT, is rooted in chaos theory]) that may have driven Heinrich-like, and associated Dansgaard-Oeschger (D-O) Events.  Indeed, the Bollings Warming/Meltwater Pulse 1A event (see the first image, and note that based on boring in coral in Tahiti Meltwater Pulse 1A included significant SLR contribution from marine ice sheets previously located on the continental shelf of West Antarctica) is but one of a series of other Dansgaard-Oeschger/Heinrich Events, that indicate the sensitivity of marine ice sheets to rapid collapse, thus indicating the likely potential abrupt collapse of the last remaining marine ice sheet, the WAIS.

For those not familiar with Chaos theory or Lorenz Attractors, I provide the following from Wikipedia:
"In 1963 Edward Lorenz was studying the patterns of rising warm air in the atmosphere. It was known at the time that air could start to move if it came into contact with a warm object. The properties of air are such that it expands a lot when heated, it is a good insulator and it flows with relative ease - technically speaking, it has a high Rayleigh number. Think of a large hot air mass in the atmosphere as rising like a hot air balloon in the shape of a mushroom cloud (!). Based on known hydrodynamics Lorenz derived a set of simplified equations for this movement and found something amazing. For certain values of the parameters, the overall movement of the atmospheric air was oscillating unpredictably (Lorenz 1963):
A major concern was that for small changes in starting conditions the system would always have an unpredictable outcome. This was the discovery of deterministic chaos and we knew there and then that we would never know the weather more than 10 days ahead without using disproportionate computing power with very little pay-off. Naturally, scientists knew about chaos from studying turbulence, which is not both smooth (deterministic) and unpredictable.
When Lorenz looked closer at his graphs, something exciting happened. A peculiar regularity emerged when he plotted the curves against each other: they were attracted to something never leaving a boxed volume. It was strange, because it was not a simple shape, but rather an entire subspace of points strangely smeared into three dimensions (see the second image).
Even stranger, the structure is occupying not just a two dimensional surface but something which is more than two dimensional and less than three dimensional: it is two-dimensional plus a fraction. It exists in a so called fractal dimension. It never truly intersects itself thus committing every trajectory to infinite solitude. The object was therefore aptly dubbed a strange attractor.
A closer look reveals where the unpredictability arises. The blue and the magenta curves are closely following each other for a time. Suddenly the magenta curve takes a wild hike and quickly finds itself far away from its companion curve (see the third image). This is known as sensitivity to initial conditions, which is seen in everyday weather."
The fourth image (from climate skeptic) illustrates how while the trend of global temperature rise is not chaotic (and can be reliably projected), periodic chaotic strange attractor (e.g. Lorenz Attractor) temperature rise events can happen (and possibly increase with rising temperature).  Perhaps the most famous/relevant example of such a periodic chaotic strange attractor (that may be increasing with rising global temperatures) is the ENSO; recent changes in which I have repeatedly stated may contribute to the rapid degradation of the WAIS, including by: (a) the current 13-year long El Nino hiatus period pumping more ocean heat content directly from the tropics (particularly the Pacific Tropics) into the ACC and thus warming and expanding the volume of the CDW; and (b) changes in ENSO have a influence of both SAM and on storms in the Southern Ocean.

Unfortunately, with regard to Heinrich events, many researchers have not previously recognized both: (a) the rapid response atmospheric/ocean periodic chaotic strange attractor mechanisms (such as the ENSO strange attractor mechanism); and (b) the importance of the short-term synchronistic (strange attractor) mechanism between Northern Hemisphere (NH) ice and Southern Hemisphere (SH) marine ice sheets.  Therefore,  I am postulating that Heinrich like events (possibly including the potential collapse of the WAIS by 2100), can also follow a pattern, of a general trend of rising radiative forcing (such as our current anthropogenic forcing) with periodic strange attractor events (ie the Heinrich [or pending WAIS collapse] events supported by ENSO and NH/SH ice synchronicity strange attractor subsystems) .   In my next series of posts, I will explore this postulated Heinrich/D-O periodic chaotic strange attractor pattern, superimposed on a longer-term global warming trend; and also how the repeated collapse of the WAIS during past interglacial peak periods has gouged troughs in the West Antarctic seafloor that increase the risk of the collapse of the current WAIS.




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

AbruptSLR

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Previously, many researchers focused on NH related causes for Heinrich events, and on slow response synchronicity NH/SH interaction such as that through the Great Oceanic Current Convey system; while much new evidence clarifies the importance of Antarctic marine ice sheets and fast response ocean/atmospheric interactions (like ENSO and SAM), on past and the possible future Heinrich like abrupt SLR events.  For those not familiar with Heinrich and D-O Events, I provide from Wikipedia (italic added for emphasis):

"Heinrich events are global climate fluctuations which coincide with the destruction of northern hemisphere ice shelves, and the consequent release of a prodigious volume of sea ice and icebergs. The events are rapid: they last around 750 years, and their abrupt onset may occur in mere years (Maslin et al. 2001). Heinrich events are observed during the last glacial period; the low resolution of the sedimentary record before this point makes it impossible to deduce whether they occurred during other glacial periods in the Earth's history.

Heinrich events occur during some, but not all, of the periodic cold spells preceding the rapid warming events known as Dansgaard-Oeschger (D-O) events, which repeat around every 1,500 years (see the first image). However, difficulties in establishing exact dates cast aspersions on the accuracy—or indeed the veracity—of this statement. Some (Broecker 1994, Bond & Lotti 1995) identify the Younger Dryas event as a Heinrich event, which would make it H0.

Several factors external to ice sheets may cause Heinrich events, but such factors would have to be large to overcome attenuation by the huge volumes of ice involved (MacAyeal 1993).
Gerard Bond suggests that changes in the flux of solar energy on a 1,500-year scale may be correlated to the Daansgard-Oeschger cycles, and in turn the Heinrich events; however the small magnitude of the change in energy makes such an exo-terrestrial factor unlikely to have the required large effects, at least without huge positive feedback processes acting within the Earth system. However, rather than the warming itself melting the ice, it is possible that sea level change associated with the warming destabilised ice shelves. A rise in sea level could begin to corrode the bottom of an ice sheet, undercutting it; when one ice sheet failed and surged, the ice released would further raise sea levels — further destabilizing other ice sheets. In favour of this theory is the non-simultaneity of ice sheet break up in H1, 2, 4, and 5, where European breakup preceded European melting by up to 1,500 years (Maslin et al. 2001).

Various mechanisms have been proposed to explain the cause of Heinrich events. Most centre around the activity of the Laurentide ice sheet, but others suggest that the unstable West Antarctic Ice Sheet played a triggering role.  Several factors external to ice sheets may cause Heinrich events, but such factors would have to be large to overcome attenuation by the huge volumes of ice involved (MacAyeal 1993).

Hunt & Malin (1998) proposed that Heinrich events are caused by earthquakes triggered near the ice margin by rapid deglaciation.

Ice core evidence from Antarctic cores suggests that the Dansgaard–Oeschger events are related to the so-called Antarctic Isotope Maxima by means of a coupling of the climate of the two hemispheres, the Bi-polar Seesaw.

…… Rohling's 2004 Bipolar model suggests that sea level rise lifted buoyant ice shelves, causing their destabilisation and destruction. Without a floating ice shelf to support them, continental ice sheets would flow out towards the oceans and disintegrate into icebergs and sea ice.

Freshwater addition has been implicated by coupled ocean and atmosphere climate modeling (Ganopolski and Rahmstorf 2001), showing that both Heinrich and Dansgaard-Oeschger events may show hysteresis behaviour. This means that relatively minor changes in freshwater loading into the Nordic Seas — a 0.15 Sv increase, or 0.03 Sv decrease — would suffice to cause profound shifts in global circulation (Rahmstorf et al. 2005). The results show that a Heinrich event does not cause a cooling around Greenland but further south, mostly in the subtropical Atlantic, a finding supported by most available paleoclimatic data. This idea was connected to D-O events by Maslin et al. (2001). They suggested that each ice sheet had its own conditions of stability, but that on melting, the influx of freshwater was enough to reconfigure ocean currents — causing melting elsewhere. More specifically, D-O cold events, and their associated influx of meltwater, reduce the strength of the North Atlantic Deep Water current (NADW), weakening the northern hemisphere circulation and therefore resulting in an increased transfer of heat polewards in the southern hemisphere. This warmer water results in melting of Antarctic ice, thereby reducing density stratification and the strength of the Antarctic Bottom Water current (AABW). This allows the NADW to return to its previous strength, driving northern hemisphere melting and another D-O cold event. Eventually, the accumulation of melting reaches a threshold, whereby it raises sea level enough to undercut the Laurentide ice sheet — causing a Heinrich event and resetting the cycle."

My subsequent posts will focus more on the specifics of the current WAIS condition and why paleo-evidence indicates that it may soon be (or already has been) triggered to be the next Heirich-like event (the last of a chain of periodic chaotic stange attractor events for marine ice sheets) with armadas of icebergs from the WAIS collapse drifting about the Southern Ocean.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Further to the previous posts, I present the following additional paleo-evidence that support the probability of the various collapse mechanisms used my hazard assessment for WAIS collapse (and their possible connection to a periodic chaotic strange attractor scenario for Heinrich events):

-   The first image from Grant et al 2012 shows a synchronicity of NH and SH climate changes and ice mass loss (sea level contribution) from GIS and Antarctic marine ice sheets from the Eemian to the present.  The clear/tight correlation between NH and SH climate and ice mass loss supports my postulation that Heinrich events has a periodic chaotic strange attractor pattern characterized by rapid response oceanic/atmospheric strange attractor mechanisms (such as ENSO/SAM) and finger print sea-level rise interaction between GIS and Antarctic marine glaciers (ie summer ice melt from the GIS destabilizes Antarctic marine ice sheets/glaciers which then rise sea level in the NH to repeat the cycle as discussed in many of my other threads).  The following bullet point on research by Weber 2012, supports this postulation.

-   From: Antarctic deglaciation since the Last Glacial Maximum – implications for the Weddell Gyre development  by Michael E. Weber, Institute of Geology and Mineralogy, University of Cologne, Zuelpicher Str. 49a, 50935 Cologne, Germany:  "We developed a chronology for the Weddell Sea sector of the East Antarctic ice sheet (EAIS) that, combined with ages from other Antarctic ice-sheets, indicates that the advance to (at 29 –28 ka) and retreat from their maximum extent (at 19 ka, and again, at 16 ka) was nearly synchronous with Northern Hemisphere ice sheets (Weber, M.E., Clark, P. U., Ricken, W., Mitrovica, J.X., Hostetler, S.W. and Kuhn, G. (2011): Interhemispheric ice-sheet synchronicity during the Last Glacial Maximum. Science 334, 1265-1269, doi: 10.1126:science.1209299).  ….   Furthermore, our new data support teleconnections involving a sea-level fingerprint forced from Northern Hemisphere ice sheets as indicated by gravitational modeling. Also, changes in North Atlantic Deep Water formation and attendant heat flux to Antarctic grounding lines may have contributed to synchronizing the hemispheric ice sheets.  …. The new data from both the Weddell Sea and the Scotia Sea challenge previous reconstructions of a late and monotonous ice-sheet retreat between 12 ka and 7 and call for a principal revision of the Antarctic deglacial history, with previously unrecognized, highly dynamic ice sheets and clear responses to all meltwater pulses, suggesting a substantially higher contribution to the last sea-level rise.

-   Furthermore it is postulated that there is extensive paleo-evidence of subglacial networks and meltwater outbursts from beneath previous West Antarctic marine ice sheets, such as that carved into the Amundsen Sea Embayment seafloor (see the second image).  As my collapse scenario for the Bellingshausen and Amundsen Sea ice stream/glaciers depends heavily on the influence of such subglacial meltwater networks and periodic meltwater outbursts (postulated to be trigger by the synchronistic finger print sea-level interaction between the GIS and Antarctic marine ice sheets); such paleo-evidence of such past behavior (during Heinrich events) supports/calibrates my hazard analysis.

-   Furthermore, patterns of seafloor/subglacial troughs both facilitate my proposed collapse mechanisms ((i) by reducing basal ice friction along the troughs (which also accelerates the ice in these ice stream thus increasing internal friction/internal ice melting feeding basal meltwater and also reducing internal ice viscosity [which is important to the postulated "Thwaites Effect"]; (ii) by the troughs channeling the basal meltwater networks; (iii) by conveying warm CDW across the continental shelves to subglacial cavity advection; and (iv) by helping to form sea passageways that change ocean currents, tidal amplifications and accelerated calving of grounded ice along the sides of the passageways), but also most likely were formed due to the ocean/land/ice/atmosphere interactions that I cite in my scenarios.  Indeed, with regard to the stability of the Thwaites Glacier an indication that the ice flow of the Thwaites Glacier is currently following troughs formed the last time that the WAIS collapsed (apparently during MIS 5.5/Eemian peak), From Boon 2011, key findings state:

"We find that roughness is greater across-flow than along-flow, and greater downstream than upstream in our study area. This spatial organization results from a combination of pre-existing topography and glacial erosion. The multi-method analysis allows us to robustly characterize basal roughness in our study area. We correlate our results with existing models of greater basal shear stress downstream, and infer the presence of subglacial water.

Our localized study of an area of Thwaites Glacier, with roughness increasing downstream as it flows onto a ridge, suggests that there is high spatial variability in bed roughness. The different metrics used to quantify roughness suggest that roughness and modeled basal shear stress are related (Joughin et al., 2009). We find differences in roughness between the upstream and downstream halves of our study area that are coincident with differences in modeled basal shear stress. This link supports the hypothesis that rougher beds provide greater resistance to ice flow. However, we cannot confirm that roughness is the only factor causing basal shear stress to increase downstream; changes in glacier thickness can also change basal shear stress. Given steady-state conditions, when a glacier thins, the basal shear stress must increase to actuate a higher velocity to drive the same amount of ice out of the thinner zone. Nonetheless, the sum of the evidence points towards bed roughness playing an important role in influencing the basal shear stress.

Taylor et al. (2004) recognized that analyzing roughness alone does not solve the causality issue of pre-existing topography and flow direction, in that we cannot determine if the glacier is simply flowing along the path of least resistance over pre-existing topography, or whether the glacier is eroding its flow path through topography. Based on geomorphology considerations, we propose below that flow in our area is occurring over pre-existing large-scale topography."

In my subsequent posts I will provide more general paleo-evidence supporting/calibrating my abrupt WAIS collapse harzard scenario.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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The following are additional paleo-evidence supporting supporting the concept that th periodic chaotic strange attractor scenario correlating past Heinrich events to the possible further collapse of the WAIS by 2100 as may have happened during the Eemian peak:
-   It is noted that the approximately 20m abrupt SLR from about 124.2 to 123.8 kyr ago, during the Eemian peak, is comparable to the approximately 500-year Meltwater Pulse 1A event (and possibly to other similar Dansgaard-Oeschger, D-O, Events), see Deschamps et al., 2012 for evidence from coral borings in Tahiti that the Meltwater Pulse 1A included substantial ice mass loss from West Antarctic marine ice sheets.
-   According to Barnes et.al. 2010 (from Global Change Biology) based on samples of Bryozoans, the WAIS essentially disappeared during the Eemian peak. Also, Strugnell et al. 2012 note that the modern distribution of the Antarctic adult Turquet's octopuses provides additional biological evidence that WAIS essentially disappeared at the peak of the Eemian.
-   The fact that the Larsen Ice Shelf B has apparently not collapsed since the MIS 5.5 (Eemian peak) period, and that the Larsen Ice Shelf C is close to a state of collapse indicates that the Earth is entering a thermal domain not seen since the last collapse of the WAIS, apparently during MIS 5.5 (Eemian Peak).
-   Muhs et al. 2012 (and other studies) present physical evidence from several sites around demonstrate that during MIS 5.5 RSLR (including a RSLR of over 6 m offshore of California) was sufficiently high that the WAIS clearly collapsed during the Eemian peak.
-   According to Fox 2012:  "The average speed of winds blowing off Antarctica's coastlines has increased by 10 to 15 percent over the past 30 years.  Wind now scours 50 billion to 150 billion metric tons of snow from Antarctica's surface each year, blowing it into the ocean, where it melts.  As winds strengthen, scouring will likely increase, potentially worsening the prognosis for ice shelves in a way no one anticipated."  Fox 2012 continues: "That more ice shelves will collapse is a foregone conclusion.  An average summer temperature of zero degrees C seems to represent the highest temperature at which an ice shelf can exist. And the invisible line where summer averages zero degrees C is creeping south along the Antarctic Peninsula tip toward the mainland, along with higher mean annual temperatures.  Every ice shelf that the line crosses has collapsed within a decade or so.  Next up, south of Larsen B and Scar Inlet, is the Larsen C ice shelf, which covers 49,000 square kilometers - twice as large as the state of Maryland, or about 820 Manhattans.  Larsen C has more glacial ice flowing into it than all the other ice shelves that have collapsed combined.  It already sees summer melt ponds on its northern end."  Fox 2012 also cite evidence that while the Prince Gustav, Larsen Inlet and Larsen A ice shelves apparently all collapsed during the period of peak Holocene mean global temperatures about 4,000 years ago, but that the Larsen B Ice Shelf which collapsed in 2002 had apparently been stable for about 100,000 years; which indicates that the earth is now entering global conditions best characterized by the Eemian peak (MIS 5.5) era as postulated by my harzard scenarios.
-   The attached image shows a comparison of 2009 ice shelf melt rates of selected Amundsen Sea ice shelves vs sea surface ocean temperatures (oC above freezing).  As a key part of my hazard scenario is that warming of the CDW both in the past and in the future leads to both ice shelf collapse and to subglacial cavity formation/interconnection (into sea passageways); the data shown in this image clear supports the position that higher seawater temperatures support more ice shelf melting (which destabilize the WAIS).

As I have a large amount of such supporting paleo-evidence but little time to organize it into a presentable fashion, I will provide addition evidence in a sporadic fashion as time permits.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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While paleo-evidence of a possible correlation between a periodic chaotic strange attractor mechanism and Heinrich-like abrupt SLR events might provide a conceptual framework supporting the probability that someday the WAIS might also collapse abruptly; but even if true this would not necessarily mean that the WAIS is going to collapse this century, or that abrupt means a 50 to 100-yr period instead of collapsing over several centuries.  Therefore, this post focuses on paleo-evidence that: (a) during the Eemain peak, and/or the Holsteinian peak, the WAIS likely collapsed abruptly, (b) that current collapse forcing conditions, equal or exceed those extant during the Holsteinian peak, and/or the Eemain peak; and (c) that the WAIS ice mass loss is currently primed to accelerate in a Heinrich-like manner:
1.   First, in 2011 seafloor samples (see Carlson et al 2011) indicated that the WAIS contributed 3.4 to 3.8 m to sea level during the Eemian; while in 2013 the North Greenland Eemian Ice Drilling (NEEM) confirmed that the WAIS contributed closer to 3.8m (which implies that about 0.4m of sea-level rise contribution of this ice mass loss came from the EAIS), than 3.4m, to sea level.  As the sea-level during the Holsteinian peak was multiple meters higher than today, there is little doubt that the WAIS had fully melted during this relatively stable interglacial peak. This means that the primary questions resolve to: (a) how fast the WAIS lost ice mass; and (b) whether the WAIS collapse could begin in the near future (or has already begun).  However, while there is no definitive proof, numerous researchers have found preliminary evidence of possible abrupt SLR during the Eemian peak including research by Blancon et al. published in Nature in 2009, examining the paleoclimate record, shows sea-level rises of 3 meters in 50 years due to the rapid melting of ice sheets around 123,000 years ago in the Eemian.
2.   Second, it is important to remember that while the Eemian peak, and/or the Holsteinian peak, may be the closest physical cases to parallel Earth's current condition; still they are clearly not some sort of physical model simulations that we can rely on without any thoughtful corrections (whether by computer model results; evidence from different interglacial peaks [such as different aspects of both the Eemian & Holsteinian peaks {MIS 5 & MIS 11c}]; or a better understanding of the complex past and present earth systems).  For instance, the Lake El’gygytgyn region of Russian seems to have been considerably warmer during MIS 11c [the Holsteinian peak] than it was during MIS 5e. This is despite the fact that summer solar radiation was less intense (though the season was longer) and greenhouse gas concentrations were similar. The researchers of sediment in the lake write, “Consequently, the distinctly higher observed [temperature and precipitation] at MIS 11c cannot readily be explained by the local summer orbital forcing or GHG concentrations alone, and suggest that other processes and feedbacks contributed to the extraordinary warmth at this interglacial, and the relatively muted response to the strongest forcing at MIS 5e.”  The Arctic is especially sensitive to climate changes (through the loss of reflective snow and ice, for example), and what happens there affects the rest of the planet as well. Figuring out which feedbacks could account for the warm temperatures during MIS 11c could be useful.  Seeing how climate responds to many different situations helps researchers obtain a deeper understanding of the climate system. And therein lies the value in climate records from disparate regions. As the researchers put it, “The observed response of the region’s climate and terrestrial ecosystems to a range of interglacial forcing provides a challenge for modeling and important constraints on climate sensitivity and polar amplification.”                     
3.   For those not familiar with the comparison of the Eemian Peak (MIS 5) with the Holsteinian Peak (MIS 11), I provide both the first image from Hansen and Sato, and the following from Wikipedia: "Marine Isotope Stage 11 or MIS 11 is the interglacial period between 424,000 and 374,000 years ago. It corresponds to the geological Hoxnian Stage.  Interglacial periods which occurred during Pleistocene times have been recently put under investigation, in order to better understand our present and future climates. In fact, paleoclimatic interpretations often depends on observations drawn from the study of modern/historical processes. In order to better estimate the ”natural range” of climatically important mechanisms, it seems crucial to attempt detailed comparisons of the present interglacial (i.e., the Holocene) with previous warm periods of the Quaternary, such as Marine isotopic stage 11. Similar orbital configurations and comparable atmospheric greenhouse gas concentrations (considering only the period before the beginning of the Industrial Revolution, i.e. 1800 AD ca.) have led to the suggestion that MIS 11 is a suitable, possibly the best, geological analogue for the natural development of Holocene and future climate. Another candidate was MIS 5, but several characteristics do not fit the present conditions. MIS 11 represents the longest and warmest interglacial interval of the last 500 kyr. In fact, it shows the highest-amplitude deglacial warming in the last 5 Myr and possibly lasted twice the other interglacial stages. MIS 11 is characterized by overall warm sea-surface temperatures in high latitudes, strong thermohaline circulation, unusual blooms of calcareous plankton in high latitudes, higher sea level than the present, coral reef expansion resulting in enlarged accumulation of neritic carbonates, and overall poor pelagic carbonate preservation and strong dissolution in certain areas.  As stated above, MIS 11 is considered the warmest interglacial period of the last 500 kyr.  Nevertheless, some issues concern the lack of evidence for the trends and degree of warming during this interval. Recent isotopic and planktonic faunal data sets from high-accumulation rate marine successions in the North and South Atlantic indicate that MIS 11 was not warmer, but even slightly cooler than the Holocene. According to these data, the warmest interglacial period was likely MIS 5, although it was shorter.  Beach deposits in Alaska, Bermuda and the Bahamas, as well as uplifted reef terraces in Indonesia, suggest that global sea level reached as much as twenty metres above the present. During MIS 11, δ18O records show isotopic depletions that are consistent with a sea-level highstand, but temperature effect cannot be confidently disentangled from glacioeustasy. Moreover, the collapse of at least one major ice sheet has to be inferred in order to produce similar high sea-levels, nevertheless, the stability of these ice sheets is one of the main questions in climate-change research: in fact, controversial geologic evidences suggest that present-day polar ice sheets might have been disrupted (or drastically shrunk) during previous Pleistocene interglacials. The increased sea level requires reduction in modern polar ice sheets and is consistent with the interpretation that both the West Antarctica and the Greenland ice sheets were absent, or at least greatly reduced, during MIS 11. However, similar conditions would have led to much lighter δ18O values than the present, in contrast to what observed in oxygen isotope records worldwide.  Unlike most other interglacials of the late Quaternary, MIS 11 cannot be explained and modeled solely within the context of Milankovitch forcing mechanisms. According to various studies, the MIS 11 interglacial period was longer than the other interglacial stages; moreover, the sustained interglacial warmth lasted as long as it did, because the eccentricity was low and the amplitude of the precessional cycle diminished, resulting in several fewer cold substages during this period and also induced an abrupt climate change at MIS 12–11 transition, the most intense of the past 500 kyr. Noteworthy, MIS 11 developed just after one of the most “heavy” Pleistocene δ18O glacials (MIS 12). According to some Authors, MIS 12 is likely to represent a “minimum” within the 400-kyr cyclicity (which is apparently “stretched” into ca. 500-kyr cycles in the Pleistocene), same as the MIS 24/MIS 22 complex (ca. 900 ka; Wang et al., 2004). In support to this inference is the fact that these dramatic glacial intervals are coincident with periods of major climate reorganisation, namely the “Mid-Brunhes Event” (Jansen et al., 1986) and the “Mid-Pleistocene Revolution” (Berger & Jansen, 1994), respectively. Considering the variability in the astronomically-driven insolation, MIS 11 is the interval in which insolation is highly correlated with predicted near future situation. Using the 2-D Northern Hemisphere climate model to simulate climate evolution over MIS 11, MIS 5 and the future, it appears that climatic feature and length of MIS 11 are very similar to the present-future interglacial. This consideration may lead to the conclusion that actual interglacial period (begun 10 kyr) will continue for approximately 20-25 kyr"
As noted in the preceeding quote: "… paleoclimatic interpretations often depends on observations drawn from the study of modern/historical processes" Therefore my next post will focus on the study of modern/historical processes required to interpret the paleo-evidence from the MIS 5 and MIS 11 periods; and the to suggest appropriate corrections to CMIP5 projections, as our current GCM projections are calibrated to match the old interpretation of the Eemian response, which does not fully capture either: (a) the likely polar amplification; or (b) periodic strange attractor considerations.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Lennart van der Linde

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ASLR,
You say:
"Beach deposits in Alaska, Bermuda and the Bahamas, as well as uplifted reef terraces in Indonesia, suggest that global sea level reached as much as twenty metres above the present."

Yes, but Raymo & Mitrovica (2012) conclude that:
http://www.moraymo.us/Raymo+Mitrovica_2012.pdf

"the elevations of these features are corrected downwards by 10 metres when we account for post-glacial crustal subsidence of these sites over the course of the anomalously long interglacial. On the basis of this correction, we estimate that eustatic sea level rose to 6–13m above the present-day value in the second half of MIS 11."

So about 10m higher global mean sea level than present seems the currently most accurate number for the Holsteinian, unless you have reasons why this wouldn't be the best available estimate?

ritter

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Well, 10 meters of sea level rise would be catastrophic, so what's another 10 meters?! :o

(I joke mostly because it is unimaginable what 20 meter rise would do to our world. And us.)

AbruptSLR

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Lennart & Ritter,

I do not have any better information than Raymo & Mitrovica (2012), so I agree that assuming a 10m higher eustatic sea level for the Holsteinian peak is probably the best value for now.  That said it took the Holsteinian epoch several thousand years to reach this level; while the focus of all of my posts have been on the risk of 5 to 6m of SLR this century.

In any event, thanks for the correction.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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This post assumes that CMIP5 projections have been calibrated to match general hind-castes of paleo-climatic behavior and that they capture the general future trends associated with climate change, but cannot accurately capture amplification mechanisms (see the first image).  Rather, this post assumes that a hazard analysis should add considerations for possible mechanisms that I am calling ratcheting quasi-static equilibrium polar amplifications associated with periodic strange attractors (or "ratcheting mechanisms" for short); as they relate to evaluating the probabilities of both past and possible future abrupt SLR, ASLR, events. As the paleo-record, and GCM hind-castes, are not adequately refined to accurately quantify the risk of 50 to 100-yr ASLR events; therefore, the following discussion focuses on paleo-interpretation of recent possible ratcheting mechanism.  The second image provides a graphical comparison of a ratcheting mechanism to a more common periodic chaotic strange attractor behavior, with both cases superimposed on a general trend of increasing climate change.
The third image provides my first example of a possible ratcheting mechanism where it is postulated that the unusually positive AO (a possible strange attractor event) from 1989 to 1995 lead to the accelerated export of multi-year Arctic Sea Ice; which in-turn could lead to accelerated Arctic Sea Ice Extent reductions.
The fourth image provides my second example of a possible ratcheting mechanism associated with the difference between the maximum Winter and the minimum Summer Arctic Sea Ice Extent from 1979 to 2011.  The continuation of such a ratcheting mechanism could contribute to accelerated Arctic Sea Ice extent loss and an associated acceleration in albedo loss radiative forcing (albedo flip); which in-turn can contribute to accelerated tropical Atlantic ocean heat uptake; that can lead to an acceleration of CDW volume increase and temperature increase.
My third example of a possible ratcheting mechanism is discussed in the "Forcing" thread where the ENSO hiatus (with La Nina of ENSO index neutral conditions) period from 1999 to 2012, drive tropical Pacific overturning that telecommunicates ocean heat content from the tropics to the CDW; thus triggering accelerated ice mass loss from both West Antarctic ice shelves and ice sheets/marine glaciers.
All three of these ratcheting mechanisms are not adequately captured by the CMIP5 models; but they all occurred in the modern era under radiative forcing conditions that are well within the conditions extant during both the Eemian (MIS 5) and the Holsteinian (MIS 11), peaks, and such ratcheting mechanisms could have triggered past ice mass loss from the WAIS and may have already triggered an ASLR event in modern times (from now to a couple of hundred years from now).  My next series of posts will focus on how the dramatic modern acceleration of anthropogenic radiative forcing may serve to induce natural amplifications of climate change sufficiently to essentially "guarantee" that such an ASLR event may happen by the turn of this century.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

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My previous posts in this thread have focused on possible previously unrecognized/unappreciated possible natural feedback pathways that could have amplified natural radiative forcing in order to better account for some of the large past high sea level events (focusing on the Eemian and Holsteinian events).  Furthermore, my series of threads on the potential collapse of the WAIS this century have been based on the assumption that anthropogenic radiative forcing will roughly follow the RCP 8.5 scenario (with some minor adjustments); which the World Bank tells us is the path that we are currently following, and the first image illustrates just how much more aggressive the rate of warming of this current "business-as-usual" radiative forcing is compared to the extreme natural radiative forcing during the PETM.  However, it is intellectually dishonest to think that as the projected temperature rise for RCP 8.5 approximately matches the extreme natural temperature rise during the PETM; that RCP 8.5 represents an upper bound for radiative forcing, because the PETM case included no anthropogenic forcing; thus for a realistic hazard assessment one needs to consider the possibility that extreme natural radiative amplification (or feed-back) will be added on top of the anthropogenic radiative forcing component of at least RCP 8.5 (note that as discussed in the "Forcing" thread anthropogenic radiative forcing is currently exceeding that assumed in RCP 8.5).  In this regard, it is important to note that the following extreme natural amplification scenarios are particularly serious in that not only do they steepen the slope of the general climate change trend line, but they also can increase the amplitude of the strange attractor temporary departures from the mean trend line; which when combined with the ratcheting mechanisms characteristic of polar amplification (see prior posts in this thread), can further accelerate/amplify the combined influence on the risk of ASLR this century.  Thus if any of the following extreme natural amplification scenarios were to occur then ASLR would be virtually guaranteed to occur this century due a collapse of the WAIS.
For my first extreme natural amplification scenario, I point out that Isaksen et al. (2011) ran a range of computer models to show that methane's atmospheric burden is greater when more methane is emitted to the atmosphere than assumed in AR4 (see the second image for Isaksen et al. (2011)'s emission rates input into computer models).  Isaksen et al (2011) found (see the second image) that as the assumed emission rate increased the chemistry of the atmosphere would change resulting in increase lifetime of methane, increased methane burden in the atmosphere and that the radiative forcing from the methane would increase (see the third image).
The methane emission rates presented in the "Forcing" thread justify the use of the findings from Isaksen et al's 7 x CH4 case for calculating a hazard revised GWP for methane, as follows: As the radiative forcing in a 50-year time horizon for 4 x CH4 additional emission of 0.80 GtCH4/yr is 2.2 Wm-2, and as the radiative forcing for the current methane emissions of 0.54 GtCH4/yr is 0.48 Wm-2, an updated GWP for methane, assuming the occurrence of Isaksen et al's 4 x CH4 case in 2040, would be: 33 (per Shindell et al 2009) times (2.2/[0.8 + 0.48]) divided by (0.54/0.48) = 50.  This first approximation of a new GWP for methane may be to be non-conservative with regard to calculating potential SLR for reasons including:
(a) Isaksen et al's (2011) 4 x CH4 case assumes that the additional methane emissions stabilize at a rate of 0.8 GtCH4/yr, while the methane emissions presented in the "Forcing" thread assumes that by 2100 the additional methane emissions (beyond 0.54 GtCH4/yr) may increase to about 1.06 GtCH4/yr.
(b) The methane emissions assumed in RCP 8.5 appear to be non-conservative (note RCP 8.5 assumes a 2011 methane emission value less than the scientific consensus, see the discussion in the "Forcing" thread).
(c) The HIAPER Pole-to-Pole Observations (HIPPO) found that in the summer of 2011 methane was being emitted into the atmosphere from the entire Atlantic sector of the Arctic Ocean, and possibly the entire Arctic Ocean, depending on the amount of the ice cover.  Thus as the ice cover declines, more methane will be emitted from the Arctic Ocean into the atmosphere.
(d) These assumptions ignore the possible increase in methane emissions from unconventional (such as shale gas), as compared to the current conventional, sources of natural gas.
(e) Currently, in the Arctic Ocean, 80% of the deep water and more than 50% of the surface water has methane levels more than eight times that of normal seawater.
It should also be remembered that many countries in the world (USA, Canada, Argentina, China, etc.) are becoming increasingly dependent on methane gathered by means of hydrofracking and that it is unlikely that the anthropogenic emissions for most shale gas operations (including both hydrofracking and transmission operations) will meet the 2 to 3 percent emissions "target" shown in the fourth image.  It is important to also remember that none of the GCM projections have yet been paleo-calibrated for black carbon's radiative effect as it a modern phenomena; and it's observed effects have exceeded most of the early estimates of this effect.
My second and third extreme natural amplification scenarios will be addressed in my next post.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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For my second extreme natural amplification scenario, the first image shows model projections of warm ocean current intrusion into the Arctic Ocean, which could possibly trigger the clathrate gun mechanism, which has been postulated to possibly drive the remarkably rapid natural temperature rise of the PETM.  The second image shows how the postulated clathrate gun mechanism may work in the Arctic Ocean. However, it is possible the clathrate gun mechanism may already be occurring on the Antarctic continental slope due to both the observed volume reduction of the AABW flow (and temperature increase) and the observed volume increase of the CDW flow (and the temperature increase).  See A4R's updates and discussions of the recent rapid increase in methane emissions from both the Arctic and Southern Oceans.  If a clathrate gun mechanism were to be triggered before the end of this century then the GWP for methane would clearly increase above the value of 50 calculated in the previous post; which taken together with the direct radiative forcing from the additional methane would clearly drive the world into the amplified albedo feedback situation discussed in my third extreme natural forcing amplification scenario.

For my third extreme natural forcing amplification scenario, as my third image I am re-posting Hansen and Sato's figure regarding the influence of albedo loss on the climate sensitivity value; which according to the figure indicates that if radiative forcing increases to between 2 to 3 Watts/sq meter above the Holocene levels (which we will likely exceed in less than 10 to 15 years); then climate sensitivity will increase to approximately 7 C from the 3 C value assumed by most CMIP5 projections.  As the radiative forcing values for the extreme methane forcing scenario (discussed in the previous post and for the clathrate gun mechanism) could clearly increase radiative forcing to between the 2 to 3 W/sq m values cited above; an amplifying feedback mechanism could readily be developed between natural methane emissions (including from the permafrost, and methane hydrates); that could drive ASLR values into the 5 to 9m range shown in the fourth accompanying image (from Kopp et al) that may have last occurred during the Eemian peak (MIS 5) [although note that the ice mass loss contributions to sea level rise from GIS, and WAIS were likely different during the Eemian peak than indicated by Kopp et al].
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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The purpose of this thread is not to make specific projections about the probability of ASLR, but rather to point out that there are a number of natural feedback/amplifying/ratcheting quasi-static equilibrium mechanisms that are supported by both the paleo-, and recent historical, evidence; that when applied to the modern anthropogenic radiative forcing, could possible drive the Earth Systems toward both abrupt climate change and ASLR.  However, I would like to point out in this post, that from a hazard analysis point of view, that anthropogenic forcing is also not bounded by the pathway defined by RCP 8.5.  The first figure shows the likely new shipping routes that industry is planned to take advantage of as the Arctic Sea Ice retreats; which will both break-up the increasingly think ice, and will introduce more black carbon directly to the Arctic.  The second image shows the relatively large amount of fossil fuels that are likely to be recovered from the Arctic; which implies the risk of oil spills and loss of albedo.  There are numerous other examples that are discussed elsewhere in this forum and in the Arctic Sea Ice blog.
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I would also like to emphasize that the true risks of ASLR must be combined together with short-term flood risks, such as storm surge, while the risks of inundation from storm surge is significantly increasing, with climate change, as discussed in the following:

Tebaldi et al. (2012) investigated the influence of RSLR on expected storm surge driven water levels and their frequencies for 55 tidal stations in the Continental United States using hourly data from 1979 to 2008 and monthly data from 1959 to 2008.  They used the Vermeer and Rahmstorf (2009) semi-empirical relationship to determine RSLR at each station (and for the global mean) for the years 2030 and 2050 and estimated the influence of RSLR on the extreme storm surge levels and associate return levels.  The first image shows in how many years will today's 100-year storm surge event recur in 2050 for each of the 55 stations evaluated by Tebaldi et al.  It is noted that: (a) as the WAIS is not expected to exhibit significant collapse before 2050, the V&R SLR projections should be reasons values to use until this date; (b) Tebaldi et al. (2012) averaged data over a 50-year epoch in order to reduce the influence of multi-decadal ocean cycles; however, this practice also fails to adequately characterize trends in rapidly changing systems; and (c) Tebaldi et. al. assume that storm intensities will remain constant with time.
It is important to note that the joint storm surge and RSLR return levels and confidence limits presented in the second and third attached images by Tebaldi et. al. (2012) do not consider contributions from such effects as: (a) collapse of the WAIS; (b) storm tide; (c) backwater effects or (d) increase in storm intensity due to global warming; nor do they include local geographical amplification affects that must be modeled by a tightly coupled circulation and wave/wind hydraulic model. 

In reference to the fourth image, Grinsted et al 2013 (PNAS) states:
“We find that 0.4 degrees Celcius warming of the climate corresponds to a doubling of the frequency of extreme storm surges like the one following Hurricane Katrina. With the global warming we have had during the 20th century, we have already crossed the threshold where more than half of all ‘Katrinas’ are due to global warming.  If the temperature rises an additional degree, the frequency will increase by 3-4 times and if the global climate becomes two degrees warmer, there will be about 10 times as many extreme storm surges. This means that there will be a ‘Katrina’ magnitude storm surge every other year.”
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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To emphasize the importance of ocean currents I thought that I would be good to repost the following article from the internet, here:

"The world’s oceans act as a massive conveyor, circulating heat, water and carbon around the planet. This global system plays a key role in climate change, storing and releasing heat throughout the world. To study how this system affects climate, scientists have largely focused on the North Atlantic, a major basin where water sinks, burying carbon and heat deep in the ocean’s interior.
But what goes down must come back up, and it’s been a mystery where, and how, deep waters circulate back to the surface. Filling in this missing piece of the circulation, and developing theories and models that capture it, may help researchers understand and predict the ocean’s role in climate and climate change.
Recently, scientists have found evidence that the missing piece may lie in the Southern Ocean — the vast ribbon of water encircling Antarctica. The Southern Ocean, according to observations and models, is a site where strong winds blowing along the Antarctic Circumpolar Current dredge waters up from the depths.
“There’s a lot of carbon and heat in the interior ocean,” says John Marshall, the Cecil and Ida Green Professor of Oceanography at MIT. “The Southern Ocean is the window by which the interior of the ocean connects to the atmosphere above.”
Marshall and Kevin Speer, a professor of physical oceanography at Florida State University, have published a paper in Nature Geoscience in which they review past work, examine the Southern Ocean’s influence on climate and draw up a new schematic for ocean circulation.
A revised conveyor
For decades, a “conveyor belt” model, developed by paleoclimatologist Wallace Broecker, has served as a simple cartoon of ocean circulation. The diagram depicts warm water moving northward, plunging deep into the North Atlantic; then coursing south as cold water toward Antarctica; then back north again, where waters rise and warm in the North Pacific.
However, evidence has shown that waters rise to the surface not so much in the North Pacific, but in the Southern Ocean — a distinction that Marshall and Speer illustrate in their updated diagram.
A new schematic emphasizes the role of the Southern Ocean in the world’s ocean circulation. The upper regions of ocean circulation are fed predominantly by broad upwelling across surfaces at mid-depth over the main ocean basins (rising blue-green-yellow arrows). Upwelling to the ocean surface occurs mainly around Antarctica in the Southern Ocean (rising yellow-red arrows) with wind and eddies playing a central role. Image: John Marshall and Kevin Speer
Marshall says winds and eddies along the Southern Ocean drag deep waters — and any buried carbon — to the surface around Antarctica. He and Speer write that the updated diagram “brings the Southern Ocean to the forefront” of the global circulation system, highlighting its role as a powerful climate mediator.
Indeed, Marshall and Speer review evidence that the Southern Ocean may have had a part in thawing the planet out of the last Ice Age. While it’s unclear what caused Earth to warm initially, this warming may have driven surface wind patterns poleward, pulling up deep water and carbon — which would have been released into the atmosphere, further warming the climate.
Shifting winds
In a cooling world, it appears that winds shift slightly closer to the Equator, and are buffeted by the continents. In a warming world, winds shift toward the poles; in the Southern Ocean, unimpeded winds whip up deep waters. The researchers note that two manmade atmospheric trends — ozone depletion and greenhouse gas emissions from fossil fuels — have a large effect on winds over the Southern Ocean: As the ozone hole recovers, greenhouse gases rise and the planet warms, winds over the Southern Ocean are likely to shift, affecting the delicate balance at play. In the future, if the Southern Ocean experiences stronger winds displaced slightly south of their current position, Antarctica’s ice shelves may be more vulnerable to melting — a phenomenon that may also have contributed to the end of the Ice Age.
“There are huge reservoirs of carbon in the interior of the ocean,” Marshall says. “If the climate changes and makes it easier for that carbon to get into the atmosphere, then there will be an additional warming effect.”


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

AbruptSLR

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Considering the importance of ocean currents in the Arctic Ocean, I thought that I would post this figure from Polyakov et al 2005; showing how warm pulses of ocean currents can travel around the edge of the Arctic continental slope; where it could promote the Clathrate Gun mechanism as the ocean current water temperature rises.
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I believe that I may have made the following point in one of my other posts; but if so it bears repeating.

The first image from Fasullo and Trenberth 2012 illustrates how a review of the projections of the 16 leading global circulation models, demonstrates that regarding the critical topic of humidity/cloud-cover in the tropics atmosphere (critical because of the reflectivity of clouds in the tropics) that the GCM projections that assume an equilibrium climate sensitivity, ECS, of 4.5 C matched the observations much better over the last about 20-years than those models that used the 3 C ECS assumed (calibrated to) by most CMIP5 projections. 

Furthermore, the second image shows that rapid rate of increase of global specific humidity in the past 25 years.  The indicated rate of increase in global specific humidity is much faster than projected by CMIP5 models; thus indicating that the Earth System's fast response mechanisms may well be faster than assumed by the projections made in IPCC AR5 SOD.  Obviously, if verified, this rapid fast response (supporting a current ECS of about 4.5 C)  would increase the risk of ASLR this century, as compared to current thinking.
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The first image, from Hansen, et al 2011, shows the results of a sensitivity study to examine the response of both global mean surface temperature and planetary energy imbalance as a function of changes to the GCM response function as indicated in the second image.  This sensitivity study clearly indicates that if the rate of response of some climate feedback mechanism (such as Arctic or Antarctic albedo) were to increase, then the global mean surface temperature will also increase.  The first image shows Green's function calculation of global mean surface temperature change and planetary energy imbalance for different response functions (as indicated), from Hansen et al. 2011.  Hansen et al's 2011 results illustrate that if researchers do not fully understand the rates of response for the various feedback mechanisms that they are modeling; then the actual hazard to society may be considerably higher than projected by the CMIP5 results.
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AbruptSLR

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With regards to the immediate prior post, the following are examples of phenomena that were once modeled to have slow response rates in the GCM analyses, which in ASLR hazard analysis process should provide a SLR correction for the probability that they may actually have fast response rates:
•   Reduced albedo from Arctic Sea Ice during the Summer months;
•   Reduced albedo from: (a) Ross and Weddell Sea Ice Shelves; (b) From Pine Island, Thwaites, and other WAIS glaciers/ice-stream flows during the austral summer months.
•   Reduced albedo from: (a) loss of permafrost; (b) plants moving north; (c) increase in lake surface area; and (d) increase in wild fires.
•   Reduced land absorption of CO2 due to (counters to more farming and increased plant growth rate due to warmer weather and plants moving north): (a) release of CO2 from warmer tropical rain forest floor and Northern wetlands/permafrost; and (b) Amazon droughts;
•   Reduced ocean absorption of CO2 due to: (a) acidification of oceans killing marine life and making the partial pressure different; and (b) slowing of ocean currents;
•   Relative reduction of air pollution in Asia and Africa, over several decades, thus reducing this negative aerosol feedback effect that has been masking the influence of GHG emitted from at least 1990 until the point where the aerosol effect is decreased.
•   More rapid ice mass loss due to non-uniform global distribution of temperature increase (note the temperature of the Arctic/West Antarctic/Antarctic Peninsula regions are warming faster than any other region of the world.
•   Potential acceleration of Greenland Ice Sheet mass loss due to such factors as: (a) reduction of buttressing from reduced Arctic Sea Ice and increase ocean water temperatures; and (b) change in albedo due to reduction of snow;
•   Ratcheting to quasi-equilibrium states driven by oscillations such as: solar cycles, Arctic Oscillation Index/Arctic dipoles (inducing sea ice flushing from the Arctic through the Fram Straits); and ENSO cycles
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The following addresses a few points from Weitzman 2011:
(1) Regarding systemic inertia and learning, Weitzman states: "The issue of how to deal with deep structural uncertainties of climate change would be completely different and immensely simpler if systemic inertias, such as the time required for the system to naturally remove extra atmospheric CO2, were short, as is the case for many airborne pollutants like sulfur dioxide, nitrous oxides, and particulates.  An important component of an optimal strategy might be along the lines of "wait and see."  With strong reversibility, an optimal climate change policy would logically involve (among other elements) waiting to learn how far out on the bad fat tail the planet will end up, followed by midcourse corrections if we seem to be headed for a disaster.  Alas, the problem of climate change seems bedeviled at almost every turn by significant stock-accumulation inertias ---- in atmospheric CO2, in the absorption of heat or CO2 by the oceans, and in many other relevant physical and biological processes ---- that are slow to respond to attempts at reversal."
(2) Weitzman concludes: "Taking fat tails into account has implications for climate change research and policy.  For example, perhaps more emphasis should be placed on research about the extreme tails of relevant PDFs rather than on research about central tendencies.  As another example, the fatness of the bad fat tail of proposed solutions (such as, perhaps, the possibility that buried CO2 might escape) needs to be weighed against the fatness of the tail of the climate change problem itself. With fat tails generally, we might want more explicit contingency planning for bad outcomes, including, perhaps, a niche role for last-resort portfolio options like geoengineering.
   Qualitatively, fat tails favor more aggressive policies to lower GHGs than "standard" BCA (Benefit Cost Analysis).  Alas, the quantitative implications are less clear.  As this article has stressed, the natural consequence of fat-tailed uncertainty should be to make economists less confident about climate change BCA and to make them adopt a more modest tone that befits less robust policy advice.  My own conclusion is that the sheer magnitude of the deep structural uncertainties concerning catastrophic outcomes, and the way we express this in our models, is likely to influence plausible application of BCA to the economics of climate change for the foreseeable future."
While Weitzman's theoretical fat-tailed methodology is primarily focused on issues (such as policy for GHG reductions) and on timeframes (typically well beyond 2100) that are beyond my hazard analysis for ASLR this century; nevertheless, his proposed methodology brings focus to many of the issues addressed in the different threads that I started, including:
•   The need to recognize that deep structural uncertainties are not beneficial to society at large (while such uncertainties may allow individuals to acquire short-term benefits ala the "Tyranny of the Commons") as such deep structural uncertainties tend to stifle human will to take the robust/resilient measures appropriate to deal with fat-tailed risks (including ASLR this century).
•   The need to recognize that while most scientists/policy makers admit that for high-cases like RCP 8.5 that systemic climatic inertias will subject future generations to millennia of the consequences of severe global warming; nevertheless, most scientists (e.g. IPCC)/policy makers fail to admit that localized systemic climatic inertias within their models (e.g. CMIP5) are masking (in the short-term) the identification of polar/oceanic amplification/ratcheting/feedback mechanisms that will greatly accelerate the observed consequences of global warming once sufficient momentum has been gained (e.g. by such means as polar albedo flip; permafrost decomposition warming of ocean currents in both the Arctic and the Southern Oceans; intensification of winds & storms and associated increase in upwelling around Antarctica; etc.), so that abrupt SLR from the collapse of the WAIS may happen in this century.
•   The need to refocus attention from the mean/mode on to the fat end of the PDFs associated with RSLR/ASLR design.  Focusing on mean/mode values is particularly hazardous when evaluating the risk of the WAIS collapsing this century, for example: (a) many people average WAIS trends together with EAIS trends, which is not advisable as the WAIS is the only remaining marine ice sheet in the world, thus it would make more sense to average the GIS and EAIS trends with regard to ice mass loss; and (b) many people focus on how ocean thermal inertia slow the rate of global temperature rise but down play that much of the ocean heat uptake/content has be directed (via currents) into the CDW where it is rapidly accelerating ice mass loss from the WAIS.
•   The need to not only consider that systemic inertia from such factors related to climate sensitivity as the thermal inertia of the ocean which can delay the response of the global-mean temperature by decades from the time of the initial radiative forcing; but that it is also important to consider such systemic inertia as the current dependence of the modern economic system on fossil fuels and the amount of time that it will take transition to more sustainable energy sources.
•   The need to address the fact that currently rates of radiative forcing are one hundred to one thousand times faster than for any period in the past several hundreds of millions of years (and over 100,000 times faster that the MIS 5 and 11 interglacial periods that many GCM projections are calibrated to) ; which, will create thermal imbalances around the planet leading to extreme weather/oceanic events that can iteratively ratchet the global's quasi-static equilibrium level to higher energy states, as can be observed by earlier discussion in this thread, and by mechanisms as NOAA's "Warm Arctic Cold Continent" paradigm.
•   The need to correct most GCM, and most BCA, projections that have assumed thin tailed (or Normal) PDFs for functions that actually have fat tailed (or Pareto) PDFs.  Most hard civil marine/coastal need to be designed with a 95% CL, and at this level Weitzman demonstrates that incorrectly using a thin tailed PDF when a fat tailed PDF is correct, can result in a large difference (several times) in projected damage functions.
•   The need to correctly account for all earth system feedback mechanisms (such as GHG from melting permafrost, peat bogs, and man-induced wild fires), including feedback from the feedback itself.   
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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The information at the following wiki sites provides additional supporting information regarding the modern risk of abrupt climate change and supporting paleo-evidence:

http://en.wikipedia.org/wiki/Runaway_climate_change

http://en.wikipedia.org/wiki/Abrupt_climate_change

However, no matter how much supporting evidence is provided (and there is new supporting evidence reported every week); due to the "deep structural uncertainties" and "systemic inertias" discussed by Weitzman 2011; it will never be possible to make thin-tailed projections about the risks of abrupt SLR from a potential collapse of the WAIS this century; until the probabilities and consequences of ASLR are unavoidable.  Therefore, I will close my planned posts to this thread by again stating that decision makers should plan for robust/resilient behave of our infrastructure that is at risk of inundation this century, while there is still some time for such adaptive engineering measures to be taken.
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Hi Abrupt SLR!

My concerns rest with a sudden collapse of the Roosevelt Island side of the Ross Ice Shelf? Pat Warmings have not only had WAIS ice free but also an island with a sea channel from Ross to Weddell.

With the Warm Bottom waters now at Ross surely undercutting is occuring? Radar plots of Ross show a 'crumple' in the ice showing a rapid halt to it's past fast movement (as the ice welded to the Sea bed?). This would suggest that there is a point where the back pressure will overcome the resistance that the shelf currently provides. Undercutting might not lead to calving events but may lead to allowing a sudden forward surge (and then calving?).

Without Ross we have EAIS drain glaciers as well as the gradual meltdown of WAIS?
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AbruptSLR

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Gray-Wolf,

You may well be right (only time will tell), and I use to have the same concerns as you.  However, as cited in my posts in the "Hazard Analysis for FRIS/RIS for the 2012 to 2060" thread, I now believe that the "protective circulation patterns" beneath the RIS will only allow for about 1km to 2km/yr of iceshelf face retreat (due to calving) until about 2040-2050 afterwhich I expect warm CDW to start circulating under RIS.  While the warming of the AABW is important, I do not believe that by itself it can adequately disrupt the "protective circulation patterns" beneath RIS (without the help of the warming CDW coming across the continental shelf and entering the Ross Sea Embayment through the shallow trough on the west side (opposite Roosevelt Island)).

My biggest concern in the near-term is still the PIG/Thwaites system as I discuss in my posts in the "Hazard Analysis for PIG/Thwaites in the 2012 to 2040-2060 Timeframe"; however, you may well be right the RIS (Ross Ice Shelf) is a bigger risk.  I will open a thread on links to websites to monitor in order to watch what is happening in the Antarctic; however, things in the Antarctic are not changing as dynamically as in the Arctic, and there is less information available in real-time about the Antarctic; thus we may all need to patient to see what is going to unfold in the near-term.
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AbruptSLR

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I found this article on the internet that is related to my first post, but which clarifies that part of the Northern Hemisphere/Southern Hemisphere synergistic interaction during paleo-interglacial periods is due to the collapse of the WAIS raising sea level sufficiently as to drive more warm Pacific ocean water into the Arctic Ocean through the Bering Strait:

"Loss of Antarctic ice could trigger super-interglacial
21 June 2012 by Michael Marshall
At least eight times in the last 2.8 million years, the Arctic experienced super-interglacials – periods in which summers there were 5 °C warmer than they are today.
Climate models cannot explain these unusually warm spells, but there could be an unexpected cause: the collapse of the West Antarctic ice sheet (WAIS), on the other side of the planet. The sheet could collapse again as the world warms, perhaps heralding super-interglacial number nine.
The evidence for the super-interglacials comes from a sediment core drilled from the bed of Lake El'gygytgyn in north-east Russia by Martin Melles of the University of Köln in Germany, and his colleagues.
Toasty warm
The Arctic ice sheets have been advancing and retreating for the last 2.6 million years, as temperatures fell and rose. Warmer periods – including the one we now live in – are known as interglacials. The Lake El'gygytgyn core confirms that Arctic temperatures during eight of these periods were on average 4 to 5 °C warmer than in the region today. "That's really a lot," says Melles.
What triggered these super-interglacials? Earlier studies hinting that they occurred encouraged Paul Valdes at the University of Bristol, UK, to try to find out. Last year he discovered that standard climate models couldn't simulate them (Journal of Quaternary Science, DOI: 10.1002/jqs.1525).
Melles ran into the same problem. He used a state-of-the-art climate model that included key positive feedbacks, such as vegetation moving north and thus absorbing more heat. But he could not trigger a super-interglacial in his simulations.
He turned to sediment records from Antarctica for further clues. These records suggest that the WAIS disintegrated during each of the super-interglacials.
All around the world
Despite being half a world away, the collapse of the ice sheet might be the trigger for an Arctic super-interglacial, says Melles. As the WAIS disintegrates, it would raise global sea levels by about 5 metres. This would push more warm water from the Pacific Ocean through the Bering Strait into the Arctic Ocean, warming the Arctic region.
Valdes agrees such a process could well be important, particularly as it was not included in the models he studied last year. So a collapsing WAIS would not just drive up sea levels, it might also heat up the Arctic. The $64,000 question is, will it collapse again in the near future?
"What we see today is a dramatic decrease of the WAIS," Melles says. Some scientists think it will start to break up this century. But Melles says it could be centuries before the whole thing goes, and the effects would then take time to reach the Arctic.
"I don't think we know what it will take to lose the WAIS," says Valdes, "but if it goes, it would have climate consequences for the whole globe."
Journal reference: Science, DOI: 10.1126/science.1222135"

Science 20 July 2012:
Vol. 337 no. 6092 pp. 315-320
DOI: 10.1126/science.1222135
2.8 Million Years of Arctic Climate Change from Lake El’gygytgyn, NE Russia
1.   Martin Melles,
2.   Julie Brigham-Grette,
3.   Pavel S. Minyuk,
4.   Norbert R. Nowaczyk,
5.   Volker Wennrich,
6.   Robert M. DeConto,
7.   Patricia M. Anderson,
8.   Andrei A. Andreev,
9.   Anthony Coletti,
10.   Timothy L. Cook,
11.   Eeva Haltia-Hovi,
12.   Maaret Kukkonen,
13.   Anatoli V. Lozhkin,
14.   Peter Rosén,
15.   Pavel Tarasov,
16.   Hendrik Vogel,
17.   Bernd Wagner

ABSTRACT
"The reliability of Arctic climate predictions is currently hampered by insufficient knowledge of natural climate variability in the past. A sediment core from Lake El’gygytgyn in northeastern (NE) Russia provides a continuous, high-resolution record from the Arctic, spanning the past 2.8 million years. This core reveals numerous “super interglacials” during the Quaternary; for marine benthic isotope stages (MIS) 11c and 31, maximum summer temperatures and annual precipitation values are ~4° to 5°C and ~300 millimeters higher than those of MIS 1 and 5e. Climate simulations show that these extreme warm conditions are difficult to explain with greenhouse gas and astronomical forcing alone, implying the importance of amplifying feedbacks and far field influences. The timing of Arctic warming relative to West Antarctic Ice Sheet retreats implies strong interhemispheric climate connectivity."

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

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According to the following internet article, the RICE program may help clarify where abrupt SLR can occur in 50 yrs or 500 yrs:

"Christmas came early to a remote corner of Antarctica last year. After two summers of drilling, the 12-member crew of the Roosevelt Island Climate Evolution Project (RICE) finally made it through nearly 800 metres of solid ice, to bedrock, on December 20, 2012.
In doing so they had, figuratively speaking, travelled back in time more than 100,000 years, to the Earth’s last interglacial period, when the Earth’s ice caps receded and global sea levels rose.
The nine-nation team had spent three months in this remote location on the Ross Ice Shelf — a white expanse roughly the size of France — sleeping in tents, working laboriously in layers of extreme-cold-weather clothing, enduring the regular storms that make even an Antarctic summer a savage environment.
If they toasted their breakthrough, however, it was not without the knowledge that their findings could be cause for anything but celebration.
Because contained within the solid ice cores — which they had painstakingly extracted with the drill rig — lies information that could support a hypothesis that large parts of the frozen continent are more delicate, more dynamic and changing more rapidly than previously thought.
The ice cores are right now locked within two super-refrigerated containers onboard the last ship out of McMurdo Sound before the Antarctic winter closes in, and due to arrive in New Zealand in early March.
It is all precious cargo, but there is one sample that is of particular interest. When the very last ice core was drawn up from a depth of 763 metres, it showed imprints of the sediment on which it had been resting. The team sent the drill down one more time and managed to draw up a little of this sediment — which has the consistency of frozen mud.
The RICE team believes there is a strong probability it will turn out to be marine sediment, most likely from the interglacial period before the last ice age, 105,000 to 130,000 years ago, when temperatures were only a little higher than they are today.
If confirmed, it would mean Roosevelt Island was under water during that interglacial phase. This in turn would mean the Ross Ice Shelf was much smaller than it is today, or had in fact disappeared altogether. The huge West Antarctic ice sheet behind it would have been significantly smaller too.
“Of course,” says ice-core climatologist and RICE project leader Nancy Bertler, “that would mean we are far more susceptible to change than we might think.”
In other words, the pace and scale of Antarctic melting — and therefore the kind of rise in sea levels we all fear — could happen much faster than previously imagined.

COASTAL ICE CORE RESEARCH IS RELATIVELY NEW. Previously, scientists believed the great Antarctic interior, where the ice sheet can reach depths of 4 km, would yield the most useful results.
But in the coastal regions, where the sheet is thinner and the records correspondingly shorter, the cores have provided a complementary picture to those from the interior. “Being at the coast is right at the interface between the ocean and the atmosphere and the ice sheet. This is really where the change is most visible.”
The Roosevelt Island site, then, provides a measure of climatic conditions from the last interglacial period to the present. Within the past 30,000 years of that span, from the end of the last ice age to now, the Earth has experienced a temperature increase of about six degrees. That was enough to melt ice sheets in the northern hemisphere and cause the Ross Ice Shelf to contract up to a thousand kilometres southward to its present perimeter.
As a consequence of this melting, sea levels rose and the big West and East Antarctic ice sheets thinned a little. Throughout this period, Roosevelt Island has been quietly recording a year-by-year snapshot of global warming.
The data extracted from the ice cores will allow the historical CO2 record to be reconstructed, atmospheric and sea-surface temperatures to be calculated, and the sea-ice extent to be estimated. “It allows us now to establish how quickly the Ross Ice Shelf can react to warming and how quickly it retreats because of that warming, both in the ocean and in the atmosphere,” says Bertler.
Roosevelt Island sits at one edge of the Ross Ice Shelf. At the other edge lies Ross Island, home to New Zealand’s Scott Base, which serves as the transport and provisioning hub for the RICE expedition. The $NZ7 million project is a massive logistical operation, involving the transport of some 200 tonnes of cargo 600 kilometres across the ice to the drill site.
At the heart of the site lies a 30-metre-long trench, 10 metres at its deepest point, dug out with chainsaws and shovels. A small complex of caves off to the side serves as storage for the ice cores once they have been hauled up.
Inside the trench and beneath a sheltering tent sits the rig itself, purpose-built for the conditions and with a new hydraulic system designed to break off each ice core sample as cleanly and gently as possible.
According to Bertler, there was some initial skepticism from veteran ice-core drillers about the hydraulic innovation, but it proved ideal for coping with the peculiarities of Antarctic ice.
That is, when under intense pressure beyond a depth of a few hundred metres, Antarctic ice becomes what is known as “brittle ice”. The tiny bubbles of prehistoric atmosphere within — vital for analysing the climatic conditions when they were first formed — react dramatically to even the slightest warming.
Place a sample in your hand, for instance, and it may explode with a radius of several metres. “Imagine when you send an electro-mechanical drill down, then you pull with almost a tonnne of weight on it,” explains Bertler. “Very often this brittle ice comes up in bags rather than cores.”
The ice at Roosevelt Island may be tricky to extract, but it offers a clear window into our planet’s weather history. The island — to the naked eye nothing more than a large rise in the white expanse — is one of the “pinning points” of the Ross Ice Shelf (the other being Ross Island). That is, it anchors the mass of sea ice within the Ross Embayment.
The regular storm tracks that circle Antarctica inevitably penetrate the Ross Sea and the ice shelf, which means Roosevelt Island is a veritable databank of snow precipitation. “And this is our business,” Bertler says. “We read snow. We turn this into climate records.”
THE RICE PROJECT WAS IN PART DESIGNED TO SOLVE A MYSTERY left by a previous New Zealand-led drilling project, known as Andrill. Andrill involved the exploration of Antarctic marine sediment from the mid-Pliocene period, about three to five million years ago, and it showed that at some point during that epoch the entire Ross Ice Shelf had disintegrated.
The mid-Pliocene is important because we have to go that far back to find atmospheric CO2 concentrations equivalent to those of today. At about 400 parts per million (ppm) they were slightly higher than our 397 ppm, and the temperatures were slightly warmer than we’re experiencing now. But human activity is increasing current CO2 levels by about two ppm per year, with temperatures following close behind — suggesting we are rapidly approaching a known tipping point.
As Bertler points out, the collapse of the Ross Ice Shelf would have been dramatic in itself, but because the shelf is made of sea ice it already displaces its own mass and does not affect sea levels. However, what Andrill also showed was that the whole West Antarctic ice sheet had collapsed.
While the West Antarctic ice sheet is smaller than the East Antarctic sheet, it still contains more than two million cubic kilometres of frozen fresh water. The ice mass is so heavy it depresses the underlying rock by up to a kilometre.
When it previously collapsed — in conditions which also caused the northern hemisphere ice sheets to melt, and the margins of the East Antarctic sheet to collapse — global sea levels rose about 20 metres. “That’s very significant, obviously,” says Bertler with admirable understatement.
What Andrill couldn’t show, due to the much lower resolution of sedimentary records, but what RICE is expected to reveal, is how quickly the sea ice retreated or the ice sheet collapsed. It might have taken anywhere between 50 and 500 years — the blink of an eye in geological terms.
Such a broad margin of error poses huge problems for policy makers, who need more accurate predictions when planning for the potentially alarming consequences of multi-metre rises in sea level. “This is where Roosevelt Island comes in,” says Bertler.
As she puts it, ice contains a “memory” within its compressed crystals that we can now recover and interpret, to determine not just what happened in the past, but what will happen in the future.
There are many variables influencing these major climate shifts, from the Earth’s elliptical orbit around the sun to the feedback loops created by ocean warming or ice-sheet accumulation.
And we are only now beginning to understand the true relationship between atmospheric CO2 levels and rising temperatures. As the New York Times recently reported, more sophisticated ice core analysis suggests there is a much closer link than previously argued by some climate change sceptics.
By reconstructing a past that is comparable to our present, Bertler explains, we can “train” our computer climate models to accurately “predict the past”, which in turn will give us more confidence in their ability to forecast future climate conditions.
This is the huge advantage ice cores have over Andrill’s sedimentary record. “We can read the cores like a seasonal diary. So we can tell you exactly what a summer 29,000 years ago looked like in this area.”
The cores’ records aren’t quite as obvious to the eye as the rings of a tree, but are as clear as day to scientists with the right measuring equipment. Bertler: “You see wonderful oscillations, you see warmer and colder temperatures from summers and winters, you see marine air masses dominating during the summer, the sea ice extent that has its maximum sometime in August then reduces to its minimum in January or February. We can see those things for each year, every year, in the ice-core record.”
The RICE research, like the other ice-core projects around Antarctica, exists in the context of a rapidly expanding field of knowledge about the West Antarctic ice sheet’s recent, disconcerting behaviour. Satellite imagery now shows the ice sheet has a negative “mass balance”; that is, the rate of melt is outstripping the rate of snow precipitation, and therefore West Antarctica is losing mass very quickly.
At the inaccessible and inhospitable Amundsen Sea Embayment, the massive Pine Island Glacier, which drains about 10 per cent of West Antarctica’s ice sheet directly into the sea, has been moving faster and thinning out over the past decade, as has the nearby Thwaites Glacier.
Because much of the ice sheet is grounded on rock thousands of metres below sea level, the danger is that sea water will eventually pour in over the lip of the continent and effectively float the ice above it.
“At the moment,” says Bertler, the loss of mass balance “is all due to melt ice being transported into the ocean. But if the water reaches underneath, as soon as you lift that mass, you increase the sea level by the equivalent of that mass.” Such a lifting of the entire West Antarctic sheet “could cause a five- to seven-metre rise in sea levels, but just the Pine Island area [could] raise levels by one to two metres”.
At the same time the Southern Ocean is absorbing more CO2, and warming faster and to a greater depth than previously imagined. Instead of only the first hundred or so metres of water being affected, temperatures have risen at depths of up to 3,000 metres. The increase might be very small (0.2 degrees Celsius in a decade), but the amount of energy required to warm such a vast body of water is huge. The fact that the ocean is absorbing so much of the warming also explains why atmospheric temperatures haven’t risen as steeply as might have been expected.
“In the short term that is really great,” Bertler suggests, “because it buys us a little time. But in the long term it is really bad. The ocean has a very long memory, and the warmth we are currently putting into the ocean will be with us for a very long time. So we are committed to that for many generations to come.”
Pine Island is one indicator of the possible consequences of this warming. Back at Roosevelt Island, the same rules apply for the Ross Ice Shelf. “If you put warm water under an ice shelf, ice shelves don’t like that. They warm rather quickly and melt quickly from underneath. You can’t see that until it collapses.”
In May this year representatives from all the RICE member nations will arrive at the New Zealand Ice Core Research Facility in Wellington to begin analysing the ice cores from Roosevelt Island. Working around the clock and using an ultra-pure nickel disk to melt each sample, they will begin with the most recent cores and work back (or down) towards the past. Hundreds of thousands of measurements will be taken to reveal the history of this surprisingly sensitive and dynamic part of the planet.
But that crucial sample of frozen mud from the surface of the sub-glacial rock will be analysed much more quickly, hopefully by mid-March. If, as the researchers have hypothesised, it turns out to be marine sediment, it will be yet more evidence of the potentially alarming implications of global warming."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Laurent

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What do you think the inertia is ?
Is it 50 years as some people say or 150 years as the ice cores where suggesting (I don't know anymore because of these new studies changing the relative date between temperatures and CO2).
Or is it something like 1000 years like this graph suggest ?

AbruptSLR

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Laurent,

The inertial value is one question, the rate radiative forcing is another, climate sensitivity still another, and the starting time for the WAIS collapse is still another.  But roughly speaking, I agree with the people who take the ocean thermal inertia to be about 50-yrs; and I believe that if we follow RCP 8.5 95% CL, the WAIS will have collapsed by 2100.
« Last Edit: March 26, 2013, 02:49:43 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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For those who don't know what I am talking about in my prior post:

As the earth must increase it's longwave, LW, emissions to space in order to re-establish its energy balance due to changes in radiative forcing, deltaF (in W m-2), due to GHG concentrations as a first approximation it can be assumed that this increased LW emission is proportional to the global surface temperature change deltaT, which gives the equation:
deltaF = landa times deltaT +deltaQ
Where:        landa = the climate feedback parameter (in W m-2 C-1), and
                  deltaQ  = the thermal inertia = the imbalance between the climate forcing and the response (in W m-2), which is dominated by ocean influence and thus is generally referred to as the ocean heat uptake (and is currently estimated to be 0.85 +/- 0.15 W m-2 and is currently dominated by the ocean heat uptake, but which is decreasing slightly with time at the as the Arctic Sea Ice is disappearing rapidly).  This term typically causes a 1 to 40-yr lag between time for a given change in a radiative forcing with fast feedback sensitivity and the final equilibrium change in temperature (the lag time for slow feedback sensitivity maybe say 40 to hundreds of years).
« Last Edit: March 26, 2013, 02:51:08 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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I have zoomed in on the relevant area near the Eemain peak (MIS 5e) from Figure 2 of Grant et al 2012 (doi:10.1038/nature11593) in the attached image of relative sea level from the Red Sea in that era (125 to 130 thousand years ago [kya]).  This figure clear indicates that for a 95% Confidence Level (CL) that during MIS 5e sea level could have easily increased over 6m in a century, with a most probable RSLR of about 1.4m/century (for conditions which historically most closely match those of today).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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I thought that I would post the abstract from:
Ice Volume and Sea Level During the Last Interglacial
by A. Dutton and K. Lambeck; in Science

"During the last interglacial period, ~125,000 years ago, sea level was at least several
meters higher than at present, with substantial variability observed for peak sea level at
geographically diverse sites. Speculation that the West Antarctic ice sheet collapsed during
the last interglacial period has drawn particular interest to understanding climate and ice-sheet
dynamics during this time interval. We provide an internally consistent database of coral
U-Th ages to assess last interglacial sea-level observations in the context of isostatic modeling
and stratigraphic evidence. These data indicate that global (eustatic) sea level peaked 5.5
to 9 meters above present sea level, requiring smaller ice sheets in both Greenland and
Antarctica relative to today and indicating strong sea-level sensitivity to small changes in
radiative forcing
."

I underlined the last sentence to emphasize the "... strong sea-level sensitivity to small changes in radiative forcing."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

icebgone

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Gray Wolf, The crumple zones in the Ross Ice Shelf might also be stretch marks that reflect differences in speeds between parts of the shelf.  As Lunar cycles come and go the floating section of the shelf gets tugged by tidal currents while the anchored sections remain locked in place.  Eventually melting from underneath will thin the floating portion of the shelf to the extent that it will become a very large free floating berg.  Probably in the 2200-2300 time frame?

AbruptSLR

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Icebgone,

While your timeframe for the RIS to collapse is the 2200 to 2300 is what many models project; but from a risk point of view, I do not trust the model projections.  In my thread entitled "Hazard Analysis for the FRIS/RIS in the 2012 to 2060 Timeframe" I make the case that RIS might collapse between 2060 and 2070 timeframe.

ASLR
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AbruptSLR

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While I have provided many comparisons to the Eemian (MIS 5e) era sea level (largely due to the high thermal inertia of the ocean), the attached figure indicates that when the ocean comes into equilibrium with the possible 2100 mean global temperature, then the eustatic sea level may eventually be over 50m higher than today (based on historical comparisons to periods with comparable mean global temperatures).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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If the Antarctic Pennisula can serve as a harbinger of what may happen in the WAIS in a couple of decades time, then the following information from Nerilie Abram of Australian National University regarding ice cores from the James Ross Island (JRI) in the Antarctic Pennisula is not good news.  The following report comes from Joel Pedro, who is an Honorary Research Fellow, Antarctic Climate & Ecosystems CRC at University of Tasmania:

"Their results demonstrate that surface summer melting at James Ross Island is now occurring “at a level that is unprecedented in the past 1,000 years”; indeed, there has been “a nearly-tenfold increase in melt intensity since the late 1400s”.

A concerning aspect of their finding is that the melt rate appears to respond non-linearly to temperature increase. Abram and colleagues explain: “as average summer temperature increases and positive temperature days [days above 0°C] become warmer and more frequent, the amount of melt produced exhibits an exponential increase”. Their conclusion is that ice on the Antarctic Peninsula appears to be crossing a threshold where it is particularly susceptible to rapid increases in melt caused by warming summer temperatures. This could translate to a “poleward extension of areas where glaciers and ice shelves are undergoing decay by atmospheric-driven melting”.

The attached images shows an ice core record of temperature and surface melt over the past 1,000 years at James Ross Island (JRI), Antarctic Peninsula. In the upper panel, the thin green line represents average temperature at the site expressed relative to the average between 1981 and 2001. In the lower panel, the thin red represents snow melt at the surface, expressed in per cent of annual snowfall. The thick lines are smoothed versions of the annual data. Dashed lines show the 1981—2001 averages. Figure adapted from Abram et al.
« Last Edit: May 03, 2013, 11:48:06 PM by AbruptSLR »
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icebgone

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AbruptSLR,  What measurements would be needed to define an abrupt (2060) RIS melt out in progress.  Do we drill ice cores in 5 year increments?  Is there a quantification of predecessor events and their timing?  How do we separate out natural fluctuations from accelerated feed backs?  Is SLR the primary trigger for mechanical leveraging of ice fractures?  I suppose a 3D chart which integrates the primary drivers similar to the one demonstrating the retreat of Arctic Ice Volume might be a good place to start?  I agree that early loss of RIS and other buttresses of ice flow would have devastating impacts on global SLR.  It is difficult to imagine the loss of a mass of ice as thick as RIS in such a short period of time.  How many extra joules of energy would the ocean have to deliver over the next 50 years to make it possible?  I say extra because the floating ice beyond the RIS would have to be melted first each year.

AbruptSLR

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icebgone,

In my opinion the most likely mechanism for the RIS to collapse circa 2060 is the meltpond mechanism as is believed to happen to the Larsen B Ice Shelf; which only requires a limited amount of the RIS to melt inplace, for the remainder of the ice shelf to float away into the Southern Ocean (where it could melt gradually over a couple of decades.  It has been estimated that if the RIS were to collapse the loss of buttressing action on the adjoining ice streams/ice sheets would cause the SLR contributions for these ice streams/ice sheets to increase by a factor of over five times. Currently, the front edge of the center part of the RIS is calving at a rate on the order of 1.8 km per year, so I speculated that this retreat could allow a warm current of CDW to flow along a trough in the seafloor leading across the continental shelf to the base of the Byrd Glacier, and from there (within a few year) arround the perimeter of the Ross Sea Embayment; where it would thin the thickness of the ice shelf near the grounding line.  Furthermore, there is evidence that the surface temperature in the RIS area could have warmed sufficiently that circa 2060 there could be substantial surface ice melting and associated ponding of this meltwater.  Next according to the meltpond theory, thermal stresses of the ice shelf could cause the formation of crevasses around the thinned (due to the circulated warm current of CDW) perimeter of RIS (near the grounding line); which the meltponds could then flow into the crevasses causing them to split to the bottom of the shelf all around the perimeter; thus allowing the lion share of the RIS to break-up and float out to the Southern Ocean.

Therefore, evidence that this could happen include: (a) continued monitoring of the rate of surface temperature increase [particularly in non-El Nino hiatus periods], which could allow the meltponds to form; (b) monitoring of the calving of the front edge; and (c) changes of the ocean currents beneath the RIS to induce sufficient ice thinning for the crevasses to form around the perimeter of the shelf.  Note that a similar mechanism could cause the FRIS to collapse around the same time.
 
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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icebgone,

If you would like a more detailed discussion of my thoughts on the things to monitor regarding the risks of the RIS (and the FRIS) collapsing circa 2060 then please review my posts in the "RIS/FRIS 2012-2060 Timeframe: thread on the second page of the Antarctic folder, here:

https://forum.arctic-sea-ice.net/index.php/topic,117.0.html

Also, from Bromirski et al 2010 and 2011 (see references both), I discuss some of the addtional risks that infragravity waves have on the RIS:

Bromirski, P.D., Miller, A.J., Flick, R.E, and Auad, G., (2011), "Dynamical Suppression of Sea Level Rise Along the Pacific Coast of North America: Indications for Imminent Acceleration" Journal of Geophysical Research, Vol. 116, C07005, doi: 10.1029/2010JC006759, July 2011.
Bromirski, P. D., O. V. Sergienko, and D. R. MacAyeal (2010), Transoceanic infragravity waves impacting Antarctic ice shelves, Geophys. Res. Lett., 37, L02502, doi:10.1029/2009GL041488.

Oceanic Infragravity Waves
Infragravity waves are surface gravity waves with frequencies lower than the wind waves – consisting of both wind sea and swell – so corresponding with the part of the wave spectrum lower than the frequencies directly generated by forcing through the wind.
Infragravity waves consist of long-period oceanic waves generated along continental coastlines by nonlinear wave interactions of storm-forced shoreward-propagating ocean swells. These differ from normal oceanic gravity waves, which are created by wind acting on the surface of the sea. Normal gravity waves typically have a frequency on the order of 50 millihertz (i.e., a period of 20 seconds). Interactions of these waves with coastlines filters out the frequencies with periods about 30 seconds, but nonlinear processes convert some of this energy to sub-harmonics with periods ranging from 50 seconds (20 mHz) to 350 seconds (3 mHz). Infragravity waves are these sub-harmonics of the impinging gravity waves.
Technically, infragravity waves are simply a subcategory of gravity waves and refer to all gravity waves with periods greater than 30 s. Although they include phenomena such as tides and oceanic Rossby waves, in the common literature their use is limited to gravity waves that are generated by the topography of the bottom.
According to Bromirski, Sergienko and MacAyeal, 2010: "Long-period oceanic infragravity (IG) waves (ca. [250, 50] s period) are generated along continental coastlines by nonlinear wave interactions of storm-forced shoreward propagating swell. Seismic observations on the Ross Ice Shelf show that free IG waves generated along the Pacific coast of North America propagate transoceanically to Antarctica, where they induce a much higher amplitude shelf response than ocean swell (ca. [30, 12] s period). Additionally, unlike ocean swell, IG waves are not significantly damped by sea ice, and thus impact the ice shelf throughout the year. The response of the Ross Ice Shelf to IG-wave induced flexural stresses is more than 60 dB greater than concurrent ground motions measured at nearby Scott Base. This strong coupling suggests that IG-wave forcing may produce ice-shelf fractures that enable abrupt disintegration of ice shelves that are also affected by strong surface melting. Bolstering this hypothesis, each of the 2008 breakup events of the Wilkins Ice Shelf coincides with wave-model-estimated arrival of IG-wave energy from the Patagonian coast."

According to Bromirski, storm-driven ocean swells travel across the Pacific Ocean and break along the coastlines of North and South America, where they are transformed into very long-period ocean waves called "infragravity waves" that travel long distances to Antarctica.

In Bromirski, Sergienko and MacAyeal, 2010, it is proposed that the southbound travelling infragravity waves "may be a key mechanical agent that contributes to the production and/or expansion of the pre-existing crevasse fields on ice shelves," and that the infragravity waves also may provide the trigger necessary to initiate the calving collapse process.
The researchers used seismic data collected on the Ross Ice Shelf to identify signals generated by infragravity waves that originated along the Northern California and British Columbia coasts, and modeled how much stress an ice shelf suffers in response to infragravity wave impacts. The study found that each of the Wilkins Ice Shelf breakup events in 2008 coincided with the estimated arrival of infragravity waves. The authors note that such waves could affect ice shelf stability by opening crevasses, reducing ice integrity through fracturing and initiating a collapse. "Infragravity waves may produce ice-shelf fractures that enable abrupt disintegration of ice shelves that are also affected by strong surface melting," the authors note in the paper.

Whether increased infragravity wave frequency and energy induced by heightened storm intensity associated with climate change ultimately contribute to or trigger ice shelf collapse is an open question at this point, needing more study, including on the observed trend of increase cyclone frequency and intensity in the Amundsen and Ross Seas, due to climate change.

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sidd

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Long period waves might trigger, but the shelf wouldn't collapse unless preweakened. Eventually as it rots out, a few thousand penguins might do it ...

I am beginning to think of instabilities of ice sheets and ice shelves in terms of self organized criticality as one forces them with stressors. 

sidd

AbruptSLR

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Sidd,

I very much look forward to reading your input regarding your statement that:

"I am beginning to think of instabilities of ice sheets and ice shelves in terms of self organized criticality as one forces them with stressors."
 
Certainly there are a large number of stressors on both ice sheets and ice shelves (such as the RIS), and while have discusses many of them in my various (scattered) posts, and while I have discussed many different feedback mechanisms and possible abupt failure scenarios in my many scattered posts; nevertheless, I thought that I would aggregate some of my previously thought regarding weakening the RIS up to about 2040 (on the chance that if might assist some of your thinking on self-organized criticality), as presented in this post and in my next two posts in this thread:

My second attached image shows that in my opinion, by circa 2040, there is a good chance that not only will PIG and TG be lossing ice mass volume above floatation (VAF), but also the Siple Coast ice streams will be, because I believe the following scenario (started in this post and continued in the next two posts) is likely:

- The current rate of ice calving from the RIS front edge (see the first and third images) will either continue, or will accelerate (possibly due both to thinning of the thickness of the front edge ice due to sub-ice shelf basal melting from warm ocean water brought in by tides [see the fourth image], and by increased storm wave, and infragravity wave, -action).
« Last Edit: May 26, 2013, 02:38:11 PM by AbruptSLR »
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AbruptSLR

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- by 2040 the extent of calving should have caused the front edge of the RIS to have retreated sufficiently (including influence from the periodic encounter with crevasses and the periodic influence of tsunami's [see the first attached image showing a sequence of how the Honshu Earthquake Generated Tsunami led to significant calving from the Sulzberger Ice Shelf near the Ross Ice Shelf]), sufficiently that the tidally induced flexure of the RIS (see the second image) should cause the Siple Coast ice stream flow rate to increase due to the daily tidally induced up-lift of the grounding line due to tidal action.

- The third image shows that the front edge of the RIS is already less than 200 m thick, and continued basal melting from both long-term warming of the CDW and due to periodic increases in local upwelling from events such as strong El Nino events and both increased local cyclonic action and swells from increased distant cyclonic action; should contribute to continued high rates of calving of the RIS in the future.

- The fourth images shows how periodic interaction of the prevailing wind directions can influence the ocean temperature offshore of the RIS; which can periodically influence the temperature of the ocean water causing sub-iceshelf basal melting/thinning.
« Last Edit: May 26, 2013, 03:05:50 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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- The attached image shows historical storm tracks of strong cyclone/hurricanes, and note that the cyclones in the South Pacific approach the Southern Ocean before they decay;which means that these periodic strong storm should send large swells to the entire Pacific Antarctic Coast, including the front edge of the RIS (note that with global warming such large tropically cyclones are projected to increase significantly in frequency).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Sidd,

I provide the following abstracts from the Nineteenth Annual WAIS Workshop, 2012, that are relevant to my prior posts from the past couple of days in this thread:

1.  "Ice--‐2--‐O: Interactions between ice shelves, sea ice and ocean
Laurence Padman, Scott Springer

The mass budgets of ice shelves, marine-terminating glaciers and the adjacent grounded ice sheets can change rapidly as the adjacent ocean state varies. The three water components – glacial ice, sea ice, and liquid ocean – interact in complex ways to affect not just the ice sheet mass balance, but also the production of dense water masses and the flux of sea ice northwards over the Southern Ocean. We use a model of the Ross Sea, including its ice shelf, to motivate a discussion of some climatically important interactions between these water components. We also consider the implications for mass loss mechanisms for large "cold water" ice shelves such as the Ross and Filchner-Ronne. We focus on the hypothesis that their future mass loss will be via frontal retreat caused by accelerated melting in, and associated calving of, the Ice Shelf Frontal Zone (ISFZ) rather than by thinning that is either concentrated near the grounding lines or broadly distributed under the ice shelf. The modeling points to the need to accurately represent the seasonality of sea ice production and advection when projecting ice sheet response to changing ocean state. Improved calving laws are also required to incorporate this potential mass loss process into projections of ice sheet mass change."

2. "Ice--‐shelf tidal flexure and subglacial pressure variations
Ryan T. Walker, Byron R. Parizek, Richard B. Alley, Sridhar Anandakrishnan, Kiya L.
Wilson, Knut Christianson
We develop a model of an ice shelf-ice stream system as a viscoelastic beam partially supported by an elastic foundation. When bedrock near the grounding line acts as a fulcrum, leverage from the ice shelf dropping at low tide can cause significant (~1 cm) uplift in the first few kilometers of grounded ice. This uplift and the corresponding depression at high tide lead to basal pressure variations of sufficient magnitude to influence subglacial hydrology. Tidal flexure may thus affect basal lubrication, sediment flow, and till strength, all of which are significant factors in ice-stream dynamics and grounding-line stability. Under certain circumstances, our results suggest the possibility of seawater being drawn into the subglacial water system. The presence of seawater beneath grounded ice would significantly change the radar reflectivity of the grounding zone and complicate the interpretation of grounded versus floating ice based on ice-penetrating radar observations."

3. "The influence of stick--‐slip motion on the present deceleration of the Whillans Ice Stream
Paul Winberry, Sridhar Anandakrishnan, Richard B. Alley, and Doug Wiens

The Whillans Ice Stream (WIS) is major route for ice transiting from the interior of the West Antarctic Ice Sheet (WAIS) into the Ross Sea. It has been observed that the WIS has been slowing, contributing to a positive mass balance in the Ross Sea sector of the WAIS. Superimposed on this decadal-scale deceleration is a tidally modulated stick-slip characterized by extended periods (6-24 hours) of minimal motion followed by brief periods (30 minutes) of rapid motion when the ice stream lurches forward by ~ 0.5 m. Comparison of new results collected during 2010-2011 with earlier measurements show that the deceleration has continued and the timing of slip events has become less regular, often slipping only once during a day instead of previously observations that documented two slip events daily. The reduced regularity of slip events has resulted in a less efficient release of stored elastic strain during slip events.  These observations highlight non-linear feedbacks at the daily-scale that influence the decadal time-scale behavior of the ice stream."

« Last Edit: May 26, 2013, 07:40:09 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Sidd,

I also provide the following from the Eighteenth Annual WAIS Workshop, 2011:

Sea ice and West Antarctic ice-shelf stability
Kelly M. Brunt, Emile A. Okal, and Douglas R. MacAyeal

Sea ice plays a critical role in ice-shelf stability. It does so in two ways: 1) sea ice dampens sea swell incident on ice-shelf calving fronts and 2) fast ice can act to buttress an ice shelf, similar to the way an ice shelf buttresses an ice sheet. We examine the sea-ice conditions during two March 2011 calving events, from two different West Antarctic ice shelves. In particular, we examine a calving event on the McMurdo Ice Shelf and a tsunami-triggered calving event on Sulzberger Ice Shelf. We use satellite imagery and aerial photography to assess sea-ice conditions, and long-term ice-shelf stability, prior to these calving events.

• Sulzberger Ice Shelf calving event
– Distant teleconnection (13,000 km)
– Links unrelated phenomena
– Tsunami‐induced swell occurs when Sulzberger Bay is devoid of sea ice
• McMurdo Ice Shelf calving event
– Loss of 40,000 km2 of ‘persistent’ sea ice
– Mild storm event triggers calving
• Sea ice plays a critical role in ice‐shelf stability Controls on calving/collapse include
– Thermodynamic (e.g., Larsen B)
– Mechanical (e.g., Sulzberger, McMurdo, Wilkins)
– Sea ice
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

sidd

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I haven't got my thoughts clear on a treatment outline. The classic example of a sandpile constantly added to from above undergoing avalanches at all scales governed by power law distribution was in my mind. One thing I want to look at is the distribution of breakup events as a function of volume of ice loss in each event, and see if a scaling relation like a power law can be found.  Such a treatment might be applicable to sea ice in the Arctic, perhaps even GIS, but I am currently thinking of Antarctica. A great difficulty for land based ice in Antarctica is the unconditional Weertman instability of ice sheet on retrograde bed, even without CDW forcing. This might manifest as increasing ice loss in larger scale events than would be predicted by power law distribution. So ice shelf breakup might be a better place to begin.

As you can tell, I haven't started calculating yet, just trying to think this through first, and explore the data in the literature. For as I have often discovered before, several weeks of calculation or coding save me an afternoon in a library ...
   
sidd

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Sidd,

I agree that starting with an ice shelf should be more productive that starting with an ice sheet. 

Here are some more abstracts, that might be relevant:

From the Eighteenth Annual WAIS Workshop:

"Emergence of tidewater and ice shelf calving dynamics using a granular model of iceJeremy N. Bassis
Department of Atmospheric, Oceanic and Space Sciences, University of Michigan
Ice sheets and glaciers have traditionally been modeled as thin films of non-Newtonian fluids.  This approximation is, however, incompatible with the extensive fracturing of ice that precedes and is occasionally part of the iceberg calving process. In this study, the explosive disintegration of ice shelves and rapid retreat and even advance of tidewater glaciers is explained by instead assuming that glacier ice is heavily fractured to the extent that it behaves in a manner that is more akin to a granular material than a continuous fluid. The conceptual granular ice model thus approximates the ice as a large number of discrete spheres or blocks of ice that interact through friction, damped elastic collisions and elastic bonds. The spectrum of intact to completely disarticulated ice is accommodated by allow bonds connecting adjacent blocks of ice to break.  This model is shown to reproduce many of the observed features of calving including (i) the detachment of tabular bergs from ice tongues, (i) explosive disintegration of ice shelves and; (iii) smaller more frequent ice thickness sized bergs that detach from tidewater glaciers. The distinction between modes of calving is controlled by the fraction of bonds broken, ice thickness and near terminus water depth. However, it is shown that if the ice is already heavily fractured, the factor limiting retreat is the transport and export of ice away from the terminus rather than fracturing of the ice. It is possible that analogous continuum granular models can also formulated based on plasticity theory. This would return ice dynamics full circle to a version of the discarded plastic rheology glaciologists once favored."

From the Nineteenth Annual WAIS Workshop:

"Propagation of an active rift in the Ross Ice Shelf, Antarctica
Christine LeDoux
Understanding propagation behavior of large rifts in ice shelves is important for understanding shelf adjustments to change and for parameterizing calving in models. We use satellite images and a comparison of two epochs of the MOA (MODIS Mosaic of Antarctica) to study the propagation of an active rift within a rift system near the western front of the Ross Ice Shelf.  Between 1992 and 2012, the most upstream rift within the rift system propagated over 90 km.  We observe large jumps and two types of episodic propagation. We use a numerical model to study recent propagation behavior of test fractures within a stress field. Our observations and model simulations support findings on the Ross and other large ice shelves regarding the importance of lateral propagation and the roles of transverse compressive stress, fracture length, and material inhomogeneity in controlling propagation behavior."


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

icebgone

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I am glad they are returning to a plastic rheology model for understanding ice dynamics.  IMHO it is necessary for a complete understanding of ice behavior.  It helps to describe the relationship between ice and underlying geology across time and sites.  In response to the missing years of ice coring samples, Did they do an inter comparison of the cores from various locations or are we dealing with just one or two cores?  I ask, because pits and holes formed from glacier sliding or ice sheet settling can result in bottom seizure and ice shearing.  If you happen to drill downstream of a pit a discontinuity may result.  Inter comparisons removes that possibility.   Lastly, A sampling of the ice milk at the ice/bedding plane interface  provides evidence for ice sheet chemistry and movement through the bedding plane over time.  Difficult to get though!

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Icebgone,

As I am a bit out of my depth, as to how to interpret these findings, I will simply post a few more related abstracts from the Nineteenth Annual WAIS Workshop (2012):

1. "Near--‐continuous monitoring of Antarctic ice shelf and sub--‐ice shelf ocean temperatures
Holland, David; Tyler, Scott; Zagorodnov, Victor; Stern, Alon; Taylor, Kendrick; Sladek, Chris; and Kob, Scott

During the Austral spring of 2011, two instrumented boreholes were completed through the McMurdo Ice Shelf (MIS) at Windless Bight to test rapid drilling and continuous monitoring methods. The boreholes were drilled using an approach combining ice coring for the upper portion of the borehole, with a new hot-point method for the final penetration through the
Ice-ocean interface. Each borehole was drilled through 190 m of ice to the ocean using two person drilling team. The core drilling provided a 130mm diameter open borehole that remained dry through the drilling period. A hot point drill was used to penetrate into the ocean, and provided a 40 mm diameter borehole. The boreholes were instrumented with distributed temperature sensing (DTS) fiber-optic cables temperature measurements within the ~190m thick ice shelf and into the ocean below. The boreholes were also instrumented with traditional thermistors both in the ice shelf and in the ocean column and pressure transducers all attached to the armored DTS cables. Borehole BH1 is instrumented with fiber optic temperature sensing cable through the ice shelf and extending 30m into the ocean below. BH2, located 40 north of BH1, was used to test measurements to depths of 800m and also to demonstrate the potential for multiple independent installations through the same borehole. BH2 is completed with one DTS cable extending 600m below the ice/ocean interface, a logging pressure transducer and thermister located 450m below the ice/ocean interface and four additional logging thermistors.  Temperature measurements are made every 1 meter along each optical fiber. The measurements are repeated hourly through the summer, and 4 times per day in winter months to conserve power. Data are transmitted off site via satellite link. After 3 months of operation (February 2012), there has been warming trend (~0.5oC) in the upper ocean column that began in late December, consistent with previous measurements in the vicinity."



2. "Ice stream stick--‐slip, sticky spots and rate--‐and--‐state friction
J. N. Bassis
Department of Atmospheric, Oceanic and Space Sciences, University of Michigan
The Whillans ice plain is highly unusual in that it is nearly stagnant during most of the day, but lurches forward twice daily by nearly half a meter during short-lived stick-slip events. These highly repeatable sliding events are choreographed to the rhythmic waxing and waning of the ocean tides. This behavior presents an interesting, but significant challenge to ice sheet models for two reasons. First, the stick-slip of the WIS requires elastic deformation of the ice with viscous flow of the ice only playing a secondary role. Second, the stick-slip behavior of the WIS is inconsistent with the array of sliding laws conventionally used in ice sheet models; stick-slip requires resistance from friction that decreases with increasing velocity.  Most sliding laws, in contrast, are velocity strengthening. These inconsistencies hint that simulations of ice sheet evolution may require models that not only include viscoelasticity, but are also capable of resolving individual stick-slip events. In this study, I use an elastic slider block model to show that rate-and-state friction laws, analogous to those used in earthquake studies, are consistent with stick-slip and tidally modulated ice stream flow. In this model stick-slip corresponds to slight velocity weakening, roughly consistent with rock-on-rock contact as would be the case if basal debris entrained within the ice is rubbing again exposed bedrock. Tidal modulation, in contrast, is consistent with slight velocity strengthening consistent with laboratory experiments in which sliding occurs through till deformation. Both velocity strengthening and velocity weakening sliding laws can be tuned to mimic more conventional sliding laws (and vice versa), but the distinction between velocity weakening and strengthening is crucial when examining the response of individual ice streams to perturbations. While these results remain speculative, it suggests that basal friction does not remain constant in time and understanding how friction evolves over time is likely to be both critical and difficult to predict."

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

AbruptSLR

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Icebgone,

In your post you said:
"In response to the missing years of ice coring samples, Did they do an inter comparison of the cores from various locations or are we dealing with just one or two cores?  I ask, because pits and holes formed from glacier sliding or ice sheet settling can result in bottom seizure and ice shearing.  If you happen to drill downstream of a pit a discontinuity may result.  Inter comparisons removes that possibility.   Lastly, A sampling of the ice milk at the ice/bedding plane interface  provides evidence for ice sheet chemistry and movement through the bedding plane over time.  Difficult to get though!"

If this comment is directed towards the finding of the WAIS Divide borehole, then see my post today in the thread on that topic.  Also, those researchers said that they did not want to drill down into the bed material because they did not want to contaminate the subglacial meltwater; but they did take downhole heat measurements that allowed them to estimate that the basal melt rate is currently about 1.5 +/- 0.5 cm per year; which is very high and could easily account for "missing years of ice core samples" because at that rate at least 30,000 years worth of basal ice thickness would have melted (on average).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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I have not posted much about the semi-empirical evidence supporting the risks of abrupt SLR but the attached image from Stefan Rahmstorf's January 2013 article from the following website indicates the recent historical evidence of the risks of potentially high rates of SLR this century if the current trend for global mean warming continues:

http://www.realclimate.org/index.php/archives/2013/01/sea-level-rise-where-we-stand-at-the-start-of-2013/

The following is the caption for this non-linear figure:
"Rate of global sea-level rise based on the data of Church & White (2006), and global mean temperature data of GISS, both smoothed. The satellite-derived rate of sea-level rise of 3.2 ± 0.5 mm/yr is also shown. The strong similarity of these two curves is at the core of the semi-empirical models of sea-level rise. Graph adapted from Rahmstorf (2007)."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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The following reference – abstract-attached image, provides a paleo-example of the rapid retreat of a marine glacier in the Younger Dryas Fjord in Western Norway, circa 11,600 to 11,100 BP.  While this example is different that WAIS glacier, it is comparable and provides a valuable point of reference the potential rapid retreat of WAIS glaciers:

Collapse of marine-based outlet glaciers from the Scandinavian Ice Sheet
by: Jan Mangerud; Brent M. Goehring; Øystein S. Lohne; John Inge Svendsen; and Richard Gyllencreutz; Quaternary Science Reviews; Volume 67, 1 May 2013, Pages 8–16

Accessible from:

http://www.sciencedirect.com/science/article/pii/S0277379113000395

"Abstract
We present a reconstruction of the timing and retreat rates of more than 2000 m thick Younger Dryas (YD) fjord glaciers in western Norway using a detailed chronology of 10Be exposure ages from lateral moraines and 14C dated end moraines. A primary conclusion is that ice margins retreated up the 120–170 km long fjords at mean rates of 240–340 m yr−1 during the early Holocene. We further show that part of the south-western sector of the Scandinavian Ice Sheet collapsed in two distinct steps. The first step occurred between 19.5 and 18.5 ka BP as break-up of the Norwegian Channel Ice Stream, which drained the ice sheet during the Last Glacial Maximum (LGM). The second step was the rapid retreat up the fjords mentioned above, dated to 11.6–11.1 ka BP. During the intervening ∼7000 years no net retreat occurred despite oscillations of the ice margin. This stepwise ice margin retreat strongly contrasts with the more monotonic decay of the ice sheet as a whole, indicating that water depths set the pace for climate-triggered ice margin retreat in this part of the ice sheet. Calving and melting of marine margins has dominated mass-loss from modern ice sheets in recent decades; however, the mechanisms and long-term (100–1000 yr) rate of ice-front retreat is less certain and empirical examples such as those given here may help in developing better numerical models."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Focusing on paleo-temperature records is not sufficient to fully appreciate the risks of abrupt climate change; therefore, I provide the following reference related to prehistoric postglacial hydrological evidence from China (note such hydrological records can be cross correlated to the WAIS Divide borehole records via calibrated GCMs):

http://geology.gsapubs.org/content/early/2013/06/27/G34318.1.abstract

Concordant monsoon-driven postglacial hydrological changes in peat and stalagmite records and their impacts on prehistoric cultures in central China
by:Shucheng Xie et al., The Geological Society of America, First published on 28 June 2013, doi: 10.1130/G34318.1.

"Abstract
Asian monsoon records are widely documented, but specific proxies of monsoonal rainfall are limited. We present here two new independent proxy records from peatland and stalagmite archives that indicate a high degree of concordance between monsoon-driven hydrological changes occurring since the last deglaciation in a broad region of central China. The wet periods elevated the water table in the Dajiuhu peatland, as recorded by reduced mass accumulation rates of hopanoids, biomarkers for aerobic microbes, confirmed by molecular phylogenic analyses. The hopanoid-based reconstruction is supported by the first report of the environmental magnetism parameter ARM/SIRM (anhysteretic remanent magnetization / saturation isothermal remanent magnetization; ratio of fine magnetic particles to total ferrimagnetic particles) in a stalagmite from Heshang Cave in central China. Heavy rainfall resulted in the enhanced transport of coarse particles to the cave and thus low ARM/SIRM values in the stalagmite. The hydrological conditions inferred from the two records reveal three relatively long wet periods in central China: 13–11.5 k.y. ago, 9.5–7.0 k.y. ago, and 3.0–1.5 k.y. ago. Archaeological evidence for the hydrological impacts on regional populations comes from the observation that temporal shifts among six distinctive cultures of the Neolithic Period to the Iron Age in central China occurred during wet periods or flood episodes. Spatiotemporal distributions of >1600 prehistoric settlement sites correlate with the proxy-inferred fluctuating hydrological conditions, with enhanced flooding risk forcing major relocations of human settlements away from riparian zones."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson