Ice Apocalypse - Multiple Meters Sea Level Rise

[prokaryotes]

Rapid collapse of Antarctic glaciers could flood coastal cities by the end of this century. Based on an article written by Eric Holthaus.

[gerontocrat]

Why a dedicated thread for this?

[Neven]

Why a dedicated thread for this?

On the one hand, I agree. On the other hand, it's an interesting video.

[prokaryotes]

This is kind of a summary, though planning to publish a video on surface melt vs basal.

[GeoffBeacon]

Was the article by Holthaus this one on grist?

It was criticised by Tamsin Edwards in the Guardian e.g.

But Eric is wrong to say Antarctica’s ‘ice budget’ has tipped out of balance due to our burning of fossil fuels. Not only has it been out of balance before – such as the ancient West Antarctic collapse that causes concern – but the reason for the Amundsen Sea changes, where most ice is being lost, is that the ring of deep warm water around Antarctica has welled up onto the continental shelf and is melting the ice from underneath. We don’t know if human activities made this more likely.

Any comments?

[AbruptSLR]

Any comments?

Geoff,

I enjoyed watching the short video, as it offers a nice summary in a manner that the general public can digest.  Regarding Tamsin Edwards' criticism, I would say that it is irrelevant whether we know, as a proven fact, that human activity has caused the Amundsen Sea Embayment, ASE, marine glaciers to cross their tipping points, as climate models combined with field observation make an almost certain fact.  For example:

1. Proistosescu & Huybers (2017) demonstrate convincingly that since 1750 anthropogenic activity has slowly been increasing the heat content of both the Tropical Pacific Ocean and the Southern Ocean; which not only increases ocean driving ice mass loss from West Antarctic marine glaciers, but also has activated a slow-response positive feedback mechanism that is currently increasing ECS to at least the upper end of the AR5 range.

Cristian Proistosescu and Peter J. Huybers (05 Jul 2017), "Slow climate mode reconciles historical and model-based estimates of climate sensitivity", Science Advances, Vol. 3, no. 7, e1602821, DOI: 10.1126/sciadv.1602821

http://advances.sciencemag.org/content/3/7/e1602821

Thus, not only are humans responsible for increasing the heat content of the Southern Ocean but the associated increase of the current ECS value means that the hydrofracturing mechanism described by DeConto & Pollard could begin as soon as 2040; which would greatly accelerate ice mass loss from all of the WAIS.

2.  There is no serious doubt that human activity caused the ozone hole over Antarctica, which accelerated the westerly wind velocities into a 'sweet spot' for promoting the increased upwelling of relatively warm circumpolar deepwater, CDW, onto the continental shelves that lead to key marine glaciers in the ASE (and other Antarctic marine glaciers).  Thus not only are we responsible for increasing the heat content of the CDW, but we are responsible for the mechanism that delivers this heat content to the grounding line of key marine glaciers.

3.  It is my opinion that human activity has accelerated surface ice mass loss from Greenland (including due to both decreased albedo from air pollution and from increased surface temperatures), which most likely caused a 'cold spot' in the North Atlantic, which most likely has somewhat slowed the Meridional Overturning Circulation, MOC.  Hansen et al (2016) indicates that this slowing of the MOC has reduced the formation of polynas in the Weddell Sea area, which has promoted an increase in Antarctic sea ice area, which has protected the upwelled CDW from cooling as much as it use to; which promotes grounding line retreat of key Antarctic marine glaciers.  This bipolar seesaw action contributes to Hansen's ice-climate feedback which further increases ECS and which further increases the risk of hydrofracturing of key ASE marine glaciers circa 2040.

I could go on, but my main point is that reticent scientists do not hesitate to dream-up any highly improbably scenario (like SSP1) to indicate that we may never cross the 2C limit; but then they do not hesitate to imply that much more probable scenarios that lead to GMSTAs approaching at least 2.7C (at which point DeConto & Pollard's ice cliff and hydrofracturing mechanisms kick into high gear) are not absolutely proven and thus do not merit serious consideration by busy decision makers who are bedeviled by other fat-tailed risks.  Such a reticent scientific posture is not good science.

Best,
ASLR

[Neven]

Tamsin Edwards is an apologist for climate risk denial, like a good Brit phlegmatically adding a couple of big paving stones to the road to hell.

[magnamentis]

Any comments?

Geoff,

I enjoyed watching the short video, as it offers a nice summary in a manner that the general public can digest.  Regarding Tamsin Edwards' criticism, I would say that it is irrelevant whether we know, as a proven fact, that human activity has caused the Amundsen Sea Embayment, ASE, marine glaciers to cross their tipping points, as climate models combined with field observation make an almost certain fact.  For example:

1. Proistosescu & Huybers (2017) demonstrate convincingly that since 1750 anthropogenic activity has slowly been increasing the heat content of both the Tropical Pacific Ocean and the Southern Ocean; which not only increases ocean driving ice mass loss from West Antarctic marine glaciers, but also has activated a slow-response positive feedback mechanism that is currently increasing ECS to at least the upper end of the AR5 range.

Cristian Proistosescu and Peter J. Huybers (05 Jul 2017), "Slow climate mode reconciles historical and model-based estimates of climate sensitivity", Science Advances, Vol. 3, no. 7, e1602821, DOI: 10.1126/sciadv.1602821

http://advances.sciencemag.org/content/3/7/e1602821

Thus, not only are humans responsible for increasing the heat content of the Southern Ocean but the associated increase of the current ECS value means that the hydrofracturing mechanism described by DeConto & Pollard could begin as soon as 2040; which would greatly accelerate ice mass loss from all of the WAIS.

2.  There is no serious doubt that human activity caused the ozone hole over Antarctica, which accelerated the westerly wind velocities into a 'sweet spot' for promoting the increased upwelling of relatively warm circumpolar deepwater, CDW, onto the continental shelves that lead to key marine glaciers in the ASE (and other Antarctic marine glaciers).  Thus not only are we responsible for increasing the heat content of the CDW, but we are responsible for the mechanism that delivers this heat content to the grounding line of key marine glaciers.

3.  It is my opinion that human activity has accelerated surface ice mass loss from Greenland (including due to both decreased albedo from air pollution and from increased surface temperatures), which most likely caused a 'cold spot' in the North Atlantic, which most likely has somewhat slowed the Meridional Overturning Circulation, MOC.  Hansen et al (2016) indicates that this slowing of the MOC has reduced the formation of polynas in the Weddell Sea area, which has promoted an increase in Antarctic sea ice area, which has protected the upwelled CDW from cooling as much as it use to; which promotes grounding line retreat of key Antarctic marine glaciers.  This bipolar seesaw action contributes to Hansen's ice-climate feedback which further increases ECS and which further increases the risk of hydrofracturing of key ASE marine glaciers circa 2040.

I could go on, but my main point is that reticent scientists do not hesitate to dream-up any highly improbably scenario (like SSP1) to indicate that we may never cross the 2C limit; but then they do not hesitate to imply that much more probable scenarios that lead to GMSTAs approaching at least 2.7C (at which point DeConto & Pollard's ice cliff and hydrofracturing mechanisms kick into high gear) are not absolutely proven and thus do not merit serious consideration by busy decision makers who are bedeviled by other fat-tailed risks.  Such a reticent scientific posture is not good science.

Best,
ASLR

another top post as always, must be mentioned from time to time

[A-Team]

Tamsin Edwards is an apologist for climate risk denial.

Here is an amusing commentary on their low-ball Antarctic scenario from G Laden and RB Alley.

I did not care for the timing (as it undercut a good public outreach effort from E Holthaus) nor the self-promotional tone of the Guardian piece, nor the barrage of followup tweets, from a minor figure in climate science seemingly assuming a major role as media spokesperson.

I wonder if she will morph into another Dahl-Jensen, Judith Curry, Andrew Rifken, or Bjorn Lomberg, the last thing we need right now in communicating climate risk. Or maybe just naive (as only a scientist can be) to how the Guardian post will be utilized by industry to muddy the risk waters.

I located her researchgate page and the never--published, never-cited 2006 dissertation on Z bosons; this constant recitation of being a particle physicist despite never having worked in that area in a professional capacity. It's not a qualification any more than neurosurgery because the physics of climate change is entirely nineteenth century newtonian (outside a few things like isotopes).

http://gregladen.com/blog/2015/11/22/antarctic-ice-sheet-deterioration-study-left-out-important-factors/
http://www.annualreviews.org/doi/abs/10.1146/annurev-earth-060614-105344?journalCode=earth
http://www.annualreviews.org/doi/abs/10.1146/annurev-earth-060614-105344?journalCode=earth
https://www.researchgate.net/profile/Tamsin_Edwards/contributions
https://www-d0.fnal.gov/results/publications_talks/thesis/edwards/thesis.pdf

"An engineer, a theoretical physicist [ie TE], and a paleoclimatologist are at a wedding. There is a ice large sculpture of a swan on a flat topped table, for decoration. The three start a betting pool on how long it will take for the entire swan, which has already started to melt, to end up on the floor.

The engineer notices some of the meltwater dribbling off the back of the table. She places a set of beer mugs under the streams of water, and records how long it takes for a measured amount of liquid to accumulate. She uses this to generate a graph showing melting over time, estimating the volume of the swan by looking it up in his manual on Ice Sculpture Specifications, and suggests that it will take eleven hours.

The theoretical physicist estimates the volume of ice by assuming a spherical swan, measures the air temperature, and calculates the rate of conversion from ice to water using thermodynamics. He comes up with a different estimate, because the engineer forgot to account for density differences in ice vs water. He estimates that the swan will be entirely the floor in eight and a half hours.

The paleoclimatologist disagrees, and says, “It will take between one and three hours for that swan to be on the floor.”

“Why do you think that, you are clearly an idiot, and I am clearly a physicist, so I must be right!” says the theoretical physicist.

Just as the paleoclimatologist is about to answer, the already melting neck of the swan breaks, and the upper part of the neck and head fall backwards, knocking off one of the large wings. All of those pieces slide off the table and crash on the floor. The stress of the impact causes the second wing to break off, but it stays on the table, but it begins to slowly slide toward the edge, clearly about to fall off as well.

“Because,” the paleoclimatologist says. “Last wedding I went to, that happened.”

[AbruptSLR]

I concur that paleo researchers can share a lot of insights with ESM modelers (see the linked open access reference), and one insight that CMIP6 modelers could learn would be to make some of their runs including subroutines of DeConto and Pollard's ice cliff failure and hydrofracturing mechanism, because without the introduction of such freshwater hosing into their models, they will never be able to match the climate responses indicated in the paleo record for Super Interglacials:

Anna S. von der Heydt, Peter Ashwin (Submitted on 12 Apr 2016), "State-dependence of climate sensitivity: attractor constraints and palaeoclimate regimes",    arXiv:1604.03311


http://arxiv.org/abs/1604.03311
&
http://arxiv.org/pdf/1604.03311v1.pdf

Abstract: "Equilibrium climate sensitivity is a frequently used measure to predict long-term climate change. However, both climate models and observational data suggest a rather large uncertainty on climate sensitivity (CS). The reasons for this include: the climate has a strong internal variability on many time scales, it is subject to a non-stationary forcing and it is, on many timescales, out of equilibrium with the changes in the radiative forcing. Palaeo records of past climate variations give insight into how the climate system responds to various forcings although care must be taken of the slow feedback processes before comparing palaeo CS estimates with model estimates. In addition, the fast feedback processes can change their relative strength and time scales over time. Consequently, another reason for the large uncertainty on palaeo climate sensitivity may be the fact that it is strongly state-dependent. Using a conceptual climate model, we explore how CS can be estimated from unperturbed and perturbed model time series. Even in this rather simple model we find a wide range of estimates of the distribution of CS, depending on climate state and variability within the unperturbed attractor. For climate states perturbed by instantaneous doubling of CO2, the sensitivity estimates agree with those for the unperturbed model after transient decay back the attractor. In this sense, climate sensitivity can be seen as a distribution that is a local property of the climate attractor. We also follow the classical climate model approach to sensitivity, where CO2 is prescribed and non-dynamic, leading to CS values consistently smaller than those derived from the experiments with dynamic CO2. This suggests that climate sensitivity estimates from climate models may depend significantly on future dynamics, and not just the level of CO2."

Extract: “... the presence of variability on the attractor on a number of timescales means there are clear and non-trivial distributions of sensitivities, even for unperturbed climates. The distribution of sensitivities depends strongly on the background state as well as on the timescale considered. This suggests that it could be useful to think of the unperturbed climate sensitivity as a local property of the “climate attractor”. For a perturbed system (we have considered instantaneously doubled CO2) this is still useful once an initial transient has decayed. This transient will depend in particular on ocean heat uptake, though also on carbon cycle and biosphere processes that act on time scales roughly equivalent with the forcing time scale. If the climate system has more than one attractor, the perturbed system may clearly evolve to a completely different set of states than the original attractor – a situation that did not occur in the climate model used here. In less extreme cases, there may still be very long transients for some perturbations associated parts of the climate system that are associated with slow feedbacks.

Such perturbations (illustrated in Fig. 1b,d) are not normally applied in climate models used for climate predictions [IPCC, 2013], where climate sensitivity is derived from model simulations considering prescribed, non-dynamic atmospheric CO2. In our conceptual model, we have derived climate sensitivities from both types of perturbations and find that the classical climate model approach (section 2.2, Fig. 4f) leads to significantly lower values of the climate sensitivity than the perturbations away from the attractor with dynamic CO2 (section 2.3, Fig. 11a). This emphasises the importance of including dynamic carbon cycle processes into climate prediction models. Moreover, it supports the idea that the real observed climate response may indeed be larger than the model predicted."

Edit, see also:

https://link.springer.com/article/10.1007/s40641-016-0049-3
&
https://pubs.geoscienceworld.org/gsa/geology/article-abstract/45/7/643/207872/el-nino-southern-oscillation-like-variability-in-a?redirectedFrom=fulltext

[GeoffBeacon]

I've just posted excerpts of one of AbruptSLR's comments and Neven's on the Guardian's site.

I might go back later to add some of A-Team's comment.

[GeoffBeacon]

Not much of a surprise when the Guardian removed my comment and left

This comment was removed by a moderator because it didn't abide by our community standards. Replies may also be deleted. For more detail see our FAQs.

This may be off-topic. I have started a new thread Censorship by the good guys

[prokaryotes]

There is another new study on winds due to CO2 increase, causing more upwelling, and may cause through this mechanism warm water intrusion at Totten glacier -- holds more than 11 feet of sea level rise, located in East Antarctica


Press release https://news.utexas.edu/2017/11/01/winds-driving-warm-water-under-east-antarctic

[AbruptSLR]

I've just posted excerpts of one of AbruptSLR's comments and Neven's on the Guardian's site.

I might go back later to add some of A-Team's comment.

Geoff,

It can be tiresome to play games with reticent scientists/denialist as they hide behind the inherent complexity and uncertainties of climate change, with the essence of their game plan captured by Cardinal Richelieu's following quote:

"If you give me six lines written by the hand of the most honest of men, I will find something in them which will hang him."

https://en.wikiquote.org/wiki/Cardinal_Richelieu

Nevertheless, as I believe that this is a topic of some fundamental importance, I will try to provide a series of posts, over the coming days/weeks, that can provide some counter arguments to Tamsin Edwards' points, in order to illustrate that the risks of the possible early collapse of the WAIS is likely higher than she implies.

In this regards:

My first image shows NOAA's 2017 SLR guidance; which recommends that significant coastal structures (such as power plants, etc.) should consider 2.5m of SLR by 2100; which is improbably without significant SLR contribution from the WAIS.  I start with this image because NOAA is a conservative US authority on SLR and their guidance can be used as a baseline to which more possible SLR contributions from the WAIS this century and be added.

My second image from DeConto & Pollard (2016) extended data, illustrates that Edwards is correct that in this initial assessment using RCP 8.5 with ECS about 3C, that the peak SLR contribution from the WAIS does not occur until about 2150; however, when DeConto & Pollard use RCP 8.5 together with Hansen's ice-climate interaction, the peak SLR contribution from the WAIS shifts to about 2100 (which is more contribution than assumed by NOAA's 2017 guidance).

Next, DeConto & Pollard's work indicates that their cliff failure and hydrofracturing mechanisms become highly activated before GMSTA reaches 2.7C.  However, as the third image indicates that when following CMIP5 (as DeConto & Pollard (2016) did) this threshold is not reached until about 2070; while if one uses the paleo-calibrated estimate of ECS provided by Tobias Friedrich et al (2016), one sees that we may cross this threshold around 2045 (I note that Hansen's ice-climate work assumed a value for ECS that was compatible with CMIP5).  Thus DeConto & Pollard's extended data peak contribution with ice-climate interaction of about 2100 could be moved forward in time to about 2075, using Friedrich et al's estimate for ECS.

Lastly (for this post), the fourth image from SkS's response to work by Cristian Proistosescu and Peter J. Huybers (05 Jul 2017), therein PH17, indicate that there is substantial fat-tailed risk that Friedrich et al's value for ECS may be two low, and that more advanced ESM projections indicate a risk that ECS may be between 6 and 8C (which could move the date for the peak SLR contribution from the WAIS to a date meaningful earlier than 2075).

Best,
ASLR

[AbruptSLR]

As a follow-on to my last post, the Bakker et al (2017) reference, cited below, presents a worked example of how to calibrate a scenario (see the first image for part of the calibration process using both paleo ,and observed, data) for the potential collapse of the WAIS this century.  Bakker et al (2017) then effectively summarize the findings from their calibrated scenario, w.r.t. to its impact on SLR, in an easily understood plot (see the second attached image) of Sea level with time and scenarios with varying degrees of 'deep uncertainty.  Also, I note that Bakker et al (2017) indicate that: "Around 2040-2050, a large and uncertain contribution of the GIS becomes important …"

Alexander M. R. Bakker, Tony E. Wong, Kelsey L. Ruckert & Klaus Keller (2017), "Sea-level projections representing the deeply uncertain contribution of the West Antarctic ice sheet", Scientific Reports 7, Article number: 3880; doi:10.1038/s41598-017-43134-5

http://www.nature.com/articles/s41598-017-04134-5

Abstract: "There is a growing awareness that uncertainties surrounding future sea-level projections may be much larger than typically perceived. Recently published projections appear widely divergent and highly sensitive to non-trivial model choices. Moreover, the West Antarctic ice sheet (WAIS) may be much less stable than previous believed, enabling a rapid disintegration. Here, we present a set of probabilistic sea-level projections that approximates the deeply uncertain WAIS contributions. The projections aim to inform robust decisions by clarifying the sensitivity to non-trivial or controversial assumptions. We show that the deeply uncertain WAIS contribution can dominate other uncertainties within decades. These deep uncertainties call for the development of robust adaptive strategies. These decision-making needs, in turn, require mission-oriented basic science, for example about potential signposts and the maximum rate of WAIS-induced sea-level changes."

Extract: "Our sea-level projections are constructed to support robust decision frameworks by i) being explicit about the relevant uncertainties, both shallow and deep; ii) communicating plausible ranges of sea-level rise, including the deep uncertainties surrounding future climate forcings and potential WAIS collapse; and iii) tending to err on the side of underconfident versus overconfident when possible.

Model design. We design the projections to be probabilistic where reasonable and explicit about deep uncertainties (e.g. resulting from non-trivial model choices) when needed. Robust decision frameworks often apply plausible rather than probabilistic ranges to represent and communicate uncertainties. In the case of sea-level projections, the bounding of the plausible range usually involves both a probabilistic interpretation of the surrounding uncertainties and estimates of which probabilities are still relevant. For example, a full disintegration of the major ice sheets is often not taken into account because the probabilities of this occurring are considered too
small to be relevant. What probability is relevant is highly dependent on the decision context and therefore it makes sense to be explicit about the probabilities. Moreover, probabilities are the easiest and most unambiguous way to communicate uncertainties.

Our projections are designed to highlight the relatively large deep uncertainties, notably those resulting from future climate forcings and those surrounding potential WAIS collapse (even though representations of deep uncertainty often implicitly encompass probabilistic interpretations). The future climate forcing is, to a large extent, controlled by future human decisions.

The probability of a WAIS collapse is potentially much larger than previously thought due to the combined effects of Marine Ice Sheet Instability (MISI), ice cliff failure and hydrofracturing. The discovery of this new mechanism puts earlier expert elicitations in a different light as it is unclear if those were based on this combined effect. One approach when faced with deeply uncertain model structures and priors is to present a potential WAIS collapse as deeply uncertain by means of a plausible range. We stress that this range is not meant to represent an implicit probabilistic projection of the WAIS contribution to sea-level rise.

We merge some small deep uncertainties into the probabilistic part of the projections. According to Herman et al. “… a larger risk lies in sampling too narrow a range (thus ignoring potentially important vulnerabilities) rather than too wide a range which, at worst, will sample extreme states of the world in which all alternatives fail”.  Thus, in the context of informing robust decision making, it can be preferable to be slightly under- than slightly overconfident. To minimize the risk of producing overconfident projections we only use observational data with relatively uncontroversial and well-defined error structure.

Model setup. We use a relatively simple (39 free physical and statistical parameters), but a mechanistically motivated model framework to link transient sea-level rise to radiative concentration pathways applying sub-models for the global climate, thermal expansion (TE), and contributions of the Antarctic ice sheet (AIS), Greenland ice sheet (GIS) and glaciers and small ice caps (GSIC) (see Methods). This approach extends on the semi-empirical model setup recently reported by Mengel et al..

We use a Bayesian calibration method, wherein paleoclimatic data is assimilated with the AIS model separately from the calibration for the rest of the model, which assimilates only modern observations. Modern model simulations are then run at parameters drawn from the two resulting calibrated parameter sets (AIS and rest-of-model) and compared to global mean sea-level (GMSL) data (see Methods). Only model realizations which agree with each GMSL data point to within 4σ are admitted into the final ensemble for analysis. 4σ was chosen so the spread in the model ensemble characterizes well the uncertainty in the GMSL data (Fig. 1f). We choose, at this time, not to use paleo-reconstructions nor reanalyses, beyond incorporating a windowing
approach into our calibration method for the Antarctic ice-sheet parameters. This choice is motivated by the highly complex and uncertain error structure of these data sets. Failure to account for such complex error structure can result in considerable overconfidence, especially for low-probability events."

Furthermore, Bakker et al (2017) cite the second linked reference which provides a worked example of how the potential bias of a current model can be quantified by comparing its projections against the projections of a dynamical model with 'deep uncertainty', in this cases one that includes the dynamical mechanism of cliff failures and hydrofracturing w.r.t. to SLR contributions from the Antarctic ice sheet.  To the best of my understanding none of the Earth System Models in CMIP6 include the dynamical cliff failures, and hydrofracturing, mechanisms, apparently due to 'deep uncertainty'.  Nevertheless, even if CMIP6/AR6 do not present projections including the impacts of the dynamical cliff failures, and hydrofractuing, mechanisms, they could still numerically present the potential bias of their projections by following the methodology presented by Ruckert et al (2017), & in this regards see the last two attached images.


Kelsey L. Ruckert, Gary Shaffer, David Pollard, Yawen Guan, Tony E. Wong, Chris E. Forest &Klaus Keller (2017), "Assessing the impact of retreat mechanisms in a simple Antarctic ice sheet model using Bayesian Calibration", PLoS ONE, 12, 1-15, https://doi.org/10.1371/journal.pone.0170052

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0170052

Abstract: "The response of the Antarctic ice sheet (AIS) to changing climate forcings is an important driver of sea-level changes. Anthropogenic climate change may drive a sizeable AIS tipping point response with subsequent increases in coastal flooding risks. Many studies analyzing flood risks use simple models to project the future responses of AIS and its sea-level contributions. These analyses have provided important new insights, but they are often silent on the effects of potentially important processes such as Marine Ice Sheet Instability (MISI) or Marine Ice Cliff Instability (MICI). These approximations can be well justified and result in more parsimonious and transparent model structures. This raises the question of how this approximation impacts hindcasts and projections. Here, we calibrate a previously published and relatively simple AIS model, which neglects the effects of MICI and regional characteristics, using a combination of observational constraints and a Bayesian inversion method. Specifically, we approximate the effects of missing MICI by comparing our results to those from expert assessments with more realistic models and quantify the bias during the last interglacial when MICI may have been triggered. Our results suggest that the model can approximate the process of MISI and reproduce the projected median melt from some previous expert assessments in the year 2100. Yet, our mean hindcast is roughly 3/4 of the observed data during the last interglacial period and our mean projection is roughly 1/6 and 1/10 of the mean from a model accounting for MICI in the year 2100. These results suggest that missing MICI and/or regional characteristics can lead to a low-bias during warming period AIS melting and hence a potential low-bias in projected sea levels and flood risks."

Extract: " We calibrate a simple AIS model (that does not include a cliff instability mechanism nor is able to capture regional characteristics) with observational constraints over the past 240,000 years using a Bayesian inversion considering the heteroskedastic nature of the data. Using the hindcasts and projections, we compare our results to those from a pre-calibration method and expert assessments with potentially more realistic models. We approximate how neglecting fast processes (i.e., the MICI mechanism) in an AIS model can lead to biases in the AIS hindcasts and projections during warming periods. For the specific example considered, we show how missing MICI produces a lower mean hindcast (roughly 26% or 1 m smaller) during the LIG, a period when the marine ice sheet is suggested to have deglaciated. Additionally, the model is unable to account for roughly 96 and 100% of future AIS contributions predicted by a physically more realistic model accounting for MISI, MICI, and hydro-fracturing yet reproduces the projected median melt in other expert assessments in the year 2100. Overall, accounting for retreat mechanisms can potentially increase warming period AIS melt and reduce model discrepancy."

[AbruptSLR]

Edwards' claim that BAU is best represented by the Paris Accord path forward, is nothing more than her personal opinion, as the first attached image issued by the Global Carbon Project compares the SSP scenarios vs the observed projected thru 2017 for the fossil fuel and land use change CO2 emissions.  This plot indicates that we are currently following the SSP5 Baseline pathway, and not SSP3 which roughly represents the Paris Accord path forward.  This point is clarified by the second attached image where the authors of the Shared Socioeconomic Pathways, SSPs, label both SSP5 and SSP3 as baseline scenario depending on the decision maker's point of view.  However, I note that even SSP5 baseline can be taken to be optimistic as the third image indicates that SSP5 assumes a world population of about 8.5 billion by 2050; while the fourth image of the 2017 UN projection of global population gives a 50-50 chance that the world population will be 9.8 billion by 2050.  Thus taking SSP5/RCP 8.5 as BAU is fully supported by the IPCC process.

Also, I note that NASA's 12-month running GISTEMP value for GMSTA corrected to a pre-industrial baseline thru October 2017 is currently 1.159C, which is high, and that CO2e is over 521ppm to 530ppm (depending on how one treats ozone's contribution), which is also high.  So both of these parameters support the idea that we are currently following a SSP5/RCP 8.5 pathway.

[A-Team]

Not much of a surprise when the Guardian removed my comment and left "This comment was removed by a moderator because it didn't abide by our community standards. Replies may also be deleted.

Right, good effort Geoff. They probably wanted you to express views in your own words. Copy/paste opens too many doors to mass orchestrated submissions.

However ... newspapers are always looking for free content and seeking 'balance'. The Guardian is driven financially by investment income from its giant charitable endowment. I don't imagine they are invested in high risk, low-return Puerto Rican reconstruction bonds nor feel-good green energy projects but rather have a conventional large cap stock portfolio, meaning their income -- and the paper's very survival -- rises and falls with capitalism and ponzical growth. So it 'makes sense' to have climate coverage in alignment.

While we don't know if the Guardian has contracted with T Edwards to spin future climate coverage, I don't expect them to hit rock bottom like the NYTimes, all those years of Revkin followed by firing the entire environmental desk. Meanwhile Chris Mooney for the WaPo/Bezos is making them look stupid; and Masters/Benson climate commentary at Wunderground is so far being tolerated by new owner IBM.

tiresome to play games with reticent scientists/denialist/delayers/minimizers

Right. Some climate scientists are not going to stay on message, no matter what the societal costs. The whole idea is be different, get noticed as an iconoclastic paradigm-challenger. Journals favor controversy-engendering articles that bump citation rankings; universities hire full-time PR staff to hype mundane faculty accomplishments. The planets are in alignment.

How many times has Antarctica been modeled in the last twenty years? I'm going to say 1000 papers. Picture yourself in early career about to write #1001, knowing a choice of internal parameters for your ensemble runs that merely affirms #1000 would be unpublishable and possibly fatal to your livelihood.  Whereas a different choice would get you noticed, all the more so if backed by non-stop horn-tooting.

Alternatively, imagine you ran down your machine time budget before finally realizing what you should have done -- what to do with what you did? Publish it.

There's no need to feel guilty because 'everyone does it' plus #1002 will come along soon enough, overwriting your societal damage because those authors need to conflict with #1001. There are unrealistic pressures on young researchers today.

[AbruptSLR]

T. Edwards' comment that no other model other than Pollard and DeConto (2016) indicates such rapid ice mass loss from the WAIS ignores the significance of modeling efforts such as the following:

David Pollard, Won Chang, Murali Haran, Patrick Applegate, and Robert DeConto (2016), "Large ensemble modeling of the last deglacial retreat of the West Antarctic Ice Sheet: comparison of simple and advanced statistical techniques", Geosci. Model Dev., 9, 1697–1723, doi:10.5194/gmd-9-1697-2016

http://www.geosci-model-dev.net/9/1697/2016/gmd-9-1697-2016.pdf
www.geosci-model-dev.net/9/1697/2016/


Abstract. A 3-D hybrid ice-sheet model is applied to the last deglacial retreat of the West Antarctic Ice Sheet over the last ~20 000 yr. A large ensemble of 625 model runs is used to calibrate the model to modern and geologic data, including reconstructed grounding lines, relative sea-level records, elevation–age data and uplift rates, with an aggregate score computed for each run that measures overall model–data misfit. Two types of statistical methods are used to analyze the large-ensemble results: simple averaging weighted by the aggregate score, and more advanced Bayesian techniques involving Gaussian process-based emulation and calibration, and Markov chain Monte Carlo. The analyses provide sea-level-rise envelopes with well-defined parametric uncertainty bounds, but the simple averaging method only provides robust results with full-factorial parameter sampling in the large ensemble. Results for best-fit parameter ranges and envelopes of equivalent sea-level rise with the simple averaging method agree well with the more advanced techniques.  Best-fit parameter ranges confirm earlier values expected from prior model tuning, including large basal sliding coefficients on modern ocean beds.

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Won Chang, Murali Haran, Patrick Applegate, David Pollard (October 7, 2015), "Improving Ice Sheet Model Calibration Using Paleoclimate and Modern Data"

http://arxiv.org/pdf/1510.01676.pdf

Abstract: "Human-induced climate change may cause significant ice volume loss from the West Antarctic Ice Sheet (WAIS). Projections of ice volume change from ice-sheet models and corresponding future sea-level rise have large uncertainties due to poorly constrained input parameters. In most future applications to date, model calibration has utilized only modern or recent (decadal) observations, leaving input parameters that control the long-term behavior of WAIS largely unconstrained. Many paleo-observations are in the form of localized time series, while modern observations are non-Gaussian spatial data; combining information across these types poses nontrivial statistical challenges. Here we introduce a computationally efficient calibration approach that utilizes both modern and paleo-observations to generate better-constrained ice volume projections.

Using fast emulators built upon principal component analysis and a reduced dimension calibration model, we can efficiently handle high-dimensional and non-Gaussian data. We apply our calibration approach to the PSU3D-ICE model which can realistically simulate long-term behavior of WAIS. Our results show that using paleo observations in calibration significantly reduces parametric uncertainty, resulting in sharper projections about the future state of WAIS. One benefit of using paleo observations is found to be that unrealistic simulations with overshoots in past ice retreat and projected future regrowth are eliminated."

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David Pollard, Robert DeConto, Won Chang, Patrick Applegate and Murali Haran (Dec 18, 2015), "Modeling of past and future variations of the Antarctic Ice Sheet with Large Ensembles" AGU Fall Meeting, Paper 60833.

https://agu.confex.com/agu/fm15/meetingapp.cgi/Paper/60833

Abstract: "Recent observations of thinning and retreat of the Pine Island and Thwaites Glaciers identify the Amundsen Sea Embayment (ASE) sector of West Antarctica as particularly vulnerable to future climate change. To date, most future modeling of these glaciers has been calibrated using recent and modern observations. As an alternate approach, we apply a hybrid 3-D ice sheet-shelf model to the last deglacial retreat of Antarctica, making use of geologic data from ~20,000 years BP to present, focusing on the ASE but including other sectors of Antarctica.
Following several recent ice-sheet studies, we use Large Ensemble statistical methods, performing sets of ~600 runs over the last 30,000 years with systematically varying model parameters. Objective scores for each run are calculated using modern data and past reconstructed grounding lines, relative sea level records, cosmogenic elevation-age data and uplift rates. Two types of statistical methods are used to analyze the Large-Ensemble results: simple averaging weighted by the aggregate score, and more advanced Bayesian emulation and calibration methods that rigorously account for some of the uncertainties in the model and observations.

Results for best-fit parameter ranges and envelopes of equivalent sea-level rise with the simple averaging method agree quite well with the more advanced techniques, but only for a Large Ensemble with dense (Full Factorial) parameter sampling. Runs are extended into the future using RCP scenarios, with drastic retreat mechanisms of hydrofracturing and structural ice-cliff failure. In most runs this produces grounding-line retreat into the West Antarctic interior, and into East Antarctic basins for RCP8.5, and the Large Ensemble analysis provides sea-level-rise envelopes with well defined parametric uncertainty bounds."

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E. Gasson, R.M. DeConto, D. Pollard, and R.H. Levy (2016), "Dynamic Antarctic ice sheet during the early to mid-Miocene", Proceedings of the National Academy of Sciences, pp. 201516130, doi: 10.1073/pnas.1516130113

http://www.pnas.org/content/early/2016/02/17/1516130113

Significance: "Atmospheric concentrations of carbon dioxide are projected to exceed 500 ppm in the coming decades. It is likely that the last time such levels of atmospheric CO2 were reached was during the Miocene, for which there is geologic data for large-scale advance and retreat of the Antarctic ice sheet. Simulating Antarctic ice sheet retreat is something that ice sheet models have struggled to achieve because of a strong hysteresis effect. Here, a number of developments in our modeling approach mean that we are able to simulate large-scale variability of the Antarctic ice sheet for the first time. Our results are also consistent with a recently recovered sedimentological record from the Ross Sea presented in a companion article."

Abstract: "Geological data indicate that there were major variations in Antarctic ice sheet volume and extent during the early to mid-Miocene. Simulating such large-scale changes is problematic because of a strong hysteresis effect, which results in stability once the ice sheets have reached continental size. A relatively narrow range of atmospheric CO2 concentrations indicated by proxy records exacerbates this problem. Here, we are able to simulate large-scale variability of the early to mid-Miocene Antarctic ice sheet because of three developments in our modeling approach. (i) We use a climate–ice sheet coupling method utilizing a high-resolution atmospheric component to account for ice sheet–climate feedbacks. (ii) The ice sheet model includes recently proposed mechanisms for retreat into deep subglacial basins caused by ice-cliff failure and ice-shelf hydrofracture. (iii) We account for changes in the oxygen isotopic composition of the ice sheet by using isotope-enabled climate and ice sheet models. We compare our modeling results with ice-proximal records emerging from a sedimentological drill core from the Ross Sea (Andrill-2A) that is presented in a companion article. The variability in Antarctic ice volume that we simulate is equivalent to a seawater oxygen isotope signal of 0.52–0.66‰, or a sea level equivalent change of 30–36 m, for a range of atmospheric CO2 between 280 and 500 ppm and a changing astronomical configuration. This result represents a substantial advance in resolving the long-standing model data conflict of Miocene Antarctic ice sheet and sea level variability."

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Dewi Le Bars, Sybren Drijfhout and Hylke de Vries (3 April 2017), "A high-end sea level rise probabilistic projection including rapid Antarctic ice sheet mass loss",
Environmental Research Letters, Volume 12, Number 4 , https://doi.org/10.1088/1748-9326/aa6512

http://iopscience.iop.org/article/10.1088/1748-9326/aa6512
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http://iopscience.iop.org/article/10.1088/1748-9326/aa6512/pdf

Abstract: "The potential for break-up of Antarctic ice shelves by hydrofracturing and following ice cliff instability might be important for future ice dynamics. One recent study suggests that the Antarctic ice sheet could lose a lot more mass during the 21st century than previously thought. This increased mass-loss is found to strongly depend on the emission scenario and thereby on global temperature change. We investigate the impact of this new information on high-end global sea level rise projections by developing a probabilistic process-based method. It is shown that uncertainties in the projections increase when including the temperature dependence of Antarctic mass loss and the uncertainty in the Coupled Model Intercomparison Project Phase 5 (CMIP5) model ensemble. Including these new uncertainties we provide probability density functions for the high-end distribution of total global mean sea level in 2100 conditional on emission scenario. These projections provide a probabilistic context to previous extreme sea level scenarios developed for adaptation purposes."

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Furthermore, T. Edwards ignores the linked reference which discusses state of the art surface temperature at the West Antarctic Divide for the past ~ 40,000 years, that indicate that current climate models are challenged to hind cast the observed findings and that models with low climate sensitivities can be eliminated from consideration.  Furthermore, they find that an Antarctic Amplification of 2 to 3 time GMSTA. 

Kurt M. Cuffey, Gary D. Clow, Eric J. Steig, Christo Buizert, T. J. Fudge, Michelle Koutnik, Edwin D. Waddington, Richard B. Alley, and Jeffrey P. Severinghaus (2016), "Deglacial temperature history of West Antarctica", PNAS, vol. 113 no. 50, 14249–14254, doi: 10.1073/pnas.1609132113

http://www.pnas.org/content/113/50/14249

Abstract: "The most recent glacial to interglacial transition constitutes a remarkable natural experiment for learning how Earth’s climate responds to various forcings, including a rise in atmospheric CO2. This transition has left a direct thermal remnant in the polar ice sheets, where the exceptional purity and continual accumulation of ice permit analyses not possible in other settings. For Antarctica, the deglacial warming has previously been constrained only by the water isotopic composition in ice cores, without an absolute thermometric assessment of the isotopes’ sensitivity to temperature. To overcome this limitation, we measured temperatures in a deep borehole and analyzed them together with ice-core data to reconstruct the surface temperature history of West Antarctica. The deglacial warming was 11.3±1.8 ∘  11.3±1.8∘ C, approximately two to three times the global average, in agreement with theoretical expectations for Antarctic amplification of planetary temperature changes. Consistent with evidence from glacier retreat in Southern Hemisphere mountain ranges, the Antarctic warming was mostly completed by 15 kyBP, several millennia earlier than in the Northern Hemisphere. These results constrain the role of variable oceanic heat transport between hemispheres during deglaciation and quantitatively bound the direct influence of global climate forcings on Antarctic temperature. Although climate models perform well on average in this context, some recent syntheses of deglacial climate history have underestimated Antarctic warming and the models with lowest sensitivity can be discounted."

Extract: "Of greatest immediate interest, however, is our demonstration that the global deglacial temperature change was amplified by a factor of 2–3 in the Antarctic, that Antarctic warming was largely achieved by 15 ka in coherence with records from Southern Hemisphere mountain ranges, and that climate models of the deglaciation perform well on average, but that the ones with lowest sensitivity can be discounted. The early warming of the Southern Hemisphere, which our study helps to quantify, arose from combined effects of reduced northward oceanic heat transport, increased insolation, and increasing atmospheric CO2. Quantitative simulation of this phenomenon could provide an illuminating challenge for model studies."

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Furthermore, T. Edwards ignores the already increasing risks of hydrofracture events in the WAIS as illustrated by the two linked sources (the attached image comes from the first linked source):

"Scientists stunned by Antarctic rainfall and a melt area bigger than Texas"

https://www.washingtonpost.com/news/energy-environment/wp/2017/06/15/scientists-just-documented-a-massive-melt-event-on-the-surface-of-antarctica/?utm_term=.526054dc4fdf

Extract: "Scientists have documented a recent, massive melt event on the surface of highly vulnerable West Antarctica that, they fear, could be a harbinger of future events as the planet continues to warm.

In the Antarctic summer of 2016, the surface of the Ross Ice Shelf, the largest floating ice platform on Earth, developed a sheet of meltwater that lasted for as long as 15 days in some places. The total area affected by melt was 300,000 square miles, or larger than the state of Texas, the scientists report."
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The second linked reference finds that: "The increase in the number of extreme El Niño events projected for the twenty-first century could expose the WAIS to more frequent major surface melt events.":

Julien P. Nicolas et. al. (2017), "January 2016 extensive summer melt in West Antarctica favoured by strong El Niño", Nature Communications 8, Article number: 15799, doi:10.1038/ncomms15799

http://www.nature.com/articles/ncomms15799

Abstract: "Over the past two decades the primary driver of mass loss from the West Antarctic Ice Sheet (WAIS) has been warm ocean water underneath coastal ice shelves, not a warmer atmosphere. Yet, surface melt occurs sporadically over low-lying areas of the WAIS and is not fully understood. Here we report on an episode of extensive and prolonged surface melting observed in the Ross Sea sector of the WAIS in January 2016. A comprehensive cloud and radiation experiment at the WAIS ice divide, downwind of the melt region, provided detailed insight into the physical processes at play during the event. The unusual extent and duration of the melting are linked to strong and sustained advection of warm marine air toward the area, likely favoured by the concurrent strong El Niño event. The increase in the number of extreme El Niño events projected for the twenty-first century could expose the WAIS to more frequent major melt events."

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T. Edwards also ignores the implications of both the extensive subglacial meltwater drainage system and the high subglacial geothermal heat flux as indicated in the linked references and attached images:

The linked reference studies a subglacial draining event beneath Thwaites Glacier from June 2013 to January 2014:

Smith et. al. (2017), "Connected subglacial lake drainage beneath Thwaites Glacier, West Antarctica", The Cryosphere, 11, 451–467, doi:10.5194/tc-11-451-2017

http://www.the-cryosphere.net/11/451/2017/tc-11-451-2017.pdf

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Yasmina M. Martos, Manuel Catalan, Tom A. Jordan,Alexander Golynsky, Dmitry Golynsky, Graeme Eagles & David G. Vaughan (6 November 2017), "Heat flux distribution of Antarctica unveiled", Geophysical Research Letters, DOI: 10.1002/2017GL075609 

http://onlinelibrary.wiley.com/doi/10.1002/2017GL075609/abstract?utm_content=buffer4cbb3&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

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Furthermore, T. Edwards ignores the dynamical periodic multistate nature of the Earth's Systems; where ENSO is but one of several different interacting positive reinforcements of various Earth Systems (Arctic Amplification, Bipolar Seesaw, Permafrost degradation, PDO/ENSO, Ice-Climate Feedback, Hadley Cell expansion, etc.); which Chaos Theory calls Strange (or Lorenz) Attractors.  I believe that such strange attractors can progressively/interactively ratchet-up different Earth System States (see the first attached image) so as to increase the effective climate sensitivity so that some "slow-response" feedbacks (see the second figure from Andrew – Ringberg 2015, where the middle panel indicates an effective climate sensitivity of about 5C) occur within decades rather than millennia. This potential acceleration of the rate of activation of "slow-response" feedbacks is driven by anthropogenic behavior including:

(a) We are radiatively forcing the Earth at well over 10 times the rate experienced during the PETM;

(b) Rapid deforestation and ocean acidification are slowly decreasing the capacity of both land and the ocean, respectively, to serve as CO₂ sinks.

(c) Anthropogenic aerosols have been temporarily masking the impacts of anthropogenic radiative forcing; much as dust in paleo times resulted in negative forcing that caused cooling.  However, reticent science has discounted the efficiency of both of these mechanisms leaving the modern world subject to unexpectedly high rates of GMST increases due to the GHGs that accumulated in the atmosphere during the recent faux hiatus.

Indeed the first linked reference indicates that when analyzing modern day observations: "Severe testing is applied to observed global and regional surface and satellite temperatures and modelled surface temperatures to determine whether these interactions are independent, as in the traditional signal-to-noise model, or whether they interact, resulting in steplike warming."  The reference concludes that indeed steplike warming occurs due to "… a store-and-release mechanism from the ocean to the atmosphere…" like the classical Lorenzian attractor case of ENSO decadal cycles.  Such steplike behavior confirms the mechanism that I call "Ratcheting of Quasi-static Equilibrium States" (see the first attachment).  As the authors point-out reticent science likely missed this behavior because: "This may be due in part to science asking the wrong questions."; and they advise that such reticent AR5/CMIP5 researchers should change how they view the output from their models.  For example, the third attached image (see panel "e" of that Figure 6) from the reference shows global warming increasing much faster for a steplike response if ECS is 4.5 than for a the traditional AR5/CMIP5 interpretation; which means that ESLD researchers are exposing society to far more risk of the consequences of high ECS values than AR5/CMIP5 are leading us to believe:

Jones, R. N. and Ricketts, J. H.: Reconciling the signal and noise of atmospheric warming on decadal timescales, Earth Syst. Dynam. Discuss., doi:10.5194/esd-2016-35, in review, 2016.

http://www.earth-syst-dynam-discuss.net/esd-2016-35/
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http://www.earth-syst-dynam-discuss.net/esd-2016-35/esd-2016-35.pdf


Extract: "This finding does not invalidate the huge literature that assesses long-term (>50 years) climate change as a relatively linear process, and the warming response as being broadly additive with respect to forcing (e.g., Lucarini et al., 2010; Marvel et al., 2015). However, on decadal scales, this is not the case – warming appears to be largely governed by a storage and release process, where heat is stored in the ocean and released in bursts projecting onto modes of climate variability as suggested by Corti et al. (1999). We discuss this further in another paper (Jones and Ricketts, 2016).

This has serious implications for how climate change is understood and applied in a whole range of decision-making contexts.  The characterisation of changing climate risk as a smooth process will leave climate risk as being seriously underdetermined, affecting how adaptation is perceived, planned and undertaken (Jones et al., 2013).

The interaction of change and variability is typical of a complex, rather than mechanistic, system. The possibility of Lorenzian attractors in the ocean-atmosphere acting on decadal time scales was raised by Palmer (1993) and, despite later discussions about the potential for nonlinear responses on those timescales (e.g., Lucarini and Ragone, 2011;Tsonis and Swanson, 2012), very little progress has been made in translating this into applied research that can portray a better understanding of changing climate risk. This may be due in part to science asking the wrong questions.

The signal to noise model of a gradually changing mean surrounded by random climate variability poorly represents warming on decadal timescales. The separation of signal and noise into ‘good’ and ‘bad, likewise, is poor framing for the purposes of understanding and managing risk in fundamentally nonlinear systems (Koutsoyiannis, 2010; Jones, 2015b). However, as we show, the presence of such changes within climate models shows their current potential for investigating nonlinearly changing climate risks. Investigating step changes in temperature and related variables does not indicate a need to fundamentally change how climate modelling is carried out. It does, however, indicate a need to change how the results are analysed."

The second reference indicates global warming is increasing the frequency of extreme El Ninos.  As strong El Ninos increase both the temperature and induce droughts in the tropics it is clear that CO₂ emissions increase from the tropical land vegetation during strong El Ninos:

Wenju Cai, Agus Santoso, Guojian Wang, Sang-Wook Yeh, Soon-Il An, Kim M. Cobb, Mat Collins, Eric Guilyardi, Fei-Fei Jin, Jong-Seong Kug, Matthieu Lengaigne, Michael J. McPhaden, Ken Takahashi, Axel Timmermann, Gabriel Vecchi, Masahiro Watanabe & Lixin Wu (2015), "ENSO and greenhouse warming", Nature Climate Change, Volume: 5, Pages: 849–859, doi:10.1038/nclimate2743


http://www.nature.com/nclimate/journal/v5/n9/full/nclimate2743.html

Abstract: "The El Niño/Southern Oscillation (ENSO) is the dominant climate phenomenon affecting extreme weather conditions worldwide. Its response to greenhouse warming has challenged scientists for decades, despite model agreement on projected changes in mean state. Recent studies have provided new insights into the elusive links between changes in ENSO and in the mean state of the Pacific climate. The projected slow-down in Walker circulation is expected to weaken equatorial Pacific Ocean currents, boosting the occurrences of eastward-propagating warm surface anomalies that characterize observed extreme El Niño events. Accelerated equatorial Pacific warming, particularly in the east, is expected to induce extreme rainfall in the eastern equatorial Pacific and extreme equatorward swings of the Pacific convergence zones, both of which are features of extreme El Niño. The frequency of extreme La Niña is also expected to increase in response to more extreme El Niños, an accelerated maritime continent warming and surface-intensified ocean warming. ENSO-related catastrophic weather events are thus likely to occur more frequently with unabated greenhouse-gas emissions. But model biases and recent observed strengthening of the Walker circulation highlight the need for further testing as new models, observations and insights become available."

In summary, I provide the fourth image that illustrates how periodic climate attractors (triggered by the combination of anthropogenic radiative forcing and freshwater hosing from the collapse of the WAIS) could stepwise drive us into a very dynamical anthropogenic state, with high sea level, high storm activity and high temperatures.

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Furthermore, T. Edwards ignores the fact that all glacial models included in CMIP5 and CMIP6 cannot match the paleo-record, nor the observed-record, for ice mass loss from marine glaciers, and that they all err far on the side of least drama.  Therefore I post selected images (from a slide show compiled by Bill Lipscomb's team from the US - DOE and Los Alamos National Lab.) regarding recent research using the Community Ice Sheet Model (CISM), that illustrate the challenges that such models face (which will take decades to resolve to the point where they could match the paleo-record):

- The first image shows key software in CISM
- The second image shows the concept of using software packages to fight on many challenging fronts at once for both GIS and WAIS types of ocean, atmosphere, land, ice situations.
- The third image shows a listing of progress by the team on these many fronts.
- The fourth image shows the coupling required between the various software packages

Due to the four image limit per post I will present images related to a  BISICLES analysis for the West Antarctic in my next post.

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The following images continue from the preceeding post with figures related to analysis for the Western Antarctic focused on marine glaciers and ice shelves:

- The first shows the boundary layer conditions for such an analysis.
- The second images shows future/planned moving boundaries for such models to account for subglacial cavity growth and sub-ice-shelf melting.
- The third images shows the results of a convergence study for the LCM indicating that they need a resolution of at least 1 km which means that there model is too local to capture advective interactions between PIG and Thwaites (as I discuss in the "Surge" thread).  Thus computers will need to become bigger and faster before complex regional interactions can be captured
- The fourth image shows the subglacial hydrological system used in the LCM which does not include geothermal heating comparable to that measured in the BSB (Byrd Subglacial Basin) that is creating relatively large volumes of basal meltwater, sufficient to feed a key subglacial lake, which is also not included in the LCM system.  Furthermore, I have postulated that the basal meltwater entering the ocean through the Thwaites Gateway Trough act as a positive feedback for the advective formation of a subglacial cavity in the trough (which is not captured in this LCM model).

These images show how much work remains to be done (including refinement of the gird resolution of non-linear models) before projections from the combined GCM, RCM, and LCM efforts can be depended upon for reasonably accurate SLR projections.

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The following extracts come from the linked Scribbler article entitled: "From Ice Apocalypse to Mega-Thunderstorms, Continuing to Burn Fossil Fuels Makes the World Scary as all Hell", which also has a link to the 'Chasing Ice' video of a 2012 ice cliff failure event at the Jakobshavn Glacier.  Scribbler provides some descriptions of ice cliff failures that the general public can relate too; however, he: (1) limits his stated concerns about DeConto & Pollard (2016)'s findings to issues related to sea level rise; which ignores dynamical issues such as ice-climate interaction and associated mega-storms cited by Hansen; and (2) his mentioning of a relatively low probability of occurrence of 10 to 20 percent for DeConto & Pollard's scenario is highly subjective and is likely to bias readers to err on the side of least drama as the true probability is certainly much higher than 10 to 20 percent.

https://robertscribbler.com/2017/11/22/from-ice-apocalypse-to-mega-thunderstorms-continuing-to-burn-fossil-fuels-makes-the-world-scary-as-all-hell/

Extract: "Ice cliff stability is a pretty technical term. One that may make the eyes of your typical reader gloss over. But when we consider that the glaciers of Greenland and Antarctica can be upwards of two miles high, then the question of whether or not the cliffs of those great ice mountains are stable may start to generate a flicker of warning. May conjure up a phantom of the titanic roar set off when such ice giants tumble away into the sea as has happened throughout the deep history of Earth whenever the world warmed up by a certain amount.
When I think of the words ice cliff stability, my mind’s eye pictures a vast wall of numbing white-blue stretching hundreds of feet high. It expands both left and right as far as I can see. And it looms over an endless warming ocean. Waiting for a colossal fall if just that right amount of extra heat is applied.
Ice is fragile. It’s not like stone. It doesn’t flex much. It doesn’t give much. And even minor stresses are enough to make it shatter.
…
But the problem with the DeConto study, as with any other form of serious climate risk, is that there are plausible scenarios in which terrible catastrophic events are possible even if their degree of likelihood is still somewhat debatable. And reasonable precaution would dictate that even if there were just a 10-20 percent chance of DeConto like events coming to pass, we would do everything we could to avoid them. The risk of this scenario emerging, however, is probably a bit higher. As numerous studies have identified the potential for 6, 8, or even 12 feet of sea level rise by as early as 2100."

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Perhaps T. Edwards' most valid issue for debate is: How long will it take for the ice plug in the Thwaites Gateway to degrade to the point that cliff failures will begin in earnest in this part of the WAIS?  In this regards, the first attached image of the ice sheet in the Wilkes Basin illustrates how an ice plug (that is similar to that for Thwaites) can temporarily make a marine glacier stable for a relatively long period until ocean/atmospheric heat (or hydrofracturing) causes a sufficient retreat down a negative bottom slope for cliff failures (and hydrofracturing) to drive a rapid retreat as per DeConto & Pollard.

DeConto & Pollard (2016)'s ice sheet model has a relatively coarse grid resolution, and thus largely relies on hydrofracturing to both eliminate the ice shelf buttressing and the ice plug for Thwaites; which is why their projections rely on GMSTA approaching 2.7C (I note that conservative estimates give less than a 5% chance that we will stay below 2C) before significant cliff failure activity occurs.  DeConto & Pollard's reliance on hydrofracturing to kick-start serious cliff failure activity not only saves then from using a fine grid resolution but also from the trouble of modeling the influence of:

(a) The basal meltwater drainage system and high geothermal heat flux for Thwaites (which I previously mentioned);

(b) The PIG-Thwaites interaction especially via the Southwest, SW, Tributary Glacier, whose activation by the retreat of the Pine Island Ice Shelf, PIIS, calving face upstream of the SW Tributary Glacier's calving face (which per the second attached image could occur in the next year or two), would reduce the ice flow restraint associated with Thwaites' eastern shear margin (see the third image);

(c) The fourth image shows that several years ago both the Thwaites Eastern Ice Shelf and the Thwaites Ice Tongue, were pinned by offshore submerged seamounts, but now the Thwaites Ice Tongue is no longer pinned, and the Eastern Ice Shelf shows signs that it may break apart (largely due to basal melting from ocean heat) long before hydrofracturing may begin.

This post just cites some of the reasons that DeConto & Pollard (2016)'s projection of how soon the Thwaites ice plug may be lost, likely errs on the side of least drama; while in future posts, I plan to cite several other reasons (including the influence of the 'trough' that passes through the Thwaites ice plug shown in the fourth image).

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As a follow-on to my last post [focused on specific local reasons that the Thwaites Ice Plug could degrade earlier than projected by DeConto & Pollard (2016)], in this post I provide the two more reasons:

(a) The first image shows a Nov 1 2017 image of the degraded conditions of both the Thwaites Eastern Ice Shelf and the Thwaites Ice Tongue, while the second image shows portions of these features before January 2012 together with superimposed coloring indicating where an abrupt drop in surface ice elevation occurred after January 2012 near the bases of both the Ice Shelf and the Ice Tongue, in the area of the 'trough' shown in the fourth image of my last post.  Furthermore the third image shows a 2013 close-up of this collapsed area of ice indicating a 'checkerboard' pattern of floating icebergs that are currently trapped by the outboard ice mélange of the residual Thwaites Ice Tongue, that could readily float away once ocean currents/storms have adequately cleared away this ice mélange.  This 'checkerboard' of penned-in icebergs are located in the 'trough' through the Thwaites Ice Plug shown in the fourth image of my last post, and thus once these penned-in icebergs float away, the water depth in the 'trough' is deep enough to initiate local cliff failures that could accelerate the degradation of the ice plug together with the loss of buttressing associated with the potential early loss of the ice shelf (discussed in my last post).

(b) The fourth image (from Fogt et al 2011) shows how atmospheric Rossby waves telecommunicate atmospheric heat energy directly from the Tropical Pacific to the WAIS according to the indicated patterns of La Nina, El Nino and SAM events.  This telecommunicated heat energy could accelerate rapidly in the next few decades as global warming is projected to accelerate the frequency of Super El Nino (& to a lesser extent Super La Nina) events.  If so this could start hydrofracturing around the WAIS sooner than assumed by DeConto & Pollard (2016).

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Further to my last two posts about local considerations that could lead to an early (relative to DeConto & Pollard 2016's projection) degradation of the Thwaites ice plug, this post focuses on the influence of the ENSO cycle on the Amundsen Sea Low (or Amundsen Bellingshausen Sea Low), ASL (or ABSL) and the advection of more than usual wind-driven warm CDW into the ASE.
In this regards, the first attached image from Bertler et al 2006 (see reference below), which shows pictorially the relationship between the location of the ASL (or ABSL) and either a La Nina or an El Nino event.  This implies that future El Nino events will shift the location of the ASL to blow wind directly into the ASE.  Furthermore, the winds blowing into the ASE will likely be stronger than in the past recent past due both to the lower Amundsen sea pressure associated with AMO effect and the projected increase in the frequency of Super El Nino events with continued global warming.

The second image shows the deepwater changes across the Amundsen Sea continental shelf through which the warm CDW flows towards the grounding lines of key marine glaciers.
The third image shows a computer simulation of the pattern of warm CDW flow in the Amundsen Sea continental shelf area; which indicates how warm CDW can flow from the PIG to the Thwaites grounding line.

The fourth image shows that the submerged ridge seaward of Thwaites can help direct the warm CDW come from the PIG towards the 'trough' that crosses the Thwaites ice plug.

Bertler, N.A., Naish, T.T., Mayewski, P.A. and Barrett, P.J., (2006), "Opposing oceanic and atmospheric ENSO influences on the Ross Sea Region, Antarctica", Advances in Geosciences, 6, pp 83-88, SRef-ID: 1680-7359/adgeo/2006-6-83.

Next, the second linked reference indicates that from January to June the ASL typically moves from about 110 degrees W (where it is in position to help direct warm CDW into the ASE) to about 150 degrees W (where it does not help to direct warm CDW into the ASE).  I note also that:
(a) As the SAM has become more positive, due to global warming, the ASL has become more intensity and has tended to drift more to the west than previously; and

(b) El Nino events do not typically occur in the January to June timeframe but rather in the October to Dec timeframe, which helps to explain way more warm CDW flows into the ASE during El Nino events

Turner, J., Phillips, T., Hosking, J. S., Marshall, G. J. and Orr, A. (2013), The Amundsen Sea low. Int. J. Climatol., 33: 1818–1829. doi: 10.1002/joc.3558

http://onlinelibrary.wiley.com/doi/10.1002/joc.3558/abstract

Abstract: "We develop a climatology of the Amundsen Sea low (ASL) covering the period 1979–2008 using ECMWF operational and reanalysis fields. The depth of the ASL is strongly influenced by the phase of the Southern annular mode (SAM) with positive (negative) mean sea level pressure anomalies when the SAM is negative (positive). The zonal location of the ASL is linked to the phase of the mid-tropospheric planetary waves and the low moves west from close to 110°W in January to near 150°W in June as planetary waves 1 to 3 amplify and their phases shift westwards. The ASL is deeper by a small, but significant amount, during the La Niña phase of El Niño-Southern Oscillation (ENSO) compared to El Niño. The difference in depth of the low between the two states of ENSO is greatest in winter. There is no statistically significant difference in the zonal location of the ASL between the different phases of ENSO. Over 1979–2008 the low has deepened in January by 1.7 hPa dec−1 as the SAM has become more positive. It has also deepened in spring and autumn as the semi-annual oscillation has increase in amplitude over the last 30 years. An increase in central pressure and eastward shift in March has occurred as a result of a cooling of tropical Pacific SSTs that altered the strength of the polar front jet."

Next, the third linked reference ties the warming of the Tropical Atlantic SST to a strengthening of both the Antarctic Circumpolar Winds and the Amundsen Bellingshausen Sea Low (ABSL/ASL) via atmospheric Rossby waves in all seasons except the austral summer. 

XICHEN LI, EDWIN P. GERBER, DAVID M. HOLLAND, AND CHANGHYUN YOO, (2015), "A Rossby Wave Bridge from the Tropical Atlantic to West Antarctica", J. Climate, 28, 2256–2273, doi: http://dx.doi.org/10.1175/JCLI-D-14-00450.1


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-14-00450.1
&
http://polarmet.osu.edu/ACCIMA/li_gerber_jc_2015.pdf

Abstract: "Tropical Atlantic sea surface temperature changes have recently been linked to circulation anomalies around Antarctica during austral winter. Warming in the tropical Atlantic associated with the Atlantic multidecadal oscillation forces a positive response in the southern annular mode, strengthening the Amundsen–Bellingshausen Sea low in particular. In this study, observational and reanalysis datasets and a hierarchy of atmospheric models are used to assess the seasonality and dynamical mechanism of this teleconnection.  Both the reanalyses and models reveal a robust link between tropical Atlantic SSTs and the Amundsen–Bellingshausen Sea low in all seasons except austral summer. A Rossby wave mechanism is then shown to both explain the teleconnection and its seasonality. The mechanism involves both changes in the excitation of Rossby wave activity with season and the formation of a Rossby waveguide across the Pacific, which depends critically on the strength and extension of the subtropical jet over the west Pacific. Strong anticyclonic curvature on the poleward flank of the jet creates a reflecting surface, channeling quasi-stationary Rossby waves from the subtropical Atlantic to the Amundsen–Bellingshausen Sea region. In summer, however, the jet is weaker than in other seasons and no longer able to keep Rossby wave activity trapped in the Southern Hemisphere. The mechanism is supported by integrations with a comprehensive atmospheric model, initial-value calculations with a primitive equation model on the sphere, and Rossby wave ray tracing analysis."

Extract: "Antarctic climate is also influenced by other tropical–polar teleconnections (Fogt et al. 2011; Ding et al. 2012), and key questions remain concerning the relative importance of these effects. The time scales of tropical SST variability differs significantly from one region to another (e.g., ENSO and the east Pacific dominate on interannual time scales, while the AMO and Pacific decadal oscillation are more significant on longer time scales). Moreover, SSTs in different tropical ocean basins may interact with each other through tropical ocean interbasin teleconnections. It is thus important to further investigate the relative importance and the relationship between the teleconnections from different tropical ocean sectors as a function of time scale."

Finally, the fourth linked 2017 reference confirms that the ENSO is directly associated with surface air temperatures across the interior of West Antarctica, and I note that the frequency of Super El Nino events is projected to double when the global mean surface temp. anom. gets to 1.5C:

Kyle R. Clem, James A. Renwick, and James McGregor (2017), "Large-Scale Forcing of the Amundsen Sea Low and its Influence on Sea Ice and West Antarctic Temperature", Journal of Climate, https://doi.org/10.1175/JCLI-D-16-0891.1

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0891.1?utm_content=buffer2e94d&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Using empirical orthogonal function (EOF) analysis and atmospheric reanalyses, we examine the principal patterns of seasonal West Antarctic surface air temperature (SAT) and their connection to sea ice and the Amundsen Sea Low (ASL). During austral summer, the leading EOF (EOF1) explains 35% of West Antarctic SAT variability and consists of a widespread SAT anomaly over the continent linked to persistent sea ice concentration anomalies over the Ross and Amundsen Seas from the previous spring. Outside of summer, EOF1 (explaining ~40-50% of the variability) consists of an east-west dipole over the continent with SAT anomalies over the Antarctic Peninsula opposite those over western West Antarctica. The dipole is tied to variability in the Southern Annular Mode (SAM) and in-phase El Niño-Southern Oscillation (ENSO) / SAM combinations that influence the depth of the ASL over the central Amundsen Sea (near 105°W). The second EOF (EOF2) during autumn, winter, and spring (explaining ~15-20% of the variability) consists of a dipole shifted approximately 30 degrees west of EOF1 with a widespread SAT anomaly over the continent. During winter and spring, EOF2 is closely tied to variability in ENSO and a tropically-forced wavetrain that influences the ASL in the western Amundsen / eastern Ross Seas (near 135°W) with an opposite sign circulation anomaly over the Weddell Sea; the ENSO-related circulation brings anomalous thermal advection deep onto the continent. We conclude the ENSO-only circulation pattern is associated with SAT variability across interior West Antarctica, especially during winter and spring, while the SAM circulation pattern is associated with an SAT dipole over the continent."

[AbruptSLR]

Another reason that DeConto & Pollard (2016)'s projection for the loss of the Thwaites ice plug may be too slow, is that they (and essentially all other modelers) have based their estimates of current ice mass loss from the ASE largely on data from the GRACE satellite.  However, the past GRACE data may have been corrected using a conservative estimate of the associated glacial isostatic adjustment, GIA, in this area.

Thus I post the following abstract which indicates that after updated GIA correction the Amundsen Sea sector is contributing more to SLR than previously projected:

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 image shows how post-glacial rebound for current ice mass loss from a marine glacier consists of both quick elastic rebound and slower rebound due to the flow of magma in the mantle.  I note that the current GIA corrections to GRACE data are based on conservative assumptions about the viscosity of the magma beneath the Byrd Subglacial Basin, BSB; but numerous indications are that this magma has a slower viscosity than assumed, which may mean that the GRACE ice mass loss projections for the ASE glaciers may need to be increased by more 40%.

The third and fourth images show the GRACE data from 2003 to 2009 which likely needs to be increase by more 40% than previously reported.  I note that the GRACE satellite has now fallen out of obit, but should be replaced by an upgraded system in 2018.

[AbruptSLR]

While my last series of posts have focused on factors that could accelerate (earlier than assumed by DeConto & Pollard 2016) ice mass loss from the ASE marine glaciers, in this post I provide some factors that could cause ice mass losses from other portions of the WAIS earlier than assumed by DeConto & Pollard (2016).

The first four following references on both Oceanic Rossby Waves (see the first attached image) and Oceanic Infragravity Waves that telecommunicate energy from the Pacific Ocean to West Antarctica, and which promote ice calving events.

Pierre St-Laurent, John M. Klinck and Michael S. Dinniman (2012), "On the Role of Coastal Troughs in the Circulation of Warm Circumpolar Deep Water on Antarctic Shelves", JPO.

Bromirski, P.D., Miller, A.J., Flick, R.E, and Auad, G., (2011), "Dynamical Suppression of Sea Level Rise Along the Pacific Coast of North America: Indications for Imminent Acceleration" Journal of Geophysical Research, Vol. 116, C07005, doi: 10.1029/2010JC006759, July 2011.

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

The fourth (linked) reference provides recent field evidence of the impacts of tsunami and infragravity waves on the Ross Ice Shelf and concludes that such very long period waves can reduce the stability of Antarctic ice shelves; which could then reduce the buttressing on the associated marine glacial, and thus can serve to accelerate the rate of sea level rise (and the ice-climate feedback mechanism).

P. D. Bromirski et al. (20 July 2017), "Tsunami and infragravity waves impacting Antarctic ice shelves", JGR Oceans, DOI: 10.1002/2017JC012913 

http://onlinelibrary.wiley.com/doi/10.1002/2017JC012913/full

Abstract: "The responses of the Ross Ice Shelf (RIS) to the 16 September 2015 8.3 (Mw) Chilean earthquake tsunami (>75 s period) and to oceanic infragravity (IG) waves (50–300 s period) were recorded by a broadband seismic array deployed on the RIS from November 2014 to November 2016. Here we show that tsunami and IG-generated signals within the RIS propagate at gravity wave speeds (∼70 m/s) as water-ice coupled flexural-gravity waves. IG band signals show measureable attenuation away from the shelf front. The response of the RIS to Chilean tsunami arrivals is compared with modeled tsunami forcing to assess ice shelf flexural-gravity wave excitation by very long period (VLP; >300 s) gravity waves. Displacements across the RIS are affected by gravity wave incident direction, bathymetry under and north of the shelf, and water layer and ice shelf thicknesses. Horizontal displacements are typically about 10 times larger than vertical displacements, producing dynamical extensional motions that may facilitate expansion of existing fractures. VLP excitation is continuously observed throughout the year, with horizontal displacements highest during the austral winter with amplitudes exceeding 20 cm. Because VLP flexural-gravity waves exhibit no discernable attenuation, this energy must propagate to the grounding zone. Both IG and VLP band flexural-gravity waves excite mechanical perturbations of the RIS that likely promote tabular iceberg calving, consequently affecting ice shelf evolution. Understanding these ocean-excited mechanical interactions is important to determine their effect on ice shelf stability to reduce uncertainty in the magnitude and rate of global sea level rise."

Plain Language Summary
"A major source of the uncertainty in the magnitude and rate of global sea level rise is the contribution from Antarctica. Ice shelves buttress land ice, restraining land ice from reaching the sea. We present the analysis of seismic data collected with a broadband seismic array deployed on the Ross Ice Shelf, Antarctica. The characteristics of ocean gravity-wave-induced vibrations, that may expand existing fractures in the ice shelf and/or trigger iceberg calving or ice shelf collapse events, are described. The mechanical dynamic strains induced can potentially affect ice shelf integrity, and ultimately reduce or remove buttressing restraints, accelerating sea level rise."

&

The second attached figure by Fogt et al 2011 indicates that trends for cyclones storm in both the Ross Sea, and Bellingshausen Sea, Basins has been of increased intensity (ie lower cental pressure) and increase storm frequency.  This will tend to increase calving from ice shelves/tongues in these areas.

&

I note that the conventional thinking is that the cold FRIS/RIS ice shelves will largely remain intact until well after 2300 possibly due to their belief in the stationary nature of both: (a) the water adjoining the FRIS/RIS  in the Continential Zone, within the Continental Water Boundary, CWB, shown in the third attached image; and (b) the protective circulation pattern beneath a cold ice shelf that helps to keep warm CDW out from beneath as cold ice shelf, per Hellmer et al 2012.  However, in the next linker reference, Hellmer et al (2017) demonstrates that warm CDW will circulate beneath the FRIS circa 2070.

Hartmut H. Hellmer et al. (2017), "The Fate of the Southern Weddell Sea Continental Shelf in a Warming Climate", Journal of Climate, https://doi.org/10.1175/JCLI-D-16-0420.1

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0420.1
http://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-16-0420.1

Abstract: "Warm water of open ocean origin on the continental shelf of the Amundsen and Bellingshausen Seas causes the highest basal melt rates reported for Antarctic ice shelves with severe consequences for the ice shelf/ice sheet dynamics. Ice shelves fringing the broad continental shelf in the Weddell and Ross Seas melt at rates orders of magnitude smaller. However, simulations using coupled ice–ocean models forced with the atmospheric output of the HadCM3 SRES-A1B scenario run (CO2 concentration in the atmosphere reaches 700 ppmv by the year 2100 and stays at that level for an additional 100 years) show that the circulation in the southern Weddell Sea changes during the twenty-first century. Derivatives of Circumpolar Deep Water are directed southward underneath the Filchner–Ronne Ice Shelf, warming the cavity and dramatically increasing basal melting. To find out whether the open ocean will always continue to power the melting, the authors extend their simulations, applying twentieth-century atmospheric forcing, both alone and together with prescribed basal mass flux at the end of (or during) the SRES-A1B scenario run. The results identify a tipping point in the southern Weddell Sea: once warm water flushes the ice shelf cavity a positive meltwater feedback enhances the shelf circulation and the onshore transport of open ocean heat. The process is irreversible with a recurrence to twentieth-century atmospheric forcing and can only be halted through prescribing a return to twentieth-century basal melt rates. This finding might have strong implications for the stability of the Antarctic ice sheet."

Extract: "Our experiments indicate that the link between the hydrography on the southern Weddell Sea continental shelf and melt rates beneath the Filchner–Ronne Ice Shelf is controlled by a positive feedback mechanism: Once the reversal of the near-bottom density gradient across the Filchner Trough, together with a rising coastal thermocline, facilitates the direct inflow of the slope current into the trough, warm deep water flushes the ice shelf cavity, causing its warming, enhanced basal mass loss, and a vigorous outflow of glacial meltwater. The latter further freshens the shelf water and thus maintains a density and flow structure at the sill that supports further access of warm water to the ice shelf cavity. The increase in basal melting accelerates the cavity circulation, drawing in even more warm water of open ocean origin—a self-intensifying mechanism. Although the initial trigger for this transition is freshening on the continental shelf as a result of atmosphere–ocean interactions, once the system is in the warm-shelf phase, the only way to stop the inflow of the warm water is to return to twentieth-century atmospheric conditions and to reduce the meltwater input. At first, the latter could be realized by a reduction in the floating portion of the ice sheet. However, the resulting loss of buttressing of the inland ice sheet would accelerate the draining ice streams. The discharge of ice from the relevant catchment basin and a significant contribution to global sea level will be inevitable."

&

Lastly I note that the following linked (open access) reference cites research on four decades of marine glacier grounding line retreat in the Bellingshausen margin (see fourth attached image), which is losing ice mass faster than most researchers previously expected, primarily due to oceanic heat effects:

Frazer D.W. Christie, Robert G. Bingham, Noel Gourmelen, Simon F.B. Tett & Atsuhiro Muto (22 May 2016), "Four-decade record of pervasive grounding line retreat along the Bellingshausen margin of West Antarctica", Geophysical Research Letters, DOI: 10.1002/2016GL068972

http://onlinelibrary.wiley.com/doi/10.1002/2016GL068972/abstract

Abstract: "Changes to the grounding line, where grounded ice starts to float, can be used as a remotely-sensed measure of ice-sheet susceptibility to ocean-forced dynamic thinning. Constraining this susceptibility is vital for predicting Antarctica's contribution to rising sea levels. We use Landsat imagery to monitor grounding line movement over four decades along the Bellingshausen margin of West Antarctica, an area little monitored despite potential for future ice losses. We show that ~65% of the grounding line retreated from 1990-2015, with pervasive and accelerating retreat in regions of fast ice flow and/or thinning ice shelves. Venable Ice Shelf confounds expectations in that despite extensive thinning, its grounding line has undergone negligible retreat. We present evidence that the ice shelf is currently pinned to a sub-ice topographic high which, if breached, could facilitate ice retreat into a significant inland basin, analogous to nearby Pine Island Glacier."

[AbruptSLR]

In my last post I cited some factors that may contribute to significant ice mass loss, before 2100, from key regions of the WAIS in addition to the Amundsen Sea Embayment, ASE, marine glaciers.  Here I present the first two images (& I note that the second image show up to 120 meters of total post glacial rebound in the BSB, which was not considered by DeConto & Pollard's model) from Vaughan et al. 2011, that indicate that during previous collapses of the WAIS, seaways opened between the various regions of the WAIS.  If such seaways were to open during the future WAIS collapse postulated by DeConto & Pollard (2016), the associated oceanic heat impacts and loss of ice surface elevations would likely result in faster image mass loss than DeConto & Pollard (2016) assumed.  In this regards, I note that the main reason that current Antarctic Amplification is lower than current Arctic Amplification, is due to the high elevation of the glacial ice in Antarctica.  Thus, if a postulated collapse of the WAIS were to occur this century, Antarctic Amplification would increase to the range of 2 to 3 times GMSTA.

Also, I note that the third image illustrates a clear bipolar seesaw mechanism between freshwater hosing events since MIS 5 (the Eemian), thus as both the Greenland Ice Sheet and the WAIS are concurrently losing ice mass during the Anthropocene, one can expect more impact on/from the MOC than for the paleo periods the DeConto & Pollard (2016) conservatively calibrated their model for.

Lastly, for this post, I note that researchers have identified numerous positive feedback mechanisms related to the methane cycle that could result in significant natural pulses of methane emissions into the atmosphere in the 2050 to 2100 timeframe including from: flooded tropical peatlands/rainforests, methane hydrates beneath the WAIS and from Arctic thermokarst lakes (see the fourth attached image for RCP 8.5 forcing), none of which were including in DeConto & Pollard (2016)'s forcing scenario.

[AbruptSLR]

In my last post, I briefly mentioned the risk of abrupt release of methane from hydrate beneath the WAIS, during a potential near-future collapse of the WAIS. In this regards, the linked reference provides paleo evidence that subglacial gas hydrates within zones of the basal sediment served to reduce ice flow velocities in the marine glaciers of the Barents-Sea-Fennoscandian ice sheet approximately 20,000 years ago.  As there are projected to be large amounts of gas hydrates in the marine sediments beneath the WAIS, these findings may help to partially explain why the ice flow velocities of key WAIS marine glaciers like the PIG and Thwaites have plateaued recently (rather than continuing to accelerate rapidly).  However, if this is the case and if cliff failures and hydrofracturing occurs in the WAIS before GMST anoms reach 2.7C (as forecast by DeConto 2016), then such postulated basal hydrates could release significant volumes of methane if/when the WAIS collapses:

Monica Winsborrow, Karin Andreassen, Alun Hubbard, Andreia Plaza-Faverola, Eythor Gudlaugsson, Henry Patton. Regulation of ice stream flow through subglacial formation of gas hydrates. Nature Geoscience, 2016; DOI: 10.1038/ngeo2696

http://www.nature.com/ngeo/journal/v9/n5/full/ngeo2696.html


Abstract: "Variations in the flow of ice streams and outlet glaciers are a primary control on ice sheet stability, yet comprehensive understanding of the key processes operating at the ice-bed interface remains elusive. Basal resistance is critical, especially sticky spots-localized zones of high basal traction-for maintaining force balance in an otherwise well-lubricated/high-slip subglacial environment. Here we consider the influence of subglacial gas-hydrate formation on ice stream dynamics, and its potential to initiate and maintain sticky spots. Geophysical data document the geologic footprint of a major palaeo-ice-stream that drained the Barents Sea-Fennoscandian ice sheet approximately 20,000 years ago. Our results reveal a ∼250 km2 sticky spot that coincided with subsurface shallow gas accumulations, seafloor fluid expulsion and a fault complex associated with deep hydrocarbon reservoirs. We propose that gas migrating from these reservoirs formed hydrates under high-pressure, low-temperature subglacial conditions. The gas hydrate desiccated, stiffened and thereby strengthened the subglacial sediments, promoting high traction-a sticky spot-that regulated ice stream flow. Deep hydrocarbon reservoirs are common beneath past and contemporary glaciated areas, implying that gas-hydrate regulation of subglacial dynamics could be a widespread phenomenon."

https://www.sciencedaily.com/releases/2016/04/160413084735.htm

Extract: "One of the major questions today is: What are the ice sheets going to do in an ever-warming climate? Ice sheets of Greenland and Antarctica are major contributors to the sea level rise, which can make life difficult for many coastal nations in the near future.

To understand the ice sheets we need to understand their drainage system -- a key component of this is ice streams, fast-flowing rivers of ice, that deliver ice from the centre of the ice sheet to the oceans. Many of these ice streams are speeding up, which may be seen as the logical consequence of the warming climate. But some are slowing down, even stopping, examples of this may be found in the Ross ice streams of West Antarctica.

A new study in Nature Geoscience suggests that a 250km2 sticky spot made up of sediments with gas hydrates in them, slowed down an ice stream in the Barents Sea. This happened sometime during the last ice age, 20,000 years ago, when the Barents Sea was covered with an ice sheet.
…
Gas hydrate sticky spots under ice streams are a potentially widespread feature also today.
"If there are gas hydrates under today's ice sheets, they can slow the ice streams. There are studies indicating that there may be vast reservoirs of hydrates under the West Antarctic Ice sheet. Anywhere you have a hydrocarbon reservoir, water, high pressure and low temperature, you will get gas hydrate." says Winsborrow.

Ice streams of today are extensively monitored with GPS tracking systems, but it is very difficult to gaze beneath three kilometres of ice to see what is going on at the bottom. But scars left by the Barents Sea Ice sheet are visible on the ocean floor today. That makes this ancient ice sheet an important analogue, especially for the modern West Antarctica Ice Sheet, as both are based in marine environments.

"We need these analogies from the past. Understanding what is happening at the base of ice streams is important for modelling and predicting the future of the ice sheets.""

&

The following linked reference presents new findings that the retreat of the Barents Sea Ice Sheet at the end of the last ice age resulted in the explosive release of methane from Arctic seafloor hydrates as overpressure from the ice sheet disappeared.  The researchers find that serves as a good past analogy of what may likely happen in the near-term future if the WAIS were to collapse (see the attached image).  As methane has a GWP100 of about 35 such explosive releases of methane could have a significant impact on global warming this century.  Such short-term methane forcings would be superimposed on top of Hansen's ice-climate feedback mechanism.

K. Andreassen, A. Hubbard, M. Winsborrow, H. Patton, S. Vadakkepuliyambatta, A. Plaza-Faverola, E. Gudlaugsson, P. Serov, A. Deryabin, R. Mattingsdal, J. Mienert & S. Bünz (02 Jun 2017), "Massive blow-out craters formed by hydrate-controlled methane expulsion from the Arctic seafloor", Science, Vol. 356, Issue 6341, pp. 948-953
DOI: 10.1126/science.aal4500

http://science.sciencemag.org/content/356/6341/948

Abstract: "Widespread methane release from thawing Arctic gas hydrates is a major concern, yet the processes, sources, and fluxes involved remain unconstrained. We present geophysical data documenting a cluster of kilometer-wide craters and mounds from the Barents Sea floor associated with large-scale methane expulsion. Combined with ice sheet/gas hydrate modeling, our results indicate that during glaciation, natural gas migrated from underlying hydrocarbon reservoirs and was sequestered extensively as subglacial gas hydrates. Upon ice sheet retreat, methane from this hydrate reservoir concentrated in massive mounds before being abruptly released to form craters.  We propose that these processes were likely widespread across past glaciated petroleum provinces and that they also provide an analog for the potential future destabilization of subglacial gas hydrate reservoirs beneath contemporary ice sheets."

[AbruptSLR]

At around minute 42 of the linked video entitled: ""Sea-Level Rise: Inconvenient, or Unmanageable?" Richard B. Alley", Alley notes that the ASE marine glaciers could begin to hydrofacture with subsequent cliff failures in about 50-years +/- 50 years:

[A-Team]

I sure hope you are planning to pull all this together into a comprehensive arXiv-type journal review article as hosted by Cornell. They have a section called Atmospheric and Oceanic Physics with el nino articles etc where it would fit in and receive a permanent citable doi. It might involve less quoting and more paraphrasing of source material and endnotes for the refs (though I haven't looked at their exact requirements). Such posts can then serve as a springboard to submission to regular peer-reviewed journals if you want to go that route.

https://arxiv.org/list/physics.ao-ph/recent

Scribbler note on Holthaus:
https://robertscribbler.com/category/climate-change-2/

[AbruptSLR]

I sure hope you are planning to pull all this together into a comprehensive arXiv-type journal review article as hosted by Cornell. They have a section called Atmospheric and Oceanic Physics with el nino articles etc where it would fit in and receive a permanent citable doi. It might involve less quoting and more paraphrasing of source material and endnotes for the refs (though I haven't looked at their exact requirements). Such posts can then serve as a springboard to submission to regular peer-reviewed journals if you want to go that route.

https://arxiv.org/list/physics.ao-ph/recent

Scribbler note on Holthaus:
https://robertscribbler.com/category/climate-change-2/

Thanks for the pointer, but as I work as a fulltime engineer, I find it easier to critique the work of real scientists rather than to pretend to be one myself.  Nevertheless, the following linked abstract (I do not have access to EGU papers), indicates that DeConto & Pollard are working hard to improve the calibration of the model that they used in the 2016 paper.

Rob DeConto, David Pollard, and Ed Gasson (2017), "Potential for future sea-level contributions from the Antarctic ice sheet", Geophysical Research Abstracts, Vol. 19, EGU2017-15929,

http://meetingorganizer.copernicus.org/EGU2017/EGU2017-15929.pdf

Abstract: "Recent Antarctic ice-sheet modeling that includes the effects of surface meltwater on ice-sheet dynamics (through hydrofracturing and ice-cliff collapse) has demonstrated the previously underappreciated sensitivity of the ice sheet to atmospheric warming in addition to sub-ice oceanic warming. Here, we improve on our modeling of future icesheet retreat by using time-evolving atmospheric climatologies from a high-resolution regional climate model, synchronized with SSTs, subsurface ocean temperatures, and sub-ice melt rates from the NCAR CCSM4 GCM. Ongoing improvements in ice-sheet model physics are tested and calibrated relative to observations of recent and ancient (Pliocene, Last InterGlacial, and Last Deglaciation) ice-sheet responses to warming. The model is applied to a range of future greenhouse-gas emissions scenarios, including modified RCP scenarios corresponding to the 1.5º and 2.0º targets of the Paris Agreement and higher emissions scenarios including RCP8.5. The results imply that a threshold in the stability of the West Antarctic Ice Sheet and outlet glaciers in East Antarctica might be exceeded in the absence of aggressive mitigation policies like those discussed in Paris. We also explore the maximum potential for Antarctica to contribute to future sea-level rise in high greenhouse gas emissions scenarios, by testing a range of model physical parameters within the bounds of observations."

[FishOutofWater]

Let me add that the southward expansion of the subtropical highs is an known predicted consequence of adding heat to the climate system. There are numerous papers on it. The combination of the southward expansion of the high pressure areas and the cooling caused by ozone killing chemicals has increased the temperature gradient north of Antarctica. That has caused an increase of westerly winds closer to the continent.

Our theoretical physicist is ignorant of the meteorology and oceanography of the southern ocean. The tightening winds around Antarctica are driving the warm waters under the ice shelves. There are papers on the effects of the tightening winds on the ocean currents around the Antarctic Peninsula.

That joke about the paleoclimatologist, physicist and engineer was good for a big laugh. Thanks.

[FishOutofWater]

Thanks for the video. There are a few redundancies but it has excellent visualizations that will help non-scientists and scientists alike understand what's happening.

Another piece of information our theroetical physicist doesn't know. The fresh water layer caused by melting will greatly reduce heat loss from warmer water below. It will act as a lid on heat loss.  A blanket of insulating ice in the winter may actually expand in area, but the glaciers will continue to melt from below because warm intermediate water will not be caught up in deep convection.

[FishOutofWater]

ASLR if you can't access scientific reports any other way try this link.
http://sci-hub.bz/

[AbruptSLR]

ASLR if you can't access scientific reports any other way try this link.
http://sci-hub.bz/

Thanks, but I already looked there & I could not find DeConto & Pollard's 2017 EGU paper (if it exists).

[GeoffBeacon]

A-Team

I sure hope [A-team is] planning to pull all this together into a comprehensive arXiv-type journal review article as hosted by Cornell.

But who is going to get the message through to Guardian readers?  These might even include some policy makers or policy influencers.

[AbruptSLR]

It seems to me that when glacial scientists like Richard Alley says that major portions of the WAIS could begin rapid ice cliff failures and hydrofracturing within 50-years plus or minus 50-years; and when climate scientists like James Hansen warned that global mean sea level could be up to 5m higher than pre-industrial by 2100, and when Bakker et al. 2100 carefully layout the probabilities for scenarios leading up to 5m of sea level rise by 2100 (see the first image); then both decision makers and the public have already been adequately warned, and it societies addiction to cheap power (largely fossil fuels) that will keep us on a RCP8.5/SSP5 pathway through about 2050 (when a socio-economic collapse will unfold until about 2060).

The second image shows that by 2050 following RCP 8.5 (which does not include any freshwater hosing events) that anthropogenic radiative forcing (planetary energy imbalance) will be about 5 Watts/sq meter, which herein I will assume will stop increasing (due to socio-economic collapse) but will remain constant thru 2100 (due to the long life of CO₂ in the atmosphere).  However, the third image (from Hansen et al 2016) shows that an abrupt freshwater hosing event circa 2050 will cause pulse increase of radiative forcing of about 2.5 Watts/sq meter that is additive to the 5 Watts/sq meter, for a total radiative forcing of about 7.5 Watts/sq meter circa 2060; which is very close to RCP 8.5's assumed 8.5 Watts/sq meter of radiative forcing by 2100.

Now, the two following Bintanja et al. (2017) referencing indicate that in the 2091 to 2100 timeframe most of the strongly increase volume of precipitation in the Arctic will fall as rain, rather than as show; which my by logic cited in the preceding paragraph would begin circa 2060 if the WAIS collapse reaches a peak circa 2060.  However, the fourth attached image (from Hansen & Sato 2012) indicates that with an albedo flip (herein assumed to occur due to Arctic rainfall), together with the assumed freshwater hosing event, that ECS would reach about 7C.  Also, the possible pulses of methane discussed in Replies #30 & 31 (from thermokarst lakes, tropical wetlands and from Antarctic marine hydrates), we could be on a pathway to a runaway-greenhouse (with an equable climate in the NH) effect indicated in the fourth image to occur when radiative forcing reaches about 8.5 Watts/sq meter.

Richard Bintanja and Olivier Andry (2017), “Towards a rain-dominated Arctic”, Geophysical Research Abstracts Vol. 19, EGU2017-4402

http://meetingorganizer.copernicus.org/EGU2017/EGU2017-4402.pdf

Abstract: “Current climate models project a strong increase in Arctic precipitation over the coming century, which has been attributed primarily to enhanced surface evaporation associated with sea-ice retreat. Since the Arctic is still quite cold, especially in winter, it is often (implicitly) assumed that the additional precipitation will fall mostly as snow. However, very little is known about future changes in rain/snow distribution in the Arctic, notwithstanding the importance for hydrology and biology. Here we use 37 state-of-the-art climate models in standardised twenty-first century (2006–2100) simulations to show that 70◦ – 90◦N average annual Arctic snowfall will actually decrease, despite the strong increase in precipitation, and that most of the additional precipitation in the future (2091– 2100) will fall as rain. In fact, rain is even projected to become the dominant form of precipitation in the Arctic region. This is because Arctic atmospheric warming causes a greater fraction of snowfall to melt before it reaches the surface, in particular over the North Atlantic and the Barents Sea. The reduction in Arctic snowfall is most pronounced during summer and autumn when temperatures are close to the melting point, but also winter rainfall is found to intensify considerably. Projected (seasonal) trends in rain/snowfall will heavily impact Arctic hydrology (e.g. river discharge, permafrost melt), climatology (e.g. snow, sea ice albedo and melt) and ecology (e.g. water and food availability).”

See also:

R. Bintanja et al. Towards a rain-dominated Arctic, Nature Climate Change (2017). DOI: 10.1038/nclimate3240

http://www.nature.com/nclimate/journal/v7/n4/full/nclimate3240.html

Extract: "Rain causes more (extensive) permafrost melt, which most likely leads to enhanced emissions of terrestrial methane  (a powerful greenhouse gas), more direct runoff (a smaller seasonal delay) and concurrent freshening of the Arctic Ocean. Rainfall also diminishes snow cover extent and considerably lowers the surface albedo of seasonal snow, ice sheets and sea ice, reinforcing surface warming and amplifying the retreat of ice and snow; in fact, enhanced rainfall will most likely accelerate sea-ice retreat by lowering its albedo (compared with that of fresh snowfall)."

[A-Team]

I do not have access to EGU papers

That is just an abstract for a talk at EGU2017. There is no further pdf associated with it. The powerpoints shown during the talk are not available either. An older paper with a very similar title was written by these authors from 2016, DOI 10.1038/nature17145. Neither author is on ResearchGate.

However RE Kopp is there, co-authoring this April 2017 arxiv preprint (comments accepted) with DeConto et al:

Implications of ice-shelf hydrofracturing and ice-cliff collapse mechanisms for sea-level projections
https://arxiv.org/abs/1704.05597

A title search of the 2016 paper at google reveals 275 follow-up citations by subsequent articles which is a lot. These hits can be sorted by date. Some of them are on-topic, others off in the weeds.

Here are some other 2017 DeConto resources (in addition to Google Scholar 2017 hits):



http://www.scientia.global/dr-david-pollard-dr-robert-deconto-birth-death-ice-sheets-understanding-past-predicting-future-pennsylvania-state-university-university-massachusetts/

But who is going to get the message through to Guardian readers?  These might even include some policy makers or policy influencers.

Good question, Geoff. Outreach at that level is a full-time job. In the meantime "A lie can travel halfway around the world while the truth is still putting on its shoes".

Jonathan Swift on this in “The Examiner” back in 1710:

"Besides, as the vilest Writer has his Readers, so the greatest Liar has his Believers; and it often happens, that if a Lie be believ’d only for an Hour, it has done its Work, and there is no farther occasion for it. Falsehood flies, and the Truth comes limping after it; so that when Men come to be undeceiv’d, it is too late; the Jest is over, and the Tale has had its Effect…"

https://quoteinvestigator.com/2014/07/13/truth/

[AbruptSLR]

In my last post, I truncated the RCP 8.5 anthropogenic radiative forcing at 2050 (due to an assumed socio-economic collapse), and then added radiative forcing from a freshwater hosing event (per Hansen et al 2016) & an Arctic Albedo Flip (per Hansen and Sato 2012) & unspecified amount of methane emissions from thermokarst lakes, Antarctic methane hydrates and tropical wetlands.  In this post, I discuss some of the implications of decision makers being out of date on the implications of current methane concentrations.  In this regards, the first image shows the CO2e concentrations (per Wikipedia) for the various RCP scenarios, assume the conversion factors assumed prior to AR5.  This image shows an assumed CO2e concentration for RCP 8.5 of about 425 for 2017 and of about 630 ppm by 2050.

However, the total radiative forcings, RFs, from the linked ORNL website article by Blasing, T.J. (that updates such RF values reported in April 2016) are used in the linked Wikipedia article to calculate a CO2e value of 526.6ppm; which assuming the current rate of annual increase in CO2e of about 3.5ppm indicates that early in 2017 CO2e exceeded 530ppm:

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


Extract: "To calculate the CO2e of the additional radiative forcing calculated from April 2016's updated data: ∑ RF(GHGs) = 3.3793, thus CO2e = 280 e3.3793/5.35 ppmv = 526.6 ppmv."

http://cdiac.ornl.gov/pns/current_ghg.html


This value of 530ppm for CO2e for 2017 is well above the 425ppm value assumed by RCP 8.5 (used to force climate models for AR5); thus it seems highly likely that the true CO2e value in 2050 will be well above 750ppm

Also, see the associated 2008 article entitled: "Possible Origin of Methane in Ice Core Records"; which concludes that the methane in both Antarctic and Greenland ice cores for the Late Quaternary period (0.5-1.0 million years ago) is likely associated with methane emitted from marine hydrates

https://www.sciencedaily.com/releases/2008/02/080217093816.htm

Next, I provide a links to Jagniecki et al. (2015) (and an associated article); indicating that early Eocene climatic optimum (EECO) conditions (with an equable climate) may have occurred with atmospheric CO₂ concentrations between 680ppm and 1260ppm (see the second attached image); and that under such conditions the effective climate sensitivity (ESS) may have been twice that previously assumed by Royer et al (2012) (see link to reference below) as indicates in the third attached image, and could be very high for a CO2e concentration over 750ppm per the fourth image.

Jagniecki,Elliot A. et al. (2015), "Eocene atmospheric CO2from the nahcolite proxy", Geology, http://dx.doi.org/10.1130/G36886.1


http://geology.gsapubs.org/content/early/2015/10/23/G36886.1

ftp://rock.geosociety.org/pub/reposit/2015/2015357.pdf

Abstract: "Estimates of the atmospheric concentration of CO2, [CO2]atm, for the "hothouse" climate of the early Eocene climatic optimum (EECO) vary for different proxies. Extensive beds of the mineral nahcolite (NaHCO3) in evaporite deposits of the Green River Formation, Piceance Creek Basin, Colorado, USA, previously established [CO2]atm for the EECO to be >1125 ppm by volume (ppm). Here, we present experimental data that revise the sodium carbonate mineral equilibria as a function of [CO2] and temperature. Co-precipitation of nahcolite and halite (NaCl) now establishes a well-constrained lower [CO2]atm limit of 680 ppm for the EECO. Paleotemperature estimates from leaf fossils and fluid inclusions in halite suggest an upper limit for [CO2]atm in the EECO from the nahcolite proxy of ∼1260 ppm. These data support a causal connection between elevated [CO2]atm and early Eocene global warmth, but at significantly lower [CO2]atm than previously thought, which suggests that ancient climates on Earth may have been more sensitive to a doubling of [CO2]atm than is currently assumed."

Extract: "These results show that [CO₂]atm may not have been as high as previously thought during the warmest interval of the Cenozoic, implying a climate sensitivity for CO₂ that is roughly twice as high as is currently assumed (Royer et al., 2012)."

See also:
https://www.sciencenews.org/article/eocene-temperature-spike-caused-half-much-co2-once-thought

Extract: "During the Eocene around 50 million years ago, climbing CO2 levels heated the planet by more than 5 degrees Celsius. By examining crystals grown in this “hothouse” climate, researchers discovered that Eocene CO2 levels were as low as 680 parts per million. That’s nearly half the 1,125 ppm predicted by previous, less accurate crystal experiments, the researchers report online October 23 in Geology."

This supports my concern that if we stay on a BAU pathway until 2050, we could trigger a runaway climate change situation driven by methane from hydrates (see the following Wikipedia article on the Clathrate gun hypothesis) after say 2100, even if humans stop new GHG emissions all together in 2050.

Title: "Clathrate gun hypothesis"

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

Extract: "The sudden release of large amounts of natural gas from methane clathrate deposits in runaway climate change could be a cause of past, future, and present climate changes. The release of this trapped methane is a potential major outcome of a rise in temperature; some have suggested that this was a main factor in the planet warming 6 °C, which happened during the end-Permian extinction, as methane is much more powerful as a greenhouse gas than carbon dioxide. Despite its atmospheric lifetime of around 12 years, it has a global warming potential of 72 over 20 years, 25 over 100 years, and 33 when accounted for aerosol interactions. The theory also predicts this will greatly affect available oxygen and hydroxyl radical content of the atmosphere.
…
Another kind of exception is in clathrates associated with the Arctic ocean, where clathrates can exist in shallower water stabilized by lower temperatures rather than higher pressures; these may potentially be marginally stable much closer to the surface of the sea-bed, stabilized by a frozen 'lid' of permafrost preventing methane escape.

The so-called self-preservation phenomenon has been intensively studied by Russian geologists starting in the late 1980s. This metastable clathrate state can be a basis for release events of methane excursions, such as during the interval of the last glacial maximum. A study from 2010 concluded with the possibility for a trigger of abrupt climate warming based on metastable methane clathrates in the East Siberian Arctic Shelf (ESAS) region."

[Susan Anderson]

[edit and further apology for not reading from the beginning: I see Prokaryotes opened this discussion with a reference to this article. The continuing discussion is fascinating if a bit above my level.]

With apologies for an amateur interruption, while admiring all this excellent work. Just caught up my reading on a link I'd saved for when I had time from Eric Holthaus (Grist, 21 November 2017). It is a layperson's overview. I'm inclined to tamp down on exaggeration, but this is both convincing and terrifying. https://grist.org/article/antarctica-doomsday-glaciers-could-flood-coastal-cities/

Ice Apocalypse: Rapid collapse of Antarctic glaciers could flood coastal cities by the end of this century.
....
The glaciers of Pine Island Bay are two of the largest and fastest-melting in Antarctica. (A Rolling Stone feature earlier this year dubbed Thwaites “The Doomsday Glacier.”) Together, they act as a plug holding back enough ice to pour 11 feet of sea-level rise into the world’s oceans — an amount that would submerge every coastal city on the planet. For that reason, finding out how fast these glaciers will collapse is one of the most important scientific questions in the world today.

To figure that out, scientists have been looking back to the end of the last ice age, about 11,000 years ago, when global temperatures stood at roughly their current levels. The bad news? There’s growing evidence that the Pine Island Bay glaciers collapsed rapidly back then, flooding the world’s coastlines — partially the result of something called “marine ice-cliff instability.”

The ocean floor gets deeper toward the center of this part of Antarctica, so each new iceberg that breaks away exposes taller and taller cliffs. Ice gets so heavy that these taller cliffs can’t support their own weight. Once they start to crumble, the destruction would be unstoppable.

“Ice is only so strong, so it will collapse if these cliffs reach a certain height,” explains Kristin Poinar, a glaciologist at NASA’s Goddard Space Flight Center. “We need to know how fast it’s going to happen.”

In the past few years, scientists have identified marine ice-cliff instability as a feedback loop that could kickstart the disintegration of the entire West Antarctic ice sheet this century — much more quickly than previously thought.

Minute-by-minute, huge skyscraper-sized shards of ice cliffs would crumble into the sea, as tall as the Statue of Liberty and as deep underwater as the height of the Empire State Building. The result: a global catastrophe the likes of which we’ve never seen.

There are more references and caveats in the article, which appears to me to raise the probability of sea level rise which will inundate good parts of, for example, my home city Boston sooner than previously projected and make the low estimates for 2100 less likely than the higher ones.

[AbruptSLR]

As I only attach four images per post, I provide the four attached images to catch-up to the points made in by last two posts. 

The first image from Tobias Friedrich et al. (2016), indicates that when using an effective ECS based on calibration to data during warm conditions over the past 784,000 years, the global mean SAT could become as high as 8C above pre-industrial with radiative forcing of 6 Watts/sq meter (see also the following associated caption)

Caption for the first image: "Fig. 3  Sensitivity of global mean SAT anomalies to radiative forcing anomalies:  Scatter diagram (circles) of reconstructed global mean SAT anomalies (K) (Fig. 2B) versus net radiative forcing anomalies (W/m2) (Fig. 2D) for the last 784,000 years. Anomalies are calculated with respect to PI values. Two-dimensional kernel density estimate of paleo-SAT/radiative forcing data (blue shading). The thick dashed yellow curve represents nonlinear regression of paleo-SAT/radiative forcing data, along with uncertainty ranges (dashed black curves; see Materials and Methods). The thick cyan line represents linear regression for cold phases. The slope represents Scold. The thick red line represents linear regression for warm phases. The slope represents Swarm. Dashed horizontal lines denote warm (orange) and cold (blue) phases using 1 SD of the reconstructed global mean SAT anomalies as a separator. Cold (warm) phases are defined by SAT anomalies of <−5.12 K (>−1.66 K). The CMIP5 transient model projections using the RCP8.5 forcing scenario are presented by purple circles. Using Swarm (orange shading) and taking into account the ocean heat uptake efficiency, we can calculate the transient response to the RCP8.5 radiative forcing. The resulting paleo-based projection with the corresponding uncertainty ranges is represented by cyan shading (see Materials and Methods)."

The second image shows a table of CH4 direct, CH4 indirect and associate indirect radiative forcing from O3/H₂O/CO₂ from the indicated change in CH4 burden in the atmosphere; which is associated with the third image that describes the cases, with a highest case associated with a pulse of methane from hydrates.  The second & third images are from Isaksen et al. (2011).

The fourth image shows the total net positive cloud feedback per degree C increase in GMSTA (global mean surface temperature anom.); which helps to explain why ECS increases with increasing GMSTA.

[AbruptSLR]

The linked reference studies the paleo decay of the Cordilleran ice sheet and finds that it lost most of its ice mass earlier than consensus science previously thought, and it lost much of its ice mass over a relatively short period.  Personally, I am concerned about the impact of rainfall at increasingly high latitudes (with warming) on both the Greenland Ice Sheet, GIS, on Arctic permafrost, and on the WAIS and the EAIS, and I note that some researchers indicate that based on these new findings that the GIS could lose all of its ice mass in as little as 500 years (which would contribute to freshwater hosing from both the WAIS and the EAIS):

B. Menounos et al (10 Nov 2017), "Cordilleran Ice Sheet mass loss preceded climate reversals near the Pleistocene Termination", Science, Vol. 358, Issue 6364, pp. 781-784, DOI: 10.1126/science.aan3001

http://science.sciencemag.org/content/358/6364/781

Abstract: "The Cordilleran Ice Sheet (CIS) once covered an area comparable to that of Greenland. Previous geologic evidence and numerical models indicate that the ice sheet covered much of westernmost Canada as late as 12.5 thousand years ago (ka). New data indicate that substantial areas throughout westernmost Canada were ice free prior to 12.5 ka and some as early as 14.0 ka, with implications for climate dynamics and the timing of meltwater discharge to the Pacific and Arctic oceans. Early Bølling-Allerød warmth halved the mass of the CIS in as little as 500 years, causing 2.5 to 3.0 meters of sea-level rise. Dozens of cirque and valley glaciers, along with the southern margin of the CIS, advanced into recently deglaciated regions during the Bølling-Allerød and Younger Dryas."

Disappearance of an ice sheet

The Cordilleran Ice Sheet is thought to have covered westernmost Canada until about 13,000 years ago, even though the warming and sea level rise of the last deglaciation had begun more than a thousand years earlier. This out-of-phase behavior has puzzled glaciologists because it is not clear what mechanisms could account for it. Menounos et al. report measurements of the ages of cirque and valley glaciers that show that much of western Canada was ice-free as early as 14,000 years ago—a finding that better agrees with the record of global ice volume (see the Perspective by Marcott and Shakun). Previous reconstructions seem not to have adequately reflected the complexity of ice sheet decay.

In the attached image showing the results of a straw-man poll of experts, I would believe that the risk of a WAIS collapse, and ENSO amplitude increase, are seriously underestimated (but the risk of the GIS collapse seems reasonable).  Also, I note that a dynamical analysis would clearly demonstrate that all of these indicated tipping mechanisms are interlinked and feedback on each other.  Also, I note that rainfall in the Arctic would do more that just reduce sea ice albedo, but would also reduce the albedo of snow-covered land.

[AbruptSLR]

Here are four more misc. images that are relevant to this topic.

The first image shows how warm ocean water can leak from the West Pacific Warm Pool into the Southern Ocean, and this mechanism should result in more advected warm water with continued global warming and with increase amplitude of El Nino events.

The second images observed data illustrating how quickly the volume of warm CDW has increase in the Southern Ocean in recent years.  This not only promotes ice mass loss from Antarctic marine glaciers, but it also promotes the slow response positive feedback mechanism between the Tropical Pacific and the Southern Ocean.

The third image shows how the discharge of fresh basal meltwater at the cliff face of a marine glacier produces turbulent convection at the ice face, which can promote the occurrence of cliff failures.

The fourth image shows how relatively thin the lithosphere is in much of West Antarctica, which not only promotes geothermal heat flux, but also promotes both seismic and volcanic activity; both of which can be triggered by sufficient ice mass loss.

[AbruptSLR]

While the ice in the Totten Glacier Catchment (see the first image) in East Antarctica, may not collapse until 2100 or later, this issue is still a serious concern.  The second image shows the Totten Gateway with a deep channel in the seafloor leading to the warm CDW indicated in the third and fourth attached images.

See also the video linked in Reply #12.

[sidd]

" I note that some researchers indicate that based on these new findings that the GIS could lose all of its ice mass in as little as 500 years "

Do tell ? References would be helpful. Losing all icemass from GIS in 500 years is not something I have seen.

sidd

[A-Team]

Losing all ice from GIS in 500 years is not something I have seen

Right, sidd. No such claim has ever been made in a peer-reviewed article. For Greenland's floating ice shelves, those are all but gone already. These do not contribute to sea level rise, nor does what's left significantly buttress ice streams in the case of Jakobshavn and Petermann, contrary to repeated nonsense in newspapers. Zachariae - Nioghalvfjerdsfjorden's shelves might, but like the name says it's at 79ºN and adjacent to a steady stream of Fram ice floes.

Instead, there has been a long-running argument between the soil surface Be¹⁰ people and the Danish PI of ice core drilling about whether Greenland even melted out during the last interglacial, the Eemian, which was warmer than today and lasted for a few thousand years.

The beryllium data shows beyond any reasonable doubt that central and western Greenland did in fact melt out. (Note no one is suggesting that the 3000 m marginal mountains on the east side were snow-free.) Moderately old bottom ice in Greenland has been identified but drilling to date has taken place elsewhere.

The focus today is getting additional soil and rock cores from beneath the ice sheet, both for geothermal gradient and melt history. Stay tuned while the back-and-forth continues over Greenland's paleo contributions to sea level rise.
 
The whole problem with paleo setting risk policy is when you get it wrong, like here, Storegga, and numerous late Pleistocene - early Holocene event correlations now known from gold standard dendrochronology to be incorrectly dated by C¹⁴ plateauing and ice core annual layer mis-counting.