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AbruptSLR

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Antarctic Interactions with, and Lessons from, Greenland
« on: August 17, 2013, 06:03:33 PM »
There are many Antarctic interactions with, and lessons to be learned from, Greenland that are not fully discussed in the Greenland folder, therefore, I am opening this new folder on this important topic.

In the "Surge" thread I raised the prospect that the large increase in Greenland's contribution to SLR in 2012 might have triggered a temporarily large outflow of subglacial meltwater from beneath the WAIS via a postulated increase in local sea level around West Antarctic (due to the fingerprint effect of ice mass loss from Greenland), temporarily lifting up the grounding lines of key West Antarctic glaciers, thereby temporarily breaking the seal and allowing the basal melt water to surge out (and to also temporarily increase ice flow velocity).  While the "Surge" thread does document small surges of the Thwaites, and Ferrigano, Ice Tongues; the subsequent published GRACE data indicated that at best there was only a very minor surge in WAIS ice mass loss in 2012. 

Nevertheless, the 2012 experience does not mean that the postulated interaction between Greenland and AIS mass loss many not be more significant in the next few decades, as not only is Greenland's surface ice mass loss projected to increase in the near future, but as indicated by the following article, which discusses dynamic ice mass loss for four key marine terminating Greenland glaciers; which are projected to accelerate sharply in the next few decades before slowing down through 2200.  Therefore, there is a reason likelihood that the projected temporary surge in Greenland ice mass loss in the coming decades could trigger an acceleration of ice mass loss from key glaciers in the AIS (particularly in the WAIS):


http://www.nature.com/nature/journal/v497/n7448/full/nature12068.html


Future sea-level rise from Greenland’s main outlet glaciers in a warming climate
by: Faezeh M. Nick, Andreas Vieli, Morten Langer Andersen, Ian Joughin, Antony Payne, Tamsin L. Edwards, Frank Pattyn & Roderik S. W. van de Wal; Nature; 497,235–238(09 May 2013)doi:10.1038/nature12068


"Over the past decade, ice loss from the Greenland Ice Sheet increased as a result of both increased surface melting and ice discharge to the ocean. The latter is controlled by the acceleration of ice flow and subsequent thinning of fast-flowing marine-terminating outlet glaciers. Quantifying the future dynamic contribution of such glaciers to sea-level rise (SLR) remains a major challenge because outlet glacier dynamics are poorly understood. Here we present a glacier flow model that includes a fully dynamic treatment of marine termini. We use this model to simulate behaviour of four major marine-terminating outlet glaciers, which collectively drain about 22 per cent of the Greenland Ice Sheet. Using atmospheric and oceanic forcing from a mid-range future warming scenario that predicts warming by 2.8 degrees Celsius by 2100, we project a contribution of 19 to 30 millimetres to SLR from these glaciers by 2200. This contribution is largely (80 per cent) dynamic in origin and is caused by several episodic retreats past overdeepenings in outlet glacier troughs. After initial increases, however, dynamic losses from these four outlets remain relatively constant and contribute to SLR individually at rates of about 0.01 to 0.06 millimetres per year. These rates correspond to ice fluxes that are less than twice those of the late 1990s, well below previous upper bounds. For a more extreme future warming scenario (warming by 4.5 degrees Celsius by 2100), the projected losses increase by more than 50 per cent, producing a cumulative SLR of 29 to 49 millimetres by 2200."



This hypothesis is further supported by the recent finding (see the following reference) that the lithosphere below Greenland is thinner than previously thought; and therefore, one can expect that ice mass loss from Greenland will be faster than previously estimated (including faster than projected by the first article cited in this post):

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo1898.html

Petrunin, A. G., Rogozhina, I., Vaughan, A. P. M., Kukkonen, I. T., Kaban, M. K., Koulakov, I. & Thomas, M., Heat flux variations beneath central Greenland’s ice due to anomalously thin lithosphere, Advance Online Publication, Nature Geoscience, 11. 08. 2013, http://dx.doi.org/10.1038/ngeo1898)



"Greenland ice is melting - even from below: Heat flow from the mantle contributes to the ice melt.  Modeled basal ice temperatures of the present-day Greenland Ice Shield across the Summit region, GRIP and GISP2 indicate borehole locations.
 
07.08.2013 | Potsdam: The Greenland ice sheet is melting from below, caused by a high heat flow from the mantle into the lithosphere. This influence is very variable spatially and has its origin in an exceptionally thin lithosphere. Consequently, there is an increased heat flow from the mantle and a complex interplay between this geothermal heating and the Greenland ice sheet. The international research initiative IceGeoHeat led by the GFZ German Research Centre for Geosciences establishes in the current online issue of Nature Geosciences (Vol 6, August 11, 2013) that this effect cannot be neglected when modeling the ice sheet as part of a climate study.

The continental ice sheets play a central role in climate. Interactions and feedback processes between ice and temperature rise are complex and still a current research topic. The Greenland ice sheet loses about 227 gigatonnes of ice per year and contributes about 0.7 millimeters to the currently observed mean sea level change of about 3 mm per year. Existing model calculations, however, were based on a consideration of the ice cap and considered the effect of the lithosphere, i.e. the earth's crust and upper mantle, too simplistic and primarily mechanical: the ice presses the crust down due to its weight. GFZ scientists Alexey Petrunin and Irina Rogozhina have now coupled an ice/climate model with a thermo-mechanical model for the Greenland lithosphere. "We have run the model over a simulated period of three million years, and taken into account measurements from ice cores and independent magnetic and seismic data", says Petrunin. "Our model calculations are in good agreement with the measurements. Both the thickness of the ice sheet as well as the temperature at its base are depicted very accurately. "

The model can even explain the difference in temperature measured at two adjacent drill holes: the thickness of the Greenland lithosphere and thus the geothermal heat flow varies greatly in narrow confines.
What does this mean for climate modeling? "The temperature at the base of the ice, and therefore the current dynamics of the Greenland ice sheet is the result of the interaction between the heat flow from the earth's interior and the temperature changes associated with glacial cycles," explains corresponding author Irina Rogozhina (GFZ) who initiated IceGeoHeat. "We found areas where the ice melts at the base next to other areas where the base is extremely cold."

The current climate is influenced by processes that go far back into the history of Earth: the Greenland lithosphere is 2.8 to 1.7 billion years old and is only about 70 to 80 kilometers thick under Central Greenland. It remains to be explored why it is so exceptionally thin. It turns out, however, that the coupling of models of ice dynamics with thermo-mechanical models of the solid earth allows a more accurate view of the processes that are melting the Greenland ice."




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AbruptSLR

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #1 on: August 17, 2013, 06:15:31 PM »
In the way of lessons learned from the GIS, the following website (and extracted quote) indicates that data from a significant number of new boreholes in Greenland indicates that current ice sheet models (both for the GIS and the AIS) currently do not capture critical processes including the probability that as "... ice sheets accelerate, the acceleration itself opens up space between the ice and bedrock and expands the drainage network."  This means that model projections of ice mass loss from both the GIS and the AIS (particulary for the WAIS) need to be revised upward, once the models are corrected to account for such previously unrecognized ice sheet behavior.


http://www.sciencedaily.com/releases/2013/08/130815161541.htm

"Once the data was analyzed, the research team discovered that it didn't match up with the working hypotheses for water flow beneath the ice sheet. This led the scientists to surmise that there are other critical processes at work that had been missing -- one possibility being that as the ice sheet accelerates, the acceleration itself opens up space between the ice and bedrock and expands the drainage network.
"This process is largely neglected in current interpretations," Meierbachtol said. "We need to pull ourselves away from the narrow vision and start to explore some of the other options for transient growth."
Future warming likely will be enhanced over the Arctic. This body of research will provide a more accurate assessment of the impacts of future warming on Greenland."


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

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #2 on: August 17, 2013, 08:16:01 PM »
Those who have read my posts in the "Hazard Analysis for PIG/Thwaites in the 2012 to 2040/2060 Timeframe" thread know that I have already applied lessons learned from the Jakobshavn Effect to postulate an even more dynamic ice mass loss effect that I named the "Thwaites Effect" (see the following link):

http://forum.arctic-sea-ice.net/index.php/topic,72.0.html

Now the recent analysis of the Jakobshavn glacier rapid retreat discussed in the following reference (and abstract copied below; while the following link leads to a free pdf of the paper), indicates that not only is geometry important in the Jakobshaven Effect but so is the modeled "softening" of the basal restraint conditions; which I note can occur due to soften of the basal ice due to increased basal friction as the ice accelerates and/or as the volume and/or temperature of the basal meltwater increases.  This new lesson learned from Greenland supports the case for a fat-tailed probability distribution for the collapse of the WAIS this century:

http://www.the-cryosphere-discuss.net/7/2153/2013/tcd-7-2153-2013.pdf

Changing basal conditions during the speed-up of Jakobshavn Isbræ, Greenland
By: M. Habermann, M. Truffer, and D. Maxwell; The Cryosphere Discuss., 7, 2153–2190, 2013; www.the-cryosphere-discuss.net/7/2153/2013/; doi:10.5194/tcd-7-2153-2013

"Abstract
Ice-sheet outlet glaciers can undergo dynamic changes such as the rapid speed-up of Jakobshavn Isbræ following the disintegration of its floating ice tongue. These changes are associated with stress changes on the boundary of the ice mass. We investigate the basal conditions throughout a well-observed period of rapid change and evaluate parameterizations currently used in ice-sheet models. A Tikhonov inverse method with a Shallow Shelf Approximation forward model is used for diagnostic inversions for the years 1985, 2000, 2005, 2006 and 2008. Our ice softness, model norm, and regularization parameter choices are justified using the data-model misfit metric and the L-curve method. The sensitivity of the inversion results to these parameter choices is explored.  We find a lowering of basal yield stress in the first 7 km of the 2008 grounding line and no significant changes higher upstream. The temporal evolution in the fast flow area is in broad agreement with a Mohr–Coulomb parameterization of basal shear stress, but with a till friction angle much lower than has been measured for till samples. The lowering of basal yield stress is significant within the uncertainties of the inversion, but it cannot be ruled out that there are other significant contributors to the acceleration of the glacier."
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AbruptSLR

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #3 on: August 17, 2013, 10:24:22 PM »
It is likely that most of the short-term (decadal) interactions between Antarctica and Greenland will be led by developments in Greenland first with the interaction in Antarctica occurring sometime later.  However, towards the end of this century the developments in Antarctica may become so significant that they induce a significant reponse in Greenland.  While I have posted the following reference about Antarctic Intermediate Water, AAIW (see the following Wiki link) in the "Trends of the Southern Ocean" thread; I did not note there that after 2100 the referenced non-linear response to an increase in the AAIW (due to significant ice mass loss from Antarctica); could lead to a negative feedback on global warming due to the associated slow-down of the meridional ocean heat transport (the THC), which may lead to some ice mass gain in Greenland (and the rest of the North Hemisphere).


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

Non-linear climate responses to changes in Antarctic Intermediate Water
by: Jennifer A. Graham;  David P. Stevens & Karen J. Heywood; Journal of Climate 2013; doi: http://dx.doi.org/10.1175/JCLI-D-12-00767.1 

Abstract
"The global impact of changes in Antarctic Intermediate Water (AAIW) properties is demonstrated using idealized perturbation experiments in a coupled climate model. Properties of AAIW were altered between 10 and 20°S in the Atlantic, Pacific and Indian oceans separately. Potential temperature was changed by ±1°C, along with density-compensating changes in salinity. For each of the experiments, sea surface temperature responds to changes in AAIW, when anomalies surface at higher latitudes (> 30°). Anomalous sea-to-air heat fluxes leave density anomalies in the ocean, resulting in non-linear responses to opposite sign perturbations. In the Southern Ocean, these affect the meridional density gradient, leading to changes in Antarctic Circumpolar Current transport. The response to cooler, fresher AAIW is both greater in magnitude and significant over a larger area than that for warmer, saltier AAIW. The North Atlantic is particularly sensitive to cool, fresh perturbations, with density anomalies causing reductions in the meridional overturning circulation of up to 1 Sv. Resultant changes in meridional ocean heat transport, along with surfacing anomalies, cause basin-wide changes in the surface ocean and overlying atmosphere on multi-decadal time-scales."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #4 on: August 21, 2013, 05:54:54 PM »
The following link leads to a free pdf (see also the attached image of the simplified model used in the study) of a good paper about the millennial scale interactions between the NH (including Greenland) and the SH (including Antarctica) via changes in wind induced surface stress on the Meridional Overturning Circulation, MOC.  While I do not believe that these changes will be important for ASLR this century; it is possible that such changes could be important for SLR in the next century if anthropogenic forcing remains high for an extended period of time:

http://stockage.univ-brest.fr/~oarzel/publis/Arzel_England.CD2012.pdf

Wind-stress feedback amplification of abrupt millennial-scale
climate changes; Olivier Arzel • Matthew H. England; Clim Dyn; 2012
DOI 10.1007/s00382-012-1288-1

Abstract:
"The influence of changes in surface wind-stress on the properties (amplitude and period) and domain of existence of thermohaline millennial oscillations is studied by means of a coupled model of intermediate complexity set up in an idealized spherical sector geometry of the Atlantic basin. Using the atmospheric CO2 concentration as the control parameter, bifurcation diagrams of the model are built to show that the influence of wind-stress changes on glacial abrupt variability is threefold. First, millennialscale oscillations are significantly amplified through windfeedback- induced changes in both northern sea ice export and oceanic heat transport. Changes in surface wind-stress more than double the amplitude of the strong warming events that punctuate glacial abrupt variability obtained under prescribed winds in the model. Second, the average duration of both stadials and interstadials is significantly lengthened and the temporal structure of observed variability is better captured under interactive winds. Third, the generation of millennial-scale oscillations is shown to occur for significantly colder climates when wind-stress feedback is enabled. This behaviour results from the strengthening of the negative temperature-advection feedback associated with stronger northward oceanic heat transport under interactive winds."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #5 on: December 28, 2013, 09:19:59 AM »
The following linked paper indicates that in the short-term marine terminating glaciers in Greenland will experience accelerating ice mass loss (before stabilizing), thus in the several years to several decades, one can expect ice mass loss from Greenland to continue to increasing sea levels in the Southern Ocean, which should contribute to de-stabilizing Antarctic marine ice sheets:

http://www.nature.com/nature/journal/v497/n7448/full/nature12068.html

Faezeh M. Nick, Andreas Vieli, Morten Langer Andersen, Ian Joughin, Antony Payne, Tamsin L. Edwards, Frank Pattyn & Roderik S. W. van de Wal, (2013), "Future sea-level rise from Greenland’s main outlet glaciers in a warming climate"; Nature, 497, pp. 235–238; (09 May 2013), doi:10.1038/nature12068

Abstract:
"Over the past decade, ice loss from the Greenland Ice Sheet increased as a result of both increased surface melting and ice discharge to the ocean. The latter is controlled by the acceleration of ice flow and subsequent thinning of fast-flowing marine-terminating outlet glaciers. Quantifying the future dynamic contribution of such glaciers to sea-level rise (SLR) remains a major challenge because outlet glacier dynamics are poorly understood. Here we present a glacier flow model that includes a fully dynamic treatment of marine termini. We use this model to simulate behaviour of four major marine-terminating outlet glaciers, which collectively drain about 22 per cent of the Greenland Ice Sheet. Using atmospheric and oceanic forcing from a mid-range future warming scenario that predicts warming by 2.8 degrees Celsius by 2100, we project a contribution of 19 to 30 millimetres to SLR from these glaciers by 2200. This contribution is largely (80 per cent) dynamic in origin and is caused by several episodic retreats past overdeepenings in outlet glacier troughs. After initial increases, however, dynamic losses from these four outlets remain relatively constant and contribute to SLR individually at rates of about 0.01 to 0.06 millimetres per year. These rates correspond to ice fluxes that are less than twice those of the late 1990s, well below previous upper bounds. For a more extreme future warming scenario (warming by 4.5 degrees Celsius by 2100), the projected losses increase by more than 50 per cent, producing a cumulative SLR of 29 to 49 millimetres by 2200."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #6 on: December 28, 2013, 09:24:32 AM »
The linked paper indicates that a substantial amount of liquid water is being accumulated in firn within the Greenland ice sheet, which will likely be releases in the next several years, or several decades, which will contribute to sea level rise in the Southern Ocean, which will help to de-stabilize Antarctic marine ice sheets:


http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2043.html

Richard R. Forster, Jason E. Box, Michiel R. van den Broeke, Clément Miège, Evan W. Burgess, Jan H. van Angelen, Jan T. M. Lenaerts, Lora S. Koenig, John Paden, Cameron Lewis, S. Prasad Gogineni, Carl Leuschen & Joseph R. McConnell, (2013), Extensive liquid meltwater storage in firn within the Greenland ice sheet; Nature Geoscience; doi:10.1038/ngeo2043

Abstract:
"Mass loss from the Greenland ice sheet contributes significantly to present sea level rise. High meltwater runoff is responsible for half of Greenland’s mass loss. Surface melt has been spreading and intensifying in Greenland, with the highest ever surface area melt and runoff recorded in 2012. However, how surface melt water reaches the ocean, and how fast it does so, is poorly understood. Firn—partially compacted snow from previous years—potentially has the capacity to store significant amounts of melt water in liquid or frozen form, and thus delay its contribution to sea level. Here we present direct observations from ground and airborne radar, as well as ice cores, of liquid water within firn in the southern Greenland ice sheet. We find a substantial amount of water in this firn aquifer that persists throughout the winter, when snow accumulation and melt rates are high. This represents a previously unknown storage mode for water within the ice sheet. We estimate, using a regional climate model, aquifer area at about 70,000 km2 and the depth to the top of the water table as 5–50 m. The perennial firn aquifer could be important for estimates of ice sheet mass and energy budget."
« Last Edit: December 28, 2013, 05:37:05 PM by AbruptSLR »
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wili

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #7 on: December 28, 2013, 03:56:16 PM »
I noticed this article. Do you think this water could suddenly enter the ocean? If so, what might be the effect on slr and AMOC?

One wonders what other surprises may lie beneath the ice.
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AbruptSLR

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #8 on: December 28, 2013, 06:01:29 PM »
wili,

The abstract of the following linked companion article, indicates that if all of this reservoir were released at once it would contribute 0.4mm to eustatic SLR (or about 0.6mm of SLR in the Southern Ocean); and that it is located in the firn at depths between 12m and 37m.  Also, the researchers could not determine whether this widely spread reservoir currently communicates directly to the ocean, or not, but in any event it is most likely that it will take at least several decades for such liquid water to drain into the ocean (unless surface melting on Greenland's ice sheet accelerates very quickly, say due to a large increase in rainfall):

http://onlinelibrary.wiley.com/doi/10.1002/2013GL058083/abstract

Koenig LS et al. 2013. Initial in situ measurements of perennial meltwater storage in the Greenland firn aquifer. Geophysical Research Letters, published online; doi: 10.1002/2013GL058083

Abstract
"A perennial storage of water in a firn aquifer was discovered in Southeast Greenland in 2011. We present the first in situ measurements of the aquifer, including densities and temperatures. Water was present at depths between ~12 and 37 m and amounted to 18.7 ± 0.9 kg in the extracted core. The water filled the firn to capacity at ~35 m. From April to June 2013, the aquifer temperature remained at the melting point, representing a large heat reservoir within the firn. Using model results of liquid water extent and aquifer surface depth from radar measurements, we extend our in situ measurements to the Greenland Ice Sheet. The estimated water volume is 140 ± 20 Gt, representing ~0.4 mm of sea level rise (SLR). It is unknown if the aquifer temporary buffers SLR or contributes to SLR through drainage and/or ice dynamics."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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wili

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #9 on: December 28, 2013, 09:10:03 PM »
Thanks, ASLR. That puts some perspective on it. Even though parenthetical, the comment "unless surface melting on Greenland's ice sheet accelerates very quickly, say due to a large increase in rainfall" seemed interesting to me--something I hadn't thought of. At the point that the snow melts down to this level, it will be...interesting...to see what happens. On the one hand, that will mean that the overlying snow will no longer be insulating it; but, on the other hand, that melt will likely happen during the summer, so who knows.

Do you think there may be other large reservoirs of free water of various sorts that we don't kow about, hidden in the ice caps, that could rush out suddenly under the right conditions?
"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

AbruptSLR

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #10 on: December 29, 2013, 06:17:40 PM »
wili,

I suspect that the Greenland firn reservoir of liquid is currently the largest in the world, but I would also guess that the firns in many small glaciers (including in the Antarctic Peninsula) and in tundra areas also contain smaller versions of such reservoirs.  However, I think that such reservoirs will be released gradually (over decades in the worst cases); but I believe that they represent an additional source of SLR that most guidance organizations have ignored.  Rather than pointing to these reservoirs as a major source of SLR contribution by themselves, the purpose of my post was intended to indicate that there are tens, to hundreds, of small positive feedback mechanisms (please review my earlier posts in the various threads of the Antarctic folder for others) for SLR that all interact non-linearly to potentially lead to initiations of catastrophic collapses of portions of the WAIS (and peripheral portions of the EAIS) within the next few decades.

Unfortunately, this is like watching a very slow motion tsunami and the public can easily get bored thinking of tens, to hundreds, of small positive feedback mechanisms (see the following links), when they only want one simple storyline to follow (which is not the case), before they are willing to support money being spent to reduce these risks.

Current climate change communications are boring:

http://abcnews.go.com/International/filmmaker-randy-olson-climate-change-bo-ho-horing/story?id=21344670

Reassigning responsibility (or the blame game: note that historically China's rice crops have contributed a lot of methane to the atmosphere) for GHG emissions:

http://www.nytimes.com/2013/12/25/business/economy/what-if-consumers-not-producers-paid-for-emissions.html?pagewanted=2&_r=0

Shadow carbon footprint:

http://www.nytimes.com/interactive/2013/12/25/business/shadow-carbon-footprints.html?src=recg
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #11 on: February 18, 2014, 10:29:30 AM »
I am not saying that the linked article, or the attached images, are proof of any kind, but I find it suspicious that the rapid acceleration of ice mass loss (both discharge and surface mass balance) from Greenland appear to begin circa 1998, the year of the last large El Nino.  This makes me apprehensive about where the rate of acceleration of ice mass loss from Greenland will increase again the next time that we have a very large El Nino event (possibly as early as in the next year or two).  If so, this would disproportionately increase regional sea level off the coast of West Antarctica, which would serve to reduce the stability of the marine glaciers there:


https://www.skepticalscience.com/Why-is-Greenlands-ice-loss-accelerating.html


Caption for first image: "Greenland mass balance and its components Surface Mass Balance (SMB) and Discharge (D). Before 1996, D and hence SMB - D, are poorly constrained and therefore not shown."

Caption for second image: "Surface Mass Balance (blue) and its components precipitation (red), runoff (orange) and sublimation (green)."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #12 on: February 18, 2014, 05:54:34 PM »
And it's looking more and more as if we are heading for an El Nino, possibly starting this summer (though ultimately, it's too early to say for certain):

Latest NOAA forecast is out, and it says...

Quote
models predict either ENSO-neutral or El Niño (greater or equal to
+0.5ºC) during the Northern Hemisphere summer 2014
(p. 26)

Quote
...El Niño starting in May-July 2014
(p. 27)

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/lanina/enso_evolution-status-fcsts-web.pdf
"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #13 on: February 18, 2014, 09:04:52 PM »
Here are some papers on Greenland and Antarctica, some of these have been mentioned already. I poste this on realclimate, but i think it has relevance here


1) Enderlin(2014) doi: 10.1002/2013GL059010

Cohort from Byrd Polar Research Center and Utrecht

Mass waste from all causes 2009-2012 378+/-50 Gtonne/yr (more than 1mm/yr sea level rise,) accelerating at 27+/-9 GTonne/yr^2 (will double in 15yr)

SMB has taken over in Greenland since 2006.

“Our results confirm a decline in the relative importance of discharge to ice sheet mass loss (Figure 3). The 17% increase in discharge between 2000 and 2005 accounted for 58% of the mass loss during that time. This fraction decreased to 36% in 2005–2009 and again to 32% between 2009 and 2012. Since 2009, nearly all (84%) of the increase in the rate of mass loss has been due to increased surface melting and runoff.”

They do say that (under some assumptions):
“…21st century sea level rise from Greenland glacier discharge should not exceed 80 mm.”

but go on to temper it with:

“Given the large variability in discharge and SMB observed within the past decade and the potential for unaccounted positive feedback within the ice-climate system, however, the contribution of GrIS discharge to future sea level rise remains highly uncertain.”

Sing it. Glacier discharge 80mm and SMB how much ? Looks to me like SMB is accelerating too, from fig 3. SMB is already larger than discharge. And Greenland albedo is dropping. Our worst cases grow direr.

2) Meanwhile basal melt drives Antarctica

Depoorter(2013) doi:10.1038/nature12567

Depoorter judges that total basal melt and calving are just about balanced in terms of quantity. (1321+/-144Gtonne/yr calving, 1454+/-174Gtonne/yr basal melt). The two big ice shelves still lose mass predominantly through calving, Thwaites shelf is balanced between the two, PIG is more basal melt. Their map of shelf thinning rates is on fire in the Amundsen sea, and more uneasily, between Totten and Moscow U. The latter are included in their list of glaciers “vulnerable to oceanic forcing.”

Pitchard(2012) doi:10.1038/nature10968

Pritchard points out that basal melt is a control on total mass waste “… through a reduction in buttressing of the adjacent ice sheet leading to accelerated glacier flow.” They conclude:
“…the most profound contemporary changes to the ice sheets and their contribution to sea level rise can be attributed to ocean thermal forcing that is sustained over decades and may already have triggered a period of unstable glacier retreat.”

Rignot(2013) doi:10.1126/science.1235798

Has about the same figures for basal melting than Depoorter (1325+/-235 Gtonne/yr basal melt) but lower for calving (1089+/-139Gtonne/yr.) They point out that most of the basal melt come from “small warm cavity ice shelves” and warn about the same stretch near Totten:

” “Modified” warm deep water at a temperature near 0°C has been reported 40 km south of the continental shelf break northeast of Totten (30). By analogy with observations in the Amundsen Sea, our results suggest the presence of seawater at similar temperatures under several East Antarctic ice shelves. Even zero-degree seawater at outer continen tal shelf depths could expose ice shelves with deep grounding lines like the Totten (2.2 km), Moscow (2.0 km) and Shackleton (1.8 km) to temperatures more than 3°C above their melting points.”

They conclude with another warning:
“…if major shifts in sea ice cover and ocean circulation tip even large ice shelf cavities from cold to warm (35), there could be major changes in ice shelf and thus ice sheet mass balance.”

Thwaites is the one that keeps me awake at night.

sidd



AbruptSLR

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #14 on: February 19, 2014, 04:28:27 PM »
sidd,

I couldn't agree more that Thwaites can keep one awake at night.  The deep trough near the base of the residual Thwaites Ice Tongue represents a weak spot in the Thwaites Gateway for numerous reasons (that you are well aware of) including:
 
(a) As the ice thins in this area (due to relatively high ice velocities) the vertical restraint from the side walls of the trough result in the rift/crevasse cracking pattern that resulting in the approximately 1km by 1km blocks in the residual Thwaites Ice Tongue that can easily float away in the future.
(b) This trough is directly connected to the Thwaites subglacial hydrological drainage system (including: swamps, channels and a few small subglacial lakes), which tend to build-up hydraulic pressure in the basal melt-water; which periodically (with increasing frequency) bursts through the gravitational ice seal in the trough; resulting in period increases in ice velocity, associated ice thinning, associated rifting & crevasse formation, and associated ice mass loss.  I also believe that the advection of warm CDW is increased during these periodic out-bursts of basal melt-water.
(c) The geothermal induced basal melting is higher in the BSB than any other marine glacial basin that I am aware of in the world, and virtually all of this melt-water drains through the trough.
(d) There are some buried seamounts (pinnacles) near the trough, that induce area of high basal friction in the ice stream that induces relatively high rates of friction induced basal ice melting near the trough.

Also, I am concerned about the synergy between PIG and Thwaites, both through ocean water advection, through the SW tributary and the eastern shear margin, and through future changes in the boundary between these two ice drainage basins.

Best,
ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #15 on: February 19, 2014, 10:51:35 PM »
For all my worries about Thwaites and WAIS, Greenland is going faster. I noted some time ago that Greenland will melt in place, SMB is winning out as Enderlin shows. The best measurements i can see is that GRIS is wasting twice as fast as AIS + AIP, and  more, that acceleration of mass waste is also twice as large as Antarctica. I am watching that saddle at 67N north, to see the Gregory instability kick in. But this will of course have profound effect at the other pole, with Greenland at 1mm/yr or bettr now, doubling in 15, with Mitrovica amplification raising up ice shelves down south, lessening basal stress, while increasing grounding line depth ...

sidd

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #16 on: February 19, 2014, 11:45:14 PM »
sidd,

While the first figure shows that you are right that the GIS (GRIS) is currently contributing twice as much to SLR as the AIS, according to Sasgen et al. 2012, for GRACE data from 2002 to 2011 (& without the probably 25% increase in SLR contribution from the BSB due to the GIA correction); the EAIS is actually gaining ice mass (snow) so averaging its numbers with those for the WAIS make the WAIS look less dynamic than it actually is (see the second and third and fourth images from Sasgen et al 2012):

Also, see the revised GRACE Antarctic ice mass trend & accelerations cited in the following:

Simon D.P. Williams Philip Moore, Matt A. King, & Pippa L. Whitehouse; (2014) "Revisiting GRACE Antarctic ice mass trends and accelerations considering autocorrelation",
Earth and Planetary Science Letters; Volume 385, 1 January 2014, Pages 12–21; http://dx.doi.org/10.1016/j.epsl.2013.10.016

http://www.sciencedirect.com/science/article/pii/S0012821X13005797

"Abstract
Previous GRACE-derived ice mass trends and accelerations have almost entirely been based on an assumption that the residuals to a regression model (including also semi-annual, annual and tidal aliasing terms) are not serially correlated. We consider ice mass change time series for Antarctica and show that significant autocorrelation is, in fact, present. We examine power-law and autoregressive models and compare them to those that assume white (uncorrelated) noise. The data do not let us separate autoregressive and power-law models but both indicate that white noise uncertainties need to be scaled up by a factor of up to 4 for accelerations and 6 for linear rates, depending on length of observations and location. For the whole of Antarctica, East Antarctica and West Antarctica the scale factors are 1.5, 1.5 and 2.2 respectively for the trends and, for the accelerations, 1.5, 1.5 and 2.1. Substantially lower scale-factors are required for offshore time series, suggesting much of the time-correlation is related to continental mass changes. Despite the higher uncertainties, we find significant (2-sigma) accelerations over much of West Antarctica (overall increasing mass loss) and Dronning Maud Land (increasing mass gain) as well as a marginally significant acceleration for the ice sheet as a whole (increasing mass loss)."
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sidd

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #17 on: February 20, 2014, 04:30:25 AM »
I don't really weight the the Simon paper too much, since Shepherd(2012) and others used multiple datasets, not just GRACE. The noise being correlated does not bother me too much either, remember, the "noise" is just those degrees of freedom one is _not_ keeping track of. There is information in the "noise", that information just isn't included in the analytical model that was used. Witness the paper (I forget, it was in Physics Today a few years ago) on the D-O oscillations.  The little wiggles in the ice rafted debris data was telling us something that was very important, but was dismissed as noise in earlier treatments.


sidd

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #18 on: February 20, 2014, 04:37:01 AM »
I  completely forgot to add that in the large I agree with you but I have the feeling that WAIS will become the major player after 2050. And Greenland will contribute by forcing SLR among other effects on the climate: e.g. if freshwater input from GRIS slows northbound heat transport from southern hemisphere, the latter will heat even faster as heat is retained down south. There are probably other horrible forcings lurking.

sidd

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #19 on: February 20, 2014, 05:20:46 PM »
sidd,

While your feeling that the WAIS will only become a major player in SLR after 2050, certainly seems reasonable (probable); still one of the horrible scenarios lurking at the fat end of the SLR PDF, includes the risk of abrupt SLR from the ASE glaciers by 2050 [note that the NRC 2013 report "Abrupt Impacts of Climate Change - Anticipating Surprises" cites that the time scale for the collapse of the GRIS could be many centuries to millennia, while this same report states: "A retreat of Thwaites Glacier in West Antarctica could give a much wider and deeper calving front than any observed today, so the "speed limits" suggested by Pfeffer et al. (2008) may not apply (Parizek et al. 2013)."]. 

In this regard it should be noted that up to 9% of the world's GDP [see "Coastal flood damage and adaptation costs under 21st century sea-level rise" by Hinkel et al 2014 (PNAS). DOI: 10.1073/pnas.1222469111] could be lost per year to a 0.9m sea level rise for a world that does not take any protective measure; which would probably be the case for an abrupt sea level rise of 0.9m by 2050.  As PIG has a potential of a 0.33m sea level rise contribution and Thwaites could raise sea level by another 0.67m; one only needs to ask oneself how confident they are that the ASE ice shelves are sound, and that the Thwaites Gateway is sound against an activation of it eastern shear margin (due to an acceleration of the SW Tributary) and against a local (within the ASE) increase in sea level both from a major El Nino event and from SLR induced by a rapid 30-mile retreat of the Jakobshavn Glacier [note that while Jakobshavn is current at a basal "speed bump" it could rapidly get past this bump if surface melting (say from an EL Nino event) filled melt water into the crevasses near the calving face of Jakobshavn].

The credible possibility (per NRC 2013) that the ASE glaciers could abruptly contribute 0.7 to 0.9m to SLR within a 30-year period, represents a multi-trillion dollar per year risk to the world between 2050 and 2100.
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AbruptSLR

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #20 on: February 20, 2014, 07:02:39 PM »
sidd,

For some reason after making my last post about the risks of ASLR (1m of sea level rise in a 30-year period), from the ASE, I felt it appropriate to post the following quote from Dirty Harry:

"I know what you're thinking. "Did he fire six shots or only five?" Well, to tell you the truth, in all this excitement I kind of lost track myself. But being as this is a .44 Magnum, the most powerful handgun in the world, and would blow your head clean off, you've got to ask yourself one question: "Do I feel lucky?" Well, do ya, punk?"

Maybe not a very scientific quote, but it does seem to me that the world is playing Russian Roulette with regard to the (in)stability of the ASE glaciers.

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

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #21 on: February 20, 2014, 08:01:04 PM »
As I have opened myself up for criticism by quoting from the movie "Dirty Harry" once, I thought that I would post that following dialog between the Mayor of San Francisco and Harry Callahan, from that movie:

"Mayor: I don't want any more trouble like you had last year in the Fillmore District. Understand? That's my policy.
Insp. Harry Callahan: Yeah, well, when an adult male is chasing a female with intent to commit rape, I shoot the bastard; that's my policy.
Mayor: Intent? How did you establish that?
Insp. Harry Callahan: When a naked man is chasing a woman through an alley with a butcher knife and a hard-on, I figure he isn't out collecting for the Red Cross.
Mayor: [after Callahan has left] I think he's got a point."
 

In this dialog, I imagine that the Mayor sounds like policy makers following "process-based" SLR projections (eg. the AR5 projections); while Dirty Harry sounds like a policy maker following Bayesianist projections of SLR based on real world experience of the risks of abrupt sea level rise; all we need to do is to cross the burden of proof of intent in a world: (a) following a BAU emission pathway; (b) with an average fast response climate sensitivity of 4.5 instead of 3 degrees C; (c) where the "slow response" climate sensitivity associated with the change in Arctic albedo is already about ¼ of the radiative forcing contribution from CO2; (d) where the frequency of large El Nino events may well double with continued global warming; and (e) where the stability of the ASE marine glaciers is poorly understood, while the measured ice mass loss from the ASE is accelerating at an ever increasing rate.
« Last Edit: February 20, 2014, 11:03:05 PM by AbruptSLR »
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sidd

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #22 on: February 20, 2014, 09:33:05 PM »
In addition to Hinkel(2014), there are two other papers i use for impacts:

the first paper is by a co-author of Hinkel:

Nicholls(2011) "Sea-level rise and its possible impacts given a 'beyond 4°C world' in the twenty-first century", Phil. Trans. R. Soc. A 2011 369, doi: 10.1098/rsta.2010.0291

 Mondal and Tatem( 2012), Uncertainties in Measuring Populations Potentially Impacted by Sea Level Rise and Coastal Flooding. PLoS ONE 7(10):e48191. doi:10.1371/journal.pone.0048191

Hundreds of millions of people at risk in all studies.

sidd

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #23 on: February 21, 2014, 01:01:48 AM »
I have put together some thoughts on the ice sheets, discussing GRACE measurements, basal melt in Antarctica and albedo in Greenland, together with some impact figures from Nicholls(2011) and Mondal(2012) at

http://membrane.com/sidd/fireice/

An amusing animation of the 2012 melt in Greenland is linked from that page.

sidd

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #24 on: February 21, 2014, 01:59:45 AM »
sidd,

Thanks for the linked information, which presents a very nice summary statement.

ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #25 on: February 21, 2014, 05:16:08 AM »
I added the video of the full year 2012 and full field of view rather than just Greenland to the link to the Greenland albedo page.  You can see the ice and the weather systems in th arctic and subarctic down to the english channel. I have made flv,avi and mp4 formats, they are all linked on the albedo page

sidd

AbruptSLR

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #26 on: March 17, 2014, 02:28:13 AM »
The linked reference indicates that previous process-based projections have underestimated ice mass loss from the Northeast Greenland Ice Sheet; which implies that due to the fingerprint effect, sea level around Antarctica will raise more than previously expected; which in turn will serve to destabilize the Antarctic marine glaciers more than previously expected:

Shfaqat A. Khan, Kurt H. Kjær, Michael Bevis, Jonathan L. Bamber, John Wahr, Kristian K. Kjeldsen, Anders A. Bjørk, Niels J. Korsgaard, Leigh A. Stearns, Michiel R. van den Broeke, Lin Liu, Nicolaj K. Larsen & Ioana S. Muresan, (2014), "Sustained mass loss of the northeast Greenland ice sheet triggered by regional warming", Nature Climate Change, doi:10.1038/nclimate2161

http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2161.html

Abstract: "The Greenland ice sheet has been one of the largest contributors to global sea-level rise over the past 20 years, accounting for 0.5 mm yr−1 of a total of 3.2 mm yr−1. A significant portion of this contribution is associated with the speed-up of an increased number of glaciers in southeast and northwest Greenland. Here, we show that the northeast Greenland ice stream, which extends more than 600 km into the interior of the ice sheet, is now undergoing sustained dynamic thinning, linked to regional warming, after more than a quarter of a century of stability. This sector of the Greenland ice sheet is of particular interest, because the drainage basin area covers 16% of the ice sheet (twice that of Jakobshavn Isbræ) and numerical model predictions suggest no significant mass loss for this sector, leading to an under-estimation of future global sea-level rise. The geometry of the bedrock and monotonic trend in glacier speed-up and mass loss suggests that dynamic drawdown of ice in this region will continue in the near future."
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AbruptSLR

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #27 on: May 19, 2014, 04:39:00 PM »
The linked reference from Morlighem et al 2014 indicates that the risk of more rapid SLR contribution from Greenland, this century, is more likely than previously expected by the scientific mainstream.  As SLR contribution from Greenland serves to destabilize marine glaciers in Antarctica, this clearly increases the probability that the WAIS could make an abrupt contribution to SLR this century:

M. Morlighem, E. Rignot, J. Mouginot, H. Seroussi & E. Larour, (2014), "Deeply incised submarine glacial valleys beneath the Greenland ice sheet", Nature Geoscience,  doi:10.1038/ngeo2167

Abstract: "The bed topography beneath the Greenland ice sheet controls the flow of ice and its discharge into the ocean. Outlet glaciers move through a set of narrow valleys whose detailed geometry is poorly known, especially along the southern coasts. As a result, the contribution of the Greenland ice sheet and its glaciers to sea-level change in the coming century is uncertain. Here, we combine sparse ice-thickness data derived from airborne radar soundings with satellite-derived high-resolution ice motion data through a mass conservation optimization scheme. We infer ice thickness and bed topography along the entire periphery of the Greenland ice sheet at an unprecedented level of spatial detail and precision. We detect widespread ice-covered valleys that extend significantly deeper below sea level and farther inland than previously thought. Our findings imply that the outlet glaciers of Greenland, and the ice sheet as a whole, are probably more vulnerable to ocean thermal forcing and peripheral thinning than inferred previously from existing numerical ice-sheet models."
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Bruce Steele

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #28 on: May 19, 2014, 05:29:59 PM »
ASLR, I was wondering about the long term consequences of the slowdown in deep water formation processes. If the cold saline waters that form along the Antarctic continent do not sink into the bottom waters will the cold waters they normally carry stay closer to the surface? Same question for the North Atlantic deep water formation processes if they begin to decline as has been documented for Antarctic bottom waters. Ventilation of the bottom waters will decline but the timeframes involved are centuries long. The consequences of the cold staying closer to the surface would be a shorter time frame because the circulation of surface and intermediate waters are faster than bottom waters. I don't recall reading anything about what happens to the heat/cold effects of water that doesn't sink.

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #29 on: May 19, 2014, 06:49:19 PM »
Fig 1 from Morlinghem(2014) attached. Quotes, the first is, i think echoes a point from Bindschadler, that might have been reassuring when he made it, but we know better now:

"It has however been suggested that the current acceleration and retreat of these marine-terminating glaciers will decrease in the near future, as the ice sheet will lose contact with the ocean waters because the bed elevation of these glaciers rises above sea level within tens of kilometres of the coast"

but they knock this one down:

"If these 107 glaciers were to retreat at an average rate of 110 m/yr in the coming century, as they have between 2000 and 2012 , only 30 of them would disconnect from the ocean by the end of the century."

"More important, out of these 123 marine-terminating glaciers, 60 drain 88% of the ice sheet in area and are grounded below 300 m depth at their termini, meaning they are deep enough to interact with subsurface warm Atlantic waters and undergo massive rates of subaqueous melting"

"Numerical models for the ice sheet therefore employ a shallow, smoothed bed topography that restrains the outflow of glacier ice into the ocean and suppresses contact with the ocean waters in most fjords. Unsurprisingly, the numerical models tend to predict thickening of the ice sheet along the periphery, and a weak sensitivity to ocean thermal forcing, which are both in contrast to recent observations."

sidd

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #30 on: May 19, 2014, 08:07:15 PM »
Bruce,

The question that you raise in Reply #28 can either be addressed with a more accurate complex response, or a simple less accurate response.  As the discussion about the AABW is spread throughout numerous threads in this Antarctic folder including in the following, I am going to skip the complex option:

http://forum.arctic-sea-ice.net/index.php/topic,214.0.html

In the way of a simple response: (a) the slowdown in the AABW is most closely related to the basal ice melting of the Antarctic ice shelves (and also to melting from the AIS); but is also related to changes in local ocean currents related to changes in the westerly circumpolar winds; and you also relate this issue conceptually to the formation of North Atlantic deep water, NADW; which has its own (and different) characteristics; however, (b) if we solely focus on the question of the accumulation of cold low salinity melt-water near the surface of both the North Atlantic and the Southern Ocean then:
(I) It is highly unlikely that this volume of melt water (in any reasonable scenario) will be sufficient to stop either AABW, or NADW, formation, but will only slow this formation down for several centuries.
(II) Certainly, in the Southern Ocean the accumulation of cold fresher water at the surface contributes to the formation of more sea ice for several decades to come; however, the sea ice does nothing to slow the access of the warm CDW from melting the bottom of Antarctic ice shelves or to slow the rate of grounding line retreat for Antarctic marine glaciers.  Therefore, more melt-water will be produced over the next several decades, but Hansen et al shows that while this accumulation of cold fresher water at the sea surface is a negative feedback for global warming, this feedback is insufficient to meaningfully slow the ice sheet calving/melting.
(III) Similarly, in the North Atlantic studies have shown that the colder fresher sea surface water is insufficient to either stop the great ocean conveyor belt current, or to meaningfully slow ice mass loss from Greenland marine terminating glaciers.

Eventually, (in centuries) global warming eliminates these cold fresher water layers, and at some point in the distant future (over 1,000 year) the ocean bottom waters could become anaerobic due to lack of ventilation (as you know better than I do).

So my bottom line response as to what happens to the colder fresher surface water, is that it somewhat slows the rate of warming of the upper North Atlantic, and the upper Southern Ocean, but not enough to change the long-term trend of any of the climate change trends (global warming, SLR, etc).

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

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #31 on: June 16, 2014, 05:10:59 AM »
The following linked reference was provided by LRC1962; which includes the following summary: "Researchers have found evidence of widespread refreezing of ice at the bottom of the Greenland Ice Sheet (see attached image and associated caption); some of these features coincide with faster flows. The newly revealed forms may help scientists understand more about how ice sheets behave and how they will respond to a warming climate."

Clearly, significant refreezing of ice at the bottom of the GIS warms the adjoining ice, which reduces its viscosity (ie softens it), which causes the adjoining ice to accelerate.  Any accelerated ice mass loss from the GIS would tend to accelerate ice mass loss from the AIS due to the fingerprint influenced rise in local sea level around the Southern Ocean.  As the AIS warms, this behavior may gain more significance in Antarctica:

Robin E. Bell, Kirsteen Tinto, Indrani Das, Michael Wolovick, Winnie Chu, Timothy T. Creyts, Nicholas Frearson,  Abdulhakim Abdi & John D. Paden, (2014), "Deformation, warming and softening of Greenland’s ice by refreezing meltwater", Nature Geoscience, doi:10.1038/ngeo2179

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2179.html

Abstract: "Meltwater beneath the large ice sheets can influence ice flow by lubrication at the base or by softening when meltwater refreezes to form relatively warm ice. Refreezing has produced large basal ice units in East Antarctica. Bubble-free basal ice units also outcrop at the edge of the Greenland ice sheet, but the extent of refreezing and its influence on Greenland’s ice flow dynamics are unknown. Here we demonstrate that refreezing of meltwater produces distinct basal ice units throughout northern Greenland with thicknesses of up to 1,100 m. We compare airborne gravity data with modelled gravity anomalies to show that these basal units are ice. Using radar data we determine the extent of the units, which significantly disrupt the overlying ice sheet stratigraphy. The units consist of refrozen basal water commonly surrounded by heavily deformed meteoric ice derived from snowfall. We map these units along the ice sheet margins where surface melt is the largest source of water, as well as in the interior where basal melting is the only source of water. Beneath Petermann Glacier, basal units coincide with the onset of fast flow and channels in the floating ice tongue. We suggest that refreezing of meltwater and the resulting deformation of the surrounding basal ice warms the Greenland ice sheet, modifying the temperature structure of the ice column and influencing ice flow and grounding line melting."

Image caption: "Melting and refreezing at the bottom of ice sheets warps the layer-cake structure above, as seen in this radar image from Greenland."

See also:

http://www.sciencedaily.com/releases/2014/06/140615143832.htm
« Last Edit: June 16, 2014, 11:37:56 PM by AbruptSLR »
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AbruptSLR

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #32 on: June 25, 2014, 02:38:54 AM »
The following linked research on marine terminating glaciers in Greenland confirms the importance of the ocean in accelerating ice mass loss; which indicates to me that as we enter a long period of positive PDO we can expect more frequent intense advection of warm CDW into the ASE and a faster acceleration of ice mass loss from these key Antarctic marine glaciers:

Externally forced fluctuations in ocean temperature at Greenland glaciers in non-summer months by Rebecca H. Jackson, Fiammetta Straneo & David A. Sutherland published in Nature Geoscience doi:10.1038/ngeo2186
http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2186.html

Abstract: "Enhanced submarine melting of outlet glaciers has been identified as a plausible trigger for part of the accelerated mass loss from the Greenland ice sheet, which at present accounts for a quarter of global sea level rise. However, our understanding of what controls the submarine melt rate is limited and largely informed by brief summer surveys in the fjords where glaciers terminate. Here, we present continuous records of water properties and velocity from September to May in Sermilik Fjord (2011–2012) and Kangerdlugssuaq Fjord (2009–2010), the fjords into which the Helheim and Kangerdlugssuaq glaciers drain. We show that water properties, including heat content, vary significantly over timescales of three to ten days in both fjords. This variability results from frequent velocity pulses that originate on the shelf outside the fjord. The pulses drive rapid water exchange with the shelf and renew warm water in the fjord more effectively than any glacial freshwater-driven circulation. Our observations suggest that, during non-summer months, the glacier melt rate varies substantially and depends on externally forced ocean flows that rapidly transport changes on the shelf towards the glaciers’ margins."
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AbruptSLR

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #33 on: June 29, 2014, 03:45:20 PM »
The following linked reference indicates that the southern portion of the Greenland Ice Sheet, GIS, is less stable than previously thought; and as SLR contribution from the GIS serve to destabilize the marine glaciers in Antarctica, this new research increases the probability of the collapse of the WAIS this century:

South Greenland ice-sheet collapse during Marine Isotope Stage 11 by Alberto V. Reyes, Anders E. Carlson, Brian L. Beard, Robert G. Hatfield, Joseph S. Stoner, Kelsey Winsor, Bethany Welke & David J. Ullman published in Nature 510, 525–528 (26 June 2014) doi:10.1038/nature13456.

http://www.nature.com/nature/journal/v510/n7506/full/nature13456.html


Abstract: "Varying levels of boreal summer insolation and associated Earth system feedbacks led to differing climate and ice-sheet states during late-Quaternary interglaciations. In particular, Marine Isotope Stage (MIS) 11 was an exceptionally long interglaciation and potentially had a global mean sea level 6 to 13 metres above the present level around 410,000 to 400,000 years ago, implying substantial mass loss from the Greenland ice sheet (GIS). There are, however, no model simulations and only limited proxy data to constrain the magnitude of the GIS response to climate change during this ‘super interglacial, thus confounding efforts to assess climate/ice-sheet threshold behaviour and associated sea-level rise. Here we show that the south GIS was drastically smaller during MIS 11 than it is now, with only a small residual ice dome over southernmost Greenland. We use the strontium–neodymium–lead isotopic composition of proglacial sediment discharged from south Greenland to constrain the provenance of terrigenous silt deposited on the Eirik Drift, a sedimentary deposit off the south Greenland margin. We identify a major reduction in sediment input derived from south Greenland’s Precambrian bedrock terranes, probably reflecting the cessation of subglacial erosion and sediment transport as a result of near-complete deglaciation of south Greenland. Comparison with ice-sheet configurations from numerical models suggests that the GIS lost about 4.5 to 6 metres of sea-level-equivalent volume during MIS 11. This is evidence for late-Quaternary GIS collapse after it crossed a climate/ice-sheet stability threshold that may have been no more than several degrees above pre-industrial temperatures."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #34 on: September 28, 2014, 04:39:58 AM »
The link leads to an open access pdf that provides valuable information about the bed topography of both Jakobshavn (Greenland), and Byrd (Antarctica), Glaciers.

S. GOGINENI, J.-B. YAN, J. PADEN, C. LEUSCHEN, J. LI, F. RODRIGUEZ-MORALES, D. BRAATEN, K. PURDON, Z. WANG, W. LIU, & J. GAUCH, (2014), "Bed topography of Jakobshavn Isbræ, Greenland, and Byrd Glacier, Antarctica", Journal of Glaciology, Vol. 60, No. 223, 2014 doi: 10.3189/2014JoG14J129

http://www.igsoc.org/journal/60/223/j14j129.pdf

Edit: I thought that I would also provide the attached associated image of the new topology beneath the Byrd Glacier.
« Last Edit: October 06, 2014, 02:29:08 AM by AbruptSLR »
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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #35 on: December 16, 2014, 01:24:05 AM »
Both of the following references indicate that the Greenland Ice Sheet will probably contribute more to SLR than previously expected; which of course will raise future sea levels around Antarctica, which will serve to help destabilize Antarctic marine glaciers in the future:

Beata M. Csatho, Anton F. Schenk, Cornelis J. van der Veen, Gregory Babonis, Kyle Duncan, Soroush Rezvanbehbahani, Michiel R. van den Broeke, Sebastian B. Simonsen, Sudhagar Nagarajan, and Jan H. van Angelen, (2014), "Laser altimetry reveals complex pattern of Greenland Ice Sheet dynamics", PNAS, doi: 10.1073/pnas.1411680112

http://www.pnas.org/content/early/2014/12/12/1411680112.abstract

Abstract: "We present a new record of ice thickness change, reconstructed at nearly 100,000 sites on the Greenland Ice Sheet (GrIS) from laser altimetry measurements spanning the period 1993–2012, partitioned into changes due to surface mass balance (SMB) and ice dynamics. We estimate a mean annual GrIS mass loss of 243 ± 18 Gt⋅y−1, equivalent to 0.68 mm⋅y−1 sea level rise (SLR) for 2003–2009. Dynamic thinning contributed 48%, with the largest rates occurring in 2004–2006, followed by a gradual decrease balanced by accelerating SMB loss. The spatial pattern of dynamic mass loss changed over this time as dynamic thinning rapidly decreased in southeast Greenland but slowly increased in the southwest, north, and northeast regions. Most outlet glaciers have been thinning during the last two decades, interrupted by episodes of decreasing thinning or even thickening. Dynamics of the major outlet glaciers dominated the mass loss from larger drainage basins, and simultaneous changes over distances up to 500 km are detected, indicating climate control. However, the intricate spatiotemporal pattern of dynamic thickness change suggests that, regardless of the forcing responsible for initial glacier acceleration and thinning, the response of individual glaciers is modulated by local conditions. Recent projections of dynamic contributions from the entire GrIS to SLR have been based on the extrapolation of four major outlet glaciers. Considering the observed complexity, we question how well these four glaciers represent all of Greenland’s outlet glaciers."


A. A. Leeson, A. Shepherd, K. Briggs, I. Howat, X. Fettweis, M. Morlighem & E. Rignot,  (2014), "Supraglacial lakes on the Greenland ice sheet advance inland under warming climate", Nature Climate Change, doi:10.1038/nclimate2463

http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate2463.html

Abstract: "Supraglacial lakes (SGLs) form annually on the Greenland ice sheet and, when they drain, their discharge enhances ice-sheet flow by lubricating the base and potentially by warming the ice. Today, SGLs tend to form within the ablation zone, where enhanced lubrication is offset by efficient subglacial drainage. However, it is not clear what impact a warming climate will have on this arrangement. Here, we use an SGL initiation and growth model to show that lakes form at higher altitudes as temperatures rise, consistent with satellite observations. Our simulations show that in southwest Greenland, SGLs spread 103 and 110 km further inland by the year 2060 under moderate (RCP 4.5) and extreme (RCP 8.5) climate change scenarios, respectively, leading to an estimated 48–53% increase in the area over which they are distributed across the ice sheet as a whole. Up to half of these new lakes may be large enough to drain, potentially delivering water and heat to the ice-sheet base in regions where subglacial drainage is inefficient. In such places, ice flow responds positively to increases in surface water delivered to the bed through enhanced basal lubrication and warming of the ice, and so the inland advance of SGLs should be considered in projections of ice-sheet change."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #36 on: January 13, 2015, 05:30:30 PM »
The linked article concludes that the predicted outflow of surface GIS meltwater "… based on climate models alone, without recognition of subglacial processes, may overestimate true meltwater release from the ice sheet."  However, I note that if such events as the 2012 GIS surface melting occurrence are currently contributing less to SLR than previously expected (because some of the surface meltwater is retained within the body of the ice sheet), this it is likely that the AIS is contributing more to the measured SLR than previously expected (which is more troubling to me than if the GIS were contributing more because the AIS is less stable):

Laurence C. Smith Vena W. Chu, Kang Yang, Colin J. Gleason, Lincoln H. Pitcher, Asa K. Rennermalm,Carl J. Legleiter, Alberto E. Behar, Brandon T. Overstreet, Samiah E. Moustafa, Marco Tedesco, Richard R. Forster, Adam L. LeWinter, David C. Finnegan, Yongwei Sheng, and James Balog, (2015), "Efficient meltwater drainage through supraglacial streams and rivers on the southwest Greenland ice sheet", PNAS, doi: 10.1073/pnas.1413024112


http://www.pnas.org/content/early/2015/01/07/1413024112

Abstract: "Thermally incised meltwater channels that flow each summer across melt-prone surfaces of the Greenland ice sheet have received little direct study. We use high-resolution WorldView-1/2 satellite mapping and in situ measurements to characterize supraglacial water storage, drainage pattern, and discharge across 6,812 km2 of southwest Greenland in July 2012, after a record melt event. Efficient surface drainage was routed through 523 high-order stream/river channel networks, all of which terminated in moulins before reaching the ice edge. Low surface water storage (3.6 ± 0.9 cm), negligible impoundment by supraglacial lakes or topographic depressions, and high discharge to moulins (2.54–2.81 cm⋅d−1) indicate that the surface drainage system conveyed its own storage volume every <2 d to the bed. Moulin discharges mapped inside ∼52% of the source ice watershed for Isortoq, a major proglacial river, totaled ∼41–98% of observed proglacial discharge, highlighting the importance of supraglacial river drainage to true outflow from the ice edge. However, Isortoq discharges tended lower than runoff simulations from the Modèle Atmosphérique Régional (MAR) regional climate model (0.056–0.112 km3⋅d−1 vs. ∼0.103 km3⋅d−1), and when integrated over the melt season, totaled just 37–75% of MAR, suggesting nontrivial subglacial water storage even in this melt-prone region of the ice sheet. We conclude that (i) the interior surface of the ice sheet can be efficiently drained under optimal conditions, (ii) that digital elevation models alone cannot fully describe supraglacial drainage and its connection to subglacial systems, and (iii) that predicting outflow from climate models alone, without recognition of subglacial processes, may overestimate true meltwater export from the ice sheet to the ocean."

See also:
http://www.latimes.com/science/sciencenow/la-sci-sn-catastrophic-greenland-melt-20150112-story.html

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

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Re: Antarctic Interactions with, and Lessons from, Greenland
« Reply #37 on: January 09, 2018, 05:29:13 PM »
What happens to the meltwater in the Greenland Ice Sheet deep percolation zone could have a major impact on mass loss from Greenland in the coming decades.  The linked reference discusses a new field method for better monitoring the accumulation of meltwater in this zone.  Obviously, ice mass loss from Greenland impacts ice mass loss from Antarctica via the bipolar seesaw mechanism:

Heilig, A., Eisen, O., MacFerrin, M., Tedesco, M., and Fettweis, X.: Seasonal monitoring of melt and accumulation within the deep percolation zone of the Greenland Ice Sheet and comparison with simulations of regional climate modeling, The Cryosphere Discuss., https://doi.org/10.5194/tc-2017-277, in review, 2018.

https://www.the-cryosphere-discuss.net/tc-2017-277/

Abstract. Increasing melt over the Greenland ice sheet (GrIS) recorded over the past years has resulted in significant changes of the percolation regime of the ice sheet. It remains unclear whether Greenland's percolation zone will act as meltwater buffer in the near future through gradually filling all pore space or if near-surface refreezing causes the formation of impermeable layers, which provoke lateral runoff. Homogeneous ice layers within perennial firn, as well as near-surface ice layers of several meter thickness are observable in firn cores. Because firn coring is a destructive method, deriving stratigraphic changes in firn and allocation of summer melt events is challenging. To overcome this deficit and provide continuous data for model evaluations on snow and firn density, temporal changes in liquid water content and depths of water infiltration, we installed an upward-looking radar system (upGPR) 3.4 m below the snow surface in May 2016 close to Camp Raven (66.4779° N/46.2856° W) at 2120 m a.s.l. The radar is capable to monitor quasi-continuously changes in snow and firn stratigraphy, which occur above the antennas. For summer 2016, we observed four major melt events, which routed liquid water into various depths beneath the surface. The last event in mid-August resulted in the deepest percolation down to about 2.3 m beneath the surface. Comparisons with simulations from the regional climate model MAR are in very good agreement in terms of seasonal changes in accumulation and timing of onset of melt. However, neither bulk density of near-surface layers nor the amounts of liquid water and percolation depths predicted by MAR correspond with upGPR data. Radar data and records of a nearby thermistor string, in contrast, matched very well, for both, timing and depth of temperature changes and observed water percolations. All four melt events transferred a cumulative mass of 56 kg/m2 into firn beneath the summer surface of 2015. We find that continuous observations of liquid water content, percolation depths and rates for the seasonal mass fluxes are sufficiently accurate to provide valuable information for validation of model approaches and help to develop a better understanding of liquid water retention and percolation in perennial firn.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson