Hansen et al paper: 3+ meters SLR by 2100

[Andruin]

Tossed and then eroded?

[AbruptSLR]

Tossed and then eroded?

I would say yes, that "Tossed and then eroded" is the most likely scenario.

[bbr2314]

Question:

The Hansen maps show declines in temperatures surrounding areas affected by the NATL cold pool, with anomalies increasing (in a negative direction) as the Greenland melt accelerates.

Could the lingering Hudson Bay ice and the very cold Quebec this summer also be a result of this, and if the positive feedback continues accelerating, perhaps it's possible that higher elevations of both Scotland and Quebec see re-glaciation over the next few centuries, while Greenland gradually melts out?

[AbruptSLR]

Question:

The Hansen maps show declines in temperatures surrounding areas affected by the NATL cold pool, with anomalies increasing (in a negative direction) as the Greenland melt accelerates.

Could the lingering Hudson Bay ice and the very cold Quebec this summer also be a result of this, and if the positive feedback continues accelerating, perhaps it's possible that higher elevations of both Scotland and Quebec see re-glaciation over the next few centuries, while Greenland gradually melts out?

I believe that the lesson to be learned from Hansen et al. 2015 is that the slow-down of the AMOC will contribute changes in the Jetstream between the Ferrel and the Polar Cells sufficiently to cause blocking weather patterns (such as the RRR) that will generally cause warmer dry patterns on western side of continents (like in Washington, & California and Western Europe) and colder conditions towards the eastern side of continents (like Quebec).  This will result in increased storm activity and behavior like the Polar Vortex that will keep Quebec unusually cold but will not cause glaciation in Quebec if for no other reason than because the effect forecast by Hansen et al. (2015) of increased Planetary Energy Imbalance due to abrupt ice sheet melting, only lasts for about five to ten decades.

[bbr2314]

Question:

The Hansen maps show declines in temperatures surrounding areas affected by the NATL cold pool, with anomalies increasing (in a negative direction) as the Greenland melt accelerates.

Could the lingering Hudson Bay ice and the very cold Quebec this summer also be a result of this, and if the positive feedback continues accelerating, perhaps it's possible that higher elevations of both Scotland and Quebec see re-glaciation over the next few centuries, while Greenland gradually melts out?

I believe that the lesson to be learned from Hansen et al. 2015 is that the slow-down of the AMOC will contribute changes in the Jetstream between the Ferrel and the Polar Cells sufficiently to cause blocking weather patterns (such as the RRR) that will generally cause warmer dry patterns on western side of continents (like in Washington, & California and Western Europe) and colder conditions towards the eastern side of continents (like Quebec).  This will result in increased storm activity and behavior like the Polar Vortex that will keep Quebec unusually cold but will not cause glaciation in Quebec if for no other reason than because the effect forecast by Hansen et al. (2015) of increased Planetary Energy Imbalance due to abrupt ice sheet melting, only lasts for about five to ten decades.

I thought it was only modeled out to a certain point, and the effects would have lasted several hundred years, as they would endure for the duration of Greenland's significant melt (which probably cannot happen in its entirety in under a few centuries tho I could be wrong)

[AbruptSLR]

Hansen et al. (2015) assume relatively rapid ice mass loss from either Greenland, Antarctica or both at rates as slow as having doubling times for ice mass loss of 20-years to 40-years and then they cap the total sea level rise contribution from all sources to 5meters.  If the ice sheet melting occurs very slowly then the AMOC will behavior differently than indicated by Hansen et al.

[bbr2314]

Hansen et al. (2015) assume relatively rapid ice mass loss from either Greenland, Antarctica or both at rates as slow as having doubling times for ice mass loss of 20-years to 40-years and then they cap the total sea level rise contribution from all sources to 5meters.  If the ice sheet melting occurs very slowly then the AMOC will behavior differently than indicated by Hansen et al.

Right, but isn't the total available from both Greenland and Antarctica more like 100 meters of SLR? And wouldn't it continue & accelerate on both until the ice is depleted? Of course one shouldn't make assumptions but you would think that such a continuation of what his models showed in the recent paper would result in extending the resultant anomalies out for several centuries as the melt continues...

[AbruptSLR]

Hansen et al. (2015) assume relatively rapid ice mass loss from either Greenland, Antarctica or both at rates as slow as having doubling times for ice mass loss of 20-years to 40-years and then they cap the total sea level rise contribution from all sources to 5meters.  If the ice sheet melting occurs very slowly then the AMOC will behavior differently than indicated by Hansen et al.

Right, but isn't the total available from both Greenland and Antarctica more like 100 meters of SLR? And wouldn't it continue & accelerate on both until the ice is depleted? Of course one shouldn't make assumptions but you would think that such a continuation of what his models showed in the recent paper would result in extending the resultant anomalies out for several centuries as the melt continues...

I believe that most of the abrupt SLR contribution from ice sheets comes from marine glaciers and surface ice melting of Greenland. As discussed in the following thread, the marine glacier contribution can occur particularly quickly due to calving events (ala cliff failures & hydrofracturing), and one this volume of marine glaciers subject to cliff failures & hydrofracturing is diminished / depleted then one would expect the rate of SLR contribution from ice sheets to slow down.  Apparently, Hansen et al. (2015) believe that this slowdown will occur after about 5m of SLR; and thereafter they would probably propose changing to a different math relationship than say a 10-year doubling time. 

http://forum.arctic-sea-ice.net/index.php/topic,874.0.html

[P-maker]

Andruin & ASLR,

A new and thorough response to Hansen et al.'s interpretation of the parabolic dunes has been posted here:

http://www.atmos-chem-phys-discuss.net/15/C6270/2015/acpd-15-C6270-2015.pdf

I couldn't have done it better myself.

However, their second part about the tumbled boulders is in my view not yet to the point. I may elaborate on this later, when I have more time to collect the evidence. I'm still inclined towards an aeolian origin.

Cheers P

[AbruptSLR]

Andruin & ASLR,

A new and thorough response to Hansen et al.'s interpretation of the parabolic dunes has been posted here:

http://www.atmos-chem-phys-discuss.net/15/C6270/2015/acpd-15-C6270-2015.pdf

I couldn't have done it better myself.

However, their second part about the tumbled boulders is in my view not yet to the point. I may elaborate on this later, when I have more time to collect the evidence. I'm still inclined towards an aeolian origin.

Cheers P

P-maker,

Thank you for the link.  However, as you yourself acknowledge the commentators agree with Hansen et al. (2015) that the boulders were tossed into place as they state:

"In view of the extraordinary transport capacities of infragravity waves observed during Supertyphoon Haiyan (Roeber and Bricker, 2015) or the potential of numerically modelled, locally generated landslide tsunamis (Hasler et al., 2010), further supported by the convex-bankward shape of the bank margin in this area (Mullins and Hine, 1989; Fig. 2), neither storm waves generated in a present day-like climate nor a near-field tsunami, respectively, can be excluded to have dislocated the blocks near Glass Window on Eleuthera."

Please note that the commentators qualify their statement that storm waves generated in a "present day-like climate" could transport the boulders; however, Hansen et al. (2015) believe it likely that during the late Eemian the climate was more violent than today w.r.t. storm activity.  Infragravity waves can do amazing things (like break-off state-sized pieces of ice shelves); so I would say that Hansen et al. (2015) evidence, while not bullet-proof, is sufficiently compelling to require advanced Earth Systems models such as ACME to include the introduction of abrupt ice sheet meltwater scenarios, to check to see whether violent super-storms (with associated infragravity waves) by soon be part of our common future.

Best regards,
ASLR

[AbruptSLR]

In the following linked article & associated videos NASA's Goddard Space Center voices their concern about the rate of ice sheet mass loss:

http://www.nasa.gov/feature/goddard/warming-seas-and-melting-ice-sheets


Edit: See also the following link & associated image (with a recent up-turn in SLR):

http://www.cbsnews.com/news/nasa-sea-level-rise-could-be-worse-than-we-thought/

[AbruptSLR]

Further to my Reply #259 that mentioned that infragravity waves can do amazing things (including lifting multi-ton boulders and triggering ice shelf collapse); and in this regard I provide the following link to an open access pdf of Bromirski et al 2010 showing how transoceanic infragravity waves could travel from the area around the ridiculously resilient ridge do to the Ross Ice Shelf (RIS), to potentially trigger ice berg calving events (see the attached image).  Thus if Hansen et al. (2015) is correct then the increased storm activity initiated say by the collapse of the Amundsen Sea Embayment marine glacier, could create sufficiently large transoceanic infragravity waves to contribute to the early collapse of the RIS (say around 2060-2070) leading to a positive feedback on more West Antarctic ice sheet mass loss, more storms and more SLR:

Bromirski, P. D., O. V. Sergienko, and D. R. MacAyeal (2010), Transoceanic infragravity waves impacting Antarctic ice shelves, Geophys. Res. Lett., 37, L02502, doi:10.1029/2009GL041488.

http://iod.ucsd.edu/~peter/pdfs/Bromirski_etal_GRL_RossIG_2010.pdf

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

In Bromirski, Sergienko and MacAyeal, 2010, it is proposed that the southbound travelling infragravity waves "may be a key mechanical agent that contributes to the production and/or expansion of the pre-existing crevasse fields on ice shelves," and that the infragravity waves also may provide the trigger necessary to initiate the calving collapse process.

[AbruptSLR]

The SkS provides a re-post of an article discussing the Hansen et al. (2015) draft paper:

https://www.skepticalscience.com/how-to-make-sense-of-alarming-sea-level-rise-forecasts.html

[P-maker]

ASLR,

resuming my reflections on the Hansen et al. draft, I will now turn to the problem of the tumbled boulders on Bahamas.

As before, I had to consult my old textbook on the subject: Greeley & Iversen (1985): Wind as a geological process. Pages 118-144 describes various erosional land forms. The boulders on Bahamas are either ventifacts, yardangs or a mixture of the two, if they have an aeolian origin. The boulders - by the way - show a striking similarity with pictures of wind abraded blocks on Mars… (their figures 4.17 and 4.18, although size of blocks on Mars is smaller).

Size does matter, and I do acknowledge the findings after Supertyphoon Haiyan, that “dislocation of extremely large clasts (a-axis up to 9 m) was attributed to long-period infragravity waves” (c.f. Engel et al. 2015).

Dislocation is however not the same as “tossing”. Coastal engineers around the world have guidelines for boulder sizes in breakwaters depending on expected wave climate. You can’t just toss boulders around like that and certainly not more than 20 meters into the air to let them land on their pointed end.

Hansen et al. (in prep.) show in their fig 24 (f) that relative sea level during MIS 5e was at maximum about 15 m higher than today. Thus, the “tossing hypothesis” needs some quantification in order to go down well.

On the other hand, if Engel et al. (2015) are correct, that the contemporary parabolic dunes were deposited by winds at a relative sea level some 2.5-6 m above present, then the boulders would have had to be “tossed” even higher into the air. Giant storm waves or tsunamis able to “dislocate” 10-15 m high boulders should also have destroyed the aeolian deposits as well as deposited a number of other landforms, which have not yet been identified in the area.

Hearty’s (1997) original paper on the giant boulders does contain a number of observations, some of which have later been confirmed by other studies:

1)   Bedding in the boulders is as steep as 30-70 degrees (even up to 85 degrees) (“eolonites”)
2)   Some of the boulders are located on “pedestrals” (“entisols”)
3)   Some of the boulders have pedogenice calcrete and lateritic palaeosols (on the leeward side) attached to the lower parts above the “entisols”.

Hearty (1997) describes Boulder 4 as a “displaced boulder” (his Fig 7c), whereas some of the others are plainly described as  “Boulders”.

And now back to my interpretation:

Ad 1) These calcite blocks may have been formed in situ and exposed by aeolian abrasion/erosion over the years. In order to observe bedding angles above 30-33 degrees today, at least some of these boulders must have tumbled from their original setting.

Ad 2) If the boulders tumbled from a former pedestral onto an already existing entisol (formed during 100-200 years), then  bedding angles may have increased from 30-33 to somewhere between 70 and 85 degrees.

Ad 3) following tumbling, some of the boulders may have acted as obstructions to the wind and sand and soils may have been deposited on the leeward (SW) side of the boulders and new soil profiles may have developed around the boulders during the last 100.000 years.

Since then, similar processes may have exposed the boulders again and formed new pedestrals and re-exposed former entisols under the tumbled boulders.

You see, no need to include neither tsunamis nor giant waves to explain these phenomena.

Cheers P

[AbruptSLR]

ASLR,

resuming my reflections on the Hansen et al. draft, I will now turn to the problem of the tumbled boulders on Bahamas.

...

You see, no need to include neither tsunamis nor giant waves to explain these phenomena.

Cheers P

P-maker,

While I do not find your counter arguments very convincing; I will still reserve judgment until Hansen et al respond to the related comments posted on the ACPD website.

Best,
ASLR

Edit: I will note that no one is talking about the boulder being toss through the air but yourself; as it is clear to ever one except yourself that Hansen et al. 2015 are talking about the boulders being lifted by a long-period wave that has surged up onto the land.  Also, if the boulders were lifted by a wave (or by different waves), when they set-down on land they would likely be seated in other debris deposited by the wave(s), debris which could have been later eroded by wind and rain, leaving a boulder on a point.

[P-maker]

ASLR,

just to make one thing clear:

"I will note that no one is talking about the boulder being toss through the air but yourself;

When I say "into the air", I do not mean "flying boulders", just that these boulders would have had to be lifted vertically 20-30 meters. I will also remind you, that I did not introduce the word "toss" in this thread.

[AbruptSLR]

ASLR,

just to make one thing clear:

"I will note that no one is talking about the boulder being toss through the air but yourself;

When I say "into the air", I do not mean "flying boulders", just that these boulders would have had to be lifted vertically 20-30 meters. I will also remind you, that I did not introduce the word "toss" in this thread.

P-maker,

Thanks for the clarification, & I remind you that I did not introduce the word "tossed" in this thread either, as perhaps "rolled/tumbled" would be more appropriate for a surging infragravity wave action.

Best,
ASLR

[Andruin]

It was Hansen: "The bedding planes are at a variety of angles, as expected for boulders tossed from the ocean."

[Richard Rathbone]

Ad 1) These calcite blocks may have been formed in situ and exposed by aeolian abrasion/erosion over the years. In order to observe bedding angles above 30-33 degrees today, at least some of these boulders must have tumbled from their original setting.

I thought Hansen had quite thoroughly demolished this contention is a response already. Older rock does not form on younger rock.

[AbruptSLR]

J. Nissen has posted a comment at the following link:

http://www.atmos-chem-phys-discuss.net/15/C6300/2015/acpd-15-C6300-2015.pdf

[crandles]

J. Nissen has posted a comment at the following link:

http://www.atmos-chem-phys-discuss.net/15/C6300/2015/acpd-15-C6300-2015.pdf

Of relevance at this blog perhaps:

The trend in Arctic sea ice, established over at least two decades, is for exponential decrease in volume.

and later

Most alarming are the observations of sea ice thickness over thirty years, confirming an
exponential decline in sea ice, which if continued for a few years would lead to the low
ice state.

While PIOMAS volume output may look like exponential volume decline, it also looks like several other forms of decline and therefore the observations neither establish nor confirm the decline to be exponential. At best these comments are badly worded.

While some things being said seem reasonably sensible, many seem outside the scope of a broad ranging paper and I can't think it sensible to extend the scope of Hansen's paper so much further. IMHO, Discussion at ACPD would be better focussed without such comments.

[AbruptSLR]

crandles,

While I agree with your comments in your immediate past post; Hansen et al. chose to use the open review format of the ACPD; so we should expect to deal with some sloppy comments from both sides of this issue.

Best,
ASLR

[crandles]

Yes lots of crazy comments. At least they have 'closed' the crazy thread that is much worse than this short comment (with an implication that comments by Swedan were not scientifically sound).

with the comment policy being

To keep the peer review process efficient and avoid diluting the scientific discussion, only members of the scientific community are invited to post expert comments in the scientific discussion forums of the EGU interactive open access journals. People from outside the scientific community are welcome to read and follow the public review and discussion in the scientific discussion forums, but should pursue further (non-expert) discussions in other more appropriate venues (blogs etc.). Speaking informally: “scientific community” can be broadly defined as scientific researchers with an expert knowledge on the subject of the study under discussion…

they should be in a position to close down such nonsense pretty quickly but I guess high profile papers will attract some.

[sidd]

I have been rereading Pollard (open access) http://dx.doi.org/10.1016/j.epsl.2014.12.035 which is of course referenced in Hansen. This time i read the appendices and the supplementaries with more care, as i think Hansen did, but did not dwell on. i include a graph from Pollard, and some reasons why i think the danger is greater than it shows.

Pollard etal. have attempted to incorporate the Bassis cliff failure mechanism into their ice sheet models.  Note that this effect is almost independent of buttressing. The acknowledge several features which weaken their analysis, which cause me much more misgiving now that i reread.

1) ice cliff fails at 1Km total height from grounding. They put this in as a retreat of the cliff, but cap it at 3Km/yr max, which they admit is conservative: Appendix A:
" ...maximum value of 3 km/yr is conservatively based on observations of ice vs. terminus velocities at Jakobshavn Isbrae (Joughin et al., 2012; up to ∼12 km/yr ) and Crane Glacier’s terminus retreat (Scambos et al., 2011; ∼5 km/yr ) following recent disintegrations of their ice shelves; the sensitivity of results to other values is examined in Supplementary Material Section S.7."

Supplementary S.7 examines increasing the rate to 5Km/yr. I fear it will be much worse.

2)Supplementary S.2.1:
"The numerical treatment makes an implicit choice representing real physics: whether normal dynamical flux and small-scale calving events continue at high frequency between large discrete cliff-failure events, as observed at the Jakobshavn grounding line today (Amundson et al., 2010), or whether cliff failure essentially shuts down the normal processes. The latter assumption is more conservative (less total ice is lost), and is made in the current model."

so i wonder what the model does when you put in what we see on Jacobshawn.

3) A cautionary note in the S2.1 at the end is that they do not really put this in as a boundary condition, so in a sense the the treatment is phenomenological and not rigorous:

" ... physical ice-removal processes, applied in the vertically averaged ice-thickness advection equation  ... in principle they would enter as boundary conditions in the derivation of that equation from 3-D primitive equations ..."

This bothers me, i think someone like Schoof should do this correctly. It might be very important.

4)"As mentioned above, the mode of cliff failure may have no analog today, and for subaerial cliffs, may involve explosive expelling of fractured ice near the water line (the approximate location of maximum imbalance in hydrostatic stress), with associated avalanching of ice from above and violent flotation of ice below, so that cuboid bergs do not occur."

didnt we just see some explosive expulsion into Disko Bay ?

5) S.2.3:

"However, it is sobering to note that observed oceanic melt rates of some modern tidewater glacier fronts in Greenland are on the order of 3 m/day (Rignot et al., 2010), which would be sufficient to overcome the dynamical supply of ice flowing across ~1 km deep grounding lines (100’s to ~1000 m/yr) Furthermore, on smaller scales at least, the actual wastage rate into the ice face may be up to ten times the oceanic melt rate (O’Leary and Christoffersen, 2013; Bartholomaus et al., 2013; cf. Cook S. et al., 2013)."
 
that factor of 10 is disconcerting. I have been basing some of my calculation on the magnitude of heat flux delivered by ocean to glacier face.

So the graph i attach might be too optimistic. I suspect what Thwaites will do once grounding line hits the km+ deep holes will dwarf Jacobshawn, in speed and fury.


sidd

[AbruptSLR]

sidd,

Your last post has inspired  me to conceptualize that rather than watching helplessly as armadas of icebergs come pouring out of the Amundsen Sea Embayment, ASE, into the Southern Ocean (possibly beginning as early as around 2030 - 2040), we could use vessels to nudge such icebergs out of the Antarctic Circumpolar Current, ACC, to move north along either the West and/or East Coast of South America.  Once deflected, and depending on the local winds and currently (see the two attached nullschool map for Sept 2015 for surface winds and surface ocean currents, respectively), these icebergs would slowly float northward towards the Eastern Tropical Pacific and/or the Western Tropical Atlantic (possibly assisted by towing if needed).  This form of geoengineering would:

(a) Reduce the high latitude thermal gradient projected by Hansen et al. (2015) to produce super storms;

(b) Cool the Tropical Pacific and Atlantic Ocean areas thus further reducing the thermal gradient and possibly reducing ECS positive feedback associated with the projected increase in the elevation of tropical ocean cloud cover;

(c) Possible introduce iron from the icebergs into the waters along the routes of the icebergs, which might promote plankton growth.

The first related link leads to a discussion of one plan to tow icebergs for freshwater supply; which has proven to date to be uneconomical compared to desalination:

http://www.3ds.com/icedream/

The second lined article indicates that iceberg wrangling is an annual event offshore of Newfoundland, and Eastern Canada:

http://www.cbc.ca/news/canada/nova-scotia/iceberg-wrangled-in-north-atlantic-by-atlantic-towing-crew-1.3065018

Best regards,
ASLR

Edit: The third and fourth attached images show that icebergs from the Southern Ocean could also be deflected to float northward along the western coast of Australia (plus possibly fresh water to Perth); where they could provide the benefits to the Tropical Indian Ocean that I previously cited for both the Tropical Pacific & Atlantic Oceans.

[sidd]

Re: Nudging icebergs

1) considering the size of these bergs, i doubt that this can be done
2)the southern ocean is home to some of the most furious weather on earth. I pity the tugboat captains who dare brave those seas with an iceberg attached.
3)I recall some discussion, possibly on the gcaptain fora, on the feasibility of towing bergs from the south for freshwater supply; the consensus then seemed to be in the negative.

[AbruptSLR]

Re: Nudging icebergs

1) considering the size of these bergs, i doubt that this can be done
2)the southern ocean is home to some of the most furious weather on earth. I pity the tugboat captains who dare brave those seas with an iceberg attached.
3)I recall some discussion, possibly on the gcaptain fora, on the feasibility of towing bergs from the south for freshwater supply; the consensus then seemed to be in the negative.

When I was college I wrote a paper on towing Antarctic icebergs for water supply to Southwestern Australia, & I found that there were no technical problems, only economic challenges.  Fortunately, icebergs from cliff failure mechanisms from the ASE would be much smaller than large tabular icebergs from major ice shelf calving events, and such smaller icebergs could even be roped together to form trains for ease of towing.  Furthermore, nudging such icebergs out of the ACC and into an adjoining northbound  current; would be hundreds of times more practicable than previously evaluated water harvesting schemes.

In any event, we have until about 2030 before we need to take any action, and such a plan need only be considered as a last ditch effort if all of our other efforts come-up short.




To see what NOAA thinks about towing Antarctic icebergs go to the following link:
http://oceanexplorer.noaa.gov/edu/learning/player/lesson12/l12la1.html

[AbruptSLR]

If Hansen et al. 2015 is correct, then the following linked article (& associated image) shows that a lot of tons of methane could be released over some unknown timeframe:

http://news.nationalgeographic.com/news/2012/08/120831-antarctica-methane-global-warming-science-environment/

Extract: "Deep stacks of sediment would have accumulated in those marine basins, as they do in coastal water today. Inevitably, methane-producing microbes would have been hard at work in that mud, digesting the organic matter—around 21 trillion tons of it, the researchers estimate. The microbes are still at it."

[sidd]

1)i submit towing enuf iceberg to satisfy freshwater needs for a ciry is trivial compared to towing enuf to ameliorate  a Petatonne a year coming outtta thwaites
2)there are people who have sailed those waters on this forum, so i will leave it to them to extend the feasibility discussion. perhaps a different thread.

sidd

[bligh8]

I thought the Hansen paper was most illuminating and did generate a lot of reasonable conversation.  But to your point…Towing an Ice Berg out of the Southern Oceans is not going to happen ever.   

 http://www.theatlantic.com/technology/archive/2011/08/the-many-failures-and-few-successes-of-zany-iceberg-towing-schemes/243364/


w

[AbruptSLR]

sidd/bligh8,

Let's take this discuss to the following new thread entitled "Possible Iceberg Wrangling in the Southern Ocean" in the "Policy and solutions" folder:

http://forum.arctic-sea-ice.net/index.php/topic,1389.0.html

Best,
ASLR

[Lennart van der Linde]

Two new papers that seem relevant to Hansen et al:
http://www.washingtonpost.com/news/energy-environment/wp/2015/09/07/new-studies-deepen-concerns-about-a-climate-change-wild-card/

[Lennart van der Linde]

Jason Box posted a short comment on Hansen et al:
http://www.atmos-chem-phys-discuss.net/15/C6715/2015/acpd-15-C6715-2015.pdf

His main point: Hansen et al may underestimate the potential non-linear response of GIS.

[crandles]

Jason Box posted a short comment on Hansen et al:
http://www.atmos-chem-phys-discuss.net/15/C6715/2015/acpd-15-C6715-2015.pdf

His main point: Hansen et al may underestimate the potential non-linear response of GIS.

Surely he is just querying a sentence saying
"“rapid nonlinear growth of ice melt is not likely."
and suggesting it is a little dubious.

The full sentence being queried is

Multiple submarine valleys make much of the Greenland ice sheet vulnerable to
thermal forcing by a warming ocean (Morlighem et al., 2014), but with a few exceptions
(Khan et al., 2014) the valleys are prograde and thus rapid nonlinear growth of ice melt
is not likely.

Perhaps that is the same as saying 'Hansen et al may underestimate the potential non-linear response of GIS" but my reaction is that would seem to require a lot more effort to understand whether what Hansen is putting in for estimates for Greenland is adequate or not. That doesn't seem to be present in Box's comment.

Maybe I am being too pedantic.
(Edit: 'rapid nonlinear growth' is going to be faster than linear but this doesn't mean it is going to be faster than exponential that Hansen seems to assume with 10 20 and 40 year doubling times. However maybe there is more detail than this so that Hansen assumes much less from Greenland than from Antarctica which would make comparison difficult. Anyway, I think it best to avoid suggestion that Box is saying response is going to be worse than 10 20 or 40 year doubling times, he isn't saying that. He is just saying that sentence saying 'rapid nonlinear growth of ice melt is not likely' needs further consideration.)

[sidd]

I read the Box comment as follows: that Hansen's reliance on the relative absence of retrograde glacier beds in Greenland to forestall large mass waste there is not supported by recent data showing that surface ablation now dominates mass waste in Greenland. Greenland will now waste mass from the surface faster than the sea melts it at the fringes.

[AbruptSLR]

As the Box comment refers to his Huffington Post interview, I provide the following extract that indicates that Box is concerned that ice sheet models under estimate ice mass losses from both surface melting and from marine terminating glaciers in Greenland:

http://www.huffingtonpost.com/jason-e-box/ice-melt-fast_b_7927186.html

Extract: "Despite decades of progress by many clever scientists engaged with climate modeling, climate models used to inform policymakers don't yet encode key pieces of physics that have ice melting so fast. They don't incorporate thermal collapse -- ice softening due to increasing meltwater infiltration.

Climate models also don't yet incorporate increasing forced ocean convection at the ocean fronts of glaciers that forces a heat exchange between warming water and ice at the grounding lines.

Climate models don't yet include ice algae growth that darkens the bare ice surface.

Climate models don't yet prescribe background dark bare ice from outcropping dust on Greenland from the dusty last ice age.

Climate models don't include increasing wildfire delivering more light-trapping dark particles to bright snow covered areas, yielding earlier melt onset and more intense summer melting.

As a result of some of these factors and probably some as yet unknown others, climate models have under-predicted the loss rate of snow on land by a factor of four and the loss of sea ice by a factor of two.

Climate models also don't yet sufficiently resolve extended periods of lazy north-south extended jet streams that produce the kind of sunny summers over Greenland (2007-2012 and 2015) that resulted in melting that our models didn't foresee happening until 2100.

While individual climate models come close to observations on this or that piece of the complex big picture, what ends up in global assessment reports intended to help guide policy decisions and national discussions of climate change are very conservative averages of dozens of models that don't include the latest, higher sensitivity physics."

[AbruptSLR]

The linked article about research by Stephen Rintoul provide more details of the risks, including those of:
(a) Advection of warm CDW to the grounding line of Totten Glacier thus accelerating ice mass loss [thus increasing the risk of abrupt SLR this century as indicated by Hansen et al. 2015];
(b) increased rainfall over the Southern Ocean is contributing to the freshening of the surface water which is contributing to the associated positive feedback mechanism identified by Hansen et al. (2015); and
(c) that the slowdown in the formation of the AABW is contributing to a warming of the CDW; which also contributes to the positive feedback mechanism identified by Hansen et al. (2015)

http://m.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=11512463

Extract: "CSIRO physical oceanographer and climate scientist Dr Stephen Rintoul, who was onboard the Australian icebreaker research ship Aurora Australis when it managed to reach the remote glacier, said the region that the Totten drains holds enough ice to produce an equivalent 3.9 metres of global sea level rise - about half the amount that could come from the Greenland ice sheet in the Northern Hemisphere.
"There was good evidence from other places in Antarctica that the ocean was responsible for the thinning of glaciers, like the Pine Island glacier in West Antarctica, but we couldn't say why the Totten was thinning because no one had been there before," said Dr Rintoul …

…

"What we found was, sure enough, there was warm water reaching the glacier - and that really goes counter to what we'd long thought.
"While the ice sheet in West Antarctica has grown and shrunk over time, East Antarctica, we'd always thought, was pretty stable and unlikely to make much of a contribution to sea level rise.
"Our observations, along with new geological evidence that East Antarctica contributed to sea level rise in the past, suggest that we need to reassess that assumption, and realise that East Antarctica may play a bigger role in future sea level rise than we thought."
While the West Antarctic Ice Sheet would respond more quickly to climate change, Dr Rintoul said the new evidence warranted shifting more of the scientific focus to the east.
The first direct evidence that ocean heat was able to erode the ice shelf in the east added to evidence that East Antarctica was more dynamic than we understood.
"For example, if we go back to the last time in Earth's history when atmospheric CO2 was as high as it is today - which was about three million years ago - the sea level during that climate was about 20 metres higher than it is today.
"Twenty metres is an important number because it means even if we melted all of the ice on Greenland at that time, along with all of the ice in West Antarctica, that's still not enough to give 20 metres of sea level rise.
"The only other place that ice could have melted is East Antarctica."
While that climate period, called the Pliocene, was not a perfect analogue for what might happen in the future, it did tell us that East Antarctica wasn't just a big chunk of ice that sat at the bottom of the globe and didn't change over time.

…

…if climate change caused the ocean to take up less heat, and less carbon dioxide, that would tend to speed up the rate of climate change."
Presently, data collected from ships and ARGO floats - torpedo-like instruments deployed around the globe - showed that the Southern Ocean was taking up much of the heat, and that its waters were "freshening", or becoming less saline.
"The freshening is important because ocean waters get fresher either because there's more rainfall than evaporation, or if it's from melting ice - in the Southern Ocean, both of those things are happening."
Another focus of Dr Rintoul's lecture were important changes in the very deepest part of the ocean - particularly around Antarctica.
"What we've found there is the waters that sink around the edge of Antarctica and fill the bottom of the ocean are not being formed at the same rate as they used to - those waters are becoming lighter, and the dense layers are contracting.
"If we look in the bottom of the ocean, the layer of dense water that used to be about 1000 metres thick in the mid-1990s is only about half that thick today.
"Those changes in the deepest part of the oceans are reflecting changes in the climate around the edge of Antarctica, and the melt of glaciers is probably contributing to those changes.""

[AbruptSLR]

The linked reference finds that considering only hosing from the PIG collapse is sufficient to alter climate model projections for such matters as: CDW temperatures, surface water temperatures, Southern Ocean sea ice extent, and AMOC activity.  This work clearly substantiates the Hansen et al. 2015 findings, and also indicates how sensitive climate response is to different input combinations:

J.A.M. Green and A. Schmittner (2015), "Climatic consequences of a Pine Island Glacier collapse", Journal of Climate; doi: http://dx.doi.org/10.1175/JCLI-D-15-0110.1


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0110.1


Abstract: "An intermediate complexity climate model is used to simulate the impact of an accelerated Pine Island Glacier mass loss on the large-scale ocean circulation and climate. Simulations are performed for pre-industrial conditions using hosing levels consistent with present day observation of 3,000 m3 s-1, at an accelerated rate of 6,000 m3 s-1, and at a total collapse rate of 100,000 m3 s-1, and in all experiments the hosing lasted 100 years. It is shown that even a modest input of meltwater from the glacier can introduce an initial cooling over the upper part of the Southern Ocean due to increased stratification and ice cover leading to a reduced upward heat flux from Circumpolar Deep Water. This causes global ocean heat content to increase and global surface air temperatures to decrease. The Atlantic Meridional Overturning Circulation (AMOC) increases, presumably due to changes in the density difference between Antarctic Intermediate Water and North Atlantic Deep Water. Simulations with a simultaneous hosing and increases of atmospheric CO2 concentrations show smaller effects of the hosing on global surface air temperature and ocean heat content, which we attribute to the melting of Southern Ocean sea ice. The sensitivity of the AMOC to the hosing is also reduced as the warming by the atmosphere completely dominates the perturbations."

[AbruptSLR]

The WAIS contains approximately 2.2 million km3 of grounded ice, and Bamber et al. 2009 have estimated that 3.3 meters of equivalent SLR of the total 4.8 meters of equivalent SLR contribution, is susceptible to accelerated collapse from ocean forcing.  Thus following a 10-year double rate of SLR contribution we could assume that 2.2 million x 3.3/4.8 = 1.5 million km³ of ice by 2100 that may be susceptible to cliff failure and hydrofracturing ala Pollard et al. (2015).  Further, if we assume that 5% of this volume is in the form of methane hydrates, this implies that 75,000 km³ of methane hydrates could be susceptible to rapid decomposition from about 2040 to 2100, or a possible average rate of 1,250 km³ per year.  If this hydrate contains about 150 cu meter of gas per cu meter of hydrate, then this could mean a release of 187,500 billion cu meters of methane per year.  This is an enormous number, which, if approximately correct, could explain paleo-evidence tying past events where a WAIS collapse was followed by a period of subsequent rapid warming.  This does not speak well for our future if Hansen et al. (2015) is correct, and an armada of Antarctic icebergs contribute to an abrupt rate of SLR this century.

[Richard Rathbone]

The WAIS contains approximately 2.2 million km3 of grounded ice, and Bamber et al. 2009 have estimated that 3.3 meters of equivalent SLR of the total 4.8 meters of equivalent SLR contribution, is susceptible to accelerated collapse from ocean forcing.  Thus following a 10-year double rate of SLR contribution we could assume that 2.2 million x 3.3/4.8 = 1.5 million km³ of ice by 2100 that may be susceptible to cliff failure and hydrofracturing ala Pollard et al. (2015).  Further, if we assume that 5% of this volume is in the form of methane hydrates, this implies that 75,000 km³ of methane hydrates could be susceptible to rapid decomposition from about 2040 to 2100, or a possible average rate of 1,250 km³ per year.  If this hydrate contains about 150 cu meter of gas per cu meter of hydrate, then this could mean a release of 187,500 billion cu meters of methane per year.  This is an enormous number, which, if approximately correct, could explain paleo-evidence tying past events where a WAIS collapse was followed by a period of subsequent rapid warming.  This does not speak well for our future if Hansen et al. (2015) is correct, and an armada of Antarctic icebergs contribute to an abrupt rate of SLR this century.

It doesn't look like a large number spread out over the globe. 2e11 / 5e14 = 4e-4 m thickness. Atmospheric thickness is about 1e4 m so thats 4e-8 concentration compared to around 2e-6 today. It would have a measurable effect on atmospheric concentration while it lasted, but thats all. Even sustained indefinitely, it only puts global concentration up by a factor of 1.2

[AbruptSLR]

The WAIS contains approximately 2.2 million km3 of grounded ice, and Bamber et al. 2009 have estimated that 3.3 meters of equivalent SLR of the total 4.8 meters of equivalent SLR contribution, is susceptible to accelerated collapse from ocean forcing.  Thus following a 10-year double rate of SLR contribution we could assume that 2.2 million x 3.3/4.8 = 1.5 million km³ of ice by 2100 that may be susceptible to cliff failure and hydrofracturing ala Pollard et al. (2015).  Further, if we assume that 5% of this volume is in the form of methane hydrates, this implies that 75,000 km³ of methane hydrates could be susceptible to rapid decomposition from about 2040 to 2100, or a possible average rate of 1,250 km³ per year.  If this hydrate contains about 150 cu meter of gas per cu meter of hydrate, then this could mean a release of 187,500 billion cu meters of methane per year.  This is an enormous number, which, if approximately correct, could explain paleo-evidence tying past events where a WAIS collapse was followed by a period of subsequent rapid warming.  This does not speak well for our future if Hansen et al. (2015) is correct, and an armada of Antarctic icebergs contribute to an abrupt rate of SLR this century.

It doesn't look like a large number spread out over the globe. 2e11 / 5e14 = 4e-4 m thickness. Atmospheric thickness is about 1e4 m so thats 4e-8 concentration compared to around 2e-6 today. It would have a measurable effect on atmospheric concentration while it lasted, but thats all. Even sustained indefinitely, it only puts global concentration up by a factor of 1.2

Richard,
Unless I am making a math error, then 187,500 billion cu meters of methane per year times 0.66 kg/m³ (density of methane) = 123,750 Tg/year; which according to the linked GISS/NASA site is about 250 times the current anthropogenic methane emission rate. 
I would say that this is an enormous average emission rate; and if combined with other possible natural accelerated methane emissions that are currently being ignored by AR5 (such as Arctic permafrost and Arctic marine hydrates) then such emission rates could readily increase the hundred-year GWP for methane from 35 closer to 50 by 2100.
Best,
ASLR


http://icp.giss.nasa.gov/education/methane/intro/cycle.html

Extract: "Researchers have estimated that natural methane sources totaled about ~180-380 Tg (1012 g) methane per year (Chappellaz et al., 1993). Wetlands were the dominant source with small contributions from wild fires, animals and oceans.
Since methane is chemically as well as radiatively active, atmospheric concentrations can increase because the terrestrial sources are increasing and/or because the sinks are declining. An important atmospheric sink for methane is the OH (hydroxyl) radical. The reaction of methane with OH radicals is the first step in a series of reactions which eventually leads to compounds that are readily removed from the atmosphere by precipitation or uptake at the surface. OH radicals also act as a chemical sink for other trace gases. For this reason, OH radicals are known as "the detergent of the atmosphere" (Crutzen, 1995).
During the last two hundred years, atmospheric methane concentrations have more than doubled to ~1800 ppbv and are still increasing. During the same period, the total annual emission of methane has increased to ~450-500 Tg (see Table above), about two times what it was during the pre-industrial period when natural sources dominated. Most of this increase in sources is due to the anthropogenic perturbation to the methane cycle, though climate variations may also contribute to changes in emission from wetlands and from wildfires."

[AbruptSLR]

My estimates that methane from abrupt calving of WAIS marine glaciers could be a major source methane emissions from the relatively rapid decomposition of methane hydrates from the bottom of such marine glaciers, assumes that hydrofracturing and cliff failures result in small enough icebergs that they flip either 90 or 180 degrees so that the hydrates are exposed to warm surface waters and/or to the atmosphere. And to appreciate the potential size of these possible methane emissions I provide the attached image showing that the methane emissions assumed in RCP 8.5 are at least 100 times lower than this possible WAIS contribution.


Furthermore, to support my claim that such potentially high WAIS methane emission rates could increase the hundred-year GWP of atmospheric methane by 2100 to about 50, see the following Isaksen et al. (2011) reference:

Isaksen, I. S. A., M. Gauss, G. Myhre, K. M. Walter Anthony, and C. Ruppel (2011), "Strong atmospheric chemistry feedback to climate warming from Arctic methane emissions", Global Biogeochem. Cycles, 25, GB2002, doi:10.1029/2010GB003845.

[Richard Rathbone]

ASLR,

I misread your 2e14 as 2e11. I agree 2e14 is a large number in this context.

[AbruptSLR]

ASLR,

I misread your 2e14 as 2e11. I agree 2e14 is a large number in this context.

Richard,
Per the following linked reference the entire WAIS contains tens of billions of tonnes of carbon in the form of methane hydrates (see also the attached figure).  Still, even if my estimates are off by a factor of ten, we are still talking about 25 time current anthropogenic methane emissions, so I think that scientists should take this matter seriously (and not like a grey swan).

J. L. Wadham, S. Arndt, S. Tulaczyk, M. Stibal, M. Tranter, J. Telling, G. P. Lis, E. Lawson, A. Ridgwell, A. Dubnick, M. J. Sharp, A. M. Anesio & C. E. H. Butler (30 August 2012), "Potential methane reservoirs beneath Antarctica", Nature, Volume: 488, Pages: 633–637, doi:10.1038/nature11374


http://www.nature.com/nature/journal/v488/n7413/full/nature11374.html


Abstract: "Once thought to be devoid of life, the ice-covered parts of Antarctica are now known to be a reservoir of metabolically active microbial cells and organic carbon. The potential for methanogenic archaea to support the degradation of organic carbon to methane beneath the ice, however, has not yet been evaluated. Large sedimentary basins containing marine sequences up to 14 kilometres thick and an estimated 21,000 petagrams (1 Pg equals 1015 g) of organic carbon are buried beneath the Antarctic Ice Sheet. No data exist for rates of methanogenesis in sub-Antarctic marine sediments. Here we present experimental data from other subglacial environments that demonstrate the potential for overridden organic matter beneath glacial systems to produce methane. We also numerically simulate the accumulation of methane in Antarctic sedimentary basins using an established one-dimensional hydrate model3 and show that pressure/temperature conditions favour methane hydrate formation down to sediment depths of about 300 metres in West Antarctica and 700 metres in East Antarctica. Our results demonstrate the potential for methane hydrate accumulation in Antarctic sedimentary basins, where the total inventory depends on rates of organic carbon degradation and conditions at the ice-sheet bed. We calculate that the sub-Antarctic hydrate inventory could be of the same order of magnitude as that of recent estimates made for Arctic permafrost. Our findings suggest that the Antarctic Ice Sheet may be a neglected but important component of the global methane budget, with the potential to act as a positive feedback on climate warming during ice-sheet wastage."


See also:
http://news.nationalgeographic.com/news/2012/08/120831-antarctica-methane-global-warming-science-environment/

Best,
ASLR

[AbruptSLR]

The following linked reference provides new findings from the WAIS Divide and the EDML ice cores, Antarctica, and indicates that the atmospheric methane record in Antarctica is much different than that for Greenland, indicating a local source of methane, including during Meltwater Pulse 1a, when the collapse of Antarctic marine glaciers could have resulted in local Antarctic methane emissions from associated icebergs:

Winstrup, M., Vinther, B.M., Sigl, M., McConnell, J., Svensson, A.M. and Wegner, A. (2014)
Development and comparison of layer-counted chronologies from the WAIS Divide and EDML ice cores, Antarctica, over the last glacial transition (10-15 ka BP)
EGU General Assembly 2014, held 27 April - 02 May 2014 in Vienna, Austria, id. EGU2014-12193-1

http://waisdivide.unh.edu/Publications/DisplayArticle.shtml?REF_ID=1365

[AbruptSLR]

In prior posts in this tread I have shown that if the WAIS were to undergo main phase collapse between 2040 and 2100, that it is conceivable that associated methane hydrate decomposition from the armada of icebergs from such a collapse (such as occurred during Meltwater Pulse 1a) might contribute to an associated pulse of natural methane emissions with annual emission rates from 250 to 25 time current annual anthropogenic methane emission rates.  Also, I should that the WAIS divide ice cores show that during Meltwater Pulse 1a that the atmospheric methane over Antarctica did not come from the NH; which raises the possibility that much of this methane could have come from methane hydrates associated marine glaciers that collapsed around Antarctica during Meltwater Pulse 1a.
Now, I take a larger paleo-overview to elaborate (see related earlier posts in this thread) on why it is also possible that paleo-evidence from MIS 11c (the Holsteinian Peak), may ) also support the idea that methane emission pulses from hydrates may have occurred during earlier interglacial WAIS collapse events (I focus on MIS 11c here, while Hansen et al. (2015) considered the WAIS collapse during MIS 5e).

In many ways I feel that the MIS 11c is more relevant to our current/modern climate change risks for reasons including:
- MIS 11c occurred after a long period of relatively warm climatic conditions such as we have experienced to date during the Holocene.
- MIS 11c had comparable atmospheric greenhouse gas concentrations (considering only the period before the beginning of the Industrial Revolution, i.e. 1800 AD ca.),
- MIS 11c shows the highest-amplitude response to forcing for deglacial warming in the last 5 Myr,
- The period prior to MIS 11c, although cooler than the Holocene, is characterized by overall warm sea-surface temperatures in high latitudes, strong thermohaline circulation, unusual blooms of calcareous plankton in high latitudes, higher sea level than the present, coral reef expansion resulting in enlarged accumulation of neritic carbonates, and overall poor pelagic carbonate preservation and strong dissolution in certain areas. 
- Considering the variability in the astronomically-driven insolation, MIS 11 is the interval in which insolation is highly correlated with predicted near future situation.

Unlike most other interglacials of the late Quaternary, MIS 11 still cannot be explained and modeled solely within the context of Milankovitch forcing mechanisms; which, indicates that some as yet unacknowledged additional positive feedback mechanism (such as rapid methane emission rates from WAIS methane hydrate decomposition) remains to be added to climate models (hopefully such as ACME).

Next I provide the following Berger (2013) reference that shows the Milankovitch Sensitivity, MS, during the Quaternary increased after the Brunhes transition (see the first attached image, which is Berger's Figure 3), which characterizes MS by the oxygen isotope record.  Berger indicates that the high MS after the Brunhes transition is associated with system state conditions (such as the build-up of large Antarctic ice sheet mass), rather than directly to ECS or ESS.  Furthermore, the second attached image shows that the oxygen isotope index (in standard deviations) during MIS 11c was as high as what occurred leading to the Holocene; which the third attached image (Berger's Figures 1 & 2) show that the rate of change of the oxygen isotope record can be read as meters of sea-level change per decade.

Berger, W. H.: On the Milankovitch sensitivity of the Quaternary deep-sea record, Clim. Past, 9, 2003-2011, doi:10.5194/cp-9-2003-2013, 2013.

http://www.clim-past.net/9/2003/2013/cp-9-2003-2013.html

Abstract. The response of the climate system to external forcing (that is, global warming) has become an item of prime interest, especially with respect to the rate of melting of land-based ice masses. The deep-sea record of ice-age climate change has been useful in assessing the sensitivity of the climate system to a different type of forcing; that is, to orbital forcing, which is well known for the last several million years. The expectation is that the response to one type of forcing will yield information about the likely response to other types of forcing. When comparing response and orbital forcing, one finds that sensitivity to this type of forcing varies greatly through time, evidently in dependence on the state of the system and the associated readiness of the system for change. The changing stability of ice masses is here presumed to be the chief underlying cause for the changing state of the system. A buildup of vulnerable ice masses within the latest Tertiary, when going into the ice ages, is thus here conjectured to cause a stepwise increase of climate variability since the early Pliocene.


Extract: "Traditionally, the assessment of MS relies on globally relevant proxy records thought to be Milankovitch driven, commonly the oxygen isotope record of either benthic or planktonic foraminifers. Remarkably, the difference between the two types of proxy records is not important in the context (Fig. 4). This suggests that both records reflect the dominant parameter of climate change (ice mass) or else that other parameters that matter (such as local temperature) are highly correlated to the primary one (that is, to ice mass).

…

Trends of increasing variability in climate response, when moving into the Quaternary, at the end of the late Tertiary, suggest that the buildup of large polar ice masses was responsible for the increased sensitivity of the system to disturbance, in agreement with the theory formulated by Milankovitch (1930). As the amplitudes of change became larger, the carbon cycle became increasingly involved as one element in the climatic variations.


Next, I provide the following Holden et al. (2011) reference entitled: "The Mid-Brunhes Event and West Antarctic ice sheet stability" (see the fourth attached image and the associated caption below).  This reference shows that:
- Due to erosion that stability of the WAIS has been decreasing for the past 800 ka.
- Positive feedback from the collapse of the WAIS during MIS 11c contributed to the exceptionally high MS documented during this period.

Holden, P. B.; Edwards, N. R.; Wolff, E. W.; Valdes, P. J. and Singarayer, J. S. (2011), "The Mid-Brunhes Event and West Antarctic ice sheet stability", Journal of Quaternary Science, 26(5) pp. 474–477.

http://oro.open.ac.uk/28967/2/Mid_brunhes_event.pdf

Abstract: "The complex cyclical nature of Pleistocene climate, driven by the evolving orbital configuration of the Earth, is well known but not well understood. A major climatic transition took place at the Mid-Brunhes Event (MBE), ~430 ka BP after which the amplitude of the ~100 ka climate oscillations increased, with substantially warmer interglacials, including periods warmer than the present. Recent modelling has indicated that whilst the timing of these Warmer-than-Present-Transient (WPT) events is consistent with southern warming due to a deglaciation-forced slowdown of Atlantic Meridional Overturning Circulation, the magnitude of warming requires a local amplification, for which a candidate is the feedback of significant West Antarctic Ice Sheet (WAIS) retreat. We here extend this argument, based on the absence of WPTs in the early ice-core record (450 to 800 ka BP), to hypothesise that the MBE could be a manifestation of decreased WAIS stability, triggered by ongoing subglacial erosion."

Extract: "Snapshot simulations with HadCM3 demonstrated that the magnitude of post-MBE interglacial warming is reproduced under the assumption of significant WAIS retreat with precipitation-weighted East Antarctic temperatures ~5ºC above pre-industrial (Holden et al 2010). This warming signal arises from the combined effects of reduced West Antarctic albedo and seasonal biasing by increased East Antarctic summer precipitation. The climate simulations are therefore consistent with the possibility that repeated WAIS retreat occurred in recent interglacials. We here suggest the possibility that the MBE may have been a manifestation of decreased WAIS stability.
…

A possible explanation for progressively decreasing WAIS stability relates to ongoing erosion. The modern WAIS bedrock profile is primarily a consequence of subglacial erosion (Anderson 1999). Ice streams are today responsible for more than 90% of the discharge of Antarctic ice and are potentially key to WAIS stability (Bennett 2003).

…

In summary, several lines of both observational and modelling evidence indicate that the warmth during the early stages of the last three interglacials was driven by the bipolar seesaw during terminations. Recent modelling suggested that a feedback associated with significant WAIS retreat would supply the observed magnitude of Antarctic warming. However, prior to the MBE, Antarctic interglacial temperatures are readily simulated under the assumption of the modern Antarctic ice sheet configuration, requiring no additional amplification, such as that supplied by substantial WAIS retreat. These arguments suggest the possibility that the MBE may have been a manifestation of decreasing WAIS stability, consistent with ongoing erosion of the submarine bedrock. We note that the location of potential points of WAIS instability are climate dependent, with increased accumulation, decreased ice temperature or lower sea-levels acting to stabilize the ice sheet (Schoof 2007), so that this inference does not conflict with the obliquity-paced WAIS retreats that were inferred during the warmer climate of the Pliocene (Naish et al 2009). We note that relative strength of the obliquity component of the DOME C deltaD power spectra has been increasing over the last 800,000 years (Jouzel et al 2007). The inferred initial retreat during MIS 11, not associated with the termination but occurring in the middle of the long interglacial, and apparently consistent with an observed strengthening of Atlantic overturning at 415 kyr BP (Dickson et al 2009), would presumably have been accompanied by further erosion, reducing topographic buttressing and leading to further destabilisation. Two recent studies suggest possible ways to test this hypothesis. Firstly, an ice-sheet model incorporating the necessary parameterisation of grounding-line dynamics (Pollard and DeConto 2009) coupled to an Earth System Model of appropriate complexity, would enable an investigation of coupled ice-sheet/ocean/climate feedbacks and the role of changing bedrock gradients on WAIS stability. Secondly, spatial variation of the Antarctic isotopic signature during warm interglacials has been demonstrated, suggesting the possibility that existing deltaD reconstructions may in fact underestimate the magnitude of warm interglacials (Sime et al 2009). An extension of this analysis could be used to test the impacts of bipolar warming and WAIS retreat on the isotopic record and provide an improved evaluation of the consistency of the hypothesis with Antarctic ice core records. However, new observational constraints on the size of WAIS during recent interglacials could provide more direct evidence needed to support or reject these ideas."


Caption: "(a) deltaD-inferred temperature anomaly from DOME C (Jouzel et al 2007). (b) GENIE-1 temperature anomaly with respect to pre-industrial (sea-level equivalent, annually averaged across East Antarctica, south of 71°S), from the simulation described in Holden et al (2010). Boundary conditions (orbital forcing, prescribed atmospheric CO2, transient ice sheets and associated meltwater fluxes) are described in the text. (c) The difference between observations and simulations (a-b) highlighting the absence of interglacial warmth in the simulated post-MBE temperature optima that are the focus of this work. (d) GENIE-1 temperature anomaly with respect to pre-industrial (sealevel equivalent, annually averaged across East Antarctica, south of 71°S) when orbital (orange), Laurentide and Eurasian ice sheet (blue) and CO2 (green) forcing are applied in isolation. The dominant feedbacks in this configuration of GENIE arise from dynamical changes in ocean circulation, vegetation, sea ice and snow cover. (e) The meltwater-induced Antarctic temperature anomaly (the difference between simulations that include and neglect meltwater forcing). The early interglacial optima during MIS 5.5, 7.5, 9.3 and 19.3 are illustrated with vertical dashed lines."

Finally, I conclude by re-posting the Coletti et al. (2015) reference that shows that even the most advanced modern analysis of the MIS 11c event cannot yet full account for the exceptionally high MS during this period; which again raises the prospect that a rapid methane emission rate from the possible future collapse of the WAIS could raise climate response well beyond any current climate model projection.

Coletti, A. J., DeConto, R. M., Brigham-Grette, J., and Melles, M.: A GCM comparison of Pleistocene super-interglacial periods in relation to Lake El'gygytgyn, NE Arctic Russia, Clim. Past, 11, 979-989, doi:10.5194/cp-11-979-2015, 2015.

http://www.clim-past.net/11/979/2015/cp-11-979-2015.pdf
http://www.clim-past.net/11/979/2015/cp-11-979-2015.html

Abstract: "Until now, the lack of time-continuous, terrestrial paleoenvironmental data from the Pleistocene Arctic has made model simulations of past interglacials difficult to assess. Here, we compare climate simulations of four warm interglacials at Marine Isotope Stages (MISs) 1 (9 ka), 5e (127 ka), 11c (409 ka) and 31 (1072 ka) with new proxy climate data recovered from Lake El'gygytgyn, NE Russia. Climate reconstructions of the mean temperature of the warmest month (MTWM) indicate conditions up to 0.4, 2.1, 0.5 and 3.1 °C warmer than today during MIS 1, 5e, 11c and 31, respectively. While the climate model captures much of the observed warming during each interglacial, largely in response to boreal summer (JJA) orbital forcing, the extraordinary warmth of MIS 11c compared to the other interglacials in the Lake El'gygytgyn temperature proxy reconstructions remains difficult to explain. To deconvolve the contribution of multiple influences on interglacial warming at Lake El'gygytgyn, we isolated the influence of vegetation, sea ice and circum-Arctic land ice feedbacks on the modeled climate of the Beringian interior. Simulations accounting for climate–vegetation–land-surface feedbacks during all four interglacials show expanding boreal forest cover with increasing summer insolation intensity. A deglaciated Greenland is shown to have a minimal effect on northeast Asian temperature during the warmth of stages 11c and 31 (Melles et al., 2012). A prescribed enhancement of oceanic heat transport into the Arctic Ocean does have some effect on Lake El'gygytgyn's regional climate, but the exceptional warmth of MIS 11c remains enigmatic compared to the modest orbital and greenhouse gas forcing during that interglacial."

Extract: "The timing of significant warming in the circum-Arctic can be linked to major deglaciation events in Antarctica, demonstrating possible interhemispheric linkages between the Arctic and Antarctic climate on glacial–interglacial timescales, which have yet to be explained."


See also:
http://www.nature.com/nature/journal/v494/n7436/abs/nature11790.html
&
https://en.wikipedia.org/wiki/Mid-Brunhes_Event

Extract: "The Mid-Brunhes Event (MBE) is a climatic shift evident in a number of marine sediment and Antarctic ice cores. It corresponds to an increase in amplitude of glacial-interglacial cycles.[1]
The MBE roughly corresponds to the transition between MIS 12 and MIS 11 (Termination V) about 430 kyr ago."

[AbruptSLR]

In my last post, I failed to note that the increase in Milankovitch sensitivity during the Brunhes due to Earth System state sensitivity (including increases sensitivity due to increased ice sheet size), could also be due to the temporary increase in planetary energy imbalance shown by Hansen et al. (2015) in the first attached image, as well as possibly being due to marine ice sheet related methane hydrates; or possibly due to both phenomena.

I also remind readers that if increased methane emissions do increase in the 2040-2100 timeframe due to abrupt iceberg calving from the WAIS (and/or East Antarctic marine glaciers); these increased emissions may likely be superimposed on the methane emissions associated with thermokarst activity as indicated in the second image, particularly for RCP 8.5 (which would likely increase the GWP of all methane within the atmosphere in that timeframe).

[Lennart van der Linde]

Comment by Drijfhout et al on Hansen et al:
http://www.atmos-chem-phys-discuss.net/15/C6867/2015/acpd-15-C6867-2015-supplement.pdf

A long quote:
"to our opinion the paper and its framing in the public arena sometimes tend to cross the thin line between opinion and scientific evidence. On one hand, the evidence compiled by Hansen et al. to conclude that global warming is highly dangerous is based on rational arguments. The analysis does not contain any process that is physically impossible (albeit sometimes unlikely), nor present principally flawed interpretations of the paleo data (albeit often biased to the upper end of uncertainty measures). As such we can support the conclusions that the scenarios sketched in this paper could be interpreted as an extreme high‐end scenario that describes the upper bound of what one might expect in the coming centuries to happen with our current climate if carbon emissions continue at present‐day rate. The philosophy on which the construction of this “upper‐end” scenario is funded does not fundamentally differ from the previously released “Delta‐committee” scenario that was published by Katsman et al. (2011), with the notion that the Hansen et al. scenario is even more extreme and unlikely to occur, that is, it resides in the end of the tail of the probability distribution of future climate change.

The title of the paper is more suggestive than is justified by the scientific evidence. The conclusions cannot be regarded as being robust, as they are insufficiently supported by both modeling results and observations. Our arguments for inferring this assessment are based on four points, namely:
1) The climate model used possesses large biases, cannot be considered to be state‐of‐the‐art and misses essential processes.
2) There are issues with timing of the events inferred from the paleodata.
3) The Eemian cannot be directly compared to any future climate that we might anticipate.
4) Even if all these issues would not exist, the extreme, abrupt events reported in this article need some preconditioning and would be much more likely to occur after 2100 or even after 2200 than in the coming century.

Therefore, we would recommend present this work with a lower level of “alarmism”, and avoid terminology as “dangerous” in the title and upfront displays of the paper. Below we discuss in more detail the points that in our view make this scenario unlikely and not fit for a more realistic, best estimate projection of future climate change in the coming centuries.

Specific comments

Sea level rise
In Section 2.1 the authors discuss literature on Eemian sea level variations, and conclude that there have been 2 peaks, separated by one sea level fall (implying ice sheet growth). To our understanding, this is not as evident as the authors suggest: various evidence for either one, two, three or even four peaks exists (see for a review Dutton et al, 2015). Related to this subject, the explanation for a mid‐Eemian sea level minimum they provide is not sound (page 20074‐20075):
“We suggest that the explanation for a mid‐Eemian sea level minimum is a substantial late‐Eemian collapse of the Antarctic ice sheet facilitated by the positive warm‐season insolation anomaly on Antarctica and the Southern Ocean during the late Eemian (Fig. 3b).”

A collapse of the Antarctic ice sheet can explain a sea level rise, however it cannot explain a mid‐ Eemian sea level minimum. Ice sheet growth is needed for a sea level minimum, but physical mechanisms for such regrowth are not discussed explicitly. It is mentioned that Eemian sea level fluctuations are the result of a combination of processes including NH cooling due to the solar forcing, and feedbacks affecting the Antarctica ice sheet. But the degree to which this leads to a sea level minimum is unclear.

For Sections 3.2, 3.3 and 4.1 we have noticed that the freshwater forcing scenarios seem somewhat unrealistic, being 360 Gt yr‐1 (1 mm yr‐1 SLR, over 2003‐2015), then growing with 5, 10 and 20 yr doubling times. The problem is not on the initial value, but lies in the exponential growth that is assumed. It implies that values in the order of 1 Sv are reached, which equals 30,000 Gt yr‐1. It is not likely that these magnitudes of ice loss can be reached. The choice for this extreme freshwater forcing scenario is not extensively motivated, apart from some notions that ice in Greenland and Antarctica is widely connected to the ocean via outlet glaciers and basins with bedrock below sea level, and that feedbacks like albedo and surface lowering can increase the ice melt. Later in the paper (section 7.3) a review on recent ice sheet changes is given, but no direct physical justification is given for a continuous exponential growth of ice sheet mass loss, apart from a fairly loose statement:
“We do not argue for this specific input function, but we suggest that rapid meltwater increase is likely if GHGs continue to grow rapidly.” (page 20078)

In fact, there are estimates of how much ice can be melted from Antarctica via a WAIS collapse: Bamber et al. (2009) estimate this to be 3.5 m. With this as upper limit an exponential growth rate is not realistic. Furthermore, the authors argue that paleoclimate data reveals that sea level rise of several meters in one century have occurred before. But this occurred during terminations of glacial periods, hence with much more ice available on the planet. To put the scenarios used here in context of the recently published assessment by Church et al. (2013): the lowest scenario by Hansen et al. is still 2‐3 times higher than the Church et al. estimate in 2100, and Hansens highest estimate is more than 3000 times higher.

Referring to the comment on page 20079, line 17‐19: “Actual current freshwater flux may be about a factor of four higher than assumed in these initial runs, as we will discuss, and thus effects may occur ~20 years earlier.”: The suggestion that the simulated effects of an exponentially growing freshwater flux may occur ~20 yr earlier is only based upon a possible underestimation of the initial freshwater flux. This is strange reasoning, because the timing of the effects strongly rely on the exponential growth curve, which is highly uncertain (see above), not on the initial value. As a consequence of these over the top melt scenarios, an unrealistic fresh water flux is generated leading to a strong response in the ocean. Model results with more realistic ice melt fluxes don’t show this behaviour. In other words, a large part of the results depends on the extreme ice melt down scenarios for which support lacks."

So they seem to be saying, in my words: Hansen et al could be right, but probably they're not, because that would seem unrealistic in view of past slower SLR.

They simply ignore the main argument of Hansen et al, namely that the current forcing is many times stronger than in the past.

Isn't that strange?

[AbruptSLR]

Lennart,

Thanks for the post.  Hansen has been commenting about scientific reticence for years, and it appears to me that scientific consensus is as subject to "group-think" as any other human endeavor.  As ice sheet models will not be sufficiently accurate to even begin to approximate the timing of the start and the rate of acceleration for main phase WAIS collapse; scientific consensus feels very comfortable in calling this grey swan scenario a black swan, thus indicating to society that we do not need to worry about such scenarios so that society does not need to take appropriately aggressive action to prevent such a grey swan occurrence. 

Viewed in this light scientific reticence (erring on the side of least drama) is a positive feedback factor for more climate change.  Scientists need to learn to take responsibility for their actions (or in actions) in the Anthropocene.

Best,
ASLR   

[Lennart van der Linde]

scientific reticence (erring on the side of least drama) is a positive feedback factor for more climate change

Indeed. Drijfhout et al seem overly confident in their judgement that Hansen et al are being alarmist. How can they be so sure they have a better understanding of this system than Hansen cs? Is that hubris? Or was it hubris when Rignot said in a conference call with journalists:
http://www.newyorker.com/news/daily-comment/if-we-burned-all-the-fossil-fuel-in-the-world

“Sea-level rise is one foot per century, and we are talking about the possibility of this being three feet per century or even thirty feet per century.”

Or is it that Drijfhout et al cannot deal with the stress of suspecting there's a risk of truly catastrophic SLR? They may think it's unlikely, but they can't be sure the risk is not there, as they even acknowledge themselves. So why would it not be dangerous to ignore such risk? They think Hansen et al are overplaying the risk, but their arguments seem really weak and to miss the main points. Hopefully Hansen et al will reply soon.