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Author Topic: Hansen et al paper: 3+ meters SLR by 2100  (Read 101033 times)

sidd

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #100 on: July 29, 2015, 06:19:42 AM »
Cliff failure event without hydrofracture scares me from that Bassis graf showing unconditional failure at 1km. When does Thwaites grounding retreat to 1K  is a key question in my mind, after that a 55Km wide failing front, way into the BSB

A-Team

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #101 on: July 29, 2015, 07:18:16 AM »
I'm a big fan of Joe Romm overall. I don't really see how someone can demonstrate a better track record -- a doctorate in physics from a first-tier university in oceanic tomography, years of being inside the belly of the DC policy beast and decades of highly effective blogging. I'm seeing a whole lot of public service here: https://en.wikipedia.org/wiki/Joseph_J._Romm

At the same time we need to respond strongly, the sooner the better, to our situation so I can agree with AbruptSLR that it is stupid to leisurely titrate our response in accordance with convenient magical thinking about lots of time being left. That's like having a brain tumor and waiting for the very last minute that it's still operable. Most people would get right on it.

can someone else comment on Eemian in Greenland and Atlantic meridional overturning current components of the Hansen paper.

I'll leave AMOC to someone else. I'm disinclined to rush to summary judgement without first building up some context. If people want to skip the details, I would say we know very little for sure about the Eemian in Greenland. However the take in the Hansen paper is defensible and supported by its cites.

The paper, while dated June and even having 2015 bibliographic entries, can hardly be faulted for not covering -- or arguably being undercut -- by research to be published in mid-August and beyond. However I am going to move the goal posts forward to the Paris meeting decision and report on a newly accepted paper with very disturbing implications that has crossed my desk:

Something is rotten in the state of Denmark ice core analysis. Because they pwned deep and shallow Greenland ice core research via major grant support and heroic but ultimately successful bedrock drilling projects, most of what we think we know about paleo climate conditions in the Northern Hemisphere is at the mercy of their core analyses. What happens, despite sincerest efforts, if those are in error?

Nothing is worse for climate modeling than an offset in annual layer dating, especially if in a defective core like DYE3 whose layer count gets cloned to subsequent cores using mis-attributed internal tie points like Vesuvius. And nothing is more troubling than multiple offset errors in the easy years, historic and Holocene. Later years, with thinner layers and deformed ice, are then only going to be worse. I posted earlier on dating errors within the written observational record and now have more details on that. But the bigger news is that even larger dating errors are now confirmed back to the 8.2 kyr event. I'll explain the significance of that to the Hansen paper shortly.
« Last Edit: July 30, 2015, 12:47:22 AM by A-Team »

Sleepy

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #102 on: July 29, 2015, 08:10:21 AM »
Well, we do have a brain tumor as I see it. And we are injecting steroids to make it grow faster.
http://www.vox.com/2015/7/7/8908179/coal-global-climate-change

The ice is growing in the Arctic, I can read here in Sweden this week. We are entering an ice age. We need to mitigate responsibly and keep our dirty coalbusiness in Germany to protect our money and keep our fossilgussling cars and trust that our energy needs will be saved by future technologies like fusion.

Sorry for the OT, just a bit grumpy today...

P-maker

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #103 on: July 29, 2015, 10:40:39 AM »
A-Team

” Something is rotten in the state of Denmark ice core analysis.”

I totally concur, although you should also know, that a very small minority of it’s inhabitants have over the years tried to put the record straight. However, for exactly the reasons you give, it has turned more than difficult to get core scientists to even discuss the issue. One reason might be the often cited “reticence” of researchers, who do not wish to “rock the boat” with a harsh Eemian verdict ( with immense consequences for our future ) in a small, low lying country fostering such infamous characters as Bjørn Lomborg.

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #104 on: July 29, 2015, 12:42:57 PM »
Richard Alley on potential 4m SLR from WAIS alone within 100 yrs (in the Northern Hemisphere), once collapse starts, around 2050 maybe (?):
https://youtu.be/yCunWFmvUfo?t=35m49s

And Alley on potential 7m SLR from GIS within 300 yrs if CO2 gets high enough, say 800 ppm (?), with 400 ppm now, rising more than 2 ppm/yr now:
https://youtu.be/yCunWFmvUfo?t=34m30s

So under BAU this could imply maybe 8m of total SLR by 2150, if following Hansen et al we assume 1m by 2060, 4m by 2100 and 8m by 2150, with maybe 1m from thermal expansion + small glaciers/ice caps, 4m from WAIS, 2m from GIS and 1m from EAIS?

Add maybe 2m more from GIS and EAIS until 2200 would give maybe 10m total SLR by that time?

No matter how often I reflect on these numbers, they keep boggling my mind...
« Last Edit: July 29, 2015, 01:45:34 PM by Lennart van der Linde »

Shared Humanity

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #105 on: July 29, 2015, 01:41:56 PM »
Fig.S22 in Hansen et al, attached below, shows the potential effects of 6 and 25 meters of SLR.

I am surprised that 25m doesn't have more effect on area submerged than shown above. Of course even 2 or 3m would be devastating to small islands.

With 25m sea level rise, it looks like land area would only decline around(rough eyeball) 3%? Patchy of course: Bangladesh and small islands losing large proportions of their land but plenty of other countries losing little area.

Oldest son lives in the Marshall Islands, Majuro now but on an outer island, Ailinglaplap, 3 years ago. The highest elevation on any of the islands is 3 meters. They already have serious problems caused by SLR and the entire 2000 island nation will be abandoned well before 2100.

This abandoning will occur even if the most optimistic projections for SLR are correct.
« Last Edit: July 29, 2015, 02:04:10 PM by Shared Humanity »

AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #106 on: July 29, 2015, 05:09:13 PM »
Richard Alley on potential 4m SLR from WAIS alone within 100 yrs (in the Northern Hemisphere), once collapse starts, around 2050 maybe (?):
https://youtu.be/yCunWFmvUfo?t=35m49s

And Alley on potential 7m SLR from GIS within 300 yrs if CO2 gets high enough, say 800 ppm (?), with 400 ppm now, rising more than 2 ppm/yr now:
https://youtu.be/yCunWFmvUfo?t=34m30s

So under BAU this could imply maybe 8m of total SLR by 2150, if following Hansen et al we assume 1m by 2060, 4m by 2100 and 8m by 2150, with maybe 1m from thermal expansion + small glaciers/ice caps, 4m from WAIS, 2m from GIS and 1m from EAIS?

Add maybe 2m more from GIS and EAIS until 2200 would give maybe 10m total SLR by that time?

No matter how often I reflect on these numbers, they keep boggling my mind...

Lennart,

If we group the adjoining portions of the EAIS (such as Recovery Glacier) together with WAIS, then I would say that your numbers are roughly what we are talking about.  So this primarily leaves our discussion to how likely is such a possible scenario to occur.  In this regards I quote from Rignot's June 2015 interview: ".. I would rather hear Jim’s upper bounds being discussed than the overly conservative scenarios from existing, poorly skilled numerical models."


I provide the following link to a YouTube talk by David Bromwich on general background issues related to the potential WAIS collapse risk.  While, rather long and general in nature, it does explain how the teleconnection of Tropical Pacific energy to WAIS can result in surface ice melting that could drive the hydrofracturing modeled by Pollard et al 2015:

https://www.youtube.com/watch?v=8kf1Tv7-8NI

It can be very difficult to discuss the probability of uncertain ice sheet mass loss this century beyond that quantified by our current poorly skilled numerical models; however, as most experts agree that once hydrofracturing & cliff failures begin in the BSB they can proceed very quickly; what we are left with discussing is the timing and the probability of the loss of the "plug ice" at the thresholds of the various Antarctic marine glaciers including the BSB, Recovery, Totten etc.  The stability of all of these "ice plugs" are addressed in the Antarctic Folder, but I would like to note that the calving face of Jakobshavn is currently rapidly approaching a region of seafloor with a negative slope, and as it is also subjected to risk of hydrofracturing we may learn many lessons from this Greenland glacier that are applicable to helping to model the risk of the collapse of the Antarctic marine glaciers (note that the BSB/Thwaites system is a 3D collapse risk as compared to the 2D behavior of Jakobshavn, and thus BSB/Thwaites will likely receive relatively little buttressing support from any mélange that forms in front of it).

Best,
ASLR
“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: Hansen et al paper: 3+ meters SLR by 2100
« Reply #107 on: July 29, 2015, 06:07:28 PM »
For those who don't want to watch the Bromwich video in my last post (or for those who watched it & did not understand some of the key risk factors for marine glacier collapse), I provide the four attached images that illustrate some key concepts:

The first image shows how wind patterns can blow warm circumpolar deep water, CDW, over the continental shelf to the groundling line of marine glaciers, where it can contribute to rapid grounding line retreat.

The second image shows the bathymetry of the threshold area for Thwaites/BSB (this is the area where the current "ice plug" exists), showing that there are numerous pathways for warm CDW to reach this glacier's grounding line; particularly when the wind patterns associated with a strong El Nino (& 2015-2016 will likely experience a super El Nino) push extra CDW into the Amundsen Sea Embayment, ASE, where it can also accelerate degradation of both the Pine Island Ice Shelf and the Thwaites Eastern Ice Shelf.

The third image shows how many crevasses are already in the Thwaites threshold area, and as El Nino events not only bring warm CDW into the ASE, but also warm atmospheric surface temperatures, we can expect some surface ice melting in the Thwaites threshold area in January 2016, which could accelerate calving of the Thwaites Eastern Ice Shelf and adjoining areas due to surface melt water flowing into the pre-existing crevasses.

The fourth image is from Bassis & Jacobs (2013) showing how flaws in thick ice sheets can accelerate calving such as that currently be observed in Jakobshavn and postulated by Pollard et al 2015 to occur in numerous WAIS and EAIS marine glaciers (with continued warming to Pliocene like conditions that we are rapidly approaching circa 2035) due to hydrofracturing and cliff failures.


See also:
Bassis, J.N., and Jacobs,S., (2013), "Diverse calving patterns linked to glacier geometry", Nature Geoscience, 6, 833–836, doi:10.1038/ngeo1887.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Bruce Steele

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #108 on: July 29, 2015, 07:04:53 PM »
What is the maximum sea level rise you would expect by 2100?
< 1 meter
2 (4%)1.0 meters
2 (4%)1.5 meters
12 (24%)2.0 meters
9 (18%)2.5 meters
6 (12%)3.0 meters
2 (4%)> 3 meters
17 (34%)
Total Members Voted: 50


OLN organized this poll back in 2013. Does the Hansen paper change anyones prior vote? Maybe 
3.5 and 4 meter bins would draw votes also.

AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #109 on: July 29, 2015, 07:27:49 PM »
What is the maximum sea level rise you would expect by 2100?
< 1 meter
2 (4%)1.0 meters
2 (4%)1.5 meters
12 (24%)2.0 meters
9 (18%)2.5 meters
6 (12%)3.0 meters
2 (4%)> 3 meters
17 (34%)
Total Members Voted: 50


OLN organized this poll back in 2013. Does the Hansen paper change anyones prior vote? Maybe 
3.5 and 4 meter bins would draw votes also.

Bruce,

Without a pdf this question could mean different things to different people.  Therefore, my first attachment shows a pdf in blue for California SLR assuming a BAU pathway thru 2100 (note the red curves show a pdf for 2070).

Second, while I am posting I provide the second attached image from a March 2014 Michael Mann Sci Am article that correlates different ECS values, with the faux hiatus (or observed global mean surface temperatures), and the corresponding projected global mean surface temperature in the coming decades.  Mann takes this figure to support the idea that ECS is lower than 4C and close to 3C; however, I do not believe that this is necessarily a correct interpretation as numerous researchers have shown that the surplus heat during the faux hiatus entered both the Southern Pacific and the Indian Oceans (where it almost certainly has increased the volume of CDW in the Southern Ocean, which means that there is more CDW available to spill over more continental shelves to trigger not only Thwaites, but Recovery, Wilkes, Totten etc marine glaciers).  This also leaves the probability that a 4C ECS may rapidly increase surface temperatures over the WAIS in the coming decades, thus contributing to surface melt and hydrofracturing.

Best,
ASLR
“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: Hansen et al paper: 3+ meters SLR by 2100
« Reply #110 on: July 29, 2015, 08:34:06 PM »
Further to my comment that during the faux hiatus that ocean heat content was leaking from the Tropical Pacific into the Southern Pacific and the Indian Oceans (and from there into the Southern Ocean), see the following references and associate images:


Lee, S. K. et al (2015), "Pacific origin of the abrupt increase in Indian Ocean heat content during the warming hiatus", Nature Geoscience (2015) DOI: 10.1038/ngeo2438

http://www.nature.com/articles/ngeo2438.epdf?referrer_access_token=9BJgiYXdhYH99_2ymUOCl9RgN0jAjWel9jnR3ZoTv0ObkVE5338xGv8uBOQWlRnAab4qPXFs4O3SZb6IxKfW2PnJo_T3XFSFHOLhlVP5DuGMj1m9zXfhUpQNo49qcfXDEiah-FdrNW9ptu6fWbPhE1c9_C5YRZri4QlC1kisr1NrPzt4KRR2GdIZazw2xlww80jv4_iErazAtxWMImsP1HDoFRm1OW3P6nlXyMUnlxs%3D&tracking_referrer=www.nature.com

Abstract: "Global mean surface warming has stalled since the end of the twentieth century, but the net radiation imbalance at the top of the atmosphere continues to suggest an increasingly warming planet. This apparent contradiction has been reconciled by an anomalous heat flux into the ocean, induced by a shift towards a La Niña-like state with cold sea surface temperatures in the eastern tropical Pacific over the past decade or so. A significant portion of the heat missing from the atmosphere is therefore expected to be stored in the Pacific Ocean. However, in situ hydrographic records indicate that Pacific Ocean heat content has been decreasing9. Here, we analyse observations along with simulations from a global ocean–sea ice model to track the pathway of heat. We find that the enhanced heat uptake by the Pacific Ocean has been compensated by an increased heat transport from the Pacific Ocean to the Indian Ocean, carried by the Indonesian throughflow. As a result, Indian Ocean heat content has increased abruptly, which accounts for more than 70% of the global ocean heat gain in the upper 700 m during the past decade. We conclude that the Indian Ocean has become increasingly important in modulating global climate variability."


See also:
Julia Rosen (2015), "Indian Ocean may be key to global warming 'hiatus' - Upper ocean may be storing heat, giving atmosphere a break", Nature, doi:10.1038/nature.2015.17505

http://www.nature.com/news/indian-ocean-may-be-key-to-global-warming-hiatus-1.17505
&
http://phys.org/news/2015-05-global-captured-pacific-ocean-indian.html

“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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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #111 on: July 29, 2015, 10:23:36 PM »
Good piece on Hansen et al in Ars Technica:
http://arstechnica.com/science/2015/07/no-scientists-arent-predicting-10ft-higher-sea-level-by-2050/

So the "likely this century" statement was not in an earlier draft, but in a 10 page summary for journalists.

Sigmetnow

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #112 on: July 30, 2015, 12:56:12 AM »
@TheBradBlog: Starting now on the @KPFK #BradCast: @MichaelEMann on bombshell new sea level rise study & much more! 3p PT. LISTEN: http://t.co/I0TY83klvz

Some technical difficulties reported....

@MichaelEMann: @DRTucker @TheBradBlog @KPFK That's unfortunate. I think the full clip will be available a bit later this evening...
People who say it cannot be done should not interrupt those who are doing it.

A-Team

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #113 on: July 30, 2015, 01:13:38 AM »
The second peer-reviewer has not yet surfaced in the commenting area. They are at 24 comments already, unheard of.  However a few people seem to just be having a discussion among themselves.

I wish there was some way to filter out comments from people who have not themselves published 3 or more scientific papers, each with 10 or more cites. The discussion will stay open until 17 Sep 15. That still leaves a very generous period before the Paris meeting during which the paper will have been out of peer review.

Six fresher discussion papers are now piled on top of Hansen et al and more than 30 are below. Will the NY Times severely criticize several hundred more scientists for using open review? No, all these article will pass unnoticed. It just goes to show how politically disturbed the dotEarth agenda is.

http://www.atmos-chem-phys-discuss.net/15/20059/2015/acpd-15-20059-2015-discussion.html

The ArsTechnica was a little on the snarky side (does this guy think AGU chats and posters are peer-reviewed articles? -- no one complains about non-stop press releases there) but had some good additional information, such as an essay on Hansen's  Columbia University page where he writes:

“My conclusion, based on the total information available, is that continued high emissions would result in multi-meter sea level rise this century and lock in continued ice sheet disintegration such that building cities or rebuilding cities on coast lines would become foolish.”

http://www.columbia.edu/~jeh1/mailings/2015/20150727_SeaLevelDisaster.pdf

Here is a list of 13 scientific journals with identical open peer review practices published by the European Geoscience Union. Of the tens of thousands of articles that first appeared as discussion papers, only one has ever drawn the wrath of commentators.

 I'm currently reading four in-review articles* -- if you're a researcher wanting to be keep up with the competition, you'd better be reading them too. Quite a few authors will not only answer questions but also ply you with even fresher pdfs they're readying for submission.

Annales Geophysicae (ANGEO)
Atmospheric Chemistry and Physics*
Atmospheric Measurement Techniques
Biogeosciences
Climate of the Past**
Earth Surface Dynamics
Earth System Dynamics
Geoscientific Instrumentation, Methods and Data Systems
Geoscientific Model Development
Hydrology and Earth System Sciences
Natural Hazards and Earth System Sciences
Nonlinear Processes in Geophysics
Ocean Science
SOIL
The Cryosphere*
« Last Edit: July 30, 2015, 02:02:37 AM by A-Team »

Sleepy

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #114 on: July 30, 2015, 06:48:27 AM »
From the ArsTechnica article above.
The problem is, all those headlines describe a study, and that study doesn’t predict anything. It certainly doesn’t predict 10 feet of sea level rise by 2100 (or even 2050) as a number of stories have claimed.
Sure, but to regular people this is just playing with words. And who needs to understand where we are heading? Regular people, non scientists.

On another blog, I selected the exact same qoute as A-team above from the essay on Hansens webpage on the 27th, and another part. Why? I do believe normal people who don't care to read papers are more affected by Hansens personal opinions. Even (especially) deniers...

Discussing science is one thing, communicating where we are heading it is another. I think Hansen is doing the right thing here. I like it.

A-Team

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #115 on: July 30, 2015, 07:42:17 AM »
Sure, but to regular people this is just playing with words. And who needs to understand where we are heading? Regular people, non scientists. Discussing science is one thing, communicating where we are heading it is another. I think Hansen is doing the right thing here. I like it.

My sentiments exactly. Hansen's essay is expert opinion from an honorable guy with fifty years of relevant research experience. He could have dispensed with this paper altogether. My guess is he just wanted to pull it all together one last time, not for how it's going to turn out (he knows that already), but just to lay out the sequence of falling dominoes  for those who want that level of detail. 

Here is the bio of Scott K. Johnson / Associate Writer for Ars Techica: "master's in hydrogeology from the University of Wisconsin. He has taught Earth science at Madison Community College and worked as a hydrogeologist for the Wisconsin DNR and the Wisconsin Geological and Natural History Survey. His keen interest in fluid flow led to a closet brewery"

It's clear to Scott that had he been given oversight on Hansen's group, they wouldn't have made so many stupid mistakes in their article. Maybe he and Revkin could pull an authoritative synthesis of climate change. Revkin earned a BS from Brown University in 1978 in biology and later received a master's in journalism. That's nice but the barrista working at the coffee kiosk has a Ph.D in physical chemistry.

AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #116 on: July 30, 2015, 04:22:48 PM »
From the ArsTechnica article above.
The problem is, all those headlines describe a study, and that study doesn’t predict anything. It certainly doesn’t predict 10 feet of sea level rise by 2100 (or even 2050) as a number of stories have claimed.

Sure, but to regular people this is just playing with words. And who needs to understand where we are heading? Regular people, non scientists.

On another blog, I selected the exact same qoute as A-team above from the essay on Hansens webpage on the 27th, and another part. Why? I do believe normal people who don't care to read papers are more affected by Hansens personal opinions. Even (especially) deniers...

Discussing science is one thing, communicating where we are heading it is another. I think Hansen is doing the right thing here. I like it.


Sleepy,

I concur with you, and I have always found your posts to be well grounded in common sense.

That said, many/most policymakers will only accept a projection from a computer model as adequate political cover for taking any action, and they will not accept paleo-analogies from the late-Eemian, nor estimates (say 10-year doubling time) of probable ice mass loss from the WAIS no matter how intelligent or experienced the researcher (say Hansen).  Unfortunately for the BSB/Thwaites case, most existing ice models leave the "ice plug" effectively blocking the basin threshold for one to two hundred years before the main phase collapse begins; however, as Rignot notes (& in my opinion no one speaks with more authority on this topic) these existing models are incomplete and at best represent a lower bound.  This leaves policymakers free to do as little as possible on this matter, and as indicated by the following clip when Alley provided heavily hedged (milk-toast) testimony to a Republican congressman who wanted to enact a carbon pricing plan, Alley did not give his fellow Republican adequate ammunition so the whole measure failed (leaving the world at risk):

https://www.youtube.com/watch?v=4tMeqjbA94I

Now Alley feels that he was protecting scientific integrity; however, in the following clip he is well aware of the risks of a BSB/Thwaites collapse, but instead of communicating them holistically as Hansen does he prefers to focus on getting more research dollars to support his graduate students by focusing on incremental improvements to old ice models; while poo-pooing significant risk factors that would be difficult for his team to model for the BSB/Thwaites threshold area (I do acknowledge his many valuable scientific contributions including input to the hydrofracturing and cliff failure mechanisms).


https://www.youtube.com/watch?v=yCunWFmvUfo

For example in Alley's April INSTAAR talk (linked above) on possible WAIS collapse, he admits that he has a proposal to make a more detailed model of the Thwaites threshold area; however, as far as I can tell from looking at the clip Alley missed: 1. Hydrodynamic water pressure pulse from cliff failure calving event; 2. influence of increasing Southern Ocean cyclones & associated storm surge on flushing-out Thwaites mélange; 3. local ASE sea level has not changed due to GIS contribution & magma inflow to keep gravitational attraction of seawater surface; 3. influence of ENSO (we are entering a period of increased EL Nino intensity & frequency), & IPO (we are existing a two decade long negative IPO phase) on CDW inflow into the ASE; 4. projected changes in local ocean currents, including the influence of advective flow out of the Pine Glacier on the current flow to the Thwaites grounding line (see the first two attached image); 5. The influence of the outflow of buoyant basal water from beneath Thwaites (see the third attached image) on both surging of the Thwaites Ice Tongue and on cutting channels on the underside of both the Thwaites Ice Tongue and Ice Shelf; and 6. The probable early loss of the pinning points on the Thwaites Ice Shelf and Ice Tongue due to accelerated calving and break-up around these pinning points (see the fourth image).

Furthermore, I suspect that Alley will use computer generated estimates of the warm CDW flow into the ASE; which as indicated by the following underestimates observations of the CDW in the Southern Ocean during the recent period of negative IPO:

Sunke Schmidtko, Karen J. Heywood, Andrew F. Thompson, Shigeru Aoki (2014), "Multidecadal warming of Antarctic waters", Science 5 December 2014: Vol. 346 no. 6214 pp. 1227-1231 DOI: 10.1126/science.1256117



http://www.sciencemag.org/content/346/6214/1227

Abstract: "Decadal trends in the properties of seawater adjacent to Antarctica are poorly known, and the mechanisms responsible for such changes are uncertain. Antarctic ice sheet mass loss is largely driven by ice shelf basal melt, which is influenced by ocean-ice interactions and has been correlated with Antarctic Continental Shelf Bottom Water (ASBW) temperature. We document the spatial distribution of long-term large-scale trends in temperature, salinity, and core depth over the Antarctic continental shelf and slope. Warming at the seabed in the Bellingshausen and Amundsen seas is linked to increased heat content and to a shoaling of the mid-depth temperature maximum over the continental slope, allowing warmer, saltier water greater access to the shelf in recent years. Regions of ASBW warming are those exhibiting increased ice shelf melt."


https://robertscribbler.wordpress.com/tag/circumpolar-deep-water/

Extract: "For a study this week confirmed that Antarctica is now seeing a yearly loss of ice equal to one half the volume of Mt Everest every single year. A rate of loss triple that seen just ten years ago. An acceleration that, should it continue, means a much more immediate threat to coastal regions from sea level rise than current IPCC projections now estimate.

According to a new study led by Sunke Schmidtko, this deep water current has been warming at a rate of 0.1 degrees Celsius per decade since 1975. Even before this period of more rapid deep water warming, the current was already warmer than the continental shelf waters near Antarctica’s great glaciers. With the added warming, the Circumpolar Deep Water boasts temperatures in the range of 33 to 35 degrees Fahrenheit — enough heat to melt any glacier it contacts quite rapidly.
Out in the deep ocean waters beyond the continental shelf zone surrounding Antarctica, the now warmer waters of this current can do little to effect the great ice sheets. Here Sunke’s study identifies the crux of the problem — the waters of the Circumpolar Deep Water are surging up over the continental shelf margins to contact Antarctica’s sea fronting glaciers and ice shelves with increasing frequency.
In some cases, these warm waters have risen by more than 300 feet up the continental shelf margins and come into direct contact with Antarctic ice — causing it to rapidly melt. This process is most visible in the Amundsen Sea where an entire flank of West Antarctica is now found to be undergoing irreversible collapse. The great Pine Island Glacier, the Thwaites Glacier and many of its tributaries altogether composing enough ice to raise sea levels by 4 feet are now at the start of their last days. All due to an encroachment of warm water rising up from the abyss."

Furthermore, the following Weber et al 2014 reference makes it clear, by studying ice-rafted debris from the 26,000–19,000 years ago, how important the ocean temperature is on determining ice mass loss:

M. E. Weber, P. U. Clark, G. Kuhn, A. Timmermann, D. Sprenk, R. Gladstone, X. Zhang, G. Lohmann, L. Menviel, M. O. Chikamoto, T. Friedrich, & C. Ohlwein (05 June 2014), "Millennial-scale variability in Antarctic ice-sheet discharge during the last deglaciation", Nature, Volume: 510, Pages: 134–138, doi:10.1038/nature13397

http://www.nature.com/nature/journal/v510/n7503/abs/nature13397.html

Abstract: "Our understanding of the deglacial evolution of the Antarctic Ice Sheet (AIS) following the Last Glacial Maximum (26,000–19,000 years ago) is based largely on a few well-dated but temporally and geographically restricted terrestrial and shallow-marine sequences. This sparseness limits our understanding of the dominant feedbacks between the AIS, Southern Hemisphere climate and global sea level. Marine records of iceberg-rafted debris (IBRD) provide a nearly continuous signal of ice-sheet dynamics and variability. IBRD records from the North Atlantic Ocean have been widely used to reconstruct variability in Northern Hemisphere ice sheets, but comparable records from the Southern Ocean of the AIS are lacking because of the low resolution and large dating uncertainties in existing sediment cores. Here we present two well-dated, high-resolution IBRD records that capture a spatially integrated signal of AIS variability during the last deglaciation. We document eight events of increased iceberg flux from various parts of the AIS between 20,000 and 9,000 years ago, in marked contrast to previous scenarios which identified the main AIS retreat as occurring after meltwater pulse 1A and continuing into the late Holocene epoch. The highest IBRD flux occurred 14,600 years ago, providing the first direct evidence for an Antarctic contribution to meltwater pulse 1A. Climate model simulations with AIS freshwater forcing identify a positive feedback between poleward transport of Circumpolar Deep Water, subsurface warming and AIS melt, suggesting that small perturbations to the ice sheet can be substantially enhanced, providing a possible mechanism for rapid sea-level rise."

http://www.climatecentral.org/news/warm-water-invasion-fueling-striking-antarctic-ice-melt-18401

Extract: "What the team found was that the waters circulating around the Antarctic continental shelf have warmed considerably in some areas. In the Bellingshausen and Amundsen Seas, the waters had warmed by about 0.2 to 0.5°F per decade since the 1990s, which meshed with the melting trends seen in both areas.
In fact, the other new study found that the melt rate of the glaciers of the Amundsen Sea Embayment had tripled in just the past decade.
"The mass loss of these glaciers is increasing at an amazing rate," study co-author Isabella Velicogna, also of UC Irvine and JPL, said in a statement.
That study compared data of ice loss from the glaciers from four different sources and found that they all told a similar story.
“It’s sort of a confirmation because it’s using multiple techniques and the signal is so big you can’t miss it,” Rignot, who was not involved with either new study, said."

Therefore, due to difficulties with modeling the true risks, I suspect that policymakers will continue to take inadequate action no matter how masterfully Hansen et al explain the over all risk from ASLR.

Very 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: Hansen et al paper: 3+ meters SLR by 2100
« Reply #117 on: July 30, 2015, 04:56:26 PM »
Just to add to my immediately prior post:

The first Landsat 8 image of the Thwaites Ice Shelf & Ice Tongue from March 2015, shows both: (a) a significant calving event on the eastern side (top of the image) of the Thwaites Eastern Ice Shelf; and (b) the fractured and partially collapsed condition of the Thwaites Ice Tongue.

The second image (click on it to animate) was compiled by Wipneus & shows the growth in a crack in the Pine Island Ice Shelf from May to June 2015; which in my opinion could lead to another major calving event for the PIIS by the November to December 2015 timeframe; which reduces buttressing action on the Southwest Tributary Glacier; which influences the Thwaites Threshold area stability (so the entire ASE area adjoining the Thwaites Threshold must be modeled including PIG, Haynes, etc, see the third NASA model image of ice velocity in this ASE area).

The fourth image shows how basal pinning point could possibly stabilize the Thwaites Threshold area; however, Rignot has found that some key pinning points that some researchers previously estimated were in the threshold area are in reality not there.  Furthermore, as this fourth image indicates, as the groundling retreats due to ice melting from advection of warm CDW, whatever remaining pinning points that do exist in the threshold area will sooner or later (I am guessing by 2035 due to the current positive phase of the IPO that will last at least that long) become irrelevant as the ice will float over the tops of such pinning points.

Thus while simplified computer models of the BSB/Thwaites threshold area may project that it will be stable for one to two hundred years; the reality (as supported by Rignot) is that it is already destabilizing at an accelerating rate.
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #118 on: July 30, 2015, 05:14:37 PM »
In one of my earlier posts in this thread I noted that I hoped that Hansen et al 2015's findings would stimulate the DOE to modify their ACME program to refocus on the ASLR issue; and as the ACME computer code is based on the CESM code I provide the four attached images from a discussion of the modeling challenges from a few years ago for the CESM/CISM code.
Furthermore, in this post I briefly list some of additional challenges (beyond what Hansen et al cite) that such GCMs and RCMS (preferably ESMs) should not ignore when they publish projections for future SLR responses including:

- They should consider regional methane emissions (see the "Antarctic Methane" thread in the Antarctic folder started by A4R).
- They should consider accelerating regional ice mass loss from ice shelves (including RIS and FRIS) and terrestrial ice, and changes to: SST, sea ice, currents and winds (see all of the threads for periods from 2012 to 2060 in the Antarctic folder started by me)
-  They should consider the risk of regional collapse of the WAIS, and the resulting changes to ocean currents (see all the threads for the period from 2060 to 2100 from me in the Antarctic folder, including discussion of new sea passageways)
-  They should evaluate the risk of regional collapse of AABW production (also see the discussion in the, influence of dust (which could increase the albedo of the AIS) from the desertification of South Africa and Australia due to the pole-ward expansion of the atmospheric Hadley Cells.
- RCMs should consider input of correct boundary conditions from the GCMs (preferably from Earth Systems Models, ESMs)
-  They should link dynamically to get input of correct ice mass loss from local circulation models, LCMs, of advective cells melting glaciers, ice shelves and ice sheets
- They should use different radiative forcing scenarios than the IPCC's cited probabilities of occurrences of the Recommended Concentration Pathways, RCPs, for AR5 which are highly misleading and should be corrected before used to interpret any GCM, RCM, or LCM, projections.
- Readers (policy makers) of GCM, RCM and LCM projections should not focus on median projections and they should remember that uncertainties increase with time into the future (meaning more risk).
« Last Edit: July 30, 2015, 06:45:26 PM by AbruptSLR »
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wili

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #119 on: July 30, 2015, 06:16:16 PM »
D. Archer has now weighed in on the Hansen et al. paper, mostly positively: http://www.atmos-chem-phys-discuss.net/15/C5209/2015/acpd-15-C5209-2015.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: Hansen et al paper: 3+ meters SLR by 2100
« Reply #120 on: July 30, 2015, 07:09:51 PM »
The U.S. Navy's former top expert on man-made climate change, retired Rear Adm. David Titley supports a holistic approach to recognizing climate change risks, and as the extract below states we do not need to know every detail about the future before we take appropriate action; while his calls-out denialist for obstructing appropriate action by stating that the case is not air-tight.

http://www.timesunion.com/tuplus-local/article/Navy-climate-change-expert-sees-opponents-6401711.php

Extract: "Titley's presentation in Hudson is entitled "Climate Change and National Security: People not Polar Bears." In it, he said he will discuss "multiple, independent lines of evidence," the history of climate change as seen within the U.S. Department of Defense and U.S. Navy, and challenges to national security that arise from climate change and in particular, the associated changes in the Arctic.
"We know enough to take significant action now, even if we don't know every detail about the future," he said. "We will figure this out. We did not get out of Stone Age because we ran out of stones. We just found something better.""
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #121 on: July 30, 2015, 11:12:16 PM »
Most excellent coverage and context, AbruptSLR. This is a far better commentary than what they are getting over at the poor journal.

I'm wondering if somewhere in this opus whether they indicate the use of 'inverse methods'. Everyone breezes by thinking  they know what those two little words mean but actually they can involve many pages of math on the methodological side (or just a cite elsewhere). Whether they literally used that exact phrase or not, this could be the origin for press seeing 'nothing predicted' in the article vs seeing prediction specifics on SLR amount and timing in the essay and interviews.

I am rather distracted right about now with the Alaska drilling protests just to my north. Tsk-tsk, it seems Shell cannot get their ship to drydock with those people hanging off the bridge and kayakers there. It is a little problematic for me to get my inflatable up there, 104ºF.

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #122 on: July 30, 2015, 11:22:39 PM »
This is normal for the middle of the Antarctic winter, right?
http://forum.arctic-sea-ice.net/index.php/topic,429.msg58797/topicseen.html#msg58797
BYE BYE
Edit:  GIFed it up, images from 7/17 to 7/30.  There was another shot at 7/23, with no sign of the collapse coming.

Edit:  Added the frame for the 23rd because you can see the ice field collapsing.
FNORD

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #123 on: July 30, 2015, 11:58:20 PM »
This is normal for the middle of the Antarctic winter, right?
http://forum.arctic-sea-ice.net/index.php/topic,429.msg58797/topicseen.html#msg58797
BYE BYE
Edit:  GIFed it up, images from 7/17 to 7/30.  There was another shot at 7/23, with no sign of the collapse coming.

Edit:  Added the frame for the 23rd because you can see the ice field collapsing.


solartim27,

Thank you very much for the link to this major Pine Island Ice Shelf, PIIS, calving event.  The first attached image shows this July 30 2015 calving of PIIS, and the second image shows the current condition of the degrading Thwaites Ice Shelf & Tongue (also from today's Polarview image).  The last major calving event for the PIIS also occurred in the dead of the austral winter as indicated as indicated by the third attached image from July 8 2013 (only two years ago).

I believe that today's PIIS calving event must be related to the strong El Nino event that is currently getting stronger and is driving warm CDW into the ASE (as indicated by the very thin sea ice in the area).  This also indicates that major calving events are accelerating (in frequency) and this PIIS event should reduce some of the buttressing action of the PIIS on the SW Tributary Glacier; which may soon add stress on the Thwaites Eastern Shear Margin.

As our current El Nino could reach a super status by October, and may last through March 2016, we may see a lot more calving events in this critical area this season.

Best regards,
ASLR
« Last Edit: July 31, 2015, 12:11:26 AM by AbruptSLR »
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #124 on: July 31, 2015, 01:28:09 AM »
Most excellent coverage and context, AbruptSLR. This is a far better commentary than what they are getting over at the poor journal.

A-Team,

Thank you.  This information is mostly pulled directly from my old posts in the Antarctic folder (of which there are many more); however, it can be hard to see the forest from the trees in the Antarctic folder because the information is spread around between so many different threads.

Best,
ASLR

PS: Because I thought it would be good to provide some new information, the attached image is from the Earth nullschool for July 30 2015, and shows the surface winds together with the mean sea level pressure.  This image shows how the Amundsen Sea Low is directing wind flow directly into the Amundsen Sea Embayment, ASE; which drags the warm circumpolar deep water, CDW into the ASE; which is accelerating the calving of the local ice shelves and also accelerating the retreat of the grounding lines for the various ASE marine glaciers.
« Last Edit: July 31, 2015, 01:42:49 AM by AbruptSLR »
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #125 on: July 31, 2015, 05:15:53 PM »
As it is a bit boring repeating information already available (but dispersed) information about potential ASLR, I provide the following link to the summary thread of observations about the risk of a WAIS collapse this century:

http://forum.arctic-sea-ice.net/index.php/topic,106.0.html

While reviewing that summary thread the following quote from Reply #12 of that thread struck me, which is:

"Communicating Uncertainties in Natural Hazard Forecasts" by Stein & Geller, EOS, Transactions, AGU Vol. 93 No 38, 2012
›   "One major challenge is that real uncertainties often turn out to have been underestimated.  In many applications, 20%-45% of results are surprises, falling outside the previously assumed 98% confidence limits [Hammitt and Shyakhter, 1999]. …. This effect arise in predicting river floods [Merz, 2012] and earthquake ground motions and may arise for the IPCC uncertainty estimates [Curry, 2011]."

Hansen has been saying for decades that scientific reticence (or erring on the side of least drama, ESLD) has been causing scientist's to under-report the risks of abrupt sea level rise, ASLR, for decades.

For example Alley publically admits that in AR4 he and this fellow IPCC panel members intentionally (and willfully) did not address the risk of ASLR (from ice sheet collapse), and in a footnote left it to others to address/define this risk to the common good.  By AR5 evidence that the ozone hole over Antarctica had accelerated the circumpolar winds sufficiently to drive warm CDW to the grounding lines of so many Antarctic marine glaciers that the IPCC could not ignore this observed behavior, but they still refused to consider a collapse scenario so instead they took the response observed during the satellite era and applied a feel good estimate of acceleration (ala Tad Pfeffer et al) and added this "rapid ice mass loss" for both the GIS and the AIS, to effectively increase the AR4 SLR projection by about 50%.

Unfortunately, the satellite era has been dominated by a negative PDO/IPO phase and thus is uncharacteristic of the true forcing profile, and thus the AR5 SLR projections are once again based on ESLD; and we all bear the risks of main phase ASLR being triggered by 2035-2040 via stronger forcing associated with the two to three decade long positive PDO/IPO phase.

Furthermore, I would like to note that many people (including many scientists) feel reassured by the relatively slow rates of SLR in the paleo-record, and even during the late-Eemian addressed by Hansen et al 2015, and by the fact that the AR5 GCM projections do not indicate a significant risk of an ASLR event this century.  To this type of magic thinking, I point-out that:

- The paleo-record does not include either an ozone-hole over Antarctica, nor anthropogenic radiative forcing that is many times that ever experience in the paleo-record.  Thus it is not surprising that an ASLR event should occur now at a very fast pulse rate.

- The AR5 GCM projections are proven to include: (a) double-intertropical convergence zone bias (particularly in the Pacific Ocean, see Baijun Tian (2015)), which limits their telecommunication of tropical energy to the WAIS; and (b) Per Sherwood at the 2015 Ringberg conference do not adequately include the influence of aerosols (including those from phytoplankton) that reflect light and promote Antarctic sea ice growth (and Hansen et al 2015 show that Antarctic sea ice growth is a positive feedback factor for ice sheet ice mass loss). 

Thus indicating that the scientific establishment (& particularly AR5) shows ESLD behavior and refuses to acknowledge their true uncertainties as quantified by Stein & Geller (2012).
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #126 on: July 31, 2015, 10:45:09 PM »
As a follow-on to Reply #123 about a July 2015 major calving event for the Pine Island Ice Shelf, PIIS; I thought that some would be interested in seeing some images of the 2012 major calving event of the Thwaites Ice Tongue (you can compare the attached images to the Sentential 1a image from July 30 2015 in Reply #123):

The first image show an over-view of the ASE region prior to 2012 by Rignot (provided for orientation).

The second 2012 image shows a sequence of the outer end of the Ice Tongue breaking off and rotating away.

The third image show that between Jan. 2012 and Jan 2013 the ice surface elevation at the base of the Thwaites Ice Tongue dropped by over 6 meters as the ice surged seaward (due to the loss of buttressing).

The fourth image shows the Ice Tongue in Feb 2012, Feb 2013 and March 2013 showing ice movement (also note that the grounded iceberg at the tip of the residual Thwaites Ice Tongue has moved downstream from March 2013 until July 2015, see Reply #123).

If I am correct that the stronger than normal intrusion of warm CDW into the ASE associated with our current strong El Nino, then we may soon see the grounded iceberg at the tip of the residual Thwaites Ice Tongue float-away (due to basal ice melting by the warm CDW) this austral summer, resulting in another acceleration of ice flow (and an associated drop in the ice surface elevation) at the base of the ice tongue.
« Last Edit: July 31, 2015, 10:52:31 PM by AbruptSLR »
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #127 on: July 31, 2015, 11:02:16 PM »
While I am posting, I thought that I would provide two more images.

The first attached figure is from Manabe et al 1989 (Manabe is a highly regarded researcher), showing the output of a computer model illustrating the flux of heat from the tropics to the Southern Ocean from 1989 to 2059.  This shows that the Southern Ocean is now & will continue to be the faster warming ocean on the planet; which, will continue to support ice mass loss from Antarctic marine glaciers.

The second attached image shows that advection of water (warm CDW & basal meltwater) forms grooves (or channels) beneath Antarctic ice shelves, which then facilitate the creation of crevasses in the ice shelves as the shelves flex from tidal movements.  These crevasses and basal grooves (or channels) promote major calving events such as the 2012 Thwaites Ice Tongue calving event and the July 2015 PIIS calving event.
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #128 on: July 31, 2015, 11:22:06 PM »
Just for fun, as Richard Alley frequently poo-poos risks from both subsea hydrate methane emissions and from subglacial volcanoes in the Byrd Subglacial Basin, I thought that I would post the two following images:

The first image from NOAA shows the atmospheric methane concentration in ppb on July 30 2015 at 600-hPa.  Not only are the methane concentrations in the northern hemisphere unusually high for this time of year (up to 2262ppb), but also the coastline of Antarctica is fringed with atmospheric methane (in the dead of the austral winter), indicating to me that with continued CDW warming and continued retreat of Antarctic marine glacier grounding lines that Antarctic methane emissions from the seafloor may well accelerate.

The second image shows the locations of active and inactive subglacial volcanoes in West Antarctica, and as the ice sheet degrades in this area magma will upwell in this area; which could reactive such subglacial volcanoes (maybe sometime after 2060).
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #129 on: August 01, 2015, 01:43:32 AM »
The linked reference (with an open access pdf) provides historical information indicating that continued global warming will increase ENSO activity and will telecommunicate more atmospheric energy to Antarctica (particularly West Antarctica), which will increase surface temperatures, and will increase the propensity for surface ice melting (which could fuel more hydrofracturing).

Turney, C. S. M., Fogwill, C. J., Klekociuk, A., van Ommen, T. D., Curran, M. A. J., Moy, A. D., and Palmer, J. G.  (2015), "Tropical and mid-latitude forcing of continental Antarctic temperatures", The Cryosphere Discuss., 9, 4019-4042, doi:10.5194/tcd-9-4019-2015.

http://www.the-cryosphere-discuss.net/9/4019/2015/tcd-9-4019-2015.html
http://www.the-cryosphere-discuss.net/9/4019/2015/tcd-9-4019-2015.pdf

Abstract. Future changes in atmospheric circulation and associated modes of variability are a major source of uncertainty in climate projections. Nowhere is this issue more acute than across the mid- to high-latitudes of the Southern Hemisphere (SH) which over the last few decades has experienced extreme and regional variable trends in precipitation, ocean circulation, and temperature, with major implications for Antarctic ice melt and surface mass balance. Unfortunately there is a relative dearth of observational data, limiting our understanding of the driving mechanism(s). Here we report a new 130-year annually-resolved record of δ D – a proxy for temperature – from the South Geographic Pole where we find a significant influence from extra-tropical pressure anomalies which act as "gatekeepers" to the meridional exchange of air masses. Reanalysis of global atmospheric circulation suggests these pressure anomalies play a considerably larger influence on mid- to high-latitude SH climate than hitherto believed, modulated by the tropical Pacific Ocean. Our findings suggest that future increasing tropical warmth will strengthen meridional circulation, exaggerating current trends, with potentially significant impacts on Antarctic surface mass balance.

Extract: "By extending historical observations over the South Pole and in combination with reanalysis products we find that meridional circulation changes associated with centres of pressure anomalies are part of a broader change observed over recent decades. Of particular note is the marked decrease in rainfall in southwest Australia since the 1970s. Our results demonstrate this trend is part of a hemispheric pattern of alternating northerly and southerly airflow linked to changes in the southwest Pacific and the tropical Pacific. We explore possible teleconnections via a strengthening of the Ferrel Cell and weakening Polar Cell. Comparison of 30-year running means of isotopic and climate datasets suggest the continuing trend to lower pressure anomalies in the southwest Pacific – with largely stable values in the Indian Ocean – are consistent with increased ENSO variability, implying precipitation will continue to decline in southwest.  Australia if El Niños become more frequent, and lead to greater warming over the
Antarctic, potentially impacting the future surface mass balance."
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #130 on: August 01, 2015, 11:11:09 AM »
As I previously mentioned the ACME program, I provide the following information from the Antarctic folder:
The US DoE's Accelerated Climate Modeling for Energy (ACME), will include extensive sub-routines focused on the Antarctic Ice Sheet, AIS, (as well as the Greenland Ice Sheet, GIS) and possible abrupt SLR:

Bader D, W Collins, R Jacob, P Jones, P Rasch, M Taylor, P Thornton, and D Williams. "Accelerated Climate Modeling for Energy (ACME) Project Strategy and Initial Implementation Plan." 2014

http://climatemodeling.science.energy.gov/sites/default/files/publications/acme-project-strategy-plan_0.pdf
Extract: "2.2.1.3 Cryosphere System
Could a dynamical instability in the Antarctic Ice Sheet be triggered within the next 40 years?

The objective is to examine the near-term risk of initiating the dynamic instability and onset of the collapse of the Antarctic Ice Sheet due to rapid melting by warming waters adjacent to the ice-sheet grounding lines. The experiment would be the first fully coupled global simulation to include dynamic ice shelf–ocean interactions for addressing the potential instability associated with grounding line dynamics in marine ice sheets around Antarctica. It will utilize several significant advances in the new ACME model, including the ability to enhance spatial resolution in both the ice sheet and ocean model to resolve grounding-line processes while still maintaining global extent in a coupled system and throughput for decadal simulations. The simulation will include an eddy-resolving Southern Ocean as well to better represent Circumpolar Deep Water (CDW) and dynamics associated with bringing this water onto the continental shelf under the ice sheet. Including the sea-ice model captures the process of buttressing at the ice shelf–sea-ice boundary. Finally, a fully coupled system is able to simulate changes in atmospheric forcing (e.g., poleward displacement of jets) that could influence the behavior of the Southern Ocean and sea ice.
The specific experiment will be a fully coupled simulation from 1970–2050 to explore whether rapid ice-sheet instability is triggered in this time frame. An ensemble would be desirable to address the likelihood of such an event, though this is not likely to be affordable in our configuration in this timeframe. The model configuration for this experiment will be a modified version of the standard high-resolution ACME configuration described below. The base configuration includes the atmosphere/land on a 0.25° cubed-sphere grid using the ACME-modified CAM5-SE atmosphere model. The subgrid orography modifications will be needed to resolve Antarctic surface mass balance at the ice-sheet margins. The ocean component will be MPAS-O on a Spherical Centroidal Voronoi Tesselations (SCVT) mesh with 15-km grid spacing at the equator, decreasing to 5 km in the Southern Ocean region. The default mesh will be extended southward to include critical Antarctic embayments and the resolution in these regions will be further enhanced if affordable. The vertical grid will be a hybrid coordinate with 100 vertical levels. The sea-ice component will be MPAS-CICE on the same ocean grid. Finally, we will add an Antarctic Ice Sheet model with resolution of 0.5–1 km near likely grounding-line locations and coarser resolution (~10 km) throughout the interior. For initial conditions, we will follow a similar spin-up procedure as with previous high-resolution simulations, with an ocean/ice state from an ocean/ice reanalysis-forced spin-up. For the ice sheet, an optimized initial condition should be available from the PISCEES project.
This first-of-its-kind coupled simulation will be focused largely on the ocean–ice shelf feedbacks and potential for dynamical instability and rapid SLR. It represents a first step toward a comprehensive SLR and impacts capability needed by the DOE to assess threats to coastal facilities. As work proceeds toward the more comprehensive experiments planned in the 10-year timeframe, we will be incrementally adding additional features. For example, work will begin under this project to develop an initial implementation of icebergs and primitive calving laws to capture the transport and distribution of ice and other material as the ice sheets flow into the ocean. Work also continues (as part of related projects) on a Greenland Ice Sheet model so that we can capture SLR contributions from both major ice sheets. We will also begin to include isostasy and ice-sheet self-gravity that can have a first-order effect on the regional SLR signature around the coastal U.S. We anticipate all of these effects to be included in a following ACME version. Further releases will begin to include wave models, further focusing of resolution in coastal and storm-track regions, and other capabilities needed to further refine SLR impact at regional scales.

2.2.2.3 Cryosphere System
How will regional variations in sea level rise interact with more extreme storms to enhance the coastal impacts of SLR?
The aim of this simulation is to determine the potential impacts on the nation’s coastal zones due to SLR exacerbated by regional variations in SLR and extreme storm surges. The novel aspects of this simulation are:
1. Fully coupled models of the cryosphere, including both major land ice sheets, the floating ice shelves surrounding Antarctica, the interactions with surrounding sea ice, and icebergs calved from Antarctica and Greenland
2. Complete treatments of the impacts of time-evolving isostasy and ice-sheet self-gravity on SLR
3. Addition of wave models to the ocean component
4. Deployment of enhanced resolution in all components to resolve dynamics at ice-sheet margins, sea-ice behavior, and the effects of severe weather on sea state in the major storm tracks

This experiment is based upon DOE’s advances in dynamic and adaptive ice-sheet modeling combined with the capacity for ultrahigh resolution of the land ice sheets and surrounding oceans using upcoming advances toward extreme-scale computing.

4.4 Ice Sheets
The ice-sheet model brings in a new set of interactions that must be understood and monitored for development or reduction of biases. The state of the atmosphere is essential to the surface mass balance, which in turn must be compared against other mass loss terms (iceberg calving, submarine melting). Along with monitoring of changes in grounded ice area and volume and these related mass balance terms, some of which may prove useful as metrics in a coupled context, a research problem we intend to take on is the development of Circumpolar Deep Water (CDW) metrics. Where waters are all near freezing, the relatively warm CDW, often found below colder and fresher waters, has a strong potential to accelerate submarine melting and therefore to strongly impact the overall mass balance of the Antarctic Ice Sheet. Stronger winds can drive greater upwelling and bring these warm waters in contact with the ice shelf. Research to understand the controls on CDW state and variability will be undertaken, facilitating the establishment of metrics focused on CDW mean state and variability, ensuring that transitions to or from rapid submarine melt states are not modeling artifacts but are robust and well understood. This effort will be critical for successfully answering the cryospheric driving question."

See also:
http://www.forbes.com/sites/jamesconca/2014/10/13/the-great-climate-model/

Extract: "We need a Great Climate Model.

The national laboratories of the Department of Energy are working on just such a model. Teamed with the National Center for Atmospheric Research, four academic institutions and one private company to form the Accelerated Climate Modeling for Energy, or ACME project, the national labs will help develop the most complete, fully coupled, state-of-the-science Earth system model to date.

Pacific Northwest National Laboratory (PNNL), Argonne, Brookhaven, Lawrence Berkeley, Lawrence Livermore, Los Alamos, Oak Ridge and Sandia will conduct simulations and modeling on the highest performance computing systems in the world. That includes over a hundred petaflop machines and the soon-to-be-operational exascale supercomputers."

&

http://www.scientificcomputing.com/news/2014/09/developing-most-advanced-earth-system-computer-model-yet-created

Extract: "LOS ALAMOS, NM — With President Obama announcing climate-support initiatives at the 2014 United Nations Climate Summit, the U.S. Department of Energy national laboratories are teaming with academia and the private sector to develop the most advanced climate and Earth system computer model yet created. For Los Alamos National Laboratory researchers, it is a welcome advance for an already vibrant high-performance computing community.
Accelerated Climate Modeling for Energy, or ACME, is designed to accelerate the development and application of fully coupled, state-of-the-science Earth system models for scientific and energy applications."

Caption for first Image: "The oceans play an important role in the earth's climate; they transport heat from equator to pole, provide moisture for rain, and absorb carbon dioxide from the atmosphere. Ocean models, such as this one from Los Alamos National Laboratory, help explain interactions between individual eddies that may be altered in a changing climate. This visualization, courtesy of the Lab's MPAS-Ocean Model, shows ocean currents and eddies in a high-resolution global ocean simulation with the Antarctic in the center. Colors show speed, where white is fast and blue is slow."

Also, separately, the second attached image shows that during the Argos era, essentially all of the ocean's heat gain has occurred in the Southern Latitudes

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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #131 on: August 01, 2015, 05:56:03 PM »
The first linked web article by Kitware, elaborates on the three key goals [focused on water cycle, biochemistry, and cryosphere systems] for the first three years of the ACME (Accelerated Climate Model – Energy) program, with the cryosphere effort focused on determining the stability of the AIS for the coming 40-years.

http://www.prweb.com/releases/2015/02/prweb12539509.htm


The second linked article discusses Kitware's efforts to achieve economical Input/output form large programs such as ACME (including for the ASLR issue):

The following link provide much the same information as the first link:

http://www.kitware.com/news/home/browse/Kitware%3F2015_02_25%26Kitware+Part+of+Team+to+Address+Climate+Change+Issues

https://datascience.lanl.gov/data/papers/SC14.pdf
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #132 on: August 01, 2015, 06:48:51 PM »
Per the linked reference (with an open access pdf) the austral Spring-Summer albedo increased due to Antarctic sea ice trends from 1982 to 2009.  Furthermore, as shown by the extract below this increase in Antarctic sea ice albedo was also accompanied by an increase in snowfall on this sea ice.  Both of these findings support Hansen et al 2015's conclusions, and support the idea that ice mass loss from Antarctica is currently accelerating (as the increased sea ice cover results in both a greater Planetary Energy Imbalance and greater access for warm CDW to the grounding lines of Antarctic marine glaciers, and increased snowfall on the sea ice means generally less snowfall on grounded marine glaciers), and is trending towards still further acceleration:

Zhu-De Shao and Chang-Qing Ke (2015), "Spring–summer albedo variations of Antarctic sea ice from 1982 to 2009", Environ. Res. Lett. 10 064001

http://iopscience.iop.org/1748-9326/10/6/064001/article

Extract: "The increasing albedo means that Antarctic sea ice region reflects more solar radiation and absorbs less, leading to a decrease in temperature and much snowfall on sea ice, and further resulted in an increase in albedo."

See also:
http://environmentalresearchweb.org/cws/article/news/62032

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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #133 on: August 01, 2015, 07:19:01 PM »
One of the criticisms of the Hansen et al 2015 paper was that the model that they used was too simple; however, the two linked references using state-of-the-art software from NOAA's Geophysical Fluid Dynamics Laboratory, GFDL, both present model results that support the findings of Hansen et al 2015.  The first linked reference indicates that GFDL CM2.1 finds that the AMOC is changing to increase warming of the subpolar gyre (SPG, see the attached image), while cooling the adjoining Gulf Stream region, as projected by Hansen et al 2015.  The second linked reference indicates that using CMIP5 input together with HiRAM, indicates that the tropical cyclone season will lengthen in the 21st century, both supporting Hansen et al 2015's projection of increased storm activity and also as tropical cyclones convey heat to the polar regions this identified trend will increase the changes of accelerated ice mass loss from both the GIS and the AIS (& particularly from the WAIS):

Zhang, J, and Rong Zhang, July 2015: On the Evolution of Atlantic Meridional Overturning Circulation (AMOC) Fingerprint and Implications for Decadal Predictability in the North Atlantic. Geophysical Research Letters, 42(13), DOI:10.1002/2015GL064596.

http://onlinelibrary.wiley.com/doi/10.1002/2015GL064596/abstract

Abstract: "It has been suggested previously that the Atlantic Meridional Overturning Circulation (AMOC) anomaly associated with changes in the North Atlantic Deep Water formation propagates southward with an advection speed north of 34°N. In this study, using Geophysical Fluid Dynamics Laboratory Coupled Model version 2.1 (GFDL CM2.1), we show that this slow southward propagation of the AMOC anomaly is crucial for the evolution and the enhanced decadal predictability of the AMOC fingerprint—the leading mode of upper ocean heat content (UOHC) in the extratropical North Atlantic. A positive AMOC anomaly in northern high latitudes leads to a convergence/divergence of the Atlantic meridional heat transport (MHT) anomaly in the subpolar/Gulf Stream region, thus warming in the subpolar gyre (SPG) and cooling in the Gulf Stream region after several years. Recent decadal prediction studies successfully predicted the observed warm shift in the SPG in the mid-1990s. Our results here provide the physical mechanism for the enhanced decadal prediction skills in the SPG UOHC."


Dwyer, John, S J Camargo, A Sobel, M Biasutti, K A Emanuel, Gabriel A Vecchi, Ming Zhao, and M K Tippett, August 2015: Projected Twenty-First-Century Changes in the Length of the Tropical Cyclone Season. Journal of Climate, 28(15), DOI:10.1175/JCLI-D-14-00686.1.

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-14-00686.1

Abstract: "This study investigates projected changes in the length of the tropical cyclone season due to greenhouse gas increases. Two sets of simulations are analyzed, both of which capture the relevant features of the observed annual cycle of tropical cyclones in the recent historical record. Both sets use output from the general circulation models (GCMs) of either phase 3 or phase 5 of the CMIP suite (CMIP3 and CMIP5, respectively). In one set, downscaling is performed by randomly seeding incipient vortices into the large-scale atmospheric conditions simulated by each GCM and simulating the vortices’ evolution in an axisymmetric dynamical tropical cyclone model; in the other set, the GCMs’ sea surface temperature (SST) is used as the boundary condition for a high-resolution global atmospheric model (HiRAM). The downscaling model projects a longer season (in the late twenty-first century compared to the twentieth century) in most basins when using CMIP5 data but a slightly shorter season using CMIP3. HiRAM with either CMIP3 or CMIP5 SST anomalies projects a shorter tropical cyclone season in most basins. Season length is measured by the number of consecutive days that the mean cyclone count is greater than a fixed threshold, but other metrics give consistent results. The projected season length changes are also consistent with the large-scale changes, as measured by a genesis index of tropical cyclones. The season length changes are mostly explained by an idealized year-round multiplicative change in tropical cyclone frequency, but additional changes in the transition months also contribute."

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

bluesky

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #134 on: August 02, 2015, 03:33:25 PM »
Just wonder if the recent "Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation" (S. Rahmstorf et al, Nature) and other similar research papers,  already discussed there
http://forum.arctic-sea-ice.net/index.php/topic,1199.msg49283.html#msg49283
give more credit to Hansen et al. paper, as one its "controversial" assumption is the amount of fresh water in the model and the consequences on local SST and shutting down some of the existing MOC or equivalent, or maybe I am just confusing things?

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #135 on: August 02, 2015, 11:56:19 PM »
While the Byrd Subglacial Basin (which includes the Thwaites Glacier) is clearly the most imminent threat w.r.t. ASLR, the East Antarctic Ice Sheet, EAIS, also has numerous marine glaciers that are also susceptible to collapse once (if/when) their "ice plugs" degrade.  In this regard the four accompanying images regarding the Wilkes Basin briefly illustrate the mechanism of the "ice plug" and subsequent collapse of the marine glacier once the  plug is removed.

The first images shows the general logistics of the Wilkes Basin.  The second image shows two cross-sectional profiles illustrating the location of the "ice plug" (which has both a stable portion and a portion prone to collapse) and the portion of the marine glacier subject to collapse once the plug is removed.  The third image illustrates just how abruptly the marine glacier becomes unstable (due to ice calving, ala cliff failures and/or hydrofracturing) once the ice plug is removed.  The fourth image shows how calved icebergs carry entrapped rock debris that progressively falls to the seafloor as the iceberg progressively melts, while it is floating away to the Southern Ocean.  I note that researchers have found numerous examples of iceberg debris fields on the Southern Ocean seafloor, confirming that once initiated large volumes of ice mass can be lost due to iceberg calving.

While most researchers currently point to the influx of warm CDW to remove the "ice plug" (which can take multiple decades to centuries depending on the particular conditions of any given marine glacier); in my next few posts I plan to not only consider the influence of warm CDW (circumpolar deep water) on the ice plug for the Thwaites threshold/gateway, I also plan to address other mechanisms that could accelerate the removal of the Thwaites ice plug sooner than many/most researchers currently admit.

P.S. I note that when warm CDW causes the ice at a marine glacier's grounding line to melt in-place the debris fall directly down, so researchers can clearly tell the difference between debris fields from iceberg debris vs those where basal ice melting forms an ice self (as is currently the case for the Pine Island Glacier / Ice Shelf).
« Last Edit: August 03, 2015, 12:05:22 AM by AbruptSLR »
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #136 on: August 03, 2015, 12:27:23 AM »
The first figure from Goldberg et al 2012 shows the change in ice Volume Above Floatation, VAF, for a representative ice plug with bathymetry idealized after the Thwaites Gateway/Threshold; when subjected to different temperatures of warm CDW advection.  After about 20-years the lose in VAF is shown to slow as the grounding line retreated to an assumed pinning point in the model (I note that one previously assumed pinning in the Thwaites Gateway was proven not to exist by Rignot et al 2014).  This figure helps to illustrate when some researchers seem to believe that the Thwaites Glacier will be stable for another one to two hundred years.

The second figure shows the temperature above freezing (which is a function of depth) observed CDW temperatures above freezing for 1994, 2000, 2007 and 2009 beneath the Pine Island Ice Shelf, PIIS; indicating values as high as 3.3C by 2009.  While temperatures previously observed in front of Thwaites where not as high as for the PIIS; the CDW temperatures in front of Thwaites may increase with strong El Nino events and continued global warming.

The third image (by Fogt 2011) shows that El Nino & La Nina events can alternate in the location of atmospheric heat transported to the WAIS by atmospheric Rossby waves; which can cause alternating cycles for cracking the ice followed by potential surface melting events (which could contribute to cliff failures and hydrofracturing in the future).

The fourth image (by Rignot et al 2014) shows the ice flux from key ASE marine glaciers from 1974 to 2013; which shows that ice flux from the Thwaites Glacier is still accelerating.
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #137 on: August 03, 2015, 12:58:34 AM »
The first image shows an early (prior to 2011) estimate of the subglacial drainage network beneath the Thwaites Glacier.  While the details of this old network are crude it illustrates both the relatively large size of the network and that network primarily drains out the deep submarine trough at the base of the Thwaites Ice Tongue.

The second image by Motyka et al 2003 shows how the outlet of fresh basal meltwater can accelerate convective mixing at a cliff face grounding line; which can accelerate local ice calving; which could be of importance to future calving in the next decade or two for the ice near the submarine trough at the base of the Thwaites Ice Tongue.

The third image is from the PISM ice sheet model guide material & illustrates how this program accounts for the influence of enthalpy in different types of glaciers [note the Antarctic case is closer to that shown in panel (b)].  Enthalpy is not only a function of ice temperature but also of meltwater content within the ice mass.  As the Byrd Subglacial Basin has exceptionally high geothermal heat flux, the deep portions of the Thwaites Glacier high enthalpy basal conditions which results in low viscosity; which could accelerate calving once the ice plug has been removed.

The fourth image comes from an analysis of contour velocities for the Jakobshavn Glacier (in Greenland) for different basal viscosity, basal drag and gravitational driving force conditions. This analysis shows for a case with ice cliff failures that velocities increase with: decreasing viscosity, increasing basal drag, and increasing gravitational forcing.  These conditions are generally worse for the Thwaites Glacier (once the ice plug is removed) than for the Jakobshavn Glacier.
« Last Edit: August 03, 2015, 01:49:56 AM by AbruptSLR »
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #138 on: August 03, 2015, 01:29:05 AM »
When I posted an image in Reply #126 of the 6m drop in ice surface elevation in 2012, and the subsequent crevasse pattern in the ice at the base of the Thwaites Ice Tongue in Reply #107; I did not discuss how this created a relatively large number of roughly 1km by 2km icebergs that are ready to float away once the large grounded (on a submerged pinnacle) iceberg (at the former tip of the Ice Tongue) floats away (note this grounded iceberg can be observed to be shifting now by Sentential 1a).  Furthermore if/when this roughly 1km by 2km icebergs float away (maybe in the next year or two); this will likely result in cliff failures of the adjoining fractured ice grounded in the trough at the base of the Thwaites Ice Tongue.  Also, if such cliff failure calving events manages to clear ice out of the trough within the next decade, or so, this will allow warm CDW to penetrate deeper into the Thwaites Gateway than any current model has evaluated.  This issue is partially illustrated by the following four images:

The first image provides a perspective overview of the 2009 ice elevations in the PIG/Thwaites area & illustrates how strong the gravitational driving force would be to support any cliff failures of the ice in the trough at the base of the Thwaites Ice Tongue.

The second image from Goddard shows the drop in ice surface elevation from 2002 to 2011 for the ASE marine glaciers; which shows at least a 20m drop in elevation at the base of the Thwaites Ice Tongue, which together with the 6m drop in 2012, brings this drop to at least 26m; which increases the propensity for floatation of ice in this area.

The third image from Bassis et al 2013 shows that the ice cliffs (exposed once the icebergs float away) for the ice in the trough would have geometry highly favorable for both cliff failure and floatation.

The fourth image provides an overview of the trough, the offshore pinning points and the general bathymetry for the Thwaites Gateway/Threshold.

If it comes to pass that with the next 10 to 15 years that both: (a) cliff failures occur in the ice at the base of the Thwaites Ice Tongue; and (b) the activation of the SW Tributary glacier (due to probably reductions in buttressing from the PIIS) activates the Thwaites Eastern Shear Margin; then Hansen et al 2015, assumption that main phase marine glacier collapse will begin around 2035 to 2040; may well actually begin in the Byrd Subglacial Basin.
« Last Edit: August 03, 2015, 01:48:36 AM by AbruptSLR »
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #139 on: August 03, 2015, 05:30:49 AM »
For those interested in the following links and information on symposia on: (a) Contemporary Ice-Sheet Dynamics: Ocean interaction, Meltwater and Non-linear effects; and (b) the Twenty-Second Annual WAIS Workshop :


International Symposium on Contemporary Ice-Sheet Dynamics: Ocean interaction, Meltwater and Non-linear effects
Where & When: Cambridge, UK, 16 August 2015 to 21 August 2015

http://www.igsoc.org/symposia/2015/cambridge/
http://www.igsoc.org/symposia/2015/cambridge/draft_cambridge_program(1).pdf

Extractact: "Session 4 Ice sheet modeling
David Pollard: "Large-Ensemble modeling of last deglacial and future variations of the Antarctic Ice Sheet" ,IGSOC ID: 73A1780

Johannes Sutter: "Antarctic Eemian ice sheet-shelf dynamics controlled by sustained ocean warming", IGSOC ID: 73A1873

Frank Pattyn: "Ensemble predictions of future Antarctic mass loss with the FETISH model", 73A1954

Dan Martin: "Response of the Antarctic Ice Sheet to a Warming Ocean Using the POPSICLES Coupled Ice Sheet-Ocean Model", 73A1884"



See also:
http://www.arcus.org/events/arctic-calendar/21235


Twenty-Second Annual WAIS Workshop
September 16-19, 2015
Sylvan Dale Ranch, Loveland, CO, U.S.A.

https://www.waisworkshop.org/workshop-2015


Extract: "This year's meeting is being held back-to-back with two other Antarctic meetings, all at the same venue!
September 19-20: Amundsen / Bellingshausen Coastal Dome Project (contact Nancy Bertler)
September 20-23: 2015 Interdisciplinary Antarctic Earth Science Meeting with Shackleton Camp Planning workshop

Friday afternoon will feature a discussion on future international collaboration on Thwaites Glacier.

Themes for this year are based on Western film titles:
• Cowboys and Aliens --- US - international collaborations
• The Big Valley ---- Thwaites, Pine Island, and the Amundsen Sea Embayment: ice, ocean, and climate interaction.
• Paint Your Wagon --- Traverses, aircraft, and satellite work
• Westworld --- Ice sheet modeling
• The Wild Bunch --- Recent fieldwork in WAIS and related areas
• High Plains Drifter --- Climate, meteorology, and surface mass balance on WAIS and EAIS
• True Grit --- marine sediments, sub-glacial hydrology, and ice-bedrock interaction
• A Fistful of Dollars  --- funding needs and status, including NSF update."

See also:
https://www.waisworkshop.org/bibliography
https://www.waisworkshop.org/wais-science-plan
https://www.waisworkshop.org/
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #140 on: August 03, 2015, 07:59:11 AM »
"While most researchers currently point to the influx of warm CDW to remove the "ice plug" (which can take multiple decades to centuries depending on the particular conditions of any given marine glacier); ..."

No.The plug is not static. it flows. the glen's law exponent will kill ya as the temperature rises. CDW does not only melt, it warms.

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #141 on: August 03, 2015, 08:03:38 AM »
Also, (this is unfair, since Hansen(2015) is yet in review) no model includes the feedback he seems to have found if the insulating meltwater cap

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #142 on: August 03, 2015, 12:30:02 PM »
"While most researchers currently point to the influx of warm CDW to remove the "ice plug" (which can take multiple decades to centuries depending on the particular conditions of any given marine glacier); ..."

No.The plug is not static. it flows. the glen's law exponent will kill ya as the temperature rises. CDW does not only melt, it warms.

I concur that the ice plug is not static; however, the warm CDW does not always flow with the same volume over the continental shelf (in the ASE this volume fluctuates with the ENSO, which is not included in most local models) and the rate of increase of the average temperature of the CDW at the grounding line of Thwaites may be slow (and is not included except as sensitivity cases in most local models).  Thus, cliff failures of the ice in the trough at the base of the Thwaites Ice Tongue may work synergistically with the warm CDW to destabilize the Thwaites Ice Plug faster than most local models (which consider Glenn's Law) project.
« Last Edit: August 03, 2015, 04:19:33 PM by AbruptSLR »
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Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #143 on: August 03, 2015, 02:04:35 PM »

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #144 on: August 03, 2015, 02:09:22 PM »
Just to put some amusing quotes on the permanent record here from Hansen's popular article up on the Huffington Post for a week now. We've heard very similar grievances expressed here over the years:

Did you read any of the recent papers that concluded ice sheets may be disintegrating and might cause large sea level rise in 200-900 years? The time needed for ice sheets to respond to climate change is uncertain, and there are proponents for time scales covering a huge range. However, 200-900 years should cause a scientist to scratch his head. If it is uncertain by an order of magnitude or more, why not 100-1000? Where does the 200-900 precision come from?

Why the peculiar 900 years instead of the logical 1000? Probably because nobody cares about matters 1000 years in the future (they may not care about 900, but 200-900 does not seem like infinity). A scientist knowing that sea level is a problem does not want the reader to dismiss it.

Why 200 years? For one thing, 100 years would require taking on the formidable IPCC, which estimates that even the huge climate forcing for a hypothetical 936 ppm CO2 in 2100 would yield less than one meter sea level rise. For another thing, incentives for scientists strongly favor conservative statements and militate against any "alarmist" conclusion; this is the "reticence" phenomenon that infects the sea level rise issue. "Scientific Reticence and Sea Level Rise" will be the subject of a session at the American Geophysical Union meeting this year.

IPCC conclusions about sea level rise rely substantially on models. Ice sheet models are very sluggish in response to forcings. It is important to recognize a great difference in the status of atmosphere-ocean climate models and ice sheet models. Climate models are based on general circulation models that have a long pedigree. The fundamental equations they solve do a good job of simulating atmosphere and ocean circulations. Uncertainties remain in climate models, such as how well they handle the effect of clouds on climate sensitivity. However, the climate models are extensively tested, and paleoclimate changes confirm their approximate sensitivities.

In contrast, we show in a prior paper and our new paper that ice sheet models are far too sluggish compared with the magnitude and speed of sea level changes in the paleoclimate record. This is not surprising, given the primitive state of ice sheet modeling. For example, a recent ice sheet model sensitivity study finds that incorporating the physical processes of hydrofracturing of ice and ice cliff failure increases their calculated sea level rise from 2 meters to 17 meters and reduces the potential time for West Antarctic collapse to decadal time scales.

Other researchers show that part of the East Antarctic ice sheet sits on bedrock well below sea level. Thus, West Antarctica is not the only potential source of rapid change; part of the East Antarctic ice sheet is also susceptible to rapid retreat because of its direct contact with the ocean and because the bed beneath the ice slopes landward, which makes it less stable.

Our simulations were aimed to test my suspicion that ice sheet disintegration is a very nonlinear phenomena and that the IPCC studies were largely omitting what may be the most important forcing of the ocean: the effect of cold freshwater from melting ice. Rather than use an ice sheet model to estimate rates of freshwater release, we use observations for the present ice melt rate and specify several alternative rates of increase of ice melt. Our atmosphere-ocean model shows that the freshwater spurs amplifying feedbacks that would accelerate ice shelf and ice sheet mass loss, thus providing support for our assumption of a nonlinear ice sheet response.

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #145 on: August 03, 2015, 02:49:32 PM »
The second peer reviewer has still not surfaced.

There is also a new review comment from William Colgan who must have been on the maligned IPCC committee, noting they did in fact gesticulate in the general direction of non-linear SLR in the context of cryo-hydrological warming -- rapid warming of glacier ice temperatures due to the latent heat released by refreezing meltwater, modifying temperature-dependent ice rheology with relatively small increases in ice temperature resulting in relatively large increases in ice deformation and flow.

Note that per se doesn't speak to linear vs non-linear, just to a large proportionality but see http://williamcolgan.net/blog/?p=319 where he notes:

Of the many strange material properties of ice, the non-linear temperature dependence of its viscosity is especially notable; ice at 0 °C deforms almost ten times more than ice at -10 °C at the same stress. This temperature-dependent viscosity makes ice flow very sensitive to ice temperature...  resulting in an ice dynamic drawdown of the ice sheet, causing a 5 ± 2 % ice sheet volume reduction within 500 years. This is equivalent to a global mean sea-level rise contribution of 33 ± 18 cm. Of course, the vast majority of the sea level rise associated with thermal-viscous collapse would occur over subsequent millennia.

Cryo-hydrological warming however is mostly a Greenland story as Antarctica is rather cold for much meltwater production, so this would not get IPCC off the hook. Five cites are provided, including Colgan's own 'Considering thermal-viscous collapse of the Greenland ice sheet' Earth’s Future. 3: 2015doi:10.1002/2015EF000301.

http://www.atmos-chem-phys-discuss.net/15/C5493/2015/acpd-15-C5493-2015.pdf

M Pelto notes doublings of volume loss are easy at first but difficult to sustain as the numbers get larger. Further the situation in Antarctica is quite heterogeneous regionally in physical oceanography and basal topograpny, meaning without introducing particulars, no one triggering mechanism can suffice. Ocean warming is not observed to cause much basal ice melt in some major regions today.

AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #146 on: August 03, 2015, 04:55:15 PM »
Also see Mauri Pelto's comment on Hansen et al:
http://www.atmos-chem-phys-discuss.net/15/C5538/2015/acpd-15-C5538-2015.pdf


Thanks for the link.  Mauri Pelto is a serious researcher and he makes many worthwhile points in his comments on Hansen et al 2015; however, he seems to miss the point that Hansen's rates of doubling are merely rules-of-thumb, and that no one would argue that they are meant to be a precise projection of decade by decade ice response.  Nevertheless, many of Pelto's points are naive as indicated by his summary comment below:

Extract: "The point is that it is not all Antarctic glaciers are behaving the same or will follow the same path of behavior evolution. This will make it quite difficult to sustain a doubling rate as envisioned in this paper. This does not mean that volume losses cannot double from current levels and continue to rise thereafter."

No one is more aware of the various differences (as a whole) between the various Antarctic marine glaciers than Rignot, so having Pelto point this matter out is superfluous.  Furthermore, pointing-out that the volume losses can double from current levels and then can continue to rise thereafter, has almost no relevant meaning at all as he does not make any specific time projections himself, while he feels free to point out this short-coming in others.  Also, much of Hansen's ocean modeling is dependent on freshening of the ocean which includes not only changes in VAF, but also in the melting of already floating glacial ice.  Pelto, would benefit from reviewing the latest findings by Pollard, Applegate, DeConto, Haran and others as cited in the Antarctic folder (with some brief related points summarized in this thread); who have found that assuming the higher RCP scenarios significant increases (measured in meters) in sea level would occur this century due to ice mass loss from Antarctica.
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Csnavywx

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #147 on: August 03, 2015, 06:17:43 PM »
Yeah, I think some folks are kind of missing the point in the comments. I felt like the real question and research that Hansen et al. was trying to provoke was: At what point will this excessive freshwater input become a serious issue?

We don't yet have ice sheet models that can seriously help us with this, so using a simpler assumption (like doubling times) can at least put us in the ballpark.

It's interesting that the model increases sea ice area in response to freshwater injection. We already seem to be doing just that.

AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #148 on: August 03, 2015, 06:59:54 PM »
Yeah, I think some folks are kind of missing the point in the comments. I felt like the real question and research that Hansen et al. was trying to provoke was: At what point will this excessive freshwater input become a serious issue?

We don't yet have ice sheet models that can seriously help us with this, so using a simpler assumption (like doubling times) can at least put us in the ballpark.

It's interesting that the model increases sea ice area in response to freshwater injection. We already seem to be doing just that.


Csnavywx,
I fully agree with you, and as I imagine that many reading this thread do not go to the Antarctic folder, I provide the following two recent abstracts (and the attached figure by Pollard et al of the influence of Pliocene-type conditions on Antarctic contribution to SLR, Edit: I note that if we continue on a BAU pathway we could be at Pliocene-type conditions as early at 2035-2040), showing what current models are beginning to be able to do.  However, that said it would be best if the ACME were to include such recent modeling methodology in their high resolution mesh (mesh resolution is very important in such matters):

David Pollard, Robert DeConto, Won Chang, Patrick Applegate, and Murali Haran (2015), "Large-Ensemble modeling of last deglacial and future variations of the Antarctic Ice Sheet", Geophysical Research Abstracts, Vol. 17, EGU2015-5717, EGU General Assembly 2015


http://meetingorganizer.copernicus.org/EGU2015/EGU2015-5717.pdf

Abstract: "Recent observations of thinning and retreat of the Pine Island and Thwaites Glaciers identify the Amundsen Sea Embayment (ASE) sector of West Antarctica as particularly vulnerable to future climate change. To date, most future modeling of these glaciers has been calibrated using recent and modern observations.

As an alternate approach, we apply a hybrid 3-D ice sheet-shelf model to the last deglacial retreat of Antarctica, making use of geologic data from ~20,000 years BP to present, focusing on the ASE but including other sectors of Antarctica.  Following several recent ice-sheet studies, we use Large-Ensemble statistical techniques, performing sets of ~500 to 1000 runs with varying model parameters.  The model is run for the last 40 kyrs on 10 to 20-km grids, both on continental domains and also on nested domains over West Antarctica. Various types of objective scores for each run are calculated using reconstructed past grounding lines, relative sea level records, measured uplift rates, and cosmogenic elevation-age data. Runs are extended into the future few millennia using RCP scenarios. The goal is to produce calibrated probabilistic ranges of model parameter values and quantified envelopes of future ice retreat.  Preliminary results are presented for Large Ensembles with (i) Latin HyperCube sampling in high-dimensional parameter space, using statistical emulators and Markov Chain Monte Carlo techniques, and (ii) dense "factorial" sampling with a smaller number of parameters. Different ways of combining the types of scores listed above are explored. One robust conclusion is that for the warmer future RCP scenarios, most reasonable parameter combinations produce retreat deep into the West Antarctic interior. Recently proposed mechanisms of hydrofracturing and ice-cliff failure accelerate future West Antarctic retreat, and later produce retreat into East Antarctic basins."

Johannes Sutter, Malte Thoma, Klaus Grosfeld, Paul Gierz, and Gerrit Lohmann (2015), "Learning from the past: Antarctic Eemian ice sheet dynamics as an analogy for future warming", Geophysical Research Abstracts, Vol. 17, EGU2015-13255-2, EGU General Assembly 2015


http://meetingorganizer.copernicus.org/EGU2015/EGU2015-13255-2.pdf


Abstract: "Facing considerable warming during this century the stability of the West Antarctic Ice Sheet is under increasing scrutiny. Recent observations suggest that the marine ice sheet instability of the WAIS has already started. We investigate the dynamic evolution of the Antarctic Ice Sheet during the last interglacial, forcing a state of the art 3D ice sheet model with Eemian boundary conditions. We elucidate the role of ocean warming and surface mass balance on the coupled ice sheet/shelf and grounding line dynamics. Special focus lies on an ice sheet modeling assessment of Antarctica’s potential contribution to global sea level rise during the Eemian. The transient model runs are forced by time slice experiments of a fully coupled atmosphere-ocean global circulation model, as well as different sets of sea level and bedrock reconstructions. The model result show strong evidences for a severe ice-sheet retreat in West Antarctica, leading to substantial contribution to global sea level from the Southern Hemisphere.  Additionally we compare future warming scenarios of West Antarctic Ice Sheet dynamics to our paleo ice sheet modeling studies."
Best,
ASLR
« Last Edit: August 03, 2015, 07:09:55 PM by AbruptSLR »
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #149 on: August 03, 2015, 10:17:54 PM »
I have referred to the abrupt SLR portion of the ACME program in several posts now, and I have recently stated that I hope that the ACME program learns some lessons from the recent findings of researchers such as Pollard, DeConto, Applegate, Sutter and others; because while ACME is developing state-of-the-art software and hardware, their methodology is still essentially a lower bound approach and does not consider ice mass loss mechanisms such as hydrofracturing & cliff failures.  As far as I know ACME's ASLR effort currently uses a combination of CISM-BISICLES (for the ice sheets) and POP2x (for Ocean Circulation); which together they call POPSICLES.

The linked reference used BISICLES (with a relatively high-resolution mesh) to examine "Century-scale simulations of the response of the West Antarctic Ice Sheet to a warming climate" and produced results such as that shown in the three attached images; which compare to the Pollard et al 2015 results when they do not consider a combination of hydrofracturing & cliff failures.  Again, hopefully the ACME program will learn from the recent advance of other researchers:

S. L. Cornford, D. F. Martin, A. J. Payne, E. G. Ng, A. M. Le Brocq, R. M.,  Gladstone, T. L. Edwards, S. R. Shannon, C. Agosta, M. R. van den Broeke, H. H. Hellmer, G. Krinner, S. R. M. Ligtenberg, R. Timmermann, D. G. Vaughan (March 23, 2015) "Century-scale simulations of the response of the West Antarctic Ice Sheet to a warming climate", The Cryosphere Discussions, doi: 10.5194/tcd-9-1887-2015

http://www.the-cryosphere-discuss.net/9/1887/2015/tcd-9-1887-2015.html

Abstract: "We use the BISICLES adaptive mesh ice sheet model to carry out one, two, and three century simulations of the fast-flowing ice streams of the West Antarctic Ice Sheet. Each of the simulations begins with a geometry and velocity close to present day observations, and evolves according to variation in meteoric ice accumulation, ice shelf melting, and mesh resolution. Future changes in accumulation and melt rates range from no change, through anomalies computed by atmosphere and ocean models driven by the E1 and A1B emissions scenarios, to spatially uniform melt rates anomalies that remove most of the ice shelves over a few centuries. We find that variation in the resulting ice dynamics is dominated by the choice of initial conditions, ice shelf melt rate and mesh resolution, although ice accumulation affects the net change in volume above flotation to a similar degree. Given sufficient melt rates, we compute grounding line retreat over hundreds of kilometers in every major ice stream, but the ocean models do not predict such melt rates outside of the Amundsen Sea Embayment until after 2100. Sensitivity to mesh resolution is spurious, and we find that sub-kilometer resolution is needed along most regions of the grounding line to avoid systematic under-estimates of the retreat rate, although resolution requirements are more stringent in some regions – for example the Amundsen Sea Embayment – than others – such as the Möller and Institute ice streams."


See also:
http://crd.lbl.gov/departments/applied-mathematics/ANAG/about/staff/dan-martin/
http://crd.lbl.gov/assets/pubs_presos/Martin-LIWG-2015-final.pdf

P.S: I suspect that in its current state of development that POPSICLES would have a difficult time matching the paleo SLR data for either the late-Eemian or the Pliocene.
« Last Edit: August 03, 2015, 10:25:33 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