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Messages - AbruptSLR

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1
With a hat-tip to vox mundi, the linked reference validates the use of RCP 8.5 (or SSP5) for climate simulations:

Christopher R. Schwalm el al., "RCP8.5 tracks cumulative CO2 emissions," PNAS (2020). www.pnas.org/cgi/doi/10.1073/pnas.2007117117

https://www.pnas.org/content/early/2020/07/30/2007117117

Abstract: "Climate simulation-based scenarios are routinely used to characterize a range of plausible climate futures. Despite some recent progress on bending the emissions curve, RCP8.5, the most aggressive scenario in assumed fossil fuel use for global climate models, will continue to serve as a useful tool for quantifying physical climate risk, especially over near- to midterm policy-relevant time horizons. Not only are the emissions consistent with RCP8.5 in close agreement with historical total cumulative CO2 emissions (within 1%), but RCP8.5 is also the best match out to midcentury under current and stated policies with still highly plausible levels of CO2 emissions in 2100."

2
For those who think that a Super El Nino is the only perturbation that might trigger an MICI-type of collapse of the Thwaites/BSB ice, I note that 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), and that these subglacial lakes can refill within 20-years which indicates that another associated surge of ice in the Thwaites Ice Tongue may occur in the 2032 to 2033 timeframe:

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

http://www.the-cryosphere.net/11/451/2017/tc-11-451-2017.pdf

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".

http://www.washington.edu/news/2017/02/08/hidden-lakes-drained-under-west-antarcticas-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."

3
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: August 03, 2020, 10:18:20 PM »
The attached image is just a reminder that thru 2019 our CO2 emissions were still closely tracking the RCP 8.5 emissions scenario.

4
For those who still do not believe that once unpinned that the icebergs within the Thwaites Ice Tongue can float away to the northwest I attach an image of the ice tongue from May 31, 2020 annotated by baking where the feature that he names the 'Shear Zone' are going just that and the feature that he names 'Calving Zone' indicates the iceberg that I believe could expose ice cliffs once they float away due to a perturbation (such as a Super El Nino event).

5
For those who doubt that the pinned icebergs at the base of the Thwaites Ice Tongue cannot float-away, then look at the two images from Jordan et al (2020) that show that once unpinned these icebergs could float away in a northwest direction around the current subsea mount/ridge that is currently pinning the Thwaites Ice Tongue:

Jordan, T. A., Porter, D., Tinto, K., Millan, R., Muto, A., Hogan, K., Larter, R. D., Graham, A. G. C., and Paden, J. D.: New gravity-derived bathymetry for the Thwaites, Crosson and Dotson ice shelves revealing two ice shelf populations, The Cryosphere Discuss., https://doi.org/10.5194/tc-2019-294, in review, 2020.

https://www.the-cryosphere-discuss.net/tc-2019-294/

Extract: "Airborne gravity provides a good first order estimate of sub-ice-shelf bathymetry. Despite the relatively high uncertainty (~100 m standard deviation) comparisons with different gravity inversion techniques, and new observational bathymetric data, indicate that the pattern of sub-ice-shelf bathymetry is well resolved.

Thwaites Glacier is connected to the deep ocean by a major trough >800 m deep and 20 km wide. In contrast the grounding lines of the of Dotson and Crosson ice shelves are accessible through relatively narrow channels and thin sub shelf cavities. In the Thwaites, Dotson and Crosson region, areas of ice shelf which developed before and after 1993 form distinct populations. The most recently un-grounded areas are underlain by thin cavities (average 112 m) where the ice shelf base closely tracks the underlying bed topography."

Caption of image 2: "Figure 2: New bathymetry and cavity maps. a) Final topography from terrain shift method. White lines A-D mark profiles in Fig. 3. Yellow outline encloses region constrained by gravity data. Pink line shows -800m depth contour. Light grey lines mark grounding lines and ice shelf edge."

Caption of image 3: "Figure 3: Profiles across ice shelves. Upper panel shows ice surface from REMA DEM (Howat et al., 2019) and base of ice shelf calculated assuming hydrostatic equilibrium, together with gravity-derived bathymetric estimates. Second panel shows input freeair gravity anomaly. Third panel shows magnetic anomalies derived from ITGC survey data (REF data doi) and ADMAP2 (Golynsky et al., 2018). a) Thwaites Eastern Ice Shelf. b) Thwites Glacier Tongue. c) Crosson Ice Shelf. d) Dotson Ice Shelf. Note 520 thin cavity in regions of ice sheet grounding line retreat since 1993 (grey boxes)."

6
For those who do not know how much at risk the grounded icebergs at the base of the Thwaites Ice Tongue (see the first image from 2013) already have a negative height above floatation at Point B shown in the second attached image (from Milillo et al. 2019) and thus could easily float away (likely exposing an ice cliff face) once the melange downstream of Point B is disrupted, say due to a coming Super El Nino.

P. Milillo et al. (30 Jan 2019), "Heterogeneous retreat and ice melt of Thwaites Glacier, West Antarctica", Science Advances, Vol. 5, no. 1, eaau3433, DOI: 10.1126/sciadv.aau3433

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

Caption: "Fig. 2 Changes in ice surface elevation, h, of Thwaites Glacier.
(A to F) from TDX data (blue dots) for the time period 2011–2017 over grounded ice (red domain, dh/dt) at locations A to F, with height above floatation, hf (red lines), and 1σ uncertainty (dashed red lines), converted into change in ice thickness, H, over floating ice (blue domain, dH/dt) in meters per year. Black triangles are TDX dates in (G) to (J). (G and H) Main trunk. (I and J) TEIS. Grounding line position is thin black for 2016–2017 and white dashed blue for 2011."

Edit: For those who cannot see the heights above floatation for the indicated Points A, B, C, D, E & F, I provide the last two attached images.

7
While the 'Chasing Ice' video is a great example of ice cliff failures at Jakobshavn, I am primarily concerned about slumping calving failures (see the first linked article & associated first linked reference & the associated image) in the BSB/Thwaites that would produce somewhat shallow draft icebergs (at least shallower than tabular icebergs) that can readily float out of the Thwaites gateway that would allow more calving leading to an MICI-type of collapse.  Also, see the second linked reference on ice cliff failures of Jakobshavn and see also the linked video:

Title: "Tall ice-cliffs may trigger big calving events -- and fast sea-level rise"

https://www.sciencedaily.com/releases/2019/03/190322163342.htm

Extract: "Glaciers that drain ice sheets such as Antarctica or Greenland often flow into the ocean, ending in near-vertical cliffs. As the glacier flows into the sea, chunks of the ice break off in calving events. Although much calving occurs when the ocean melts the front of the ice, and ice cliff above falls down, a new study presents another method of calving: slumping. And this process could break off much larger chunks of ice at a quicker rate.

The ice-cliff research was spurred by a helicopter ride over Jakobshavn and Helheim glaciers on Greenland's eastern coast. Helheim ends abruptly in the ocean, in near-vertical ice-cliffs reaching 30-stories high (100 meters). On the flight, scientists viewed large cracks (called crevasses) on top of the ice that marched towards the end of the glacier."

See also:

Byron R. Parizek, Knut Christianson, Richard B. Alley, Denis Voytenko, Irena Vaňková, Timothy H. Dixon, Ryan T. Walker, David M. Holland. Ice-cliff failure via retrogressive slumping. Geology, 2019; DOI: 10.1130/G45880.1

https://pubs.geoscienceworld.org/gsa/geology/article/47/5/449/569567/Ice-cliff-failure-via-retrogressive-slumping

&

Xie, S., Dixon, T. H., Voytenko, D., Deng, F., and Holland, D. M.: Grounding line migration through the calving season of Jakobshavn Isbræ, Greenland, observed with terrestrial radar interferometry, The Cryosphere Discuss., https://doi.org/10.5194/tc-2017-231, in review, 2018.

https://www.the-cryosphere-discuss.net/tc-2017-231/

Abstract. "Ice velocity variations near the terminus of Jakobshavn Isbræ, Greenland were observed with a terrestrial radar interferometer (TRI) during three summer campaigns in 2012, 2015, and 2016. Ice velocity variations appear to be largely modulated by ocean tides. We estimate a ∼ 1 km wide floating zone near the calving front in early summer of 2015 and 2016, where ice moves in phase with ocean tides. Digital Elevation Models (DEMs) generated by the TRI show that the glacier front here is thin (ice surface is < 125 m above local water level). However, in late summer 2012, there is no evidence of a floating ice tongue in the TRI observations. Ice surface elevation near the glacier front was also higher, > 140 m above local sea level within a very short distance (< 1 km) from the ice cliff. We hypothesize that during Jakobshavn Isbræ's recent calving seasons, the ice front advances ∼ 3 km from winter to spring, forming a > 1 km floating ice tongue. During the subsequent calving season in mid- and late-summer, the glacier retreats by losing its floating portion through a sequence of iceberg calving events. By late summer, the entire glacier is likely grounded. In addition to ice velocity variations driven by tide rise and fall, we also observed a transverse velocity variation in the mélange and floating ice front. This across flow-line signal is in phase with the first time derivative of tidal height, and is likely associated with tidal currents or bed topography."

&




8
As a follow-on to my last post:

The first image shows the relationship between the ENSO cycle and the surface elevation of the ice shelves in the Amundsen Sea Sector; clearly increasing that these ice shelves float up on El Nino events and down on La Nina events; which causes flexure and cracking of the ice shelves (which weakens them and makes them more susceptible to the influence of warm CDW).

The second image shows how during the combination of an El Nino event and a positive SAM event tropical heat energy is advected from the Tropical Pacific directly to the coastal West Antarctica; where it can episodically accelerate local ice mass loss (along the coastal areas).

The third image shows how the Amundsen Bellingshausen Sea Low, ABSL (or ASL), can direct winds directly into the ASE, which also drags along ocean currents that advect more warm CDW into the ASE which accelerates local ice mass loss.

The fourth image shows the average potential temperature of the warm CDW (above freezing) typically being advected into the ASE, and the associate marine glacier ice flow velocities (because of the reduced buttressing from the degrading ice shelves and the retreating grounding lines).  Also, I note that relatively rapid ice flow velocities cause internal friction within the ice of the marine glaciers, which induces more basal meltwater beneath the marine glaciers (which further destabilize the marine glaciers).

The first linked reference concludes with regard to the Amundsen Sea Region, ASR, that:

"In contrast, the El Niño–ASR teleconnection in austral summer, which more closely resembles the Southern Annular Mode, is found to increase linearly for El Niño amplitudes up to 3 K."

As austral summer is also when surface ice melting occurs in the Amundsen Sea Region, and as El Nino events push warm CDW into the Amundsen Sea Embayment, ASE, we should be very concerned about the impacts of coming Super El Nino events on marine glaciers in the ASE.

Yu Yeung Scott Yiu and Amanda C. Maycock (2020 Apr), "The linearity of the El Niño teleconnection to the Amundsen Sea region", Q J R Meteorol Soc.; 146, (728), 1169–1183, doi: 10.1002/qj.3731

https://rmets.onlinelibrary.wiley.com/doi/full/10.1002/qj.3731

Abstract: El Niño Southern Oscillation (ENSO) drives interannual variability in West Antarctic climate through altering atmospheric circulation in the Amundsen Sea region (ASR). The El Niño–ASR teleconnection is known to be strongest in austral winter and spring, but its variation with El Niño amplitude is underexplored. This study uses experiments from the HadGEM3‐A climate model to investigate the El Niño–ASR teleconnection for a range of imposed SST perturbations spanning weak (0.75 K) to strong (3 K) amplitudes. In austral winter, the El Niño–ASR teleconnection behaves linearly for El Niño amplitudes up to 2.25 K, but is found to weaken for stronger forcing (3 K). The anomalous Rossby wave source in the subtropical South Pacific increases monotonically with El Niño amplitude. However, a Rossby wave reflection surface originally located in the western South Pacific sector extends progressively eastward with increasing El Niño amplitude, reducing wave propagation into the ASR. The wave reflection surface is associated with curvature in the upper tropospheric zonal winds which intensifies as the subtropical jet strengthens under El Niño forcing. In contrast, the El Niño–ASR teleconnection in austral summer, which more closely resembles the Southern Annular Mode, is found to increase linearly for El Niño amplitudes up to 3 K. The results explicitly demonstrate that a linear approximation of the El Niño teleconnection to the ASR is reasonable based on the range of El Niño amplitudes observed in recent history.

See also:

Dätwyler, C., Grosjean, M., Steiger, N. J., and Neukom, R.: Teleconnections and relationship between the El Niño–Southern Oscillation (ENSO) and the Southern Annular Mode (SAM) in reconstructions and models over the past millennium, Clim. Past, 16, 743–756, https://doi.org/10.5194/cp-16-743-2020, 2020.

https://cp.copernicus.org/articles/16/743/2020/

Abstract
The climate of the Southern Hemisphere (SH) is strongly influenced by variations in the El Niño–Southern Oscillation (ENSO) and the Southern Annular Mode (SAM). Because of the limited length of instrumental records in most parts of the SH, very little is known about the relationship between these two key modes of variability over time. Using proxy-based reconstructions and last-millennium climate model simulations, we find that ENSO and SAM indices are mostly negatively correlated over the past millennium. Pseudo-proxy experiments indicate that currently available proxy records are able to reliably capture ENSO–SAM relationships back to at least 1600 CE. Palaeoclimate reconstructions show mostly negative correlations back to about 1400 CE. An ensemble of last-millennium climate model simulations confirms this negative correlation, showing a stable correlation of approximately −0.3. Despite this generally negative relationship we do find intermittent periods of positive ENSO–SAM correlations in individual model simulations and in the palaeoclimate reconstructions. We do not find evidence that these relationship fluctuations are caused by exogenous forcing nor by a consistent climate pattern. However, we do find evidence that strong negative correlations are associated with strong positive (negative) anomalies in the Interdecadal Pacific Oscillation and the Amundsen Sea Low during periods when SAM and ENSO indices are of opposite (equal) sign.

9
I am less pessimistic than someone like AbruptSLR, I think the timeline is more like 100 years before we really see massive ice sheet instabilities.

But again I trying to see which glacier will go first.
One vote for Jakobshavn it is.

While Jakobshavn is already undergoing ice cliff failures and may very well undergo and temporary acceleration of ice cliff failures once the grounding line / calving front reaches the retrograde bed slope, but once that bed slope changes to a prograde slope then the temporary acceleration will stop and the ice cliff failures will slowdown to something like their current rate of calving.  Thus, if you are asking which glacier will be the first to lead to a collapse of a ice sheet, then the only marine glacier that is reasonable to cite is the Thwaites Glacier.

To me, it is more productive to discuss the validity of the reasons that I have previously cited (& for which I have previously provided references) as to why Thwaites Glacier has a good probability of triggering a MICI-type of collapse of the WAIS before 2045.  While it is not possible to cite one specific scenario I am slowly preparing a summary, but here I cite a few key points.

A freshwater hosing event (like the temporary collapse of Jakobshavn's calving front and/or as short-term reversal of the Beaufort Gyre) say between 2025 and 2035, could slow the MOC sufficiently to trigger a Super El Nino  say by 2035 to 2040 that would cause both a sufficient perturbation of both CDW pulse into the ASE and surface ice melting to trigger an ice cliff front at the base of the current Thwaites Ice Tongue in the bed trough leading to the BSB.

See also:

Title: "NASA Space Laser Missions Map 16 Years of Ice Sheet Loss"

https://www.nasa.gov/feature/goddard/2020/nasa-space-laser-missions-map-16-years-of-ice-sheet-loss

10
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: August 01, 2020, 07:53:31 PM »
The linked reference cites that increased rainfall is already accelerating permafrost degradation in Alaska; which, means it is likely already happening in Siberia; which leads to more Arctic Amplification.

Thomas A. Douglas, Merritt R. Turetsky, Charles D. Koven. Increased rainfall stimulates permafrost thaw across a variety of Interior Alaskan boreal ecosystems. npj Climate and Atmospheric Science, 2020; 3 (1) DOI: 10.1038/s41612-020-0130-4

https://www.nature.com/articles/s41612-020-0130-4

Abstract: "Earth’s high latitudes are projected to experience warmer and wetter summers in the future but ramifications for soil thermal processes and permafrost thaw are poorly understood. Here we present 2750 end of summer thaw depths representing a range of vegetation characteristics in Interior Alaska measured over a 5 year period. This included the top and third wettest summers in the 91-year record and three summers with precipitation close to mean historical values. Increased rainfall led to deeper thaw across all sites with an increase of 0.7 ± 0.1 cm of thaw per cm of additional rain. Disturbed and wetland sites were the most vulnerable to rain-induced thaw with ~1 cm of surface thaw per additional 1 cm of rain. Permafrost in tussock tundra, mixed forest, and conifer forest was less sensitive to rain-induced thaw. A simple energy budget model yields seasonal thaw values smaller than the linear regression of our measurements but provides a first-order estimate of the role of rain-driven sensible heat fluxes in high-latitude terrestrial permafrost. This study demonstrates substantial permafrost thaw from the projected increasing summer precipitation across most of the Arctic region."

11
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: August 01, 2020, 03:08:28 PM »
With a hat tip to Tom Mazanec, the linked reference concludes that:

"We argue that the Arctic is currently experiencing an abrupt climate change event, and that climate models underestimate this ongoing warming."

This indicates that Arctic Amplification is likely higher than assumed by consensus climate models.

Jansen, E., Christensen, J.H., Dokken, T. et al. Past perspectives on the present era of abrupt Arctic climate change. Nat. Clim. Chang. 10, 714–721 (2020). https://doi.org/10.1038/s41558-020-0860-7

https://www.nature.com/articles/s41558-020-0860-7

Abstract: "Abrupt climate change is a striking feature of many climate records, particularly the warming events in Greenland ice cores. These abrupt and high-amplitude events were tightly coupled to rapid sea-ice retreat in the North Atlantic and Nordic Seas, and observational evidence shows they had global repercussions. In the present-day Arctic, sea-ice loss is also key to ongoing warming. This Perspective uses observations and climate models to place contemporary Arctic change into the context of past abrupt Greenland warmings. We find that warming rates similar to or higher than modern trends have only occurred during past abrupt glacial episodes. We argue that the Arctic is currently experiencing an abrupt climate change event, and that climate models underestimate this ongoing warming."

12
Science / Re: Beaufort Gyre Reversal and a Return to 1960's Level SIE
« on: August 01, 2020, 01:44:14 AM »
The linked reference discusses the stability of the Arctic halocline and the use of available potential energy (APE) as a measure of the vulnerability of Arctic sea ice to the upward heat fluxes from the interior of the Arctic Ocean.  In this regard, the first image (Figure 5 of the reference) shows how APE has allowed freshwater to accumulate in the Beaufort Gyre (as compared to earlier periods) and the reference indicates that if the APE changes in the future to allow much of the surplus freshwater in the Beaufort Gyre (see the second image) that this could abruptly disrupt the Arctic Ocean halocline, which could result in the abrupt reduction of Arctic Sea Ice Extent via the upward migration of ocean heat energy previously trapped beneath the halocline.  Furthermore, if the Arctic Sea Ice Extent were to be abruptly reduced then the depth of the wind mixed thermocline would increase thus potentially exposing the seafloor on various Arctic Ocean continental shelves to higher temperatures.  Furthermore, an abrupt release of freshwater from the Beaufort Gyre into the North Atlantic would cause much of the heat content of the Gulf Steam to penetrate deeper in the Arctic Ocean.

Igor V Polyakov et al (2018), "Stability of the arctic halocline: a new indicator of arctic climate change", Environ. Res. Lett., 13, 125008,

https://iopscience.iop.org/article/10.1088/1748-9326/aaec1e
https://iopscience.iop.org/article/10.1088/1748-9326/aaec1e/pdf

Abstract: "In this study, we propose a new Arctic climate change indicator based on the strength of the Arctic halocline, a porous barrier between the cold and fresh upper ocean and ice and the warm intermediate Atlantic Water of the Arctic Ocean. This indicator provides a measure of the vulnerability of sea ice to upward heat fluxes from the ocean interior, as well as the efficiency of mixing affecting carbon and nutrient exchanges. It utilizes the well-accepted calculation of available potential energy (APE), which integrates anomalies of potential density from the surface downwards through the surface mixed layer to the base of the halocline. Regional APE contrasts are striking and show a strengthening of stratification in the Amerasian Basin (AB) and an overall weakening in the Eurasian Basin (EB). In contrast, Arctic-wide time series of APE is not reflective of these inter-basin contrasts. The use of two time series of APE—AB and EB—as an indicator of Arctic Ocean climate change provides a powerful tool for detecting and monitoring transition of the Arctic Ocean towards a seasonally ice-free Arctic Ocean. This new, straightforward climate indicator can be used to inform both the scientific community and the broader public about changes occurring in the Arctic Ocean interior and their potential impacts on the state of the ice cover, the productivity of marine ecosystems and mid-latitude weather."

Caption for first image: "Figure 5. Strength of Arctic halocline illustrated by the APE as an indicator of Arctic Ocean climate change. (a) Map showing APE difference between two selected periods of time. (b), (c) Time series showing APE averaged over (b) the entire Arctic Ocean and (c) Amerasian (red) and Eurasian (blue) basins. (d) Conceptual model of change of Arctic halocline strength showing: (i) decrease in time of sea ice, (ii) enhanced impact of Arctic High on ocean circulation, (iii) increase of thickness of SML and halocline in the AB and decrease in the EB, (iv) increase of influx of Pacific Water (PI), (v) reduction of EB halocline.

Extract: "The potential significance of the proposed Arctic climate change indicator is far reaching. In addition to providing fundamental knowledge regarding the dynamics of the Arctic halocline (figure 5), this indicator will provide impetus for improved representation of Arctic sea-ice responses to halocline changes in climate models. It may serve as a measure that delivers lead warning of impending changes in Arctic Ocean water mass structure and potential impacts on ice cover, upper ocean biology related to light and nutrient availability, and impacts on human activities (fisheries, shipping) and mid-latitudes. Further, the proposed indicator provides a foundation for the development of further hypotheses about Arctic climate system functionality. Thus, the proposed indicator will be an important contributor to the existing sets of Arctic climate change indicators."

Next, to reiterate about the risks associated with a potential abrupt release of relatively fresh and relatively warm water from the Beaufort Gyre, the third image shows the current weather pattern trend that has allowed a surplus of fresh/warm water to be accumulated in the Beaufort Gyre, and the fourth image shows the weather pattern trend that would allow for the release of this surplus of fresh/warm water first into the Arctic Ocean and then into the North Atlantic where calculations indicate that the current volume of surplus fresh/warm water is sufficient to abruptly slow the MOC once released into the North Atlantic.

13
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 31, 2020, 05:45:55 PM »
It certainly is not good news (w.r.t. Arctic Amplification) that two Arctic ice caps have already disappeared:

Title: "Going, Going, GONE: Two Arctic Ice Caps Have Disappeared"

https://www.discovermagazine.com/environment/going-going-gone-two-arctic-ice-caps-have-disappeared

Extract: "Two little Arctic ice caps that Mark Serreze studied as a graduate student in the early 1980s might not have been as grand and dramatic as other features of our planet's cryosphere, but to him they nonetheless were quite special.

Were quite special — past tense — because Serreze, who now directs the National Snow and Ice Data Center, has confirmed that the two ice caps on the Hazen Plateau of Canada's Ellsmere Island have disappeared. They're the victims of human-caused warming that has occurred three times more rapidly in the Arctic than anywhere else.

The disappearance was confirmed using recent images from the ASTER instrument aboard NASA’s Terra satellite."

14
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 31, 2020, 04:06:02 PM »
...findings certainly support the concept that episodic bipolar MICI events between the marine glaciers in the NH and the SH may well have dominated SLR in this period.
This may be much different today, given different novel atmospheric chemistry (ie. ozone loss at both poles), and because of the CO2 buildup rate. Thus, where is the bipolarity now, the geological record will show both poles recording responses.


...

No paleo case matches today's situation and yet all scientists (consensus and otherwise) understand that there are lessons to be learned from the past behavior of various Earth Systems that can then be applied to ESMs in order to improve projections of future behavior.  Furthermore, when attempting to learn from paleo cases it is helpful to ask questions about the Earth Systems that are relevant rather than focusing on irrelevant cases (such as suggesting that because there are no paleo cases where the aerosol and/or ozone cases match our current anthropogenically driven situation that this invalidates the possibility of learning about the bipolar seesaw from paelo-evidence).

For example, the first image shows how the SST in the North Atlantic is associated with heat advected through the atmosphere from the North Atlantic to the Tropical Pacific where it can then be advected to either the WAIS or the Bering Sea area (depending on ENSO & SAM) as shown in the second image.  The SST of the North Atlantic can be impacted by freshwater hosing events whether due to paleo ice cliff calving from a marine glacier in the Barents Sea (see the third image) or due to a reversal of the Beaufort Gyre (see the fourth image) in a few years flushing freshwater into the North Atlantic; which could trigger a bipolar seesaw mechanism by advecting energy to the Tropical Pacific and then on to the WAIS.

15
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 31, 2020, 12:05:31 AM »
While the linked reference does not prove that MICI dominated SLR during Meltwater Pulse 1A; its findings certainly support the concept that episodic bipolar MICI events between the marine glaciers in the NH and the SH may well have dominated SLR in this period.  Also, ice note that during this period there is a lot of direct evidence of ice-rafted debris accumulations in both the NH and the SH and that ice-rafted debris must come from MICI events as MISI ice mass loss occurs in marine glaciers with ice shelves which cannot generate ice-rafted debris (see the first image from the second linked reference).  So while consensus climate scientists can (and do) refuse to incorporate MICI mechanism into their climate models; there is a lot of ice-rafted debris (see the second image) around the would that suggests that they would be wise if they should do so:

Brendryen, J., Haflidason, H., Yokoyama, Y. et al. Eurasian Ice Sheet collapse was a major source of Meltwater Pulse 1A 14,600 years ago. Nat. Geosci. 13, 363–368 (2020). https://doi.org/10.1038/s41561-020-0567-4

https://www.nature.com/articles/s41561-020-0567-4?proof=true%3Ca+href%3D

Abstract: "Rapid sea-level rise caused by the collapse of large ice sheets is a threat to human societies. In the last deglacial period, the rate of global sea-level rise peaked at more than 4 cm yr−1 during Meltwater Pulse 1A, which coincided with the Bølling warming event some 14,650 years ago. However, the sources of the meltwater have proven elusive, and the contribution from Eurasian ice sheets has been considered negligible. Here, we present a regional carbon-14 calibration curve for the Norwegian Sea and recalibrate marine 14C dates linked to the Eurasian Ice Sheet retreat. We find that marine-based sectors of the Eurasian Ice Sheet collapsed at the Bølling transition and lost an ice volume of 4.5–7.9 m sea-level equivalents (SLE) over 500 years. During peak melting, 3.3–6.7 m SLE of ice was lost, potentially explaining up to half of Meltwater Pulse 1A. A mean meltwater flux of 0.2 Sv over 300 years was injected into the Norwegian Sea and the Arctic Ocean at a time when proxy evidence suggests vigorous Atlantic meridional overturning circulation. Our reconstruction shows that massive marine-based ice sheets can collapse in as little as 300–500 years."

See also:
Smith, J.A., Graham, A.G.C., Post, A.L. et al. The marine geological imprint of Antarctic ice shelves. Nat Commun 10, 5635 (2019). https://doi.org/10.1038/s41467-019-13496-5

https://www.nature.com/articles/s41467-019-13496-5

Abstract: "Reductions in the thickness and extent of Antarctic ice shelves are triggering increased discharge of marine-terminating glaciers. While the impacts of recent changes are well documented, their role in modulating past ice-sheet dynamics remains poorly constrained. This reflects two persistent issues; first, the effective discrimination of sediments and landforms solely attributable to sub-ice-shelf deposition, and second, challenges in dating these records. Recent progress in deciphering the geological imprint of Antarctic ice shelves is summarised, including advances in dating methods and proxies to reconstruct drivers of change. Finally, we identify several challenges to overcome to fully exploit the paleo record."

16
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 30, 2020, 08:34:39 AM »
The linked reference confirms that the ocean is warming globally and that the AMOC has been observed to be currently slowing and is expected to continue slowing with continuing global warming:

Johnson, G.C., Lyman, J.M. Warming trends increasingly dominate global ocean. Nat. Clim. Chang. (2020). https://doi.org/10.1038/s41558-020-0822-0

https://www.nature.com/articles/s41558-020-0822-0
&
https://www.nature.com/articles/s41558-020-0822-0.epdf?sharing_token=XAe_EpnEyT3mMAOw2OZDodRgN0jAjWel9jnR3ZoTv0Mu-QJ5YGgHpvNJjdXiiG_qsknU8mrV_B-C6CX0vjXjFxpmNGcEQwLX8XSvp4LTRyEDVYltt34LeVCrAc_rDGn1A8vK8pSfCRMMpEF6hZ3-YibM4CvAT9JASjTXDvQz998%3D

Abstract: "The ocean takes up about 93% of the global warming heat entering Earth’s climate system. In addition, the associated thermal expansion contributes substantially to sea-level rise. Hence, quantifying the oceanic heat uptake rate and its statistical significance has been a research focus. Here we use gridded ocean heat content maps to examine regional trends in ocean warming for 0–700 m depth from 1993–2019 and 1968–2019, periods based on sampling distributions. The maps are from four research groups, three based on ocean temperature alone and one combining ocean temperature with satellite altimeter sea-level anomalies. We show that use of longer periods results in larger percentages of ocean area with statistically significant warming trends and less ocean area covered by statistically significant cooling trends. We discuss relations of these patterns to climate phenomena, including the Pacific Decadal Oscillation, the Atlantic Meridional Overturning Circulation and global warming."

Extract: "The 1993–2019 trend towards a warmer upper ocean (and higher sea levels) along the east coast of North America and cooling (with lower sea levels) in the subpolar North Atlantic (Fig. 1) is highly reminiscent of a pattern that has been linked to a reduction in the strength of the AMOC in models. Similar trends are visible for the 1968–2019 period, with the subpolar cooling muted over the longer period. A reduction in AMOC strength starting in 2009 relative to 2004–2008 has also been documented observationally and discussed, with 2004 being the first year of AMOC observations with a trans-Atlantic moored array. Our analysis indicates that the changes are large and long-term enough to support a statistically significant pattern in the 1993–2019 trends of upper-ocean heat content and even the 1968–2019 trends. However, the link of the cooling in the subpolar North Atlantic to reductions in the AMOC is difficult to disentangle, with a strong interannual cool event centred around 2015 being caused mostly by strong heat loss from the ocean to the atmosphere, rather than reduced advection of warm water northward associated with an AMOC reduction, which is expected to occur on longer timescales."


17
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 30, 2020, 08:16:43 AM »
The linked reference offers hope that regional climate forecasts may improve in the future by better representing the atmospheric eddy spectrum; however, it also indicates that a lot of physics is still missing from the current generation of climate models:

Smith, D.M., Scaife, A.A., Eade, R. et al. North Atlantic climate far more predictable than models imply. Nature 583, 796–800 (2020). https://doi.org/10.1038/s41586-020-2525-0

https://www.nature.com/articles/s41586-020-2525-0

Abstract: "Quantifying signals and uncertainties in climate models is essential for the detection, attribution, prediction and projection of climate change. Although inter-model agreement is high for large-scale temperature signals, dynamical changes in atmospheric circulation are very uncertain. This leads to low confidence in regional projections, especially for precipitation, over the coming decades. The chaotic nature of the climate system may also mean that signal uncertainties are largely irreducible. However, climate projections are difficult to verify until further observations become available. Here we assess retrospective climate model predictions of the past six decades and show that decadal variations in North Atlantic winter climate are highly predictable, despite a lack of agreement between individual model simulations and the poor predictive ability of raw model outputs. Crucially, current models underestimate the predictable signal (the predictable fraction of the total variability) of the North Atlantic Oscillation (the leading mode of variability in North Atlantic atmospheric circulation) by an order of magnitude. Consequently, compared to perfect models, 100 times as many ensemble members are needed in current models to extract this signal, and its effects on the climate are underestimated relative to other factors. To address these limitations, we implement a two-stage post-processing technique. We first adjust the variance of the ensemble-mean North Atlantic Oscillation forecast to match the observed variance of the predictable signal. We then select and use only the ensemble members with a North Atlantic Oscillation sufficiently close to the variance-adjusted ensemble-mean forecast North Atlantic Oscillation. This approach greatly improves decadal predictions of winter climate for Europe and eastern North America. Predictions of Atlantic multidecadal variability are also improved, suggesting that the North Atlantic Oscillation is not driven solely by Atlantic multidecadal variability. Our results highlight the need to understand why the signal-to-noise ratio is too small in current climate models, and the extent to which correcting this model error would reduce uncertainties in regional climate change projections on timescales beyond a decade."

See also:

Title: "Missed wind patterns are throwing off climate forecasts of rain and storms"

https://www.sciencemag.org/news/2020/07/missed-wind-patterns-are-throwing-climate-forecasts-rain-and-storms

Extract: "Kirtman thinks something fundamental is wrong with the models’ code. For the time being, he says, “You’re probably making pretty profound mistakes in your climate change assessment” by relying on regional forecasts. For example, models predicted that the Horn of Africa, which is heavily influenced by Indian Ocean winds, would get wetter with climate change. But since the early 1990s, rains have plummeted and the region has dried.

The missing predictability also undermines so-called event attribution, which attempts to link extreme weather to climate change by using models to predict how sea surface warming is altering wind patterns. The changes in winds, in turn, affect the odds of extreme weather events, like hurricanes or floods. But the new work suggests “the probabilities they derive will probably not be correct,” Smith says.

What’s not clear yet is why climate models get circulation changes so wrong. One leading hypothesis is that the models fail to capture feedbacks into overall wind patterns from individual weather systems, called eddies. “Part of that eddy spectrum may simply be missing,” Smith says. Models do try to approximate the effects of eddies, but at just kilometers across, they are too small to simulate directly. The problem could also reflect poor rendering of the stratosphere, or of interactions between the ocean and atmosphere. “It’s fascinating,” says Jennifer Kay, a climate scientist at the University of Colorado, Boulder. “But there’s also a lot left unanswered.”"

18
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 29, 2020, 04:29:40 PM »
The linked articles (& associated linked references) indicate that anthropogenic GHG emissions is causing the mesosphere above Antarctica to cool at rates up to 10 times faster than the rate of increase of GMSTA.  Furthermore, this research identifies a new natural cycle not previously identified in the Antarctic upper atmosphere; which is a four-year cycle that the authored called the Quasi-Quadrennial Oscillation (QQO), which caused observed mesosphere temperatures to vary by 3-4 degrees C.  As it is not likely that the CMIP projections to date account for this QQO cycle in their models future generations (CMIP7) of ESM projects should be adjusted to simulate this signal which plausibly arises from an ocean–atmosphere response, and appears to have a signature in Antarctic sea ice extent.  Lastly, I note that the current ozone hole over Antarctica also serves to cool the upper atmosphere over Antarctica; so as the ozone hole heals itself this GHG driven cooling of the mesosphere over Antarctica will likely maintain current conditions that have causes the westerly winds over the Southern Ocean to accelerate since the 1970s; which will likely at least maintain the current upwelling volumes of warm CDW that has been accelerating ocean related ice melting around the Antarctic coastline since the 1970s.


Title: "Carbon Emissions Are Chilling The Atmosphere 90 Km Above Antarctica"

https://www.sciencealert.com/carbon-emissions-are-chilling-the-atmosphere-90km-above-antarctica-at-the-edge-of-space

Extract: "While greenhouse gases are warming Earth's surface, they're also causing rapid cooling far above us, at the edge of space.

In fact, the upper atmosphere about 90 kilometres (56 miles) above Antarctica is cooling at a rate 10 times faster than the average warming at the planet's surface.

Rising greenhouse gas emissions are contributing to the temperature changes we recorded, but a number of other influences are also at play. These include the seasonal cycle (warmer in winter, colder in summer) and the Sun's 11-year activity cycle (which involves quieter and more intense solar periods) in the mesosphere.

One challenge of the research was untangling all these merged "signals" to work out the extent to which each was driving the changes we observed.

Surprisingly in this process, we discovered a new natural cycle not previously identified in the polar upper atmosphere. This four-year cycle which we called the Quasi-Quadrennial Oscillation (QQO), saw temperatures vary by 3-4 degrees C in the upper atmosphere.

But the finding has big implications for climate modelling. The physics that drive this cycle are unlikely to be included in global models currently used to predict climate change. But a variation of 3-4 degrees C every four years is a large signal to ignore.

We don't yet know what's driving the oscillation. But whatever the answer, it also seems to affect the winds, sea surface temperatures, atmospheric pressure and sea ice concentrations around Antarctica.

See also:

Title: "Antarctic research unlocks mysteries of the upper atmosphere"

https://www.antarctica.gov.au/news/2020/antarctic-research-unlocks-mysteries-of-the-upper-atmosphere/

&

French, W. J. R., Mulligan, F. J., and Klekociuk, A. R.: Analysis of 24 years of mesopause region OH rotational temperature observations at Davis, Antarctica – Part 1: long-term trends, Atmos. Chem. Phys., 20, 6379–6394, https://doi.org/10.5194/acp-20-6379-2020, 2020.

https://www.atmos-chem-phys.net/20/6379/2020/acp-20-6379-2020.html

Abstract
The long-term trend, solar cycle response, and residual variability in 24 years of hydroxyl nightglow rotational temperatures above Davis research station, Antarctica (68∘ S, 78∘ E) are reported. Hydroxyl rotational temperatures are a layer-weighted proxy for kinetic temperatures near 87 km altitude and have been used for many decades to monitor trends in the mesopause region in response to increasing greenhouse gas emissions. Routine observations of the OH(6-2) band P-branch emission lines using a scanning spectrometer at Davis station have been made continuously over each winter season since 1995. Significant outcomes of this most recent analysis update are the following: (a) a record-low winter-average temperature of 198.3 K is obtained for 2018 (1.7 K below previous low in 2009); (b) a long-term cooling trend of −1.2±0.51 K per decade persists, coupled with a solar cycle response of 4.3±1.02 K per 100 solar flux units; and (c) we find evidence in the residual winter mean temperatures of an oscillation on a quasi-quadrennial (QQO) timescale which is investigated in detail in Part 2 of this work.
Our observations and trend analyses are compared with satellite measurements from Aura/MLS version v4.2 level-2 data over the last 14 years, and we find close agreement (a best fit to temperature anomalies) with the 0.00464 hPa pressure level values. The solar cycle response (3.4±2.3 K per 100 sfu), long-term trend (−1.3±1.2 K per decade), and underlying QQO residuals in Aura/MLS are consistent with the Davis observations. Consequently, we extend the Aura/MLS trend analysis to provide a global view of solar response and long-term trend for Southern and Northern Hemisphere winter seasons at the 0.00464 hPa pressure level to compare with other observers and models.

&

French, W. J. R., Klekociuk, A. R., and Mulligan, F. J.: Analysis of 24 years of mesopause region OH rotational temperature observations at Davis, Antarctica – Part 2: Evidence of a quasi-quadrennial oscillation (QQO) in the polar mesosphere, Atmos. Chem. Phys., 20, 8691–8708, https://doi.org/10.5194/acp-20-8691-2020, 2020.

https://www.atmos-chem-phys.net/20/8691/2020/

Abstract
Observational evidence of a quasi-quadrennial oscillation (QQO) in the polar mesosphere is presented based on the analysis of 24 years of hydroxyl (OH) nightglow rotational temperatures derived from scanning spectrometer observations above Davis research station, Antarctica (68∘ S, 78∘ E). After removal of the long-term trend and solar cycle response, the residual winter mean temperature variability contains an oscillation over an approximately 3.5–4.5-year cycle with a peak-to-peak amplitude of 3–4 K. Here we investigate this QQO feature in the context of the global temperature, pressure, wind, and surface fields using satellite, meteorological reanalysis, sea surface temperature, and sea ice concentration data sets in order to understand possible drivers of the signal. Specifically, correlation and composite analyses are made with data sets from the Microwave Limb Sounder on the Aura satellite (Aura/MLS v4.2) and the Sounding of the Atmosphere using Broadband Emission Radiometry instrument on the Thermosphere Ionosphere Mesosphere Energetics Dynamics satellite (TIMED/SABER v2.0), ERA5 reanalysis, the Extended Reconstructed Sea Surface Temperature (ERSST v5), and Optimum-Interpolation (OI v2) sea ice concentration. We find a significant anti-correlation between the QQO temperature and the meridional wind at 86 km altitude measured by a medium-frequency spaced antenna radar at Davis (R2∼0.516; poleward flow associated with warmer temperatures at ∼0.83±0.21 K (ms−1)−1). The QQO signal is also marginally correlated with vertical transport as determined from an evaluation of carbon monoxide (CO) concentrations in the mesosphere (sensitivity 0.73±0.45 K ppmv−1 CO, R2∼0.18). Together this relationship suggests that the QQO is plausibly linked to adiabatic heating and cooling driven by the meridional flow. The presence of quasi-stationary or persistent patterns in the ERA5 data geopotential anomaly and the meridional wind anomaly data during warm and cold phases of the QQO is consistent with tidal or planetary waves influencing its formation, which may act on the filtering of gravity waves to drive an adiabatic response in the mesosphere. The QQO signal plausibly arises from an ocean–atmosphere response, and appears to have a signature in Antarctic sea ice extent.

Edit:  The first image shows that the Stratosphere and Troposphere are at much lower altitudes than the mesosphere (at 90km up), the second image shows that the ozone hole produces an atmospheric geopotential well over all of Antarctic and the third image shows that the low pressure typically over Antarctica (which is associated with the atmospheric geopotential well) not only contributes to accelerated westerly winds over the Southern Ocean but also contributes to accelerated katabatic winds that can contribute to accelerated surface ice melting along the Antarctic coastal areas as occurred over the Ross Ice Shelf a few years ago.

19
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 29, 2020, 04:13:07 PM »
The linked reference indicates that in addition to the freshwater accumulated in the Beaufort Gyre the entire Arctic Ocean surface layer has been accumulating atypically high volumes of freshwater that are only recently beginning to leak atypically high volumes of freshwater into the North Atlantic.  This implies that for many years now the fully impacts of unusually high (anthropogenically driven) discharges of freshwater into the Arctic Ocean (and then on to the North Atlantic) have been masked.  As thick layers of freshwater in the Arctic Ocean reduce the rate of heat flux from the deeper/warming layers of ocean water into the Arctic atmosphere, this atypically high accumulation of freshwater in the Arctic Ocean surface layers implies that in recent years the Arctic has been cooler than it otherwise would have been (without this atypically high accumulation).  Thus if/when the Beaufort Gyre finally reverses it will likely not only release excessively high freshwater volumes accumulated in the Gyre into the North Atlantic, but it would likely also flush excess freshwater from the atypically high accumulations from the ocean surface layers in much of the Arctic Ocean and would likely melt large portions of the existing sea ice; which, would flush even more freshwater into the North Atlantic where as of this additional freshwater flux would serve to rapidly slow the AMOC:

Alexandra Jahn and Rory Laiho (27 July 2020), "Forced Changes in the Arctic Freshwater Budget Emerge in the Early 21st Century", Geophysical Research Letters, https://doi.org/10.1029/2020GL088854

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL088854?af=R

Abstract
Arctic liquid freshwater (FW) storage has shown a large increase over the past decades, posing the question: Is the Arctic FW budget already showing clear signs of anthropogenic climate change, or are the observed changes the result of multi‐decadal variability? We show that the observed change in liquid and solid Arctic FW storage is likely already driven by the changing climate, based on ensemble simulations from a state‐of‐the‐art climate model. Generally, the emergence of forced changes in Arctic FW fluxes occurs earlier for oceanic fluxes than for atmospheric or land fluxes. Nares Strait liquid FW flux is the first to show emergence outside the range of background variability, with this change potentially already occurring. Other FW fluxes have likely started to shift but have not yet emerged into a completely different regime. Future emissions reductions have the potential to avoid the emergence of some FW fluxes beyond the background variability.

Plain Language Summary
The surface waters of the Arctic Ocean are fresher than the rest of the world oceans, due to the input of large amounts of river runoff. The very fresh surface ocean affects the ocean circulation and climate not just in the Arctic Ocean, but also at lower latitudes, especially in the North Atlantic. The last two decades have seen a freshening of the surface Arctic Ocean, for reasons that are currently unknown. Here we demonstrate that this freshening is likely already driven by climate change. Furthermore, we find that due to man‐made climate change, Arctic freshwater fluxes to the North Atlantic are also likely to soon start showing signs of change beyond the range of the variability we have observed in the past. The information provided here about the expected timing of the emergence of climate change signals will allow us to monitor upcoming changes in real time, to better understand how changes in the Arctic Ocean can impact climate worldwide.

Key points
•   The observed increase in Arctic liquid freshwater (FW) storage is likely already driven by climate change
•   A forced change in liquid FW flux through Nares Strait is likely to emerge within the next decade
•   The already changing nature of many FW budget terms can delay detection of shift and emergence from observations

20
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 29, 2020, 04:00:00 PM »
The linked reference confirms that, within the study area, a multidecadal trend of decreasing anthropogenic aerosol emissions has been observed.  While this is good, as aerosol radiative forcing/feedback is negative, it means that if the tend continues (as expected) that anthropogenic GHG emissions need to be cut-back to a net zero scenario as soon as possible:

Collaud Coen, M., Andrews, E., Alastuey, A., Arsov, T. P., Backman, J., Brem, B. T., Bukowiecki, N., Couret, C., Eleftheriadis, K., Flentje, H., Fiebig, M., Gysel-Beer, M., Hand, J. L., Hoffer, A., Hooda, R., Hueglin, C., Joubert, W., Keywood, M., Kim, J. E., Kim, S.-W., Labuschagne, C., Lin, N.-H., Lin, Y., Lund Myhre, C., Luoma, K., Lyamani, H., Marinoni, A., Mayol-Bracero, O. L., Mihalopoulos, N., Pandolfi, M., Prats, N., Prenni, A. J., Putaud, J.-P., Ries, L., Reisen, F., Sellegri, K., Sharma, S., Sheridan, P., Sherman, J. P., Sun, J., Titos, G., Torres, E., Tuch, T., Weller, R., Wiedensohler, A., Zieger, P., and Laj, P.: Multidecadal trend analysis of in situ aerosol radiative properties around the world, Atmos. Chem. Phys., 20, 8867–8908, https://doi.org/10.5194/acp-20-8867-2020, 2020.

https://www.atmos-chem-phys.net/20/8867/2020/

Abstract
In order to assess the evolution of aerosol parameters affecting climate change, a long-term trend analysis of aerosol optical properties was performed on time series from 52 stations situated across five continents. The time series of measured scattering, backscattering and absorption coefficients as well as the derived single scattering albedo, backscattering fraction, scattering and absorption Ångström exponents covered at least 10 years and up to 40 years for some stations. The non-parametric seasonal Mann–Kendall (MK) statistical test associated with several pre-whitening methods and with Sen's slope was used as the main trend analysis method. Comparisons with general least mean square associated with autoregressive bootstrap (GLS/ARB) and with standard least mean square analysis (LMS) enabled confirmation of the detected MK statistically significant trends and the assessment of advantages and limitations of each method. Currently, scattering and backscattering coefficient trends are mostly decreasing in Europe and North America and are not statistically significant in Asia, while polar stations exhibit a mix of increasing and decreasing trends. A few increasing trends are also found at some stations in North America and Australia. Absorption coefficient time series also exhibit primarily decreasing trends. For single scattering albedo, 52 % of the sites exhibit statistically significant positive trends, mostly in Asia, eastern/northern Europe and the Arctic, 22 % of sites exhibit statistically significant negative trends, mostly in central Europe and central North America, while the remaining 26 % of sites have trends which are not statistically significant. In addition to evaluating trends for the overall time series, the evolution of the trends in sequential 10-year segments was also analyzed. For scattering and backscattering, statistically significant increasing 10-year trends are primarily found for earlier periods (10-year trends ending in 2010–2015) for polar stations and Mauna Loa. For most of the stations, the present-day statistically significant decreasing 10-year trends of the single scattering albedo were preceded by not statistically significant and statistically significant increasing 10-year trends. The effect of air pollution abatement policies in continental North America is very obvious in the 10-year trends of the scattering coefficient – there is a shift to statistically significant negative trends in 2009–2012 for all stations in the eastern and central USA. This long-term trend analysis of aerosol radiative properties with a broad spatial coverage provides insight into potential aerosol effects on climate changes.

21
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 29, 2020, 03:54:33 PM »
The linked reference (which includes Gavin Schmidt as a co-author) finds that:

"ECS estimates from ≥300‐year coupled simulations from current US models range from 3.1°C to 7.0°C ..."

However, the reference also cautions that different modeling assumptions and different methodologies result in different values for ECS and that:

"Such variations between methods argues for caution in comparison and interpretation of ECS estimates across models."

John P. Dunne et al. (23 July 2020), "Comparison of equilibrium climate sensitivity estimates from slab ocean, 150‐year, and longer simulations", Geophysical Research Letters, https://doi.org/10.1029/2020GL088852

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL088852?af=R

Abstract

We compare equilibrium climate sensitivity (ECS) estimates from pairs of long (≥ 800‐year) control and abruptly quadrupled CO2 simulations with shorter (150, 300 year) coupled atmosphere‐ocean simulations and Slab Ocean Models (SOM). Consistent with previous work, ECS estimates from shorter coupled simulations based on annual averages for years 1‐150 underestimate those from SOM (‐8% ± 13%) and long (‐14% ± 8%) simulations. Analysis of only years 21‐150 improved agreement with SOM (‐2% ± 14%) and long (‐8% ± 10%) estimates. Use of pentadal averages for years 51‐150 results in improved agreement with long simulations (‐4% ± 11%). While ECS estimates from current generation US models based on SOM and coupled annual averages of years 1‐150 range from 2.6°C to 5.3°C, estimates based longer simulations of the same models range from 3.2°C to 7.0°C. Such variations between methods argues for caution in comparison and interpretation of ECS estimates across models.

Plain Language Summary
Precise definition and estimation of Equilibrium Climate Sensitivity (ECS) continues to challenge model inter‐comparison. While annual analyses of years 1‐150 of coupled atmosphere‐ocean models agree with slab ocean model simulations, they underestimate coupled ECS estimates from multi‐centennial to millennial scale simulations. However, long‐term ECS estimates can be largely recovered through a combination of 1) ignoring the first 50 years of abrupt 4x preindustrial CO2 simulation dominated by early timescales of ocean response and 2) using pentadal (5‐year) averages instead of annual ones for years 51‐150. This variation between methods argues for reconsideration of ECS estimation and application acknowledging that slab‐ocean estimates systematically ignore potential sources of enhanced sensitivity and simulations longer than 150 years are necessary for precise estimation of the long‐term trend.

Key Points
•   Equilibrium Climate Sensitivity (ECS) estimates for a single coupled model can vary by more than 1°C (20%) depending on analysis method
•   ECS estimates from ≥300‐year coupled simulations from current US models range from 3.1°C to 7.0°C, another method giving 2.7°C to 5.3°C
•   Analysis of years 21‐150 agrees with slab ocean ECS, but pentadal analysis of years 51‐150 reduces bias against long, coupled simulations


22
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 29, 2020, 03:44:14 PM »
The linked reference indicates that current ESM projections (such as the high-end CMIP6 models like E3SMv1) that include Antarctic ice shelf melting do not yet account for tidal impacts; which according to the reference significantly increases ice shelf melting and should be accounted for in future (CMIP7) generations of projections.  When this tidal impacts are included, future projections will likely project most significant future slowing of the MOC.

Richter, O., Gwyther, D. E., King, M. A., and Galton-Fenzi, B. K.: Tidal Modulation of Antarctic Ice Shelf Melting, The Cryosphere Discuss., https://doi.org/10.5194/tc-2020-169, in review, 2020.

https://tc.copernicus.org/preprints/tc-2020-169/

Abstract. Tides influence basal melting of individual Antarctic ice shelves, but their net impact on Antarctic-wide ice-ocean interaction has yet to be constrained. Here we quantify the impact of tides on ice shelf melting and the continental shelf seas by means of a 4 km resolution circum-Antarctic ocean model. Activating tides in the model increases the total basal mass loss by 57 Gt/yr (4 %), while decreasing continental shelf temperatures by 0.04 °C, indicating a slightly more efficient conversion of ocean heat into ice shelf melting. Regional variations can be larger, with melt rate modulations exceeding 500 % and temperatures changing by more than 0.5 °C, highlighting the importance of capturing tides for robust modelling of glacier systems and coastal oceans. Tide-induced changes around the Antarctic Peninsula have a dipolar distribution with decreased ocean temperatures and reduced melting towards the Bellingshausen Sea and warming along the continental shelf break on the Weddell Sea side. This warming extends under the Ronne Ice Shelf, which also features one of the highest increases in area-averaged basal melting (150 %) when tides are included. Further, by means of a singular spectrum analysis, we explore the processes that cause variations in melting and its drivers in the boundary layer over periods of up to one month. At most places friction velocity varies at tidal timescales (one day or faster), while thermal driving changes at slower rates (longer than one day). In some key regions under the large cold-water ice shelves, however, thermal driving varies faster than friction velocity and this can not be explained by tidal modulations in boundary layer exchange rates alone. Our results suggest that large scale ocean models aiming to predict accurate ice shelf melt rates will need to explicitly resolve tides.

23
Antarctica / Re: The State of Wilkes Basin Glaciers
« on: July 27, 2020, 07:13:42 PM »
Regarding what is the real 'doomsday glacier', the IPCC’s SROCC says that “Thwaites Glacier is particularly important because it extends into the interior of the WAIS, where the bed is >2000m below sea level in places”. 

Although, the SROCC also notes that while MISI requires a retrograde bed slope to occur, MICI could even happen on a flat or seaward-inclined bed where combined with hydrofracturing (see the first attached image from the SROCC).  So a key question regarding the Wilkes MICI stability is when will the local coastal surface temperatures (say at EL +100m) be high enough to induce frequent ice surface melting in the January to February timeframe; which is a function of both TCR and ECS (see the second image from E3SMv1 which includes the influence of a slowdown of the MOC due to projected freshening of the North Atlantic and Southern Ocean surface waters).

24
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 26, 2020, 03:09:26 PM »
Don't worry, ASLR, we can wait.

While we all wait a year (or so) for me to create an annual summary of long-tailed climate risk issues in a tightly grouped series of cross-correlated posts, I present the attached images (from the two linked references) showing the bathymetries of key ASE marine glaciers and how the Thwaites gateway at base of the Thwaites Ice Tongue is deep enough to sustain ice-cliff failure mechanisms that could propagate upstream into the BSB once initiated:

Hogan, K. A., Larter, R. D., Graham, A. G. C., Arthern, R., Kirkham, J. D., Totten Minzoni, R., Jordan, T. A., Clark, R., Fitzgerald, V., Anderson, J. B., Hillenbrand, C.-D., Nitsche, F. O., Simkins, L., Smith, J. A., Gohl, K., Arndt, J. E., Hong, J., and Wellner, J.: Revealing the former bed of Thwaites Glacier using sea-floor bathymetry, The Cryosphere Discuss., https://doi.org/10.5194/tc-2020-25, in review, 2020.

https://www.the-cryosphere-discuss.net/tc-2020-25/

Caption of image 1: "Figure 2: (a) New MBES grid for the inner Amundsen Sea Embayment. Ice-velocity data from the MEaSUREs V2 dataset (Mouginot et al., 2019); grounding lines for 1992 and 2011 are from Rignot et al. (2011), and that for 2017 from Milillo et al. (2019); red arrows delineate CDW pathways after Dutrieux et al. (2014) and Milillo et al. (2019). The black dashed line marks the boundaries of the drainage basin of Thwaites Glacier (Vaughan et al., 2001). (b) NBP19-02 data coverage versus other MBES datasets (Table 1). The dark blue coastline illustrates the ice-shelf and ice-mélange extent during survey on NBP19-02 and was digitised from Landsat 8 imagery."

&

Jordan, T. A., Porter, D., Tinto, K., Millan, R., Muto, A., Hogan, K., Larter, R. D., Graham, A. G. C., and Paden, J. D.: New gravity-derived bathymetry for the Thwaites, Crosson and Dotson ice shelves revealing two ice shelf populations, The Cryosphere Discuss., https://doi.org/10.5194/tc-2019-294, in review, 2020.

https://www.the-cryosphere-discuss.net/tc-2019-294/

Extract: "Airborne gravity provides a good first order estimate of sub-ice-shelf bathymetry. Despite the relatively high uncertainty (~100 m standard deviation) comparisons with different gravity inversion techniques, and new observational bathymetric data, indicate that the pattern of sub-ice-shelf bathymetry is well resolved.

Thwaites Glacier is connected to the deep ocean by a major trough >800 m deep and 20 km wide. In contrast the grounding lines of the of Dotson and Crosson ice shelves are accessible through relatively narrow channels and thin sub shelf cavities. In the Thwaites, Dotson and Crosson region, areas of ice shelf which developed before and after 1993 form distinct populations. The most recently un-grounded areas are underlain by thin cavities (average 112 m) where the ice shelf base closely tracks the underlying bed topography."

Caption of image 2: "Figure 2: New bathymetry and cavity maps. a) Final topography from terrain shift method. White lines A-D mark profiles in Fig. 3. Yellow outline encloses region constrained by gravity data. Pink line shows -800m depth contour. Light grey lines mark grounding lines and ice shelf edge."

Caption of image 3: "Figure 3: Profiles across ice shelves. Upper panel shows ice surface from REMA DEM (Howat et al., 2019) and base of ice shelf calculated assuming hydrostatic equilibrium, together with gravity-derived bathymetric estimates. Second panel shows input freeair gravity anomaly. Third panel shows magnetic anomalies derived from ITGC survey data (REF data doi) and ADMAP2 (Golynsky et al., 2018). a) Thwaites Eastern Ice Shelf. b) Thwites Glacier Tongue. c) Crosson Ice Shelf. d) Dotson Ice Shelf. Note 520 thin cavity in regions of ice sheet grounding line retreat since 1993 (grey boxes)."

The forth image shows conceptual models for the formation of the subglacial cavities for the key ASE marine glaciers

25
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 25, 2020, 10:39:55 PM »
etc. etc. etc.
Also would love to publish a post from you on my blog, perhaps could even make it into a narrated video with graphs, animations etc.

Unfortunately, currently I do not have sufficient time to take you up on your offer.

26
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 25, 2020, 04:45:36 PM »
In this talk from October 2019, Eric Rignot suggests the possibility of 4 meters of sea level rise per century.
...

Rignot is a very honorable climate scientist who acknowledges that there is a lot of deep uncertainties associated ice sheet instability in the coming century, which raises the risk of 4 meter eustatic SLR this century (whether 2000 or 2020).  Unfortunately, this long-tail ice mass climate risk is too complicated for him to effectively express to either the public and/or to decision makers; and I get the feeling that this thread is at best a small flashlight peering into a large black cave; where most readers forget what they just saw as the flashlight moves around the cave.  As I have other work to do today, I will just mention a very few fat-tail ice-climate risk factors that Rignot's talk did not have the time to express:

1. Abrupt ice sheet mass loss can quickly slow the MOC; which can abruptly increase climate sensitivity.
2. Anthropogenic warming has been occurring for 250-years since pre-industrial times so many slow-response positive feedback mechanisms are already being activated today.
3. The frequency of Super El Nino events are projected to increase with continued global warming; which will accelerate the telecommunication of Tropical Pacific heat energy directly to West Antarctica.
4. If/when the ASE marine glaciers collapse, this will advect a pulse of freshened surface ocean water counter-clockwise around the coast of Antarctica (all the way to the Weddell Sea) that will accelerate the upwelling of warm CDW to the grounding line of key marine glaciers in both East and West Antarctica.
5. Marine ice cliff instability can progress back/up along a mild prograde bed slope.
6. The grounding line at the base of the Thwaites Ice Tongue has progressed further upstream than Rignot's 2019 talk indicates.
7. Rignot did not mention the probability of a cascade of freshwater hosing tipping events between the NH and the SH that characterized the Meltwater Pulse 1A event that Rignot cited as evidence that 4m of eustatic SLR might occur this century.

I need to go now, but readers should not forget to use the search function of this thread to look up past posts that discuss issues like: a) seismic/volcanic activity, b) geothermal heat flux, c) aerosol masking, d) methane feedback mechanisms etc. etc. etc.

27
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 24, 2020, 10:26:43 PM »
Very good.

28
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 24, 2020, 09:14:21 PM »
...
Thanks for trying to help me understand this topic. So does this mean that CS is a dynamic value, could be today 3C, and in 30 years increase to 5C?

...

Currently working on a video which ends with this, 'Both the Aurora, and Wilkes Basin ice is prone to the so called marine ice sheet instability, the potential for ice sheets grounded below sea level to destabilize in a runaway fashion.'

Regarding your first question on changes of climate sensitivity (CS) with time; this is a complex topic to appreciate the numerous subtle issues; nevertheless, CS does change with GMST as clearly indicated by the paleorecord (with warmer periods having higher CS values), but also with the rate of radiative forcing, initial climate parameters (such as the ozone hole over Antarctica, etc).  Some feedbacks impact both TCR (& consequently ECS) such as the ice content of the clouds over the Southern Ocean (as shown by several high end CMIP6 projections) and possible slowing of the MOC due for freshwater hosing (as partially demonstrated by E3SMv1).  Furthermore, ECS can progressively increase due to tipping points of Earth Systems such as: permafrost, rainforest carbon sinks and changes in albedo (such as from changes in snow cover and/or sea ice coverage).  Also, ECS might currently be masked (say by highly negative aerosol forcing) to say effectively be 3C (see the first image) as measured by observations, but its true value of say 5C (see the second image) could be unmasked in say 30 years if there were to be a marked decrease in anthropogenic aerosol emissions in that time.  Finally, an abrupt freshwater hosing event would temporarily increase the planetary imbalance of radiative forcing (see the third image) and which might increase the tropical ocean SSTA by say 5C, which would increase high-energy evaporation from the tropical ocean which would produce more high altitude clouds (an fewer low altitude clouds) for a marked increase in net radiative forcing (see the fourth image) that might abruptly increase both TCR and ECS over several decades time.

Also, when you make your video on marine ice sheet instability (MISI) try to explain the difference between MISI and MICI and note that different marine glaciers could experience tipping points in a cascade, where say the initial collapse of Thwaites Glacier could trigger the collapse of other marine glaciers in Antarctic and/or via the bipolar seesaw of marine terminating glaciers in Greenland.

29
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 24, 2020, 07:01:10 PM »
Here two more consensus climate science-based images related to TCR vs ECS, both of which ignore decadal freshwater hosing events such as a freshwater release from the Beaufort Gyre and/or an abrupt (MICI-type of) collapse of the WAIS.

30
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 24, 2020, 04:54:41 PM »
Transient Climate Response, TCR, only addresses fast feedback mechanisms (and not the slow feedback mechanisms) and thus TCR is smaller than ECS.  Furthermore, IPCC's AR5 explicitly calculates a Carbon Budget using TCR values, and they ignore uncertainties in estimating TCR such as cloud feedback uncertainties, aerosol feedback uncertainties (see the first image) and freshwater hosing uncertainties (see the second image from E3SMv1 where the high 2.93C value for TCR has been attributed to hosing images on the MOC).

Also, both TCR and ECS (see the third image) have numerous different definitions depending on timeframe and method of approximation.  Lastly, all AR and CMIP projections of both TCR and ECS assume that we will not cross a tipping point (see the fourth image) possibly leading to an abrupt increasing in climate sensitivity within the next hundred years.

31
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 24, 2020, 12:52:57 AM »
While the linked reference does not consider the impacts of meltwater from the AIS; nevertheless its analysis represents an improvement on earlier studies with regard to the effects of buoyancy and wind forcing on the Southern Ocean:

Jia-Rui Shi, Lynne D. Talley, Shang-Ping Xie, Wei Liu and Sarah T. Gille (2020), "Effects of Buoyancy and Wind Forcing on Southern Ocean Climate Change", J. Climate, 1–53, https://doi.org/10.1175/JCLI-D-19-0877.1

https://journals.ametsoc.org/jcli/article/doi/10.1175/JCLI-D-19-0877.1/353484/Effects-of-Buoyancy-and-Wind-Forcing-on-Southern?searchresult=1

Abstract
Observations show that since the 1950s, the Southern Ocean has stored a large amount of anthropogenic heat and has freshened at the surface. These patterns can be attributed to two components of surface forcing: poleward-intensified westerly winds and increased buoyancy flux from freshwater and heat. Here we separate the effects of these two forcing components by using a novel partial-coupling technique. We show that buoyancy forcing dominates the overall response in the temperature and salinity structure of the Southern Ocean. Wind stress change results in changes in subsurface temperature and salinity that are closely related to intensified  . As an important result, we show that buoyancy and wind forcing result in opposing changes in salinity: the wind-induced surface salinity increase due to upwelling of saltier subsurface water offsets surface freshening due to amplification of the global hydrological cycle. Buoyancy and wind forcing further lead to different vertical structures of Antarctic Circumpolar Current (ACC) transport change; buoyancy forcing causes an ACC transport increase (3.1±1.6 Sv; 1Sv ≡ 106m3s−1) by increasing the meridional density gradient across the ACC in the upper 2000m, while the wind-induced response is more barotropic, with the whole column transport increased by 8.7±2.3 Sv. While previous research focused on the wind effect on ACC intensity, we show that surface horizontal current acceleration within the ACC is dominated by buoyancy forcing. These results shed light on how the Southern Ocean might change under global warming, contributing to more reliable future projections.

32
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 23, 2020, 08:21:26 PM »
Gavin Schmidt makes a few good points about Sherwood et al (2020) in the linked article:

Title: "Climate Sensitivity: A new assessment"

http://www.realclimate.org/index.php/archives/2020/07/climate-sensitivity-a-new-assessment/#more-23158

Extract: "The paper is exhaustive (and exhausting – coming in at 166 preprint pages!) and concludes that equilibrium climate sensitivity is likely between 2.3 and 4.5 K, and very likely to be between 2.0 and 5.7 K.

I should be clear that although (I think) this is the best and most thorough assessment of climate sensitivity to date, I don’t think it is the last word on the subject. During the research on this paper, and the attempts to nail down each element of the uncertainty, there were many points where it was clear that more effort (with models or with data analysis) could be applied (see the paper for details). In particular, we could still do a better job of tying paleo-climate constraints to the other two classes. Additionally, new data will continue to impact the estimates – whether it’s improvements in proxy temperature databases, cloud property measurements, or each new year of historical change. New, more skillful, models will also help, perhaps reducing the structural uncertainty in some of the parameters (though there is no guarantee they will do so)."


33
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 23, 2020, 08:07:28 PM »
As of July 23, 2020 the World Population is over 7.8 billion people and counting.

34
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 23, 2020, 07:36:36 PM »
The linked reference finds that:

An interesting feature in aerosol-induced circulation changes is a characteristic dipole pattern with intensification of the Icelandic Low and an anticyclonic anomaly over southeastern Europe, inducing warm air advection towards the northern polar latitudes in winter.

Zanis, P., Akritidis, D., Georgoulias, A. K., Allen, R. J., Bauer, S. E., Boucher, O., Cole, J., Johnson, B., Deushi, M., Michou, M., Mulcahy, J., Nabat, P., Olivié, D., Oshima, N., Sima, A., Schulz, M., Takemura, T., and Tsigaridis, K.: Fast responses on pre-industrial climate from present-day aerosols in a CMIP6 multi-model study, Atmos. Chem. Phys., 20, 8381–8404, https://doi.org/10.5194/acp-20-8381-2020, 2020.

https://www.atmos-chem-phys.net/20/8381/2020/

Abstract
In this work, we use Coupled Model Intercomparison Project Phase 6 (CMIP6) simulations from 10 Earth system models (ESMs) and general circulation models (GCMs) to study the fast climate responses on pre-industrial climate, due to present-day aerosols. All models carried out two sets of simulations: a control experiment with all forcings set to the year 1850 and a perturbation experiment with all forcings identical to the control, except for aerosols with precursor emissions set to the year 2014. In response to the pattern of all aerosols effective radiative forcing (ERF), the fast temperature responses are characterized by cooling over the continental areas, especially in the Northern Hemisphere, with the largest cooling over East Asia and India, sulfate being the dominant aerosol surface temperature driver for present-day emissions. In the Arctic there is a warming signal for winter in the ensemble mean of fast temperature responses, but the model-to-model variability is large, and it is presumably linked to aerosol-induced circulation changes. The largest fast precipitation responses are seen in the tropical belt regions, generally characterized by a reduction over continental regions and presumably a southward shift of the tropical rain belt. This is a characteristic and robust feature among most models in this study, associated with weakening of the monsoon systems around the globe (Asia, Africa and America) in response to hemispherically asymmetric cooling from a Northern Hemisphere aerosol perturbation, forcing possibly the Intertropical Convergence Zone (ITCZ) and tropical precipitation to shift away from the cooled hemisphere despite that aerosols' effects on temperature and precipitation are only partly realized in these simulations as the sea surface temperatures are kept fixed. An interesting feature in aerosol-induced circulation changes is a characteristic dipole pattern with intensification of the Icelandic Low and an anticyclonic anomaly over southeastern Europe, inducing warm air advection towards the northern polar latitudes in winter.

35
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 23, 2020, 07:21:47 PM »
The linked open access reference recommends that "… the best strategy would be to consider multiple fingerprints to provide early detection of all likely AMOC changes."

L. C. Jackson and R. A. Wood (2020), "Fingerprints for Early Detection of Changes in the AMOC
J. Climate, 33 (16): 7027–7044, https://doi.org/10.1175/JCLI-D-20-0034.1

https://journals.ametsoc.org/jcli/article/33/16/7027/347834/Fingerprints-for-Early-Detection-of-Changes-in-the

Abstract
Different strategies have been proposed in previous studies for monitoring the Atlantic meridional overturning circulation (AMOC). As well as arrays to directly monitor the AMOC strength, various fingerprints have been suggested to represent an aspect of the AMOC based on properties such as temperature and density. The additional value of fingerprints potentially includes the ability to detect a change earlier than a change in the AMOC itself, the ability to extend a time series back into the past, and the ability to detect crossing a threshold. In this study we select metrics that have been proposed as fingerprints in previous studies and evaluate their ability to detect AMOC changes in a number of scenarios (internal variability, weakening from increased greenhouse gases, weakening from hosing and hysteresis) in the eddy-permitting coupled climate model HadGEM3-GC2. We find that the metrics that perform best are the temperature metrics based on large-scale differences, the large-scale meridional density gradient, and the vertical density difference in the Labrador Sea. The best metric for monitoring the AMOC depends somewhat on the processes driving the change. Hence the best strategy would be to consider multiple fingerprints to provide early detection of all likely AMOC changes.

Extract: "Current arrays monitoring the AMOC directly (RAPID and OSNAP) are shown to perform well, although fingerprints can provide added value. Results here show that some metrics are useful fingerprints; however, the best metric may depend on the question being asked. The results do point to continued monitoring of densities, surface temperatures, and mixed layer depths, particularly in the subpolar gyre. A successful monitoring strategy for climate-relevant AMOC changes is likely to involve using multiple fingerprints and physical understanding."

36
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 23, 2020, 07:13:49 PM »
For those who think of the application of the Precautionary Principle as a form of doomer dogma, the linked reference recommends the adoption of a conceptual framework to use pitchfork bifurcation and to analyze the early‐warning signals in temperature time series for critical slowing down prior to both the early 20th century global warming and heat waves.

Chenghao Wang, Zhi‐Hua Wang and Linda Sun (15 July 2020), "Early‐Warning Signals for Critical Temperature Transitions", Geophysical Research Letters, https://doi.org/10.1029/2020GL088503

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2020GL088503?af=R

Abstract
Critical transitions of the state variable (temperature) in dynamic climate systems often lead to catastrophic consequence, whereas the effort to reverse the transitions usually lags behind. However, these transitions are characterized by the slowing down of recovery from perturbations, carrying early‐warning signals that can be used to predict system bifurcation. In this study, we employ the conceptual framework of pitchfork bifurcation and analyze the early‐warning signals in temperature time series for critical slowing down prior to both the early 20th century global warming and heat waves. We also investigate the urban signature in these heat waves. The emergence of early‐warning signals before heat waves provides new insights into the underlying mechanisms (e.g., possible feedback via land‐atmosphere interactions). In particular, given the increasing frequency and intensity of heat extremes, the results will facilitate the design of countermeasures to reserve the tipping and restore the resilience of climate systems.

Plain Language Summary
Critical transitions have been identified in global and regional climate systems, during which a small perturbation can lead to a qualitative change. They are notoriously difficult to predict and can have potential catastrophic impacts on ecosystems and human society. However, certain characteristics may exist prior to such transitions and can serve as the early‐warning signals to predict critical transitions in climate systems. Here we investigate the early‐warning signals in global warming and regional heat waves based on temperature records. We identify clear early‐warning signals before the early 20th century global warming period and several heat waves during recent years. The early‐warning signals for heat waves are possibly due to the interplay of multiple environmental determinants, such as the drying soil during droughts and the heat accumulated in the atmosphere. Furthermore, we observe differences in the early‐warning signals between urban and rural temperature records. Our study highlights the presence of early‐warning signals days (years) prior to heat waves (abrupt global warming). With the higher frequency and intensity of heat wave events in a warming future, the results can be used to design mitigation and adaptation strategies beforehand to attenuate their negative impacts (such as heat stress) and proactively combat climate change.

37
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 23, 2020, 12:51:30 AM »
...
Thanks ASLR for linking to this new, major study.

Their approach to not using GCM's is refreshing: "...we avoid relying on GCMs to tell us what values to expect for key feedbacks except where the feedback mechanisms can be calibrated against other evidence." (p 8 of a total of 184 pages)

I believe this is good advice for everyone.

To me human bias (including bias by consensus climate science) is what got us all in to the current climate emergency that we are all facing; and thinking that humans will find a path forward through this crisis without using the best ESMs available now and incrementally in the future (such as E3SMv4 calibrated using machine learning ) is shortsighted.

38
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 22, 2020, 10:34:54 PM »
As the E3SM program gets ready for the transition to non-linear exascale climate modeling using E3SMv4; they are currently using machine learning to ensure the reproducibility of the statics of their ESM simulations.  In this regard, I believe that climate modeling is so complicated that machine learning is needed as humans love to use linear interpretations of data:

Title: "Machine Learning Approaches to Ensure Statistical Reproducibility of ESM Simulations"

https://e3sm.org/wp-content/uploads/2020/07/200709_S_Mahajan_opt1.pdf


39
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 22, 2020, 07:10:24 PM »
To me, the linked reference, and associated article, represent an incremental refinement of consensus climate science where the authors limit their definition of ECS to exclude short-term freshwater hosing events, which to me means that only their findings limiting the lower bound of ECS to values above 2.6C are meaningful; while their suggested limits on the upper bound of the true ECS is influenced by their limited definition of ECS.  Therefore, while the climate sensitivity projections from E3SMv1 are not definitive, I believe that the findings of Sherwood et al. (2020) do not eliminate the risk that the higher end CMIP6 ECS values may be in the right range of values (as acknowledged in the last paragraph of the associated article):

S. Sherwood et al. (22 July 2020), "An assessment of Earth's climate sensitivity using multiple lines of evidence", Reviews of Geophysics, https://doi.org/10.1029/2019RG000678

https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2019RG000678

Abstract
We assess evidence relevant to Earth's equilibrium climate sensitivity per doubling of atmospheric CO2, characterized by an effective sensitivity S . This evidence includes feedback process understanding, the historical climate record, and the paleoclimate record. An S value lower than 2 K is difficult to reconcile with any of the three lines of evidence. The amount of cooling during the Last Glacial Maximum provides strong evidence against values of S greater than 4.5 K. Other lines of evidence in combination also show that this is relatively unlikely. We use a Bayesian approach to produce a probability density (PDF) for S given all the evidence, including tests of robustness to difficult‐to‐quantify uncertainties and different priors. The 66% range is 2.6‐3.9 K for our Baseline calculation, and remains within 2.3‐4.5 K under the robustness tests; corresponding 5‐95% ranges are 2.3‐4.7 K, bounded by 2.0‐5.7 K (although such high‐confidence ranges should be regarded more cautiously). This indicates a stronger constraint on S than reported in past assessments, by lifting the low end of the range. This narrowing occurs because the three lines of evidence agree and are judged to be largely independent, and because of greater confidence in understanding feedback processes and in combining evidence. We identify promising avenues for further narrowing the range in S , in particular using comprehensive models and process understanding to address limitations in the traditional forcing‐feedback paradigm for interpreting past changes.

Plain Language Summary
Earth's global “climate sensitivity” is a fundamental quantitative measure of the susceptibility of Earth's climate to human influence. A landmark report in 1979 concluded that it probably lies between 1.5‐4.5°C per doubling of atmospheric carbon dioxide, assuming that other influences on climate remain unchanged. In the 40 years since, it has appeared difficult to reduce this uncertainty range. In this report we thoroughly assess all lines of evidence including some new developments. We find that a large volume of consistent evidence now points to a more confident view of a climate sensitivity near the middle or upper part of this range. In particular, it now appears extremely unlikely that the climate sensitivity could be low enough to avoid substantial climate change (well in excess of 2°C warming) under a high‐emissions future scenario. We remain unable to rule out that the sensitivity could be above 4.5°C per doubling of carbon dioxide levels, although this is not likely. Continued research is needed to further reduce the uncertainty and we identify some of the more promising possibilities in this regard.

See also:

Title: "Guest post: Why low-end ‘climate sensitivity’ can now be ruled out"

https://www.carbonbrief.org/guest-post-why-low-end-climate-sensitivity-can-now-be-ruled-out

Extract: "Our findings, published in Reviews of Geophysics, narrow the likely range in “equilibrium climate sensitivity” (ECS) – a measure of how much the world can be expected to warm for a doubling of CO2 above pre-industrial levels.

Now, bringing together evidence from observed warming, Earth’s distant past and climate models, as well as advances in our scientific understanding of the climate, our findings suggest that the range of ECS is likely to be between 2.6C and 4.1C.

This narrowed range indicates that human society will not be able to rely on a low sensitivity to give us more time to tackle climate change. But the silver lining to this cloud is that our findings also suggest that very high ECS estimates are unlikely."

However, our study is not definitive and there is still space in the statistics for values at the high end of ECS, in particular, as this is less well constrained than our lower end. Therefore, our work cannot definitively rule out these high-end models.

Further, other studies have found that in many ways simulations with high ECS values are improved. Therefore, it remains a useful precautionary measure to include these high ECS models when assessing future risks."

Edit, see also:

Title: "Range of global warming scenarios is more severe than thought, study shows"

https://www.axios.com/global-warming-climate-study-8a887793-5ec0-4e06-872a-c43579a144e5.html

Extract: "The bottom line: It now appears "extremely unlikely" that Earth's global climate sensitivity "could be low enough to avoid substantial climate change" if carbon emissions continue unabated, according to the researchers."

Edit2, for a pdf of the reference see the following link:

https://climateextremes.org.au/wp-content/uploads/2020/07/WCRP_ECS_Final_manuscript_2019RG000678R_FINAL_200720.pdf

40
...
This is a reminder to readers that if the BSB were to experience an MICI-type of collapse beginning possibly as early as 2030 due to hydrofacturing of the calving front of the Thwaites Ice Tongue due to a Super El Nino event, then it is possible that significant amounts of methane could be emitted into the atmosphere from the associated rapid degradation of seabed methane hydrates in the BSB bed.

The linked open access reference provides more details bout the nature of methane hydrate seeps from the seafloor around Antarctica:

Andrew R. Thurber, Sarah Seabrook and Rory M. Welsh (22 July 2020), "Riddles in the cold: Antarctic endemism and microbial succession impact methane cycling in the Southern Ocean", Proceedings of the Royal Society B, https://doi.org/10.1098/rspb.2020.1134

https://royalsocietypublishing.org/doi/10.1098/rspb.2020.1134

Abstract
Antarctica is estimated to contain as much as a quarter of earth's marine methane, however we have not discovered an active Antarctic methane seep limiting our understanding of the methane cycle. In 2011, an expansive (70 m × 1 m) microbial mat formed at 10 m water depth in the Ross Sea, Antarctica which we identify here to be a high latitude hydrogen sulfide and methane seep. Through 16S rRNA gene analysis on samples collected 1 year and 5 years after the methane seep formed, we identify the taxa involved in the Antarctic methane cycle and quantify the response rate of the microbial community to a novel input of methane. One year after the seep formed, ANaerobic MEthane oxidizing archaea (ANME), the dominant sink of methane globally, were absent. Five years later, ANME were found to make up to 4% of the microbial community, however the dominant member of this group observed (ANME-1) were unexpected considering the cold temperature (−1.8°C) and high sulfate concentrations (greater than 24 mM) present at this site. Additionally, the microbial community had not yet formed a sufficient filter to mitigate the release of methane from the sediment; methane flux from the sediment was still significant at 3.1 mmol CH4 m−2 d−1. We hypothesize that this 5 year time point represents an early successional stage of the microbiota in response to methane input. This study provides the first report of the evolution of a seep system from a non-seep environment, and reveals that the rate of microbial succession may have an unrealized impact on greenhouse gas emission from marine methane reservoirs.

41
In my last post, I briefly mentioned the risk of abrupt release of methane from hydrate beneath the WAIS, during a potential near-future collapse of the WAIS. In this regards, the linked reference provides paleo evidence that subglacial gas hydrates within zones of the basal sediment served to reduce ice flow velocities in the marine glaciers of the Barents-Sea-Fennoscandian ice sheet approximately 20,000 years ago.  As there are projected to be large amounts of gas hydrates in the marine sediments beneath the WAIS, these findings may help to partially explain why the ice flow velocities of key WAIS marine glaciers like the PIG and Thwaites have plateaued recently (rather than continuing to accelerate rapidly).  However, if this is the case and if cliff failures and hydrofracturing occurs in the WAIS before GMST anoms reach 2.7C (as forecast by DeConto 2016), then such postulated basal hydrates could release significant volumes of methane if/when the WAIS collapses:

Monica Winsborrow, Karin Andreassen, Alun Hubbard, Andreia Plaza-Faverola, Eythor Gudlaugsson, Henry Patton. Regulation of ice stream flow through subglacial formation of gas hydrates. Nature Geoscience, 2016; DOI: 10.1038/ngeo2696

http://www.nature.com/ngeo/journal/v9/n5/full/ngeo2696.html


Abstract: "Variations in the flow of ice streams and outlet glaciers are a primary control on ice sheet stability, yet comprehensive understanding of the key processes operating at the ice-bed interface remains elusive. Basal resistance is critical, especially sticky spots-localized zones of high basal traction-for maintaining force balance in an otherwise well-lubricated/high-slip subglacial environment. Here we consider the influence of subglacial gas-hydrate formation on ice stream dynamics, and its potential to initiate and maintain sticky spots. Geophysical data document the geologic footprint of a major palaeo-ice-stream that drained the Barents Sea-Fennoscandian ice sheet approximately 20,000 years ago. Our results reveal a ∼250 km2 sticky spot that coincided with subsurface shallow gas accumulations, seafloor fluid expulsion and a fault complex associated with deep hydrocarbon reservoirs. We propose that gas migrating from these reservoirs formed hydrates under high-pressure, low-temperature subglacial conditions. The gas hydrate desiccated, stiffened and thereby strengthened the subglacial sediments, promoting high traction-a sticky spot-that regulated ice stream flow. Deep hydrocarbon reservoirs are common beneath past and contemporary glaciated areas, implying that gas-hydrate regulation of subglacial dynamics could be a widespread phenomenon."

https://www.sciencedaily.com/releases/2016/04/160413084735.htm

Extract: "One of the major questions today is: What are the ice sheets going to do in an ever-warming climate? Ice sheets of Greenland and Antarctica are major contributors to the sea level rise, which can make life difficult for many coastal nations in the near future.

To understand the ice sheets we need to understand their drainage system -- a key component of this is ice streams, fast-flowing rivers of ice, that deliver ice from the centre of the ice sheet to the oceans. Many of these ice streams are speeding up, which may be seen as the logical consequence of the warming climate. But some are slowing down, even stopping, examples of this may be found in the Ross ice streams of West Antarctica.

A new study in Nature Geoscience suggests that a 250km2 sticky spot made up of sediments with gas hydrates in them, slowed down an ice stream in the Barents Sea. This happened sometime during the last ice age, 20,000 years ago, when the Barents Sea was covered with an ice sheet.

Gas hydrate sticky spots under ice streams are a potentially widespread feature also today.
"If there are gas hydrates under today's ice sheets, they can slow the ice streams. There are studies indicating that there may be vast reservoirs of hydrates under the West Antarctic Ice sheet. Anywhere you have a hydrocarbon reservoir, water, high pressure and low temperature, you will get gas hydrate." says Winsborrow.

Ice streams of today are extensively monitored with GPS tracking systems, but it is very difficult to gaze beneath three kilometres of ice to see what is going on at the bottom. But scars left by the Barents Sea Ice sheet are visible on the ocean floor today. That makes this ancient ice sheet an important analogue, especially for the modern West Antarctica Ice Sheet, as both are based in marine environments.

"We need these analogies from the past. Understanding what is happening at the base of ice streams is important for modelling and predicting the future of the ice sheets.""

&

The following linked reference presents new findings that the retreat of the Barents Sea Ice Sheet at the end of the last ice age resulted in the explosive release of methane from Arctic seafloor hydrates as overpressure from the ice sheet disappeared.  The researchers find that serves as a good past analogy of what may likely happen in the near-term future if the WAIS were to collapse (see the attached image).  As methane has a GWP100 of about 35 such explosive releases of methane could have a significant impact on global warming this century.  Such short-term methane forcings would be superimposed on top of Hansen's ice-climate feedback mechanism.

K. Andreassen, A. Hubbard, M. Winsborrow, H. Patton, S. Vadakkepuliyambatta, A. Plaza-Faverola, E. Gudlaugsson, P. Serov, A. Deryabin, R. Mattingsdal, J. Mienert & S. Bünz (02 Jun 2017), "Massive blow-out craters formed by hydrate-controlled methane expulsion from the Arctic seafloor", Science, Vol. 356, Issue 6341, pp. 948-953
DOI: 10.1126/science.aal4500

http://science.sciencemag.org/content/356/6341/948

Abstract: "Widespread methane release from thawing Arctic gas hydrates is a major concern, yet the processes, sources, and fluxes involved remain unconstrained. We present geophysical data documenting a cluster of kilometer-wide craters and mounds from the Barents Sea floor associated with large-scale methane expulsion. Combined with ice sheet/gas hydrate modeling, our results indicate that during glaciation, natural gas migrated from underlying hydrocarbon reservoirs and was sequestered extensively as subglacial gas hydrates. Upon ice sheet retreat, methane from this hydrate reservoir concentrated in massive mounds before being abruptly released to form craters.  We propose that these processes were likely widespread across past glaciated petroleum provinces and that they also provide an analog for the potential future destabilization of subglacial gas hydrate reservoirs beneath contemporary ice sheets."

This is a reminder to readers that if the BSB were to experience an MICI-type of collapse beginning possibly as early as 2030 due to hydrofacturing of the calving front of the Thwaites Ice Tongue due to a Super El Nino event, then it is possible that significant amounts of methane could be emitted into the atmosphere from the associated rapid degradation of seabed methane hydrates in the BSB bed.

42
Antarctica / Re: Methane in Antarctica
« on: July 22, 2020, 05:45:05 PM »
Fascinating presentation.

That graph at 9 minutes is interesting.

I guess that you mean the attached image, where the red indicates atmospheric methane concentration and the blue means atmospheric CO2 concentrations.

Edit: I note that the GWP for methane is higher than the 25 value cited on this image.

43
Antarctica / Re: Antarctic Methane Concentrations
« on: July 22, 2020, 05:20:56 PM »
The linked reference discusses how gas hydrates in the bed sediment beneath marine glaciers can cause 'sticky spots' that can regulate ice stream flow rates:

Winsborrow, M., K. Andreassen, A. Hubbard, A. Plaza-Faverola, E. Gudlaugsson and H. Patton (2016). "Regulation of ice stream flow through subglacial formation of gas hydrates." Nature Geosci 9(5): 370-374, DOI: 10.1038/NGEO2696

https://www.nature.com/articles/ngeo2696
&
http://www.nature.com/articles/ngeo2696.epdf?referrer_access_token=IHHHsNRUI3lD2eFpTMWvl9RgN0jAjWel9jnR3ZoTv0N6H6twa9eus1zouX_OVF0HHps81v4XTc0_11DCSpeGLDxz98tw1yul2mr16lbVJL4uOjHYggNVEvnorXQDpPb-4F8Dx03N10vp8xTpF1OSQUCQuGQbrx_agiKHwJMiE0Vb3p9RlZE1kgUDa_7CPZDbIHfa0-zC2RtwAc1-HEOzfwPw5ovCnEJWlCwr6K4nmQjxYGctlb4MLBBjUrGaOUBg&tracking_referrer=austhrutime.com

 Abstract: "Variations in the flow of ice streams and outlet glaciers are a primary control on ice sheet stability, yet comprehensive understanding of the key processes operating at the ice–bed interface remains elusive. Basal resistance is critical, especially sticky spots—localized zones of high basal traction—for maintaining force balance in an otherwise well-lubricated/high-slip subglacial environment. Here we consider the influence of subglacial gas-hydrate formation on ice stream dynamics, and its potential to initiate and maintain sticky spots. Geophysical data document the geologic footprint of a major palaeo-ice-stream that drained the Barents Sea–Fennoscandian ice sheet approximately 20,000 years ago. Our results reveal a ∼250 km sticky spot that coincided with subsurface shallow gas accumulations, seafloor fluid expulsion and a fault complex associated with deep hydrocarbon reservoirs. We propose that gas migrating from these reservoirs formed hydrates under high-pressure, low-temperature subglacial conditions. The gas hydrate desiccated, stiffened and thereby strengthened the subglacial sediments, promoting high traction—a sticky spot— that regulated ice stream flow. Deep hydrocarbon reservoirs are common beneath past and contemporary glaciated areas, implying that gas-hydrate regulation of subglacial dynamics could be a widespread phenomenon."

Also see:

Title: "Regulation of Ice Stream Flow Through Subglacial Formation of Gas Hydrates"

http://austhrutime.com/ice_stram_flow_regulation_subglacial_gas_hydrates.htm

Extract: "Based on the presence of extensive sedimentary basins and modelling studies (Wadham et al., 2012; Wallmann et al., 2012) it is proposed that abundant gas hydrate accumulations are present beneath the ice sheets of Greenland and Antarctica. Also, gas hydrates have been identified in ice core samples obtained from above the subglacial Lake Vostok in East Antarctica (Uchida et al., 1994). The role of potentially widespread gas hydrate reservoirs in the modification of the thermomechanical regime at the base of contemporary ice sheets, which makes them critically sensitive, as well as their impact on ice steam force balance and dynamics has, so far, not been recognised. This control that was previously unforeseen, given the current lack of knowledge with regard to the distribution of gas hydrate, represents a significant unknown in attempts to model the current and future discharge and evolution of contemporary ice sheets, as well as their contribution to rising global sea levels."

I remind readers that if the Byrd Subglacial Basin, BSB, were to sustain an MICI-type of collapse in the coming decades that it is probably that a meaningful about of methane would be released from the methane hydrates in the bed of the Thwaites, and adjoining, glaciers.

44
...

As it only takes one sufficiently intensive surface ice melt event to hydrofracture an ice shelf, looking at averages (even for just the ASE) is not good science, as intense surface ice melt events happen more frequently during intense El Nino events as occurred in January 2016.  In this regard, the first attached image comes from the first linked source:

"Scientists stunned by Antarctic rainfall and a melt area bigger than Texas"

https://www.washingtonpost.com/news/energy-environment/wp/2017/06/15/scientists-just-documented-a-massive-melt-event-on-the-surface-of-antarctica/?utm_term=.526054dc4fdf

Extract: "Scientists have documented a recent, massive melt event on the surface of highly vulnerable West Antarctica that, they fear, could be a harbinger of future events as the planet continues to warm.

In the Antarctic summer of 2016, the surface of the Ross Ice Shelf, the largest floating ice platform on Earth, developed a sheet of meltwater that lasted for as long as 15 days in some places. The total area affected by melt was 300,000 square miles, or larger than the state of Texas, the scientists report."
&
The second linked reference finds that: "The increase in the number of extreme El Niño events projected for the twenty-first century could expose the WAIS to more frequent major surface melt events.":

Julien P. Nicolas et. al. (2017), "January 2016 extensive summer melt in West Antarctica favoured by strong El Niño", Nature Communications 8, Article number: 15799, doi:10.1038/ncomms15799

http://www.nature.com/articles/ncomms15799

Abstract: "Over the past two decades the primary driver of mass loss from the West Antarctic Ice Sheet (WAIS) has been warm ocean water underneath coastal ice shelves, not a warmer atmosphere. Yet, surface melt occurs sporadically over low-lying areas of the WAIS and is not fully understood. Here we report on an episode of extensive and prolonged surface melting observed in the Ross Sea sector of the WAIS in January 2016. A comprehensive cloud and radiation experiment at the WAIS ice divide, downwind of the melt region, provided detailed insight into the physical processes at play during the event. The unusual extent and duration of the melting are linked to strong and sustained advection of warm marine air toward the area, likely favoured by the concurrent strong El Niño event. The increase in the number of extreme El Niño events projected for the twenty-first century could expose the WAIS to more frequent major melt events."

Furthermore, I repost the second attached image to remind readers that the recent past observed rate of warming of the Southern Ocean is not relevant to a possible MICI-type of event in the WAIS in coming decades, because what matters is the increase in temperature of the warm CDW that is advected over the various continental shelves to the grounding lines of the key West Antarctic marine glaciers (which the second image show will increase by about 1.5C by 2050 as compared to 1960).

I reiterate that surface melt from the next Super El Nino might be sufficient to cause a hydro-fracturing triggered MICI-type of failure beginning at the base of the Thwaites Ice Tongue say around 2030-2035.  Furthermore, I note that since the AIS formed about 30 million years ago, there has likely been a lot of MICI-types of failures initiating in this same area; which has likely pre-conditioned the glacial/sea bed to facilitate such failures.  This implies that it is now more likely that a MICI-type of failure of the BSB is more probable than during say the Eemian.

45
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 22, 2020, 02:27:40 AM »
The linked article indicates that NSF has now approved $3 million for ice coring on the WAIS/EAIS divide to help determine whether the WAIS collapsed during the Eemian as some climate scientists believe:

Title: "NSF campaign will drill for ice capturing West Antarctica’s last collapse", Jul. 10, 2020

https://www.sciencemag.org/news/2020/07/nsf-campaign-will-drill-ice-capturing-west-antarctica-s-last-collapse

Extract: "Next week, the National Science Foundation will fund a 5-year project, costing more than $3 million, that will seek evidence of this collapse from gases trapped in tiny bubbles encased in a 2.5 kilometer-long tube of ice. The core drilling, likely to start in 2023, will target Hercules Dome, an expanse of ice 400 kilometers from the South Pole. Hercules sits at the saddle between the continent’s western and eastern ice sheets; if the western one collapsed, “Hercules Dome would be sitting on the waterfront, so to speak,” says Eric Steig, the project’s principal investigator and a glaciologist at the University of Washington, Seattle.

The Eemian, the last warm period between the ice ages, lasting from 129,000 to 116,00 years ago, is one of the best analogs for modern Earth. Temperatures were about 1° warmer than now, yet sea levels were 6 meters to 9 meters higher. And recent work, some still unpublished, has suggested much of this melt must have come from Antarctica."

46
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 22, 2020, 12:19:02 AM »
The first reference indicates that in West Antarctica subglacial lake formation/filling is related to ice velocities.  The second reference and associated image show the catchment area and ice velocities for the PIG and Thwaite Glacier.  Furthermore, I highlight the following passage from the second reference (as the active subglacial lakes, in a cascade system-type, beneath the trunk of Thwaites Glacier, are currently refilling and could readily cause a surge in ice flow at the base of the Thwaites Ice Tongue circa 2030 to 2035):

"… the subglacial water drainage area of TG is bigger than previously thought and recent investigations (e.g., Smith et al., 2017) have demonstrated the presence of active subglacial lakes, in a cascade system-type, beneath the trunk of TG. Any water accumulation/drainage (e.g., chain of active subglacial lakes) in this area may affect the basal friction of the ice and therefore the ice flow velocity."

E. J. MacKie, D. M. Schroeder, J. Caers, M. R. Siegfried and C. Scheidt (08 March 2020), "Antarctic Topographic Realizations and Geostatistical Modeling Used to Map Subglacial Lakes", JGR Earth Surface, https://doi.org/10.1029/2019JF005420

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JF005420

Abstract
Antarctic subglacial lakes can play an important role in ice sheet dynamics, biology, geology, and oceanography, but it is difficult to definitively constrain their character and locations. Subglacial lake locations are related to factors including heat flux, ice surface slope, ice thickness, and bed topography, though these relationships are not fully quantified. Bed topography is particularly important for determining where water flows and accumulates, but digital elevation models of the ice sheet bed rely on interpolation and are unrealistically smooth, biasing estimates of subglacial lake location and surface area. To address this issue, we use geostatistical methods to simulate realistically rough bed topography. We use our simulated topography to predict subglacial lake distribution across the continent using a binomial logistic regression, which uses physical parameters and known lake locations to calculate the probabilities of lake occurrences. Our results suggest that topography models interpolated without appropriate geostatistics overestimate subglacial lake surface area and that total lake surface area is lower than previously predicted. We find that radar‐detected lakes are more likely to occur in the interior of East Antarctica, while altimetry‐detected (active) lakes are expected to be found in West Antarctica and near the grounding line. We observe that radar‐detected lakes have a high correlation with heat flux and ice thickness, while active lakes are associated with higher ice velocity.

&

Felipe Napoleoni et al. (20 March 2020), "Subglacial lakes and hydrology across the Ellsworth Subglacial Highlands, West Antarctica", The Cryosphere Discussions, http://doi.org/10.5194/tc-2020-68

https://tc.copernicus.org/preprints/tc-2020-68/tc-2020-68.pdf

Extract: "The subglacial hydrological catchments of Pine Island and Thwaites Glaciers We observe that most of the subglacial water draining towards ASE is routed through the Bentley Subglacial Trench in the upper part of the hydrological catchment and driven through the Byrd Subglacial Basin towards the trunk of Thwaites Glacier. The high topography in the mid PIG catchment (Vaughan et al., 2006) means that the hydrological drainage system does not link to the faster flowing trunk of PIG. Instead, the basal hydrological system is captured by Thwaites. This drainage pattern has two main implications. Firstly, the subglacial hydrological catchments of PIG and Thwaites do not correspond to the ice catchments; they do not coincide either in position or size. Secondly, the hydrological system of TG trunk (Schroeder et al., 2013) may be fed by water sourced in the upper glaciological catchment of PIG, within the ESH.

Any change in the water catchment of the TG, at the head of PIG, could therefore have important glaciological consequences for the ice dynamics of Thwaites Glacier and the wider ASE. This is particularly critical since the subglacial water drainage area of TG is bigger than previously thought and recent investigations (e.g., Smith et al., 2017) have demonstrated the presence of active subglacial lakes, in a cascade system-type, beneath the trunk of TG. Any water accumulation/drainage (e.g., chain of active subglacial lakes) in this area may affect the basal friction of the ice and therefore the ice flow velocity. Conversely, this pattern may have a reduced importance for PIG in terms of magnitude or timing due to the topographic barrier disconnecting the drainage upstream with the lower/marginal section of PIG. If we are to clearly understand the potential role of subglacial water on the ice dynamics of the PIG and Thwaites systems, then more investigations of the detailed subglacial and hydrological conditions are required."

Caption: "Figure 9. Mean annual ice surface velocity (Mouginot et al., 2019) of Pine Island Glacier, Rutford Ice Stream, Institute Ice Stream, Bindschedler Ice Stream and Thwaites Glacier. Black line shows ice surface velocities higher than 250 myr−1 . The red line indicates the boundary of the water catchment. The blue lines show the subglacial water drainage and the arrows indicates the general flow direction. The Cryosat-2 Elevation model (1 km), virtual hillshade (Helm et al., 2014) is showed in the background. ASE: Amundsen Sea Embayment; BSB: Byrd Subglacial Basin; BST: Bentley Subglacial Trench. Projection: Antarctic Polar Stereographic (EPSG 3031). B) shows the histogram of surface ice velocity over the central part of each subglacial lakes."

47
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 21, 2020, 11:46:30 PM »
With a hat-tip to BornFromTheVoid, the attached images shows a Landsat 8 RGB composite of Petermann Glacier, from July 17th (click to see a larger image).

https://twitter.com/Icy_Samuel/status/1285656073517531138

I wonder how the implied up-coming major calving event will impact the 'Cold Blob' when the resulting icebergs finally float down into the North Atlantic.

48
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 21, 2020, 08:39:25 PM »
For those who are interested, I provide the following open access linked reference (& associated article) about the thermal and compositional structure of the Antarctic lithosphere (which is thin beneath the WAIS):

F. Pappa, J. Ebbing, F. Ferraccioli and W. van der Wal (25 October 2019), "Modeling Satellite Gravity Gradient Data to Derive Density, Temperature, and Viscosity Structure of the Antarctic Lithosphere", Journal of Geophysical Research: Solid Earth, Volume 124, Issue 11, https://doi.org/10.1029/2019JB017997

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JB017997

Abstract
In this study we combine seismological and petrological models with satellite gravity gradient data to obtain the thermal and compositional structure of the Antarctic lithosphere. Our results indicate that Antarctica is largely in isostatic equilibrium, although notable anomalies exist. A new Antarctic Moho depth map is derived that fits the satellite gravity gradient anomaly field and is in good agreement with independent seismic estimates. It exhibits detailed crustal thickness variations also in areas of East Antarctica that are poorly explored due to sparse seismic station coverage. The thickness of the lithosphere in our model is in general agreement with seismological estimates, confirming the marked contrast between West Antarctica (<100 km) and East Antarctica (up to 260 km). Finally, we assess the implications of the temperature distribution in our model for mantle viscosities and glacial isostatic adjustment. The upper mantle temperatures we model are lower than obtained from previous seismic velocity studies. This results in higher estimated viscosities underneath West Antarctica. When combined with present‐day uplift rates from GPS, a bulk dry upper mantle rheology appears permissible.

Plain Language Summary
The solid Earth structure of the Antarctic continent is still poorly explored due to the coverage of up to 4‐km‐thick ice sheets and its remote location. Robust knowledge of its characteristics is, however, essential to understand the Earth's response to ice mass changes (glacial isostatic adjustment). Of particular interest are the depth and geometry of the main subsurface boundaries, which are the interface between crustal and mantle rocks (Moho discontinuity) and the base of the rigid tectonic plate (lithosphere). Since both of them are accompanied by changes in rock density, we used gravimetric data from the Gravity Field and Steady‐State Ocean Circulation Explorer satellite to build a 3‐D model of Antarctica's deep structure. Rock composition according to temperature and pressure is taken into account. Rock composition according to temperature and pressure is taken into account and the model as a whole is internally consistent. As a result, we present a continental‐scale Moho depth map that shows novel details. From the temperature distribution in our model, we derive present‐day uplift rates of the solid Earth's surface, which are a key parameter in estimating the future ice sheet evolution.

&

Title: "GOCE reveals what’s going on deep below Antarctica"

https://yubanet.com/scitech/goce-reveals-whats-going-on-deep-below-antarctica/

Extract: "“Under West Antarctica, Earth’s crust is comparatively thin at about 25 kilometres, and the mantle is viscous at less than 100 kilometres. East Antarctica, on the other hand, is an old cratonic shield. Here, the mantle rock still has solid properties at a depth of more than 200 kilometres.”"

49
The linked reference evaluates the implications of more accurately considering a 3-D viscoelastic Earth models as opposed to the less accurate assumption of elastic response on the sea-level fingerprint implications of an abrupt collapse of the WAIS.  Their findings conclude that "… when viscous effects are included, the peak sea-level fall predicted in the vicinity of WAIS during a melt event will increase by ~25% and ~50%, relative to the elastic case, for events of duration 25 years and 100 years, respectively."  This is important w.r.t. global sea level rise as the further the local sea-level drops around West Antarctica, the higher sea level will raise at distance away from West Antarctica.

Carling C. Hay, Harriet C. P. Lau, Natalya Gomez, Jacqueline Austermann, Evelyn Powell, Jerry X. Mitrovica, Konstantin Latychev, and Douglas A. Wiens (2016), "Sea-level fingerprints in a region of complex Earth structure: The case of WAIS", Journal of Climate, DOI: http://dx.doi.org/10.1175/JCLI-D-16-0388.1


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0388.1


Abstract: "Sea-level fingerprints associated with rapid melting of the West Antarctic Ice Sheet (WAIS) have generally been computed under the assumption of a purely elastic response of the solid Earth. We investigate the impact of viscous effects on these fingerprints by computing gravitationally self-consistent sea-level changes that adopt a 3-D viscoelastic Earth model in the Antarctic region consistent with available geological and geophysical constraints. In West Antarctica, the model is characterized by a thin (~65 km) elastic lithosphere and sub-lithospheric viscosities that span three orders of magnitude, reaching values as low as ~4 × 1018 Pa s beneath WAIS. Our calculations indicate that sea-level predictions in the near field of WAIS will depart significantly from elastic fingerprints in as little as a few decades. For example, when viscous effects are included, the peak sea-level fall predicted in the vicinity of WAIS during a melt event will increase by ~25% and ~50%, relative to the elastic case, for events of duration 25 years and 100 years, respectively. Our results have implications for studies of sea-level change due to both ongoing mass loss from WAIS over the next century and future, large scale collapse of WAIS on century-to-millennial time scales."

For those who do not know, the magma beneath the WAIS has a particularly low viscosity; which implies that the WAIS would contribute to more future SLR than previously assumed by consensus climate science.

Edit, for details of how low the magma viscosity is beneath the WAIS (however, I note that the reference's statement that a low magma viscosity increases the stability of the WAIS is predicated on the assumption of MISI-type of behavior instead of MICI-type of behavior), see:

Barletta et al. (22 Jun 2018), "Observed rapid bedrock uplift in Amundsen Sea Embayment promotes ice-sheet stability," Science, Vol. 360, Issue 6395, pp. 1335-1339, DOI: 10.1126/science.aao1447.

http://science.sciencemag.org/content/360/6395/1335

Abstract
The marine portion of the West Antarctic Ice Sheet (WAIS) in the Amundsen Sea Embayment (ASE) accounts for one-fourth of the cryospheric contribution to global sea-level rise and is vulnerable to catastrophic collapse. The bedrock response to ice mass loss, glacial isostatic adjustment (GIA), was thought to occur on a time scale of 10,000 years. We used new GPS measurements, which show a rapid (41 millimeters per year) uplift of the ASE, to estimate the viscosity of the mantle underneath. We found a much lower viscosity (4 × 1018 pascal-second) than global average, and this shortens the GIA response time scale from tens to hundreds of years. Our finding requires an upward revision of ice mass loss from gravity data of 10% and increases the potential stability of the WAIS against catastrophic collapse.

50
Antarctica / Re: Ice Apocalypse - MULTIPLE METERS SEA LEVEL RISE
« on: July 21, 2020, 07:43:58 PM »
The linked reference (& associated article) reminds us that with continued global warming, Super El Nino events will become more frequent; which will more frequently telecommunicate large amounts of atmospheric heat energy from particularly the Central Tropical Pacific to the West Antarctica coastal regions, where it may likely accelerate the risk of hydro-fracturing inducing calving events, say for Thwaites:

Bin Wang, Xiao Luo, Young-Min Yang, Weiyi Sun, Mark A. Cane, Wenju Cai, Sang-Wook Yeh, and  Jian Liu (November 5, 2019), "Historical change of El Niño properties sheds light on future changes of extreme El Niño", PNAS, 116 ,(45), 22512-22517; https://doi.org/10.1073/pnas.1911130116

https://www.pnas.org/content/116/45/22512

Significance
How the magnitude of El Niño will change is of great societal concern, yet it remains largely unknown. Here we show analysis of how changing El Niño properties, due to 20th century climate change, can shed light on changes to the intensity of El Niño in the future. Since the 1970s, El Niño has changed its origination from the eastern Pacific to the western Pacific, along with increased strong El Niño events due to a background warming in the western Pacific warm pool. This suggests the controlling factors that may lead to increased extreme El Niño events in the future. If the observed background changes continue under future anthropogenic forcing, more frequent extreme El Niño events will induce profound socioeconomic consequences.

Abstract
El Niño’s intensity change under anthropogenic warming is of great importance to society, yet current climate models’ projections remain largely uncertain. The current classification of El Niño does not distinguish the strong from the moderate El Niño events, making it difficult to project future change of El Niño’s intensity. Here we classify 33 El Niño events from 1901 to 2017 by cluster analysis of the onset and amplification processes, and the resultant 4 types of El Niño distinguish the strong from the moderate events and the onset from successive events. The 3 categories of El Niño onset exhibit distinct development mechanisms. We find El Niño onset regime has changed from eastern Pacific origin to western Pacific origin with more frequent occurrence of extreme events since the 1970s. This regime change is hypothesized to arise from a background warming in the western Pacific and the associated increased zonal and vertical sea-surface temperature (SST) gradients in the equatorial central Pacific, which reveals a controlling factor that could lead to increased extreme El Niño events in the future. The Coupled Model Intercomparison Project phase 5 (CMIP5) models’ projections demonstrate that both the frequency and intensity of the strong El Niño events will increase significantly if the projected central Pacific zonal SST gradients become enhanced. If the currently observed background changes continue under future anthropogenic forcing, more frequent strong El Niño events are anticipated. The models’ uncertainty in the projected equatorial zonal SST gradients, however, remains a major roadblock for faithful prediction of El Niño’s future changes.

See also:

Title: "Super El Niño events may become more frequent as the climate warms"

https://www.washingtonpost.com/weather/2019/10/22/super-el-nio-events-may-become-more-frequent-climate-warms/

Extract: "Study co-author Mark Cane of Columbia University, who is a pioneer in El Niño forecasting, says computer models have failed to accurately simulate changes in the tropical Pacific Ocean during the past few decades.

He says if the West Pacific heats up faster than the East Pacific, it’ll cause more El Niño events to be centered toward the international date line, rather than farther east."

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