Ice Apocalypse - Multiple Meters Sea Level Rise

[vox_mundi]

Sea Ice Plays Pacemaker Role in Abrupt Climate Change
https://phys.org/news/2019-03-sea-ice-pacemaker-role-abrupt.html

A new study looking at variations in past sea ice cover in the Norwegian Sea found the shrinkage and growth of ice was instrumental in several abrupt climate changes between 32,000 and 40,000 years ago.

The growth or shrinkage of sea ice is often viewed as a symptom of climate change, but new research shows it may have played a more causative role in abrupt climate changes thousands of years ago.

The study, which was led by Dr. Henrik Sadatzki from the Department of Earth Science and Bjerknes Centre for Climate Research, University of Bergen (Norway), analysed marine sediment cores from the Norwegian sea to reconstruct changes in sea ice during the last glacial period, focusing on the abrupt climate change events. This was complemented by climate model simulations of the last glacial period.

The abrupt climate changes – known as Dansgaard–Oeschger climate events – had global implications and comprised temperature shifts of up to 15°C over the Greenland ice sheet and happened within decades.

While the underlying mechanisms of these dramatic changes are not yet fully understood, the study confirms that changes in sea ice cover in the Norwegian Sea played a key role in driving the enigmatic events.

Open Access: Henrik Sadatzki et al. Sea ice variability in the southern Norwegian Sea during glacial Dansgaard-Oeschger climate cycles, Science Advances (2019).

[AbruptSLR]

Kent A. Peacock (12 Sep 2018) "A Different Kind of Rigor: What Climate Scientists Can Learn from Emergency Room Doctors", Ethics, Policy & Environment, Volume 21, 2018 - Issue 2, Pages 194-214, https://doi.org/10.1080/21550085.2018.1509483
https://www.tandfonline.com/doi/full/10.1080/21550085.2018.1509483

Peacock says:
"There is a genuine possibility, however, remote, that the whole contents of the Bentley trench could shatter in a matter of weeks or months, raising global mean sea level by 3 m or more almost immediately."

What peer-reviewed publication supports this statement? I think Pollard, DeConto & Alley 2015 have said they can't rule out this is possible in a matter of "decades" (3m in 3 decades?):
https://www.sciencedirect.com/science/article/pii/S0012821X14007961

"In summary, applying a simple Pliocene-like warming scenario to our model, the combined mechanisms of MISI, melt-driven hydrofracturing and cliff failure cause a very rapid collapse of West Antarctic ice, on the order of decades."

I have not seen "weeks or months". Anyone else?

Lennart,

First, the Peacock paper is peer-reviewed, but that said, I have not seen another comparable statement about the stability of the ice above the Bentley Subglacial Trench.

Second, the statement from Pollard, DeConto & Alley (2015) addresses a collapse of the entire WAIS within decades; while the Peacock (2018) comment was limited to the Bentley trench.  Also, Pollard, DeConto & Alley (2015) limited the rate of ice-cliff retreat to less than half (i.e. 5 km/a) of the maximum observed for the Jakobshavn Glacier of about 13 km/a (see the Youtube video & Reply #268):

https://www.youtube.com/watch?time_continue=3029&v=aqVPlBf4ydo

However:

a. Jakobshavn ice flow is restrained on both sides by the wall of the fjord; while the ice in the Bentley trench does not have comparable side restraints.

b. Jakobshavn is currently retreating up a positively sloped ice bed; while this would not be the case for an ice cliff with the Bentley trench formed some years after the initiation of a MICI collapse triggered at the threshold of the Thwaites Glacier.

c. The current height of the Jakobshavn ice face is in the 100 to 120m range, while after a few tens of kilometers of retreat, the ice face for the Thwaites Glacier could be several hundred meters high and with a relative water depth w = D/H (water dept/ice face height) of 0.6 to 0.8; for such a case Schlemm & Levermann (2018) indicates that the actual retreat rate would be well (likely by many times) over 60 km/a (see also Reply #278).

Tanja Schlemm and Anders Levermann (2018), "A simple stress-based cliff-calving law", The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-205

https://www.the-cryosphere-discuss.net/tc-2018-205/tc-2018-205.pdf

Fourth, the linked Ivanovic et al. (2018) reference indicates that paleo-signals from meltwater pulse events in the NH override any such paleo-signals from SH meltwater pulse events.  Thus one would not likely able to find any evidence of a meltwater pulse event in the paleo-record from a meltwater pulse event associate with the Bentley Subglacial Trench.

R. F. Ivanovic et al. (04 June 2018), "Climatic Effect of Antarctic Meltwater Overwhelmed by Concurrent Northern Hemispheric Melt", Geophysical Research Letters 45, Issue 11
https://doi.org/10.1029/2018GL077623

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL077623

Abstract
Records indicate that 14,500 years ago, sea level rose by 12–22 m in under 340 years. However, the source of the sea level rise remains contentious, partly due to the competing climatic impact of different hemispheric contributions. Antarctic meltwater could indirectly strengthen the Atlantic Meridional Overturning Circulation (AMOC), causing northern warming, whereas Northern Hemisphere ice sheet meltwater has the opposite effect. This story has recently become more intriguing, due to increasing evidence for sea level contributions from both hemispheres. Using a coupled climate model with freshwater forcing, we demonstrate that the climatic influence of southern‐sourced meltwater is overridden by northern sources even when the Antarctic flux is double the North American contribution. This is because the Southern Ocean is quickly resalinized by Antarctic Circumpolar water. These results imply that the pattern of surface climate changes caused by ice sheet melting cannot be used to fingerprint the hemispheric source of the meltwater.

Plain Language Summary
The fastest major sea level rise ever recorded took place 14,500 years ago, when sea level rose by 12–22 m in under 340 years. The extra water came from melting ice sheets, which stretched across North America and northern Europe as well as Greenland and Antarctica. We ran a climate model to test the impact of different meltwater contributions from Antarctica and the Northern Hemisphere ice sheets (North America, Greenland, and Eurasia). Our simulations demonstrate that northern meltwater has a much stronger and longer lasting effect on ocean circulation and climate than Southern Hemisphere melt. Consequently, northern melting overrides the impact of southern melting even when the flux of water from North America is only half the magnitude of the Antarctic flux. This means that past climate records cannot be used to identify the contribution of meltwater from different ice sheets: the northern signal can override the southern signal.

Fifth, the two images from Bassis & Walker (2011) show that any ice cliff in the Bentley trench would inherently be unstable and would collapse with the slightest perturbation.

J. N. Bassis & C. C. Walker (23 November 2011), "Upper and lower limits on the stability of calving glaciers from the yield strength envelope of ice", Proceedings of the Royal Society A, https://doi.org/10.1098/rspa.2011.0422

https://royalsocietypublishing.org/doi/full/10.1098/rspa.2011.0422

Abstract
Observations indicate that substantial changes in the dynamics of marine-terminating ice sheets and glaciers are tightly coupled to calving-induced changes in the terminus position. However, the calving process itself remains poorly understood and is not well parametrized in current numerical ice sheet models. In this study, we address this uncertainty by deriving plausible upper and lower limits for the maximum stable ice thickness at the calving face of marine-terminating glaciers, using two complementary models. The first model assumes that a combination of tensile and shear failure can render the ice cliff near the terminus unstable and/or enable pre-existing crevasses to intersect. A direct consequence of this model is that thick glaciers must terminate in deep water to stabilize the calving front, yielding a predicted maximum ice cliff height that increases with increasing water depth, consistent with observations culled from glaciers in West Greenland, Antarctica, Svalbard and Alaska. The second model considers an analogous lower limit derived by assuming that the ice is already fractured and fractures are lubricated by pore pressure. In this model, a floating ice tongue can only form when the ice entering the terminus region is relatively intact with few pre-existing, deeply penetrating crevasses.

Caption for the first image: "Contours showing maximum stable ice thickness as a function of water depth for different crevasse penetration depths for a constant yield strength of 1 MPa. The contours represent different crevasse penetration ratios r, ranging from 0 (no crevasses) to 1 (completely fractured). The arrows indicate the maximum dry calving cliff thickness when crevasse depths are computed according to the Nye theory (110 m) and when the ice is assumed to be intact with no pre-existing crevasses (221 m). The dashed black line shows the thickness at buoyancy for a given ice thickness. Inset: the maximum floating termini thickness for different fractions of intact ice."

Caption for second image: "Comparison of observed height-above-buoyancy and water depth against predicted bounds. The shaded region shows allowed values for the height-above-buoyancy determined using S3 (C0=1 MPa,α=0) with no crevasses. The dashed black line shows the maximum height-above-buoyancy permitted when surface and bottom crevasses are included. The dotted line shows a constant height-above-buoyancy of 50 m. Density of ice ρi=920 kg m−3 and density of water ρw=1020 kg m−3. CG, Columbia Glacier, Alaska; AK, Alaska; Sb, Svalbard; WG, West Greenland; HG, Helheim Glacier, Greenland."

Best,
ASLR

For ease of reference, I provide the third attached image from Schlemm and Levermann (2018)

[sidd]

In my previous comment i mentioned i could not see an efficient method for heat into the ice sheets except rain. As we see, hard rain fallin on greenland. Fast rain induced collapse there is far more likely today than in antarctica.  I watch melt on the 67N saddle, that will be the first to go. Then south dome. thats a meter or so of SLR, not to be sneezed at.

The question is, as always, how fast ? Gregoire saw time scales on the order of a century in the last deglaciation in north american collapse, so mebbe add a meter from 67N saddle/south dome collapse to the high end of SLR projection for 2100.

sidd
 

[gerontocrat]

In my previous comment i mentioned i could not see an efficient method for heat into the ice sheets except rain. As we see, hard rain fallin on greenland. Fast rain induced collapse there is far more likely today than in antarctica. 
sidd

New paper on Greenland rain -  posted on "what's new in Greenland"
https://forum.arctic-sea-ice.net/index.php/topic,1090.msg191421.html#msg191421

links to
https://www.the-cryosphere.net/13/815/2019/ and
https://www.bbc.co.uk/news/science-environment-47485847

[Sleepy]

Thanks for all the updates here!
No offense but the last one was posted yesterday by ASLR, gc.

When reading the discussion around Bentley I started thinking about this study about the mantle thermal anomalies beneath it. You guys are probably aware of it:
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015JB012455

[Lennart van der Linde]

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.'

[AbruptSLR]

Re: "weeks or months" for collapse of bentley trench

I think that is impossible under current conditions. First, as Mercer pointed out, oh, so many decades ago, you need the 0C isotherm to migrate into the bentley trench, and then remain there for large fraction of summer. Then you might have substantial surface melt and hydrofracture enuf to meet up with basal crevasses. And then you might have icecube collapse in a few decades.

But the ice wont stay in place. Long b4 that glacier flow rate will skyrocket due to glen's law exponent dependence on temperature and we shall have iceberg armadas in southern ocean thru calving.

So watch the grounding lines rather than surface melt for now. When the westerlies around antarctica start breaking down enuf to allow 0C isotherm incursion deep into heart of WAIS, then you might see Peacock's apocalypse stretched out over a decade or three.  But that will b after a lot of other apocalypse.

From a physics point of view, the problem is  moving enuf heat into the ice sheet fast enuf to cause icecube collapse; fast enuf to surpass and overcome ice export thru flow rate increase due to glen's law exponent increase. I really see no way to do that except rain. CDW incursion really doesn't get into the bulk of the ice, its a basal and frontal thing. And we wont get rain until westerlies break down massively and Mercer's 0C isotherm acts up.

Blanchon(2009) has some interesting graphs which i have posted b4 about rates of SLR. Worst case seems to be a meter evry 20 yrs continuing for 500 yr.

doi:10.1038/nature07933

sidd

First, Mercer was not aware of the MICI failure mechanism, which most likely explains why he needed to assume that the 0C isotherm needs to move down to the Byrd Subglacial Basin before it became destabilized.

Second, Pollard & DeConto have shown that for abrupt sea level rise in the next few decades, one only needs excessive surface water on top of the key ice shelves, which are near sea level and which are also susceptible to surface warming from katabatic winds (which happened recently for the Ross Ice Shelf.

Third, once the buttressing action of the ice shelves are lost due to hydrofracturing, Pollard/DeConto show that the ice flow velocity for the key marine glaciers accelerate sufficiently to active a MISI mechanism which in turn activates the MICI mechanism before the end of the century, and the MICI mechanism can result in the loss of the bulk of WAIS ice mass without the need for surface water (from rain or ice melt) in places like the heart of the Byrd Subglacial Basin.

Fourth, Pollard and DeConto's models likely err on the side of least drama, ESLD, for a number of reasons including:
a. The use global circulation models that project nominal values of ECS around 3C; which likely ESLD.
b. At the base of the Thwaites Ice Tongue, the water depths and ice profiles are sufficient to active local ice cliff failures without the need to active MISI mechanisms.
c. As I have shown Pollard & DeConto limited the rate of MICI propagation to 5km/a, when in the Bentley trench it could be many times 60km/a.
d. I believe that the ASE ice shelves are already in a much more degraded condition that assumed by Pollard & DeConto.

Thus rainfall is not need for the WAIS to collapse this century.

[AbruptSLR]

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

Lennart,

Thank you for the link to Dewi Le Bars' reflections on Edwards et al (2019) & Golledge et al (2019) w.r.t. DeConto & Pollard (2016), as Le Bars' comments reminds me of the linked reference (with a hat tip to jai) that 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."

In my opinion many consensus climate scientists (such as those involved in CMIP5), are reticent to accept new findings with more dramatic implications (such as those of Pollard & DeConto 2016), and thus AR6 and CMIP6 are likely to only accept a small fraction of new research into their consensus climate projections.  The 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 cause consensus climate scientists to exhaust themselves on chasing Type 1 errors, leaving them with less energy/stomach to chase Type 2 errs (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, I add the following partial list of Type 2 errs that consensus scientists' models (both CMIP5 and soon 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 err, 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 err).  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 hindcast the degree of Arctic Amplification observed in the paleo-record, and thus these consensus climate models are clearly committing Type 2 errs 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 errs (such as the positive feedback associated with the project future redistribution of anthropogenic aerosol emissions, and projected changes in VOCs from forests).

Best,
ASLR

[AbruptSLR]

The linked reference indicates that the net feedback of phytoplankton in the Arctic will likely be positive leading to greater Arctic Amplification than current assumed by consensus Earth System Models:

Lim et al. (March 2019), "Biogeophysical feedback of phytoplankton on Arctic climate. Part II: Arctic warming amplified by interactive chlorophyll under greenhouse warming", Climate Dynamics, pp 1–14, https://doi.org/10.1007/s00382-019-04693-5

https://link.springer.com/article/10.1007%2Fs00382-019-04693-5

Abstract: "It has been shown that the interaction between marine phytoplankton and climate systems may intensify Arctic warming in the future via shortwave heating associated with increased spring chlorophyll bloom. However, the changes of chlorophyll variability and its impact on the Arctic future climate are uncomprehended. Lim et al. (Clim Dyn.  https://doi.org/10.1007/s00382-018-4450-6, 2018a) (Part I) suggested that two nonlinear rectifications of chlorophyll variability play cooling role in present-day climate. In this study, we suggest that the decreased interannual chlorophyll variability may amplify Arctic surface warming (+ 10% in both regions) and sea ice melting (− 13% and − 10%) in Kara-Barents Seas and East Siberian-Chukchi Seas in boreal winter, respectively. Projections of earth system models show a future decrease in chlorophyll both mean concentration and interannual variability via sea ice melting and intensified surface-water stratification in summer. We found that suggested two nonlinear processes in Part I will be reduced by about 31% and 20% in the future, respectively, because the sea ice and chlorophyll variabilities, which control the amplitudes of nonlinear rectifications, are projected to decrease in the future climate. The Arctic warming is consequently enhanced by the weakening of the cooling effects of the nonlinear rectifications. Thus, this additional biological warming will contribute to future Arctic warming. This study suggests that effects of the mean chlorophyll and its variability should be considered to the sensitivity of Arctic warming via biogeophysical feedback processes in future projections using earth system models."

[AbruptSLR]

Thanks for all the updates here!
No offense but the last one was posted yesterday by ASLR, gc.

When reading the discussion around Bentley I started thinking about this study about the mantle thermal anomalies beneath it. You guys are probably aware of it:
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015JB012455

Sleepy,

Thanks for the link to Lloyd et al (2015), for which I provide the following information and the associated attached first image that clear shows the relationship of the study area to the Thwaites drainage basin, the Byrd Subglacial Basin and the Bentley Subglacial Trench; which was the subject of Lennart's question about Peacock's assessment of the risk of ice mass loss from the Bentley trench area.

Lloyd et al (2015), "A seismic transect across West Antarctica: Evidence for mantle thermal anomalies beneath the Bentley Subglacial Trench and the Marie Byrd Land Dome", JGR Solid Earth, https://doi.org/10.1002/2015JB012455

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015JB012455

Abstract: "West Antarctica consists of several tectonically diverse terranes, including the West Antarctic Rift System, a topographic low region of extended continental crust. In contrast, the adjacent Marie Byrd Land and Ellsworth‐Whitmore mountains crustal blocks are on average over 1 km higher, with the former dominated by polygenetic shield and stratovolcanoes protruding through the West Antarctic ice sheet and the latter having a Precambrian basement. The upper mantle structure of these regions is important for inferring the geologic history and tectonic processes, as well as the influence of the solid earth on ice sheet dynamics. Yet this structure is poorly constrained due to a lack of seismological data. As part of the Polar Earth Observing Network, 13 temporary broadband seismic stations were deployed from January 2010 to January 2012 that extended from the Whitmore Mountains, across the West Antarctic Rift System, and into Marie Byrd Land with a mean station spacing of ~90 km. Relative P and S wave travel time residuals were obtained from these stations as well as five other nearby stations by cross correlation. The relative residuals, corrected for both ice and crustal structure using previously published receiver function models of crustal velocity, were inverted to image the relative P and S wave velocity structure of the West Antarctic upper mantle. Some of the fastest relative P and S wave velocities are observed beneath the Ellsworth‐Whitmore mountains crustal block and extend to the southern flank of the Bentley Subglacial Trench. However, the velocities in this region are not fast enough to be compatible with a Precambrian lithospheric root, suggesting some combination of thermal, chemical, and structural modification of the lithosphere. The West Antarctic Rift System consists largely of relative fast uppermost mantle seismic velocities consistent with Late Cretaceous/early Cenozoic extension that at present likely has negligible rift related heat flow. In contrast, the Bentley Subglacial Trench, a narrow deep basin within the West Antarctic Rift System, has relative P and S wave velocities in the uppermost mantle that are ~1% and ~2% slower, respectively, and suggest a thermal anomaly of ~75 K. Models for the thermal evolution of a rift basin suggest that such a thermal anomaly is consistent with Neogene extension within the Bentley Subglacial Trench and may, at least in part, account for elevated heat flow reported at the nearby West Antarctic Ice Sheet Divide Ice Core and at Subglacial Lake Whillans. The slowest relative P and S wave velocity anomaly is observed extending to at least 200 km depth beneath the Executive Committee Range in Marie Byrd Land, which is consistent with warm possibly plume‐related, upper mantle. The imaged low‐velocity anomaly and inferred thermal perturbation (~150 K) are sufficient to support isostatically the anomalous long‐wavelength topography of Marie Byrd Land, relative to the adjacent West Antarctic Rift System."

In addition to information from Lloyd et al (2015), I provide the following linked information from Martos et al. (2017) which provides the second attached image of geothermal heat flux from the Bentley trench area.  Such high geothermal flux from the Bentley trench area further destabilizes the ice in this area more than that associated with ice cliff failure mechanisms:

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

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

Abstract: "Antarctica is the largest reservoir of ice on Earth. Understanding its ice sheet dynamics is crucial to unraveling past global climate change and making robust climatic and sea level predictions. Of the basic parameters that shape and control ice flow, the most poorly known is geothermal heat flux. Direct observations of heat flux are difficult to obtain in Antarctica, and until now continent-wide heat flux maps have only been derived from low-resolution satellite magnetic and seismological data. We present a high resolution heat flux map and associated uncertainty derived from spectral analysis of the most advanced continental compilation of airborne magnetic data. Small-scale spatial variability and features consistent with known geology are better reproduced than in previous models, between 36% and 50%. Our high-resolution heat-flux map and its uncertainty distribution provide an important new boundary condition to be used in studies on future subglacial hydrology, ice-sheet dynamics and sea-level change."

Best,
ASLR

[AbruptSLR]

ughes et al (2011) (see following link to a free access pdf and the abstract) discusses the ice-bed coupling beneath and beyond ice streams using information related to a 2004 surge in the flow of the Byrd Glacier associated with the basal drainage of two large subglacial lakes.  The Thwaites Glacier also has a well-developed subglacial basal water hydrological system and surges in the Thwaites ice stream flow (particularly of the Thwaites Ice Tongue) have also been related to episodic basal water discharges of subglacial lakes; and the Hughes et al 2011 reference shows how during such surges the ice flow accelerates above the bed as controlled by the floating friction (phi) that is influenced by the internal ice structure in the ice sheet (see the first attached image and associated caption).  The subglacial basal water hydrological system is also partially feed by the high geothermal heat flux within both the Bentley trench and the Byrd Subglacial Basin.

Hughes, Terence J.; Sargent, Aitbala; and Fastook, James L., "Ice-Bed Coupling Beneath and Beyond Ice Streams: Byrd Glacier, Antarctica" (2011). Earth Science Faculty Scholarship. Paper 49. http://digitalcommons.library.umaine.edu/ers_facpub/49  (citation: Hughes, T., A. Sargent, and J. Fastook (2011), Ice‐bed coupling beneath and beyond ice streams: Byrd Glacier, Antarctica, J. Geophys. Res., 116, F03005, doi:10.1029/2010JF001896.)

http://digitalcommons.library.umaine.edu/cgi/viewcontent.cgi?article=1048&context=ers_facpub

Abstract: "Ice sheet thickness is determined mainly by the strength of ice‐bed coupling that controls holistic transitions from slow sheet flow to fast streamflow to buttressing shelf flow. Byrd Glacier has the largest ice drainage system in Antarctica and is the fastest ice stream entering Ross Ice Shelf. In 2004 two large subglacial lakes at the head of Byrd Glacier suddenly drained and increased the terminal ice velocity of Byrd Glacier from 820 m yr−1 to 900 m yr−1. This resulted in partial ice‐bed recoupling above the lakes and partial decoupling along Byrd Glacier. An attempt to quantify this behavior is made using flowband and flowline models in which the controlling variable for ice height above the bed is the floating fraction phi of ice along the flowband and flowline. Changes in phi before and after drainage are obtained from available data, but more reliable data in the map plane are required before Byrd Glacier can be modeled adequately. A holistic sliding velocity is derived that depends on phi, with contributions from ice shearing over coupled beds and ice stretching over uncoupled beds, as is done in state‐of‐the‐art sliding theories.

Caption for the first attached image of the Byrd Glacier: "The geometrical force balance on an ice stream ending as a confined ice shelf. (top) Stresses that resist gravitational flow along x. The bed supports ice in the shaded area. Ice in the unshaded area is supported by “effective” basal water pressure. (middle) Gravitational forces at x represented as triangles and a rectangle are linked to specific resisting stresses. The area inside the thick border is linked to compressive stress sC. Heights hI, hW, and hF are measured from the bed for x > 0. (bottom) Resisting stresses and gravitational forces along Dx. Resisting and gravitational forces are balanced along x and Dx [see Hughes, 2009a]."

Edit, see also the following Hughes 1981 reference, and the associated second image:

Hughes, Terence J., "The Weak Underbelly of the West Antarctic Ice-Sheet" (1981). Earth Science Faculty Scholarship. Paper 156. http://digitalcommons.library.umaine.edu/ers_facpub/156

http://digitalcommons.library.umaine.edu/cgi/viewcontent.cgi?article=1155&context=ers_facpub

Extract: "Thwaites Glacier terminates as a huge floating ice tongue 200 km long. Floating ice tongues form when the ice-stream velocity exceeds the iceberg calving rate, which is most likely toward the beginning of a surge."

[Tony Mcleod]

Just want to thank you AbruptSLR for your ongoing posting of these fascinating abstracts, links and your accompanying comments. I wouldn't know where to begin to find all this stuff out but you manage to to distill it out in wonderful digest. Most appreciative.
Tony

[AbruptSLR]

Returning to Terence Hughes' 2012 insights about AIS kinematics and internal structure, in the following linked reference (with a free access pdf), he expands on his earlier theory of thermal convection in the AIS, citing evidence and proposed tests to verify his insight.  The evidence again focuses on the Byrd Glacier (see the first image and associated caption) about converging and dispersing tributary flows which changes ice flow speeds, boundary conditions and thermal energy that influences convection rolls shown in the second attached image (see also the second associated caption).  Obviously, ice is not a liquid therefore its thermal convection is heavily influence by creep as indicated by the third and fourth attached images (and associated captions).  If this theory is verified by field measurements it could have a significant influence on understanding ice sheet flow and how heat (say from internal ice friction [note as the ice stream velocity increases so does the amount of internal ice melting due to internal friction], geothermal, surface meltwater penetrating surface crevasses, or other sources) feedback mechanisms could accelerate local ice streams (such as Thwaites and other ASE marine glaciers) leading to possible ice sheet (say WAIS) destruction:

Terence J. Hughes, (2012), " Thermal convection in ice sheets: New data, new tests", Natural Science, Vol.4 No.7, Article ID:20743,10 pages DOI:10.4236/ns.2012.47056

http://file.scirp.org/Html/1-8301678_20743.htm

Abstract: "Thermal convection in the Antarctic Ice Sheet was proposed in 1970. Demonstrating its existence proved to be elusive. In 2009, tributaries to ice streams were postulated as the surface expression of underlying thermal convection rolls aligned in directions of advective ice flow. Two definitive tests of this hypothesis are now possible, using highly accurate ice elevations and velocities provided by the European, Japanese, and Canadian Space Agencies that allow ice-stream tributaries and their velocities to be mapped. These tests are 1) measuring lowering of tributary surfaces to see if lowering is due only to advective ice thinning, or also requires lowering en masse in the broad descending part of convective flow, and 2) measuring transverse surface ice velocities to see if ice entering tributaries from the sides increases while crossing lateral shear zones, as would be required if this flow is augmented by convective flow ascending in the narrow side shear zones and diverted into tributaries by advective ice flow. If 1) and 2) are applied to tributaries converging on Byrd Glacier, the same measurements can be conducted when tributaries pack together to become “flow stripes” down Byrd Glacier and onto the Ross Ice Shelf to see if 2) is reduced when lateral advection stops. This could determine if thermal convection remains active or shuts down as ice thins. Thermal convection in the Antarctic Ice Sheet would raise three questions. Can it cause the ice sheet to self-destruct as convective flow turns on and off? Does it render invalid climate records extracted at depth from ice cores? Can the ice sheet be studied as a miniature mantle analogous in some respects to Earth’s mantle?"

Selected extracts: "Recrystallization begins at a creep strain of about 10 percent for a given applied stress. The strain rate, initially infinite, gives an infinite Rayleigh number. Both decrease over time and the Rayleigh number can fall below its critical value before slow steady state creep is established. Then convective flow stops. If the Rayleigh number remains above its critical value, recrystallization can take place and allow fast steady state creep to produce a higher Rayleigh number that allows faster convective flow. This component of ice-sheet flow can therefore turn on and off, and thereby regulate the 90 percent of ice discharged by ice streams in the Antarctic Ice Sheet. In the extreme, the faster discharge may allow the ice sheet to self-destruct, if more ice leaves than can be replaced by precipitation over the surface.
…
As in rifted crustal ridges, ice pulls away from ice divides, but ice is too slow and soft to produce rifts. Ice converges on ice streams that supply ice shelves, which calve instead of collide like crustal plates. This understanding of ice-sheet dynamics would draw wide interest, and be a great boon to glaciology. The glaciology of ice sheets would undergo a Scientific Revolution comparable to plate tectonics if convection rolls were shown to underlie ice-stream tributaries."

Caption for the first image of the Byrd Glacier Flow Pattern: "A Radarsat image of Byrd Glacier, including converging tributaries at its head and lateral rifts where it enters Ross Ice Shelf. The trace of tributaries continues on Byrd Glacier and onto the Ross Ice Shelf as flow stripes."

Caption of the second image of theoretical convective ice stream flow pattern: "A cartoon showing thermal convection rolls in transverse cross-section beneath ice-stream tributaries. Letters T, C, and S show respective regions of tensile, compressive, and shear flow caused by convection. Top: For an isolated tributary, lateral advective flow moves down the side slopes into the tributary and augments convective flow into the tributary. Similar flow of subglacial water may produce a lake under the tributary. Bottom: Lateral advective flow stops when tributaries get packed together as they enter an ice stream."

Caption of the third image of creep curves: "Creep curves for simple shear in polycrystalline ice at −3˚C for applied shear stresses of 117 kPa (curve A) and 55 kPa (curve B). Transient creep dominates for the first 50 to 100 hours of strain, depending on the applied stress. Recrystallization begins at about 20 percent strain. Shear displacements dz were measured on planes normal to x, so ezx = 1/2 (¶dz/¶x + ¶dx/¶z) gives strain ¶dz/¶x = 2ezx. At 55 kPa, recrystallization would begin when 2ezx = 2000 hours, about 17 days."

Caption of the fourth image of creep spectrum: "The viscoplastic creep spectrum for both slow and fast steady-state creep respectively before and after recrystallization. Viscoplastic viscosity hV is the tangent-slope to curves at applied stress s. At plastic yield stress sO the strain rate is change in epsilono for all values of n. Recrystallization produces an easyglide fabric for which sO is reduced. Two viscoplastic yield criteria are shown for ice at viscoplastic yield stress sV at n = 3. The maximum stress-curvature criterion gives sV = 0.386sO. The stress-intercept tangent line at change in epsilono  gives sV = 0.667sO."

[AbruptSLR]

Just want to thank you AbruptSLR for your ongoing posting of these fascinating abstracts, links and your accompanying comments. I wouldn't know where to begin to find all this stuff out but you manage to to distill it out in wonderful digest. Most appreciative.
Tony

Tony,

Thank you for your thoughtful words.  One of my biggest concerns is that consensus climate science is so complex that the general-public cannot appreciate the risks posed by the large number of caveats that a document like AR5 contains.  For example, most people do not know that the CMIP5 projections do a particularly poor job of predicting decadal-scale climate dynamics.  In this regards, the linked reference provides state-of-the-art modeling work with nonlinear decadal-scale interactions between the atmosphere and ocean (see the attached image for an example of how much the Zhang & Kirtman (2019) interactive ensemble (IE) predictions of North Atlantic sea surface temperatures, SSTs, vary from the consensus control predictions:


Wei Zhang & Ben Kirtman (07 March 2019), "Estimates of Decadal Climate Predictability from an Interactive Ensemble Model", Geophysical Research Letters, https://doi.org/10.1029/2018GL081307

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL081307

Abstract: "Decadal climate predictability has received considerable scientific interest in recent years; yet, the limits and mechanisms for decadal predictability are currently not well known. It is widely accepted that noise due to internal atmospheric dynamics at the air‐sea interface influences predictability. The purpose of this paper is to use the interactive ensemble (IE) coupling strategy to quantify how internal atmospheric noise at the air‐sea interface impacts decadal predictability. The IE technique can significantly reduce internal atmospheric noise and has proven useful in assessing seasonal‐to‐interannual variability and predictability. Here we focus on decadal timescales and apply the Nonlinear Local Lyapunov Exponent (NLLE) method to the Community Climate System Model comparing control simulations with IE simulations. This is the first time the NLLE has been applied to the state‐of‐the‐art coupled models. The global patterns of decadal predictability are discussed from the perspective of internal atmospheric noise and ocean dynamics."

Best,
ASLR

P.S.: Obviously, if consensus climate science models currently have a tough time projecting decadal-scale climate change patterns; how can we have confidence that the ocean-ice interaction will not destabilize key Amundsen Sea Embayment, ASE, marine glaciers within the next few decades?

[mitch]

I worry more about nonlinear effects--warming of ice sheets and decrease of viscosity. There is roughly an order of magnitude decrease as an ice sheet warms from -10C to near freezing:
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2015EF000301

The paper is open source.  Colgan et al were arguing for a potential for ice sheet collapse via meltwater transfer of heat to the base of Greenland glaciers. The 'good' news is that it may take 4 centuries. 

[AbruptSLR]

It was previously noted in this thread that the average Antarctic ice mass loss between 2012 and 2017 was three times the average from the 1990s to the 2010s.  Nevertheless, I provide extracts from the first linked article & the linked video & I note that:

a) The first attached image show that prior to 2007 the SLR contribution from small glaciers and icecaps exceeded the combined SLR contributions from the GIS and the AIS; however, the second attached image (from AR5) shows that by 2012 the SLR contribution from small glaciers and icecaps had plateaued while the contributions from the GIS and the AIS were accelerating nonlinearly.  Thus, the rate of measured SLR since 2012 (4.5 mm/yr) is not currently accelerating largely because both the rate of ice mass loss from small glaciers & icecaps is decreasing and also because land storage of water is temporarily increasing.

b) The fact that the GIS is most stable than the WAIS, is only of moderate comfort to me as: 1) the GIS has several large marine terminating glacier that are much less stable that the average GIS stability; and ice-climate feedback from these key Greenland marine terminating glaciers can help to further destabilize the WAIS, via the bipolar seesaw mechanism; and 2) during the Meltwater Pulse 1A (MWP-1A) SLR rose at rates of up to 1m per twenty years, and per Kopp (2012) rapid mass loss from Antarctica predominated the SLR contributions during these high periods (see the third image).

c) Lastly, I note the fourth image shows that the subglacial drainage system beneath the Thwaites Glacier outlets in a concentrated stream near the base of the Thwaites Ice Tongue; which is the least stable part of the WAIS.

Title: "Antarctic ice loss tripled – should we be worried?"

https://citizensclimatelobby.org/antarctic-ice-loss-tripled-should-we-be-worried/

Extracts: "Since the 1990s until the 2010s, about 40% of sea level rise was due to thermal expansion (water expanding as it warms). That’s now down to 30% because melting ice is contributing more and more to sea level rise.

For example, Greenland only contributed about 5% to sea level rise in 1993; now that’s up to 25%. Glacier melt is now up from 20% to about 25% of sea level rise too. The big news from Antarctica brings its contribution up from about 6% to 20% of global sea level rise.

Overall, the rate of sea level rise has accelerated from 1.4 millimeters per year (mm/yr) in the first half of the 20th century to 3.2 mm/yr since the 1990s, and now to 4.5 mm/yr since 2012.  That acceleration is due to the increase in melting ice.
…
… there have been periods in the past when sea level rose as fast as 1 meter every 20 years due to rapidly melting ice.
…
As James Hansen has noted, there’s been about a 100- to 400-year lag before sea level has responded to past natural climate changes, but the current human influence on the climate is much bigger than natural effects, so it could happen even faster this time around."

See also the linked 2013 YouTube video:

Title: "Scientists' Concerns Challenge Conservative Sea-Level Rise Projections"



Kopp (2012), "Tahitian record suggests Antarctica Collapse", Nature 483, 549-550, https://doi.org/10.1038/s483549a

https://www.nature.com/articles/483549a

Extract: "But for the moment, the geographical patterns seen in the sea-level records of MWP-1A argue that the event was caused predominantly by rapid Antarctic melting

See also:

Deschamps, P. et al. (2012), "Ice-sheet collapse and sea-level rise at the Bølling warming 14,600 years ago", Nature 483, 559–564, doi: 10.1038/nature10902

https://www.nature.com/articles/nature10902

Abstract: "Past sea-level records provide invaluable information about the response of ice sheets to climate forcing. Some such records suggest that the last deglaciation was punctuated by a dramatic period of sea-level rise, of about 20 metres, in less than 500 years. Controversy about the amplitude and timing of this meltwater pulse (MWP-1A) has, however, led to uncertainty about the source of the melt water and its temporal and causal relationships with the abrupt climate changes of the deglaciation. Here we show that MWP-1A started no earlier than 14,650 years ago and ended before 14,310 years ago, making it coeval with the Bølling warming. Our results, based on corals drilled offshore from Tahiti during Integrated Ocean Drilling Project Expedition 310, reveal that the increase in sea level at Tahiti was between 12 and 22 metres, with a most probable value between 14 and 18 metres, establishing a significant meltwater contribution from the Southern Hemisphere. This implies that the rate of eustatic sea-level rise exceeded 40 millimetres per year during MWP-1A."

[AbruptSLR]

It is convenient to focus on GMSTA (global mean surface temperature anom.) when talking about climate change projections; however, I have come to appreciate the importance of also tracking Sea Surface Temperature Anom., SSTA, with particular focus on Tropical SSTA.  However, when thinking about SSTA trends, one must simultaneously bear in mind the decadal-scale oscillations of SSTA (& particularly tropical SSTA) when interpreting both the data and the projections.  In this regard, I provide the linked NOAA document issued Feb 14, 2019 entitled: "2018 Annual Ocean Review".  The first attached image from this document shows the global and key regional trends in mean annual SSTA thru 2018.  Interpreting such mean SSTA data can be challenging but I note the following:

a. The global mean annual SSTA has increased rapidly since 2011, reflecting the decreasing influence of La Nina events; which likely means ECS is higher than assumed by consensus climate science.

b. The N. Pac. mean annual SSTA is critical for El Nino formation and this value increased in 2018, just as it did in 2014 (which led to the 2015-16 Super El Nino).

c. The S. Ocean mean annual SSTA increased in 2018, which for me is a very bad signal w.r.t. both Antarctic marine glacier ice, and sea ice, stability.

Also, per the linked NOAA document: "All models favor continuation of El Nino conditions through at least spring 2019".

The last three attached associate images make it clear that the 2018 ENSO behavior has strong similarities to the 2014 ENSO behavior, and we should all remember that the 2014 ENSO behavior led directly to the 2015-16 Super El Nino year.

Title: "2018 Annual Ocean Review" by NCEP/NOAA issued Feb. 14, 2019

https://www.cpc.ncep.noaa.gov/products/GODAS/ocean_briefing_gif/global_ocean_monitoring_current.pdf

Caption for first image:
"- The ERSSTv5 (white line) is compared with daily OISST (DOISST) and HadSST.3.1.0.0. The differences are largely within the 2-σ STD (grey shading).
 
- There was a cooling from 2017 to 2018 in all ocean basins except in the North Pacific and South Ocean, which was probably associated with the impacts of the La Nina of 2017/18. The linear trend of globally averaged SSTA based on ERSSTv5 (oC/decade) is 0.16 in 2000-2018 and 0.1 in 1950–2018.
 
- The largest warming trend (oC/decade) in 1950-2018 was observed in the tropical Indian (0.14), smallest warming in the North Pacific (0.07).
Yearly"

Caption for second image:
"- Compared to the historical El Nino events since 1980, the El Nino development in 2018, measured by NINO3 and NINO4, started with cooler conditions, but cached up after summer, with an amplitude similar to other weak El Ninos.

- Although the evolution of NINO4 and NINO3 in 2018 is very different from that in 2014 in the first half of the year, the conditions in fall/winter are very similar in the two years."

Caption for third image:
"The common features in the El Nino development in 2018 and 2014 include: 
- easterly wind anom. and associated upwelling oceanic Kelvin waves in early summer, and SST cooling in the central-eastern Pacific in summer;
- a late onset of El Nino warming in Oct;
- absence of persistent westerly wind anom. associated with the warming"

Caption for fourth image:
"- Compared to other El Nino events, the WWV in 2018, based on the ensemble mean of 6 ocean reanalyses, was highest in the fall/winter of Year 0. But it has declined rapidly since Oct 2018 and became comparable to other weak warming events in Jan 2019. The current positive WWV provides the necessary conditions for development of a second year warming in 2019."

[AbruptSLR]

When reading the linked article by Jeff Masters on the influence of climate change on the frequency of major (with return periods of 200 to 1,000 years) atmospheric river events for California (ARkStorm events); remember that these evaluations do not consider either high values of ECS nor ice-climate feedback mechanisms:

Title: "A Nearly $1 Trillion California Flood Likely to Occur Within 40 Years" by Jeff Masters issued March 5, 2019

https://www.wunderground.com/cat6/Nearly-1-Trillion-California-Flood-Likely-Occur-Within-40-Years

Extract: "The odds of a 1-in-200-year flood in California costing nearly $1 trillion (4% of U.S. GDP) are steadily rising due to climate change, with a greater than 50% chance of one occurring in the next 40 years.
…
Storms capable of causing a $1 trillion flood in California have hit multiple times in the past, so it is only a matter of time before one occurs again. The most recent one occurred back in the winter of 1861 – 1862. A 45-day period of torrential rains from multiple storms carrying a strong “atmospheric river” (AR) of tropical moisture impacted the state, turning California’s Central Valley into a lake 300 miles long and over 20 miles wide. The resulting floods put downtown Sacramento under 10+ feet of water, forcing movement of the state capital to San Francisco. Sediment research has found that six storms even more severe than the 1861 – 1862 storm hit California in the years 212, 440, 603, 1029, 1418, and 1605 AD.

If a storm with an equivalent amount of precipitation were to hit California now, it might do $900 billion (2019 dollars) in damage, according to a 2011 study by the USGS called the “ARkStorm Scenario” (the “AR” stands for Atmospheric River, and the “k” stands for the number one thousand, since the storm could be expected to bring 1-in-1000-year rains to some locations). The storm they modeled could flood up to 25% of all buildings in the state, breach approximately 50 levees, and force the evacuation of 1.5 million people.
…
The recently released Fourth National Climate Assessment states, “The frequency and severity of landfalling ‘atmospheric rivers’ on the U.S. West Coast … will increase as a result of increasing evaporation and resulting higher atmospheric water vapor that occurs with increasing temperature. (Medium confidence).” The 2018 study led by Swain obtained the same result. They used the NCAR Community Earth System Model to simulate California’s climate in the high-emissions or “business as usual” scenario (RCP8.5, the path humanity is currently on). The model showed that a steadily warmer climate can be expected to make rare 1-in-200-year ARkStorms occur once every 40 or 50 years. The authors wrote, “Strikingly, these findings suggest that California’s major urban centers (including San Francisco and Los Angeles) are more likely than not to experience at least one such extremely severe storm sequence between 2018 and 2060 on a business-as-usual emissions trajectory." That means multiple $1 trillion floods will probably happen in California in coming decades--unless major upgrades to the state's flood-control infrastructure are performed.

Caption for the first image: "Figure 2. Areas of California expected to flood (colored blue) under the 2011 “ARkStorm Scenario” modeled by the USGS."

Caption for the second image: " Figure 3. Number of ARkStorm-like events predicted under a business-as-usual emissions scenario (RCP8.5, thick blue line) by 40 climate simulations from the NCAR Community Earth System Model, along with the number expected in the climate from pre-industrial times (dashed line). The light blue shaded area represents where two-thirds of the model runs predicted an ARkStorm. Image credit: Swain et al., 2018, Increasing precipitation volatility in twenty-first century California, Nature Climate Change.

See also:

Swain et al. (2018), "Increasing precipitation volatility in twenty-first-century California", Nature Climate Change, https://doi.org/10.1038/s41558-018-0140-y

https://www.nature.com/articles/s41558-018-0140-y
&
https://www.nature.com/articles/s41558-018-0140-y.epdf?author_access_token=SpNm1AkLDEG2WYpjrokbt9RgN0jAjWel9jnR3ZoTv0N5WVXwZkTOMe5YxQC6t2N_038NWJlpDOtWZcE65BM0CfIUOL9naHt1EdpF1wss04QU_5ph14XmBsju5RABLAPbKzI7wsRPl9_D-YWN9uCCHA%3D%3D

Abstract: "Mediterranean climate regimes are particularly susceptible to rapid shifts between drought and flood—of which, California’s rapid transition from record multi-year dryness between 2012 and 2016 to extreme wetness during the 2016–2017 winter provides a dramatic example. Projected future changes in such dry-to-wet events, however, remain inadequately quantified, which we investigate here using the Community Earth System Model Large Ensemble of climate model simulations. Anthropogenic forcing is found to yield large twenty-first-century increases in the frequency of wet extremes, including a more than threefold increase in sub-seasonal events comparable to California’s ‘Great Flood of 1862’. Smaller but statistically robust increases in dry extremes are also apparent. As a consequence, a 25% to 100% increase in extreme dry-to-wet precipitation events is projected, despite only modest changes in mean precipitation. Such hydrological cycle intensification would seriously challenge California’s existing water storage, conveyance and flood control infrastructure."

[AbruptSLR]

As a follow-on to my last post about a $1 Trillion ARkStorm event, the linked article focues on the impact of a $1 Trillion Cat. 5 Hurricane event on the world's financial/insurance markets.  Think about Hansen's projections in "Storms of My Grandchildren", when considering the fuller meaning of an 'Ice Apocalypse':

Title: "The $1 Trillion Storm: How a Single Hurricane Could Rupture the World Economy"

https://www.vice.com/en_us/article/wjm78x/the-dollar1-trillion-storm-how-a-single-hurricane-could-rupture-the-world-economy

Extract: "Climate change and a potentially vulnerable insurance market could cause a disaster that starts in South Florida but spreads over the entire globe.
…
… a warmer climate is making hurricanes more severe and destructive. Above-average temperatures are increasing the rainfall of tropical cyclones between 5 to 10 percent, while rising seas add to the intensity of flooding.

At the same time, there are structural aspects of the insurance industry that are more opaque and perhaps riskier than the public thinks, creating the potential for localized financial damage from a massive hurricane to quickly spread internationally, a process similar to what happened during the subprime mortgage crisis in 2008.
…
One version of a worst-case hurricane for Florida is a storm that makes landfall just south of Miami, heads slightly inland, then moves steadily up the east coast.
…
Based on historical experience, it’s reasonable to conclude that even the most destructive catastrophes pose relatively little risk to the wider economy.

But damage over $1 trillion may challenge that logic. “That’s the threshold when these losses have a noticeable impact and spread to the global economy,” Carpenter explained. The Centre for Risk Studies estimated someone with a high quality investment portfolio could see a 6 percent drop in returns following the worst-case Miami hurricane. As financial fallout from the disaster spreads from Florida it may put $2.35 trillion of world GDP at risk.
…
“There are not many journalists paying any attention to the insurance industry,” Ross Hammond, who works on the activist campaign Insure Our Future, told VICE. “But when insurance insiders are making comparisons to the subprime mortgage crash it’s probably worth looking into.”

It blows Hammond’s mind that industry leaders—and our entire society for that matter—continue to treat climate change as an easily predictable threat. “In the case of a Category 5 hurricane hitting Miami,” he said. “That ain’t going to be gradual.”"

[AbruptSLR]

The linked FiveThirtyEight article makes a lot of good points about 'Why Good Politics and Good Climate Science Don't Mix"; and which in my opinion helps to appreciate why consensus climate science tries so hard to ignore dramatic maximum-credible scenarios such as those discussed in this 'Ice Apocalypse' thread (i.e. because consensus scientists are playing politics which does not mix well with good climate science).

Title: "Why Good Politics And Good Climate Science Don’t Mix"

https://fivethirtyeight.com/features/good-climate-science-is-all-about-nuance-good-politics-is-not/

Extract: "Imagine two people walking through a field. One of them tiptoes gingerly, zigging and zagging from one side to another. The other strides confidently straight ahead. Who looks more like they know what they’re doing?

Now what if I told you the field is full of land mines?

Confidence doesn’t equal competence. But our brains tend to assume it does. And that can create big problems when scientific evidence collides with political rhetoric.
…
“Denialism has an advantage. Absolutely. There’s no question,” said Stephan Lewandowsky, professor of cognitive psychology at the University of Bristol in the UK.
…
… the simpler the words are to understand, the clearer and more consistent the narrative is and the more absolute and concrete the claims, the more likely people are to nod along. Anything that makes us briefly confused or makes our train of thought stumble will make an idea less believable.
…
Pretty often, we’re just working off intuition about what seems reasonable, Newman said. And this effect matters to political debates about climate change because scientists and advocates of climate change action often sacrifice smoothness of narrative and ease of processing in favor of nuance and accuracy.

Case in point: The Intergovernmental Panel on Climate Change report.

This is the document that summarizes climate science for politicians and the public. It’s pretty crucial to lay understandings of climate risks and to the crafting of policy meant to address those risks. But a 2015 study showed that the language used in the IPCC report tends to be more cautious, more complex, and less confident than language used by a factually misleading denialist report. The IPCC had more tentative words, more modifiers, more use of passive voice. The other report confidently told a narrative with fewer caveats.

“They have a rhetorical advantage because they don’t have to be scientific. They want to be politically effective. And that makes it very easy to come across as being convincing,” Lewandowsky said.
…
… research has shown that telling people there’s a scientific consensus on climate change makes them more likely to believe in it.
…
Our gut instinct is more likely to believe a person we know, who shares our identities and ideologies. And that means political leadership matters. So when psychologists see bills like the New Green Deal changing the arguments we’re having about climate change policy or Republican politicians coming out as believing in climate change and opposing denialism — those things look like viable paths forward."

As I have indicated before, one way that consensus scientists could engage in better (more effective) climate science reporting would be to create a family of Maximum-credible Climate-risk Scenarios (or MCS similar to the SRES, RCP and SSPs families of scenario) that would better help to evaluate all of the caveats that consensus scientists put in to AR5 (and/or into AR6). 

As consensus climate scientists are genuinely concerned about the nonlinearities associate with assessing the risks of extreme climate hazards; I recommend that such MCSs through 2100 be created by only the top climate change experts in each field.  An example of such a MCS associated with the version of the 'Ice Apocalypse' that I have presented (using guidance from top experts like Hansen, Rignot, Pollard, DeConto etc.) in this thread might roughly go something like the following:

1. Assume that Mid-Pliocene conditions could occur as early as 2040 +/- 5 years (see the first image showing that GMSTA will exceed 2C by 2040 for the mean probability of SSP5-Baseline).  Also, assume that all ASE ice shelves have collapsed before 2040.

2. Use per DeConto, Pollard & Alley (2018) to estimate the amount of freshwater hosing from 2040 to 2100 (see the second attached image), and introduce Pollard's hydrofracturing and ice cliff model, with this calibration, into E3SM.  Run this updated version of E3SM [calibrated per DeConto, Pollard & Alley (2018)] using SSP5-Baseline thru 2060, followed by an assumed worldwide socioeconomic collapse.

3. Also, upgrade E3SM to use the aerosol cloud radiative forcing feedback sensitivity reported by Rosenfeld et al (2019), see Reply #519, and assume that after 2060 anthropogenic aerosol emissions drop to near zero, and that anthropogenic GHG emissions drop to SSP1 (starting with the SSP1 value for 2060).

It would be interesting to see what such an upgraded version of E3SM would project, following the MCS case cited above.

[Sleepy]

This EPA report from 1983 showed 2°C in 2040.
Record emissions in 2018 and continuing warm ENSO conditions projected for 2019 won't delay warming.

Can we delay a greenhouse warming?
The Effectiveness and Feasibility of Options to Slow a Build-up of Carbon Dioxide in the Atmosphere
https://cfpub.epa.gov/ols/catalog/advanced_brief_record.cfm?&FIELD1=AUTHOR&INPUT1=STEPHEN%20AND%20L.&TYPE1=ALL&LOGIC1=AND&COLL=&SORT_TYPE=MTIC&item_count=34&item_accn=61312
http://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=9101HEAX.PDF

[AbruptSLR]

To stay current on our GHG situation and local temperature changes, you can visit the following linked sites:

Title: "Greenhouse Gas Factsheets"

http://greenhousegases.science.unimelb.edu.au/#!/view

Extract: "This webpage offers comprehensive, interactive plots, factsheets and data download options for atmospheric surface concentrations of 43 greenhouse gases and 3 equivalent gas time series from 2000 years ago to the year 2500.

& The electronic input of the SSP series into CMIP6 can be found at:

Title: "input4MIPs: Boundary Condition and Forcing Datasets for CMIP6"

https://esgf-node.llnl.gov/projects/input4mips/

Also see:

Title: "Mapped: How every part of the world has warmed – and could continue to warm"

https://www.carbonbrief.org/mapped-how-every-part-of-the-world-has-warmed-and-could-continue-to-warm

[vox_mundi]

Game Over Man; Game Over! ...

Few Pathways to an Acceptable Climate Future Without Immediate Action
https://phys.org/news/2019-03-pathways-climate-future-action.html

...The massive analysis shows that meeting the 2.00 C target is exceptionally difficult in all but the most optimistic climate scenarios. One pathway is to immediately and aggressively pursue carbon-neutral energy production by 2030 and hope that the atmosphere's sensitivity to carbon emissions is relatively low, according to the study. If climate sensitivity is not low, the window to a tolerable future narrows and in some scenarios, may already be closed.

... If the climate sensitivity is greater than 3.00K (median of assumed distribution), the pathway to a tolerable future is likely already closed. 



Robust abatement pathways to tolerable climate futures require immediate global action, Nature Climate Change (2019).

[AbruptSLR]

This EPA report from 1983 showed 2°C in 2040.
...

Also, the linked 2016 reference calibrated an effective/specific equilibrium climate sensitivity (S) based on warming cycles during the past 784,000 years.  Their findings for the upper end risk (e.g. RCP 8.5) indicated that the projected average GMSTA would slightly exceed 2C by 2040 (see the attached images).

Tobias Friedrich, Axel Timmermann, Michelle Tigchelaar, Oliver Elison Timm and Andrey Ganopolski (09 Nov 2016), "Nonlinear climate sensitivity and its implications for future greenhouse warming", Science Advances, Vol. 2, no. 11, e1501923, DOI: 10.1126/sciadv.1501923

http://advances.sciencemag.org/content/2/11/e1501923

Edit: For those who do not know, SSP5-Baseline is more aggressive than RCP 8.5, so the Friedrich et al. 2016 projection is conservative.

[AbruptSLR]

As a follow-on to Replies #719 & #723:

I note that Hawkins et al (2017) defines the pre-industrial baseline to be from 1720-1800 for determining GMSTA, and indicates that as both the CMIP5 and the AR5 projections were baselined to the 1896-2005 baseline (see first image that gives various AR5 baselines), one needs to add between 0.55 and 0.80C (which has a mean value of 0.675C) to the published CMIP5 and AR5 projections values to get correct values for GMSTA.

As the second image from the second linked article by Clive Best indicates that the mean value of the CMIP5 runs for RCP 8.5 in 2040 is about 1.7C, this implies that referenced to pre-industrial for RCP 8.5 (which is less aggressive than SSP5-Baseline) GMSTA in 2040 would be about 2.375C (which is above Mid-Pliocene conditions):

Ed Hawkins et al. (2017), "Estimating Changes in Global Temperature since the Preindustrial Period", BAMS, https://doi.org/10.1175/BAMS-D-16-0007.1

https://journals.ametsoc.org/doi/full/10.1175/BAMS-D-16-0007.1

Abstract: "The United Nations Framework Convention on Climate Change (UNFCCC) process agreed in Paris to limit global surface temperature rise to “well below 2°C above pre-industrial levels.” But what period is preindustrial? Somewhat remarkably, this is not defined within the UNFCCC’s many agreements and protocols. Nor is it defined in the IPCC’s Fifth Assessment Report (AR5) in the evaluation of when particular temperature levels might be reached because no robust definition of the period exists. Here we discuss the important factors to consider when defining a preindustrial period, based on estimates of historical radiative forcings and the availability of climate observations. There is no perfect period, but we suggest that 1720–1800 is the most suitable choice when discussing global temperature limits. We then estimate the change in global average temperature since preindustrial using a range of approaches based on observations, radiative forcings, global climate model simulations, and proxy evidence. Our assessment is that this preindustrial period was likely 0.55°–0.80°C cooler than 1986–2005 and that 2015 was likely the first year in which global average temperature was more than 1°C above preindustrial levels. We provide some recommendations for how this assessment might be improved in the future and suggest that reframing temperature limits with a modern baseline would be inherently less uncertain and more policy relevant."
&

Extract: "We have examined estimates of historical radiative forcings to determine which period might be most suitable to be termed preindustrial and used several approaches to estimate a change in global temperature since this preindustrial reference period. The main conclusions are as follows:

1.   The 1720–1800 period is most suitable to be defined as preindustrial in physical terms, although we have incomplete information about the radiative forcings and very few direct observations during this time. However, this definition offers a target period for future analysis and data collection to inform this issue.
2.   The 1850–1900 period is a reasonable pragmatic surrogate for preindustrial global mean temperature. The available evidence suggests it was slightly warmer than 1720–1800 by around 0.05°C, but this is not statistically significant.
3.   We assess a likely range of 0.55°–0.80°C for the change in global average temperature from preindustrial to 1986–2005.
4.   We also consider a likely lower bound on warming from preindustrial to 1986–2005 of 0.60°C, implying that the AR5 estimate of warming was probably too small and that 2015 was the first year to be more than 1°C above preindustrial levels."
&

Title: "A comparison of CMIP5 Climate Models with HadCRUT4.6" January 21, 2019 by Clive Best

http://clivebest.com/blog/?p=8788

Caption for the second image: Model comparisons to HadCRUT4.6. Spaghetti are individual annual model results for each RCP. Solid curves are model ensemble annual averages.

[AbruptSLR]

The thing that I do not feel good about my last Reply #724, is that per the attached image (second panel) from Kriegler et al (2017), for 2040 RCP 8.5 indeed does project a GMSTA of 1.7C while SSP5 projects a value of 2C; which implies that they are both using 1986-2005 as a reference baseline datum.

Kriegler et al (2017), "Fossil-fueled development (SSP5): An energy and resource intensive scenario for the 21st century", Global Environmental Change, Volume 42, Pages 297-315, https://doi.org/10.1016/j.gloenvcha.2016.05.015

https://www.sciencedirect.com/science/article/pii/S0959378016300711

Therefore if Hawkins et al. (2017) is correct and to get from a 1986-2005 baseline to a preindustrial baseline on needs to add an average of 0.675C then the SSP5-Baseline projection for 2040 would be 2C + 0.675C = 2.675C (which to me implies that CMIP6 models assume that ECS is significantly higher than 3C).

Edit:

Per the linked Gavin Schmidt tweeter thread, for a 20yr loess trend line Gavin is predicting that the GMSTA in 2019 will be 1.2+/-0.15C (see the see second attached image) or 1.23C for a 15yr loess trend line (see the extract below).  I note that this prediction is in line with the SSP5-Baseline projection for 2019 shown in the first image:

https://twitter.com/ClimateOfGavin/status/1068336654887337984

Extract: "ENSO forecast for DJF here: https://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/ … (I used 1±0.6 (95% CI)). Note there is also some dependence on the smoothing; predictions for 2019 would be 1.23 or 1.17 using a 15yr or 30yr loess smooth....1.2±0.15 ºC above the late 19th C. A warmer yr than 2018 (which will #4), almost certain >1ºC yr, and 1 in 3 chance of a new record."

[AbruptSLR]

In my last post, the second image shows Gavin Schmidt's GMSTA predictions using Goddard Institute for Space Studies (GISS) temperature data which gives a value of GMSTA in 2018 of about 1.05C (above the late 19th Century).  However, it is a matter of opinion as to whether GISS temperature data accurately represents GMSTA, therefore I provide the linked information that indicates that Berkeley Earth calculated a value of GMSTA in 2018 of 1.16C (above the late 19th Century); which is 0.11C above Gavin's prediction.  Thus Gavin's prediction for 2019 may very well be underestimating GMSTA by about 0.11C; and if adjusted his 1.23C (with 15-yr smoothing) value might well be about 1.36C.

However, Hawkins et al. (2017) indicates that the mid-18th Century was about 0.05C cooler than the late 19th Century.  So if we were to again correct Gavin's GISS-based GMSTA prediction for 2019, we would get a value of about 1.41C above 'preindustrial'. 

Title: "Global Temperature Report for 2018"

http://berkeleyearth.org/2018-temperatures/

Extract: "In our estimation, temperatures in 2018 were around 1.16 °C (2.09 °F) above the average temperature of the late 19th century, from 1850-1900, a period often used as a pre-industrial baseline for global temperature targets."

Consensus climate scientists are perfectly capable of calculating and presenting GMSTA predictions (above preindustrial) for 2019 of 1.41C; however, they choose to present less dramatic values for political reasons.

Note I provide the attached Berkeley Earth chart of Land and Ocean temperature anomalies (relative to the late 19th Century) from 1850 to 2018 in order to emphasis that the land and ocean temperature anomalies began to diverge from each other prior to 1900; which means that slow response ocean positive feedback mechanisms have been slowly begun activating since at least 1900.  Also, note that land surface temp. anomalies have been increasing at twice the rate of SSTA, and as well all live on the land, we should be aware of that trend.

[AbruptSLR]

One of the reasons that SSP5-Baseline is more aggressive than RCP 8.5, is that RCP 8.5 assumed that methane emissions would be better regulated than the subsequently observed methane emissions have indicated.  Also, I note that SSP5-Baseline uses MAGICC to calculate the effective radiative forcing of methane emissions (see the first image) where are higher than previously assumed by consensus science.

The linked reference shows the significant impact of methane on climate change, when appropriately considering both the direct and indirect forcing contributions (see the attached image):

Ocko, I. B., Naik, V., and Paynter, D.: Rapid and reliable assessment of methane impacts on climate, Atmos. Chem. Phys., 18, 15555-15568, https://doi.org/10.5194/acp-18-15555-2018, 2018.

https://www.atmos-chem-phys.net/18/15555/2018/

Abstract. It is clear that the most effective way to limit global temperature rise and associated impacts is to reduce human emissions of greenhouse gases, including methane. However, quantification of the climate benefits of mitigation options are complicated by the contrast in the timescales at which short-lived climate pollutants, such as methane, persist in the atmosphere compared to carbon dioxide. Whereas simple metrics fail to capture the differential impacts across all timescales, sophisticated climate models that can address these temporal dynamics are often inaccessible, time-intensive, require special infrastructure, and include high unforced interannual variability that makes it difficult to analyse small changes in forcings. On the other hand, reduced-complexity climate models that use basic knowledge from observations and complex Earth system models offer an ideal compromise in that they provide quick, reliable insights into climate responses, with only limited computational infrastructure needed. They are particularly useful for simulating the response to forcings of small changes in different climate pollutants, due to the absence of internal variability. In this paper, we build on previous evaluations of the freely available and easy-to-run reduced-complexity climate model MAGICC by comparing temperature responses to historical methane emissions to those from a more complex coupled global chemistry–climate model, GFDL-CM3. While we find that the overall forcings and temperature responses are comparable between the two models, the prominent role of unforced variability in CM3 demonstrates how sophisticated models are potentially inappropriate tools for small forcing scenarios. On the other hand, we find that MAGICC can easily and rapidly provide robust data on climate responses to changes in methane emissions with clear signals unfettered by variability. We are therefore able to build confidence in using reduced-complexity climate models such as MAGICC for purposes of understanding the climate implications of methane mitigation.

Furthermore, the linked Columbia website (reflective James Hansen's thinking, see the second attached image, and note that Hansen et al 2017 values for effective radiative forcing for methane are close to the sum of the direct and indirect radiative forcing for methane shown in the first attached image) discusses effective radiative forcing, and it calculates the effective radiative forcing of methane to include: "… simulated CH4-induced changes of O3 and stratospheric H2O …".

Title: "Radiative Forcings"

http://www.columbia.edu/~mhs119/Forcings/

Extract: "Fe provides a good prediction of the response to different forcing amounts.

The time dependent effective forcings relative to 1850 for the agents used in our computations are shown individually and as the total in the graph below."

See also:

Hansen et al (2017), "Young people’s burden: requirement of negative CO₂ emissions", Earth Syst. Dynam., 8, 577–616, https://doi.org/10.5194/esd-8-577-2017

https://www.earth-syst-dynam.net/8/577/2017/esd-8-577-2017.pdf

Extract: "The CH4 forcing includes its indirect effects, as increasing atmospheric CH4 causes tropospheric ozone (O3) and stratospheric water vapor to increase (Myhre et al., 2013)."

Such estimates of the effective radiative forcing contribution from methane, help to explain why we will likely reach Pliocene conditions by 2040.

[AbruptSLR]

Two first two linked studies published last year in Nature suggest the AMOC had slowed down by 15 per cent since the mid-20th century, which raises the probability that changes in the MOC could be one of the key mechanisms that could contribute to the WAIS beginning a MICI type of collapse mode by 2040; which in-turn could trigger a cascade of tipping points (including an abrupt slow down of the MOC):

Caesar, L. et al. Observed fingerprint of a weakening Atlantic Ocean overturning circulation. Nature (2018). DOI: 10.1038/s41586-018-0006-5

https://www.nature.com/articles/s41586-018-0006-5

Extract: "Continued global warming is likely to further weaken the AMOC in the long term, via changes to the hydrological cycle, sea-ice loss and accelerating melting of the Greenland Ice Sheet, causing further freshening of the northern Atlantic.  Given that the AMOC is one of the well documented 'tipping elements', it is of considerable concern that the proximity of the Atlantic to this threshold is still poorly known."
&

Lozier, M.S. et al. A sea change in our view of overturning in the subpolar North Atlantic. 2019. Science. Vol. 363, Issue 6426, pp. 516-521. DOI: 10.1126/science.aau6592.

http://science.sciencemag.org/content/363/64

Abstract: "To provide an observational basis for the Intergovernmental Panel on Climate Change projections of a slowing Atlantic meridional overturning circulation (MOC) in the 21st century, the Overturning in the Subpolar North Atlantic Program (OSNAP) observing system was launched in the summer of 2014.The first 21-month record reveals a highly variable overturning circulation responsible for the majority of the heat and freshwater transport across the OSNAP line. In a departure from the prevailing view that changes in deep water formation in the Labrador Sea dominate MOC variability, these results suggest that the conversion of warm, salty, shallow Atlantic waters into colder, fresher, deep waters that move southward in the Irminger and Iceland basins is largely responsible for overturning and its variability in the subpolar basin.:

See also:

Rhein, M. Taking a close look at ocean circulation. Science (2019). DOI: 10.1126/science.aaw3111

[AbruptSLR]

As the effective GWP for methane emissions is at least 34, the linked reference on methane and carbon dioxide fluxes from a tropical flooded forest should be cause for concept.  Further, I note that if ENSO induced droughts accelerate the degradation of the Amazon rainforest in the next few decades, the methane emissions associated with the seasonally submerged dead vegetation will continue/accelerate; while the absorption of carbon dioxide will decrease sharply:

Higo J. Dalmagro et al. (10 March 2019), "Radiative forcing of methane fluxes offsets net carbon dioxide uptake for a tropical flooded forest", Global Change Biology, https://doi.org/10.1111/gcb.14615

https://onlinelibrary.wiley.com/doi/abs/10.1111/gcb.14615

Abstract: "Wetlands are important sources of methane (CH4) and sinks of carbon dioxide (CO2). However, little is known about CH4 and CO2 fluxes and dynamics of seasonally flooded tropical forests of South America in relation to local carbon (C) balances and atmospheric exchange. We measured net ecosystem fluxes of CH4 and CO2 in the Pantanal over 2014‐2017 using tower‐based eddy covariance along with C measurements in soil, biomass and water. Our data indicate that seasonally‐flooded tropical forests are potentially large sinks for CO2 but strong sources of CH4, particularly during inundation when reducing conditions in soils increase CH4 production and limit CO2 release. During inundation when soils were anaerobic, the flooded forest emitted 0.11±0.002 g CH4‐C m−2 d−1 and absorbed 1.6±0.2 g CO2‐C m−2 d−1 (mean±95% confidence interval for the entire study period). Following the recession of floodwaters, soils rapidly became aerobic and CH4 emissions decreased significantly (0.002±0.001 g CH4‐C m−2 d−1) but remained a net source, while the net CO2 flux flipped from being a net sink during anaerobic periods to acting as a source during aerobic periods. CH4 fluxes were 50 times higher in the wet season; DOC was a minor component in the net ecosystem carbon balance. Daily fluxes of CO2 and CH4 were similar in all years for each season, but annual net fluxes varied primarily in relation to flood duration. While the ecosystem was a net C sink on an annual basis (absorbing 218 g C m−2 (as CH4‐C+CO2‐C) in anaerobic phases and emitting 76 g C m−2 in aerobic phases), high CH4 effluxes during the anaerobic flooded phase and modest CH4 effluxes during the aerobic phase indicate that seasonally flooded tropical forests can be a net source of radiative forcings on an annual basis, thus acting as an amplifying feedback on global warming."

[AbruptSLR]

The linked reference explains a critical risk to permafrost degradation in both northern Canada and eastern Siberia.  That is that the recent "… enhanced summertime blocking activity in the Greenland region seems responsible for the positive trend in the geopotential height …", which causes atmospheric moisture fluxes over these regions, which enhances downward infrared radiation to the surface.  This is a positive feedback mechanism for accelerating Arctic Amplification:

Sai Wang et al. (11 March 2019), "Recent strengthening of Greenland blocking drives summertime surface warming over northern Canada and eastern Siberia", Journal of Climate, https://doi.org/10.1175/JCLI-D-18-0410.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-18-0410.1

Abstract: "In the last three decades, rapid surface warming is observed in the land areas of northern high-latitudes during boreal summer months. Although the warming trend is thought to be driven by early snowmelt, however, the exact causes, especially its relationship with atmospheric circulation changes remains a subject of debate. By analyzing the ERA-Interim data, this study examines the possible factors for rapid sub-Arctic warming. It is found that more than half of the warming trend over whole sub-Arctic and 80% over Northern Canada and Eastern Siberia (regions with maximum amplification) can be explained by an enhanced downward infrared radiation (IR). Downward IR is largely drives by horizontal atmospheric moisture flux convergence and warm air advection. The positive trend in geopotential height over the Greenland region is the key for moisture fluxes convergence over northern Canada and over eastern Siberia through changes in the storm tracks. An enhanced summertime blocking activity in the Greenland region seems responsible for the positive trend in the geopotential height."

[AbruptSLR]

For those who are interested, machine learning is now providing improved estimates of climate feedbacks:

Tingting Zhu et al. (10 March 2019), "Estimating Climate Feedbacks Using a Neural Network", JGR Atmospheres, https://doi.org/10.1029/2018JD029223

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018JD029223

Abstract: "A nonlinear method has been developed to estimate climate feedbacks based on the Neural Network (NN) taking advantage of its self‐learning skills. The NN model developed here is trained using a reanalysis dataset and predicts radiation flux globally from atmospheric and surface variables. The radiative feedbacks of temperature, water vapor, surface albedo and cloud in the interannual climate variations estimated from the NN method are in agreement with those from a broadly used kernel method. However, the NN method demonstrates significant advantages: 1) it withdraws the linearity assumption of the kernel method and accounts for the nonlinear effects of the feedbacks. In the case of large climate perturbations, such as that in the Arctic caused by sea ice melt, the NN method achieves better radiation closure. 2) The method can directly calculate the radiative feedback of cloud and its components. We find that the high, middle and low cloud feedback components analyzed from the NN method are linearly additive in the interannual climate variations, although there is a considerable nonlinear effect arising from the interactions between cloud and noncloud variables."

[AbruptSLR]

In this post I make a very few comments about the SSP scenarios in general and about SSP5-Baseline in particular:

1. The SSP scenarios are primarily an expression of the priorities of the Intergovernmental Panel on Climate Change, IPCC, and they are not an expression of the IPCC of what probably will happen with regards to future radiative forcing.  Being a governmental body the IPCC reviews and accepts the SSP scenarios, but all of the Assessment Reports contain a disclaimer disavowing any responsibility that any of the SSPs will likely represent what will actually happen.

2. Consensus climate scientist are spending a great deal of time and resources evaluating SSP scenarios within CMIP6; which clearly will never happen; which in my opinion means that they are diverting both resources and public attention away from higher risk scenarios which have a higher probability of actually happening.  Such a diversion of resources and attention away higher risk scenarios increases the probability that such high risk scenarios will actually happen (including events like: strong ice-climate events; wars, socioeconomic collapse, famine, climate related mass human migration, disease, and bad governmental policies & decisions).

3. With regard to SSP5-Baseline:
a) We have seen that it uses 1986-2005 as a temperature reference baseline datum; while if Hawkins et al. (2017) is correct one needs to add about 0.675C (or at least 0.6C) to the projected values; which means not only are we closer to Mid-Pliocene conditions than most people assume, but also that ECS is higher than AR5 assumes.

b) This scenario assumes that human population will peak around 8 billion people, while next month human population should reach about 7.7 billion people, and appears to have a 50%-50% chance of reaching 10 billion by 2050.  Governmental policies focuses on decreasing the price of sustainable energy without increasing the price of carbon energy, will likely increase the per capita energy use of around 10 billion people by 2050.

c) This scenario focuses too much on continued fossil fuel use after the 2050 to 2060 timeframe, which causes critics to dismiss it as being improbable, while we are currently following it and are not likely to get off a BAU pathway before 2040.  This focus on GHG radiative forcing after the 2040 to 2060 timeframe diverts attention and effort from such radiative forcing agents as freshwater hosing events and changes in aerosols that could very likely replace any change in radiative forcing associated with a socioeconomic drop in fossil fuel GHG emissions in the 2040 to 2060 timeframe.

[AbruptSLR]

While the authors of the linked reference are not the first researchers to use a chemistry-climate model to assess climate impacts of abrupt increases in atmospheric methane concentrations, their work and findings are an improvement on earlier published efforts in this matter.  Some of their improved findings include that an abrupt increase in methane concentration (say from permafrost, peatland and/or tropical rainforest degradation together with high anthropogenic methane emissions) would help to sustain the Antarctic ozone hole; which would sustain strong westerly winds around the Southern Ocean; which would sustain/accelerate rapid ice mass loss from associated Antarctic marine glaciers:

Franziska Winterstein et al. (2019), "Implication of extreme atmospheric methane concentrations for chemistry-climate connections", Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2019-41

https://www.atmos-chem-phys-discuss.net/acp-2019-41/acp-2019-41.pdf

Abstract. Methane (CH4) is the second most important greenhouse gas, which atmospheric concentration is influenced by human activities. In this study, numerical simulations with a chemistry-climate model (CCM) are performed aiming to assess possible consequences of significantly enhanced CH4 concentrations in the Earth’s atmosphere for the climate.

We analyze experiments with 2xCH4 and 5xCH4 present day (2010) mixing ratio and its quasi-instantaneous chemical impact on the atmosphere. The massive increase in CH4 strongly influences the tropospheric chemistry by reducing the hydroxyl radical (OH) abundance and thereby extending the CH4 lifetime as well as the residence time of other chemical pollutants. The region above the tropopause is impacted by a substantial rise in stratospheric water vapor (SWV). The stratospheric ozone (O3) column increases overall, but SWV induced stratospheric cooling also leads to a enhanced ozone depletion in the Antarctic lower stratosphere. Regional patterns of ozone change are affected by modification of stratospheric dynamics, i.e. increased tropical up-welling and stronger meridional transport towards the polar regions. We calculate the net radiative impact (RI) of the 2xCH4 experiment to be 0.69 W/m2 and for the 5xCH4 experiment to be 1.79 W/m2. A substantial part of the RI is contributed by chemically induced O3 and SWV changes, in line with previous radiative forcing estimates.

To our knowledge this is the first numerical study using a CCM with respect to two/fivefold CH4 concentrations and it is therefore an overdue analysis as it emphasizes the impact of possible strong future CH4 emissions on atmospheric chemistry and its feedback on climate.

[AbruptSLR]

Without getting too specific, in the linked article Kate Marvel indicates that in her experience the scientists who study paleo-climate events are most concerned about Earth's future climate.  Then she notes that we may very well be headed towards future dynamic climatic responses that are more extreme than anything observed in past 'Deep Time' (say at least over the past hundred million years):

Title: "Deep Time" by Kate Marvel, in SciAm, March 11, 2019

https://blogs.scientificamerican.com/hot-planet/deep-time/

Extract: "I have found that the scientists who study the Earth's past are often the most alarmed about its future.
…
We may be headed to something far different than anything in the whole history of Earth."

[AbruptSLR]

I suspect that the bipolar seesaw has something to do with observed trends of the Southern Ocean carbon sink; but who knows what the future holds for this issue.

R. Ritter et al. (4 December 2017), "Observation-based Trends of the Southern Ocean Carbon Sink", Geophysical Research Letters, DOI: 10.1002/2017GL074837

http://onlinelibrary.wiley.com/doi/10.1002/2017GL074837/abstract?utm_content=buffer0a4fc&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "The Southern Ocean (SO) carbon sink has strengthened substantially since the year 2000, following a decade of a weakening trend. However, the surface ocean pCO2 data underlying this trend reversal are sparse, requiring a substantial amount of extrapolation to map the data. Here, we use 9 different pCO2 mapping products to investigate the SO trends and their sensitivity to the mapping procedure. We find a robust temporal coherence for the entire SO, with 8 of the 9 products agreeing on the sign of the decadal trends, i.e., a weakening CO2 sink trend in the in the 1990s (on average 0.22±0.24 Pg C yr−1 decade−1), and a strengthening sink trend during the 2000s (-0.35±0.23 Pg C yr−1 decade−1). Spatially, the multi-product mean reveals rather uniform trends, but the confidence is limited, given the small number of statistically significant trends from the individual products, particularly during the data sparse 1990-1999 period."

[AbruptSLR]

The linked article compares the atmospheric carbon accumulation rates for both PETM and Modern emission rates and presents the attached image that indicates that following RCP 8.5 carbon emission rates we could reach the minimum estimates for the PETM within 140 years (from 2019).  However, I note that SSP5-Baseline assumes higher carbon emission rates than does RCP 8.5; and also I note that abrupt temporary perturbations to radiative forcing say from decades long ice-climate feedback from a WAIS collapse and methane emissions from thermokarst lakes and a sharp drop in aerosol emissions, we could cascade to an equable climate well before reaching PETM levels of accumulated carbon in the atmosphere:

Philip D. Gingerich (30 January 2019), "Temporal Scaling of Carbon Emission and Accumulation Rates: Modern Anthropogenic Emissions Compared to Estimates of PETM Onset Accumulation", Paleoceanography and Paleoclimatology, https://doi.org/10.1029/2018PA003379

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018PA003379

Abstract
The Paleocene‐Eocene thermal maximum (PETM) was caused by a massive release of carbon to the atmosphere. This is a benchmark global greenhouse warming event that raised temperatures to their warmest since extinction of the dinosaurs. Rates of carbon emission today can be compared to those during onset of the PETM in two ways: (1) projection of long‐term PETM rates for comparison on an annual time scale and (2) projection of short‐term modern rates for comparison on a PETM time scale. Both require temporal scaling and extrapolation for comparison on the same time scale. PETM rates are few and projection to a short time scale is poorly constrained. Modern rates are many, and projection to a longer PETM time scale is tightly constrained—modern rates are some 9–10 times higher than those during onset of the PETM. If the present trend of anthropogenic emissions continues, we can expect to reach a PETM‐scale accumulation of atmospheric carbon in as few as 140 to 259 years (about 5 to 10 human generations).

Plain Language Summary
The Paleocene‐Eocene thermal maximum (PETM) is a global greenhouse warming event that happened 56 million years ago, causing extinction in the world's oceans and accelerated evolution on the continents. It was caused by release of carbon dioxide and other greenhouse gases to the atmosphere. When we compare the rate of release of greenhouse gases today to the rate of accumulation during the PETM, we must compare the rates on a common time scale. Projection of modern rates to a PETM time scale is tightly constrained and shows that we are now emitting carbon some 9–10 times faster than during the PETM. If the present trend of increasing carbon emissions continues, we may see PETM‐magnitude extinction and accelerated evolution in as few as 140 years or about five human generations.

Caption for the attached image: "Model for carbon accumulation as the sum of carbon emissions, based on the steady increase in emissions and emission rates shown in Figure 1. Red circles are annual accumulations through 2015. If the recent trend in emissions continues, we can expect to reach the minimum estimate for PETM‐scale carbon accumulation in the year 2159 and the maximum estimate for PETM‐scale carbon accumulation in the year 2278. The light red band illustrates the range of PETM values for carbon accumulation (Table 1). The range of PETM values brackets the mass of carbon thought to remain in fossil fuel reserves (Archer et al., 2009). Finally, the petagrams of carbon trajectory shown here, logged, resembles the upper bound for carbon emissions in the Representative Concentration Pathway or RCP 8.5 model of the Intergovernmental Panel on Climate Change (Ciais et al., 2013). PETM = Paleocene‐Eocene thermal maximum."

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The linked reference presents findings the lead time for triggering releases of equatorial Pacific warm water volume (WWV) eastward has decreased from 6 to 9 months before 2000 to 3 months since 2000.  This could help to explain the increasing frequency of El Nino events (note that if the WWV is not released eastward, it spills over into the Indian Ocean).  This is an indication that ECS has increased since 2000:

S. Neske and S. McGregor (25 January 2018), "Understanding the Warm Water Volume Precursor of ENSO Events and its Interdecadal Variation", Geophysical Research Letters, https://doi.org/10.1002/2017GL076439

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2017GL076439

Abstract: "A wind forced ocean model is used to decompose the equatorial Pacific warm water volume (WWV) between 1980 and 2016 into two components: the (i) adjusted wind response, which is found by letting the model evolve unforced for three months, and (ii) instantaneous wind response, which are the instantaneous WWV changes due to Ekman transports. Our results suggest that roughly half of WWV variability is only as predictable as the winds that drive the instantaneous change. Separate examinations of pre‐2000 and post‐2000 periods reveal (i) nearly equal importance of instantaneous and adjusted responses for the pre‐2000 period and (ii) dominance of the instantaneous response during the post‐2000 period, which is most apparent during the recharged phase. This increasing instantaneous contribution prominence explains the post‐2000 reduction in WWV/El Niño‐Southern Oscillation sea surface temperature lead times (from six to nine months pre‐2000 down to three months post‐2000) and is consistent with the reduction in post‐2000 El Niño‐Southern Oscillation prediction skill."

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The linked reference indicates that ocean circulation (which will be increasingly influenced by ice-climate feedback mechanisms in coming decades) has a stronger influence on the Atlantic Multidecadal Oscillation, AMO, than recognized by most current climate models.  Hopefully, CMIP6 models will improve upon past climate model performance in this regard:

Robert C. J. Wills, Kyle C. Armour, David S. Battisti, and Dennis L. Hartmann (2019), "Ocean–Atmosphere Dynamical Coupling Fundamental to the Atlantic Multidecadal Oscillation", Journal of Climate, https://doi.org/10.1175/JCLI-D-18-0269.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-18-0269.1

Abstract: "The North Atlantic has shown large multidecadal temperature shifts during the twentieth century. There is ongoing debate about whether this variability arises primarily through the influence of atmospheric internal variability, through changes in ocean circulation, or as a response to anthropogenic forcing. This study isolates the mechanisms driving Atlantic sea surface temperature variability on multidecadal time scales by using low-frequency component analysis (LFCA) to separate the influences of high-frequency variability, multidecadal variability, and long-term global warming. This analysis objectively identifies the North Atlantic subpolar gyre as the dominant region of Atlantic multidecadal variability. In unforced control runs of coupled climate models, warm subpolar temperatures are associated with a strengthened Atlantic meridional overturning circulation (AMOC) and anomalous local heat fluxes from the ocean into the atmosphere. Atmospheric variability plays a role in the intensification and subsequent weakening of ocean overturning and helps to communicate warming into the tropical Atlantic. These findings suggest that dynamical coupling between atmospheric and oceanic circulations is fundamental to the Atlantic multidecadal oscillation (AMO) and motivate approaching decadal prediction with a focus on ocean circulation."

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Similar to my last post, the linked reference finds that the Pacific Decadal Oscillation, PDO, is heavily influenced by ocean circulation patterns (which will be increasingly influenced by ice-climate feedback mechanisms in coming decades).  As the PDO plays a major role in the ENSO and El Nino frequency, it will be interesting to see how continued global warming influences the PDO-ENSO dynamic:

Robert C. J. Wills et al. (15 January 2019), "Ocean Circulation Signatures of North Pacific Decadal Variability", Geophysical Research Letters, https://doi.org/10.1029/2018GL080716

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2018GL080716

Abstract
The Pacific Decadal Oscillation (PDO) is the dominant pattern of observed sea surface temperature variability in the North Pacific. Its characteristic pattern of eastern intensified warming and cooling within the Kuroshio‐Oyashio Extension is pervasive across timescales. We investigate the mechanisms for its decadal persistence in coupled climate models, focusing on the role of ocean circulation changes. We use low‐frequency component analysis to isolate the mechanisms relevant at decadal and longer timescales from those acting at shorter timescales. The PDO warm phase is associated with strengthening and expansion of the North Pacific subpolar gyre in response to a deepening of the Aleutian Low. The subpolar gyre takes several years to respond to wind stress forcing through baroclinic ocean Rossby wave adjustment, such that white noise atmospheric forcing is integrated into red noise, increasing variability at long timescales. Sea level anomalies within the Kuroshio‐Oyashio Extension provide an observable ocean circulation signature of North Pacific decadal variability.

Plain Language Summary
North Pacific sea surface temperatures vary from decade to decade with a characteristic pattern, where temperature anomalies near North America are opposite to those off the coast of Japan. These ocean changes influence fish populations as well as climate over the surrounding land regions. Here we investigate the physical mechanisms for this sea surface temperature variability using global climate models that include interactions between the atmosphere and ocean. We find that ocean currents change together with the changes in sea surface temperature and that the time it takes for these ocean currents to adjust to changes in the prevailing wind patterns gives this variability its persistence from decade to decade.

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The linked article and associated websites consider lessons learn from the Pliocene w.r.t. ice sheet contributions to sea level rise, and indicates that in order to correctly interpret Pliocene ice mass losses, multiple model simulations need to be run, in order to understand the complex interaction between the GIS and the AIS; and the different responses of the GIS and the AIS to radiative forcing:

Title: "Global warming – we have lessons to learn from the Pliocene epoch"

https://phys.org/news/2018-02-global-lessons-pliocene-epoch.html

Extract: "Recent research by a team of scientists, including PLIOTRANS, has been considering how the planet responded to Pliocene warmth. They have published a new paper presenting, for the first time, the transient nature of ice sheets and sea level during the late Pliocene. They show that the Greenland and Antarctic ice sheets might have responded differently to Pliocene heat, melting at different times.

Their transient ice sheet predictions are forced by multiple climate snapshots derived from a climate model set up with late Pliocene boundary conditions with different orbital forcing scenarios appropriate to two Marine Isotope Stages (MISs): KM5c (from 3.226 to 3.184 million years ago), and K1 (from 3.082 to 3.038 million years ago).

Their findings support previous studies, which have shown model results indicate peak MIS KM5c and K1 interglacial temperatures were not globally synchronous: there are leads and lags in temperature in different regions.

When it comes to modeling, this highlights the potential pitfalls of aligning peaks in proxy-derived temperatures across geographically diverse data sites. A single climate model simulation for an interglacial event is inadequate to capture peak temperature change in all regions."

See also:

Title: "PLIOcene TRANSient Climate Modelling: Towards a global consensus between ice volume, temperature and relative sea level for the Late Pliocene"

https://cordis.europa.eu/project/rcn/196017/factsheet/en
&
https://cordis.europa.eu/project/rcn/196017/reporting/en

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The linked article discusses a report by the Zurich Insurance Group about coming risks, including climate change risks. The report notes that '… it is likely to become more difficult to make collective progress on emerging global challenges …' due to problems like geo-economic and geo-political global tensions & technological instabilities (like cyber & AI risks).

The report also indicates that the insurance industry has concluded that world leaders appear to be collectively less likely to tackle climate risks while the climate change challenges are growing.  Indeed, the attached image from the report implies that the insurance industry believes that 'extreme weather events' are the most likely future risk we will face, while 'failure of climate change mitigation and adaption' is most likely to have the largest impact on future societies.  This implies that the insurance industry see major climate impacts as essentially inevitable and that our leaders' mitigation and adaption measure will most likely be inadequate to meet the coming climate impacts.

As insurance is the largest industry on the planet, consensus climate science would be wise to recognize the insurance industry's climate impact assessments and should add a chapter on 'Deep Climate Risks' to AR6:

Title: "We are drifting deeper into global problems"

https://www.zurich.com/en/knowledge/articles/2019/01/we-are-drifting-deeper-into-global-problems

Extract: "Global risks are intensifying but the collective will to tackle them appears to be lacking. Instead, divisions are hardening.
…
As environmental risks crystallize with increasing frequency and severity, there is urgent need to build resilience, for human health, food and water security, critical infrastructure and global value chains."

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The linked reference on peatland establishment and persistence concludes that: "These results show that northern peatlands accumulate significant C stocks during warmer times, indicating their potential for C sequestration during the warming Anthropocene."  The problem with this assessment is that it implies that the authors suspect that the world is head for a multimillennial warm period, as permafrost degradation can emit carbon from previously sequestered peatland sources in about a century, while sequestering new carbon in northern peatlands will take millennia (i.e. long after any socioeconomic collapse has occurred).

Treat et al. (February 25, 2019), "Widespread global peatland establishment and persistence over the last 130,000 y", PNAS March 12, 2019 116 (11) 4822-4827; https://doi.org/10.1073/pnas.1813305116

https://www.pnas.org/content/116/11/4822.short

Significance
During the Holocene (11,600 y ago to present), northern peatlands accumulated significant C stocks over millennia. However, virtually nothing is known about peatlands that are no longer in the landscape, including ones formed prior to the Holocene: Where were they, when did they form, and why did they disappear? We used records of peatlands buried by mineral sediments for a reconstruction of peat-forming wetlands for the past 130,000 y. Northern peatlands expanded across high latitudes during warm periods and were buried during periods of glacial advance in northern latitudes. Thus, peat accumulation and burial represent a key long-term C storage mechanism in the Earth system.

Abstract
Glacial−interglacial variations in CO2 and methane in polar ice cores have been attributed, in part, to changes in global wetland extent, but the wetland distribution before the Last Glacial Maximum (LGM, 21 ka to 18 ka) remains virtually unknown. We present a study of global peatland extent and carbon (C) stocks through the last glacial cycle (130 ka to present) using a newly compiled database of 1,063 detailed stratigraphic records of peat deposits buried by mineral sediments, as well as a global peatland model. Quantitative agreement between modeling and observations shows extensive peat accumulation before the LGM in northern latitudes (>40°N), particularly during warmer periods including the last interglacial (130 ka to 116 ka, MIS 5e) and the interstadial (57 ka to 29 ka, MIS 3). During cooling periods of glacial advance and permafrost formation, the burial of northern peatlands by glaciers and mineral sediments decreased active peatland extent, thickness, and modeled C stocks by 70 to 90% from warmer times. Tropical peatland extent and C stocks show little temporal variation throughout the study period. While the increased burial of northern peats was correlated with cooling periods, the burial of tropical peat was predominately driven by changes in sea level and regional hydrology. Peat burial by mineral sediments represents a mechanism for long-term terrestrial C storage in the Earth system. These results show that northern peatlands accumulate significant C stocks during warmer times, indicating their potential for C sequestration during the warming Anthropocene.

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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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The linked reference provides paleo evidence from about 11,500 year ago, that indicates that portions of the WAIS are very sensitivity to collapse, even under conditions that were cooler than today:

J. Kingslake et al. (2018), "Extensive retreat and re-advance of the West Antarctic Ice Sheet during the Holocene", Nature, https://doi.org/10.1038/s41586-018-0208-x

http://www.nature.com/articles/s41586-018-0208-x.epdf?referrer_access_token=lOkN7hgTt7KBVbuYuXMwc9RgN0jAjWel9jnR3ZoTv0PagDqQuHClF_KBoNEwt0qCDswVby5xisTUuro2GVqEdVyNRmUsMYB32-gwCy-WQGiOJuRHvpbmk3l6OEkAKwxOiPNDPRAKMIlDGFP4EHQgKD_G1qFJE2DhzFl3IkCeDuHh2Xln7I7LeJAB1tog4tIasE0yBRLzYo4hLBA3XhRCpg%3D%3D&tracking_referrer=news.nationalgeographic.com

Abstract: "To predict the future contributions of the Antarctic ice sheets to sea-level rise, numerical models use reconstructions of past ice-sheet retreat after the Last Glacial Maximum to tune model parameters. Reconstructions of the West Antarctic Ice Sheet have assumed that it retreated progressively throughout the Holocene epoch (the past 11,500 years or so). Here we show, however, that over this period the grounding line of the West Antarctic Ice Sheet (which marks the point at which it is no longer in contact with the ground and becomes a floating ice shelf) retreated several hundred kilometres inland of today’s grounding line, before isostatic rebound caused it to re-advance to its present position. Our evidence includes, first, radiocarbon dating of sediment cores recovered from beneath the ice streams of the Ross Sea sector, indicating widespread Holocene marine exposure; and second, ice-penetrating radar observations of englacial structure in the Weddell Sea sector, indicating ice-shelf grounding. We explore the implications of these findings with an ice-sheet model. Modelled re-advance of the grounding line in the Holocene requires ice-shelf grounding caused by isostatic rebound. Our findings overturn the assumption of progressive retreat of the grounding line during the Holocene in West Antarctica, and corroborate previous suggestions of ice-sheet re-advance. Rebound-driven stabilizing processes were apparently able to halt and reverse climate-initiated ice loss. Whether these processes can reverse present-day ice loss on millennial timescales will depend on bedrock topography and mantle viscosity—parameters that are difficult to measure and to incorporate into ice-sheet models."

See also:

Title: "The West Antarctic Ice Sheet Seems to Be Good at Collapsing"

https://news.nationalgeographic.com/2018/06/west-antarctic-ice-sheet-collapse-climate-change/

Extract: "SCIENTISTS HAVE DISCOVERED that the West Antarctic Ice Sheet underwent a major retreat between 10,000 and 12,000 years ago, at a time when the world was actually cooler than it is today. The collapse happened at the close of the last Ice Age, and it left the ice sheet 135,000 square miles smaller than it is today – a difference nearly as large as the state of Montana.

“That the ice sheet could retreat beyond where it is today, in a climate that was likely quite a bit colder than today, points to extraordinary sensitivity,” says Robert DeConto, a glaciologist at the University of Massachusetts Amherst, who was not involved in the research."

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The linked 2018 reference provides useful background discussions about modeling ice-climate feedback mechanisms in ESMs; however, it essentially ignores the MICI mechansims:

Jeremy Fyke et al. (23 April 2018), "An Overview of Interactions and Feedbacks Between Ice Sheets and the Earth System", Review of Geophysics", https://doi.org/10.1029/2018RG000600

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018RG000600

Abstract
Ice sheet response to forced changes—such as that from anthropogenic climate forcing—is closely regulated by two‐way interactions with other components of the Earth system. These interactions encompass the ice sheet response to Earth system forcing, the Earth system response to ice sheet change, and feedbacks resulting from coupled ice sheet/Earth system evolution. Motivated by the impact of Antarctic and Greenland ice sheet change on future sea level rise, here we review the state of knowledge of ice sheet/Earth system interactions and feedbacks. We also describe emerging observation and model‐based methods that can improve understanding of ice sheet/Earth system interactions and feedbacks. We particularly focus on the development of Earth system models that incorporate current understanding of Earth system processes, ice dynamics, and ice sheet/Earth system couplings. Such models will be critical tools for projecting future sea level rise from anthropogenically forced ice sheet mass loss.

Plain Language Summary
Sea level rise from ice sheets depends closely on interactions between ice sheets and the surrounding Earth system. These interactions determine how forcings to the climate system (such as from anthropogenic climate influences) translate to ice sheet change, which in turn impact the surrounding environment. This set of two‐way interactions between ice sheets and the Earth system forms the basis for important, yet poorly understood feedback loops. This review article describes the current state of knowledge of ice sheet/Earth system interactions and feedbacks and describes promising observational techniques for better understanding their behavior. It also highlights challenges and opportunities in modeling these interactions and feedbacks using coupled ice sheet/Earth system models, which will ultimately be used to predict future sea level rise caused by ice sheet loss.

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For those who want to gain a better appreciation of how inexact chaos theory calculations (say using an exascale supercomputer) can be used to better estimate climate risks associated with extreme climate events and tipping points, I recommend watching the hour long video entitled: "Climate Change, Chaos, and Inexact Computing".

Title: "Tim Palmer Public Lecture: Climate Change, Chaos, and Inexact Computing"



Extract: "How well can we predict climate change? The forecast for our future may lie at the intersection of chaos theory and a new breed of supercomputing, Tim Palmer explains in his public lecture from Perimeter Institute on May 4, 2016."

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While downplaying the potential significance of a MICI-driven WAIS collapse this century, the linked article provides a nice summary of many key issues associate with the current and potential future ice mass losses from Antarctica:

Title: "Antarctica is colder than the Arctic, but it’s still losing ice"

https://www.climate.gov/news-features/features/antarctica-colder-arctic-it%E2%80%99s-still-losing-ice

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Information such as that provided in the linked reference is needed to better assess the stability of the marine terminating glaciers in Southeast Greenland:

C. L. Batchelor et al. (11 March 2019), "Submarine moraines in Southeast Greenland fjords reveal contrasting outlet‐glacier behaviour since the Last Glacial Maximum", Geophysical Research Letters, https://doi.org/10.1029/2019GL082556

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL082556

Abstract: "Knowledge of the past behaviour of the outlet glaciers of Southeast (SE) Greenland is necessary to understand and model spatial differences in the response of the Greenland Ice Sheet (GIS) to climatic changes. Here, we use bathymetric data to map the distribution of more than 50 major moraines in SE Greenland fjords. Inner‐fjord moraines are widespread along the SE Greenland margin, occurring in 65% of the surveyed fjords. We identify, for the first time, 9 mid‐fjord moraines that span the c.150 km long eastern margin of the Julianehåb Ice Cap (JIC). In contrast, mid‐fjord moraines are generally absent from the deeper and wider fjords of the SE GIS. The variable distribution of mid‐fjord moraines along the SE Greenland margin reveals contrasting behaviour of the SE GIS and the eastern JIC during the last deglaciation, which probably reflects differences in fjord geometry and exposure to ocean heat."

[kassy]

Re 744.

Have you seen the news in #64 here.

https://forum.arctic-sea-ice.net/index.php/topic,2449.msg191933.html

"The plant assemblages indicate that there was an abrupt and major shift in the vegetation from wet, cold conditions at Pilauco to warm, dry conditions," Kennett said. According to him, the atmospheric zonal climatic belts shifted "like a seesaw," with a synergistic mechanism, bringing warming to the Southern Hemisphere even as the Northern Hemisphere experienced cooling and expanding sea ice.

They could be related?