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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #200 on: August 08, 2015, 02:44:41 AM »
My apologies, as the answer to my isostatic rebound question is mostly in your following post showing the 40% impact of GIA in Amundsen Bay area, but still do wonder if there is a negative feedback with subsidence in the surrounding

bluesky,

This may seem confusing, but the models that I was referring to were models including the viscosity of the mantle; which assumed too high of values of viscosity meaning that they assumed that more residual rebound was still occurring in the ASE than is actually the case (see the attached image of projected current residual rebound from the end of the last ice age about 12,000 years ago, so that with low viscosity there is very little current residual rebound left, but with a high assumed viscosity there is still significant rebound occurring).  This is important because if significant residual rebound is currently occurring (which is not the case) then mass change measurements made by the GRACE satellite are 40% associated with this residual rebound (and thus the researchers subtracted it before reporting their results); however, as the actual residual rebound is very low essentially all of the GRACE mass change contribution should be attributed to ice mass loss.

Best,
ASLR
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sidd

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #201 on: August 08, 2015, 07:58:33 AM »
"Slowing the rate of flow of the AMOC (via reduced AABW production); which would cause the North Atlantic current to get hotter and carry more heat into the Arctic"

As i understand it, AMOC steals heat from the South and warms the North, decrease in AMOC would relatively cool the north (but the effect would be swamped by AGW ...)

AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #202 on: August 08, 2015, 04:19:35 PM »
"Slowing the rate of flow of the AMOC (via reduced AABW production); which would cause the North Atlantic current to get hotter and carry more heat into the Arctic"

As i understand it, AMOC steals heat from the South and warms the North, decrease in AMOC would relatively cool the north (but the effect would be swamped by AGW ...)

sidd,
The bipolar seesaw hypothesis has been around for a number of years and indicates that the temperatures of the NH & SH are out of phase and linked (see the Wikipedia link below).  This bipolar seesaw mechanism is not only influenced by discharges of fresh water (melt water) in high latitudes, but also by Agulhas Current Leakage from the Indian Ocean into the Atlantic Ocean, and by shifts in the Intertropical Convergence Zones (ITCZ), all of which can contribute to abrupt climate change as highlighted by Hansen et al 2015 (also by the references cited below)
https://en.wikipedia.org/wiki/Polar_see-saw


The first linked paper provides evidence supporting the "bipolar seesaw theory of abrupt climate change." "Theoretical models and observational data have long suggested that the Northern and Southern Hemisphere climates behave in a seesaw-like fashion: when the northern ocean warms, the southern ocean cools and vice versa."

Kyoung-nam Jo, Kyung Sik Woo, Sangheon Yi, Dong Yoon Yang, Hyoun Soo Lim, Yongjin Wang, Hai Cheng & R. Lawrence Edwards  (17 April 2014), "Mid-latitude interhemispheric hydrologic seesaw over the past 550,000 years", Nature, Volume: 508, Pages: 378–382, doi:10.1038/nature13076


http://www.nature.com/nature/journal/v508/n7496/full/nature13076.html


Abstract: "An interhemispheric hydrologic seesaw—in which latitudinal migrations of the Intertropical Convergence Zone (ITCZ) produce simultaneous wetting (increased precipitation) in one hemisphere and drying in the other—has been discovered in some tropical and subtropical regions. For instance, Chinese and Brazilian subtropical speleothem (cave formations such as stalactites and stalagmites) records show opposite trends in time series of oxygen isotopes (a proxy for precipitation variability) at millennial to orbital timescales, suggesting that hydrologic cycles were antiphased in the northerly versus southerly subtropics. This tropical to subtropical hydrologic phenomenon is likely to be an initial and important climatic response to orbital forcing. The impacts of such an interhemispheric hydrologic seesaw on higher-latitude regions and the global climate system, however, are unknown. Here we show that the antiphasing seen in the tropical records is also present in both hemispheres of the mid-latitude western Pacific Ocean. Our results are based on a new 550,000-year record of the growth frequency of speleothems from the Korean peninsula, which we compare to Southern Hemisphere equivalents. The Korean data are discontinuous and derived from 24 separate speleothems, but still allow the identification of periods of peak speleothem growth and, thus, precipitation. The clear hemispheric antiphasing indicates that the sphere of influence of the interhemispheric hydrologic seesaw over the past 550,000 years extended at least to the mid-latitudes, such as northeast Asia, and that orbital-timescale ITCZ shifts can have serious effects on temperate climate systems. Furthermore, our result implies that insolation-driven ITCZ dynamics may provoke water vapour and vegetation feedbacks in northern mid-latitude regions and could have regulated global climate conditions throughout the late Quaternary ice age cycles."

The linked Marino & Zahn (2015) reference (and first attached image) shows how Agulhas Leakage can interact with the AMOC to strengthen of 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

Extract: "The Agulhas Leakage is a key component of the Atlantic Meridional Overturning Circulation. Unraveling the past patterns of leakage variability and associated heat and salt anomalies into the Atlantic Ocean holds clues for their role in ocean and climate changes."


The next linked reference (with a free access pdf, & see the second attached image) indicates that the leakage of warm saline water from the Agulhas Current into the Atlantic Ocean (see attached image), 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

Abstract: "Future projections of climate suggest our planet is moving into a ‘super-interglacial’. Here we report a global synthesis of ice, marine and terrestrial data from a recent palaeoclimate equivalent, the Last Interglacial (ca. 130–116 ka ago). Our analysis suggests global temperatures were on average ∼1.5°C higher than today (relative to the AD 1961–1990 period). Intriguingly, we identify several Indian Ocean Last Interglacial sequences that suggest persistent early warming, consistent with leakage of warm, saline waters from the Agulhas Current into the Atlantic, intensifying meridional ocean circulation and increasing global temperatures. This mechanism may have played a significant positive feedback role during super-interglacials and could become increasingly important in the future. These results provide an important insight into a future 2°C climate stabilisation scenario."


The next linked reference documents the bipolar seesaw control during the last interglacial period:

G. Marino, E. J. Rohling, L. Rodríguez-Sanz, K. M. Grant, D. Heslop, A. P. Roberts, J. D. Stanford & J. Yu (11 June 2015), "Bipolar seesaw control on last interglacial sea level", Nature, Volume: 522, Pages: 197–201, doi:10.1038/nature14499


http://www.nature.com/nature/journal/v522/n7555/full/nature14499.html


Abstract: "Our current understanding of ocean–atmosphere–cryosphere interactions at ice-age terminations relies largely on assessments of the most recent (last) glacial–interglacial transition, Termination I (T-I). But the extent to which T-I is representative of previous terminations remains unclear. Testing the consistency of termination processes requires comparison of time series of critical climate parameters with detailed absolute and relative age control. However, such age control has been lacking for even the penultimate glacial termination (T-II), which culminated in a sea-level highstand during the last interglacial period that was several metres above present. Here we show that Heinrich Stadial 11 (HS11), a prominent North Atlantic cold episode, occurred between 135 ± 1 and 130 ± 2 thousand years ago and was linked with rapid sea-level rise during T-II. Our conclusions are based on new and existing6, data for T-II and the last interglacial that we collate onto a single, radiometrically constrained chronology. The HS11 cold episode punctuated T-II and coincided directly with a major deglacial meltwater pulse, which predominantly entered the North Atlantic Ocean and accounted for about 70 per cent of the glacial–interglacial sea-level rise. We conclude that, possibly in response to stronger insolation and CO2 forcing earlier in T-II, the relationship between climate and ice-volume changes differed fundamentally from that of T-I. In T-I, the major sea-level rise clearly post-dates Heinrich Stadial 1. We also find that HS11 coincided with sustained Antarctic warming, probably through a bipolar seesaw temperature response12, and propose that this heat gain at high southern latitudes promoted Antarctic ice-sheet melting that fuelled the last interglacial sea-level peak."


The last linked reference discusses how Antarctic ice mass loss during Meltwater Pulse 1A reduced Southern Ocean overturning (including the AMOC), thus contributing to warming

N. R. Golledge, L. Menviel, L. Carter, C. J. Fogwill, M. H. England, G. Cortese & R. H. Levy, (2014), "Antarctic contribution to meltwater pulse 1A from reduced Southern Ocean overturning", Nature Communications, 5, Article number: 5107, doi:10.1038/ncomms6107


http://www.nature.com/ncomms/2014/140929/ncomms6107/abs/ncomms6107.html


Abstract: "During the last glacial termination, the upwelling strength of the southern polar limb of the Atlantic Meridional Overturning Circulation varied, changing the ventilation and stratification of the high-latitude Southern Ocean. During the same period, at least two phases of abrupt global sea-level rise—meltwater pulses—took place. Although the timing and magnitude of these events have become better constrained, a causal link between ocean stratification, the meltwater pulses and accelerated ice loss from Antarctica has not been proven. Here we simulate Antarctic ice sheet evolution over the last 25 kyr using a data-constrained ice-sheet model forced by changes in Southern Ocean temperature from an Earth system model. Results reveal several episodes of accelerated ice-sheet recession, the largest being coincident with meltwater pulse 1A. This resulted from reduced Southern Ocean overturning following Heinrich Event 1, when warmer subsurface water thermally eroded grounded marine-based ice and instigated a positive feedback that further accelerated ice-sheet retreat."

Again, I note that all of this supports the Hansen et al 2015 findings.

Very best,
ASLR

Edit: Note that in the first attached image that when the Southern Ocean Subtropical Front moves northward (say by 2040 due to the initial of a main phase collapse of the WAIS) the Agulhas Leakage is reduced, which would help warm the North Atlantic (in a bipolar seesaw manner)
« Last Edit: August 08, 2015, 05:48:53 PM by AbruptSLR »
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #203 on: August 08, 2015, 05:13:26 PM »
Quote
it appears that climatic feature and length of MIS 11 are very similar to the present-future interglacial. This consideration may lead to the conclusion that actual interglacial period (begun 10 kyr) will continue for approximately 20-25 kyr"

Ruddiman 2008 and 2013 shows that the early human ag contributed significantly to global CO2.

without this early human influence on the global climate we would have moved into a new ice age sometime around 2,000 B.C.E.

see discussion here:  http://www.realclimate.org/index.php/archives/2015/04/a-scientific-debate/

jai,

Thanks.  I will try to me more careful when/what I copy and paste from Wikipedia, see original text at:

https://en.wikipedia.org/wiki/Marine_Isotope_Stage_11

Nevertheless, I believe that MIS 11 is a valuable case to consider, especially when calibrating ice sheet models like that used in the ACME program, or by Pollard et al.

See also:
http://forum.arctic-sea-ice.net/index.php/topic,852.0.html



jai,

After a little bit more thought, I believe that the point that the Wikipedia quote was making was not that the natural Holocene (without anthropogenic input) was comparable to the MIS 11 but rather that the current Anthropocene (with both natural and anthropogenic forcing) may be comparable to the MIS 11 peak particularly with regard to sea level (which as about 10m higher during MIS 11 than now) as it might that thousands of years (if we do not use geoengineering) to remove the CO2 levels that we will almost certainly reach by 2050, when making any reasonable set of assumptions for success of the CoP21 conference in Paris.

Best,
ASLR
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #204 on: August 08, 2015, 06:47:00 PM »
As we are just now entering the two to three decade long negative phase of the Atlantic Multidecadal Oscillation (AMO); the findings of the linked research that this negative phase will result in more intense El Nino events during this period, is bad news, as it increases the likelihood that the Amundsen Sea Embayment, and the Bellingshausen Sea, marine glaciers will initiate a main phase collapse by circa 2035-2040, as assumed by Hansen et al 2015:

Mi-Kyung Sung, Soon-Il An, Baek-Min Kim & Jong-Seong Kug (28 June 2015), "Asymmetric impact of Atlantic Multidecadal Oscillation on El Niño and La Niña characteristics", Geophysical Research Letters, Volume 42, Issue 12, Pages 4998–5004, DOI: 10.1002/2015GL064381

http://onlinelibrary.wiley.com/doi/10.1002/2015GL064381/abstract

Abstract: "The long-lasting cold surface conditions of North Atlantic, i.e., the negative phase of Atlantic Multidecadal Oscillation (AMO), can intensify the El Niño–Southern Oscillation through the enhanced air-sea coupling under the increased central-to-eastern tropical Pacific mean sea surface temperature. However, the impact of warmer mean sea surface temperature (SST) is more efficient in the intensifying El Niño than La Niña, because of the nature of the exponential growth of atmospheric convection to SST change. Moreover, the farther eastward shift of the atmospheric convection during the negative AMO leads to the stronger El Niño due to the longer delayed negative feedback by oceanic waves. Therefore, the AMO mainly influences the El Niño intensity rather than La Niña intensity."
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #205 on: August 08, 2015, 06:59:06 PM »
I imagine that evidence presented in this thread supporting Hansen et al 2015's warnings about the risk & consequences of a potential collapse of the WAIS, leaves many people wondering about the effectiveness of the use of stratospheric sulfate aerosols (a form of geoengineering) to counter these risks & consequences.  However, the linked reference indicates that injecting sulfate aerosols would not be effective in inhibiting a WAIS collapse; while in contrast, removing the anthropogenic GHGs would be effective:

K. E. McCusker, D. S. Battisti & C. M. Bitz (28 June 2015), "Inability of stratospheric sulfate aerosol injections to preserve the West Antarctic Ice Sheet", Geophysical Research Letters, Volume 42, Issue 12, Pages 4989–4997, DOI: 10.1002/2015GL064314


http://onlinelibrary.wiley.com/doi/10.1002/2015GL064314/abstract

Abstract: "Injection of sulfate aerosols into the stratosphere has the potential to reduce the climate impacts of global warming, including sea level rise (SLR). However, changes in atmospheric and oceanic circulation that can significantly influence the rate of basal melting of Antarctic marine ice shelves and the associated SLR have not previously been considered. Here we use a fully coupled global climate model to investigate whether rapidly increasing stratospheric sulfate aerosol concentrations after a period of global warming could preserve Antarctic ice sheets by cooling subsurface ocean temperatures. We contrast this climate engineering method with an alternative strategy in which all greenhouse gases (GHG) are returned to preindustrial levels. We find that the rapid addition of a stratospheric aerosol layer does not effectively counteract surface and upper level atmospheric circulation changes caused by increasing GHGs, resulting in continued upwelling of warm water in proximity of ice shelves, especially in the vicinity of the already unstable Pine Island Glacier in West Antarctica. By contrast, removal of GHGs restores the circulation, yielding relatively cooler subsurface ocean temperatures to better preserve West Antarctica."
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #206 on: August 08, 2015, 07:19:33 PM »
In addition to the current positive phase of the PDO and the negative phase of the AMO; both of which contribute to strong El Nino events; the linked reference indicates that anthropogenic global warming also contributes to the increased frequency of Super El Nino events; all of which not only increase these risks of WAIS collapse, but also of increased mean global surface temperatures, in the coming decades:

Mojib Latif, Vladimir A. Semenov & Wonsun Park (June 2015), "Super El Niños in response to global warming in a climate model", Climatic Change, DOI 10.1007/s10584-015-1439-6

http://rd.springer.com/article/10.1007%2Fs10584-015-1439-6

Abstract: "Extraordinarily strong El Niño events, such as those of 1982/1983 and 1997/1998, cause havoc with weather around the world, adversely influence terrestrial and marine ecosystems in a number of regions and have major socio-economic impacts. Here we show by means of climate model integrations that El Niño events may be boosted by global warming. An important factor causing El Niño intensification is warming of the western Pacific warm pool, which strongly enhances surface zonal wind sensitivity to eastern equatorial Pacific sea surface temperature anomalies. This in conjunction with larger and more zonally asymmetric equatorial Pacific upper ocean heat content supports stronger and longer lasting El Niños. The most intense events, termed Super El Niños, drive extraordinary global teleconnections which are associated with exceptional surface air temperature and rainfall anomalies over many land areas."
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #207 on: August 08, 2015, 07:55:56 PM »
Hansen has previously assumed that evidence from the last glacial maximum, LGM, effectively constrained the equilibrium climate sensitivity (ECS) to approximately 3C.  However, the linked (open access) paper shows that CMIP5 cannot constrain ECS to approximately 3C; as the changes in the tropical surface air temperature (especially the tropical Pacific) with future warming could support relative high values of ECS (see especially the third attached image).  Thus even Hansen et al 2015 could be engaging in incomplete (or wishful) thinking:

Peter O. Hopcroft & Paul J. Valdes (July 16, 2015), "How well do simulated last glacial maximum tropical temperatures constrain equilibrium climate sensitivity?", Geophysical Research Letters, Volume 42, Issue 13, Pages 5533–5539, DOI: 10.1002/2015GL064903

http://onlinelibrary.wiley.com/doi/10.1002/2015GL064903/abstract
http://onlinelibrary.wiley.com/doi/10.1002/2015GL064903/full

For the key support material, see:

http://onlinelibrary.wiley.com/store/10.1002/2015GL064903/asset/supinfo/grl53123-sup-0001-documentS1.pdf?v=1&s=57211311f2b41c4fa1d4dd61e37d7110b6c6b4f7

Abstract: "Previous work demonstrated a significant correlation between tropical surface air temperature and equilibrium climate sensitivity (ECS) in PMIP (Paleoclimate Modelling Intercomparison Project) phase 2 model simulations of the last glacial maximum (LGM). This implies that reconstructed LGM cooling in this region could provide information about the climate system ECS value. We analyze results from new simulations of the LGM performed as part of Coupled Model Intercomparison Project (CMIP5) and PMIP phase 3. These results show no consistent relationship between the LGM tropical cooling and ECS. A radiative forcing and feedback analysis shows that a number of factors are responsible for this decoupling, some of which are related to vegetation and aerosol feedbacks. While several of the processes identified are LGM specific and do not impact on elevated CO2 simulations, this analysis demonstrates one area where the newer CMIP5 models behave in a qualitatively different manner compared with the older ensemble. The results imply that so-called Earth System components such as vegetation and aerosols can have a significant impact on the climate response in LGM simulations, and this should be taken into account in future analyses."


Extract: "… simulations with these same models conducted as part of CMIP5 shows a strong relationship between ECS and tropical warming…

The correlation between ECS and tropical temperature changes is positive in both the RCP8.5 and abrupt4×CO2 simulations (see supporting information Figure S1). The abrupt4×CO2 output shows relatively little change in global vegetation distributions in the CMIP5 models which include dynamic vegetation, while the changes in aerosol loading are smaller than those simulated for the LGM in these models."

Note that Figure S1 is the third attached image.

Caption for first image: "The relationship between ECS and tropical lgm-piControl temperature anomalies (ΔTtrop) for PMIP2 and CMIP5-PMIP3 ensembles of LGM and preindustrial simulations. The correlation for eight PMIP2 models is −0.8 and is +0.1 for nine PMIP3 simulations. The linear regression of the PMIP2 models is shown by the black line."

Caption for second image: "Short-wave cloud radiative feedbacks in PMIP2, PMIP3, and abrupt4×CO2 simulations. The SW cloud feedback is calculated using the approximate partial radiative perturbation method [Taylor et al., 2007] and is normalized by the simulated surface temperature change averaged over the same region. The linear regression of the PMIP2 models is shown by the black line."
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jai mitchell

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #208 on: August 08, 2015, 08:06:59 PM »


Nevertheless, I believe that MIS 11 is a valuable case to consider, especially when calibrating ice sheet models like that used in the ACME program, or by Pollard et al.

See also:
http://forum.arctic-sea-ice.net/index.php/topic,852.0.html

I agree, I am not criticizing but rather clarifying as best I can the awesome work that is being put up here. 

One question that is not clear in my mind is the ice dynamic effects of the global GHG forcing and how very different this global effect is when compared to previous interglacials.  Among many stark differences between the two a primary one in my mind is the Milankovitch cycle driven (and Meridional Overturning Circulation driven) "seesaw" effect. 

It seems to me that the NH/SH warming/cooling seesaw may have significant impact differences when compared to a total global warming event.  I suspect that Hansen et al have a good handle on this and that this is why their predictions break away from previous work that relied on the Paleo MIS-5a and MIS-11 analogues.
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #209 on: August 08, 2015, 08:37:36 PM »


Nevertheless, I believe that MIS 11 is a valuable case to consider, especially when calibrating ice sheet models like that used in the ACME program, or by Pollard et al.

See also:
http://forum.arctic-sea-ice.net/index.php/topic,852.0.html

I agree, I am not criticizing but rather clarifying as best I can the awesome work that is being put up here. 

One question that is not clear in my mind is the ice dynamic effects of the global GHG forcing and how very different this global effect is when compared to previous interglacials.  Among many stark differences between the two a primary one in my mind is the Milankovitch cycle driven (and Meridional Overturning Circulation driven) "seesaw" effect. 

It seems to me that the NH/SH warming/cooling seesaw may have significant impact differences when compared to a total global warming event.  I suspect that Hansen et al have a good handle on this and that this is why their predictions break away from previous work that relied on the Paleo MIS-5a and MIS-11 analogues.

jai,

I concur that Hansen et al 2015 model results seem to have a better handle on the potentially abrupt NH/SH seesaw effect associated with potential ice sheet collapse than many/any earlier model results; or that of analogies to paleo cases that were subjected to much different (much less intense) forcing pathways.  Hopefully, global decision makers will be able to see the writing on the wall and take some action; as I am concerned that even programs like ACME by 2024 will still not be able to represent the full risks of abrupt climate change.

I guess that we will all see together.

Best,
ASLR
« Last Edit: August 09, 2015, 08:03:52 PM by AbruptSLR »
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #210 on: August 09, 2015, 01:08:06 AM »
So far in this thread I have mostly posted reasons supporting the idea that the ASE marine glacier may start to experience main phase collapse (characterized by cliff failures and hydrofracturing); so in this post, I provide some reasons supporting the idea that by the 2060-2070 timeframe both the Filchner-Ronne Ice Shelf, FRIS, and the Ross Ice Shelf, will break-up sufficiently to start rapidly accelerating the marine glaciers in the Weddell, and Ross, Sea Sectors. In brief, I suspect that:

(1) A "horizontal" advective cell (driven by a salinity gradient of the fresh sub-ice-shelf meltwater and the inflowing CDW through the Filchner Trough) has already been established beneath the FRIS and is (or will be) reinforced by: (a) an increasing volume and temperature of the CDW within a warm tongue of current feeding from the ACC through the Weddell Gyre current; (b) increasing volumes of sub-ice-shelf ice meltwater; (c) decreasing production of AABW; and after 2060, (d) a rapid decline in Antarctic sea ice area, causing both: (i) wind shear to blow more warm CDW into the Filchner Trough (FT) [see the first and second attached images]; and (ii) an associated increase in surface temperatures.  The establishment of this "horizontal" advective cell (pumping water from the northeastern edge of the FRIS through the FT to the northwestern edge of the FRIS) was facilitated early by interactions between the Antarctic Peninsula & SAM (temporally/periodically disrupting the "protective" sub-ice-shelf circulation pattern) and an intrusion of a warm CDW current from the north.

(2)  A weaker "horizontal" advective cell will be established for RIS [see the third attached image] after 2050 when the ice shelf face has retreated sufficiently (through calving) in order to direct a warm CDW current (allowed to form when the Getz iceshelf melting slows) towards the Byrd Glacier which will drive as side branch of the warm CDW towards the grounding line of the RIS along the Siple Coast, and then out throught the northeast edge of RIS as a cold current.

(3) In both cases between 2060 and 2070 melt pond mechanisms [see the fourth attached image] may likely lead to the rapid collapse of most of both of the two ice shelves.
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #211 on: August 09, 2015, 12:32:12 PM »
The linked reference indicates that Transient Climate Response to cumulative Emissions (TCRE) varies with the rate of radiative forcing, and finds that:

"TCRE has a complex relationship with emission rates; TCRE is largest for both low (2 GtC/yr) and high (25 GtC/yr) emissions and smallest for present-day emissions (5–10 GtC/yr)."


Krasting, J. P., J. P. Dunne, E. Shevliakova, and R. J. Stouffer (2014), "Trajectory sensitivity of the transient climate response to cumulative carbon emissions", Geophys. Res. Lett., 41, 2520–2527, doi:10.1002/2013GL059141.

http://onlinelibrary.wiley.com/doi/10.1002/2013GL059141/abstract

Abstract: "The robustness of Transient Climate Response to cumulative Emissions (TCRE) is tested using an Earth System Model (Geophysical Fluid Dynamics Laboratory-ESM2G) forced with seven different constant rates of carbon emissions (2 GtC/yr to 25 GtC/yr), including low emission rates that have been largely unexplored in previous studies. We find the range of TCRE resulting from varying emission pathways to be 0.76 to 1.04°C/TtC. This range, however, is small compared to the uncertainty resulting from varying model physics across the Fifth Coupled Model Intercomparison Project ensemble. TCRE has a complex relationship with emission rates; TCRE is largest for both low (2 GtC/yr) and high (25 GtC/yr) emissions and smallest for present-day emissions (5–10 GtC/yr). Unforced climate variability hinders precise estimates of TCRE for periods shorter than 50 years for emission rates near or smaller than present day values. Even if carbon emissions would stop, the prior emissions pathways will affect the future climate responses."

As fossil fuel emissions are estimated to be about 10.1 GtC yr-1 in 2014, we have now entered the range of increasing TCRE, and that does not consider the influence of the likely acceleration of carbon-cycle emissions with continued global warming.
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #212 on: August 09, 2015, 06:48:05 PM »
This multi-part post shows how Rignot et al 2015's findings (see first linked paper) about the great of Greenland's marine-terminating glaciers contributing sooner to SLR, highlights the need for greater physical investigation [see the OMG program links below) and numerical investigation (note the discussion about the ACME involvement (see William Lipscomb's comments) and the Naval Postgraduate School in Monterey, California].  While in general terms Greenland's ice sheet is more stable than Antarctica's ice sheets; nevertheless, Greenland's marine-terminating glaciers are particularly susceptible to early ice mass loss due to ocean interaction due to the newly recognized depth of the fjords that these marine-terminating glacier occupy.
Furthermore, I find it particularly plausible that a pulse of meltwater from the Greenland marine-terminating glaciers (say in ten, to twenty, years) could help trigger (edit: say both sending a gravitational pulse through the Global MOC via the bipolar seesaw, and by pulsing up the local Antarctic sea level by a few extra millimeters) the marine phase collapse of the Amundsen Sea Embayment, ASE, marine glaciers starting around 2035.

Eric Rignot, Ian Fenty, Yun Xu, Cilan Cai & Chris Kemp (28 July 2015), "Undercutting of marine-terminating glaciers in West Greenland", Geophysical Research Letters, Volume 42, Issue 14
Pages 5909–5917, DOI: 10.1002/2015GL064236


http://onlinelibrary.wiley.com/doi/10.1002/2015GL064236/abstract

Abstract: "Marine-terminating glaciers control most of Greenland's ice discharge into the ocean, but little is known about the geometry of their frontal regions. Here we use side-looking, multibeam echo sounding observations to reveal that their frontal ice cliffs are grounded deeper below sea level than previously measured and their ice faces are neither vertical nor smooth but often undercut by the ocean and rough. Deep glacier grounding enables contact with subsurface, warm, salty Atlantic waters (AW) which melts ice at rates of meters per day. We detect cavities undercutting the base of the calving faces at the sites of subglacial water (SGW) discharge predicted by a hydrological model. The observed pattern of undercutting is consistent with numerical simulations of ice melt in which buoyant plumes of SGW transport warm AW to the ice faces. Glacier undercutting likely enhances iceberg calving, impacting ice front stability and, in turn, the glacier mass balance."

The next series of links discuss the Oceans Melting Greenland (OMG) mission.  Josh Willis of NASA will lead the OMG mission to explore the risk associated with the oceans contributing ice melting in Greenland and to pave the way for improved SLR estimates.


http://science.nasa.gov/missions/omg/

Summary: "Global sea level rise will be one of the major environmental challenges of the 21st Century. Oceans Melting Greenland (OMG) will pave the way for improved estimates of sea level rise by addressing the question:  To what extent are the oceans melting Greenland’s ice from below? Over a five-year campaign, OMG will observe changing water temperatures on the continental shelf surrounding Greenland, and how marine glaciers react to the presence of warm, salty Atlantic Water. The complicated geometry of the sea floor steers currents on the shelf and often determines whether Atlantic Water can reach into the long narrow fjords and interact with the coastal glaciers. Because knowledge of these pathways is a critical component of modeling the interaction between the oceans and ice sheet, OMG will facilitate improved measurements of the shape and depth of the sea floor in key regions as well.
OMG will use NASA’s G-III to fly the Glacier and Ice Surface Topography Interferometer (GLISTIN) in order to generate high resolution, high precision elevation measurements of Greenland’s coastal glaciers during the spring. Annual surveys by GLISTIN will measure glacier thinning and retreat over the preceding season. A second aircraft, the NASA S-3, will be deployed each year to release over 200 expendable temperature and salinity probes along the continental shelf to measure the volume, extent, of warm, salty Atlantic Water. These data, along with fundamental new and critical observations of airborne marine gravity and ship-based observations of the sea floor geometry will provide a revolutionary data set for modeling ocean/ice interactions and lead to improved estimates of global sea level rise.
Beyond addressing the scientific questions on Greenland posed by the 2007 NASA Earth Science Decadal Survey, the campaign will provide observations connected to the overall NASA Earth Science Question from the NASA 2010 Science Plan: How is the Earth changing and what are the consequences for life on Earth? It will also directly address 3 of the 4 sub-components of this question (Characterize, Understand and Predict changes in the Earth system).Jet Propulsion Laboratory(JPL) is a Federally Funded Research and Development Center (FFRDC) managed and operated by Caltech under a contract from NASA."

Jeff Tollefson ((30 July 2015), "NASA launches mission to Greenland - Ship and planes will probe water–ice interface in fjords", Nature, Volume: 523, Pages: 510–511, doi:10.1038/523510a


http://www.nature.com/news/nasa-launches-mission-to-greenland-1.18085

Extract: "Called Oceans Melting Greenland (OMG), the US$30-million NASA project will help scientists to predict the future of the Greenland ice sheet …

When simulating glacier dynamics, current global climate models consider only ice’s interactions with the atmosphere, says William Lipscomb, an ice modeller at Los Alamos National Laboratory in New Mexico. He is working to incorporate ice–ocean inter¬actions around Antarctica into a climate model being developed by the US Department of Energy. But in Greenland, the intricately carved coastline makes this much more difficult. The department plans to give researchers at the Naval Postgraduate School in Monterey, California, $466,000 over 2 years to build a detailed model that will link the land ice and oceans around Greenland. OMG data will help to validate that model, says project leader Frank Giraldo.

Work by OMG participant Eric Rignot, a glaciologist at the University of California, Irvine, underscores the importance of detailed data….
..
When the aerial phase of OMG begins next year, planes will fly inland from the coast, taking measurements of slight changes in gravitational pull that can be used to produce low-resolution maps of the topography under both water and ice. Planes will also drop more than 200 temperature and salinity probes into fjords and coastal waters, and take radar measurements along the coast to track large-scale ice loss over five years. Analysing that ice loss in light of the new topographical and oceanographic data will help researchers to determine where, and to what extent, deeper saltwater currents affect glaciers.
Lipscomb says that all these OMG data should help modellers as they incorporate ocean–ice interactions around Greenland into their models. That work is still in its early stages, he says, “but the data that they are getting in this project is exactly what we need”."



Also see:
http://www.theguardian.com/environment/2015/aug/09/omg-nasa-project-oceans-melting-greenland

Extract: "According to a recent report, scientists who studied three particularly important fjords found that existing maps underestimate their depths by several hundred metres. In addition they found that glaciers flowing into these fjords were also doing so to a far greater depth than had previously been estimated and could reach the warm, salty layer of water that flows up from the Atlantic. This would make those glaciers more vulnerable to melting than had been previously anticipated. “With OMG, we are going to reveal the depth of those fjords,” project scientist Eric Rignot, a glaciologist at the University of California Irvine, told Nature."

« Last Edit: August 09, 2015, 08:08:24 PM by AbruptSLR »
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #213 on: August 10, 2015, 05:08:23 AM »
In Reply #128 I briefly referred to an image of key active and inactive subglacial volcanoes in West Antarctica; and while in Reply #199 I cited evidence of the thin crust and low viscosity of the magma beneath the WAIS (and in particular beneath the Byrd Subglacial Basin, BSB); and in this post I add some additional discussion about the tectonic risks associated with abrupt ice mass loss in the WAIS.

The first linked reference (Compton et al 2015, and associated trailing linked articles) cites research in Iceland indicates the glacial ice mass loss there has resulted in an isostatic rebound rate of more than 30mm/yr, and has contributed to an increase in volcanic activity. Furthermore, Alley has pointed out that paleo occurrences of episodic ice mass loss from the BSB has contributed to the past volcanic activity in this area, and the second linked reference (Adhikari et al 2014) points out that the current isostatic rebound rate at the Pine Island Bay is already about 45 mm/yr.

The third (Schroeder et al 2014) and fourth (Damiani et al 2014) references both discuss the unusually high geotechnical heat flux at bed of the WAIS (& in particular of the BSB), see the attached images; which also contributes to unusually high basal ice melt rates, relatively low basal ice viscosities and also promotes advection of warm CDW at the grounding line of the Thwaites Ice Tongue (which is collapsing faster than previously expected by researchers.

Taken holistically with the other points presented in this thread and by Hansen et al 2015; this information adds to the increasingly compelling assessment of the risks and consequences of abrupt ice sheet mass loss, this century:


Kathleen Compton, Richard A. Bennett & Sigrún Hreinsdóttir (16 February 2015), "Climate-driven vertical acceleration of Icelandic crust measured by continuous GPS geodesy", Geophysical Research Letters, Volume 42, Issue 3, Pages 743–750, DOI: 10.1002/2014GL062446


http://onlinelibrary.wiley.com/doi/10.1002/2014GL062446/abstract

Abstract: "Earth's present-day response to enhanced glacial melting resulting from climate change can be measured using Global Positioning System (GPS) technology. We present data from 62 continuously operating GPS instruments in Iceland. Statistically significant upward velocity and accelerations are recorded at 27 GPS stations, predominantly located in the Central Highlands region of Iceland, where present-day thinning of the Iceland ice caps results in velocities of more than 30 mm/yr and uplift accelerations of 1–2 mm/yr2. We use our acceleration estimates to back calculate to a time of zero velocity, which coincides with the initiation of ice loss in Iceland from ice mass balance calculations and Arctic warming trends. We show, through a simple inversion, a direct relationship between ice mass balance measurements and vertical position and show that accelerated unloading is required to reproduce uplift observations for a simple elastic layer over viscoelastic half-space model."


See also:
http://www.icenews.is/2015/08/08/iceland-volcanic-eruptions-could-be-a-consequence-of-melting-glaciers/
and

http://time.com/3687893/volcanoes-climate-change/

Quote: “As the glaciers melt, the pressure on the underlying rocks decreases,” Compton said in an e-mail to TIME. “Rocks at very high temperatures may stay in their solid phase if the pressure is high enough. As you reduce the pressure, you effectively lower the melting temperature.” The result is a softer, more molten subsurface, which increases the amount of eruptive material lying around and makes it easier for more deeply buried magma chambers to escape their confinement and blow the whole mess through the surface.
“High heat content at lower pressure creates an environment prone to melting these rising mantle rocks, which provides magma to the volcanic systems,…”

S. Adhikari, E. Ivins, E. Larour, H. Seroussi, M. Morlighem, and S. Nowicki, (2014), "Future Antarctic bed topography and its implications for ice sheet dynamics", Solid Earth Discuss., 6, 191–228, 2014, www.solid-earth-discuss.net/6/191/2014/; doi:10.5194/sed-6-191-2014

http://www.solid-earth-discuss.net/6/191/2014/sed-6-191-2014-print.pdf

Abstract: "The Antarctic bedrock is evolving as the solid Earth responds to the past and ongoing evolution of the ice sheet. A recently improved ice loading history suggests that the Antarctic Ice Sheet (AIS) is generally losing its mass since the last glacial maximum (LGM). In a sustained warming climate, the AIS is predicted to retreat at a greater pace primarily via melting beneath the ice shelves. We employ the glacial isostatic adjustment (GIA) capability of the Ice Sheet System Model (ISSM) to combine these past and future ice loadings and provide the new solid Earth computations for the AIS. We find that the past loading is relatively less important than future loading on the evolution of the future bed topography. Our computations predict that the West Antarctic Ice Sheet (WAIS) may uplift by a few meters and a few tens of meters at years 2100 and 2500AD, respectively, and that the East Antarctic Ice Sheet (EAIS) is likely to remain unchanged or subside minimally except around the Amery Ice Shelf.  The Amundsen Sea Sector in particular is predicted to rise at the greatest rate; one hundred years of ice evolution in this region, for example, predicts that the coastline of Pine Island Bay approaches roughly 45mmyr−1 in viscoelastic vertical motion. Of particular importance, we systematically demonstrate that the effect of a pervasive and large GIA uplift in the WAIS is associated with the flattening of reverse bed, reduction of local sea depth, and thus the extension of grounding line (GL) towards the continental shelf. Using the 3-D higher-order ice flow capability of ISSM, such a migration of GL is shown to inhibit the ice flow. This negative feedback between the ice sheet and the solid Earth may promote the stability to marine portions of the ice sheet in future."


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

http://www.pnas.org/content/111/25/9070.full.pdf

Theresa M. Damiani, Tom A. Jordan, Fausto Ferraccioli, Duncan A. Young, and Donald D. Blankenship, (2014), "Variable crustal thickness beneath Thwaites Glacier revealed from airborne gravimetry, possible implications for geothermal heat flux in West Antarctica", Earth and Planetary Science Letters Volume 407, 1, Pages 109–122, DOI: 10.1016/j.epsl.2014.09.023

http://www.sciencedirect.com/science/article/pii/S0012821X14005780


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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #214 on: August 10, 2015, 04:07:38 PM »
Rignot 2015 mentioned in #212 is really quite the landmark paper on ocean-glacier interaction in Greenland. Unfortunately paywalled, it is highly relevant to many issues we discuss on these forums.

First off, ship sonar showed newly compiled IBCAO bathymetry was way off the mark in intra-coastal fjords. These were overdeepened by paleo-glaciation several hundred meters beyond IBCAO in some instances, meaning more than deep enough for warm 'Atlantic Water' to reach the bases of marine-terminating glaciers today.

This water is significant not so much for slow passive melting of the underwater portion of the calving front but rather for rapid melting just above bedrock where accumulated inland surface meltwater exits from its conduits. That meltwater, being fresh, is buoyant relative to seawater and creates a turbulent (and turbid) plume rising to the surface, entraining warm Atlantic Water to move across the ice surface.

Moving water is much more effective at heat transfer than a stagnant film the same temperature as the ice. (Put a block of ice in the kitchen sink filled with cold water and watch the ice sit there overnight. Repeat, turning the faucet on so cold water falls directly on the block, the ice is gone in twenty minutes.)

The net effect of hollowing out the base of the calving front at depth, leaving the tremendous weight of calving front ice perched above these caverns unsupported. The Rignot group was able to image the actual undercut geometry of the face of the calving front for three outlet glaciers north of Jakobshavn, namely Store, Rink and Kangilernata.

Greenland glaciers have to be analyzed one at a time (unbeknownst to armchair modelers). Here bathymetry and face geometry of nearby Eqip Sermia, Sermilik and Perdlerfiup Sermia showed these glaciers are grounded at the end of deep fjords but sit on shallow plateaus of ~ 100 m depth meaning the calving front at bedrock is submerged in cold fresh Pacific Water rather warm salty Atlantic Water and so are not subjected to the same effect from emergent meltwater plumes.

They did not provide killer graphics to illustrate their point so there is a great opportunity here for Andy Lee Robinson or others.

Perhaps surprisingly, the massively hollowed out calving fronts of Store and Rink are not retreating -- Store for example hasn't budged since 1948. That's because the intrinisic forward speed of these glaciers is driven by the gravitational force acting on them from the summit ridge on down, as retarded by bedrock resistance and cold rheology. There is little buttressing at the calving front from winter melange so its disappearance doesn't matter.

They address a perennial confusion on our forums: sea water cannot force its way under grounded glaciers  -- here 350 to 980 m below sea level at the calving front -- when the ice overburden hydrostatic pressure is greater than the seawater pressure. Indeed meltwater under greater pressure fire-hoses out into the sea water, not vice versa (sea water squirting out moulins).

However stasis won't continue under rapid climate change because meltwater will surge to unprecedented volume and velocity later in the season, greatly exacerbating melt at the exit conduits and so calving (first graphic). However the glaciers may also speed up, leaving the net effect on calving front uncertain. The real issue for sea level rise is volume calved (rather, SMB); calving front position is not a reliable proxy for that.

Indeed the authors conclude "the sensitivity of Greenland glaciers to ocean warming and enhanced ice sheet runoff may have been underestimated and projections of sea level rise from the Greenland Ice Sheet will need to be revised upward."

Quote
This mechanism differs from ice melt at the water line for lake-terminating glaciers, the buoyant flexure and fracture of semi-floating sections at tidewater margins, the viscous bending of ice shelf fronts caused by vertical differences between hydrostatic and seawater pressure or the fracturing of ice by tensile stresses and water propagating down cracks.

Undercutting will alter the stress regime of the glacier front compared to that of a vertical face because it increases its bending moment. Bending and cracking are likely to operate on relatively short timescales (days to weeks) because melt is measured in meters per day, whereas the viscous bending of ice operates on monthly time scales for a 400 m thick ice slab at −8∘C [see Benn 2007,  James 2014, Reeh, 1968]

Fig. 4 legend: Ice melt rate in meter per day for a 150 m wide × 800 m high vertical face vs depth below the sea level for thermal forcing of 4ºC, and one subglacial water  channel 1 m in height with a flow speed of 0.5 m/s (and various variations). The thin line  averages over the entire face; the thick line is only above the SGW channel itself.
« Last Edit: August 10, 2015, 05:24:35 PM by A-Team »

AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #215 on: August 10, 2015, 04:37:06 PM »
In the first linked reference Schuur et al 2015 (and the immediate following associated linked PowerPoint presentation) focus on the mean CO2 emissions and in the first attached image cite an mean estimate of about 130 to 160 Pg cummulative carbon emissions from permafrost degradation by 2100 (which would need to be added to the Anthropogenic emissions to see which RCP pathway we follow).  However, Schuur et al 2015 acknowledge that they may well be underestimating the methane emissions from such sources a abrupt thermokarst response (and/or from hydrates), as discussed in the second linked reference by von Deimling et al 2015, where the risk of abrupt methane emissions by 2050 is highlighted in the second attached image.

With carbon-cycle accelerated GHG emission scenarios such as these, it will be difficult to get off RCP scenarios leading to abrupt ice sheet mass loss:
 

Schuur, E. A. G. et al. (2015), "Climate change and the permafrost carbon feedback", Nature, 520, 171–179; doi:10.1038/nature14338

http://www.nature.com/nature/journal/v520/n7546/full/nature14338.html

Abstract: "Large quantities of organic carbon are stored in frozen soils (permafrost) within Arctic and sub-Arctic regions. A warming climate can induce environmental changes that accelerate the microbial breakdown of organic carbon and the release of the greenhouse gases carbon dioxide and methane. This feedback can accelerate climate change, but the magnitude and timing of greenhouse gas emission from these regions and their impact on climate change remain uncertain. Here we find that current evidence suggests a gradual and prolonged release of greenhouse gas emissions in a warming climate and present a research strategy with which to target poorly understood aspects of permafrost carbon dynamics.

Also see:
http://www.lter.uaf.edu/symposium_2015/F0830_BNZsymposium2015_Schuur.pdf



Schneider von Deimling, T., Grosse, G., Strauss, J., Schirrmeister, L., Morgenstern, A., Schaphoff, S., Meinshausen, M., and Boike, J.: Observation-based modelling of permafrost carbon fluxes with accounting for deep carbon deposits and thermokarst activity, Biogeosciences, 12, 3469-3488, doi:10.5194/bg-12-3469-2015, 2015.

http://www.biogeosciences.net/12/3469/2015/bg-12-3469-2015.html

Abstract. High-latitude soils store vast amounts of perennially frozen and therefore inert organic matter. With rising global temperatures and consequent permafrost degradation, a part of this carbon stock will become available for microbial decay and eventual release to the atmosphere. We have developed a simplified, two-dimensional multi-pool model to estimate the strength and timing of future carbon dioxide (CO2) and methane (CH4) fluxes from newly thawed permafrost carbon (i.e. carbon thawed when temperatures rise above pre-industrial levels). We have especially simulated carbon release from deep deposits in Yedoma regions by describing abrupt thaw under newly formed thermokarst lakes. The computational efficiency of our model allowed us to run large, multi-centennial ensembles under various scenarios of future warming to express uncertainty inherent to simulations of the permafrost carbon feedback.

Under moderate warming of the representative concentration pathway (RCP) 2.6 scenario, cumulated CO2 fluxes from newly thawed permafrost carbon amount to 20 to 58 petagrams of carbon (Pg-C) (68% range) by the year 2100 and reach 40 to 98 Pg-C in 2300. The much larger permafrost degradation under strong warming (RCP8.5) results in cumulated CO2 release of 42 to 141 Pg-C and 157 to 313 Pg-C (68% ranges) in the years 2100 and 2300, respectively. Our estimates only consider fluxes from newly thawed permafrost, not from soils already part of the seasonally thawed active layer under pre-industrial climate. Our simulated CH4 fluxes contribute a few percent to total permafrost carbon release yet they can cause up to 40% of total permafrost-affected radiative forcing in the 21st century (upper 68% range). We infer largest CH4 emission rates of about 50 Tg-CH4 per year around the middle of the 21st century when simulated thermokarst lake extent is at its maximum and when abrupt thaw under thermokarst lakes is taken into account. CH4 release from newly thawed carbon in wetland-affected deposits is only discernible in the 22nd and 23rd century because of the absence of abrupt thaw processes. We further show that release from organic matter stored in deep deposits of Yedoma regions crucially affects our simulated circumpolar CH4 fluxes. The additional warming through the release from newly thawed permafrost carbon proved only slightly dependent on the pathway of anthropogenic emission and amounts to about 0.03–0.14 °C (68% ranges) by end of the century. The warming increased further in the 22nd and 23rd century and was most pronounced under the RCP6.0 scenario, adding 0.16 to 0.39 °C (68% range) to simulated global mean surface air temperatures in the year 2300.
« Last Edit: August 10, 2015, 05:14:47 PM by AbruptSLR »
“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 #216 on: August 10, 2015, 05:08:43 PM »
Just to let ye know, Jim Hansen is doing a Q&A on reddit.com/r/science on Wednesday. I'll post a link to it when it's live.

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #217 on: August 10, 2015, 06:50:14 PM »
There are so many goodies left in the Rignot 2015 article that I wanted to pass a bit more along. Rignot has also worked extensively on Antarctic glaciers and as co-author of the Hansen paper would have ensured that article reflected current understanding ("SLR will be faster than IPCC says") on those and West Greenland glaciers. The Hansen article thus does not put a one-year moratorium on data that it will consider (like IPCC) and so will have a longer shelf life.

Store Gletscher flows into a 6 km wide, 850 m deep, steep-walled fjord at 9 meters per day at the calving front, the fifth fastest speed in Greenland. It drains roughly  2% of Greenland (30,466 km2) with a balance discharge of 8.7 Gt/yr and an ice discharge of 11.0 Gt/yr over 2008–2011 only marginally higher (10%) than in 1992. The flat bottom profile of Ikerasak fjord (ie not U-shaped) can be attributed to extensive sedimentary deposits: rain-out of fine-grained debris in turbid meltwater rather than old glacial moraines. The fjord overdeepens to 1400 m in the west which is nearly a mile below sea level. A few rocky mounds emerge from the sediments.

There’s a remarkable submarine channel (50 m deep by 300 wide and 30 km in length) that the authors attribute to turbidity current erosion (downslope flow of dense  sediment-rich water), drawing on the detailed paleo-geology perspective provided in Dowdeswell  2014 [free full https://dspace.lboro.ac.uk/dspace-jspui/bitstream/2134/17834/3/1-s2.0-S0277379113003430-main.pdf]. This channel then does not have the same basis as the so-called Grand Canyon exiting by Petermann; the ice shelf bathymetery there is not known in detail but is being investigated this very month.

A sedimentary wedge occurs to the side of where buoyant meltwater emerges at the base of the calving front. Here again see Dowdeswell for how to interpret sonar features in regions of advancing and retreating glaciers; this will be applicable to new results from Petermann as well.

The glacier front is grounded on a two km long sill plateau at 560 m depth that spans the entire width of the glacier without dipping to the side. In 2013, the ice front at Store extended 420 m seaward of the 2012 position with ice floating ~30 m above the seafloor vs a grounded ice front in 2012 —a small floating section can form at the glacier center at the edge of the sill plateau. This configuration would stabilize the glacier front itself because floating tongues lack support from glacier sides and therefore break up rapidly from buoyancy forces, as discussed in TD James 2014 “Buoyant flexure and basal crevassing in dynamic mass loss at Helheim Glacier”, paywalled. Store Glacier is thus quite relevant to future behavior of certain Antarctic glaciers.

The deepest zones of undercutting of the Store Glacier ice fron are found where meltwater emerges. Some 73% of the ice front is undercut on average by 100 m, with a maximum of 350 m. Undercutting amounts to 30% of glacier depth and is three times larger than at Kangilernata.

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #218 on: August 10, 2015, 07:22:19 PM »
Talking of Store, some people may find some of this of use:
http://www.bbc.co.uk/programmes/p00tvcnx/clips

The programme was pushed in a slightly hyperbolic way, but if you ignore that there is/was some interesting stuff in the programme one that's related to A-Team's post above (there was discussion of the undercutting and calving, as well as the melt water channels), as well as off-topic stuff. Programme two was about one of the Petermann bergs, so whilst interesting to watch, very off-topic in this thread.

If this post is considered too OT, please move it... :)

AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #219 on: August 10, 2015, 08:42:26 PM »
Moving water is much more effective at heat transfer than a stagnant film the same temperature as the ice. (Put a block of ice in the kitchen sink filled with cold water and watch the ice sit there overnight. Repeat, turning the faucet on so cold water falls directly on the block, the ice is gone in twenty minutes.)

Obviously, bathymetry & ice is half of the Oceans Melting Greenland, OMG, story, while the linked reference discusses the ocean half of this story, the attached image showing relatively high ocean water temperatures at depth that can actively melt marine glacial ice provided that there is sufficient advection within a given fjord to circulate the water.  I image that the Monterey Naval Academy and the ACME project with be looking at this question very closely:

Andreas Münchow, Kelly K. Falkner & Humfrey Melling (2015), "Baffin Island and West Greenland Current Systems in northern Baffin Bay", Progress In Oceanography, 132:305-317, DOI: 10.1016/j.pocean.2014.04.001


http://muenchow.cms.udel.edu/papers/muenchow2014Baffin.pdf


Abstract: "Temperature, salinity, and direct velocity observations from northern Baffin Bay are presented from a summer 2003 survey. The data reveal interactions between fresh and cold Arctic waters advected southward along Baffin Island and salty and warm Atlantic waters advected northward along western Greenland. Geostrophic currents estimated from hydrography are compared to measured ocean currents above 600 m depth. The Baffin Island Current is well constrained by the geostrophic thermal wind relation, but the West Greenland Current is not. Furthermore, both currents are better described as current systems that contain multiple velocity cores and eddies. We describe a surface-intensified Baffin Island  Current seaward of the continental slope off Canada and a bottom-intensified West Greenland Current over the continental slope off Greenland. Acoustic Doppler current profiler observations suggest that the West Greenland Current System advected about 3.8 ± 0.27 Sv (Sv = 106 m3 s!1) towards the northwest at this time. The most prominent features were a surface intensified coastal current advecting 0.5 Sv and a bottom intensified slope current advecting about 2.5 Sv in the same direction. Most of this north-westward circulation turned southward in the Baffin Island Current System. The Baffin Island system was transporting 5.1 ± 0.24 Sv to the south-east at the time that includes additional contributions from Nares Strait to the north (1.0 ± 0.2 Sv) and Lancaster Sound to the east (1.0 ± 0.2 Sv). Net freshwater fluxes were 72 and 187 mSv for the West Greenland and Baffin Island Currents, respectively. Empirical uncertainty arises from unknown temporal variations at weekly time scales and pertubations introduced by unresolved eddies. Eddies with 10 km horizontal and 400 m vertical scales were common and recirculated up to 1 Sv. Our 2003 observations represent conditions when the North-Atlantic Oscillation index (NAO) was close to zero. Analysis of historical hydrographic data averaged along isobaths during NAO-positive years reveals a baroclinic circulation in Baffin Bay more intense than 2003 with stronger southward flow of fresher Arctic waters along Baffin Island and stronger northward inflow of saltier Atlantic waters along Greenland. During negative NAO years this cyclonic circulation weakens as evidenced by a 1979 synoptic survey of the hydrography along Baffin Island."
“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 #220 on: August 10, 2015, 11:48:19 PM »
As I just posted about ocean conditions in Baffin Bay, I thought that I should make a few observations about the Southern Ocean.

First, as shown in the first accompanying figure 4a (from Purkey & Johnson 2013) warm CDW has (prior to 2013) surged from the north southward into the Weddell-Enderby Basin at depths shallower than 1000m (depths that can feed directly into the Filchner Trough leading beneath the FRIS.

The second image shows that in addition to the Antarctic Circumpolar Current in the Southern Ocean, there are three major gyres: the Ross Gyre and the Weddell Gyre (both of which could feed warm CDW beneath the RIS and FRIS respectively sometime after 2060) and an un-named Gyre that could feed warm CDW into the gateway for Totten Glacier.

The third image shows a representative Antarctic coastal current situation, where the Antarctic slope front & current can hinder CDW from gaining access over the continental shelf, and can promote mixing of the CDW with the AABW.

The fourth image shows that while warm CDW advected beneath an Antarctic ice shelf can melt glacial ice near the grounding line and lower portions of the ice shelf, that frazil ice can adhere to the underside of the high portions of the ice shelf.

Sarah G. Purkey, and Gregory C. Johnson (2013), "Antarctic Bottom Water warming and freshening: Contributions to sea level rise, ocean freshwater budgets, and global heat gain", Journal of Climate; doi: http://dx.doi.org/10.1175/JCLI-D-12-00834.1

Abstract: "Freshening and warming of Antarctic Bottom Water (AABW) between the 1980s and 2000s are quantified, assessing the relative contributions of water-mass changes and isotherm heave. The analysis uses highly accurate, full-depth, ship-based, conductivity-temperature-depth measurements taken along repeated oceanographic sections around the Southern Ocean. Fresher varieties of AABW are present within the South Pacific and South Indian oceans in 2000s compared to the 1990s, with the strongest freshening in the newest waters adjacent to the Antarctic continental slope and rise indicating a recent shift in the salinity of AABW produced in this region. Bottom waters in the Weddell Sea exhibit significantly less water-mass freshening than those in the other two southern basins. However, a decrease in the volume of the coldest, deepest waters is observed throughout the entire Southern Ocean. This isotherm heave causes a salinification and warming on isobaths from the bottom up to the shallow potential temperature maximum. The water-mass freshening of AABW in the Indian and Pacific sectors is equivalent to a freshwater flux of 73 ±26 Gt yr-1, roughly half of the estimated recent mass loss of the West Antarctic Ice Sheet. Isotherm heave integrated below 2000 m and south of 30 °S equates to a net heat uptake of 34 ±3 TW of excess energy entering the deep ocean from deep volume loss of AABW and 0.37 ±0.15 mm yr-1 of sea level rise from associated thermal expansion."
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #221 on: August 11, 2015, 12:02:17 AM »
The two attached figures from Purkey and Johnson 2013 show:

In the first image how a large amount of "Water Mass" largely due to ice shelf meltwater can combine with isotherm heave, salinity changes and the local AABW warming to result in a relatively high rate of local (Southern Ocean) SLR.

In the second image how isotherm heave can cause significant amounts of heat flux into the AABW.

Edit: Besides noting that the Purkey & Johnson 2013 images are relevant both to the issue of the freshening of the Southern Ocean and the slow-down of the Global MOC; the images specifically indicate that ice meltwater in the Southern Ocean helps to prevent the sea level around Antarctica from declining (as it loses ice mass) as indicated in the third attached image.  Note that maintaining sea level helps to destabilize the Antarctic marine glaciers.

Caption for the third attached image: "Multi-mission map of Sea Level Anomalies on 2012/01/01 exploiting 4 altimeters: Jason-2, Jason-1, Envisat and Cryosat-2. Credits Cnes-Ssalto/Duacs-Esa"
« Last Edit: August 11, 2015, 04:45:37 PM by AbruptSLR »
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #222 on: August 11, 2015, 12:31:08 AM »
The cartoon of the week from SkS:
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #223 on: August 11, 2015, 11:48:17 PM »
First I note that the following linked article in Skeptical Science (see abstract), indicates that due to recently identified carbon-cycle issues anthropogenic GHG emissions could be about 400 GtC smaller than identified in RCP 8.5, while still achieving the same atmospheric GHG concentrations assumed by RCP 8.5:

https://www.skepticalscience.com/CCFBRCP85.html

Abstract: "The worst-case emissions pathway, RCP8.5, is a scenario that burns a huge amount of fossil fuels, especially coal. The model has sometimes been criticized as implausible because of its huge resource consumption and emissions of ~1700 billion tonnes of carbon (GtC) over the century. Those emissions are based in part on carbon cycle model assumptions, which recent work suggests may be too optimistic. New research shows that future plant growth may be restricted by nutrient availability, turning the land carbon sink into a source. Also, permafrost feedbacks (not considered in IPCC CMIP5 models) may also add significant emissions to the atmosphere under the RCP8.5 pathway. In addition, the latest research on the Amazon Basin reveals that the tropical forest carbon sinks may already be diminishing there. Together, these feedbacks suggest that the greenhouse gas concentrations in the RCP8.5 case could be achieved with ~400 GtC smaller human emissions, making the RCP8.5 worst-case scenario more plausible."

Next, while I do not mean to appear to be too simple minded; however, if one were to assume that:

(a) Due to the carbon-cycle input of about 400 GtC by 2100, that we stay on RCP 8.5 which would result in radiative forcing, RF, of 8.5 W/m² by 2100.

(b) The ice meltwater planetary energy imbalance identified by Hansen et al 2015 will add about 2 W/m² to this total RF by 2100

(c) If one is interested in the planet response and it turns out that ECS is 4.5 instead of 3 then there could be a 1.5 factor to apply to model output.

Then if one were to look at the model results of Sagoo et al 2013 about the Early Eocene equable climate evaluation and one were to note that:

(a) The primary difference in cloud radiative feedback from the pre-industrial to the early Eocene conditions was attributed to an increase in atmospheric convection in the tropics; and

(b) Per the first attached image from Sagoo et al showing that the net cloud radiative forcing in the Early Eocene was about 15 +/- 0.5 W/m²; then

(c) One wonders if (8.5 +2)1.5 = 15.75 means that our atmosphere could assume an equable climate configuration by 2100 as shown in the second attached image; which suggests the tropical Eocene atmosphere exhibit extensive deep convective mixing (ala Sherwood et al).


Navjit Sagoo, Paul Valdes, Rachel Flecker, and Lauren Gregoire (2013) "The Early Eocene equable climate problem: Can perturbations of climate model parameters identify possible solutions?", Royal Society Philosophical Transactions A

http://www.paleo.bris.ac.uk/~ggdjl/warm_climates/sagoo_etal.pdf


Abstract:
"Geological data for the early Eocene (56 Ma to 47.8 Ma) indicates extensive global warming, with very warm temperatures at both poles. However, despite numerous attempts to simulate this warmth, there are remarkable data–model differences in the prediction of these polar surface temperatures, resulting in the so called “equable climate problem”.

In this paper, for the first time an ensemble with a perturbed climate-sensitive model parameters approach has been applied to modelling the early Eocene climate. We performed more than 100 simulations with perturbed physics parameters, and identified two simulations which have an optimal fit with the proxy data. We have simulated the warmth of the early Eocene at 560 ppmv CO2 which is a much lower CO2 level than many other models. We investigate the changes in atmospheric circulation, cloud properties and ocean circulation that are common to these simulations and how they differ from the remaining simulations in order to understand what mechanisms contribute to the polar warming.  The parameter set from one of the optimal early Eocene simulations also produces a favourable fit for the Last Glacial Maximum boundary climate and outperforms the control parameter set for the present day. Although this does not “prove” that this model is correct, it is very encouraging that there is a parameter set that creates a climate model able to simulate well very different paleoclimates and the present day climate.  Interestingly, to achieve the great warmth of the early Eocene this version of the model does not have a strong future climate change Charney climate sensitivity. It produces a Charney climate sensitivity of 2.7 °C whereas the mean value of the 18 models in the AR4 is 3.26 °C ± 0.69 °C.  Thus this value is within the range and below the mean of the models included in the IPCC Fourth Assessment Report (AR4)."

See also:
http://fallmeeting.agu.org/2012/files/2012/12/Final_poster_AGU.pdf

Edit: I thought it might help if I added two more images, with: (a) the third image from Sagoo et al 2013 showing that the continents were in a different configuration in the Eocene, which indicates that it took less radiative forcing during the Eocene to get the atmosphere to flip into an equable configuration than it would take today; and (b) the fourth image from a 2009 SkS article on Planetary Energy Imbalance showing the cumulative modern day negative forcings that I have glossed over, which also make it more difficult to flip into an equable pattern for the modern case.
« Last Edit: August 12, 2015, 04:50:25 PM by AbruptSLR »
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #224 on: August 12, 2015, 12:20:30 AM »
Further to my last post, the following linked reference (with a free access pdf), raises several concerns about state-dependent climate sensitivity and its implications for future climate change.  Caballero & Huber 2013 (C&H 2013) present a thoughtful and balanced discussion such as that indicated by the first attached figure 1 that compares the changes in Mean Average Temperature, MAT, with atmospheric carbon dioxide concentrations for both the Paleogene (~65 to 35 Mya) the modern boundary conditions, indicating a consistent ~5oC lower MAT for modern conditions than for Paleogene conditions.
 
http://www.pnas.org/content/110/35/14162.abstract

State-dependent climate sensitivity in past warm climates and its implications for future climate projections; by: Rodrigo Caballero and Matthew Huber; PNAS August 27, 2013 vol. 110 no. 35 pp 14162-14167, doi: 10.1073/pnas.1303365110



"Abstract
Projections of future climate depend critically on refined estimates of climate sensitivity. Recent progress in temperature proxies dramatically increases the magnitude of warming reconstructed from early Paleogene greenhouse climates and demands a close examination of the forcing and feedback mechanisms that maintained this warmth and the broad dynamic range that these paleoclimate records attest to. Here, we show that several complementary resolutions to these questions are possible in the context of model simulations using modern and early Paleogene configurations. We find that (i) changes in boundary conditions representative of slow “Earth system” feedbacks play an important role in maintaining elevated early Paleogene temperatures, (ii) radiative forcing by carbon dioxide deviates significantly from pure logarithmic behavior at concentrations relevant for simulation of the early Paleogene, and (iii) fast or “Charney” climate sensitivity in this model increases sharply as the climate warms. Thus, increased forcing and increased slow and fast sensitivity can all play a substantial role in maintaining early Paleogene warmth. This poses an equifinality problem: The same climate can be maintained by a different mix of these ingredients; however, at present, the mix cannot be constrained directly from climate proxy data. The implications of strongly state-dependent fast sensitivity reach far beyond the early Paleogene. The study of past warm climates may not narrow uncertainty in future climate projections in coming centuries because fast climate sensitivity may itself be state-dependent, but proxies and models are both consistent with significant increases in fast sensitivity with increasing temperature."



The C&H 2013 quote below, indicate that changes in cloud cover associated with a weakening of the atmospheric Hadley Cell (presumably related to a transition from a three cell to a one cell configuration) results in a marked increase in the fast or "Charney" climate sensitivity at a MAT of about 23 oC (which they associate with a modern atmospheric carbon dioxide concentration of about 4,000 ppm, see the attached figure).  Thus the C&H 2013 findings would appear to indicate that the modern Earth has a long way to go before possibly changing to an equable climate atmospheric circulation pattern.  However, I would like to note that from a hazard assessment point of view regarding out modern condition: (a) we do not know how fast the "slow" climate sensitivity factors will change (such as a possible sudden albedo flip; or rapid methane releases from either the permafrost or from methane hydrates); and (b) we do not know whether the current very rapid rate of radiative forcing might temporarily support several years of Madden-Julian oscillation type conditions that could convey large amounts of tropical atmospheric heat directly to the Arctic regions.

Extract: "Finally, fast-feedback sensitivity in the present model is strongly nonuniform, increasing rapidly at high temperatures due mostly to positive short-wave cloud feedbacks. These changes in cloud cover and cloud radiative forcing (CRF) are coincident with major changes in the model’s general circulation. As shown in previous work, the 23 °C threshold marks the transition to a regime in which large-amplitude equatorial waves reminiscent of the Madden–Julian oscillation converge sufficient zonal momentum onto the equator to drive mean superrotating (i.e., westerly) winds along the equatorial upper troposphere. This transition is also observed in a “superparameterized” version of the atmosphere model, where the standard convective parameterization is replaced by an embedded cloud-resolving model within each column that is arguably closer to physical reality. The transition coincides with a substantial weakening of the Hadley cell, which is consistent with decreased high- and midlevel cloud cover in the deep tropics and with low-level clouds in the subtropics (Fig. S2). Moreover, as temperature increases, the midlatitude storm tracks become weaker and shift poleward, resulting in decreased low and midlevel clouds, especially in the southern midlatitudes (Fig. S2). There is observational support for the notion that such a shift in storm tracks is associated with positive cloud feedback."


Also see:
For the Langford paper:
http://www.math.ualberta.ca/ami/CAMQ/pdf_files/vol_17/17_1/17_1e.pdf

For the Langford PPT pdf:
http://slideonline.com/presentation/6848-hadley-cell-expansion-langford-pdf

The second attached image is from the Landford PPT pdf.

Edit: To add two more figures to better indicate the risks of following a BAU radiative forcing pathway, I add: (a) the third figure shows the CO2 emissions pledges following the 2014 China-USA agreement (i.e. pre-CoP-21), and I note that the cumulative 400 GtC carbon-cycle emission to 2100 cited in my immediate prior post is equal to about 19 Billion tons per year until 2100, which would return us right back to the RCP 8.5 curve shown in the third image; and (b) the fourth image shows that RCP 8.5 continues to increase after 2100, indicating risk of continued anthropogenic radiative forcing after 2100.
« Last Edit: August 12, 2015, 06:00:36 PM by AbruptSLR »
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BornFromTheVoid

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #225 on: August 12, 2015, 02:04:59 PM »
The Jim Hansen AMA (Q&A) is up now:

PLOS Science Wednesday: We're Jim Hansen, a professor at Columbia’s Earth Institute, and Paul Hearty, a professor at UNC-Wilmington, here to make the case for urgent action to reduce carbon dioxide emissions, which are on the verge of locking in highly undesirable consequences, Ask Us Anything

Hi Reddit,
I’m Jim Hansen, a professor at Columbia University’s Earth Institute[1] .http://www.earthinstitute.columbia.edu/sections/view/9[2] Today I make the case for urgent action to reduce carbon dioxide (CO2) emissions, which are on the verge of locking in highly undesirable consequences, leaving young people with a climate system out of humanity's control. Not long after my 1988 testimony to Congress, when I concluded that human-made climate change had begun, practically all nations agreed in a 1992 United Nations Framework Convention to reduce emissions so as to avoid dangerous human-made climate change. Yet little has been done to achieve that objective.
I am glad to have the opportunity today to discuss with researchers and general science readers here on redditscience an alarming situation — as the science reveals climate threats that are increasingly alarming, policymakers propose only ineffectual actions while allowing continued development of fossil fuels that will certainly cause disastrous consequences for today's young people. Young people need to understand this situation and stand up for their rights.
To further a broad exchange of views on the implications of this research, my colleagues and I have published in a variety of open access journals, including, in PLOS ONE[3] , Assessing Dangerous Climate Change: Required Reduction of Carbon Emissions to Protect Young People, Future Generations and Nature (2013)[4] , PLOS ONE[5] , Assessing Dangerous Climate Change: Required Reduction of Carbon Emissions to Protect Young People, Future Generations and Nature (2013)[6] , and most recently, Ice Melt, Sea Level Rise and Superstorms: Evidence from the Paleoclimate Data, Climate Modeling that 2 C Global Warming is Highly Dangerous[7] , in Atmos. Chem. & Phys. Discussions[8] (July, 2015).
One conclusion we share in the latter paper is that ice sheet models that guided IPCC (Intergovernmental Panel on Climate Change)[9] sea level projections and upcoming United Nations meetings in Paris are far too sluggish compared with the magnitude and speed of sea level changes in the paleoclimate record. An implication is that continued high emissions likely would result in multi-meter sea level rise this century and lock in continued ice sheet disintegration such that building cities or rebuilding cities on coast lines would become foolish.
The bottom line message we as scientists should deliver to the public and to policymakers is that we have a global crisis, an emergency that calls for global cooperation to reduce emissions as rapidly as practical. We conclude and reaffirm in our present paper that the crisis calls for an across-the-board rising carbon fee and international technical cooperation in carbon-free technologies. This urgent science must become part of a global conversation about our changing climate and what all citizens can do to make the world livable for future generations.
Joining me is my co-author, Professor Paul Hearty, a professor at University of North Carolina — Wilmington.
I’ll be answering your questions from 1 – 2pm ET today. Ask Us Anything!


https://www.reddit.com/r/science/comments/3gporh/plos_science_wednesday_were_jim_hansen_a/

AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #226 on: August 12, 2015, 04:31:33 PM »
In the "Pig has calved" thread in the Antarctic folder, solartim27 has recently posted the attached animation between August 1st and 11th 2015, showing:

(a) The generally degraded condition of the Thwaites Eastern Ice Shelf and Ice Tongue; which appears to primarily degrading due to the advection of warm CDW in their basal areas; and

(b) A recent calving event of the glacial ice face to the west of the Thwaites Ice Tongue, as indicated by the arrow.

I note that Hansen et al 2015 did not highlight the influence of a strong El Nino event (such as we have now) on accelerating the advection of warm CDW to the Thwaites Gateway/Threshold; but if the Thwaites Ice Shelf collapses in the next few years due to such strong ocean interaction; then ice mass loss from the BSB will almost certainly accelerate rapidly.
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #227 on: August 12, 2015, 04:38:26 PM »
Have to salute a great outreach effort!  Hopefully AbruptSLR gets in there with some deeper questions from an unexpected direction. Byrd Subglacial Basin (BSB)? Hearty is the Bahama boulder geologist; super-storms have been an unfortunate  distraction from the main issue in my view. Meanwhile, the second peer-reviewer has still not surfaced with (RC) comments, though serial postings by crazies has fallen off.

http://www.atmos-chem-phys-discuss.net/15/20059/2015/acpd-15-20059-2015-discussion.html

AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #228 on: August 12, 2015, 09:56:44 PM »
Have to salute a great outreach effort!  Hopefully AbruptSLR gets in there with some deeper questions from an unexpected direction. Byrd Subglacial Basin (BSB)? Hearty is the Bahama boulder geologist; super-storms have been an unfortunate  distraction from the main issue in my view. Meanwhile, the second peer-reviewer has still not surfaced with (RC) comments, though serial postings by crazies has fallen off.

http://www.atmos-chem-phys-discuss.net/15/20059/2015/acpd-15-20059-2015-discussion.html

A-Team,

In response to one of my posts on Reddit, it was suggested that I provide a comment on ACPD.  So if the general public is permitted to post such a comment, then I will work on writing one this weekend.  If the general public is not permitted to post comments on ACPD, let me know & I will focus on something else.

Best,
ASLR
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #229 on: August 12, 2015, 10:34:12 PM »
Yes, anyone can register to comment, some of THEM did and some who weren't even up to THEIR level did as well. You in contrast are eminently well-qualified to comment on the topic of this paper.

I think it would be your time well spent for it creates a permanent citeable discussion paper record, a clean pdf that people can pass around as an email attachment that pulls together the published record and its interpretation, reaches a broader and more influential audience than here, and above all may stimulate some re-thinking on the part of the authors as they will have to respond in detail to a substantive comment (which they actually will be glad to receive).

It seems too that you might be outflanking them on the precautionary side and that too would be welcomed as it positions them as more moderate.

I would caution you to simplify to a few main points, not throw too much material at them, and not quote abstracts but use your own words (or paraphrases), citing papers only as references. This is a big job to put together all the material you have and I for one applaud the effort that it takes to marshal the evidence succinctly (there are actually no limits on either text or images) and so look forward to reading your ACP commentary!

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #230 on: August 13, 2015, 12:04:19 AM »
Yes, anyone can register to comment, some of THEM did and some who weren't even up to THEIR level did as well. You in contrast are eminently well-qualified to comment on the topic of this paper.

I think it would be your time well spent for it creates a permanent citeable discussion paper record, a clean pdf that people can pass around as an email attachment that pulls together the published record and its interpretation, reaches a broader and more influential audience than here, and above all may stimulate some re-thinking on the part of the authors as they will have to respond in detail to a substantive comment (which they actually will be glad to receive).

It seems too that you might be outflanking them on the precautionary side and that too would be welcomed as it positions them as more moderate.

I would caution you to simplify to a few main points, not throw too much material at them, and not quote abstracts but use your own words (or paraphrases), citing papers only as references. This is a big job to put together all the material you have and I for one applaud the effort that it takes to marshal the evidence succinctly (there are actually no limits on either text or images) and so look forward to reading your ACP commentary!

Thanks for the words of wisdom.  I will put my best-foot-forward this weekend, and I will try to post constructive comments next Monday or Tuesday.
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #231 on: August 17, 2015, 05:23:19 PM »
The first image shows NOAA's latest official guidance (from Parris et al. 2014) for SLR through 2100; where the curve marked Highest - 2m is appropriate for use in the design of new coastal infrastructure with a design life of comparable age.

The second image shows an extended scenario pdf for 2100 for Pfeffer et al. (2008) per Lempert et al. (2012), showing that there is still fat-tailed risk, by Pfeffer's way of thinking, for SLR beyond 2m by 2100.

The third image is from Grinsted (2014) showing his understanding of the SLR expert's (including NASA) opinions (prior to 2014) of the risk of SLR through 2100.

The fourth image shows Hansen et al (2015)'s SLR scenarios for 5-year, 10-year and 20-year doubling rates.  This image clearly shows that the 20-year doubling scenario is close to the 50% CL level for NOAA, Pfeffer et al. (2008) and Grinsted's 2014 interpretation of SLR expert opinion; while NOAA's (Parris et al. 2012's) highest – 2m SLR guidance curve falls between the 10-year and the 20-year doubling rate.

Hansen et al. 2015 demonstrate that all of their SLR scenarios cause significant positive feedback associated with the introduction of fresh ice sheet meltwater to the high latitude oceans.  This indicates that if SLR experts wish to truly safeguard the financial investments currently being made for coastal infrastructure around the world they would immediately introduce appropriate amounts of ice sheet meltwater into their GCM's (e.g. those for IPCC-AR5 and those coming for AR6), and they would immediately begin to investigate the risks of SLR by 2100 above 2m.
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AbruptSLR

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #232 on: August 17, 2015, 06:41:29 PM »
The first image shows a Earth Ocean Current & SSTA Map for August 15 2015, showing the synchronization of the anomalously low SSTA in the North Atlantic (associated with the cooling phase of the AMOC, and possibly by the slowdown in AABW production) and the anomalously high SSTA in the Eastern North Pacific; which reminds me of the synchronization discussed by Praetorius & Mix (2014) that preceded two abrupt climate change events during Termination I.

Praetorius, S. K. and Mix, A. C.: Synchronization of North Pacific and Greenland climates preceded abrupt deglacial warming, Science 25 July 2014: Vol. 345 no. 6195 pp. 444-448, 2014.

Furthermore, Sung et al. (2015) discuss how the AMO can work to strengthen El Nino events.

Sung, M.-K., An, S.-ll, Kim, B.-M. & Kug, J.-S.: Asymmetric impact of Atlantic Multidecadal Oscillation on El Niño and La Niña characteristics, Geophysical Research Letters, Volume 42, Issue 12, Pages 4998–5004, 2015.

The second images shows an Earth Surface Wind & MSLP Map for August 17 2015, showing how: (a) Strong El Nino events telecommunicate atmospheric energy from the Tropical Pacific to the WAIS via atmospheric Rossby Waves; and (b) how Strong El Nino events tend to direct wind and consequently warm CDW towards the ASE in West Antarctica, as discussed by Dutrieux et al. (2014).

Dutrieux, P., De Rydt, J., Jenkins, A., Holland, P. R., Ha, H. K., Lee, S. H., Steig, E. J., Ding, Q., Abrahamsen, E. P., and Schröder, M.: Strong Sensitivity of Pine Island Ice-Shelf Melting to Climatic Variability, Science, 2014.

Both of these trends indicate to me that we are now enter a period of strengthening positive feedbacks that may support the abrupt SLR scenarios assumed by Hansen et al. (2015).
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #233 on: August 18, 2015, 09:54:58 PM »
Nice comment on Hansen et al by Dale Berner:
http://www.atmos-chem-phys-discuss.net/15/C5966/2015/acpd-15-C5966-2015.pdf

Can't wait for their response!

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #234 on: August 19, 2015, 12:03:11 AM »
Strong effort went into that comment, my congratulations to the author for his work both there and in other fora.

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #235 on: August 19, 2015, 01:36:22 AM »
Quote
Can't wait for their response!
Most excellent -- both on the risk management and the science side! They might just end up citing the Comment in its entirety somewhere in the final to spare themselves a line-by-line response.

Alternatively, reviewer RC2 might be lurking until close to comment-close in September and then assimilate all the good stuff in previous comments by quotation. It would suffice then for the authors to just respond to RC1 and RC2.

I'm not sure if this journal has a written policy on a cut-off date for 2015 publications the Hansen paper has to consider. It was submitted on June 9th so surely nothing after that. How about April 9th and earlier? That gives them two months to assimilate new information.

Yet what I've seen authors do is say newish stuff is 'beyond the scope' of the present paper, or the paper is already too long, or it will be discussed in another mss in review. Usually the editor allows authors a fair amount of discretion here so they could probably get away with a cut-off of Dec 2014. Which would be unfortunate for a Sept 2015 official appearance given the need for a paper fully reflective of the best available data.

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #236 on: August 19, 2015, 06:12:09 AM »
For a while, i thought that one needs ice model in detail to understand marine ice instability on retrograde bed. I used to think that to melt ice, you got to get heat to the ice, perhaps in rain, or as we see, by ocean. But over the last couple years i realized that you can, instead, take the ice to the heat. And thats perhaps why Hansen, being much wiser than I, didn't bother to develop detail ice model.

If I were a malevolent sea deity, call me Neptune, who wanted to collapse WAIS, what would I do? I have mighty stores of heat available, and I am cleverer than sidd. All I got to do is melt the WAIS marine front back to a klick total depth on the retrograde bed and sit back and watch. The front is unstable, as Bassis informs, so collapses, meltwater efflux flushes the bergs out to warmer ocean where they melt at leisure. Every gram of ice floated north and melted is 80 calories of heat going south, that conveyor of mass is really a conveyor of heat the other way. Makes me think of icebergs in a whole new light.

So the key is not the Dutrieux estimate of a GWatt of heat per km of deep trough into Antarctica, (which adds up to a mm/yr or so SLR,) but the mass flux outta Antarctica in ice that can be transported north. How fat and how fast can that conveyor belt get ?

And then we have the effect Hansen has found of the meltwater cap which does two things for Mr. Neptune. a) it inhibits heat loss from CDW, so more remains available to melt icefronts back to 1 Km instability point and b) cooler surface drops precip north of Antarctic mainland onto floating ice  preventing mass gain on grounded ice which would lessen SLR. As a side effect, this makes the freshwater cap thicker.

But wait, there's more, Neptune has many tentacles. Meltwater cap reduces AABW formation, which coupled with GIS melt suppression of AMOC, reduces heat thievery by the North from the South, and leaves even more heat available for his conveyor belt in and outta WAIS

And what the hell, Neptune makes league with Aeolus, and dumps rain on GIS as well, to keep things lively.

So mebbe the ocean model is more important than the ice model. Hansen postulates sufficient ice transport, but has no eddy resolving, detail ocean model either. But we do have Weber on ice rafted debris with that disturbing MWP1A "coincidence", and the ANDRILL results showing 1 kyr collapse, so it has happened before.

sidd

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #237 on: August 19, 2015, 02:44:35 PM »
Quote
Can't wait for their response!
I'm not sure if this journal has a written policy on a cut-off date for 2015 publications the Hansen paper has to consider. It was submitted on June 9th so surely nothing after that. How about April 9th and earlier? That gives them two months to assimilate new information.

Yet what I've seen authors do is say newish stuff is 'beyond the scope' of the present paper, or the paper is already too long, or it will be discussed in another mss in review. Usually the editor allows authors a fair amount of discretion here so they could probably get away with a cut-off of Dec 2014. Which would be unfortunate for a Sept 2015 official appearance given the need for a paper fully reflective of the best available data.

As all of the 2015 references support the author's position and as the Hansen et al. 2015 authors are a little bit more fervent than the typical scientific author, so even if the editor sets a Dec 2014 cut-off date, then perhaps the authors will see fit to include discussion about the new 2015 references in the Supplemental Material.
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #238 on: August 19, 2015, 04:25:35 PM »
For a while, i thought that one needs ice model in detail to understand marine ice instability on retrograde bed. I used to think that to melt ice, you got to get heat to the ice, perhaps in rain, or as we see, by ocean. But over the last couple years i realized that you can, instead, take the ice to the heat. And thats perhaps why Hansen, being much wiser than I, didn't bother to develop detail ice model.

If I were a malevolent sea deity, call me Neptune, who wanted to collapse WAIS, what would I do? I have mighty stores of heat available, and I am cleverer than sidd. All I got to do is melt the WAIS marine front back to a klick total depth on the retrograde bed and sit back and watch. The front is unstable, as Bassis informs, so collapses, meltwater efflux flushes the bergs out to warmer ocean where they melt at leisure. Every gram of ice floated north and melted is 80 calories of heat going south, that conveyor of mass is really a conveyor of heat the other way. Makes me think of icebergs in a whole new light.

So the key is not the Dutrieux estimate of a GWatt of heat per km of deep trough into Antarctica, (which adds up to a mm/yr or so SLR,) but the mass flux outta Antarctica in ice that can be transported north. How fat and how fast can that conveyor belt get ?

And then we have the effect Hansen has found of the meltwater cap which does two things for Mr. Neptune. a) it inhibits heat loss from CDW, so more remains available to melt icefronts back to 1 Km instability point and b) cooler surface drops precip north of Antarctic mainland onto floating ice  preventing mass gain on grounded ice which would lessen SLR. As a side effect, this makes the freshwater cap thicker.

But wait, there's more, Neptune has many tentacles. Meltwater cap reduces AABW formation, which coupled with GIS melt suppression of AMOC, reduces heat thievery by the North from the South, and leaves even more heat available for his conveyor belt in and outta WAIS

And what the hell, Neptune makes league with Aeolus, and dumps rain on GIS as well, to keep things lively.

So mebbe the ocean model is more important than the ice model. Hansen postulates sufficient ice transport, but has no eddy resolving, detail ocean model either. But we do have Weber on ice rafted debris with that disturbing MWP1A "coincidence", and the ANDRILL results showing 1 kyr collapse, so it has happened before.

sidd

sidd,

To add to your list of abrupt SLR risk mechanisms:

(1) Currently in Greenland, surface meltwater typically occurs so close to the coastline that when it runs down  moulins to the bed, the now basal meltwater soon bores an outlet to the ocean via concentrated channels and thus has limited opportunity to change either the basal ice viscosity and/or the hydrostatic basal uplift pressure.  However, Rignot 2015 points out that:
(a) As surface temperatures increase with continued global warming, and
(b) As the surface elevation of the coastal ice sheet drops the local surface temperature will increase; thus in the near future Greenland's surface melt-ponds will occur further from the coastline; and thus when it becomes basal water it will have appreciably greater opportunity to both decrease the basal ice viscosity and to maintain relatively high basal hydrostatic pressures.

(2) While currently there is moderately little surface ice melt in West Antarctica, in the future with:
(a) An elevation drop in the surface of coastal ice sheets,
(b) Increase in mean global surface temperatures and
(c) A telecommunication of Tropical Pacific atmospheric energy to the WAIS; surface ice melting in the WAIS could contribute to increased: hydrofracturing, basal hydrostatic uplift pressures, turbulent ocean water mixing (and associated ice mass loss) at the cliff face where concentrated basal water discharges (i.e. the base of the Thwaites Ice Tongue), and also a decrease in basal ice viscosity.

(3) The warm CDW is rapidly collapsing ice shelves around Antarctica (particularly in the ASE) which will decrease buttressing (particularly of the SW Tributary Glacier and the Thwaites Glacier); which will accelerate ice flow velocities in the adjoining marine glaciers.

Obviously, I could include increased storm activity (and associated increases in storm surge), the possibility of future rainfall instead of snowfall, etc. but I have to go now.

Best,
ALSR.

edit: I forgot to mention that your malevolent sea deity, Neptune, has many more tentacles including (now that Jakobshavn is in rapid retreat) the bipolar seesaw where a temporary surge in ice mass loss from Greenland marine-terminating glacier could contribute to a destabilization of Antarctic marine glaciers both by: (a) temporarily raising local sea level in Antarctica and (b) by slowing the AMOC that helps keep heat in the CDW.
« Last Edit: August 19, 2015, 04:48:12 PM by AbruptSLR »
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #239 on: August 20, 2015, 07:41:30 PM »
The second referee's comments (by Peter Thorne) are now available at:

http://www.atmos-chem-phys-discuss.net/15/C6089/2015/acpd-15-C6089-2015.pdf

See also:

http://icarus.nuim.ie/people/thorne-peter
« Last Edit: August 20, 2015, 07:49:00 PM by AbruptSLR »
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #240 on: August 20, 2015, 08:49:22 PM »
Thorne says:
"there is certainly a place for exploration of potential high impact event outcomes. Sadly, the only tools to hand that enable any meaningful insights are palaeo records and models no matter how imperfect each of these tools are. However, as Carl Sagan popularized “Extraordinary claims require extraordinary evidence”. It is not clear to me that the findings described herein raise to the status of extraordinary evidence. In my view further analyses are required to reach such a point. I therefore find myself conflicted over a recommendation as to whether to publish in the full ACP journal or not. Hence I make no explicit recommendation at this time. I may, based upon the multitude of comments received, come back with a firmer recommendation nearer the conclusion of the review period."

Of course further analyses are required, but why would that be a reason for this analysis not to be published? He thinks use of only one model is not enough, but analysis has to start somewhere so one model seems like a good start. Other models aren't perfect either, as Hansen et al point out, so their paper seems like a good start for further analyzing and improving those models. That exponential ice mass loss growth can't go on forever is clear, but isn't the point of the paper to show the plausibility of a new reinforcing meltwater feedback that makes exponential ice mass loss for a longer period more likely?

Well, Hansen et al will answer and we will see what they think of Thorne's comments.

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #241 on: August 21, 2015, 03:48:12 AM »
Quote
I therefore find myself conflicted over a recommendation as to whether to publish in the full ACP journal or not. Hence I make no explicit recommendation at this time. I may, based upon the multitude of comments received, come back with a firmer recommendation nearer the conclusion of the review period."

It doesn't get any woozier than that.

This paper admittedly is not an easy one to review as it requires an encyclopedic knowledge of many areas of climate science.

Thorne is legitimate enough, not atypcial for what could be expected from the ACP atmospheric focus, comments not atypical from the peer-reviewer pool, my sense is an IPCC and int'l committee guy rather than active researcher. He writes 'my main emphasis: temperature and humidity changes from in-situ measurements (marine, land and weather balloon). Lead Author on 5th Assessment report of the Intergovernmental Panel on Climate Change and the 2014 US National Climate Assessment. atmospheric temperature trends.

I wondered from day one, why this particular journal. My guess is there is possibly an editor there known to be sympathetic to the overall concerns of climate change. So unless the RC are totally thumbs down, the paper will go forward in Sept. Hansen could just have stuck the paper into the far more prestigious PNAS since he has been a member since 1996. He has used this ACP journal twice before, not recently, out of 175 papers. I see nothing out of the ordinary in any of this.

# citations (requires google or researchGate account, some author names too common to search)
 1,721  Peter Thorne
 3,885 George Tselioudis
 4,781 A-Team [off-topic]
 5,276 Isabella Velicogna
14,463 Eric Rignot
16,380 Valérie Masson-Delmotte
[175 papers] James Hansen http://pubs.giss.nasa.gov/authors/jhansen.html

Hansen, J., M. Sato, P. Kharecha, and K. von Schuckmann, 2011: Earth's energy imbalance and implications. Atmos. Chem. Phys., 11, 13421-13449, doi:10.5194/acp-11-13421-2011.

Dangerous human-made interference with climate: A GISS modelE study. Atmos. Chem. Phys., 7, 2287-2312, doi:10.5194/acp-7-2287-2007.

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #242 on: August 21, 2015, 05:51:57 AM »
Thorne says:
"there is certainly a place for exploration of potential high impact event outcomes. Sadly, the only tools to hand that enable any meaningful insights are palaeo records and models no matter how imperfect each of these tools are. However, as Carl Sagan popularized “Extraordinary claims require extraordinary evidence”. It is not clear to me that the findings described herein raise to the status of extraordinary evidence. In my view further analyses are required to reach such a point. I therefore find myself conflicted over a recommendation as to whether to publish in the full ACP journal or not. Hence I make no explicit recommendation at this time. I may, based upon the multitude of comments received, come back with a firmer recommendation nearer the conclusion of the review period."

Of course further analyses are required, but why would that be a reason for this analysis not to be published? He thinks use of only one model is not enough, but analysis has to start somewhere so one model seems like a good start. Other models aren't perfect either, as Hansen et al point out, so their paper seems like a good start for further analyzing and improving those models. That exponential ice mass loss growth can't go on forever is clear, but isn't the point of the paper to show the plausibility of a new reinforcing meltwater feedback that makes exponential ice mass loss for a longer period more likely?

Well, Hansen et al will answer and we will see what they think of Thorne's comments.

Dale Berner has posted a response to Peter Thorne's comment at:

http://editor.copernicus.org/index.php/acpd-15-C6113-2015.pdf?_mdl=msover_md&_jrl=10&_lcm=oc108lcm109w&_acm=get_comm_file&_ms=30888&c=93054&salt=4330690381857704242
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #243 on: August 21, 2015, 06:50:26 AM »
Re: Thorne comment on Hansen paper

Section : "Scientific Queries/Concerns"

Para 2) and 3) detail ocean and ice models, or rather, the lack thereof: I agree. With this caveat, as i remarked earlier, the ocean thing might b more important, and perhaps easier ... we already know WAIS can disappear quite quickly, so we dont need anything but a timescale from the ice model,  so why deal with complicated phase change if you can approximate with a single phase ocean model as Hansen tries to do ?

Para 4)  mmm, he doesnt buy the greenland melt causing cold spot

On the other sections, this looks like he is unrecommending without revision, and i actually agree. Make the thing shorter, for sure.

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #244 on: August 21, 2015, 05:12:40 PM »
Re: Thorne comment on Hansen paper

Section : "Scientific Queries/Concerns"

Para 2) and 3) detail ocean and ice models, or rather, the lack thereof: I agree. With this caveat, as i remarked earlier, the ocean thing might b more important, and perhaps easier ... we already know WAIS can disappear quite quickly, so we dont need anything but a timescale from the ice model,  so why deal with complicated phase change if you can approximate with a single phase ocean model as Hansen tries to do ?

Para 4)  mmm, he doesnt buy the greenland melt causing cold spot

On the other sections, this looks like he is unrecommending without revision, and i actually agree. Make the thing shorter, for sure.

I am also taken aback by the fact that Thorne indicates that he believes that the Holocene has been a period of remarkable stability, so why should be believe that this stability is coming to an end; when the attached figure by Ruddiman indicates that it is highly likely that anthropogenic radiative forcing has been luckily keeping the decline in natural Holocene temperatures in balance, and that with the arrival of the industrial age this balance is now disrupted.
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #245 on: August 21, 2015, 08:35:58 PM »
Re: Thorne comment on Hansen paper

Section : "Scientific Queries/Concerns"

Para 2) and 3) detail ocean and ice models, or rather, the lack thereof: I agree. With this caveat, as i remarked earlier, the ocean thing might b more important, and perhaps easier ... we already know WAIS can disappear quite quickly, so we dont need anything but a timescale from the ice model,  so why deal with complicated phase change if you can approximate with a single phase ocean model as Hansen tries to do ?

Para 4)  mmm, he doesnt buy the greenland melt causing cold spot

On the other sections, this looks like he is unrecommending without revision, and i actually agree. Make the thing shorter, for sure.

He also states that the cold spot is not necessarily unprecedented in the recent history, this is in direct opposition to Rahmstorf et. al (2015)  http://www.nature.com/nclimate/journal/v5/n5/full/nclimate2554.html

the slowdown of the AMOC is really happening and it is happening MUCH more rapidly than the models held.  This is a direct consequence of the changes in the arctic and will lead to increased storm strength, changes in weather activity and sea level rise on the east coast of the United States.
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #246 on: August 23, 2015, 08:10:38 PM »
With reference to remarks starting a # 40 in this thread and my comment over at the ASIB:

http://neven1.typepad.com/blog/2015/08/jakobshavn-record-retreat.html?cid=6a0133f03a1e37970b01bb0866d9db970d#comment-6a0133f03a1e37970b01bb0866d9db970d

I will have to come back to the Bahamas “evidence” of the Hansen “storms of my grandfathers”.


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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #247 on: August 24, 2015, 02:54:48 AM »
With reference to remarks starting a # 40 in this thread and my comment over at the ASIB:

http://neven1.typepad.com/blog/2015/08/jakobshavn-record-retreat.html?cid=6a0133f03a1e37970b01bb0866d9db970d#comment-6a0133f03a1e37970b01bb0866d9db970d

I will have to come back to the Bahamas “evidence” of the Hansen “storms of my grandfathers”.


At the first link, Hansen provides a summary explanation of why the Bahamas Boulder support the idea of very strong North Atlantic storms during the late-Eemian (see also the discussion at the second link, and the two Hearty references at the end of this post:

http://csas.ei.columbia.edu/2015/08/04/boulders-in-the-bahamas/

Extract: "In plain English, the boulders are old rock of “hammer-ringing” hardness. They sit on younger softer (“punky”) Eemian-era substrate. The boulders are limestone formed on the floor of the North Atlantic Ocean at least 300-400 thousand years ago.
The boulders had to be placed there (on the cliff facing the North Atlantic) in the late Eemian or immediately thereafter before sea level had fallen much from its high Eemian level. It required powerful long-period waves from the Northeast to scour the ocean floor and lift the boulders. The boulders are all located at the apex of a narrowing horseshoe-shaped embayment; ocean waves funneled into this embayment generate huge surge and splash as they reach the cliffs.
One might have guessed that the boulders were deposited by a tsunami, but accompanying (V-shaped) “chevron” ridges and run-up deposits suggest otherwise. The chevron ridges and run-up deposits are located along the 900 kilometer eastern front of the Bahamian Islands at places most susceptible to ocean incursion. The power of the storms is indicated by the fact that the chevrons extend as much as several kilometers inland and the run-up deposits on hills immediately adjacent to the chevrons reach heights as great as 30-40 m above today’s sea level."
See also the following discussion by Hansen:

http://csas.ei.columbia.edu/2015/08/14/boulders-and-superstorms-redux/

Extract: "Hearty suggests three possible means by which the boulders could have been thrown up to their present level, where they rest on younger soils: (1) a tsunami, (2) backwash from a major bank margin collapse, thus somewhat analogous to a tsunami, or (3) powerful sustained storms from the northeast, with long-period waves that could scour the coastal ocean bottom. None of these three can be ruled out, but parsimony favors #3, because only it can account for the extensive (V-shaped) “chevron” ridges and run-up deposits …."

Hearty, P.J., J.T. Hollin, A.C. Neumann, M.J. O’Leary & M. McCulloch: Global sea-level fluctuations during the Last Interglaciatlion (MIS 5e), Quatern. Sci. Rev. 26, 2090-2112, 2007.

Hearty, P.J.: Boulder deposits from large waves during the last interglaciation on North Eleuthera Island, Bahamas, Quatern. Res. 48, 326-338, 1997.
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #248 on: August 25, 2015, 01:19:13 AM »
ASLR,

Thanks for providing context.

I spent the evening reading through a handful of Hearty et al. papers and some abstracts. Two key findings – 1) the perched boulders & 2) the parabolic ridges found in Bahamas are consistently being interpreted as the results of giant waves (crests more than 30 meter high and waves moving faster than 20 m/s in one direction from ENE).

I have a number of remarks.

First of all, I agree that these features may have been formed during the MIS 5e (Late Eemian Period) appr. 125,000 years ago. I also agree that these features were formed during a regression phase after a period with higher sea level than today. Hearty is consistently estimating the maximum sea level somewhere between 2.5 and 6 m above present at the time of formation.

However, I think that Hansen et al. also got a number of things wrong:

1)   Waves of that size are not unthinkable, but I am not convinced that Hansen’s modelling (see his figure 13) of appr. 10 % higher wind speeds from a NE direction around a stronger high pressure area in the NW Atlantic is enough to explain palaeo-waves, which should have been 10 x stronger in order to lift 2000 t boulders more than 20 m into the air.
2)   Hearty (1997) provides amble documentation, that these perched boulders were not deposited by waves. Giant waves would never leave boulders like these standing on their smallest end and they would never ever be able to move boulders likes these several hundred meter inland crossing a 20 m high coastal cliff on the way.
3)   Hearty et al (1998) provides amble documentation, that the parabolic ridges (socalled “Chevrons”) were not deposited by waves. First of all, waves would never leave ridges like this with their highest parts in the distal apex. This depositional landform, which is mainly found in low lying parts of the Bahamas (but also seen creeping up to 40-50 m above current sea level in some places) all show a striking resemblance  with ordinary parabolic dunes.
4)   Parabolic dunes found in Denmark were mainly formed during the Little Ice, when sea level temporarily fell a few decimeters. The lowering of the sea level provided amble sand from intertidal flats for the winds to pick up. Since most of the forests had been cleared by humans, these blowouts quickly spread from the coast and turned into elongated parabolic dunes, which moved several km’s across the landscape during the course of a few hundred years. Nearly all these dunes moved from WNW to ESE, but no traces whatsoever of giant waves have been seen.

So, my initial interpretation would be that both perched boulders and parabolic dunes may have been formed by winds from an ENE'ly direction at roughly the same time. I see the boulders as erosional remnants carved out by drifting sand from the beach, whereas the dunes are the depositional land forms also built up by amble sand from a marine regression.

I think I will leave it here for the night.

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #249 on: August 25, 2015, 02:03:51 AM »
P-maker,

Perhaps you should read Hansen et al. (2015)'s response to A. Revkin on this topic in the pdf at the following link:

http://www.atmos-chem-phys-discuss.net/15/C5615/2015/acpd-15-C5615-2015.pdf

Erosion of the boulders in place is not an option as the boulder are older than the ground they are resting on. Also, per Hansen: "Also the orientation of the original bedding planes of the boulders (i.e., the horizontal level at the time the limestone was formed from carbonate sediments on the ocean floor) can readily be discerned. The bedding planes are at a variety of angles, as expected for boulders tossed from the ocean."
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