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Sigmetnow

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Hansen et al paper: 3+ meters SLR by 2100
« on: July 20, 2015, 04:50:10 PM »
The new Hansen et al paper looks to be a very important one.  Ties in with ASIF threads like SLR, Places Becoming Less Livable, and discussions of the 2°C target.
 
@EricHolthaus: James Hansen: Sea level rise could top 10 feet by 2100. Peer reviewed study with 16 co-authors. Yikes.   
http://t.co/r69oYcqYm5

@EricHolthaus: Today's paper by Hansen et al could prove a turning point on climate change action. NYC may have only ~50 yrs left.
http://t.co/r69oYcqYm5

https://twitter.com/ericholthaus/status/623130549234733056

The Daily Beast article:
James Hansen, the former NASA scientist whose congressional testimony put global warming on the world’s agenda a quarter century ago, is now warning that humanity could confront “sea level rise of several meters” before the end of the century unless greenhouse gas emissions are slashed much faster than currently contemplated.

This roughly ten feet of sea level rise—well beyond previous estimates—would render coastal cities such as New York, London and Shanghai uninhabitable.  “Parts of [our coastal cities] would still be sticking above the water,” Hansen says, “but you couldn’t live there.”

http://www.thedailybeast.com/articles/2015/07/20/climate-seer-james-hansen-issues-his-direst-forecast-yet.html
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jai mitchell

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #1 on: July 20, 2015, 04:59:37 PM »
hah!  just posted same on SLR and social cost of carbon thread!

have not yet read the report but this is already in line with adjustments coming from studies in antarctica and greenland.
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Sigmetnow

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #2 on: July 20, 2015, 07:17:22 PM »
No reason it can't be discussed on multiple threads -- and no doubt it will -- but this can be a place to post when no particular thread seems quite right.
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Sigmetnow

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #3 on: July 22, 2015, 02:57:18 AM »
The Hansen et al paper has not yet been peer-reviewed -- in part to speed the publication and assure the information is available before the Paris climate talks in December.

The article serves as a sobering wakeup call to those who still dispute the threat posed by our ongoing burning of fossil fuels," he said.

But the study could also be met with skepticism from the scientific community, Mann and other scientists said. Whereas peer review is traditionally done before a study is published, Atmospheric Chemistry and Physics is an open access journal where peer review takes place after publication. Scientists and the public submit their comments and concerns to the study authors, who then address them and update the paper if needed. Only then is the paper considered "accepted."

This type of publishing process is a "bit new and unusual," said Mann, "and it will take time, I imagine, for the scientific community to fully embrace this alternative approach to publication. But it is increasingly widespread and, in my view, totally legitimate."

It is even more rare for such a study to be publicized before the peer review process is complete, said Andrew Shepherd, a polar scientist at the University of Leeds, in England. "I would not recommend reporting on a paper ahead of peer review," he said.

Shepherd said Hansen and his colleagues used a relatively short time period—15 years—to calculate the accelerated loss of ice from Greenland and Antarctica due to climate change, and that he would "exercise caution when interpreting such numbers."

Mann also said he is skeptical that the paper assumed melting of the ice shelves would accelerate constantly with time, and that it used a low-resolution climate model to examine how this meltwater would affect ocean circulation.

Still, Mann said, "the authors have done a real service to the scientific discourse by putting forward some interesting and provocative ideas."

Hansen told reporters during a press call on Monday that he and he colleagues decided to publish the paper in an open access, open peer review journal to ensure the results were available to international leaders ahead of the Paris climate treaty talks in December. Hansen said he will spend the next few months educating treaty delegates on the study, but declined to provide further detail about who he would be meeting with, or when.

http://insideclimatenews.org/news/21072015/new-study-says-even-2-degrees-warming-highly-dangerous
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Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #4 on: July 23, 2015, 03:47:58 PM »

A-Team

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #5 on: July 23, 2015, 05:53:35 PM »
There's been numerous ill-informed and outright erroneous takes on peer review here that has distracted greatly from the actual content of the paper.

Here the authors sent in a submission on 11 June 2015, it was accepted by an editor of Atmos. Chem. Phys. of Copernicus Publications (part of the European Geosciences Union) as a discussion paper on July 9th and posted online July 23rd. All this rush for a December conference?

Anyone can register with the journal and submit a pdf critique; if it's not substantive, it won't be posted. The authors then post a line-by-line response. Especially to comments of the two peer-reviewers assigned to the article by the editor.

After activity dies down, the journal editor reads it all, decides whether or not to promote the original or amended article out of the discussion area, ie from ACPD to ACP. That is the peer review process at this family of journals and one that I find -- having been on both sides of traditional peer review -- find both satisfactory and superior.

It's superior in that referees are more numerous and their comments are public. That eliminates a lot of snarky unsubstantative remarks right there, only designated reviewer comments can be anonymous. I often find expert comments more interesting than the original article ... shop talk, sitting in the dugout listening to Inside Baseball minutiae.

But the biggest gain with this style of peer review is shaving 6 months off the period of darkness. Before, the article was presented at meetings and circulated among a few insiders but with 99% not having a clue until the (already stale) article appeared. I call this Botticellian peer-review whereby the article, like The Birth of Venus, abruptly appears as fully adult.

It's true reporters don't have the scientific background to read a discussion paper and are incapable of evaluating it on their own. This creates a very dangerous dependency on peer-review approval since a lot of crap makes it through peer review as any scientist can tell you.

I find this a bogus complaint because once the discussion paper is in the public domain, reporters can ask any number of outside scientists who read it for their take. I don't see how a reporter can conflate this with a white paper issued by think tank to advance some agenda. These are PR pieces not written by qualified academics and will never even be submitted to a journal.

Here the press releases should never have been issued until the discussion paper was ready to link because 'a lie can travel half way around the world before the truth can even get it boots on' (http://quoteinvestigator.com/2014/07/13/truth/). However I expect the content to stand up quite well to the scrutiny it will receive.

When I was peer-reviewing (it's unpaid), I resented spending a lot of time on an article, only to have all my effort tossed away in a go/no go decision by the editor. It was not unusual to call out mistakes and see them sail through; the bigger picture is the editor has to fill up an issue and the authors need to get their mss out the door and move on to the next one.

I saw an interesting case recently over at The Cryosphere where a Jakobshavn article was ultimately declined even though the authors agreed to (too many) amendments. A better version was eventually published two years later in a different journal but the original and comments stayed up in the discussion sector, another great idea.

It's worth noting too that big meetings like AGU fill the air with press releases that all too often are missing any pdf or ppt or video of what the scientists actually said. No one complains about it -- people who couldn't attend like to hear the news.
« Last Edit: July 26, 2015, 06:59:01 PM by A-Team »

Lennart van der Linde

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Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #7 on: July 23, 2015, 10:33:31 PM »
Andy Revkin on Hansen et al 2015:
http://dotearth.blogs.nytimes.com/2015/07/23/whiplash-warning-when-climate-science-is-publicized-before-peer-review-and-publication/?smid=fb-share

Seems the published version of the paper is slightly different from the one journalists had seen before.

A-Team

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #8 on: July 24, 2015, 04:19:24 AM »
I really don't like the sound of this Glover Park Group. No business communicating science... science can speak for itself. Like Refkin, I wonder who paid for them, how much (talking many ten$ of thousand$ here) and out of whose grant budget. I can't really see a European journal paying for DC PR. And who bungled the press release timing, conflated the articles, and sent around different versions? Maybe it was pro bono?

Whoever, this will be a huge turn-off to working scientists regardless of article merit.

Refkin still has one thing wrong. There is no separate 'discussion journal' ACPD. There is only a holding tank for ACP, a conventional journal that uses this peer-review mechanism, though in the interests of transparency (it's all open access), they archive the comment proceedings permanently in ACPD. It's the editor's file cabinet, a folder for each submission, not a journal.

If it isn't promoted to ACP, it didn't pass peer review. There could still be value in it. I even saw a case of an author later citing his rejected paper, which sounds sketchy. However citations at the end of journal articles need only be to the source, whatever that might be.

Elementary particle physics has thrown all this to the winds. Anyone, including certifiable nut cases, can upload their article to a pre-print server, arXiv. Of the tens of thousands of article per year, not 0.1% will ever be submitted to a peer-review journal. Which is just as well, little of value has been added to 1967 Weinberg/Salam theory by these half-million articles.

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« Last Edit: July 24, 2015, 07:22:41 AM by A-Team »

A-Team

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #9 on: July 24, 2015, 06:17:22 AM »
Enough socio, on to the scientific content ... I may put in a word or two on the Eemian paleo but otherwise pass the baton on Southern Ocean commentary to AbruptSLR, collecting here cross-posts if those posts are scattered around other forums.

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #10 on: July 24, 2015, 07:11:54 AM »
On a first reading, the paper reminds me of a previous Hansen paper, "Climate Change and Trace Gases" at the Royal Society, but less tightly argued. In many parts it is more a review article, but the model runs are, of course, his own work, as is the unification of various lines of evidence.

The main argument, as i see it, is the the feedback from enhanced ocean stratification due to ice melt in both hemispheres. Cold freshwater caps warmer seawater, trapping heat which is then more available to melt basal ice grounded at kilometer depth. In the South, freshwater freezes easier, adding more ice above the water column, deepening the trap. Suppression of the MOC increases available heat in the South. Much paleo evidence is marshalled in support.

Increased nebulosity in the South, expansion of subtropical deserts are other effects. The first is related to shift in the energy imbalance toward the tropics, and is somewhat counterintuitive, at least to my intuition.

Two questions spring to my mind:

1)the ansatz of exponential melt: his Velicogna and IMBIE graphs demonstrate that a constant acceleration is as good a fit as an exponential one. Of course, the argument can be turned on its head, that one cannot rule out exponential melt. But lacking an ice model coupled to ocean/atmosphere, i think he has not made the case. Having more ocean heat available at ice basal depth is necessary but not sufficient; how can the heat get into the ice fast enuf, or alternatively, how can the ice flow fast enuf to the hot ocean ? Paleo evidence indicates this did happen at the end of the Eemian, but my cavilling soul is unsatisfied without detail.

2) I think the model does not capture the effect of rain on Greenland. He mentions Neff(2014)  and the atmospheric river of 2012, but does not link to his model predicting larger storms.

That said, i recall seeing and reading his senate testimony in 1988. And I do recall that was unconvinced then, and it took me more than a decade to realize he was right, long after the model successes after Pinatubo and other eruptions, and much laborious calculation on my part.

sidd

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #11 on: July 24, 2015, 08:06:11 AM »
Nice comment, sidd. That 2007 Hansen article you mention would be free full @ http://rsta.royalsocietypublishing.org/content/365/1856/1925. Curiously, in support of your observation of similarity, Hansen told Refkin he has been working on today's article for 8 years. Three co-authors are on both papers.

W Neff 2014 is below but the 2012 Greenland event is done better (109 cites), certainly the ice core history, by SV Nghiem 2012 among others. Rain on snow seems more significant in mobilizing the western half of Greenland. About half this area is land-terminating and so not in contact with ocean; only 7 of 55 marine-terminating ice shelves are left today and the effect on grounded termini comes from current circulation bringing in water from elsewhere that was already warmer:
during a week of warm, wet cyclonic weather in late August and early September 2011 extreme surface runoff from melt and rainfall led to a widespread acceleration in ice flow that extended 140 km into the ice-sheet interior.

http://woodland.ucsd.edu/wp-content/uploads/2014/04/Neff_etal_2014.pdf
http://onlinelibrary.wiley.com/doi/10.1029/2012GL053611/full
http://www.sciencedaily.com/releases/2015/07/150713113447.htm

What is your take on Trenberth's (condescending) assessment in the dot earth column? Trenberth sent this out as a press release of his own (not waiting for a journalist to ask). So far it's not suitable as an ACPD comment: 

The new Hansen et al study is provocative and intriguing but rife with speculation and “what if” scenarios. It has many conjectures and huge extrapolations based on quite flimsy evidence, but evidence nonetheless. In that regard it raises good questions and topics worthy of further exploration, but it is not a document that can be used for setting policy for anthropogenic climate change, although it pretends to be so.
« Last Edit: July 24, 2015, 02:14:17 PM by A-Team »

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #12 on: July 24, 2015, 09:07:52 AM »
Hansen et al say (p.20078-79):
"Freshwater injection is specified as 360Gtyr−1 (1mm sea level) in 2003–2015, then growing with 5, 10 or 20 year doubling time (Fig.8 ). Injection ends when input to global sea level reaches 1 or 5m. The sharp cut-off aids separation of immediate forcing effects and feedbacks. We do not argue for this specific input function, but we suggest that rapid meltwater increase is likely if GHGs continue to grow rapidly. Greenland and Antarctica have outlet glaciers occupying canyons with bedrock below sea level well back into the ice sheet (Fretwell et al., 2013; Morlighem et al., 2014; Pollard et al., 2015). Feedbacks, including ice sheet darkening due to surface melt (Hansen et al., 2007b; Robinson et al., 2012; Tedesco et al., 2013; Box et al., 2012) and lowering and thus warming of the near-coastal ice sheet surface, make increasing ice melt likely...
We add freshwater to the North Atlantic (ocean area within 52–72◦N and 15◦E–65◦N) or Southern Ocean (ocean south of 60◦S), or equally divided between the two oceans. Ice sheet discharge (icebergs plus meltwater) is mixed as fresh water with mean temperature−15◦C into top three ocean layers (Fig. S7)."

They find (p.20079-81):
"Temperature change in 2065, 2080 and 2096 for 10 year doubling time (Fig.9) should be thought of as results when sea level rise reaches 0.6, 1.7 and 5m, because the dates depend on initial freshwater flux. Actual current freshwater flux may be about a factor of four higher than assumed in these initial runs, as we will discuss, and thus effects may occur ∼20 years earlier. A sea level rise of 5m in a century is about the most extreme in the paleo record (Fairbanks, 1989; Deschamps et al., 2012), but the assumed 21st century climate forcing is also more rapidly growing than any known natural forcing. Meltwater injected on the North Atlantic has larger initial impact, but Southern Hemisphere ice melt has a greater global effect for larger melt as the effectiveness of more meltwater in the North Atlantic begins to decline. The global effect is large long before sea level rise of 5m is reached. Meltwater reduces global warming about half by the time sea level rise reaches 1.7m. Cooling due to ice melt more than eliminates A1B warming in large areas of the globe. The large cooling effect of ice melt does not decrease much as the ice melting rate varies between doubling times of 5, 10 or 20 years (Fig. 10a). In other words, the cumulative ice sheet melt, rather than the rate of ice melt, largely determines the climate impact for the range of melt rates covered by 5, 10 and 20 year doubling times. Thus if ice sheet loss occurs even to an extent of 1.7m sea level rise (Fig. 10b), a large impact on climate and climate change is predicted...
Global cooling due to ice melt causes a large increase in Earth’s energy imbalance (Fig. 10b), adding about +2Wm−2, which is larger than the imbalance caused by increasing GHGs. Thus, although the cold fresh water from ice sheet disintegration provides a negative feedback on regional and global surface temperature, it increases the planet’s energy imbalance, thus providing more energy for ice melt (Hansen, 2005). This added energy is pumped into the ocean. Increased downward energy flux at the top of the atmosphere is not located in the regions cooled by ice melt. On the contrary, those regions suffer a large reduction of net incoming energy (Fig. 11a). The regional energy reduction is a consequence of increased cloud cover (Fig. 11b) in response to the colder ocean surface. However, the colder ocean surface reduces upward radiative, sensible and latent heat fluxes, thus causing a large (∼50Wm−2) increase of energy into the North Atlantic and a substantial but smaller flux into the Southern Ocean (Fig. 11c). Below we conclude that the principal mechanism by which this ocean heat increases ice melt is via its effect on ice shelves. Discussion requires examination of how the freshwater injections alter the ocean circulation and internal ocean temperature."

So to me a core question seems to be how much of this extra 2W/m2 global energy imbalance will/could reach the ice shelves/sheets.
« Last Edit: July 24, 2015, 09:14:08 AM by Lennart van der Linde »

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #13 on: July 24, 2015, 01:49:48 PM »
Hansen et al say (p.20092):
"The critical issue is whether human-spurred ice sheet mass loss can be approximated as an exponential process during the next few decades. Such nonlinear behavior depends upon amplifying feedbacks, which, indeed, our climate simulations reveal in the Southern Ocean."

p.20102:
"CO2 is more recalcitrant than snow and ice, i.e., its response time is longer. CO2 inserted into the climate system, by humans or plate tectonics, remains in the climate system of order 100000 years before full removal by weathering (Archer, 2005). Even CO2 exchange between the atmosphere (where it affects climate) and ocean has a lag of the order a millennium (Fig. 24). In contrast, correlations of paleo temperatures and sea level show that lag of sea level change behind temperature is of order a century, not a millennium (Grant et al., 2012). We suggest that limitations on the speed of ice volume (thus sea level) changes in the paleo record are more a consequence of the pace of orbital changes and CO2 changes, as opposed to being a result of lethargic ice physics."

P.20112-13:
"Loss of ice shelves that buttress the ice sheets potentially can lead to large sea level rise (Mercer, 1978). The ocean depths with largest warming in response to surface freshening (Fig. 16) encompass ice shelf grounding lines that exert the strongest restraining force (Jenkins and Doake, 1991). The impact of warming CDW varies among ice shelves because of unique geometries and proximity to the CDW current, but eventually a warming ocean will likely affect them all. As ice shelves weaken and ice sheet discharge increases the process is self-amplifying via the increasing freshwater discharge. Weber et al. (2014) used ocean cores near Antarctica to study the deglacial evolution of the Antarctic ice sheet following the last glacial maximum. They identified eight episodes of large iceberg flux, with the largest flux occurring ∼14600 years ago, providing evidence of an Antarctic contribution to Meltwater Pulse 1A, when sea level rose an average of 3–5mcentury−1 for a few centuries (Fairbanks, 1989). Ice sheets today may not have as much vulnerable ice as they had during the ice age. On the other hand, CO2 and the global climate forcing are increasing much more rapidly today, and heat is being pumped into the ocean at a high rate via the resulting positive (incoming) planetary energy imbalance (Hansen et al., 2011; Roemmich et al., 2015) providing ample energy to spur increasing ice melt."

P.20114:
"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 and 40 year doubling times require 50 and 200 years, respectively."

P.20117:
"Ice mass losses from Greenland, West Antarctica and Totten/Aurora basin in East Antarctica are growing nonlinearly with doubling times of order 10 years. Continued exponential growth at that rate seems unlikely for Greenland, and reduced mass loss in the past two years (Fig. S20) is consistent with a slower growth of the mass loss rate for Greenland. However, if GHGs continue to grow, the amplifying feedbacks in the Southern Ocean, including expanded sea ice and SMOC slowdown likely will continue to grow and facilitate increasing Antarctic mass loss."

P.20119:
"Our analysis paints a different picture than IPCC (2013) for how this Hyper-Anthropocene phase is likely to proceed if GHG emissions grow at a rate that continues to pump energy at a high rate into the ocean. We conclude that multi-meter sea level rise would become practically unavoidable. Social disruption and economic consequences of such large sea level rise could be devastating. It is not difficult to imagine that conflicts arising from forced migrations and economic collapse might make the planet ungovernable, threatening the fabric of civilization. This image of our planet with accelerating meltwater includes growing climate chaos and storminess, as meltwater causes cooling around Antarctica and in the North Atlantic while the tropics and subtropics continue to warm. Rising seas and more powerful storms together are especially threatening, providing strong incentive to phase down CO2 emissions rapidly.
Humanity faces near certainty of eventual sea level rise of at least Eemian proportions, 5–9m, if fossil fuel emissions continue on a business-as-usual course, e.g., IPCC scenario A1B that has CO2 ∼700ppm in 2100 (Fig. S21). It is unlikely that coastal cities or low-lying areas such as Bangladesh, European lowlands, and large portions of the United States eastern coast and northeast China plains (Fig. S22) could be protected against such large sea level rise. Rapid large sea level rise may begin sooner than generally assumed. Amplifying feedbacks, including slowdown of SMOC and cooling of the near-Antarctic ocean surface with increasing sea ice, may spur nonlinear growth of Antarctic ice sheet mass loss. Deep submarine valleys in West Antarctica and the Wilkes Basin of East Antarctica, each with access to ice amounting to several meters of sea level, provide gateways to the ocean. If the Southern Ocean forcing (subsurface warming) of the Antarctic ice sheets continues to grow, it likely will become impossible to avoid sea level rise of several meters, with the largest uncertainty being how rapidly it will occur."

P.20120-22:
"sea level rise sets the lowest limit on allowable human-made climate forcing and CO2, because of the extreme sensitivity of sea level to ocean warming and the devastating economic and humanitarian impacts of a multi-meter sea level rise. Ice sheet response time is shorter than the time for natural geologic processes to remove CO2 from the climate system, so there is no morally defensible excuse to delay phase-out of fossil fuel emissions as rapidly as possible.
We conclude that the 2◦C global warming “guardrail”, affirmed in the Copenhagen Accord (2009), does not provide safety, as such warming would likely yield sea level rise of several meters along with numerous other severely disruptive consequences for human society and ecosystems. The Eemian, less than 2◦C 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◦C, 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. Our finding of global cooling from ice melt calls into question whether global temperature is the most fundamental metric for global climate in the 21st century. The first order requirement to stabilize climate is to remove Earth’s energy imbalance, which is now about +0.6Wm−2, more energy coming in than going out. If other forcings are unchanged, removing this imbalance requires reducing atmospheric CO2 from ∼40020 to∼350ppm (Hansen et al., 2008, 2013a). The message that the climate science delivers to policymakers, instead of defining a safe “guardrail”, is that fossil fuel CO2 emissions must be reduced as rapidly as practical... Given the inertia of the climate and energy systems, and the grave threat posed by continued high emissions, the matter is urgent and calls for emergency cooperation among nations."

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #14 on: July 24, 2015, 02:09:28 PM »
I'm wondering what Hansen et al 2015 may imply for DeConto & Pollard 2015 (and vice versa), who presented these results at the AGU-conference earlier this year (paper to be published coming fall):
http://meetingorganizer.copernicus.org/EGU2015/EGU2015-8104.pdf

"the magnitude and rate of Antarctic ice sheet retreat are highly dependent on which future greenhouse gas scenario is followed, but even the lower emission scenarios produce an Antarctic contribution of several meters within the next several centuries. Once atmospheric CO2 concentrations exceed 2x preindustrial levels, we find that hydrofracturing by surface melt on ice shelves can trigger large-scale ice sheet retreat, regardless of circum-Antarctic ocean warming. Hence, unlike the LIG, atmospheric (not ocean) warming has the potential to become the primary mechanism driving future retreat of the Antarctic ice sheet. In simulations without atmospheric warming, we find small amounts of ocean warming can still produce large-scale retreat of the West Antarctic Ice Sheet, although the timescale of ocean-driven retreat is slower than atmospherically driven retreat."

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #15 on: July 24, 2015, 02:18:58 PM »
I'm also wondering what Trenberth thinks of Anderegg et al 2014:
http://journals.ametsoc.org/doi/full/10.1175/BAMS-D-13-00115.1

Abstract
"Treatment of error and uncertainty is an essential component of science and is crucial in policy-relevant disciplines, such as climate science. We posit here that awareness of both “false positive” and “false negative” errors is particularly critical in climate science and assessments, such as those of the Intergovernmental Panel on Climate Change. Scientific and assessment practices likely focus more attention to avoiding false positives, which could lead to higher prevalence of false-negative errors. We explore here the treatment of error avoidance in two prominent case studies regarding sea level rise and Himalayan glacier melt as presented in the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. While different decision rules are necessarily appropriate for different circumstances, we highlight that false-negative errors also have consequences, including impaired communication of the risks of climate change. We present recommendations for better accounting for both types of errors in the scientific process and scientific assessments."

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #16 on: July 24, 2015, 02:25:53 PM »
On risk assessment also see this recent report by David King et al:
http://www.csap.cam.ac.uk/projects/climate-change-risk-assessment/

"This report argues that the risks of climate change should be assessed in the same way as risks to national security, financial stability, or public health. That means we should concentrate especially on understanding what is the worst that could happen, and how likely that might be."

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #17 on: July 24, 2015, 02:51:24 PM »
So, what if Hansen et al are right on the potential/probable nonlinear response of the ice sheets to global warming due to rising CO2?

What if IPCC is indeed under-estimating the strength of this response, not only after 2100, as IPCC itself thinks likely, but already before 2100?

Is it possible, as Hansen et al suspect, that ice mass loss may double every 10-20 years for at least the next 100 years, or even 150 years? Are the amplifying feedbacks strong enough to keep accelerating ice sheet melt for so long? And how much of this potential acceleration have we already committed too?

Even a 20 year doubling time would lead to circa 5m of SRL by 2150 or so, with circa 4m of those from 2100-2150. IPCC does not really exclude this possibility. That would imply (over) a meter/decade of SLR by the last decades of this period, assuming kinematic constraints (Pfeffer et al 2008) would not limit this acceleration before.

A-Team

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #18 on: July 24, 2015, 02:55:58 PM »
I was curious about what specialties the 16 other co-authors contributed so looked up their most recent publications. Five of them seem to only co-publish with Hansen and are listed first. The other 11 have credibility in a wide range of climate topics relevant to this study. Six additional scientists are thanked at the end for providing additional information: A Carlson, E Cortijo, N Irvali, K Lambeck, S Lehman, and U Ninnemann.

The acknowledgements section does not state who did what; today that is increasingly required by journals and should be fixed in the final. Sometimes people will agree to comment a manuscript section extensively in exchange for a publication (ie without really participating in the research). Here co-authors are out of alphabetic order so presumably in contribution order. The study was funded entirely by private donors and charitable foundations, no grants.

Now I am wondering if these same donors are financing Glover Park Group throughout the whole campaign to the Paris conference (and beyond).

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Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #19 on: July 24, 2015, 03:00:04 PM »
Earlier Hansen was talking about 'the iceberg cooling' effect as a negative feedback for surface warming, but now it seems this still could be an amplifying feedback for ice melt.

jai mitchell

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #20 on: July 24, 2015, 05:05:38 PM »
how much of this potential acceleration have we already committed too?


At least several decades worth.

As aggressive decarbonization of the global economy continues, we will experience a rapid decline in anthropogenic aerosols.  These aerosols are preventing 40-60% of the current GHG abundance warming effect from impacting the climate.  During this period we will also continue to emit GHGs.

Since there is a 10-year time lag for full effect of warming upon GHG emission (due to water vapor and lapse-rate feedbacks) this means that the current global experience of warming, (as measured by ocean heat content gain) will increase by between 30 and 60% over the next 20 years. 

In addition, continued declines in arctic sea ice during the melt season, as well as increased negative snow cover anomalies in the NH, will produce significant albedo shifts that will yield additional increases in global heat gains. 

Sea Ice albedo effect:  http://fallmeeting.agu.org/2014/files/2014/12/CERES_AGU_final_PL.pdf
and:  http://climate.nasa.gov/news/2208/

snow anomalies:  http://climate.rutgers.edu/snowcover/chart_anom.php?ui_set=1&ui_region=nhland&ui_month=6

A recent paper showed how a single warm weather cyclonic event on greenland produced 15% of the total annual melt in 2011 due to rainfall on the ice cap.  The Hansen paper indicates that this will become a significant factor for SLR in coming years as the AMOC continues to slow down.

paper here: http://forum.arctic-sea-ice.net/index.php/topic,1329.0.html
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JimD

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #22 on: July 24, 2015, 06:10:26 PM »
In another thread someone asked this question, "would it not be possible to have someone of high standing like Hansen convince the President to issue a special order for that?

I snarked back about the likelyhood of the White House having had a little afterwork party the day Hansen retired as he would no longer be an 'official' thorn in their side and they could completely ignore him. 

A jest but very accurate I believe.  Hansen is now an official climate change 'activist' and will be perceived and treated as such.  He was a huge pain when he was an official person.  Hansen does not have 'high' standing in any meaningful sense of the word as having it would imply he has the power to effect change.  And he clearly does not.

I note that not only has Trenberth been dismissive of the new paper, but also Gavin Schmidt.  A quote from Schmidt's response,

"Gavin Schmidt, a climate scientist with NASA’s Goddard Institute for Space Studies, says the Hansen report is merely “one scenario, and not evidence for that scenario.”

Schmidt says the study “might add to the discussions” but is far enough from conventional thinking that it is unlikely to change mainstream climate views, international negotiations on reducing carbon, or the IPCC’s recommendations to world governments."

Gavin I would point out is still an 'official' climate scientist.

There seems to be some irrational sense that pronouncements from folks like Hansen will have some ability to cause or generate fast change.  Why people think this just amazes me and such thoughts fly in the face of all prior evidence.  It amounts to wishful thinking.

I am happy that some of the climate scientists are now using language which is much more alarmist than the 'official' climate scientists are willing to do - yet.  But the reason to do that and its hoped for effect have little to do with the government agreements, the IPCC or the 'official' world.  What we need to do is scare the living crap out of the public.  They are a little useful for that purpose.  What we 'need' is a catastrophic climate disaster - and that is just so unlikely to happen for some time yet.
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sidd

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #23 on: July 24, 2015, 08:33:15 PM »
Re: comment by Trenberth on Hansen(2015) in Revkin:

I do not support the adjective "flimsy" as applied to the evidence, the paleo evidence is quite strong. I agree with the points about limitations in the model, especially in neglect of  ENSO  and PDO  but that should spur us to better models. In this regard I see that Manabe agrees with me about the pressing importance of developing realistic ice sheet simulations. I agree that a comparison with present day observations might strengthen the paper, but so might many other things. I find it odd that Trenberth calls for such a comparison, but then goes on to bemoan the lack of such data in the Southern Ocean, and the complicating effects of the (largely imaginary) "hiatus," both of which would decrease the utility of such a comparison. 

The language of the comment is perhaps too strong for my taste. Most of the so called "speculation" is backed up (to varying degrees) by argument and data. Trenberth has taken issue with the findings of reduced precipitation over Antarctica, but he does not tell us why the argument by Hansen on the effects of freshwater  in the Southern Ocean is faulty.

As to Revkin: Revkin is a shill and his blog is a sewer. Many years ago, before i gave up on most Internet fora,  I commented there that he had turned into George Will before our eyes.  I see nothing in his latest to disabuse me of my opinion, or to tempt me back to his cesspit.

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Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #24 on: July 24, 2015, 10:42:56 PM »
I agree that a comparison with present day observations might strengthen the paper, but so might many other things. I find it odd that Trenberth calls for such a comparison, but then goes on to bemoan the lack of such data in the Southern Ocean, and the complicating effects of the (largely imaginary) "hiatus," both of which would decrease the utility of such a comparison. 

The irony may be that Hansen et al are pointing to a potential 'mega-hiatus' around 2050, with surface cooling but increased warming of the ocean.

What I don't understand: why don't Trenberth and others simply respond specifically to Hansen's main argument?

He's been saying for at least/almost a decade now that the current/future human climate forcing is much stronger than past natural forcings, so ice sheet response may be much stronger than in the past as well. The question is: how much stronger? This is a highly relevant question, but very difficult to answer. Hansen is trying his best and others are contributing as well, but it's too early for definitive answers. As long as I haven't seen any convincing refutation of Hansen's suspicion he may eventually well turn out to be (largely) right, for all I know.

For risk assessment scientifically argued suspicions like Hansen's seem very relevant, even if politically very inconvenient to powerful interests. Hansen in my opinion deserves the highest praise for his high quality scientific work, as far as I can tell as a layman, and his courage to not let himself be intimidated by those powerful interests. I don't know why colleagues like Trenberth and Schmidt do not give him stronger support, but it may be that they do feel more initimidated by the permanent pushback from vested interests, or maybe they just don't share Hansen's probably broader, deeper, fuller understanding of the climate system, and therefore his stronger concern?

wili

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #25 on: July 24, 2015, 11:04:38 PM »
Good point about risk assessment, LfdL, and nice take down of Refkin, sidd.

Here's a nice summary of the paper by rs: http://robertscribbler.com/2015/07/24/warning-from-scientists-halt-fossil-fuel-burning-fast-or-age-of-superstorms-3-20-feet-of-sea-level-rise-is-coming-soon/#comment-45703

    Warning From Scientists — Halt Fossil Fuel Burning Fast or Age of Superstorms, 3-20 Foot Sea Level Rise is Coming Soon

    First the good news. James Hansen, one of the world’s most recognized climate scientists, along with 13 of his well-decorated fellows believe that there’s a way out of this hothouse mess we’re brewing for ourselves. It’s a point that’s often missed in media reports on their most recent paper — Ice Melt, Sea Level Rise, and Superstorms. A paper that focuses on just two of the very serious troubles we’ll be visiting on ourselves in short order if we don’t heed their advice.

    The way out? Reduce global carbon emissions by 6% each year and manage the biosphere such that it draws carbon down to 350 ppm levels or below through the early 22nd Century. To Hansen and colleagues this involves a scaling carbon fee and dividend or a similarly ramping carbon tax to rapidly dis-incentivize carbon use on a global scale. Do that and we might be relatively safe. Safe, at least in the sense of not setting off a catastrophe never before seen on the face of the Earth. That’s pretty good news. Pretty good news when we consider that some of the best climate scientists in the world see an exit window to a hothouse nightmare we’re already starting to visit upon ourselves.

    The bad news? According to Hansen and colleagues, even if we just continue to burn fossil fuels and dump carbon into the atmosphere at a ‘moderate’ pace some of the terrifically catastrophic impacts of human caused climate change are not too far off.



    It’s worth noting that the 5-9 meter sea level rise during the Eemian occurred in the context of global temperatures that are now similar to our own (1-2 C above 1880s values).

    But it’s also worth considering that the underlying CO2 and greenhouse gas conditions for the current age are far, far worse.

    As the undersides of ice shelves erode and more fresh water laden ice bergs are pulled out into the ocean, these ice bergs begin to melt en mass. This massive ice melt develops into an enormous and expanding pool of fresh water at the surface.

    And its this troublesome demon that traps heat in the deeper ocean levels.

    So, in other words, as the ice from the land glaciers floats away and melts it traps and focuses more heat at the base of these great glaciers.

    It’s an amplifying feedback...

    In the worst case (5-10 year melt rate doubling times), it’s possibly

>>3 meters of sea level rise by mid Century, perhaps

>>7 meters by end Century under business as usual fossil fuel emissions.

    Even in the more moderate cases (10-20 year melt rate doubling times),

>>1 meter of sea level rise by mid Century and

>>3 meters or more of sea level rise by end Century is not entirely out of the question
"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."

A-Team

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #26 on: July 24, 2015, 11:20:20 PM »
There seems to be some irrational sense that pronouncements from folks like Hansen will have some ability to cause or generate fast change.  Why people think this just amazes me and such thoughts fly in the face of all prior evidence.  It amounts to wishful thinking.

I wish we could move the needle to wishful in my town but this may just be magical thinking on my part.

What we 'need' is a catastrophic climate disaster - and that is just so unlikely to happen for some time yet.

Arctic Ocean blowout is our best bet. Imagine six fraternity brothers gathering each New Year's eve to play another round of Russian Roulette with their six-shooter advanced to the next chamber. It's bound to end badly but we can't predict just when. That's us in late July with no real idea if the weather will finish off this round of melt season.

Revkin is a shill and his blog is a sewer.

It's there because it aligns with business interests of his employer. The Washington Post has been doing a much better job reporting climate coverage.

Hansen deserves the highest praise for his high quality scientific work. I don't know why colleagues like Trenberth and Schmidt do not give him stronger support, but it may be  they just don't share Hansen's probably broader, deeper, fuller understanding of the climate system, and therefore his stronger concern?

Indeed Hansen has made a great effort for many years. This quixotic  paper had zero prospects of changing the debate. Right now, maybe 5 new papers a week cross my desk all saying things are moving way faster than IPCC and such-and-such runaway feedback wasn't considered. Right.

People in my inland town couldn't care less about coastal flooding whether it's 20 or 40 years off; replacing all that infrastructure creates j.o.b.s and raises the value of their real estate. Between two oceans, a border fence and all the channels choices, climate refugee woes can be tuned out.

All this unbelievable nastiness from former colleagues? Over a much-stronger-than-average journal article??? Being an academic myself, I would say they're jealous of all the attention Hansen attracts. There must be quite the backstory here though. They're scrambling to fill the power vaccuum created by his retirement. With themselves.

jai mitchell

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #27 on: July 24, 2015, 11:28:21 PM »

5 new papers a week cross my desk all saying things are moving way faster than IPCC

mind starting a thread with just Doi?

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A-Team

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #28 on: July 25, 2015, 12:21:15 AM »
mind starting a thread with just Doi? I am trying to keep a running database

Interesting concept, be great to retrieve exactly what is wanted. It seems the many hands here could make light work of keeping up with research; in some sense we do now. Note forum itself can be text-searched periodically for doi.

I am the last person to consult about organization though ... maybe 50 pdfs open that I've been meaning to 'get to'. Hundreds of other files that need to be put away. I tend to just do another internet search rather than find something locally.

Greenland here has a "what's new" forum, far from exhaustive. It doesn't separate newspaper from campus press releases from actual articles. We have a whole lot of forums though.

There was a Finnish fellow on Skeptical Science or similar who for years posted titles of every single climate article article that came out, too broad for me to wade through. Index terms for sure, a good idea  but which mouse wants to put a bell on the cat.

Google Scholar in effect already maintains this running database, as well as the all-important forward cites (here of Hansen et al), and often points to open access links not on regular Google search. Neither provides consistent doi's or abstracts. Searching is an art form if you don't have a really high entropy search term. Also very repetitive. I don't think they dive into discussion articles that I want. Setting up enough alerts could get really tedious. PubMed is another comprehensive system for access, abstracts, overall biblio and links but very spotty outside of biomedical.

I wonder if there is interest in a 'best reads' forum. This would consist of well-written, not overly geeky, authoritative recent articles especially suited to learning something from. Just a list of title, author, abstract, open access link organized what topic you could learn about. For example, Arctic ocean stratification, inflows, outflows, surface and other currents. Wikipedia articles are very uneven and it's a real tussle to fix one.

In summary, it seems to be a lose-lose situation: lot of overhead to either disorganized and organized.

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #29 on: July 25, 2015, 01:57:39 AM »
Some how I feel that I should write something in this thread as the Hansen et al 2015 paper states very well many of the points that I have been saying that scientists should be at least acknowledging in documents like AR5 and NOAA guidance on SLR (which gives a high range of 2m by 2100).  Unfortunately, I am traveling through Monday, so I will limit myself to the following random points:

- Hansen's co-authors are serious scientists and the fact that they would put their names on this paper speaks volumes to me about how seriously they take this matter.  Whether policymakers listen to them, or not, is a totally separate matter; but I do believe that this paper will put more pressure on business-as-usual climate scientists to look a lot harder at the increasingly fat-tailed of the climate change risk pdf (note that I saying increasingly fat-tailed because as more information identifies more positive feedbacks, the old pdfs are history and should be ignored).
- Lennart raised the question about how Hansen et al's findings will impact the Pollard & DeConto projections about ASLR from hydrofracturing and cliff failure mechanism (which is dependent on atmospheric driving to achieve the hydrofracturing); and I note that the atmospheric cooling at high latitudes projected by Hansen et al does not occur until after massive amounts of iceberg armadas have been launched and have melted (which could take decades).  So this issue will not stop the collapse of the WAIS.
- The temporary increase in planetary energy imbalance cited by Hansen et al associated with the high latitude cooling associated with ice mass melting needs to be added on top of all of the other climate sensitivity mechanisms including the approximately 4.1C ECS identified by Trenberth & Sherwood, the high carbon-cycle GHG emissions, reductions in negative feedbacks, reductions in aerosol masking and anthropogenic cheating on CoP21 pledges.
- Lastly, I would like to note that while current ice sheet models (including the module in the ACME program) cannot project ASLR this provides no assurance that such ASLR will not occur in the coming decades, but without the ice sheet models making such specific projections, BAU climate scientists & policymakers will never acknowledge this risk so that risk will be carried by this and future generations without appropriate guidance.

I will post more next week,

Best,
ASLR
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sidd

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #30 on: July 25, 2015, 05:16:02 AM »
"There was a Finnish fellow on Skeptical Science or similar .."

Ari Jokimaki, https://agwobserver.wordpress.com/

Also, Tenney Naumer has a very useful site

http://climatechangepsychology.blogspot.com/

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #31 on: July 25, 2015, 09:22:34 AM »
Tad Pfeffer on Hansen et al, interviewed via Skype by, dare I say, Andy Revkin (sound quality is not too good):
https://www.youtube.com/watch?v=1Dqar1x-F70

He argues that to be policy relevant Hansen et al should have given a date by which the fastest SLR would be reached, and if that is more than say a century away, then policy makers will not be worried enough. I think Hansen et al do argue that 4m of SLR between 2100-2150, or even earlier, is not unthinkable, and that this risk is highly policy relevant at this moment, even if many policy makers do not (want to) recognize this (yet).

He also says no(t enough) work is being done on finding out how long it would take for the big Antarctic ice shelves to melt away, as a precondition for WAIS-disintegration to really speed up. He didn't mention Pollard et al 2015, but they are working on this, and more work is certainly needed. Hopefully the coming paper by DeConto & Pollard, mentioned above, will shed more light on this.

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #32 on: July 25, 2015, 09:58:33 AM »
Lennart raised the question about how Hansen et al's findings will impact the Pollard & DeConto projections about ASLR from hydrofracturing and cliff failure mechanism (which is dependent on atmospheric driving to achieve the hydrofracturing); and I note that the atmospheric cooling at high latitudes projected by Hansen et al does not occur until after massive amounts of iceberg armadas have been launched and have melted (which could take decades). So this issue will not stop the collapse of the WAIS.

If we look at figures 9 and 20 in Hansen et al we see substantial surface cooling around Antarctica around 2060. Depending on how fast the big ice shelves disappear in the modelling by DeConto & Pollard, this may slow down their disintegration by hydrofracturing, I suppose. On the other hand, if more ocean surface cooling lets more deeper warm water eat away the 'buttress of the buttress' as Hansen et al suggest, then this may speed up cliff failure more than DeConto & Pollard think, depending on the extent to which they reckon with such stronger stratification.

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #33 on: July 25, 2015, 10:13:26 AM »
Also relevant may be this post by ASLR in the Antarctica folder some time ago:

DeConto R, and Pollard D., (2014), "Antarctica's potential contribution to future sea-level rise", SCAR - COMNAP Symposium

http://www.scar2014.com/assets/SCAR_and_COMNAP_2014_Abstract_Document.pdf

Abstract: "A hybrid ice sheet-shelf model with freely migrating grounding lines is improved by accounting for 1) surface meltwater enhancement of ice shelf calving; and 2) the structural stability of thick (>800 m), marine-terminating (tidewater) grounding lines. When coupled to a high-resolution atmospheric model with imposed or simulated ocean temperatures, the new model is demonstrated to do a good job simulating past geologic intervals with high (albeit uncertain) sea levels including the Pliocene (3Ma; +20 ±10m) and the Last Interglacial (130-115ka; +4-9m).  When applied to future IPCC CMIP5 RCP greenhouse gas forcing scenarios with ocean temperatures provided by the NCAR CCSM4, the same model shows the potential for massive ice and freshwater discharge beginning in the second half of this century. In both RCP2.6 and 8.5 scenarios considerable retreat begins in the Pine Island Bay region of West Antarctica. In the more aggressive (and arguably more likely) RCP8.5 scenario, Pine Island Bay retreat is followed by more massive retreat of the entire WAIS, and eventual ice retreat into deep East Antarctic basins. During peak rates of retreat, freshwater discharge exceeds 1 Sv and exceeds 0.2 Sv for several centuries with potential to disrupt ocean circulation in addition to contributing between 2m and 9m sea level rise within the next 500 years. Here, we demonstrate that large portions of the Antarctic Ice Sheet (in West and East Antarctica) can retreat on relatively short (decadal to centennial) timescales, posing a serious threat to global populations."

Note that as 1 Sv = 86mm of SLR per year, this research indicates that the WAIS might plausibly contribute over 0.86 meters per decade to SLR before the end of this century. In addition to other SLR sources, this could resulting in over 3m of SLR, and over 4m of Regional SLR for the Continental U.S.A. for a RCP 8.5 pathway.


It seems this abstract has been removed since, but maybe this will be integrated into their coming paper.

Edit: the abstract is still available here, at p.86:
http://www.researchgate.net/profile/Tanya_Oneill/publication/267752555_Relief_analysis_in_periglacial_environments_on_selected_ice-free_areas_of_the_South_Shetland_Islands/links/54599bd10cf2cf516483d7a4.pdf
« Last Edit: July 25, 2015, 10:25:08 AM by Lennart van der Linde »

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #34 on: July 25, 2015, 10:50:53 AM »
Hansen et al use a global peak freshwater discharge of 2-4 Sv for their 20-10 year doubling time experiments (see their fig.8 ). DeConto & Pollard have peak discharge of more than 1 Sv from Antarctica alone, so will probably stay below the rates that Hansen et al use. But as ASLR pointed out: 1 Sv peak discharge, if lasting a decade, still amounts to circa 86 cm of SLR in that decade. If lasting five decades that would be more than 4m of SLR in half a century, comparable to what Hansen et al use in their 20 yr doubling scenario.

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #35 on: July 25, 2015, 03:10:41 PM »
Lennart raised the question about how Hansen et al's findings will impact the Pollard & DeConto projections about ASLR from hydrofracturing and cliff failure mechanism (which is dependent on atmospheric driving to achieve the hydrofracturing); and I note that the atmospheric cooling at high latitudes projected by Hansen et al does not occur until after massive amounts of iceberg armadas have been launched and have melted (which could take decades). So this issue will not stop the collapse of the WAIS.

If we look at figures 9 and 20 in Hansen et al we see substantial surface cooling around Antarctica around 2060. Depending on how fast the big ice shelves disappear in the modelling by DeConto & Pollard, this may slow down their disintegration by hydrofracturing, I suppose. On the other hand, if more ocean surface cooling lets more deeper warm water eat away the 'buttress of the buttress' as Hansen et al suggest, then this may speed up cliff failure more than DeConto & Pollard think, depending on the extent to which they reckon with such stronger stratification.

With an ECS of 4.1C we could be at peak Eemian surface temperature conditions by 2036 (or so); which would provide 2060-2036 = 24 years of WAIS collapse before any surface cooling provides a negative feedback on hydrofracturing (unless atmospheric rivers & or volcanic action causes surface melt).
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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #36 on: July 25, 2015, 05:24:21 PM »
Probably noted already on another forum ... positive oxygen isotope anomalies at Hercules Dome would prove WAIS collapsed during the Eemian, ie that issue is not resolved today but could be.

It's amazing to me, the scientific back-and-forth on the Eemian in Greenland, multiple groups saying it hardly melted but a Science paper and a metadata review saying it was a major contributor to SLR (at the expense of Antarctica). All in June/July 2015. The Eemian was not so long ago -- if it can't be used yet for ice sheet response calibration, reliably modeling future behavior seems very problematic.

Influence of West Antarctic Ice Sheet collapse on Antarctic surface climate
E Steig et al 18 June 2015 DOI: 10.1002/2015GL063861
http://www.atmos.washington.edu/~dargan/papers/set_submitted.pdf

...The lowered topography following WAIS collapse produces anomalous cyclonic circulation with increased flow of warm, maritime air toward the South Pole and cold-air advection from the East Antarctic plateau toward the Ross Sea and Marie Byrd Land, West Antarctica. Relative to the background climate, areas in East Antarctica that are adjacent to the WAIS warm, while substantial cooling (several ∘C) occurs over parts of West Antarctica.

Anomalously low isotope-paleotemperature values at Mount Moulton, West Antarctica, compared with ice core records in East Antarctica, are consistent with collapse of the WAIS during the last interglacial period, Marine Isotope Stage 5e. More definitive evidence might be recoverable from an ice core record at Hercules Dome, East Antarctica, which would experience significant warming and positive oxygen isotope anomalies if the WAIS collapsed.

The Greenland Ice Sheet during the last glacial cycle: Current ice loss and contribution to sea-level rise from a palaeoclimatic perspective
K Vasskoga et al https://www.sciencedirect.com/science/article/pii/S0012825215300167
During the Last Interglacial the Greenland Ice Sheet contributed 0.5–4.2 m to SLR. This is not sufficient to explain the 6–9 m MSL rise estimated for the LIG, which implies that a significant contribution to the LIG highstand came from Antarctica. Following the LIG the GrIS grew and attained its maximum volume of about 12 m global sea-level equivalents (SLEs) between 18 and 16 ka BP...

The GrIS probably reached its minimum Holocene extent around 4 ka BP, and modelling studies suggest that it contributed to a rise in global MSL of less than 0.2 m...Currently the GrIS occupies an area of ~ 1.7 × 106 km2 and features a volume of ~ 2.96 × 106 km3, which amounts to ~ 7.4 m SLE.  The GrIS is expected to contribute about 0.1–0.3 m to global MSL rise by the end of the 21st century. In a longer time perspective, modelling suggests that melting of the GrIS may replace ocean thermal expansion as the most important factor in future sea-level rise, potentially contributing with 0.7–2.6 m SLE within the next 500 years. Multi-millennial simulations show that the entire ice sheet (~ 7.4 m SLE) might disappear completely within less than three thousand years under high-emission scenarios.
« Last Edit: July 25, 2015, 05:31:54 PM by A-Team »

Clare

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #37 on: July 26, 2015, 08:38:29 AM »
I was surprised to see this being covered by this particular TV channel, AND that they have made a simulated flyover of what parts of Auckland would be underwater with 3m SLR. 

"A study led by arguably the world's best-known authority on climate change says a sea level rise of three metres in the next century is likely – and the effects on New Zealand would be devastating."

https://www.tvnz.co.nz/one-news/new-zealand/simulation-shows-unavoidable-3m-auckland-sea-level-rise-q02974.html

Clare

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #38 on: July 26, 2015, 09:10:23 AM »
Interesting update from Revkin, on the Bahama-boulders in particular:
http://dotearth.blogs.nytimes.com/2015/07/25/a-rocky-first-review-for-a-climate-paper-warning-of-a-stormy-coastal-crisis/?smid=tw-share&_r=0

On the ice shelves vulnerability, the paper could maybe be strengthened, as suggested by Pfeffer.

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #39 on: July 26, 2015, 10:47:44 AM »
Hansen et al say (p.20090):
"We take freshwater injection to be 720 Gtyr−1 from Antarctica and 360 Gtyr−1 in the North Atlantic in 2011, with injection rates at earlier and later times defined by assumption of a 10 year doubling time. Resulting mean freshwater injection around Antarctica in 1992–2011 is ∼400 Gtyr−1, similar to the estimate of Rye et al. (2014)." [with land ice mass loss of about 50-90 Gtyr-1 in 1992-2011, so ice shelves contribute about 80% or more of the Antarctic freshwater contribution; see pp.20088-89]

They find (p.20091):
"Global temperature has a peak at +1.2◦C in the 2040s for the modified forcings (Fig. 19). Ice melt cooling is advanced as global ice melt reaches 1m of sea level in 2060, 1/3 from Greenland and 2/3 from Antarctica. Actual sea level rise could be less than 1m, depending on the portion of melt from ice shelves (which has little effect on sea level), but contributions from ocean thermal expansion and mountain glacier melt would probably make global mean sea level rise at least of the order of 1m."

How crucial is "depending on the portion of melt from ice shelves", in light of the comment by Pfeffer? The shelves need to melt in order to enable further WAIS-collapse later (if doubling of ice mass is to continue for more than a few decades), but the earlier they do, the less sea level rises initially, in this experiment. Or maybe I misunderstand?

And how much is melt of the shelves accelerating? It seems Hansen et al don't give an estimate on this, or I've missed it?

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #40 on: July 26, 2015, 10:54:01 AM »
On the Bahama-boulders Hansen et al say (p.20069):
"The boulders must have been transported to their present position by waves, as two of the largest ones (Fig. 1) are located on the crest of the island’s ridge, eliminating the possibility that they were moved downward by gravity (Hearty, 1998) or are the karstic remnants of some ancient landscape."

So this needs to be cleared up, since Revkin shows that some argue they may be the result of erosion. This part of the argument, however, seems irrelevant to the argument of faster potential SLR than IPCC thinks likely, or even possible/plausible.

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #41 on: July 26, 2015, 01:31:13 PM »
On accelerating Antarctic ice shelves loss Paolo et al 2015 seems most relevant:
http://www.sciencemag.org/content/348/6232/327

Abstract
"The floating ice shelves surrounding the Antarctic Ice Sheet restrain the grounded ice-sheet flow. Thinning of an ice shelf reduces this effect, leading to an increase in ice discharge to the ocean. Using 18 years of continuous satellite radar altimeter observations, we have computed decadal-scale changes in ice-shelf thickness around the Antarctic continent. Overall, average ice-shelf volume change accelerated from negligible loss at 25 ± 64 cubic kilometers per year for 1994–2003 to rapid loss of 310 ± 74 cubic kilometers per year for 2003–2012. West Antarctic losses increased by ~70% in the past decade, and earlier volume gain by East Antarctic ice shelves ceased. In the Amundsen and Bellingshausen regions, some ice shelves have lost up to 18% of their thickness in less than two decades."

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #42 on: July 26, 2015, 05:27:47 PM »
Rignot et al 2013 on Antarctic ice shelves melting:
http://www.sciencemag.org/content/341/6143/266

Abstract
"We compare the volume flux divergence of Antarctic ice shelves in 2007 and 2008 with 1979 to 2010 surface accumulation and 2003 to 2008 thinning to determine their rates of melting and mass balance. Basal melt of 1325 ± 235 gigatons per year (Gt/year) exceeds a calving flux of 1089 ± 139 Gt/year, making ice-shelf melting the largest ablation process in Antarctica. The giant cold-cavity Ross, Filchner, and Ronne ice shelves covering two-thirds of the total ice-shelf area account for only 15% of net melting. Half of the meltwater comes from 10 small, warm-cavity Southeast Pacific ice shelves occupying 8% of the area. A similar high melt/area ratio is found for six East Antarctic ice shelves, implying undocumented strong ocean thermal forcing on their deep grounding lines."

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #43 on: July 26, 2015, 05:35:59 PM »
Depoorter et al 2013 on Antarctic ice shelves melting:
http://www.nature.com/nature/journal/vaop/ncurrent/abs/nature12567.html

Abstract
"Iceberg calving has been assumed to be the dominant cause of mass loss for the Antarctic ice sheet, with previous estimates of the calving flux exceeding 2,000 gigatonnes per year. More recently, the importance of melting by the ocean has been demonstrated close to the grounding line and near the calving front. So far, however, no study has reliably quantified the calving flux and the basal mass balance (the balance between accretion and ablation at the ice-shelf base) for the whole of Antarctica. The distribution of fresh water in the Southern Ocean and its partitioning between the liquid and solid phases is therefore poorly constrained. Here we estimate the mass balance components for all ice shelves in Antarctica, using satellite measurements of calving flux and grounding-line flux, modelled ice-shelf snow accumulation rates and a regional scaling that accounts for unsurveyed areas. We obtain a total calving flux of 1,321 ± 144 gigatonnes per year and a total basal mass balance of −1,454 ± 174 gigatonnes per year. This means that about half of the ice-sheet surface mass gain is lost through oceanic erosion before reaching the ice front, and the calving flux is about 34 per cent less than previous estimates derived from iceberg tracking. In addition, the fraction of mass loss due to basal processes varies from about 10 to 90 per cent between ice shelves. We find a significant positive correlation between basal mass loss and surface elevation change for ice shelves experiencing surface lowering and enhanced discharge. We suggest that basal mass loss is a valuable metric for predicting future ice-shelf vulnerability to oceanic forcing."

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #44 on: July 26, 2015, 05:48:57 PM »
Hansen et al refer to Rignot et al 2013 and Depoorter et al 2013 (p.20089):

"Rignot et al. (2013) and Depoorter et al. (2013) independently assessed the freshwater mass fluxes from Antarctic ice shelves. Their respective estimates for the basal melt are 1500±237 and 1454±174Gtyr−1. Their respective estimates for calving are 1265±139 and 1321±144Gtyr−1. This estimated freshwater loss via the ice shelves (∼2800Gtyr−1) is larger than freshwater gain by the Antarctic surface. Vaughan et al. (1999) estimated the net surface mass balance of the continent as +1811 and +2288Gtyr−1 including precipitation on ice shelves. IPCC (2013) estimates the net Antarctic surface mass balance as +1983±122Gtyr−1 excluding ice shelves. Thus comparison of continental freshwater input with ice shelf output suggests a net export of freshwater to the Southern Ocean of several hundred Gtyr−1 in recent years. However, substantial uncertainty exists in the difference between these two large numbers."

Somehow they cite slightly different numbers from Rignot et al 2013: 1500 vs 1325 Gt/yr for basal melting and 1265 vs 1089 Gt/yr for calving.

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #45 on: July 26, 2015, 05:55:09 PM »
Antarctic ice shelves have a total area of a little over 1,500,000 km2:
https://en.wikipedia.org/wiki/List_of_Antarctic_ice_shelves

So on average they thin by almost 1m/yr by basal melting.

A-Team

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #46 on: July 26, 2015, 07:49:32 PM »
Hansen et al refer to Rignot et al 2013

Rignot being one of the co-authors here, perhaps the two 2015 papers from him and Joughin (not a co-author) on imminent and irreversible Antarctic ice shelf collapse came too late for this draft.

I am still choking on the overly broad sweep of the Hansen article -- two of the building blocks have crumbled (see #36) since this paper was put together (6-8 weeks ago).

Below I dug into a very recent fiasco/scandal concerning the seeming slam-dunk issue of synchronizing Greenland and Antarctic ice cores over just the last 2,500 years, assigning stratospheric volcanoes to dates and modeling their cooling effects on climate through sulfate aerosols.

Mind you, the Sigl paper (first link below) is really excellent but frankly I do not see here an 'offset' or 'seven year bias' in ice core dates, but instead seven years of dating blunders by a cryosphere community that mistakenly deprecated dendrochronology, followed by years of rubbish and denial from climate aerosol modelers who write and tediously defend papers based on the misinterpreted record (notably ME Mann).

How much confidence can we have in a 115ka Greenland ice core chronology with the first 2.5ka proving such a struggle and extension to the Holocene seemingly a pipe dream? Very little, based on wholesale revisions of radar stratigraphy and Eemian nitrogen isotope dates. Yet a whole lot of paleo and forecast climatology is contingent on this. And this does not get to a tenth of the factual assumptions underlying the Hansen paper. Crawl before walking, walk before flying and all that.

Naturally the Sigl article shows very little curiosity about sources of ice dating mistakes, other than Vesuvius attribution which was nonsense from the get-go and corrected earlier by Baillie. (Indeed, the paper might well have gone point by point through every issue raised by the Baillie papers.)  Systemic errors in ice core analytics — such as flat-melt CFA and non-utilization of split beam optics to detect layer distortion —  are likely to have even larger cumulative effects in deeper deformed ice. Indeed, after so many siting errors such as NEEM, the new Renland core was drilled precisely where parallel layers could be obtained according to the sled radar grid.
 
It seems the seven extra years in the ice core chronology were inserted earlier than the 1257 Samalas event but later than 994 Be10 and C14 anomalies, an interval of 263 years. Is this better understood yet, that is, how much is still wrong (ie earlier than 1257 but not correctly dated initially in the ice chronology)?

The Sigl paper states that revised ice-core timescales are now accurate to <5 years, with revised age models pointing to previous 11 year errors in Greenland and 14 years in Antarctica. I didn’t quite follow why residual errors are still so high — dendrochronology has zero annual error on this scale, indeed I recall the Inyo bristlecone alone provide a continuous 9 ka record of the Holocene. Is the 5 year error attributable to deference to the Hidden Markov Matrix algorithm now being used on ice cores?

I am very familiar with scientific applications of HMM and 'maximal likelihood' statistics. The first thing to say here is HMM is just an algorithm within a particular non-Bayesian school of parametric statistics; despite the name, it does not necessarily find a more likely outcome than ordinary common sense and does not purport be objective (as the Sigl paper asserts): it merely carries out someone's code written to various buried subjective assumptions not necessarily met by the data feed. I'm ok with HMM on ice cores as a convenient first step that suggests an initial neutral (or at least uniform) baseline for multiple cores.

The real reason people use HMM is because it provides ‘error' estimates, leaving peer-reviewers with less to complain about. The issue getting lost here is formal error within the HMM framework vs real error in the real world.

I can’t envision HMM ever outperforming an expert human annotator in ice corp interpretation. Case in point: right here. The more holistic Baillie approach already has a better outcome than 5 year error. The misunderstanding about subjectivity may have arisen from the checkered history with different sunspot observers where indeed each observer had to be assigned an individual scaling factor.

There’s a fascinating backstory on what actually caused the C14 and B10 excursion in the tree rings and ice. I’ve included the better articles on those as well. How was it even possible for the C14 extravaganza in 775 to be missed by so many for so long? How many historic dates are based on what we now see as erroneous calibration?

Timing and climate forcing of volcanic eruptions for the past 2,500 years
M. Sigl and 24 others 2015
http://www.nature.com/nature/journal/vaop/ncurrent/full/nature14565.html

Tree ring effects and ice core acidities clarify the volcanic record of the first millennium
MGL Baillie and J McAneney 2015
http://www.clim-past.net/11/105/2015/cp-11-105-2015.html

The mystery of the offset chronologies: Tree rings and the volcanic record of the 1st millennium
J McAneney 2015
http://www.realclimate.org/index.php/archives/2015/02/the-mystery-of-the-offset-chronologies-tree-rings-and-the-volcanic-record-of-the-1st-millennium/

Volcanoes, ice-cores and tree-rings: one story or two?
MGL Bailli 2010
http://dx.doi.org/10.1017/S0003598X00099877

Proposed re‐dating of the European ice core chronology by seven years prior to the 7th century AD
MGL Baillie 2008
http://onlinelibrary.wiley.com/doi/10.1029/2008GL034755/full

Tree rings and volcanic cooling
KJ Anchukaitis 2012
http://dx.doi.org/10.1038/ngeo1645       

Dendrochronology raises questions about the nature of the AD 536 dust-veil event
MGL Baillie The Holocene, 4, 212–217, 1994

http://www.realclimate.org/index.php/archives/2012/11/responses-to-volcanoes-in-tree-rings-and-models/
Mann, M., Fuentes, J. & Rutherford, S. Nature Geosci. 5, 202–205 (2012).
Mann, M., Fuentes, J. & Rutherford, S. Nature Geosci. 5, 837–838 (2012).
Mann, M. E. et al. J. Geophys. Res. A. 118, 7617–7627 (2013)

Cosmic ray event of AD 774–775 shown in quasi‐annual 10Be data from the Antarctic Dome Fuji ice core
F Miyake 2015
http://onlinelibrary.wiley.com/doi/10.1002/2014GL062218/abstract

On a solar origin for the cosmogenic nuclide event of 775 AD
EW Cliver 2014
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150007938.pdf

A solar super-flare as cause for the 14C variation in AD 774/5?
R. Neuhäuser 2014
http://onlinelibrary.wiley.com/doi/10.1002/asna.201412071/abstract

Solar activity around AD 775 from aurorae and radiocarbon
R Neuhäuser 2015
http://arxiv.org/abs/1503.01581

The AD775 cosmic event revisited: the Sun is to blame
IG Usoskin 2013
http://arxiv.org/abs/1302.6897

« Last Edit: July 26, 2015, 08:01:51 PM by A-Team »

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #47 on: July 26, 2015, 08:19:21 PM »
Hansen et al experiment with a 10 yr doubling time for freshwater discharge from Antarctica, starting with 720 Gt/yr of ice mass loss in 2011.

Doubling every 10 yrs implies:
- 1440 Gt/yr in 2021
- 2880 Gt/yr in 2031
- 5760 Gt/yr in 2041
- 11520 Gt/yr in 2051
- 23040 Gt/yr in 2061

In total this would imply about 450,000 Gt of ice mass loss by about 2064, of which maybe half from ice shelves and the other half from the ice sheet, rising sea level by about 62 cm, and contributing about 3 cm/yr at this point?
Total SLR could be almost 1m by 2060 and total rate of SLR could then be ca 5 cm/yr (assuming the GIS-contribution wouldn't accelerate all the way upto 3 cm/yr), so by 2100 total SLR could be about/almost 3m, with no further acceleration.

Maybe we can also assume that in this scenario basal melting will double every 10 yrs:
- 2m/yr in 2021
- 4m/yr in 2031
- 8m/yr in 2041
- 16m/yr in 2051
- 32m/yr in 2061

The Ross Ice Shelve with an area of ca 487,000 km2 seems to be about 500m thick on average, from 300m at the front to 700m near the grounding line. So by about 2060 the RIS could be (almost/half?) gone in this scenario, by basal melting alone and some help from calving (cliff failure, hydrofracturing), although currently it seems to thin by only about 14 cm/yr, according to Depoorter et al 2013:
http://www.staff.science.uu.nl/~lenae101/pubs/Depoorter2013.pdf

Losing RIS would inject about 240,000 km3 of freshwater into the Ross Sea, so maybe half could be gone by 2060 in this scenario, with the other half gone by 2070?

Maybe ALSR can improve on my back of the envelope calculations :)

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #48 on: July 26, 2015, 08:35:51 PM »
Rignot being one of the co-authors here, perhaps the two 2015 papers from him and Joughin (not a co-author) on imminent and irreversible Antarctic ice shelf collapse came too late for this draft.

I am still choking on the overly broad sweep of the Hansen article -- two of the building blocks have crumbled (see #36) since this paper was put together (6-8 weeks ago).

Rignot et al 2014 is in the references, but not Joughin, indeed. Maybe they find him too 'conservative'?

And why have two building blocks crumbled? I don't see what you mean immediately...

Lennart van der Linde

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Re: Hansen et al paper: 3+ meters SLR by 2100
« Reply #49 on: July 26, 2015, 08:50:26 PM »
On ice shelves melting and calving also see Liu et al 2015:
http://www.pnas.org/content/112/11/3263.full.pdf

Abstract
"Iceberg calving from all Antarctic ice shelves has never been directly measured, despite playing a crucial role in ice sheet mass balance. Rapid changes to iceberg calving naturally arise from the sporadic detachment of large tabular bergs but can also be triggered by climate forcing. Here we provide a direct empirical estimate of mass loss due to iceberg calving and melting from Antarctic ice shelves. We find that between 2005 and 2011, the total mass loss due to iceberg calving of 755 ± 24 gigatonnes per year (Gt/y) is only half the total loss due to basal melt of 1516 ± 106 Gt/y. However, we observe widespread retreat of ice shelves that are currently thinning. Net mass loss due to iceberg calving for these ice shelves (302 ± 27 Gt/y) is comparable in magnitude to net mass loss due to basal melt (312 ± 14 Gt/y). Moreover, we find that iceberg calving from these decaying ice shelves is dominated by frequent calving events, which are distinct from the less frequent detachment of isolated tabular icebergs associated with ice shelves in neutral or positive mass balance regimes. Our results suggest that thinning associated with ocean-driven increased basal melt can trigger increased iceberg calving, implying that iceberg calving may play an overlooked role in the demise of shrinking ice shelves, and is more sensitive to ocean forcing than expected from steady state calving estimates."