Ice Apocalypse - Multiple Meters Sea Level Rise

[AbruptSLR]

Peter A. Tuckett et al. (2019), "Rapid accelerations of Antarctic Peninsula outlet glaciers driven by surface melt", Nature Communications,  10, Article number: 4311, DOI: https://doi.org/10.1038/s41467-019-12039-2

I would assume this lubricating effect applies to glacier beds above sea level.  Those below sea level must be wet all the time.  But do these drainage events effect both above and below in the same way?

Ice flow dynamics of marine and marine-terminating glaciers is a complex topic; which I attempt to simplify by focusing in this post on Terry Hughes' conceptualization of key mechanisms governing these ice flow dynamics.  I begin with Hughes et al (2011) (see following link to a free access pdf and the abstract) that discusses the ice-bed coupling beneath and beyond ice streams using information related to a 2004 surge in the flow of the Byrd Glacier associated with the basal drainage of two large subglacial lakes.  The Hughes et al 2011 reference shows how episodic basal water discharges trigger accelerating ice flow surges that are controlled by the floating friction (phi) that is influenced by the internal ice structure in the ice sheet (see the first attached image and associated caption).  Here I believe that it is important to note that the first image shows that when/as surface meltwater penetrates into the glacial ice (via fissures, etc.) it raises the hydrostatic water level (phreatic surface) in the glacial ice to elevations well above sea level.  Thus, the influence of surface meltwater when it reaches the basal level of the marine, and/or marine-terminating, glacier has a buoyant up-lifting action that reduces the basal friction force (which is a function of the normal force on the glacial bed).  Thus, my prior post is relevant to the subsea portions of both marine, and marine-terminating, glaciers.

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

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

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

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

The next linked reference by Hughes et al (2015) presents analysis about something Hughes called the Jakobshavn Effect (Hughes, 1986), and it focus on progressive ice-bed uncoupling due to such factors as: basal meltwater, buoyancy friction (particularly with changing surface elevation), boundary constraints of the fjord.  This work has relevance to multiple marine-terminating, and marine, glaciers in both Greenland and Antarctica:

Hughes, T., Sargent, A., Fastook, J., Purdon, K., Li, J., Yan, J.-B., and Gogineni, S.: Sheet, stream, and shelf flow as progressive ice-bed uncoupling: Byrd Glacier, Antarctica, and Jakobshavn Isbrae, Greenland, The Cryosphere Discuss., 9, 4271-4354, doi:10.5194/tcd-9-4271-2015, 2015.

http://www.the-cryosphere-discuss.net/9/4271/2015/tcd-9-4271-2015.pdf

Abstract. The first-order control of ice thickness and height above sea level is linked to the decreasing strength of ice-bed coupling alone flowlines from an interior ice divide to the calving front of an ice shelf. Uncoupling progresses as a frozen bed progressively thaws for sheet flow, as a thawed bed is progressively drowned for stream flow, and as lateral and/or local grounding vanish for shelf flow. This can reduce ice thicknesses by 90 % and ice elevations by 99 % along flowlines. Original work presented here includes (1) replacing flow and sliding laws for sheet flow with upper and lower yield stresses for creep in cold overlying ice and basal ice sliding over deforming till, respectively, (2) replacing integrating the Navier–Stokes equations for stream flow with geometrical solutions to the force balance, and (3) including resistance to shelf flow caused by lateral confinement in a fjord and local grounding at ice rumples and ice rises. A comparison is made between our approach and two approaches based on continuum mechanics. Applications are made to Byrd Glacier in Antarctica and Jakobshavn Isbrae in Greenland.

Extract: "Warming in high polar latitudes can, in principle, trigger a succession of positive feedback mechanisms called the Jakobshavn Effect (Hughes, 1986). Buoyancy fraction phiB combines the two dominant mechanisms, reduced ice-bed coupling when surface meltwater floods the bed under an ice stream and reduced ice-shelf buttressing when an ice shelf disintegrates beyond the ice stream. For Greenland, the Jakobshavn Effect would move northward along the east and west coasts, affecting all calving ice streams."

Lastly, the next reference relates the Jakobshavn to the Byrd response to ice-bed uncoupling (including from an influx of basal meltwater), Hughes et al 2016 present a discussion of such matters on the progression/acceleration of marine glacial flow/retreat with continued global warming.  The authors also relate their findings to other critical marine glaciers in both Greenland and Antarctica.  The last two attached images relate ice-bed uncoupling for Jakobshavn and to the Jakobshavn Effect, respectively.

Hughes, T., Sargent, A., Fastook, J., Purdon, K., Li, J., Yan, J.-B., and Gogineni, S.: Sheet, stream, and shelf flow as progressive ice-bed uncoupling: Byrd Glacier, Antarctica and Jakobshavn Isbrae, Greenland, The Cryosphere, 10, 193-225, doi:10.5194/tc-10-193-2016, 2016

http://www.the-cryosphere.net/10/193/2016/

Abstract. The first-order control of ice thickness and height above sea level is linked to the decreasing strength of ice-bed coupling along flowlines from an interior ice divide to the calving front of an ice shelf. Uncoupling progresses as a frozen bed progressively thaws for sheet flow, as a thawed bed is progressively drowned for stream flow, and as lateral and/or local grounding vanish for shelf flow. This can reduce ice thicknesses by 90 % and ice elevations by 99 % along flowlines. Original work presented here includes (1) replacing flow and sliding laws for sheet flow with upper and lower yield stresses for creep in cold overlying ice and basal ice sliding over deforming till, respectively, (2) replacing integrating the Navier–Stokes equations for stream flow with geometrical solutions to the force balance, and (3) including resistance to shelf flow caused by lateral confinement in a fjord and local grounding at ice rumples and ice rises. A comparison is made between our approach and two approaches based on continuum mechanics. Applications are made to Byrd Glacier in Antarctica and Jakobshavn Isbrae in Greenland.

Extract: Our ice-sheet modeling approach is based on the first-order dependence of ice-sheet thickness on the strength of ice-bed coupling, such that ice 3000m high and 4000m thick at an interior ice divide can lower to 100m high and 1000m thick when ice margins become afloat, and lower further to 30m high and 300m thick at the front of calving ice shelves, a 99% reduction of ice elevations, all due to reduced ice-bed coupling. We began by quantifying ice-bed uncoupling as an increase in thawed fraction f of the bed for sheet flow, of floating fraction phi of ice for stream flow, and of unbuttressed fraction phiO of ice for shelf flow. Our treatment is holistic in the sense it provides smooth transitions from sheet flow to stream flow to shelf flow for steady-state conditions along surface flowlines.

We compared our treatment for ice sheets with two treatments based on continuum mechanics, one by Schoof and Hindmarsh (2010) and one by Pattyn (2003). All three treatments avoided flow “laws” and sliding “laws” of dubious reliability for sheet flow. We substituted respective upper and lower yield stresses applied to cold ice over a frozen bed and to temperate ice sliding over bedrock and/or deforming till for sheet flow, with cold ice above temperate basal ice in ice streams and ice shelves. Schoof and Hindmarsh (2010) introduced “slip” and “no-slip” interfaces at the bed linked to separate deviator stress tensors that can be applied to sheet, stream, and shelf flow. Pattyn (2003) reduced basal drag as a frozen bed thaws. His approach can also be applied to sheet, stream, and shelf flow.

…
Our results for both Byrd Glacier and Jakobshavn Isbrae are compatible with basal buoyancy fraction phiB = phiphiO in Table 2 used to quantify a hypothetical “life cycle” of ice streams. The product of fraction phi linked to ice-bed uncoupling and fraction phiO linked to ice-shelf unbuttressing is maximized when surface meltwater floods the bed under an ice stream, and when its buttressing ice shelf shelf disintegrates. Hughes (1986) postulated these two processes, augmented by other processes, are sufficient to collapse marine portions of an ice sheet, and to that extent contribute to Termination of glaciation cycles lasting approximately 90 000 years during the Quaternary Ice Age in which we now live. He called this the Jakobshavn Effect because all the processes were active for Jakobshavn Isbrae. Contributing processes include additional surface melting when crevasses are ubiquitous, analyzed by Pfeffer and Bretherton (1987), warm ocean water entering Jakobshavn Isfjord, reported by Holland et al. (2008) and restricted flow of outlet glaciers in curving and branching fjords like Jakobsahvn Isfjord (Pfeffer
et al., 2008).

We conclude the Jakobshavn Effect may have a long-term impact in Greenland if global warming allows these processes to migrate northward, causing successive ice streams to surge, thereby completing their life cycles. Some processes are already appearing in ice streams draining the east, west, and northwest parts of the Greenland Ice Sheet (Rignot and Kanagaratnam, 2006). Schoof (2010) shows how ongoing acceleration and thinning of Jakobshavn Isbrae reported by Joughin et al. (2014) could continue for a century. Various paths can be taken by phi and phiO in Table 2 during a life cycle, including reversals, as documented by Engelhardt and Kamb (2013) for Kamb Ice Stream. Hughes (2011) used Table 2 to determine where major Antarctic ice streams are in their life cycles today. When the Jakobshavn Effect is nearly simultaneous for many ice streams, Table 2 can be used to identify stadials and interstadials within Quaternary glaciation cycles, and to account for Terminations of cycles, all linked to global sea level (Denton et al., 1986) and the Jakobshavn Effect.
…
These ice streams bracket ice-bed uncoupling ranging from no surface meltwater lubricating the bed and a massive buttressing ice shelf for Byrd Glacier to massive surface meltwater lubricating the bed and an ice shelf that has recently disintegrated for Jakobshavn Isbrae.
…
Today, Byrd Glacier has low values of phi and phiO, but both values are substantially higher for Jakobshavn Isbrae. For Byrd Glacier we temporarily increased phi when two subglacial lakes at its head drained rapidly in 2006–2007 (Stearns and others, 2008). For Jakobshavn Isbrae, we set phiO = 1 when its buttressing ice shelf suddenly disintegrated in 2002 (Thomas, 2004).
…
Warming in high polar latitudes can, in principle, trigger a succession of positive feedback mechanisms called the Jakobshavn Effect (Hughes, 1986). Buoyancy fraction phiB combines the two dominant mechanisms: reduced icebed coupling when surface meltwater floods the bed under an ice stream and reduced ice-shelf buttressing when an ice shelf disintegrates beyond the ice stream. For Greenland, the Jakobshavn Effect would move northward along the east and west coasts, affecting all calving ice streams. For Antarctica, it would affect the northernmost ice streams, which are primarily in East Antarctica, but also ice streams entering the Pine Island Bay polynya in West Antarctica (Hughes, 1987, 2011; Pingree et al., 2011)."

[AbruptSLR]

We should all remember the impact of arctic animal populations on arctic permafrost degradation as discussed in the following summary of the linked research project.  I note that the range of arctic ground squirrels will move northward with continuing global warming, resulting in a positive feedback for more warming.  Currently, consensus climate models ignore this positive feedback mechanism (including on Arctic Amplification):

Title: "Effects of arctic ground squirrel abundance and distribution on carbon cycling and ecosystem dynamics"

https://necsc.umass.edu/projects/effects-arctic-ground-squirrel-abundance-and-distribution-carbon-cycling-and-ecosystem

Summary: "Increasing atmospheric greenhouse gases have caused global warming, resulting in considerable shifts in ecosystem function and structure, particularly in sensitive cold climates like the Arctic. As the Arctic continues to warm, the ground thaws and permafrost degrades, resulting in changes to shrub communities. These changes can cause northern tundra soils, which have twice as much below ground carbon (C) as atmospheric carbon, to shift from sinks to sources of C. The fate of this large C pool may be driven not only by climatic conditions, but also by ecosystem changes brought about by arctic animal populations. For example, grazing, burrowing, and defecating are expected to alter nutrients and soil decomposition, although this area of research has not been well explored. In this project I will quantify the effects of arctic ground squirrels, Urocitellus parryii, activity on soil respiration and other characteristics in interior Alaska. Ground squirrels create subterranean burrows that mix soil layers, increase aeration, alter soil moisture and temperature, and redistribute soil nutrients, all of which may impact microbial decomposition. I will compare habitat characteristics of areas with and without ground squirrels to measure differences in C inputs and decomposition between sites utilizing long-term incubation experiments. I will then compare thaw depth, soil respiration, and other habitat characteristics to estimate the effects of climate-induced shifts in ground squirrels distribution. I will use these results to examine impacts of ground squirrels on permafrost and soil C vulnerability under future warming scenarios of habitat shifts in the Arctic. Results will improve understanding of biological feedbacks on C mobilization and serve as a model for how to use wildlife activity to reduce uncertainty in global earth climate model projections of carbon flux. In addition, this research will provide information for natural resource planning to conserve arctic habitat by identifying the extent of risk for ground squirrels from climate change and highlighting conservation priorities."

See also:

Title: "Permafrost"

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

[AbruptSLR]

Also, let's not forget about the degradation happening now to Brazil's Cerrado (a mosaic of savannah, grassland and forest) regions, as I dare to point-out that consensus climate models do not capture this climate risk:

Title: "The Amazon burns. But another part of Brazil is being destroyed faster"

https://www.cnn.com/2019/09/22/americas/brazil-cerrado-soy-intl/index.html

Extract: "Brazil's Cerrado -- a "mosaic" habitat made up of savannah, grassland and forest -- is the world's most biodiverse such region, and spans around 200 million hectares.
…
Like in the Amazon, Cerrado habitats are being cleared because of global demand for meat -- to make way for cattle ranches, and later converted to grow soy which is used to feed livestock or exported to other parts of the world.
…
The destruction of the habitat is also bad news for climate change: the Cerrado, the WWF says, locks up a "deceptively large amount of carbon" in its deep root systems.

"It is a forest in a different way -- it is an upside-down forest, because a lot of the biomass is underground," de Oliviera Rosa told CNN.

In a recent report, Greenpeace suggested that the remaining original vegetation of the region contains a carbon store of equivalent to 13.7 gigatonnes of equivalent carbon dioxide.

[AbruptSLR]

While the influence of beavers on regional carbon flux (both CO2 & CH4) is complex; the first linked reference indicates that invasive species of beavers can result in significant increases in carbon flux when they invade new forests made accessible by polar amplification.  As beavers migrate polar ward (primarily in the Arctic regions) this phenomenon will likely result in another net positive climate change feedback (particularly on Arctic Amplification) that is currently not modelled by consensus climate scientists:

Chloe Margaret Papier et al, Invasive species and carbon flux: the case of invasive beavers (Castor canadensis) in riparian Nothofagus forests of Tierra del Fuego, Chile, Climatic Change (2019). DOI: 10.1007/s10584-019-02377-x

https://link.springer.com/article/10.1007%2Fs10584-019-02377-x

Abstract: "Forests are important moderators of global atmospheric CO2 emissions, making them a key focus of terrestrial C-cycling research. The 5th assessment report of the Intergovernmental Panel on Climate Change explicitly calls upon nations to enhance C-stock accounting and mitigate losses of global forest C sinks, which inherently will require more accurate and higher spatial resolution carbon accounting. Monitoring and predicting how disturbances, such as invasive species, influence forest C stocks and the transfer of C from live to dead pools remains a high priority both in the scientific and policy communities. We documented the effects of invasive North American beavers (Castor canadensis) on C-sequestration of riparian Nothofagus forests in Tierra del Fuego, Chile. Our paired plot sampling design quantified significant losses from beaver invasion in total aboveground, live standing, dead standing, and dead and downed C stocks (P < 0.001, paired t tests). We extrapolated stand-level C losses to the entire study area using a Maxent habitat suitability model and estimated that 1.177 (± 0.103) Tg C would be lost if all of the predicted 18,384 ha of invasible habitat (14% of the total forested area) were colonized by beavers. These results document the impacts of invasive mammals on large terrestrial C sinks and highlight the need for understanding the magnitude of such effects across both landscape- and regional-scales."

See also:

Title: "Invasive beavers: Bad for the climate"

https://phys.org/news/2019-05-invasive-beavers-bad-climate.html

Extract: "Scientists documented the effects of invasive North American beavers (Castor canadensis) on carbon sequestration of a riparian forest in Tierra del Fuego.

Scientists estimated that 1.177 (+/- 0.103) megatonnes of carbon would be lost if all of the predicted 18,384 hectares (70 square miles) of habitat (14 percent of the total forested area) were colonized by beavers."

Also see:

Petri Nummi et al. Beavers affect carbon biogeochemistry: both short-term and long-term processes are involved, Mammal Review (2018). DOI: 10.1111/mam.12134

[kassy]

Thanks for another nice selection of articles.

Enjoyed the animal ones and i cross posted the CAA glaciers (to What is new in the Arctic) and the Cerrado article.

[AbruptSLR]

I will believe that we will get off the RCP 8.5 scenario, if/when it happens, and not before:

Title: "Trump threatens to overshadow U.N. climate push"

https://www.politico.com/story/2019/09/23/trump-united-nations-climate-summit-1758605

Extract: "No one — neither the European nor Asian governments that are here, nor the U.S. that isn’t — is cutting emissions fast enough to address many scientists’ warnings of looming catastrophe in the coming decades. China’s are still rising rapidly.
…
By announcing his decision to pull out of the 2015 Paris climate pact ratified by 185 nations, Trump slowed the diplomatic and policy momentum behind a coordinated global response. At home, citing his claims of harm to the economy, the U.S. president rolled back the Obama administration’s regulations on greenhouse gas limits for cars, trucks and power plants, and pushed the U.S. to burn a lot more coal. He’s the spoiler at the global climate bash in New York this week."

[AbruptSLR]

While I concur with Thunberg's statement to the U.N., I am concerned that young people still have a way to go (a ways to go) before they fully understand the extent of betrayal of coming generations by current (& past) global decision makers:

Title: "Greta Thunberg to world leaders: "You are failing us" on climate change"

https://www.axios.com/climate-change-greta-thunberg-speech-un-873a3fd2-6288-4a89-9320-1e3cedb4566f.html

Extract: "Thunberg, who is usually not especially emotive when she talks, was uniquely emotional in this speech, notably tearing up and showing anger. "You are failing us, but the young people are starting to understand your betrayal," Thunberg said.

•   "We will not let you get away with this.""

[AbruptSLR]

The linked reference provides new data (that is not included in current consensus climate models) about how much instantaneous radiative forcing increases when brown carbon is deposited (say from wildfires) on snow.  These findings will likely increase consensus estimates for Arctic Amplification in coming decades:

Beres, N. D., Sengupta, D., Samburova, V., Khlystov, A. Y., and Moosmüller, H.: Deposition of brown carbon onto snow: changes of snow optical and radiative properties, Atmos. Chem. Phys. Discuss., https://doi.org/10.5194/acp-2019-761, in review, 2019.

https://www.atmos-chem-phys-discuss.net/acp-2019-761/

Abstract. Light-absorbing organic carbon aerosol – colloquially known as brown carbon (BrC) – is emitted from combustion processes and has a brownish or yellowish visual appearance, caused by enhanced light absorption at shorter visible and ultraviolet wavelengths (0.3 μm ≲ λ ≲ 0.5 μm). Recently, optical properties of atmospheric BrC aerosols have become the topic of intense research, but little is known about how BrC deposition onto snow surfaces affects the spectral snow albedo, which can alter the resulting radiative forcing and in-snow photochemistry. Wildland fires in close proximity to the cryosphere, such as peatland fires that emit large quantities of BrC, are becoming more common at high latitudes, potentially affecting nearby snow and ice surfaces.

In this study, we describe the artificial deposition of BrC aerosol with known optical, chemical, and physical properties onto the snow surface and we monitor its spectral radiative impact and compare it directly to modeled values. First, using small-scale combustion of Alaskan peat, BrC aerosols were artificially deposited onto the snow surface. UV-vis absorbance and total organic carbon (TOC) concentration of snow samples were measured for samples with and without artificial BrC deposition. These measurements were used to estimate the imaginary part of the refractive index of deposited BrC aerosol with a volume mixing rule. Single particle optical properties were calculated using Mie theory, and these values were used to show that the measured spectral snow albedo of snow with deposited BrC was in general agreement with modeled spectral snow albedo using calculated BrC optical properties.

The instantaneous radiative forcing by impurities present in the snow before the deposition experiments was found to increase the instantaneous radiative forcing at the surface of the natural snow at our site by 1.23 (+0.14/−0.11) W m−2 per ppm of BrC deposited. However, we estimate that deposition onto a clean snowpack without light-absorbing impurities would have resulted in a more than twice as large instantaneous radiative forcing of 2.68 (+0.27/−0.22) W m−2 per ppm of BrC deposited.

[nanning]

Thank you very much for your post about Greta Thunberg's speech ASLR!

There's betrayal in all the countries of the world. All of our youth, our new young humans, are facing a bleak future life. A nice prospect when you're a teenager or even younger. Not!
If they realise this, their growing anger and acts will be fully justified.
I have empathy, they have my deepest sympathy.

[AbruptSLR]

The findings of the linked reference are not good news for the stability of the WAIS, as it implies that the Antarctic ozone hole will likely last longer than previously expected by consensus climate scientists:

Fang, X., J.A. Pyle, M.P. Chipperfield, J.S. Daniel, S. Park and R.G. Prinn (2019), "Challenges for the recovery of the ozone layer", Nature Geoscience, 12, 592-596, doi: 10.1038/s41561-019-0422-7

https://www.nature.com/articles/s41561-019-0422-7

Abstract: "The stratospheric ozone layer, which protects us from the sun’s ultraviolet radiation, has recovered considerably from past depletion since the implementation of the 1987 Montreal Protocol in 1987 and subsequent amendments, which phased out the production and consumption of major ozone-depleting substances (ODSs). But unexpected observed and potential emissions of long- and short-lived ODSs could delay the return of stratospheric ozone levels to 1980 levels by years to decades.

Recognizing the threat that unconstrained ODSs pose to the continued restoration of the ozone layer, this study provides an overview of these substances and the steps needed to control them in alignment with the Montreal Protocol."

Edit, see also:

Title: "NASA-Supported Monitoring Network Assesses Ozone Layer Threats"

https://www.nasa.gov/feature/goddard/2019/nasa-supported-network-assesses-threats-to-ozone

Extract: "On the heels of the first definitive signs of the ozone layer recovery last year, an international team of scientists discovered that production and emission of a banned, potent ozone-depleting chemical is on the rise again. A new research finding, published in Nature on May 23, locates the source region for about half of those new emissions. Since 2013, they found that an increase of about 7000 tons per year of trichlorofluromethane, or CFC-11, added to the atmosphere originates from eastern China."

[AbruptSLR]

The linked reference confirms that the ENSO underwent a change in state around the later 1990's (say after the 97-98 El Nino event), changing the period of El Nino events from ~4-5 years to ~ 2-3 years.  As El Nino events contribute to global warming, these findings support the concept that ECS may likely already be increasing due to anthropogenic global warming:

Zongci Huang et al. (24 September 2019), "Recent Shift in State of the Western Pacific Subtropical High due to ENSO change: Journal of Climate, https://doi.org/10.1175/JCLI-D-18-0873.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-18-0873.1

Abstract: "The boreal summer western Pacific subtropical high (WPSH) exhibits a remarkable decadal shift in its spatial pattern and periodicity around the late 1990s. In the former period, the WPSH is primarily characterized by a large-scale uniform pattern over Asia and its surrounding area with an oscillating period of ∼4-5 year. However, the WPSH-related atmospheric circulations shift to a dipole structure and oscillate at ∼2-3 year in the recent period. We found that this decadal shift is largely contributed by the ENSO regime change. During the former period, the tropical Pacific was dominated by the conventional eastern Pacific (EP) El Niño-Southern Oscillation (ENSO) with an oscillating period of ∼4-5 year. Strong anticyclone anomalies usually maintain over the western North Pacific (WNP) during the EP El Niño decaying summer, accounting for most of the WPSH temporal and spatial variability. In contrast, the recent period is featured by much more frequent occurrence of central Pacific (CP) El Niño events in the tropical Pacific with a ∼2-3 year oscillating period. A dipole structure in the WNP and Indian Ocean is evident during both developing and decaying summers of CP El Niño, consistent with the WPSH leading mode after the late 1990s. The results have important implications for seasonal prediction of the WPSH and associated Asian summer climate anomalies."

Edit, w.r.t. the increased frequency of central Pacific El Nino events, see also:

Qinghua Ding et al. (April 2011), "Winter warming in West Antarctica caused by central Pacific warming", Nature Geoscience 4(6):398-403, DOI: 10.1038/ngeo1129

https://www.nature.com/articles/ngeo1129

Abstract: "The Pacific sector of Antarctica, including both the Antarctic Peninsula and continental West Antarctica, has experienced substantial warming in the past 30 years. An increase in the circumpolar westerlies, owing in part to the decline in stratospheric ozone concentrations since the late 1970s, may account for warming trends in the peninsula region in austral summer and autumn. The more widespread warming in continental West Antarctica (Ellsworth Land and Marie Byrd Land) occurs primarily in austral winter and spring, and remains unexplained. Here we use observations of Antarctic surface temperature and global sea surface temperature, and atmospheric circulation data to show that recent warming in continental West Antarctica is linked to sea surface temperature changes in the tropical Pacific. Over the past 30 years, anomalous sea surface temperatures in the central tropical Pacific have generated an atmospheric Rossby wave response that influences atmospheric circulation over the Amundsen Sea, causing increased advection of warm air to the Antarctic continent. General circulation model experiments show that the central tropical Pacific is a critical region for producing the observed high latitude response. We conclude that, by affecting the atmospheric circulation at high southern latitudes, increasing tropical sea surface temperatures may account for West Antarctic warming through most of the twentieth century."

[AbruptSLR]

The linked reference provides evidence that during the period from 2007 to 2012 (the faux hiatus period), the relatively cool east-central tropical Pacific sea surface temperature; helped to telecommunicate energy from the tropical Pacific thru the atmosphere to the Arctic where it contributed to high rates of Artic sea ice loss during this period.

Ian Baxter et al. (18 September 2019), "How tropical Pacific surface cooling contributed to accelerated sea ice melt from 2007 to 2012 as ice is thinned by anthropogenic forcing", Journal of Climate, https://doi.org/10.1175/JCLI-D-18-0783.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-18-0783.1?af=R

Abstract: "Over the past 40 years the Arctic sea ice minimum in September has declined. The period between 2007 and 2012 showed accelerated melt contributed to the record minima of 2007 and 2012. Here, observational and model evidence shows that the changes in summer sea ice since the 2000s reflects a continuous anthropogenically forced melting masked by interdecadal variability of Arctic atmospheric circulation. This variation is partially driven by teleconnections originating from sea surface temperature (SST) changes in the east-central tropical Pacific via a Rossby wave train propagating into the Arctic (hereafter referred to as the “Pacific-Arctic teleconnection (PARC)”), which represents the leading internal mode connecting the pole to lower latitudes. This mode has contributed to accelerated warming and Arctic sea ice loss from 2007 to 2012, followed by slower declines in recent years, resulting in the appearance of a slowdown over the past 11 years. A pacemaker model simulation, in which we specify observed SST in the tropical eastern Pacific, demonstrates a physically plausible mechanism for the PARC mode. However, the model-based PARC mechanism is considerably weaker and only partially accounts for the observed acceleration of sea ice loss from 2007 to 2012. We also explore features of large-scale circulation patterns associated with extreme melting periods in a long (1800-yr) CESM preindustrial simulation. These results further support that remote SST forcing originating from the tropical Pacific can excite significant warm episodes in the Arctic. However, further research is needed to identify the reasons for model limitations in reproducing the observed PARC mode featuring a Cold Pacific - Warm Arctic connection."

[AbruptSLR]

The linked reference indicates that when accounting for the efficacy of land ice changes (which is assumed by consensus climate scientists for be a long-term process) in deriving climate sensitivity based on paleodata that ECS would be 5.8 +/- 1.3K; which is much higher than that indicated by AR5.  Thus, if MICI results in a collapse of the WAIS in coming decades, we can expect a marked increase in ECS:

Including the efficacy of land ice changes in deriving climate sensitivity from paleodata", Earth Syst. Dynam., 10, 333–345, https://doi.org/10.5194/esd-10-333-2019
https://www.earth-syst-dynam.net/10/333/2019/

Abstract: "The equilibrium climate sensitivity (ECS) of climate models is calculated as the equilibrium global mean surface air warming resulting from a simulated doubling of the atmospheric CO2 concentration. In these simulations, long-term processes in the climate system, such as land ice changes, are not incorporated. Hence, climate sensitivity derived from paleodata has to be compensated for these processes, when comparing it to the ECS of climate models. Several recent studies found that the impact these long-term processes have on global temperature cannot be quantified directly through the global radiative forcing they induce. This renders the prevailing approach of deconvoluting paleotemperatures through a partitioning based on radiative forcings inaccurate. Here, we therefore implement an efficacy factor εli that relates the impact of land ice changes on global temperature to that of CO2 changes in our calculation of climate sensitivity from paleodata. We apply our refined approach to a proxy-inferred paleoclimate dataset, using εli =0.45 +0.34 −0.20  based on a multi-model assemblage of simulated relative influences of land ice changes on the Last Glacial Maximum temperature anomaly. The implemented εli is smaller than unity, meaning that per unit of radiative, forcing the impact on global temperature is less strong for land ice changes than for CO2 changes. Consequently, our obtained ECS estimate of 5.8±1.3 K, where the uncertainty reflects the implemented range in εli is ∼50 % higher than when differences in efficacy are not considered."

Edit: With regard to the is post, the attached figure from Hansen and Sato 2012 indicates that as radiative forcing increases for a period (say due to an MICI type of collapse for the WAIS) the associated reduction in albedo resulting from such events as the loss of Arctic Sea Ice, a decrease in winter snow cover and the lost of the WAIS, will significantly increase the climate sensitivity of the earth; possibly this century.

[AbruptSLR]

The linked reference documents how while large Antarctic icebergs melt they provide nutrients into the nearby waters that induce local plankton blooms that absorb CO₂, and thus act as a negative feedback mechanism as more large icebergs are calved with continuing global warming.  While their research should be used to update ESM projections, the authors do not consider the case of the WAIS collapsing this century, which (which would abruptly freshen the surface waters of the Southern Ocean) could result in more Southern Ocean plankton die-offs and fewer plankton blooms, eventually resulting in a positive feedback for global warming (which is not considered by current consensus ESM projections):

Luis P. A. M. Duprat, Grant R. Bigg & David J. Wilton (2016), "Enhanced Southern Ocean marine productivity due to fertilization by giant icebergs", Nature Geoscience, doi:10.1038/ngeo2633

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2633.html

Abstract: "Primary productivity is enhanced within a few kilometres of icebergs in the Weddell Sea owing to the input of terrigeneous nutrients and trace elements during iceberg melting. However, the influence of giant icebergs, over 18 km in length, on marine primary production in the Southern Ocean is less well studied. Here we present an analysis of 175 satellite images of open ocean colour before and after the passage of 17 giant icebergs between 2003 and 2013. We detect substantially enhanced chlorophyll levels, typically over a radius of at least 4–10 times the iceberg’s length, that can persist for more than a month following passage of a giant iceberg. This area of influence is more than an order of magnitude larger than that found for sub-kilometre scale icebergs or in ship-based surveys of giant icebergs. Assuming that carbon export increases by a factor of 5–10 over the area of influence, we estimate that up to a fifth of the Southern Ocean’s downward carbon flux originates with giant iceberg fertilization. We suggest that, if giant iceberg calving increases this century as expected, this negative feedback on the carbon cycle may become more important."

[AbruptSLR]

Many scientists are concerned that the Earth may be headed towards a Pliocene type of climate this century due to global warming.  The linked reference indicates that changes in cloud cover/albedo for such conditions would rapidly induce the Equatorial Pacific Ocean into a permanent El Nino-like state.  As cloud albedo is a rapid response feedback mechanism, such a change could happen in as little as a few decades from now (say 2040-2050). Permanent El Nino-like conditions would telecommunicate large amounts of heat from the Equatorial Pacific directly to West Antarctica.

N. J. Burls and A. V. Fedorov, (2014), "Simulating Pliocene warmth and a permanent El Niño-like state: the role of cloud albedo", Paleoceanography, DOI: 10.1002/2014PA00264

http://onlinelibrary.wiley.com/doi/10.1002/2014PA002644/abstract

Abstract: "Available evidence suggests that during the early Pliocene (4-5 Ma) the mean east–west sea surface temperature (SST) gradient in the equatorial Pacific Ocean was significantly smaller than today, possibly reaching only 1-2°C. The meridional SST gradients were also substantially weaker, implying an expanded ocean warm pool in low latitudes. Subsequent global cooling led to the establishment of the stronger, modern temperature gradients. Given our understanding of the physical processes that maintain the present-day cold tongue in the east, warm pool in the west and hence sharp temperature contrasts, determining the key factors that maintained early Pliocene climate still presents a challenge for climate theories and models. This study demonstrates how different cloud properties could provide a solution. We show that a reduction in the meridional gradient in cloud albedo can sustain reduced meridional and zonal SST gradients, an expanded warm pool and warmer thermal stratification in the ocean, weaker Hadley and Walker circulations in the atmosphere. Having conducted a range of hypothetical modified cloud albedo experiments, we arrive at our Pliocene simulation, which shows good agreement with proxy SST data from major equatorial and coastal upwelling regions, the tropical warm pool, mid and high latitudes, and available subsurface temperature data. As suggested by the observations, the simulated Pliocene-like climate sustains a robust ENSO despite the reduced mean east–west SST gradient. Our results demonstrate that cloud albedo changes may be a critical element of Pliocene climate and that simulating the meridional SST gradient correctly is central to replicating the geographical patterns of Pliocene warmth."

[AbruptSLR]

The linked reference (with an open access pdf) proves that the Southern Ocean has been absorbing more heat than previously assumed by the CMIP5 projections; which, implies that ECS is meaningfully higher than 3.0 degrees.  This proves that the IPCC AR5 mean global temperature rise projections have erred on the low side:

Paul J. Durack, Peter J. Gleckler, Felix W. Landerer and Karl E. Taylor, (2014), "Quantifying Underestimates of Long-term Upper-Ocean Warming", Nature Climate Change, 4 (11), DOI: 10.1038/nclimate2389

http://www-pcmdi.llnl.gov/about/staff/Durack/dump/oceanwarming/140926a_Duracketal_UpperOceanWarming.pdf

Abstract: "The global ocean stores more than 90% of the heat associated with observed greenhouse‐gas‐attributed global warming (Levitus et al., 2005; Church et al., 2011; Otto et al., 2013; Rhein et al., 2013). Using satellite altimetry observations and a large suite of climate models, we conclude that observed estimates of 0‐700 dbar global ocean warming since 1970 are likely biased low. This underestimation is attributed to poor sampling of the Southern Hemisphere, and limitations of the analysis methods that conservatively estimate temperature changes in data‐sparse regions (Gregory et al., 2004; Gouretski & Koltermann, 2007; Gille, 2008). We find that the partitioning of northern and southern hemispheric simulated sea surface height changes are consistent with precise altimeter observations, whereas the hemispheric partitioning of simulated upper‐ocean warming is inconsistent with observed in‐situ‐based ocean heat content estimates. Relying on the close correspondence between hemispheric‐scale ocean heat content and steric changes, we adjust the poorly constrained Southern Hemisphere observed warming estimates so that hemispheric ratios are consistent with the broad range of modelled results. These adjustments yield large increases (2.2‐7.1 x 1022 J 35yrs‐1) to current global upper‐ocean heat content change estimates, and have important implications for sea level, the planetary energy budget and climate sensitivity assessments."

[AbruptSLR]

I have previously cited the new IPCC special report (SR) on the ocean and cryosphere thus here I will only provide the link to this new SR (& a link to an associated article); and I will say that while this report is an improvement on the AR5 coverage of this matter, this SR still errs on the side of least drama:

Title: "Special Report on the Ocean and Cryosphere in a Changing Climate"

https://www.ipcc.ch/srocc/home/
https://www.ipcc.ch/srocc/download-report/


See also:

Title: "Rising Seas Aren’t Even the Scariest Part of Climate Change in the Oceans"

https://www.motherjones.com/environment/2019/09/rising-seas-arent-even-the-scariest-part-of-climate-change-in-the-oceans/

Extract: "Some places are already “reaching adaptation limits.”"

[AbruptSLR]

The linked reference indicates that dimethylamine can significantly facilitate cloud formation, unfortunately ocean acidification is threatening to significantly reduce the amount of natural dimethylamine emitted into the atmosphere so unless society is interested in using dimethylamine in geoengineering, we are likely headed towards accelerating global warming as the ocean continues to acidify:

Kürten, A., Jokinen, T., Simon, M., Sipilä, M., Sarnela, N., Junninen, H., Adamov, A., Almeida, J., Amorim, A., Bianchi, F., Breitenlechner, M., Dommen, J., Donahue, N. M., Duplissy, J., Ehrhart, S., Flagan, R. C., Franchin, A., Hakala, J., Hansel, A., Heinritzi, M., Hutterli, M., Kangasluoma, J., Kirkby, J., Laaksonen, A., Lehtipalo, K., Leiminger, M., Makhmutov, V., Mathot, S., Onnela, A., Petäjä, T., Praplan, A. P., Riccobono, F., Rissanen, M. P., Rondo, L., Schobesberger, S., Seinfeld, J. H., Steiner, G., Tomé, A., Tröstl, J., Winkler, P. M., Williamson, C., Wimmer, D., Ye, P., Baltensperger, U., Carslaw, K. S., Kulmala, M., Worsnop, D. R., and Curtius, J., (2014), "Neutral molecular cluster formation of sulphuric acid-dimethylamine observed in real-time under atmospheric conditions", Proc. Natl. Acad. Sci., doi/10.1073/pnas.1404853111.


http://www.pnas.org/content/early/2014/10/02/1404853111

Abstract: "For atmospheric sulfuric acid (SA) concentrations the presence of dimethylamine (DMA) at mixing ratios of several parts per trillion by volume can explain observed boundary layer new particle formation rates. However, the concentration and molecular composition of the neutral (uncharged) clusters have not been reported so far due to the lack of suitable instrumentation. Here we report on experiments from the Cosmics Leaving Outdoor Droplets chamber at the European Organization for Nuclear Research revealing the formation of neutral particles containing up to 14 SA and 16 DMA molecules, corresponding to a mobility diameter of about 2 nm, under atmospherically relevant conditions. These measurements bridge the gap between the molecular and particle perspectives of nucleation, revealing the fundamental processes involved in particle formation and growth. The neutral clusters are found to form at or close to the kinetic limit where particle formation is limited only by the collision rate of SA molecules. Even though the neutral particles are stable against evaporation from the SA dimer onward, the formation rates of particles at 1.7-nm size, which contain about 10 SA molecules, are up to 4 orders of magnitude smaller compared with those of the dimer due to coagulation and wall loss of particles before they reach 1.7 nm in diameter. This demonstrates that neither the atmospheric particle formation rate nor its dependence on SA can simply be interpreted in terms of cluster evaporation or the molecular composition of a critical nucleus."

[AbruptSLR]

Biogenic volatile organic compounds, associated with the conversion of forests to agriculture (in addition to associated changes in CO₂ emissions and surface albedo), have been masking global warming.  According to the following linked reference the amount of this masking from 1850 to 2000 was a net global radiative impact of −0.11 ± 0.17 W m−2 (cooling).  As global warming stresses plant growth, this masking factor will stop and global warming will accelerate.

Nadine Unger, (2014), "Human land-use-driven reduction of forest volatiles cools global climate", Nature Climate Change, Volume: 4, Pages: 907–910, doi:10.1038/nclimate2347

http://www.nature.com/nclimate/journal/v4/n10/full/nclimate2347.html

Abstract: "Human conversion of forest ecosystems to agriculture is a major driver of global change. Conventionally, the impacts of the historical cropland expansion on Earth’s radiation balance have been quantified through two opposing effects: the release of stored carbon to the atmosphere as CO2 (warming) versus the increase in surface albedo (cooling). Changing forest cover has a third effect on the global radiation balance by altering emissions of biogenic volatile organic compounds (BVOCs) that control the loadings of multiple warming and cooling climate pollutants: tropospheric ozone (O3), methane (CH4) and aerosols. Although human land cover change has dominated BVOC emission variability over the past century, the net effect on global climate has not been quantified. Here, I show that the effects of the global cropland expansion between the 1850s and 2000s on BVOC emissions and atmospheric chemistry have imposed an additional net global radiative impact of −0.11 ± 0.17 W m−2 (cooling). This magnitude is comparable to that of the surface albedo and land carbon release effects. I conclude that atmospheric chemistry must be considered in climate impact assessments of anthropogenic land cover change and in forestry for climate protection strategies."

Edit, see also:

Mikael Ehn, Joel A. Thornton, Einhard Kleist, Mikko Sipilä, Heikki Junninen, Iida Pullinen, Monika Springer, Florian Rubach, Ralf Tillmann, Ben Lee, Felipe Lopez-Hilfiker, Stefanie Andres, Ismail-Hakki Acir, Matti Rissanen, Tuija Jokinen, Siegfried Schobesberger, Juha Kangasluoma, Jenni Kontkanen, Tuomo Nieminen, Theo Kurtén, Lasse B. Nielsen, Solvejg Jørgensen, Henrik G. Kjaergaard, Manjula Canagaratna, Miikka Dal Maso et al (2014), " A large source of low-volatility secondary organic aerosol", Nature, 506, 476–479, doi:10.1038/nature13032

http://www.nature.com/nature/journal/v506/n7489/full/nature13032.html

Abstract: "Forests emit large quantities of volatile organic compounds (VOCs) to the atmosphere. Their condensable oxidation products can form secondary organic aerosol, a significant and ubiquitous component of atmospheric aerosol, which is known to affect the Earth’s radiation balance by scattering solar radiation and by acting as cloud condensation nuclei. The quantitative assessment of such climate effects remains hampered by a number of factors, including an incomplete understanding of how biogenic VOCs contribute to the formation of atmospheric secondary organic aerosol. The growth of newly formed particles from sizes of less than three nanometres up to the sizes of cloud condensation nuclei (about one hundred nanometres) in many continental ecosystems requires abundant, essentially non-volatile organic vapours, but the sources and compositions of such vapours remain unknown. Here we investigate the oxidation of VOCs, in particular the terpene α-pinene, under atmospherically relevant conditions in chamber experiments. We find that a direct pathway leads from several biogenic VOCs, such as monoterpenes, to the formation of large amounts of extremely low-volatility vapours. These vapours form at significant mass yield in the gas phase and condense irreversibly onto aerosol surfaces to produce secondary organic aerosol, helping to explain the discrepancy between the observed atmospheric burden of secondary organic aerosol and that reported by many model studies. We further demonstrate how these low-volatility vapours can enhance, or even dominate, the formation and growth of aerosol particles over forested regions, providing a missing link between biogenic VOCs and their conversion to aerosol particles. Our findings could help to improve assessments of biosphere–aerosol–climate feedback mechanisms, and the air quality and climate effects of biogenic emissions generally."

Also, see the link to the following related reference:

Paasonen, P., et. al. (2013), "Evidence for negative climate feedback: warming increases aerosol number concentrations,", Nature Geoscience, 6, Pages: 438–442, doi: 10.1038/NGEO1800

http://www.nature.com/ngeo/journal/v6/n6/full/ngeo1800.html

[AbruptSLR]

I note here that since the 1950's the Antarctic Circumpolar Current, ACC, has been moving southward, in large part due to the increase in the Westerly winds over the Southern Ocean due to anthropogenic climate change and the Antarctic ozone hole.  Furthermore, as the ACC moves southward (note that the Subtropical Front marks the north boundary of the ACC, see the image at the Cape of Good Hope) more warm salty ocean water from the Indian Ocean's Agulhas Current leaks (Agulhas Leakage) into the South Atlantic Ocean (around the Cape of Good Hope), where it stimulates the great oceanic conveyor belt current, which in turn then carries more warm ocean water via the "Gulf Stream" into the North Atlantic, where it can contribute to Arctic Amplification.

See also the following linked reference about the positive feedback between Agulhas Leakage and the bipolar seesaw:

Gianluca Marino and Rainer Zahn (2015), "The Agulhas Leakage: the missing link in the interhemispheric climate seesaw?" PAGES Magazine, Vol 23, No. 1

http://www.pages-igbp.org/download/docs/magazine/2015-1/PAGESmagazine_2015(1)_22-23_Marino.pdf

Extract: "The Agulhas Leakage is a key component of the Atlantic Meridional Overturning Circulation. Unraveling the past patterns of leakage variability and associated heat and salt anomalies into the Atlantic Ocean holds clues for their role in ocean and climate changes."

[AbruptSLR]

The linked research discusses the matter that consensus climate science (like AR5 & CMIP5) underestimated of the impacts of Black Carbon on global warming:

Øivind Hodnebrog, Gunnar Myhre, & Bjørn H. Samset, (2014), "How shorter black carbon lifetime alters its climate effect", Nature Communications, Volume: 5, Article number: 5065, doi:10.1038/ncomms6065

http://www.nature.com/ncomms/2014/140925/ncomms6065/abs/ncomms6065.html

Abstract: "Black carbon (BC), unlike most aerosol types, absorbs solar radiation. However, the quantification of its climate impact is uncertain and presently under debate. Recently, attention has been drawn both to a likely underestimation of global BC emissions in climate models, and an overestimation of BC at high altitudes. Here we show that doubling present day BC emissions in a model simulation, while reducing BC lifetime based on observational evidence, leaves the direct aerosol effect of BC virtually unchanged. Increased emissions, together with increased wet removal that reduces the lifetime, yields modelled BC vertical profiles that are in strongly improved agreement with recent aircraft observations. Furthermore, we explore the consequences of an altered BC profile in a global circulation model, and show that both the vertical profile of BC and rapid climate adjustments need to be taken into account in order to assess the total climate impact of BC."

Edit, see also (& note that if Black Carbon (BC) emission were higher than assumed by consensus climate scientists from 1960 to 2000, then ECS must have been higher than consensus climate scientists have previously assumed because BC acts as negative radiative forcing, so more BC emissions mean less radiative forcing in the observed record, which means that ECS must be higher than previously assumed to match the recorded GMSTA):

T. Sun et al. (12 March 2019), "Constraining a Historical Black Carbon Emission Inventory of the United States for 1960–2000", JGR Atmospheres, https://doi.org/10.1029/2018JD030201
 
https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018JD030201

Abstract
We present an observationally constrained United States black carbon emission inventory with explicit representation of activity and technology between 1960 and 2000. We compare measured coefficient of haze data in California and New Jersey between 1965 and 2000 with predicted concentration trends and attribute discrepancies between observations and predicted concentrations among several sources based on seasonal and weekly patterns in observations. Emission factors for sources with distinct fuel trends are then estimated by comparing fuel and concentration trends and further substantiated by in‐depth examination of emission measurements. We recommend (1) increasing emission factors for preregulation vehicles by 80–250%; (2) increasing emission factors for residential heating stoves and boilers by 70% to 200% for 1980s and before; (3) explicitly representing naturally aspired off‐road engines for 1980s and before; and (4) explicitly representing certified wood stoves after 1985. We also evaluate other possible sources for discrepancy between model and measurement, including bias in modeled meteorology, subgrid spatial heterogeneity of concentrations, and inconsistencies in reported fuel consumption. The updated U.S. emissions are higher than the a priori estimate by 80% between 1960 and 1980, totaling 690 Gg/year in 1960 and 620 Gg/year in 1970 (excluding open burning). The revised inventory shows a strongly decreasing trend that was present in the observations but missing in the a priori inventory.

&

Title: "Previous Research Has Underestimated Black Carbon Emissions "

https://eos.org/research-spotlights/previous-research-has-underestimated-black-carbon-emissions

Extract: "New observational constraints suggest that U.S. emissions of this heat-absorbing aerosol were 80% higher during the late 20th century than prior estimates have indicated.
…
The far-reaching results suggest that modeling simulations based on earlier emission estimates, and potentially the inventories of other combustion by-products, will need to be reevaluated."

[Sciguy]

The linked research discusses the matter that consensus climate science (like AR5 & CMIP5) underestimated of the impacts of Black Carbon on global warming:

Øivind Hodnebrog, Gunnar Myhre, & Bjørn H. Samset, (2014), "How shorter black carbon lifetime alters its climate effect", Nature Communications, Volume: 5, Article number: 5065, doi:10.1038/ncomms6065

http://www.nature.com/ncomms/2014/140925/ncomms6065/abs/ncomms6065.html

Abstract: "Black carbon (BC), unlike most aerosol types, absorbs solar radiation. However, the quantification of its climate impact is uncertain and presently under debate. Recently, attention has been drawn both to a likely underestimation of global BC emissions in climate models, and an overestimation of BC at high altitudes. Here we show that doubling present day BC emissions in a model simulation, while reducing BC lifetime based on observational evidence, leaves the direct aerosol effect of BC virtually unchanged. Increased emissions, together with increased wet removal that reduces the lifetime, yields modelled BC vertical profiles that are in strongly improved agreement with recent aircraft observations. Furthermore, we explore the consequences of an altered BC profile in a global circulation model, and show that both the vertical profile of BC and rapid climate adjustments need to be taken into account in order to assess the total climate impact of BC."

Edit, see also (& note that if Black Carbon (BC) emission were higher than assumed by consensus climate scientists from 1960 to 2000, then ECS must have been higher than consensus climate scientists have previously assumed because BC acts as negative radiative forcing, so more BC emissions mean less radiative forcing in the observed record, which means that ECS must be higher than previously assumed to match the recorded GMSTA):
...

Actually, black carbon is a strong positive forcing, as it absorbs solar radiation.  See the linked webpage for more information about black carbon.

https://www.ccacoalition.org/en/slcps/black-carbon

Here's the forcings chart from the IPCC AR5, which shows it a a positive forcing, unlike other aerosols, which reflect sunlight and are therefore negative forcings.



So if black carbon emissions have been underestimated, does that mean ECS would be lower?

[AbruptSLR]

The linked reference, and associated article, indicate that as society reduces anthropogenic aerosol emissions in the future, GMSTA will likely increase faster than previously assumed by consensus climate scientists (e.g. CMIP5):

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

https://science.sciencemag.org/content/363/6427/eaav0566

Structured Abstract
INTRODUCTION
Human-made emissions of particulate air pollution can offset part of the warming induced by emissions of greenhouse gases, by enhancing low-level clouds that reflect more solar radiation back to space. The aerosol particles have this effect because cloud droplets must condense on preexisting tiny particles in the same way as dew forms on cold objects; more aerosol particles from human-made emissions lead to larger numbers of smaller cloud droplets. One major pathway for low-level cloud enhancement is through the suppression of rain by reducing cloud droplet sizes. This leaves more water in the cloud for a longer time, thus increasing the cloud cover and water content and thereby reflecting more solar heat to space. This effect is strongest over the oceans, where moisture for sustaining low-level clouds over vast areas is abundant. Predicting global warming requires a quantitative understanding of how cloud cover and water content are affected by human-made aerosols.

RATIONALE
Quantifying the aerosol cloud–mediated radiative effects has been a major challenge and has driven the uncertainty in climate predictions. It has been difficult to measure cloud-active aerosols from satellites and to isolate their effects on clouds from meteorological data. The development of novel methodologies to retrieve cloud droplet concentrations and vertical winds from satellites represents a breakthrough that made this quantification possible. The methodologies were applied to the world’s oceans between the equator and 40°S. Aerosol and meteorological variables explained 95% of the variability in the cloud radiative effects.

RESULTS
The measured aerosol cloud–mediated cooling effect was much larger than the present estimates, especially via the effect of aerosols on the suppression of precipitation, which makes the clouds retain more water, persist longer, and have a larger fractional coverage. This goes against most previous observations and simulations, which reported that vertically integrated cloud water may even decrease with additional aerosols, especially in precipitating clouds. The major reason for this apparent discrepancy is because deeper clouds have more water and produce rainfall more easily, thus scavenging the aerosols more efficiently. The outcome is that clouds with fewer aerosols have more water, but it has nothing to do with aerosol effects on clouds. This fallacy is overcome when assessing the effects for clouds with a given fixed geometrical thickness.
The large aerosol sensitivity of the water content and coverage of shallow marine clouds dispels another belief that the effects of added aerosols are mostly buffered by adjustment of the cloud properties, which counteracts the initial aerosol effect. For example, adding aerosols suppresses rain, so the clouds respond by deepening just enough to restore the rain amount that was suppressed. But the time scale required for the completion of this adjustment process is substantially longer than the life cycle of the cloud systems, which is mostly under 12 hours. Therefore, most of the marine shallow clouds are not buffered for the aerosol effects, which are inducing cooling to a much greater extent than previously believed.

CONCLUSION
Aerosols explain three-fourths of the variability in the cooling effects of low-level marine clouds for a given geometrical thickness. Doubling the cloud droplet concentration nearly doubles the cooling. This reveals a much greater sensitivity to aerosols than previously reported, meaning too much cooling if incorporated into present climate models. This argument has been used to dismiss such large sensitivities. To avoid that, the aerosol effects in some of the models were tuned down. Accepting the large sensitivity revealed in this study implies that aerosols have another large positive forcing, possibly through the deep clouds, which is not accounted for in current models. This reveals additional uncertainty that must be accounted for and requires a major revision in calculating Earth’s energy budget and climate predictions. Paradoxically, this advancement in our knowledge increases the uncertainty in aerosol cloud–mediated radiative forcing. But it paves the way to eventual substantial reduction of this uncertainty.

Also see:

Title: "We need to rethink everything we know about global warming"

https://www.sciencedaily.com/releases/2019/01/190122104611.htm
Extract: "New calculations show scientists have grossly underestimated the effects of air pollution
…
New research shows that the degree to which aerosols cool the earth has been grossly underestimated, necessitating a recalculation of climate change models to more accurately predict the pace of global warming."

[AbruptSLR]

...
Actually, black carbon is a strong positive forcing, …

Thanks for the catch.

Edit: As BC is an aerosol it may be difficult to separate its misestimated impact from the misestimated impact of other aerosols (largely with negative forcing/feedback) as discussed in my last post (Reply #1622).

[AbruptSLR]

As wildfires: emit GHGs, degrade carbon sinks and emit both black and brown carbon, it can be difficult for climate models to accurately project the climate impact of wildfire, but that does not change the risks associated with such wildfires:

Title: "Human-Caused Wildfires Caused the Sky to Change Color in Indonesia"

https://www.vice.com/en_us/article/ywab8x/human-caused-wildfires-caused-the-sky-to-change-color-in-indonesia

Extract: "The nation's worst fire season since 2015 spurred one Twitter user to say, "This is Earth, not the planet Mars."
…
Climate change has also created drier conditions in forests, boosting the reach and intensity of fires, while the flames in turn belch out greenhouse gases, which fuels further climate change.

This feedback loop is especially troubling in Indonesia because of the nation’s widespread peatland environments, which are highly combustible during dry seasons and store disproportionate amounts of carbon. Though peatland only accounts for 3 percent of global land area, it is estimated to hold 21 percent of the world’s soil carbon, making Indonesia’s fires especially noxious on both local and planetary scales.

More than 800,000 acres of forest has been burned so far this season, and the fires are expected to rage until October or November. The smoky haze underscores the need for more stringent regulations against slash-and-burn practices and better policies to protect and restore Indonesia’s forests."

[nanning]

Re: Restoring tropical rainforests after they are burned down.

If I liken the original biodiverse forest to an exquisite painting:
They are burning the Mona Lisa.
"Restore Indonesia's forests" is simply not a possibility
You'll never get another Mona Lisa but an empty frame.

These important and beautiful forests are lost forever! Turned into boring lifeless monoculture soya paintings on a canvas of catastrophic climate change.

All those ecosystems, the vibrant colours, sounds and richness of life.. gone.
Our brothers and sisters the Orangutangs.. gone.

[AbruptSLR]

For those who want a summary for the SROCC, I provide the following like to a CarbonBrief article that provides just such a summary.  However, I make two minor observations about the SROCC:

a) The accompanying image from the SROCC shows that the sea surface temperature anomaly (SSTA) of the Southern Ocean has cooled (here in March but also in general) at least from 1982 to 2017.  I imagine that some/most decision makers will take this good news that GMSTA is not increasing as fast as it would without this statistical trend in SSTA, while in reality the cooling trend in SSTA is dominated by the freshening of the surface water of the Southern Ocean primarily due to the relatively rapid ice mass loss from key Antarctic ice shelves; which is not good news at all.  Thus, by not emphasizing this reality the SROCC ESLD on this issue.

b) The SROCC calls the MICI mechanism 'hypothetical' and thus do not include any of the projections of MICI models in the values that the SROCC reports.  While it is true that the MICI models are 'hypothetical' the SROCC fails to note that all consensus climate model projections are also 'hypothetical', but the SROCC feels no need to point this out because they are consensus projections and thus do not in their opinion merit the moniker of 'hypothetical' even though the mean ECS value per AR5 is around 3C while the preliminary mean values for the eight best CMIP6 models give values well over 5C.  Thus if the eight best CMIP6 preliminary projections are correct then the current consensus climate models are indeed only 'hypothetical' and consensus climate scientists may well adopt a new consensus in AR6 and indeed by AR7 MICI projections may well be considered not longer hypothetical but consensus values:

Title: "In-depth Q&A: The IPCC’s special report on the ocean and cryosphere"

https://www.carbonbrief.org/in-depth-qa-the-ipccs-special-report-on-the-ocean-and-cryosphere

Extract: "The maps below show observed changes for 1982−2017 in sea surface temperature …
…
Another potential factor highlighted in the report is “marine ice cliff instability”, a hypothetical process by which vanishing ice leaves behind frozen cliffs that collapse into the ocean. It notes that this idea “remains unproven” and is characterised by “deep uncertainty”.

The report concludes there is “limited evidence and high agreement” that recent Antarctic ice sheet melting could be “irreversible over decades to millennia”.

In the SPM, the authors note “considering the consequences of sea level rise that a collapse of parts of the Antarctic Ice Sheet entails, this high impact risk merits attention”."

[AbruptSLR]

To me the linked article makes a valid case the 'left-tail' (of the right-skewed probability density function, pdf) accusations of 'Groupthink' against consensus climate scientists is indeed '... not a valid argument against climate science'; however, it does not convince me that 'right-tail' pdf accusations of 'Groupthink' against consensus climate scientists defends consensus climate scientists from erring on the side of least drama.  For instance the article suggests that when the public need to decide how to deal with climate change uncertainty, that they should think critically about who is challenging the consensus position; and when I think about who is warning about 'right-tailed' ice-climate feedback risks, I think of men like James Hansen, David Pollard, and Rob DeConto and I think that consensus climate scientists would be wise to martial their resources (including their reports like AR6) to better convey to the public that risk is equal to probability times consequences and that thus the right-tailed risk is many orders of magnitude greater than the left-tailed risk that consensus climate scientists spend so much effort addressing.  Thus, I think that it is not appropriate that consensus climate scientists tell the public that we have something like 12 more years (to control GHG emissions) before we cross that threshold towards serious climate consequences, when there is a very high right-tailed risk that such statement err on the side of least drama:

Title: "'Groupthink' is not a valid argument against climate science"

https://phys.org/news/2019-09-groupthink-valid-argument-climate-science.html

Extract: "From the "inside" looking out, it seems clear to scientists that groupthink has not taken over, and there is no danger that it will. Nevertheless, the public perception and (some) media portrayals of the climate scientists as being unwilling to listen to dissenters, combined with an unassailable belief in the correctness of their position, still persists. How do scientists overcome this gap in trust?

One solution might simply be for the public to realise that science is never black and white. As scientists are at pains to point out, there is very rarely incontrovertible evidence in any field, and science can only provide a current summary of the accumulated knowledge that has withstood the scrutiny of the scientific method. In other words, science doesn't claim to be infallible, but it is the best we can do using rigorous techniques of inquiry and testing.

Some research suggests that people who think of science as debate between alternative positions are more persuaded by messages that communicate high uncertainty than those who see science as the search for absolute truth. This is important because it suggests a way to overcome the ever-present problem of embracing the uncertainty that is inherent in any prediction, without leading people to conclude that nobody really knows anything and so we should not worry. Uncertainty is inevitable.

Another solution is for us all to think critically about the source of the information. If a climate scientist refuses to debate someone who is challenging their position, is this evidence for insularity and ignoring dissent? Only if those challengers are credible rather than mouthpieces for vested interests, as is often the case.

Scientists have to walk a fine line between communicating the science clearly and getting embroiled in advocacy, or divisive rhetoric. Indeed, some have argued that misleading arguments—such as there being a hiatus in global warming—can "seep" into scientific discussion (and research) partly through the pressure to engage in "faux" debate.

As members of the public it might be effortful to engage our cognitive resources and do a level of fact-checking or trust-assessment, but it is crucial. To disengage now could have disastrous consequences for us all."

[AbruptSLR]

In the linked 2019 article, Rob DeConto (a very straight shooter) says that the basic conclusions of the DeConto & Pollard (2016) reference about MICI risks remains unchanged:

Title: "Doomsday Postponed? The Takeaway From the Big New Antarctica Studies"

https://www.motherjones.com/environment/2019/02/doomsday-postponed-the-takeaway-from-the-big-new-antarctica-studies/

Extract: "“We still see a dangerous threat,” Rob DeConto, one of the authors of the 2016 paper, said in an email to Grist. “I don’t really see ice fracture as an optional process that can be excluded from ice sheet models.”

“If the pace of calving we observe in Greenland today someday becomes widespread around the edges of the vastly bigger Antarctic ice sheet, it could cause very fast sea-level rise,” DeConto said. “This was the take home message from our 2016 paper. Based on all the work that has followed, that basic conclusion remains unchanged.”"

[Hefaistos]

... the SROCC fails to note that all consensus climate model projections are also 'hypothetical', but the SROCC feels no need to point this out because they are consensus projections and thus do not in their opinion merit the moniker of 'hypothetical' even though the mean ECS value per AR5 is around 3C while the preliminary mean values for the eight best CMIP6 models give values well over 5C.  Thus if the eight best CMIP6 preliminary projections are correct then the current consensus climate models are indeed only 'hypothetical' and consensus climate scientists may well adopt a new consensus in AR6 ...

I wonder, what is it in your opinion that makes these eight models to be the "best"?
Is it that they are demonstrating very high ECS values?

I also believe it's doubtful to claim that the projections produced by CMIP5 GCMs "are consensus projections". Specifically, how do you reconcile these "best" CMIP6 models with the fact that the ensamble of CMIP5 models are 'running hot' in their projections compared to actual temperature observations?

Figure with updated data from
www.climate-lab-book.ac.uk

[AbruptSLR]

...
I wonder, what is it in your opinion that makes these eight models to be the "best"?
Is it that they are demonstrating very high ECS values?

I also believe it's doubtful to claim that the projections produced by CMIP5 GCMs "are consensus projections". Specifically, how do you reconcile these "best" CMIP6 models with the fact that the ensamble of CMIP5 models are 'running hot' in their projections compared to actual temperature observations?
...

For convenience I repost Reply #1177 from May 24, 2019 in this thread:

"I provide the linked article to remind readers that eight of the most sophisticated ESMs for CMIP6, are projecting ECS values will increase to over 5C in the coming decades, and that
increasing ECS values means increasing climate variability, which means increased risk of a coming abrupt change in climate state (such as occurred in the Mid-Pliocene period due to an Arctic albedo flip, e.g. see my last post).

Title: "New climate models predict a warming surge"

https://www.sciencemag.org/news/2019/04/new-climate-models-predict-warming-surge

Extract: "But a host of global climate models developed for the United Nations' next major assessment of global warming, due in 2021, are now showing a puzzling but undeniable trend. They are running hotter than they have in the past.
…
But in at least eight of the next-generation models, produced by leading centers in the United States, the United Kingdom, Canada, and France, that “equilibrium climate sensitivity” has come in at 5°C or warmer.""

So by 'best' I mean the most sophisticated/advanced next-generation models from the USA, the UK, Canada and France.  The preliminary hind cast projections from these eight model had no trouble matching the observed record and yet all eight project mean ECS values of over 5C, so if CMIP5 hind casts were 'running hot' it may be because they were not sophisticated enough to deal with cloud feedback mechanisms so they underestimated many of these mechanism by acknowledging large uncertainty band for these cloud feedback mechanism (which include aerosol cloud interactions that were highly negative during the historical record, but which may be much less negative in the future as many types of aerosols are decreased). 

Furthermore, the CMIP5 models may have provided 'hot' hind casts because: high ECS values (such as those preliminarily projected by the eight most sophisticated CMIP6 models) result in greater variability of Earth Systems including the ENSO cycle, so the 'faux hiatus' period was not an indication of low ECS but rather that strong La Nina activity in that period was sequestering heat from the Tropical Pacific surface deeper into the ocean where it was conveyed to the Southern Ocean, where it has contributed to accelerated ice mass loss.  I note that CMIP5 also underestimated the amount of measured ocean heat content; which indicates that the CMIP5 models are not sophisticated enough to accurately project nonlinear Earth Systems behavior.

Edit: In case readers have forgot, CMIP5 projections have also underestimated the measured ice mass loss and sea level rise, since CMIP5 was released (see the SROCC).  This indicates to me that GMSTA is probably not the best measure of climate change risk as it downplays all of the heat content going into both the ocean and the cryosphere.

Edit2: I also note that the average altitude of clouds has been observed to be increasing faster than CMIP5 projected, and as high altitude clouds generally have positive climate change feedback, while low altitude clouds generally have negative climate change feedback; this is yet another reason why the more sophisticated CMIP6 model projections may well prove to be more accurate than the old CMIP5 model projections.

Edit3: From Reply #1626 about the SROCC findings, regarding the attached image: "The maps below show observed changes for 1982−2017 in sea surface temperature …".  This image makes it clear that during the 'faux hiatus' the SSTA for the Southern Ocean was decreasing due to a spurt/surge of ice shelf mass loss (associated with upwelling of the relatively warm CDW associated with the Antarctic ozone hole formation) which provided sufficient cold freshwater to cool the surface temperature of the Southern Ocean (while the circumpolar deep water, CDW, was warming from heat advected from the tropical ocean surface water).  However, the same figure shows that after 2017 the surface temperature of the Southern Ocean is projected to increase (as these projections do not consider MICI-types of potential ice mass loss from Antarctica).  In other words the freshening of the surface water of the Southern Ocean during the 'faux hiatus' temporarily cooled this surface, which also contributed to the measured temporary slowdown of the trend of increasing GMSTA; which is yet another reason why CMIP5 projections were 'running hot' during this 'faux hiatus' period as they underestimated the upwelling of warm CDW along the Antarctic coastlines & thus underestimated the ice mass loss from the key Antarctic ice shelves and thus underestimated the cooling of the SSTA of the Southern Ocean.

Edit4: I also remind readers that BC emissions (with a positive feedback) never occur by themselves, but rather occur together with other aerosol emissions that typically have negative feedbacks.  Thus a recognition of past under reported BC emissions likely means that other anthropogenic aerosol emissions have also been under reported, and if so the net feedback would like be negative (but less negative than if the unreported BC emission were ignored).

[AbruptSLR]

The linked 2018 RealClimate article (by Gavin Schmidt) confirms that the AR5 projection of ocean heat uptake (see image, where AR5 projections are shown by the dark blue line) was lower than what was observed thru 2017, and that same trend has either continued or accelerated since 2017.  This indicates that climate change risks (particularly for ice-climate feedback mechanism) are accelerating faster than consensus climate scientists are stating publicly:

Title: "The long story of constraining ocean heat content"

http://www.realclimate.org/index.php/archives/2018/11/the-long-story-of-constraining-ocean-heat-content/

Extract: "The evidence suggests that ocean heat uptake has accelerated over the last couple of decades, and is likely higher than was reported in IPCC in 2013."

[AbruptSLR]

With regards to the Indo-Pacific Warm Pool (IPWP, & see the first image), and particularly w.r.t. the Western Pacific Warm Pool, the first linked reference states:

"We similarly conclude that the IPWP was warmer in the early Holocene compared to the late Holocene. However, with the new data we are able to argue against a western displacement/expansion of the IPWP and suggest a warmer southern IPWP in the early Holocene. … Additionally, the late deglacial section of the records mostly show a gradual IPWP warming similar in structure to the atmospheric CO2 and/or Antarctica rising temperatures."

While it can be difficult to correctly interpret paleodata, the fact that during the late deglacial period leading to the Holocene the southern IPWP grew to be warmer than today, indicates to me the possibility/probability that periodic abrupt ice mass losses in both the NH and particularly in the SH (where the Antarctic ice mass losses could only be due to MICI-types of local marine glacier ice mass loss, & see the last three links and the last three images), slowed the MOC sufficiently to warm the southern IPWP.  If this is true, then an abrupt MICI-type of collapse of the WAIS in coming decades would likely also lead to a rapid increase in the temperature of the southern IPWP (which is in the Western Pacific Warm Pool), which would likely result in a rapid increase in the frequency of large El Nino events, which would increase the effect value of ECS during that period:

Paola Moffa‐Sanchez et al. (11 June 2019), "Temperature Evolution of the Indo‐Pacific Warm Pool Over the Holocene and the Last Deglaciation", Paleoceanography and Paleoclimatology, Volume 34, Issue 7, https://doi.org/10.1029/2018PA003455

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018PA003455

Abstract: "The Indo‐Pacific Warm Pool (IPWP) contains the warmest surface ocean waters on our planet making it a major source of heat and moisture to the atmosphere. Changes in the extent and position of the IPWP likely impacted the tropical and global climate in the past and may also do in the future. With the aim to put recent ocean changes into a longer temporal context, we present new paleoceanographic sea surface temperature reconstructions from the heart of the Western Pacific Warm Pool, which is the warmest region
within the IPWP, across the last 17,000 years. To provide an improved spatial and temporal regional context we use new and published sea surface temperature records from the IPWP and update previous compilation efforts (Linsley et al., 2010, https://doi.org/10.1038/ngeo1920). We similarly conclude that the IPWP was warmer in the early Holocene compared to the late Holocene. However, with the new data we are able to argue against a western displacement/expansion of the IPWP and suggest a warmer southern IPWP in the early Holocene. We explore the potential drivers of the Holocene IPWP cooling and propose a combination of processes including changes in the monsoonal winds associated with the position of the rain belt, the tropical Pacific mean climate, and upper water column mixing. The proposed climatic processes differentially impacted the IPWP subregions resulting in spatially diverse trends. Additionally, the late deglacial section of the records mostly show a gradual IPWP warming similar in structure to the atmospheric CO2 and/or Antarctica rising temperatures."

See also:

Weber, M.E., P.U. Clark, G. Kuhn, A. Timmermann, D. Sprenk, R. Gladstone, X. Zhang, G. Lohmann, L. Menviel, M.O. Chikamoto, T. Friedrich, and C. Ohlwein (2014), "Millennial-scale variability in Antarctic ice-sheet discharge during the last deglaciation", Nature. 510(7503),134–138, doi: 10.1038/nature13397

https://www.nature.com/articles/nature13397

Abstract: "Our understanding of the deglacial evolution of the Antarctic Ice Sheet (AIS) following the Last Glacial Maximum (26,000-19,000 years ago) is based largely on a few well-dated but temporally and geographically restricted terrestrial and shallow-marine sequences. This sparseness limits our understanding of the dominant feedbacks between the AIS, Southern Hemisphere climate and global sea level. Marine records of iceberg-rafted debris (IBRD) provide a nearly continuous signal of ice-sheet dynamics and variability. IBRD records from the North Atlantic Ocean have been widely used to reconstruct variability in Northern Hemisphere ice sheets, but comparable records from the Southern Ocean of the AIS are lacking because of the low resolution and large dating uncertainties in existing sediment cores. Here we present two well-dated, high-resolution IBRD records that capture a spatially integrated signal of AIS variability during the last deglaciation. We document eight events of increased iceberg flux from various parts of the AIS between 20,000 and 9,000 years ago, in marked contrast to previous scenarios which identified the main AIS retreat as occurring after meltwater pulse 1A and continuing into the late Holocene epoch. The highest IBRD flux occurred 14,600 years ago, providing the first direct evidence for an Antarctic contribution to meltwater pulse 1A. Climate model simulations with AIS freshwater forcing identify a positive feedback between poleward transport of Circumpolar Deep Water, subsurface warming and AIS melt, suggesting that small perturbations to the ice sheet can be substantially enhanced, providing a possible mechanism for rapid sea-level rise."

&

Title: "Meltwater pulse 1A"

https://en.wikipedia.org/wiki/Meltwater_pulse_1A

Extract: "Between 20,000 and 9,000 calendar years ago, this study documented eight well-defined periods of increased iceberg Ice calving and discharge from various parts of the Antarctic Ice Sheet. The highest period of discharge of icebergs recorded in both cores is known as AID6 (Antarctic Iceberg Discharge event 6). AID6 has a relatively abrupt onset at about 15,000 calendar years ago. The peak interval of greatest iceberg discharge and flux from the Antarctic Ice sheet for AID6 is between about 14,800 and 14,400 calendar years ago. The peak discharge is followed by gradual decline in flux until 13,900 calendar years ago, when it abruptly ends. The peak period of iceberg discharge for AID6 is synchronous with the onset of the Bølling interstadial in the Northern Hemisphere meltwater pulse 1A. Weber and others estimated that the flux of icebergs from Antarctica during AID6 contributed a substantial (at least 50%) to the global mean sea-level rise that occurred during meltwater pulse 1A."
&

Title: "Meltwater pulse 1B"

https://en.wikipedia.org/wiki/Meltwater_pulse_1B

Extract: "Between 20,000 and 9,000 calendar years ago, Weber and others documented eight well-defined periods of increased iceberg calving and discharge from various parts of the Antarctic Ice Sheet. Five of these periods, AID5 through AID2 (Antarctic Iceberg Discharge events), are comparable in duration and have a repeat time of about 800–900 calendar years. The largest of the Antarctic Iceberg Discharge events is AID2. Its peak intensity at about 11,300 calendar years ago, which is synchronous with meltwater pulse 1B in the Barbados sea-level record, is consistent with a significant Antarctic contribution to meltwater pulse 1B. The lack of a sea level response in the Tahiti coral record might indicate a regionally specific sea-level response to a deglaciation event only from the Pacific sector of the Antarctica Ice Sheet."

[AbruptSLR]

Bolivia is currently experiencing its worst fire season in over two decades:

Title: "Firefighters in Bolivia lose hope of taming blazes as burned area doubles"

http://news.trust.org/item/20190922093504-v5w0k/

Extract: "The fires this year are Bolivia's worst in at least two decades, with the size of burned land across the country nearly doubling in under three weeks, destroying swaths of biodiverse forest and ranches and farms that sustain thousands of people."

[AbruptSLR]

While I admire Prof. Schellnhuber's approach of multiplying climate change risk (consequence x probability) times urgency (time needed to react divided by time left for intervention); I note that he ignoring ice-climate feedback mechanisms and consequently his 'time left for intervention' is too long.

Title: "‘I would like people to panic’ – Top scientist unveils equation showing world in climate emergency"

https://horizon-magazine.eu/article/i-would-people-panic-top-scientist-unveils-equation-showing-world-climate-emergency.html

Extract: " A new equation showing that the world is ‘deep in a climate emergency’ was unveiled on 24 September by Professor Hans Joachim Schellnhuber, one of the world’s leading authorities on climate change, who said that people still don’t want to see the truth about the state we’re in.
…
To make his assessment, Prof. Schellnhuber, founder of the Potsdam Institute for Climate Impact Research, Germany, has devised a formula that defines the level of emergency as risk multiplied by urgency. To calculate risk, he used the insurance industry’s approach of multiplying the amount of damage done by the probability of the event. For urgency, he followed the model used by air traffic controllers, which divides the time needed to react by time left for intervention.
‘If we go into a runaway climate effect, the damage may be between €100 trillion and the loss of civilisation,’ he said. ‘The probability, I would say, is about 10% that this is going to happen. And when it comes to the urgency of decarbonising society and keeping the forests alive, we need at least 20 years. We have only 30 years left to do this."

[AbruptSLR]

The linked article takes consensus science projections for a radiative forcing scenario where decision makers do not take quick effective action to fight climate change, and then add in the impact of relatively fragile societal issues stressed by those consensus climate change projection like human mass migration, disease, the impacts of natural disasters on the economy, wars etc.; and finds that global society could collapse by 2050 even while ignoring right-tailed climate change risks.  Our current global society was constructed on the assumption that mankind could continue (endlessly) exploiting various Earth Systems and is not prepared to deal with a world with limits on numerous Earth Systems.  In this sense, the fragility of our current global socio-economic system represents several more domino tiles that contribute to the risk of tipping point cascades which increase the probability of occurrence of right-tailed climate change events.  Here, I emphasize that the probability of abrupt right-tail events (& risks) increase both with increasing radiative forcing and with the likely impacts from our fragile socio-economic system on various key Earth Systems (so what is a right-tail chain of events today may well be a mean probability chain of events by 2040).

Title: "Society could collapse by 2050 under strain of climate change and conflict, paper warns"

https://globalnews.ca/news/5350048/climate-change-impact-society/

Extract: "An Australian policy paper warning that society could collapse amid climate change-related strife by 2050 is “plausible” if countries fail to take action, a leading Canadian climate scientist says.

The 12-page policy paper paints a scenario in which the international order breaks down after humans fail to band together and address the effects of climate change within the next two decades. Food supplies run low, economies collapse, disease kills millions, natural disasters ravage communities and mass migration strains many nations to the breaking point. Countries stop co-operating, and conflict eventually breaks out, plunging the world into war.
…
He says the scenario outlined in the paper is “plausible” based on the assumption that no one will work together to stop climate change. He described the paper as an “appropriate part of the scientific discourse” because it connects some of the dots for climate scientists who are reluctant to sound too alarmist.
…
He also points out that the paper’s doomsday scenario isn’t necessarily caused by climate change alone. Instead, climate change is merely a factor that puts strain on other problems in the geopolitical system, such as migration patterns, income inequality and climate-change denial.
…
Climate change is already presenting a national security threat in many parts of the world, according to several experts who spoke at the Planetary Security Conference at The Hague in February.

“Climate change fuels the roots of conflict around the globe and poses a direct threat to populations and installations in coastal areas and small islands,” Gen. Tom Middendorp, a former Dutch defence chief, said at the conference."

[Hefaistos]

...
So by 'best' I mean the most sophisticated/advanced next-generation models from the USA, the UK, Canada and France.  The preliminary hind cast projections from these eight model had no trouble matching the observed record and yet all eight project mean ECS values of over 5C, so if CMIP5 hind casts were 'running hot' it may be because they were not sophisticated enough to deal with cloud feedback mechanisms so they underestimated many of these mechanism by acknowledging large uncertainty band for these cloud feedback mechanism (which include aerosol cloud interactions that were highly negative during the historical record, but which may be much less negative in the future as many types of aerosols are decreased). 

...
Edit2: I also note that the average altitude of clouds has been observed to be increasing faster than CMIP5 projected, and as high altitude clouds generally have positive climate change feedback, while low altitude clouds generally have negative climate change feedback; this is yet another reason why the more sophisticated CMIP6 model projections may well prove to be more accurate than the old CMIP5 model projections.

/my emphases throughout/

I focus here on the major obstacle that climate models (GCM) have to model water vapor and cloud formation, and aerosols. This is what the GISS/NASA International Satellite Cloud Climatology Project (ISCCP) has to say on that topic:
"The challenge for climate models is to account for the most important physical processes, including cloud microphysics and cloud dynamics, and their complex interactions accurately enough to carry climatic predictions tens of years into the future. When contemporary models are given information about Earth's present condition — the size, shape and topography of the continents; the composition of the atmosphere; the amount of sunlight striking the globe — they create artificial climates that mathematically resemble the real one: their temperatures and winds are accurate to within about 5%, but their clouds and rainfall are only accurate to within about 25-35%.  ...

Unfortunately, such a margin of error is much too large for making a reliable forecast about climate changes, such as the global warming will result from increasing abundances of greenhouse gases in the atmosphere. A doubling in atmospheric carbon dioxide (CO2), predicted to take place in the next 50 to 100 years, is expected to change the radiation balance at the surface by only about 2 percent. Yet according to current climate models, such a small change could raise global mean surface temperatures by between 2-5°C (4-9°F), with potentially dramatic consequences. If a 2 percent change is that important, then a climate model to be useful must be accurate to something like 0.25%. Thus today's models must be improved by about a hundredfold in accuracy, a very challenging task. To develop a much better understanding of clouds, radiation and precipitation, as well as many other climate processes, we need much better observations."

Due to the greenhouse effect, the weather patterns, and the associated clouds, do change quite a lot, not least on regional scales.  GISS/ISCCP: "But it is not known whether the resulting cloud changes would diminish the warming (a negative feedback) or enhance the warming (a positive feedback)". - We definitely don't even know the sign of this feedback on the grid scale that GCMs operate.

There is no qualitative difference between CMIP5 and CMIP6 models in these respects. Both model generations are unable to correctly simulate projected water vapor and convection processes in clouds, and in many cases (e.g. on grid cell level) we don't even know the sign of the cloud feedback.

Models have these issues because there is a lack of theory on water vapor and cloud formation in a warming climate. Many phase changes occur in the clouds and are a major influence in the extremely complex convective activity taking place.

There is also a disturbing lack of data on the scale where convection takes place.
Models are furthermore by construction unable to resolve the water vapor issue (the processes of convection) because of the big grid size they have to operate on, (due to computational restraints and lack of data). GCMs typically use 100 km grid cells, whereas modelling of convective activity would require something like 0.1 km - 1 km cells. To reach this definition in a GCM would require in the order 10^10 times more powerful computers, as well as correspondig feed of input data. This won't happen in any foreseeable future.

In conclusion, how can we trust the simulated projections of GCMs when the models aren't able to correctly model the most important GHG of them all, water vapor? If we, according to the climate scientists at ISCCP don't even know where and when clouds have a positive, or a negative feedback? It's not for nothing that IPCC has to operate with the current huge interval of ECS values.

Thus, I reject calling any of these models "the best".

https://isccp.giss.nasa.gov/role.html

[AbruptSLR]

For those who are interested, the first linked article presents a somewhat scientifically-light discussion about the potential collapse of the Thwaites Glacier, which includes a light review of the MICI mechanism as it relates to Thwaites.  However, I note that neither this first overview article nor DeConto & Pollards (2016) MICI model consider the influence of the extensive subglacial water systems under both the PIG and Thwaites which also serve to destabilize these two interconnected marine glaciers.  Therefore, I provide links to the last two scientific references for those who want to better understand how these subglacial water systems (& a currently growing subglacial cavity, nearly the size of Manhattan, at the gateway to the Thwaites Glacier) could help trigger an MICI type of a collapse of large portions of the WAIS in the coming decades:

Title: "If Thwaites Glacier collapses, it would change global coastlines forever"

https://interactive.pri.org/2019/05/antarctica/thwaites-glacier-collapse.html

Extract: "“How quickly can you feasibly collapse something like Thwaites?” Graham said. “Is it over a century, over a thousand years, or can you do in a decade? I don't think anyone can, hand on heart, say which of those it is yet. And that's a concern.”
…
In a paper that outlined this marine ice cliff instability theory in 2016, authors Rob DeConto from the University of Massachusetts, Amherst, and David Pollard from Penn State University raised alarm by predicting that Antarctica by itself could contribute up to 3 feet of sea level rise by 2100.
…
DeConto said they are still working to identify the exact tipping point that would trigger this dramatic fracturing of the West Antarctic ice sheet, but work he presented at the American Geophysical Union meeting this past winter suggests it’s somewhere between 2-3 degrees Celsius of warming. If every country met its Paris Agreement commitments, the world would warm to 2.7 degrees Celsius.
…
Scientists studying Thwaites Glacier hope to give policymakers a better sense of just how fast sea levels might rise in coming decades, and whether it’s still possible to halt the kind of massive sea level rise it could cause, or just slow its onset."

&

P. Milillo, E. Rignot, P. Rizzoli, B. Scheuchl, J. Mouginot, J. Bueso-Bello, P. Prats-Iraola. Heterogeneous retreat and ice melt of Thwaites Glacier, West Antarctica. Science Advances, 2019; 5 (1): eaau3433 DOI: 10.1126/sciadv.aau3433

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

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

&

James D, Kirkham et al. (2019), "Past water flow beneath Pine Island and Thwaites glaciers West Antarctica", The Cryosphere, 13 1959-1981, https://doi.org/10.5194/tc-13-1959-2019.

https://www.the-cryosphere.net/13/1959/2019/
&
https://www.the-cryosphere.net/13/1959/2019/tc-13-1959-2019.pdf

Abstract: "Outburst floods from subglacial lakes beneath the Antarctic Ice Sheet modulate ice-flow velocities over periods of months to years. Although subglacial lake drainage events have been observed from satellite-altimetric data, little is known about their role in the long-term evolution of ice-sheet basal hydrology. Here, we systematically map and model past water flow through an extensive area containing over 1000 subglacial channels and 19 former lake basins exposed on over 19 000 km2 of seafloor by the retreat of Pine Island and Thwaites glaciers, West Antarctica. At 507 m wide and 43 m deep on average, the channels offshore of present-day Pine Island and Thwaites glaciers are approximately twice as deep, 3 times as wide, and cover an area over 400 times larger than the terrestrial meltwater channels comprising the Labyrinth in the Antarctic Dry Valleys. The channels incised into bedrock offshore of contemporary Pine Island and Thwaites glaciers would have been capable of accommodating discharges of up to 8.8×106 m3 s−1. We suggest that the channels were formed by episodic discharges from subglacial lakes trapped during ice-sheet advance and retreat over multiple glacial periods. Our results document the widespread influence of episodic subglacial drainage events during past glacial periods, in particular beneath large ice streams similar to those that continue to dominate contemporary ice-sheet discharge."

[AbruptSLR]

…
Thus, I reject calling any of these models "the best".

https://isccp.giss.nasa.gov/role.html

I prefer to think of the scientific method as a process that is continually improving climate change models, and as an example of the next generation (of new & improved) climate change models, I provide the following link to special issues of the JGR Atmospheres publication, update September 13, 2019, focused on the Energy Exascale Earth System Model (E3SM), which is one of the CMIP6 preliminarily indicating that the mean value of ECS is currently over 5C (as discussed earlier in this thread):

Title: "The Energy Exascale Earth System Model"

https://agupubs.onlinelibrary.wiley.com/doi/toc/10.1002/(ISSN)2169-8996.ENERGY1

Edit: Also note that recent models (e.g. see Reply #1642) indicate that with ice shelf & MISI ice mass loss, ice-climate interaction (including slowing of the MOC & heating of the tropical oceans [which promotes the formation of high elevation clouds]) become significant without MICI mechanisms.

[AbruptSLR]

The linked reference cites some of the reasons that it will likely be more difficult for the global socio-economic system to reach a 'Net-Zero' condition than my consensus climate scientists assume:

Duncan P. McLaren et al. (21 August 2019), "Beyond “Net-Zero”: A Case for Separate Targets for Emissions Reduction and Negative Emissions", Front. Clim., https://doi.org/10.3389/fclim.2019.00004

https://www.frontiersin.org/articles/10.3389/fclim.2019.00004/full

Abstract: "Targets and accounting for negative emissions should be explicitly set and managed separately from existing and future targets for emissions reduction. Failure to make such a separation has already hampered climate policy, exaggerating the expected future contribution of negative emissions in climate models, while also obscuring the extent and pace of the investment needed to deliver negative emissions. Separation would help minimize the negative impacts that promises and deployments of negative emissions could have on emissions reduction, arising from effects such as temporal trade-offs, excessive offsetting, and technological lock-in. Benefits for international, national, local, organizational, and sectoral planning would arise from greater clarity over the role and timing of negative emissions alongside accelerated emissions reduction."

See also:

Title: "Guest post: The problem with net-zero emissions targets"

https://www.carbonbrief.org/guest-post-the-problem-with-net-zero-emissions-targets

Extract: "Both the IPCC and the UK’s Climate Change Committee have also highlighted the likely need for negative emissions, in addition to increased efforts to cut greenhouse gas outputs, if emissions are to fall to ‘net-zero’.

However, our newly published research – based on findings from expert interviews and stakeholder deliberations – suggests that combining emissions reductions and negative emissions into a single target of reaching “net-zero” may create problems. These could include delayed emissions cuts, but also insufficient focus on developing negative emissions technologies.
…
In questioning net-zero, however, we also want to ensure that it is not seen as the last word in targets. Even if emissions were brought to net-zero by 2050, the world would likely still need to achieve “net-negative” emissions for a period, to reduce atmospheric CO2 concentrations back to safer levels. At least some countries and sectors will need to go “beyond net-zero”."

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For those who are interested, the first linked article presents a somewhat scientifically-light discussion about the potential collapse of the Thwaites Glacier, which includes a light review of the MICI mechanism as it relates to Thwaites.  However, I note that neither this first overview article nor DeConto & Pollards (2016) MICI model consider the influence of the extensive subglacial water systems under both the PIG and Thwaites which also serve to destabilize these two interconnected marine glaciers.  Therefore, I provide links to the last two scientific references for those who want to better understand how these subglacial water systems (& a currently growing subglacial cavity, nearly the size of Manhattan, at the gateway to the Thwaites Glacier) could help trigger an MICI type of a collapse of large portions of the WAIS in the coming decades:
…

The linked reference provides convincing evidence that subglacial drainage of basal meltwater can induce rapid ice mass loss on a 'continental-scale ice sheet' in West Antarctica:

Cooper W. Elsworth & Jenny Suckale (31 October 2016), "Subglacial drainage may induce rapid ice flow rearrangement in West Antarctica", Geophysical Research Letters, DOI: 10.1002/2016GL070430

http://onlinelibrary.wiley.com/doi/10.1002/2016GL070430/abstract

Abstract: "Ice streams are corridors of rapid ice flow draining the ice sheets. They can exhibit astonishing spatial variability on annual to centennial time scales. We propose that changes in the subglacial drainage of meltwater could induce these sudden rearrangements of ice streams. We develop a two-dimensional, thermo-mechanical model representing an ice stream cross-section and couple it to a plastically deforming bed with spatially variable meltwater influx. We find that where ice flows over deformable sediments and lacks significant topographic control, the efficiency of subglacial water drainage exerts direct control on the velocity, location and width of ice streams. This implies that meltwater percolation at the meter scale could have a significant effect on the short-term variability in ice loss from a continental-scale ice sheet. We verify our model against previous analytical results and validate it against surface observations from the Siple Coast of West Antarctica."

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The linked reference provides evidence that the NEGIS marine terminating glacier in Greenland, has high basal/geothermal heat flux, which results in its relatively dynamic behavior.  Here, I note that large areas of the WAIS have higher geothermal heat flux values than does the NEGIS.  Thus, if/when key WAIS marine glaciers lose buttressing from their ice shelves one can expect their dynamic response to accelerate, which will cause more internal ice melting, which will result in more subglacial meltwater; which will act as a positive feedback for more ice acceleration:

Smith-Johnsen, S., de Fleurian, B., Schlegel, N., Seroussi, H., and Nisanciolgu, K. (2019), "Exceptionally High Geothermal Heat Flux Needed to Sustain the Northeast Greenland Ice Stream", The Cryosphere Discuss., https://doi.org/10.5194/tc-2019-212

https://www.the-cryosphere-discuss.net/tc-2019-212/

Abstract. The Northeast Greenland Ice Stream (NEGIS) currently drains more than 10 % of the Greenland Ice Sheet area, and has recently undergone significant dynamic changes. It is therefore critical to accurately represent this feature when assessing the future contribution of Greenland to sea level rise. At present, NEGIS is reproduced in ice sheet models by inferring basal conditions using observed surface velocities. This approach helps estimate conditions at the base of the ice sheet, but cannot be used to estimate the evolution of basal drag in time, so it is not a good representation of the evolution of the ice sheet in future climate warming scenarios. NEGIS is suggested to be initiated by a geothermal heat flux anomaly close to the ice divide, left behind by the movement of Greenland over the Icelandic plume. However, the heat flux underneath the ice sheet is largely unknown, except for a few direct measurements from deep ice core drill sites. Using the Ice Sheet System Model (ISSM), with ice dynamics coupled to a subglacial hydrology model, we investigate the possibility of initiating NEGIS by inserting hotspots with various locations and intensities. We find that a minimum geothermal heat flux value of 970 mW/m2 located close to EastGRIP is required locally to reproduce the observed NEGIS velocities, consistent with previous estimates. By including high geothermal heat flux and the effect of water on sliding, we successfully reproduce the main characteristics of NEGIS in an ice sheet model without using data assimilation.

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The linked reference indicates that even relatively small ice mass losses (not included in CMIP5 models, and not including any MICI mechanism) from Antarctica and Greenland are sufficient to slow the MOC, thus increasing climate variability which is a sign of increasing ECS.  Imagine the ice-climate feedbacks associated with a MICI-type of collapse of the WAIS in coming decades.

Nicholas R. Golledge et al. (2019), "Global environmental consequences of twenty-first-century ice-sheet melt", Nature,  566, 65–72, DOI: https://doi.org/10.1038/s41586-019-0889-9

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

Abstract: "Government policies currently commit us to surface warming of three to four degrees Celsius above pre-industrial levels by 2100, which will lead to enhanced ice-sheet melt. Ice-sheet discharge was not explicitly included in Coupled Model Intercomparison Project phase 5, so effects on climate from this melt are not currently captured in the simulations most commonly used to inform governmental policy. Here we show, using simulations of the Greenland and Antarctic ice sheets constrained by satellite-based measurements of recent changes in ice mass, that increasing meltwater from Greenland will lead to substantial slowing of the Atlantic overturning circulation, and that meltwater from Antarctica will trap warm water below the sea surface, creating a positive feedback that increases Antarctic ice loss. In our simulations, future ice-sheet melt enhances global temperature variability and contributes up to 25 centimetres to sea level by 2100. However, uncertainties in the way in which future changes in ice dynamics are modelled remain, underlining the need for continued observations and comprehensive multi-model assessments."

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The linked Youtube video describes a major calving event for the Amery Ice Shelf (East Antarctica).  This reminds us that ice mass loss from ice shelves in Eastern Antarctica are actively contributing to the freshening of the Southern Ocean, and thus is contributing in real time to ice-climate feedback mechanisms like the slowing of the MOC:

Title: "City-sized iceberg separates from Antarctic ice shelf"



Extract: "A gigantic iceberg has broken away from the Amery ice shelf in east Antarctica. The tabular iceberg, officially named D28, is 1,636 square kilometres in size, or about 50 x 30 kilometres - the size of greater London or greater Sydney. It separated from the ice shelf last week, on 26 September but scientists said it was not related to climate change."

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…
Thus, I reject calling any of these models "the best".

https://isccp.giss.nasa.gov/role.html

I prefer to think of the scientific method as a process that is continually improving climate change models, and as an example of the next generation (of new & improved) climate change models, I provide the following link to special issues of the JGR Atmospheres publication, update September 13, 2019, focused on the Energy Exascale Earth System Model (E3SM), which is one of the CMIP6 preliminarily indicating that the mean value of ECS is currently over 5C (as discussed earlier in this thread):

Title: "The Energy Exascale Earth System Model"

https://agupubs.onlinelibrary.wiley.com/doi/toc/10.1002/(ISSN)2169-8996.ENERGY1

Edit: Also note that recent models (e.g. see Reply #1642) indicate that with ice shelf & MISI ice mass loss, ice-climate interaction (including slowing of the MOC & heating of the tropical oceans [which promotes the formation of high elevation clouds]) become significant without MICI mechanisms.

Two French model projections for CMIP6 have now been officially released, and they confirm their preliminary findings that ECS is likely over 5C, and per Olivier Boucher, head of the Institute Pierre Simon Laplace Climate Modelling Centre in Paris: "The most respected ones—from the United States, and Britain's Met Office—also show a higher ECS" than the previous generation of models:

Title: "Earth warming more quickly than thought, new climate models show"

https://phys.org/news/2019-09-earth-quickly-climate.html

Extract: "'Tipping points'

A core finding of the new models is that increased levels of CO2 in the atmosphere will warm Earth's surface more—and more easily—than earlier calculations had suggested.

If confirmed, this higher "equilibrium climate sensitivity", or ECS, means humanity's carbon budget—our total emissions allowance—is likely to shrink.

"CMIP6 clearly includes the latest modelling improvements," even as important uncertainties remain, Joeri Rogelj, an associate professor at Imperial College London and an IPCC lead author, told AFP.

These include increased supercomputing power and sharper representations of weather systems, natural and man-made particles, and how clouds evolve in a warming world.

"We have better models now," said Boucher. "They have better resolution, and they represent current climate trends more accurately."

The French models are the first to be released.

"The French modelling groups are to be congratulated for being the first to complete their simulations," said Piers Forster, director of the Priestley International Centre for Climate at the University of Leeds.

But other models developed independently have come to the same unsettling conclusion, Boucher confirmed.

"The most respected ones—from the United States, and Britain's Met Office—also show a higher ECS" than the previous generation of models, he said."

[AbruptSLR]

Information from the linked articles and references can help scientists to between compare abrupt climate change events in the past with the changes that are happening in modern times:

Title: "Humanity's emissions '100-times greater' than volcanoes"

https://phys.org/news/2019-10-humanity-emissions-times-greater-volcanoes.html

Extract: "The Deep Carbon Observatory (DCO), a 500-strong international team of scientists, released a series of papers outlining how carbon is stored, emitted and reabsorbed by natural and manmade processes.
…
Celina Suarez, Associate Professor of Geology at the University of Arkansas, said modern manmade emissions were the "same magnitude" as past carbon shocks that precipitated mass extinction.

See also:

Giancarlo Tamburello et al. Global-scale control of extensional tectonics on CO2 earth degassing, Nature Communications (2018). DOI: 10.1038/s41467-018-07087-z

J.M. de Moor et al. Short-period volcanic gas precursors to phreatic eruptions: Insights from Poás Volcano, Costa Rica, Earth and Planetary Science Letters (2016). DOI: 10.1016/j.epsl.2016.02.056

Brendan McCormick Kilbride et al. Observing eruptions of gas-rich compressible magmas from space, Nature Communications (2016). DOI: 10.1038/ncomms13744

Louis Johansson et al. The Interplay Between the Eruption and Weathering of Large Igneous Provinces and the Deep-Time Carbon Cycle, Geophysical Research Letters (2018). DOI: 10.1029/2017GL076691

Peter B. Kelemen et al. Reevaluating carbon fluxes in subduction zones, what goes down, mostly comes up, Proceedings of the National Academy of Sciences (2015). DOI: 10.1073/pnas.1507889112

&

Title: "Scientists quantify global volcanic CO2 venting; estimate total carbon on Earth"

https://phys.org/news/2019-10-scientists-quantify-global-volcanic-co2.html

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While I like the concept of developing calibrated language to better communicate the results of extreme event attribution studies, I do not like the language recommended in the linked study.  Nevertheless, I provide this information for those who might have use for the study's findings.

Also, I note that as an increase in climate variability is an indication of increasing climate sensitivity, attribution is a important topic:

Sophie C. Lewis et al. (27 August 2019), "Toward Calibrated Language for Effectively Communicating the Results of Extreme Event Attribution Studies", Earth's Future, https://doi.org/10.1029/2019EF001273

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019EF001273

Abstract: "Extreme event attribution studies attempt to quantify the role of human influences in observed weather and climate extremes. These studies are of broad scientific and public interest, although quantitative results (e.g., that a specific event was made a specific number of times more likely because of anthropogenic forcings) can be difficult to communicate accurately to a variety of audiences and difficult for audiences to interpret. Here, we focus on how results of these studies can be effectively communicated using standardized language and propose, for the first time, a set of calibrated terms to describe event attribution results. Using these terms and an accompanying visual guide, results are presented in terms of likelihood of event changes and the associated uncertainties. This standardized language will allow clearer communication and interpretation of probabilities by the public and stakeholders."

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Given the importance of the various snow/ice albedo feedback mechanisms wr.t. the risk of abrupt climate change, I provide following three linked references, all of which indicate that snow/ice albedo will likely be significantly reduced in coming decades:

Jieru Ma (2019), "The Dominant Role of Snow/Ice Albedo Feedback Strengthened by Black Carbon in the Enhanced Warming over the Himalayas", Journal of Climate, https://doi.org/10.1175/JCLI-D-18-0720.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-18-0720.1

Abstract: "An obvious warming trend in winter over the Tibetan Plateau (TP) in the recent decades has been widely discussed, with studies emphasizing the dominant effects of local radiative factors, including those due to black carbon (BC). The Himalayas are one of the largest snowpack- and ice-covered regions in the TP, and an ideal area to investigate local radiative effects on climate change. In this study, the coupled climate feedback response analysis method (CFRAM) is applied to quantify the magnitude of warming over the Himalayas induced by different external forcing factors and climate feedback processes. The results show that snow/ice albedo feedback (SAF) resulted in a warming of approximately 2.6°C and was the primary contributor to enhanced warming over the Himalayas in recent decades. This warming was much greater than the warming induced by dynamic and other radiative factors. In particular, the strong radiative effects of BC on the warming over the Himalayas are identified by comparing control and BC-perturbed experiments of the Community Earth System Model (CESM). As a result of strong BC effects on the Himalayas, evaporation and reduced precipitation were strengthened, accounting for local drying and land degradation, which intensified warming. These results suggest that more investigations on the local radiative effects on the climate and ecosystem are needed, especially in the high-altitude cryosphere."

&

Adrienne M. Marshall et al.  (08 August 2019), "Projected Changes in Interannual Variability of Peak Snowpack Amount and Timing in the Western United States", Geophysical Research Letters, https://doi.org/10.1029/2019GL083770

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019GL083770

Abstract
Interannual variability of mountain snowpack has important consequences for ecological and socioeconomic systems, yet changes in variability have not been widely examined under future climates. Physically based snowpack simulations for historical (1970–1999) and high‐emission scenario (RCP 8.5) mid‐21st century (2050–2079) periods were used to assess changes in the variability of annual maximum snow water equivalent (SWEmax) and SWEmax timing across the western United States. Models show robust declines in the interannual variability of SWEmax in regions where precipitation is projected to increasingly fall as rain. The average frequency of consecutive snow drought years (SWEmax < historical 25th percentile) is projected to increase from 6.6% to 42.2% of years. Models also project increases in the variability of SWEmax timing, suggesting reduced reliability of when SWEmax occurs. Differences in physiography and regional climate create distinct spatial patterns of change in snowpack variability that will require adaptive strategies for environmental resource management.

Plain Language Summary
A wealth of research has established that warming temperatures associated with climate change in the western United States will generally reduce snowpack accumulation and result in earlier snowmelt timing, with important consequences for water resources and ecosystems. However, changes in the variability of snowpack conditions between years have not been well established. We analyze simulated snowpack data for historical and future climate scenarios and find that changes in variability differ across the western United States. Variability of annual maximum snowpack between years decreases while the timing of peak snow accumulation becomes more variable, particularly in areas transitioning from snow‐ to rain‐dominated precipitation. We also find that consecutive years with very low or early snowpack will become much more frequent. These findings highlight the need to consider changes in snowpack variability in climate change impact assessments and adaptation planning

&

Chunxia Zhou et al. (2019), "The Characteristics of Surface Albedo Change Trends over the Antarctic Sea Ice Region during Recent Decades", Remote Sens., 11(7), 821, doi: 10.3390/rs11070821

https://www.mdpi.com/2072-4292/11/7/821

Abstract: "Based on a long-time series (1982–2015) of remote sensing data, we analyzed the change in surface albedo (SAL) during summer (from December to the following February) for the entire Antarctic Sea Ice Region (ASIR) and five longitudinal sectors around Antarctica: (1). the Weddell Sea (WS), (2). Indian Ocean, (3). Pacific Ocean (PO), (4). Ross Sea, and (5). Bellingshausen–Amundsen Sea (BS). Empirical mode decomposition was used to extract the trend of the original signal, and then a slope test method was utilized to identify a transition point. The SAL provided by the CM SAF cloud, Albedo, and Surface Radiation dataset from AVHRR data-Second Edition was validated at Neumayer station. Sea ice concentration (SIC) and sea surface temperature (SST) were also analyzed. The trend of the SAL/SIC was positive during summer over the ASIR and five longitudinal sectors, except for the BS (−2.926% and −4.596% per decade for SAL and SIC, correspondingly). Moreover, the largest increasing trend of SAL and SIC appeared in the PO at approximately 3.781% and 3.358% per decade, respectively. However, the decreasing trend of SAL/SIC in the BS slowed down, and the increasing trend of SAL/SIC in the PO accelerated. The trend curves of the SST exhibited a crest around 2000–2005; thus, the slope lines of the SST showed an increasing–decreasing type for the ASIR and the five longitudinal sectors. The evolution of summer albedo decreased rapidly in the early summer and then maintained a relatively stable level for the whole ASIR. The change of it mainly depended on the early melt of sea ice during the entire summer. The change of sea ice albedo had a narrow range when compared with composite albedo and SIC over the five longitudinal sectors and reached a stable level earlier. The transition point of SAL/SIC in several sectors appeared around the year 2000, whereas that of the SST for the entire ASIR occurred in 2003–2005. A high value of SAL/SIC and a low value of the SST existed in the WS which can be displayed by the spatial distribution of pixel average. In addition, the lower the latitude was, the lower the SAL/SIC and the higher the SST would be. A transition point of SAL appeared in 2001 in most areas of West Antarctica. This transition point could be illustrated by anomaly maps. The spatial distribution of the pixel-based trend of SAL demonstrated that the change in SAL in East Antarctica has exhibited a positive trend in recent decades. However, in West Antarctica, the change of SAL presented a decreasing trend before 2001 and transformed into an increasing trend afterward, especially in the east of the Antarctic Peninsula."

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The linked reference confirms the important role that SST of the Western Tropical Pacific will likely play in increasing ECS with continued anthropogenic radiative forcing (& I note that increasing glacial ice mass loss, in the future, will work to slow the MOC, which will serve to warm the Western Tropical Pacific:

Dong, Y., C. Proistosescu, K.C. Armour, D.S. Battisti (2019): Attributing historical and future evolution of radiative feedbacks to regional warming patterns using a Green’s function approach: The preeminence of the western Pacific. Journal of Climate, https://doi.org/10.1175/JCLI-D-18-0843.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-18-0843.1

Abstract
Global radiative feedbacks have been found to vary in global climate model (GCM) simulations. Atmospheric GCMs (AGCMs) driven with historical patterns of sea surface temperatures (SSTs) and sea ice concentrations produce radiative feedbacks that trend toward more negative values, implying low climate sensitivity, over recent decades. Freely evolving coupled GCMs driven by increasing CO2 produce radiative feedbacks that trend toward more positive values, implying increasing climate sensitivity, in the future. While this time variation in feedbacks has been linked to evolving SST patterns, the role of particular regions has not been quantified. Here, a Green’s function is derived from a suite of simulations within an AGCM (NCAR’s CAM4), allowing an attribution of global feedback changes to surface warming in each region. The results highlight the radiative response to surface warming in ascent regions of the western tropical Pacific as the dominant control on global radiative feedback changes. Historical warming from the 1950s to 2000s preferentially occurred in the western Pacific, yielding a strong global outgoing radiative response at the top of the atmosphere (TOA) and thus a strongly negative global feedback. Long-term warming in coupled GCMs occurs preferentially in tropical descent regions and in high latitudes, where surface warming yields small global TOA radiation change but large global surface air temperature change, and thus a less-negative global feedback. These results illuminate the importance of determining mechanisms of warm pool warming for understanding how feedbacks have varied historically and will evolve in the future.

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One significant reason (others include: more than expected heat has gone into the oceans and into melting ice and that the negative impact of aerosols were greater than previously assumed) that estimates of ECS based on observed changes in mean global temperature are lower than what society is likely going to face for the rest of this century is that a surge of plant growth has temporarily absorbed meaningful amounts of CO2 from the atmosphere.  However, the linked article (base on per reviewed research) indicates that 'vegetated coastal ecosystems' are susceptible to release carbon back into the atmosphere when subjected stressed by such factors as: storms, heatwaves, dredging, etc., and 'vegetated coastal ecosystems' are currently being degraded globally twice as fast as rain forests.  It does not take much imagination to see the significant risk that global biosystems may turn from carbon sinks into carbon sources this century:

Title: "Australia’s vast carbon sink releasing millions of tonnes of CO2 back into atmosphere "

https://www.theguardian.com/environment/2019/oct/01/australias-vast-carbon-sink-releasing-millions-of-tonnes-of-co2-back-into-atmosphere

Extract: "Australia’s mangroves, tidal marshes and seagrass meadows are absorbing about 20m tonnes of carbon dioxide every year, according to a major new study that is the first to measure in detail the climate benefits of the coastal ecosystems.

But the study, published in the journal Nature Communications, warns that degradation of these “vegetated coastal ecosystems” was already seeing 3 million tonnes of CO2 per year being released back into the atmosphere.

The study reveals Australia’s vast coastlines represent between 5% and 11% of all the so called “blue carbon” locked up in mangroves, seagrasses and tidal marshes globally.
...
Serrano said: “When these ecosystems are damaged by storms, heatwaves, dredging or other human development, the carbon dioxide stored in their biomass and soils beneath them can make its way back into the environment, contributing to climate change.

“Globally, vegetated coastal ecosystems are being lost twice as fast as tropical rainforests despite covering a fraction of the area.”"