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Author Topic: Hansen et al paper: 3+ meters SLR by 2100  (Read 172711 times)

sidd

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #650 on: April 26, 2017, 06:46:00 PM »
Hansen not so farfetched: 3m SLR by 2100 doi: 10.1088/1748-9326/aa6512

I see Drijfhout is an author. They put in DeConto-Polard model for Antarctica and a couple other tweaks. Open access. Read all about it

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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #651 on: May 05, 2017, 09:53:51 AM »
The linked reference indicates that freshwater hosing events in the North Atlantic can result in warming of the Nordic Seas (see the attached image); which can accelerate Arctic Amplification:

Mélanie Wary et. al. (2017), "Regional seesaw between North Atlantic and Nordic Seas
during the last glacial abrupt climate events", Clim. Past Discuss., doi:10.5194/cp-2017-14

http://www.clim-past-discuss.net/cp-2017-14/cp-2017-14.pdf

Abstract. Dansgaard-Oeschger oscillations constitute one of the most enigmatic features of the last glacial cycle.  Their cold atmospheric phases have been commonly associated with cold sea-surface temperatures and expansion of sea ice in the North Atlantic and adjacent seas. Here, based on dinocyst analyses from the 48-30 ka BP interval of four sediment cores from the northern Northeast Atlantic and southern Norwegian Sea, we provide direct and quantitative evidence of a regional paradoxical seesaw pattern: cold Greenland and North Atlantic phases coincide with warmer sea-surface conditions and shorter seasonal sea-ice cover durations in the Norwegian Sea as compared to warm phases. Combined with additional paleorecords and multi-model hosing simulations, our results suggest that during cold Greenland phases, reduced Atlantic meridional overturning circulation and cold North Atlantic sea-surface conditions were accompanied by the subsurface propagation of warm Atlantic waters that re-emerged in the Nordic Seas and provided moisture towards Greenland summit.
« Last Edit: November 06, 2017, 06:39:55 PM by AbruptSLR »
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #652 on: May 05, 2017, 06:42:10 PM »
The linked video entitled: "Climate Change: Hansen Paper: Multimeter Sea Level Rise by 2075?", provides an easily accessible overview of the key points of Hansen et al (2016):


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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #653 on: July 10, 2017, 04:31:17 AM »
The linked reference indicates that much of the weaker polar amplification of Antarctica as compared to the Arctic is due to its (high) surface elevation.  This makes me wonder how much the Antarctic polar amplification will increase if/when the WAIS collapses:

Salzmann, M. (2017) The polar amplification asymmetry: Role of antarctic surface height, Earth Systems Dynamics,doi:10.5194/esd-8-323-2017

http://www.earth-syst-dynam.net/8/323/2017/esd-8-323-2017.pdf

Abstract: “Previous studies have attributed an overall weaker (or slower) polar amplification in Antarctica compared to the Arctic to a weaker Antarctic surface albedo feedback and also to more efficient ocean heat uptake in the Southern Ocean in combination with Antarctic ozone depletion. Here, the role of the Antarctic surface height for meridional heat transport and local radiative feedbacks, including the surface albedo feedback, was investigated based on CO2-doubling experiments in a low-resolution coupled climate model. When Antarctica was assumed to be flat, the north–south asymmetry of the zonal mean top of the atmosphere radiation budget was notably reduced… between 24 and 80%… of the polar amplification asymmetry was explained by the difference in surface height, but… might to some extent also depend on model uncertainties.”
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #654 on: July 18, 2017, 07:49:00 PM »
The 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 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."
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #655 on: July 31, 2017, 02:02:57 AM »
The linked reference discusses how decreasing cloud cover over the Greenland Ice Sheet is contributing to accelerated ice mass loss; which could progressively feed into Hansen's ice-climate feedback:

Stefan Hofer, Andrew J. Tedstone, Xavier Fettweis & Jonathan L. Bamber (28 June 2017), “Decreasing cloud cover drives the recent mass loss on the Greenland Ice Sheet”, Science Advances, Vol. 3, no. 6, e1700584, DOI: 10.1126/sciadv.1700584

http://advances.sciencemag.org/content/3/6/e1700584

Abstract: “The Greenland Ice Sheet (GrIS) has been losing mass at an accelerating rate since the mid-1990s. This has been due to both increased ice discharge into the ocean and melting at the surface, with the latter being the dominant contribution. This change in state has been attributed to rising temperatures and a decrease in surface albedo. We show, using satellite data and climate model output, that the abrupt reduction in surface mass balance since about 1995 can be attributed largely to a coincident trend of decreasing summer cloud cover enhancing the melt-albedo feedback. Satellite observations show that, from 1995 to 2009, summer cloud cover decreased by 0.9 ± 0.3% per year. Model output indicates that the GrIS summer melt increases by 27 ± 13 gigatons (Gt) per percent reduction in summer cloud cover, principally because of the impact of increased shortwave radiation over the low albedo ablation zone. The observed reduction in cloud cover is strongly correlated with a state shift in the North Atlantic Oscillation promoting anticyclonic conditions in summer and suggests that the enhanced surface mass loss from the GrIS is driven by synoptic-scale changes in Arctic-wide atmospheric circulation.”
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #656 on: July 31, 2017, 03:14:31 AM »
The linked reference indicates that new decadal-scale model projections for the Southern Ocean indicate that some component of the recent high levels of sea ice extents has been associated with weakening of the AABW cell in the Weddell Sea.  To me this weakening of this AABW cell supports Hansen's ice-climate feedback mechanism:

Zhang, Liping, Thomas L Delworth, Xiaosong Yang, Richard G Gudgel, Liwei Jia, Gabriel A Vecchi, and Fanrong Zeng, July 2017: Estimating decadal predictability for the Southern Ocean using the GFDL CM2.1 model. Journal of Climate, 30(14), DOI:10.1175/JCLI-D-16-0840.1

http://journals.ametsoc.org/doi/10.1175/JCLI-D-16-0840.1

Abstract: “This study explores the potential predictability of the Southern Ocean (SO) climate on decadal time scales as represented in the GFDL CM2.1 model using prognostic methods. Perfect model predictability experiments are conducted starting from 10 different initial states, showing potentially predictable variations of Antarctic bottom water (AABW) formation rates on time scales as long as 20 years. The associated Weddell Sea (WS) subsurface temperatures and Antarctic sea ice have potential predictability comparable to that of the AABW cell. The predictability of sea surface temperature (SST) variations over the WS and the SO is somewhat smaller, with predictable scales out to a decade. This reduced predictability is likely associated with stronger damping from air–sea interaction. As a complement to this perfect predictability study, the authors also make hindcasts of SO decadal variability using the GFDL CM2.1 decadal prediction system. Significant predictive skill for SO SST on multiyear time scales is found in the hindcast system. The success of the hindcasts, especially in reproducing observed surface cooling trends, is largely due to initializing the state of the AABW cell. A weak state of the AABW cell leads to cooler surface conditions and more extensive sea ice. Although there are considerable uncertainties regarding the observational data used to initialize the hindcasts, the consistency between the perfect model experiments and the decadal hindcasts at least gives some indication as to where and to what extent skillful decadal SO forecasts might be possible.”
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #657 on: August 01, 2017, 11:48:24 PM »
The linked reference discusses state of the art surface temperature at the West Antarctic Divide for the past ~ 40,000 years (see image bottom panel).  Findings indicate that current climate models are challenged to hind cast the observed findings and that models with low climate sensitivities can be eliminated from consideration.  Furthermore, they find that an Antarctic Amplification of 2 to 3 time GMSTA.  These findings do not bode well for the stability of the WAIS with continued global warming:

Kurt M. Cuffey, Gary D. Clow, Eric J. Steig, Christo Buizert, T. J. Fudge, Michelle Koutnik, Edwin D. Waddington, Richard B. Alley, and Jeffrey P. Severinghaus (2016), "Deglacial temperature history of West Antarctica", PNAS, vol. 113 no. 50, 14249–14254, doi: 10.1073/pnas.1609132113

http://www.pnas.org/content/113/50/14249

Abstract: "The most recent glacial to interglacial transition constitutes a remarkable natural experiment for learning how Earth’s climate responds to various forcings, including a rise in atmospheric CO2. This transition has left a direct thermal remnant in the polar ice sheets, where the exceptional purity and continual accumulation of ice permit analyses not possible in other settings. For Antarctica, the deglacial warming has previously been constrained only by the water isotopic composition in ice cores, without an absolute thermometric assessment of the isotopes’ sensitivity to temperature. To overcome this limitation, we measured temperatures in a deep borehole and analyzed them together with ice-core data to reconstruct the surface temperature history of West Antarctica. The deglacial warming was 11.3±1.8 ∘  11.3±1.8∘ C, approximately two to three times the global average, in agreement with theoretical expectations for Antarctic amplification of planetary temperature changes. Consistent with evidence from glacier retreat in Southern Hemisphere mountain ranges, the Antarctic warming was mostly completed by 15 kyBP, several millennia earlier than in the Northern Hemisphere. These results constrain the role of variable oceanic heat transport between hemispheres during deglaciation and quantitatively bound the direct influence of global climate forcings on Antarctic temperature. Although climate models perform well on average in this context, some recent syntheses of deglacial climate history have underestimated Antarctic warming and the models with lowest sensitivity can be discounted."

Extract: "Of greatest immediate interest, however, is our demonstration that the global deglacial temperature change was amplified by a factor of 2–3 in the Antarctic, that Antarctic warming was largely achieved by 15 ka in coherence with records from Southern Hemisphere mountain ranges, and that climate models of the deglaciation perform well on average, but that the ones with lowest sensitivity can be discounted. The early warming of the Southern Hemisphere, which our study helps to quantify, arose from combined effects of reduced northward oceanic heat transport, increased insolation, and increasing atmospheric CO2. Quantitative simulation of this phenomenon could provide an illuminating challenge for model studies."
« Last Edit: August 02, 2017, 12:04:35 AM by AbruptSLR »
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #658 on: September 24, 2017, 04:29:18 PM »
The linked reference uses the ice sheet model Glimmer (I note that all current ice sheet models cannot yet adequately model ice sheet behavior to accurately replicate abrupt ice mass loss from ice sheets) to improve our understanding of the differences between MIS 11 and MIS 5e, and identifies the AMOC as the contributing to the largest difference.  Given the WAIS's instability and Hansen's ice-climate feedback mechanism, and the bipolar seesaw mechanism; I do not find this to be particularly surprising nor particularly comforting:

R. Rachmayani, M. Prange, D. J. Lunt, E. J. Stone & M. Schulz (23 September 2017), "Sensitivity of the Greenland Ice Sheet to interglacial climate forcing: MIS 5e versus MIS 11", Paleoceanography, DOI: 10.1002/2017PA003149 

http://onlinelibrary.wiley.com/doi/10.1002/2017PA003149/abstract?utm_content=buffer05e1a&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "The Greenland Ice Sheet (GrIS) is thought to have contributed substantially to high global sea levels during the interglacials of Marine Isotope Stage (MIS) 5e and 11. Geological evidence suggests that the mass loss of the GrIS was greater during the peak interglacial of MIS 11 than MIS 5e, despite a weaker boreal summer insolation. We address this conundrum by using the three-dimensional thermomechanical ice-sheet model Glimmer forced by CCSM3 climate model output for MIS 5e and MIS 11 interglacial time slices. Our results suggest a stronger sensitivity of the GrIS to MIS 11 climate forcing than to MIS 5e forcing. Besides stronger greenhouse gas radiative forcing, the greater MIS 11 GrIS mass loss relative to MIS 5e is attributed to a larger oceanic heat transport towards high latitudes by a stronger Atlantic meridional overturning circulation. The vigorous MIS 11 ocean overturning, in turn, is related to a stronger wind-driven salt transport from low to high latitudes promoting North Atlantic Deep Water formation. The orbital insolation forcing, which causes the ocean current anomalies, is discussed."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #659 on: September 30, 2017, 06:44:33 PM »
The linked reference used climate models that include eddies in the ocean to confirm many of the ice-climate feedback mechanisms cited by Hansen.  Hopefully, CMIP6 models will benefit these lessons:

Paul B. Goddard, Carolina O. Dufour, Jianjun Yin, Stephen M. Griffies & Michael Winton (17 September 2017), "CO2-Induced Ocean Warming of the Antarctic Continental Shelf in an Eddying Global Climate Model", JGR Oceans, DOI: 10.1002/2017JC012849

http://onlinelibrary.wiley.com/doi/10.1002/2017JC012849/abstract

Abstract: "Ocean warming near the Antarctic ice shelves has critical implications for future ice sheet mass loss and global sea level rise. A global climate model with an eddying ocean is used to quantify the mechanisms contributing to ocean warming on the Antarctic continental shelf in an idealized 2xCO2 experiment. The results indicate that relatively large warm anomalies occur both in the upper 100 m and at depths above the shelf floor, which are controlled by different mechanisms. The near-surface ocean warming is primarily a response to enhanced onshore advective heat transport across the shelf break. The deep shelf warming is initiated by onshore intrusions of relatively warm Circumpolar Deep Water (CDW), in density classes that access the shelf, as well as the reduction of the vertical mixing of heat. CO2-induced shelf freshening influences both warming mechanisms. The shelf freshening slows vertical mixing by limiting gravitational instabilities and the upward diffusion of heat associated with CDW, resulting in the build-up of heat at depth. Meanwhile, freshening near the shelf break enhances the lateral density gradient of the Antarctic Slope Front (ASF) and disconnect isopycnals between the shelf and CDW, making cross-ASF heat exchange more difficult. However, at several locations along the ASF, the cross-ASF heat transport is less inhibited and heat can move onshore. Once onshore, lateral and vertical heat advection work to disperse the heat anomalies across the shelf region. Understanding the inhomogeneous Antarctic shelf warming will lead to better projections of future ice sheet mass loss."
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #660 on: October 06, 2017, 10:45:36 PM »
The linked reference concludes: "An ensemble of transient meltwater simulations shows that Antarctic-sourced salinity anomalies can generate climate changes that are propagated globally via an atmospheric Rossby wave train".  This research confirms that a fresh water hosing event from the WAIS can impact the Northern Hemisphere within months, via the bipolar seesaw mechanism.

Turney et al (2017), "Rapid global ocean-atmosphere response to Southern Ocean freshening during the last glacial", Nature Communications, doi:20.2038/s41467-017-00577-6

https://www.nature.com/articles/s41467-017-00577-6
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #661 on: October 06, 2017, 10:49:38 PM »
The linked reference concludes: "An ensemble of transient meltwater simulations shows that Antarctic-sourced salinity anomalies can generate climate changes that are propagated globally via an atmospheric Rossby wave train".  This research confirms that a fresh water hosing event from the WAIS can impact the Northern Hemisphere within months, via the bipolar seesaw mechanism.

Turney et al (2017), "Rapid global ocean-atmosphere response to Southern Ocean freshening during the last glacial", Nature Communications, doi:20.2038/s41467-017-00577-6

https://www.nature.com/articles/s41467-017-00577-6

See also:

https://theconversation.com/how-antarctic-ice-melt-can-be-a-tipping-point-for-the-whole-planets-climate-83776
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #662 on: October 07, 2017, 05:26:15 PM »
The linked reference discusses the impact of large ice sheet contributions to sea level rise on the behavior of tides, and warns that changes in the location of tidal mixing fronts and ocean currents could induce continental shelves to contribute carbon to global carbon cycles:

Sophie-Berenice Wilmes et al (6 October 2017), "Global Tidal Impacts of Large-Scale Ice-Sheet Collapses", Journal of Geophysical Research, DOI: 10.1002/2017JC013109 

http://onlinelibrary.wiley.com/doi/10.1002/2017JC013109/abstract?utm_content=buffer2e484&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract: "Recent studies show that the glaciers draining both the West Antarctic and the Greenland ice sheets are experiencing an accelerated ice loss, highlighting the possibility of large-scale ice-sheet retreat and sea-level rise in the coming centuries and millennia. These sea-level changes would vary spatially, and could significantly alter global tides as the latter are highly dependent on bathymetry (or water column thickness under ice shelves) and basin shape. This paper investigates how the principal semi-diurnal (M2) tidal amplitudes and energy dissipation respond to the non-uniform sea-level changes induced by complete ice-sheet collapses. The sea-level changes are calculated using gravitationally self-consistent sea-level theory, and the tides are simulated using an established tidal model. Results from the simulations show global and spatially heterogeneous changes in tidal amplitudes. In addition, pronounced changes in tidal energy dissipation occur in both the open ocean and in shelf seas, also altering the location of tidal mixing fronts. These changes have the potential to impact ocean mixing, and hence large-scale currents and climate patterns, and the contribution of shelf-sea to the global carbon cycle. The new results highlight the importance of considering changes in the tides in predictions of future climate and reconstructions of past climate phases such as the Last Interglacial."
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sidd

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #663 on: October 12, 2017, 09:48:22 PM »
Hearty and Tormey review in Marine Geology of late Eemian sea level evidence from the Bahamas and Bermuda:

" ... during a global climate transition late in the MIS 5e interglacial, abrupt sea-level changes occurred, and concurrently coastlines of the Bahamas and Bermuda were impacted by massive storms, resulting in a unique trilogy of wave-transported deposits: mega-boulders, chevron storm beach ridges, and runup deposits on eolian ridges. A composite MIS 5e sea-level curve (Hearty et al., 2007b; O'Leary et al., 2013) indicates early stability around + 2.5–3 m, followed by a slight regression, and ending the interglacial with a rapid rise to + 6–9 m. This rise overtopped coral reefs and shifted depocenters kilometers landward and bankward. Regression of sea level after this peak left a series of massive storm-beach and dune ridges (Suppl. Figs. S1–S3). Such rapid sea-level shifts require ice sheet growth and melting, comparable with the last deglaciation meltwater events (Edwards et al., 1993; Blanchon andShaw, 1995; Tu et al., 2001; Golledge et al., 2014; DeConto and Pollard,2016)"

"This sediment and rock record provides a perspective into natural and non-human driven climate changes at a time when atmospheric CO 2 was at ~ 275 ppm and global temperatures were only about 1 °C warmer than today. Under climatic conditions with considerably less CO 2 forcing and only slightly warmer temperatures, sea levels ranged between + 2.5 and +9 m above present sea level. At the close of the interglacial, steeper temperature and pressure gradients in the North Atlantic Ocean generated superstorms and large, long period waves on higher sea levels, impacting Bermuda and the eastern margin of the Bahamas."

The reference list is magisterial and I would retain the paper for that alone. But the whole paper is good. Read all about it. Open access.

http://dx.doi.org/10.1016/j.margeo.2017.05.009

sidd


sidd

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #664 on: October 18, 2017, 08:49:23 PM »
I must apologize for  an error, that paper by Hearty is not open access.

sidd

TerryM

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #665 on: October 18, 2017, 10:23:37 PM »
sidd
Do we now have storms of anywhere near these magnitudes? I've seen how modern tsunamis have redrawn coastlines, how flash floods have carved new canyons, and the tracks left by retreating glaciers, but mega-boulders always gone down hill.


Terry

sidd

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #666 on: October 19, 2017, 01:48:08 AM »
To my knowledge, none in this deglaciation cycle even during MWP1A. But i could be wrong and  Hearty confines himself to the Eemian.

AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #667 on: October 19, 2017, 02:33:18 AM »
To my knowledge, none in this deglaciation cycle even during MWP1A. But i could be wrong and  Hearty confines himself to the Eemian.

That would be none yet in this (Holocene/Anthropocene) deglaciation.
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TerryM

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #668 on: October 19, 2017, 06:35:50 AM »
We're talking the end of civilization.
Terry



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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #669 on: October 19, 2017, 09:29:52 AM »

With events of this magnitude….yea we are.
bligh

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #670 on: October 21, 2017, 09:32:22 PM »
The linked reference provides paleo data (from the past 360,000 years) that the ENSO assumes a La Nina like pattern during glacial periods and assumes an El Nino like pattern during rapidly changing portions of interglacial periods.  As we are in the most rapidly changing interglacial period on record, this is not good news (as El Nino like Earth System patterns can result in effective ECS values in the range of 5C):

Zhang, S., Li, T., Chang, F. et al. Chin. J. (2017), "Correspondence between the ENSO-like state and glacial-interglacial condition during the past 360 kyr", Ocean. Limnol., 35: 1018. https://doi.org/10.1007/s00343-017-6082-9

https://link.springer.com/article/10.1007/s00343-017-6082-9#citeas

Abstract: "In the warming world, tropical Pacific sea surface temperature (SST) variation has received considerable attention because of its enormous influence on global climate change, particularly the El Niño-Southern Oscillation process. Here, we provide new high-resolution proxy records of the magnesium/calcium ratio and the oxygen isotope in foraminifera from a core on the Ontong-Java Plateau to reconstruct the SST and hydrological variation in the center of the Western Pacific Warm Pool (WPWP) over the last 360 000 years. In comparison with other Mg/Ca-derived SST and δ18O records, the results suggested that in a relatively stable condition, e.g., the last glacial maximum (LGM) and other glacial periods, the tropical Pacific would adopt a La Niña-like state, and the Walker and Hadley cycles would be synchronously enhanced. Conversely, El Niño-like conditions could have occurred in the tropical Pacific during fast changing periods, e.g., the termination and rapidly cooling stages of interglacial periods. In the light of the sensitivity of the Eastern Pacific Cold Tongue (EPCT) and the inertia of the WPWP, we hypothesize an inter-restricted relationship between the WPWP and EPCT, which could control the zonal gradient variation of SST and affect climate change."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #671 on: October 23, 2017, 08:18:03 PM »
The 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, and/or if marine terminating glaciers in Greenland were to retreat rapidly.  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."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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Shared Humanity

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #672 on: October 26, 2017, 04:08:43 PM »
I apologize; this is way off topic,

Well, you're right about that.

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #673 on: October 26, 2017, 05:56:43 PM »
Evidence of paleoclimate Pine Island Glacier Cliff effect collapse during end of last ice age.

https://www.washingtonpost.com/news/energy-environment/wp/2017/10/26/new-science-suggests-the-ocean-could-rise-more-and-faster-than-we-thought/?tid=ss_tw&utm_term=.cf16ef3c6d1b

What’s critical about the markings, explains lead study author Matthew Wise of the University of Cambridge, is their maximum depth — 848 meters, or around 2,800 feet. Because ice floats with 10 percent of its mass above the surface and the remaining 90 percent below it, this suggests that when the ice broke from the glacier, close to 100 meters (over 3oo feet) of it was extending above the water surface.

That’s a key number, because scientists are converging on the belief that ice cliffs of about this height above the water level are no longer sustainable and collapse under their own weight — meaning that when you get a glacier this tall up against the ocean, it tends to crumble and crumble, leading to fast retreat and potentially fast sea level rise.

“If we think about how thick these icebergs would have needed to be considering these float with 90 percent of their mass and thickness beneath the sea,” Wise said, “we think of an ice cliff that was at the maximum thickness implied by the physics of the ice.”

The problem is that if it happened then, well, it could happen again. Both Pine Island glacier and its next door neighbor, Thwaites, are known to get thicker as one travels inland away from the sea, which means they are capable of once again generating ice cliffs taller than the critical size detected by the current study.

“If a cliff even higher than the ~100 m subaerial/900 m submarine cliffs were to form, as might occur with retreat of Thwaites Glacier in West Antarctica, it might break repeatedly with much shorter pauses than now observed, causing very fast grounding line retreat and sea level rise,” explained Richard Alley, a glaciologist at Penn State University, by email after reviewing the current study for the Post.
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sidd

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #674 on: November 02, 2017, 07:09:48 AM »
Apparently you wouldnt need superstorms in the Eemian to put the Eleuthera boulders where they are, because sa level was higher. A storm like Sandy could do it.

Rovere et al. "Giant boulders and Last Interglacial storm intensity in the North Atlantic," PNAS, 2017

doi: 10.1073/pnas.1712433114

"Putting this all together, our results show that it is not necessary to invoke LIG superstorms to explain the current position of the Eleuthera Cow and Bull boulders. At the minimum assumed LIG sea level (~5 m), or even slightly lower (3.5 m above present, Fig. 3A) waves generated by an event analogous to Hurricane Sandy (2012) could have produced flows great enough to transport the Cow and Bull boulders from the cliff edge to their modern position (Fig. 3 A and C). Waves from Hurricane Andrew (1992) could have moved both boulders at RSL = 12.5 m, which is still in the range of possible LIG sea levels in the area. The waves modeled for the Perfect Storm (1991) can hardly move even the smaller boulder (Cow) in any RSL scenario."

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #675 on: November 02, 2017, 09:05:16 AM »
Apparently you wouldnt need superstorms in the Eemian to put the Eleuthera boulders where they are, because sa level was higher. A storm like Sandy could do it.

Rovere et al. "Giant boulders and Last Interglacial storm intensity in the North Atlantic," PNAS, 2017

doi: 10.1073/pnas.1712433114

"Putting this all together, our results show that it is not necessary to invoke LIG superstorms to explain the current position of the Eleuthera Cow and Bull boulders. At the minimum assumed LIG sea level (~5 m), or even slightly lower (3.5 m above present, Fig. 3A) waves generated by an event analogous to Hurricane Sandy (2012) could have produced flows great enough to transport the Cow and Bull boulders from the cliff edge to their modern position (Fig. 3 A and C). Waves from Hurricane Andrew (1992) could have moved both boulders at RSL = 12.5 m, which is still in the range of possible LIG sea levels in the area. The waves modeled for the Perfect Storm (1991) can hardly move even the smaller boulder (Cow) in any RSL scenario."

sidd


An piece of good news, unusual and appreciated. :)
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #676 on: November 02, 2017, 08:51:16 PM »
Of course, that Rovere paper is just one piece of evidence and does not address all the arguments made by Hearty and Hansen. For example it dismisses the amino acid racemization dates as "controversial" and does not address othe arguments such as  chevrn beach ridges, or ooid sediments and inclusions. Rovere concentrates on two boulders, while Hearty has looked at at lest seven. I must admit that these issues are off the top of my head, and i have not done a close comparison of the Rovere paper with the Hearty paper yet.

So I am not yet convinced of Rovere's thesis, and certainly Hearty and Hansen have impressive track records.

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #677 on: November 03, 2017, 10:13:49 PM »
It is difficult to ignore Hansen's warnings about the ice-climate feedback mechanism when confronted with direct evidence of the SLR fingerprint effect as discussed in the linked article:

Title: "Evidence of sea level 'fingerprints'"
https://climate.nasa.gov/news/2626/evidence-of-sea-level-fingerprints/

Extract: "Researchers from NASA’s Jet Propulsion Laboratory in Pasadena, California, and the University of California, Irvine, have reported the first detection of sea level “fingerprints” in ocean observations: detectable patterns of sea level variability around the world resulting from changes in water storage on Earth’s continents and in the mass of ice sheets. The results will give scientists confidence they can use these data to determine how much the sea level will rise at any point on the global ocean as a result of glacier ice melt."
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #678 on: November 10, 2017, 07:57:06 PM »
The Mid-Brunhes Event (MBE) coincides with MIS 11 (the Holsteinian) about 400,000 to 350,000 years ago, and marks a major transition to subsequent enhanced Arctic Amplification as discussed in the open access linked reference (see the first three attached images while the fourth image from another source help to clarify that after the MBE interglacial peak global mean peak temperatures have been higher).  Furthermore, the reference associates this change with the bipolar seesaw and episodic collapses of the WAIS.  This research clearly associates the bipolar seesaw mechanism with Hansen's ice-climate feedback and with Arctic Amplification. 

Cronin et al (2017), "Enhanced Arctic Amplification Began at the Mid-Brunhes Event ~400,000 years ago", Scientific Reports 7, Article No. 14475, doi: 10.1038/s41598-017-13821-2

https://www.nature.com/articles/s41598-017-13821-2

Extract: "Enhanced Arctic amplification at the MBE suggests a major climate threshold was reached at ~400 ka involving Atlantic Meridional Overturning Circulation (AMOC), inflowing warm Atlantic Layer water, ice sheet, sea-ice and ice-shelf feedbacks, and sensitivity to higher post-MBE interglacial CO₂ concentrations.

Southern Hemisphere ocean-atmosphere-sea ice processes are critical for understanding the MBE, specifically the idea that there is a bipolar seesaw operating between Northern and Southern Hemispheres on millennial timescales explain warmer interglacial condition in the Southern Hemisphere.  Barker et al. (2011) demonstrated that abrupt millennial-scale AMOC variability characterized the last 800 ka, albeit without the large amplitude shift seen in our Arctic records.  Holden et al. proposed a role for decreased stability of the West Antarctic Ice Sheet following the MBE, leading to AMOC slowdown during deglacials.  Thus, it is possible that ice sheet/ice shelf instability characterized both hemispheres providing the necessary non-linear dynamics to explain large amplitude temperature events in the Arctic Ocean.  However establishing the relationship between bottom temperature, sea ice and productivity during stadial and interstadial periods – require better sediment core resolution in the Arctic.  Nonetheless, the large shift in Arctic land ice, ice shelves and sea ice at the MBE, suggests an amplification of Arctic climate sensitivity related to higher interglacial CO₂ concentrations and associated feedbacks involving ice shelves and ice sheets, Heinrich-like events, AMOC-forcing Arctic Ocean temperature oscillations, and deeper submergence of Atlantic water in the central Arctic Basin."

Furthermore, the next linked reference studies the Last Glacial Termination, LGT, from 18,000 to 11,650 kya, and reconstructs the dynamic response of the Antarctic ice sheets to warming in this period and it clarifies the important role that the Pacific Ocean (and the ENSO) plays in both the bipolar seesaw and the ice-climate feedback mechanism.  The abstract from the linked reference concludes: "Given the anti-phase relationship between inter-hemispheric climate trends across the LGT our findings demonstrate that Southern Ocean-AIS feedbacks were controlled by global atmospheric teleconnections.  With increasing stratification of the Southern Ocean and intensification of mid-latitude westerly winds today, such teleconnections could amplify AIS mass loss and accelerate global sea-level rise."

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

https://www.nature.com/articles/srep39979

See also the associated article entitled: "How Antarctic ice melt can be a tipping point for the whole planet’s climate"

https://theconversation.com/how-antarctic-ice-melt-can-be-a-tipping-point-for-the-whole-planets-climate-83776

Extract: "To explore how melting Antarctic ice might cause such dramatic change in the global climate, we used a climate model to simulate the release of large volumes of freshwater into the Southern Ocean. The model simulations all showed the same response, in agreement with our climate reconstructions: regardless of the amount of freshwater released into the Southern Ocean, the surface waters of the tropical Pacific nevertheless warmed, causing changes to wind patterns that in turn triggered the North Atlantic to warm too."
« Last Edit: November 12, 2017, 08:43:42 AM by AbruptSLR »
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bligh8

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #679 on: November 19, 2017, 04:20:16 AM »
Sea-level projections representing the deeply uncertain contribution of the West Antarctic ice sheet

·   Alexander M. R. Bakker,
·   Tony E. Wong,
·   Kelsey L. Ruckert &
·   Klaus Keller

Abstract:

There is a growing awareness that uncertainties surrounding future sea-level projections may be much larger than typically perceived. Recently published projections appear widely divergent and highly sensitive to non-trivial model choices. Moreover, the West Antarctic ice sheet (WAIS) may be much less stable than previous believed, enabling a rapid disintegration. Here, we present a set of probabilistic sea-level projections that approximates the deeply uncertain WAIS contributions. The projections aim to inform robust decisions by clarifying the sensitivity to non-trivial or controversial assumptions. We show that the deeply uncertain WAIS contribution can dominate other uncertainties within decades. These deep uncertainties call for the development of robust adaptive strategies. These decision-making needs, in turn, require mission-oriented basic science, for example about potential signposts and the maximum rate of WAIS-induced sea-level changes.

Extract:

We presented a set of sea-level projections designed to represent important deep uncertainties and to inform robust decision-making frameworks. Our simple model framework includes semi-empirical models of the climate and sea-level contributions from thermal expansion, the Antarctic ice sheet, the Greenland ice sheet, and glaciers and small ice caps. Its relative simplicity is chosen to result in a transparent model structure and to enable a data-model fusion. Our calibration is designed to avoid over constraining the projections. We hence only utilize observational data accompanied with clear uncertainty estimates, and aim for relatively non-informative prior distributions. We communicate divergent expert assessments and large structural uncertainties as deep uncertainties surrounding the projections.

bligh

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #680 on: November 19, 2017, 04:56:37 AM »
Reference please, Mr. Bligh ?

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #681 on: November 19, 2017, 06:46:47 AM »
Reference please, Mr. Bligh ?

sidd

I believe that would be:

Alexander M. R. Bakker, Tony E. Wong, Kelsey L. Ruckert & Klaus Keller (2017), "Sea-level projections representing the deeply uncertain contribution of the West Antarctic ice sheet", Scientific Reports 7, Article number: 3880; doi:10.1038/s41598-017-43134-5

http://www.nature.com/articles/s41598-017-04134-5
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #682 on: November 19, 2017, 07:20:59 AM »
Thanks for the reference. They note Greenland as becoming an important source of uncertainty around midcentury as well.

"Around 2040–2050, a large and uncertain contribution of the GIS becomes important ... "

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #683 on: November 19, 2017, 03:23:31 PM »
Mr. sidd.....so sorry about not including the reference link.  Thanks for bringing that to my attention.

Fair Winds
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #684 on: December 04, 2017, 11:48:40 PM »
The paleo findings of the following linked reference indicate to me that we are playing Russian roulette w.r.t. the possible collapse of the WAIS this century.  The extreme storm activity and high sea levels in the Bahamas cited in Hearty & Tormey (2017) and in Rovere et al. (2017) indicate to me that the ice-climate feedback was very strong during the late MIS 5e highstand (circa 119.5 kya).  Furthermore, when one looks at the sea level error bars in the attached image [from O'Leary et al. (2013)] around 119.5 kya it is clear that there is a reasonable probability that the WAIS could substantially collapse in less than a century.  People who demand absolute proof of such a possible event, are likely to be able to directly observe it from 2040 to 2100.

P.J. Hearty & B.R. Tormey (1 August 2017), "Sea-level change and superstorms; geologic evidence from the last interglacial (MIS 5e) in the Bahamas and Bermuda offers ominous prospects for a warming Earth", Marine Geology, Volume 390, Pages 347-365, https://doi.org/10.1016/j.margeo.2017.05.009

http://www.sciencedirect.com/science/article/pii/S0025322717302700

Extract: "Geological observations from last interglacial (LIG; MIS 5e, Eemian) carbonate landscapes in the Bahamas and Bermuda reveal a turbulent climate transition at the close of the peak interglacial. The interval is associated with rapid, multi-meter shifts in sea level as major ice sheets melted and/or collapsed. Sedimentary evidence from the eastern Bahamas includes wave-transported megaboulders, lowland chevron storm ridges, and hillside runup deposits. This “trilogy” collectively provides direct geological evidence of frequent, intense storms generating sustained long-period waves from the northeast Atlantic Ocean. Penecontemporaneous with wave deposits is the subtidal production and flux of a massive volume of ooid sediments associated with amplified winds and storminess during the latter half of MIS 5e that resulted in exponential island growth. Steeper temperature and pressure gradients were evident in the North Atlantic Ocean, while the Southern Ocean appears to have had a major role in affecting atmospheric CO2, as warming of the Southern Ocean drives ventilation of the deep ocean. CO2 in turn, acts as a tight control knob on global climate.

The dramatic oceanographic and island building events of late MIS 5e are unique among other interglacial periods of the past half million years. The LIG record reveals that strong climate forcing is not required to yield major impacts on the ocean and ice caps. Antarctic ice cores document that LIG atmospheric CO2 was ~ 275 ppm, while global temperature was < 1 °C warmer than present. Despite only slightly warmer conditions than pre-Industrial times, relative sea level (RSL) persisted at + 2–3 m for several thousand years during the early and mid LIG. Later in the LIG, sea level abruptly rose an additional 3–5 m meters to + 6–9 m RSL.

In terms of Lyellian uniformitarian principles, the trilogy of coeval deposits of MIS 5e described herein do not translate to our modern climate parameters, and further cannot be explained by coincidental megatsunami. In our industrial world, rapidly increasing atmospheric CO2 rates (> 2 ppm/yr) have surpassed 408 ppm, levels not achieved since the Pliocene 3 Ma ago, while global temperature increased ~ 1 °C since the 1870s. With greatly increased CO2 forcing at unmatched rates, except perhaps during global extinction events, dramatic change is certain. In the interest of our future world, we must seek to understand the complex set of linked natural events and field observations that are revealed in the geology of past warmer climates."
&

Title: "Geologic evidence is the forerunner of ominous prospects for a warming Earth"

https://www.sciencedaily.com/releases/2017/10/171012114839.htm

&

Alessio Rovere et al. (2017), "Giant boulders and Last Interglacial storm intensity in the North Atlantic", PNAS, doi: 10.1073/pnas.1712433114

http://www.pnas.org/content/114/46/12144.abstract

Abstract: "As global climate warms and sea level rises, coastal areas will be subject to more frequent extreme flooding and hurricanes. Geologic evidence for extreme coastal storms during past warm periods has the potential to provide fundamental insights into their future intensity. Recent studies argue that during the Last Interglacial (MIS 5e, ∼128–116 ka) tropical and extratropical North Atlantic cyclones may have been more intense than at present, and may have produced waves larger than those observed historically. Such strong swells are inferred to have created a number of geologic features that can be observed today along the coastlines of Bermuda and the Bahamas. In this paper, we investigate the most iconic among these features: massive boulders atop a cliff in North Eleuthera, Bahamas. We combine geologic field surveys, wave models, and boulder transport equations to test the hypothesis that such boulders must have been emplaced by storms of greater-than-historical intensity. By contrast, our results suggest that with the higher relative sea level (RSL) estimated for the Bahamas during MIS 5e, boulders of this size could have been transported by waves generated by storms of historical intensity. Thus, while the megaboulders of Eleuthera cannot be used as geologic proof for past “superstorms,” they do show that with rising sea levels, cliffs and coastal barriers will be subject to significantly greater erosional energy, even without changes in storm intensity."

&

Michael J. O’Leary, Paul J. Hearty, William G. Thompson, Maureen E. Raymo, Jerry X. Mitrovica and Jody M.Webster (2013), "Ice sheet collapse following a prolonged period of stable sea level during the last interglacial", Nature Geoscience 6, 796-800, doi:10.1038/ngeo1890.

https://www.nature.com/articles/ngeo1890

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sidd

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #685 on: December 05, 2017, 04:51:34 AM »
In another thread there was a reference to the Scambos review doi:10.1016/j.gloplacha.2017.04.008
Open access, good review. I noted Fig 4 which I attach. As is my wont, i often whine about the Mercer warning of the 0C midsummer isotherm. Fig 4 in Scambos is a depiction of surface melt on WAIS fringe. I imagine 0C midsummer isotherm is not far behind.

Doom is nigh.

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #686 on: December 11, 2017, 06:44:00 PM »
Personally, I think that the first linked article and the associated second linked reference increases the probability that the WAIS will enter a main phase collapse period by 2040.  The article indicates that ice mass loss from Greenland has been contributing to feedback mechanisms that has caused the Beaufort Gyre to progressively stockpile more freshwater than all of the great lakes combined (see the first image).  While some consensus scientists will undoubtable emphasize that an eventual release of this freshwater in coming years will result in a temporary cooling of the North Atlantic and Europe, which may decrease GMSTA; I note that

Title: "How a Wayward Arctic Current Could Cool the Climate in Europe"

http://e360.yale.edu/features/how-a-wayward-arctic-current-could-cool-the-climate-in-europe

Extract: "The Beaufort Gyre, a key Arctic Ocean current, is acting strangely. Scientists say it may be on the verge of discharging a huge amount of ice and cold freshwater that could kick off a period of lower temperatures in northern Europe.

…something is amiss with this vital plumbing system in the Arctic, a region warming faster than any other on the planet. Thanks in part to rising air temperatures, steadily disappearing sea ice, and the annual melting of 270 billion tons of ice from Greenland’s ice cap, the gyre is no longer functioning as it has predictably done for more than a half century. And now, scientists are anticipating that a sudden change in the Beaufort Gyre could set in motion events that — in a steadily warming world — would actually lead to a temporary but significant cooling of the North Atlantic region.

During the second half of the 20th century — and, most likely, earlier — the gyre adhered to a cyclical pattern in which it would shift gears every five to seven years and temporarily spin in a counter-clockwise direction, expelling ice and freshwater into the eastern Arctic Ocean and the North Atlantic. But for more than a dozen years, this carousel of ice and, increasingly, freshwater has been spinning faster in its usual clockwise direction, all the while collecting more and more freshwater from three sources: melting sea ice, huge volumes of runoff flowing into the Arctic Ocean from Russian and North American rivers, and the relatively fresh water streaming in from the Bering Sea….
The gyre’s strange behavior is likely linked, at least in part, to the profound warming of the Arctic, and it demonstrates how disruptions in one rapidly changing region of the world can affect ecosystems hundreds, even thousands, of miles away. In a recent paper, Krishfield, Proshutinsky, and other scientists suggest that frigid freshwater pouring into the north Atlantic Ocean from the rapidly melting Greenland ice sheet is forming a cap on the North Atlantic that results in stratification that prevents storm-triggering heat from the northern end of the Gulf Stream from rising to the surface. The scientists say this may be inhibiting the formation of cyclones that would cause the motion of the gyre to weaken or temporarily reverse.

If that is the case, it may mean the gyre will continue to grow and spin clockwise for years to come."
See also:

Andrey Proshutinsky, Dmitry Dukhovskoy, Mary-Louise Timmermans, Richard Krishfield, Jonathan L. Bamber (2015), "Arctic circulation regimes", Philosophical Transactions of the Royal Society A, DOI: 10.1098/rsta.2014.0160

http://rsta.royalsocietypublishing.org/content/373/2052/20140160

Abstract: "Between 1948 and 1996, mean annual environmental parameters in the Arctic experienced a well-pronounced decadal variability with two basic circulation patterns: cyclonic and anticyclonic alternating at 5 to 7 year intervals. During cyclonic regimes, low sea-level atmospheric pressure (SLP) dominated over the Arctic Ocean driving sea ice and the upper ocean counterclockwise; the Arctic atmosphere was relatively warm and humid, and freshwater flux from the Arctic Ocean towards the subarctic seas was intensified. By contrast, during anticylonic circulation regimes, high SLP dominated driving sea ice and the upper ocean clockwise. Meanwhile, the atmosphere was cold and dry and the freshwater flux from the Arctic to the subarctic seas was reduced. Since 1997, however, the Arctic system has been under the influence of an anticyclonic circulation regime (17 years) with a set of environmental parameters that are atypical for this regime. We discuss a hypothesis explaining the causes and mechanisms regulating the intensity and duration of Arctic circulation regimes, and speculate how changes in freshwater fluxes from the Arctic Ocean and Greenland impact environmental conditions and interrupt their decadal variability."

&

The third linked Marino & Zahn (2015) reference (and second attached image) shows how a cooling of the North Atlantic can cause warming around Antarctica and an increase of Agulhas Leakage which can interact with the AMOC to strengthen Arctic Amplification and the bipolar seesaw:

Gianluca Marino and Rainer Zahn (January 2015), "The Agulhas Leakage: the missing link in the interhemispheric climate seesaw?", Past Global Changes Magazine, SCIENCE HIGHLIGHTS: Glacial terminations and interglacials

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

&

With continued global warming one can expect more Agulhas leakage (see the third image); which per the fourth linked reference means that one can expect the AMOC to continue slowing; which should work synergistically with Hansen's ice-climate feedback, particularly if the WAIS collapses in coming decades:

Kathryn A. Kelly, Kyla Drushka, LuAnne Thompson, Dewi Le Bars & Elaine L. McDonagh (25 July 2016), "Impact of slowdown of Atlantic overturning circulation on heat and freshwater transports", Geophysical Research Letters, DOI: 10.1002/2016GL069789

http://onlinelibrary.wiley.com/doi/10.1002/2016GL069789/abstract

&

The fifth linked reference about the influence of the recent increased Agulhas leakage on tropical Atlantic warming and the response of the AMOC:

Joke F. Lübbecke, Jonathan V. Durgadoo, and Arne Biastoch (2015), "Contribution of increased Agulhas leakage to tropical Atlantic warming", Journal of Climate, doi: http://dx.doi.org/10.1175/JCLI-D-15-0258.1


http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-15-0258.1

&

The sixth linked reference (with a free access pdf) indicates that the leakage of warm saline water from the Agulhas Current into the Atlantic Ocean, caused a positive feedback mechanism contributing to polar amplification during the Eemian; and that this mechanism could become increasingly important with increasing global warming today:

Turney, C. S.M. and Jones, R. T. (2010), Does the Agulhas Current amplify global temperatures during super-interglacials?. J. Quaternary Sci., 25: 839–843. doi: 10.1002/jqs.1423

http://onlinelibrary.wiley.com/doi/10.1002/jqs.1423/full
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #687 on: December 11, 2017, 11:11:53 PM »
Due to the importance of the coming freshwater flux from the Beaufort Gyre in to the North Atlantic (particularly w.r.t. Hansen's freshwater hosing-climate feedback mechanism & see Reply #686), I provide the following selected information about the 2018 Ocean Science Meeting Session entitled: " HE003: Freshwater Fluxes in the Arctic Ocean – North Atlantic Climate System"

https://agu.confex.com/agu/os18/preliminaryview.cgi/Session23525

Summary: "Oceanic and sea ice freshwater fluxes in the Arctic Ocean – North Atlantic climate system impact thermohaline and convective processes, with far-reaching influence on climate. Increased freshwater fluxes to the Arctic Ocean along with the wind-driven anticyclonic circulation have resulted in growing freshwater content in the Beaufort Gyre. There is no observational evidence of significant changes in freshwater fluxes between the Arctic Ocean and the North Atlantic. Yet freshwater flux from the Greenland Ice Sheet is clearly increasing and may be impacting thermohaline processes in the North Atlantic. It is a priority to discern the driving mechanisms, the role and consequences of changing freshwater fluxes into the Arctic Ocean and North Atlantic. This session solicits papers addressing issues related to oceanic freshwater fluxes (liquid and sea ice) in the Arctic Ocean – North Atlantic climate system. Possible topics include: Propagation mechanisms, pathways and time scales of fresh water anomalies; residence time of fresh water; impacts of changes to the cryosphere; the role of freshwater in the future Arctic climate; the sensitivity of thermohaline circulation to freshwater fluxes; the relationship between sea ice and freshwater content in the ocean; and, biological and environmental consequences of increased freshwater fluxes."

Laura de Steur, et al (2018), "Increased freshwater export though Fram Strait contributes to freshening in the North Atlantic (301769)"

Andrey Yu Proshutinsky, Richard A Krishfield, Mary-Louise Timmermans and William James Williams (2018), "Causes and Consequences of Beaufort Gyre Freshwater Content Changes in 2003-2017 (303087)"

Dmitry S Dukhovskoy (2018), "Freshwater pathways in the Arctic Ocean and northern North Atlantic from a numerical experiment with passive tracers (304003)"

Oleg Saenko et al (2018), "Response of the North Atlantic Dynamic Sea Level and Circulation to Greenland Meltwater under Present and Projected Climates (304135)"

Elizabeth Douglass (2018), "Impact of Freshwater from Arctic Rivers in a High-Resolution Model (305887)"

Subrahmanyam Bulusu (2018), "Recent changes in the Arctic Circulation and Freshwater Fluxes (Invited) (306593)"

Freshwater fluxes between the Arctic Ocean and the North Atlantic from water stable isotopes: study of coastal currents and interior of the subpolar gyre. (308866)

A new record of North Atlantic sea surface salinity and temperature from 1896–2015 reveals modes of variability and long–term trends (309308)
Andrew Ronald Friedman1, Gilles P Reverdin2, Myriam Khodri1 and Guillaume Gastineau1, (1)Sorbonne-Universités, LOCEAN, CNRS/IRD/UPMC/MNHN, Paris, France, (2)LOCEAN - Sorbonne Universités - UPMC/CNRS/IRD/MNHN, Paris, France
Marion Benetti et al. (2018), "Observed Greenland Glacial Melt Water Distribution in the Greenland Sea (310757)"

Caroline A Katsman et al (2018), "Impacts of Arctic precipitation changes on the downwelling limb of the Atlantic Meridional Overturning Circulation (310762)

Heather Regan (2018), "Investigating the Spatial and Temporal Variability of the Beaufort Gyre from Satellite Observations (311439)"
 
Cristian Florindo-Lopez  et al (2018), "Observational Evidence of Multi-Decadal Changes in Arctic Freshwater Transport to the Subpolar North Atlantic (313117)"

Nathan Grivault (2018), "Frequency of Volume and Freshwater Events Leaving the Arctic Ocean: A Numerical Study. (314363)"

Gilles Garric (2018), "Dependencies of Arctic Freshwater Content and Transport to Surface Atmospheric Conditions (316214)"

Per Pemberton et al. (2018), "The response of the Arctic Ocean to freshwater and wind perturbations (317179)"

Helen Johnson et al (2018), "Response of Arctic Ocean Freshwater Content to Large Scale Atmospheric Forcing Changes in a Coupled Climate Model  (317606)"

Rory Laiho et al. (2018), "Internal Variability in the Arctic Freshwater Budget as Simulated by the CESM Large Ensemble (321495)"

Clark William Pennelly et al. (2018), "Numerical modeling in the northern Atlantic: Labrador Sea freshwater. (321605)"

Marilena Oltmanns et al (2018), "Rapid North Atlantic Cooling Induced by Fresh, Cold and Shallow Mixed Layers in the Subpolar Gyre (321700)"

Jiayan Yang, (2018), "A process-modeling study of the Arctic-Atlantic Ocean exchanges and their role in the Arctic Ocean freshwater export (322447)"
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #688 on: December 12, 2017, 12:16:49 AM »
For those who have trouble envisioning how increased Agulhas Leakage triggered by a cooling of the North Atlantic could lead to Arctic Amplification (see Reply #686) associated with the transfer of energy through the atmosphere from the Tropical Atlantic directly to the Arctic, I provide the attached image & associate caption from the linked reference, which show how this occurs due to Rossby Waves:

Merryfield, W. J., F. J. Doblas-Reyes, L. Ferranti, J.-H. Jeong, Y. J. Orsolini, R. I. Saurral, A. A. Scaife, M. A. Tolstykh, and M. Rixen (2017), Advancing climate forecasting, Eos, 98, https://doi.org/10.1029/2017EO086891

https://eos.org/project-updates/advancing-climate-forecasting?utm_source=eos&utm_medium=email&utm_campaign=EosBuzz120117

Caption: "Fig. 1. Averaged atmospheric response during winter in the Northern Hemisphere to recent El Niño events, connecting atmospheric changes in the tropics with those at latitudes farther north and south. Dots represent approximate pathways of planetary waves [after Scaife et al., 2017]. Colors show associated changes in sea level pressure (SLP) in hectopascals (hPa), indicative of atmospheric circulation changes. In the Northern Hemisphere, changes are clockwise for positive contours, represented by warm colors, and counterclockwise for negative contours, represented by cool colors; these directions are opposite in the Southern Hemisphere. Credit: Adam Scaife"
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #689 on: December 14, 2017, 04:31:19 PM »
This ice mass loss is already contributing to Hansen's ice-climate feedback mechanism, and this trend will likely get worse in coming years:

Andreas P. Ahlstrøm et al. (13 Dec 2017), "Abrupt shift in the observed runoff from the southwestern Greenland ice sheet", Science Advances, Vol. 3, no. 12, e1701169, DOI: 10.1126/sciadv.1701169

http://advances.sciencemag.org/content/3/12/e1701169?utm_source=VancePak+%28updated+6%2F30%2F2017%29&utm_campaign=988468d293-EMAIL_CAMPAIGN_2017_12_08&utm_medium=email&utm_term=0_56c46682ac-988468d293-126675293

Abstract: "The recent decades of accelerating mass loss of the Greenland ice sheet have arisen from an increase in both surface meltwater runoff and ice flow discharge from tidewater glaciers. Despite the role of the Greenland ice sheet as the dominant individual cryospheric contributor to sea level rise in recent decades, no observational record of its mass loss spans the 30-year period needed to assess its climatological state. We present for the first time a 40-year (1975–2014) time series of observed meltwater discharge from a >6500-km2 catchment of the southwestern Greenland ice sheet. We find that an abrupt 80% increase in runoff occurring between the 1976–2002 and 2003–2014 periods is due to a shift in atmospheric circulation, with meridional exchange events occurring more frequently over Greenland, establishing the first observation-based connection between ice sheet runoff and climate change."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #690 on: December 18, 2017, 02:13:24 AM »
As a follow-on to my last few posts, I note that both Helheim, and Jakobshavn, glaciers are currently experiences significant grounding line retreat due to cliff failures, and they both contribute icebergs that feed into the subpolar gyre and subpolar North Atlantic (which directly influence the AMOC as well as the Beaufort Gyre). The first attached image shows that both the Jakobshavn (labelled 1) bedmap and the Helheim (labelled 2) bedmap are the two most significant areas for potential contribution of icebergs to cool the subpolar North Atlantic from Southern Greenland.  Furthermore, the second image for Jakobshavn and the third image for Helheim, indicate that the grounding lines for both of these marine terminating glaciers (see the Greenland folder for the current location of these grounding lines) are at, or near, regions of bed with negative slopes that indicate that icebergs calvings for both of these glaciers are likely to accelerate from the next boreal summer thru about 2030.

Finally, the fourth image from the following linked reference shows the complex relationship between the marine glaciers in both the western and eastern South Greenland, iceberg calving, the local oceanic currents, the subpolar gyre and consequently the AMOC.  This relationship could both limit flushing of freshwater from the Beaufort Gyre, BG, into the North Atlantic (thus allowing the BG to accumulate still more freshwater) and could cause westerly winds around Antarctica to accelerate due to the bipolar seesaw; both of which would contribute to Hansen's ice-climate feedback:

Camilla S. Andresen et al. (2017), "Exceptional 20th century glaciological regime of a major SE Greenland outlet glacier", Scientific Reports 7, Article number: 13626, doi:10.1038/s41598-017-13246-x

http://www.nature.com/articles/s41598-017-13246-x?WT.feed_name=subjects_climate-sciences

Abstract: "The early 2000s accelerated ice-mass loss from large outlet glaciers in W and SE Greenland has been linked to warming of the subpolar North Atlantic. To investigate the uniqueness of this event, we extend the record of glacier and ocean changes back 1700 years by analyzing a sediment core from Sermilik Fjord near Helheim Glacier in SE Greenland. We show that multidecadal to centennial increases in alkenone-inferred Atlantic Water SSTs on the shelf occurred at times of reduced solar activity during the Little Ice Age, when the subpolar gyre weakened and shifted westward promoted by atmospheric blocking events. Helheim Glacier responded to many of these episodes with increased calving, but despite earlier multidecadal warming episodes matching the 20th century high SSTs in magnitude, the glacier behaved differently during the 20th century. We suggest the presence of a floating ice tongue since at least 300 AD lasting until 1900 AD followed by elevated 20th century glacier calving due to the loss of the tongue. We attribute this regime shift to 20th century unprecedented low sea-ice occurrence in the East Greenland Current and conclude that properties of this current are important for the stability of the present ice tongues in NE Greenland."

Extract: "Our results imply that model predictions of dynamic loss from ice streams in North Greenland need to account for threshold effects from sea-ice to better predict the future evolution of Greenland coastal glaciers in a warming North Atlantic Ocean."

Caption for the attached image:"Map of the North Atlantic region showing the major surface ocean currents (colour of arrows indicate temperature; red = warm, blue = cold, yellow = mixture) and location of sites referred to in Fig. 3a–f. HG = Helheim Glacier; KG = Kangerdlugssuaq Glacier; JI = Jakobshavn Isbræ. Magenta circles show location of sediment cores discussed in the text and shown on Figs 2 and 3. The magenta box delineates the extent of the inset map. Bathymetric data are from IBCAO v3. Terrestrial topographic data are from the ETOPO1 Global Relief model and the GIMP surface digital elevation model. The inset map of Sermilik Fjord shows the location of sediment core ER07 and the local bathymetry."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson