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sidd

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #600 on: September 30, 2016, 06:23:36 AM »
"Suppression of AABW formation has so far been observed at  the Weddell location," said I, mere moments ago. Now it is seen elsewhere.

More diving seals. Amery melt (one of my pet fears). Open access. Read all about it.

doi: 10.1038/ncomms12577

sidd

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #601 on: September 30, 2016, 07:53:53 AM »
Thanks, sidd.

Williams et al 2016, The suppression of Antarctic bottom water formation by melting ice shelves in Prydz Bay:
http://www.nature.com/ncomms/2016/160823/ncomms12577/full/ncomms12577.html

Abstract
A fourth production region for the globally important Antarctic bottom water has been attributed to dense shelf water formation in the Cape Darnley Polynya, adjoining Prydz Bay in East Antarctica. Here we show new observations from CTD-instrumented elephant seals in 2011–2013 that provide the first complete assessment of dense shelf water formation in Prydz Bay. After a complex evolution involving opposing contributions from three polynyas (positive) and two ice shelves (negative), dense shelf water (salinity 34.65–34.7) is exported through Prydz Channel. This provides a distinct, relatively fresh contribution to Cape Darnley bottom water. Elsewhere, dense water formation is hindered by the freshwater input from the Amery and West Ice Shelves into the Prydz Bay Gyre. This study highlights the susceptibility of Antarctic bottom water to increased freshwater input from the enhanced melting of ice shelves, and ultimately the potential collapse of Antarctic bottom water formation in a warming climate.

AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #602 on: October 08, 2016, 12:34:14 AM »
The linked reference indicates 14,000 years ago when the Laurentide Ice Sheet collapsed, the ENSO abruptly strengthened by about 25%.  This paleo ice-climate feedback mechanism makes me wonder what will happen to the ENSO if/when the WAIS collapses this century:

Lu, Z., Liu, Z. & Zhu, J. (2016), "Abrupt intensification of ENSO forced by deglacial ice-sheet retreat in CCSM3", Clim Dyn,  46: 1877. doi:10.1007/s00382-015-2681-3


http://link.springer.com/article/10.1007/s00382-015-2681-3


Abstract: "The influence of ice-sheet retreat on the El Niño–Southern Oscillation (ENSO) variability is studied using a transient simulation in NCAR-CCSM3 forced only by variations in continental ice sheets during the last deglaciation. The most striking feature is an abrupt strengthening of ENSO (by ~25 %) at 14 thousand years before present (ka BP) in response to a significant retreat (an equivalent ~25 m sea-level rise) of the Laurentide ice sheet (LIS). This abrupt intensification of ENSO is caused mainly by a sudden weakening of the equatorial annual cycle through the nonlinear mechanism of frequency entrainment, rather than an increase in the coupled ocean–atmosphere instability. The weakened annual cycle corresponds to a reduced north–south cross-equatorial annual mean SST contrast in the eastern Pacific. This reduced interhemispheric SST gradient—significant cooling north of the equator—is forced predominantly by an anomalous easterly from an abrupt polarward shift of the jet stream in the Northern Hemisphere, which extends to the northeastern tropical Pacific Ocean surface and is reinforced by the wind-evaporation-SST feedback then propagates equatorward; it could also be contributed by a fast sea-ice expansion and a consequent cooling in the North Pacific and North Atlantic that is induced by the retreat of the LIS."
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #603 on: October 27, 2016, 05:34:18 PM »
The linked article indicates that as there are still large ice sheets in both Greenland and Antarctica, we are technically still in an "ice age" and thus it is not surprising that Hansen's ice-climate interaction could drive world temperatures much higher (with, or without, more Anthropogenic radiative forcing), as this has happened during previous ice ages as the ice sheets collapsed.

http://www.businessinsider.com/why-ice-ages-happen-in-cycles-2016-10

Extract: " When oceans are colder, they can absorb more carbon dioxide. As the temperature increases, more gas molecules leave the water than enter it. This theory also provides an explanation for how global warming is related to the increase of carbon in the atmosphere.

"You can start with a small change in climate, which changes the amount of carbon dioxide in the atmosphere, and then leads to a bigger change in climate," Lear said.

The Earth is currently in a warm spell, as the most recent ice age occurred about 11,000 years ago. There is no particular temperature that signifies an ice age; they are just defined as periods of time when large ice sheets cover the planet.

"Technically we are still in an ice age now, as we have a large ice sheet on Antarctica and Greenland," Lear said."
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johnm33

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #604 on: December 05, 2016, 10:37:37 AM »
Just a comment on the conversation taking place on the 2016 freezing season thread, regarding the addition of ice into the north Atlantic. Surely this is exactly what we have been observing for the last 40 years, as the huge volume of Arctic ice has melted and flowed south, as ice or meltwater, joining the Atlantic in Denmark strait or the Labrador sea. For all this time it has cooled the north Atlantic and now, it seems to me it, has reached a point where the flow is enhanced/established sufficiently to be constantly recycled. The smoothed underside topography of the now thin ice being unable to accomodate anything like the volume of melt/freshwater it once did we now see bottom meltwater being created and escaping the Arctic in december.
The Younger Dryas is easier to understand from the 'catastrophist' point of veiw.

jai mitchell

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #605 on: December 05, 2016, 01:14:14 PM »
NASA's Ice penetrating radar shows clearly that a vast majority of the ice on Greenland melted during the last interglacial when temperatures in the region were very similar to todays current values.

see video here:

https://www.youtube.com/watch?v=wzC-iHOqJuo

all of the models are wrong.
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #606 on: December 05, 2016, 05:26:26 PM »
This is a re-post from the Antarctic folder that indicates that the ocean-ice shelf interaction will likely accelerate the loss of the Pine Island Ice Shelf, PIIS, which will accelerate the loss of both the Pine Island Glacier, PIG and the adjoining Thwaites Glacier:

"The linked Climate Central article is entitled: "Odd Rifts in Antarctic Ice Could Mean ‘Sayonara, Glacier’", and it cites an ocean-ice interaction mechanism that could accelerate the loss of the PIIS and subsequently the loss of the PIG (beyond current consensus projections):

http://www.climatecentral.org/news/rifts-antarctic-ice-sayonara-glacier-20923

Extract: "The key question for the future of Pine Island Glacier is whether rifts will keep forming in these valleys further and further inland. If they do, more and more icebergs could calve off at a quicker pace than is typical, diminishing the ice shelf and speeding the retreat of the glacier.
The study shows “a new mechanism for potentially rapid collapse,” Mankoff said. “It’s a little bit scary.”
Or, as Howat put it, if this mechanism does continue like this, “then it’s going to be, ‘Sayonara, glacier.’”"
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ritter

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #607 on: December 05, 2016, 05:57:54 PM »

all of the models are wrong.

Elaborate, please.

AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #608 on: December 05, 2016, 09:08:09 PM »
The linked article is entitled: "During last period of global warming, Antarctica warmed 2 to 3 times more than planet average".  The 2.75 amplification factor is toward the higher end of the consensus range, but does eliminate some of the lower-end model projection.

http://www.pnas.org/content/early/2016/11/22/1609132113.full

Extract: "Following Earth’s last ice age, which peaked 20,000 years ago, the Antarctic warmed between two and three times the average temperature increase worldwide, according to a new study by a team of American geophysicists.

The disparity – Antarctica warmed about 11 degrees Celsius, nearly 20 degrees Fahrenheit, between about 20,000 and 10,000 years ago, while the average temperature worldwide rose only about 4 degrees Celsius, or 7 degrees Fahrenheit …"

See also:

http://www.pnas.org/content/early/2016/11/22/1609132113.full

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bbr2314

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #609 on: December 05, 2016, 11:47:44 PM »
NASA's Ice penetrating radar shows clearly that a vast majority of the ice on Greenland melted during the last interglacial when temperatures in the region were very similar to todays current values.

see video here:

https://www.youtube.com/watch?v=wzC-iHOqJuo

all of the models are wrong.
Hansen's models probably give a decent idea but they are too slow.

AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #610 on: December 07, 2016, 11:49:18 PM »
The linked article is entitled: "Studies open deep history of Greenland's ice sheet—and raise new questions about its stability".  If both of the cited references are correct then the Greenland Ice Sheet may be more susceptible to both rapid deglaciation, and re-glaciation, than previously appreciated.


http://phys.org/news/2016-12-deep-history-greenland-ice-sheetand.html

Extract: "How much of Greenland's ice melted during past periods of global warming? Two first-of-their-kind studies in Nature look much deeper into the history of Greenland than previous techniques allowed. One of the studies, led by University of Vermont geologist Paul Bierman, concludes that East Greenland -- like the coastal scene shown in this image from near Tasiilaq -- has been actively scoured by glacial ice for much of the last 7.5 million years. The other study presents contrasting results suggesting the disappearance of the ice sheet over the center of Greenland during at least some of the Pleistocene. The two studies improve our understand of Greenland's deep past, while raising questions about both the past and future of its giant ice sheet in a changing climate. Credit: Joshua Brown/UVM

The dynamics of Antarctica's giant ice sheet is full of questions and the disastrous potential. "But there's enough sea-level rise tied-up in Greenland alone to put a lot of cities and long stretches of coastline underwater," says Paul Bierman, "including Donald Trump's property in Florida." "

See also:

Joerg M. Schaefer et al, Greenland was nearly ice-free for extended periods during the Pleistocene, Nature (2016). DOI: 10.1038/nature20146

http://www.nature.com/nature/journal/v540/n7632/full/nature20146.html

Abstract: "The Greenland Ice Sheet (GIS) contains the equivalent of 7.4 metres of global sea-level rise. Its stability in our warming climate is therefore a pressing concern. However, the sparse proxy evidence of the palaeo-stability of the GIS means that its history is controversial (compare refs 2 and 3 to ref. 4). Here we show that Greenland was deglaciated for extended periods during the Pleistocene epoch (from 2.6 million years ago to 11,700 years ago), based on new measurements of cosmic-ray-produced beryllium and aluminium isotopes (10Be and 26Al) in a bedrock core from beneath an ice core near the GIS summit. Models indicate that when this bedrock site is ice-free, any remaining ice is concentrated in the eastern Greenland highlands and the GIS is reduced to less than ten per cent of its current volume. Our results narrow the spectrum of possible GIS histories: the longest period of stability of the present ice sheet that is consistent with the measurements is 1.1 million years, assuming that this was preceded by more than 280,000 years of ice-free conditions. Other scenarios, in which Greenland was ice-free during any or all Pleistocene interglacials, may be more realistic. Our observations are incompatible with most existing model simulations that present a continuously existing Pleistocene GIS. Future simulations of the GIS should take into account that Greenland was nearly ice-free for extended periods under Pleistocene climate forcing."

&

Paul R. Bierman et al, A persistent and dynamic East Greenland Ice Sheet over the past 7.5 million years, Nature (2016). DOI: 10.1038/nature20147

http://www.nature.com/nature/journal/v540/n7632/full/nature20147.html

Abstract: "Climate models show that ice-sheet melt will dominate sea-level rise over the coming centuries, but our understanding of ice-sheet variations before the last interglacial 125,000 years ago remains fragmentary. This is because terrestrial deposits of ancient glacial and interglacial periods are overrun and eroded by more recent glacial advances, and are therefore usually rare, isolated and poorly dated. In contrast, material shed almost continuously from continents is preserved as marine sediment that can be analysed to infer the time-varying state of major ice sheets. Here we show that the East Greenland Ice Sheet existed over the past 7.5 million years, as indicated by beryllium and aluminium isotopes (10Be and 26Al) in quartz sand removed by deep, ongoing glacial erosion on land and deposited offshore in the marine sedimentary record. During the early Pleistocene epoch, ice cover in East Greenland was dynamic; in contrast, East Greenland was mostly ice-covered during the mid-to-late Pleistocene. The isotope record we present is consistent with distinct signatures of changes in ice sheet behaviour coincident with major climate transitions. Although our data are continuous, they are from low-deposition-rate sites and sourced only from East Greenland. Consequently, the signal of extensive deglaciation during short, intense interglacials could be missed or blurred, and we cannot distinguish between a remnant ice sheet in the East Greenland highlands and a diminished continent-wide ice sheet. A clearer constraint on the behaviour of the ice sheet during past and, ultimately, future interglacial warmth could be produced by 10Be and 26Al records from a coring site with a higher deposition rate. Nonetheless, our analysis challenges the possibility of complete and extended deglaciation over the past several million years."
« Last Edit: December 08, 2016, 12:54:16 AM by AbruptSLR »
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #611 on: December 12, 2016, 01:07:35 AM »
The linked reference indicates that the collapse of an ice sheet can result in the abrupt reorganization of the associated jet stream in less than 100 years.  Thus a collapse of the WAIS this century could result in atmospheric changes in the Southern Hemisphere beyond those projected by Hansen et al (2016).

Juan M. Lora, Jonathan L. Mitchell & Aradhna E. Tripati (22 November 2016), "Abrupt reorganization of North Pacific and western North American climate during the last deglaciation", Geophysical Research Letters, DOI: 10.1002/2016GL071244


http://onlinelibrary.wiley.com/doi/10.1002/2016GL071244/full

Abstract: "Dramatic hydroclimate shifts occurred in western North America during the last deglaciation, but the timing and mechanisms driving these changes are uncertain and debated, and previous modeling has largely relied on linear interpolations between equilibrium snapshot simulations. Using a published transient climate simulation and a range of proxy records, we analyze the region's climate evolution in order to identify the mechanisms governing hydroclimate shifts. A rapid loss of ice around 14,000 years ago causes an abrupt reorganization of the circulation, which precipitates drying and moistening of southwestern and northwestern North America, respectively. The atmospheric circulation transitions between two states on a timescale of decades to centuries, during which time the westerly jet shifts north by about 7°. In contrast to previous studies, we find that changes in the water budget of western North America prior to this event are not attributable to variations in the position of the jet, but rather to the intensity of moisture transport into the continent."
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #612 on: December 12, 2016, 06:29:27 PM »
Most climate models do not include wind-albedo interaction that is currently inducing surface melting in portions of East Antarctica, but the linked reference documents field evidence for this mechanism that could contribute to a faster rate of EAIS destabilization with global warming then currently projected:

J. T. M. Lenaerts, et. al.  (2016), "Meltwater produced by wind–albedo interaction stored in an East Antarctic ice shelf", Nature Climate Change, doi:10.1038/nclimate3180

http://www.nature.com/nclimate/journal/vaop/ncurrent/full/nclimate3180.html

Abstract: "Surface melt and subsequent firn air depletion can ultimately lead to disintegration of Antarctic ice shelves causing grounded glaciers to accelerate and sea level to rise. In the Antarctic Peninsula, foehn winds enhance melting near the grounding line, which in the recent past has led to the disintegration of the most northerly ice shelves. Here, we provide observational and model evidence that this process also occurs over an East Antarctic ice shelf, where meltwater-induced firn air depletion is found in the grounding zone. Unlike the Antarctic Peninsula, where foehn events originate from episodic interaction of the circumpolar westerlies with the topography, in coastal East Antarctica high temperatures are caused by persistent katabatic winds originating from the ice sheet’s interior. Katabatic winds warm and mix the air as it flows downward and cause widespread snow erosion, explaining >3 K higher near-surface temperatures in summer and surface melt doubling in the grounding zone compared with its surroundings. Additionally, these winds expose blue ice and firn with lower surface albedo, further enhancing melt. The in situ observation of supraglacial flow and englacial storage of meltwater suggests that ice-shelf grounding zones in East Antarctica, like their Antarctic Peninsula counterparts, are vulnerable to hydrofracturing."
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #613 on: December 12, 2016, 06:42:11 PM »
The linked reference provides field evidence supporting Hansen's ice-climate interaction mechanism.

Pepijn Bakker et al, Centennial-scale Holocene climate variations amplified by Antarctic Ice Sheet discharge, Nature (2016). DOI: 10.1038/nature20582

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature20582.html

Abstract: "Proxy-based indicators of past climate change show that current global climate models systematically underestimate Holocene-epoch climate variability on centennial to multi-millennial timescales, with the mismatch increasing for longer periods. Proposed explanations for the discrepancy include ocean–atmosphere coupling that is too weak in models, insufficient energy cascades from smaller to larger spatial and temporal scales, or that global climate models do not consider slow climate feedbacks related to the carbon cycle or interactions between ice sheets and climate. Such interactions, however, are known to have strongly affected centennial- to orbital-scale climate variability during past glaciations, and are likely to be important in future climate change. Here we show that fluctuations in Antarctic Ice Sheet discharge caused by relatively small changes in subsurface ocean temperature can amplify multi-centennial climate variability regionally and globally, suggesting that a dynamic Antarctic Ice Sheet may have driven climate fluctuations during the Holocene. We analysed high-temporal-resolution records of iceberg-rafted debris derived from the Antarctic Ice Sheet, and performed both high-spatial-resolution ice-sheet modelling of the Antarctic Ice Sheet and multi-millennial global climate model simulations. Ice-sheet responses to decadal-scale ocean forcing appear to be less important, possibly indicating that the future response of the Antarctic Ice Sheet will be governed more by long-term anthropogenic warming combined with multi-centennial natural variability than by annual or decadal climate oscillations."


See also the linked article entitled: "Antarctic Ice Sheet study reveals 8,000-year record of climate change".

http://phys.org/news/2016-12-antarctic-ice-sheet-reveals-year.html

Extract: "An international team of researchers has found that the Antarctic Ice Sheet plays a major role in regional and global climate variability - a discovery that may also help explain why sea ice in the Southern Hemisphere has been increasing despite the warming of the rest of the Earth.


Global climate models that look at the last several thousand years have failed to account for the amount of climate variability captured in the paleoclimate record, according to lead author Pepijn Bakker, a climate modeller from the MARUM Center for Marine Environmental Studies at the University of Bremen in Germany.

The researchers first turned their attention to the Scotia Sea. "Most icebergs calving off the Antarctic Ice Sheet travel through this region because of the atmospheric and oceanic circulation," explained Weber. "The icebergs contain gravel that drop into the sediment on the ocean floor - and analysis and dating of such deposits shows that for the last 8,000 years, there were centuries with more gravel and those with less."

The research team's hypothesis is that climate modellers have historically overlooked one crucial element in the overall climate system. They discovered that the centuries-long phases of enhanced and reduced Antarctic ice mass loss documented over the past 8,000 years have had a cascading effect on the entire climate system.

Using sophisticated computer modelling, the researchers traced the variability in iceberg calving (ice that breaks away from glaciers) to small changes in ocean temperatures."
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #614 on: January 03, 2017, 05:44:57 PM »
The linked article is entitled: "Greenland Ice Melt Could Push Atlantic Circulation to Collapse".  This research indicates that the GIS represents more of a long-term risk w.r.t. to the potential collapse of the thermohaline circulation; but it does not assess the risks from either the WAIS and/or the EAIS:

https://www.hakaimagazine.com/article-short/greenland-ice-melt-could-push-atlantic-circulation-collapse

Extract: "New research gives a glimpse of the potential long-term consequences of anthropogenic warming.

Notably, Bakker’s calculations of how much AMOC-suppressing meltwater could flow into the North Atlantic were more conservative than some previous estimates, including Hansen’s widely reported paper. Hansen’s group projected massive freshwater runoff from Greenland and a catastrophic collapse of the AMOC. That paper also predicted violent superstorms, mega-waves throwing massive boulders onto shorelines, and a stratification of the ocean with cold water on top and warm water on the bottom.

Bakker says he thinks Hansen’s paper was unrealistic, but adds that a collapse in the AMOC would have devastating consequences. Sediment cores drilled from Greenland and Antarctica show that during the last ice age, the AMOC weakened suddenly and dramatically, nearly to the point of collapse, just before periods of wild climate change in the northern and southern hemispheres."
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Pmt111500

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #615 on: January 03, 2017, 06:19:37 PM »
Collapse of thermohaline circulation in Northern Atlantic... Didn't this happen during Minor Dryas? Given that the temperature drop was 1-2 degrees i guess, and the fact that the glacier involved was the more southerly Laurentian, I'd guess that at most this would take the NA region back to the 1970s temperatures, with little effect further over the continents. (sarcastically practising getting along with Trump government , Well, a couple of cities would drown but they're probably not that important (end sarc)
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #616 on: January 03, 2017, 06:36:58 PM »
Collapse of thermohaline circulation in Northern Atlantic... Didn't this happen during Minor Dryas? Given that the temperature drop was 1-2 degrees i guess, and the fact that the glacier involved was the more southerly Laurentian, I'd guess that at most this would take the NA region back to the 1970s temperatures, with little effect further over the continents. (sarcastically practising getting along with Trump government , Well, a couple of cities would drown but they're probably not that important (end sarc)

Setup ( boundary conditions and initial conditions ) is very different. Unlikely trajectory is the same.
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #617 on: January 04, 2017, 02:11:47 AM »
The linked article is entitled: "Greenland Ice Melt Could Push Atlantic Circulation to Collapse".  This research indicates that the GIS represents more of a long-term risk w.r.t. to the potential collapse of the thermohaline circulation; but it does not assess the risks from either the WAIS and/or the EAIS:

The slowdown of the thermohaline circulation in previous years coincidents with a short pulse in the rate of CO2 accumulation in the earth's atmosphere.  This circulation is important in many ways, the least of which is pushing new water with low CO2 concentrations to the surface (so that it can absorb more from the ocean).  I estimate that a total halt of the thermohaline would reduce ocean uptake of CO2 by (at least) 7% (about 0,5 GT CO2 per year
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #618 on: January 05, 2017, 03:29:30 AM »
The linked article is entitled: "Study finds potential instability in Atlantic Ocean water circulation system", and if the AMOC is less stable than previously thought then Hansen's ice-climate interaction is more likely than currently assumed by mainstream climate scientists:

http://news.yale.edu/2017/01/04/study-finds-potential-instability-atlantic-ocean-water-circulation-system

Extract: "One of the world’s largest ocean circulation systems may not be as stable as today’s weather models predict, according to a new study.

In fact, changes in the Atlantic Meridional Overturning Circulation (AMOC) — the same deep-water ocean current featured in the movie “The Day After Tomorrow” — could occur quite abruptly, in geologic terms, the study says. The research appears in the Jan. 4 online edition of the journal Science Advances.

“We show that the possibility of a collapsed AMOC under global warming is hugely underestimated,” said Wei Liu, a postdoctoral associate in the Department of Geology and Geophysics at Yale University and lead author of the study. Liu began the research when he was a graduate student at the University of Wisconsin-Madison, and continued it at the Scripps Institution of Oceanography, prior to coming to Yale."
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #619 on: January 05, 2017, 03:34:53 AM »
For convenience below I provide a link to the reference cited in my Reply #618:

Wei Liu, Shang-Ping Xie, Zhengyu Liu and Jiang Zhu (04 Jan 2017), "Overlooked possibility of a collapsed Atlantic Meridional Overturning Circulation in warming climate", Science Advances, Vol. 3, no. 1, e1601666, DOI: 10.1126/sciadv.1601666

http://advances.sciencemag.org/content/3/1/e1601666

Abstract: "Changes in the Atlantic Meridional Overturning Circulation (AMOC) are moderate in most climate model projections under increasing greenhouse gas forcing. This intermodel consensus may be an artifact of common model biases that favor a stable AMOC. Observationally based freshwater budget analyses suggest that the AMOC is in an unstable regime susceptible for large changes in response to perturbations. By correcting the model biases, we show that the AMOC collapses 300 years after the atmospheric CO2 concentration is abruptly doubled from the 1990 level. Compared to an uncorrected model, the AMOC collapse brings about large, markedly different climate responses: a prominent cooling over the northern North Atlantic and neighboring areas, sea ice increases over the Greenland-Iceland-Norwegian seas and to the south of Greenland, and a significant southward rain-belt migration over the tropical Atlantic. Our results highlight the need to develop dynamical metrics to constrain models and the importance of reducing model biases in long-term climate projection."
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #620 on: January 05, 2017, 04:48:10 PM »
As a follow-on to my Replies #618 & 619 , also see the associated commentary by Rahmstorf entitled: "The underestimated danger of a breakdown of the Gulf Stream System"

http://www.realclimate.org/index.php/archives/2017/01/the-underestimated-danger-of-a-breakdown-of-the-gulf-stream-system/

Extract: "According to the observational data, the AMOC is exporting freshwater, which is why freshwater will accumulate in the Atlantic when the AMOC breaks down. That is precisely the instability described by Stommel 1961 and Broecker 1987. In the models, on the other hand, the AMOC in most cases imports freshwater, so the flow is fundamentally stable there. The differences in AMOC stability between different models cannot be understood without the fundamental criterion of whether the AMOC imports or exports freshwater, and by what amount. Liu et al. 2014 have identified a known common bias in all coupled climate GCMs without flux adjustments, the “tropical bias”, which makes them import freshwater in contrast to what observations show for the real ocean. A model bias towards stability is also consistent with the fact that most models underestimate the cooling trend observed in the subpolar Atlantic, which is indicative of an ongoing significant AMOC weakening, as we have argued (Rahmstorf et al. 2015).
...
There are, therefore, two reasons why thus far we could have underestimated the risk of a breakdown of the Gulf Stream System. First, climate models probably have a systematic bias towards stable flow. Secondly, most of them do not take into account the melting ice of Greenland. As the new studies show, each of these factors alone can lead to a much stronger weakening of the Gulf Stream system. We now need to study how these two factors work together. I hope these worrying new results will encourage as many other research groups as possible to pursue this question with their own models!"
« Last Edit: January 05, 2017, 04:56:23 PM by AbruptSLR »
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #621 on: January 06, 2017, 04:42:38 PM »
As a follow-on to my last post Reply #620: with continued global warming one can expect more Agulhas leakage; which per the 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

Abstract: "Recent measurements of the strength of the Atlantic overturning circulation at 26°N show a 1 year drop and partial recovery amid a gradual weakening. To examine the extent and impact of the slowdown on basin wide heat and freshwater transports for 2004–2012, a box model that assimilates hydrographic and satellite observations is used to estimate heat transport and freshwater convergence as residuals of the heat and freshwater budgets. Using an independent transport estimate, convergences are converted to transports, which show a high level of spatial coherence. The similarity between Atlantic heat transport and the Agulhas Leakage suggests that it is the source of the surface heat transport anomalies. The freshwater budget in the North Atlantic is dominated by a decrease in freshwater flux. The increasing salinity during the slowdown supports modeling studies that show that heat, not freshwater, drives trends in the overturning circulation in a warming climate."
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #622 on: February 05, 2017, 12:51:04 PM »
The linked reference indicates that the rate of freshening of the AABW is accelerating rapidly, thus supporting Hansen's ice-climate feedback mechanism:

Viviane V. Menezes, Alison M. Macdonald and Courtney Schatzman (25 Jan 2017), "Accelerated freshening of Antarctic Bottom Water over the last decade in the Southern Indian Ocean", Science Advances, Vol. 3, no. 1, e1601426, DOI: 10.1126/sciadv.1601426

http://advances.sciencemag.org/content/3/1/e1601426

Extract: "Southern Ocean abyssal waters, in contact with the atmosphere at their formation sites around Antarctica, not only bring signals of a changing climate with them as they move around the globe but also contribute to that change through heat uptake and sea level rise. A repeat hydrographic line in the Indian sector of the Southern Ocean, occupied three times in the last two decades (1994, 2007, and, most recently, 2016), reveals that Antarctic Bottom Water (AABW) continues to become fresher (0.004 ± 0.001 kg/g decade−1), warmer (0.06° ± 0.01°C decade−1), and less dense (0.011 ± 0.002 kg/m3 decade−1). The most recent observations in the Australian-Antarctic Basin show a particularly striking acceleration in AABW freshening between 2007 and 2016 (0.008 ± 0.001 kg/g decade−1) compared to the 0.002 ± 0.001 kg/g decade−1 seen between 1994 and 2007. Freshening is, in part, responsible for an overall shift of the mean temperature-salinity curve toward lower densities. The marked freshening may be linked to an abrupt iceberg-glacier collision and calving event that occurred in 2010 on the George V/Adélie Land Coast, the main source region of bottom waters for the Australian-Antarctic Basin. Because AABW is a key component of the global overturning circulation, the persistent decrease in bottom water density and the associated increase in steric height that result from continued warming and freshening have important consequences beyond the Southern Indian Ocean."

See also the associated article entitled: "Antarctic Bottom Waters Freshening at Unexpected Rate".

https://scripps.ucsd.edu/news/antarctic-bottom-waters-freshening-unexpected-rate

Extract: "Shift could disturb ocean circulation and hasten sea level rise, researchers say.

The team found that the previously detected warming trend has continued, though at a somewhat slower pace. The biggest surprise, however, was its lack of saltiness: AABW in the  region off East Antarctica’s Adélie Land has grown fresher four times faster in the past decade than it did between 1994 and 2007."
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #623 on: February 05, 2017, 01:10:33 PM »
The linked reference helps to explain why the Antarctic deep water is freshening unexpectedly quickly; which likely will accelerate the slowing of the thermohaline circulation.  This research also indicates that the Antarctic sea ice extent will likely retreat faster than previously expected.

Alberto C. Naveira Garabato, Alexander Forryan, Pierre Dutrieux, Liam Brannigan, Louise C. Biddle, Karen J. Heywood, Adrian Jenkins, Yvonne L. Firing & Satoshi Kimura (2017), "Vigorous lateral export of the meltwater outflow from beneath an Antarctic ice shelf", Nature; doi:10.1038/nature20825

http://www.nature.com/articles/nature20825.epdf?author_access_token=DF62yOZXCaJUnJISA1g1PNRgN0jAjWel9jnR3ZoTv0MR1tk45gxKLxa6eT2BdeuvYwxU8paCVQ2zahPfQktn7LRlJScf53AShbsmYwaBPWLsy2X11W9kCUj_9XPaD8Mz

Abstract: "The instability and accelerated melting of the Antarctic Ice Sheet are among the foremost elements of contemporary global climate change. The increased freshwater output from Antarctica is important in determining sea level rise, the fate of Antarctic sea ice and its effect on the Earth’s albedo, ongoing changes in global deep-ocean ventilation, and the evolution of Southern Ocean ecosystems and carbon cycling. A key uncertainty in assessing and predicting the impacts of Antarctic Ice Sheet melting concerns the vertical distribution of the exported meltwater. This is usually represented by climate-scale models as a near-surface freshwater input to the ocean, yet measurements around Antarctica reveal the meltwater to be concentrated at deeper levels. Here we use observations of the turbulent properties of the meltwater outflows from beneath a rapidly melting Antarctic ice shelf to identify the mechanism responsible for the depth of the meltwater. We show that the initial ascent of the meltwater outflow from the ice shelf cavity triggers a centrifugal overturning instability that grows by extracting kinetic energy from the lateral shear of the background oceanic flow. The instability promotes vigorous lateral export, rapid dilution by turbulent mixing, and finally settling of meltwater at depth. We use an idealized ocean circulation model to show that this mechanism is relevant to a broad spectrum of Antarctic ice shelves. Our findings demonstrate that the mechanism producing meltwater at depth is a dynamically robust feature of Antarctic melting that should be incorporated into climate-scale models."

See also the linked article entitled: "Scientists Say They Now Know Why Antarctic Meltwater Stays Below Ocean Surface".

http://blogs.ei.columbia.edu/2017/02/02/scientists-say-they-now-know-why-antarctic-meltwater-stays-below-ocean-surface/

Extract: " Scientists believe that the depth at which meltwater enters the ocean can affect global ocean circulation and, in turn, climate. Fresh surface meltwater makes the upper layers of the Southern Ocean lighter. This is thought to slow down the sinking of surface water, and to favor the expansion of Antarctic sea ice. Injecting the same meltwater further down is believed to have the opposite effect, favoring sinking of surface waters and the retreat of Antarctic sea ice.

The potential effects of such processes were taken to the extreme in the 2004 movie The Day After Tomorrow, in which floating meltwater produced by warming climate caused the North Atlantic to freeze over almost instantly, in turn locking much of the United States in ice within days. “While no one expects our climate to change in the space of a few days, like the movie, we do know that fresh water flowing into our seas could dramatically affect sea levels and ocean circulation,” said study coauthor Alexander Forryan of the University of Southampton. “As such, it is vital our models take into account the presence of both surface and deep meltwater to maximize their accuracy.”"
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jai mitchell

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #624 on: February 05, 2017, 10:13:08 PM »
I wonder if, (when) the rate of freshwater cold flow continues to increase that it will (has already) increased the surface stratification of the CDW and increased the rate of undercutting of the Antarctic glaciers.
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #625 on: February 06, 2017, 03:02:32 AM »
I wonder if, (when) the rate of freshwater cold flow continues to increase that it will (has already) increased the surface stratification of the CDW and increased the rate of undercutting of the Antarctic glaciers.

Explaining the hydrodynamics of the Southern Ocean is complex, so I will just cut to the key consideration that the volume of CDW flow is both expanding and moving southward; and thus is increasingly presented with the possibility of advecting beneath Antarctic ice shelves, thus increasing the rate is ice mass loss.
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #626 on: February 06, 2017, 06:17:07 AM »
are you aware of a teleconnection between CDW source and the Pacific Warm Pool, perhaps through internal wave action? https://www.scientificamerican.com/article/long-a-mystery-how-500-me/
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #627 on: February 06, 2017, 06:07:32 PM »
are you aware of a teleconnection between CDW source and the Pacific Warm Pool, perhaps through internal wave action? https://www.scientificamerican.com/article/long-a-mystery-how-500-me/

Thanks.  While I am aware of ENSO related telecommunications of energy from the Pacific Warm Pool to the Southern Ocean, I was not aware of this specific mechanism.  It may be a long time before climate change models capture all of the various mechanisms that can feed into a possible strange attractor driven upward ratcheting of the climate state.
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #628 on: February 08, 2017, 05:05:19 PM »
jai,

I have been (& continue to be) distracted for a while now, but here are some references on both Oceanic Rossby Waves and Oceanic Infragravity Waves that telecommunicate energy from the Pacific Ocean to West Antarctica, and which promote ice calving events.


Pierre St-Laurent, John M. Klinck and Michael S. Dinniman (2012), "On the Role of Coastal Troughs in the Circulation of Warm Circumpolar Deep Water on Antarctic Shelves", JPO.

Bromirski, P.D., Miller, A.J., Flick, R.E, and Auad, G., (2011), "Dynamical Suppression of Sea Level Rise Along the Pacific Coast of North America: Indications for Imminent Acceleration" Journal of Geophysical Research, Vol. 116, C07005, doi: 10.1029/2010JC006759, July 2011.

Bromirski, P. D., O. V. Sergienko, and D. R. MacAyeal (2010), Transoceanic infragravity waves impacting Antarctic ice shelves, Geophys. Res. Lett., 37, L02502, doi:10.1029/2009GL041488.

Best,
ASLR
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #629 on: February 08, 2017, 05:52:47 PM »
The linked reference discounts the observed positive trend in the SAM to conclude that natural variability overwhelms the anthropogenic radiative forcing response in the high-latitude Southern Hemisphere.  To me discounting the observed positive trend in the SAM is a very bad idea as the first attached image from Fogt et. al. (2011) shows that during a La Nina event (as NOAA just called for 2016-17) combined with a positive SAM leads to atmospheric telecommunication of energy from the Tropical Pacific to West Antarctica  as is supported by the atypically low current Antarctic sea ice extent in West Antarctica as indicated in the second attachment.

Jones, J.M., Gille, S.T., Goosse, H., Abram, N.J., Canziani, P, Charman, D., Clem, K., Crosta, X., de Lavergne, C., Eisenman, I., M. H. England, Fogt, R., Frankcombe, L., Marshall, G.J., Masson-Delmotte, V., Morrison, A.K., Orsi, A., Raphael, M., Renwick, J., Schneider, D., Simpkins, G., Steig, E., Stenni, B., Swingedouw, D., and Vance, T.R., 2016: Assessing recent trends in high-latitude Southern Hemisphere surface climate. Nature Climate Change, 6, 917-926

http://web.science.unsw.edu.au/~matthew/nclimate3103.pdf

Extract: "Understanding the causes of recent climatic trends and variability in the high-latitude Southern Hemisphere is hampered by a short instrumental record. Here, we analyse recent atmosphere, surface ocean and sea-ice observations in this region and assess their trends in the context of palaeoclimate records and climate model simulations. Over the 36-year satellite era, significant linear trends in annual mean sea-ice extent, surface temperature and sea-level pressure are superimposed on large interannual to decadal variability. Most observed trends, however, are not unusual when compared with Antarctic palaeoclimate records of the past two centuries. With the exception of the positive trend in the Southern Annular Mode, climate model simulations that include anthropogenic forcing are not compatible with the observed trends. This suggests that natural variability overwhelms the forced response in the observations, but the models may not fully represent this natural variability or may overestimate the magnitude of the forced response."
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #630 on: February 17, 2017, 04:26:27 PM »
While this research has been previously cited in other threads, I believe that it belongs also in this thread as Bassis et al (2017) model supports the 'cliff failure' mechanism used by DeConto & Pollard.  Also the Bassis et al (2017) work indicates that the PIG-Thwaites basins in Antarctica are currently experiencing ocean temperatures that should lead to 'cliff failures', and with continued warming (to a GMSTA of about 2.6C above pre-industrial) DeConto indicates that 'hydrofracturing' will act synergistically with the 'cliff failure' mechanism to greatly accelerate ice mass loss from the WAIS.

Jeremy N. Bassis, Sierra V. Petersen, L. Mac Cathles. Heinrich events triggered by ocean forcing and modulated by isostatic adjustment. Nature, 2017; 542 (7641): 332 DOI: 10.1038/nature21069

http://www.nature.com/nature/journal/v542/n7641/full/nature21069.html

Abstract: "During the last glacial period, the Laurentide Ice Sheet sporadically discharged huge numbers of icebergs through the Hudson Strait into the North Atlantic Ocean, leaving behind distinct layers of ice-rafted debris in the ocean sediments. Perplexingly, these massive discharge events—Heinrich events—occurred during the cold portion of millennial-scale climate oscillations called Dansgaard–Oeschger cycles. This is in contrast to the expectation that ice sheets expand in colder climates and shrink in warmer climates. Here we use an ice sheet model to show that the magnitude and timing of Heinrich events can be explained by the same processes that drive the retreat of modern marine-terminating glaciers. In our model, subsurface ocean warming associated with variations in the overturning circulation increases underwater melt along the calving face, triggering rapid margin retreat and increased iceberg discharge. On millennial timescales, isostatic adjustment causes the bed to uplift, isolating the terminus from subsurface warming and allowing the ice sheet to advance again until, at its most advanced position, it is poised for another Heinrich event. This mechanism not only explains the timing and magnitude of observed Heinrich events, but also suggests that ice sheets in contact with warming oceans may be vulnerable to catastrophic collapse even with little atmospheric warming."

See also:
https://www.sciencedaily.com/releases/2017/02/170215131551.htm

Extract: ""There is currently large uncertainty about how much sea level will rise and much of this uncertainty is related to whether models incorporate the fact that ice sheets break," Bassis said. "What we are showing is that the models we have of this process seem to work for Greenland, as well as in the past so we should be able to more confidently predict sea level rise."

He added that portions of Antarctica have similar geography to Laurentide: Pine Island, Thwaites glacier, for example.

"We're seeing ocean warming in those region and we're seeing these regions start to change. In that area, they're seeing ocean temperature changes of about 2.7 degrees Fahrenheit," Bassis said. "That's pretty similar magnitude as we believe occurred in the Laurentide events, and what we saw in our simulations is that just a small amount of ocean warming can destabilize a region if it's in the right configuration, and even in the absence of atmospheric warming.""
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #631 on: February 18, 2017, 09:16:22 PM »
In the linked reference, researchers us a model to show that crevasses receiving firn-aquifer water will hydrofracture through to the bed, ~1000 m below, in 10–40 days.  This represents a risk for accelerating ice mass loss to the ocean, that was not previously recognized.

Kristin Poinar et al (07 February 2017), "Drainage of Southeast Greenland Firn Aquifer Water through Crevasses to the Bed", Front. Earth Sci., | https://doi.org/10.3389/feart.2017.00005

http://journal.frontiersin.org/article/10.3389/feart.2017.00005/full

Abstract: "A firn aquifer in the Helheim Glacier catchment of Southeast Greenland lies directly upstream of a crevasse field. Previous measurements show that a 3.5-km long segment of the aquifer lost a large volume of water (26,000–65,000 m2 in cross section) between spring 2012 and spring 2013, compared to annual meltwater accumulation of 6000–15,000 m2. The water is thought to have entered the crevasses, but whether the water reached the bed or refroze within the ice sheet is unknown. We used a thermo-visco-elastic model for crevasse propagation to calculate the depths and volumes of these water-filled crevasses. We compared our model output to data from the Airborne Topographic Mapper (ATM), which reveals the near-surface geometry of specific crevasses, and WorldView images, which capture the surface expressions of crevasses across our 1.5-km study area. We found a best fit with a shear modulus between 0.2 and 1.5 GPa within our study area. We show that surface meltwater can drive crevasses to the top surface of the firn aquifer (~20 m depth), whereupon it receives water at rates corresponding to the water flux through the aquifer. Our model shows that crevasses receiving firn-aquifer water hydrofracture through to the bed, ~1000 m below, in 10–40 days. Englacial refreezing of firn-aquifer water raises the average local ice temperature by ~4°C over a ten-year period, which enhances deformational ice motion by ~50 m year−1, compared to the observed surface velocity of ~200 m year−1. The effect of the basal water on the sliding velocity remains unknown. Were the firn aquifer not present to concentrate surface meltwater into crevasses, we find that no surface melt would reach the bed; instead, it would refreeze annually in crevasses at depths <500 m. The crevasse field downstream of the firn aquifer likely allows a large fraction of the aquifer water in our study area to reach the bed. Thus, future studies should consider the aquifer and crevasses as part of a common system. This system may uniquely affect ice-sheet dynamics by routing a large volume of water to the bed outside of the typical runoff period."

See also the linked article is entitled: "NASA study identifies new pathway for Greenland meltwater to reach ocean".

https://climate.nasa.gov/news/2551/nasa-study-identifies-new-pathway-for-greenland-meltwater-to-reach-ocean/

Extract: "Cracks in the Greenland Ice Sheet let one of its aquifers drain to the ocean, new NASA research finds. The aquifers, discovered only recently, are unusual in that they trap large amounts of liquid water within the ice sheet. Until now, scientists did not know what happened to the water stored away in this reservoir — the discovery will help fine tune computer models of Greenland’s contribution to sea level rise.
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #632 on: February 25, 2017, 08:01:19 PM »
The linked reference by Sgubin, et. al. (2017) is entitled: Abrupt cooling over the North Atlantic in modern climate model", Nature Communications, doi:10.1038/ncomms14375; and it indicates that the CMIP5 ensemble underestimates the risk of future abrupt cooling of the subpolar North Atlantic, SPG.  This increases the probability of the reality of Hansen's ice-climate feedback mechanism.

http://www.nature.com/articles/ncomms14375

Abstract: "Observations over the 20th century evidence no long-term warming in the subpolar North Atlantic (SPG). This region even experienced a rapid cooling around 1970, raising a debate over its potential reoccurrence. Here we assess the risk of future abrupt SPG cooling in 40 climate models from the fifth Coupled Model Intercomparison Project (CMIP5). Contrary to the long-term SPG warming trend evidenced by most of the models, 17.5% of the models (7/40) project a rapid SPG cooling, consistent with a collapse of the local deep-ocean convection. Uncertainty in projections is associated with the models’ varying capability in simulating the present-day SPG stratification, whose realistic reproduction appears a necessary condition for the onset of a convection collapse. This event occurs in 45.5% of the 11 models best able to simulate the observed SPG stratification. Thus, due to systematic model biases, the CMIP5 ensemble as a whole underestimates the chance of future abrupt SPG cooling, entailing crucial implications for observation and adaptation policy."

See also the linked article is entitled: "Drastic cooling in North Atlantic beyond worst fears, scientists warn".

https://www.theguardian.com/environment/2017/feb/24/drastic-cooling-north-atlantic-beyond-worst-fears-scientists-warn

Extract: "Climatologists say Labrador Sea could cool within a decade before end of this century, leading to unprecedented disruption…"
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #633 on: February 28, 2017, 07:00:18 PM »
Good talk about SLR:

Weather & Climate Summit 2017 (Part II): Dr Ben Strauss (January 2017)


https://youtu.be/8qwh-TTCqRE

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #634 on: March 23, 2017, 06:19:35 PM »
The linked article is entitled: "New Video: It's Alive – Microbes and Melt on the Greenland Ice Sheet"; and I recommend watching the associated video as it discusses an important positive feedback mechanism for both global warming and for sea level rise that was not included in AR5 projections; but which increases the probable occurrence of Hansen's ice-climate positive feedback mechanism (which also was not included in AR5 projections).

https://www.skepticalscience.com/microbes-melt-gis.html

Extract: "In recent years, several research groups have been looking in detail at the darkening of the ice sheet – and understanding that, as the planet warms, and ice melts, more liquid water means more habitat for bugs, more darkening, more melt,..you get the picture."
« Last Edit: March 23, 2017, 07:10:25 PM by AbruptSLR »
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #635 on: March 23, 2017, 07:01:11 PM »
In H.G.Well's "War of The Worlds" in the end it was the microbes wot did the biz on  the Martians. Ironic ?

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #636 on: March 24, 2017, 10:24:00 PM »
Gregoire has a new openaccess  paper out, refining the connections between MWP1A, saddle collapse and Bolling warming.

doi: 10.1002/2016GL070356

Read all about it.

sidd

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #637 on: April 10, 2017, 05:24:24 PM »
The linked Scribbler article is entitled: "An Armada of Icebergs Has Just Invaded The North Atlantic".  This is evidence indicate that we are likely, & rapidly, approaching a tipping point w.r.t. the stability of many Greenland marine terminating glaciers; which in-turn makes Hansen's ice-climate feedback mechanism more probable (this century).

https://robertscribbler.com/2017/04/08/an-armada-of-ice-bergs-has-just-invaded-the-north-atlantic/

Extract: "This week an unprecedented 481 icebergs swarmed into the shipping lanes of a storm-tossed North Atlantic. Strong hurricane force winds had ripped these bergs from their sea ice moored haven of Baffin Bay and thrust them into the ocean waters off Newfoundland. The week before, there were only 37 such icebergs in the Atlantic’s far northern waters. And the new number this week is nearly 6 times the annual average for this time of year at 83. To be very clear, there is no record, at present, of such a large surge of icebergs entering these waters in so short a period at any time in the modern reckoning."
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #638 on: April 10, 2017, 06:01:52 PM »
The linked Scribbler article is entitled: "An Armada of Icebergs Has Just Invaded The North Atlantic".  This is evidence indicate that we are likely, & rapidly, approaching a tipping point w.r.t. the stability of many Greenland marine terminating glaciers; which in-turn makes Hansen's ice-climate feedback mechanism more probable (this century).

https://robertscribbler.com/2017/04/08/an-armada-of-ice-bergs-has-just-invaded-the-north-atlantic/

Extract: "This week an unprecedented 481 icebergs swarmed into the shipping lanes of a storm-tossed North Atlantic. Strong hurricane force winds had ripped these bergs from their sea ice moored haven of Baffin Bay and thrust them into the ocean waters off Newfoundland. The week before, there were only 37 such icebergs in the Atlantic’s far northern waters. And the new number this week is nearly 6 times the annual average for this time of year at 83. To be very clear, there is no record, at present, of such a large surge of icebergs entering these waters in so short a period at any time in the modern reckoning."

The only problem I have with that comparison to Heinrich events, is the abundance of ice sheets in the previous cases. Their collapse gave rise to armadas Robert describes. This time around ? Not many sources other than Greenland.
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #639 on: April 10, 2017, 11:12:16 PM »
Good points, Dr. T.

But it is not just the total ice mass available for melt, but the rate at which it is melting.

We are heating the planet very fast, so, while we won't dump the total amount, we will likely see some very rapid changes. So it won't be exactly like earlier Heinrich events imho, but could have similar effects. As I recall, Hansen expects the Northern Atlantic to cool from significant melt off of Greenland, perhaps enough ocean cooling to cause general GW to pause briefly on its incessant march to the hell on earth we have created for ourselves.
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #640 on: April 10, 2017, 11:25:27 PM »
Good points, Dr. T.

But it is not just the total ice mass available for melt, but the rate at which it is melting.

We are heating the planet very fast, so, while we won't dump the total amount, we will likely see some very rapid changes. So it won't be exactly like earlier Heinrich events imho, but could have similar effects. As I recall, Hansen expects the Northern Atlantic to cool from significant melt off of Greenland, perhaps enough ocean cooling to cause general GW to pause briefly on its incessant march to the hell on earth we have created for ourselves.


The linked article entitled: "Heinrich event", reminds us that while the Lauentide ice sheet is most frequently associated with Heinrich events, the West Antarctic ice sheet has also been correlated, and it is extant today (& Hansen has warned us of a possible armada of icebergs around the Southern Ocean, should the WAIS collapse.

http://dictionary.sensagent.com/Heinrich%20event/en-en/

Extract: "Various mechanisms have been proposed to explain the cause of Heinrich events. Most centre around the activity of the Laurentide ice sheet, but others suggest that the unstable West Antarctic Ice Sheet played a triggering role."
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sidd

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #641 on: April 11, 2017, 05:15:25 AM »
"The only problem I have with that comparison to Heinrich events, is the abundance of ice sheets in the previous cases."

I was of that opinion myself, but learning about the evidence of late Eemian spike in SLR made me rethink. The Eemian was just about as warm as we are now.

sidd

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #642 on: April 11, 2017, 11:28:16 PM »
"The only problem I have with that comparison to Heinrich events, is the abundance of ice sheets in the previous cases."

I was of that opinion myself, but learning about the evidence of late Eemian spike in SLR made me rethink. The Eemian was just about as warm as we are now.

sidd

For those who do not know what sidd is talking about:
The first figure is from Muhs et al 2012, & shows that for California sea-level rapidly increased to just over 6m above today's sea level at the Eemian Peak (MIS 5.5, circa 120 kya) and then was flat for a long prior.

The second attached figure is from O'Leary et al (2013) and shows an abrupt contributions to SLR (circa 119kya)

Lastly, the third image is from Robert M. DeConto & David Pollard (31 March 2016), "Contribution of Antarctica to past and future sea-level rise", Nature, Volume: 531, Pages: 591–597, doi:10.1038/nature17145; which demonstrates that there is currently plenty of marine glacier ice in the WAIS to contribute to an abrupt SLR this century.
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #643 on: April 15, 2017, 01:48:37 AM »
Although the research discussed in the linked article entitled: "New study shows worrisome signs for Greenland ice", has been cited elsewhere in this forum, I believe it also belongs here, as it increases the probability of Hansen's ice-climate feedback mechanism:

https://www.theguardian.com/environment/climate-consensus-97-per-cent/2017/apr/14/new-study-shows-worrisome-signs-for-greenland-ice

Extract: "Greenland ice is melting fast, and could potentially cause many meters of sea level rise".
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #644 on: April 16, 2017, 06:47:52 PM »
Can you imagine how the timing of a rain-dominated Arctic will be affected by Hansen's ice-climate feedback mechanism driven by a WAIS collapse circa 2040-2060 (which almost all ESM projections currently ignore), and or pulses of methane emission from thermokarst lakes?  I also note that there is increasing evidence that ECS is higher than the 3C assumed by the cited research.

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

http://meetingorganizer.copernicus.org/EGU2017/EGU2017-4402.pdf

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

See also:

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

http://www.nature.com/nclimate/journal/v7/n4/full/nclimate3240.html
« Last Edit: April 16, 2017, 07:00:10 PM by AbruptSLR »
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sidd

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #645 on: April 16, 2017, 07:38:46 PM »
From the Bintanja paper:

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

They do not look at the effect of increased rain on the mass balance of Greenland, but I think the result will not be pretty. The Greenland ice sheet gains mass through precipitation, if this precipitation does not remain on the ice sheet but promptly runs off to the ocean, then the mass balance will go even more negative even quicker.

sidd

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #646 on: April 20, 2017, 12:33:30 PM »
The Last Glacial Termination, LGT, occurred from 18,000 to 11,650 kya, and the following reference, reconstructs the dynamic response of the Antarctic ice sheets to warming in this period in order to better evaluate Hansen's ice-climate feedback mechanisms.  The abstract 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:
http://www.geosci-model-dev-discuss.net/gmd-2017-18/gmd-2017-18.pdf
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wili

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #647 on: April 20, 2017, 01:51:59 PM »
Thanks for this info. It sound like most coastal dwellers in the US will be deep 'underwater' financially long before the actual wet stuff closes over their houses.

https://www.nytimes.com/2017/04/18/magazine/when-rising-seas-transform-risk-into-certainty.html?ref=oembed

"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #648 on: April 20, 2017, 11:02:49 PM »
The linked reference studies ice-climate feedback calibrated to 'freshwater hosing' events in the North Atlantic over the past 720,000 years, in order to study state dependence of climatic instabilities within a CMIP class of climate model.  Such research can help to calibrate models for such 'freshwater hosing' events such as the possible collapse of the WAIS this century:

Ayako Abe-Ouchi, et. al. (2017), "State dependence of climatic instability over the past 720,000 years from Antarctic ice cores and climate modeling", Science Advances, Vol. 3, no. 2, e1600446, DOI: 10.1126/sciadv.1600446

http://advances.sciencemag.org/content/3/2/e1600446
&
http://repository.kulib.kyoto-u.ac.jp/dspace/bitstream/2433/218067/1/sciadv.1600446.pdf

Abstract: "Climatic variabilities on millennial and longer time scales with a bipolar seesaw pattern have been documented in paleoclimatic records, but their frequencies, relationships with mean climatic state, and mechanisms remain unclear.  Understanding the processes and sensitivities that underlie these changes will underpin better understanding of the climate system and projections of its future change. We investigate the long-term characteristics of climatic variability using a new ice-core record from Dome Fuji, East Antarctica, combined with an existing long record from the Dome C ice core. Antarctic warming events over the past 720,000 years are most frequent when the Antarctic temperature is slightly below average on orbital time scales, equivalent to an intermediate climate during glacial periods, whereas interglacial and fully glaciated climates are unfavourable for a millennial-scale bipolar seesaw. Numerical experiments using a fully coupled atmosphere-ocean general circulation model with freshwater hosing in the northern North Atlantic showed that climate becomes most unstable in intermediate glacial conditions associated with large changes in sea ice and the Atlantic Meridional Overturning Circulation. Model sensitivity experiments suggest that the prerequisite for the most frequent climate instability with bipolar seesaw pattern during the late Pleistocene era is associated with reduced atmospheric CO2 concentration via global cooling and sea ice formation in the North Atlantic, in addition to extended Northern Hemisphere 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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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #649 on: April 24, 2017, 05:59:26 PM »
As deep convective clouds (DCC) are a significant positive feedback mechanism, the fact that they increase rapidly with warming of the tropical ocean, is a major consideration of Hansen's ice-climate feedback mechanism, because freshwater hosing of the Southern Ocean will slow the thermohaline circulation of the great ocean conveyor-belt current circulation; which will back-up ocean surface heat in the tropical oceans.  Thus, the linked reference errs on the side of least drama by ignoring the effects of:

(a)a potential collapse of the WAIS this century (see also the first attached image that shows the increase in GMSTA at 30N & 30S latitude since 2003, which is associated with DCC); and/or
 
(b) a relatively high ECS (in the 5C +/- 0.5C range as indicated by the middle panel of the second attached image).

Aumann, H. H., Ruzmaikin, A., and Behrangi, A.: Increase in the Frequency of Tropical Deep Convective Clouds with Global Warming, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2017-135, in review, 2017.

http://www.atmos-chem-phys-discuss.net/acp-2017-135/

Abstract. Deep Convective Clouds (DCC) are extreme rain events associated with large thunderstorms. They form in 0.6 % of the area of the tropical oceans. As the tropical oceans warm in a future climate, the frequency of occurrence of DCC may change. Between 2003 and 2016 the yearly mean temperature of the tropical ocean varied by almost 1 K. We use Atmospheric Infrared Sounder (AIRS) data for this time period to derive the probability of the DCC process as function of the Sea Surface Temperature (SST). The onset of the DCC process shifts about 0.5 K per 1 K of warming of the mean tropical SST. When these results are applied to the temperature distribution predicted by CMIP5 climate models for the end of this century, we find that the frequency of DCC, i.e. the percent of the area of the tropical oceans associated with DCC, which is 0.6 percent in the current climate, increases to 0.9 %, close to a 50 % increase.


Summary: "We derive the probability of the DCC process as function of the Sea Surface Temperature (SST) associated with DCC identified with AIRS between the years 2003 and 2016 for the tropical oceans (30S-30N). During this time the annual mean value of the SST varied by almost 1K, producing measureable shifts in the temperature of the onset of the DCC process. We find that the temperature of the onset of the DCC formation process shifts at the rate of about +0.50 K per K of the warming of the mean tropical ocean temperature. We use the probability of the DCC process to predict the change in the frequency of DCC in a future climate, based on the temperature distribution of the tropical oceans predicted by the CMIP5 models. The average of the 36 CMIP5 models (RCP 8.5 scenario) predicts 2.7 K of warming of the mean SST of the tropical oceans by the end of this century. As a result the percent of the area of the tropical oceans associated with DCC, in the current climate 0.6 percent, increases to 0.9% by the end of the century, close to a 50% increase.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson