Hansen et al paper: 3+ meters SLR by 2100

[Sleepy]

Thank you for your kind words above, ASLR. Having a hard time contributing and my comments have been even more erratic than before thanks to a useless ISP. Online (again) hoping to stay since I'm back to my old ISP now. And I can see that I have a lot more reading to do.

A news release from the University of Zurich.
Glaciers melt faster than ever.
http://www.mediadesk.uzh.ch/articles/2015/gletscher-verlieren-mehr-eis-als-je-zuvor_en.html

«The observed glaciers currently lose between half a metre and one metre of its ice thickness every year – this is two to three times more than the corresponding average of the 20th century», explains Michael Zemp, Director of the World Glacier Monitoring Service and lead author of the study. «Exact measurements of this ice loss are reported from a few hundred glaciers only. However, these results are qualitatively confirmed from field and satellite-based observations for tens of thousands of glaciers around the world.»

Historically unprecedented global glacier decline in the early 21st century.
http://www.ingentaconnect.com/content/igsoc/jog/pre-prints/content-ings_jog_15j017

Observations show that glaciers around the world are in retreat and losing mass. Internationally coordinated for over a century, glacier monitoring activities provide an unprecedented dataset of glacier observations from ground, air and space. Glacier studies generally select specific parts of these datasets to obtain optimal assessments of the mass-balance data relating to the impact that glaciers exercise on global sea-level fluctuations or on regional runoff. In this study we provide an overview and analysis of the main observational datasets compiled by the World Glacier Monitoring Service (WGMS). The dataset on glacier front variations (~42 000 since 1600) delivers clear evidence that centennial glacier retreat is a global phenomenon. Intermittent readvance periods at regional and decadal scale are normally restricted to a subsample of glaciers and have not come close to achieving the maximum positions of the Little Ice Age (or Holocene). Glaciological and geodetic observations (~5200 since 1850) show that the rates of early 21st-century mass loss are without precedent on a global scale, at least for the time period observed and probably also for recorded history, as indicated also in reconstructions from written and illustrated documents. This strong imbalance implies that glaciers in many regions will very likely suffer further ice loss, even if climate remains stable.

EDIT; There you go, I cant keep up... LVDL started a new thread in more appropriate section.
http://forum.arctic-sea-ice.net/index.php/topic,1350.0.html

[AbruptSLR]

Sleepy,

It is great to have you posting more regularly again.  Your point that mountain glaciers are losing ice mass two to three times the average rate of the 20th century re-emphasizes Hansen et al 2015's basic point that we are already too warm and that if we were smart we would plant forests to back down from our current atmospheric CO2 concentration of over 400ppm down to about 350 ppm.

The importance of not believing the IPCC's remaining Carbon Budget can readily be seen by the following line of logic.

1) Pollard, DeConto & Alley 2015 show that once the mean global surface temperature reaches about 2C above modern conditions (note by at least one scale we are already at 1C of pre-industrial and we are only 1/2 way through our current strong El Nino event), and just stays constant from there on (intended to roughly match Pliocene conditions), that within 100-years the Antarctic could contribute 3m to SLR and after 200-year it could contribute about 5m to SLR.  Noting that we are currently follow about the 90% CL level of radiative forcing for RCP8.5; even if CoP 21 gets us down to RCP 4.5 by 2050; the mean global surface temperature will almost certainly by over 2C above pre-industrial between 2035 & 2040; which is precisely when Hansen et 2015 rule-of thumb 10-year double time SLR rate of rise matches the slope of the sea level rise curve shown in my Reply #148 from Pollard, DeConto & Alley 2015 for Pliocene-like conditions.

2) The first attached image from Pollard, DeConto & Alley 2015 shows that within 100-years of reaching 2C above pre-industrial the Amundsen, Bellingshausen and Weddell Sea will all be interconnected due to WAIS ice mass loss; which will cause a massive change in local ocean current circulation patterns (which will further accelerate local ice mass loss).  Furthermore, the second attached image shows that since 2009 the ice mass loss not only in the ASE but also in the Bellingshausen Sea area have accelerated rapidly; which adds support to Pollard, DeConto & Alley 2015's projections.

3) The third attached image shows historical reconstructed surface temperature data gathered from the WAIS Divide location; illustrating the rapid acceleration of increasing surface temperature in this critical area within the past few decades.  Continuing this trend will result in extensive austral summer surface ice melting events by 2040.

4) The fourth attached image shows a profile view through the Thwaites Glacier (from 2006).  This image shows that when the current grounding line retreats by about 70km an assumed vertical ice cliff face would extend from -1km to +1km; which would be very susceptible to a cliff failure (like nowhere else on Earth).

Again, this scenario assumes only that we reach 2C above pre-industrial between 2035 & 2040 and then stay at that temperature for another one to two hundred years.

Best,
ASLR

Edit: the following link provides evidence that we are already 1/2 the way to a 2C temperature rise from the mid-18 Hundreds:

https://www.newscientist.com/article/mg22730324-200-earth-now-halfway-to-un-global-warming-limit/

[AbruptSLR]

As I have noted the following information in the Antarctic folder, I thought that I would note it here as well.

In the first attached image (from about 74.5S, 106W to about 76.25S, 108W) there is a submarine channel/trench that runs straight from the Pine Island Ice Shelf, PIIS< directly to the trough at the base of the Thwaites residual Ice Tongue.   Inspired by the second attached image of modeled temperatures of ocean current flows within the ASE, I have previously speculated that the warm CDW advected out from the PIIS follows this submarine channel/trench and delivers warm CDW directly to the grounding line of the trough at the base of the ice tongue.

If I am correct that within the next 10 to 15 years that cliff failure calving events clear ground ice from the trough, then next super El Nino event (say circa 2025 to 2030) could deliver significant quantities of warm CDW all the way to within about 20km of a submarine canyon leading straight into the heart of the Byrd Subglacial Basin, BSB, (this fact was also noted by Tinto & Bell 2011).  If so, then by about 2035 to 2040 the grounding line locally could retreat all the way to the steeply negative slope of the BSB; which, in my opinion presents a major risk of extremely active local cliff failure and hydrofracting calving events, on a scale that could make the current Jakobshavn calving events look very small in comparison.

Such a possible scenario combined with the possible activation of the Thwaites Eastern Shear Margin due to the possible acceleration of the SW Tributary Glacier associated with the retreat of the calving face of the PIIS to upstream of the SW Tributary Glacier calving face circa 2035 to 2040; should be carefully evaluated by any researcher (including especially the ACME team by 2017, when their preliminary ASLR findings are due) claiming that there is little risk of significant SLR contribution from the BSB this century.

[Lennart van der Linde]

Hansen et al reply to Andy Revkin's comment:
http://www.atmos-chem-phys-discuss.net/15/C5615/2015/acpd-15-C5615-2015.pdf

Ruddiman et al comment on Hansen et al:
http://www.atmos-chem-phys-discuss.net/15/C5549/2015/acpd-15-C5549-2015.pdf

[JimD]

Re: the several comments about Joe Romm

Yeah he is smart and yeah he has a PhD from MIT.  BUT, he is a political animal from the Progressive camp and he is TOTALLY wedded to the Green-BAU approach.  He cannot see the facts because his way of life will not allow him to.

He always shies away from taking the data to where it points to all the time, and ops instead to promote technologies, economic tactics, and progressive social ideology that seeks to maintain our ultra wealthy lifestyle so no one will have to suffer.  Green-BAU. 

He is not going to accept any data or interpretation of data which indicates that it is not possible to maintain our current civilizational structure and economic systems.

Population levels, carrying capacity and climate change.   All have to be solved simultaneously or none will be solved. 

[AbruptSLR]

Jason Box opines that sea level rise will occur sooner and go faster than currently expected by most other scientists:

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

Extract: "... when it comes to ice, how fast it can go and how fast the sea will rise, if I were a betting man, I'd put my money on it going faster than forecast."

[Lennart van der Linde]

Jim,
I think Romm doesn't push an economic paradigm shift, but sometimes he recognizes its necessity, sort of:
http://thinkprogress.org/climate/2013/06/06/2112091/robert-f-kennedy-challenged-our-ponzi-scheme-pursuit-of-growth-for-growths-sake-when-will-come-another/

In this respect, however, he's not very different from planetary boundaries scientists like Hansen and Rockstrom, it seems, who argue for 350 ppm, but who believe this is still compatible with economic growth, even though their co-author Costanza thinks those are not compatible:
http://www.ecologyandsociety.org/vol14/iss2/art32/

Costanza and others argue for this economic paradigm shift, for example here:
http://www.un.org/esa/dsd/dsd_aofw_sdkp/sdkp_pdf/sdkp_workshop_0510/joint_statement.pdf

And here:
https://sustainabledevelopment.un.org/content/documents/Building_a_Sustainable_and_Desirable_Economy-in-Society-in-Nature.pdf

But I agree that taking Hansen et al and other recent (and not so recent) science seriously should lead to this economic paradigm shift, even if Hansen himself doesn't think or say so (yet?).

[Lennart van der Linde]

KCRW-radio in LA with Hansen, John Englander, retired admiral Bouchard and New York City planner on the risks of SLR:
http://www.kcrw.com/news-culture/shows/to-the-point/rising-seas-are-threatening-americas-cities

Undoubtedly all the (inter-) national media are waiting for the peer review process to complete...

[sidd]

Not being a geologist, i decided to ask one about Bahamian beach chevrons and perched boulders. She had been to those beaches and is familiar with the coasts there, and immediately told me to trust Hearty over Myrolie. Hansen is more polite than she was, but does have a good zinger or two:

"A geologist visiting the site would recognize that the boulders, with highly disoriented original bedding, are much older than the substrate."

In short, grandmothers and sucking eggs.

sidd

[A-Team]

ask a geologist about Bahamian beach chevrons and perched boulders:  trust Hearty

Puzzled by why a few rocks have been such a emotional flashpoint in geology for so long, I read through a whole bunch of papers on putative signatures of Caribbean mega-storm. Recent Hearty papers address all the concerns without backing off in the slightest from the mid-90's papers. Interesting but the superstorm topic is totally tangential to the Hansen paper.

The first thing to understand about geology is its absolute fixation on gradualism. This had its historical roots in nasty 19th century battles with biblical creationists. Anything that smacks of abrupt change, like the Missoula Floods, Yucatan meteorite, volcanoes cooling climate, massive tectonic subsidence of the Oregon coast in 1701, 30 meters of sedimentation from one Gulf hurricane, Bahaman boulders -- the list of reflexive denial runs into the thousands.

I'm ok with burden-of-proof falling on claim originators and extraordinary claims requiring extarordinary evidence but geology can get really overly emo on some fairly petty matters. However there is in fact a steady drumbeat of preposterous modern catastrophists like Firestone and the "Clovis Comet", see https://en.wikipedia.org/wiki/Younger_Dryas_impact_hypothesis

several comments about Joe Romm from JimD

Nice description. I've seen Romm make the most ignorant comments imaginable about biodiversity and extinction. Like he has spent the last 45 Earth Days under a rock. People who work inside the DC Beltway often have peculiar views.

My interest in Romm has to do with the high visibility of his blog, its generally accurate take on climate change, his clever put-downs of denier scams, and his effective writing style that explains complex issues simply. It's worth studying how he does this.

It was a huge mistake turning over his blog to Think Progress. It has noticeably deteriorated since with ghostwritten pieces, far less science, and above all loss of authenticity. For what?

You should really stop calling this Green-BAU. Maybe Renewables + BAU? It has very little overlap with values of the green (environmental) movement in the US.

To see the distinction, consider the solar abomination called Ivanpah. Renewable energy yes but as brown as it gets -- sucking down subsidies, destroying the Mojave, killing all those endangered tortoises, incinerating everything that flies through from peregrine falcons to bats to butterflies -- all for a piddling amount of electric easily and better done with rooftop solar. One of the largest green groups sued over that; I've served on their Advisory Board for many years and am very familiar with the facts surrounding this installation.

[Lennart van der Linde]

On Romm and the need, or political strategy, to push for an economic paradigm shift, see his discussion with Naomi Klein, who bases herself more on the likes of Kevin Anderson and Tim Jackson:
http://thinkprogress.org/climate/2014/09/16/3567322/this-changes-everything-naomi-klein-capitalism-climate/

Before her book came out, Romm took more issue with her critique of "Big Green" for not pushing for the needed economic paradigm shift:
http://thinkprogress.org/climate/2013/09/09/2577331/naomi-klein-denialism/

I'm more with Klein on this. But this thread started with the climate science and there I think Romm follows Hansen et al quite closely. It's on the economic implications of this science that Romm (and Hansen himself, as noted) don't push for the paradigm shift that seems unavoidable, and that Anderson, Klein, Costanza, Jackson, Gilding and others are pushing for.

In the end this may be more of a difference of opinion on political strategy, or as Jim suggests of a willingness to fundamental lifestyle changes, or of different roles in the transition to a sustainable economy. I'm not sure if this is the thread to pursue this part of the discussion, although Hansen et al also touch upon the political implications of their scientific findings.

[TerryM]

A-Team
In complete agreement re. Ivanpah with the addition of flooding damage during the next major rain event. I'd sailed that lake bed for decades and I've seen what water streaming down from the mountains can do.


However


After collecting Black Mat samples from Northern Mexico to Southern Ontario I'm not ready to toss Firestone out just yet. A friend who's in charge of the megafauna displays at the Royal Ontario Museum assures me that every Mammoth tusk he's checked tests positive for iridium particles drilled deep in the upper surfaces of the ivory.
In the south west you won't find evidence of Clovis, or any ice age megafauna, unless they're covered by the mat & we were well aware of this decades before Firestone came up with a convincing answer as to why.  Visit any mammoth dig in N. America & look around for the distinctive strata.
I now live on the Algonquin Ridge, one of the few places in Ontario that may have been ice free at that time. Other than an area near Long Point I've found no traces here as of yet. When I do I will let you know.


Terry

[A-Team]

ice age megafauna

We should really do more here on a dedicated paleoclimate forum. Just in passing, 23 Jul 15:

http://phys.org/news/2015-07-mammoths-abrupt-climate.html
http://www.sciencemag.org/content/early/2015/07/22/science.aac4315

[AbruptSLR]

The linked reference & following summary discusses the positive feedback caused by the acidification of the oceans reducing sulfur flux from the ocean which then results in more radiative forcing (see the attached image) particularly over the Southern Ocean; however, I wonder what all of the fresh water (cited by Hansen et al 2015) will do the plankton producing all of this dimethylsulphide.  If the freshwater kills the associated plankton then this could also be a very strong positive feedback mechanism (that Hansen et al 2015 do not consider):

http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate1981.html

Global warming amplified by reduced sulphur fluxes as a result of ocean acidification; Katharina D. Six, Silvia Kloster, Tatiana Ilyina, Stephen D. Archer, Kai Zhang & Ernst Maier-Reimer; Nature Climate Change;  (2013); doi:10.1038/nclimate1981


http://www.mpimet.mpg.de/nc/en/communication/news/single-news/article/climate-change-ocean-acidification-amplifies-global-warming.html

Summary:

"Scientists at the Max Planck Institute for Meteorology (MPI-M), Dr. Katharina Six, Dr. Silvia Kloster, Dr. Tatiana Ilyina, the late Dr. Ernst Maier-Reimer and two co-authors from the US, demonstrate that ocean acidification may amplify global warming through the biogenic production of the marine sulfur component dimethylsulphide (DMS).

It is common knowledge that fossil fuel emissions of CO2 lead to global warming. The ocean, by taking up significant amounts of CO2, lessens the effect of this anthropogenic disturbance. The "price" for storing CO2 is an ongoing decrease of seawater pH (ocean acidification1), a process that is likely to have diverse and harmful impacts on marine biota, food webs, and ecosystems. Until now, however, climate change and ocean acidification have been widely considered as uncoupled consequences of the anthropogenic CO2 perturbation2. Recently, ocean biologists measured in experiments using seawater enclosures (mesocosms)3 that DMS concentrations were markedly lower in a low-pH environment (Figure 1).
When DMS is emitted to the atmosphere it oxidizes to gas phase sulfuric acid, which can form new aerosol particles that impact cloud albedo and, hence, cool the Earth's surface. As marine DMS emissions are the largest natural source for atmospheric sulfur, changes in their strength have the potential to notably alter the Earth's radiation budget. Based on the results from the mesocosm studies the researchers from the MPI-M have established relationships between pH changes and DMS concentrations in seawater. They projected changes in DMS emissions into the atmosphere in a future climate with enhanced ocean acidification using the MPI-M Earth system model4. In the journal Nature Climate Change it is demonstrated, that modeled DMS emissions decrease by about 18 (±3)% in 2100 compared to preindustrial times as a result of the combined effects of ocean acidification and climate change. The reduced DMS emissions induce a significant positive radiative forcing of which 83% (0.4 W/m2) can, in the model, be attributed to the impact of ocean acidification alone (Figure 2).
Compared to the Earth system response to a doubling of atmospheric CO2 this is tantamount to an equilibrium temperature increase between 0.23 and 0.48 K. Simply put, their research shows that ocean acidification has the potential to speed up global warming considerably.

References:
1. Gattuso, J-P. & Hansson, L. in Ocean Acidification (eds Gattuso, J-P. & Hansson, L.) 1_20 (Oxford Univ. Press, 2011).
2. Doney, S. C., Fabry, V. J., Feely, R. A. & Kleypas, J. A. Ocean acidification: The other CO2 problem. Annu. Rev. Mar. Sci. 1,
dx.doi.org/10.1146/annurev.marine.010908.163834, 169-192 (2009).
3. Archer, S. D. et al. Contrasting responses of DMS and DMSP 102 to ocean acidification in Arctic waters. Biogeosciences 10, 103,
dx.doi.org/10.5194/bg-10-1893-2013 (2013).
4. Jungclaus, J. H. et al. Climate and carbon-cycle variability over the last millennium. Clim. Past 6, dx.doi.org/10.5194/cp-6-723-2010, 723-737 (2010)."


Furthermore, the linked 2013 article focuses on changes in the Arctic Ocean, and indicates that changes in the plankton there could also result in a positive feedback (that will likely become more important with time) associated both with lower dimethyl sulphide production and lower CO2 absorption, and again I wonder whether freshwater in the North Atlantic from possible GIS ice mass loss my kill these plankton and thus strengthen the positive feedback mechanism: 

http://www.egu.eu/news/76/tiny-plankton-could-have-big-impact-on-climate/

This article states:

""If the tiny plankton blooms, it consumes the nutrients that are normally also available to larger plankton species,” explains Ulf Riebesell, a professor of biological oceanography at the GEOMAR Helmholtz Centre for Ocean Research Kiel in Germany and head of the experimental team. This could mean the larger plankton run short of food.

Large plankton play an important role in carbon export to the deep ocean, but in a system dominated by the so-called pico- and nanoplankton, less carbon is transported out of surface waters. “This may cause the oceans to absorb less CO2 in the future,” says Riebesell.

The potential imbalance in the plankton food web may have an even bigger climate impact. Large plankton are also important producers of a climate-cooling gas called dimethyl sulphide, which stimulates cloud-formation over the oceans. Less dimethyl sulphide means more sunlight reaches the Earth’s surface, adding to the greenhouse effect. “These important services of the ocean may thus be significantly affected by acidification.”

Ecosystems in the Arctic are some of the most vulnerable to acidification because the cold temperatures here mean that the ocean absorbs more carbon dioxide. “Acidification is faster there than in temperate or tropical regions,” explains the coordinator of the European Project on Ocean Acidification (EPOCA), Jean-Pierre Gattuso of the Laboratory of Oceanography of Villefranche-sur-Mer of the French National Centre for Scientific Research (CNRS).

The increasing acidity is known to affect some calcifying organisms in the Arctic, including certain sea snails, mussels and other molluscs. But scientists did not know until now how ocean acidification alters both the base of the marine food web and carbon transport in the ocean. ..."


Furthermore, this article points to the free pdfs available on this topic from the following special issue of Biogenosciences

http://www.biogeosciences.net/special_issue120.html

[AbruptSLR]

ice age megafauna

We should really do more here on a dedicated paleoclimate forum. Just in passing, 23 Jul 15:

http://phys.org/news/2015-07-mammoths-abrupt-climate.html
http://www.sciencemag.org/content/early/2015/07/22/science.aac4315

The is already a thread on the "Early Anthropocene" that includes discussion on this topic, here:


http://forum.arctic-sea-ice.net/index.php/topic,852.0.html

[AbruptSLR]

The first linked reference by the Royal Netherlands Meteorological Institute (KNMI) presents relatively recent information (and the attached images) about the influence of glacial melt water on the Southern Ocean, focused on: (a) expanding Southern Ocean sea ice; (b) protection of warm CDW from cooling; and (c) cooling of the surface temperature of the Southern Ocean.  The second linked reference by de Lavergne et al (2014) discusses how the freshening of the Southern Ocean is slowing the Antarctic Bottom Water, AABW, formation. Both of these references add background to the Hansen et al 2015 paper, and in my next post I plan to address some of the influences of reduced rates of AABW (and NADW) on the Global MOC circulation:


 
R. Bintanja, G. J. van Oldenborgh, S. S. Drijfhout, B. Wouters & C. A. Katsman, (2013), "Important role for ocean warming and increased ice-shelf melt in Antarctic sea-ice expansion", Nature Geoscience, Volume: 6, 376–379, (2013), doi:10.1038/ngeo1767.

http://www.nature.com/ngeo/journal/v6/n5/full/ngeo1767.html


Abstract: "Changes in sea ice significantly modulate climate change because of its high reflective and strong insulating nature. In contrast to Arctic sea ice, sea ice surrounding Antarctica has expanded, with record extent in 2010. This ice expansion has previously been attributed to dynamical atmospheric changes that induce atmospheric cooling. Here we show that accelerated basal melting of Antarctic ice shelves is likely to have contributed significantly to sea-ice expansion. Specifically, we present observations indicating that melt water from Antarctica’s ice shelves accumulates in a cool and fresh surface layer that shields the surface ocean from the warmer deeper waters that are melting the ice shelves. Simulating these processes in a coupled climate model we find that cool and fresh surface water from ice-shelf melt indeed leads to expanding sea ice in austral autumn and winter. This powerful negative feedback counteracts Southern Hemispheric atmospheric warming. Although changes in atmospheric dynamics most likely govern regional sea-ice trends, our analyses indicate that the overall sea-ice trend is dominated by increased ice-shelf melt. We suggest that cool sea surface temperatures around Antarctica could offset projected snowfall increases in Antarctica, with implications for estimates of future sea-level rise."

see also: doi:10.1038/nature.2013.12709,
http://www.nature.com/news/global-warming-expands-antarctic-sea-ice-1.12709

The linked reference indicates that observed and projected reductions in deep convection in the Southern Ocean due to climate change, will result in a continuing reduction in AABW production which represents a positive feedback for global warming.


Casimir de Lavergne, Jaime B. Palter, Eric D. Galbraith, Raffaele Bernardello & Irina Marinov, (2014), "Cessation of deep convection in the open Southern Ocean under anthropogenic climate change", Nature Climate Change, 4, 278–282, doi:10.1038/nclimate2132


http://www.nature.com/nclimate/journal/v4/n4/full/nclimate2132.html


Abstract: "In 1974, newly available satellite observations unveiled the presence of a giant ice-free area, or polynya, within the Antarctic ice pack of the Weddell Sea, which persisted during the two following winters. Subsequent research showed that deep convective overturning had opened a conduit between the surface and the abyssal ocean, and had maintained the polynya through the massive release of heat from the deep sea. Although the polynya has aroused continued interest, the presence of a fresh surface layer has prevented the recurrence of deep convection there since 1976, and it is now largely viewed as a naturally rare event. Here, we present a new analysis of historical observations and model simulations that suggest deep convection in the Weddell Sea was more active in the past, and has been weakened by anthropogenic forcing. The observations show that surface freshening of the southern polar ocean since the 1950s has considerably enhanced the salinity stratification. Meanwhile, among the present generation of global climate models, deep convection is common in the Southern Ocean under pre-industrial conditions, but weakens and ceases under a climate change scenario owing to surface freshening. A decline of open-ocean convection would reduce the production rate of Antarctic Bottom Waters, with important implications for ocean heat and carbon storage, and may have played a role in recent Antarctic climate change."

[AbruptSLR]

The attached images are from the Marshall & Speer 2012 paper that can be found at the first following linked site.  With continued freshening of the Southern Ocean (were Antarctic Bottom Water, AABW, formation rate is slowing) and the North Atlantic where the North Atlantic Deep Water, NADW, is formed, the Global MOC is projected to slow per Hansen et al 2015; which should backup ocean heat in the tropical equatorial zones of the oceans (see the images).  This could have profound impact on the Double Inter-tropical Convergence Zone and the associated high ECS as discussed by Baijun Tian (2015)

http://www-pord.ucsd.edu/~ltalley/sio219/marshall_speer_natgeo2012.pdf

Closure of the meridional overturning circulation through Southern Ocean upwelling
By: John Marshall and Kevin Speer; NATURE GEOSCIENCE j VOL 5 j MARCH 2012 j www.nature.com/naturegeoscience

The first attached image from this paper shows an overview of the global MOC

The second attached image show a north-south cross section through the MOC with air-sea flux patterns.

The third attached images shows an idealized simulation of the ACC.

The fourth attached image elaborates on the wind – sea energy flux relationship in the Southern Ocean.


The Double Inter-Tropical Convergence Zone bias causes artificially low ECS response in the models, discussed in the linked Tian reference:

http://onlinelibrary.wiley.com/doi/10.1002/2015GL064119/full

Spread of Model Climate Sensitivity Linked to Double-Intertropical Convergence Zone Bias†
Baijun Tian, DOI: 10.1002/2015GL064119

[TerryM]

ice age megafauna

We should really do more here on a dedicated paleoclimate forum. Just in passing, 23 Jul 15:

http://phys.org/news/2015-07-mammoths-abrupt-climate.html
http://www.sciencemag.org/content/early/2015/07/22/science.aac4315

Thanx

[Bruce Steele]

ASLR, Large changes in surface water salinity may change how plankton communities respond to future ocean productivity in the North Atlantic and around the Antarctic due to increased freshwater inputs from melt but other areas may see productivity increased due to increased mixing and upwelling  where open water and wind fetch results from a seasonal decrease in Arctic pack ice. So an increase in productivity in one area may compensate for a decrease in another.
 As I understand Riebesell's 2013 paper you linked it is a change from large phytoplankton to
Nano- and Pico-phytoplankton communities that is responsible for the change in DMS production.
Even though the phytoplankton communities that develop in the soon be be open waters of the Arctic may also be similarly disposed to Nano and Pico-Phytoplankton communities they still would be producing DMS in areas that aren't as productive now as they will be as the sea ice decreases.
 

[AbruptSLR]

ASLR, Large changes in surface water salinity may change how plankton communities respond to future ocean productivity in the North Atlantic and around the Antarctic due to increased freshwater inputs from melt but other areas may see productivity increased due to increased mixing and upwelling  where open water and wind fetch results from a seasonal decrease in Arctic pack ice. So an increase in productivity in one area may compensate for a decrease in another.
 As I understand Riebesell's 2013 paper you linked it is a change from large phytoplankton to
Nano- and Pico-phytoplankton communities that is responsible for the change in DMS production.
Even though the phytoplankton communities that develop in the soon be be open waters of the Arctic may also be similarly disposed to Nano and Pico-Phytoplankton communities they still would be producing DMS in areas that aren't as productive now as they will be as the sea ice decreases.
 

Bruce,

Thanks for the insight.  With all of this complexity, my hope is that the new ACME model considers all of these potentially rapid changes in carbon-cycle and ECS (Double Inter-tropical Convergence Zones); due to potentially abrupt freshwater ice mass discharge in to the North Atlantic & the Southern Ocean.  If not by 2017 (when the preliminary output is due) then maybe by 2024 when the current project is complete (unless extensions are granted for the ACME program; which seems likely); as this impacts appear to be potentially significant (in addition to those identified by Hansen et al 2015).

Also, as I have stated before, I am concerned that increased hurricane activity and strength along the US Atlantic seaboard could convey large amounts of periodic rain and heat directly to the GIS (which could result in unexpectedly large ice mass losses).  Per the attached image (from Grinsted 2013) red represents hurricane projections with one degree (C) global warming; blue represents no warming. The gap between these lines suggests that a warmer climate will produce more frequent hurricanes; the gap is widest at the top, meaning the biggest increase will be with the biggest storms.  Furthermore, if Hansen et al 2015 are correct about the freshening of the North Atlantic and the Southern Ocean inducing still stronger storms, then the Grinsted 2013 projections will be non-conservative from a public safety point of view.

Best,
ASLR

[AbruptSLR]

While discussing possible rapid carbon-cycle positive feedback mechanisms that require complex modeling (comparable to ACME) to determine the influence of abrupt ocean freshening include the ventilation of CO2 associate with upwelling as discussed in the following thread:

http://forum.arctic-sea-ice.net/index.php/topic,888.msg31200.html#msg31200

[Bruce Steele]

ASLR, I read the Marshal & Speer 2012 you linked above. I will reread it a couple more times before it sinks in a little better. The two layers of MOC described is going to take me awhile to incorporate into the little mental picture I have developed re. " the conveyor ".  I was wondering if the upper layer is more " intermediate water " than deep water formation like I typically think of the MOC but I will reserve that as a question I need to track down an answer for.
 Thanks for the links and I will try to keep up with reading your insightful posts as well as the supporting documents.  Maybe the difference of trying to get an education over the Internet and an official one is having a sounding board of teachers and other students to get feedback on questions where here online we have to figure things out things alone.   
   

[Lennart van der Linde]

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.

A-Team,
Curious to hear your thoughts on:
http://www.realclimate.org/index.php/archives/2015/08/ice-core-dating-corroborates-tree-ring-chronologies/?utm_source=twitterfeed&utm_medium=twitter

And what the implications for Hansen et al may or may not be...

[Tor Bejnar]

Bruce's mention of "DMS production" made me realize I recently read about "DMS emissions".  Searching the internet, the following seems to be (closer to) the source material of what I read.

Climate Change: Ocean acidification amplifies global warming (2013)

Scientists at the Max Planck Institute for Meteorology (MPI-M), Dr. Katharina Six, Dr. Silvia Kloster, Dr. Tatiana Ilyina, the late Dr. Ernst Maier-Reimer and two co-authors from the US, demonstrate that ocean acidification may amplify global warming through the biogenic production of the marine sulfur component dimethylsulphide (DMS).
...
In the journal Nature Climate Change it is demonstrated, that modeled DMS emissions decrease by about 18 (±3)% in 2100 compared to preindustrial times as a result of the combined effects of ocean acidification and climate change.
…
Simply put, their research shows that ocean acidification has the potential to speed up global warming considerably.

[Bruce Steele]

Tor Bejnar, I was commenting on ASLR' post #163 above and I should have included a reference back to it. ASLR has a link above to the article you are quoting. The original mesocosm studies done by Riebesell and published 2013 were done in the North Atlantic and the followup mesocosm studies were in the Antarctic.  That different phytoplankton communities in different ocean regimes responded similarly gives weight to the theory that acidification will cause a decrease in worldwide DMS production , the caveat being some compensatory increases in the arctic. The graph included in the
Six et al 2013 paper do show an increase in DMS in far northerly latitudes so there is some compensation to the reduction in DMS worldwide . Hard to quantify I would think however before we better understand productivity increases for the Arctic peripheral seas.     

[AbruptSLR]

ASLR, I read the Marshal & Speer 2012 you linked above. I will reread it a couple more times before it sinks in a little better. The two layers of MOC described is going to take me awhile to incorporate into the little mental picture I have developed re. " the conveyor ".  I was wondering if the upper layer is more " intermediate water " than deep water formation like I typically think of the MOC but I will reserve that as a question I need to track down an answer for.
 Thanks for the links and I will try to keep up with reading your insightful posts as well as the supporting documents.  Maybe the difference of trying to get an education over the Internet and an official one is having a sounding board of teachers and other students to get feedback on questions where here online we have to figure things out things alone.   
   

Bruce,
While you're doing homework, please note that in both the Marshall & Speer 2012 paper, and the following link (and associated map), there are multiple sources for AABW that feed not only into the Atlantic, but also the Pacific and Indian Oceans; thus if you have and insights on how freshening of the Southern Ocean surface water would affect all of these different interconnected ocean circulation patterns, I would be pleased to hear them.

http://wwwoa.ees.hokudai.ac.jp/research/polar_e.html


Extract: "Antarctic bottom water is, along with North Atlantic deep water, a source of deep and bottom water for all the world's oceans. The amount of Antarctic bottom water generated governs the relative strength of global deep ocean circulation. The Weddell and Ross Seas are well known regions of Antarctic bottom water formation, but in recent years it has emerged that the waters off Adelie Land in the vicinity of East 140 degrees Longitude is also an important region for bottom water generation (Refer to right figure)."

Also, as Nano and Pico-Phytoplankton do not produce as much DMS as larger phytoplankton and also do not sink to the bottom of the seafloor as well as larger phytoplankton, I suspect that if acidification and reduced water salinity kills off much of the older larger phytoplankton only to be replace new small phytoplankton; we will still wind-up with a net positive feedback that could be triggered within the next few decades.

Best,
ASLR

[Lennart van der Linde]

Did anyone have a look at the comments of Matt Whipple yet?
He very much doubts the Eemian-interpretation of Hansen et al:
http://www.atmos-chem-phys-discuss.net/15/C5284/2015/acpd-15-C5284-2015.pdf

No idea how well founded those doubts are.

[AbruptSLR]

Did anyone have a look at the comments of Matt Whipple yet?
He very much doubts the Eemian-interpretation of Hansen et al:
http://www.atmos-chem-phys-discuss.net/15/C5284/2015/acpd-15-C5284-2015.pdf

No idea how well founded those doubts are.

After reading Matt Whipple's comments, my impression is that Hansen et al 2015 know far more about this topic than Whipple does; and I expect that their response to his comment will likely clearly support my impression (i.e. I believe that Hansen et al 2015 interpretation of the late-Eemian period and that the Antarctic is likely the largest source for SLR in this period, is most likely nearly correct).

[Tor Bejnar]

Thanks, Bruce, for the context. 
That's what I get for not reading this thread thoroughly.

[AbruptSLR]

For anyone who thinks that ice mass loss from marine, and marine-terminating, glaciers, only happens at glacial speeds, then I recommend watching the linked YouTube video from the "Chasing Ice" documentary for the Jakobshavn Glacier (or Ilulissat Glacier):



Per the description of the video the event happened in 2008 at the: "...  Ilulissat Glacier in Western Greenland. The calving event lasted for 75 minutes and the glacier retreated a full mile across a calving face three miles wide. The height of the ice is about 3,000 feet, 300-400 feet above water and the rest below water."

If the Byrd Subglacier Basin glacial ice were to undergo cliff failures and hydrofacturing; such future events would almost certainly dwarf this 2008 Jakobshavn event.

[A-Team]

After reading Matt Whipple's comments, my impression is that Hansen et al 2015 know far more about this

Snarky millennial? Too important/busy to take time to develop comment, fix grammar etc. Ok, then I am too busy/important to figure out what his point is.

Whipple has just complete his dissertation at Bristol, no publications but 3rd author on a meeting talk and an abstract modestly sharing 'insights' from his thesis. Never set foot in Antarctica. His expertise manifestly dwarfs that of all the authors on the Hansen paper put together.

His next move should be to take an English class -- absolute disgrace so many foreigners write better scientific English than the natives.

The last interglaciation represents a period of warmer climates and higher sea levels, and a useful analogue to future climate. While many studies have focussed on the response of the Greenland Ice sheet, far less is known about the response of the Antarctic ice sheet. Here, I present the summarised results of my PhD thesis "Constraints on the minimum extent of the Antarctic ice sheet during the last interglaciation".

Firstly, I cover the timings of interglaciation in Antarctica, and their differences with respect to the Northern Hemisphere timings, based on paleo sea level indicators, and oceanic temperature records. I move on to cover climate forcings, and how they influence the ice sheet, relative to present, and early Holocene.

Secondly, I present thesis results, from looking at ice core stable water isotopes. These are compared with Isostatic and Climatic modelling results, for various different Ice sheet scenarios, as to the resulting Climate, from changes in Elevation, Temperature, Precipitation, and Sublimation, all contributing to the recorded stable water isotope record.

Thirdly, I move on to looking at the mid-field relative sea level records, from Australia and Argentina. Using isostatic modelling, these are used to assess the relative contribution of the Eastern and Western Antarctic Ice sheets. Although data uncertainties result in us being to identify the contribution from West Antarctica.

Overall, using model-data comparison, we find a lack of evidence for a substantial retreat of the Wilkes Subglacial basin. No data location is close enough to determine the existence of the marine based West Antarctic Ice sheet. Model uncertainty is unable to constrain evidence of variations in ice thickness in East Antarctica

.

Global sea level during the last interglacial is likely to have been between 5.5 and 9m above present (Dutton and Lambeck, 2012). Recent calculations, taking into account latest NEEM ice core information, suggest that Greenland would probably not have contributed more than 2.2m to this (Stone et al, 2013), implying a considerable contribution from Antarctica.

Previous studies have suggested a significant loss from the West Antarctic ice-sheet (e.g. Holden et al, 2010), which could be initiated following a collapse of the Atlantic Meridional Overturning Circulation (AMOC) and resultant warming in the Southern Ocean. Here, model simulations with FAMOUS and HadCM3 have been performed of the last interglacial under various scenarios of reduced Greenland and Antarctic ice-sheet configurations, and with and without collapsed AMOC.

Thermal expansion and changes in regional density structure (resulting from ocean circulation changes) can also influence sea level, in addition to ice mass effects discussed thus far. The HadCM3 and FAMOUS simulations will be used to estimate the contribution to global and regional sea level change in interglacials from the latter two factors using a similar methodology to the IPCC TAR/AR4 estimations of future sea level rise (Gregory and Lowe, 2000). The HadCM3 and FAMOUS both have a rigid lid in their ocean model, and consequently a fixed ocean volume. Thermal expansion can, however, be calculated as a volume change from in-situ density (a prognostic variable from the model). Relative sea surface topography will then be estimated from surface pressure gradients and changes in atmospheric pressure

[AbruptSLR]

A couple of years ago I downloaded the attached sea level PDF for 2100, produced by Richard Alley to convey his belief that the US Congress's attention was mostly focused on possible sea levels below the UN - IPCC projections for any given RCP forcing scenario; while he was recommending giving more consideration to the "fat-tailed" risk that he labels: abrupt climate change ice sheet collapse. 

However, if the Hansen et al 2015 "rule-of-thumb" estimates of the possible range of sea level rise scenarios (5-, 10- or 20-yr double times) are correct, then not only are the US Congress and the IPCC are engaging in wishful thinking, but so is Richard Alley (with all due respect to a talented, energetic and capable researcher).

[AbruptSLR]

ASLR, I read the Marshal & Speer 2012 you linked above. I will reread it a couple more times before it sinks in a little better. The two layers of MOC described is going to take me awhile to incorporate into the little mental picture I have developed re. " the conveyor ".  I was wondering if the upper layer is more " intermediate water " than deep water formation like I typically think of the MOC but I will reserve that as a question I need to track down an answer for.
 Thanks for the links and I will try to keep up with reading your insightful posts as well as the supporting documents.  Maybe the difference of trying to get an education over the Internet and an official one is having a sounding board of teachers and other students to get feedback on questions where here online we have to figure things out things alone.   
   

Possibly the following reference can shine some light on this rather complex matter:

Farneti, R., S.M. Downes, S.M. Griffies, S.J. Marsland, E. Behrens, M. Bentsen, D. Bi, A. Biastoch, C. Böning, A. Bozec, V.M. Canuto, E. Chassignet, G. Danabasoglu, S. Danilov, N. Diansky, H. Drange, P.G. Fogli, A. Gusev, R.W. Hallberg, A. Howard, M. Ilicak, T. Jung, M. Kelley, W.G. Large, A. Leboissetier, M. Long, J. Lu, S. Masina, A. Mishra, A. Navarra, A.J. George Nurser, L. Patara, B.L. Samuels, D. Sidorenko, H. Tsujino, P. Uotila, Q. Wang, and S.G. Yeager (2015), "An assessment of Antarctic Circumpolar Current and Southern Ocean Meridional Overturning Circulation during 1958-2007 in a suite of interannual CORE-II simulations", Ocean Model., doi:10.1016/j.ocemod.2015.07.009.

http://www.sciencedirect.com/science/article/pii/S1463500315001183

Abstract: "In the framework of the second phase of the Coordinated Ocean-ice Reference Experiments (CORE-II), we present an analysis of the representation of the Antarctic Circumpolar Current (ACC) and Southern Ocean Meridional Overturning Circulation (MOC) in a suite of seventeen global ocean-sea ice models. We focus on the mean, variability and trends of both the ACC and MOC over the 1958-2007 period, and discuss their relationship with the surface forcing. We aim to quantify the degree of eddy saturation and eddy compensation in the models participating in CORE-II, and compare our results with available observations, previous fine-resolution numerical studies and theoretical constraints. Most models show weak ACC transport sensitivity to changes in forcing during the past five decades, and they can be considered to be in an eddy saturated regime. Larger contrasts arise when considering MOC trends, with a majority of models exhibiting significant strengthening of the MOC during the late 20th and early 21st century. Only a few models show a relatively small sensitivity to forcing changes, responding with an intensified eddy-induced circulation that provides some degree of eddy compensation, while still showing considerable decadal trends. Both ACC and MOC interannual variability are largely controlled by the Southern Annular Mode (SAM). Based on these results, models are clustered into two groups. Models with constant or two-dimensional (horizontal) specification of the eddy-induced advection coefficient κ show larger ocean interior decadal trends, larger ACC transport decadal trends and no eddy compensation in the MOC. Eddy-permitting models or models with a three-dimensional time varying κ show smaller changes in isopycnal slopes and associated ACC trends, and partial eddy compensation. As previously argued, a constant in time or space κ is responsible for a poor representation of mesoscale eddy effects and cannot properly simulate the sensitivity of the ACC and MOC to changing surface forcing. Evidence is given for a larger sensitivity of the MOC as compared to the ACC transport, even when approaching eddy saturation. Future process studies designed for disentangling the role of momentum and buoyancy forcing in driving the ACC and MOC are proposed.

[A-Team]

Curious to hear your thoughts on yet another insipid McAneney post at RealClimate. And implications for Hansen et al?

I already reviewed the excellent Sigl paper and provided the same key graphic. It has two very great peculiarities, the first not profusely crediting dendrochronologist Billie for the detection of the dating error much earlier in 3 publications and even earlier in tactful but pointed remarks to Danish ice core researchers at a Niels Bohr Institute seminar in 1995, it taking some nerve to rosalindfranklin somebody in the same journal in 2015.

The second is the article's utter lack of interest in identifying where and how the Danish ice core people blundered so badly for so long on the no-brainer task of counting annual layers, refusing to listen to overwhelming evidence that they were wrong.

Without coming to grips with the error source, it is only going to get repeated and get worse going farther back in the Holocene. Indeed they are soon off by a couple of decades according to a very recent C¹⁴ paper. There is a zero-error tree ring record back 8200 kyr so we are really entitled to a zero-error ice layer attribution.

So don't believe anything you've read about impacts of stratospheric sulfur injection on Holocene climate (or models thereof) if they were tied to GICC05 and the wrong volcano. (This won't materially affect the Hansen paper.) My take on where things went wrong: cloning the chronology off older crummy Greenland cores, not recognizing a mid-first milennium event as two closely spaced volcanoes , and above all fixation on a mis-attributed Vesuvius tie point.

Then or now, the Danes simply cannot wrap their heads around the idea that their schoolbook's favorite Plinian eruption, which Pliny the Younger himself saw blow the wrong way, not to mention the 40.8º longitude and a middling VEI of 4, did not put a big ash layer down in north-central Greenland.

Nothing scientists like less than admitting to a mistake, unless it be when someone from the humanities (history) has
pointed it out. It's embarrassing, in the same league as your spouse finding a big invoice from AshleyMadison.com, but climate change is important and we need to root out the methodological errors and set the record straight.

McAneney in the post you mention kinda touches on this but not for long:

The one thing not mentioned though is how the error in GICC05 originated. The ice core dates for Eldgja and Hekla of 934 and 1104 have been in print since 1980  and they have been replicated in each Greenland ice core up to now, culminating in the GICC05 timescale. There are similar offsets with Antarctica ice cores that have been dated independently of the GICC05 timescale. An understanding of the origin of this error could help to evaluate the robustness of all ice core dating.

[sidd]

1)  Bintanja(2013) certainly agrees with the subject paper regarding the meltwater cap, but as important, in the reduced snowfall on Antarctica (and is, of course, referenced in the subject paper.) I like Bintanja, and I look forward to a day when he might collaborate with Curry (the Good) on a paper on the Southern Ocean.

2)Whipple's comment  is unconvincing in that, for one, it it becoming clear that GIS alone could not account for Eemian SLR, and absent WAIS it is difficult to see what might have done it.  I wish he would not have prefaced his comment with all the things he could talk about, but wasn't going to. And bringing up "not a very confident analysis"  in the next para ...

3)Another paper that supports the subject paper is the pretty Weber(2014) doi:10.1038/nature13397 work which is concerned with a later period than the Eemian, but does vividly exhibit the episodic melt pulses after LGM, and in addition:

" .. our model results show considerable Southern Ocean surface cooling,
expansion of sea ice, formation of a halocline, reduction of Antarctic
Bottom Water formation and subsurface warming at depths of 100–
1,500 m through poleward migration of Circumpolar Deep Water (Fig. 4).
Consistent with previous modelling experiments18,19, we suggest that
this ocean thermal forcing accelerated thinning of ice shelves by basal
melting, inducing a positive feedback by causing grounding-line retreat,
calving and subsequent release of more fresh water."

Didn't i just read this in the subject paper, and Bintanja ... ?

sidd

[AbruptSLR]

Hansen et al 2015 extensively discusses Heinrich events, including that recent evidence clarifies the importance of NH interaction with the Antarctic marine ice sheets and fast response ocean/atmospheric interactions (like ENSO and SAM), on past and the possible future Heinrich like abrupt SLR events.  As background to elaborate on this NH/SH interaction (via abrupt ice mass discharges), I provide the following Wikipedia extract & associated image:

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

Extract: "Gerard Bond suggests that changes in the flux of solar energy on a 1,500-year scale may be correlated to the Dansgaard-Oeschger cycles, and in turn the Heinrich events; however the small magnitude of the change in energy makes such an exo-terrestrial factor unlikely to have the required large effects, at least without huge positive feedback processes acting within the Earth system. However, rather than the warming itself melting the ice, it is possible that sea level change associated with the warming destabilised ice shelves. A rise in sea level could begin to corrode the bottom of an ice sheet, undercutting it; when one ice sheet failed and surged, the ice released would further raise sea levels — further destabilizing other ice sheets. In favour of this theory is the non-simultaneity of ice sheet break up in H1, 2, 4, and 5, where European breakup preceded European melting by up to 1,500 years (Maslin et al. 2001).
The Atlantic Heat Piracy model suggests that changes in oceanic circulation cause one hemisphere's oceans to become warmer at the other's expense (Seidov and Maslin 2001). Currently, the Gulf stream redirects warm, equatorial waters towards the northern Nordic Seas. The addition of fresh water to northern oceans may reduce the strength of the Gulf stream, and allow a southwards current to develop instead. This would cause the cooling of the northern hemisphere, and the warming of the southern, causing changes in ice accumulation and melting rates and possibly triggering shelf destruction and Heinrich events (Stocker 1998).
Rohling's 2004 Bipolar model suggests that sea level rise lifted buoyant ice shelves, causing their destabilisation and destruction. Without a floating ice shelf to support them, continental ice sheets would flow out towards the oceans and disintegrate into icebergs and sea ice.
Freshwater addition has been implicated by coupled ocean and atmosphere climate modeling (Ganopolski and Rahmstorf 2001), showing that both Heinrich and Dansgaard-Oeschger events may show hysteresis behaviour. This means that relatively minor changes in freshwater loading into the Nordic Seas — a 0.15 Sv increase, or 0.03 Sv decrease — would suffice to cause profound shifts in global circulation (Rahmstorf et al. 2005). The results show that a Heinrich event does not cause a cooling around Greenland but further south, mostly in the subtropical Atlantic, a finding supported by most available paleoclimatic data. This idea was connected to D-O events by Maslin et al.. (2001). They suggested that each ice sheet had its own conditions of stability, but that on melting, the influx of freshwater was enough to reconfigure ocean currents — causing melting elsewhere. More specifically, D-O cold events, and their associated influx of meltwater, reduce the strength of the North Atlantic Deep Water current (NADW), weakening the northern hemisphere circulation and therefore resulting in an increased transfer of heat polewards in the southern hemisphere. This warmer water results in melting of Antarctic ice, thereby reducing density stratification and the strength of the Antarctic Bottom Water current (AABW). This allows the NADW to return to its previous strength, driving northern hemisphere melting and another D-O cold event. Eventually, the accumulation of melting reaches a threshold, whereby it raises sea level enough to undercut the Laurentide ice sheet — causing a Heinrich event and resetting the cycle."

Caption: "Chronology of climatic events of importance for the Last Glacial Period (~last 120 000 years) as recorded in polar ice cores, and approximate relative position of Heinrich events, initially recorded in marine sediment cores from the North Atlantic Ocean. Light violet line: δ18O from the NGRIP ice core (Greenland), permil (NGRIP members, 2004). Orange dots: temperature reconstruction for the NGRIP drilling site (Kindler et al., 2014). Dark violet line: δ18O from the EDML ice core (Antarctica), permil (EPICA community members, 2006). Grey areas: major Heinrich events of mostly Laurentide origine (H1, H2, H4, H5). Grey hatch: major Heinrich events of mostly European origine (H3, H6). Light grey hatch and numbers C-14 to C-25: minor IRD layers registered in North Atlantic marine sediment cores (Chapman et al., 1999). HS-1 to HS-10: Heinrich Stadial (HS, Heinrich, 1988; Rasmussen et al., 2003; Rashid et al., 2003). GS-2 to GS-24: Greenland Stadial (GS, Rasmussen et al., 2014). AIM-1 to AIM-24: Antarctic Isotope Maximum (AIM, EPICA community members, 2006). Antarctica and Greeland ice core records are shown on their common timescale AICC2012 (Bazin et al., 2013; Veres et al., 2013)."

[AbruptSLR]

My last post focused on Heinrich events for the past 120,000 years and their NH/SH interaction.  However, such NH/SH interactions have been going on for a long time as indicated by the following 2012 internet article and associated paper, that clarify that part of the Northern Hemisphere/Southern Hemisphere synergistic interaction during paleo-interglacial periods is due to the collapse of the WAIS raising sea level sufficiently as to drive more warm Pacific ocean water into the Arctic Ocean through the Bering Strait.  Furthermore, the first attached image of GCM model results from Lawrence Berkeley Laboratories (circa 2010), shows that with continued warming (and stratification of the North Atlantic which slows the AMOC) that by 2035 more warm NADW will be entering the Arctic Basin from the Atlantic Ocean, which will not only acceleration Arctic Sea Ice loss then, but will also increase the risk of increased hydrate methane emissions from the Arctic continental shelf areas via heat induced submarine landslides (caused by the warm intermediate water from the Atlantic weakening the soil shear strength by melting some of the interstitial ice/hydrates in the soil on the slope) as illustrated by the Clathrate Gun hypothesis shown in the second attached image:

Extract: "Loss of Antarctic ice could trigger super-interglacial"
21 June 2012 by Michael Marshall

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


Martin Melles, Julie Brigham-Grette, Pavel S. Minyuk, Norbert R. Nowaczyk, Volker Wennrich, Robert M. DeConto, Patricia M. Anderson, Andrei A. Andreev, Anthony Coletti, Timothy L. Cook, Eeva Haltia-Hovi, Maaret Kukkonen, Anatoli V. Lozhkin, Peter Rosén, Pavel Tarasov, Hendrik Vogel & Bernd Wagner (20 July 2012), "2.8 Million Years of Arctic Climate Change from Lake El’gygytgyn, NE Russia", Science, Vol. 337 no. 6092 pp. 315-320, DOI: 10.1126/science.1222135

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

Edit: see also:
http://www.geo.umass.edu/faculty/jbg/
http://www.clim-past.net/special_issue48.html
http://www.sciencemag.org/content/340/6139/1421.abstract

[AbruptSLR]

Both of the following references indicate that the Greenland Ice Sheet will probably contribute more to SLR than previously expected; which of course will raise future sea levels around Antarctica, which will serve to help destabilize Antarctic ice shelves and marine glaciers in the future:

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

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

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


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

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

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

[AbruptSLR]

This post is a follow-up to my Reply #186, and presents a July 2015 updated paper (see also the attached image) on the paleo hypothesis that and abrupt collapse of the WAIS helps to trigger Arctic amplification.  As DeConto is one of the primary authors and he is also one of the main authors of the Pollard, DeConto and Alley 2015 on ASLR from Antarctic cliff failures and hydrofracturing; I think that we should all take these paleo findings very seriously when evaluating Hansen et al 2015's warming about the risks of ASLR this century:

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 timingof 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."

[AbruptSLR]

In many ways I feel that the Holsteinian Peak (MIS 11c) is more relevant to our current risks; therefore, for those not familiar with the comparison of the Eemian Peak (MIS 5) with the Holsteinian Peak (MIS 11), I provide both the first image from Hansen and Sato, and the following from Wikipedia: "Marine Isotope Stage 11 or MIS 11 is the interglacial period between 424,000 and 374,000 years ago. It corresponds to the geological Hoxnian Stage.  Interglacial periods which occurred during Pleistocene times have been recently put under investigation, in order to better understand our present and future climates. In fact, paleoclimatic interpretations often depends on observations drawn from the study of modern/historical processes. In order to better estimate the ”natural range” of climatically important mechanisms, it seems crucial to attempt detailed comparisons of the present interglacial (i.e., the Holocene) with previous warm periods of the Quaternary, such as Marine isotopic stage 11. Similar orbital configurations and comparable atmospheric greenhouse gas concentrations (considering only the period before the beginning of the Industrial Revolution, i.e. 1800 AD ca.) have led to the suggestion that MIS 11 is a suitable, possibly the best, geological analogue for the natural development of Holocene and future climate. Another candidate was MIS 5, but several characteristics do not fit the present conditions. MIS 11 represents the longest and warmest interglacial interval of the last 500 kyr. In fact, it shows the highest-amplitude deglacial warming in the last 5 Myr and possibly lasted twice the other interglacial stages. MIS 11 is characterized by overall warm sea-surface temperatures in high latitudes, strong thermohaline circulation, unusual blooms of calcareous plankton in high latitudes, higher sea level than the present, coral reef expansion resulting in enlarged accumulation of neritic carbonates, and overall poor pelagic carbonate preservation and strong dissolution in certain areas.  As stated above, MIS 11 is considered the warmest interglacial period of the last 500 kyr.  Nevertheless, some issues concern the lack of evidence for the trends and degree of warming during this interval. Recent isotopic and planktonic faunal data sets from high-accumulation rate marine successions in the North and South Atlantic indicate that MIS 11 was not warmer, but even slightly cooler than the Holocene. According to these data, the warmest interglacial period was likely MIS 5, although it was shorter.  Beach deposits in Alaska, Bermuda and the Bahamas, as well as uplifted reef terraces in Indonesia, suggest that global sea level reached as much as twenty metres above the present. During MIS 11, δ18O records show isotopic depletions that are consistent with a sea-level highstand, but temperature effect cannot be confidently disentangled from glacioeustasy. Moreover, the collapse of at least one major ice sheet has to be inferred in order to produce similar high sea-levels, nevertheless, the stability of these ice sheets is one of the main questions in climate-change research: in fact, controversial geologic evidences suggest that present-day polar ice sheets might have been disrupted (or drastically shrunk) during previous Pleistocene interglacials. The increased sea level requires reduction in modern polar ice sheets and is consistent with the interpretation that both the West Antarctica and the Greenland ice sheets were absent, or at least greatly reduced, during MIS 11. However, similar conditions would have led to much lighter δ18O values than the present, in contrast to what observed in oxygen isotope records worldwide.  Unlike most other interglacials of the late Quaternary, MIS 11 cannot be explained and modeled solely within the context of Milankovitch forcing mechanisms. According to various studies, the MIS 11 interglacial period was longer than the other interglacial stages; moreover, the sustained interglacial warmth lasted as long as it did, because the eccentricity was low and the amplitude of the precessional cycle diminished, resulting in several fewer cold substages during this period and also induced an abrupt climate change at MIS 12–11 transition, the most intense of the past 500 kyr. Noteworthy, MIS 11 developed just after one of the most “heavy” Pleistocene δ18O glacials (MIS 12). According to some Authors, MIS 12 is likely to represent a “minimum” within the 400-kyr cyclicity (which is apparently “stretched” into ca. 500-kyr cycles in the Pleistocene), same as the MIS 24/MIS 22 complex (ca. 900 ka; Wang et al., 2004). In support to this inference is the fact that these dramatic glacial intervals are coincident with periods of major climate reorganisation, namely the “Mid-Brunhes Event” (Jansen et al., 1986) and the “Mid-Pleistocene Revolution” (Berger & Jansen, 1994), respectively. Considering the variability in the astronomically-driven insolation, MIS 11 is the interval in which insolation is highly correlated with predicted near future situation. Using the 2-D Northern Hemisphere climate model to simulate climate evolution over MIS 11, MIS 5 and the future, it appears that climatic feature and length of MIS 11 are very similar to the present-future interglacial. This consideration may lead to the conclusion that actual interglacial period (begun 10 kyr) will continue for approximately 20-25 kyr"
As noted in the preceeding quote: "… paleoclimatic interpretations often depends on observations drawn from the study of modern/historical processes"

[AbruptSLR]

The following YouTube video features interviews of Bamber, Rignot, Velicogana, Pelto, Alley & others about the cryosphere & ice sheet SLR contributions, suggesting that the WAIS is past the tipping point:



Also, I would like to note that the stratification of the high latitude oceans postulated by Hansen et al 2015 is very insidious in that it not only allows warm deep water to reach the Greenland and Antarctic ice sheets, and not only backs-up the ocean heat in the tropics (thus promoting deep atmospheric convection that may increase ECS; Edit the first attached image by Sherwood et al 2014 shows how deep atmospheric convection in the Equatorial Pacific might mean that ECS is between 3 & 5C; while the second attached image from the Andrews Ringberg 2015 presentation shows how strong ocean warming in the Eastern Equatorial Pacific Ocean could mean an ECS values as high as 5C); but it also allows for Arctic Amplification by reducing both Arctic sea ice area-extent and Northern Hemisphere snow cover.

[AbruptSLR]

It seems to me that people should think of the Hansen et al 2015 analysis as more of a sophisticated thought experiment to characterize some key aspects of the possible abrupt introduction of fresh ice melt water to the high latitude oceans, in much the same way as the IPCC uses the RCP scenarios to characterize uncertainties about anthropogenic forcing and uncertainties about feedback mechanisms.

The key problem is that decision makers will only address the outputs of integrated models; whether those models are incomplete and/or inaccurate; and all of the current AR5 GCM (ESM) models do not evaluate the risks of the possible abrupt high latitude ocean surface water freshening events entail; and while Hansen et al 2015's thought experiment goes further than anyone else's attempts to characterize these risks; the Hansen et al 2015 output cannot be taken as a comprehensive projection of possible future events; which theoretically more comprehensive programs such are ACME are intended to try to do; hopefully after evaluating the findings of numerous researchers including Hansen et al 2015.

I have previously pointed at some of the risks that Hansen et al 2015's model my not have captured including positive feedback from: (a) changes in phytoplankton CO2 sequestration and DSM emissions; (b) changes in CO2 ventilation from ocean waters (largely associated with upwelling); (c) fast response Arctic Amplification; (d) ENSO, PDO, and IPO feedbacks, (e) deep atmospheric convective mixing feedbacks in the Tropical Pacific (e.g. see Sherwood et al 2014) and (f) possible Clathrate Gun triggering by warm NADW and CDW.  However, I would also like to note that Hansen has previously warned about the risks of slow response positive feedback mechanisms accelerating (say by the planetary energy imbalance that he demonstrates would happen due to the abrupt high-latitude ocean water freshening); which might include such mechanisms as: (a) accelerated permafrost degradation both due to fast response Artic Amplification and due to flooding of Arctic coastal areas due to ASLR; and (b) increase of methane's Global Warming Potential (GWP) as the increasing future concentration of atmospheric methane reduces the concentration of hydroxyl ions that chemically react with methane to convert it into other gases like CO2.

[AbruptSLR]

For those who want to read more about the slowing of the AMOC (noted by Hansen et al 2015) and the possible role of melt ice from Greenland, you can see the following linked reference, and attached image:

Rahmstorf, S., J.E. Box, G. Feulner, M.E. Mann, A. Robinson, S. Rutherford, and E.J. Schaffernicht (2015), Exceptional twentieth-century slowdown in Atlantic Ocean overturning circulation, Nature Clim. Change, 23 March 2015, doi: 10.1038/NCLIMATE2554

http://www.nature.com/nclimate/journal/v5/n5/full/nclimate2554.html

Abstract: "Possible changes in Atlantic meridional overturning circulation (AMOC) provide a key source of uncertainty regarding future climate change. Maps of temperature trends over the twentieth century show a conspicuous region of cooling in the northern Atlantic. Here we present multiple lines of evidence suggesting that this cooling may be due to a reduction in the AMOC over the twentieth century and particularly after 1970. Since 1990 the AMOC seems to have partly recovered. This time evolution is consistently suggested by an AMOC index based on sea surface temperatures, by the hemispheric temperature difference, by coral-based proxies and by oceanic measurements. We discuss a possible contribution of the melting of the Greenland Ice Sheet to the slowdown. Using a multi-proxy temperature reconstruction for the AMOC index suggests that the AMOC weakness after 1975 is an unprecedented event in the past millennium (p > 0.99). Further melting of Greenland in the coming decades could contribute to further weakening of the AMOC."


See also:
http://oceanbites.org/cooling-in-north-atlantic-defies-global-warming/

Extract: "Increased meltwater from glaciers due to global climate change increases the amount of low salinity seawater in the North Atlantic, thereby causing a slowdown in the AMOC. Although a permanent AMOC shutdown in the future remains very unlikely, short-term consequences from sluggish circulation are expected. Likely impacts include a rise in sea level along the US eastern seaboard that would impact cities like New York and Boston, more severe winter storms over Europe, and negative impacts on marine ecosystems and fisheries. Although these findings are significant, there is still much uncertainty about the natural variability and evolution of the AMOC over time due to unattainable continuous and direct measurements. This study is unique because it uses inferred evidence based on coral proxies to make hypotheses about past changes in ocean circulation. To what extent will global climate change affect the strength of the AMOC in the future? We may just have to wait and see. If the Greenland Ice Sheet continues to melt and the Arctic to freshen, the AMOC may continue to weaken over the next century, leading to more severe weather and extreme events."

[AbruptSLR]

I note that most current SLR projections do not consider the glacial isostatic rebound of the WAIS & adjoining marine glacial areas that could collapse abruptly; therefore, I provide the first image of the bedmap2 bottom elevations (with the ice removed without GIA), in contract to the second image of the Antarctic bottom elevations (with the ice removed and with GIA).  It is very clear that the indicated rebound will eventually add meters to future SLR.

[AbruptSLR]

As my last post discussed the long-term implications of Glacial Isostatic Adjustment, GIA; I thought that it would be helpful to note that the following reference indicates that after GIA correction the Amundsen Sea sector is contributing more to SLR than model GRACE measurements indicate, possibly by as much as 40%:

An investigation of Glacial Isostatic Adjustment over the Amundsen Sea sector, West Antarctica
by: A. Groh; H. Ewert, M. Scheinert, M. Fritsche, A. Rülke, A. Richter, R. Rosenau, R. Dietrich
http://dx.doi.org/10.1016/j.gloplacha.2012.08.001

Abstract
The present study focuses on the Amundsen Sea sector which is the most dynamical region of the Antarctic Ice Sheet (AIS). Based on basin estimates of mass changes observed by the Gravity Recovery and Climate Experiment (GRACE) and volume changes observed by the Ice, Cloud and Land Elevation Satellite (ICESat), the mean mass change induced by Glacial Isostatic Adjustment (GIA) is derived. This mean GIA-induced mass change is found to be 34.1 ± 11.9 Gt/yr, which is significantly larger than the predictions of current GIA models. We show that the corresponding mean elevation change of 23.3 ± 7.7 mm/yr in the Amundsen Sea sector is in good agreement with the uplift rates obtained from observations at three GPS sites. Utilising ICESat observations, the observed uplift rates were corrected for elastic deformations due to present-day ice-mass changes. Based on the GRACE-derived mass change estimate and the inferred GIA correction, we inferred a present-day ice-mass loss of − 98.9 ± 13.7 Gt/yr for the Amundsen Sea sector. This is equivalent to a global eustatic sea-level rise of 0.27 ± 0.04 mm/yr. Compared to the results relying on GIA model predictions, this corresponds to an increase of the ice-mass loss or sea-level rise, respectively, of about 40%.

The first accompanying figure shows an overview of the Amundsen Sea sector, West Antarctica. The red line defines the generalised drainage basins of Pine Island Glacier, Thwaites Glacier and Smith Glacier (PITS). Locations of three GPS campaign sites are marked by red triangles.

The second figures shows the GRACE data from 2003 to 2009 which the papers says needs to be corrected to indicate about 40% more ice mass loss than previously reported

[jai mitchell]

it appears that climatic feature and length of MIS 11 are very similar to the present-future interglacial. This consideration may lead to the conclusion that actual interglacial period (begun 10 kyr) will continue for approximately 20-25 kyr"

Ruddiman 2008 and 2013 shows that the early human ag contributed significantly to global CO2.

without this early human influence on the global climate we would have moved into a new ice age sometime around 2,000 B.C.E.



see discussion here:  http://www.realclimate.org/index.php/archives/2015/04/a-scientific-debate/

[AbruptSLR]

it appears that climatic feature and length of MIS 11 are very similar to the present-future interglacial. This consideration may lead to the conclusion that actual interglacial period (begun 10 kyr) will continue for approximately 20-25 kyr"

Ruddiman 2008 and 2013 shows that the early human ag contributed significantly to global CO2.

without this early human influence on the global climate we would have moved into a new ice age sometime around 2,000 B.C.E.



see discussion here:  http://www.realclimate.org/index.php/archives/2015/04/a-scientific-debate/

jai,

Thanks.  I will try to me more careful when/what I copy and paste from Wikipedia, see original text at:

https://en.wikipedia.org/wiki/Marine_Isotope_Stage_11

Nevertheless, I believe that MIS 11 is a valuable case to consider, especially when calibrating ice sheet models like that used in the ACME program, or by Pollard et al.

See also:
http://forum.arctic-sea-ice.net/index.php/topic,852.0.html

[bluesky]

AbruptSLR post 5241:
Extract: "The timingof 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."

May I ask you whether you would have an explanation for the possibile connection between Antartic melting and Arctic?

In relation to isostatic renound, i just wonder whether the effect on SLR is really significant as during glaciation period the lithosphere below the ice sheet subsides while the land outside bulges upward, once the ice sheet melt the isostatic rebound under the former ice sheet is taking place at the same time the earth subside in the surrounding. Maybe the the volume of subsidence/ rebound on one side  and bulging/subsidence on the other side are not equivalent? But even summing the 2 does it make a real impact compared to SLR from melting ice sheet? The isostatic rebound seems to be quite a long process (still going on in Scotland going up and London down, same in Scandinavia and Eastern Canada) although decaying and a exponential rate, so presumably could be significant at the beginning of the process but to which extent?

All the research papers are just incredibly interesting, i wish i had time to read them all, and effectively seem to give ground to Hansen et al scenario.
One thing which worries me is that climate change is extraordinarily complex and counter intuitive in many respect, and the knowledge gap between the scientific community including the small circle of people reading this blog (i know there are thousands reading it, but unfortunatly this is still small compared to the hundred of millions browsing the internet every day) and the wider public keeps increasing which is one of the reason why the decision maker are not doing much about it. There was an interesting arcticle in the New Scientists a couple of weeks ago "33 reasons we can't think clearly about climate change", and it is probably more urgent than ever to address these (is it discussed in another thread somewhere in the forum?)

[bluesky]

My apologies, as the answer to my isostatic rebound question is mostly in your following post showing the 40% impact of GIA in Amundsen Bay area, but still do wonder if there is a negative feedback with subsidence in the surrounding

[AbruptSLR]

AbruptSLR post 5241:
Extract: "The timingof 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."

May I ask you whether you would have an explanation for the possibile connection between Antartic melting and Arctic?

In relation to isostatic renound, i just wonder whether the effect on SLR is really significant as during glaciation period the lithosphere below the ice sheet subsides while the land outside bulges upward, once the ice sheet melt the isostatic rebound under the former ice sheet is taking place at the same time the earth subside in the surrounding. Maybe the the volume of subsidence/ rebound on one side  and bulging/subsidence on the other side are not equivalent? But even summing the 2 does it make a real impact compared to SLR from melting ice sheet? The isostatic rebound seems to be quite a long process (still going on in Scotland going up and London down, same in Scandinavia and Eastern Canada) although decaying and a exponential rate, so presumably could be significant at the beginning of the process but to which extent?

All the research papers are just incredibly interesting, i wish i had time to read them all, and effectively seem to give ground to Hansen et al scenario.
One thing which worries me is that climate change is extraordinarily complex and counter intuitive in many respect, and the knowledge gap between the scientific community including the small circle of people reading this blog (i know there are thousands reading it, but unfortunatly this is still small compared to the hundred of millions browsing the internet every day) and the wider public keeps increasing which is one of the reason why the decision maker are not doing much about it. There was an interesting arcticle in the New Scientists a couple of weeks ago "33 reasons we can't think clearly about climate change", and it is probably more urgent than ever to address these (is it discussed in another thread somewhere in the forum?)

bluesky,

I do not have much time now, so I will try to respond to what I can. 

First, you are referring to Reply # 193, as my number of posts (you cite 5,241 keep increasing).

Second, for your first question a paleo-collapse of the WAIS could increase temperatures in the Arctic by: 1. Slowing the rate of flow of the AMOC (via reduced AABW production); which would cause the North Atlantic current to get hotter and carry more heat into the Arctic; and 2. the increase in sea level associated with the WAIS collapse would deepen the Bering Strait which would allow more warm Pacific water to enter the Arctic Basin.

Third, as per the first attached image, GIA (or post-glacial rebound) has two components: 1. Elastic rebound, and 2. Visco-elastic rebound; and I suspect that you are ignoring the first; because when you consider both, the Amundsen Sea Embayment, ASE, has the highest rate of post-glacial rebound in the world at between 42 mm/year and 45mm/year (see the second image); which is partially due to the low mantle viscosity and the high rate of ice mass loss.

Fourth, as the ASE is roughly contribution about 0.5mm/yr to SLR, and as Hansen et al 2015 postulate about 3m of SLR from the ASE by 2100 for a 10-yr doubling rate; this implies that Hansen et al envision at least a rate 30mm/yr of SLR contribution from the WAIS.  Thus if one were to use linear extrapolation, if 0.5mm/yr SLR gives 45mm/yr of rebound then 30mm/yr SLR would give 2.7meter of rebound per year (or over 100-yrs about 270meter of rebound by 2140 in the greater Byrd Subglacial Basin, BSB).

Best,
ASLR

Edit: The third attached image by Vaughan et al 2011 verifies that the full Airy Isostatic Adjustment would be over 300m, and with a low mantle viscosity in the BSB, all of the Isostatic Adjustment would occur within 100 to 200 years (per the following linked video):

http://www.iris.edu/hq/webinar/2015/06/antarctic_seismology_revealing_the_secrets_of_an_icecovered_continent

Abstract: "The dynamics of ice sheets and their interaction with the solid earth is an important topic, with crucial implications for climate change and sea-level rise. Projections of ice sheet retreat and sea level rise are heavily influenced by solid earth properties such as basal heat flow, bed properties, lithospheric thickness and mantle viscosity. Recently installed seismic networks in Antarctica and developments in technology allowing year-round unattended seismograph operation even in the coldest regions now allow us to use seismology to investigate these interactions. We use seismic velocity maps to constrain parameters important for ice sheet models such as heat flow and mantle viscosity. Inferred mantle viscosity is lowest beneath Marie Byrd Land and highest beneath East Antarctica, and the variation is large enough to have a first order effect on glacial isostatic adjustment (GIA). Inferred mantle viscosity in West Antarctica is much lower than used in recent GIA models, and limits the GIA response to ice sheet mass changes to the last several hundred years. The Transantarctic Mountains lie along a first order boundary in mantle viscosity, probably leading to a complicated GIA response poorly modeled by 1-D viscosity models. West Antarctica shows low mantle seismic velocities associated with late Cenozoic rift systems and with a large mantle thermal anomaly supporting the Marie Byrd Land dome. These structures suggest high geothermal heat flow may have a first order effect on glacial dynamics in West Antarctica, as indicated by recent high heat flow measurements from the WAIS ice core. In addition, the recent discovery of deep-long period volcanic earthquakes beneath the ice sheet in Marie Byrd Land demonstrates the existence of active subglacial magmatic systems and suggests volcanic eruptions may have an important effect on the ice sheet."

Vaughan, D.G., Barnes, D.K.A., Fretwell, P.T., and Bingham, R.G., (2011), "Potential seaways across West Antarctica", Geochemistry Geophysics Geosystems, Vol. 12, No. 10, 7 October 2011, doi: 10.1029/2011GC003688