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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2150 on: December 06, 2019, 05:51:15 PM »
So a natural super-interglacial has been turned by us into a super-super-interglacial, and maybe we're even tipping the planet into a Hothouse Earth state:
https://www.pnas.org/content/115/33/8252

Again, I should have formulated more precisely, as Steffen et al 2018 do in their Hothouse Earth paper, referring to Ganopolski et al 2016:
"the rapid trajectory of the climate system over the past half-century along with technological lock in and socioeconomic inertia in human systems commit the climate system to conditions beyond the envelope of past interglacial conditions. We, therefore, suggest that the Earth System may already have passed one “fork in the road” of potential pathways, a bifurcation (near A in Fig. 1) taking the Earth System out of the next glaciation cycle (11)."

Maybe we've already passed this fork in the road, or maybe not. In risky territory we certainly seem to be.

I note that consensus climate science tends to use large ensemble of model projections (like those coming from CMIP6) in order to better address the 'signal-to noise' paradox in climate science as discussed in the linked reference (& associated linked article & first attached image).  While this may be an effect strategy to address the 'signal-to-noise' problem for ensembles of models that do not contain inherent bias in their formulations, if our current Earth Systems are subject to a cascade of Earth System tipping points changing our current 'climate state' to a 'Hothouse' Earth, then ensembles like CMIP6 could well be erring on the side of least drama.  For instance, CMIP6 excludes a large number of potential ice-climate feedback mechanism, largely by indicating that the participants calibrated their models against paleo-events that considered Heinrich and Dansgaard-Oeschger events as noise (see the second image); however, typically these ensembles cannot accurately project the super-interglacial periods cited by Lennart; which in my opinion is associated with the likely situation that super-interglacial periods are typically triggered by the collapse of marine ice sheets (such as the WAIS) while most Heinrich and Dansgaard-Oeschger events are related to ice calving from land, or land-terminating, ice sheets.  Furthermore, ensembles are not good at modeling decadal-scale feedback mechanisms; thus a MICI-type of collapse of the WAIS would likely not be simulated by the CMIP6 ensemble even if the modelers including MICI-mechanisms, which they do not:


Scaife, A.A., Smith, D. A signal-to-noise paradox in climate science. npj Clim Atmos Sci 1, 28 (2018) doi:10.1038/s41612-018-0038-4

https://www.nature.com/articles/s41612-018-0038-4

Abstract: "We review the growing evidence for a widespread inconsistency between the low strength of predictable signals in climate models and the relatively high level of agreement they exhibit with observed variability of the atmospheric circulation. This discrepancy is particularly evident in the climate variability of the Atlantic sector, where ensemble predictions using climate models generally show higher correlation with observed variability than with their own simulations, and higher correlations with observations than would be expected from their small signal-to-noise ratios, hence a ‘signal-to-noise paradox’. This unusual behaviour has been documented in multiple climate prediction systems and in the response to a number of different sources of climate variability. However, we also note that the total variance in the models is often close in magnitude to the observed variance, and so it is not a simple matter of models containing too much variability. Instead, the proportion of Atlantic climate variance that is predictable in climate models appears to be too weak in amplitude by a factor of two, or perhaps more. In this review, we provide a range of examples from existing studies to build the case for a problem that is common across different climate models, common to several different sources of climate variability and common across a range of timescales. We also discuss the wider implications of this intriguing paradox."

Extract: "We have provided a wide range of evidence for a ‘signal-to-noise paradox’ in climate science. The paradox lies in the fact that climate models are better able to predict observed climate variability than would be expected from their low signal-to-noise ratio. However, in many cases, the total amount of variability found in ensemble member simulations closely matches that found in observations, and so it is not just a simple case of models being too ‘noisy’ or containing too much variability. We instead conclude that the amplitude of predictable signals in response to boundary conditions or external forcing may be much too weak, especially in the Atlantic sector. This helps to explain why so many climate modelling studies show clear relationships between model and observations only after anomalies are ‘standardised’. These anomalously weak signals in predictions hamper the use of seasonal and decadal predictions, inhibit the validity of probabilistic and ensemble approaches and prevent the accurate estimation of forced climate variability in the Atlantic sector."

Caption for the first image: "Figure 1. This graph shows how ensemble predictions are better at predicting the real-world North Atlantic Oscillation (in black) than simulated ones (blue). The horizontal axis indicates the number of individual simulations contributing to each ensemble prediction, while the vertical axis measures the correlation between the ensemble average prediction and the year to year variations in the North Atlantic Oscillation (real or simulated)."

&

Title: "Clarity from Chaos: How Climate Models Could Be Better than We Think"

http://physicsbuzz.physicscentral.com/2019/08/clarity-from-chaos-how-climate-models.html

Extract: "Since Lorenz’s research took the field by storm, climate scientists have found the need to relinquish the traditional scientific love of causality. Weather and climate patterns are technically deterministic—if a perfect computer simulation had perfectly precise measurements of the millions of factors affecting the atmosphere, it could hypothetically predict future behavior exactly.  However, the impossibility of this task means that in practice, even a small error in measurement early on, or a slight misjudgment of, say, the number of butterflies passing through can easily compound.

Last year, Adam Scaife and Doug Smith of the UK’s Met Office published a review article in Nature Climate and Atmospheric Science which highlighted what they consider a “paradox” in ensemble predictions. The crux of the matter is this: for many models, the ensemble predictions provide a poor measure of the likelihood of a single simulated outcome… this might just suggest that chaos rules and there is little predictability, except for the surprising fact that the ensemble produces much more accurate predictions of the single real-world outcome. In other words, these models are better at predicting the real world than they are at predicting themselves!"
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2151 on: December 06, 2019, 06:51:47 PM »
Some interesting reflections by Dewi Le Bars on the implications of two recent papers for the projections by DeConto & Pollard and for ice-climate feedback modelling (as proposed by Hansen et al, amongst others):
https://sites.google.com/site/dewilebars/sea-level-monthly-review/february-2019

On Edwards et al 2019:
'The claim that MICI is "not necessary" to reproduce past sea level high stands is both not really true and not really useful. The uncertainty range about what could have been the contribution of Antarctica to sea level during the Pliocene is 5-20 m and during the Last Interglacial it is 3.6-7.4 m. DeConto and Pollard’s model without MICI can reproduce up to 6 m and 5.5 m respectively for these two period (see Edwards et al. E.D. Fig. 4). So yes it can reproduce the lower part of the ranges. But most of the Pliocene range cannot be reproduced with the no-MICI assumption. What the figure shows is that the model with MICI covers a much bigger par of the possible Antarctic contribution for these periods. And still, even including MICI, the model can only explain a maximum of 12 m contribution for the Pliocene. Which means additional mechanisms would be necessary to cover the whole range of possible Antarctic contribution for that period. The claim that MICI is “not necessary” is also not very useful practically because projections with MICI are used to make high-end sea level scenarios. The important information is then is it possible or not? If it was not possible then it would be good news and decision makers wouldn't need to take it into account. "Not necessary" only has an impact on low-end scenarios, for which MICI would already not be used anyways.'

On Golledge et al 2019:
'Current state of the art (CMIP5 type) climate models do not include ice sheet models so the coupled effects between ice sheets and climate are a blind spot. In these climate models the ice sheets are just white mountains that do not change over time. They might have a snow layer on top of them but no ice. So snow falls on them accumulate a little bit and when it melts it is put in the nearest ocean grid box. If too much accumulates then it is put directly in the ocean to avoid infinite accumulation. What is missing is a model to transform the snow to ice and then transport it back to the sides of the ice sheet or to the ocean under the force of gravity. This is what ice sheet models do. Golledge et al. use the PISM ice sheet model for Greenland and Antarctica and couple them offline to LOVECLIM, an intermediate complexity climate model. Intermediate complexity means lower resolution and simpler physics compared to CMIP5 type climate models. It is the type of models generally used for long paleoclimate simulations.

What they find is that allowing feedbacks between the ice sheets and the climate model leads to strengthen both Antarctic and Greenland mass loss, by 100% and 30% respectively. For Antarctica this is not a surprise, although the magnitude is much bigger than I expected. Freshwater from the melting of ice leads to increase the ocean stratification, because it is is very light. This reduces vertical ocean mixing and as a result the surface of the ocean cools down while the subsurface warms up. Antarctica mostly looses mass from ice shelves basal melt and calving which is strengthened by warmer subsurface ocean temperature. For Greenland, it comes as a surprise to me that the feedback would increase the mass loss, because Greenland mostly looses mass from surface melt and a cooler atmosphere temperature would tend to reduce surface melt. Unfortunately the paper does not explain the mechanisms at play there (or did I miss it?).

There are a few issues with the ice sheet models that reduce my confidence in the projections. For Greenland the model is not able to reproduce the recent fast mass loss acceleration. Therefore the authors artificially impose the mass loss on the model in two ways: (1) decrease the friction between the ice and the bed (basal traction) to have a faster flow between 2000 and 2015 and (2) reduce the snowpack refreezing between 2000 and 2025. Refreezing is important for the mass balance because on ice sheets more than half of the snow that melts in the summer refreezes locally. It never reaches the ocean. Michiel van den Broeke had a similar comments in Trouw (in Dutch). You can force the model to agree with observations but if the model does not have the proper dynamics to explain observations there is no reason it is doing a good job for the future. For Antarctica, the model starts with enormous mass accumulation (1000 Gt/year in 1900) and accumulates mass until the 1980th. This is clearly not possible, such an accumulation would have been seen by tide gauge measurements. In fact as I said in the last review it is expected that Antarctica was slowly loosing mass in the 20th century. Also, the internal variability of grounded ice is so large in the model (Fig. 1a-d) that I do not understand what is going on physically (please let me know if you do).

In conclusion, the paper’s goal is important and it is the first time that two high resolution ice sheet models are coupled to a climate model. This is a big step in the right direction. However, I am not convinced by the results because of the issues mentioned above concerning the ice sheet models. Nevertheless, it is very instructive as it shows the long way that is left for ice sheet models to reach the level at which we can trust their future projections.'

As many left-tail advocates on this thread like to imply that Edwards et al. (2019) and Golledge et al. (2019), allows consensus climate science to effectively ignore MICI-type of ice-climate mechanism, I encourage readers to both re-read Lennart's quoted post from last March, and to consider:

1. The first image shows an abrupt SLR event about 127,000 year ago (during the Eemian) that Edwards et al. (2019) cannot replicate; and thus this significantly raises the risk that MICI-type of mechanisms are very relevant to our current situation w.r.t. a potential near-term collapse of the WAIS.

2. The second image shows how the pdf for ECS shifts to the right as more feedback mechanisms are considered (note that observation-based estimates of ECS not only ignore all slow-response mechanisms but also many fast response mechanisms).  However, as consensus climate science chooses to define ECS based on a doubling of CO2 (or CO2 equivalent) it ignores many ice-climate feedback mechanisms this century including both MISI and MICI mechanisms, which if considered would screw the effective ECS pdf still further to the right.  Furthermore, as the IPCC report use confidence levels centered on median values rather than average values of ECS, as illustrated by the third image, when the IPCC ignores many ice-climate feedback mechanisms for effective ECS they ignore that likelihood that the average effective ECS has shifted further to the right, which raises the risk of Earth Systems shifting into a high climate state during the Anthropocene as illustrated by the fourth attached image.


For reference see:

Edwards, T. L. et al. (2019) Revisiting Antarctic ice loss due to marine ice-cliff instability, Nature, doi:10.1038/s41586-019-0901-4

https://www.nature.com/articles/s41586-019-0901-4

&

Golledge, N. R. et al. (2019) Global environmental consequences of twenty-first-century ice-sheet melt, Nature, doi:10.1038/s41586-019-0889-9

https://www.nature.com/articles/s41586-019-0889-9
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2152 on: December 06, 2019, 08:39:48 PM »
As a follow-on to my last post, the linked reference discusses the implications of both Type 1 (false positive) and Type 2 (false negative) errors in climate science and assessments (see the attached image).

Anderegg, W.L. et. al. (September 2014), "AWARENESS OF BOTH TYPE 1 AND 2 ERRORS IN CLIMATE SCIENCE AND ASSESSMENT", BAMS - American Meteorological Society, DOI:10.1175/BAMS-D-13-00115.1

https://journals.ametsoc.org/doi/full/10.1175/BAMS-D-13-00115.1
&
https://journals.ametsoc.org/doi/pdf/10.1175/BAMS-D-13-00115.1

Abstract: "Treatment of error and uncertainty is an essential component of science and is crucial in policy-relevant disciplines, such as climate science. We posit here that awareness of both “false positive” and “false negative” errors is particularly critical in climate science and assessments, such as those of the Intergovernmental Panel on Climate Change. Scientific and assessment practices likely focus more attention to avoiding false positives, which could lead to higher prevalence of false-negative errors. We explore here the treatment of error avoidance in two prominent case studies regarding sea level rise and Himalayan glacier melt as presented in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. While different decision rules are necessarily appropriate for different circumstances, we highlight that false-negative errors also have consequences, including impaired communication of the risks of climate change. We present recommendations for better accounting for both types of errors in the scientific process and scientific assessments."

Anderegg et al (2014) reference extensively discusses the Type 1 (false positive) statement in AR4 about the Himalayan glacier melt contribution to sea level rise; the correction of which in AR5, in my opinion, has caused consensus climate scientists to exhaust themselves on chasing Type 1 errors, leaving them with less energy to chase Type 2 errors (i.e. case where consensus scientists assume that no relationship exists when in fact one due exist [i.e. MICI mechanisms]).  Therefore, in addition to the points raised by Le Bars about Edwards et al. (2019), I add the following partial list of Type 2 errors that consensus scientists' models (both CMIP5 and to some degree CMIP6) are most probably making with regard to characterization of the risk of abrupt ice mass loss this century:

1. Consensus scientists over emphasize that Greenland is contributing about twice as much to current SLR than Antarctica. This can lead to a Type 2 error, of ignoring the freshening of the Southern Ocean associate with both ice mass loss from Antarctic ice shelves and increasing precipitation into the Southern Ocean, neither of which contribute to SLR, but both of which contribute to the early activation of ice-climate feedback mechanisms around Antarctica, which will contribute to more significant MICI action than consensus scientists are currently prepared to acknowledge.

2. The initial conditions and boundary conditions of virtually all consensus climate models err on the side of least drama with regard to such matters as: a) slowing of the MOC, b) sensitivity of the ENSO to shift towards more frequent El Nino events (which indicates higher end values for ECS) & initial Ocean Heat Content; c) negative forcing from aerosols which mask higher end values of ECS; d) the key Antarctic ice shelves are currently in much worse condition than assumed by essentially all climate models that I am aware of; e) finer meshes virtually always lead to greater marine glacier sensitivity to climate forcing, and current consensus models are far to coarse to capture key ice behavior (such as that at the base of the Thwaites Ice Tongue); f) new satellite information confirms that low level tropical cloud cover is dissipating with more global warming which implies that fast response climate sensitivity is increasing with time.

3. Many nonlinearly increasing positive carbon feedback mechanisms (such as permafrost, soil and forest degradation) are currently being masked by the likely increase in carbon absorption by vegetation that is temporarily benefiting from more atmospheric CO₂ and warming temperatures.  This is what Hansen calls a Faustian bargain, where consensus scientists do not need to acknowledge the nonlinearly increasing positive carbon feedback mechanisms (which is a Type 2 error).  Furthermore, biological systems are highly susceptible to damage from abrupt climate change, but most consensus climate models downplay the degree of this sensitivity; therefore most consensus models underestimate the likely coming damage to both terrestrial and oceanic carbon sinks with continuing anthropogenic forcing (including pollution, and land use changes).

4.  Consensus climate models cannot hind cast the degree of Arctic Amplification observed in the paleo-record, and thus these consensus climate models are clearly committing Type 2 errors by ignoring positive feedback mechanisms that contribute to Arctic Amplification (& thus to Antarctic marine glacial instability via bipolar seesaw mechanisms).

I could go on, but I am mere listing arguments that I have already made earlier in this thread, so those who are interested can scroll back to see other Type 2 errors (such as the positive feedback associated with the project future redistribution of anthropogenic aerosol emissions, and projected changes in VOCs from forests).
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2153 on: December 06, 2019, 09:24:30 PM »
The linked article and associated linked reference confirms that GHG emissions during the peak of the PETM were occurring about 10 times slower than current anthropogenic GHG emissions:

Title: "Carbon emissions from volcanic rocks can create global warming"

https://www.sciencedaily.com/releases/2019/12/191205073024.htm

Extract: "Geologists at the University of Birmingham have created the first mechanistic model of carbon emissions changes during the Paleocene-Eocene Thermal Maximum (PETM) -- a short interval of maximum temperature lasting around 100,000 years some 55 million years ago.

During PETM initiation, release of 0.3-1.1 PgC yr-1 of carbon as greenhouse gases to the ocean-atmosphere system drove 4-5°C of global warming over less than 20,000 years -- a relatively short period of time."

See also:

Stephen M. Jones, Murray Hoggett, Sarah E. Greene & Tom Dunkley Jones. Large Igneous Province thermogenic greenhouse gas flux could have initiated Paleocene-Eocene Thermal Maximum climate change. Nature Communications, 2019 DOI: 10.1038/s41467-019-12957-1

https://www.nature.com/articles/s41467-019-12957-1.epdf?shared_access_token=eJinQbvdEZd9ahXxNcs1ytRgN0jAjWel9jnR3ZoTv0NKzrEQ0tfq0ywvPqEwgn3CRBhC0EOyZalzcBDc1uFjXMiJ4lPtxegf_Pj0b5pds-B9v1i7Z55UIOQQnGSZzaa0zS67-jh5N7-FXcA10MuDGQ%3D%3D


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vox_mundi

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2154 on: December 06, 2019, 09:36:35 PM »
Research Reveals Past Rapid Antarctic Ice Loss Due to Ocean Warming
https://phys.org/news/2019-12-reveals-rapid-antarctic-ice-loss.html

New research from the University of Otago has found the sensitive West Antarctic Ice Sheet collapsed during a warming period just over a million years ago when atmospheric carbon dioxide levels were lower than today.

Using biomarkers to reconstruct past ocean temperatures, and through ice sheet computer models, the study published in Quaternary Science Reviews shows that the accepted maximum global warming of 1.5°C under the Paris Agreement could lead to a runaway retreat of the West Antarctic Ice Sheet.

The study found that one million years ago in the ocean surrounding Antarctica, the summer ocean temperature was on average 5°C (±1.2°C) warmer than today.

"Using the data, the ice sheet simulation indicates a complete collapse of the West Antarctic Ice Sheet with additional melting of the East Antarctic Ice Sheet resulting in sustained global sea-level rise of centimetre to decimetres per decade."

The study proposes a two-step model for West Antarctic ice loss which initially involves mild ocean warming forcing ice margin retreat, followed by a rapid warming primarily driven by the extensively modified oceanic and hydrologic system following further ice sheet retreat.



Beltran Catherine et al. Southern Ocean temperature records and ice-sheet models demonstrate rapid Antarctic ice sheet retreat under low atmospheric CO2 during Marine Isotope Stage 31, Quaternary Science Reviews (2019)

Highlights

• Quantification of the Southern Ocean warming during MIS31 using molecular temperature reconstructions at high latitudes.

• Sustained surface Southern Ocean warming & collapse of the sub-Antarctic ocean fronts under low atmospheric CO2 conditions.

• Use of sea surface temperature data to test scenarios for the AIS retreat using coupled ice-sheet/ice-shelf model.

• Two steps WAIS retreat: 1) mild ocean warming forcing ice margin retreat 2) rapid ocean warming as the ice sheet retreats.

We show that the Paris Agreement target temperature of 1.5°C is sufficient to drive runaway retreat of the WAIS.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2155 on: December 06, 2019, 10:43:05 PM »
...
We show that the Paris Agreement target temperature of 1.5°C is sufficient to drive runaway retreat of the WAIS.

vox,

Thank you for the links to Beltran et al. (2019); which complements and adds details for the MIS 31 super interglacial that I posted about in Reply #2005, and by Coletti et al. (2015), see attached image; which also documents an interhemispheric linkage between the Arctic and Antarctic during super interglacial periods. 

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

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

Abstract: "Until now, the lack of time-continuous, terrestrial paleoenvironmental data from the Pleistocene Arctic has made model simulations of past interglacials difficult to assess. Here, we compare climate simulations of four warm interglacials at Marine Isotope Stages (MISs) 1 (9 ka), 5e (127 ka), 11c (409 ka) and 31 (1072 ka) with new proxy climate data recovered from Lake El'gygytgyn, NE Russia. Climate reconstructions of the mean temperature of the warmest month (MTWM) indicate conditions up to 0.4, 2.1, 0.5 and 3.1 °C warmer than today during MIS 1, 5e, 11c and 31, respectively. While the climate model captures much of the observed warming during each interglacial, largely in response to boreal summer (JJA) orbital forcing, the extraordinary warmth of MIS 11c compared to the other interglacials in the Lake El'gygytgyn temperature proxy reconstructions remains difficult to explain. To deconvolve the contribution of multiple influences on interglacial warming at Lake El'gygytgyn, we isolated the influence of vegetation, sea ice and circum-Arctic land ice feedbacks on the modeled climate of the Beringian interior. Simulations accounting for climate–vegetation–land-surface feedbacks during all four interglacials show expanding boreal forest cover with increasing summer insolation intensity. A deglaciated Greenland is shown to have a minimal effect on northeast Asian temperature during the warmth of stages 11c and 31 (Melles et al., 2012). A prescribed enhancement of oceanic heat transport into the Arctic Ocean does have some effect on Lake El'gygytgyn's regional climate, but the exceptional warmth of MIS l1c remains enigmatic compared to the modest orbital and greenhouse gas forcing during that interglacial."

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

Certainly, the model results by Beltran et al. (2019) suggest that the current upwelling of modified CDW and advection to groundling lines of key Antarctic marine glaciers may well trigger sufficient ice mass loss to cause extensive modifications to oceanic and hydrologic systems that could lead directly to the collapse of the WAIS.

Beltran, Catherine et al. (2019 online or 15 January 2020), "Southern Ocean temperature records and ice-sheet models demonstrate rapid Antarctic ice sheet retreat under low atmospheric CO2 during Marine Isotope Stage 31, Quaternary Science Reviews, Volume 228, 10606, https://doi.org/10.1016/j.quascirev.2019.106069

https://www.sciencedirect.com/science/article/abs/pii/S0277379119306122?via%3Dihub

Abstract: "Over the last 5 million years, the Earth’s climate has oscillated between warm (interglacial) and cold (glacial) states. Some particularly warm interglacial periods (i.e. ‘super-interglacials’) occurred under low atmospheric CO2 and may have featured extensive Antarctic ice sheet collapse. Here we focus on an extreme super-interglacial known as Marine Isotope Stage 31 (MIS31), between 1.085 and 1.055 million years ago and is the subject of intense discussion. We reconstructed the first Southern Ocean and Antarctic margin sea surface temperatures (SSTs) from organic biomarkers and used them to constrain numerical ice sheet-shelf simulations. Our SSTs indicate that the ocean was on average 5 °C (±1.2 °C) warmer in summer than today between 50 °S and the Antarctic ice margin. Our most conservative ice sheet simulation indicates a complete collapse of the West Antarctic Ice Sheet (WAIS) with additional deflation of the East Antarctic Ice Sheet. We suggest the WAIS retreated because of anomalously high Southern Hemisphere insolation coupled with the intrusion of Circumpolar Deep Water onto the continental shelf under poleward-intensified winds leading to a shorter sea ice season and ocean warming at the continental margin. In this scenario, the extreme warming we observed likely reflects the extensively modified oceanic and hydrologic system following ice sheet collapse. Our work highlights the sensitivity of the Antarctic ice sheets to minor oceanic perturbations that could also be at play for future changes."

Best,
ASLR
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2156 on: December 07, 2019, 02:28:23 AM »
...

Certainly, the model results by Beltran et al. (2019) suggest that the current upwelling of modified CDW and advection to groundling lines of key Antarctic marine glaciers may well trigger sufficient ice mass loss to cause extensive modifications to oceanic and hydrologic systems that could lead directly to the collapse of the WAIS.

...

I thought it would be good to remind readers that Milillo et al. (2019) stated that: "We interpret the results in terms of buoyancy/slope-driven seawater intrusion along preferential channels at tidal frequencies leading to more efficient melt in newly formed cavities. Such complexities in ice-ocean interaction are not currently represented in coupled ice sheet/ocean models."

P. Milillo, E. Rignot, P. Rizzoli, B. Scheuchl, J. Mouginot, J. Bueso-Bello and P. Prats-Iraola (Jan 2019), "Heterogeneous retreat and ice melt of Thwaites Glacier, West Antarctica", Science Advances  30, Vol. 5, no. 1, eaau3433, DOI: 10.1126/sciadv.aau3433

https://advances.sciencemag.org/content/5/1/eaau3433

Abstract
The glaciers flowing into the Amundsen Sea Embayment, West Antarctica, have undergone acceleration and grounding line retreat over the past few decades that may yield an irreversible mass loss. Using a constellation of satellites, we detect the evolution of ice velocity, ice thinning, and grounding line retreat of Thwaites Glacier from 1992 to 2017. The results reveal a complex pattern of retreat and ice melt, with sectors retreating at 0.8 km/year and floating ice melting at 200 m/year, while others retreat at 0.3 km/year with ice melting 10 times slower. We interpret the results in terms of buoyancy/slope-driven seawater intrusion along preferential channels at tidal frequencies leading to more efficient melt in newly formed cavities. Such complexities in ice-ocean interaction are not currently represented in coupled ice sheet/ocean models.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2157 on: December 07, 2019, 03:27:55 AM »
I just remind readers that researchers including Hellmer et al. (2012) [see the attached image comparing E3SM projections for FRIS vs Hellmer et al. (2012)] and Darelius et al. (2016) find that changes in sea ice extent near the Weddell Sea are changing local wind patterns that are currently driving warm modified CDW beneath the FRIS which should result in accelerated ice mass loss from the FRIS in coming decades:


Hellmer, H., Kauker, F., Timmermann, R. et al. Twenty-first-century warming of a large Antarctic ice-shelf cavity by a redirected coastal current. Nature 485, 225–228 (2012) doi:10.1038/nature11064

https://www.nature.com/articles/nature11064

Abstract: "The Antarctic ice sheet loses mass at its fringes bordering the Southern Ocean. At this boundary, warm circumpolar water can override the continental slope front, reaching the grounding line through submarine glacial troughs and causing high rates of melting at the deep ice-shelf bases. The interplay between ocean currents and continental bathymetry is therefore likely to influence future rates of ice-mass loss. Here we show that a redirection of the coastal current into the Filchner Trough and underneath the Filchner–Ronne Ice Shelf during the second half of the twenty-first century would lead to increased movement of warm waters into the deep southern ice-shelf cavity. Water temperatures in the cavity would increase by more than 2 degrees Celsius and boost average basal melting from 0.2 metres, or 82 billion tonnes, per year to almost 4 metres, or 1,600 billion tonnes, per year. Our results, which are based on the output of a coupled ice–ocean model forced by a range of atmospheric outputs from the HadCM3 climate model, suggest that the changes would be caused primarily by an increase in ocean surface stress in the southeastern Weddell Sea due to thinning of the formerly consolidated sea-ice cover. The projected ice loss at the base of the Filchner–Ronne Ice Shelf represents 80 per cent of the present Antarctic surface mass balance. Thus, the quantification of basal mass loss under changing climate conditions is important for projections regarding the dynamics of Antarctic ice streams and ice shelves, and global sea level rise."

&

Darelius, E., Fer, I. & Nicholls, K. Observed vulnerability of Filchner-Ronne Ice Shelf to wind-driven inflow of warm deep water. Nat Commun 7, 12300 (2016) doi:10.1038/ncomms12300

https://www.nature.com/articles/ncomms12300

Abstract: "The average rate of melting at the base of the large Filchner-Ronne Ice Shelf in the southern Weddell Sea is currently low, but projected to increase dramatically within the next century. In a model study, melt rates increase as changing ice conditions cause a redirection of a coastal current, bringing warm water of open ocean origin through the Filchner Depression and into the Filchner Ice Shelf cavity. Here we present observations from near Filchner Ice Shelf and from the Filchner Depression, which show that pulses of warm water already arrive as far south as the ice front. This southward heat transport follows the eastern flank of the Filchner Depression and is found to be directly linked to the strength of a wind-driven coastal current. Our observations emphasize the potential sensitivity of Filchner-Ronne Ice Shelf melt rates to changes in wind forcing."
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― Leon C. Megginson

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2158 on: December 07, 2019, 03:34:03 AM »

The linked (open access) reference focuses on the impacts of marine instability primarily of the Wilkes Basin (but also other basins as indicated by the attached images showing impacts on AABW formation due to different assumed marine glacier instability scenarios in different basins) on Southern Ocean dynamics.  This research supports the Hansen et al (2016) findings:

Phipps, S. J., Fogwill, C. J., and Turney, C. S. M.: Impacts of marine instability across the East Antarctic Ice Sheet on Southern Ocean dynamics, The Cryosphere Discuss., doi:10.5194/tc-2016-111, in review, 2016.

http://www.the-cryosphere-discuss.net/tc-2016-111/

Abstract. Recent observations and modelling studies have demonstrated the potential for rapid and substantial retreat of large sectors of the East Antarctic Ice Sheet (EAIS). This has major implications for ocean circulation and global sea level. Here we examine the effects of increasing meltwater from the Wilkes Basin, one of the major marine-based sectors of the EAIS, on Southern Ocean dynamics. Climate model simulations reveal that the meltwater flux rapidly stratifies surface waters, leading to a dramatic decrease in the rate of Antarctic Bottom Water formation. The surface ocean cools but, critically, the Southern Ocean warms by more than 1 ºC at depth. This warming is accompanied by a Southern Ocean-wide "domino effect", whereby the warming signal propagates westward with depth. Our results suggest that melting of one sector of the EAIS could result in accelerated warming across other sectors, including the Weddell Sea sector of the West Antarctic Ice Sheet. Thus localised melting of the EAIS could potentially destabilise the wider Antarctic Ice Sheet.


Caption for attached image: "Figure 3. Rate of AABW formation (Sv) in the control simulation (black), and in experiments WILKES (red), WEST (green) and EAST (blue). Thin lines indicate individual ensemble members; thick lines indicate the ensemble means. The values shown are 100-year running means. Vertical dashed lines indicate the years in which the freshwater hosing begins and ends."

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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2159 on: December 07, 2019, 04:06:25 AM »
I think that the linked op/ed by Naomi Oreskes et al. (2019) is worth reading in its entirety as I only extract a few short sections:

Title: "Scientists Have Been Underestimating the Pace of Climate Change"

https://blogs.scientificamerican.com/observations/scientists-have-been-underestimating-the-pace-of-climate-change/

Extract: "… it was reported recently that in the one place where it was carefully measured, the underwater melting that is driving disintegration of ice sheets and glaciers is occurring far faster than predicted by theory—as much as two orders of magnitude faster—throwing current model projections of sea level rise further in doubt.

Consistent underestimation is a form of bias—in the literal meaning of a systematic tendency to lean in one direction or another—which raises the question: what is causing this bias in scientific analyses of the climate system?

In our new book, Discerning Experts, we explored the workings of scientific assessments for policy, with particular attention to their internal dynamics, as we attempted to illuminate how the scientists working in assessments make the judgments they do. Among other things, we wanted to know how scientists respond to the pressures—sometimes subtle, sometimes overt—that arise when they know that their conclusions will be disseminated beyond the research community—in short, when they know that the world is watching. The view that scientific evidence should guide public policy presumes that the evidence is of high quality, and that scientists’ interpretations of it are broadly correct. But, until now, those assumptions have rarely been closely examined."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2160 on: December 07, 2019, 10:07:29 AM »
Now that Hausfather et al. (2019) has indicated that earlier/simpler climate models have a good record as compared to the observer record, and as in the following linked Carbon Brief article, Hausfather indicates that the majority of simpler climate models in CMIP6 are indicating lower values of ECS than the more sophisticated CMIP6 model projections; I strongly suspect that all of the left-tail advocates are already lining-up their strategies to keep the AR6 range for ECS as close as possible to the current AR5 range for ECS.

Title: "CMIP6: the next generation of climate models explained"

https://www.carbonbrief.org/cmip6-the-next-generation-of-climate-models-explained

Extract: "SSP5-3.4OS is an overshoot scenario (OS) where emissions follow a worst-case SSP5-8.5 pathway until 2040, after which they decline extremely rapidly with lot of late-century use of negative emissions.

However, despite making the models more realistic, it is not yet clear whether these improvements are translating into more accurate estimates of ECS. For example, a number of climate scientists have expressed scepticism of the high-end values, arguing that they are inconsistent with evidence from palaeoclimate records and other lines of evidence.

It remains to be seen how the IPCC AR6 will reconcile the high ECS from some models with other sources of evidence, and if they will update the “likely” sensitivity range."


Unfortunately, much of the risks of higher ECS values are associated with the Antarctic/Southern Ocean; which generally have not been modelled well by the CMIP5 and earlier models due to limited availability of data.  For instance, in Hausfather's Carbon Brief article he states:

"Researchers are currently looking into what is driving these high ECS values. In a number of models the increase in ECS appears to be due to their improved representation of clouds and aerosols; for example, how models treat supercooled clouds (below freezing but still liquid) in the Southern oceans can make a big difference in resulting sensitivity."

Furthermore, the CMIP5 and earlier climate models has all underestimated the ice-climate feedback mechanisms already being activated in the Antarctic/Southern Ocean system, as not only demonstrated by observed ice mass loss and ice shelve loss, but also by such recent paleo findings as Beltran et al. (2019 online or 15 January 2020 in print).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Hefaistos

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2161 on: December 07, 2019, 02:32:33 PM »

...
The study found that one million years ago in the ocean surrounding Antarctica, the summer ocean temperature was on average 5°C (±1.2°C) warmer than today.

"Using the data, the ice sheet simulation indicates a complete collapse of the West Antarctic Ice Sheet with additional melting of the East Antarctic Ice Sheet resulting in sustained global sea-level rise of centimetre to decimetres per decade."
...
We show that the Paris Agreement target temperature of 1.5°C is sufficient to drive runaway retreat of the WAIS.

Sorry, I don't follow this argument. The Southern Ocean is supposed to warm with 5 °C within a GST rise of only 1.5 °C. How many millenia is that supposed to take?

There is nothing simple with the Southern Ocean. Some parts show depth temperature inversion, some not.
"Southern Ocean mixed‐layer depth from Argo float profiles" by Dong et al.
"This common thermally stabilized stratification makes up 76% of the total Argo profiles in our study region. The rest of the profiles experience temperature inversions //24%// because of the influence of salinity. Temperature inversions are common within and near the boundaries of the ACC, and they are frequently found in the Argo profiles (Figure 1b and 1c). Depending on the location and time of year, temperature inversions show different vertical structures. "
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2006JC004051

The Southern Ocean is cooling, not warming. Surface temperatures cool, and there is some warming on deeper levels. How much is unclear.

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2162 on: December 07, 2019, 04:10:52 PM »
The linked article provides clear warning that climate change and nutrient pollution are both driving oxygen from the oceans, which is threatening many species of fish.  What is not stated is that a some point the loss of fish species will contribute to the stratification of the oceans, as many specifies of fish contribute to the mixing of seawater in the upper levels of the ocean (note that the video imbedded in the article presented a simple/clear message about some of the risks of climate change):

Title: "Climate change: Oceans running out of oxygen as temperatures rise"

https://www.bbc.com/news/science-environment-50690995

Extract: "Climate change and nutrient pollution are driving the oxygen from our oceans, and threatening many species of fish.

That's the conclusion of the biggest study of its kind, undertaken by conservation group IUCN.

As more carbon dioxide is released enhancing the greenhouse effect, much of the heat is absorbed by the oceans. In turn, this warmer water can hold less oxygen. The scientists estimate that between 1960 and 2010, the amount of the gas dissolved in the oceans declined by 2%.

That may not seem like much as it is a global average, but in some tropical locations the loss can range up to 40%.

Even small changes can impact marine life in a significant way. So waters with less oxygen favour species such as jellyfish, but not so good for bigger, fast-swimming species like tuna."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2163 on: December 07, 2019, 05:34:33 PM »

Sorry, I don't follow this argument. The Southern Ocean is supposed to warm with 5 °C within a GST rise of only 1.5 °C. How many millenia is that supposed to take?

...
The Southern Ocean is cooling, not warming. Surface temperatures cool, and there is some warming on deeper levels. How much is unclear.

To help limit the spread of your misunderstandings my first attachment is a pdf of Beltan et al. (2019 online, where the lead author is mistakenly identified as B. Catherine), which makes it clear that the authors are referring to a 5 oC increase of the surface water temperature within the study area in the Antarctic coastal waters and is associated with various factors including stratification of regional waters (due to freshening), warming of the surface water from the atmosphere and local upwelling of warm CDW.  Furthermore the first attached image (Fig 5) shows that within 1000 years of the majority of local ice mass loss has occurred; while the second image (Fig 6) shows the two step paleo warming process (& I note that in the modern world we are currently past Step 1).  Also, I note that the model that Beltran et al. (2019 online) could simulate MISI behavior but not MICI behavior thus I include the third attached image from Pollard and DeConto showing that using one version of an MICI model projected similar ice mass loss from Antarctica by 2170 that took the Beltran et al (2019) model approximately 1000 years to achieve.

Extract from Beltran et al. (2019 online): "We propose that the exceptional surface ocean warming during the MIS31 super-interglacial occurred in two steps (Fig. 6). [Step 1] The unusual MIS31 orbital configuration resulted in an extended period (~2000 years) of warm and long-lasting summer seasons that caused mild warming of Southern Ocean surface waters and the reduction of sea ice development or survival.  Concomitantly, the prevailing Southern Hemisphere Westerly Winds and the easterly coastal winds migrated to the south (Fig. 6).  The poleward shifted winds warmed the coastal waters, thus bring heat southwards thereby initiating basal melting of ice shelves and the retreat of marine-based groundling lines.  Our numerical ice sheet model demonstrates that a 0.5 oC ocean warming at the ice margin for c. 200 years is sufficient to cause ice retreat and that most of it can occur in less than 2000 years.  [Step 2] The surface warming in the coastal regions (9.5 oC at ODP Site 1101 and 5 oC at IODP Site 1361) could only take place after complete loss of the WAIS (Fig. 6) and would likely be amplified by ocean stratification feedbacks."


Caption for second image: "Fig. 6. Schematic evolution of ice retreat during MIS31 in response to poleward wind shift and subsequent ocean warming.  Step 1 shows the increased advection of warmer deep waters (red arrow, see Pedro et al., 2016).  Step 2 represents the run over ice melting at the maximum of MIS31 warmth.

Edit: I note that to access the pdf you need to click on the link named 10.10@j.quascirev.2019.106069
« Last Edit: December 07, 2019, 05:41:44 PM by AbruptSLR »
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2164 on: December 07, 2019, 05:45:22 PM »
Dear Abrupt, The oxygen minimum zone is expanding here along the west coast of North America.
Anchovy and sardines are major components of forage for many fish, bird and mammal populations and if their range contracts due to oxygen reductions then so too will the range and populations of predators dependent upon them. This is also an issue in the Humboldt current ecosystem. Eastern boundary current ecosystems provide about a fifth of all fish harvested by humans from the oceans and forage fish like sardines and anchovy make up a large portion of the catch. Here is a link to a video on the oxygen declines in the Calif. Current and how anchovy stocks will contract and move north. These changes will cause widespread problems for charismatic species.

57
Consequences / Re: Ocean Temps
« on: September 09, 2019, 05:47:06 AM »
Modeling shows anchovy populations may crash in Southern Calif. offshore waters. We have long term biological data sets and monitoring efforts stretching back seventy years, called CAL COFI . Anchovy and sardine population and egg counts are sampled by ocean cruises on an annual basis. As the ocean heats it also stratifies. The bacterial remineralization of primary production and the heating results in decreased oxygen levels. Those low levels of oxygen are already affecting anchovy populations by pushing the anchovy into shallower coastal waters where oxygen levels are higher. The habitat range is shrinking. Any long term restriction in the biomass of an important forage component of the ecosystem will reverberate up through higher trophic levels.
 Curtis Deutsch has a presentation on the hypoxia issues that are affecting the Anchovy and it's future in Southern Calif. on this you tube presentation

https://m.youtube.com/watch?feature=youtu.be&v=VOlZUorIRK0

Yes it will take an hour of listening to get through the first two presentations but considering that there have only been 17 views so far you might get info most people never see. I am always kinda careful with work that may still be embargoed so sorry if I can't upload more.

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2165 on: December 07, 2019, 05:49:53 PM »
As a follow-on to my last post I note that most of the ice mass loss modeled by Beltran et al. (2019 online) occurs both due to upwell of warm CDW (which the first image indicates is currently accelerating) and due to redirected warm ocean currents beneath key ice shelves (which is currently progressing for the FRIS as indicated by the second two image) due to changes in the local sea ice extent and the associate changes in local wind patterns.  Finally, I provide the fourth image to remind readers that we are currently near a fork in the road that may lead to a Hothouse Earth.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2166 on: December 08, 2019, 04:12:25 PM »
It is important to remember that while during the MIS 31, the Eemian peak, and the Holsteinian peak, Earth Systems were similar to their current condition; still these paleo-cases are clearly not some sort of physical model simulations that we can rely on without any thoughtful corrections (whether by computer model results; evidence from different interglacial peaks [such as different aspects of both the Eemian & Holsteinian peaks {MIS 5 & MIS 11c}]; or a better understanding of the complex past and present earth systems).  For instance, the Lake El’gygytgyn region of Russian seems to have been considerably warmer during MIS 11c [the Holsteinian peak] than it was during MIS 5e. This is despite the fact that summer solar radiation was less intense (though the season was longer) and greenhouse gas concentrations were similar. The researchers of sediment in the lake write, “Consequently, the distinctly higher observed [temperature and precipitation] at MIS 11c cannot readily be explained by the local summer orbital forcing or GHG concentrations alone, and suggest that other processes and feedbacks contributed to the extraordinary warmth at this interglacial, and the relatively muted response to the strongest forcing at MIS 5e.”  The Arctic is especially sensitive to climate changes (through the loss of reflective snow and ice, for example), and what happens there affects the rest of the planet as well. Figuring out which feedbacks could account for the warm temperatures during MIS 11c could be useful.  Seeing how climate responds to many different situations (such as the potential collapse of the WAIS) helps researchers obtain a deeper understanding of the climate system. And therein lies the value in climate records from disparate regions. As the researchers put it, “The observed response of the region’s climate and terrestrial ecosystems to a range of interglacial forcing provides a challenge for modeling and important constraints on climate sensitivity and polar amplification.”

For example, see:

Martin Melles, et al. (20 July 2012), "2.8 Million Years of Arctic Climate Change from Lake El’gygytgyn, NE Russia", Science, Vol. 337 no. 6092 pp. 315-320, DOI: 10.1126/science.1222135

https://science.sciencemag.org/content/337/6092/315

ABSTRACT: "The reliability of Arctic climate predictions is currently hampered by insufficient knowledge of natural climate variability in the past. A sediment core from Lake El’gygytgyn in northeastern (NE) Russia provides a continuous, high-resolution record from the Arctic, spanning the past 2.8 million years. This core reveals numerous “super interglacials” during the Quaternary; for marine benthic isotope stages (MIS) 11c and 31, maximum summer temperatures and annual precipitation values are ~4° to 5°C and ~300 millimeters higher than those of MIS 1 and 5e. Climate simulations show that these extreme warm conditions are difficult to explain with greenhouse gas and astronomical forcing alone, implying the importance of amplifying feedbacks and far field influences. The timing of Arctic warming relative to West Antarctic Ice Sheet retreats implies strong interhemispheric climate connectivity."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2167 on: December 08, 2019, 04:19:05 PM »
The linked reference indicates that during the Eocene polar amplification was so strong that the climate in portions of Antarctica were like Florida:

"Pronounced zonal heterogeneity in Eocene southern high-latitude sea surface temperatures" by Peter M. J. Douglas, Hagit P. Affek, Linda C. Ivany, Alexander J. P. Houben, Willem P. Sijp, Appy Sluijs, Stefan Schouten, and Mark Pagani published in PNAS doi: 10.1073/pnas.1321441111

http://www.pnas.org/content/early/2014/04/16/1321441111.abstract?sid=416fb7a8-dbf3-43d0-9dba-8b4bbcf0c1a0

Abstract: " Paleoclimate studies suggest that increased global warmth during the Eocene epoch was greatly amplified at high latitudes, a state that climate models cannot fully reproduce. However, proxy estimates of Eocene near-Antarctic sea surface temperatures (SSTs) have produced widely divergent results at similar latitudes, with SSTs above 20 °C in the southwest Pacific contrasting with SSTs between 5 and 15 °C in the South Atlantic. Validation of this zonal temperature difference has been impeded by uncertainties inherent to the individual paleotemperature proxies applied at these sites. Here, we present multiproxy data from Seymour Island, near the Antarctic Peninsula, that provides well-constrained evidence for annual SSTs of 10–17 °C (1σ SD) during the middle and late Eocene. Comparison of the same paleotemperature proxy at Seymour Island and at the East Tasman Plateau indicate the presence of a large and consistent middle-to-late Eocene SST gradient of ∼7 °C between these two sites located at similar paleolatitudes. Intermediate-complexity climate model simulations suggest that enhanced oceanic heat transport in the South Pacific, driven by deep-water formation in the Ross Sea, was largely responsible for the observed SST gradient. These results indicate that very warm SSTs, in excess of 18 °C, did not extend uniformly across the Eocene southern high latitudes, and suggest that thermohaline circulation may partially control the distribution of high-latitude ocean temperatures in greenhouse climates. The pronounced zonal SST heterogeneity evident in the Eocene cautions against inferring past meridional temperature gradients using spatially limited data within given latitudinal bands."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2168 on: December 08, 2019, 04:26:36 PM »
Not to over-generalize, but the Pliocene is considered by many researchers to represent a paleo-condition that the Earth is rapidly headed towards, and the linked reference indicates that there was considerable surface ice sheet melting in this period (2.6-5.3 Ma) in the WAIS, which was sufficient to feed major subglacial hydrological meltwater systems that resulted in considerable amount of subglacial erosion. This research supports the concern that the extensive existing subglacial meltwater networks may well contribute to the substantial collapse of the WAIS before the end of this century:

Kathryn Rose, Neil Ross, Robert Bingham, Hugh Corr, Fausto Ferraccioli, Tom Jordan, Anne LeBrocq, David Rippin, and Martin Siegert, (2014), "Major Subglacial Meltwater Channels Reveal Former Dynamic Ice Sheet in West Antarctica", Geophysical Research Abstracts, Vol. 16, EGU2014-7128, 2014

http://meetingorganizer.copernicus.org/EGU2014/EGU2014-7128.pdf

Abstract: "The Eocene-Oligocene boundary (ca. 34 Ma) marks the onset of widespread, continental-scale glaciation in Antarctica, due to declining atmospheric carbon dioxide levels and the opening of the Drake Passage. The marine-based West Antarctic Ice Sheet (WAIS) is considered highly susceptible to change, experiencing numerous oscillations since its formation. In order to assess how past changes to the WAIS are relevant for understanding its future behaviour, it is important to comprehend the glaciological processes involved in those changes. Central to this is an appreciation of climate and ice flow regimes, in particular the extent to which former ice sheets have experienced surface melting (as in Greenland today). Geomorphic analysis of subglacial topography has played a key role in reconstructing the nature of former ice masses in Antarctica, as landscape form can be linked to glacial process. While radio-echo sounding (RES) is the primary tool used to map boundary conditions beneath ice sheets, recent developments have demonstrated that satellite imagery of the ice surface can provide insights into subglacial topography, where RES is unavailable.
 
Using this combination of datasets, we have identified a series of major, elongate subglacial features, which we interpret as preserved subglacial channels, developed through the action of water. They are incised into a subglacial plateau in the region between the Möller and Foundation ice streams (MIS and FIS, respectively), in West Antarctica. The channels are observed across an area of ~17,700 km2 and extend 200 km inland from the grounding line. They are located below sea level and track over present-day reverse slopes, indicating a subglacial (rather than pre-glacial) fluvial origin. In order to form, these channels require significant, probably periodic (seasonal), meltwater inputs to the base of the ice sheet. We suggest the channels are the result of meltwater inputs to the subglacial environment from the ice surface, in a setting analogous to present-day Greenland. This allows us to bracket the most recent date at which this may have occurred.

The Pliocene (2.6-5.3 Ma) represents the most recent period in the geologic past when atmospheric temperatures for West Antarctica were high enough to generate surface melt comparable to that observed on the Greenland Ice Sheet today. These features provide evidence for temperate basal thermal conditions and thus, a former ice flow regime that differs markedly from the present-day polar ice sheet conditions of West Antarctica.  We envisage bed channel formation occurred under temperate ice sheet conditions, when the subglacial plateau was overridden by a temperate ice mass. If this interpretation is correct, it means that ice was still present (at least periodically) in this location, during the warm conditions of the Pliocene. The discovery of these channels also highlights what little was known about this large region of West Antarctica, prior to the Institute-Möller geophysical survey."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2169 on: December 08, 2019, 04:36:06 PM »
The linked reference address how the collapse of the WAIS can alter oceanic and atmospheric patterns, leading to Super Interglacial conditions:

Flavio Justino, Douglas Lindemann, Fred Kucharski, Aaron Wilson, David Bromwich, and Frode Stordal (2017), "Oceanic response to changes in the WAIS and astronomical forcing during the MIS31 superinterglacial", Clim. Past, 13, 1081–1095, https://doi.org/10.5194/cp-13-1081-2017

https://www.clim-past.net/13/1081/2017/cp-13-1081-2017.pdf

Abstract: "Marine Isotope Stage 31 (MIS31, between 1085 and 1055 ka) was characterized by higher extratropical air temperatures and a substantial recession of polar glaciers compared to today.  Paleoreconstructions and model simulations have increased the understanding of the MIS31 interval, but questions remain regarding the role of the Atlantic and Pacific oceans in modifying the climate associated with the variations in Earth’s orbital parameters. Multi-century coupled climate simulations, with the astronomical configuration of the MIS31 and modified West Antarctic Ice Sheet (WAIS) topography, show an increase in the thermohaline flux and northward oceanic heat transport (OHT) in the Pacific Ocean.  These oceanic changes are driven by anomalous atmospheric circulation and increased surface salinity in concert with a stronger meridional overturning circulation (MOC). The intensified northward OHT is responsible for up to 85% of the global OHT anomalies and contributes to the overall reduction in sea ice in the Northern Hemisphere (NH) due to Earth’s astronomical configuration. The relative contributions of the Atlantic Ocean to global OHT and MOC anomalies are minor compared to those of the Pacific.  However, sea ice changes are remarkable, highlighted by decreased (increased) cover in the Ross (Weddell) Sea but widespread reductions in sea ice across the NH."

Extract: "Based on coupled climate simulations performed under present day and boundary conditions representative of Marine Isotope Stage 31 (MIS31), our analyses provide evidence that under MIS31 climate conditions there was a remarkable reduction in sea ice distribution across the NH due to the astronomical configuration of that epoch. This contrasts with increases in sea ice area across the SH. The climate response to collapsing the WAIS is prominent in the vicinity of the Antarctic continent, whereas the effect of modification in the Earth orbital configuration extends worldwide.

It has furthermore been demonstrated that the MIS31 interglacial experienced significant changes in the Meridional Overturning Circulation (MOC). In the Atlantic, increases in the MOC are related to an intensified westerly atmospheric flow in the northern North Atlantic, leading to strong convective mixing. The main convection sites in MIS31 have also been shifted poleward compared to the control simulation (CTR) in concert with changes in the position of the meridional thermal gradient."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2170 on: December 08, 2019, 04:58:08 PM »
AbruptSLR, how has continental drift affected Antarctica since the Eocene?
SHARKS (CROSSED OUT) MONGEESE (SIC) WITH FRICKIN LASER BEAMS ATTACHED TO THEIR HEADS

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2171 on: December 08, 2019, 07:28:17 PM »
Tom,

It is never easy to provide simple answers to complex questions, as continental drift was not the only difference between the Eocene epoch and modern times, as for instance the AIS did not form until the Eocene was over, so the only real way to answer your question would be to use a state-of-the-art climate model calibrated for Eocene conditions and then to swap in the current position of continents into that model.  That said the first linked reference by Sagoo et al. (2013), ran an early climate model and found that to get an equable climate, they not only had CO2 at 560ppm, they also rewound 50 million years of continental drift too, but when they ran the same model with modern geography, it didn't get close to being equable at 560pmm (note that CO2 atmospheric concentrations are only now beginning to approach these levels).

A draft pdf copy of the of Sagoo et al. (2013) is available at the link provided below. 


The Early Eocene equable climate problem: Can perturbations of climate model parameters identify possible solutions? by: by Navjit Sagoo, Paul Valdes, Rachel Flecker, and Lauren Gregoire; Royal Society Philosophical Transactions A; 2013

http://www.paleo.bris.ac.uk/~ggdjl/warm_climates/sagoo_etal.pdf

Abstract:
"Geological data for the early Eocene (56 Ma to 47.8 Ma) indicates extensive global warming, with very warm temperatures at both poles. However, despite numerous attempts to simulate this warmth, there are remarkable data–model differences in the prediction of these polar surface temperatures, resulting in the so called “equable climate problem”.

In this paper, for the first time an ensemble with a perturbed climate-sensitive model parameters approach has been applied to modelling the early Eocene climate. We performed more than 100 simulations with perturbed physics parameters, and identified two simulations which have an optimal fit with the proxy data. We have simulated the warmth of the early Eocene at 560 ppmv CO2 which is a much lower CO2 level than many other models. We investigate the changes in atmospheric circulation, cloud properties and ocean circulation that are common to these simulations and how they differ from the remaining simulations in order to understand what mechanisms contribute to the polar warming.  The parameter set from one of the optimal early Eocene simulations also produces a favourable fit for the Last Glacial Maximum boundary climate and outperforms the control parameter set for the present day. Although this does not “prove” that this model is correct, it is very encouraging that there is a parameter set that creates a climate model able to simulate well very different paleoclimates and the present day climate.  Interestingly, to achieve the great warmth of the early Eocene this version of the model does not have a strong future climate change Charney climate sensitivity. It produces a Charney climate sensitivity of 2.7 °C whereas the mean value of the 18 models in the AR4 is 3.26 °C ± 0.69 °C.  Thus this value is within the range and below the mean of the models included in the IPCC Fourth Assessment Report (AR4)."

For ease of reference the first two attached images are from the following Wikipedia article on the Eocene:

Title: "Eocene"

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

Also, the following linked reference discusses the modeling uncertainties associated with modeling the Eocene-Oligocene transiton:

A. T. Kennedy‐Asser et al. (21 December 2018), "Assessing Mechanisms and Uncertainty in Modeled Climatic Change at the Eocene‐Oligocene Transition", Paleoceanography and Paleoclimatology, https://doi.org/10.1029/2018PA003380

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018PA003380
https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2018PA003380

Abstract
The Earth system changed dramatically across the Eocene‐Oligocene Transition (EOT) on a variety of spatial and temporal scales. Understanding the many complex and interacting factors affecting the Earth's atmosphere and oceans at the EOT requires the combination of both data and modeling approaches and an understanding of the uncertainty in both of these elements. Here uncertainty in the Earth system response to various imposed forcings typical of changes at the EOT is assessed. By using an ensemble of simulations from the fully coupled general circulation model, HadCM3L, the uncertainty due to differences in the boundary conditions and insufficient model spin‐up is quantified. The surface temperature response in high‐latitude ocean regions, particularly where deep water formation occurs, is found to be highly sensitive to differences in boundary conditions (i.e., have the greatest magnitude of uncertainty), while low‐latitude oceans are the most insensitive to differences in boundary conditions (i.e., have the lowest magnitude of uncertainty). The length of spin‐up (or how far the model is from equilibrium) can have a significant effect on the response to some forcings and on the magnitude of uncertainty due to differences in boundary conditions. These findings are important to consider for future modeling work and for interpreting previous published simulations.

Plain Language Summary
Around 34 million years ago, the first major ice sheet formed over Antarctica. Understanding why the Earth cooled at this time and how this would have impacted on global climate requires the use of geologic data and computer models. Here multiple coupled climate‐ocean model simulations are used to assess changes in modeled climate around this period in the Earth's history. Specifically, the climatic sensitivity to subtle changes in the model setup and how long the simulations are run for (the model spin‐up) are evaluated. The temperature response in certain regions is found to be particularly sensitive to changes in the model setup and lack of spin‐up. This is the case particularly for high‐latitude ocean regions, making it harder to build up a consistent picture of how the climate of these regions changed at this time. Lower latitude oceans are much less sensitive, giving us higher confidence in model results for these regions. In these simulations, the global changes that occurred around 34 million years ago are best described by declining atmospheric pCO2.

ASLR

Edit: One should remember that if the WAIS were to collapse in coming decades, this would induce a multidecadal surge in the planetary energy imbalance (which was not possible during the Eocene as the AIS did not exist in the Eocene) which might possibly push the Earth into an equable climate which would like not be reversible for millennia.
« Last Edit: December 09, 2019, 04:22:01 PM by AbruptSLR »
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2172 on: December 08, 2019, 10:51:23 PM »
When I first started investigating climate change, I found the linked five-part 2011 article by Steve Brown in clarifying the limits and advantages of comparing the Eemian (LIG or MIS 5e) with the Holocene and future projections for the Anthropocene.  While the article makes many different points, I like the conclusions of the fifth article the opines that: a. MIS 11 (the Holsteinian), with its relatively high climate sensitivity, may provide a better paleo-case to calibrate state-of-the-art climate models against, and that b. the current exceedingly high rate of radiative forcing is taking us collectively into uncharted waters w.r.t. future Earth System responses:

Title: "The Last Interglacial - An Analogue for the Future?" Part I

https://skepticalscience.com/LIG1-0706.html

Extract: "The Last Interglacial, also known as the Eemian in Europe and broadly corresponding to the global  interglacial record of Marine Isotope Stage 5e (MIS 5e), was a period with significantly higher temperatures in many parts of the Northern Hemisphere compared to the present day (IPCC AR4) and similar to some predictions for the next century by current research.  The Last Interglacial offers several benefits for comparison with the present day in that continental configuration, flora and fauna are near identical to today, as well as being a recent enough period to provide a range of high-resolution palaeoenvironmental proxy indicators.  The Last Interglacial was also a period with higher global sea-level and a corresponding reduction in ice sheet area and volume,  which are consistent with IPCC predictions for responses to future global warming.  The period also had an atmospheric CO2 level of up to 300 ppm; similar to the pre-industrial era."

&

Title: "The Last Interglacial Part Two - Why was it so warm?"

https://skepticalscience.com/LIG2-1906.html

Extract: "The most important terrestrial controls of climate relate to albedo effects and changes in land surface, which determine the reflectivity of the Earth and how much energy from the Sun can be absorbed.  For example, reduction in ice-sheet extent can expose lower albedo soil, rock and vegetation, which enhances surface warming.  There was less glacial ice on Earth during the Last Interglacial compared to the present day, which suggests a significant reduction in the size of the Greenland and Antarctic Ice Sheets (IPCC AR4). This would support the view that an increase in land area exhibiting a lower albedo might have played some part in increased warming during the Last Interglacial."


Title: "The Last Interglacial Part Three - Melting Ice and Rising Seas:

https://skepticalscience.com/LIG3-1207.html

Extract: "Ocean circulation is pivotal in its role for transferring heat around the globe, as well as being a significant factor in regional climate and weather patterns.  Did the large volume of cold freshwater that returned to the ocean from the melting ice sheets affect this circulation and influence changes to climate and weather patterns?"

&


Title: "The Last Interglacial Part Four - Oceanic Influences"

https://skepticalscience.com/LIG4-3008.html

Extract: "Surface freshwater plays an important role for ocean circulation by its influence on the formation of deep water masses.   A stronger deep circulation may increase northward heat transport by the AMOC, while a weaker deep circulation may promote less northward heat transport (Born et al., 2009).  Barreiro et al. (2008) found that northern Atlantic waters have freshened rapidly in the past few decades and heat transported northward by the thermohaline circulation has decreased.  It's expected that this freshening could increase further through intensified high-latitiude precipitation and glacial melt-water related to global warming.  Vellinga et al. (2008) examined various model results that attempt to quantify how the AMOC responds to different melt-water fluxes from Greenland.  In one model a large enough flux, or rate of flow,  of melt-water to shutdown the AMOC was created, which resulted in a cooling of surface air temperature in excess of 15oC over the Norwegian and Barents Seas, with a lesser degree of cooling over the whole hemisphere.  Most models that investigate increasing greenhouse gas scenarios predict that the AMOC will slow down as a result of such forcing (Driesschaert et al., 2007; Meehl et al., 2007).  However, other model results suggest that anthropogenic aerosols may have delayed a greenhouse gas induced weakening of the AMOC by reflecting inbound solar radiation and partially offsetting greenhouse gas warming."

Title: "The Last Interglacial Part Five - A Crystal Ball?"

https://skepticalscience.com/LIG5-1110.html

Extract: "Comparing the influences on the Last Interglacial climate with those assumed in future climate projections is problematic owing to fundamental differences, especially orbital forcing, seasonal warming, and greenhouse gas concentrations.  Palaeoclimate studies show that differences in the manner in which the Earth orbited the Sun during the Last Interglacial are sufficient to explain the higher temperatures over most parts of the Northern Hemisphere, particularly due to greater axial tilt and eccentricity compared with the present day orbital configuration.  This greater axial tilt provided stronger insolation (solar heating) at high latitudes and weaker insolation at low latitudes.  Perihelion, when the Earth is nearest the Sun, occurred during summer in the Northern Hemisphere, which amplified seasonal insolation, while perihelion occurs in winter during the present day.

The difference in greenhouse gas concentration combined with significantly different orbital parameters and seasonal insolation may limit the validity of using the Last Interglacial as an analogue for predicted future changes to the climate system.  The proxy coverage of the period in the Southern Hemisphere and large parts of the Northern Hemisphere is poor, giving a bias towards Europe and the North Atlantic region.   The value of the Last Interglacial in aiding prediction of future climate change is restricted to mainly Europe and the North Atlantic.  To improve our ability to predict the potential impacts of future climate change it is essential that the search for proxy data in new locations with a more comprehensive geographical spread are sought out in order to get a more global picture of ancient climate with better resolution.

Acknowledging the problems and benefits of using the Last Interglacial as an analogue for a future warming climate begs the question of whether there may be a more suitable analogue in the past.  Loutre and Berger (2002) suggest that Marine Isotope Stage 11 (MIS 11) from 405 to 340 ka would make a better analogue for future climate than the Last Interglacial, due to it being a warmer interglacial period, but with an orbital insolation signal that correlates closely with the recent past and future, giving a much better comparison of orbital forcing.  MIS 11 also appears to have been possibly the warmest and longest interglacial of the past 5 million years and had an extended period with little or no continental ice, which is projected to occur under some future global warming scenarios.

Because the observed and predicted rate of increase in greenhouse gas concentrations and global warming is faster than seems to have happened during the Last Interglacial may mean that we are heading into uncertain territory."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2173 on: December 08, 2019, 11:29:53 PM »
The linked article summarizes some of the positions made by Lenton et al. (2019) and note that: "Lenton and his co-authors accept there is speculation involved, but argue that “given its huge impact and irreversible nature… to err on the side of danger is not a responsible option.”".

However, while doing a better job that AR5, in my opinion Lenton et al. (2019) still manage to err on the side of least drama w.r.t to such matters as:

1. GMSTA in 2019 will exceed 1.1C rather than the 1C cited in the article;
2. The article underestimates the risk of an MICI-type of collapse of the WAIS in coming decades;
3. Lenton et al. (2019) likely do not consider that ECS may currently be close to 5C.

Title: "As Climate Change Worsens, A Cascade of Tipping Points Looms"

https://e360.yale.edu/features/as-climate-changes-worsens-a-cascade-of-tipping-points-looms

Extract: "Some of the most alarming science surrounding climate change is the discovery that it may not happen incrementally — as a steadily rising line on a graph — but in a series of lurches as various “tipping points” are passed. And now comes a new concern: These tipping points can form a cascade, with each one triggering others, creating an irreversible shift to a hotter world. A new study suggests that changes to ocean circulation could be the driver of such a cascade.

A group of researchers, led by Tim Lenton at Exeter University, England, first warned in a landmark paper 11 years ago about the risk of climate tipping points. Back then, they thought the dangers would only arise when global warming exceeded 5 degrees Celsius (9 degrees Fahrenheit) above pre-industrial levels. But last week, Lenton and six co-authors argued in the journal Nature that the risks are now much more likely and much more imminent. Some tipping points, they said, may already have been breached at the current 1 degree C of warming.

The new warning is much starker than the forecasts of the Intergovernmental Panel on Climate Change, which critics say has until now played down the risks of exceeding climate tipping points, in part because they are difficult to quantify.

The potential tipping points come in three forms: runaway loss of ice sheets that accelerate sea level rise; forests and other natural carbon stores such as permafrost releasing those stores into the atmosphere as carbon dioxide (CO2), accelerating warming; and the disabling of the ocean circulation system."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2174 on: December 09, 2019, 04:29:59 PM »
As some readers have indicated to me that they do not understand where the magma would come from to cause the rebound of the glacial bed if the WAIS were to collapse in the coming decades, I provide the attached image, that shows that it comes from beneath the surrounding seafloor which bulged up when the magna flowed out from beneath the WAIS in the past.  The figure also shows what happens to the ocean water elevation due to the associated change in ice mass.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2175 on: December 09, 2019, 05:01:33 PM »
The linked website provides access to the CONSTRAIN-EU titled document and associated graphics about the remaining carbon budget and the coming decadal warming rates.  In this regard, a) the first image shows that carbon budgets are based on TCR not ECS (which if feedbacks are nonlinear is not appropriate); and b) if we follow SSP5-8.5 for a few more decades per CMIP6 the decadal warming rate by range from 0.23C/decade to over 0.7C/decade with a current median value well over 0.3C/decade (close to 0.35C/decade per the green dot).  None of this is particularly good news:

Title: "Zero in on: - The remaining carbon budget & - Decadal warming rates"

http://constrain-eu.org/

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2176 on: December 09, 2019, 05:33:18 PM »
As shown in the attached figure, unlike the Arctic that has a convex geopotential height topology which tends to disperse local methane emissions; the Antarctic has a concave geopotential height topology which tends to concentrate any local methane emissions.  Furthermore, the extreme cold over the East Antarctic reduces the rate of chemical oxidation of the methane to carbon dioxide thus resulting in a further concentration of methane in the troposphere over the East Antarctic.  However, as GHG contributes to the concavity of the geopotential height topology over Antarctica; this provides a positive feedback mechanism to further accelerate (or at least maintain) the velocity of the circumpolar winds, which should increase the circumpolar current velocity (as well as moving it to the south); which should push more warm CDW onto the Antarctic continental shelf thus decomposing more methane hydrate; resulting in an increased rate of local ice sheet mass loss and an increased probability of the collapse of the WAIS this century than what is current (AR5) projected by any LCM, RCM or GCM.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2177 on: December 09, 2019, 05:41:43 PM »
The linked article indicates that the ocean has been the main driver of Antarctic ice sheet retreat throughout the Holocene which has had an atypically warm plateau as compare to earlier interglacial periods (see also the Early Anthropocene thread, in the Science folder).  This implies that the WAIS is more susceptible to abrupt collapse than consensus climate science likes to admit:

Xavier Crosta et al. (2018), "Ocean as the main driver of Antarctic ice sheet retreat during the Holocene", Global and Planetary Change, https://doi.org/10.1016/j.gloplacha.2018.04.007

https://www.sciencedirect.com/science/article/pii/S0921818118300249

Abstract: "Ocean-driven basal melting has been shown to be the main ablation process responsible for the recession of many Antarctic ice shelves and marine-terminating glaciers over the last decades. However, much less is known about the drivers of ice shelf melt prior to the short instrumental era. Based on diatom oxygen isotope (δ18Odiatom; a proxy for glacial ice discharge in solid or liquid form) records from western Antarctic Peninsula (West Antarctica) and Adélie Land (East Antarctica), higher ocean temperatures were suggested to have been the main driver of enhanced ice melt during the Early-to-Mid Holocene while atmosphere temperatures were proposed to have been the main driver during the Late Holocene. Here, we present a new Holocene δ18Odiatom record from Prydz Bay, East Antarctica, also suggesting an increase in glacial ice discharge since ~4500 years before present (~4.5 kyr BP) as previously observed in Antarctic Peninsula and Adélie Land. Similar results from three different regions around Antarctica thus suggest common driving mechanisms. Combining marine and ice core records along with new transient accelerated simulations from the IPSL-CM5A-LR climate model, we rule out changes in air temperatures during the last ~4.5 kyr as the main driver of enhanced glacial ice discharge. Conversely, our simulations evidence the potential for significant warmer subsurface waters in the Southern Ocean during the last 6 kyr in response to enhanced summer insolation south of 60°S and enhanced upwelling of Circumpolar Deep Water towards the Antarctic shelf. We conclude that ice front and basal melting may have played a dominant role in glacial discharge during the Late Holocene."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2178 on: December 09, 2019, 06:40:11 PM »
For those not familiar with the recent history of Antarctic ice sheet modelling, the linked article provides an overview (see the first image).  However, while this article makes clear the many advances in such modeling, I note that we only have one world to live on and it is dangerous for such modelers to assume that Antarctic ice mass lost will only occur on the century to millennial time-scales in the future, as if consensus climate scientists are wrong in this assumption (i.e. by ignoring MICI-type mechanisms even in CMIP6) we will not get another change to get our projections right as an abrupt collapse of the WAIS could abruptly add over 2 W/m2 of forcing (see the second image) for several decades, which might put numerous Earth Systems into higher climate states:

Pattyn, F. (2018), "The paradigm shift in Antarctic ice sheet modelling", Nat Commun 9, 2728, doi:10.1038/s41467-018-05003-z

https://www.nature.com/articles/s41467-018-05003-z

Extract: "Antarctic ice sheet modelling has taken a big step forward based on an improved understanding of key processes and the development of assimilation methods leading to the ability to reproduce observed ice sheet changes and by making refined future projections."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2179 on: December 09, 2019, 07:31:31 PM »
Evidence for increased submarine melting of tidewater glaciers (& ice shelves?)


Geophysical Research Letters
Meltwater intrusions reveal mechanisms for rapid submarine melt at a tidewater glacier
R.H. Jackson  J.D. Nash  C. Kienholz  D.A. Sutherland  J.M. Amundson  R.J. Motyka  D. Winters  E. Skyllingstad  E. Pettit
First published: 25 November 2019 https://doi.org/10.1029/2019GL085335
Quote
Abstract
Submarine melting has been implicated as a driver of glacier retreat and sea level rise, but to date melting has been difficult to observe and quantify. As a result, melt rates have been estimated from parameterizations that are largely unconstrained by observations, particularly at the near‐vertical termini of tidewater glaciers. With standard coefficients, these melt parameterizations predict that ambient melting (the melt away from subglacial discharge outlets) is negligible compared to discharge‐driven melting for typical tidewater glaciers. Here, we present new data from LeConte Glacier, Alaska that challenges this paradigm. Using autonomous kayaks, we observe ambient meltwater intrusions that are ubiquitous within 400 m of the terminus, and we provide the first characterization of their properties, structure, and distribution. Our results suggest that ambient melt rates are substantially higher ($\x100$) than standard theory predicts and that ambient melting is a significant part of the total submarine melt flux. We explore modifications to the prevalent melt parameterization to provide a path forward for improved modeling of ocean‐glacier interactions.

Plain Language Summary
Tidewater glaciers discharge ice into the ocean through iceberg calving and submarine melting. Submarine melting has been implicated as a driver of glacier retreat and sea level rise, but melt rates have been difficult to directly observe and quantify. As a result, melt rates are typically estimated using a theory that has not been tested with observations at any tidewater glaciers. Two types of melting are expected at tidewater glaciers: where subglacial discharge drains from outlets in the terminus, energetic upwelling plumes rise along the ice face, and theory predicts vigorous melting. Away from discharge outlets, weaker plumes form from ambient melting, and theory predicts that these ambient melt rates are effectively negligible compared to discharge‐driven melting. Here, we present new data from LeConte Glacier, Alaska that challenges this paradigm. Using autonomous kayaks, we observe intrusions of meltwater ‐‐ the product of ambient melt plumes ‐‐ that are only found within 400 m of the terminus, and we provide the first characterization of their properties, structure, and distribution. Their ubiquity suggests that ambient melt rates are substantially higher than standard theory predicts and that ambient melting is a significant ‐‐ but often neglected ‐‐ part of the total submarine melt flux.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2180 on: December 09, 2019, 07:39:44 PM »
The attached 2017 reference discusses modeling Thwaites Glacier in the 21st Century; however, w.r.t. the attached image showing the author's concept of the size and integrity of both the Thwaites Ice Shelf and the Thwaites Ice Tongue, and I note that the initial condition of both of these two features err significantly on the side of least drama.  Furthermore, while I have not seen images of how either of these two features have been modeled in the CMIP6 models; I am concerned that many of the initial configurations for Thwaites in the CMIP6 models were developed in this 2017 timeframe, and are most likely biased to the same degree regarding the current structural integrity of these features:

T.A.Scambo  et al. (June 2017), "How much, how fast?: A science review and outlook for research on the instability of Antarctica's Thwaites Glacier in the 21st century", Global and Planetary Change, Volume 153, Pages 16-34; https://doi.org/10.1016/j.gloplacha.2017.04.008

https://www.sciencedirect.com/science/article/pii/S092181811630491X

Abstract
Constraining how much and how fast the West Antarctic Ice Sheet (WAIS) will change in the coming decades has recently been identified as the highest priority in Antarctic research (National Academies, 2015). Here we review recent research on WAIS and outline further scientific objectives for the area now identified as the most likely to undergo near-term significant change: Thwaites Glacier and the adjacent Amundsen Sea. Multiple lines of evidence point to an ongoing rapid loss of ice in this region in response to changing atmospheric and oceanic conditions. Models of the ice sheet's dynamic behavior indicate a potential for greatly accelerated ice loss as ocean-driven melting at the Thwaites Glacier grounding zone and nearby areas leads to thinning, faster flow, and retreat. A complete retreat of the Thwaites Glacier basin would raise global sea level by more than three meters by entraining ice from adjacent catchments. This scenario could occur over the next few centuries, and faster ice loss could occur through processes omitted from most ice flow models such as hydrofracture and ice cliff failure, which have been observed in recent rapid ice retreats elsewhere. Increased basal melt at the grounding zone and increased potential for hydrofracture due to enhanced surface melt could initiate a more rapid collapse of Thwaites Glacier within the next few decades.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2181 on: December 09, 2019, 07:43:51 PM »
Evidence for increased submarine melting of tidewater glaciers (& ice shelves?)

Their ubiquity suggests that ambient melt rates are substantially higher than standard theory predicts and that ambient melting is a significant ‐‐ but often neglected ‐‐ part of the total submarine melt flux.

I certainly hope that CMIP7 corrects the current underestimation in ice shelf models of the rate of basal ice melting.
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2182 on: December 09, 2019, 10:37:18 PM »
The linked research provides more evidence that a slowing of the AMOC will lead to increased warming at high latitudes due to abrupt warming during the summer months.  This helps to confirm Hansen's ice-climate feedback projections:

G. Bromley et al. (06 April 2018), "Interstadial Rise and Younger Dryas Demise of Scotland's Last Ice Fields", Paleoceanography and Paleoclimatology, Vol. 33, Issue 4, https://doi.org/10.1002/2018PA003341

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2018PA003341

Abstract

Establishing the atmospheric expression of abrupt climate change during the last glacial termination is key to understanding driving mechanisms. In this paper, we present a new 14C chronology of glacier behavior during late‐glacial time from the Scottish Highlands, located close to the overturning region of the North Atlantic Ocean. Our results indicate that the last pulse of glaciation culminated between ~12.8 and ~12.6 ka, during the earliest part of the Younger Dryas stadial and as much as a millennium earlier than several recent estimates. Comparison of our results with existing minimum‐limiting 14C data also suggests that the subsequent deglaciation of Scotland was rapid and occurred during full stadial conditions in the North Atlantic. We attribute this pattern of ice recession to enhanced summertime melting, despite severely cool winters, and propose that relatively warm summers are a fundamental characteristic of North Atlantic stadials.

Plain Language Summary
Geologic data reveal that Earth is capable of abrupt, high‐magnitude changes in both temperature and precipitation that can occur well within a human lifespan. Exactly what causes these potentially catastrophic climate‐change events, however, and their likelihood in the near future, remains frustratingly unclear due to uncertainty about how they are manifested on land and in the oceans. Our study sheds new light on the terrestrial impact of so‐called “stadial” events in the North Atlantic region, a key area in abrupt climate change. We reconstructed the behavior of Scotland's last glaciers, which served as natural thermometers, to explore past changes in summertime temperature. Stadials have long been associated with extreme cooling of the North Atlantic and adjacent Europe and the most recent, the Younger Dryas stadial, is commonly invoked as an example of what might happen due to anthropogenic global warming. In contrast, our new glacial chronology suggests that the Younger Dryas was instead characterized by glacier retreat, which is indicative of climate warming. This finding is important because, rather than being defined by severe year‐round cooling, it indicates that abrupt climate change is instead characterized by extreme seasonality in the North Atlantic region, with cold winters yet anomalously warm summers.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2183 on: December 09, 2019, 10:39:42 PM »
The linked reference indicates that much of the weaker polar amplification of Antarctica as compared to the Arctic is due to its (high) surface elevation.  This makes me wonder how much the Antarctic polar amplification will increase if/when the WAIS collapses:

Salzmann, M. (2017) The polar amplification asymmetry: Role of antarctic surface height, Earth Systems Dynamics,doi:10.5194/esd-8-323-2017

http://www.earth-syst-dynam.net/8/323/2017/esd-8-323-2017.pdf

Abstract: “Previous studies have attributed an overall weaker (or slower) polar amplification in Antarctica compared to the Arctic to a weaker Antarctic surface albedo feedback and also to more efficient ocean heat uptake in the Southern Ocean in combination with Antarctic ozone depletion. Here, the role of the Antarctic surface height for meridional heat transport and local radiative feedbacks, including the surface albedo feedback, was investigated based on CO2-doubling experiments in a low-resolution coupled climate model. When Antarctica was assumed to be flat, the north–south asymmetry of the zonal mean top of the atmosphere radiation budget was notably reduced… between 24 and 80%… of the polar amplification asymmetry was explained by the difference in surface height, but… might to some extent also depend on model uncertainties.”
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2184 on: December 09, 2019, 10:42:14 PM »
The linked open access reference is highly relevant to Hansen's ice-climate feedback mechanism, as an abrupt collapse of key WAIS marine glaciers, would increase ocean temperatures at key Greenland marine-terminating glaciers via the bipolar seesaw:

Tabone, I., Blasco, J., Robinson, A., Alvarez-Solas, J., and Montoya, M.: The sensitivity of the Greenland Ice Sheet to glacial–interglacial oceanic forcing, Clim. Past, 14, 455-472, https://doi.org/10.5194/cp-14-455-2018, 2018.

https://www.clim-past.net/14/455/2018/

Abstract. Observations suggest that during the last decades the Greenland Ice Sheet (GrIS) has experienced a gradually accelerating mass loss, in part due to the observed speed-up of several of Greenland's marine-terminating glaciers. Recent studies directly attribute this to warming North Atlantic temperatures, which have triggered melting of the outlet glaciers of the GrIS, grounding-line retreat and enhanced ice discharge into the ocean, contributing to an acceleration of sea-level rise. Reconstructions suggest that the influence of the ocean has been of primary importance in the past as well. This was the case not only in interglacial periods, when warmer climates led to a rapid retreat of the GrIS to land above sea level, but also in glacial periods, when the GrIS expanded as far as the continental shelf break and was thus more directly exposed to oceanic changes. However, the GrIS response to palaeo-oceanic variations has yet to be investigated in detail from a mechanistic modelling perspective. In this work, the evolution of the GrIS over the past two glacial cycles is studied using a three-dimensional hybrid ice-sheet–shelf model. We assess the effect of the variation of oceanic temperatures on the GrIS evolution on glacial–interglacial timescales through changes in submarine melting. The results show a very high sensitivity of the GrIS to changing oceanic conditions. Oceanic forcing is found to be a primary driver of GrIS expansion in glacial times and of retreat in interglacial periods. If switched off, palaeo-atmospheric variations alone are not able to yield a reliable glacial configuration of the GrIS. This work therefore suggests that considering the ocean as an active forcing should become standard practice in palaeo-ice-sheet modelling.
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2185 on: December 09, 2019, 11:15:28 PM »
Currently, a layer of cold relatively freshwater existing in the North Atlantic over a lower layer of warm salty water.  The linked research raises the possibility that with continued warming the lower layer of warm salty water could abruptly raise to the surface; which would like abruptly warm the Northern Hemisphere.

Xiaoxu Shi, Hu Yang, Gerrit Lohmann and Gregor Knorr (2019), "Modelled abrupt climate change under persisted freshwater hosing", Geophysical Research Abstracts, Vol. 21, EGU2019-6028

https://meetingorganizer.copernicus.org/EGU2019/EGU2019-6028.pdf

Abstract: "With the use of a state-of-the-art climate model in high and coarse resolutions over the North Atlantic subpolar region, we perform hosing experiments with 0.1Sv freshwater input over the IRD belt under LGM climate state.  Both experiments are able to show a weak mode of AMOC in the beginning of the meltwater pulse.  However, after 550 model years, high-resolution experiment produces an abrupt warming over the Northern Hemisphere, accompanied by an overshoot of AMOC.  Such abruptness lies on the warming occurred at sub-surface sea water in the North Atlantic.  This warm salty water (WSW) layer, situated beneath the colder surface freshwater, generated ocean convective available potential energy (OCAPE).  At on point the accumulation of OCAPE was released abruptly into kinetic energy of thermobaric cabbeling convection, resulting in the warmer salty waters getting to the surface and subsequently surface warming.  We also illustrate that only high-resolution models have potential ability to present the abrupt warming.  With low resolution, no overshoot of AMOC happens, instead, a slight recovering trend is detected.  Our results provide an implication for the abrupt climate changes in the past (for example the DO events and Blling-Allerd warming) and rise our attention to the importance of resolution in simulating climate system."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2186 on: December 10, 2019, 03:28:34 AM »
If you think that examples of abrupt climate change only occurred in the deep past then read the linked article about the Younger Dryas when the surface temperature of Greenland rose 10C in one decade:

Title: "The Younger Dryas"

https://www.ncdc.noaa.gov/abrupt-climate-change/The%20Younger%20Dryas

Extract: "The end of the Younger Dryas, about 11,500 years ago, was particularly abrupt. In Greenland, temperatures rose 10°C (18°F) in a decade (Alley 2000). Other proxy records, including varved lake sediments in Europe, also display these abrupt shifts (Brauer et al. 2008)."
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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2187 on: December 10, 2019, 05:17:05 PM »
The USA in the 2020's is not setting a good example for developing countries with regard to the production of new oil and gas as discussed in the linked article:

Title: "The U.S. Dominates New Oil And Gas Production"

https://www.forbes.com/sites/judeclemente/2019/12/08/the-us-dominates-new-oil-and-gas-production/#66b796ff1cce

Extract: "The American fracking for oil and natural gas boom will continue on through the 2020s. And why not? Since fracking took off in 2008, we have more than doubled our proven oil reserves to ~65 billion barrels. Natural gas reserves have surged over 80% to ~430 trillion cubic feet. Already the largest oil and gas producer, the U.S. is set to increase its share of ~17% of global oil production and ~23% of gas. In the 2020s, the U.S. is set to supply over 60% of new oil and gas (see Figure below)."
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Ken Feldman

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2188 on: December 10, 2019, 05:35:01 PM »
The USA in the 2020's is not setting a good example for developing countries with regard to the production of new oil and gas as discussed in the linked article:

Title: "The U.S. Dominates New Oil And Gas Production"

https://www.forbes.com/sites/judeclemente/2019/12/08/the-us-dominates-new-oil-and-gas-production/#66b796ff1cce

Extract: "The American fracking for oil and natural gas boom will continue on through the 2020s. And why not? Since fracking took off in 2008, we have more than doubled our proven oil reserves to ~65 billion barrels. Natural gas reserves have surged over 80% to ~430 trillion cubic feet. Already the largest oil and gas producer, the U.S. is set to increase its share of ~17% of global oil production and ~23% of gas. In the 2020s, the U.S. is set to supply over 60% of new oil and gas (see Figure below)."

Well, if you believe everything the IEA, EIA and the gas producers sell you, yeah.  I wonder if those projections take into account the fact that the fracking industry has been debt fueled for years while producers tried to increase market share.  That lead to a supply glut and investors are now calling in the debts.

https://oilprice.com/Energy/Natural-Gas/Shales-Debt-Fueled-Drilling-Boom-Is-Coming-To-An-End.html

Quote
Shale’s Debt-Fueled Drilling Boom Is Coming To An End
By Nick Cunningham - Dec 04, 2019

The financial struggles of the U.S. shale industry are becoming increasingly hard to ignore, but drillers in Appalachia are in particularly bad shape.

The Permian has recently seen job losses, and for the first time since 2016, the hottest shale basin in the world has seen job growth lag the broader Texas economy. The industry is cutting back amid heightened financial scrutiny from investors, as debt-fueled drilling has become increasingly hard to justify.

But E&P companies focused almost exclusively on gas, such as those in the Marcellus and Utica shales, are in even worse shape. An IEEFA analysis found that seven of the largest producers in Appalachia burned through about a half billion dollars in the third quarter.

Quote
The outlook is not encouraging. The gas glut is expected to stick around for a few years. Bank of America Merrill Lynch has repeatedly warned that unless there is an unusually frigid winter, which could lead to higher-than-expected demand, the gas market is headed for trouble. “A mild winter across the northern hemisphere or a worsening macro backdrop could be catastrophic for gas prices in all regions,” Bank of America said in a note in October.

The problem for Appalachian drillers is that Permian producers are not really interested in all of the gas they are producing. That makes them unresponsive to price signals. Gas prices in the Permian have plunged close to zero, and have at times turned negative, but gas production in Texas really hinges on the industry’s interest in oil. This dynamic means that the gas glut becomes entrenched longer than it otherwise might. It’s a grim reality plaguing the gas-focused producers in Appalachia.

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2189 on: December 10, 2019, 05:51:34 PM »
...
Well, if you believe everything the IEA, EIA and the gas producers sell you, yeah.
...

The article and the image clearly show that this new data "... is according to experts at Rystad Energy, “an independent energy consulting services and business intelligence data firm” based in Norway."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2190 on: December 10, 2019, 06:10:01 PM »
The linked reference indicates that ice shelf melt rates in the ASE requires complex modeling but indicates that this issue will likely contribute to an acceleration of grounding line retreats for both PIG and Thwaites, in coming decades:

Marion Donat-Magnin et al. (6 December 2017), "Ice-Shelf Melt Response to Changing Winds and Glacier Dynamics in the Amundsen Sea Sector, Antarctica", JGR Oceans, DOI: 10.1002/2017JC013059

http://onlinelibrary.wiley.com/doi/10.1002/2017JC013059/abstract?utm_content=buffer9d542&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "It has been suggested that the coastal Southern Ocean subsurface may warm over the 21st century in response to strengthening and poleward shifting winds, with potential adverse effects on West Antarctic glaciers. However, using a 1/12° ocean regional model that includes ice-shelf cavities, we find a more complex response to changing winds in the Amundsen Sea. Simulated offshore subsurface waters get colder under strengthened and poleward shifted winds representative of the SAM projected trend. The buoyancy-driven circulation induced by ice-shelf melt transports this cold offshore anomaly onto the continental shelf, leading to cooling and decreased melt below 450 m. In the vicinity of ice-shelf fronts, Ekman pumping contributes to raise the isotherms in response to changing winds. This effect overwhelms the horizontal transport of colder offshore waters at intermediate depths (between 200 and 450 m), and therefore increases melt rates in the upper part of the ice-shelf cavities, which reinforces the buoyancy-driven circulation and further contributes to raise the isotherms. Then, prescribing an extreme grounding line retreat projected for 2100, the total melt rates simulated underneath Thwaites and Pine Island are multiplied by 2.5. Such increase is explained by a larger ocean/ice interface exposed to CDW, which is then amplified by a stronger melt-induced circulation along the ice draft. Our main conclusions are that (1) outputs from ocean models that do not represent ice shelf cavities (e.g. CMIP5 models) should not be directly used to predict the thermal forcing of future ice shelf cavities; (2) coupled ocean/ice sheet models with a velocity-dependent melt formulation are needed for future projections of glaciers experiencing a significant grounding line retreat."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2191 on: December 10, 2019, 06:14:49 PM »
The linked reference finds that, even when using a MISI-type of analysis, with regards to ice mass loss from the BSB that: " Grounding line retreats that begin faster proceed more rapidly because the shorter time interval for the grounding line to erode into the grounded ice sheet means relatively thicker ice and larger driving stress upstream of the boundary."  This indicates that it is a very bad idea to continue following a BAU forcing pathway as mankind has been doing since the pre-industrial era.

M. S. Waibel, C. L. Hulbe, C. S. Jackson & D. F. Martin (16 January 2018), "Rate of mass loss across the instability threshold for Thwaites Glacier determines rate of mass loss for entire basin", Geophysical Research Letters, DOI: 10.1002/2017GL076470

http://onlinelibrary.wiley.com/doi/10.1002/2017GL076470/abstract?utm_content=buffer0799e&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Rapid change now underway on Thwaites Glacier (TG) raises concern that a threshold for unstoppable grounding line retreat has been or is about to be crossed. We use a high-resolution ice sheet model to examine the mechanics of TG self-sustained retreat by nudging the grounding line just past the point of instability. We find that by modifying surface slope in the region of the grounding line, the rate of the forcing dictates the rate of retreat, even after the external forcing is removed. Grounding line retreats that begin faster proceed more rapidly because the shorter time interval for the grounding line to erode into the grounded ice sheet means relatively thicker ice and larger driving stress upstream of the boundary. Retreat is sensitive to short-duration re-advances associated with reduced external forcing where the bathymetry allows re-grounding, even when an instability is invoked."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2192 on: December 10, 2019, 06:17:22 PM »
For the sake of completeness, I provide the linked reference, which considers possible interactions between the PIG and Thwaites glacier:

Dustin M. Schroeder et al. Ocean access beneath the southwest tributary of Pine Island Glacier, West Antarctica, Annals of Glaciology (2017). DOI: 10.1017/aog.2017.45

https://www.cambridge.org/core/journals/annals-of-glaciology/article/ocean-access-beneath-the-southwest-tributary-of-pine-island-glacier-west-antarctica/EFF449338C7D7D088CCB7BC48D40B150

Abstract: "The catchments of Pine Island Glacier and Thwaites Glacier in the Amundsen Sea Embayment are two of the largest, most rapidly changing, and potentially unstable sectors of the West Antarctic Ice Sheet. They are also neighboring outlets, separated by the topographically unconfined eastern shear margin of Thwaites Glacier and the southwest tributary of Pine Island Glacier. This tributary begins just downstream of the eastern shear margin and flows into the Pine Island ice shelf. As a result, it is a potential locus of interaction between the two glaciers and could result in cross-catchment feedback during the retreat of either. Here, we analyze relative basal reflectivity profiles from three radar sounding survey lines collected using the UTIG HiCARS radar system in 2004 and CReSIS MCoRDS radar system in 2012 and 2014 to investigate the extent and character of ocean access beneath the southwest tributary. These profiles provide evidence of ocean access ~12 km inland of the 1992–2011 InSAR-derived grounding line by 2014, suggesting either retreat since 2011 or the intrusion of ocean water kilometers inland of the grounding line."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2193 on: December 10, 2019, 06:20:09 PM »
The linked reference concludes that the groundling line for the PIG has a several km wide "flush zone" where seawater intrudes beneath the glacier on high tides and where there is "… continuous draining/filling of subglacial lakes proximal to the grounding line."  Further, it concludes that: "At present, numerical models of ice flow do not account for a flush zone. The existence of a flush zone should make the glacier more prone to retreat in response to warmer ocean waters."

Pietro Milillo, Eric Rignot, Jeremie Mouginot, Bernd Scheuchl, Mathieu Morlighem, Xin Li & Jacqueline T. Salzer (31 August 2017), "On the short-term grounding zone dynamics of Pine Island glacier, West Antarctica observed with COSMO-SkyMed interferometric data", Geophysical Research Letters, DOI: 10.1002/2017GL074320 

http://onlinelibrary.wiley.com/doi/10.1002/2017GL074320/abstract?utm_content=buffer19afa&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Using radar satellite data from the Italian COSMO-SkyMed (CSK) constellation and the German TanDEM-X formation, we present comprehensive measurements of the bi-weekly grounding line dynamics of Pine Island Glacier, West Antarctica, from August to December 2015. The one-day repeat cycle of CSK reveals tidally-induced, grounding line migration on the scale of kilometers and extensive seawater intrusion within the grounding zone, which significantly exceeds that predicted for a stiff bed but are consistent with that calculated for a deformable bed. The deformable bed also explains the continuous draining/filling of subglacial lakes proximal to the grounding line. After correction for oceanic tides, we estimate a retreat rate for 2011-2015 of 0.3 km/yr at the glacier center and 0.5 km/yr on the sides, which is three times slower than for 1994-2011 (1.2 km/yr at the center). We attribute the decrease in retreat rate to colder ocean conditions in 2012-2013 relative to 2000-2011."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2194 on: December 10, 2019, 06:20:47 PM »
The linked 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 extreme 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."
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AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2195 on: December 10, 2019, 06:23:01 PM »
The linked reference indicates that the PIIS is calving further upstream than in the past due to oceanic driven disintegration of the northern shear margin mélange and intensified melting with basal crevasses.  As the ocean in this area will remain relatively warm for a long time, this indicates that the PIIS will continue to calve more rapidly than in the past and will calve further and further upstream, with time:

Seongsu Jeong, Ian M. Howat & Jeremy N. Bassis (28 November 2016), "Accelerated ice shelf rifting and retreat at Pine Island Glacier, West Antarctica", Geophysical Research Letters, DOI: 10.1002/2016GL071360

http://onlinelibrary.wiley.com/doi/10.1002/2016GL071360/full

Abstract: "Pine Island Glacier has undergone several major iceberg calving events over the past decades. These typically occurred when a rift at the heavily fractured shear margin propagated across the width of the ice shelf. This type of calving is common on polar ice shelves, with no clear connection to ocean-ice dynamic forcing. In contrast, we report on the recent development of multiple rifts initiating from basal crevasses in the center of the ice shelf, resulted in calving further upglacier than previously observed. Coincident with rift formation was the sudden disintegration of the ice mélange that filled the northern shear margin, resulting in ice sheet detachment from this margin. Examination of ice velocity suggests that this internal rifting resulted from the combination of a change in ice shelf stress regime caused by disintegration of the mélange and intensified melting within basal crevasses, both of which may be linked to ocean forcing."
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vox_mundi

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2196 on: December 10, 2019, 06:39:23 PM »
Greenland Ice Losses Rising Faster Than Expected
https://phys.org/news/2019-12-greenland-ice-losses-faster.html

Greenland is losing ice seven times faster than in the 1990s and is tracking the Intergovernmental Panel on Climate Change's high-end climate warming scenario, which would see 40 million more people exposed to coastal flooding by 2100.

... The findings, published today in Nature today, show that Greenland has lost 3.8 trillion tonnes of ice since 1992—enough to push global sea levels up by 10.6 millimetres. The rate of ice loss has risen from 33 billion tonnes per year in the 1990s to 254 billion tonnes per year in the last decade—a seven-fold increase within three decades.

In 2013, the Intergovernmental Panel on Climate Change (IPCC) predicted that global sea levels will rise by 60 centimetres by 2100, putting 360 million people at risk of annual coastal flooding. But this new study shows that Greenland's ice losses are rising faster than expected and are instead tracking the IPCC's high-end climate warming scenario, which predicts 7 centimetres more.



Mass balance of the Greenland Ice Sheet from 1992 to 2018, Nature (2019)
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Hefaistos

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2197 on: December 10, 2019, 07:25:19 PM »
The linked research provides more evidence that a slowing of the AMOC will lead to increased warming at high latitudes due to abrupt warming during the summer months.  This helps to confirm Hansen's ice-climate feedback projections:


However, the claim that the AMOC is slowing is disputed. Seems that the AMOC slowdown has reversed, and that it has incredibly large variability.
Measured and reported in paper "Atlantic Meridional Overturning Circulation: Observed Transport and Variability"
Eleanor Frajka-Williams, et al. 2019, pdf attached to this post.

"From first transbasin measurements retrieved at 26◦N by the RAPID array, a number of startling results have emerged (summarized in Srokosz and Bryden, 2015): that the AMOC ranged from 4 to 35 Sv over a single year, had a seasonal cycle with amplitude over 5 Sv, and that the dip in 2009/10 of 30% exceeded the range of interannual variability found in climate models. The international efforts to measure the AMOC in the Atlantic at a range of latitudes have delivered new understanding of AMOC variability, its structure and meridional coherence. In situ mooring arrays form the primary measurements of the large-scale meridional circulation,[/b]."

AMOC has been above its historic mean for the last 5 years or so, see attached graph.

Figure caption: FIGURE 6 | A time series of AMOC transport (MOCρ ) at the OVIDE section (eastern subpolar gyre: Portugal to Cape Farewell) for 1993–2017, constructed from altimetry and hydrography. The gray line is from altimetry combined with a time-mean of Argo velocities; the green curve is low-pass filtered using a 2-year running mean. The black curve is from altimetry and Argo. Red circles are estimates from OVIDE hydrography with associated errors given by the red lines. The mean of the gray curve is given by the black dashed line (Updated from Mercier et al., 2015).
« Last Edit: December 10, 2019, 07:30:41 PM by Hefaistos »

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2198 on: December 10, 2019, 08:38:35 PM »
...
However, the claim that the AMOC is slowing is disputed. Seems that the AMOC slowdown has reversed, and that it has incredibly large variability.


While I concur that the current nature of the trendline for the AMOC is not 'settled science', I also note that uncertainty is not our friend, nor is the high variability of the AMOC w.r.t. climate risks.  Indeed, Fraika-Williams (2019) conclude that '… the observational records of the AMOC transport variability are relatively short …"; and when one looks at a longer time period such as that shown in the attached image, the trendline indicating slowing is clearer than that may, or may not, be indicated by shorter periods; which are more easily influenced by temporal variability:

Eleanor Frajka-Williams et al. (2019), "Atlantic Meridional Overturning Circulation: Observed Transport and Variability", Front. Mar. Sci., 07, https://doi.org/10.3389/fmars.2019.00260

https://www.frontiersin.org/articles/10.3389/fmars.2019.00260/full
&
https://www.frontiersin.org/articles/10.3389/fmars.2019.00260/full#supplementary-material

Abstract: "The Atlantic Meridional Overturning Circulation (AMOC) extends from the Southern Ocean to the northern North Atlantic, transporting heat northwards throughout the South and North Atlantic, and sinking carbon and nutrients into the deep ocean. Climate models indicate that changes to the AMOC both herald and drive climate shifts. Intensive trans-basin AMOC observational systems have been put in place to continuously monitor meridional volume transport variability, and in some cases, heat, freshwater and carbon transport. These observational programs have been used to diagnose the magnitude and origins of transport variability, and to investigate impacts of variability on essential climate variables such as sea surface temperature, ocean heat content and coastal sea level. AMOC observing approaches vary between the different systems, ranging from trans-basin arrays (OSNAP, RAPID 26°N, 11°S, SAMBA 34.5°S) to arrays concentrating on western boundaries (e.g., RAPID WAVE, MOVE 16°N). In this paper, we outline the different approaches (aims, strengths and limitations) and summarize the key results to date. We also discuss alternate approaches for capturing AMOC variability including direct estimates (e.g., using sea level, bottom pressure, and hydrography from autonomous profiling floats), indirect estimates applying budgetary approaches, state estimates or ocean reanalyses, and proxies. Based on the existing observations and their results, and the potential of new observational and formal synthesis approaches, we make suggestions as to how to evaluate a comprehensive, future-proof observational network of the AMOC to deepen our understanding of the AMOC and its role in global climate."

Extract: "While the observational records of the AMOC transport variability are relatively short, we have learned a great deal about the structure and variability of the AMOC volume, heat and freshwater transports, its response to wind forcing, and its meridional coherence (or lack thereof) between latitudes."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE (narrated video)
« Reply #2199 on: December 10, 2019, 09:56:46 PM »
We should not forget that meltwater from Greenland has formed a cool spot in the North Atlantic (see image); which, is activity contributing to the slowing of the AMOC:

Title: "The North Atlantic ocean current, which warms northern Europe, may be slowing

https://skepticalscience.com/north-atlantic-current-slowing.html

Extract: "The current depends on the saltiness of the North Atlantic to create the sinking motion of water, that is, it’s the “pump” driving the current. Saltier water is heavier than fresh water.

As the Greenland ice sheet melts, large volumes of fresh water enter the North Atlantic and freshen the very salty sea water, slowing the “pump,” Jorgen Peder Steffensen of the University of Copenhagen explains in the video, produced for Yale Climate Connections by independent videographer Peter Sinclair of Midland, Michigan.

“That would make it terribly cold in Denmark, where I come from,” Steffensen says. “In principle, there’s no reason why Earth could not get warmer but still northern Europe and North America could get cold. Still, that area is not large compared to the global area.”

Melting ice from Greenland largely explains the freshening North Atlantic, Box agrees.

“We are 50 to a hundred years ahead of schedule with the slowdown of this ocean circulation pattern, relative to the models,” according to Mann. “The more observations we get, the more sophisticated our models become, the more we’re learning that things can happen faster, and with a greater magnitude, than we predicted just years ago.”"
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson