Sea Level Rise and Social Cost of Carbon

[Ned W]

Reply #49 on: Today at 12:01:43 AM

Oh, good grief.

That is an opinion piece by some journalist or blogger named "Dady Cherry" or "Chery" (the byline is inconsistent).  His or her qualifications are listed as "co-editor in chief of News Junkie Post", whatever that is.

The article is entirely based on the work of Eric Rignot but completely ignores his own comments about the likely magnitude of 21st century sea level rise.  Instead, it paints a lurid picture of a global catastrophe following 3 to 5 meters of sea level rise in the next "decades".

Can you seriously not understand how non-credible a source that is?  This isn't WUWT.  Can't we leave that kind of "motivated reasoning" for the other side?

[jai mitchell]

With regard to best case/worst case scenarios.

Yes, this analysis does not include the potential for a radical global break from fossil fuel use.  Nor does it include the potential for widescale geoengineering as a world-ending moral hazard.

My analysis considers the following:



full image here:
http://oi57.tinypic.com/b4gwn8.jpg

Over 90% of this cumulative global heat accumulation is being deposited into the oceans.

[AbruptSLR]

We should recognize that there is only going to be one SLR scenario that plays out by the end of this century and that no one can identify that exact scenario today, but the tribal concession case (i.e. the case that society is willing to acknowledge) need not be that single SLR scenario.  So at our best today we need to rely on expert opinion, which is something that changes with time and on who you are asking.  Nevertheless, I am prepared to accept the panel of experts that Horton vetted; which provided the opinions presented in the attached image when asked what their best projections are for RCP 8.5 by 2100.

Many people believe that RCP 8.5 is an extreme case, but it is actually the BAU case that we are currently following, and rather than being an extreme physical case, it seems to me to be the most extreme case that society is prepared to consider.  That said, I cannot believe that we will get off this pathway before 2050, and I believe that this case is highly relevant to a discussion about SLR that is dominated by the ocean's thermal inertia.

In this survey distribution the possibility of exceeding 1m of eustatic SLR by 2100 is well over 50%, and at least one true expert (not some outlier) believes that following a RCP 8.5 scenario will result in a 50%CL of 6m of eustatic SLR this century.  Some people feel good about these kinds of odds; however, I do not, as that one 6m projection might be right.

[Ned W]

For the unmitigated warming scenario (RCP 8.5), the likely ranges are 0.7–1.2 m by AD 2100 and 2–3 m by AD 2300.

That seems about right to me.

[wili]

Thanks for that clear graph, ASLR. But do note that the newest info on WAIS and GIS should presumably make that 2013 piece out of date and so wrong (so anyone agreeing with it is agreeing with something we know to be wrong). Specifically, it should be skewed toward the right. The question is, by how much?

I'm looking for anyone out there who is making guestimates at this point, since we will have to wait for another survey of experts. The whole point of blogs like this is to speculate based on most recent findings, isn't it?

I would also point out that Climate Central, the Guardian and The Environmentalist are generally well regarded sources (as MSM sources go), though not, of course, at the level of peer reviewed papers or surveys of experts.

[AbruptSLR]

wili,

Your point is well taken with regard to the median value of the Horton survey; however, I believe that the fat tail of the distribution likely will not change much, as I suspect that the experts at this end of the graph have been aware of such as Rignot et al (2014) for some time.

Best,
ASLR

[Ned W]

But do note that the newest info on WAIS and GIS should presumably make that 2013 piece out of date and so wrong (so anyone agreeing with it is agreeing with something we know to be wrong).

I am pretty sure that Eric Rignot understands the implications of "the newest info on WAIS and GIS"  since he was lead author on the WAIS paper and 2nd author on the GIS paper.  He is quoted as saying that SLR by 2100 is likely to be near the upper end of the AR5 range, i.e. around 98cm.  Which is right at the peak of the distribution in Horton 2013. 

[wili]

Good point, ASLR.

Just to emphasize that I am interested in discussing a range of views, not engaging in some kind of high school debate, here is the latest on the issue from PhysOrg:

"All of our simulations show it will retreat at less than a millimeter of sea level rise per year for a couple of hundred years, and then, boom, it just starts to really go," Joughin said in a news release from the University of Washington...

Cochran agreed: The papers' message is "that … over the next couple hundred years, there's going to be a significant rise in sea level, and at this point we can't stop it." But, he added, "it doesn't say give up on trying to cut emissions. … [Just] don't buy land in Florida."

http://phys.org/news/2014-05-clock-west-antarctic.html#jCp

[AbruptSLR]

wili,

I appreciate all of the different sources of information that you are providing, and I also am not interested in winning a high school debate, or a popularity contest.  There is only one Earth that we all live on, and I also get frustrated that more scientists and policy makers want to follow the path of least drama when evaluating a situation that could push civil society past the tipping point.  Nevertheless, the best thing to do is to: (a) keep clarifying the facts/confusion; and (b) to help people to see that while this is a big problem, what they do as individuals matters.

That said, I would like to clarify that both Rignot et al's and Joughln's models can be taken as lower bound solutions to complex problems and cannot account for such positive feedback mechanisms for WAIS ice mass loss as:
(a) Likely calving from both the Pine Island Ice Shelf, PIIS, and the Eastern Thwaites Ice Shelf (note that the Thwaites Ice Tongue shown in the Rignot model currently has only a fraction of the structural integrity indicated by his model, due to extensive fracturing in the tongue); could both reduce buttressing support of both the PIG and the Thwaites Glacier, and also could trigger the SW tributary glacier feeding into PIIS, which in turn could activate the Eastern Shear Margin of the Thwaites Glacier.
(b) Most of the period that the models were calibrated to occurred during the recent hiatus period (including a low frequency of El Nino events) which certainly resulted in lower than potential ice mass loss from the ASE glaciers; and we can certainly expect this ice mass loss to accelerate during the coming positive Interdecadal Pacific Oscillation, IPO, phase (15 to 25 years or so).
(c) The models cannot replicate the Jakobshavn Effect that the ASE glaciers are subject to.
(d) As ice mass loss from the GIS results in amplified RSLR in Antarctica, the fact that the marine terminating glaciers in Greenland can contribute more to SLR than previously expected, will serve to destabilize the WAIS more in the future than previously expected.
(e) The basal melt water system beneath the ASE glaciers cannot have been fully modeled in either the Rignot or the Joughin projections, but this basal meltwater will increase as: (i) the glacier accelerate; (ii) as magma moves under the WAIS lithosphere due to isostatic rebound; and (c) due to increasing surface melting in the future.

Best,
ASLR

[sidd]

dear god:look at the numbers.
   
a) look at "glaciers and icecaps"  search term "GIC"   e.g.   doi:10.1038/nature10847
thats half a mm/yr  right now
b)look at antarctic peninsula search term "APIS"
c)Greenland SMB
d)WAIS

a) and b) will waste first and fastest. than  and there are tens  of centimeters SLR there.
GIS will undergo saddle collapse at 67N,

Sea level rise from the north, amplified by fingerprint effect will raise antarctic ice shelves and bathytherms, melting the gut outta WAIS.

But: we can help a) and b) and c) by cutting at least black carbon as fast as we can _today_, and CO2 to decrease radiative imbalance

This is important because

Sea level rise from the north, amplified by fingerprint effect will raise antarctic ice shelves and bathytherms, melting the gut outta WAIS.

Anyone who imagines the ocean will not rise much faster than before (this will be true for several centuries)  is deluded, or selling coastal real estate, fake insurance, or fossil fuel. Or worse.

We are committed to retreating coastline for centuries. May our children have mercy on our souls.
But perhaps we can buy them some precious time.

sidd

[Lennart van der Linde]

ASLR,

Your (attached) figure showing results from Horton et al. is the same as figure 3 in this post by Stefan Rahmstorf on RealClimate:
http://www.realclimate.org/index.php/archives/2013/11/sea-level-rise-what-the-experts-expect/

The caption to his figure 3 says:
"Distribution of the experts’ answers to the upper limit of the ‘likely’ range for the RCP8.5 scenario by the year 2100. (These numbers can be compared to the value of 98 cm given in the IPCC report.)"

I think this means the experts estimate there's about a 17% chance of SLR around or over this upper limit. So, I'm not sure what you mean when you say:

at least one true expert (not some outlier) believes that following a RCP 8.5 scenario will result in a 50%CL of 6m of eustatic SLR this century

I think "50%" should be "17%". But maybe I misunderstand?

Figure 2 in Horton et al. itself (also attached) shows the distribution of the upper limit of the 'very likely' range:
https://marine.rutgers.edu/pubs/private/HortonQSR_2013.pdf

The caption to this figure reads:
"Box plots of survey results from all experts who provided at least partial responses to questions. The number of respondents for each of the four questions is shown in the top left corner; it is lower than the total of 90 participants since not all answered each question. Participants were asked to estimate likely (17th-83rd percentiles) and very likely (5th-95th percentiles) sea-level rise under two temperature scenarios and at two time points (AD 2100 and AD 2300), resulting in four sets of responses. Shaded boxes represent the range between the first and third quantiles of responses. Dashed horizontal line within the box is the median response. Whiskers (solid lines) represent two standard deviations of the responses. Filled circles show individual responses that are beyond two standard deviations of the median."

For 2100 apparently 5 out of 82 experts (6%) think a worst-case of 3m or more has about a 5% chance of occurring following BAU. About 50% of the experts think 1.5m or more has about a 5% chance of occurring in this scenario. About 33% think this worst-case risk is 2m or more. One expert even thinks this risk is 7m or more by 2100.

So depending on your criteria for a worst-case estimate it could be 1.5 to 7m by 2100. I think it's significant that 33% of experts think there's a 5% chance of 2m or more by 2100 under BAU. This was not in the IPCC-report, but it seems highly relevant to societal and political discussion on mitigation and adaptation options and negotiations.

[AbruptSLR]

Lennart,

Thanks for expanding on the Horton survey.  It appears that Rahmstorf is correct that the figure he called figure 3 is at the upper limit of the 'likely' range for the RCP8.5 scenario by 2100, which would correspond to a 83%CL for that scenario. I focused on the term 'likely' which extends from the 17th-83rd percentile, and on the fact that the respondents are essentially guessing (and that scientific surveys have demonstrated that scientists typically select the least dramatic option for their estimates). 

Also, thanks for pointing out that at the 95%CL for this scenario that one researcher cited the possibility of a 7m eustatic SLR.  It is important to recognize that due to the fingerprint effect a 7m eustatic SLR by 2100 could mean 5m to 9m RSLR depending on location relative to the melted ice sheets.

Finally, I believe that wili has a point, that in a non-stationary world that surveys like Horton should be repeated at least annually if decision makers are suppose to base their decisions on such findings.

Best,
ASLR

[Gray-Wolf]

Maybe a little less 'cutting edge' than all I've read above but the collective memories/cultural myths about a 'flood' event in humanities past would seem to suggest that we do see a phase of SSL that is near instant/daily rises?

Surely this is not just some echo of the Black sea inundation but a truly global event at the end of the last ice age where catastrophic collapse, and subsequent melt occurred?

We have already seen an Antarctic ice shelf collapse due to the storm swell sent by an Alaskan storm so should we not expect further such events from floating glacier tongues/shelfs?

Bad combinations of tide and swell could lead to pneumatic hammering type fractures of ice bodies that have sea water inundation. The nastiest area for this to happen ( in my mind) is the east of the Ross embayment ? We know that recent collapses of the WAIS has seen the channel linking Ross and Weddell opening up and looking at how the continent is today it makes more sense for such an event to begin from the ross side of the channel?

When we look at the amount of Sea level rise locked up in Ross then any partial collapse of the shelf could bring multiple feet of SLR over a period of less then a decade?

[Lennart van der Linde]

ASLR,

Thanks for pointing out that the fingerprint effect will mean even higher SLR of up to 30% in some places. The same can probably be said for subsidence of cities like Jakarta.

And I agree that surveys like these should be repeated regularly.

[Lennart van der Linde]

Gray-Wolf,

Maybe these flood memories/myths were related to Meltwater Pulse 1A about 14.500 years ago:
http://www.nature.com/nature/journal/v483/n7391/full/nature10902.html

Average SLR was probably over 4 meters/century for several centuries back then, so over 40 cm/decade. People would surely have noticed such exceptionally rapid SLR. Maybe their stories were the (or an important) basis for all the various flood legends that have been chronicled world-wide?

[Shared Humanity]

I would prefer that we not use "biblical stories" to speculate on sea level rise. This is little different than deniers using Viking accounts to argue for natural variation.

[tombond]

We know for certain that sea level is rising in response to global warming caused by rising GHG emissions and will continue to rise for centuries. 

What is uncertain, is how fast this sea level rise will be. 

The IPCC gives us two extremes. 

The first extreme is a low emissions scenario (RCP 2.6) where sea level rise (SLR) is expected to be under 0.5 of a metre by 2100.  This estimation is based on the belief that the global community will co-operate and substantially reduce emissions to almost zero by 2100.  With GHG emissions increasing at 2% per year so far this century, from a risk assessment point of view, this belief currently seems unlikely.

The second extreme is the high emissions scenario (RCP 8.5) where SLR is expected to be about 1 metre by 2100.  This estimation is based on the scientific belief that polar land ice melt will be minimal during this century.  With the polar land ice melt rate observations, as measured by satellite, currently doubling about every 10 years, from a risk assessment point of view, this belief also currently seems unlikely. 

Jim Hansen explores this ice melt doubling period scenario in this paper at www.columbia.edu/~jeh1/.../20121226_GreenlandIceSheetUpdate.pdf

Using polar land ice melt doubling rates, Hansen calculates that for 5, 7 and 10 year doubling rates, that if maintained will give a 1 metre SLR about mid century or just after, much earlier than the more conservative, consensual IPCC predictions.

From a risk assessment point of view this is a more creditable estimation as it is based on current real world observations and data, not beliefs.

For SLR, global governments and communities would be wise to continually monitor the polar land ice melt doubling rates and use this data as the priority prediction input into SLR coastal planning. 

When adapting to continuous SLR whether it be short term protection or staged retreat, the impact on coastal communities can always be reduced by timely, long lead-time planning . 

[wili]

Thanks all for info and speculations on slr issue.

Hank at RC suggested this article as one good starting point for how things looked to many experts before the latest findings:http://www.theguardian.com/environment/climate-consensus-97-per-cent/2014/feb/18/scientists-worried-ipcc-underestimate-sea-level-rise

The Vision Prize survey mentioned here is distinct from the Horton study referenced earlier (though the Guardian article then goes on to discuss that survey as well).

In its latest survey, the Vision Prize asked participants questions about technologies to limit climate change, and about the latest IPCC report. Two of these questions asked about the likelihood that global average sea level will rise less than the IPCC lowest estimate (0.25 meters, or 10 inches), or more than the IPCC highest estimate (0.91 meters, or 3 feet) by 2100. These estimates are about 60 percent higher than in the 2007 IPCC report, which intentionally left out dynamic processes that cause effects like the calving of ice shelves into the ocean, because at the time they were not well understood. As expected, research has shown that the previous IPCC report underestimated the rate of sea level rise.

The Vision Prize results revealed that despite the much higher sea level rise estimates this time around, the survey participants are worried that the IPCC is still underestimating future sea level rise. 41 percent responded that it's likely or very likely that sea level rise will exceed the IPCC highest estimate, and 71 percent answering that it's at least as likely as not. Conversely, only 5 percent responded that it's likely sea level rise will be less than the IPCC lowest estimate, and 83 percent called this scenario unlikely.

It strikes me that these experts did not say that their own highest estimate was higher than the IPCCs high estimat, but that they thought that, as I read it, actual sea level rise would exceed IPCC’s highest estimate of about a meter. One wonders, then, what their highest estimate would be. Especially in the light of the most recent research.

Presumably at this point we can conclude that most experts would expect actual sea level rise to exceed one meter by 2100. The questions remain:

>>By how much?
>>And what would the high-end estimates be, the ones that are so important for doing accurate risk assessment?
>>And how much faster do we expect these levels of sea rise to appear?

Any further light that any of our experts or search sleuths can throw on these important issues would be most welcome.

[Lennart van der Linde]

Wili,

Thanks for the link to the Guardian article on the Vision Prize survey. Indeed it also mentions the Horton et al. survey:

"In this survey, 90 researchers who'd published sea level research in the last 5 years concluded that sea level rise by 2100 is likely to be between 0.7 and 1.2 meters if we continue on a business-as-usual greenhouse gas emissions path. Two-thirds of the experts responded that sea level could rise more than the upper end of the IPCC's projected range by 2100, consistent with the Vision Prize survey results."

[Lennart van der Linde]

It seems the Vision Prize survey also implicitly asks the experts to make an estimate of the likelihood of BAU or mitigation. That's different from the Horton et al. survey which asked for estimates under BAU and under strong mitigation.

[AbruptSLR]

Another consideration that I think that is important to remember with regard to the expert surveys, is that the experts are given the scenarios RCP 3-PD-2.6 & RCP 8.5, and they are not allowed to question this input.  Personally, I do not believe that RCP 3-PD2.6 is anything but a fantasy (this scenario assumes that the third world stayed relatively underdeveloped since the 1980's on, rather than experiencing relatively explosive economic growth), furthermore, as RCP 8.5 is calibrated to assume an ECS of about 3 degrees C, it could very easily be assuming 50% too low of forcing if say the Earth System Sensitivity, ESS, is 4.5 degrees C (many readers here would not be surprised if the Arctic Sea Ice extent and the Northern Hemisphere snow extent, both seasonally dropped markedly in the next decade, not to mention that the hiatus period is ending (for about 15 to 25 yrs), and that air pollution will likely be relatively reduced in the future).  If these ice experts were allowed to determine their own input values to their models, would they have higher projected ice mass loss values?

Furthermore, we have not cited any semi-empirical SLR projections, which uniformly have higher values than the AR5 SLR projections, so if you were to combine higher forcing values together with semi-empirical SLR functions, one should not be surprised if SLR well exceeds one meter by the end of this century.

[Yuha]

I've been reading the recent paper by Joughin, Smith and Medley (doi: 10.1126/science.1249055). Many places mention the 200-900 years until the collapse of the Thwaites Glacier but I don't think the 200 years should be taken as an absolute worst case. ASRL has already made this point but I'm adding my support.

In my interpretation, the paper is stating: "According to simulations, the Thwaites Glacier will collapse 200 to 300 years from now if it continues to melt at the rate observed in 1996-2013." More details and justification is provided by the following quotes from the paper:

We simulated Thwaites Glacier’s response to subshelf melt using a prognostic, finite-element, depth-averaged, shallow-shelf model (12, 22, 23).

Our simulations are not coupled to a global climate model to provide forcing nor do they include an ice-shelf cavity-circulation model to derive melt rates. Few if any such fully coupled models presently exist (13). As such, our simulations do not constitute a projection of future sea level in response to projected climate forcing.

The observed losses from 1996 to 2013 (Fig. 3A) fall between the results from our highest-melt (m = 3 and 4) simulations. Over this period, the average simulated melt of 84 Gt/year for m = 4 agrees well with recent melt estimates of 69 to 97 Gt/year (7,8), indicating that the higher-melt simulations’ early stages reasonably approximate present conditions.

Strong melt (m = 2 to 4) produces ice loss at rates of <0.25 mm/year of sea-level equivalent (sle) for the first century, beyond which there is a period in each strong-melt simulation when the grounding line retreats abruptly, producing greater ice loss (0.25 to 0.5 mm/year of sle).

When simulated losses exceed 1 mm/year of sle, much greater losses generally follow within a few years. Using our basin-scale model, however, such rapid collapse is difficult to model, especially because interaction with other basins becomes increasingly important. Thus, we take 1 mm/year of sle to be a threshold that, once crossed, marks the onset of rapid (decades) collapse as the grounding line reaches the deepest regions of the marine basin.

Table 1. Year in simulation when losses first exceed 1 mm/year of sle for standard and weak-margin models.

m Standard model (year) Weak-margin model (years)
0.5 >1000 >1000
1.0 870 573
2.0 460 342
3.0 343 253
4.0 292 212

Eric Rignot seems to agree that the worst case may be less than 200 years according to a News&Analysis piece in Science (doi: 10.1126/science.344.6185.683):

Eric Rignot, a climate scientist at the University of California, Irvine, and the lead author of the GRL study, is skeptical of Joughin’s timeline because the computer model used estimates of future melting rates instead of calculations based on physical processes such as changing sea temperatures. “These simulations ought to go to the next stage and include realistic ocean forcing,” he says. If they do, he says, they might predict an even more rapid retreat.

[wili]

Thanks for those insights and quote, Yuha.

"According to simulations, the Thwaites Glacier will collapse 200 to 300 years from now if it continues to melt at the rate observed in 1996-2013."

Holy smokes! Does anyone really think the rate is going to remain linear? Has it in the past. Compare the first 20 year period to the second in this graph from the Guardian article:



From my eyeballing, it looks like the rate essentially doubled, from 3 cm in 20 years up to 1990 to 6 cm in the following 20 years. Why should not this acceleration increase? Was there some peculiarity about this time period that we should not expect to repeat in future decades? On the contrary, aren't there now many feedbacks kicking in or about to do so that weren't in evidence in the last century? It sounds to me as if we can say pretty much for sure based on these assumptions that the collapse will come sooner than two centuries out. Am I missing something obvious?

...

ETA: RaenorShine posted these on the Greenland Melt thread, but they seem particularly relevant to this discussion, too:

Dr Jason Box on new Greenland Glacier Bottom Maps
http://climatecrocks.com/2014/05/27/greenland-dark-snow-project-now-more-important-than-ever/

Dr Richard Alley on the latest Antarctic and Greenland Studies
https://soundcloud.com/inquiringminds/35-richard-alley-west-antarctica-is-melting-and-we-cant-stop-it

The actual Alley interview starts just after the 16 minute mark. At about minute 22, Alley points out that at some point there is a runaway--tipping points where the ice flow increases dramatically. He then mentions 'centuries or maybe decades " but I'm unclear as to whether he means that these are periods from now within which we can expect to see these tipping points, or if he means these are the time periods after the tipping points over which we can expect all the ice to flow into the ocean.

I'm thinking/hoping it's the latter.

But then at 25:50 he says that the authors 'did not run the worst case scenario.'

He says, by the end of the century, the most likely slr is a couple of feet or so. It could be a little less than that (but not by much), or it could be a bit more than that. But there's a slight chance that it could be a lot more than that.

(Sorry to be giving this blow by blow, but this is the first 'expert' I've heard weigh in on these matters, rather than just authors of articles in MSM.)

Just before minute 33, the interviewer points out that already last year Archer had said that there is a possibility of WAIS collapse by the end of the century, though he considered it a small possibility at that point. Pressed by the interviewer whether that possibility was now larger, Archer pointed out how little we really know about the potential dynamics of these systems. He then points out that the usual thing we see in reconstructions of earlier melts of ice sheets is long periods of relatively slow melt followed by extremely rapid melt--as in not even pausing for a few months during winter.

We are dealing with a switch, not a dial. It is very easy to know what will happen if you very slowly move a dial. But with a switch, it is very hard to know ahead of time how hard of a push it takes till suddenly you are in a completely different state. WAIS is a switch, and it's very hard to know when it will flip.

[AbruptSLR]

I attached the Mean Sea Level trend plot from circa 1993 to 2014 from the University of Colorado, issued May 23 2014 with data through mid-March 2014.  I also provide the following recent data from that same source (see the link):

http://sealevel.colorado.edu/files/2014_rel4/sl_ns_global.txt

year      msl_ib_ns(mm)
2013.9450   54.943
2013.9721   59.019
2013.9993   62.872
2014.0264   64.153
2014.0536   62.231
2014.0807   57.746
2014.1079   60.575
2014.1350   63.326
2014.1621   66.086
2014.1893   67.650

While the MSL trend from 1993-2014 is 3.2 +/- 0.4 mm/yr this period (note that before this period the MSL trend rate was about 1.7 mm/yr) includes the hiatus period  (including reduced frequency of El Nino's) from about 1998.5 to 2014, and as sea level rises more during El Nino years, the Joughin et al (2014) assumption is very conservative.  This is indicated by the fact that precursor El Nino conditions in 2014 began with a Equatorial Kelvin Wave, EKW, around the end of January; which is reflected in the fact that sea level has increased about 1mm between the end of January and mid-March 2014.

[jai mitchell]

So,

Am I completely off base in expecting a non-linear 0-700M warming event for the Amundsen Sea over the next 40 years?



http://www.atmos.washington.edu/~david/Steig_etal_2012.pdf
Tropical forcing of Circumpolar Deep Water Inflow and outlet
glacier thinning in the Amundsen Sea Embayment, West Antarctica

http://blogs.ei.columbia.edu/2010/12/14/deep-ocean-heat-is-melting-antarctic-ice/

Martinson said that heat stored in deep waters far from Antarctica is being pushed southward and becoming entrained in the Antarctic Circumpolar Current, a vast, wind-driven water mass that constantly circles the frozen continent. The evidence comes from 18 years of Antarctic voyages Martinson has made to measure water temperature, salinity and other qualities at different depths. He called the increases in ocean heat in the past few decades “jaw dropping.”

In view of the projected exponential growth in heat accumulation in the deep oceans over the next 6 decades, how does the fact that they did not project increasing warming into their scenarios makes 1M of sea level rise the new minimum expected rise by 2100?

[AbruptSLR]

jai,

What the fundamental problem is that scientist are trained to only report what their models say, and the models are not yet sophisticated enough to correctly model the influence of the ocean heat on the ASE glaciers, and decision makers are not held accountable by the public for projecting beyond what the scientist tell them.  To be fair, glacial speeds for most of this century have been slow (glacial); but when they hit a certain point they accelerate exponentially as the Jakobshavn Glacier (in Greenland) has already started to do.  So the ready big uncertainty is when does the exponential acceleration begin (which is when the grounding line has retreated past the lip of the sea floor into a negative slope, and when the throat of the gateway widens enough for all the calving ice (due to a Jakobshavn Effect) to float out of the gateway)?  This could not start before 2040 in my opinion but it could be longer.

Also, separately, see the attached fingerprint map of RSLR associated with only the collapse of the WAIS.

Best,
ASLR

[Anne]

Does that chart show feet or metres? 
Feet, I hope.
*Edit* I guess not

[Shared Humanity]

Does that chart show feet or metres? 
Feet, I hope.
*Edit* I guess not

I believe that is a multiple of the average. If average sea level  increases 1 meter than the east coast of the U.S. will see 1.4 meters.

[crandles]

More details and justification is provided by the following quotes from the paper:

Our simulations are not coupled to a global climate model to provide forcing nor do they include an ice-shelf cavity-circulation model to derive melt rates. Few if any such fully coupled models presently exist (13). As such, our simulations do not constitute a projection of future sea level in response to projected climate forcing.

The observed losses from 1996 to 2013 (Fig. 3A) fall between the results from our highest-melt (m = 3 and 4) simulations. Over this period, the average simulated melt of 84 Gt/year for m = 4 agrees well with recent melt estimates of 69 to 97 Gt/year (7,8), indicating that the higher-melt simulations’ early stages reasonably approximate present conditions.

Strong melt (m = 2 to 4) produces ice loss at rates of <0.25 mm/year of sea-level equivalent (sle) for the first century, beyond which there is a period in each strong-melt simulation when the grounding line retreats abruptly, producing greater ice loss (0.25 to 0.5 mm/year of sle).

When simulated losses exceed 1 mm/year of sle, much greater losses generally follow within a few years. Using our basin-scale model, however, such rapid collapse is difficult to model, especially because interaction with other basins becomes increasingly important. Thus, we take 1 mm/year of sle to be a threshold that, once crossed, marks the onset of rapid (decades) collapse as the grounding line reaches the deepest regions of the marine basin.

Table 1. Year in simulation when losses first exceed 1 mm/year of sle for standard and weak-margin models.

m Standard model (year) Weak-margin model (years)
0.5 >1000 >1000
1.0 870 573
2.0 460 342
3.0 343 253
4.0 292 212

Thank you for these quotes.

The current 69-97 GT range averages to ~83GT. it takes 360GT to raise global sea level by 1mm and they are saying if the rate reaches 1mm per year, much greater losses generally follow.

So it only takes two doublings in the rate of loss to get pretty close to this. While I was a bit incredulous about doubling every 4-7 years, doubling every 20-40 years seems much more plausible than assuming the same linear rate as now. That would give a timescale of 40-80 years before even more rapid accelerations?

or am I misunderstanding?

[sidd]

Joughin addresses Thwaites, which is the biggie. But it's not just Thwaites. Right there are PIG,Smith Haynes,Pope,Kohler. All bedded submarine.

i attach fig 1 and part of 3 from Rignot(2014) doi: 10.1002/2014GL060140

Fig 1 is self explanatory. The frames from Fig 3 are improved bedrock topo for b) PIG, d)Thwaites and Haynes f)Smith and Kohler.

Couple meters SLR right there.

sidd

[jai mitchell]

Study #1:
Shepherd et. al
Science 30 November 2012:
Vol. 338  no. 6111  pp. 1183-1189 
DOI: 10.1126/science.1228102

A Reconciled Estimate of Ice-Sheet Mass Balance

Between 1992 and 2011, the ice sheets of

East Antarctica, ---------  +14 ± 43
West Antarctica, ---------   –65 ± 26
Antarctic Peninsula ----------–20 ± 14

changed in mass gigatonnes per year.

Study #2
Mcmillian, Shepherd et. al
DOI: 10.1002/2014GL060111
AGU Letters:  2014

Between 2010 and 2013,
West Antarctica, ---------  −134 ± 27
East Antarctica, and the ----------  −3 ± 36
Antarctic Peninsula ------  −23 ± 18

changed in mass in Gt yr−1

please pardon the hand drawn images.



http://www.theguardian.com/environment/2014/may/19/doubling-of-antarctic-ice-loss-revealed-by-european-satellite

The new data, published in journal Geophysical Research Letters, comes from the European Space Agency’s CryoSat-2 satellite, which was launched in 2010.

It shows that the western Antarctica ice sheet is where 87% of the lost ice is being shed, with the east Antarctic and the Antarctic peninsula shedding the rest. The data collected from 2010-2013 was compared to that from 2005-2010.

So we see a real step-change in west mass loss beginning in 2006 and being maintained through 2013. 

With increased penetration into the continental valleys, there will be a greater exposure to warm waters, combine this with an increase in the temperature of the waters, likely a non-linear increase, which was not included in the model and we reach 1mm/year mass loss very quickly (1-2 decades).

[AbruptSLR]

jai,

While I to believe that the WAIS will contribute to abrupt SLR this century, I believe that it is not likely that the Thwaites Glacier will start showing Jakobshavn type behavior within 1 to 2 decades.

If you scan through the posts in the "Surge" thread of the Antarctic folder (see link below), you will find extensive discussion on just this topic:

http://forum.arctic-sea-ice.net/index.php/topic,21.100.html

In particular, I note that while the McMillian, Shepherd et. al, DOI: 10.1002/2014GL060111, AGU Letters:  2014, findings based on corrected Cryosat data maybe new, the trend that you present in your hand drawn figures are not news to NASA, or to Rignot et al, at all as indicated by the GRACE satellite figure (see first attached figure) from December 2012, which you can also find in Reply #61 of the "Surge" thread; and NASA/Rignot merely prefer to error on the side of least drama in projecting ice mass loss.

Furthermore, if you look at the second attached figure (and Reply # 71 of the "Surge" thread) then you will see that there is reason to suspect that the GRACE satellite (and the McMillian et al 2014) is indicating too low of ice mass loss from the ASE as magma is moving back under the crust in the Byrd Subglacial Basin; which may infer a 2003 to 2009 average ice-mass loss of − 98.9 ± 13.7 Gt/yr for the Amundsen Sea sector alone (note that the British Antarctic Survey and others are currently gathering GPS data to confirm this behavior).

Lastly, I draw your attention to Reply #100 to #103 in the "Surge" thread that indicates some evidence that the subglacial cavity (or local area of grounding line retreat) beneath the Thwaites Ice Tongue may have been filled by surging ice (or the local area of the grounding line advanced) in the boreal Fall of 2012 (austral Spring of 2012), which is the main subject of the "Surge" thread.  Therefore, you cannot assume that grounding line retreat will occur in exactly the same manner in the Thwaites Glacier as is being observed in the PIG, and these differences can add decades to the onset of Jakobshavn type behavior in the Thwaites Glacier.

Best,
ASLR

[jai mitchell]

SLR

Thank you for your post, so many really good posts on the thread.  I have learned so much!!

The ideas that Rignot did not include projected future warming to determine the Thwaites critical failure threshold in 200 to 300 years was illuminating.

Also, the GRACE image that you posted.

To clarify, I was referring to TOTAL Antarctica 1mm/year contribution, not THE Thwaites 1mm/year critical failure threshold of 1mm per year.

 The paleoclimate record is clear, there has been times when a 5cm per year rise has occurred, under normal Milankovitch cycle events.  We know that global ocean heat content is projected to accumulate 166% more energy in the next 30 years than it gained in the last 30 years.  (as a minimum).

Observations from the Circumpolar Deep Water show the recent tropical heating is moving into this Antarctic melt-source via some, currently low understood mechanism.

The observed change in West Antarctic mass loss rate also shows the increased deep water warming.

Therefore, the potential for current AR5 sea level rise projections over the next 20, 50 and 100 years, even the worst case scenarios, are now recognized to be extreme underestimates.

The increased accumulation of 20cm in the next 30 years will effectively double the current value of the social cost of carbon.  (at a ridiculously high 2.5% discount rate) of $57.00 per tonne

Therefore, instead of a double at 2.5% to $114.00 per metric tonne, the value that should be used (at 1.5% per metric tonne - following the Stern Report guidelines) would be closer to $250.00 per metric tonne.

http://www.whitehouse.gov/sites/default/files/omb/inforeg/social_cost_of_carbon_for_ria_2013_update.pdf

[AbruptSLR]

I note that the most dramatic things that could happen in the next few years to either PIG and/or Thwaites would be for their ice shelves/tongue to break apart.  This topic is discussed in the following thread:

http://forum.arctic-sea-ice.net/index.php/topic,429.150.html

The first attached image from Sentinal-1A radar image (I believe from late April 2014) shows how fractured both the Eastern Thwaites Ice Shelf and Ice Tongue are.

The second attached image from the Aqua satellite from March 29 2014, shows how concentrated the calving of the Pine Island Ice Shelf has been in the Northeastern corner over the past austral summer (which could lead to a future major calving event as occurred in November of 2013).

[AbruptSLR]

I just made a new post in the "Paleo-Evidence" thread of the Antarctic folder (see link below), about new evidence that directly ties major collapses of portions of the Antarctic Ice Sheet, particularly with Meltwater Pulse 1A, when sea level rose about 4m in about 100-years:

http://forum.arctic-sea-ice.net/index.php?board=13.0

Editorial note: I have corrected the point that sea level rose up to 4m in about 100-years during MWP 1A.

[jai mitchell]

Thanks for that SLR.

There is so much evidence now for a 95% contribution of WAIS during the late Eemian melt pulse http://www.bitsofscience.org/eemian-sea-level-rise-greenland-antarctica-2487/. 

Even the regional fauna indicate TOTAL WAIS collapse and population mixing between the Ross and Weddell seas during this time.  http://www.sciencedaily.com/releases/2012/05/120509111453.htm


http://planetearth.nerc.ac.uk/multimedia/story.aspx?id=1401&cookieConsent=A

As you posted earlier, this secondary collapse of the entire WAIS happened after a long period of Eemain warming with a sudden and catastrophic (8 meters in 1000 years at the tail end of that interglacial) - the 1000 years window being the highest sample resolution, the likely response time to modern warming is expected to be much less. 

Now that the grounding lines are retreating in depth and distance into the continent this will produce an increased pumping mechanism as warmer high-salinity water is pushed further into the continent and the surface wall of the grounding line is forced deeper into the valley. 

Combining this with the observed increase in southern ocean abyssal waters http://journals.ametsoc.org/doi/abs/10.1175/2010JCLI3682.1 

I see no other option but significant increases in melt rates for at least the next several decades.

[sidd]

" ... increases in melt rates for at least the next several decades."

That last word is really  "centuries"

sidd

[AbruptSLR]

Most of this thread focuses on eustatic sea level rise, but we all need to remember that this is only a fraction of the total future sea level change at any one give location.  I previously, posted an image showing that a 1m eustatic SLR contribution from the WAIS due to the fingerprint effect results in 1.4m of local SLR for most of the continental US, but this is only the start of determining the total future sea level change for say New York Harbor.

The first attached image shows the tide gage readings (in feet relative to MLLW) at the Battery Tide Station, NY at the peak water level during Super Storm Sandy, with the chart showing: (a) the high astronomical tide, HAT of just over 6-feet (1.83m); and (b) the observed maximum water level was 13.87-ft (4.23m).  The second attached image show the results from a NOAA SLOSH analysis showing the water height (relative to MLLW) at the entrance to New York Harbor during a Cat 4 Hurricane could be about 28-ft (8.54m) at today's sea level, during a high tide.

The third image shows a visual representation of the primary contributors to local sea level change including: eustatic SLR, regional SLR, tides, local land movements, and regional sea level variability.  The fourth image shows a plot from NOAA of sea level anomalies on May 23 2014, showing a sea level anomaly at the mouth of New York Harbor of about 0.25m (as an example of combined regional sea level variability and steric SLR)


Now it is important to realize that storm surge increases with SLR and for New York at a rate of about half of the RSLR.  So a 1m eustatic SLR contribution from the WAIS gives a 1.4m local SLR at New York Harbor, plus regional variability of say 0.25m, plus the conventional eustatic SLR at New York (say 1m by 2100, see Haigh et al 2014, nature communications, DOI: 10.1038/ncomms4635), gives a total RSLR of about 2.65m by 2100, plus the 50% increase effect on storm surge or 2.65m x 1.5 = 3.975m plus the storm tide of 8.54m for a Cat 4 event gives at total sea level change for inundation of 12.5 m compared to the 4.23m experienced during Super Storm Sandy.  So when you are reading scientific findings about SLR, I hope that you all are translating this into meaningful sea level changes that will impact society.

[Shared Humanity]

Such a  storm  surge would permanently alter the barrier islands along Long Island.

[Laurent]

AbruptSLR don't you forget the thermal expansion ? I hear 5% sometimes 50% ? 5% of what ? The whole volume of oceans ?

[AbruptSLR]

SH,
Of course while Cat 4 hurricanes have hit New York in the past, their level of storm surge is dependent on the track that they take, and the surge that I show assumes a track similar to that of Hurricane Sandy.  However, with increasing global warming the number of Cat 4 hurricanes hitting New York should increase rapidly.  I believe that Super Storm Sandy was not even a Cat 1 Hurricane when it made landfall, and Hurricane Katrina was a Cat 3 when it made landfall, so we both can imagine how much damage a future Cat 4 Hurricane would have on greater NY/NJ if it were follow a Sandy type storm track.


Laurent,
The thermal expansion was included in the 0.25m of regional variability, and the 1m of process-based projected SLR, values that I assumed.

Best,
ASLR

[AbruptSLR]

The following link leads to advanced abstracts from the International Glacial Society Proceedings 65; which has a lot of information related to Marine Ice Sheet stability and its likely effects on sea level rise projection.  As there are so many abstracts, I just extracted the following three quotes related to our discussion here, and in the next day, or so, I will post many relevant abstracts in the Antarctic folder:

http://www.igsoc.org/symposia/2014/chamonix/proceedings/procsfiles/procabstracts_65.htm

The following Payne et al 2014 extract indicates that the authors try to identify likely SLR contribution ranges associated with Marine Ice Sheet instability not considered in AR5:
 
PAYNE et al (2014), "70A0915 - Ice sheets and sea-level projections in the Fifth Assessment Report of the IPCC", IGSOC Proceedings 65.

"Projections of sea-level rise by 2100 are presented as a likely range, which equates to a likelihood of about two-thirds. The assessed likely range does not allow for a Marine Ice Sheet Instability. Particular attention is paid to this possibility and a further assessment is made of the additional contribution that might arise from it."

I have investigated the collapse of the Paleo-Pine Island glacier, and while not confirmed it is highly likely that this collapse event occurred during Meltwater Pulse 1A, which would indicate that the Paleo-Pine Island glacier may have contributed up to 2m of the 4m total SLR that occurred over a 100-year period during MWP 1A, and the following extract from Schroeder et al 2014 indicates that the Thwaites Glacier is primed to degrade in a similar character and pacing:

SCHROEDER et al, (2014) "70A0914 - Radar-sounding observations of basal water, sediments and geothermal heat flux and their implications for the past and future sea-level contribution of the Amundsen Sea sector of West Antarctica", IGSOC Proceedings 65.

"We conclude that a transition in the basal hydrology of Paleo Pine Island was characteristic of its relatively rapid retreat across exposed bedrock on the inner continental shelf and that Thwaites Glacier may be currently configured for a retreat that is similar in character and pacing."

The following extract from Nias et al 2014 confirms that the Thwaites Glacier, TG, will degrade in a different manner than the PIG currently is exhibiting:

NIAS et. al., (2014), "70A0919  -  Contrasting dynamics and sensitivity of the Amundsen Sea ice streams", IGSOC Proceedings 65.

"Using BISICLES, we ran a perturbed model ensemble for PIG and TG. Latin hypercube sampling was used to generate sets of parameter values for a range of physical conditions, including ice rheology, basal sliding and bed topography. We present probability density functions of the likelihood of sea-level contributions from PIG and TG under the same oceanic forcing. Initial results suggest that these probability density functions are very different."

[Laurent]

I found that wikipedia stuff...if it does help...
https://en.wikipedia.org/wiki/Current_sea_level_rise

[AbruptSLR]

See the linked article (with a free access pdf) which states: " … the proportion of Category 4 and 5 hurricanes has increased at a rate of ~25–30 % per °C of global warming after accounting for analysis and observing system changes."  This supports my assumption of taking a Cat 4 hurricane for flood risks for New York Harbor by the end of this century, see Reply #91.

Greg Holland • Cindy L. Bruye`re (2014), "Recent intense hurricane response to global climate change", Clim Dyn (2014) 42:617–627, DOI 10.1007/s00382-013-1713-0


http://link.springer.com/article/10.1007%2Fs00382-013-1713-0

Abstract: "An Anthropogenic Climate Change Index (ACCI) is developed and used to investigate the potential global warming contribution to current tropical cyclone activity. The ACCI is defined as the difference between the means of ensembles of climate simulations with and without anthropogenic gases and aerosols. This index indicates that the bulk of the current anthropogenic warming has occurred in the past four decades, which enables improved confidence in assessing hurricane changes as it removes many of the data issues from previous eras. We find no anthropogenic signal in annual global tropical cyclone or hurricane frequencies. But a strong signal is found in proportions of both weaker and stronger hurricanes: the proportion of Category 4 and 5 hurricanes has increased at a rate of ~25–30 % per °C of global warming after accounting for analysis and observing system changes. This has been balanced by a similar decrease in Category 1 and 2 hurricane proportions, leading to development of a distinctly bimodal intensity distribution, with the secondary maximum at Category 4 hurricanes. This global signal is reproduced in all ocean basins. The observed increase in Category 4–5 hurricanes may not continue at the same rate with future global warming. The analysis suggests that following an initial climate increase in intense hurricane proportions a saturation level will be reached beyond which any further global warming will have little effect."

[AbruptSLR]

While the linked article is a few months old, the following quote makes it painfully clear that with increasing storminess and increasing SLR we could see $100 trillion/year in storm surge damage by 2100, if we don't do something to stop it:

http://www.theecologist.org/News/news_round_up/2268503/storm_surges_to_cost_100_trillion_a_year_as_sea_levels_rise.html

Quote: "According to a study published in the Proceedings of the National Academy of Sciences, global average storm surge damages could increase from about $10-$40 billion per year today to up to $100,000 billion per year by the end of century, if no adaptation action is taken."

[AbruptSLR]

Many researchers like to look to the Mid-Pliocene as a paleo-example of what the GCMs estimate the Earth could be like in the late 21st century, with regard to surface temperatures ( but not with regard to sea level which was at least 15 to 25 meter above modern levels, as the sea/ice responds more slowly than the atmosphere).  The following quote from the IPCC puts the Mid-Pliocene into context:

http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch6s6-3-2.html

Quote: "The Mid-Pliocene (about 3.3 to 3.0 Ma) is the most recent time in Earth’s history when mean global temperatures were substantially warmer for a sustained period (estimated by GCMs to be about 2°C to 3°C above pre-industrial temperatures; Chandler et al., 1994; Sloan et al., 1996; Haywood et al., 2000; Jiang et al., 2005), providing an accessible example of a world that is similar in many respects to what models estimate could be the Earth of the late 21st century. The Pliocene is also recent enough that the continents and ocean basins had nearly reached their present geographic configuration. Taken together, the average of the warmest times during the middle Pliocene presents a view of the equilibrium state of a globally warmer world, in which atmospheric CO2 concentrations (estimated to be between 360 to 400 ppm) were likely higher than pre-industrial values (Raymo and Rau, 1992; Raymo et al., 1996), and in which geologic evidence and isotopes agree that sea level was at least 15 to 25 m above modern levels (Dowsett and Cronin, 1990; Shackleton et al., 1995), with correspondingly reduced ice sheets and lower continental aridity (Guo et al., 2004)."

Furthermore, I discuss the following linked reference (with a free access pdf) in both the "Forcing" thread (Reply #197) and the "PIG/Thwaites 2012 to 2040-2060" thread in the Antarctic folder, and the first attached image from Hill et al 2014 shows that polar amplification results in about 10 degrees C higher Surface Air Temperatures (SAT) in the Amundsen Sea Embayment, ASE, during the Mid-Pliocene than today, and that this amplification was largely related to reductions in clear sky albedo (see the second attached image), due to such factors as reduction in sea ice.

Hill, D. J., Haywood, A. M., Lunt, D. J., Hunter, S. J., Bragg, F. J., Contoux, C., Stepanek, C., Sohl, L., Rosenbloom, N. A., Chan, W.-L., Kamae, Y., Zhang, Z., Abe-Ouchi, A., Chandler, M. A., Jost, A., Lohmann, G., Otto-Bliesner, B. L., Ramstein, G., and Ueda, H.: Evaluating the dominant components of warming in Pliocene climate simulations, Clim. Past, 10, 79-90, doi:10.5194/cp-10-79-2014, 2014.

http://www.clim-past.net/10/79/2014/cp-10-79-2014.html

To emphasize that while currently Antarctic sea ice extent is trending upward (a trend that is projected to reverse after 2080), currently the austral summer sea ice extent in the ASE is actually trending downward as illustrated by the third attached image of an Antarctic sea ice extent map for January 29 2014, and while the fourth attached image shows that solar insolation in Antarctic in January is actually higher than in the Arctic in July.

Taken together, this evidence indicates that by the late 21st century that we can expect extensive ice surface melting in the ASE during the austral summer; which will not only contribute to ice mass loss due to austral summertime runoff, but more importantly preliminary findings indicate that the presence of surface water can markedly accelerate ice mass loss due to the Jakobshavn Effect.  This is a very serious matter that could significantly accelerate SLR after about 2070.

[AbruptSLR]

As frustrating as it is that neither Rignot et al 2014 nor Joughin et al 2014,  used the full RCP ocean forcing in their projections about the irreversibility, and coming acceleration, of ice mass loss from the Amundsen Sea Embayment, ASE, marine glaciers; I find it particularly worrisome that the RCP scenarios are calibrated using a nominal Equilibrium Climate Sensitivity, ECS, value of about 3 degrees C; while the following research indicates the true ECS is closer to 4 degrees C (and may be about 4.5 degrees C; see the "Forcing" thread in the Antarctic folder).  The linked video, quote, and attached image, indicates that this higher ECS value is related to differences between actual and previously modeled (in the RCP scenarios) in atmospheric convective mixing resulting in differences in tropical cloud cover.  As we enter a positive PDO phase for the next 15 to 25 years, the importance of these differences should be clearly demonstrated by an acceleration in the rate of SLR:

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 video: “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.
“Rises in global average temperatures of this magnitude will have profound impacts on the world and the economies of many countries if we don’t urgently start to curb our emissions."

See also:

Shindell, D.T., (2014), "Inhomogeneous forcing and transient climate sensitivity", Nature Climate Change, Vol.: 4, pp: 274–277, doi:10.1038/nclimate2136.

http://www.nature.com/nclimate/journal/v4/n4/full/nclimate2136.html

and also:

Fasullo, J.T. and Trenberth, K.E., (2012), "A Less Cloudy Future: The Role of Subtropical Subsidence in Climate Sensitivity", Science, vol. 338, pp. 792-794, 2012. http://dx.doi.org/10.1126/science.1227465.

http://www.sciencemag.org/content/338/6108/792

[AbruptSLR]

I realize that I may be confusing some people by talking about Equilibrium Climate Sensitivity, ECS, sometimes, Transient Climate Response, TCR, sometimes, and Earth System Sensitivity, ESS, sometimes.  Therefore, I provide the following extract from Wikipedia, related to these terms:

http://en.wikipedia.org/wiki/Climate_sensitivity


Extract: "The equilibrium climate sensitivity (ECS) refers to the equilibrium change in global mean near-surface air temperature that would result from a sustained doubling of the atmospheric (equivalent) carbon dioxide concentration (ΔTx2).
….
A model estimate of equilibrium sensitivity thus requires a very long model integration; fully equilibrating ocean temperatures requires integrations of thousands of model years. A measure requiring shorter integrations is the transient climate response (TCR) which is defined as the average temperature response over a twenty-year period centered at CO2 doubling in a transient simulation with CO2 increasing at 1% per year. The transient response is lower than the equilibrium sensitivity, due to the "inertia" of ocean heat uptake.
…
A less commonly used concept, the Earth system sensitivity (ESS), can be defined which includes the effects of slower feedbacks, such as the albedo change from melting the large ice sheets that covered much of the northern hemisphere during the last glacial maximum. These extra feedbacks make the ESS larger than the ECS — possibly twice as large —
 …."

In my last post I indicated that Sherwood et al (2014) and Fasullo and Trenberth (2012) indicate that ECS is likely between 4 and 4.5 degrees C; and Shindell (2014) indicates that TCR is also likely proportionally higher than the AR5 assumes.  Furthermore, while traditional process-based thinking assumes that ESS reaches it's full potential over a period of millennia, James Hansen warns that a significant fraction of the full potential of an ESS value can be realized within say one hundred years.

In this regards, the linked reference by Pagani et al 2009 (with a free pdf) and attached figure, indicate that in the early Pliocene (over 4 million years ago, when the world was about 4 degrees warmer than pre-industrial era and CO₂ concentrations were about 415ppm) that Earth Systems Sensitivity, ESS, was about 9.6 +/- 1.4 degrees C.

Mark Pagani, Zhonghui Liu, Jonathan LaRiviere, Ana Christina Ravelo (2009), "High Earth-System Climate Sensitivity determined from Pliocene CO2 Concentrations", Nature geoscience, doi:10.1038/NGEO724

http://people.earth.yale.edu/sites/default/files/files/Pagani/1_2009%20Pagani_NatureGeosci.pdf

As the Arctic Sea Ice, the Northern Hemisphere snow cover, Antarctic Sea Ice and the WAIS, also show signs of potentially collapsing before the end of this century if we stay on a BAU pathway, it does not seem unreasonable to be concerned that 6 degree C of the ESS full potential could be realized this century, with potentially severe consequences on SLR this century.

[AbruptSLR]

For those who are concerned that I may be over-stating the reasonable values for ESS this century, please review my Reply #151 in the "Potential Collapse Scenario for the WAIS" thread at the following link:

http://forum.arctic-sea-ice.net/index.php/topic,31.150.html

This post cites a large number of factors that can be temporarily "masking" the true magnitude of the ESS; which may be more fully expressed in a few decades time due to changes such as: (a) reductions in the relative amount of air pollution/aerosols (particularly in China); (b) stress to much of the worlds vegetation from such factors as: heat, drought, floods, insects, and wildfires; (c) the coming positive PDO phase; (d) the coming acceleration in methane and CO2 emissions from both tundra and tropical wetlands; (e) the coming warming phase of the “Atlantic Multidecadal Oscillation” or “AMO”; and (f) a possible reduction in the relatively high recent number of significant volcanic eruptions.

[Shared Humanity]

ASLR...

Thank you for these posts. Until you posted it, I was only aware of ECS. TCR and ESS are completely new to me.