Ice Apocalypse - Multiple Meters Sea Level Rise

[AbruptSLR]

In Reply #642 I cited Schneider et al (2019), but as this is an important paper, I provide the following improved citation including abstract, extracts and attached images.  The extracts and images make it clear that it is not fact the that CO₂ levels raise above 1,200ppm that causes the stratocumulus clouds to abruptly dissipate, but rather it is that fact that the tropical ocean SST temperature increases by 5C (from 27C to 32C) that causes the stratocumulus clouds to abruptly dissipate.  This is an important distinction because a collapse of the WAIS beginning circa 2040 would cause the MOC to slow, which would increase the tropical ocean SST without any increase in CO₂ levels.  Furthermore, the hysteresis loops in Figures 3 & 4 make it clear that once the stratocumulus clouds dissipate (say partially due to a temporary decades-long perturbation like the collapse of the WAIS and associated feedbacks, and partially due to a temporary pulse of methane emission from Arctic thermokarst lakes [as well as a rapid reduction in anthropogenic aerosols]), it is difficult for them to reestablish themselves even at CO2-equivalent levels well below 1,200ppm.

Tapio Schneider , Colleen M. Kaul and Kyle G. Pressel (2019), "Possible climate transitions from breakup of stratocumulus decks under greenhouse warming", Nature Geoscience, https://doi.org/10.1038/s41561-019-0310-1

https://www.nature.com/articles/s41561-019-0310-1

Abstract: "Stratocumulus clouds cover 20% of the low-latitude oceans and are especially prevalent in the subtropics. They cool the Earth by shading large portions of its surface from sunlight. However, as their dynamical scales are too small to be resolvable in global climate models, predictions of their response to greenhouse warming have remained uncertain. Here we report how stratocumulus decks respond to greenhouse warming in large-eddy simulations that explicitly resolve cloud dynamics in a representative subtropical region. In the simulations, stratocumulus decks become unstable and break up into scattered clouds when CO2 levels rise above 1,200 ppm. In addition to the warming from rising CO2 levels, this instability triggers a surface warming of about 8 K globally and 10 K in the subtropics. Once the stratocumulus decks have broken up, they only re-form once CO2 concentrations drop substantially below the level at which the instability first occurred. Climate transitions that arise from this instability may have contributed importantly to hothouse climates and abrupt climate changes in the geological past. Such transitions to a much warmer climate may also occur in the future if CO2 levels continue to rise."

Extract: "The CO2 level at which the instability occurs depends on how largescale dynamics change with climate, which is heuristically parameterized in our simulations and hence is uncertain. In particular, the large-scale subsidence in the troposphere weakens under warming, which lifts the cloud tops and counteracts the instability. Indeed, when we weaken the parameterized large-scale subsidence by 1 or 3% per Kelvin of tropical SST increase (within the range of GCM responses to warming), the stratocumulus instability occurs at higher CO2 levels: around 1,400 ppm with 1% K–1 subsidence weakening, and around 2,200 ppm with 3% K–1 (Fig. 4). The hysteresis when the CO2 levels drop thereafter remains, but it narrows: stratocumulus decks reform once the CO2 levels drop below 500 ppm for a 1% K–1 subsidence weakening, and once they drop below 1,900 ppm for one of 3% K–1.
…
For the future, our results suggest that stratocumulus decks may break up if CO2 levels continue to rise. Equivalent CO2 concentrations around 1,300 ppm—the lowest level at which the stratocumulus instability occurred in our simulations—can be reached within a century under high-emission scenarios. However, it remains uncertain at which CO2 level the stratocumulus instability occurs because we had to parameterize rather than resolve the large-scale dynamics that interact with cloud cover. To be able to quantify more precisely at which CO2 level the stratocumulus instability occurs, how it interacts with large-scale dynamics and what its global effects are, it is imperative to improve the parameterizations of clouds and turbulence in climate models."

[AbruptSLR]

While the Trump administration is authorized to replace the acting NOAA administrator, Tim Gallaudet, this move disappoints me sufficiently to note that the existence of the Trump administration is yet another factor contributing to the increased likelihood of an "Ice Apocalypse" this century.  As the extract from the linked article notes Gallaudet earned plaudits for his excellent work on ocean and atmospheric science, and his abrupt departure is a clear loss to the agency.

Title: "Sudden leadership shake-up hits NOAA"

https://www.axios.com/sudden-leadership-shakeup-hits-oceans-and-climate-agency-fb8427ca-d501-4eb5-8a5b-8c437350bcd5.html

Extract: "Tim Gallaudet, the acting administrator of the National Oceanic and Atmospheric Administration (NOAA), was suddenly replaced on Monday by the No. 3 official at the agency, former weather industry scientist Neil A. Jacobs.

Why it matters: The agency has been operating without a Senate-confirmed administrator for the longest time since it was created in 1970. Gallaudet, a retired U.S. Navy rear admiral, had earned plaudits for advancing the agency's priorities in ocean and atmospheric sciences without succumbing to political interference with climate research, as other agencies have during the Trump administration.
…
Details: An email went out to NOAA employees on Monday to announce the leadership swap, stating that it was ordered by Commerce Secretary Wilbur Ross."

[AbruptSLR]

...
The extracts and images make it clear that it is not the fact that CO₂ levels raise above 1,200ppm that causes the stratocumulus clouds to abruptly dissipate, but rather it is that fact that the tropical ocean SST temperature increases by 5C (from 27C to 32C) that causes the stratocumulus clouds to abruptly dissipate. 
...

For those who do not remember Reply #633, the linked article shows that the risk that if the equatorial SST increases from about 27C to about 32C the atmosphere for the North Hemisphere could be abruptly transitioned from modern to equable climate (or 'hot house') conditions.  Such a 5C SST increase in the equatorial oceans, could conceivable occur this century from a combination of: a) ice-climate feedbacks from the collapse of the WAIS & bipolar seesaw interaction with the Arctic & Greenland; b) a cascade of other tipping points (including methane feedbacks) and c) a rapid decrease/redistribution of anthropogenic aerosol emissions:


Title: "The Effects of Ocean Freshening on Marine and Atmospheric Circulation: Impacts and Solutions"

https://www.sciencebuzz.com/the-effects-of-ocean-freshening-on-marine-and-atmospheric-circulation-impacts-and-solutions/

Extract: "If the equatorial SST were raised from the average 27°C to 32°C then the tropopause would be heated 37°C above average. A 5°C SST increase, combined with other factors, would hypothetically cause the Hadley cells to increase in height allowing them to reach the poles. This effect terminates Ferrel and Polar cell convection and replaces it with a large Hadley cell (Figure 5). This causes global climates to become more equable than previously existed as temperatures are more evenly distributed across the globe (Piana n.d.)."

[AbruptSLR]

The linked articles on 'deep adaptation' to coming climate change ignores almost all ice-climate feedbacks, but it does provide discussion of philosophical considerations of 'deep adaptation':

Title: "The End of the Line – A Climate in Crisis"

https://www.counterpunch.org/2018/08/03/the-end-of-the-line-a-climate-in-crisis/

Extract: “Disruptive impacts from climate change are now inevitable. Geoengineering is likely to be ineffective or counter-productive. Therefore, the mainstream climate policy community now recognizes the need to work much more on adaptation to the effects of climate change… societies will experience disruptions to their basic functioning within less than ten years due to climate stress. Such disruptions include increased levels of malnutrition, starvation, disease, civil conflict and war – and will not avoid affluent nations.”

See also:

"Deep Adaptation: A Map for Navigating Climate Tragedy", 2018 by Jem Bendel

https://www.lifeworth.com/deepadaptation.pdf

&

https://jembendell.wordpress.com/2018/07/26/the-study-on-collapse-they-thought-you-should-not-read-yet/

[AbruptSLR]

The linked reference discusses paleo evidence for abrupt shifts in circumpolar westerly winds around Antarctica due to Dansgaard-Oeschger (DO) events in the North Atlantic.  The bipolar seesaw mechanism associated with this long-distance telecommunication includes both an oceanic component with about a 200-year lag time, and an atmospheric component that occurs essentially currently with the DO event.  This research confirms that significant portions of bipolar seesaw mechanisms rapidly occur via the atmosphere.

Buizert C, Sigl M, Severi M, Markle BR, Wettstein JJ, McConnell JR, Pedro JB, Sodemann H, Goto-Azuma K, Kawamura K, Fujita S, Motoyama H, Hirabayashi M, Uemura R, Stenni B, Parrenin F, He F, Fudge TJ, Steig EJ (2018) Abrupt ice-age shifts in southern westerly winds and Antarctic climate forced from the north, Nature, 563, 681-685. https://doi.org/10.1038/s41586-018-0727-5

https://www.nature.com/articles/s41586-018-0727-5

See also:

Brook & Buizert (2018), "Antarctic and global climate history viewed from ice cores", Nature, 558, 200-208, https://doi.org/10.1038/s41586-018-0172-5

https://www.nature.com/articles/s41586-018-0172-5

[AbruptSLR]

I provide the following two images for those who think that Antarctic Amplification is irrelevant to the potential collapse of the WAIS in the coming decades because the surface elevation for most of the ice mass is so high that the surface temperature will remain below freezing for many decades into the future.

The first image from Eric Steig shows average Antarctic surface 50-year warming trends (in C/decade) from the mid-1950's; which the second image from the WAIS divide shows that this warming trend is accelerating for the WAIS with over 0.8 C/decade of surface warming between 1987 and 2007.  DeConto and Pollard essentially only use the hydrofracturing mechanism to collapse key West Antarctic ice shelves (which are at sea level and thus are not protected by cooling due to surface elevation); thus these images imply that with continued warming there should be sufficient surface warming of key Amundsen Sea Embayment ice shelves for hydrofracturing to collapse such ice shelve before 2040.

Caption for the first image: "Antarctic surface temperature trends. Red represents areas where temperatures have increased the most during the last 50 years, particularly in West Antarctica. The temperature trends are given in °C/decade. Credit: Eric Steig, University of Washington, with NASA/GSFC Scientific Visualization Studio"

[AbruptSLR]

The two linked articles make it clear that Russian political leadership view rapid Arctic climate change as an economic benefit to the Russian economy and they are investing money in order to exploit such regional economic benefits.  However, the indicated rapid climate change in Russia's Arctic regions will most likely have dire consequences to the rest of the world's population due to such positive feedback mechanism as methane emissions from Russia thermokarst lakes and impact from reduced albedo from both Russia sea ice area losses and snow coverage losses on land.  Also, in this regards I note that the Trump Administration's reversal on progress to fight climate change mirror's that of the Putin Administration and will geopolitically benefit Russia.

Title: "With more dark clouds in horizon, Russian Arctic meteorologists get almost a billion for studies of the weather"

https://thebarentsobserver.com/en/arctic/2019/02/more-dark-clouds-horizon-russian-arctic-meteorologists-get-almost-billion-studies

Extract: "The Russian government this week announced that it is allocating 868.75 million rubles (€11.6 million) to the Transarktika-2019 program, an initiative managed by the country’s state meteorological institute Roshydromet.
…
The Transarktika-2019 starts as the Russian Arctic is undergoing unprecedented climate change with average temperatures far beyond normal. In parts of the region, the average temperatures have increased with up to five degrees Celsius in less than 30 years.

At the same time, regional Russian industrial activities are rapidly on the increase and shipping on the Northern Sea Route is bigger than ever. And far more is to come. The target set by President Putin is 80 million tons of goods on the route by year 2024, an 8-fold increase from year 2017."

&

Title: "Under the surface of Russia’s Arctic super-region is a looming disaster"

https://thebarentsobserver.com/en/node/4894

Extract: "Our mission is to produce hydrocarbons and deliver to the markets, regional governor Dmitry Artyukhov underlined in an address delivered at the event. He shrugged off questions about the need for alternative energy sources and focus on climate change.
…
The Panel’s latest climate report says that the likelihood of an Arctic Ocean  free of sea ice in summer would be at least once per decade with 2°C global temperature increase. A similar picture is drawn up by the Russian researchers working in federal meteorological institute Roshydromet.

According to Roshydromet, average temperatures in the Kara Sea have since 1998 increased with as much as 4,95 C degrees. Ice is retreating and the permafrost melting. Data from measuring points in the country’s European parts of the Arctic in 2017 showed an average shrinking of the permafrost layer by about 10 cm.
…
«If you look at statements from political leaders you see that there has been a turn from the international focus under President Dmitry Medvedev and till today.»

«The image of being a responsible player has changed,» he says."

Edit: The response of Russia's current political leaders to climate change, increases the probability of the occurrence of an "Ice Apocalypse".

[AbruptSLR]

The linked article (& associated reference) discusses direct observational data that demonstrates that strong El Nino events result in significant ice mass loss from key West Antarctic ice shelves.  As the frequency of strong El Nino events is projected to increase with continued global warming, this findings indicate that the stability of the WAIS will be reduced due to reduced buttressing from key ice shelves:

Title: "Strong El Niño events cause large changes in Antarctic ice shelves"

https://www.sciencedaily.com/releases/2018/01/180108121618.htm

Extract: "Oscillations of water temperature in the tropical Pacific Ocean can induce rapid melting of Antarctic ice shelves
…
After further analysis of the data, the scientists found that although a strong El Niño changes wind patterns in West Antarctica in a way that promotes flow of warm ocean waters towards the ice shelves to increase melting from below, it also increases snowfall particularly along the Amundsen Sea sector. The team then needed to determine the contribution of the two effects. Is the atmosphere adding more mass than the ocean is taking away or is it the other way around?

"We found out that the ocean ends up winning in terms of mass. Changes in mass, rather than height, control how the ice shelves and associated glaciers flow into the ocean," Paolo said. While mass loss by basal melting exceeds mass gain from snowfall during strong El Niño events, the opposite appears to be true during La Niña events."

See also:

F. S. Paolo, L. Padman, H. A. Fricker, S. Adusumilli, S. Howard, M. R. Siegfried. Response of Pacific-sector Antarctic ice shelves to the El Niño/Southern Oscillation. Nature Geoscience, 2018; DOI: 10.1038/s41561-017-0033-0

https://www.nature.com/articles/s41561-017-0033-0

[AbruptSLR]

Ice mass loss from Antarctica and Greenland are both slightly slowing the MOC; and as more ice sheet mass is lost in the future this slowing of the MOC should become more pronounced.  Furthermore, as the MOC slows the AMOC will push further into the Arctic Ocean Basin, and the linked reference presents analysis about how the intrusion of Atlantic Ocean water into the Arctic Ocean translates into altered thermohaline-shear instability, which will impact heat transfer from depth to the ocean surface.  To me this will effect the rate of loss of sea ice area, and thus this physical phenomenon should be included in future climate change models:

Timour Radko (08 January 2019), "Thermohaline‐Shear Instability", Geophysical Research Letters", https://doi.org/10.1029/2018GL081009

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL081009

Abstract
This study presents the linear theory of thermohaline‐shear instability, which is realized in oceanic flows that are dynamically and diffusively stable. The framework is based on the unbounded Couette model, which makes it possible to decouple the destabilizing effects of spatially uniform shear from instabilities caused by the presence of inflection points in velocity profiles. The basic state is assumed to be time dependent, which reflects the role of internal waves in controlling fine‐scale shear. Linear stability analysis suggests that conditions for thermohaline‐shear instability are met in most ocean regions where temperature and salinity concurrently increase downward. We conclude that thermohaline‐shear instability represents a plausible mechanism for the initiation of active diffusive convection, which, in turn, is essential for the formation of thermohaline staircases and maintenance of double‐diffusive interleaving.

Plain Language Summary
Warming and decline in sea ice coverage of the Arctic Ocean represent an unambiguous indicator of the ongoing climate change. A critical process in the transition of the Arctic to the new state involves heating of near‐surface waters from below. Relatively warm waters enter the Arctic from the Atlantic Ocean and spread throughout the basin at depths of 150–900 m. These waters contain more than enough heat to melt all the sea ice, but it is not clear how this heat can be transferred upward to the surface. In particular, above the warm Atlantic Water lies a region marked by the presence of horizontal layers of 1–10 m thick with almost uniform temperatures in each layer. Stacks of these layers are often called “staircases,” in a neat reference to step‐like changes of temperature. Staircases act as a heat transport bottleneck in the upper Arctic, which demands full understanding of their physics for the purpose of climate prediction. This study explains their origin by showing that smooth temperature patterns are inherently unstable for the conditions commonly realized in the upper Arctic. Thus, even if nature initially creates a smooth temperature distribution, such stratification can spontaneously buckle due to its instability and form a staircase.

[sidd]

Where does the Radko paper state anything about amplifying sea ice loss ? As  far as i see, it merely suggests a physical process for the layer stucture of arctic waters.

sidd
 

[AbruptSLR]

The linked article reminds us that during warming ENSO years (see the first image), that the associated warmer and drier air (particularly in the Amazon Basin) results in reduced terrestrial carbon uptake, resulting in higher atmospheric CO₂ concentrations (see the second image).  First, this is a positive feedback that promotes climate change.  Second, this behavior will accelerate the rate of loss of the Amazon rainforest. Third, as the ice-climate feedback mechanisms promote more frequent El Nino events, as more ice sheet mass loss occurs, we can expect many terrestrial and oceanic carbon sinks to progressively (or abruptly) decrease their carbon uptake:

Title: "Faster CO2 rise expected in 2019"

https://phys.org/news/2019-01-faster-co2.html

Extract: "With emissions already at a record high, the build-up of carbon-dioxide in the atmosphere could be larger than last year due to a slower removal by natural carbon sinks.
…
Weather patterns linked to year-by-year swings in Pacific Ocean temperatures are known to affect the uptake of carbon-dioxide by land ecosystems. In years with a warmer tropical Pacific, many regions become warmer and drier, which limits the ability of plants to grow and absorb CO₂. The opposite occurs when the Pacific is cool, as happened a year ago."

Caption for second image: "Figure 1: Forecast CO₂ concentrations at Mauna Loa over 2019 (orange), along with previous forecast concentrations for 2016 (blue), 2017 (green), 2018 (pink) and Scripps Institute measurements (black). Credit: University of Exeter "

[AbruptSLR]

Where does the Radko paper state anything about amplifying sea ice loss ? As  far as i see, it merely suggests a physical process for the layer stucture of arctic waters.

sidd

I have modified the wording in that post to emphasize that the physical process in question will impact the rate of heat transfer from the increased quantity of relatively warm Atlantic water to the surface of the regional Arctic Ocean; which should impact the rate of sea ice loss.  And I note that the physical process in question is not included in current consensus climate model projections.

[AbruptSLR]

While the climate change induced damage to terrestrial ecosystems is tragic in and of itself (see the two associated linked sources), my Reply #660, reminds us that we all rely on terrestrial ecosystems to act as carbon sinks, and climate change damage to our collective terrestrial ecosystems will likely accelerate the rate of the reduction of carbon uptake from these systems.  Furthermore, ice-climate feedbacks are already accelerating the of such damage, and consensus climate models do not consider such ice-climate feedbacks.

Sebastian Ostberg et al. (09 January 2018), "The Biosphere Under Potential Paris Outcomes", Earth's Future, https://doi.org/10.1002/2017EF000628

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017EF000628

Abstract
Rapid economic and population growth over the last centuries have started to push the Earth out of its Holocene state into the Anthropocene. In this new era, ecosystems across the globe face mounting dual pressure from human land use change (LUC) and climate change (CC). With the Paris Agreement, the international community has committed to holding global warming below 2°C above preindustrial levels, yet current pledges by countries to reduce greenhouse gas emissions appear insufficient to achieve that goal. At the same time, the sustainable development goals strive to reduce inequalities between countries and provide sufficient food, feed, and clean energy to a growing world population likely to reach more than 9 billion by 2050. Here, we present a macro‐scale analysis of the projected impacts of both CC and LUC on the terrestrial biosphere over the 21st century using the Representative Concentration Pathways (RCPs) to illustrate possible trajectories following the Paris Agreement. We find that CC may cause major impacts in landscapes covering between 16% and 65% of the global ice‐free land surface by the end of the century, depending on the success or failure of achieving the Paris goal. Accounting for LUC impacts in addition, this number increases to 38%–80%. Thus, CC will likely replace LUC as the major driver of ecosystem change unless global warming can be limited to well below 2°C. We also find a substantial risk that impacts of agricultural expansion may offset some of the benefits of ambitious climate protection for ecosystems.

Plain Language Summary
Ecosystems across the world are under increasing pressure from man‐made climate change and humanity's use of land for agriculture. While countries have agreed to limit climate change to less than 2 degrees in the 2015 Paris Agreement the success of climate protection is currently uncertain. At the same time, continued population growth is causing demand for food and bioenergy to rise. We use computer simulations to explore which ecosystems are at risk of major change due to climate change and land use by the end of the 21st century. We find that climate change could transform between 16% and 65% of all ecosystems worldwide substantially, depending on how successful greenhouse gas emissions can be reduced. 11% to 25% of ecosystems may also experience severe impacts from land use, depending on how much land is needed for agriculture. In the worst case we studied, climate change and land use change risk transforming up to 80% of the land biosphere into a completely new state, putting many species at risk of extinction if they cannot adapt to their rapidly changing environment.

See also:

Title: "Climate Change Could Leave Big Mark on Earth’s Landscape"

https://eos.org/scientific-press/climate-change-could-leave-big-mark-on-earths-landscape

Extract: "In the case that the world reduces greenhouse gas emissions, but is unable to limit global warming to 2 degrees Celsius above pre-industrial levels, the researchers’ model projects climate change will cause major changes to 34 percent of Earth’s biosphere while land use change will impact 11 to 13 percent of the global land surface by 2100.

If the world fails to reduce carbon emissions, climate change and land use change will bring major changes to 73 percent of the global landscape by the end of the century, according to the model. In this scenario, the researchers predict climate change alone would account for almost three-quarters of this change."

[AbruptSLR]

The linked (associated) sources indicate how sensitive like on Earth is to abrupt climate change:

Title: "Global warming increases the risk of an extinction domino effect"

https://phys.org/news/2018-11-global-extinction-domino-effect.html

Extract: "In the case of global warming, predictions that fail to take into account this cascading effect might underestimate extinctions by up to 10 times.

As an obvious, direct consequence of climate change, plants and animals living in a given area are driven to extinction when the local environmental conditions become incompatible with their tolerance limits, just like fish in an aquarium with a broken thermostat.
…
According to the simulations, 5-6°C of warming would be enough to wipe out most life on the virtual Earths the scientists created."

See also:

Giovanni Strona et al. Co-extinctions annihilate planetary life during extreme environmental change, Scientific Reports (2018). DOI: 10.1038/s41598-018-35068-1

https://www.nature.com/articles/s41598-018-35068-1

[AbruptSLR]

Yet another concern about the sensitivity of Antarctic marine glaciers to ocean-driven melting in the coming decades:

R. H. Levy, S. R. Meyers, T. R. Naish, N. R. Golledge, R. M. McKay, J. S. Crampton, R. M. DeConto, L. De Santis, F. Florindo, E. G. W. Gasson, D. M. Harwood, B. P. Luyendyk, R. D. Powell, C. Clowes, D. K. Kulhanek. Antarctic ice-sheet sensitivity to obliquity forcing enhanced through ocean connections. Nature Geoscience, 2019; DOI: 10.1038/s41561-018-0284-4

https://www.nature.com/articles/s41561-018-0284-4

Extract; "Our reconstruction of the Antarctic ice-sheet history suggests that if sea-ice decreases in the coming decades, ocean-driven melting at the ice-sheet margin will be amplified."

See also:

https://www.sciencedaily.com/releases/2019/01/190114114237.htm

Extract: "Marine ice sheets, note Levy and Meyers, are especially sensitive to heat delivered by ocean currents. Fast flowing inland ice streams of the West Antarctic are buttressed by floating ice shelves, which -- if diminished or lost -- raise the possibility of a runaway flow of West Antarctica's marine ice.

The new research suggests that a reduction in sea ice due to climate change would erode the barrier keeping the ice sheet -- including the parts of it below sea level -- in place.

"Sea ice creates a barrier between the ocean and the ice. If we fail to achieve carbon dioxide emissions targets and Earth's average temperature warms more than 2 degrees Celsius, sea ice will diminish and we jump into a world that is more similar to that last experienced during the early to mid-Miocene," says Levy, referencing a geological epoch that ended about 14 million years ago when the Earth and its polar regions were much more temperate, with an atmosphere supercharged with carbon dioxide and global temperatures, on average, warmer by 3 to 4 degrees Celsius (7 to 9 degrees Fahrenheit).""

[AbruptSLR]

The open-access linked reference provides basal ice melt rates for the Pine Island Ice Shelf thru 2015, which are high.  Since that time, things have gotten worse:

Shean, D. E., Joughin, I. R., Dutrieux, P., Smith, B. E., and Berthier, E.: Ice shelf basal melt rates from a high-resolution DEM record for Pine Island Glacier, Antarctica, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-209, in review, 2018.

https://www.the-cryosphere-discuss.net/tc-2018-209/

Abstract. Ocean-induced basal melting is directly and indirectly responsible for much of the Amundsen Sea Embayment ice loss in recent decades, but the total magnitude and spatiotemporal evolution of this melt is poorly constrained. To address this problem, we generated a record of high-resolution Digital Elevation Models (DEMs) for Pine Island Glacier (PIG) using commercial sub-meter satellite stereo imagery and integrated additional 2002–2015 DEM/altimetry data. We implemented a Lagrangian elevation change (Dh/Dt) framework to estimate ice shelf basal melt rates at 32–256-m resolution. We describe this methodology and consider basal melt rates and elevation change over the PIG shelf and lower catchment from 2008–2015. We document the evolution of Eulerian elevation change (dh/dt) and upstream propagation of thinning signals following the end of rapid grounding line retreat around 2010. Mean full-shelf basal melt rates for the 2008–2015 period were ~82–93 Gt/yr, with ~ 200–250 m/yr basal melt rates within large channels near the grounding line, ~ 10–30 m/yr over the main shelf, and ~ 0–10 m/yr over the North and South shelves, with the notable exception of a small area with rates of ~ 50–100 m/yr near the grounding line of a fast-flowing tributary on the South shelf. The observed basal melt rates show excellent agreement with, and provide context for, in situ basal melt rate observations. We also document the relative melt rates for km-scale basal channels and keels at different locations on the shelf and consider implications for ocean circulation and heat content. These methods and results offer new indirect observations of ice-ocean interaction and constraints on the processes driving sub-shelf melting beneath vulnerable ice shelves in West Antarctica.

[sidd]

Re: Radko

I have read the paper more carefully and it does have this to say about diffusive heat transport and sea ice melt:

" Turner (2010) concludes that diffusive convection has contributed significantly to the observed increase in sea ice melting during the past few decades. Polyakov et al. (2017) reinforce this suggestion by demonstrating that the impact of the diffusive heat transport from AW on the sea ice loss in the Eurasian Basin is now comparable to, or possibly exceeds, the level attributed to atmospheric forcing. The staircase region today is about 100 m shallower, and layer thicknesses have doubled in comparison to measurements taken in 1985 (Padman & Dillon, 1987; Timmermans et al., 2008). The systematic increase in mean layer thickness, in turn, implies the systematic amplification of diffusive heat transport. Remarkably, despite the undeniable significance of thermohaline staircases for high‐latitude ocean dynamics, the physical mechanism of their formation has not been fully explained after more than half a century of observation.

Another diffusively generated phenomenon that is widespread in polar oceans is thermohaline interleaving (e.g., Rudels et al., 2009). Interleaving is characterized by lateral intrusive flows that mix adjacent water masses with different T‐S properties (Ruddick & Kerr, 2003; Ruddick & Richards, 2003). Fully developed intrusions are readily recognized in temperature and salinity profiles by alternating patterns of positive and negative vertical T‐S gradients. In the Arctic, intrusions spread relatively warm and salty AW from boundary currents at the basin periphery into fresher and colder interior regions. They can reach extraordinary large scales of up to a hundred meters in height and remain laterally coherent over hundreds of kilometers (e.g., Carmack et al., 1999; Merryfield, 2002)."

sidd

[sidd]

Re: Radko

After thinking about it some more, I wonder if the instability against layering manifests in the Southerm Hemisphere ? CDW and neighbours are quite different from AMOC but the analysis seems quite general. I shall have to reread Dutrieux and others, in particular Hellmer on warm/cold cavities under ice shelves, in this light. The ocean transects by the current Thwaites effort should illuminate.

sidd
 

[AbruptSLR]

The first two associated linked sources indicate both that Arctic cloud cover is a net positive feedback mechanism and that Arctic cloud formation is highly enhanced (more so than in most other areas of the Earth) by the presence of aerosols.  These sources warn that allowing increase ship traffic into the Arctic Ocean would thus increase Arctic Amplification more than previously assumed.

Title: "Arctic Clouds Highly Sensitive to Air Pollution"

https://eos.org/scientific-press/arctic-clouds-highly-sensitive-to-air-pollution

Extract: "Scientists have been interested in the effects of pollution on Arctic clouds because of their potential warming effect. In other parts of the world, clouds can cool the surface because their white color reflects solar energy back out into space.

“In the Arctic, the cooling effect isn’t as large because the sea-ice at the surface is already bright,” Garrett says. “Just as clouds reflect radiation efficiently, they also absorb radiation efficiently and re-emit that energy back to warm the surface.” Droplets of water can form around particulate matter in the air. More particles make for more droplets, which makes for a cloud that warms the surface more.
…
Controlling current particulate matter sources could ease pollution in the Arctic, decrease cloud cover, and slow down warming. All of those gains could be offset, other researchers have suggested, if the Arctic becomes a shipping route and sees industrialization and development. Emissions from those activities could have a disproportionate effect on Arctic clouds compared to emissions from other parts of the world, Garrett says."
&

Q. Coopman et al. (09 November 2017), "High Sensitivity of Arctic Liquid Clouds to Long‐Range Anthropogenic Aerosol Transport", Geophysical Research Letters, https://doi.org/10.1002/2017GL075795

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2017GL075795

Abstract: "The rate of warming in the Arctic depends upon the response of low‐level microphysical and radiative cloud properties to aerosols advected from distant anthropogenic and biomass‐burning sources. Cloud droplet cross‐section density increases with higher concentrations of cloud condensation nuclei, leading to an increase of cloud droplet absorption and scattering radiative cross sections. The challenge of assessing the magnitude of the effect has been decoupling the aerosol impacts on clouds from how clouds change solely due to natural meteorological variability. Here we address this issue with large, multi‐year satellite, meteorological, and tracer transport model data sets to show that the response of low‐level clouds in the Arctic to anthropogenic aerosols lies close to a theoretical maximum and is between 2 and 8 times higher than has been observed elsewhere. However, a previously described response of arctic clouds to biomass‐burning plumes appears to be overstated because the interactions are rare and modification of cloud radiative properties appears better explained by coincident changes in temperature, humidity, and atmospheric stability."
__________

The next linked reference indicates that natural emissions of dimethyl sulfide (DMS) is accelerating around the Arctic, largely due to the increasing existence of free-surface bodies of water (e.g. melt ponds) in the Arctic.  As DMS is an aerosol that promotes cloud formation, and as clouds are a net positive feedback mechanism in the Arctic, this research indicates that Arctic Amplification will increase faster than previously assumed, due to the increasing formation of DMS in Arctic regions:

Abbatt, J. P. D., Leaitch, W. R., Aliabadi, A. A., Bertram, A. K., Blanchet, J.-P., Boivin-Rioux, A., Bozem, H., Burkart, J., Chang, R. Y. W., Charette, J., Chaubey, J. P., Christensen, R. J., Cirisan, A., Collins, D. B., Croft, B., Dionne, J., Evans, G. J., Fletcher, C. G., Galí, M., Ghahremaninezhad, R., Girard, E., Gong, W., Gosselin, M., Gourdal, M., Hanna, S. J., Hayashida, H., Herber, A. B., Hesaraki, S., Hoor, P., Huang, L., Hussherr, R., Irish, V. E., Keita, S. A., Kodros, J. K., Köllner, F., Kolonjari, F., Kunkel, D., Ladino, L. A., Law, K., Levasseur, M., Libois, Q., Liggio, J., Lizotte, M., Macdonald, K. M., Mahmood, R., Martin, R. V., Mason, R. H., Miller, L. A., Moravek, A., Mortenson, E., Mungall, E. L., Murphy, J. G., Namazi, M., Norman, A.-L., O'Neill, N. T., Pierce, J. R., Russell, L. M., Schneider, J., Schulz, H., Sharma, S., Si, M., Staebler, R. M., Steiner, N. S., Thomas, J. L., von Salzen, K., Wentzell, J. J. B., Willis, M. D., Wentworth, G. R., Xu, J.-W., and Yakobi-Hancock, J. D.: Overview paper: New insights into aerosol and climate in the Arctic, Atmos. Chem. Phys., 19, 2527-2560, https://doi.org/10.5194/acp-19-2527-2019, 2019.

https://www.atmos-chem-phys.net/19/2527/2019/

Abstract
Motivated by the need to predict how the Arctic atmosphere will change in a warming world, this article summarizes recent advances made by the research consortium NETCARE (Network on Climate and Aerosols: Addressing Key Uncertainties in Remote Canadian Environments) that contribute to our fundamental understanding of Arctic aerosol particles as they relate to climate forcing. The overall goal of NETCARE research has been to use an interdisciplinary approach encompassing extensive field observations and a range of chemical transport, earth system, and biogeochemical models. Several major findings and advances have emerged from NETCARE since its formation in 2013. (1) Unexpectedly high summertime dimethyl sulfide (DMS) levels were identified in ocean water (up to 75 nM) and the overlying atmosphere (up to 1 ppbv) in the Canadian Arctic Archipelago (CAA). Furthermore, melt ponds, which are widely prevalent, were identified as an important DMS source (with DMS concentrations of up to 6 nM and a potential contribution to atmospheric DMS of 20 % in the study area). (2) Evidence of widespread particle nucleation and growth in the marine boundary layer was found in the CAA in the summertime, with these events observed on 41 % of days in a 2016 cruise. As well, at Alert, Nunavut, particles that are newly formed and grown under conditions of minimal anthropogenic influence during the months of July and August are estimated to contribute 20 % to 80 % of the 30–50 nm particle number density. DMS-oxidation-driven nucleation is facilitated by the presence of atmospheric ammonia arising from seabird-colony emissions, and potentially also from coastal regions, tundra, and biomass burning. Via accumulation of secondary organic aerosol (SOA), a significant fraction of the new particles grow to sizes that are active in cloud droplet formation. Although the gaseous precursors to Arctic marine SOA remain poorly defined, the measured levels of common continental SOA precursors (isoprene and monoterpenes) were low, whereas elevated mixing ratios of oxygenated volatile organic compounds (OVOCs) were inferred to arise via processes involving the sea surface microlayer. (3) The variability in the vertical distribution of black carbon (BC) under both springtime Arctic haze and more pristine summertime aerosol conditions was observed. Measured particle size distributions and mixing states were used to constrain, for the first time, calculations of aerosol–climate interactions under Arctic conditions. Aircraft- and ground-based measurements were used to better establish the BC source regions that supply the Arctic via long-range transport mechanisms, with evidence for a dominant springtime contribution from eastern and southern Asia to the middle troposphere, and a major contribution from northern Asia to the surface. (4) Measurements of ice nucleating particles (INPs) in the Arctic indicate that a major source of these particles is mineral dust, likely derived from local sources in the summer and long-range transport in the spring. In addition, INPs are abundant in the sea surface microlayer in the Arctic, and possibly play a role in ice nucleation in the atmosphere when mineral dust concentrations are low. (5) Amongst multiple aerosol components, BC was observed to have the smallest effective deposition velocities to high Arctic snow (0.03 cm s−1).

See also

Title: "How one little molecule influences Earth's climate"
https://blogs.scientificamerican.com/culturing-science/how-one-little-molecule-influences-earthe28099s-climate/
&

Title: "Dimethyl Sulfide"
https://en.wikipedia.org/wiki/Dimethyl_sulfide

[El Cid]

Concerning sulfur and shipping - mentioned above - I do not know how well the new IMO (International Maritime Organization) 2020 regulations are known to you.

From 2020 Jan 1, the sulfur content of fuel used by ships will be reduced from 3,5% to 0,5% (yes, from three-and-a-half to half percent). That is a major change and is going to happen very soon:

see for example here:

http://www.seatrade-maritime.com/images/PDFs/SOMWME-whitepaper_Sulphur-p2.pdf

[AbruptSLR]

Re: Radko

After thinking about it some more, I wonder if the instability against layering manifests in the Southerm Hemisphere ? CDW and neighbours are quite different from AMOC but the analysis seems quite general. I shall have to reread Dutrieux and others, in particular Hellmer on warm/cold cavities under ice shelves, in this light. The ocean transects by the current Thwaites effort should illuminate.

sidd

I have had similar thoughts but the CDW patterns in the ASE (as indicated by the attached model output) are much more complicated (including dependence on ENSO and ice-climate feedback mechanisms) than is the case for Atlantic Water intruding into the Arctic Ocean.  But whether researchers can model this degree of complexity is unclear to be, but it is clear that Mother Nature has no problem at all with resolving the most complex situations into actual responses in the field.

[AbruptSLR]

Concerning sulfur and shipping - mentioned above - I do not know how well the new IMO (International Maritime Organization) 2020 regulations are known to you.

From 2020 Jan 1, the sulfur content of fuel used by ships will be reduced from 3,5% to 0,5% (yes, from three-and-a-half to half percent). That is a major change and is going to happen very soon:

see for example here:

http://www.seatrade-maritime.com/images/PDFs/SOMWME-whitepaper_Sulphur-p2.pdf

I am not sure that China and Russia share Western sensitivities when it comes to their likely exploitation of the 'Polar Silk Road' and all of the soon to be accessible resources around the Arctic Ocean:

Title: "Putin and Xi Are Dreaming of a Polar Silk Road"

https://foreignpolicy.com/2018/03/08/putin-and-xi-are-dreaming-of-a-polar-silk-road-arctic-northern-sea-route-yamal/

Extract: "China is dreamy-eyed about the prospects of shipping goods from Asia to Europe across the top of Russia, with visions of transpolar shipping dominating its brand-new Arctic strategy. Some specialized tankers are making headlines by crossing the Arctic alone — in the dead of winter, something that was almost impossible before.

And Russia is convinced that the melting Arctic will open up a new economic frontier rich in oil, natural gas, and lucrative transport routes between the world’s workshop and the world’s consumers. Russian President Vladimir Putin, whose government plans to invest tens of billions of dollars by 2030 to develop ships, shipbuilders, navigational aids, and ports along the Northern Sea Route, last week reiterated his conviction that polar shipping is the next big thing.
…
The Donald Trump administration is pushing Arctic energy development off the coast of Alaska, but otherwise hasn’t made the region a priority. Unlike in years past, there is no Arctic envoy at the State Department.

“It’s in no one’s urgent inbox, and there’s no budget behind it,” Conley says. “Meanwhile, Russia and China’s interest and activity in the Arctic is only increasing.”"
&

Title: "Russian Ministers Try to Fulfill Putin’s Arctic Shipping Goals" January 21, 2019

https://www.maritime-executive.com/editorials/russian-ministers-try-to-fulfill-putin-s-arctic-shipping-goals

Extract: "Ever since Russian President Vladimir Putin decreed last year that shipping traffic through the Arctic’s Northern Sea Route must increase to a soaring 80 million tons annually within a mere five years, the emperor’s wish has been treated as a reality.

The May presidential decree had the ring of the old-fashioned Stalinist five-year plans, which, throughout the communist era, were the economic yardstick of the Soviet economy. The penalties for coming up short were harsh, with under-producing bureaucrats singled out for public humiliation, the Gulag and worse.
…
According to documents, the ministry calculated that by 2024, LNG shipments along the Arctic will reach only some 40 million tons, followed by 9.2 million tons of oil, and 3.2 million tons of mineral ores from Norilsk Nickel, one of the world’s largest nickel producers located in Northern Siberia.
…
One of these promises came from Dmitry Bosov, one of the heads of VostokCoal, a Russian coal mining company with lavish backing from the Kremlin. Bosov made headlines in November with a commitment to ship out 30 million tons of anthracite coal per year from the Arctic’s Taymyr Peninsula. But the Natural Resources Ministry laid the odds of Bosov fulfilling that goal at only about one in five."

[AbruptSLR]

The first two associated linked sources indicate both that Arctic cloud cover is a net positive feedback mechanism and that Arctic cloud formation is highly enhanced (more so than in most other areas of the Earth) by the presence of aerosols.  These sources warn that allowing increase ship traffic into the Arctic Ocean would thus increase Arctic Amplification more than previously assumed.

Title: "Arctic Clouds Highly Sensitive to Air Pollution"

https://eos.org/scientific-press/arctic-clouds-highly-sensitive-to-air-pollution

Just a reminder that not only will increasing Arctic cloud cover act as an increasingly positive feedback mechanism in the atmosphere, but the associated rainfall (see the following linked article) will accelerate permafrost degradation and associated thermokarst lake formation; which is yet another positive feedback mechanism (due to the associated CO2 & CH4 emissions):

Title: "Study suggests a big increase in Arctic precipitation over the coming century, much of it rain"

https://phys.org/news/2017-03-big-arctic-precipitation-century.html

Extract: "A pair of researchers with the University of Groningen in the Netherlands has found via climate modeling that it appears likely that the Arctic is likely to see substantially more precipitation over the next century, much of it in the form of rain. In their paper published in the journal Nature Climate Change, Richard Bintanja and Olivier Andry describe their results when running 37 climate models programed to describe Arctic conditions over the years 2091 to 2100."

See also:

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

[AbruptSLR]

Sentinel-3's data will allow us to monitor the coming rapid changes in Antarctica's ice surface elevations:

McMillan, M., Muir, A., Shepherd, A., Escolà, R., Roca, M., Aublanc, J., Thibaut, P., Restano, M., Ambrozio, A., and Benveniste, J.: Sentinel-3 Delay-Doppler altimetry over Antarctica, The Cryosphere, 13, 709-722, https://doi.org/10.5194/tc-13-709-2019, 2019.

https://www.the-cryosphere.net/13/709/2019/

Abstract
The launch of Sentinel-3A in February 2016 represented the beginning of a new long-term series of operational satellite radar altimeters, which will provide Delay-Doppler altimetry measurements over ice sheets for decades to come. Given the potential benefits that these satellites can offer to a range of glaciological applications, it is important to establish their capacity to monitor ice sheet elevation and elevation change. Here, we present the first analysis of Sentinel-3 Delay-Doppler altimetry over the Antarctic ice sheet, and assess the accuracy and precision of retrievals of ice sheet elevation across a range of topographic regimes. Over the low-slope regions of the ice sheet interior, we find that the instrument achieves both an accuracy and a precision of the order of 10 cm, with ∼98 % of the data validated being within 50 cm of co-located airborne measurements. Across the steeper and more complex topography of the ice sheet margin, the accuracy decreases, although analysis at two coastal sites with densely surveyed airborne campaigns shows that ∼60 %–85 % of validated data are still within 1 m of co-located airborne elevation measurements. We then explore the utility of the Sentinel-3A Delay-Doppler altimeter for mapping ice sheet elevation change. We show that with only 2 years of available data, it is possible to resolve known signals of ice dynamic imbalance and to detect evidence of subglacial lake drainage activity. Our analysis demonstrates a new, long-term source of measurements of ice sheet elevation and elevation change, and the early potential of this operational system for monitoring ice sheet imbalance for decades to come.

Caption for second image: "Figure 7(a) Rates of Antarctic surface elevation change derived from Sentinel-3A Delay-Doppler altimetry acquired between May 2016 and June 2018. The background image is a shaded relief derived from a DEM (Slater et al., 2018), overlaid upon the MODIS Mosaic of Antarctica (MOA) (Haran et al., 2006). The white line shows, for reference, the CryoSat-2 mode mask boundary, which separates regions where CryoSat-2 operates in low-resolution mode (interior regions) and in SAR interferometric mode (coastal regions). The absence of Sentinel-3 elevation rate data in the region surrounding the South Pole is due to the 81.35∘ latitudinal limit of the satellite orbit. (b) Localized surface lowering resolved by Sentinel-3A across a 30 km track segment in East Antarctica (location shown by red box in panel a), indicating a possible subglacial lake drainage event."

[AbruptSLR]

As I believe that decision makers and consensus climate scientists will not effectively address the reality of our current climate crisis until the people create an appropriate sense of urgency, I support the Youth Climate Strikers:

Title: "Youth climate strikers: 'We are going to change the fate of humanity'"

https://www.theguardian.com/environment/2019/mar/01/youth-climate-strikers-we-are-going-to-change-the-fate-of-humanity

Extract: "Students issue an open letter ahead of global day of action on 15 March, when young people are expected to strike across 50 nations
…
“United we will rise on 15 March and many times after until we see climate justice. We demand the world’s decision makers take responsibility and solve this crisis. You have failed us in the past. [But] the youth of this world has started to move and we will not rest again.”"


Caption for image: "Swedish climate activist Greta Thunberg speaking at a protest in front of the city hall in Hambourg, Germany. Photograph: Axel Heimken/Getty"

[jai mitchell]

The first two associated linked sources indicate both that Arctic cloud cover is a net positive feedback mechanism and that Arctic cloud formation is highly enhanced (more so than in most other areas of the Earth) by the presence of aerosols.  These sources warn that allowing increase ship traffic into the Arctic Ocean would thus increase Arctic Amplification more than previously assumed.

Title: "Arctic Clouds Highly Sensitive to Air Pollution"

https://eos.org/scientific-press/arctic-clouds-highly-sensitive-to-air-pollution


Q. Coopman et al. (09 November 2017), "High Sensitivity of Arctic Liquid Clouds to Long‐Range Anthropogenic Aerosol Transport", Geophysical Research Letters, https://doi.org/10.1002/2017GL075795

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2017GL075795

These are gold, especially the second one.

[AbruptSLR]

While I have previously cited the linked reference on potential percolation of seawater in into Antarctic ice shelves where layers of firn are located below sea level, here, I emphasize that the Thwaites ice shelf is most likely to have the highest degree of seawater intrusion of any identified Antarctic ice shelf.  This is not a good thing as this means that the Thwaites ice shelf is more susceptible hydrofracturing than previously assumed by consensus climate science:

Cook, S., Galton-Fenzi, B. K., Ligtenberg, S. R. M., and Coleman, R.: Brief Communication: Widespread potential for seawater infiltration on Antarctic ice shelves, The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-146, in review, 2018.

https://www.the-cryosphere.net/12/3853/2018/tc-12-3853-2018.pdf


Abstract. ."Antarctica’s future contribution to sea level change depends on the fate of its fringing ice shelves. One factor which may affect the rate of iceberg calving from ice shelves is the presence of liquid water, including the percolation of seawater into permeable firn layers. Here, we present evidence that most ice shelves around Antarctica have regions where permeable firn exists below sea level. We find that seawater infiltration into ice shelves may be much more widespread in Antarctica than previously recognised. Finally, we identify the locations where seawater infiltration is most likely to occur, with the intention that the results maybe used to direct future radar studies."

Caption for the first image: " Figure1. Map of potential brine zones areas around Antarctica. Map shows areas where permeable firn lies below sea level (the brine zone), with the threshold for firn permeability defined as 750kgm−3 (red), 800kgm−3 (yellow) and 830kgm−3 (blue) calculated using Bedmap2 surface elevation. Bar charts show the mean percentage area of selected ice shelves covered by the brine zone."

Caption for the second image: "Figure2. Previous observations of firn and brine around Antarctica. Coloured areas show potential brine zones as described in Fig.1. Closed circles indicate boreholes where brine has been observed. Open circles are firn cores which penetrated below sea level but found no brine. Observations of brine using ice-penetrating radar are marked with black stars. Grey boxes on the main map indicate the extent of regions mapped in subfigures:(b) Wilkins Ice Shelf, (c) Ross Ice Shelf, (d) Princess Ragnhild Coast and (e) McMurdo Ice Shelf. Panel (b) is adapted from (Vaughan et al., 1993) with thin black lines showing the full network of radar flight paths over the ice shelf. Thick black lines indicate areas where no brine was detected. Observations are described in detail in Tables S4 and S5."

See also, and the third image of firn air depletion:

Peter KUIPERS MUNNEKE et al. (2014), "Firn air depletion as a precursor of Antarctic ice-shelf collapse", Journal of Glaciology, Vol. 60, No. 220, 2014 doi: 10.3189/2014JoG13J183

https://www.igsoc.org/journal/60/220/t13J183.pdf

Abstract: "ABSTRACT. Since the 1970s, the sudden, rapid collapse of ~20% of ice shelves on the Antarctic Peninsula has led to large-scale thinning and acceleration of its tributary glaciers. The leading hypothesis for the collapse of most of these ice shelves is the process of hydrofracturing, whereby a water-filled crevasse is opened by the hydrostatic pressure acting at the crevasse tip. This process has been linked to observed atmospheric warming through the increased supply of meltwater. Importantly, the low-density firn layer near the ice-shelf surface, providing a porous medium in which meltwater can percolate and refreeze, has to be filled in with refrozen meltwater first, before hydrofracturing can occur at all. Here we build upon this notion of firn air depletion as a precursor of ice-shelf collapse, by using a firn model to show that pore space was depleted in the firn layer on former ice shelves, which enabled their collapse due to hydrofracturing. Two climate scenario runs with the same model indicate that during the 21st century most Antarctic Peninsula ice shelves, and some minor ice shelves elsewhere, are more likely to become susceptible to collapse following firn air depletion. If warming continues into the 22nd century, similar depletion will become widespread on ice shelves around East Antarctica. Our model further suggests that a projected increase in snowfall will protect the Ross and Filchner–Ronne Ice Shelves from hydrofracturing in the coming two centuries."

[AbruptSLR]

The linked 2017 article entitled "Ice Apocalypse" reconfirms many of the points made in this thread:

Title: "Ice Apocalypse"

https://grist.org/article/antarctica-doomsday-glaciers-could-flood-coastal-cities/

Extract: "In the past few years, scientists have identified marine ice-cliff instability as a feedback loop that could kickstart the disintegration of the entire West Antarctic ice sheet this century — much more quickly than previously thought.
Minute-by-minute, huge skyscraper-sized shards of ice cliffs would crumble into the sea, as tall as the Statue of Liberty and as deep underwater as the height of the Empire State Building. The result: a global catastrophe the likes of which we’ve never seen.
…
A wholesale collapse of Pine Island and Thwaites would set off a catastrophe. Giant icebergs would stream away from Antarctica like a parade of frozen soldiers. All over the world, high tides would creep higher, slowly burying every shoreline on the planet, flooding coastal cities and creating hundreds of millions of climate refugees.

All this could play out in a mere 20 to 50 years — much too quickly for humanity to adapt."

[AbruptSLR]

The linked reference and associated article (& the first image) indicate that the number of global average ocean heatwave days has tripled in recent years. As this trend in the number of ocean heatwave days is closely linked to ENSO trends, this information supports James Hansen's position (see second attached image) that El Nino events are already becoming more frequent (which implies that ECS is likely higher than assumed by consensus climate science):

Dan A. Smale (2019), "Marine heatwaves threaten global biodiversity and the provision of ecosystem services", Nature Communications, https://doi.org/10.1038/s41558-019-0412-1.

https://www.nature.com/articles/s41558-019-0412-1.epdf?referrer_access_token=nbXlSefHuxLXsPggbRYaYdRgN0jAjWel9jnR3ZoTv0MZYsBsaXIKb-fVObm0N-AgwEnED6cZs5J51AHSuQ0zO55Cxccyq0tvhgH5IAV31I-9Px-9gnq1z6PsxoTtPF4bG_WqGkWHE8p1T-QRgWSgiUG45bF2W3cI396usEMgl9AZ4LINfkDQ7dYOrngJpW_-EgIKVKrd_Xbpy28i_lMzJMq8eSBjDAm0OhWYZEqsE7pbO1hZyfDMbQW_klGyweoHtDoeYWiP4SGCef_-IaoWUDgjiapezbjlAY8R9gxJvBsimjBBIwlZEgtVWrTmMR31&tracking_referrer=www.theguardian.com

Abstract: "The global ocean has warmed substantially over the past century, with far-reaching implications for marine eco-systems. Concurrent with long-term persistent warming, discrete periods of extreme regional ocean warming (marine heatwaves, MHWs) have increased in frequency. Here we quantify trends and attributes of MHWs across all ocean basins and examine their biological impacts from species to ecosystems. Multiple regions in the Pacific, Atlantic and Indian Oceans are particularly vulnerable to MHW intensification, due to the co-existence of high levels of biodiversity, a prevalence of species found at their warm range edges or concurrent non-climatic human impacts. The physical attributes of prominent MHWs varied considerably, but all had deleterious impacts across a range of biological processes and taxa, including critical foundation species (corals, seagrasses and kelps). MHWs, which will probably intensify with anthropogenic climate change, are rapidly emerging as forceful agents of disturbance with the capacity to restructure entire ecosystems and disrupt the provision of ecological goods and services in coming decades."

See also the associated article, and attached image, at:

Title: "Heatwaves sweeping oceans ‘like wildfires’, scientists reveal"

https://www.theguardian.com/environment/2019/mar/04/heatwaves-sweeping-oceans-like-wildfires-scientists-reveal

[AbruptSLR]

The linked article indicates that many climate scientists are worried about the recent increase in atmospheric methane concentrations (see the attached image).

Title: "Methane in the atmosphere is surging, and that’s got scientists worried"

https://www.latimes.com/science/sciencenow/la-sci-sn-methane-atmosphere-accelerating-20190301-story.html

Caption for accompanying image: "The concentration of methane in the atmosphere, indicated by green circles, is not consistent with a climate scenario that aggressively limits global warming (the solid green line labeled RCP 2.6). The other pathways lead to more warming. (Martin Manning / Victoria University of Wellington)"

[Shared Humanity]

The linked reference and associated article (& the first image) indicate that the number of global average ocean heatwave days has tripled in recent years.

Every chart I have seen tracking some component of climate change shows an exponential trend. This heat wave chart is no exception.

[Shared Humanity]

The linked article indicates that many climate scientists are worried about the recent increase in atmospheric methane concentrations (see the attached image).

Title: "Methane in the atmosphere is surging, and that’s got scientists worried"

https://www.latimes.com/science/sciencenow/la-sci-sn-methane-atmosphere-accelerating-20190301-story.html

Nice interactive atmospheric methane chart...

https://www.methanelevels.org/

[AbruptSLR]

In the linked article Gavin Schmidt notes that consensus climate model projections missed the impact of the Antarctic ozone hole (which has greatly accelerated ice mass loss from Antarctica), and acknowledges that other candidates for surprise impacts to consensus climate change projections include potential: a) positive feedbacks from climate sensitive species; b) positive feedbacks associated with the sensitivity of the WAIS, c) the sensitivity of the MOC, and d) positive carbon feedbacks from the Arctic (primarily from the permafrost).  Hopefully, Gavin will venture from the "safe harbors" of his recent climate model projections "…to explore the more treacherous shores of uncertainty . ." of the under-appreciated positive feedback mechanisms that he cites in his article:

Title: "The best case for worst case scenarios"

http://www.realclimate.org/index.php/archives/2019/02/the-best-case-for-worst-case-scenarios/#more-20520

Extract: "To be clear, “unknown unknowns” are real. A classic example in environmental science is the Antarctic polar ozone hole which was not predicted ahead of time (see my previous post on that history) and occurred as a result of chemistry that was theoretically known about but not considered salient and thus not implemented in predictions.

Possible candidates for “surprises in the greenhouse”, are shifts in ecosystem functioning because of the climate sensitivity of an under-appreciated key species (think pine bark beetles and the like), under-appreciated sensitivities in the West Antarctic Ice Sheet, or the North Atlantic overturning, and/or carbon feedbacks in the Arctic.
…
Indeed, the true worst case scenario might be one where we don’t venture out from our safe harbors of knowledge to explore the more treacherous shores of uncertainty. As we do, we will need to be careful as well as bold as we map those shoals."

[Shared Humanity]

also nifty with sea level rise...

https://www.sealevels.org/

[AbruptSLR]

Hopefully, more and more climate modelers will come to appreciate that the Exascale Computing commercial market is growing rapidly and that within the next three to four years they should be able to purchase computing time on Exascale super computers other than those ordered by the DOE for the E3SM project. 

Title: "Trends in Exascale Computing Market: Business Analysis 2018-2025 by CAGR, Share, Revenue and Prominent Key Players"

https://www.marketwatch.com/press-release/trends-in-exascale-computing-market-business-analysis-2018-2025-by-cagr-share-revenue-and-prominent-key-players-2019-02-20

Extract: "The exascale Market is segmented on the basis of component, hardware type, service type, and industry verticals, in which the hardware segment is expected to grow significantly and will reach $1.3 bn by 2023.
…
Exascale Computing refers to the processing frameworks that are capable of processing one exaFLOPS, or a billion billion (… quintillion) computations every second. It takes the High Performance Computing (HPC) to a different dimension - to the level of quintillion calculations per second. This level of computational performance is essential for solving the complex problems like climate research …
…
The key players from Exascale Computing market covered in this study are Advanced Micro Devices, Amazon Web Services, Atos, Cisco Systems, Cray Inc., DELL Technologies Inc., Fujitsu Ltd, Hewlett Packard Enterprise, IBM Corporation, Intel Corporation, Lenovo Group Ltd, Microsoft Corporation, NEC Corporation, NVIDIA, Rackspace US Inc."

&

Title: "Interview with 2019 Person to Watch Lori Diachin, Deputy Director, Exascale Computing Project" February 28, 2019

https://www.hpcwire.com/2019/02/28/2019-person-to-watch-interview-lori-diachin-deputy-director-ecp/

Extract: "First up we are happy to bring you our interview with Lori Diachin, deputy director for the U.S. Department of Energy’s Exascale Computing Project (ECP).
…
For the ECP in particular what I’ve found really exciting is the fact that it’s one of the largest and most important computing projects that the DOE has sponsored. We’re focused on developing a capable exascale computing ecosystem comprising application development, software technologies, and advanced hardware design. What we are doing could have a tremendous impact on our nation; both from the perspective of the applications we are developing and the investments we are making to keep the high performance computing ecosystem healthy.
…
There are approximately 1,000 researchers at 16 different laboratories working on over 100 different subprojects in the ECP, tracking the integration that’s happening among all of those efforts is an interesting challenge."

[AbruptSLR]

The linked reference uses 10-years of CALIPSO data to indicate that CMIP5 is likely underestimating the net positive feedback (for global warming) associated with the reduction in marine tropical low-cloud cover (LCC) as the local ocean surface warms (delta SST).  As ice-climate feedback mechanisms tend to slowdown the MOC, they induce more rapid warming of the tropical ocean surface, and thus this research supports the idea that ice-climate feedbacks will make the net cloud feedback progressively more positive:

Cesana, G., Del Genio, A. D., Ackerman, A. S., Kelley, M., Elsaesser, G., Fridlind, A. M., Cheng, Y., and Yao, M.-S.: Evaluating models' response of tropical low clouds to SST forcings using CALIPSO observations, Atmos. Chem. Phys., 19, 2813-2832, https://doi.org/10.5194/acp-19-2813-2019, 2019.

https://www.atmos-chem-phys.net/19/2813/2019/

Abstract
Recent studies have shown that, in response to a surface warming, the marine tropical low-cloud cover (LCC) as observed by passive-sensor satellites substantially decreases, therefore generating a smaller negative value of the top-of-the-atmosphere (TOA) cloud radiative effect (CRE). Here we study the LCC and CRE interannual changes in response to sea surface temperature (SST) forcings in the GISS model E2 climate model, a developmental version of the GISS model E3 climate model, and in 12 other climate models, as a function of their ability to represent the vertical structure of the cloud response to SST change against 10 years of CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) observations. The more realistic models (those that satisfy the observational constraint) capture the observed interannual LCC change quite well (ΔLCC/ΔSST=−3.49±1.01ΔLCC/ΔSST=-3.49±1.01 % K−1 vs. ΔLCC/ΔSSTobs=−3.59±0.28ΔLCC/ΔSSTobs=-3.59±0.28 % K−1) while the others largely underestimate it (ΔLCC/ΔSST=−1.32±1.28ΔLCC/ΔSST=-1.32±1.28 % K−1). Consequently, the more realistic models simulate more positive shortwave (SW) feedback (ΔCRE/ΔSST=2.60±1.13ΔCRE/ΔSST=2.60±1.13  W m−2 K−1) than the less realistic models (ΔCRE/ΔSST=0.87±2.63ΔCRE/ΔSST=0.87±2.63  W m−2 K−1), in better agreement with the observations (ΔCRE/ΔSSTobs=3±0.26ΔCRE/ΔSSTobs=3±0.26 W m−2 K−1), although slightly underestimated. The ability of the models to represent moist processes within the planetary boundary layer (PBL) and produce persistent stratocumulus (Sc) decks appears crucial to replicating the observed relationship between clouds, radiation and surface temperature. This relationship is different depending on the type of low clouds in the observations. Over stratocumulus regions, cloud-top height increases slightly with SST, accompanied by a large decrease in cloud fraction, whereas over trade cumulus (Cu) regions, cloud fraction decreases everywhere, to a smaller extent.

Extract: "In response to interannual surface warming, the marine tropical low-cloud cover (LCC) as observed by the active sensor from the CALIPSO satellite over a 10-year period significantly decreases (ΔLCC/ΔSST=−3.59ΔLCC/ΔSST=-3.59 % K−1). This reduction of the LCC is larger than that found using results from passive-sensor satellites (ΔLCC=−1ΔLCC=-1 to −2.95 % K−1), albeit consistent in terms of sign and magnitude (e.g., McCoy et al., 2017; Qu et al., 2015; Seethala et al., 2015). Overall, the ensemble mean of CMIP5 models captures the sign and the shape of the observed interannual low-cloud cover change (ΔLCC∕ΔSST) quite well. However, its magnitude is underestimated and the model variability is large (ΔLCC/ΔSST=−2.25±1.58ΔLCC/ΔSST=-2.25±1.58 % K−1), with some models (2 out of 14) even producing the wrong sign (a gain instead of a loss)."

[AbruptSLR]

The linked reference indicates that for a BAU pathway, Greenland permafrost will likely be a significant source of future methane emissions; which is yet another positive feedback mechanism that is underestimated by consensus climate science:

Marilena Sophie Geng, Jens Hesselbjerg Christensen and Torben Røjle Christensen (2019), "Potential future methane emission hot spots in Greenland", Environmental Research Letters, Volume 14, Number 3

https://iopscience.iop.org/article/10.1088/1748-9326/aaf34b/meta

Abstract
Climate models have been making significant progress encompassing an increasing number of complex feedback mechanisms from natural ecosystems. Permafrost thaw and subsequent induced greenhouse gas emissions, however, remain a challenge for climate models at large. Deducing permafrost conditions and associated greenhouse gas emissions from parameters that are simulated in climate models would be a helpful step towards estimating emission budgets from permafrost regions. Here we use a regional climate model with a 5 km horizontal resolution to assess future potential methane (CH4) emissions over presently unglaciated areas in Greenland under an RCP8.5 scenario. A simple frost index is applied to estimate permafrost conditions from the model output. CH4 flux measurements from two stations in Greenland; Nuuk representing sub-Arctic and Zackenberg high-Arctic climate, are used to establish a relationship between emissions and near surface air temperature. Permafrost conditions in Greenland change drastically by the end of the 21st century in an RCP8.5 climate. Continuous permafrost remains stable only in North Greenland, the north-west coast, the northern tip of Disko Island, and Nuussuaq. Southern Greenland conditions only sustain sporadic permafrost conditions and largely at high elevations, whereas former permafrost in other regions thaws. The increasing thawed soil leads to increasing CH4 emissions. Especially the area surrounding Kangerlussuaq, Scoresby Land, and the southern coast of Greenland exhibit potentially high emissions during the longer growing season. The constructed maps and budgets combining modelled permafrost conditions with observed CH4 fluxes from CH4 promoting sites represent a useful tool to identify areas in need of additional monitoring as they highlight potential CH4 hot spots.

[AbruptSLR]

If consensus climate science provided sufficiently accurate projections in a timely manner for engineers, regulators and other decision makers to take appropriate action, then the number of climate change lawsuits would not be proliferating at their current high rate.  Consensus climate scientists should emphasize to decision makers that they do not have all the answers to our complex climate change situation, so that the decisions makers can more easily be held legally accountable for not taking appropriate precautions to better address our current high risk situation:

Joana Setzer et al. (04 March 2019), "Climate change litigation: A review of research on courts and litigants in climate governance", WIREs Climate Change, https://doi.org/10.1002/wcc.580

https://onlinelibrary.wiley.com/doi/abs/10.1002/wcc.580

Abstract
Studies of climate change litigation have proliferated over the past two decades, as lawsuits across the world increasingly bring policy debates about climate change mitigation and adaptation, as well as climate change‐related loss and damage to the attention of courts. We systematically identify 130 articles on climate change litigation published in English in the law and social sciences between 2000 and 2018 to identify research trajectories. In addition to a budding interdisciplinarity in scholarly interest in climate change litigation we also document a growing understanding of the full spectrum of actors involved and implicated in climate lawsuits and the range of motivations and/or strategic imperatives underpinning their engagement with the law. Situating this within the broader academic literature on the topic we then highlight a number of cutting edge trends and opportunities for future research. Four emerging themes are explored in detail: the relationship between litigation and governance; how time and scale feature in climate litigation; the role of science; and what has been coined the “human rights turn” in climate change litigation. We highlight the limits of existing work and the need for future research—not limited to legal scholarship—to evaluate the impact of both regulatory and anti‐regulatory climate‐related lawsuits, and to explore a wider set of jurisdictions, actors and themes. Addressing these issues and questions will help to develop a deeper understanding of the conditions under which litigation will strengthen or undermine climate governance.

[AbruptSLR]

While the linked reference does not make a bulletproof case, its general point is a good one that climate change scientists needed to do a better job communicating climate risks to both the public and decision makers, as we collectively approach cascading tipping points.  I do not attach any of Sharpe's plots because I believe that they underestimate our true risks:

Sharpe, S.: Telling the boiling frog what he needs to know: why climate change risks should be plotted as probability over time, Geosci. Commun. Discuss., https://doi.org/10.5194/gc-2019-1, in review, 2019.

https://www.geosci-commun-discuss.net/gc-2019-1/

Abstract. Humanity's situation with respect to climate change is sometimes compared to that of a frog in a slowly-boiling pot of water, meaning that change will happen too gradually for us to appreciate the likelihood of catastrophe and act before it is too late. I argue that the scientific community is not yet telling the boiling frog what he needs to know. I use a review of the figures included in two reports of the Inter-governmental Panel on Climate Change to show that much of the climate science communicated to policymakers is presented in the form of projections of what is most likely to occur, as a function of time (equivalent to: in 5 minutes' time, the water you are sitting in will be two degrees warmer). I argue from first principles that a more appropriate means of assessing and communicating the risks of climate change would be to produce assessments of the likelihood of crossing non-arbitrary thresholds of impact, as a function of time (equivalent to: the probability of you being boiled to death will be 1% in five minutes' time, rising to 100% in twenty minutes' time if you don't jump out of the pot). This would be consistent with approaches to risk assessment in fields such as insurance, engineering, and health and safety. Importantly, it would ensure decision-makers were informed of the biggest risks, and hence of the strongest reasons to act. I suggest ways in which the science community could contribute to promoting this approach, taking into account its inherent need for cross-disciplinary research and for engagement with decision-makers before the research is conducted, instead of afterwards.

[AbruptSLR]

Consensus climate change modelers use families of SSP (or RCP/SRES) scenarios to address/cover their uncertainties associated with future anthropogenic carbon emissions; therefore, it is logical that to evaluate right-tail risks they should be willing to generate comparable families of 'right-tail' uncertainties associated with the following: radiative forcings, feedback mechanisms and initial model conditions:

1. The linked reference indicates that consensus climate science is underestimating the cooling effect of anthropogenic aerosols, which means that the climate sensitivity values assumed by consensus climate scientists.  Thus 'right-tail' uncertainties scenarios could include a number of likely warming mechanism that have been masked by the underestimated cooling aerosol mechanism, such as: a) more high-altitude clouds, b) extant ice-climate feedbacks and/or c) greater lapse rate effects.

Daniel Rosenfeld, Yannian Zhu, Minghuai Wang, Youtong Zheng, Tom Goren, Shaocai Yu. Aerosol-driven droplet concentrations dominate coverage and water of oceanic low level clouds. Science, 2019; eaav0566 DOI: 10.1126/science.aav0566

http://science.sciencemag.org/content/early/2019/01/16/science.aav0566

2. The measured ocean heat content (OHC) has exceeded consensus model hindcasts.  Therefore, 'right-tailed' uncertainties scenarios could include mechanisms such as: a) in recent decades ENSO cycles have been more efficient sequestering tropical ocean heat but with warming the tropical ocean SST will increase faster than assumed; b) in recent decades the MOC was faster, but now that it is slowing down the tropical ocean SST will increase faster than assumed; and c) as the OHC has been increasing sense around 1750, more slow response oceanic positive feedback mechanisms are already being activated.

3. Most consensus climate models have ignored the fact that volatile organic compounds emitted by forests promote the formation of low-level clouds; which act as a negative feedback (for warming).  Thus, the fact that deforestation accelerated with the beginning of the industrial revolution, implies that estimates of climate sensitivity based on observations before the deforestation accelerated would understate the true values for ECS (see the linked reference).  Thus 'right-tail' uncertainties scenarios could correct for this oversight:

Lejeune et al (2018), "Historical deforestation locally increased the intensity of hot days in northern mid-latitudes", Nature Climate Change 8, https://doi.org/10.1038/s41558-018-0131-z

https://www.nature.com/articles/s41558-018-0131-z

Edit, see also:

Octaviani, M., Tost, H., and Lammel, G.: Global Simulation of Semivolatile Organic Compounds – Development and Evaluation of the MESSy Submodel SVOC (v1.0), Geosci. Model Dev. Discuss., https://doi.org/10.5194/gmd-2019-19, in review, 2019.

https://www.geosci-model-dev-discuss.net/gmd-2019-19/
___________

If you scroll back through this thread you will find numerous other 'right-tail' uncertainties that have been underestimated by current consensus climate science models, that could be addressed by potential future 'right-tail' uncertainties scenarios.

[AbruptSLR]

Per the attached images, it is likely that the 2018-19 and the 2019-2020 ENSO seasons may likely have back-to-back El Nino events (per the NOAA definition).  If so this would support Hansen's observation the frequency of El Nino event is increasing with global warming.

[AbruptSLR]

The linked reference provides optical properties of "rotten" Arctic sea ice which are distinct from the well-studied summertime sea ice properties.  Consensus climate change models should be updated to include this new information, as the properties of the "rotten" sea ice can has a significant impact on fluid and heat exchange in the upper Arctic Ocean:

Frantz, C. M., Light, B., Farley, S. M., Carpenter, S., Lieblappen, R., Courville, Z., Orellana, M. V., and Junge, K.: Physical and optical characteristics of heavily melted “rotten” Arctic sea ice, The Cryosphere, 13, 775-793, https://doi.org/10.5194/tc-13-775-2019, 2019.

https://www.the-cryosphere.net/13/775/2019/

Abstract
Field investigations of the properties of heavily melted “rotten” Arctic sea ice were carried out on shorefast and drifting ice off the coast of Utqiaġvik (formerly Barrow), Alaska, during the melt season. While no formal criteria exist to qualify when ice becomes rotten, the objective of this study was to sample melting ice at the point at which its structural and optical properties are sufficiently advanced beyond the peak of the summer season. Baseline data on the physical (temperature, salinity, density, microstructure) and optical (light scattering) properties of shorefast ice were recorded in May and June 2015. In July of both 2015 and 2017, small boats were used to access drifting rotten ice within ∼32 km of Utqiaġvik. Measurements showed that pore space increased as ice temperature increased (−8 to 0 ∘C), ice salinity decreased (10 to 0 ppt), and bulk density decreased (0.9 to 0.6 g cm−3). Changes in pore space were characterized with thin-section microphotography and X-ray micro-computed tomography in the laboratory. These analyses yielded changes in average brine inclusion number density (which decreased from 32 to 0.01 mm−3), mean pore size (which increased from 80 µm to 3 mm), and total porosity (increased from 0 % to > 45 %) and structural anisotropy (variable, with values of generally less than 0.7). Additionally, light-scattering coefficients of the ice increased from approximately 0.06 to > 0.35 cm−1 as the ice melt progressed. Together, these findings indicate that the properties of Arctic sea ice at the end of melt season are significantly distinct from those of often-studied summertime ice. If such rotten ice were to become more prevalent in a warmer Arctic with longer melt seasons, this could have implications for the exchange of fluid and heat at the ocean surface.

[AbruptSLR]

In the linked article, Zeke Hausfather performs a valuable service by debunking information presented on WUWT, by presenting consensus science information (see the attached images) of reconstructed temperatures in Greenland during the Holocene.

Title: "Factcheck: What Greenland ice cores say about past and present climate change" by Zeke Hausfather, March 5, 2019

https://www.carbonbrief.org/factcheck-what-greenland-ice-cores-say-about-past-and-present-climate-change

However, I note that while Hausfather is performing a valuable service by presenting consensus science information; he, and virtually all other consensus scientists, fails to note that the IPCC projections that he presents fail to consider conditional probabilities of how cascading thresholds could be crossed as various times of the assumed emission pathway; which (if considered) would likely increase projected temperature increases (in the images for Greenland up to 2100).  Therefore, the readers of such consensus climate science articles are left with an incorrect evaluation of likely future responses to climate change.

[AbruptSLR]

In Reply #682 I noted that Gavin Schmidt essentially acknowledged that CMIP5 did not address several potentially significant feedback mechanisms that are included in CMIP6; and I essentially gave him an 'atta boy' for his work to continue to update consensus science.  That said, in the linked article Gavin indicates that he does not believe that consensus scientists exhibit reticence (in contract to Hansen's statements that they do); and depending on how one defines 'worst cases' the extracted statement below Gavin indicates that he believes that consensus climate scientists would have to be both 'incredibly stupid' and 'incredibly unlucky' for such worst cases to occur (as they are absent from consensus science projections). Gavin then goes on to state "… who should be listened to and trusted on these questions?"  Seeing as most people are concerned about worst case scenarios that occur by 2100, I provide the four attached images from sources that I recommend that Gavin should trust when the GISS makes its CMIP6 runs:

a) The first image shows NOAA's (Sweet et al. 2017) SLR projections that provide the H++ scenario with the WAIS collapse considered.  I suggest that Gavin trust NOAA's judgement for timing and magnitude.

b) The second image (from Bronselaer et al 2018) shows how quickly ice-climate feedback mechanisms can both raise and warm CDW off the coast of Antarctica (due largely to Antarctic ice mass loss). I suggest that Gavin trust Bronselaer et al's result w.r.t. what (& when) ocean heat to apply to the grounding lines of key Antarctic marine glaciers.

c) The third image shows Brown & Caldeira 2017 projections for GMSTA increases through 2100 & I recommend that Gavin trust Brown & Caldeira's calibrated projections for GMSTA.

d) The fourth image from the US National Academy of Science, NAS, gives an idea of how fat they suspect that the right tail of abrupt impact pdfs can be.  I recommend that Gavin trust the NAS in this matter.

Finally, while CMIP6 will clearly be an improvement over CMIP5 (w.r.t. characterizing climate risks), just as clearly it will not be the last word on this matter as I imagine that CMIP7 will indicate greater climate risks than CMIP6 will.
__________

Title: "The best case for worst case scenarios" by Gavin Schmidt

http://www.realclimate.org/index.php/archives/2019/02/the-best-case-for-worst-case-scenarios/#more-20520

Extract: "Summary
To get to the worst cases, two things have to happen – we have to be incredibly stupid and incredibly unlucky. Dismissing plausible worst case scenarios adds to the likelihood of both. Conversely, dwelling on impossible catastrophes is a massive drain of mental energy and focus. But the fundamental question raised by the three points above is who should be listened to and trusted on these questions?"

See also:

Bronselaer, B. et al. (2018) Change in future climate due to Antarctic meltwater, Nature, doi:s41586-018-0712-z

https://www.nature.com/articles/s41586-018-0712-z

[AbruptSLR]

We should always remember that both the GIS and the AIS are losing ice mass, and both contribute to ice-climate feedback mechanism.  The linked reference cites impact of the North Atlantic Warming Hole (i.e. a cool region) has on the mean atmospheric circulation & the North Atlantic jet:

Melissa Gervais (2019), "Impacts of the North Atlantic Warming Hole in Future Climate Projections: Mean Atmospheric Circulation and the North Atlantic jet", Journal of Climate; https://doi.org/10.1175/JCLI-D-18-0647.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-18-0647.1

Abstract: "In future climate simulations there is a pronounced region of reduced warming in the subpolar gyre of the North Atlantic ocean known as the North Atlantic warming hole (NAWH). This study investigates the impact of the North Atlantic warming hole on atmospheric circulation and midlatitude jets within the Community Earth System model (CESM). A series of large-ensemble atmospheric model experiments with prescribed sea surface temperature (SST) and sea ice are conducted, in which the warming hole is either filled or deepened. Two mechanisms through which the NAWH impacts the atmosphere are identified: a linear response characterized by a shallow atmospheric cooling and increase in sea level pressure shifted slightly downstream of the SST changes; and a transient eddy forced response whereby the enhanced SST gradient produced by the NAWH leads to increased transient eddy activity that propagates vertically and enhances the midlatitude jet. The relative contributions of these two mechanisms and the details of the response are strongly dependent on the season, time period, and warming hole strength. Our results indicate that the NAWH plays an important role in midlatitude atmospheric circulation changes in CESM future climate simulations."

[AbruptSLR]

The linked reference argues that consensus climate science is only now being faced with the challenge of making life-or-death decisions on how to offer concrete advice about climate risk, under the conditions of uncertainty; and considers the pending collapse of the WAIS as a case study of how scientific reticence can make our collective situation worse.  Certainly, waiting for seven sigma confirmation will result in many, many unnecessary deaths, and this reference offer the guidelines governing the behavior of doctors and engineers as a means to prevent consensus climate scientists from erring too much on the side of least drama.  Per Hansen: "We may come to rue reticence if it serves to lock in future disasters."

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

Abstract: "James Hansen and others have argued that climate scientists are often reluctant to speak out about extreme outcomes of anthropogenic carbonization. According to Hansen, such reticence lessens the chance of effective responses to these threats. With the collapse of the West Antarctic Ice Sheet (WAIS) as a case study, reasons for scientific reticence are reviewed. The challenges faced by scientists in finding the right balance between reticence and speaking out are both ethical and methodological. Scientists need a framework within which to find this balance. Such a framework can be found in the long-established practices of professional ethics."

Edit: I provide the attached image as a reminder of how engineers deal with uncertainties.

[AbruptSLR]

I provide the attached image as a reminder of how much the ASE ice shelves change between 2000 and 2011; and I note that now the SW Tributary Glacier is no longer buttressed by the Pine Island Ice Shelf.

[Lennart van der Linde]

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?

[sidd]

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

 

[AbruptSLR]

The linked reference (& associate article) indicate that year-round cyclonic precipitation events are participating in the decline of the Greenland Ice Sheet, and that this behavior caught consensus scientists by surprise (i.e. it is not included in their models):

Marilena Oltmanns, Fiammetta Straneo, and Marco Tedesco (2019), "Increased Greenland melt triggered by large-scale, year-round cyclonic moisture intrusions", The Cryosphere, 13, 815–825, 2019 https://doi.org/10.5194/tc-13-815-2019

https://www.the-cryosphere.net/13/815/2019/tc-13-815-2019.pdf

Abstract.
Surface melting is a major driver of Greenland’s mass loss. Yet, the mechanisms that trigger melt are still insufficiently understood because seasonally based studies blend processes initiating melt with positive feedbacks. Here, we focus on the triggers of melt by examining the synoptic atmospheric conditions associated with 313 rapid melt increases, detected in a satellite-derived melt extent product, equallydistributedthroughouttheyearovertheperiod1979– 2012. By combining reanalysis and weather station data, we show that melt is initiated by a cyclone-driven, southerly flow of warm, moist air, which gives rise to large-scale precipitation. A decomposition of the synoptic atmospheric variability over Greenland suggests that the identified, melt-triggering weather pattern accounts for ∼40% of the net precipitation, but increases in the frequency, duration and areal extent of the initiated melting have shifted the line between mass gain and mass loss as more melt and rainwater run off or accumulate in the snowpack. Using a regional climate model, we estimate that the initiated melting more than doubled over the investigated period, amounting to ∼28% of the overall surface melt and revealing that, despite the involved mass gain, year-round precipitation events are participating in the ice sheet’s decline.

See also:

Title: "Climate change: Rain melting Greenland ice sheet 'even in winter'"

https://www.bbc.com/news/science-environment-47485847

Extract: "Rain is becoming more frequent in Greenland and accelerating the melting of its ice, a new study has found.

Scientists say they're "surprised" to discover rain falling even during the long Arctic winter."