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Messages - AbruptSLR

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The linked reference provides evidence that it will be difficult to get politically conservative individuals to fully accept climate change risks simply by using logic and data.  This implies that it will be more difficult to get off over our current BAU pathway then many individuals believe:

Matthew S. Nurse & Will Grant (16 Jun 2019), "I’ll See It When I Believe It: Motivated Numeracy in Perceptions of Climate Change Risk", Environmental Communication,

Abstract: "People’s attitudes about Anthropogenic Climate Change (ACC) risks are not only influenced by scientific data, such as the likelihood of harm, the consequences of failing to act and the cost and effectiveness of mitigation. Instead, when people receive information about controversial topics of decision-relevant science like ACC they often defer to their political attitudes. Recent research has shown that more numerate people can be more polarized about these topics despite their better ability to interpret the scientific data. In this study, we investigated whether the motivated numeracy effect originally found by Kahan, Peters, Dawson, and Slovic [2017. Motivated numeracy and enlightened self-government. Behavioural Public Policy, 1(1)] on the controversial topic of gun control laws in the United States also applies to people when assessing ACC risks. This randomized controlled experiment (N = 504) of Australian adults extends the motivated reasoning thesis by finding evidence that highly numerate people who receive scientific data about ACC use motivated numeracy to rationalize their interpretations in line with their attitudes."

The linked (open access) reference indicates that during the mid-Pliocene wildfires were more common in the Arctic than they are today.  Hopefully, climate models will include this climate risk into their future projections:

Fletcher, T. L., Warden, L., Sinninghe Damsté, J. S., Brown, K. J., Rybczynski, N., Gosse, J. C., and Ballantyne, A. P.: Evidence for fire in the Pliocene Arctic in response to amplified temperature, Clim. Past, 15, 1063-1081,, 2019.

Abstract: "The mid-Pliocene is a valuable time interval for investigating equilibrium climate at current atmospheric CO2 concentrations because atmospheric CO2 concentrations are thought to have been comparable to the current day and yet the climate and distribution of ecosystems were quite different. One intriguing, but not fully understood, feature of the early to mid-Pliocene climate is the amplified Arctic temperature response and its impact on Arctic ecosystems. Only the most recent models appear to correctly estimate the degree of warming in the Pliocene Arctic and validation of the currently proposed feedbacks is limited by scarce terrestrial records of climate and environment. Here we reconstruct the summer temperature and fire regime from a subfossil fen-peat deposit on west–central Ellesmere Island, Canada, that has been chronologically constrained using cosmogenic nuclide burial dating to 3.9+1.5/−0.5 3.9+1.5/-0.5 Ma.

The estimate for average mean summer temperature is 15.4±0.8 ∘C using specific bacterial membrane lipids, i.e., branched glycerol dialkyl glycerol tetraethers. This is above the proposed threshold that predicts a substantial increase in wildfire in the modern high latitudes. Macro-charcoal was present in all samples from this Pliocene section with notably higher charcoal concentration in the upper part of the sequence. This change in charcoal was synchronous with a change in vegetation that included an increase in abundance of fire-promoting Pinus and Picea. Paleo-vegetation reconstructions are consistent with warm summer temperatures, relatively low summer precipitation and an incidence of fire comparable to fire-adapted boreal forests of North America and central Siberia.

To our knowledge, this site provides the northernmost evidence of fire during the Pliocene. It suggests that ecosystem productivity was greater than in the present day, providing fuel for wildfires, and that the climate was conducive to the ignition of fire during this period. The results reveal that interactions between paleo-vegetation and paleoclimate were mediated by fire in the High Arctic during the Pliocene, even though CO2 concentrations were similar to modern values."

The linked reference discusses efforts to calibrate the Community Earth System Model, CESM, to better project the poleward migration of moisture to Antarctica.  Such work can be used to better project the risk of future rainfall events (at low elevations) in West Antarctica and their potential impact on hydrofracturing risks to destabilize West Antarctic ice shelves:

Adriana Bailey et al. (20 June 2019), "Evaluating a Moist Isentropic Framework for Poleward Moisture Transport: Implications for Water Isotopes over Antarctica", Geophysical Research Letters,

Abstract: "The ability to identify moisture source regions and sinks, and to model the transport pathways that link them in simple yet physical ways, is critical for understanding climate today and in the past. Using water tagging and isotopic tracer experiments in the Community Earth System Model, this work shows that poleward moisture transport largely follows surfaces of constant moist entropy. The analysis not only provides insight into why distinct zonal bands supply moisture to high‐ and low‐elevation polar sites but also explains why changes in these source regions are inherently linked to changes in temperature and rainout. Moreover, because the geometry, and specifically length, of the moist isentropic surfaces describes how much integrated rainout occurs, the analysis provides a physical framework for interpreting the isotopic composition of water in poleward‐moving air, thus indicating how variations in moisture transport might influence Antarctic ice cores."

At least the US House of Representative realizes that we are already in a 'Climate Crisis':

House Select Committee on the Climate Crisis

As consensus climate scientists typically 'err on the side of least drama' (ESLD), they would undoubtable contribute more to reducing climate risks by applying 'Drama theory' to their own actions as well as that of the general-public, and decision makers, before they make recommendations such as the Carbon Budgets:

Title: "Drama theory"

Extract: "Drama-theorists build and analyze models (called card tables or options boards) that are isomorphic to game models, but unlike game theorists and most other model-builders, do not do so with the aim of finding a 'solution'. Instead, the aim is to find the dilemmas facing characters and so help to predict how they will re-define the model itself – i.e., the game that will be played. Such prediction requires not only analysis of the model and its dilemmas, but also exploration of the reality outside the model; without this it is impossible to decide which ways of changing the model in order to eliminate dilemmas might be rationalized by the characters.

The relation between drama theory and game theory is complementary in nature. Game theory does not explain how the game that is played is arrived at – i.e., how players select a small number of players and strategies from the virtually infinite set they could select, and how they arrive at common knowledge about each other's selections and preferences for the resulting combinations of strategies. Drama theory tries to explain this, and also to explain how the 'focal point' is arrived at for the 'game with a focal point' that is finally played. On the other hand, drama theory does not explain how players will act when they finally have to play a particular 'game with a focal point', even though it has to make assumptions about this. This is what game theory tries to explain and predict."

The linked reference discusses the impact that microorganisms may have on climate change on human wellbeing, and warns that consensus climate science model projections should more fully consider the interactions between microorganisms and climate change:

Ricardo Cavicchioli et al. (2019), "Scientists’ warning to humanity: microorganisms and climate change", Nature Reviews Microbiology, DOI:

Abstract: "In the Anthropocene, in which we now live, climate change is impacting most life on Earth. Microorganisms support the existence of all higher trophic life forms. To understand how humans and other life forms on Earth (including those we are yet to discover) can withstand anthropogenic climate change, it is vital to incorporate knowledge of the microbial ‘unseen majority’. We must learn not just how microorganisms affect climate change (including production and consumption of greenhouse gases) but also how they will be affected by climate change and other human activities. This Consensus Statement documents the central role and global importance of microorganisms in climate change biology. It also puts humanity on notice that the impact of climate change will depend heavily on responses of microorganisms, which are essential for achieving an environmentally sustainable future."

As Antarctic Bottom Water (AABW) formation is a major driver of the meridional overturning current; the finding of the linked reference (which in my opinion errs on the side of least drama) that projected Antarctic ice mass loss (following either RCP 4.5 or RCP 8.5) will result in '… a near complete shutdown of AABW formation within just 50 years …', is a positive ice-climate feedback mechanism that is omitted from almost all current consensus climate model projections.

Véronique Lago, and Matthew H. England (2019), "Projected slowdown of Antarctic Bottom Water formation in response to amplified meltwater contributions", Journal of Climate,

Abstract: "The sinking and recirculation of Antarctic Bottom Water (AABW) is a major regulator of the storage of heat, carbon and nutrients in the ocean. This sinking is sensitive to changes in surface buoyancy, particularly due to freshening as salinity plays a greater role in determining density at cold temperatures. Acceleration in Antarctic ice-shelf and land-ice melt could thus significantly impact the ventilation of the world’s oceans, yet future projections do not usually include this effect in models. Here we use an ocean-sea-ice model to investigate the potential long-term impact of Antarctic meltwater on ocean circulation and heat storage. The freshwater forcing is derived from present-day estimates of meltwater input from drifting icebergs and basal melt, combined with RCP2.6, RCP4.5 and RCP8.5 scenarios of projected amplification of Antarctic meltwater. We find that the additional freshwater induces a substantial slowdown in the formation rate of AABW, reducing ventilation of the abyssal ocean. Under both the RCP4.5 and RCP8.5 meltwater scenarios, there is a near complete shutdown of AABW formation within just 50 years, something not captured by climate model projections. The abyssal overturning at ∼30oS also weakens, with a ∼20 year delay relative to the onset of AABW slowdown. After 200 years, up to ∼50% of the original volume of AABW has disappeared due to abyssal warming, induced by vertical mixing in the absence of AABW ventilation. This suggests that climate change could induce the disappearance of present day abyssal water-masses, with implications for the global distribution of heat, carbon and nutrients."

Boaty McBoatface has identified a mechanism that enables the Southern Ocean's Westerly winds '... to increase turbulence deep in the Southern Ocean, causing warm water a mid depths to mix with cold, dense water in the abyss.' 
Unfortunately, current models do not simulate this newly identified mechanism; which in my book increases our collective risk of potential future abrupt sea level rise:

Title: "Boaty McBoatface mission gives new insight into warming ocean abyss"

Extract: "In recent decades, winds blowing over the Southern Ocean have been getting stronger due to the hole in the ozone layer above Antarctica and increasing greenhouse gases. The data collected by Boaty, along with other ocean measurements collected from research vessel RRS James Clark Ross, have revealed a mechanism that enables these winds to increase turbulence deep in the Southern Ocean, causing warm water at mid depths to mix with cold, dense water in the abyss.

The resulting warming of the water on the sea bed is a significant contributor to rising sea levels. However, the mechanism uncovered by Boaty is not built into current models for predicting the impact of increasing global temperatures on our oceans."

Edit: I note that the new mechanism identified by Boaty McBoatface works to slow-down the velocity of the global meridional overturning current; which, then causes tropical ocean surface temperatures to increase; which, is a positive ice-climate feedback mechanism.

Why is it that consensus climate scientist say that we still have time to cut GHG emissions, but a growing number of climate scientists now think that geoengineering may be essential?

Title: "More Scientists Now Think Geoengineering May Be Essential"

Notice anything unusual in this year data in the attached plot of Greenland Surface Ice Melt Extent Area thru the second week of June 2019?

The attached image shows that primary energy consumptions is growing even faster than CO2 emissions, while the linked article indicates that this is significantly due to the recent rapid growth in natural gas as a primary energy fuel.  However, it would be better if media articles reported CO2-equivalent emissions and used a GWP-100 value of 35 for methane rather than the 25 value unscientifically used by NOAA:

Title: "In-depth: BP data reveals record CO2 emissions in 2018 driven by surging use of gas"

Extract: "Gas was the largest driver of energy-use growth in 2018, responsible for more than 40% of the increase. This, along with increased use of oil and coal, led to global CO2 emissions rising by 2% in 2018, the largest year-on-year increase in seven years."

See also:

Title: "The world goes the wrong way on carbon emissions"

For what it is worth, the attached BoM Nino 3.4 Outlook forecast was issued today based on models runs from June 8, 2019; which projects the current mild El Nino event to last throughout 2019 (which will increase GMSTA this year).

The first linked reference indicates the relatively unique relationship between the African rift valley and the West Antarctic Rift, WAR, established about 180 million years ago as Gondwana (Pangaea) split apart (see first and second images).

Caption for the second image: " Schematic cross-section of the Karoo continental flood basalt province c. 180 million years ago. 1) Mantle melts extensively and the 2) melts intrude the lithosphere (=crust + brittle upper mantle), where they form large magma chambers and mix with it. 3) The contaminated melts proceed upwards and 4) erupt from shield volcanoes or fissures. 5) Some rare melts do not assimilate lithosphere and preserve the original mantle-derived geochemical signature. Image: Luomus / Jussi Heinonen"

Quote: "Our latest findings indicate that the enormous melt generation was caused by at least two processes: 1) Gondwana supercontinent functioned like a "lid on a cooking pot" and prevented the cooling of the sublithospheric mantle. High amount of accumulated heat caused more efficient melting of the mantle (Heinonen et al., 2010). 2) Some portions of the sublithospheric mantle were relatively Fe-rich and melted more efficiently than ambient mantle materials. Such portions were formed by mixing with ancient parts of oceanic crust that sank in to the mantle at subduction zones (Heinonen et al., 2013, 2014)."

Furthermore, the second linked reference shows how the sub-lithospheric interconnection between Africa's rift valley and WAR may have changed with some interconnection possibly being maintained via mantle plumes, such as beneath the Erebus volcano (see the third and fourth images).  Thus as the WAIS loses ice mass, we may witness changes in mantle dynamics as far away as Central Africa and South America:

Philip J. Heron (19 November 2018), "Mantle plumes and mantle dynamics in the Wilson cycle",
Geological Society, London, Special Publications, 470,

Caption for third image: "A cartoon of a simple supercontinent, the starting point for this review. Step 1, a supercontinent is amassed through a super-downwelling. Step 2, subduction then forms on the margins of the continent, generating sub-continental plumes due to mantle return flow and warming of the mantle through continental insulation (step 3). Step 4, the continental plumes facilitate the dispersal of the supercontinent."

Edit, see also Replies #: 101, 102, 103, 113, 115, 117, 147, 167, 168, 170, 172, 178, 442, 900 & 1,149.

The linked website provides a number of downloadable reports from the Australian 'Breakthrough National Centre for Climate Rehabilitation', including its latest report entitled: "What Lies Beneath - The Understatement of Existential Climate Risk" by Spratt & Dunlop (2019)

Extract: "This latest Breakthrough report argues for an urgent risk reframing of climate research and the IPCC reports. What Lies Beneath is the inside story of how climate policy-making has become embedded in a culture of failure and scientific reticence. The report brings together the voices of some of the world’s leading scientists."

Edit: Unfortunately, none of these reports appropriately address the risks of positive ice-climate feedback mechanisms.

Re: hysteresis

Yes, there are such effects. ASLR has posted on many, not a few on this very thread.


For convenience, the following are some selected extracts from some of my posts in this thread on hysteresis:

Furthermore, the hysteresis loops in Figures 3 & 4 make it clear that once the stratocumulus clouds dissipate (say partially due to a temporary decades-long perturbation like the collapse of the WAIS and associated feedbacks, and partially due to a temporary pulse of methane emission from Arctic thermokarst lakes [as well as a rapid reduction in anthropogenic aerosols]), it is difficult for them to reestablish themselves even at CO2-equivalent levels well below 1,200ppm.

Tapio Schneider , Colleen M. Kaul and Kyle G. Pressel (2019), "Possible climate transitions from breakup of stratocumulus decks under greenhouse warming", Nature Geoscience,

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

Extract: "The CO2 level at which the instability occurs depends on how largescale dynamics change with climate, which is heuristically parameterized in our simulations and hence is uncertain. In particular, the large-scale subsidence in the troposphere weakens under warming, which lifts the cloud tops and counteracts the instability. Indeed, when we weaken the parameterized large-scale subsidence by 1 or 3% per Kelvin of tropical SST increase (within the range of GCM responses to warming), the stratocumulus instability occurs at higher CO2 levels: around 1,400 ppm with 1% K–1 subsidence weakening, and around 2,200 ppm with 3% K–1 (Fig. 4). The hysteresis when the CO2 levels drop thereafter remains, but it narrows: stratocumulus decks reform once the CO2 levels drop below 500 ppm for a 1% K–1 subsidence weakening, and once they drop below 1,900 ppm for one of 3% K–1.

For the future, our results suggest that stratocumulus decks may break up if CO2 levels continue to rise. Equivalent CO2 concentrations around 1,300 ppm—the lowest level at which the stratocumulus instability occurred in our simulations—can be reached within a century under high-emission scenarios. However, it remains uncertain at which CO2 level the stratocumulus instability occurs because we had to parameterize rather than resolve the large-scale dynamics that interact with cloud cover. To be able to quantify more precisely at which CO2 level the stratocumulus instability occurs, how it interacts with large-scale dynamics and what its global effects are, it is imperative to improve the parameterizations of clouds and turbulence in climate models."

If nothing else, the findings of the linked reference could be used to better calibrate state-of-the-art ESM climate change projections w.r.t. 'the role of the Southern Ocean in abrupt transitions and hysteresis' in the MOC:

Sophia K.V. Hines, Andrew F. Thompson, Jess F. Adkins (15 March 2019), "The Role of the Southern Ocean in Abrupt Transitions and Hysteresis in Glacial Ocean Circulation", Paleoceanography and Paleoclimatology,

Abstract: "High‐latitude Northern Hemisphere climate during the last glacial period was characterized by a series of abrupt climate changes, known as Dansgaard‐Oeschger events, which were recorded in Greenland ice cores as shifts in the oxygen isotopic composition of the ice. These shifts in inferred Northern Hemisphere high‐latitude temperature have been linked to changes in Atlantic meridional overturning strength. The response of ocean overturning circulation to forcing is nonlinear and a hierarchy of models have suggested that it may exist in multiple steady state configurations. Here, we use a time‐dependent coarse‐resolution isopycnal model with four density classes and two basins, linked by a Southern Ocean to explore overturning states and their stability to changes in external parameters. The model exhibits hysteresis in both the steady state stratification and overturning strength as a function of the magnitude of North Atlantic Deep Water formation. Hysteresis occurs as a result of two nonlinearities in the model—the surface buoyancy distribution in the Southern Ocean and the vertical diffusivity profile in the Atlantic and Indo‐Pacific basins. We construct a metric to assess circulation configuration in the model, motivated by observations from the Last Glacial Maximum, which show a different circulation structure from the modern. We find that circulation configuration is primarily determined by North Atlantic Deep Water density. The model results are used to suggest how ocean conditions may have influenced the pattern of Dansgaard‐Oeschger events across the last glacial cycle."


The linked reference finds that:
"… Labrador Sea deep convection and the AMOC have been anomalously weak over the past 150 years or so (since the end of the Little Ice Age, LIA, approximately AD 1850) compared with the preceding 1,500 years.

We suggest that enhanced freshwater fluxes from the Arctic and Nordic seas towards the end of the LIA – sourced from melting glaciers and thickened sea ice that developed earlier in the LIA – weakened Labrador Sea convection and the AMOC.  The lack of a subsequent recovery may have resulted from hysteresis or from twentieth-century melting of the Greenland Ice Sheet."

These findings support Hansen's ice-climate feedback mechanism.

Thornalley et al. (2018), "Anomalously weak Labrador Sea convection and Atlantic overturning during the past 150 years", Nature, doi:10.1038/s41586-018-0007-4

E. Gasson, R.M. DeConto, D. Pollard, and R.H. Levy (2016), "Dynamic Antarctic ice sheet during the early to mid-Miocene", Proceedings of the National Academy of Sciences, pp. 201516130, doi: 10.1073/pnas.1516130113

Significance: "Atmospheric concentrations of carbon dioxide are projected to exceed 500 ppm in the coming decades. It is likely that the last time such levels of atmospheric CO2 were reached was during the Miocene, for which there is geologic data for large-scale advance and retreat of the Antarctic ice sheet. Simulating Antarctic ice sheet retreat is something that ice sheet models have struggled to achieve because of a strong hysteresis effect. Here, a number of developments in our modeling approach mean that we are able to simulate large-scale variability of the Antarctic ice sheet for the first time. Our results are also consistent with a recently recovered sedimentological record from the Ross Sea presented in a companion article."

We are in general, including the experts, notoriously overconfident and optimistic when it comes to predictions.

The linked scientific reference finds that AR5 (as a reflection of consensus climate science) does not adequately communicate the trur level of climate change risks:

Salvador Herrando-Pérez, Corey J A Bradshaw, Stephan Lewandowsky, David R Vieites. Statistical Language Backs Conservatism in Climate-Change Assessments. BioScience, 2019; 69 (3): 209 DOI: 10.1093/biosci/biz004

Abstract: "The scientific evidence for anthropogenic climate change is empirically settled, but communicating it to nonscientific audiences remains challenging. To be explicit about the state of knowledge on climate science, the Intergovernmental Panel on Climate Change (IPCC) has adopted a vocabulary that ranks climate findings through certainty-calibrated qualifiers of confidence and likelihood. In this article, we quantified the occurrence of knowns and unknowns about “The Physical Science Basis” of the IPCC's Fifth Assessment Report by counting the frequency of calibrated qualifiers. We found that the tone of the IPCC's probabilistic language is remarkably conservative (mean confidence is medium, and mean likelihood is 66%–100% or 0–33%), and emanates from the IPCC recommendations themselves, complexity of climate research, and exposure to politically motivated debates. Leveraging communication of uncertainty with overwhelming scientific consensus about anthropogenic climate change should be one element of a wider reform, whereby the creation of an IPCC outreach working group could enhance the transmission of climate science to the panel's audiences."

As a follow on to my comments in Reply #1175:

The first image shows the turbulent convective mixing of the warm modified CDW and the fresh basal meltwater in front of an ice cliff in Antarctica.  In my opinion this type of turbulent convection is significantly contribution to the observed expansion of the subglacial cavity in the trough area between the Big and Little Ears of the Thwaites Ice Shelf/Ice Tongue.

The second image shows the conceptual degradation of methane hydrates from the paleo-bed of the retreating paleo-marine ice sheet in the Barents Sea during the last interglacial.  I note that as it is believed that the bed beneath the Thwaites Glacier also contains methane hydrates, and abrupt retreat of the Thwaites grounding line in the relatively shallow Thwaites Gateway, could result in a similar release of methane into the atmosphere from the potential degradation of methane hydrates in the Thwaites Gateway, in the coming decades.

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

Title: "New climate models predict a warming surge"

Extract: "But a host of global climate models developed for the United Nations' next major assessment of global warming, due in 2021, are now showing a puzzling but undeniable trend. They are running hotter than they have in the past.

But in at least eight of the next-generation models, produced by leading centers in the United States, the United Kingdom, Canada, and France, that “equilibrium climate sensitivity” has come in at 5°C or warmer."

As a follow on to my last post, I present four images in an attempt to get readers oriented in the area where I first expect ice cliff failures for Thwaites Glacier between to bed areas that I have labelled Big Ear and Little Ear in this series of images.

With a hat tip to Sleepy, the first image shows the ear relative to the growth of the subglacial cavity at the base of the Thwaites Ice Tongue (near the Big Ear)

The second image shows the locations of the Big & Little Ears relative to a collapse of the cavity that lead to a surge of the Thwaites Ice Tongue after January 2012.

The third image shows the location of Big & Little Ears on a Sentinel 1 image from May 23, 2019.  This image shows ice bergs floating near the Little Ear location.

The fourth image shows the bathymetry of the Thwaites Gateway prior to 2013, where the location of the Big & Little Ears is self-evident, so I have not labelled them.

It's my experience so far in California that a 'carbon' tax isn't doing what it's supposed to do, and that is because the oil companies wont sell the farm. I am SERIOUSLY worried that the carbon tax will fail to cut emissions, here is NO guarantee it will work. We don't need some wishy-washy idea of tax and dividend that makes everyone seem like we are saving the planet but it turns out to be greenwashing.

Not all Carbon Fee and Dividend plans are the same (& it is definitely not a cap & trade plan; which Hansen does not support), but the linked plan by 'Citizens' Climate Lobby' is supported by James Hansen and many others:

Title: "The Basics of Carbon Fee and Dividend"

The devil is in the details.


Thank you for your observations of how adult bullshit has been leading us all on a path to climate breakdown for decades.  As James Hansen have communicated for decades the solutions to climate change are well known, it is clearly adult dishonesty that has prevented the implementation of even building a firm foundation for effective climate action (such as Hansen's Carbon Fee and Dividend program).

While not to highjack this thread I have observed that unless adult climate change bullshitters are shown a plan to effectively deal with climate change, they will continue to obstruct climate action.  Therefore, I link to an article on the youth movement and climate action, as it is harder to pervert someone like Greta Thunberg, and at least EU leaders are seeing the reality of this current situation:

Title: "The Kids Are Taking Charge of Climate Change"

Extract: "“We’ve been telling the politicians exactly this for years, and they brushed us off. But the young people, they’re honest, innocent in a way, and speak straight to the problems, which they didn’t create but will have to pay for.” There’s more action on the political level in the last month than he has seen in a decade, he said, even if there has been no overhaul of policy yet. “If the politicians don’t act,” Quaschning said, “they’ll lose this younger generation. They’re worried.”

The shift in discourse may not have changed policy yet, but it is obviously wind in the sails of the pro-climate voices in Merkel’s cabinet, the EU, and elsewhere. Germany’s environment minister, Svenja Schulze, will be heading up a new climate cabinet that will coordinate emissions reduction efforts across various ministries to reach the country’s 2030 climate targets, namely 55 percent reduction of emissions by 2030, compared with 1990 levels. The government will develop a climate law to chart the way, which Spiegel magazine reported this week may include a serious tax on carbon, which hadn’t originally been in the plans."


The word of the street seems to be that not all scientists are fully convinced that marine cliff instability will play out as current models predict. It would help if it could be observed to happen in nature.


While SH's posts demonstrates that no one questions the reality of ice cliff failures (such as those regularly observed for Jakobshavn), it seems that you are not only asking about well documented cases of marine ice cliff instability (MICI); but also whether current models of MICI can precisely determine a WAIS collapse scenario to the decadal-scale.

In this regards, no observed MICI event has been recorded my modern instruments (SH's recorded Jakobshavn's ice-cliff failure event was not an MICI event); however, the linked reference provides good documentation of a paleo-MICI event in Pine Island Bay from about 12.3kya to before 11.2kya (see the first attached image). 

You might say that a 1,100 yr MICI-event is a lot longer than the century-, to decadal-, scale MICI events projected by some recent MICI models.  Nevertheless, the second attached image shows that this 12.3kya to 11.2kya MICI event occurred between Meltwater Pulse (MWP) event 1A and MWP event 1B; both of which had ice mass loss rates comparable to those projected by Pollard & DeConto's MICI-model.

You might then say that the MICI-events associated with the MWP events shown in the second image involved different marine glaciers than exist in the WAIS today, and while that is true, if you search this thread (using the search function) for MICI, you while find a lot of references where MICI models have been calibrated against the paleo record for key interglacial periods over the past 3 million years, such as for the Pliocene when GMSTA was about 2C above pre-industrial.

You might then say that the peak periods for interglacials such as the Pliocene occurred over thousands of years, so this proves nothing.  But there is no recorded paleo warming rate as fast as we are currently experiencing, so if you demand an exact match for the projected WAIS MICI-event, then you will need to wait a few decades as we are current conducting a one of a kind experiment on Earth.

Wise et al. (2017), "Evidence of marine ice-cliff instability in Pine Island Bay from iceberg-keel plough marks", Nature 550, 506-510, doi:10.1038/nature24458

Abstract: "Marine ice-cliff instability (MICI) processes could accelerate future retreat of the Antarctic Ice Sheet if ice shelves that buttress grounding lines more than 800 metres below sea level are lost. The present-day grounding zones of the Pine Island and Thwaites glaciers in West Antarctica need to retreat only short distances before they reach extensive retrograde slopes. When grounding zones of glaciers retreat onto such slopes, theoretical considerations and modelling results indicate that the retreat accelerates. It is thought that MICI is triggered when this retreat produces ice cliffs above the water line with heights approaching about 90 metres. However, observational evidence confirming the action of MICI has not previously been reported. Here we present observational evidence that rapid deglacial ice-sheet retreat into Pine Island Bay proceeded in a similar manner to that simulated in a recent modelling study, driven by MICI. Iceberg-keel plough marks on the sea-floor provide geological evidence of past and present iceberg morphology, keel depth and drift direction. From the planform shape and cross-sectional morphologies of iceberg-keel plough marks, we find that iceberg calving during the most recent deglaciation was not characterized by small numbers of large, tabular icebergs as is observed today, which would produce wide, flat-based plough marks or toothcomb-like multi-keeled plough marks. Instead, it was characterized by large numbers of smaller icebergs with V-shaped keels. Geological evidence of the form and water-depth distribution of the plough marks indicates calving-margin thicknesses equivalent to the threshold that is predicted to trigger ice-cliff structural collapse as a result of MICI. We infer rapid and sustained ice-sheet retreat driven by MICI, commencing around 12,300 years ago and terminating before about 11,200 years ago, which produced large numbers of icebergs smaller than the typical tabular icebergs produced today. Our findings demonstrate the effective operation of MICI in the past, and highlight its potential contribution to accelerated future retreat of the Antarctic Ice Sheet."


Re: "Obviously, AR5 climate scientists were most likely ignoring cumulative ECS risk mechanisms "

I will disagree. AR5 (as is happening in AR6) scientists are tasked to put together literature review of current science. They are not asked for their opinions on the literature, peer review occurs before publication. Accusing them of ignoring relevant literature is something  I will not do, since I have no evidence.  In the case of MICI, The Bassis and Walker paper came after the deadline for AR5.


I note that this forum is filled with tens of thousands of post documenting observed climate change's damaging impacts, yet there are virtually no significant carbon pricing programs implemented by world governments to date.  In my opinion this is partially due to the fact that AR5 issued a carbon budget based on left-tail assumptions about climate sensitivity including about ice-climate feedback mechanisms.  The AR5 carbon budgets (written by consensus climate scientists) tell decision makers that they have decades of time before it is too late to stay well below the 2C GMSTA target.  However, the two associated linked articles (parts 1 & 2); demonstrate that when the risks (probabilities times consequences) associated with worse plausible cases are considered, even very high social costs of carbon, SCC, are justified to be added to the prices of fossil fuels (preferably together with a UBI, or dividend, program).

Title: "On Buying Insurance, and Ignoring Cost-Benefit Analysis"

Extract: "The damages expected from climate change seem to get worse with each new study. Reports from the IPCC and the U.S. Global Change Research Project, and a multi-author review article in Science, all published in late 2018, are among the recent bearers of bad news.

In fact, a crash program to decarbonize the economy is obviously the right answer. There are just a few things you need to know about the economics of climate policy, in order to confirm that Adam Smith and his intellectual heirs have not overturned common sense on this issue. Three key points are worth remembering.

For uncertain, extreme risks, policy should be based on the credible worst-case outcome, not the expected or most likely value. This is the way people think about insurance against disasters.

As the careful qualifications in the IPCC and other reports remind us, climate change could be very bad, surprisingly soon, but almost no one is willing to put a precise number or date on the expected losses.

One group does rush in where scientists fear to tread, guessing about the precise magnitude and timing of future climate damages: economists engaged in cost-benefit analysis (CBA).

The disastrous worst-case risks are all on the benefits, or avoided climate damages, side of the ledger. The scientific uncertainties about climate change concern the timing and extent of damages. Therefore, the urgency of avoiding these damages, or conversely the cost of not avoiding them, is intrinsically uncertain, and could be disastrously large."

Title: "Climate Damages: Uncertain but Ominous, or $51 per Ton?"

Abstract: "According to scientists, climate damages are deeply uncertain, but could be ominously large (see the previous post). Alternatively, according to the best-known economic calculation, lifetime damages caused by emissions in 2020 will be worth $51 per metric ton of carbon dioxide, in 2018 prices.
These two views can’t both be right. This post explains where the $51 estimate comes from, why it’s not reliable, and the meaning for climate policy of the deep uncertainty about the value of damages.

The “social cost of carbon” (SCC) is the value of present and future climate damages caused by a ton of carbon dioxide emissions.

Expected climate damages are uncertain over a wide range, including the possibility of disastrously large impacts. The SCC is a monetary valuation of expected damages per ton of carbon dioxide. Therefore, SCC values should be uncertain over a wide range, including the possibility of disastrously high values.

As explained in the previous post in this series, deep uncertainty about the magnitude and timing of risks stymies the use of cost-benefit analysis for climate policy. Rather, policy should be set in an insurance-like framework, focused on credible worst-case losses rather than most likely outcomes. Given the magnitude of the global problem, this means “self-insurance” – investing in measures that make worst cases less likely.

In short, we already know that doing everything on the least-cost emission reduction path will cost less, per ton of carbon dioxide, than worst-case climate damages.

That’s it: end of economic story about evaluating climate policy. We don’t need more exact, accurate SCC estimates; they will not be forthcoming in time to shape policy, due to the uncertainties involved. Since estimated worst-case damages are rising over time, while abatement costs (such as the costs of renewables) are falling, the balance is tipping farther and farther toward “do everything you can, now.” That was already the correct answer some years ago, and only becomes more correct over time."


Would someone mind explaining the relationship between the ozone hole and CDW upwelling? I'd like to understand if someone is willing to spell it out.


The first image shows that the ozone hole over Antarctica deepens the upper atmospheric geopotential well, which then tightens the geopotential contours as shown in the second image.  These tighter geopotential contours cause the westerly winds that nearly continuously blow around the Southern Ocean to both accelerate and consequently to shift southward (like a spinning ice skater pulling inward [southward] her arms, causing her to spin faster).  This intensification, and southward shift, of the westerly winds, causes the associated circumpolar ocean surface currents to both accelerate and to be generated further to the south.  Furthermore, the Coriolis effect causes moving ocean currents (& all other moving objects) to deflect to the left in the Southern Hemisphere.  Thus, the faster westerly moving surface ocean currents deflect northward, which induces more upwelling of warm CDW onto the continental shelf where they advect with increasing frequency to beneath key Antarctic ice shelves.

Also, as shown in the third image, unlike the Arctic that has a convex geopotential height topology which tends to disperse local atmospheric methane concentrations; the Antarctic has a concave geopotential height topology which tends to concentrate any local methane emissions (see the fourth image and note that methane is lighter than air and thus floats upward).  Furthermore, the extreme cold over the East Antarctic reduces the rate of chemical oxidation of the methane to carbon dioxide thus resulting in a further concentration of methane in the troposphere over the South Pole.  However, as GHG contributes to the concavity of the geopotential height topology over Antarctica; this provides a positive feedback mechanism to further accelerate (or at least maintain) the velocity of the circumpolar winds, which should increase the circumpolar current velocity (as well as moving it to the south); which should push more warm CDW onto the Antarctic continental shelf thus causing more basal ice melting for local ice shelves; which reduces surface seawater salinity which causes more upwelling of warm CDW (by a different mechanism than that associated with the ozone hole).

Also, below I repost Reply #306:

The linked reference indicates that the projected increase (with continued global warming) of more frequent strong El Nino events combined with the projected increase in positive SAM, will significantly increase ice mass loss from the ASE, which will increase the risk of a collapse of the WAIS:

Deb, P., A. Orr, D. H. Bromwich, J. P. Nicolas, J. Turner, and J. S. Hosking, 2018: Summer drivers of atmospheric variability affecting ice shelf thinning in the Amundsen Sea Embayment, West Antarctica. Geophy. Res. Lett., 45. doi: 10.1029/2018GL077092.

Abstract:  "Satellite data and a 35-year hindcast of the Amundsen Sea Embayment summer climate using the Weather Research and Forecasting model are used to understand how regional and large-scale atmospheric variability affects thinning of ice shelves in this sector of West Antarctica by melting from above and below (linked to intrusions of warm water caused by anomalous westerlies over the continental shelf edge). El Niño episodes are associated with an increase in surface melt but do not have a statistically significant impact on westerly winds over the continental shelf edge. The location of the Amundsen Sea Low and the polarity of the Southern Annular Mode (SAM) have negligible impact on surface melting, although a positive SAM and eastward shift of the Amundsen Sea Low cause anomalous westerlies over the continental shelf edge. The projected future increase in El Niño episodes and positive SAM could therefore increase the risk of disintegration of West Antarctic ice shelves."

Extract: "Our study suggests that ASE ice shelves could experience an intensification of melt in the future from both above and below as a result of both regional and large-scale atmospheric changes, potentially increasing the risk of their disintegration, which in turn could potentially trigger a collapse of the West Antarctic ice sheet (DeConto & Pollard, 2016). To better understand this threat will require further detailed investigation of the impacts of ENSO, the polarity of the SAM, and the depth/location of the ASL on ASE ice shelves. Also necessary is improving the reliability of future projections, such as ENSO and its teleconnections, as well as the response of the SAM to recovery of the Antarctic ozone hole and increased greenhouse gas emissions (Polvani, Waugh, et al., 2011)."

Finally, see my comments in Reply #920.


I've learned a lot thanks to this topic, and my personal feeling is that future SLR is greatly underestimated due to uncertainties in the science behind it.

However most papers about marine ice sheet instabilities seem to be written by or referring to papers written by Pollard and DeConto. Is MISI/MICI type scenarios only a two man show and are their results approved or contested by other experts? I'm asking because I don't know and not to start a flame war :)

First, Pollard and DeConto are experts in MISI and include it in their MICI models.

Second, MICI research is not a two man show, as indicated by the following brief list of related references (however, MICI modeling is still maturing and has not yet been embraced by consensus climate science):

1.   Ben Seiyon Lee, Murali Haran, Robert Fuller, David Pollard, Klaus Keller (24 March 2019), "A Fast Particle-Based Approach for Calibrating a 3-D Model of the Antarctic Ice Sheet", arXiv:1903.10032v1

2.   David Pollard, Robert M. DeConto, Richard B. Alley (13 March 2018), "A continuum model of ice mélange and its role during retreat of the Antarctic Ice Sheet", Geosci. Model Dev. Discuss.,

3.   Tanja Schlemm and Anders Levermann (2018), "A simple stress-based cliff-calving law", The Cryosphere Discuss.,

4.   J. N. Bassis & C. C. Walker (23 November 2011), "Upper and lower limits on the stability of calving glaciers from the yield strength envelope of ice", Proceedings of the Royal Society A,

5.   D. Pollard et al. (11 September 2018), "Estimating Modern Elevations of Pliocene Shorelines Using a Coupled Ice Sheet‐Earth‐Sea Level Model", JGR Earth Surface,

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

7.   Byron R. Parizek et al. Ice-cliff failure via retrogressive slumping, Geology (2019). DOI: 10.1130/G45880.1

8.   Edward Gasson, Robert M. DeConto, David Pollard and Richard H. Levy (2016), "Dynamic Antarctic ice sheet during the early to mid-Miocene", PNAS,

She blogged about that story here:
It's much quicker to read it than watch a freaking video.

She's clearly very smart with a PhD in particle physics. She's clearly an expert at physical modelling. What she appears to lack is training in the earth or ocean sciences. Brilliant physicists who are modelling experts may not have the same appreciation for how the earth works as someone who has done a large amount of field study. At least, that's my personal experience.

In my opinion, I concur that Tamsin Edwards is short on real world experience (& per Reply #1089 it appears that both David Pollard and Klaus Keller & others agree).  Furthermore, I repost A-Team's Reply #8 below:

Tamsin Edwards is an apologist for climate risk denial.
Here is an amusing commentary on their low-ball Antarctic scenario from G Laden and RB Alley.

I did not care for the timing (as it undercut a good public outreach effort from E Holthaus) nor the self-promotional tone of the Guardian piece, nor the barrage of followup tweets, from a minor figure in climate science seemingly assuming a major role as media spokesperson.

I wonder if she will morph into another Dahl-Jensen, Judith Curry, Andrew Rifken, or Bjorn Lomberg, the last thing we need right now in communicating climate risk. Or maybe just naive (as only a scientist can be) to how the Guardian post will be utilized by industry to muddy the risk waters.

I located her researchgate page and the never--published, never-cited 2006 dissertation on Z bosons; this constant recitation of being a particle physicist despite never having worked in that area in a professional capacity. It's not a qualification any more than neurosurgery because the physics of climate change is entirely nineteenth century newtonian (outside a few things like isotopes).

"An engineer, a theoretical physicist [ie TE], and a paleoclimatologist are at a wedding. There is a ice large sculpture of a swan on a flat topped table, for decoration. The three start a betting pool on how long it will take for the entire swan, which has already started to melt, to end up on the floor.

The engineer notices some of the meltwater dribbling off the back of the table. She places a set of beer mugs under the streams of water, and records how long it takes for a measured amount of liquid to accumulate. She uses this to generate a graph showing melting over time, estimating the volume of the swan by looking it up in his manual on Ice Sculpture Specifications, and suggests that it will take eleven hours.

The theoretical physicist estimates the volume of ice by assuming a spherical swan, measures the air temperature, and calculates the rate of conversion from ice to water using thermodynamics. He comes up with a different estimate, because the engineer forgot to account for density differences in ice vs water. He estimates that the swan will be entirely the floor in eight and a half hours.

The paleoclimatologist disagrees, and says, “It will take between one and three hours for that swan to be on the floor.”

“Why do you think that, you are clearly an idiot, and I am clearly a physicist, so I must be right!” says the theoretical physicist.

Just as the paleoclimatologist is about to answer, the already melting neck of the swan breaks, and the upper part of the neck and head fall backwards, knocking off one of the large wings. All of those pieces slide off the table and crash on the floor. The stress of the impact causes the second wing to break off, but it stays on the table, but it begins to slowly slide toward the edge, clearly about to fall off as well.

“Because,” the paleoclimatologist says. “Last wedding I went to, that happened.”"

See also:

Title: "Tamsin Edwards"

Extract: "She will be a lead author for Chapter 9 (Ocean, cryosphere, and sea level change) of the sixth assessment report of the Intergovernmental Panel on Climate Change."

Title: "Working Group I contribution to the IPCC Sixth Assessment Report (AR6-WG1)"

Whether one agrees with Tamsin Edwards, or not, she is a lead author of the IPCC AR6, so it is worth watching the following 2018 video entitled: "How soon will the ice apocalypse come? (CCCR2018)", that she presented at the 2018 Cambridge Conference on Catastrophic Risk:

I selected the two attached images from the 'Early Anthropocene' thread in the Science folder, to point that it appears likely that the Earth was headed towards a cooling cycle (as in headed towards a glacial period) before mankind started impacting both atmospheric carbon dioxide and methane concentrations.  Thus it is plausible that some of mankind's recent contributions to increasing GMSTA has been partially masked from the observed measurements by offsetting transient negative feedbacks associated with such a long-term/slow cooling trend.  Thus it is plausible that this is one more consideration (together with such masking factors as negative aerosol forcing) that may surprise consensus science projections if/when it turns out that the positive feedback mechanisms have been stronger than indicated by the masked GMSTA data.

As noted in Reply #243, the linked reference (see also the first attached image and associated caption below, and the second image that shows the basal meltwater drainage system beneath Thwaites) provides more evidence of high geothermal flux and associated basal melt water beneath the Thwaites Glacier, both of which will threaten its future stability, and they both work to refill the recently drained subglacial lakes beneath Thwaites:

Dustin M. Schroeder, Donald D. Blankenship, Duncan A. Young, and Enrica Quartini, (2014), "Evidence for elevated and spatially variable geothermal flux beneath the West Antarctic Ice Sheet", PNAS, doi: 10.1073/pnas.1405184111

Also see:

Caption for first image: "This map shows the locations of geothermal flow underneath Thwaites Glacier in West Antarctica that were identified with airborne ice-penetrating radar. The dark magenta triangles show where geothermal flow exceeds 150 milliwatts per square meter, and the light magenta triangles show where flow exceeds 200 milliwatts per square meter. Letters C, D and E denote high melt areas: in the western-most tributary, C; adjacent to the Crary mountains, D; and in the upper portion of the central tributaries, E. Credit: University of Texas Institute Geophysics"

The linked article (& associated reference) discuss new findings that help to explain why the Earth warms so rapidly at the end of the late Pleistocene ice ages (see image).  They attribute part of this rapid warming to radiative forcing associated with carbon dioxide 'released into the ocean from geologic reservoirs located on the seafloor when the oceans began to warm.

During to the thermal inertia of the oceans, I would be surprised if such a feedback had much impact sooner than century timescales.  Nevertheless, ice-climate feedback mechanisms over this coming century might be sufficient to active such carbon dioxide hydrate related feedback mechanisms next century; which would be bad news for future generations:

Title: "Deep sea carbon reservoirs once superheated the Earth – could it happen again?"

Extract: "It is now clear from these studies that abrupt warming events are built into Earth’s climate system. They have occurred when disturbances in carbon storage at Earth’s surface released greenhouse gases into the atmosphere. One of the grand challenges for climate scientists like me is to determine where these releases came from before humans were present, and what triggered them. Importantly, we want to know if such an event could happen again.

In a recently published study, my colleagues Katie Harazin, Nadine Krupinski and I discovered that at the end of the last glacial era, about 20,000 years ago, carbon dioxide was released into the ocean from geologic reservoirs located on the seafloor when the oceans began to warm.

This finding is a potential game-changer. Naturally occurring reservoirs of carbon in the modern ocean could be disturbed again, with potentially serious effects to Earth’s oceans and climate.

Over the past two decades, ocean scientists have discovered that there are reservoirs of liquid and solid carbon dioxide accumulating at the bottom of the ocean, within the rocks and sediments on the margins of active hydrothermal vents. At these sites, volcanic magma from within the Earth meets superheated water, producing plumes of carbon dioxide-rich fluids that filter through crevices in the Earth’s crust, migrating upward towards the surface.

When a plume of this fluid meets cold seawater, the carbon dioxide can solidify into a form called hydrate. The hydrate forms a cap that traps carbon dioxide within the rocks and sediments and keeps it from entering the ocean. But at temperatures above roughly 48 degrees Fahrenheit (9 degrees Celsius), hydrate will melt, releasing buoyant liquid or gaseous carbon dioxide directly into the overlying water.

These discoveries are changing scientists’ understanding of the marine carbon system. Climate scientists have not included deep sea carbon reservoirs in current models that explore the potential impacts of future warming, because little is known about the size and distribution of these carbon sources.

Earth’s oceans are warming rapidly, and climate models project that they will warm fastest near the poles, where deep currents form that carry warming waters downward from the surface.

As these warm waters sink into the ocean’s interior, they transport excess heat towards sites where carbon dioxide reservoirs can form. Those warmer waters will eventually destabilize the hydrate seals that keep liquid carbon dioxide trapped.

Importantly, warm hydrothermal fluids are rising from below the carbon dioxide reservoir toward the surface. As the oceans continue to warm, the temperature difference between cold ocean waters and warmer hydrothermal fluids will decrease. This will cause the hydrate to thin, potentially to a point where it will no longer keep liquid carbon dioxide from escaping.

To date there has been no research to assess whether these ocean carbon dioxide reservoirs are vulnerable to rising ocean temperatures. But Earth’s pre-historic record clearly demonstrates that geologic reservoirs can be destabilized – and that when they are, it leads to rapid increases in atmospheric carbon dioxide and global warming. In my view, this represents an important unknown risk that cannot be ignored."
See also:

Lowell D Stott, Kathleen M Harazin and Nadine B Quintana Krupinski (15 February 2019), "Hydrothermal carbon release to the ocean and atmosphere from the eastern equatorial Pacific during the last glacial termination", Environmental Research Letters, Volume 14, Number 2

Abstract: "Arguably among the most globally impactful climate changes in Earth's past million years are the glacial terminations that punctuated the Pleistocene epoch. With the acquisition and analysis of marine and continental records, including ice cores, it is now clear that the Earth's climate was responding profoundly to changes in greenhouse gases that accompanied those glacial terminations. But the ultimate forcing responsible for the greenhouse gas variability remains elusive. The oceans must play a central role in any hypothesis that attempt to explain the systematic variations in pCO2 because the Ocean is a giant carbon capacitor, regulating carbon entering and leaving the atmosphere. For a long time, geological processes that regulate fluxes of carbon to and from the oceans were thought to operate too slowly to account for any of the systematic variations in atmospheric pCO2 that accompanied glacial cycles during the Pleistocene. Here we investigate the role that Earth's hydrothermal systems had in affecting the flux of carbon to the ocean and ultimately, the atmosphere during the last glacial termination. We document late glacial and deglacial intervals of anomalously old 14C reservoir ages, large benthic-planktic foraminifera 14C age differences, and increased deposition of hydrothermal metals in marine sediments from the eastern equatorial Pacific (EEP) that indicate a significant release of hydrothermal fluids entered the ocean at the last glacial termination. The large 14C anomaly was accompanied by a ~4-fold increase in Zn/Ca in both benthic and planktic foraminifera that reflects an increase in dissolved [Zn] throughout the water column. Foraminiferal B/Ca and Li/Ca results from these sites document deglacial declines in [ ] throughout the water column; these were accompanied by carbonate dissolution at water depths that today lie well above the calcite lysocline. Taken together, these results are strong evidence for an increased flux of hydrothermally-derived carbon through the EEP upwelling system at the last glacial termination that would have exchanged with the atmosphere and affected both Δ14C and pCO2. These data do not quantify the amount of carbon released to the atmosphere through the EEP upwelling system but indicate that geologic forcing must be incorporated into models that attempt to simulate the cyclic nature of glacial/interglacial climate variability. Importantly, these results underscore the need to put better constraints on the flux of carbon from geologic reservoirs that affect the global carbon budget."

The linked reference indicates that many earlier CESM projections did not consider cloud radiative feedbacks with the ENSO cycles; however, it finds that when such feedbacks do indeed work synergistically with the ENSO.

Eleanor A. Middlemas et al. (8 May 2019), "Cloud radiative feedbacks and El Niño Southern Oscillation", Journal of Climate,

Cloud radiative feedbacks are disabled via “cloud-locking” in the Community Earth System Model, version 1.2, (CESM1.2) to result in a shift in El Niño Southern Oscillation (ENSO) periodicity from 2-7 years to decadal timescales. We hypothesize that cloud radiative feedbacks may impact the periodicity in three ways: by (1) modulating heat flux locally into the equatorial Pacific subsurface through negative shortwave cloud feedback on sea surface temperature anomalies (SSTA), (2) damping the persistence of subtropical Southeast Pacific SSTA such that the South Pacific Meridional Mode impacts the duration of ENSO events, or (3) controlling the meridional width of off-equatorial westerly winds, which impact the periodicity of ENSO by initiating longer Rossby waves. The result of cloud-locking in CESM1.2 contrasts that of another study which found that cloud-locking in a different global climate model led to decreased ENSO magnitude across all timescales due to a lack of positive longwave feedback on the anomalous Walker circulation. CESM1.2 contains this positive longwave feedback on the anomalous Walker circulation, but either its influence on the surface is decoupled from ocean dynamics or the feedback is only active on interannual timescales. The role of cloud radiative feedbacks in ENSO in other global climate models are additionally considered. In particular, it is shown that one cannot predict the role of cloud radiative feedbacks in ENSO through a multimodel diagnostic analysis. Instead, they must be directly altered.

What studies in the next couple years that we could do would clarify the likelihood of this scenario (in the video) eventuating within a century?

You can review the program conducted this past austral summer in the ASE (Amundsen Sea Embayment) in Reply #824.  So if decision makers had more will power they could perform similar field and modeling work for the next two years.  Also, if DoD was so inclined they could introduce ice-cliff failure and hydrofracturing routines to E3SM within the next year so that we could check James Hansen's ice-climate feedback mechanism projections.

Unfortunately, I would be surprised if the Trump Administration would authorize any such accelerated work.

Edit, the following are reposts that I made in back 2013 in this folder (in the 'Recommendations and Summary wrt the WAIS Collapse Hazard', thread):

1) The following recommendations are from: Abrupt Climate Change a report by the U.S. Climate Change Science Program and the Subcommittee on Global Change Research, U.S. Geological Survey, Reston, VA. Lead Author: Konrad Steffen, University of Colorado:
•   Reduce uncertainties in estimates of mass balance. This includes continuing mass-balance measurements on small glaciers and completing the World Glacier Inventory.
•   Maintain climate networks on ice sheets to detect regional climate change and calibrate climate models.
•   Derive better measurements of glacier and ice-sheet topography and velocity through improved observation of glaciers and ice sheets. This includes utilizing existing satellite interferometric synthetic aperture radar (InSAR) data to measure ice velocity.
•   Use observations of the time-varying gravity field from satellites to estimate changes in ice sheet mass.
•   Survey changes in ice sheet topography using tools such as satellite radar (e.g., Envisat and Cryosat-2), laser (e.g., ICESat-1/2), and wide-swath altimeters.
•   Monitor the polar regions with numerous satellites at various wavelengths to detect change and to understand processes responsible for the accelerated ice loss of ice sheets, the disintegration of ice shelves, and the reduction of sea ice. It is the integrated satellite data evaluation that provides the tools and understanding to model the future response of cryospheric processes to climate change.
•   Utilize aircraft observations of surface elevation, ice thickness, and basal characteristics to ensure that such information is acquired at high spatial resolution along specific routes, such as glacier flow lines, and along transects close to the grounding lines.
•   Improve coverage of longer term (centennial to millennial) records of ice sheet and ocean history from geological observations.
•   Support field, theoretical, and computational investigations of physical processes beneath and along ice shelves and beneath glaciers, especially near to the grounding lines of the latter, with the goal of understanding recent increases in mass loss.
•   Develop ice-sheet models on a par with current models of the atmosphere and ocean. Particular effort is needed with respect to the modeling of ocean/ice-shelf interactions and physical processes, of surface mass balance from climatic information, and of all (rather than just some, as now) of the forces which drive the motion of the ice.

2) - Develop a sophisticated box model for the Thwaites Glacier (including the postulated subglacial cavity) to see how the grounding line retreats into the BSB.
- Run various ice sheet models with the initial starting conditions that have been presented here; particularly the conditions postulated for the Thwaites Glacier after 2060, including the basal melt rate measured at the WAIS-Divide bore hole.
- Run ice shelf models for both FRIS and RIS with CDW (with flow and temperature parameter calibrated to match the reduction of AABW in these respective areas) introduced beneath them in order to evaluate the rate of ice shelf thinning thru 2100.
- Try to hydraulically model the advective (horizontal) interaction between the PIG and Thwaites system to determine whether there is any synergistic advective action.
- Model the hydraulic action of the postulated interconnected sea passageways and side spurs, and their possible influences on local currents around a degraded WAIS (after 2070).
Possible Field Studies:
- Send a research vessel to the Northeast edge of the FRIS to see whether it is true that warm CDW is already entering the Filchner Trough, and monitor the water flow at outer edge of the RIS for indications of possible CDW fluxes.
- Conduct high-resolution ground penetrating radar examinations of the grounding line of the marine ice sheets for Basins A & B near the Southwest edge of the Filchner Ice Shelf, in order to see whether the grounding line has begun to retreat down the negative slope.
- Refine the ground penetrating survey of the ice in the Thwaites drainage basin, in order to more accurately locate, and delineate, the subglacial lakes in this area.
- Deploy a submersible ROV to survey the: (a) Thwaites Hollow/Subglacial cavity; and (b) the gateway to the Ferrigno Glacier to see if a subglacial cavity has formed there.

Edit 2:  With regard to current modeling efforts of the ocean - cryosphere interaction (i.e. the preponderance of ice-climate feedbacks), see Replies #781 & #990.

The linked reference discusses how 'a recent shift toward an El Nino-like ocean state in the Tropical Pacific' "… is linked to the recent acceleration of global ocean warming":

Sang‐Chul Cha et al. (05 November 2018), "A Recent Shift Toward an El Niño‐Like Ocean State in the Tropical Pacific and the Resumption of Ocean Warming", Geophysical Research Letters,

Since approximately 2011, the tropical Pacific has been sharply shifting toward an opposite phase to that observed in the previous decade. This shift has coincided with a recent resumption of global warming after a hiatus in the 2000s. Based on a model‐data analysis using an ensemble empirical mode decomposition, we identified a distinct low‐frequency mode of the sea level in the tropical Pacific and showed its connection to global ocean warming and the suppression of global warming during the early 2000s, as well as the resumption of warming during recent years. Hindcast and model experiments conducted to illustrate the physical mechanism linking the decadal mode to the Pacific Decadal Oscillation‐related trade winds, which regulate the strength of the Equatorial Undercurrent and the surface temperature of the tropical Pacific Ocean, revealed an El Niño‐like state for the last several years.

Plain Language Summary

In contrast to previous decade, since roughly 2011, sea level in the western tropical Pacific has declined, while sea level in the central‐to‐eastern tropical Pacific has increased. This study focuses on a decadal shift in the tropical Pacific Ocean toward a low‐frequency El Niño‐like state, which coincides with a recent resumption of global warming after a hiatus in the 2000s. Here we identify whether the recent shift is a short‐term change associated with ENSO or longer‐term change and examine how the decadal shift in the Pacific is linked to the recent acceleration of global ocean warming. The model‐data analysis allows us to gain insight into the evolution of sea level and ocean circulation in the Pacific Ocean on decadal time scale, as well as the accuracy and reliability of observed decadal fluctuation. The decadal mode presented here could lead to a better understanding of how sea level and ocean circulation respond to the Pacific climate variability.

Christ AbruptSLR...I don't visit for a few hours and you dump a day's worth of reading on me!

Shared Humanity,

Please excuse my irregular posting (due to my irregular schedule); however, from my point of view theses posts are all re-posts of prior points that I have made before, that I have merely concentrated in one sequence for those who get lost in the noise of a blog.

Best regards,


The linked reference has relevance to my last post:

Slater, D., Straneo, F., Felikson, D., Little, C., Goelzer, H., Fettweis, X., and Holte, J.: Past and future response of Greenland's tidewater glaciers to submarine melting, The Cryosphere Discuss.,, in review, 2019.

Abstract. The effect of the North Atlantic Ocean on the Greenland Ice Sheet through submarine melting of Greenland's tidewater glacier calving fronts is thought to be a key driver of widespread glacier retreat, dynamic mass loss and sea level contribution from the ice sheet. Despite its critical importance, problems of process complexity and scale hinder efforts to represent the influence of submarine melting in ice sheet-scale models. Here we propose parameterizing tidewater glacier terminus position as a simple linear function of submarine melting, with submarine melting in turn estimated as a function of subglacial runoff and ocean temperature. The relationship is tested, calibrated and validated using datasets of terminus position, runoff and ocean temperature covering the full ice sheet and surrounding ocean from the period 1960–present. We demonstrate a statistically significant link between multi-decadal tidewater glacier terminus position and submarine melting and show that the proposed parameterisation has predictive power when considering a population of glaciers. An illustrative 21st century projection is considered suggesting that tidewater glaciers in Greenland will undergo little further retreat in a low emissions RCP2.6 scenario. In contrast, a high emissions RCP8.5 scenario results in a median retreat of ∼6 km, with 35 % of glaciers experiencing retreat exceeding 10 km. Our study provides a long-term and ice sheet-wide assessment of the sensitivity of tidewater glaciers to submarine melting and proposes a practical and empirically validated means of incorporating ocean forcing into models of the Greenland ice sheet.

Edit, for fun I note that the linked reference does not consider ice-cliff failure mechanisms, but the attached images indicate that at least Jakobshavn & Helheim are primed to experience at least a spurt of ice-climate failures as their ice faces retreat down negative bed-slopes in the next decade or two:

The first attached image is from Espen, where: "Helheim (1.) is qualified to be on of the four super iceways of Greenland together with Jakobshavn (2.), Petermann / Humboldt (3.) and Zachariae (4.)"

The second image shows Jakobshavn bathymetry with the ice calving face thru 2017; which indicates that the ice face is retreating toward the negative bed-slope at location A15; and where the third image shows a profile of Jakobshavn where the negative bed-slope is at AA' distance 12km.

The fourth image shows that the calving ice face of the Helheim Glacier is also approaching a negative bed-slope.

Edit 2: Just a reminder that James Hanson warned in the 1980's that for modern society to be fully safe from significant negative climate impacts, the atmospheric carbon dioxide concentration should remain below 350ppm.

As a follow-on to my last five posts, I reiterate that: The first image shows key marine glacial basins in Antarctica (focused on the Totten Glacier catchment basin), and the second image shows seaways that could form in the WAIS basin due to MICI-type failures in this areas in the decades from circa 2030 to circa 2100.  The associated slowing of the meridional overturning current would advect more warm Atlantic water to key marine terminating glaciers in Southern and Northeast Greenland (see the third and fourth images) via the bipolar seesaw mechanism; which would accelerate ice mass loss from the GIS.

Finally, I remind readers that this possible scenario is not dependent upon GMSTA reading 2C above pre-industrial (as cited by Alley, Pollard, DeConto etc 2018), and is largely dependent only upon heat content that is already in the ocean.

As a follow-on to my last post, here I reiterate that: The first image shows that through 2015 key Antarctic ice shelves have already provided (& continue to provide) significant quantities of freshwater to the coastal Antarctic surface water without contributing to measured SLR. The second image shows how during El Nino events (which are becoming more frequent with continued global warming) and negative SAM conditions, atmospheric heat is advected from the Tropical Pacific to the coastal West Antarctic. This second image also shows how El Nino conditions lead to a low pressure system (the blue blob in the image) off of coast of the Bellingshausen-Amundsen Seas; which pins the Amundsen Sea Low (ASL) off this coast; which as indicated in the third image blows wind landward, which drags still more warm CDW into the ASE.  Once the warm CDW is beneath the key ASE ice shelves, the fourth image shows how this warm water 'burns' upward through basal crevasses in these ice shelves, which leads to early calving events such as we are observing for the PIIS.

The linked reference applies mathematical modeling to state change in a natural lake ecosystem and '...  resolves a previously unclear issue as to the nature of the tipping point involved.'  Hopefully, such lessons learned can be applied to abrupt climate state change.

Boettiger, C. & Batt, R. J. (2019), "Bifurcation or state tipping: assessing transition type in a model trophic cascade", Math. Biol.,

Abstract: "Ecosystems can experience sudden regime shifts due to a variety of mechanisms. Two of the ways a system can cross a tipping point include when a perturbation to the system state is large enough to push the system beyond the basin of attraction of one stable state and into that of another (state tipping), and alternately, when slow changes to some underlying parameter lead to a fold bifurcation that annihilates one of the stable states. The first mechanism does not generate the phenomenon of critical slowing down (CSD), whereas the latter does generate CSD, which has been postulated as a way to detect early warning signs ahead of a sudden shift. Yet distinguishing between the two mechanisms (s-tipping and b-tipping) is not always as straightforward as it might seem. The distinction between “state” and “parameter” that may seem self-evident in mathematical equations depends fundamentally on ecological details in model formulation. This distinction is particularly relevant when considering high-dimensional models involving trophic webs of interacting species, which can only be reduced to a one-dimensional model of a tipping point under appropriate consideration of both the mathematics and biology involved. Here we illustrate that process of dimension reduction and distinguishing between s- and b-tipping for a highly influential trophic cascade model used to demonstrate tipping points and test CSD predictions in silico, and later, in a natural lake ecosystem. Our analysis resolves a previously unclear issue as to the nature of the tipping point involved."

For the first time the linked insurance industry survey found '… climate change ranked as both the top current risk and leading emerging risk ..':

Title: "Twelfth Annual Survey of Emerging Risks: Summary of Finding"

Extract: "For the first time in the survey’s history, climate change ranked as both the top current risk and leading emerging risk – breaking cyber risk’s four-year streak as number one – according to the Twelfth Annual Emerging Risks Survey of Risk Managers from the Joint Risk Management Section (JRMS) of the Canadian Institute of Actuaries (CIA), Casualty Actuarial Society (CAS) and the Society of Actuaries (SOA)."

Maybe the term 'Anthropocene' should be changed to 'Absurdocene':

Aarssen, Lonnie (2019). "Meet Homo absurdus--the only creature that refuses to be what it is", Ideas in Ecology and Evolution, 11, doi:10.24908/iee.2018.11.13.e.

Extract: "Homo sapiens sapiens ('wise human') may describe a distant human ancestor, but if it ever did, the name no longer suits us.  As Cribb (2011) put it, "An animal that imperils its own future and that of most other life forms and ecosystems does not merit a single 'sapiens', let alone the two we now bear." … Homo absurdus – human that spends its whole life trying to convince itself that its existence is not absurd.  As Albert Camus (1956) put it, "Man is the only creature who refuses to be what he is.

"The world of human aspirations is largely fictitious, and if we do not understand this, we understand nothing about man.  ...""

Edit, see also:

Title: "Earth hurtles toward extinction crisis — 1 million species at risk"

Extract: "By the numbers:

- 8 million: Total estimated number of plant and animal species on Earth (includes insects).

- Up to 1 million: Total number of species threatened with extinction.

- Tens to hundreds of times: "The extent to which the current global rate of species extinction is higher compared to average over the last 10 million years." This rate is accelerating, the report finds.


In "Climatic Thresholds for WAIS Retreat: Onset of Widespread Ice Shelf Hydrofracturing and Ice Cliff Calving in a Warming World", Rob DeConto, David Pollard, Knut Christianson, Richard B. Alley & Byron R. Parizek only project widespread ice shelf hydrofracturing after GMSTA reaches about 2C above pre-industrial; which following SSP5-Baseline is projected to occur circa 2040.

However, this is a quick note to remind readers that the PIIS and Thwaites Eastern Ice Shelf could collapse earlier than when GMSTA reaches about 2C above pre-industrial; primarily due to (channelized) basal ice melting beneath these key ice shelves; which in my opinion could result in these ice shelves effectively disappearing as early at 2030; which might then trigger an MICI-type of collapse of the WAIS of the subsequent decades.  The first attached image (from MacGregor et al. 2012) indicates that as late as 2011 both the PIIS, the Thwaites Eastern Ice Shelf, and the Thwaites Ice Tongue were in much better condition than any of them are today.

Edit: I note that the ocean has been accumulating anthropogenic heat for at least the past two hundred and seventy years, and most of this excess ocean heat content has been advected to the Southern Ocean; where it represents a threat to the stability of Antarctic ice shelves.

Edit 2: The condition of the key ice shelves in the ASE is illustrated both by Schroeder et al. (2018), and by the recent retreat of the PIIS calving face to be upstream of the SW Tributary Glacier (see the second attached image {showing a recent crevasse in PIIS on May 5, 2019} & note that in Reply #931 I projected another major PIIS calving event still further upstream in July 2019).

Schroeder et al (2018) indicate that: "… thickness change of the Thwaites Eastern Ice Shelf between 1978 and 2009, revealing the loss of over half of its thickness over the past three decades."  As the Eastern Thwaites Ice Shelf continues to thin, its risk of abrupt collapse increases rapidly in coming decades:

Edit 3: Needless to say, but if key ASE ice shelves collapse simply due to the heat content that is already in the Southern Ocean, then no matter what radiative forcing pathway the global socio-economic system following in the coming decades, we may have already past the tipping point for a MICI-type of collapse for the WAIS this century.

The GRACE satellite was an amazing tool from April 2002 until June 2017 & I look forward to seeing even better results from GRACE-FO:

Byron D. Tapley, et al. (2019), "Contributions of GRACE to understanding climate change", Nature Climate Change, volume 9, pages358–369, DOI:

Abstract: "Time-resolved satellite gravimetry has revolutionized understanding of mass transport in the Earth system. Since 2002, the Gravity Recovery and Climate Experiment (GRACE) has enabled monitoring of the terrestrial water cycle, ice sheet and glacier mass balance, sea level change and ocean bottom pressure variations, as well as understanding responses to changes in the global climate system. Initially a pioneering experiment of geodesy, the time-variable observations have matured into reliable mass transport products, allowing assessment and forecast of a number of important climate trends, and improvements in service applications such as the United States Drought Monitor. With the successful launch of the GRACE Follow-On mission, a multi-decadal record of mass variability in the Earth system is within reach."

See also:

Title: "GRACE mission data contributes to our understanding of climate change"

•   Extract: "GRACE enabled a measure of the quantity of heat added to the ocean and the location for said heat that remains stored in the ocean. GRACE has provided detailed observations, confirming that the majority of the warming occurs in the upper 2,000 meters of the oceans.
•   GRACE has observed that of the 37 largest land-based aquifers, 13 have undergone critical mass loss. This loss, due to both a climate-related effect and an anthropogenic (human-induced) effect, documents the reduced availability of clean, fresh water supplies for human consumption.
•   The information gathered from GRACE provides vital data for the federal agency United States Drought Monitor and has shed light on the causes of drought and aquifer depletion in places worldwide, from India to California"
Image caption: "Global representation of trends and variability in ice and water mass recovered by GRACE over 15 years. The top figure, which shows trend maps over Antarctica, Greenland and part of the Arctic, represent changes in ice mass. The middle trend map mainly represents changes in the terrestrial water storage. The bottom figure shows variability in ocean bottom pressure. In the last figure, the color scales represent variability, with the highest variability shown in red. Credit: Cockrell School of Engineering, The University of Texas at Austin"

See also:

Title: "GRACE-FO"

The Drawdown organization ranked disposal of old refrigerant materials (CFCs, HCFCs and HFCs) as the #1 ranked priority for limiting GMSTA increase by 2050.  The National Geographic Society is majority owned by 21st Century Fox; thus it is not surprising that the linked article by the National Geographic, cites this as '... an incredibly important solution."  As the risk of leakage of old refrigerant materials into the atmosphere is not considered in the SSP baseline scenarios, this matter actually represents a climate risk (of 17 years worth of US CO2 emissions equivalent if it is not dealt with) rather than a solution:

Title: "One overlooked way to fight climate change? Dispose of old CFCs."

Extract: "Last year, a coalition of scientists and policy experts at the nonprofit Drawdown ranked the top one hundred climate change solutions by level of impact. No one guessed that refrigerant management, which includes CFCs and two other classes of chemicals known as HCFCs and HFCs, would top the list. But it did.

The Drawdown study estimated that properly disposing of old refrigerants, rather than letting them leak into the air, would be equivalent to preventing nearly 90 gigatons of carbon dioxide from reaching the atmosphere. That’s more than 17 years of U.S. CO2 emissions.

“It’s an incredibly important solution,” said Chad Frishmann, Drawdown’s Research Director.

But in order to achieve consensus, negotiators of the Montreal Protocol had to be forward-looking. The nations of the world agreed to ban future production of ozone-depleting chemicals but quantities of ozone-depleting gases that already existed, materials that have come to be known as “banks,” were left out of the agreement. The banks weren’t insignificant either. In 1988, the year before the protocol went into effect, the size of the CFC bank was slightly more than that year’s global emissions of CO2."

See also:

Extract: "Materials - Refrigerant Management

Extract: "In October 2016, officials from more than 170 countries met in Kigali, Rwanda, to negotiate a deal to address this problem. Through an amendment to the Montreal Protocol, the world will phase out HFCs—starting with high-income countries in 2019, then some low-income countries in 2024 and others in 2028. Substitutes are already on the market, including natural refrigerants such as propane and ammonium.

Scientists estimate the Kigali accord will reduce global warming by nearly one degree Fahrenheit. Still, the bank of HFCs will grow substantially before all countries halt their use. Because 90 percent of refrigerant emissions happen at end of life, effective disposal of those currently in circulation is essential. After being carefully removed and stored, refrigerants can be purified for reuse or transformed into other chemicals that do not cause warming."

Edit: I note that any potential 'solution' to our climate change situation is not a solution unless it is actually implemented.  Consensus climate science has been identifying potential 'solutions' since at least the 1980's and yet since that time we have continuously followed a BAU pathway.

As a follow-on to my last post, the following linked references future illustrate paleo cases that climate models find difficult to match:

The first linked Ivanovic et al. (2018) reference indicates that paleo-signals from meltwater pulse events in the NH override any such paleo-signals from SH meltwater pulse events.  Thus it is difficult to find evidence of a meltwater pulse event in the paleo-record from a meltwater pulse event associate with an abrupt MICI collapse of the WAIS.

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

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

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

The second linked reference [Erhardt et al. (2019)] indicates that Dansgaard-Oeschger warming effects can be trigger by decadal-scale atmospheric circulation changes including changes in precipitation (such as increased rainfall in Arctic and Antarctic areas):

Erhardt, T., Capron, E., Rasmussen, S. O., Schüpbach, S., Bigler, M., Adolphi, F., and Fischer, H.: Decadal-scale progression of the onset of Dansgaard–Oeschger warming events, Clim. Past, 15, 811-825,, 2019.

During the last glacial period, proxy records throughout the Northern Hemisphere document a succession of rapid millennial-scale warming events, called Dansgaard–Oeschger (DO) events. A range of different mechanisms has been proposed that can produce similar warming in model experiments; however, the progression and ultimate trigger of the events are still unknown. Because of their fast nature, the progression is challenging to reconstruct from paleoclimate data due to the limited temporal resolution achievable in many archives and cross-dating uncertainties between records. Here, we use new high-resolution multi-proxy records of sea-salt (derived from sea spray and sea ice over the North Atlantic) and terrestrial (derived from the central Asian deserts) aerosol concentrations over the period 10–60 ka from the North Greenland Ice Core Project (NGRIP) and North Greenland Eemian Ice Drilling (NEEM) ice cores in conjunction with local precipitation and temperature proxies from the NGRIP ice core to investigate the progression of environmental changes at the onset of the warming events at annual to multi-annual resolution. Our results show on average a small lead of the changes in both local precipitation and terrestrial dust aerosol concentrations over the change in sea-salt aerosol concentrations and local temperature of approximately one decade. This suggests that, connected to the reinvigoration of the Atlantic meridional overturning circulation and the warming in the North Atlantic, both synoptic and hemispheric atmospheric circulation changes at the onset of the DO warming, affecting both the moisture transport to Greenland and the Asian monsoon systems. Taken at face value, this suggests that a collapse of the sea-ice cover may not have been the initial trigger for the DO warming.

The third linked reference [Coletti et al. (2015)] elaborates on the fact that even the most advanced modern analysis of the MIS 11c event cannot yet full account for the exceptionally high Arctic Amplification which may have been associated with a paleo-collapse of the WAIS.

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

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

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

I would like to remind readers that all current and planned (e.g. E3SMv2) models that simulate glacial ice responses are not sufficiently sophisticated to match both paleo and observed behavior; much of which is highly dependent on: a) initial conditions; b) boundary conditions, c) chaotic reinforcement of fluctuations and d) synergy between adjoining glacial bodies (e.g. the Pine Island  Glacier drainage basin and the Byrd Subglacial Basin) and between glacial bodies, the ocean, the atmosphere and the glacial beds. 

Examples of observed behavior (all previously cited in this thread) that local Antarctic models are currently not getting correct include:

a) The southward migration of mixed CDW; b) the subglacial cavity at the base of the Thwaites Ice Tongue; c) the periodic discharge of subglacial lakes, including those beneath the Thwaites Glacier and d) the dynamic circulation of mixed CDW within the ASE.

Examples of possible future events that are not considered in global or local models include:

a) future changes in local in Antarctic sea ice contentations and of local winds; which may advect more mixed CDW beneath ice shelves such as the FRIS and the RIS; b) future increases in storm activity over the Southern Ocean can increase storm surge, increase rainfall on ice shelves and increase snowfall at higher elvations on marine glaciers which can increase both ice cliff heights and gravitational driving forces; c) future increased El Nino frequencies can drive more CDW into the ASE (including via the ASL) and increase advected heat from the Tropical Pacific to the west coast of the WAIS and d) future ice-climate feedbacks can reinforce cascades of other positive feedback mechanisms that can increase ECS in coming decades.

Examples of anthropogenic radiative forcing that are not fully considered by the SSP scenarios include:

a) A relocation of aerosol sources away from the Arctic could abruptly accelerate Arctic Amplification which could result in a rapid reduction of Arctic Sea Ice Extent that could trigger an associated albedo flip; b) a drive for sustainable energy without reducing fossil fuel production could support a rapid increase in the use of refrigeration and air conditioning in the Third World without reducing GHG emissions; c) SSP5 assumes population peaks around 8 billion while we are already at 7.7 billion people and the associate demand for meat is growing faster than the population growth; and d) a drive to push BECCS could devastate bio-diversity which could result in a rapid reduction of thenatural terrestial CO2 sink.

Now I note that the fact that Pollard, DeConto and Alley (2015 [not 2016 as you cited]), assumed a uniformly warm ocean is irrelevant to what happens beneath the ASE ice shelves and grounding lines, because Bronselar et al. (2018) clearly shows that for modern day conditions the warm CDW will upwell into the ASE, locally creating the warmth of water comparable to mid-Pliocene conditions.

Furthermore, it is conservative for Pollard, DeConto, Alley and others to assume instant local mid-Pliocene conditions (which I say may very well happen circa 2040) because the local ice shelf condition is much worse than assumed by such authors due to decades (since the 1970's) of periodic warm CDW intrusions into the ASE associated with the formation of the Antarctic ozone hole.  The condition of the key ice shelves in the ASE is illustrated by Schroeder et al. (2018), and by the recent retreat of the PIIS calving face to be upstream of the SW Tributary Glacier.

Schroeder et al (2018) indicate that: "… thickness change of the Thwaites Eastern Ice Shelf between 1978 and 2009, revealing the loss of over half of its thickness over the past three decades."  As the Eastern Thwaites Ice Shelf continues to thin, its risk of abrupt collapse increases rapidly in coming decades:

Also, the first attached image from Kriegler et al. (2017), shows that SSP5 projects that by 2040 GMSTA will be about 2C above a 1986-2005 baseline.

Kriegler et al (2017), "Fossil-fueled development (SSP5): An energy and resource intensive scenario for the 21st century", Global Environmental Change, Volume 42, Pages 297-315,

Therefore if Hawkins et al. (2017) is correct and to get from a 1986-2005 baseline to a preindustrial baseline one needs to add an average of 0.675C then the SSP5-Baseline projection for 2040 would be 2C + 0.675C = 2.675C.

I note that Hawkins et al (2017) defines the pre-industrial baseline to be from 1720-1800 for determining GMSTA.

Ed Hawkins et al. (2017), "Estimating Changes in Global Temperature since the Preindustrial Period", BAMS,

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

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

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

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

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

Edit: Also, I note that Pollard, DeConto & Alley (2018) ice mass loss projections only use hydrofracturing to collapse key ice shelves which are essentially at sea level, thus for a MICI-type of collapse surface temperatures only need to be above freezing (in the Austral Summer) at sea level in order to generate sufficient surface meltwater to cause hydrofracturing of the key WAIS ice shelves.

The linked reference clearly states the consensus climate science position (i.e.: "Climate change scientists should instead communicate and engage with policy makers (and the public) on those things that we know with confidence.") that I strongly object to, and which I believe contributes to greater climate change risk.  This consensus climate science position empowered climate skeptics to define what is acceptable to communicate to both policy makers and the public, which is not only bad science but also a very bad idea:

Nafees Meah (2019), "Climate uncertainty and policy making—what do policy makers want to know?", Regional Environmental Change, pp 1–11, DOI:

Abstract: "In climate change science, the existence of a high degree of uncertainty seems to be the cause of anxiety for many scientists because it appears to undermine the authority of the science. One of the assertions made by the so-called sceptics against the scientific consensus on climate change is that because the science is so uncertain, there is no basis for taking action. The response of the climate change science community has been to develop in-depth analyses of uncertainty of increasing sophistication and complexity. In most areas of policy making, the normal situation is characterised by complexity, ambiguity and uncertainty. Therefore, dealing with uncertainty is not an unusual state of affairs for policy makers. However, the overemphasis given to uncertainty in the climate science discourse by scientists working in the field has been self-defeating as it has led to confusion among the intended recipients of the policy relevant scientific knowledge and allowed room for scepticism to grow. Climate change scientists should instead communicate and engage with policy makers (and the public) on those things that we know with confidence."

Consensus climate science (e.g. WGI) has deemphasized communication of climate risk assessments to both decision makers and to the public (see the linked open source reference).  If consensus scientists think that risk assessment is not part of science, then they should either change their way of thinking or find another profession:

Rowan T. Sutton (23 April 2019), "Climate science needs to take risk assessment much more seriously", BAMS,

Abstract: "For decision makers, climate change is a problem in risk assessment and risk management. It is, therefore, surprising that the needs and lessons of risk assessment have not featured more centrally in the consideration of priorities for physical climate science research, or in the Working Group I contributions to the major Assessment Reports of the Intergovernmental Panel on Climate Change. This article considers the reasons, which include a widespread view that the job of physical climate science is to provide predictions and projections - with a focus on likelihood rather than risk - and that risk assessment is a job for others. This view, it is argued, is incorrect. There is an urgent need for physical climate science to take the needs of risk assessment much more seriously. The challenge of meeting this need has important implications for priorities in climate research, climate modelling and climate assessments."

The linked reference indicates that ice mass loss has increased sixfold from the 1980s until 2018; this is significantly more than recognized previously by consensus climate science

Jérémie Mouginot, Eric Rignot, Anders A. Bjørk, Michiel van den Broeke, Romain Millan, Mathieu Morlighem, Brice Noël, Bernd Scheuchl, and Michael Wood (April 22, 2019), "Forty-six years of Greenland Ice Sheet mass balance from 1972 to 2018", PNAS,


We reconstruct the mass balance of the Greenland Ice Sheet for the past 46 years by comparing glacier ice discharge into the ocean with interior accumulation of snowfall from regional atmospheric climate models over 260 drainage basins. The mass balance started to deviate from its natural range of variability in the 1980s. The mass loss has increased sixfold since the 1980s. Greenland has raised sea level by 13.7 mm since 1972, half during the last 8 years.

We reconstruct the mass balance of the Greenland Ice Sheet using a comprehensive survey of thickness, surface elevation, velocity, and surface mass balance (SMB) of 260 glaciers from 1972 to 2018. We calculate mass discharge, D, into the ocean directly for 107 glaciers (85% of D) and indirectly for 110 glaciers (15%) using velocity-scaled reference fluxes. The decadal mass balance switched from a mass gain of +47 ± 21 Gt/y in 1972–1980 to a loss of 51 ± 17 Gt/y in 1980–1990. The mass loss increased from 41 ± 17 Gt/y in 1990–2000, to 187 ± 17 Gt/y in 2000–2010, to 286 ± 20 Gt/y in 2010–2018, or sixfold since the 1980s, or 80 ± 6 Gt/y per decade, on average. The acceleration in mass loss switched from positive in 2000–2010 to negative in 2010–2018 due to a series of cold summers, which illustrates the difficulty of extrapolating short records into longer-term trends. Cumulated since 1972, the largest contributions to global sea level rise are from northwest (4.4 ± 0.2 mm), southeast (3.0 ± 0.3 mm), and central west (2.0 ± 0.2 mm) Greenland, with a total 13.7 ± 1.1 mm for the ice sheet. The mass loss is controlled at 66 ± 8% by glacier dynamics (9.1 mm) and 34 ± 8% by SMB (4.6 mm). Even in years of high SMB, enhanced glacier discharge has remained sufficiently high above equilibrium to maintain an annual mass loss every year since 1998.

Edit, the attached image provides specific numbers for the ice mass loss in Greenland from 1972 to 2018:

Caption: "Cumulative anomalies in SMB (blue), discharge (D, red), and mass (M, purple) in gigatons (gigaton = 10121012 kg) for the time period 1972–2018 for the seven regions of Greenland and the entire ice sheet component: (A) SW, (B) CW, (C) NW, (D) NO, (E) NE, (F) DE, (G) SE, and (H) GIS."

The linked reference projects an increase in methane emissions from lakes and impoundments equal to 18 to 33% of annual anthropogenic CO₂ emissions by 2100.  This is not good.

Jake J. Beaulieu, Tonya Del Sontro & John A. Downing (2019), "Eutrophication will increase methane emissions from lakes and impoundments during the 21st century", Nature Communications, volume 10, Article number: 1375,

Abstract: "Lakes and impoundments are an important source of methane (CH4), a potent greenhouse gas, to the atmosphere. A recent analysis shows aquatic productivity (i.e., eutrophication) is an important driver of CH4 emissions from lentic waters. Considering that aquatic productivity will increase over the next century due to climate change and a growing human population, a concomitant increase in aquatic CH4 emissions may occur. We simulate the eutrophication of lentic waters under scenarios of future nutrient loading to inland waters and show that enhanced eutrophication of lakes and impoundments will substantially increase CH4 emissions from these systems (+30–90%) over the next century. This increased CH4 emission has an atmospheric impact of 1.7–2.6 Pg C-CO2-eq y−1, which is equivalent to 18–33% of annual CO2 emissions from burning fossil fuels. Thus, it is not only important to limit eutrophication to preserve fragile water supplies, but also to avoid acceleration of climate change."

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