Ice Apocalypse - Multiple Meters Sea Level Rise

[AbruptSLR]

The linked reference indicates that as the Atlantic warm pool (AWP) continues to warm (& I note that a slowing of the AMOC acts to warm the AWP), enhance telecommunications from the AWP to the Pacific, increases the frequency of El Nino events; which increases ECS, and the telecommunication of heat energy from the Tropical Pacific to West Anarctica:

Park, JH., Li, T., Yeh, SW. et al. (2019), "Effect of recent Atlantic warming in strengthening Atlantic–Pacific teleconnection on interannual timescale via enhanced connection with the pacific meridional mode", Clim Dyn, https://doi.org/10.1007/s00382-018-4591-7

https://link.springer.com/article/10.1007%2Fs00382-018-4591-7

Abstract: "The Atlantic warm pool (AWP), which features the highest sea surface temperature (SST) in the western Hemisphere in boreal summer to early fall, has been known to have a significant influence on the climate in its surrounding regions. It is reported that the AWP has become warmer and warmer, so that AWP–SST during a couple of recent decades has been higher than any other period since the twentieth century. Under the increased mean AWP–SST, atmospheric responses to the anomalous AWP–SST are intensified, which corresponds to a higher possibility of deep convection formation. Through Rossby wave propagation induced by the deep convection, AWP signals are able to reach further west toward the central North Pacific. At this moment, anomalous northerly winds are introduced over the North Pacific, which advects negative moist static energy (MSE) into the subtropics and simultaneously contributes to a SST cooling by interacting with northerly mean trade winds. Owing to the Gill-type response to a negative heating anomaly associated with the anomalous SST cooling and the negative MSE, the anomalous northerly winds are further developed over the North Pacific. Such air–sea coupling persists throughout fall to winter, leading to Pacific meridional mode development in the following spring. Subsequently, the PMM acts to boost El Niño and Southern Oscillation events. Coupled model experiments were carried out to investigate the extent to which the mean AWP–SST warming strengthens the Atlantic–Pacific interbasin teleconnection on interannual timescales, and it is proven to support observational analysis."

[AbruptSLR]

I have previously speculated that when the Getz Ice Shelf eventually collapses, the associated regional changes in seawater temperatures and current flows could contribute to an acceleration of the degradation of the Ross Ice Shelf, RIS (see the Hazard Analysis for the FRIS/RIS in the 2012 to 2060 Timeframe).  In this regards, I provide the following linked reference that verifies the relationship of changes (climate change related) to the local winds that changed the local upwelling of warm CDW and consequent increasing in ice mass loss from the Getz Ice Shelf:

K. M. Assmann et al. (04 January 2019), "Warm Circumpolar Deep Water at the western Getz Ice Shelf Front, Antarctica", Geophysical Research Letters, https://doi.org/10.1029/2018GL081354

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL081354

Abstract
The Getz Ice Shelf is one of the largest sources of fresh water from ice shelf basal melt in Antarctica. We present new observations from three moorings west of Siple Island 2016‐18. All moorings show a persistent flow of modified Circumpolar Deep Water towards the western Getz Ice Shelf. Unmodified Circumpolar Deep Water with temperatures up to 1.5° C reaches the ice shelf front in frequent episodes. These represent the warmest water observed at any ice shelf front in the Amundsen Sea. Mean currents within the warm bottom layer of 18‐20 cm s−1 imply an advection time scale of 7 days from shelf break to ice shelf front. Zonal wind stress at the shelf break affects heat content at the ice shelf front on weekly to monthly time scales. Our two‐year mooring records also evince that upwelling over the shelf break controls thermocline depth on sub‐annual to annual time scales.

Plain Language Summary
The recent retreat of the West Antarctic Ice Sheet has been linked to changes in the transport of warm ocean water up to 1.5C to the floating ice shelves in the Amundsen Sea. One of these is the Getz Ice Shelf that produces one of the largest amounts of ice shelf melt water in Antarctica. To measure how much ocean heat is transported towards this ice shelf, we deployed a series of temperature, salinity and current sensors at its western end from 2016‐2018. We find a constant flow of warm water towards the ice shelf cavity. Comparing our ocean observations with wind data from the area we found that stronger easterly winds in the area make it harder for the warm water to reach the ice shelf front by depressing the warm bottom layer over the shelf break. Climate projections indicate that these easterlies will weaken in future, making it easier for the warm water to reach the ice shelf base. Gradients in the wind field over the shelf break control the thickness of the warm layer on longer time scales. This provides the missing ocean evidence for previous studies that have linked this wind mechanism to ice sheet changes.

[AbruptSLR]

The linked reference indicates that models of key Antarctic ice shelves currently underestimate observes ice melt rates, indicating that both more refined  local meshing needs to be employed as well as improved ice-ocean interaction, otherwise we are underestimating our associated risk levels:

D. N. Goldberg et al. (31 December 2018), "How Accurately Should We Model Ice Shelf Melt Rates?", Geophysical Research Letters, https://doi.org/10.1029/2018GL080383

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL080383

Abstract
Assessment of ocean‐forced ice sheet loss requires that ocean models be able to represent sub‐ice shelf melt rates. However, spatial accuracy of modeled melt is not well investigated, and neither is the level of accuracy required to assess ice sheet loss. Focusing on a fast‐thinning region of West Antarctica, we calculate spatially resolved ice‐shelf melt from satellite altimetry and compare against results from an ocean model with varying representations of cavity geometry and ocean physics. Then, we use an ice‐flow model to assess the impact of the results on grounded ice. We find that a number of factors influence model‐data agreement of melt rates, with bathymetry being the leading factor; but this agreement is only important in isolated regions under the ice shelves, such as shear margins and grounding lines. To improve ice sheet forecasts, both modeling and observations of ice‐ocean interactions must be improved in these critical regions.

Plain Language Summary
The Antarctic coastline is fringed by large floating ice shelves, often the size of cities or larger. They play a crucial role as a stopgap against acceleration of the ice sheet, and their loss could lead to considerable sea level rise. Many of these ice shelves are exposed to warm waters from farther north, leading to considerable melting underneath. Scientists use models of the ice sheet and the ocean in order to understand the link between warming oceans and sea levels, and how this might change in the future. In our study we focus on one of these fast‐thinning ice shelves and determine through satellite imagery that melting is not uniform across the ice shelf but is highly focused in certain areas due to ocean currents. Using state‐of‐the‐art ice and ocean models, we investigate what information will be needed in order to predict how the Antarctic Ice Sheet will respond to climate change. Our findings suggest that improved knowledge of ocean depth under ice shelves, as well as improved understanding of ocean flow just below the ice bottom, will be vital in determining the effects of climate change on ice shelves and ice sheets.

[AbruptSLR]

The linked reference indicates that projected increases of rainfall in Arctic permafrost regions will result in an increase in methane, that will "… increase near‐term global warming associated with permafrost thaw …", which is currently not considered in consensus science projections:

R. B. Neumann et al. (03 January 2019), "Warming effects of spring rainfall increase methane emissions from thawing permafrost", Geophysical Research Letters, https://doi.org/10.1029/2018GL081274

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL081274

Abstract
Methane emissions regulate the near‐term global warming potential of permafrost thaw, particularly where loss of ice‐rich permafrost converts forest and tundra into wetlands. Northern latitudes are expected to get warmer and wetter, and while there is consensus that warming will increase thaw and methane emissions, effects of increased precipitation are uncertain. At a thawing wetland complex in Interior Alaska, we found that interactions between rain and deep soil temperatures controlled methane emissions. In rainy years, recharge from the watershed rapidly altered wetland soil temperatures, warming the top ~80 cm of soil in spring and summer, and cooling it in autumn. When soils were warmed by spring rainfall, methane emissions increased by ~30%. The warm, deep soils early in the growing season likely supported both microbial and plant processes that enhanced emissions. Our study identifies an important and unconsidered role of rain in governing the radiative forcing of thawing permafrost landscapes.

Plain Language Summary
Because the world is getting warmer, permanently frozen ground around the arctic, known as permafrost, is thawing. When permafrost thaws, the ground collapses and sinks. Often a wetland forms within the collapsed area. Conversion of permanently frozen landscapes to wetlands changes the exchange of greenhouse gases between the land and atmosphere, which impacts global temperatures. Wetlands release methane into the atmosphere. Methane is a potent greenhouse gas. The ability of methane to warm the Earth is 32‐times stronger than that of carbon dioxide over a period of 100 years. In our study, we found that methane release from a thaw wetland in Interior Alaska was greater in rainy years when rain fell in spring. When spring rainwater entered the wetland, it rapidly warmed wetland soils. Rain has roughly the same temperature as the air, and during springtime in northern regions, the air is warmer than the ground. The microbial and plant processes that generate methane increase with temperature. Therefore, wetland soils, warmed by spring rainfall, supported more methane production and release. Northern regions are expected to receive more rainfall in the future. By warming soils and increasing methane release, this rainfall could increase near‐term global warming associated with permafrost thaw.

[AbruptSLR]

The linked reference uses machine learning to demonstrate the consensus climate science underestimate the risk of carbon emissions that may occur from coastal temperate rainforests, with continued warming:

Gavin McNicol, Chuck Bulmer, David D'Amore, Paul Sanborn, Sari Saunders, Ian Giesbrecht, Santiago Gonzalez Arriola, Allison Bidlack, David Butman and Brian Buma (3 January 2019), "Large, climate-sensitive soil carbon stocks mapped with pedology-informed machine learning in the North Pacific coastal temperate rainforest", Environmental Research Letters, Volume 14, Number 1, https://doi.org/10.1088/1748-9326/aaed52

http://iopscience.iop.org/article/10.1088/1748-9326/aaed52/meta

Abstract
Accurate soil organic carbon (SOC) maps are needed to predict the terrestrial SOC feedback to climate change, one of the largest remaining uncertainties in Earth system modeling. Over the last decade, global scale models have produced varied predictions of the size and distribution of SOC stocks, ranging from 1000 to >3000 Pg of C within the top 1 m. Regional assessments may help validate or improve global maps because they can examine landscape controls on SOC stocks and offer a tractable means to retain regionally-specific information, such as soil taxonomy, during database creation and modeling. We compile a new transboundary SOC stock database for coastal watersheds of the North Pacific coastal temperate rainforest, using soil classification data to guide gap-filling and machine learning approaches to explore spatial controls on SOC and predict regional stocks. Precipitation and topographic attributes controlling soil wetness were found to be the dominant controls of SOC, underscoring the dependence of C accumulation on high soil moisture. The random forest model predicted stocks of 4.5 Pg C (to 1 m) for the study region, 22% of which was stored in organic soil layers. Calculated stocks of 228 ± 111 Mg C ha−1 fell within ranges of several past regional studies and indicate 11–33 Pg C may be stored across temperate rainforest soils globally. Predictions compared very favorably to regionalized estimates from two spatially-explicit global products (Pearson's correlation: ρ = 0.73 versus 0.34). Notably, SoilGrids 250 m was an outlier for estimates of total SOC, predicting 4-fold higher stocks (18 Pg C) and indicating bias in this global product for the soils of the temperate rainforest. In sum our study demonstrates that CTR ecosystems represent a moisture-dependent hotspot for SOC storage at mid-latitudes.

[Lennart van der Linde]

There is not yet a compelling theory for the magnetic field or magnetic polar wander. There is almost certainly a coupling between the location of the spin axis and the magnetic poles, but the nature of this coupling is not understood, probably because the nature of the magnetic field is not well understood. There is a Nobel waiting for anyone who comes up with answers.

Could small changes in the position of the spin axis maybe cause changes in convection in the outer core, and could those in turn cause (small) changes in the position of the magnetic pole, as one factor amongst others?

Here someone says:
http://all-geo.org/highlyallochthonous/2008/03/where-the-earths-magnetic-field-comes-from/
“Earth’s rotation… has a strong influence on the patterns of convection in the outer core. Most significantly, it has a tendency to produce helical convection currents which align with the spin axis…”.

The geographical pole apparently moves partly due to convection in the Earth mantle:
https://phys.org/news/2018-09-scientists-id-earth-axis-drift.html
“Using observational and model-based data spanning the entire 20th century, NASA scientists have for the first time identified three broadly-categorized processes responsible for this drift—contemporary mass loss primarily in Greenland, glacial rebound, and mantle convection... Mantle convection is responsible for the movement of tectonic plates on Earth’s surface. It is basically the circulation of material in the mantle caused by heat from Earth’s core. Ivins describes it as similar to a pot of soup placed on the stove. As the pot, or mantle, heats, the pieces of the soup begin to rise and fall, essentially forming a vertical circulation pattern—just like the rocks moving through Earth’s mantle.”

Or is this hypothesis too farfetched?

[sidd]

Re: "Or is this hypothesis too farfetched?"

Can you put some numbers on the coupling between spin axis change and convection ? And then convection change and magnetic pole wander ?

 I have thought about this and i cannot.  This seems very difficult since mantle convection is very poorly understood ...

sidd

[Lennart van der Linde]

I wish I could

[Shared Humanity]

ASLR...

Thank you for the Plain Language Summaries on your posts.

[AbruptSLR]

The two linked articles indicate that the Northwestern portion of the Ross Ice Shelf, RIS, is currently being destabilized by a previously unverified mechanism, i.e. local basal ice melting induced by '… seasonal masses of warm water near the ocean surface in front of the ice shelf.'  The attached image (which shows ice velocities from 2009) shows that a local weakening of buttressing action in the Northwestern portion of the RIS would likely lead to an acceleration of ice stream velocities for the important Byrd Glacier:

Title: "Antarctica's Largest Ice Shelf Could Be at Risk of Melting"

https://www.insidescience.org/news/antarcticas-largest-ice-shelf-could-be-risk-melting

Extract: "The ROSETTA-Ice researchers have built a computer model of the interconnected factors that control the Ross Ice Shelf, including seasonal conditions, ocean currents, and the structure of ice and bedrock on the adjacent continent. The model is based on data collected by the ROSETTA-Ice team using instruments mounted on aircraft and on undersea robots.

The findings suggest that a spot on the northwestern side of the ice shelf is melting in a way researchers have not seen before -- neither hydrofracture nor deep currents at the grounding line. Instead, the Ross's problem is seasonal masses of warm water near the ocean surface in front of the ice shelf.
…
The lost ice is currently being replaced by ice flowing down from the continent, so the shelf is not yet getting thinner. But it could easily start to thin as the climate continues to warm, and current projections don't take the processes the ROSETTA-Ice team observed into account, said Padman.
Most of the grounded glacier ice that is being held back by the Ross Ice Shelf is unlikely to melt anytime soon, in part because it is also held in place by the shape of underlying mountains and valleys, said Padman. But the melting corner of the Ross happens to be located right in front of a particularly vulnerable swathe of ice on the continent."

See also the associated presentation abstract:

Title: "C11A-04: Ice Shelf Vulnerability to Increased Seasonal Upper Ocean Warming" by Padman et al. (2018).

https://agu.confex.com/agu/fm18/meetingapp.cgi/Paper/446984

Abstract: "Ice shelf vulnerability to climate change is strongly controlled by the interactions between ice, ocean and atmosphere. Most studies of ice shelves have focused on changes in melt rates near the deep grounding lines, driven by deep intrusions of warm water. Increased melting at the grounding line leads to mass imbalance and grounding line retreat, with potentially long-lasting consequences for ice dynamics. However, mass loss from anywhere on the ice shelf can alter the back-stress acting on the grounded ice. For Ross Ice Shelf, basal melting near the grounding line is governed by deep circulation of cold, dense water that is formed by winter convection in polynyas near the ice front. Circulation of this dense water is primarily controlled by seafloor bathymetry and is resistant to change. In contrast, melt rates close to the ice front are known to vary on seasonal and interannual time scales, and ice-sheet models indicate that grounded ice flow into the ice shelf is sensitive to changes in ice thickness near the ice front.

We use data from new radar surveys of Ross Ice Shelf to measure multi-decadal averaged basal melt rates within a key region of the ice shelf near Ross Island. These rates are comparable to estimates from satellite altimetry, suggesting that ocean processes governing melt near the ice front have been stable for several decades. However, ocean models suggest that melt in this region is caused by warm surface waters in summer intruding beneath the ice shelf where ice draft is shallow. These results indicate that the common assumption of Ross Ice Shelf stability during the next century may be incorrect, if the summer upper ocean temperature in the western Ross Sea increases significantly in response to a longer period free of sea ice or a decrease in summertime cloudiness. Our findings emphasize the importance of processes beyond the grounding line and call for a rethinking of the vulnerability of ice shelves in large-scale models of future ice sheet behavior."

[AbruptSLR]

As a supplement to my last post, I estimate that by 2050 that the calving face of RIS should have retreated at least 40km (using the current rate of retreat), and I postulate that this retreat of the ice shelf face will cause the Ross Gyre current (see the first attached image) to follow the retreating face until the gyre current is directed at the shallow bed trough leading to the base of the Byrd Glacier (see the second image).  Also, by 2050 I believe that that the AABW production will be sufficiently reduced (by both changing atmospheric patterns and the strengthening of the CDW volume & temperature) so that the cold AABW entrained in the Ross Gyre will not be able to adequately dilute the CDW entrained in the Ross Gyre (assuming also that the ice melt from the Getz Ice Shelf has slowed sufficiently to reduce the dilution of the CDW crossing the continental shelf with meltwater).  Therefore, I postulate that a warm tongue of CDW will make its way to the grounding line for the Byrd Glacier, which will help to trigger a positive feedback cycle that will alternate the circulation patterns in the Ross Sea Embayment so as to direct the warm tongue from the Byrd Glacier southward along the grounding lines of the Siple Coast ice streams (note that there is a pre-existing shallow trough leading from the Byrd Glacier to the Siple Coast; with the resulting cold ice melt water from the Siple Coast ice streams existing out through another shallow trough along the east side of the Ross Sea Embayment.  As the RIS is already thinner than the FRIS, and the CDW will be warmer by then, I postulate that a large portion of the RIS will be subject to a melt-pond collapse mechanism between 2060 & 2070; which, will reduce the buttressing of the RIS on the Siple Coast ice streams that the thinning ice streams will induce a grounding line treat pattern.

[AbruptSLR]

The linked reference indicates that Antarctica is currently losing ice mass at a rate six times that during the 1980s; which should not surprise anyone following this thread:

Eric Rignot, Jérémie Mouginot, Bernd Scheuchl, Michiel van den Broeke, Melchior J. van Wessem, and Mathieu Morlighem (January 14, 2019), "Four decades of Antarctic Ice Sheet mass balance from 1979–2017", PNAS https://doi.org/10.1073/pnas.1812883116

https://www.pnas.org/content/early/2019/01/08/1812883116

Abstract: "We use updated drainage inventory, ice thickness, and ice velocity data to calculate the grounding line ice discharge of 176 basins draining the Antarctic Ice Sheet from 1979 to 2017. We compare the results with a surface mass balance model to deduce the ice sheet mass balance. The total mass loss increased from 40 ± 9 Gt/y in 1979–1990 to 50 ± 14 Gt/y in 1989–2000, 166 ± 18 Gt/y in 1999–2009, and 252 ± 26 Gt/y in 2009–2017. In 2009–2017, the mass loss was dominated by the Amundsen/Bellingshausen Sea sectors, in West Antarctica (159 ± 8 Gt/y), Wilkes Land, in East Antarctica (51 ± 13 Gt/y), and West and Northeast Peninsula (42 ± 5 Gt/y). The contribution to sea-level rise from Antarctica averaged 3.6 ± 0.5 mm per decade with a cumulative 14.0 ± 2.0 mm since 1979, including 6.9 ± 0.6 mm from West Antarctica, 4.4 ± 0.9 mm from East Antarctica, and 2.5 ± 0.4 mm from the Peninsula (i.e., East Antarctica is a major participant in the mass loss). During the entire period, the mass loss concentrated in areas closest to warm, salty, subsurface, circumpolar deep water (CDW), that is, consistent with enhanced polar westerlies pushing CDW toward Antarctica to melt its floating ice shelves, destabilize the glaciers, and raise sea level."

Significance Statement

We evaluate the state of the mass balance of the Antarctic Ice Sheet over the last four decades using a comprehensive, precise satellite record and output products from a regional atmospheric climate model to document its impact on sea-level rise. The mass loss is dominated by enhanced glacier flow in areas closest to warm, salty, subsurface circumpolar deep water, including East Antarctica, which has been a major contributor over the entire period. The same sectors are likely to dominate sea-level rise from Antarctica in decades to come as enhanced polar westerlies push more circumpolar deep water toward the glaciers.

See also the following related article:

Title: "Antarctica is losing ice six times faster than in 1980s"

https://www.axios.com/antarctica-ice-loss-has-grown-sixfold-in-past-4-decades-ad1ed0e1-ef89-4b80-9b14-242c847ac863.html

[sidd]

The paper is open access. Nice work, has detail for every basin. I note that WAIS went from 56GT/y in 1999-2009 to 160 GT/yr in 2009-2017. Thats a tripling in 9 years, call it a doubling in 6. Not reassuring.

sidd

[sidd]

That Rignot latest table 1 includes decadal glacier discharge. I note that apart from the two biggies, that all "the glaciers next door" as a recent paper called them, Haynes, Crosson, Dotson, Getz are increasing discharge, to me clear signs of hot water lapping at their foundations.

6 yr doubling for WAIS mass waste, we will have half inch a year of SLR from WAIS alone by 2050.

A couple years ago I seem to recall either Joughin or Rignot remarking that mass waste models for WAIS blow up once you get to a few mm/yr SLR. Lets hope they got better.

sidd

[AbruptSLR]

It appears that carbon pricing (& dividend) is facing trouble not only from the right, but now increasingly from the left.  It is hard for me to imagine that without strong carbon pricing measures, that the Green New Deal will make much headway against our current BAU pathway before 2040 (when I project that the WAIS will reach an irreversible tipping point towards collapse):

Title: "Carbon taxes are facing new troubles on the left"

https://www.axios.com/green-new-deal-carbon-tax-climate-change-85a5c503-fc5c-4610-89d5-8dff9be81a4f.html

Extract: "The bottom line: the biggest barrier to carbon pricing remains extremely widespread GOP resistance. But the idea is also fighting for air on the left."

[AbruptSLR]

The fact that the Western Pacific warm pool has predominant influence on ECS, is bad news for those who believe in the ice-climate feedback mechanisms, as a slowing of the MOC (due to increasing ice mass loss) will directly increase the temperature of the Western Pacific, and thus will increase the frequency of El Nino events and the associated telecommunication of Tropical Pacific heat energy poleward:

Yue Dong, Cristian Proistosescu, Kyle Armour & David S. Battisti (Dec 19, 2018), "Attributing Historical and Future Evolution of Radiative Feedbacks to Regional Warming Patterns using a Green’s Function Approach: The Preeminence of the Western Pacific"

https://eartharxiv.org/tdrmx/

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 (SST) 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 regions.

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 TOA and producing 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 changes, and thus a less-negative global feedback.  These results illuminate the importance of determining mechanism of warm pool warming for understanding how feedbacks have varied historically and will evolve in the future."

[AbruptSLR]

The linked reference examines large-scale climate forcing associated with West Antarctic surface ice melting; which is one of the numerous positive feedbacks associated with the ice-climate mechanism:

Ryan C. Scott et al. (2019), "Meteorological Drivers and Large-Scale Climate Forcing of West Antarctic Surface Melt", Journal of Climate, https://doi.org/10.1175/JCLI-D-18-0233.1

https://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-18-0233.1

Abstract: "Understanding the drivers of surface melting in West Antarctica is crucial for understanding future ice loss and global sea level rise. This study identifies atmospheric drivers of surface melt on West Antarctic ice shelves and ice sheet margins and relationships with tropical Pacific and high-latitude climate forcing using multidecadal reanalysis and satellite datasets. Physical drivers of ice melt are diagnosed by comparing satellite-observed melt patterns to anomalies of reanalysis near-surface air temperature, winds, and satellite-derived cloud cover, radiative fluxes, and sea ice concentration based on an Antarctic summer synoptic climatology spanning 1979–2017. Summer warming in West Antarctica is favored by Amundsen Sea (AS) blocking activity and a negative phase of the southern annular mode (SAM), which both correlate with El Niño conditions in the tropical Pacific Ocean. Extensive melt events on the Ross–Amundsen sector of the West Antarctic Ice Sheet (WAIS) are linked to persistent, intense AS blocking anticyclones, which force intrusions of marine air over the ice sheet. Surface melting is primarily driven by enhanced downwelling longwave radiation from clouds and a warm, moist atmosphere and by turbulent mixing of sensible heat to the surface by föhn winds. Since the late 1990s, concurrent with ocean-driven WAIS mass loss, summer surface melt occurrence has increased from the Amundsen Sea Embayment to the eastern Ross Ice Shelf. We link this change to increasing anticyclonic advection of marine air into West Antarctica, amplified by increasing air–sea fluxes associated with declining sea ice concentration in the coastal Ross–Amundsen Seas."

[rboyd]

Extract: "The bottom line: the biggest barrier to carbon pricing remains extremely widespread GOP resistance. But the idea is also fighting for air on the left."

I think that the following quote from the article you linked to sums it up well:
"A carbon price should not be the centerpiece of legislation, it should be about spending and regulations to get the economy on an ambitious decarbonization pathway. ... Carbon prices and tax may have a role, but more to change market incentives and break up concentrations of wealth and income."

A carbon tax by itself will simply dump the cost predominantly on the poorer members of society. Fee + Flat Dividend helps redistribute, but it is not a silver bullet and requires extensive government spending (the military, infrastructure etc.) changes, together with regulations (e.g. applying the clean water act and the EPA to fracking etc., building codes ...). Probably could have worked in the 1990's, but we are already too far gone for such policies.

A true "WW2" type effort would ban over-consumption as an ethical issue given the need to fight climate change, just as happened in WW2 when things like private car production was banned. Ethics and shaming need to be employed, not just driving individuals and corporations cost-benefit analyses through pricing changes.

[oren]

The two linked articles indicate that the Northwestern portion of the Ross Ice Shelf, RIS, is currently being destabilized by a previously unverified mechanism, i.e. local basal ice melting induced by '… seasonal masses of warm water near the ocean surface in from of the ice shelf.' 

Seeing that the Ross Sea ice extent has decreased sharply in summer in the last few years, I expect these seasonal masses of warm water near the ocean surface to be increasing. Bad news indeed.

[AbruptSLR]

More paleo-evidence indicating that we may already have initiated conditions leading to a WAIS collapse at least as severe as that during the Eemian maximum (MIS-5e):

Paul Voosen. Antarctic ice melt 125,000 years ago offers warning, Science (2018). DOI: 10.1126/science.362.6421.1339

http://science.sciencemag.org/content/362/6421/1339

Abstract: "Some 125,000 years ago, during the last brief warm period between ice ages, Earth was flooded, with sea levels 6 to 9 meters higher than they are today. Temperatures during this time, called the Eemian, were barely higher than in today's greenhouse-warmed world. Scientists have now identified the source of all that water: a collapse of the West Antarctic Ice Sheet. Glaciologists worry about the present-day stability of this formidable ice mass. Its base lies below sea level, at risk of being undermined by warming ocean waters, and glaciers fringing it are retreating fast. The discovery, teased out of a sediment core and reported at a meeting of the American Geophysical Union in Washington, D.C., provides evidence that the ice sheet disappeared in the recent geological past under climate conditions similar to today's. The Eemian is not a perfect analog, as its sea levels were likely driven by slight changes in Earth's orbit and spin axis. But the work, if it holds up, could suggest the recent melt at the ice sheet is the start of a similar collapse, rather than a short-term variation."

[AbruptSLR]

The two linked articles indicate that the Northwestern portion of the Ross Ice Shelf, RIS, is currently being destabilized by a previously unverified mechanism, i.e. local basal ice melting induced by '… seasonal masses of warm water near the ocean surface in from of the ice shelf.' 

Seeing that the Ross Sea ice extent has decreased sharply in summer in the last few years, I expect these seasonal masses of warm water near the ocean surface to be increasing. Bad news indeed.

The attached image shows that seasonal wind tend to blow sea ice seaward from the northeast edge of the RIS:

[AbruptSLR]

The linked reference provides paleo-evidence that supports Hansen's interpretation of the ice-climate feedback mechanisms:

R.H. Levy et al. (2019), "Antarctic ice-sheet sensitivity to obliquity forcing
enhanced through ocean connections", Nature Geoscience, https://doi.org/10.1038/s41561-018-0284-4.

https://www.nature.com/articles/s41561-018-0284-4
&
https://www.nature.com/articles/s41561-018-0284-4.epdf?referrer_access_token=aCfwVc-RjgcGTd4MgHtGUNRgN0jAjWel9jnR3ZoTv0Ot_gu31-eQPxiztIuzStKFE6UdtLeqWzC_6QrFMHEaeupppjQfCG98e2wXxANtbC327DQWNypC7fIGTwbf37zfNbJuLl77xXlrAQ2hrla4hYmrO40qS9t3kY86lxyogxudK-e_txRwdssl87Qb6t3ioWYdHwuv5_PeCFAqfOE0lFWZ0IjRlZQMNgN4Ir-NxvIj62uPf18Ix08nKiMIBtHa&tracking_referrer=www.livescience.com

Abstract: "Deep sea geological records indicate that Antarctic ice-sheet growth and decay is strongly influenced by the Earth’s astronomical variations (known as Milankovitch cycles), and that the frequency of the glacial–interglacial cycles changes through time. Here we examine the emergence of a strong obliquity (axial tilt) control on Antarctic ice-sheet evolution during the Miocene by correlating the Antarctic margin geological records from 34 to 5 million years ago with a measure of obliquity sensitivity that compares the variance in deep sea sediment core oxygen-isotope data at obliquity timescales with variance of the calculated obliquity forcing. Our analysis reveals distinct phases of ice-sheet evolution and suggests the sensitivity to obliquity forcing increases when ice-sheet margins extend into marine environments. We propose that this occurs because obliquity-driven changes in the meridional temperature gradient affect the position and strength of the circum-Antarctic easterly flow and enhance (or reduce) ocean heat transport across the Antarctic continental margin. The influence of obliquity-driven changes in ocean dynamics is amplified when marine ice sheets are extensive, and sea ice is limited. Our reconstruction of the Antarctic ice-sheet history suggests that if sea-ice cover decreases in the coming decades, ocean-driven melting at the ice-sheet margin will be amplified."

See also:

Title: "Earth's Tilt May Exacerbate a Melting Antarctic"

https://www.livescience.com/64507-antarctica-ice-melt-earth-tilt.html

Extract: "At times of high tilt, the polar regions warm and the temperature differences between the equator and the poles become less extreme. This, in turn, alters wind and current patterns — which are largely driven by this temperature difference — ultimately increasing the flow of warm ocean water to Antarctica's edge.
…
This history spells trouble for Antarctica's future. In 2016, the level of carbon dioxide in Earth's atmosphere leapt past 400 ppm, permanently. The last time in Earth's geologic history that carbon dioxide was this high, there was no year-round sea ice in Antarctica, Levy said. If emissions continue as they are, the sea ice will falter, Levy said, "and we will jump back to a world that hasn't existed for millions of years."

"Antarctica's vulnerable marine-based ice sheets will feel the effect of our current relatively high tilt, and ocean warming at Antarctica's margins will be amplified," he said."

[AbruptSLR]

For those who do not know what Marine Ice Sheet Instability, MISI, is, I provide the first linked article.

Title: "Marine Ice Sheet Instability “For Dummies”"

https://blogs.egu.eu/divisions/cr/2016/06/22/marine-ice-sheet-instability-for-dummies-2/

Extract: "The MISI hypothesis states that when the bedrock slopes down from the coast towards the interior of the marine ice sheet, which is the case in large parts of West Antarctica, the grounding line is not stable (in the absence of back forces provided by ice shelves, see next section for more details). To explain this concept, let us take the schematic example shown in Figure 4:
1.   The grounding line is initially located on a bedrock sill (Figure 4a). This position is stable: the ice flux at the grounding line, which is the amount of ice passing through the grounding line per unit time, matches the total upstream accumulation.
2.   A perturbation is applied at the grounding line, e.g. through the incursion of warm Circumpolar Deep Water (CDW, red arrow in Figure 4) below the ice shelf as observed in the Amundsen Sea Embayment.
3.   These warm waters lead to basal melting at the grounding line, ice-shelf thinning and glacier acceleration, resulting in an inland retreat of the grounding line.
4.   The grounding line is then located on a bedrock that slopes downward inland (Figure 4b), i.e. an unstable position where the ice column at the grounding line is thicker than previously (Figure 4a). The theory shows that ice flux at the grounding line is strongly dependent on ice thickness there (Weertman, 1974; Schoof, 2007), so a thicker ice leads to a higher ice flux.
5.   Then, the grounding line is forced to retreat since the ice flux at the grounding line is higher than the upstream accumulation.
6.   This is a positive feedback and the retreat only stops once a new stable position is reached (e.g. a bedrock high), where both ice flux at the grounding line and upstream accumulation match.

   In summary, the MISI hypothesis describes the condition where a marine ice sheet is unstable due to being grounded below sea level on land that is sloping downward from the coast to the interior of the ice sheet.
   This configuration leads to potential rapid retreat of the grounding line and speed up of ice flow from the interior of the continent into the oceans."
&
For those who do not know the difference between MISI and Marine Ice Cliff Instability, MICI, I provide the following linked article:

Title: "Marine ice sheet instability"

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

Extract: "Marine ice sheet instability (MISI) describes the potential for ice sheets grounded below sea level to rapidly destabilize in a runaway fashion.
…
A related process known as Marine Ice Cliff Instability (MICI) posits that due to the physical characteristics of ice, subaerial ice cliffs exceeding ~90 meters in height are likely to collapse under their own weight, and could lead to runaway ice sheet retreat in a fashion similar to MISI.  For an ice sheet grounded below sea level with an inland-sloping bed, ice cliff failure removes peripheral ice, which then exposes taller, more unstable ice cliffs, further perpetuating the cycle of ice front failure and retreat. Surface melt can further enhance MICI through ponding and hydrofracture."

[AbruptSLR]

For what it is worth, the linked MIT Earth System Model updated using somewhat updated data (thru 2010) indicates that climate sensitivity is higher than previously projected:

Libardoni, A.G., C.E. Forest, A.P. Sokolov and E. Monier (2018): Estimates of climate system properties incorporating recent climate change. Advances in Statistical Climatology, Meteorology and Oceanography, 4(1/2),19-36 (doi:10.5194/ascmo-4-19-2018) (https://www.adv-stat-clim-meteorol-oceanogr.net/4/19/2018/)

https://www.adv-stat-clim-meteorol-oceanogr.net/4/19/2018/

Summary
We present new probabilistic estimates of model parameters in the MIT Earth System Model using more recent data and an updated method. Model output is compared to observed climate change to determine which sets of model parameters best simulate the past. In response to increasing surface temperatures and accelerated heat storage in the ocean, our estimates of climate sensitivity and ocean diffusivity are higher. Using a new interpolation algorithm results in smoother probability distributions.

Abstract
Historical time series of surface temperature and ocean heat content changes are commonly used metrics to diagnose climate change and estimate properties of the climate system. We show that recent trends, namely the slowing of surface temperature rise at the beginning of the 21st century and the acceleration of heat stored in the deep ocean, have a substantial impact on these estimates. Using the Massachusetts Institute of Technology Earth System Model (MESM), we vary three model parameters that influence the behavior of the climate system: effective climate sensitivity (ECS), the effective ocean diffusivity of heat anomalies by all mixing processes (Kv), and the net anthropogenic aerosol forcing scaling factor. Each model run is compared to observed changes in decadal mean surface temperature anomalies and the trend in global mean ocean heat content change to derive a joint probability distribution function for the model parameters. Marginal distributions for individual parameters are found by integrating over the other two parameters. To investigate how the inclusion of recent temperature changes affects our estimates, we systematically include additional data by choosing periods that end in 1990, 2000, and 2010. We find that estimates of ECS increase in response to rising global surface temperatures when data beyond 1990 are included, but due to the slowdown of surface temperature rise in the early 21st century, estimates when using data up to 2000 are greater than when data up to 2010 are used. We also show that estimates of Kv increase in response to the acceleration of heat stored in the ocean as data beyond 1990 are included. Further, we highlight how including spatial patterns of surface temperature change modifies the estimates. We show that including latitudinal structure in the climate change signal impacts properties with spatial dependence, namely the aerosol forcing pattern, more than properties defined for the global mean, climate sensitivity, and ocean diffusivity.

[AbruptSLR]

While the Wall Street Journal (owned by Rupert Murdoch) is a questionable source, at least if a carbon fee & dividend is passed into US law, and it proves insufficient, then regulations and other climate change policies could be added as needed:

Title: "Former Fed chairmen and Nobel economists voice support for carbon tax"

https://www.axios.com/economists-back-carbon-dividend-to-tackle-climate-change--b84a96c6-6217-4e90-9ea0-93367c6b4832.html

Extract: "The increasing consensus among economists that the best thing to do with any money raised with a carbon tax is to return it to Americans is a significant policy marker as Washington debates to what degree, if at all, it will address Earth’s rising temperatures.

Details: All four of the still-living former Federal Reserve chairs, nearly 30 Nobel economists and all but one former chair of the White House’s Council of Economic Advisers have signed onto a statement laying out their support for a carbon-tax policy — one that has been gaining support from big oil companies, environmental groups and others across the political spectrum.
The plan includes a tax on carbon emissions that rises over time, with the proceeds sent back to Americans via quarterly dividend checks."

See also:

Title: "Economists’ Statement on Carbon Dividends"

https://www.wsj.com/articles/economists-statement-on-carbon-dividends-11547682910?mod=searchresults&page=1&pos=1

[kassy]

Paul Voosen. Antarctic ice melt 125,000 years ago offers warning

Did he give any time-line for the collapse in the article?

[AbruptSLR]

Paul Voosen. Antarctic ice melt 125,000 years ago offers warning

Did he give any time-line for the collapse in the article?

He does not provide a time-line, but he does indicate that we are already experiencing conditions under which a WAIS collapse has already been initiated for MISI, but if/when MICI initiates the collapse rate will accelerate to decadal timescales per Pollard, DeConto and Alley.

[AbruptSLR]

The attached image shows that both the Institute and Möller Ice Streams (West Antarctica) are on the threshold of MISI this century, while the linked reference indicates that ice melting of the grounding line to the reverse bed slope is the most likely trigger for such MISI behavior:

Martin J. Siegert et al. (2016), "Subglacial controls on the flow of Institute Ice Stream, West Antarctica", Annals of Glaciology, https://doi.org/10.1017/aog.2016.17

https://www.cambridge.org/core/journals/annals-of-glaciology/article/subglacial-controls-on-the-flow-of-institute-ice-stream-west-antarctica/145176FC3A09FCB3CE964966FCD5FF10
&
https://www.geos.ed.ac.uk/homes/rbingha2/44_2016_Siegert.pdf

Abstract: "The Institute Ice Stream (IIS) rests on a reverse-sloping bed, extending >150 km upstream into the ~1.8 km deep Robin Subglacial Basin, placing it at the threshold of marine ice-sheet instability. Understanding IIS vulnerability has focused on the effect of grounding-line melting, which is forecast to increase significantly this century. Changes to ice-flow dynamics are also important to IIS stability, yet little is known about them. Here we reveal that the trunk of the IIS occurs downstream of the intersection of three discrete subglacial features; a large ‘active’ subglacial lake, a newly-discovered sharp transition to a zone of weak basal sediments and a major tectonic rift. The border of IIS trunk flow is confined by the sediment on one side, and by a transition between basal melting and freezing at the border with the Bungenstock Ice Rise. By showing how basal sediment and water dictate present-day flow of IIS, we reveal that ice-sheet stability here is dependent on this unusual arrangement."

[AbruptSLR]

Many consensus climate scientists discount the MICI projections by such researchers as Pollard and DeConto, because they use statistic to bypass some of the calving physics that the linked reference begin to address.  Such calving models may not be available to significantly impact AR6, but that doesn't mean that Mother Nature will give mankind an extension on the timing of a WAIS collapse, with continued warming:

Douglas I. Benn & Jan A. Åström (2018) "Calving glaciers and ice shelves" Advances in Physics: X, https://doi.org/10.1080/23746149.2018.1513819

https://www.tandfonline.com/doi/full/10.1080/23746149.2018.1513819

Abstract: "Calving, or the release of icebergs from glaciers and floating ice shelves, is an important process transferring mass into the world’s oceans. Calving glaciers and ice sheets make a large contribution to sea-level rise, but large uncertainty remains about future ice sheet response to alternative carbon scenarios. In this review, we summarize recent progress in understanding calving processes and representing them in the models needed to predict future ice sheet evolution and sea-level rise. We focus on two main types of calving models: (1) discrete element models that represent ice as assemblages of particles linked by breakable bonds, which can explicitly simulate fracture and calving processes; and (2) continuum models, in which calving processes are parameterized using simple calving laws. With a series of examples using both synthetic and real-world ice geometries, we show how explicit models are yielding a detailed, process-based understanding of system physics that can be translated into predictive capability via improved calving laws."

[AbruptSLR]

The linked article confirms that 2018 was the warmest year on record for ocean heat content (which is most important for the pending collapse of the WAIS, see the attached image) and that CO₂, methane and nitrous oxide concentrations all reached record levels in the atmosphere:

Title: "State of the climate: How the world warmed in 2018"

https://www.carbonbrief.org/state-of-the-climate-how-world-warmed-2018

Extract: "A number of records for the Earth’s climate were set in 2018:

•   It was the warmest year on record for ocean heat content, which increased markedly between 2017 and 2018.
•   …
•   Greenhouse gas concentrations reached record levels for CO2, methane, and nitrous oxide."

[AbruptSLR]

Many people tend to forget/neglect that as GHG emissions are reduced, anthropogenic aerosol coemissions will also be reduced.  The linked reference estimates that: "Removing aerosols induces a global mean surface heating of 0.5–1.1°C, and precipitation increase of 2.0–4.6%. Extreme weather indices also increase." (note the attached image comes from another source):

B. H. Samset et al. (08 January 2018), "Climate Impacts From a Removal of Anthropogenic Aerosol Emissions", Geophysical Research Letters, https://doi.org/10.1002/2017GL076079

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL076079

Abstract
Limiting global warming to 1.5 or 2.0°C requires strong mitigation of anthropogenic greenhouse gas (GHG) emissions. Concurrently, emissions of anthropogenic aerosols will decline, due to coemission with GHG, and measures to improve air quality. However, the combined climate effect of GHG and aerosol emissions over the industrial era is poorly constrained. Here we show the climate impacts from removing present‐day anthropogenic aerosol emissions and compare them to the impacts from moderate GHG‐dominated global warming. Removing aerosols induces a global mean surface heating of 0.5–1.1°C, and precipitation increase of 2.0–4.6%. Extreme weather indices also increase. We find a higher sensitivity of extreme events to aerosol reductions, per degree of surface warming, in particular over the major aerosol emission regions. Under near‐term warming, we find that regional climate change will depend strongly on the balance between aerosol and GHG forcing.

Plain Language Summary
To keep within 1.5 or 2° of global warming, we need massive reductions of greenhouse gas emissions. At the same time, aerosol emissions will be strongly reduced. We show how cleaning up aerosols, predominantly sulfate, may add an additional half a degree of global warming, with impacts that strengthen those from greenhouse gas warming. The northern hemisphere is found to be more sensitive to aerosol removal than greenhouse gas warming, because of where the aerosols are emitted today. This means that it does not only matter whether or not we reach international climate targets. It also matters how we get there.

[AbruptSLR]

The linked reference provides evidence that CMIP5 model projections 'have underestimated the cooling effect that aerosol particles have had on climate in recent decades"; which 'suggests that the models are not sensitive enough to increasing greenhouse gas concentrations in the atmosphere'.  In other words, this reference finds that the CMIP5 models (as a group) underestimate both TCR & ECS:

Trude Storelvmo et al. (29 August 2018), "Lethargic response to aerosol emissions in current climate models", Geophysical Research Letters, https://doi.org/10.1029/2018GL078298

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GL078298

Abstract
The global temperature trend observed over the last century is largely the result of two opposing effects – cooling from aerosol particles and greenhouse gas (GHG) warming. While the effect of increasing GHG concentrations on Earth's radiation budget is well‐constrained, that due to anthropogenic aerosols is not, partly due to a lack of observations. However, long‐term surface measurements of changes in downward solar radiation (SDSR), an often‐used proxy for aerosol radiative impact, are available worldwide over the last half‐century. We compare SDSR changes from ∼1,400 stations to those from the CMIP5 global climate simulations over the period 1961‐2005. The observed SDSR shows a strong early downward trend followed by a weaker trend‐reversal, broadly consistent with historical aerosol emissions. However, despite considerable changes to known aerosol emissions over time, the models show negligible SDSR trends, revealing a lethargic response to aerosol emissions, and casting doubt on the accuracy of their future climate projections.

Plain Language Summary
Observations of incoming solar radiation, as measured at approximately 1400 surface stations worldwide, show a strong downward trend from the 1960s to the 1980s, followed by a weaker trend reversal thereafter. These trends are thought to be due to changes in the amount of aerosol particles in the atmosphere, and we find support for that here in the temporal evolution of anthropogenic aerosol emissions. This is expected because aerosol particles reflect and/or absorb sunlight back to space, and have a net cooling effect on Earth's climate. However, we find that the current generation of climate models simulate negligible solar radiation trends over the last half‐century, suggesting that they have underestimated the cooling effect that aerosol particles have had on climate in recent decades. Despite this, climate models tend to reproduce surface air temperature over the time period in question reasonably well. This, in turn, suggests that the models are not sensitive enough to increasing greenhouse gas concentrations in the atmosphere, with important implications for their ability to simulate future climate.

[AbruptSLR]

Alley (2019) provides a convenient overview of some of the considerations associated with the potential collapse of the Thwaites Glacier within the next "… few decades":

Richard B. Alley (2019), "Is Antarctica Collapsing?", SciAm, Vol 320, No. 2,

https://www.scientificamerican.com/magazine/sa/2019/02-01/

Extract: "In Brief

Big glaciers on Greenland, such as Jakobshavn, are flowing quickly into the ocean, raising sea level slightly.  The much larger Thwaites Glacier in West Antarctica has begun flowing faster, too.  The key factor determining its fate is whether it will retreat into the great Bentley Subglacial Trench behind it.  If it does retreat, that would create very high ice cliffs that would break off into the ocean.  If Thwaites starts to crumble, it could raise sea level by as much as 11 feet in just a few decades."

[AbruptSLR]

It is frustrating (to me at least) that the current generation of Earth System Models, ESMs (e. g. CMIP5), do not adequately address dynamical climate sensitivity.  Hopefully, CMIP6 and future phases of E3SM, will improve upon the accuracy of our current projections.

In this regards, the first linked reference (and associated image) calibrated an effective/specific equilibrium climate sensitivity (S) based on warming cycles during the past 784,000 years.  There findings for the upper end risk (e.g. RCP 8.5) indicated that the projected GMSTA range could be between 4.78C to 7.36C by 2100, based on one set of calculations.

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

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

Extract: "Global mean surface temperatures are rising in response to anthropogenic greenhouse gas emissions. The magnitude of this warming at equilibrium for a given radiative forcing—referred to as specific equilibrium climate sensitivity (S)—is still subject to uncertainties. We estimate global mean temperature variations and S using a 784,000-year-long field reconstruction of sea surface temperatures and a transient paleoclimate model simulation. Our results reveal that S is strongly dependent on the climate background state, with significantly larger values attained during warm phases. Using the Representative Concentration Pathway 8.5 for future greenhouse radiative forcing, we find that the range of paleo-based estimates of Earth’s future warming by 2100 CE overlaps with the upper range of climate simulations conducted as part of the Coupled Model Intercomparison Project Phase 5 (CMIP5). Furthermore, we find that within the 21st century, global mean temperatures will very likely exceed maximum levels reconstructed for the last 784,000 years. On the basis of temperature data from eight glacial cycles, our results provide an independent validation of the magnitude of current CMIP5 warming projections."

While Friedrich et. al. (2016) is a useful starting point, its use of an effective/specific equilibrium climate sensitivity (S) calibrated to the last 784,000 years of warming cycles, means that it is missing the aperiodic dynamical climate sensitivity illustrated in the third image, the risk of Hansen's ice-climate feedback mechanism and the risk that we may well exceed the value of S calibrated to the last 784,000 years, as the fourth attached image shows that S increases in value with increasing values of GMST.

In regards S increasing with GMST, per the following linked NOAA article is entitled: "Global Climate Report - Annual 2016"

https://www.ncdc.noaa.gov/sotc/global/201613#gtemp

Extract: "The average global temperature across land and ocean surface areas for 2016 was 0.94°C (1.69°F) above the 20th century average of 13.9°C (57.0°F), surpassing the previous record warmth of 2015 by 0.04°C (0.07°F)."


The immediate following linked reference clarifies the relationship of ECS and the dynamical sensitivity of climate models.:

Kevin M. Grise & Lorenzo M. Polvani (28 April 2016), "Is climate sensitivity related to dynamical sensitivity?", Journal of Geophysical Research Atmospheres, DOI: 10.1002/2015JD024687


http://onlinelibrary.wiley.com/doi/10.1002/2015JD024687/abstract

Abstract: "The atmospheric response to increasing CO2 concentrations is often described in terms of the equilibrium climate sensitivity (ECS). Yet, the response to CO2 forcing in global climate models is not limited to an increase in global-mean surface temperature: for example, the mid-latitude jets shift poleward, the Hadley circulation expands, and the subtropical dry zones are altered. These changes, which are referred to here as “dynamical sensitivity,” may be more important in practice than the global-mean surface temperature.

This study examines to what degree the inter-model spread in the dynamical sensitivity of 23 CMIP5 models is captured by ECS. In the Southern Hemisphere, inter-model differences in the value of ECS explain ~60% of the inter-model variance in the annual-mean Hadley cell expansion, but just ~20% of the variance in the annual-mean mid-latitude jet response. In the Northern Hemisphere (NH), models with larger values of ECS significantly expand the Hadley circulation more during winter months, but contract the Hadley circulation more during summer months. Inter-model differences in ECS provide little significant information about the behavior of the Northern Hemisphere subtropical dry zones or mid-latitude jets.

The components of dynamical sensitivity correlated with ECS appear to be driven largely by increasing sea surface temperatures, whereas the components of dynamical sensitivity independent of ECS are related in part to changes in surface temperature gradients. These results suggest that efforts to narrow the spread in dynamical sensitivity across global climate models must also consider factors that are independent of global-mean surface temperature."

Finally, I provide the following reference related to the calibration of dynamical sensitivity of climate models using paleodata.

The first following four linked references and I note that der Heydt et. al. 2016 concludes: "Such perturbations (illustrated in Fig. 1b,d) are not normally applied in climate models used for climate predictions [IPCC, 2013], where climate sensitivity is derived from model simulations considering prescribed, non-dynamic atmospheric CO2. In our conceptual model, we have derived climate sensitivities from both types of perturbations and find that the classical climate model approach (section 2.2, Fig. 4f) leads to significantly lower values of the climate sensitivity than the perturbations away from the attractor with dynamic CO2 (section 2.3, Fig. 11a). This emphasises the importance of including dynamic carbon cycle processes into climate prediction models. Moreover, it supports the idea that the real observed climate response may indeed be larger than the model predicted one, because those models never will include all feedback processes in the climate system.“

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

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

The second linked reference on the application of "dynamical systems theory" supports the position that the current effective ECS may be as high as 4.35C (but is masked both by lag times and by aerosol impacts):

Egbert H. van Nes, Marten Scheffer, Victor Brovkin, Timothy M. Lenton, Hao Ye, Ethan Deyle and George Sugihara (2015), "Causal feedbacks in climate change", Nature Climate Change, doi:10.1038/nclimate2568

http://www.nature.com/nclimate/journal/v5/n5/full/nclimate2568.html


The third linked reference examines the state dependency of ECS using paledata from the past 5 millions years and similarly finds that the effective ECS is higher than more CMIP5 models assume.

Köhler, P., de Boer, B., von der Heydt, A. S., Stap, L. B., and van de Wal, R. S. W. (2015), "On the state dependency of the equilibrium climate sensitivity during the last 5 million years", Clim. Past, 11, 1801-1823, doi:10.5194/cp-11-1801-2015.


http://www.clim-past.net/11/1801/2015/cp-11-1801-2015.html
http://www.clim-past.net/11/1801/2015/cp-11-1801-2015.pdf


The fourth linked reference could not make it more clear that paleo-evidence from inter-glacial periods indicates that ECS is meaningfully higher than 3C and that climate models are commonly under predicting the magnitude of coming climate change.  Furthermore, these finding concur with those of Köhler et al (2015) which indicates that inter-glacial values for specific ECS was about 45% higher than during glacial periods.

Dana L. Royer (2016), "Climate Sensitivity in the Geologic Past", Annual Review of Earth and Planetary Sciences, Vol. 44

http://www.annualreviews.org/doi/abs/10.1146/annurev-earth-100815-024150?src=recsys

[sidd]

I see nothing in the van Nes paper on climate sensitivity ?

sidd

[jai mitchell]

Hopefully, CMIP6 and future phases of E3SM, will improve upon the accuracy of our current projections.

Yes and the E3SM Equilibrium Climate Sensitivity of 5.3K is based on the dynamical sensitivity effects you linked below, including a split of the ITCZ, greatly decreasing albedo (among many other impacts).

The immediate following linked reference clarifies the relationship of ECS and the dynamical sensitivity of climate models.:

Kevin M. Grise & Lorenzo M. Polvani (28 April 2016), "Is climate sensitivity related to dynamical sensitivity?", Journal of Geophysical Research Atmospheres, DOI: 10.1002/2015JD024687


http://onlinelibrary.wiley.com/doi/10.1002/2015JD024687/abstract

Abstract: "The atmospheric response to increasing CO2 concentrations is often described in terms of the equilibrium climate sensitivity (ECS). Yet, the response to CO2 forcing in global climate models is not limited to an increase in global-mean surface temperature: for example, the mid-latitude jets shift poleward, the Hadley circulation expands, and the subtropical dry zones are altered. These changes, which are referred to here as “dynamical sensitivity,” may be more important in practice than the global-mean surface temperature.

This study examines to what degree the inter-model spread in the dynamical sensitivity of 23 CMIP5 models is captured by ECS. In the Southern Hemisphere, inter-model differences in the value of ECS explain ~60% of the inter-model variance in the annual-mean Hadley cell expansion, but just ~20% of the variance in the annual-mean mid-latitude jet response. In the Northern Hemisphere (NH), models with larger values of ECS significantly expand the Hadley circulation more during winter months, but contract the Hadley circulation more during summer months. Inter-model differences in ECS provide little significant information about the behavior of the Northern Hemisphere subtropical dry zones or mid-latitude jets.

The components of dynamical sensitivity correlated with ECS appear to be driven largely by increasing sea surface temperatures, whereas the components of dynamical sensitivity independent of ECS are related in part to changes in surface temperature gradients. These results suggest that efforts to narrow the spread in dynamical sensitivity across global climate models must also consider factors that are independent of global-mean surface temperature."

Finally, I provide the following reference related to the calibration of dynamical sensitivity of climate models using paleodata.

Wanted to share this one.

http://eprints.whiterose.ac.uk/132373/8/IMBIE2_accepted_v16.pdf
Mass balance of the Antarctic Ice Sheet from 1992 to 2017

Ocean-driven melting has caused rates of ice loss from West Antarctica to rise from 53 ± 29 Gt/yr in the 1990s to 159 ± 26 Gt/yr in the 2010s. Ice shelf collapse has driven Antarctic Peninsula ice loss up from 7 ± 13 Gt/yr in the 1990s to 33 ± 16 Gt/yr in the 2010s. We find large variations in and among model estimates of surface mass balance and glacial isostatic adjustment in East Antarctica, and its 25-year mass trend (5 ± 46 Gt/yr) is still the least certain.

[AbruptSLR]

I see nothing in the van Nes paper on climate sensitivity ?

sidd

For improved clarity, my point was that van Nes et al (2015) explains 'dynamical climate sensitivity', which has been used by other researchers such at Köhler et al (2015) to demonstrate that: "During Pleistocene intermediate glaciated climates and interglacial periods, S[CO2,LI] is on average ~ 45 % larger than during Pleistocene full glacial conditions."

While climate researchers who relied on paleo findings that during recent full glacial periods ECS was about 3.0C, did not know that during interglacial periods this value would be 45% larger, or 4.35C.

Köhler, P., de Boer, B., von der Heydt, A. S., Stap, L. B., and van de Wal, R. S. W. (2015), "On the state dependency of the equilibrium climate sensitivity during the last 5 million years", Clim. Past, 11, 1801-1823, doi:10.5194/cp-11-1801-2015.

http://www.clim-past.net/11/1801/2015/cp-11-1801-2015.html
http://www.clim-past.net/11/1801/2015/cp-11-1801-2015.pdf

Abstract: "It is still an open question how equilibrium warming in response to increasing radiative forcing – the specific equilibrium climate sensitivity S – depends on background climate. We here present palaeodata-based evidence on the state dependency of S, by using CO2 proxy data together with a 3-D ice-sheet-model-based reconstruction of land ice albedo over the last 5 million years (Myr). We find that the land ice albedo forcing depends non-linearly on the background climate, while any non-linearity of CO2 radiative forcing depends on the CO2 data set used. This non-linearity has not, so far, been accounted for in similar approaches due to previously more simplistic approximations, in which land ice albedo radiative forcing was a linear function of sea level change. The latitudinal dependency of ice-sheet area changes is important for the non-linearity between land ice albedo and sea level. In our set-up, in which the radiative forcing of CO2 and of the land ice albedo (LI) is combined, we find a state dependence in the calculated specific equilibrium climate sensitivity, S[CO2,LI], for most of the Pleistocene (last 2.1 Myr). During Pleistocene intermediate glaciated climates and interglacial periods, S[CO2,LI] is on average ~ 45 % larger than during Pleistocene full glacial conditions. In the Pliocene part of our analysis (2.6–5 Myr BP) the CO2 data uncertainties prevent a well-supported calculation for S[CO2,LI], but our analysis suggests that during times without a large land ice area in the Northern Hemisphere (e.g. before 2.82 Myr BP), the specific equilibrium climate sensitivity, S[CO2,LI], was smaller than during interglacials of the Pleistocene. We thus find support for a previously proposed state change in the climate system with the widespread appearance of northern hemispheric ice sheets. This study points for the first time to a so far overlooked non-linearity in the land ice albedo radiative forcing, which is important for similar palaeodata-based approaches to calculate climate sensitivity. However, the implications of this study for a suggested warming under CO2 doubling are not yet entirely clear since the details of necessary corrections for other slow feedbacks are not fully known and the uncertainties that exist in the ice-sheet simulations and global temperature reconstructions are large."

Extracts: "…. important feedbacks of the climate system are not incorporated into all models. For example, when coupling a climate model interactively to a model of stratospheric chemistry, including ozone, the calculated transient warming on a 100-year timescale differs by 20% from results without such an interactive coupling (Nowack et al., 2015).

…

A major restriction of any geological-data-based estimate of climate sensitivity is that there was no period in Earth’s history during which the atmospheric CO2 concentration and global temperature changed as rapidly as today. Therefore, in all these data-based approaches (including our study here), ECS defined as global equilibrium temperature rise in response to a doubling of atmospheric CO2 can only be roughly estimated.

…

Slow feedbacks are of interest in a more distant future (Zeebe, 2013) but are not yet considered in climate simulations using fully coupled climate models underlying the fifth assessment report of the IPCC (Stocker et al., 2013)."

[AbruptSLR]

While the findings of the linked reference typically address much higher atmospheric concentrations of GHG than exist on Earth today; nevertheless, it finds that paleoclimates indicate ECS is typically higher than that assumed by consensus climate models:

E. T. Wolf et al. (22 October 2018), "Evaluating Climate Sensitivity to CO2 Across Earth's History", JGR Atmospheres, https://doi.org/10.1029/2018JD029262

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018JD029262#.XEFCy-h8SyQ.twitter

Abstract: "CO2‐driven changes to climate have occurred during many epochs of Earth's history when the solar insolation, atmospheric CO2 concentration, and surface temperature of the planet were all significantly different than today. Each of these aspects affects the implied radiative forcings, climate feedbacks, and resultant changes in global mean surface temperature. Here we use a three‐dimensional climate system model to study the effects of increasing CO2 on Earth's climate, across many orders of magnitude of variation, and under solar inputs relevant for paleo, present, and future Earth scenarios. We find that the change in global mean surface temperature from doubling CO2 (i.e., the equilibrium climate sensitivity) may vary between 2.6 and 21.6 K over the course of Earth's history. In agreement with previous studies, we find that the adjusted radiative forcing from doubling CO2 increases at high concentrations up to about 1.5 bars partial pressure, generally resulting in larger changes in the surface temperature. We also find that the cloud albedo feedback causes an abrupt transition in climate for warming atmospheres that depends both on the mean surface temperature and the total solar insolation. Climate sensitivity to atmospheric CO2 has probably varied considerably across Earth's history."


Extract: "Thus, when phrased in terms of equilibrium climate sensitivity, paleoclimates (under weak solar insolation but with implicitly larger CO2 inventories) experience relatively larger (~10 Wm-2) changes in the adjusted radiative forcings for each CO2 doubling.  This change in forcing generally results in correspondingly larger changes in temperature compared with estimates of ECS made for anthropogenic climate change studies."

[Hefaistos]

In the paper by Wolf et al they say in the Abstract, as quoted by ASLR:

"We also find that the cloud albedo feedback causes an abrupt transition in climate for warming atmospheres that depends both on the mean surface temperature and the total solar insolation."

As the paper is paywalled I remain in the dark about what this could possibly mean. Especially interesting would be to learn at what latitudes such abrupt transition might happen.
Anyone has access to the full text?

[Lennart van der Linde]

Anyone has access to the full text?

They're talking about quite warm climates:
https://sci-hub.tw/https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018JD029262

"ECS for the first three CO2 doublings beyond the present day Earth (up to 2880 μbar CO2) fall within the IPCC estimated range, with values of 3.8 K, 4.0 K, and 4.1 K respectively (gray box in Figure 1b). At the 4th CO2 doubling (5760 μbar CO2) ECS exceeds the IPCC estimated range, reaching 5.8 K. Thus, the sensitivity of climate accelerates under potential anthropogenic CO2 increases, in agreement with recent studies [Meraner et al., 2013; Russell et al., 2013; Caballero and Huber, 2013]. We find a sharp maximum in ECS of 16.0 K evident at the 6th CO2 doubling (0.02304 bar CO2) beyond present day Earth conditions... warming climate leads to reductions in the cloud albedo, thus constituting a positive climate feedback and leading to further warming. The sharp transition between temperate and moist greenhouse climate states centered at Ts ~ 320 K is associated with the minima in cloud albedo"

[sidd]

That Wolf paper has very little to do with present day earth, it has to do with mostly hypothetical climates, and hot ones at that. They use present day continents, fainter and brighter suns and they vary CO2 levels.

But

1) permanent land glaciers over Antarctica and Greenland have been replaced with bare soil

2) thermodynamic slab ocean model of 50‐m depth

3) We assume a 1‐bar N2 background ... we have ignored the formation of stratospheric ozone and the presence of oxygen in the atmosphere.

I attach Fig 1 and 6

To the question of a cloud albedo transitions:

"Similarly, here we find that the global mean cloud albedo varies in proportion with the solar insolation at all values of Ts (Figure 6b), and across a range of insolations. Under all solar constants cloud feedbacks have a destabilizing effect on climate for 280 ≤ Ts ≤ 330 K. That is, warming climate leads to reductions in the cloud albedo, thus constituting a positive climate feedback and leading to further warming. The sharp transition between temperate and moist greenhouse climate states centered at Ts ~320 K is associated with the minima in cloud albedo (Figure 6b), and is caused by the convective stabilization of warm atmospheres and subsequent dissipation of low‐lying clouds as reported in Wolf and Toon (2015)."

I dont really believe the accuracy of their cloud model. First off, their grid is 4x5 degrees in a modified CESM model, so they rely on parametrization for cloud effects. Their ocean is laughably simple. They have no biology. But as Box said, "all models are wrong but some are useful" This one is not very useful to me, i prefer Hansen and the Russel model he uses for simple, quick looks at the rape of things to come.

But, as always, thats just me, your mileage may vary
.
sidd

[AbruptSLR]

Currently, consensus climate science assumes that climate sensitivity is too complicated for bodies such as the IPCC's WG1 (e.g. AR5) to differentiate between such measures of ECS at: paleo-values, observed-record values, Earth System Model values, inferred values, true values, etc.  Therefore, AR5 lumped all such published measures together and provided their interpretation of probable ranges of values for ECS.  Now that more published papers (see prior posts on this topic and the following linked reference) are available on the topic of climate sensitivity (including ice-climate feedback), I hope that AR6 does a better job differentiating (& reporting) different values of ECS including probable ranges of dynamical climate sensitivity for different time periods (as with continued warming dynamical climate sensitivity will likely increase):

Steven J. Lade et al. (2018), "Analytically tractable climate–carbon cycle feedbacks under 21st century anthropogenic forcing", Earth System Dynamics

http://macroecointern.dk/pdf-reprints/Lade_ESD_2018.pdf

Abstract: "Changes to climate–carbon cycle feedbacks may significantly affect the Earth system’s response to greenhouse gas emissions. These feed backs are usually analysed from numerical output of complex and arguably opaque Earth system models. Here, we construct a stylised global climate–carbon cycle model, test its output against comprehensive Earth system models, and investigate the strengths of its climate–carbon cycle feedbacks analytically. The analytical expressions we obtain aid understanding of carbon cycle feed backs and the operation of the carbon cycle. Specific results include that different feedback formalisms measure fundamentally the same climate–carbon cycle processes; temperature dependence of the solubility pump, biological pump, and CO2 solubility all contribute approximately equally to the ocean climate–carbon feedback; and concentration–carbon feedbacks may be more sensitive to future climate change than climate–carbon feedbacks. Simple models such as that developed here also provide “workbenches” for simple but mechanistically based explorations of Earth system processes, such as interactions and feedbacks between the planetary boundaries, that are currently too uncertain to be included in comprehensive Earth system models."

[AbruptSLR]

In the paper by Wolf et al they say in the Abstract, as quoted by ASLR:

"We also find that the cloud albedo feedback causes an abrupt transition in climate for warming atmospheres that depends both on the mean surface temperature and the total solar insolation."

As the paper is paywalled I remain in the dark about what this could possibly mean. Especially interesting would be to learn at what latitudes such abrupt transition might happen.
Anyone has access to the full text?

While I certainly appreciate the additional background that both sidd and Lennart provided on the Wolf et al. (2018) paper; we cannot neglect (see also Reply #236) to consider the fact that the current high rate of anthropogenic radiative forcing (at least 100 times faster than during the PETM) together with the positive ice-climate feedback mechanism both increase the risk that a cascade (domino effect) of activated positive feedback mechanisms could abruptly drive the Earth irreversibly (at least for millennia) towards a 'hothouse' condition, if we allow the Earth to temporarily reach Mid-Pliocene conditions (which will cause abrupt ice mass loss from Antarctica), as shown in Steffen et al. (2018) & by the first two associated images.

Will Steffen, Johan Rockström, Katherine Richardson, Timothy M. Lenton, Carl Folke, Diana Liverman, Colin P. Summerhayes, Anthony D. Barnosky, Sarah E. Cornell, Michel Crucifix, Jonathan F. Donges, Ingo Fetzer, Steven J. Lade, Marten Scheffer, Ricarda Winkelmann, Hans Joachim Schellnhuber (2018), "Trajectories of the Earth System in the Anthropocene", Proc. Nat. Acad. Sci., https://doi.org/10.1073/pnas.1810141115

http://www.pnas.org/content/115/33/8252

Abstract: "We explore the risk that self-reinforcing feedbacks could push the Earth System toward a planetary threshold that, if crossed, could prevent stabilization of the climate at intermediate temperature rises and cause continued warming on a “Hothouse Earth” pathway even as human emissions are reduced. Crossing the threshold would lead to a much higher global average temperature than any interglacial in the past 1.2 million years and to sea levels significantly higher than at any time in the Holocene. We examine the evidence that such a threshold might exist and where it might be. If the threshold is crossed, the resulting trajectory would likely cause serious disruptions to ecosystems, society, and economies. Collective human action is required to steer the Earth System away from a potential threshold and stabilize it in a habitable interglacial-like state. Such action entails stewardship of the entire Earth System—biosphere, climate, and societies—and could include decarbonization of the global economy, enhancement of biosphere carbon sinks, behavioral changes, technological innovations, new governance arrangements, and transformed social values."

Furthermore, the third image shows well before GMSTA reached 2.7C, WAIS may collapse (possibly beginning as early as 2040); and the fourth image shows how climate sensitivity can abruptly increase once certain tipping points are crossed (possibly by a perturbation such as a WAIS collapse, and/or seasonal loss of Arctic Sea Ice).

[wdmn]

I find it hard to understand how ECS could be anything less than 3 given what we already know about the warming that's occurred.

Here's my back of the envelope:

10 year lag for temperatures to catch up to radiative forcing of any given CO2ppm level.

Temperatures now are the result of concentration 10 years ago, which was 385ppm

Change in temperature from 1880 to now is ~1C

In 1880 CO2 was 290ppm.

Half of double would be 435ppm

385 is ~65.5% of 435.

If 65.5% of half double gets us to an anomaly of ~1C then we should be able to calculate where we would be, ceteris paribus, at half double, and double.

If half double is x, then x(0.655)=1
x=1/0.655
x=1.526

Anything less than ECS 3 seems to be ruled out.
Of course this does not account for aerosols, or possible increase in warming rate due to other positive feedbacks.

So it seems very conservative to say ECS is at least 3.


Hopefully it wasn't in basic math that I made my mistakes...

[AbruptSLR]

With a hat-tip to jai (for the linked reference and image), Persad & Caldeira (2018) show that if (in the coming decades) anthropogenic aerosol emissions shift from such regions as: Western Europe), the USA and China to such areas as: India and its neighbors; then the negative feedback associated for those coming emissions will be less than assumed by 'many scientific and policy discussions'; which will would mean that the associated global warming would likely be higher than assumed by consensus climate science:

Persad & Caldeira (2018), "Divergent global-scale temperature effects from identical aerosols emitted in different regions", Nature Communications, https://doi.org/10.1038/s41467-018-05838-6

https://www.nature.com/articles/s41467-018-05838-6

Abstract: "The distribution of anthropogenic aerosols’ climate effects depends on the geographic distribution of the aerosols themselves. Yet many scientific and policy discussions ignore the role of emission location when evaluating aerosols’ climate impacts. Here, we present new climate model results demonstrating divergent climate responses to a fixed amount and composition of aerosol—emulating China’s present-day emissions—emitted from 8 key geopolitical regions. The aerosols’ global-mean cooling effect is fourteen times greater when emitted from the highest impact emitting region (Western Europe) than from the lowest (India). Further, radiative forcing, a widely used climate response proxy, fails as an effective predictor of global-mean cooling for national-scale aerosol emissions in our simulations; global-mean forcing-to-cooling efficacy differs fivefold depending on emitting region. This suggests that climate accounting should differentiate between aerosols emitted from different countries and that aerosol emissions’ evolving geographic distribution will impact the global-scale magnitude and spatial distribution of climate change."

[AbruptSLR]

That Wolf paper has very little to do with present day earth, it has to do with mostly hypothetical climates, and hot ones at that. They use present day continents, fainter and brighter suns and they vary CO2 levels.

...

Per the linked Twitter thread, Dessler indicates that Wolf et (2018) indicates that ECS (with modern solar insolation might reach 16C for a CO₂-equivalent of about 3000 ppmv.  While Wolf et al (2018) may be wrong, I certainly hope that Hansen et al (2016)'s ice-climate feedback doesn't result in a multidecadal surge of CO₂ & CH₄ due to rapid permafrost, and methane-hydrate, degradation:

https://twitter.com/AndrewDessler/status/1086098135250804736

Extract: "Key figure: shows ECS (for modern solar insolation) reaches 16°C! for about 3000 ppmv of CO2. let's hope that's not right — and that we don't hit 3000 ppmv!"


Edit: The attached image shows the projected permafrost carbon flux (atmospheric emission in billions of short tons per year) [from: NOAA and the National Snow and Ice Data Center (NSIDC), 2011].

[Lennart van der Linde]

the current high rate of anthropogenic radiative forcing (at least 100 times faster than during the PETM)

This may well happen later this century, but currently it seems more like 10x faster than during the PETM, according to Diffenbaugh & Field 2013 (see attachments below):
http://denning.atmos.colostate.edu/readings/Impacts/Ecosystems.Science-2013-Diffenbaugh-486-92.pdf

Such fast warming may indeed cause ECS to increase to levels that are higher than the natural ECS at the same temperature in the past, as far as I know (I would have to look for specific references).

[AbruptSLR]

the current high rate of anthropogenic radiative forcing (at least 100 times faster than during the PETM)

This may well happen later this century, but currently it seems more like 10x faster than during the PETM, according to Diffenbaugh & Field 2013 (see attachments below):
http://denning.atmos.colostate.edu/readings/Impacts/Ecosystems.Science-2013-Diffenbaugh-486-92.pdf

Such fast warming may indeed cause ECS to increase to levels that are higher than the natural ECS at the same temperature in the past, as far as I know (I would have to look for specific references).

Lennart,

Thanks for the catch (sometimes I type too fast), as indeed the current rate of CO₂ emissions is somewhere to 10 to 15 time the rate during the PETM (depending on which part of the PETM we compare to and whether we consider CO₂-equiv emission rates), see the attached image & associated linked article).

Title: "PETM: Global Warming, Naturally"

https://www.wunderground.com/climate/PETM

As to ECS increasing with continued warming, I believe that this is dynamically dependent on both radiative forcing path and rate.

Best,
ASLR

[Lennart van der Linde]

indeed the current rate of CO₂ emissions is somewhere to 10 to 15 time the rate during the PETM (depending on which part of the PETM we compare to add whether we consider CO₂-equiv emission rates)

Scanning several papers on the PETM again I see estimates on the rate of emissions and warming vary significantly, so it's hard to have much confidence in any particular estimate, whether it was 10x slower than currently, 100x slower, or maybe even as fast as currently.

As Turner 2018 concludes:
https://royalsocietypublishing.org/doi/full/10.1098/rsta.2017.0082

"After more than 25 years of intense study, the PETM continues to be the best analogue for future CO2-driven global warming. However, the aspect of the PETM that is most relevant for understanding future impacts—the duration of carbon release—is extremely challenging to constrain using the typical methods for determining age in the geologic record (biomagnetostratigraphy and cyclostratigraphy). Combined data and modelling studies offer a potential way forward by suggesting simulacra of the traces left in the geologic record that indicate a short carbon input duration. Each of the age-model independent methods outlined here has caveats in its application; however, a consensus appears to be emerging that the carbon emissions that drove the CIE occurred over just a few thousand years. This still suggests emissions rates about 10× slower than the current annual average, but is similar to predicted rates of additional carbon release from natural carbon cycle feedbacks..."

However, 10x slower emissions 56 million years ago when CO2 levels were higher to begin with and the sun was somewhat weaker than now implies CO2-forcing is currently already probably substantially more than 10x stronger than during the PETM, and rising fast as long as we don't eliminate our emissions. What that does to ECS humanity will find out in coming decades and centuries, assuming there will be humans around and they will still be able to determine ECS.

[AbruptSLR]

For those who do not care to scroll back to Reply #42, I provide the following updated extracts:

The total radiative forcings, RFs, from the linked ORNL website article by Blasing, T.J. (that updates such RF values reported in April 2016) are used in the linked Wikipedia article to calculate a CO2e value of 526.6ppm; which assuming the current rate of annual increase in CO2e of about 3.5ppm indicates that early in 2019 CO2e will exceed 537ppm (when including the radiative forcing from stratospheric ozone when computing CO2e):

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


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

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

…

Next, I provide links to Jagniecki et al. (2015) (and an associated article); indicating that early Eocene climatic optimum (EECO) conditions (with an equable climate) may have occurred with atmospheric CO₂ concentrations between 680ppm and 1260ppm (see the attached image); and that under such conditions the effective climate sensitivity (ESS) may have been twice that previously assumed by Royer et al (2012) …

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


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

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

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

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