Please support this Forum and Neven's Blog

Author Topic: Hansen et al paper: 3+ meters SLR by 2100  (Read 105924 times)

Lennart van der Linde

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #50 on: July 26, 2015, 10:28:30 PM »
Here's the full Paolo et al 2015:
http://www.ccpo.odu.edu/~klinck/Reprints/PDF/paoloScience15.pdf

"The total circum-Antarctic ice-shelf volume loss was negligible (25 ± 64 km3/year) during 1994-2003 and then declined rapidly by 310 ± 74 km3/year after 2003. Overall, from 1994 to 2012 Antarctic ice-shelf volume changed on average by -166 ± 48 km3/year, with mean acceleration of -31 ± 10 km3/year2 (-51 ± 33 km3/year2 for the period 2003-2012)."

So the acceleration of ice-shelf-volume loss seems to be accelerating, and so far the doubling time seems to be less than 10 yrs, more like 6 yrs in fact.

Lennart van der Linde

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #51 on: July 26, 2015, 11:22:44 PM »
And here the full Rignot et al 2013:
http://www.ccpo.odu.edu/~klinck/Reprints/PDF/rignotScience13.pdf

They say:
"The grounding-line flux of all surveyed ice shelves accounts for 83 +/- 7% of the total ice discharge into the Southern Ocean (Table 1). Total Antarctic grounded ice discharge is 352 +/- 30 Gt/year higher than our grounding-line flux because of additional discharge from smaller ice shelves and ice walls that terminate in the ocean. An equal partitioning of these missing areas between calving and basal melting (sees upplementary materials) would increase in situ meltwater production to 1500 +/- 237 Gt/year and ice-front flux to 1265 +/- 139 Gt/year."

So those were the numbers used by Hansen et al.

A-Team

  • ASIF Upper Class
  • Posts: 1656
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #52 on: July 26, 2015, 11:56:35 PM »
two building blocks crumbled? I don't see what you mean immediately...

Well, the Hansen article is saying sea level will rise a lot faster than IPCC thought, maybe 3 m rather than 1 in this century, attributing that primarily to Antarctica rather than thermal expansion or to Greenland melt.

Why then even study Greenland SLR? The funding should be pulled and given to the Antarctic; after all, it dominated SLR in the Eemian. In post #36, I show the decades of back-and-forth on interglacial SLR attribution has not settled down as of July 2015. Thus it is not a solid building block for more sweeping syntheses such as Hansen et al. And that's before even considering what happens to Greenland if the Arctic Ocean has ice-free summers (new forum).

Post #46 looks what we know about the effect on solar forcing of volcanic aerosols, an important arena for validating of earth system models which must be vetted on paleo coolings and greenhouse gas levels, which is to say the polar ice core record after surges in non sea salt sulfur.

Here it emerges just this week that the dating scheme for ice layers has been way off, even for the last two millenia. Since stratospheric volcanoes can be independently dated, this throws off the phasing of sulfate aerosol injection vis-a-vis temporary global cooling. This means the ice cores haven't been a solid building block and the models fitted on them are seriously wrong.

What's new here? Science marches on, never quite there, forever under revision, more studies always needed. Maybe once the necessary revisions are made, projects like Hansen's can just be re-run and asymptotically refined. My view however is the foundation is not laid, the building blocks have not set up properly, thus it is way too early to build a wall. I'll post on other fundamental blocks in future posts as new papers come in on them.

I am not looking here for 'consensus' nor finding fault with the overall narrative of train wreck to which we are all supposed to adhere, but rather that we need to get the experimentally supported foundations under much better control. And that is slowly happening, Renland and eGrip in northeast Greenland, million-year ice in Allen Hills, Antarctica and so forth.

I've seen train wrecks before in science itself where model club car overtakes the experimental engine and there's no better example of that than what happened to physics with string theory.

Lennart van der Linde

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #53 on: July 27, 2015, 12:23:48 AM »
two building blocks crumbled? I don't see what you mean immediately...

Well, the Hansen article is saying sea level will rise a lot faster than IPCC thought, maybe 3 m rather than 1 in this century, attributing that primarily to Antarctica rather than thermal expansion or to Greenland melt.

Why then even study Greenland SLR? The funding should be pulled and given to the Antarctic; after all, it dominated SLR in the Eemian. In post #36, I show the decades of back-and-forth on interglacial SLR attribution has not settled down as of July 2015. Thus it is not a solid building block for more sweeping syntheses such as Hansen et al. And that's before even considering what happens to Greenland if the Arctic Ocean has ice-free summers (new forum).

Post #46 looks what we know about the effect on solar forcing of volcanic aerosols, an important arena for validating of earth system models which must be vetted on paleo coolings and greenhouse gas levels, which is to say the polar ice core record after surges in non sea salt sulfur.

Here it emerges just this week that the dating scheme for ice layers has been way off, even for the last two millenia. Since stratospheric volcanoes can be independently dated, this throws off the phasing of sulfate aerosol injection vis-a-vis temporary global cooling. This means the ice cores haven't been a solid building block and the models fitted on them are seriously wrong.

Well, yes, uncertainty ranges on GIS vs WAIS in Eemian and aerosol forcing are large, so Hansen et al may turn out to have made more or less incorrect assumptions on those topics. But they may still turn out to have been more right than wrong, right? We don't know at this point, so while recognizing the uncertanties, we still need to take their hypothesis seriously, I think. Unless you can show why these new findings you mention would make their hypothesis totally unfounded without any reasonable doubt.

Lennart van der Linde

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #54 on: July 27, 2015, 12:26:14 AM »
Also interesting to hear the Hansen press conference call of last monday:
https://soundcloud.com/andrewrevkin/science-reporters-and-jim-hansen-discuss-a-portentous-climate-paper-released-prior-to-peer-review

Made available by Andy Revkin.

Lennart van der Linde

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #55 on: July 27, 2015, 12:42:30 AM »
And Hansen on CNN tonight explaining in a few seconds the meaning of "10 feet in 50 years":
http://edition.cnn.com/videos/tv/2015/07/25/exp-gps-hansen-sot-climate.cnn

LRC1962

  • ASIF Citizen
  • Posts: 392
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #56 on: July 27, 2015, 01:49:40 AM »
I am not looking here for 'consensus' nor finding fault with the overall narrative of train wreck to which we are all supposed to adhere, but rather that we need to get the experimentally supported foundations under much better control. And that is slowly happening, Renland and eGrip in northeast Greenland, million-year ice in Allen Hills, Antarctica and so forth.

I've seen train wrecks before in science itself where model club car overtakes the experimental engine and there's no better example of that than what happened to physics with string theory.
Which would be better? Presume the train wreck will happen at the accelerated speeds Hansen is claiming and at accordingly or wait for the conclusive evidence to come in an therefore maybe really find ourselves in a pile of manure. An example comes to mind. There are those that claim the 2k bug in computers was a fiction and all the money spent to fix it was the industry creating a scare to make more money. What is failed to acknowledge is that the bug failed not because it did not exist but that it was successfully prevented from happening in the first place. If we keep on arguing over how much, how fast and at the same time not explain this is not an end point but part of a process that will continue on till all coastal areas WILL be gone, in regards to SLR, the BAU side will successfully claim that the cost benefit risk assessment best guess is to not take action because science has no clue what is going on. Dr. Allen said it best. The best guess is 1 foot (that the time of talk) by 2100. The problem is all possible other outcomes are not equal on both sides of the 1 foot, all of them come on the worst side of the outcome. Therefore if one is to hedge your bets, the only bet is to take the Hansen version or worse.
"All truth passes through three stages: First, it is ridiculed; Second,  it is violently opposed; and Third, it is accepted as self-evident."
       - Arthur Schopenhauer

wili

  • ASIF Upper Class
  • Posts: 1792
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #57 on: July 27, 2015, 02:56:33 AM »
Thanks for the Hansen stuff, LdvL. Let me know if you run across a transcript of the conference call tape.
"A force de chercher de bonnes raisons, on en trouve; on les dit; et après on y tient, non pas tant parce qu'elles sont bonnes que pour ne pas se démentir." Choderlos de Laclos "You struggle to come up with some valid reasons, then cling to them, not because they're good, but just to not back down."

AbruptSLR

  • ASIF Emperor
  • Posts: 10942
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #58 on: July 27, 2015, 03:59:05 AM »
As ice sheet models are not likely to be able to reasonably replicate the key mechanisms that will likely contribute to a possible collapse of the WAIS this century, until (at the earliest) possibly the end of the DOE's Accelerated Climate Model Energy, ACME, program in 2024; paleo-evidence remains prominent in guiding our climate change policy.  In this regard, Hansen et al 2015 have performed an excellent service by providing extensive paleo discussion, much of which is directed towards the North Atlantic and Greenland, which I will let other discuss; as in this post I focus primarily on the late Eemain (late MIS 5e) event driven by Antarctic ice mass loss, when sea level rose to about 9m above present beginning at: "119 ky b2k and peak sea level at 118.1 +/- 1.4 ky b2k" (see the first image from O'Leary et al 2013) and the following extract from page 20066 of Hansen et al 2015:


page 20066
Extract: "O’Leary et al. (2013) provide a new perspective on Eemian sea level change using over 100 well-dated U-series coral reefs at 28 sites along the 1400 km west coast of Australia and incorporating GIA corrections on regional sea level. In agreement with Hearty et al. (2007), their analyses suggest that sea level was relatively stable at 3–4m in most of the Eemian, followed by a rapid (<1000 yr) late-Eemian sea level rise to about +9 m. U-series dating of the corals has the sea level rise begin at 119 ky b2k and peak sea level at 118.1_1.4 ky b2k. This dating of peak sea level is consistent with the estimate of Hearty and Neumann (2001) of _118 ky b2k as the time of rapid climate changes and extreme storminess.

End-Eemian sea level rise would seem to be a paradox, because orbital forcing then favored growth of Northern Hemisphere ice sheets.  We will find evidence, however, that the sea level rise and increased storminess are consistent, and likely related to events in the Southern Ocean."

 

The second image shows that in the 118 +/- 5 ky b2k time frame the spring and summer insolation anom. north of 60oN was negative while south of 60oS it was positive; which indicates that this abrupt SLR event is primarily associate with a partial collapse of the AIS as indicated by the following extract from page 20074 to 20075 of Hansen et al 2015:
Extract: "Late Eemian sea level rise is seemingly a paradox, because glacial-interglacial sea level change is mainly a result of the growth and decay of Northern Hemisphere ice sheets. Northern warm-season insolation anomalies were negative and declining in the latter part of the Eemian (Fig. 3a), so Northern Hemisphere ice sheets should have been growing. We suggest that the explanation for a mid-Eemian sea level minimum is a substantial late-Eemian collapse of the Antarctic ice sheet facilitated by the positive warm-season insolation anomaly on Antarctica and the Southern Ocean during the late Eemian (Fig. 3b).

Persuasive presentation of this interpretation requires analysis of relevant climate mechanisms with a global model as well as a detailed discussion of paleoclimate data.  We will show that these analyses in turn help to explain ongoing climate change today, with implications for continuing climate change this century."

 

The following extract from page 20107-20108 of Hansen et al 2015, cites still more paleo evidence that the SLR surge at the late-Eemian was driven by AIS ice mass loss, particularly in the WAIS, and calls for "… higher resolution models with more realistic sea ice distribution and seasonal change than our present model produces
Extract: "We suggest that the Southern Hemisphere was the source for brief late-Eemian sea level rise. The positive warm-season insolation anomaly on the Southern Ocean and AMOC slowdown due to C26 added to Southern Ocean heat, causing ice shelf melt, ice sheet discharge, and sea level rise. Rapid Antarctica ice loss would cool the Southern Ocean and increase sea ice cover, which may have left telltale evidence in ice cores. Indeed, Masson-Delmotte et al. (2011) suggest that abrupt changes of _18O in the EDML and TALDICE ice cores (those most proximal to the coast) indicate a change in moisture origin, likely due to increased sea ice. Further analysis of Antarctic data for the late Eemian might help pinpoint the melting and help assess vulnerability of Antarctic ice sheets to ocean warming, but this likely will require higher resolution models with more realistic sea ice distribution and seasonal change than our present model produces."

The third image provides an example of the type of global relative SLR pattern that occurs due to the collapse of the WAIS, which must be applied both to correctly interpret paleo sea level data and also future sea level projections.
 

The following extract from page 20113 to 20114 of Hansen et al 2015 and the fourth image discuss/show both observed and projected trends in (a) the Southern Merdional Overturning Circulation (in Sverdrups) and (b) the Southern Hemisphere mean sea ice area anomaly.  This comparison shows both the importance of the recent freshwater influx into the Southern Ocean both on the SMOC and the SH ice area anom. that support Hansen et al 2015 main warning that current GCM projections are underestimating the possibly profound importance of ASLR on both further planetary energy imbalance and on future storminess.
Extract: "The Weddell and Ross Sea regions have large freshwater flux that is mainly icebergs. In contrast, the large Amundsen- Bellingshausen fresh water flux is mainly basal melt. This distinctive spatial variation may help account for observed sea ice increasing in the Weddell and Ross Seas, while decreasing in the Amundsen and Bellingshausen Seas. Note also that the Weddell Sea and Ross Sea sectors are respectively the regions where the EDML and TALDICE Antarctic ice cores are suggestive of expanding sea ice (Masson-Delmotte et al., 2011) at end-Eemian time."


 

The Hansen et al 2015 conclusion on page 20121 includes the following extract emphasis that the observed impacts of the freshening of the Southern Ocean are occurring even faster than their own model projects (which indicates that their findings may be conservative in a scientific sense):
Extract: "The Eemian, less than 2 oC warmer than pre-industrial Earth, itself provides a clear indication of the danger, even though the orbital drive for Eemian warming differed from today’s human-made climate forcing. Ongoing changes in the Southern Ocean, while global warming is less than 1 oC, provide a strong warning, as observed changes tend to confirm the mechanisms amplifying change. Predicted effects, such as cooling of the surface ocean around Antarctica, are occurring even faster than modeled."

Furthermore, I not that in the following Pollard, DeConto & Alley (2015) reference the authors show that without the inclusion of their postulated hydrofracturing and ice cliff failure mechanism, it is impossible to replicate the observed paleo SLR evidence from the Paleocene (including the Eemian)
Pollard, D., R.M. DeConto and R.B. Alley (2015) "Potential Antarctic Ice Sheet retreat driven by hydrofracturing and ice cliff failure", Earth Plan. Sci. Lett., 412, 112-121

Finally, I re-post the following reference by Alley et al (2015) that examines paleo-evidence (focused on WAIS behavior) to concluded that: " Although sea-level histories and physical understanding allow the possibility that ice-sheet response could be quite fast, no strong constraints are yet available on the worst-case scenario. Recent work also suggests that the Greenland and East Antarctic Ice Sheets share some of the same vulnerabilities to shrinkage from marine influence."

Alley, R.B., S. Anandakrishnan. K. Christianson, H.J. Horgan, A. Muto, B.R. Parizek, D. Pollard and R.T. Walker (2015) "Oceanic forcing of ice-sheet retreat: West Antarctica and more", Ann. Rev. Earth Plan. Sci., 43, 7.1-7.25.

http://www.annualreviews.org/doi/abs/10.1146/annurev-earth-060614-105344?journalCode=earth

Abstract: "Ocean-ice interactions have exerted primary control on the Antarctic Ice Sheet and parts of the Greenland Ice Sheet, and will continue to do so in the near future, especially through melting of ice shelves and calving cliffs. Retreat in response to increasing marine melting typically exhibits threshold behavior, with little change for forcing below the threshold but a rapid, possibly delayed shift to a reduced state once the threshold is exceeded. For Thwaites Glacier, West Antarctica, the threshold may already have been exceeded, although rapid change may be delayed by centuries, and the reduced state will likely involve loss of most of the West Antarctic Ice Sheet, causing >3 m of sea-level rise. Because of shortcomings in physical understanding and available data, uncertainty persists about this threshold and the subsequent rate of change. Although sea-level histories and physical understanding allow the possibility that ice-sheet response could be quite fast, no strong constraints are yet available on the worst-case scenario. Recent work also suggests that the Greenland and East Antarctic Ice Sheets share some of the same vulnerabilities to shrinkage from marine influence."

“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

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #59 on: July 27, 2015, 08:20:25 AM »
A glowing review of Hansen et al by David Archer:
http://www.atmos-chem-phys-discuss.net/15/C5209/2015/acpd-15-C5209-2015.pdf

"This is another Hansen masterwork of scholarly synthesis, modeling virtuosity, and insight, with profound implications... Perhaps a more usual strategy, from a researcher who is less of a creative and intellectual volcano than Hansen, would be to publish the storminess part separately. This paper is breathtakingly rich and panoramic... Due to its important conclusions, primarily about the ice sheet melting climate feedback, I expect this paper will be widely read, but it will make its readers work for it."
« Last Edit: July 27, 2015, 09:40:50 AM by Lennart van der Linde »

Lennart van der Linde

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #60 on: July 27, 2015, 01:04:00 PM »
Hansen in the Huffington Post, very eloquently making his case, including a link to his draft paper with figures included in the text:
http://www.huffingtonpost.com/dr-james-hansen/multi-meter-sea-level-rise-is-an-issue-for-todays-public_b_7875828.html

AbruptSLR

  • ASIF Emperor
  • Posts: 10942
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #61 on: July 27, 2015, 01:24:29 PM »
My last post provides tantalizing paleo evidence both that: (a) the WAIS and portions of the EAIS are quite sensitivity to rapid ice mass loss due to relatively low levels of forcing (such as those experienced during the late-Eemian); and (b) that we are rapidly approaching conditions similar (or worse than) the late-Eemian where sea level surged abruptly above modern sea levels.  Nevertheless, this tantalizing paleo-evidence does not prove that: (a) we are rapidly (by 2035 to 2040) approaching the main phase collapse of at least the WAIS; (b) the main phase collapse will occur at a rate to produce multiple meters of SLR by 2100; nor (c) the possible initial main phase collapse of the WAIS will extend into abrupt collapse of key (marine ice sheet) portions of the EAIS and key marine terminating glacial portions of the GIS, to possibly produce up to 5m +/- of SLR by circa 2100 as indicated in the first attached image from Hansen et al 2015 (focused on a 10-year doubling scenario)
 

While Hansen et al 2015 provide only limited justification for evaluating ice sheet freshwater melt flux scenarios with 5, 10 and 20 year doubling times; in this & my next several posts I will provide further discussion to justify the scenarios summarized by the first attached image.
Due to lack of space per post, I start by reiterating that Hansen's model only assumes that ECS is 3C as indicated by the second attached image (by Hansen & Sato, 2012).  However, both Baijun Tian (2015) and Sherwood et al (2014) found that ECS cannot be less than 3C, and is likely currently in the 4.1C range.  Also, everyone should remember that the effective ECS is not a constant, and models project that following a BAU pathway will result in the effective ECS increasing this century:

Baijun Tian (2015), "Spread of Model Climate Sensitivity Linked to Double-Intertropical Convergence Zone Bias", Geophysical Research Letters, DOI: 10.1002/2015GL064119

Sherwood, S.C., Bony, S. and Dufresne, J.-L., (2014) "Spread in model climate sensitivity traced to atmospheric convective mixing", Nature; Volume: 505, pp 37–42, doi:10.1038/nature12829

http://www.nature.com/nature/journal/v505/n7481/full/nature12829.html


Quote from Sherwood (2014): “Climate sceptics like to criticize climate models for getting things wrong, and we are the first to admit they are not perfect, but what we are finding is that the mistakes are being made by those models which predict less warming, not those that predict more,” said Prof. Sherwood.


Furthermore, the following linked Wang et al (2015) reference indicates that the cause of the double-ITCZ bias in the CAM5 model is focused on its modeling of the Eastern Tropical Pacific, which may help to explain why Stevens misses the positive cloud feedback signal as he does not give as much significance to the Eastern Tropical Pacific (which is heavily influenced by the ENSO) as do researchers such as Trenberth and Sherwood, who pay particular attention to the Tropical Pacific and the influence of the ENSO.

On the face of it, this evidence seems to strengthen the probability that ECS is relatively close to 4.1C.

Chia-Chi Wang, Wei-Liang Lee, Yu-Luen Chen, and Huang-Hsiung Hsu (2015), "Processes Leading to Double Intertropical Convergence Zone Bias in CESM1/CAM5", J. Climate, 28, 2900–2915, doi: http://dx.doi.org/10.1175/JCLI-D-14-00622.1

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-14-00622.1

"The double intertropical convergence zone (ITCZ) bias in the eastern Pacific in the Community Earth System Model version 1 with Community Atmosphere Model version 5 (CESM1/CAM5) is diagnosed. In CAM5 standalone, the northern ITCZ is associated with inertial instability and the southern ITCZ is thermally forced. After air–sea coupling, the processes on both hemispheres are switched because the spatial pattern of sea surface temperature (SST) is changed.
Biases occur during boreal spring in both CAM5 and the ocean model. In CAM5 alone, weaker-than-observed equatorial easterly in the tropical eastern South Pacific leads to weaker evaporation and an increase in local SST. The shallow meridional circulation overly converges in the same region in the CAM5 standalone simulation, the planetary boundary layer and middle troposphere are too humid, and the large-scale subsidence is too weak at the middle levels. These biases may result from excessive shallow convection behavior in CAM5. The extra moisture would then fuel stronger convection and a higher precipitation rate in the southeastern Pacific.
In the ocean model, the South Equatorial Current is underestimated and the North Equatorial Countercurrent is located too close to the equator, causing a warm SST bias in the southeastern Pacific and a cold bias in the northeastern Pacific. These SST biases feed back to the atmosphere and further influence convection and the surface wind biases in the coupled simulation. When the convection in the tropical northeastern Pacific becomes thermally forced after coupling, the northern ITCZ is diminished due to colder SST, forming the so-called alternating ITCZ bias."


Also see Sherwood's (2015) presentation at the Ringberg workshop:

http://www.mpimet.mpg.de/fileadmin/atmosphaere/WCRP_Grand_Challenge_Workshop/Ringberg_2015/Talks/Sherwood_24032015.pdf

I conclude this post by noting that Trenberth criticized Hansen et al (2015) for not adequately accounting for influence of the ENSO and the Equatorial Pacific in general; which can telecommunicate energy (via both the atmosphere & the ocean) from the tropical Pacific directly to West Antarctica thereby warming the WAIS much faster than the AIS as indicated by the third attached image.

Edit: The fourth attached image indicates that Fasullo & Trenberth 2012 concur with the position that ECS may currently be near 4.1C
« Last Edit: July 27, 2015, 04:50:38 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Laurent

  • ASIF Governor
  • Posts: 2512
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #62 on: July 27, 2015, 02:53:06 PM »
I did not see the link of the hansen paper seen in the huffington post article on this tread, so I put it here in case you haven't read it.

http://www.columbia.edu/~jeh1/2015/20150704_IceMelt.pdf

Lennart van der Linde

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #63 on: July 27, 2015, 03:42:24 PM »
Hansen et al in their experiments use 3 doubling times: 5, 10 and 20 yrs.

But then on p.40 (of the Huffington version), and in the abstract as well, they suddenly talk of 10, 20 and 40 yrs:
"The fundamental question we raise is whether ice sheet melt in response to rapid global warming will be nonlinear and better characterized by a doubling time for its rate of change or whether more linear processes dominate. Hansen (2005, 2007) argued on heuristic grounds that ice sheet disintegration is likely to be nonlinear if climate forcings continue to grow, and that sea level rise of several meters is possible on a time scale of the order of a century. Given current ice sheet melt rates, a 20-year doubling rate produces multi-meter sea level rise in a century, while 10-year and 40-year doubling times require 50 years and 200 years, respectively."

This should still be 5, 10 and 20 yrs, right?

If the current ice sheet melt rate is 1 mm/yr from 2000-2010, then a 10 yr doubling time gives:

2010-2020:   2 mm/yr
2020-2030:   4 mm/yr
2030-2040:   8 mm/yr
2040-2050: 16 mm/yr
2050-2060: 32 mm/yr
2060-2070: 64 mm/yr

This would give 63 cm of SLR by ice sheet melt from 2000-2060, with maybe 21 cm from GIS and 42 cm from AIS.
Adding thermal expansion + small glaciers/ice caps could add maybe another 37 cm by 2060.
So total SLR by 2060 would be about 1m, or in the order of a meter, as Hansen et al say.

Even without any further acceleration after 2060 this would give:

2060-2100: 64 mm/yr

This would add another 256 cm by 2100.
Thermal expansion + small glaciers/ice caps could add maybe another 24 cm by 2100.
So total SLR by 2100 would be about 3.8m, or almost 4m, in this scenario.
By 2200 SLR could then maybe reach 9-10m.

If the doubling time would be 20 yrs instead of 10 yrs, we would reach 1m around 2100 and 4m around 2200. This is about the worst-case the Dutch Delta Committee imagined in 2008, and what they ('we') somehow thought manageable, for The Netherlands at least.

So what if Hansen et al are right and this is somehow more like a best case, and the worst-case is more than twice as bad? It should wake the Dutch up from their risk denial and work for much stronger mitigation than they've been willing to consider. But so far they still want to continue their sweet dreams of a safe future without any strong mitigation. So hopefully the courts will uphold the recent order for stronger mitigation, and who knows, maybe they will even strengthen that order...

Lennart van der Linde

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #64 on: July 27, 2015, 04:12:42 PM »
The 10 yr doubling scenario of Hansen et al is about the worst-case (0.1% probability) given in figure 2 and table 1 (attached below) of Kopp et al 2014:
http://onlinelibrary.wiley.com/doi/10.1002/2014EF000239/full

For 2100 Kopp et al estimate more than 2.45m is not possible/plausible.
For 2200 they estimate 9.5m is the upper thinkable limit.
So if Hansen et al stays as it is, Kopp et al may have to update their estimates.

Lennart van der Linde

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #65 on: July 27, 2015, 04:25:41 PM »
Some in the sea level expert community do share the concerns of Hansen et al, according to the survey by Horton et al 2014:
http://ac.els-cdn.com/S0277379113004381/1-s2.0-S0277379113004381-main.pdf?_tid=73b46cfe-346a-11e5-98f4-00000aacb35f&acdnat=1438006931_a78511bcc8622299c7d961f3436d17a9

Although according to their figure 2, attached below, it may be that only Hansen himself thinks 9.5m in 2200 is possible (intrapolating from the 15m by 2300 in RCP8.5).

Lennart van der Linde

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #66 on: July 27, 2015, 04:38:13 PM »
Rohling et al estimate 1m/decade as the maximum thinkable rate of SLR, according to their fig2a (attached below):
http://www.nature.com/srep/2013/131212/srep03461/full/srep03461.html

They consider about 1.8m by 2100 and 5m by 2200 as worst-cases, as shown in their fig3b below.

A-Team

  • ASIF Upper Class
  • Posts: 1656
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #67 on: July 27, 2015, 05:45:30 PM »
People are starting to post their peer-review comments to the ACP discussion site. I've never heard of such a thing before but journalist Refkin was the first to post on the super-storm component (he is going all-out to discredit this paper).

E Stabenau and D Archer also have comments in. Stabenau is an oceanographer and coastal ocean modeler with the Natl Park Service in Florida -- his comment is just a brief question about supporting data in the coming decade. Archer is one of the designated reviewers and a well-known entity in climate change research.

You can tell what's what by AC: Author Comment | RC: Referee Comment | SC: Short Comment | EC: Editor Comment. The authors have not yet responded to any of them. Don't be confused by the 'Reply' button -- that's for you, not a link to author response which gets an AC label.

If you go to https://scholar.google.com/scholar and search with something like "David Archer climate", then sort results by post 2011, you can greatly enrich for the proper person, pick up middle initials and alternate versions of names, institution, use that to refine the search and finally get a list of all  their recent research activities.

Then go back to regular Google search and look for the person at the right institution at ResearchGate. Don't trust search at ResearchGate itself, their tool is haphazard. There are 8 distinct David Archers including a second one at U Chicago. Our guy is not yet fully up and running there. Stabenau is just getting going on his career so not there and Revkin is not a researcher. (I'm not sure if you can open an account without any publications.)

I like to take a quick look at the #citations by other scientists to see what sort of career dent someone unknown to me has made. (For reference, I'm at 4,695 citations which is 77.5th percentile with a somewhat scary 232 people having checked out my profile. Stalkers?!?) 

ResearchGate otherwise is a great place to get free full text. If not posted, RG will send a request out to the set of authors without you having to know their emails. This nudges researchers to post their pdfs to save on future bother. People often attach a brief note with the document and will answer a question or two, again w/o a need to disclose direct emails. I usually preface my question by saying I'm writing a commentary piece for the Arctic Sea Ice Forum; they usually know what this is and it opens the door. I've gotten some really good supplemental information in this way.

http://www.atmos-chem-phys-discuss.net/15/20059/2015/acpd-15-20059-2015-discussion.html
https://www.researchgate.net/home
« Last Edit: July 27, 2015, 05:55:50 PM by A-Team »

Lennart van der Linde

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #68 on: July 27, 2015, 07:21:48 PM »
Finally Joe Romm comments on Hansen et al:
http://thinkprogress.org/climate/2015/07/27/3684564/james-hansen-climate-danger-hyper-anthropocene/

Very to the point, as usual.

Lennart van der Linde

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #69 on: July 27, 2015, 08:32:11 PM »
Michael Mann radio interview on the Hansen paper:
http://paulharrisonline.blogspot.nl/2015/07/michael-mann-on-climate-change.html

Quite supportive, as I would've expected.

Lennart van der Linde

  • ASIF Middle Class
  • Posts: 653
    • View Profile

AbruptSLR

  • ASIF Emperor
  • Posts: 10942
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #71 on: July 27, 2015, 08:49:09 PM »
Finally Joe Romm comments on Hansen et al:
http://thinkprogress.org/climate/2015/07/27/3684564/james-hansen-climate-danger-hyper-anthropocene/

Very to the point, as usual.


Lennart,

While Joe Romm is generally rather complementary to the Hansen et al 2015 paper, I take exception to the following extract from his write-up:

"I also think Hansen is pushing the speculative possibility of 10 feet of sea level rise this century harder than he needs to. Yes, there are many experts who consider that a real possibility now, so it would be imprudent to ignore the warning. But the fact is, on our current emissions path, we now appear to be headed toward the ballpark of 4-6 feet of sea level rise in 2100 — with seas rising up to one foot per decade after that — which should be more than enough of a “beyond adaptation” catastrophe to warrant strongest of action ASAP."

Romm thinking about ASLR appears to be stuck in the 2008 thinking presented by Tad Pfeffer et al (see the top pdf in the first attached image); which was subsequently formally adopted by NOAA in their Dec. 2012 SLR guidance document.

Since 2008 there have been numerous findings including most prominently by Rignot et al in 2015 showing that the WAIS is less stable than previously believed (i.e. by Pfeffer et al 2008); yet people like Romm fail to update their thinking to reflect such new findings.  Examples of other considerations ignored by people like Romm include: (a) the newly identified & well develop subglacial meltwater drainage systems below the WAIS; (b) the greater geothermal heating below the WAIS (see the second & third images) and (c) possible/probable activation of the Thwaites Glacier Eastern Shear Margin by a retreat of the PIIS face so as to accelerate the ice flow down the SW Tributary Glacier shown in the fourth image.

Many public figures such as Romm feel comfortable ignoring the recent research (most significantly by Rignot who is one of Hansen's co-authors), and instead clinging to 2008 interpretations just because NOAA is slow to update their old reports.

Best,
ASLR
“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

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #72 on: July 27, 2015, 09:55:04 PM »
Romm thinking about ASLR appears to be stuck in the 2008 thinking presented by Tad Pfeffer et al (see the top pdf in the first attached image); which was subsequently formally adopted by NOAA in their Dec. 2012 SLR guidance document.

Since 2008 there have been numerous findings including most prominently by Rignot et al in 2015 showing that the WAIS is less stable than previously believed (i.e. by Pfeffer et al 2008); yet people like Romm fail to update their thinking to reflect such new findings.  Examples of other considerations ignored by people like Romm include: (a) the newly identified & well develop subglacial meltwater drainage systems below the WAIS; (b) the greater geothermal heating below the WAIS (see the second & third images) and (c) possible/probable activation of the Thwaites Glacier Eastern Shear Margin by a retreat of the PIIS face so as to accelerate the ice flow down the SW Tributary Glacier shown in the fourth image.

Many public figures such as Romm feel comfortable ignoring the recent research (most significantly by Rignot who is one of Hansen's co-authors), and instead clinging to 2008 interpretations just because NOAA is slow to update their old reports.


Hi ASLR,
In his Hansen-comment Romm links to his earlier comment on Rignot et al 2014:
http://thinkprogress.org/climate/2014/05/13/3437033/coastal-cities-abandoned/

I read him as saying that Hansen doesn't need to be more sure of 3m by 2100 than the science at this point can warrant, and that we shouldn't forget that even if 3m by 2100, or earlier, would not be reached, that doesn't mean that the risk of 1-2m by 2100 isn't urgent enough to justify very strong mitigation. Hansen has a suspicion, and it doesn't need to turn out right to be justified. That he could be right is reason enough to take his suspicion very seriously, and justifies even stronger mitigation (and adaptation) than the risk of 1-2m by 2100 does. I think that's what Romm is saying, and I agree with that.

AbruptSLR

  • ASIF Emperor
  • Posts: 10942
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #73 on: July 27, 2015, 10:07:40 PM »
While I am pointing out the need to update the 2008 Pfeffer et al SLR pdf, I add four more figures illustrating additional risk factors for more rapid ASLR:

The first figure, by MacGregor et al 2012 illustrates how rapidly the ice shelves in the ASE (Amundsen Sea Embayment) have collapsed in recent years, which indicates to me that within the next one to five years: (a) the SW Tributary Glacier ice flow velocity could be accelerated by about five times with a few more major calving events on the Pine Island Ice Shelve, PIIS, and (b) both the remaining Thwaites ice shelf and ice tongue could collapse; thus allowing the Thwaites Glacier ice flow to accelerate.

The second figure shows how during a strong El Nino event (like this year) the Amundsen Sea Low, ASL, can drive the warm Circumpolar Deep Water, CDW, shown with a Bottom Potential Temperature of 1.4 C  (see the third image) deep into the ASE; where it accelerates the basal ice melting of both the associated ice shelves and grounding line ice.

The fourth image shows the location of the number of melt days in Antarctica during the month of January 2005; which shows that after the collapse of key portions of the ASE ice shelves; hydrofacturing could occur at almost any austral summer thereafter.
“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

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #74 on: July 27, 2015, 10:08:55 PM »
ASLR,
I do think Romm/ClimateProgress missed the Pollard et al 2015 study on hydrofracture and cliff failure. Or at least I can't find any mention of it right now.

Lennart van der Linde

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #75 on: July 27, 2015, 10:23:08 PM »
Here's Greg Laden on Hansen et al:
http://scienceblogs.com/gregladen/2015/07/27/catastrophic-sea-level-rise/

My comment:
Hansen et al don't model ice melt, I think; they assume exponential melt increase and see what happens with ocean and surface temperatures. Their suspicion is that this could happen in the coming decades/centuries and they give arguments why this may be plausible, or even likely.

AbruptSLR

  • ASIF Emperor
  • Posts: 10942
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #76 on: July 27, 2015, 10:25:05 PM »
Romm thinking about ASLR appears to be stuck in the 2008 thinking presented by Tad Pfeffer et al (see the top pdf in the first attached image); which was subsequently formally adopted by NOAA in their Dec. 2012 SLR guidance document.

Since 2008 there have been numerous findings including most prominently by Rignot et al in 2015 showing that the WAIS is less stable than previously believed (i.e. by Pfeffer et al 2008); yet people like Romm fail to update their thinking to reflect such new findings.  Examples of other considerations ignored by people like Romm include: (a) the newly identified & well develop subglacial meltwater drainage systems below the WAIS; (b) the greater geothermal heating below the WAIS (see the second & third images) and (c) possible/probable activation of the Thwaites Glacier Eastern Shear Margin by a retreat of the PIIS face so as to accelerate the ice flow down the SW Tributary Glacier shown in the fourth image.

Many public figures such as Romm feel comfortable ignoring the recent research (most significantly by Rignot who is one of Hansen's co-authors), and instead clinging to 2008 interpretations just because NOAA is slow to update their old reports.


Hi ASLR,
In his Hansen-comment Romm links to his earlier comment on Rignot et al 2014:
http://thinkprogress.org/climate/2014/05/13/3437033/coastal-cities-abandoned/

I read him as saying that Hansen doesn't need to be more sure of 3m by 2100 than the science at this point can warrant, and that we shouldn't forget that even if 3m by 2100, or earlier, would not be reached, that doesn't mean that the risk of 1-2m by 2100 isn't urgent enough to justify very strong mitigation. Hansen has a suspicion, and it doesn't need to turn out right to be justified. That he could be right is reason enough to take his suspicion very seriously, and justifies even stronger mitigation (and adaptation) than the risk of 1-2m by 2100 does. I think that's what Romm is saying, and I agree with that.


Lennart,

Thanks for the response (and all your other great posts on this topic); however:

(a) All of Rignot's most disturbing papers about ASLR (see the Antarctic folder) were published in 2015 not 2014, so Romm is out-of-date on the true risks of over 2m of SLR, and
(see also: Rignot on potential EAIS ice loss:
http://climatestate.com/2015/06/09/eric-rignot-observations-suggest-that-ice-sheets-and-glaciers-can-change-faster-sooner-and-in-a-stronger-way-than-anticipated/ )

(b) Romm seems to be downplaying the risk of the temporary radiative forcing imbalance that is related to the volume of melt water released from the ice sheets; and as shown in the attached image from Hansen et al 2015, the Antarctic melt water has more impact on the temporary change in radiative forcing than does Greenland melt water.

Thus even though Romm may be correct that 2m of SLR by 2100 may be horrible; the fat-tail of the SLR PDF is getting fatter, and it does no one any good to ignore this advance in our understanding of the situation.

Very best,
ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 10942
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #77 on: July 27, 2015, 10:35:18 PM »
Here's Greg Laden on Hansen et al:
http://scienceblogs.com/gregladen/2015/07/27/catastrophic-sea-level-rise/

My comment:
Hansen et al don't model ice melt, I think; they assume exponential melt increase and see what happens with ocean and surface temperatures. Their suspicion is that this could happen in the coming decades/centuries and they give arguments why this may be plausible, or even likely.


I believe that you are correct that Hansen et al 2015 do not explicitly model the ice melt; however, they do point to the last-Eemian multi-meter SLR event; which they cite as justification for assuming the exponential ice melt behavior.  However, as ice sheet models cannot yet match the late-Eemian SLR case it is difficult to fault the Hansen et al 2015 assumptions for possible ice mass loss.  Certainly, it will be many years before we have reasonably definitive information; but if we due experience multiple meters of SLR this century, at least we will not be able to say that we weren't warned.
“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

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #78 on: July 27, 2015, 11:16:43 PM »
ASLR,
Sorry, but which 2015-papers by Rignot are you referring to?
As far as I know the high impact papers on WAIS/AIS are from 2014:
https://scholar.google.com/citations?hl=en&user=Am3-eqEAAAAJ&view_op=list_works&sortby=pubdate

The fat tail is getting fatter, yes, I think Romm agrees with that, as far as I understand.
Hansen may even think the fat tail is turning into the best estimate, and he may be right.

But it's hard to prove that at this point, and all Romm is saying, I believe, is that Hansen doesn't need to prove that a 10 yr doubling time is likely to be taken seriously, exactly because, as you say, it will take many years before we have reasonably definitive information.

A-Team

  • ASIF Upper Class
  • Posts: 1656
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #79 on: July 27, 2015, 11:28:33 PM »
Romm should know better to perpetuate Refkin's  "discussion journal" ploy. There's no such thing. ACP is a conventional journal; articles are peer-reviewed by two outside reviewers and a designated editor. The article is being peer-reviewed by ACP for ACP. One of the reviewers is more distinguished than need be, the other is not yet known.

This journal and many others have moved towards transparency and permanence of the peer review process. The wrapper for that is called ACPD. It cannot be interpreted as a separate journal because authors are then publishing the same thing twice, forbidden. The article was submitted in June; the ACP's editorial decision is due in early September, a normal time frame. ACPD does not have any buildings, post office boxes, bank accounts, editors, reviewers or subscribers -- it is just the submission database for ACP.

But, but what about them traditional non-discussion journals, isn't there a big difference?
No difference at all, all journals have the same workflow. Their submission database pipeline is structured exactly like ACP's, same fields. You just don't get to see it.

But, but the peer review process is highly opaque for a reason. Sometimes a reviewer didn't read the paper too closely, has no understanding of this field, or just didn't follow the reasoning. Or needs to take revenge on a competitor or just unload some bile. The field will suffer if we have to wash our dirty linen in public.
What goes around, comes around. You've just made a strong case for transparency.

I practically invented catastrophism, yet my theories weren't cited #immanuelVelikovsky
Only open peer review enables people like you to submit substantive comments for consideration.

I read a preprint once. I am too trusting maybe, believe everything I read. It had some typos and I came down with a cold afterwards. Now I'm repeating those same errors in my own papers.
You always have the freedom to wait until September to read the Hansen paper. Disclosure: it could still have some mistakes.

I found a number of simple-minded blunders just in the first couple of pages (too busy to write 'em up). I have better things to do than read preprints that will never get out of peer review.
Your best option then is wait until September to see if the Hansen paper is accepted for publication. It's a pity you are too busy to share these putative errors in a discussion comment. Aren't you concerned reviewers won't catch them?

I dunno. Shouldn't we go back to journal-of-record mode printed on glossy paper? This online stuff doesn't have any heft or credibility. My PC crashed the other day. Millennials/discussion papers are disruptive.
Paper journals, pay phones on the corner, pay-to-view newspapers, checks in the mail, taxis ...

If the second reviewer also has suggestions but generally a positive take, the odds are overwhelming (99+%) that it will be formally accepted by the journal largely as it stands.

I do expect fixed typos, minor wording changes, revised paragraphs, clarified phrases, toned down language in assertions, clearer graphics, better legends, working urls, and additional citations in the final. I have never heard of an article that sailed through verbatim. Nor one that did a 180º. The vast majority of authors won't budge an inch. They'd rather withdraw the mss and submit it elsewhere.

So at the risk of repeating myself:

The Hansen article WAS submitted to a conventional peer-reviewed journal.
The peer review process there has nothing out of the ordinary (except internet-age transparency)
There will be some text changes before the article migrates into ACP's final repository.
There will be no significant changes in the article's thrust based on 1st reviewer's comments.

The Hansen article WAS submitted to a conventional peer-reviewed journal.
The peer review process there has nothing out of the ordinary (except internet-age transparency)
There will be some text changes before the article migrates into ACP's final repository.
There will be no significant changes in the article's thrust based on 1st reviewer's comments

The Hansen article WAS submitted to a conventional peer-reviewed journal.
The peer review process there has nothing out of the ordinary (except internet-age transparency)
There will be some text changes before the article migrates into ACP's final repository.
There will be no significant changes in the article's thrust based on 1st reviewer's comments
« Last Edit: July 28, 2015, 06:16:59 AM by A-Team »

A-Team

  • ASIF Upper Class
  • Posts: 1656
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #80 on: July 27, 2015, 11:32:57 PM »
but which 2015-papers by Rignot are you refering to

The same one I was above. Please take a moment to re-read the above post on Google Scholar, general Google, and ResearchGate searches. Start by seeing if you can reproduce the output below. 

None of the 2015 papers by co-author Rignot are cited in the Hansen paper. Surely Rignot remembers them. I can just guess what happened here: the usual. They have been reworking drafts since forever. It is a mid-size collaboration with endless ccing of mss suggestions and changes. Rignot is a very busy guy mid-way down the author list, he did his bit back in 2014 and moved on. The 2015 articles themselves were probably still hung up in peer review but for sure he knew what was in them as he wrote his bit for the Hansen article.

If the 2015 Rignots appeared substantially before this article was submitted on June 9th, reviewers could suggest (or even demand) that the Hansen article encompass their results and cite them. The authors could refuse the first by saying Rignot already did.

The evolving instability of the remnant Larsen B Ice Shelf and its tributary glaciers
A Khazendar, CP Borstad, B Scheuchl, E Rignot… - Earth and Planetary …, 2015 - Elsevier
Abstract Following the 2002 disintegration of the northern and central parts of the Larsen B
Ice Shelf, the tributary glaciers of the southern surviving part initially appeared relatively
unchanged and hence assumed to be buttressed sufficiently by the remnant ice shelf. ...
 
Supraglacial lakes advance inland on the Greenland ice sheet under warming climate
…, X Fettweis, M Morlighem, E Rignot - EGU General …, 2015 - adsabs.harvard.edu
Abstract Supraglacial lakes (SGLs) form annually on the Greenland ice sheet and, when
they drain, their discharge enhances ice-sheet flow by lubricating the base and potentially
by warming the ice. Today, SGLs tend to form within the ablation zone, where enhanced ...

Undercutting of marine‐terminating glaciers in West Greenland
E Rignot, I Fenty, Y Xu, C Cai… - Geophysical Research …, 2015 - Wiley Online Library
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 ...
« Last Edit: July 28, 2015, 12:35:28 AM by A-Team »

AbruptSLR

  • ASIF Emperor
  • Posts: 10942
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #81 on: July 27, 2015, 11:33:26 PM »
ASLR,
Sorry, but which 2015-papers by Rignot are you referring to?
As far as I know the high impact papers on WAIS/AIS are from 2014:
https://scholar.google.com/citations?hl=en&user=Am3-eqEAAAAJ&view_op=list_works&sortby=pubdate

The fat tail is getting fatter, yes, I think Romm agrees with that, as far as I understand.
Hansen may even think the fat tail is turning into the best estimate, and he may be right.

But it's hard to prove that at this point, and all Romm is saying, I believe, is that Hansen doesn't need to prove that a 10 yr doubling time is likely to be taken seriously, exactly because, as you say, it will take many years before we have reasonably definitive information.


Lennart,
The following 2015 interview with Rignot addresses exactly his thoughts on this matter
http://climatestate.com/2015/06/09/eric-rignot-observations-suggest-that-ice-sheets-and-glaciers-can-change-faster-sooner-and-in-a-stronger-way-than-anticipated/
Extract: "Machens: Hansen (2007), assumed an ice sheet contribution of 1 cm for the decade 2005–15, with a potential ten year doubling time for sea-level rise, based on a nonlinear ice sheet response, which would yield 5 m this century. Considering past sea level sometimes rose quickly, jumps associated with catastrophic ice-sheet collapses, Hansen appears plausible. Thus, are we getting closer to modeling ice sheet dynamics in a nonlinear fashion?
Rignot: Jim’s calculations are back of the envelope calculations that do not include any ice physics. That ice sheet loss will proceed in a non linear fashion is certainly a given but from there on a whole variety of scenarios are possible, and we do not have the tools in hand to answer that question.
We need fully coupled ice sheet/ocean/sea ice/atmosphere models and we do not have them now. 5 m this century is hard to conceive, because even a speed up of all glaciers in Antarctica and Greenland by a factor 10 would not get us there in time. But I would rather hear Jim’s upper bounds being discussed than the overly conservative scenarios from existing, poorly skilled numerical models."

Furthermore, the following extract (edited by Alley) comes from the National Research Council, NRC, (2013), Abrupt Impacts of Climate Change Anticipating Surprises, The National Academies Press, Washington D.C.:
"A retreat of Thwaites Glacier in West Antarctica could give a much wider and deeper calving front than any observed today, so the "speed limits" suggested by Pfeffer et al. (2008) may not apply (Parizek et al., 2013)."

This extract indicates that accepting the Pfeffer et al (2008) SLR pdf may be inappropriate from a public safety point of view.

I (and Rignot & Alley) know that there is a lot of uncertainty about both when any main stage collapse of the WAIS will begin and at what rate it will proceed at, but I still do not think that Romm should say:
"But the fact is, on our current emissions path, we now appear to be headed toward the ballpark of 4-6 feet of sea level rise in 2100 — with seas rising up to one foot per decade after that…."

Very best,
ASLR

P.S. I will look-up the 2015 Rolling Stone interview with Rignot soon.
« Last Edit: July 28, 2015, 02:01:24 AM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 10942
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #82 on: July 28, 2015, 12:32:23 AM »
P.S. I will look-up the 2015 Rolling Stone interview with Rignot soon.


I think that I was wrong about a 2015 Rolling Stone interview with Rignot, but I did find the following extract from the 2014 article from the Washington Post

http://www.washingtonpost.com/national/health-science/research-casts-alarming-light-on-decline-of-west-antarctic-ice-sheets/2014/12/04/19efd3e4-7bbe-11e4-84d4-7c896b90abdc_story.html

Extract: "So how fast could the loss of West Antarctica unfold? Velicogna’s co-author, Eric Rignot of UC-Irvine, suggested that in his view, within 100 to 200 years, one-third of West Antarctica could be gone.
Rignot noted that the scientific community “still balks at this” — particularly the 100-year projection — but said he thinks observational studies are showing that ice sheets can melt at a faster pace than model-based projections take into account."

Also, NRC (2013) consider abrupt SLR to be at least a 1m of SLR within an approximately 30-year period (or a rate of SLR of 33 mm/yr over such a 30-year period by 2100), and NRC 2013 singles out the WAIS as a possible specific source for such abrupt GLSR

Extract: "However, a large part of the West Antarctic Ice Sheet (WAIS), representing 3-4 m of potential sea-level rise, is capable of flowing rapidly into deep ocean basins. Because the full suite of physical processes occurring where ice meets ocean is not included in comprehensive icesheet models, it remains possible that future rates of sea-level rise from the WAIS are underestimated, perhaps substantially. Improved understanding of key physical processes and inclusion of them in models, together with improved projections of changes in the surrounding ocean, are required to notably reduce uncertainties and to better quantify worst-case scenarios. Because large uncertainties remain, the Committee judges an abrupt change in the WAIS within this century to be plausible, with an unknown although probably low probability."


Also see:
http://www.motherjones.com/environment/2015/07/earth%E2%80%99s-most-famous-climate-scientist-issues-bombshell-sea-level-warning
http://www.motherjones.com/environment/2014/05/west-antarctic-ice-sheet-collapse
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

  • ASIF Emperor
  • Posts: 10942
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #83 on: July 28, 2015, 01:37:48 AM »
ASLR,
I do think Romm/ClimateProgress missed the Pollard et al 2015 study on hydrofracture and cliff failure. Or at least I can't find any mention of it right now.

I concur, but Pollard et al 2015 was about postulated conditions broadly representative of a warm Pliocene period (could be a little warmer than the late-Eemian assumed by Hansen et al 2015), which may, or many not, match the conditions assumed by Hansen et al 2015's future cases; however, as hydrofracturing and ice cliff failure was not considered before 2015, we should be very careful about relying on older SLR projections like Pfeffer et al 2008.
« Last Edit: July 28, 2015, 01:58:55 AM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

sidd

  • ASIF Middle Class
  • Posts: 987
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #84 on: July 28, 2015, 06:44:18 AM »
I agree with Mr. van der Linde, in that it will take many years to get definitive information. But this is the situation as i understand

0)Marine fronted ice sheets on retrograde beds are unstable. Antarctica has many.

1)Melt begets melt is the proposal in the subject paper, this is explicitly exponential, even in the absence of 0)

2)A host of other ills from from anthro fossil loading of the air affect the great ice sheets, speed melt, and together, are explicitly at least nonlinear, even excluding 0) and 1)

3)The ice sheet contribution to sea level rise will increase at at least nonlinear rate, and if the subject paper is also correct, at exponential rate. In worst case AIS will waste mass at superexponential rate

4)The first sign of nonlinearity will be increase in ice sheet contribution to sea level rise, which we already see.

5)It will get worse. Every day it will get worse faster.

sidd
« Last Edit: July 28, 2015, 07:01:43 AM by sidd »

Lennart van der Linde

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #85 on: July 28, 2015, 07:55:19 AM »
I (and Rignot & Alley) know that there is a lot of uncertainty about both when any main stage collapse of the WAIS will begin and at what rate it will proceed at, but I still do not think that Romm should say:
"But the fact is, on our current emissions path, we now appear to be headed toward the ballpark of 4-6 feet of sea level rise in 2100 — with seas rising up to one foot per decade after that…."

What would be a better way of putting it, you think? Maybe you're right that Romm doesn't stress the new findings enough, although he does mention them and says we should take them into account.

sidd

  • ASIF Middle Class
  • Posts: 987
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #86 on: July 28, 2015, 08:08:25 AM »
The paper, as Prof. Archer put it, is strenuous. I just got my jaws around the Jenkins and Doake, 1991 reference and i include figure 14 which shows the buttressing force maximum at the grounding line. This, of course, becomes important when hot water gets there.

sidd

Lennart van der Linde

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #87 on: July 28, 2015, 08:18:11 AM »
but which 2015-papers by Rignot are you refering to

The same one I was above. Please take a moment to re-read the above post on Google Scholar, general Google, and ResearchGate searches. Start by seeing if you can reproduce the output below. 

Ok, if those are the ones you're talking about. I assumed both of you meant the 2014-papers on WAIS. My mistake.

Lennart van der Linde

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #88 on: July 28, 2015, 08:23:26 AM »
Hansen on his blog, apologizing to Joughin and others for attacking the 200-900 timeframe in the way that he did on his blog:
http://csas.ei.columbia.edu/2015/07/27/ice-sheet-200-900-year-time-scale/

"Yikes! It has been pointed out to me that the specificity of 200-900 years in my post about ice sheet time scales has the potential to be very unfair to specific individuals. The example that was shown to me was a paper by Ian Joughin published in Science 16 May 2014 in which that range of time scales is mentioned. Joughin is a brilliant young scientist making major contributions to our understanding of ice sheets via numerous field investigations in Greenland and Antarctica, as well as via state-of-the-art modeling, a combination of skills that most of us can only dream of. The time scales that he obtains come out of the modeling, not from pressure to avoid the uncomfortable 100 year time scale that policymakers consider relevant.

I apologize to Joughin, his co-authors and any other scientists who may have a similar situation. It was my fault for not thinking through possible repercussions of my presentation. I should have stuck to discussion of the amplifying feedbacks that we identified and their potential to reduce the time scale for large sea level rise."

Lennart van der Linde

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #89 on: July 28, 2015, 08:29:00 AM »
And here the part he apologizes for:
http://csas.ei.columbia.edu/2015/07/27/darn-sea-level-disaster-ahead-in-200-900-years-when/

"let me mention some curious numerology to get you thinking about scientific reticence.

Did you read any of the recent papers that concluded ice sheets may be disintegrating and might cause large sea level rise in 200-900 years? The time needed for ice sheets to respond to climate change is uncertain, and there are proponents for time scales covering a huge range. However, 200-900 years should cause a scientist to scratch his head. If it is uncertain by an order of magnitude or more, why not 100-1000? Where does the 200-900 precision come from?

Why the peculiar 900 years instead of the logical 1000? Probably because nobody cares about matters 1000 years in the future (they may not care about 900, but 200-900 does not seem like infinity). A scientist knowing that sea level is a problem does not want the reader to dismiss it.

Why 200 years? For one thing, 100 years would require taking on the formidable IPCC4, which estimates that even the huge climate forcing for a hypothetical 936 ppm CO2 in 2100 would yield less than one meter sea level rise. For another thing, incentives for scientists strongly favor conservative statements and militate against any “alarmist” conclusion; this is the “reticence” phenomenon that infects the sea level rise issue2. “Scientific Reticence and Sea Level Rise” will be the subject of a session at the American Geophysical Union meeting this year4.

IPCC conclusions about sea level rise rely substantially on models. Ice sheet models are very sluggish in response to forcings. It is important to recognize a great difference in the status of (atmosphere-ocean) climate models and ice sheet models. Climate models are based on general circulation models that have a long pedigree. The fundamental equations they solve do a good job of simulating atmosphere and ocean circulations. Uncertainties remain in climate models, such as how well they handle the effect of clouds on climate sensitivity. However, the climate models are extensively tested, and paleoclimate changes confirm their approximate sensitivities.

In contrast, we show in a prior paper5 and our new paper3 that ice sheet models are far too sluggish compared with the magnitude and speed of sea level changes in the paleoclimate record. This is not surprising, given the primitive state of ice sheet modeling. For example, a recent ice sheet model sensitivity study6 finds that incorporating the physical processes of hydrofracturing of ice and ice cliff failure increases their calculated sea level rise from 2 meters to 17 meters and reduces the potential time for West Antarctic collapse to decadal time scales. Other researchers7,8 show that part of the East Antarctic ice sheet sits on bedrock well below sea level. Thus West Antarctica is not the only potential source of rapid change; part of the East Antarctic ice sheet is also susceptible to rapid retreat because of its direct contact with the ocean and because the bed beneath the ice slopes landward (Fig. 1), which makes it less stable.

Our simulations were aimed to test my suspicion that ice sheet disintegration is a very nonlinear phenomena and that the IPCC studies were largely omitting what may be the most important forcing of the ocean: the effect of cold freshwater from melting ice. Rather than use an ice sheet model to estimate rates of freshwater release, we use observations for the present ice melt rate and specify several alternative rates of increase of ice melt. Our atmosphere-ocean model shows that the freshwater spurs amplifying feedbacks that would accelerate ice shelf and ice sheet mass loss, thus providing support for our assumption of a nonlinear ice sheet response.

Our analysis, however, is based on much more than the climate simulations, as it relies on a huge body of research by the relevant scientific communities, as indicated by the 300 references. Our analysis is based on about equal parts of information gleaned from paleoclimate studies, climate modeling, and modern observations of ongoing climate changes."

Lennart van der Linde

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #90 on: July 28, 2015, 02:48:44 PM »
Hansen et al argue that ice sheet melt over the past few decades had about a 10 yr doubling time or less. Their fig.S20, attached below, shows how large the yearly swings in ice melt are, which makes it hard to determine the acceleration factor on such a short timescale. Shown are a linear (Velicogna) and an exponential (10 yr doubling) melt acceleration, besides the year to year fluctuations.

Lennart van der Linde

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #91 on: July 28, 2015, 02:53:21 PM »
Fig.S22 in Hansen et al, attached below, shows the potential effects of 6 and 25 meters of SLR.

crandles

  • ASIF Upper Class
  • Posts: 1591
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #92 on: July 28, 2015, 05:11:25 PM »
Fig.S22 in Hansen et al, attached below, shows the potential effects of 6 and 25 meters of SLR.

I am surprised that 25m doesn't have more effect on area submerged than shown above. Of course even 2 or 3m would be devastating to small islands.

With 25m sea level rise, it looks like land area would only decline around(rough eyeball) 3%? Patchy of course: Bangladesh and small islands losing large proportions of their land but plenty of other countries losing little area.


Lennart van der Linde

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #93 on: July 28, 2015, 05:44:26 PM »
I don't know about 25m, but for 10m this study gives 2% of area and 10% of world population, so 600-700 million people currently, and probably growing rapidly:
http://eau.sagepub.com/content/19/1/17

A-Team

  • ASIF Upper Class
  • Posts: 1656
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #94 on: July 28, 2015, 06:01:58 PM »
Not to mention storm surges and salt water intrusion into drinking water and agricultural aquifers which will already be very costly at 0.5 meters.

This map is also a disaster cartographically speaking, in terms of scaling (do we really need to emphasize the Himalayas or should coastal ramping be the sole focus?). The palette is compressed but seemingly not as the usual log. This map has been done better many times before with zoomable maps. Note however Supplemental Material does not fall under peer review and Fig.S22 is very unlikely be revised or improved.

The second image shows the exceedingly poor quality of the map for the western US -- no impacts to the port of Portland, the San Joaquin Valley already under water, the Imperial Valley ag hotspot not flooding even though it is already way below sea level, the Sea of Cortez mysteriously flooding some more and so forth. Somewhere they had co-registration issues.

It is not rocket science to find a nice DEM of world elevation on the internet and assign a pretty palette to low contours at 1 m intervals. Two minutes work?

The other curious aspect of this map is how many people experience only minor inconveniences (eg US west of Texas: winter lettuce at risk) other than being asked to pay, like now, for people on East Coast barrier islands who have been wiped out many times before despite innumerable warning because their home insurance payments are outsourced to people in the MidWest and West Coast. Florida too, warnings go back decades, how many times do they have to be told before they take responsibility upon themselves? Given the current level of animosity towards New Yorkers etc where I live, I'd be surprised to see a measurable level concern for problems foreign people having overseas. Watch a youTube on Africa: a zebra gets taken by the lions but the rest of the herd goes right back to grazing.

In terms of superstorms, I have to say that they would be very popular in the US. Turn on the weather channel now and it is all about disaster weather. Somewhere else preferably. This is what the viewers want. Another very popular show here was called the Agony of Defeat, endless clips of ski jumpers crashing or pole vaulters missing the cushion. So I don't know that sea level and storms were the right topics to elevate concern about climate change (but then what is, 2º?).

To their credit, the native resolution of the authors' submission is twice that in the post above, 1009 x 662 below (which won't display properly here without an additional click). As explained many times before, these can be extracted in ImageJ or online tools like http://www.extractpdf.com/ It's the very first thing to do in reading a scientific article.
« Last Edit: July 28, 2015, 10:15:40 PM by A-Team »

AbruptSLR

  • ASIF Emperor
  • Posts: 10942
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #95 on: July 28, 2015, 06:35:49 PM »
I (and Rignot & Alley) know that there is a lot of uncertainty about both when any main stage collapse of the WAIS will begin and at what rate it will proceed at, but I still do not think that Romm should say:
"But the fact is, on our current emissions path, we now appear to be headed toward the ballpark of 4-6 feet of sea level rise in 2100 — with seas rising up to one foot per decade after that…."

What would be a better way of putting it, you think? Maybe you're right that Romm doesn't stress the new findings enough, although he does mention them and says we should take them into account.

I guess that besides agreeing that Hansen et al 2015 have not proven that ASLR will occur this century, and that there is still sufficient doubt/uncertainty for policymakers (and commentators like Romm) to hide behind this uncertainty so as not to take any responsibility to safeguard the public from this risk, I provide the attached image to help clarify the point that I was trying to make.  This figure shows four different cases where new data (indicated by the red pdf) is combined with old priors to create new posterior pdfs.  In the top case the new findings can be considered linear so it merely fattens the tail of the new posterior pdf (and as policymaker ignore the tail, they do not need to do much).  In the second case the new finding can be considered somewhat non-linear so that not only is the tail of the pdf fattened but it shift the whole pdf to the right (so policymakers only need to take moderate action).  While the bottom two cases show new findings that are increasingly non-linear, with increasingly more significant impacts.

Now, Hansen et al 2015, not only showed that during the late-Eemian that ice mass loss from the WAIS (& adjoining EAIS marine glacier area) is very sensitive to forcing and thus is non-linear, and that there is a positive ocean-ice melt interaction feedback that is also non-linear.  To that I showed that Hansen et al 2015 ignored the risks of higher ECS, geothermal heating in the WAIS, subglacial basal ice melting in the WAIS, and the impact of strong El Ninos (like this year), all of which have non-linear impacts on the posterior pdf.  Now I note a few more non-linear risks: (a) hurricanes and/or atmospheric river events dropping warm rain on Greenland; (b) the recent faux hiatus pumping more heat into the ocean than the atmosphere so that we are further down the ice mass loss hole (which is driven by ocean forcing) than the IPCC projections consider; and (c) anthropogenic (and anthropogenically triggered carbon-cycle contributions to atmospheric GHG concentrations) forcing (including reductions in negative anthropogenic aerosol forcing) may be much harder to slow than most decision makers are willing to admit.

Therefore, while Romm is welcome to hedge this prognostications however he sees fit; I imagine that in ten to fifteen years time when our fully coupled ESM models can handle the very complex ASLR case, people like Romm will just say "who would have thought", when in reality they had been fully warned by experts such as Hansen et al 2015.

« Last Edit: July 28, 2015, 07:13:13 PM by AbruptSLR »
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

Sleepy

  • Guest
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #96 on: July 28, 2015, 07:11:40 PM »
Joining to follow the thread.
 
I don't think that map in the paper is accurate enough. As an example, Gothenburg doesn't show any blue spots. They are planning for three levees there with the IPCC levels in mind. At est. ~20billion SEK. At the same time they are planning to build a city tunnel for trains...
http://cityplanneronline.com/cityplanner/project/webgl/index.do;jsessionid=CB1DB532D84F95BEA6B83420A254F49E?uid=ZD1mr6Yb&lang=en
The southern part in the map will be an island at higher levels since the water will enter from further south and surround it without levees. The place that I grew up in will be a beach property at 3m, unfortunately the nearest city centre (not Gothenburg) will be under water.

I can't imagine the costs world wide for a 3m sea level rise...

Lennart van der Linde

  • ASIF Middle Class
  • Posts: 653
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #97 on: July 28, 2015, 10:32:39 PM »
while Romm is welcome to hedge this prognostications however he sees fit; I imagine that in ten to fifteen years time when our fully coupled ESM models can handle the very complex ASLR case, people like Romm will just say "who would have thought", when in reality they had been fully warned by experts such as Hansen et al 2015.

I don't see Romm hedging and I think he's taken Hansen very seriously from the beginning, which for him is since Katrina in 2005. My reading of Romm is that he sees Hansen saying that "multi-meter SLR this century is likely under BAU", but apparently this statement was taken out of the draft/summary sent to journalists, since it's not in the final discussion paper submitted for review.

So Hansen thinks it's likely, but not (all of) his co-authors. Or Hansen thinks it's likely, but he cannot make this case strongly enough yet in a scientific sense. And Romm says he doesn't need to, to still have a very strong case for much stronger mitigation. That's all, I think, but of course I may well be wrong.

A-Team

  • ASIF Upper Class
  • Posts: 1656
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #98 on: July 29, 2015, 01:18:45 AM »
That may have been put in by the PR communications team, thinking to be helpful. There's no voting or vetoing by co-authors in a largish collaborative article, far too ponderous. A co-author can mention their druthers a few times but Hansen as senior author makes all the final decisions; that's understood at the time you sign on.

This paper is a godsend for co-authors: name on instant classic, bump in exposure for the home institution, tonne of later cites to skew the Dean's metrics. No one is going to fall on their sword nitpicking "in this century" as it is in decent alignment with the article.

Keep in mind the paper itself was locked down on the date they handed it over to ACP, June 9. Who knows when and by whom this summary/PR piece was written or what all it consisted of, or who if anyone on the science side issued an approval.
« Last Edit: July 30, 2015, 12:48:30 AM by A-Team »

AbruptSLR

  • ASIF Emperor
  • Posts: 10942
    • View Profile
Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #99 on: July 29, 2015, 05:48:17 AM »
while Romm is welcome to hedge this prognostications however he sees fit; I imagine that in ten to fifteen years time when our fully coupled ESM models can handle the very complex ASLR case, people like Romm will just say "who would have thought", when in reality they had been fully warned by experts such as Hansen et al 2015.

I don't see Romm hedging and I think he's taken Hansen very seriously from the beginning, which for him is since Katrina in 2005. My reading of Romm is that he sees Hansen saying that "multi-meter SLR this century is likely under BAU", but apparently this statement was taken out of the draft/summary sent to journalists, since it's not in the final discussion paper submitted for review.

So Hansen thinks it's likely, but not (all of) his co-authors. Or Hansen thinks it's likely, but he cannot make this case strongly enough yet in a scientific sense. And Romm says he doesn't need to, to still have a very strong case for much stronger mitigation. That's all, I think, but of course I may well be wrong.

Lennart,

I very much appreciate your points above, and I do not want to be beating a dead horse (as policymakers probably will not do more than what they are already doing, note that CoP21 may yet prove to be toothless).  Nevertheless, the implications if Hansen et al 2015 are correct are so disturbing to me that I think that more needs to said on this matter:

1) Pollard et al 2015 found that in the Pliocene cases that they modeled that they could not replicate the observed paleo sea levels without hydrofracturing and cliff failures.  I imagine that very few bloggers here have examined the susceptibility of the Byrd Subglacial Basin to rapid and extensive hydrofracturing and cliff failures but I have examined it off and on for over three years now, and it honestly frightens me, regardless of whether or not computer models can demonstrate such a rapid collapse mechanism or not.   Furthermore, with regard to the WAIS, I do not believe that the Pliocene cases examined by Pollard et al 2015 were that much worse than the late-Eemian considered by Hansen et al 2015.  Also, with a projected increase in ENSO activity and the uncertainty about the impact of the faux hiatus on Southern Ocean CDW temperatures; I believe that it is short sighted to believe it unlikely that the WAIS will not experience forcing comparable to the late-Eemian by about 2035 to 2040.

2) Given that under Hansen et al 2015's assumed conditions that the planetary energy imbalance could peak dramatically, it seems highly irresponsible to not at least dramatically increase the field and modeling budgets for examining the AIS ice loss case.

3) In the way of a general comment, I have read that capable people are frequently susceptible to addictive behavior, and it seems to me that at least the IPCC scientists (yes including Alley) fall into this category.  They are so good at dreaming-up magical reasons that ASLR is not likely this century, that they can rationalize anything to discount this risk, such as: (a) the fact that we have been exceeding RCP 8.5 forcing for years is irrelevant and says nothing about future political will power; (b) the fact that the observed Southern Ocean deep water is warming much faster than the IPCC models predicted has uncertain consequences and is difficult to model so it is best not to worry and (c) the fact that chaotic systems such as the Tropical Pacific - WAIS system can resonant and produce highly non-linear responses are again too difficult to model so it is best not talk about it.

Finally, I hope that the scientific community takes Hansen et al 2015 seriously enough to modify the ACME project to better evaluate the implications of possible abrupt ice sheet collapse this century.

Very best,
ASLR
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson