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Messages - AbruptSLR

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I have not had time to review the linked reference, so I am just posting here without comment:

Qin Wen and Jie Yao (2018), "Decoding Hosing and Heating Effects on Global Temperature and Meridional Circulations in a Warming Climate", Journal of Climate,


I have now reviewed Wen et al (2018), and perhaps I am over reacting to the fact that several media reports that I saw headlined the finding that: '… freshwater change has a significant cooling effect that can mitigate the global surface warming by as much as ~30%. … In terms of global temperature and Earth’s energy balance, the freshwater change plays a stabilizing role in a warming climate.'.  Nevertheless, I first note that 'All models are wrong, but some models are useful', and I offer the following comments about the following extracts and first two images from Wen et al (2018), as related to the following three linked references:

1. The extract and the second linked reference shows that the authors used an older version of CESM that has been superseded since June 2018 by a version with many improvements/corrections including improved subroutines for ice sheet behavior and for cloud feedback, which are both important when talking about 'Decoding Hosing and Heating Effects on Global Temperature and Meridional Circulations in a Warming Climate'.

2. The first two images make it clear that the authors' model considers a relatively slow rate of ice mass loss from the GIS and the AIS over many hundreds of years, and thus clearly does not consider abrupt ice mass loss such as that induced by ice-cliff failures and/or hydrofracturing.  Thus, the estimated 30% reduction in global warming occurs over a 2,000 year period, while Hansen et al (2016)'s larger reduction in global warming occurs over several decades and then this cooling dissipates in subsequent decades.  Furthermore, Wen et al (2018)'s findings that freshwater hosing stabilizes the Earth's energy balances is likely similarly related to the hosing scenario that they assume [which is radically less dynamic than that of Hansen et al (2016)].

3. Wen et al. (2018) acknowledge that they only consider two feedback mechanisms (i.e. the long wave and short wave radiation due to surface temperature and the impacts on the MOC) of the may involved in the net ice-climate feedback mechanism. and they ignore other such hosing feedback mechanisms as the influence of: '… the wind-driven circulations and subduction in the midlatitudes, the intermediate water formation in the subpolar Antarctic, and the atmospheric monsoon system? How are climate variabilities, such as El Niño–Southern Oscillation, the Pacific decadal oscillation, and the Atlantic multidecadal oscillation, modulated by freshwater change and radiation forcing?'. In this regards the authors' findings would have more meaning if they had bothered to calibrate their models response to match paleo data [see the third linked reference, Maier et al (2018)], as E3SM has done and I note that CESM 2.0 (which superseded the version used by the authors) adopted many of the calibrations identified by E3SM.

4. The authors define numerous terms that are consistent within the reference (and thus acceptable in peer review), but that differ from common usage, e.g.: their definition of 'sea ice' includes marine glacial ice.

5. I could go on with my critiques but leave it to say that within the author's limited set of assumptions their work appears to be consistent with other CMIP5 era of projections, but in my option they fall behind the CMIP6 level of sophistication, so I look forward to seeing the CMIP6 (and AR6) findings for freshwater hosing impact (while noting that none of them are currently considering ice-cliff failures nor hydrofracting of ice sheets).

Extract: "The hosing effect, in this work, refers to ocean freshwater flux change, which can directly change ocean salinity (Durack and Wijffels 2010) and thus upper-ocean buoyancy, affecting mainly the thermohaline circulation and thus the oceanic heat transport (OHT) (Swingedouw et al. 2007, 2009; Yang et al. 2013, 2017).

In this study, the heating and hosing effects are separated in a coupled climate model through two groups of global warming experiments. It is shown that the freshwater change has a significant cooling effect that can mitigate the global surface warming by as much as ~30%. Two significant regional cooling centers appear: one in the subpolar Atlantic and one in the Southern Ocean; both are triggered by sea ice melting but are sustained by different mechanisms. The subpolar Atlantic cooling is maintained by the weakened AMOC in the NH, while the Southern Ocean surface cooling is maintained by the enhanced northward Ekman flow related to strengthened westerly wind (Ferreira et al. 2015; Kostov et al. 2017). In these two regions, the effect of freshwater flux change dominates over that of radiation flux change, controlling the SST change in the warming climate.

The model used in this study is the Community Earth System Model (CESM) of the National Center for Atmospheric Research (NCAR), which was used in our previous studies (e.g., Dai et al. 2017). CESM is a fully coupled global climate model that provides state-of-the-art simulations of Earth’s past, present, and future climate states ( CESM (version 1.0) consists of five components and one coupler: The Community Atmosphere Model, version 5 (CAM5; Park et al. 2014); the Community Land Model, version 4 (CLM4; Lawrence et al. 2012); the Community Ice Code, version 4 (CICE4; Hunke and Lipscomb 2008); the Parallel Ocean Program, version 2 (POP2; Smith et al. 2010); the Community Ice Sheet Model (Glimmer-CISM); and the CESM coupler, version 7 (CPL7). CESM1.0 is widely used and validated by researchers in the community.

This work is the first step toward quantifying the individual contributions of the heating and hosing effects to an evolving climate. Only the surface temperature and large-scale circulations are examined in this paper. Many other aspects have not been considered in the present study. For example, how do the hosing effect and the heating effect influence the wind-driven circulations and subduction in the midlatitudes, the intermediate water formation in the subpolar Antarctic, and the atmospheric monsoon system? How are climate variabilities, such as El Niño–Southern Oscillation, the Pacific decadal oscillation, and the Atlantic multidecadal oscillation, modulated by freshwater change and radiation forcing? It should be recognized that climate models have many limitations and that a climate shift in the model experiments may also exist. Many questions remain about the roles of the hydrological cycle in global change."

Caption for the first image: "FIG. 1. (a) Temporal evolutions of globally integrated net radiative flux (black), net downward SW (blue), and outgoing LW (red) at TOA (PW; positive for downward anomaly) under 2CO2 forcing. The red line at the top denotes the CO2 forcing. (b),(c) As in (a), but showing the hosing effect and heating effect, respectively. Each curve is smoothed with a 20-yr running mean. (d) Radiative flux change at the TOA in stage I of global warming, with net radiative flux (black), SW (blue), and LW (red). Stage I spans the years 200–500. (e),(f) As in (d), but showing the hosing effect and heating effect, respectively."

Caption for the second image: "FIG. 2. Temporal evolutions of (a)–(c) SST (thick solid curves) and SAT (thin dashed curves) averaged over the globe (black), NH (red), and SH (blue) (°C); (d)–(f) percentage changes of the AMOC (black), the Indo-Pacific STC (blue), and HC (red; %); and (g)–(i) AHT (red), global OHT (blue), Atlantic OHT (green), and Indo-Pacific OHT (light blue) averaged over 30°–70°N (PW). The AMOC index is defined as the maximum of the streamfunction in the range of 0°–10°C isotherms over 20°–70°N in the Atlantic. The Indo-Pacific STC is similarly defined, but in the range of 20°–30°C isotherms over 0°–30°N. The HC index is defined as the maximum streamfunction between 200 and 1000 hPa over 0°–30°N. All indexes are normalized by their time-mean values in CTRL, which are 18, 36, and 92 Sv, respectively (1 Sv = 106 m3 s−1 for the ocean; 1 Sv = 109 kg s−1 for the atmosphere). Each curve is smoothed with a 20-yr running mean. Stage I spans the years 200–500 and represents an earlier quasi-equilibrium stage of global warming, based on the AMOC evolution. Stage II spans the years 800–1100 and represents the recovery stage of the AMOC. Stage III spans the years 1700–2000 and represents the equilibrium stage of global warming for (a),(d),(g) 2CO2 forcing; (b),(e),(h) hosing effect; and (c),(f),(i) heating effect."

See also:

Qianzi Yang et al. (2018), "Understanding Bjerknes Compensation in Meridional Heat Transports and the Role of Freshwater in a Warming Climate", Journal of Climate,

Abstract: "The Bjerknes compensation (BJC) under global warming is studied using a simple box model and a coupled Earth system model. The BJC states the out-of-phase changes in the meridional atmosphere and ocean heat transports. Results suggest that the BJC can occur during the transient period of global warming. During the transient period, the sea ice melting in the high latitudes can cause a significant weakening of the Atlantic meridional overturning circulation (AMOC), resulting in a cooling in the North Atlantic. The meridional contrast of sea surface temperature would be enhanced, and this can eventually enhance the Hadley cell and storm-track activities in the Northern Hemisphere. Accompanied by changes in both ocean and atmosphere circulations, the northward ocean heat transport in the Atlantic is decreased while the northward atmosphere heat transport is increased, and the BJC occurs in the Northern Hemisphere. Once the freshwater influx into the North Atlantic Ocean stops, or the ocean even loses freshwater because of strong heating in the high latitudes, the AMOC would recover. Both the atmosphere and ocean heat transports would be enhanced, and they can eventually recover to the state of the control run, leading to the BJC to become invalid. The above processes are clearly demonstrated in the coupled model CO2 experiment. Since it is difficult to separate the freshwater effect from the heating effect in the coupled model, a simple box model is used to understand the BJC mechanism and freshwater’s role under global warming. In a warming climate, the freshwater flux into the ocean can cool the global surface temperature, mitigating the temperature rise. Box model experiments indicate clearly that it is the freshwater flux into the North Atlantic that causes out-of-phase changes in the atmosphere and ocean heat transports, which eventually plays a stabilizing role in global climate change."

Title: "CESM - Community Earth System Model"

Extract: "Subsequently, a major milestone was the long-waited, community release of the CESM version 2.0, CESM2.0, in early June 2018. This new version contains many substantial science and infrastructure improvements and capabilities for use of the broader CESM and international community. These new advancements include: an atmospheric model component that incorporates significant improvements to its turbulence and convection representations, opening the way for an analysis of how these small-scale processes can impact the climate; improved ability to simulate modes of tropical variability that can span seasons and affect global weather patterns; a land ice sheet model component for Greenland that can simulate the complex way the ice sheet moves – sluggish in the middle and much more quickly near the coast – and does a better job of simulating calving of the ice into the ocean; …

AMWG CSL resources were used to address a serious defect, i.e., cooling of the global mean surface temperatures over the mid- to late 20th century, that appeared in CESM2 with the introduction of CMIP6 emissions data. A number of explanations were considered for this behavior. Studies of cloud properties influenced by volcanic sulfate emissions (Malavelle et al. 2017) suggested that CAM6 microphysics may be overestimating the 2nd indirect aerosol effect (the ‘lifetime’ effect). The lifetime effect is essentially a consequence of a droplet number effect on auto conversion rates that goes as ~ N− where N is the cloud droplet number concentration, which is directly related to aerosol concentrations. As the exponent  becomes larger, auto conversion rates become slower so that “dirtier” air leads to longer lived cloud. Removing the N dependence altogether, i.e., =0, appeared to resolve the cooling. However, this is not considered a physically plausible option. Extensive experimentation with alternate formulations of the auto conversion dependence on N was conducted. A compromise formulation with =1.1 similar to that used in DOE’s E3SM was adopted."

E. Maier et al. (2018), "North Pacific freshwater events linked to changes in glacial ocean circulation", Nature, Vol. 559,

Abstract: "There is compelling evidence that episodic deposition of large volumes of freshwater into the oceans strongly influenced global ocean circulation and climate variability during glacial periods. In the North Atlantic region, episodes of massive freshwater discharge to the North Atlantic Ocean were related to distinct cold periods known as Heinrich Stadials. By contrast, the freshwater history of the North Pacific region remains unclear, giving rise to persistent debates about the existence and possible magnitude of climate links between the North Pacific and North Atlantic oceans during Heinrich Stadials4,5. Here we find that there was a strong connection between changes in North Atlantic circulation during Heinrich Stadials and injections of freshwater from the North American Cordilleran Ice Sheet to the northeastern North Pacific. Our record of diatom δ18O (a measure of the ratio of the stable oxygen isotopes 18O and 16O) over the past 50,000 years shows a decrease in surface seawater δ18O of two to three per thousand, corresponding to a decline in salinity of roughly two to four practical salinity units. This coincided with enhanced deposition of ice-rafted debris and a slight cooling of the sea surface in the northeastern North Pacific during Heinrich Stadials 1 and 4, but not during Heinrich Stadial 3. Furthermore, results from our isotope-enabled model suggest that warming of the eastern Equatorial Pacific during Heinrich Stadials was crucial for transmitting the North Atlantic signal to the northeastern North Pacific, where the associated subsurface warming resulted in a discernible freshwater discharge from the Cordilleran Ice Sheet during Heinrich Stadials 1 and 4. However, enhanced background cooling across the northern high latitudes during Heinrich Stadial 3—the coldest period in the past 50,000 years—prevented subsurface warming of the northeastern North Pacific and thus increased freshwater discharge from the Cordilleran Ice Sheet. In combination, our results show that nonlinear ocean– atmosphere background interactions played a complex role in the dynamics linking the freshwater discharge responses of the North Atlantic and North Pacific during glacial periods."

Extract: "The results of our data–model comparison provide compelling evidence that, during North Atlantic cold stadials characterizing the past 50,000 years, perturbations to the AMOC could have been teleconnected to the northeastern North Pacific region, triggering freshwater discharge events via interactions between low and high latitudes and between oceans and the atmosphere. Until now, such North Pacific freshwater input events have not been considered as standard forcing components in glacial climate simulations; the incorporation of this freshwater forcing scenario provides a new basis for research that could reconcile the discrepancies within proxy data regarding the responses of North Pacific ocean circulation to AMOC changes."

Caption for the third image: "Fig. 2 | Proxy data from the North Pacific and North Atlantic (50 kyr to 5 kyr bp). a–f, Data from northeastern North Pacific core SO202-27-6 (in b, e and f, data for the past 25 kyr bp are from ref. 12). a, Ice-rafted debris. b, δ18Odiat. data; error bars show the errors of replicate analyses or the long-term reproducibility of standards (1σ). c, Surface δ18Osw; dark grey and light grey envelopes show 68% and 95% confidence intervals, respectively. d, Sea-surface salinity calculated from surface δ18Osw; green envelopes show 95% confidence intervals, assuming a CIS meltwater δ18O of −20‰ (light green) or −30‰ (dark green). e, Subsurface δ18Opl.foram. data from sinistral N. pachyderma. f, Alkenone-based SSTs. g, Alkenone-based (solid line) and magnesium/calcium-based (dashed line) SSTs (from the eastern Equatorial Pacific, core MD02-2529; ref. 25). h, Sediment total reflectance (from the Cariaco Basin; ref. 24). L*, lightness; sm200, 200-point running mean. i, 231Pa/230Th ratio (Ocean Drilling Program (ODP) site 1063; ref. 3). j, NGRIP δ18O record7. EEP, eastern Equatorial Pacific; HS, Heinrich Stadial; ITCZ, Intertropical Convergence Zone. Arrows indicate the direction of proxy changes during Heinrich Stadials 1, 3 and 4."

The first image shows the Antarctic Bedmap with the ice instantly removed, while the second image shows the Antarctic Bedmap with the ice removed and all associated isostatic rebound recovered.  Also, the dotted lines on the five cross-sections thru the WAIS on the third image shows the hundreds of meters of rebound that would be recovered if the WAIS were to abruptly collapse.  This much rebound would certainly contribute to an increase in local seismic and volcanic activity.

Edit: For a plan view of the candidate seaways proposed by Vaughan in the third image, see Reply #328

The attached image is from the linked open access reference & provides background information relevant to different possible definitions for the Anthropocene.  This image implies that without anthropogenic radiative forcing Earth would now be headed for another glacial period; and I wonder whether this temperature trend may also act as yet another factor masking a relatively high value of ECS; also I wonder whether the upward tend of atmospheric methane concentration since 5,000 years ago, makes the Anthropocene's radiative forcing signature much different than past interglacial periods such as that for the Mid-Pliocene.

Lewis, S. L.; Maslin, M. A. (12 March 2015). "Defining the Anthropocene". Nature 519: 171–180. doi:10.1038/nature14258


Considering that you frequently talk about the importance of ENSO events to the pace of Antarctic melt, I thought I should post this new paper (out yesterday) here:

Increased variability of eastern Pacific El Niño under greenhouse warming Wenju Cai, Guojian Wang, Boris Dewitte, Lixin Wu, Agus Santoso, Ken Takahashi, Yun Yang, Aude Carréric & Michael J. McPhaden

This is an indication of both increasingly high values of ECS and of increasingly high levels of telecommunication of energy from the Tropical Pacific directly to West Antarctica.

With regards to my last post, some readers may wonder what Steffen et al (2018) mean by 'Hothouse' conditions (as opposed to Pliocene or Miocene conditions).  Generally, 'Hothouse' conditions can be taken as Early Eocene Climatic Optimum (EECO; ∼52–50 Ma) conditions as discussed in the linked reference Evans et al. (2018) and the associated attached images.  Note that as the reference demonstrates that no current ESM (including FAMOUS which has been tailored for the EECO) can accurately project the full extent of Polar Amplification during the EECO; this means that if we keep following SSP5-Baseline long enough to reach atmospheric CO₂ concentrations around 560 ppm, then depending on the history of our climate change momentum, the Earth's climate could flip into an equable conditions (characterized by warm poles):

David Evans, Navjit Sagoo, Willem Renema, Laura J. Cotton, Wolfgang Müller, Jonathan A. Todd, Pratul Kumar Saraswati, Peter Stassen, Martin Ziegler, Paul N. Pearson, Paul J. Valdes, and Hagit P. Affek (January 22, 2018), "Eocene greenhouse climate revealed by coupled clumped isotope-Mg/Ca thermometry", PNAS February 6, 2018 115 (6) 1174-1179;

Reconstructing the degree of warming during geological periods of elevated CO2 provides a way of testing our understanding of the Earth system and the accuracy of climate models. We present accurate estimates of tropical sea-surface temperatures (SST) and seawater chemistry during the Eocene (56–34 Ma before present, CO2 >560 ppm). This latter dataset enables us to reinterpret a large amount of existing proxy data. We find that tropical SST are characterized by a modest warming in response to CO2. Coupling these data to a conservative estimate of high-latitude warming demonstrates that most climate simulations do not capture the degree of Eocene polar amplification.


Past greenhouse periods with elevated atmospheric CO2 were characterized by globally warmer sea-surface temperatures (SST). However, the extent to which the high latitudes warmed to a greater degree than the tropics (polar amplification) remains poorly constrained, in particular because there are only a few temperature reconstructions from the tropics. Consequently, the relationship between increased CO2, the degree of tropical warming, and the resulting latitudinal SST gradient is not well known. Here, we present coupled clumped isotope (Δ47)-Mg/Ca measurements of foraminifera from a set of globally distributed sites in the tropics and midlatitudes. Δ47 is insensitive to seawater chemistry and therefore provides a robust constraint on tropical SST. Crucially, coupling these data with Mg/Ca measurements allows the precise reconstruction of Mg/Casw throughout the Eocene, enabling the reinterpretation of all planktonic foraminifera Mg/Ca data. The combined dataset constrains the range in Eocene tropical SST to 30–36 °C (from sites in all basins). We compare these accurate tropical SST to deep-ocean temperatures, serving as a minimum constraint on high-latitude SST. This results in a robust conservative reconstruction of the early Eocene latitudinal gradient, which was reduced by at least 32 ± 10% compared with present day, demonstrating greater polar amplification than captured by most climate models.

Caption for second image: "Fig. 2 Seawater Mg/Ca reconstruction for the Eocene and early Oligocene based on coupled Δ47-Mg/Ca LBF and ridge-flank CaCO3 vein (CCV) data, shown in the context of previous Cenozoic reconstructions (33, 34, 56, 57) and box models (refs. 35, 36, and 58; WA89, SH98, and HS15, respectively), that are commonly used for calculating planktonic and deep-benthic foraminifera Mg/Ca data. Coral-derived data younger than 20 Ma are omitted. The 95% confidence intervals on our Eocene Mg/Casw curve are derived from bootstrapping 1,000 locally weighted scatterplot smoothing (LOWESS) fits, including both geochemical and dating uncertainties."

Caption for third image: "Fig. 5. Early Eocene (48–56 Ma) model-data comparison. (A) Zonally averaged latitudinal gradients based on proxy CO2 and SST data (gray box) and climate models over a range of CO2 (circles) (12, 46–48, 60). Proxy CO2 range is from ref. 1; the gradient uncertainty is the combined 2 SE of the tropical and high-latitude proxy data (see text). Proxy-derived gradient is shown relative to present day; Eocene climate model simulations are shown relative to their preindustrial counterpart. Most model simulations do not capture the reduced latitudinal gradient within the range of proxy CO2 (<2,250 ppm). (B) Site-specific model-data comparison for both the tropics and high latitudes. Model SST competency assessed by comparing the mean difference between the model and proxy data for low and high latitudes. Quadrants reflect different overall patterns of model-data offset. Hypothetical simulations falling on the 1:1 line would reconstruct the same latitudinal gradient as the data but not the same absolute SST, except at the origin. All models fall below this line, indicating that Eocene polar amplification is underestimated."

I note that I remember four different definitions of pre-industrial in AR5, while the summary declines to specify which definition policy makers should follow.  Furthermore, the linked reference indicates that the proper definition of the pre-industrial baseline could add up to +0.2C to IPCC projections of GMSTA; while the Paris Accord has declined to adopt Schurer et al. (2017)'s proposed definition.

Schurer et al (2017), "Importance of the pre-industrial baseline for likelihood of exceeding Paris goals", Nature Climate Change 7, 563-567, doi:10.1038/nclimate3345

Abstract: "During the Paris conference in 2015, nations of the world strengthened the United Nations Framework Convention on Climate Change by agreeing to holding ‘the increase in the global average temperature to well below 2◦C above pre-industrial levels and pursuing efforts to limit the temperature increase to 1.5◦C’ (ref. 1). However, ‘pre-industrial’ was not defined. Here we investigate the implications of different choices of the pre-industrial baseline on the likelihood of exceeding these two temperature thresholds. We find that for the strongest mitigation scenario RCP2.6 and a medium scenario RCP4.5, the probability of exceeding the thresholds and timing of exceedance is highly dependent on the pre-industrial baseline; for example, the probability of crossing 1.5◦C by the end of the century under RCP2.6 varies from 61% to88% depending on how the baseline is defined. In contrast, in the scenario with no mitigation, RCP8.5, both thresholds will almost certainly be exceeded by the middle of the century with the definition of the pre-industrial baseline of less importance. Allowable carbon emissions for threshold stabilization are similarly highly dependent on the pre-industrial baseline. For stabilization at 2◦C, allowable emissions decrease by as much as 40% when earlier than nineteenth-century climates are considered as a baseline."
Extract: "In total, spatially complete blended global temperatures from 23 simulations, from 7 different models, were analysed with the means of each model for the period 1401–1800 found to be cooler than the late-nineteenth-century baseline (1850–1900) by 0.03◦C to 0.19◦C (multi-model mean of 0.09◦C, Fig.2b). In these simulations, and in temperature reconstructions of the past millennium, there is considerable centennial variability. Some periods, such as the sixteenth century, are of comparable warmth to the late nineteenth century, while other periods have a multi-model mean nearly 0.2◦C cooler."

Caption of attached image: "Figure2 | Model-simulated difference in global mean temperature between different pre-industrial periods and 1850–1900. a, Range of ensemble means for different models, and for different forcing combinations. Model distribution fitted with a kernel density estimate (violin plot)—red, all forcings combined; green, greenhouse gas forcing alone; blue, volcanic forcing alone; yellow, solar forcing alone. Model mean: circle; 10–90% model range: bar. Differences refer to the mean of the period enclosed by the dashed lines; except on the far right, where they are means for the full period 1401–1800 (relative to 1850–1900). b–e, Model means for different forcing combinations—colours, ensemble means for individual models; black line, mean over all models."

Obviously, such definitions matter when we are trying to decide by which decade we have approached Mid-Pliocene conditions, and can also impact estimates of ECS.

As anthropogenic forcing is the largest source of climate change, one of the 'Deepest Uncertainties' is whether decision makers will accept that the probability of near-term abrupt climate change is serious enough to do something effective about it.  In this regard, I provide the attached image from the linked article that indicates that scientific education about climate change is insufficient to prevent tribalism among conservatives, but rather it takes 'science curiosity' to be open-minded enough to accept this risk.  It is not clear to me that decision makers exhibit sufficient 'science curiosity' to avoid ice-climate induced abrupt climate change in the coming decades:

Title: "Why Smart People Are Vulnerable to Putting Tribe Before Truth" by Dan Kahan, SciAm 2018.

Extract: "Science literacy is important, but without the parallel trait of 'science curiosity," it can lead us astray."

First, I note that a jökulhlaup is a glacial outburst of meltwater, and the first linked article demonstrates that with Antarctic subglacial lakes and drainage systems such event can be regulated by the nature of pressure waves passing through the system over multiple years; and that the pressures associated with such waves can regulate the glacial ice flow velocities.

C. F. Dow et al. (22 March 2018), "Dynamics of Active Subglacial Lakes in Recovery Ice Stream", JGR Earth Surface,

Recovery Ice Stream has a substantial number of active subglacial lakes that are observed, with satellite altimetry, to grow and drain over multiple years. These lakes store and release water that could be important for controlling the velocity of the ice stream. We apply a subglacial hydrology model to analyze lake growth and drainage characteristics together with the simultaneous development of the ice stream hydrological network. Our outputs produce a good match between modeled lake location and those identified using satellite altimetry for many of the lakes. The modeled subglacial system demonstrates development of pressure waves that initiate at the ice stream neck and transit to within 100 km of the terminus. These waves alter the hydraulic potential of the ice stream and encourage growth and drainage of the subglacial lakes. Lake drainage can cause large R‐channels to develop between basal overdeepenings that persist for multiple years. The pressure waves, along with lake growth and drainage rates, do not identically repeat over multiple years due to basal network development. This suggests that the subglacial hydrology of Recovery Ice Stream is influenced by regional drainage development on the scale of hundreds of kilometers rather than local conditions over tens of kilometers.

Plain Language Summary
Ice streams are fast‐flowing areas of the Antarctic ice sheet that drain large quantities of ice into the ocean, contributing to sea level rise. We have run a model of water flow underneath Recovery Ice Stream to examine lakes that build up and drain underneath kilometers of ice to find out whether they have an impact on the speed of the overlying ice. We find that the timing of the lake growth and drainage is determined by the hydrological conditions underneath the entirety of the ice stream, stretching over hundreds of kilometers. As the lakes drain, they melt channels that connect as sub‐ice rivers between the drainage basins. We also find that the regions of highest water pressure, and therefore the fastest‐moving overlying ice, are concentrated in the deepest parts of the trough that the ice stream flows through. This is an important finding for determining the controls on fast ice stream flow speed and therefore the stability of the Antarctic ice sheet.

Extract: "Antarctic subglacial lakes have been modeled within synthetic ice dynamics models (Pattyn, 2008; Sergienko et al., 2007) and as basins that are filled and drained by tuning with satellite altimetry data (Carter & Fricker, 2012; Carter et al., 2009, 2011). Recent work by Carter et al. (2017) suggests that Antarctic lake dynamics cannot be influenced by the formation of Röthlisberger (R-) channels that melt upward into the ice, instead arguing that sediment canals are necessary to allow lake drainage. These treatments of Antarctic subglacial lakes are different from those models that examine ice marginal lake outburst floods or subglacial jökulhlaups, where rapid (on the scale of days to weeks) drainage occurs. Models examining the latter focus on the water pressure allowing ice uplift and downstream lake drainage (e.g., Ng & Liu, 2009; Nye, 1976) or negative pressure gradients that prevent outflow of the lakes until they are reversed by hydrological development (e.g., Evatt et al., 2006; Fowler, 1999; Kingslake, 2015). In contrast, the active Antarctic subglacial lakes differ because they drain over a timescale of years and can become much larger (>10km2), although often shallower (e.g., <10m deep) than ice marginal or jökulhlaup lakes. The work of Dow et al. (2016) found that at no time were hydraulic pressure gradients reversed when applying a synthetic hydrology model to Antarctic lakes. Instead, lake dynamics were driven by spatially and temporally varying conductivity of the basal drainage system including the growth of R-channels that drained the lake. The Dow et al. (2016) study applied a synthetic, planar topography with one overdeepening, designed to emulate Recovery Ice Stream. However, until now, a 2-D approach to catchment-scale hydrology modeling with Antarctic topography including multiple lake basins has not been attempted.

This suggests that the water pressure plays a more important role in the ice stream velocity than the water thickness, which as we demonstrate with our model outputs is not always coincident with water pressure, either spatially or temporally."

Next, I note that the first two attached images are from the second linked reference, and they show the extensive subglacial lake and meltwater drainage systems in Antarctica (with increasing warming these systems should become more extensive and important in the future):

S. J. Livingstone, C. D. Clark, and J. Woodward (2013), "Predicting subglacial lakes and meltwater drainage pathways beneath the Antarctic and Greenland ice sheets", The Cryosphere Discuss., 7, 1177–1213,, doi:10.5194/tcd-7-1177-2013

The caption for the first image is: "In (B), the blue colour illustrates regions below the pressure melting point. This is used as a simple mask to remove all subglacial lakes that fall within the cold-bedded zones. Note, the subglacial drainage network is still treated as though the bed was wholly warm based."

The caption for the second image is:  "(B) the fraction of the grounded ice-sheet bed occupied by subglacial lakes vs ice-sheet area, with both the Antarctic and Greenland subglacial lake data plotted."

Next, the following link leads to findings presented at the AGU 2013 conference about new evidence characterizing the nature of the subglacial hydrological system in Antarctica:

In the third attached image, the red dots mark surface changes that scientists think are caused by water moving beneath Antarctica's ice. The blue and magenta colors indicate ice velocity, with the magenta showing the fastest-moving ice.

Finally, the following linked reference by Bell discusses the importance of correctly modeling the influence of subglacial hydrology on ice mass loss from AIS:

Robin E. Bell (2008), "The role of subglacial water in ice-sheet mass balance", Nature Geoscience, doi:10.1038/ngeo186

Abstract: "In the coming decades, significant changes in the polar regions will increase the contribution of ice sheets to global sea-level rise. Under the ice streams and outlet glaciers that deliver ice to the oceans, water and deformable wet sediments lubricate the base, facilitating fast ice flow. The influence of subglacial water on fast ice flow depends on the geometry and capacity of the subglacial hydrologic system: water moving rapidly through a well-connected system of conduits or channels will have little impact on ice-sheet velocities, but water injected into a spatially dispersed subglacial system may reduce the effective pressure at the base of the ice sheet, and thereby trigger increased ice-sheet velocities. In Greenland, the form of the subglacial hydrologic system encountered by increasing surface melt water will determine the influence of changing atmospheric conditions on ice-sheet mass balance. In Antarctica, subglacial lakes have the capacity to both modulate velocities in ice streams and outlet glaciers and provide nucleation points for new fast ice-flow tributaries. Climate models of ice-sheet responses to global change remain incomplete without a parameterization of subglacial hydrodynamics and ice dynamics."

The linked refence works to try to explain why the surface temperatures for the Early Pliocene was so much warmer than for the Mid-Pliocene, and points to this nonlinear saddlenode bifurcation being associated with primarily Arctic Amplification but also probably due to both increased El Nino frequency and an expanded Hadley Cell (see the first image).  As I have previously noted that ice-climate feedback from a collapse of the WAIS would contribute to all three (Arctic Amplification, more frequent El Nino events and an expanded Hadley Cell); it is possible/probable that as early as 2060 Earth could be in conditions comparable to the Early Pliocene (with GMSTA up to +3.6C) even if we stop following SSP5-Baseline after 2035.  To emphasize this point I repost the second image of how such a bifurcation can lead to an abrupt change in climate state (due to a tipping perturbation such as abrupt ice mass loss from the WAIS).  Also as precaution, I note that Energy Balance Models are associated with inferred climate sensitivity which is lower than true climate sensitivity as shown in the third image.

Brady Dortmans et al. (2018), "An Energy Balance Model for Paleoclimate Transitions', Clim. Past Discuss.,

Abstract. A new energy balance model (EBM) is presented and is used to study Paleoclimate transitions. While most previous EBMs dealt only with the globally averaged climate, this new EBM has three variants: Arctic, Antarctic and Tropical climates. This EBM incorporates the greenhouse warming effects of both carbon dioxide and water vapour, and also includes ice-albedo feedback. The main conclusion to be drawn from the EBM is that the climate system possesses multiple equilibrium states, both warm and frozen, which coexist mathematically. 5 While the actual climate can exist in only one of these states at any given time, the climate can undergo transitions between the states, via mathematical saddlenode bifurcations. This paper proposes that such bifurcations have actually occurred in Paleoclimate transitions. The EBM is applied to the study of the Pliocene Paradox, the Glaciation of Antarctica and the so-called warm, equable climate problem of both the mid-Cretaceous Period and the Eocene Epoch. In all cases, the EBM is in qualitative agreement with the geological record.

Extract: "During the early Pliocene Epoch, 3–5 Ma, the climate of the Arctic region of Earth changed abruptly from ice-free to ice-capped. The climate forcing factors then (solar constant, orbital parameters, CO2 concentration and locations of the continents) were all very similar to today. Therefore, it is difficult to explain why the early Pliocene climate was so different from that of today. That problem is known as the Pliocene Paradox, (Cronin (2010); Fedorov et al. (2006, 2010)). This paper presents a plausible explanation of the Pliocene paradox.

As stated above, a key feature of this family of mathematical models is that they incorporate physical principles that are nonlinear. As is well known, nonlinear equations can have multiple solutions, unlike linear equations which can have only one unique solution (if well-posed). In our mathematical models, the same set of equations can have two or more co-existing solutions, for example an ice-capped solution (like today’s climate) and an ice-free solution (like the Cretaceous climate), even with the same values of the forcing parameters. The determination of which solution is actually realized by the planet at a given time is dependent on past history. Changes in forcing parameters may drive the system abruptly from one stable state to another, at so-called “tipping points”. In this paper, these tipping points are investigated mathematically, and are shown to be bifurcation points, which can be investigated using mathematical bifurcation theory. Bifurcation theory tells us that the existence of bifurcation points is preserved (but the numerical values may change) under small deformations of the model equations. Thus, even though this conceptual model may not give us precise quantitative information about climate changes, qualitatively there is good reason to believe that the existence of the bifurcation points in the model will be preserved in similar more refined models and in the real world.

The change from ice-free to ice-covered in the Arctic occurred abruptly, during the Pliocene Epoch, 5.3 to 2.6 Ma. It has been a longstanding challenge for paleoclimatologists to explain this dramatic change in the climate.

During the Pliocene Epoch, all of the important forcing factors that determine climate were very similar to those of today. The Earth orbital parameters, the CO2 concentration, solar radiation intensity, position of the continents, ocean currents and atmospheric circulation all had values close to the values they have today. Yet, in the early Pliocene, 4–5 million years ago, the Arctic climate was much milder than that of today. Arctic surface temperatures were 8−19_C warmer than today and global sea levels were 15−20 m higher than today, and yet CO2 levels are estimated to have been 340−400 ppm, about the same as 20th Century values; see Ballantyne et al. (2010); Csank et al. (2011); Tedford and Harington (2003). As mentioned in the Introduction, the problem of explaining how such different climates could exist with such similar forcing parameter values has been called the Pliocene Paradox (Cronin (2010); Fedorov et al. (2006, 2010)).

Another interesting paradox concerning Polar glaciation is the fact that, although both poles have transitioned abruptly from ice-free to ice-covered, they did so at very different geological times. The climate forcing conditions of Earth are highly symmetric between the two hemispheres and for most of the history of Earth the climates of the two poles have been very similar. However, there was an anomalous period of about 30 million years, from the Eocene-Oligocene boundary (34 Ma) to the early Pliocene (4 Ma), when the Antarctic was largely ice-covered but the Arctic was ice-free.

Thus, the EBM presented here, as illustrated in Figure 7, provides a plausible explanation for the Pliocene paradox. The slowly-acting physical forcings of decreasing CO2 concentration and decreasing ocean heat transport FO were amplified by the mechanisms of ice-albedo feedback and water vapour feedback, both of which act very strongly when the temperature crosses the freezing point of water. For millions of years before the Pliocene, while the Arctic temperature remained well above freezing, the climate changed very little. However, once the freezing temperature was reached, the Arctic climate changed abruptly via a saddlenode bifurcation as in Figure 7 b), to a new frozen state. This simple mechanism suffices to explain the Pliocene paradox. No more complicated explanations are necessary.

Several other explanations have been proposed for the Pliocene paradox. There is convincing evidence that, at the beginning of the Pliocene, there was a permanent El Niño condition in the tropical Pacific ocean, see Cronin (2010); Fedorov et al. (2006, 2010). (However, some have disputed this finding, see Watanabe et al. (2011).) It has been suggested that a permanent El Niño condition could explain the warm early Pliocene, and that the onset of the El Niño – La Niña Southern Oscillation (ENSO) was the cause of sudden cooling of the Arctic during the Pliocene. Today, it is known that ENSO can influence weather patterns as far away as the Arctic.

Another suggestion is that Hadley cell feedback contributed to the abrupt cooling of the Arctic during the Pliocene. Recent work shows that an increase in pole-to-equator temperature gradient causes the Hadley cells to contract towards the equator, while increasing in circulation velocity, see Lewis and Langford (2008); Langford and Lewis (2009). This would cause a decrease in equator to pole atmospheric heat transport, which would in turn accelerate Arctic cooling; this is called Hadley cell feedback.  Further work on modelling this mechanism is in progress. It is conjectured here that Hadley cell feedback may in fact have caused the end of a permanent El Niño condition in the Pliocene, as follows. It is known that the La Niña phase of ENSO is forced in part by the Trade Winds blowing East to West across the tropical Pacific Ocean. The Trade Winds are the surface component of the Hadley circulation. Therefore, acceleration of the Hadley circulation would strengthen the Trade Winds, enhancing the conditions for La Niña and ending the permanent El Niño. Further work on this conjecture also is in progress.

In the Tropics, many of the values of the forcing parameters are different from their values in the Arctic and Antarctic, see Table 2. The geological record shows little change in the tropical climate over the past 100 million years, other than a little cooling. Even when Arctic climate changed dramatically in the Pliocene, the Tropical climate changed very little.

The new entry in this Table, one that did not appear in the polar models, is FC, which represents transport of heat away from the surface to the atmosphere, by conduction / convection / change of state of water. The most important of these is the upward transport of latent heat. Surface water evaporates, taking heat from the surface. As warm moist air rises and cools, the water vapour condenses, releasing its latent heat into the surrounding atmosphere."

Caption for the first attached image: "Figure 7. Pliocene Arctic EBM (36)(37). Parameter values δ = 0.67, FA = 115; other parameters as in Table 1. Subfigure a): CO2 takes valuesµ = 1200, 1000, 800, 600, 400, 200ppm,from top to bottom on the blue curves, with fixed FO = 50 Wm−2. The warm equilibrium state disappears as µ decreases. Subfigure b): Bifurcation Diagram for the Pliocene Paradox. Here, CO2 concentration µ and ocean heat transport FO decrease simultaneously, with increasing ν, (0≤ν ≤1), as given by equations (42). As ν increases, the warm equilibrium solution (τS > 1) disappears in a saddlenode bifurcation, at approximately ν = 0.9, corresponding to forcing parameter µ = 343 ppm and FO = 51 Wm2. To the right of this point, only the frozen equilibrium state exists. To the left of this point, the frozen and warm equilibrium states coexist, separated by the unstable intermediate state."

Edit, W.r.t. coming Arctic Amplification, see the following linked article:

Title: "New and emerging threats continue to appear in Arctic as region warms, 2018 Arctic Report Card says"

Extract: "The Arctic Ocean has lost 95 percent of its oldest, thickest ice. In 2018, Arctic sea ice remained younger and thinner and covered less area than in the past. The 12 lowest extents in the satellite record have occurred in the last 12 years, according to the report."

For what it is worth, SSP5 will be used in the upcoming AR6, and per the linked reference & associated image), following the SSP5-Baseline scenario through at least 2035 (due to the lag in time between the forcing and the change in surface temperature), GMSTA (above pre-industrial) would be about +1.6C in 2030 and +2C in 2040, which agrees with my estimates in Reply #344:

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

Abstract: "This paper presents a set of energy and resource intensive scenarios based on the concept of Shared Socio-Economic Pathways (SSPs). The scenario family is characterized by rapid and fossil-fueled development with high socio-economic challenges to mitigation and low socio-economic challenges to adaptation (SSP5). A special focus is placed on the SSP5 marker scenario developed by the REMIND-MAgPIE integrated assessment modeling framework. The SSP5 baseline scenarios exhibit very high levels of fossil fuel use, up to a doubling of global food demand, and up to a tripling of energy demand and greenhouse gas emissions over the course of the century, marking the upper end of the scenario literature in several dimensions. These scenarios are currently the only SSP scenarios that result in a radiative forcing pathway as high as the highest Representative Concentration Pathway (RCP8.5). This paper further investigates the direct impact of mitigation policies on the SSP5 energy, land and emissions dynamics confirming high socio-economic challenges to mitigation in SSP5. Nonetheless, mitigation policies reaching climate forcing levels as low as in the lowest Representative Concentration Pathway (RCP2.6) are accessible in SSP5. The SSP5 scenarios presented in this paper aim to provide useful reference points for future climate change, climate impact, adaption and mitigation analysis, and broader questions of sustainable development."

We should also keep in mind the ice-climate feedback risks associated with both nonlinear surface melting of the GIS (see the first linked reference and image); and of increasing rainfall around the Artic (see the second linked reference) and in Greenland (see the third linked reference w.r.t. atmospheric rivers):

Trusel, L. D., Das, S. B., Osman, M. B., Evans, M. J., Smith, B. E., Fettweis, X., … van den Broeke, M. R. (2018). Nonlinear rise in Greenland runoff in response to post-industrial Arctic warming. Nature, 564(7734), 104–108. doi:10.1038/s41586-018-0752-4,

Abstract: "The Greenland ice sheet (GrIS) is a growing contributor to global sea-level rise, with recent ice mass loss dominated by surface meltwater runoff. Satellite observations reveal positive trends in GrIS surface melt extent, but melt variability, intensity and runoff remain uncertain before the satellite era. Here we present the first continuous, multi-century and observationally constrained record of GrIS surface melt intensity and runoff, revealing that the magnitude of recent GrIS melting is exceptional over at least the last 350 years. We develop this record through stratigraphic analysis of central west Greenland ice cores, and demonstrate that measurements of refrozen melt layers in percolation zone ice cores can be used to quantifiably, and reproducibly, reconstruct past melt rates. We show significant (P < 0.01) and spatially extensive correlations between these ice-core-derived melt records and modelled melt rates and satellite-derived melt duration across Greenland more broadly, enabling the reconstruction of past ice-sheet-scale surface melt intensity and runoff. We find that the initiation of increases in GrIS melting closely follow the onset of industrial-era Arctic warming in the mid-1800s, but that the magnitude of GrIS melting has only recently emerged beyond the range of natural variability. Owing to a nonlinear response of surface melting to increasing summer air temperatures, continued atmospheric warming will lead to rapid increases in GrIS runoff and sea-level contributions."

Caption for the image: "Fig. 4 | Exceptional rise in Greenland ice-sheet runoff and climate warming context. a, GrIS-integrated meltwater runoff, as simulated by regional climate models (coloured lines; 5-year smoothed) and reconstructed using the NU and CWG ice-core-derived melt records (black line; 95% confidence interval shaded; see Methods). b, Median onset of significant trends (vertical black dotted lines) and climate emergence above pre-industrial (vertical red dotted lines) for mean  Arctic temperatures (top), our ice-core-derived runoff reconstruction (middle) and two summer Arctic sea-ice extent datasets (bottom;  Methods). Median absolute deviations of trend onsets and climate  emergence shown as shaded boxes. Thin and bold black lines denote  15-year and 50-year Gaussian smoothed series. c, Recent modelled evolution of mean summer (JJA) near-surface air temperature and surface
melt (in millimetres of water equivalent per year) across CWG. Ice core sites are shown as coloured points, and a Jakobshavn basin (basin 7.1; Fig. 1) elevational transect as grey points from RACMO2.3p2 (circles) and MARv3.7 (squares). Means over the past 20 years of the ice-core records (1994–2013) at core sites are denoted by points with single black border, and peak melting in 2012 by double black borders. The evolution of CWG ice-sheet melt in response to a warming climate is well represented by an exponential function (black curve). Recent melt rates at our percolation zone core sites approach conditions where the models have recently begun to simulate meltwater runoff (blue dashed line indicates mean runoff-linked melt rate and the shaded region corresponds to ±1 s.d.; see Methods for details)."

Richard Bintanja and Olivier Andry (2017), “Towards a rain-dominated Arctic”, Geophysical Research Abstracts Vol. 19, EGU2017-4402

Abstract: “Current climate models project a strong increase in Arctic precipitation over the coming century, which has been attributed primarily to enhanced surface evaporation associated with sea-ice retreat. Since the Arctic is still quite cold, especially in winter, it is often (implicitly) assumed that the additional precipitation will fall mostly as snow. However, very little is known about future changes in rain/snow distribution in the Arctic, notwithstanding the importance for hydrology and biology. Here we use 37 state-of-the-art climate models in standardised twenty-first century (2006–2100) simulations to show that 70◦ – 90◦N average annual Arctic snowfall will actually decrease, despite the strong increase in precipitation, and that most of the additional precipitation in the future (2091– 2100) will fall as rain. In fact, rain is even projected to become the dominant form of precipitation in the Arctic region. This is because Arctic atmospheric warming causes a greater fraction of snowfall to melt before it reaches the surface, in particular over the North Atlantic and the Barents Sea. The reduction in Arctic snowfall is most pronounced during summer and autumn when temperatures are close to the melting point, but also winter rainfall is found to intensify considerably. Projected (seasonal) trends in rain/snowfall will heavily impact Arctic hydrology (e.g. river discharge, permafrost melt), climatology (e.g. snow, sea ice albedo and melt) and ecology (e.g. water and food availability).”

Also as a repost of Reply #195: continued global warming should increase the frequency with which atmospheric rivers reach Greenland, we may be in for some rude surprises in the coming decades (w.r.t. increasing rates of ice mass loss from the Greenland Ice Sheet):

William Neff (2018), "Atmospheric rivers melt Greenland", Nature Climate Change 8, 857-858, DOI:

Abstract: "Recent years have seen increased melting of the Greenland Ice Sheet, contributing to accelerated rates of sea-level rise.  New research suggests that this melting due to an increased frequency of atmospheric rivers, narrow filaments of moist air moving polewards."

As a follow-on to my last post, the first two images from the first linked website entitled "Figures from the Global Carbon Budget 2018", show (respectively) that we are currently following the SSP5 baseline scenario, and that we are above the SSP scenarios required to state below the 1.5C goal.

Also, by the end of 2018 the world population will be about 7.7 million people, which, per the third & fourth images, slightly exceeds that assumed by SSP5.


It's hard to reconcile mid-Pliocene conditions beginning around 2030 with the IPCC report.

Not to repeat myself, but 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 first attached image) or 1.23C for a 15yr loess trend line (see the extract below).  I note that this prediction is in line with Hansen's prediction that I cited in Reply #220 and as is indicated by the second attached image.  So if one takes Gavin's estimate of +1.23C by the end of 2019 together with Hansen's value of 0.38C/decade one gets GMSTAs of +1.61C by 2030 and +1.99C by 2040 (note in most of my posts I take 2040 as the date when conditions for key West Antarctic marine glaciers reaching Mid-Pliocene oceanic and atmospheric conditions).

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."

Next, it is somewhat unclear what Mid-Pliocene conditions, in West Antarctica, actually means.  Per the third image, from Sweet et al. 2017) GMSTA (from pre-industrial) during the Pliocene ranges from +1.8C to +3.6C; while the fourth image from Hansen & Sato shows Pliocene GMSTA relative to the Holocene Optimum.

Thus to begin to reconcile Mid-Pliocene conditions circa 2040 with AR5, one needs to believe (at least) that IPCC underestimates:

a) ECS and negative forcing from anthropogenic aerosols,
b) the role of ENSO (& IPO) in determining GMSTA in the coming decades,
c) the role of ice-climate feedback mechanisms that have already been triggered.

Edit, there currently are 2,387 posts in the "Conservative Scientists & its Consequences" thread related to why the IPCC is likely erring of the side of least drama in its climate change projections:,1053.0.html

Edit2, with regard to the 2030 date, I suspect that Burke et al (2018) are likely referring to the CO2 concentration by 2030 (see the CO2 concentrations given in the third image).

As a follow-on to my last two posts, I note that:

1. The first image [from Wilson et al (2018)], highlights that the sea level rise during MIS 11 (the Holsteinian) was higher (6 to 13m) than for MIS5 (the Eemian, 6 to 9m), even though its radiative forcing and Antarctic temperature increase were both less than for MIS 5.  As no current ESM projection can match the sensitivity of MIS 11, this is an indication that all reported projections err on the side of least drama.

Wilson, D. J., Bertram, R. A., Needham, E. F., van de Flierdt, T., Welsh, K. J., McKay, R. M., … Escutia, C. (2018). Ice loss from the East Antarctic Ice Sheet during late Pleistocene interglacials. Nature. doi:10.1038/s41586-018-0501-8

Caption for the first attached image: "Fig. 3 | Comparison of U1361A records to regional palaeoclimate and global sea level records. a, Antarctic ice core temperature difference (ΔT, difference from mean values of the last millennium) derived from deuterium isotopes at EPICA Dome C (EDC)11 plotted on EDC3 age scale. bp, before present. b, Southern Ocean bottom water temperature (BWT) from Mg/Ca at Ocean Drilling Program (ODP) Site 1123 (ref. 18).  c, Southern Ocean sea surface temperature (SST) from alkenones at ODP Site 1090 (ref. 19). d, Ba/Al ratios (XRF-scanner counts; three-point smoothed) in U1361A. e, Bulk detrital sediment Nd isotopes in U1361A (error bars are 2 s.d. external reproducibility). f, Sea level proxy from benthic oxygen isotopes28, labelled with MIS numbers and sea level estimates17 from MIS 5e and MIS 11. Shading in a–c, f represents intervals with values above modern (or late Holocene core top); red dashed line in e indicates the core top εNd value of U1361A. For chronostratigraphic constraints on U1361A, see Supplementary Table 8 and Methods."

2. The second image [from Weber et al (2014)] shows that an iceberg armada from the ASE (Amundsen Sea Embayment, say from 2040 to 2060) would be initially carried eastward by the Antarctic Coastal Current where it would provide meltwater that would disrupt AABW formation in East Antarctica until it was kicked northward in 'Iceberg Alley' in the Weddell Sea, into the ACC stream.  This parallels the scenario modeled by Fogwill et al with a figure showing impact on AABW formation in my Reply #338.

3. The third image shows the findings of a field survey of the Recovery Ice Stream, indicating the presences of subglacial lakes that could well accelerate ice mass loss from this EAIS glacier beyond that indicated by Pollard, DeConto and Alley (2018) for Pliocene conditions. The linked article talks about the IceBridge mission to investigate the Recovery Glacier area from which the third image was taken:

Also, I note that almost all other key Antarctic marine glacier have extensive systems of subglacial lakes and streams that could accelerate ice flow in the near-term future with continued global warming.

4.  The fourth image shows the location of key gyres around Antarctica including the 'Unnamed Gyre' that is probably driving upwelling of warm CDW towards the grounding line of Totten Glacier (and thus likely which is accelerating ice mass loss from this key EAIS marine glacier beyond that accounted for in any model that I know of).

Re: ITCZ, question for abruptSLR

in the ACME modelling efforts, have they fixed the double ITCZ problem that most GCMs have ?


That last time I looked it was still there, but who knows what changes that they are continually making as they transform ACME into E3SM.

Edit: You can monitor the progress being made on the E3SM model at:

I think it could be argued that the period highlighted was blighted by the flip side of the global warming coin, that of global dimming?


Thanks for your comments.  Certainly the variable and chaotic nature of both natural and anthropogenic forcing adds to the 'Deep Uncertainty' that tends to obscure the very real risks of abrupt ice-climate feedback this century.  The truth is that mankind is headed into uncharted waters within the next couple of decades, and we are not appropriately facing the warning provided by researchers such as James Hansen, & others, all of whom have to partially mute their warning in order to even be published [witness the difficulties that were encountered getting Hansen et al (2016) published and how infrequently it has been cited by consensus climate science].

I strongly suspect that mankind will not be willing to accept the risks of abrupt ice-climate feedback until it is both manifest and unstoppable (at least for the next few centuries).


One key problem associated with reducing the 'Deep Uncertainty' associate with ice-climate feedback mechanisms is the problems of correct attribution, especially when consensus climate change studies such as the first linked report (for decision makers) essentially ignore this consideration, even though Hansen's book "Storms of my Grandchildren" clearly warns about the consequence of this important feedback:

Title: "Fingerprints Everywhere 2018"

Indeed, the second linked reference highlights the difficulties of climate change attribution; which makes it even harder for ice-climate feedback mechanisms to gain traction in the attribution game:

Judith L. Lean (22 February 2018), "Observation‐based detection and attribution of 21st century climate change", WIREs Climate Change,

Abstract: "Climate change detection and attribution have proven unexpectedly challenging during the 21st century. Earth’s global surface temperature increased less rapidly from 2000 to 2015 than during the last half of the 20th century, even though greenhouse gas concentrations continued to increase. A probable explanation is the mitigation of anthropogenic warming by La Niña cooling and declining solar irradiance. Physical climate models overestimated recent global warming because they did not generate the observed phase of La Niña cooling and may also have underestimated cooling by declining solar irradiance. Ongoing scientific investigations continue to seek alternative explanations to account for the divergence of simulated and observed climate change in the early 21st century, which IPCC termed a “global warming hiatus.” Amplified by media commentary, the suggestions by these studies that “missing” mechanisms may be influencing climate exacerbates confusion among policy makers, the public and other stakeholders about the causes and reality of modern climate change.

Understanding and communicating the causes of climate change in the next 20 years may be equally challenging. Predictions of the modulation of projected anthropogenic warming by natural processes have limited skill. The rapid warming at the end of 2015, for example, is not a resumption of anthropogenic warming but rather an amplification of ongoing warming by El Niño. Furthermore, emerging feedbacks and tipping points precipitated by, for example, melting summer Arctic sea ice may alter Earth’s global temperature in ways that even the most sophisticated physical climate models do not yet replicate."

For example, when non-experts think of the impacts of ice loss on the climate they typically think of the ice-albedo feedback and the potential rapid loss of Arctic Sea Ice; however, the third linked reference indicates the attribution problems associated with this feedback due to the influences of both natural GHG emissions and of anthropogenic aerosol forcing (which have been suppressing Arctic Sea Ice losses for decades until the recent reduction in anthropogenic aerosol emissions).  Furthermore, ice-albedo feedback can be one of the many different mechanisms contributing to ice-climate feedback, which further complicates attribution.

B. L. Mueller et al (2018), "Attribution of Arctic Sea Ice Decline from 1953 to 2012 to Influences from Natural, Greenhouse Gas, and Anthropogenic Aerosol Forcing", Journal of Climate,

Abstract: "The paper presents results from a climate change detection and attribution study on the decline of Arctic sea ice extent in September for the 1953–2012 period. For this period three independently derived observational datasets and simulations from multiple climate models are available to attribute observed changes in the sea ice extent to known climate forcings. Here we direct our attention to the combined cooling effect from other anthropogenic forcing agents (mainly aerosols), which has potentially masked a fraction of greenhouse gas–induced Arctic sea ice decline. The presented detection and attribution framework consists of a regression model, namely, regularized optimal fingerprinting, where observations are regressed onto model-simulated climate response patterns (i.e., fingerprints). We show that fingerprints from greenhouse gas, natural, and other anthropogenic forcings are detected in the three observed records of Arctic sea ice extent. Beyond that, our findings indicate that for the 1953–2012 period roughly 23% of the greenhouse gas–induced negative sea ice trend has been offset by a weak positive sea ice trend attributable to other anthropogenic forcing. We show that our detection and attribution results remain robust in the presence of emerging nonstationary internal climate variability acting upon sea ice using a perfect model experiment and data from two large ensembles of climate simulations."

The linked video of a May 28, 2008 calving event of Ilulissat Glacier (also called Jakobshavn Glacier) gives some idea of the dynamic nature of cliff failures.  As noted below the height of the ice cliff face (above water) for Ilulissat/Jakobshavn is 300 to 400-ft; while the height of the ice cliff face for Thwaites could be many times this height if/when the grounding line retreats down the retrograde stream bed:

Title: "Chasing Ice"

Extract: " This rare footage has gone on record as the largest glacier calving event ever captured on film, by the 2016 Guiness Book of World Records.

On May 28, 2008, Adam LeWinter and Director Jeff Orlowski filmed a historic breakup at the Ilulissat Glacier in Western Greenland. The calving event lasted for 75 minutes and the glacier retreated a full mile across a calving face three miles wide. The height of the ice is about 3,000 feet, 300-400 feet above water and the rest below water."

P.S. While many have already seen this video, its dynamic nature never fails to impress me.

Edit: For those who are not familiar with the profile (elevations in kilometers) of the Thwaites Glacier, I provide the attached representative image.

The first linked article entitled: "SkS Analogy 4 - Ocean Time Lag" illustrates how consensus based 'scientific' call to action can greatly underplay the risks associated with regard to dynamical climate sensitivity as illustrated by the second linked reference associated with the influences that the IPO as short-term GMSTA.  The first attached image is from the first reference & indicates that due to a 30-year lag we will not reach 2C warming until 2035 + 30 – 2065.  However, the second & third images, from the second reference, indicate respectively that we appear to have entered a warm IPO period (which may well last until ~2035); which indicates that we could reach +1.8C by 2034 (when considering the confidence range).

Extract: "Greenhouse gases (GHG) determine amount of warming, but oceans delay the warming.

This figure therefore shows the temperature anomaly starting in 1970, the year when the temperature increase due to greenhouse gases began to emerge from the background noise. This figure indicates 3 things: (1) the time lag between emitting greenhouse gases and when we see the principle effect is about 30 years, due mostly to the time required to heat the oceans, (2) the rate of temperature increase predicted by a climate sensitivity of 3°C tracks well with the observed rate of temperature increase, and (3) we have already locked in more than 1.5°C warming. As of 2017 we have reached 406 ppm CO2. At the current increase of 2 ppm CO2/yr., this implies that we will reach 440 ppm and lock in 2°C warming by 2035 … if we don’t act now."

The second reference is:

Henley, B. J and King, A. D. (2017) Trajectories toward the 1.5C Paris target: Modulation by the Interdecadal Pacific Oscillation, Geophysical Research Letters, doi:10.1002/2017GL073480

Abstract: "Global temperature is rapidly approaching the 1.5°C Paris target. In the absence of external cooling influences, such as volcanic eruptions, temperature projections are centered on a breaching of the 1.5°C target, relative to 1850–1900, before 2029. The phase of the Interdecadal Pacific Oscillation (IPO) will regulate the rate at which mean temperature approaches the 1.5°C level. A transition to the positive phase of the IPO would lead to a projected exceedance of the target centered around 2026. If the Pacific Ocean remains in its negative decadal phase, the target will be reached around 5 years later, in 2031. Given the temporary slowdown in global warming between 2000 and 2014, and recent initialized decadal predictions suggestive of a turnaround in the IPO, a sustained period of rapid temperature rise might be underway. In that case, the world will reach the 1.5°C level of warming several years sooner than if the negative IPO phase persists."

Plain Language Summary
Global temperature is rapidly approaching the 1.5°C Paris target. In this study, we find that in the absence of external cooling influences, such as volcanic eruptions, the midpoint of the spread of temperature projections exceeds the 1.5°C target before 2029, based on temperatures relative to 1850–1900. We find that the phase of the Interdecadal Pacific Oscillation (IPO), a slow-moving natural oscillation in the climate system, will regulate the rate at which global temperature approaches the 1.5°C level. A transition to the positive phase of the IPO would lead to a projected exceedance of the target centered around 2026. If the Pacific Ocean remains in its negative phase, however, the projections are centered on reaching the target around 5 years later, in 2031. Given the temporary slowdown in global warming between 2000 and 2014, and recent climate model predictions suggestive of a turnaround in the IPO, a sustained period of rapid temperature rise might be underway. In that case, the world will reach the 1.5°C level of warming several years sooner than if the negative IPO phase persists.

See also the associated following article entitled: "Pacific Ocean shift could see 1.5C limit breached within a decade":

The linked reference points out that per their 1D models the Arctic continental shelf methane hydrate stability zone (HSZ) can take ~ 10 to 20 kyrs to respond to changes in initial temperature conditions associated with the end of the last ice age.  However, while it is pleasant to think of middle of the 10 to 20 kya range, as the attached image indicates the Holocene began about 11 kya and thus we should now start to see portions of the HSZ becoming unstable due to the global temperature increase leading to the beginning of the Holocene.  This emphasizes that modelers need to get their initial conditions correct:

Valentina V. Malakhova & Alexey V. Eliseev (2017), "The role of heat transfer time scale in the evolution of the subsea permafrost and associated methane hydrates stability zone during glacial cycles", Global and Planetary Change,

Abstract: "Climate warming may lead to degradation of the subsea permafrost developed during Pleistocene glaciations and release methane from the hydrates, which are stored in this permafrost. It is important to quantify time scales at which this release is plausible. While, in principle, such time scale might be inferred from paleoarchives, this is hampered by considerable uncertainty associated with paleodata. In the present paper, to reduce such uncertainty, one–dimensional simulations with a model for thermal state of subsea sediments forced by the data obtained from the ice core reconstructions are performed. It is shown that heat propagates in the sediments with a time scale of ∼ 10-20 kyr. This time scale is longer than the present interglacial and is determined by the time needed for heat penetration in the unfrozen part of thick sediments. We highlight also that timings of shelf exposure during oceanic regressions and flooding during transgressions are important for simulating thermal state of the sediments and methane hydrates stability zone (HSZ). These timings should be resolved with respect to the contemporary shelf depth (SD). During glacial cycles, the temperature at the top of the sediments is a major driver for moving the HSZ vertical boundaries irrespective of SD. In turn, pressure due to oceanic water is additionally important for SD ≥ 50 m. Thus, oceanic transgressions and regressions do not instantly determine onset s of HSZ and/or its disappearance. Finally, impact of initial conditions in the subsea sediments is lost after ∼ 100 kyr. Our results are moderately sensitive to intensity of geothermal heat flux."

For those interested in an overview of atmospheric bridges, oceanic tunnels and global climatic telecommunications, I offer the following linked 2007 open access reference.  However, I warn that it only provides a low level overview and does not explicitly address issues such as ice-climate feedback (ala Hansen et al 2016) nor issues like the role of Agulhus Leakage in the bipolar seesaw mechanism:

Zhengyu Liu & Mike Alexander (23 June 2007), "Atmospheric bridge, oceanic tunnel, and global climatic teleconnections', Reviews of Geophysics; DOI: 10.1029/2005RG000172

Abstract: "We review teleconnections within the atmosphere and ocean, their dynamics and their role in coupled climate variability. We concentrate on teleconnections in the latitudinal direction, notably tropical-extratropical and interhemispheric interactions, and discuss the timescales of several teleconnection processes. The tropical impact on extratropical climate is accomplished mainly through the atmosphere. In particular, tropical Pacific sea surface temperature anomalies impact extratropical climate variability through stationary atmospheric waves and their interactions with midlatitude storm tracks. Changes in the extratropics can also impact the tropical climate through upper ocean subtropical cells at decadal and longer timescales. On the global scale the tropics and subtropics interact through the atmospheric Hadley circulation and the oceanic subtropical cell. The thermohaline circulation can provide an effective oceanic teleconnection for interhemispheric climate interactions."

The first attached image shows an oceanic Rossby Wave Train that can propagate from the Equatorial Pacific to West Antarctica in a timeframe of months.

The second image shows that during a paleo (45 kya) North Atlantic hosing (D-O) event, warm Gulf Stream water flowed under the less saline (but colder) surface water in order to warm the Norwegian Sea.  Also, the third image shows that under extant conditions with both cool North Pacific and North Atlantic ocean temperatures, atmospheric Rossby waves can still telecommunicate heat from the tropical oceans directly to Arctic regions (as indicated).

The Last Glacial Termination, LGT, occurred from 18,000 to 11,650 kya, and the following reference, reconstructs the dynamic response of the Antarctic ice sheets to warming in this period in order to better evaluate Hansen's ice-climate feedback mechanisms.  The abstract from the second linked reference concludes: "Given the anti-phase relationship between inter-hemispheric climate trends across the LGT our findings demonstrate that Southern Ocean-AIS feedbacks were controlled by global atmospheric teleconnections.  With increasing stratification of the Southern Ocean and intensification of mid-latitude westerly winds today, such teleconnections could amplify AIS mass loss and accelerate global sea-level rise."

Fogwill, et. al. (2017), "Antarctic ice sheet discharge driven by atmosphere-ocean feedbacks at the last Glacial Termination", Scientific Reports 7, Article number 39979, doi:10.1038/srep39979

Also a rain-dominated Arctic would be affected by Hansen's ice-climate feedback mechanism driven by a WAIS collapse beginning circa 2040 (which almost all ESM projections currently ignore), and or pulses of methane emission from thermokarst lakes.   Also the second linked reference assumes that ECS is only around 3C.

Richard Bintanja and Olivier Andry (2017), “Towards a rain-dominated Arctic”, Geophysical Research Abstracts Vol. 19, EGU2017-4402

Abstract: “Current climate models project a strong increase in Arctic precipitation over the coming century, which has been attributed primarily to enhanced surface evaporation associated with sea-ice retreat. Since the Arctic is still quite cold, especially in winter, it is often (implicitly) assumed that the additional precipitation will fall mostly as snow. However, very little is known about future changes in rain/snow distribution in the Arctic, notwithstanding the importance for hydrology and biology. Here we use 37 state-of-the-art climate models in standardised twenty-first century (2006–2100) simulations to show that 70◦ – 90◦N average annual Arctic snowfall will actually decrease, despite the strong increase in precipitation, and that most of the additional precipitation in the future (2091– 2100) will fall as rain. In fact, rain is even projected to become the dominant form of precipitation in the Arctic region. This is because Arctic atmospheric warming causes a greater fraction of snowfall to melt before it reaches the surface, in particular over the North Atlantic and the Barents Sea. The reduction in Arctic snowfall is most pronounced during summer and autumn when temperatures are close to the melting point, but also winter rainfall is found to intensify considerably. Projected (seasonal) trends in rain/snowfall will heavily impact Arctic hydrology (e.g. river discharge, permafrost melt), climatology (e.g. snow, sea ice albedo and melt) and ecology (e.g. water and food availability).”

See also the following linked reference:

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

Extract: "Rain causes more (extensive) permafrost melt [Refs. 7,26], which most likely leads to enhanced emissions of terrestrial methane [Ref. 27] (a powerful greenhouse gas), more direct runoff (a smaller seasonal delay) and concurrent freshening of the Arctic Ocean [Ref 18]. Rainfall also diminishes snow cover extent and considerably lowers the surface albedo of seasonal snow, ice sheets and sea ice [Ref. 9] , reinforcing surface warming and amplifying the retreat of ice and snow; in fact, enhanced rainfall will most likely accelerate sea-ice retreat by lowering its albedo (compared with that of fresh snowfall) "

In regards to my last post, 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 drainage 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: "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"

In September 2012 the Thwaites Ice Tongue flow rate surged and continued flowing at a high rate through the end of 2012 (and this high flow rate can be associated with the surface elevation depression shown in the first image)

In this regards, the linked reference studies a subglacial draining event beneath Thwaites Glacier from June 2013 to January 2014 (see the last three attached images):

Smith et. al. (2017), "Connected subglacial lake drainage beneath Thwaites Glacier, West Antarctica", The Cryosphere, 11, 451–467, doi:10.5194/tc-11-451-2017

Abstract. We present conventional and swath altimetry data from CryoSat-2, revealing a system of subglacial lakes that drained between June 2013 and January 2014 under the central part of Thwaites Glacier, West Antarctica (TWG). Much of the drainage happened in less than 6 months, with an apparent connection between three lakes spanning more than 130 km. Hydro-potential analysis of the glacier bed shows a large number of small closed basins that should trap water produced by subglacial melt, although the observed largescale motion of water suggests that water can sometimes locally move against the apparent potential gradient, at least during lake-drainage events. This shows that there are important limitations in the ability of hydro-potential maps to predict subglacial water flow. An interpretation based on a map of the melt rate suggests that lake drainages of this type should take place every 20–80 years, depending on the connectivity of the water flow at the bed. Although we observed an acceleration in the downstream part of TWG immediately before the start of the lake drainage, there is no clear connection between the drainage and any speed change of the glacier."

There is more information on the June 2013 to Jan 2014 drainage of four subglacial lakes beneath the Thwaites Glacier.  The article is entitled: "Hidden lakes drain below West Antarctica’s Thwaites Glacier".

Extract: "Researchers at the University of Washington and the University of Edinburgh used data from the European Space Agency’s CryoSat-2 to identify a sudden drainage of large pools below Thwaites Glacier, one of two fast-moving glaciers at the edge of the ice sheet. The study published Feb. 8 in The Cryosphere finds four interconnected lakes drained in the eight months from June 2013 and January 2014. The glacier sped up by about 10 percent during that time, showing that the glacier’s long-term movement is fairly oblivious to trickles at its underside.

Melting at the ice sheet base would refill the lakes in 20 to 80 years, Smith said. Over time meltwater gradually collects in depressions in the bedrock. When the water reaches a certain level it breaches a weak point, then flows through channels in the ice. As Thwaites Glacier thins near the coast, its surface will become steeper, Smith said, and the difference in ice pressure between inland regions and the coast may push water coastward and cause more lakes to drain."

Obviously, when these subglacial lakes have refilled by the basal meltwater drainage system, in the coming decades, Thwaites will be primed for another surge.

 I re-post the following from the Potential Collapse Scenario for the WAIS" thread

"Based on my interpretation of the two linked references, I suspect that local ice cliff failures near the base of the Thwaites Ice Tongue (see the four images) will begin sometime 2025 and 2033, and will be initiated due to influences from Super El Nino events in that timeframe:

Yu, H., Rignot, E., Morlighem, M., & Seroussi, H. (2017). Iceberg calving of Thwaites Glacier, West Antarctica: full-Stokes modeling combined with linear elastic fracture mechanics. The Cryosphere, 11(3), 1283, doi:10.5194/tc-11-1283-2017

Abstract. "Thwaites Glacier (TG), West Antarctica, has been losing mass and retreating rapidly in the past few decades.  Here, we present a study of its calving dynamics combining a two-dimensional flow-band full-Stokes (FS) model of its viscous flow with linear elastic fracture mechanics (LEFM) theory to model crevasse propagation and ice fracturing.  We compare the results with those obtained with the higher-order (HO) and the shallow-shelf approximation (SSA) models coupled with LEFM. We find that FS/LEFM produces surface and bottom crevasses that are consistent with the distribution of depth and width of surface and bottom crevasses observed by NASA’s Operation IceBridge radar depth sounder and laser altimeter, whereas HO/LEFM and SSA/LEFM do not generate crevasses that are consistent with observations.  We attribute the difference to the nonhydrostatic condition of ice near the grounding line, which facilitates crevasse formation and is accounted for by the FS model but not by the HO or SSA models. We find that calving is enhanced when pre-existing surface crevasses are present, when the ice shelf is shortened or when the ice shelf front is undercut. The role of undercutting depends on the timescale of calving events. It is more prominent for glaciers with rapid calving rates than for glaciers with slow calving rates. Glaciers extending into a shorter ice shelf are more vulnerable to calving than glaciers developing a long ice shelf, especially as the ice front retreats close to the grounding line region, which leads to a positive feedback to calving events. We conclude that the FS/LEFM combination yields substantial improvements in capturing the stress field near the grounding line of a glacier for constraining crevasse formation and iceberg calving."

Extract: "In our simulations, we find that crevasses propagate significantly faster near the ice front when the ice shelf is shortened.

The reason for the propagation of crevasses is the existence of a nonhydrostatic condition of ice immediately downstream of the grounding line, which is not accounted for in simplified models that assume hydrostatic equilibrium everywhere on the ice shelf.  We also find that calving is enhanced in the presence of pre-existing surface crevasses or shorter ice shelves or when the ice front is undercut.  We conclude that it is important to consider the full stress regime of ice in the grounding line region to replicate the conditions conducive to calving events, especially the nonhydrostatic condition that is critical to propagate the crevasses."


The second linked reference confirms that the ENSO is directly associated with surface air temperatures across the interior of West Antarctica, and I note that the frequency of extreme El Nino events is projected to double when the global mean surface temp. anom. gets to 1.5C:

Kyle R. Clem, James A. Renwick, and James McGregor (2017), "Large-Scale Forcing of the Amundsen Sea Low and its Influence on Sea Ice and West Antarctic Temperature", Journal of Climate,

Abstract: "Using empirical orthogonal function (EOF) analysis and atmospheric reanalyses, we examine the principal patterns of seasonal West Antarctic surface air temperature (SAT) and their connection to sea ice and the Amundsen Sea Low (ASL). During austral summer, the leading EOF (EOF1) explains 35% of West Antarctic SAT variability and consists of a widespread SAT anomaly over the continent linked to persistent sea ice concentration anomalies over the Ross and Amundsen Seas from the previous spring. Outside of summer, EOF1 (explaining ~40-50% of the variability) consists of an east-west dipole over the continent with SAT anomalies over the Antarctic Peninsula opposite those over western West Antarctica. The dipole is tied to variability in the Southern Annular Mode (SAM) and in-phase El Niño-Southern Oscillation (ENSO) / SAM combinations that influence the depth of the ASL over the central Amundsen Sea (near 105°W). The second EOF (EOF2) during autumn, winter, and spring (explaining ~15-20% of the variability) consists of a dipole shifted approximately 30 degrees west of EOF1 with a widespread SAT anomaly over the continent. During winter and spring, EOF2 is closely tied to variability in ENSO and a tropically-forced wavetrain that influences the ASL in the western Amundsen / eastern Ross Seas (near 135°W) with an opposite sign circulation anomaly over the Weddell Sea; the ENSO-related circulation brings anomalous thermal advection deep onto the continent. We conclude the ENSO-only circulation pattern is associated with SAT variability across interior West Antarctica, especially during winter and spring, while the SAM circulation pattern is associated with an SAT dipole over the continent.""

As this is the Ice Apocalypse thread, we cannot neglect to consider the fact that the current high rate of anthropogenic radiative forcing (at least 100 times faster than during the PETM) increases the risk that a cascade (domino effect) of activated positive feedback mechanisms could drive the Earth irreversibly towards a 'hothouse' condition, if we allow the Earth to temporarily reach Mid-Pliocene conditions (which will cause abrupt ice mass loss from Antarctica), as shown in Steffen et al. (2018) & the three associated images, and the associated article.

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

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

Extract: "The initial domino stones could form the tipping points, which already react to a relatively small increase in global temperatures, such as the melting of the West Antarctic and Greenland Ice Sheet and the Arctic sea ice. As this continues to fuel warming through positive feedback loops, it could then be "swept" by tipping points with slightly higher thresholds, such as the Gulf Stream ocean current or the Southern Ocean's buffering of global CO2. Once such a cascade is triggered, it might cause a runaway effect that could catapult Earth's climate out of its stable phase even as human emissions are reduced. The earth could be 4–5 °C warmer than pre-industrial temperatures and have sea levels 10–60 m higher than today."

Furthermore, Fischer et al. (2018) (& the associated article) supports the concern that if we allow the world to reach Mid-Pliocene conditions we could lock-in a cascade of positive feedbacks that could effectively double the current value of climate sensitivity.

Fischer et al. (2018), "Palaeoclimate constraints on the impact of 2 °C anthropogenic warming and beyond", Nature Geoscience, vol. 11, 474–485,

Abstract: "Over the past 3.5 million years, there have been several intervals when climate conditions were warmer than during the preindustrial Holocene. Although past intervals of warming were forced differently than future anthropogenic change, such periods can provide insights into potential future climate impacts and ecosystem feedbacks, especially over centennial-to-millennial timescales that are often not covered by climate model simulations. Our observation-based synthesis of the understanding of past intervals with temperatures within the range of projected future warming suggests that there is a low risk of runaway greenhouse gas feedbacks for global warming of no more than 2 °C. However, substantial regional environmental impacts can occur. A global average warming of 1–2 °C with strong polar amplification has, in the past, been accompanied by significant shifts in climate zones and the spatial distribution of land and ocean ecosystems. Sustained warming at this level has also led to substantial reductions of the Greenland and Antarctic ice sheets, with sea-level increases of at least several metres on millennial timescales. Comparison of palaeo observations with climate model results suggests that, due to the lack of certain feedback processes, model-based climate projections may underestimate long-term warming in response to future radiative forcing by as much as a factor of two, and thus may also underestimate centennial-to-millennial-scale sea-level rise."


Title: "Global warming may be twice what climate models predict"

Extract: "Observations of past warming periods suggest that a number of amplifying mechanisms, which are poorly represented in climate models, increase long-term warming beyond climate model projections," said lead author, Prof Hubertus Fischer of the University of Bern.

"This suggests the carbon budget to avoid 2°C of global warming may be far smaller than estimated, leaving very little margin for error to meet the Paris targets."

To get their results, the researchers looked at three of the best-documented warm periods, the Holocene thermal maximum (5000-9000 years ago), the last interglacial (129,000-116,000 years ago) and the mid-Pliocene warm period (3.3-3 million years ago).

The warming of the first two periods was caused by predictable changes in the Earth's orbit, while the mid-Pliocene event was the result of atmospheric carbon dioxide concentrations that were 350-450ppm – much the same as today."

Furthermore, Liu et al. (2018) confirms that a sufficient perturbance of the AMOC into the Arctic Ocean (say due to abrupt ice mass loss from Antarctic beginning in 2040) could lead "… to a rapid Arctic sea ice retreat within 5 years after the perturbations are activated."  Such possible activation of the positive Arctic ice-albedo mechanism, could then trigger other positive feedback mechanisms.

Wei Liu et al. (2018), "The mechanisms of the Atlantic Meridional Overturning Circulation slowdown induced by Arctic sea ice decline", Journal of Climate,

Abstract: "We explore the mechanisms by which Arctic sea ice decline affects the Atlantic Meridional Overturning Circulation (AMOC) in a suite of numerical experiments perturbing Arctic sea ice radiative budget within a fully coupled climate model. The imposed perturbations act to increase the amount of heat available to melt ice, leading to a rapid Arctic sea ice retreat within 5 years after the perturbations are activated. In response, the AMOC gradually weakens over the next ∼100 years. The AMOC changes can be explained by the accumulation in the Arctic and subsequent downstream propagation to the North Atlantic of buoyancy anomalies controlled by temperature and salinity. Initially, during the first decade or so, the Arctic sea ice loss results in anomalous positive heat and salinity fluxes in the subpolar North Atlantic, inducing positive temperature and salinity anomalies over the regions of oceanic deep convection. At first, these anomalies largely compensate one another, leading to a minimal change in upper ocean density and deep convection in the North Atlantic. Over the following years, however, more anomalous warm water accumulates in the Arctic and spreads to the North Atlantic. At the same time, freshwater that accumulates from seasonal sea ice melting over most of the upper Arctic Ocean also spreads southward, reaching as far as south of Iceland. These warm and fresh anomalies reduce upper ocean density and suppress oceanic deep convection. The thermal and haline contributions to these bouyancy anomalies, and therefore to the AMOC slowdown during this period, are found to have similar magnitudes. We also find that the related changes in horizontal wind-driven circulation could potentially push freshwater away from the deep convection areas and hence strengthen the AMOC, but this effect is overwhelmed by mean advection."

Edit: To help convey how close we currently are to reaching Mid-Pliocene conditions, I attach the fourth image of Fischer et al. (2018) Figure 1.

From Replies #219 & #220 there is a strong case to be made that key portions of the Antarctic Ice Sheet may be initially subject to cliff-failures and hydrofracturing by about 2040 when GMSTA may be between 1.5 and 1.8C above pre-industrial.  Furthermore, the first linked reference Zhuan et al. (2018) demonstrates that climate sensitivity [aka climate model response (M) combined with internal climate variability (V)] dominates the rate of increase of GMSTA vs GHG emissions in this timeframe.  Unfortunately, contrarians (and/or those who prefer to err on the side of least drama) like to point at incomplete and biased definitions of climate sensitivity that give low estimates ECS, and TCR, which decision makers are all too willing to use in their policies.  Therefore, in this post I provide some more insight as to why the true ECS values (over the next 20 years) is higher that the ~3C value recommended by IPCC.

Meijia Zhuan et al. (12 November 2018), "A method for investigating the relative importance of three components in overall uncertainty of climate projections", International Journal of Climatology,

Abstract: "Climate model response (M) and greenhouse gas emissions (S) uncertainties are consistently estimated as spreads of multi‐model and multi‐scenario climate change projections. There has been less agreement in estimating internal climate variability (V). In recent years, an initial condition ensemble (ICE) of a climate model has been developed to study V. ICE is simulated by running a climate model using an identical climate forcing but different initial conditions. Inter‐member differences of an ICE manifestly represent V. However, ICE has been barely used to investigate relative importance of climate change uncertainties. Accordingly, this study proposes a method of using ICEs, without assuming V as constant, for investigating the relative importance of climate change uncertainties and its temporal‐spatial variation. Prior to investigating temporal‐spatial variation in China, V estimated using ICE was compared to that using multi‐model individual time series at national scale. Results show that V using ICE is qualitatively similar to that using multi‐model individual time series for temperature. However, V is not constant for average and extreme precipitations. V and M dominate before 2050s especially for precipitation. S is dominant in the late 21st century especially for temperature. Mean temperature change is projected to be 30%‐70% greater than its uncertainty until 2050s, while uncertainty becomes 10%‐40% greater than the change in the late 21st century. Precipitation change uncertainty overwhelms its change by 70%‐150% throughout 21st century. Cold regions (e.g. northern China, Qinghai‐Tibetan Plateau) tend to have greater temperature change uncertainties. In dry regions (e.g. northwest China), all three uncertainties tend to be great for changes in average and extreme precipitations. This study emphasizes the importance of considering climate change uncertainty in impact studies, especially taking into account that V is irreducible in the future. Using ICEs without assuming V as constant is an appropriate approach to study climate change uncertainty."

First, Skeie et al. (2018) demonstrate that: "Sensitivity analysis performed by merging the upper (0–700m) and the deep-ocean OHC or using only one OHC dataset (instead of four in the main analysis) both give an enhancement of the mean ECSinf by about 50% from our best estimate."  Thus considering increases in ocean heat content considerable increases estimates of effective ECS above those currently used by policymakers and indeed that used by Hansen et al. (2016).  Furthermore, we all need to remember that the ocean has been warming from pre-industrial conditions for nearly 270 years, and unlike previous interglacial warming periods, the oceans had the entire Holocene to absorb heat, which, is important when evaluating the stability of subsea methane hydrates (particularly in the Arctic Ocean).

Skeie, R. B., Berntsen, T., Aldrin, M., Holden, M., and Myhre, G.: Climate sensitivity estimates – sensitivity to radiative forcing time series and observational data, Earth Syst. Dynam., 9, 879-894,, 2018.

Abstract: "Inferred effective climate sensitivity (ECSinf) is estimated using a method combining radiative forcing (RF) time series and several series of observed ocean heat content (OHC) and near-surface temperature change in a Bayesian framework using a simple energy balance model and a stochastic model. The model is updated compared to our previous analysis by using recent forcing estimates from IPCC, including OHC data for the deep ocean, and extending the time series to 2014. In our main analysis, the mean value of the estimated ECSinf is 2.0°C, with a median value of 1.9°C and a 90% credible interval (CI) of 1.2–3.1°C. The mean estimate has recently been shown to be consistent with the higher values for the equilibrium climate sensitivity estimated by climate models. The transient climate response (TCR) is estimated to have a mean value of 1.4°C (90% CI 0.9–2.0°C), and in our main analysis the posterior aerosol effective radiative forcing is similar to the range provided by the IPCC. We show a strong sensitivity of the estimated ECSinf to the choice of a priori RF time series, excluding pre-1950 data and the treatment of OHC data. Sensitivity analysis performed by merging the upper (0–700m) and the deep-ocean OHC or using only one OHC dataset (instead of four in the main analysis) both give an enhancement of the mean ECSinf by about 50% from our best estimate."

Second, not only do we need to consider heat absorbed by the oceans, but Sallee (2018) notes that: "Since 2006, an estimated 60%–90% of global ocean heat content change associated with global warming is based in the Southern Ocean."  Thus most of this recent increase in ocean heat content is available to destabilize key Antarctic marine glaciers (see the first attached image & associated caption below).

Sallée, J.-B. (2018), "Southern Ocean warming", Oceanography 31(2),

Abstract: "The Southern Ocean plays a fundamental role in global climate. With no continental barriers, it distributes climate signals among the Pacific, Atlantic, and Indian Oceans through its fast-flowing, energetic, and deep-reaching dominant current, the Antarctic Circumpolar Current. The unusual dynamics of this current, in conjunction with energetic atmospheric and ice conditions, make the Southern Ocean a key region for connecting the surface ocean with the world ocean’s deep seas. Recent examinations of global ocean temperature show that the Southern Ocean plays a major role in global ocean heat uptake and storage. Since 2006, an estimated 60%–90% of global ocean heat content change associated with global warming is based in the Southern Ocean. But the warming of its water masses is inhomogeneous. While the upper 1,000 m of the Southern Ocean within and north of the Antarctic Circumpolar Current are warming rapidly, at a rate of 0.1°–0.2°C per decade, the surface subpolar seas south of this region are not warming or are slightly cooling. However, subpolar abyssal waters are warming at a substantial rate of ~0.05°C per decade due to the formation of bottom waters on the Antarctic continental shelves. Although the processes at play in this warming and their regional distribution are beginning to become clear, the specific mechanisms associated with wind change, eddy activity, and ocean-ice interaction remain areas of active research, and substantial challenges persist to representing them accurately in climate models."

Caption for first image: "FIGURE 1. Schematic showing temperature trends in different layers of the Southern Ocean. The layers are defined as main water masses of the Southern Ocean: Subtropical Water (TW), Mode Water (MW), Intermediate Water (IW), Circumpolar Deep Water (CDW), and Bottom Water (BW). Black arrows show the main overturning pathways in the basin, and the dashed black contours show a vertical slice of the deep-reaching Antarctic Circumpolar Current circulating clockwise around the Antarctic continent. The red arrows and associated numbers represent processes at play in the warming of the Southern Ocean and are discussed in the text: 1 increased surface stratification and shallowing of CDW layer, 2 increased heat uptake in the subpolar basins, 3 increased northward heat transport associated with increased subpolar heat uptake, 4 reduced eddy- mediated southward heat transport across the Antarctic Circumpolar Current, 5 intrusion of CDW onto the continental shelves, and 6 warming of the bottom water ventilating the abyssal ocean."

Second, Purkey & Johnson show that the increase in the Antarctic Westerly wind velocities associated with the Antarctic ozone hole has advected the warm CDW southward when it can more easily destabilize key marine glaciers.  As shown in the second accompanying image figure 4a the warm CDW has surged from the north into the Weddell-Enderby Basin at depths shallower than 1000m (depths that can feed directly into the Filchner Trough leading beneath the FRIS. 

Sarah G. Purkey and Gregory C. Johnson (2012), "Global Contraction of Antarctic Bottom Water between the 1980s and 2000s", Journal of Climate,

Abstract: "A statistically significant reduction in Antarctic Bottom Water (AABW) volume is quantified between the 1980s and 2000s within the Southern Ocean and along the bottom-most, southern branches of the meridional overturning circulation (MOC). AABW has warmed globally during that time, contributing roughly 10% of the recent total ocean heat uptake. This warming implies a global-scale contraction of AABW. Rates of change in AABW-related circulation are estimated in most of the world’s deep-ocean basins by finding average rates of volume loss or gain below cold, deep potential temperature (θ) surfaces using all available repeated hydrographic sections. The Southern Ocean is losing water below θ = 0°C at a rate of −8.2 (±2.6) × 106 m3 s−1. This bottom water contraction causes a descent of potential isotherms throughout much of the water column until a near-surface recovery, apparently through a southward surge of Circumpolar Deep Water from the north. To the north, smaller losses of bottom waters are seen along three of the four main northward outflow routes of AABW. Volume and heat budgets below deep, cold θ surfaces within the Brazil and Pacific basins are not in steady state. The observed changes in volume and heat of the coldest waters within these basins could be accounted for by small decreases to the volume transport or small increases to θ of their inflows, or fractional increases in deep mixing. The budget calculations and global contraction pattern are consistent with a global-scale slowdown of the bottom, southern limb of the MOC."

Caption: "FIG. 4. (a)–(c) Total rates of volume change for select basins (legends) below each potential isotherm (DV curves, solid lines) with 95% confidence intervals (shading) along three of the four northward pathways for AABW out of the Southern Ocean from south to north (orange through green to purple). Minimum u values spreading from the orange to the green basins (lower horizontal black lines) and the green to the purple basins (upper horizontal black lines) are estimated from a climatology (Gouretski and Koltermann 2004). Color-coded numbers along the right axis indicate mean depths of selected us for the corresponding basin."
Third, Hansen has warned that changing ENSO patterns (due to global warming) are disproportionately working to destabilize Antarctic marine glaciers, and as noted by Cha et al (2018), all the changes in the ENSO pattern that Hansen warned about are coming true now (i.e. more frequent El Nino events, less frequent La Nina events, and more frequent warming of the Nino 3 region that is primarily responsible for advecting tropical Pacific Ocean heat energy to West Antarctica via atmospheric Rossby waves)

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.


Fourth, I noted that freshwater hosing of the North Atlantic from both ice mass loss from Greenland [see Bondzio et al. (2018) and Ying et al. (2018)] and from a likely pulse of low salinity water released from the Beaufort Sea Gyre (likely sometime in the next two decades); would further slow the global overturning current [see Buarque et al (2018)]; which via the bipolar seesaw mechanism will both further destabilize Antarctic marine glaciers and will increase tropical ocean surface temperatures.

Johannes H. Bondzio et al. (15 November 2018), "Control of ocean temperature on Jakobshavn Isbræ's present and future mass loss", Geophysical Research Letters,


Large uncertainties in model parameterizations and input datasets make projections of future sea level rise contributions of outlet glaciers challenging. Here, we introduce a novel technique for weighing large ensemble model simulations that uses information of key observables. The approach is robust to input errors and yields calibrated means and error estimates of a glacier's mass balance. We apply the technique to Jakobshavn Isbræ, using a model that includes a dynamic calving law, and closely reproduce the observed behavior from 1985 until 2018 by forcing the model with ocean temperatures only. Our calibrated projection suggests that the glacier will continue to retreat and contribute about 5.1 mm to eustatic sea level rise by 2100 under present‐day climatic forcing. Our analysis shows that the glacier's future evolution will strongly depend on the ambient oceanic setting.


Jun Ying et al. (2018), "Inter-model uncertainty in the change of ENSO’s amplitude under global warming: Role of the response of atmospheric circulation to SST anomalies", Journal of Climate,

Abstract: "This study investigates the mechanism of the large inter-model uncertainty in the change of ENSO’s amplitude under global warming, based on 31 CMIP5 models. We find that the uncertainty in ENSO’s amplitude is significantly correlated to that of the change in the response of atmospheric circulation to SST anomalies (SSTAs) in the eastern equatorial Pacific Niño3 region. This effect of the atmospheric response to SSTAs mainly influences the uncertainty in ENSO’s amplitude during El Niño (EN) phases, but not during La Niña (LN) phases, showing pronounced nonlinearity. The effect of the relative SST warming and the present-day response of atmospheric circulation to SSTAs are the two major contributors to the inter-model spread of the change in the atmospheric response to SSTAs, of which the latter is more important. On the one hand, models with a stronger (weaker) mean-state SST warming in the eastern equatorial Pacific, relative to the tropical-mean warming, favor a larger (smaller) increase in the change in the response of atmospheric circulation to SSTAs in the eastern equatorial Pacific during EN. On the other hand, models with a weaker (stronger) present-day response of atmospheric circulation to SSTAs during EN tend to exhibit a larger (smaller) increase in the change under global warming. The result implies that an improved simulation of the present-day response of atmospheric circulation to SSTAs could be effective in lowering the uncertainty in ENSO’s amplitude change under global warming."


Ramos Buarque, S. and Salas y Melia, D.: Link between the North Atlantic Oscillation and the surface mass balance components of the Greenland Ice Sheet under preindustrial and last interglacial climates: a study with a coupled global circulation model, Clim. Past, 14, 1707-1725,, 2018.

Abstract. The relationship between the surface mass balance (SMB) components (accumulation and melting) of the Greenland Ice Sheet (GrIS) and the North Atlantic Oscillation (NAO) is examined from numerical simulations performed with a new atmospheric stretched grid configuration of the Centre National de Recherches Météorologiques Coupled Model (CNRM-CM) version 5.2 under three periods: preindustrial climate, a warm phase (early Eemian, 130kaBP) and a cool phase (late Eemian, 115kaBP) of the last interglacial. The horizontal grid of the atmospheric component of CNRM-CM5.2 is stretched from the tilted pole on Baffin Bay (72°N, 65°W) in order to obtain a higher spatial resolution on Greenland. The correlation between simulated SMB anomalies averaged over Greenland and the NAO index is weak in winter and significant in summer (about 0.6 for the three periods). In summer, spatial correlations between the NAO index and SMB components display different patterns from one period to another. These differences are analyzed in terms of the respective influence of the positive and negative phases of the NAO on accumulation and melting. Accumulation in south Greenland is significantly correlated with the positive (negative) phase of the NAO in a warm (cold) climate. Under preindustrial and 115kaBP climates, melting along the margins is more correlated with the positive phase of the NAO than with its negative phase, whereas at 130kaBP it is more correlated with the negative phase of the NAO in north and northeast Greenland.

Thanks again for all of the well wishes.

Additionally, to be clear past interglacial periods do not service as analogues for projecting future modern-day climate change; for which state-the-art Earth System Models, ESMs, (with ice-cliff and hydrofracturing mechanisms included) are the best tool for projecting coming climate change.  That said, paleo-information from past glacial and interglacial periods can be helpful in calibrating ESM projections.  In this regard the first linked reference (& associated article) by Rehfeld et al (2018) demonstrates that: "… AWI researchers have now demonstrated that, though climate change has decreased around the globe from glacial to interglacial periods, the difference is by no means as pronounced as previously assumed."  This of course means that climate sensitivity (which is positively correlated with climate variability) is currently higher than consensus scientists previously assumed:

Kira Rehfeld et al, Global patterns of declining temperature variability from the Last Glacial Maximum to the Holocene, Nature (2018). DOI: 10.1038/nature25454

Abstract: "Changes in climate variability are as important for society to address as are changes in mean climate1. Contrasting temperature variability during the Last Glacial Maximum and the Holocene can provide insights into the relationship between the mean state of the climate and its variability. However, although glacial–interglacial changes in variability have been quantified for Greenland, a global view remains elusive. Here we use a network of marine and terrestrial temperature proxies to show that temperature variability decreased globally by a factor of four as the climate warmed by 3–8 degrees Celsius from the Last Glacial Maximum (around 21,000 years ago) to the Holocene epoch (the past 11,500 years). This decrease had a clear zonal pattern, with little change in the tropics (by a factor of only 1.6–2.8) and greater change in the mid-latitudes of both hemispheres (by a factor of 3.3–14). By contrast, Greenland ice-core records show a reduction in temperature variability by a factor of 73, suggesting influences beyond local temperature or a decoupling of atmospheric and global surface temperature variability for Greenland. The overall pattern of reduced variability can be explained by changes in the meridional temperature gradient, a mechanism that points to further decreases in temperature variability in a warmer future."

See also:
Title: "Researchers compare global temperature variability in glacial and interglacial periods"

Extract: "On the basis of a unique global comparison of data from core samples extracted from the ocean floor and the polar ice sheets, AWI researchers have now demonstrated that, though climate change has decreased around the globe from glacial to interglacial periods, the difference is by no means as pronounced as previously assumed."

To better quantify the implications of Rehfeld et al (2018)'s finding, the following linked reference by Dessler & Forster (2018) clearly demonstrate that the likely range for ECS in the period from 2000 to 2017 was 2.4 to 4.6C (with a mode and a mean of 2.9 and 3.3C, respectively) as opposed to AR5's cited likely range of 1.5 to 4.5C.

Furthermore, it is important to remember that ECS is not a fixed value but rather is projected to increase with continued global warming, this century:

A. E. Dessler and P.M. Forster (07 August 2018), "An estimate of equilibrium climate sensitivity from interannual variability', Journal of Geophysical Research Atmospheres,

Estimating the equilibrium climate sensitivity (ECS; the equilibrium warming in response to a doubling of CO2) from observations is one of the big problems in climate science. Using observations of interannual climate variations covering the period 2000 to 2017 and a model‐derived relationship between interannual variations and forced climate change, we estimate ECS is likely 2.4‐4.6 K (17‐83% confidence interval), with a mode and median value of 2.9 and 3.3 K, respectively. This analysis provides no support for low values of ECS (below 2 K) suggested by other analyses. The main uncertainty in our estimate is not observational uncertainty, but rather uncertainty in converting observations of short‐term, mainly unforced climate variability to an estimate of the response of the climate system to long‐term forced warming.

Plain language summary
Equilibrium climate sensitivity (ECS) is the amount of warming resulting from doubling carbon dioxide. It is one of the important metrics in climate science because it is a primary determinant of how much warming we will experience in the future. Despite decades of work, this quantity remains uncertain: the last IPCC report stated a range for ECS of 1.5‐4.5 deg. Celsius. Using observations of interannual climate variations covering the period 2000 to 2017, we estimate ECS is likely 2.4‐4.6 K. Thus, our analysis provides no support for the bottom of the IPCC's range."

You can obtain a copy of the paper here:

Finally, Dessler & Forster (2018)'s findings combined with those of Brown & Caldeira 2017 and Caldwell 2018 should place best estimates of the current value of ECS at 3.5 or greater.  This is important in that it increases the probability of abrupt ice mass loss from the WAIS within the next couple of decades.  Also, Rehfeld et al (2018)'s findings confirm Hansen's projections about the coming of superstorms when the ice mass loss from the WAIS cools the surface of the Southern Ocean, and warms the tropical oceans, thus increasing the atmospheric thermal gradient from the tropics to the poles.

Great to see you back ASLR, even if on a limited fashion. Your scientific contributions are sorely missed. Hopefully they will increase again as time goes by, as there are many subjects you have been covering that have been suffering as a result of your absence.


You (& others who are so inclined) should feel free to re-post any information that I provide in this thread to other threads where you feel that contrarians (and/or those who err on the side of least drama) are putting their collective thumbs on the scales.

For example, in the 'Hansen e al paper: 3+ meters SLR by 2100' thread, Reply #713 indicated that the findings of Polyak et al. (2018) that "Altogether, the data show that the MIS-5e highstand began by 126.6  ± 0.4 ka and ended no earlier than 116.0  ± 0.8 ka, representing 10.5 kyr of remarkable Western Mediterranean RSL stability between 1.4 and 2.9 m.a.p.s.l.", induced sidd to state:

"I find this striking because part of my concern for WAIS stability stems from the evidence for late Eemina sea level rise. If that did not actually happen, my concern is (slightly) diminished.",1327.700.html

In this regard, I note that the correct interpretation of paleo-SLR data is notoriously challenging and includes many uncertainties that could easily change Polyak et al. (2018)'s conclusions such as is illustrated by their own Fig. 3 (see the first attached image), including:

1. They show that their calculated RSL values (ranging from +1.4m to well over +14m) depend significantly on what GIA model and GIA assumptions that they utilize.
2. Their simplified GIA assumptions do not effectively consider phased ice mass loss scenarios from the NH and the SH.

See also:

Title: "Scientists find stable sea levels during last interglacial"

Extract: ""This is the most accurate, best resolved sea level record for MIS-5e of the last interglacial period," said Polyak. "It provides exceptionally accurate timing of the sea level history during the above mentioned period and shows that it rose to 6 meters above present sea level ~127,000 years ago, it would have gradually fell to 2 meters by 122,000 years ago, and would have stayed at that elevation for the remainder of the sea level highstand to 116,000 years ago," says Onac. "The results suggest that if the pre-industrial temperature will be surpassed by 1.5 to 2°C, sea level will respond and rise 2 to 6 meters (7 to 20 feet) above present sea level.""

& see:

Victor J. Polyak, Bogdan P. Onac, Joan J. Fornós, Carling Hay, Yemane Asmerom, Jeffrey A. Dorale, Joaquín Ginés, Paola Tuccimei, Angel Ginés. A highly resolved record of relative sea level in the western Mediterranean Sea during the last interglacial period. Nature Geoscience, 2018; DOI: 10.1038/s41561-018-0222-5

Abstract: "The magnitude and trajectory of sea-level change during marine isotope stage (MIS) 5e of the last interglacial period is uncertain. In general, sea level may have been 6–9 m above present sea level, with one or more oscillations of up to several metres superimposed. Here we present a well-dated relative sea-level record from the island of Mallorca in the western Mediterranean Sea for MIS-5e, based on the occurrence of phreatic overgrowths on speleothems forming near sea level. We find that relative sea-level in this region was within a range of 2.15 ±  0.75 m above present levels between 126,600 ±  400 and 116,000 ±  800 years ago, although centennial-scale excursions cannot be excluded due to some gaps in the speleothem record. We corrected our relative sea-level record for glacio-isostatic adjustment using nine different glacial isostatic models. Together, these models suggest that ice-equivalent sea-level in Mallorca peaked at the start of MIS-5e then gradually decreased and stabilized by 122,000 years ago, until the highstand termination 116,000 years ago. Our sea-level record does not support the hypothesis of rapid sea-level fluctuations within MIS-5e. Instead, we suggest that melting of the polar ice sheets occurred early in the interglacial period, followed by gradual ice-sheet growth."

Additional information Supplementary information is available for this paper at s41561-018-0222-5.

As further evidence that Polyak et al. (2018) may be erring on the side of least drama, Stocchi et al. (2018) find that: "Evidences of two MIS 5e RSL stands are found in Mallorca, northern Tyrrhenian coast of Italy, southeastern Sardinia and Tunisia."; which directly contradicts Polyak et al. (2018)'s conclusion.


Stocchi et al. (2018), "MIS 5e relative sea-level changes in the Mediterranean Sea: Contribution of isostatic disequilibrium", Quaternary Science Reviews 185, 122-134,

Abstract: "Sea-level indicators dated to the Last Interglacial, or Marine Isotope Stage (MIS) 5e, have a twofold value. First, they can be used to constrain the melting of Greenland and Antarctic Ice Sheets in response to global warming scenarios. Second, they can be used to calculate the vertical crustal rates at active margins. For both applications, the contribution of glacio- and hydro-isostatic adjustment (GIA) to vertical displacement of sea-level indicators must be calculated. In this paper, we re-assess MIS 5e sea-level indicators at 11 Mediterranean sites that have been generally considered tectonically stable or affected by mild tectonics. These are found within a range of elevations of 2–10 m above modern mean sea level. Four sites are characterized by two separate sea-level stands, which suggest a two-step sea-level highstand during MIS 5e. Comparing field data with numerical modeling we show that (i) GIA is an important contributor to the spatial and temporal variability of the sea-level highstand during MIS 5e, (ii) the isostatic imbalance from the melting of the MIS 6 ice sheet can produce a >2.0 m sea-level highstand, and (iii) a two-step melting phase for the Greenland and Antarctic Ice Sheets reduces the differences between observations and predictions. Our results show that assumptions of tectonic stability on the basis of the MIS 5e records carry intrinsically large uncertainties, stemming either from uncertainties in field data and GIA models. The latter are propagated to either Holocene or Pleistocene sea-level reconstructions if tectonic rates are considered linear through time."

Extract: "Conclusions
1. The observed range of MIS 5e RSL highstand from 11 tectonically stable sites in the Mediterranean is comprised between 2 and 10m above present msl.  The observed highstands are not necessarily coeval.  Evidences of two MIS 5e RSL stands are found in Mallorca, northern Tyrrhenian coast of Italy, southeastern Sardinia and Tunisia.
2. The GIA-induced RSL changes across the Mediterranean are characterized by significant regional variability throughout the MIS 5e.  The Earth is in isostatic imbalance and a generalized RSL above present sea level is predicted. …
3. According to GIA, the MIS 5e RSL highstand occurs at different times as a function of the geographical location in the Mediterranean.
4. To precisely quantify the GrIS and AIS retreat during MIS5e on the basis on RSL data, requires that the maximum extent, thickness and retreat of the MIS 6 ice sheets, and in particular of Fennoscandia, are constrained.
5. A two-step melting chronology where the GrIS and AIS retreat is out of phase is capable of reconciling predictions and observation provided that the GIA processes are included.
6. Neglecting the uncertainties that are related to RSL indicators and GIA may lead to over or underestimations of local crustal motions even at sites that are considered tectonically stable.  As a consequence, we suggest that caution should be exercised when extrapolating long-term tectonic rates from MIS 5e shorelines."

Furthermore Barlow et al. (2018) find no evidence that RSL fell (note that it takes longer to form new ice sheets and it can take for them to collapse) significantly from the circa 127kya peak (see the second attached image) during the MIS 5e (Eemian).

Barlow NLM, McClymont EL, Whitehouse PL, Stokes CR, Jamieson SSR, Woodroffe SA, Bentley MJ, Callard SL, Ó Cofaigh C, Evans DJA, Horrocks JR, Lloyd JM, Long AJ, Margold M, Roberts DH & Sanchez-Montes ML (2018), "Lack of evidence for a substantial sea-level fluctuation within the Last Interglacial", Nature Geoscience, vol. 11, 627–634,

Abstract: "During the Last Interglacial, global mean sea level reached approximately 6 to 9 m above the present level. This period of high sea level may have been punctuated by a fall of more than 4 m, but a cause for such a widespread sea-level fall has been elusive. Reconstructions of global mean sea level account for solid Earth processes and so the rapid growth and decay of ice sheets is the most obvious explanation for the sea-level fluctuation. Here, we synthesize published geomorphological and stratigraphic indicators from the Last Interglacial, and find no evidence for ice-sheet regrowth within the warm interglacial climate. We also identify uncertainties in the interpretation of local relative sea-level data that underpin the reconstructions of global mean sea level. Given this uncertainty, and taking into account our inability to identify any plausible processes that would cause global sea level to fall by 4 m during warm climate conditions, we question the occurrence of a rapid sea-level fluctuation within the Last Interglacial. We therefore recommend caution in interpreting the high rates of global mean sea-level rise in excess of 3 to 7 m per 1,000 years that have been proposed for the period following the Last Interglacial sea-level lowstand."

Extract: "In conclusion, reconstructions of GMSL during the LIG4,5 have raised the intriguing possibility that fluctuations in ice-sheet volume occurred within the interglacial, that is, ice sheets regrew and then decayed. We have considered several possible driving mechanisms, acting alone or in combination, for multimetre changes in GMSL during the LIG. We find that the current understanding of ice-sheet histories during MIS 6 is not adequate enough to rule out the possibility that limitations in the modelling of the solid Earth response could be contributing to the appearance of a GMSL fall during the LIG3,11. However, if the GMSL fall was driven by changes in ice-sheet mass balance, it would require 1.15–3.45 million km3 of ice to form in less than 1,000 years; we found little geomorphological or sedimentary evidence for such substantial ice-sheet regrowth during the LIG. It is also clear that large uncertainties associated with the interpretation of some local RSL data that underpin the reconstructed GMSL curve remain. Taken together, our analysis leads us to question the occurrence of a rapid GMSL fall within the LIG, which also raises important questions about the very high reconstructed rates of GMSL rise following the lowstand; reported to be approximately 3 to 7 m kyr–1 (ref. 5).

We conclude that it is critical that future reconstructions of GMSL during the LIG include a range of realistic ice-sheet scenarios from the preceding glacial (MIS 6); take into account the impact of dynamic topography on the reconstructed elevations of former RSLs; and assemble a geographically and temporally widespread dataset of local RSL, with careful interpretation of fossil sea-level indicators with respect to tidal datums and accurate chronologies. Until these issues are better resolved, we would urge caution in using rates of GMSL rise from the LIG to project future sea-level changes.

5. Kopp, R. E., Simons, F. J., Mitrovica, J. X., Maloof, A. C. & Oppenheimer, M. A probabilistic assessment of sea level variations within the last interglacial stage. Geophys. J. Int. 193, 711–716 (2013)."

Finally, the third attached image from Austermann et al. (2017) indicates that correctly paleo-SLR data to account for dynamic topography (DT) can increase calculated estimates of paleo-SLR by about a meter in the Western Mediterranean during MIS 5e (Eemian);

Austermann J, Mitrovica JX, Huybers P and Rovere A (2017), "Detection of a dynamic topography signal in last interglacial sea-level records", Science Advances, vol. 3(7), e1700457,

Abstract: "Estimating minimum ice volume during the last interglacial based on local sea-level indicators requires that these indicators are corrected for processes that alter local sea level relative to the global average. Although glacial isostatic adjustment is generally accounted for, global scale dynamic changes in topography driven by convective mantle flow are generally not considered. We use numerical models of mantle flow to quantify vertical deflections caused by dynamic topography and compare predictions at passive margins to a globally distributed set of last interglacial sea-level markers. The deflections predicted as a result of dynamic topography are significantly correlated with marker elevations (>95% probability) and are consistent with construction and preservation attributes across marker types. We conclude that a dynamic topography signal is present in the elevation of last interglacial sea-level records and that the signal must be accounted for in any effort to determine peak global mean sea level during the last interglacial to within an accuracy of several meters."

Extract: "A complication in all these studies is that various geodynamic processes contribute to the present elevation of paleo sea level records (8). A notable example of these processes is tectonic uplift or subsidence at active plate boundaries [for example, see Zazo et al. (9)], which often leads to the exclusion of these sites in reconstructions of past GMSL. Another important deformational process is the response of the Earth system to changes in ice and ocean loading during ice age cycles (10, 11), or glacial isostatic adjustment (GIA), a process first studied in the context of the LIG by Lambeck and Nakada (12). The accuracy of model-derived corrections for this global process is subject to uncertainties in ice history and mantle viscoelastic structure [for example, see Lambeck et al. (13)]. Additionally, the redistribution of sediment can lead to sea level changes through the buildup of topography and loading-induced deformation of the solid Earth and gravity field (14, 15).

Earth’s surface is further deflected by viscous stresses associated with buoyancy variations and flow within Earth’s convective mantle that can alter the elevation of sea-level markers subsequent to their formation (16–22). Effects of this so-called dynamic topography (DT) on the current elevation of sea-level markers dating to the mid-Pliocene (~3 million years ago) have been documented (23–25) and imply meter-scale displacements for LIG sea-level markers (24). Kopp et al. (4) incorporated uncertainties due to vertical land movement and applied nonzero rates in several passive margin regions. Although this correction may implicitly include the DT process, effects of DT are generally not addressed in sea level studies of Pleistocene interglacials and have not previously been shown to be detectable during the LIG. Here, we quantify and analyze the effects of DT on globally distributed markers of local peak sea level during the LIG."


Thank you all.


As stated in the first linked article, when Hansen et al. (2016) clearly presented their case/scenarios for abrupt SLR and associated coming superstorms in the coming decades; it "… met with skepticism from a number of other climate scientists."  However, this first linked article and the associated reference by Alessandro Silvano et al (18 Apr 2018), provides some concrete evidence that at least portions of Hansen's ice-climate feedback mechanism (e.g. reduced global overturning circulation) are already being activated. 

Title: "One of the most worrisome predictions about climate change may be coming true"

Extract: "Two years ago, former NASA climate scientist James Hansen and a number of colleagues laid out a dire scenario in which gigantic pulses of fresh water from melting glaciers could upend the circulation of the oceans, leading to a world of fast-rising seas and even superstorms.

Hansen’s scenario was based on a computer simulation, not hard data from the real world, and met with skepticism from a number of other climate scientists. But now, a new oceanographic study appears to have confirmed one aspect of this picture — in its early stages, at least.

The new research, based on ocean measurements off the coast of East Antarctica, shows that melting Antarctic glaciers are indeed freshening the ocean around them. And this, in turn, is blocking a process in which cold and salty ocean water sinks below the sea surface in winter, forming “the densest water on the Earth,” in the words of study lead author Alessandro Silvano, a researcher with the University of Tasmania in Hobart."


Alessandro Silvano et al (18 Apr 2018), "Freshening by glacial meltwater enhances melting of ice shelves and reduces formation of Antarctic Bottom Water", Science Advances, Vol. 4, no. 4, eaap9467, DOI: 10.1126/sciadv.aap9467

Abstract: "Strong heat loss and brine release during sea ice formation in coastal polynyas act to cool and salinify waters on the Antarctic continental shelf. Polynya activity thus both limits the ocean heat flux to the Antarctic Ice Sheet and promotes formation of Dense Shelf Water (DSW), the precursor to Antarctic Bottom Water. However, despite the presence of strong polynyas, DSW is not formed on the Sabrina Coast in East Antarctica and in the Amundsen Sea in West Antarctica. Using a simple ocean model driven by observed forcing, we show that freshwater input from basal melt of ice shelves partially offsets the salt flux by sea ice formation in polynyas found in both regions, preventing full-depth convection and formation of DSW. In the absence of deep convection, warm water that reaches the continental shelf in the bottom layer does not lose much heat to the atmosphere and is thus available to drive the rapid basal melt observed at the Totten Ice Shelf on the Sabrina Coast and at the Dotson and Getz ice shelves in the Amundsen Sea. Our results suggest that increased glacial meltwater input in a warming climate will both reduce Antarctic Bottom Water formation and trigger increased mass loss from the Antarctic Ice Sheet, with consequences for the global overturning circulation and sea level rise."

Indeed, the second reference Caesar et al. (2018) (and the associated linked RealClimate article), provide further proof that the AMOC is slowing as projected by Hansen et al (2016).

Caesar et al. (April 12, 2018) "Observed fingerprint of a weakening Atlantic Ocean overturning circulation", Nature, Vol 556,

Abstract: "The Atlantic meridional overturning circulation (AMOC)—a system of ocean currents in the North Atlantic—has a major impact on climate, yet its evolution during the industrial era is poorly known owing to a lack of direct current measurements. Here we provide evidence for a weakening of the AMOC by about 3 ± 1 sverdrups (around 15 per cent) since the mid-twentieth century. This weakening is revealed by a characteristic spatial and seasonal sea-surface temperature ‘fingerprint’—consisting of a pattern of cooling in the subpolar Atlantic Ocean and warming in the Gulf Stream region—and is calibrated through an ensemble of model simulations from the CMIP5 project. We find this fingerprint both in a high-resolution climate model in response to increasing atmospheric carbon dioxide concentrations, and in the temperature trends observed since the late nineteenth century. The pattern can be explained by a slowdown in the AMOC and reduced northward heat transport, as well as an associated northward shift of the Gulf Stream. Comparisons with recent direct measurements from the RAPID project and several other studies provide a consistent depiction of record-low AMOC values in recent years."

See also:

Title: "If you doubt that the AMOC has weakened, read this"

Furthermore, the third linked reference (Pedro et al. (2018)) demonstrates that the bipolar seesaw (associated with changes in the global overturning circulation) is indeed part of a larger 'interhemispheric coupling' that is a bigger part of Hansen's ice-climate feedback mechanism.  However, while Pedro et al (2018) focus on calibrating their computer model for 'interhemispheric coupling' first triggered by ice mass loss from the Greenland Ice Sheet, GIS; the associated first image clearly shows paleo-evidence that 'interhemispheric coupling' triggered by ice mass loss from the Antarctic Ice Sheet, AIS, leads to an abrupt warming of the GIS.  This indicates that if my various posts in this thread are correct that the AIS may contribute multiple meters to SLR in the coming decades, then this will likely trigger a rapid warming of the GIS in the subsequent decades; which would then drive further abrupt SLR & more superstorms.

Joel B. Pedro , Markus Jochum, Christo Buizert, Feng He, Stephen Barker & Sune O. Rasmussen (15 July 2018), "Beyond the bipolar seesaw: Toward a process understanding of interhemispheric coupling", Quaternary Science Reviews, Volume 192, , Pages 27-46,

Abstract: "The thermal bipolar ocean seesaw hypothesis was advanced by Stocker and Johnsen (2003) as the ‘simplest possible thermodynamic model’ to explain the time relationship between Dansgaard–Oeschger (DO) and Antarctic Isotope Maxima (AIM) events. In this review we combine palaeoclimate observations, theory and general circulation model experiments to advance from the conceptual model toward a process understanding of interhemispheric coupling and the forcing of AIM events. We present four main results: (1) Changes in Atlantic heat transport invoked by the thermal seesaw are partially compensated by opposing changes in heat transport by the global atmosphere and Pacific Ocean. This compensation is an integral part of interhemispheric coupling, with a major influence on the global pattern of climate anomalies. (2) We support the role of a heat reservoir in interhemispheric coupling but argue that its location is the global interior ocean to the north of the Antarctic Circumpolar Current (ACC), not the commonly assumed Southern Ocean. (3) Energy budget analysis indicates that the process driving Antarctic warming during AIM events is an increase in poleward atmospheric heat and moisture transport following sea ice retreat and surface warming over the Southern Ocean. (4) The Antarctic sea ice retreat is itself driven by eddy-heat fluxes across the ACC, amplified by sea-ice–albedo feedbacks. The lag of Antarctic warming after AMOC collapse reflects the time required for heat to accumulate in the ocean interior north of the ACC (predominantly the upper 1500 m), before it can be mixed across this dynamic barrier by eddies."

Finally for this post, the second attached image from the Sentinel satellite for Nov 23 2018, shows that the Southwest Tributary Ice Shelf is no longer blocked by the Pine Island Ice Shelf; which means that the ice flow velocity of the Southwest Tributary Glacier is currently accelerating; which in turn means that the east shear margin of the Thwaites Glacier (see the third image) well progressively offer less stabilization to the Thwaites Glacier; which in turn may well trigger the abrupt collapse of major portions of the Byrd Subglacial Basin within the next one to two decades (when considering concurrent influences from the ENSO & ASL interactions).

Welcome back ASLR.

With a limited bandwidth ;)


As I said that I would make a few posts (which I take to mean three posts today), I provide the following like to an article that cites research that confirms that current ice mass loss is contributing (see blue line in the attached image) to the drift of the Earth's rotational axis about the poles:

Scientists Identified Three Reasons Responsible for Earth’s Spin Axis Drift

Extract: "A typical desk globe is designed to be a geometric sphere and to rotate smoothly when you spin it. Our actual planet is far less perfect—in both shape and in rotation.

Earth is not a perfect sphere. When it rotates on its spin axis—an imaginary line that passes through the North and South Poles—it drifts and wobbles. These spin-axis movements are scientifically referred to as "polar motion." Measurements for the 20th century show that the spin axis drifted about 4 inches (10 centimeters) per year. Over the course of a century, that becomes more than 11 yards (10 meters).

Using observational and model-based data spanning the entire 20th century, NASA scientists have for the first time identified three broadly-categorized processes responsible for this drift—contemporary mass loss primarily in Greenland, glacial rebound, and mantle convection.

"The traditional explanation is that one process, glacial rebound, is responsible for this motion of Earth's spin axis. But recently, many researchers have speculated that other processes could have potentially large effects on it as well," said first author Surendra Adhikari of NASA's Jet Propulsion Laboratory in Pasadena, California."

As a follow-on to my last post I note that, Pollard, DeConto & Alley (2018) use their Antarctic Ice Sheet, AIS, model with ice-cliff and hydrofracturing failure mechanisms together with ice mélange back pressures calibrated to that currently observed for the Jakobshavn marine terminating glacier in Greenland.  Pollard et al (2018) then assumed the abrupt imposition of warm mid-Pliocene climate conditions (which roughly have a GMSTA above pre-industrial of over 1.5C and ocean water temperatures beneath the ice of key AIS marine glaciers comparable to those found by Bronselaer et al (2018) after 2040).  Assuming these approximations Antarctica could look like the illustrations shown in column 'b' in the first image, and may contributed about 3 m to SLR, by roughly 2090, per panel 'a' of the second attached image.  Furthermore, the third attached image (from Hansen (2018)) show that currently GMSTA is about 1.05C and that the most recent two La Ninas imply a warming rate of 0.38°C per decade; which indicates that by 2040 GMSTA may be over 1.8C (which would match Mid-Pliocene conditions).  Finally, the last attached image (from Hansen et al (2016)) shows gold colored curves for abrupt ice sheet mass loss beginning circa 2040, that show such an ice mass loss would temporarily cool GMSTA, but would also temporarily increase the global energy imbalance, which implies an abrupt & temporary increase in climate sensitivity that would wreak severe storm activity around the planet:

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.,

Abstract: "Rapidly retreating thick ice fronts can generate large amounts of mélange (floating ice debris), which may affect episodes of rapid retreat of Antarctic marine ice. In modern Greenland fjords, mélange provides substantial back pressure on calving ice faces, which slows ice-front velocities and calving rates. On the much larger scales of West Antarctica, it is unknown if mélange could clog seaways and provide enough back pressure to act as a negative feedback slowing retreat.  Here we describe a new mélange model, using a continuum mechanical formulation that is computationally feasible for long-term continental Antarctic applications. It is tested in an idealized rectangular channel and calibrated very basically using observed modern conditions in Jakobshavn fjord, West Greenland. The model is then applied to drastic retreat of Antarctic ice in response to warm mid-Pliocene climate. With mélange parameter values that yield reasonable modern Jakobshavn results, Antarctic marine ice still retreats drastically in the Pliocene simulations, with little slowdown despite the huge amounts of mélange generated. This holds both for the rapid early collapse of West Antarctica, and later retreat into major East Antarctic basins. If parameter values are changed to make the mélange much more resistive to flow, far outside the range for reasonable Jakobshavn results, West Antarctica still collapses and retreat is slowed or prevented only in a few East Antarctic basins."

While in other threads I have stated that I would no longer post in the ASIF, I have decided that as the risk of abrupt sea level rise, SLR, this century is so much higher than many decisionmakers appreciate; I will periodically post in this one ASIF thread.  In this regard, I make a few posts illustrating how decisionmakers are confused about the topic of abrupt SLR, and I begin by providing the first linked reference by Pattyn (2018), which points out that many (most) current consensus ice-sheet model projections of Antarctic Ice Sheet, AIS, contribution to SLR used inappropriate equilibrium initial states for their models; while dynamical initial states are necessary for short-term projections on the order of decades.  Furthermore, Pattyn (2018) notes that such dynamical initial conditions need to properly account for not only Marine Ice Sheet Instability, MISI, but also for Marine Ice Cliff Instability, MICI, and for hydro-fracturing mechanisms (see the first attached image).

Frank Pattyn (2018 Jul 16), "The paradigm shift in Antarctic ice sheet modelling", Nat Commun. 2018; 9: 2728; doi:  10.1038/s41467-018-05003-z

Abstract: "The Antarctic ice sheet is one of the largest potential contributors to future sea level rise. Predicting its future behaviour using physically-based ice sheet models has been a bottleneck for the past decades, but major advances are ongoing."

Extract: "A key aspect of projecting future Antarctic mass loss with dynamical ice sheet models is related to the initial state of the model. Since ice sheet models were initially applied for palaeo-climatic studies on long time scales, initialisation was generally obtained from a long spin-up time leading to a steady-state ice sheet (both in terms of geometry and thermodynamics). However, for predictions on shorter time scales (decades to centuries), a stable spin-up generally leads to an ice sheet geometry far different from the one currently observed, which is one of the reasons why such ice sheet models may respond differently than observations suggest. Moreover, using a steady-state for initialising the ice sheet prevents models from properly accounting for the dynamical mass losses observed over the last decade, as the present-day ice sheet is not in steady state. Motivated by the increasing ice sheet imbalance of the ASE glaciers over the last 20 years, and supported by the recent boom in satellite data availability, data-assimilation methods are progressively used to evaluate unknown fields using time-evolving states accounting for the transient nature of observations and the model dynamics."

Next I note that, Bronselaer et al (2018) used an AIS model that does not account for MICI nor hydro-fracturing (which are not likely to be significant before 2040) to show that by 2040 upwelling of relatively warm circumpolar deep water, CDW, around Antarctic will shift the potential ice melting temperature difference upward from below 1,000 m depth to roughly 750 m depth, and will increasingly advect this warm CDW towards the grounding line (see the second attached image) for key marine glaciers such as the Pine Island Glacier, PIG (see the third image wrt the water depth of the grounding line) and the Thwaites Glacier (see the fourth image).  What is critical to note wrt Bronselaer et al (2018) is that by 2040 the temperature of the Southern Ocean would be thousands of years from full equilibrium, but for key AIS marine glaciers both the top and bottom ice surfaces exposed to air and water respectively will experience ice mass loss sufficient to trigger localized MICI and hydro-fracturing mechanisms (if they had been included in Bronselaer et al (2018)'s model.

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

Abstract: "Meltwater from the Antarctic Ice Sheet is projected to cause up to one metre of sea-level rise by 2100 under the highest greenhouse gas concentration trajectory (RCP8.5) considered by the Intergovernmental Panel on Climate Change (IPCC). However, the effects of meltwater from the ice sheets and ice shelves of Antarctica are not included in the widely used CMIP5 climate models, which introduces bias into IPCC climate projections. Here we assess a large ensemble simulation of the CMIP5 model ‘GFDL ESM2M’ that accounts for RCP8.5-projected Antarctic Ice Sheet meltwater. We find that, relative to the standard RCP8.5 scenario, accounting for meltwater delays the exceedance of the maximum global-mean atmospheric warming targets of 1.5 and 2 degrees Celsius by more than a decade, enhances drying of the Southern Hemisphere and reduces drying of the Northern Hemisphere, increases the formation of Antarctic sea ice (consistent with recent observations of increasing Antarctic sea-ice area) and warms the subsurface ocean around the Antarctic coast. Moreover, the meltwater-induced subsurface ocean warming could lead to further ice-sheet and ice-shelf melting through a positive feedback mechanism, highlighting the importance of including meltwater effects in simulations of future climate."

Caption for the second attached image: "Fig. 5 | Mechanism for ocean warming. a, Hovmoller diagram of the meltwater-induced ocean temperature anomaly, averaged along the Antarctic coast, as a function of time. The black dotted line indicates the maximum warming in a given year. b, c, Schematic of the meltwater-induced Southern Ocean subsurface warming, shown as a zonal-mean cross-section. In the pre-industrial state (b), isopycnals (black lines) are tilted towards the ocean surface by westerly winds (black circles, directed out of the page), away from the continental shelf, with an upward heat flux transporting heat from the warm CDW (orange water) towards the cooler surface (blue water), as shown by the red arrow. In the perturbed state (c), meltwater from the Antarctic Ice Sheet freshens the surface (blue), depressing isopycnals (solid to dashed black lines) so that isopycnal mixing transports heat towards the continent rather than towards the ocean surface (red arrow), leading to coastal warming at depth around the shelf and cooling at the surface."

The rest / Re: Mueller Investigation & Cohen Investigation
« on: November 11, 2018, 04:43:05 PM »
The linked article provides still more evidence that Acting AG Whitaker is little more than an alt-right tool, who should be removed (by the courts) from his current responsibility for making sure that federal laws are not violated:

Title: "Whitaker said he supports state's rights to nullify federal law"

Extract: "Matthew Whitaker, the new acting attorney general, has said that states have the right to nullify federal law, but that they need the political courage to do so."

Antarctica / Re: PIG has calved
« on: November 08, 2018, 06:13:15 PM »
The attached Nullschool weather image shows MSLP and surface wind patterns for Nov 8 2018.  This image shows that (likely due to the current El Nino condition) the Amundsen Sea Low, ASL, is positioned so as to direct surface winds directly into the Amundsen Sea Embayment, ASE; which tends to induce upwelling of relatively warm circumpolar deep water, CDW, into the ASE; which then accelerates basal ice melting of both the sea ice and floating ice shelves, therein.  If such conditions continue for several months this will promote ice loss from both the PIIS and the SWTIS (not to mention also the Thwaites Ice Shelf).

The forum / Re: Forum Decorum
« on: November 06, 2018, 12:43:31 AM »
Re: "TPTB give permission for conservative posts in this forum to be more reactionary, because they expect it."

Re: "in my opinion the Forum Decorum imposed on this forum supports bothsidesism"

Examples supporting these statements might bolster them.


While there are more examples than I care to cite, I find it an example of bothsidesism that this forum has a thread entitled "ECS is 2.5" in the science folder (see Reply #37 in that thread).  Having a thread with this title: a) promotes inaction on climate change which promotes consumption and b) as indicated by Reply #33 in that thread it is bothsidesism to compare calculation of ECS from a spreadsheet with calculations of ECS from state of the art climate models such as those presented by Andrew Dessler.

The forum / Re: Forum Decorum
« on: November 05, 2018, 11:50:15 PM »
... snip ...

And what does this have to do with Forum Decorum?

It is my opinion that TPTB give permission for conservative posts in this forum to be more reactionary, because they expect it.


Meaning that in my opinion the Forum Decorum imposed on this forum supports bothsidesism; which is scientifically indefensible; as bothsidesism resulting in delaying climate change action and promotes consumption by allowing conservatives to promote such behavior without providing adequate evidence of their positions.

The forum / Re: Forum Decorum
« on: November 05, 2018, 07:40:58 PM »
... snip ...

And what does this have to do with Forum Decorum?

It is my opinion that TPTB give permission for conservative posts in this forum to be more reactionary, because they expect it.

Antarctica / Re: PIG has calved
« on: October 30, 2018, 09:38:49 PM »
The PIIS is surely in record retreat territory. I am hoping for a long-term animation or graphic showing the current calving front against the past few years of PIIS advance and calving activity.
Turns out Stef Lhermitte has posted such an animation going back to 1973. The retreat is indeed into record territory, and especially so at the important junction of the SW tributary and the PIIS.

Edit: this is the same animation appearing in ASLR's link above.

Here is a screen grab from Stef Lhermittee's animation on his site:

The linked reference provides paleo-evidence that prior to the PETM, many of the Earth's carbon cycles became destabilized (i.e. weakened negative feedbacks and greater sensitivity to small shocks).  This is not good news, but this information may be useful in helping to better calibrate state-of-the-art Earth System Models:

Armstrong McKay, D. I. and Lenton, T. M.: Reduced carbon cycle resilience across the Palaeocene–Eocene Thermal Maximum, Clim. Past, 14, 1515-1527,, 2018.

Abstract. Several past episodes of rapid carbon cycle and climate change are hypothesised to be the result of the Earth system reaching a tipping point beyond which an abrupt transition to a new state occurs. At the Palaeocene–Eocene Thermal Maximum (PETM) at  ∼ 56Ma and at subsequent hyperthermal events, hypothesised tipping points involve the abrupt transfer of carbon from surface reservoirs to the atmosphere. Theory suggests that tipping points in complex dynamical systems should be preceded by critical slowing down of their dynamics, including increasing temporal autocorrelation and variability. However, reliably detecting these indicators in palaeorecords is challenging, with issues of data quality, false positives, and parameter selection potentially affecting reliability. Here we show that in a sufficiently long, high-resolution palaeorecord there is consistent evidence of destabilisation of the carbon cycle in the  ∼ 1.5Myr prior to the PETM, elevated carbon cycle and climate instability following both the PETM and Eocene Thermal Maximum 2 (ETM2), and different drivers of carbon cycle dynamics preceding the PETM and ETM2 events. Our results indicate a loss of resilience (weakened stabilising negative feedbacks and greater sensitivity to small shocks) in the carbon cycle before the PETM and in the carbon–climate system following it. This pre-PETM carbon cycle destabilisation may reflect gradual forcing by the contemporaneous North Atlantic Volcanic Province eruptions, with volcanism-driven warming potentially weakening the organic carbon burial feedback. Our results are consistent with but cannot prove the existence of a tipping point for abrupt carbon release, e.g. from methane hydrate or terrestrial organic carbon reservoirs, whereas we find no support for a tipping point in deep ocean temperature.

The rest / Re: The Trump Presidency (was "Presidential Poll")
« on: October 17, 2018, 10:00:43 PM »
The linked article has details from the gruesome tape that Turkey made of Khashoggi's alleged torture/execution?

Title: "What we know about what happened to Jamal Khashoggi"

•   "On whether he has asked for the audio and video evidence: "We have asked for it, if it exists... I'm not sure yet that it exists — probably does, possibly does."

•   However, the WSJ reports that "Turkish officials said they shared... the details of an audio recording with both the U.S. and Saudi Arabia.""

Policy and solutions / Re: UN Climate Agreement - Paris 2015 and beyond
« on: October 17, 2018, 04:41:33 PM »
When thinking about future GHG emissions from coal it is important to take a holistic viewpoint, and to consider how countries like Indonesia, Taiwan, Vietnam, Malaysia, Thailand, Philippines, Pakistan and other Asian countries are trending (especially as China's Belt and Road Initiative shift coal consumption from China to its neighbors):

Title: "The Center of Coal Demand Keeps Shifting"

Extract: "Coal accounted for 44 percent of energy-related CO2 emissions in 2016, even though it provided 27 percent of the world’s primary energy. The world needs to either curb coal use or develop technologies that limit carbon emissions from coal to meet its climate goals. In policy circles, this challenge is often framed around specific countries—the need for Germany, China, or the United States, for example, to reduce coal use. But this conversation, while essential, tends to underrate how much of the world’s coal challenge is now an Asian challenge. Unless Asia can find other energy sources to meet its needs, our efforts to curb CO2 emissions from coal will likely fail.

Asian demand is dominated by China, whose consumption has weakened in recent years (down 4 percent relative to the 2013 peak). But demand outside China is growing. In part, this is due to India, although its coal use is still less than a fourth of China’s. Among the countries in the Organization for Economic Co-operation and Development (OECD), demand is falling in Australia, rising in Korea and remaining near all-time highs in Japan. Together with New Zealand, these countries make up 10 percent of regional coal demand—with modest growth.

The most dynamic part, however, is the rest: a group of countries that includes Indonesia, Taiwan, Vietnam, Malaysia, Thailand, Philippines, Pakistan, and others (ordered by 2017 demand). Demand in that sub-group rose 45 percent in the last decade. Soon, this region could surpass the European Union, whose demand was 13 percent higher in 2017. Indonesia now consumes more coal than Poland, and in a few years, it might overtake Germany. Indonesia and Vietnam together use more coal than South Africa, and Vietnam’s coal use has more than quadrupled since 2007. Malaysia is a latecomer, but its coal consumption has more than doubled in the last 10 years—it consumes more coal than the Czech Republic, Spain or the United Kingdom. And demand for energy in these countries keeps growing—energy use per capita is low, and electrification rates and electricity consumption are rising.

This is the challenge in simple terms: while the world beyond Asia might reduce its coal consumption, demand keeps rising in Asia; and this demand growth is not concentrated only in China, or even China and India, but in several other emerging economies that see coal as an answer to their energy needs. The solution to this problem, however, is harder to see. The most common answer, to use more gas, is not quite working, and in several countries in Southeast Asia coal is being used because gas cannot compete or gas is being exported instead. Renewable energy holds great promise, but Southeast Asia needs to do more to scale up its renewable energy potential. China’s Belt and Road Initiative risks entrenching coal further, despite Beijing’s stated desire to maintain the initiative’s green and environmental credentials. Absent a more concerted effort to channel funds that support non-coal energy, the region will keep using more coal, and the world’s success elsewhere might easily be muted by Asia."

Science / Re: Early Anthropocene
« on: October 15, 2018, 10:20:30 PM »
Move evidence that Ruddiman (2003) roughly knew what he was talking about:

Title: "Pre-industrial anthropogenic CO2 emissions: How large?"

Extract: "Fifteen years after publication of Ruddiman (2003), the early anthropogenic hypothesis is still debated, with relevant evidence from many disciplines continuing to emerge. Recent findings summarized here lend support to the claim that greenhouse-gas emissions from early agriculture (before 1850) were large enough to alter atmospheric composition and global climate substantially."

The rest / Re: Systemic Isolation
« on: October 14, 2018, 08:50:31 PM »
While the linked research confirms that a single concrete reality does not exist; HIOTTOE's timelessly evolved free-will information network remains plausible as it posits that free-will creates a constantly changing timeless illusion of reality (rupa):

Title: "Famous Experiment Dooms Alternative to Quantum Weirdness"

Extract: "Oil droplets guided by “pilot waves” have failed to reproduce the results of the quantum double-slit experiment, crushing a century-old dream that there exists a single, concrete reality."

Consequences / Re: Conservative Scientists & its Consequences
« on: October 08, 2018, 04:08:35 PM »
Consensus climate scientists have decided to err on the side of least drama and thus ignore the Precautionary Principle in order to extend the period for the 66% confidence level carbon budget from the AR5 estimated 3-year period to 10-years to be committed to a 1.5C increase in GMSTA above pre-industrial (whatever those words mean).  If they are wrong, mankind will suffer what it must because it doesn't have the strength to face the reality of our current situation:

Title: "Analysis: Why the IPCC 1.5C report expanded the carbon budget"

Extract: "The newly published Intergovernmental Panel on Climate Change’s (IPCC) special report on 1.5C (SR15) significantly expands the budget for a 66% chance of avoiding 1.5C to the equivalent of 10 years of current emissions. This compares to the IPCC’s fifth assessment report (AR5), which put it at around three years.

Based on estimates made in the IPCC’s fifth assessment report (AR5), there would be around 120 gigatonnes of CO2 (GtCO2) remaining from the beginning of 2018 – or around three years of current emissions – for a 66% chance of avoiding 1.5C warming. For a 50/50 chance of exceeding 1.5C, the remaining budget was a modestly larger 268GtCO2 – or around seven years of current emissions.

The IPCC’s new SR15 significantly revises these numbers. It raises the budget for a 66% of avoiding 1.5C to 420GtCO2 – or 10 years of current emissions. Similarly, the budget for a 50/50 chance of exceeding 1.5C is increased to 580GtCO2 – 14 years of current emissions.

Even with the revised 1.5C carbon budget is unlikely to be the end of the debate, however, given a number of large remaining uncertainties. These include:

•   The precise meaning of the 1.5C target.
•   Disagreement about what “surface temperature” actually refers to.
•   The definition of the “pre-industrial” period.
•   What observational temperature datasets should be used.
•   What happens to non-CO2 factors that influencing the climate.
•   Whether Earth-system feedbacks like melting permafrost are taken into account.

Finally, the emission scenarios considered in the new SR15 also tend to emit far more than the budget would allow, but make up for it with the large-scale use of negative emissions in the future.

The carbon budgets featured in the IPCC AR5 were based on this subset of 20 climate models that could calculate both past temperature change and emissions, rather than on actual observations of temperature and emissions. Because some of these models had emissions and temperature changes that diverged significantly from observations, it caused a number of problems in calculating the carbon budget.

The main change in the way carbon budgets are calculated in the new IPCC SR15 report is the use of observations – rather than values from ESMs – to determine the amount of warming and emissions between the mid-1800s and present. The relationship between cumulative emissions and temperatures – based on ESMs and observational constraints from the IPCC AR5 – is then used to calculate the remaining budget from present.

This approach, originally proposed by Millar and colleagues in a 2017 paper, effectively eliminates the problems associated with ESMs underestimating historical cumulative CO2 emissions and projecting temperatures warmer than have been observed.

Correcting both of these issues is broadly accepted by the scientific community. There is no doubt that using observations rather than model estimates leads to a more accurate estimate of the remaining budget for the 1.5C and 2C targets."

See also:

The rest / Re: The Trump Presidency (was "Presidential Poll")
« on: October 07, 2018, 05:47:08 PM »
Trump is progressively pushing the US towards a police state:

Title: "Kavanaugh’s first vote could be in Trump executive power fight"

Extract: "Justice Brett Kavanaugh’s first vote as a member of the Supreme Court could come as soon as Tuesday or Wednesday on a Trump administration request testing how much power courts should wield over top executive branch officials.

The administration has already made one unsuccessful run at the high court on the issue: asking Justice Ruth Bader Ginsburg last week to step in to block depositions of Commerce Secretary Wilbur Ross and Justice Department civil rights chief John Gore in lawsuits challenging Ross’ decision to put a question about citizenship on the 2020 U.S. Census.

Ginsburg rebuffed the stay request, but Justice Department attorneys have indicated they plan to return to the Supreme Court with another emergency stay application within days unless they get full relief from lower courts, which seems unlikely.

Justice Department lawyers argue the depositions of Ross and Gore ordered by a federal judge in New York City constitute an unwarranted intrusion into executive authority and could prove distracting to senior officials with important duties.

It’s the kind of argument that could have appeal to Kavanaugh, who has advocated for broad views of executive power. However, deferring to the Trump administration within days of joining the court could appear to confirm many of Kavanaugh’s critics’ claims that he’s likely to be a rubber stamp for Trump and his agenda.

“It certainly seems likely that, if the Court is divided 4-4 as to whether to grant a stay, Justice Kavanaugh is going to have to participate in resolving the Ross dispute,” University of Texas law professor Stephen Vladeck said."

As continued global warming should increase the frequency with which atmospheric rivers reach Greenland, we may be in for some rude surprises in the coming decades (w.r.t. increasing rates of ice mass loss from the Greenland Ice Sheet):

William Neff (2018), "Atmospheric rivers melt Greenland", Nature Climate Change 8, 857-858, DOI:

Abstract: "Recent years have seen increased melting of the Greenland Ice Sheet, contributing to accelerated rates of sea-level rise.  New research suggests that this melting due to an increased frequency of atmospheric rivers, narrow filaments of moist air moving polewards."

The rest / Re: GOP Losing Ground for the 2018 Mid-Term Election
« on: October 01, 2018, 06:41:28 PM »
The FBI's investigation should note that Kavanaugh repeatedly lied (under oath) about his drinking in both high school and college.  If Kavanaugh is not confirmed and the Democrats win control of both the House and the Senate in the midterms, the Supreme Court could remain in a 4-4 balance until at least 2021:

Title: "Brett Kavanaugh wrongly claimed he could drink legally in Maryland in high school"

Extract: "Supreme Court nominee Brett Kavanaugh has repeatedly said that he was legally allowed to consume beer as a prep school senior in Maryland. In fact, he was never legal in high school because the state's drinking age increased to 21 at the end of his junior year, while he was still 17."


Title: "Yale classmate to tell FBI of Kavanuagh's 'violent drunken' behavior"

Extract: "Charles Ludington, a classmate of Supreme Court nominee Brett Kavanaugh at Yale University, will provide information to the FBI on Monday, he confirmed to NBC News.

News of Ludington's involvement was first reported by The Washington Post, which said he planned to give a statement to the FBI at its field office in Raleigh, North Carolina, "detailing violent drunken behavior by Kavanaugh in college.""

The rest / Re: GOP Losing Ground for the 2018 Mid-Term Election
« on: October 01, 2018, 11:55:10 AM »
Here is a link to the letter that Senator Feinstein sent to both Don McGahn and Christopher Wray, asking for a copy of the written instructions to the FBI regarding their probe of Kavanaugh.  I note that it may be the case that Trump's tweets about the nature of the FBI investigation cannot overrule McGahn's written instructions:

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